LIPIDS By Henry Wormser, Ph.D. PSC 3110 Fall semester 2008 Introduction Definition: water insoluble compounds Most lipids are fatty acids or ester of fatty acid They are soluble in non-polar solvents such as petroleum ether, benzene, chloroform Functions Energy storage Structure of cell membranes Thermal blanket and cushion Precursors of hormones (steroids and prostaglandins) Types: Fatty acids Neutral lipids Phospholipids and other lipids Fatty acids Carboxylic acid derivatives of long chain hydrocarbons Nomenclature (somewhat confusing) Stearate stearic acid C 18:0 n-octadecanoic acid General structure: Fatty acids Common fatty acids n = 4 butyric acid (butanoic acid) n = 6 caproic acid (hexanoic acid) n = 8 caprylic acid (octanoic acid) n = 10 capric acid (decanoic acid) Fatty acids common FAs: n = 12: lauric acid (n-dodecanoic acid; C 12:0 ) n = 14: myristic acid (n-tetradecanoic acid; C 14:0 ) n = 16: palmitic acid (n-hexadecanoic acid; C 16:0 ) n = 18; stearic acid (n-octadecanoic acid; C 18:0 ) n = 20; arachidic (eicosanoic acid; C 20:0 ) n= 22; behenic acid n = 24; lignoceric acid n = 26; cerotic acid Less common fatty acids iso isobutyric acid anteiso odd carbon fatty acid propionic acid hydroxy fatty acids ricinoleic acid, dihydroxystearic acid, cerebronic acid cyclic fatty acids hydnocarpic, chaulmoogric acid PHYTANIC ACID A plant derived fatty acid with 16 carbons and branches at C 3, C7, C11 and C15. Present in dairy products and ruminant fats. A peroxisome responsible for the metabolism of phytanic acid is defective in some individuals. This leads to a disease called Refsums disease Refsums disease is characterized by peripheral polyneuropathy, cerebellar ataxia and retinitis pigmentosa Less common fatty acids These are alkyne fatty acids Fatty acids Fatty acids can be classified either as: saturated or unsaturated according to chain length: short chain FA: 2-4 carbon atoms medium chain FA: 6 10 carbon atoms long chain FA: 12 26 carbon atoms essential fatty acids vs those that can be biosynthesized in the body: linoleic and linolenic are two examples of essential fatty acid Unsaturated fatty acids Monoenoic acid (monounsaturated) Double bond is always cis in natural fatty acids. This lowers the melting point due to kink in the chain Unsaturated fatty acids Dienoic acid: linoleic acid Unsaturated fatty acids Various conventions are in use for indicating the number and position of the double bond(s) Unsaturated fatty acids Polyenoic acid (polyunsaturated) Unsaturated fatty acids Monoenoic acids (one double bond): 16:1, 9 7: palmitoleic acid (cis-9-hexadecenoic acid 18:1, 9 9: oleic acid (cis-9-octadecenoic acid) 18:1, 9 9: elaidic acid (trans-9-octadecenoic acid) 22:1, 13 9: erucic acid (cis-13-docosenoic acid) 24:1, 15 9: nervonic acid (cis-15-tetracosenoic acid) Unsaturated fatty acids Trienoic acids (3 double bonds) 18:3;6,9,12 6 : -linolenic acid (all cis-6,9,12- octadecatrienoic acid) 18:3; 9,12,15 3 : -linolenic acid (all-cis-9,12,15- octadecatrienoic acid) Tetraenoic acids (4 double bonds) 20:4; 5,8,11,14 6: arachidonic acid (all-cis- 5,8,11,14-eicosatetraenoic acid) Unsaturated fatty acids Pentaenoic acid (5 double bonds) 20:5; 5,8,11,14,17 3: timnodonic acid or EPA (all-cis-5,8,11,14,17-eicosapentaenoic acid)* Hexaenoic acid (6 double bonds) 22:6; 4,7,10,13,16,19 3: cervonic acid or DHA (all-cis-4,7,10,13,16,19- docosahexaenoic acid)* Both FAs are found in cold water fish oils Typical fish oil supplements Properties of fats and oils fats are solids or semi solids oils are liquids melting points and boiling points are not usually sharp (most fats/oils are mixtures) when shaken with water, oils tend to emulsify pure fats and oils are colorless and odorless (color and odor is always a result of contaminants) i.e. butter (bacteria give flavor, carotene gives color) Examples of oils Olive oil from Oleo europa (olive tree) Corn oil from Zea mays Peanut oil from Arachis hypogaea Cottonseed oil from Gossypium Sesame oil from Sesamum indicum Linseed oil from Linum usitatissimum Sunflower seed oil from Helianthus annuus Rapeseed oil from Brassica rapa Coconut oil from Cocos nucifera Non-drying, semi-drying and drying oils based on the ease of autoxidation and polymerization of oils (important in paints and varnishes) the more unsaturation in the oil, the more likely the drying process Non-drying oils: Castor, olive, peanut, rapeseed oils Semi-drying oils Corn, sesame, cottonseed oils Drying oils Soybean, sunflower, hemp, linseed, tung, oiticica oils Fatty acid reactions salt formation ester formation lipid peroxidation Soaps Process of formation is known as saponification