Antagonism of Metal Pyridinethiones and Their Degradation Products toward Estrogen Receptor : A Combination of In Vitro, In Vivo, and In Silico Approaches

Metal pyrithiones (MePTs) are used as emerging antifouling biocides. Our recent studies have shown that one of the degradation products of MePTs, 2,2 '-dithio-bis-pyridine, is a potential endocrine-disrupting chemical. However, the direct target remains unknown. This study was conducted to determine whether MePTs and their degradation products interact with estrogen receptor alpha (ER alpha). Electrochemical biosensors showed that MePTs and their degradation products bound to ER alpha. A two-hybrid yeast assay and E-screen indicated that co-exposure of MePTs and their degradation products to 17 beta-estradiol (E2) significantly inhibited E2-induced beta-galactosidase activities and MCF-7 cell proliferation, with 30% inhibition concentrations ranging from 6.39 x 10(-9) to 4.56 x 10(-5), suggesting their anti-estrogenic activities in vitro. Among the eight compounds, 2-mercaptopyridine N-oxide (HPT) showed the most potent antagonism. Confocal microscope observation indicated that 10(-7) mol/L HPT exposure caused an ectopic location of a partial primordial germ cell in EGFP-nanos-3 ' UTR transgenic line zebrafish embryos, and an enzyme-linked immunosorbent assay showed that 10(-7) mol/L HPT exposure downregulated hepatic vitellogenin protein levels in wild-type adult female zebrafish, indicating its ER alpha antagonism at an environmentally relevant concentration in vivo. Molecular docking showed that Glu353 participated in the hydrogen bond interaction of HPT with ER alpha. This study demonstrates that MePTs and their degradation products act as antagonists toward ER alpha.