Modulation of the Expression of Human LDL-Apo B-100 Epitopes by Lipids

The purpose of the present study was to determine the immunochemical properties of apolipoprotein (apo) B-100 associated with low density lipoprotein (LDL) in relation to lipid and apolipoprotein composition. LDLs were isolated by sequential ultracentrifugation (1.019<rf< 1.050 g/mL) from two healthy volunteers and 21 dyslipidemic patients to obtain heterogeneous samples of LDL. Lipid (free cholesterol, cholesteryl esters, triglycerides, and phospholipids) and apolipoprotein contents (apo B, apo C-III, apo E) were determined in each LDL sample. Immunoreactivities of apo B were tested in solid-phase competitive-binding radioimmunoassays using seven monoclonal anti-LDL antibodies that reacted with defined epitopes of apo B-100. The relation between lipid and/or protein variables and the immunoreactivity of apo B was evaluated by successive use of Spearman's rank simple correlation, partial correlation, and canonical correlation analyses. The canonical correlation analysis showed that apo B-100 immunoreactivity on LDL is highly dependent on lipid and apolipoprotein composition simultaneously. The results confirmed the influence of surface and core lipids on the expression of the apo B-100 epitopes, independent of their location on the molecule. However, the lipid requirement of LDL strongly influences the expression of epitopes mapped in the LDL receptor-recognition domain. In contrast to apo E, apo C-III does not seem to influence the expression of the apo B-100 epitopes in the LDL range studied. T