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

How to Preserve Steatotic Liver Grafts for Transplantation

Liver allograft steatosis is a significant risk factor for postoperative graft dysfunction and has been associated with inferior patient and graft survival, particularly in the case of moderate or severe macrovesicular steatosis. In recent years, the increasing incidence of obesity and fatty liver disease in the population has led to a higher proportion of steatotic liver grafts being used for transplantation, making the optimization of their preservation an urgent necessity. This review discusses the mechanisms behind the increased susceptibility of fatty livers to ischemia-reperfusion injury and provides an overview of the available strategies to improve their utilization for transplantation, with a focus on preclinical and clinical evidence supporting donor interventions, novel preservation solutions, and machine perfusion techniques.

The effect of transient oxygenation on stem cell mobilization and ischemia/reperfusion heart injury

For general anesthesia, pre-oxygenation is routinely performed prior to intubation. It is well-known that ischemic/hypoxic preconditioning induces stem cell mobilization and protects against ischemia/reperfusion (I/R) injury. In this study, we investigated the effect of transient oxygenation on stem cell mobilization and I/R injury of the heart. Mice were exposed to 100% oxygen for 5 or 20 minutes. We evaluated the number of c-kit+ stem/progenitor cells and the levels of SDF-1α and VEGF in peripheral blood at 1, 3, 6, and 24 hours after oxygenation. We also induced I/R injury of the heart at 3 hours post-oxygenation for 5 minutes and then examined stem cell recruitment and fibrotic changes in the heart 3 or 14 days later. The number of c-kit+ cells in peripheral blood was significantly increased at 1 or 24 hours after oxygenation for either 5 or 20 minutes. Oxygenation for 5 or 20 minutes did not significantly change the SDF-1α level measured in plasma. However, the plasma VEGF level was decreased at 3 hours post-oxygenation for 20 minutes (p = 0.051). Oxygenation for 5 minutes did not significantly alter the fibrotic area or cell apoptosis. Although oxygenation for 5 minutes increased the number of c-kit+ cells in hearts damaged by I/R injury, this difference was not significant between groups due to large variation between individuals (p = 0.14). Although transient oxygenation induces stem cell mobilization, it does not appear to protect against I/R injury of the heart in mice.

A systematic review and meta-analysis of donor ischaemic preconditioning in liver transplantation

Ischaemic preconditioning (IPC) is a strategy to reduce ischaemia-reperfusion (IR) injury. Its benefit in human liver transplantation is unclear. The aim of this study was to analyse the current evidence for donor IPC in liver transplantation. Systematic review and meta-analysis of studies involving IPC of liver transplant donors. Ovid Medline, Embase and Cochrane CENTRAL were searched up until January 2015. Data retrieved included the primary outcomes of 1-year mortality, incidence of primary graft non-function (PGNF) and retransplantation. Secondary outcomes included aspartate aminotransferase (AST) levels on day 3 post-op. Pooled odds ratios (ORs) were calculated for dichotomous data and mean weighted ratios for continuous data. Ten studies included 593 patients (286 IPC; 307 control). IPC was associated with a reduction in mortality at 1 year (6% vs. 11%) although this was not statistically significant (OR 0.54, 95% C.I. 0.28-1.04, P = 0.06). The IPC group had a significantly lower day 3 AST level (WMD -66.41iU, P = 0.04). This meta-analysis demonstrates that IPC reduces liver injury following transplantation and produces a large reduction in 1-year mortality which was not statistically significant. Confirmation of clinical benefit from IPC requires an adequately powered prospective RCT.

Pharmacological Preconditioning by Adenosine A2a Receptor Stimulation: Features of the Protected Liver Cell Phenotype

Ischemic preconditioning (IP) of the liver by a brief interruption of the blood flow protects the damage induced by a subsequent ischemia/reperfusion (I/R) preventing parenchymal and nonparenchymal liver cell damage. The discovery of IP has shown the existence of intrinsic systems of cytoprotection whose activation can stave off the progression of irreversible tissue damage. Deciphering the molecular mediators that underlie the cytoprotective effects of preconditioning can pave the way to important therapeutic possibilities. Pharmacological activation of critical mediators of IP would be expected to emulate or even to intensify its salubrious effects. In vitro and in vivo studies have demonstrated the role of the adenosine A2a receptor (A2aR) as a trigger of liver IP. This review will provide insight into the phenotypic changes that underline the resistance to death of liver cells preconditioned by pharmacological activation of A2aR and their implications to develop innovative strategies against liver IR damage.

