Erythrocyte glutathione peroxidase levels in hyperthyroidism–effect of treatment with methimazole

• Author Details:   
• Sreekumari RG
• Sandhya CV

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Background: The hypermetabolic state seen in hyperthyroidism causes increased oxygen consumption resulting in an increased formation of Reactive Oxygen Species leading to tissue injury. Increased oxidative stress characterised by elevated levels of free radicals and diminished antioxidant status has been described in animal models as well as in patients with hyperthyroidism. Thyroid gland is characterized by high activity of the antioxidant enzyme Glutathione Peroxidase (GSHPx) and this has been studied much reflecting the imbalance of antioxidant enzyme systems in thyroid dysfunction. However, contradictory results have been obtained regarding plasma and erythrocyte GSHPx levels in hyperthyroidism. Studies have also shown that antithyroid drugs like Methimazole and propyl thiouracil have antioxidant effects. How the treatment with these drugs affect the antioxidant status is also a matter of debate. Hence, the present study aimed to evaluate the erythrocyte Glutathione Peroxidase levels in hyperthyroidism in comparison with normal controls and evaluate the effect of methimazole treatment.
Methods: The study was carried out in patients attending the special investigation laboratory in the department of Biochemistry of our college for assessment of their thyroid function. The study groups included: Group 1 (n = 40) consisting of healthy euthyroid controls. Group 2: (n=30) clinically diagnosed hyperthyroid patients, 17 were untreated fresh cases (series1) and 13 patients were undergoing treatment with methimazole for the past one month (series2). Erythrocyte Glutathione peroxidase enzyme levels were analyzed in blood samples collected from these subjects along with thyroid function tests T3, T4 and TSH.
Results & Conclusion: Comparison of the mean values showed that the elevated levels of thyroid hormones have come down in the Methimazole (MMI) treatment group as expected. There were very low TSH levels in the untreated group whereas in treated group TSH levels were at the lower limit of normal range. The mean GSH Px levels in untreated hyperthyroid patients were significantly elevated (6.970± 0.302?moles/L) compared to normal controls (6.117 ± 0.133?moles/L). The GSHPx levels in the treated group were closer to the GSHPx values of the control group.(6.125 ± 0.482?moles/L)

Keywords: Hyperthyroidism, Methimazole, Glutathione peroxidase, Oxidative stress, Antioxidant status, Reactive Oxygen Species