Natural Compounds Toxicology

C H A P T E R

40

Natural Compounds J. WESTENDORF

Department of Toxicology, University Medical School, Hamburg, Germany

I N T R O D U C T I O N

The use of chemical compounds for defense or at- tack is common in nature and an important tool of the evolution. Poisons are present in almost all classes of organisms from the most primitive bacteria to the highly developed vertebrates. The variation of natural poisons with respect to their chemical structures and biological action is enormous. The highest concentration of toxic organisms is located at places of maximal population density, such as tropical rain forests and coral reefs. Because a sufficient treatise on the entire field of natural poisons is not possible here, this chapter will only give an overview of the most important principles of action with some selected examples.

The use of plant- and animal-derived toxins by humans has been reported throughout history. Such poisons have been used for hunting purposes (arrow poisons), for occult ceremonies (belladonna, psilocybe, and opium) for executing victims (Conium maculatum), as abortives, and especially to treacherously murder people. Although poisons had been used as medicine in antiquity, it was Paracelsus (1493-1451), who recognized the dualistic principle of many poisons of their curative and deadly actions; "dosis sola facit venenum" (only the dose makes the poison). Modern pharmacology is a product of the knowledge of the special biological actions of compounds derived from plants and animals.

A N I M A L V E N O M S A N D P O I S O N S

Animals use poisons and venoms for defense against potential enemies and to paralyze or kill their prey. In the latter case, the venom is located in special glands and transferred by bite or sting. If the venom or poison is only used for defense, it may be located also in the skin, or inner organs. The toxicity of such animals is often supported by conspicuous colors (e.g., frogs of the Dendrobate family and salamanders) to warn potential enemies "be careful, I am toxic." Some animals contain poisons that are derived from other organisms. This is often the case in aquatic systems, where certain dinoflagellates are the primary source of the toxic compounds, which are transferred to higher organisms by the food chain or via symbiosis.

The chemical composition of animal-derived venoms and toxins is, in most cases, very complex and contains proteins, peptides, glycosides, alkaloids, neurotransmitters, ketones, and even hydrocarbons. The poisons are often highly specialized and target the nervous system very efficiently. The components of complex toxins are often synergistic with respect to their adverse effects. Typical poisons of Hymenop- tera, snakes, scorpions, and spiders contain

Amines: histamine, serotonine, acetylcholine, and kinines; these act as inflammatory agents, cause pain, and decrease blood pressure.

TOXICOLOGY 959 Copyright 9 1999 Academic Press.

All rights of reproduction in any form reserved.

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Enzymes: hyaluronidase (loosening up connecting tissue); and phospholipases (destroys cell membranes and increases the synthesis of inflammatory compounds, e.g., prostaglandines).

Polypeptides: these act as neurotoxins, myotoxins, and cardiotoxins.

The peptides are often the main toxicants in such complex mixtures and responsible for the death of the victim, whereas the other components act as adjuvans to help the peptides to reach its target (e.g., the nerve system receptors and heart). The protein components may cause allergic reactions after repeated application of the poison, which may also cause lethal anaphylactic-shock reactions.

Aquatic Animals The aquatic ecosystem is characterized by a great

complexity of species, many of which use toxic compounds to survive. The greatest concentration of different and, therefore, toxic species is located at tropical coral reefs. To swim or dive in such regions may be dangerous, especially for inexperienced people. The number of accidents caused by poisonous aquatic animals worldwide is between 40,000 and 50,000. An- other 20,000 intoxications are caused by eating poisonous fish or mollusks.

Coelenterata (Coelenterate)

Poisonous representatives can be found among the hydras, jellyfish, sea anemones, and corals, all of which are marine inhabitants of the warm belt between the 30th parallels. In the warm Atlantic Gulf Stream, they can be found up to the 60th parallel. The toxins of these animals are usually polypeptides, which serve to catch prey or to protect against potential voracious enemies.

Upon touching the tentacle of these animals, which are covered with cnidoblasts (nematocysts), a sophisticated apparatus (cnidocile) rushes out. A kind of flagellum with numerous bristles and barbed hooks penetrates the skin, injecting the poison. The most dangerous representatives live in the tropical coral reefs. Among the most dreaded jellyfishes are the Por- tuguese man-of-war (Physalia physalis) and the sea wasp (Chironex fleckeri). Contact with these animals is followed by extreme pain caused by histamine, kinines, and prostaglandines, all contents of the poison. The victim may become unconscious because the pain is so violent and drown. Death may also occur by the poison itself. The toxic peptides of these Coelenterates are sodium channel blockers, which cause an extreme

prolongation of the action potential of the synapses and neuromuscular endplate, causing very painful muscular contractions, paralysis, shock symptoms, and respiratory arrest. Antidotes do not exist and the treatment is symptomatic. The iv application of calcium, glucocorticoids, and plasma expanders is necessary in cases of shock. Topical application of local anesthetics is helpful because the contact with the poison is very painful. In most cases of accidents with poisonous Coelenterates, no medical care is immediately available. Information about the local situation and avoidance of any contact with such animals is, therefore, most important.

Mollusks (Mollusca)

Among these are the genera for mussels (Lamelli- branchiata) and snails (Gastropoda). Poisoning by these species is, in most cases, caused by ingestion. Dino- flagellates are often the primary source of the toxins. The mollusks concentrate their toxins during their consumption of these organisms. The presentation of these toxins, which occur also in some fish species, is given elsewhere in this book.

Among the active toxic mollusks are Conidae (Tox- oglossa), inhabiting the tropical marine areas. The animals possess a sophisticated venom apparatus serving as an offensive weapon for the gaining of food. It may also be used to a lesser extent as a defensive weapon. The apparatus consists of a muscular bulb, a venom duct, the radula, and the radular teeth, which are formed like little harpoons from 1 to 10 mm in length. The venom is forced under pressure from the venom duct into the radula and taken up by the radular teeth, which are then transported through the phar- ynx into the proboscis. The animals use this organ like a gun in shooting toxic arrows into the prey. The different Conidae are specialized to different prey (worms, snails, fish). Only those species preying on vertebrates (fish) are dangerous for humans. The venom contains basic peptides with a chain length of 13 to 29 amino acids. Three main species are distin- guishable, c~-Conotoxins possess a curare-like action on nicotinergic acetylcholine receptors at the neuromuscular endplate, a~-Conotoxins are calcium channel-blockers in the synapses of the neuromuscular endplate. /~-Conotoxins block sodium channels in muscle cell membranes. The actions of the different peptides are perfectly coordinated in order to block the nerve function with maximum efficiency. Normal prey is paralyzed almost immediately after being attacked by Conidae. This is important because these animals are slowly moving and not able to follow

Natural Compounds 961

their prey. Some species of Conidae are quite able to kill humans (e.g., Conus geographus and Conus tulipa).

Conidae live in the shallow regions of tropic marine areas and are often collected as souvenirs because most are very pretty. This should be performed with great care and only dead shells should be picked up. The sting of fish-hunting Conidae results in a local numbness that spreads through the whole body, followed by paralysis of the muscles and finally heart arrest. No specific antidote is available, and the treatment has, therefore, to be symptomatic.

Echinoderms (Echinodermata)

The genus of Echinoderms contains two groups, the Pelmatozoa and Eleutherozoa. Most of the poisonous species belong to the Eleutherozoa. Among these are Asteroidea (starfishes), Ophioidea, Echinoidea (sea urchins), and Holothurioidea (sea cucumbers). Echino- derms are benthic organisms spread all over the oceans. However, most of the toxic species live in tropical areas.

Starfish use their poison most probably for preying on other organisms. For this purpose they produce a toxin located in skin glands, which is released into the water. The toxins are able to paralyze mussels, snails, and shrimps. After one touche a poisonous starfish, the stings may penetrate the skin, causing great pain and local inflammation. The toxins of starfish are steroid glycosides, which act as detergents, similar to the saponines occurring in many plant species. Figure 1 shows the toxic principle of the starfish Acanthaster planci. The toxin of this starfish decreases the blood pressure after parenteral application in mammals. This is believed to be mediated by endogenous ara- chidonic acid metabolites, such as prostacyclin.

Sea urchins cause painful wounds with their pointed stings, which break off after drilling into the skin. The stings of some species contain a venom, that causes great pain and inflammation. Sometimes systemic reactions, such as paresthesia, gastrointestinal symptoms, headache, and allergic reactions occur. Fa- tal cases are rare. The poisons are not only located in the stings but also in the genital organs. Eating sea urchins is, therefore, not recommended, especially during the spawning period. The chemistry of the sea urchin toxins is unknown. The toxins are most probably high molecular-weight compounds, which decom- pose during the procedure of isolation.

Among the sea cucumbers there are many poisonous species. Some of their toxins are located in skin glands. More important, however, are special organs, which are called as "Cuvierian tubules." In case of

danger these tubules are extruded through the anus, releasing a mixture of toxic compounds that act as repellents for possible predators. The main toxic principles of sea cucumbers are saponins of the lanosterin- type, such as holothurin A (Fig. 1). Skin contact with sea cucumbers may cause painful symptoms, which normally disappear soon. In some Asian countries sea cucumbers are used as food (trepang). This sometimes causes intoxication dominated by gastrointestinal symptoms, such as vomiting and diarrhea. After absorption of considerable amounts of holothurin A, hemolysis and paralysis may occur. Fatal cases have also been reported.

Fishes (Pisces) Most of the venomous or poisonous fishes live in

the area of tropical coral reefs. They are distinguished as active (venomous) and passive (poisonous) species. Some of the poisons are produced by microorganisms living in a symbiosis with the fish.

Venomous fishes have venom glands and stings, which are used for defensive purposes. These fishes are in most cases lazy and stationary. Their toxic nature serves as a substitute for flight from predators. Among the around 200 species living in marine areas are stingrays (Dasyatidae), scorpionfishes (Scorpaeni- dae), weevers (Trachinidae), catfishes (Siluroideae) and others. The toxins consist of a complex mixture of very unstable proteins. The specific toxicity (LD50 in mice) varies between 200/zg/kg (stonefish) and several mg/kg. Stings from these fishes are sometimes extremely painful and cause local inflammation and necrosis with a bad prognosis for healing. The most toxic venomous fish, the stonefish (Synaceja horrida) was used by the native Malays on hunting darts.

After systemic application, the toxins exert pronounced myotoxic action. Affected are the heart, the blood circulatory system, and the skeletal muscles. Lethal doses cause a paralysis of the extremities and a circulatory collapse. Most dangerous are the stonefish species Synaceja horrida and Synaceja trachinus. The animals live in shallow marine areas and spend most of the time buried in the sand waiting for prey. Their color is so perfectly adapted to the neighboring environment that, even if not buried, they are almost in- visible. Accidents occur in most cases by stepping on the fish. The dorsal spines penetrate the skin and the venom is injected by the pressure of the victim's weight into the wound. Fatal cases are not rare. Death occurs normally 8-24 hours after the envenomation.

Treatment first consists of removal of the sting fragments and cleaning the wound carefully. The af-

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fected extremity should be treated with hot water (40-50~ for at least 30 minutes. This results in a decrease in the pain and a partial washout of the venom. In severe cases of intoxication the iv injection of an antivenin is recommended. However, in many cases an antivenin may not be available and the treatment has to be only symptomatic. The best way to prevent complications is to avoid any contact with these fishes. In areas known to be the habitats of stonefishes, the wearing of bathing shoes is recommended.

Other toxic fish species excrete their toxins through the skin. These are called "crinotoxic." An example is the boxfish (Ostracion lentiginosus), which excretes a toxin called pahutoxin. It is a choline ester of 3-acetox- yhexadecanoic acid (Fig. 2). Because of its ampho- philic character, the compound acts as a detergent. Once released into the water, it has a strong repelling action on fishes, even on sharks, and other aquatic animals. If it is impossible to escape the toxin (e.g., as in an aquarium), the victims develop a decrease in movement, loss of equilibrium and locomotion, and, finally, sporadic convulsions and death. After parenteral application to mammals, the toxin, like other

detergents, causes severe hemolysis. The LDs0 in mice is 200 mg/kg.

Some fish contain toxic gonads, whereas the rest of the body is free from toxins. These fishes are called "ichtyootoxic." Most of these species live in freshwa- ter and only a few live in marine environments. Among these is the Cabezon (Scorpenichtys marmora- tus), which inhabits the Pacific coastal areas between California and British Columbia. The fish weighs up to 20 pounds and is a valuable food fish. Eating of the roe will cause intoxication with mainly gastrointestinal symptoms. In more severe cases arrhythmia, chest

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pain, convulsion, and coma may occur. Lethal events are rare.

Some fishes contain toxins only in their blood and are, therefore, called "ichtyohematoxic." Among these are eels and muraena. Intoxication occurs if greater amounts of blood from these fishes are ingested. Nothing is known about the chemistry of the toxins, except that they are labile upon heating. The eating of cooked fish is, therefore, safe.

Passive toxic fishes contain toxins originally produced by certain microorganisms, such as bacteria, protozoa, or algae. The toxins are sometimes extremely potent and may be present in all tissues or only in certain organs of the fish. The term "ciguatera" characterizes an intoxication caused by eating groupers, barracudas, sharks, and other predatory fishes living in some tropical or subtropical marine areas, mainly near coral reefs. The phenomenon is frequent in certain areas of the Caribbean Sea and the Gulf of Mexico. The term ciguatera is derived from the Spanish word for a snail living on the isle of Cuba, erroneously thought to be responsible for the intoxication. The primary source of the toxin are epi- phytic dinoflagellates living on macrophytic algae. The toxin is concentrated in the food chain (dinoflagellate to herbivorous fish to predatory fish). The highest concentrations occur in the gut and liver; however, the concentration of the toxin in muscular tissue is high enough to cause intoxication after eating contaminated fish. It is very hard to predict whether a fish is contaminated with the ciguatera toxin. Certain species of fish should, therefore, not be used for food in areas with a known history of ciguatera intoxication. A more detailed presentation of the symptoms of the ciguatera intoxication follows elsewhere.

A toxin derived from bacteria and concentrated in the gonads and liver of certain pufferfishes is tetrodotoxin (Fig. 3). The pufferfish (Sphaeroides), known in Japan as fugu, is very popular because of its delicious meat. The fish is cut into very thin slices and eaten raw. Very strict qualifications are required for cooks preparing the fugu. The problem is to avoid cutting the inner organs, which contain the toxin. Neverthe- less about 75 fatal cases of intoxication from fugu are reported every year from Japan alone. Worldwide the number is about 125. Tetrodotoxin occurs not only in pufferfish, but also in other fish species (Diodontidae, Molidae, Gobius ssp.) and in other aquatic animals, such as starfish, crab, worms, and blue-ringed octo- pus, and even in some terrestric animals, such as the amphibians Taricha torosa and Atelopus ssp.

There is no doubt that tetrodotoxin is synthesized by bacteria, however, the exact species is unknown. An Alteromonas species and different marine species of Pseudomonas and Vibrio have been demonstrated to synthesize tetrodotoxin and the analogs epitetrodo- toxin and anhydrotetrodotoxin in culture. It is thought that the bacteria enter the GI tract of the fishes via their food. The toxin is produced by the bacteria in a fish's gut and transported to the liver and the ovary after absorption. The highest concentration of the toxin occurs immediately before spawning. This gives rise to the suggestion that the accumulation process can be controlled by the fish. The toxin is most probably intended to protect the eggs from predators. It was also shown that pufferfish born in aquariums were not toxic. After releasing the fish into the natural environment, they became toxic very soon.

Tetrodotoxin blocks the sodium transport across the axoplasma membrane without influencing the opposite potassium transport. This inhibits the formation of action potentials. The specific side of action at the central nerve conduction is responsible for the extreme potency of the poison. The LD50 in mice after ip injection is 10/~g/kg. After oral administration, it is 322 ~g/kg, still an extremely low value. If the toxin is taken up by humans via contaminated food, a tin- gling occurs 5 to 30 minutes later at the lips, tongue, and throat, followed by a paresthesia. The symptoms spread to the extremities. Other symptoms follow; among these are hyperthermia, hypotension, nausea, chest pain, and, for severe intoxication, muscle pain, convulsion, and respiratory arrest, which finally leads to death. Because of the lack of a specific antidote, only symptomatic therapy is possible. Gastric lavage and induction of vomiting is recommended. The oral application of charcoal is intended to bind the toxin still in the lumen and prevent its absorption. Addi- tional treatment consists of oxygen, iv substitution of

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fluids, and the application of atropine. Some decades ago most of the victims died. Due to the modern intensive care about half of the patients now survive.

Terrestrial Animals

Arthropods This phylum contains spiders and scorpions (Ar-

achnoidea) and insects (Hexapoda). The venomous species transfer their venom by sting or bite. Almost all spiders are toxic, but only a few species, most of which are living in tropical areas are dangerous to humans. Most of the scorpions are toxic, too, whereas most insects are not toxic; however, some of the toxic species are responsible for numerous fatal cases, caused by allergic rather than toxic reactions.

Spiders (Araneae) Around 25,000 species of spiders are known; how-

ever, only 1% have fangs (chelizera) long and strong enough to penetrate the skin and are of real danger. Some of the dangerous species live in the Mediterra- nean area of southern Europe, but most of the fatal cases occur in Central and South America, Africa, and Australia. Among the dangerous genera of spiders are Atrax ssp., Trechona ssp. (funnel-web spider), Harpac- tirella ssp. (trapdoor spider), Phoneutria ssp. (hunting spider), Loxosceles ssp. (brown or violin spider), Lycosa ssp. (wolf spider), and Latrodectus ssp. (widow spiders).

The black widow spider (Latrodectus mactans) is the best-known species of its genus and is responsible for most of the spider accidents in the European area. This and other widow spiders are found nearly glob- ally. The name "widow spider" is related to the fact that the females kill and eat their mates after mating. Due to their bigger size (10-18 mm), only the females have fangs (chelizera) large and strong enough to penetrate the human skin when they bite. The venom of the black widow spider contains a variety of peptides, some of which are only toxic to insects. The fraction that is toxic for humans is called a-latrotoxin and consists of a peptide with a molecular weight of 130,000. The animals contain median amounts of 0.22 mg of the toxin. The LD50 in mice (iv) is 0.55 mg/kg. The fact that sometimes fatal cases in humans occur (3% of cases) suggests that humans are more sensitive to the toxins than rodents. The symptoms after a bite consists of local inflammation, painful swelling of lymph nodes, spontaneous muscle contractions, hyperthermia, hypertension, headache, and nausea. Fear and hallucinations sometimes occur. At particular risk

are patients with diseases of the heart and circulatory system. Death is often caused by a stroke or heart arrest. The best therapy consists of the injection of calcium and Latrodectus mactans antivenin. Because the progression of the symptoms is usually slow, there is enough time to start with the antivenin application. One should, however, consider that antivenins sometimes cause anaphylactic reactions. It is, therefore, not recommended that it be used in the less severe cases of intoxication.

