Metabolism of VLDL

Synthesis of Apo B-100 in liver.

2. Assembly of VLDL, packaging and release of nascent VLDL.

·        Hepatocyte synthesizes TAG, cholesterol ester, phospholipid and free cholesterol endogenously.

·        Endogenously produced lipids assemble with apo B-100 to make nascent VLDL.

·        Nascent VLDL is then secreted from the liver by exocytosis to hepatic sinusoids and thence to general circulation.

3. Modification of nascent VLDL in plasma.

4. Exchange of lipids with HDL

VLDL receives cholesterol ester from HDL and in exchange gives TAG and free cholesterol to HDL. This is mediated by CETP.

5. Degradation of TAG of VLDL in peripheral tissues by lipoprotein lipase and formation of VLDL remnant.

6. Clearance of IDL

·        50% of IDL goes to liver. Hepatocytes recognize IDL with the help of ApoE and then internalize them through receptor mediated endocytosis for further metabolism of their constituents within hepatocytes. Just prior to endocytosis apo-E is returned to HDL.

·        Remaining 50% of IDL in circulation matures to LDL with return of apo E back to HDL.