L5 N Lipoproteins 1445.pptx-------------

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1. Lipoproteins L5 W.M & A.M(1445)

2. Outlines Lipid plasma profile Analytical methods Lipid abnormalities

3. Step 3 Liver releases bile acids to solubilize lipid products in mixed micelles Step 2 Pancreas releases: Lipase (+ colipase ) cholesterol esterase phospholipase A 2 Lipids: Triacylglycerol Cholesterol esters Phospholipids pancreas liver Step 4 Lipids absorbed from micelles into epithelial cells Step 5 Chylomicrons form and travel through lymphatics Lingual Lipase Gastric Lipase STEP 1 Five steps of lipid digestion and absorption small intestine stomach

4. What is lipoprotein? Lipoproteins are complex particles that have a central hydrophobic core of non-polar lipids, primarily cholesterol esters and triglycerides. This hydrophobic core is surrounded by a hydrophilic membrane consisting of phospholipids, free cholesterol, and apolipoproteins. Plasma lipoproteins are divided into classes based on size, lipid composition, and apolipoproteins

5. What is lipoprotein?

6. Are the protein moieties associated with the plasma lipoprotein Apoprotein (Apo)

7. Apoprotein (Apo)

8. Classification of Lipoproteins Based on density - They are separated by Ultracentrifugation . Depending upon the floatation constant (Sf), Five major groups of lipoproteins have been identified that are important physiologically and in clinical diagnosis. Lipoproteins with high lipid content will have low density, larger size and so float on centrifugation Based on electrophoretic mobilities : Lipoproteins may be separated according to their electrophoretic properties into - α, pre β, β , and broad beta lipoproteins . The mobility of a lipoprotein is mainly dependent upon protein content . Those with higher protein content will move faster towards the anode and those with minimum protein content will have minimum mobility .

9. Classification of Lipoproteins

10. Classification of Lipoproteins Each group nearly contain all types of lipids (Cholesterol, Triglycerides, Phospholipids & FFA) but differ in: 1- The main lipid content 2- Source of each group 3-Type and amount of the associated protein .

11. Formed in the intestinal mucosal cells Absorbed into: the lymph vessels, the moves into the blood Rich in exogenous TG Contain Apo-B-48 Apo-E, Apo-C, Apo-A Deliver TG’s to body cells to be used as fuel 1-Chylomicron s A high-fat meal leads to the formation of large chylomicron particles due to the increased amount of triglyceride being transported whereas in the fasting state, the chylomicron particles are small carrying decreased quantities of triglyceride.

12. 1-Chylomicron s Chylomicrons comprise: 81% triglyceride, 7% phospholipids, 9% cholesterol , and 2%proteins . Also they have low density (in lipemic serum specimen found creamy top layer , 4-6 o C , for 16 hrs ) Chylomicrons are responsible for transporting dietary triglycerides and some cholesterol to the rest of the body . The clearance time from the formation of Chylomicrons after meal and the removal of remnants of the liver in about six hours . Normally, chylomicrons are not found in 12 to 14 hour fasting blood specimen.

13. 2- VLDL s Synthesized in the liver , These particles are produced by the liver and are triglyceride-rich. Rich in endogenous TGs Contain: Apo-B-100 (Reuptake), C-II, C-III( TG metabolism) and Apo-E (Reuptake)

14. 2- VLDL s Comprise: 50% triglycerides, 22% cholesterol , 26% phospholipids , and 7% proteins Excess dietary intake of carbohydrates enhances the hepatic synthesis of triglyceride , which, in turn, increased VLDL production. Fatty liver occurs in clinical conditions in which there is an imbalance between hepatic TG syntheses and secretion of VLDL ( uncontrolled DM, hepatitis, alcohol ingestion).

