Ischaemic preconditioning of the liver: a preliminary study

Ischaemic preconditioning - Current knowledge and potential future applications after 30 years of experience

Ischaemic preconditioning (IPC) phenomenon has been known for thirty years. During that time several studies showed that IPC provided by brief ischaemic and reperfusion episodes prior to longer ischaemia can bestow a protective effect to both preconditioned and also remote organs. IPC affecting remote organs is called remote ischaemic preconditioning. Initially, most IPC studies were focused on enhancing myocardial resistance to subsequent ischaemia and reperfusion injury. However, preconditioning was found to be a universal phenomenon and was observed in various organs and tissues including the heart, liver, brain, retina, kidney, skeletal muscles and intestine. Currently, there are a lot of simultaneous studies are underway aiming at finding out whether IPC can be helpful in protecting these organs. The mechanism of local and remote IPC is complex and not well known. Several triggers, intracellular pathways and effectors, humoral, neural and induced by genetic changes may be considered potential pathways in the protective activity of local and remote IPC. Local and remote IPC mechanism may potentially serve as heart protection during cardiac surgery and may limit the infarct size of the myocardium, can be a strategy for preventing the development of acute kidney injury development and liver damage during transplantation, may protect the brain against ischaemic injury. In addition, the method is safe, non-invasive, cheap and easily applicable. The main purpose of this review article is to present new advances which would help to understand the potential mechanism of IPC. It also discusses both its potential applications and utility in clinical settings.

Ischemic preconditioning vs adenosine vs prostaglandin E1 for protection against liver ischemia/reperfusion injury

Ischemia/reperfusion injury is still a major cause of morbidity and mortality during liver surgery and transplantation. A variety of surgical and pharmacological therapeutic strategies have been investigated to minimize the effects of ischemia/reperfusion. The aim of our study was to analyze and compare preventive influences of ischemic preconditioning, adenosine and prostaglandin E1 in the experimental model of hepatic ischemia/reperfusion injury. Adult chinchilla rabbits were divided into four groups: 10 rabbits subjected to liver ischemic preconditioning (3-min period of inflow occlusion followed by a 5-min period of reperfusion) followed by 45 min of Pringle maneuver; 10 rabbits subjected to pre-treatment with intraportal injection of adenosine followed by 45 min of Pringle maneuver; 10 rabbits subjected to pre-treatment with intraportal injection of prostaglandin E1 followed by 45 min of Pringle maneuver; and control group of 10 rabbits subjected to 45 min of inflow liver ischemia without any preconditioning. On the second postoperative day, blood samples were obtained and biochemical parameters of liver function were measured and compared. Liver tissue samples were also obtained and histopathological changes were compared. Based on biochemical and histopathological parameters, it was demonstrated that ischemic preconditioning provided the best protection against hepatic ischemia/reperfusion injury. This was probably due to a wider range of mechanisms of action of this method oriented to reduce oxidative stress and inflammation, and restore liver microcirculation and hepatocyte energy compared to the examined pharmacological strategies.

Remote Ischemic Preconditioning Fails to Benefit Pediatric Patients Undergoing Congenital Cardiac Surgery: A Meta-Analysis of Randomized Controlled Trials

Remote ischemic preconditioning (RIPC) has been proven to reduce the ischemia-reperfusion injury. However, its effect on children receiving congenital cardiac surgery (CCS) was inconsistent. We therefore performed the current meta-analysis of randomized controlled trials (RCTs) to comprehensively evaluate the effect of RIPC in pediatric patients undergoing CCS.PubMed, Embase, and Cochrane library were searched to identify RCTs assessing the effect of RIPC in pediatric patients undergoing CCS. The outcomes included the duration of mechanical ventilation (MV), intensive care unit (ICU) length of stay, postoperative cardiac troponin (cTnI) level, hospital length of stay (HLOS), postoperative inotropic score, and mortality. Subgroup and sensitivity analysis were also performed as predesigned. The meta-analysis was performed with random-effects model despite of heterogeneity. Sensitivity and subgroup analysis were predesigned to identify the robustness of the pooled estimate.Nine RCTs with 697 pediatric patients were included in the meta-analysis. Overall, RIPC failed to alter clinical outcomes of duration of MV (standard mean difference [SMD] -0.03, 95% confidence interval [CI] -0.23-0.17), ICU length of stay (SMD -0.22, 95% CI -0.47-0.04), or HLOS (SMD -0.14, 95% CI -0.55-0.26). Additionally, RIPC could not reduce postoperative cTnI (at 4-6 hours: SMD -0.25, 95% CI -0.73-0.23; P = 0.311; at 20-24 hours: SMD 0.09, 95% CI -0.51-0.68; P = 0.778) or postoperative inotropic score (at 4-6 hours: SMD -0.19, 95% CI -0.51-0.14; P = 0.264; at 24 hours: SMD -0.15, 95% CI -0.49-0.18; P = 0.365).RIPC may have no beneficial effects in children undergoing CCS. However, this finding should be interpreted with caution because of heterogeneity and large-scale RCTs are still needed.

The challenge of translating ischemic conditioning from animal models to humans: the role of comorbidities

Following a period of ischemia (local restriction of blood supply to a tissue), the restoration of blood supply to the affected area causes significant tissue damage. This is known as ischemia-reperfusion injury (IRI) and is a central pathological mechanism contributing to many common disease states. The medical complications caused by IRI in individuals with cerebrovascular or heart disease are a leading cause of death in developed countries. IRI is also of crucial importance in fields as diverse as solid organ transplantation, acute kidney injury and following major surgery, where post-operative organ dysfunction is a major cause of morbidity and mortality. Given its clinical impact, novel interventions are urgently needed to minimize the effects of IRI, not least to save lives but also to reduce healthcare costs. In this Review, we examine the experimental technique of ischemic conditioning, which entails exposing organs or tissues to brief sub-lethal episodes of ischemia and reperfusion, before, during or after a lethal ischemic insult. This approach has been found to confer profound tissue protection against IRI. We discuss the translation of ischemic conditioning strategies from bench to bedside, and highlight where transition into human clinical studies has been less successful than in animal models, reviewing potential reasons for this. We explore the challenges that preclude more extensive clinical translation of these strategies and emphasize the role that underlying comorbidities have in altering the efficacy of these strategies in improving patient outcomes.

