title: In vitro fluorescence displacement investigation of thyroxine transport disruption by bisphenol A.
abstract: Bisphenol A (BPA) is a chemical with high production volume and wide applications in many industries. Although BPA is known as an endocrine disruptor, its toxic mechanisms have not been fully characterized. Due to its structural similarity to thyroid hormones thyroxine (T4) and triiodothyronine (T3), one possible mechanism of BPA toxicity is disruption of hormone transport by competitive binding with the transport proteins. In this study, the binding interactions of BPA, T4, and T3 with three thyroid hormone transport proteins, human serum albumin (HSA), transthyretin (TTR), and thyroxine-binding globulin (TBG) were investigated by fluorescence measurement. Using two site-specific fluorescence probes dansylamide and dansyl-L-proline, the binding constants of BPA with HSA at drug site I and site II were determined as 2.90 x 10(4) and 3.14 x 10(4) L/mol, respectively. By monitoring the intrinsic fluorescence of tryptophan, a binding constant of 4.70 x 10(3) L/mol was obtained. Similarly, by employing 8-anilino-1-naphthalenesulfonic acid as fluorescence probe, the binding affinity of BPA with TTR and TBG was measured to be 3.10 x 10(5) and 5.90 x 10(5) L/mol, respectively. In general, BPA showed lower binding affinity with the proteins than T3 did, and even lower affinity than T4. Using these binding constants, the amount of BPA which would bind to the transport proteins in human plasma was estimated. These results suggest that the concentrations of BPA commonly found in human plasma are probably not high enough to interfere with T4 transport.
authors.affiliation: State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. caojiercees@l126.com
authors.forename: Jie
authors.initials: J
authors.lastname: Cao
authors.forename: Liang-Hong
authors.initials: LH
authors.lastname: Guo
authors.forename: Bin
authors.initials: B
authors.lastname: Wan
authors.forename: Yin
authors.initials: Y
authors.lastname: Wei
mesh_terms: D001559:Benzhydryl Compounds; D001692:Biological Transport; D052244:Endocrine Disruptors / Q000097:blood / Q000633:toxicity*; D005456:Fluorescent Dyes / Q000378:metabolism*; D006801:Humans; D010636:Phenols / Q000097:blood / Q000633:toxicity*; D013974:Thyroxine / Q000378:metabolism*; D014284:Triiodothyronine / Q000378:metabolism; D000098826:Bisphenol A Compounds
chemical_list: D001559:Benzhydryl Compounds; D052244:Endocrine Disruptors; D005456:Fluorescent Dyes; D010636:Phenols; D013974:Thyroxine; D014284:Triiodothyronine; C006780:bisphenol A; D000098826:Bisphenol A Compounds