The venom of the Loxosceles genus causes severe necrotic action. The brown recluse (Loxosceles reclusa) contains approximately 70/zg of a toxic protein, composed of different fractions. The LD50 for guinea pigs (ip) is 0.43 mg/kg. After bites from Loxosceles ssp., extensive local necroses occur, leaving irreversible tissue damage in most cases. After systemic distribution of greater amounts of the venom, extensive hemolysis occurs resulting in considerable hematuria and, sometimes, kidney failure. After less severe envenomation, the symptoms may be restricted to fever, nausea, vomiting, jaundice, splenic enlargement, and disturbance of coagulation. Similar symptoms are also common after bites of Lycosa ssp. Local and systemic application of glucocorticoids are recommended for the treatment of the cytotoxic action of the venom components. Systemic effects have to be treated sympto- matically. The use of antivenins is not always successful.

The most toxic spider is the black banana spider (Phoneutria nigriventer). Three neurotoxic peptide fractions have been isolated from the raw venom. The LD50 for mice is in the range of 50 /zg/kg. Severe symptoms of intoxication occur almost immediately. After a bite, mice will be paralyzed almost within seconds. In humans, the first symptoms occur after 10-20 minutes and are dominated by great pain. Cen- tral symptoms are fever, heavy sweating, tachycardia, arrhythmia, nausea, vomiting, hypertonia, visual disturbance, heavy convulsions, and, finally, respiratory arrest. Immediate application of an antivenin together with symptomatic treatment is the only sufficient therapy.

Scorpions (Scorpiones) About 75 of the 800 species of scorpions are dan-

gerous to humans. They live in almost all tropical and subtropical areas. Most of the accidents occur in houses, especially the primitive ones, where it is easy for the scorpion to enter. The animals like to hide themselves in clothing and shoes at the night. In the morning, when people put on this clothing, the scorpions feel attacked and sting. Children are at higher


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LDs0 of venom Genus species Occurrence (mg/kg mice, sc)

Androctonus spp. A. australis A. oeneas oeneas A. mauretanicus mauretanicus A. crassicauda A. amoreuxi

Buthus spp. B. occitanus tunetanus B. occitanus paris

Buthotus spp. B. judaicus B. minax

Centruroides spp. C. limpidus

Leiurus spp. L. quiquestriatu

Parabuthus spp. P. transvaalicus

Tityus spp. T. serrulatus T. bahiensis T. trinitatis

North Africa, Middle East

France, Spain, North Africa, Middle East

Africa, Middle East, Central Asia

North America, Central America, South America

North Africa, Middle East

South Africa

Central America, South America

6.00 0.31 0.32 0.40 0.75

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risk than adults because they are less careful and have a lower body weight. Worldwide about 150,000 accidents due to scorpions are registered per year, most occur in Latin America (Mexico) and North Africa. The overall mean mortality is 2%, but among children it is 20%. Some data for medically relevant scorpions are shown in Table 1. The LD50 data have been derived from experiments with mice. With respect to the relative toxicity, humans usually are much more sensitive.

The scorpion's venom is composed mainly of neurotoxic peptides with a chain length of 60-70 amino acids. Biogenic amines have been observed in the venom of some species. Stings of scorpions are normally very painful. Numbness may occur after a certain time. The systemic effects consist of convulsions, tachycardia, arrhythmia, nausea, vomiting, visual disturbances, and respiratory distress. Death normally occurs from respiratory arrest. If the victim survives the first 24 hours after the sting, the prognosis is relatively good. The best results are observed after the injection of specific antivenins. It is important that sufficient amounts be given intravenously shortly after the sting (up to 30 ml). Since specific antivenins have become available, the mortality from scorpion

stings has decreased dramatically, especially in children.

Insects (Hexapoda) The insects are the most successful animal class on

Earth, contributing to more than 90% of the biomass of terrestrial animals. Many of the numerous species are active or passive toxic. Although the amount of toxin in one individual is not dangerous to humans, many fatal cases occur after insect stings, such as from bees and wasps. In almost all cases, this is due to a systemic allergic reaction, resulting in an anaphylactic-shock reaction. Some species contain a lot of interesting chemically toxins that have structures more common with the plant kingdom rather than with animals. Some myriapods (millipedes and centipedes) contain repellents consisting of hydrocyanide, nitriles, phenols, quinones, and aromatic nitro compounds. Saturated and unsaturated hydrocarbons, alcohols, esters, and fatty acids were observed in the repellents of bedbugs (Hemiptera).

The toxin of the spanish fly (Lytta vesicatoria), which is actually a bug, is famous as an aphrodisiac. The active toxin is cantharidin, an inner ether of tetrahy- drophtalic acid anhydride (Fig. 4). The compound ex-

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erts characteristic blisters on the skin and is a strong mucous-membrane irritant. Poisoning in humans are not rare and in most cases is due to an overdose of pulverized bugs. The stimulating action is due to an irritation of the mucous membrane of the urethra, causing spontaneous erections. After oral uptake of toxic amounts of cantharidin, strong irritation occurs in all parts of the intestinal and urogenital tract. The symptoms consist of the formation of blisters on the tongue and throat, accompanied by salivation, nausea, vomiting, and spastic contractions of musculature in the stomach and intestine. The mucous membrane of the urogenital tract gets irritated and hemorrhages. Tachycardia occurs, followed later by bradycardia. Tetanic convulsions, delirium, and coma may also occur. The lesions on the gastric and intestinal epithelium may lead to intraluminal accumulation of fluid followed by a hypovolemic shock. The lethal dose of pulverized spanish flies for an adult is several grams; however, 10 mg of pure cantharidin may be lethal. A case has been reported in which a patient survived 75 mg. In absence of a specific antidote the therapy is symptomatic.

Some insects take up toxic compounds from plants and accumulate it in their bodies. Sometimes the uptake occurs in the larval stage and persists during the metamorphosis. In these cases the adult insects contain the toxins without consuming the toxic plants. This is observed in some species of butterflies, which consume plant leaves in the larval and nectar in the adult stage. Toxic compounds are often found in plant leaves but are rare in plant nectar. The toxins protect the insects against predators. Other insects accumulat- ing toxic plant constituents are bed bugs and some bug species. Their toxic food plants are oleander (cardiac glycosides), Aristolochia clematitis (aristolochic acid), and Senecio ssp. (unsaturated pyrrolizidine alkaloids).

Hymenoptera In this genus are ants, bees, wasps, and hornets.

The insects have a special venomous apparatus, con-

sisting of a venom gland and an injecting tool, the sting. Stings by bees and wasps can happen to almost everyone once in his or her life. Although the stings are often very painful, they are normally harmless, unless hundreds occur at the same time. Nevertheless, there are no other animals, scorpions and snakes in- cluded, that are responsible for so many fatal cases. The reason is that many people develop an allergy to the venom after the first event. The allergic reaction gets worse after every sting and it may result in an anaphylactic-shock reaction. Patients with a known history of an allergy to the stings of bees or wasps should be extremely careful and carry a kit in their pockets containing an antihistamine and epinephrine, in case of a sting from these insects.

The venom of Hymenoptera contains biogenic amines, kinines, peptides, and enzymes, such as phospholipases and hyaluronidase. The amines are responsible for the pain reaction, whereas the enzymes result in a local destruction of tissue connection. Kin- ines are found only in the venom of wasps and hornets and are responsible for a decrease of the blood pressure.

The venom of bees is well investigated and the structure of the toxic peptides is known. Apamin, making up 2% of the dry weight, consists of 18 amino acids. It acts at the central nervous system (CNS), causing a hypermotility. With 50% of dry weight, mellitin is the main constituent of bee venom. It is a strong basic peptide (pKa 10) with 26 amino acids. Interestingly the peptide lacks sulfur containing (Cys, Met), aromatic (Phe, Tyr), and heterocyclic (His) amino acids. It acts as a strong detergent and has, therefore, a hemolytic activity. Additionally the toxin damages mast cells and platelets. Mellitin also con- tracts the smooth muscles. Small doses stimulate the heart, which is inhibited by high doses. The LDs0 in mice after iv injection is 3.5 mg/kg. The third peptide in bee venom is the mast cell degranulating peptid (MCDR). It contains 22 amino acids and makes up 2% of the bee venom. The LDs0 (in mice, iv) is 40 mg/kg. This peptid destroys mast cells, which release inflammatory agents, such as histamine, serotonine, and kinines.

Ants (Formicidae) In this family are biting and stinging representa-

tives. The latter inject their venom, similar to bees and wasps. Ants consist of approximately 6000 species, most of which are harmless to humans. Fire ants (So- lenopsis), which are endemic in the southern parts of the United States are dangerous. The reaction after a sting may vary from a weak skin rash to a severe dermatitis, accompanied by local inflammation and


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necrosis. Anaphylactic reactions may occur after repeated stings. Different toxic piperidine derivatives have been isolated from the venom of fire ants.

Amphibia

Most amphibians are classifiable as toxic. Their toxins are thought to protect their hosts from predators and from skin contamination from microorganisms. The toxins are produced in special skin glands. They are impressive because of their diversity in interesting chemical structures and biological actions. Some amphibians (Dendrobatidae) produce the most potent toxins occurring in animals.

Indol derivatives The skin of some toad species (Bufonidae) contains

biogenic amines, related to serotonin. Among these are bufotenin (N, N-dimethyl serotonin) and its methyl ether. Other compounds are bufotenidine, bu- foviridine, and the tricyclic derivatives bufothionine and dehydrobufotenine (Fig. 5).

N-alkylated indol derivatives have a high affinity to serotoninergic (5-HT2-) receptors in the CNS. This is the reason for their psychodelic action. The compounds exert an LSD-like action, with hallucinations and spectral visions. O-Methylbufotenin is most active in this regard, with an effective dose of 50/zg/kg. Recently it has been shown that the N-methylation of serotonin takes place in the CNS of mammals under

the control of the enzyme indolethylamin-N-methyl- transferase. It is suggested that the resulting bufotenin plays a role in certain psychotic diseases, such as schizophrenia.

The hallucinogenic action of extracts prepared from toads was known long ago and many witch recipes are based on it. An example is given in the following two text phrases from William Shakespeare's Macbeth.

Third Act: 9 . . Round about the cauldron go; In the poison'd entrails throw. Toad, that under cold stone Days and nights has thirty-one Swelter'd venom sleeping got, Boil thou first i' the charmed pot.

Fifth Act: 9 . . The juice of toad, the oil of adder. Those will make the younker madder.

Obviously it was well known at that time that the slime of toads is rich in compounds acting on the brain.

The toxins of toads are not dangerous to humans under normal circumstances because the penetration through the skin is low after touching the animals. Rodents are less sensitive than humans after systemic application of the toxins. The lethal doses of bufotenin and 5-methylbufotenin in mice (ip) are 290 m g / k g and 115 rng/kg, respectively. Much less sensitive are the amphibians themselves. Frogs tolerate up to 2500 m g / k g without any symptoms, whereas doses of 1

968 Westendorf

m g / k g are lethal to sheep. Death occurs after a series of tremors and convulsions and, finally, respiratory arrest.

Steroids The chemical structure of the steroid-like toad tox-

ins is related to cardiac glycosides present in some plant species (e.g., oleander and purple foxglove). The toxins are synthesized in the parotis glands and excreted with the saliva. Representatives of genins (bu- fotaline) and glycosides (bufotoxin) are shown in Fig. 6. The biological action is mainly targeted on the heart and consists of an inhibition of Na§ resulting in a negatively chronotropic and inotropic action. High doses cause arrest. Beside the action on the heart, the toxins act as local anesthetics. The lethal doses are relatively independent of the species and vary between 200-1000/~g/kg.

An interesting group of steroids with a ring system consisting of seven carbon atoms occurs in some species of salamanders. The benefit for the animals is most likely related to its antibiotic action. A pronounced inhibition of the growth of bacteria and fungi was demonstrated. The compounds are, however, also toxic to higher organisms. The LD50 values for most rodents is below several mg/kg. The action is targeted to the CNS. Muscle contractions and arrest of breathing occur after application of the toxins.

Alkaloids The most toxic amphibians live in the rain forest of

Central and South America and belong to the families Dendrobatidae and Phyllobatidae. They are small, very colorful frogs, climbing on branches (Greek den- dros) or leaves (Greek phyllos), where they wait for insects. Because of the pretty colors, which function as a warning signal to their possible predators, they are also called as color frogs; however, they are better known as poison dart frogs, because the Indians of Colombia and Panama use the toxins on hunting darts. The Choco imitate the whistling of the frogs, which attracts the animals. To protect the skin of their palms from the extremely toxic slime, they cover them with leaves before catching the frogs. The animals are then speared on pointed sticks and put near a fire. This extreme stress causes the frogs to excrete lots of their toxin. The toxic slime is spread on the darts by direct contact with the frog's skin. About 50 darts can be toxified by a single frog. The most toxic species (Phyllobates terribilis) contains enough poison to kill 20,000 mice or 10 humans.

The toxins belong to the alkaloids and are divided into batrachotoxins (from Phyllobates aurotaenia), pum- iliotoxins (from Dendrobates pumilio), and histrionico-

toxins (from Dendrobates histrionicus) (Fig. 8). All of these are strong nerve and muscle toxins. Batracho- toxin is among the most potent natural toxins (LD50 in mice, sc, 2/~g/kg) known so far. The action is related to an inhibition of the sodium channel of nerve and muscle cells, which is unable to collapse after an action potential occurred. This will result in a permanent depolarization. The action is opposite to that of tetrodotoxin, which inhibits the opening of the sodium channel.

Pumiliotoxin B causes the liberation of Ca 2+ from intracellular reservoirs of muscle cells and inhibits the reabsorbtion into the endoplasmatic reticulum. This causes long-acting muscular contractions. The spasmogenic action is promoted by an increase of the Ca 2§ influx into nerve cells, followed by an increase in the liberation of neurotransmitters. Pumiliotoxin C, gephyrotoxin, and the histrionicotoxins inhibit the transmembraneous flux of Na § and K § initiated by ace- teylcholine at the neuromuscular endplate, resulting in a paralysis of the skeletal muscles.

Peptides The skins of most amphibian species contain a va-

riety of pepfides related to biogenic peptides. Among these are physalein, caerulein, and ranatensin. Like other biogenic peptides, present in mammals, such as bradykinin, the compounds contract smooth muscles, decrease the blood pressure, and increase the permeability of capillary walls.

Reptiles Lizards

Two poisonous species of lizards live in the southern part of the United States and in northern Mexico, Heloderma suspectum and Heloderma horridum. The animals inject their venom during a bite, which mainly consists of serotonin and a variety of enzymes. Among these are hyaluronidase, phospholipase A, aminooxidase, and proteases. The LDs0 (in mice, ip) of the raw toxin is 1.4 mg/kg. Fatal cases are very rare. In most cases the victims recover spontaneously a few days to 2 weeks later. If large amounts of venom are injected, the blood pressure and the circulating fluid may decrease, resulting in a responding tachycardia. Death may result from a lack in ventricular contractil- ity. Specific antivenins are not available.

Snakes Human beings have been fascinated by snakes

throughout time, due to the deadly hazard associated


0 I / N H ~ C O - ( C H 2 ) 6 - C O - N H - C H - ( C H ~ h - N H - C \ \

I N H C O O H

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with many snake species. Among the 3500 species there are only 375 (i.e., 10%) that are venomous. These snakes are subdivided into four classes.

1. Elapidae (e.g., coral snakes, kraits, mambas, and cobras).

2. Viperidae (e.g., vipers). 3. Crotalidae (e.g., rattlesnakes). 4. Hydrophiidae (e.g., seasnakes).

Venomous snakes contain a venom apparatus consisting of venom glands, which are comparable to the parotis glands, and teeth that function like injection needles. Approximately 1.7 million accidents with venomous snakes occur every year worldwide and 40,000 (2.35%) end with the death of the victim. The mortality rate is dependent on the snake species.

European viper (Vipera berus) 1% Indian cobra (Naja naja) 32% Black mamba (Dendroaspis polylepis) ~100%

An overview about the toxicity of snake venoms is given in Table 2. The ratio of the injected amount of venom during one bite and the toxic potential of the venom (the lethality coefficient of a bite) is the same for the Indian cobra and black mamba; however, the lethality observed is different. This is due to the fact

that mambas bite preferentially at the head and neck whereas cobras prefer the legs and arms. In the latter case it is possible to prevent the distribution of the venom by tying up the affected extremity. With respect to the lethality coefficient, bites from European adders should not be lethal to humans at all. The few lethal events reported may be due to an unfortunate direct application of venom into a greater blood vessel or an extreme sensitivity of the victim. Repeated bites may also cause in an anaphylactic-shock reaction.

The composition of snake venom is rather compli- cated. The different components often have a synergistic action. The actually toxic compounds are peptides with a chain length of 60-70 amino acids. The peptides contain numerous disulfide bridges, responsible for the formation of a characteristic three-dimen- sional structure. Like at all other higher venomous animals, the toxic action of the peptides is directed preferentially against the central and peripheral nerve system. This will result in a fast paralysis of the prey or attacker.

The toxins of Elapids and Hydrophiids are preferentially directed against acetylcholine receptors at post- synaptic membranes and neuromuscular endplate. /3-Bungarotoxin (Bungarus multicinctus) acts at the presynaptic membrane, resulting in a gradual depletion

HN OO V.O H HN ~ S a m a n d a r i n S a m a n d a r i d i n

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970 Westendorf

~I CH3 H CH3 ~ C ~ \

H H"-,~ K'~ O 1-t '~ HO-~'~ A ~ ] H a c ~ N

'H ~ " I : I I N--CH~

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Batrachotoxin Pumiliotoxin B Pumiliotoxin C

C ' --H

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Histrionicotoxin Gephyrotoxin

of acetylcholine. The toxins of some viper species result in cardiovascular shock. It is suggested that their site of action is located in the medulla oblongata. These toxins are different from the others also in that their chain lengths are shorter (30-40 amino acids). A variety of enzymes occurring in snake venom promote the distribution of the toxic peptides by disintegrating the tissue at the bite side.

About 25 different enzymes have been isolated from snake venom so far. Their catalytic action is cat- egorized into four groups (Table 3).

Proteolytic enzymes catalyze the hydrolysis of proteins. They are mainly distributed in crotalids and responsible for the tissue necrosis reactions often observed after rattlesnake bites. Fewer of these enzymes are present in Viperides and the venom of Elapids and

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Ejected amount of Species venom/bite Lethal dose for humans

Elapidae Naja naja (Indian cobra) 210 mg 15 mg Naja bungarus (King cobra) 100 mg 12 mg Bungarus candidus (Malayan krait) 5 mg 1 mg Bungarus caeruleus (Indian krait) 10 mg 6 mg Dendroaspis polylepis (Black mamba) 1000 mg 120 mg

Viperidae Vipera russeli (Russel's viper) 70 mg 42 mg Vipera carinatus 12 mg 5 mg Vipera berus (European viper) 10 mg 75 mg

Crotalidae Bothrops neuwiedii (Urutu) 200 mg 200 mg Trimeresurus gramineus 14 mg 100 mg

aAccording to Habermehl (1994).


