4. Biochemistry of Fat and NSAIDs (1).pdf

MODULE 2 4 BIOCHEMISTRY OF FAT AND NSAIDS 5 LIPID METABOLISM 1  MODULE 2 4 BIOCHEMISTRY OF FAT AND NSAIDS 5 LIPID METABOLISM 2 4 BIOCHEMISTRY OF FAT AND NSAIDS...

MODULE 2 4 BIOCHEMISTRY OF FAT AND NSAIDS 5 LIPID METABOLISM 1  MODULE 2 4 BIOCHEMISTRY OF FAT AND NSAIDS 5 LIPID METABOLISM 2 4 BIOCHEMISTRY OF FAT AND NSAIDS 3  4. BIOCHEMISTRY OF FAT AND NSAIDS — CONTENTS — I. BIOCHEMISTRY OF FAT Classification of lipids Storage lipids fatty acids and triacylglycerols Omega-3 and Omega-6 fatty acids Membrane lipids Glycerophospholipids and phospholipases II. NSAIDS Synthesis of prostaglandins Prostaglandin synthase, COX-1, and COX-2 NSAIDs Aspirin Other NSAIDs COX-2 inhibitors III. ACETAMINOPHEN Doses Metabolism Hepatotoxicity 4  4. BIOCHEMISTRY OF FATS AND NSAIDS – LEARNING OBJECTIVES – Distinguish based on their properties saturated-, unsaturated-, and trans fats Describe the FDA qualified health claims for omega-3-fatty acids Outline the activities of phospholipases on glycerophospholipids Describe the activity of prostaglandin synthase and distinguish COX-1 and COX-2 Explain the mechanism of action of aspirin and compare it to other NSAIDs Discuss the acetaminophen-induced hepatotoxicity 5 I. BIOCHEMISTRY OF FAT 6  I. BIOCHEMISTRY OF FAT Classification of Lipids Lipids can be classified into storage lipids and membrane lipids. Storage lipids are neutral whereas membrane lipids are polar. Both storage or membrane lipids have an alcohol as the backbone: either glycerol or sphingosine. There is a third class of membrane lipids, the sterols, mainly cholesterol. storage lipids membrane lipids (polar) phospholipids glycolipids triacylglycerols glycerophospholipids sphingolipids sphingosine sphingosine fatty acid fatty acid glycerol glycerol fatty acid fatty acid fatty acid fatty acid fatty acid Pi alcohol Pi choline glucose/galactose 7  storage lipids membrane lipids (polar) phospholipids glycolipids triacylglycerols glycerophospholipids sphingolipids sphingosine sphingosine fatty acid fatty acid glycerol glycerol fatty acid fatty acid fatty acid fatty acid fatty acid Pi alcohol Pi choline glucose/galactose 8  I. BIOCHEMISTRY OF FAT Storage Lipids: Fatty acids and triacylglycerols Fatty acids are hydrocarbon derivatives that contain a terminal storage lipids carboxyl group. In some fatty acids this chain is fully saturated (there are no double bonds); the basic formula of completely saturated fatty acids is CH3—(CH2)n—COOH triacylglycerols Others are unsaturated, i.e., contain one or more double bonds. If unsaturated fatty acids contain more than one double bond, they fatty acid are usually separated by a methylene group (—CH2—). glycerol —CH2—CH=CH—CH2 —CH=CH—CH2— fatty acid Carbon atoms are numbered with the carboxyl group as number 1, fatty acid and double bond locations are designated by the number of the carbon atom on the carboxyl side of it. 9  I. BIOCHEMISTRY__ saturated OF FAT fatty acid __ ______ unsaturated fatty acid ______ carboxyl– carboxyl O –O Storage Lipids: Properties of fatty acids group O O group C C Fatty acids esterifying glycerol can be saturated or unsaturated. When an unsa- hydrocarbon hydrocarbon chain chain turated fatty acid esterifies glycerol, it introduces a bend or kink in the molecule structure. this double bond is rigid and creates a glycerol kink in the chain backbone glycerol backbone fatty acids fatty acids Triacylglycerol Triacylglycerol The fatty acids esterifying glycerol One of the fatty acids esterifying are all saturated glycerol is unsaturated, thus introducing a bend or kink in the molecule structure 10  I. BIOCHEMISTRY OF FAT Storage Lipids: Fatty acid composition in natural foods C16 + C18 C16 + C18 C4 to C14 saturated unsaturated saturated 100 Fatty Acids (% of Total) UNSATURATED