Types of soaps: Sodium soap ordinary hard soap Potassium soap soft soap (shaving soaps are potassium soaps of coconut and palm oils) Castile soap sodium soap of olive oil Green soap mixture of sodium and potassium linseed oil Transparent soap contains sucrose Floating soap contains air Calcium and magnesium soaps are very poorly water soluble (hard water contains calcium and magnesium salts these insolubilize soaps) Lipid peroxidation a non-enzymatic reaction catalyzed by oxygen may occur in tissues or in foods (spoilage) the hydroperoxide formed is very reactive and leads to the formation of free radicals which oxidize protein and/or DNA (causes aging and cancer) principle is also used in drying oils (linseed, tung, walnut) to form hard films Hydrogenated fats hydrogenation leads to either saturated fats and or trans fatty acids the purpose of hydrogenation is to make the oil/fat more stable to oxygen and temperature variation (increase shelf life) example of hydrogenated fats: Crisco, margarine Neutral lipids Glycerides (fats and oils) ;glycerides Glycerol Ester of glycerol - mono glycerides, diglycerides and triglycerides Waxes simple esters of long chain alcohols GLYCERIDES Function: storage of energy in compact form and cushioning Stereospecific numbering carbon 2 of triglycerides is frequently asymmetric since C-1 and C-3 may be substituted with different acyl groups by convention we normally draw the hydroxyl group at C-2 to the left and use the designation of sn2 for that particular substituent C-1 and C-3 of the glycerol molecule become sn1 and sn3 respectively Analytical methods to evaluate lipids saponification number iodine value (Hanus method) free fatty acids acetyl number Reichert-Meissl number HPLC/GC (for more precise analysis) Saponification number gives some clue as to the average size of fatty acids in a given sample of fat defined as the number of milligrams of KOH needed to neutralize the fatty acids in 1 Gm of fat butter (large proportion of short chain FAs) sap. no. 220 230 oleomargarine (long chain FAs) sap. No is 195 or less Iodine number measures the degree of unsaturation in a given amount of fat or oil the iodine number is the number of grams of iodine absorbed by 100 grams of fat Cottonseed oil: 103 111 Olive oil: 79 88 Linseed oil: 175 202 frequently used to determine adulteration of commercial lots of oils Acetyl number some fatty acids have hydroxyl groups The acetyl number gives the proportion of these hydroxyl-containing fatty acids in a given sample of fat or oil Acetyl number the acetyl number is the number of milligrams of KOH needed to neutralize the acetic acid of 1 Gm of acetylated fat examples: castor oil 146 150 cod liver oil 1.1 cottonseed oil 21 25 olive oil 10.5 peanut oil 3.5 Reichert Meissl number measures the amount of volatile fatty acids (low MW and water soluble Fas) the R-M number is the number of milliliters of 0.1N alkali required to neutralize the soluble fatty acids distilled from 5 Gm of fat butter fat has a high R-M number WAXES simple esters of fatty acids (usually saturated with long chain monohydric alcohols) Beeswax also includes some free alcohol and fatty acids Spermaceti contains cetyl palmitate (from whale oil) useful for Pharmaceuticals (creams/ointments; tableting and granulation) Carnauba wax from a palm tree from brazil a hard wax used on cars and boats Bees wax Spermaceti source Carnauba wax source Waxes Examples of long chain monohydric alcohols found in waxes Phospholipids the major components of cell membranes phosphoglycerides Phospholipids are generally composed of FAs, a nitrogenous base, phosphoric acid and either glycerol, inositol or sphingosine Phosphatidyl inositol Commonly utilized in cellular signaling Sphingolipids Based on sphingosine instead of glycerol Sphingomyelin (a ceramide) It is a ubiquitous component of animal cell membranes, where it is by far the most abundant sphingolipid. It can comprise as much as 50% of the lipids in certain tissues, though it is usually lower in concentration than phosphatidylcholine Ether glycerophospholipids Possess an ether linkage instead of an acyl group at the C-1 position of glycerol PAF ( platelet activating factor) A potent mediator in inflammation, allergic response and in shock (also responsible for asthma-like symptom The ether linkage is stable in either acid or base Plasmalogens: cis , -unsaturated ethers The alpha/beta unsaturated ether can be hydrolyzed more easily Ether glycerophospholipids glycolipids There are different types of glycolipids: cerebrosides, gangliosides, lactosylceramides GLYCOLIPIDS Cerebrosides One sugar molecule Galactocerebroside