Requirement for interleukin-12 in the pathogenesis of warm hepatic ischemia/reperfusion injury in mice

Pre-Ischemic Hypothermic Oxygenated Perfusion Alleviates Protective Molecular Markers of Ischemia-Reperfusion Injury in Rat Liver

To expand the pool of organs, hypothermic oxygenated perfusion (HOPE), one of the most promising perfusion protocols, is currently performed after cold storage (CS) at transplant centers (HOPE-END). We investigated a new timing for HOPE, hypothesizing that performing HOPE before CS (HOPE-PRE) could boost mitochondrial protection allowing the graft to better cope with the accumulation of oxidative stress during CS. We analyzed liver injuries at 3 different levels. Histologic analysis demonstrated that, compared to classical CS (CTRL), the HOPE-PRE group showed significantly less ischemic necrosis compared to CTRL vs HOPE-END. From a biochemical standpoint, transaminases were lower after 2 hours of reperfusion in the CTRL vs HOPE-PRE group, which marked decreased liver injury. qPCR analysis on 37 genes involved in ischemia-reperfusion injury revealed protection in HOPE-PRE and HOPE-END compared to CTRL mediated through similar pathways. However, the CTRL vs HOPE-PRE group demonstrated an increased transcriptional level for protective genes compared to the CTRL vs HOPE-END group. This study provides insights on novel biomarkers that could be used in the clinic to better characterize graft quality improving transplantation outcomes.

How Machine Perfusion Ameliorates Hepatic Ischaemia Reperfusion Injury

The increasing disparity between the number of patients listed for transplantation and the number of suitable organs has led to the increasing use of extended criteria donors (ECDs). ECDs are at increased risk of developing ischaemia reperfusion injury and greater risk of post-transplant complications. Ischaemia reperfusion injury is a major complication of organ transplantation defined as the inflammatory changes seen following the disruption and restoration of blood flow to an organ—it is a multifactorial process with the potential to cause both local and systemic organ failure. The utilisation of machine perfusion under normothermic (37 degrees Celsius) and hypothermic (4–10 degrees Celsius) has proven to be a significant advancement in organ preservation and restoration. One of the key benefits is its ability to optimise suboptimal organs for successful transplantation. This review is focused on examining ischaemia reperfusion injury and how machine perfusion ameliorates the graft’s response to this.

Beneficial effects of natural compounds on experimental liver ischemia-reperfusion injury

Liver ischemia-reperfusion injury (IRI) is a phenomenon inherent to hepatic surgery that severely compromises the organ functionality, whose underlying mechanisms involve cellular and molecular interrelated processes leading to the development of an excessive inflammatory response. Liver resident cells and those recruited in response to injury generate pro-inflammatory signals such as reactive oxygen species, cytokines, chemokines, proteases and lipid mediators that contribute to hepatocellular necrosis and apoptosis. Besides, dying hepatocytes release damage-associated molecular patterns that actívate inflammasomes to further stimulate inflammatory responses leading to massive cell death. Since liver IRI is a complication of hepatic surgery in man, extensive preclinical studies have assessed potential protective strategies, including the supplementation with natural compounds, with the objective to downregulate nuclear factor-κB functioning, the main effector of inflammatory responses. This can be accomplished by either the activation of peroxisome proliferator-activated receptor-α, G protein-coupled receptor 120 or antioxidant signaling pathways, the synthesis of specific pro-resolving mediators, downregulation of Toll-like receptor 4 activity or additional contributory mechanisms that are beginning to be understood. The latter aspect is a crucial issue to be accomplished in preclinical studies, in order to establish adequate conditions for the supplementation with natural products before major liver surgeries in man involving warm IR, such as hepatic trauma or resection of large intrahepatic tumors.

Nanotheranostics for the Management of Hepatic Ischemia-Reperfusion Injury

Hepatic ischemia-reperfusion injury (IRI), in which an insufficient oxygen supply followed by reperfusion leads to an inflammatory network and oxidative stress in disease tissue to cause cell death, always occurs after liver transplantations and sections. Although pharmacological treatments favorably prevent or protect the liver against experimental IRI, there have been few successes in clinical applications for patient benefits because of the incomprehension of complicated IRI-induced signaling events as well as short blood circulation time, poor solubility, and severe side reactions of most antioxidants and anti-inflammatory drugs. Nanomaterials can achieve targeted delivery and controllable release of contrast agents and therapeutic drugs in desired hepatic IRI regions for enhanced imaging sensitivity and improved therapeutic effects, emerging as novel alternative approaches for hepatic IRI diagnosis and therapy. In this review, the application of nanotechnology is summarized in the management of hepatic IRI, including nanomaterial-assisted hepatic IRI diagnosis, nanoparticulate systems-mediated remission of reactive oxygen species-induced tissue injury, and nanoparticle-based targeted drug delivery systems for the alleviation of IRI-related inflammation. The current challenges and future perspectives of these nanoenabled strategies for hepatic IRI treatment are also discussed.

Safety and feasibility of laparoscopic living donor right hepatectomy for adult liver transplantation: a meta-analysis

BACKGROUND

Laparoscopic living donor right hepatectomy (LDRH) was a controversial topic due to its unknown safety and feasibility.

METHODS

PubMed, EMBASE and Cochrane Library databases were searched for studies comparing LDRH with open living donor right hepatectomy (ODRH), which were published between the date of database establishment and June 2020. Revman5.3 was used for statistical analysis.

RESULTS

Fourteen studies were included. For the donors, there was no significant difference in warm ischemic time, hospital stay, graft weight, hepatic arterial anomalies (HAA), hepatic vein anomalies (HVA), portal vein anomalies (PVA), biliary anomalies, bleeding, wound infection, severe complication rate and readmission rate. The estimated blood loss, incidence of complication, intra-abdominal fluid rate in the LDRH group were significantly lower than those in the ODRH group, while the operation time, time to remove liver in the LDRH group were significantly higher than those in the ODRH group. For the recipients, there was no significant difference in complication rate, bleeding, HAA, PVA, biliary anomalies, graft failure and mortality. The HVA rate in the LDRH group was significantly higher than that in the ODRH group.

CONCLUSION

LDRH is safe and feasible for adult living donor liver transplantation compared with ODRH and it can reduce intraoperative bleeding and postoperative complication in donors, which requires further verification by more multi-center comparative studies with large sample and high quality.

Silibinin-hydroxypropyl-β-cyclodextrin (SLB-HP-β-CD) complex prevents apoptosis in liver and kidney after hepatic ischemia-reperfusion injury

BACKGROUND

We investigated the protective effect of silibinin on rat liver and kidney after hepatic inschemia/reperfusion (I/R) injury.

METHODS AND MATERIALS

Sixty three male Wistar-type rats (median age 13 weeks; average weight 314 g) were subjected to I/R injury of the liver. They were randomly divided into three groups: Sham (n = 7), Control (C, n = 28) and Silibinin (Si, n = 28). The last group received intravenously silibinin. The C and Si groups were each subdivided in four subgroups according to euthanasia times (i.e., 60, 120, 180, 240 min). We assessed expression of caspase-3 and TUNEL assay, and biochemical and histological parameters.

RESULTS

At 240 min, expression of caspase-3 and TUNEL assay were statistically significantly lower in the Si compared to the C group for both liver and kidney. SGOT and SGPT were also statistically significantly lower in the Si than in the C group at all time points. Histological parameters of the liver were also improved in the Si group.

CONCLUSION

Silibinin was found to exhibit a protective effect on liver and kidney after hepatic I/R injury. The present results are encouraging for further studies and future clinical application.