UNSATURATED FATTY ACIDS OOLIVE OIL LIVE OIL FISHOILOIL FISH FATTY ACIDS 50 0 olive oil butter beef fat (liquid) (soft solid) (hard solid) ______ Natural Fats at 25°C ______ SATURATED SATURATED FATTY ACIDS ANIMAL FAT ANIMAL FAT BBUTTER UTTER FATTY ACIDS 11  I. BIOCHEMISTRY OF FAT Storage Lipids: Fatty acid composition in natural foods: Omega-3 (w-3) and omega-6 (w-6) fatty acids Omega-3 (w-3) and omega-6 (w-6) fatty acids contain a double bond at the third or sixth carbon, respectively, from the end of the carbon chain (opposite to C1 that contains the carboxylic group). w-6) fatty acids (linoleic acid) present in different oils (safflower, sunflower, corn, soybean, 18 17 etc). 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 CH3–CH2–CH=CH–CH2–CH=CH–CH2–CH=CH–CH 2–CH 2–CH 2–CH22–CH 2–CH 2–CH 2–COOH Linoleni 17 16 n Linoleic 15 14 acid 13 (18:2) 12 11 and 10 arachidonic 9 8 7acid6 (20:4) 5 are 4 examples 3 of w-6 1 fatty acids, the 18:3 (9,1 –CH2–CH=CH–CH 2–CH=CH–CH2–CH=CH–CH2–CH2–CH2–CH2–CH2–CH2–CH2–COOH Linolenic Acid ω ____ 3 ____ 9 major dietary sources being plant oils and different types of nuts. 18:3 (9,12,15) 18:3 (Δ __ 3 ____ 18:3 (Δ9,12,15) 18:3 (ω 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 18:31(ω-3) CH –CH2–CH2–CH2–CH2–CH=CH–CH2–CH=CH–CH –CH2–CH2–CH2–CH2–CH2–CH2–COOH Linoleic 7 16 n 153 14 13 12 11 10 9 8 7 6 52 4 3 2 1 18:2 (9 CH2–CHω 2–CH 2–CH2–CH=CH–CH ____________ 2–CH=CH–CH2–CH2–CH2–CH2–CH2–CH2–CH2–COOH Linoleic Acid 18:2 (Δ 6 ______________ 18:2 (9,12) ________ 6 ______________ 18:2 (Δ9,12) 18:2 (ω 18:2 (ω-6) 12  I. BIOCHEMISTRY OF FAT w-3 fatty acids in plants is linolenic acid (contains three cis double bonds between carbon 9 and 10, between 12 and 13, and between 15 and 16): 18:3 (D9,12,15). 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 CH3–CH2–CH=CH–CH2–CH=CH–CH2–CH=CH–CH 2–CH 2–CH 2–CH 2–CH 2–CH2–CH2–COOH Linole 7 16 15 n 14 13 12 11 10 9 8 7 6 5 4 3 2 1 18:3 (9 CH2–CH=CH–CH 2–CH=CH–CH2–CH=CH–CH2–CH2–CH2–CH2–CH2–CH2–CH2–COOH Linolenic Acid ω ____ 3 ____ 18:3 (9,12,15) 18:3 (Δ 3 ____ 18:3 (Δ9,12,15) 18:3 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 18:3 2 (ω-3) 1 CH –CH –CH –CH –CH –CH=CH–CH2–CH=CH–CH –CH –CH2–CH2–CH2–CH2–CH2–COOH Linole 16 n15 3 14 2 13 2 12 2 11 2 10 9 8 7 6 5 2 4 2 3 2 1 18:2 H2–CH2–CH Examples of 2–CH2–CH=CH–CH ω ____________ w-3 fatty2–CH=CH–CH acids in marine2–CH 6 ______________ oils 2are –CH eicosapentaenoic 2–CH2–CH2–CHacid 2–CH (EPA) 2–COOH(a 20-carbon fatty Linoleic Acid 18:2 (9,12) 18:2 ( ______ 6 ______________ 18:2 acid that contains five cis double bonds) and docosahexanoic acid (DHA) (a 22-carbon (Δ9,12 18:2fatty acid ) 18:2 (ω-6) with 6 cis double bonds). Present in oily fish (salmon, herring, sardines), fish oil, walnuts. 13  I. BIOCHEMISTRY OF FAT Storage Lipids: Fatty acid composition in natural foods Omega-3 (w-3) and omega-6 (w-6) fatty acids FDA ANNOUNCED QUALIFIED HEALTH CLAIMS FOR OMEGA-3-FATTY ACIDS JUNE 19, 2019 The Food and Drug Administration (FDA) announced today that it does not intend to object to the use of certain qualified health claims stating that consuming eicosa- pentaenoic acid (EPA) and docosahexaenoic acid (DHA) omega-3 fatty acids in food or dietary supplements may reduce the risk of hypertension and coronary heart disease. Specifically, the FDA responded to a health claim petition submitted by The Global Organization for EPA and DHA omega 3s in a letter of enforcement discretion. The agency found that while there is some credible evidence suggesting that combined intake of EPA and DHA from conventional foods and dietary supplements may reduce the risk of hypertension by lowering blood pressure, this evidence is inconclusive and highly inconsistent. EPA and DHA omega-3 fatty acids are found primarily in some fatty fish, fish oils and dietary supplements. Omega-3 