The anti-hypertensive peptide catestatin limits reperfusion injury

Background: The Chromogranin A (CgA)-derived anti-hypertensive peptide catestatin (Cts) plasma levels result decreased in hypertensive patients and in their still-normotensive offsprings. Moreover, Cts antagonizes catecholamine secretion, and is negative myocardial inotrope acting via a nitric oxide-dependent mechanism. Exogenous Cts also diminished stress-induced increments in blood pressure and heart rate. Whether Cts is involved in post-ischemic protection has not been investigated yet. Since ischemic postconditioning (PostC), i.e. brief cycles of ischemia/reperfusion (I/R) after prolonged ischemia, induces a significant reduction of ischemia/reperfusion (I/R) injuries via RISK (Reperfusion Injury Salvage Kinases) pathway, which include nitric oxide-dependent mechanism, we hypothesized that Cts may have a cardioprotective role. Here we tested whether Cts could improve post-ischemic cardiac function and cardiomyocyte survival using two experimental models: the isolated rat heart and cardiac isolated cells. Methods: Three groups of isolated perfused hearts from adult Wistar Rats underwent 30-min ischemia and 120-min reperfusion (I/R, Group-1), or were postconditioned by brief ischemic episodes (PostC, 5-cycles of 10-sec I/R at the beginning of 120-min reperfusion, Group-2), or with exogenous Cts (75 nM for 20-min, Cts-PostC, Group-3) at the onset of reperfusion. Perfusion pressure and left ventricular pressure (LVP) were monitored. Infarct size was evaluated with nitroblue-tetrazolium staining. The role of RISK pathway was studied with western blotting at the end of reperfusion. The Cts (5 nM) effects were also tested in simulated ischemia/reperfusion experiments on cardiomyocytes isolated from young-adult rats, evaluating cell survival with propidium-iodide labeling. Results: In isolated rat hearts, infarct size was about 60% of risk area in hearts subjected to I/R only. Ischemic PostC and Cts-PostC reduced infarct size to about 35% of risk area (p<0.05 vs I/R for both). Cts-PostC reduced post-ischemic rise of diastolic LVP, an index of contracture, and significantly improved post-ischemic recovery of developed LVP. The improvements of post-ischemic cardiac function obtained with Cts were greater than those obtained with ischemic PostC. The western blotting analysis demonstrated that the Cts-PostC significantly enhanced the phosphorylation of key elements (Akt and ERK) of the RISK pathway, and induced phosphorylation/inactivation of GSK-3beta, one of the end-effectors of RISK pathway. In isolated cardiomyocytes, Cts increased the cell viability rate by about 65% after simulated ischemia/reperfusion. Conclusions: These results suggest a novel cardioprotective role for Cts, which appears mainly due to a direct reduction of post ischemic myocardial damages and dysfunction, rather than to an involvement of adrenergic terminals and/or endothelium. RISK pathway may play a role in this Cts-induced protection. Recently we demonstrated that the ischemic PostC cardioprotection is blunted in the hypertensive rat model. Next step will be to test Cts protection in hypertensive animals.