Endocrine Abstracts

Background and objectives: Recent studies have identified pleiotropic roles for the Nrf2 antioxidant response in the physiology of the thyroid gland and in the pathophysiology of various thyroid diseases. Various natural compounds have antioxidant properties and/or thyroidal effects, but it is not well known whether and how the two are related. The aim of the present study was to characterize in a systematic manner the thyroidal and antioxidant effects of natural compounds.

Methods: We performed a low-throughput manual chemical screen of >400 natural compounds in thyroid follicular cell lines stably transfected with reporter constructs. We used the rat PCCL3 cell line in its wild-type form as well as a PCCL3 Nrf2-knockout clone generated via CRISPR/Cas9 mutagenesis. The following read-outs were assessed: Nrf2 transcriptional activity (ARE-luciferase); Nrf1 protein stabilization (Nrf1-delta-luciferase); cell viability (CellTiter-Glo); reporter gene expression of the thyroid hormone precursor thyroglobulin (TG-luciferase); reporter gene expression of the sodium-iodide symporter (NIS-luciferase); and iodine uptake by the cells. For compounds showing activity in the respective assays, the mRNA and protein levels of NIS, TG, and the antioxidant gene Nqo1 were assayed by qRT-PCR and Western blot, respectively.

Results: Among other findings, we observed that certain compounds paradoxically induced higher transcriptional activation of the ARE in Nrf2-knockout cells than in wild-type cells. Further studies showed that these compounds were potent activators of Nrf1, which is highly expressed in the thyroid in vivo. As a further example, the flavonoid compound bavachin was found to increase iodine uptake by the cells in an Nrf2-independent manner. Importantly, bavachin was also able to reverse the decrease in iodine uptake that is induced by exposure to lithium, a drug used in the treatment of bipolar disorder.

Conclusions: In conclusion, screening of natural compounds in thyroid cell lines can yield relevant hits with potential therapeutic relevance in thyroid diseases.