Role of endothelins and nitric oxide in hepatic reperfusion injury in the rat

Cellular and molecular mechanisms of hepatic ischemia-reperfusion injury: The role of oxidative stress and therapeutic approaches

Ischemia-reperfusion (IR) or reoxygenation injury is the paradoxical exacerbation of cellular impairment following restoration of blood flow after a period of ischemia during surgical procedures or other conditions. Acute interruption of blood supply to the liver and subsequent reperfusion can result in hepatocyte injury, apoptosis, and necrosis. Since the liver requires a continuous supply of oxygen for many biochemical reactions, any obstruction of blood flow can rapidly lead to hepatic hypoxia, which could quickly progress to absolute anoxia. Reoxygenation results in the increased generation of reactive oxygen species and oxidative stress, which lead to the enhanced production of proinflammatory cytokines, chemokines, and other signaling molecules. Consequent acute inflammatory cascades lead to significant impairment of hepatocytes and nonparenchymal cells. Furthermore, the expression of several vascular growth factors results in the heterogeneous closure of numerous hepatic sinusoids, which leads to reduced oxygen supply in certain areas of the liver even after reperfusion. Therefore, it is vital to identify appropriate therapeutic modalities to mitigate hepatic IR injury and subsequent tissue damage. This review covers all the major aspects of cellular and molecular mechanisms underlying the pathogenesis of hepatic ischemia-reperfusion injury, with special emphasis on oxidative stress, associated inflammation and complications, and prospective therapeutic approaches.

Role of Mitochondrial Pathways in Cell Apoptosis during He-Patic Ischemia/Reperfusion Injury

Hepatic ischemia-reperfusion injury is a major cause of post-operative hepatic dysfunction and liver failure after transplantation. Mitochondrial pathways can be either beneficial or detrimental to hepatic cell apoptosis during hepatic ischemia/reperfusion injury, depending on multiple factors. Hepatic ischemia/reperfusion injury may be induced by opened mitochondrial permeability transition pore, released apoptosis-related proteins, up-regulated B-cell lymphoma-2 gene family proteins, unbalanced mitochondrial dynamics, and endoplasmic reticulum stress, which are integral parts of mitochondrial pathways. In this review, we discuss the role of mitochondrial pathways in apoptosis that account for the most deleterious effect of hepatic ischemia/reperfusion injury.

Effects of silibinin on hepatic warm ischemia-reperfusion injury in the rat model

OBJECTIVES

Liver ischemia-reperfusion injuries (I/RI) are typically the main causes of liver dysfunction after various types of liver surgery especially liver transplantation. Radical components are the major causes of such direct injuries. We aimed to determine the beneficial effects of silibinin, a potent radical scavenger on liver I/RI.

MATERIALS AND METHODS

Thirty-two rats were divided into 4 groups. Group I: VEHICLE, the rats underwent laparotomy and received DMSO, group II: SILI, laparotomy was done and silibinin was administered. Group III: I/R, the rats received DMSO and were subjected to a liver I/R procedure and group IV: I/R+SILI, the animals underwent the I/R procedure and received silibinin. After 1 hr of ischemia followed by 3 hr reperfusion, blood was collected to evaluate the serum marker of liver injuries. Hepatic tissue was harvested to investigate glycogen content, histological changes, and vasoregulatory gene expression.

RESULTS

Results showed that serum AST, ALT, LDH, GGT, ALP, and hyaluronic acid (HA) increased significantly in I/R group compared with the VEHICLE group. Silibinin reduced this elevation except for GGT. Silibinin inhibited hepatocyte vacuolization and degeneration, endothelium damages, sinusoidal congestion and inflammation, and glycogen depletion during I/R. ET-1 mRNA was overproduced in the I/R group compared with the VEHICLE group which was decreased by silibinin. KLF2 and eNOS expression was reduced during I/R compared with the VEHICLE group. Silibinin elevated KLF2 expression but had no meaningful effect on eNOS expression.

CONCLUSION

Silibinin protected the liver from I/RI. Silibinin could improve liver circulation by preventing sinusoidal congestion, inflammation, and perhaps modification of the vasoregulatory gene expression.

The Impact of Liver Graft Injury on Cancer Recurrence Posttransplantation

Liver transplantation is the most effective treatment for selected patients with hepatocellular carcinoma. However, cancer recurrence, posttransplantation, remains to be the critical issue that affects the long-term outcome of hepatocellular carcinoma recipients. In addition to tumor biology itself, increasing evidence demonstrates that acute-phase liver graft injury is a result of hepatic ischemia reperfusion injury (which is an inevitable consequence during liver transplantation) and may promote cancer recurrence at late phase posttransplantation. The liver grafts from living donors, donors after cardiac death, and steatotic donors have been considered as promising sources of organs for liver transplantation and are associated with high incidence of liver graft injury. The acute-phase liver graft injury will trigger a series of inflammatory cascades, which may not only activate the cell signaling pathways regulating the tumor cell invasion and migration but also mobilize the circulating progenitor and immune cells to facilitate tumor recurrence and metastasis. The injured liver graft may also provide the favorable microenvironment for tumor cell growth, migration, and invasion through the disturbance of microcirculatory barrier function, induction of hypoxia and angiogenesis. This review aims to summarize the latest findings about the role and mechanisms of liver graft injury resulted from hepatic ischemia reperfusion injury on tumor recurrence posttransplantation, both in clinical and animal cohorts.

Effect of cardamonin on hepatic ischemia reperfusion induced in rats: Role of nitric oxide

Ischemia reperfusion (I/R) injury is a cellular damage in a hypoxic organ following the restoration of oxygen delivery. It may occur during organ transplantation, trauma and hepatectomies. Nitric oxide (NO) effects during hepatic I/R are complicated. The iNOS-derived NO has a deleterious effect, whereas eNOS-derived NO has a protective effect in liver I/R. Cardamonin (CDN) is an anti-inflammatory molecule and a novel iNOS inhibitor, and Nω-Nitro-L-arginine (L-NNA) is a NOS inhibitor. L-Arginine is a precursor of NOS. This study was designed to investigate the possible protective effects of CDN on hepatic I/R and the role of NO. Wistar rats were randomly divided into 5 groups (Sham, I/R, CDN, L-NNA and L-arginine). Liver ischemia was induced for 45min then reperfusion was allowed for 1h. L-Arginine and CDN ameliorated the deleterious effects of I/R through reducing the oxidative stress and hepatocyte degeneration. Both molecules decreased the elevated inflammatory cytokines and increased the antiapoptotic marker, Bcl2. Both agents increased NO and eNOS expression and decreased iNOS expression. In conclusion, increased NO/eNOS and suppression of iNOS expression have protective effects on I/R injury. While inhibition of eNOS and reduction of NO have deleterious effects on I/R injury. For the first time, we demonstrated that cardamonin improved functional and structural abnormalities of the liver following I/R by improving oxidative stress and inflammation and increasing the availability of NO produced by eNOS. Treatment with cardamonin could be a promising strategy in patients with hepatic I/R injury in different clinical situations.

