OXIDATION OF HUMAN HIGH-DENSITY-LIPOPROTEINS BY (OH)-O-CENTER-DOT AND(OH)-O-CENTER-DOT O-2(CENTER-DOT-) FREE-RADICALS/

The aim of this work was to specify the mechanisms involved in the rad ical oxidation of human high-density lipoprotein (HDL) and to compare these mechanisms with those described previously for the oxidation of low-density lipoprotein (LDL) under the same experimental conditions ( Bonnefont-Rousselot et al., Radiat. Res, 134, 271-282, 1993), The oxid ation of HDL, initiated by (OH)-O-. or (OH)-O-./O-2(-) free radicals f rom gamma radiolysis of water, was evaluated as a function of increasi ng radiation dose by analyzing quantitatively the decrease of endogeno us alpha-tocopherol and the formation of oxidation products (thiobarbi turic acid-reactive substances and conjugated dienes). All qualitative conclusions were supported by quantitative data (radiation yields and concentrations of the oxidation markers at high radiation doses) and by the mechanisms of the kinetics, (OH)-O-. free radicals in the absen ce of oxygen were less efficient in initiating HDL oxidation than in t he presence of oxygen (action of (OH)-O-./O-2(.-) free radicals), whic h was in agreement with the enhancement of the action of (OH)-O-. free radicals by oxygen. The remaining significant level of vitamin E in H DLs at high radiation doses in the absence of oxygen could be explaine d by a regeneration of vitamin E by an oxidation product that was able to reduce the alpha-tocopheroxyl radical, The yields related to the d ecrease in the vitamin E content of HDLs after exposure to radiation w ith (OH)-O-. or (OH)-O-./O-2(.-) free radicals were slightly higher th an those obtained previously in LDLs under similar experimental condit ions, Moreover, in the presence of oxygen, (OH)-O-. free radicals led to a lower formation of thiobarbituric acid-reactive substances in HDL s than in LDLs. Such discrepancies in the behavior of these two lipopr otein fractions could be related to the differences in the chemical co mposition of HDLs and LDLs, (C) 1997 by Radiation Research Society.