Protein kinase activation by warm and cold hypoxia- reoxygenation in primary-cultured rat hepatocytes-JNK(1)/SAPK(1) involvement in apoptosis

Human Antigen R (HuR): A Regulator of Heme Oxygenase-1 Cytoprotection in Mouse and Human Liver Transplant Injury

BACKGROUND AND AIMS

Ischemia-reperfusion injury (IRI) represents a risk factor in liver transplantation (LT). We have shown that overexpression of heme oxygenase-1 (HO-1) mitigates hepatic IRI in LT recipients. Here, we hypothesized that human antigen R (HuR), the stabilizer of adenylate-uridylate (AU)-rich mRNAs, is required for hepatoprotection in LT.

APPROACH AND RESULTS

In an experimental arm, HuR/HO-1 protein expression was correlated with hepatic IRI phenotype. In an in vitro inflammation mimic model of hepatic warm IRI, induction of HuR/HO-1 and cytoplasmic localization following cytokine preconditioning were detected in primary hepatocyte cultures, whereas HuR silencing caused negative regulation of HO-1, followed by enhanced cytotoxicity. Using the HuR-inhibitor, we showed that HuR likely regulates HO-1 through its 3' untranslated region and causes neutrophil activation (CD69+/lymphocyte antigen 6 complex locus G [Ly6-G]). HuR silencing in bone marrow-derived macrophages decreased HO-1 expression, leading to the induction of proinflammatory cytokines/chemokines. RNA sequencing of HuR silenced transcripts under in vitro warm IRI revealed regulation of genes thymus cell antigen 1 (THY1), aconitate decarboxylase 1 (ACOD1), and Prostaglandin E Synthase (PTGES). HuR, but not hypoxia-inducible protein alpha, positively regulated HO-1 in warm, but not cold, hypoxia/reoxygenation conditions. HuR modulated HO-1 in primary hepatocytes, neutrophils, and macrophages under reperfusion. Adjunctive inhibition of HuR diminished microtubule-associated proteins 1A/1B light chain 3B (LC3B), a marker for autophagosome, under HO-1 regulation, suggesting a cytoprotective mechanism in hepatic IR. In a clinical arm, hepatic biopsies from 51 patients with LT were analyzed at 2 hours after reperfusion. Graft HuR expression was negatively correlated with macrophage (CD80/CD86) and neutrophil (Cathepsin G) markers. Hepatic IRI increased HuR/HO-1 expression and inflammatory genes. High HuR-expressing liver grafts showed lower serum alanine aminotransferase/serum aspartate aminotransferase levels and improved LT survival.

CONCLUSIONS

This translational study identifies HuR as a regulator of HO-1-mediated cytoprotection in sterile liver inflammation and a biomarker of ischemic stress resistance in LT.

Interleukin 18 binding protein ameliorates ischemia/reperfusion-induced hepatic injury in mice

Inflammation-associated oxidative stress contributes to hepatic ischemia/reperfusion injury (IRI). Detrimental inflammatory event cascades largely depend on activated Kupffer cells (KCs) and neutrophils, as well as proinflammatory cytokines, including tumor necrosis factor α (TNF-α) and interleukin (IL) 18. The aim of our study was to evaluate the effects of IL 18 binding protein (IL 18Bp) in hepatic IRI of mice. Thirty C57BL/6 mice were allocated into 3 groups: sham operation, ischemia/reperfusion (I/R), and I/R with intravenous administration of IL 18Bp. Hepatic ischemia was induced for 30 minutes by Pringle's maneuver. After 120 minutes of reperfusion, mice were euthanized, and the liver and blood samples were collected for histological, immunohistochemical, molecular, and biochemical analyses. I/R injury induced the typical liver pathology and upregulated IL-18 expression in the liver of mice. Binding of IL 18 with IL 18Bp significantly reduced the histopathological indices of I/R liver injury and KC apoptosis. The I/R-induced increase of TNF-α, malondialdehyde, aspartate aminotransferase, and alanine aminotransferase levels was prevented in statistically significant levels because of the pretreatment with IL 18Bp. Likewise, blocking of IL 18 ablated the I/R-associated elevation of nuclear factor kappa B, c-Jun, myeloperoxidase, and IL 32 and the up-regulation of neutrophils and T-helper lymphocytes. Administration of IL 18Bp protects the mice liver from I/R injury by intervening in critical inflammation-associated pathways and KC apoptosis.

Systemic lupus erythematosus patients in the low-latitude plateau of China: altitudinal influences

The current study was to investigate the features of hospitalized patients with systemic lupus erythematosus (SLE) at different altitudes. The correlation between SLE activity and altitudinal variations was also explored. Medical records of 1029 patients were retrospectively reviewed. Activity of SLE in each organ system was recorded using the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI). There was no significant correlation between SLE activity and altitudes (r = 0.003, p = 0.159). Age at onset for SLE patients at high altitudes was significantly younger than that at low and moderate altitudes (p = 0.022 and p = 0.004, respectively). Age at SLE admission at low altitudes was significant older than those at moderate and high altitudes (p = 0.011 and p < 0.001, respectively). Patients at high altitudes had shorter duration from disease onset to admission than those at moderate altitudes (p = 0.009). Incidence of Sm antibodies-positive for resident patients at high altitudes was 36.4%, which were higher than that at moderate altitudes (p = 0.003). We found increasing trends of CNS activity in active patients; immunological and renal activities in inactive patients were correlated with elevated altitudes (p = 0.024, p = 0.004, p = 0.005), while arthritis scores in active patients showed the tendency of decreasing with the rise of elevation (p = 0.002). Hemoglobin level, red blood cell and platelet counts at high altitudes were significantly lower than those at low altitudes (p < 0.05, respectively). There was no significant difference in hemoglobin level between moderate- and low-altitude groups (p > 0.05). No significant difference in platelet counts between moderate- and high-altitude groups was observed (p > 0.05). Our findings suggest that some clinical features, laboratory tests and activity of main organs in SLE are influenced by altitudes. Furthermore, organ activities of active and inactive SLE patients have different patterns of altitudinal variations. These distinctive variations likely reveal that peculiar environmental factors at high altitudes can affect the development of SLE.

Pinocembrin protects human brain microvascular endothelial cells against fibrillar amyloid-β(1-40) injury by suppressing the MAPK/NF-κB inflammatory pathways

Cerebrovascular accumulation of amyloid-β (Aβ) peptides in Alzheimer's disease (AD) may contribute to disease progression through Aβ-induced microvascular endothelial pathogenesis. Pinocembrin has been shown to have therapeutic effects in AD models. These effects correlate with preservation of microvascular function, but the effect on endothelial cells under Aβ-damaged conditions is unclear. The present study focuses on the in vitro protective effect of pinocembrin on fibrillar Aβ₁₋₄₀ (fAβ₁₋₄₀) injured human brain microvascular endothelial cells (hBMECs) and explores potential mechanisms. The results demonstrate that fAβ₁₋₄₀-induced cytotoxicity in hBMECs can be rescued by pinocembrin treatment. Pinocembrin increases cell viability, reduces the release of LDH, and relieves nuclear condensation. The mechanisms of this reversal from Aβ may be associated with the inhibition of inflammatory response, involving inhibition of MAPK activation, downregulation of phosphor-IKK level, relief of IκBα degradation, blockage of NF-κB p65 nuclear translocation, and reduction of the release of proinflammatory cytokines. Pinocembrin does not show obvious effects on regulating the redox imbalance after exposure to fAβ₁₋₄₀. Together, the suppression of MAPK and the NF-κB signaling pathways play a significant role in the anti-inflammation of pinocembrin in hBMECs subjected to fAβ₁₋₄₀. This may serve as a therapeutic agent for BMEC protection in Alzheimer's-related deficits.

