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Perchlorate, a chemical used to propel rockets and airbags, accumulates in the environment as a pollutant. A new study suggests that perchlorate can enter the water supply and might be more detrimental to human health than previously thought.

Perchlorate is transported from the blood into the thyroid gland by the sodium/iodide symporter, or NIS, which usually transports iodide and sodium. Iodide, the negatively charged form of iodine, is involved in producing thyroid hormone, which plays an important role in metabolism and development.

Previous research has demonstrated that sodium and iodide are co-transported by the NIS symporter in a two to one ratio in an energetically favorable reaction. The current study investigated the mechanism by which perchlorate affects the function of this transporter.

The authors of this cell culture study used radioactive iodine to determine how perchlorate influenced iodide transport across the NIS symporter. Using varying concentrations of perchlorate, they measured how much iodide was transported compared to sodium.

The authors found that perchlorate inhibited the transport of iodide in two ways. First, it competed with iodide for a receptor site. In a second mechanism, perchlorate altered the shape of the transporter by blocking one of the two sodium binding sites. Normally, iodide is co-transported into thyroid cells with two sodium ions, providing the energy required to drive iodide into the cell. When perchlorate blocks one of the sodium binding sites, a single sodium ion is transported with iodide in a less energetic reaction. This slower iodide transport means that less iodide reaches the thyroid gland leading to lower thyroid hormone production.

These findings suggest that perchlorate in the environment, even at low levels, can decrease the amount of iodide taken up by the thyroid gland. The resulting reduction in thyroid hormone production can be harmful to health, particularly to sensitive populations, including pregnant women, fetuses, and nursing infants.

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