Characterization of Novel Ligands of ERα, Erβ, and PPARγ: The Case of Halogenated Bisphenol A and Their Conjugated Metabolites

The capability of the flame retardants tetrabromobisphenol A (TBBPA) and tetrachlorobisphenol A (TCBPA) to activate peroxysome proliferator-activated receptors (PPARs) alpha, beta, and gamma and estrogen receptors (ERs) alpha and beta has been recently investigated, but the activity of their biotransformation products and of their lower molecular weight analogues formed in the environment remains unexplored. The aim of this study was to investigate the relationship between the degree of halogenation of BPA analogues and their affinity and activity towards human PPAR gamma and ERs and to characterize active metabolites of major marketed halogenated bisphenols. The biological activity of all compounds was studied using reporter cell lines expressing these nuclear receptors (NRs). We used NR-based affinity columns to rapidly evaluate the binding affinity of halogenated bisphenols for PPAR gamma and ERs and to trap active metabolites of TBBPA and TCBPA formed in HepG2 cells. The agonistic potential of BPA analogs highly depends on their halogenation degree: the bulkier halogenated BPA analogs, the greater their capability to activate PPAR gamma. In addition, PPAR gamma-based affinity column, HGELN-PPAR gamma reporter cell line and crystallographic analysis clearly demonstrate that the sulfation pathway, usually considered as a detoxification process, leads for TBBPA and TCBPA, to the formation of sulfate conjugates which possess a residual PPAR gamma-binding activity. Our results highlight the effectiveness NR-based affinity columns to trap and characterize biologically active compounds from complex matrices. Polyhalogenated bisphenols, but also some of their metabolites, are potential disrupters of PPAR gamma activity.