Hepatocyte proliferation/growth arrest balance in the liver of mice during E. multilocularis infection: a coordinated 3-stage course

Background

Alveolar echinococcosis (AE) is characterized by the tumor-like growth of Echinococcus (E.) multilocularis. Very little is known on the influence of helminth parasites which develop in the liver on the proliferation/growth arrest metabolic pathways in the hepatocytes of the infected liver over the various stages of infection.

Methodology/Principal Findings

Using Western blot analysis, qPCR and immunohistochemistry, we measured the levels of MAPKs activation, Cyclins, PCNA, Gadd45β, Gadd45γ, p53 and p21 expression in the murine AE model, from day 2 to 360 post-infection. Within the early (day 2–60) and middle (day60–180) stages, CyclinB1 and CyclinD1 gene expression increased up to day30 and then returned to control level after day60; Gadd45β, CyclinA and PCNA increased all over the period; ERK1/2 was permanently activated. Meanwhile, p53, p21 and Gadd45γ gene expression, and caspase 3 activation, gradually increased in a time-dependent manner. In the late stage (day180–360), p53, p21 and Gadd45γ gene expression were significantly higher in infected mice; JNK and caspase 3 were activated. TUNEL analysis showed apoptosis of hepatocytes. No significant change in CyclinE, p53 mRNA and p-p38 expression were observed at any time.

Conclusions

Our data support the concept of a sequential activation of metabolic pathways which 1) would first favor parasitic, liver and immune cell proliferation and survival, and thus promote metacestode fertility and tolerance by the host, and 2) would then favor liver damage/apoptosis, impairment in protein synthesis and xenobiotic metabolism, as well as promote immune deficiency, and thus contribute to the dissemination of the protoscoleces after metacestode fertility has been acquired. These findings give a rational explanation to the clinical observations of hepatomegaly and of unexpected survival of AE patients after major hepatic resections, and of chronic liver injury, necrosis and of hepatic failure at an advanced stage and in experimental animals.

Multiphoton microscopy can visualize zonal damage and decreased cellular metabolic activity in hepatic ischemia-reperfusion injury in rats

Ischemia-reperfusion (I/R) injury is a common occurrence in liver surgery. In orthotopic transplantation, the donor liver is exposed to periods of ischemia and when oxygenated blood is reintroduced to the liver, oxidative stress may develop and lead to graft failure. The aim of this project was to investigate whether noninvasive multiphoton and fluorescence lifetime imaging microscopy, without external markers, were useful in detecting early liver damage caused by I/R injury. Localized hepatic ischemia was induced in rats for 1 h followed by 4 h reperfusion. Multiphoton and fluorescence lifetime imaging microscopy was conducted prior to ischemia and up to 4 h of reperfusion and compared to morphological and biochemical assessment of liver damage. Liver function was significantly impaired at 2 and 4 h of reperfusion. Multiphoton microscopy detected liver damage at 1 h of reperfusion, manifested by vacuolated cells and heterogeneous spread of damage over the liver. The damage was mainly localized in the midzonal region of the liver acinus. In addition, fluorescence lifetime imaging showed a decrease in cellular metabolic activity. Multiphoton and fluorescence lifetime imaging microscopy detected evidence of early I/R injury both structurally and functionally. This provides a simple noninvasive technique useful for following progressive liver injury without external markers.

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.

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.

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.

Attenuation of liver ischemia/reperfusion induced apoptosis by epigallocatechin-3-gallate via down-regulation of NF-kappaB and c-Jun expression

INTRODUCTION

Hepatic ischemia/reperfusion (I/R) activates Kupffer cells and initiates severe oxidative stress with enhanced production of reactive oxygen species (ROS) and tumor necrosis factor-alpha (TNF-alpha). ROS and TNF-alpha mediate the expression of nuclear factors and kinases, activating the signal transduction pathway, and triggering apoptosis. The aim of our study was to evaluate the potential protective effect of (-)-epigallocatechin-3-gallate (EGCG) administration in inhibition of apoptosis by attenuating the expression of NF-kappaB, c-Jun, and caspase-3 in a model of severe hepatic I/R.

MATERIALS AND METHODS

Thirty Wistar rats were allocated into three groups. Sham operation, I/R, and I/R-EGCG 50mg/kg. Hepatic ischemia was induced for 60min by Pringle's maneuver. Malondialdehyde (MDA), myeloperoxidase (MPO), light histology, scanning electron microscopy, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), and immunocytochemistry for NF-kappaB, c-Jun, caspase-3, analysis on liver specimens and aspartate (AST), and alanine (ALT) transferases analysis in serum, were performed 120min after reperfusion.

RESULTS

Apoptosis as indicated by TUNEL and caspase-3 was widely expressed in the I/R group but very limited in the EGCG treated group. Liver was stained positive for NF-kappaB and c-Jun in the I/R group but failed to be stained positive in the EGCG treated group. MDA, MPO, AST, and ALT showed marked increase in the I/R group and significant decrease in EGCG treated group. Significant alterations of liver specimens were observed by light histology and transmission electron microscopy whilst pretreatment with EGCG resulted in parenchymal preservation.

CONCLUSIONS

Administration of EGCG is likely to inhibit I/R-induced apoptosis and protect liver by down-regulating NF-kappaB and c-Jun signal transduction pathways.

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.

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.

Role of ischaemic preconditioning in liver regeneration following major liver resection and transplantation

Liver ischaemic preconditioning (IPC) is known to protect the liver from the detrimental effects of ischaemic-reperfusion injury (IRI), which contributes significantly to the morbidity and mortality following major liver surgery. Recent studies have focused on the role of IPC in liver regeneration, the precise mechanism of which are not completely understood. This review discusses the current understanding of the mechanism of liver regeneration and the role of IPC in this setting. Relevant articles were reviewed from the published literature using the Medline database. The search was performed using the keywords “liver”, “ischaemic reperfusion”, “ischaemic preconditioning”, “regeneration”, “hepatectomy” and “transplantation”. The underlying mechanism of liver regeneration is a complex process involving the interaction of cytokines, growth factors and the metabolic demand of the liver. IPC, through various mediators, promotes liver regeneration by up-regulating growth-promoting factors and suppresses growth-inhibiting factors as well as damaging stresses. The increased understanding of the cellular mechanisms involved in IPC will enable the development of alternative treatment modalities aimed at promoting liver regeneration following major liver resection and transplantation.

Glial-derived neurotrophic factor (GDNF) prevents ethanol (EtOH) induced B92 glial cell death by both PI3K/AKT and MEK/ERK signaling pathways

We investigated the neuroprotective effect of glial-derived neurotrophic factor (GDNF) upon alcohol-exposed B92 cultures, as well as the role of the cytoskeleton and mitogen-activated protein kinase (MAPK) pathways in this effect. Ethanol (EtOH) was added to cultures, either alone or in combination with 30 ng/ml GDNF. Exposure to EtOH (86 and 172 mM; 60 and 120 min) increased the frequency of apoptotic cells identified by nuclear DNA staining with 4,6-diamidino-2-phenylindole (DAPI). Cultures treated with GDNF showed a decrease in ethanol-induced apoptosis. A jun N-terminal kinase (JNK) pathway is activated by EtOH and their pharmacological inhibition (by SP600125) neutralized ethanol-induced apoptosis, suggesting a role for JNK in EtOH neurotoxicity. Immunocytochemically detected phospho-JNK (p-JNK) showed an unusual filamental expression, and localized together with actin stress fibers. Examination of the cytoskeleton showed that EtOH depolymerized actin filaments, inducing p-JNK dissociation and translocation to the nucleus, which suggests that released p-JNK may contribute to glial cell death after EtOH exposure. Treatment with GDNF, in turn, may neutralize the ethanol-induced cell death pathway. Either a phosphatidylinositol 3-kinase (PI3K)/AKT pathway inhibitor (LY294002) or an inhibitor of the extracellular signal-regulated kinase (ERK) 1, 2 pathways (UO126) failed to neutralize GDNF protective effects. However, the simultaneous use of both inhibitors blocked the protective effect of GDNF, suggesting a role for both signaling cascades in the GDNF protection. These findings provide further insight into the mechanism involved in ethanol-induced apoptosis and the neurotrophic protection of glial cells.

