[Role of nitric oxide synthase III and guanosine 3':5'- cyclic monophosphate in the protection exerted by nitric oxide on hepatic ischemia-reperfusion injury]

The hepatic soluble guanylyl cyclase-cyclic guanosine monophosphate pathway mediates the protection of remote ischemic preconditioning on the microcirculation in liver ischemia-reperfusion injury

BACKGROUND

Remote ischemic preconditioning (RIPC) protects against liver ischemia reperfusion (IR) injury. An essential circulating mediator of this protection is nitric oxide (NO) induced by lower limb RIPC. One of the mechanisms through which NO generally acts is the soluble guanylyl cyclase-cyclic GMP (sGC-cGMP) pathway. The present study aimed to assess the role of hepatic sGC-cGMP in lower limb RIPC-induced protection against liver IR injury.

METHODS

Mice were allocated to 4 groups: 1.Sham; 2.IR: 40 min of lobar hepatic ischemia and 2 hr reperfusion; 3.RIPC+IR: 6 cycles of 4x4 min IR of the lower limb followed by IR group procedure; (4) 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (ODQ)+RIPC+IR: ODQ (sGC inhibitor) was administered followed by RIPC+IR group procedure. Hepatic microcirculatory blood flow (MBF) was measured throughout the experiment. Plasma transaminases, hepatic histopathological and transmission electron microscopy studies were performed at the end of the experiment. Hepatic cGMP levels were measured in groups 1-3 in addition to an RIPC alone group.

RESULTS

Compared to liver IR alone, RIPC+IR increased hepatic MBF during liver reperfusion (P<0.05), and reduced plasma transaminases (P<0.05) and ultrastructural markers of injury. In contrast compared to RIPC+IR, ODQ+RIPC+IR decreased hepatic MBF (P<0.05) and ultrastructural markers of injury. However, plasma transaminases were not significantly different in the ODQ+RIPC+IR compared to the RIPC+IR group. Hepatic cGMP levels were significantly elevated in the RIPC compared to sham group.

CONCLUSIONS

The hepatic sGC-cGMP pathway is required for mediating the protective effects of lower limb RIPC on hepatic MBF in liver IR injury.

The nitric oxide pathway--evidence and mechanisms for protection against liver ischaemia reperfusion injury

Ischaemia reperfusion (IR) injury is a clinical entity with a major contribution to the morbidity and mortality of liver surgery and transplantation. A central pathway of protection against IR injury utilizes nitric oxide (NO). Nitric oxide synthase (NOS) enzymes manufacture NO from L-arginine. NO generated by the endothelial NOS (eNOS) isoform protects against liver IR injury, whereas inducible NOS (iNOS)-derived NO may have either a protective or a deleterious effect during the early phase of IR injury, depending on the length of ischaemia, length of reperfusion and experimental model. In late phase hepatic IR injury, iNOS-derived NO plays a protective role. In addition to NOS consumption of L-arginine during NO synthesis, this amino acid may also be metabolized by arginase, an enzyme whose release is increased during prolonged ischaemia, and therefore diverts L-arginine away from NOS metabolism leading to a drop in the rate of NO synthesis. NO most commonly acts through the soluble guanylyl cyclase-cyclic GMP- protein kinase G pathway to ameliorate hepatic IR injury. Both endogenously generated and exogenously administered NO donors protect against liver IR injury. The beneficial effects of NO on liver IR are not, however, universal, and certain conditions, such as steatosis, may influence the protective effects of NO. In this review, the evidence for, and mechanisms of these protective actions of NO are discussed, and areas in need of further research are highlighted.

Evaluation of Rana snk esculenta blood cell response to chemical stressors in the environment during the larval and adult phases

The assessment of the biological effects on aquatic vertebrate species is frequently employed to monitor water pollution, as it provides significant information on bioavailability and actual concentration levels. In anamniote vertebrates (fish and amphibians), significant correlations have been observed between exposure to contaminants - both natural and experimental - and blood modification. We investigated the changes in some circulating blood cell parameters of green frog (Rana snk esculenta) tadpoles and adults collected at two sample rice fields, one heavily polluted and the other relatively unpolluted. The frequency of eosinophilic leucocytes, mitotic, anucleated and micronucleated erythrocytes was evaluated also regarding the haemopoietic/haemocatheretic and NOS expression of the liver. Haematological indicators in polluted samples were found to be significantly different from controls as regards both larval and adult exposure, and provided information on long-term background pollution of the habitats under investigation. The population of the polluted area showed evident effects of chronic exposure to contaminants, to a degree which could lead to sub-lethal alterations of their health status. The general nature of responses to this kind of stress emphasizes the role of amphibian peripheral blood as a sensitive indicator regarding contamination in aquatic environments.

