Calpain inhibition prevents sinusoidal endothelial cell apoptosis in the cold ischemic rat liver

Protective Effect of Calpain Inhibition During Cold Ischemia on Ischemia-reperfusion Injury After Lung Transplantation

BACKGROUND

Necroptosis, one of the types of regulated necrosis, causes ischemia-reperfusion (IR) lung injury. N-acetyl-leucyl-leucyl-norleucinal (ALLN), a calpain inhibitor, is known to attenuate necroptosis and apoptosis, and the purpose of this study was to evaluate the protective effect of ALLN during cold ischemia against IR injury in a rat lung transplant model.

METHODS

Male Lewis rats (250-350 g) were divided into 3 groups: sham group (n = 4), nontransplantation; control group (n = 8), transplantation with IR lung injury; and ALLN group (n = 8), transplantation with IR lung injury/ALLN. Rats in the sham group underwent a simple thoracotomy, and the remaining 2 groups of rats underwent an orthotopic left lung transplant. Cold ischemic time was 15 h. After 2 h of reperfusion, physiological function, inflammatory cytokine expression, pathway activation, and the degrees of necroptosis and apoptosis were evaluated.

RESULTS

Lung gas exchange (PaO 2 /FiO 2 ) was significantly better, and pulmonary edema was significantly improved in the ALLN group compared with the control group ( P = 0.0009, P = 0.0014). Plasma expression of interleukin-1β was significantly lower in the ALLN group than in the control group ( P = 0.0313). The proportion of necroptotic and apoptotic cells was significantly lower in the ALLN group than in the control group ( P = 0.0009), whereas the proportion of apoptotic cells remained unchanged ( P = 0.372); therefore, the calpain inhibitor was thought to suppress necroptosis.

CONCLUSIONS

The administration of ALLN during cold ischemia appears to improve IR lung injury in a lung transplant animal model via the inhibition of necroptosis.

New insights into host-pathogen interactions during Entamoeba histolytica liver infection

Amoebiasis is the third worldwide disease due to a parasite. The causative agent of this disease, the unicellular eukaryote Entamoeba histolytica, causes dysentery and liver abscesses associated with inflammation and human cell death. During liver invasion, before entering the parenchyma, E. histolytica trophozoites are in contact with liver sinusoidal endothelial cells (LSEC). We present data characterizing human LSEC responses to interaction with E. histolytica and identifying amoebic factors involved in the process of cell death in this cell culture model potentially relevant for early steps of hepatic amoebiasis. E. histolytica interferes with host cell adhesion signalling and leads to diminished adhesion and target cell death. Contact with parasites induces disruption of actin stress fibers and focal adhesion complexes. We conclude that interference with LSEC signalling may result from amoeba-triggered changes in the mechanical forces in the vicinity of cells in contact with parasites, sensed and transmitted by focal adhesion complexes. The study highlights for the first time the potential role in the onset of hepatic amoebiasis of the loss of liver endothelium integrity by disturbance of focal adhesion function and adhesion signalling. Among the amoebic factors required for changed LSEC adherence properties we identified the Gal/GalNAC lectin, cysteine proteases and KERP1.

The current state of knowledge of hepatic ischemia-reperfusion injury based on its study in experimental models

The present review focuses on the numerous experimental models used to study the complexity of hepatic ischemia/reperfusion (I/R) injury. Although experimental models of hepatic I/R injury represent a compromise between the clinical reality and experimental simplification, the clinical transfer of experimental results is problematic because of anatomical and physiological differences and the inevitable simplification of experimental work. In this review, the strengths and limitations of the various models of hepatic I/R are discussed. Several strategies to protect the liver from I/R injury have been developed in animal models and, some of these, might find their way into clinical practice. We also attempt to highlight the fact that the mechanisms responsible for hepatic I/R injury depend on the experimental model used, and therefore the therapeutic strategies also differ according to the model used. Thus, the choice of model must therefore be adapted to the clinical question being answered.

Once initiated, how does toxic tissue injury expand?

Once initiated, how tissue injury expands after high toxicant doses, even after their complete elimination, is not understood. Free-radical generation was initially proposed to mediate progression of injury. However, mechanisms proposed thus far have remained unsubstantiated. Necrotic injury is characterized by loss of osmoregulation, cell swelling, blebbing, and cell rupture. This exposes cytosolic enzymes, including proteases, phospholipases, and lysosomal Ca(2+)-dependent enzymes, to high extracellular calcium (Ca(2+)). Activated hydrolytic enzymes, termed 'death proteins,' hydrolyze their substrates in the plasma membrane of neighboring cells, commencing self-perpetuated injury progression. Likewise, ischemia-reperfusion injury exposes the hydrolytic enzymes to high Ca(2+), fuelling the progression of tissue injury. This mechanism is independent of the offending toxicant that initiates the injury. I present here a case for therapeutic intervention with inhibitors directed against death proteins as a means to avert organ failure and death well after the poisoning event.

Biological modulation of liver ischemia-reperfusion injury

PURPOSE OF REVIEW

This review gives a broad overview of the key factors of ischemic injury to the liver and presents the current modifications of preservation solutions and the few strategies of biological modulation in clinical use today.

RECENT FINDINGS

Protective effects in human-liver transplantation were shown by methylprednisolone treatment in decreased donors, and by inhalation of a nontoxic dose of nitric oxide in recipients. In addition, recent results showed rescue of pig livers, donated after cardiac death by application of a cocktail of substances addressing several previously identified mechanisms of ischemia-reperfusion injury.

SUMMARY

The future of a pharmacological approach attenuating or preventing ischemia-reperfusion injury lies in a combination of drugs acting simultaneously on several steps of the injury cascades. Applying these substances during flush, before, and during implantation appears as an attractive strategy to protect extended criteria liver grafts.