Involvement of protein kinase B and mitogen-activated protein kinases in experimental normothermic liver ischaemia-reperfusion injury

BACKGROUND

This study evaluated the role of protein kinase B (PKB), phosphatidylinositol 3-kinase (PI3-K), Bcl-2-associated death protein (BAD) and mitogen-activated protein kinases (MAPKs) in normothermic ischaemia-reperfusion (IR)-induced apoptosis in rat liver.

METHODS

Rats were divided into two groups that received either phosphate-buffered saline (control) or the caspase inhibitor Z-Asp-2,6-dichorobenzoyloxymethylketone (Z-Asp-cmk), injected intravenously 2 min before the induction of 120 min of normothermic liver ischaemia. Liver apoptosis was assessed by the terminal deoxyribonucleotidyltransferase-mediated dUTP nick end labelling (TUNEL) method. PI3-K, PKB, BAD and MAPK activities were measured in ischaemic and non-ischaemic lobes at various times after reperfusion.

RESULTS

The number of TUNEL-positive cells was significantly decreased after pretreatment with Z-Asp-cmk. In controls, PI3-K and PKB activities and BAD phosphorylation were inhibited in ischaemic liver lobes. The MAPKs (extracellular signal-regulated kinases, c-Jun N-terminal kinase and p38) showed different patterns of activation during IR. PKB activity was not modified by pretreatment with Z-Asp-cmk.

CONCLUSION

Induction of apoptosis during IR liver injury might be triggered by inactivation of the antiapoptotic PI3-K-PKB pathway and activation of the proapoptotic MAPKs.

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.

MAPKs are differentially modulated in arctic ground squirrels during hibernation

Hibernating animals are very tolerant of trauma to the central nervous system such that dramatic fluctuations in cerebral blood flow occur during hibernation and arousal without apparent damage. Indeed, it was demonstrated that Arctic ground squirrels (AGS) experience acute and severe systemic hypoxia along with the dramatic fluctuation in cerebral blood flow when the animals are aroused from hibernation. While initial hypotheses concerned protective mechanisms in the hibernating state, recent evidence of sustained elevation of HIF1alpha in euthermic AGS from our laboratory suggests that a preparatory program of protective gene expression is chronically expressed in euthermic AGS. In this study we evaluated potential neuroprotective adaptations by examining the alteration of intracellular MAPK pathways that may be modulated by hypoperfusion/reperfusion in AGS during hibernation and arousal. We found that ERK and JNK are activated in both euthermic and aroused AGS compared to the hibernating group which positively correlated with HIF1alpha levels. The activation of ERK and JNK associated with HIF1alpha may play an important role in mediating neuroprotective adaptations that is essential for successful hibernation. Interestingly, p38 is activated in euthermic AGS but not in aroused AGS, which shows strong correlation with iNOS induction. Therefore, the attenuation of p38 activation and iNOS induction in hibernating and aroused animals may contribute to the attenuation of inflammation that plays important neuroprotective roles during hibernation. Taken together, the differential modulation of the MAPK pathways may be critical for neuroprotection of AGS necessary for fluctuations in oxygen and nutrient delivery during hibernation.

JNK mediates hepatic ischemia reperfusion injury

BACKGROUND/AIMS

Hepatic ischemia followed by reperfusion (I/R) is a major clinical problem during transplantation, liver resection for tumor, and circulatory shock, producing apoptosis and necrosis. Although several intracellular signal molecules are induced following I/R including NF-kappaB and c-Jun N terminal kinase (JNK), their roles in I/R injury are largely unknown. The aim of this study is to assess the role of JNK during warm I/R injury using novel selective JNK inhibitors.

METHODS

Male Wistar rats (200+/-25 g) are pretreated with vehicle or with one of three compounds (CC0209766, CC0223105, and CC-401), which are reversible, highly selective, ATP-competitive inhibitors of JNK. In the first study, rats are assessed for survival using a model of ischemia to 70% of the liver for 90 min followed by 30% hepatectomy of the non-ischemic lobes and then reperfusion. In the second study, rats are assessed for liver injury resulting from 60 or 90 min of ischemia followed by reperfusion with analysis over time of hepatic histology, serum ALT, hepatic caspase-3 activation, cytochrome c release, and lipid peroxidation.

RESULTS

In the I/R survival model, vehicle-treated rats have a 7-day survival of 20-40%, while rats treated with the three different JNK inhibitors have survival rates of 60-100% (P<0.05). The decrease in mortality correlates with improved hepatic histology and serum ALT levels. Vehicle treated rats have pericentral necrosis, neutrophil infiltration, and some apoptosis in both hepatocytes and sinusoidal endothelial cells, while JNK inhibitors significantly decrease both types of cell death. JNK inhibitors decrease caspase-3 activation, cytochrome c release from mitochondria, and lipid peroxidation. JNK inhibition transiently blocks phosphorylation of c-Jun at an early time point after reperfusion, and AP-1 activation is also substantially blocked. JNK inhibition blocks the upregulation of the pro-apoptotic Bak protein and the degradation of Bid.

CONCLUSIONS

Thus, JNK inhibitors decrease both necrosis and apoptosis, suggesting that JNK activity induces cell death by both pathways.

Balance between hypertrophic and hypoxic stimulus in caspase-3 activation during rat heart development

During heart development, cell hyperplasia and hypertrophy are the main mechanisms by which cardiac mass grows. Both these processes along with programmed cell death lead to complete growth and function. In addition, since the establishment of cardiac function depends on the relationship between oxygen supply and demand, we investigated some of the molecular mechanisms at the basis of rat myocardial cell response to hypoxic stress at different times of neonatal life. In particular, the role played by hypertrophic and survival factors like NF-kB and IAP-1 (Inhibiting Apoptosis Protein) and by death factors ASK-1 (Apoptosis Signal Regulating Kinase), JNK/SAPK (Jun-N-Terminal-Kinase/Stress-Activated Protein Kinase) pathways in regulating caspase-3 expression and activity has been evaluated by immunohistochemical and Western blotting analyses, respectively. Level of phosphorylation of IkBalpha and IAP-1 expression were substantial in 8-day-old hypoxic hearts, suggesting the persistence of NF-kB driven hypertrophic signal along with a rescue attempt against hypoxic stress. In contrast, ASK-1 mediated JNK/SAPK activation, regulating Bcl(2) levels, allows Bax homodimerization and caspase-3 activation in the same experimental conditions. Thus, a regulation carried out by NF-kB and JNK/SAPK pathways on caspase-3 activation at day 8 of neonatal life can be suggested as the main factor for the heart 'adaptive' response to hypoxia.

