Differential requirement for c-Jun NH2-terminal kinase in TNFalpha- and Fas-mediated apoptosis in hepatocytes

Celecoxib abrogates concanavalin A-induced hepatitis in mice: Possible involvement of Nrf2/HO-1, JNK signaling pathways and COX-2 expression

Concanavalin A (ConA) is an established model for inducing autoimmune hepatitis (AIH) in mice, mimicking clinical features in human. The aimof the current study is to explore the possible protective effect of celecoxib, a cyclooxygenase-2 inhibitor,on immunological responses elicited in the ConA model of acute hepatitis. ConA (20 mg/kg) was administered intravenously to adult male mice for 6 h. Prior to ConA intoxication, mice in the treatedgroups received daily doses of celecoxib (30 and 60 mg/kg in CMC) for 7 days. Results revealed that administration of celecoxib 60 mg/kg for 7 days significantly protected the liver from ConA-induced liver damage revealed by significant decrease in ALT and AST serum levels. Celecoxib 30 and 60 mg/kg pretreatment enhanced oxidant/antioxidant hemostasis by significantreduction of MDA and NO content and increase hepatic GSH contents and SOD activity. In addition, celecoxib 30 and 60 mg/kg caused significant increase in hepatic nuclear factor erythroid 2-related factor 2 (Nrf2) and the stress protein heme oxygenase-1 (HO-1) levels. Moreover, celecoxib 30 and 60 mg/kg inhibited the release of proinflammatory markers including IL-1β and TNF-α along with significant decrease in p-JNK, AKT phosphorylation ratio and caspase-3 expression. Besides, Con A was correlated to high expression of cyclooxygenase COX-2 and this increasing was improved by administration of celecoxib. These changes were in good agreement with improvement in histological deterioration. The protective effect of celecoxib was also associated with significant reduction of autophagy biomarkers (Beclin-1 and LC3II). In conclusion, celecoxib showed antioxidant, anti-inflammatory, anti-apoptotic and anti-autophagy activity against Con A-induced immune-mediated hepatitis. These effects could be produced by modulation of Nrf2/HO-1, IL-1B /p-JNK/p-AKT, JNK/caspase-3, and Beclin-1/LC3II signaling pathways.

The Possible Connection of Two Dual Function Processes: The Relationship of Ferroptosis and the JNK Pathway

Ferroptosis represents a typical process that has dual functions in cell fate decisions since the reduction and/or inhibition of ferroptosis is desirable for the therapies of diseases such as neurological disorders, localized ischemia-reperfusion, kidney injury, and hematological diseases, while the enhanced ferroptosis of cancer cells may benefit patients with cancer. The JNK pathway also has a real dual function in the fate of cells. Multiple factors suggest a potential link between the ferroptotic and JNK pathways; (i) both processes are ROS mediated; (ii) both can be inhibited by lipid peroxide scavengers; (iii) RAS mutations may play a role in the initiation of both pathways. We aimed to investigate the possible link between ferroptosis and the JNK pathway. Interestingly, JNK inhibitor co-treatment could enhance the cancer cytotoxic effect of the ferroptosis inducers in NRAS and KRAS mutation-harboring cells (HT-1080 and MIA PaCa-2). Since cancer’s cytotoxic effect from the JNK inhibitors could only be suspended by the ferroptosis inhibitors, and that sole JNK-inhibitor treatment did not affect cell viability, it seems that the JNK inhibitors “just” amplify the effect of the ferroptosis inducers. This cancer cell death amplifying effect of the JNK inhibitors could not be observed in other oxidative stress-driven cell deaths. Hence, it seems it is specific to ferroptosis. Finally, our results suggest that GSH content/depletion could be an important candidate for switching the anti-cancer effect of JNK inhibitors.

Therapeutic Effects of Resveratrol on Nonalcoholic Fatty Liver Disease Through Inflammatory, Oxidative Stress, Metabolic, and Epigenetic Modifications

The prevalence of nonalcoholic fatty liver disease (NAFLD) is increasing around the world, in association with the progressive elevation in overweight and obesity. The accumulation of lipids in NAFLD patients contributes to the development of insulin resistance, inflammation and oxidative stress in hepatocytes, and alteration of blood lipids and glycaemia. There are currently no effective pharmacological therapies for NAFLD, although lifestyle and dietary modifications targeting weight reduction are among the prevailing alternative approaches. For this reason, new approaches should be investigated. The natural polyphenol resveratrol represents a potential new treatment for management of NAFLD due to anti-inflammatory and antioxidant properties. Although preclinical trials have demonstrated promising results of resveratrol against NALFD, the lack of conclusive results creates the need for more trials with larger numbers of patients, longer time courses, and standardized protocols.

The MAP2K4/JNK/c-Jun Signaling Pathway Plays A Key Role In Dexmedetomidine Protection Against Acetaminophen-Induced Liver Toxicity

Purpose

Dexmedetomidine [DEX; (S)-4-[1-(2,3-dimethylphenyl)ethyl]-3H-imidazole] is a selective α₂-adrenergic receptor (α₂-AR) agonist that attenuates the liver damage associated with local or systemic inflammation. However, it remains unclear whether DEX has protective effects against acetaminophen (Paracetamol, PARA)-induced liver toxicity (PILT).

Methods

PILT mice were established by intraperitoneal administration of a hepatotoxic dose of acetaminophen (300 mg/kg). Thirty minutes later, the mice were treated with DEX at a concentration of 0, 5, 25, or 50 μg/kg. Blood and liver samples were obtained for further analysis.

Results

DEX treatment significantly attenuated PILT in mice, with the strongest beneficial effects at a dose of 25 μg/kg. The levels of hepatic cytokines, tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6), in addition to myeloperoxidase (MPO) activity, were significantly decreased following DEX treatment. Moreover, DEX treatment reduced macrophage recruitment around the area of hepatotoxicity and the expression levels of hepatic phosphorylated mitogen-activated protein kinase kinase 4 (MAP2K4), c-jun N-terminal kinase (JNK), and c-Jun expression induced by acetaminophen overdose.

Conclusion

The data suggest that DEX likely downregulates the JNK signaling pathway and its downstream effectors to promote its hepatoprotective effect, providing a clinical application of DEX for the attenuation of PILT.

Prolonged high-fat-diet feeding promotes non-alcoholic fatty liver disease and alters gut microbiota in mice

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) has become an epidemic largely due to the worldwide increase in obesity. While lifestyle modifications and pharmacotherapies have been used to alleviate NAFLD, successful treatment options are limited. One of the main barriers to finding safe and effective drugs for long-term use in NAFLD is the fast initiation and progression of disease in the available preclinical models. Therefore, we are in need of preclinical models that (1) mimic the human manifestation of NAFLD and (2) have a longer progression time to allow for the design of superior treatments.

AIM

To characterize a model of prolonged high-fat diet (HFD) feeding for investigation of the long-term progression of NAFLD.

METHODS

In this study, we utilized prolonged HFD feeding to examine NAFLD features in C57BL/6 male mice. We fed mice with a HFD (60% fat, 20% protein, and 20% carbohydrate) for 80 wk to promote obesity (Old-HFD group, n = 18). A low-fat diet (LFD) (14% fat, 32% protein, and 54% carbohydrate) was administered for the same duration to age-matched mice (Old-LFD group, n = 15). An additional group of mice was maintained on the LFD (Young-LFD, n = 20) for a shorter duration (6 wk) to distinguish between age-dependent and age-independent effects. Liver, colon, adipose tissue, and feces were collected for histological and molecular assessments.

RESULTS

Prolonged HFD feeding led to obesity and insulin resistance. Histological analysis in the liver of HFD mice demonstrated steatosis, cell injury, portal and lobular inflammation and fibrosis. In addition, molecular analysis for markers of endoplasmic reticulum stress established that the liver tissue of HFD mice have increased phosphorylated Jnk and CHOP. Lastly, we evaluated the gut microbial composition of Old-LFD and Old-HFD. We observed that prolonged HFD feeding in mice increased the relative abundance of the Firmicutes phylum. At the genus level, we observed a significant increase in the abundance of Adercreutzia, Coprococcus, Dorea, and Ruminococcus and decreased relative abundance of Turicibacter and Anaeroplasma in HFD mice.

CONCLUSION

Overall, these data suggest that chronic HFD consumption in mice can mimic pathophysiological and some microbial events observed in NAFLD patients.

