Dissection of the multiple mechanisms of TNF-alpha-induced apoptosis in liver injury

TNFα-induced apoptosis in human myeloid cell lines HL-60 and K562 is dependent of intracellular ROS generation

The present study determines the role of reactive oxygen species (ROS) production and calcium signaling evoked by the tumor necrosis factor-alpha (TNFα) on apoptosis in the human leukemia HL-60 and K562 cell lines. The results show that treatment of both cell lines cells with 10 ng/mL TNFα resulted in a rise in the percentage of apoptotic cells after 6 h of treatment. It was also observed that the administration of 10 ng/mL TNFα increased intracellular ROS production, as well as a time-dependent increase in caspase-8, -3, and -9 activities. The present results also show that the pretreatment with well-known antioxidants such as trolox and N-acetyl cysteine partially reduced the caspase activation caused by the administration of TNFα. The findings suggest that TNFα-induced apoptosis is dependent on alterations in intracellular ROS generation in human leukemia HL-60 and K562 cells.

Chronological changes in circulating levels of soluble tumor necrosis factor receptors 1 and 2 in rats with carbon tetrachloride-induced liver injury

Carbon tetrachloride (CCl₄) facilitates the generation of hepatotoxins that can result in morphologic abnormalities, and these abnormalities are reasonably characteristic and reproducible for each particular toxin. It is also known that tumor necrosis factor-alpha (TNF-α) may participate in CCl₄-induced liver injury (CILI). In this study, we observed the chronological changes in circulating soluble tumor necrosis factor receptors 1 and 2 (sTNF-R1 and -R2) in rats with CILI. Laboratory data; circulating levels of TNF-α, sTNF-R1, and sTNF-R2; and TNF-α levels in liver tissues were measured at various time-points. In the CCl₄ group, the plasma aspartate aminotransferase (AST, 7694±3041IU/l)/alanine aminotransferase (ALT, 3241±2159 IU/l) levels peaked at 48 h after CCl₄ administration, but the other laboratory data did not differ significantly from the corresponding data in the controls. Centrilobular hepatocyte necrosis and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive cells near the central vein area were observed via hematoxylin eosin (HE) and TUNEL staining, respectively, at 24 and 48 h after CCl₄ administration. Compared to the control group, the CCl₄ group did not show significantly the increased circulating TNF-α levels. But TNF-α levels in the liver tissues first peaked at 1h (5261±2253 pg/g liver), and a second peak was observed at 12h (3806±533 pg/g liver) after CCl₄ administration. Compared to the control group, the CCl₄ group showed significantly increased circulating levels of both sTNF-R1 (797±121pg/ml) and sTNF-R2 (5696±626 pg/ml) 1h after CCl₄ administration. Since the hepatocyte apoptosis may be resulted from binding of TNF-α with TNF-R1 at 24h after administration, and consequently the circulating TNF-R2 level might be approximately 10-fold higher than the circulating TNF-R1 level. In conclusion, increased circulating levels of sTNF-R1 and -R2 potentially contribute to drug-induced liver injury, together with AST/ALT.

Induction of autophagy, a promising approach for treating liver injury

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.

Kolaviron, a Garcinia biflavonoid complex ameliorates hyperglycemia-mediated hepatic injury in rats via suppression of inflammatory responses

BACKGROUND

Chronic inflammation plays a crucial role in hyperglycemia-induced liver injury. Kolaviron (KV), a natural biflavonoid from Garcinia kola seeds have been shown to possess anti- inflammatory properties which has not been explored in diabetes. To our knowledge, this is the first study to investigate the effect of KV on pro-inflammatory proteins in the liver of diabetic rats.

METHODS

Diabetes was induced by a single intraperitoneal injection of streptozotocin (STZ) (50 mg/kg) in male Wistar rats. Kolaviron (100 mg/kg) was administered orally five times a week for six weeks. The concentrations of cytokines and chemokine were measured using Bio-plex Pro™ magnetic bead-based assays (Bio-Rad Laboratories, Hercules, USA). Plasma glucose and serum biomarkers of liver dysfunction were analyzed with diagnostic kits in an automated clinical chemistry analyzer. Insulin concentration was estimated by radioimmunoassay (RIA).

RESULT

Kolaviron (100mg/kg) treatment significantly ameliorated hyperglycemia and liver dysfunction. Serum levels of hepatic marker enzymes were significantly reduced in kolaviron treated diabetic rats. Kolaviron prevented diabetes induced increase in the hepatic levels of proinflammatory cytokines; interleukin (IL)-1beta, IL-6, tumour necrosis factor (TNF-α) and monocyte chemotactic protein (MCP-1).

CONCLUSION

The results of this study demonstrate that the hepatoprotective effects of kolaviron in diabetic rats may be partly associated with its modulating effect on inflammatory responses.

Targeting TNF-α and NF-κB activation by bee venom: role in suppressing adjuvant induced arthritis and methotrexate hepatotoxicity in rats

Low dose methotrexate is the cornerstone for the treatment of rheumatoid arthritis. One of its major drawbacks is hepatotoxicity, resulting in poor compliance of therapy. Dissatisfied arthritis patients are likely to seek the option of complementary and alternative medicine such as bee venom. The combination of natural products with modern medicine poses the possibility of potential interaction between the two groups and needs investigation. The present study was aimed to investigate the modulatory effect of bee venom acupuncture on efficacy, toxicity, and pharmacokinetics and tissue disposition of methotrexate. Complete Freund's adjuvant induced arthritic rats were treated for 3 weeks with methotrexate and/or bee venom. Arthritic score, ankle diameter, paw volume and tissue expression of NF-κB and TNF-α were determined to assess anti-arthritic effects, while anti-nociceptive effects were assessed by gait score and thermal hyperalgesia. Methotrexate toxicity was assessed by measuring serum TNF-α, liver enzymes and expression of NF-κB in liver. Combination therapy of bee venom with methotrexate significantly improved arthritic parameters and analgesic effect as compared to methotrexate alone. Bee venom ameliorated serum TNF-α and liver enzymes elevations as well as over expression of NF-κB in liver induced by methotrexate. Histological examination supported the results. And for the first time bee venom acupuncture was approved to increase methotrexate bioavailability with a significant decrease in its elimination.

CONCLUSION

bee venom potentiates the anti-arthritic effects of methotrexate, possibly by increasing its bioavailability. Also, it provides a potent anti-nociceptive effect. Furthermore, bee venom protects against methotrexate induced hepatotoxicity mostly due to its inhibitory effect on TNF-α and NF-κB.

Pentoxifylline in liver ischemia and reperfusion

Pentoxifylline is a methylxanthine compound which was first filed in 1973 and registered in 1974 in the United States by Sanofi-Aventis Deustchland Gmbh for the treatment of intermittent claudication for chronic occlusive arterial disease. This methylxanthine was later discovered to be a phosphodiesterase inhibitor. Furthermore, its hemorheological properties and its function as an inhibitor of inflammatory cytokines, like TNF-α, allowed researchers to study its effects in organ ischemia and reperfusion and transplantation. Although this drug has demonstrated beneficial effects, the mechanisms by which Pentoxifylline exerts a protective effect are not fully understood. This paper focuses on reviewing the literature to define the effect of Pentoxifylline when used in liver ischemia and reperfusion injury. Our research shows different animal models in which Pentoxifylline has been used as well as different doses and time of administration, as the ideal dose and timing have not yet been ascertained in liver ischemia and reperfusion. In conclusion, Pentoxifylline has shown positive effects in liver ischemia and reperfusion injury, and the main mechanism seems to be associated with the inhibition of TNF-α.

