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1) OBESITY & high plasma triglycerides Adipose cells, adipocytokines . . White fat cells store a large lipid droplet of triglycerides and cholesteryl ester.
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1) OBESITY & high plasma triglyceridesAdipose cells, adipocytokines . • White fat cells store a large lipid droplet of triglycerides and cholesteryl ester. • Synthesise and secrete leptin167(aminoacids), peptide hormone, binds to receptors in hypothalamic nuclei “satiety center” regulates energy). Leptin signals a decrease in appetite. Prooxidant like fructose. • Adiponectin (244aa) , most abundant protein in adipocyte, (similar structure to TNFα) & released into the blood. Higherin females. Antioxidant. • adipocyte oxidative stress (insulin activates NADPH oxidase (Nox4) • body weight , mitoch.fatty acid oxidation,gluconeogenesis, insulin resistance. Insulin causes lipogenesis and fatty acid release ( fatty liver) . • Plasma adiponectin decr. & leptin incr. in obesity (promotes breast cancer). • Brown fat (babies) mitochondria make heat.
Adipocyte dysfunction & Metabolic disease • Obesity due to overnutrition (high fat or sugar diet ) & inactivity causes metabolic disease . • Insulin resistance & diabetes mellitus • Hypertension • Hyperlipidemia , nonalcoholic steatohepatitis (NASH), alcoholic liver disease, chronic hepatitis, liver cancer • Therapy: caloriesexercise,taurine,salicylate,thiazolidinediones, • Research : how to increase adiponectin levels • J.Gastroenterol(2008)43,811-822,Clinical Chemistry (2008)54,945-55
Fatness increases cancer risk • Fatness cancer rate may exceed cancer from smoking soon. • Breast cancer, esophagus, colorectal, pancreas, ovary. • gall bladder,endometrium, liver (after cirrhosis) NASH. • NOT prostate,bladder, mouth, lung, skin, cervix, nasopharynx,skin cancer • Associated with energy-dense foods,fast food,sugary drinks,sedentary living,TV/computers. • 2007 WCRF/AICR report
Adipocyte dysfunction & Metabolic disease • Obesity due to overnutrition (high fat or sugar diet ) & inactivity causes metabolic disease . • Cancer rate may exceed that from smoking in 10y! • Insulin resistance & diabetes mellitus • Hypertension • Hyperlipidemia , nonalcoholic steatohepatitis (NASH), alcoholic liver disease, chronic hepatitis, liver cancer • Therapy: caloriesexercise,taurine,salicylate,thiazolidinediones, • Research : how to increase adiponectin levels? • J.Gastroenterol(2008)43,811-822,Clinical Chemistry (2008)54,945-55
Figure 1 Following chronic alcohol ingestion, endotoxin is released from certain intestinal bacteria. Endotoxin moves from the gut into the bloodstream and the liver where it activates Kupffer cells- a type of immune cell (resident liver macrophages) - by interacting with CD14 causing nuclear factor kappa B (NFκB) production.This generates superoxide radicals (O2) and various signaling molecules (the cytokine TNF–α) which injures hepatocytes. (Alcohol Res Health. 2003; 27(4):300-6.)
2) High plasma cholesterol and atherosclerosis Clinical chemistry Fat Absorption Liver cell synthesis of LDL and HDL Cholesterol Synthesis Drug Therapy Fibroblasts and other extrahepatic tissues for membrane biosynthesis Atherosclerosis Genetic Disorders
Lipoproteins, Cholesterol and Atherosclerosis • A) Clinical chemistry - Lipoproteins • Conjugated proteins in which the prosthetic group • are lipids • Responsible for the transport and distribution of • lipids: • - Lipid hormones • - Lipids absorbed by the intestine • - Fat-soluble vitamins
Plasma cholesterol >6.2mM (change diet); 5.5-6.2mM (borderline); <5.5mM normal Percent contribution of cholesterol and saturated fat from fats/oils, meats, dairy products and eggs in the US diet. Biochim. et Biophys. Acta 1529 (2000) 310-320
A lipoprotein: Horton Fig 17-5
B) Stage 1 - Fat Absorption • Chylomicrons • Found in lymph draining the intestine not hepatic • portal systems • Largest ones are microscopically visible (diameter • 500 nm) (floats upon centrifugation) • Responsible for the lipemic (milky turbidity) of the • blood following food digestion and disappears at 5 hours • Contains 1% protein - formed by intestinal cell • triglycerides (apo AI and II, B)
Dietary cholesterol chylomicron & HDL formed in intestinal epithelial cell remnant lymph vessel taken up by adipose cells & extrahepatic tissues B48 M.W. = 300,000 (chylomicrons, chylomicron remnants)
C) Stage 2 : LDL activity and function LDL(apoB100) synthesised by liver moves cholesterol to the tissues (taken up by the apoB100 receptor of tissues). LDL carries 75% plasma cholesterol and HDL carries 25%.
