Reperfusion injury to donor livers stored for transplantation

In vivo imaging of hepatic hemodynamics and light scattering property during ischemia-reperfusion in rats based on spectrocolorimetry

A red-green-blue camera-based imaging method is proposed for estimating spatial maps of concentrations of oxyhemoglobin (CHbO), deoxyhemoglobin (CHbR), total hemoglobin (CHbT), tissue oxygen saturation (StO2), and scattering power (b) in liver tissue. Hemodynamic responses to hepatic ischemia-reperfusion of in vivo rat liver tissues induced by portal triad occlusion were evaluated. Upon portal triad occlusion, this method yielded images of decreased CHbO, CHbT, StO2, and b, and increased CHbR followed by a progressive increase in CHbO and StO2 during reperfusion. Time courses of the changes in CHbO, CHbR, CHbT, and StO2 over different regions of interest (ROIs) revealed that ischemia results in an abrupt significant (P<0.05) reduction in CHbO, CHbT, and StO2 with a simultaneous increase in CHbR compared to the baseline level, indicative of the hemodynamic responses during hepatic ischemia-reperfusion. Upon reperfusion, there was a gradual increase in CHbO and StO2, and decrease in CHbR. The change in average scattering power b implies the presence of morphological alterations in the cellular and subcellular structures induced by ischemia or anoxia. This study shows the potential of monitoring spatiotemporal changes in hemodynamic parameters and morphological changes in studies of hepatic pathophysiology.

Impact of Temperature on Porcine Liver Machine Perfusion From Donors After Cardiac Death

Normothermic machine perfusion (NMP) has been introduced as a promising technology to preserve and possibly repair marginal liver grafts. The aim of this study was to compare the effect of temperature on the preservation of donation after cardiac death (DCD) liver grafts in an ex vivo perfusion model after NMP (38.5°C) and subnormothermic machine perfusion (SNMP, 21°C) with a control group preserved by cold storage (CS, 4°C). Fifteen porcine livers with 60 min of warm ischemia were preserved for 10 h by NMP, SNMP or CS (n = 5/group). After the preservation phase all livers were reperfused for 24 h in an isolated perfusion system with whole blood at 38.5°C to simulate transplantation. At the end of transplant simulation, the NMP group showed significantly lower hepatocellular enzyme level (AST: 277 ± 69 U/L; ALT: 22 ± 2 U/L; P < 0.03) compared to both SNMP (AST: 3243 ± 1048 U/L; ALT: 127 ± 70 U/L) and CS (AST: 3150 ± 1546 U/L; ALT: 185 ± 97 U/L). There was no significant difference between SNMP and CS. Bile production was significantly higher in the NMP group (219 ± 43 mL; P < 0.01) compared to both SNMP (49 ± 84 mL) and CS (12 ± 16 mL) with no significant difference between the latter two groups. Histologically, the NMP livers showed preserved cellular architecture compared to the SNMP and CS groups. NMP was able to recover DCD livers showing superior hepatocellular integrity, biliary function, and microcirculation compared to SNMP and CS. SNMP showed some significant benefit over CS, yet has not shown any advantage over NMP.

Intestinal ischemic preconditioning ameliorates hepatic ischemia/reperfusion injury in rats: role of heme oxygenase 1 in the second window of protection

Preconditioning by brief ischemia protects not only the concerned organ but also other distant organs against subsequent lethal damage; this is called remote ischemic preconditioning (RIPC). This study was designed to investigate the impact of intestinal RIPC on hepatic ischemia/reperfusion injury (IRI) with a special interest in heme oxygenase 1 (HO-1) induction in the second window of protection (SWOP). Male Wistar rats were randomly assigned to 1 of 2 groups: an RIPC group or a sham group. Before hepatic IRI, either intestinal RIPC, consisting of 2 cycles of 4-minute superior mesenteric artery clamping separated by 11 minutes of declamping (RIPC group), or a sham procedure (sham group) was performed. After 48 hours of recovery, the rats were exposed to 30 minutes of total hepatic IRI. Transaminase releases and proinflammatory cytokines were determined at several time points after reperfusion. Histopathological analysis and animal survival were also investigated. Intestinal RIPC significantly lowered transaminase release (alanine aminotransferase at 2 hours: 873.3 ± 176.4 IU/L for the RIPC group versus 3378.7 ± 871.1 IU/L for the sham group, P < .001) as well as proinflammatory cytokine production (tumor necrosis factor α at 2 hours: 930 ± 42 versus 387 ± 17 pg/μL, P < .001). The morphological integrity of the liver and the ileum was maintained significantly better with intestinal RIPC; this reached statistical significance not only in Suzuki's liver injury score (3.5 ± 0.2 versus 0.7 ± 0.5, P = .007) but also in Park's score for intestinal damage (4.0 ± 0.4 versus 2.0 ± 0.2, P = .007). Animal survival was also markedly improved (83.1% versus 15.4%, P < .001). As a mechanism underlying this protection, HO-1 was substantially induced in liver tissue, especially in hepatocytes, with remarkable up-regulation of bradykinin in the portal blood, whereas HO-1 protein induction in enterocytes was not significant. In conclusion, intestinal RIPC remarkably attenuates hepatic IRI in the SWOP, presumably by HO-1 induction in hepatocytes.

Improved hypothermic short-term storage of isolated mouse islets by adding serum to preservation solutions

Preserving isolated islets at low temperature appears attractive because it can keep islet quantity comparable to freshly isolated islets. In this study, we evaluated the effect of serum as an additive to preservation solutions on islet quality after short-term hypothermic storage. Isolated mouse islets were preserved at 4°C in University of Wisconsin solution (UW) alone, UW with serum, M-Kyoto solution (MK) alone or MK with serum. We then assessed islet quantity, morphology, viability and function in vitro as well as in vivo. Islet quantity after storage in all four solutions was well maintained for up to 120 h. However, islets functioned for different duration; glucose-stimulated insulin release assay revealed that the duration was 72 h when islets were stored in UW with serum and MK with serum, but only 24 h in UW alone, and the islet function disappeared immediately in MK alone. Viability assay confirmed that more than 70% islet cells survived for up to 48 h when islets are preserved in UW with serum and MK with serum, but the viability decreased rapidly in UW alone and MK alone. In in vivo bioassays using 48-h preserved isogeneic islets, all recipient mice restored normal blood glucose concentrations by transplants preserved in UW with serum or MK with serum, whereas 33.3% recipients and no recipient restored diabetes by transplants preserved in UW alone and in MK alone respectively. Adding serum to both UW and MK improves their capability to store isolated islets by maintaining islet functional viability.