New progress in roles of nitric oxide during hepatic ischemia reperfusion injury

Hepatic ischemia reperfusion injury (HIRI) is a clinical condition which may lead to cellular injury and organ dysfunction. The role of nitric oxide (NO) in HIRI is complicated and inconclusive. NO produced by endothelial nitric oxide synthase (eNOS) activation plays a protective role during early HIRI. But eNOS overexpression and the resulting excessive NO bioavailability can aggravate liver injury. NO induced by inducible nitric oxide synthase (iNOS) may have either a protective or a deleterious effect during the early phase of HIRI, but it may protect the liver during late HIRI. Here, we reviewed the latest findings on the role of NO during HIRI: (1) NO exerts a protective effect against HIRI by increasing NO bioavailability, downregulating p53 gene expression, decreasing inflammatory chemokines, reducing ROS via inhibiting the mitochondrial respiratory chain, activating sGC-GTP-cGMP signal pathway to reduce liver cell apoptosis, and regulating hepatic immune functions; (2) eNOS protects against HIRI by increasing NO levels, several eNOS/NO signal pathways (such as Akt-eNOS/NO, AMPK-eNOS/NO and HIF-1α-eNOS/NO) participating in the anti-HIRI process, and inhibiting over-expression of eNOS also protects against HIRI; and (3) the inhibition of iNOS prevents HIRI. Thus, the adverse effects of NO should be avoided, but its positive effect in the clinical treatment of diseases associated with HIRI should be recognized.

Serum levels of endothelin-1 after liver resection as an early predictor of postoperative liver failure. A prospective study

AIM

Besides the residual liver volume, damage of the microcirculation secondary to increased portal blood flow is a main determinant of postoperative liver failure (PLF). Endothelin-1 (ET-1), produced by sinusoidal endothelial cells, plays a key role in the regulation of hepatic microcirculation. The aim of this study was to determine whether ET-1 levels has any prognostic utility in predicting PLF.

METHODS

Patients undergoing liver resection for primary or secondary liver tumors at San Raffaele Hospital, Milan, were prospectively enrolled in the study. Serial postoperative serum ET-1 levels in patients undergoing liver resections were correlated with indices of inflammatory response, liver failure and death.

RESULTS

A total of 144 patients were included. ET-1 levels in patients who underwent major or extended liver resection were significantly higher than in patients who had a minor resection on postoperative day (POD) 1 (P = 0.003), POD 2 (P = 0.0001) and POD 5 (P = 0.0001). Eight patients developed PLF and ET-1 was significantly higher compared with patients without PLF on POD 2 (P = 0.002) and POD5 (P = 0.006). Serum ET-1 concentration on POD 2 was an independent predictor of PLF in multivariate analysis.

CONCLUSION

ET-1 is as an early index of PLF and provides a rationale for therapeutic manipulation, with many potential clinical implications to prevent PLF onset and reduce its severity.

Protective Effect of Nitric Oxide on Liver Circulation from Ischemia Reperfusion Injury

INTRODUCTION

The reduction of endogenous nitric oxide (NO) production during hepatic ischemia-reperfusion injury, generally via a reduction in endothelial NO synthase activity, leads to liver injury. We hypothesized that administration of an exogenous NO donor into the portal vein may ameliorate hepatic blood flow reduction after a period of ischemia.

MATERIAL AND METHODS

A total of 90 min of ischemia (portal vein and hepatic artery) was applied in 15 anesthetized pigs, using the Pringle method under sevoflurane anesthesia. All animals were administered either saline (control group, n = 8) or sodium nitroprusside (SNP, n = 7) as exogenous NO donor drugs into the portal vein, 30 min before and after ischemia. The portal venous blood flow and hepatic artery blood flow were measured continuously using transonic flow probes attached to each vessel. Endogenous NO (NOx = NO2- + NO3-) production was measured every 10 min using a microdialysis probe placed in the left lobe of the liver.

RESULTS

In the SNP group, portal venous flow remained unchanged and hepatic artery flow significantly increased compared to baseline. Although the production of liver tissue NOx transiently decreased to 60% after ischemia, its level in the SNP group remained higher than the control saline group.

CONCLUSION

Regional administration of SNP into the portal vein increases hepatic arterial flow during ischemia reperfusion periods without altering mean systemic arterial pressure. We speculate that administration of an exogenous NO donor may be effective in preventing liver injury via preservation of total hepatic blood flow.

Modulating CD4+ T cell migration in the postischemic liver: hepatic stellate cells as new therapeutic target?

BACKGROUND

CD4+ T cells play a critical role during hepatic ischemia-reperfusion (I/R) injury although the mechanisms of their migration in the postischemic liver remain unclear. We answered the questions of whether hepatic stellate cells (HSCs) interact with CD4+ T cells during I/R of the liver and whether modulation of HSC activity affects T cell-dependent I/R injury.

METHODS

In mice, migration of CD4+ T cells was analyzed in vivo using conventional intravital microscopy and two-photon microscopy. CD4+ T cell-HSC interactions were visualized after infusion of fluorescence-labeled CD4+ T cells into Cx3CR1 mice (mice exhibiting GFP-labeled HSCs) after I/R. Because the activation of HSC is controlled by endocannabinoid receptors, CB-1 and CB-2, the mice received treatment before I/R with the CB-2 agonist JWH-133 to reach HSC depletion or the CB-1 agonist arachidonylcyclopropylamide to activate HSCs. Sinusoidal perfusion and liver transaminases were used as markers of I/R injury.

RESULTS

Hepatic I/R induced CD4+ T cell recruitment in sinusoids. More than 25% of adherent CD4+ T cells were colocalized with HSCs during reperfusion, suggesting a direct cell-cell interaction. The HSC deactivation with JWH-133 significantly attenuated the CD4+ T cell recruitment in the postischemic liver and reduced I/R injury as compared to the vehicle-treated group. The HSC hyperactivation by CB-1, however, did not affect T-cell migration and even increased perfusion failure.

CONCLUSION

Our in vivo data suggest that CD4+ T cells interact with HSCs on their migration into the hepatic parenchyma, and a depletion or deactivation of HSCs protects the liver from T cell-dependent I/R injury.

The role of hepatic ischemia-reperfusion injury and liver parenchymal quality on cancer recurrence

Hepatic ischemia/reperfusion (I/R) injury is a common clinical challenge. Despite accumulating evidence regarding its mechanisms and potential therapeutic approaches, hepatic I/R is still a leading cause of organ dysfunction, morbidity, and resource utilization, especially in those patients with underlying parenchymal abnormalities. In the oncological setting, there are growing concerns regarding the deleterious impact of I/R injury on the risk of post-surgical tumor recurrence. This review aims at giving the last updates regarding the role of hepatic I/R and liver parenchymal quality injury in the setting of oncological liver surgery, using a "bench-to-bedside" approach. Relevant medical literature was identified by searching PubMed and hand scanning of the reference lists of articles considered for inclusion. Numerous preclinical models have depicted the impact of I/R injury and hepatic parenchymal quality (steatosis, age) on increased cancer growth in the injured liver. Putative pathophysiological mechanisms linking I/R injury and liver cancer recurrence include an increased implantation of circulating cancer cells in the ischemic liver and the upregulation of proliferation and angiogenic factors following the ischemic insult. Although limited, there is growing clinical evidence that I/R injury and liver quality are associated with the risk of post-surgical cancer recurrence. In conclusion, on top of its harmful early impact on organ function, I/R injury is linked to increased tumor growth. Therapeutic strategies tackling I/R injury could not only improve post-surgical organ function, but also allow a reduction in the risk of cancer recurrence.