Ultrastructural, immunohistochemical and biochemical investigations of the rat liver exposed to experimental diabetes und acute hypoxia with and without application of Ginkgo extract

The aim of this paper was to investigate the effect of streptozotocin-induced diabetes by i.p. bolus injection of streptozotocin at 60 mg per kg bodyweight over four months and additional acute respiratory hypoxia (20 min. duration, 5% oxygen v/v), and also the protective effect of Ginkgo biloba extract (EGb 761) on Wistar rat liver under these experimental conditions. Diabetic and additional hypoxic alterations in histology and ultrastructure were subjected to qualitative and quantitative analysis, collagen was investigated by immunohistochemistry, and some biochemical parameters of oxidative stress were determined. Diabetes caused an increase in the size of the hepatocytes and their nuclei with a decrease in nucleus-to-plasma ratio and glycogen content. Connective tissue was variably increased in individual cases as shown by routine histological staining. EGb did not influence these data. Ultrastructural morphometry revealed a significant reduction in rough endoplasmic reticulum (rER) and a significant increase in smooth endoplasmic reticulum (sER) through diabetes, an increase under EGb protection, with no significant alteration under hypoxia. The volume fraction of mitochondria was significantly increased after induction of diabetes but less increased in the protected group. Additional hypoxia reduced this parameter. The mean cross-section area of mitochondria was significantly elevated in all diabetic groups compared to controls. Volume density of mitochondrial cristae was significantly diminished in all diabetic groups; EGb could only improve this parameter in the diabetic-hypoxic group.

Hepatic cytoprotection by nitric oxide and the cGMP pathway after ischaemia-reperfusion in the rat

Many studies in diverse models suggest that nitric oxide (NO) may be protective against liver injury due to ischaemia-reperfusion (IR). We evaluated, in an experimental in vivo model of rat liver partial ischaemia, the effects of pretreatment by an NO donor (spermineNONOate, 5mg/kg), and exogenous cGMP (8Br-cGMP, 16 mg/kg) or an endogenous cGMP producer (ANP, 10 microg/kg), to assess their beneficial effects. After 6h of reperfusion, 8Br-cGMP completely prevented the adverse effect of Nomega-nitro-L-arginine (10mg/kg) and 8Br-cGMP alone showed a protective action on both hepatocytes (AST, -25%, LDH, -55%) and endothelial cells (plasma hyaluronic acid (HA), -30%). ANP caused a marked decrease in AST and LDH activities only after 1h of reperfusion (AST, -30%, LDH, -40%). Pretreatment with spermineNONOate prevented hepatocyte injury after 1 and 6h of reperfusion (AST, -22%, LDH, -27%). However, neither spermineNONOate nor ANP had any protective effect on endothelial cell damage. These results confirm the beneficial effect of an NO donor and strongly suggest the implication of a cGMP pathway that does not involve a blockade of inflammatory cytokines production (IL-6 generation was unaffected by 8Br-cGMP pre-treatment). In our model, 8Br-cGMP showed a greater protective effect than ANP or spermineNONOate and so might be used to prevent hepatic injury after IR. Finally, we propose a schematic representation of the different routes for the actions of NO in protecting the liver against IR damage.

Kupffer cells protect liver from ischemia-reperfusion injury by an inducible nitric oxide synthase-dependent mechanism