Hepatic blood flow plays an important role in ischemia-reperfusion injury

Severe ischemia/reperfusion (IR) injury is associated with poor hepatic microperfusion. The aim of this study was to investigate the role of hepatic artery flow (HAF) and portal vein flow (PVF) in IR injury. From January 2004 to June 2008, 566 patients underwent orthotopic liver transplantation (OLT). The data were retrospectively reviewed via the transplant database. Patients with hepatic artery (HA) or portal vein (PV) thrombosis and retransplant patients were excluded. Intraoperative PVF and HAF values and graft weights were measured routinely, and the central venous pressure, mean arterial pressure, cardiac output, and cardiac index were recorded with hepatic blood flow measurements. Complete data were available for 312 primary OLT recipients (215 males and 97 females; mean age = 54 ± 10 years). The patients' follow-up ranged from 215 to 1746 days (705 ± 408 days). IR injury was defined by the aspartate aminotransferase (AST) level on postoperative day (POD) 2, and the patients were divided into 3 groups: (1) mild IR injury [AST < 500 U/L; n = 160 (51%)], (2) moderate IR injury [AST = 500-1000 U/L; n = 85 (27%)], and (3) severe IR injury [AST > 1000 U/L; n = 67 (21%)]. The demographics and pre-OLT variables (the Model for End-Stage Liver Disease score (MELD), platelet counts, PV thrombosis, transjugular intrahepatic portosystemic shunts, and shunts on computed tomography scans) were similar in all groups. The graft survival rate was 99% in group 1, 95.2% in group 2 (P = 0.02), and 92.3% in group 3 (P = 0.016). The patient survival rates were similar in the 3 groups. The cold ischemia time (CIT) was significantly higher in group 3 versus group 1 (P < 0.007). In the statistical analysis, low HAF, PVF, total liver blood flow (TLBF), and augmented HAF values were associated with a greater likelihood of elevated AST levels on POD 2. The strongest univariate predictors of AST were reduced augmented HAF (mL/minute/100 g) values (P < 0.001) and reduced TLBF (mL/minute/100 g) values (P < 0.001). In a covariate analysis with adjustments for CIT and donor variables, the blood flow parameters remained important predictors of graft function. In conclusion, this report demonstrates for the first time that reduced hepatic blood flow is a significant finding in patients with severe hepatic IR injury.

S-nitroso-N-acetylcysteine: a promising drug for early ischemia/reperfusion injury in rat liver

BACKGROUND/AIMS

Ischemia-reperfusion (I/R) injury is among the major causes of poor graft function early after liver transplantation that adversely influences patient survival. A variety of mediators have been implicated in the pathogenesis of I/R vascular injury, including nitric oxide (NO). Because of the beneficial effects of NO during preconditioning and reperfusion, strategies to prevent or ameliorate I/R injury through the stimulation of hepatic NO production are an area of significant clinical interest. We evaluated the role of S-nitroso-N-acetylcysteine (SNAC) as an NO donor in the prevention of liver I/R injury in an animal model.

METHODS

Adult male Wistar rats were randomly assigned to 3 experimental groups containing 5 animals each: the University of Wisconsin (UW) solution group; SNAC solution group; and SNAC-containing UW solution (SNAC+UW) group. Aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) were determined in samples of the cold storage solution at 2, 4, and 6 hours of preservation. After 6 hours of cold storage, We applied a 15-minute reperfusion period. Thereafter, the reperfusion was interrupted with blood samples obtained to measure AST, ALT, LDH, and thiobarbituric acid reactive substances (TBARS). Hepatic fragments were processed for histologic analysis, and to determine of TBARS, catalase, and glutathione levels.

RESULTS

During cold preservation, AST and LDH were significantly lower among the SNAC than the UW group or the SNAC+UW group (P = .004 and P = .03, respectively). ALT was comparable among the groups (P = .3). After reperfusion, serum levels of AST, ALT, and LDH, as well as of hepatic TBARS and catalase showed no differences among the groups. Glutathione concentration was lower in the SNAC and SNAC+UW group (P < .001) compared with the UW group. We did not observe histologic signs of preservation injury.

CONCLUSION

The SNAC solution showed a greater protective effect to preserve rat livers during cold storage, but it was comparable with UW.

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.

Inhibition of endogenous hedgehog signaling protects against acute liver injury after ischemia reperfusion

PURPOSE

Although Hedgehog (Hh) signaling is required for endodermal commitment and hepatogenesis, the possibility that it regulates liver injury after ischemia reperfusion (I/R) has not been considered. Therefore, we determined the expression pattern of Hh signaling and its role in liver injury following I/R using Hh antagonist cyclopamine (CYA).

METHODS

Sprague-Dawley rats were randomly divided into three groups. Sham group underwent a sham operation with no liver I/R. Vehicle or CYA preconditioned I/R groups underwent liver ischemia for 90 min followed by reperfusion for 1 h. Liver tissue and blood were analyzed for gene expression, histological and biochemical evaluation.

RESULTS

Hedgehog ligands were upregulated after reperfusion injury. Serum levels of aspartate transaminase and alanine transaminase, inflammatory cytokines, neutrophil infiltration, and tissue damage were significantly less in CYA-pretreated rats compared with vehicle-pretreated rats. CYA also decreased the phosphorylated form of JNK and ERK.

CONCLUSIONS

This study provides evidence that endogenous Hh signaling is an early mediator of liver injury and inflammation after I/R. CYA abrogates normothermic I/R injury in rats by inhibiting the MAPK pathway and decreasing the acute inflammatory response. This novel strategy of preconditioning livers with Hh antagonist may have effective therapeutic potential in preventing acute liver injury.

Heme oxygenase-1 protects donor livers from ischemia/reperfusion injury: the role of Kupffer cells

AIM

To examine whether heme oxygenase (HO)-1 overexpression would exert direct or indirect effects on Kupffer cells activation, which lead to aggravation of reperfusion injury.

METHODS

Donors 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 before transplantation. Kupffer cells were isolated and cultured for 6 h after liver reperfusion.

RESULTS

Postoperatively, serum transaminases were significantly lower and associated with less liver injury when donors were pretreated with CoPP, as compared with the ZnPP group. Production of the cytokines tumor necrosis factor-alpha and interleukin-6 generated by Kupffer cells decreased in the CoPP group. The CD14 expression levels (RT-PCR/Western blots) of Kupffer cells from CoPP-pretreated liver grafts reduced.

CONCLUSION

The study suggests that the potential utility of HO-1 overexpression in preventing ischemia/reperfusion injury results from inhibition of Kupffer cells activation.