Impact of ischaemic preconditioning on experimental steatotic livers following hepatic ischaemia-reperfusion injury: a systematic review

BACKGROUND

Steatotic livers are vulnerable to the deleterious effects of ischaemia-reperfusion injury (IRI) that occur after hepatic surgery. Ischaemic preconditioning (IPC) has been shown to abrogate the effects of IRI in patients undergoing hepatic surgery. Experimental studies have suggested that IPC may be beneficial in steatotic livers subjected to IRI.

OBJECTIVE

The aim of this systematic review was to evaluate the effects of IPC on steatotic livers following hepatic IRI in experimental models.

METHODS

An electronic search of the OVID Medline and EMBASE databases was performed to identify studies that reported clinically relevant outcomes in animal models of hepatic steatosis subjected to IPC and IRI.

RESULTS

A total of 1093 articles were identified, of which 18 met the inclusion criteria. There was considerable heterogeneity in the type of animal model, and duration and type of IRI. Increased macrovesicular steatosis (> 30%) was associated with a poor outcome following IRI. Ischaemic preconditioning was found to be beneficial in > 30% steatotic livers and provided for decreased histological damage, improved liver function findings and increased survival.

CONCLUSIONS

Experimental evidence supports the use of IPC in steatotic livers undergoing IRI. These findings may be applicable to patients undergoing liver surgery. However, clinical studies are required to validate the efficacy of IPC in this setting.

Rodent models of hepatic ischemia-reperfusion injury: time and percentage-related pathophysiological mechanisms

Ischemia and reperfusion (IR) injury remains one of the major problems in liver surgery and transplantation, which determines the viability of the hepatic tissue after resection and of the grafted organ. This review aims to elucidate the mechanisms involved in IR injury of the liver in rodent experimental studies and the preventative methods and pharmacologic agents that have been applied. Many time- and percentage-related liver IR injury rodent models have been used to examine the pathophysiological mechanisms and the parameters implicated with different morbidity, mortality, and pathology findings. The most preferred experimental rodent model of liver IR is the induction of 70% IR for 45 min, which is associated with almost 100% survival. In this model, plasma levels of several parameters such as alanine transaminase, aspartate aminotransferase, gamma-glutamyltransferase, endothelin-1, malonodialdehyde, tumor necrosis factor α, interleukin 1b, inducible nitric oxide synthase, and caspases are increased. The increase of caspases is associated with the initiation of hepatic cellular apoptosis. The main injuries observed 24 h after reperfusion are nuclear pyknosis, cytoplasmic hypereosinophilia, severe necrosis, and loss of intercellular borders. Both ischemic pre- and post-conditioning preventative methods and pharmacologic agents are successfully applied to alleviate the IR injuries. The selection of the time- and percentage-related liver IR injury rodent model and the potential preventative method should be related to the clinical question being answered.

The impact of hepatic steatosis on hepatic ischemia-reperfusion injury in experimental studies: a systematic review

Background. The impact of hepatic steatosis on outcome following hepatic ischemia-reperfusion injury (IRI) remains controversial with conflicting clinical results. A number of experimental studies have been published examining the relationship between hepatic steatosis and IRI. This systematic review evaluates these experimental studies. Methods. An electronic search of the Medline and Embase databases (January 1946 to June 2012) was performed to identify studies that reported relevant outcomes in animal models of hepatic steatosis subjected to IRI. Results. A total of 1314 articles were identified, of which 33 met the predefined criteria and were included in the study. There was large variation in the type of animal model, duration, and type of IRI and reporting of histological findings. Increased macrovesicular steatosis (>30%) was associated with increased histological damage, liver function derangement, and reduced survival. Increased duration of warm or cold ischemia had a negative impact on all outcomes measured. Microvesicular steatosis did not influence outcome. Conclusions. Findings from this systemic review support the hypothesis that livers with >30% macrovesicular steatosis are less tolerant of IRI. Clinically, it is likely that these findings are applicable to patients undergoing hepatic resection, but further studies are required to confirm these data.

