Current status of ischemia and reperfusion injury in the liver

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

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

Diannexin, a novel annexin V homodimer, protects rat liver transplants against cold ischemia-reperfusion injury

Ischemia/reperfusion injury (IRI) remains an important problem in clinical transplantation. Following ischemia, phosphatidylserine (PS) translocates to surfaces of endothelial cells (ECs) and promotes the early attachment of leukocytes/platelets, impairing microvascular blood flow. Diannexin, a 73 KD homodimer of human annexin V, binds to PS, prevents attachment of leukocytes/platelets to EC, and maintains sinusoidal blood flow. This study analyzes whether Diannexin treatment can prevent cold IRI in liver transplantation. Rat livers were stored at 4 degrees C in UW solution for 24 h, and then transplanted orthotopically (OLT) into syngeneic recipients. Diannexin (200 microg/kg) was infused into: (i) donor livers after recovering and before reperfusion, (ii) OLT recipients at reperfusion and day +2. Controls consisted of untreated OLTs. Both Diannexin regimens increased OLT survival from 40% to 100%, depressed sALT levels, and decreased hepatic histological injury. Diannexin treatment decreased TNF-alpha, IL-1beta, IP-10 expression, diminished expression of P-selectin, endothelial ICAM-1, and attenuated OLT infiltration by macrophages, CD4 cells and PMNs. Diannexin increased expression of HO-1/Bcl-2/Bcl-xl, and reduced Caspase-3/TUNEL+ apoptotic cells. Thus, by modulating leukocyte/platelet trafficking and EC activation in OLTs, Diannexin suppressed vascular inflammatory responses and decreased apoptosis. Diannexin deserves further exploration as a novel agent to attenuate IRI, and thereby improve OLT function/increase organ donor pool.

Heme Oxygenase-1 Mediated Cytoprotection Against Liver Ischemia and Reperfusion Injury: Inhibition of Type-1 Interferon Signaling

BACKGROUND

Toll-like receptor (TLR)-4 signaling plays a key role in initiating exogenous antigen-independent innate immunity-dominated liver ischemia/reperfusion injury (IRI). Heme oxygenase (HO)-1, a heat-shock protein 32, exerts potent adaptive anti-oxidant and anti-inflammatory functions. Signal transducers and activator of transcription (STAT)-1 activation triggers interferon (IFN)-inducible protein 10 (CXCL-10), one of major products of type-1 IFN pathway downstream of TLR4. This study focuses on the role of type-1 IFN pathway in the mechanism of HO-1 cytoprotection during liver IRI.

METHODS AND RESULTS

Cobalt protoporphyrin (CoPP)-induced HO-1 overexpression ameliorated liver damage in a well-defined mouse model of liver warm IRI, as evidenced by improved hepatic function (serum alanine aminotransferase levels) and liver histology (Suzuki's scores). HO-1 downregulated phospho-STAT-1 and its key product, CXCL-10. In contrast, TLR4 expression remained elevated regardless of the IRI status. To dissect the mechanism of HO-1 upon CXCL-10, we cultured RW 264.7 (macrophage) cells with exogenous rIFN-beta to stimulate CXCL-10 production via TLR4 pathway in vitro. Indeed, CoPP-induced HO-1 suppressed otherwise highly upregulated rIFN-beta-triggered CXCL-10. Moreover, consistent with our in vitro data, CoPP pretreatment diminished rIFN-beta-induced CXCL-10 production in normal mouse livers.

CONCLUSION

Hepatic IRI activates TLR4 signaling in vivo to elaborate CXCL-10. HO-1 overexpression downregulates activation of STAT1 via type-1 IFN pathway downstream of TLR4, which in turn decreases CXCL-10 production. This study provides evidence for a novel mechanism by which HO-1 exerts adaptive cytoprotective and anti-inflammatory functions in the context of innate TLR4 activation.

Effects of Diethyldithiocarbamate (DETC) on Liver Injury Induced by Ischemia-Reperfusion in Rats

PURPOSE

In organ transplantation, ischemia-reperfusion injury (I/R) is a constant occurrence. Dithiocarbamates, a class of antioxidants, have been reported to inhibit nuclear factor-kappaB (NF-kappaB), a critical transcription factor in the intracellular inflammatory cascade. We studied the effects of diethyldithiocarbamate (DETC) on liver injury induced by I/R.

MATERIALS AND METHODS

Male Wistar rats were pretreated with DETC (100 mg/kg IV) 10 minutes before hepatic ischemia, which was followed by 2 hours reperfusion, or 10 minutes prior to the reperfusion. Blood samples were obtained at the end of the reperfusion period to determine the biochemical markers of liver injury. Results were compared using the one-way analysis of variance (ANOVA), followed by the Bonferroni posttest, and presented as mean values +/- SEM.

RESULTS

I/R produced significant increases in aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH), and gamma-glutamyl transferase (gamma-GT) serum levels compared with sham-operated rats. Administration of DETC prior to the onset of reperfusion significantly reduced the liver injury. However, DETC administered before the ischemic period failed to protect the liver from an I/R injury.

CONCLUSION

DETC, administered just before the reperfusion period, resulted in a significant decrease in the I/R injury to the liver, an observation that may have therapeutic implications.

Prospective randomized study of the benefits of preoperative corticosteroid administration on hepatic ischemia-reperfusion injury and cytokine response in patients undergoing hepatic resection

BACKGROUND

Hepatic injury secondary to warm ischemia and reperfusion (I/R) remains an important clinical issue following liver surgery. The aim of this prospective, randomized study was to determine whether steroid administration may reduce liver injury and improve short-term outcome.

PATIENTS AND METHODS

Forty-three patients undergoing liver resection were randomized to a steroid group or a control group. Patients in the steroid group received 500 mg of methylprednisolone preoperatively. Serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin, anti-thrombin III (AT-III), prothrombin time (PT), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF-alpha) were compared between the two groups. Length of stay and type and number of complications were recorded.

RESULTS

Postoperative serum levels of ALT, AST, total bilirubin, and inflammatory cytokines were significantly lower in the steroid group than in controls. The postoperative level of AT-III in the control group was significantly lower than in the steroid group (ANOVA p < 0.01). The incidence of postoperative complications in the control group tended to be significantly higher than that in the steroid group.

CONCLUSION

These results suggest that steroid pretreatment represents a potentially important biologic modifier of I/R injury and may contribute to maintenance of coagulant/anticoagulant homeostasis.