Metabolic disorder induces fatty liver in Japanese seabass, Lateolabrax japonicas fed a full plant protein diet and regulated by cAMP-JNK/NF-kB-caspase signal pathway

A 10-week growth trial was conducted to investigate the effects of replacing dietary fishmeal with plant proteins on nutrition metabolism, immunity, inflammation and apoptosis responses in liver tissues of Japanese seabass, Lateolabrax japonicas (initial body weight = 10.42 ± 0.01 g). Two isonitrogenous and isoenergetic diets were formulated. A basal diet containing 54% fishmeal (FM), whereas another diet was prepared by totally replacing FM with a plant protein blend (PP) composed with soybean protein concentrate and cottonseed protein concentrate. Although essential amino acids, fatty acids, and available phosphorus had been balanced according to the FM diet profile, the significantly lower growth performance, metabolic disorder, and fatty liver symptom were observed in the PP group. Compared with the FM group, fish in the PP group showed significantly lower plasma free EAA level and PPV. Glucose metabolism disorder was expressed as the uncontrollable fasting glycolysis and pyruvate aerobic oxidation at postprandial 24 h with significantly up-regulated GK, PK and PDH genes expression, which potentially over-produced acetyl-CoA as the substrate for protein and lipid synthesis. Significantly reduced plasma GLU, but increased GC level, along with very significantly reduced liver GLY storage could be observed in the PP group. Plasma TG and hepatic NEFA contents were significantly decreased, but the hepatic TC content was very significantly increased in the PP group, in addition, hepatocyte vacuolation appeared. The significantly up-regulated cholesterol synthesis gene (HMGCR) expression but down-regulated bile acid synthesis gene (CYP7A1) expression could be the main reason for the fatty liver induced by cholesterol accumulation. The reduced plasma IgM content accompanied by the up-regulated mRNA levels of pro-inflammatory cytokines (TNFα and IL1β) and activated apoptosis signals of liver tissues were found in the PP group. The hyperthyroidism (higher plasma T3 and T4) and the accelerated energy metabolism rate decreased the growth performance in the PP group. The activated p65NF-kB may promote the hepatocytes apoptosis via the extrinsic pathway (caspase8/caspase3). Simultaneously, a "self-saving" response could be observed that activated cAMP promoted the lipolysis/β-oxidation process and up-regulated gene expression of anti-inflammatory cytokine IL10 via promoting CREB expression, further inhibited the over-phosphorylation of JNK protein, which might impede the intrinsic apoptosis pathway (caspase9/caspase3). In conclusion, the nutrient and energy metabolic disorder induced fatty liver related to the cholesterol accumulation in Japanese seabass fed full PP diet, which was under the regulation by cAMP-JNK/NF-kB-caspase signaling pathway. The hemostasis phosphorylation of JNK protein protected the liver tissues from more serious damage.

Loss of PDK4 switches the hepatic NF-κB/TNF pathway from pro-survival to pro-apoptosis

It has been established that nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) members promote survival by upregulating antiapoptotic genes and that genetic and pharmacological inhibition of NF-κB is required for tumor necrosis factor (TNF)-induced hepatocyte apoptosis. In this study, we demonstrate that this pro-survival pathway is switched to pro-apoptosis under pyruvate dehydrogenase kinase 4 (PDK4)-deficient conditions. PDK4-deficiency triggered hepatic apoptosis concomitantly with increased numbers of aberrant mitochondria, reactive oxygen species (ROS) production, sustained c-Jun N-terminal Kinase (JNK) activation, and reduction of glutathione (GSH). Interestingly, PDK4 retained p65 in cytoplasm via a direct protein-protein interaction. Disruption of PDK4-p65 association promoted p65 nuclear translocation. This, in turn, facilitated p65 binding to the TNF promoter to activate TNF-TNFR1 apoptotic pathway. Pdk4^-/- livers were sensitized to Jo2 and D-(+)-Galactosamine /Lipopolysaccharide (GalN/LPS)-mediated apoptotic injury which was prevented by the inhibition of p65 or TNFR1. The pro-survival activity of TNF was shifted, which was switched to a pro-apoptotic activity in Pdk4^-/- hepatocytes as a result of impaired activation of pro-survival NF-κB targets. Conclusion: PDK4 is indispensable to dictate the fate of TNF/NF-κB-mediated hepatocyte apoptosis. (Hepatology 2018).

Pathophysiology of Nonalcoholic Fatty Liver Disease/Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) encompasses a spectrum of liver disorders ranging from hepatic steatosis to nonalcoholic steatohepatitis (NASH) and ultimately may lead to cirrhosis. Hepatic steatosis or fatty liver is defined as increased accumulation of lipids in hepatocytes and results from increased production or reduced clearance of hepatic triglycerides or fatty acids. Fatty liver can progress to NASH in a significant proportion of subjects. NASH is a necroinflammatory liver disease governed by multiple pathways that are not completely elucidated. This review describes the main mechanisms that have been reported to contribute to the pathophysiology of NAFLD and NASH.

Pentamidine blocks hepatotoxic injury in mice

Toxin-induced liver diseases lack effective therapies despite increased understanding of the role factors such as an overactive innate immune response play in the pathogenesis of this form of hepatic injury. Pentamidine is an effective antimicrobial agent against several human pathogens, but studies have also suggested that this drug inhibits inflammation. This potential anti-inflammatory mechanism of action, together with the development of a new oral form of pentamidine isethionate VLX103, led to investigations of the effectiveness of this drug in the prevention and treatment of hepatotoxic liver injury. Pretreatment with a single injection of VLX103 in the d-galactosamine (GalN) and lipopolysaccharide (LPS) model of acute, fulminant liver injury dramatically decreased serum alanine aminotransferase levels, histological injury, the number of terminal deoxynucleotide transferase-mediated deoxyuridine triphosphate nick end-labeling (TUNEL)-positive cells and mortality compared with vehicle-injected controls. VLX103 decreased GalN/LPS induction of tumor necrosis factor (TNF) but had no effect on other proinflammatory cytokines. VLX103 prevented the proinflammatory activation of cultured hepatic macrophages and partially blocked liver injury from GalN/TNF. In GalN/LPS-treated mice, VLX103 decreased activation of both the mitochondrial death pathway and downstream effector caspases 3 and 7, which resulted from reduced c-Jun N-terminal kinase activation and initiator caspase 8 cleavage. Delaying VLX103 treatment for up to 3 hours after GalN/LPS administration was still remarkably effective in blocking liver injury in this model. Oral administration of VLX103 also decreased hepatotoxic injury in a second more chronic model of alcohol-induced liver injury, as demonstrated by decreased serum alanine and aspartate aminotransferase levels and numbers of TUNEL-positive cells.

CONCLUSION

VLX103 effectively decreases toxin-induced liver injury in mice and may be an effective therapy for this and other forms of human liver disease. (Hepatology 2017;66:922-935).

Mitochondria-meditated pathways of organ failure upon inflammation

Liver failure induced by systemic inflammatory response (SIRS) is often associated with mitochondrial dysfunction but the mechanism linking SIRS and mitochondria-mediated liver failure is still a matter of discussion. Current hypotheses suggest that causative events could be a drop in ATP synthesis, opening of mitochondrial permeability transition pore, specific changes in mitochondrial morphology, impaired Ca²⁺ uptake, generation of mitochondrial reactive oxygen species (mtROS), turnover of mitochondria and imbalance in electron supply to the respiratory chain. The aim of this review is to critically analyze existing hypotheses, in order to highlight the most promising research lines helping to prevent liver failure induced by SIRS. Evaluation of the literature shows that there is no consistent support that impaired Ca⁺⁺ metabolism, electron transport chain function and ultrastructure of mitochondria substantially contribute to liver failure. Moreover, our analysis suggests that the drop in ATP levels has protective rather than a deleterious character. Recent data suggest that the most critical mitochondrial event occurring upon SIRS is the release of mtROS in cytoplasm, which can activate two specific intracellular signaling cascades. The first is the mtROS-mediated activation of NADPH-oxidase in liver macrophages and endothelial cells; the second is the acceleration of the expression of inflammatory genes in hepatocytes. The signaling action of mtROS is strictly controlled in mitochondria at three points, (i) at the site of ROS generation at complex I, (ii) the site of mtROS release in cytoplasm via permeability transition pore, and (iii) interaction with specific kinases in cytoplasm. The systems controlling mtROS-signaling include pro- and anti-inflammatory mediators, nitric oxide, Ca²⁺ and NADPH-oxidase. Analysis of the literature suggests that further research should be focused on the impact of mtROS on organ failure induced by inflammation and simultaneously providing a new theoretical basis for a targeted therapy of overwhelmed inflammatory response.

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Relationship between mitochondrial dysfunction and high lethality upon sepsis.

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Criteria to define critical for lethality mitochondrial dysfunction.

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ATP, calcium, mitochondrial ultrastructure and apoptosis, upon inflammation.

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Regulation of inflammatory processes by mitochondrial ROS.

FK866 attenuates acute hepatic failure through c-jun-N-terminal kinase (JNK)-dependent autophagy

FK866 exhibits a protective effect on D-galactosamine (GaIN)/lipopolysaccharide (LPS) and concanavalin A (ConA)-induced acute liver failure (ALF), but the mechanism by which FK866 affords this benefit has not yet been elucidated. Autophagy has a protective effect on acute liver injury. However, the contribution of autophagy to FK866-conferred hepatoprotection is still unclear. This study aimed to investigate whether FK866 could attenuate GaIN/LPS and ConA-induced ALF through c-jun-N-terminal kinase (JNK)-dependent autophagy. In vivo, Mice were pretreated with FK866 at 24, 12, and 0.5 h before treatment with GaIN/LPS and ConA. 3-methyladenine (3MA) or rapamycin were used to determine the role of autophagy in FK866-conferred hepatoprotection. In primary hepatocytes, autophagy was inhibited by 3MA or autophagy-related protein 7 (Atg7) small interfering RNA (siRNA). JNK was suppressed by SP600125 or Jnk siRNA. FK866 alleviated hepatotoxicity and increased autophagy while decreased JNK activation. Suppression of autophagy abolished the FK866-conferred protection. Inhibition of JNK increased autophagy and exhibited strongly protective effect. Collectively, FK866 could ameliorate GaIN/LPS and ConA-induced ALF through induction of autophagy while suppression of JNK. These findings suggest that FK866 acts as a simple and applicable preconditioning intervention to protect against ALF; autophagy and JNK may also provide therapeutic targets for ALF treatment.

