‹#› 1 Lipids and Steroids ã Department of Biochemistry (J.D.), 2010 ‹#› 2 Types of lipids •Simple •triacylglycerols •waxes •ceramides •non-polar •insoluble in water •soluble in lipophilic solvents • •Complex •glycerophospholipids •sphingophospholipids •glycosphingolipids •polar and non-polar have the character of tenside concentrate on phase interface see Med.Chem. II App. 4 ‹#› 3 Lipophilic solvents are very toxic trichloroethene Cl2C=CHCl (hepatotoxic) tetrachloroethene Cl2C=CCl2 (hepatotoxic) chloroform CHCl3 (hepatotoxic) tetrachloromethane CCl4 (N extremely hepatotoxic!!) benzene C6H6 (N carcinogen!!) toluene C6H5-CH3 (lung damages, addictive inhalant) nitrobenzene C6H5-NO2 (N methemoglobinemia) carbon disulfide CS2 (N neurotoxic) ‹#› 4 Fatty acids (FA) ‹#› 5 The three features of „fatty“ •1. Non-polar •= hydrophobic •= insoluble in water •= lipophilic •= soluble in organic solvents (CHCl3, CCl4, benzene) • 1. •2. Lighter than water •= density < 1 g/cm3 •= floats on water surface •= makes upper liquid phase 3. Contains long C-H chains and/or cycles ‹#› 6 oil on water water any fatty substance (oil, hydrocarbon) makes the upper phase ‹#› 7 Three types of fatty acids •SAFA saturated fatty acids •MUFA monounsaturated fatty acids •PUFA polyunsaturated fatty acids •aliphatic, monocarboxylic acid •even number of C atoms, biosynthesis from acetyl-CoA (2C) •saturated or unsaturated (configuration cis) •free FA are non-polar compouds, insoluble in water •very weak acids (pKA ~ 10) ‹#› 8 Three groups of SAFA C Acid Occurence Commentary 4 6 8 10 butyric caproic caprylic capric butter butter butter butter easily digestible, absorbed directly to blood metabolic fuel for enterocytes and liver Lat. butyrum, i, n. butter Lat. capra, ae, f. goat 12 14 16 lauric myristic palmitic coconut fat coconut fat animal fats atherogenic, increase blood cholesterol coconut fat is used to make ice cream etc. 18 stearic animal fats cocoa butter does not elevate blood cholesterol ‹#› 9 Biochemical role of SAFA •source of energy, for most tissues (not for brain) •excessive intakes leads to obesity, atherosclerosis (especially FA C12, C14, C16), increase total and LDL-cholesterol in blood •it is recommended to reduce the intake of SAFA •occurence: lard, butter, fatty meat, hardened fats, coconut fat •exception: cocoa butter – contains mainly C18, stearic acid does not harm, in addition cocoa is very rich in antioxidants ‹#› 10 Average ox. num. C = 0.0 Average ox. num. C = 0.0 Average ox. num. C = -1.8 Þ C is the most reduced Fatty acids possess the highest energy from nutrients Lipids Saccharides Proteins 38 kJ/g 17 kJ/g 17 kJ/g ‹#› 11 MUFA prevail in olive and rape seed oils •16:1(9) palmitoleic •18:1(9) oleic ‹#› 12 Biochemical role of MUFA •mainly oleic acid, source of energy •beneficial influence on blood lipids, decreases LDL-cholesterol, lipoproteins rich in MUFA are more resistent to lipoperoxidation •phenolic compounds in extra virgin olive oil increase antioxidant capacity of LDL •Mediterranean diet – low occurence of cardiovascular and cancer diseases •sufficient intake of MUFA is recommended •occurence: triacylglycerols of olive and rape seed oil ‹#› 13 Pyramid of Mediterranean diet red meat fish, poultry, eggs, sweets bread, pasta, vegetables, legumes, fruits, nuts, olives, olive oil, feta, yoghurt, light wines Daily Several times per month Several times a week ‹#› 14 PUFA •18:2 (9,12) linoleic n-6 essential •18:3 (9,12,15) a-linolenic n-3 essential •20:4 (5,8,11,14) arachidonic n-6 •20:5 (5,8,11,14,17) eicosapentaenoic (EPA) n-3 •22:6 (4,7,10,13,16,19) docosahexaenoic (DHA) n-3 ‹#› 15 18:3 (n–3) or ω-3 C O O– 18 15 12 9 n n-3 n-6 n-9 Linolenic acid (neutral compound), Linolenate (anion) 18 : 3 (9,12,15) positions of double bonds number of double bonds total number of carbon atoms Nomenclature of PUFA Example: all-cis-octadeca-9,12,15-trienoic acid (systematic name) Linguistic analysis: octadeca - tri - en - oic acid Name component Explanation octadeca 18 (from Greek) = the number of C atoms tri 3 = the number of double bonds en infix, indicates a double bond oic acid suffix, indicates a compound type (carboxylic acid) ‹#› 16 Essential fatty acids: linoleic acid (LA), α-linolenic acid (ALA) •cannot be created in the body, we do not have enzymes for corresponding desaturations •desaturation in human body proceeds only from C1 to C9 •n-3 and n-6 desaturations occur only in plants •essential FA must be supplied by food •recommended intake of total PUFA: around 20 g •optimal ratio LA : ALA = 1:1, not higher than 5:1 • ‹#› 17 Biochemical roles of PUFA •structural components of membrane phospholipids •the precursors of eicosanoids •primarily not source of energy •beneficial influence on blood cholesterol •CAUTION: excessive intake of PUFA is harmful, they are sensitive to lipoperoxidation •excess of LA-derived eicosanoids exhibit unfavourable health effects (increased blood coagulation etc.) •PUFA occurence: sunflower oil and soybean oil (ω-6), fish oil, nuts, linseed oil (ω-3) ‹#› 18 Physiological effects of n-6 and n-3 PUFA are not the same. They are given by the opposite effects of corresponding eicosanoids n-6 n-3 Decrease blood cholesterol Decrease blood TAG Increase blood coagulation (platelet aggregation) Decrease blood coagulation (platelet aggregation) Inflammatory effect Anti-inflammatory effect Necessary for the development of brain in children ‹#› 19 Essential FA are the substrates for desaturations and elongations PUFA with double bonds beyond C9 (n-6 and n-3) are synthesized by plants. If dietary intake is sufficient, linoleate and α-linolenate are precursors of other PUFA such as arachidonate (n-6) and eicosapentaenoate (n-3), from which eicosanoids are formed. Linoleate 18:2 (9,12) γ-Linolenate 18:3 (6,9,12) Eicosatrienoate 20:3 (8,11,14) Arachidonate 20:4 (5,8,11,14) α-Linolenate 18:3 (9,12,15) Octadecatetraenoate 18:4 (6,9,12,15) Eicosatetraenoate 20:4 (8,11,14,17) Eicosapentaenoate 20:5 (5,8,11,14,17) 6-desaturation elongation 5-desaturation 6-desaturation elongation 5-desaturation n-6 n-3 ‹#› 20 Simple lipids are triesters of glycerol saturated triacylglycerol (TAG) ‹#› 21 Dispersion interactions between saturated TAG (linear molecules) are very extensive Higher melting point – solid fats tristearoylglycerol ‹#› 22 Dispersion interactions between unsaturated TAG (spherical molecules) are limited Lower m.p. – liquid fats (oils) trilinoloylglycerol ‹#› 23 Chemical conversion of lipids •hydrogenation (in vitro) •re-esterification (in vitro) •hydrolysis (in vitro, in vivo) •lipoperoxidation (in vitro, in vivo) •rancidification (in vitro) fat hardening ‹#› 24 Hydrolysis of triacylglycerols •acidic ® glycerol + 3 FA •alkaline ® glycerol + 3 salts of FA •enzymatic: lipase action (see later) ‹#› 25 Acidic hydrolysis provides free FA ‹#› 26 Alkaline hydrolysis provides soap Soap (sodium salt of fatty acid) is anionic surfactant linguistic paradox ‹#› 27 Composition of soap Aqua, Sodium Tallowate, Sodium Lardate, Sodium Cocoate, Perfume, Glycerine, Almond Extract, Sodium Chloride, Titanium Dioxide, EDTA, CI 15510 See Seminars, p. 24 tallow = fat obtained from beef cattle and sheep lard = pig fat coconut fat = fat obtained from the flesh of coconut fruit ‹#› 28 Lipoperoxidation in vivo •Reaction of PUFA with free radicals (•OH, •OR, •OOR) •Chain reaction, non-specific •Products: higher aldehydes, alkanes malondialdehyde (MDA) O=CH-CH2-CH=O •MDA attacks proteins and other biomolecules ‹#› 29 Lipids in food: Various aspects Pure (100%) plant oils, lard, hardened kitchen fats Emulsified with water butter, margarins Obvious (explicit) see above Hidden (latent) meat products, cheese, ice cream, cookies etc. Atherogenic SAFA, especially C12, C14, C16 most animal fats, coconut fat Anti-atherogenic MUFA, PUFA olive oil, rape seed oil, nuts, sea fish Suitable for frying resistent to oxidation (SAFA, MUFA) cholesterol-free Unsuitable for frying containing: higher portion of PUFA / cholesterol / water ‹#› 30 Average content of FA in selected kitchen fats (%) Fat SAFA MUFA ω-3 PUFA ω-6 PUFA Rape seed oil 10 60 10 20 Sunflower oil 10 25 1 64 Soybean oil 16 24 7 53 Olive oil 15 75 1 9 Coconut fat 90 7 0 3 Lard 43 48 1 8 Butter* 67 28 0 2 Poultry fat 42 37 1 20 Fish oil 28 52 15 5 Cocoa butter 60 38 0 2 * The difference to 100 % is made by 3 % of trans-FA. ‹#› 31 Nutritional recommendations about fats •2/3 plant oils, 1/3 animal fat •avoid fats with SAFA (mostly contain cholesterol) •prefer olive oil, rape seed oil, and sea fish •be careful with sunflower oil and soybean oil •prefer margarins to butter •avoid trans-FA •avoid dead-burn fats and fried meals ‹#› 32 Fat content in meat varies in the big range Type of meat Fat content (%) Long-life salamis 40-60 Sausages, wursts, hot dogs etc. 20-50 Pork 40 Goose, duck 20-40 Pork lean 20 Sea fish (herring, mackerel, salmon) 10-20 Sardines 7-9 Rabbit 7 Chicken, turkey 5-6 Beef lean 3 Carp (fish) 3 Venison 1 Codfish 0,6 Chicken brest 0,5 Zander (fish) 0,4 Pangasius (fish) 0,4 Turkey breast 0,3 ‹#› 33 trans-Fatty acids contribute to coronary heart disease •Natural occurence •tallow (3-7 %) •butter (3 %) •Synthetic origin •kitchen fats hardened by hydrogenation •food products containg hardened fats (cookies etc.) • saturated ‹#› 34 Other lipid-like substances •lipophilic vitamins (retinol, tocopherol, calciol, phylloquinone) •terpenes, antioxidants etc. •cholesterol, phytosterols Severe lipid-free diets lead to the deficit of lipophilic vitamins, antioxidants, and essential FA. ‹#› 35 Lipophilic vitamins and antioxidants Compound Structure type Main food sources Retinol Carotenoids Phylloquinone Tocopherol Calciol isoprene isoprene naphtoquinone chroman cholesterol butter, egg yolk, liver, vegetables colored vegetables and fruits green vegetables, made in intestine nuts, seeds, cold pressed plant oils fish oil, butter, made in skin (UV) ‹#› 36 Biochemical conversions of lipids ‹#› 37 Enzymatic hydrolysis in small intestine pancreatic lipase 2-acylglycerol is non-ionic surfactant free FA dissociates and makes anionic surfactant pH of pancreatic juice 7.5-8.8 ‹#› 38 Natural tensides in fat digestion Tenside Type Origin Bile acids 2-Acylglycerol FA anions Phospholipids anionic non-ionic anionic amphoteric from cholesterol in liver TAG hydrolysis in gut TAG hydrolysis in gut food They all together make a mixed micelle which enters enterocyte ‹#› 39 Lipases in human body Lipase Substrate Organ location Pancreatic lipase exogenous TAG small intestine Hormon-sensitive lipase (HSL) endogenous TAG adipose tissue Lipoprotein lipase (LPL) TAG of chylomicrons and VLDL capillaries of peripheral tissues (muscles etc.) Hepatic lipase (HL) TAG of HDL liver sinusoids ‹#› 40 triacylglycerols (adipose tissue) fatty acids acetyl-CoA ketone bodies lipolysis b-oxidation ketogenesis in liver if excess of acetyl-CoA CO2 + H2O + energy citrate cycle + respiratory chain utilization of ketone bodies in extrahepatic tissues Catabolic pathway of lipids ‹#› 41 Ketone bodies beta-hydroxybutyrate acetoacetate acetone ‹#› 42 glucose from food glucose from food acetyl-CoA pyruvate