Cholesteryl ester transfer protein promotes the association of HDL apolipoproteins A-I and A-II with LDL: potentiation by oleic acid

Abstract

The association of apolipoprotein (apo) A-I and apo A-II with apo-B-containing particles was measured after incubation at 37°C of either total plasma or low-density lipoproteins (LDL) and high-density lipoproteins-3 (HDL 3) in the presence of partially purified cholesteryl ester transfer protein (CETP). At the end of the incubation, apo-B-containing lipoproteins were separated by immunoprecipitation with an anti-apo B γ-globulin fraction. In mixtures containing LDL and HDL 3, either maintained at 4°C or incubated at 37°C, optimal concentrations of anti-apo B antibodies induced the precipitation of more than 95% of apo B without precipitation of apo A-I and apo A-II. When total plasma was incubated at 37°C for 24 h, a significant proportion of apo A-I and apo A-II became associated with apo-B-containing lipoproteins. The fraction of HDL apoproteins associated with apo-B-containing lipoproteins was significantly reduced when plasma was supplemented with TP2 anti-CETP monoclonal antibodies, which are known to inhibit CETP activity. Incubation of LDL and HDL 3 for 24 h at 37°C in the presence of purified CETP also induced the association of a significant proportion of apo A-I and apo A-II with apo-B-containing particles. This effect was dependent on CETP concentration in the incubation mixtures and could be suppressed by the addition of anti-CETP monoclonal antibodies. While oleic acid alone, at a final concentration of 0.2 mmol/l, did not promote any association of HDL-apolipoproteins with LDL, it was able, at this concentration, to greatly enhance the CETP-mediated association of apo A-I and apo A-II with apo-B-containing particles. In the presence of both CETP and oleic acid, the association of apo A-I and apo A-II with apo-B-containing particles was apparent within 3 h of commencing the incubation. Approximately 3 mol of apo A-I and 1 mol of apo A-II co-precipitated with each mol of apo B after a 24 h incubation of LDL, HDL 3 and CETP. When oleic acid was added to the incubation mixture in addition to CETP, up to 5.5 mol of apo A-I and 2.3 mol of apo A-II were associated with each mol of apo B. The present study has demonstrated that CETP can promote the association of apo A-I and apo A-II with apo-B-containing particles and that this process is enhanced by oleic acid.