Liver graft exposure to carbon monoxide during cold storage protects sinusoidal endothelial cells and ameliorates reperfusion injury in rats

Hepatic ischemia/reperfusion (I/R) injury significantly influences short-term and long-term outcomes after liver transplantation (LTx). The critical step initiating the injury is known to include sinusoidal endothelial cell (SEC) alteration during the cold preservation period. As carbon monoxide (CO) has potent cytoprotective functions on vascular endothelial cells, this study examined if CO treatment of excised liver grafts during cold storage could protect SECs and ameliorate hepatic I/R injury. Rat liver grafts were preserved in University of Wisconsin (UW) solution containing 5% CO (CO-UW solution) for 18 to 24 hours and were transplanted into syngeneic Lewis rats. After 18 hours of cold preservation, SEC damage was evident with propidium iodide (PI) nuclear staining on SECs, and the frequency of PI(+) SECs was significantly lower in grafts stored in CO-UW solution versus those stored in control UW solution. SEC protection with CO was associated with decreased intercellular cell adhesion molecule translocation and less matrix metalloproteinase release during cold preservation. After LTx with 18 hours of cold preservation, serum alanine aminotransferase levels and hepatic necrosis were significantly less in the CO-UW group than in the control UW group. With 24 hours of cold storage, 35% (7/20) survived with control UW solution, whereas the survival with CO-UW solution improved to 80% (8/10). These beneficial effects of CO-UW solution were associated with a significant reduction of neutrophil extravasation, down-regulation of hepatic messenger RNA for tumor necrosis factor alpha and intercellular cell adhesion molecule 1, and less hepatic extracellular signal-regulated kinase activation. Liver grafts from Kupffer cell-depleted donors or pseudogerm-free donors showed less SEC death during cold preservation, and CO-UW solution further reduced SEC death. In conclusion, CO delivery to excised liver grafts during cold preservation efficiently ameliorates SEC damage and hepatic I/R injury.

Nitric oxide: A useful indicator in acute allograft rejection after liver transplantation

The aim of this study was to monitor serum nitric oxide levels at various times, intraoperatively and following liver transplantation in humans. Nitric oxide production was assessed by cadmium reduction method in 15 patients undergoing liver transplantation. We observed strong correlation between nitric oxide production and allograft rejection. Sustained rise in nitric oxide level after transplantation might provide an indication of acute allograft rejection. Therefore measurement of nitric oxide, a stable end product appears to be an excellent marker that can help in the development of strategies intended to improve graft viability and patient's survival.

Ischemic preconditioning in hepatic ischemia and reperfusion

PURPOSE OF REVIEW

Ischemic preconditioning that consists of a short period of hepatic inflow occlusion followed by reperfusion has the potential to increase tolerance to a subsequent prolonged ischemic insult. This review outlines current insight into ischemic preconditioning for hepatic ischemia and reperfusion injury in experimental and clinical settings.

RECENT FINDINGS

Experimental evidence suggests that interleukin-6 signaling and increased phosphorylation of STAT3 (signal transducer and activator of transcription-3) are involved in the protective effects of ischemic preconditioning. The benefit of ischemic preconditioning is restricted, however, by old liver and prolonged ischemic time (>60 min). To overcome this, ascorbic acid or glucose administration combined with ischemic preconditioning potentially can maintain the integrity of hepatic mitochondrial function through signal transduction pathways. The influence of ischemic preconditioning on hepatic regeneration varies with partial hepatectomy or small-for-size liver graft models, and remains controversial. Clinically, ischemic preconditioning in deceased donors protects against ischemia and reperfusion injury, as demonstrated by lowered liver enzyme levels, reduced incidence of primary nonfunction, and increased hepatic hypoxia-induced factor-1alpha concentrations.

SUMMARY

Enhanced understanding of the mechanisms of organ tolerance induced by ischemic preconditioning would strengthen the significance of this potential therapeutic strategy in liver transplantation.

Sinusoidal endothelial cell repopulation following ischemia/reperfusion injury in rat liver transplantation

We evaluated the kinetics by which rat liver sinusoidal endothelial cells (LSECs) are repopulated in the reperfused transplanted liver after 18 hours of cold ischemic storage. We found that the majority of LSECs in livers cold-stored for 18 hours in University of Wisconsin solution are seriously compromised and often are retracted before transplantation. Sinusoids rapidly re-endothelialize within 48 hours of transplantation, and repopulation is coincident with up-regulation of hepatocyte vascular endothelial growth factor expression and vascular endothelial growth factor receptor-2 expression on large vessel endothelial cells and repopulating LSECs. Although re-endothelialization occurs rapidly, we show here, using several high-resolution imaging techniques and 2 different rat liver transplantation models, that engraftment of bone marrow-derived cells into functioning LSECs is routinely between 1% and 5%.

CONCLUSION

Bone marrow plays a measurable but surprisingly limited role in the rapid repopulation and functional engraftment of bone marrow-derived LSECs after cold ischemia and warm reperfusion.

New preservation strategies for preventing liver grafts against cold ischemia reperfusion injury

BACKGROUND

In spite of improvements in University of Wisconsin (UW) preservation solution, the injury from grafts during cold storage is an unresolved problem in liver transplantation. The aim of the present study was to evaluate the beneficial effect on ischemia-reperfusion injury associated with liver transplantation of the inversion of K(+) and Na(+) concentrations and the replacement of hydroxyethyl starch (HES) by polyethylene glycol (PEG) in UW preservation solution.

METHODS

Using an orthotopic liver transplantation model, the effects on rat liver preservation of a modified preservation solution (UW-PEG) were evaluated, based on the inversion of K(+) and Na(+) concentration and the replacement of HES by PEG 35 kDa (0.03 mmol/L) in UW preservation solution.

RESULTS

The use of UW-PEG preservation solution ameliorated the biochemical and histological parameters of hepatic damage. Thus, at 24 h after transplantation, transaminase levels were reduced significantly when livers were preserved during 8 h in UW-PEG preservation solution compared with the original UW solution. In addition, histological findings revealed fewer and smaller areas of hepatocyte necrosis. The benefits of UW-PEG solution cannot be explained by modifications in oxidative stress or neutrophil accumulation associated with liver transplantation. However, the results of hepatic and portal blood flow indicated that the benefits of this modified preservation solution, UW-PEG were associated with improvements in the microcirculatory disorders after reperfusion.

CONCLUSIONS

The UW-PEG solution, while retaining all the advantages of UW solution, improved hepatic ischemia-reperfusion injury associated with liver transplantation.

Gene transduction of an active mutant of akt exerts cytoprotection and reduces graft injury after liver transplantation

Akt is expected to be an effective target for the treatment of ischemia-reperfusion injury (I/R) due to its anti-apoptotic properties and its ability to activate the endothelial nitric oxide synthase (eNOS) enzyme. Therefore, this study was aimed to determine the efficacy of an active mutant of Akt (myr-Akt) to decrease I/R injury in a model of orthotopic liver transplantation in pigs. In addition, we analyzed the contribution of nitric oxide in the Akt-mediated effects by using an eNOS mutant (S1179DeNOS) that mimics the phosphorylation promoted by Akt in the eNOS sequence. Donors were treated with adenoviruses codifying for myr-Akt, S1179DeNOS or beta-galactosidase 24 h before liver harvesting. Then, liver grafts were orthotopically transplanted into their corresponding recipients. Levels of transaminases and lactate dehydrogenase (LDH) increased in all recipients after 24 h of transplant. However, transaminases and LDH levels were significantly lower in the myr-Akt group compared with vehicle. The percentage of apoptotic cells and the amount of activated-caspase 3 protein were also markedly reduced in myr-Akt-treated grafts after 4 days of liver transplant compared with vehicle and S1179DeNOS groups. In conclusion, myr-Akt gene therapy effectively exerts cytoprotection against hepatic I/R injury regardless of the Akt-dependent eNOS activation.

