Equol-Producing Bacteria and Estrogen Metabolism

摘要

Intestinal bacteria are involved in estrogen metabolism. Thus, inter- individual differences in intestinal bacterial populations may contribute to variation breast cancer risk via effects on estrogen metabolism. One-third to one-half of the population harbors the yet-to be-identified bacteria that metabolize daidzein, a soy isoflavone, to equol. Studies suggest that equol production may be associated with reduced breast cancer risk, but mechanisms for this relationship are unknown. Our objective was to determine whether fecal bacterial metabolism of estrogens differs according to equol-producer phenotype. A method was developed for the extraction and gas chromatography- mass spectrometry quantification of estrogens from fecal incubations. Previously frozen fecal samples from female equol producers (n=20) and non- producers (n=l3) were incubated anaerobically in media for 5d at 37C with the following estrogens: estrone, estradiol, estriol, 2-hydroxyestrone, l6alpha- hydroxyestrone, and 2-methoxyestrone. Fecal bacteria from equol-producers were more likely than non-producers to convert 2-hydroxyestrone to 2- hydroxyestradiol. Furthermore, equol-producers, compared to non- producers, converted significantly more estrone to estradiol, and l6alpha-hydroxyestrone to estriol. These findings suggest diffenences may exist between equol- producers and non-producers in bacterial estrogen metabolism. However, the conversion of 16alpha-hydroxyestrone to estriol, and the conversion of estrone to estradiol could represent potentially beneficial and detrimental, respectively, pathways in terms of breast cancer risk.