Enzyme Occurrence

Proteolytic enzymes Proteinases Proteases Peptidases Endopeptidases Argininesterhydrolase

Nucleotidases Phosphomonoesterase

Phosphodiesterase 5'-Nucleotidase NAD-Nucleotidase DNase RNase

Tissue-disintegrating enzymes Collagenase Hyaluronidase Phospholipasen

Other enzymes Acetylcholinesterase Lactatdehydrogenase L-Aminos/iureoxidase Thrombin-like enzymes

Crotalidae, Viperidae Crotalidae, Viperidae Crotalidae, Viperidae Crotalidae, Viperidae Crotalidae, Viperidae,

Hydrophiidae

All venomous snakes (except Colubrides)

All venomous snakes All venomous snakes All venomous snakes All venomous snakes Rare (exp. Naja oxiana)

Crotalidae, Viperadae All venomous snakes All venomous snakes

Elapidae, Viperidae Elapidae All venomous snakes Crotalidae, Viperidae

Hydrophiids is almost free of it. Especially after bites of seasnakes, no necrotic reactions are observed.

Nucleotide-degrading enzymes are present in almost all snake venoms. They destroy fundamental energy-carrying molecules (ATP), second messengers (cAMP), and redox-coenzymes (NAD, NADH, NADP, NADPH). These enzymes interfere, therefore, with the most fundamental biochemical processes, which makes them strongly cytotoxic. Enzymes, such as acetylcholinesterase, L-aminoacidoxidase, or lactatdehydrogenase, occur in some snake venoms.

Some enzymes act on the connective tissue. Among these are collagenase and hyaluronidase, which cause the tissue next to the bite side to loosen. Phospholi- pases exert a destructive action on cell membranes. This enables cytotoxic enzymes to enter the cells. The destruction of red blood cells by these enzymes causes a severe hemolysis. The venom of Viperidae and Cro- talidae contains thrombin-like enzymes, causing a clot- ting of plasma or pure fibrinogen solution in vitro.

The clinical course of a snake bite is dependent on a number of variables, such as the age, body weight, and constitution of the victim, as well as the toxicity and size of the snake. The location of the bite is also important. Systemic effects, such as disturbances of

the cardiovascular system or CNS, will occur almost immediately if the bite hits a blood vessel. Severe necrosis accompanied by great pain often occurs after bites of Crotalidae and Viperidae. If a patient has a history of other snake bites, an anaphylactic-shock reaction may occur.

Many patients survive snake bites today because of the availability of specific antivenins. It is, however, most important that not too much time be lost before the beginning of treatment. If the symptoms of the intoxication occur soon, compression of the affected extremity should be initiated if possible. It is important that the compression affects only the veins and lymph drains and not the arteries. The incision of the bite location is not recommended. This will cause lengthy bleeding and promote the invasion of the venom into the bloodstream. The application of a sedative may be useful to decrease the patient's irritation. Peripheral or central analgesics should be given if great pain is present. Because of the possibility of allergic reactions, the infusion of an antivenin should only be performed in serious cases of envenornation (25% of all snake bites). Anaphylactic-shock reactions with fatal outcomes occur in approximately 0.3% of the cases.

The amount of the antivenin is dependent on the amount of the venom injected by the snake and not on the body weight of the patient. It may vary between 10-300 ml. Monovalent as well as polyvalent antivenins are available. If possible, a monovalent antivenin should be used.

TOXINS OF P R O T O Z O A AND ALGAE

Marine phytoplankton contain numerous species that produce strong toxins. Most belong to the dinoflagellates. Toxins are mainly observed in the genus Protogonyaulax, Gonyaulax, Pyrodinium, Gambierdiscus, Gymnodinium, and Ptychodiscus. At certain times of the year these algae proliferate enormously ("red tide"). This may result in a considerable loss of the endemic fish fauna. Human poisoning may occur via the food chain from mollusks to shrimps to fish.

Saxitoxin

Dinoflagellates, such as Gonyaulax tamarensis, Gon- yaulax catenella, Gonyaulax excavata, Ptychodiscus (Gym- nodinium) breve, and Ptychodiscus veneficum, contain the extraordinarily toxic compound saxitoxin (Fig. 9). This compound is possibly synthesized by bacteria, living in symbiosis with the dinoflagellates. The phy-

972 Westendorf

H2N"~ O- H

OHN ~'~ NH + ~.. L . , ~:NH2

Saxitoxin ~: ~..,~,~ . . . . . . . . . . . . . .

The mechanism of the toxicity of saxitoxin is similar to tetrodotoxin. Both compounds are sodium- channel blockers. They inhibit the transmission of excitation signals from pre- to post-synaptic neurons and to muscle cells. The LD50 for mice (i.p.) is 10/~g/ kg. The lethal dose for humans is approximately 1 mg. This amount may be eventually present in only a few mussels. In the United States and Canada, the limit value is 80/~g/100 g mussel meat. The treatment of saxitonin poisoning consists of gastric lavage and symptomatic treatment, especially artificial respiration.

toplankton is then trapped by mussels, which concentrate the toxin. The mussels themselves are not sensitive to the toxic action of the poison. At certain seasons, mainly in the summer, poisoning of humans occurs after they consume the mussels. The disease is known as paralytic shellfish poisoning. The symptoms begin with a prickling of the tongue and lips, followed by a paralysis of the musculature in the mouth. Later the muscle paralysis progresses all over the body. When the paralysis affects the diaphragm, death occurs from suffocation.

Brevetoxins

In the Gulf of Mexico a phenomenon occurs at certain times, called "red tide". It is caused by a massive proliferation of the dinoflagellate Ptychodiscus (Gym- nodinium) breve and accompanied by the death of thousands or millions of fishes. Ptychodiscus contains a variety of toxins, which are different from saxitoxin with respect to their chemical structure as well as toxic action. The brevetoxins (Fig. 10) consist of an unusual structure of linearly linked polycyclic ethers. The toxins bind to the lipophilic domain of the sodium channel of the synapses and lead to depolariza-

OH ~~/CHO

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0 , 0

0 OH .~//CHO

Brevetoxin-B 0 , , ~ ~ 0

, 0 0 0 , 0

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O H " - . . . . .~ -. I OH

OH

tion. The resulting liberation of acetylcholine at the neuromuscular endplate causes fascicular twitching. If the depolarization persists, the nerves will lose their irritability completely and paralysis occurs. The increased liberation of noradrenalin at the heart causes ventricular arrhythmia and fibrillation. The action of tetrodotoxin and local anesthetics are antagonistic to the depolarizing action of brevetoxin. Related to brevetoxin are the dinophysistoxins and ocadaic acid (Fig. 11), which also occur in dinoflagellates.

Cigateratoxin Poisonings from edible fishes, such as barracudas,

snappers, and sharks, occur in some tropical marine areas. The toxin responsible for these cases is called ciguateratoxin and is found in the dinoflagellate (Gambierdiscus toxicus), living epiphytically on macrophytic algae in reef areas. The algae are taken up by herbivorous fishes, which are then consumed by predatory fishes. The poison accumulates via the food chain and is stored in the liver and gonads of these fishes. Considerable amounts of the toxin may, however, also be present in the muscular tissue and cause poisoning after consuming the fishes.

The lethal dose of ciguateratoxin is extremely low (in mice, ip, 45 ng/kg). The structure of the long stretched molecule, which is related to some part to ocadaic acid, is shown in Fig. 12. The action is directed to the sodium channel and consists of an increase of the permeability of Na +. This will cause ex- citatory reactions. The action of ciguateratoxin is antagonistic to tetrodotoxin and saxitoxin, both of which inhibit the sodium channel.

The symptoms of ciguatera poisoning begin with irritations of the mucous membranes in the mouth and throat, followed by a generalized weakness, diarrhea, rigor, fever, motion, insomnia, and shortness of breath. If lethal doses are taken up, death occurs by arrest of breathing. After the uptake of sublethal doses, the symptoms may persist for months. In the

absence of any causal therapy, the treatment has to be symptomatic. The infusion of mannitol ( l g /kg in 45 minutes) may be advantageous. The protective mechanism is possibly due to an inhibition of the formation of edemas in the neuronal tissue.

Another toxin, maitotoxin, often occurs concomi- tantly with ciguateratoxin. In contrast to ciguateratoxin the action of maitotoxin is directed to the calcium channel. The compound increases the permeability of nerve and muscle cells for Ca 2+, resulting in a calcium overload of these cells. This causes the liberation of neurotransmitters in the nerve cells and lead to long-acting muscle contractions and heart arrhythmia.

M Y C O T O X I N S

The fungi are divided into lower (monocellular) fungi (Ascomycetae) and higher (multicellular) fungi (Basidiomycetae). About 300,000 species have been characterized so far. Most produce a large spectrum of secondary metabolites. Among these are also many toxic compounds.

Toxins from Ascomycetae Many lower fungi produce toxic metabolites that

are distributed in the environment, most probably to inhibit the growth of other microorganisms. Poisoning by mycotoxins is a common phenomenon, because molds of the genus Aspergillus, Penicillium, and Fusar- ium often contaminate food. In industrial nations, such food will normally go to waste. In many devel- oping countries, however, where food is scarce, people will eat it regardless of mold contamination. The growth of molds is supported in such countries by the often hot and humid climate.

The actions of mycotoxins vary from weak irritation to severe damage. Some of the compounds are even teratogenicic and carcinogenic. A summary of the most important mycotoxins is given in Table 4.

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HO

N H~ ~ . . ~ ~ " ' ~ ~ u ~ y OH HO ~ OH

-. HO. ~ " L . ~ .OH "-oH "I i

H O ~ . ~ . O H O - i /

O'H IOH ~ O H

HO | .OH I i O O CH~ OH CHa OH " ~ ~ O..../x..

H ~ c ~ O . / ~ ~ ~ . / ~ ~ . .~ /OH ~ / "r" v v "r" "OH O" Y o ; H~C-- -~ i CH~ OHoH CH, HO Nv~-.OH

OH HO "_'oHOH OH

Ciguateratoxin OH

The presentation of the mycotoxins in the following will be in botanical order, although there are many overlaps in compounds.

Aspergillus Species Aflatoxins

The fungi Aspergillus flavus, Aspergillus parasiticus, and Aspergillus oryzae synthesize a variety of related mycotoxins known as aflatoxins (Fig. 13). The fungi often contaminate food, such as peanuts, wheat, rice, corn, and soybeans. The aflatoxins M 1 and M 2 occur also in the milk of cattle and sheep, if the animals' food is contaminated with the fungi. A limit value for the aflatoxin concentration in many countries is 50 ng/liter. Endemic poisoning from aflatoxins occurs in animals as well as in humans. The target organ of most aflatoxins is the liver. The aflatoxins B1, G1, and M1 are converted under the catalytic action of cyto- chrome P450 to highly reactive epoxides, which then form covalent adducts with nucleophilic molecules of the liver cells. AFB~ forms C7 adducts with the gua- nine moieties of DNA and RNA. The saturated afla-

toxins G2 and M 2 a r e less toxic and not carcinogenic. AFB 2 is, however, partially converted in the liver to the unsaturated and highly toxic AFB1.

After the uptake of high doses of aflatoxins, liver necrosis occur and the victim may die from liver failure. Damage to the kidney tubules occur sometimes. The lethal dose for humans is approximately 1-10 m g / k g AFB 1. The chronic uptake of smaller doses may cause liver cirrhosis or liver tumors. The daily amount of A F B 1 causing liver cirrhosis in children is 9-18/~g. The sources of the toxin are often contaminated peanuts. Liver damage was also observed in infants whose lactating mothers consumed aflatoxin- contaminated food. AFB1 is the most potent hepato- carcinogen in rats. Sufficient evidence of the hepato- carcinogenic action in humans was derived from epidemiological studies. A correlation was observed between the excretion of aflatoxins in the urine and the incidence of hepatocarcinomas (HCC) (Fig. 14). Very high incidences of HCC occur in some African countries, such as Mozambique, Swaziland, Kenya, and Uganda, where the aflatoxin contamination of the food is high.


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Aflatoxin B 1 A. flavus, Aflatoxin B 2 A. parasiticus, Aflatoxin G 1 A. oryzae, Aflatoxin G 2 P. puperulum Aflatoxin M 1 A. flavus Aflatoxin M 2 Aspertoxin A. flavus, A. versicolor Citreoviridin P. citreo-viride Citrinin P. citrinum Cyclochlorotin P. islandicum

Cytochalasin A Helminthosporium Cytochalasin B dematioideum Cytochalasin C Metarrhizium anisopliae Cytochalasin D Zygosporium mansonii Cytochalasin E A. clavatus Islanditoxin P. islandicum Luteoskyrin Maltoryzin A. oryzae

Moniliformin Fusarium ssp. Ochratoxin A A. ochraceus Patulin Penicillium ssp. Penicillic acid Penicillium ssp. Roquefortin P. roqueforti Rubratoxin A P. rubrum

Rubratoxin B P. rubrum Sterigmatocystin A. nidulans, A.

versicolor Trichothecenes Fusarium ssp.

1.7 mg/kg (rat, po) 84.8/~g/50g (duck I day old, po) 39.2/~g/50g (duck 1 day old, po)

172.5/~g/50g (duck, 1 day old, po) 16.6 ~g/duck (duck, 1 day old, po) 62/~g/duck (duck, 1 day old, po) 0.7 ~g/egg (duck) 3.6 mg/kg (rat, sc)

67 mg/kg (rat, sc) 470/~g/kg (mice, sc)

1.9 mg/kg (mice, ip) 2.6 mg/kg (rat, ip)

338/~g/kg (mice, iv) 145 mg/kg (mice, ip)

3 mg/kg (mice, ip)

29 mg/kg (mice, ip) 20 mg/kg (rat, po) 30 mg/kg (rat, po)

100 mg/kg (mice, po) 18 mg/kg (mice, ip) 6.6 mg/kg (mice, ip)

3 mg/kg (mice, ip) 800 mg/kg (mice, po)

Hepatotoxic, Nephrotoxic

Hepatocancerogenic

Hepatotoxic, hepatocancerogenic

Hepatotoxic, hepatocancerogenic Neurotoxic Hepatotoxic, nephrotoxic Respiration and circulation toxin,

hepatotoxic Damage of cytosceleton, teratogenic

Hepatotoxic, hepatocancerogenic Hepatotoxic, hepatocancerogenic Hepatotoxic, nephrotoxic,

neurotoxic Local irritatant Nephrotoxic Local irritant Hepatotoxic, cytotoxic Neurotoxic Local irritant, mutagenic Teratogenic Hepatotoxic Hepatotoxic, hepatocancerogenic

Local irritant, hematotoxic, neurotoxic

S teri gmatocystin

Sterigmatocystin is structurally related to the aflatoxins (Fig. 15), and occurs in Aspergillus versicolor, Aspergillus nidulans, and Aspergillus bipolaris, which, together with aflatoxin-producing fungi, frequently contaminate food. Although the toxic potency of sterigmatocystin is less than the aflatoxins, the former compound is usually present in much higher concentrations. The mode of action is similar to that of the aflatoxins. The compound damages mainly the liver and, additionally, the kidney and the myocardium. Liver tumors in rats were observed after long-term oral treatment with the compound. The metabolic conversion (hydroxylation) of sterigmatocystin leads to aspertoxin (Fig. 15), which is also toxic.

Patulin

The mold species Aspergillus clavatus, Aspergillus gi- ganteus, Penicillium patulinum, Penicillium expansum, and Penicillium urticae produce a toxin called patulin (Fig. 16). It was observed in flour, meat, and particu- larly in apple juice. The toxin has a high affinity to SH groups and damages cell membranes especially. Membrane-bound ATPases are inhibited. Skin contact results in local irritation. Mucous membrane irritation, nausea, vomiting, and diarrhea occur after oral consumption of contaminated food. Edemas and hemorrhages of the lung and brain were observed after oral application of patulin in experimental animals. The amounts usually occuring in hu m an food is not sufficient to cause these symptoms.

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0 0

0

Aflatoxin G~

0 0 0 0

R 0 ~ 0

R = H Aflatoxin B~ Aflatoxin G=a R = OH Aflatoxin M~

O O

OCH~

0 0 0 0

o I R 0

oc.

Aflatoxin G~ R = H Aflatoxin B~ Aflatoxin B=a R = OH Aflatoxin M~

A carcinogenic action of patulin could not be demonstrated in laboratory animal after either oral or in- traperitoneal application. Sarcomas, observed after s.c. injection of patulin in rats, were more the result of a local irritation rather than a carcinogenic action of the compound. A teratogenic action was observed only in chicken embryos but not in mammals. How- ever, chromosomal aberrations in the bone marrow were observed in Chinese hamsters after treatment with patulin.

Ochratoxin A Aspergillus ochraceus frequently contaminates cere-

als, peanuts, and vegetables. The mold synthesizes a variety of structurally related toxins, called ochra- toxins. Especially toxic is the chlorine-containing ochratoxin A (Fig. 17). The phenylalanyl moiety of the molecule binds to the enzyme phenylalanyl-t-RNA- synthetase, which results in an inhibition of the protein synthesis. This mechanism is most probably responsible for the observed teratogenic action of the compound in mice. Malformations occurred mainly in the CNS. The application of sublethal doses in young chickens leads to damage of the hematopoietic system. Immunosupressive effects were also observed in mice after i.p. application of 10/zg/kg ochratoxin A.

The organs especially affected by ochratoxin are the kidneys. Necrosis occurs in the proximal tubules, resulting in severe inhibition of the kidney function, finally leading to anuria. An endemic nephropathia observed in humans and livestock living in some

Mediterranian countries (e.g., Bosnia and Croatia) correlated with the ochratoxin A content of the food. Considerable amounts of the toxin were also observed in the meat of pigs.

Ochratoxin A is not genotoxic in Salmonella or yeast. However, tumors (adenomas) were observed in the livers and kidneys of mice fed a diet containing 40 ppm of the toxin. In rats only a few kidney but no liver tumors were observed.

HCC - incidence (per year and 100.000 people) 20

10

5

(3

J - / ,.

I I

0 50 100 150

Daily uptake of Aflatoxin B1 (ng/kg)

200


o oH 0 0

OH O~~OH

Sterigmatocystin Aspertoxin

Maltoryzin and Kojic Acid The fungus Aspergillus oryzae is used in eastern

Asia for the fermentation of foods and spices, such as soy sauce, sake, and miso. The fungus synthesizes the mycotoxins maltoryzin and kojic acid (Fig. 18). In the foods the concentration of the mycotoxins remains normally below critical values. Of greater concern is the contamination of food for the livestock. Acute toxic doses result in convulsions and arrest of breathing whereas sublethal doses damage nearly all parenchymatous organs and the CNS. Kojic acid is mutagenic in Salmonella typhimurium.

Penicillium Species Citrinin

Citrinin, an antibiotic active compound (Fig. 19) is synthesized by the fungi P. citrinum, P. viridicatum, P. expansum, P. notatum, P. citreoviride, and P. chryso- genum. These species prefer moderate temperatures. Therefore, their occurrence is limited to the moderate climate zones. Citrinin is also produced by some As- pergillus species (A. candidus, A. niveus, A. terreus, and A. flavipes). The antibiotic action of the compound is not used therapeutically because of its considerable toxicity. In rats acute toxic doses were demonstrated to cause vasoconstriction, bronchoconstriction, and

fascicular twitching. Sublethal doses, especially after chronic administration, lead to damage of the proximal renal tubules, resulting in a progressive renal dysfunction. It is suggested that citrinin is accumu- lated in the renal tubules by the acid transport carrier. The cytotoxic action is probably based on an inhibition of RNA synthesis.

