In vivo and in vitro antioxidant activity of ghrelin: Attenuation of gastric ischemic injury in the rat

BACKGROUND AND AIM: Gherlin, an endogenous ligand for the growth hormone secretagogue receptor (GHS-R), is produced by stomach cells. It regulates food intake, gastric secretion and motility. However, its role as a protective agent in gastric ischemia/reperfusion (I/R) injury has not yet been investigated. Therefore, the objectives of the present study were to: (i) test the in vivo effect of peripherally administered ghrelin on gastric I/R-induced lesions in rats; and (ii) investigate in vitro the effect of ghrelin on reactive oxygen species (ROS) production by human polymorphoneuclear (PMN) cells. METHODS: The present study was carried out on three groups of rats (six per group): control (sham-operated), I/R (clamping of celiac artery for 30 min and reperfusion for 1 h), and I/R + ghrelin (200 ng/kg i.v., 15 min before ischemia and before reperfusion, respectively). Histological assessment of hematoxylin and eosin stained sections was performed and immunostaining with inducible nitric oxide (iNOS) antibody were performed on a gastric paraffin embedded section. Oxidative stress markers thiobarbituric acid reactive substance (TBARS) and glutathione (GSH) were measured in gastric tissue homogenates. Serum lactic acid dehydrogenase (LDH) was determined. Tumor necrosis factor-alpha (TNF-alpha) was assayed in gastric tissue homogenate. Gastric permeability was assessed calorimetrically using Evans blue dye. In vitro studies were carried out on isolated human PMN cells incubated with ghrelin and tested for ROS generation as measured by chemiluminecence (CL). RESULTS: Peripheral administration of ghrelin attenuated gastric injury by reducing ulceration, tissue congestion, cellular infiltration and vascular permeability. Serum level of LDH and tissue content of TNF-alpha were markedly reduced. A decrement in TBARS and an increment in GSH were observed. Ghrelin treatment attenuated iNOS protein expression which was upregulated by gastric ischemic injury. In vitro studies showed for the first time that ghrelin inhibited ROS generation by human PMN in a dose-dependent manner. CONCLUSIONS: These results provide evidence that peripherally administered ghrelin protects against gastric I/R injury. We also demonstrated that this protection is possibly accomplished through the antioxidant activity of ghrelin observed in vivo and in vitro.