The aim of this study was to investigate the role of nitric oxide (NO) in rat hepatic ischemia-reperfusion (I/R) injury. Animals were divided into four groups: Group I, control; Group II, gadolinium chloride (GdCl3), a Kupffer cell depleting agent, pretreated; Group III, S-methylisothiourea (SMT), a potent inducible NO synthase (iNOS) inhibitor, pretreated; Group IV, pretreated with SMT, then treated with S-Nitroso-N-acetylpenicillamine (SNAP), a NO donor, after ischemia. Sprague-Dawley rats underwent left lateral and median lobe ischemia for 60 min and reperfusion for 120 min. The left lateral and median lobes were used as ischemic lobes, and the right lateral lobe in the same rat was used as a control lobe. The total NOS (tNOS), iNOS, constitutive NOS (cNOS) activity, and liver protein were determined. The liver tissue malonaldehyde (MDA) level was measured as an index of lipid peroxidation. Liver histology was also examined. The liver tNOS activity in ischemic lobes of Group I, II, III, and IV was increased by 214%, 86%, 61%, and 45%, respectively. The increase in tNOS activity is mainly due to the induction of iNOS activity in the ischemic lobes of rat liver. GdCl3 significantly decreased the tNOS by 66% in the ischemic lobes. GdCl3 significantly increased MDA by 39% in the ischemic lobes. SMT significantly decreased tNOS and iNOS activity by 66% and 85% in ischemic lobes. SMT increased MDA by 67% in the ischemic lobes. SMT + SNAP treatment increased iNOS activity by 117% in the ischemic lobes in comparison with the ischemic lobes of the SMT group. SMT + SNAP treatment decreased MDA by 39% in the ischemic lobes. SMT + SNAP treatment also decreased the sinusoidal congestion and spotty necrosis of hepatocytes in the ischemic lobes. iNOS immunostaining showed an obvious increase in sinusodial area of the ischemic lobes where most Kupffer cells were interspersed. In conclusion, in this model of liver I/R injury, I/R increased the activity of tNOS and iNOS, but not the cNOS activity. Kupffer cells might be the major source of the induction of iNOS activity. The iNOS specific inhibitor SMT increased the lipid peroxidation and the tissue damage in hepatic I/R injury. On the contrary, the NO donor SNAP increased the activity of iNOS and decreased the hepatic injury in this study. Kupffer cells could protect liver from I/R injury by an iNOS-dependent mechanism, thus NO production has a beneficial role in hepatic IR injury.

Combined use of adenosine and amrinone inhibits reperfusion injury of rat liver

Although intraportal infusion of adenosine suppressed the oxidative stress caused by activated neutrophils and attenuated ischemia-reperfusion injury of canine liver, high doses of adenosine elicit systemic hypotension. The present work demonstrates that combined use of low doses of adenosine and amrinone, a phosphodiesterase inhibitor, strongly inhibited reperfusion injury of the liver without eliciting hypotension. After 45 min ischemia followed by 60 min reperfusion of rat liver, low doses of adenosine and amrinone were administrated intraportally, resulting in significantly increased hepatic levels of cGMP, cAMP, nitrite plus nitrate in plasma, and decreased alanine aminotransferase in plasma without changing hemodynamics. Thus, intraportal administration of low doses of adenosine and amrinone increased the cyclic nucleotides, thereby improved microcirculation and attenuated reperfusion injury of the liver.

Signal transduction of nitric oxide donor-induced protection in hydrogen peroxide-mediated apoptosis in H9C2 cardiomyoblasts

Nitric oxide (NO) attenuates hydrogen peroxide (H2O2)-mediated injury to H9C2 cardiomyoblasts. To examine the role of nitric oxide, cultured H9C2 cardiomyoblasts were treated with H2O2 for 2 h in the presence or absence of the NO donor, diethylamine nitric oxide (DEANO). DEANO (30 microM) attenuated H2O2-induced apoptosis in H9C2 cells. H2O2-exposed H9C2 cells resulted in apoptosis in a time-dependent manner estimated by DNA fragmentation assay, nuclear morphology stained with fluorescent dye, Hoechst 33258 and Annexin V staining. Pretreatment with z-VAD-FMK, a pancaspase inhibitor, or z-DEVD-CHO, a specific caspase-3 inhibitor, completely suppressed the DNA ladder in response to H2O2. An increase in caspase-3-like protease (DEVDase) activity was observed during apoptosis, but no caspase-1 activity (YVADase) was detected. Treatment of H9C2 cells with 100 microM H2O2, resulted in a strong activation of JNK/SAPK. However, the activation of JNK/ SAPK was clearly attenuated by 30 microM DEANO. Furthermore, the dominant negative JNK and SEK1-expressing cells displayed a marked decrease in a number of apoptotic cells. This inhibition of JNK1 in the system is involved in the protection of H2O2-induced apoptosis in H9C2 cardiomyoblasts.