The impact of transient elevation of intra-abdominal pressure on liver regeneration in the rat

Transient increased intra-abdominal pressure (IIAP) due to carbon dioxide insufflation is suspected to cause a form of ischemia-reperfusion injury. Considering this, a study was designed to assess the effect of transient IIAP on liver regeneration in a rat model. Six groups of animals (each n = 6) were studied. While experiments in Group 1 (IIAP+PHR) were subjected to IIAP, following partial hepatic resection (PHR), those in Group 2 (IIAP) experiments were subjected to IIAP. Animals in Group 3 (IR+PHR) were subjected to liver ischemia-reperfusion (IR) following PHR, and those in Group 4 (IR) underwent only IR. Group 5 (PHR) and Group 6 (healthy) served as controls. Blood was taken for assessment of tumor necrosis factor (TNF)-alpha and interleukin (IL)-6 with enzyme-linked immunosorbent assay (ELISA) at day 5 postoperatively. Each rat was then given a lethal injection of pentobarbital. Gravimetric analysis and immunohistochemistry staining for proliferating cell nuclear antigen (PCNA) were used for assessments of liver regeneration. Apoptosis was assessed by immunohistochemical TUNEL index, expressed as the number of positive cells/per total number of cells at the same time. Although mean liver regeneration rates of Group 1 and Group 3 were the same, that of Group 5 was the highest (p = .04). Serum TNF-alpha levels of Group 1 versus Group 3 were 340 pg/ml versus 352 pg/ml. Serum IL-l levels of Group 1 versus Group 3 were 124 pg/ml versus 135 pg/ml. Serum TNl-alpha and IL-6 levels of Group 1 and Group 3 were the same at the first day of surgical procedure (p > .05). Mean serum TNF-alpha levels of Group 5 (387 pg/ml) were significantly higher than those of both Group 1 and Group 3 at 24 h of operation. Serum IL-6 levels of Group 5 (174 pg/ml) at the same time was higher than those of Group 1 and Group 3 at the same time (p = .01). Proliferating cell nuclear antigen indices of Group 1, Group 2, Group 3, Group 4, and Group 6 were the same; however, the mean PCNA-labeling index of Group 5 was higher than those of the others. There were no significant differences between the groups (p > .05). Liver regeneration is suppressed by transient IIAP. However, the effect of IIAP on liver apoptosis needs to be clarified.

Pro- and anti-apoptotic roles of c-Jun N-terminal kinase (JNK) in ethanol and acetaldehyde exposed rat hepatocytes

We have examined the significance of the activation of c-Jun N-terminal kinase (JNK) and p42/44 mitogen-activated protein kinase (MAPK) by ethanol and acetaldehyde in rat hepatocyte apoptosis. Acetaldehyde induced rapid and transient (15 min) activation of p42/44 MAPK followed by activation of JNK, which remained above control up to 1 h. Ethanol activated JNK for up to 4 h. Both ethanol and acetaldehyde caused apoptosis as determined by DNA fragmentation, caspase-3 activation and 2'[4-ethoxyphenyl]-5-[4-methyl-piperazinyl]-2,5'-bi-1H-benzimidazole (Hoechst 33342) staining. Ethanol-induced apoptosis was blocked by JNK inhibitor 1,9-pyrazoloanthrone (SP600125), indicating that JNK activation is pro-apoptotic. In contrast, acetaldehyde-induced apoptosis was not suppressed by this inhibitor. In fact, SP600125 potentiated acetaldehyde-induced apoptosis, suggesting that JNK activation is anti-apoptotic. Inhibition of p42/44 MAPK by MAPK kinase (MKK1) inhibitor, 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene (U0126), potentiated apoptosis by acetaldehyde or ethanol, suggesting anti-apoptotic role of p42/44 MAPK. The activation of JNK by ethanol or acetaldehyde was insensitive to the genistein (tyrosine kinase inhibitor), GF109203X (2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl)maleimide, protein kinase C [PKC] inhibitor) and N-acetylcysteine (N-AC) (antioxidant), whereas p42/44 MAPK activation by acetaldehyde was inhibited by genistein and GF109203X. Furthermore, p42/44 MAPK activation is not necessary for the JNK activation. In summary, transient activation of JNK by acetaldehyde is anti-apoptotic, whereas sustained activation of JNK by ethanol is pro-apoptotic. The activation of p42/44 MAPK appears to be anti-apoptotic for both ethanol and acetaldehyde. Thus, JNK activation by ethanol and acetaldehyde can be both pro- and anti-apoptotic in hepatocytes.

Hypoxia tolerance in mammalian heterotherms

Heterothermic mammals tolerate severe hypoxia, as well as a variety of central nervous system insults, better than homeothermic mammals. Tolerance to hypoxia may stem from adaptations associated with the ability to survive hibernation and periodic arousal thermogenesis. Here, we review evidence and mechanisms of hypoxia tolerance during hibernation, euthermy and arousal in heterothermic mammals and consider potential mechanisms for regenerative-like processes, such as synaptogenesis, observed within hours of hypoxic stress associated with arousal thermogenesis.

Cell apoptosis and regeneration of hepatocellular carcinoma after transarterial chemoembolization

AIM: To evaluate whether cell apoptosis and regeneration were existed in normal liver cells adjacent to carcinoma after transarterial chemoembolization (TACE).

METHODS: Fifty rabbits with hepatic carcinoma were divided into 5 groups at random: group A (control group), groups B and C (TACE treatment groups), groups D and E (partial hepatectomy groups). There were 10 rabbits in each group. Rabbits in groups B-E were treated by transarterial chemoembolization (TACE) and partial hepatectomy (PH) respectively. The changes of S-phase cell fraction (SPF), proliferation index (PI) and cell apoptosis in the normal liver tissue were determined with flow cytometry (FCM) after operations on the first and third days. We determined the mitosis index (MI) with histo-pathological method and the apoptosis index (AI) with TUNEL method at the same time.

RESULTS: Twenty-four hours after operations, compared with control group, the rabbits in TACE group had much higher index of SPF, PI and MI (MI: t = 4.89, P < 0.001; SPF: t = 5.27, P < 0.001; PI: t = 4.87, P < 0.001). Moreover, the proliferation of liver cells in TACE group was much weaker than that of the cells treated by partial hepatectomy, and the differences were significant (MI: t = 7.02, P < 0.001; SPF: t = 4.06, P < 0.001; PI: t = 2.70, P < 0.05). Seventy-two h after operations, FCM showed a small sub-G1 peak in TACE group and PH group, compared with the control group, but there was no difference between them (t = 0.41, P > 0.05). TACE showed that AI in the treated rabbits was higher than that in control group (t = 3.07, P < 0.05), and there were no differences between TACE group and PH group, either (t = 0.93, P > 0.05).

CONCLUSION: Cell apoptosis and regeneration exist in rabbit liver tissues after TACE in some degree, which may be associated with the selective embolization of iodised oil, chemotherapeutic drug and free radical damage.

