Optimization of an ex vivo model to test the ability of chemicals to disrupt thyroid hormone synthesis.

Thyroid hormone (TH) synthesis and secretion can be perturbed by endocrine disrupting chemicals (EDCs). Traditional 2D cell culture models are useful for studying specific effects on enzymes and transporters involved in hormone synthesis; however, they lack the structural organization required for hormone production. In this study, we refine the conditions for an ex vivo rat thyroid gland model that supports robust thyroxine (T4) production and to evaluate the inhibition of T4 output using a model inhibitor. Thyroid glands from postnatal day 6 were excised and cultured for 7 or 9 days. We assessed the influence of medium composition (RPMI or StemPro™-34), culture method (hanging drop or filter inserts), thyroid stimulating hormone (TSH) concentration and iodide supplementation by measuring T4 secretion into the culture medium, evaluating tissue morphology and quantifying expression of key genes in TH synthesis machinery. Cultivating on filter inserts in StemPro™-34 media with iodide addition and 5 mU/mL TSH was the superior condition for enhanced T4 production while preserving tissue morphology. By challenging the ex vivo model with the antithyroid drug methimazole (MMI) T4 release was markedly reduced after 9 days of culture, and gene expression levels of Tpo and Slc5a5(NIS) were significantly upregulated. Together, these results demonstrate that the optimized ex vivo rat model supports sustained T4 production and is sensitive to a TH synthesis inhibitor, making it a promising model for studying the thyroid gland and the effects of thyroid-disrupting chemicals.