Strategies to rescue steatotic livers before transplantation in clinical and experimental studies

The shortage of donor livers has led to an increased use of organs from expanded criteria donors. Included are livers with steatosis, a metabolic abnormality that increases the likelihood of graft complications post-transplantation. After a brief introduction on the etiology, pathophysiology, categories and experimental models of hepatic steatosis, we herein review the methods to rescue steatotic donor livers before transplantation applied in clinical and experimental studies. The methods span the spectrum of encouraging donor weight loss, employing drug therapy, heat shock preconditioning, ischemia preconditioning and selective anesthesia on donors, and the treatment on isolated grafts during preservation. These methods work at different stages of transplantation process, although share similar molecular mechanisms including lipid metabolism stimulation through enzymes or nuclear receptor e.g., peroxisomal proliferator-activated receptor, or anti-inflammation through suppressing cytokines e.g., tumor necrosis factor-α, or antioxidant therapies to alleviate oxidative stress. This similarity of molecular mechanisms implies possible future attempts to reinforce each approach by repeating the same treatment approach at several stages of procurement and preservation, as well as utilizing these alternative approaches in tandem.

Influence of Kupffer cells and platelets on ischemia-reperfusion injury in mild steatotic liver

AIM: To investigate the effect of mild steatotic liver on ischemia-reperfusion injury by focusing on Kupffer cells (KCs) and platelets.

METHODS: Wistar rats were divided into a normal liver group (N group) and a mild steatotic liver group (S group) induced by feeding a choline-deficient diet for 2 wk. Both groups were subjected to 20 min of warm ischemia followed by 120 min of reperfusion. The number of labeled KCs and platelets in sinusoids and the blood perfusion in sinusoids were observed by intravital microscopy (IVM), which was performed at 30, 60 and 120 min after reperfusion. To evaluate serum alanine aminotransferase as a marker of liver deterioration, blood samples were taken at the same time as IVM.

RESULTS: In the S group, the number of platelets adhering to KCs decreased significantly compared with the N group (120 after reperfusion; 2.9 ± 1.1 cells/acinus vs 4.8 ± 1.2 cells/acinus, P < 0.01). The number of KCs in sinusoids was significantly less in the S group than in the N group throughout the observation periods (before ischemia, 19.6 ± 3.3 cells/acinus vs 28.2 ± 4.1 cells/acinus, P < 0.01 and 120 min after reperfusion, 29.0 ± 4.3 cells/acinus vs 40.2 ± 3.3 cells/acinus, P < 0.01). The blood perfusion of sinusoids 120 min after reperfusion was maintained in the S group more than in the N group. Furthermore, elevation of serum alanine aminotransferase was lower in the S group than in the N group 120 min after reperfusion (99.7 ± 19.8 IU/L vs 166.3 ± 61.1 IU/L, P = 0.041), and histological impairment of hepatocyte structure was prevented in the S group.

CONCLUSION: Ischemia-reperfusion injury in mild steatotic liver was attenuated compared with normal liver due to the decreased number of KCs and the reduction of the KC-platelet interaction.

Immediately transcripted genes in various hepatic ischemia models

PURPOSE

To elucidate the characteristic gene transcription profiles among various hepatic ischemia conditions, immediately transcribed genes and the degree of ischemic injury were compared among total ischemia (TI), intermittent clamping (IC), and ischemic preconditioning (IPC).

METHODS

Sprague-Dawley rats were equally divided into control (C, sham-operated), TI (ischemia for 90 minutes), IC (ischemia for 15 minutes and reperfusion for 5 minutes, repeated six times), and IPC (ischemia for 15 minutes, reperfusion for 5 minutes, and ischemia again for 90 minutes) groups. A cDNA microarray analysis was performed using hepatic tissues obtained by partial hepatectomy after occluding hepatic inflow.

