ApoB and lipoprotein metabolism

Apolipoprotein B is the main apolipoprotein of chylomicrons and low-density lipoproteins (LDL). It occurs in the plasma in two main forms, apoB48 and apoB100. The first is synthesized exclusively by the intestine, the second by the liver. ApoB is thus essential for lipoprotein assembly and apoB-100 serves as the principal ligand ensuring interaction between LDL and the apoB,E receptor.

Several common mutations have been found in the human apoB gene. Owing to the protein's dual role as a transport protein and a peripheral recognition signal for LDL clearance, these mutations have been shown to result either in reduced VLDL secretion or in hypercholesterolaemia (LDL accumulation). Several studies have investigated the influence of some of the apoB polymorphisms on responses to change from high-fat to low-fat diets (or the opposite). Three polymorphisms have been mostly associated with diet-induced LDL cholesterol changes: a XbaI restriction site located in exon 26, an EcoRI site in exon 29 and a MspI site. Lopez-Miranda et al. (1997) reported that subjects with the homozygous absence of the XbaI site have a greater postprandial response (retinyl palmitate and apoB48 levels) to a fat-rich meal than the subjects with the presence of the XbaI site. More recently, it has been shown that a high-fat diet also induced a larger increase in plasma LDL cholesterol in subjects presenting the homozygous absence of the EcoRI restriction site. Subjects displaying the homozygous presence of the MspI restriction site were also more responsive to such a diet than heterozygous subjects (Rantala et al., 2000).

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