Basal Rather Than Induced Heme Oxygenase-1 Levels Are Crucial in the Antioxidant Cytoprotection

Heme oxygenase-1 (HO-1) overexpression protects against tissue injury in many inflammatory processes, including ischemia/reperfusion injury (IRI). This study evaluated whether genetically decreased HO-1 levels affected susceptibility to liver IRI. Partial warm ischemia was produced in hepatic lobes for 90 min followed by 6 h of reperfusion in heterozygous HO-1 knockout (HO-1(+/-)) and HO-1(+/+) wild-type (WT) mice. HO-1(+/-) mice demonstrated reduced HO-1 mRNA/protein levels at baseline and postreperfusion. This corresponded with increased hepatocellular damage in HO-1(+/-) mice, compared with WT. HO-1(+/-) mice revealed enhanced neutrophil infiltration and proinflammatory cytokine (TNF-alpha, IL-6, and IFN-gamma) induction, as well as an increase of intrahepatic apoptotic TUNEL(+) cells with enhanced expression of proapoptotic genes (Bax/cleaved caspase-3). We used cobalt protoporphyrin (CoPP) treatment to evaluate the effect of increased baseline HO-1 levels in both WT and HO-1(+/-) mice. CoPP treatment increased HO-1 expression in both animal groups, which correlated with a lower degree of hepatic damage. However, HO-1 mRNA/protein levels were still lower in HO-1(+/-) mice, which failed to achieve the degree of antioxidant hepatoprotection seen in CoPP-treated WT. Although the baseline and postreperfusion HO-1 levels correlated with the degree of protection, the HO-1 fold induction correlated instead with the degree of damage. Thus, basal HO-1 levels are more critical than the ability to up-regulate HO-1 in response to the IRI and may also predict the success of pharmacologically induced cytoprotection. This model provides an opportunity to further our understanding of HO-1 in stress defense mechanisms and design new regimens to prevent IRI.

FK330, a novel inducible nitric oxide synthase inhibitor, prevents ischemia and reperfusion injury in rat liver transplantation

Nitric oxide (NO), produced via inducible NO synthase (iNOS), is implicated in the pathophysiology of liver ischemia/reperfusion injury (IRI). We examined the effects of a novel iNOS inhibitor, FK330 (FR260330), in well-defined rat liver IRI models. In a model of liver cold ischemia followed by ex vivo reperfusion, treatment with FK330 improved portal venous flow, increased bile production and decreased hepatocellular damage. FK330 prevented IRI in rat model of 40-h cold ischemia followed by syngeneic orthotopic liver transplantation (OLT), as evidenced by: (1) increased OLT survival (from 20% to 80%); (2) decreased hepatocellular damage (serum glutamic oxaloacetic transaminase/glutamic pyruvic transaminase levels); (3) improved histological features of IRI; (4) reduced intrahepatic leukocyte infiltration, as evidenced by decreased expression of P-selectin/intracellular adhesion molecule 1, ED-1/CD3 cells and neutrophils; (5) depressed lymphocyte activation, as evidenced by expression of pro-inflammatory cytokine (TNF-alpha, IL-1beta, IL-6) and chemokine (IP-10, MCP-1, MIP-2) programs; (6) prevented hepatic apoptosis and down-regulated Bax/Bcl-2 ratio. Thus, by modulating leukocyte trafficking and cell activation patterns, treatment of rats with FK330, a specific iNOS inhibitor, prevented liver IRI. These results provide the rationale for novel therapeutic approaches to maximize organ donor pool through the safer use of liver grafts despite prolonged periods of cold ischemia.

CXCR3+CD4+ T cells mediate innate immune function in the pathophysiology of liver ischemia/reperfusion injury

Ischemia-reperfusion injury (IRI), an innate immune-dominated inflammatory response, develops in the absence of exogenous Ags. The recently highlighted role of T cells in IRI raises a question as to how T lymphocytes interact with the innate immune system and function with no Ag stimulation. This study dissected the mechanism of innate immune-induced T cell recruitment and activation in rat syngeneic orthotopic liver transplantation (OLT) model. Liver IRI was induced after cold storage (24-36 h) at 4 degrees C in University of Wisconsin solution. Gene products contributing to IRI were identified by cDNA microarray at 4-h posttransplant. IRI triggered increased intrahepatic expression of CXCL10, along with CXCL9 and 11. The significance of CXCR3 ligand induction was documented by the ability of neutralizing anti-CXCR3 Ab treatment to ameliorate hepatocellular damage and improve 14-day survival of 30-h cold-stored OLTs (95 vs 40% in controls; p < 0.01). Immunohistology analysis confirmed reduced CXCR3+ and CD4+ T cell infiltration in OLTs after treatment. Interestingly, anti-CXCR3 Ab did not suppress innate immune activation in the liver, as evidenced by increased levels of IL-1beta, IL-6, inducible NO synthase, and multiple neutrophil/monokine-targeted chemokine programs. In conclusion, this study demonstrates a novel mechanism of T cell recruitment and function in the absence of exogenous Ag stimulation. By documenting that the execution of innate immune function requires CXCR3+CD4+ T cells, it highlights the critical role of CXCR3 chemokine biology for the continuum of innate to adaptive immunity in the pathophysiology of liver IRI.

Vascular endothelial growth factor antagonist modulates leukocyte trafficking and protects mouse livers against ischemia/reperfusion injury

Although hypoxia stimulates the expression of vascular endothelial growth factor (VEGF), little is known of the role or mechanism by which VEGF functions after ischemia and reperfusion (I/R) injury. In this report, we first evaluated the expression of VEGF in a mouse model of liver warm ischemia. We found that the expression of VEGF increased after ischemia but peaked between 2 and 6 hours after reperfusion. Mice were treated with a neutralizing anti-mouse VEGF antiserum (anti-VEGF) or control serum daily from day -1 (1 day before the initiation of ischemia). Treatment with anti-VEGF significantly reduced serum glutaminic pyruvic transaminase levels and reduced histological evidence of hepatocellular damage compared with controls. Anti-VEGF also markedly decreased T-cell, macrophage, and neutrophil accumulation within livers and reduced the frequency of intrahepatic apoptotic terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling-positive cells. Moreover, there was a reduction in the expression of pro-inflammatory cytokines (tumor necrosis factor-alpha and interferon-gamma), chemokines (interferon-inducible protein-10 and monocyte chemoattractant protein-1) and adhesion molecules (E-selectin) in parallel with enhanced expression of anti-apoptotic genes (Bcl-2/Bcl-xl and heme oxygenase-1) in anti-VEGF-treated animals. In conclusion, hypoxia-inducible VEGF expression by hepatocytes modulates leukocyte trafficking and leukocyte-induced injury in a mouse liver model of warm I/R injury, demonstrating the importance of endogenous VEGF production in the pathophysiology of hepatic I/R injury.

Heme oxygenase 1 expression in postischemic reperfusion liver damage: effect of L-Arginine

Ischemia/reperfusion (I/R) injury is a multifactorial process that affects liver function after transplantation and resectional surgery. Alterations in hepatic microcirculation and decreased hepatic flow can cause local hypoxia and consequently liver damage, which is worsened by reperfusion. The aim of this study was to evaluate if treatment with L-arginine improved hepatic function in rats with I/R injury. Animals were treated with L-arginine, ischemized for 30 min, and reperfused for 3 h. Plasmatic levels of GOT, GPT, lipid hydroperoxides (LOOH), and total thiol groups (RSH) were evaluated. In addition, we analyzed hepatic LOOH and RSH levels, DNA fragmentation, heme oxygenase 1 (HO-1) expression, and histological modifications. Our results demonstrate a significant improvement in hepatic function of I/R rats compared to the control group. Treatment with L-arginine increased the expression of HO-1. These data suggest that L-arginine could be useful in preventing oxidative damage during hepatic surgery.

