LIPOPROTEINS MUHAMMAD MUSTANSAR FJMC LAHORE

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LIPOPROTEINS

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LIPOPROTEINS MUHAMMAD MUSTANSAR FJMC LAHORE

  1. 1. PLASMA LIPOPROTEINSDR MUHAMMAD MUSTANSAR
  2. 2. Plasma LipidsPlasma lipids are usually measured after 12 hours fasting. The mean value of plasma lipids is 470 mg/dl. The different types of Plasma lipids are : Triglyceride  normal range 50 – 150 (mean value 100 mg/dl) Cholesterol  normal range 100– 200(mean value 150 mg/dl) Phospholipids  normal range 150 –250 (mean value 200 mg/dl) Free fatty acids  normal range 10 – 30 (mean value 20 mg/dl)2
  3. 3. Lipid transport in the circulationLipids are insoluble in plasma. In order to be transported they are combinedwith specific proteins to form lipoproteins: Proteins (apoproteins) HO O Non polar lipids in coreCholesterol R (TAG and cholesterol esters) O R HO H HOApoproteins are only weakly associated with a particular lipoprotein and areeasily transferred to another lipoprotein of a different class. Apoproteins havevarious functions including:• Structural role• Binding sites for receptors• Activators or co-enzymes for enzymes involved with lipid metabolism
  4. 4. Plasma LipoproteinsAll Lipids in plasma are transported in the form lipoproteins.Any lipoprotein has: central core: formed of non- polar lipids (triglycerids & cholesterol esters). outer layer: formed of the more polar lipids (phospholipids & non- esterified cholesterol), and proteins (apoproteins) 5
  5. 5. Structure of lipoprotein INTEGRAL APOPROTEINS MONOLAYER OF PHOSPHOLIPIDCHOLESTEROL AND CHOLESTERLOL CORE ESTERSTRIGLYCERIDES PERIPHERAL APOPROTEINS
  6. 6. Apoproteins Are either peripheral (can be transferred) or integral (cannot be transferred). Function: They act as activator for the enzymes that act on lipoproteins They are important for receptor recognition to uptake the lipoproteins by certain tissues. 7
  7. 7. General Functions of Lipoproteins 1. Keep lipids soluble as they transport them in plasma 2. Provide an efficient mechanism for delivering their lipid content to tissues8
  8. 8. Plasma lipoproteins can be separated into different fractions by two methods, electrophoresis and ultracentrifugation.Ultracentrifugation Electrophoresis Non-mobile Chylomicrons fraction VLDL β-lipoproteins LDL Pre β- lipoproteins HDL α - lipoproteins Free FA –Albumin (+) 9
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  10. 10. The five classes of lipoprotein (all contain characteristic amounts TAG, cholesterol, cholesterol esters, phospholipids and apoproteins) Diameter Major apoliproteins Class (nm) Source and function Chylomicrons 500 Intestine. Transport of A, B48, C(I,II,III) E (CM) dietary TAG Very low density 43 Liver. Transport of B100, C(I,II,III) , EIncreasing density lipoproteins endogenously synthesised (VLDL) TAG Low density lipoproteins 22 Formed in circulation by B100 (LDL) partial breakdown of IDL. Delivers cholesterol to peripheral tissues High density lipoproteins 8 Liver. Removes “used” A, C(I,II,III), D, E (HDL) cholesterol from tissues and takes it to liver. Donates apolipoproteins to CM and VLDL
  11. 11. &% Types ofLipoproteins Lipid Content Origin apoprotein s 2% • TAG 90% (Main lipid) Chylomicrons A, B48, C-II • Cholesterol (free & esters) 5% Intestine &E • Phospholipids 3% VLDL • TAG 60% (Main lipid) (very low % 10 B100, C, E • Phospholipids 15% Liver density • Cholesterol ( free & esters)15%lipoproteins) IDL • Cholesterol (free & esters)(intermediate % 11 45% (Main lipid) Breakdown density B100, E • Phospholipids 25 % of VLDL lipoproteins) • TAG 30 % • Cholesterol (free & esters) Breakdown LDL 20 % 50% (Main lipid)(low density B100 • Phospholipids 22 % of VLDL via lipoproteins) • TAG 8 % IDL • Cholesterol (free & esters) 15% HDL 50 % • Phospholipids 30% (Main(high density Liver A,C,D,E lipid) 13
  12. 12. Lipoprotein Functions Clinical significance •Transport dietary TAG Increased inChylomicron (mainly), cholesterol & deficiency of cholesterol esters from the lipoprotein lipase s intestine to the peripheral tissues •Transport endogenous TAG Defect in their VLDL from the liver to the peripheral synthesis leads to tissues (Mobilize fat from fatty liver liver) LDL •Transport cholesterol from the Their increase liver to the peripheral tissues leads to atherosclerosis. •Remove free cholesterol from Their decrease peripheral tissues & esterifies leads to 14 HDL
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  14. 14. Uptake of LDL & its regulation The uptake of LDL occurs mainly in the liver (75%), adrenals and adipose tissue. LDL are taken up by cells by LDL receptor- mediated endocytosis. The interaction of LDL with LDL receptors requires the presence of apoB100 which is found only on LDL). The endocytosed membrane vesicles (endosomes) fuse with lysosomes, in which the apoproteins are degraded and the cholesterol esters are hydrolyzed to yield free cholesterol.

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