Possible mechanisms of toxic effects of per-and polyfluoroalkyl substances exposure on thyroid

Per- and polyfluoroalkyl substances (PFASs) are persistent organic pollutants (POPs). They are widely used in food packaging, tableware coating, stain resistant furniture, and other industrial production. Humans are exposed to PFASs on a daily basis through drinking water and intaking food, use of consumer products containing PFASs, and occupational exposure during the production of PFASs or related products. A growing body of toxicological studies has shown that PFASs exposure disrupts the thyroid hormone (TH) system and causes hypothyroidism, which is further supported by population epidemiological studies. PFASs can damage thyroid follicular cells and sodium/iodine transporters to impair iodine uptake by thyroid cells. They interfere with the synthesis of thyroglobulin, reduce the activity of thyroid peroxidase, and affect the synthesis and secretion of TH. They interfere with TH transportation and biological effects via TH competitive binding thyroid transporter or thyroid hormone receptor. They suppress TH signaling pathway and deiodinase activity, interfere negative feedback mechanism, and accelerate TH metabolism and excretion. The processes of TH synthesis, transport, degradation, and biological effects may all be affected by PFASs exposure. This paper described possible toxic mechanisms of PFASs on the thyroid from four aspects: TH biosynthesis, transport, action on target cells, and metabolic excretion stage, and summarized the thyroid toxicity associated with PFASs exposure.