Pharmacological strategies against cold ischemia reperfusion injury

IMPORTANCE OF THE FIELD

Good organ preservation is a determinant of graft outcome after revascularization. The necessity of increasing the quality of organ preservation, as well as of extending cold storage time, has made it necessary to consider the use of pharmacological additives.

AREAS COVERED IN THIS REVIEW

The complex physiopathology of cold-ischemia-reperfusion (I/R) injury--and in particular cell death, mitochondrial injury and endoplasmic reticulum stress--are reviewed. Basic principles of the formulation of the different preservation solutions are discussed.

WHAT THE READER WILL GAIN

Current strategies and new trends in static organ preservation using additives such as trimetazidine, polyethylene glycols, melatonin, trophic factors and endothelin antagonists in solution are presented and discussed. The benefits and mechanisms responsible for enhancing organ protection against I/R injury are also discussed. Graft preservation was substantially improved when additives were added to the preservation solutions.

TAKE HOME MESSAGE

Enrichment of preservation solutions by additives is clinically useful only for short periods. For longer periods of cold ischemia, the use of such additives becomes insufficient because graft function deteriorates as a result of ischemia. In such conditions, the preservation strategy should be changed by the use of machine perfusion in normothermic conditions.

Preconditioning, organ preservation, and postconditioning to prevent ischemia-reperfusion injury to the liver

Ischemia and reperfusion lead to injury of the liver. Ischemia-reperfusion injury is inevitable in liver transplantation and trauma and, to a great extent, in liver resection. This article gives an overview of the mechanisms involved in this type of injury and summarizes protective and treatment strategies in clinical use today. Intervention is possible at different time points: during harvesting, during the period of preservation, and during implantation. Liver preconditioning and postconditioning can be applied in the transplant setting and for liver resection. Graft optimization is merely possible in the period between the harvest and the implantation. Given that there are 3 stages in which a surgeon can intervene against ischemia-reperfusion injury, we have structured the review as follows. The first section reviews the approaches using surgical interventions, such as ischemic preconditioning, as well as pharmacological applications. In the second section, static organ preservation and machine perfusion are addressed. Finally, the possibility of treating the recipient or postconditioning is discussed.

Ischemic preconditioning and intermittent clamping confer protection against ischemic injury in the cirrhotic mouse liver

Surgery on cirrhotic livers is fraught with complications, and many surgeons refrain from operating on patients with cirrhosis. Surgical procedures include temporal occlusion of blood flow resulting in ischemia. The mechanisms of protective strategies to prevent ischemic injury in patients with cirrhosis are not fully understood. The aim of this study was to evaluate how the cirrhotic liver tolerates an ischemic insult, whether mechanisms other than those observed in the normal liver are active, and whether intermittent clamping and preconditioning, which are known as safe surgical strategies in normal and steatotic livers, confer protection to the cirrhotic liver. We applied partial hepatic inflow occlusion to cirrhotic mice fed carbon tetrachloride according to different vascular occlusion protocols: intermittent clamping with 15 or 30 minute cycles of ischemia or ischemic preconditioning prior to 60 or 75 minutes of ischemia. Continuous ischemia (60 or 75 minutes) served as controls. The results showed that the cirrhotic liver was significantly more susceptible to 60 minutes of ischemia than the normal liver. Apoptosis was higher in the normal liver, whereas necrosis was a predominant feature in the cirrhotic liver. Both protocols of intermittent vascular occlusion and ischemic preconditioning dramatically prevented injury compared to continuous occlusion for 60 minutes. This protection was associated with reduced necrosis and apoptosis, and particularly reduced activation of the apoptotic pathway through mitochondria. In conclusion, this study extends the protective effects of ischemic preconditioning and intermittent clamping to the cirrhotic liver, highlighting a diminished apoptotic pathway with dramatic improvement in the development of necrosis.

Reperfusion injury in liver transplantation

Reperfusion injury occurring in the transplanted liver is a complex lesion and has been the focus of considerable research over the past decade. This section will review recent major developments in understanding the mechanisms involved and their application to clinical transplantation.

A caspase inhibitor, IDN-6556, ameliorates early hepatic injury in an ex vivo rat model of warm and cold ischemia

This study examined the efficacy of the caspase inhibitor, IDN-6556, in a rat model of liver ischemia-reperfusion injury. Livers from male Sprague-Dawley rats were reperfused for 120 minutes after 24 hours of 4 degrees C cold storage in University of Wisconsin solution. Portal blood flow measurements estimated sinusoidal resistance, and bile production, alanine aminotransferase activities, and Suzuki scores were evaluated as parameters of hepatocyte/liver injury. Treated livers were exposed to 25 or 50 microM of IDN-6556 in University of Wisconsin storage solution and/or the perfusate. All treatment regimens with IDN-6556 significantly improved portal blood flow measured at 120 minutes, and significant improvements were seen as early as 30 minutes when inhibitor was also present in the perfusate (P < 0.01). All treatment groups with IDN-6556 significantly increased bile production by 3-4-fold compared with controls (P < 0.01), and reductions in alanine aminotransferase activities were seen within 90 minutes of reperfusion (P < 0.05). These data were confirmed by improved Suzuki scores (less sinusoidal congestion, necrosis, and vacuolization) in all treated groups. Livers from the IDN-6556-treated groups had markedly reduced caspase activities and TUNEL (terminal deoxynucleotidyl transferase dUTP nick-end labeling)-positive cells, suggesting reductions in apoptosis. IDN-6556 present in cold storage media ameliorated liver injury due to cold ischemia and reperfusion injury and may be a rational therapeutic approach to reduce the risk of liver ischemia in the clinical setting.

