Very low density lipoprotein
From Free net encyclopedia
Very Low Density Lipoprotein (VLDL) is a lipoprotein subclass. It is assembled in the liver from cholesterol and apolipoproteins. It is converted in the bloodstream to low density lipoprotein (LDL). VLDL particles have a diameter of 30-80 nm. VLDL transports endogenous products where chylomicrons transport exogenous (dietary) products.
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Function
VLDL transports endogenous triglycerides, phospholipids, cholesterol and cholesteryl esters. It functions as the body's internal transport mechanism for lipid.
Composition
Nascent (young) VLDL is released into the blood from the liver with the apolipoprotein B-100 (ApoB-100) marker. At this point, the VLDL consists of ~50% triglycerides, ~18 phospholipids, ~20% cholesterol and 10% protein (hence the name, very low density lipoprotein).
Changes During Circulation
Nascent VLDL circulates in blood and picks up apoliprotein C-II and apolipoprotein E donated from High Density Lipoprotein (HDL). At this point, the nascent VLDL becomes a mature VLDL. Once in circulation, the VLDL will come in contact with Lipoprotein Lipase (LPL) in the capillary beds in the body (adipose, cardiac and skeletal muscle). The LPL will remove triglycerides from the VLDL for storages or energy production.
The VLDL now meets back up with HDL where apoC-II and apoE are transferred back to the HDL. In addition to this, the HDL transfers cholesteryl esters to the VLDL in exchange for phospholipids and triglycerides (via cholesteryl ester transfer protein).
As more and more triglycerides are removed from the VLDL, the composition of the molecule changes, and it becomes intermediate density lipoprotein (IDL). When cholesterol content of the IDL becomes greater than the triglyceride content, it becomes low-density lipoprotein (LDL), with the primary apolipoprotein being apoB-100. The LDL is taken into a cell via the LDL receptor (endocytosis) where the contents are either stored, used for cell membrane structure, or converted into other products (steroid hormones or bile acids).
VLDL and Disease
VLDL is prone to accelerate atherosclerosis, and is elevated in a number of diseases and metabolic states.