RESULTS

THE CDNA MICROARRAY REVEALED THE FOLLOWING: interleukin (IL)-1β expression was 2-fold greater in the TI group than in the C group. In the IC group, IL-1α/β expression increased by 2.5-fold, and Na+/K+ ATPase β1 expression decreased by 2.4-fold. In the IPC group, interferon regulatory factor-1, osteoprotegerin, and retinoblastoma-1 expression increased by approximately 2-fold compared to that in the C group, but the expression of Na+/K+ ATPase β1 decreased 3-fold.

CONCLUSION

The current findings revealed characteristic gene expression profiles under various ischemic conditions. However, additional studies are needed to clarify the mechanism of protection against IPC.

Nitric oxide is an essential mediator of the protective effects of remote ischaemic preconditioning in a mouse model of liver ischaemia/reperfusion injury

NO (nitric oxide) may protect the liver from IR (ischaemia/reperfusion) injury. RIPC (remote ischaemic preconditioning) also protects against liver IR injury; however, the molecular mediator(s) of RIPC are currently unknown. The aim of the present study was to assess the role of NO in hindlimb RIPC-induced protection against liver IR injury. Mice were allocated to the following groups: sham group; RIPC group (six cycles of 4×4 min IR of hindlimb); IR group [40 min lobar (70%) hepatic ischaemia and 2-h reperfusion]; RIPC+IR group (RIPC followed by IR group procedures); and C-PTIO [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt]+RIPC+IR group [C-PTIO (a direct NO scavenger) was administered, followed by the RIPC+IR group procedure]. Hepatic MBF (microcirculatory blood flow) was measured throughout the experiment. Circulating NOx (nitrite and nitrate) levels, plasma liver transaminases, hepatic histopathological and TEM (transmission electron microscopy) studies were performed at the end of the experiment. NOx concentrations were significantly elevated (P<0.05) in the RIPC and RIPC+IR groups. Compared with liver IR alone, RIPC+IR preserved hepatic MBF during liver reperfusion (P<0.05). In contrast, C-PTIO+RIPC+IR reduced MBF compared with RIPC+IR (P<0.05). RIPC+IR reduced plasma transaminases (P<0.05), and histopathological and ultrastructural features of injury compared with IR alone. The protective effects of RIPC+IR in reducing liver IR injury were abrogated in the group that received antecedent C-PTIO (C-PTIO+RIPC+IR). In conclusion, NO is an essential mediator of the protection afforded by hindlimb RIPC against liver IR injury. The mechanisms underlying this protection involve preservation of the sinusoidal structure and maintenance of blood flow through the hepatic microcirculation.

Ischemia/reperfusion injury in liver resection: a review of preconditioning methods

Ischemic preconditioning is one of the therapeutic interventions aiming at preventing ischemia/reperfusion-related injury. Numerous experimental studies and a few clinical series have shown that during liver resections, ischemic preconditioning is a promising strategy for optimizing the postoperative outcome. Moreover, various types of pharmacological intervention as well as different types of preconditioning, such as remote preconditioning, the use of heat shock, and hyperbaric oxygen, have been developed to attenuate the functional impairment accompanying ischemia/reperfusion injury. This review summarizes the various forms of preconditioning, thus suggesting that close cooperation between surgeons and anesthesiologists paves the way to apply novel strategies to improve the outcome of liver resection.

Intermittent ischaemia maintains function after ischaemia reperfusion in steatotic livers

BACKGROUND

Ischaemic preconditioning (IPC) and intermittent ischaemia (INT) reduce liver injury after ischaemia reperfusion (IR). Steatotic livers are at a higher risk of IR injury, but the protection offered by IPC and INT is not well understood. The aim of the present study was to determine the effectiveness of IPC and INT in maintaining liver function in steatotic livers.

MATERIAL AND METHODS

A model of segmental hepatic ischaemia (45 min) and reperfusion (60 min) was employed using lean and obese Zucker rats. Bile flow recovery was measured to assess dynamic liver function, hepatocyte fat content quantified and blood electrolytes, metabolites and bile calcium measured to assess liver and whole body physiology. Liver marker enzymes and light and electron microscopy were employed to assess hepatocyte injury.

