JNK mediates hepatic ischemia reperfusion injury

Hepatic preconditioning using lipopolysaccharide: association with specific negative regulators of the Toll-like receptor 4 signaling pathway

BACKGROUND

Preconditioning using lipopolysaccharide (LPS), a Toll-like receptor (TLR)-4 ligand, has been demonstrated to attenuate ischemia-reperfusion injury (IRI) in several organs but has not been sufficiently elucidated in the liver. We investigated the molecular mechanism of protection induced by LPS preconditioning against hepatic IRI.

METHODS

BALB/c mice underwent 70% hepatic ischemia for 90 min. LPS was injected intraperitoneally 20 hr before ischemia at a range of 1 to 1000 μg/kg. Hepatic injury was evaluated based on serum alanine aminotransferase levels and histopathology. Inflammatory cytokine expression, nuclear factor-κB activation, and c-Jun N-terminal kinase phosphorylation were investigated after reperfusion. Additionally, preischemic expression of negative feedback inhibitors of the TLR4 cascade was examined.

RESULTS

Only the 100 μg/kg LPS pretreatment significantly reduced serum alanine aminotransferase levels and histopathologic damage 6 hr after reperfusion; there was no difference among other LPS concentrations. In mice pretreated with LPS, intrahepatic expression of tumor necrosis factor-α and interleukin (IL)-6 as well as activation of nuclear factor-κB and c-Jun N-terminal kinase were inhibited 1 hr after reperfusion, whereas expression of IL-10, an anti-inflammatory cytokine, was induced. Suppressor of cytokine signaling (SOCS)-1, SOCS-3 and IL-1 receptor-associated kinase-M were upregulated by LPS exposure in the preischemic period.

CONCLUSIONS

Hepatic LPS preconditioning elicited the upregulation of specific negative regulators in the TLR4 signaling pathway. Preischemic induction of these regulators plays an important role as immunologic preparation for the subsequent ischemia-reperfusion and produces resistance to liver injury. Preoperative modulation of the TLR4 pathway might become an alternative therapeutic strategy against hepatic IRI.

Role of JNK signaling pathway-mediated apoptosis in diseases

C-Jun N-terminal kinases (JNKs), also referred to as stress-activated kinases (SAPKs), constitute a subfamily of the mitogen-activated protein kinase (MAPK) superfamily. Apoptosis induced by a variety of extracellular stimuli (such as stress, Fas, TNF-α) is mediated by JNK, and the JNK signaling pathway is involved in apoptosis of many cell types and plays an important role in the pathogenesis of many diseases and pathological injuries, such as neurodegenerative diseases, tumors, type I diabetes, chronic viral hepatitis B and ischemia/reperfusion injury. Therefore, components of the JNK signaling pathway represent potential molecular targets for the treatment of related diseases. This review aims to elucidate the basic composition of the JNK signaling pathway and mechanisms behind JNK-mediated apoptosis, and to highlight the role of JNK signaling pathway-mediated apoptosis in diseases.

Cyclosporin-A does not prevent cold ischemia/reperfusion injury of rat livers

Cyclosporin-A (CsA) has been reported to protect livers from warm ischemia/reperfusion (I/R) injury. To study if CsA has also a protective effect on cold I/R injury, two models were used: the isolated perfused rat liver (IPRL) and the orthotopic rat liver transplantation (ORLT). (1) IPRL: Livers were preserved for 24 h (5°C) in University of Wisconsin (UW) solution alone (group 1), with CsA (400 nM) dissolved in dimethylsulfoxide (50 μM) (group 2), and with dimethylsulfoxide (DMSO) alone (group 3). Livers were reperfused for 60 min (37°C) (n = 8/group). Cell necrosis was evaluated by trypan blue uptake and apoptosis by laddering and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay, and by caspase-3 activation. Marked and similar sinusoidal endothelial cell necrosis was found in the three groups while apoptosis was found similarly deceased in groups 2 and 3 compared with group 1. (2) ORLT: Donors received either CsA (5 mg/kg) or corn oil 24 h before transplantation. Recipients were sacrificed after 240 min; cell necrosis and apoptosis were then evaluated. No difference was found between treated and control groups. The current data strongly suggest that CsA has no protective effect on hepatic cold I/R injury. Hepatocyte apoptosis can be reduced by antioxidants, as occurred with DMSO, but introduction of CsA does not provide additional protective effect.

The role of excessive versus acute administration of erythropoietin in attenuating hepatic ischemia-reperfusion injury

Ischemia-reperfusion injury (I/R) is the main cause of primary graft nonfunction. Our aim was to evaluate the effect of excessive versus acute administration of erythropoietin (EPO) in attenuating the hepatic injury induced by I/R in mice. The effect of segmental (70%) hepatic ischemia was evaluated in a transgenic mouse line with constitutive overexpression of human EPO cDNA and in wild-type (WT) mice. Mice were randomly allocated to 5 main experimental groups: (i) WT-sham, (ii) WT ischemia, (iii) WT ischemia + recombinant human erythropoietin (rhEPO), (iv) transgenic-sham, and (v) transgenic ischemia. The EPO-pretreated mice showed a significant reduction in liver enzyme levels and intrahepatic caspase-3 activity and fewer apoptotic hepatocytes (p < 0.05 for all) compared with the WT untreated I/R group. EPO decreased c-Jun N-terminal kinase (JNK) phosphorylation and nuclear factor-κB (NF-κB) expression during I/R. In transgenic I/R livers, baseline histology showed diffused hepatic injury, and no significant beneficial effect was noted between the WT untreated and the transgenic I/R mice. In conclusion, acute pretreatment with EPO in WT mice attenuated in vivo I/R liver injury. However, in excessive EPO overexpression, the initial liver injury abolished the beneficial effect of EPO. These findings have important implications for the potential use of acute EPO in I/R injury during liver transplantation.

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

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

Oral methylthioadenosine administration attenuates fibrosis and chronic liver disease progression in Mdr2-/- mice

BACKGROUND

Inflammation and fibrogenesis are directly related to chronic liver disease progression, including hepatocellular carcinoma (HCC) development. Currently there are few therapeutic options available to inhibit liver fibrosis. We have evaluated the hepatoprotective and anti-fibrotic potential of orally-administered 5'-methylthioadenosine (MTA) in Mdr2(-/-) mice, a clinically relevant model of sclerosing cholangitis and spontaneous biliary fibrosis, followed at later stages by HCC development.

METHODOLOGY

MTA was administered daily by gavage to wild type and Mdr2(-/-) mice for three weeks. MTA anti-inflammatory and anti-fibrotic effects and potential mechanisms of action were examined in the liver of Mdr2(-/-) mice with ongoing fibrogenesis and in cultured liver fibrogenic cells (myofibroblasts).

PRINCIPAL FINDINGS

MTA treatment reduced hepatomegaly and liver injury. α-Smooth muscle actin immunoreactivity and collagen deposition were also significantly decreased. Inflammatory infiltrate, the expression of the cytokines IL6 and Mcp-1, pro-fibrogenic factors like TGFβ2 and tenascin-C, as well as pro-fibrogenic intracellular signalling pathways were reduced by MTA in vivo. MTA inhibited the activation and proliferation of isolated myofibroblasts and down-regulated cyclin D1 gene expression at the transcriptional level. The expression of JunD, a key transcription factor in liver fibrogenesis, was also reduced by MTA in activated myofibroblasts.