Aristolochia manshuriensis Kom ethyl acetate extract protects against high-fat diet-induced non-alcoholic steatohepatitis by regulating kinase phosphorylation in mouse

Aristolochia manshuriensis Kom (AMK) is an herb used as a traditional medicine; however, it causes side effects such as nephrotoxicity and carcinogenicity. Nevertheless, AMK can be applied in specific ways medicinally, including via ingestion of low doses for short periods of time. Non-alcoholic steatohepatitis (NASH) induced the hepatocyte injury and inflammation. The protective effects of AMK against NASH are unclear; therefore, in this study, the protective effects of AMK ethyl acetate extract were investigated in a high-fat diet (HFD)-induced NASH model. We found decreased hepatic steatosis and inflammation, as well as increased levels of lipoproteins during AMK extract treatment. We also observed decreased hepatic lipid peroxidation and triglycerides, as well as suppressed hepatic expression of lipogenic genes in extract-treated livers. Treatment with extract decreased the activation of c-jun N-terminal kinase 1/2 (JNK1/2) and increased the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2). These results demonstrate that the protective effect of the extract against HFD-induced NASH occurred via reductions in reactive oxygen species production, inflammation suppression, and apoptosis related to the suppression of JNK1/2 activation and increased ERK1/2 phosphorylation. Taken together, these results indicate that that ethyl acetate extract of AMK has potential therapeutic effects in the HFD-induced NASH mouse model.

Dissociation of JNK Activation from Elevated Levels of Reactive Oxygen Species, Cytochrome c Release, and Cell Death in NGF-Deprived Sympathetic Neurons

Withdrawal of nerve growth factor (NGF) from sympathetic neurons causes their apoptotic death. Activation of c-Jun NH2-terminal kinase (JNK) may contribute to this death by the induction and phosphorylation of pro-apoptotic Bcl-2 proteins, such as Bax, that are involved in cytochrome c release from mitochondria and reactive oxygen species (ROS) production. Induction of either JNK or ROS may stimulate the other, and both may regulate release of apoptogenic factors from the mitochondria. In order to discern the relationship between JNK and ROS in apoptosis, we treated NGF-deprived, mouse sympathetic neurons with a JNK inhibitor and examined the effect on several important apoptotic events. Block of JNK activation prevented induction of c-Jun expression and resulted in a dose-dependent, yet surprisingly modest, increase in cell survival after 48 h of NGF deprivation. JNK suppression was also not sufficient to prevent the elevation in ROS or the release of cytochrome c from the mitochondria in NGF-deprived sympathetic neurons. Bax deletion prevents apoptotic death of NGF-deprived neurons by preventing release of cytochrome c from their mitochondria. It also prevents increased ROS on NGF deprivation. However, we found that induction of c-Jun in cells lacking Bax was equivalent to that in wild-type neurons. Our results suggest that while JNK activation plays an important role in many forms of apoptosis, it may not be a crucial regulator of Bax-dependent events involved in the apoptotic death of mouse sympathetic neurons deprived of NGF and that ROS is not involved in its activation in these cells.

Autophagy confers resistance to lipopolysaccharide-induced mouse hepatocyte injury

During sepsis, bacterial products, particularly LPS, trigger injury in organs such as the liver. This common condition remains largely untreatable, in part due to a lack of understanding of how high concentrations of LPS cause cellular injury. In the liver, the lysosomal degradative pathway of autophagy performs essential hepatoprotective functions and is induced by LPS. We, therefore, examined whether hepatocyte autophagy protects against liver injury from septic levels of LPS. Mice with an inducible hepatocyte-specific knockout of the critical autophagy gene Atg7 were examined for their sensitivity to high-dose LPS. Increased liver injury occurred in knockout mice, as determined by significantly increased serum alanine aminotransferase levels, histological evidence of liver injury, terminal deoxynucleotide transferase-mediated deoxyuridine triphosphate nick end-labeling, and effector caspase-3 and -7 activation. Hepatic inflammation and proinflammatory cytokine induction were unaffected by the decrease in hepatocyte autophagy. Although knockout mice had normal NF-κB signaling, hepatic levels of Akt1 and Akt2 phosphorylation in response to LPS were decreased. Cultured hepatocytes from knockout mice displayed a generalized defect in Akt signaling in response to multiple stimuli, including LPS, TNF, and IL-1β. Akt activation mediates hepatocyte resistance to TNF cytotoxicity, and anti-TNF antibodies significantly decreased LPS-induced liver injury in knockout mice, indicating that the loss of autophagy sensitized to TNF-dependent liver damage. Hepatocyte autophagy, therefore, protects against LPS-induced liver injury. Conditions such as aging and steatosis that impair hepatic autophagy may predispose to poor outcomes from sepsis through this mechanism.

Therapeutic effects of 1,25-dihydroxyvitamin D3 on diabetes-induced liver complications in a rat model

It has been suggested that 1,25-dihydroxyvitamin D3 (vitamin D) plays a protective role against inflammation and insulin resistance (IR) in type 2 diabetes mellitus (T2DM). The present study investigate the hypothesis that vitamin D may exert beneficial effects on the liver in a rat model of T2DM by regulating the expression of inflammation-related cytokines and ameliorating IR induced by inflammation. Normal control group rats were fed a basic diet (NC). Experimental rats received a high-fat diet for 8 weeks and were then injected with streptozotocin (STZ) to induce T2DM. Half of the T2DM model rats received vitamin D (0.03 µg/kg/day) for 8 weeks (vitamin D-treated group; VD; n=11), while the other (T2DM group; DM; n=10) and NC group received an equivalent quantity of peanut oil. Following sacrifice, fasting plasma glucose (FPG) and fasting insulin (FINS) were recorded and homeostasis model assessment of IR (HOMA-IR) was calculated. Liver histopathology was examined using hematoxylin and eosin staining. The levels of the inflammatory cytokines C-Jun N-terminal kinase, C-Jun, tumor necrosis factor-α and interleukin-1β were measured using immunohistology, quantitative polymerase chain reaction and western blot analyses. The results revealed that treatment with vitamin D markedly alleviated the pathological alterations of liver and reduced the expression of inflammatory cytokines at the protein and mRNA levels. Furthermore, decreased levels of FPG, HOMA-IR and increased FINS were detected. In conclusion, the results of the present study indicate that vitamin D has therapeutic effects on diabetes-induced liver complications in T2DM model rats, which may involve the modulation of the inflammatory response, attenuating the crosstalk' between inflammation and IR and ameliorating hyperglycemic state.

Hepatocyte Nicotinamide Adenine Dinucleotide Phosphate Reduced Oxidase 4 Regulates Stress Signaling, Fibrosis, and Insulin Sensitivity During Development of Steatohepatitis in Mice

BACKGROUND & AIMS

Reactive oxidative species (ROS) are believed to be involved in the progression of nonalcoholic steatohepatitis (NASH). However, little is known about the sources of ROS in hepatocytes or their role in disease progression. We studied the effects of nicotinamide adenine dinucleotide phosphate reduced oxidase 4 (NOX4) in liver tissues from patients with NASH and mice with steatohepatitis.

METHODS

Liver biopsy samples were obtained from 5 patients with NASH, as well as 4 patients with simple steatosis and 5 patients without steatosis (controls) from the University of California, Davis Cancer Center Biorepository. Mice with hepatocyte-specific deletion of NOX4 (NOX4(hepKO)) and NOX4(floxp+/+) C57BL/6 mice (controls) were given fast-food diets (supplemented with high-fructose corn syrup) or choline-deficient l-amino acid defined diets to induce steatohepatitis, or control diets, for 20 weeks. A separate group of mice were given the NOX4 inhibitor (GKT137831). Liver tissues were collected and immunoblot analyses were performed determine levels of NOX4, markers of inflammation and fibrosis, double-stranded RNA-activated protein kinase, and phospho-eIF-2α kinase-mediated stress signaling pathways. We performed hyperinsulinemic-euglycemic clamp studies and immunoprecipitation analyses to determine the oxidation and phosphatase activity of PP1C.

RESULTS

Levels of NOX4 were increased in patients with NASH compared with controls. Hepatocyte-specific deletion of NOX4 reduced oxidative stress, lipid peroxidation, and liver fibrosis in mice with diet-induced steatohepatitis. A small molecule inhibitor of NOX4 reduced liver inflammation and fibrosis and increased insulin sensitivity in mice with diet-induced steatohepatitis. In primary hepatocytes, NOX4 reduced the activity of the phosphatase PP1C, prolonging activation of double-stranded RNA-activated protein kinase and phosphorylation of extracellular signal-regulated kinase-mediated stress signaling. Mice with hepatocyte-specific deletion of NOX4 and mice given GKT137831 had increased insulin sensitivity.