Modulation of apoptosis as a target for liver disease

Apoptosis mediated via extrinsic or intrinsic pathways is essential for maintaining cellular homeostasis in the liver. The extrinsic pathway is triggered from the cell surface by engagement of death receptors as CD95, TRAIL (TNF-related apoptosis inducing ligand) and TNF (tumour necrosis factor) or TGF-beta (transforming growth factor beta) receptors. The intrinsic pathway is initiated from the mitochondria and can be influenced by Bcl-2 family members. Both pathways are intertwined and play a physiological role in the liver. Dysregulation of apoptosis pathways contributes to diseases as hepatocellular carcinoma, viral hepatitis, autoimmune hepatitis, ischaemia-reperfusion injury, iron or copper deposition disorders, toxic liver damage and acute liver failure. The apoptosis defects are often central pathogenetic events; hence molecular mechanisms of apoptosis give not only insight into disease mechanisms but also provide potential corresponding therapeutic candidates in liver disease. The focus of this review is the identification of apoptotic signalling components in the liver as therapeutic targets.

Ischemic preconditioning modulates the expression of several genes, leading to the overproduction of IL-1Ra, iNOS, and Bcl-2 in a human model of liver ischemia-reperfusion

Ischemia triggers an inflammatory response that precipitates cell death during reperfusion. Several studies have shown that tissues are protected by ischemic preconditioning (IP) consisting of 10 min of ischemia followed by 10 min of reperfusion just before ischemia. The molecular basis of this protective effect is poorly understood. We used cDNA arrays (20K) to compare global gene expression in liver biopsies from living human liver donors who underwent IP (n=7) or not (n=7) just before liver devascularization. Microarray data were analyzed using pairedt test with a type I error rate fixed at alpha = 2.5 10(6) (Bonferroni correction). We found that 60 genes were differentially expressed (36 over- and 24 underexpressed in preconditioning group). After IP, the most significantly overexpressed gene was IL-1Ra. This was confirmed by immunoblotting. Differentially expressed were genes involved in apoptosis (NOD2, ephrin-A1, and calpain) and in the carbohydrate metabolism. A significant increase in the amount of the anti-apoptotic protein Bcl-2 in preconditioned livers but no change in the cleavage of procaspase-3, -8, and -9 was observed. We also observed an increase in the amount in the inducible nitric oxide synthase. Therefore, the benefits of IP may be associated with the overproduction of IL-1Ra, Bcl-2, and NO countering the proinflammatory and proapoptotic effects generated during ischemia-reperfusion.

Liver Transplantation in Italy: Analysis of Risk Factors Associated with Graft Outcome

Objective

To analyze the graft outcome after liver transplantation in Italy in the years 1995 to 2000.

Methods

We performed a longitudinal study with follow-up at 3 months, 1 year, 3 years, and 5 years on 1987 liver grafts. The effect of several variables on graft survival was also analyzed.

Results

Several variables affect graft survival: Donor and recipient older age, gender mismatching, prolonged cold ischemia time, acute hepatic necrosis, and retransplantation are reported to significantly affect liver graft survival. Donors older than 60 years show a relative risk of 1.59 (95% CI, 1.23–2.05) compared with donors with an age between 19 and 60 years; recipients older than 50 years show a relative risk of 1.29 (95% CI, 1.04–1.60) compared with recipients aged 19 to 50 years. A cold ischemia time of 12 hours or longer doubled the risk of failure (relative risk = 2.01, 95% CI, 1.36–2.96) compared with a cold ischemia time of less than 6 hours.

Conclusions

The results show that the overall quality of liver transplantation in Italy is satisfying and comparable to the outcome reported by international registries. Follow-up studies on large numbers of liver transplants are useful to define predictors of outcome, and subsequently modify the criteria for organ allocation.

Apoptosis and necrosis in the liver: a tale of two deaths?

Death of hepatocytes and other hepatic cell types is a characteristic feature of liver diseases as diverse as cholestasis, viral hepatitis, ischemia/reperfusion, liver preservation for transplantation and drug/toxicant-induced injury. Cell death typically follows one of two patterns: oncotic necrosis and apoptosis. Necrosis is typically the consequence of acute metabolic perturbation with ATP depletion as occurs in ischemia/reperfusion and acute drug-induced hepatotoxicity. Apoptosis, in contrast, represents the execution of an ATP-dependent death program often initiated by death ligand/death receptor interactions, such as Fas ligand with Fas, which leads to a caspase activation cascade. A common event leading to both apoptosis and necrosis is mitochondrial permeabilization and dysfunction, although the mechanistic basis of mitochondrial injury may vary in different settings. Prevention of these modes of cell death is an important target of therapy, but controversies still exist regarding which mode of cell death predominates in various forms of liver disease and injury. Resolution of these controversies may come with the recognition that apoptosis and necrosis frequently represent alternate outcomes of the same cellular pathways to cell death, especially for cell death mediated by mitochondrial permeabilization. An understanding of processes leading to liver cell death will be important for development of effective interventions to prevent hepatocellular death leading to liver failure and to promote cancer and stellate cell death in malignancy and fibrotic disease.

