Pharmacodynamics

Pharmacodynamics - study of the physiological effects of drugs on the body or

on microorganisms or parasites within - and the mechanisms of drug action and the relationship between drug concentration and

effect.

L +R = L.Rwhere L=ligand (drug), R=receptor (attachment

site)

PK PD analysis

Pharmacodynamics is often summarized as the study of what a drug does to the body,

whereas pharmacokinetics is the study of what the body does to a drug.

Pharmacodynamics is abbreviated as "PD", and when referred to in conjunction with pharmacokinetics can be referred to as

"PKPD"

Effects on the bodyThe majority of drugs either (a) mimic or inhibit normal physiological/biochemical

processes or inhibit pathological processes in animals (b) inhibit vital processes of endo or ectoparasites and

microbial organisms.There are 5 main drug actions:• Depressing• Stimulating • Destroying cells (cytotoxicity) • Irritation • Replacing substances

Desired activityThe desired activity of a drug is mainly due to one

of the following:• Cellular membrane disruption (of the pathogen)• Chemical reaction• Interaction with enzyme proteins • Interaction with structural proteins • Interaction with carrier proteins • Interaction with ion channels • Ligand binding to receptors

– Hormone receptors – Neuromodulator receptors – Neurotransmitter receptors

Few of them – their mode of action• General anesthetics - work by disordering the neural

membranes, thereby altering the Na+ influx.• Antacids and chelating agents combine chemically in

the body. Ex. Enzyme-substrate binding is a way to alter the

production or metabolism of key endogenous chemicals, for example aspirin irreversibly inhibits the enzyme prostaglandin synthetase (cyclooxygenase) thereby preventing inflammatory response.

• Colchicine, a drug for gout, interferes with the function of the structural protein tubulin.

• Digitalis, a drug still used in heart failure, inhibits the activity of the carrier molecule, Na-K-ATPase pump

NEED LESS TO SAY

The widest class of drugs act as ligands which bind to receptors which determine

cellular effects. Upon drug binding, receptors can elicit

their normal action (agonist), blocked action (antagonist), or even action

opposite to normal (inverse agonist).

Undesirable effects (Unwanted effects or side effects)

Undesirable effects of a drug include:• Increased probability of cell mutation

(carcinogenic activity) • A multitude of simultaneous assorted actions

which may be deleterious • Interaction (additive, multiplicative, or

metabolic) • Induced physiological damage, or abnormal

chronic conditions

Therapeutic WindowThe therapeutic window is the amount of a

medication between the amount that gives an effect (effective dose) and the amount that gives

more of adverse effects than desired effects. For instance, medication with a small therapeutic

window must be administered with care and control, e.g. by frequently measuring blood

concentration of the drug, since it easily loses effects or gives adverse effects

The therapeutic index (also known as therapeutic ratio), is a comparison of the amount of a therapeutic agent that causes

the therapeutic effect to the amount that causes death. A therapeutic index is the lethal dose of a drug for 50% of the

population (LD50) divided by the minimum effective dose for 50% of the population (ED50).

A high therapeutic index is preferable to a low one: this corresponds to a situation in which one would have to take a much higher dose of a drug to reach the lethal threshold than

the dose taken to elicit the therapeutic effect.

One of the more commonly used measures of toxicity is the LD50.

The LD50 (the lethal dose for 50 percent of the animals tested) of a poison is usually expressed in milligrams of chemical per kilogram of body weight (mg/kg). A chemical with a small LD50 (like 5 mg/kg) is very highly toxic. A chemical with a large LD50 (1,000 to 5,000 mg/kg) is

practically non-toxic.

DOSE RESPONSE RELATIONSHIP

The characteristics of exposure to a chemical and the spectrum of effects caused by the chemical come

together in a correlative relationship that toxicologists call the dose-response relationship. This relationship is

the most fundamental and pervasive concept in toxicology. To understand the potential hazard of a specific chemical, toxicologists must know both the type of effect it produces and the amount, or dose,

required to produce that effect.

DOSE RESPONSE RELATIONSHIP

The dose-response relationship, or exposure-response relationship, describes the change in effect on

an organism caused by differing levels of exposure (or doses) to a stressor (usually a chemical) after a

certain exposure time . This may apply to individuals (e.g.: a small amount has no significant effect, a large

amount is fatal), or to populations (e.g.: how many people or organisms are affected at different levels of

exposure).

DOSE RESPONSE RELATIONSHIP

A dose-response curve is a simple X-Y graph relating the magnitude of a stressor (e.g. concentration of a pollutant, amount of a drug, temperature, intensity of radiation) to the response of the receptor (e.g. organism under study). The response may be a physiological or biochemical response, or

even death (mortality), and thus can be counts (or proportion, e.g., mortality rate), ordered descriptive categories (e.g., severity of a lesion), or

continuous measurements (e.g., blood pressure). A number of effects (or endpoints) can be studied, often at different organizational levels (e.g.,

population, whole animal, tissue, cell).

The measured dose (usually in milligrams, micrograms, or grams per kilogram of body-weight for oral

exposures or milligrams per cubic meter of ambient air for inhalation exposures) is generally plotted on the X axis and the response is plotted on the Y axis. Other

dose units include moles per body-weight, moles per animal, and for dermal exposure, moles per square centimeter. In some cases, it is the logarithm of the

dose that is plotted on the X axis, and in such cases the curve is typically sigmoidal, with the steepest portion in

the middle.

