Application of a nonradioactive assay for high throughput screening for inhibition of thyroid hormone uptake via the transmembrane transporter MCT8

Thyroid hormones (THs) play important roles in almost all physiological processes. High-throughput screening (HTS) assays are needed to screen the vast numbers of chemicals for their potential to disrupt TH signalling. The current work has confirmed the ability of a rapid assay to identify substances inhibiting TH uptake through monocarboxylate transporter (MCT) 8. Perturbation of MCT8 function results in significant developmental impairments, suggesting substances inhibiting MCT8 may be important developmental toxicants. We examined the accuracy and consistency of a recently described method to identify TH inhibitors via MCT8, using MDCK cells overexpressing human MCT8 gene. We confirmed the method detected T3 uptake in a concentration/time-dependent manner, and this effect was blocked by substances previous reported to block TH uptake via MCT8. Assay performance was assessed extensively and the system was found to have high signal dynamic range and Z' factor. The assay was also validated with a diverse set of training chemicals. This assay was then used to screen chemicals suspected to disrupt TH signalling. Other than bisphenol A (BPA), all substances tested were negative. Our results suggest that this assay could be part of a battery of screening assays to predict the potential thyroid disrupting activity of chemicals.