Molecular mechanisms of hepatocellular apoptosis induced by trovafloxacin-tumor necrosis factor-alpha interaction

Idiosyncratic drug-induced liver injury (IDILI) continues to be a significant human health problem. IDILI is characterized as occurring in a minority of individuals exposed to a drug, yet it accounts for as much as 17% of all cases of acute liver failure. Despite these concerns, the mechanisms underlying IDILI remain unknown. Trovafloxacin (TVX), which causes IDILI in humans, also causes hepatocellular death in vitro when combined with tumor necrosis factor-alpha (TNF) treatment. However, the molecular mechanisms involved in this toxicity are not fully characterized. The purpose of this study was to identify mechanisms by which TVX and TNF interact to cause hepatocellular death, with a focus on a human hepatocyte cell line. TVX and TNF interacted to cause cytotoxicity in HepG2 cells at drug concentrations similar to those in people undergoing TVX therapy. TVX/TNF treatment caused apoptosis and DNA damage in HepG2 cells that depended on caspase activation. Prolonged activation of JNK occurred in TVX/TNF-induced cytotoxicity, and treatment with the JNK selective inhibitor SP600125 attenuated cytotoxicity. TVX/TNF cotreatment also caused cytotoxicity in isolated primary murine hepatocytes that was dependent on caspase activation. These results increase understanding of molecular signaling pathways involved in hepatocellular death caused by a drug with idiosyncratic liability in the presence of TNF.

Tumor necrosis factor-α attenuates starvation-induced apoptosis through upregulation of ferritin heavy chain in hepatocellular carcinoma cells

BACKGROUND

Tumor microenviroment is characteristic of inflammation, ischemia and starvation of nutrient. TNF-α, which is an extraordinarily pleiotropic cytokine, could be an endogenous tumor promoter in some tumor types. The basic objective of this study was to investigate the effects of TNF-α on the cell viability and apoptosis of hepatocellular carcinoma cells under serum starvation, and to identify the molecular mechanisms involved.

METHODS

For this purpose, five different concentrations of TNF-α and two different serum settings (serum-cultured and serum-deprived) were used to investigate the effects of TNF-α on the cell viability and apoptosis of Hep3B and SMMC-7721 cells.

RESULTS

TNF-α (10 ng/ml) attenuated serum starvation-induced apoptosis of hepatocellular carcinoma cells, and autophagy conferred this process. BAY11-7082, a specific inhibitor of NF-κB, reversed the suppression of serum starvation-induced apoptosis by TNF-α. Moreover, TNF-α-induced NF-κB transactivation was suppressed by autophagy inhibitor 3-MA. In addition, TNF-α up-regulated Ferritin heavy chain (FHC) transiently by NF-κB activation and FHC levels were correlated with the TNF-α-induced protection against serum starvation-mediated apoptosis of hepatocellular carcinoma cells. Furthermore, FHC-mediated inhibition of apoptosis depended on suppressing ROS accumulation.

CONCLUSIONS

Our findings suggested that autophagy conferred the TNF-α protection against serum starvation-mediated apoptosis of hepatocellular carcinoma cells, the mechanism involved with the activation of the TNF-α/ NF-κB /FHC signaling pathway.

Mechanism for hepato-protective action of Liangxue Huayu Recipe (LHR): blockade of mitochondrial cytochrome c release and caspase activation

ETHNOPHARMACOLOGICAL RELEVANCE

Liangxue Huayu Recipe (LHR) as a classical prescription is clinically employed to treat liver diseases in traditional Chinese medicine.

AIM OF STUDY

In this study, we attempt to show that LHR attenuates hepatocyte apoptosis and hepatic injury induced by lipopolysaccharide (LPS) and D-galactosamine (GalN) in rats. The present study was also designed to examine whether LHR had the protective effects on d-GalN and tumor necrosis factor-α (TNF-α)-treated human L02 hepatocytes and its possible association with the mitochondrial pathway.

MATERIALS AND METHODS

LHR is composed of three traditional Chinese medicines: Herba Rehmannia, Rhubarb and Radix Paeoniae Rubra. LHR at 541, 1082 and 2164 mg/kg was orally administered to model and normal rats for 7 days. The effects of LHR on serum levels of liver enzymes, including alanine aminotransferase (ALT) and aspartate aminotransferase (AST), were measured. Hepatocyte apoptosis in vivo was assessed by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL) method. Apoptosis in vitro and related morphological changes of human L02 hepatocytes were determined by high content screening (HCS) assay. The expression levels of Bcl-2, Bax and cytochrome c were detected by Western-blot analysis in L02 cells. In addition, the activities of caspase-3 and caspase-9 were tested by enzyme-linked immunosorbent detector.

RESULTS

It revealed that LHR pretreatment effectively ameliorated the GalN/LPS-induced elevation of serum ALT and AST levels, and attenuated hepatocyte apoptosis in the rat model characterized by the addition of GalN/LPS. In subsequent experiments in vitro, LHR also attenuated GalN/TNF-α-induced apoptosis in human L02 hepatocytes. Furthermore, LHR improved the mitochondrial function, inhibited the upregulation of Bax/Bcl-2 protein ratio, decreased the release of cytochrome c from the mitochondria into the cytosol, as well as inhibited caspase-3 and caspase-9 activation in this cell model.

CONCLUSIONS

These results indicate that LHR is effective in attenuating hepatocyte apoptosis both in vivo and in vitro, and this effect is partly mediated through the activation of the mitochondrial pathway and subsequent regulation of particular pro-apoptotic gene expression.

Hepatoprotective evaluation of the total flavonoids extracted from flowers of Abelmoschus manihot (L.) Medic: In vitro and in vivo studies

ETHNOPHARMACOLOGICAL RELEVANCE

The decoction of the flowers of Abelmoschus manihot (L.) Medic is traditionally used for the treatment of jaundice and various types of chronic and acute hepatitis in Anhui and Jiangsu Provinces of China. Phytochemical studies have indicated that total flavonoids extracted from flowers of Abelmoschus manihot (L.) Medic (TFA) were the major constituents of the flowers. The present study was designed to investigate the hepatoprotective effect of the plant extracts against carbon tetrachloride (CCl4) induced hepatocyte damage in vitro and liver injury in vivo.

MATERIAL AND METHODS

In the in vitro studies, freshly isolated rat hepatocytes were exposed to CCl4 (1%) along with/without various concentrations of TFA (4.5-72mg/L). Cell damage was assessed by the trypan blue exclusion method and alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP) in the medium were analyzed. In the in vivo studies, the hepatoprotective activity of TFA (125, 250 and 500mg/kg) were investigated on CCl4-induced liver damages in mice. The levels of ALT, AST and ALP, gamma glutamyltransferase (γ-GT), tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β) and nitric oxide (NO) were determined in serum. Hepatic malondialdehyde (MDA), glutathione (GSH), superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT) and glutathione transferase (GST) were measured in the liver homogenates. Cytokine transcript levels of TNF-α, IL-1β and inducible nitric oxide synthase (iNOS) in the liver tissues of mice were measured using reverse transcription-polymerase chain reaction (RT-PCR). Livers were dissected out and evaluated for histomorphological changes.

