1) OBESITY & high plasma triglycerides

Adipose cells, adipocytokines .

• White fat cells store large lipid droplets of triglycerides and cholesterol ester.

• Leptin (167aa) synthesised and secreted, peptide hormone, binds to receptors in hypothalamic nuclei

“satiety center.”

Regulates energy.Signals a decrease in appetite. Prooxidant.

• Adiponectin (244aa) , most abundant protein in adipocyte, (similar structure to TNFα) & released

into the blood. Higher in 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. 1

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

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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

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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.)

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2) High plasma cholesterol and atherosclerosis

A. Clinical chemistryB. Fat AbsorptionC. Liver cell synthesis of LDL and HDLD. Cholesterol SynthesisE. Drug TherapyF. Fibroblasts and other extrahepatic tissues for

membrane biosynthesisG. Incr. heart attacks,strokes,atheroscelerosisH. Genetic Disorders

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Lipoproteins, Cholesterol and Atherosclerosis

A) Clinical chemistry - Lipoproteins

• Conjugated proteins in which the prosthetic group are lipids:• Lipoproteins responsible for the transport/distribution of lipids:

- Lipid hormones- Lipids absorbed by the intestine- Fat-soluble vitamins

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Percent contribution of saturated fat and cholesterol from fats/oils, meats, dairy products and eggs in the US diet.

Biochim. et Biophys. Acta 1529 (2000) 310-320

Plasma cholesterol >6.2mM (change diet); 5.5-6.2mM (borderline); <5.5mM normal

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A lipoprotein:Horton Fig 17-5

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B) Stage 1 - Fat AbsorptionChylomicrons•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)

Particle Size(nm)

Electroph. Origin

Chylomicron >75 - IntestineVLDL 25-75 A2 LiverLDL BAD 19-26 B VLDLHDL GOOD 7-19 A1 Liver, intestine

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B48 M.W. = 300,000(chylomicrons, chylomicron remnants)

Dietary cholesterol chylomicron & HDL formed in intestinal epithelial cell remnant lymph vessel taken up by adipose cells & extrahepatic tissues

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C) Stage 2 : LDL activity and functionLDL(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%.

1. Intestine

2. Liver(Synthesis)

chylomicrons

VLDL

tissues for oxidation

adipose tissuefor storage

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Liver cell synthesis of LDL,VLDL and HDL

B-100A,C,E

i.e. LDL, VLDL, HDL

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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.

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Liver mitochondrial fatty acid oxidation inhibited by some drugs causing FATTY LIVER

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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 pitsb) Receptor-LDL complex is internalised by endocytosisc) Vesicles containing LDL fuse with lysosomes (proteases, esterases)

LDL Protein amino acids

LDL Cholesterol esters cholesterol + fatty acid LINOLEATE

LDL receptor returns to plasma membrane (10min. - turnover ever 24 hours)

proteases

esterases

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Steps (cont’d)d) Free cholesterol in the cell is used or stored

Cholesterol Membrane biosynthesis

+ Linoleate Cholesterol esteri.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

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The LDL receptor

Membrane spanningdomain

The LDL receptor consistsof five domains withdifferent functions: anLDL-binding domain, 292residues; a domain bearingN-linked sugars, 350 residues; a domain bearingO-linked sugars, 58 residues; a membrane-spanning domain, 22residues; and a cytosolicdomain, 50 residues.

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Four 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

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Genetic disorders (cont.)

e.g. Familial hypercholesterolemia (Type II) - Autosomal dominant trait 1:500Cholesterol 680 mg/100 mL instead of 175 mg/100 mLDie 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

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Extrahepatic tissue(e.g.fibroblasts) take up cholesterol via LDL receptors and store it as cholesterol esters in lysosomes

Voet et al., Fig 19-37

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Cholesterol Ester Synthesis

Endoplasmic reticulum

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Acid proteases (cathepsins)Cholesterol ester esteraseNucleasesAcid phospholipasesRequire acid pH

Amino acidsCholesterolNucleotidesFatty acids

Stores dietary CoQCoQ reduction maintains acid pH

ACID pHACID pH

H+ CoQ

ROS Cyt b5

FAD NADH

Autophagic vacuoleAged proteins,Nucleic acids,

lipids

LYSOSOMES recycle proteins,lipids,nucleic acids

Arch Biochem Biophys. 375, 347-54, (2000).

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G) Atherosclerosis – cholesterol plaque formation

An atherosclerotic plaque(marked by the arrow)blocks most of the lumen ofthis blood cell. The plaqueis rich in cholesterol.

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B100

NH2

LDL

B100NH2

OOH

LIPID PEROXIDE

(H2O2/Fe or Cu)

LEUKOCYTES, ENDOTHELIAL CELLS

ANTIOXIDANTe.g. PROBUCOL (500mg/day) -SCISSION

B100

NH2

+ H

O

H

O

MALONDIALDEHYDE

B100

NH

HC CH

CHOSCHIFF BASE

MODIFIED LDL

Don't bind to apo B LDL receptoror peripheral cellsBUT recognised by scavenger receptor of macrophage

macrophageaccumulates chol.

transformation

Forms atherosclerotic plaque Foam Cell

Atherosclerosis mechanism: oxidised LDL taken up by macrophage scavenger receptors

M.W.ELECTROPH. MOBILITYFLUORESC.

Liver

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