CONCLUSIONS

NOX4 regulates oxidative stress in the liver and its levels are increased in patients with NASH and mice with diet-induced steatohepatitis. Inhibitors of NOX4 reduce liver inflammation and fibrosis and increase insulin sensitivity, and might be developed for treatment of NASH.

Carotenoids and non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a growing health problem around the world, especially in developed countries. NAFLD includes all cases of fatty liver disease from simple steatosis to cirrhosis, without excessive alcohol intake, use of steatogenic medication or hereditary disorders. Pathogenesis is associated with dietary high fat intake, decreased free fatty acid (FFA) oxidation, increased hepatic lipogenesis and lipolysis from the adipose tissue. These metabolic alterations contribute to the hepatic fat accumulation. Consequently, stimulated oxidative stress and inflammation play a major role in hepatocellular damage. Therefore, antioxidant and anti-inflammatory agents may have a role in the prevention of this disease. Carotenoids are potent antioxidant and anti-inflammatory micronutrients, which have been investigated in the prevention and treatment of NAFLD. The main sources of the carotenoids are fruits and vegetables. In this article we review the potential role and possible molecular mechanism of carotenoids in NAFLD.

Paediatric non-alcoholic fatty liver disease: an overview

Non-alcoholic fatty liver disease (NAFLD) is a progressive disease that encompasses a spectrum of liver diseases, ranging from simple steatosis to non-alcoholic steatohepatitis (NASH). Data related to survival in children are scarce, but these data firmly associate NAFLD with higher risks of hepatic and non-hepatic morbidities and mortalities compared with the general population. More recently, the association between NAFLD and cardiovascular disease among children has increasingly been recognized. Given that obesity is a major risk factor for the disease, paediatric NAFLD is becoming a global issue, paralleling the dramatic rise in obesity worldwide. NASH, which is more common in obese children, has the potential to advance to liver fibrosis and failure. It is unclear why certain patients undergo such transformation but this susceptibility is likely related to an interaction between a genetically susceptible host and the surrounding environment. Currently, treatment is largely conservative and includes lifestyle modification, attainable through healthy weight reduction via diet and exercise. In this review, current knowledge about NAFLD in children is summarized. This review aims to increase the awareness of the medical community about a hidden public health issue and to identify current gaps in the literature while providing directions for future research.

Protective effects of astaxanthin on ConA-induced autoimmune hepatitis by the JNK/p-JNK pathway-mediated inhibition of autophagy and apoptosis

OBJECTIVE

Astaxanthin, a potent antioxidant, exhibits a wide range of biological activities, including antioxidant, atherosclerosis and antitumor activities. However, its effect on concanavalin A (ConA)-induced autoimmune hepatitis remains unclear. The aim of this study was to investigate the protective effects of astaxanthin on ConA-induced hepatitis in mice, and to elucidate the mechanisms of regulation.

MATERIALS AND METHODS

Autoimmune hepatitis was induced in in Balb/C mice using ConA (25 mg/kg), and astaxanthin was orally administered daily at two doses (20 mg/kg and 40 mg/kg) for 14 days before ConA injection. Levels of serum liver enzymes and the histopathology of inflammatory cytokines and other maker proteins were determined at three time points (2, 8 and 24 h). Primary hepatocytes were pretreated with astaxanthin (80 μM) in vitro 24 h before stimulation with TNF-α (10 ng/ml). The apoptosis rate and related protein expression were determined 24 h after the administration of TNF-α.

RESULTS

Astaxanthin attenuated serum liver enzymes and pathological damage by reducing the release of inflammatory factors. It performed anti-apoptotic effects via the descending phosphorylation of Bcl-2 through the down-regulation of the JNK/p-JNK pathway.

CONCLUSION

This research firstly expounded that astaxanthin reduced immune liver injury in ConA-induced autoimmune hepatitis. The mode of action appears to be downregulation of JNK/p-JNK-mediated apoptosis and autophagy.

Cathepsin inhibition-induced lysosomal dysfunction enhances pancreatic beta-cell apoptosis in high glucose

Autophagy is a lysosomal degradative pathway that plays an important role in maintaining cellular homeostasis. We previously showed that the inhibition of autophagy causes pancreatic β-cell apoptosis, suggesting that autophagy is a protective mechanism for the survival of pancreatic β-cells. The current study demonstrates that treatment with inhibitors and knockdown of the lysosomal cysteine proteases such as cathepsins B and L impair autophagy, enhancing the caspase-dependent apoptosis of INS-1 cells and islets upon exposure to high concentration of glucose. Interestingly, treatment with cathepsin B and L inhibitors prevented the proteolytic processing of cathepsins B, D and L, as evidenced by gradual accumulation of the respective pro-forms. Of note, inhibition of aspartic cathepsins had no effect on autophagy and cell viability, suggesting the selective role of cathepsins B and L in the regulation of β-cell autophagy and apoptosis. Lysosomal localization of accumulated pro-cathepsins in the presence of cathepsin B and L inhibitors was verified via immunocytochemistry and lysosomal fractionation. Lysotracker staining indicated that cathepsin B and L inhibitors led to the formation of severely enlarged lysosomes in a time-dependent manner. The abnormal accumulation of pro-cathepsins following treatment with inhibitors of cathepsins B and L suppressed normal lysosomal degradation and the processing of lysosomal enzymes, leading to lysosomal dysfunction. Collectively, our findings suggest that cathepsin defects following the inhibition of cathepsin B and L result in lysosomal dysfunction and consequent cell death in pancreatic β-cells.

Haematopoietic cell-derived Jnk1 is crucial for chronic inflammation and carcinogenesis in an experimental model of liver injury

BACKGROUND & AIMS

Chronic liver injury triggers complications such as liver fibrosis and hepatocellular carcinoma (HCC), which are associated with alterations in distinct signalling pathways. Of particular interest is the interaction between mechanisms controlled by IKKγ/NEMO, the regulatory IKK subunit, and Jnk activation for directing cell death and survival. In the present study, we aimed to define the relevance of Jnk in hepatocyte-specific NEMO knockout mice (NEMO(Δhepa)), a genetic model of chronic inflammatory liver injury.

METHODS

We generated Jnk1(-/-)/NEMO(Δhepa) and Jnk2(-/-)/NEMO(Δhepa) mice by crossing NEMO(Δhepa) mice with Jnk1 and Jnk2 global deficient animals, respectively, and examined the progression of chronic liver disease. Moreover, we investigated the expression of Jnk during acute liver injury, evaluated the role of Jnk1 in bone marrow-derived cells, and analysed the expression of NEMO and p-JNK in human diseased-livers.

RESULTS

Deletion of Jnk1 significantly aggravated the progression of liver disease, exacerbating apoptosis, compensatory proliferation and carcinogenesis in NEMO(Δhepa) mice. Conversely, Jnk2(-/-)/NEMO(Δhepa) displayed hepatic inflammation. By using bone marrow transfer, we observed that Jnk1 in haematopoietic cells had an impact on the progression of chronic liver disease in NEMO(Δhepa) livers. These findings are of clinical relevance since NEMO expression was downregulated in hepatocytes of patients with HCC whereas NEMO and p-JNK were expressed in a large amount of infiltrating cells.

CONCLUSIONS

A synergistic function of Jnk1 in haematopoietic cells and hepatocytes might be relevant for the development of chronic liver injury. These results elucidate the complex function of Jnk in chronic inflammatory liver disease.

CYLD deletion triggers nuclear factor-κB-signaling and increases cell death resistance in murine hepatocytes

AIM: To analyze the role of CYLD for receptor-mediated cell death of murine hepatocytes in acute liver injury models.

METHODS: Hepatocyte cell death in CYLD knockout mice (CYLD^-/-) was analyzed by application of liver injury models for CD95- (Jo2) and tumor necrosis factor (TNF)-α- [D-GalN/lipopolysaccharide (LPS)] induced apoptosis. Liver injury was assessed by measurement of serum transaminases and histological analysis. Apoptosis induction was quantified by cleaved PARP staining and Western blotting of activated caspases. Nuclear factor (NF)-κB, ERK, Akt and jun amino-terminal kinases signaling were assessed. Primary Hepatocytes were isolated by two step-collagenase perfusion and treated with recombinant TNF-α and with the CD95-ligand Jo2. Cell viability was analyzed by MTT-assay.

RESULTS: Livers of CYLD^-/- mice showed increased anti-apoptotic NF-κB signaling. In both applied liver injury models CYLD^-/- mice showed a significantly reduced apoptosis sensitivity. After D-GalN/LPS treatment CYLD^-/- mice exhibited significantly lower levels of alanine aminotransferase (ALT) (295 U/L vs 859 U/L, P < 0.05) and aspartate aminotransferase (AST) (560 U/L vs 1025 U/L, P < 0.01). After Jo injection CYLD^-/- mice showed 2-fold lower ALT (50 U/L vs 110 U/L, P < 0.01) and lower AST (250 U/L vs 435 U/L, P < 0.01) serum-levels compared to WT mice. In addition, isolated CYLD^-/- primary murine hepatocytes (PMH) were less sensitive towards death receptor-mediated apoptosis and showed increased levels of Bcl-2, XIAP, cIAP1/2, survivin and c-FLIP expression upon TNF- and CD95-receptor triggering, respectively. Inhibition of NF-κB activation by the inhibitor of NF-κB phosphorylation inhibitor BAY 11-7085 inhibited the expression of anti-apoptotic proteins and re-sensitized CYLD^-/- PMH towards TNF- and CD95-receptor mediated cell death.

