Question

6. Explain how VLDL is metabolized by lipases to intermediate-density lipoprotein (IDL) which may be cleared by the liver or converted to lowdensity lipoprotein (LDL), which functions to deliver cholesterol from the liver to extrahepatic tissues via the LDL (apoB100, E) receptor.

7. Explain how high-density lipoprotein (HDL) is synthesized, indicate the mechanisms by which it accepts cholesterol from extrahepatic tissues and returns it to the liver in reverse cholesterol transport.

8. Describe how the liver plays a central role in lipid transport and metabolism and how hepatic VLDL secretion is regulated by the diet and hormones.

9. Indicate the roles of LDL and HDL in promoting and retarding, respectively, the development of atherosclerosis.

10. Indicate the causes of alcoholic and nonalcoholic fatty liver disease (NAFLD).

Answer 1

.The metabolism of VLDL. Very low density lipoprotein (VLDL) particles are produced by the liver and share with chylomicrons (CM) a common removal pathway mediated by lipoprotein lipase (LPL). At the level of LPL, increased competition occurs between CM and VLDL particles. VLDL remnants (cholesterol-rich and triglyceride-poor particles) are the intermediate density lipoprotein (IDL) cholesterol, which are further catabolized to low density lipoprotein (LDL) cholesterol under the action of hepatic lipase (HL) and LPL. IDL and LDL particles are removed by the liver by LDL receptor and LDL receptor-related protein. Cholesteryl ester (CE) can be transferred from LDL to CM and VLDL by cholesteryl ester transfer protein (CETP) in exchange for triglycerides (TG). The TGs contained in the TG-rich LDL particle are then hydrolyzed by HL or LPL to produce smaller and denser LDL particles.

LDL-receptor LDL-receptor related protein circulation endothelial cells liver.ㅡㅡㅡㅡㅡㅡ+ VLD + LPL LPL, HL TG CETP CM. VLDL CE TG-rich LDL HL, LPL small dense LDL