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.
We tested the hypothesis that OH-PBDEs would interact with and alter activity of estrogen receptor-α (ER-α).
We tested estrogenicity using two assays: 3H-estradiol ( 3H-E 2) 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.
Reporter gene activity was increased by DE-71 that had been subjected to microsomal metabolism. DE-71 did not displace E 2 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 E 2. Coadministration of E 2 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.
The observations—that the DE-71 mixture did not displace 3H-E 2 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 E 2, suggest a secondary, undetermined mechanism from classical ER-α activation.