Calpain is activated in degenerating photoreceptors in the rd1 mouse

The retinal degeneration (rd)1 mouse displays an inherited retinal degeneration and therefore allows studies of the molecular mechanisms behind the blinding disease retinitis pigmentosa. Activation of the calcium-dependent protease calpain has been suggested to play an important role in cell death in various tissues, but little is known about the expression and activity of calpain during inherited retinal degeneration. Using microarray techniques, transcript levels of cyclic AMP response element-binding protein (CREB)-1, calpastatin and of various calpain genes were analysed in the rd1 mouse compared with its wild-type control. Expression of distinct calpain isoforms and calpastatin was investigated using immunofluorescence and immunoblotting. Gene transcription and protein expression levels were compared with calpain activity using an enzymatic assay that allowed monitoring of calpain activity at the cellular level. We found that CREB-1 and calpastatin expression was reduced in rd1 retinas, whereas calpain activity was substantially increased in rd1 photoreceptors. Calpain activity peaked at postnatal day 13, together with rd1 photoreceptor cell death. Calpain-specific inhibitors decreased calpain activity in situ. These results indicate that activation of calpains correlates with rd1 photoreceptor cell death, which raises the possibility of using calpain inhibitors to prevent or delay photoreceptor degeneration.

Effect of adenosine A2A receptor agonist (CGS) on ischemia/reperfusion injury in isolated rat liver

Ischemia/reperfusion injury during liver transplantation is a major cause of primary nonfunctioning graft for which there is no effective treatment other than retransplantation. Adenosine prevents ischemia-reperfusion-induced hepatic injury via its A2A receptors. The aim of this study was to investigate the role of A2A receptor agonist on apoptotic ischemia/reperfusion-induced hepatic injury in rats. Isolated rat livers within University of Wisconsin solution were randomly divided into four groups: (1) continuous perfusion of Krebs-Henseleit solution through the portal vein for 165 minutes (control); (2) 30-minute perfusion followed by 120 minutes of ischemia and 15 minutes of reperfusion; (3) like group 2, but with the administration of CGS 21680, an A2A receptor agonist, 30 microg/100 ml, for 1 minute before ischemia; (4) like group 3, but with administration of SCH 58261, an A2A receptor antagonist. Serum liver enzyme levels were measured by biochemical analysis, and intrahepatic caspase-3 activity was measured by fluorometric assay; apoptotic cells were identified by morphological criteria, the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) fluorometric assay, and immunohistochemistry for caspase-3. Results showed that at 1 minute of reperfusion, there was a statistically significant reduction in liver enzyme levels in the animals pretreated with CGS (p < 0.05). On fluorometric assay, caspase-3 activity was significantly decreased in group 3 compared to group 2 (p < 0.0002). The reduction in postischemic apoptotic hepatic injury in the CGS-treated group was confirmed morphologically, by the significantly fewer apoptotic hepatocyte cells detected (p < 0.05); immunohistochemically, by the significantly weaker activation of caspase-3 compared to the ischemic group (p < 0.05); and by the TUNEL assay (p < 0.05). In conclusion, the administration of A2A receptor agonist before induction of ischemia can attenuate postischemic apoptotic hepatic injury and thereby minimize liver injury. Apoptotic hepatic injury seems to be mediated through caspase-3 activity.

[Calpains and cardiac diseases]

Calpains are a large family of cytosolic cysteine proteases composed of at least fourteen distinct isoforms. The family can be divided into two groups on the basis of distribution: ubiquitous and tissue-specific. Our current knowledge about calpains properties apply mainly to the ubiquitous isozymes, micro- and milli-calpain (classic calpains). These forms are activated after autolysis. Translocation and subsequent interactions with phospholipids of these enzymes increase their activity. Calpains are able to cleave a subset of substrates, as enzymes, structural and signalling proteins. Cardiac pathologies, such as heart failure, atrial fibrillation or clinical states particularly ischemia reperfusion, are associated with an increase of cytosolic calcium and in this regards, calpain activation has been evoked as one of the mediators leading to myocardial damage. Calpain activities have been shown to be increased in hearts experimentally subjected to ischemia reperfusion or during hypertrophy, but also in atrial tissue harvested from patients suffering from atrial fibrillations. These activities have been related to an increase of the proteolysis of different myocardial components, particularly, troponins, which are major regulators of the contraction of cardiomyocytes. Moreover, recent works have demonstrated that calpains are involved in the development of myocardial cell death by necrosis or apoptosis.

Caspase inhibition prevents the increase in caspase-3, -2, -8 and -9 activity and apoptosis in the cold ischemic mouse kidney

Prolonged cold ischemic time is a risk factor for the development of delayed graft function. The adverse impact of cold ischemia may be associated with tubular cell death in the kidney. Caspase-3 is a major mediator of apoptotic cell death. We hypothesized that caspase inhibition would reduce apoptosis and other features of cold ischemia. Kidneys of C57BL/6 mice were perfused with cold University of Wisconsin solution containing a pancaspase inhibitor or vehicle via the left ventricle. The contralateral right kidney was used as a control. The left kidney was stored for 48 h at 4 degrees C to produce cold ischemia. Caspase-3 activity was massively (100-fold) increased in cold ischemic kidneys compared with controls. On immunoblot analysis, the processed form of caspase-3 was increased in cold ischemic kidneys compared with controls. The increase in caspase-3 was associated with significantly more renal tubular apoptosis and brush-border injury. In addition, caspase-2, -8 and -9 activities were increased in cold ischemic kidneys. The pancaspase inhibitor prevented the formation of the processed form of caspase-3 and the increase in caspase activity, and reduced apoptosis and brush-border injury. Caspase inhibition may prove useful in kidney preservation.