Donor graft adenoviral iNOS gene transfer ameliorates rat liver transplant preservation injury and improves survival

The exact role of inducible NOS (iNOS) in liver ischemia/reperfusion (I/R) injury is controversial. This study was designed to investigate whether donor liver pretreatment with adenovirus encoding iNOS (AdiNOS) ameliorates I/R injury associated with liver transplantation. Orthotopic syngeneic LEW rat liver transplantation (OLT) was performed after 18 or 24 hours' preservation in cold UW. AdiNOS or control gene vector (AdLacZ) was delivered to the liver by donor intravenous pretreatment 4 days before graft harvesting. Uninfected grafts also served as control. Recipients were sacrificed 1 to 48 hours posttransplantation. An abundant hepatic iNOS protein expression and marked serum NO elevation was observed in the AdiNOS-treated group, without affecting endothelial nitric oxide synthase (eNOS) expression, before harvesting and after OLT. AdiNOS pretreatment markedly improved liver function assessed by serum aspartate aminotransferase/alanine aminotransferase levels and reduced liver necrosis formation. AdiNOS treatment also was associated with reduced ICAM-1 mRNA expression and neutrophil accumulation in the liver graft after OLT compared with untransfected or AdLacZ-treated group. Furthermore, AdiNOS delivery significantly improved transplant survival, compared with AdLacZ or saline controls. AdiNOS pretreatment did not attenuate I/R-induced apoptotic cell death in the liver graft. Administration of a selective inhibitor for iNOS abrogated the protection afforded by AdiNOS pretreatment. In conclusion, donor pretreatment with AdiNOS led to improved liver graft injury and posttransplantation survival. Downregulation of ICAM-1 mRNA and neutrophil infiltration may be associated with the mechanisms by which AdiNOS pretreatment confer the protection against transplant-associated hepatic I/R injury.

Initial hepatic microcirculation correlates with early graft function in human orthotopic liver transplantation

Microcirculatory disturbances are an initial causative determinant in hepatic ischemia/reperfusion injury. The aim of this study was to assess sinusoidal perfusion during human liver transplantation using orthogonal polarization spectral imaging and to evaluate the significance of intraoperative microcirculation for early postoperative graft function. Hepatic microcirculation was measured in 27 recipients undergoing full-size liver transplantation and compared to a group of 32 healthy living-related liver donors. The microvascular parameters were correlated with postoperative aspartate aminotransferase and bilirubin levels. Hepatic perfusion following liver transplantation was found to be significantly decreased when compared with the control group. Volumetric blood flow within the individual sinusoids increased due to sinusoidal dilatation and enhanced flow velocity. Regression analysis of postoperative aspartate aminotransferase and bilirubin with microvascular parameters revealed significant correlations. The extent of volumetric blood flow increased within the first 30 minutes after reperfusion and showed a significant correlation with postoperative aspartate aminotransferase release and bilirubin elimination. In conclusion, postischemic hepatic microvascular perfusion was analyzed in vivo, demonstrating significant microvascular impairment during liver transplantation. Sinusoidal hyperperfusion appears to confer protection against postischemic liver injury, as given by the correlation with aspartate aminotransferase and bilirubin levels. Thus, these findings may have therapeutic importance with respect to mechanisms mediating postischemic reactive hyperemia.

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

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

Role of free radicals in failure of fatty liver grafts caused by ethanol

Alcohol is associated with accidental deaths and suicides leading to organ donation, and hepatic steatosis is an important risk factor for initial poor function and failure of human liver grafts. Mechanisms of fatty graft failure are not fully understood, but increased oxidative stress may be a major factor. To characterize the role of free radical stress and the efficacy of antioxidant treatments in fatty liver graft injury, donors for orthotopic rat liver transplantation were treated chronically (3 or more weeks) and acutely (single dose) with ethanol. After transplantation, necrosis and alanine aminotransferase release were threefold to fourfold higher in recipients of fatty grafts from donors treated with ethanol either acutely or chronically compared with findings for recipients of grafts from untreated donors. Moreover, graft survival decreased from nearly 100% to less than 20%. Free radical adducts, as measured by electron spin resonance spectroscopy, were detected in the blood and bile of rats receiving fatty grafts caused by ethanol. Markers of lipid peroxidation also increased after transplantation. Destruction of Kupffer cells with gadolinium chloride decreased free radical production and improved graft survival. Leukocyte adhesion increased beginning early after implantation, and adherent white blood cells obtained from transplanted fatty livers produced the same free radical species as were detected in blood. Therefore, Kupffer cells and adherent white blood cells are important sources of free radicals. Free radicals not only damage fatty grafts directly but also lead to enhanced inflammation and disturbed microcirculation. Delivery of superoxide dismutase-1 and superoxide dismutase-2 genes, free radical-scavenging polyphenols, and antioxidant-containing Carolina Rinse solution reduced injury and improved survival of fatty grafts caused by ethanol. Taken together, these findings indicate that free radicals increase in fatty grafts after transplantation and play an important role in injury of fatty grafts obtained from ethanol-exposed donors. Treatment of fatty donor livers with antioxidants and free radical scavengers may thus be an effective clinical therapy to prevent failure of fatty grafts.

New Insights into the Cellular and Molecular Mechanisms of Cold Storage Injury

Solid organ grafts, but also other biologic materials requiring storage for a few hours to a few days, are usually stored under hypothermic conditions. To decrease graft injury during cold storage, organ preservation solutions were developed many years ago. However, since then, modern biochemical and cell biologic methods have allowed further insights into the molecular and cellular mechanisms of cold storage injury, including further insights into alterations of the cellular ion homeostasis, the occurrence of a mitochondrial permeability transition, and the occurrence of free–radical-mediated hypothermic injury and cold-induced apoptosis. These new aspects of cold storage injury, which are not covered by preservation solutions in current clinical use and offer the potential for improvement of organ and tissue preservation, are presented here.

Effect of cold-ischemia time on nuclear factor-κB activation and inflammatory response in graft after orthotopic liver transplantation in rats

AIM: To study the mechanism and effect of nuclear factor-κB (NF-κB) activation and inflammatory response on the extended cold-preserved graft injury after orthotopic liver transplantation (OLT).

METHODS: OLT was performed in rats with varying time of cold ischemia grafts (6, 18 and 24 h in University Wisconsin solution at 4 °C). We determined the time of NF-κB activation and expression of tumor necrosis factor-α(TNF-α), cytokine-inducible neutrophil chemoattractant (CINC), and intercellular adhesion molecule-1 (ICAM-1) within 6 h after reperfusion. Serum alarming aminotransferase (ALT), neutrophil sequestration, circulating neutrophil CD11b and L- selectin expression were also evaluated.