CONCLUSION: CYLD is a central regulator of apoptotic cell death in murine hepatocytes by controlling NF-κB dependent anti-apoptotic signaling.

Pathogenesis and therapeutic approaches for non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease affects approximately one-third of the population worldwide, and its incidence continues to increase with the increasing prevalence of other metabolic disorders such as type 2 diabetes. As non-alcoholic fatty liver disease can progress to liver cirrhosis, its treatment is attracting greater attention. The pathogenesis of non-alcoholic fatty liver disease is closely associated with insulin resistance and dyslipidemia, especially hypertriglyceridemia. Increased serum levels of free fatty acid and glucose can cause oxidative stress in the liver and peripheral tissue, leading to ectopic fat accumulation, especially in the liver. In this review, we summarize the mechanism underlying the progression of hepatic steatosis to steatohepatitis and cirrhosis. We also discuss established drugs that are already being used to treat non-alcoholic fatty liver disease, in addition to newly discovered agents, with respect to their mechanisms of drug action, focusing mainly on hepatic insulin resistance. As well, we review clinical data that demonstrate the efficacy of these drugs, together with improvements in biochemical or histological parameters.

Stathmin mediates hepatocyte resistance to death from oxidative stress by down regulating JNK

Stathmin 1 performs a critical function in cell proliferation by regulating microtubule polymerization. This proliferative function is thought to explain the frequent overexpression of stathmin in human cancer and its correlation with a bad prognosis. Whether stathmin also functions in cell death pathways is unclear. Stathmin regulates microtubules in part by binding free tubulin, a process inhibited by stathmin phosphorylation from kinases including c-Jun N-terminal kinase (JNK). The involvement of JNK activation both in stathmin phosphorylation, and in hepatocellular resistance to oxidative stress, led to an examination of the role of stathmin/JNK crosstalk in oxidant-induced hepatocyte death. Oxidative stress from menadione-generated superoxide induced JNK-dependent stathmin phosphorylation at Ser-16, Ser-25 and Ser-38 in hepatocytes. A stathmin knockdown sensitized hepatocytes to both apoptotic and necrotic cell death from menadione without altering levels of oxidant generation. The absence of stathmin during oxidative stress led to JNK overactivation that was the mechanism of cell death as a concomitant knockdown of JNK1 or JNK2 blocked death. Hepatocyte death from JNK overactivation was mediated by the effects of JNK on mitochondria. Mitochondrial outer membrane permeabilization occurred in stathmin knockdown cells at low concentrations of menadione that triggered apoptosis, whereas mitochondrial β-oxidation and ATP homeostasis were compromised at higher, necrotic menadione concentrations. Stathmin therefore mediates hepatocyte resistance to death from oxidative stress by down regulating JNK and maintaining mitochondrial integrity. These findings demonstrate a new mechanism by which stathmin promotes cell survival and potentially tumor growth.

Cell death and cell death responses in liver disease: mechanisms and clinical relevance

Hepatocellular death is present in almost all types of human liver disease and is used as a sensitive parameter for the detection of acute and chronic liver disease of viral, toxic, metabolic, or autoimmune origin. Clinical data and animal models suggest that hepatocyte death is the key trigger of liver disease progression, manifested by the subsequent development of inflammation, fibrosis, cirrhosis, and hepatocellular carcinoma. Modes of hepatocellular death differ substantially between liver diseases. Different modes of cell death such as apoptosis, necrosis, and necroptosis trigger specific cell death responses and promote progression of liver disease through distinct mechanisms. In this review, we first discuss molecular mechanisms by which different modes of cell death, damage-associated molecular patterns, and specific cell death responses contribute to the development of liver disease. We then review the clinical relevance of cell death, focusing on biomarkers; the contribution of cell death to drug-induced, viral, and fatty liver disease and liver cancer; and evidence for cell death pathways as therapeutic targets.

TNF receptors: signaling pathways and contribution to renal dysfunction

Tumor necrosis factor (TNF), initially reported to induce tumor cell apoptosis and cachexia, is now considered a central mediator of a broad range of biological activities from cell proliferation, cell death and differentiation to induction of inflammation and immune modulation. TNF exerts its biological responses via interaction with two cell surface receptors: TNFR1 and TNFR2. (TNFRs). These receptors trigger shared and distinct signaling pathways upon TNF binding, which in turn result in cellular outputs that may promote tissue injury on one hand but may also induce protective, beneficial responses. Yet the role of TNF and its receptors specifically in renal disease is still not well understood. This review describes the expression of the TNFRs, the signaling pathways induced by them and the biological responses of TNF and its receptors in various animal models of renal diseases, and discusses the current outcomes from use of TNF biologics and TNF biomarkers in renal disorders.

TNF and TNF-receptors: From mediators of cell death and inflammation to therapeutic giants - past, present and future

Tumor Necrosis Factor (TNF), initially known for its tumor cytotoxicity, is a potent mediator of inflammation, as well as many normal physiological functions in homeostasis and health, and anti-microbial immunity. It also appears to have a central role in neurobiology, although this area of TNF biology is only recently emerging. Here, we review the basic biology of TNF and its normal effector functions, and discuss the advantages and disadvantages of therapeutic neutralization of TNF - now a commonplace practice in the treatment of a wide range of human inflammatory diseases. With over ten years of experience, and an emerging range of anti-TNF biologics now available, we also review their modes of action, which appear to be far more complex than had originally been anticipated. Finally, we highlight the current challenges for therapeutic intervention of TNF: (i) to discover and produce orally delivered small molecule TNF-inhibitors, (ii) to specifically target selected TNF producing cells or individual (diseased) tissue targets, and (iii) to pre-identify anti-TNF treatment responders. Although the future looks bright, the therapeutic modulation of TNF now moves into the era of personalized medicine with society's challenging expectations of durable treatment success and of achieving long-term disease remission.

Chemoprevention of nonalcoholic fatty liver disease by dietary natural compounds

Nonalcoholic fatty liver disease (NAFLD) refers to a wide spectrum of liver disease that is not from excess alcohol consumption, but is often associated with obesity, type 2 diabetes, and metabolic syndrome. NAFLD pathogenesis is complicated and involves oxidative stress, lipotoxicity, mitochondrial damage, insulin resistance, inflammation, and excessive dietary fat intake, which increase hepatic lipid influx and de novo lipogenesis and impair insulin signaling, thus promoting hepatic triglyceride accumulation and ultimately NAFLD. Overproduction of proinflammatory adipokines from adipose tissue also affects hepatic metabolic function. Current NAFLD therapies are limited; thus, much attention has been focused on identification of potential dietary substances from fruits, vegetables, and edible plants to provide a new strategy for NAFLD treatment. Dietary natural compounds, such as carotenoids, omega-3-PUFAs, flavonoids, isothiocyanates, terpenoids, curcumin, and resveratrol, act through a variety of mechanisms to prevent and improve NAFLD. Here, we summarize and briefly discuss the currently known targets and signaling pathways as well as the role of dietary natural compounds that interfere with NAFLD pathogenesis.

PARP inhibition attenuates acute kidney allograft rejection by suppressing cell death pathways and activating PI-3K-Akt cascade

BACKGROUND

Novel immunosuppressive therapy facilitates long term allograft survival, but acute tubular necrosis and ischemia-reperfusion during transplantation can compromise allograft function. These processes are related to oxidative stress which activates poly- (ADP-ribose) polymerase (PARP) contributing to the activation of cell death pathways. Here we raised the possibility that PARP inhibition curbs cell death pathways and shifts kinase signaling to improved graft survival.

METHODS FINDINGS

In an acute rat kidney rejection model, we provided evidence that the PARP inhibitor 4-hydroxy-quinazoline (4OHQ) attenuates rejection processes initiated oxidative/nitrosative stress, nuclear poly-ADP-ribosylation and the disintegration of the tubulo-interstitial structures. The PARP inhibitor attenuated rejection processes induced pro-apoptotic pathways by increasing Bcl-2/Bax ratio and suppressing pro-apoptotic t-Bid levels. In transplanted kidneys, the cell death inducing JNK1/2 is normally activated, but PARP inhibition suppressed this activation with having only modest effects on ERK1/2 and p38 MAP kinases. In untreated transplanted kidneys, no significant alterations were detected in the cytoprotective PI-3K-Akt pathway, but the PARP inhibitor significantly activated Akt (by S473 phosphorylation) and suppressed GSK-3β, as well as activated acute NF-kappaB activation contributing to graft protection.

CONCLUSION

These data show the protective role of PARP inhibition on graft survival by attenuating poly-ADP-ribosylation, oxidative stress, suppressing pro-apoptotic and increasing anti-apoptotic protein level, and by shifting MAP kinases and PI-3-K-Akt pathways to cytoprotective direction. Thus, addition of PARP inhibitors to standard immunosuppressive therapies during kidney transplantation may provide increased protection to prolong graft survival.