MAP kinase signaling in diverse effects of ethanol

Chronic ethanol abuse is associated with liver injury, neurotoxicity, hypertension, cardiomyopathy, modulation of immune responses and increased risk for cancer, whereas moderate alcohol consumption exerts protective effect on coronary heart disease. However, the signal transduction mechanisms underlying these processes are not well understood. Emerging evidences highlight a central role for mitogen activated protein kinase (MAPK) family in several of these effects of ethanol. MAPK signaling cascade plays an essential role in the initiation of cellular processes such as proliferation, differentiation, development, apoptosis, stress and inflammatory responses. Modulation of MAPK signaling pathway by ethanol is distinctive, depending on the cell type; acute or chronic; normal or transformed cell phenotype and on the type of agonist stimulating the MAPK. Acute exposure to ethanol results in modest activation of p42/44 MAPK in hepatocytes, astrocytes, and vascular smooth muscle cells. Acute ethanol exposure also results in potentiation or prolonged activation of p42/44MAPK in an agonist selective manner. Acute ethanol treatment also inhibits serum stimulated p42/44 MAPK activation and DNA synthesis in vascular smooth muscle cells. Chronic ethanol treatment causes decreased activation of p42/44 MAPK and inhibition of growth factor stimulated p42/44 MAPK activation and these effects of ethanol are correlated to suppression of DNA synthesis, impaired synaptic plasticity and neurotoxicity. In contrast, chronic ethanol treatment causes potentiation of endotoxin stimulated p42/44 MAPK and p38 MAPK signaling in Kupffer cells leading to increased synthesis of tumor necrosis factor. Acute exposure to ethanol activates pro-apoptotic JNK pathway and anti-apoptotic p42/44 MAPK pathway. Apoptosis caused by chronic ethanol treatment may be due to ethanol potentiation of TNF induced activation of p38 MAPK. Ethanol induced activation of MAPK signaling is also involved in collagen expression in stellate cells. Ethanol did not potentiate serum stimulated or Gi-protein dependent activation of p42/44 MAPK in normal hepatocytes but did so in embryonic liver cells and transformed hepatocytes leading to enhanced DNA synthesis. Ethanol has a 'triangular effect' on MAPK that involve direct effects of ethanol, its metabolically derived mediators and oxidative stress. Acetaldehyde, phosphatidylethanol, fatty acid ethyl ester and oxidative stress, mediate some of the effects seen after ethanol alone whereas ethanol modulation of agonist stimulated MAPK signaling appears to be mediated by phosphatidylethanol. Nuclear MAPKs are also affected by ethanol. Ethanol modulation of nuclear p42/44 MAPK occurs by both nuclear translocation of p42/44 MAPK and its activation in the nucleus. Of interest is the observation that ethanol caused selective acetylation of Lys 9 of histone 3 in the hepatocyte nucleus. It is plausible that ethanol modulation of cross talk between phosphorylation and acetylations of histone may regulate chromatin remodeling. Taken together, these recent developments place MAPK in a pivotal position in relation to cellular actions of ethanol. Furthermore, they offer promising insights into the specificity of ethanol effects and pharmacological modulation of MAPK signaling. Such molecular signaling approaches have the potential to provide mechanism-based therapy for the management of deleterious effects of ethanol or for exploiting its beneficial effects.

Bile acids up-regulate death receptor 5/TRAIL-receptor 2 expression via a c-Jun N-terminal kinase-dependent pathway involving Sp1

Bile acids up-regulate death receptor 5 (DR5)/TRAIL-receptor 2 (TRAIL-R2) expression thereby sensitizing hepatocytes to TRAIL-mediated apoptosis. However, the precise mechanism by which bile acids enhance DR5/TRAIL-R2 expression is unknown. Although several bile acids enhanced DR5/TRAIL-R2 expression, deoxycholic acid (DCA) was the most potent. DCA stimulated JNK activation and the JNK inhibitor SP600125 blocked DCA-induced DR5/TRAIL-R2 mRNA and protein expression. Reporter gene analysis identified a 5'-flanking region containing two Sp1 binding sites within the DR5/TRAIL-R2 promoter as bile acid responsive. Sp1 binding to one of the two sites was enhanced by DCA treatment as evaluated by electrophoretic mobility shift assays and chromatin immunoprecipitation studies. JNK inhibition with SP600125 also blocked binding of Sp1 to the DR5/TRAIL-R2 promoter. Finally, point mutations of the Sp1 binding site attenuated promoter activity. In conclusion, Sp1 is a bile acid-responsive transcription factor that mediates DR5/TRAIL-R2 gene expression downstream of JNK.

Atrial natriuretic peptide preconditioning protects against hepatic preservation injury by attenuating necrotic and apoptotic cell death

BACKGROUND/AIMS

Preconditioning of livers with the atrial natriuretic peptide (ANP) markedly reduces hepatic ischemia-reperfusion injury. Aim of this study was to characterize the influence of ANP preconditioning on necrotic and apoptotic cell death and on proliferation.

METHODS

Rat livers were perfused with Krebs-Henseleit buffer with or without ANP or its second messenger analogue 8-Bromo cyclic guanosine monophosphate (8-Br cGMP) for 20 min, stored in cold University of Wisconsin solution (24 h), and reperfused for up to 120 min. Apoptosis and necrosis were determined using biochemical and morphological criteria, proliferation was assessed by Ki67 histochemistry.

RESULTS

Apoptosis peaked after 24 h of cold ischemia. Preconditioning with both ANP and 8-Br-cGMP significantly reduced caspase-3-like activity and the number of triphosphate nick-end labelling-positive cells. Reduction of apoptosis was significant for hepatocytes, but not for endothelial cells. After ischemia, degenerative cell changes were clearly reduced in ANP pretreated livers. After reperfusion, ANP preconditioning led to a significant reduction of necrotic hepatocytes and endothelial cells in periportal zones. Cell proliferation was not affected by preconditioning.

CONCLUSIONS

ANP reduces necrotic and apoptotic cell death without affecting the proliferation status. The protection takes place mainly in the periportal area and seems to be most prominent against necrosis of hepatocytes and endothelial cells during reperfusion.

Rat liver ischemia-reperfusion-induced apoptosis and necrosis are decreased by FK506 pretreatment

The aim of this study was to demonstrate that tacrolimus (FK506) has a hepatoprotective effect by reducing ischemia-reperfusion-induced apoptosis and necrosis, both of which lead to post-surgical liver dysfunction. An ischemia-reperfusion model and primary cultured rat hepatocytes subjected to hypoxic and reoxygenation phases, mimicking the surgical process, were used. c-Jun N-terminal kinase 1/stress-activated protein kinase 1 (JNK1/SAPK1) activation leads to caspase 3 activation, a trigger of apoptosis. The activation status of JNK1/SAPK1 was evaluated by immunoprecipitation or Western-blotting experiments. Apoptosis was assessed by measuring caspase activation and by TUNEL (terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate-biotin nick-end labeling) reaction. Necrosis was assessed histologically. Tacrolimus improved the survival rate of rats subjected to ischemia-reperfusion. After FK506 pretreatment, the liver necrosis rate was reduced, and ischemia-reperfusion-induced JNK1/SAPK1 activation and apoptosis were significantly decreased. In hypoxia-reoxygenation-subjected hepatocytes, tacrolimus reduced JNK1/SAPK1 and caspase 3 activation. In the liver, tacrolimus prevented ischemia-reperfusion-induced apoptosis and necrosis.

The activation of c-Jun NH2-terminal kinase (JNK) by DNA-damaging agents serves to promote drug resistance via activating transcription factor 2 (ATF2)-dependent enhanced DNA repair

The activating transcription factor 2 (ATF2) is a member of the ATF/cAMP-response element-binding protein family of basic-leucine zipper proteins involved in cellular stress response. The transcription potential of ATF2 is enhanced markedly by NH2-terminal phosphorylation by c-Jun NH2-terminal kinase (JNK) and mediates stress responses including DNA-damaging events. We have observed that four DNA-damaging agents (cisplatin, actinomycin D, MMS, and etoposide), but not the cisplatin isomer, transplatin, which does not readily damage DNA, strongly activate JNK, p38, and extracellular signal-regulated kinase (ERK), and strongly increase phosphorylation and ATF2-dependent transcriptional activity. Selective inhibition studies with PD98059, SB202190, SP600125, and the dominant negative JNK indicate that activation of JNK but not p38 kinase or ERK kinase is required for the phosphorylation and transcriptional activation of ATF2. Stable expression of ATF2 in human breast carcinoma BT474 cells increases transcriptional activity and confers resistance to the four DNA-damaging agents, but not to transplatin. Conversely, stable expression of a dominant negative ATF2 (dnATF2) quantitatively blocks phosphorylation of endogenous ATF2 leading to a marked decrease in transcriptional activity by endogenous ATF2 and a markedly increased sensitivity to the four agents as judged by decreased cell viability. Similarly, application of SB202190 at 50 micro m or SP600125 inhibited JNK activity, blocked transactivation, and sensitized parental cells to the four DNA-damaging drugs. Moreover, the wild type ATF2-expressing clones exhibited rapid DNA repair after treatment with the four DNA-damaging agents but not transplatin. Conversely, expression of dnATF2 quantitatively blocks DNA repair. These results indicate that JNK-dependent phosphorylation of ATF2 plays an important role in the drug resistance phenotype likely by mediating enhanced DNA repair by a p53-independent mechanism. JNK may be a rational target for sensitizing tumor cells to DNA-damaging chemotherapy agents.