Damage also occurs after citrinin uptake at other organs, such as liver, spleen, and bone marrow. Tera- togenic effects were demonstrated in rats, mice, and chickens. Adenomatous hyperplasias were observed in the liver and kidneys of rats after long-term treatment with citrinin. In tissue culture (V79 cells), the compound produced chromosomal aberrations after the addition of rat liver microsomes ($9).

Penicillic Acid Penicillic acid is, like patulin, an a,/3-unsaturated

lactone. The compound (Fig. 19) occurs in numerous Aspergillus and Penicillium species, which often contaminate human and animal food. The cytotoxic compound has a high affinity for SH groups and depletes glutathion. This is the reason for the hepatotoxic action, observed after higher doses. The administration of glutathion or cystein has, therfore, a protective action against poisoning from penicillic acid. A hepato-

OH

Patulin

o

0~- CH3 HHO~ O~H 0

Ochratoxin A

978 Westendorf

~~ CH2OH OH O

HO O H O \ ~

Kojic acid Maltoryzin

carcinogenic action was observed in mice after chronic application of the compound.

Citreoviridin Rice is often contaminated by the mold Penicillium

citreoviride, which produces the mycotoxin citreoviridin. The compound (Fig. 19) has a neurotoxic and cardiotoxic potential and is responsible for the endemic occurrence of the heart disease "Cardiac beri beri." Damage of the liver and kidneys have also been correlated with the uptake of citreoviridin. It is suggested that the compound inhibits a mitochondrial ATPase, which is important for the cells, energy support. Especially sensitive are nerve and muscle cells, which have a higher energy requirement to support their electrical potentials.

Luteoskyrin and Rugulosin Two other molds frequently contaminate rice in

Asia, Penicillium islandicum and P. rugulosum. The color of the rice turns to yellow after being contaminated, which is caused by the mycotoxins luteoskyrin (P. islandicum) and rugulosin (P. rugulosum). The two bis-anthraquinones (Fig. 20) are hepatotoxic and he- patocarcinogenic in laboratory animals. It is believed that a considerable percentage of liver tumors in Asia is due to food contamination with these compounds. Both compounds have been demonstrated to accumulate to a high degree in the liver. It is believed that luteoskyrin induces liver injuries via the formation of active oxygen species generated in the process of au- toxidation of the luteoskyrin semiquinone radical, which is produced in the one-electron redox systems catalyzed by the liver NAD(P)H-dependent cyto- chrome reductases. Because the mycotoxins are not mutagenic, an epigenetic process via oxidative stress may be responsible for the hepatocarcinogenicity.

Islanditoxin (Cyclochlorotin) Islanditoxin, a mixture of closely related cyclic pep-

tides (Fig. 20) with a L-dichloroproline moiety, also occurs in Penicillium islandicum. The toxin is very potent in mice (LD50 of 0.45 mg/kg). The toxicity mainly targets the liver. The mechanism of action is based on a binding of the compound to actin fibers. After contact of the liver cells with islanditoxin, the shape of

OCH~ ~.~ ~CH~ I "/ IT H~C OH

O / ~ o ~ C H ~ (~H~ 0--~ "OH

CH~ Citreoviridin

OH H O O C ~ . ~ OCH~.. /H

O-- T N}/ "CH~ C H = ~ ---~'~O CH~ CH~ H~C

Citrinin Penicillic acid


OH O OH ~ CH3 OH O OH H3C I ~ ' : 0

OH O OH

(-) Luteoskyrin

OH O OH

~ ' ~ C H 3

H3C.

OH O OH

(+) Rugulosin

0

R1 O ~ R , R,~NH

' C l Cl R1 = CH2OH R2 = CzHs R3 = Cell5

Islanditoxin

the cells changes and numerous blisters occur at the surface of the cell membrane. After rodents are fed 50 /~g/kg/day, necroses at periportal liver areas occur, leading to cirrhosis and hepatomas. It has been demonstrated that the presence of chlorine in the molecule is essential for the toxic action.

Cyclopiaconic acid and Penitrem A The mold Penicillium cyclobium frequently contami-

nates cereal. It produces the neurotoxic compounds

cyclopiaconic acid and penitrem A (Fig. 21). The compounds seem to act at presynaptic sites in the CNS and to interfere with the neurotransmitters GABA, glutamic acid, and aspartic acid.

Fusarium Species Fusarium species are common molds contaminating

cereal, hay, and other liverstock food. The fungi produce a variety of extraordinarily toxic compounds,

H OH

Cyclopiazonic acid

H3C CH3 H2C -- ~ ~"'~O

H ~ O H

Penitrem A

980 Westendorf

exerting neurotoxic, immunotoxic, and cytotoxic actions.

Trichotecenes

The most important group of fusarian toxins is that of the trichotecenes (Table 5). These compounds form a family with more than 60 structurally related compounds divided into four subclasses. The compounds have in common an epoxy group at C-12, 13 and a double bond between C-8, 9. Some important examples are shown in Fig. 22. The toxic action is related to the nature of the side chain. The fact that the toxicity is almost the same after enteral or parenteral application indicates a good absorption from the GI tract. The toxicity of the derivative diacetoxyscirpenol increases from mice to rats to rabbits to guinea pigs. It is suspected that humans are even more sensitive.

The trichotecenes are cytotoxic compounds that bind to a 60S subunit of eucaryotic ribosomal proteins, resulting in an inhibition of protein synthesis. Procaryotes are much less sensitive. The epoxy group of the toxins is essential for the action. Hydrolysis of this group abolishes the activity. This is an important

inactivation pathway, taking place in liver cells. The side chain is important for the affinity of the toxins to the ribosomal-binding proteins. SH groups are involved in the binding process.

The high cytotoxic potential is responsible for the irritation of mucous membranes in the GI tract, causing nausea, vomiting, and severe diarrhea. After absorption, the toxic symptoms are dominated by the cytotoxic action on the bone marrow. The resulting im- munosuppression is responsible for many secondary effects observed in humans and livestock after consuming cereal contaminated with Fusarium species. Teratogenic actions were observed after the administration of some trichotecenes (T-2 and deoxyniva- lenol) to laboratory animals. T-2 also induced chromosomal aberrations in the bone marrow of Chinese hamsters. No mutagenic or direct carcinogenic action of trichotecenes could be observed; however, after in- itiation with DMBA the compounds acted as tumor promotors. Epidemiologic studies in South Africa re- vealed a correlation between the food content of deox- ynivalenol and the incidence of esophagus cancer. The mechanism could be either a tumor-promoting or im- munosuppressive action of the trichotecenes. An op-

al

R~ CH=Rz

Trichothecenes

R~ R2 R3 R~ R5 T2-Toxin OH OAc OAc H (CH3)2CHCH2OCO HT2-Toxin OH OH OAc H (CHB)2CHCH2OCO Diacetoxyscirpenol OH OAc OAc H H Neosolaniol OH OAc OAc H OH Nivalenol OH OH OH OH O Fusarenon X OH OAc OH OH O Diacetylnivalenol OH OAc OAc OH O Tetraacetylnivalenol OAc OAc OAc OAc O Dehydronivalenol OH H OH OH O Dehydronivalenol AC H OH OH O Trichothecin H CH3CH--CHOCO H H O Trichothecolon H OH H H O

~ ..... ~ ................. q~ii~!~ < < ~ ~ i ! ~ ~ ~ ~ i


Group Trichotecen Animal Mode of application LDs0 (mg/kg)

A T-2 toxin M o u s e ip 5.2 po 10.5

Rat po 5.2 Gu inea pig iv 1.2 Ch icken po 4.0 Trou t po 6.1

Diace toxysc i rpenol M o u s e ip 23.0 po 7.3

Rabbi t iv 1.0 G u i n e a p ig iv 0.37

B Niva leno l M o u s e ip 4.1 Deoxyn iva leno l M o u s e po 46.0

Duck sc 27.0 F u s a r e n o n X M o u s e ip 3.4

po 4.5 Rat po 4.4 Cat sc 5.0

C Cro toc in M o u s e po 1000 ip 810

D Ror id in A M o u s e iv 1.0 Ver rucar in A M o u s e iv 1.5

Rat iv 0.87 Rabbi t iv 0.54

Ver ruca r in B M o u s e iv 7.0 Ver rucar in J M o u s e ip 0.5

aAccord ing to Ueno (1985).

erating immune system is important as a natural defense system against cancer.

Moniliformin Corn is frequently contaminated wi th Fusarium

moniliforme, which leads to considerable losses of this cereal. The mold produces several toxins, of which moniliformin is most important. The compound is a cyclobutadiene derivative (Fig. 23) with a high toxic potential. After administration of lethal doses to rats, mice, and chickens, the animals die of arrest of

OH 0 ii H CH~

~ O H HO

Moniliformin trans-Zearalenon

!~:i ~ ................ ~:'~" "~::~ "~ ~:~:::":::::'~:~;~:r ~: ~:~!ill ~ ~i~ ~i~ ~': ~d4 !~ ~!'~ Ii~ ~ ~' ~i ~ili!i~:~:~ li~ ~i ~i~t ~ ~: ~'~ ~t ~ ~ ~ i l ~I ~!~i~ ~ ~ ~ l i

breathing. Sublethal doses lead to myocardial injury. The mechanism of action consists of an irreversible inhibition of the enzyme pyruvat dehydrogenase, resulting in an inhibition of the citric acid cycle and, thus, the energy support of the cells. Muscle, especially cardial, cells have an higher energy requirement than most other cells, which may be the reason for their special sensitivity to these toxins.

Zearalenon Fusarium gramineum is a mold that not only con-

taminates corn and hay but also other types of herbal foodstuff. The fungus produces a toxin, zearalenon (Fig. 23), which exerts an estrogenic action. Typical symptoms in female domestic animals consuming contaminated food consist of uterus hyperplasia, vul- vovaginitis, and a decrease in fertility (which also effects male animals). The milk of cows consuming contaminated hay may contain considerable amounts of zearalenon. Drinking contaminated milk causes an ac- celerated maturation of the genital organs in girls, a disturbance of the estrous cycle in adult women, and a decrease of fertility in men.

982 Westendorf

O OH O ii

, , , ,~ U,~ R

CH30 O OH I O

HOl t NH2

R = H: Daunorubicin R = OH" Doxorubicin

I . ~ OH

O

I ~ CH3

O C H ~ ~ O OH CH3 O

Aclacinomycin A

It was shown that zearalenon binds at the intracellular estrogen receptor of the uterus. The compound binds also to estrogen receptors in the hypothalamus and the pituitary gland. This results in a disturbance of the estrogen-feedback mechanism. The use of zearalenon as a substitute for estrogen in post-menopausal women was stopped after the observation of a carcinogenic action in laboratory animals. In the mean- time, however, it is well known that estrogen itself promotes the development of breast and uterine tumors. Zearalenon was teratogenic in rats and pigs. The malformations were especially prevalent in the skeleton. With respect to this observation, it should be noted that osteoporosis is a common complication in post-menopausal woman.

Toxins of Other Monocellular Fungi Cytochalasins

The cytochalsins form a class of structurally related mycotoxins produced by the fungi Helminthosporium dematioideum (cytochalasin A and B), Metarrhizium anisopliae (cytochalasin C), Zygosporium mansonii (cytochalasin D), and Aspergillus clavatus (cytochalasin E). Acute toxic doses initiate severe damage of the capillary walls, leading to massive loss of intravasal proteins, systemic edema, and shock. The compounds are useful tools in experimental pharmacology and cell physiology because they bind to and inhibit the function of tubulin and actin.

Antitumor Antibiotics The red-colored mycotoxins daunorubucin and

doxorubicin (Fig. 24) are synthesized by Streptomyces

peucetius and S. peucetius var. caesius, respectively. The compounds belong to the group of anthracyclines and are used therapeutically as antineoplastic agents. Dox- orubicin has a broad spectrum of activity and is used for the treatment of leukemia and several solid tumors, whereas daunorubicin is used almost exclusively for the treatment of leukemia. The yellow an- thracycline derivative aclacinomycin A (Fig. 24) is produced by Streptomyces galileus. This compound is also used for the treatment of leukoblastoses and some solid tumors. Although the biological action of the anthracyclines has been the subject of thousands of papers, the exact mechanism of action is not known. It is most likely the result of a summary of different actions. Among these are the intercalation between the base pairs in the DNA helix the formation of reactive oxygen species, and interactions with the cytoplasmic membrane. Similar to most other antineoplastic agents, the treatment with anthracyclines is accompanied by severe side effects, which are mainly directed against proliferating tissues, such as the epithelium of the GI tract and the bone marrow. Daunorubicin and doxorubicin exert a cardiotoxic action, which is related to radical formation in heart muscle cell mitochondria. The effect is cumulative and limits the total dose used in a treatment schedule. Both anthracyclines are mutagenic in bacterial and mammalian in vitro systems and carcinogenic in rodents after a single i.v. injection of a sublethal dose. The primary amino group of the sugar moiety is essential for the genotoxic and carcinogenic action of anthracyclines. Aclacinomycin A, which has a N,N- dimethylated sugar moiety is, therefore, not mutagenic and does not induce tumors in rats.


OH CtHs H 0 I --C2H~

~/~ I~NI~~__N CH~ " ~ ..<-.. ~~N~i~ .~CH~

HN~ HN Ergotamine Lycergic acid diethylamid, LSD

Claviceps Alkaloids The parasitic fungus Claviceps purpurea, also known

as Secale cornutum, grows parasitically on wheat, rye, and various other grasses. The fungus consists of a long, black, slightly curved body, the sclerotium, which contains a variety of alkaloids, known as "ergot" (Fig. 25). During harvest and threshing, the sclerotia get into the grain. Modern techniques allow the separation of the sclerotia from the grain before it is ground. In recent times, however, endemic poisoning sometimes occurred when a great amount of Secale was present in the grain and, thus the flour and bread. Directives of the European Community restrict the ergot content of grain to less than 0.1%.

Two forms of chronical poisoning are known, gangrene ergotism and convulsive ergotism. The latter form causes paresthesias of the extremities and, because of a permanent constriction of the arteries, is- chemia and gangrene develop. The affected extremities may become subject to amputation. The convulsive form is characterized by tonoclonic convulsions, which are very painful. Ergot alkaloids act also on the CNS, resulting in psychotic disorders, which may end in dementia. Because of its contractile action on plain muscles, ergot was used in folk medicine as a birth-accelerating drug and an abortive. In modern medicine, the alkaloid ergotamine is used in the therapy of migraine headache.

Lysergic acid is produced after hydrolysis of ergotamine. Its conversion into the N,N-diethylamid yields one of the most powerful hallucinogenic drugs, called LSD. The psychogenic action of LSD is accompanied by spectral visions and erotic feelings. The drug, which was first synthesized by the German chemist A. Hofmann at Ciba-Geigy in Basel, Switzerland, was very famous during the "hippie movement," which

started in the late 1960s. The effective dose range to cause hallucinations is 0.5-2 /~g/kg. Higher doses may lead to a phenomenon known as "horror trip," which is characterized by fear and manic episodes. Sometimes the symptoms last for several weeks. Irre- versible parachromatism and schizophrenia have also been observed after the use of high doses of LSD.

Toxins from Mushrooms (Basidiomycetae) Among the higher fungi (mushrooms) are many

toxic species, which are responsible for severe, sometimes lethal poisoning in humans. Most of the toxic mushrooms belong to the genus of Amanita, Inocybe, and Cortinarius. The collection and cooking of toxic instead of edible mushrooms is, in most cases, due to a lack of botanical knowledge. Fortunately, lethal poisonings are rare. However, gastroenteritic discomfort is common after the ingestion of toxic mushrooms. A survey of the most important species of toxic mushrooms follows.

Amanita Species (A. phalloides, A. virosa, A. citrina, and A. verna)

Up to 90% of the fatalities of mushroom poisoning are caused by Amanita phalloides or other Amanita species. The toxic principles consist of two groups of cyclic peptides, the amatoxins (Fig. 26) and the phallotoxins (Fig. 27). The amatoxins block the transcrip- tion process via an inhibition of the RNA polymerase. This causes an intracellular depletion of mRNA, followed by a gradual depletion of proteins, finally causing cell death. The liver is the main target organ of the toxins, which is due to an intensive first-pass effect. Damage also occurs in the GI tract and the kid-

984 Westendorf

I CO

/"~-CH

HO N

H~CR2 I

HCR~ I

H3C ~CH I

H N ~ C H ~ C O ~ N H ~ C H ~CO ~ N H ~ C H 2 ~ C O

H~C~I ~ NH CH~

0 +" R4 HC~CH

HzC CO CH3 I I

O C ~ C H ~ N H ~ CO~CH~NH ~ C O ~ C H z ~ NH

H~C ~COR~

R~ R2 R3 R4 LDs0(Mice p.o.)

r162 OH OH NH2 OH 0.3 m g / k g

~-Amanitin OH OH OH OH 0.5 m g / k g

~-Amanitin OH H NH2 OH 0.2 m g / k g

e-Amanitin OH H OH OH 0.3 m g / k g

Amanin OH OH OH H 0.5 m g / k g

Amanull in H H NH2 OH > 20 m g / k g

. . . . . . . . . . . . . . . . . . . . . ~ .. . . . . . . ~ ; ~ ............ ~ ~ ~ y ~ i ~ , : ' i ~ ~'~F,~',:~,'~ ~ i ~ i ~ . ~ '~" ~ " ~ ~ " ~"*';:~ ~ : : ~ ~ ~ " " ~ ~ ~ a ~ . . . . . ~ ~ ~ .... ~ ~ ~ ~ . . . . . . . . . ~ ~ ~ . . . . . . . ~ii~;~i~ ~ 9 i ~ , ~ i ~ ~ ~ ~ ~ ! ~ i ~ i ~ i ~

neys. In most cases of amanita poisoning, the hepatotoxic action is first recognized 1-2 days after ingestion. At this time, the degree of liver damage is usually severe and irreversible.

The phallotoxins bind to actin fibers at the cell membrane, resulting in changes of the membrane permeability, which finally leads to cell death. Their action is comparable to that of the cytochalasins. In contrast to the amatoxins, the phallotoxins exert their action a few hours after ingestion. The amatoxins are much more potent than the phallotoxins. If large masses of mushrooms are ingested, the symptoms of intoxication may be dominated by the earlier- acting phallotoxins. The lethal doses for amatoxins and phallotoxins are 0.1 mg and 5-10 mg, respectively. A quantity of 100 g fresh Amanita phalloides contains up to 17 mg amatoxins. A single mature mushroom is, therefore, sufficient to kill a whole family.

The symptomatic therapy of amanita poisoning is very complex. Gastric lavage is important to remove undigested material. Ingestion of activated charcoal is helpful to bind toxins that still remain in the GI tract. Infusions of fluid and plasma expanders are essential

in cases of shock. Further treatment requires the infusion of high doses of vitamins, fibrinogen, antibiotics, glucocorticoids, and, eventually, cardiac glycosides. Modern intensive care has reduced the lethality rates below 20%. After the severe progression of liver damage, liver transplantation is the last possibility to save the patient's life.

