α-Tocopherol induces proatherogenic changes to HDL2 & HDL3: an in vitro and ex vivo investigation.

INTRODUCTION: High density lipoproteins (HDL) have considerable potential for improving cardiovascular health. Additionally, epidemiological studies have identified an inverse relationship between α-tocopherol intake and cardiovascular disease, which has not been translated in randomised controlled trials. OBJECTIVES: This study assessed if increased α-tocopherol within HDL(2) and HDL(3) (HDL(2&3)) influenced their antiatherogenic potential. In the first of two in vitro investigations, the oxidation potential of HDL(2&3) was assessed when α-tocopherol was added following their isolation. In the second, their oxidation potential was assessed when HDL(2&3) were isolated from serum pre-incubated with α-tocopherol. Additionally, a 6-week placebo-controlled intervention with α-tocopherol assessed if α-tocopherol influenced the oxidation potential and activities of HDL(2&3)-associated enzymes, paraoxonase-1 (PON-1) and lecithin cholesteryl acyltransferase (LCAT). RESULTS: Conflicting results arose from the in vitro investigations, whereby increasing concentrations of α-tocopherol protected HDL(2&3) against oxidation in the post-incubated HDL(2&3), and promoted HDL(2&3)-oxidation when they were isolated from serum pre-incubated with α-tocopherol. Following the 6-week placebo-controlled investigation, α-tocopherol increased in HDL(2&3), while HDL(2&3) became more susceptible to oxidation, additionally the activities of HDL(2&3)-PON-1 and HDL(2)-LCAT decreased. CONCLUSION: These results have shown for the first time that α-tocopherol induces changes to HDL(2&3), which could contribute to the pathophysiology of cardiovascular disease.

Distinct HDL subclasses present similar intrinsic susceptibility to oxidation by HOCl.

The heme protein myeloperoxidase (MPO) functions as a catalyst for lipoprotein oxidation. Hypochlorous acid (HOCl), a potent two-electron oxidant formed by the MPO-H(2)O(2)-chloride system of activated phagocytes, modifies antiatherogenic high-density lipoprotein (HDL). The structural heterogeneity and oxidative susceptibility of HDL particle subfractions were probed with HOCl. All distinct five HDL subfraction were modified by HOCl as demonstrated by the consumption of tryptophan residues and free amino groups, cross-linking of apolipoprotein AI, formation of HOCl-modified epitopes, increased electrophoretic mobility and altered content of unsaturated fatty acids in HDL subclasses. Small, dense HDL3 were less susceptible to oxidative modification than large, light HDL2 on a total mass basis at a fixed HOCl:HDL mass ratio of 1:32, but in contrast not on a particle number basis at a fixed HOCl:HDL molar ratio of 97:1. We conclude that structural and physicochemical differences between HDL subclasses do not influence their intrinsic susceptibility to oxidative attack by HOCl.

Partial suppression of CETP activity beneficially modifies the lipid transfer profile of plasma.

Cholesteryl ester transfer protein (CETP) regulates human lipoprotein metabolism. Because reducing CETP increases plasma HDL, CETP inhibitors are currently being investigated for their pharmacologic value. However, complete CETP deficiency may have undesirable consequences. In contrast, based on previous studies with purified components, we hypothesized that partial CETP inhibition, which will still elevate HDL, may induce beneficial changes in plasma lipid metabolism. To address this, CETP activity in human plasma was variably inhibited with monoclonal antibody. In control plasma, VLDL to LDL lipid transfer was >2-fold higher than to HDL(3) with lipid transfer to HDL(2) intermediate. However, individual lipid transfer events were uniquely sensitive to CETP suppression such that when CETP activity was inhibited by 60%, lipid transfer from VLDL to LDL, HDL(2) and HDL(3) were equal. The ratio of lipid transfers to LDL versus HDL declined linearly with CETP inhibition. In mass lipid transfer experiments, 25-50% inhibition of CETP significantly reduced lipid flux between VLDL and LDL but minimally affected cholesteryl ester (CE) loss from HDL. Complete CETP inhibition did not reduce cholesterol esterification rates but completely blocked the delivery of new CE to VLDL, whereas, 50% inhibition of CETP reduced this CE flux to VLDL by <20%. Thus, inhibition of CETP by