Differential Effects of Estrogen and Progestin on Apolipoprotein B100 and B48 Kinetics in Postmenopausal Women.

The distinct effects of the estrogen and progestin components of hormonal therapy on the metabolism of apolipoprotein (apo) B-containing lipoproteins have not been studied. We enrolled eight healthy postmenopausal women in a placebo-controlled, randomized, double-blind crossover study. Each subject received placebo, conjugated equine estrogen (CEE, 0.625 mg/day) and CEE plus medroxyprogesterone acetate (MPA, 2.5 mg/day) for 8 weeks in a randomized order, with a 4-week washout between phases. Main outcomes were the fractional catabolic rate (FCR) and production rate (PR) of apo B100 in triglyceride-rich lipoproteins (TRL), intermediate-density lipoproteins (IDL) and low -density lipoprotein (LDL) and of apo B48 in TRL. Compared to placebo, CEE increased TRL apo B100 PR (p = 0.04). CEE also increased LDL apo B100 FCR (p = 0.02), but this effect was offset by a significant increase in LDL apo B100 PR (p = 0.04). Adding MPA to CEE negated the CEE effects resulting in no significant changes in TRL apo B100 PR and LDL apo B100 FCR and PR relative to placebo. Relative to placebo, during CEE there was a trend toward a reduction in plasma apo B48 concentrations and PR (p = 0.07 and p = 0.12, respectively). Compared with CEE, CEE + MPA significantly increased TRL apo B48 FCR (p = 0.02) as well as apo B48 PR (p = 0.01), resulting in no significant changes in apo B48 concentration. Estrogen and progestin have independent and opposing effects on the metabolism of the atherogenic apo B100- and apo B48-containing lipoproteins.

Effects of CETP inhibition on triglyceride-rich lipoprotein composition and apoB-48 metabolism.

Cholesteryl ester transfer protein (CETP) facilitates the transfer of HDL cholesteryl ester to triglyceride-rich lipoproteins (TRL). This study aimed to determine the effects of CETP inhibition with torcetrapib on TRL composition and apoB-48 metabolism. Study subjects with low HDL cholesterol (<40 mg/dl), either untreated (n = 9) or receiving atorvastatin 20 mg daily (n = 9), received placebo for 4 weeks, followed by torcetrapib 120 mg once daily for the next 4 weeks. A subset of the subjects not treated with atorvastatin participated in a third phase (n = 6), in which they received torcetrapib 120 mg twice daily for an additional 4 weeks. At the end of each phase, all subjects received a primed-constant infusion of [5,5,5-(2)H(3)]L-leucine, while in the constantly fed state, to determine the kinetics of TRL apoB-48 and TRL composition. Relative to placebo, torcetrapib markedly reduced TRL CE levels in all groups (≥-69%; P < 0.005). ApoB-48 pool size (PS) and production rate (PR) decreased in the nonatorvastatin once daily (PS: -49%, P = 0.007; PR: -49%, P = 0.005) and twice daily (PS: -30%, P = 0.01; PR: -27%, P = 0.13) cohorts. In the atorvastatin cohort, apoB-48 PS and PR, which were already lowered by atorvastatin, did not change with torcetrapib. Our findings indicate that CETP inhibition reduced plasma apoB-48 concentrations by reducing apoB-48 production but did not have this effect in subjects already treated with atorvastatin.

Effects of cholesteryl ester transfer protein inhibition on apolipoprotein A-II-containing HDL subspecies and apolipoprotein A-II metabolism.

This study was designed to establish the mechanism responsible for the increased apolipoprotein (apo) A-II levels caused by the cholesteryl ester transfer protein inhibitor torcetrapib. Nineteen subjects with low HDL cholesterol (<40 mg/dl), nine of whom were also treated with 20 mg of atorvastatin daily, received placebo for 4 weeks, followed by 120 mg of torcetrapib daily for the next 4 weeks. Six subjects in the nonatorvastatin cohort participated in a third phase, in which they received 120 mg of torcetrapib twice daily for 4 weeks. At the end of each phase, subjects underwent a primed-constant infusion of [5,5,5-(2)H(3)]L-leucine to determine the kinetics of HDL apoA-II. Relative to placebo, torcetrapib significantly increased apoA-II concentrations by reducing HDL apoA-II catabolism in the atorvastatin (-9.4%, P < 0.003) and nonatorvastatin once- (-9.9%, P = 0.02) and twice- (-13.2%, P = 0.02) daily cohorts. Torcetrapib significantly increased the amount of apoA-II in the alpha-2-migrating subpopulation of HDL when given as monotherapy (27%, P < 0.02; 57%, P < 0.003) or on a background of atorvastatin (28%, P < 0.01). In contrast, torcetrapib reduced concentrations of apoA-II in alpha-3-migrating HDL, with mean reductions of -14% (P = 0.23), -18% (P < 0.02), and -18% (P < 0.01) noted during the atorvastatin and nonatorvastatin 120 mg once- and twice-daily phases, respectively. Our findings indicate that CETP inhibition increases plasma concentrations of apoA-II by delaying HDL apoA-II catabolism and significantly alters the remodeling of apoA-II-containing HDL subpopulations.