Inflammatory responses in a new mouse model of prolonged hepatic cold ischemia followed by arterialized orthotopic liver transplantation

The current models of liver ischemia/reperfusion injury (IRI) in mice are largely limited to a warm ischemic component. To investigate the mechanism of hepatic "cold" IRI, we developed and validated a new mouse model of prolonged cold preservation followed by syngeneic orthotopic liver transplantation (OLT). Two hundred and forty-three OLTs with or without rearterialization and preservation in University of Wisconsin solution at 4 degrees C were performed in Balb/c mice. The 14-day survivals in the nonarterialized OLT groups were 92% (11/12), 82% (9/11), and 8% (1/12) after 1-hour, 6-hour and 24-hour preservation, respectively. In contrast, hepatic artery reconstruction after 1-hour, 6-hour, and 24-hour preservation improved the outcome as evidenced by 2-week survival of 100% (12/12), 100% (10/10), and 33% (4/12), respectively, and diminished hepatocellular damage (serum alanine aminotransferase /histology). Moreover, 24-hour (but not 1-h) cold preservation of rearterialized OLTs increased hepatic CD4+ T-cell infiltration and proinflammatory cytokine (tumor necrosis factor-alpha, interleukin 2, interferon-gamma) production, as well as enhanced local apoptosis, and Toll-like receptor 4/caspase 3 expression. These cardinal features of hepatic IRI validate the model. In conclusion, we have developed and validated a new mouse model of IRI in which hepatic artery reconstruction was mandatory for long-term animal survival after prolonged (24-h) OLT preservation. With the availability of genetically manipulated mouse strains, this model should provide important insights into the mechanism of antigen-independent hepatic IRI and help design much needed refined therapeutic means to combat hepatic IRI in the clinics.

Ischemia and reperfusion injury in liver transplantation

Ischemia/reperfusion (I/R) injury is a multifactorial process detrimental to liver graft function. An understanding of the mechanisms involved in I/R injury is essential for the design of therapeutic strategies to improve the outcome of liver transplantation. The generation of reactive oxygen species subsequent to reoxygenation inflicts tissue damage and initiates a cellular cascade leading to inflammation, cell death, and ultimate organ failure. The accruing evidence suggests that Kupffer cells and T cells mediate the activation of neutrophil inflammatory responses. Activated neutrophils infiltrate the injured liver in parallel with increased expression of adhesion molecules on endothelial cells. The heme oxygenase (HO) system is among the most critical of the cytoprotective mechanisms activated during the cellular stress, exerting anti-oxidant and anti-inflammatory functions, modulating the cell cycle, and maintaining the microcirculation. The activation of toll-like receptors (TLR) on Kupffer cells may provide the triggering signal for pro-inflammatory responses in the I/R injury sequence. Indeed, dissecting TLR downstream signaling pathways plays a fundamental role in exploring novel therapeutic strategies based on the concept that hepatic I/R injury represents a case for host "innate" immunity.

Toll-like receptor and heme oxygenase-1 signaling in hepatic ischemia/reperfusion injury

Ischemia/reperfusion injury (IRI) represents the major problem in clinical liver transplantation. We have shown that toll-like receptor 4 (TLR4) signaling is specifically required in initiating antigen-independent IRI leading to liver inflammation, whereas local induction of anti-oxidant heme oxygenase-1 (HO-1) is cytoprotective. This study analyzes in vivo interactions between HO-1 and sentinel TLR system in the pathophysiology of liver IRI. Using a 90-min lobar warm ischemia model, wild type (WT), TLR4 KO/mutant and TLR2 KO mice were first assessed for the severity of hepatocellular damage at 6 h postreperfusion. Unlike in WT or TLR2-deficient mice, disruption/absence of TLR4 pathway reduced IRI, as manifested by liver function (serum alanine aminotransferase levels), histology (Suzuki's scores), neutrophil infiltration (myeloperoxidase activity) and local/systemic TNF-alpha production (mRNA/protein levels). Moreover, defective TLR4 but not TLR2 signaling increased mRNA/protein HO-1 expression. In contrast, tin protoporphyrin-mediated HO-1 inhibition restored hepatic damage in otherwise IRI-resistant TLR4 mutant/KO mice. CoPP-induced HO-1 overexpression ameliorated hepatic damage in IRI-susceptible TLR2 KO mice, comparable with WT controls, and concomitantly diminished TLR4 levels. In conclusion, this study highlights the importance of cross talk between HO-1 and TLR system in the mechanism of hepatic IRI. Hepatic IRI represents a case for innate immunity in which HO-1 modulates proinflammatory responses that are triggered via TLR4 signaling, a putative HO-1 repressor.

The CD154-CD40 T-cell co-stimulation pathway in liver ischemia and reperfusion inflammatory responses

BACKGROUND

Ischemia-reperfusion (I/R) injury is a prime antigen-independent inflammatory factor in the dysfunction of liver transplants. The precise contribution of T cells in the mechanism of I/R injury remains to be elucidated. As the CD154-CD40 co-stimulation pathway provides essential second signal in the initiation and maintenance of T-cell-dependent immune responses, this study was designed to assess the role of CD154 signaling in the pathophysiology of liver I/R injury.

METHODS

A mouse model of partial 90-min warm hepatic ischemia followed by 6 hr of reperfusion was used. Three animal groups were studied: (1) wild-type (WT) mice treated with Ad-(-gal versus Ad-CD40 immunoglobulin; (2) untreated WT versus CD154 (MR1) monoclonal antibody-treated WT mice; and (3) untreated WT versus CD154 knockout mice.

RESULTS

The disruption of CD154 signaling in all three animal groups ameliorated otherwise fulminant liver injury, as evidenced by depressed serum glutamic oxaloacetic transaminase levels, compared with controls. These beneficial effects were accompanied by depressed hepatic T-cell sequestration, local decrease of vascular endothelial growth factor expression, inhibition of tumor necrosis factor-(and T-helper type 1 cytokine production, and induction of antiapoptotic (Bcl-2/Bcl-xl) but depression of proapoptotic (caspase-3) proteins.

CONCLUSIONS

By using in parallel a gene therapy approach, pharmacologic blockade, and genetically targeted mice, these findings document the benefits of disrupting CD154 to selectively modulate inflammatory responses in liver I/R injury. This study reinforces the key role of CD154-CD40 T-cell co-stimulation in the pathophysiology of liver I/R injury.

Ethyl pyruvate ameliorates liver ischemia-reperfusion injury by decreasing hepatic necrosis and apoptosis

BACKGROUND

Hepatic ischemia-reperfusion injury (I/R) occurs in the settings of transplantation, trauma, and elective liver resections. Reactive oxygen species (ROS) have been shown to play a major role in organ I/R injury. Pyruvate, a key intermediate in cellular metabolism, is an effective scavenger of ROS. The purpose of this study was to test the hypothesis that ethyl pyruvate (EP), a soluble pyruvate derivative, is effective in preventing hepatic I/R injury.

METHODS

Lewis rats underwent 60 minutes of partial warm hepatic ischemia. Three doses of EP dissolved in lactated Ringer's solution or lactated Ringer's solution (LR) alone were given by intravenous injection. Serum and tissue samples were obtained at 1 to 24 hours postreperfusion.