Comparative Effects of Ischemic Preconditioning and Iron Chelation in Hepatectomy

PURPOSE/AIM

Major hepatectomies can result in severe ischemia/reperfusion (I/R) injury of the liver. The aim of this survey is to comparatively evaluate the effects of a surgical and a pharmacological hepatoprotective modality on the liver remnant in a porcine model of hepatectomy.

MATERIAL AND METHODS

Twenty-one Landrace pigs were randomly divided into three groups: a control group (CON) (n = 7), an Ischemic Preconditioning (PRE) group (n = 7) and a Desferoxamine (DFX) treated one (n = 7). Animals were subjected to 120 min of liver ischemia with subsequent 75% hepatectomy followed by 24-hr reperfusion. In all animals, continuous intracranial pressure (ICP) monitoring was employed. Blood samples were collected at t0, t6, t12, and t24 hrs after reperfusion. Liver remnant specimens were excised for histological examination.

RESULTS

In the PRE group, ICP was statistically lower at t6 time point compared to CON group and in comparison with t0. In addition, ICP was significantly lower at all-time points after reperfusion in the DFX group. Finally, with regard to DFX and PRE group correlation, ICP was significantly lower at t0, t12, and t24 time points after reperfusion in the DFX group. In the PRE group, NH3 levels were significantly lower at t12 after reperfusion compared to CON and DFX groups. Histological evaluation elucidated significantly less hepatocellular necrosis, apoptosis, and degeneration in the PRE and DFX groups correlated to CON group.

CONCLUSIONS

Both hepatoprotective modalities including PRE and DFX administration are associated with lower ICP levels and correlated with attenuated liver remnant injury.

Endothelial nitric oxide synthase and heme oxygenase-1 act independently in liver ischemic preconditioning

BACKGROUND

ischemic preconditioning (IPC) protects against liver ischemia-reperfusion (IR) injury. The mechanism involves nitric oxide metabolism but the importance of endothelial nitric oxide synthase (eNOS) has not been established. Heme oxygenase-1 (HO-1) protects against liver IR but it is unclear if this depends on nitric oxide synthase.

MATERIALS AND METHODS

A mouse model of IPC with liver IR using wild-type (WT) and eNOS transgenic knockout (eNOS-/-) mice was developed to study the role of eNOS and its relationship to HO-1. Serum alanine aminotransferase level, liver histopathologic injury scores, and liver microcirculatory blood flow were measured. Western blots measured liver HO-1/2, eNOS, phosphorylated eNOS, inducible nitric oxide synthase, and reverse transcription-polymerase chain reaction (HO-1). A set of 24-h recovery experiments was undertaken on WT mice with measurement of serum alanine aminotransferase level, histologic injury score, and HO-1 by Western blot.

RESULTS

In WT animals, IPC preceding IR resulted in a reduction in hepatocellular and histologic injury, and improvement in parenchymal perfusion. In contrast, IPC in the eNOS-/- model did not protect the animals from IR injury. There was no difference between the eNOS and phosphorylated eNOS expression in all the WT groups. HO-1 protein was not detected in the nonrecovery groups but HO-1 messenger RNA was detected in all groups. In WT recovery experiments, IPC was protective against IR injury. HO-1 protein was detected in the IPC + IR and IR only groups but not in the sham group.

CONCLUSIONS

This study developed and used an eNOS-/- model to demonstrate that eNOS mediates protection against liver IR injury by IPC. The eNOS expression and activity and HO-1 expression are increased independently in liver IPC and IR, with HO-1 expression increased in the later stages of IPC and IR.

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.

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.

EFFECTS OF ISCHEMIC PRECONDITIONING ON RAT LUNG: ROLE OF NITRIC OXIDE

Recent studies suggest that ischemic preconditioning (IP) of the lung may have a protective effect in ischemia-reperfusion (I/R) injury. The purpose of the present study was to investigate the preconditioning hypothesis in rat pulmonary vascular bed and to examine the role of nitric oxide (NO) in IP. Isolated rat lung was perfused with Krebs-Henseleit solution containing indomethacin at a constant flow rate and perfusion pressure changes was recorded by a pressure transducer. In rat pulmonary vascular bed, 2 hours of hypothermic ischemia significantly attenuated histamine-induced vasodilator responses without affecting sodium nitroprusside (SNP) vasodilation when compared to sham values. However, 2 cycles of 5 minutes of ischemia and reperfusion that were applied prior to 2 hours of ischemia (IP protocol) prevented the attenuation of histamine-induced vasodilation. On the other hand, IP failed to prevent pulmonary edema after ischemia. Histopathological examination of rat lungs demonstrated that IP was able to protect endothelial cells and type II pneumocytes in lung. Moreover, in IP group, malondialdehyde (MDA) contents of the lung tissue were significantly lower and tissue glutathione (GSH) contents were significantly higher than those in I/R group. Administration of NO synthase inhibitor, N(G)-nitro-L-arginine-methyl ester (L-NAME) prior to the IP protocol abolished the protective effects of IP, but not affected the tissue malondialdehyde and glutathione levels. These results suggest that I/R impaired endothelium-dependent vasodilatory response, whereas endothelium-independent SNP-induced responses were preserved in rat pulmonary vascular bed. IP prevented the impairment of pulmonary vascular endothelium-dependent responses, and these effects may be partially mediated by NO.