Effects of the cholesteryl ester transfer protein inhibitor torcetrapib on VLDL apolipoprotein E metabolism.

Cholesteryl ester transfer protein (CETP) inhibition leads to changes in lipoprotein metabolism. We studied the effect of the CETP inhibitor torcetrapib on VLDL apolipoprotein E (apoE) metabolism. Subjects, pretreated with atorvastatin (n = 9) or untreated (n = 10), received placebo followed by torcetrapib (4 weeks each). After each treatment, subjects underwent a primed-constant infusion of D(3)-leucine to determine the VLDL apoE production rate (PR) and fractional catabolic rate (FCR). Torcetrapib alone reduced the VLDL apoE pool size (PS) (-28%) by increasing the VLDL apoE FCR (77%) and leaving the VLDL apoE PR unchanged. In subjects pretreated with atorvastatin, torcetrapib increased the VLDL apoE FCR (25%) and PR (21%). This left the VLDL apoE PS unchanged but increased the VLDL apoE content, likely enhancing VLDL clearance and reducing LDL production in this group. Used alone, torcetrapib reduces the VLDL apoE PS by increasing the apoE FCR while leaving the VLDL apoE content unchanged. In contrast, torcetrapib added to atorvastatin treatment increases both the VLDL apoE FCR and PR, leaving the VLDL apoE PS unchanged. Adding torcetrapib to atorvastatin treatment increases the VLDL apoE content, likely leading to decreased conversion of VLDL to LDL, reduced LDL production, and lower levels of circulating VLDL and LDL.

Effects of the cholesteryl ester transfer protein inhibitor torcetrapib on apolipoprotein B100 metabolism in humans.

OBJECTIVE: Cholesteryl ester transfer protein (CETP) inhibition with torcetrapib not only increases high-density lipoprotein cholesterol levels but also significantly reduces plasma triglyceride, low-density lipoprotein (LDL) cholesterol, and apolipoprotein B (apoB) levels. The goal of the present study was to define the kinetic mechanism(s) by which CETP inhibition reduces levels of apoB-containing lipoproteins. METHODS AND RESULTS: Nineteen subjects, 9 of whom were pretreated with 20 mg atorvastatin, received placebo for 4 weeks, followed by 120 mg torcetrapib once daily for 4 weeks. Six subjects in the nonatorvastatin group received 120 mg torcetrapib twice daily for an additional 4 weeks. After each phase, subjects underwent a primed-constant infusion of deuterated leucine to endogenously label newly synthesized apoB to determine very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL) and LDL apoB100 production, and fractional catabolic rates (FCRs). Once-daily 120 mg torcetrapib significantly reduced VLDL, IDL, and LDL apoB100 pool sizes by enhancing the FCR of apoB100 within each fraction. On a background of atorvastatin, 120 mg torcetrapib significantly reduced VLDL, IDL, and LDL apoB100 pool sizes. The reduction in VLDL apoB100 was associated with an enhanced apoB100 FCR, whereas the decreases in IDL and LDL apoB100 were associated with reduced apoB100 production. CONCLUSIONS: These data indicate that when used alone, torcetrapib reduces VLDL, IDL, and LDL apoB100 levels primarily by increasing the rate of apoB100 clearance. In contrast, when added to atorvastatin treatment, torcetrapib reduces apoB100 levels mainly by enhancing VLDL apoB100 clearance and reducing production of IDL and LDL apoB100.

Effects of cholesteryl ester transfer protein inhibition on high-density lipoprotein subspecies, apolipoprotein A-I metabolism, and fecal sterol excretion.