Hepatic ischemia-reperfusion injury in liver transplant setting: mechanisms and protective strategies

Hepatic ischemia-reperfusion injury is a major cause of liver transplant failure, and is of increasing significance due to increased use of expanded criteria livers for transplantation. This review summarizes the mechanisms and protective strategies for hepatic ischemia-reperfusion injury in the context of liver transplantation. Pharmacological therapies, the use of pre-and post-conditioning and machine perfusion are discussed as protective strategies. The use of machine perfusion offers significant potential in the reconditioning of liver grafts and the prevention of hepatic ischemia-reperfusion injury, and is an exciting and active area of research, which needs more study clinically.

Modelling of the SDF-1/CXCR4 regulated in vivo homing of therapeutic mesenchymal stem/stromal cells in mice

Background

Mesenchymal stem/stromal cells (MSCs) are a promising tool for cell-based therapies in the treatment of tissue injury. The stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor 4 (CXCR4) axis plays a significant role in directing MSC homing to sites of injury. However in vivo MSC distribution following intravenous transplantation remains poorly understood, potentially hampering the precise prediction and evaluation of therapeutic efficacy.

Methods

A murine model of partial ischemia/reperfusion (I/R) is used to induce liver injury, increase the hepatic levels of SDF-1, and study in vivo MSC distribution. Hypoxia-preconditioning increases the expression of CXCR4 in human bone marrow-derived MSCs. Quantitative assays for human DNA using droplet digital PCR (ddPCR) allow us to examine the in vivo kinetics of intravenously infused human MSCs in mouse blood and liver. A mathematical model-based system is developed to characterize in vivo homing of human MSCs in mouse models with SDF-1 levels in liver and CXCR4 expression on the transfused MSCs. The model is calibrated to experimental data to provide novel estimates of relevant parameter values.

Results

Images of immunohistochemistry for SDF-1 in the mouse liver with I/R injury show a significantly higher SDF-1 level in the I/R injured liver than that in the control. Correspondingly, the ddPCR results illustrate a higher MSC concentration in the I/R injured liver than the normal liver. CXCR4 is overexpressed in hypoxia-preconditioned MSCs. An increased number of hypoxia-preconditioned MSCs in the I/R injured liver is observed from the ddPCR results. The model simulations align with the experimental data of control and hypoxia-preconditioned human MSC distribution in normal and injured mouse livers, and accurately predict the experimental outcomes with different MSC doses.

Discussion

The modelling results suggest that SDF-1 in organs is an effective in vivo attractant for MSCs through the SDF-1/CXCR4 axis and reveal the significance of the SDF-1/CXCR4 chemotaxis on in vivo homing of MSCs. This in vivo modelling approach allows qualitative characterization and prediction of the MSC homing to normal and injured organs on the basis of clinically accessible variables, such as the MSC dose and SDF-1 concentration in blood. This model could also be adapted to abnormal conditions and/or other types of circulating cells to predict in vivo homing patterns.

IL-23 mediates murine liver transplantation ischemia-reperfusion injury via IFN-γ/IRF-1 pathway

Interleukin-23 (IL-23) is a proinflammatory cytokine initially studied in autoimmune disease that has been more recently linked to innate immunity. We observed that the expression of IL-23 is upregulated during hypoxia in a hepatocyte and nonparenchymal cell (NPC) coculture system, as well as during ischemia-reperfusion (I/R) injury in the liver. Interferon regulatory factor-1 (IRF-1) is a transcription factor that induces expression of multiple inflammatory cytokines and has been shown to play a critical role in liver I/R injury. We observed that IL-23 signaling induces not only the IL-17/chemokine (C-X-C motif) ligand 2 (CXCL2) pathway but also the IFN-γ/IRF-1 pathway. Quantification of cytokine genes revealed increased liver expression of IL-17a, CXCL2, and IRF-1 messenger RNA during liver transplantation. Recombinant IL-23 treated hepatocytes, and NPC coculture led to IL-17, CXCL2, IFN-γ, and IRF-1 expression. With anti-IL-17 and anti-Ly6G antibody neutralization, neutrophil recruitment and IFN-γ production were decreased during warm I/R injury. Overexpression of IL-23 in vivo through use of an adenovirus vector also led to expression of IL-17, CXCL2, IFN-γ, and IRF-1. The increased expression of IL-23 also led to increased apoptosis in the liver. By neutralization of IL-23 through use of an anti-IL-23p19 antibody, we were able to attenuate liver damage in a wild-type but not a natural killer T (NKT) cell-deficient mouse. This suggests that IL-23 signaling shares a common pathway with NKT cells. In conclusion, IL-23 is induced early by I/R in the liver. Its signaling leads to activation of the IL-17/CXCL2 and IFN-γ/IRF-1 pathways, resulting in increased apoptosis and necrosis. NEW & NOTEWORTHY IL-23 is expressed early during cold ischemia-reperfusion (I/R), and this expression is associated with expression of IL-17 and chemokine (C-X-C motif) ligand 2. Neutralization of IL-23 during cold I/R can significantly reduce liver damage as well as decrease cytokine production and neutrophil infiltration in the liver. IL-23 appears to activate IFN-γ production in natural killer T cells within the liver which, in turn, activates interferon regulatory factor-1, a known inflammatory transcription factor during I/R injury.

Age-dependent loss of induced regulatory T cell function exacerbates liver ischemia-reperfusion injury

Previous studies demonstrate that the number of induced regulatory T cells (iTregs) increases in aged mice. However, these studies do not characterize iTregs across different ages or how these immune modulators contribute to the dysregulation of immunity in murine disease models. Therefore, this study aimed to examine the relationship between age and iTreg function using a mouse model of hepatic ischemia-reperfusion injury (IRI). In this model, aged-mice suffered more serious injury than Young-mice, with higher serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) and higher histological scores from liver biopsies. iTregs isolated from Young-mice exhibited stronger immunosuppressive ability in vitro and had a greater response during IRI in vivo. In addition, aged-mice that were pretreated with iTregs generated in Young-mice (Y-iTregs) had alleviated injury compared with mice pretreated with iTregs from aged-mice (A-iTregs) or no treatment group. Adoptive transfer of iTregs ameliorated liver IRI and promoted liver recovery with decreased levels of interferon-γ (IFN-γ) and interleukin-17 (IL-17). These results demonstrate that the exacerbated IRI observed in aged-mice is a result of decreased iTreg function. Therefore, improving iTreg function is important for disease treatment in elder patients.

Hepatic Ischemia/Reperfusion: Mechanisms of Tissue Injury, Repair, and Regeneration

Hepatic ischemia/reperfusion (I/R) injury is a major complication of liver surgery, including liver resection, liver transplantation, and trauma surgery. Much has been learned about the inflammatory injury response induced by I/R, including the cascade of proinflammatory mediators and recruitment of activated leukocytes. In this review, we discuss the complex network of events that culminate in liver injury after I/R, including cellular, protein, and molecular mechanisms. In addition, we address the known endogenous regulatory mediators that function to maintain homeostasis and resolve injury. Finally, we cover more recent insights into how the liver repairs and regenerates after I/R injury, a setting in which physical mass remains unchanged, but functional liver mass is greatly reduced. In this regard, we focus on recent work highlighting a novel role of CXC chemokines as important regulators of hepatocyte proliferation and liver regeneration after I/R injury.

Peritransplant Energy Changes and Their Correlation to Outcome After Human Liver Transplantation

BACKGROUND

The ongoing shortage of donor livers for transplantation and the increased use of marginal livers necessitate the development of accurate pretransplant tests of viability. Considering the importance energy status during transplantation, we aimed to correlate peritransplant energy cofactors to posttransplant outcome and subsequently model this in an ex vivo setting.

METHODS

Sequential biopsies were taken from 19 donor livers postpreservation, as well as 30 minutes after portal venous reperfusion and hepatic arterial reperfusion and analyzed by liquid chromatography-mass spectrometry for energetic cofactors (adenosine triphosphate [ATP]/adenosine diphosphate [ADP]/adenosine monophosphate [AMP], nicotinamide adenine dinucleotide /NAD, nicotinamide adenine dinucleotide phosphate / nicotinamide adenine dinucleotide phosphate , flavin adenine dinucleotide , glutathione disulfide/glutathione). Energy status was correlated to posttransplant outcome. In addition, 4 discarded human donation after circulatory death livers were subjected to ex vivo reperfusion, modeling reperfusion injury and were similarly analyzed for energetic cofactors.

