A review on disruption of thyroid hormones caused by polybrominated diphenyl ethers and associated mechanism
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Abstract
Polybrominated diphenyl ethers (PBDEs) have been widely used as additive flame retardants in electronic devices, plastic products, building materials, etc. However, a large amount of studies have demonstrated that PBDEs are a kind of persistent organic pollutants. Due to the similarity of chemical structure between PBDEs and thyroid hormones (THs), many researchers have focused on THs disruption caused by PBDEs. We summarized the epidemiological studies on the interference of PBDEs on human THs levels, and found that exposure to PBDEs was very likely to interfere with the homeostasis of THs, but the results differed, which might be closely related to their interference mechanisms. Therefore, we analyzed the possible mechanisms of PBDEs and their major metabolites on THs disruptions from four aspects:THs synthesis and secretion, transportation, activation and metabolism, and the hypothalamus-pituitary-thyroid hormone axis. PBDEs and their metabolites can interfere with the synthesis and secretion of THs. By virtue of their similar structure to THs, PBDEs and their metabolites can competitively bind to THs transporters, feedback regulate the activity and expression levels of deiodinase (Dio) through various mechanisms, and bind to nuclear receptors in order to accelerate the metabolism of THs. In addition, PBDEs exposure can also regulate thyroid stimulating hormone (TSH), thyroid hormone receptor (TR), and even thyrotropin releasing hormone (TRH) levels. Facing the changes of THs level caused by various factors, the body initiates a feedback protection mechanism to keep the level of biologically active THs stable.
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