Primary hepatocytes and their cultures in liver apoptosis research

Apoptosis not only plays a key role in physiological demise of defunct hepatocytes, but is also associated with a plethora of acute and chronic liver diseases as well as with hepatotoxicity. The present paper focuses on the modelling of this mode of programmed cell death in primary hepatocyte cultures. Particular attention is paid to the activation of spontaneous apoptosis during the isolation of hepatocytes from the liver, its progressive manifestation upon the subsequent establishment of cell cultures and simultaneously to strategies to counteract this deleterious process. In addition, currently applied approaches to experimentally induce controlled apoptosis in this in vitro setting for mechanistic research purposes and thereby its detection using relevant biomarkers are reviewed.

Tumour necrosis factor in infectious disease

TNF signals through two distinct receptors, designated TNFR1 and TNFR2, which initiate diverse cellular effects that include cell survival, activation, differentiation, and proliferation and cell death. These cellular responses can promote immunological and inflammatory responses that eradicate infectious agents, but can also lead to local tissue injury at sites of infection and harmful systemic effects. Defining the molecular mechanisms involved in TNF responses, the effects of natural and experimental genetic diversity in TNF signalling and the effects of therapeutic blockade of TNF has increased our understanding of the key role that TNF plays in infectious disease.

JNK activation is required for TNFα-induced apoptosis in human hepatocarcinoma cells

BACKGROUND

A frequent distinctive feature of tumors, hepatocellular carcinomas included, is resistance to apoptosis induced by a variety of agents, among which the pleiotropic cytokine tumor necrosis factor-α (TNF). Compared to other cell types, hepatocytes and hepatoma-derived cell lines are poorly susceptible to TNF-induced apoptosis, which is largely ascribed to activation of the prosurvival transcription factor NF-κB and can be overcome by associating TNF to low doses of protein synthesis inhibitors or other drugs.

AIMS

This study analyses the molecular mechanisms by which TNF, in combination with cycloheximide (CHX), induces apoptosis in human hepatoma-derived Huh7 cells, focusing on the role played by JNK.

METHODS

Huh7 cell cultures were treated with TNF + CHX in the presence or in the absence of the pancaspase inhibitor zVADfmk or of the JNK inhibitor SP600125 as well as after suppression of JNK expression by RNAi. Apoptosis was assessed both by light microscopy and by flow cytometry, JNK and caspase activation by western blotting and/or enzymatic assay.

RESULTS

TNF + CHX-induced death of Huh7 cells involved JNK activation since it was partially prevented by suppressing JNK activity or expression. Moreover, apoptosis was significantly reduced also by zVADfmk, while SP600125 and zVADfmk combined totally abrogated cell death in an additive fashion.

CONCLUSIONS

These results demonstrate a causal role for JNK and caspases in TNF+CHX-induced apoptosis of Huh7 human hepatoma cells. Therefore, strategies aimed at enhancing both pathways should provide a profitable basis to overcome the resistance of hepatocarcinoma cells to TNF-dependent apoptosis.

MAPK Signal Transduction Pathway Regulation: A Novel Mechanism of Rat HSC-T6 Cell Apoptosis Induced by FUZHENGHUAYU Tablet

FUZHENGHUAYU Tablets have been widely used in the treatment of liver fibrosis in China. Here, we investigate the apoptotic effect of FUZHENGHUAYU Tablet in rat liver stellate cell line HSC-T6. HSC-T6 cells were incubated with control serum or drug serum from rats fed with 0.9% NaCl or FUZHENGHUAYU Tablet, respectively. Cells exposed to drug serum showed higher proportions of early and late apoptotic cells than controls. The mRNA levels of collagens I and III, TGF-β1 and α-SMA were reduced by drug serum compared to control serum. Differentially expressed mRNAs and miRNAs were analyzed by microarray and sequencing, respectively. We identified 334 differentially expressed mRNAs and also 60 GOs and two pathways related to the mRNAs. Seventy-five differentially expressed miRNAs were down-regulated by drug serum and 1963 target genes were predicted. 134 GOs up-regulated in drug serum group were linked to miRNA targets, and drug serum also regulated 43 miRNA signal transduction pathways. Protein levels were evaluated by Western blot. Drug serum down-regulated (phospho-SAPK/JNK)/(SAPK/JNK) and up-regulated phospho-p38/p38 ratios. The study showed that FUZHENGHUAYU Tablet induced apoptosis in rat HSC-T6 cells possibly in part by activating p38 and inhibiting SAPK/JNK.

Inhibition of hepatocyte autophagy increases tumor necrosis factor-dependent liver injury by promoting caspase-8 activation

Recent investigations have demonstrated a complex interrelationship between autophagy and cell death. A common mechanism of cell death in liver injury is tumor necrosis factor (TNF) cytotoxicity. To better delineate the in vivo function of autophagy in cell death, we examined the role of autophagy in TNF-induced hepatic injury. Atg7Δhep mice with a hepatocyte-specific knockout of the autophagy gene atg7 were generated and cotreated with D-galactosamine (GalN) and lipopolysaccharide (LPS). GalN/LPS-treated Atg7Δhep mice had increased serum alanine aminotransferase levels, histological injury, numbers of TUNEL (terminal deoxynucleotide transferase-mediated deoxyuridine triphosphate nick end-labeling)-positive cells and mortality as compared with littermate controls. Loss of hepatocyte autophagy similarly sensitized to GalN/TNF liver injury. GalN/LPS injury in knockout animals did not result from altered production of TNF or other cytokines. Atg7Δhep mice had accelerated activation of the mitochondrial death pathway and caspase-3 and -7 cleavage. Increased cell death did not occur from direct mitochondrial toxicity or a lack of mitophagy, but rather from increased activation of initiator caspase-8 causing Bid cleavage. GalN blocked LPS induction of hepatic autophagy, and increased autophagy from beclin 1 overexpression prevented GalN/LPS injury. Autophagy, therefore, mediates cellular resistance to TNF toxicity in vivo by blocking activation of caspase-8 and the mitochondrial death pathway, suggesting that autophagy is a therapeutic target in TNF-dependent tissue injury.

Proapoptotic effects of the chemokine, CXCL 10 are mediated by the noncognate receptor TLR4 in hepatocytes

Aberrant expression of the chemokine CXC chemokine ligand (CXCL)10 has been linked to the severity of hepatitis C virus (HCV)-induced liver injury, but the underlying molecular mechanisms remain unclear. In this study, we describe a yet-unknown proapoptotic effect of CXCL10 in hepatocytes, which is not mediated through its cognate chemokine receptor, but the lipopolysaccharide receptor Toll-like receptor 4 (TLR4). To this end, we investigated the link of CXCL10 expression with apoptosis in HCV-infected patients and in murine liver injury models. Mice were treated with CXCL10 or neutralizing antibody to systematically analyze effects on hepatocellular apoptosis in vivo. Direct proapoptotic functions of CXCL10 on different liver cell types were evaluated in detail in vitro. The results showed that CXCL10 expression was positively correlated with liver cell apoptosis in humans and mice. Neutralization of CXCL10 ameliorated concanavalin A-induced tissue injury in vivo, which was strongly associated with reduced liver cell apoptosis. In vitro, CXCL10 mediated the apoptosis of hepatocytes involving TLR4, but not CXC chemokine receptor 3 signaling. Specifically, CXCL10 induced long-term protein kinase B and Jun N-terminal kinase activation, leading to hepatocyte apoptosis by caspase-8, caspase-3, and p21-activated kinase 2 cleavage. Accordingly, systemic application of CXCL10 led to TLR4-induced liver cell apoptosis in vivo.

CONCLUSION

The results identify CXCL10 and its noncognate receptor, TLR4, as a proapoptotic signaling cascade during liver injury. Antagonism of the CXCL10/TLR4 pathway might be a therapeutic option in liver diseases associated with increased apoptosis.

Involvement of the apelin receptor APJ in Fas-induced liver injury

BACKGROUND

Apelin-APJ signalling is known to play important roles in heart physiology and pathology; however, its functions in liver physiology and pathology remain unclear. On the other hand, Fas is an important molecule in hepatitis and other liver disease that belongs to the death receptor family. The aim of this study was to assess the relationship between apelin-APJ signaling and Fas-mediated liver injury in mice.

METHODS

APJ(-/-) mice and wild type (WT) mice were administered an intraperitoneal injection of an agonistic anti-Fas antibody (clone; Jo2), and sacrificed after 3 or 6 h to assess the liver histology. The expression levels of apelin and APJ, plasma levels of transaminases, activities of hepatic caspases and activations of stress-activated protein kinases were also analysed.

RESULTS

Before the Jo2 injection, APJ was weakly expressed in the hepatocytes in spots; on the other hand, after the Jo2 injection, it had spread into whole hepatocytes. Moreover, the mRNA expression level of apelin and APJ in the liver increased after Jo2 injection. In the APJ(-/-) mice, the liver injuries and apoptotic changes were significantly inhibited as compared with those in the WT mice. Dramatic increase in JNK activation was observed in the WT mice after Jo2 injection, whereas such activation was completely absent in the APJ(-/-) mice. JNK inhibitor partially, but significantly suppressed Jo2-mediated liver injury in WT mice.

CONCLUSION

Apelin-APJ signalling may promote Fas-induced liver injury at least partially via JNK activation, and may thus serve as a potential therapeutic target in cases of acute liver injury.

