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In Vitro Screening for Chemical Inhibition of the Iodide Recycling Enzyme, Iodotyrosine Deiodinase
Citation:
Olker, J., J. Korte, J. Denny, J. Haselman, Philip Hartig, M. Cardon, M. Hornung, AND S. Degitz. In Vitro Screening for Chemical Inhibition of the Iodide Recycling Enzyme, Iodotyrosine Deiodinase. TOXICOLOGY IN VITRO. Elsevier Science Ltd, New York, NY, 71:105073, (2021). https://doi.org/10.1016/j.tiv.2020.105073
Impact/Purpose:
Iodotyrosine deiodinase (IYD) has an important role in vertebrate thyroid hormone homeostasis through catalyzing iodide recycling and promoting retention of iodide in thyroid follicular cells. This manuscript describes the development of an assay for inhibition of human IYD in a 96-well plate format and the application of this assay to screen a large set of chemicals. Included are the results from screening over 1,800 chemicals from the ToxCast phase 1_v2, phase 2, and e1k chemical libraries for inhibition of human IYD activity. Further concentration-response testing was completed for 154 of these chemicals to calculate IC50s and rank order potency. This assay can be used for future screening of large chemical libraries for inhibition of IYD activity. This work supports the U.S. EPA Endocrine Disruptor Screening Program’s need for higher-throughput screening assays to address additional molecular initiating events, beyond those currently in the ToxCast suite of assays, with the potential to disrupt normal thyroid function
Description:
Environmental contaminants can disrupt thyroid function through a variety of molecular mechanisms; however, some molecular targets have little known of their toxicological relevance, including susceptibility to chemical perturbation and resulting adverse organismal effects. The iodide recycling enzyme, iodotyrosine deiodinase (IYD), is one conserved potential molecular target that plays an essential role in maintaining adequate levels of free iodide for thyroid hormone synthesis. Thyroid disruption following in vivo IYD inhibition has been documented in mammals and was recently demonstrated in an amphibian model. These effects, along with human clinical data with failure of IYD due to genetic mutations, support the biological importance of IYD for proper thyroid function. Here we present development and application of a screening assay to assess susceptibility of IYD to chemical perturbation. With recombinant human IYD enzyme, a 96-well plate in vitro assay was developed to screen chemicals for inhibition of IYD enzyme activity. This assay was then used to screen the U.S. EPA ToxCast phase 1_v2, phase 2, and e1k chemical libraries. Of the over 1,800 unique chemicals tested, less than 200 (~11%) produced inhibition of IYD enzyme activity by 20% or greater at a single target concentration of 200 µM. Further testing of 154 chemicals in concentration-response was conducted to determine IC50 and rank-order potency; this set of chemicals included 84 that produced inhibition of 50% or greater, 20 that produced low to moderate inhibition (20-50%), and 50 non-inhibitors. These results greatly expand the number of compounds tested for inhibition of IYD and expands the coverage of molecular targets for which chemicals can be screened for potential thyroid disruption. Furthermore, the in vitro screening results presented here set the groundwork for development and evaluation of structure-activity relationships and aid in prioritizing chemicals for targeted in vivo testing to evaluate thyroid-related adverse outcomes.
URLs/Downloads:
DOI: In Vitro Screening for Chemical Inhibition of the Iodide Recycling Enzyme, Iodotyrosine Deiodinase