Avaliação do estresse oxidativo em pacientes com tireotoxicose subclínica

Abstract

Thyroid hormones (TH) increase both basal and adaptive metabolism, and the production of Reactive Oxygen Species (ROS). Unbalance between excessive production of ROS and antioxidant defenses causes oxidative stress (OS), which may lead to cell dysfunctions. Whether minimal TH increase, as observed in subclinical thyrotoxicosis (ScT), increases OS is unknown. The aim of our study was to evaluate the impact of exogenous ScT on OS. Twenty-one women with hypothyroidism, aged 44±10 years, were evaluated in ScT and in euthyrodism (EU) after adjustment of L-thyroxine dosis by measuring serum TH (free thyroxin - FT4 and total T3 - TT3) and thyroid stimulant hormone (TSH) levels, and hematological and biochemical profile. OS parameters used were superoxide dismutase (SOD), catalase (CAT), nitrite/nitrate (NO) and malonaldehyde (MDA). Comparisons between the same variable in ScT and EU were analyzed using paired t-test or Wilcoxon as appropriate, significance level set as P < 0.05, and GraphPad Prism 5.0 and SPSS 21 were used. No significant differences in hematological and biochemical profiles were observed. As compared to euthyroid state, patients in ScT had higher levels of FT4 (1.05 ± 0.18 vs 0.93 ± 0.14 ng/dL; P = 0.014) and lower levels of TSH (0.11 ± 0.1 vs 2.01 ± 1.49 µUI/mL; P < 0.001). OS parameters were similar in both situations (ScT vs EU, respectively): SOD (1390 ± 453.5 vs 1509 ± 364 act/min; P = 0.48); CAT (57.68 ± 22.91 vs 62.91 ± 18.62 act/min; P = 0.435); NO (35.05 ± 20.3 vs 30.15 ± 12.21 mg/L; P = 0.18) and MDA (2.91 ± 0.51 vs 3.00 ± 0.61 µM; P = 0.73). These data suggest that exogenous subclinical thyrotoxicosis does not increase the markers of oxidative stress.