Effects of dietary vitamin C and E supplementation on the copper mediated oxidation of HDL and on HDL mediated cholesterol efflux

Copper mediated oxidative modification of high density lipoprotein (HDL) diminishes its capacity to promote cholesterol efflux from cells in culture. In the present study, HDL was isolated from eight subjects before and after a 10 day administration of the antioxidant vitamins C and E. After incubation of HDL (1.25 mg protein/ml) with 10 mu M copper for 0-4 h or with 0-20 mu M copper for 4 h, thiobarbituric acid reactive substances (TEARS) production was significantly decreased following vitamin administration suggesting that the vitamins decreased the susceptibility of HDL to oxidation. However, two other assays of lipoprotein oxidation, trinitrobenzene sulfonic acid reactivity and conjugated diene formation, did not show a consistent effect of vitamin administration. To study cholesterol efflux, J774 macrophages were labeled with H-3 cholesterol (0.1 mu Ci/ml, 50 mu g/ml) and incubated with HDL or oxidized HDL (100 mu g protein/ml) for 24 h. HDL isolated before vitamins and oxidized in vitro was 39% less effective in mediating efflux compared to unmodified HDL, while HDL isolated after vitamins and oxidized was 22% less effective (before vs. after vitamins, P < 0.015). HDL oxidation determined by measuring TEARS production correlated with decreased cholesterol efflux (r = -0.73, P < 0.050). These data suggest that oxidation of HDL interferes with its role in reverse cholesterol transport and that antioxidant vitamins have a protective effect.