RESULTS

A rapid shift toward higher energy adenine nucleotides was observed following clinical reperfusion, with a 2.45-, 3.17- and 2.12-fold increase in ATP:ADP, ATP:AMP and energy charge after portal venous reperfusion, respectively. Seven of the 19 grafts developed early allograft dysfunction. Correlation with peritransplant cofactors revealed a significant difference in EC between early allograft dysfunction and normal functioning grafts (0.09 vs 0.31, P < 0.05). In the simulated reperfusion model, a similar trend in adenine nucleotide changes was observed.

CONCLUSIONS

A preserved energy status appears critical in the peritransplant period. Levels of adenine nucleotides change rapidly after reperfusion and ratios of ATP/ADP/AMP after reperfusion are significantly correlated to graft function. Using these markers as a viability test in combination with ex vivo reperfusion may provide a useful predictor of outcome that incorporates donor, preservation, and reperfusion factors.

Warm ischemia time-dependent variation in liver damage, inflammation, and function in hepatic ischemia/reperfusion injury

BACKGROUND

Hepatic ischemia/reperfusion (I/R) injury is characterized by hepatocellular damage, sterile inflammation, and compromised postoperative liver function. Generally used mouse I/R models are too severe and poorly reflect the clinical injury profile. The aim was to establish a mouse I/R model with better translatability using hepatocellular injury, liver function, and innate immune parameters as endpoints.

METHODS

Mice (C57Bl/6J) were subjected to sham surgery, 30min, or 60min of partial hepatic ischemia. Liver function was measured after 24h using intravital microscopy and spectroscopy. Innate immune activity was assessed at 6 and 24h of reperfusion using mRNA and cytokine arrays. Liver inflammation and function were profiled in two patient cohorts subjected to I/R during liver resection to validate the preclinical results.

RESULTS

In mice, plasma ALT levels and the degree of hepatic necrosis were strongly correlated. Liver function was bound by a narrow damage threshold and was severely impaired following 60min of ischemia. Severe ischemia (60min) evoked a neutrophil-dominant immune response, whereas mild ischemia (30min) triggered a monocyte-driven response. Clinical liver I/R did not compromise liver function and displayed a cytokine profile similar to the mild I/R injury model.

CONCLUSIONS

Mouse models using ≤30min of ischemia best reflect the clinical liver I/R injury profile in terms of liver function dynamics and type of immune response.

GENERAL SIGNIFICANCE

This short duration of ischemia therefore has most translational value and should be used to increase the prospects of developing effective interventions for hepatic I/R.

Hypothermia is better than ischemic preconditioning for preventing early hepatic ischemia/reperfusion in rats

BACKGROUND

Topical hypothermia (TH) and ischemic preconditioning (IPC) are used to decrease I/R injury. The efficacy of isolated or combined use of TH and IPC in the liver regarding inflammation and cytoprotection in early ischemia/reperfusion (I/R) injury needs to be evaluated.

MATERIAL AND METHODS

Wistar rats underwent 70% liver ischemia for 90 min followed by 120 min of reperfusion. Livers of animals allocated in the sham, normothermic ischemia (NI), IPC, TH, and TH+IPC groups were collected for molecular analyses by ELISA and Western blot, aiming to compare proinflammatory, anti-inflammatory, and antioxidant profiles.

RESULTS

Compared with NI, TH presented decreased tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6 and IL-12 concentrations and increased IL-10 levels. TH animals displayed lower inducible nitric oxide synthase (iNOS) and higher endothelial nitric oxide synthase (eNOS) expressions. NAD(P)H-quinone oxidoreductase-1(NQO1) expression was also lower with TH. Isolated IPC and NI were similar regarding all these markers. TH+IPC was associated with decreased IL-12 concentration and reduced iNOS and NQO1 expressions, similarly to isolated TH. Expression of Kelch-like ECH-associated protein (Keap)-1 was increased and expression of nuclear and cytosolic nuclear erythroid 2-related factor 2 (Nrf2) was decreased with TH+IPC vs. NI.

CONCLUSION

TH was the most effective method of protection against early I/R injury. Isolated IPC entailed triggering of second-line antioxidant defense enzymes. Combined TH+IPC seemed to confer no additional advantage over isolated TH in relation to the inflammatory process, but had the advantage of completely avoid second-line antioxidant defense enzymes.

Interaction between periodontitis and liver diseases

Periodontitis is an oral disease that is highly prevalent worldwide, with a prevalence of 30–50% of the population in developed countries, but only ~10% present with severe forms. It is also estimated that periodontitis results in worldwide productivity losses amounting to ~54 billion USD yearly. In addition to the damage it causes to oral health, periodontitis also affects other types of disease. Numerous studies have confirmed the association between periodontitis and systemic diseases, such as diabetes, respiratory disease, osteoporosis and cardiovascular disease. Increasing evidence also indicated that periodontitis may participate in the progression of liver diseases, such as non-alcoholic fatty liver disease, cirrhosis and hepatocellular carcinoma, as well as affecting liver transplantation. However, to the best of our knowledge, there are currently no reviews elaborating upon the possible links between periodontitis and liver diseases. Therefore, the current review summarizes the human trials and animal experiments that have been conducted to investigate the correlation between periodontitis and liver diseases. Furthermore, in the present review, certain mechanisms that have been postulated to be responsible for the role of periodontitis in liver diseases (such as bacteria, pro-inflammatory mediators and oxidative stress) are considered. The aim of the review is to introduce the hypothesis that periodontitis may be important in the progression of liver disease, thus providing dentists and physicians with an improved understanding of this issue.

RORγt(+) IL-22-producing NKp46(+) cells protect from hepatic ischemia reperfusion injury in mice

BACKGROUND & AIMS

NKp46(+) cells are major effector cells in the pathogenesis of hepatic ischemia reperfusion injury (IRI). Nevertheless, the precise role of unconventional subsets like the IL-22-producing NKp46(+) cells (NK22) remains unknown. The purpose of this study was to examine the role of NK22 cells in IRI in transplantation, particularly with respect to regulation by the transcription factor ROR-gamma-t (RORγt).

METHODS

To explore the role of NK22 cells in IRI in the absence of adaptive immunity, B6.RORγt-(gfp/wt)-reporter and B6.RORγt-(gfp/gfp)-knockout (KO) mice on a Rag KO background underwent 90min partial warm ischemia, followed by 24h of reperfusion.

RESULTS

Rag KO mice that possess fully functional NKp46(+) cells, and Rag-common-γ-chain-double-KO (Rag-γc-DKO) mice that lack T, B and NKp46(+) cells, were used as controls. We found that Rag-γc-DKO mice lacking NK22 cells show more severe levels of hepatocellular damage (GPT, histological injury) when compared to both Rag-RORγt-reporter and Rag KO mice that possess NK22 cells. Importantly, Rag-RORγt-reporter and Rag KO mice undergoing IRI expressed high protein levels of both IL-22 and GFP (RORγt), suggesting a protective role for RORγt(+) NK22 cells in IRI. Therefore, we tested the hypothesis that RORγt critically protects from IRI through the induction of hepatic NK22 cells by studying Rag-Rorγt-DKO mice under IRI conditions. We found that the lack of RORγt(+) NK22 cells in Rag-Rorγt-DKO mice significantly enhanced IR-induced hepatocellular injury, a phenotype that could be reversed upon adoptive transfer of Rag-Rorγt-reporter NK22 cells into DKO mice.

CONCLUSIONS

RORγt(+) NK22 cells play an important protective role in IRI in mice.

