Sexual Dimorphism of NADPH Oxidase/H2O2 System in Rat Thyroid Cells; Effect of Exogenous 17β-Estradiol

It has long been observed that females are more susceptible to thyroid diseases than males. Epidemiological and experimental data show that actions of hormonal factorsespecially estrogensmay explain such disparity. However, the exact cause and mechanisms of this sexual dimorphism remain so far unknown. Therefore, we aimed at evaluating the effect of 17-estradiol on the redox balance in thyroids of male and female rats. Expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, i.e., dual oxidase 1 (DUOX1), dual oxidase 2 (DUOX2) and NADPH oxidase 4 (NOX4), and hydrogen peroxide (H2O2) levels were evaluated in the primary cell cultures derived from thyroid glands of adult male or female Wistar rats. The measurement was made before and after treatment with 17-estradiol alone or with addition of one of its receptor antagonists. We found that under basal conditions female thyroid cells are exposed to higher concentrations of H2O2, most likely due to NOX/DUOX enzymes activity. Additionally, exogenous 17-estradiol stimulated NOX/DUOX expression as well as H2O2 production, and this effect was mainly mediated through ER. In conclusion, oxidative processes may constitute mechanisms responsible for sexual dimorphism of thyroid diseases. Exogenous 17-estradiol may play a crucial pathogenic role in thyroid diseases via oxidative mechanisms, however without any gender differences.