RESULTS

Serum transaminases, degree of hepatic necrosis, and neutrophil infiltration were all significantly decreased in the EP-treated rats compared with control animals. The amount of hepatic lipid peroxidation was also significantly decreased in EP-treated animals. Both circulating levels and hepatic expression of inflammatory cytokines were significantly decreased in the EP-treated animals. Furthermore, EP inhibited activation of extracellular signal-regulated kinase, p38, and c-Jun N-terminal kinase mitogen-activated protein kinases, as well as nuclear factor-kappaB, signaling pathways involved in cytokine release. Treatment with EP also inhibited hepatic apoptosis.

CONCLUSION

EP has a protective effect on hepatic I/R injury, mediated in part by decreasing lipid peroxidation, down-regulation of inflammatory mediators, and inhibition of apoptosis. Strategies using this additive to LR solution should be considered in clinical settings of ischemic liver injury to decrease organ damage.

Protective role of dehydroascorbate in rat liver ischemia-reperfusion injury

BACKGROUND

Oxidative stress plays an important role in liver ischemia/reperfusion (I/R) injury. Thus, enhancing the liver antioxidant capacity could be a promising therapeutic strategy. Ascorbate (AA) is considered the perfect antioxidant, but its therapeutic efficacy is greatly limited by its slow achievement of high intracellular levels. This might be circumvented by administering dehydroascorbate (DHA), which presents a several-fold greater uptake than AA, and undergoes rapid intracellular reduction to AA. Thus, our aim was to assess the protective role of DHA in liver I/R injury.

MATERIALS AND METHODS

Wistar rats (200-300 g bw) were pretreated iv with different doses of AA or DHA 20 min before liver ischemia, followed by 6 h reperfusion. Liver damage was assessed by biochemical and morphological indices.

RESULTS

DHA pretreatment induced a rapid increase in liver ascorbate levels, significantly higher than findings for AA, without any significant reduction in glutathione levels. Liver damage during I/R in controls showed significant increases in serum transaminases and hepatic thiobarbituric acid reactive substances with alterations of liver morphology. DHA administration induced a clear, significant protection against I/R injury, whereas liver damage was only moderately prevented by AA.

CONCLUSIONS

DHA might represent a simple, effective therapeutic option to prevent liver damage associated with ischemia/reperfusion.

Serum matrix metalloproteinase MMP-2 and MMP-9 in the late phase of ischemia and reperfusion injury in human orthotopic liver transplantation

INTRODUCTION

Ischemia and reperfusion (I/R) injury during orthotopic liver transplantation (OLT) is accompanied by neutrophil infiltration and degradation of extracellular matrix. Matrix metalloproteinases (MMP) play an important role in the turnover of extracellular matrix components. We assessed the changes in level and composition of serum MMP-2 and MMP-9 in relation with I/R injury after human OLT.

METHODS

Thirty-three patients were separated into two groups according to their peak level of aspartate aminotransferase (AST) after OLT (AST < 1500 IU/L: n = 22; AST > 1500 IU/L: n = 11). Serum MMP-2 and MMP-9 were measured before transplantation as well as 2 days and 1 week after OLT using ELISA (MMP protein) and BIA (enzymatic activity of MMP).

RESULTS

MMP-2 and MMP-9 protein concentrations were comparable before and 2 days after OLT, whereas at 1 week MMP-2 decreased and MMP-9 increased significantly. However, there were no significant differences between patients with high or low peak AST at all time points. Also, the composition of MMP-2 and MMP-9 did not differ over time between the groups of patients.

CONCLUSION

Serum MMP-2 and MMP-9 do not relate to the late phase of hepatic I/R injury after human OLT.

Interleukin 13 Gene Transfer in Liver Ischemia and Reperfusion Injury: Role of Stat6 and TLR4 Pathways in Cytoprotection

Ischemia and reperfusion injury (IRI) represents the major problem in clinical liver transplantation. We have shown that transcription of signal transducer and activator of transcription 4 (Stat4) plays a key role in the mechanism of hepatic IRI, whereas local induction of interleukin 13 (IL-13) is cytoprotective. The disruption of innate Toll-like receptor 4 (TLR4) signaling prevents mouse livers from undergoing fulminant IRI. This study analyzes in vivo interplay between innate (TLR4) and adaptive (Stat6) immunity in Ad-IL-13 (recombinant adenovirus encoding IL-13) cytoprotection in hepatic IRI. Using a partial 90-min lobar warm ischemia model, groups of wild-type and Stat6-deficient knockout mice were assessed for the severity of hepatocellular damage at 6 hr postreperfusion. Unlike in wild-type mice, treatment of Stat6 knockout recipients with Ad-IL-13 failed to improve hepatic function/histology. The expression of mRNAs encoding tumor necrosis factor alpha/IL-1 beta and IL-2/interferon gamma remained depressed in the wild-type plus Ad-IL-13 group, but not in the Stat6 knockout plus Ad-IL-13 group. Ad-IL-13 increased antioxidant heme oxygenase 1 (HO-1) expression and prevented TLR4 activation in livers of Stat6-competent (wild-type) mice. In contrast, low HO-1 expression and enhanced TLR4 expression were recorded in Stat6 knockout recipients despite Ad-IL-13 therapy. Thus (1) Stat6 is required for Ad-IL-13 to prevent IRI, and (2) depression of TLR4 activation is Stat6 dependent. In conclusion, the Stat6 pathway operates as a key negative regulator in the hepatic inflammatory ischemia-reperfusion response. This study outlines requirements for Ad-IL-13 use to maximize the organ donor pool through the use of liver transplants despite prolonged ischemia.

Dipyridamole protects the liver against warm ischemia and reperfusion injury

BACKGROUND

Adenosine, a metabolite of adenosine triphosphate degradation during ischemia, is reported to attenuate ischemia and reperfusion injury in several tissues. Dipyridamole is a nucleoside transport inhibitor that augments endogenous adenosine. In this study, we tested whether dipyridamole would attenuate hepatic I/R injury. For this purpose, dipyridamole was applied to a 2-hour total hepatic vascular exclusion model in dogs.

STUDY DESIGN

Dipyridamole (DYP) was given by continuous intravenous infusion for 1 hour before ischemia at a dose of 0.25 mg/kg (high-DYP, n = 6), 0.1 mg/kg (medium-DYP, n = 6), or 0.05 mg/kg (low-DYP, n = 6). Nontreated animals were used as ischemic controls (CT, n = 12). Two-week survival, systemic and hepatic hemodynamics, liver function tests, energy metabolism, adenosine 3', 5'-cyclic monophosphate (cyclic AMP) levels, platelet numbers, arachidonic acid metabolites, and histopathology were analyzed.

RESULTS

Two-week animal survival was 25% in CT, 17% in high-DYP, 100% in medium-DYP, and 17% in low-DYP. Dipyridamole significantly improved postreperfusion hepatic blood flow and energy metabolism, attenuated liver enzyme release and purine catabolite production, and augmented cyclic AMP levels. The medium dose of dipyridamole lessened platelet aggregation, thromboxane B2 production, and polymorphonuclear neutrophil infiltration, and improved survival.

CONCLUSIONS

We demonstrated marked hepatoprotective effects of dipyridamole against severe ischemia and reperfusion injury in canine livers. Dipyridamole is a promising agent for liver surgery and transplantation.