Sphingolipids in liver injury, repair and regeneration

Sphingolipids are not only essential components of cellular membranes but also function as intracellular and extracellular mediators that regulate important physiological cellular processes including cell survival, proliferation, apoptosis, differentiation, migration and immune responses. The liver possesses the unique ability to regenerate after injury in a complex manner that involves numerous mediators, including sphingolipids such as ceramide and sphingosine 1-phosphate. Here we present the current understanding of the involvement of the sphingolipid pathway and the role this pathway plays in regulating liver injury, repair and regeneration. The regulation of sphingolipids and their enzymes may have a great impact in the development of novel therapeutic modalities for a variety of liver injuries and diseases.

CXC chemokine receptor-4 signaling limits hepatocyte proliferation after hepatic ischemia-reperfusion in mice

The role of stromal cell-derived factor-1 (SDF-1 or CXCL12) and its receptor CXC chemokine receptor-4 (CXCR4) in ischemic liver injury and recovery has not been studied. Some reports suggest that this chemokine may aid in liver regeneration, but others suggest that it may be profibrotic through its activation of hepatic stellate cells. In this study we sought to elucidate the role of SDF-1 and its receptor CXCR4 during liver injury, recovery, and regeneration after ischemia-reperfusion (I/R). A murine model of partial (70%) I/R was used to induce liver injury and study the reparative and regenerative response. CXCR4 was expressed constitutively in the liver, and hepatic levels of SDF-1 peaked 8 h after reperfusion but remained significantly increased for 96 h. Treatment of mice with the CXCR4 antagonist AMD3100 or agonist SDF-1 had no effect on acute liver injury assessed 8 h after I/R. However, treatment with AMD3100 increased hepatocyte proliferation after 72 and 96 h of reperfusion and reduced the amount of liver necrosis. In contrast, treatment with SDF-1 significantly decreased hepatocyte proliferation. These effects appeared to be dependent on the presence of liver injury, as AMD3100 and SDF-1 had no effect on hepatocyte proliferation or liver mass in mice undergoing 70% partial hepatectomy. The data suggest that signaling through CXCR4 is detrimental to liver recovery and regeneration after I/R and that clinical therapy with a CXCR4 antagonist may improve hepatic recovery following acute liver injury.

Role of the sympathetic nervous system in carbon tetrachloride-induced hepatotoxicity and systemic inflammation

Carbon tetrachloride (CCl₄) is widely used as an animal model of hepatotoxicity and the mechanisms have been arduously studied, however, the contribution of the sympathetic nervous system (SNS) in CCl₄-induced acute hepatotoxicity remains controversial. It is also known that either CCl₄ or SNS can affect systemic inflammatory responses. The aim of this study was to establish the effect of chemical sympathectomy with 6-hydroxydopamine (6-OHDA) in a mouse model of CCl₄-induced acute hepatotoxicity and systemic inflammatory response. Mice exposed to CCl₄ or vehicle were pretreated with 6-OHDA or saline. The serum levels of aminotransferases and alkaline phosphatase in the CCl₄-poisoning mice with sympathetic denervation were significantly lower than those without sympathetic denervation. With sympathetic denervation, hepatocellular necrosis and fat infiltration induced by CCl₄ were greatly decreased. Sympathetic denervation significantly attenuated CCl₄-induced lipid peroxidation in liver and serum. Acute CCl₄ intoxication showed increased expression of inflammatory cytokines/chemokines [eotaxin-2/CCL24, Fas ligand, interleukin (IL)-1α, IL-6, IL-12p40p70, monocyte chemoattractant protein-1 (MCP-1/CCL2), and tumor necrosis factor-α (TNF-α)], as well as decreased expression of granulocyte colony-stimulating factor and keratinocyte-derived chemokine. The overexpressed levels of IL-1α, IL-6, IL-12p40p70, MCP-1/CCL2, and TNF-α were attenuated by sympathetic denervation. Pretreatment with dexamethasone significantly reduced CCl₄-induced hepatic injury. Collectively, this study demonstrates that the SNS plays an important role in CCl₄-induced acute hepatotoxicity and systemic inflammation and the effect may be connected with chemical- or drug-induced hepatotoxicity and circulating immune response.

Hepatic ischemia and reperfusion injury and trauma: current concepts

Context

Ischemia-reperfusion injury is a fascinating topic which has drawn a lot of interest in the last several years. Hepatic ischemia reperfusion injury may occur in a variety of clinical situations. These include transplantation, liver resection, trauma, and vascular surgery.

Evidence Acquisition

The purpose of this review was to outline the molecular mechanisms underlying hepatic I/R injury and present the latest approaches, both surgical and pharmacological, regarding the prevention of it. A comprehensive electronic literature search in MEDLINE/PubMed was performed to identify relative articles published within the last 2 years.

Results

The basic mechanism of hepatic ischemia – reperfusion injury is one of blood deprivation during ischemia, followed by the return of flow during reperfusion. It involves a complex series of events, such as mitochondrial deenergization, adenosine-5'-triphosphate depletion, alterations of electrolyte homeostasis, as well as Kupffer cell activation, oxidative stress changes and upregulation of proinflammatory cytokine signaling. The great number of variable pathways, with several mediators interacting with each other, leads to a high number of candidates for potential therapeutic intervention. As far as surgical approaches are concerned, the modification of existing clamping techniques and the ischemic preconditioning are the most promising techniques till recently. In the search for novel techniques of protecting against hepatic ischemia reperfusion injury, many different strategies have been used in experimental models. The biggest part of this research lies around antioxidant therapy, but other potential solutions have been explored as well.

Conclusions

The management of hepatic trauma, in spite of the fact that it has become increasingly nonoperative, there still remains the possibility of hepatic resection in the hepatic trauma setting, especially in severe injuries. Hence, clinicians should be familiar with the concept of hepatic ischemia-reperfusion injury and respond appropriately and timely.

Sterile inflammation in hepatic ischemia/reperfusion injury: present concepts and potential therapeutics

Ischemia and reperfusion (I/R) injury is an often unavoidable consequence of major liver surgery and is characterized by a sterile inflammatory response that jeopardizes the viability of the organ. The inflammatory response results from acute oxidative and nitrosative stress and consequent hepatocellular death during the early reperfusion phase, which causes the release of endogenous self-antigens known as damage-associated molecular patterns (DAMPs). DAMPs, in turn, are indirectly responsible for a second wave of reactive oxygen and nitrogen species (ROS and RNS) production by driving the chemoattraction of various leukocyte subsets that exacerbate oxidative liver damage during the later stages of reperfusion. In this review, the molecular mechanisms underlying hepatic I/R injury are outlined, with emphasis on the interplay between ROS/RNS, DAMPs, and the cell types that either produce ROS/RNS and DAMPs or respond to them. This theoretical background is subsequently used to explain why current interventions for hepatic I/R injury have not been very successful. Moreover, novel therapeutic modalities are addressed, including MitoSNO and nilotinib, and metalloporphyrins on the basis of the updated paradigm of hepatic I/R injury.

Antioxidant Stress and Anti-Inflammation of PPARα on Warm Hepatic Ischemia-Reperfusion Injury

Hepatic ischemia-reperfusion (IR) injury is a serious clinical problem. Minimizing the adverse effect of ischemia-reperfusion injury after liver surgery or trauma is an urgent need. It has been proved that besides the effect of regulating the lipid and lipoprotein metabolism, PPARα also undertakes the task of organ protection. In this paper, related literature has been summarized and we come to the conclusion that administration of PPARα agonists can strengthen the antioxidant and anti-inflammation defense system by the upregulation of the expression of antioxidant enzymes and inhibition of NF-κB activity. This may provide a potential clinical treatment for hepatic ischemia-reperfusion injury.

