EFFECT OF PLASMA ON THE DEGRADATION OF HYDROPEROXIDES OF UNESTERIFIEDLINOLEIC-ACID AND COPPER-PEROXIDIZED LDL

The determination of lipid hydroperoxides in plasma and lipoproteins r ecently reached a clinical relevance in disorders such as atherosclero sis, where oxidative reactions have been suggested to play a fundament al pathogenetic role. The peroxide content of lipoproteins is usually measured after ultracentrifugation and extraction. During this procedu re, some peroxides might decompose causing a too low recovery. To scre en this possibility, the disappearance, in the presence of human plasm a, of hydroperoxides of linoleic acid and Cu-oxidized low density lipo protein (LDL) have been investigated, using both a iodometric titratio n and an enzymatic assay. While only in the presence of GSH plasma dec omposes linoleic acid hydroperoxides quite rapidly, peroxides in Cu-ox idized LDL were stable both in presence as well as in absence of GSH. This indicated that lipid hydroperoxides are stable in plasma and that peroxides of Cu-oxidized LDL are not substrate for the glutathione-de pendent peroxidase activity in plasma. The relevant decrease of the io dometric titre of LDL peroxides observed in the presence of elevated a mounts of plasma was shown to be artifactual, since some compounds ext racted from plasma do react with iodine generated by peroxides. Whole plasma itself, indeed, has been shown to reduce back to I- appreciable amount of free iodine.