Anacetrapib lowers LDL by increasing ApoB clearance in mildly hypercholesterolemic subjects

Abstract

Background: Individuals treated with the cholesteryl ester transfer protein (CETP) inhibitor anacetrapib exhibit a reduction in both LDL cholesterol and apolipoprotein B (ApoB) in response to monotherapy or combination therapy with a statin. It is not clear how anacetrapib exerts these effects; therefore, the goal of this study was to determine the kinetic mechanism responsible for the reduction in LDL and ApoB in response to anacetrapib.

Methods: We performed a trial of the effects of anacetrapib on ApoB kinetics. Mildly hypercholesterolemic subjects were randomized to background treatment of either placebo (n = 10) or 20 mg atorvastatin (ATV) (n = 29) for 4 weeks. All subjects then added 100 mg anacetrapib to background treatment for 8 weeks. Following each study period, subjects underwent a metabolic study to determine the LDL-ApoB-100 and proprotein convertase subtilisin/kexin type 9 (PCSK9) production rate (PR) and fractional catabolic rate (FCR).

Results: Anacetrapib markedly reduced the LDL-ApoB-100 pool size (PS) in both the placebo and ATV groups. These changes in PS resulted from substantial increases in LDL-ApoB-100 FCRs in both groups. Anacetrapib had no effect on LDL-ApoB-100 PRs in either treatment group. Moreover, there were no changes in the PCSK9 PS, FCR, or PR in either group. Anacetrapib treatment was associated with considerable increases in the LDL triglyceride/cholesterol ratio and LDL size by NMR.

Conclusion: These data indicate that anacetrapib, given alone or in combination with a statin, reduces LDL-ApoB-100 levels by increasing the rate of ApoB-100 fractional clearance.

Trial registration: ClinicalTrials.gov NCT00990808.

Funding: Merck & Co. Inc., Kenilworth, New Jersey, USA. Additional support for instrumentation was obtained from the National Center for Advancing Translational Sciences (UL1TR000003 and UL1TR000040).

Figures

Figure 4. Potential mechanisms responsible for the increase in the LDL ApoB FCR observed in response to anacetrapib treatment.

(A) A reduction in the cholesterol content of the regulatory pool of intracellular cholesterol activates SREBP2, leading to increased transcription of LDLR, PCSK9, and cholesterol synthetic genes. Increased LDLR transcription increases the amount of LDLR at the cell surface of hepatocytes (indicated by “Y”), leading to an increase in LDL clearance. This scenario should be accompanied by an increase in the PCSK9 PR and cholesterol synthesis as reflected by lathosterol levels. (B) Reduced levels of PCSK9 circulating in plasma results in less targeting of the LDLR for degradation and an increase in LDL recycling. This would increase the amount of LDLR at the cell surface of hepatocytes and lead to an increase in LDL clearance. (C) A decrease in hepatic oxysterols reduces activation of the LXR, leading to reduced transcription of MYLIP, the gene that encodes IDOL, and APOA1. Reduced IDOL at the plasma membrane attenuates LDLR degradation and increases LDL recycling, leading to an increased number of LDLRs at the hepatocyte cell surface and, consequently, an increase in LDL clearance. This scenario should be accompanied by a reduced ApoA-I PR. (D) An increase in the TG/cholesterol ratio as well as an increase in LDL particle size as seen by NMR increases the affinity of LDL for the LDLR, leading to a greater degree of LDL binding to the LDLR and an increase in overall LDL clearance.

Figure 3. PCSK9 kinetics after treatment with anacetrapib.

PCSK9 kinetic parameters for subjects in panel A (n = 29) and panel B (n = 10) at the end of each treatment period. The geometric mean is shown as a bar. None of the comparisons achieved a raw P value of less than 0.05 on the basis of the linear mixed-effects models containing fixed effects for panel and treatment-within-panel and random effects for subject-within-panel.

Figure 2. ApoB kinetics in lipoprotein fractions after treatment with anacetrapib.

VLDL-, IDL-, and LDL ApoB kinetic parameters for subjects in panel A (n = 29) and panel B (n = 10) at the end of each treatment period. The geometric mean is shown as a bar with unadjusted raw P values generated using a linear mixed-effects model containing fixed effects for panel and treatment-within-panel and random effects for subject-within-panel, unless indicated by an asterisk, in which case median values are indicated by a bar, and P values obtained by a Wilcoxon signed-rank test are shown. ANA, anacetrapib; PBO, placebo.

Figure 1. CONSORT flow diagram showing the disposition of subjects participating in the current study.

*Patients are only counted once: Lost to follow-up, n = 28; lipids too low or too high, n = 35; qualified but declined, n = 8; cardiovascular risk factors, n = 11; high BMI, n = 5; taking excluded medication, n = 2; noncompliant during screening, n = 2; creatinine clearance too low, n = 4; kidney disease, n = 1; severe allergy, n = 2; glucose too high, n = 3; other, n = 17.