Gene therapy for liver transplantation using adenoviral vectors: CD40-CD154 blockade by gene transfer of CD40Ig protects rat livers from cold ischemia and reperfusion injury

Liver injury induced by ischemia/reperfusion (I/R) is the prime factor in delayed or loss graft function following transplantation. CD4+ T lymphocytes are key cellular mediators of antigen-independent inflammatory response triggered by I/R. We attempted to modulate rat liver I/R injury by targeted gene therapy with CD40Ig, which blocks the CD40-CD154 costimulation pathway. One hundred percent of Ad-CD40Ig-pretreated orthotopic liver transplants (OLTs) subjected to 24 h of cold (4 degrees C) ischemia survived > 14 days (vs 50% in untreated/Ad-beta-gal groups). Ad-CD40Ig treatment decreased sGOT levels and depressed neutrophil infiltration, compared with controls. These functional data correlated with histological Suzuki's grading of hepatic injury, which in untreated/Ad-beta-gal groups showed severe necrosis (> 60%) and moderate to severe sinusoidal congestion; the Ad-CD40Ig-pretreated group revealed minimal sinusoidal congestion/necrosis. Unlike in controls, OLT expression of mRNA coding for IL-2/IFN-gamma remained depressed, whereas that of IL-4/IL-13 reciprocally increased in the Ad-CD40Ig group. Ad-CD40Ig reduced frequency of TUNEL+ cells and pro-apoptotic Caspase-3, but enhanced antioxidant HO-1 and anti-apoptotic Bcl-2/Bcl-xl expression. Thus, prolonged blockade of CD40-CD154 by CD40Ig exerts potent cytoprotection against hepatic I/R injury. These results provide the rationale for a novel gene therapy approach to maximize the organ donor pool through the safer use of liver transplants exposed to prolonged cold ischemia.

Epigallocatechin gallate can significantly decrease free oxygen radicals in the reperfusion injury in vivo

OBJECTIVE

There is experimental evidence that oxygen-derived free radicals (Superoxide (O(2)(-))) play a key role in tissue damage in ischemia-reperfusion injury. Among various antioxidants tested in vitro, natural polyphenols like Epigallocatechine gallate (EGCG) show a 164-fold higher scavenging activity for O(2)(-) than ascorbic acid We therefore conducted an animal study in order to investigate the impact of EGCG on O(2)(-) production during reperfusion after defined periods of ischemia in the muscle tissue of the rat, using a recently developed cytochrome c-based biosensor for on-line in vivo monitoring of O(2)(-).

MATERIALS AND METHODS

Femoral artery and vein were dissected below the inguinal ligament in male Wistar rats. The cytochrome c-based biosensor was placed in the gastrocnemius muscle. Ischemia was induced by clamping the femoral vessels. Ischemia times were either 60 (n = 14) or 120 (n = 14) minutes. Six animals in each group received 4 mg/kg body weight EGCG intravenously at the time of reperfusion, another six animals in each group served as controls (no treatment). Additionally, two animals in each group received the same volume of saline instead of EGCG. The current response of the biosensor corresponding to the O(2)(-) concentrations in vivo was recorded on a PC. The gastrocnemius muscles were harvested for histological evaluation.

RESULTS

The average maximum O(2)(-) concentration after 60 minutes of ischemia was 188, 18 nmol/L (23 pA) compared to 90 nmol/L (11 pA) (P <.01) with EGCG application. The mean O(2)(-) value after 120 minutes was 220 nmol/L (27 pA) versus 135 nmol/L (16.5 pA) (P <.01) with EGCG, respectively. Histological analysis showed advanced muscle cell injury and neutrophil infiltration in the group without EGCG. No O(2)(-) reduction could be verified administering saline instead of EGCG.

CONCLUSION

For the first time the scavenging activity of an antioxidant was verified in vivo on-line. EGCG significantly diminished O(2)(-) tissue concentrations after 60 or 120 minutes of ischemia by an average of nearly 50%, suggesting its therapeutic potential.

Cytoprotective and antiapoptotic effects of IL-13 in hepatic cold ischemia/reperfusion injury are heme oxygenase-1 dependent

Liver injury caused by ischemia/reperfusion (I/R) insult represents the major problem following orthotopic liver transplantation (OLT). I/R damage has been linked to Th1-like cytokine producers. This study evaluates putative cytoprotective effects/mechanisms of Th2-type IL-13 gene transfer. IL-13 overexpression prevented hepatic insult in a rat model of 24 h cold ischemia followed by OLT, as assessed: (i) profoundly decreased hepatocellular damage (sGOT levels), and ameliorated histological signs of I/R injury (Suzuki criteria), consistent with long-term OLT survival; (ii) prevented hepatic apoptosis (TUNEL stains) and up-regulated expression of antiapoptotic (A20, Bcl-2/Bcl-xl)/antioxidant (HO-1) genes. However, inhibition of HO-1 with tin protoporphyrin reversed cytoprotective/antiapoptotic effects of IL-13. In conclusion, cytoprotection rendered by virally induced IL-13 against hepatic I/R injury in this clinically relevant rat hepatic cold I/R injury model was accomplished via decreased apoptosis and induction of antiapoptotic/antioxidant molecules. HO-1 neutralization studies suggest that HO-1 represents one of putative IL-13 downstream effectors. This study provides the rationale for novel approaches to maximize organ donor pool through the safer use of OLTs despite prolonged periods of cold ischemia.

Heavy chain ferritin acts as an antiapoptotic gene that protects livers from ischemia reperfusion injury

Heme oxygenase-1 (HO-1) is induced under a variety of pro-oxidant conditions such as those associated with ischemia-reperfusion injury (IRI) of transplanted organs. HO-1 cleaves the heme porphyrin ring releasing Fe2+, which induces the expression of the Fe2+ sequestering protein ferritin. By limiting the ability of Fe2+ to participate in the generation of free radicals through the Fenton reaction, ferritin acts as an anti-oxidant. We have previously shown that HO-1 protects transplanted organs from IRI. We have linked this protective effect with the anti-apoptotic action of HO-1. Whether the iron-binding properties of ferritin contributed to the protective effect of HO-1 was not clear. We now report that recombinant adenovirus mediated overexpression of the ferritin heavy chain (H-ferritin) gene protects rat livers from IRI and prevents hepatocellular damage upon transplantation into syngeneic recipients. The protective effect of H-ferritin is associated with the inhibition of endothelial cell and hepatocyte apoptosis in vivo. H-ferritin protects cultured endothelial cells from apoptosis induced by a variety of stimuli. These findings unveil the anti-apoptotic function of H-ferritin and suggest that H-ferritin can be used in a therapeutic manner to prevent liver IRI and thus maximize the organ donor pool used for transplantation.

Insulin in University of Wisconsin solution exacerbates the ischemic injury and decreases the graft survival rate in rat liver transplantation

BACKGROUND

Insulin keeps the liver in a metabolically vigorous state. However, organ preservation aims to decrease the metabolic rate. The objective of this study was to clarify the effect of insulin used in University of Wisconsin (UW) preservation solution on the liver graft.

METHODS

The liver grafts were preserved by UW solution with or without insulin for 7, 9, and 24 hr, respectively. The influence of insulin was studied by 7-day survival rate, liver function, morphology, and intragraft gene expression 24 hr after transplantation. Morphology was studied on the preserved grafts.