CONCLUSIONS/SIGNIFICANCE

Oral MTA administration was well tolerated and proved its efficacy in reducing liver inflammation and fibrosis. MTA may have multiple molecular and cellular targets. These include the inhibition of inflammatory and pro-fibrogenic cytokines, as well as the attenuation of myofibroblast activation and proliferation. Downregulation of JunD and cyclin D1 expression in myofibroblasts may be important regarding the mechanism of action of MTA. This compound could be a good candidate to be tested for the treatment of (biliary) liver fibrosis.

Glycine-induced cytoprotection is mediated by ERK1/2 and AKT in renal cells with ATP depletion

Glycine receptor (GlyR) activation by glycine protects cells against ATP depletion. However, the underlying mechanisms remain unclear. To define signaling pathways responsible for the GlyR mediated cytoprotection, we examined the phosphorylation status of key kinases signaling pathways in Madin-Darby canine kidney (MDCK) cells. Our results indicated that growing the ATP-depleted MDCK cells in glycine-containing media increased the level of phosphorylated extracellular signal-regulated kinase 1 and 2 (ERK1/2), Ets-like transcription factor-1 (Elk1), AKT, and Forkhead box O-class 1 (FoxO1), decreased the level of phosphorylated p38 mitogen-activated protein kinase, while having little effect on the phosphorylation status of c-Jun N-terminal kinase 1 and 2. Similar phosphorylation changes in these molecules took place in the GlyRα1 stably expressing HEK-293 cell. We also showed that treating MDCK cells with ERK1/2 inhibitor PD98059 or AKT inhibitor LY294002 diminished cytoprotection against cell death by glycine, as determined by assessment of lactate dehydrogenase release and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide activity. In contrast, treatment with p38 inhibitor SB203580 enhanced the glycine-induced cytoprotection. Finally, RNAi-mediated silencing of GlyRα1 abolished the glycine-induced changes in phosphorylation status of the above kinases in ATP-depleted cells. Taken together, our results suggest that the ERK1/2 and AKT signaling pathways are involved in the glycine-GlyR protection of MDCK cells against death induced by ATP depletion.

Delayed ischemic preconditioning protects against liver ischemia-reperfusion injury in vivo

OBJECTIVES

Ischemic preconditioning (IP) affords resistance to liver ischemia-reperfusion (IR) injury, providing an early phase of protection. Development of delayed IP against IR injury was assessed using partial IR in rat liver.

METHODS

The IP manuver (10 minutes of ischemia and up to 72 hours of reperfusion) was induced before 1 hour of ischemia and 20 hours of reperfusion. At the end of the reperfusion period, blood and liver samples were analyzed for serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), haptoglobin and tumor necrosis factor-alpha (TNF-alpha) levels, hepatic histology, protein carbonyl and glutathione (GSH) contents as well as nuclear factor-kappaB (NF-kappaB), and activating protein-1 (AP-1) DNA binding.

RESULTS

The IP manuver significantly increased protein carbonyl/GSH ratios (275%), serum ALT (42%), and AST (58%); these changes normalized after 12 hours. Serum AST, ALT, and LDH levels were significantly increased by IR (4-, 5.6-, and 7.0-fold, respectively), with significant changes in liver histology, protein carbonyl/GSH ratio (481% enhancement), and serum TNF-alpha (6.1-fold increase). Delayed IP in IR animals reduced serum AST (66%), ALT (57%), and LDH (90%) and liver GSH depletion (89%), with normalization of protein carbonyl content, serum TNF-alpha levels, and liver histology. Enhanced AP-1/NF-kappaB DNA binding ratios and diminished haptoglobin expression induced by IR were normalized by IP.

CONCLUSION

These data support that delayed IP suppresses IR-induced liver injury, oxidative stress, and TNF-alpha response, which coincide with recovery of IR-altered signaling functions represented by normal AP-1/NF-kappaB DNA binding ratios and acute phase responses.

Simvastatin reduces mortality and hepatic injury after hemorrhage/resuscitation in rats

Statins are established in the prevention and therapy of chronic cardiovascular diseases because of inhibition of HMG-CoA (3-hydroxy-3-methylglutaryl-coenzyme A), thus lowering blood cholesterol levels. However, their cholesterol-independent effects include regulation of Rho/Rho-kinases (ROCK) and eNOS, proteins centrally involved in various models of acute inflammation. Therefore, we tested the hypothesis that simvastatin confers protection after rat hemorrhage/resuscitation (H/R) and wanted to elucidate the mechanisms involved. Fifty-two female Lewis rats (180-250 g) were pretreated with simvastatin 5 mg/kg per day or vehicle for 6 days (i.p.). Then, rats were hemorrhaged to a mean arterial pressure of 30 +/- 2 mmHg for 60 min and resuscitated. Control group underwent surgical procedures without H/R. Two hours after resuscitation, tissues were harvested. Mortality was assessed 72 h after H/R. Simvastatin pretreatment increased survival after H/R from 20% to 80%. Serum alanine aminotransferase after H/R increased 2.2-fold in vehicle as compared with simvastatin-treated rats. Histopathological analysis revealed decreased hepatic necrosis in simvastatin-treated rats after H/R. Hepatic oxidative (4-hydroxynonenal) and nitrosative (3-nitrotyrosine) stress, inflammatory markers (serum IL-6 and hepatic infiltration with polymorphonuclear leukocytes), and actin cytoskeleton rearrangements were decreased after simvastatin pretreatment compared with vehicle-treated rats after H/R. Simvastatin increased eNOS and heme oxygenase 1 expression and eNOS activation. Expression of Rho/Rho-kinase and myosin phosphatase targeting subunit, Thr-MYPT1, a marker for Rho-kinase activity, decreased after simvastatin treatment compared with vehicle-treated rats after H/R. Simvastatin pretreatment exerts beneficial effects in this model of acute inflammation by supporting protective mechanisms that are important for hepatic microcirculation after H/R.

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.

Hepatocyte death: a clear and present danger

The hepatocyte is especially vulnerable to injury due to its central role in xenobiotic metabolism including drugs and alcohol, participation in lipid and fatty acid metabolism, its unique role in the enterohepatic circulation of bile acids, the widespread prevalence of hepatotropic viruses, and its existence within a milieu of innate immune responding cells. Apoptosis and necrosis are the most widely recognized forms of hepatocyte cell death. The hepatocyte displays many unique features regarding cell death by apoptosis. It is quite susceptible to death receptor-mediated injury, and its death receptor signaling pathways involve the mitochondrial pathway for efficient cell killing. Also, death receptors can trigger lysosomal disruption in hepatocytes which further promote cell and tissue injury. Interestingly, hepatocytes are protected from cell death by only two anti-apoptotic proteins, Bcl-x(L) and Mcl-1, which have nonredundant functions. Endoplasmic reticulum stress or the unfolded protein response contributes to hepatocyte cell death during alterations of lipid and fatty acid metabolism. Finally, the current information implicating RIP kinases in necrosis provides an approach to more fully address this mode of cell death in hepatocyte injury. All of these processes contributing to hepatocyte injury are discussed in the context of potential therapeutic strategies.