RESULTS

IPC was not effective in promoting bile flow recovery after IR in either lean or steatotic livers, whereas INT promoted good bile flow recovery in steatotic as well as lean livers. However, the bile flow recovery in steatotic livers was less than that in lean livers. In steatotic livers, ischaemia led to a rapid and substantial decrease in fat content. Steatotic livers were more susceptible to IR injury than lean livers, as indicated by increased blood ALT concentrations and major histological injury.

CONCLUSION

INT is more effective than IPC in restoring liver function in the acute phase of IR in steatotic livers. In obese patients, INT may be useful in promoting better liver function after IR after liver resection.

Intracellular oxygenation and cytochrome oxidase C activity in ischemic preconditioning of steatotic rabbit liver

BACKGROUND

Mild to moderate steatotic livers are used as marginal donors in liver transplantation. Very little is known about the mechanisms of ischemia reperfusion (IR) injury (IRI) in fatty liver. This study aimed to establish whether cytochrome oxidase C (COX) activity is compromised by IRI in fatty liver and whether ischemic preconditioning (IPC) can protect COX activity.

METHODS

New Zealand rabbits were fed on a high-cholesterol diet for 8 weeks to induce moderate hepatic steatosis. Three groups were tested. The IR group underwent 60 minutes of ischemia, followed by 7 hours of reperfusion. The IPC group (IPC + IR) underwent 5 minutes of ischemia, followed by 10 minutes of reperfusion and then 60 minutes of ischemia and 7 hours of reperfusion. The control group (sham) underwent the same surgical procedure, but ischemia was not induced. Deoxyhemoglobin, oxyhemoglobin, and change in the redox state of COX was continuously monitored in vivo by near-infrared spectroscopy. COX and citrate synthase (CS) activity assays were carried out on liver biopsy specimens in vitro. Bile was collected continuously during the procedure and analyzed using proton nuclear magnetic resonance spectroscopy.

RESULTS

The IR group had decreased COX activity and tissue oxygenation represented by deoxyhemoglobin, oxyhemoglobin, COX, and elevated redox ratios of lactate/pyruvate and β-hydroxybutarate/acetoacetate in vivo and a decrease in COX and CS activity in vitro. The IPC + IR group showed higher levels of all measured parameters in vivo and showed a smaller decrease in COX and CS activity in vitro.

CONCLUSION

This study shows that IRI affects COX activity in fatty livers. This is attenuated by IPC.

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.

Role of ischemic preconditioning in liver surgery and hepatic transplantation

INTRODUCTION

The purpose of this review is to summarize intraoperative surgical strategies available to decrease ischemia-reperfusion injury associated with liver resection and liver transplantation.

MATERIAL AND METHOD

We conducted a critical review of the literature evaluating the potential applications of hepatic ischemic preconditioning (IPC) for hepatic resection surgery and liver transplantation. In addition, we provide a basic bench-to-bedside summary of the liver physiology and cell signaling mechanisms that account for the protective effects seen with hepatic IPC.

The in-vivo effect of pyrrolidine dithiocarbamate on hepatic parenchymal microcirculation and oxygenation of the rat liver

OBJECTIVE

Pyrrolidine dithiocarbamate has been shown to be a potent inducer of haemeoxygenase-1. This study investigated its in-vivo effects on systemic and hepatic microcirculatory perfusion.

METHODS

Male Sprague-Dawley rats (n=12) were administered intravenously with pyrrolidine dithiocarbamate (10, 20 and 50 mg/kg body weight) or vehicle (0.2 ml physiological saline) served as control. Systemic and hepatic haemodynamics including arterial oxygen saturation, heart rate, mean arterial blood pressure and portal blood flow were monitored. Microcirculation in skeletal muscle and liver was measured by laser Doppler flowmetry and intravital fluorescence microscopy, whereas hepatic tissue oxyhaemoglobin and cytochrome oxidase CuA redox state, which is an indicative of extracellular and intracellular oxygenation were measured by near infrared spectroscopy.

RESULTS

Pyrrolidine dithiocarbamate induced a dose-dependent increase in mean arterial blood pressure and skeletal muscle microcirculation. The hepatic parenchymal microcirculation was significantly improved and an increase in sinusoidal diameter and reduction in RBC velocity were observed. Pyrrolidine dithiocarbamate also showed beneficial effect on hepatic tissue oxygenation showed by an increase in oxyhaemoglobin and cytochrome oxidase CuA redox state as well.

