LIPIDSBy Henry Wormser, Ph.D.PSC 3110 Fall semester 2008

IntroductionDefinition: water insoluble compoundsMost lipids are fatty acids or ester of fatty acidThey are soluble in non-polar solvents such as petroleum ether, benzene, chloroformFunctionsEnergy storageStructure of cell membranesThermal blanket and cushionPrecursors of hormones (steroids and prostaglandins)Types:Fatty acidsNeutral lipidsPhospholipids and other lipids

Fatty acidsCarboxylic acid derivatives of long chain hydrocarbonsNomenclature (somewhat confusing)Stearate stearic acid C18:0 n-octadecanoic acidGeneral structure:

Fatty acidsCommon fatty acidsn = 4 butyric acid (butanoic acid)n = 6 caproic acid (hexanoic acid)n = 8 caprylic acid (octanoic acid)n = 10 capric acid (decanoic acid)

Fatty acidscommon FAs: n = 12: lauric acid (n-dodecanoic acid; C12:0)n = 14: myristic acid (n-tetradecanoic acid; C14:0)n = 16: palmitic acid (n-hexadecanoic acid; C16:0)n = 18; stearic acid (n-octadecanoic acid; C18:0)n = 20; arachidic (eicosanoic acid; C20:0)n= 22; behenic acidn = 24; lignoceric acidn = 26; cerotic acid

Less common fatty acidsiso isobutyric acidanteisoodd carbon fatty acid propionic acidhydroxy fatty acids ricinoleic acid, dihydroxystearic acid, cerebronic acidcyclic fatty acids hydnocarpic, chaulmoogric acid

PHYTANIC ACIDA plant derived fatty acid with 16 carbons and branches at C 3, C7, C11 andC15. Present in dairy products and ruminant fats.A peroxisome responsible for the metabolism of phytanic acid is defectivein some individuals. This leads to a disease called Refsums disease

Refsums disease is characterized by peripheral polyneuropathy, cerebellarataxia and retinitis pigmentosa

Less common fatty acidsThese are alkyne fatty acids

Fatty acidsFatty acids can be classified either as:saturated or unsaturatedaccording to chain length:short chain FA: 2-4 carbon atomsmedium chain FA: 6 10 carbon atomslong chain FA: 12 26 carbon atomsessential fatty acids vs those that can be biosynthesized in the body:linoleic and linolenic are two examples of essential fatty acid

Unsaturated fatty acidsMonoenoic acid (monounsaturated)

Double bond is alwayscis in natural fatty acids.This lowers the meltingpoint due to kink inthe chain

Unsaturated fatty acidsDienoic acid: linoleic acid

Unsaturated fatty acidsVarious conventions are in use for indicating the number and position of the double bond(s)

Unsaturated fatty acidsPolyenoic acid (polyunsaturated)

Unsaturated fatty acidsMonoenoic acids (one double bond):16:1, 9 w7: palmitoleic acid (cis-9-hexadecenoic acid18:1, 9 w9: oleic acid (cis-9-octadecenoic acid)18:1, 9 w9: elaidic acid (trans-9-octadecenoic acid)22:1, 13 w9: erucic acid (cis-13-docosenoic acid)24:1, 15 w9: nervonic acid (cis-15-tetracosenoic acid)

Unsaturated fatty acidsTrienoic acids (3 double bonds)18:3;6,9,12 w6 : g-linolenic acid (all cis-6,9,12-octadecatrienoic acid)18:3; 9,12,15 w3 : a-linolenic acid (all-cis-9,12,15-octadecatrienoic acid)Tetraenoic acids (4 double bonds)20:4; 5,8,11,14 w6: arachidonic acid (all-cis-5,8,11,14-eicosatetraenoic acid)

Unsaturated fatty acidsPentaenoic acid (5 double bonds)20:5; 5,8,11,14,17 w3: 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 w3: 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 oilsfats are solids or semi solidsoils are liquidsmelting points and boiling points are not usually sharp (most fats/oils are mixtures)when shaken with water, oils tend to emulsifypure 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 oilsOlive oil from Oleo europa (olive tree)Corn oil from Zea maysPeanut oil from Arachis hypogaeaCottonseed oil from GossypiumSesame oil from Sesamum indicumLinseed oil from Linum usitatissimumSunflower seed oil from Helianthus annuusRapeseed oil from Brassica rapaCoconut oil from Cocos nucifera

