tert-butyl hydroperoxide-dependent microsomal release of iron and lipid peroxidation. II. Evidence for the involvement of nonheme, nonferritin iron in lipid peroxidation.
In a previous study tert-butyl hydroperoxide (t-BOOH) was found to promote reductive release of nonheme, nonferritin iron from rat liver microsomes. The reaction was catalyzed by cytochrome P450 and was strictly contingent on the availability of ADP. In this study, t-BOOH was also found to promote microsomal lipid peroxidation, as evidenced by formation of malondialdehyde. t-BOOH-dependent lipid peroxidation was stimulated by ADP, and four lines of evidence suggested that such stimulation was mediated by reductive release and subsequent redox cycling of nonheme, nonferritin iron. First, lipid peroxidation was stimulated by the same concentration of ADP that promoted iron release. Second, depletion of nonheme, nonferritin iron by pretreatment of rats with phenobarbital decreased the stimulation of lipid peroxidation by ADP. Third, the effect of ADP was maximal when the concentration of t-BOOH was adjusted to values that yielded maximum iron release. Fourth, the effect of ADP was abolished by bathophenanthroline, which is known to chelate ferrous iron in a redox inactive form. These results suggest that the reductive release of nonheme, nonferritin iron exacerbates the deleterious effects of t-BOOH on microsomal lipids.