CONCLUSION

Pyrrolidine dithiocarbamate improves hepatic parenchymal microcirculation and tissue oxygenation, suggesting that it may be used as a potential agent in pharmacological preconditioning in the liver.

Ischemic preconditioning of the liver: a few perspectives from the bench to bedside translation

Utilization of ischemic preconditioning to ameliorate ischemia/reperfusion injury has been extensively studied in various organs and species for the past two decades. While hepatic ischemic preconditioning in animals has been largely beneficial, translational efforts in the two clinical contexts--liver resection and decreased donor liver transplantation--have yielded mixed results. This review is intended to critically examine the translational data and identify some potential reasons for the disparate clinical results, and highlight some issues for further studies.

Current studies on therapeutic approaches for ischemia/reperfusion injury in steatotic livers

Steatotic livers are particularly vulnerable to ischemia/reperfusion (I/R) injury, resulting in poor outcomes following liver surgery and transplantation. Therapeutic approaches for I/R injury in steatotic livers are currently under intensive investigation. This review summarizes and discusses the approaches developed during the last few years to prevent hepatic I/R injury in steatotic livers. Among the proposed approaches, ischemic preconditioning and intermittent clamping are the two most promising approaches that have been applied in some clinical centers for liver surgery and transplantation, but most of others have not reached clinical application yet.

El preacondicionamiento isquémico del hígado: de las bases moleculares a la aplicación clínica

Ischemia-reperfusion injury is produced when an organ is deprived of blood flow (ischemia), which is then restored (reperfusion). In certain circumstances, this injury leads to irreversible organ damage. Several therapeutic strategies have been used to reduce the severity of this injury. One of these strategies is the application of brief and repetitive episodes of ischemia-reperfusion before prolonged ischemia-reperfusion (ischemic preconditioning). In the present article we review the molecular mechanisms through which ischemic preconditioning confers protection against ischemia-reperfusion injury. The application of ischemic preconditioning during liver surgery is discussed, both in normothermic situations such as liver resection and in situations of low temperature such as liver transplantation.

Heat shock proteins and mitogen-activated protein kinases in steatotic livers undergoing ischemia-reperfusion: some answers

Ischemic preconditioning protects steatotic livers against ischemia-reperfusion (I/R) injury, but just how this is achieved is poorly understood. Here, I/R or preconditioning plus I/R was induced in steatotic and nonsteatotic livers followed by investigating the effect of pharmacological treatments that modulate heat shock proteins (HSPs) and mitogen-activated protein kinases (MAPKs). MAPKs, HSPs, protein kinase C, and transaminase levels were measured after reperfusion. We report that preconditioning increased HSP72 and heme-oxygenase-1 (HO-1) at 6 and 24 hours of reperfusion, respectively. Unlike nonsteatotic livers, steatotic livers benefited from HSP72 activators (geranylgeranylacetone) throughout reperfusion. This protection seemed attributable to HO-1 induction. In steatotic livers, preconditioning and geranylgeranylacetone treatment (which are responsible for HO-1 induction) increased protein kinase C activity. HO-1 activators (cobalt(III) protoporphyrin IX) protected both liver types. Preconditioning reduced p38 MAPK and c-Jun N-terminal kinase (JNK), resulting in HSP72 induction though HO-1 remained unmodified. Like HSP72, both p38 and JNK appeared not to be crucial in preconditioning, and inhibitors of p38 (SB203580) and JNK (SP600125) were less effective against hepatic injury than HO-1 activators. These results provide new data regarding the mechanisms of preconditioning and may pave the way to the development of new pharmacological strategies in liver surgery.