Interleukin-37 reduces liver inflammatory injury via effects on hepatocytes and non-parenchymal cells

BACKGROUND AND AIM

The purpose of the present study was to determine the effects of interleukin-37 (IL-37) on liver cells and on liver inflammation induced by hepatic ischemia/reperfusion (I/R).

METHODS

Mice were subjected to I/R. Some mice received recombinant IL-37 (IL-37) at the time of reperfusion. Serum levels of alanine aminotransferase, and liver myeloperoxidase content were assessed. Serum and liver tumor necrosis factor-α (TNF-α), macrophage inflammatory protein-2 (MIP-2) and keratinocyte chemokine (KC) were also assessed. Hepatic reactive oxygen species (ROS) levels were assessed. For in vitro experiments, isolated hepatocytes and Kupffer cells were treated with IL-37 and inflammatory stimulants. Cytokine and chemokine production by these cells were assessed. Primary hepatocytes underwent induced cell injury and were treated with IL-37 concurrently. Hepatocyte cytotoxicity and Bcl-2 expression were determined. Isolated neutrophils were treated with TNF-α and IL-37 and neutrophil activation and respiratory burst were assessed.

RESULTS

IL-37 reduced hepatocyte injury and neutrophil accumulation in the liver after I/R. These effects were accompanied by reduced serum levels of TNF-α and MIP-2 and hepatic ROS levels. IL-37 significantly reduced MIP-2 and KC productions from lipopolysaccharide-stimulated hepatocytes and Kupffer cells. IL-37 significantly reduced cell death and increased Bcl-2 expression in hepatocytes. IL-37 significantly suppressed TNF-α-induced neutrophil activation.

CONCLUSIONS

IL-37 is protective against hepatic I/R injury. These effects are related to the ability of IL-37 to reduce proinflammatory cytokine and chemokine production by hepatocytes and Kupffer cells as well as having a direct protective effect on hepatocytes. In addition, IL-37 contributes to reduce liver injury through suppression of neutrophil activity.

Interleukin-33 is hepatoprotective during liver ischemia/reperfusion in mice

Interleukin (IL)-33 is a recently identified member of the IL-1 family that binds to the receptor, ST2L. In the current study, we sought to determine whether IL-33 is an important regulator in the hepatic response to ischemia/reperfusion (I/R). Male C57BL/6 mice were subjected to 90 minutes of partial hepatic ischemia, followed by up to 8 hours of reperfusion. Some mice received recombinant IL-33 (IL-33) intraperitoneally (IP) before surgery or anti-ST2 antibody IP at the time of reperfusion. Primary hepatocytes and Kupffer cells were isolated and treated with IL-33 to assess the effects of IL-33 on inflammatory cytokine production. Primary hepatocytes were treated with IL-33 to assess the effects of IL-33 on mediators of cell survival in hepatocytes. IL-33 protein expression increased within 4 hours after reperfusion and remained elevated for up to 8 hours. ST2L protein expression was detected in healthy liver and was up-regulated within 1 hour and peaked at 4 hours after I/R. ST2L was primarily expressed by hepatocytes, with little to no expression by Kupffer cells. IL-33 significantly reduced hepatocellular injury and liver neutrophil accumulation at 1 and 8 hours after reperfusion. In addition, IL-33 treatment increased liver activation of nuclear factor kappa light-chain enhancer of activated B cells (NF-κB), p38 mitogen-activated protein kinase (MAPK), cyclin D1, and B-cell lymphoma 2 (Bcl-2), but reduced serum levels of CXC chemokines. In vitro experiments demonstrated that IL-33 significantly reduced hepatocyte cell death as a result of increased NF-κB activation and Bcl-2 expression in hepatocytes.

CONCLUSION

The data suggest that IL-33 is an important endogenous regulator of hepatic I/R injury. It appears that IL-33 has direct protective effects on hepatocytes, associated with the activation of NF-κB, p38 MAPK, cyclin D1, and Bcl-2 that limits liver injury and reduces the stimulus for inflammation.

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.

Histamine protects against the acute phase of experimentally-induced hepatic ischemia/re-perfusion

Histamine, involved in many inflammatory reactions and immune responses, is reported to suppress--via H4R stimulation--injury concomitant with the late phase of warm hepatic ischemia/re-perfusion (I/R). The current study investigated the possible effects of histamine on the acute phase of hepatic I/R injury, and the possible underlying mechanisms like oxidative stress and release of inflammatory cytokines (e.g., tumor necrosis factor (TNF)-α nd interleukin [IL]-12). Rats were divided into naïve, sham-operated, and I/R groups. The I/R group was divided into sub-groups and pre-treated with histaminergic ligands before induction of ischemia. Anesthetized rats were subjected to warm ischemia for 30 min by occlusion of the portal vein and hepatic artery, then re-perfused for 90 min. Rats in the control I/R group showed significant increases in hepatic malondialdehyde (MDA), TNFα, and IL-12 contents, and in plasma alanine transaminase (ALT) and aspartate transaminase (AST) levels, along with significant decreases in hepatic reduced glutathione (GSH) content and marked diffuse histopathologic damage. Pre-treatment with histamine resulted in significant mitigation of each of these end-points. The protective effect of histamine was not antagonized by pre-treatment with mepyramine (H1R antagonist) or ranitidine (H2R antagonist) and completely reversed by pre-treatment with thioperamide (H3R and H4R antagonist). In addition, the histamine protective effect was mimicked by pre-treatment of rats with clozapine (H4R agonist). These observations strongly suggested that histamine has a protective effect against hepatic I/R-mediated tissue injury during the acute phase, and this effect was mediated through an H4R stimulation that led to a decrease in IL-12 and TNFα production--outcomes that consequently decreased localized oxidative stress and afforded hepatic protection in general.

The sterile immune response during hepatic ischemia/reperfusion

Hepatic ischemia and reperfusion elicits an immune response that lacks a microbial constituent yet poses a potentially lethal threat to the host. In this sterile setting, the immune system is alarmed by endogenous danger signals that are release by stressed and dying liver cells. The detection of these immunogenic messengers by sentinel leukocyte populations constitutes the proximal trigger for a self-perpetuating cycle of inflammation, in which consecutive waves of cytokines and chemokines orchestrate the influx of various leukocyte subsets that ultimately confer tissue destruction. This review focuses on the temporal organization of sterile hepatic inflammation, using surgery-induced trauma as a template disease state.

Age-related differences in hepatic ischemia/reperfusion: gene activation, liver injury, and protective effect of melatonin

BACKGROUND

Ischemia/reperfusion (I/R) causes functional and structural damage to liver cells, this being more pronounced with increasing age of the tissue. Melatonin is a pineal indole that has been shown to play an important role as a free radical scavenger and anti-inflammatory molecule.

MATERIAL AND METHODS

The age-dependent responses to I/R were compared in 2-mo-old and 14-mo-old male Wistar rats. After 35 min of hepatic ischemia followed by 36 h of reperfusion, rats were sacrificed. Sham-operated control rats underwent the same protocol without real vascular occlusion. Animals were intraperitoneally injected with 10 mg/kg melatonin 24 h before the operation, at the time of surgery, and 12 and 24 h after it. The tissues were submitted to histopathologic evaluation. The levels of ALT and AST were analyzed in plasma. The expression of TNF-α, IL-1β, IL-10, MCP-1, IFN-γ, iNOS, eNOS, Bad, Bax, Bcl2, AIF, PCNA, and NFKB1 genes were detected by RT-PCR in hepatic tissue.

RESULTS

I/R was associated with significant increases in the expression of pro-inflammatory and pro-apoptotic genes in liver. Older rats submitted to I/R were found to respond with increased liver damage as compared with young rats, with serum ALT and AST levels significantly higher than in young animals. Mature rats also showed more evident increases in expression of pro-inflammatory cytokines (IL-1β, MCP-1, and IFN-γ) as well as a decrease in the mRNA expression of IL-10 as compared with young animals. Pro-apoptotic genes (Bax, Bad, and AIF) were significantly enhanced in liver after I/R, without differences between young and mature animals. However, the expression of Bcl2 gene did not show any change. Melatonin treatment was able to lower the expression of pro-inflammatory cytokines and pro-apoptotic genes and to improve liver function, as indicated by normalization of plasma AST and ALT levels and by reduction of necrosis and microsteatosis areas.

