Determination of Oxidative Stress in Thyroid Tissue and Plasma of Patients with Graves' Disease

Background: The aim of our study was to evaluate the oxidant/antioxidant status of thyroid tissue in Graves' disease (GD) patients and to compare the results of GD thyroid tissue with plasma of patients and healthy controls.

Methods: We studied 25 consecutive patients with GD hyperthyroidism who underwent surgical treatment. The patients were divided into groups according to the duration of antithyroid drug treatment, the type of antithyroid drugs used, the presence of ophthalmopathy, and recurrence after a complete course of antithyroid drugs. Thiobarbituric acid-reacting substances (TBARS), glutathione peroxidase (GPx) activity, superoxide dismutase (SOD) activity, and total thiol (t-SH) content of tissue and plasma samples were determined.

Results: TBARS concentrations were found to be significantly increased in GD patients' plasma compared with controls' plasma (0.1+/-0.02 nmol/mg protein vs. 0.062+/-0.01 nmol/mg protein). Significantly decreased t-SH concentrations were measured in GD patients' plasma compared with controls (8.26+/-1.9 nmol/mg protein vs. 13.03+/-3.3 nmol/mg protein). Tissue TBARS, t-SH, GPx, and SOD measurements in GD patients indicated significantly increased concentrations compared with the plasma levels of patients. Patients with shorter treatment duration before the operation had significantly increased plasma and tissue TBARS and decreased plasma and tissue t-SH concentrations. Patients on propylthiouracil treatment had significantly lower plasma and tissue concentrations of TBARS than patients on methimazole. Patients with recurrence had significantly higher plasma and tissue TBARS and lower plasma and tissue t-SH concentrations than patients treated for the first time.

Conclusions: In euthyroid GD patients on antithyroid drugs, increased oxidative stress and a compensatory increase in the antioxidant defense system are more prominent in thyroid tissue than in plasma. Patients who relapsed had markers indicating increased oxidative stress. Thus, ongoing autoimmunity may contribute to increased oxidative stress in GD patients, even in the euthyroid state.