RESULTS: The accumulation of neutrophils in the graft was significantly increased in the 18 h and 24 h cold-ischemia groups within 0.5 h after reperfusion, compared with the 6 h group. But the strongly activated neutrophils was slightly increased at 2 h after reperfusion and remained at high levels 4 h after reperfusion, which was synchronized with the common situation of recipients after transplantation. Prolonged cold-preservation did not affect neutrophil accumulation and activation. NF-κB activation preceded the expression of TNF-α, CINC, and ICAM-1 in the liver, which was significantly increased with prolonged cold preservation. In prolonged cold preserved grafts, prominently elevated NF-κB activation occurred at 0.5 h and 1 h, compared with that at 2 h after reperfusion, which was consistent with greatly increased intrahepatic TNF-α response.

CONCLUSION: NF-κB activation is correlated with the expression of TNF-α, CINC, and ICAM-1 in vivo in OLT rats. Extended cold preservation of grafts might up-regulate TNF-α, CINC, and ICAM-1 expression in the grafts, most probably through elevated NF-κB activation, and might contribute to neutrophil infiltration in the grafts after reperfusion. Elevated NF-κB activity is harmful to inflammatory response in the grafts, and inhibited NF-κB activity might protect against early graft injury after liver transplantation.

Significance of and contributing factors for a high resistive index on Doppler sonography of the hepatic artery immediately after surgery: prognostic implications for liver transplant recipients

OBJECTIVE

The goal of our study was to investigate the contributing factors, clinical repercussions, and implications for prognosis of high-resistance flow at the hepatic artery detected on Doppler sonography during the period immediately after orthotopic liver transplantation.

MATERIALS AND METHODS

We retrospectively studied the transplanted livers of 90 patients who had been examined on Doppler sonography within the first 3 days after grafting. Seventeen variables from organ donors, transplant recipients, graft characteristics, and surgical procedures were investigated. Early clinical evolution was also analyzed. Follow-up was performed for 5 years.

RESULTS

Forty-one (45.6%) of the 90 patients showed a high resistive index at the hepatic artery during the first 72 hr after transplantation. Two factors showed a statistically significant effect on the occurrence of a high resistive index at the hepatic artery immediately after transplantation: an older liver donor (p = 0.008) and extended preservation time (p = 0.005). No relation with early graft function was detected. The incidence of bile duct complications, retransplantation, or death was not higher at follow-up in patients with high-resistance flow than in those with normal flow.

CONCLUSION

High-resistance flow at the hepatic artery detected on Doppler sonography during the period immediately after transplantation is a frequent finding and is related to older donor age and prolonged period of ischemia. This finding has neither significant clinical repercussions nor prognosis implications for early and long-term follow-up.

Clinical implications of hepatic preservation injury after adult liver transplantation

Several advances in organ preservation have allowed for improved results after liver transplantation; however, little information is available regarding the clinical impact of preservation injury on the postoperative course. The medical records of 889 liver transplants were retrospectively reviewed. Preservation injury was classified according to postoperative aspartate aminotransferase values as minor (<1000 U/L), moderate (1000-5000 U/L), or severe (>5000 U/L). The following criteria were analyzed and compared according to the extent of preservation injury: patient and graft survival, retransplantation rate, duration of hospitalization and postoperative ventilation, as well as incidence of rejection, infection, and hemodialysis. The majority of patients received a liver with minor preservation injury (75.9%), whereas 22.7% and 1.3% of grafts showed moderate or severe injury. Graft survival was significantly lower in patients with severe preservation injury, when compared to minor or moderate injury. The relative risk for initial nonfunction was 39.36-fold increased (95% confidence interval (ci): 10.3-150.2), as it was increased for duration of postoperative ventilation (6.92-fold; 95%ci: 2.1-22.3) and hemodialysis (6.13-fold; 95%ci: 1.9-19.3). Since the incidence of retransplantation was significantly increased (50%), patient survival remained comparable between all groups. Severe preservation injury had a tremendous impact on the postoperative clinical course, requiring the maximum medical effort to achieve adequate patient survival.

Bilirubin rinse: A simple protectant against the rat liver graft injury mimicking heme oxygenase-1 preconditioning

Heme oxygenase (HO)-1 preconditioning through genetic or pharmacologic interventions was shown experimentally to improve posttransplant outcome of liver grafts. However, its clinical application requires careful consideration because of the complexity and economic costs of the procedures. This study aimed to examine if graft preconditioning with HO-1 could be substituted by a simple treatment with heme-degrading products such as bilirubin. Rats were pretreated with or without hemin, an HO-1 inducer for preconditioning. Their livers were harvested as grafts in University of Wisconsin (UW) solution for 16 hours at 4 degrees C and followed by reperfusion ex vivo or by transplantation in vivo. The control grafts were also treated with a rinse buffer containing varied concentrations of unconjugated bilirubin with different time intervals. The HO-1-preconditioned grafts ex vivo exhibited a marked improvement of bile output and cell injury that was cancelled by blocking HO with zinc protoporphyrin-IX. The aggravation of the graft viability by the inhibitor was repressed by supplementation of bilirubin but not by that of carbon monoxide. Furthermore, a short-term rinse treatment with micromolar levels of bilirubin attenuated biliary dysfunction and cell injury of the grafts both ex vivo and in vivo even without HO-1 preconditioning. The protective effects of HO-1 preconditioning or bilirubin rinse appeared to involve its inhibitory effects on lipid peroxidation in hepatocytes. In conclusion, these results suggest that bilirubin rinse serves as a simple strategy to ameliorate hyperacute oxidative stress and hepatobiliary dysfunction of the transplanted grafts, mimicking effects of HO-1-mediated preconditioning.

Enhanced energy metabolism during cold hypoxic organ preservation: studies on rat liver after pyruvate supplementation

Previous studies have indicated that pyruvate is able to reduce ischaemia/reperfusion (I/R) injury in a variety of tissues, but a full understanding of the effects is lacking. In this current preliminary study, magnetic resonance spectroscopy (MRS) was used to investigate the biochemical effects of differing concentrations of pyruvate (3 and 15mM) on liver metabolism during the cold hypoxic preservation period itself, in order to gain insight into possible mechanisms. Hepatic lactate, alanine, and succinate levels were increased in livers preserved with 15mM pyruvate added to the University of Wisconsin (UW) solution and were generally elevated (but to a lesser degree) in livers flushed with 3mM pyruvate, compared to those cold stored in UW alone. Further, from enzymatic assays of adenine nucleotides, 15mM levels of pyruvate were found to maintain higher ATP levels during short periods (up to 4h) of cold hypoxic storage than in UW stored livers, whilst energy charge ratios (after 4 and 24h) were also higher (P<0.01 in each case). This may arise from enhanced glycolysis secondary to an improved redox status in the pyruvate-treated livers, as evident by the increase in the levels of lactate.

