Effects of dichloroacetate on the lactate/ pyruvate ratio and on aspartate and leucine metabolism in cultured rat skeletal muscle cells

Abstract

Dichloroacetate accelerates pyruvate and lactate metabolism in many tissues and has often been shown to increase the lactate/pyruvate (L/P) ratio, which is assumed to be in equilibrium with the cytosolic NADH/NAD + ratio. The cause of the drug-induced increase in L/P ratio is not known, but abnormalities in the malate-aspartate hydrogen shuttle have been implicated in perfused skeletal muscle. In addition, indirect studies in perfused skeletal muscle suggest that dichloroacetate inhibits branched chain amino acid oxidation. In the present studies, cultured rat skeletal muscle cells were used to examine the effect of dichloroacetate on the L/P ratio and on the metabolism of aspartate and of leucine. Dichloroacetate increased the L/P ratio after only 60 min of incubation, and the process was saturable with an ED 50 of 1.0 mM. Drug treatment resulted in marked decreases in cell lactate, pyruvate, and alanine, but no significant differences were observed in cell ATP or in cell levels of compounds of the malate-aspartate shuttle (e.g. malate, aspartate, glutamate or α-ketoglutarate). In addition, dichloroacetate had no consistent effect on aspartate oxidation or on aspartate conversion into glutamate. However, action of the drug did result in an inhibition of leucine oxidation, an effect which contrasts with dichloroacetate action in heart or liver, wherein the drug stimulates leucine oxidation. These results confirm other studies showing that dichloroacetate raises the L/P ratio in skeletal muscle, but do not provide evidence for drug-induced alterations of the malate-aspartate cycle, the principal cytosolic hydrogen shuttle system.