Amanita muscaria and Amanita pantherina Both of these mushrooms contain the anticholiner-

gic compounds ibotenic acid, also converted into muscimol and the cholinergic compound muscarine (Fig. 28). After the ingestion of the mushrooms, mainly anticholinergic symptoms, such as tachycardia, hyperthermia, and mydriasis, dominate. Parasympathetic symptoms, such as bradycardia, salivation, and miosis, are also sometimes observed. Similar to the anticholinergic compound atropine, ibotenic acid and muscimol enter the CNS and cause reactions, such as dizziness, ataxia, delirium, hallucinations, and erotic feelings. Because of its psychotic actions, the mushrooms have been used historically at cult ceremonies and in the preparation of witch recipes. Lethal intoxication is rare. It sometimes occurs when the toxic


H I

H 3 C - - C ~ C O ~ N H m C H ~ C O - - N H - - I H2C-,.~ . ~

I CO ~ S N L H2C H

I N ~ C O - - C H

/ I OH

HI H2C-R1

C ~ CH2-- C ~ CH2Rz

CO I NH

HC ~R3 I

NH--CO m C H ~ N H ~ C O

OH

H--C ~OH R4

R1 R2 R3 R4 LDso (Mice p.o.) Phalloidin OH H C H 3 C H 3 2.0 mg/kg Phalloin H H C H 3 C H 3 1.5 mg/kg Phallisin OH OH C H 3 C H 3 2.5 mg/kg Phallacidin OH H CH(CH3) 2 COOH 2.5 mg/kg

mushroom Amanita pantherina (lethal dose, 110 g fresh weight) is mistakenly collected instead of the edible species Aminita rubescens. Almost no fatal cases have been reported for A. muscaria, which is less toxic than A. panhterina; also the intense red color of this mushroom prevents it from being erroneously collected.

H3~__CH2~ OE)

Muscimol

| H 3 N - - C H ~ _ / N

C~ OOE) O

Ibothenic acid

OH CH3 I|

H3C CH2--N I

CH3

CH3

Muscarin

i iiiiii

Inocybe Species Most of the approximately 130 Inocybe species are

toxic. Some also cause fatal intoxication (e.g., Inocybe patoulliardi). The mushrooms contain great amounts of muscarin, which acts on post-synaptic acetylcholi- nergic (muscarinic) receptors (Fig. 28). The symptoms of intoxication are, therefore, characterized by excessive parasympathetic excitement (salivation, lacrima- tion, sweating, gastrointestinal spasms, severe diarrhea, bradycardia, and bronchospasm). If medical care is soon available, the prognosis is good, because all the symptoms are reversible after administration of atropine. If no atropine is given, the symptoms pro- gress to coma and respiratory or heart arrest. Further toxic mushrooms are listed in Table 6 (Fig. 29).

P L A N T T O X I N S

Many plants contain compounds that are toxic to animals and humans. Some of these compounds serve as repellents against herbivorous animals, fungi, or bacteria. Others may be just accidentally, toxic. Toxic plants have been used by humans for different purposes as long as they have existed. Modern methods of chemical analysis made the chemical structures of

986 Westendorf

~ =~ ~ , ,~ ~ $ ~ , ~ . ~ , = , ~ , ~ = ~ ~ ! ~ = ~ ~y,.~ ............... @ ~ , ~ , ~., ,~, ~o,. , . ~ , ~ ~ , ~ = ~ ,,~ . 7 ; ~ , o i : . . ..... . . . . . . . . . ~-- , =~:~ .--.~,~. :... ......... .::,~.:i~..'--:..~..~:.-- ~,.-~.-.~ , .~::~,..~ ~ ;~ .-. ~ - . ~ = ~ i ~ ; , . : ~ , - . i ~ -=. ~ , .~ ........ - ~ .

Mushroom Poison Symptoms

Amanita phalloides Amatoxins Hepatotoxic Amanita verna Amatoxins Hepatotoxic Amanita v i r o s a Amatoxins Hepatotoxic Amanita pantherina Ibotenic ac id Parasymphatolytic Amanita muscaria Ibotenic ac id Parasymphatolytic Cortinarius ssp. O r e l l a n i n e s Nephrotoxic Galerina ssp. Amatoxins Hepatotoxic Gyromitra esculenta Gyromitrin Hepatotoxic Inocybe ssp. Muscarin Parasympathomimetic Lactarius ssp. Nectaronon Gastrointestinal Omphalotus olearius Sesquiterpenes Gastrointestinal Paxillus involutus Unknown Anaphylactic shock

many toxic plant ingredients available, and their pharmacological and toxicological mechanisms have been investigated.

Poisoning by plants is mainly due to oral ingestion of plants or parts of plants. At special risk are little children, who are more careless than adults and often attracted by the appearance of plants (e.g., the nice color of purple foxglove or the appetizing appeal of the fruits of belladonna). In the case of adults, a lack of botanical knowledge may lead to the mistaken use of toxic plants for food or preparation of phytothera- peutics. Finally, toxic plants are also used as abortives, and in suicides and homicides.

A differentiation of toxic plants by their site of action is difficult, because the toxicity is often the result of a complex mixture of compounds with different modes of action (Table 7). Moreover, individual dif- ferences in sensitivity may lead to different symptoms, especially if allergic reactions are involved. Plant toxins are normally less target directed than are animal toxins. Plants also often contain compounds with antagonistic properties, whereas the components of animal toxins act synergistically, in most cases.

Compounds with Action on the Gastrointestinal System

Irritation of the mucous membranes of the GI tract is caused by most plant toxins ingested orally. Some toxins exert their action almost exclusively at this site. Among these are the saponines, a group of glycosidic compounds containing a lipophilic aglycone and a hydrophilic sugar moiety. Their name "saponines" is based on the Latin word for soap (principium sapo- neum) and characterizes the action of the compounds as detergents. Saponines are widely distributed in the

CHz -CH -N- N: CHz'" "CHO

Gyromitrin

HI N N ~ O H

Nectaronon

" N'oH H O . . N ~ O H

Orellanin

~ .. ~i~;i~ a.-'~.=~'...~:~ %

plant kingdom and cause many plants to be inedible. An example for a saponine-containing plant that caused endemic poisoning in past centuries in west- ern Europe is Argostemma githago L. The seeds of this plant, which sometimes grows together with cereals, contain the saponine githagin glycoside. The ingestion of bread prepared from flour with Argostemma-contamination caused endemic poisoning with many fatal cases. Poisoning was also observed in domestic animals. The toxic dose for humans is approximately 3 - 5 g of Argostemma seeds. Another saponine-containing plant is Cyclamen purpurescens, a popular indoor plant. The bulbs contain the triterpenglycoside cyclamin. The purple foxglove (Digitalis purpurea L.) contains the saponine digitonin (Fig. 30). A well-known saponine plant is the horse chestnut (Aesculus hippocastanum L.). The chestnuts contain a mixture of triterpenegly- cosides called aescin. In North America, the American pokeweed (Phytolacca americana L.) is used in folk medicine as a remedy against rheumatism. All parts of the plant, especially the roots, contain triterpene glycosides. Poisoning occurred from overdosing from tea preparations made from the roots or leaves of the plant (pokeroot tea). The symptoms are directed mainly to the GI tract. Other saponine-containing plants with rare cases of human poisoning are: Pri- mula L. (primrose), Viola purpurea L. (violet), Astraga- lus glycyphyllos L. (licorice milkvetch), Panax ginseng C. Meyer (ginseng), and Equisetum arvense L. (field horsetail).

Compound Occurrence

I~ :~!i~J ~i '~ ~ ~i~ lI!~ ~ 0,~,0,~i,~,~,~,,~i ......... ~ ! ~ ~ ~ ~ 1 7 6 ~ l ~ I ~ l ~ i ~

Toxicity a Action

Abrin Abrus precatorius LDs0 (M ip) 0.02 mg/kg Cytotoxic, gastroenteritis, Aconitin Aconitum spp LDs0 (M iv) 0.16 mg/kg Increase nerve excitability, later paralysis Adonitoxin Adonis vernalis LDso (M) 191/zg/kg Heart glycoside ~Aescin Aesculus hipp. LD50 (M po/iv) 400/2 mg/kg Oral: gastroenteritis, parenteral: H/imolysis Aethusin Aethusa cynap. Spasmogenic Allylisothiocyanat Brassica nigra LD50 (M po) 108 mg/kg Mucous membrane irritant Amygdalin Cotoneaster spp. Cyanogen, asphyxia Anabasine Nicotiana tabacum LD (H) 22 mg Ganglia blocking Arecolin Areca catechu LDs0 (M sc) 100 mg/kg Parasympathomimetic Aristolochic acid Aristolochia clematitis LD50 (M po) 30 mg/kg Gastroenteritis, carcinogenic Atropin Atropa belladonna LD (H) 60-100 mg Parasympatholytic Berberin Berberis vulgaris LDs0 (M ip) 100 mg/kg Gastroenteritis, nephritis Brucin Strychnos nux-vomica LDlo (H) 30 mg Spasmogenic Bulbocapnin Corydalis cava LDs0 (M sc) 195 mg/kg Paralysis, hypnotic Caffeine Coffea arabica LD50(R po) 200 mg/kg Inhibition of phosphodiesterase Cannabinol Cannabis sativa LDs0 (R po) 670 mg/kg Hallucinogenic Capsaicin Capsicum ssp. LDlo (C iv) 1.6 mg/kg Mucous membrane irritant, hypothermia Cheirosid A Cheiranthus cheiri Heart glycoside Cheirotoxin Cheiranthus cheiri LDlo (C iv) 0.12 mg/kg Heart glycoside Chelidonin Chelidonium majus LDs0 (M iv) 35 mg/kg Mitotic arrest Chrysarobin Andira araroba LDlo (M ip) 4 mg/kg Cytotoxic, tumor promoting Cicutoxin Cicuta virosa LDlo (C po) 7 mg/kg Spasmogenic Cocaine Erythroxylum coca LD50 (R iv) 17.5 mg/kg Local anesthetic, exciting Colchicine Colchicum autumnale LD (H) 20 mg Mitotic arrest Coniine Conium maculatum LD (H) 500 mg Paralysis Convallatoxin Convallaria majalis LD (F iv) 0.3 mg/kg Heart glycoside Cotinine Nicotiana tabacum Ganglia blocking Cycasin Cycas revoluta LDs0 (R po) 562 mg/kg Carcinogenic Cyclamin Cyclamen purpurescens Gastroenteritis, hemolysis Cytisin Laburnum anagyroides LD50 (C po) 3 mg/kg Ganglia blocking Digitonin Digitalis purpurea Gastroenteritis, hemolysis Digitoxin Digitalis purpurea LDs0 (C po) 0.18 mg/kg Heart glycoside Digoxin Digitalis purpurea LDs0 (C po) 0.2 mg/kg Heart glycoside Emetin Cephaelis ipecacuana LD50 (R ip) 12 mg/kg Cytotoxic, gastroenteritis Ephedrine Ephedra vulgaris LD (M po) 400 mg/kg Sympathomimetic Gitoxigenin Digitalis ssp. LDs0 (C iv) 3 mg/kg Heart glycoside Hellebrin Helleborus ssp. LDlo (GP po) 0.6 mg/kg Gastroenteritis, CNS excitation L-Hyoscyamine Solanaceae LD (H) 60-100 mg Parasympatholytic Hypericin Hypericum ssp. Phototoxic, MAO-inhibitor Khellin Ammi visnaga LDs0 (R po) 80 mg/kg Spasmolytic Lycorin Ammarillaceae Gastroenteritis, skin irritating Mescaline Lophophora Williamsii LDs0 (M ip) 212 mg/kg Hallucinogenic, teratogenic Morphine Papaver somniferum LD (H) 300-500 mg Central analgesic, respiratory depressant Narcotine Papaver somniferum LDs0 (M po) 0.83 mg/kg Spasmolytic Nicotine Nicotiana tabacum LDlo (H) 40 mg Ganglia blocking Nomicotine Nicotiana tabacum LDs0 (Rip) 23.5 mg/kg Ganglia blocking Oenanthotoxin Oenanthe crocata LD (M ip) 0.83 mg/kg Spasmogenic Papaverine Papaver somniferum LDs0 (R po) 750 mg/kg Spasmolytic Phasin Phaseolus vulgaris Cytotoxic, hemagglutinine Phorbolester Croton tiglium Skin irritant, tumor promoting Physostigmin Physostigma venenosum LD50 (M po) 3 mg/kg Inhibition of acetylcholinesterase Picrotoxin Anamirta cocculus LDs0 (M ip) 4 mg/kg Spasmogenic Pilocarpin Pilocarpus jaborandi LD50 (R po) 911 mg/kg Parasympathomimetic Protoanemonine Helleborus ssp. LD50 (M ip) 190 mg/kg Gastroenteritis, skin irritant, paralysis Psilocybin Psilocybe ssp. LDs0 (M ip) 275 mg/kg Hallucinogenic Psoralen Citrus ssp. Skin irritant Quinidine Cinchona pubescens LDs0 (C iv) 22 mg/kg Heart poison Quinine Cinchona pubescens LDlo (GP po) 300 mg/kg Heart poison Reserpine Rauvolfia serpentina Antisympathicotonic Retrorsin Senecio ssp. LDs0 (M iv) 59 mg/kg Hepatotoxic, carcinogenic Ricin Ricinus communis LDs0 (M iv) 12/zg/kg Cytotoxic, gastroenteritis Safrol Sassafras albidum LDs0 (R po) 1950 mg/kg Skin irritant, carcinogenic Scopolamine Solanaceae LD50 (M iv) 163 mg/kgp Parasympathicolytic Senecionin Senecio ssp. LDs0 (M iv) 64 mg/kg Hepatotoxic, carcinogenic Senldrkin Tussilago farfara Hepatotoxic, carcinogenic Solanin Solanaceae LDlo (H) 400 mg Gastroenteritis, hemolysis, CNS disturbance Sparteine Genista tinctoria LDlo (RB iv) 30 mg/kg Heart arrest g-Strophantin Strophantus ssp. LD (C iv) 0.15 mg/kg Gastroenteritis, heart arrest Strychnine Strychnos nux-vomica LDlo (H) 30 mg Spasmogenic Tetrahydrocannabiol Cannabis sativa LD50 (R iv) 29 mg/kg HaUuzinogenic Thujon Thuja ssp. LD (Rip) 240 mg/kg Nerve poison Tubocurarine Chondrodendron LD (H) 50-120 mg Paralysis of motoric endplate

tomentosum Urushioles Rhus toxicodendron Severe skin irritant Vicin Vicia faba H/imolytic anemia Vinblastine Catharantus roseus LDs0 (M iv) 17 mg/kg Mitotic arrest Vincristine Catharantus roseus LD50 (M iv) 2 mg/kg Mitotic arrest Yohimbine Pausinystalia yohimba LD (H) > 1.8 g Aphrodisiacic, alpha-2-agonistic

LDlo (M iv) 16 mg/kg Sympathomimetic

aAbbreviations: F = Frog, C = cat, M = mouse, H = human, GP = guinea pig, R = rat, RB = rabbit.

988 Westendorf

Xyl\ ,Arab-Gluc- Gluc"

H3C CHO H,C

L2 H3C ~

I H3C CH3 Xyl

I (Gal)2

I

Cyclamin (Gluc)2 Digitonin

CH3

i i ~ i i ! ~i~ i! !iiiii~iiii~ii~i!iiiiiii! iiii~i!~i i!i i ii ii ii~iii~i~!i~i~!i!~iiiiiiiii!i!i!i!~!ii ~ii~!~ ii~iiiiiiiiiiiiii~iiiiiiii i!iiiii i iii iiiiiiii iiiiiiii~ii i il iiiiii i il

Saponines are weakly absorbed by the intestine. Because of their action as a detergent they concentrate in the lipid layer of the cell membranes of the gastric and intestinal epithelium, which is damaged. This causes severe irritation, characterized by burning of mouth and stomach, cough, salivation, and lacrima- tion; followed by nausea, vomiting, and diarrhea; and sometimes resulting in severe loss of fluids and electrolytes. Reflexes via the autonomic nerve system may cause disturbances to heart function and circulatory system. Death is often the result of shock reaction. Although saponines are normally poorly absorbed, the local irritation of the mucous membranes may enhance the permeability via damage to the intestinal wall. Systemic reactions of saponines after absorption are mainly directed to red blood cells and may consist of severe hemolysis, causing anoxia and kidney failure as secondary reactions.

The therapy for saponine poisoning consists of the oral application of activated charcoal in order to ab- sorb and, thus, inactivate the saponines. Slime preparations of rice and oats or paraffin should be admin- istered as a mucous-membrane protective. The substitution of electrolytes and fluid is essential after extensive episodes of vomiting and diarrhea. If the patient is excited, sedatives should be given and artificial respiration is necessary if arrest of breathing occurs. Due to modern intensive care, fatal poisonings by saponine-containing plants are very rare.

Another group of plant toxins with irritating action on the GI tract are hydroxyanthraquinones (HA). They occur in numerous medicinal plants, most of which are used as laxatives. Anthraquinone-containing drugs are aloe (Aloe barbadensis P. Mill. and A. ferox Mill.), sennae folium, and sennae fructus (Cassia angustifolia Vahl.), rhei radix (Rheum officinale Baillon,

Chinese rhubarb) and rhamni frangulae cortex (Rham- nus ssp., buckthorn). They contain the anthraquinones rhein, aloe-emodin, chrysophanol, and physcion as free aglycones and as glycosides (Fig. 31). Intestinal bacteria reduce the anthraquinones (glycosides) to very reactive anthrones, which increase the net secretion of fluid into the lumen by irritation of the intestinal wall. This process causes the laxative action. The presence of two hydroxy groups in 1,8-position is essential for the laxative action. Upon chronic use of anthraquinones, its laxative potency decreases, ending up in a vicious circle (Fig. 32).

Some of the anthraquinones (Fig. 31) are genotoxic (e.g., aloe-emodin, and emodin) in a variety of in vitro short-term assays. All HA with hydroxygroups in 1,8- position (i.e., laxative active ones) act as tumor pro- moters in primary liver cell cultures (via induction of mitosis) and in C3H-mouse fibroblasts (via enhance- ment of malignant transformation after low-dose treatment with an initiating carcinogen). A carcinogenic action in rodents was demonstrated after feeding rats and mice danthron and 1-hydroxyanthraqui- none. There is also limited evidence that long-term abuse of anthraquinone laxatives is correlated with colon cancer. The action of the HA is most probably related to oxidative stress.

The toxic proteins ricin, abrin, and phasin occur in the seeds of Ricinus communis L (castor bean), Abrus precatorius L. (jequirity bean), Phaseolus vulgaris L. (kidney bean), and Phaseolus coccineus L. (scarlet run- ner). The compounds, which belong to the lectines, are destroyed upon cooking the plants; however, they are resistant to digestive enzymes. Ricin and abrin are among the most potent plant poisons known. After IV injection into mice the LDs0 is approximately 0.1 ~g / kg. The lethal dose after oral consumption by hu-


OH 0 OH J.8 "U9 .,

0

Rhein

Glu-O O OH

~ ~ ~ - ~ C O O H .COOH

Glu-O O OH Sennosid

OH O OH

~"~ ~ ' ~ " / / ' % ' C H 3 O

Chrysophanol

H3C

HO O OH HO O OH

O O

HO O OH

H3C OCH3 O

Emodin Emodin Physcion

OH O OH OH O OH

, CH OH O H Glu

Aloe-Emodin Aloin

l/IIIi1 mans is approximately 5 ~g/kg. If jequirity beans or castor beans are ingested without chewing, the liberation of the poison is inhibited by the tough skin. After the beans are chewed, however, lethal intoxication may occur. Pulverized jequirity beans were used by jealous Aztec women, who mixed it into the food of their unfaithful husbands. Kidney beans are toxic if ingested raw because of their phasin content. Fatal cases in children occurred after ingestion of 5 -6 raw beans.

