Hydroxylated benzo[a]pyrene metabolites are responsible for in vitro estrogen receptor-mediated gene expression induced by benzo[a]pyrene, but do not elicit uterotrophic effects in vivo

The estrogenic activities of benzo[a]pyrene (B[a]P) and 10 metabolites (1, 3-, 7-, and 9-hydroxy-B[a]P; 4,5-, 7,8-, and 9,10-dihydrodihydroxy-B[a]P; and 1,6-, 3,6-, and 6,12-B[a]P-dione) were investigated, in vitro, B[a]P did not displace tritiated 17 beta -estradiol ([H-3]E2) from either a bacterially expressed fusion protein consisting of glutathione-S-transferase linked to the D, E, and F domains of human ER alpha (GST-hER alpha def), or from full-length human ER beta (hER beta) at concentrations as high as 60 muM. However, 10 muM B[a]P demonstrated partial agonist activity in human Ga14-ER alpha def and mouse Ga14-ER beta def reporter gene assays in transiently transfected MCF-7 cells, relative to 10 nM E2. 1-, 3-, 7-, and 9-hydroxy-B[a]P were found to bind to both receptor isoforms, each showing a higher affinity for the P isoform. At 10 muM the four monohydroxylated metabolites were able to induce Ga14-hER alpha def- and Ga14-mER beta def-mediated reporter gene expression to levels 20-100% of that caused by 10 nM E2, suggesting that these metabolites, and not the parent compound, induced reporter gene expression following B[a]P treatment of transiently transfected MCF-7 cells. In addition, the effect of B[a]P on two estrogen-inducible end points, uterine weight and lactoferrin mRNA levels, was determined in ovariectomized DBA/2 and C57BL/6 mice. Neither orally administered B[a]P at doses as high as 10 mg/kg body weight nor subcutaneously injected 3- or 9-hydroxy-B[a]P at doses as high as 20 mg/kg induced effects on uterine wet weight or uterine lactoferrin mRNA levels in either strain. These data suggest that B[a]P metabolites that are estrogenic at high concentrations in vitro do not induce estrogenic effects in the mouse uterus.