Novel nitric oxide donor (FK409) ameliorates liver damage during extended liver resection with warm ischemia in dogs

Role of Nitric Oxide and Protein S-Nitrosylation in Ischemia-Reperfusion Injury

Ischemia-reperfusion injury (IRI) is a process in which damage is induced in hypoxic tissue when oxygen supply is resumed after ischemia. During IRI, restoration of reduced nitric oxide (NO) levels may alleviate reperfusion injury in ischemic organs. The protective mechanism of NO is due to anti-inflammatory effects, antioxidant effects, and the regulation of cell signaling pathways. On the other hand, it is generally known that S-nitrosylation (SNO) mediates the detrimental or protective effect of NO depending on the action of the nitrosylated target protein, and this is also applied in the IRI process. In this review, the effect of each change of NO and SNO during the IRI process was investigated.

Role of nitric oxide in liver transplantation: Should it be routinely used?

Ischemia-reperfusion injury (IRI) continues to be a major contributor to graft dysfunction, thus supporting the need for therapeutic strategies focused on minimizing organ damage especially with growing numbers of extended criteria grafts being utilized which are more vulnerable to cold and warm ischemia. Nitric oxide (NO·) is highly reactive gaseous molecule found in air and regarded as a pollutant. Not surprising, it is extremely bioactive, and has been demonstrated to play major roles in vascular homeostasis, neurotransmission, and host defense inflammatory reactions. Under conditions of ischemia, NO· has consistently been demonstrated to enhance microcirculatory vasorelaxation and mitigate pro-inflammatory responses, making it an excellent strategy for patients undergoing organ transplantation. Clinical studies designed to test this hypothesis have yielded very promising results that includes reduced hepatocellular injury and enhanced graft recovery without any identifiable complications. By what means NO· facilitates extra-pulmonary actions is up for debate and speculation. The general premise is that they are NO· containing intermediates in the circulation, that ultimately mediate either direct or indirect effects. A plethora of data exists explaining how NO·-containing intermediate molecules form in the plasma as S-nitrosothiols (e.g., S-nitrosoalbumin), whereas other compelling data suggest nitrite to be a protective mediator. In this article, we discuss the use of inhaled NO· as a way to protect the donor liver graft against IRI in patients undergoing liver transplantation.

Protective effect of eNOS overexpression against ischemia/reperfusion injury in small-for-size liver transplantation

Ischemia/reperfusion (I/R) injury can occur during small-for-size liver transplantation, resulting in delayed graft function and decreased long-term graft survival. The aim of the present study was to evaluate the effects of genetic overexpression of endothelial nitric oxide synthase (eNOS) in protecting hepatocytes against I/R injury in a rat model of small-for-size liver transplantation. L02 liver cells were transfected with the eNOS gene using an adenovirus (Ad-eNOS). eNOS expression was detected using quantitative polymerase chain reaction and western blot analysis. To evaluate the effect of eNOS overexpression, L02 cells were placed in a hypoxic environment for 12 h and immediately transferred to an oxygen-enriched atmosphere. For in vivo testing, rats pretreated with Ad-eNOS or control underwent small-for-size liver transplantation. At 6 h after reperfusion, the bile quantity, serum transaminase and nitric oxide (NO) levels, and histological outcomes were evaluated. Cell apoptosis was assessed by flow cytometry or TUNEL assay. In vitro, Ad-eNOS prevented apoptosis in L02 cells with an increase in the level of NO in culture supernatant. In vivo, Ad-eNOS pre-treatment significantly increased bile production, improved abnormal transaminase levels, diminished apoptosis among liver cells, and decreased hepatocellular damage at 6 h after I/R injury. The eNOS-mediated renal protective effects might be associated with the downregulation of tumor necrosis factor-α and a reduction in macrophage activation in the early stage of reperfusion in small-for-size liver allografts. eNOS-derived NO production significantly attenuates hepatic I/R injury. Thus, eNOS overexpression constitutes a promising therapeutic approach to prevent liver I/R injury following small-for-size liver transplantation.

Protective effect of lisinopril on hepatic ischemia/reperfusion injury in rats

Objective:

Ischemia/reperfusion (I/R) injury plays a key role in the pathogenesis of hepatic failure in several clinical settings such as liver resection or transplantation. Lisinopril, a widely prescribed drug for various cardiovascular conditions, has been reported to have diverse pharmacological properties. The aim of this study, therefore, was to evaluate a potential protective effect of lisinopril on hepatic I/R injury in rats.

Materials and Methods:

In anesthetized rats, partial hepatic ischemia was applied for one hour followed by two hours reperfusion. Biochemical analysis of serum and hepatic tissue was done. Hepatic tissue was also subjected to electron microscopy.