Liver cell synthesis of LDL,VLDL and HDL B-100 A,C,E i.e. LDL, VLDL, HDL
Electron micrograph of a part of a liver cell actively engaged in the synthesis and secretion of very low density lipoprotein (VLDL). The arrow points to a vesicle that is releasing its content of VLDL particles. Liver mitochondrial fatty acid oxidation inhibited by some drugs causing FATTY LIVER 10
F) Stage 3- Fibroblasts and other extrahepatic tissues - cholesterol taken up for membrane biosynthesis Extrahepatic tissues obtain cholesterol from plasma LDL & NOT by synthesis STEPS: a) ApoB100 protein of LDL binds to receptor in coated pits b) Receptor-LDL complex is internalised by endocytosis c) Vesicles containing LDL fuse with lysosomes (proteases, esterases) proteases LDL Protein amino acids LDL Cholesterol esters cholesterol + fatty acid LINOLEATE esterases LDL receptor returns to plasma membrane (10min. - turnover ever 24 hours)
Steps (cont’d) d) Free cholesterol in the cell is used or stored Cholesterol Membrane biosynthesis + Linoleate Cholesterol ester i.e., store for cholesterol Acyl-CoA: cholesterol acyl transferase Regulation: When excess, the synthesis of new LDL receptors is stopped, therefore LDL not taken up by cells
The LDL receptor The LDL receptor consists of five domains with different functions: an LDL-binding domain, 292 residues; a domain bearing N-linked sugars, 350 residues; a domain bearing O-linked sugars, 58 residues; a membrane- spanning domain, 22 residues; and a cytosolic domain, 50 residues. Membrane spanning domain
Mutations affecting LDL receptors 1) no receptor is synthesised 2) receptors are synthesised but lack signals for transport don’t reach plasma membrane 3) receptors reach cell surface but don’t bind LDL normally 4) receptors don’t cluster in coated pits
Genetic disorders e.g. Familial hypercholesterolemia (Type II) - Autosomal dominant trait 1:500 - Cholesterol 680 mg/100 mL instead of 175 mg/100 mL - Die of heart disease before 20 years (homozygous) - Die of heart disease before 40 years (heterozygous– inherit one defective and one normal gene) 1.LDL receptor is unable to bind to coated pitsrandomly distributed in membrane LDL binds but can’t be absorbed by endocytosis 2. Faulty LDL receptor formed which can’t bind LDL
Extrahepatic tissues take up cholesterol via LDL receptors e.g. fibroblasts and stored as cholesterol esters in lysosomes Voet et al., Fig 19-37
Cholesterol Ester Synthesis Endoplasmic reticulum
LYSOSOMES Autophagic vacuole Aged proteins, Nucleic acids, lipids NADH FAD Acid proteases (cathepsins) Cholesterol ester esterase Nucleases Acid phospholipases Require acid pH ROS Cyt b5 Amino acids Cholesterol Nucleotides Fatty acids CoQ H+ ACID pH Stores dietary CoQ CoQ reduction maintains acid pH Arch Biochem Biophys. 375, 347-54, (2000).
G) Atherosclerosis - metabolic biochemistry An atherosclerotic plaque (marked by the arrow) blocks most of the lumen of this blood cell. The plaque is rich in cholesterol.
D) Stage 4 HDL : Reverse cholesterol transport and function 1. HDL is synthesised and secreted from the liver and the intestine. HDL contains 65% protein + free fatty acids, cholesterol, triacylglyceride and phospholipids. 2 Function: HDL picks up cholesterol released into the plasma from dying cells and from membranes undergoing turnover and returns it to the liver 3. HDL contains cholesterol, cholesterol ester, phospholipid and Lecithin:Cholesterol Acyl Transferase (LCAT) - synthesised in the liver that catalyses : LECITHIN + CHOLESTEROL LYSOLECITHIN + CHOLESTEROL ESTER LCAT is activated by apo-A1 and deficiency in LCAT means that HDL can’t take up cholesterol from tissue, therefore cholesterol and lecithin in tissue
Raising HDL to decrease tissue cholesterol • Niacin best • Fibrate drugs • bile acid binding resins • Exercise , -3 fatty acids,red wine,orange juice,beans, soy,oat bran • Not trans fatty acids, high carbohydrates
E) Cholesterol synthesis Step 1 Mitochondria Biochim. et Biophys. Acta. 1529 (2000) 89-102.
