Journal of Lipid Research (Feb 1999)
Effects of estrogenic oral contraceptives on the lipoprotein B particle system defined by apolipoproteins E and C-III content
Abstract
Apolipoproteins E and C-III are modulators of lipoprotein metabolism that could affect development of atherosclerosis. The prevalence in plasma of apoB-containing particles (LpB) that contain either apoE or apoC-III, both or neither, and the effect of estrogen on these lipoproteins are unknown. The LpB particle system, defined by the presence or absence of apoE or C-III, was studied in 13 normolipidemic women, 7 nonusers and 6 users of oral contraceptives. Fasting plasma was separated by anti-apoE and C-III affinity chromatography and ultracentrifugation into four types of VLDL, IDL, and LDL particles: with apoE but not apoC-III (E+C−), apoC-III but not apoE (E−C+), both (E+C+) or neither (E−C−). The predominant VLDL particles were E−C− (42% in nonusers, 56% in users) and E+C+ (39% in nonusers, 24% in users), suggesting that apoE and apoC-III mainly exist together in VLDL. In IDL, E−C− was the major fraction (74% nonusers, 81% users), and in LDL, it was 99% in both groups. The triglycerides in VLDL and IDL were mainly contained in C+ particles (79% and 66% of the total VLDL and IDL triglycerides, respectively). Within VLDL, IDL, and LDL, E−C− particles had the smallest size and E+C+ or E−C+ the largest. Users had higher concentrations of VLDL E−C− (280%) and IDL E−C− (90%) particles than nonusers. They also had higher free cholesterol and cholesteryl ester concentrations associated with these fractions and with VLDL E−C+. The triglyceride contents of VLDL E−C− particles were lower in users of oral contraceptives than in nonusers. This study demonstrates that the elevated VLDL TG concentrations in users of estrogen-dominant oral contraceptives is mainly caused by an increased concentration of small VLDL particles that have reduced TG content, and that do not have apoE and C-III. These particles may have lower atherogenicity than particles enriched with apoE and C-III.—Khoo, C., H. Campos, H. Judge, and F. M. Sacks. Effects of estrogenic oral contraceptives on the lipoprotein B particle system defined by apolipoproteins E and C-III content. J. Lipid Res. 1999. 40: 202–212.