in neuronal membranes Glucocerebrosides elsewhere in the body Sulfatides or sulfogalactocerebrosides A sulfuric acid ester of galactocerebroside Globosides: ceramide oligosaccharides Lactosylceramide 2 sugars ( eg. lactose) Gangliosides Have a more complex oligosaccharide attached Biological functions: cell-cell recognition; receptors for hormones Gangliosides complex glycosphingolipids that consist of a ceramide backbone with 3 or more sugars esterified,one of these being a sialic acid such as N-acetylneuraminic acid common gangliosides: G M1, G M2, G M3, G D1a, G D1b, G T1a, GT 1b, G q1b Ganglioside nomenclature letter G refers to the name ganglioside the subscripts M, D, T and Q indicate mono-, di-, tri, and quatra(tetra)-sialic- containing gangliosides the numerical subscripts 1, 2, and 3 designate the carbohydrate sequence attached to ceramide Ganglioside nomenclature Numerical subscripts: 1. Gal-GalNAc-Gal-Glc-ceramide 2. GalNAc-Gal-Glc-ceramide 3. Gal-Glc-ceramide A ganglioside (G M1 ) Cardiolipids A polyglycerol phospholipid; makes up 15% of total lipid-phosphorus content of the myocardium associated with the cell membrane Cardiolipids are antigenic and as such are used in serologic test for syphilis (Wasserman test) Sulfolipids also called sulfatides or cerebroside sulfates contained in brain lipids sulfate esters of cerebrosides present in low levels in liver, lung, kidney, spleen, skeletal muscle and heart function is not established Lipid storage diseases also known as sphingolipidoses genetically acquired due to the deficiency or absence of a catabolic enzyme examples: Tay Sachs disease Gauchers disease Niemann-Pick disease Fabrys disease/lipid_storage_diseases.htmhttp://www.ninds.nih.gov/disorders/lipid_storage_diseases /lipid_storage_diseases.htm Genetic defects in ganglioside metabolism leads to a buildup of gangliosides (ganglioside G M2 ) in nerve cells, killing them Tay-Sachs disease a fatal disease which is due to the deficiency of hexosaminidase A activity accumulation of ganglioside G M2 in the brain of infants mental retardation, blindness, inability to swallow a cherry red spot develops on the macula (back of the the eyes) Tay-Sachs children usually die by age 5 and often sooner Genetic defects in globoside metabolism Fabrys disease: Accumulation of ceramide trihexoside in kidneys of patients who are deficient in lysosomal - galactosidase A sometimes referred to as ceramide trihexosidase Skin rash, kidney failure, pains in the lower extremities Now treated with enzyme replacement therapy: agalsidase beta (Fabrazyme) Genetic defects in cerebroside metabolism Krabbes disease: Also known as globoid leukodystrophy Increased amount of galactocerebroside in the white matter of the brain Caused by a deficiency in the lysosomal enzyme galactocerebrosidase Gauchers disease: Caused by a deficiency of lysosomal glucocerebrosidase Increase content of glucocerebroside in the spleen and liver Erosion of long bones and pelvis Enzyme replacement therapy is available for the Type I disease (Imiglucerase or Cerezyme) Also miglustat (Zavesca) an oral drug which inhibits the enzyme glucosylceramide synthase, an essential enzyme for the synthesis of most glycosphingolipids Miglustat (Zavesca) Genetic defects in ganglioside metabolism Metachromatic leukodystrophy accumulation of sulfogalactocerebroside (sulfatide) in the central nervous system of patient having a deficiency of a specific sulfatase mental retardation, nerves stain yellowish-brown with cresyl violet dye (metachromasia) Generalized gangliosidosis accumulation of ganglioside GM1 deficiency of GM1 ganglioside: -galactosidase mental retardation, liver enlargement, skeletal involvement Niemann-Pick disease principal storage substance: sphingomyelin which accumulates in reticuloendothelial cells enzyme deficiency: sphingomyelinase liver and spleen enlargement, mental retardation Blood groups determined by various glycolipids on RBCs A antigens B antigens H antigens not recognized by anti-A or anti-B antibodies (found on type O blood cells) Cholesterol and cholesterol esters STEROID NUMBERING SYSTEM STEREOCHEMISTRY OF STEROIDS Cholesterol sources, biosynthesis and degradation diet: only found in animal fat biosynthesis: primarily synthesized in the liver from acetyl-coA; biosynthesis is inhibited by LDL uptake degradation: only occurs in the liver Cholesterol and cholesterol esters The hydroxyl at C-3 is hydrophilic; the rest of the molecule is hydrophobic; also 8 centers of asymmetry Cholesterol and cholesterol esters Functions: -serves as a component of membranes of cells (increases or moderates membrane fluidity -precursor to steroid hormones -storage and transport cholesterol esters Functions of cholesterol serves as a component of membranes of cells (increases or moderates membrane fluidity) precursor to steroid hormones and bile acids storage and transport cholesterol esters Prostaglandins and other eicosanoids (prostanoids) local hormones, unstable, key mediators of inflammation derivatives of prostanoic acid SUBSTITUTION PATTERN OF PROSTANOIDS Prostacyclins, thromboxanes and leukotrienes PGH 2 in platelets is converted to thromboxane A 2 (TXA 2 ) a vasoconstrictor which also promotes platelet aggregation PGH 2 in vascular endothelial cells is converted to PGI 2, a vasodilator which inhibits platelet aggregation Aspirins irreversible inhibition of platelet COX leads to its anticoagulant effect Functions of eicosanoids Prostaglandins particularly PGE 1 block gastric production and thus are gastric protection agents Misoprostol (Cytotec) is a stable PGE 1 analog that is used to prevent ulceration by long term NSAID treatment PGE 1 also has vasodilator effects Alprostadil (PGE 1 ) used to treat infants with congenital heart defects Also used in impotance (Muse) Functions of eicosanoids PGF 2 causes constriction of the uterus Carboprost; Hebamate (15-Me-PGF 2 ) induces abortions PGE 2 is applied locally to help induce labor at term Examples of drugs derived from prostaglandins Leukotrienes are derived from arachidonic acid via the enzyme 5-lipoxygenase which converts arachidonic acid to 5-HPETE (5-hydroperoxyeicosatetranoic acid) and subsequently by dehydration to LTA 4 peptidoleukotrienes Leukotrienes Leukotrienes are synthesized in neutrophils, monocytes, macrophages, mast cells and keratinocytes. Also in lung, spleen, brain and heart. A mixture of LTC4, LTD4 and LTE4 was previously known as the slow-reacting substance of anaphylaxis peptidoleukotrienes Leukotrienes Non-peptidoleuktrienes: LTA 4 is formed by dehydration of 5-HPETE, and LTB 4 by hydrolysis of the epoxide of LTA 4 Leukotrienes Biological activities of leukotrienes 1. LTB 4 - potent chemoattractent - mediator of hyperalgesia - growth factor for keratinocytes 2. LTC 4 - constricts lung smooth muscle - promotes capillary leakage 1000 X histamine 3. LTD 4 - constricts smooth muscle; lung - airway hyperactivity - vasoconstriction 4. LTE x less potent than LTD4 (except in asthmatics) Leukotriene receptor antagonists Montelukast (Singulair) Zafirlukast (Accolate) Lipid-linked proteins Lipid-linked proteins (different from lipoproteins) lipoproteins that have lipids covalently attached to them these proteins are peripheral membrane proteins Lipid-linked proteins 3 types are most common: Prenylated proteins Farnesylated proteins (C15 isoprene unit) Geranylgeranylated proteins (C20 isoprene unit) Fatty acylated proteins Myristoylated proteins (C14) Palmitoylated proteins (C16) Lipid-linked proteins glycosylphosphatidylinositol-linked proteins (GPI-linked proteins) occur in all eukaryotes, but are particularly abundant in parasitic protozoa located only on the exterior surface of the plasma membrane Fatty acylated proteins Prenylated proteins GPI-linked proteins Lipoproteins particles found in plasma that transport lipids including cholesterol lipoprotein classes chylomicrons: take lipids from small intestine through lymph cells very low density lipoproteins (VLDL) intermediate density lipoproteins (IDL) low density lipoproteins (LDL) high density lipoproteins (HDL) Terpenes Lipoprotein class Density (g/mL) Diameter (nm) Protein % of dry wt Phosphol ipid % Triacylglycerol % of dry wt HDL LDL1.019 IDL VLDL0.95 chylomicrons< Composition and properties of human lipoproteins most proteins have densities of about 1.3 1.4 g/mL and lipid aggregates usually have densities of about 0.8 g/mL Lipoprotein structure LDL molecule The apolipoproteins major components of lipoproteins often referred to as aproteins classified by alphabetical designation (A thru E) the use of roman numeral suffix describes the order in which the apolipoprotein emerge froma chromatographic column responsible for recognition of particle by receptors HELICAL WHEEL PROJECTION OF A PORTION OF APOLIPOPROTEIN A-I LIPOPROTEINS spherical particles with a hydrophobic core (TG and esterified cholesterol) apolipoproteins on the surface large: apoB (b-48 and B-100) atherogenic smaller: apoA-I, apoC-II, apoE classified on the basis of density and electrophoretic mobility (VLDL; LDL; IDL;HDL; Lp(a) Apoproteins of human lipoproteins A-1 (28,300)- principal protein in HDL 90 120 mg% in plasma A-2 (8,700) occurs as dimer mainly in HDL 30 50 mg % B-48 (240,000) found only in chylomicron