Obestatin affords cardioprotection to the ischemic-reperfused isolated rat heart and inhibits apoptosis in cultures of similarly stressed cardiomyocytes

Obestatin affords cardioprotection to the ischemic/reperfused isolated rat heart and inhibits apoptosis in cultured cardiomyocytes- Obestatin, a newly discovered peptide encoded by the ghrelin gene, induces expression of genes regulating pancreatic β-cell differentiation, insulin biosynthesis and glucose metabolism. It also activates anti-apoptotic signalling pathways such as PI3K and ERK1/2 in pancreatic β-cells and human islets. Since these kinases have been shown to protect against myocardial injury, we sought to investigate whether obestatin would exert cardioprotective effects. Both isolated perfused rat heart and cultured cardiomyocyte models of ischemia/reperfusion (I/R) were used, measuring infarct size and cell apoptosis as end points of injury. The presence of specific obestatin receptors on cardiac cells, as well as the signalling pathways underlying the obestatin effect were also studied. In isolated heart, the addition before ischemia of rat obestatin-(1-23), reduced infarct size and contractile dysfunction in a concentration-dependent manner, whereas obestatin-(23-1), a synthetic analogue with inverse aminoacid sequence, was ineffective. The cardioprotective effect of obestatin-(1-23) was observed at concentrations of 10-50 nmol/L and was abolished by inhibiting PI3K or PKC by addition of wortmannin (100 nmol/L) or chelerythrine, (5 µmol/L), respectively. In rat H9c2 cardiac cells or isolated ventricular myocytes subjected to I/R, 50 nmol/L obestatin-(1-23) reduced cardiomyocyte apoptosis and reduced caspase-3 activation; the anti-apoptotic effect was blocked by inhibition of PKC, PI3K or ERK1/2 pathways. In keeping with these functional findings, radioreceptor binding results revealed the presence of specific high-affinity obestatin binding sites, mainly localized on membranes of ventricular myocardium and cardiomyocytes. Our data suggest that, acting on specific receptors, obestatin-(1-23) activates PI3K, PKCε, PKCδ and ERK1/2 signalling and protects cardiac cells against myocardial injury and apoptosis induced by I/R