Peripheral parameters of oxidative stress in Graves' disease: the effects of methimazole and 131 iodine treatments

BACKGROUND Increased oxidative stress, with elevated levels of free radicals, together with diminished antioxidation have been described previously in models of hyperthyroidism and in patients with Graves' disease. However, controversial results have been found about the antioxidant status and its response to treatment. AIM To evaluate the antioxidant/oxidant balance in active Graves' disease and the effects of treatment with methimazole (MMI) and 131 iodine (I-131). PATIENTS AND METHODS We studied 69 hyperthyroid (H) patients, 58 female and 11 male, 16-50 years old; total T3:8 +/- 2 nmol/l, total T4:264 +/- 65 nmol/l (all mean +/- SD), TSH: 0.1 +/- 0.1 mIU/l, TSH receptor antibody 41 +/- 21%, highest (131)Iodine uptake: 67 +/- 16%. As a control group (C), 19 normal adults were studied. DESIGN Parameters evaluated were: tert-butyl hydroperoxide initiated chemiluminiscence (CL), superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), glutathione peroxidase (GPx) and total reactive antioxidant potential (TRAP). RESULTS In patients vs. controls there was an increase in CL levels (6207 +/- 1434 vs. 3000 +/- 851 cpm/mg of haemoglobin, P< 0.001), decrease in SOD (0.4 +/- 0.1 vs. 0.7 +/- 0.2 U/mg prot, P < 0.05; corresponding to 0.15 mug/ml), CAT (2.8 +/- 0.6 vs. 3.8 +/- 0.7 pmol/mg prot, P < 0.001) and GSH (1.2 +/- 0.4 vs. 2 +/- 0.7 mmol/l erythrocytes, P < 0.05). The decrease in GPx and TRAP did not show significant differences. The parameters were also recorded in 30 patients who became euthyroid after treatment: 20 of them under MMI therapy (2-12 months) and the rest 3-6 months after (131)Iodine administration. All the parameters evaluated were normalized after MMI; however, CL levels stayed high after I-131 and only CAT and GSH levels returned to normal values. CONCLUSION Our results confirm the imbalance of the antioxidant/oxidant status in hyperthyroid patients. MMI treatment was more effective than I-131 therapy to improve that balance. We speculate on the benefits of antioxidant therapy administrated together with the habitual treatment of hyperthyroidism, especially in patients after I-131 therapy.