OBJECTIVE: Pharmacological inhibition of the cholesteryl ester transfer protein (CETP) in humans increases high-density lipoprotein (HDL) cholesterol (HDL-C) levels; however, its effects on apolipoprotein A-I (apoA-I) containing HDL subspecies, apoA-I turnover, and markers of reverse cholesterol transport are unknown. The present study was designed to address these issues. METHODS AND RESULTS: Nineteen subjects, 9 of whom were taking 20 mg of atorvastatin for hypercholesterolemia, received placebo for 4 weeks, followed by the CETP inhibitor torcetrapib (120 mg QD) for 4 weeks. In 6 subjects from the nonatorvastatin cohort, the everyday regimen was followed by a 4-week period of torcetrapib (120 mg BID). At the end of each phase, subjects underwent a primed-constant infusion of (5,5,5-2H3)-L-leucine to determine the kinetics of HDL apoA-I. The lipid data in this study have been reported previously. Relative to placebo, 120 mg daily torcetrapib increased the amount of apoA-I in alpha1-migrating HDL in the atorvastatin (136%; P<0.001) and nonatorvastatin (153%; P<0.01) cohorts, whereas an increase of 382% (P<0.01) was observed in the 120 mg twice daily group. HDL apoA-I pool size increased by 8+/-15% in the atorvastatin cohort (P=0.16) and by 16+/-7% (P<0.0001) and 34+/-8% (P<0.0001) in the nonatorvastatin 120 mg QD and BID cohorts, respectively. These changes were attributable to reductions in HDL apoA-I fractional catabolic rate (FCR), with torcetrapib reducing HDL apoA-I FCR by 7% (P=0.10) in the atorvastatin cohort, by 8% (P<0.001) in the nonatorvastatin 120 mg QD cohort, and by 21% (P<0.01) in the nonatorvastatin 120 mg BID cohort. Torcetrapib did not affect HDL apoA-I production rate. In addition, torcetrapib did not significantly change serum markers of cholesterol or bile acid synthesis or fecal sterol excretion. CONCLUSIONS: These data indicate that partial inhibition of CETP via torcetrapib in patients with low HDL-C: (1) normalizes apoA-I levels within alpha1-migrating HDL, (2) increases plasma concentrations of HDL apoA-I by delaying apoA-I catabolism, and (3) does not significantly influence fecal sterol excretion.

ATP binding cassette transporter G5 and G8 genotypes and plasma lipoprotein levels before and after treatment with atorvastatin.

The mechanisms responsible for interindividual variation in response to statin therapy remain uncertain. It has been shown that hepatic cholesterol synthesis is associated with ATP binding cassette transporter G5 and G8 (ABCG5/8) activities. To test the hypothesis that genetic variation in ABCG5/8 might influence the plasma lipid response to statin therapy, we examined five nonsynonymous polymorphisms at the ABCG5/8 loci (Q604E, D19H, Y54C, T400K, and A632V) in 338 hypercholesterolemic patients treated with 10 mg atorvastatin. In carriers of the D19H variant, means of posttreatment values and adjusted percent reductions in LDL cholesterol (LDLC) were significantly lower (P = 0.028) and greater (P = 0.036) (112 mg/dl, 39.7%) than those of noncarriers (119 mg/dl, 36.2%), respectively, while no significant difference was observed in percent reductions in total cholesterol. Stepwise multiple regression analysis revealed significant and independent associations with absolute or percent reduction between D19H genotype and posttreatment LDL cholesterol levels. The other polymorphisms were not significantly associated with treatment effects. These results suggest that, in patients with hypercholesterolemia, the ABCG8 D19H variant is associated with greater LDLC-lowering response to atorvastatin therapy.

Apolipoprotein composition of HDL in cholesteryl ester transfer protein deficiency.

Our purpose was to compare HDL subpopulations, as determined by nondenaturing two-dimensional gel electrophoresis followed by immunoblotting for apolipoprotein A-I (apoA-I), apoA-II, apoA-IV, apoCs, and apoE in heterozygous, compound heterozygous, and homozygous subjects for cholesteryl ester transfer protein (CETP) deficiency and controls. Heterozygotes, compound heterozygotes, and homozygotes had CETP masses that were 30, 63, and more than 90% lower and HDL-cholesterol values that were 64, 168, and 203% higher than those in controls, respectively. Heterozygotes had approximately 50% lower pre-beta-1 and more than 2-fold higher levels of alpha-1 and pre-alpha-1 particles than controls. Three of the five heterozygotes' alpha-1 particles also contained apoA-II, which was not seen in controls. Compound heterozygotes and homozygotes had very large particles not observed in controls and heterozygotes. These particles contained apoA-I, apoA-II, apoCs, and apoE. However, these subjects did not have decreased pre-beta-1 levels. Our data indicate that CETP deficiency results in the formation of very large HDL particles containing all of the major HDL apolipoproteins except for apoA-IV. We hypothesize that the HDL subpopulation profile of heterozygous CETP-deficient patients, especially those with high levels of alpha-1 containing apoA-I but no apoA-II, represent an improved anti-atherogenic state, although this might not be the case for compound heterozygotes and homozygotes with very large, undifferentiated HDL particles.