Acute Effect of Ghrelin on a Rat Model of Cerebral Ischemia/ Reperfusion: Possible Role of Autophagy

Background: Ghrelin, a peptide 28 amino acid hormone and an endogenous ligand for growth hormone secretagogue (GHS) receptor 1a (GHS-R 1a) exerts multiple physiological functions. It has recently been investigated for its neuroprotective effects. However, the effect of ghrelin on ischemic reperfusion (I/R) injury of the brain during the acute period (1-24h) has not been the focus of much attention and the effect of ghrelin on autophagy in model of cerebral ischemia has not yet been examined. Therefore, the aim of the present study was to examine the acute effect of ghrelin in I/R rat brain model. Exploring its neuroprotective mechanisms including autophagy. Material and Methods: 36 male albino rats, weighing 150-200g, were randomly divided into three groups: Control group: Sham operation (n=12), ischemia/reperfusion (I/R) + saline treatment vehicle group (n=12) and ischemia/reperfusion + ghrelin treatment (n=12). I/R injury of the brain was induced by occlusion of bilateral common carotid arteries for 12min. Ghrelin was administered in a dose of 0.4mg/Kg intraperitoneally after the insult. Animals were sacrificed 6 and 24hrs after ischemia (n=6 per group and per time point. Superoxide dismutase (SOD) activity and caspase-3 activity were measured. HSP70 was measured by ELISA. Gene expression of NF-kB, UCP-2, GH-R beclin were assayed in brain tissue by Real-time RT-PCR. Results: I/R of rat brain model caused oxidative stress resulting in significant decrease in SOD level and significant increase in NF-kB mRNA, HSP70 level, caspase-3 level and UCP-2 mRNA. With more significant increase in NF-kB, caspase-3 and UCP-2 at 24h than at 6h measured after the I/R. Also our results showed significant decrease in gene expression of beclin and ghrelin receptor in I/R of rat brain. Ghrelin treatment significantly attenuated I/R injury of rat brain as our results showed significant increase in SOD level and beclin mRNA, there were significant decrease in NF-kB mRNA, UCP-2 mRNA caspase-3 level and HSP70 level, also NF-kB mRNA, UCP-2 mRNA, caspase-3 level and beclin mRNA were returned to their control values in I/R of rat brain model with ghrelin administration. Ghrelin increased gene expression of its receptor with more significant increase at 24h than measured at 6h. Conclusion: Our results indicate that ghrelin protected rat bain against I/R injury and its administration immediately after cerebral I/R can improve neuronal cell survival. The possible mechanisms of action including anti-apoptotic, anti-inflammatory, anti-oxidant effects of ghrelin. Also our results showed that ghrelin induced autophagy and increased gene expression of its receptor. We suggest that early ghrelin treatment may be a useful intervention after stroke in the clinic.