RESULTS

The morphology of the graft in the insulin group showed more severe ischemia-reperfusion injury. The 7-day graft survival rates of the 7-hr subgroups with and without insulin were 55% and 93%, respectively (P=0.02). In the 9-hr subgroups, the survival rates were 0% and 78%, respectively (P=0.002). The serum levels of aspartate aminotransferase (AST) (P=0.008) and alanine aminotransferase (ALT) (P=0.032) were higher in the 7-hr subgroup with insulin. The same trend was found in the 9-hr subgroups (AST, P=0.016; ALT, P=0.016). The expression level of 215 genes were much lower at 24 hr after transplantation in the grafts preserved with insulin than in those preserved without insulin, and most of the genes were related to metabolic activities.

CONCLUSIONS

Insulin in UW solution may exacerbate graft ischemic injury and decrease the graft survival rate in rat liver transplantation. Insulin, in the absence of glucose in UW solution, may exhaust the metabolic activity of the liver graft. It is harmful rather than helpful for isolated rat liver grafts preserved in UW solution.

Interleukin-13 gene transfer protects rat livers from antigen-independent injury induced by ischemia and reperfusion

BACKGROUND

Ischemia-reperfusion (I/R) injury is a prime inflammatory factor in the dysfunction of orthotopic liver transplants. Interleukin (IL)-13 suppresses macrophage production of proinflammatory mediators. This study explores the effects of adenovirus (Ad)-based IL-13 gene transfer in rat models of hepatic I/R injury.

METHODS

The authors used a model of warm in situ ischemia followed by reperfusion, and ex vivo cold ischemia followed by transplantation.

RESULTS

In a model of warm in situ ischemia followed by reperfusion, Ad-based IL-13 significantly diminished hepatocellular injury, assessed by serum glutamic oxaloacetic transaminase (SGOT) levels, as compared with Ad-based beta-galactosidase (gal)-treated livers. In a model of ex vivo cold ischemia followed by transplantation, the survival of liver grafts increased from 50% in Ad-beta-gal untreated controls to 100% after Ad-IL-13 gene therapy. This beneficial effect correlated with improved liver function (SGOT levels), preservation of hepatic histologic integrity and architecture (Suzuki criteria), and depression of neutrophil infiltration (myeloperoxidase assay). Ad-IL-13 diminished activation of macrophage-neutrophil-associated tumor necrosis factor-alpha, macrophage inflammatory protein-2, and endothelial-dependent E-selectin, but increased type 2 IL-4 and IL-13 expression.

CONCLUSIONS

This study documents striking cytoprotective effects of virally induced IL-13 against hepatic I/R injury in two clinically relevant rat models of hepatic I/R injury. These data provide the rationale for novel therapeutic approaches to maximize the organ donor pool through the safer use of liver transplants despite prolonged periods of warm or cold ischemia, or both.

Hepatic ischemia/reperfusion injury--a fresh look

Ischemia/reperfusion (I/R) injury is a multifactorial process that affects graft function after liver transplantation. An understanding of the mechanisms involved in I/R injury is essential for the design of therapeutic strategies to improve the outcome of liver transplantation. The generation of reactive oxygen species subsequent to reoxygenation inflicts tissue damage and initiates a cascade of deleterious cellular responses leading to inflammation, cell death, and ultimate organ failure. Increased experimental evidence has suggested that Kupffer cells and T cells mediate the activation of neutrophil inflammatory responses. Activated neutrophils infiltrate the injured liver in parallel with increased expression of adhesion molecules on endothelial cells. The heme oxygenase system is among the most critical of the cytoprotective mechanisms activated during cellular stress, exerting antioxidant and anti-inflammatory functions, modulating the cell cycle, and maintaining the microcirculation. Finally, the activation of toll-like receptors on Kupffer cells may play a fundamental role in exploring new therapeutic strategies based on the concept that hepatic I/R injury represents a case for a host "innate" immunity.

Stat4 and Stat6 signaling in hepatic ischemia/reperfusion injury in mice: HO-1 dependence of Stat4 disruption-mediated cytoprotection

Ischemia/reperfusion (I/R) injury remains an important problem in clinical organ transplantation. There is growing evidence that T lymphocytes, and activated CD4+ T cells in particular, play a key role in hepatic I/R injury. This study analyzes the role of signal transducer and activator of transcription 4 (Stat4) and Stat6 signaling in liver I/R injury. Using a partial lobar warm ischemia model, groups of wild-type (WT), T cell-deficient, Stat4-/Stat6-deficient knockout (KO) mice were assessed for the extent/severity of I/R injury. Ninety minutes of warm ischemia followed by 6 hours of reperfusion induced a fulminant liver failure in WT and Stat6 KO mice, as assessed by hepatocellular damage (serum alanine aminotransferase [sALT] levels), neutrophil accumulation (myeloperoxidase [MPO] activity) and histology (Suzuki scores). In contrast, T cell deficiency (nu/nu mice) or disruption of Stat4 signaling (Stat4 KO mice) reduced I/R insult. Unlike adoptive transfer of WT or Stat6-deficient T cells, infusion of Stat4-deficient T cells failed to restore hepatic I/R injury and prevented tumor necrosis factor alpha (TNF-alpha) production in nu/nu mice. Diminished TNF-alpha/Th1-type cytokine messenger RNA (mRNA)/protein elaborations patterns, along with overexpression of heme oxygenase-1 (HO-1)-accompanied hepatic cytoprotection in Stat4 KO recipients. In contrast, HO-1 depression restored hepatic injury in otherwise I/R resistant Stat4 KOs. In conclusion, Stat4 signaling is required for, whereas Stat4 disruption protects against, warm hepatic I/R injury in mice. The cytoprotection rendered by Stat4 disruption remains HO-1-dependent.

FTY720 pretreatment reduces warm hepatic ischemia reperfusion injury through inhibition of T-lymphocyte infiltration

Ischemia and reperfusion (IR) injury remains a significant problem in clinical liver transplantation. We investigated the effects of lymphocyte depletion with FTY720 in models of warm hepatic IR. Using 60-min partial warm hepatic IR, three groups of rats were studied: Sham--laparotomy alone; Control--water p.o. x 3 d before ischemia; Treatment--FTY720 p.o. x 3 d before ischemia. Animals were sacrificed for analysis at 6 h and 24 h post reperfusion. The effect of FTY720 pretreatment on survival was also studied using 150 min total hepatic IR with portojugular shunt. FTY720 treatment significantly reduced serum glutamic pyruvic transaminase and peripheral blood lymphocytes compared to controls at 6h and 24h (p < 0.0005). Histological grade was significantly improved in treated livers vs. controls (p < 0.05). CD3 immunocytochemical analysis revealed a significant reduction in T-cell infiltration in FTY720-treated livers (p < 0.0002). No difference in tissue myeloperoxidase levels was observed. Seven-day survival was significantly improved in treated rats vs. controls following total hepatic ischemia (p < 0.05). In conclusion, FTY720 ameliorates the biochemical and histological manifestations of hepatic IR by preventing T-lymphocyte infiltration and prolongs survival following a more severe ischemic insult. Myeloperoxidase data suggest this mechanism is independent of neutrophil activation. These results indicate that T lymphocytes are pivotal mediators in hepatic IR and may have important implications in liver transplantation.

