Effects of hyperthyroidism on the cellular antioxidant system and the expression of DNMT-1 in peripheral blood mononuclear cells of patients with Graves' disease

SABAN M.; CURRIA M.; KLECHA A.; CREMASCHI G.; COSTILLA M.; DI CUGNEO M.; BARREIRO ARCOS M.L.

Rosario, Santa Fé

Congreso; Reunión Anual de la Sociedad Argentina de Fisiología; 2019

Sociedad Argentina de Fisiología

Introduction: Graves' disease is the most frequent cause of hyperthyroidism. It is characterized by the presence of autoantibodies anti-TSH receptor, which causes overproduction of T3 and T4. Although its etiology has not been fully clarified, it is due to the complex interaction between genetic and environmental factors. Objectives: Analyze the effect of oxidative stress induced by the hyperthyroid state, on the cellular antioxidant system and the expression of DNMT-1, an enzyme that could regulate the transcription of genes involved in autoimmune processes. Methodology: Peripheral blood mononuclear cells (PBMC) of euthyroid subjects, patients with Graves' disease recently diagnosed or treated with methimazole were purified by Ficoll-Hypaque. Serum levels of T3, T4 and autoantibodies were quantified by immunoassays. Reactive oxygen species (ROS) and apoptosis were evaluated by cytometry. Nuclear morphology was analyzed by microscopy. Catalase activity was determined by spectrophotometry and glutathione concentration was quantified by HPLC/MS. The genomic and protein expression of catalase and DNMT-1 was determined by PCR and western blot. Results: PBMC of patients with Graves' disease had increased levels of ROS that were reverted to control by preincubation with N-acetyl cysteine (NAC, 2 mM). ROS levels in patients treated with methimazole were similar to the euthyroid subjects. Only the PBMC of patients with Graves' disease had a significant increase in the expression and activity of catalase and decreased levels of GSH. They also showed a higher genomic and protein expression of DNMT-1, which decreased in the presence of NAC. PBMC of patients treated with methimazole expressed levels of DNMT-1 similar to controls. Cellular apoptosis was similar in the three study groups. Conclusions: The oxidative stress regulates the antioxidant system, increasing the expression and activity of catalase and decreasing the content of GSH. ROS detoxification protects cells from apoptosis. On the other hand, ROS induces the expression of DNMT-1, enzyme responsible for DNA methylation, silencing immunoregulatory genes and contributing to the pathogenesis of Graves' disease.