Effect of ghrelin on chronic liver injury and fibrogenesis in male rats: possible role of nitric oxide

Recent studies have revealed that ghrelin may be an antioxidant and anti-inflammatory agent in many organs, however its role in chronic liver injury (CLI) remains unclear. The role of nitric oxide (NO) in CLI is controversial as evidence suggests that NO is either a primary mediator of liver cell injury or exhibits a protective effect against injurious stimuli. Recent evidence demonstrated that the therapeutic potential for ghrelin was through eNOS activation and increase in NO production. However, its role on NO production in the liver has not been previously investigated. The aim of this study was to investigate the role of ghrelin in treatment of CLI, and whether this action is mediated through NO. Forty male rats were divided into four groups: Group I: Control; Group II: chronic liver injury (CLI); Group III: CLI+Ghrelin; and Group IV: CLI+Ghrelin+l-NAME. Liver enzymes and tumor necrosis factor alpha (TNF-α), were measured to assess hepatocellular injury. Liver tissue collagen content, malondialdehyde (MDA), gene expression of Bax, Bcl-2, and eNOS were assessed to determine the mechanism of ghrelin action. Results showed that ghrelin decreased serum liver enzymes and TNF-α levels. Ghrelin also reduced liver tissue collagen, MDA, and Bax gene expression, and increased Bcl-2 and eNOS gene expression. The effects on TNF-α, collagen, MDA, Bax, and eNOS were partially reversed in Group IV, suggesting that ghrelin's action could be through modulation of NO levels. Therefore, ghrelin's hepatoprotective effect is partially mediated by NO release.

Graft cholangiopathy: etiology, diagnosis, and therapeutic strategies

BACKGROUND

Graft cholangiopathy has been recognized as a significant cause of morbidity, graft loss, and even mortality in patients after orthotopic liver transplantation. The aim of this review is to analyze the etiology, pathogenesis, diagnosis and therapeutic strategies of graft cholangiopathy after liver transplantation.

DATA SOURCE

A PubMed database search was performed to identify articles relevant to liver transplantation, biliary complications and cholangiopathy.

RESULTS

Several risk factors for graft cholangiopathy after liver transplantation have been identified, including ischemia/reperfusion injury, cytomegalovirus infection, immunological injury and bile salt toxicity. A number of strategies have been attempted to prevent the development of graft cholangiopathy, but their efficacy needs to be evaluated in large clinical studies. Non-surgical approaches may offer good results in patients with extrahepatic lesions. For most patients with complex hilar and intrahepatic biliary abnormalities, however, surgical repair or re-transplantation may be required.

CONCLUSIONS

The pathogenesis of graft cholangiopathy after liver transplantation is multifactorial. In the future, more efforts should be devoted to the development of more effective preventative and therapeutic strategies against graft cholangiopathy.

Inhibition of glycogen synthase kinase (GSK)-3-β improves liver microcirculation and hepatocellular function after hemorrhagic shock

Ischemia and reperfusion may cause liver injury and are characterized by hepatic microperfusion failure and a decreased hepatocellular function. Inhibition of glycogen synthase kinase (GSK)-3β, a serine-threonine kinase that has recently emerged as a key regulator in the modulation of the inflammatory response after stress events, may be protective in conditions like sepsis, inflammation and shock. Therefore, aim of the study was to assess the role of GSK-3β in liver microcirculation and hepatocellular function after hemorrhagic shock and resuscitation (H/R). Anesthetized male Sprague-Dawley rats underwent pretreatment with Ringer´s solution, vehicle (DMSO) or TDZD-8 (1 mg/kg), a selective GSK-3β inhibitor, 30 min before induction of hemorrhagic shock (mean arterial pressure 35±5 mmHg for 90 min) and were resuscitated with shed blood and Ringer´s solution (2h). 5h after resuscitation hepatic microcirculation was assessed by intravital microscopy. Propidium iodide (PI) positive cells, liver enzymes and alpha-GST were measured as indicators of hepatic injury. Liver function was estimated by assessment of indocyanine green plasma disappearance rate. H/R led to a significant decrease in sinusoidal diameters and impairment of liver function compared to sham operation. Furthermore, the number of PI positive cells in the liver as well as serum activities of liver enzymes and alpha-GST increased significantly after H/R. Pretreatment with TDZD-8 prevented the changes in liver microcirculation, hepatocellular injury and liver function after H/R. A significant rise in the plasma level of IL-10 was observed. Thus, inhibition of GSK-3β before hemorrhagic shock modulates the inflammatory response and improves hepatic microcirculation and hepatocellular function.

Protective effects of branched-chain amino acids on hepatic ischemia-reperfusion-induced liver injury in rats: a direct attenuation of Kupffer cell activation

We determined whether there is a protective effect of branched-chain amino acid (BCAA) on hepatic ischemia-reperfusion (I/R)-induced acute liver injury. Wister rats were divided into the following four groups: simple laparotomy with vehicle; simple laparotomy with BCAA (1 g/kg body wt orally); I/R (30 min clamp) with vehicle; and I/R with BCAA. Serum liver function tests and the gene expression of adhesion molecules (intercellular adhesion molecule and vascular cell adhesion molecule) and vasoconstrictor-related genes (endothelin-1) in the liver were examined. In the in vivo study, portal venous pressure, leukocyte adhesion, and hepatic microcirculation were evaluated. Furthermore, Kupffer cells were isolated and cultured with various concentrations of BCAA in the presence or absence of lipopolysaccharide (LPS). Increased levels of liver function tests following I/R were significantly attenuated by BCAA treatment. The increased expression of adhesion molecules and endothelin-1 was also significantly attenuated by BCAA treatment. Moreover, increased portal venous pressure, enhanced leukocyte adhesion, and deteriorated hepatic microcirculation following I/R were all improved by BCAA treatment. In the experiment using isolated Kupffer cells, the expression of interleukin-6, interleukin-1β, and endothelin-1 in response to LPS stimulation was attenuated by BCAA in a dose-dependent fashion. These results indicate that perioperative oral administration of BCAA has excellent therapeutic potential to reduce I/R-induced liver injury. These beneficial effects may result from the direct attenuation of Kupffer cell activation under stressful conditions.

