Abstract 16185: CETP Inhibitor Anacetrapib Downregulates Both LDL Receptor and PCSK9 Expression in Cultured Liver Cells Through a SREBP Dependent Mechanism
The plasma protein cholesteryl ester transfer protein (CETP) mediates the exchange of cholesteryl esters (CE) and TG between HDL and apoB-containing lipoprotein particles. Thus, inhibition of CETP activity raises plasma HDL-C and lowers LDL-C. Anacetrapid (ANA) and dalcetrapid (DAL) are potent CETP inhibitors and their effects on raising plasma HDL-C are demonstrated in clinical trials. Particularly, ANA monotherapy increases HDL-C by over 100% and lowers LDL-C by 30-40% in dyslipidemic patients. Besides CETP, PCSK9 is another promising therapeutic target. Plasma PCSK9 binds to hepatic LDL receptor (LDLR), promoting its degradation, and consequently raising plasma LDL-C. It was recently reported that CETP inhibitors (ANA, DAL, and K-312) exhibited negative effects on PCSK9 expression in HepG2 cells, which could be potentially a causal factor for LDL-C reduction observed in humans, additional to CETP activity inhibition. The current study aimed to evaluate the direct effects of ANA and DAL on LDLR and PCSK9 expression in cultured hepatic cells and to further elucidate the underlying mechanism. Unexpectedly, we found that ANA treatment of HepG2 cells significantly reduced protein levels of PCSK9 and LDLR to 70% and 50% of control at 1 μM and 10 μM concentrations, while DAL up to 10 μM had no effect. We further examined the effects of ANA on human primary hepatocytes. The data generated from 3 independent donors showed 41% reduction of LDLR protein (p<0.01) and 27% reduction in PCSK9 protein levels (p<0.05) by 3 μM ANA after 24 h treatment. The inhibitory action of ANA on LDLR/PCSK9 was further demonstrated in mouse primary hepatocytes and mouse hepatoma cell lines, thereby suggesting an action independent of CETP protein. Q-PCR analysis showed a similar degree of decrease in LDLR/PCSK9 mRNA levels by ANA comparable to its effects on their respective proteins. LDLR and PCSK9 promoter analyses further suggested that ANA inhibits LDLR/PCSK9 expression at the level of transcription. Finally, we observed that treating HepG2 cells with ANA reduced the amount of mature SREBP2, the common trans-activator of LDLR and PCSK9. In summary, these novel findings suggest that ANA most likely affects SREBP2 processing which leads to attenuated transcriptions of LDLR and PCSK9.
- © 2013 by American Heart Association, Inc.