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Thyroid hormone activity during pregnancy altered by endocrine-disrupting chemicals
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Thyroid activity at the cellular level can be disrupted by polychlorinated biphenyls that infiltrate the placenta during pregnancy, according to recent study findings published in The Journal of Clinical Endocrinology & Metabolism.
“As endocrine-disrupting chemicals, [polychlorinated biphenyls] interfere with the way the thyroid hormone functions, but they don’t actually change the amount of the hormone found in the body,” R. Thomas Zoeller, PhD, of the University of Massachusetts, said in a press release. “Although these effects are largely invisible in scientific studies that only judge thyroid activity by measuring hormone levels, they may be having a real impact on infants’ brain development.”
R. Thomas Zoeller
Zoeller and colleagues evaluated 164 pregnant women to determine the effect of low-dose chemical exposure on the fetus. The researchers examined the placenta for enzyme CYP1A1, which changes endocrine-disrupting chemicals into a form that can directly interfere with thyroid hormone receptors.
“Whatever is happening in the placenta likely reflects what is happening in the fetus,” Zoeller said. “To truly understand how endocrine-disrupting chemicals may be affecting pregnancies, the findings show we need to study not only hormone levels, but hormone activity at the cellular level.”
Overall, 132 placental samples had detectable CYP1A1 levels. According to the researchers, when higher amounts of CYP1A1 were present in the placenta, the tissue also had signs of thyroid disruption. Although the mother’s overall thyroid hormone levels did not change, those pregnancies had higher levels of two thyroid-regulated genes.
“In summary, we report a robust correlation in human placenta between CYP1A1 and mRNA levels of two [thyroid hormone]-regulated genes ([placental lactogen] and GH-V) and an even tighter correlation between these two [thyroid hormone]-regulated genes suggesting a common stimulus,” the researchers wrote. “Because CYP1A1 was not otherwise associated with [thyroid hormone] levels, these findings are consistent with the action of xenobiotic chemical (eg, [polychlorinated biphenyls]) being metabolized by CYP1A1 in these placental samples and acting in a manner that increases the [thyroid hormone] activity within the placenta. We put forward that the relationship between CYP1A1 expression and [thyroid hormone]-regulated genes may be an important biomarker of environmental impacts on [thyroid hormone] action that can be used in epidemiological studies.”
Disclosure: See the complete study for a full list of the researchers’ financial disclosures.
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