fatty acid ethyl esters Lovaza Antihyperlipidemic 14 I. BIOCHEMISTRY OF FAT Storage Lipids: Trans fatty acids Although most unsaturated fatty acids possess their double bond in the cis configuration, there are some unsaturated fatty acids with the double bond in the trans 18:0 18:1 18:1 stearic acid oleic acid elaidic acid configuration. The trans fatty acids originate (saturated) CH3 CH3 (cis unsaturated) (trans unsaturated) CH3 | | | CH2 CH2 CH2 mainly from food processing, chemical | | | CH2 CH2 CH2 | | | CH2 CH2 CH2 | | | hydrogenating polyunsaturated fatty acids for CH2 | CH2 CH2 | CH2 CH2 | CH2 | | | CH2 CH2 CH2 stability. Examples are margarine, shortenings, | | | CH2 CH2 CH2 | | | CH2 C—H C—H | H and fried foods. Trans-fatty acids are generally CH2 C— | 2 CH2 H— C CH| | | 2 CH| CH2 CH2 CH 2 solid but with a softer texture (margarine | CH| | CH2 CH2 CH| 2 | | | CH| 2 CH2 CH2 | CH| 2 | versus butter). Trans-fatty acids, like saturated CH2 CH2 CO| 2 H | | O CH2 CH2 | | CH2 CH2 fatty acids, have been suggested to increase | | COOH CH2 | COOH serum cholesterol levels. 15  storage lipids membrane lipids (polar) phospholipids glycolipids triacylglycerols glycerophospholipids sphingolipids sphingosine sphingosine fatty acid fatty acid glycerol glycerol fatty acid fatty acid fatty acid fatty acid fatty acid Pi alcohol Pi choline glucose/galactose 16  I. BIOCHEMISTRY OF FAT Membrane Lipids (Polar) The main feature of biological membranes is a double layer of lipids that constitutes a barrier to the passage of polar molecules. There are three major types of membrane lipids: glycerophospholipids, in which the hydrophobic regions are composed to two fatty acids joined to glycerol. sphingolipids, in which a single fatty acid is joined to an amino alcohol, sphingosine. sterols, compounds characterized by a rigid system of four fused hydrocarbon rings. membrane lipids (polar) phospholipids glycolipids glycerophospholipids sphingolipids sphingosine sphingosine fatty acid glycerol fatty acid fatty acid fatty acid Pi alcohol Pi choline glucose/galactose 17  I. BIOCHEMISTRY OF FAT 3 Membrane Lipids (Polar) a. Glycerophospholipids Glycerophospholipids are derivatives of phosphatidic acid. In glycerophospholipids, a polar alcohol is joined to C-3 of glycerol through a phosphodiester bond. Glycerophospholipids are named for their polar head groups (e.g., phosphatidyl-choline and phosphatidyl-ethanolamine). The fatty storage acids lipids in glycerophospholipids can be any of a wide variety, but generally a saturated fatty acid (e.g., palmitic acid) and an unsaturated fatty acid (e.g., oleic). O || fatty acid H2C—O—C—R triacylglycerols | O glycerol || ethanolamine --------------- phosphatidylethanolamine fatty acid HC—O—C—R choline----------------------- phosphatidylcholine | O fatty acid || serine------------------------ phosphatidylserine alcohol H2C—O—P—O—X Pi glycerol | glycerol---------------------- phosphatidylglycerol fatty acid O– inositol ---------------------- phosphatidylinositol phosphatidyl glycerol------ cardiolipin fatty acid 18  GLYCEROPHOSPHOLIPIDS AND PHOSPHOLIPASES There is a specific hydrolytic enzyme (phospholipase) for each of the bonds in a glycero-phospholipid. Phospholipase A1 removes the fatty acid in position 1 and phospholipase A2 that in position 2 of glycerol. Phospholipase C cleaves phosphatidylinositols, releasing diacyl- glycerol and inositol phosphates, which serve as signaling molecules. Phospholipase D removes the alcohol from the phospholipid. phospholipase A1 O || CH2—O—C—R1 | O || CH—O—C—R2 | O– phospholipase A2 | CH2—O—P—O—alcohol || O phospholipase D phospholipase C 19  SYNTHESIS OF PROSTAGLANDINS When the fatty acid in C2 of glycerol is arachidonic acid, the action of phospholipase A2 releases free arachidonic acid, a precursor in the synthesis of