CONCLUSIONS

Melatonin treatment was able to reduce the I/R-stimulated pro-inflammatory and pro-apoptotic genes in the rat liver. Since older animals showed a more marked increase in inflammation and in liver injury, the treatment was more effective in those subjects.

Mechanistic overview of reactive species-induced degradation of the endothelial glycocalyx during hepatic ischemia/reperfusion injury

Endothelial cells are covered by a delicate meshwork of glycoproteins known as the glycocalyx. Under normophysiological conditions the glycocalyx plays an active role in maintaining vascular homeostasis by deterring primary and secondary hemostasis and leukocyte adhesion and by regulating vascular permeability and tone. During (micro)vascular oxidative and nitrosative stress, which prevails in numerous metabolic (diabetes), vascular (atherosclerosis, hypertension), and surgical (ischemia/reperfusion injury, trauma) disease states, the glycocalyx is oxidatively and nitrosatively modified and degraded, which culminates in an exacerbation of the underlying pathology. Consequently, glycocalyx degradation due to oxidative/nitrosative stress has far-reaching clinical implications. In this review the molecular mechanisms of reactive oxygen and nitrogen species-induced destruction of the endothelial glycocalyx are addressed in the context of hepatic ischemia/reperfusion injury as a model disease state. Specifically, the review focuses on (i) the mechanisms of glycocalyx degradation during hepatic ischemia/reperfusion, (ii) the molecular and cellular players involved in the degradation process, and (iii) its implications for hepatic pathophysiology. These topics are projected against a background of liver anatomy, glycocalyx function and structure, and the biology/biochemistry and the sources/targets of reactive oxygen and nitrogen species. The majority of the glycocalyx-related mechanisms elucidated for hepatic ischemia/reperfusion are extrapolatable to the other aforementioned disease states.

Receptor activator of nuclear factor-κB ligand (RANKL) protects against hepatic ischemia/reperfusion injury in mice

The transcription factor nuclear factor kappaB (NF-κB) plays diverse roles in the acute injury response to hepatic ischemia/reperfusion (I/R). Activation of NF-κB in Kupffer cells promotes inflammation through cytokine expression, whereas activation in hepatocytes may be cell protective. The interaction of receptor activator of NF-κB (RANK) and its ligand (RANKL) promotes NF-κB activation; however, this ligand-receptor system has not been studied in acute liver injury. In the current study, we sought to determine if RANK and RANKL were important in the hepatic response to I/R. Mice were subjected to partial hepatic ischemia followed by reperfusion. In some experiments, mice received recombinant RANKL or neutralizing antibodies to RANKL 1 hour prior to surgery or at reperfusion to assess the role of RANK/RANKL signaling during I/R injury. RANK was constitutively expressed in the liver and was not altered by I/R. RANK was strongly expressed in hepatocytes and very weakly expressed in Kupffer cells. Serum RANKL concentrations increased after I/R and peaked 4 hours after reperfusion. Serum levels of osteoprotegerin (OPG), a decoy receptor for RANKL, steadily increased over the 8-hour period of reperfusion. Treatment with RANKL, before ischemia or at reperfusion, increased hepatocyte NF-κB activation and significantly reduced liver injury. These beneficial effects occurred without any effect on cytokine expression or liver inflammation. Treatment with anti-RANKL antibodies had no effect on liver I/R injury.

CONCLUSION

During the course of injury, endogenous OPG appears to suppress the effects of RANKL. However, exogenous administration of RANKL, given either prophylactically or postinjury, reduces liver injury in a manner associated with increased hepatocyte NF-κB activation. The data suggest that RANK/RANKL may be a viable therapeutic target in acute liver injury.

Inhibition of TNF-α protects against hepatic ischemia-reperfusion injury in rats via NF-κB dependent pathway

Hepatic ischemia-reperfusion injury (I/R) is a serious health problem associated with liver transplantation, resection surgery, and various types of shock especially hemorrhagic shock. In the present investigation, the effect of inhibition of tumor necrosis factor-alpha (TNF-α) using pentoxifylline or infliximab against hepatic I/R injury induced in rats by 45-min ischemia and 1-h reperfusion was studied. It was observed that both pentoxifylline and infliximab-treated groups showed a significantly lower extent and severity of liver injury. This is attributed to (1) a decrease in oxidative stress markers, (2) reduction of the expression of TNF-α, TNF-α type-1 receptors, and nuclear factor kappa B (NF-κB). Thus TNF-α inhibition may be one of the therapeutic interventions to overcome the deleterious effects of I/R on liver via reduction of oxidative stress and inhibition of inflammatory cascade.

CXC chemokine signaling in the liver: impact on repair and regeneration

The process of liver repair and regeneration following hepatic injury is complex and relies on a temporally coordinated integration of several key signaling pathways. Pathways activated by members of the CXC family of chemokines play important roles in the mechanisms of liver repair and regeneration through their effects on hepatocytes. However, little is known about the signaling pathways used by CXC chemokine receptors in hepatocytes. Here we review our current understanding of the pathways involved in both CXC chemokine receptor signaling in other cell types, most notably neutrophils, and similar pathways operant during hepatocyte proliferation/liver regeneration to formulate a basis for the function of CXC chemokine receptor signaling in hepatocytes.

Role of IL-17A in neutrophil recruitment and hepatic injury after warm ischemia-reperfusion mice

Recent evidence suggests that IL-17A regulates neutrophil-dependent organ injury. Accordingly, the purpose of this study was to determine the role of IL-17A in neutrophil recruitment after ischemia-reperfusion (I/R) and in subsequent liver injury. Two mouse models including wild-type and IL-17A knockout mice were evaluated for I/R injury. The medial largest lobe of the liver was clamped for 90 min. In another set of experiments, recombinant mouse (rm)IL-17A homodimer or rmIL-17A/F heterodimer were administered to knockout mice before I/R, and liver injury was investigated. Isolated Kupffer cells were incubated with rmIL-17A or rmIL-17F, and production of TNF-α was measured. Studies evaluating the extent of liver injury as measured by serum transaminase levels demonstrated similar levels in the acute phase (6 h) in these two models. In contrast, in the subacute phase (20 h) after I/R, both serum transaminase levels and percent of hepatic necrosis were significantly reduced in the knockout mice compared with the wild-type mice. This reduction in liver injury seen in the knockout mice was associated with suppression of chemokine and adhesion molecule expression and reduction in infiltration of neutrophils into the liver. Administration of rmIL-17A homodimer, but not IL-17A/F heterodimer, increased liver injury in the subacute phase of I/R in KO mice. TNF-α production by isolated Kupffer cells increased significantly in the cells incubated with rmIL-17A compared with rmIL-17F. These results indicate that IL-17A is a key regulator in initiating neutrophil-induced inflammatory responses and hepatic injury in the subacute phase after reperfusion.

