It has been proposed that in the heart, ranolazine shifts the energy source from fatty acids to glucose oxidation by inhibiting fatty acid oxidation. Up to now no mechanism for this inhibition has been proposed. The purpose of this study was to investigate if ranolazine also affects hepatic fatty acid oxidation, with especial emphasis on cell membrane permeation based on the observations that the compound interacts with biological membranes. The isolated perfused rat liver was used, and [1-(14)C]oleate transport was measured by means of the multiple-indicator dilution technique. Ranolazine inhibited net uptake of [1-(14)C]-oleate by impairing transport of this fatty acid. The compound also diminished the extra oxygen consumption and ketogenesis driven by oleate and the mitochondrial NADH/NAD(+) ratio, but stimulated (14)CO(2) production. These effects were already significant at 20 μM ranolazine. Ranolazine also inhibited both oxygen consumption and ketogenesis driven by endogenous fatty acids in substrate-free perfused livers. In isolated mitochondria ranolazine inhibited acyl-CoA oxidation and β-hydroxybutyrate or α-ketoglutarate oxidation coupled to ADP phosphorylation. It was concluded that ranolazine inhibits fatty acid uptake and oxidation in the liver by at least two mechanisms: inhibition of cell membrane permeation and by an inhibition of the mitochondrial electron transfer via pyridine nucleotides.

Flavonols, which possess the B-catechol ring, as quercetin, are capable of producing o-hemiquinones and to oxidize NADH in a variety of mammalian cells. The purpose of this study was to investigate whether fisetin affects the liver energy metabolism and the mitochondrial NADH to NAD+ ratio. The action of fisetin on hepatic energy metabolism was investigated in the perfused rat liver and isolated mitochondria. In isolated mitochondria, fisetin decreased the respiratory control and ADP/O ratios with the substrates α-ketoglutarate and succinate. In the presence of ADP, respiration of isolated mitochondria was inhibited with both substrates, indicating an inhibitory action on the ATP-synthase. The stimulation of the ATPase activity of coupled mitochondria and the inhibition of NADH-oxidase activity pointed toward a possible uncoupling action and the interference of fisetin with mitochondrial energy transduction mechanisms. In livers from fasted rats, fisetin inhibited ketogenesis from endogenous sources. The β-hydroxybutyrate/ acetoacetate ratio, which reflects the mitochondrial NADH/NAD+ redox ratio, was also decreased. In addition, fisetin (200 μM) increased the production of (14)CO2 from exogenous oleate. The results of this investigation suggest that fisetin causes a shift in the mitochondrial redox potential toward a more oxidized state with a clear predominance of its prooxidant activity.

The action mechanism of ranolazine, an antiangina drug, could be at least partly metabolic, including inhibition of fatty acid oxidation and stimulation of glucose utilization in the heart. The purpose of the present work was to investigate if ranolazine affects hepatic carbohydrate metabolism. For this purpose, the hemoglobin-free isolated perfused rat liver was used as the experimental system. Ranolazine increased glycolysis and glycogenolysis and decreased gluconeogenesis. These effects were accompanied by an inhibition of oxygen consumption. The drug also changed the redox state of the NAD + -NADH couple. For the cytosol, increased NADH/NAD + ratios were observed both under glycolytic conditions as well as under gluconeogenic conditions. For the mitochondria, increased NADH/NAD + ratios were found in the present work in the absence of exogenous fatty acids in contrast with the previous observation of a decreasing effect when the liver was actively oxidizing exogenous oleate. It seems likely that ranolazine inhibits gluconeogenesis and increases glycolysis in consequence of its inhibitory actions on energy metabolism and fatty acid oxidation and by deviating reducing equivalents in favour of its own biotransformation. This is in line with the earlier postulates that ranolazine diminishes fatty acid oxidation, shifting the energy source from fatty acids to glucose.