Protective effect of MDL28170 against thioacetamide-induced acute liver failure in mice

Liver injury is known to often progress even after the hepatotoxicant is dissipated. The hydrolytic enzyme calpain, which is released from dying hepatocytes, destroys the surrounding cells and results in progression of injury. Therefore, control of calpain activation may be a suitable therapeutic intervention in cases of fulminant hepatic failure. This study evaluated the effects of a potent cell-permeable calpain inhibitor, MDL28170, and its mechanisms of action on thioacetamide (TAA)-induced hepatotoxicity in mice. We found that MDL28170 significantly decreased mortality and change in serum transaminase after TAA administration. The necroinflammatory response in the liver was also suppressed. Furthermore, a significant suppression of hepatocyte apoptosis could be found by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling assay. The upregulation of inducible nitric oxide synthase (iNOS) and tumor necrosis factor-alpha (TNF-alpha), both of which are known to mediate the propagation of inflammation, was abolished. MDL2810 also effectively blocked hepatic stellate cell activation, which is assumed to be the early step in liver fibrosis. These results demonstrated that MDL28170 attenuated TAA-induced acute liver failure by inhibiting hepatocyte apoptosis, abrogating iNOS and TNF-alpha mRNA upregulation and blocking hepatic stellate cell activation.

Sinusoidal endothelial cell and hepatocyte death following cold ischemia-warm reperfusion of the rat liver

Cold ischemia-warm reperfusion (CI-WR) injury of the liver is characterized by marked alterations of sinusoidal endothelial cells (SECs), whereas hepatocytes appear to be relatively unscathed. However, the time course and mechanism of cell death remain controversial: early versus late phenomenon, necrosis versus apoptosis? We describe the occurrence and nature of cell death after different periods of CI with University of Wisconsin (UW) solution and after different periods of WR in the isolated perfused rat liver model. After 24- and 42-hour CI (viable and nonviable livers, respectively), similar patterns of liver cell death were seen: SEC necrosis appeared early after WR (10 minutes) and remained stable for up to 120 minutes. After 30 minutes of WR, apoptosis increased progressively with WR length. Based on morphological criteria, apoptotic cells were mainly hepatocytes within liver plates or extruded in the sinusoidal lumen. In addition, only after 42-hour CI were large clusters of necrotic hepatocytes found in areas of congested sinusoids. In these same livers, the hepatic microcirculation, evaluated by means of the multiple-indicator dilution technique, revealed extracellular matrix disappearance with no-flow areas. In conclusion, different time courses and mechanisms of cell death occur in rat livers after CI-WR, with early SEC necrosis followed by delayed hepatocyte apoptosis. These processes do not appear to be of major importance in the mechanism of graft failure because they are similar under both nonlethal and lethal conditions; this is not the case for the loss of the extracellular matrix found only under lethal conditions and associated with hepatocyte necrosis.

Calpain released from dying hepatocytes mediates progression of acute liver injury induced by model hepatotoxicants

Liver injury is known to progress even after the hepatotoxicant is long gone and the mechanisms of progressive injury are not understood. We tested the hypothesis that hydrolytic enzymes such as calpain, released from dying hepatocytes, destroy the surrounding cells causing progression of injury. Calpain inhibitor, N-CBZ-VAL-PHE-methyl ester (CBZ), administered 1 h after a toxic but nonlethal dose of CCl(4) (2 ml/kg, ip) to male Sprague Dawley rats substantially mitigated the progression of liver injury (6 to 48 h) and also led to 75% protection against CCl(4)-induced lethality following a lethal dose (LD75) of CCl(4) (3 ml/kg). Calpain leakage in plasma and in the perinecrotic areas increased until 48 h and decreased from 72 h onward paralleling progression and regression of liver injury, respectively, after CCl(4) treatment. Mitigation of progressive injury was accompanied by substantially low calpain in perinecrotic areas and in plasma after CBZ treatment. Normal hepatocytes incubated with the plasma collected from CCl(4)-treated rats (collected at 12 h when most of the CCl(4) is eliminated) resulted in extensive cell death prevented by CBZ. Cell-impermeable calpain inhibitor E64 also protected against progression of CCl(4)-induced liver injury, thereby confirming the role of released calpain in progression of liver injury. Following CCl(4) treatment, calpain-specific breakdown of alpha-fodrin increased, while it was negligible in rats receiving CBZ after CCl(4). Hepatocyte cell death in incubations containing calpain was completely prevented by CBZ. Eighty percent of Swiss Webster mice receiving a lethal dose (LD80) of acetaminophen (600 mg/kg, ip) survived if CBZ was administered 1 h after acetaminophen, suggesting that calpain-mediated progression of liver injury is neither species nor chemical specific. These findings suggest the role of calpain in progression of liver injury.

Leukocyte infiltration and inflammatory antigen expression in cadaveric and living-donor livers before transplant

BACKGROUND

There is evidence to indicate that organs obtained from cadaveric donors may be injured as a result of inflammatory events occurring at around the time of brain death. The aim of this study was to investigate whether there are differences in the expression of proinflammatory molecules between cadaveric and living-donor livers before transplant and to determine whether there is any association with donor factors and posttransplant graft function.

METHODS

A comparison of biopsies obtained before implantation from cadaveric (n=22) and living-related donor (LRD) (n=10) livers was performed. Cryostat tissue sections were stained with antibodies to leukocyte subpopulations, adhesion molecules, and human leukocyte antigen class II antigens.

RESULTS

Significantly higher levels of CD3+ lymphocytes (1.5%+/-0.8% vs. 0.5%+/-0.3%; P=0.00004), CD68+ monocytes and macrophages (4.0%+/-1.2% vs. 2.7%+/-0.6%; P=0.0003), and Fas-ligand staining (4.2%+/-2.6% vs. 1.5%+/-1.1%; P=0.0003) were detected in cadaveric livers compared with LRD livers before transplantation. Furthermore, higher levels of intercellular adhesion molecule-1 expression were detected in cadaveric donor livers and found to be associated with longer periods of ventilation (P=0.01), infection in the donor (P=0.013), and administration of dopamine (P=0.03). Although there were no differences in neutrophil infiltration between cadaveric and LRD livers, significantly higher levels were found in cadaveric donors with infection (P=0.01).