Results:

Pre-ischemic treatment with lisinopril (10 mg/kg) exerted protection against I/R-induced hepatocellular injury as evident by significant decrease in serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), and total bilirubin levels, along with hepatic lipid peroxidation, expressed as malondialdehyde content, with a concurrent increase in hepatic nitric oxide content as compared to I/R group. The electron microscopic examination indicated that lisinopril can effectively protect against hepatic I/R injury.

Conclusion:

Lisinopril provides a protection against hepatic I/R injury in rats. The protective effect is associated with reduction of oxidative stress-induced lipid peroxidation level and enhancement of nitric oxide availability.

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.

Role of nitric oxide in hepatic ischemia-reperfusion injury

Hepatic ischemia-reperfusion injury (IRI) occurs upon restoration of hepatic blood flow after a period of ischemia. Decreased endogenous nitric oxide (NO) production resulting in capillary luminal narrowing is central in the pathogenesis of IRI. Exogenous NO has emerged as a potential therapy for IRI based on its role in decreasing oxidative stress, cytokine release, leukocyte endothelial-adhesion and hepatic apoptosis. This review will highlight the influence of endogenous NO on hepatic IRI, role of inhaled NO in ameliorating IRI, modes of delivery, donor drugs and potential side effects of exogenous NO.

The hepatic microcirculation: mechanistic contributions and therapeutic targets in liver injury and repair

The complex functions of the liver in biosynthesis, metabolism, clearance, and host defense are tightly dependent on an adequate microcirculation. To guarantee hepatic homeostasis, this requires not only a sufficient nutritive perfusion and oxygen supply, but also a balanced vasomotor control and an appropriate cell-cell communication. Deteriorations of the hepatic homeostasis, as observed in ischemia/reperfusion, cold preservation and transplantation, septic organ failure, and hepatic resection-induced hyperperfusion, are associated with a high morbidity and mortality. During the last two decades, experimental studies have demonstrated that microcirculatory disorders are determinants for organ failure in these disease states. Disorders include 1) a dysregulation of the vasomotor control with a deterioration of the endothelin-nitric oxide balance, an arterial and sinusoidal constriction, and a shutdown of the microcirculation as well as 2) an overwhelming inflammatory response with microvascular leukocyte accumulation, platelet adherence, and Kupffer cell activation. Within the sequelae of events, proinflammatory mediators, such as reactive oxygen species and tumor necrosis factor-alpha, are the key players, causing the microvascular dysfunction and perfusion failure. This review covers the morphological and functional characterization of the hepatic microcirculation, the mechanistic contributions in surgical disease states, and the therapeutic targets to attenuate tissue injury and organ dysfunction. It also indicates future directions to translate the knowledge achieved from experimental studies into clinical practice. By this, the use of the recently introduced techniques to monitor the hepatic microcirculation in humans, such as near-infrared spectroscopy or orthogonal polarized spectral imaging, may allow an early initiation of treatment, which should benefit the final outcome of these critically ill patients.

NO Donor Ameliorates Ischemia–Reperfusion Injury of the Rat Liver With iNOS Attenuation

This study investigated the effect of a spontaneous nitric oxide (NO) donor, FK409 (FK), in a rat model of segmental hepatic ischemia. Rats were allocated to four experimental groups. Two of the groups underwent segmental hepatic ischemia of 60 min duration and received FK (0.4 mg/kg, iv) or vehicle alone before inducing ischemia and again 5 min before reperfusion. Sham-FK and sham groups were treated identically, but did not have vascular occlusion. Serum aspartate transaminase (AST), alanine transaminase (ALT), and lactate dehydrogenase (LDH) were measured, and the livers were examined for histological evidence of injury, polymorphonuclear neutrophil (PMN) infiltration, and immunohistochemical expression of inducible NO synthase (iNOS) before and 6 h after reperfusion. AST, ALT, and LDH levels were significantly (p < .05) reduced 6 h after reperfusion in the FK-treated group compared with the vehicle-treated control group. FK treatment also reduced the degree of hepatic damage apparent on histopathology and reduced PMN infiltration and iNOS expression. Thus, FK treatment is protective against hepatic ischemia reperfusion injury and attenuates neutrophil infiltration and iNOS expression.

