Effects of unopposed conjugated equine estrogen on lipoprotein composition and apolipoprotein-E distribution

Responses of HDL subclasses, Lp(A-I) and Lp(A-I:A-II) levels and lipolytic enzyme activities to continuous oral estrogen-progestin and transdermal estrogen with cyclic progestin regimens in postmenopausal women

Seventy postmenopausal women took part in the study. Subjects received either continuous oral 17 beta-estradiol 2 mg/day combined with norethisterone acetate 1 mg/day (E2/NETA, Kliogest) or transdermal treatment consisting of 28 day cycles with patches delivering 17 beta-estradiol 50 micrograms/day (Estraderm) combined with cyclic medroxyprogesterone acetate 10 mg/day (E2/MPA, Provera), on days 17-28. At baseline the serum lipid and lipoprotein concentrations, composition and concentrations of high density lipoprotein (HDL) subclasses, lipoprotein (Lp)(AI) and Lp(A-I:A-II) levels were comparable in the two groups. In the E2/NETA group, after 12 months hormone replacement therapy (HRT), the HDL2 cholesterol concentration decreased by 17% (P < 0.01) and the HDL3 cholesterol remained unchanged. The concentrations of HDL2b, HDL2a and HDL3a were reduced by 30, 26 and 15%, respectively, P < 0.001, and the cholesterol:triglyceride ratio decreased significantly in all HDL subclasses. Apolipoprotein (apo) A-I concentration decreased by 5% (P < 0.05), but apo A-II, Lp(A-I) and Lp(A-I:A-II) concentrations remained unchanged. In the E2/MPA group the HDL2 and HDL3 cholesterol levels were both reduced by 6% (P < 0.05) and the HDL3a, HDL3b and HDL3c concentrations decreased by 14, 12 and 17% during the E2/MPA phase compared with baseline (P < 0.01). No major changes in the composition of HDL subclasses occurred in the E2 MPA group during treatment. The apo A-I and Lp(A-I) levels were not changed, but apo A-II and Lp(A-I:A-II) concentrations decreased by 8 and 5%, P < 0.001 and P < 0.05, respectively. At 12 months the postheparin plasma hepatic lipase (HL) activity decreased only in the E2/NETA group (by 12%, P < 0.05). The cholesteryl ester transfer protein (CETP) activity was not affected by either HRT regimen. The results of our study show that the 2 HRT regimens have multiple effects on HDL particles and HRT induced changes in HDL are not associated with changes in activities of lipolytic enzymes or CETP.