Very Low Density Lipoprotein (VLDL)

Triglyceride (TG) or more accurately triacylglycerol is simply a compound of three acyl groups (fatty acids) attached to a glycerol molecule. They are easily measured in the laboratory and reported as serum TG level: it actually refers to all of the TG that are being trafficked within all of the lipoproteins that exist in a deciliter of plasma. A physiologic fasting TG concentration is on average 30 mg/dL with one standard deviation ranging from 10 to 70 mg/dL. The two major lipoproteins that transport TG are chylomicrons and very low density lipoprotein (VLDL). Since chylomicrons are basically postprandial lipoproteins with very short half life’s (and hour or so) most of the TG reported are in VLDLs (4-6 hour half life). The purpose of the triglyceride-rich lipoproteins (TGRLP), VLDL and chylomicrons are to transport energy in the form of fatty acids (FA) trafficked as triglycerides (TG), to the energy-requiring tissues (muscles) or the energystoring tissues, the adipocytes. If the muscles do not require the fuel, the FA in the TG will then be delivered for storage in adipocytes. Normally the liver (hepatocytes) packages TG, cholesterol and phospholipids with a single, molecule of apolipoprotein B100 (apoB) and the enterocytes package the lipids with a truncated version of apoB; termed apolipoprotein B48 (has 48% of the molecular weight of hepatically produced apoB100). A normally composed VLDL particle has five times more TG than cholesterol (a 5:1 ratio) and since most TG are presumed to be in VLDLs; the VLDL-C is calculated as TG/5. If 150 mg/dL is a normal TG, then a normal VLDL-C is < 30 mg/dL. A high VLDL-C implies a high TG level. In conditions of elevated TG, many of the VLDL will be very large and TG-rich. If hepatic TG levels are not elevated the liver produces fewer as well as smaller VLDL particles (VLDL-C is reduced).