Non-drying, semi-drying and drying oilsbased 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 processNon-drying oils:Castor, olive, peanut, rapeseed oilsSemi-drying oilsCorn, sesame, cottonseed oilsDrying oilsSoybean, sunflower, hemp, linseed, tung, oiticica oils

Fatty acid reactionssalt formation

ester formation

lipid peroxidation

SoapsProcess of formation is known as saponificationTypes of soaps:Sodium soap ordinary hard soapPotassium soap soft soap (shaving soaps are potassium soaps of coconut and palm oils)Castile soap sodium soap of olive oilGreen soap mixture of sodium and potassium linseed oilTransparent soap contains sucroseFloating soap contains airCalcium and magnesium soaps are very poorly water soluble (hard water contains calcium and magnesium salts these insolubilize soaps)

Lipid peroxidationa non-enzymatic reaction catalyzed by oxygenmay 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 fatshydrogenation leads to either saturated fats and or trans fatty acidsthe 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 lipidsGlycerides (fats and oils) ;glyceridesGlycerol

Ester of glycerol - mono glycerides, diglycerides and triglycerides

Waxes simple esters of long chain alcohols

GLYCERIDESFunction: storage of energy in compact form and cushioning

Stereospecific numberingcarbon 2 of triglycerides is frequently asymmetric since C-1 and C-3 may be substituted with different acyl groupsby convention we normally draw the hydroxyl group at C-2 to the left and use the designation of sn2 for that particular substituentC-1 and C-3 of the glycerol molecule become sn1 and sn3 respectively

Analytical methods to evaluate lipidssaponification numberiodine value (Hanus method)free fatty acidsacetyl numberReichert-Meissl numberHPLC/GC (for more precise analysis)

Saponification numbergives some clue as to the average size of fatty acids in a given sample of fatdefined as the number of milligrams of KOH needed to neutralize the fatty acids in 1 Gm of fatbutter (large proportion of short chain FAs) sap. no. 220 230oleomargarine (long chain FAs) sap. No is 195 or less

Iodine numbermeasures the degree of unsaturation in a given amount of fat or oilthe iodine number is the number of grams of iodine absorbed by 100 grams of fatCottonseed oil: 103 111Olive oil: 79 88Linseed oil: 175 202frequently used to determine adulteration of commercial lots of oils

Acetyl numbersome fatty acids have hydroxyl groupsThe acetyl number gives the proportion of these hydroxyl-containing fattyacids in a given sample of fat or oil

Acetyl numberthe acetyl number is the number of milligrams of KOH needed to neutralize the acetic acid of 1 Gm of acetylated fatexamples:castor oil 146 150cod liver oil 1.1cottonseed oil 21 25olive oil 10.5peanut oil 3.5

Reichert Meissl numbermeasures 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 fatbutter fat has a high R-M number

WAXESsimple esters of fatty acids (usually saturated with long chain monohydric alcohols)Beeswax also includes some free alcohol and fatty acidsSpermaceti contains cetyl palmitate (from whale oil) useful forPharmaceuticals (creams/ointments; tableting and granulation)Carnauba wax from a palm tree from brazil a hard wax used oncars and boats

Bees waxSpermaceti sourceCarnauba wax source

WaxesExamples of long chain monohydric alcohols found in waxes

Phospholipidsthe major components of cell membranesphosphoglyceridesPhospholipids are generally composed of FAs, a nitrogenous base, phosphoricacid and either glycerol, inositol or sphingosine

Phosphatidyl inositolCommonly utilized in cellular signaling

SphingolipidsBased 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 glycerophospholipidsPossess an ether linkage instead of an acyl group at the C-1 position of glycerolPAF ( platelet activating factor)A potent mediator in inflammation, allergic response and in shock (also responsible for asthma-like symptomThe ether linkage is stable in either acid or basePlasmalogens: cis a,b-unsaturated ethers

The alpha/beta unsaturated ether can be hydrolyzed more easily

Ether glycerophospholipids

glycolipidsThere are different types of glycolipids: cerebrosides, gangliosides,lactosylceramides

