The cardioprotective effect of mildronate is diminished after co-treatment with L-carnitine

Mildronate, an inhibitor of L-carnitine biosynthesis and uptake, is a cardioprotective drug whose mechanism of action is thought to rely on the changes in concentration of L-carnitine in heart tissue. In the present study, we compared the cardioprotective effect of mildronate (100 mg/kg) and a combination of mildronate and L-carnitine (100 + 100 mg/kg) administered for 14 days with respect to the observed changes in l-carnitine level and carnitine palmitoyltransferase I (CPT-I)-dependent fatty acid metabolism in the heart tissues. Concentrations of L-carnitine and its precursor γ-butyrobetaine (GBB) were measured by ultraperformance liquid chromatography with tandem mass spectrometry. In addition, mitochondrial respiration, activity of CPT-I, and expression of CPT-IA/B messenger RNA (mRNA) were measured. Isolated rat hearts were subjected to ischemia-reperfusion injury. Administration of mildronate induced a 69% decrease in L-carnitine concentration and a 6-fold increase in GBB concentration in the heart tissue as well as a 27% decrease in CPT-I-dependent mitochondrial respiration on palmitoyl-coenzyme A. In addition, mildronate treatment induced a significant reduction in infarct size and also diminished the ischemia-induced respiration stimulation by exogenous cytochrome c. Treatment with a combination had no significant impact on L-carnitine concentration, CPT-I-dependent mitochondrial respiration, and infarct size. Our results demonstrated that the mildronate-induced decrease in L-carnitine concentration, concomitant decrease in fatty acid transport, and maintenance of the intactness of outer mitochondrial membrane in heart mitochondria are the key mechanisms of action for the anti-infarction activity of mildronate.