Abstract 15120: Anacetrapib Alters Triglyceride Trafficking and Clearance in Rhesus Macaques: Interrogating the Mechanism Behind V/LDL-Cholesterol Reduction

Abstract

Cholesterol Ester Transfer Protein (CETP) facilitates the exchange of cholesteryl esters and triglycerides (TG) between HDL particles and apoB containing lipoproteins. Assessment of CETP activity has been mainly based upon in vitro transfer assays and, therefore, may not reflect the activity of CETP mediated exchange in vivo. Novel isotope tracer methods were developed to study the transfer of lipids in vivo. We used these techniques to systematically study lipid fluxes in lipoprotein particles from fed and fasted rhesus macaques before and after 10 days of treatment with the CETPi , anacetrapib. In two separate studies, dual isotopes of oleic acid, [²H₁₁] p.o. in heavy cream and [¹³C₁₈]i.v., were administered before and after treatment with anacetrapib 150 mg/kg Q.D.. Plasma samples, collected at eight times postprandially and at 24 h, were analyzed for total cholesterol and TG using biochemical methods, and lipoprotein fractions were analyzed for isotope labeled lipids using liquid chromatography and mass spectrometry. Treatment with anacetrapib increased total plasma cholesterol by >70%, and HDL cholesterol by >110%. A >90% (p<0.01) decrease in newly synthesized TG transfer to HDL was observed with anacetrapib treatment, reflecting a decrease in CETP activity. This was calculated based on labeled TG in non-HDL as the substrate and labeled-TG in HDL as the product of CETP activity. In addition, the 1 hour post-prandial HDL TG pool size was decreased by >85% (p<0.001). An effect of anacetrapib on overall TG clearance is further implied since circulating levels of total plasma TG reach baseline level within 2 hours with treatment compared with 5 hours on vehicle. In support of this, we have found a temporal change in PCSK9 levels, as measured by ELISA, suggesting a link of anacetrapib to increased clearance of TG rich particles. Tracking these changes in lipid trafficking has shed light on a possible mechanism to explain how anacetrapib reduces V/LDL-cholesterol in rhesus macaques. These findings are consistent with the increase in VLDL apoB FCR observed in a clinical lipoprotein kinetic study with anacetrapib.