Interferon regulatory factor 1 mediates acetylation and release of high mobility group box 1 from hepatocytes during murine liver ischemia-reperfusion injury

Damage-associated molecular patterns (DAMPs) initiate inflammatory pathways that are common to both sterile and infectious processes. The DAMP, high-mobility group box 1 (HMGB1), and the transcription factor, interferon regulatory factor 1 (IRF-1), have been independently associated as key players in ischemia-reperfusion (I/R) injury. Our study demonstrates that IRF-1 contributes to hepatocellular release of HMGB1 and further that IRF-1 is a necessary component of HMGB1 release in response to hypoxia or after liver I/R. We also link the nuclear upregulation of IRF-1 to the presence of functional Toll-like receptor 4 (TLR4), a pattern recognition receptor also important in sterile and infectious processes. Using IRF-1 chimeric mice, we show that IRF-1 upregulation in hepatic parenchymal cells, and not in the bone marrow-derived immune cells, is responsible for HMGB1 release during ischemic liver injury. Finally, our study also demonstrates a role for IRF-1 in modulating the acetylation status and subsequent release of HMGB1 through histone acetyltransferases. We found that serum HMGB1 is acetylated after liver I/R and that this process was dependent on IRF-1. Additionally, liver I/R induced a direct association of IRF-1 and the nuclear histone acetyltransferase enzyme p300. Together, these findings suggest that I/R-induced release of acetylated HMGB1 is a process that is dependent on TLR4-mediated upregulation of IRF-1.

Glycyrrhizin prevents liver injury by inhibition of high-mobility group box 1 production by Kupffer cells after ischemia-reperfusion in rats

High-mobility group box 1 (HMGB1) acts as an early mediator of inflammation and organ damage in hepatic ischemia-reperfusion (I/R) injury. Glycyrrhizin is a natural anti-inflammatory and antiviral triterpene in clinical use. The purpose of this study was to investigate the effect of glycyrrhizin on liver injury caused by I/R and production of HMGB1 by Kupffer cells in rats. In the first test period, rats were given saline or glycyrrhizin 20 min before segmental hepatic warm I/R. Serum alanine aminotransferase and HMGB1 levels and hepatic histopathological findings were evaluated after I/R. Furthermore, expression of HMGB1 in the liver was assessed by immunohistochemical staining after I/R. Kupffer cells were isolated by collagenase digestion and differential centrifugation, and production of HMGB1 was assessed. In another set of experiments, the effect of inhibition of Kupffer cells by injection of liposome-entrapped dichloromethylene diphosphonate (lipo-MDP) on liver injury and expression of HMGB1 were investigated after I/R. Liver injury was prevented in the glycyrrhizin group compared with the control group. Furthermore, serum HMGB1 levels were also significantly blunted in the glycyrrhizin group compared with the control group. Cells expressing HMGB1 were detected in the hepatic sinusoid by immunohistochemistry and recognized morphologically as Kupffer cells. Furthermore, the expression of HMGB1 was reduced in the glycyrrhizin group compared with the control group. Production of HMGB1 was reduced in Kupffer cells isolated from the glycyrrhizin group compared with the control group. It is noteworthy that treatment with lipo-MDP significantly blunted serum HMGB1 levels and prevented liver injury after I/R. These results suggest that glycyrrhizin has the therapeutic potential to prevent warm I/R-induced injury during hepato-biliary surgery.

Marginal copper deficiency increases liver neutrophil accumulation after ischemia/reperfusion in rats

Copper deficiency can cause a host of major cardiovascular complications including an augmented inflammatory response through effects on both neutrophils and the microvascular endothelium. In the present study, we evaluated the effect of marginal copper deficiency on the neutrophilic response to hepatic ischemia/reperfusion injury, a condition that induces an inflammatory response. Male weanling Sprague-Dawley rats were fed purified diets which were either copper-adequate (6.3 mg/kg) or copper-marginal (1.62 mg/kg) for 4 weeks prior to undergoing 90 min of partial hepatic ischemia followed by 8 h of reperfusion. Liver injury was assessed by serum levels of alanine aminotransferase and by liver histology. Liver neutrophil accumulation was determined by tissue myeloperoxidase content. There was no significant difference in liver injury between copper-adequate and copper-marginal rats. However, liver neutrophil accumulation was significantly increased in copper-marginal rats. These findings were confirmed histologically. Liver expression of the adhesion molecule, intercellular adhesion molecule-1 (ICAM-1), was increased in copper-marginal rats compared to copper-adequate rats. The results suggest that neutrophil accumulation is increased through enhanced ICAM-1 expression in liver of copper-marginal rats after ischemia/reperfusion, but that this does not result in increased liver injury.

Hepatic ischemia-reperfusion injury and therapeutic strategies to alleviate cellular damage

Warm hepatic ischemia-reperfusion injury is a significant medical problem in many clinical conditions such as liver transplantation, hepatic surgery for tumor excision, trauma and hepatic failure after hemorrhagic shock. Partial or, mostly, total interruption of hepatic blood flow is often necessary when liver surgery is performed. This interruption of blood flow is termed "warm ischemia" and upon revascularization, when molecular oxygen is reintroduced, the organ undergoes a process called "reperfusion injury" that causes deterioration of organ function. Ischemia reperfusion results in cellular damage and tissue injury associated with a complex series of events. Pathophysiological mechanisms leading to tissue injury following ischemia-reperfusion will be discussed and therapies targeted to reduce liver damage will be summarized within this review.

Molecular biology of liver ischemia/reperfusion injury: established mechanisms and recent advancements

Hepatic ischemia/reperfusion (I/R) injury occurs in a variety of clinical contexts, including transplantation, liver resection surgery, trauma, and hypovolemic shock. The mechanism of organ damage after I/R has been studied extensively and consists of complex interactions of multiple inflammatory pathways. The major contributors to I/R injury include production of reactive oxygen species, release of proinflammatory cytokines and chemokines, and activation of immune cells to promote inflammation and tissue damage. Recent research has focused on the mechanisms by which these immune responses are initially activated through signaling molecules and their cellular receptors. Thorough understanding of the pathophysiology of liver I/R may yield novel therapeutic strategies to reduce I/R injury and lead to improved clinical outcomes.

Critical role of interferon regulatory factor-1 in murine liver transplant ischemia reperfusion injury

Interferon regulatory factor-1 (IRF-1) is a transcription factor that regulates gene expression during immunity. We hypothesized that IRF-1 plays a pivotal role in liver transplant (LTx) ischemia/reperfusion (I/R) injury. Mouse orthotopic LTx was conducted after 24 hours cold storage in University of Wisconsin (UW) solution in wildtype (WT) C57BL/6 and IRF-1 knockout (KO) mice. IRF-1 deficiency in liver grafts, but not in recipients, resulted in significant reduction of hepatocyte apoptosis and liver injury, as well as improved survival. IRF-1 mRNA up-regulation was typically seen in graft hepatocytes in WT-->WT LTx. Deficiency of IRF-1 signaling in graft resulted in significantly reduced messenger RNA (mRNA) levels for death ligands and death receptors in hepatocytes, as well as decreased caspase-8 activities, indicating that IRF-1 mediates death ligand-induced hepatocyte death. Further, a smaller but significant IRF-1 mRNA up-regulation was seen in WT graft nonparenchymal cells (NPC) and associated with interferon gamma (IFN-gamma) mRNA up-regulation exclusively in NPC. IFN-gamma mRNA was significantly reduced in IRF-1 KO graft. Thus, IRF-1 in graft hepatocytes and NPC has distinct effects in hepatic I/R injury. However, LTx with chimeric liver grafts showed that grafts lacking hepatocellular IRF-1 had better protection compared with those lacking IRF-1 in NPC. The study identifies a critical role for IRF-1 in liver transplant I/R injury.