BIOCHEMICAL BASIS OF TOXICITY

DETOXIFICATIONOR

BIOTRANSFORMATIONOR

METABOLISM OF XENOBIOTICS

BIOTRANSFORMATION

Process that converts the parent compound into metabolites and then forms conjugates

Can happen in 2 phases

Phase I Phase II

BIOTRANSFORMATION

Considered as the mechanism of detoxification by host organisms

But some times the metabolites are more toxic than the parent compound

Bioactivation

BIOTRANSFORMATION

Phase I – involves oxidation, reduction and hydrolysis (may be considered as degradation reactions)Phase II – involves the production of compound (a conjugate) that is biosynthesized from the toxicant or its metabolite Example : Benzene Phase I Phenol

Phase IIconjugates with sulfate

Hepatic microsomal enzymes (oxidation, conjugation)

Extrahepatic microsomal enzymesExtrahepatic microsomal enzymes (oxidation, conjugation)(oxidation, conjugation)

Hepatic non-microsomal enzymes Hepatic non-microsomal enzymes (acetylation, sulfation,GSH, (acetylation, sulfation,GSH, alcohol/aldehyde dehydrogenase,alcohol/aldehyde dehydrogenase,hydrolysis, ox/red)hydrolysis, ox/red)

Drug Metabolism

http://en.wikipedia.org/wiki/File:Xenobiotic_metabolism.png

Phase I vs Phase IIEnzyme Phase I Phase II

Types of reactions HydrolysisOxidationReduction

Conjugations

Increase inhydrophilicity

Small Large

General mechanism Exposes functionalgroup

Polar compound addedto functional group

Consquences May result inmetabolic activation

Facilitates excretion

The Phase I System The Phase I detoxification system, composed

mainly of the cytochrome P450 supergene family of enzymes, is generally the first

enzymatic defense against foreign compounds.

Most pharmaceuticals are metabolized through Phase I biotransformation

The Phase I SystemIn a typical Phase I reaction, a cytochrome P450 enzyme (CypP450)

uses oxygen and NADH as a cofactor, to add a reactive group, such as a hydroxyl radical.

reactive molecules which may be more toxic than the parent molecule

If these reactive molecules are not further metabolized by Phase II conjugation, they may cause damage to proteins, RNA, and DNA

within the cell.

The Phase I System Several studies have shown evidence of

associations between induced Phase I and/or decreased Phase II activities and an increased

risk of disease, such as cancer, SLE , and Parkinson’s disease

Compromised Phase I and/or Phase II activity has also been implicated in adverse drug

responses

CYP P 450Cytochrome P450 (abbreviated CYP, P450,

infrequently CYP450) is a very large and diverse superfamily of hemoproteins found in all domains of

life. Cytochromes P450 use a plethora of both exogenous and

endogenous compounds as substrates in enzymatic reactions.

Usually they form part of multi-component electron transfer chains, called P450-containing systems.

The most common reaction catalysed by cytochrome P450 is a monooxygenase reaction, e.g. insertion of one atom of oxygen into an organic substrate (RH) while the other oxygen atom is reduced to water:

RH + O2 + 2H+ + 2e– → ROH + H2O

CYP P 450• CYP enzymes have been identified from all lineages

of life, including mammals, birds, fish, insects, worms, sea squirts, sea urchins, plants, fungi, slime molds, bacteria and archaea.

• More than 11500 distinct CYP sequences are known and named .

• The name cytochrome P450 is derived from the fact that these are colored ('chrome') cellular ('cyto') proteins, with a "pigment at 450 nm", so named for the characteristic Soret peak formed by absorbance of light at wavelengths near 450 nm when the heme iron is reduced (often with sodium dithionite) and complexed to carbon monoxide.

Electron flow in microsomal drug oxidizing system

CO

hCYP-Fe+2

Drug

CO

O2

e-

e-

2H+

H2O

Drug

CYPR-Ase

NADPH

NADP+

OHDrug

CYP Fe+3

PC Drug

CYP Fe+2

Drug

CYP Fe+2

Drug

O2

CYP Fe+3

OHDrug

Cytochrome P450 Isoforms (CYPs) - An Overview

• NADPH + H+ + O2 + DrugNADP+ + H2O + Oxidized Drug

• Carbon monoxide binds to the reduced Fe(II) heme and absorbs at 450 nm (origin of enzyme family name)

• CYP monooxygenase enzyme family is major catalyst of drug and endogenous compound oxidations in liver, kidney, G.I. tract, skin, lungs

• Oxidative reactions require the CYP heme protein, the reductase, NADPH, phosphatidylcholine and molecular oxygen

• CYPs are in smooth endoplasmic reticulum in close association with NADPH-CYP reductase in 10/1 ratio

• The reductase serves as the electron source for the oxidative reaction cycle

Phase I - Hydrolysis

• Carboxyesterases & peptidases– hydrolysis of esters, eg: valacyclovir, midodrine – hydrolysis of peptide bonds, eg: insulin (peptide)

• Epoxide hydrolase– H2O added to epoxides, eg: carbamazepine

Phase I - Reduction• Azo reduction

– N=N to 2 -NH2 groups– eg: prontosil to sulfanilamide

• Nitro reduction– N=O to one -NH2 group– eg: 2,6-dinitrotoluene activation

• N-glucuronide conjugate hydrolyzed by gut microflora• Hepatotoxic compound reabsorbed

• Carbonyl reduction– Alcohol dehydrogenase (ADH)

• Chloral hydrate is reduced to trichlorothanol• Disulfide reduction

– First step in disulfiram metabolism• Sulfoxide reduction

– NSAID prodrug Sulindac converted to active sulfide moiety

Phase I - Reduction• Quinone reduction

– Cytosolic flavoprotein NAD(P)H quinone oxidoreductase• two-electron reduction, no oxidative stress• high in tumor cells; activates diaziquone to more potent form

– Flavoprotein P450-reductase• one-electron reduction, produces superoxide ions• metabolic activation of paraquat, doxorubicin

• Dehalogenation– Reductive (H replaces X)

• Enhances CCl4 toxicity by forming free radicals– Oxidative (X and H replaced with =O)

• Causes halothane hepatitis via reactive acylhalide intermediates– Dehydrodechlorination (2 X’s removed, form C=C)

