Inhibition of lipid peroxidation by estradiol and 2-hydroxyestradiol

We investigated the inhibition mechanism of lipid peroxidation by estrogens. Estradiol and 2-hydroxyestradiol showed strong inhibitory activities toward NADPH and ADP-Fe3+-dependent lipid peroxidations in the microsomes from rat livers only when the steroids were added to the reaction system before the start of the peroxidation reaction. These steroids also strongly inhibited oxygen uptake only when added before the start of the reaction. These results suggest that estradiol and 2-hydroxyestradiol inhibit the initial stage of microsomal lipid peroxidation. Lipid peroxidation of erythrocyte membranes induced by the systems of xanthine oxidase-hypoxanthine and ascorbate was strongly inhibited by 2 hydroxyestradiol but not by estradiol. Lipid peroxidation of erythrocyte membranes induced by 2,2'-azobis- (amidinopropane) dihydrochloride was not markedly inhibited by estradiol and 2,hydroxyestradiol, suggesting that the steroids have low reactivity with lipid peroxyl radicals. However lipid peroxidation induced by t-butyl hydroperoxide-Fe2+ was strongly inhibited only by 2-hydroxyestradiol: It seems that 2-hydroxyestradiol may interact with alkoxyl rather than with peroxyl radicals during lipid peroxidation.