Antioxidative properties of pyruvate and protection of the ischemic rat heart during cardioplegia

Formation of oxygen free radicals during heart transplantation seems to be related to the alterations occurring during ischemia and reperfusion and co uld explain the short preservation time of donor hearts. The aim of our stu dy was (a) to analyze the protective effects of pyruvate during cold cardio plegia and ischemia/reperfusion sequence, and (b) to investigate in vitro t he radical scavenging properties of this compound. After 30 min of perfusio n, isolated working rat hearts were arrested by cardioplegic solution, stor ed 4 h in B21 solutions at 4 degrees C, and reperfused with Krebs-Henseleit buffer for 45 min. Pyruvate (2 mM) was added to Krebs-Henseleit, cardiople gic, and storage solutions, and functional parameters were recorded through out the experiments. In a second part, control hearts and hearts treated wi th pyruvate were cannulated via the aorta and perfused for 30 min by the La ngendorff method, arrested by cardioplegic solution, stored 4 h in B21 solu tions at 4 degrees C, and reperfused for 45 min by the Langendorff method. Malonedialdehyde and alpha-tocopherol levels were determined on heart homog enate. In situ detection of apoptotic cells also was performed on tissue sa mples (left ventricle) at the end of the ischemia/reperfusion sequence. To demonstrate in vitro the antioxidant effects of pyruvate, we monitored (a) its hydroxyl radical scavenging properties by using electron para-magnetic resonance (EPR) spectroscopy, and (b) the decrease of fluorescence of allop hycocyanin, in the presence of a Fenton system (H2O2/Cu2+). Ischemia for 4 h, followed by myocardial reperfusion, resulted in substantially reduced me chanical function. Hearts subjected to this ischemia and pretreated with py ruvate showed a significant improvement in the function recovery. After the ischemia/reperfusion protocol, no significant decrease of malonedialdehyde levels was shown on hearts treated with pyruvate. However, alpha-tocophero l levels were higher in the pyruvate group compared with the control group. At the end of the reperfusion period, levels of apoptotic cells were signi ficantly lower in hearts treated with pyruvate compared with control hearts . EPR studies showed that pyruvate was an efficient hydroxyl scavenger, wit h a median inhibitory concentration (IC50) of 8 mM. The allophycocyanin ass ay also showed a dose-dependent effect of pyruvate against hydroxyl radical s. In conclusion, these findings showed that pyruvate could prevent reperfu sion injuries in the isolated heart, probably by its antioxidative properti es. The application of pyruvate may contribute to the preservation of heart s for organ transplantation.