• DDT to DDE

Phase I: Oxidation-Reduction

• Alcohol dehydrogenase– Alcohols to aldehydes (Genetic polymorphism-

Asians metabolize alcohol rapidly)– Inhibited by ranitidine, cimetidine, aspirin

• Aldehyde dehydrogenase– Aldehydes to carboxylic acids– Inhibited by disulfiram

Phase I: Monooxygenases

• Flavin-containing mono-oxygenases– Generally results in detoxification– Microsomal enzymes– Substrates: nicotine, cimetidine, chlopromazine,

imipramine– Repressed rather than induced by phenobarbital,

3-methylcholanthrene

Phase I: Monooxygenases• Monoamine oxidase

– Primaquine, haloperidol, tryptophan are substrates– Activates 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine

(MPTP) to neurotoxic toxic metabolite in nerve tissue, resulting in Parkinsonian-like symptoms

• Peroxidases couple oxidation to reduction of H2O2 & lipid hydroperoxidase– Prostaglandin H synthetase (prostaglandin metabolism)

• Causes nephrotoxicity by activating aflatoxin B1, acetaminophen to DNA-binding compounds

– Lactoperoxidase (mammary gland)– Myleoperoxidase (bone marrow)

• Causes bone marrow suppression by activating benzene to DNA-reactive compound

Phase I Effects

Biotransformation by liver or gut enzymes before compound reaches systemic circulation

&Results in lower systemic bioavailbility of parent

compound

The Phase II SystemPhase II conjugation reactions generally follow

Phase I activation, resulting in a xenobiotic that has been transformed into a water-soluble compound that can be excreted

through urine or bile. Several types of conjugation reactions are seen

in PII - glucuronidation, sulfation, and glutathione and amino acid conjugation

The Phase II System In phase II reactions, the activated xenobiotic

metabolites are conjugated with charged species such as glutathione (G-SH), sulfate,

glycine, or glucuronic acid. These reactions are catalysed by a large group of broad-specificity

transferases, which in combination can metabolise almost any hydrophobic

compound that contains nucleophilic or electrophilic groups.

The Phase II System

One of the most important of these groups are the glutathione S-transferases (GSTs). The

addition of large anionic groups (such as G-SH) detoxifies reactive electrophiles and produces

more polar metabolites that cannot diffuse across membranes, and may, therefore, be

actively transported.

The Phase II System

These reactions requirecofactors which must be replenished through

dietary sources.

Phase II - GlucuronidationMajor Phase II pathway in mammals

UDP-glucuronyltransferase forms O-, N-, S-, C- glucuronides; six forms in human liver

Cofactor: UDP-glucuronic acidInducers: Phenobarbital, indoles,

3-methylcholanthrene, cigarette smokingSubstrates : dextrophan, methadone, morphine,

p-nitrophenol, valproic acid, NSAIDS, bilirubin, steroid hormones

Conjugation Reactions Glucuronidation

OOH

OHOOH

CO2H

P O P O

O

HO

OH

O

CH2

O NNH

O

O

OOH

OHOH

CO2HO R

+ ROH

orR3N

UGT

UDP- -D-glucuronic acidO

OH

OHOH

CO2HN+ R

R

R

O-glucuronide

N+-glucuronide

Liver has several soluble UDP-Gluc-transferases

Phase II – Sulfation

- Sulfotransferases are widely-distributed enzymes - Cofactor is 3’-phosphoadenosine-5’-phosphosulfate

(PAPS)- Produce highly water-soluble sulfate esters,

eliminated in urine, bile- Xenobiotics & endogenous compounds are sulfated

(phenols, catechols, amines, hydroxylamines)

Conjugation Reactions Sulfation

Examples: ethanol, p-hydroxyacetanilide, 3-hydroxycoumarin

(PAPS, 3’-phosphoadenosine-5’-phosphosulfate)

R OH

R O S OH

O

O H H

NH2

N

NN

N

OH

O

H HHO

O P

OH

O

O SOH

O

O

+

Phase II – Acetylation

- Major route of biotransformation for aromatic amines, hydrazines

- Generally decreases water solubilityN-acetyltransferase (NAT)

- Cofactor is AcetylCoenzyme A

- Humans express two formsSubstrates include sulfanilamide, isoniazid, dapsone

Conjugation ReactionsAcetylation

Examples: Procainamide, isoniazid, sulfanilimide, histamine

NAT enzyme is found in many tissues, including liver

Ar NH2

R SH

R OH

R NH2

+

Ar NCH3

O

H

Acetyl transferase

CoA SO

R NO

CH3H

R OO

CH3

R SO

CH3

METHYLATION

- Common, minor pathway which generally decreases water solubility

- Enzyme involved is Methyltransferases- Cofactor: S-adenosylmethionine (SAM)

- Reaction (-CH3 ) transfer to O, N, S, C- Substrates include phenols, catechols, amines,

heavy metals (Hg, As, Se)

AMINO ACID CONJUGATION

- Alternative to glucuronidationTwo principle pathways

- COOH group of substrate conjugated with -NH2 of glycine, serine, glutamine, requiring CoA activation

(e.g: conjugation of benzoic acid with glycine to form hippuric acid)

(or)- Aromatic -NH2 or NHOH conjugated with -COOH of

serine, proline, requiring ATP activation

AMINO ACID CONJUGATION

- Substrates: bile acids, NSAIDs- Species specificity in amino acid acceptors mammals: glycine (benzoic acid) birds: ornithine (benzoic acid)

dogs, cats: taurine (bile acids)nonhuman primates: glutamine

- Metabolic activation(Serine or proline N-esters of hydroxylamines are unstable & degrade to reactive electrophiles)

GLUTATHIONE CONJUGATION

- Enormous array of substrates- Glutathione-S-transferase catalyzes

conjugation with glutathione - Glutathione is a tripeptide of glycine, cysteine,

glutamic acid-Formed by -glutamylcysteine synthetase,

glutathione synthetase- Buthione-S-sulfoxine is inhibitor

GLUTATHIONE CONJUGATION

- Two types of reactions with glutathione1. Displacement of halogen, sulfate, sulfonate, phospho, nitro group

2. Glutathione added to activated double bond or strained ring system

- Glutathione substrates are hydrophobic, containing electrophilic atom- Can react with glutathione nonenzymatically

GLUTATHIONE CONJUGATION

- Excretion of glutathione conjugates - Excreted intact in bile - Converted to mercapturic acids in

kidney and excreted in urine

- Enzymes involved are - glutamyltranspeptidase, aminopeptidase

Environmental Toxicology

“What is there that is not poison?

