Antioxidants in the treatment of Graves disease.

An antioxidant mixture (LAROTABE) was evaluated in the treatment of Graves disease. Fifty-six hyperthyroid patients were treated with methimazol (MMI) (A), LAROTABE (B), or MMI plus LAROTABE (C). According to a clinical score, improvement was obtained at 8 weeks in A and 4 weeks in B and C. Group A diminished their thyroid hormone concentration to normal levels, while patients with LAROTABE did not reduce T3 and T4 unless MMI was introduced. Hyperthyroid patients had increased malondialdehyde (MDA) content and SOD activity and decreased catalase activity compared to controls. Within group A, MDA decreased to control values while SOD was reduced 38.3% and catalase increased 21.6%. Similar results were obtained for MDA and for both enzymes after treatment with LAROTABE. Signs and symptoms of Graves disease might be related to an increase in free radicals; antioxidants could be a new therapeutic tool to improve the clinical manifestation of this illness.

Reduction of nitrofuran compounds by heart lipoamide dehydrogenase: role of flavin and the reactive disulfide groups.

In order to elucidate the mechanism of the biological activation of nitrofurans, the interaction of these compounds with lipoamide dehydrogenase (LipDH)** was investigated. LipDH catalysed one-electron reduction of several nitrofuran derivatives. The reaction could be demonstrated spectroscopically and was enhanced by cadmium, arsenite and anaerobiosis. The role of flavin in the nitroreductase activity was supported by (a) the nitrofuran effect on the spectral properties of anaerobic, arsenite-inhibited, NADH-reduced LipDH; (b) FAD catalytic activity in a NADH-nitrofuran model system; and (c) the nitroreductase activity of LipDH monomer. Two-electron nitrofuran reduction to less oxidized products was inhibited by cadmium, arsenite and NAD+. The possible role of reactive nitrosofuran derivatives as intermediates of the nitrofuran reduction sequence was supported by the LipDH capability for catalysing 2-nitroso-1-naphthol redox-cycling. The nitroso naphthol reduction was inhibited by cadmium and arsenite, like the two-electron nitrofuran reduction.

Superoxide anion production by lipoamide dehydrogenase redox-cycling: effect of enzyme modifiers.

Redox-cycling of porcine heart lipoamide dehydrogenase in the presence of NADH and oxygen produced O2-. (NADH-oxidase activity) as demonstrated by (a) reduction of cytochrome c; (b) reduction of the Fe(III)-ADP complex; (c) lucigenin luminescence and (d) the inhibitory effect of superoxide dismutase. NAD+ and p-chloromercuribenzoate inhibited O2-. generation whereas arsenite enhanced it. Comparison of heart and yeast enzyme preparations revealed a close correlation between lipoamide reductase and NADH-oxidase activities. It is concluded that O2-. production is a molecular property of lipoamide dehydrogenase.

Catalysis of nitrofuran redox-cycling and superoxide anion production by heart lipoamide dehydrogenase.

Heart lipoamide dehydrogenase (LADH) catalyzed redox-cycling and O2-. production by (5-nitro-2-furfurylidene)amino derivatives using NADH as electron donor. NADH was a much more effective electron donor than NADPH for the nitroreductase activity. O2-. production was demonstrated by cytochrome c reduction, adrenochrome formation and the effect of superoxide dismutase. Under optimum conditions, nitroreductase activity was about 1% of LADH activity. One electron oxygen reduction and NADH oxidation correlated in 2:1 stoichiometry. The nitroreductase kinetics was in accordance with an ordered bi-bi mechanism. Nitrofuran derivatives bearing unsaturated five- or six-membered nitrogen heterocycles were more effective substrates than those bearing other groups, namely nifurtimox, nitrofurazone, nitrofurantoin and 5-nitro-2-furoic acid. Other nitro compounds (chloramphenicol, benznidazole, 2-nitroimidazole and 5-nitroindole) were ineffective. With the triazole, traizine and imidazole nitrofuran derivatives, the nitroreductase pH curve showed a maximum at pH 8.8, different from the pH optimum for the lipoamide reductase and diaphorase activities. Spectroscopic observations demonstrated pH-dependent structural changes in the triazole(I) and triazine derivatives which would affect their behavior as nitroreductase substrates. The nitroreductase activity was inhibited by p-chloromercuribenzoate and enhanced by cadmium and arsenite, whereas the NADH-induced LADH inactivation failed to affect the nitroreductase activity. In the absence of oxygen. LADH catalyzed nitrofuran reduction to products more reduced than the nitroanion, which were not reoxidized by oxygen. The anaerobic nitrofuran reduction was inhibited by cadmium and arsenite. The assayed nitrofuran compounds did not inhibit LADH lipoamide reductase activity, at variance with their action on glutathione reductase (Grinblat et al., Biochem Pharmacol 38: 767-772, 1989).

Nitrofuran inhibition of yeast and rat tissue glutathione reductases. Structure-activity relationships.

Nitrofuran derivatives bearing unsaturated five- or six-membered nitrogen heterocycles or related substituents were more effective inhibitors of yeast and rat tissue glutathione reductases than those bearing other groups, such as nifurtimox, nitrofurazone and 5-nitro-2-furoic acid. The inhibitory action proved independent of electron withdrawal from the reduced enzyme, as a consequence of redoxcycling of the nitro group. Uncompetitive kinetics was obtained with nitrofurantoin and nifurtimox. Most of the assayed nitrofurans inhibited the yeast enzyme Coenzyme A glutathione disulfide reductase activity, though less than oxidized glutathione reduction. The transhydrogenase activity was not inhibited to a significant degree. Benznidazole (a 2-nitroimidazole derivative), 2-nitroimidazole, 5-nitroindole and chloramphenicol did not inhibit glutathione reductase. Under the same experimental conditions, liver glutathione peroxidase was not affected by the nitro compounds.