Gisa Tiegs

Concanavalin A - induced T-cell - mediated hepatic injury in mice : The role of tumor necrosis factor

Concanavalin A activates T lymphocytes in vitro and causes T‐cell‐dependent hepatic injury in mice. T lymphocytes were previously identified as effector cells of concanavalin A‐induced liver injury. Here we report that hepatic injury is characterized by apoptotic cell death. On concanavalin A challenge, the cytokines tumor necrosis factor‐α (TNF α), interleukin‐2, granulocyte macrophage‐colony stimulating factor, and interferon‐γ were detectable in the circulation of the mice. Pretreatment of mice with anti‐mouse TNF‐α antiserum protected them from concanavalin A‐induced liver injury. Nude mice failed to release TNF‐α or interleukin‐2 after concanavalin A challenge and were protected from liver injury. Lymph node cell transfer from responder mice to resistant nude mice resulted in susceptibility of the latter towards concanavalin A, i.e., to induction of cytokine release and hepatotoxicity. These experiments suggest that immunocompetent T cells play a pivotal role in concanavalin A‐stimulated TNF‐α release in vivo. After intravenous administration of fluorescein isothiocyanate‐labeled concanavalin A to mice, the most fluorescence was found within the liver. In vitro, concanavalin A stimulation of separate cultures of mouse lymph node cells or nonparenchymal liver cells induced the release of minute amounts of TNF, whereas stimulation of cocultures of these cells resulted in production of substantial amounts of TNF‐α. These findings may explain the hepatotropic effect of concanavalin A. In conclusion, T‐cell‐dependent concanavalin A‐induced apoptotic liver injury in mice is related to immunological and cytokinemediated disorders and possibly to autoreactive hepatic processes. (Hepatology 1995;21:190–198).

A novel biologically active seleno-organic compound—II: Activity of PZ 51 in relation to Glutathione Peroxidase

The anti-inflammatory compound 2-phenyl-1,2-benzoisoselenazol-3(2H)-on (PZ 51) catalysed GSSG formation from GSH in the presence of hydroperoxides in an NADPH/GSSG reductase system with the following rates (delta log GSH/min per molar selenium): 1.1 X 10(6) with H2O2, 1.2 X 10(6) with butylhydroperoxide, 1.7 X 10(6) with cumenehydroperoxide. The reaction catalysed by the sulphur analogue of PZ 51 was negligible. Similar results were obtained in a direct assay of GSH-Px activity based on GSH estimation by dithionitrobenzoate. The activation energy of the reaction was determined as 55 kJ/mol . deg in the presence of 30 mumol/1 PZ 51 compared to 36.5 kJ/mol . deg obtained in the presence of 1 nmol/1 pure GSH-Px isolated from bovine red blood cells. In mouse liver microsomes, NADPH-dependent aminopyrine dealkylation was totally inhibited in the presence of 50 mumol/1 PZ 51. In vivo experiments with Se-deficient mice showed that the Se-moiety of PZ 51 is not available for the synthesis of the selenoenzyme GSH-Px after dietary treatment or i.p. doses up to 25 mg Se as PZ 51 per kg body wt. After oral administration of labelled PZ 51, unlike with selenite, no radioactivity was incorporated into GSH-Px within 48 hr. The data suggest that several similarities between PZ 51 and the active site of GSH-Px exist, resulting in the capability of the compound to catalyse the GSH-Px reaction. An extracellular pharmacodynamic action of the drug seems likely.

Tumor necrosis factor is a terminal mediator in galactosamine/endotoxin-induced hepatitis in mice

Intravenous injection of murine recombinant tumor necrosis factor alpha(TNF-alpha) to male NMRI albino mice in doses greater than 4 micrograms/kg (specific activity 4 x 10(7) U/mg) resulted in a fulminant hepatitis when animals had been sensitized 1 hr before by intraperitoneal administration of 700 mg/kg galactosamine. Liver injury was assessed by measurement of serum transaminases as well as sorbitol dehydrogenase activity 8 hr after administration of TNF-alpha. Pretreatment with either galactosamine or 40 micrograms/kg TNF-alpha alone did not cause hepatitis. Pretreatment of galactosamine/TNF-alpha-injured mice with 800 mg/kg uridine or with 6 mg/kg calmidazolium fully protected the animals, while administration of either verapamil or nifedipine (100 mg/kg, respectively) had no significant effect. The following inhibitors of generation or action of leukotriene D4, which were previously shown to block galactosamine/endotoxin-induced hepatitis in mice, failed to protect against galactosamine/TNF-alpha-induced intoxication: 200 micrograms/kg dexamethasone, 174 mg/kg BW 755 C or 13 x 10 mg/kg FPL 55712. In addition, unlike in the galactosamine/endotoxin model no prevention was achieved by pretreatment of galactosamine/TNF-alpha-injured animals with the following substances blocking the development of an ischemia/reperfusion syndrome: 2 x 100 mg/kg allopurinol, 3.3 x 10(4) U/kg superoxide dismutase, 10(6) U/kg catalase or 10 micrograms/kg iloprost. We conclude from our results that tumor necrosis factor alpha is likely to act as a final mediator of endotoxin action in a sequence of events which includes formation of leukotriene D4 and reactive oxygen species.