dihydroxyacetone-P fatty acid fats from food glycerol-3-P + acyl-CoA phosphatidate glycerophospholipids (cell membranes) triacylglycerols glycolysis oxidative decarboxylation synthesis of FA glycolysis hydrogenation activation Anabolic pathway- biosynthesis of lipids ‹#› 43 Schematic diagrams of complex lipids The "head“ group Glycolipids Sphingophospholipids The "head“ group Glycerophospholipids see MCH II App. 4 ‹#› 44 Complex lipids are tensides glycerophospholipid sphingophospholipid polar head two non-polar tails ‹#› 45 Phosphatidic acid is the main structure of glycerophospholipids 1,2-diacylglycerol-3-phosphoric acid ‹#› 46 Distinguish •Phosphatidate = anion of phosphatidic acid (after removing H+) • • •Phosphatidyl = acyl of phosphatidic acid (after removing –OH group) ‹#› 47 Glycerophospholipids diester of phosphoric acid dissociated – negative charge X is polar component choline ethanolamine serine inositol ‹#› 48 Polar components – Metabolic origin serine ethanolamine choline decarboxylation methylation (SAM) inositol From food ‹#› 49 Phosphatidylcholine is amphoteric tenside ‹#› 50 FA acyl Non-polar part Polar part cation phosphate ‹#› 51 A pictogram of phospholipid shows one polar head and two non-polar tails ‹#› 52 Phospholipids make a bilayer of cell membranes Cell mebrane is predominantly non-polar system. Non-polar substances penetrate easily (O2, CO2, some toxins and drugs). Polar (glucose) and ionic species (Na+, Ca2+) require specific transporters. ‹#› 53 Dipalmitoylphosphatidylcholine is the main component of pulmonary surfactant inspiration expiration atelectasis • decreases surface tension of alveoli • prevents the collapse of lungs during expiration • facilitates the opening of alveoli during inspiration • lack of surfactant Þ respiratory distress (atelectasis) ‹#› 54 Phosphatidylinositol It makes up to 20 % of phospholipids in cell membranes. ‹#› 55 PIP2 is a precursor of the second messenger phosphatidylinositol-4,5-bisphosphate (PIP2) Second messengers: inositol trisphosphate (IP3) and diacylglycerol (DAG) are released after hydrolysis of PIP2 ‹#› 56 Sphingolipids – Schematic diagrams Glycolipids Sphingophospholipids The "head“ group Ceramide N-Acylsphingosine ‹#› 57 Sphingosine has 18 carbons (16 from palmitic acid, 2 from serine) serine (3C) palmitoyl-CoA (16C) amino group binds FA Prim. alcohol group binds phosphate or sugar ‹#› 58 Ceramides are amides fatty acid sphingosine amide linkage ‹#› 59 Sphingomyelines FA – lignoceric 24:0 and nervonic 24:1(15) fatty acid sphingosine phosphate choline ‹#› 60 Glycosphingolipids •Neutral •cerebrosides (monoglycosylceramides) •oligoglycosylceramides •contain galactose (Gal) and/or glucose (Glc) •attached by O-glycosidic bond •Acidic •sulfoglycosphingolipids (esters of sulfuric acid) •gangliosides (contain sialic acid) • ‹#› 61 Cerebroside (monoglycosylceramide) galactosylceramide ceramide galactose O-glycosidic bond ‹#› 62 Glycolipids can be sulfated C3 hydroxyl of galactose is esterified by sulfuric acid ‹#› 63 Gangliosides (sialoglycosphingolipids) Sialic acid is attached in terminal position to oligosaccharide ‹#› 64 cyclopentanoperhydrophenanthrene (sterane) phenanthrene (fused aromatic benzene rings) perhydrophenanthrene (fused cyclohexane rings) Steroids ‹#› 65 The rings in steroids are denoted by the letters A, B, C, and D: Carbon atoms in steroids are numbered: 1 10 2 3 4 5 9 6 7 8 11 15 14 16 17 13 12 A B C D Carbons outside the rings: 17 22 23 27 26 25 21 20 19 18 24 ‹#› 66 The two fused cyclohexane rings in chair conformations trans fusion cis fusion A trans fusion yields a nearly planar structure, whereas a cis fusion gives a buckled structure. ‹#› 67 5a-Gonane From the eight stereoisomers