The toxic lectines consist of two protein chains (A and B), connected by a disulfide bridge. The B-chain binds covalently to the surface of the cell membrane, whereas the A-chain enters the cell and inhibits the ribosomal protein synthesis by splitting off adenine from the rRNA. It is believed that a single molecule of abrin or ricin is sufficient to kill a cell. After oral ingestion of the compounds, the mucosa cells of the GI tract are first damaged. Severe vomiting and diarrhea may lead to death by hypovolemic-shock syn-

drome. After absorption of the toxic proteins, other organs, especially the liver and kidney, are damaged. The latency period between ingestion of the toxin and death is normally 2 -3 days. After parenteral application (caused by contact of the toxin with a predam- aged skin) the symptoms soon occur and are not directed to the GI tract.

A local irritation of the GI tract mucosa is also achieved by uptake of capsaicin (Fig. 33), which is in hot spices, such as pepper. The highest amounts (up to 1%) are present in cayenne pepper (Capsicum frutescens L.). The burning taste of capsaicin is still de- tectable after dilution of 1:2,000,000. Mustard and horseradish contain the irritating compound allyliso- thiocyanate (Fig. 33). After the ingestion of greater amounts of these compounds, severe irritation of the GI tract may cause vomiting and diarrhea. The func- tions of the heart and kidneys may also be disturbed. A carcinogenic action of the compounds was demonstrated in laboratory animals.

990 Westendorf

Damage of intestinal wall and myenteric nerve plexi

Inhibition of myenteric activity

Potassium deficiency

Obstipation

Intestinal Loss of potassium

Intestinal

Laxatives

k i Intestinal

Loss of water and sodium

Increase of aldosterone secretion

N Compounds with Action on the Heart

Cardiotoxic compounds are glycosides, present in Digitalis purpurea L. and Digitalis lanata Ehrh. (foxglove species), Convallaria majalis L. (European lily of the valley), Nerium oleander L. (oleander), Cheiranthus cheiri L., Adonis vernalis L. (spring pheasant's eye), Helleborus niger L. (black hellbore), Euonymus euro- paeus L. (spindle tree), and Scilla bifolia L. All cardiac glycosides have similar chemical structures. The main structure consists of a steroid ring system, connected

H

H~CO/~i/OH N O~~~kx.

CH~ =CH-CH=- N-C= S AI lyli sothiocyanat

HO---~CH~ - N-C-S Capsaicin p-Hydroxybenzylisothiocyanat

. . . . . . . . . . .

at C17 with a monounsaturated 7-1actone ring (car- denolid group) or a bis-unsaturated &lactone ring. Examples for both groups are shown in Fig. 34. Deriv- atives of the bufadienolid group are also present in the saliva of toads (bufo means toad). The aglycones of the plant-derived cardiac glycosides are linked to sugar moieties, such as D-glucose, D-fructose, D-fu- cose, L-rhamnose, and some characteristic 2-deoxy- or 3-O-methyl sugars.

The glycosidic moiety and the lactone rings are not essential for the action of the compounds, although the latter are involved in the potency. The compounds possess a high affinity for the Na+-K+-ATPases of the heart muscle cells. Binding results in an inhibition of the active Na+-K § fluxes across the cell membrane and an increase of the intracellular Ca 2+ concentration. Small doses create a positive inotropic effect, which is therapeutically used in patients with cardiac insuffi- ciency. The therapeutic dose range is narrow. Intoxi- cation may occur at 60% overdose only. Reduction of the blood-potassium level as a result of the use of diuretics, hyperaldosteronism, or diarrhea increases the toxicity of cardiac glycosides.

Intoxication with cardiac glycosides are characterized by a massive intracellular loss of K § followed by bradycardia and arrhythmia and, finally, ventricular fibrillation and heart failure. The lethal dose of digi-


O ~ OH

0 HO Ouabain

OH

HO

OH

O O O O O O~.~ /

ON ON

H

Digitoxin O

o /

OH /OH ~ H H O ' 7 ~ o - ~ O 0

HO 0 HO 0

OH Scillaren A

tonin is approximately 10 mg, occurring in only 2 -3 leaves of purple foxglove.

The bark of Cinchona pubescens Vahl (quinine) contains the alkaloids quinine and quinidine (Fig. 35). The compounds are used therapeutically for the treatment of malaria and as an antiarrhythmic. Both compounds inhibit the spontaneous contractions of the heart muscles at high doses, finally leading to heart arrest. Similar actions are exerted by the compound spartein, occurring in the genus Genista and Lupinus.

Taxus baccata L. (yew tree) contains a mixture of related toxic alkaloids, the taxanes (Fig. 36). The poison is present in the needles and the fruit pits of the plant. The fruit pulp is free of poison and edible.

Poisoning often occurs in domesticated animals, such as horses, cattle, and pigs. The lethal dose for a horse is approximately 500 g of needles. The toxicity is mainly caused by taxin (Fig. 36), a mixture of two components with strong cardiotoxic activity. After ingestion of toxic amounts of the plant, severe bradycardia occurs leading to diastolic heart arrest. The action is most probably due to an inhibition of the transmembraneous flux of Na § and Ca 2+.

Compounds with Action on the Liver

The liver is the central detoxification organ. All compounds taken up orally pass through the liver

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H~CO H~CO

N N

Quinin Quinidin

Spartein

first after absorption from the GI tract. It is, therefore, likely that the liver is also the target for many toxins entering our bodies. However, only a few toxins are liver specific. Among these are secondary toxic compounds, which are activated by the xenobiotic metab- olism of the liver cells to highly reactive intermediates that bind almost completely to macromolecules of the liver.

An important group of plant compounds with toxicity to the liver are the pyrrolizidine alkaloids (PA), occurring in about 350 plant species. Among these are numerous medicinal plants, such as Tussilago farfara L. (coltsfoot), Symphytum officinale L. (comfrey), Petas- ites hybridus (L.) P.G. Gaertn., B. Mey., & Scherb (but- terbur, butterfly dock), Cynoglossum officinale L.

OH HO\ .,' CH~

) . . ~OH

R OH CH~

Taxicin I: R = OH Taxicin I1: R = H

O~ _ R, R

R; R, ~-N~.~ OR"~'XOHR~

Echimidin-type

R R4 OH r13% ~ ~ R , _ R, OH R2 R2 . .

CH3 Senecio nin- type Senki rkin- type

(hound's tongue), and various Senecio ssp. (ragwort). The pyrrolizidine alkaloids consist of about 200 derivatives, containing a heterocyclic ring system, the necin base, which is connected with two acid moieties, often part of a macrocyclic two-basic acid. There are two main classes of PAs, a saturated and an unsaturated necin moiety. Only unsaturated PAs are toxic. Fig. 37 shows some typical structures of PA.

After absorption, the PAs are oxidized by liver mixed functional oxidases to highly reactive pyrrole derivatives, which bind covalently to macromolecules of the liver cells. The ingestion of toxic doses may result in necrotic liver damage, known as veno-occlu- sive syndrome. In some areas of Central America and the Caribbean islands (e.g., Jamaica), endemic liver cirrhosis was observed in babies and little children treated with "bush teas" made from plants often containing senecio species; these are used as folk medi- cines against various diseases. Endemic poisoning with PAs was also reported from other parts of the world. Outbreaks of severe liver damage occurred in Afghanistan after the consumption of cereals contaminated with the seeds of Heliotropium and Crotalaria species. About 100 million sheep in Australia suffer from liver damage caused by ingestion of Heliotropium species. The animals normally avoid these plants as long as other (nontoxic) food plants are available, but this is not the case during especially the dry season.

PAs also represent an important class of natural carcinogens. It was demonstrated that PAs, after metabolic activation, bind covalently to liver DNA.


o\~...o ,H ~--0 O ~ o H 0

R/ ~ a ~ O ' Cyt P450 R2 ' / ~ a / ~ O

OH P y r r o l i z i d i n e a l k a l o i d

- H20

N u c 2 ~ Nuc1 + Nuc~ e , k-- O + Nuc2e R2 /- -

.. R1 - R~COO e

Addukt - R2COOO Pyrrolderivative

PA diesters are able to cross-link DNA (Fig. 38). The compounds are mutagenic in numerous in vitro assays and teratogenic in laboratory animals. Rats developed characteristic tumors of the liver after long-term feeding on PAs or plants containing such compounds.

Compounds with Toxicity on the Kidneys Many xenobiotic compounds concentrate in the

kidneys during the process of excretion. It is, therefore, not surprising that the kidneys are often involved in the toxic action of chemical compounds. Indirect mechanisms may also lead to kidney dysfunction and damage. Severe intravasal hemolysis may cause in a crystallization of heme crystals in the kidney tubules and thus lead to kidney failure. Oligo- and anuria may also be a result of electrolyte-balance disturbances occurring after episodes of severe diarrhea or vomiting, frequent symptoms of poisoning from plants. In this case, kidney failure is the result of an activation of the renin-angiotensin-aldosterone system. Very few plant toxins act specifically at the kidneys.

The seeds of a tree (Pithecolobium lobatum) belonging to the plant family of leguminoses contain the sulfur-containing amino acid djencolic acid. The beans of this tree are often eaten on the islands of Java and Sumatra. Djencolic acid is composed of two cysteine moieties bridged by a-S-CH2-S-chain. The compound is poorly water soluble, leading to crystallization in the kidney tubules during the process of concentration and excretion. The symptoms are related to the

amount of the compound ingested and vary from cases of slight oliguria to complete anuria. Similar symptoms are caused by excessive uptake of oxalic acid, which occurs in some vegetable plants, such as rhubarb, spinach, and celery. Damage to the kidney tubules is caused by crystallization of Ca oxalate.

Plants with Hematotoxic Action Many plants contain saponines that cause hemoly-

sis after absorption. Because of the poor intestinal absorption of saponines, the symptoms of poisoning by such plants are mainly restricted to the GI tract. If considerable amounts are absorbed, severe hemolysis may occur, resulting in cyanosis and kidney failure. The horse chestnut saponin aescin was used clinically for the treatment of or as a prophylactic for post- operative brain edema. Overdosing in children caused some fatal cases in Germany.

Lectines consist of a group of compounds with action on the blood cells. These compounds, which occur in numerous plants, bind to specific sugar moieties of the cell membrane. Ricin, abrin, and phasin have already been discussed. Another lectin is con- canavalin A, occurring in the bean Canavalia ensiformis (L.) D.C. Lectines cause the agglutination of blood cells. Some derivatives stimulate the mitosis of lymphocytes, acting in a way similar to antigens. The action is, however, not specific. Lectines are also used diagnostically for blood-group determination.

A syndrome called "favism" occurs after the consumption of the edible bean Vicia faba L. (horsebean)

994 Westendorf

NH2 NH2 HOrN HOrN OH

Divicin Isouramil

by susceptible persons. The patients suffer from massive hemolysis, often with a fatal outcome. The susceptibility is correlated with a recessive X-chromosomal abnormality, leading to a lack of glucose-6- phosphate-dehydrogenase (GPDH) of the erythrocytes. The abnormality is frequent in blacks, Asiatics, and people living in Mediterranean areas. The enzyme is important for the synthesis of NADPH, which regulates the level of reduced glutathione (GSH). A lack of GSH leads to oxidative damage of the erythrocytes followed by hemolysis. Horsebeans contain the compounds divicin and isouramil (Fig. 39), which cause the oxidation of GSH to GSSG. Persons with normal concentrations of GPDH contain enough NADPH to compensate for the oxidative stress due to the toxins. In sensitive persons, however, the GSH concentration of the erythrocytes may be reduced to only 6% of the normal value.

Plant Toxins with Neurotoxic and Myotoxic Action

Numerous plant-derived toxins act on the conduction of the central and autonomic nerve systems and on the skeletal muscles. Most of these compounds belong to the alkaloids, which mimic or inhibit the action of endogenous neurotransmitters. Some compounds act directly on transmembraneous ion fluxes. Such compounds purified from plants, as well as plant extracts or the plants itself, are used for medicinal purposes, such as blood-pressure regulates, spas- molytics, analgesics, analeptics, and psychopharma- c o n s .

Compounds with Action on the Autonomic Nerve System

These compounds are divided into those acting on the sympathetic or parasympathetic nerves and those acting on the autonomic ganglia, influencing the total

Nicotine Nor nicotine Myosmine

~ H

O Anatabine Anabasine Cytisin

~'t~

~

autonomic nerve system. To the latter ones belong the pyridine alkaloids occurring in tobacco (Nicotiana tabacum L.) (Fig. 40). The action is related mainly to nicotine, which leads to a depolarization of all autonomic ganglia. Small doses of nicotine have a stimulating action. The anorectic action is also due to the liberation of epinephrine, which leads to glycogenol- ysis followed by an increase of the blood-glucose level. Higher doses also cause parasympathetic excitement with symptoms of sweating and intestinal spasms. The lethal dose for adult humans is 40-60 mg nicotine, the content of one-half cigar or two cigarettes. The fact that acute poisoning is normally not observed after smoking is due to the slow uptake of nicotine by the lungs and its rapid metabolic inactivation. Additionally, a nicotine tolerance occurs in heavy smokers. Intoxication is, however, frequently observed after oral ingestion of nicotine, occurring, for example, after the eating of cigarettes by little children. Lethal intoxication may also occur after careless handling or suicidal ingestion of nicotine-based pesti- cides. Toxic amounts of nicotine may also penetrate the skin after contact with aqueous tobacco extracts. Lethal amounts of nicotine lead to short episodes of convulsions followed by respiratory and cardiac arrest.

Cytisin (Fig. 40), occurring in laburnum species, such as Laburnum anagyroides Medik., a popular garden plant, is similar to nicotine with respect to its structure and pharmacological action. The poison is located mainly in the seeds. Ingestion of 15-20 seeds is lethal for an adult, whereas only five seeds may be sufficient to kill a child. Cytisin intoxication was also reported after consuming goat milk. Goats, which are


relatively insensitive to the toxic action of cytisin, excrete the compound with their milk after feeding on the plant. The symptoms of a cytisin intoxication are similar to that caused by nicotine; however, the central stimulating effects directed to the medulla oblongata are more pronounced. The symptoms begin with an increase in blood pressure as a result of vasoconstriction and tachycardia, followed by tonoclonic spasms, unconsciousnes, and respiratory arrest. Treat- ment of the patients is symptomatic after the removal of plant material by gastric lavage.

Pilocarpine (Fig. 41), the active principal of jaborandi leaves (Pilocarpus jaborandi Holmes), stimulates the parasympathetic receptor mechanism. The pure compound is used pharmaceutically for the treatment of glaucoma. The symptoms of pilocarpine intoxication consist of an excessive stimulation of the parasympathetic nerve system with symptoms of salivation, sweating, miosis, spasms of the almost all smooth muscles, and bradycardia. Severe intoxication occurs after ingestion of more than 20 mg of pilocarpine. Another compound with action on parasympathetic receptors is muscarine, which occurs in basidi- omycte species (see the section on mycotoxins).

Physostigmine, occurring in the African plant Phy- sostigma venenosum Balf. (calabar bean) exerts its cholinergic action by a reversible inhibition of the enzyme acetylcholinesterase. This will cause in an excessive accumulation of endogenous acetylcholine. The symptoms consist mainly in parasympathetic reactions. In contrast to the direct-acting compound pilocarpine, physostigmine also causes fascicular twitching of striped muscles. The therapy of intoxication consists of the administration of atropine and diazepam.

Tropa alkaloids act as antagonists on cholinergic receptors. Among such compounds are L-hyoscyamine, its racemate atropine and the atropine epoxide scopolamine (Fig. 42). The compounds occur in different species of the plant family of Solanaceae (night- shade). High concentrations occur in Atropa belladonna

/CH3 /J"'N"

i , CHa

o--~ 0

H3C

H3C/NH ~ N ~ \CH3 CH3

P il oca rpin e Ph ysost i g mine

L. (atropa), Hyoscyamus niger L. (black henbane), Da- tura stramonium L. (jimson weed), and Mandragora of- ficinarum L. (mandrake). Where the plants grow wild, the black (pseudo-) berries of belladonna and the seeds of datura are often eaten by children. The berries of atropa look appetizing and have an agreeable, slightly sweet taste. Only 2-3 berries may be fatal in children, whereas the lethal dose in adults is about 20 berries. Poisoning with Solanacea plants is also due to overdosing of herbal remedies.

After the ingestion of atropa berries (or other sources of atropine), the symptoms of poisoning begin with dryness of the mouth and throat, a scarlet flush of the face, and dialation of the pupils. Symptoms of central excitement occur a little later. The patient is lively, merry, and agitated. Spectral illusions and erotic feeling are often perceived. The condition may then change to an anxious or furious state. The pulse is quick and faint, and the respiration is stertorous. In fatal cases, the symptoms of excitement disappear slowly and deep coma occurs. Death is normally caused by respiratory arrest.

Extracts of Solanacea plants, such as jimson weed, black henbane, and mandrake, were used in Europe in the Middle Ages in the preparation of special ointments by witches. The ointments were applied to the mucous membranes of the genital organs to produce a condition of ecstasy and erotic feeling. Jimson weed was also known to the native people of North and Latin America. The Aztecs worshipped the plant and used it for cult purposes and for punishments. A special application was the insertion of rolled-up leaves into the anus. Beside cult purposes, Solanacea plants have also been extensively used for murdering people.

Plant Toxins with Action on Sympathetic Nerves The plant Ephedra distachya L. (joint fir), which oc-

curs mainly in Mediterranean areas, contains the alkaloid ephedrine (Fig. 43), which acts in a way similar to norepinephrine. The compound is also in the horse- taiMike shrub Catha edulis (Vahl) Forsskal ex Endl (khat). Because of its stimulating action, chewing of the khat leaves is common in countries of the Middle East and North Africa. The pharmacological action of ephedrine is due to the liberation of norepinephrine in the peripheral nerve endings and of norepinephrine, serotonine, and dopamine in the CNS. This produces an increase in attention and fitness and a decrease in tiredness and hunger. Chronic use of the drug causes addiction and tolerance (tachyphylaxia). Sweating, mydriasis, insomnia, retention of urine, and constipation occur after overdosing on the drug. Toxic

996 Westendorf

CH3 CH~ I N N

o o

"O--C--CH "O--C-- CH I CH2OH CH2OH

Atropine Scopolamine

iiii i iii

doses lead to convulsions, shock, and respiratory arrest.

Other plant compounds with action on the sympathetic system are indol alkaloids occurring in Rauvolfia serpentina (L.) Benth. ex Kurz (serpentine wood). The most important derivative is reserpine (Fig. 44). The compound acts by an inhibition of the re-uptake of norepinephrine into the vesicles of sympathetic nerve endings, which are gradually depleted. The resulting decrease of sympathetic reactions was used for the treatment of hypertension. Because of the central symptoms, consisting of sedation and depression, the drug was replaced by synthetic compounds with less central side effects. Toxic doses lead to bradycardia, arrhythmia, and finally heart arrest.