All things are poison and nothing is without

poison.Solely the dose

determines that a thing is not a poison.”

In other words, “the dose makes the poison”

Paracelsus

Terms

• Toxicology – study of exposure to and adverse effects of chemicals in living organisms

• Toxicant – A toxic chemical of human origin• Toxin – A natural toxic chemical usually a

protein• Exposure – Chemicals come in contact with, and

are absorbed into organisms• Effect – Absorbed chemicals interact with a

molecular target and cause a (generally adverse) change

Major Routes of Chemical Entry• Ingestion – via the gastro-intestinal [GI] tract• Inhalation – via the lungs• Dermal – via the skin

Exposure Duration• Acute – Less than 24 hours – generally a single dose• Repeated Exposures – usually dietary• Subacute – Repeated exposure for 1 month or less• Subchronic – Repeated exposure for 1 to 3 months• Chronic – Repeated exposure for greater than 3

months

Acute and Chronic ExposuresCan Lead to Very Different Outcomes

Benzene• Acute exposure – Central nervous system

narcosis• Chronic exposure – bone marrow damage and

leukemiaCigarette Smoke

• Acute exposure – Nervous system stimulation, calming (nicotine)

• Chronic exposure – Cancer of mouth, pharynx, larynx, lung, esophagus, pancreas and bladder; emphysema

InorganicMetalsToxic metals• Lead · Mercury· Cadmium · Silver · Thallium ·

Tin · Beryllium · CobaltDietary minerals• Manganese · Copper · Iron · Chromium · Zinc·

SeleniumMetalloids• ArsenicNonmetals/halogen compounds• Fluoride · ChlorineOther• Radiation poisoningOrganic Phosphorus• Pesticides: OrganophosphatesNitrogen• CyanideCHO• alcohol (Ethanol, Methanol, Ethylene glycol)

Carbon monoxide · Oxygen toxicity

PharmaceuticalsDrug overdosesOn nervous system• Salicylate · Paracetamol ·

Opioids · Benzodiazepines · TCAs · Anticholinesterase

On cardiovascular system• Digoxin toxicity• DipyridamoleVitamins• Vitamin A• Vitamin D• Vitamin E

Biological(including venom, toxin, food poisoning)

Fish/seafood• Shellfis poisoning (Paralytic shellfish poisoning, Diarrheal shellfish

poisoning, Amnesic shellfish poisoning, Neurotoxic shellfish poisoning) · Ciguatera · Ichthyoallyeinotoxism· Scombroid · Haff disease

Other vertebrates• snake venom(Alpha-Bungarotoxin, Ancrod, Batroxobin) amphibian

venom: Batrachotoxin · Bombesin · Bufotenin · Physalaemin birds/quail: Coturnism

Arthropods• arthropod venom: Bee sting/bee venom (Apamin, Melittin) · spider

venom (Latrotoxin/Latrodectism) · scorpion venom (Charybdotoxin)Tick paralysis

Poisonous plants/ derivatives• Mushroom poisoning · Lathyrism · Ergotism · Strychnine poisoning ·

Cinchonism · Locoism (Pea struck)

Toxicity

• Tissue specific toxicity (Hepatotoxicity)• Genotoxicity• Pesticide toxicity• Food toxicity• Occupational toxicity• Environmental toxicity

HepatotoxicityImplies chemical-driven liver damage. The liver plays a central role in transforming and clearing chemicals and is susceptible to the toxicity from

these agents. Certain medicinal agents when taken in overdoses and sometimes even when

introduced within therapeutic ranges may injure the organ. Other chemical agents such as those

used in laboratories and industries, natural chemicals (e.g. microcystins- non ribosomal

peptides produced by cyanobacteria) and herbal remedies can also induce hepatotoxicity.

Chemicals that cause liver injury are called hepatotoxins.

Hepatotoxicity

More than 900 drugs have been implicated in causing liver injury and it is the most common

reason for a drug to be withdrawn from the market. Chemicals often cause subclinical

injury to liver which manifests only as abnormal liver enzyme tests. Drug induced

liver injury is responsible for 5% of all hospital admissions and 50% of all acute liver failures.

Drug metabolism in liver

Drug metabolism in liver: transferases are : glutathione, sulfate, acetate, glucoronic acid. P-450 is cytochrome P-450 enzymes. 3 different pathways are depicted for Drugs A, B and C

Hepatotoxicity• The human body identifies almost all drugs as foreign

substances (i.e. xenobiotics) and subjects them to various chemical processes (i.e. metabolism) to make them suitable for elimination.

• This involves chemical transformations to (a) reduce fat solubility (b) to change biological activity.

Although almost all tissue in the body have some ability to metabolize chemicals, smooth endoplasmic reticulum in liver is the principal "metabolic clearing house" for both endogenous chemicals (e.g., cholesterol, steroid hormones, fatty acids, and proteins), and exogenous substances (e.g. drugs).The central role played by liver in the clearance and transformation of chemicals also makes it susceptible to drug induced injury.

HepatotoxicityFactors influencing drug induced hepatotoxicity• Age • Ethnicity and race • Gender • Nutritional status • underlying liver disease • Renal function • Pregnancy • Duration and dosage of drug • Enzyme induction • Drug- drug interaction

Hepatotoxicity• Drugs continue to be taken off the market due

to late discovery of hepatotoxicity. Due to its unique feature and close relationship with the gastrointestinal tract, the liver is susceptible to injury from drugs and other substances.