RESULTS

A concentration-dependent increase in the percentage viability was observed when CCl4-exposed hepatocytes were treated with different concentrations of TFA. Levels of ALT, AST and ALP in the medium were significantly decreased. In the animal studies, TFA showed significant protection with the depletion of ALT, AST, ALP and γ-GT in serum as was raised by the induction of CCl4. Moreover, TFA decreased the MDA level and elevated the content of GSH in the liver as compared to those in the CCl4 group. Furthermore, activities of antioxidative enzymes, including SOD, GPx, CAT and GST, were enhanced dose dependently with TFA. Meanwhile, the inflammatory mediators (e.g., TNF-α, IL-1β and NO) were inhibited by TFA treatment both at the serum and mRNA levels. Additionally, histological analyses also showed that TFA reduced the extent of liver lesions induced by CCl4.

CONCLUSION

These results suggested that TFA protected mice against CCl4-induced liver injury through antioxidant stress and antiinflammatory effects. This finding justified the use of this plant in traditional medicine for the treatment of liver disease.

The protective role of the transmembrane thioredoxin-related protein TMX in inflammatory liver injury

AIMS

Accumulating evidence indicates that oxidative stress is associated with inflammation, and the cellular redox status can determine the sensitivity and the final outcome in response to inflammatory stimuli. To control the redox balance, mammalian cells contain a variety of oxidoreductases belonging to the thioredoxin superfamily. The large number of these enzymes suggests a complex mechanism of redox regulation in mammals, but the precise function of each family member awaits further investigations.

RESULTS

We generated mice deficient in transmembrane thioredoxin-related protein (TMX), a transmembrane oxidoreductase in the endoplasmic reticulum (ER). When exposed to lipopolysaccharide (LPS) and d-(+)-galactosamine (GalN) to induce inflammatory liver injury, mutant mice were highly susceptible to the toxicants and developed severe liver damage. LPS-induced production of inflammatory mediators was equivalent in both wild-type and TMX(-/-) mice, whereas neutralization of the proinflammatory cytokine tumor necrosis factor-α suppressed the toxic effects of LPS/GalN in the mutant mice. Liver transcriptional profiles revealed enhanced activation of the p53-signaling pathway in the TMX(-/-) mice after LPS/GalN treatment. Furthermore, TMX deficiency also caused increased sensitivity to thioacetamide, which exerts its hepatotoxicity through the generation of reactive oxygen species.

INNOVATION

The present study is the first to address the role of the oxidoreductase TMX in inflammatory liver injury. The phenotype of mice deficient in TMX suggests a functional link between redox regulation in the ER and susceptibility to oxidative tissue damage.

CONCLUSION

We conclude that TMX plays a major role in host defense under the type of inflammatory conditions associated with oxidative stress.

Mitophagy: mechanisms, pathophysiological roles, and analysis

Abstract Mitochondria are essential organelles that regulate cellular energy homeostasis and cell death. The removal of damaged mitochondria through autophagy, a process called mitophagy, is thus critical for maintaining proper cellular functions. Indeed, mitophagy has been recently proposed to play critical roles in terminal differentiation of red blood cells, paternal mitochondrial degradation, neurodegenerative diseases, and ischemia or drug-induced tissue injury. Removal of damaged mitochondria through autophagy requires two steps: induction of general autophagy and priming of damaged mitochondria for selective autophagic recognition. Recent progress in mitophagy studies reveals that mitochondrial priming is mediated either by the Pink1-Parkin signaling pathway or the mitophagic receptors Nix and Bnip3. In this review, we summarize our current knowledge on the mechanisms of mitophagy. We also discuss the pathophysiological roles of mitophagy and current assays used to monitor mitophagy.

Kupffer cell-mediated hepatic injury induced by silica nanoparticles in vitro and in vivo

Silica nanoparticles (SiO₂ NPs) have been shown to exert cytotoxic effects in hepato-cytes and to cause liver injury. In the liver, Kupffer cells (KCs), as the resident macrophages, play an important role in the normal physiology and homeostasis of the liver. Nevertheless, few studies have attempted to clarify the role of KCs in hepatic injury induced by SiO₂ NPs. In this study, we treated Buffalo rat liver (BRL) cells with the supernatants of SiO₂ NP-stimulated KCs to determine KC-mediated hepatotoxicity and its underlying preliminary mechanism. We also examined the response of KCs and liver injury in vivo after the administration of SiO₂ NPs. The results showed that KCs stimulated by SiO₂ NPs release large amounts of reactive oxygen species, tumor necrosis factor-α and nitric oxide. After BRL cells were cultured with the supernatants of SiO₂ NP-stimulated KCs, the viability of BRL cells was reduced, and increases in aspartate aminotransferase and lactate dehydrogenase leakage were observed. Exposure to SiO₂ NPs in vivo caused KC hyperplasia, hepatic inflammation, and oxidative stress, which led to changes in the biochemical composition of the liver. These data suggest that SiO₂ NPs activate KCs to mediate hepatic injury and that the preliminary mechanism involves the release of bioactive substances from KCs.

Beta-catenin-NF-κB interactions in murine hepatocytes: a complex to die for

Wnt/β-catenin signaling plays an important role in hepatic homeostasis, especially in liver development, regeneration, and cancer, and loss of β-catenin signaling is often associated with increased apoptosis. To elucidate how β-catenin may be regulating hepatocyte survival, we investigated the susceptibility of β-catenin conditional knockout (KO) mice and their wild-type (WT) littermates to Fas and tumor necrosis factor-α (TNF-α), two common pathways of hepatocyte apoptosis. While comparable detrimental effects from Fas activation were observed in WT and KO, a paradoxical survival benefit was observed in KO mice challenged with D-galactosamine/lipopolysaccharide. KO mice showed significantly lower morbidity and liver injury due to early, robust, and protracted activation of NF-κB in the absence of β-catenin. Enhanced NF-κB activation in KO mice was associated with increased basal inflammation and Toll-like receptor 4 expression and lack of the p65/β-catenin complex in hepatocytes. The p65/β-catenin complex in WT livers underwent temporal dissociation allowing for NF-κB activation to regulate hepatocyte survival following TNF-α-induced hepatic injury. Decrease of total β-catenin protein but not its inactivation induced p65 activity, whereas β-catenin stabilization either chemically or due to mutations repressed it in hepatomas in a dose-dependent manner, whereas β-catenin stabilization repressed it either chemically or due to mutations.

CONCLUSION

The p65/β-catenin complex in hepatocytes undergoes dynamic changes during TNF-α-induced hepatic injury and plays a critical role in NF-κB activation and cell survival. Modulation of β-catenin levels is a unique mode of regulating NF-κB activity and thus may present novel opportunities in devising therapeutics in specific hepatic injuries.