Melatonin treatment protects liver of Zucker rats after ischemia/reperfusion by diminishing oxidative stress and apoptosis

Fatty livers occur in up to 20% of potential liver donors and increase cellular injury during the ischemia/reperfusion phase, so any intervention that could enable a better outcome of grafts for liver transplantation would be very useful. The effect of melatonin on liver ischemia/reperfusion injury in a rat model of obesity and hepatic steatosis has been investigated. Forty fa/fa Zucker rats were divided in 4 groups. 3 groups were subjected to 35 min of warm hepatic ischemia and 36 h of reperfusion. One experimental group remained untreated and 2 were given 10mg/kg melatonin intraperitoneally or orally. Another group was sham-operated. Plasma ALT, AST and hepatic content of ATP, MDA, hydroxyalkenals, NOx metabolites, antioxidant enzyme activity, caspase-9 and DNA fragmentation were determined in the liver. The expression of iNOS, eNOS, Bcl2, Bax, Bad and AIF were determined by RT-PCR Melatonin was effective at decreasing liver injury by both ways as assessed by liver transaminases, markers of apoptosis, of oxidative stress and improved liver ATP content. Melatonin administration decreased the activities or levels of most of the parameters measured in a beneficial way, and our study identified also some of the mechanisms of protection. We conclude that administration of melatonin improved liver function, as well as markers of pro/antioxidant status and apoptosis following ischemia/reperfusion in obese rats with fatty liver. These data suggest that this substance could improve outcome in patients undergoing liver transplantation who receive a fatty liver implant and suggest the need of clinical trials with it in liver transplantation.

Regulatory mechanisms of injury and repair after hepatic ischemia/reperfusion

Hepatic ischemia/reperfusion injury is an important complication of liver surgery and transplantation. The mechanisms of this injury as well as the subsequent reparative and regenerative processes have been the subject of thorough study. In this paper, we discuss the complex and coordinated responses leading to parenchymal damage after liver ischemia/reperfusion as well as the manner in which the liver clears damaged cells and regenerates functional mass.

Real-time monitoring of liver damage during experimental ischaemia–reperfusion using a nitric oxide sensor

Background

Hepatic ischaemia–reperfusion (IR) injury may lead to liver damage during liver surgery, and intrahepatic nitric oxide (NO) levels may play a role in this context. The aim of this study was to demonstrate real-time changes in intrahepatic NO concentration during IR and to correlate potential hepatic NO production with liver damage using a selective NO sensor.

Methods

Wistar rats were exposed to 15 min of hepatic ischaemia followed by reperfusion, after which changes in intrahepatic NO levels were measured using an NO sensor. Additionally, rats were exposed to five successive periods of IR, each consisting of 15 min ischaemia followed by 5 or 15 min reperfusion, and hepatic damage was evaluated by blood tests and histological examination. Hepatic expression of Akt, phosphorylated Akt, endothelial nitric oxide synthase (eNOS) and phosphorylated eNOS was examined at different time points during and after IR by western blot and immunohistochemical analysis.

Results

During ischaemia, intrahepatic NO levels increased and reached a plateau at approximately 10 min. Repeated 15 min ischaemia–5 min reperfusion cycles reduced the maximum amount of NO produced during ischaemia gradually, and almost no NO production was observed during the fifth period of ischaemia. NO production following repeated ischaemia was proportional to the degree of hepatic viability. Phosphorylated eNOS was upregulated and correlated with the level of NO production during hepatic ischaemia.

Conclusion

Intrahepatic NO levels decrease during repeated IR in rats. Real-time monitoring of intrahepatic NO levels is useful for the prediction of IR-related liver injury during experimental liver surgery.

Pravastatin for thioacetamide-induced hepatic failure and encephalopathy

BACKGROUND

Nitric oxide (NO) inhibition aggravates hepatic damage and encephalopathy and increases mortality in rats with thioacetamide (TAA)-induced acute liver failure. Statins enhance NO production but whether they influence the above parameters are unknown.

MATERIAL AND METHODS

Male Sprague-Dawley rats were used. In the first series, TAA (350 mg/kg per day, i.p. for 3 days) was administered to induce acute liver failure. Control rats received saline. Rats received distilled water or pravastatin (20 mg/kg per day, p.o.) from 2 days before to 3 days after TAA or saline injection. In the second series, liver cirrhosis was induced by common bile duct ligation (BDL). Sham-operated rats served as controls. Rats received distilled water or pravastatin for 5 or 14 days until the 42nd day after operation. On the last day of treatment, survival, motor activities, serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), bilirubin, ammonia and brain histology were evaluated.

RESULTS

Thioacetamide and BDL rats showed higher ALT, AST, bilirubin and ammonia levels and lower motor activity counts compared with their corresponding control groups. In TAA rats, pravastatin elicited higher total and ambulatory motor activity counts and lower AST and total bilirubin levels. Survival was improved, whereas brain H&E staining was not significantly different in TAA rats with or without pravastatin treatment. In BDL groups, rats with or without pravastatin treatment were not different in motor activity counts and liver biochemistry.

CONCLUSIONS

Pravastatin ameliorates hepatic encephalopathy and liver biochemistry and improves survival in rats with acute liver failure, but not in those with cirrhosis.

How Institut Georges Lopez preservation solution protects nonsteatotic and steatotic livers against ischemia-reperfusion injury

The Institut Georges Lopez preservation solution (IGL-1) is a serum-free organ preservative that has been shown to protect steatotic livers against hepatic ischemia-reperfusion injury. Although several hypotheses have been proposed to explain the graft protection mechanisms induced by IGL-1 solution, they have not been fully investigated. This review assessed possible IGL-1 mechanisms responsible for the increased liver tolerance of ischemia-reperfusion injury with special emphasis on vasodilatator mediators such as nitric oxide, on oxidative stress prevention, on protection against mitochondrial damage, and finally on induction of cytoprotective factors.

Innate immunity of the liver microcirculation

The liver is a complex organ with a unique microcirculation and both synthetic and immune functions. Innate immune responses have been studied in response to single inflammatory mediators and several clinically relevant models of infection and injury. While standard histological techniques have been used in many models, the liver microcirculation is also amenable to in vivo examination using epifluorescent, confocal and transillumination intravital microscopy. These techniques have begun to clarify not only the molecular mechanisms but also the specific cell populations involved in the liver inflammation. In this review, we discuss the cells and mediators involved in hepatic innate immunity in simple and complex models of injury and infection, and present the view that the liver microcirculation utilizes non-classical pathways for leukocyte recruitment.

Hepatic ischaemia-reperfusion injury from bench to bedside

BACKGROUND

Vascular occlusion to prevent haemorrhage during liver resection causes ischaemia-reperfusion (IR) injury. Insights into the mechanisms of IR injury gathered from experimental models have contributed to the development of therapeutic approaches, some of which have already been tested in randomized clinical trials.

METHODS

The review was based on a PubMed search using the terms 'ischemia AND hepatectomy', 'ischemia AND liver', 'hepatectomy AND drug treatment', 'liver AND intermittent clamping' and 'liver AND ischemic preconditioning'; only randomized controlled trials (RCTs) were included.

RESULTS

Twelve RCTs reported on ischaemic preconditioning and intermittent clamping. Both strategies seem to confer protection and allow extension of ischaemia time. Fourteen RCTs evaluating pharmacological interventions, including antioxidants, anti-inflammatory drugs, vasodilators, pharmacological preconditioning and glucose infusion, were identified.

