RELEASE OF IRON FROM FERRITIN STORAGE BY REDOX CYCLING OF STILBENE AND STEROID ESTROGEN METABOLITES - A MECHANISM OF INDUCTION OF FREE-RADICAL DAMAGE BY ESTROGEN

Estrogens induce hydroxyl radical-mediated DNA and protein damage and lipid peroxidation, As part of a study of the mechanism of hydroxyl ra dical generation by estrogens, we investigated the in vitro mobilizati on of Fe2+ from ferritin by redox cycling of the stilbene or steroid e strogen metabolites diethylstilbestrol-4',4''-quinone (DESQ), equileni n-3,4-quinone (EQ), or estrone-3,4-quinone (3,4EQ). Aerobic cytochrome P450 reductase-mediated redox cycling of 35.50 mu M DESQ, 0.35 mu M E Q, or 3.55 mu M 3,4EQ increased the reduction of succinoylated cytochr ome c, a measure of superoxide radical formation, by 19-20% over contr ol values (24.5 +/- 0.3 mu M) in the absence of estrogen quinone subst rate, Rates of Fe2+ release from horse spleen ferritin by cytochrome P 450 reductase-mediated redox cycling of 35.50 mu M DESQ, 0.35 mu M EQ, or 3.55 mu M 3,4EQ were 94.4 +/- 0.6, 117.2 +/- 9.4, or 137.7 +/- 19. 9 pmol Fe2+/ min, respectively, compared to 67.3 +/- 2.3 pmol Fe2+/ mi n in the absence of estrogen substrates. Redox cycling of 35.5 mu M DE SQ, EQ, or 3,4EQ medial-ed by microsomes of hamster kidney, a target o rgan of estrogen-induced carcinogenesis, released 511 +/- 30.10, 516.9 1 +/- 22.90, or 410.27 +/- 28.49 pmol Fe2+/min, respectively. Correspo nding values with microsomes of hamster liver, where tumors do not dev elop by estrogen treatment, were 272.27 +/- 43.10, 222.25 +/- 21.78, o r 91.36 +/- 8.54 pmol Fe2+/min, respectively. Diethylstilbestrol, equi lenin, and 4-hydroxyestrone do not induce detectable iron release from ferritin under these conditions. The cytochrome P450 reductase-mediat ed redox cycling of DESQ, EQ, or 3,4EQ in the presence of iron resulte d in the hydroxylation of benzoic acid by hydroxyl radical attack. The se data demonstrate that redox cycling of estrogen metabolites release s Fe2+ from ferritin, which in tarn generates hydroxyl radicals by a F enton reaction. This estrogen-induced hydroxyl radical damage may cont ribute to tumor initiation in hormone target tissues, including breast cancer. (C) 1997 Academic Press.