Pathophysiological Significance of Hepatic Apoptosis

Apoptosis is a classical pathological feature in liver diseases caused by various etiological factors such as drugs, viruses, alcohol, and cholestasis. Hepatic apoptosis and its deleterious effects exacerbate liver function as well as involvement in fibrosis/cirrhosis and carcinogenesis. An imbalance between apoptotic and antiapoptotic capabilities is a prominent characteristic of liver injury. The regulation of apoptosis and antiapoptosis can be a pivotal step in the treatment of liver diseases.

Using ASMase knockout mice to model human diseases

Acid sphingomyelinase (ASMase) is a key initiator of sphingomyelin/ceramide signal transduction activated by many stress stimuli. Over the past two decades, much progress has been made in defining the clinical relevance of sphingomyelin/ceramide signaling in numerous diseases using ASMase knockout mice. Organs that operate this pathway are numerous and the disease states regulated are diverse, with ceramide generation governing injury in tumor, gut, ovary, brain, lung, heart, liver, and during infection. This chapter emphasizes evolutionary conservation of sphingolipid stress signaling and mammalian adaptations that permit transduction of organotypic responses. Recognition that the sphingomyelin/ceramide transducer calibrates extent of tissue injury, ultimately acting as a molecular switch that determines organ fate, is driving development of new pharmacologic concepts and tools to intervene therapeutically.

Apoptosis induction by OTA and TNF-α in cultured primary rat hepatocytes and prevention by silibinin

In cultures of primary rat hepatocytes, apoptosis occurred after application of 20 ng/mL tumor necrosis factor alpha (TNF-α). However, this was only in the presence of 200 ng/mL of the transcriptional inhibitor actinomycin D (ActD). This toxic effect was completely prevented in the presence of 25 µg/mL soluble TNF-α receptor I (sTNFR I) in the supernatant of hepatocyte cell cultures. Apoptosis also occurred after application of 12.5 µmol/L ochratoxin A (OTA). However, that was not prevented by up to 500 µg/mL sTNFR I, indicating that TNF-α/TNFR I is not involved in OTA mediated apoptosis in hepatocytes. The antioxidative flavanolignan silibinin in doses from 130 to 260 µmol/L prevented chromatin condensation, caspase-3 activation, and apoptotic DNA fragmentation that were induced by OTA, by 10 mmol/L hydrogen peroxide (H₂O₂) and by ultraviolet (UV-C) light (50 mJ/cm²), respectively. To achieve protection by silibinin, the drug was applied to the cell cultures for 2 h in advance. OTA stimulated lipid peroxidation on cultured immortalized rat liver HPCT cells, as was revealed by malondialdehyde (MDA) production. Lipid peroxidation occurred further by H₂O₂ and ActD/TNF-α incubation. These reactions were also suppressed by silibinin pretreatment. We conclude that the anti-apoptotic activity of silibinin against OTA, H₂O₂ and ActD/ TNF-α is caused in vitro by the antioxidative effects of the flavanolignan. Furthermore, cytotoxicity of the pro-apoptotic toxins was revealed by MTT-test. When applied separately, ActD and TNF-α showed no cytotoxic effects after 24 h, but were cytotoxic if applied in combination. The used concentrations of OTA, H₂O₂ and the dose of UV-C caused a substantial decrease in viability within 36 h that was prevented mostly by silibinin. We conclude that silibinin is a potent protective compound against apoptosis and cytotoxicity caused by OTA and the investigated compounds.

C-phycocyanin attenuates cisplatin-induced nephrotoxicity in mice

Although cisplatin is a highly effective antineoplastic agent, nephrotoxicity is its major clinical problem. Recently, it was reported that Spirulina, a blue-green algae, has potent antioxidant properties. The aim of this study was to establish the possible protective role of C-phycocyanin (PC), one of the active ingredients of Spirulina, against cisplatin-induced nephrotoxicity. This study was carried out using human kidney-2 (HK-2) cells and male C57BL6 mice. Cells and mice were divided into four groups; untreated control group, PC-treated control group, cisplatin-treated group, and PC plus cisplatin-treated group. The molecular, functional, and structural parameters were measured. PC significantly attenuated blood urea nitrogen, serum creatinine, renal histological damages, and apoptotic cell death in cisplatin-treated mice. The cisplatin-induced cell death was significantly attenuated in cells pretreated with PC. PC also significantly attenuated the elevation of p-ERK, p-JNK, and p-p38 induced by cisplatin treatment. The expression of Bax, caspase-9, and caspase-3 in cisplatin-treated cells were also decreased by PC treatment. In conclusion, PC ameliorates cisplatin-induced nephrotoxicity and, at least in part, suppression of p-ERK, p-JNK, p-p38, Bax, caspase-9, and caspase-3 may be involved in this mechanism.

Mechanistic overview of reactive species-induced degradation of the endothelial glycocalyx during hepatic ischemia/reperfusion injury

Endothelial cells are covered by a delicate meshwork of glycoproteins known as the glycocalyx. Under normophysiological conditions the glycocalyx plays an active role in maintaining vascular homeostasis by deterring primary and secondary hemostasis and leukocyte adhesion and by regulating vascular permeability and tone. During (micro)vascular oxidative and nitrosative stress, which prevails in numerous metabolic (diabetes), vascular (atherosclerosis, hypertension), and surgical (ischemia/reperfusion injury, trauma) disease states, the glycocalyx is oxidatively and nitrosatively modified and degraded, which culminates in an exacerbation of the underlying pathology. Consequently, glycocalyx degradation due to oxidative/nitrosative stress has far-reaching clinical implications. In this review the molecular mechanisms of reactive oxygen and nitrogen species-induced destruction of the endothelial glycocalyx are addressed in the context of hepatic ischemia/reperfusion injury as a model disease state. Specifically, the review focuses on (i) the mechanisms of glycocalyx degradation during hepatic ischemia/reperfusion, (ii) the molecular and cellular players involved in the degradation process, and (iii) its implications for hepatic pathophysiology. These topics are projected against a background of liver anatomy, glycocalyx function and structure, and the biology/biochemistry and the sources/targets of reactive oxygen and nitrogen species. The majority of the glycocalyx-related mechanisms elucidated for hepatic ischemia/reperfusion are extrapolatable to the other aforementioned disease states.

Loss of caspase-8 protects mice against inflammation-related hepatocarcinogenesis but induces non-apoptotic liver injury

BACKGROUND & AIMS

Disruption of the nuclear factor-κB (NF-κB) essential modulator (NEMO) in hepatocytes of mice (NEMO(Δhepa) mice) results in spontaneous liver apoptosis and chronic liver disease involving inflammation, steatosis, fibrosis, and development of hepatocellular carcinoma. Activation of caspase-8 (Casp8) initiates death receptor-mediated apoptosis. We investigated the pathogenic role of this protease in NEMO(Δhepa) mice or after induction of acute liver injury.

METHODS

We created mice with conditional deletion of Casp8 in hepatocytes (Casp8(Δhepa)) and Casp8(Δhepa)NEMO(Δhepa) double knockout mice. Acute liver injury was induced by Fas-activating antibodies, lipopolysaccharides, or concanavalin A. Spontaneous hepatocarcinogenesis was monitored by magnetic resonance imaging.

