Factors contributing to the resistance of the thyrocyte to hydrogen peroxide

Abstract

We studied the mechanism that may explain the relative resistance of thyrocytes to H₂O₂ compared to other cell types. Ability to degrade H₂O₂, glutathione peroxidase (GPx) activity, heme oxygenase-1 (HO-1) expression, cell survival and capacity to repair DNA damage after H₂O₂ exposure or irradiation were measured in human thyrocytes in primary culture and compared to the values obtained in human T-cells and different cell lines. Compared to other cell types, thyrocytes presented a low mortality rate after H₂O₂ exposure, rapidly degraded extracellular H₂O₂ and presented a high basal seleno-dependent GPx activity. Only in thyrocytes, H₂O₂ up-regulated GPx activity and expression of HO-1 mRNA. These effects were not reproduced by irradiation. DNA damage caused by H₂O₂ was more slowly repaired than that caused by irradiation and not repaired at all in T-cells. Our study demonstrates that the thyrocyte has specific protective mechanisms against H₂O₂ and its mutagenic effects.

Keywords: Antioxidant enzymes; DNA damage; Hydrogen peroxide; Thyroid.