Screening for endocrine disrupting chemicals inhibiting monocarboxylate 8 (MCT8) transporter facilitated thyroid hormone transport using a modified nonradioactive assay

Early neurodevelopmental processes are strictly dependent on spatial and temporally modulated of thyroid hormone (TH) availability and action. Thyroid hormone transmembrane transporters (THTMT) are critical for regulating the local concentrations of TH, namely thyroxine (T4) and 3,5,3′-tri-iodothyronine (T3), in the brain. Monocarboxylate transporter 8 (MCT8) is one of the most prominent THTMT. Genetically induced deficiencies in expression, function or localization of MCT8 are associated with irreversible and severe neurodevelopmental adversities. Due to the importance of MCT8 in brain development, studies addressing chemical interferences of MCT8 facilitated T3 uptake are a crucial step to identify TH system disrupting chemicals with this specific mode of action. Recently a non-radioactive in vitro assay has been developed to rapidly screen for endocrine disrupting chemicals (EDCs) acting upon MCT8 mediated transport. This study explored the use of an UV-light digestion step as an alternative for the original ammonium persulfate (APS) digestion step. The non-radioactive TH uptake assay, with the incorporated UV-light digestion step of TH, was then used to screen a set of 31 reference chemicals and environmentally relevant substances to detect inhibition of MCT8-depending T3 uptake. This alternative assay identified three novel MCT8 inhibitors: methylmercury, bisphenol-AF and bisphenol-Z and confirmed previously known MCT8 inhibitors.