RESULTS

Hepatocyte-specific deletion of Casp8 protected mice from induction of apoptosis and liver injury by Fas or lipopolysaccharides but increased necrotic damage and reduced survival times of mice given concanavalin A. Casp8(Δhepa)NEMO(Δhepa) mice were protected against steatosis and hepatocarcinogenesis but had a separate, spontaneous phenotype that included massive liver necrosis, cholestasis, and biliary lesions. The common mechanism by which inactivation of Casp8 induces liver necrosis in both injury models involves the formation of protein complexes that included the adaptor protein Fas-associated protein with death domain and the kinases receptor-interacting protein (RIP) 1 and RIP3-these have been shown to be required for programmed necrosis. We demonstrated that hepatic RIP1 was proteolytically cleaved by Casp8, whereas Casp8 inhibition resulted in accumulation of RIP complexes and subsequent liver necrosis.

CONCLUSIONS

Inhibition of Casp8 protects mice from hepatocarcinogenesis following chronic liver injury mediated by apoptosis of hepatocytes but can activate RIP-mediated necrosis in an inflammatory environment.

An evaluation of the effects of Lactobacillus ingluviei on body weight, the intestinal microbiome and metabolism in mice

BACKGROUND

Food can modify the intestinal flora, and Lactobacillus ingluviei has been shown to cause weight gain in chicks and ducks but not in mammals.

METHODOLOGY

Female BALB/c mice were divided into a control and two experimental groups and were inoculated either once or twice with L. ingluviei or with PBS. Faecal samples were collected and tested using qPCR in order to detect and quantify Lactobacillus spp., Bacteroidetes spp. and Firmicutes spp. Gene expression was examined in liver and adipose tissue by microarray and qPCR. Metabolic indicators in the plasma were also measured.

RESULTS

Mice that were inoculated with 4 × 10(10) L. ingluviei presented a significant increase in weight gain and liver weight and significant increases in Lactobacillus spp. and Firmicutes DNA copy numbers in their faeces. The mRNA levels of fatty acyl synthase (Fas), sterol regulatory element binding factor 1 (Srebp1c), tumour necrosis factor alpha (Tnf), cytochrome P450 2E1 (Cyp2e1), 3-phosphoinositide-dependent protein kinase-1 (Pdpk1), acyl-Coenzyme A dehydrogenase 11 (Acad11), ATP-binding cassette sub family member G (ABCG2) and DEAD box polypeptide 25 (Ddx25) were significantly elevated in the liver tissues of animals in the experimental group. In gonadal adipose tissue, the expression levels of leptin, peroxisome proliferator-activated receptor γ (Pparg) and Srebp1c were significantly higher in animals from the experimental group, whereas the expression of adiponectin was significantly lower in these animals.

CONCLUSIONS

The inoculation of L. ingluviei in mice resulted in alterations in the intestinal flora, increased weight gain and liver enlargement, accelerated metabolism and increased inflammation.

The functional expression of TLR3 in EPCs impairs cell proliferation by induction of cell apoptosis and cell cycle progress inhibition

Toll-like receptor 3 (TLR3), a member of the TLR family that recognizes double-stranded RNA (dsRNA), plays an important role in antiviral immunity. TLR3 is widely expressed in various cells and the activation of TLR3 induces cell apoptosis in some cells. However, the effect of TLR3 on cell proliferation in endothelial progenitor cells (EPCs) is unclear. In this study, we found that EPCs expressed high levels of TLR1, 3, 4, and 6 and low levels of TLR2, 5, 7, 8, and 10. The treatment of EPCs with TLR3 agonist Poly I:C up-regulated the expression of cytokines IL-1β, IL-6, IL-8, TNF-α, IFN-α, and IFN-β, indicating that EPCs expressed functional TLR3. Moreover, Poly I:C treatment induced cell cycle progress inhibition and cell apoptosis, leading to the inhibition of cell proliferation. Further studies indicated that IL-1β was involved in TLR3-induced cell proliferation inhibition, as IL-1β inhibited cell proliferation in a dose-dependent manner, and the IL-1β receptor type I (IL-1R1)-neutralizing antibody ameliorated Poly I:C-induced cell proliferation inhibition. Taken together, these results suggest that Poly I:C impairs cell proliferation by inducing cell cycle progress inhibition and cell apoptosis via TLR3 in EPCs.

Protective effects of luteolin against apoptotic liver damage induced by D-galactosamine/lipopolysaccharide in mice

In this study, the protective effects of luteolin (1, a major component of Cirsium japonicum) were examined against d-galactosamine (GalN)/lipopolysaccharide (LPS)-induced fulminant hepatic failure. Mice received an intraperitoneal injection of 1 (25, 50, 100, and 200 mg·kg(-1)) 1 h before treatment with GalN (700 mg·kg(-1))/LPS (10 μg·kg(-1)). Treatment with GalN/LPS resulted in increased mortality and serum aminotransferase activity. These increases were attenuated by pretreatment with 1. Treatment with GalN/LPS induced an increase in the serum level of tumor necrosis factor-α (TNF-α) and protein expression of TNF-α receptor-associated death domain, and these increases were prevented by 1. In addition, 1 attenuated apoptosis induced by GalN/LPS treatment, which was analyzed using a caspase-3 and -8 activity assay, as well as by proapoptotic BH3-only protein and cytochrome c protein expression, and by a terminal deoxynuleotidyl transferase-mediated dUTP nick end-labeling method. After GalN/LPS injection, nuclear phosphorylated c-Jun levels showed a significant increase, which were attenuated by 1. The present findings suggest that luteolin ameliorates D-GalN/LPS-induced liver injury and that this protection is likely due to inhibition of the extrinsic and intrinsic apoptotic pathways.

A glutamine synthetase inhibitor increases survival and decreases cytokine response in a mouse model of acute liver failure

BACKGROUND

Acute liver failure (ALF) can be induced in mice by administering Escherichia coli lipopolysaccharide (LPS) and D-galactosamine (D-GalN), which induce an inflammatory response involving tumour necrosis factor (TNF)-α production and a hepatocyte-specific transcriptional block. Under these conditions, binding of TNF-α to its cognate receptor on hepatocytes eventually leads to their apoptosis.

AIMS

As part of an effort to identify drugs to treat this disease model, we have investigated whether the glutamine synthetase inhibitor methionine sulfoximine (MSO) could play a protective role, given its effectiveness in the inhibition of brain swelling associated with hyperammonaemia.

METHODS

Mouse survival, glutamine synthetase activity, hepatocyte apoptosis and induction of inflammatory cytokines were measured in mice treated with MSO before an intraperitoneal injection of LPS/D-GalN. The effect of MSO on viability and on TNF-α release was also assessed on inflammatory and liver cells.

RESULTS

We have found that, in mice treated with LPS/D-GalN, MSO (i) drastically increases animal survival; (ii) sharply reduces glutamine synthetase activity, without inhibiting its other target, γ-glutamyl cysteine synthetase; (iii) inhibits death receptor-mediated apoptosis in hepatocytes upstream to cytokine binding; (iv) strongly reduces the overall inflammatory cytokine response, including a significant decrease in TNF-α induction in vivo and ex vivo, and in the interferon-γ level and signalling.