Nitric oxide mechanism of protection in ischemia and reperfusion injury

In 1992 nitric oxide (NO) was declared molecule of the year by Science magazine, and ever since research on this molecule continues to increase. Following this award, NO was shown to be a mediator/protector of ischemia and reperfusion injury in many organs, such as the heart, liver, lungs, and kidneys. Controversy has existed concerning the actual protective effects of NO. However, literature from the past 15 years seems to reinforce the consensus that NO is indeed protective. Some of the protective actions of NO in ischemia and reperfusion are due to its potential as an antioxidant and anti-inflammatory agent, along with its beneficial effects on cell signaling and inhibition of nuclear proteins, such as NF-kappa B and AP-1. New therapeutic potentials for this drug are also continuously emerging. Exogenous NO and endogenous NO may both play protective roles during ischemia and reperfusion injury. Sodium nitroprusside and nitroglycerin have been used clinically with much success; though only recently have they been tested and proven effective in attenuating some of the injuries associated with ischemia and reperfusion. NO inhalation has, in the past, mostly been used for its pulmonary effects, but has also recently been shown to be protective in other organs. The potential of NO in the treatment of ischemic disease is only just being realized. Elucidation of the mechanism by which NO exerts its protective effects needs further investigation. Therefore, this paper will focus on the mechanistic actions of NO in ischemia and reperfusion injury, along with the compound's potential therapeutic benefits.

Prevention of hepatic ischemia/reperfusion injury by prolonged delivery of nitric oxide to the circulating blood in mice

BACKGROUND

To protect hepatocytes from ischemia/reperfusion injury in mice, prolonged delivery of nitric oxide (NO) to the liver was performed by a bolus intravenous injection of polyethylene glycol (PEG)-conjugated bovine serum albumin (BSA) with about 10 NO molecules attached via an S-nitrosothiol linkage (PEG-poly SNO-BSA).

METHODS

A hepatic ischemia/reperfusion injury was induced in mice by occluding the portal vein and the hepatic artery for 15 min followed by 6 hours of reperfusion. Each NO donor was injected into the tail vein just before the initiation of the reperfusion at a dose of 2 micromol NO/kg.

RESULTS

The ischemia followed by reperfusion resulted in a striking increase in plasma alanine aminotransferase and aspartate aminotransferase activities. S-nitroso-N-acetyl penicillamine and NO-BSA, two classical S-nitrosothiols, had no statistically significant effect in preventing elevation of the markers. In marked contrast, PEG-poly SNO-BSA significantly (P<0.01) suppressed it. In addition, PEG-poly SNO-BSA significantly (P<0.01) reduced the number of neutrophils infiltrating into the liver and prevented the excessive production of NO from inducible NO synthase in the liver.

CONCLUSIONS

These results indicate that PEG-poly SNO-BSA can be used to prevent hepatic ischemia/reperfusion injury.

New preservation strategies for preventing liver grafts against cold ischemia reperfusion injury

BACKGROUND

In spite of improvements in University of Wisconsin (UW) preservation solution, the injury from grafts during cold storage is an unresolved problem in liver transplantation. The aim of the present study was to evaluate the beneficial effect on ischemia-reperfusion injury associated with liver transplantation of the inversion of K(+) and Na(+) concentrations and the replacement of hydroxyethyl starch (HES) by polyethylene glycol (PEG) in UW preservation solution.

METHODS

Using an orthotopic liver transplantation model, the effects on rat liver preservation of a modified preservation solution (UW-PEG) were evaluated, based on the inversion of K(+) and Na(+) concentration and the replacement of HES by PEG 35 kDa (0.03 mmol/L) in UW preservation solution.

RESULTS

The use of UW-PEG preservation solution ameliorated the biochemical and histological parameters of hepatic damage. Thus, at 24 h after transplantation, transaminase levels were reduced significantly when livers were preserved during 8 h in UW-PEG preservation solution compared with the original UW solution. In addition, histological findings revealed fewer and smaller areas of hepatocyte necrosis. The benefits of UW-PEG solution cannot be explained by modifications in oxidative stress or neutrophil accumulation associated with liver transplantation. However, the results of hepatic and portal blood flow indicated that the benefits of this modified preservation solution, UW-PEG were associated with improvements in the microcirculatory disorders after reperfusion.

CONCLUSIONS

The UW-PEG solution, while retaining all the advantages of UW solution, improved hepatic ischemia-reperfusion injury associated with liver transplantation.

eNOS gene therapy exacerbates hepatic ischemia-reperfusion injury in diabetes: a role for eNOS uncoupling

Previous studies indicate that endothelial nitric oxide synthase (eNOS) function is impaired in diabetes as a result of increased vascular generation of reactive oxygen species. We hypothesized that eNOS gene therapy would augment NO. bioavailability and protect against hepatic ischemia-reperfusion (I-R) injury in type 2 diabetes mellitus. We developed a transgenic (Tg) diabetic mouse in which eNOS is systemically overexpressed. We also examined the effects of hepatic eNOS adenovirus therapy in diabetic mice. Diabetic (db/db) and nondiabetic mice were subjected to hepatic I-R injury. In nondiabetic mice, genetic overexpression of eNOS (both eNOS-Tg and eNOS adenovirus) resulted in hepatoprotection. In contrast, hepatic I-R injury was significantly increased in the db/db eNOS-Tg mouse, as serum alanine aminotransaminase (ALT) levels were increased by 3.3-fold compared with diabetic controls. Similarly, eNOS adenovirus treatment resulted in a 3.2-fold increase in serum ALT levels as compared with diabetic controls. We determined that hepatic eNOS was dysfunctional in the db/db mouse and increased genetic expression of eNOS resulted in greater production of peroxynitrite. Treatment with the eNOS cofactor tetrahydrobiopterin (BH4) or the BH4 precursor sepiapterin resulted in a significant decrease in serum ALT levels following I-R injury. We present clear examples of the protective and injurious nature of NO. therapy in I-R. Our data indicate that eNOS exists in an "uncoupled" state in the setting of diabetes and that "recoupling" of the eNOS enzyme with cofactor therapy is beneficial.