15. IDL are usually undetectable in normal plasma. It ’ s normally a transient intermediate lipoprotein formed during the conversion of VLDL to LDL (from catabolism of VLDL). It contains both cholesterol and endogenous triglycerides and Apo B,C,E . 3- IDL

16. LDL contains 50% cholesterol by weight and is the most cholesterol-rich of the lipoproteins. They are provided by the catabolism of VLDL. It’s responsible for transporting cholesterol from the liver to peripheral tissues. LDL is the most atherogenic lipoprotein and high serum is regarded as a major Coronary heart disease (CHD) risk factor . 4- LDL

17. 5- HDL Smallest lipoproteins Synthesized in the liver & intestine Carry cholesterol from the tissue Contain: Apo A-I, A-II [Major], Apo-CII, CIII and Apo-E

18. HDL is composed mainly of 50% proteins , phospholipids and cholesterol. HDL typically carries 20% to 35% of total plasma cholesterol , but unlike LDL, which carry cholesterol to the tissue, HDL take excess cholesterol from the tissues to the liver ( reverse transport ). 5- HDL

19. Lipoprotein metabolism

20. Lipoprotein metabolism

21. Lipoprotein metabolism Acyl-CoA-cholesterol acyltransferase (ACAT):  key intracellular enzyme for esterifying cholesterol Lecithin:cholesterol acyltransferase (LCAT) ratio:  key HDL-associated enzyme involved in the esterification of cholesterol, removed from peripheral tissue, prior to exchange for triglyceride with VLDL and LDL Cholesterol ester transfer protein (CETP):  HDL-associated protein that transfers cholesterol esters from HDLs to VLDL and LDL in exchange of triglycerides from the VLDL/LDL to HDL

22. Lipoprotein metabolism Paraoxonases (PON):  HDL-associated enzymes that impart antioxidant activity of HDL toward LDL Lipoprotein-associated phospholipase A 2  (Lp-PLA 2 ):  is one of 2 forms of platelet-activating factor acetylhydrolase (PAF-AH), major HDL-associated hydrolase that is responsible for the hydrolysis of oxidized phospholipids Lipoprotein(a) ( Lp [a]):  clinically significant apolipoprotein disulfide bonded to apoB-100 in LDL, easily oxidized and phagocytosed by macrophages-enhancing pro-inflammatory responses, inhibits the process of fibrin clot dissolution

23. Sample: Serum is preferable Pre-analytical factors: Age, sex, fasting, stress, hemolysis. Analytical procedures include Electrophoresis, Enzymatically tests, and Precipitation reagents. 1-Lipoprotein electrophoresis: LPE Separation of various lipoproteins by the difference in the net charges , method basically is protein electrophoresis Chylomicrons is application point, LDL= ß-LP, VLDL = pre ß- Lp , HDL= α - Lp Analytical procedures

24. 1-Lipoprotein electrophoresis

25. 2- E nzymatically tests Total Cholesterol, Triglycerides are measured enzymatically in serum or plasma in a series of coupled reactions that hydrolyze esters group and oxidize OH group in sample. LDL can calculated from measured values of total cholesterol, triglycerides and HDL cholesterol according to the relationship: LDL = total chol – (HDL+TG/5) 2- Enzymatically

26. 3- Precipitation reagents: Precipitate of VLDL, LDL in the serum by divalent cations Ca +2 ,Mg +2 , Mn +2 that is associated with the ultracentrifugation method, then HDL is measured in supernatant . 3-Precipitation reagents

27. Fatty liver Fatty livers fall into: More synthesis of Triglycerides . High carbohydrate diet stimulates fatty acid synthesis by Acetyl CoA and high fat feeding provides more flux of fatty acids that can be esterifies to provide excess triglycerides . Defective VLDL synthesis: the second type of fatty liver is usually due to a metabolic block in the production of plasma lipoproteins , thus allowing triacylglycerol to accumulate . Alcoholic fatty liver. Alcoholism leads to fat accumulation in the liver, hyperlipidemia , and ultimately cirrhosis . The fatty liver is caused by a combination of impaired fatty acid oxidation and increased lipogenesis .

28. Plasma lipid & atherosclerosis Atherosclerosis is a condition in which an artery wall thickens as a result of the accumulation of fatty materials such as cholesterol. Increasing in level of plasma lipid may associated with increase risk of coronary heart disease (CHD) and atherosclerosis. There is important relationship between atherosclerosis and HDL. Decreased HDL associated with increase risk of coronary heart disease (CHD) while increase HDL ( antiatherogenic properties) represent a protection against atherosclerosis.

29. By the end of this topic you able to: Define and classify lipoproteins. Known the basic information and characteristics of lipoproteins. Known the normal, physiological and pathological changes in lipoprotein Levels. Known clinical aspects of lipoprotein profiles for diagnosis of liver , heart diseases and atherosclerosis. Key points