Evacetrapib reduces preß-1 HDL in patients with atherosclerotic cardiovascular disease or diabetes.

BACKGROUND AND AIMS: Cholesteryl ester transfer protein (CETP) inhibitor-mediated induction of HDL-cholesterol has no effect on the protection from cardiovascular disease (CVD). However, the mechanism is still unknown. Data on the effects of this class of drugs on subclasses of HDL are either limited or insufficient. In this study, we investigated the effect of evacetrapib, a CETP inhibitor, on subclasses of HDL in patients with atherosclerotic cardiovascular disease or diabetes. METHODS: Baseline and 3-month post-treatment samples from atorvastatin 40 mg plus evacetrapib 130 mg (n = 70) and atorvastatin 40 mg plus placebo (n = 30) arms were used for this purpose. Four subclasses of HDL (large HDL, medium HDL, small HDL, and preß-1 HDL) were separated according to their size and quantified by densitometry using a recently developed native polyacrylamide gel electrophoresis (PAGE) system. RESULTS: Relative to placebo, while evacetrapib treatment dramatically increased large HDL and medium HDL subclasses, it significantly reduced small HDL (27%) as well as preß-1 HDL (36%) particles. Evacetrapib treatment reduced total LDL, but also resulted in polydisperse LDL with LDL particles larger and smaller than the LDL subclasses of the placebo group. CONCLUSION: Evacetrapib reduced preß-1 HDL and small HDL in patients with ASCVD or diabetes on statin. Preß-1 HDL and medium HDL are negatively interrelated. The results could give a clue to understand the effect of CETP inhibitors on cardiovascular outcomes.

A novel role for ABCA1-generated large pre-beta migrating nascent HDL in the regulation of hepatic VLDL triglyceride secretion.

In Tangier disease, absence of ATP binding cassette transporter A1 (ABCA1) results in reduced plasma HDL and elevated triglyceride (TG) levels. We hypothesized that hepatocyte ABCA1 regulates VLDL TG secretion through nascent HDL production. Silencing of ABCA1 expression in oleate-stimulated rat hepatoma cells resulted in: 1) decreased large nascent HDL (>10 nm diameter) and increased small nascent HDL (<10 nm) formation, 2) increased large buoyant VLDL1 particle secretion, and 3) decreased phosphatidylinositol-3 (PI3) kinase activation. Nascent HDL-containing conditioned medium from rat hepatoma cells or HEK293 cells transfected with ABCA1 was effective in increasing PI3 kinase activation and reducing VLDL TG secretion in ABCA1-silenced hepatoma cells. Addition of isolated large nascent HDL particles to ABCA1-silenced hepatoma cells inhibited VLDL TG secretion to a greater extent than small nascent HDL. Similarly, addition of recombinant HDL, but not human plasma HDL, was effective in attenuating TG secretion and increasing PI3 kinase activation in ABCA1-silenced cells. Collectively, these data suggest that large nascent HDL particles, assembled by hepatic ABCA1, generate a PI3 kinase-mediated autocrine signal that attenuates VLDL maturation and TG secretion. This pathway may explain the elevated plasma TG concentration that occurs in most Tangier subjects and may also account, in part, for the inverse relationship between plasma HDL and TG concentrations in individuals with compromised ABCA1 function.

Impact of android overweight or obesity and insulin resistance on basal and postprandial SR-BI and ABCA1-mediated serum cholesterol efflux capacities.

