In vivo effects of anacetrapib on preβ HDL: improvement in HDL remodeling without effects on cholesterol absorption

Abstract

Cholesteryl ester transfer protein (CETP) transfers cholesteryl ester and triglyceride between HDL and apoB-containing lipoproteins. Anacetrapib (ANA), a reversible inhibitor of CETP, raises HDL cholesterol and lowers LDL cholesterol in dyslipidemic patients. We previously demonstrated that ANA increases macrophage-to-feces reverse cholesterol transport and fecal cholesterol excretion in hamsters, and increased preβ HDL-dependent cholesterol efflux via ABCA1 in vitro. However, the effects of ANA on in vivo preβ HDL have not been characterized. In vitro, ANA inhibited the formation of preβ, however in ANA-treated dyslipidemic hamsters, preβ HDL levels (measured by two-dimensional gel electrophoresis) were increased, in contrast to in vitro findings. Because changes in plasma preβ HDL have been proposed to potentially affect markers of cholesterol absorption with other CETP inhibitors, a dual stable isotope method was used to directly measure cholesterol absorption in hamsters. ANA treatment of hamsters (on either dyslipidemic or normal diet) had no effect on cholesterol absorption, while dalcetrapib-treated hamsters displayed an increase in cholesterol absorption. Taken together, these data support the notion that ANA promotes preβ HDL functionality in vivo, with no effects on cholesterol absorption.

Keywords: anacetrapib; apolipoprotein A1; cholesteryl ester transfer protein; dalcetrapib; high density lipoprotein.

Fig. 1.

Effects of CETP inhibitors on preβ HDL generation in vitro. Human plasma was incubated at 37°C for 21 h and preβ HDL was measured as described in Materials and Methods. A: CETP-dependence of in vitro preβ HDL generation. B: Concentration-dependent inhibition of in vitro preβ HDL generation by ANA (left) but not dalcetrapib (right). C: Inhibition of CETP activity by both ANA (left) and dalcetrapib (right).

Fig. 2.

Increased preβ HDL in dyslipidemic hamsters by ANA but not dalcetrapib. A: Preβ HDL was analyzed by 2D gel electrophoresis as described in Materials and Methods. ANA (left) increased preβ HDL as percent of total apoA-I, while dalcetrapib (right) had no effect. B: Lack of effect of treatment on total plasma apoA-I from hamsters treated with ANA (left) or dalcetrapib (right). *P < 0.05 versus vehicle (Veh). BID, twice daily.

Fig. 3.

Effect of CETP inhibition on plasma lipoproteins and fecal cholesterol in dyslipidemic hamsters. A: ANA and dalcetrapib (Dal) reduce CETP activity, with no effect of ezetimibe (Eze) (cholesterol absorption control). B: Increase in plasma HDL-C by ANA and dalcetrapib (left), reduction in LDL-C by ANA and ezetimibe (right). C: ANA and dalcetrapib increase fecal cholesterol content equivalently in dyslipidemic hamsters, but to a lesser extent than ezetimibe. **P < 0.01, ***P < 0.001 versus vehicle (Veh). CPM: counts per minute of 3H cholesteryl ester detected in the acceptor particle following LDL precipitation, as described in Materials and Methods.

Fig. 4.

Effect of CETP inhibition on plasma lipoproteins and fecal cholesterol in normolipidemic hamsters. A: ANA and dalcetrapib reduce CETP activity, with no effect of ezetimibe (cholesterol absorption control). B: Increase in plasma HDL-C by ANA and dalcetrapib (left), lack of effect of any treatment on LDL-C (right). C: Only ezetimibe increases fecal cholesterol content in normolipidemic hamsters. *P < 0.05, **P < 0.01, ***P < 0.001 versus vehicle.

Fig. 5.

Dalcetrapib (Dal), but not ANA, increases cholesterol absorption in dyslipidemic hamsters. A: Area under the curve (AUC) of the ratio of oral:iv-labeled cholesterol (measure of cholesterol absorption). B: Only ezetimibe (Eze) increases incorporation of ²H into cholesterol, a measure of de novo cholesterol synthesis. ***P < 0.001, **P < 0.01 versus vehicle (Veh).

Fig. 6.

Dalcetrapib (Dal), but not ANA, increases cholesterol absorption in normolipidemic hamsters. A: Area under the curve (AUC) of the ratio of oral:iv-labeled cholesterol (measure of cholesterol absorption). B: Only ezetimibe (Eze) increases incorporation of ²H into cholesterol, a measure of de novo cholesterol synthesis. ***P < 0.001, **P < 0.01 versus vehicle (Veh).