Hydrodynamics-based transfection of plasmid encoding receptor activator for nuclear factor kappa B-Fc protects against hepatic ischemia/reperfusion injury in mice

Hepatic ischemia/reperfusion (I/R) injury is very important in transplant surgery. To study the mechanism of receptor activator for nuclear factor kappa B-Fc (RANK-Fc) in protection against I/R injury, 90 male BALB/c mice were randomly divided into 3 groups: a phosphate-buffered saline (PBS) (sham) group, a pLNCX2-IRES-eGFP+I/R (Negative-control) group (where IRES means internal ribosome entry site and eGFP means enhanced green fluorescent protein), and a pLNCX2-RANK-Fc-IRES-eGFP+I/R (RANK-Fc) group. All mice were injected with 2.5 mL of PBS (with or without plasmids) within 6 seconds via the tail vein. After 3 days, hepatic I/R was induced under warm conditions by partial occlusion of the left and median lobes for 90 minutes followed by various periods of reperfusion. Hepatic injury was assessed by the levels of liver aminotransferases and histopathology. Tumor necrosis factor alpha, interleukin 6, and interleukin 1beta were measured by enzyme-linked immunosorbent assay, whereas RANK-Fc, phospho-c-Jun, c-Jun N-terminal kinase (JNK), hypoxia inducible factor 1 alpha (HIF-1alpha), nuclear p65, and total p65 were assessed with western blotting. Apoptosis was identified by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling. RANK-Fc was efficiently expressed in the liver. In comparison with the negative-control group, RANK-Fc reduced nuclear factor kappa B (NF-kappaB) p65 nuclear translocation, JNK phosphorylation, and HIF-1alpha expression during I/R. RANK-Fc effectively suppressed proinflammatory cytokine expression. The results indicated that RANK-Fc could protect against hepatic I/R injury in mice at least in part via the inhibition of the proinflammatory NF-kappaB pathway as well as proapoptotic JNK and HIF-1alpha pathway activation.

JNK signalling in human and experimental renal ischaemia/reperfusion injury

BACKGROUND

Ischaemia/reperfusion (I/R) is an important factor in delayed graft function in renal transplantation and is a determinant of long-term graft outcome. This study examined the role of c-Jun N-terminal kinase (JNK) signalling in human and experimental renal I/R injury.

METHODS

Biopsies obtained 15-20 min after reperfusion of human renal allografts were examined for JNK signalling by immunostaining for phospho-c-Jun. To examine the pathologic role of JNK signalling, a selective JNK inhibitor (CC-401) was administered to rats before or after the induction of a 30-min period of bilateral renal ischaemia followed by reperfusion. Renal function and tubular damage were analysed.

RESULTS

Substantial JNK activation was evident in tubular epithelial cells in kidneys from deceased donors (n = 30) which was less prominent in kidneys from live donors (n = 7) (44.6 +/- 24.8% vs 29.1 +/- 20% p-c-Jun+, respectively; P < 0.05), whereas biopsies of thin basement membrane disease exhibited little, or no, p-c-Jun staining. The degree of p-c-Jun staining correlated with ischaemic time in deceased donor allografts, but not with graft function. Administration of CC-401 to rats prior to bilateral renal I/R prevented acute renal failure and largely prevented tubular damage, leucocyte infiltration and upregulation of pro-inflammatory molecules. However, delaying CC-401 treatment until 1 h after reperfusion (after the peak of JNK activation) had no protective effect.

CONCLUSIONS

We have identified acute activation of the JNK signalling pathway following I/R in human kidney allografts. Experimental studies indicate that blockade of JNK signalling, commenced prior to this activation, can prevent acute tubular necrosis and renal dysfunction secondary to I/R injury.

Reperfusion stress induced during intermittent selective clamping accelerates rat liver regeneration through JNK pathway

BACKGROUND & AIMS

Liver resection includes temporal vascular inflow occlusion resulting in ischemia/reperfusion injury in the remnant liver. Here, we developed a rat model of selective lobe occlusion to isolate reperfusion stress from ischemia and to analyze its effect on liver regeneration.

METHODS

Left lateral and median lobes of liver were either mobilized or subjected twice for 10min to ischemia followed by 5min reperfusion prior to resection while the regenerative lobes were only subjected to reperfusion.

RESULTS

Although intermittent reperfusion stress induced higher levels of serum transaminases, analysis of cell cycle regulators revealed accelerated regenerative response compared to standard partial hepatectomy. The G0/G1 transition occurred before tissue resection, as evidenced by c-fos, junB, and IL-6 induction. Following hepatectomy, Cyclin D1 up-regulation, G1/S transition, and cell division occurred earlier than normal. Unexpectedly, liver mobilization, a component of the clamping procedure, also resulted in earlier G1/S transition. The shortened G1-phase was driven by the c-Jun N-terminal Kinase pathway and was associated with an oxidative stress response as evidenced by the expression of inducible nitric oxide synthase.

CONCLUSION

Intermittent selective clamping of lobes to be resected induced reperfusion stress on remnant liver that was beneficial for liver regeneration, suggesting this procedure could be applied in clinical practice.

Inhibition of c-Jun N-terminal kinase after hemorrhage but before resuscitation mitigates hepatic damage and inflammatory response in male rats

Inhibition of c-Jun N-terminal kinase (JNK) by a cell-penetrating, protease-resistant JNK peptide (D-JNKI-1) before hemorrhage and resuscitation (H/R) ameliorated the H/R-induced hepatic injury and blunted the proinflammatory changes. Here we tested the hypothesis if JNK inhibition at a later time point-after hemorrhagic shock but before the onset of resuscitation-in a rat model of H/R also confers protection. Twenty-four male Sprague-Dawley rats (250 - 350 g) were randomly divided into 4 groups: 2 groups of shock animals were hemorrhaged to a MAP of 32 to 37 mmHg for 60 min and randomly received either D-JNKI-1 (11 mg/kg i.p.) or sterile saline as vehicle immediately before the onset of resuscitation. Two groups of sham-operated animals underwent surgical procedures without H/R and were either D-JNKI-1 or vehicle treated. Rats were killed 2 h later. Serum activity of alanine aminotransferase and serum lactate dehydrogenase after H/R increased 3.5-fold in vehicle-treated rats as compared with D-JNKI-1-treated rats. Histopathological analysis revealed that hepatic necrosis and apoptosis (hematoxylin-eosin, TUNEL, and M30, respectively) were significantly inhibited in D-JNKI-1-treated rats after H/R. Hepatic oxidative (4-hydroxynonenal) and nitrosative (3-nitrotyrosine) stress as well as markers of inflammation (hepatic and serum IL-6 levels and hepatic infiltration with polymorphonuclear leukocytes) were also reduced in D-JNKI-1-treated rats. LPS-stimulated TNF-alpha release from whole blood from hemorrhaged and resuscitated animals was higher in vehicle-treated rats as compared with D-JNKI-1-treated rats. c-Jun N-terminal kinase inhibition after hemorrhage before resuscitation resulted in a reduced activation of c-Jun. Taken together, these results indicate that D-JNKI-1 application after hemorrhagic shock before resuscitation blunts hepatic damage and proinflammatory changes during resuscitation. Hence, JNK inhibition is even protective when initiated after blood loss before resuscitation. These experimental results indicate that the JNK pathway may be a possible treatment option for the harmful consequences of H/R.