[Hemodynamic effects of N-acetylcysteine and ischemic preconditioning in a liver ischemia-reperfusion model]

The aim of the study was to investigate whether repeated ischemic preconditioning or N-acetylcysteine (NAC) prevents ischemic-reperfusion injury as determined by having favourable hemodynamic effects during reperfusion in canine livers.

METHODS

The control group ( n = 10) underwent 60 minutes of hepatic ischemia followed by 180 minutes reperfusion. In the NAC group ( n = 5) 150 mg kg -1 of NAC was administered intravenously before inducing ischemia. In the preconditioned group ( n = 5) animals received ischemic preconditioning (10 minutes of ischemia followed by 10 minutes of reperfusion repeated three times) before clamping the portal triad.

RESULTS

18 dogs survived the study period. One dog in the NAC group died due to circulatory failure unresponsive to inotropic drugs. The cardiac index and the intrathoracic blood volume index were significantly higher in the preconditioning group compared to the controls throughout the study period.

CONCLUSIONS

Repeated ischemic preconditioning might improve hemodynamic parameters, whereas we were unable to find any significant differences between the groups regarding N-acetylcysteine.

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.

[Methods of increasing ischemic tolerance in liver surgery]

The author evaluates an experimental model of hepatic resection. The goal of the study was to investigate ischaemic tolerance during liver resection. In this model, we also investigated the protective effects of ischemic preconditioning (IP), a PARP enzyme inhibitor (PJ-34), and an antioxidant glutamine (Gln). Inbred male Wistar rats were used for the experiments. Complete segmental ischaemia of the liver was achieved with or without using IP, PJ-34 or Gln pretreatment before the ischaemia. Microcirculation was monitored using laser Doppler flowmeter (LDF) throughout the ischaemia-reperfusion period. Required standardizations and mathematical analyses were performed in order to validate statistical analysis. Histological changes, immunohistochemistry (TUNEL, caspase), liver enzymes, bilirubin, and TNF-alpha levels were all measured simultaneously.

RESULTS, CONCLUSION

30 minutes ischaemia was well tolerated by the liver and IP does not cause further improvement. 45 to 60 minutes ischaemia resulted in serious microcirculatory changes during reperfusion. 90 minutes ischaemia was unequivocally intolerable. The liver injury and microcirculatory changes caused by 45 or 60 minutes of ischemia could be reduced with IP. Improvement was observed both on histology and in survival rates. After 45 and 60 minutes, IP + I-R caused a significant decline in the TNF-alpha levels. IP, PJ-34 PARP-inhibitor and glutamine pretreatment prior to 60 minutes of ischaemia resulted in an improvement of microcirculation. Immunohistochemistry for activated caspase-3 demonstrated significantly higher apoptosis rates in the PJ-34 PARP-inhibitor and glutamine-pretreated groups, in contrast to the sham and I-R groups. Antioxidant levels in the serum and in the liver homogenates showed significant improvement in the IP and glutamine-pretreated groups.

Protocols and Mechanisms for Remote Ischemic Preconditioning: A Novel Method for Reducing Ischemia Reperfusion Injury

Ischemia reperfusion injury (IRI) results in damage to local and remote organs. Remote ischemic preconditioning (RIPC) is a strategy to protect against IRI by inducing a prior brief period(s) of IRI to an organ remote from that undergoing sustained injury. RIPC has been shown to protect organs against IRI; however, the protocols and mechanisms for RIPC are unclear. For this review, a Medline/Pubmed search (January 1985 to January 2007) was conducted and all relevant articles were included. RIPC protocols are organ and species specific and both humoral and neurogenic pathways are involved in triggering intracellular signal pathways for protection.

Advantage of ischemic preconditioning for hepatic resection in pigs

BACKGROUND

Ischemic preconditioning (IP) and intermittent inflow occlusion (IO) have provided beneficial outcomes in hepatic resection. However, comparison of these two procedures against warm hepatic ischemia-reperfusion injury has not been studied enough.

MATERIALS AND METHODS

Pigs that had undergone 65% hepatectomy were subjected to Control (120 min continuous ischemia, n = 6), IP (10 min ischemia and 10 min reperfusion, followed by 120 min continuous ischemia, n = 6), and IO (120 min ischemia in the form of eight successive periods of 15 min ischemia and 5 min reperfusion, n = 6). We evaluated hepatocyte injury by aspartate aminotransferase, lactate dehydrogenase and hepaplastin test, hepatic microcirculation by hepatic tissue blood flow (HTBF) and endothelin (ET)-1, inflammatory response by tumor necrosis factor-alpha (TNF-alpha), and histopathology after reperfusion.

RESULTS

IP prevented hepatocyte injury, HTBF disturbance, and hepatocyte necrosis in histopathology as well as IO. These two groups showed significantly better outcomes than Control. IP produced significantly less ET-1 and TNF-alpha than IO.

CONCLUSIONS

IP ameliorated hepatic warm ischemia-reperfusion injury. Furthermore, IP gained more advantages in preventing chemokine production such as ET-1 and inflammatory response over IO. IP could take the place of IO for hepatectomy.

