PHYSICOCHEMICAL CHANGES IN HUMAN HIGH-DENSITY-LIPOPROTEINS (HDL) OXIDIZED BY GAMMA RADIOLYSIS-GENERATED OXYRADICALS - EFFECT ON THEIR CHOLESTEROL EFFLUXING CAPACITY

This paper describes an oxidative process of human high-density lipoproteins (HDL) based upon the action of oxygenated free radicals produced by water radiolysis (OH. and OH./O-2(-) free radicals at pH 7), monitored by both biochemical and physical markers. Classical biochemical markers (vitamin E, thiobarbituric acid-reactive substances (TBARS), conjugated dienes and differential fluorescence) were studied as a function of the radiation dose (from 0 to 800 Gy; dose rate = 2.7 . 10(-2) Gy.s(-1)), The fluorescence polarization anisotropy (r) was measured with 1,6-diphenylhexatriene (DPH). Vitamin E decrease and formation of lipid peroxidation products (thiobarbituric acid-reactive substances and conjugated dienes) were concomitant in the case of OH. free radicals alone, whereas these products appeared after a small threshold dose when OH. and O-2(-) free radicals were simultaneously produced in solution. At high radiation doses, TBARS concentrations have reached plateau values (approx. 2 or 7 nmol/mg lipid with OH. or OH./O-2(-), free radicals, respectively) which were much lower than those obtained after copper oxidation (approx. 15 or 29 nmol/mg lipid after 12 and 24 h incubation, respectively). The free radical-induced oxidative process has led to a rigidification of the HDL and was associated with low values of cholesterol effluxing capacities when these oxidized HDL were incubated with cholesterol-loaded human fibroblasts. Similar results were obtained with copper-oxidized HDL, under our experimental conditions. Consequently, these two kinds of oxidative modification of HDL resulted both in a loss of their capacity to remove cellular cholesterol, which could be explained by the fact that this ability was under the dependence of a HDL optimum fluidity.