CONCLUSION

This study demonstrates that inflammatory changes occur in cadaveric donor livers and are associated with events occurring during the period of intensive care. These proinflammatory changes did not seem to affect the short-term clinical outcome of cadaveric liver allografts but may contribute to alloimmune responses and impairment of graft function in the long term.

Cold-induced apoptosis of rat liver endothelial cells: involvement of the proteasome

BACKGROUND

We have previously shown that in cultured liver endothelial cells the mere sequence of hypothermia and rewarming induces a pronounced, iron-dependent apoptosis that is likely to contribute to hepatic preservation injury. Here we study the involvement of proteases in this cold-induced apoptosis.

METHODS

Cultured liver endothelial cells were incubated in preservation solutions at 4 degrees C in the absence or presence of protease inhibitors. Cell injury and different protease activities were assessed.

RESULTS

Cold incubation of liver endothelial cells in University of Wisconsin or histidine-tryptophan-ketoglutarate (HTK) solution led to marked cell injury, which was strongly inhibited by the protease inhibitor 3,4-dichloroisocoumarin (DCI) (lactate dehydrogenase release: 86.0+/-2.6% in HTK and 4.0+/-0.4% in HTK + DCI after 24 hr of cold incubation). Determination of protease activity showed a doubling in the activity of a Suc-Leu-Leu-Val-Tyr-AMC-cleaving protease and some increase in a relatively low Suc-Ala-Ala-Ala-AMC-cleaving activity after 8 hr of cold incubation in HTK solution or 16 hr in University of Wisconsin solution. Further characterization of the protease activities showed that they belonged to two different proteases, with the major activity being calcium independent, inhibited by DCI, MG-132, and lactacystin, and strongly decreased by immunoprecipitation with an antiproteasome antibody. Preincubation of the cells with the iron chelator deferoxamine prevented the cold-induced increase of both activities.

CONCLUSION

These results show that (i) the proteasome and possibly, in addition, a serine protease are involved in cold-induced apoptosis of liver endothelial cells and (ii) the protease activation is downstream from the increase in intracellular chelatable iron.

Suppression of oxidative stress-induced hepatocyte injury by calpain antisense

BACKGROUND

Calpain, a cytosolic Ca(2+)-dependent proteinase, plays a pivotal role in cell injury. In this study, we investigated the effect of calpain-mu antisense oligonucleotide on oxidative stress induced-hepatocyte injury.

MATERIALS AND METHODS

Hemagglutinating virus of Japan liposome complex with one of three types of antisense oligonucleotide (AS-1, AS-2, AS-3) or scramble oligonucleotide was added to the culture medium of HuH7 cells and incubated for 6 days. The expression of calpain-mu protein was examined by Western blotting. After the addition of tert-butyl hydroperoxide, bleb formation was examined by phase contrast microscopy, and cell viability was assessed by the release of lactate dehydrogenase.

RESULTS

Incubation of HuH7 cells with AS-2 resulted in a decrease in the amount of calpain on day 4 and a further decrease to almost undetectable levels on day 6, whereas scramble oligonucleotide had no effect. Bleb formation was observed 120 min after the addition of tert-butyl hydroperoxide in scramble oligonucleotide-treated cells as in untreated cells. In contrast, it was rarely observed in AS-2-treated cells. Lactate dehydrogenase release was significantly suppressed in AS-2-treated cells, compared with that in scramble oligonucleotide treated-cells.

CONCLUSIONS

Our findings suggest that calpain activation is involved in the pathogenesis of oxidative stress injury and that transfection of calpain antisense may potentially protect against ischemia/reperfusion liver injury.

Cold preservation-warm reperfusion perturbs cytosolic calcium ion homeostasis in rat liver sinusoidal endothelial cells

Increases in intracellular calcium ion (Ca(2+)) levels of sinusoidal endothelial cell (SEC) may have a crucial role in mediating the expression of adhesion molecules and thus contribute to the microcirculatory disturbances observed in primary graft dysfunction. The effect of changes in the composition and/or temperature of the reperfusion solution on cytosolic Ca(2+) was studied in isolated rat SECs. Cells were preserved in cold University of Wisconsin (UW) solution for 0, 12, or 24 hours and loaded with Fura-2AM dye (Cedarlane, Eugene, OR) at 20 degrees C in N-2-hydroxyethylpiperazine-propanesulfonic acid (HEPES)-buffered physiological solution (HEPES 20 degrees C) or UW solution (UW 20 degrees C). SEC Ca(2+) levels were measured by cytofluorimetry. Basal steady-state Ca(2+) levels were much lower when SECs were loaded in UW 20 degrees C (37 +/- 2 nmol/L) than in HEPES 20 degrees C (114 +/- 32 nmol/L). In unstored controls (0 hour), going from UW 20 degrees C to HEPES 37 degrees C induced a large transient increase (185 +/- 31 nmol/L) in SEC Ca(2+) levels, which was greatly inhibited (43 +/- 13 nmol/L) in Ca(2+)-free HEPES 37 degrees C. A similar large transient increase was observed going from UW 20 degrees C to HEPES 20 degrees C (163 +/- 22 nmol/L). Changing temperature only (20 degrees C to 37 degrees C) in UW or HEPES solution had a much smaller effect on SEC Ca(2+) levels (14 +/- 2 and 60 +/- 18 nmol/L, respectively). These changes were similar in cold-preserved cells. In unstored controls, solution changes greatly attenuated the intensity of subsequent Ca(2+) responses to the purinergic agonist adenosine triphosphate (ATP). Cold preservation (CP) greatly attenuated both the frequency of appearance and intensity of ATP-induced Ca(2+) responses. Hence, changing reperfusion solution composition has a greater impact on SEC steady-state Ca(2+) levels than changing temperature. Cold preservation does not significantly affect changes in SEC steady-state Ca(2+) levels, but greatly impairs the capacity of SECs to subsequently respond to Ca(2+)-mobilizing agonists.