Deletion of CD39 on natural killer cells attenuates hepatic ischemia/reperfusion injury in mice

Natural killer (NK) cells play crucial roles in innate immunity and express CD39 (Ecto-nucleoside triphosphate diphosphohydrolase 1 [E-NTPD1]), a rate-limiting ectonucleotidase in the phosphohydrolysis of extracellular nucleotides to adenosine. We have studied the effects of CD39 gene deletion on NK cells in dictating outcomes after partial hepatic ischemia/reperfusion injury (IRI). We show in mice that gene deletion of CD39 is associated with marked decreases in phosphohydrolysis of adenosine triphosphate (ATP) and adenosine diphosphate to adenosine monophosphate on NK cells, thereby modulating the type-2 purinergic (P2) receptors demonstrated on these cells. We note that CD39-null mice are protected from acute vascular injury after single-lobe warm IRI, and, relative to control wild-type mice, display significantly less elevation of aminotransferases with less pronounced histopathological changes associated with IRI. Selective adoptive transfers of immune cells into Rag2/common gamma null mice (deficient in T cells, B cells, and NK/NKT cells) suggest that it is CD39 deletion on NK cells that provides end-organ protection, which is comparable to that seen in the absence of interferon gamma. Indeed, NK effector mechanisms such as interferon gamma secretion are inhibited by P2 receptor activation in vitro. Specifically, ATPgammaS (a nonhydrolyzable ATP analog) inhibits secretion of interferon gamma by NK cells in response to interleukin-12 and interleukin-18, providing a mechanistic link between CD39 deletion and altered cytokine secretion.

CONCLUSION

We propose that CD39 deficiency and changes in P2 receptor activation abrogate secretion of interferon gamma by NK cells in response to inflammatory mediators, thereby limiting tissue damage mediated by these innate immune cells during IRI.

Toll-like receptor 9 inhibition confers protection from liver ischemia-reperfusion injury

Endogenous ligands such as high-mobility group box 1 (HMGB1) and nucleic acids are released by dying cells and bind Toll-like receptors (TLRs). Because TLR9 sits at the interface of microbial and sterile inflammation by detecting both bacterial and endogenous DNA, we investigated its role in a model of segmental liver ischemia-reperfusion (I/R) injury. Mice were subjected to 1 hour of ischemia and 12 hours of reperfusion before assessment of liver injury, cytokines, and reactive oxygen species (ROS). Wild-type (WT) mice treated with an inhibitory cytosine-guanosine dinucleotide (iCpG) sequence and TLR9(-/-) mice had markedly reduced serum alanine aminotransferase (ALT) and inflammatory cytokines after liver I/R. Liver damage was mediated by bone marrow-derived cells because WT mice transplanted with TLR9(-/-) bone marrow were protected from hepatic I/R injury. Injury in WT mice partly depended on TLR9 signaling in neutrophils, which enhanced production of ROS, interleukin-6 (IL-6), and tumor necrosis factor (TNF). In vitro, DNA released from necrotic hepatocytes increased liver nonparenchymal cell (NPC) and neutrophil cytokine secretion through a TLR9-dependent mechanism. Inhibition of both TLR9 and HMGB1 caused maximal inflammatory cytokine suppression in neutrophil cultures and conferred even greater protection from I/R injury in vivo.

CONCLUSION

TLR9 serves as an endogenous sensor of tissue necrosis that exacerbates the innate immune response during liver I/R. Combined blockade of TLR9 and HMGB1 represents a clinically relevant, novel approach to limiting I/R injury.

Interleukin-18 exacerbates pulmonary injury after hepatic ischemia/reperfusion in mice

BACKGROUND

Hepatic ischemia/reperfusion has been shown to cause both local hepatic and distant organ (such as lung) injury caused by accumulation of neutrophils in the local and distant organs, leading to neutrophil-dependent organ injury. Interleukin (IL) -18 is required for facilitating neutrophil-dependent local hepatic injury by suppressing anti-inflammatory cytokine expression, but less is known about the involvement of this cytokine in distant organ injury. The objective of this study was to determine whether IL-18 contributes to pulmonary injury induced by hepatic ischemia/reperfusion.

METHODS

C57BL/6 mice and IL-18 knockout mice (C57BL/6 background) were subjected to 90 min of partial hepatic ischemia and subsequent reperfusion. Neutrophil accumulation in the lung was assessed by pulmonary myeloperoxidase contents. Pulmonary expressions of keratinocyte derived chemokine (KC, CXCL1), macrophage chemoattractant protein-1 (MCP-1, CCL2), tumor necrosis factor-alpha, interferon-gamma, IL-4, and IL-10 were measured by tissue enzyme-linked immunosorbent assay (ELISA). Lung edema was quantified by the pulmonary wet to dry weight ratios.

RESULTS

Hepatic ischemia/reperfusion caused significant increases in pulmonary neutrophil recruitment and lung edema. Also, pulmonary expression of KC and MCP-1 were up-regulated. In the IL-18 knockout mice, hepatic ischemia/reperfusion-induced increases in pulmonary neutrophil recruitment, lung injury defined by lung edema, and pulmonary chemokine expression were attenuated. Furthermore, pulmonary expression of an anti-inflammatory cytokine IL-4 and systemic IL-10 expression were significantly up-regulated in the IL-18 knockout mice.

CONCLUSIONS

The data suggested that IL-18 plays an important role in the development of pulmonary injury after hepatic ischemia/reperfusion by up-regulating proinflammatory mediators and possibly suppressing anti-inflammatory cytokine expression.

Kupffer cell and interleukin-12-dependent loss of natural killer T cells in hepatosteatosis

Hepatosteatosis is associated with increased expression of tumor necrosis factor alpha (TNF-alpha) and interleukin (IL)-12, major T helper (Th) 1 cytokines, and reduced hepatic natural killer T (NKT) cell numbers. The relationship between lipid accumulation, cytokine expression, and hepatic NKT cells is not known. This study was conducted to assess the role of IL-12 in the development of hepatic steatosis and its potential impact on liver NKT cells. Male C57Bl/6 wildtype (WT) and IL-12-deficient (IL-12(-/-)) mice were fed a choline-deficient diet (CDD) for 0, 10, or 20 weeks. CDD led to marked hepatosteatosis, reduced hepatic but not splenic NKT cell numbers and function, and increased hepatic expression of the T(h)1-type cytokines IL-12, interferon gamma (IFN-gamma), and TNF-alpha in WT mice. The absence of IL-12 resulted in similar CDD-induced hepatosteatosis, but preserved hepatic NKT cells and significantly reduced hepatic IFN-gamma and TNF-alpha expression. Treatment of CDD-fed mice with lipopolysaccharide led to a significant increase in hepatic IL-12 expression, and Kupffer cell (KC) depletion reduced liver IL-12 expression and restored NKT cells in CDD-induced fatty liver. Interestingly, KCs from CDD-fed mice failed to produce increased quantities of IL-12 upon activation in vitro when compared to similarly treated KCs from control fed mice, suggesting that secondary factors in vivo promote heightened IL-12 production. Finally, human livers with severe steatosis showed a substantial decrease in NKT cells.

CONCLUSION

Hepatosteatosis reduces the numbers of hepatic NKT cells in a KC-and IL-12-dependent manner. Our results suggest a pivotal and multifunctional role of KC-derived IL-12 in the altered immune response in steatotic liver, a process that is likely active within human nonalcoholic fatty liver disease.

CXC chemokines play a critical role in liver injury, recovery, and regeneration

BACKGROUND

Hepatic ischemia/reperfusion (I/R) injury is a principal consideration of trauma, resectional liver surgery, and transplantation. Despite improvements in supportive care, hepatic I/R injury continues to negatively impact patient outcomes because of significant tissue damage and organ dysfunction. CXC chemokines have been implicated as key mediators in the deleterious inflammatory cascade after hepatic I/R and also as important, beneficial regulators of liver recovery and regeneration. As such, their potential to mediate both beneficial and detrimental effects on hepatocytes makes them a key target for therapy. Herein, we provide a review of the inflammatory mechanisms of hepatic I/R injury, with a focus on the divergent functions of CXC chemokines in this response compared with other liver insults, and offer an explanation of this apparent paradox.

DATA SOURCES

MEDLINE and PubMed.

CONCLUSIONS

CXC chemokines are key mediators of both the inflammatory response to hepatic I/R as well as the recovery from this injury. Their contrasting functions in the regeneration of liver mass after an ischemic insult indicates that therapeutic manipulation of these mediator pathways should differ depending on the surgical milieu.