75% of blood coming to the liver arrives directly from gastrointestinal organs and then spleen via portal veins which bring drugs and

xenobiotics in concentrated form. Several mechanisms are responsible for either

inducing hepatic injury or worsening the damage process.

Hepatotoxicity• Many chemicals damage mitochondria, an intracellular organelle that produce energy. Its

dysfunction releases excessive amount of oxidants which in turn injures hepatic cells. Activation of some enzymes in the cytochrome P-450 system

such as CYP2E1 also lead to oxidative stress.Injury to hepatocyte and bile duct cells lead to

accumulation of bile acid inside liver. This promotes further liver damage. Non-parenchymal cells such as Kupffer cells, fat storing stellate cells

and leukocytes (i.e. neutrophil and monocyte) also have role in the mechanism.

HepatotoxicitySpecific histo-pathological patterns of liver

injury from drug induced damage are discussed below.

Zonal Necrosis - This is the most common type of drug induced liver cell necrosis where the injury is largely confined to a particular zone of the liver lobule. It may manifest as very high level of ALT and severe disturbance of liver function leading to acute liver failure.

Causes include: • Paracetamol, carbon tetrachloride

Hepatotoxicity Hepatitis In this pattern hepatocellular necrosis is

associated with infiltration of inflammatory cells. There can be three types of drug induced hepatitis.(A) viral hepatitis - is the commonest, where histological features are similar to acute viral hepatitis. (B) Focal hepatitis - lymphocytic infiltrate. (C) chronic hepatitis - is very similar to autoimmune hepatitis clinically, serologically as well as histologically.

Causes: (a) Viral hepatitis like: Halothane, isoniazid, phenytoin (b) Focal hepatitis: Aspirin (c) Chronic hepatitis: Methyldopa, diclofenac

HepatotoxicityCholestasis Liver injury leads to impairment of bile flow

and clinical picture is predominated by itching and jaundice. Histology may show inflammation (cholestatic hepatitis) or it can be bland without any parenchymal inflammation. In rare occasions it can produce features similar to primary biliary cirrhosis due to progressive destruction of small bile ducts (Vanishing duct syndrome).

Causes: (a) Bland: Oral contraceptive pills, anabolic steroid,

androgens (b) Inflammatory: Allopurinol, co-amoxiclav,

carbamazepine (c) Ductal: Chlorpromazine, flucloxacillin

HepatotoxicitySteatosis Hepatotoxicity may manifest as triglyceride

accumulation which leads to either small droplet (microvesicular) or large droplet (macrovesicular) fatty liver. There is a separate type of steatosis where phospholipid accumulation leads to a pattern similar to the diseases with inherited phospholipid metabolism defects (e.g. Tay-Sachs disease)

Granuloma Drug induced hepatic granulomas are usually associated with granulomas in other tissues and patients typically have features of systemic vasculitis and hypersensitivity. More than 50 drugs have been implicated.

Causes: • Allopurinol, phenytoin, isoniazid, quinine, penicillin,

quinidine

HepatotoxicityVascular lesions• They result from injury to the vascular endothelium.Causes: Venoocclusive disease: Chemotherapeutic agents, bush tea Peliosis hepatis: anabolic steroid Hepatic vein thrombosis: Oral contraceptives NeoplasmNeoplasms have been described with prolonged exposure to

some medications or toxins. Hepatocellular carcinoma, angiosarcoma and liver adenomas are the ones usually reported.

Causes: Vinyl chloride, combined oral contraceptive pill, anabolic

steroid, arsenic, thorotrast

Genotoxicity

Genotoxicity describes a deleterious action on a cell's genetic material affecting its integrity. Genotoxic substances are known to be potentially mutagenic or carcinogenic, specifically those capable of causing genetic mutation and of contributing to the development of tumors. This includes both certain chemical compounds and certain types of radiation.

Genotoxicity

Typical genotoxins like aromatic amines are believed to cause mutations because they are nucleophilic and form strong covalent bonds with DNA resulting with the formation of Aromatic Amine-DNA Adducts, preventing accurate replication.

• Genotoxins affecting sperm and eggs can pass genetic changes down to descendants who have never been exposed to the genotoxin.

PESTICIDE TOXICITYPesticide is a collective term for natural or

synthetic substances, which inhibit or kill insects (insecticides), nematodes (nematicides), snails (molluscicides), bacteria (bactericides), fungi

(fungicides) and weeds (herbicides). • Nevertheless, most often the term is used as synonymous with insecticides. While there are several insecticides of biological origin, such as

the products of the bacterium Bacillus thuringiensis, the neem tree and others, control

of crop insect pests has been dominated by synthetic insecticides for over half a century. Some insecticides may also be bactericidal or

fungicidal

PESTICIDE TOXICITYThere are more than 1100 officially recognized

synthetic organic (that contain carbon) insecticides, which belong to a vast array of chemical groups, the more important being

a) Organophosphates (OPs), with subgroups like organothiophosphates, derived from phosphoric acid

b)Organochlorines (OCs), derived from chlorine. c) Carbamates and Pyrethroids are some of the

other groups. Insecticides are referred by their common names,

derived from the cumbersome scientific names

PESTICIDE TOXICITY• Insecticides are not just crop pest specific.

They pose a serious risk to farm labour and farm animals, and most other animals in the environment that feed on insecticide sprayed crops, all of which suffer from insecticide poisoning, by dermal contact, inhalation or ingestion.

• The lack of target specificity and an indiscriminate and excessive insecticide application has disturbed large components of biodiversity of agricultural lands.

PESTICIDE TOXICITY• Most insecticides are not completely

degraded and so leave residues in the food, feed, other agricultural produce, soil and water. Insecticide (pesticide) residues are poisonous, when the food or feed from insecticide sprayed crops was consumed, without proper cleaning. Insecticides and their residues also contaminate soil and water. In the process the natural food chain gets contaminated.