Inhibition of hepatic mitochondrial aldehyde dehydrogenase by carbon tetrachloride through JNK-mediated phosphorylation

The aim of this study was to investigate the mechanism of inhibition of mitochondrial aldehyde dehydrogenase (ALDH2) by carbon tetrachloride (CCl(4)). CCl(4) administration caused marked hepatocyte ballooning and necrosis in the pericentral region. CCl(4) also inhibited hepatic ALDH2 activity in a time-dependent manner without altering the protein level, suggesting ALDH2 inhibition through covalent modifications such as phosphorylation by JNK. To demonstrate phosphorylation, the isoelectric point (pI) of ALDH2 in CCl(4)-exposed rats was compared to that of untreated controls. Immunoblot analysis revealed that immunoreactive ALDH2 bands in CCl(4)-exposed rats were shifted to acidic pI ranges on two-dimensional electrophoresis (2-DE) gels. Incubation with alkaline phosphatase significantly restored the suppressed ALDH2 activity with a concurrent alkaline pI shift of the ALDH2 spots. Both JNK and activated JNK were translocated to mitochondria after CCl(4) exposure. In addition, incubation with catalytically active JNK led to significant inhibition of ALDH2 activity, with an acidic pI shift on 2-DE gels. Furthermore, immunoprecipitation followed by immunoblot analysis with anti-phospho-Ser-Pro antibody revealed phosphorylation of a Ser residue(s) of ALDH2. These results collectively indicate a novel underlying mechanism by which CCl(4) exposure activates JNK, which translocates to mitochondria and phosphorylates ALDH2, contributing to inhibition of ALDH2 activity accompanied by decreased cellular defense capacity and increased lipid peroxidation.

Modulation of hepatic fibrosis by c-Jun-N-terminal kinase inhibition

BACKGROUND & AIMS

c-Jun N-terminal kinase (JNK) is activated by multiple profibrogenic mediators; JNK activation occurs during toxic, metabolic, and autoimmune liver injury. However, its role in hepatic fibrogenesis is unknown.

METHODS

JNK phosphorylation was detected by immunoblot analysis and confocal immunofluorescent microscopy in fibrotic livers from mice after bile duct ligation (BDL) or CCl(4) administration and in liver samples from patients with chronic hepatitis C and non-alcoholic steatohepatitis. Fibrogenesis was investigated in mice given the JNK inhibitor SP600125 and in JNK1- and JNK2-deficient mice following BDL or CCl(4) administration. Hepatic stellate cell (HSC) activation was determined in primary mouse HSCs incubated with pan-JNK inhibitors SP600125 and VIII.

RESULTS

JNK phosphorylation was strongly increased in livers of mice following BDL or CCl(4) administration as well as in human fibrotic livers, occurring predominantly in myofibroblasts. In vitro, pan-JNK inhibitors prevented transforming growth factor (TGF) beta-, platelet-derived growth factor-, and angiotensin II-induced murine HSC activation and decreased platelet-derived growth factor and TGF-beta signaling in human HSCs. In vivo, pan-JNK inhibition did not affect liver injury but significantly reduced fibrosis after BDL or CCl(4). JNK1-deficient mice had decreased fibrosis after BDL or CCl(4), whereas JNK2-deficient mice displayed increased fibrosis after BDL but fibrosis was not changed after CCl(4). Moreover, patients with chronic hepatitis C who displayed decreased fibrosis in response to the angiotensin receptor type 1 blocker losartan showed decreased JNK phosphorylation.

CONCLUSIONS

JNK is involved in HSC activation and fibrogenesis and represents a potential target for antifibrotic treatment approaches.

Signal transduction pathways involved in drug-induced liver injury

Hepatocyte death following drug intake is the critical event in the clinical manifestation of drug-induced liver injury (DILI). Traditionally, hepatocyte death caused by drugs had been attributed to overwhelming oxidative stress and mitochondria dysfunction caused by reactive metabolites formed during drug metabolism. However, recent studies have also shown that signal transduction pathways activated/inhibited during oxidative stress play a key role in DILI. In acetaminophen (APAP)-induced liver injury, hepatocyte death requires the sustained activation of c-Jun kinase (JNK), a kinase important in mediating apoptotic and necrotic death. Inhibition of JNK using chemical inhibitors or knocking down JNK can prevent hepatocyte death even in the presence of extensive glutathione (GSH) depletion, covalent binding, and oxidative stress. Once activated, JNK translocates to mitochondria, to induce mitochondria permeability transition and trigger hepatocyte death. Mitochondria are central targets where prodeath kinases such as JNK, prosurvival death proteins such as bcl-xl, and oxidative damage converge to determine hepatocyte survival. The importance of mitochondria in DILI is also observed in the Mn-SOD heterozygous (+/-) model, where mice with less mitochondrial Mn-SOD are sensitized to liver injury caused by certain drugs. An extensive body of research is accumulating suggesting a central role of mitochondria in DILI. Drugs can also cause redox changes that inhibit important prosurvival pathways such as NF-kappaB. The inhibition of NF-kappaB by subtoxic doses of APAP sensitizes hepatocyte to the cytotoxic actions of tumor necrosis factor (TNF). Many drugs will induce liver injury if simultaneously treated with LPS, which promotes inflammation and cytokine release. Drugs may be sensitizing hepatocytes to the cytotoxic effects of cytokines such as TNF, or vice versa. Overall many signaling pathways are important in regulating DILI, and represent potential therapeutic targets to reduce liver injury caused by drugs.

CYP2E1 potentiation of LPS and TNFα-induced hepatotoxicity by mechanisms involving enhanced oxidative and nitrosative stress, activation of MAP kinases, and mitochondrial dysfunction

The mechanisms by which alcohol causes cell injury are not clear. A major mechanism that is the focus of considerable research is the role of lipid peroxidation and oxidative stress in alcohol toxicity. Many pathways have been suggested to play a role in how alcohol induces oxidative stress. Considerable attention has been given to alcohol-elevated production of lipopolysaccharide (LPS) and TNFα and to alcohol induction of CYP2E1. These two pathways are not exclusive of each other, however, associations and interactions between them, especially in vivo, have not been extensively evaluated. We have shown that increased oxidative stress from induction of CYP2E1 in vivo sensitizes hepatocytes to LPS and TNF toxicity and that oxidants, such as peroxynitrite, activation of p38 and JNK MAP kinases, inactivation of NF-kB protective pathways and mitochondrial dysfunction are downstream mediators of this CYP2E1-LPS/TNF potentiated hepatotoxicity. This review will summarize studies showing potentiated interactions between these two risk factors in promoting liver injury and the mechanisms involved.

Role of p38 and JNK in liver ischemia and reperfusion

BACKGROUND/PURPOSE

The signal transduction of mitogen-activated protein kinases (MAPKs) has appeared to be an important mediator of ischemic-related events. Because of this, we analyzed the participation of p38 and JNK in liver ischemia and reperfusion, as two individual members of the MAPK family of proteins.

METHODS

All papers referred to in PubMed for the past 15 years were analyzed to determine how and when these MAPKs were considered to be an intricate part of the ischemic event. References were cross-studied to ascertain whether other papers could be found in the literature.

RESULTS

The role of p38 and JNK in liver ischemia was confirmed in the literature. The activation of these mediators was associated with the induction of apoptosis and necrosis. Inhibitors of p38 and JNK reduced the liver ischemia and reperfusion damage, probably through the mechanisms mentioned before.

CONCLUSIONS

The development of effective inhibitors of p38 and JNK protein mediators is important for minimizing the harmful effects associated with liver ischemia and reperfusion.

