Examination of the Estrogenicity of 2,4,6,2´,6´-Pentachlorobiphenyl (PCB 104), Its Hydroxylated metabolite 2,4,6,2´,6´-Pentachloro-4-Biphenylol (HO-PCB 104), and a Further Chlorinated Derivative, 2,4,6,2´,4´,6´-Hexachlorobiphenyl (PCB 155) Mark R. Fielden,
1
Ih Chen,
2
Brock Chittim,
3
Stephen H. Safe,
2
and Timothy R. Zacharewski
1
1
Department of Pharmacology and Toxicology, University of Western Ontario, London, Ontario, Canada
2
Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine, Texas A&M University, College Station, TX 77843 USA
3
Wellington Laboratories, Guelph, Ontario, Canada Abstract Several studies have reported that polychlorinated biphenyls (PCBs) exhibit estrogenic activity ; however, it is not clear if these responses are associated with the polychlorinated hydrocarbon or its hydroxylated metabolite. In order to further test this hypothesis, a battery of in vitro and in vivo assays were used to investigate the estrogenic and antiestrogenic activities of 2,4,6,2´,6´-pentachlorobiphenyl (PCB 104) , its para -hydroxylated derivative 2,4,6,2´,6´-pentachloro-4-biphenylol (HO-PCB 104) , and its para -chlorinated derivative 2,4,6,2´,4´,6´-hexachlorobiphenyl (PCB 155) . PCB 104 was found to 1) compete with tritiated 17ß-estradiol (E 2 ) for binding to the mouse uterine estrogen receptor (ER) ; 2) induce gene expression in MCF-7 human breast cancer cells transiently transfected with the Gal4-human ER chimeric construct (Gal4-HEGO) and the Gal4-regulated luciferase reporter gene (17m5-G-Luc) ; and 3) increase MCF-7 cell proliferation in a dose-dependent manner. HO-PCB 104 exhibited greater estrogenic activity than PCB 104 in the in vitro assays examined. However, gas chromatographic-mass spectrophotometric analysis of extracts prepared from MCF-7 cells incubated with PCB 104 failed to detect the presence of the expected major metabolite HO-PCB 104. The estrogenic activity of the para -chlorinated derivative, PCB 155, was minimal compared to PCB 104 and HO-PCB 104, but it did exhibit significant antiestrogenic activity following co-treatment with 1 nM E 2 . Co-treatment of PCB 104 with 1 nM E 2 had no effect on reporter gene expression compared to E 2 alone, while 10 µM HO-PCB 104 exhibited additivity with 1 nM E 2 . At a dose of 202 mg/kg, PCB 104 increased uterine wet weight in ovariectomized CD-1 mice and induced vaginal epithelial cell cornification at 202, 16, and 1.7 mg/kg in a dose-dependent manner. These studies demonstrate that in addition to the hydroxylated metabolites, selected parent PCB congeners may also exhibit estrogenic and antiestrogenic activities. Key words : environmental estrogen, estrogenicity, estrogen receptor, hydroxylation, in vitro , in vivo , polychlorinated biphenyls. Environ Health Perspect 105:1238-1248 (1997) . Address correspondence to T. Zacharewski, Department of Biochemistry, Michigan State University, Biochemistry Building, Wilson Road, East Lansing, MI 48824-1319 USA. This work was supported by a NSERC Strategic Grant, the National Institutes of Health (ES04917) , and funds from the Canadian Breast Cancer Foundation. T.R.Z. is supported by a PMAC-HRF/MRC Research Career Award in Medicine. M.R.F. was awarded a PMAC-HRF/MRC Summer Research Studentship. Received 28 April 1997 ; accepted 11 July 1997. The full version of this article is available for free in HTML format. |