Protective effect of local temporary ischemia depends on applied dose of radiation

The aim of this study was to verify hypothesis that protective effect of local temporary ischemia depends on dose of radiation. 56 male WAG-strain rats were used. Total body irradiation with 3 x 3 and 3 x 5 Gy was performed. Local temporary ischemia was induced by clamping the tail base. The biochemical parameters were the thiobarbituric acid-reactive substances (TBA-RS). In bone marrow smears the polychromatic erythrocyte (PCE) numbers were counted and the numbers of micronucleated PCEs were analyzed. In small intestines the numbers of crypts were calculated. The levels of TBA-RS in the serum of the animals irradiated with a 3 x 3 Gy dose were significantly different (P < 0.002). Also in animals irradiated with a dose of 3 x 3 Gy the numbers of intestinal crypts were different (P < 0.05). In animals irradiated with dose 3 x 5 Gy, for analyzed parameters differences did not achieve statistical significance. Local temporary ischaemia provides general protection against radiation damage for lower dose. This protective effect disappeared after applications of a higher dose of radiation.

Hypoxia-reoxygenation-induced chemokine transcription is not prevented by preconditioning or intermittent hypoxia, in mice hepatocytes

Prolonged ischemia used in liver surgery and/or transplantation causes cellular damage resulting in apoptosis and necrosis. Ischemia-reperfusion (I/R) led Kupffer cells to pro-inflammatory cytokines secretion [tumor necrosis factor (TNF)-alpha, interleukin-1] which involve chemokines secretion by hepatocytes. These chemokines have neutrophil chemotactic properties and neutrophils are involved in the development of I/R-induced necrosis. The aim of this study was to specify the consequence of partial oxygen pressure variation on hepatocyte chemokines synthesis and to verify if intermittent hypoxia and/or preconditioning could decrease it. It was performed on primary cultured mice hepatocytes and Kupffer cells, subjected to continuous, intermittent hypoxia or preconditioning phases, mimicking surgical processes. The chemokine secretion was evaluated by RNase protection assay and enzyme-linked immunosorbent assay method. Only monocyte chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein-2 (MIP-2) mRNA formation were observed, especially after 1-h hypoxia followed by 10-h (for MCP-1) or 24-h reoxygenation (for MIP-2). In conclusion, TNF-alpha and coculture with Kupffer cells increased hepatocyte chemokines mRNA transcription, whereas surgical split up protocols (intermittent hypoxia and preconditioning) had no significant effect.

Hepatic vascular occlusion: which technique?

Each vascular occlusion technique has a place in major and minor hepatic resectional surgery, based on the tumor location, presence of associated underlying liver disease, patient cardiovascular status, and experience of the operating surgeon. Understanding of the potential application of different techniques, anticipation of the expected and potential hemodynamic responses, and knowledge of the limitations of each technique are fundamental to appropriate surgical planning adapted to each patient. Experience with the various clamping methods enables an aggressive but safe approach to surgical treatment of hepatobiliary diseases, with acceptable blood loss and transfusion requirements. In all cases, surgical strategy should be defined with the anesthesiologist, particularly in regard to hemodynamic monitoring, in order to optimize perioperative patient management and to minimize the risk for complications such as bleeding and air embolism. Importantly, randomized study has shown that the added dissection, operative, and postoperative risks associated with HVE are not balanced by decreased blood loss compared with hepatic pedicle clamping, except in exceptional cases when tumors involve the major hepatic veins or vena cava. In addition, dissection in preparation for clamping may be used as safe approach techniques to tumors in difficult locations, even when eventual clamping is not performed. Similarly, the liver-hanging maneuver enables resection without mobilization, compression, and manipulation of large tumors. In the future, renewed interest in the impact of hepatic ischemia and reperfusion may reveal that some clamping methods, in particular inflow occlusion, act as a means of preconditioning before a period of prolonged hepatic ischemia, for complex hepatic resection or for graft harvest from a living donor. Finally, the addition of infrahepatic caval clamping may add a new, simple, effective technique to the armamentarium of the liver surgeon, particularly as more routine hepatic surgery moves from the specialized center to the community.

Ischemic preconditioning and methylprednisolone both equally reduce hepatic ischemia/reperfusion injury

BACKGROUND

Ischemic preconditioning (I/P) and methylprednisolone (MP) have been suggested to protect against ischemia-reperfusion (IR) injury, which results in an increased tolerance against organ hypoxia.

METHODS

Before 45 minutes of hepatic ischemia, male Wistar rats were pretreated with either I/P (5/30 minutes) or MP (30 mg/kg BW). The degree of IR injury and the postischemic inflammatory (leukocyte infiltration, myeloperoxidase, intercellular adhesion molecule-1) and apoptotic (TUNEL, caspase 3, cytochrome C) activity was measured in both groups and compared with non-pretreated (ischemic) animals.

RESULTS

Histology and enzyme release revealed that I/P and MP treatment provided significant protection as compared with ischemic controls. TUNEL-positive cells, as well as caspase 3 and cytochrome C expression, were clearly reduced in hepatic tissue of MP-treated animals and partially reduced in I/P-treated animals when compared with ischemic animals. The inflammatory response was considerably reduced in MP- and I/P-treated animals, especially in the early period after ischemia. NF-kappaB/Rel-binding activity was increased after I/P and decreased in MP-treated animals, whereas ischemic controls showed a constant binding activity.

CONCLUSIONS

MP (probably by downregulation of NF-kappaB-binding activity) and I/P attenuated the postischemic apoptotic and inflammatory response. Both treatments equally reduced IR-related hepatocellular damage, and, thus, may also be applied equally in surgery involving warm organ hypoxia.

