Hypoxic postconditioning reduces cardiomyocyte loss by inhibiting ROS generation and intracellular Ca²⁺ overload

Abstract

We have shown that intermittent interruption of immediate reflow at reperfusion (i.e., postconditioning) reduces infarct size in in vivo models after ischemia. Cardioprotection of postconditioning has been associated with attenuation of neutrophil-related events. However, it is unknown whether postconditioning before reoxygenation after hypoxia in cultured cardiomyocytes in the absence of neutrophils confers protection. This study tested the hypothesis that prevention of cardiomyocyte damage by hypoxic postconditioning (Postcon) is associated with a reduction in the generation of reactive oxygen species (ROS) and intracellular Ca(2+) overload. Primary cultured neonatal rat cardiomyocytes were exposed to 3 h of hypoxia followed by 6 h of reoxygenation. Cardiomyocytes were postconditioned after the 3-h index hypoxia by three cycles of 5 min of reoxygenation and 5 min of rehypoxia applied before 6 h of reoxygenation. Relative to sham control and hypoxia alone, the generation of ROS (increased lucigenin-enhanced chemiluminescence, SOD-inhibitable cytochrome c reduction, and generation of hydrogen peroxide) was significantly augmented after immediate reoxygenation as was the production of malondialdehyde, a product of lipid peroxidation. Concomitant with these changes, intracellular and mitochondrial Ca(2+) concentrations, which were detected by fluorescent fluo-4 AM and X-rhod-1 AM staining, respectively, were elevated. Cell viability assessed by propidium iodide staining was decreased consistent with increased levels of lactate dehydrogenase after reoxygenation. Postcon treatment at the onset of reoxygenation reduced ROS generation and malondialdehyde concentration in media and attenuated cardiomyocyte death assessed by propidium iodide and lactate dehydrogenase. Postcon treatment was associated with a decrease in intracellular and mitochondrial Ca(2+) concentrations. These data suggest that Postcon treatment reduces reoxygenation-induced injury in cardiomyocytes and is potentially mediated by attenuation of ROS generation, lipid peroxidation, and intracellular and mitochondrial Ca(2+) overload.

Delayed Hypoxic Postconditioning Protects Against Cerebral Ischemia in the Mouse

“…8 Similar to our results previously obtained for hypoxic preconditioning, 12 hypoxia with 0.1% O 2 applied 14 hours after OGD reduced neuronal death induced by OGD, whereas 2% O 2 had no effect. It is well known that brain tolerance involves transcriptional factors such as the nuclear factor B 16 and cAMP-responsive element-binding protein.…”

“…The protection has been associated with the activation of the protein kinase Akt. 4,5 Besides ischemic postconditioning, the existence of hypoxic postconditioning has been described in the heart 8 but not in the brain neither in vivo nor in vitro.…”

Cardioprotection and mitochondrial S-nitrosation: Effects of S-nitroso-2-mercaptopropionyl glycine (SNO-MPG) in cardiac ischemia–reperfusion injury

“…Such a pathway would result in slow re-introduction of electrons to the respiratory chain at the onset of reperfusion. A similar mechanism may underlie the cardioprotective benefits of slowreperfusion or postconditioning [69].…”

Endogenous Adenosine Selectively Modulates Oxidant Stressviathe A1Receptor in Ischemic Hearts

“…Additionally, A 1 ARs (and not A 2A or A 3 ARs) limit oxidant-mediated myocyte Ca 2þ entry via L-type channels (51). Preconditioning and postconditioning responses, known to involve ARs, also limit oxidant accumulation and oxidative stress (37,49,52).…”