Metabolism of bisphenol A in isolated rat hepatocytes and oestrogenic activity of a hydroxylated metabolite in MCF-7 human breast cancer cells.
1. The metabolites of bisphenol A (BPA; 2,2-bis(4-hydroxyphenyl)propane) in freshly isolated rat hepatocytes and the oestrogenic activities of BPA and its metabolites, particularly 3-hydroxybisphenol A (3-OH-BPA), in MCF-7 cells and competitive binding assays have been studied, respectively. 2. During a 2-h incubation, almost all of the BPA (0.25 mM) added to the hepatocyte suspensions was rapidly converted to a major conjugate, monoglucuronide (approximately 75% of total metabolites), and two minor conjugates, which were tentatively identified as monosulphates of BPA and a hydroxylated intermediate, 3-OH-BPA, as determined by mass spectroscopy coupled with HPLC or GC/MS. On the other hand, free 3-OH-BPA was identified as a trace metabolite, whose level was approximately 1 or 2 microM at 1 h in hepatocyte suspensions treated with 0.25 or 0.5 mM BPA, respectively. 3. In another experiment, 3-OH-BPA as well as BPA displaced competitively 17beta-oestradiol bound to the recombinant human oestrogen receptor alpha in a concentration dependent-manner: IC50 of diethylstilbestrol, BPA and 3-OH-BPA were approximately 2.5 x 10(-8), 10(-5) and 5 x 10(-5) M, respectively. Further, BPA and 3-OH-BPA at intermediate concentrations (10(-7) - 10(-6) M) caused proliferation of MCF-7 human breast cancer cells, whereas the effect of BPA was more potent than that of 3-OH-BPA. At higher concentrations, both BPA (> 10(-4)) and 3-OH-BPA (> 10(-5) M) were cytotoxic. 4. Based on the proliferative potency in MCF-7 cells and the IC50 for the competitive binding, the oestrogenic activity of 3-OH-BPA was less than that of BPA. These results indicate that BPA itself rather than its metabolite acts as a xeno-oestrogen and that 3-OH-BPA is cytotoxic, possibly acting via reactive semiquinone and/or quinone metabolites, rather than a xeno-oestrogenic mechanism, in MCF-7 cells.
Nakagawa
Y
Y
Department of Toxicology, Tokyo Metropolitan Research Laboratory of Public Health, Japan. yoshio@tokyo-eiken.go.jp
Suzuki
T
T
D000818:Animals; D001559:Benzhydryl Compounds; D001667:Binding, Competitive; D001943:Breast Neoplasms / Q000378:metabolism; D002455:Cell Division; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D004305:Dose-Response Relationship, Drug; D047628:Estrogen Receptor alpha; D004967:Estrogens / Q000378:metabolism; D004968:Estrogens, Non-Steroidal / Q000737:chemistry / Q000378:metabolism / Q000493:pharmacokinetics; D008401:Gas Chromatography-Mass Spectrometry; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D006900:Hydroxylation; D020128:Inhibitory Concentration 50; D008297:Male; D010636:Phenols / Q000737:chemistry* / Q000378:metabolism* / Q000493:pharmacokinetics; D011485:Protein Binding; D051381:Rats; D011916:Rats, Inbred F344; D011960:Receptors, Estrogen / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D013997:Time Factors; D014407:Tumor Cells, Cultured; D000098826:Bisphenol A Compounds
D001559:Benzhydryl Compounds; D047628:Estrogen Receptor alpha; D004967:Estrogens; D004968:Estrogens, Non-Steroidal; D010636:Phenols; D011960:Receptors, Estrogen; D011994:Recombinant Proteins; C006780:bisphenol A; D000098826:Bisphenol A Compounds