PESTICIDE TOXICITYThe nature and intensity of insecticidal toxicity depends upon the

• chemical structure of the insecticide • the mode of its action and not on whether it is

natural or synthetic. The level of exposure and the concentration of the insecticide or its residue in the body are critical factors.

PESTICIDE TOXICITYThere are two states of insecticide poisoning, both of which are equally dangerous:

1. Acute State is when a single very high dose that may be lethal was administered

2. Chronic State is one in which several sub-lethal doses were consumed over a long period of time, resulting in high concentrations in the body. Some insecticides may accumulate in the body and cumulatively reach hazardous concentrations. Chronic situations have indicated that about 60 per cent of the synthetic insecticides may cause cancer or Parkinson’s disease.

PESTICIDE TOXICITY OPs and carbamates are very potent neurotoxins that inhibit

the enzyme choline esterase, leading to the loss of control of acetylcholine, the most important neurotransmitter. The OPs are degraded rapidly on exposure to light, air, soil and water.

The symptoms of OP poisoning are running nose, chest tightness, shortness of breath, sweating, nausea, vomiting, stomach cramps, muscle twitching, confusion, seizers, paralysis, and coma, which lead to death. OPs can also cause the Mad Cow Disease.The symptoms of OC poisoning are tremors, headache, dermal irritation, respiratory problems, dizziness, nausea, and seizures. They may also cause neurological and respiratory illnesses and are implicated in cancer. The OCs are more persistent in nature, but are relatively less toxic than the OPs.

PESTICIDE TOXICITYStudies on the safety of chemicals are conducted on rats since human subjects cannot be used. The critical concentrations are estimated as milligrams per kg of body weight, that would kill 50 per cent of the rats in the study group, a factor called LD50 (Lethal Dose Fifty) with an alternative measure LC50 (Lethal Concentration Fifty).

• Chemicals with LD50 of less than five mg/kg are super toxic

• Chemicals that have values above 15,000 are practically non-toxic.

• For insecticides the LD50 values range from 13 mg/kg (parathion) to 1375 mg/kg (malathion), which means that the former is extremely toxic and the latter is mildly toxic.

PESTICIDE TOXICITY• The LD50 values depend upon so many factors and so there is

actually no standard.• Though such results cannot be directly extrapolated to humans,

they are the only means of evaluating toxicity potential. In general, children and small-bodied people (and animals) are at a greater risk.

The farm workers and farm animals that are in direct contact with insecticides should be periodically tested for toxic concentrations. Farm animals should not be allowed to graze on crop stubble that was exposed to extensive pesticide application. The local medical, veterinary and agricultural professionals are expected to be familiar with the safe use insecticides and treatment of people and animals that were affected, but more often than not, no such professional support is available. The levels of awareness among consumers are poor and illness from toxicity of insecticides and their residues often goes unrecognized.

FOOD TOXICITY• Any substance in food may have a degree of toxicity or

'poisonousness', whether it is natural, deliberately added, or a contaminant. There is nothing special about natural chemicals in food and no distinction should be made between natural and other substances when deciding if a food is likely to be hazardous.

• For example, a potato contains a number of poisonous substances such as nitrate, arsenic and solanine but in the amounts in which potatoes are normally eaten these natural substances are not hazardous. For this reason it is important not to consume large amounts of a small number of foods , but to consume a wide variety of foods. This not only minimizes the amount of a particular potentially hazardous substance but also ensures that a range of essential nutrients are consumed.

FOOD TOXICITYAflatoxin• Peanuts, peanut products, corn, wheat, rice, that

are grown or stored under conditions that favour mould growth

- Liver damage, possibility of liver cancerAllergens• Cereals (rice, wheat, barley, etc.), peanuts, peas,

lentils, soya beans, strawberries, bananas, mangoes, pineapples, sesame, poppy and caraway seeds, tea, chocolate, coffee, yeasts, alcoholic beverages, honev and other foods likely to contain pollen

- Eczema, hives, hay fever, asthma, headaches, abdominal distress, behavioural abnormalities

FOOD TOXICITYCaffeine• Tea, coffee, cola-type soft drinks- Increased urination, nervousness, upset stomach,

tremors, irritability, possibility of birth defects, possibility of behavioural change

Cyanide• Apricot kernels, peach kernels, apple seeds,

young bamboo shoots, bitter almonds, coloured varieties of lima beans

- Abdominal pain, vomiting, mental confusion, sensory loss, respiratory distress, spastic weakness

FOOD TOXICITYFavism• Broad beans• Anaemia due to an inborn error of metabolism; the disease has an

ethnic distribution around the Mediterranean and some other areas

Goitrogens• Cabbage, Brussels sprouts, broccoli, kale, turnips, mustard seeds,

horseradish• Goitre, particularly in areas where the iodine content of food is lowHaemagglutinins• Uncooked legumes (castor beans, kidney beans, lima beans, soya

beans, lentils, peas)• Retarded growth, diarrhoeaLathyrogens• Chickpeas• Paralysis of the legs, skeletal abnormalities

FOOD TOXICITYMycotoxins: • Ergotism, Alimentary toxic aleukia • Mouldy rice, mouldy grain• Vomiting, damage to bone marrow, convulsions,

psychotic behaviourOxalic acid• Spinach, rhubarb• Fatal poisoning is probably mythical; there is little

danger from eating normal amounts of oxalic-acid containing plants

Nitrates and nitrites• Celery, lettuce, spinach, cabbage, cured meats• Decreased oxygen-carrying ability of blood in infants

with gastro-enteritis; possible risk of gastric cancer

FOOD TOXICITYPyrrolizidine alkaloids• Comfrey, some 'herbal' teas• Possibility of liver disease and liver cancerSolanine• Sprouted and 'greening' potatoes• Vomiting, diarrhoea, abdominal pain,

headache, throat irritation

FOOD TOXICITY• Usually these effects have occurred only when

excessive amounts of a food containing these substances have been eaten. In fact, for most of us there is little hazard from these foods. The concentration of these poisonous substances is so low in the food we eat that we would have to consume huge amounts over a long time for the toxic effect to show up. Nevertheless, it is import to realize that there are many potentially hazardous substances in our diet without any obvious effects on our health, and that this applies equally to 'natural' and processed foods. Natural foods can be harmful if they are contaminated with excessive amounts of environmental contaminants, or aflatoxin or other mycotoxins produced by some moulds.

