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Cholesteryl ester transfer protein (CETP) mediates the transfer of HDL cholesteryl esters for triglyceride (TG) in VLDL/LDL. CETP inhibition, with anacetrapib, increases HDL-cholesterol, reduces LDL-cholesterol, and lowers TG levels. This study describes the mechanisms responsible for TG lowering by examining the kinetics of VLDL-TG, apoC-II, apoC-III, and apoE. Mildly hypercholesterolemic subjects were randomized to either placebo (N = 10) or atorvastatin 20 mg/qd (N = 29) for 4 weeks (period 1) followed by 8 weeks of anacetrapib, 100 mg/qd (period 2). Following each period, subjects underwent stable isotope metabolic studies to determine the fractional catabolic rates (FCRs) and production rates (PRs) of VLDL-TG and plasma apoC-II, apoC-III, and apoE. Anacetrapib reduced the VLDL-TG pool on a statin background due to an increased VLDL-TG FCR (29%; P = 0.002). Despite an increased VLDL-TG FCR following anacetrapib monotherapy (41%; P = 0.11), the VLDL-TG pool was unchanged due to an increase in the VLDL-TG PR (39%; P = 0.014). apoC-II, apoC-III, and apoE pool sizes increased following anacetrapib; however, the mechanisms responsible for these changes differed by treatment group. Anacetrapib increased the VLDL-TG FCR by enhancing the lipolytic potential of VLDL, which lowered the VLDL-TG pool on atorvastatin background. There was no change in the VLDL-TG pool in subjects treated with anacetrapib monotherapy due to an accompanying increase in the VLDL-TG PR., (Copyright © 2017 by the American Society for Biochemistry and Molecular Biology, Inc.)

Lipoprotein lipase (LPL), the major enzyme responsible for the hydrolysis of triglycerides, is primarily synthesized by adipocytes and myocytes. In addition to synthesis, degradation of cell surface-associated LPL is thought to be important in regulating production of the enzyme. We studied LPL metabolism in the LPL synthesizing adipocyte cell line BFC-1 beta and assessed the contributions of cell surface heparan sulfate proteoglycans (HSPG), low density lipoprotein receptor related protein (LRP), and glycosylphosphatidylinositol (GPI)-linked proteins to LPL uptake and degradation by these cells. Adipocytes degraded 10-12% of total cell surface I-labeled LPL in 2 h and 23-28% in 4 h. In 1 h, 30-54% of the degradation was inhibited by the 39 kDa receptor associated protein (RAP), an inhibitor of ligand binding to LRP. At 4 h, only 19-23% of the LPL degradation was RAP inhibitable. This suggested that two pathways with different kinetics were important for LPL degradation. Heparinase/heparitinase treatment of cells showed that most LPL degradation required the presence of HSPG. Treatment with phosphatidylinositol-specific phospholipase C (PIPLC) inhibited 125I-labeled LPL degradation by 13%. However, neither RAP nor PIPLC treatment of adipocytes significantly increased the amount of endogenously produced LPL activity in the media. To determine whether direct uptake of LPL bound to HSPG could account for the non-RAP sensitive LPL uptake and degradation, proteoglycan metabolism was assessed by labeling cells with 35SO4. Of the total pericellular proteoglycans, 14% were PIPLC releasable; surprisingly, 30% were dissociated from the cells with heparin. The amount of labeled pericellular proteoglycans decreased 26% in 2 h and 50% in 8 h, rapid enough to account for at least half of the degradation of cell surface LPL. We conclude that adipocytes degrade a fraction of the cell surface LPL, and that this process is mediated by both proteoglycans and RAP-sensitive receptors.