CATECHOL ESTROGEN PRODUCTION IN RAT MICROSOMES AFTER TREATMENT WITH INDOLE-3-CARBINOL, ASCORBIGEN, OR BETA-NAPHTHAFLAVONE - A COMPARISON OF STABLE-ISOTOPE DILUTION GAS-CHROMATOGRAPHY MASS-SPECTROMETRY AND RADIOMETRIC METHODS

Compounds like indole-3-carbinol (13C) have been shown to increase catechol estrogen formation and reduce mammary tumor, incidence in mice. These compounds may exert a protective effect for breast cancer development by decreasing the overall estrogen pool available for the formation of 16 alpha-hydroxyestrone (16 alpha-OHE(1)), a metabolite that retains significant estrogenic activity, may be mutagenic and could represent a potential carcinogenic intermediate of estradiol degradation. 13C and ascorbigen originate fr om the breakdown of glucobrassicin. We have compared the inductive effects of 13C with ascorbigen and beta-naphthaflavone (Bnf) in microsomes from rats pretreated with these compounds using isotope dilution GC-MS and a radiometric method. Incubated microsomes from rats pretreated with 13C and ascorbigen yielded high levels of 2-hydroxyestradiol (2-OHE(2)) that were comparable to levels induced by Bnf and were significantly above control group levels (p < 0.005). Absolute values determined by the radiometric method were approximately 40% lower than 2-OHE(2) concentrations determined by CC-MS, although the relative changes in each group were the same. These differences may be attributed to the radiolabel becoming trapped in microsomal intermediates in the sequence leading to tritium entering the aqueous compartment. Both ascorbigen- and Bnf-treated animals exhibited significant increases in 2-hydroxyestrone (2-OHE(1)) (p < 0.05). The ability of ascorbigen to induce estradiol C-2 hydroxylation has not been previously reported. Based on these data, we speculate that ascorbigen will act as an anticarcinogenic agent and will inhibit or reduce the incidence of mammary tumor formation.