Inhibitory effect of local ischaemic preconditioning in total body irradiated rats

The aim of this study was to explore the relationship between local ischaemic preconditioning and the effectiveness of fractionated radiotherapy. The rat serum, bone marrow, and small intestine were examined for oxidative changes induced by total body irradiation with gamma rays with applied local ischaemic preconditioning immediately before irradiation. Serum concentrations of TBA-RS examined 12 hours after the last irradiation did not reveal any differences among the groups of animals analyzed. Twenty-four hours after the last dose of irradiation, the serum concentrations of TBA-RS varied in particular groups (P<0.0001). The concentration of triglycerides in the serum of local preconditioned ischaemia and irradiated animals showed a reversed shape similar to the TBA-RS fluctuation (P<0.003). The level of uric acid in the serum of animals treated only with radiation is slightly higher than the level of this acid in the serum of the local preconditioned ischaemia radiation group (P<0.58). The number of bone marrow polychromatic erythrocytes did not appear to differ substantially in both irradiated groups. At the first 12 hours after irradiation, the frequency of micronucleated polychromatic erythrocytes is significantly different in the bone marrow of both groups either in combination with ischaemic preconditioned radiation or with radiation alone (P<0.0002). In irradiated animals without ischaemic preconditioning, on the 3rd day after irradiation the number of crypts increased and in the next days decreased achieving the level of the control group on the 7th day. Irradiated rats with local ischaemic preconditioning did not reveal an increase in the number of crypts. The difference was statistically significant (P<0.05). These data indicate that the local ischaemic preconditioning modifies the radiation peroxidising effects through inhibition of free radical-dependent lipid peroxidation and, probably, other unrecognized mechanisms.

Ischemic preconditioning protects from hepatic ischemia/reperfusion-injury by preservation of microcirculation and mitochondrial redox-state

BACKGROUND/AIMS

Ischemic preconditioning (IP) is known to protect hepatic tissue from ischemia-reperfusion injury. However, the mechanisms involved are not fully understood yet.

METHODS

Using intravital multifluorescence microscopy in the rat liver, we studied whether IP exerts its beneficial effect by modulating postischemic Kupffer cell activation, leukocyte-endothelial cell interaction, microvascular no-reflow, mitochondrial redox state, and, thus, tissue oxygenation.

RESULTS

Portal triad cross-clamping (45 min) followed by reperfusion induced Kupffer cell activation, microvascular leukocyte adherence, sinusoidal perfusion failure (no-reflow) and alteration of mitochondrial redox state (tissue hypoxia) (P<0.05). This resulted in liver dysfunction and parenchymal injury, as indicated by decreased bile flow and increased serum glutamate dehydrogenase (GLDH) levels (P<0.05). IP (5 min ischemia and 30 min intermittent reperfusion) was capable to significantly reduce Kupffer cell activation (P<0.05), which was associated with a slight attenuation of leukocyte adherence. Further, IP markedly ameliorated sinusoidal perfusion failure (P<0.05), and, thereby, preserved adequate mitochondrial redox state (P<0.05). As a consequence, IP prevented the decrease of bile flow (P<0.05) and the increase in serum GLDH levels (P<0.05).

CONCLUSIONS

IP may exert its beneficial effects on hepatic ischemia-reperfusion injury by preserving mitochondrial redox state, which is guaranteed by the prevention of reperfusion-associated Kupffer cell activation and sinusoidal perfusion failure.

Renal protection by brief liver ischemia in rats

BACKGROUND

In this study, we evaluated the beneficial effect of brief ischemia and reperfusion, which was shown to have local effects on liver previously, on kidney as a remote organ in rats.

METHODS

Male Wistar rats were divided into three groups: group I, sham; group II, renal ischemia for 45 min; and group III, 10 min of brief hepatic ischemia and 10 min of reperfusion after 45 min of renal ischemia. Biochemical determination, tumor necrosis factor (TNF)-alpha and tissue thiobarbituric acid-reactive substances (TBARS) levels, and histopathologic findings were evaluated at 45 min and 24 hr of reperfusion.

RESULTS

Although blood urea nitrogen and creatinine levels were similar at 45 min in groups II and III, these levels were lower in group III at 24 hr. Creatine clearance values were higher and fraction excretion of sodium values were lower in group II than in group III at 24 hr. Lactate dehydrogenase levels of groups III and II were similarly elevated at 45 min, whereas group III values decreased more rapidly than those of group II at 24 hr. At 45 min of reperfusion, TNF-alpha and tissue TBARS levels were found lower in group III than in group II. Histopathologic parameters including congestion and tubular vacuolization, tubular cell detachment, and necrosis were significantly reduced in group III as compared with results of group II 45 min after ischemia. All histopathologic parameters were defined as statistically better in group II at 24 hr.

CONCLUSIONS

The beneficial effect of brief ischemia of liver on renal ischemia as a remote organ was confirmed by biochemical, histopathologic, and ultrastructural findings.

The relationship of hepatic tissue oxygenation with nitric oxide metabolism in ischemic preconditioning of the liver

Ischemic preconditioning (IPC) may increase the hepatic tolerance of ischemic injury during liver surgery and transplantation via nitric oxide (NO) formation. This study investigates the effect of IPC on hepatic tissue oxygenation and the role of NO stimulation and inhibition on the preconditioning effect in the rat liver. Study groups had 1) sham laparotomy; 2) 45-min lobar liver ischemia and 2-h reperfusion (IR); 3) IPC with 5-min ischemia and 10-min reperfusion before IR; 4) L-arginine before IR; and 5) Nw-Nitro-L-arginine methyl ester (L-NAME) + IPC before IR. Hepatic tissue oxygenation was monitored by near-infrared spectroscopy. Plasma alanine aminotransferase and plasma nitrite/nitrate were measured. Following IR there was significant decrease in oxyhemoglobin and cytochrome oxidase and an increase in deoxyhemoglobin (PA redox state, PL-arginine did not attenuate the impairment in hepatic tissue oxygenation after IR (P>0.05 vs IR). In contrast, inhibition of NO synthesis blocked the effect of IPC and further impaired tissue oxygenation (decreased cytochrome oxidase CuA redox state and increased deoxyhemoglobin, both PL-arginine and increased by NO blockade with L-NAME (Plasma ALT, all P< 0.05 vs IR). Hepatic tissue oxygenation correlated significantly with ALT and plasma nitrite/nitrate. Ischemic preconditioning significantly improved hepatic intra cellular oxygenation and reduced hepatocellular injury. NO stimulation reduced hepatocellular injury, whereas inhibition of nitric oxide synthesis blocked the effect of IPC and reduced tissue oxygenation and increased hepatocellular injury.

