Clinical value of apolipoprotein measurement.

Low density and very low density lipoproteins contain apolipoprotein B100 which is synthesized in the liver. Chylomicrons have apolipoprotein B48, which consists of part of the apolipoprotein B100 sequence, and which is produced in the gut by the same gene that encodes for apolipoprotein B100. Both apolipoprotein B100 and apolipoprotein B48 are important for the secretion of triglyceride-rich lipoproteins whereas apolipoprotein B100, which can bind to the low density lipoprotein receptor, is also important for low density lipoprotein catabolism. Apolipoprotein (a) has structural homology with plasminogen and exists as a complex with apolipoprotein B100 in lipoprotein (a). Apolipoprotein AI is the main lipoprotein in high density lipoproteins, whilst apolipoprotein E, present in chylomicrons and intermediate density lipoproteins, plays a major role in their catabolism. Serum apolipoprotein B and apolipoprotein AI have potential in the evaluation of coronary risk. Apolipoprotein B may be of particular value in patients with hypertriglyceridaemia and normal low density lipoprotein cholesterol levels. Apolipoprotein (a) has also been reported to be an important indicator of coronary risk, especially in the presence of elevated apolipoprotein B. Lack of standardization and the limited availability of prospective data at present limit the routine use of apolipoprotein B, AI and (a) measurements. The determination of apolipoprotein E phenotypes has proved useful in the diagnosis of remnant (type III) hyperlipoproteinaemia.