CONCLUSION

Several strategies to prevent hepatic IR have been developed, but few have been incorporated into clinical practice. Although some pharmacological strategies showed promising results with improved clinical outcome there is not sufficient evidence to recommend them.

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.

Simvastatin for rats with thioacetamide-induced liver failure and encephalopathy

BACKGROUND AND AIM

Nitric oxide (NO) inhibition aggravates hepatic damage and encephalopathy and increases mortality in rats with thioacetamide (TAA)-induced acute liver failure. Statins enhance NO synthase expression beyond their lipid-lowering capability, but the impact on encephalopathy remains unexplored. The aim of this study was to assess the effects of simvastatin on rats with TAA-induced acute liver damage and hepatic encephalopathy.

METHODS

Sprague-Dawley rats received TAA (350 mg/kg/day) or normal saline (NS) by intraperitoneal injection for 3 consecutive days. Two days before injections, each group was divided into three subgroups, taking (i) distilled water; (ii) simvastatin (20 mg/kg/day); or (iii) simvastatin plus N(G)-nitro-l-arginine methyl ester (L-NAME, 25 mg/kg/day) by oral gavage for 5 days. On the fifth day, severity of encephalopathy was assessed and plasma levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin and ammonia were measured.

RESULTS

The TAA subgroups showed higher ALT, AST, bilirubin and ammonia levels and lower motor activity counts as compared with the NS subgroups. Among the TAA-treated subgroups, rats with simvastatin treatment exerted higher motor activity counts and survival rate (P = 0.043), and a trend of lower ALT, AST, bilirubin and ammonia levels than those receiving saline. All rats that underwent simvastatin plus L-NAME treatment died during or after TAA injections.

CONCLUSIONS

Simvastatin improved encephalopathy and survival in TAA-administered rats. The beneficial effect was offset by L-NAME, suggesting the role of NO in liver damage and encephalopathy.

Gene expression profiling of human liver transplants identifies an early transcriptional signature associated with initial poor graft function

Liver ischemia-reperfusion injury occurring in orthotopic liver transplantation (OLT) may be responsible for early graft failure. Molecular mechanisms underlying initial poor graft function (IPGF) have been poorly documented in human. The purpose of this study was to identify the major transcriptional alterations occurring in human livers during OLT. Twenty-one RNA extracts derived from liver transplant biopsies taken after graft reperfusion were compared with 7 RNA derived from normal control livers. Three hundred seventy-one genes were significantly modulated and classified in molecular pathways relevant to liver metabolism, inflammatory response, cell proliferation and liver protection. Grafts were then subdivided into two groups based on their peak levels of serum aspartate amino transferase within 72 h after OLT (group 1, non-IPGF: 14 patients; group 2, IPGF: 7 patients). The two corresponding data sets were compared using a supervised prediction method. A new set of genes able to correctly classify 71% of the patients was defined. These genes were functionally associated with oxidative stress, inflammation and inhibition of cell proliferation. This study provides a comprehensive picture of the transcriptional events associated with human OLT and IPGF. We anticipate that such alterations provide a framework for the elucidation of the molecular mechanisms leading to IPGF.

Hepatic microcirculatory failure

Liver ischemia has been considered a frequent problem in medical practice, and can be associated to a number of surgical and clinical situations, such as massive hepatic resections, sepsis, liver trauma, circulatory shock and liver transplantation. After restoring blood flow, the liver is further subjected to an additional injury more severe than that induced by ischemia. On account of the complexity of mechanisms related to pathophysiology of ischemia and reperfusion (I/R) injury, this review deals with I/R effects on sinusoidal microcirculation, especially when steatosis is present. Alterations in hepatic microcirculation are pointed as a main factor to explain lower tolerance of fatty liver to ischemia-reperfusion insult. The employment of therapeutic strategies that interfere directly with vasoactive mediators (nitric oxide and endothelins) acting on the sinusoidal perfusion seem to be determinant for the protection of the liver parenchyma against I/R. These approaches could be very suitable to take advantage of marginal specimens as fatty livers, in which the microcirculatory disarrangements hamper its employment in liver transplantation.

Enhanced iNOS Gene Expression in the Steatotic Rat Liver after Normothermic Ischemia

BACKGROUND

Impaired hepatic microcirculation in the steatotic liver has been identified as a considerable factor for increased vulnerability after ischemia/reperfusion (I/R). Changes in regulation and synthesis of vasoactive mediators, such as nitric oxide (NO) and endothelin (ET-1), may result in functional impairment of postischemic sinusoidal perfusion. The aim of the current study was to assess the impact of I/R injury on postischemic gene expression of NO and ET-1 in steatotic livers.

MATERIALS AND METHODS

Male Sprague-Dawley rats with or without hepatic steatosis (induced by carbon tetrachloride treatment) were subjected to normothermic I/R injury. Steady-state mRNA levels were assessed using RT-PCR to study the expression of genes encoding ET-1, NO synthase (endothelial cell NO synthase and inducible NO synthase, iNOS). Immunohistochemistry was performed for detection of iNOS.

RESULTS

I/R injury was followed by increased iNOS gene expression (RT-PCR/immunohistochemistry) in animals with hepatic steatosis, predominately in hepatocytes with fatty degeneration. A mild increase in mRNA levels for ET-1 was found in steatotic rat livers. I/R induced a further increase in ET-1 gene expression in some but not all reperfused steatotic livers.

CONCLUSIONS

We show an enhanced gene expression of iNOS in postischemic steatotic rat livers. Hepatocytes with fatty degeneration appear to be the major source for NO generation. Furthermore, I/R may also induce ET-1 gene expression. Dysregulation of sinusoidal perfusion by NO and ET-1 is therefore likely to contribute to I/R injury of the steatotic liver.

Possible protection of sinusoidal endothelial cells by endothelin B receptor during hepatic warm ischemia-reperfusion

PURPOSE

Endothelins (ETs) are important regulators of the hepatic microcirculation. We investigated the pure biological roles of endothelin B receptors (ETB-Rs) on hepatic warm ischemia-reperfusion (I/R) injury using ETB-R deficient spotting lethal (sl) rats.

METHODS

Homozygous (sl/sl) and wild-type (+/+) rats were exposed to 60 min of 92% partial hepatic ischemia and then were killed at 2, 6, and 24 h, and 3 and 7 days after reperfusion. We measured the serum alanine aminotransferase (ALT) levels to assess hepatocyte injury, and the serum hyaluronic acid (HA) levels and factor VIII-related antigen (FVIIIRAg) staining to assess sinusoidal endothelial cell (SEC) injury. We also measured the concentrations of ET-1 and nitrite (NO2-) and nitrate (NO3-) of liver tissue samples.

RESULTS

Although no significant difference was observed in the ALT levels, the HA levels were significantly elevated at an early stage after reperfusion in the sl/sl rats. Regarding FVIIIRAg staining, positive SECs were enhanced in the sl/sl rats. The ET-1 levels were also significantly elevated at an early stage after reperfusion in the sl/sl rats. Regarding the NO2- and NO3- levels, no significant difference was observed.

