OXIDATION OF HIGH-DENSITY-LIPOPROTEINS - CHARACTERIZATION AND EFFECTSON CHOLESTEROL EFFLUX FROM J774 MACROPHAGES

Oxidative modification of high density lipoproteins (HDL) may alter th eir capacity to mediate cellular cholesterol efflux. We studied the ki netics of copper-mediated oxidation of HDL and cholesterol efflux medi ated by unmodified and oxidized HDL (oxHDL). Oxidation was measured by increases in absorbance at 234 nm (Delta A234), production of thiobar bituric acid reactive substances (TEARS) and loss of trinitrobenzene s ulfonic acid reactivity. Oxidation was dependent on copper concentrati on and showed a lag phase and propagation phase. Efflux of cholesterol from J774 macrophages measured by appearance of cellular [H-3]cholest erol in the medium was lower by 16% after 4 h and 36% after 24 h with oxHDL compared to HDL. OxHDL-mediated efflux was also lower by 27% to 37% at lipoprotein concentrations of 10 to 200 mu g protein/ml. Choles terol efflux correlated negatively with TEARS production(r = -0.97, P < 0.003) and Delta A234 (r = - 0.77, P < 0.080), There was no differen ce in efflux mediated by apoproteins prepared from HDL and oxHDL. Effl ux measured by change in cholesterol mass in medium was 78% lower with oxHDL. Inhibition of oxidation with butylated hydroxytoluene maintain ed the capacity of HDL to stimulate efflux. These results suggest that oxidation of HDL may impair its protective role against atheroscleros is.