U.S. Environmental Protection Agency.
Office of Research and Development.
Toxicol Sci. 2019 Apr 1;168(2):430-442. doi: 10.1093/toxsci/kfy302.
Deiodinase enzymes play an essential role in converting thyroid hormones between active and inactive forms by deiodinating the pro-hormone thyroxine (T4) to the active hormone triiodothyronine (T3) and modifying T4 and T3 to inactive forms. Chemical inhibition of deiodinase activity has been identified as an important endpoint to include in screening chemicals for thyroid hormone disruption. To address the lack of data regarding chemicals that inhibit the deiodinase enzymes, we developed robust in vitro assays that utilized human deiodinase types 1, 2, and 3 and screened over 1800 unique chemicals from the U.S. EPA's ToxCast phase 1_v2, phase 2, and e1k libraries. Initial testing at a single concentration identified 411 putative deiodinase inhibitors that produced inhibition of 20% or greater in at least 1 of the 3 deiodinase assays, including chemicals that have not previously been shown to inhibit deiodinases. Of these, 228 chemicals produced enzyme inhibition of 50% or greater; these chemicals were further tested in concentration-response to determine relative potency. Comparisons across these deiodinase assays identified 81 chemicals that produced selective inhibition, with 50% inhibition or greater of only 1 of the deiodinases. This set of 3 deiodinase inhibition assays provides a significant contribution toward expanding the limited number of in vitro assays used to identify chemicals with the potential to interfere with thyroid hormone homeostasis. In addition, these results set the groundwork for development and evaluation of structure-activity relationships for deiodinase inhibition, and inform targeted selection of chemicals for further testing to identify adverse outcomes of deiodinase inhibition.
脱碘酶在将甲状腺激素从无活性形式转化为活性形式方面发挥着重要作用，通过将前体激素甲状腺素 (T4) 脱碘转化为活性激素三碘甲状腺原氨酸 (T3)，以及将 T4 和 T3 转化为无活性形式。化学抑制脱碘酶活性已被确定为筛选甲状腺激素干扰化学物质的一个重要终点。为了解决缺乏抑制脱碘酶的化学物质的数据问题，我们开发了强大的体外测定法，利用人类脱碘酶 1 型、2 型和 3 型，并筛选了美国环保署的 ToxCast 第 1_v2 期、第 2 期和 e1k 库中的 1800 多种独特化学物质。在单一浓度下的初步测试确定了 411 种假定的脱碘酶抑制剂，这些抑制剂在至少 1 种 3 种脱碘酶测定中产生了 20%或更高的抑制作用，其中包括以前未显示抑制脱碘酶的化学物质。其中，228 种化学物质产生了 50%或更高的酶抑制作用；这些化学物质进一步在浓度反应中进行测试，以确定相对效力。这些脱碘酶测定的比较确定了 81 种产生选择性抑制的化学物质，只有 1 种脱碘酶的抑制率达到 50%或更高。这组 3 种脱碘酶抑制测定为扩大用于识别具有干扰甲状腺激素动态平衡潜力的化学物质的有限数量的体外测定提供了重要贡献。此外，这些结果为脱碘酶抑制的构效关系的开发和评估奠定了基础，并为有针对性地选择化学物质进行进一步测试以识别脱碘酶抑制的不良后果提供了信息。