Caspase-independent photoreceptor apoptosis in vivo and differential expression of apoptotic protease activating factor-1 and caspase-3 during retinal development

Apoptosis is the mode of photoreceptor cell death in many retinal dystrophies. Exposure of Balb/c mice to excessive levels of light induces photoreceptor apoptosis and represents an animal model for the study of retinal degenerations. Caspases have emerged as central regulators of apoptosis, executing this tightly controlled death pathway in many cells. Previously we have reported that light-induced photoreceptor apoptosis occurs independently of one the key executioners of apoptosis, caspase-3. This present study extends these results reporting on the lack of activation of other caspases in this model including caspases-8, -9, -7, and -1. Furthermore, photoreceptor apoptosis cannot be inhibited with the broad range caspase inhibitor zVAD-fmk indicating that light-induced retinal degeneration is caspase-independent. We demonstrate that cytochrome c does not translocate from mitochondria to the cytosol during photoreceptor apoptosis. We also show that during retinal development apoptotic protease activating factor (Apaf-1) protein levels are markedly decreased and this is associated with the inability to activate the mitochondrial caspase cascade in the mature retina. In addition, there is also a significant reduction in expression of caspases-3 and -9 during retinal maturation and these levels do not increase following light exposure. Finally, we show that the calcium-dependent proteases calpains are active during light-induced retinal degeneration and establish that the calcium channel blocker D-cis-diltiazem completely inhibits photoreceptor apoptosis.

Ischemic preconditioning attenuates the oxidant-dependent mechanisms of reperfusion cell damage and death in rat liver

In an in vivo rat model of liver ischemia followed by reperfusion a consistent appearance of necrosis and activation of biochemical pathways of apoptosis was reproduced and monitored after 30 minutes reperfusion. Preconditioning by application of a short cycle of ischemia-reperfusion (10 minutes + 10 minutes) positively conditioned recovery of the organ at reperfusion, attenuating both necrotic and apoptotic events. Preconditioning at least halved cell oxidative damage occurring early at reperfusion, and as a major consequence, the increase of cytolysis and apoptosis occurring at reperfusion was about 50% less. The attenuation of both pathways of cell death by preconditioning appeared at least partly related to its modulate action on H(2)O(2) and 4-hydroxy-2,3-trans-nonenal production. The overall data point to a marked diminished oxidant generation and oxidative reactions as one major possible mechanism through which ischemic preconditioning exerts protection against necrotic and apoptotic insult to the postischemic liver.

A highly specific isolation of rat sinusoidal endothelial cells by the immunomagnetic bead method using SE-1 monoclonal antibody

BACKGROUND/AIMS

To develop a specific isolation method of hepatic sinusoidal endothelial cells (SEC), we applied the immunomagnetic method using a monoclonal antibody (SE-1) that recognizes a membranous antigen expressed only in rat SEC.

METHODS

Cells were isolated by incubating mixed non-parenchymal cells, which were obtained by collagenase digestion of the liver, with SE-1-conjugated superparamagnetic polystyrene beads. The conventional Percoll method was also performed in parallel to compare with the immunomagnetic method. The isolated cells were cultured on glass coverslips coated with type I collagen in the presence of various growth factors for 6 days.

RESULTS

Approximately 98% of the isolated cells were positive for SE-1 and the contamination of Kupffer cells or stellate cells was less than 1%. The purity was significantly better than that obtained by the Percoll method. The cultured cells showed typical SEC features, such as sieve plates and uptake of acetylated low-density lipoprotein. Although the cells continuously underwent apoptotic cell death after 2 days, they started robust cell growth after 3 days and were well maintained during the culture period.

CONCLUSIONS

Our simple and specific isolation method enables us to culture SEC with high purity and should be useful for the biological analysis of SEC.

Ischemic preconditioning protects against cold ischemic injury through an oxidative stress dependent mechanism

BACKGROUND/AIMS

Ischemic injury in cold preserved livers is characterized by sinusoidal endothelial cell (SEC) detachment and matrix metalloproteinase activity. Upon reperfusion reversible ischemic injury becomes permanent with SEC rapidly undergoing apoptosis. Ischemic preconditioning prevents reperfusion injury after normothermic ischemia. We hypothesized that ischemic preconditioning, through an oxygen free radical burst, protects against injury during cold preservation and reperfusion.

METHODS

Ischemic preconditioning was achieved in rats by clamping blood supply to the left and median lobes for 10 min followed by 15 min of reperfusion prior to preservation in cold University of Wisconsin solution for 30 h. In a second set of experiments, rats were pretreated with N-acetyl-cysteine (NAC). SEC apoptosis upon reperfusion was assessed in an isolated perfused rat liver (IPRL) model.

RESULTS

SEC detachment and activities of matrix metalloproteinase were significantly reduced in preconditioned livers. A decrease of SEC apoptosis after 1h of reperfusion in the IPRL was noted in preconditioned livers compared to controls. Pretreatment with NAC reversed the beneficial effects of ischemic preconditioning on SEC detachment and apoptosis.

CONCLUSIONS

Ischemic preconditioning is an effective strategy to prevent injury during cold preservation and after reperfusion. The protective effect is possibly mediated by oxygen free radicals.