The protective effect of N-acetylcysteine on apoptotic lung injury in cecal ligation and puncture-induced sepsis model

Apoptotic loss of parenchymal cells may lead to organ dysfunctions in critically ill patients with septic states. As an antioxidant, the protective effects of N-acetylcysteine (NAC) are documented in many experimental and clinical studies. In this experimental study, we investigated the role of chronically used NAC in septic lung injury on a cecal ligation and puncture (CLP) model. To evaluate this, 30 male Wistar rats were randomly divided into four groups as sham (n = 7), CLP (n = 8), sham + NAC (n = 7) and CLP + NAC (n = 8) groups. NAC was administered 150 mg kg(-1) day through intramuscular route beginning 6 h after the operations and lasting for a period of 1 week. One week later, histopathology and epithelial apoptosis were assessed by hematoxylin-eosin and immunohistochemically by M30 and caspase 3 staining to demonstrate septic lung injury. Additionally, lung tissue myeloperoxidase (MPO) activity, malondialdehyde (MDA), and nitrite/nitrate levels were measured. The MPO activity and MDA levels in lung homogenates were found to be increased in CLP group and the administration of NAC prevented their increase significantly (P < 0.05). However, there were no significant differences among the groups regarding nitrite/nitrate levels. The number of apoptotic cells was significantly lower in CLP+NAC group than CLP group, and this finding was supported by M30 and caspase 3 expression in lung (P < 0.05). Lung histopathology was also protected by NAC in CLP-induced sepsis. In conclusion, the chronic use of NAC inhibited MPO activity and lipid peroxidation, which resulted in reduction of apoptosis in lung in this CLP model. Because lung tissue nitrite/nitrate levels did not change significantly, organs other than the lungs may be responsible for producing the increased nitric oxide during sepsis. The chronic use of NAC needs further investigation for its possible antiapoptotic potential in septic states besides its documented antioxidant and antiinflammatory effects.

Low levels of glutathione peroxidase 1 activity in selenium-deficient mouse liver affect c-Jun N-terminal kinase activation and p53 phosphorylation on Ser-15 in pro-oxidant-induced aponecrosis

Low levels of hepatic selenium (Se)-dependent glutathione peroxidase 1 (GPX1) activity have been shown to protect against oxidative liver injury in Se-deficient mice. The objective of the present study was to determine if the GPX1 protection was associated with phosphorylations of c-Jun N-terminal kinase (JNK) and p53 on Ser-15, two key signalling events in oxidative-stress-mediated cell death. Both Se-deficient GPX1 knockout (GPX1(-/-)) and wild-type (WT) mice ( n =64) were pretreated with an intraperitoneal injection of Se (as sodium selenite, 50 microg/kg body weight) 6 h before an intraperitoneal injection of paraquat (12.5 mg/kg). Liver aponecrosis, a mixed form of cell death sharing apoptosis and necrosis, was induced by paraquat in both groups of mice. However, its appearance was remarkably delayed and the severity was decreased by the repletion of hepatic GPX1 activity to <4% of the normal level by the Se injection in the WT mice, compared with that in the GPX1(-/-) mice. Consistently, the WT mice had lower levels of hepatic phospho-JNK, p53 and phospho-p53 (Ser-15) when compared with the GPX1(-/-) mice at 1-10 h after paraquat injection. Incubating liver homogenates with antibodies raised against JNK or phospho-JNK resulted in co-immunoprecipitation of phospho-p53 (Ser-15), and the amounts of the precipitated phospho-p53 were greater in the GPX1(-/-) mice when compared with that in the WT mice. The co-precipitated complex by the anti-phospho-JNK antibody was capable of phosphorylating intrinsic or extrinsic p53 on Ser-15. In conclusion, phospho-JNK may catalyse phosphorylation of p53 on Ser-15 in Se-deficient mouse liver under moderate oxidative stress, and attenuation of that cascade by low levels of GPX1 activity is associated with its protection against the pro-oxidant-induced liver aponecrosis.

Low-dose TNF-alpha protects against hepatic ischemia-reperfusion injury in mice: implications for preconditioning

Tumor necrosis factor alpha (TNF-alpha) is implicated in the pathogenesis of hepatic ischemia reperfusion injury but can also prime hepatocytes to enter the cell cycle. Ischemic preconditioning protects against ischemia-reperfusion (IR) liver injury and is associated with activation of nuclear factor kappaB (NF-kappaB) and cell cycle entry. We examined the pattern of TNF-alpha release during hepatic IR in the presence or absence of ischemic preconditioning, and we tested whether a single low-dose injection of TNF could mimic the biologic effects of ischemic preconditioning. In naïve mice, hepatic and plasma levels of TNF-alpha rose during hepatic ischemia, reaching high levels after 90 minutes; values remained elevated during reperfusion until 44 hours. Following the ischemic preconditioning stimulus, there was an early rise in hepatic and serum TNF-alpha levels, but, during a second prolonged ischemic interval peak, TNF-alpha values were lower than in naïve mice and declined to negligible levels by 2 hours reperfusion. An injection with 1 microg or 5 microg/kg body weight TNF-alpha 30 minutes prior to hepatic IR substantially reduced liver injury determined by liver histology and serum alanine aminotransferase (ALT) levels. As in ischemic preconditioning, TNF-alpha pretreatment activated NF-kappaB DNA binding, STAT3, cyclin D1, cyclin-dependent kinase 4 (cdk4) expression, and cell cycle entry, determined by proliferating cell nuclear antigen (PCNA) staining of hepatocyte nuclei. In conclusion, the hepatoprotective effects of "preconditioning" can be simulated by TNF-alpha injection, which has identical downstream effects on cell cycle entry. We propose that transient increases in TNF-alpha levels may substitute for, as well as, mediate the hepatoprotective effects of ischemic preconditioning against hepatic IR injury.

Novel function of rare catechin, epigallocatechin-3-(3″-O-methyl)gallate, against cold injury in primary rat hepatocytes

Epigallocatechin-3-(3''-O-methyl)gallate (EGCg-3''-OMe) is a rare component in green tea leaf and its bioactivity is hardly known. In this paper, we report that EGCg-3''-OMe has the function for cold preservation of primary rat hepatocytes. Confluent primary cultured hepatocytes were suspended in a storage solution, culture medium or cell banker (CB). EGCg-3''-OMe was tested as a supplement in the storage solution together with a general cryoprotectant, dimethylsulfoxide (DMSO). After 24 h cold preservation of cells at 4 degrees C followed by 1 h rewarming, cell viability and urea-synthesizing activity, one of the most important liver functions, were measured. EGCg-3''-OMe dose-dependently maintained cell viability and this effect was equal to that of a commercial CB at the highest concentration. Cell viability was also maintained after a further 24 h incubation at 37 degrees C of the cold-preserved hepatocytes. Conversely, urea-synthesizing activity was dose-dependently reduced by EGCg-3''-OMe. Cell protection by EGCg-3''-OMe due to the decrease in metabolic activity in cold-preserved cells was suggested. The decreased hepatic function of cells caused by EGCg-3''-OMe was rescued after a further 24 h incubation of cells at 37 degrees C.