Plant-derived compounds with spasmolytic action are papaverine and narcotine, both occurring in Pa- paver somniferum L. (opium poppy) and khellin, a component of Visnaga daucoides Gaertn. or Ammi visnaga (toothpickweed) (Fig. 45). The compounds, which act as inhibitors of the calcium flux through the membrane of smooth muscle cells, are used pharmaceutically for the treatment of spasms in various

smooth-muscle-containing hollow organs. Overdos- ing causes severe hypotension and heart paralysis.

Plant Toxins wi th Action on Striped Muscles

These are divided into compounds causing paralysis and those convulsions. Among the paralytic-acting compounds is curare, a mixture of alkaloids occurring in the tropic climber Chondrodendron tomentosum Ruiz & Pavon. The active principles (+)- tubocurarin and C-toxiferin I (Fig. 46) act as inhibitors of acetylcholine receptors at the neuromuscular endplate. The Indians in the South American jungles impregnate hunting darts with extracts of the plant. After the toxin has entered the blood stream, the victim is paralyzed almost immediately. Both toxins are very potent. The LDs0 of tubocurarin in mice after application is 130 /zg/kg; it is only 23/zg/kg for C-toxiferin. As quater- nary ammonium salts, the compounds are not absorbed after oral ingestion. Animals killed by curare darts are, therefore, edible without danger of being poisonous, as long as the epithelium of the GI tract is

OH ~ ~ N CH3

---CH3 H

Ephedrine

lii2i H 5i!ii !JiUii ii!

H3CO

H 3 C ~ ~ OCH3

H H3CO H~'~O "OCH3

Reserpine


H 3 C O ~ 0 ~ ~

t . . - ~ ~ O C H ~ ~ H~CO O / ' ~ / ~ "]I "OCH~ /

OCH~

P apaveri ne N a rcoti ne

H~CO 0 . . . . . ~ / ~ )~CH~

HaCO O

Khellin

ii !

intact. If sufficient amounts of the toxins enter the circulatory system, a rapid paralysis of all striped muscles occurs. Suffocation occurs as a result of the inability to contract the diaphragm. The use of tubocurarin as a muscle relaxant in surgery was abolished because of the histamine release, leading sporadically to anaphylactic reactions.

Another compound with paralytic action is coniin (Fig. 47), occurring in Conium maculatum L. (poison hemlock) and Aethusa cynapium L. (fool's parsley). The

volatile compound is distributed in all parts of the plants. Concentrations up to 3.5% occur in the seeds of poison hemlock. The bad smell of coniin, which is similar to the urine of mice, prevents the ingestion of the plant by humans in most cases. Intoxication is more common in greasing animals. The ancient Greeks used extracts of the poison hemlock for exe- cutions. The most famous case was the execution of Socrates (399 A.D.), precisely reported by his friend Plato. The lethal dose for adult humans is approxi-

H3CO

H3: IH3 2CI

. . . . . . I |

H~C~-QN i

R = H" (+ ) -Tubocu ra r i nch l o r i de R = CH~; Chond rocu ra r i n i umch lo r i de

C-Toxiferin I

i l ................ i~ '~'~=~'i ~!iiii~y~:~'~i~i~:iiiii~ii ~'i~~i~Fi'iiiiiiliiiiiilii~i!?,~'~i~iii~ '~i!iiii~Iilililiiiiii~!iii!t~i~i~iiiiilililiiii~?~::~]~ii'=~iTi=ili[ ]~i~iiIiiiiiii~iii~iiiii~iill ~'~liiiiiii!iiiiiililFiiiiiiiiiiiiiiiii~F~'~iiiiiiiiiiiiiii~iiiiiiiiiiii~ilil ~' ;~ti~ilFi~'~iiiiiiiiilii#~iiiiiiiii!iiiiiiiiiiiii~ii~iiiiiiitliiiiiii~i ~iiii!!ii~iiiiiti~!ii!iiiili ~'~ii~i~|

998 Westendorf

Coniin

.Ni##i: :...~. ~N~ ~"~N:

~NNN~CzH~ H

mately 500 mg coniin. The compound is easily absorbed by the GI tract and also through the skin. After uptake of toxic doses, the symptoms of intoxication begin with a short period of excitement followed by paralysis, starting at the lower extremities and rising slowly to the head. When the paralysis reaches the diaphragm, death occurs by suffocation. Because con- sciousness is not affected, the victim experiences all phases of the intoxication until the end. Coniin exerts teratogenic effects in animals.

The convulsive compounds are divided into those acting at the medulla and the spinal cord. Among the central-acting compounds is picrotoxin, occurring in the seeds of the Asiatic climber Anamirta cocculus Wight et Arnott (levent berry, cockles). Picrotoxin is a mixture of two components, the toxic compound picrotoxinin and the nontoxic compound picrotin (Fig. 48). Because aquatic animals are extremely sensitive to the toxin, extracts of the plant have been used by native people for catching fish. Picrotoxin is used medicinally as an analeptic. Doses < 10 mg stimulate the respiration and the vasomotor center. This effect is

HO. CH~ H2C~ CH~

O _._.~....~) H ~ C H~ OH

H a C ' ~ - ~ O H~C

"O O O

Picrotin Picrotoxinin

H~C - (CHz)z - CH -(CH = CH)~- CH -CH -C - C-C -C I 1 OH HOH=C - (CH~)

Cicutoxin

H~C -CH -CH -(C-C)~ - (CH :CH)2-CH~-CH~ Ethusin

\ \ OH \ OH

Oenathetoxin

~ ~:~ ~ . . . . . . ~ ........ ~'~ ~]i~!~ ~ .......... ~;%~,~!~!i~ . . . . . ~ ..... ~" ~Ii ~ ~ ;~ i i ! i~ i~ l ~I

used for the treatment of beginning respiratory arrest. Toxic doses cause convulsions, similar to epilepsy. The LDs0 in mice (iv) is 4 mg/kg .

Cicuta virosa L. (Mackenzie's water hemlock) is one of the most toxic plants, growing in swampy areas of the moderate zones. The bulbs, which look similar to celery bulbs, contain a light yellow-orange juice located in caverns. The whole plant, especially the bulb contains the toxic polyinol cicutoxin (Fig. 49). Poison- ing occurs mainly by children who mistakenly eat the bulb. The plant was also used for suicide or homicide. Cicutoxin, like picrotoxin, causes excitement of the medulla. A single bite into the bulb of cicuta may be lethal. The symptoms of poisoning are extreme tor- ment. Very painful epileptiform seizures occur every 15-20 minutes and lead to total exhaustion (ATP depletion). Death occurs by heart or respiratory arrest.

The toxic polyinol oenanthotoxin (Fig. 49) is present in Oenanthe crocata L. (waterdropwort). The bulbs of this plant have a pleasant pastinak-like taste. The LD50 of the toxin for mice (iv) is less than 1 m g / kg. Aethusa cynapium L. (fool's parsley) contains an unsaturated aliphatic hydrocarbon, ethusin (Fig. 49), together with the paralyzing toxin coniin. Intoxication sometimes occurs by the erroneous use of the plant instead of parsley (Petroselinum crispum L.). The symptoms of intoxication depend on the proportion of the two toxins in the plant and may be either paralysis or convulsion.

Strychnine and brucine (Fig. 50), two related toxins occurring in Strychnus nux vomica L. (poison-nut tree) and Strychnus ignatii Berg., act at the medulla spinalis.


Like picrototoxin, strychnine is used as an analeptic. Because of the easy access (strychnine was used as a rodenticide) and its toxic potential (the lethal amount is 100 mg for adults and 1-5 mg for children), the toxin was often used in homicide. Strychnine and brucine inhibit post-synaptic inhibitory neurons, thus in- tensifying central neural impulses. Small doses cause an increase of sensory perceptions, whereas tetanoid convulsions occur after uptake of toxic doses. Epi- sodic convulsions occur either spontaneously or after minimal external stimuli, such as noise, light, or touching. Isolation of the patient in a dark quiet room is, therefore, an essential part of the therapy. Death occurs by central vasomotor or respiratory inhibition.

Compounds with Hypnotic or Psychotropic Action

Hypnotics The coagulated juice of the incised seed capsules of

Papaver somniferum L. (opium poppy), known as opium, contains about 20 alkaloids of the phenantrene or isoquinoline type. The spasmolytic-acting isoquinoline derivatives papaverine and narcotine have already been discussed. The phenanthrene derivatives in opium, represented by morphine, codeine, and thebaine (Fig. 51), act as hypnotics, analgesics, and psy- chotropics. Especially the last property is responsible for the abuse of opium for thousands of years. The use of opium was reported 4000 years ago by the Sumerians and later by the ancient Egyptians, Greeks, and Romans. Paracelsus (1493-1541) named opium "laudanum" and used it for many medicinal purposes. In the 19th century, opium advanced to a fash- ionable drug, especially among poets. The list of opium users includes Friedrich Schlegel, Novalis, E.T.A. Hoffmann, Edgar Allen Poe, and Charles Bau- delair.

Morphine is used in modern medicine as an effective central analgesic, whereas codeine is mainly used as an antitussive agent. Morphine and its derivatives act as agonists of the opioid (endorphine) receptors, which belong to the endogenic analgesic system. Long-time use leads to tolerance and addiction.

Poisoning by opium alkaloids is not rare and mainly due to the widespread abuse of narcotics, especially of the semisynthetic morphine analog heroin (Fig. 51). The diacetylation of the two hydroxygroups in morphine increases the lipophilicity. Heroin, therefore, enters the central nervous system more rapidly than morphine and the psychotropic action is more pronounced. Opium alkaloids easily pass through the placenta, causing tolerance and addiction in the new- born infant. The compounds are also excreted in the

N

H

H

( - ) -S t rychn ine

milk. It is, however, not clear, whether the doses are high enough to affect the nursling.

The symptoms of intoxication occur 30-60 minutes after oral ingestion and almost immediately after the injection of toxic doses of opium alkaloids. They consist of dizziness, drowsiness, general sedation, and increasing depression of respiration. Finally the victim falls into a deep coma. The combination of three symptoms is important for the diagnosis~miosis, respiratory depression, and unconsciousness. The contraction of the pupils is maximal (pin-point pupils) and is released if asphyxia occurs. The sphincters of the intestine and urinary bladder are spastically con- tracted. Death occurs by central respiratory arrest.

Plant Toxins with Psychotropic Properties The use of plants with psychotropic properties for

ceremonial purposes was common in almost all his-

H

Morph ine : R = R ~ = H Codeine: R = CH~; R~ = H Thebaine: R= R~ = CH~ Her.oin: R = R~ = COCH~

~ ~ ~,~ ............................. ~ ' ~ ~o~ .~ : ~ . . . . . . . . . . . . . . . . ~ ~ " ~ d , ~ ~ , ~,~ ~ ~

1000 Westendorf

CH3 I o N II ~ C--O --CH~

0

o

I H H I CH~ CH~

Cocaine Cuscohygri ne

torical cultures. The drugs were used help to get into contact with demons and the spirits of deceased rela- tives. The use of such drugs has never ceased and most modern nations have considerable problems with the abuse of psychotropic drugs. Although the trade in and even the possession of many psychotropic drugs are prohibited, the money earned by illegal trade in such compounds exceeds that of the most legal therapeutics by far.

In the hot and humid highlands of South America and Java grows the shrub Erytroxylum coca Lam. (coca). The leaves contain 0.7-2.5% alkaloids, mainly consisting of (-)-cocaine and cuskohygrin (Fig. 52). Al- though chemically related to atropine, cocaine is de- void of parasympatholytic properties. The compound inhibits the re-uptake of norepinephrine into axonic vesicles and is, therefore, adrenergic. It also inhibits the catecholamine-degrading enzyme monoaminooxi- dase (MAO). Especially after parenteral application (sniffing), it leads to excitation, euphoria, and hallucinations. The active oral dose is 50 mg, whereas much lower amounts are sufficient if taken by nasal application. The lethal dose is normally 1-2 g; however, fatal cases have been reported after uptake of only 100-200 mg. The LDs0 (iv) in rats is 17.5 mg/kg. The symptoms of intoxication consist of psychic exite- ment, convulsions, and, finally, respiratory arrest. On the mucous membranes and after subcutaneous injection, cocaine acts as a local anesthetic. This action is no longer used medicinally, but it is still useful for a simple identification of the drug; cocaine causes a feeling of numbness after contact with the tongue.

Great amounts of cocaine are produced in illegal laboratories. For this purpose, the leaves are used for extraction first with diluted hydrochloric acid. The hydrolyzed ester alkaloids are then isolated, esterified with methanol, and then benzoylated. Great amounts of pure cocaine are produced in Colombia, Bolivia, and Peru, from where it is illegally transported to the

CH3

H• OH

H 3 C - ~ o ~ . / " ~ ' - - CsH11 H3C

Tetrahydrocannabinol

black markets of North America and Europe. Cocaine leads to an addiction similar to that of opium alkaloids. Chronic abuse leads to physical and mental destruction. Consuming cocaine during pregnancy increases the incidence of malformations considerably.

The Indians of South America chew coca leaves after mixing them with lime or bone ash. This leads to a hydrolysis of the ester alkaloids. The resulting ecgonin exerts a stimulating effect similar to that of caffeine and decreases the feeling of hunger, which is important for poor people, such as the Indians in South America. In contrast to the parenteral application of cocaine, the chewing of coca does not produce addiction.

Canabis sativa L. ssp, Indica (Indian hemp) is used for the production of the psychedelic drugs marijuana (from the dry tips of the female plant) and hashish (from the brown resin made from the leaves and flowers of the female plant). The main areas of cultivation are the Middle East, India, and Mexico. The psychotropic actions are caused by the compound &-9,10- tetrahydrocannabinol (THC) (Fig. 53). The drug is most effectively used as a mixture of marijuana or hashish with tobacco and smoked in cigarettes ("joints") or pipes. A dose of I g of marijuana or 0.3 g of hashish, containing 5-20 mg THC, is necessary for one "trip." The drug is also effective after oral ingestion (as a tea); however, greater amounts are necessary because of the less-effective absorption. The action of the drug consists of euphoria and hallucinations. Overdosing may result in long-acting psychiatric disorders and unpredictable reactions ("horror trips"). Whether the drug causes addiction is a matter for discussion; however, marijuana consum- ers often change to stronger drugs, such as heroine and cocaine.


O

HN H '~"~N- -CH3

Lycergic acid amide

H3CO ~ N H 2

H3CO OCH3

Mescaline

OR I

H CH3

Ps i loc ine R = H | Psilocybine: R + HPO3

j

The Indians of North and Central America used a cactus that they called peyotl for cult ceremonies. Its psychotropic action is caused by mescaline (Fig. 54). Because of its relatively simple chemical structure, mescaline was synthesized in great amounts, mainly around 1970 and used instead of the more potent LSD as a psychedelic drug during the "hippie movement" (by the "people of flower power"). The effective dose is 200-500 mg. Today mescaline has been almost completely replaced by much more potent derivatives, such as 4-methyl-2,5,dimethoxy-c~-methylphen- ylethylamine (DOM). The action of mescaline and DOM is comparable to that of LSD and caused by its action on central tryptamine receptors. It consists mainly of spectral and acoustic visions, as well as an increased sense of touch. Mescaline was demonstrated to be teratogenic in animal experiments.

Similar symptoms are produced by psilocybine (Fig. 54), occurring in the mushroom Psilocybe mexicana Heims, which grows in Mexico. With an effective dose of 10 rag, psilocybine is much more potent than mescaline. The symptoms after the ingestion of psilocybine are similar to that of mescaline and LSD and are also due to an action on central tryptamine receptors. Like mescaline, psilocybine was shown to be teratogenic in laboratory animals. Other tryptamine derivatives occur in the seeds of a tree growing at the Orinoco river and on the isle of Trinidad. The tree, known by the native people as Yopo (Piptadenia peregrina (L.) Benth.), contains the compounds N,N- dimethyltryptamin (DMT) N-methyltryptamin, 5-me- thoxy-N-methyltryptamin and N,N-dimethyl-5-hy- droxytryptamin (bufotenin). The Indians pulverize the seeds, mix it with ash, and blow it in breathe through the nose. The seeds of two winding flowers growing in Mexico, Rivea corymbosa L. Hall and Ipom- oea tricolor Car. (morning glory; Nauhaut, coatlxoxo- uhqui) contain the amide of lysergic acid, which acts similar to, although less potent than, LSD. The effective dose is 2-10 mg. The native people liked to use the plants for cult ceremonies, as well.

Plant Toxins with Cytotoxic Action Some plant-derived compounds with cytotoxic ac-

tion have already been discussed earlier in this chapter (the lectines ricin, abrin, and phasin). Colchicine (Fig. 55), occurring in Colchicum autumnale L. (autumn crocus) acts as an inhibitor of cell mitosis. It is a very potent poison. The lethal dose is 20 mg for adults and 5 mg for children. After ingestion of the plant, the first symptoms of poisoning occur 2 -6 hours later and consist of severe gastrointestinal irritation with vomiting and diarrhea. An advancing paralysis occurs af-

H 3 C O / ' ~ ~ ~ / ~ H

"N--C-CH3 H3CO iO I 9

H3CO ' ~

OCH3

/~.."---CH3

"f I I CH3 I R CH3 CH3

Colchicine Vincristine R = CHO Vinblastine: R = CH 3

1002 Westendorf

CH3 CH3 .... ~ ~ : ~ O H

,,

H3C CH3 H3C CH~ a-Thujon ,8-Thujon

ter the absorption of colchicine. Death occurs after a latent period of 2 days by respiratory arrest. The con- sciousness is retained until the end. Cochicine reacts with cellular tubulin, causing a depolymerization of the microtubules. ~t~e mitosis is inhibited during the anaphase. This property is used in tissue culture for the investigation of chromosomes.

A similar action is caused by the vinca alkaloids (Fig. 55), occurring in the shrub Catharantus roseus (L.) G. Don. Vincristine and vinblastine are used as chemotherapeutic agents in the treatment of cancer. Both compounds have severely toxic side effects, consisting mainly in neurotoxic reactions with sometimes irreversible paresthesia. Both compounds cause leu- kopenia, which is more pronounced after the application of vinblastine and is dose limiting.

Among the monoterpenes there are also compounds with a high cytotoxic potential. Most important is thujon (Fig. 56), present in Thuja occidentalis L. (Eastern arborvitae) and Artemisia absinthium L. (absinthe) Acute intoxication causes severe irritation of the GI tract, as well as kidney and liver damage. Fi- nally paralysis of the central nervous system occurs. Chronic intoxication was common in the 1800s from the drinking of absinthe, an alcoholic beverage made by the distillation of brandy over vermouth, anise, and fennel. In this case, the symptoms of intoxication consist in the degeneration of the brain, leading to a total mental and physical disintegration. Today the production of and trade in absinthe are prohibited.

Plant Toxins with Skin-Irritating and Allergic Actions

Skin irritation and allergic skin reactions from plants or plant products are common and of growing concern because of the increasing popularity of "nat-

ural" cosmetics and skin-care products. Skin-irritating plants cause inflammation reactions without the in- volvement of immune reactions. These actions are produced, for example, by amines, such as acetylcholine, histamine, or serotonin, occurring in the bristles of Urtica dioica L. (stinging nettle). The tips of the silicated bristles break upon contact with the skin and the pointed stalks penetrate the skin. The amines cause erythema and itching. Severe symptoms, even fatal shock reactions, may occur if large areas of the skin are involved.