GLYCOLIPIDSCerebrosidesOne sugar moleculeGalactocerebroside in neuronal membranesGlucocerebrosides elsewhere in the bodySulfatides or sulfogalactocerebrosidesA sulfuric acid ester of galactocerebrosideGlobosides: ceramide oligosaccharidesLactosylceramide2 sugars ( eg. lactose)GangliosidesHave a more complex oligosaccharide attachedBiological functions: cell-cell recognition; receptors for hormones

Gangliosidescomplex glycosphingolipids that consist of a ceramide backbone with 3 or more sugars esterified,one of these being a sialic acid such as N-acetylneuraminic acidcommon gangliosides: GM1, GM2, GM3, GD1a, GD1b, GT1a, GT1b, Gq1b

Ganglioside nomenclatureletter G refers to the name gangliosidethe subscripts M, D, T and Q indicate mono-, di-, tri, and quatra(tetra)-sialic-containing gangliosidesthe numerical subscripts 1, 2, and 3 designate the carbohydrate sequence attached to ceramide

Ganglioside nomenclatureNumerical subscripts:1. Gal-GalNAc-Gal-Glc-ceramide2. GalNAc-Gal-Glc-ceramide3. Gal-Glc-ceramide

A ganglioside (GM1)

CardiolipidsA polyglycerol phospholipid; makes up 15% of total lipid-phosphoruscontent of the myocardium associated with the cell membraneCardiolipids are antigenic and as such are used in serologic test forsyphilis (Wasserman test)

Sulfolipidsalso called sulfatides or cerebroside sulfatescontained in brain lipidssulfate esters of cerebrosidespresent in low levels in liver, lung, kidney, spleen, skeletal muscle and heartfunction is not established

Lipid storage diseasesalso known as sphingolipidosesgenetically acquireddue to the deficiency or absence of a catabolic enzymeexamples:Tay Sachs diseaseGauchers diseaseNiemann-Pick diseaseFabrys disease

http://www.ninds.nih.gov/disorders/lipid_storage_diseases/lipid_storage_diseases.htm

Genetic defects in ganglioside metabolismleads to a buildup of gangliosides (ganglioside GM2) in nerve cells, killing them

Tay-Sachs diseasea fatal disease which is due to the deficiency of hexosaminidase A activityaccumulation of ganglioside GM2 in the brain of infantsmental retardation, blindness, inability to swallowa 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 metabolismFabrys disease:Accumulation of ceramide trihexoside in kidneys of patients who are deficient in lysosomal a-galactosidase A sometimes referred to as ceramide trihexosidaseSkin rash, kidney failure, pains in the lower extremitiesNow treated with enzyme replacement therapy: agalsidase beta (Fabrazyme)

Genetic defects in cerebroside metabolismKrabbes disease: Also known as globoid leukodystrophyIncreased amount of galactocerebroside in the white matter of the brainCaused by a deficiency in the lysosomal enzyme galactocerebrosidaseGauchers disease:Caused by a deficiency of lysosomal glucocerebrosidaseIncrease content of glucocerebroside in the spleen and liverErosion of long bones and pelvisEnzyme 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 metabolismMetachromatic leukodystrophyaccumulation of sulfogalactocerebroside (sulfatide) in the central nervous system of patient having a deficiency of a specific sulfatasemental retardation, nerves stain yellowish-brown with cresyl violet dye (metachromasia)Generalized gangliosidosisaccumulation of ganglioside GM1deficiency of GM1 ganglioside: b-galactosidasemental retardation, liver enlargement, skeletal involvement

Niemann-Pick diseaseprincipal storage substance: sphingomyelin which accumulates in reticuloendothelial cellsenzyme deficiency: sphingomyelinaseliver and spleen enlargement, mental retardation

Blood groupsdetermined by various glycolipids on RBCsA antigens

B antigens

H antigensnot 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 degradationdiet: only found in animal fatbiosynthesis: primarily synthesized in the liver from acetyl-coA; biosynthesis is inhibited by LDL uptakedegradation: only occurs in the liver

Cholesterol and cholesterol estersThe hydroxyl at C-3 is hydrophilic; the rest of themolecule is hydrophobic; also 8 centers of asymmetry