A scientist revisits the atrophy-hypertrophy complex: hepatic apoptosis and regeneration

In 1898, Cantlie demonstrated his deep insight into the AHC when he wrote. "It is theoretically possible to tie the vessels of one side at the gate of the liver...leaving the other side to do the work. That one-half of the liver can hypertrophy, so as to perform the function of the whole, is attested by pathological study...I commend this subject to all those who are working on the surgery of the liver; and I believe that if, in the hands of future observers, the statements I have made receive closer investigation, surgery of the liver will be advanced a step." More than 100 years later, his foresight is coming to fruition, but the understanding of the AHC remains rudimentary. Further insight into the cellular and molecular mechanisms that initiate hepatocyte replication after contralateral atrophy may allow the development of novel therapeutic treatments or adjuncts.

Role of temperature on protein and mRNA cytochrome P450 3A (CYP3A) isozymes expression and midazolam oxidation by cultured rat precision-cut liver slices

The cytochrome P450 3A (CYP3A)-mediated midazolam oxidation was studied in rat precision-cut liver slices (PCLS) maintained for 20hr at 4, 20 and 37 degrees, and further incubated for 8hr at 37 degrees. Either at 4 or 20 degrees, midazolam was oxidised by PCLS at similar rates to that observed in freshly cut slices. Moreover, PCLS kept a regioselectivity since 4-hydroxylation was more important than 1'-hydroxylation. Conversely, PCLS totally lost their capacity to oxidise midazolam after 20hr at 37 degrees, and both CYP3A2 protein and mRNA were not detected. CYP3A1 protein was unaffected by a temperature of 37 degrees but its mRNA was totally lost. By blocking transcription with actinomycin D, the decay of both CYP3A mRNAs followed the same profile at either 20 or 37 degrees, indicating that temperature affected the CYP3A2 protein stability. Cell functionality was not involved in such an impairment since the low values of ATP, GSH and protein synthesis rates observed at 4 and 20 degrees were rapidly restored, when PCLS were further incubated at 37 degrees. The use of rat supersomes expressing either CYP3A1 or CYP3A2, strongly supported the hypothesis that 4-hydroxymidazolam was mainly formed by CYP3A2. These results suggest that: (1) CYP3A1 protein is constitutive and largely expressed in rat liver slices; (2) regioselective midazolam oxidation appears to be mainly CYP3A2 dependent; and (3) since CYP3A isoforms have similar half-lives (about 10-14hr), the loss of CYP3A2 protein at 37 degrees might be due to a selective targeting (phosphorylation ?) leading to proteolytic disposal by the proteasome.

Stimulation of p38 MAPK by hormal preconditioning with atrial natriuretic peptide

AIM: Stress-activated signaling pathways responsible for hepatic ischemia reperfusion injury and their modulation by protective interventions are widely unknown. Preconditioning of rat livers with Atrial Natriuretic Peptide (ANP) attenuates ischemia reperfusion injury (Gerbes et al^[21]Hepatology 1998, 28:1309-1317). Since ANP has recently been shown to be a regulator of the p38 MAPK pathway in endothelial cells (Kiemer et al^[25]Circ Res 2002, 90:874-881), aim of this study was to investigate activities of MAPK during ischemia and reperfusion and effects of ANP on MAPK.

METHODS: Rat livers were perfused with KH-buffer in the presence or absence of ANP for 20 min, kept in cold UW solution for 24 h, and reperfused for up to 120 min. Activities of p38 MAPK and JNK was determined by in vitro phosphorylation assays using MBP and c-jun as substrates. After SDS/PAGE electrophoresis, gels were quantified by phosphorimaging.

RESULTS: Activity of p38 MAPK in control organs decreased in the course of ischemia and reperfusion by 85%, whereas ANP increased p38 activity by up to 30-fold. JNK activation of control livers increased in the course of ischemia and reperfusion by up to three-fold. This increase in JNK activity was slightly elevated in ANP preconditioned organs.

CONCLUSION: This work represents a systematic investigation of MAPK activation during liver ischemia and reperfusion. Employing ANP, for the first time a pharmacological approach to modulate these central signal transduction molecules is presented.

Hepatic ischemic preconditioning in mice is associated with activation of NF-kappaB, p38 kinase, and cell cycle entry

A brief period of hepatic ischemia protects the liver against subsequent ischemia-reperfusion (IR) injury, but the mechanism of such preconditioning is poorly understood. We examined whether preconditioning activated nuclear factor kappa B (NF-kappaB), the stress-activated protein kinases (SAPK), c-Jun N-terminal kinase-1 (JNK-1) and p38, and entry into the cell cycle. We used a murine model of partial hepatic ischemia. Preconditioning was performed by clamping the vasculature for 2 to 20 minutes, and allowing reperfusion for 10 minutes before 90-minute ischemia or IR. As assessed by serum alanine aminotransferase (ALT) levels and liver histology, preconditioning periods of 5 and 10 minutes were highly protective against IR injury, whereas 2-, 15-, and 20-minute intervals were ineffective. Preconditioning was associated with entry of hepatocytes into the cell cycle within 2 hours of subsequent IR, as indicated by proliferating cell nuclear antigen (PCNA) nuclear staining, induction of cyclin D1 and numerous mitotic figures; in the absence of preconditioning, such changes were not seen until 24 hours. Preconditioning increased nuclear binding of NF-kappaB within 30 minutes of the subsequent ischemic interval, paralleled by degradation of inhibitory (binding) protein for NF-kappaB (IkappaBalpha). Ischemic preconditioning also activated p38 kinase and JNK-1, which are known to converge on cyclin D1 regulation. The protective effect of the preconditioning regimen was more closely associated with p38 kinase than JNK-1 activation. In conclusion, the hepatoprotective effects of ischemic preconditioning are associated with activation of NF-kappaB and SAPKs that are associated with entry of hepatocytes into the cell cycle, a critical biological effect that favors survival of the liver against ischemic and IR injury.

Temporal activation of p42/44 mitogen-activated protein kinase and c-Jun N-terminal kinase by acetaldehyde in rat hepatocytes and its loss after chronic ethanol exposure

Several cell-damaging effects of ethanol are due to its major metabolite acetaldehyde but its mechanisms are not known. We have studied the effect of acetaldehyde on p42/44 mitogen-activated protein kinase (MAPK) and p46/p54 c-Jun N-terminal kinase (JNK 1/2) in rat hepatocytes. Acetaldehyde caused peak activation of p42/44 MAPK at 10 min followed by JNK activation at 1 h. These responses were acetaldehyde dose-dependent (0.2-5 mM). There was a consistently higher activation of p46 JNK than p54 JNK. Ethanol also activated both p42/44 MAPK and p46/p54 JNK. The activation of JNK by ethanol, however, was not significantly affected by treatment of hepatocytes with 4-methylpyrazole, an alcohol dehydrogenase inhibitor. Cells treated with 200 mM ethanol for 1 h accumulated 0.35 +/- 0.02 mM acetaldehyde, but the magnitude of JNK activation was greater than that expected with 0.35 mM acetaldehyde. Thus, ethanol-activated JNK may be both acetaldehyde-dependent and -independent. The activation of JNK by ethanol or acetaldehyde was insensitive to the treatment of hepatocytes with genistein (tyrosine kinase inhibitor) and 2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl)maleimide (GF109203X) (protein kinase C inhibitor). Remarkably, in contrast to the above-mentioned effects on normal hepatocytes, acetaldehyde was unable to increase JNK activity in hepatocytes isolated from rats chronically fed ethanol for 6 weeks and indicated a loss of this acetaldehyde response. Thus, temporal activation of the p42/44 MAPK and p46/p54 JNK, the greater activation of p46 JNK than p54 JNK, and loss of JNK activation after chronic ethanol exposure indicate that these kinases are differentially affected by ethanol metabolite acetaldehyde.

