| Hydroxylated Metabolites of the Polybrominated Diphenyl Ether Mixture DE-71 Are Weak Estrogen Receptor-α Ligands Minerva Mercado-Feliciano1 and Robert M. Bigsby2 1Department of Pharmacology and Toxicology, and 2Department of Obstetrics and Gynecology, Indiana University School of Medicine, Indianapolis, Indiana, USA Abstract
Background: Polybrominated diphenyl ethers (PBDEs) are widely found in the environment and are suspected endocrine disruptors. We previously identified six hydroxylated metabolites of PBDE (OH-PBDEs) in treated mice. Objective: We tested the hypothesis that OH-PBDEs would interact with and alter activity of estrogen receptor-α (ER-α) . Methods: We tested estrogenicity using two assays: 3H-estradiol (3H-E2) displacement from recombinant ER-α, and induction of reporter gene (ERE-luciferase) in cultured cells. We incubated the PBDE mixture DE-71 with rat liver microsomes and tested the resultant metabolite mixture for estrogenic activity. We also determined relative estrogenic potential of individual hydroxylated PBDE congeners. Results: Reporter gene activity was increased by DE-71 that had been subjected to microsomal metabolism. DE-71 did not displace E2 from ER-α, but all six of the OH-PBDE metabolites did. para-Hydroxylated metabolites displayed a 10- to 30-fold higher affinity for ER-α compared with ortho-hydroxylated PBDEs, and one produced a maximal effect 30% higher than that produced by E2. Coadministration of E2 and DE-71, or certain of its metabolites, yielded reporter activity greater than either chemical alone. Two ortho-OH-PBDEs were antiestrogenic in the reporter assay. Conclusions: The observations—that the DE-71 mixture did not displace 3H-E2 from ER-α, while the hydroxylated metabolites did—suggest that the weak estrogenic effects of DE-71 are due to metabolic activation of individual congeners. However, the behavior of DE-71 and its metabolites, when co-administered with E2, suggest a secondary, undetermined mechanism from classical ER-α activation. Keywords: cytochrome P450, DE-71, endocrine disruptors, ERE-luciferase, estrogens, mice, ovariectomized, PBDEs, polybrominated diphenyl ethers. Environ Health Perspect 116:1315–1321 (2008) . doi:10.1289/ehp.11343 available via http://dx.doi.org/ [Online 27 May 2008]
Address correspondence to R.M. Bigsby, Department of Obstetrics and Gynecology, Indiana University School of Medicine, 975 W. Walnut St. (IB360) , Indianapolis, IN 46202-5121 USA. Telephone: (317) 274-8970. Fax: (317) 278-2884. E-mail: rbigsby@iupui.edu We thank G. Eckert for assistance with the statistical analysis and X. Qiu and R. Hites for the procurement of key reactants. This work was supported by grants ES013341 and ES014367 from the National Institute of Environmental Health Sciences. The authors declare they have no competing financial interests. Received 7 February 2008 ; accepted 23 May 2008.
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