Expression of CD80 on Kupffer cells is enhanced in cadaveric liver transplants

In experimental animals inhibition of T cell co-stimulation immediately after organ transplantation effectively prevents rejection. We investigated whether the expression of co-stimulatory molecules is enhanced in cadaveric liver transplants, whether their expression is influenced by the transplantation procedure, and whether variation in expression between liver transplants is related to the occurrence of acute rejection. Expression of CD80, CD86 and the macrophage marker CD68 were determined by immunohistochemistry in biopsies from 40 clinical liver transplants obtained at different time-points during the transplantation procedure, and in normal liver tissue obtained from 10 human livers. Expression of CD80 and CD86 on Kupffer cells was graded by comparison with CD68-staining. In a subgroup CD80 and CD86 mRNA was quantified by real-time detection polymerase chain reaction. CD86 was expressed in all liver transplants and normal livers on the majority of Kupffer cells. CD80 was absent or sporadically expressed in normal liver tissue, but in 18 of 40 liver transplants at least one-quarter of Kupffer cells expressed CD80. CD80- and CD86-mRNA and protein expression in liver transplants did not change during the warm ischaemic and reperfusion phases of the transplantation procedure. CD80-expression on Kupffer cells varied strongly between individual donor livers; this variation was, however, not significantly related to the occurrence of acute rejection after transplantation. In conclusion, in nearly half of cold-preserved cadaveric liver transplants an increased proportion of Kupffer cells express CD80 at the time of transplantation in comparison with normal liver tissue. The expression was not further induced by warm ischaemia and reperfusion. However, the observed variation in CD80-expression between liver transplants is not a accurate predictive measure for acute rejection.

Liver transplantation for primary biliary cirrhosis: a long-term pathologic study

Although recurrent primary biliary cirrhosis (PBC) after liver transplantation (LT) has been reported, the full spectrum of changes and progression to fibrosis and cirrhosis is not yet established. We performed a detailed retrospective clinicopathologic analysis of 43 patients who underwent LT for PBC. Eight patients (18.6%) had definite recurrent PBC with florid duct lesions, 5 patients (11.6%) had recurrence with features of autoimmune liver disease, not otherwise specified (AILD-NOS), 7 patients (16.3%) had plasmacytosis only, 4 patients (9.3%) had chronic rejection, 18 patients (41.9%) have no recurrence at present, and 1 patient (2.3%) had acquired hepatitis C. Although definite diagnoses of PBC and AILD-NOS recurrences (n = 13) were made 1 month to 14 years (median, 4 years) post-LT, all patients had plasmacytosis in their earlier biopsy specimens. Also, these patients showed similar pre-LT and post-LT clinical features, with progressive fibrosis in 4 of 8 and 2 of 5 patients, respectively. Four of 13 patients with definite recurrence and 14 of 18 patients with no recurrence were administered azathioprine (AZA) as part of their post-LT therapy (P =.01). Six of 13 and 16 of 18 patients currently are alive, with median follow-ups of 11 and 5 years, respectively. No significant differences were seen with donor-recipient group A, group B, group O blood type, sex, or HLA mismatches; native liver histological characteristics; or tacrolimus-based therapy. In conclusion, recurrent autoimmune liver disease was seen in 30% of patients after LT for PBC and had features of PBC and/or AILD-NOS. Progression seen in 46% of patients was associated with late graft failure. Patients with no recurrent disease had shorter follow-up periods and more frequent immunosuppression, including AZA; some may still develop recurrence with longer follow-up.

Nitric oxide in liver transplantation: pathobiology and clinical implications

The gaseous molecule nitric oxide is involved in a variety of liver transplant-relevant processes, including ischemia-reperfusion injury, acute cellular rejection, and circulatory changes characteristic of advanced liver disease. This review article focuses on new advances relating to the role of nitric oxide in these syndromes with an emphasis on pathobiology and potential clinical implications.

Blockade of the L-arginine/NO synthase pathway worsens hepatic apoptosis and liver transplant preservation injury

Organ graft preservation injury is a major problem complicating liver transplantation. The L-arginine/nitric oxide pathway has protective effects in several models of liver injury. The purpose of this study was to evaluate the role of the L-arginine/NO synthase (NOS) pathway on liver preservation injury and to characterize endogenous inducible NOS (iNOS) expression. Orthotopic liver transplantation was performed with 18-hour University of Wisconsin preservation solution in syngeneic rats. Recipient rats were either untreated or treated with L-arginine, D-arginine, nonspecific NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME), or iNOS selective inhibitor L-N(6)-(1-imino-ethyl)lysine (L-NIL) after revascularization. As early as 1 hour following reperfusion, circulating arginine levels decreased 10-fold and ornithine levels increased 4-fold. A corresponding increase in arginase I protein was detected in serum. To address the profound arginine deficiency, we supplemented recipients with arginine after transplantation. L-arginine (but not D-arginine) supplementation significantly reduced preservation injury 12 hours after reperfusion, suggesting that the protective effect of L-arginine was mediated through the generation of NO. iNOS protein expression peaked in the liver 6 to 12 hours following reperfusion. Blockade of the L-arginine/NO pathway with L-NAME significantly increased necrotic and apoptotic cell death in the transplanted graft. Addition of the iNOS selective inhibitor L-NIL mildly increased liver transaminase levels and also increased apoptosis in the liver graft. In conclusion, transplant recipients are profoundly arginine deficient postreperfusion due to arginase release. L-Arginine supplementation and NO synthesis decrease necrotic and apoptotic cell death and ameliorate liver transplant preservation injury.

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.

Carolina rinse solution minimizes kidney injury and improves graft function and survival after prolonged cold ischemia

BACKGROUND

Kidney damage caused by cold ischemia-reperfusion injury promotes adverse outcomes after renal transplantation. The purpose of this study was to determine whether Carolina rinse solution (CRS) used at the end of cold ischemic storage decreases kidney injury and improves graft function and survival.

METHODS

Inbred male Lewis rats were used as donors and recipients. Left kidneys were removed from donor rats, infused with cold University of Wisconsin solution, and stored for 24, 30, or 48 hr at 0-1 degrees C. Just before implantation, kidneys were flushed with either Ringer's solution or CRS at 35-37 degrees C or were not treated. Kidneys were then transplanted into recipient rats with removal of both native kidneys.

RESULTS

Survival and renal function were analyzed over a 14-day postoperative period. Among rats receiving kidneys after 24-hr cold storage, creatinine clearance was 75% greater in rats transplanted with kidneys flushed with CRS compared with Ringer's solution or nontreatment. In animals receiving kidneys after 30-hr cold storage, recipient survival after CRS was significantly higher than with Ringer's solution or without flushing (80% vs. 25% and 17%, respectively). However, CRS failed to prevent renal graft failure after 48 hr of cold storage (14% survival with CRS vs. 0% with Ringer's solution). In separate ex vivo studies, nonviable cell nuclei were labeled by trypan blue after cold preservation and brief warm reperfusion. CRS decreased podocyte and peritubular endothelial cell killing associated with cold ischemia-reperfusion injury.

CONCLUSION

Flushing renal explants with warm CRS before implantation diminishes cold ischemia-reperfusion injury and improves the function and survival of transplanted kidneys.