CONCLUSIONS

These results demonstrate that the MSO target glutamine synthetase is required for the early steps of the cytokine response to endotoxins, and that its pharmacological inhibition may be exploited to treat inflammation.

Differential roles of unsaturated and saturated fatty acids on autophagy and apoptosis in hepatocytes

Fatty acid-induced lipotoxicity plays a critical role in the pathogenesis of nonalcoholic liver disease. Saturated fatty acids and unsaturated fatty acids have differential effects on cell death and steatosis, but the mechanisms responsible for these differences are not known. Using cultured HepG2 cells and primary mouse hepatocytes, we found that unsaturated and saturated fatty acids differentially regulate autophagy and apoptosis. The unsaturated fatty acid, oleic acid, promoted the formation of triglyceride-enriched lipid droplets and induced autophagy but had a minimal effect on apoptosis. In contrast, the saturated fatty acid, palmitic acid, was poorly converted into triglyceride-enriched lipid droplets, suppressed autophagy, and significantly induced apoptosis. Subsequent studies revealed that palmitic acid-induced apoptosis suppressed autophagy by inducing caspase-dependent Beclin 1 cleavage, indicating cross-talk between apoptosis and autophagy. Moreover, our data suggest that the formation of triglyceride-enriched lipid droplets and induction of autophagy are protective mechanisms against fatty acid-induced lipotoxicity. In line with our in vitro findings, we found that high-fat diet-induced hepatic steatosis was associated with autophagy in the mouse liver. Potential modulation of autophagy may be a novel approach that has therapeutic benefits for obesity-induced steatosis and liver injury.

Potential role of leptin, adiponectin and three novel adipokines--visfatin, chemerin and vaspin--in chronic hepatitis

Chronic hepatitis C (CHC) is generally a slowly progressive disease, but some factors associated with rapid progression have been identified. Steatosis, independently of its metabolic or viral origin, leads to liver injury and fibrosis. It is suggested that hepatitis C virus may contribute to a wide spectrum of metabolic disturbances-namely, steatosis, insulin resistance, increased prevalence of impaired glucose tolerance, type 2 diabetes mellitus and lipid metabolism abnormalities. Adipokines, which are produced mainly by adipose tissue, may influence the inflammatory response and insulin sensitivity and contribute to the development of metabolic abnormalities in CHC and also regulate fibrogenesis and angiogenesis. Visfatin was described as an adipokine with immunomodulating and proinflammatory properties that promotes B-cell maturation and enhances activation of leukocytes, synthesis of adhesion molecules and production of proinflammatory cytokines. Visfatin exerts insulin-mimetic effects, decreases plasma glucose levels and regulates cell energy balance. Chemerin stimulates chemotaxis of dendritic cells, macrophages and natural killer (NK) cells toward the site of inflammation. On the other hand, it inhibits synthesis of proinflammatory mediators and enhances adiponectin production, influences adipocyte differentiation and maturation and regulates glucose uptake in adipocytes. Vaspin expression in human adipose tissue seems to be a compensatory mechanism associated with obesity and insulin resistance. Vaspin suppresses leptin, tumor necrosis factor (TNF)-α and resistin expression. Leptin protects against liver steatosis but accelerates fibrosis progression and exacerbates the inflammatory process. In contrast, adiponectin exerts a hepatoprotective effect. In this report, data indicating a possible role of these adipokines in the pathogenesis of chronic hepatitis are summarized.

Metabolomics study of alcohol-induced liver injury and hepatocellular carcinoma xenografts in mice

Alcohol abuse is one of the major causes of liver injury and a promoter for hepatocellular carcinoma (HCC). To understand the disease-associated metabolic changes, we investigated and compared the profiles of metabolites in nude mice with alcohol-induced liver injury or bearing a HCC xenograft (HCCX). Alcohol-induced liver injury was achieved by daily administration of grain liquor, and HCC xenografts were generated by subcutaneous inoculation of HepG2 cells in nude mice. Metabolites in serum samples were profiled by ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF MS). The acquired data was analyzed by principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) to identify potential disease-specific biomarkers. Results showed that the phosphatidylcholine (PC) levels were significantly higher in both liver injury and HCCX mice compared with the control. Interestingly, lysophosphatidylcholines (LPCs) that contain saturated or monounsaturated fatty acids were reduced in both liver injury and HCCX mice, but polyunsaturated fatty acids LPCs were elevated in liver injury mice only. These data delineated the disease-related metabolic alterations of LPCs in liver injury and HCC, suggesting that the LPC profile in serum may be biomarkers for these two common liver diseases.

Tumor necrosis factor alpha pathways develops liver apoptosis in type 1 diabetes mellitus

We analyzed the contribution of TNF-α intracellular pathway in the development of apoptosis in the liver of streptozotocin-induced diabetic rats. In liver tissue, diabetes promoted a significant increase of TNF-α/TNF-R1, and led to the activation of caspase-8, of nuclear factor kappa B (NFκB), and JNK signaling pathways. The activation of NFκB led to an induction of iNOS and consequent increase in NO production. As a consequence of such changes a significant increase of caspase-3 activity and of apoptotic index were observed in the liver of diabetic animals. Importantly, the treatment in vivo of diabetic rats with etanercept (TNF-α blocking antibody) or aminoguanidine (selective iNOS inhibitor) significantly attenuated the induction of apoptosis by reduction of caspase-3 activity. Overall, we demonstrated that in the diabetes enhances TNF-α in the liver, which may be a fundamental key leading to apoptotic cell death, through activation of caspase-8, NFκB and JNK pathways.

Apoptosis in nonalcoholic fatty liver disease: diagnostic and therapeutic implications

Pathological increases in cell death in the liver as well as in peripheral tissues has emerged as an important mechanism involved in the development and progression of nonalcoholic fatty liver disease (NAFLD). An increase in hepatocyte cell death by apoptosis is typically present in patients with NAFLD and in experimental models of steatohepatitis, while an increase in adipocyte cell death in visceral adipose tissue may be an important mechanism triggering insulin resistance and hepatic steatosis. The two fundamental pathways of apoptosis, the extrinsic (death receptor-mediated) and intrinsic (organelle-initiated) pathways, are both involved. This article summarizes the current knowledge related to the distinct molecular and biochemical pathways of cell death involved in NAFLD pathogenesis. In particular, it will highlight the efforts for the development of both novel diagnostic and therapeutic strategies based on this knowledge.

TNF-α treatment alters Mfn2 expression and mitochondrial morphology and function in hepatic LO2 cells

AIM: To investigate the influence of treatment with tumor necrosis factor-alpha (TNF-α) on the expression of mitofusin 2 (Mfn2) and mitochondrial morphology and function in hepatic LO2 cells.

METHODS: After pEGFP-Mfn2 plasmid was transfected into LO2 cells with Lipofectamine 2000, transfected LO2 cells were incubated with TNF-α for 12 h. The expression of Mfn2 mRNA and protein was detected by reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot, respectively. MitoTracker Mitochondrion-Selective Probes were used to detect the changes in mitochondrial morphology. ATP synthesis and reactive oxygen species (ROS) production were measured to assess mitochondrial function.