Cholesterol and cholesterol estersFunctions: -serves as a component of membranes of cells (increases or moderates membrane fluidity -precursor to steroid hormones -storage and transport cholesterol esters

Functions of cholesterolserves as a component of membranes of cells (increases or moderates membrane fluidity)precursor to steroid hormones and bile acidsstorage and transport cholesterol esters

Prostaglandins and other eicosanoids (prostanoids)local hormones, unstable, key mediators of inflammationderivatives of prostanoic acid

SUBSTITUTION PATTERN OF PROSTANOIDS

Prostacyclins, thromboxanes and leukotrienesPGH2 in platelets is converted to thromboxane A2 (TXA2) a vasoconstrictor which also promotes platelet aggregationPGH2 in vascular endothelial cells is converted to PGI2, a vasodilator which inhibits platelet aggregationAspirins irreversible inhibition of platelet COX leads to its anticoagulant effect

Functions of eicosanoidsProstaglandins particularly PGE1 block gastric production and thus are gastric protection agentsMisoprostol (Cytotec) is a stable PGE1 analog that is used to prevent ulceration by long term NSAID treatmentPGE1 also has vasodilator effectsAlprostadil (PGE1) used to treat infants with congenital heart defectsAlso used in impotance (Muse)

Functions of eicosanoidsPGF2a causes constriction of the uterusCarboprost; Hebamate (15-Me-PGF2a) induces abortionsPGE2 is applied locally to help induce labor at term

Examples of drugs derived from prostaglandins

LeukotrienesLeukotrienes are derived from arachidonic acid via the enzyme 5-lipoxygenase which converts arachidonic acid to 5-HPETE (5-hydroperoxyeicosatetranoic acid) and subsequently bydehydration to LTA4peptidoleukotrienes

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 theslow-reacting substance of anaphylaxispeptidoleukotrienesLeukotrienes

Non-peptidoleuktrienes: LTA4 is formed by dehydration of5-HPETE, and LTB4 by hydrolysis of the epoxide of LTA4Leukotrienes

Biological activities of leukotrienes1. LTB4- potent chemoattractent- mediator of hyperalgesia- growth factor for keratinocytes2. LTC4- constricts lung smooth muscle- promotes capillary leakage 1000 X histamine3. LTD4- constricts smooth muscle; lung- airway hyperactivity- vasoconstriction4. LTE4- 1000 x less potent than LTD4(except in asthmatics)

Leukotriene receptor antagonistsMontelukast(Singulair)Zafirlukast(Accolate)

Lipid-linked proteinsLipid-linked proteins (different from lipoproteins)lipoproteins that have lipids covalently attached to themthese proteins are peripheral membrane proteins

Lipid-linked proteins3 types are most common:Prenylated proteinsFarnesylated proteins (C15 isoprene unit)Geranylgeranylated proteins (C20 isoprene unit)Fatty acylated proteinsMyristoylated proteins (C14)Palmitoylated proteins (C16)

Lipid-linked proteinsglycosylphosphatidylinositol-linked proteins (GPI-linked proteins)occur in all eukaryotes, but are particularly abundant in parasitic protozoalocated only on the exterior surface of the plasma membrane

Fatty acylated proteins

Prenylated proteins

GPI-linked proteins

Lipoproteinsparticles found in plasma that transport lipids including cholesterollipoprotein classeschylomicrons: take lipids from small intestine through lymph cellsvery low density lipoproteins (VLDL)intermediate density lipoproteins (IDL)low density lipoproteins (LDL)high density lipoproteins (HDL)

Terpenes

Composition and properties of human lipoproteinsmost proteins have densities of about 1.3 1.4 g/mL and lipid aggregates usuallyhave densities of about 0.8 g/mL

Lipoprotein classDensity (g/mL)Diameter (nm)Protein % of dry wtPhospholipid %Triacylglycerol % of dry wtHDL1.063-1.215 1533298LDL1.019 1.06318 2825214IDL1.006-1.01925 - 50182231VLDL0.95 1.00630 - 80101850chylomicrons< 0.95100 - 5001 - 2784

Lipoprotein structure

LDL molecule

The apolipoproteinsmajor components of lipoproteinsoften referred to as aproteinsclassified by alphabetical designation (A thru E)the use of roman numeral suffix describes the order in which the apolipoprotein emerge froma chromatographic columnresponsible for recognition of particle by receptors

