Thyroid Disruption by Bisphenol S Analogues via Thyroid Hormone Receptor beta: in Vitro, in Vivo, and Molecular Dynamics Simulation Study

Bisphenol S (4-hydroxyphenyl sulfone, BPS) is increasingly used as a bisphenol A (BPA) alternative. The global usage of BPS and its analogues (BPSs) resulted in the frequent detection of their residues in multiple environmental media. We investigated their potential endocrine-disrupting effects toward thyroid hormone receptor (TR) beta. The molecular interaction of BPSs toward TR beta ligand binding domain (LBD) was probed by fluorescence spectroscopy and molecular dynamics (MD) simulations. BPSs caused the static fluorescence quenching of TR beta LBD. The 100 ns MD simulations revealed that the binding of BPSs caused significant changes in the distance between residue His435 at helix 11(H11) and residue Phe459 at H12 in comparison to no ligand-bound TRfi LBD, indicating relative repositioning of H12. The recombinant two-hybrid yeast assay showed that tetrabromobisphenol S (TBBPS) and tetrabromobisphenol A (TBBPA) have potent antagonistic activity toward TR beta, with an IC(10 )of 10.1 and 21.1 nM, respectively. BPS and BPA have the antagonistic activity with IC10 of 312 and 884 nM, respectively. BPSs significantly altered the expression level of mRNA of TR beta gene in zebrafish embryos. BPS and TBBPS at environmentally relevant concentrations have antagonistic activity toward TR beta, implying that BPSs are not safe BPA alternatives in many BPA-free products. Future health risk assessments for TR disruption and other adverse effects should focus more on the structure- activity relationship in the design of environmentally benign BPA alternatives.