VLDL

Very-low-density lipoprotein (VLDL) is a type of lipoprotein made by the liver. VLDL is one of the five major groups of lipoproteins (chylomicrons, VLDL, low-density lipoprotein, intermediate-density lipoprotein, high-density lipoprotein) that enable fats and cholesterol to move within the water-based solution of the bloodstream. VLDL is assembled in the liver from triglycerides, cholesterol, and apolipoproteins. VLDL is converted in the bloodstream to low-density lipoprotein (LDL) and intermediate-density lipoprotein (IDL). VLDL particles have a diameter of 30-80 nm. VLDL transports endogenous products, whereas chylomicrons transport exogenous (dietary) products. Recently both the lipid composition and protein composition of this lipoprotein were characterised in great detail.

Very low-density lipoproteins transport endogenous triglycerides, phospholipids, cholesterol, and cholesteryl esters. It functions as the body's internal transport mechanism for lipids. In addition it serves for long-range transport of hydrophobic intercellular messengers, like the morphogen Indian hedgehog (protein).

Nascent VLDL released from the liver contains Apolipoprotein B100, apolipoprotein C1 (apoC1), apolipoprotein E (apoE), cholesterol, cholesteryl esters, and triglycerides. As it circulates in blood, it picks up apolipoprotein C-II (apoC-II) and additional apoE donated from high-density lipoprotein (HDL). At this point, nascent VLDL becomes a mature VLDL. Once in circulation, VLDL will come in contact with lipoprotein lipase (LPL) in the capillary beds in the body (adipose, cardiac, and skeletal muscle). LPL will remove triglycerides from VLDL for storage or energy production. VLDL now meets back up with HDL where apoC-II is transferred back to HDL (but keeps apoE). HDL also transfers cholesteryl esters to the VLDL in exchange for phospholipids and triglycerides via cholesterylester transfer protein (CETP). As more and more triglycerides are removed from the VLDL because of the action of LPL and CETP enzymes, the composition of the molecule changes, and it becomes intermediate-density lipoprotein (IDL).

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