RESULTS: RT-PCR and Western blot analyses showed that Mfn2 was highly expressed in LO2 cells. After treatment of LO2 cells with TNF-α, Mfn2 expression was significantly suppressed (0.279 ± 0.026 vs 0.742 ± 0.018; 0.196 ± 0.024 vs 0.580 ± 0.011, P < 0.05), ATP level decreased (2.00 µmol/g ± 0.15 µmol/g vs 5.81 µmol/g ± 0.31 µmol/g, P < 0.05), ROS production increased (80.68 ± 4.02 vs 65.44 ± 3.47, P < 0.05), and the normal tubular network of mitochondria was fragmented into short rods or spheres when compared to control cells. In contrast, these changes were not significant in Mfn2-transfected LO2 cells.

CONCLUSION: TNF-α treatment may alter mitochondrial morphology and impair mitochondrial function by decreasing the expression of Mfn2 in hepatic LO2 cells.

Tumor necrosis factor and its receptors in the neuroretina and retinal vasculature after ischemia-reperfusion injury in the pig retina

PURPOSE

Numerous studies have been performed aimed at limiting the extent of retinal injury after ischemia, but there is still no effective pharmacological treatment available. The aim of the present study was to examine the role of tumor necrosis factor (TNF)α and its receptors (TNF-R1 and TNF-R2), especially considering the neuroretina and the retinal vasculature since the retinal blood vessels are key organs in circulatory failure.

METHODS

Retinal ischemia was induced in pigs by elevating the intraocular pressure to 80 mmHg in one eye, while the other eye served as a control (sham-operated). One hour of ischemia was followed by 5 or 12 h of reperfusion. Retinal circulation was examined in vivo by fundus imaging and fluorescein angiography. TNF-α levels were measured in the vitreous using an angiogenesis antibody array test. The presence and amounts of TNF-α, TNF-R1, and TNF-R2 were investigated in the neuroretina and in the retinal blood vessels, using immunofluorescence staining and real-time PCR techniques.

RESULTS

Fundus imaging showed obstructed blood flow when ischemia was induced, and reperfusion was clearly visualized using fluorescein angiography. Ischemia resulted in elevated levels of TNF-α protein in the vitreous and TNF-α mRNA in the neuroretina. TNF-α immunofluorescence staining was localized to the Müller cells and the outer plexiform layer of the neuroretina. The expression of TNF-R1 and TNF-R2 mRNA was increased in both the neuroretina and retinal arteries following ischemia-reperfusion. Immunofluorescence double staining for TNF-R1 and either smooth muscle actin or 4',6-diamidino-2-phenylindole (DAPI) indicated expression in the cell membranes of the vascular smooth muscle cells. Double staining with TNF-R1 and calbindin showed localization to the horizontal cells in the outer plexiform layer of the neuroretina.

CONCLUSIONS

Retinal ischemia results in increased expression of TNF-α and its receptors (TNF-R1 and TNF-R2). Cellular signaling pathways involving TNF may be important in the development of retinal injury following ischemia and thus an interesting target for future development of pharmacological therapeutics.

Catumaxomab--trifunctional anti-EpCAM antibody used to treat malignant ascites

IMPORTANCE OF THE FIELD

Malignant ascites is a sign of advanced tumour growth and is associated with significant morbidity and a poor prognosis with a median survival time of a few months. Paracentesis is a recommended treatment for malignant ascites, but can cause complications, for example infections, injury of abdominal organs, persistent leakage of ascites, and haematoma/haemorrhage. The European Medicines Agency (EMA) approved the use of a trifunctional bispecific antibody, catumaxomab (Removab), for the intraperitoneal (i.p.) treatment of malignant ascites in April 2009.

AREAS COVERED IN THIS REVIEW

This review describes the tailored preclinical and the clinical development of catumaxomab for the i.p. treatment of malignant ascites from 1998 to 2009.

WHAT THE READER WILL GAIN

Relevant toxicology and pharmacokinetic findings are reported as well as main results of a large international Phase II/III study that was pivotal in the EMA approval of catumaxomab.

TAKE HOME MESSAGE

Catumaxomab i.p. treatment results in a significant and clinically relevant improvement of puncture-free survival time and time to first need for puncture compared with paracentesis alone. The related side effects of catumaxomab treatment are predictable and related to the antibody's mode of action.

Tumor necrosis factor alpha and its soluble receptors in obese children with NAFLD

PURPOSE

To evaluate the serum levels of tumor necrosis factor (TNF) alpha and its soluble receptors in obese children with non-alcoholic fatty liver disease (NAFLD).

MATERIAL/METHODS

Fasting serum levels of TNFalpha and its receptors were determined in 45 consecutive obese children with suspected liver disease and 20 lean controls. The degree of liver steatosis was graded in ultrasound according to Saverymuttu. 1H-MR spectroscopy was performed with 1.5T scanner with PRESS sequence.

RESULTS

A fatty liver was confrmed in 32 children by ultrasonography (group I); 16 of them also had increased ALT activity (group Ia - NAFLD). Serum concentrations of TNFalpha and its receptors were significantly higher in obese children with NAFLD compared to controls. Significant correlation was found between ultrasonographic grade of liver steatosis and TNFalpha level but serum level of this adipokine was not significantly different in children with advanced liver steatosis (grade 2-3, n=13) compared to patients with mild steatosis (grade 1, n=19). The ability of TNFalpha and its receptors (R1, R2) to differentiate children with advanced liver steatosis from those with mild steatosis was insignificant. However, the ability of serum TNFalpha to differentiate obese children with liver steatosis from those without steatosis was significant (AUC=0.7448, p=0.0291).

CONCLUSION

Although TNFalpha does not predict advanced liver steatosis, it may be suitable serum marker in predicting liver steatosis in obese children.

A microarray analysis of early activated pathways in concanavalin A-induced hepatitis

OBJECTIVE

To explore the mechanisms of fulminant hepatitis (FH) in the early stages, and to determine the critical pathways in its initiation and progression.

METHODS

Twelve BALB/c mice were divided into four groups: one group left as negative control and sacrificed immediately after injection of phosphate-buffered saline (PBS), and another three groups with concanavalin A (Con A) administration sacrificed at 1, 3, and 6 h after injection. Affymetrix GeneChip(R) Mouse 430 2.0 Array was employed to evaluate the expression profile of each of the 12 samples. Further analysis was done on the microarray data to extract the genes that were differentially expressed. Enrichment analysis was carried out to determine relevant pathways within which regulated genes were significantly enriched.

RESULTS

A total of 393, 8354 and 11 344 differentially expressed genes were found, respectively, at three time points. During 0-1 h and 1-3 h, most of the pathways enriched with regulated genes were related to immune response and inflammation, among which Toll-like receptor (TLR) signaling and mitogen-activated protein kinase (MAPK) signaling appeared during both phases, while cytokine-cytokine receptor interaction, apoptosis, T cell receptor signaling, and natural killer (NK) cell-mediated cytotoxicity pathways emerged during the second phase. Pathways found to be significant during 3-6 h were mostly related to metabolic processes.