Metabolic changes in the liver graft monitored continuously with microdialysis during liver transplantation in a pig model

Microdialysis provides the opportunity to continuously monitor metabolic changes in tissue. The aim of the study is to monitor metabolic changes in the liver graft over time during transplantation in a pig model. Fourteen littermate female pigs with a body weight of 30 to 34 kg were used for seven orthotopic liver transplantations. Intrahepatic implantation of a microdialysis catheter into the liver graft was performed in the donor. Microdialysis samples were collected at 20-minute intervals during the donor operation, cold preservation, and for 7 hours after reperfusion in the recipient. Glucose, lactate, pyruvate, and glycerol concentrations were measured. After cold perfusion, glucose, lactate, and glycerol levels increased, whereas pyruvate levels decreased rapidly. During cold storage, glucose and glycerol levels increased, whereas lactate levels remained stable and pyruvate levels were undetectable. During implantation of the liver graft, glucose, lactate, and glycerol levels showed an accelerated increase. After portal reperfusion, glucose, lactate, and glycerol levels continued to increase for another 40 to 60 minutes, after which they decreased and finally settled at normal levels. At this time, pyruvate levels increased, with a peak within 2 hours after reperfusion, and then decreased to normal levels. Calculated lactate-pyruvate ratio increased after cold perfusion and remained stable during cold storage. During rewarming, it showed an accelerated increase, but after reperfusion, it decreased rapidly. Rewarming and reperfusion are most harmful to the liver, reflected by an accelerated increase in glucose and glycerol levels and lactate-pyruvate ratio. High intrahepatic glucose levels during ischemia appear to be a liver-specific event, which may represent glycogen degradation in injured hepatocytes.

Cold-induced apoptosis of rat liver cells in University of Wisconsin solution: the central role of chelatable iron

Although University of Wisconsin (UW) solution aims at the prevention of cold-induced cell injury, it failed to protect against cold-induced apoptosis of hepatocytes and liver endothelial cells: when incubated in UW solution at 4 degrees C for 24 hours and subsequently rewarmed at 37 degrees C, 72% +/- 8% of rat hepatocytes and 81% +/- 5% of liver endothelial cells lost viability. In both cell types, the observed cell damage occurred under an apoptotic morphology; it appeared to be mediated by a rapid increase in the cellular chelatable iron pool by a factor > or =2 (as determined in hepatocytes) and subsequent formation of reactive oxygen species (ROS). Consequently, this cell injury was decreased by iron chelators to 6 to 25% (hepatocytes) and 4% +/- 2% (liver endothelial cells). Deferoxamine nearly completely inhibited the occurrence of apoptotic morphology in both cell types. In liver endothelial cells, cold-induced apoptosis occurring during rewarming after 24 hours of cold incubation in UW solution was far more pronounced than in cell culture medium (loss of viability: 81% +/- 5% vs. 28% +/- 13%), but viability could even be maintained for 2 weeks of cold incubation by use of deferoxamine. In conclusion, this pathological mechanism might be an explanation for the strong endothelial cell injury known to occur after cold preservation. With regard to the extent of this iron-mediated injury, addition of a suitable iron chelator to UW solution might markedly improve the outcome of liver preservation.

Mammalian cell injury induced by hypothermia- the emerging role for reactive oxygen species

Hypothermia is a well-known strategem to protect biological material against injurious or degradative processes and is widely used in experimental and especially in clinical applications. However, hypothermia has also proved to be strongly injurious to a variety of cell types. Hypothermic injury to mammalian cells has long been attributed predominantly to disturbances of cellular ion homeostasis, especially of sodium homeostasis. For many years, reactive oxygen species have hardly been considered in the pathogenesis of hypothermic injury to mammalian cells. In recent years, however, increasing evidence for a role of reactive oxygen species in hypothermic injury to these cells has accumulated. Today there seems to be little doubt that reactive oxygen species decisively contribute to hypothermic injury in diverse mammalian cells. In some cell types, such as liver and kidney cells, they even appear to play the central role in hypothermic injury, outruling by far a contribution of the cellular ion homeostasis. In these cells, the cellular chelatable, redox-active iron pool appears to be decisively involved in the pathogenesis of hypothermic injury and of cold-induced apoptosis that occurs upon rewarming of the cells after a (sublethal) period of cold incubation.

Microcirculatory failure after rat liver transplantation is related to Kupffer cell-derived oxidant stress but not involved in early graft dysfunction

BACKGROUND

Microcirculatory failure, activation of Kupffer cells (KC), and the formation of reactive oxygen species (ROS) are considered pivotal mechanisms of reperfusion injury after orthotopic liver transplantation. However, the sequence of these events and their impact on early graft function remain controversial. We therefore investigated whether KC induce microcirculatory disturbances through ROS release and whether microcirculatory failure contributes to early graft function after liver transplantation.

METHODS

Donor livers of Lewis rats were pretreated either with saline or with gadolinium chloride (GdCl3), an inhibitor of KC function (n=8 each). Syngeneic OLT was performed after 24 hr of hypothermic preservation in University of Wisconsin solution.

RESULTS

Intravital microscopy revealed significantly higher sinusoidal perfusion rates in GdCl3-treated allografts (92+/-1.1% vs. 75.7+/-0.8%; P<0.001) compared with untreated controls; permanent leukocyte sticking in sinusoids (23.5+/-2.1 vs. 62.6+/-3.3 cells/lobule, P<0.001) and in postsinusoidal venules (153.1+/-10.4 vs. 446.6+/-46.4 cells/mm(2), P<0.001) were markedly attenuated in GdCl3-treated allografts. Improvement of microcirculatory parameters in GdCl3-treated livers was correlated with a significant reduction of plasma glutathione disulfide formation by KC-derived ROS (0.96+/-0.1 microM vs. 1.79+/-0.5 microM; P<0.01). Despite these beneficial effects, GdCl3-pretreatment failed to improve postischemic alanine aminotransferase release and bile flow.

CONCLUSIONS

Microcirculatory failure after liver transplantation is related to KC-derived oxidant stress but not involved in early graft dysfunction.

Hemodynamic response to continuous infusion of dobutamine in Alagille's syndrome

BACKGROUND

Alagille's syndrome is a rare condition that is characterized by paucity of interlobular bile ducts and peripheral pulmonary artery stenosis. Liver transplantation in the setting of peripheral pulmonary stenosis and right ventricular hypertension seems to be associated with a higher mortality, which raises the concern that these patients are unable to increase their cardiac output in the immediate posttransplantation period to meet the demands of reperfusion and early graft dysfunction and cope with further increases in pulmonary vascular resistance.

METHOD

Cardiac catheterization was performed in 15 children with Alagille's syndrome and peripheral pulmonary artery stenosis to measure the cardiac output response to dobutamine infusion. The cardiac output was measured before and during each increment of infusion of dobutamine at 10 microg/kg/min and 20 microg/kg/min by using a thermodilution catheter placed in the pulmonary artery.