HELICAL WHEEL PROJECTION OF A PORTION OF APOLIPOPROTEIN A-I

LIPOPROTEINSspherical particles with a hydrophobic core (TG and esterified cholesterol)apolipoproteins on the surfacelarge: apoB (b-48 and B-100) atherogenicsmaller: apoA-I, apoC-II, apoEclassified on the basis of density and electrophoretic mobility (VLDL; LDL; IDL;HDL; Lp(a)

Apoproteins of human lipoproteinsA-1 (28,300)- principal protein in HDL90 120 mg% in plasmaA-2 (8,700) occurs as dimer mainly in HDL30 50 mg %B-48 (240,000) found only in chylomicron

Apoproteins of human lipoproteinsC-1 (7,000) found in chylomicron, VLDL, HDL4 7 mg %C-2 (8,800) - found in chylomicron, VLDL, HDL3 8 mg %C-3 (8,800) - found in chylomicron, VLDL, IDL, HDL8 15 mg %D (32,500) - found in HDL8 10 mg %E (34,100) - found in chylomicron, VLDL, IDL HDL3 6 mg %

Major lipoprotein classeschylomicronsdensity

Major lipoprotein classesVLDLdensity >1.006diameter 30 - 80nmendogenous triglyceridesapoB-100, apoE, apoC-II/C-IIIprebeta in electrophoresis

Major lipoprotein classesIDL (intermediate density lipoproteins)density: 1.006 - 1.019diameter: 25 - 35nmcholesteryl esters and triglyceridesapoB-100, apoE, apoC-II/C-IIIslow pre-beta

Major lipoprotein classesHDL (high density lipoproteins)density: 1.063-1.210diameter: 5-12nmcholesteryl esters and phospholipidsapoA-I, apoA-II, apoC-II/C-IIIalpha (electrophoresis)

Major lipoprotein classesLDL (low density lipoproteins)density: 1.019 - 1.063diameter: 18-25nmcholesteryl estersapoB-100beta (electrophoresis)< 130 LDL cholesterol is desirable, 130-159 is borderline high and >160 is high

Cholesterol and lipid transport by lipoproteins

Cholesterol and lipid transport by lipoproteins

Photograph of an arterial plaque

The LDL receptorcharacterized by Michael Brown and Joseph Goldstein (Nobel prize winners in 1985)based on work on familial hypercholesterolemiareceptor also called B/E receptor because of its ability to recognize particles containing both apos B and Eactivity occurs mainly in the liverreceptor recognizes apo E more readily than apo B-100

Representation of the LDL receptor

Terpenessimple lipids, but lack fatty acid componentformed by the combination of 2 or more molecules of 2-methyl-1,3-butadiene (isoprene)monoterpene (C-10) made up of 2 isoprene unitssesquiterpene (C-15) made up of 3 isoprene unitsditerpene (C-20) made up of 4 isoprene units

MonoterpenesMonoterpenes are readily recognized by their characterisitic flavorsand odors ( limonene in lemons, citronellal in roses and geraniums,pinene in turpentine and menthol from peppermint

Sesquiterpenes

DiterpenesAll-trans-retinal

TriterpenesTriterpenes are C-30 compounds are addition products of 2 sesquiterpenes;Both squalene and lanosterol are precursors of cholesterol and other steroids

Other terpenestetraterpenes (C-40) are not as common as mono, di, and triterpenesinclude the carotenoids such as beta-carotene (precursor of vitamin A) and lycopene found in tomatoesusually colorful compounds due to highly conjugated systempolyisoprenoids or polyprenols consist of numerous isoprene adducts (8 22) examples include dolichol phosphate, undecaprenyl alcohol (bactoprenol) and the side chains of vitamins K, vitamin E and coenzyme Q

Websites on lipidshttp://www.cyberlipid.org/ web site deals mainly with an overview on all lipidshttp://www.lipidsonline.org this website focuses mainly on disease processes (atherosclerosis) and treatmenthttp://www.lipidlibrary.co.uk/ -There are two main divisions in this website, one dealing with the chemistry and biochemistry of lipids and the other with the analysis of lipids