Spin echo nuclear magnetic resonance studies on intact erythrocytes: changes in cellular metabolism as a consequence of carbimazole therapy

Evidence for carbimazole as an antioxidant?

There is evidence in the literature to support the view that antioxidants are involved in the pathogenesis of Graves disease and that antioxidants may act as free radical scavengers. This study has compared the effects of a 12 month course of conventional Carbimazole therapy on peripheral blood antioxidant levels with those of a 12 month course of a higher dose treatment regime. Fifty seven patients were enrolled into the study. Those in Group 1 (n = 23) received a 12 month course of 60 mg/day Carbimazole. Those in Group 2 (n = 34) received 45 mg/day for the first month, 30 mg/day for the second and 20 mg/day for the remaining 10 months of treatment. T3 was added in both groups after 2-4 months to maintain patients euthyroid. Baseline samples were also obtained from 30 control subjects. Blood samples were taken for the measurement of plasma thiol (PSH), lysate thiol (LSH), superoxide dismutase (SOD) and caeruloplasmin (CP) and for routine thyroid function tests (TT4, TT3 and TSH). In untreated Graves' patients, serum levels of PSH and SOD were reduced and levels of LSH increased compared to controls. Following 2 months high dose Carbimazole therapy there was a significant increase in PSH levels and a significant reduction in CP levels compared to presentation levels. In the more conventional dose Group 2 patients PSH levels also rose significantly during the first 2 months of treatment. Levels for both groups were still significantly lower than the control group. After 12 months high dose Carbimazole therapy PSH levels had decreased so that they no longer differed from untreated levels. LSH and SOD levels still remained abnormal. CP levels continued to fall. Similar findings were obtained in those patients receiving the more conventional course of treatment. At no point was their any significant difference in antioxidant levels between the two treatment groups. The abnormal levels of antioxidants in the serum of untreated Graves' patients confirm their involvement in the pathogenesis of Graves' disease. Carbimazole therapy appeared to have only short term effects on the peripheral blood levels of the antioxidants measured. Carbimazole appeared to act only on the extra cellular markers of antioxidant activity (PSH, CP) although the disease itself had marked intracellular effects (LSH, SOD). These findings suggest that Carbimazole does not act as a free radical scavenger.

Alteration of the erythrocyte glutathione redox balance by N-acetylcysteine, captopril and exogenous glutathione

The effect of the thiol containing compounds N-acetylcysteine and captopril on glutathione metabolism in human erythrocytes has been investigated non-invasively using 1H spin echo NMR. N-Acetylcysteine was found to increase the reduced form of glutathione while captopril increased the oxidized form, but no changes in the total glutathione concentration were observed. Incubation of the cells with buthionine sulphoximine to inhibit de novo glutathione synthesis did not affect the response. The results show that these compounds act by altering the redox balance of glutathione rather than by stimulating its synthesis, and that their mechanisms of action are different, and not simply due to the presence of the thiol group.

Has the use of antithyroid drugs for Graves' disease become obsolete?

In spite of an experience of almost 50 years of use of antithyroid drugs and radioiodine for the treatment of Graves' disease, the rationale for choice is often obscure. Early reports of high remission rates during thiourea therapy were followed by less optimistic ones, which along with other factors may have fueled the current major shift toward use of radioiodine. This review examines whether or not the use of antithyroid drugs indeed may have become obsolete. The intrathyroidal and extrathyroidal mechanisms of action of the drugs are reviewed with emphasis on their potential immunosuppressive effects. The latter may involve a direct effect on thyroid follicular cells, a direct suppression of TSH receptor antibody formation, or indirect effects mediated via heat shock proteins, oxygen free radicals, and the immune system. Potential factors associated with success or failure with antithyroid drug therapy are discussed, such as the effects of dose and duration of treatment, iodine milieu, and concomitant L-thyroxine therapy. The risks inherent to radioiodine therapy are only briefly described with emphasis on the possible aggravation by radioiodine of preexistent ophthalmopathy. The reader must decide whether the evidence marshalled convincingly indicates that the use of the thiourea compounds should be abandoned. The author thinks not, and is optimistic that imminent discovery of the yet elusive and enigmatic pathogenesis of Graves' disease will permit new and innovative treatment or more effective use of currently available therapies.