one of the eicosanoids that act as intracellular messengers. Eicosanoids, unlike hormones, are not transported O between tissues in the blood but act on || CH2—O—C | O the tissue in which they are produced. || 5 11 CH—O—C Arachidonic acid is metabolized to | 8 14 CH2—O—Polar Head thromboxanes, leukotrienes, and prosta- PHOSPHOLIPASE A2 glandins by the actions of thromboxane synthase, lipoxygenase, and prostaglan- O 8 5 || C-OH din synthase. CH3 11 14 arachidonic acid THROMBOXANE SYNTHASE LIPOXYGENASE PROSTAGLANDIN SYNTHASE thromboxanes leukotrienes prostaglandins 20  PROSTAGLANDIN SYNTHASE Prostaglandin synthase has two enzymatic activities: a cyclooxygenase (COX) activity and a hydroperoxidase (HPx) activity. The former incorporates two molecules of O2 into arachidonic acid yielding prostaglandin G2 (PG2); the latter converts this compound to prostaglandin H2 (PGH2). In humans, two types of cyclooxygenase are involved in eicosanoid metabolism, catalyzing the same type of reaction from arachidonic acid: arachidonic PG2 PGH2 COX HPx PROSTAGLANDIN SYNTHASE 21  PROSTAGLANDIN SYNTHASE COX-1 is distributed throughout the body and it is always present (constitutive) and involved in keeping the stomach lining intact and kidneys functioning properly. COX-2 catalyzes the same reaction, but the prostaglandin released leads to inflammation, pain, and fever. Most tissues do not express COX-2 constitu- tively, hence the labeling of COX-2 as the inducible COX COX-1 proper kidney function constitutive PG stomach lining COX inflammation COX-2 PG pain inducible fever 22  COX-1 COX-2 NONSTEROIDAL ANTI-INFLAMMATORY DRUGS (NSAIDS) MEMBRANE PHOSPHOLIPIDS Phospholipase A2 ARACHIDONIC ACID NSAIDs COX-1 COX-2 Selective COX-2 Inhibitors PROSTAGLANDINS NSAIDS have three major therapeutic actions; Reduce: Inflammation (anti-inflammatory) Pain (analgesic) Fever (antipyretic) 23  NSAIDS ASPIRIN arachidonic Aspirin acetylates (and inactivates) COX PG G2 PG H2 irreversibly. Restoration of COX activity COX will come only with the synthesis of new HPx copies of the enzyme. PROSTAGLANDIN Aspirin exhibits anti-inflammatory activity SYNTHASE only at relatively high doses; it has gained HO—Ser— more usage at lower doses for the prevention COX of cardiovascular events. active enzyme COO– This reaction irreversibly blocks the O—C—CH3 || enzyme from acting on arachidonic acid to O synthesize PGH2. Without PGH2, the COO– OH synthesis of other prostaglandins stops and the messengers that incite inflammation are reduced, thus affording relief of pain, H3C—C—O—Ser— || COX redness, and other discomfort. Thrombox- O inactive anes (potent platelet aggregators) are not enzyme synthesized, thereby reducing clotting. O || O S H2N || || 24 O N O N  SALICYLATE (ASPIRIN) POISONING Severe salicylate (aspirin) poisoning is characterized by high salicylate blood levels: 7.25 mmol/L (100 mg/dL) in acute ingestions or 40 mg/dL in chronic ingestions. Significant neurotoxicity (agitation, coma, convulsions), kidney failure, pulmonary edema, or cardiovascular instability. The triad of mild aspirin toxicity is nausea, vomiting, and dizziness. Toxicity depends on the levels of salicylate (expressed as mg/kg body mass): _______________________________________________________________________________ Severity Mild Moderate Severe 150 mg/kg 150-300 mg/kg 300-500 mg/kg ________________________________________________________________________________________ Toxicity No toxicity Mild to moderate Life-threatening expected toxicity expected toxicity expected _______________________________________________________________________________________ Symptoms Nausea, Nausea, vomiting Delirium, seizures vomiting, headache, hyper- coma, respiratory dizziness ventilation, tachi- arrest cardia, fever ________________________________________________________________________________________ There is no specific treatment for salicylate poisoning, except of consideration and following specific issues. Initial and subsequent frequent salicylate concentrations should be determined and interpreted in the individual clinical context. In moderate to severe salicylate poisoning, consider decontamination (activated charcoal) and the early enhancement of elimination (urinary alkalization with or without haemodialysis). 