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Effects of trivalent and hexavalent chromium on lipid peroxidation in rat liver microsomes.

The effects of heavy metals, especially chromium, on lipid peroxidation in rat liver microsomes were studied. Lipid peroxidation was determined as thiobarbituric acidreacting materials. At lower concentrations in the range of 1-100μM, both hexavalent and trivalent chromium inhibited lipid peroxidation induced by ascorbate or NADPH in microsomes. In the presence of ascorbate, the inhibitions decreased on treatment with sulfhydryl reagents and were partly overcome by the addition of tartaric acid. It is suggested that chromium, presumably in the trivalent form, may bind with sulfhydryl groups of protein, resulting in the inhibition of lipid peroxidation. In the presence of NADPH, hexavalent chromium showed very potent inhibition. Hexavalent and trivalent chromium did not inhibit the electron-transport system in microsomes. The hexavalent form may act as a radical scavenger, since it strongly inhibited carbon tetrachloride-stimulated lipid peroxidation, could reduce 2, 2'-diphenyl-β-picrylhydrazyl to some extent in the presence of a reducing agent such as ethanol, and inhibited NADPH-induced peroxidation markedly in the presence of sulfhydryl compounds. Above 1 mM, hexavalent chromium caused lipid peroxide formation in microsomes, apparently not associated with iron, while trivalent chromium showed an inhibitory effect.