Diltiazem reduces apoptosis in rat hepatocytes subjected to warm hypoxia-reoxygenation

Interruption of hepatic blood flow is necessary in surgery, but the liver is sensitive to ischemia and reperfusion. Hypoxia induces an increase in intracellular calcium concentration. In previous studies, we have shown that hypoxia-reoxygenation (H/R) increased calcium influx and induced JNK(1)/SAPK(1) activation which was involved in the triggering of apoptosis. The aim of this study was to demonstrate that diltiazem, a calcium inhibitor, reduced JNK(1)/SAPK(1) activation and consequently could decrease H/R-induced apoptosis. Experiments were performed, in the presence of diltiazem, on primary cultured rat hepatocytes, subjected to warm H/R phases and in a liver ischemia-reperfusion model. The activation status of JNK(1)/SAPK(1) was evaluated by immunoprecipitation and immunohistolocalisation experiments, while apoptosis was assessed by measuring caspase activity and by TUNEL labeling. Diltiazem inhibited H/R-induced JNK(1)/SAPK(1) activation and decreased apoptosis. It could be used to improve postoperative liver function.

Activation of c-Jun N-terminal kinase promotes survival of cardiac myocytes after oxidative stress

Reperfusion injury occurs when ischaemic tissue is reperfused. It involves the generation and release of reactive oxygen that activates numerous signalling pathways and initiates cell death. Exposure of isolated cardiac myocytes to chronic hypoxia followed by reoxygenation results in the early activation of c-Jun N-terminal kinase (JNK) and death by apoptosis of approx. 30% of the myocytes. Although JNK activation has been described in a number of models of ischaemia/reperfusion, the contribution of JNK activation to cell fate has not been established. Here we report that the activation of JNK by reoxygenation correlates with myocyte survival. Transfection of myocytes with JNK pathway interfering plasmid vectors or infection with adenoviral vectors support the hypothesis that JNK is protective. Transfection or infection with JNK inhibitory mutants increased the rates of apoptosis by almost 2-fold compared with control cultures grown aerobically or subjected to hypoxia and reoxygenation. Caspase 9 activity, measured by LEHD cleavage, increased >3-fold during reoxygenation and this activity was enhanced significantly at all times in cultures infected with dominant negative JNK adenovirus. Hypoxia-reoxygenation mediated a biphasic (2.6- and 2.9-fold) activation of p38 mitogen-activated protein kinase, as well as a small increase of tumour necrosis factor alpha (TNFalpha) secretion, but treatments with the p38 MAPK-specific inhibitor SB203580 or saturating levels of a TNFalpha-1 blocking antibody provided only partial protection against apoptosis. The results suggest that JNK activation is protective and that the pathway is largely independent of p38 MAPK or secreted TNFalpha.

Cyclosporin A pretreatment in a rat model of warm ischaemia/reperfusion injury

BACKGROUND/AIMS

These studies investigated the role of apoptosis following ischaemia/reperfusion (I/R) injury to the liver and the effect of pretreatment with Cyclosporin A.

METHODS

Male Sprague-Dawley rats received 30 min of warm ischaemia followed by a period of reperfusion of 6 h. Rats were given olive oil or Cyclosporin A (30 mg/kg p.o.) the day before surgery. Neutrophil numbers were assessed in haematoxylin-eosin-stained sections of liver. In situ staining of sections using TdT-mediated dUTP-fluorescein nick-end labelling was carried out to determine the extent of apoptosis, followed by electron microscopy. Semi-quantitative polymerase chain reaction (PCR) analysis of the transcript for Fas antigen was performed.

RESULTS AND CONCLUSIONS

High levels of apoptosis were observed in I/R injury, which were greatly ameliorated in Cyclosporin A-pretreated groups. PCR analysis indicated a reduction in the level of expression of Fas transcript in Cyclosporin A-treated rats. Histological analysis showed a significant increase in the number of neutrophils infiltrating I/R-injured tissue (62 +/- 10.69, n=16), which was markedly reduced by Cyclosporin A pretreatment (16 +/- 7, n=6, P<0.05). These results indicate a role of parenchymal apoptosis in the pathogenesis of I/R injury, which occurs in association with neutrophil infiltration, both of which can be significantly reduced by Cyclosporin A pretreatment.

Reoxygenation after cold hypoxic storage of cultured precision-cut rat liver slices: effects on cellular metabolism and drug biotransformation

Cultured rat precision-cut liver slices (PCLS) were used to study the influence of hypothermic preservation and reoxygenation at 37 degrees C on cellular metabolism and drug biotransformation. Cold hypoxic storage caused a depressed metabolism in rat liver slices, but reoxygenation for 8 h at 37 degrees C partially restored the levels of both ATP and GSH and totally restored the capacity to synthesize proteins. Metabolism of midazolam (CYP3A-dependent oxidation) by cold preserved liver slices was decreased by 30% but no further affected by reoxygenation, showing the same profile as freshly cut slices. Such a reoxygenation at 37 degrees C is accompanied by a dramatic loss of CYP3A2 protein while CYP3A1 protein was unaffected. These results suggest that CYP3A2 did not play a major role in midazolam oxidation. Such results are not consistent with a putative reoxygenation injury but rather with cold hypoxic damage. Since cold preserved liver slices did not respond to bacterial endotoxin stimulation (lipopolysaccharides), a minor role of non-parenchymal cells is suggested as mediators for deleterious effects developed during the cold storage.

Paclitaxel induces prolonged activation of the Ras/MEK/ERK pathway independently of activating the programmed cell death machinery

Paclitaxel is a widely used chemotherapeutic agent and is known to induce programmed cell death (apoptosis) in a variety of cell types, but the precise underlying mechanisms are poorly understood. To elucidate these mechanisms, we challenged human esophageal squamous cancer cell lines with paclitaxel and investigated its effects upon signal transduction pathways. Physiologically relevant concentrations of paclitaxel (1-1,000 nm) induced apoptosis. All three mitogen-activated protein kinase (MAPK) family members, c-Jun N-terminal kinase (JNK), p38 MAPK, and extracellular signal-regulated kinase (ERK) were activated upon paclitaxel treatment. Interestingly, JNK activation and p38 MAPK activation were delayed and peaked at 48 h, whereas ERK activity was sustained over 72 h. In addition, Ras activation and MAPK/ERK kinase (MEK) phosphorylation were observed in concordance with ERK activation. While ERK activation was completely ablated by MEK inhibitors, immunoprecipitation and Western blot analysis revealed that neither MEK-1 nor MEK-2 was involved, but instead another member of the MEK family may potentially participate. Although pretreatment with a general caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone rescued the cell death, it did not prevent Ras or ERK activation. Furthermore, inhibition of JNK, p38 MAPK, or MEK did not alter PARP cleavage and the cell death induced by paclitaxel. These results in aggregate suggest that the delayed activation of JNK, p38 MAPK, and ERK was not linked to activation of the cell death machinery.