Cisplatin prevents high mobility group box 1 release and is protective in a murine model of hepatic ischemia/reperfusion injury

The nuclear protein high mobility group box 1 (HMGB1) is an important inflammatory mediator involved in the pathogenesis of liver ischemia/reperfusion (I/R) injury. Strategies aimed at preventing its release from stressed or damaged cells may be beneficial in preventing inflammation after I/R. Cisplatin is a member of the platinating chemotherapeutic agents and can induce DNA lesions that are capable of retaining high mobility group proteins inside the nucleus of cells. In vitro studies in primary cultured rat hepatocytes show that nontoxic concentrations of cisplatin can sequester HMGB1 inside the nucleus of hypoxic cells. Similarly, the in vivo administration of nontoxic doses of cisplatin prevents liver damage associated with a well-established murine model of hepatic I/R as measured by lower circulating serum aminotransferase levels, lower hepatic inflammatory cytokine levels including tumor necrosis factor alpha and interleukin-6, lower inducible NO synthase expression, and fewer I/R-associated histopathologic changes. The mechanism of action in vivo appears to involve the capacity of cisplatin to prevent the I/R-induced release of HMGB1 as well as to alter cell survival and stress signaling in the form of autophagy and mitogen-activated protein kinase activation, respectively.

CONCLUSION

Low, nontoxic doses of cisplatin can sequester HMGB1 inside the nucleus of redox-stressed hepatocytes in vitro and prevent its release in vivo in a murine model of hepatic I/R. Furthermore, cell survival and stress signaling pathways are altered by low-dose cisplatin. Therefore, platinating agents may provide a novel approach to mitigating the deleterious effects of I/R-mediated disease processes.

Uridine-5'-triphosphate protects against hepatic- ischemic/reperfusion injury in mice

BACKGROUND AND AIM

Mitochondrial calcium overload triggers apoptosis and also regulates ATP production. ATP and uridine-5'-triphosphate (UTP) depletion from hepatic tissue after ischemia causes cell death. ATP and UTP binds to cell membranes of the hepatocytes through P2Y receptors. Our aim was to investigate the role of UTP on the hepatic injury induced by ischemia.

METHODS

Isolated mouse livers were randomly divided into five groups: (1) control group; (2) ischemic group (90 min); (3) as group 2, but with the administration of UTP; (4) as group 2, but with the administration of suramin, a P2Y antagonist; and (5) as group 3, but with the simultaneous administration of suramin and UTP.

RESULTS

There was a postischemic significant reduction in the release of liver enzymes in the animals pretreated with UTP, the intrahepatic caspase-3 activity was significantly decreased, and the intrahepatic ATP content increased compared with group 2 (ischemic untreated). UTP prevented intracellular Ca overload after hypoxia in hepatocyte cultures. In the UTP-treated groups, significantly fewer apoptotic hepatocyte cells were noted by weaker activation of caspase-3 and by the transferase-mediated dUTP nick end labeling assay. The administration of suramin prevented the beneficial effect of endogenous ATP. UTP treatment attenuated the degradation of IkappaBalpha (nuclear factor-kappaB inhibitor) by 80% during reperfusion with no effect on c-Jun N terminal kinase phosphorylation.

CONCLUSION

The administration of UTP before induction of ischemia-reperfusion can attenuate hepatic injury. UTP administration decreased cytosolic Ca overload in hypoxic conditions. UTP-mediated protective effects may be regulated through nuclear factor- kappaB inactivation. These findings have important implications for the potential use of UTP in ischemic hepatic injury.

Receptor for advanced glycation end product (RAGE)-dependent modulation of early growth response-1 in hepatic ischemia/reperfusion injury

BACKGROUND/AIMS

We previously showed that blockade of RAGE significantly attenuates hepatic ischemia/reperfusion (I/R) injury in mice. Here, we identify that early growth response-1 (Egr-1) is a downstream target of RAGE in hepatic I/R injury.

METHODS

Hepatic I/R was induced in male mice. Liver remnants were analyzed for induction of Egr-1 and cytokines, as well as regulation of apoptotic pathways after reperfusion.

RESULTS

Egr-1 was upregulated in the liver remnants after hepatic I/R injury and was suppressed by administration of soluble RAGE or deletion of the RAGE gene. RAGE-mediated increased expression of Egr-1 upregulates a central downstream gene, MIP2. In contrast, RAGE-stimulated Egr-1-independent pathways regulate TNF-alpha production and apoptosis in response to I/R. Consistent with these findings, phospho-p44/42 and phospho-JNK MAPK and c-Jun were strikingly suppressed in RAGE(-/-) versus WT mice, but not in Egr-1(-/-) mice. RAGE ligand HMGB1 was upregulated after I/R in the liver remnants. In vitro, incubation of RAGE-expressing liver dendritic cells (DCs) with recombinant HMGB-1 resulted in increased Egr-1 transcripts, in a manner suppressed by RAGE gene deletion, soluble RAGE and inhibitors of p44/p42 or JNK MAP kinase.

CONCLUSIONS

Suppression of Egr-1 may contribute to the protective mechanisms underlying the beneficial impact of RAGE blockade or deletion.

Differential effects of JNK1 and JNK2 inhibition on murine steatohepatitis and insulin resistance

Activation of c-Jun N-terminal kinase (JNK) has been implicated as a mechanism in the development of steatohepatitis. This finding, together with the reported role of JNK signaling in the development of obesity and insulin resistance, two components of the metabolic syndrome and predisposing factors for fatty liver disease, suggests that JNK may be a central mediator of the metabolic syndrome and an important therapeutic target in steatohepatitis. To define the isoform-specific functions of JNK in steatohepatitis associated with obesity and insulin resistance, the effects of JNK1 or JNK2 ablation were determined in developing and established steatohepatitis induced by a high-fat diet (HFD). HFD-fed jnk1 null mice failed to develop excessive weight gain, insulin resistance, or steatohepatitis. In contrast, jnk2(-/-) mice fed a HFD were obese and insulin-resistant, similar to wild-type mice, and had increased liver injury. In mice with established steatohepatitis, an antisense oligonucleotide knockdown of jnk1 decreased the amount of steatohepatitis in concert with a normalization of insulin sensitivity. Knockdown of jnk2 improved insulin sensitivity but had no effect on hepatic steatosis and markedly increased liver injury. A jnk2 knockdown increased hepatic expression of the proapoptotic Bcl-2 family members Bim and Bax and the increase in liver injury resulted in part from a Bim-dependent activation of the mitochondrial death pathway.

CONCLUSION

JNK1 and JNK2 both mediate insulin resistance in HFD-fed mice, but the JNK isoforms have distinct effects on steatohepatitis, with JNK1 promoting steatosis and hepatitis and JNK2 inhibiting hepatocyte cell death by blocking the mitochondrial death pathway.

Melatonin protects from hepatic reperfusion injury through inhibition of IKK and JNK pathways and modification of cell proliferation

Reactive oxygen species (ROS) are involved in pathophysiology of ischemia/reperfusion injury. Melatonin is a potent scavenger of ROS. Thus, this study was designed to elucidate its effects in a combined hepatic warm ischemia and resection model. The right lateral and caudate lobes (32% of liver volume) of Sprague-Dawley rats underwent warm ischemia for 30 min followed by reperfusion and subsequent resection of the nonischemic liver tissue. Some rats were gavaged with 50 mg/kg melatonin 2 hr before the onset of experiments. Controls received the same volume of microcrystalline cellulose. Survival, transaminases, histology, flow cytometry, inducible nitric oxide synthase (iNOS) expression, and activation of signal transduction pathways [c-Jun N-terminal kinase (JNK), cJUN, IkappaB kinase alpha (IKKalpha), proliferating cell nuclear antigen (PCNA), and Ki67] were assessed for hepatic injury, oxidative stress, and cell proliferation. Melatonin significantly improved animal survival and decreased transaminase levels, the indices for necrosis, liver damage, leukocyte infiltration, and iNOS expression. In parallel, the expression of IKKalpha, JNK1, and cJUN decreased by 35-50% after melatonin (P < 0.05). At the same time, melatonin reduced the expression of both PCNA and Ki67 in liver (P < 0.05). Melatonin is hepatoprotective most likely via mechanisms including inhibition of IKK and JNK pathways and regulation of cell proliferation.