Comparison of ischemic preconditioning and intermittent and continuous inflow occlusion in the murine liver

OBJECTIVE

To compare protection of the liver by ischemic preconditioning and intermittent inflow occlusion in a mouse model of prolonged periods of ischemia.

SUMMARY BACKGROUND DATA

Preconditioning (short ischemic stress prior to a prolonged period of ischemia) and intermittent inflow occlusion protect the liver against reperfusion injury. This is the first study comparing these two modalities with continuous inflow occlusion (control).

METHODS

Mice were subjected to 75 or 120 minutes of 70% hepatic ischemia and 3 hours of reperfusion. Each ischemic period was evaluated using three different protocols: continuous ischemia (control), preconditioning (10 minutes ischemia and 15 minutes reperfusion) prior to the prolonged ischemic insult, and intermittent clamping (cycles of 15 minutes ischemia and 5 minutes reperfusion). Organ injury was evaluated using serum levels of aspartate aminotransferase (AST), hematoxylin and eosin staining, and specific markers of apoptosis (cytochrome C release, caspase 3 activity, and TUNEL staining). Animal survival was determined using a model of total hepatic ischemia.

RESULTS

Intermittent inflow occlusion and ischemic preconditioning were both protective against ischemic insults of 75 and 120 minutes compared with controls (continuous ischemia only). Protection against 75 minutes of ischemia was comparable in the intermittent clamping and the ischemic preconditioning group, whereas intermittent clamping was superior at 120 minutes of ischemia. One hundred percent animal survival was observed after 75 minutes of total hepatic ischemia using both protective protocols, whereas all animals subjected to continuous ischemia died after surgery. After 120 minutes of ischemia, intermittent inflow occlusion was associated with better animal survival (71%) compared with preconditioning (14%).

CONCLUSIONS

Preconditioning and intermittent clamping are both protective against prolonged periods of ischemia. In the clinical setting, preconditioning is superior for ischemic periods of up to 75 minutes because it is not associated with blood loss during transection of the liver. However, for prolonged ischemic insults exceeding 75 minutes, intermittent clamping is superior to preconditioning.

Sublethal cerebral ischemia inhibits caspase-3 activation induced by subsequent prolonged ischemia in the C57Black/Crj6 strain mouse

Caspase-3 activation has been implicated in ischemic neuronal death. In the present study, we examined if cerebral ischemic tolerance induced by sublethal ischemia is associated with an attenuation of caspase-3 activation in a mouse forebrain ischemia model. Forebrain ischemia in C57Black/Crj6 strain mice was induced by bilateral common carotid artery occlusion (BCCAO) for 18 min. Two episodes of 6-min ischemia were carried out as preconditioning 48 and 72 h before the 18-min BCCAO. Caspase-3-like activity was determined by fluorescently monitoring the release of amino-4-methylcoumarin from N-acetyl-Asp-Glu-Val-Asp-7-amino-4-methylcoumarin in the striatal protein extracts at 4, 24, and 72 h after reperfusion. The results showed that the ischemic preconditioning significantly attenuated caspase-3 activation at 4, 24, and 72 h after reperfusion, and reduced neuronal loss caused by the 18-min ischemia as examined on the 7th day after reperfusion. The present results suggest that the neuroprotection achieved by ischemic preconditioning is related to an attenuation of caspase-3 activation.

O, Oliveira A. EFEITOS DO PRÉ-CONDICIONAMENTO HEPÁTICO EM RATOS CIRRÓTICOS, SUBMETIDOS À ISQUEMIA E REPERFUSÃO HEPÁTICA RESULTADOS PRELIMINARES

Baseando-se nos efeitos estimuladores do metabolismo energético pelo pré-condicionamento isquêmico (PCI) no tecido hepático, estudou-se dois grupos de ratos cirróticos submetidos a isquemia de 20 min e reperfusão de 120 min, após o PCI ou não respectivamente, determinando assim o valor do seu uso no prolongamento da manobra de Pringle e na regeneração hepática na hepatectomia.

Protective effects of ischemic preconditioning for liver resection performed under inflow occlusion in humans

OBJECTIVE

To determine whether ischemic preconditioning protects the human liver against a subsequent period of ischemia in patients undergoing hemihepatectomy, and to identify possible underlying protective mechanisms of ischemic preconditioning, such as inhibition of hepatocellular apoptosis.

SUMMARY BACKGROUND DATA

Ischemic preconditioning is a short period of ischemia followed by a brief period of reperfusion before a sustained ischemic insult. Recent studies in rodents suggest that ischemic preconditioning is a simple and powerful protective modality against ischemic injury of the liver. The underlying mechanisms are thought to be related to downregulation of the apoptotic pathway.

METHODS

Twenty-four patients undergoing hemihepatectomy for various reasons alternatively received ischemic preconditioning (10 minutes of ischemia and 10 minutes of reperfusion) before transection of the liver performed under inflow occlusion for exactly 30 minutes. Liver wedge and Tru-cut biopsy samples were obtained at the opening of the abdomen and 30 minutes after the end of the hepatectomy. Serum levels of aspartate transferase, alanine transferase, bilirubin and prothrombin time were determined daily until discharge. Hepatocellular apoptosis was evaluated by in situ terminal deoxynucleotidyl transferase mediated d-UTP nick end-labeling (TUNEL) assay and electron microscopy. Caspase 3 and 8 activities were measured in tissue using specific fluorometric assays.