OCCUPATIONAL TOXICITYWhat is Occupational Toxicology?

• The discipline which Identifies chemical, physical or biological hazards, encountered in the work environment.

• Recognizes adverse health effects that arise out of workers’ exposures to these toxicants• Establishes control measures to prevent or

minimize exposures

OCCUPATIONAL TOXICITYWork history (present and past)Type of work

a) Physical demand (increased metabolism and increase inhalation and thus absorption)b) Shift system (exposure duration & frequency)c) Working practices such as eating, drinking in the work place (other route of exposure)d) Workplace conditions (dust, mold…)

OCCUPATIONAL TOXICITYWork history (present and past) Exposures

a) Physical (noise, cold, heat, radiation)b) Biological (viruses, bacteria, fungus..)c) Chemical (dust, vapors, fumes, …)

Environmental toxicology (EnTox)

EnTox is a young (1965) and interdisciplinary science that uses both basic and applied scientific knowledge to understand natural and anthropogenic pollutants life cycle and their impacts upon structure and functions of biological and ecological systems. Research in EnTox includes both laboratory experiments and field studies. EnTox wants to answer two main questions

(1) How the released pollutant causes harmful effects?

(2) What can we do to prevent or minimize risk to biological and ecological system?

Environmental toxicologyEnTox objective is divided into a 5-steps

• Release of pollutant into the environment• Transport and fate into biota (with/out chemical transformation)• Exposure to biological and ecological system• Understanding responses and/or effects (molecular to ecological systems)• Design remediation, minimization, conservation, and risk assessment plans to eliminate, prevent or predict environmental and human health pollutions situations.

Diagnosis of toxic effects in liver

This remains a major challenge in clinical practice due to lack of reliable markers. Many other conditions

lead to similar clinical as well as pathological picture. To diagnose hepatotoxicity, a causal relationship

between the use of the toxin or drug and subsequent liver damage has to be established, but might be difficult, especially when idiosyncratic reaction is

suspected.Simultaneous use of multiple drugs may add to the

complexity

Diagnosis of toxic effects in liver

An initial step in detecting liver damage is a simple blood test to determine the presence of certain liver enzymes in the blood. Under normal circumstances, these enzymes reside

within the cells of the liver. But when the liver is injured for any reason, these enzymes are

spilled into the blood stream. Enzymes are proteins that are present throughout the body, each with a unique

function.

Diagnosis of toxic effects in liver

Among the most sensitive and widely used of these liver enzymes are the aminotransferases. They include aspartate aminotransferase (AST or SGOT) and alanine aminotransferase (ALT or SGPT). These enzymes are normally contained within liver cells. If the liver is injured, the liver cells spill the enzymes into blood, raising the enzyme levels in the blood and signaling the liver damage.

Diagnosis of toxic effects in liver• AST (SGOT) is normally found in a diversity of tissues

including liver, heart, muscle, kidney, and brain. It is released into serum when any one of these tissues is damaged. For example, its level in serum rises with heart attacks and with muscle disorders. It is therefore, not a highly specific indicator of liver injury.

• ALT (SGPT) is, by contrast, normally found largely in the liver. This is not to say that it is exclusively located in liver, but that is where it is most concentrated. It is released into the bloodstream as the result of liver injury. It therefore serves as a fairly specific indicator of liver status.

• The normal range of values for AST (SGOT) is from 5 to 40 units per liter of serum (the liquid part of the blood).

• The normal range of values for ALT (SGPT) is from 7 to 56 units per liter of serum.

Diagnosis of toxic effects in liver• AST (SGOT) and ALT (SGPT) are sensitive indicators of liver damage

or injury from different types of disease. But it must be emphasized that higher-than-normal levels of these liver enzymes should not be automatically equated with liver disease. They may mean liver problems or they may not. For example, elevations of these enzymes can occur with muscle damage. The interpretation of elevated AST and ALT levels depends upon the entire clinical evaluation of a patient, and so it is best done by doctors experienced in evaluating liver disease.

• The precise levels of these enzymes do not correlate well with the extent of liver damage or the prognosis (outlook). Thus, the exact levels of AST (SGOT) and ALT (SGPT) cannot be used to determine the degree of liver disease or predict the future. For example, patients with acute viral hepatitis A may develop very high AST and ALT levels (sometimes in the thousands of units/liter range). But most patients with acute viral hepatitis A recover fully without residual liver disease. For a contrasting example, patients with chronic hepatitis C infection typically have only a little elevation in their AST and ALT levels. Some of these patients may have quietly developed chronic liver disease such as chronic hepatitis and cirrhosis (advanced scarring of the liver).

Diagnosis of toxic effects in kidney

• Creatinine is a chemical waste molecule that is generated from muscle metabolism. Creatinine is produced from creatine, a molecule of major importance for energy production in muscles. Approximately 2% of the body's creatine is converted to creatinine every day. Creatinine is transported through the bloodstream to the kidneys. The kidneys filter out most of the creatinine and dispose of it in the urine.

• Because the muscle mass in the body is relatively constant from day to day, the creatinine level in the blood normally remains essentially unchanged on a daily basis.

Diagnosis of toxic effects in kidney

• The kidneys maintain the blood creatinine in a normal range. Creatinine has been found to be a fairly reliable indicator of kidney function.

