Cardiac peroxisome proliferator-activated receptor-α activation causes increased fatty acid oxidation, reducing efficiency and post-ischaemic functional loss

Myocardial fatty acid (FA) oxidation is regulated acutely by the FA supply and chronically at the transcriptional level owing to FA activation of peroxisome proliferator-activated receptor-alpha (PPAR alpha). However, in vivo administration of PPAR alpha ligands has not been shown to increase cardiac FA oxidation. In this study we have examined the cardiac response to in vivo administration of tetradecylthioacetic acid (TTA, 0.5% w/w added to the diet for 8 days), a PPAR agonist with primarily PPAR alpha activity. Despite the fact that TTA treatment decreased plasma concentrations of lipids [FA and triacylglycerols (TG)], hearts from TTA-treated mice showed increased mRNA expression of PPAR alpha target genes. Cardiac substrate utilization, ventricular function, cardiac efficiency, and susceptibility to ischaemia-reperfusion were examined in isolated perfused hearts. In accordance with the mRNA changes, myocardial FA oxidation was increased 2.5-fold with a concomitant reduction in glucose oxidation. This increase in FA oxidation was abolished in PPAR alpha-null mice. Thus, it appears that the metabolic effects of TTA on the heart must be owing to a direct stimulatory effect on cardiac PPAR alpha. Hearts from TTA-treated mice also showed a marked reduction in cardiac efficiency (because of a two-fold increase in unloaded myocardial oxygen consumption) and decreased recovery of ventricular contractile function following low-flow ischaemia. This study for the first time observed that in vivo administration of a synthetic PPAR alpha ligand elevated FA oxidation, an effect that was also associated with decreased cardiac efficiency and reduced post-ischaemic functional recovery.