Nilotinib protects the murine liver from ischemia/reperfusion injury

BACKGROUND & AIMS

The mitogen-activated protein kinases (MAPKs), c-Jun N-terminal kinase (JNK), and p38, mediate liver ischemia/reperfusion (I/R) injury via cell death and inflammatory cytokine expression, respectively. Nilotinib is an orally available receptor tyrosine kinase inhibitor used for chronic myelogenous leukemia that also has in vitro activity against JNK and p38. In this study, we examine its therapeutic potential against hepatic I/R injury.

METHODS

The effects of nilotinib on liver I/R injury were tested using a murine model of warm, segmental liver I/R. Serum ALT was measured and livers were analyzed by histology, RT-PCR, Western blot, and flow cytometry. The in vitro effects of nilotinib on hepatocyte and non-parenchymal cell (NPC) MAPK activation and cytokine production were also tested.

RESULTS

Mice receiving nilotinib had markedly lower serum ALT levels and less histologic injury and apoptosis following liver I/R. Nilotinib did not inhibit its known receptor tyrosine kinases. Nilotinib lowered intrahepatic expression of IL-1β, IL-6, MCP-1, and MIP-2 and systemic levels of IL-6, MCP-1, and TNF. Nilotinib reduced NPC activation of p38 MAPK signaling and decreased the recruitment of inflammatory monocytes and their production of TNF. Nilotinib attenuated JNK phosphorylation and hepatocellular apoptosis. In vitro, nilotinib demonstrated direct inhibition of JNK activation in isolated hepatocytes cultured under hypoxic conditions, and blocked activation of p38 MAPK and cytokine production by stimulated NPCs.

CONCLUSIONS

Nilotinib lowers both liver JNK activation and NPC p38 MAPK activation and may be useful for ameliorating liver I/R injury in humans.

Distinct functions of JNK and c-Jun in oxidant-induced hepatocyte death

Overactivation of c-Jun N-terminal kinase (JNK)/c-Jun signaling is a central mechanism of hepatocyte injury and death including that from oxidative stress. However, the functions of JNK and c-Jun are still unclear, and this pathway also inhibits hepatocyte death. Previous studies of menadione-induced oxidant stress demonstrated that toxicity resulted from sustained JNK/c-Jun activation as death was blocked by the c-Jun dominant negative TAM67. To further delineate the function of JNK/c-Jun signaling in hepatocyte injury from oxidant stress, the effects of direct JNK inhibition on menadione-induced death were examined. In contrast to the inhibitory effect of TAM67, pharmacological JNK inhibition by SP600125 sensitized the rat hepatocyte cell line RALA255-10G to death from menadione. SP600125 similarly sensitized mouse primary hepatocytes to menadione toxicity. Death from SP600125/menadione was c-Jun dependent as it was blocked by TAM67, but independent of c-Jun phosphorylation. Death occurred by apoptosis and necrosis and activation of the mitochondrial death pathway. Short hairpin RNA knockdowns of total JNK or JNK2 sensitized to death from menadione, whereas a jnk1 knockdown was protective. Jnk2 null mouse primary hepatocytes were also sensitized to menadione death. JNK inhibition magnified decreases in cellular ATP content and β-oxidation induced by menadione. This effect mediated cell death as chemical inhibition of β-oxidation also sensitized cells to death from menadione, and supplementation with the β-oxidation substrate oleate blocked death. Components of the JNK/c-Jun signaling pathway have opposing functions in hepatocyte oxidant stress with JNK2 mediating resistance to cell death and c-Jun promoting death.

A liver full of JNK: signaling in regulation of cell function and disease pathogenesis, and clinical approaches

c-Jun-N-terminal kinase (JNK) is a mitogen-activated protein kinase family member that is activated by diverse stimuli, including cytokines (such as tumor necrosis factor and interleukin-1), reactive oxygen species (ROS), pathogens, toxins, drugs, endoplasmic reticulum stress, free fatty acids, and metabolic changes. Upon activation, JNK induces multiple biologic events through the transcription factor activator protein-1 and transcription-independent control of effector molecules. JNK isozymes regulate cell death and survival, differentiation, proliferation, ROS accumulation, metabolism, insulin signaling, and carcinogenesis in the liver. The biologic functions of JNK are isoform, cell type, and context dependent. Recent studies using genetically engineered mice showed that loss or hyperactivation of the JNK pathway contributes to the development of inflammation, fibrosis, cancer growth, and metabolic diseases that include obesity, hepatic steatosis, and insulin resistance. We review the functions and pathways of JNK in liver physiology and pathology and discuss findings from preclinical studies with JNK inhibitors.

C-Jun N-Terminal Kinase 2 Promotes Liver Injury via the Mitochondrial Permeability Transition after Hemorrhage and Resuscitation

Hemorrhagic shock leads to hepatic hypoperfusion and activation of mitogen-activated stress kinases (MAPK) like c-Jun N-terminal kinase (JNK) 1 and 2. Our aim was to determine whether mitochondrial dysfunction leading to hepatic necrosis and apoptosis after hemorrhage/resuscitation (H/R) was dependent on JNK2. Under pentobarbital anesthesia, wildtype (WT) and JNK2 deficient (KO) mice were hemorrhaged to 30 mm Hg for 3 h and then resuscitated with shed blood plus half the volume of lactated Ringer's solution. Serum alanine aminotransferase (ALT), necrosis, apoptosis and oxidative stress were assessed 6 h after resuscitation. Mitochondrial polarization was assessed by intravital microscopy. After H/R, ALT in WT-mice increased from 130 U/L to 4800 U/L. In KO-mice, ALT after H/R was blunted to 1800 U/l (P < 0.05). Necrosis, caspase-3 activity and ROS were all substantially decreased in KO compared to WT mice after H/R. After sham operation, intravital microscopy revealed punctate mitochondrial staining by rhodamine 123 (Rh123), indicating normal mitochondrial polarization. At 4 h after H/R, Rh123 staining became dim and diffuse in 58% of hepatocytes, indicating depolarization and onset of the mitochondrial permeability transition (MPT). By contrast, KO mice displayed less depolarization after H/R (23%, P < 0.05). In conclusion, JNK2 contributes to MPT-mediated liver injury after H/R.

Molecular mechanisms of liver injury and hepatocarcinogenesis: focusing on the role of stress-activated MAPK

Hepatocellular carcinoma (HCC) is the third most common cause of cancer mortality. Short-term prognosis of patients with HCC has improved recently due to advances in early diagnosis and treatment, but long-term prognosis is still unsatisfactory. Therefore, obtaining a further understanding of the molecular carcinogenic mechanisms and the unique pathogenic biology of HCC is important. The most characteristic process in hepatocarcinogenesis is underlying chronic liver injury, which leads to repeated cycles of hepatocyte death, inflammation, and compensatory proliferation and subsequently provides a mitogenic and mutagenic environment leading to the development of HCC. Recent in vivo studies have shown that the stress-activated mitogen-activated protein kinase (MAPK) cascade converging on c-Jun NH(2)-terminal kinase (JNK) and p38 plays a central role in these processes, and it has attracted considerable attention as a therapeutic target. However, JNK and p38 have complex functions and a wide range of cellular effects. In addition, crosstalk with each other and the nuclear factor-kappaB pathway further complicate these functions. A full understanding is essential to bring these observations into clinical settings. In this paper, we discuss the latest findings regarding the mechanisms of liver injury and hepatocarcinogenesis focusing on the role of the stress-activated MAPK pathway.

Pro-domain in precursor nerve growth factor mediates cell death

Nerve growth factor (NGF) is synthesized as a precursor, proNGF that undergoes post-translational processing to generate the biologically active mature NGF. While the neurotrophic function of NGF is well established, the activity of the proNGF precursor is still unclear. In this study, we have cloned the pro-domain of the precursor NGF molecule and have elucidated its function. We have used both mature and the furin resistant pro((R/G))NGF as controls in our experiments. Both pro((R/G))NGF and mature NGF (NGF) exhibited neurotrophic activity on PC12 cells while the pro-domain itself promoted cell death. The pro-domain, has been found to mediate apoptosis possibly by promoting the formation of a signaling complex comprising of endogenous p75(NTR) receptor, Bim/Bcl2 group of proteins and JNK and MEK1/2 signaling pathways.

Fructose protects murine hepatocytes from tumor necrosis factor-induced apoptosis by modulating JNK signaling

Fructose-induced hepatic ATP depletion prevents TNF-induced apoptosis, whereas it contrarily enhances CD95-induced hepatocyte apoptosis in vitro and in vivo. By contrast, transformed liver cells are not protected against TNF due to metabolic alterations, allowing selective tumor targeting. We analyzed the molecular mechanisms by which fructose modulates cytokine-induced apoptosis. A release of adenosine after fructose-induced ATP depletion, followed by a cAMP response, was demonstrated. Likewise, cAMP and adenosine mimicked per se the modulation by fructose of CD95- and TNF-induced apoptosis. The effects of fructose on cytokine-induced apoptosis were sensitive to inhibition of protein kinase A. Fructose prevented the pro-apoptotic, sustained phase of TNF-induced JNK signaling and thereby blocked bid-mediated activation of the intrinsic mitochondrial apoptosis pathway in a PKA-dependent manner. We explain the dichotomal effects of fructose on CD95- and TNF-induced cell death by the selective requirement of JNK signaling for the latter. These findings provide a mechanistic rationale for the protection of hepatocytes from TNF-induced cell death by pharmacological doses of fructose.