Hepatic ischemia-reperfusion injury: roles of Ca2+ and other intracellular mediators of impaired bile flow and hepatocyte damage

Liver resection and liver transplantation have been successful in the treatment of liver tumors and end-stage liver disease. This success has led to an expansion in the pool of patients potentially treatable by liver surgery and, in the case of transplantation, to a shortage of liver donors. At present, there are significant numbers of potential candidates for liver resection and liver donation who have fatty livers, are aged, or have livers damaged by chemotherapy. All of these are at high risk for ischemic reperfusion (IR) injury. The aims of this review are to assess current knowledge of the clinical effectiveness of ischemic preconditioning and intermittent ischemia in reducing IR damage in liver surgery; to evaluate the use of bile flow as a sensitive indicator of IR liver damage; and to analyze the molecular mechanisms, especially intracellular Ca2+, involved in IR injury and ischemic preconditioning. It is concluded that bile flow is a sensitive indicator of IR injury. Together with reactive oxygen species (ROS) and other extracellular and intracellular signaling molecules, intracellular Ca2+ in hepatocytes plays a key role in the normal regulation of bile flow and in IR-induced injury and cell death. Ischemic preconditioning is an effective strategy to reduce IR injury but there is considerable scope for improvement, especially in patients with fatty and aged livers. The development of effective new strategies to reduce IR injury will depend on improved understanding of the molecular mechanisms involved, especially by gaining a better perspective of the relative importance of the various intrahepatocyte signaling pathways involved.

Influence of ischemic preconditioning and nitric oxide on microcirculation and the degree of rat liver injury in the model of ischemia and reperfusion

The aim of this study was to assess the influence of ischemic preconditioning (IPC) on parenchymal liver blood flow during the early phase of reperfusion after 60 minutes of ischemia, additionally modified by adding N-nitro-L-arginine methyl ester (L-NAME). Our research involved 4 groups of rats (10 animals in each group), which underwent liver ischemia and 24 hours of reperfusion. Group I, ischemia/reperfusion (IR) was performed; group II, IPC, 10 minutes of ischemia and 10 minutes of reperfusion, and IR after that; group III, L-NAME (10 mg/kg intravenous [iv]), 10 minutes before IR; and group IV, L-NAME before IPC + IR. Activity of APAT, ALAT, GGTP, and FA was marked in serum in 90 minutes and 24 hours of reperfusion. In the liver biopsies at 24 hours of reperfusion, we analyzed reaction on adenosine-3-phosphatase stimulated by Mg++ and performed histological examination. The parenchymal perfusion was measured using a laser-doppler blood flowmeter (model PeriFlux System5000, Perimed Inc., United Kingdom). IPC during reperfusion led to minor injuries of the organ, with statistically significant normalization of enzymes compared with group 1, and a better reaction to the adenosine-3-phosphatase IPC produced faster and full return of perfusion to the 68.3 value at 24 hours (59.1 in the 60 minutes). In groups III and IV at 60 minutes, the perfusion was not statistically different from that in group 1. IPC causes full and faster blood return in the early phase of reperfusion and minor injury of liver parenchyma and liver sinus. The protective effect observed, especially in the first 60 minutes of reperfusion, was limited by L-NAME and was influenced by the action of nitric oxide.

N-Acetylcysteine ameliorates the late phase of liver ischaemia/reperfusion injury in the rabbit with hepatic steatosis

Steatotic livers are highly susceptible to I/R (ischaemia/reperfusion) injury and, therefore, the aim of the present study was to evaluate the in vivo effect of NAC (N-acetylcysteine) on hepatic function in the early and initial late phase of warm liver I/R injury in steatotic rabbits. Twelve New Zealand White rabbits were fed a high-cholesterol (2%) diet. The control group (n=6) underwent lobar liver ischaemia for 1 h, followed by 6 h of reperfusion. In the treated group receiving NAC (n=6), an intravenous infusion of NAC was administered prior to and during the 6 h reperfusion period. Systemic and hepatic haemodynamics were monitored continuously. ALT (alanine aminotransferase) activity and bile production were measured. NMR spectroscopy was used to analyse bile composition. Oxidation of DHR (dihydrorhodamine) to RH (rhodamine) was used as a marker of production of reactive oxygen and nitrogen species. Moderate centrilobular hepatic steatosis was demonstrated by histology. The results showed that NAC administration significantly improved portal flow, hepatic microcirculation, bile composition and bile flow after 5 h of reperfusion. NAC administration was also associated with less hepatocellular injury, as indicated by ALT serum activity, and decreased the oxidation of DHR to RH. In conclusion, NAC administration decreased the extent of I/R injury in the steatotic liver, particularly during the late phase of reperfusion.

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.