The MAP kinase phosphatase-1 MKP-1/DUSP1 is a regulator of human liver response to transplantation

Orthotopic liver transplantation (OLT) continues to be the only remedy for end-stage liver disease. In an attempt to decrease the ever-widening gap between organ donor and recipient numbers, and ultimately make more livers amenable to transplantation, we characterized the healthy human liver's response to ischemia and reperfusion-induced injury during transplantation. This was carried out by transcriptional profiling using cDNA microarray to identify genes whose expression was modulated at the 1-h postreperfusion time point. We observed that the map kinase phosphatase-1/dual-specificity phosphatase-1 (MKP-1/DUSP1) mRNA was strongly and significantly upregulated. Validation of this observation was carried out using reverse transcriptase-polymerase chain reaction (RT-PCR), immunoblotting and immunohistochemistry. In addition, we characterized the signaling pathways regulating MKP-1 expression using the human hepatoma cell line HepG2. Finally, by combining MKP-1 silencing with reperfusion-associated stresses, we reveal the preferential role of this protein in attenuating the activity of the JNK and p38(MAPK) pathways, and the resulting apoptosis, making MKP-1 a potential target for therapeutic intervention.

JNK signaling in apoptosis

Jun N-terminal kinases or JNKs play a critical role in death receptor-initiated extrinsic as well as mitochondrial intrinsic apoptotic pathways. JNKs activate apoptotic signaling by the upregulation of pro-apoptotic genes through the transactivation of specific transcription factors or by directly modulating the activities of mitochondrial pro- and antiapoptotic proteins through distinct phosphorylation events. This review analyses our present understanding of the role of JNK in apoptotic signaling and the various mechanisms by which JNK promotes apoptosis.

Antioxidant defense in hepatic ischemia-reperfusion injury is regulated by damage-associated molecular pattern signal molecules

Hepatic ischemia-reperfusion (I/R) injury occurs in a variety of clinical settings and generates the release of endogenous noninfectious ligands called damage-associated molecular pattern (DAMP) signal molecules from damaged cells. This study investigates the effect of DAMP molecules released by Kupffer cells (KC) in I/R injury on the expression of liver manganese superoxide dismutase (MnSOD), a key mitochondrial antioxidant enzyme. We show that MnSOD expression levels are increased in rats and remain high for 24 h after 30 min of ischemia. KC were damaged and depleted after I/R, in association with MnSOD upregulation. Causality was established by treatment with gadolinium chloride, known to selectively destroy KC, which also increased MnSOD levels. Recovery from the early damage (6 h) to the liver tissue was evidenced after 24 h. A physiological protective role for MnSOD was also confirmed by the increased susceptibility of MnSOD-knockdown AML-12 hepatocyte cells to I/R-induced cell death. Inhibition of DAMP molecule high-mobility group box-1 activity by injection of neutralizing antibody partially abolished the increase in liver MnSOD after I/R. Direct injection of ATP, to animals or cells, stimulated MnSOD upregulation. Another DAMP molecule, monosodium urate, also induced MnSOD expression in hepatocyte AML-12 and FaO cell cultures. In conclusion, a connection between danger signals and upregulation of the antioxidant defense system is shown here for the first time in the context of I/R liver injury.

Oxidative inactivation of key mitochondrial proteins leads to dysfunction and injury in hepatic ischemia reperfusion

BACKGROUND & AIMS

Ischemia-reperfusion (I/R) is a major mechanism of liver injury following hepatic surgery or transplantation. Despite numerous reports on the role of oxidative/nitrosative stress and mitochondrial dysfunction in hepatic I/R injury, the proteins that are oxidatively modified during I/R damage are poorly characterized. This study was aimed at investigating the oxidatively modified proteins underlying the mechanism for mitochondrial dysfunction in hepatic I/R injury. We also studied the effects of a superoxide dismutase mimetic/peroxynitrite scavenger metalloporphyrin (MnTMPyP) on oxidatively modified proteins and their functions.

METHODS

The oxidized and/or S-nitrosylated mitochondrial proteins from I/R-injured mouse livers with or without MnTMPyP pretreatment were labeled with biotin-N-maleimide, purified with streptavidin-agarose, and resolved by 2-dimensional gel electrophoresis. The identities of the oxidatively modified proteins were determined using mass spectrometric analysis. Liver histopathology, serum transaminase levels, nitrosative stress markers, and activities of oxidatively modified mitochondrial proteins were measured.

RESULTS

Comparative 2-dimensional gel analysis revealed markedly increased numbers of oxidized and S-nitrosylated mitochondrial proteins following hepatic I/R injury. Many key mitochondrial enzymes involved in cellular defense, fat metabolism, energy supply, and chaperones were identified as being oxidatively modified proteins. Pretreatment with MnTMPyP attenuated the I/R-induced increased serum transaminase levels, histologic damage, increased inducible nitric oxide synthase expression, and S-nitrosylation and/or nitration of various key mitochondrial proteins. MnTMPyP pretreatment also restored I/R-induced suppressed activities of mitochondrial aldehyde dehydrogenase, 3-ketoacyl-CoA thiolases, and adenosine triphosphate synthase.

CONCLUSIONS

These results suggest that increased nitrosative stress is critically important in promoting S-nitrosylation and nitration of various mitochondrial proteins, leading to mitochondrial dysfunction with decreased energy supply and increased hepatic injury.

A peptide inhibitor of C-jun N-terminal kinase modulates hepatic damage and the inflammatory response after hemorrhagic shock and resuscitation

Hemorrhage and resuscitation (H/R) leads to phosphorylation of mitogen-activated stress kinases, an event that is associated with organ damage. Recently, a specific, cell-penetrating, protease-resistant inhibitory peptide of the mitogen-activated protein kinase c-JUN N-terminal kinase (JNK) was developed (D-JNKI-1). Here, using this peptide, we tested if inhibition of JNK protects against organ damage after H/R. Male Sprague-Dawley rats were treated with D-JNKI-1 (11 mg/kg, i.p.) or vehicle. Thirty minutes later, rats were hemorrhaged for 1 h to a MAP of 30 to 35 mmHg and then resuscitated with 60% of the shed blood and twice the shed blood volume as Ringer lactate. Tissues were harvested 2 h later. ANOVA with Tukey post hoc analysis or Kruskal-Wallis ANOVA on ranks, P < 0.05, was considered significant. c-JUN N-terminal kinase inhibition decreased serum alanine aminotransferase activity as a marker of liver injury by 70%, serum creatine kinase activity by 67%, and serum lactate dehydrogenase activity by 60% as compared with vehicle treatment. The histological tissue damage observed was blunted after D-JNKI-1 pretreatment both for necrotic and apoptotic cell death. Hepatic leukocyte infiltration and serum IL-6 levels were largely diminished after D-JNKI-1 pretreatment. The extent of oxidative stress as evaluated by immunohistochemical detection of 4-hydroxynonenal was largely abrogated after JNK inhibition. After JNK inhibition, activation of cJUN after H/R was also reduced. Hemorrhage and resuscitation induces a systemic inflammatory response and leads to end-organ damage. These changes are mediated, at least in part, by JNK. Therefore, JNK inhibition deserves further evaluation as a potential treatment option in patients after resuscitated blood loss.