The milk of several Euphorbiaceae contains compounds that release histamine and other neuroactive amines from endogene reservoirs, such as mast cells. The chemical structures consist mainly in di- and tri- terpenes. Among these compounds are also the phorbol esters, which are known as potent tumor-promoting agents. Plant-derived enzymes are also able to cause skin irritation. Examples are papain, occurring in the fruit of Carica papaya L. (papaya) and bromelin, occuring in Ananas comosus L. Merr. (pineapple).

Plants with Allergenic Potential

Contact with such plants causes a sensitizing reaction with participation of T lymphocytes. Lymphoki- nes and cytokines are liberated after repeated contact with plant allergens and are responsible for inflammation reactions and the occurrence of eczema. About 10,000 plant species with an allergenic potential are known so far. Most belong to the family Asteraceae (former Compositae). Of special concern are species of the family Anarcardiaceae. Some species, such as Rhus toxicodendron L. (poison ivy), are among the most potent allergenic plants that exist.

Contact allergies are often caused by garden plants, such as Primula vulgaris Huds. (English primrose), Tu- lipa sylvestris L. (tulip), and Chrysanthemum frutescens L. (marguerite); food plants, such as Helianthus annuus L. (common sunflower), Humulus lupulus L. (common hops), and Cynara scolymus L. (globe artichoke); and many medicinal plants (see Table 8). The increasing popularity and uncontrolled use of herbal remedies promotes the occurrence of allergies to medicinal plants. An example is Arnica montana L. (mountain arnica). Tinctures prepared from the blossoms of the plant are used internally as well as externally for all kinds of injury. The poisonous compounds are sesquiterpene lactones (Fig. 57). Severe skin irritation with bullous blisters may occur after external use of extracts that are too concentrated. Internal overdosing results in irritation of the mucous membranes. After absorption, the sesquiterpene lactones cause headache, and cardiovascular and respiratory disorders.


Frequency of Plant Potency allergy occurrence

Anthemis cotula L. Strong Occasional (stinking chamomile)

Arnica montana L. Strong Frequent (Mountain arnica)

Cinnamomum zeylanicum Moderate Frequent (Cinnamon tree)

Hedera helix L. Moderate Occasional (English ivy)

Helianthus annuus L. Moderate Occasional (sunflower)

Inula helenium L. Strong Occasional (Elecampane inula)

Rhus toxicodendron L. Very strong Rare (in Europe); (poison ivy) frequent (in the

United States)

aAccording to Hausen (1988).

Fatal cases have been reported. Patients who have had allergic reactions to arnica are often allergic to other plants of the Asteraceae family, as well as to sesqui- terpen-containing plants, belonging to other families (e.g., Calophyllum ssp., laurel).

The most potent plant allergen is the milky juice of Rhus toxicodendron L. (poison ivy). Even contact with the leaves may result in severe eczema. About 60- 80% of the North American population is allergic to this plant. After acquiring an allergy, the symptoms may occur even after the use of homeopathic dilution >D6. Urushioles have been recognized as the toxic and allergenic principles. The compounds are catechol derivatives with aliphatic side chains variable in length and double bonds.

Plants Containing Phototoxic Compounds Some plants contain compounds that cause derma-

titis after contact or ingestion. The symptoms occur after exposure to sunlight as a result of the UVA content. Most of the phototoxic compounds belong to the group of furocoumarines (Fig. 58). In Europe, photo- dermatitis is often produced by Heracleum mantegaz- zianum Somm. et Lev. (giant hogweed) and Heracleum sphondylium L. After injury to the plant, a white juice is released that contains a mixture of furocoumarines. The compounds are activated by wavelengths of 310- 320 nm and sometimes cause severe itching and bullous dermatitis after contact with the skin. Healing may take several weeks.

OH Urushiole

H3C

-"o O CH~

HzC

Arnicolid D

0 CH~

Anthecotulid Alantolactone

Further plants with phototoxic components are Ruta graveolens L. (common rue), Archangelica officinalis (Moench) Hoffm. or Angelica archangelica (Norwegian angelica), Peucedanum osthruthium (L.) W. D. J. Koch (masterwort), Pastinaca sativa L. (wild parsnip), and Dictamnus albus L. (gas plant). Plants containing phototoxic compounds belonging to the group of anthraquinones are Hypericum perforatum L. (common St. Johns wort) and Fagopyrum esculentum Moench (buck- wheat). The former is a popular medicinal plant, used mainly as a mild sedative, whereas the latter is used as a food plant. Photodermatoses occur after the internal use of Hypericum extracts and exposure to sunlight. Fatal cases of phototoxicity were also observed in domestic animals (mainly in horses) after ingestion of wild St. Johns wort.

Carcinogenic and Tumor-Promoting Plant Compounds

A considerable percentage of the known carcinogens are of natural origin. Most are produced by fungi, but some are also synthesized by plants. A1-

1004 Westendorf

R

o %o R,

HO I

R

R

HO

0 OH

O OH

Furocumar ine phototoxic Anthraqu inones

Xanthotox in ' R = H, R~ = OCH3 Bergapten" R = OCHa, R~ = H Imperator in ' R = H, R1 = O-CH2-CH=C(CH3)2

Fagopyrines: R = OH, R1 = CH2-[CsHs(CH3)NO] Hypericine" R = OH, R1 = CH3

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most no carcinogens are produced primarily by animals. Natural carcinogens are an important cause of human cancer, possibly exceeding the importance of anthropogenic carcinogens. The occurrence of carcinogenic compounds is not limited to special plant families and extends over the most primitive Pterido- phytes (fern) to higher developed Gymnosperms (cycas palms) and the most developed Angiosperms (Se- necio ssp.). Plant-derived carcinogens also vary greatly with respect to their chemical structures. An overview of the most important compounds is given in Table 9.

Bracken fern (Pteridium aquilinum L. Kuhn) is the most important representative of primitive plants with carcinogenic action. The plant is ubiquitous in all temperate and mid-tropic zones of the world and responsible for considerable losses of domestic animals. Many cattle and sheep die after the ingestion of the plant, either from acute poisoning or after the development of esophageal or intestinal tumors. The use of bracken fern as a human food plant was correlated with the incidence of esophageal cancer in Ja- pan. The carcinogenic action is related to aquilide A (Fig. 59). The compound is mutagenic in bacterial systems and carcinogenic in rats.

Cycad plants of the families Cycas, Zamia, Macroza- mia, Bowenia, Enzepaloartos, and Stangeria are endemic in all tropical and subtropical areas of the world. Dif- ferent parts of the plants are used in the preparat ion of food and herbal medicine in Africa, Asia, and Cen- tral America. The carcinogenic action is related to cycasin (methylazooxymethanol-13-D-gucoside), which occurs especially in some cycas species (Cycas cirinalis L. and Cycas revoluta Tunb.), used as food plants. Methylazooxymethanol, an ultimate carcinogen, is pro-

duced after the cleavage of the glycosidic linkage. The compound, which reacts covalently with DNA, is tu- morigenic in laboratory animals after long-term oral treatment. Tumors occur in the liver, kidneys, and intestine.

The chewing of betel quid is popular in Malaya, New Guinea, East Africa, and Madagascar. The total number of betel-chewing people is estimated to about 450 millions. The quid consists of the nuts of the betel palm (Areca catechu L.), the green leaves of betel pepper (Piper betel L.), and lime (Ca(OH)a). The taste is often refined by the addition of tobacco and spices. Betel-chewing people have an extraordinarily high incidence of esophageal and laryngeal cancer. The action is most probably related to the alkaloid arecoline (Fig. 59), a compound that acts on the parasympathetic nerves. Tannins may also be involved in the carcinogenicity of betel quid.

Alkylbenzene derivatives, such as safrole, isosafrole, estragole, and ]3-asarone, occur in numerous plants that are used as foods and food additives. Among these are celery, basil, sassafras, anise, carrots, bananas, black pepper, and fermented tobacco. Espe- cially high concentrations of safrole were detected in sassafras oil, produced by steam distillation of the bark and wood of the sassafras tree (Sassafras albidum (Nutt) Nees). The addition of safrole or ]3-asarone to foods or beverages (e.g., root beer and vermouth) is now prohibited. Animal experiments show that the liver is the main target of the carcinogenic action of alkylbenzenes.

Tannin, a mixture of polyphenols, occurs in numerous foods and beverages. High concentrations are usually found in red wine, black tea, and tea prepa-

Compound

~iiii~iiii~iiii!| ~l~i ~ ~'~i'~i~'~' ~'~'~| ~' ~'~i~!~|174 ~'l~| ~~ ~:~ii~i~iiil~i~i~I~!i~ii~ili : ~ i ~ | 1 7 4 ~;i~l~ii~i~ifIiii~lil~i~i~i~'~!i~!~| ~ , ~ i i i l ~ i i i : ~ i i ~ :~ ~ . . . . , .... : ~ ~ I ~ ! ..... ~ ~ " ~ii',~#!i;@~l~',iti~e~iI~ii~l~i~i!~ ~ l ~

Occurrence Species Target organ Source

Allylisothiocyanat

Aquilid A Arecoline Aristolochic acid /3-Asaron Asiaticosid Benzylacetat Capsaicin Crotonoil Coumarin

Cycasin

Estragole

Gossypol Isosafrole Limonene Psoralene

(+)Parasorbinic acid

Pyrrolizidinalkaloids Clivorine Dehydroheliotridine Dehydromonocrotaline Dehydroretronecine Heliotrine

Hydroxysenkirkine Lasiocarpine

Petasitenine Isatidine Jacobine Lycopsamine Monocrotaline Retronecine Retrorsine Riddeline Senkirkine Symphytine Reserpine Rotenone

Safrole

Sanguinarine Shikimic acid Sterculic acid

Tannines

Thiourea

Brassica-ssp. Mouse Skin, stomach Mustard, cabbage, horseradish

Pteridium aquilinum Rat Breast, intestine, bladder Bracken fern Areca catechu Mouse Liver, lung, stomach Betel nuts, drug Aristolochia clematitis Rat Stomach, kidney, bladder Drug Acorus calamus Rat Intestine Flavoring agent, drug Centella asiatica Mouse Skin Externum against wounds Jasminum ssp. Mouse Forestomach, liver Perfumes, jasmine tea Capsicum ssp. Mouse Intestine Chili, red pepper Croton tiglium Mouse Skin Contact with plant Dipteryx odorata, Rat Bile duct Food additive

Asperula odorata, fragrance, drug Cinammonum cassia Lavendula officinalis

Cycas ssp., Zamia ssp. Rat Liver, kidney, intestine, lung, Cycad nuts, starch, drug breast, brain, testis

Mouse Liver, kidney, lung, bone marrow

Hamster Liver, bone marrow Artemisia draculuncus Mouse Liver Flavoring agent, fragrance

Ocimium basilicum, Foeniculum vulgare

Gossypium hirsutum Cananga odorata Citrus ssp. Umbelliferaceae,

Rutaceae, Leguminosae, Moraceae, Orchidaceae

Sorbus aucuparia

Ligularia dentata Heliotropium ssp. Crotalaria ssp. Senecio ssp. Heliotropium ssp.

Tussilago farfara, Heliotropium ssp.

Symphytum ssp. Petasites japonicus Senecio ssp. Senecio ssp. Amsinckia intermedia Crotalaria ssp. Senecio ssp. Senecio ssp. Senecio ssp. Tussilago farfara Symphytum officinale Rauvolfia serpentina Derris ssp.,

Tephrosia ssp. Lonchocarpus ssp.

Sassafras albidum, Illicium anisatum, Myrisitica fragrans Cinammonum ssp

Argemone mexicana numerous plants Sterculia foetida

Hibiscus syriacus Cammellia sinensis,

Acacia mollissima, Hammamelis virginiana, Pteridium aquilinum, Areca catechu

Laburnum ssp.

Mouse Skin Cotton seed oil Rat Liver, esophagus Flavoring agent, fragrance Mouse Skin Citrus oil Mouse Skin Celery, fig, parsley, drug,

cosmetics

Rat Local sarkomas Jelly

Rat Liver Rat Multiple organs Drug Mouse Skin Drug, food Rat Musculature Drug, food Rat Pancreas, liver, bladder, Drug

testis Rat Brain Drug, food Rat Liver, skin, bone marrow Drug

Rat Liver Drug, food Rat Liver Drug, food Chicken Liver Drug, food Rat Pancreas Drug, food Rat Liver, lung, pancreas Drug, food Rat Pituitary, spinal cord Drug Rat Liver, kidney, lung Drug, food Rat Liver Drug, food Rat Liver Drug Rat Liver, kidney, lung Drug, food Rat Liver, adrenal, bone marrow Drug Rat Breast, thyroid gland Piscicide, insecticide

parathyroid gland

Rat Liver Root beer Mouse Liver, lung Sassafras tea, natural

drugs, black pepper, nutmeg

Rat Bladder Drug, food oil Mouse Stomach, bone marrow Green plants Trout Liver Cotton seed oil

Rat Liver Tea, red wine, fruits, Mouse Liver, bladder vegetables, leather

industry

Rat Liver, thyroid gland Drug, fungicides Mouse Thyroid gland Textile-, paper-, photo- Trout Liver industry, cosmetics

aAccording to Lai und Woo (1987).

1006 Westendorf

/--o 0

COOH

T v "NO2 OCH3

Aristolochic acid

OH

CHO oHOHCc~~~ "

Gossypol . .

H3C OIH I O

~ C H s HsC ~" "~//I ~'~

CH2OH O

OH Aquilid A

CH2OH 0 t Ho~O-CH2- N- N -CH3

OH

Cycasin

,, ~ H3C~N/~ '~OC H 3 CH2-CH-CH2

Safrol Arecoline

OH ~--~_~H/cH~

H,C ~/ ~CH3 HO ~L_~ H

7, H H 3 c ~ ~ H ~H // / ~

O OH CH2OH Phorbol

rations of mate (Ilex paraguariensis A. St. Hil.), cacao (Theobroma cacao L.), and khat (Catha edulis (Vahl) Forsskal ex Endl.). Numerous epidemiological inves- tigations suggest a correlation between the uptake of tannin and the occurrence of liver and esophageal cancer. The incidence of liver cancer is much higher in countries with a high consumption of red wine (e.g., France, Greece, and Italy), compared with those with a consumption of predominantly white wine (e.g., Germany). The gauchos of Rio Grande do Sul (Brazil) have a high incidence of esophageal cancer. A correlation with the use of mate, a stimulating tea prepared from the leaves of Ilex paraguariensis A. St. Hil., rich in tannin, is most probable. A high incidence of esophageal cancer occurs also in people living in East Africa, where the chewing of khat is common. The carcinogenic action of tannin was demonstrated in rats.

Another polyphenol with carcinogenic properties is gossypol (Fig. 59), occurring in cotton seed oil, which is used for cooking in some countries (e.g., Egypt). Gossypol in a dose of 10 m g / d a y is an effective inhibitor of the spermatogenesis. About 10,000 men in China have been treated experimentally with the compound as a contraceptive. Gossypol was shown to act as a potent tumor promoter in the mouse skin model.

Many medicinal plants contain carcinogenic compounds, for example, pyrrolizidine alkaloid-containing plants, such as Tussilago farfara L. (coltsfoot), Petas- ites hydridus L. (pestilence wort), Symphytum officinale L. (common comfrey), and many Senecio ssp (ragwort). The compounds are metabolized in the liver to toxic pyrrole derivatives, which form covalent adducts with the DNA of liver cells (Fig. 38). The hepa- tocarcinogenic action of pyrrolizidine alkaloids, such


as senkirkine, hydroxysenkirkine, senecionine, lasiocarpine, monocrotaline, dehydromonocrotal ine, retrorsine, retronecine, isatidine, riddeline, lycopsamine, intermedine, jacobine, and seneciphylline, was demonst ra ted in numerous animal studies.

A carcinogenic nitro compound of plant origin is aristolochic acid (Fig. 59), occurring in Aristolochia clematitis L. (birthwort), a plant with a long tradition as a herbal medicine. The compound was shown to produce DNA adducts and gastric tumors in rats. The preparat ion of drugs from bir thwort is prohibited in many countries, whereas other medicinal plants with carcinogenic ingredients are still in use. Among these are plants containing pyrrolizidine alkaloids and anthraquinones.

Phorbolesters (Fig. 59) belong to the most powerful tumor-promot ing agents known. They occur in plants of the family Euphorbiaceae, especially in the seeds of Croton t igl ium L. (purging croton). Ingestion of croton oil causes severe irritation of the gastrointestinal mucosa, with vomit ing and diarrhea. Irritation also occurs after epidermal contact with croton oil. The ingestion of four seeds of croton may be lethal for humans. The inflammation reactions are mediated by prostaglandins and reactive oxygen species, which are most probably also responsible for the tumor-promoting activity of croton oil.

Bibliography De Smet P. A. G. M., Keller, K., H/insel, R., and Chandler, R. F.

(eds.) (1993). "Adverse Effects of Herbal Drugs" Vol. I and II. Springer Verlag, Berlin.

Frohne, D. and Pf/inder, H. J. (1983). "Giftpflanzen. Ein Handbuch ffir Apotheker, Artzte, Toxikologen und Biologen," 2nd ed. Wiss. Verlagsgesellschaft, Stuttgart.

Habermehl, G. (1985). "Mitteleurop/iische Giftpflanzen und ihre Wirkstoffe." Springer-Verlag, Berlin.

Habermehl, G. (1987). "Gift-Tiere und ihre Waffen" (Toxic Animals and Their Weapons 4th ed. Springer Verlag, Berlin.

Harding, K. A., and Welch, K. R. G. (1980). "Venomous Snakes of the World: A Check List." Pergamon Press, Elmsford, NY.

Hausen, B. (1988). "Allergiepflanzen, Pflanzenallergene. Handbuch und Atlas der allergieinduzierenden Wild- und Kulturpflan- zen." Ecomed, Landsberg.

Mebs, D. (1992). "Gifttiere" (Toxic Animals). Wissenschaftl Verlags- gesellschaft, Stuttgart.

Lai, D. Y., and Woo Y. (1987). Naturally occurring carcinogens: An overview. J. Environ. Sci. Ilth. C5(2), 121-173.

Roth, L., Daunderer, M., and Korman, K. (1988). "Giftpflanzen, Pflanzengifte. Vorkommen, Wirkung, Therapie, Allergische und phototoxische Reaktionen," 3rd ed. Ecomed, Landsberg.

Roth, L., Frank, H., and Korman, K. (1990). "Giftpilze-Pilzgifte. Schimmelpilze Mykotoxine. Vorkommen, Inhaltssoffe, Pilzaller- gien, Nahrungsmittelvergiftungen." Ecomed, Landsberg.

Russel, F. E. (1980). "Snake Venom Poisonining." Lippincott, Phila- delphia, PA. (Reprinted Scholium International, Great Neck, NY., 1983).

Ueno, Y. (1985). The toxicology of mycotoxins. Crit. Rev. Toxicol. 14, 99-132.

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