CD154-CD40 T-cell costimulation pathway is required in the mechanism of hepatic ischemia/reperfusion injury, and its blockade facilitates and depends on heme oxygenase-1 mediated cytoprotection

BACKGROUND

Ischemia/reperfusion (I/R) injury remains an important clinical problem that affects both early and later allograft outcome. This study was designed to analyze the role of T cells and CD154-CD40 T- cell costimulation pathway in a mouse liver I/R model.

METHODS AND RESULTS

Ninety minutes of warm ischemia followed by 4 h of reperfusion in wild-type (WT) mice resulted in a significant hepatic damage, as assessed by liver function (serum alanine aminotransferase [sALT] levels), local neutrophil accumulation (myeloperoxidase activity), and histology (Suzuki's score). In contrast, T-cell deficiency (in T-cell deficient [nu/nu] mice), disruption of the CD154 signaling (in knockout [KO] mice), or its blockade in WT recipients (after MR1 monoclonal antibody [mAb] treatment), virtually prevented hepatic I/R insult. Unlike CD154-deficient T cells, adoptive transfer of WT spleen cells fully restored hepatic I/R injury in nu/nu mice. Finally, the improved hepatic function in CD154 KO recipients, WT mice treated with CD154 mAb, or nu/nu mice infused with CD154-deficient cells resulted in consistently enhanced expression of heme oxygenase-1 (HO-1), a heat-shock protein with cytoprotective functions.

CONCLUSION

This study confirms the importance of T cells, and documents for the first time the role of CD154 costimulation signals in the mechanism of hepatic I/R injury. We also show that CD154 blockade-mediated cytoprotection results and depends on HO-1 overexpression. Our data provide the rationale for human trials to target CD154-CD40 costimulation in hepatic I/R injury, particularly in the transplant patient.

17-Beta-estradiol protects the liver against warm ischemia/reperfusion injury and is associated with increased serum nitric oxide and decreased tumor necrosis factor-alpha

BACKGROUND

Ischemia/reperfusion injury (I/R injury) to the liver can occur in low-flow states associated with trauma and shock and surgical procedures such as liver transplantation. Recent studies have shown that the administration of the female sex hormone 17-beta-estradiol after trauma-hemorrhage in animals restores depressed cardiac, hepatocellular, and immune functions. In this study we evaluated the effects of 17-beta-estradiol on I/R injury to the liver.

METHODS

The medial lobe of the liver in normal male C57BL/6 mice was clamped at its base for 90 minutes. 17-Beta-estradiol was given 1 hour before I/R injury at 40 and 4000 microg/kg intraperitoneally. Biochemical analysis was performed, and liver biopsy specimens were obtained at 24 hours.

RESULTS

A dose-dependent reduction in aspartate aminotransferase level was observed in animals (n = 8) given estradiol (243 +/- 23 IU/L) compared with saline-treated animals (902 +/- 42 IU/L, P <.001). The majority (90%) of the cytoprotective effect of estradiol was reverted by ICI 182,780 (a potent estrogen receptor antagonist). A significant increase in serum nitric oxide (NO) level was observed in animals given estradiol compared with controls; the effect was reversed by ICI 182,780 and N-nitro-L-arginine-methyl ester (an inhibitor of NO synthesis). A reduction in serum tumor necrosis factor-alpha was observed after injury in animals given estradiol compared with controls (30.2 +/- 11.1 vs 75.8 +/- 17.2 pg/mL, P <.001). Estradiol treatment significantly reduced liver necrosis, disintegration of hepatic cords, and neutrophil infiltration in an estrogen receptor-dependent manner.

CONCLUSIONS

Estradiol administration significantly reduced injury after I/R to the liver, an effect that is mainly receptor-mediated and is associated with increased serum NO, decreased TNF-alpha, and decreased number of neutrophils in liver biopsy specimens. Estrogen therapy may be important in clinical conditions associated with I/R injury to the liver.

P-selectin glycoprotein ligand-1 (rPSGL-Ig)-mediated blockade of CD62 selectin molecules protects rat steatotic liver grafts from ischemia/reperfusion injury

We examined the effects of early blockade of CD62 selectin-mediated adhesive interactions in steatotic rat liver models of ex vivo cold ischemia followed by reperfusion or transplantation by administration of P-selectin glycoprotein ligand-1 (rPSGL-Ig). In the model of cold ischemia/reperfusion, livers pretreated ex vivo with rPSGL-Ig at harvesting from obese Zucker rats showed significantly decreased portal resistance, increased bile production, and diminished hepatic endothelial neutrophil infiltration, as compared with untreated controls. Pretreatment of fatty livers with rPSGL-Ig prior to transplantation extended the survival of lean Zucker rat recipients from 40% to 90%. This effect correlated with significantly improved liver function, depressed neutrophil activity, and decreased histologic features of hepatocyte injury. Intragraft expression of CD62 P-selectin was similar in both recipient groups. rPSGL-Ig treatment decreased intragraft infiltration by CD3/CD25 cells, diminished expression of pro-inflammatory TNFalpha, IL-6, iNOS, IL-2 and IFN-gamma, without significantly affecting mRNA levels coding for anti-inflammatory IL-4. Thus, rPSGL-Ig blockade of CD62-mediated adhesive interactions protects against severe ischemia/reperfusion injury suffered otherwise by steatotic rat livers. These findings document the potential utility of rPSGL-Ig in increasing the transplant donor pool through modulation of marginal steatotic livers.

Heme oxygenase-1 overexpression protects rat livers from ischemia/reperfusion injury with extended cold preservation

This study analyzes the effects and mechanisms of heme oxygenase-1 (HO-1)-mediated cytoprotection in rat livers exposed to cold preservation. In the first series, rats were pretreated with cobalt protoporphyrin (CoPP) or zinc protoporphyrin (ZnPP), HO-1 inducer and antagonist, respectively. Livers were stored at 4 degrees C for 24 h, and then perfused ex vivo for 2 h. Livers pretreated with CoPP had significantly higher portal venous blood flow and increased total bile production, as compared with the ZnPP group. This correlated with histologic (Banff) criteria of hepatocyte injury/liver function. In the second series, rat livers were stored at 4 degrees C for 24 h or 40 h, and then transplanted into syngeneic recipients. After 24 h of preservation, 80% of rats bearing CoPP-pretreated liver grafts survived 21 days (vs. 50% in controls). After 40h of cold preservation, liver transplant survival at day 1, 7 and 21 for the CoPP group was: 100%, 71% and 57%, respectively (vs. 50%, 50% and 33% in controls). This correlated with improved hepatic function/histologic (Suzuki) criteria of hepatocyte injury after HO-1 overexpression (immunohistology/Western blots) by infiltrating macrophages. This study documents the potential utility of HO-1-inducing agents in preventing ischemia/reperfusion injury resulting from prolonged storage of liver transplants.

Heme oxygenase-1 gene transfer inhibits inducible nitric oxide synthase expression and protects genetically fat Zucker rat livers from ischemia-reperfusion injury

BACKGROUND

Ischemia/reperfusion (I/R) injury is a critical factor in the dysfunction of steatotic orthotopic liver transplants. Heme oxygenase-1 (HO-1), a cytoprotective protein, may be important in ameliorating hepatic I/R injury.