Mitochondrial permeability transition in liver ischemia and reperfusion: role of c-Jun N-terminal kinase 2

The mitochondrial permeability transition (MPT) mediates hepatic necrosis after ischemia and reperfusion (I/R). Here, we studied the role of c-Jun N-terminal kinase 2 (JNK2) in MPT-induced liver injury. Wildtype (WT) and JNK2 knockout (KO) mice underwent 70% liver ischemia for 1 hr followed by reperfusion for 8 hr, after which hepatocyte injury and animal survival was assessed. Compared with WT, JNK2 KO mice had 38% less alanine transaminase release and 39% less necrosis by histology. Survival out to 14 days was also greater in JNK2 KO mice (57% vs. 11%), and overall Kaplan-Meier survival was improved. No difference in apoptosis was observed. Intravital multiphoton microscopy of potential-indicating rhodamine 123 after reperfusion revealed depolarized mitochondria in 82% of WT hepatocytes, which decreased to 43% in JNK2 KO hepatocytes. In conclusion, JNK2 contributes to hepatocellular injury and death after I/R in association with increased mitochondrial dysfunction via the MPT.

c-Jun N-Terminal Kinase Signaling Inhibitors Under Development

Targeting protein kinases has been active area in drug discovery. The c-Jun N-terminal kinases (JNKs) have also been target for development of novel therapy in various diseases, since the roles of JNK signaling in pathological conditions were revealed in studies using jnk-deficient mice. Small molecule inhibitors and peptide inhibitors are identified for therapeutic intervention of JNK signaling pathway. SP-600125, an anthrapyrazole small molecule inhibitor for JNK with high potency and selectivity has been widely used for dissecting JNK signaling pathway. CC-401 is the first JNK inhibitor that went into clinical trial for inflammation and leukemia. Inhibitor for mixed lineage kinase (MLK), CEP-1347 also negatively regulates JNK signaling, and tried for potential use in Parkinson's disease. Cell-permeable peptide inhibitor D-JNKI-1 is being developed for the treatment of hearing loss. The current status of these JNK inhibitors and safety issue is discussed in the minireview.

Inhibition of intestinal ischemia/repurfusion induced apoptosis and necrosis via down-regulation of the NF-kB, c-Jun and caspace-3 expression by epigallocatechin-3-gallate administration

Intestinal ischemia/reperfusion (I/R) produces reactive oxygen species (ROS) activating signal transduction and apoptosis. The aim of this study was to evaluate the effect of (-)-epigallocatechin-3-gallate (EGCG) administration in inhibition of apoptosis by attenuating the expression of NF-kB, c-Jun and caspace-3 in intestinal I/R. Thirty male wistar rats were used. Group A sham operation, B I/R, C I/R-EGCG 50 mg/kg ip. Intestinal ischemia was induced for 60 min by clamping the superior mesenteric artery. Malondialdehyde (MDA), myeloperoxidase (MPO), light histology, Fragment End Labelling of DNA (TUNEL), immunocytochemistry for NF-kB, c-Jun and caspace-3 analysis in intestinal specimens were performed 120 min after reperfusion. Apoptosis as indicated by TUNEL and Caspace-3, NF-kB and c-Jun was widely expressed in I/R group but only slightly expressed in EGCG treated groups. MDA and MPO showed a marked increase in the I/R group and a significant decrease in the EGCG treated group. Light histology showed preservation of architecture in the EGCG treated group. In conclusion, EGCG pre-treatment is likely to inhibit intestinal I/R-induced apoptosis by down-regulating the expression of NF-kB, c-Jun and caspase-3.

Phosphorylation of Bad at Thr-201 by JNK1 promotes glycolysis through activation of phosphofructokinase-1

The mitogen-activated protein kinase JNK1 suppresses interleukin-3 withdrawal-induced cell death through phosphorylation of the BH3-only pro-apoptotic Bcl-2 family protein Bad at Thr-201. It is unknown whether JNK1 regulates glycolysis, an important metabolic process that is involved in cell survival, and if so, whether the regulation depends on Thr-201 phosphorylation of Bad. Here we report that phosphorylation of Bad by JNK1 is required for glycolysis through activation of phosphofructokinase-1 (PFK-1), one of the key enzymes that catalyze glycolysis. Genetic disruption of Jnk1 alleles or silencing of Jnk1 by small interfering RNA abrogates glycolysis induced by growth/survival factors such as serum or interleukin-3. Proteomic analysis identifies PFK-1 as a novel Bad-associated protein. Although the interaction between PFK-1 and Bad is independent of JNK1, Thr-201 phosphorylation of Bad by JNK1 is required for PFK-1 activation. Thus, our results provide a novel molecular mechanism by which JNK1 promotes glycolysis for cell survival.

JunD protects the liver from ischemia/reperfusion injury by dampening AP-1 transcriptional activation

The AP-1 transcription factor modulates a wide range of cellular processes, including cellular proliferation, programmed cell death, and survival. JunD is a major component of the AP-1 complex following liver ischemia/reperfusion (I/R) injury; however, its precise function in this setting remains unclear. We investigated the functional significance of JunD in regulating AP-1 transcription following partial lobar I/R injury to the liver, as well as the downstream consequences for hepatocellular remodeling. Our findings demonstrate that JunD plays a protective role, reducing I/R injury to the liver by suppressing acute transcriptional activation of AP-1. In the absence of JunD, c-Jun phosphorylation and AP-1 activation in response to I/R injury were elevated, and this correlated with increased caspase activation, injury, and alterations in hepatocyte proliferation. The expression of dominant negative JNK1 inhibited c-Jun phosphorylation, AP-1 activation, and hepatic injury following I/R in JunD-/- mice but, paradoxically, led to an enhancement of AP-1 activation and liver injury in JunD+/- littermates. Enhanced JunD/JNK1-dependent liver injury correlated with the acute induction of diphenylene iodonium-sensitive NADPH-dependent superoxide production by the liver following I/R. In this context, dominant negative JNK1 expression elevated both Nox2 and Nox4 mRNA levels in the liver in a JunD-dependent manner. These findings suggest that JunD counterbalances JNK1 activation and the downstream redox-dependent hepatic injury that results from I/R, and may do so by regulating NADPH oxidases.

CXCL10 regulates liver innate immune response against ischemia and reperfusion injury

We have shown that activation of toll-like receptor 4 (TLR4) and its interferon regulatory factor 3 (IRF3)-dependent downstream signaling pathway are required for the development of liver ischemia/reperfusion injury (IRI). This study focused on the role of TLR4-IRF3 activation pathway products, in particular, chemokine (C-X-C motif) ligand 10 (CXCL10). The induction of CXCL10 by liver IR was rapid (1 hour postreperfusion), restricted (ischemic lobes), and specific (no CXCL9 and CXCL11 induction). Functionally, CXCL10 was critical for IR-induced liver inflammation and hepatocellular injury. CXCL10 knockout (KO) mice were protected from IRI, as evidenced by reduced serum alanine aminotransferase (sALT) levels and preserved liver histological detail. The induction of pro-inflammatory genes, such as tumor necrosis factor alpha (TNF-alpha), interleukin 1beta (IL-1beta), IL-6, and IL-12beta was diminished, whereas the induction of the IL-10 gene remained intact in CXCL10 KO mice, indicating an altered liver response against IR. This was accompanied by selective down-regulation of extracellular signal-regulated kinase (ERK), but intact Jun N-terminal kinase (JNK), activation in the KO IR livers. This altered liver inflammation response was (1) specific to IR, because lipopolysaccharide (LPS) induced a comparable pro-inflammatory response in CXCL10 KO and wild-type (WT) mice; and (2) responsible for liver cytoprotection from IR, because neutralization of IL-10 restored local inflammation and hepatocellular damage.