Step 2 Synthesis of isopentenyl pyrophosphate from Mevalonate occurs in the cytosol Stryer Fig 27-12 J Biol Chem. 271, 1784-8 (1996)
Step 3 Synthesis of squalene occurs in the cytosol then the e.r. peroxisome peroxisome e.r. Squalene synthase DIMERIZATION CoQ dolichol J Biol Chem. 271, 1784-8 (1996)
Step 4 Squalene Synthesis of cholesterol occurs in the ER P450, O2, NADPH Squalene epoxide cyclase Lanosterol diet sunlight Dehydrocholesterol Vitamin D3 NADPH P450 reductase Unsat. Fa acyl CoA +cholesterol acyltransferase (ACAT) CHOLESTEROL Cholesterol ester
F) Drug therapy to decrease plasma cholesterol i) The STATINS inhibit cholesterol biosynthesis to decrease plasma LDL cholesterol and cut the risk of heart attacks and strokes by at least 33% even in people with normal cholesterol. Several million Canadians are taking statins. HMG CoA reductase inhibitors but can induce rhabdomyolysis Lipitor (Atorvastatin;Pfizer); Zocor (Simvastatin prodrug; Merck) Crestor (Rosuvastatin; AstraZeneca) lowers risk of heart attack, death and stroke Merck: Lovastatin:40-80 mg/day, Squibb: Pravastatin: 20mg/day for female patients - best for persons with sleep disorders; need hepatocyte enzyme to open up lactone ring. 3-hydroxy-3-methyl- glutaryl CoA Mevinolin Mevinolin (Fungal), a competitive inhibitor of HMG CoA reductase, resembles 3-hydroxy-3-methyl-glutaryl CoA, the substrate. Pravastatin (from Penicillin) - hepatotoxic (rare), (intestinal metabolism inhibited by grapefruit juice)
But Statins may decrease plasma ubiquinone antioxidant HMG-CoA Isopentenyl-PP TYROSINE Dimethylallyl-PP Peroxisome 4-OH-benzoate Geranyl-PP ER, Golgi Decaprenyl- 4-OH benzoate transf. Polyprenyl-PP Farnesyl-PP Decaprenyl-PP trans-prenyltransf. Squalene synthase Dolichol N-glycosylates secretory proteins = Export glycoproteins Decaprenyl-4-OH-benzoate Squalene cholesterol LDL receptors (induced) LDL uptake LDL risk of atherosclerosis Coenzyme Q Cholesterol Free Rad. Biol. Med. 29, 285-94 (2000) Lancet 356, 391-5 (2000)
ii) BILE ACID BINDERS • Cholesterol is reabsorbed from intestine by forming complexes with bile acids. Liver then replaces bile acids by oxidising cholesterol (catalysed by CYP7A). • a) Prescription therapeutic resins bind bile acids and prevent cholesterol reabsorption: problem of constipation, ↓absorption of fat sol. vitamin A,D,E,K • e.g. colestipol 20g/day taken mixed with juice or apple sauce • cholestyramine • colesevelam • b) Nonprescription bulk forming laxatives (soluble fibres) • Psyllium husks (metamucil) • Ispaghula husks • Oat bran (-glucan binds bile acids ) • Action of bile acid binders • cholesterol excretion • hepatic cholesterol 7a hydroxylase (CYP7A) activity which oxidises cholesterol to bile acids. (feedback inhibitor is normally bile acids)
BILE ACID SYNTHESIS BY LIVER Endoplasmic reticulum (except CYP27) Biochemistry. 31, 4737-49, (1992)
BILE ACID SYNTHESIS BY LIVER (cont) Then efflux into bile and stored in gall bladder. Then released by bile duct into upper-small intestine (ileum). Then metabolised (deconjugation (CO2), dehydroxylation) by anaerobic bacteria of colon to deoxycholate, lithocholate, urodeoxycholate. Then actively reabsorbed and recirculates via liver 8 times / day.
