Development of a non-radioactive screening assay to detect chemicals disrupting the human sodium iodide symporter activity
- DOI
- Language of the publication
- English
- Date
- 2019-02-07
- Type
- Article
- Author(s)
- Dong, Hongyan
- Atlas, Ella
- Wade, Michael G.
- Publisher
- Elsevier
Abstract
Adequate concentration of iodide ions within thyroid epithelial cells, which is mediated by the sodium iodide symporter (NIS), is essential for proper thyroid hormone synthesis. Inhibition of NIS activity represents a potential mechanism by which goitrogens/toxicants can disrupt thyroid hormone physiology. It is necessary to develop a rapid, simple, inexpensive and sensitive screening assay to identify chemicals affecting NIS function. The current study compares the sensitivities of non-radioactive Sandell-Kolthoff (SK) reaction and radioactive iodide uptake (RAIU) in a previously described NIS assay. The EPAhNIS cell line (HEK293T stably transfected to over-express the human NIS) was tested with the reference NIS inhibitor (sodium perchlorate) across multiple log concentration range. The results from SK reaction in EPAhNIS cells showed similar performance to published RAIU results from the same cell line, in terms of assay screening coefficient (Z′) and variability (CV). Results from the reference chemicals tested in EPAhNIS cells revealed that SK reaction yielded IC50 and selectivity scores consistent with those observed for RAIU. However, RAIU seems marginally more sensitive than the SK reaction, as RAIU consistently detected weaker NIS inhibitors among the test chemicals. We developed a second hNIS assay based on the MCF-7 cell line. Applying reference anions and chemicals to MCF7hNIS cells, we found that in comparison with results from EPAhNIS cells, the SK reaction with MCF7hNIS: 1) yielded similar Z′ and CV; 2) had similar IC50 and selectivity scores for reference chemicals; 3) identified more NIS inhibitors among reference chemicals than SK reaction, but less than the RAIU assay in EPAhNIS cells. In conclusion, the SK reaction can be used with both EPAhNIS and MCF7hNIS cells to measure iodide uptake and identify NIS inhibitors, except for those presenting an extremely weak potency.
Plain language summary
As a part of its mandate to assess and manage the risks to the health of Canadians due to exposures to environmental chemicals, Health Canada contributed to an international review, through the Organisation for Economic Cooperation and Development (OECD), of testing approaches needed to identify chemicals that interfere with thyroid hormones (TH) to cause health problems. One of the important needs identified through this exercise was for a test that can identify chemicals that inhibit iodide uptake into the thyroid gland cells (thyrocytes) where iodide is incorporated to produce thyroid hormones. Sodium Iodide Symporter (NIS) is the important enzyme regulating iodide uptake in thyrocytes. In this method development work, Health Canada scientists used two cell lines in which the human NIS gene was inserted and found they were able to measure the amount of iodide uptake into these cells. By testing a broad range of chemicals that have previously known to be NIS active or inactive inhibitors, these assays are demonstrated to be highly specific at detecting iodide inhibitors. These new assays can contribute to methods to screen chemicals and provide scientific support for assessments of the health impacts of chemicals.
Subject
- Health,
- Health and safety