Free radical activity and antioxidant defense mechanisms in patients with hyperthyroidism due to Graves' disease during therapy.

Free radical-mediated oxidative stress has been implicated in the etiopathogenesis of several autoimmune disorders. We investigated the prooxidant-antioxidant status in order to evaluate the possible deleterious role of oxidative phenomena in patients with Graves' disease. Thirty patients with hyperthyroidism due to Graves' disease were investigated. Thirty age-matched healthy subjects were studied as a control group. Free radical activity indices, antioxidant defense systems, and thyroid and pituitary hormone levels were measured in fasting blood samples. Blood samples were taken before initiation of therapy and after attainment of euthyroid state. A significant increase in lipid peroxidation activity indices, i.e., conjugated dienes and thiobarbituric acid-reacting substances, was found in blood serum of the patients with untreated Graves' disease. These changes were accompanied by a decrease in plasma thiol and erythrocyte lysate thiol groups concentrations. Hyperthyroidism resulted in a marked increase in intracellular antioxidant enzymes, i.e., superoxide dismutase, catalase and glutathione peroxidase activities as compared to the controls. Extracellular anti-free radical scavenging systems potential, measured by glutathione reductase activity and total antioxidant status level, was found to be significantly decreased in untreated Graves' patients. Treatment with thiamazole resulted in normalization of the free radical and antioxidant activity indices. The obtained results indicate an enhanced generation of reactive oxygen species and impairment of cellular and extracellular antioxidant systems potential in patients with Graves' disease. The attainment of euthyroid state led to an improvement in oxidative stress indices and antioxidant potential parameters.