Induction of inducible nitric oxide synthase in hepatocytes isolated from rats with ischemia-reperfusion injury

Hepatic inducible nitric oxide synthase expression increases upon exposure to hypergravity

Stimulation by a number of conditions, including infection, cytokines, mechanical injury, and hypoxia, can upregulate inducible nitric oxide synthase (iNOS) in hepatocytes. We observed that exposure to hypergravity significantly upregulated the transcription of the hepatic iNOS gene. The aim of this study was to confirm our preliminary data, and to further investigate the distribution of the iNOS protein in the livers of mice exposed to hypergravity. ICR mice were exposed to +3 Gz for 1 h. We investigated the time course of change in the iNOS expression. Hepatic iNOS mRNA expression progressively increased in centrifuged mice from 0 to 12 h, and then decreased rapidly by 18 h. iNOS mRNA levels in the livers of centrifuged mice was significantly higher at 3, 6, and 12 h than in uncentrifuged control mice. The pattern of iNOS protein expression paralleled that of the mRNA expression. At 0 and 1 h, weak cytoplasmic iNOS immunoreactivity was found in some hepatocytes surrounding terminal hepatic venules. It was noted that at 6 h there was an increase in the number of perivenular hepatocytes with moderate to strong cytoplasmic immunoreactivity. The number of iNOS-positive hepatocytes was maximally increased at 12 h. The majority of positively stained cells showed a strong intensity of iNOS expression. The expression levels of iNOS mRNA and protein were significantly increased in the livers of mice exposed to hypergravity. These results suggest that exposure to hypergravity significantly upregulates iNOS at both transcriptional and translational levels.

Molecular mechanisms of liver ischemia reperfusion injury: Insights from transgenic knockout models

Ischemia reperfusion injury is a major obstacle in liver resection and liver transplantation surgery. Understanding the mechanisms of liver ischemia reperfusion injury (IRI) and developing strategies to counteract this injury will therefore reduce acute complications in hepatic resection and transplantation, as well as expanding the potential pool of usable donor grafts. The initial liver injury is initiated by reactive oxygen species which cause direct cellular injury and also activate a cascade of molecular mediators leading to microvascular changes, increased apoptosis and acute inflammatory changes with increased hepatocyte necrosis. Some adaptive pathways are activated during reperfusion that reduce the reperfusion injury. IRI involves a complex interplay between neutrophils, natural killer T-cells cells, CD4+ T cell subtypes, cytokines, nitric oxide synthases, haem oxygenase-1, survival kinases such as the signal transducer and activator of transcription, Phosphatidylinositol 3-kinases/Akt and nuclear factor κβ pathways. Transgenic animals, particularly genetic knockout models, have become a powerful tool at elucidating mechanisms of liver ischaemia reperfusion injury and are complementary to pharmacological studies. Targeted disruption of the protein at the genetic level is more specific and maintained than pharmacological inhibitors or stimulants of the same protein. This article reviews the evidence from knockout models of liver IRI about the cellular and molecular mechanisms underlying liver IRI.

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.