The role of nitric oxide in the modulation of hepatic microcirculation and tissue oxygenation in an experimental model of hepatic steatosis

BACKGROUND

Impairment of hepatic microcirculation in fatty liver has been assumed to reduce tolerance of the liver against ischemia-reperfusion injury. The present study was aimed to investigate the role of nitric oxide (NO) in the regulation of hepatic microcirculation and tissue oxygenation in hepatic steatosis.

METHODS

Sprague-Dawley rats (200-250 g) were fed a 2% cholesterol diet (n = 12) to induce hepatic steatosis or normal diet (n = 12) served as controls for 12 weeks. Hepatic blood flow, microcirculation, tissue oxyhemoglobin (HbO2) and cytochrome c oxidase radox status (Cyt Ox) in response to intravenous bolus administrations of l-arginine (300 mg/kg) or l-NAME (20 mg/kg) were assessed.

RESULTS

Animals which developed moderate hepatic steatosis showed significant increase in tissue level of total lipids. Portal blood flow and hepatic microcirculation were significantly reduced as compared to controls (5.7 +/- 0.9 vs. 9.7 +/- 0.9 ml/min, P = 0.003 and 114.5 +/- 9.5 vs. 167.3 +/- 10.0 flux unit, P = 0.003). l-Arginine improved hepatic arterial and portal blood flows as well as microcirculation in fatty livers (P < 0.05), while l-NAME significantly worsened these parameters (P < 0.05). Hepatic tissue HbO2 and Cyt Ox were improved both in fatty and control livers following l-arginine, while l-NAME resulted in decreased HbO2 and Cyt Ox although a transit increase in tissue oxygenation was observed in fatty livers.

CONCLUSIONS

NO is involved in the modulation of hepatic microcirculatory perfusion and oxygenation in cholesterol-induced hepatic steatosis. NO metabolisms may be regulated as a potential therapeutic strategy for impaired microcirculation in hepatic steatosis.

Protective role of endothelial nitric oxide synthase

Nitric oxide is a versatile molecule, with its actions ranging from haemodynamic regulation to anti-proliferative effects on vascular smooth muscle cells. Nitric oxide is produced by the nitric oxide synthases, endothelial NOS (eNOS), neural NOS (nNOS), and inducible NOS (iNOS). Constitutively expressed eNOS produces low concentrations of NO, which is necessary for a good endothelial function and integrity. Endothelial derived NO is often seen as a protective agent in a variety of diseases. This review will focus on the potential protective role of eNOS. We will discuss recent data derived from studies in eNOS knockout mice and other experimental models. Furthermore, the role of eNOS in human diseases is described and possible therapeutic intervention strategies will be discussed.

Ischemic preconditioning increases the tolerance of Fatty liver to hepatic ischemia-reperfusion injury in the rat

Hepatic steatosis is a major risk factor in ischemia-reperfusion. The present study evaluates whether preconditioning, demonstrated to be effective in normal livers, could also confer protection in the presence of steatosis and investigates the potential underlying protective mechanisms. Fatty rats had increased hepatic injury and decreased survival after 60 minutes of ischemia compared with lean rats. Fatty livers showed a degree of neutrophil accumulation and microcirculatory alterations similar to that of normal livers. However, in presence of steatosis, an increased lipid peroxidation that could be reduced with glutathione-ester pretreatment was observed after hepatic reperfusion. Ischemic preconditioning reduced hepatic injury and increased animal survival. Both in normal and fatty livers, this endogenous protective mechanism was found to control lipid peroxidation, hepatic microcirculation failure, and neutrophil accumulation, reducing the subsequent hepatic injury. These beneficial effects could be mediated by nitric oxide, because the inhibition of nitric oxide synthesis and nitric oxide donor pretreatment abolished and simulated, respectively, the benefits of preconditioning. Thus, ischemic preconditioning could be an effective surgical strategy to reduce the hepatic ischemia-reperfusion injury in normal and fatty livers under normothermic conditions, including hepatic resections, and liver transplantation.