The CO-releasing molecule CORM-3 protects adult cardiomyocytes against hypoxia-reoxygenation by modulating pH restoration.

Several studies have reported that CORM-3, a water-soluble carbon monoxide releasing molecule, elicits cardioprotection against myocardial infarction but the mechanism remains to be investigated. Numerous reports indicate that inhibition of pH regulators, the Na+/H+ exchanger (NHE) and Na+/HCO3- symporter (NBC), protect cardiomyocytes from hypoxia/reoxygenation injury by delaying the intracellular pH (pHi) recovery at reperfusion. Our goal was to explore whether CORM-3-mediated cytoprotection involves the modulation of pH regulation. When added at reoxygenation, CORM-3 (50 µM) reduced the mortality of cardiomyocytes exposed to 3 h of hypoxia and 2 h of reoxygenation in HCO3--buffered solution. This effect was lost when using inactive iCORM-3, which is depleted of CO and used as control, thus implicating CO as the mediator of this cardioprotection. Interestingly, the cardioprotective effect of CORM-3 was abolished by switching to a bicarbonate-free medium. This effect of CORM-3 was also inhibited by 5-hydroxydecanoate, a mitochondrial ATP-dependent K+ (mKATP) channel inhibitor (500 µM) or PD098059, a MEK1/2 inhibitor (10 µM). In additional experiments and in the absence of hypoxia-reoxygenation, intracellular pH was monitored in cardiomyocytes exposed to cariporide to block NHE activity. CORM-3 inhibited alkalinisation and this effect was blocked by PD098059 and 5-HD. In conclusion, CORM-3 protects the cardiomyocyte against hypoxia-reoxygenation injury by inhibiting a bicarbonate transporter at reoxygenation, probably the Na+/HCO3- symporter. This cardioprotective effect of CORM-3 requires the activation of mKATP channels and the activation of MEK1/2.

Comparative effect of hypothermia and adrenaline during cardiopulmonary resuscitation in rabbits.

BACKGROUND: Therapeutic hypothermia was shown to facilitate resumption of spontaneous circulation when instituted during cardiac arrest. Here, we investigated whether it directly improved the chance of successful resuscitation independently of adrenaline administration in rabbits. We further evaluated the direct effect of hypothermia on vascular function in vitro. METHODS: In a first set of experiments, four groups of anesthetized rabbits were submitted to 15 min of cardiac arrest and subsequent cardiopulmonary resuscitation (CPR). The "control" group underwent CPR with only cardiac massage and defibrillation attempts. Two other groups received cold or normothermic saline infusion during CPR (20 mL/kg of NaCl 0.9% at 4°C or 38°C, respectively). In a last group, the animals received adrenaline (15 µg/kg intravenously) during CPR. In a second set of experiments, we evaluated at 32°C vs. 38°C the vascular function of aortic rings withdrawn from healthy rabbits or after cardiac arrest. RESULTS: In the first set of experiments, cardiac massage efficiency was improved by adrenaline but neither by hypothermic nor normothermic saline administration. Resumption of spontaneous circulation was observed in five of eight animals after adrenaline as compared with none of eight in other groups. Defibrillation rates were conversely similar among groups (7/8 or 8/8). In the second set of experiments, in vitro hypothermia (32°C) was not able to prevent the dramatic alteration of vascular function observed after cardiac arrest. It also did not directly modify vasocontractile or the vasodilating functions in healthy conditions. CONCLUSION: In rabbits, hypothermia did not exert a direct hemodynamic or vascular effect that might explain its beneficial effect during CPR.