Estrogenicity of halogenated bisphenol A: in vitro and in silico investigations

Abstract

The binding interactions of bisphenol A (BPA) and its halogenated derivatives (halogenated BPAs) to human estrogen receptor α ligand binding domain (hERα-LBD) was investigated using a combined in vitro and in silico approach. First, the recombinant hERα-LBD was prepared as a soluble protein in Escherichia coli BL21(DE3)pLysS. A native fluorescent phytoestrogen, coumestrol, was employed as tracer for the fluorescence polarization assay. The results of the in vitro binding assay showed that bisphenol compounds could bind to hERα-LBD as the affinity ligands. All the tested halogenated BPAs exhibited weaker receptor binding than BPA, which might be explained by the steric effect of substituents. Molecular docking studies elucidated that the halogenated BPAs adopted different conformations in the flexible hydrophobic ligand binding pocket (LBP), which is mainly dependent on their distinct halogenation patterns. The compounds with halogen substituents on the phenolic rings and on the bridging alkyl moiety acted as agonists and antagonists for hERα, respectively. Interestingly, all the compounds in the agonist conformation of hERα formed a hydrogen bond with His524, while the compounds in the antagonist conformation formed a hydrogen bond with Thr347. These docking results suggested a pivotal role of His524/Thr347 in maintaining the hERα structure in the biologically active agonist/antagonist conformation. Comparison of the calculated binding energies vs. experimental binding affinities yielded a good correlation, which might be applicable for the structure-based design of novel bisphenol compounds with reduced toxicities and for environmental risk assessment. In addition, based on hERα-LBD as a recognition element, the proposed fluorescence polarization assay may offer an alternative to chromatographic techniques for the multi-residue determination of bisphenol compounds.

Molecular Image-Based Prediction Models of Nuclear Receptor Agonists and Antagonists Using the DeepSnap-Deep Learning Approach with the Tox21 10K Library

“…There are several conflicting reports regarding the in vitro receptor-mediated activity. Chemicals such as bisphenol A (BSA) and its halogenated analogs (tetrabromo-BSA and tetrachloro-BSA) show weak TR antagonist activity but have a potential agonist-like effect at lower concentrations [60,61]. Thus, competitive agonists and antagonists of the steroids have long been known [62][63][64].…”

Application of Various Molecular Modelling Methods in the Study of Estrogens and Xenoestrogens

“…All studies showed that a hydrogen bond with His524 for an agonist and with Thr347 for an antagonist was created, exactly as in the case of estradiol and 4-OH-tamoxifen, respectively [187,188]. What is more, just as for estradiol, the stability of helix H12 is crucial in halogenated BPAs-ER complexes [188,189]. The in silico results have been confirmed by experimentally measured affinities.…”

“…A separate set of studies investigated BPAs with halogen substituents on the phenolic rings. All studies showed that a hydrogen bond with His524 for an agonist and with Thr347 for an antagonist was created, exactly as in the case of estradiol and 4-OH-tamoxifen, respectively [ 187 , 188 ]. What is more, just as for estradiol, the stability of helix H12 is crucial in halogenated BPAs–ER complexes [ 188 , 189 ].…”

Protecting Group-Controlled Remote Regioselective Electrophilic Aromatic Halogenation Reactions

“…We also studied iodination of bis-phenols, where the two phenolic rings are not directly attached to each other. [39][40][41][42] This is an important class of compounds, especially in the polymer arena (e.g. bis-phenol A (BPA)).…”