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 17beta-estradiol ([3H]E2) from either a bacterially expressed fusion protein consisting of glutathione-S:-transferase linked to the D, E, and F domains of human ERalpha (GST-hERalphadef), or from full-length human ERbeta (hERbeta) at concentrations as high as 60 microM. However, 10 microM B[a]P demonstrated partial agonist activity in human Gal4-ERalphadef and mouse Gal4-ERbetadef 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 beta isoform. At 10 microM the four monohydroxylated metabolites were able to induce Gal4-hERalphadef- and Gal4-mERbetadef-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.
Fertuck
K C
KC
Department of Biochemistry and Molecular Biology, Michigan State University, Lansing, Michigan 48824, USA.
Matthews
J B
JB
Zacharewski
T R
TR
D000818:Animals; D001564:Benzo(a)pyrene / Q000378:metabolism / Q000633:toxicity*; D001943:Breast Neoplasms; D017931:DNA Primers / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D004958:Estradiol / Q000378:metabolism / Q000494:pharmacology; D004968:Estrogens, Non-Steroidal / Q000378:metabolism / Q000633:toxicity*; D005260:Female; D015870:Gene Expression / Q000187:drug effects*; D017930:Genes, Reporter / Q000187:drug effects; D006801:Humans; D007781:Lactoferrin / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D009929:Organ Size / Q000187:drug effects; D012333:RNA, Messenger / Q000378:metabolism; D011960:Receptors, Estrogen / Q000235:genetics* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000187:drug effects; D014599:Uterus / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology
D017931:DNA Primers; D004968:Estrogens, Non-Steroidal; D012333:RNA, Messenger; D011960:Receptors, Estrogen; D001564:Benzo(a)pyrene; D004958:Estradiol; D007781:Lactoferrin