Structure-Dependent Activity of Polybrominated Diphenyl Ethers and Their Hydroxylated Metabolites on Estrogen Related Receptor γ: in Vitro and in Silico Study

Estrogen-related receptor gamma (ERR gamma) is an orphan nuclear receptor having functional cross-talk with classical estrogen receptors. Here, we investigated whether ERR gamma is a potential target 8 of polybrominated diphenyl ethers (PBDEs) and their hydroxylated metabolites (OH-PBDEs). By using a fluorescence competitive binding method established in our laboratory, the binding potencies of 30 PBDEs/OH-PBDEs with ERR gamma were determined for the first time. All of the tested OH-PBDEs and some PBDEs bound to ERR gamma with K-d values ranging from 0.13-13.61 mu M. The OH-PBDEs showed much higher binding potency than their parent PBDEs. A quantitative structure-activity relationship (QSAR) model was developed to analyze the chemical binding potencies in relation to their structural and chemical characteristics. The QSAR model indicated that the molecular size, relative ratios of aromatic atoms, and hydrogen bond donors and acceptors were crucial factors for PBDEs/OH-PBDEs binding. By using a reporter gene assay, we found that most of the low-brominated PBDEs/OH-PBDEs exerted agonistic activity toward ERR gamma, while high-brominated PBDEs/OH-PBDEs had no effect on the basal ERR gamma activity. The docking results showed that the low-brominated PBDEs/OH-PBDEs tended to take an agonistic binding mode while the high-brominated ones tended to take an antagonistic binding mode. Overall, our results suggest ERR gamma to be a potential novel target for PBDEs/OH-PBDEs.