• As the kidneys become impaired for any reason, the creatinine level in the blood will rise due to poor clearance by the kidneys. Abnormally high levels of creatinine thus warn of possible malfunction or failure of the kidneys. It is for this reason that standard blood tests routinely check the amount of creatinine in the blood. A more precise measure of the kidney function can be estimated by calculating how much creatinine is cleared from the body by the kidneys and it is referred to creatinine clearance

Diagnosis of toxic effects in kidney

Normal levels of creatinine in the blood are approximately 0.6 to 1.2 milligrams (mg) per deciliter (dl) in adult males and 0.5 to 1.1 milligrams per deciliter in adult females. (In the metric system, a milligram is a unit of weight equal to one-thousandth of a gram, and a deciliter is a unit of volume equal to one-tenth of a liter.)

Diagnosis of toxic effects in kidney

• Muscular young or middle-aged adults may have more creatinine in their blood than the norm for the general population. Elderly persons, on the other hand, may have less creatinine in their blood than the norm. Infants have normal levels of about 0.2 or more, depending on their muscle development. In people with malnutrition, severe weight loss, and long standing illnesses the muscle mass tends to diminish over time and, therefore, their creatinine level may be lower than expected for their age.

• A person with only one kidney may have a normal level of about 1.8 or 1.9. Creatinine levels that reach 2.0 or more in babies and 10.0 or more in adults may indicate severe kidney impairment and the need for a dialysis machine to remove wastes from the blood.

Diagnosis of toxic effects in kidney

• Any condition that impairs the function of the kidneys will probably raise the creatinine level in the blood. It is important to recognize whether the process leading to kidney dysfunction (kidney failure, azotemia) is longstanding or recent.

• The most common causes of longstanding kidney disease in adults are high blood pressure and diabetes mellitus. Certain drugs can sometimes cause abnormally elevated creatinine levels. Serum creatinine can also transiently rise after ingestion of large amount of dietary meat.

BioremediationBioremediation can be defined as any process

that uses microorganisms, fungi, green plants or their enzymes to return the natural environment altered by contaminants to its original condition.

Bioremediation may be employed to attack specific soil contaminants, such as degradation of

chlorinated hydrocarbons by bacteria. An example of a more general approach is the

cleanup of oil spills by the addition of nitrate and/or sulfate fertilisers to facilitate the

decomposition of crude oil by indigenous or exogenous bacteria.

BioremediationBioremediation technologies can be generally

classified as in situ or ex situ. In situ bioremediation involves treating the

contaminated material at the site ex situ involves the removal of the

contaminated material to be treated elsewhere.

Some examples of bioremediation technologies are landfarming, bioreactor, composting, bioaugmentation, rhizofiltration, and biostimulation.

BioremediationLandfarming - performed in the upper soil zone or in biotreatment cells. Contaminated soils, sediments, or

sludges are incorporated into the soil surface and periodically turned over (tilled) to aerate the mixture

Bioreactor - bioreactor is a vessel in which is carried out a chemical process which involves organisms or

biochemically active substances derived from such organisms. This process can either be aerobic or

anaerobic . Bioreactors are designed to treat sewage and waste water

Composting - Composting is the purposeful biodegradation of organic matter, such as yard and food waste. The

decomposition is performed by micro-organisms, mostly bacteria, but also yeasts and fungi

BioremediationBioaugmentation is the introduction of a group of natural microbial strains or a genetically engineered

variant to treat contaminated soil or water.Phytoremediation describes the treatment of

environmental problems (bioremediation) through the use of plants which mitigate the environmental

problem without the need to excavate the contaminant material and dispose of it elsewhere.

Biostimulation involves the modification of the environment to stimulate existing bacteria capable of

bioremediation. This can be done by addition of various forms of rate limiting nutrients and electron acceptors, such as phosphorus, nitrogen, oxygen, or

carbon (e.g. in the form of molasses).

BioremediationThe elimination of a wide range of pollutants and wastes from the environment requires increasing our understanding of the relative

importance of different pathways and regulatory networks to carbon flux in

particular environments and for particular compounds and they will certainly accelerate

the development of bioremediation technologies and biotransformation processes

ITS ALL IN OUR HANDS TO UNDERSTAND OUR SYSTEM AND ITS LIMITATIONS – DOSE MATTERS

ReviewToxicology is the science that studies the harmful effects of

overexposure to drugs, environmental contaminants, and naturally occurring substances found in food, water, air,

and soil.– Main objectives are to establish safe doses and determine mechanisms of biologic action of chemical

substances.

A career in toxicology involves evaluating the harmful effects and mechanisms of action of chemicals in people,

other animals, and all other living things in the environment. – This work may be carried out in government, private

industry and consulting firms, or universities and other research settings.

Toxicologists routinely use many sophisticated tools to determine how chemicals are harmful.

(e.g.) computer simulations, computer chips, molecular biology, cultured cells, and genetically-engineered

laboratory animals .

Animals in Research

“Virtually every medical achievement of the last century has depended directly or indirectly on research in animals.”

U.S. Public Health Service

SummaryToxicology is a fascinating science that

makes biology and chemistry interesting and relevant.

Understanding HOW (i.e. mechanism) something produces a toxic effect can lead to new ways of preventing or treating chemically-related diseases. Animal use in research is essential for medical progress.

Many diseases are the result of an interaction between our genetics (individual variability) and chemicals in our environment.

Toxicology provides an interesting and exciting way to apply science to important problems of social, environmental, and public health significance.

TOXICOLOGY / ENV HEALTH SCIENCE – A HOOK FOR US TO THINK ABOUT

YOUR ROLE

The responsibility to help educate the next generation of citizens to better understand the world around them, and especially to understand how chemicals – man-made or

natural – present both risks and benefits to society.

Of course, everything we eat, drink, breathe, touch, or use is made of chemicals, so the task is LARGE!

We hope to make the science of toxicology ‘less obscure’ to the public.

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RECYCLE RETHINK