RESULTS

Serum levels of aspartate transferase and alanine transferase were reduced by more than twofold in patients subjected to ischemic preconditioning versus controls. The analysis of a subgroup of patients with mild to moderate steatosis indicated possible increased protective effects of ischemic preconditioning. In situ TUNEL staining demonstrated a dramatic reduction in the number of apoptotic sinusoidal lining cells in the ischemic preconditioning group. Electron microscopy confirmed features of apoptosis present in control but not in ischemic preconditioning patients. There was no significant difference in caspase 3 and 8 activity when patients with ischemic preconditioning were compared with controls.

CONCLUSIONS

Ischemic preconditioning is a simple and effective modality protecting the liver against subsequent prolonged periods of ischemia. This strategy may be a more attractive technique than intermittent inflow occlusion, which is associated with increased blood loss during each period of reperfusion.

Protective effects of ischemic preconditioning for liver resection performed under inflow occlusion in humans

OBJECTIVE

To determine whether ischemic preconditioning protects the human liver against a subsequent period of ischemia in patients undergoing hemihepatectomy, and to identify possible underlying protective mechanisms of ischemic preconditioning, such as inhibition of hepatocellular apoptosis.

SUMMARY BACKGROUND DATA

Ischemic preconditioning is a short period of ischemia followed by a brief period of reperfusion before a sustained ischemic insult. Recent studies in rodents suggest that ischemic preconditioning is a simple and powerful protective modality against ischemic injury of the liver. The underlying mechanisms are thought to be related to downregulation of the apoptotic pathway.

METHODS

Twenty-four patients undergoing hemihepatectomy for various reasons alternatively received ischemic preconditioning (10 minutes of ischemia and 10 minutes of reperfusion) before transection of the liver performed under inflow occlusion for exactly 30 minutes. Liver wedge and Tru-cut biopsy samples were obtained at the opening of the abdomen and 30 minutes after the end of the hepatectomy. Serum levels of aspartate transferase, alanine transferase, bilirubin and prothrombin time were determined daily until discharge. Hepatocellular apoptosis was evaluated by in situ terminal deoxynucleotidyl transferase mediated d-UTP nick end-labeling (TUNEL) assay and electron microscopy. Caspase 3 and 8 activities were measured in tissue using specific fluorometric assays.

RESULTS

Serum levels of aspartate transferase and alanine transferase were reduced by more than twofold in patients subjected to ischemic preconditioning versus controls. The analysis of a subgroup of patients with mild to moderate steatosis indicated possible increased protective effects of ischemic preconditioning. In situ TUNEL staining demonstrated a dramatic reduction in the number of apoptotic sinusoidal lining cells in the ischemic preconditioning group. Electron microscopy confirmed features of apoptosis present in control but not in ischemic preconditioning patients. There was no significant difference in caspase 3 and 8 activity when patients with ischemic preconditioning were compared with controls.

CONCLUSIONS

Ischemic preconditioning is a simple and effective modality protecting the liver against subsequent prolonged periods of ischemia. This strategy may be a more attractive technique than intermittent inflow occlusion, which is associated with increased blood loss during each period of reperfusion.

Ischemia impairs liver regeneration after major tissue loss in rodents: protective effects of interleukin-6

The effects of ischemia on the regenerative capacity of the liver after major tissue loss remain unclear. Interleukin-6 (IL-6) has been shown to confer protection in models of normothermic ischemia and reperfusion injury and to initiate hepatocyte proliferation after major hepatectomy. Therefore, we investigated the effects of ischemia on the regenerative capacity of the liver and evaluated the role of IL-6 in reducing reperfusion injury and enhancing hepatic proliferation in models combining ischemia and major hepatectomy. Rats subjected to 70% hepatectomy and 30 minutes of hepatic ischemia showed significantly reduced regenerative capacity (mitotic index, proliferating cell nuclear antigen, and regenerated liver weight) when compared with animals subjected to hepatectomy alone. Pretreatment of animals subjected to hepatectomy and ischemia with recombinant interleukin-6 (rIL-6) completely restored each parameter of regeneration to levels comparable with those of animals subjected to hepatectomy only. Similar results were obtained in IL-6 deficient (IL-6(-/-)) mice. IL-6(-/-) mice exposed to ischemia and hepatectomy showed impaired hepatic regeneration when compared with wild-type mice subjected to the same experimental conditions. The use of rIL-6 completely corrected each parameter of regeneration showing the specificity of IL-6 in this type of injury. The impact of IL-6 on animal survival was studied in a model combining 45 minutes of ischemia and 68% hepatectomy. Five of 7 (71%) animals pretreated with rIL-6 survived permanently, whereas all control animals died within 3 days of surgery (P =.02, Fisher's exact test). In conclusion, the study shows that ischemia dramatically impairs the regenerative capacity of the liver. IL-6 appears to be a key protective molecule in reducing injury and promoting regeneration following combined ischemia and major tissue loss.

The role of ischemic preconditioning in the recruitment of rolling and adherent leukocytes in hepatic venules after ischemia/reperfusion

BACKGROUND

We have recently shown that hepatic ischemia/reperfusion (I/R) results in rolling and adherence of leukocytes in terminal hepatic venules (THV) followed by hepatic enzyme elevation and tissue destruction. The objective of this study was to determine the effect of ischemic preconditioning on the recruitment of leukocytes in THV after liver I/R.

METHODS

Left hepatic lobe ischemia was induced for 5 min (preconditioning) in anesthetized C57B1/6 mice followed by reperfusion for 10 min and then prolonged ischemia for 30 min. The number of rolling, saltating, and adherent leukocytes in THV was measured at 0.5, 2, 5, 12, and 24 h after reperfusion using intravital video microscopy. Matching sham groups were evaluated after 30 min of ischemia.