Ablation of c-FLIP in hepatocytes enhances death-receptor mediated apoptosis and toxic liver injury in vivo

BACKGROUND & AIMS

Apoptosis is crucially involved in acute and chronic liver injury, including viral, cholestatic, toxic, and metabolic liver disease. Additionally, dysregulation of apoptosis signaling pathways has been implicated in hepatocarcinogenesis. The most prominent members of the apoptosis-mediating tumor necrosis factor receptor superfamily are the TNF-R1 (CD120a) and the CD95 (Apo-1/Fas) receptor. Although extensively studied, the intracellular signaling events in hepatocytes are only incompletely understood.

METHODS

To examine the role of the caspase-8 homolog cellular FLICE-inhibitory protein (c-FLIP) in liver injury, we generated mice with hepatocyte specific deletion of c-FLIP. Three models of acute liver injury were employed: the agonistic anti-CD95 antibody Jo2, d-galactosamine and LPS (GalN/LPS), and concanavalin A.

RESULTS

Conditional ablation of c-FLIP in hepatocytes augmented liver injury and cell death in all three models of liver injury. CD95- and GalN/LPS-induced liver injury was ameliorated by a pancaspase inhibitor, while ConA-induced injury was unaffected by caspase inhibition. Augmented activation of the MAPK JNK was observed in parallel to liver injury in c-FLIP knockout mice in all injury models; however, inhibition of JNK only affected TNF- and ConA-mediated injury.

CONCLUSIONS

In summary, c-FLIP is a central regulator of cell death in hepatocytes, involving increased activation of caspases and the MAPK JNK.

Dysregulation of the unfolded protein response in db/db mice with diet-induced steatohepatitis

In humans with nonalcoholic fatty liver, diabetes is associated with more advanced disease. We have previously shown that diabetic db/db mice are highly susceptible to methionine choline-deficient diet (MCD)-induced hepatic injury. Because activation of the unfolded protein response (UPR) is an important adaptive cellular mechanism in diabetes, obesity, and fatty liver, we hypothesized that dysregulation of the UPR may partially explain how diabetes could promote liver injury. Db/db and db/m mice were fed the MCD or control diet for 4 weeks to characterize differences in UPR activation and downstream injury. Wildtype mice (C57BLKS/J) fed the MCD or control diet were treated with SP600125; a c-Jun N-terminal kinase (JNK) inhibitor and its effect on liver injury and UPR activation was measured. The MCD diet resulted in global up-regulation of the UPR in both diabetic db/db and nondiabetic db/m mice. db/db mice had an inadequate activation of recovery pathways (GADD34, XBP-1(s)) and accentuated activation of injury pathways related to persistent eif2-α phosphorylation (activating transcription factor 4 [ATF-4], C/EBP homologous transcription factor [CHOP], oxireductase endoplasmic reticulum oxidoreductin-1 [ERO-1α], JNK, nuclear factor kappaB [NF-κB]) compared to db/m mice. This led to increased expression of inflammatory mediators such as tumor necrosis factor alpha (TNF-α), ICAM-1, and MCP-1 compared to db/m mice. Interestingly, whereas pharmacologic JNK inhibition did not prevent the development of MCD diet-induced steatohepatitis, it did attenuate UPR and downstream inflammatory signaling.

CONCLUSION

MCD-fed db/db mice develop a more proinflammatory milieu than db/m mice associated with an impaired ability to dephosphorylate eif2-α through GADD34, impairing cellular recovery. These data may enhance our understanding of why diabetics with nonalcoholic steatohepatitis are prone to develop more severe liver injury than nondiabetic patients.

Hepatotoxicity mediated by pyrazole (cytochrome P450 2E1) plus tumor necrosis factor alpha treatment occurs in c-Jun N-terminal kinase 2-/- but not in c-Jun N-terminal kinase 1-/- mice

Cytochrome P450 2E1 (CYP2E1) induction and tumor necrosis factor alpha (TNF-α) production are key risk factors in alcoholic liver injury. Increased oxidative stress from CYP2E1 induction by pyrazole in vivo sensitizes the liver to TNF-α-induced hepatotoxicity by a mechanism involving the activation of c-jun N-terminal kinase (JNK) and mitochondrial damage. The aim of this study was to evaluate whether JNK1 or JNK2 plays a role in this potentiated hepatotoxicity. Wild-type (WT), jnk1(-/-) , and jnk2(-/-) mice were used to identify changes of hepatotoxicity, damage to mitochondria, and production of oxidative stress after pyrazole plus TNF-α treatment. Increased serum alanine aminotransferase, inflammatory infiltration, and central necrosis were observed in the jnk2(-/-) and WT mice treated with pyrazole plus TNF-α, but not in the jnk1(-/-) mice. Pyrazole elevated the activity and protein level of CYP2E1 in all mice. There was a significant increase of malondialdehyde, 4-hydroxynonenal adducts, 3-nitrotyrosine, and inducible nitric oxide synthase in the jnk2(-/-) and WT mice, compared to the jnk1(-/-) mice, upon pyrazole plus TNF-α treatment, or compared to mice treated with either pyrazole alone or TNF-α alone. The antioxidants, catalase, phospholipid hydroperoxide glutathione peroxidase, thioredoxin, and glutathione were lowered, and cytochrome c was released from the mitochondria in the jnk2(-/-) and WT mice. Mitochondrial production of superoxide was increased in the jnk2(-/-) and WT mice, compared to the jnk1(-/-) mice, upon pyrazole plus TNF-α treatment. Electron microscopy showed altered mitochondrial structure in the jnk2(-/-) and WT mice, but not the jnk1(-/-) mice.

CONCLUSIONS

JNK1 plays a role in the hepatotoxicity, mitochondrial dysfunction, and oxidative stress mediated by pyrazole plus TNF-α treatment. These findings raise the question as to the potential mechanisms of JNK1 activation related to alcoholic liver injury.

Redox balance in the pathogenesis of nonalcoholic fatty liver disease: mechanisms and therapeutic opportunities

Nonalcoholic fatty liver disease (NAFLD) is currently the most common liver disease in the world. It encompasses a histological spectrum, ranging from simple, nonprogressive steatosis to nonalcoholic steatohepatitis (NASH), which may progress to cirrhosis and hepatocellular carcinoma. While liver-related complications are confined to NASH, emerging evidence suggests both simple steatosis and NASH predispose to type 2 diabetes and cardiovascular disease. The pathogenesis of NAFLD is currently unknown, but accumulating data suggest that oxidative stress and altered redox balance play a crucial role in the pathogenesis of steatosis, steatohepatitis, and fibrosis. We will examine intracellular mechanisms, including mitochondrial dysfunction and impaired oxidative free fatty acid metabolism, leading to reactive oxygen species generation; additionally, the potential pathogenetic role of extracellular sources of reactive oxygen species in NAFLD, including increased myeloperoxidase activity and oxidized low density lipoprotein accumulation, will be reviewed. We will discuss how these mechanisms converge to determine the whole pathophysiological spectrum of NAFLD, including hepatocyte triglyceride accumulation, hepatocyte apoptosis, hepatic inflammation, hepatic stellate cell activation, and fibrogenesis. Finally, available animal and human data on treatment opportunities with older and newer antioxidant will be presented.

BIM-mediated AKT phosphorylation is a key modulator of arsenic trioxide-induced apoptosis in cisplatin-sensitive and -resistant ovarian cancer cells

Background

Chemo-resistance to cisplatin-centered cancer therapy is a major obstacle to the effective treatment of human ovarian cancer. Previous reports indicated that arsenic trioxide (ATO) induces cell apoptosis in both drug-sensitive and -resistant ovarian cancer cells.

Principal Findings

In this study, we determined the molecular mechanism of ATO-induced apoptosis in ovarian cancer cells. Our data demonstrated that ATO induced cell apoptosis by decreasing levels of phosphorylated AKT (p-AKT) and activating caspase-3 and caspase-9. Importantly, BIM played a critical role in ATO-induced apoptosis. The inhibition of BIM expression prevented AKT dephosphorylation and inhibited caspase-3 activation during cell apoptosis. However, surprisingly, gene silencing of AKT or FOXO3A had little effect on BIM expression and phosphorylation. Moreover, the activation of caspase-3 by ATO treatment improved AKT dephosphorylation, not only by cleaving the regulatory A subunit of protein phosphatase 2A (PP2A), but also by increasing its activation. Furthermore, our data indicated that the c-Jun N-terminal kinases (JNK) pathway is involved in the regulation of BIM expression.

Conclusions

We demonstrated the roles of BIM in ATO-induced apoptosis and the molecular mechanisms of BIM expression regulated by ATO during ovarian cancer cell apoptosis. Our findings suggest that BIM plays an important role in regulating p-AKT by activating caspase-3 and that BIM mediates the level of AKT phosphorylation to determine the threshold for overcoming cisplatin resistance in ovarian cancer cells.