A modified nonradioactive screening assay for MCT8 disruptors based on UV and ammonium persulfate-mediated iodide release from thyroid hormone.

The monocarboxylate transporter 8 (MCT8) transports thyroid hormone (TH) across cell membranes, and plays a critical role in transporting TH across the blood brain barrier. The importance of MCT8 for TH regulation demonstrated by the congenital neurological and physical impairment that occurs in individuals with a nonfunctional MCT8 protein. Chemical inhibition of MCT8 may disrupt thyroid signaling. Previous described assay of MCT8-mediated triiodothyronine (T3) uptake relied on iodide release following high-temperature ammonium persulfate (APS) digestion which may be compromised by evaporation and degradation of plasticware. We evaluated a UV-assisted APS digestion as an alternative to heating. Using a commercial UV lamp, digestion efficiency and assay performance were compared for UV or heat-mediated MCT8 assay. UV for 40 min was comparable to heat digestion and yielded equivalent Z' factors, IC₅₀ values, and dose-response curves. Longer exposure did not improve assay performance but caused plate discoloration. The assay using UV digestion for 40 min produced results comparable to those obtained with heat digestion for known MCT8 inhibitors bromosulfophthalein (BSP) and silychristin (SC). Additional reference chemicals showed consistent results between UV digestion for 40 min and heating at 90 °C for 60 min. In summary, UV-assisted APS digestion is a reliable, faster, and lower-temperature alternative to heat digestion for screening of chemicals that may disrupt MCT8-mediated TH transport.