25 OTHER NSAIDS Ibuprofen and naproxen, and some other anti- inflammatory medications (diclofenac and indome- thacin) bind non-covalently and inhibit the enzyme, thereby producing relief from inflammation and pain. Because they are not permanently attached to the enzyme, however, eventually they leave the active site and are excreted, allowing the enzyme to become active once more. 26  COX-1 COX-2 NONSTEROIDAL ANTI-INFLAMMATORY DRUGS (NSAIDS) MEMBRANE PHOSPHOLIPIDS Phospholipase A2 ARACHIDONIC CELECOXIB is significantly more ACID selective for inhibition of COX-2 NSAIDs COX-1 COX-2 than COX-1. Unlike the inhibition Selective COX-2 of COX-1 by aspirin (which is fast Inhibitors and irreversible), the inhibition of COX-2 is reversible. Celecoxib is approved for the treatment of rheumatoid arthritis PROSTAGLANDINS and acute moderate pain. 27  Inhibitors that are specific for COX-2 would be more selective than aspirin for Aspirin targeting the inducible COX activity and Celecoxib Indomethacin they will target the inflamed tissue without (Celebrex) Naproxen the harmful side effects associated with aspirin (e.g., loss of blood clotting activity, Ibuprofen loss of protection of the gastric lining). Celecoxib Celecoxib and rofecoxib, are potent Rofecoxib Diclofenac inhibitors of COX-2. Rofecoxib shows a More More higher preference for COX-2 but has been COX–2 COX–1 withdrawn from the market because of Diclofenac adverse cardio-vascular effects. 28  ACETAMINOPHEN Acetaminophen inhibits prostaglandin synthesis in the CNS, thus having antipyretic and analgesic properties. Acetaminophen has less effects in peripheral tissues, thus a very weak anti-inflammatory activity. NON-STEROIDAL ANTI-INFLAMMATORY DRUGS (NSAIDS) Antipyretic Analgesic Anti-inflammatory ACETAMINOPHEN 29  ACETAMINOPHEN Acetaminophen inhibits prostaglandin synthesis in the CNS, thus having antipyretic and analgesic properties. Acetaminophen has less effects in peripheral tissues, thus a very weak anti-inflammatory activity. Acetaminophen is the analgesic/antipyretic of choice for children with viral infections. Recommended dose for children: 10 to 15 mg/kg every 4 to 6 hours, not to exceed 50 to 70 mg/kg in 24 hours Recommended dose for adults: 650 to 1,000 mg every 4 to 6 hours, not to exceed 4,000 mg in a 24-hour period Exceeding these doses (intentionally or unintentionally) cause severe hepato- toxicity 30  ACETAMINOPHEN Acetaminophen is metabolized by the cytochrome P450 mixed-function oxidase to the toxic intermediate N-acetyl-p-benzoquinoenimine (NAPQI). However, At therapeutic doses NAPQI reacts with the –SH group of GSH forming the non-toxic mercapturic acid. HNCOCH3 NCOCH3 At high doses, the available GSH pool in liver becomes depleted and NAPQI reacts P450 mixed function oxidase with the –SH groups of proteins forming OH O acetaminophen toxic intermediate (NAPQI) covalent bonds. Hepatic necrosis, a life- threatening condition, can result. Patients therapeutic toxic doses doses with hepatic disease or a history of alcohol- GSH ism are at higher risk of acetaminophen- induced hepatotoxicity. HNCOCH3 HNCOCH3 N-Acetyl-cysteine (NAC) which contains – SH groups to which the toxic metabolite can SG cell macromolecules OH bind, is an antidote in case of overdose. N- mercapturic acid OH (nontoxic) Acetyl-cysteine also increases the GSH CELL DEATH pool. 31