2-hydroxyestradiol and 2-2--azobis(2-amidinopropane)

We examined by using 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) as a radical generator the ability of estrogens to scavenge carbon-centered and peroxyl radicals. Electron spin resonance signals of carbon-centered radicals from AAPH were diminished by catecholestrogens but not by phenolic estrogens, showing that catecholestrogens efficiently scavenged carbon-centered radicals. However, fluorescent decomposition of R-phycoerythrin by AAPH-derived peroxyl radicals was inhibited by catecholestrogens and phenolic estrogens. Evidently, peroxyl radicals were scavenged by catecholestrogens and by phenolic estrogens. However, the scavenging ability of 4-hydroxyestradiol was less than 2-hydroxyestradiol. Strand break of DNA induced by AAPH was inhibited by catecholestrogens, but not by phenolic estrogens under aerobic and anaerobic conditions. Inactivation of lysozyme induced by AAPH was completely blocked by 2-hydroxyestradiol under aerobic and anaerobic conditions, and by 4-hyroxyestradiol only under anaerobic conditions. Peroxidation of arachidonic acid by AAPH was strongly inhibited by catecholestrogens at low concentrations. Only large amounts of phenolic estrogens markedly inhibited lipid peroxidation. These results show that catecholestrogens were antioxidant against AAPH-induced damage to biological molecules through scavenging both carbon-centered and peroxyl radicals, but phenolic estrogens partially inhibited AAPH-induced damage because they scavenged only peroxyl radicals.

Topics: Amidines; Antioxidants; Arachidonic Acid; DNA Damage; Electron Spin Resonance Spectroscopy; Estradiol; Estrogens, Catechol; Free Radical Scavengers; Free Radicals; Lipid Peroxidation; Muramidase; Mutagens; Oxidation-Reduction; Oxygen; Peroxides; Phycoerythrin; Plasmids

We investigated the inhibition mechanism of lipid peroxidation by estrogens. Estradiol and 2-hydroxyestradiol showed strong inhibitory activities toward NADPH and ADP-Fe(3+)-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-Fe3+ was strongly inhibited only by 2-hydroxyestradiol. It seems that 2-hydroxyestradiol may interact with alkoxyl rather than with peroxyl radicals during lipid peroxidation.

Topics: Adenosine Diphosphate; Amidines; Animals; Ascorbic Acid; Butylated Hydroxytoluene; Dose-Response Relationship, Drug; Erythrocyte Membrane; Estradiol; Free Radical Scavengers; Hypoxanthine; Iron; Lipid Peroxidation; Microsomes, Liver; NADP; Rats; Rats, Wistar; Thiobarbituric Acid Reactive Substances; Xanthine Oxidase