METHODS

We used adenovirus (Ad)-based HO-1 gene transfer to analyze the effects of HO-1 overexpression in a well-established fatty Zucker rat model of I/R followed by orthotopic liver transplantation.

RESULTS

Ad-HO-1 gene therapy increased recipient survival (80% vs. 40-50% in controls) and significantly diminished hepatocyte injury, as compared with untreated and Ad-beta-galactosidase (Ad-beta-Gal)-treated livers. Orthotopic liver transplants in the Ad-HO-1 group exhibited less macrophage infiltration in the portal areas, as compared with controls. Unlike untreated and Ad-beta-Gal-treated orthotopic liver transplant controls, which showed elevated levels of inducible nitric oxide synthase by infiltrating macrophages, inducible nitric oxide synthase expression in the Ad-HO-1 group was almost absent. In contrast, endothelial nitric oxide synthase was comparable in Ad-HO-1- and Ad-beta-Gal-transduced fatty orthotopic liver transplants. Intragraft expression of antiapoptotic Bcl-2 and Bag-1 was increased in Ad-HO-1-treated orthotopic liver transplants, as compared with Ad-beta-Gal controls. Moreover, increased HO enzymatic activity was accompanied by inhibition of caspase-3 protein expression.

CONCLUSIONS

HO-1 gene transfer significantly prolongs survival of steatotic orthotopic liver transplants, depresses macrophage infiltration, suppresses local expression of inducible nitric oxide synthase, and modulates pro- and antiapoptotic pathways.

Bucillamine, a thiol antioxidant, prevents transplantation-associated reperfusion injury

Ischemia/reperfusion (I/R) injury is a serious potential threat to outcomes in organ transplantation and other clinical arenas in which there is temporary interruption of blood flow. I/R is a frequent cause of primary failure in organ transplantation. We hypothesized that the antioxidant bucillamine, a potent sulfhydryl donor, would protect against I/R injury in high-risk organ transplants. Because livers subjected to prolonged ischemia and very fatty livers are highly susceptible to severe I/R injury, we studied the effect of bucillamine in three animal models of liver transplantation: two ex vivo models of isolated perfused livers, either normal or fatty rat livers, and an in vivo model of syngenic orthotopic liver transplants in rats. In all models, livers were deprived of oxygen for 24 h before either ex vivo reperfusion or transplantation. In the ex vivo models, bucillamine treatment significantly improved portal vein blood flow and bile production, preserved normal liver architecture, and significantly reduced liver enzyme release and indices of oxidative stress. Moreover, bucillamine treatment significantly increased levels of reduced glutathione in the liver and lowered levels of oxidized glutathione in both liver and blood. In rats subjected to liver transplants, bucillamine significantly enhanced survival and protected against hepatic injury. Possible mechanisms of this protection include prevention of excessive accumulation of toxic oxygen species, interruption of redox signaling in hepatocytes, and inhibition of macrophage activation. This study demonstrates the potential utility of bucillamine or other cysteine-derived thiol donors for improving outcomes in organ transplantation and other clinical settings involving I/R injury.

Ex vivo exposure to carbon monoxide prevents hepatic ischemia/reperfusion injury through p38 MAP kinase pathway

A direct role of carbon monoxide (CO), an effector-signaling molecule during heme oxygenase-1 (HO-1) catalysis of heme, in the protection against hepatic ischemia/reperfusion (I/R) injury needs to be established. This study was designed to determine the effects and downstream mechanisms of CO on cold I/R injury in a clinically relevant isolated perfusion rat liver model. After 24 hours of cold storage, rat livers perfused ex vivo for 2 hours with blood supplemented with CO (300 parts per million) showed significantly decreased portal venous resistance and increased bile production, as compared with control livers perfused with blood devoid of CO. These beneficial effects correlated with improved liver function (serum glutamic oxaloacetic transaminase levels) and diminished histological features of hepatocyte injury (Banff's scores). The CO-mediated cytoprotective effects were nitric oxide synthase- and cyclic guanine monophosphate-independent, but p38 mitogen-activated protein kinase (MAPK)-dependent. Moreover, adjunctive use of zinc protoporphyrin, a competitive HO-1 inhibitor, has shown that exogenous CO could fully substitute for endogenous HO-1 in preventing hepatic I/R insult. This study performed in a clinically relevant ex vivo cold ischemia model is the first to provide the evidence that HO-1-mediated cytoprotection against hepatic I/R injury depends on the generation of, and can be substituted by, exogenous CO. The p38 MAPK signaling pathway represents the key downstream mechanism by which CO prevents the I/R insult. In conclusion, regimens that employ exogenous CO should be revisited, as they may have potential applications in preventing/mitigating I/R injury, and thus expanding the liver donor pool for clinical transplantation.

Early graft function after pediatric liver transplantation: comparison between in situ split liver grafts and living-related liver grafts

BACKGROUND

The systematic application of living-related and cadaveric, in situ split-liver transplantation has helped to alleviate the critical shortage of suitable-sized, pediatric donors. Undoubtedly, both techniques are beneficial and advantageous; however, the superiority of either graft source has not been demonstrated directly. Because of the potential living-donor risks, we reserve the living donor as the last graft option for pediatric recipients awaiting liver transplantation. Inasmuch as no direct comparison between these two graft types has been performed, we sought to perform a comparative analysis of the functional outcomes of left lateral segmental grafts procured from these donor sources to determine whether differences do exist.

METHODS

A retrospective analysis of all liver transplants performed at a single institution between February 1984 and January 1999 was undertaken. Only pediatric (<18 years) recipients of left lateral segmental grafts procured from either living-related (LRD) or cadaveric, in situ split-liver (SLD) donors were included. A detailed analysis of preoperative, intraoperative, and postoperative variables was undertaken. Survival was estimated using the Kaplan-Meier method, and comparison of variables between groups was undertaken using the t test of Wilcoxon rank sum test.

RESULTS

There were no significant differences in the preoperative variables between the 39 recipients of SLD grafts and 34 recipients of LRD grafts. The donors did differ significantly in mean age, ABO blood group matching, and preoperative liver function testing. Postoperative liver function testing revealed significant early differences in aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, prothrombin time, and alkaline phosphatase, with grafts from LRD performing better than those from SLD. SLD grafts also had significantly longer ischemia times and a higher incidence of graft loss owing to primary nonfunction and technical complications (9 vs. 2, P<0.05). However, six of these graft losses in the SLD group were because of technical or immunologic causes, which, theoretically, should not differ between the two groups. Furthermore, these graft losses did not negatively impact early patient survival as most patients were successfully rescued with retransplantation (30-day actuarial survival, 97.1% SLD vs. 94.1% LRD, P=0.745). In the surviving grafts, the early differences in liver function variables normalized.

CONCLUSIONS

Inherent differences in both donor sources exist and account for differences seen in preoperative and intraoperative variables. Segmental grafts from LRD clearly performed better in the first week after transplantation as demonstrated by lower liver function variables and less graft loss to primary nonfunction. However, the intermediate function (7-30 days) of both grafts did not differ, and the early graft losses did not translate into patient death. Although minimal living-donor morbidity was seen in this series, the use of this donor type still carries a finite risk. We therefore will continue to use SLD as the primary graft source for pediatric patients awaiting liver transplantation.