CONCLUSION

The TLR signaling pathway dominates the early responses of Con A-induced FH in mice. It stimulates the production of type I cytokines, therefore recruiting and activating T/NK cells. Activated T/NK cells exert their cytotoxicity on hepatocytes through inducing death receptor-intermediated apoptosis, resulting in liver injury.

Flavokawain B, the hepatotoxic constituent from kava root, induces GSH-sensitive oxidative stress through modulation of IKK/NF-kappaB and MAPK signaling pathways

Kava (Piper methysticum Foster, Piperaceae) organic solvent-extract has been used to treat mild to moderate anxiety, insomnia, and muscle fatigue in Western countries, leading to its emergence as one of the 10 best-selling herbal preparations. However, several reports of severe hepatotoxicity in kava consumers led the U.S. Food and Drug Administration and authorities in Europe to restrict sales of kava-containing products. Herein we demonstrate that flavokawain B (FKB), a chalcone from kava root, is a potent hepatocellular toxin, inducing cell death in HepG2 (LD(50)=15.3 ± 0.2 μM) and L-02 (LD(50)=32 μM) cells. Hepatocellular toxicity of FKB is mediated by induction of oxidative stress, depletion of reduced glutathione (GSH), inhibition of IKK activity leading to NF-κB transcriptional blockade, and constitutive TNF-α-independent activation of mitogen-activated protein kinase (MAPK) signaling pathways, namely, ERK, p38, and JNK. We further demonstrate by noninvasive bioluminescence imaging that oral consumption of FKB leads to inhibition of hepatic NF-κB transcriptional activity in vivo and severe liver damage. Surprisingly, replenishment with exogenous GSH normalizes both TNF-α-dependent NF-κB as well as MAPK signaling and rescues hepatocytes from FKB-induced death. Our data identify FKB as a potent GSH-sensitive hepatotoxin, levels of which should be specifically monitored and controlled in kava-containing herb products.

Lysosomal-mitochondrial cross-talk during cell death

Lysosomes are membrane-bound organelles, which contain an arsenal of different hydrolases, enabling them to act as the terminal degradative compartment of the endocytotic, phagocytic and autophagic pathways. During the last decade, it was convincingly shown that destabilization of lysosomal membrane and release of lysosomal content into the cytosol can initiate the lysosomal apoptotic pathway, which is dependent on mitochondria destabilization. The cleavage of BID to t-BID and degradation of anti-apoptotic BCL-2 proteins by lysosomal cysteine cathepsins were identified as links to the mitochondrial cytochrome c release, which eventually leads to caspase activation. There have also been reports about the involvement of lysosome destabilization and lysosomal proteases in the extrinsic apoptotic pathway, although the molecular mechanism is still under debate. In the present article, we discuss the cross-talk between lysosomes and mitochondria during apoptosis and its consequences for the fate of the cell.

Non-structural and nucleocapsid proteins of Punta Toro virus induce apoptosis of hepatocytes through both intrinsic and extrinsic pathways

Punta Toro virus (PTV; family Bunyaviridae, genus Phlebovirus) causes severe hepatic damage through brisk apoptosis of hepatocytes. In the present study, two viral proteins encoded by the S segment of the viral genome, non-structural (NSs) and nucleocapsid protein (N), were examined for their roles in apoptosis. Expression of NSs in HepG2 cells led to apoptosis in 45% of transfected cells, and with N, 28%, on average. These levels represent a four- to an eightfold increase over cells transfected with the mutated protein vectors. Caspase-3, -8 and -9 activities were increased by N protein when compared with the control NC (P < 0.05), and by NSsA and NSsB, as compared to control NSsC (P < 0.01). Treatment of the transfected cells with caspase-8 or -9 inhibitors markedly decreased apoptosis. Neutralization of TNF-alpha or Fas ligand had no effect on apoptosis. These results indicate that both NSs and N are responsible for causing hepatocyte apoptosis by triggering the extrinsic caspase-8 and intrinsic caspase-9 pathways.

Visfatin serum levels in chronic hepatitis C patients

Visfatin is a new adipokine involved in several processes. The data concerning visfatin in chronic hepatitis C (CHC) is small. To assess visfatin serum concentration and to study its association with biochemical and morphological features in CHC. Seventy nonobese patients with CHC (Group 1) confirmed by the presence of serum hepatitis C virus (HCV)-RNA and 20 healthy volunteers (Group 2), similar in age and BMI with normal fasting glucose and lipid profile were included. Visfatin was significantly increased in Group 1 compared with Group 2 (55.6 +/- 23.1 vs 23.7 +/- 3.8 ng/mL; P < 0.001). Visfatin was negatively associated with necro-inflammatory activity grade (r = -0.36; P = 0.007). The lowest levels were found in patients with the most advanced inflammation: grades 3-4 - 46.8 +/- 17.1, grade 2 - 52.6 +/- 18.4 and grade 1 - 75.2 +/- 27.6 ng/mL; P = 0.017. A significant difference was also shown comparing patients with minimal inflammatory activity to the rest of the cohort (P = 0.009). Visfatin receiver operating characteristic curve analysis for different necro-inflammatory activity - grade 1 vs grades 3-4 with area under the curve 0.81 indicated a good discriminant power for differentiation of moderate/severe inflammation, with the cut-off set at 57.6 ng/mL (sensitivity 75%, specificity 90%, positive predictive value 0.90, negative predictive value 0.75). Serum visfatin concentration increases significantly in CHC patients. These findings suggest that visfatin is important in the pathogenesis of the inflammatory process in CHC. Visfatin may play a dual role as a pro-inflammatory or/and protective factor. The measurement of visfatin serum concentration may serve as an additional tool in distinguishing more advanced grades of the necro-inflammatory activity.

Stress-induced sphingolipid signaling: role of type-2 neutral sphingomyelinase in murine cell apoptosis and proliferation

Background

Sphingomyelin hydrolysis in response to stress-inducing agents, and subsequent ceramide generation, are implicated in various cellular responses, including apoptosis, inflammation and proliferation, depending on the nature of the different acidic or neutral sphingomyelinases. This study was carried out to investigate whether the neutral Mg²⁺-dependent neutral sphingomyelinase-2 (nSMase2) plays a role in the cellular signaling evoked by TNFalpha and oxidized LDLs, two stress-inducing agents, which are mitogenic at low concentrations and proapoptotic at higher concentrations.

Methodology and Principal Findings

For this purpose, we used nSMase2-deficient cells from homozygous fro/fro (fragilitas ossium) mice and nSMase2-deficient cells reconstituted with a V5-tagged nSMase2. We report that the genetic defect of nSMase2 (in fibroblasts from fro/fro mice) does not alter the TNFalpha and oxidized LDLs-mediated apoptotic response. Likewise, the hepatic toxicity of TNFalpha is similar in wild type and fro mice, thus is independent of nSMase2 activation. In contrast, the mitogenic response elicited by low concentrations of TNFalpha and oxidized LDLs (but not fetal calf serum) requires nSMase2 activation.

Conclusion and Significance

nSMase2 activation is not involved in apoptosis mediated by TNFalpha and oxidized LDLs in murine fibroblasts, and in the hepatotoxicity of TNFalpha in mice, but is required for the mitogenic response to stress-inducing agents.