RESUMEN
INTRODUCTION: We sought to verify whether isoflavin-beta (Iso-ß), a mixture of isoflavones with antioxidant properties, could prevent thyrotoxicosis-induced loss of muscle mass and the participation of oxidative stress (OS) in the mechanisms of this prevention. METHODS: Two experimental periods of thyrotoxicosis induction were used in Wistar rats: 3 and 5 days to assess Iso-ß effects before and after thyrotoxicosis-induced muscle wasting. After euthanasia, peritoneal fat and gastrocnemius muscle were collected, weighed, and muscle OS was assessed. RESULTS: Iso-ß prevented the loss of gastrocnemius mass in thyrotoxic rats through the prevention of muscle OS generation during thyrotoxicosis, increasing muscle total antioxidant capacity and decreasing mitochondrial cytochrome c oxidase activity, lipid peroxidation, and protein carbonyl content. CONCLUSION: Iso-ß decreased oxidative modification of proteins, which is known to exert a major role during proteolysis induction and is present in thyrotoxic myopathy, highlighting the potential action of Iso-ß in this complication of the disease. Muscle Nerve 56: 975-981, 2017.