Effect of superoxide generation on rat heart mitochondrial pyruvate utilization

Previous research has shown that heart mitochondria are able to produce reactive species of oxygen such as superoxide radicals, hydrogen peroxide and hydroxyl radicals [10, 11]. When these compounds are formed beyond a certain level they are not completely removed by the enzymatic and metabolic processes which neutralize their toxicity, and as a result they are able to produce structural and functional damages that impair mitochondrial function [5, 10]. In order to study the molecular mechanism/s by which the oxygen radicals may function as mediators of cellular injury a flow of these radicals by chemical, enzymatic or photochemical methods has been generated in vitro in the presence of cellular preparations. For example, the exposure of isolated subcellular particles to the enzymatic flow of oxygen radicals produced by the reaction of xanthine oxidase upon xanthine reduced both calcium uptake velocity and Ca2+-ATPase activity in sarcoplasmic reticulum [7], while it reduced Ca2+-stimulated ATPase activity in myofibrillar preparations [4]. In addition, incubation with the xanthine oxidase reaction produced an impairment of the respiratory functions associated with an increased lipid peroxidation in the isolated mitochondria [5, 10]. These negative effects were augmented in alpha-tocopherol-deficient mitochondria [3], but were opposed by the exogenous addition of superoxide dismutase [10]. This report shows that the superoxide radicals generated by the xanthine oxidase reaction reduced rat heart mitochondrial respiration induced by pyruvate. This negative effect was partially prevented by superoxide dismutase and catalase and by thiol protecting agents. Moreover, the generation of free radicals caused a significant reduction in the rate of (1-14C) -pyruvate decarboxylation, while it did not change the transport of pyruvate into mitochondria.