Something in the water: Pollutant may be more hazardous than previously thought

Date:
June 5, 2020
Source:
Johns Hopkins Medicine
Summary:
Perchlorate, a chemical compound used in rocket fuels and other
materials, may be a more hazardous pollutant than previously
thought, says a new study.



FULL STORY ========================================================================== Sometimes toxins, such as hazardous wastes and industrial byproducts, seep
into groundwater, the source of our drinking water. One such pollutant
is perchlorate, a chemical compound used in rocket fuels, fireworks, fertilizers and other materials. The compound is thought to contribute to health issues in humans such as hypothyroidism, the decreased production
of hormones from the thyroid gland, which can impact development.


==========================================================================
In a new study published May 25, 2020, in the journal Nature Structural
& Molecular Biology, researchers at Johns Hopkins Medicine, Vanderbilt University and the University of California, Irvine, report on the
mechanism that perchlorate uses to impact and damage normal functioning
of the thyroid gland.

The findings, they say, suggest that an acceptable safe concentration
of perchlorate in drinking water is 10 times less than previously thought.

The researchers focused on how perchlorate blocks a main route by which
iodide, the negatively charged form of the element iodine, enters thyroid cells. Iodide helps the thyroid make hormones that are essential to
the body's regulation of metabolism, temperature and other important
functions.

Thyroid cells control the incoming flow of iodide by using a protein
channel called the sodium/iodide symporter, also known as the Na+/I-
symporter or NIS.

Like other cellular transport systems, a "lock-and-key" approach is
used to move iodide, with NIS acting as the lock and sodium as the
key. Sodium fits into NIS at two binding sites to unlock the channel,
enabling iodide to pass through and accumulate inside a thyroid cell.

The team, led by L Mario Amzel, Ph.D., professor of biophysics and
biophysical chemistry at the Johns Hopkins University School of Medicine,
and Vanderbilt University researcher Nancy Carrasco, M.D., determined
that perchlorate blocks the channel by latching onto the NIS protein
and changing its shape. Less sodium binds to the misshaped channel,
thereby significantly lowering the amount of iodide that can be moved
inside thyroid cells.

The researchers studied how varying concentrations of perchlorate affects iodide transport by first growing thyroid cells that expressed the gene
SLC5A5, which encodes the instructions for building NIS channels. Next, perchlorate and radioactive iodine were placed outside of some of
the cells and just radioactive iodine outside the others. Finally,
the researchers tracked how much glowing iodide was allowed to enter
the cells in both groups. They found that there was much less iodide
inside thyroid cells treated with perchlorate than in untreated ones,
even at very low concentrations of the chemical.

In May 2020, the U.S. Environmental Protection Agency (EPA) ruled not
to place regulations on the amount of perchlorate that can be allowed
in drinking water.

The findings from the new study strongly suggest that this environmental pollutant is more hazardous than previously thought, raising serious
concern about the decision.

"We hope that these findings will prompt the EPA to change its mind,"
Amzel says.


========================================================================== Story Source: Materials provided by Johns_Hopkins_Medicine. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Alejandro Llorente-Esteban, Ri'an W. Manville, Andrea Reyna-Neyra,
Geoffrey W. Abbott, L. Mario Amzel, Nancy Carrasco. Allosteric
regulation of mammalian Na /I- symporter activity by
perchlorate. Nature Structural & Molecular Biology, 2020; DOI:
10.1038/s41594-020-0417-5 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200605121514.htm

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