CONCLUSION

CXCL10 regulates liver inflammation response against IRI, and its deficiency protected livers from IRI by local IL-10-mediated cytoprotection. Targeting CXCL10 may provide a novel therapeutic means to ameliorate liver IRI in clinics.

Recombinant human erythropoietin attenuates hepatic injury induced by ischemia/reperfusion in an isolated mouse liver model

INTRODUCTION

Apoptosis is a central mechanism of cell death following reperfusion of the ischemic liver. Recombinant human erythropoietin (rhEPO) have an important role in the treatment of myocardial ischemia/reperfusion (I/R) injury, by preventing apoptosis. The aim of the study was to investigate the effect of different regimens of rhEPO in preventing apoptosis following I/R-induced hepatic injury.

MATERIAL AND METHODS

Isolated mouse livers were randomly divided into five groups: (1) control group, perfused for the whole study period (105 min); (2) 30-min perfusion followed by 90 min of ischemia and 15 min of reperfusion; (3), (4) and (5) like group 2, but with administration of rhEPO 5,000 units/kg i.p. at 30 min, 24 h, or both 30 min and 24 h respectively, before induction of ischemia. Perfusate liver enzyme levels and intrahepatic caspase-3 activity were measured, and apoptotic cells were identified by morphological criteria, TUNEL assay, and immunohistochemistry for caspase-3. Using immunoblot the expression of the proapoptotic JNK and inhibitor of NFkappaB (IkappaBalpha) were also evaluated. von Willebrand factor (vWF) immunohistochemistry was used as a marker of endothelial cells.

RESULTS

Compared to the I/R livers, all 3 rhEPO pretreated groups showed: a significant reduction in liver enzyme levels (P < 0.05) and intrahepatic caspase-3 activity (P < 0.05), fewer apoptotic hepatocytes (P < 0.05) and positive vWF staining in numerous endothelial cells lining the sinusoids. EPO decreased JNK phosphorylation and the degradation of the inhibitor of NFkappaB (IkappaBalpha) during I/R. There was no added benefit of the multiple- over the single-dose rhEPO regimen.

CONCLUSION

Pretreatment with one dose of rhEPO can attenuate post-I/R hepatocyte apoptotic liver damage. NFkappaB and JNK activation is likely to play a pivotal role in the pathophysiology of I/R hepatic injury and might have a key role in EPO-mediated protective effects. This effect is associated with the increase in sinusoidal vWF immunostaining suggests an additional effect of rhEPO in liver angiogenesis recovery. These findings have important implications for the potential use of rhEPO in I/R injury during liver transplantation.

10th anniversary Inflammation and Immune Diseases Drug Discovery and Development Summit. 20-21 March 2006, New Brunswick, USA

The meeting was hosted by the Strategic Research Institute (SRi) celebrating its 10th anniversary of meetings targeting the inflammatory response. Entitled the 10th International Inflammation and Immune Diseases Drug Discovery and Development World Summit, it was held in New Brunswick, USA on 20-21 March 2006. A composition of keynote sessions and two parallel tracks, the meeting drew on the wide-ranging application of targeting drugs that modulate the immune response and have anti-inflammatory activity in a number of human diseases, including psoriasis, actinic keratosis, allergic dermatitis, rheumatoid and osteoarthritis, systemic lupus erythematosus, asthma and chronic obstructive pulmonary disease. Data were presented supporting all stages of drug discovery from target identification and validation through to lead identification and optimisation to both early- and late-stage clinical development. In addition, a number of enabling technologies were described that supported the identification of potential new therapeutics, for tracking antigen-specific B- and T cells through to the development of an immune response and for the development of novel delivery vehicles as a route to minimise toxicity profiles.

Inhibitors of c-Jun N-terminal kinases: JuNK no more?

The c-Jun N-terminal kinases (JNKs) have been the subject of intense interest since their discovery in the early 1990s. Major research programs have been directed to the screening and/or design of JNK-selective inhibitors and testing their potential as drugs. We begin this review by considering the first commercially-available JNK ATP-competitive inhibitor, SP600125. We focus on recent studies that have evaluated the actions of SP600125 in lung, brain, kidney and liver following exposure to a range of stress insults including ischemia/reperfusion. In many but not all cases, SP600125 administration has proved beneficial. JNK activation can also follow infection, and we next consider recent examples that demonstrate the benefits of SP600125 administration in viral infection. Additional ATP-competitive JNK inhibitors have now been described following high throughput screening of small molecule libraries, but information on their use in biological systems remains limited and thus these inhibitors will require further evaluation. Peptide substrate-competitive ATP-non-competitive inhibitors of JNK have also now been described, and we discuss the recent advances in the use of JNK inhibitory peptides in the treatment of neuronal death, diabetes and viral infection. We conclude by raising a number of questions that should be considered in the quest for JNK-specific inhibitors.

Exogenous biliverdin ameliorates ischemia-reperfusion injury in small-for-size rat liver grafts

OBJECTIVE

This study sought to investigate the protective potential of exogenous biliverdin (BV) for small-for-size rat liver transplants.

METHODS AND RESULTS

We employed a rat orthotopic liver transplantation model using small-for-size grafts. BV (50 mumol/kg, intravenously) given to the recipient immediately before reperfusion increased 7-day survival rates (90% vs 40% in controls) and significantly diminished hepatocyte injury, as compared with a control group. These effects correlated with improved liver function and preserved hepatic architecture. BV adjuvant increased antioxidant ability, suppressed proinflammatory tumor necrosis factor-alpha expression, down-regulated proapoptotic molecules (cytochrome C and caspase-3), and inhibited most apoptotic cells. After reperfusion, there was a significant increase of c-Jun NH(2)-terminal kinase (JNK) activation and AP-1 binding ability. BV treatment effectively repressed JNK/AP-1 activation, indicating that a beneficial effect of BV treatment may be related to suppression of the JNK/AP-1 pathway.

CONCLUSIONS

BV treatment alleviated ischemia-reperfusion injury at least in part via inhibition of the proinflammatory and proapoptotic JNK/AP-1 pathway. Our findings provide a rationale for a novel therapeutic approach using BV to maximize the availability of small-for-size liver grafts.

Mechanisms of drug-induced liver disease

Drug-induced liver injury depends initially on development of hepatocyte stress and cell death, which can be induced directly by parent drugs or by toxic metabolites. Hepatocyte stress can lead to activation of built-in death programs for apoptosis or necrosis. Subsequently, the innate immune system's participation is recruited. The interplay between proinflammatory and anti-inflammatory components of innate immune system determines the outcome of drug-induced liver injury. Both environmental factors and genetic differences in cellular responses to stress and the innate immune response may account for different susceptibilities between individuals to drug-induced liver injury.