In Vitro and in Vivo Interactions of Bisphenol A and Its Metabolite, Bisphenol A Glucuronide, with Estrogen Receptors α and β

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Abstract
The estrogenic activities of bisphenol A (BPA) and its major metabolite BPA glucuronide (BPA-G) were assessed in a number of in vitro and in vivo assays. BPA competed with [3H]-17β-estradiol (E2) for binding to mouse uterine cytosol ER, a glutathione S-transferase (GST)−human ER D, E, and F domain fusion protein (GST−hERαdef) and full-length recombinant hERβ. The IC50 values for E2 were similar for all three receptor preparations, whereas BPA competed more effectively for binding to hERβ (0.96 μM) than to either mouse uterine cytosol ER (26 μM) or GST−hERαdef (36 μM). In contrast, BPA-G did not competitively displace [3H]E2 from any of the ER preparations. In MCF-7 cells transiently transfected with Gal4-hERαdef or Gal4-hERβdef, BPA induced reporter gene activity with comparable EC50 values (71 and 39 μM, respectively). No significant induction of reporter gene activity was seen for BPA-G. Cotreatment studies showed that concentrations of (10 μM) BPA and BPA-G did not antagonize E2-induced luciferase mediated through either Gal4-hERαdef or Gal4-hERβdef. In vivo, the uterotropic effect of gavage or subcutaneous (sc) administration of 0.002−800 mg of BPA/kg of body weight/day for three consecutive days was examined in immature rats. Dose-related estrogenic effects on the rat uterus were observed at oral doses of 200 and 800 mg/kg and at sc doses of 10, 100, and 800 mg/kg. These results demonstrate that BPA competes more effectively for binding to ERβ, but induces ERα- and ERβ-mediated gene expression with comparable efficacy. In contrast, BPA-G did not exhibit any in vitro estrogenic activity. In addition, there was a clear route dependency on the ability of BPA to induce estrogenic responses in vivo.