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

Abstract

The effects of heavy metals, especially Cr, on lipid peroxidation in rat liver microsomes were studied. Lipid peroxidation was determined as thiobarbituric acid-reacting materials. At lower concentrations in the range of 1-100 .mu.M, both hexavalent and trivalent Cr 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. Cr, presumably in the trivalent form, may bind with sulfhydryl groups of protein, causing the inhibition of lipid peroxidation. In the presence of NADPH, hexavalent Cr showed very potent inhibition. Hexavalent and trivalent Cr did not inhibit the electron-transport system in microsomes. The hexavalent form may act as a radical scavenger, since it strongly inhibited CCl4-stimulated lipid peroxidation, could reduce 2,2''-diphenyl-.beta.-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 Cr caused lipid peroxide formation in microsomes, apparently not associated with Fe, while trivalent Cr showed an inhibitory effect.