Since android overweight/obesity and insulin resistance are independent risk factors for cardiovascular disease, we investigated their impact on basal and postprandial scavenger receptor BI (SR-BI) and ATP binding cassette transporter A1 (ABCA1)-mediated serum cholesterol efflux. Twelve android overweight to obese and 9 normal weight controls women underwent body composition analysis by dual energy X-ray absorptiometry, a euglycemic hyperinsulinemic clamp, and an oral fat load with blood sampling at initial time (T0), 4h (T4) and 10h (T10) after the fat load. Serum lipids and HDL-parameters, capacities of serum to promote cholesterol efflux from SR-BI expressing Fu5AH hepatoma cells or from ABCA1-expressing J774 macrophages and to abilities of serum to induce a net removal of cholesterol from macrophage foam cells were measured at T0, T4 and T10. Sera from overweight/obese exhibited moderately decreased SR-BI-mediated cholesterol efflux capacities, in accordance with reduced HDL concentrations, but importantly increased ABCA1-mediated cholesterol efflux and increased cholesterol extraction capacities over the postprandial period, partly related to higher prebeta-HDL concentrations. In multiple regression analyses, android obesity-related parameters and HDL-PL or prebeta-HDL levels remained the only independent correlates for SR-BI or ABCA1-dependent fractional cholesterol efflux while only prebeta-HDL levels remained correlated to cholesterol extraction capacities. Our results suggest that android overweight/obesity may not result in an impaired cholesterol efflux capacity.

Increased cholesterol efflux from cultured fibroblasts to plasma from hypertriglyceridemic type 2 diabetic patients: roles of pre beta-HDL, phospholipid transfer protein and cholesterol esterification.

We tested whether hypertriglyceridemia associated with type 2 diabetes mellitus is accompanied by alterations in pre beta-HDL, which are considered to be initial acceptors of cell-derived cholesterol, and by changes in the ability of plasma to promote cellular cholesterol efflux. In 28 hypertriglyceridemic and 56 normotriglyceridemic type 2 diabetic patients, and in 56 control subjects, we determined plasma lipids, HDL cholesterol and phospholipids, plasma pre beta-HDL and pre beta-HDL formation, phospholipid transfer protein (PLTP) activity, plasma cholesterol esterification (EST) and cholesteryl ester transfer (CET) and the ability of plasma to stimulate cholesterol efflux out of cultured human fibroblasts. HDL cholesterol and HDL phospholipids were lower, whereas plasma PLTP activity, EST and CET were higher in hypertriglyceridemic diabetic patients than in the other groups. Pre beta-HDL levels and pre beta-HDL formation were unaltered, although the relative amount of pre beta-HDL (expressed as % of total plasma apo A-I) was increased in hypertriglyeridemic diabetic patients. Cellular cholesterol efflux to plasma from hypertriglyceridemic diabetic patients was increased compared to efflux to normotriglyceridemic diabetic and control plasma, but efflux to normotriglyceridemic diabetic and control plasma did not differ. Multiple linear regression analysis demonstrated that cellular cholesterol efflux to plasma was positively and independently related to pre beta-HDL formation, PLTP activity and EST (multiple r=0.48), but not to the diabetic state. In conclusion, cholesterol efflux from fibroblasts to normotriglyceridemic diabetic plasma is unchanged. Efflux to hypertriglyceridemic diabetic plasma is enhanced, in association with increased plasma PLTP activity and cholesterol esterification. Unaltered pre beta-HDL formation in diabetic hypertriglyceridemia, despite low apo A-I, could contribute to maintenance of cholesterol efflux.

[Detection of qualitative abnormalities of HDL by measurement of prebeta1-HDL concentration].

Prebeta1-HDL is a native lipid-poor HDL that promotes cholesterol efflux from cell membranes. Prebeta1-HDL is a good substrate of lecithin-cholesterol acyltransferase (LCAT) and is converted into a-migrating spherical HDL by LCAT activity. Prebeta1-HDL is probably secreted from the liver and is also generated from a-HDL by several regulatory factors. At present, prebeta1-HDL concentration is determined by native two-dimensional gel electrophoresis, ultrafiltration-isotope dilution method, or immunoassay using monoclonal antibody. Plasma samples for immunoassay are pretreated with 50% sucrose, which stabilizes prebeta1-HDL during storage at -20 degrees C as well as at 4 degrees C. We determined the LCAT-dependent conversion rate of prebeta1-HDL to detect abnormal HDL metabolism. In this review, we discuss the physiological role of prebeta1 HDL and the clinical significance of plasma prebeta1-HDL concentration.