INTRODUÇÃO AOS DISRUPTORES ENDÓCRINOS (DEs)
Inhibition of Type 1 Iodothyronine Deiodinase by Bisphenol A
Resumo: Plastics are ubiquitously present in our daily life and some components of plastics are endocrine-disrupting chemicals, such as bisphenol A and phthalates. Herein, we aimed to evaluate the effect of plastic endocrine disruptors on type 1 and type 2 deiodinase activities, enzymes responsible for the conversion of the pro-hormone T4 into the biologically active thyroid hormone T3, both in vitro and in vivo. Initially, we incubated rat liver type 1 deiodinase and brown adipose tissue type 2 deiodinase samples with 0.5 mM of the plasticizers, and the deiodinase activity was measured. Among them, only BPA was capable to inhibit both type 1 and type 2 deiodinases. Then, adult male Wistar rats were treated orally with bisphenol A (40 mg/kg b.w.) for 15 days and hepatic type 1 deiodinase and brown adipose tissue type 2 deiodinase activities and serum thyroid hormone concentrations were measured. In vivo bisphenol A treatment significantly reduced hepatic type 1 deiodinase activity but did not affect brown adipose tissue type 2 deiodinase activity. Serum T4 levels were higher in bisphenol A group, while T3 remained unchanged. T3/T4 ratio was decreased in rats treated with bisphenol A, reinforcing the idea that peripheral metabolism of thyroid hormone was affected by bisphenol A exposure. Therefore, our results suggest that bisphenol A can affect the metabolism of thyroid hormone thus disrupting thyroid signaling.
Bisphenol A increases hydrogen peroxide generation by thyrocytes both in vivo and in vitro
Resumo: Bisphenol A (BPA) is the most common monomer in polycarbonate plastics and an endocrine disruptor. Though some effects of BPA on thyroid hormone (TH) synthesis and action have been described, the impact of this compound on thyroid H2O2 generation remains elusive. H2O2 is a reactive oxygen species (ROS) which could have deleterious effect on thyrocytes if in excess. Therefore, herein we aimed at evaluating the effect of BPA exposition both in vivo and in vitro on H2O2 generation in thyrocytes, besides other essential steps for TH synthesis. Female Wistar rats were treated with vehicle (control) or BPA 40 mg/Kg BW for 15 days, by gavage. We then evaluated thyroid iodide uptake, mediated by sodium-iodide symporter (NIS), thyroperoxidase (TPO) and dual oxidase (DOUX) activities (H2O2 generation). Hydrogen peroxide generation was increased, while iodide uptake and TPO activity were reduced by BPA exposition. We have also incubated the rat thyroid cell line PCCL3 with 10-9 M BPA and evaluated Nis and Duox mRNA levels, besides H2O2 generation. Similar to that found in vivo, BPA treatment also led to increased H2O2 generation in PCCL3. Nis mRNA levels were reduced and Duox2 mRNA levels were increased in BPA-exposed cells. To evaluate the importance of oxidative stress on BPA-induced Nis reduction, PCCL3 was treated with BPA in association to n-acetylcysteine, an antioxidant, which reversed the effect of BPA on Nis. Our data suggest that BPA increases ROS production in thyrocytes, what could lead to oxidative damage thus possibly predisposing to thyroid disease.
Publicado: maio de 2020.