iii) Hypolipidemic ie antihyperlipidemic FIBRATE drugs Clofibrate: 2g/day (also: Gemfibrozil) 1. ↑ lipoprotein lipase activity 2. ↑ fatty acid oxidation by inducing PEROXISOMES serum triglycerides serum triglyceride-rich lipoprotein 3.Antioxidant action prevent LDL oxidation
PEROXISOME (numerous genetic diseases) Peroxisomal fatty acid b-oxidation forms H2O2 which is removed by catalase that is also located in the peroxisomes . Medium-chain fatty acids (C8-18) prefer mitochondrial b-oxidation that doesn’t form H2O2 . Long chain or 3 or branched fatty acids MITOCHONDRIA b-oxidation Acyl carnitine Synthase Acetyl CoA oxidase* Shorter-chain fatty acid Fatty acyl CoA NADH + Acetyl CoA O2 H2O2 heat catalase Cholesterol CoQ10* Bile acids H2O + O2 H2O2 also formed by peroxisomal glycolate/glyoxylate oxidases, xanthine oxidase, uricase * Peroxisomes induced by peroxisome proliferators via a cytosolic receptor (PPAR) e.g., hypolipidemic drugs, e.g., clofibrate; plasticizers, e.g., phthalate (DEHP); endogenous steroids formed by the adrenal glands e.g., dehydroepiandrosterone. Ann Rev Biochem. 61, 157-97 (1992) Ann Rev Nutr. 14, 343-70 (1994)
iv. NIACIN(Vitamin B3) • Deficiency (maize,indian millet) causes pellagra (rough photosensitive skin, dementia ,GI). Flour now fortified with niacin ; B 1 thiamine; B2 riboflavin tryptophan niacin nicotinamide NAD NADP NADPH • Niacin 1.5-3g/day ↓ plasma LDLcholesterol & triglycerides; best for ↑ HDL (not nicotinamide) but early hot flashes, rare hepatotox., rare hyperglycemia
NIACIN INHIBITS 1) DGAT (Synthesizes triglycerides, 2) Fatty Acyl CoA Synthase AND 3) Blocks HDL uptake, 4) Prevents LDL Oxidation Daniel Meyers Current Opinion in Lipidology 2004, 15: 659-665
v.Blocking intestinal cholesterol permease • Ezetimibe , a new drug that blocks cholesterol uptake by inhibiting intestinal sterol permease (packaged with a statin). • Plant sterols eg sitosterol , a natural method
Non prescription ways of preventing cholesterol absorption Plant sterol/stanols H O SITOSTEROL (a sterol) H O SITOSTANOL (a stanol) Cholesterol lowering action of plant sterols in the diet H H H Plant sterol not absorbed by gut (2g/day) and inhibit gut absorption of cholesterol) (ester in “functional margarine”eg Benecol,Take Control) H H H
vi Natural ways of binding dietary cholesterol to prevent absorption • Chitosan (shellfish exoskeleton) (LIBRACOL is polychitosamine: amine groups bind cholesterol) • Policosanol (sugar cane wax or rice wax alcohol ie. octacosanol CH3(CH2)26CH2OH)
CONCLUSIONS • DIETARY WAYS OF DECREASING THE ATHEROSCLEROSIS RISK: • cholesterol and saturated fatty acids plant stanols • polyunsaturated fatty acids • which cholesterol oxidation to bile acids • LDL catabolism • cholesterol excretion into intestine • 3. smoking, obesity, lack of exercise, low Ca2+ • high HDL in premenopausal women protects • but not after menopause.
Dietary mechanisms to decrease cholesterol are additive (e.g., in patients resistant or intolerant to statins). • Bind bile acids to viscous fibres, e.g., oats (b-glucan), barley, psyllium (metamucil), eggplant, okra. • Competitive inhibition of cholesterol absorption from the gut, e.g., plant sterols (stanols) margarine, almonds, flaxseed. • Inhibit cholesterol synthesis and esterification, e.g., soy proteins, garlic (diallyl disulfide) • Increase LDL receptor-mediated LDL cholesterol uptake and degradation, e.g., soy proteins. • Decrease oxidized LDL using antioxidants, e.g., almonds (Vit E), soy proteins (isoflavones). Risk factor modification center, St. Michael’s Hospital, Toronto Metabolism 51(12):1596-1604 (2002)