CONCLUSION

Endothelin B receptor was shown to have a protective effect on SECs through the inhibition of ET-1 during hepatic warm I/R injury.

Perinecrotic hypoxia contributes to ischemia/reperfusion-accelerated outgrowth of colorectal micrometastases

Ischemia/reperfusion (I/R) is often inevitable during hepatic surgery and may stimulate the outgrowth of colorectal micrometastases. Postischemic microcirculatory disturbances contribute to I/R damage and may induce prolonged tissue hypoxia and consequent stabilization of hypoxia-inducible factor (HIF)-1alpha. The aim of this study was to evaluate the contribution of postischemic microcirculatory disturbances, hypoxia, and HIF-1alpha to I/R-accelerated tumor growth. Partial hepatic I/R attributable to temporary clamping of the left liver lobe induced microcirculatory failure for up to 5 days. This was accompanied by profound and prolonged perinecrotic tissue hypoxia, stabilization of HIF-1alpha, and massive perinecrotic outgrowth of pre-established micrometastases. Restoration of the microcirculation by treatment with Atrasentan and L-arginine minimized hypoxia and HIF-1alpha stabilization and reduced the accelerated outgrowth of micrometastases by 50%. Destabilization of HIF-1alpha by the HSP90 inhibitor 17-DMAG caused an increase in tissue necrosis but reduced I/R-stimulated tumor growth by more than 70%. In conclusion, prevention of postischemic microcirculatory disturbances and perinecrotic hypoxia reduces the accelerated outgrowth of colorectal liver metastases after I/R. This may, at least in part, be attributed to the prevention of HIF-1alpha stabilization. Prevention of tissue hypoxia or inhibition of HIF-1alpha may represent attractive approaches to limiting recurrent tumor growth after hepatic surgery.

Human recombinant erythropoietin protects the striated muscle microcirculation of the dorsal skinfold from postischemic injury in mice

Erythropoietin (EPO) has been proposed as a novel cytoprotectant in ischemia-reperfusion (I/R) injury of the brain, heart, and kidney. However, whether EPO exerts its protection by prevention of postischemic microcirculatory deterioration is unknown. We have investigated the effect of EPO on I/R-induced microcirculatory dysfunctions. We used the mouse dorsal skinfold chamber preparation to study nutritive microcirculation and leukocyte-endothelial cell interaction in striated muscle of the dorsal skinfold by in vivo fluorescence microscopy before 3 h of ischemia and during 5 days of reperfusion. Animals were pretreated with EPO (5,000 U/kg body wt) 1 or 24 h before ischemia. Vehicle-treated I/R-injured animals served as controls. Additional animals underwent sham operation only or were pretreated with EPO but not subjected to I/R. I/R significantly (P < 0.05) reduced functional capillary density, increased microvascular permeability, and enhanced venular leukocyte-endothelial cell interaction during early reperfusion. These findings were associated with pronounced (P < 0.05) arteriolar constriction and diminution of blood flow during late reperfusion. Pretreatment with EPO induced EPO receptor and endothelial nitric oxide synthase expression at 6 h of reperfusion (P < 0.05). In parallel, EPO significantly (P < 0.05) reduced capillary perfusion failure and microvascular hyperpermeability during early reperfusion and arteriolar constriction and flow during late reperfusion. EPO pretreatment substantially (P < 0.05) diminished I/R-induced leukocytic inflammation by reducing the number of rolling and firmly adhering leukocytes in postcapillary venules. EPO applied 1 h before ischemia induced angiogenic budding and sprouting at 1 and 3 days of reperfusion and formation of new capillary networks at 5 days of reperfusion. Thus our study demonstrates for the first time that EPO effectively attenuates I/R injury by preserving nutritive perfusion, reducing leukocytic inflammation, and inducing new vessel formation.

Bromelain ameliorates hepatic microcirculation after warm ischemia

BACKGROUND

Because of its immunomodulatory action, the protease bromelain represents a novel strategy for the treatment of hepatic ischemia/reperfusion (I/R) injury. A dose-response study was performed to investigate the effect of bromelain on liver function, microcirculation, and leukocyte-endothelium interactions in hepatic I/R injury.

MATERIALS AND METHODS

One hundred forty rats were randomized to 8 short-term or 12 long-term groups (n=7 each). A 30 min normothermic hepatic ischemia was induced by Pringle maneuver with a portocaval shunt. Animals were treated 60 min prior to ischemia with either no therapy, 0.1, 1.0, or 10 mg/kg b.w. bromelain i.v. In the short-term experiments, microcirculation was investigated 30 min after sham operation or ischemia using intravital microscopy. In the long-term experiments AST, ALT, and bradykinin levels were determined for 14 d after central venous catheter (CVC) placement only, sham operation, or ischemia. Additionally, apoptosis rate, Kupffer cell activation, endothelial cell damage, and eNOS expression were analyzed.

RESULTS

In sham-operated animals, treatment with 10 mg/kg b.w. bromelain led to a disturbed microcirculation with increased leukocyte adherence, apoptosis rate, Kupffer cell activation, and endothelial cell damage. Six h after CVC placement and administration of 10 mg/kg b.w. bromelain, AST and ALT levels were significantly increased. After I/R, rats treated with 0.1 mg/kg b.w. bromelain showed an improved microcirculation, reduction in leukocyte adhesion, apoptosis rates, Kupffer cell activation and endothelial cell damage, increased eNOS expression, and significantly lower AST levels compared with untreated animals.

CONCLUSION

Bromelain represents a novel approach to the treatment of hepatic I/R injury with a limited therapeutic window.

Steatosis as a risk factor in liver surgery

OBJECTIVE

To review present knowledge of the influence of hepatic steatosis in liver surgery as derived from experimental and clinical studies.

SUMMARY BACKGROUND DATA

Hepatic steatosis is the most common chronic liver disease in the Western world, and it is associated with obesity, diabetes, and metabolic syndrome. Fatty accumulation affects hepatocyte homeostasis and potentially impairs recovery of steatotic livers after resection. This is reflected clinically in increased mortality and morbidity after liver resection in patients with any grade of steatosis. Because of the epidemic increase of obesity, hepatic steatosis will play an even more significant role in liver surgery.

METHODS

A literature review was performed using MEDLINE and key words related to experimental and clinical studies concerning steatosis.

RESULTS

Experimental studies show the increased vulnerability of steatotic livers to various insults, attributed to underlying metabolic and pathologic derangements induced by fatty accumulation. In clinical studies, the severity of steatosis has an important impact on patient outcome and mortality. Even the mildest form of steatosis increases the risk of postoperative complications.

CONCLUSIONS

Hepatic steatosis is a major factor determining patient outcome after surgery. Further research is needed to clarify the clinical relevance of all forms and severity grades of steatosis for patient outcome. Standardized grading and diagnostic methods need to be used in future clinical trials to be able to compare outcomes of different studies.

