Determination of apolipoprotein B in apolipoprotein CII/CIII-containing lipoproteins by an immunoenzymmetric assay.

A solid phase sandwich immunoenzymmetric assay is described for the determination of apolipoprotein B in apolipoprotein CII- and/or CIII-containing lipoproteins (chylomicron remnants, VLDL, IDL). During a first incubation step the particles containing apolipoproteins CII and/or CIII are bound to antibodies against these components, while the antibodies are immobilised on microtitre plate wells. After washing, anti-apolipoprotein B is added in a second incubation step. Finally peroxidase-labelled anti-sheep IgG reacts with the bound anti-apolipoprotein B, thus allowing the quantification of complexes containing both B and CII/CIII apolipoproteins. The amounts of these complexes were correlated with total cholesterol, triacylglycerols, HDL- and LDL-cholesterol, apolipoproteins AI and B, as well as with age and sex of the subject. A total of 258 individuals was studied, including patients with lipid metabolism disorders, patients with manifest coronary heart disease, and healthy controls. The assay described in this article was compared with radial immunodiffusion after pretreatment of samples. The immunoenzymmetric assay was easier and faster to perform and had a lower detection limit than the classical VLDL apolipoprotein B determination using ultracentrifugation. Furthermore, it could be performed directly on native serum. Most importantly, the study revealed elevated apolipoprotein CII/CIII-B levels in coronary heart disease patients of both sexes compared with normal subjects. Furthermore, in male coronary heart disease patients a negative correlation was found between the concentrations of apolipoprotein CII/CIII-B and HDL-cholesterol. These results suggest a delayed VLDL-HDL exchange of lipids and proteins in these patients which results in an accumulation of atherogenic apolipoprotein B-containing VLDL and IDL.