As contractile elements of the heart, cardiomyocytes need to function at all times for as long as we live. This requires a constant ATP production which cardiomyocytes ensure through utilization of diverse substrates for metabolism. This flexibility ensures uninterrupted ATP production especially in settings where the availability of specific substances is limited. Normally, fatty acids are the primary and glucose the secondary source for energy production. However, physiological and pathophysiological conditions can influence the availability of substrates and fundamentally shift the metabolic functions. Therefore, restoration of a normal metabolic profile could be crucial to ameliorate or possibly reestablish negative effects in pathophysiological settings. As sphingosine 1-phosphate (S1P) has multiple metabolic effects, we hypothesized that it alterations of its concentrations in vivo may have an effect on the metabolic changes cardiomyocytes experience in diet-induced obesity.

For 22 weeks, Mice were fed either a normal chow, a high fat diet (HFD) or a HFD with supplementation of 4-deoxypyridoxine (DOP), an inhibitor of the S1P-degrading enzyme S1P-lyase, for the last 12 weeks. Adult cardiomyocytes were isolated by retrograde perfusion in a Langendorff setting and analyzed in parallel using distinct metabolic profiling assay types in a Seahorse Analyzer. The first (MitoStress) allows a general assessment of mitochondrial parameters using inhibitors of the electron transport chain (ETC) and measuring oxygen consumption rate (OCR) with glucose and fatty acids as substrates. The second (glycolytic rate) and third (GlycoStress) assay examine glycolytic functions, glucose oxidation and anaerobic glycolysis.

A comparison of the measured metabolic profiles showed distinct effects of above treatments. HFD with induced diet-induced obesity (DIO) resulted in a severe dysfunction in mitochondrial and glycolytic function in comparison to normal chow mice. Under normal chow cardiomyocytes show a 2.5 to 3-fold increase to baseline oxygen consumption rate levels after FCCP treatment. In contrast DIO cardiomyocytes showed almost no increase in OCR. Extracellular acidification, a marker anaerobic glycolysis, was reduced in DIO cardiomyocyte to 50% of the normal chow values. All these abnormalities were restored with in cardiomyocytes from mice on DOP. In summary, treatment of DIO mice with DOP was able to normalize the metabolic profile by increasing mitochondrial and glycolytic functions. The mechanism of how S1P affects mitochondrial and glycolytic functions is currently under investigation. We believe that normalizing metabolic disturbances in pathophysiological conditions may help protect cardiomyocytes and the heart against injury.