Cholesteryl ester transfer protein activity correlates inversely with apolipoprotein A5 levels

Cholesteryl ester transfer protein (CETP) mediates the exchange of triglycerides (TG) from apolipoprotein B (ApoB)-containing lipoproteins to high-density lipoproteins (HDL) and the reciprocal exchange of cholesterol (C) from HDL to ApoB-containing lipoproteins. CETP inhibition increases HDL-C and decreases low-density lipoprotein cholesterol (LDL-C) while modestly decreasing TG. Considering that CETP inhibitors block removal of TG from TG-rich lipoproteins (TRL), it is interesting that CETP inhibition decreases TG concentrations. TG levels are largely regulated by lipoprotein lipase (LPL), the enzyme primarily responsible for hydrolyzing TG. The angiopoietin-like 3/8 complex (ANGPTL3/8) is the most potent circulating LPL inhibitor, while the TG-lowering apolipoprotein A5 (ApoA5) acts by suppressing ANGPTL3/8-mediated LPL inhibition.

To better understand CETP biology, we studied the effects of CETP overexpression and CETP inhibition on the levels of ANGPTL3/8 and ApoA5 in circulation using dedicated immunoassays.

CETP-overexpressing transgenic mice had increased TG and normal ANGPTL3/8 levels but manifested dramatically reduced ApoA5 concentrations. Administration of the CETP inhibitor evacetrapib had no effect on ANGPTL3/8 levels in CETP-overexpressing mice or in humans. However, evacetrapib administration increased ApoA5 concentrations in both species. In human subjects, evacetrapib treatment increased circulating ApoA5 levels in the late-stage ACCELERATE and ACCENTUATE studies by 160.1% and 204.7%, respectively.

Our results uncover a previously unrecognized link between CETP and ApoA5 by showing that CETP overexpression reduces ApoA5 levels while CETP inhibition increases ApoA5 concentrations.