Role of hepatic nitric oxide synthases in rats with thioacetamide-induced acute liver failure and encephalopathy

BACKGROUND

Hepatic encephalopathy is neuropsychiatric derangement secondary to hepatic decompensation or portal-systemic shunting. Nitric oxide (NO) synthase inhibition aggravates encephalopathy and increases mortality in rats with thioacetamide (TAA)-induced acute liver failure, suggesting a protective role of NO. This study investigated the roles of endothelium-derived constitutive NO synthase (eNOS) and inducible NOS (iNOS) in the liver of rats with fulminant hepatic failure and encephalopathy.

METHODS

Male Sprague-Dawley rats (300-350 g) were randomized to receive TAA 350 mg/kg/day, by intraperitoneal injection or normal saline for 3 days. Severity of encephalopathy was assessed with the Opto-Varimex animal activity meter. Plasma levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase, and bilirubin were measured. Hepatic iNOS and eNOS RNA and protein expressions were assessed by reverse transcription-polymerase chain reaction and Western blot analyses, respectively.

RESULTS

The TAA group showed lower motor activity counts than the normal saline group. Hepatic eNOS, but not iNOS, mRNA and protein expressions were enhanced in the TAA group. In addition, hepatic eNOS mRNA expression was negatively correlated with total movement but positively correlated with ALT and AST. Protein expression of hepatic eNOS was positively correlated with ALT, AST and bilirubin.

CONCLUSION

Upregulation of hepatic eNOS was observed in rats with TAA-induced fulminant hepatic failure and encephalopathy, which might play a regulatory role.

Edaravone reduces ischemia-reperfusion injury mediators in rat liver

BACKGROUND

In hepatic ischemia-reperfusion (I/R) injury, oxidative stress both directly injures the liver and promotes an inflammatory reaction by up-regulating various inflammatory mediators. We investigated whether edaravone, a new hydroxy radical scavenger, could reduce hepatic I/R injury including expression of inflammatory mediators such as cytokines and adhesion molecules.

MATERIALS AND METHODS

Male Sprague-Dawley rats were subjected to 30 min of partial hepatic pedicle clamping (70%) followed by reperfusion. Just after initiation of reperfusion and again 1 h later, edaravone was administered intraportally. After reperfusion hepatic lipid peroxidation was measured by thiobarbituric acid assay, and hepatic injury was quantified by measuring hepatic enzymes in plasma. We serially quantified hepatic expression of mRNAs for tumor necrosis factor (TNF)-alpha and E-selectin, and histologically examined E-selectin expression and neutrophil accumulation.

RESULTS

In the edaravone group, hepatic lipid peroxidation and hepatic enzyme leakage were significantly less than in the saline group. Hepatic expression of TNF-alpha and E-selectin mRNAs was significantly lower in the edaravone than the saline group, at 2 h after initiation of reperfusion. Histologically, E-selectin immunoreactivity and neutrophil accumulation were less evident in hepatic sections from the edaravone group.

CONCLUSIONS

Edaravone reduced hepatic I/R injury by minimizing oxidative stress, and inhibited subsequent injurious inflammation by reducing expression of inflammatory cytokines and adhesion molecules.

[Ischemia-reperfusion syndrome associated with liver transplantation: an update]

Ischemia-reperfusion (I/R) injury is the main cause of both initial graft dysfunction and primary failure in liver transplantation. The search for therapeutic strategies to prevent I/R injury has led to research into promising drugs, although most have not been used clinically. Gene therapy requires better transfection techniques, avoiding vector toxicity, and ethical debate before being used clinically. Ischemic preconditioning is the first therapeutic strategy used in clinical practice to reduce I/R injury in hepatectomies for tumors. Future research will provide data on the effectiveness of ischemic preconditioning in reducing I/R injury associated with liver transplantation, and in reducing the vulnerability of steatotic grafts to I/R syndrome so that they can be used in transplantation, thus relieving the organ shortage.

Histochemical analyses of living mouse liver under different hemodynamic conditions by "in vivo cryotechnique"

Although the morphology and molecular distribution in animal liver tissues have been examined using conventional preparation methods, the findings are always affected by the technical artifacts caused by perfusion-fixation and tissue-resection. Using "in vivo cryotechnique" (IVCT), we have examined living mouse livers with histochemical, immunohistochemical and ultrastructural analyses. In samples prepared by IVCT, widely open sinusoids with many flowing erythrocytes were observed under normal blood circulation, and their collapse or blood congestion was seen in ischemic or heart-arrested mice. In contrast, the sinusoidal cavities were artificially dilated by perfusion-fixation, and collapsed by immersion-fixation and quick-freezing (QF) methods of resected tissues. The immunoreactivity of serum albumin and immunoglobulin G and intensity of periodic acid-Schiff-staining in hepatocytes were well preserved with the QF method and IVCT. Furthermore, following tissue resection, serum proteins were rapidly translocated into hepatocytes as demonstrated by immunoreactions on QF tissues frozen 1 or 5 min after resection. Translocation was not observed in IVCT samples, indicating that IVCT could be useful to examine cell membrane permeability of hepatocytes under different pathological conditions. Both dynamic morphology and immunodistribution of soluble components in living mouse livers, reflecting their physiological and pathological states, can be precisely examined by IVCT with higher time-resolution.

Cytoprotective function of tetrahydrobiopterin in rat liver ischemia/reperfusion injury

BACKGROUND

Tetrahydrobiopterin (BH(4)) is a key coenzyme of nitric oxide synthase (NOS), which is associated with a cytoprotective function in various ischemia-reperfusion (I/R) injury models. There have been a few reports on the efficacy of BH(4) in the treatment of I/R injury in other organs; therefore, the aim of this study was to investigate the effect of BH(4) related with NOS reaction in hepatic I/R injury.

METHODS

A model of 70% liver I/R injury with a 100-minute ischemic time was created in rats, and the non-ischemic lobes were then resected. The rats were given BH(4) (BH(4) group) or saline solution (saline group) before reperfusion. The specific inducible NOS blocker 1400W was used to evaluate the effect of endogenous inducible NOS in the I/R hepatic injury. Survival, nitric oxide products (nitrate and nitrite), NOS expression, and nitrotyrosine (ie, the peroxynitrite product) were measured after reperfusion.

RESULTS

On day 7, the survival rate was 62.5% in the BH(4) group, as opposed to 14.3% in the saline group (P = .0004); 1400W administration to the BH(4) group decreased the survival rate to 0% (P = .003). BH(4) prevented the significant increase in total bilirubin levels (P < .01) after 12-hour reperfusion. The increases in serum alanine transaminase levels (after 3 hours and 12 hours of reperfusion) were significantly (P < .01) attenuated in the BH(4) group. BH(4) increased the nitrate/nitrite concentrations in liver tissue (P < .05) and reduced nitrotyrosine production, and the protein assay showed that BH(4) increased inducible NOS and endothelial NOS expression. Histologic examination of the liver revealed that BH(4) mitigated the damage that was caused by liver I/R.

CONCLUSION

Exogenous BH(4) increased nitric oxide production, which attenuated the hepatic I/R injury.