Calpain inhibition protects against virus-induced apoptotic myocardial injury

Viral myocarditis is an important cause of human morbidity and mortality for which reliable and effective therapy is lacking. Using reovirus strain 8B infection of neonatal mice, a well-characterized experimental model of direct virus-induced myocarditis, we now demonstrate that myocardial injury results from apoptosis. Proteases play a critical role as effectors of apoptosis. The activity of the cysteine protease calpain increases in reovirus-infected myocardiocytes and can be inhibited by the dipeptide alpha-ketoamide calpain inhibitor Z-Leu-aminobutyric acid-CONH(CH(2))3-morpholine (CX295). Treatment of reovirus-infected neonatal mice with CX295 protects them against reovirus myocarditis as documented by (i) a dramatic reduction in histopathologic evidence of myocardial injury, (ii) complete inhibition of apoptotic myocardial cell death as identified by terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling, (iii) a reduction in serum creatine phosphokinase, and (iv) improved weight gain. These findings are the first evidence for the importance of a calpain-associated pathway of apoptotic cell death in viral disease. Inhibition of apoptotic signaling pathways may be an effective strategy for the treatment of viral disease in general and viral myocarditis in particular.

Decreased expression of high-molecular-weight calmodulin-binding protein and its correlation with apoptosis in ischemia-reperfused rat heart

A cardiac high-molecular-weight calmodulin-binding protein (HMWCaMBP) was previously identified as a homologue of the calpain inhibitor, calpastatin. In the present study, we investigated the expression of HMWCaMBP and calpains in rat heart after ischemia and reperfusion. Western blot analysis of normal rat heart extract with a polyclonal antibody raised against bovine HMWCaMBP indicated a prominent immunoreactive band of 140kDa. Both the expression and the activity of HMWCaMBP were decreased by ischemia reperfusion. Immunohistochemical studies showed strong-to-moderate HMWCaMBP immunoreactivity in normal heart and poor immunoreactivity in ischemia-reperfused heart muscle. However, the expression of micro-calpain and m-calpain in ischemia-reperfused heart was increased as compared to normal heart. The calpain inhibitory activity of ischemia-reperfused heart tissues was significantly lower as compared to normal heart tissues. The pre-ischemic and post-ischemic perfusion of hearts with a cell-permeable calpain inhibitor suppressed the increase in calpain expression but increased the HMWCaMBP expression. In-vitro HMWCaMBP was proteolyzed by micro-calpain and m-calpain. We also measured apoptosis in normal and ischemia-reperfused tissues. An increase in the number of apoptotic bodies was observed with increased duration of ischemia and reperfusion. Bcl-2 expression did not change in any of the groups, whereas Bax expression increased with ischemia-reperfusion and correlated well with the degree of apoptosis. Our findings suggest that HMWCaMBP may sequester calpains from its substrates in the normal myocardium, but it is susceptible to proteolysis by calpains during ischemia-reperfusion. Thus, decreased expression of HMWCaMBP may play an important role in myocardial injury.

Platelets induce sinusoidal endothelial cell apoptosis upon reperfusion of the cold ischemic rat liver

BACKGROUND & AIMS

Sinusoidal endothelial cell (SEC) apoptosis is a central feature of reperfusion injury in liver transplantation. Platelet sequestration occurs after transplantation with possible deleterious effects. We tested the hypothesis that platelets mediate SEC apoptosis.

METHODS

Livers were perfused after 24 hours of cold preservation in University of Wisconsin solution in an isolated perfused rat liver model. The perfusate contained isolated syngeneic red blood cells and purified platelets. Effects of inhibiting platelet adhesion on SEC apoptosis was tested using sialyl Lewis-X oligosaccharide (sLe(x)), a natural ligand of selectin adhesion molecules. Reperfusion injury was assessed by established markers of injury. Apoptosis was determined by TUNEL and electron microscopy.

RESULTS

A third of the circulating platelets was rapidly sequestered in the liver after reperfusion. This was associated with increased graft injury. Single platelets were adherent to sinusoidal lining without morphological or dynamic evidence of impairment of microcirculation. TUNEL staining revealed a 6-fold increase in the number of apoptotic SECs at 1 hour of reperfusion. No hepatocyte death or evidence of necrosis was detected up to 3 hours of reperfusion. Addition of sLe(x) inhibited adhesion and significantly reduced SEC apoptosis.

CONCLUSIONS

Platelets cause SEC apoptosis upon reperfusion of liver grafts. Prevention of adhesion is protective.

Ischemic preconditioning protects the mouse liver by inhibition of apoptosis through a caspase-dependent pathway

A short period of ischemia and reperfusion, called ischemic preconditioning, protects various tissues against subsequent sustained ischemic insults. We previously showed that apoptosis of hepatocytes and sinusoidal endothelial cells is a critical mechanism of injury in the ischemic liver. Because caspases, calpains, and Bcl-2 have a pivotal role in the regulation of apoptosis, we hypothesized that ischemic preconditioning protects by inhibition of apoptosis through down-regulation of caspase and calpain activities and up-regulation of Bcl-2. A preconditioning period of 10 minutes of ischemia followed by 15 minutes of reperfusion maximally protected livers subjected to prolonged ischemia. After reperfusion, serum aspartate transaminase (AST) levels were reduced up to 3-fold in preconditioned animals. All animals subjected to 75 minutes of ischemia died, whereas all those who received ischemic preconditioning survived. Apoptosis of hepatocytes and sinusoidal endothelial cells, assessed by in situ TUNEL assay and DNA fragmentation by gel electrophoresis, was dramatically reduced with preconditioning. Caspase activity, measured by poly (adenosine diphosphate ribose) polymerase (PARP) proteolysis and a specific caspase-3 fluorometric assay, was inhibited by ischemic preconditioning. The antiapoptotic mechanism did not involve calpain-like activity or Bcl-2 expression because levels were similar in control and preconditioned livers. In conclusion, ischemic preconditioning confers dramatic protection against prolonged ischemia via inhibition of apoptosis through down-regulation of caspase 3 activity, independent of calpain-like activity or Bcl-2 expression.