RESULTS

Hepatic I/R elicited significant increases in the number of rolling, saltating, and adherent leukocytes, with peak values observed at 30 min and 5 h after reperfusion. All of these responses were significantly attenuated in mice undergoing ischemic preconditioning. Rolling leukocytes in THV following I/R without preconditioning reached peak levels of 25.2 +/- 1.4 leuk/2 min (leukocytes/2 min) at 30 min reperfusion and 31.4 +/- 1.5 leuk/2 min at 5 h reperfusion. With ischemic preconditioning these values fell to 12.3 +/- 0.9 leuk/2 min and 14.4 +/- 1.0 leuk/2 min, respectively (P < 0.001). Similarly, adherent leukocytes in nonpreconditioned mice reached peak values of 4.8 +/- 1.3 leuk/2 min at 30 min reperfusion and 8.3 +/- 1.2 leuk/2 min at 5 h reperfusion compared with 2.0 +/- 1.5 leuk/2 min and 1.6 +/- 1.1 leuk/2 min in preconditioned mice, respectively (P < 0.001).

CONCLUSION

Ischemic preconditioning attenuates the initial events leading to leukocyte-mediated hepatic destruction following I/R injury. Delineating these mechanisms may play an important role in hepatic transplantation, resection, shock, and sepsis.

Protective effect of ischemic preconditioning on liver preservation-reperfusion injury in rats

BACKGROUND

Ischemic-preconditioning is a process whereby a brief ischemic episode confers a state of protection against subsequent long-term ischemia-reperfusion injury. Ischemic preconditioning has been studied in heart and liver ischemia-reperfusion injury; however, few studies have been performed in the model of preservation-reperfusion injury in liver transplantation. The current study was designed to evaluate the ability of ischemic preconditioning to protect liver grafts from long-term preservation-reperfusion injury.

METHODS

Male Sprague Dawley rats were used as donors and recipients of orthotopic liver transplantation. Ischemic preconditioning was done by interruption of the portal vein and hepatic artery for 5, 10, and 20 min (5-10, 10-10, and 20-10 groups). Reflow was initiated by removal of the clamp for another 10 min in all groups. The liver was removed and placed in a bath with Euro-Collins solution for different preservation times. Tolerance of the transplanted liver to cold ischemia was determined by survival time and liver function tests. Rat tumor necrosis factor was analyzed by a bioassay. Nomega-Nitro-L-arginine methyl ester, L-arginine, or adenosine was administered to block or stimulate the synthesis of nitric oxide (NO) in the rats that received long-term-preserved liver grafts.

RESULTS

Twenty percent of syngeneic rats (n=10) that received a liver graft with a 16-hr cold ischemia time in Euro-Collins solution survived for more than 1 day and 10% survived for more than 5 days. In contrast, 87.5% of rats (n=8) that received a liver graft with ischemic preconditioning (10-10 group) and 16 hr of cold ischemia survived for more than 1 day and 75% for more than 5 days. Recipients of liver grafts with ischemic preconditioning had significantly reduced levels of serum aspartate transaminase and tumor necrosis factor-alpha, as well as increased bile flow, compared with recipients of liver grafts without ischemic preconditioning. Blockage of the NO pathway using Nomega-nitro-L-arginine methyl ester, a stereospecific competitive inhibitor of NO formation, attenuated the protective effect of ischemic preconditioning. Administration of one of two precursors of NO synthesis, L-arginine or adenosine, prolonged the survival of rats that received 16-hr-preserved liver grafts. In addition, L-arginine synergized with short-term ischemic pre conditioning (5-10 group) to increase the survival of rats that received a liver graft with a 16-hr cold ischemia time, and the survival rate was 83% after 5 days. Finally, prolonged ischemic preconditioning (> or = 20 min; 20-10 group) resulted in liver damage and loss of function.

CONCLUSION

The current results show that ischemic preconditioning protects the liver graft from subsequent long-term cold preservation-reperfusion injury in a rat liver transplantation model. The protective role of ischemic preconditioning may be mediated by the endogenous production of NO.

Ischaemic preconditioning: mechanisms and potential clinical applications

PURPOSE

Brief ischaemic episodes, followed by periods of reperfusion, increase the resistance to further ischaemic damage. This response is called "ischaemic preconditioning." By reviewing the molecular basis and fundamental principals of ischaemic preconditioning, this paper will enable the anaesthetic and critical care practitioner to understand this developing therapeutic modality.

SOURCE

Articles were obtained from a Medline review (1960-1997; search terms: ischaemia, reperfusion injury, preconditioning, ischaemic preconditioning, cardiac protection). Other sources include review articles, textbooks, hand-searches (Index Medicus), and personal files. PRINCIPLE FINDING: Ischaemic preconditioning is a powerful protective mechanism against ischaemic injury that has been shown to occur in a variety of organ systems, including the heart, brain, spinal cord, retina, liver, lung and skeletal muscle. Ischaemic preconditioning has both immediate and delayed protective effects, the importance of which varies between species and organ systems. While the exact mechanisms of both protective components are yet to be clearly defined, ischaemic preconditioning is a multifactorial process requiring the interaction of numerous signals, second messengers and effector mechanisms. Stimuli other than ischaemia, such as hypoxic perfusion, tachycardia and pharmacological agents, including isoflurane, have preconditioning-like effects. Currently ischaemic preconditioning is used during minimally invasive cardiac surgery without cardiopulmonary bypass to protect the myocardium against ischaemic injury during the anastomosis.

CONCLUSION

Ischaemic preconditioning is a powerful protective mechanism against ischaemic injury in many organ systems. Future clinical applications will depend on the clarification of the underlying biochemical mechanisms, the development of pharmacological methods to induce preconditioning, and controlled trials in humans showing improved outcomes.