Inhibition of inducible nitric oxide synthase prevents hepatic, but not pulmonary, injury following ischemia-reperfusion of rat liver

The aim of this study was to investigate the contribution of inducible nitric oxide synthase (iNOS)-derived nitric oxide on the liver and lung injury following hepatic ischemia-reperfusion (I/R) using a novel and potent iNOS inhibitor, ONO-1714. Rats were subjected to 90 min of partial hepatic ischemia followed by 3, 6, 12, and 24 hr of reperfusion. Expression of iNOS mRNA peaked at 3 hr of reperfusion in the liver and lung. Plasma nitric oxide levels were increased fourfold at 24 hr of reperfusion and plasma ALT was increased, reaching a peak at 12 hr of reperfusion; both were significantly inhibited by ONO-1714. Histological examination revealed extensive liver damage, whereas this was not seen in the ONO-1714 group. Lung injury was not significantly changed in groups with versus without ONO-1714. Nitrotyrosine expression was seen in regions similar to those of the histological injuries of the liver, while this staining was absent in the ONO-1714 group. These data show that generation of peroxynitrite could be involved in the pathogenesis of liver injury but not lung injury after hepatic I/R. Inhibition of iNOS could be applied for attenuation of liver injury following hepatic I/R.

Current Understanding of Gender Dimorphism in Hepatic Pathophysiology1

Studies have shown gender dimorphic response of the liver for various hepatic stresses including ischemia/reperfusion, hemorrhagic shock-resuscitation, hepatectomy, liver cirrhosis, endotoxemia, and chronic alcoholic consumption. The mechanisms responsible for the gender dimorphic response include differences in pro-inflammatory cytokine release, production of reactive oxygen species, and alteration in hepatic vasoregulatory action. These effects were shown to be modulated by circulating sex steroid levels. In this regard, modulation of sex steroid levels by agents/drugs has been proposed as a therapeutic option for preventing hepatic damage in various hepatic stress models. Further elucidation of precise mechanisms responsible for the gender-related differences in the hepatic pathophysiology is essential for the potential clinical application of sex hormone modulation therapy. In this article, current progress in our understanding the gender difference in the hepatic pathophysiology under the condition of hepatic stress is reviewed and discussed.

Effect of ischaemic preconditioning on hepatic oxygenation, microcirculation and function in a rat model of moderate hepatic steatosis

IPC (ischaemic preconditioning) may protect the steatotic liver, which is particularly susceptible to I/R (ischaemia/reperfusion) injury. Hepatic steatosis was induced in Sprague-Dawley rats with a high-cholesterol (2%) diet for 12 weeks after which rats were subjected to I/R (ischaemia/reperfusion; 45 min of lobar ischaemia followed by 2 h of reperfusion). Rats were divided into three study groups (n=6 each) receiving: (i) sham laparotomy alone, (ii) I/R, and (iii) IPC (5 min of ischaemia, followed by 10 min of reperfusion) before I/R. Hepatic extra- and intra-cellular oxygenation and HM (hepatic microcirculation) were measured with near-infrared spectroscopy and laser Doppler flowmetry respectively. Plasma liver enzymes and hepatic tissue ATP were measured as markers of liver injury. Histology showed moderate-grade steatosis in the livers. At the end of 2 h of reperfusion, I/R significantly decreased extra- and intra-cellular oxygenation concomitant with a failure of recovery of HM (21.1+/-14.4% of baseline; P<0.001 compared with sham animals). IPC increased intracellular oxygenation (redox state of the copper centre of cytochrome oxidase; P<0.05 compared with rats receiving I/R alone) and flow in HM (70.9+/-17.1% of baseline; P<0.001 compared with rats receiving I/R alone). Hepatocellular injury was significantly reduced with IPC compared with I/R injury alone (alanine aminotransferase, 474.8+/-122.3 compared with 5436.3+/-984.7 units/l respectively; P<0.01; aspartate aminotransferase, 630.8+/-76.9 compared with 3166.3+/-379.6 units/l respectively; P<0.01]. In conclusion, IPC has a hepatoprotective effect against I/R injury in livers with moderate steatosis. These data may have important clinical implications in liver surgery and transplantation.

Effect of Trolox on altered vasoregulatory gene expression in hepatic ischemia/reperfusion

This study was designed to investigate the effect of Trolox, a hydrophilic analogue of vitamin E, on the alteration of vasoregulatory gene expression during hepatic ischemia and reperfusion (I/R). Rats were subjected to 60 min of hepatic ischemia in vivo. The rats were treated intravenously with Trolox (2.5 mg/kg) or the vehicle as a control 5 min before reperfusion. Liver samples were obtained 5 h after reperfusion for a RT-PCR analysis on the mRNA for the genes of interest. These mRNA peptides are endothelin-1 (ET-1), potent vasoconstrictor peptide, its receptor ET(A) and ET(B), vasodilator endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), heme oxygenase-1 (HO-1), tumor necrosis factor-alpha (TNF-alpha) and cyclooxygenase-2 (COX-2). It was seen that serum alanine aminotransferase and lipid peroxidation levels were markedly increased after I/R and Trolox significantly suppressed this increase. In contrast, the glutathione concentration decreased in the I/R group, and this decrease was inhibited by Trolox. ET-1 mRNA expression was increased by I/R, an increase which was prevented by Trolox. The mRNA levels for ET(A) receptor was significantly decreased, whereas ET(B) receptor transcript increased in the I/R group. The increase in ET(A) was prevented by Trolox. The mRNA levels for iNOS and HO-1 significantly increased in the I/R group and Trolox attenuated this increase. There were no significant differences in eNOS mRNA expression among any of the experimental groups. The mRNA levels for COX-2 and TNF-alpha significantly increased in I/R group and Trolox also attenuated this increase. Our findings suggest that I/R induces an imbalanced hepatic vasoregulatory gene expression and Trolox ameliorates this change through its free radical scavenging activity.

Hepatic microcirculatory dysfunction during cholestatic liver injury in rats

OBJECTIVE

: The present study was conducted to elucidate the sequential alterations in the hepatic microvascular inflammatory response to extrahepatic biliary obstruction.

METHODS

: The hepatic microvasculature in anesthetized Sprague-Dawley rats was studied by in vivo microscopy 3, 7, and 14 days after bile duct ligation (BDL) or sham operation.

RESULTS

: The numbers of adhering leukocytes and swollen sinusoidal endothelial cells were significantly increased at 3, 7, and 14 days after BDL when compared with sham-operated controls. Concomitantly, the numbers of sinusoids containing blood flow were significantly and progressively decreased by up to 30%. The phagocytic activity of hepatic macrophages was significantly elevated during the development of biliary cholestasis. In particular, centrilobular phagocytosis at 14 days after BDL was significantly increased 1.4- to 2.0-fold when compared with that at 3 and 7 days after BDL. Electron microscopy also revealed evidence of activated Kupffer cells reflected by numerous filopodia and ruffles.

CONCLUSIONS

: These results suggest that hepatic microcirculatory dysfunction subsequent to BDL contributes to cholestatic liver injury. Microcirculation (2003) 10, 421-432. doi:10.1038/sj.mn.7800208