RESULTS

There was a significant change in the baseline cardiac index (P<0.001) with an infusion of 20 microg/kg/min of dobutamine with an increase from 4.4(1.0) L/min/m2 to 6.4(1.5) L/min/m2. There was, however, a wide variation between individuals in the increase in cardiac index, ranging from 7.3-95%. There was no correlation between the baseline systolic right ventricular/aortic pressure ratios and the increase in cardiac index (r=0.1086).

CONCLUSION

The increase in cardiac index, in response to dobutamine in patients with Alagille's syndrome, is independent of the more conventional measurement of the right ventricular pressure. This method of producing a hemodynamic response is closer to the response that results after liver transplantation, and thus, it may be a better way of predicting the outcome of liver transplantation in these patients.

Protective effects of ischemic preconditioning on the cold-preserved liver are tyrosine kinase dependent

BACKGROUND

Little data exist regarding the use of ischemic preconditioning before sustained hepatic cold storage. We hypothesized that ischemic preconditioning protects hepatic grafts via a tyrosine kinase-dependent pathway.

METHODS

Six porcine livers underwent routine harvest (control). Five other livers underwent 15 min of in situ ischemia followed by 15 min of reflow before harvest (ischemic preconditioning). Another five livers were pretreated with a tyrosine kinase inhibitor (genistein) before preconditioning. Upon reperfusion and after 2 hours of cold storage, graft function, graft circulatory impairment, and markers of cellular damage were analyzed. Tissue cytoplasmic extracts were analyzed for tyrosine phosphorylation with Western blot. Significance was determined with t tests.

RESULTS

Ischemic-preconditioned grafts demonstrated enhanced bile production, augmented responses to a bile acid challenge, and elevated O2 consumption (P<0.05) compared to controls. Also, preconditioned grafts demonstrated improved hepatic tissue blood flow and decreased hepatic vascular resistance (P<0.005) compared to controls. Endothelial cell preservation (factor VIII immunostain) was improved in preconditioned graft biopsies compared to controls. With genistein pretreatment, all observed improvements returned to control levels. Analysis of cytoplasmic extracts demonstrated an increase in tyrosine phosphorylation before cold ischemia in preconditioned grafts only, but not in control or genistein-pretreated grafts.

CONCLUSIONS

The data indicate that ischemic preconditioning protects the liver from sustained cold ischemia and that tyrosine kinases are involved in preconditioning responses.

Activation of interleukin-6/STAT3 and liver regeneration following transplantation

BACKGROUND

Every liver that is procured, stored, and transplanted experiences injury from cold ischemia and reperfusion. Most recover quickly, but some grafts sustain enough injury to result in prolonged organ dysfunction or require retransplantation. The molecular mechanisms involved in early graft function and recovery following cold ischemia and reperfusion (I/R) after liver transplantation have not been well defined. Interleukin (IL)-6 is a critical factor in the mitogenic response within the liver, and is important for cell cycle progression and protection from injury. Activation of the latent transcription factor, STAT3, is dependent on IL-6 release. The role of the IL-6/STAT3 pathway and hepatocellular regeneration in graft recovery and cell cycle progression following cold ischemia and reperfusion was studied in a rat liver transplant orthotopic (OLT) model. Methods. Rat OLT was performed in a syngeneic model. The presence, time course, and magnitude of expression of IL-6, STAT3 activation, and upregulation of target immediate early genes were determined in liver grafts with minimal (<1 h) and prolonged (12 h) cold preservation times followed by transplantation. Progression of the cell cycle and replication was confirmed by BrdU uptake.

RESULTS

Prolonged cold ischemia resulted in increased IL-6 expression and STAT3 activation. This correlated with upregulation of junB, c-fos, c-myc, and c-jun, immediate early genes associated with hepatic regeneration. Extensive DNA replication was present in livers with 12-h ischemia, demonstrating successful completion of the cell cycle.

CONCLUSIONS

The participation of the IL-6/STAT3 pathway leading to cell cycle progression and regeneration is an important component in the recovery of organs immediately following cold preservation and transplantation.

Hemodynamic and metabolic variables predict porcine ex vivo liver function

Early recognition of hepatic function during initial graft reperfusion is important in beginning hepatic support perfusions as well as in liver transplantation. We hypothesized that both hemodynamic and metabolic perfusion variables obtained immediately after reperfusion predict eventual function during liver support or transplantation. Specific hemodynamic variables, i.e., portal vein pressure and hepatic vascular resistance, as well as metabolic variables, i.e., O(2) consumption and P(CO(2)) gradients, were compared with indices of hepatic function and damage, i.e., aqueous bile production, bile lipid outputs, lactate dehydrogenase levels, and histopathology, during an ex vivo support perfusion. O(2) consumption during early reperfusion correlated directly with unstimulated bile flows (P < 0.02) and histopathology scores (P < 0.05). Hepatic venous P(CO(2)) gradients correlated inversely with unstimulated bile flows (P < 0.05). Hemodynamic variables, i.e., portal vein pressure and hepatic vascular resistance, were inversely related with taurocholate-stimulated bile flows (P < 0.05). Hemodynamic and metabolic variables of early reperfusion are useful parameters in predicting eventual effectiveness of the harvested liver for ex vivo hepatic support perfusions.

Endogenous nitric oxide and exogenous nitric oxide supplementation in hepatic ischemia-reperfusion injury in the rat

BACKGROUND

Although nitric oxide (NO) is thought to be beneficial in hepatic ischemia-reperfusion (I/R), the mechanisms for this effect are not well established.

METHODS

To investigate the effects of endogenous NO and exogenous NO supplementation on hepatic I/R injury and their pathogenic mechanisms, serum ALT and hyaluronic acid (endothelial cell damage), and hepatic malondialdehyde and H2O2 (oxidative stress), myeloperoxidase activity (leukocyte accumulation), and endothelin (vasoconstrictor peptide opposite to NO) were determined at different reperfusion periods in untreated rats and rats receiving L-NAME, L-NAME+L-arginine, and spermine NONOate (exogenous NO donor).

RESULTS

After reperfusion every parameter increased in untreated animals. Endogenous NO synthesis inhibition by L-NAME increased hepatocyte and endothelial damage as compared to untreated rats, which was reverted and even improved by the addition of L-arginine. Spermine NONOate also improved this damage. However, different mechanisms account for the beneficial effect of endogenous and exogenous NO. Oxidative stress decreased by both L-NAME and L-NAME+L-arginine, but remained unmodified by spermine NONOate. Myeloperoxidase increased by L-NAME and this effect was reverted by the addition of L-arginine, whereas no change was observed with spermine NONOate. Endothelin levels were not modified by L-NAME and L-NAME+L-arginine, but decreased with spermine NONOate.

CONCLUSIONS

These results suggest that, although both endogenous and exogenous NO exert a protective role in experimental hepatic I/R injury, the mechanisms of the beneficial effect of the two sources of NO are different.