Metabolic Activation of Bisphenol A by Rat Liver S9 Fraction

Abstract

Bisphenol A (BPA) is a well-known endocrine-disrupting chemical found in the environment. To assess the metabolic modulation of estrogenic activity of BPA after ingestion, we investigated whether the incubation of BPA with rat liver S9 fraction results in metabolic activation or inactivation of estrogenic activity using a recombinant yeast expressing human estrogen receptor and MCF-7 transfected firefly luciferase plasmid for a reporter assay. When 0.1 mM BPA was incubated with rat liver S9 for 1 h, the estrogenic activity was increased about two to five times compared with that of the control, in which the S9 was inactivated prior to incubation. This metabolic activation was inhibited by SKF 525-A, an inhibitor of cytochrome P450. With increasing incubation time, the estrogenic activity increased time-dependently. Interestingly, however, the metabolic activation did not proceed with either microsomes or cytosol alone and was restored by a recombination of both fractions. The active metabolite was eluted at later retention time than that of BPA on HPLC with a reversed-phase column. Bisphenol B and methoxychlor were also activated by incubation with rat liver S9, whereas 4-tert-octylphenol and 4-nonylphenol, as well as 17beta-estradiol, were metabolically inactivated. The present results clearly indicate that BPA is metabolically activated in terms of estrogenicity under the conditions existing only with combined rat liver microsomes and cytosol.

Using a customized DNA microarray for expression profiling of the estrogen-responsive genes to evaluate estrogen activity among natural estrogens and industrial chemicals.

“…These metabolites have more estrogen activity than methoxychlor. Such a metabolic activation of estrogenic chemicals was also reported for bisphenol A and bisphenol B (Yoshihara et al 2001), 2-nitrofluorene , and styrenes . Metabolic inactivation or inactivation by modification could also occur in many chemicals.…”

Liver tumor promoting effect of orphenadrine in rats and its possible mechanism of action including CAR activation and oxidative stress

“…Microsomal fractions were obtained according to the method of Yoshihara et al (2001). Briefly, liver samples from six rats in each group were homogenized with three volumes of ice-cold 1.15% KCl-0.05 mol/l TrisHCl buffer (pH 7.4) using TissueLyser II (Qiagen).…”

Enhanced liver tumor promotion activity in rats subjected to combined administration of phenobarbital and orphenadrine

“…Microsomal fractions were obtained according to the method of Yoshihara et al (2001). Briefly, liver samples from six rats in each group were homogenized with three volumes of ice-cold 1.15% KCl-0.05 M Tris-HCl buffer (pH 7.4) using TissueLyser II (Qiagen).…”