of sterane, two are named gonanes: The fusion of the steroid rings B ands C as well as C and D is trans, the fusion of the rings A and B is either trans (so called 5α-) or cis (5β-configuration). In nearly all natural steroids the atoms attached to C-10, C-8, C-13 lie above the plane containing the four rings – they are β-oriented. The atoms (substituents) that are below the plane are α-oriented. ‹#› 68 5b-Gonane The cis fusion of the rings A and B (characteristic for the bile acids, with the buckled structure) occurs rarely. ‹#› 69 Steroidal hydrocarbons Name No. of C Substituent 17b -Substituent Gonane 17 - - Estrane 18 13-methyl - Androstane 19 10,13-dimethyl - Pregnane 21 10,13-dimethyl ethyl Cholane 24 10,13-dimethyl pentan-2-yl Cholestane 27 10,13-dimethyl 6-methylheptan-2-yl ‹#› 70 17β-Ethyl-5α-androstane 5α-Pregnane C21 ‹#› 71 5α-Cholestane C27 Eight-carbon branched side chain at C-17 ‹#› 72 C27 C24 C21 C19 C18 Cholesterol is the precursor for other steroids ‹#› 73 Cholesterol free and esterified 27 carbon atoms 1 hydroxyl (C3) 1 double bond (C5) the only polar group ‹#› 74 In blood, cholesterol occurs in lipoproteins Class Density (g/ml) Proteins (%) Cholesterol (%) TAG (%) CM VLDL LDL HDL 0.90 0.95 1.05 1.20 2 9 21 50 5 15 50 22 84 54 11 4 CM – chylomicrons VLDL – very low density lipoprotein LDL - low density lipoprotein HDL - high density lipoprotein ‹#› 75 Coprostanol is hydrogenated cholesterol The product of bacterial reduction of cholesterol in intestine. ‹#› 76 The balance of cholesterol in human body Input into body g/day Output from body g/day food biosynthesis in body Total: 0.5 g 1.0 g 1.5 g coprostanol (stool) bile acids (stool) sebum/desquamated cells Total: 0.8 g 0.5 g 0.2 g 1.5 g cholesterol in food only animal fats (including fish): lard, butter, bacon, egg yolk, mayonnaise, fat meat, fat cheese ‹#› 77 Cell membranes contain phospholipids, glycoproteins, and cholesterol cholesterol glycolipid glycoprotein fibronektin collagen proteoglycans Fibrilar protein spektrin ‹#› 78 Calciol (cholecalciferol, vitamin D3) is synthesized from 7-dehydrocholesterol by photolysis that leads to opening the ring B: See Seminars, p. 60 C27 ‹#› 79 The effects of calciol •Calciol is made in skin (UV light) •Calciol is metabolized to calcitriol – active hormone •Regulates calcium and phosphate homeostasis •Stimulates intestinal absorption of calcium • •Deficit of calciol – rickets in children, osteomalacia in adults • • ‹#› 80 Bile acids are anionic surfactants all polar groups are oriented on one side of molecule ‹#› 81 Steroid hormones Glucocorticoids Mineralocorticoids Androgens Estrogens Gestagen ‹#› 82 Steroid hormones corticosterone testosterone cortisol aldosterone C21 C21 C21 C21 C19 C18 ‹#› 83 Progesteron is a gestagen: it prepares the lining of the uterus for implantation of an ovum and is also essential for the maintenance of pregnancy. C21 ‹#› 84 Corticoids are hormones produced in the adrenal cortex. Glucocorticoids (such as cortisol) promote gluconeogenesis and the formation of glycogen, enhance the degradation of proteins and fat, and inhibit the inflammatory response. They enable animals to respond to stress. Mineralocorticoids (primarily aldosterone) act on the kidney to increase the reabsorption of Na+ and the excretion of K+, which leads to an increase in blood volume and blood pressure. C21 ‹#› 85 Testosterone 17β-Hydroxyandrost-4-ene-3-one C19 Androgens are responsible for the development of male secondary sex characteristics. ‹#› 86 Estradiol Estra-1,3,5(10)-triene-3,17β-diol C18 Estrogens are required for the development of female secondary sex characteristics and, along with progesterone, also participate in the ovarian cycle.