Can Measurement of Apolipoprotein B Replace the Lipid Profile in the Follow-up of Patients with Lipoprotein Disorders?

Abstract

Apolipoprotein B (apo B) was so called because it was the principal protein found in β lipoprotein (LDL). It was later discovered that it is the major protein component of chylomicrons, chylomicron remnants, VLDL, intermediate density lipoprotein, LDL, and lipoprotein(a); it is absent from HDL. Thus apo B is present in lipoproteins that are potentially atherogenic and absent from those that are antiatherogenic. This prompted Fredrickson to write in 1974, “Its resistance to characterization, its seeming essentiality for glyceride transport, and perhaps the added suspicion that it has something to do with atherogenesis have all transformed apo B into one of the central mysteries of lipoprotein physiology” (1). This statement was remarkably prescient; apo B proved to be essential for hepatic and intestinal triglyceride secretion and for LDL catabolism and to be intimately involved in atherogenesis. In the human, circulating hepatic apo B has 4536 amino acids and a molecular mass of ∼540 000 Da, whereas intestinal apo B present in chylomicrons has a molecular mass that is 48% that of hepatic apo B (2). Hence hepatic and intestinal apo B are termed apo B100 and apo B48, respectively. Both are the products of a single gene, but its message is edited in the enterocyte after translation of the N-terminal 2152 codons representing the amino acid sequences necessary for triglyceride-rich lipoprotein assembly and secretion. Hepatic and intestinal steatosis occur both in a-β-lipoproteinemia (reflecting mutation of the microsomal triglyceride transfer protein, which allows apo B to associate physically with triglycerides in the liver and gut) and in homozygous hypo-β-lipoproteinemia when mutations truncate apo B early in its sequence (2). The additional part of the molecule …