Importance of Kupffer Cells for T-Cell-Dependent Liver Injury in Mice

T cells seem to be responsible for liver damage in any type of acute hepatitis. Nevertheless, the importance of Kupffer cells (KCs) for T-cell-dependent liver failure is unclear. Here we focus on the role of KCs and tumor necrosis factor (TNF) production after T cell stimulation in mice. T-cell- and TNF-dependent liver injury were induced either by Pseudomonas exotoxin A (PEA), by concanavalin A (Con A), or by the combination of subtoxic doses of PEA and the superantigen Staphylococcus enterotoxin B (SEB). KCs were depleted by clodronate liposomes. Although livers of PEA-treated mice contained foci of confluent necrosis and numerous apoptotic cells, hardly any apoptotic cells were observed in the livers of Con A-treated mice. Instead, large bridging necroses were visible. Elimination of KCs protected mice from PEA-, Con A-, or PEA/SEB-induced liver injury. In the absence of KCs, liver damage was restricted to a few small necrotic areas. KCs were the main source of TNF. Hepatic TNF mRNA and protein production were strongly attenuated because of KC-depletion whereas plasma TNF levels were unaltered. Our results suggest that KCs play an important role in T cell activation-induced liver injury by contributing TNF. Plasma TNF levels are poor diagnostic markers for the severity of TNF-dependent liver inflammation.

IL‐10, regulatory T cells, and Kupffer cells mediate tolerance in concanavalin A–induced liver injury in mice

The liver appears to play an important role in immunological tolerance, for example, during allo‐transplantation. We investigated tolerance mechanisms in the model of concanavalin A (ConA)‐induced immune‐mediated liver injury in mice. We found that a single injection of a sublethal ConA dose to C57BL/6 mice induced tolerance toward ConA‐induced liver damage within 8 days. This tolerogenic state was characterized by suppression of the typical Th1 response in this model and increased IL‐10 production. Tolerance induction was fully reversible in IL‐10−/− mice and after blockade of IL‐10 responses by anti‐IL10R antibody. Co‐cultures of CD4+CD25+ regulatory T cells (Tregs) and CD4+CD25− responder cells revealed Treg from ConA‐tolerant mice being more effective in suppressing polyclonal T cell responses than Treg from control mice. Moreover, Treg from tolerant but not from control mice were able to augment in vitro IL‐10 expression. Depletion by anti‐CD25 monoclonal antibody (MAb) indicated a functional role of Tregs in ConA tolerance in vivo. Cell depletion studies revealed Tregs and Kupffer cells (KC) to be crucial for IL‐10 expression in ConA tolerance. Studies with CD1d−/− mice lacking natural killer T (NKT) cells disclosed these cells as irrelevant for the tolerogenic effect. Finally, cellular immune therapy with CD4+CD25+ cells prevented ConA‐induced liver injury, with higher protection by Treg from ConA‐tolerized mice. Conclusion: The immunosuppressive cytokine IL‐10 is crucial for tolerance induction in ConA hepatitis and is mainly expressed by CD4+CD25+ Treg and KC. Moreover, Tregs exhibit therapeutic potential against immune‐mediated liver injury. (HEPATOLOGY 2007;45:475–485.)

Inducible nitric oxide synthase is critical for immune-mediated liver injury in mice

Concanavalin A (Con A) causes severe TNF-alpha-mediated and IFN-gamma-mediated liver injury in mice. In addition to their other functions, TNF-alpha and IFN-gamma both induce the inducible nitric oxide (NO) synthase (iNOS). Using different models of liver injury, NO was found to either mediate or prevent liver damage. To further elucidate the relevance of NO for liver damage we investigated the role of iNOS-derived NO in the Con A model. We report that iNOS mRNA was induced in livers of Con A-treated mice within 2 hours, with iNOS protein becoming detectable in hepatocytes as well as in Kupffer cells within 4 hours. iNOS-/- mice were protected from liver damage after Con A treatment, as well as in another TNF-alpha-mediated model that is inducible by LPS in D-galactosamine-sensitized (GalN-sensitized) mice. iNOS-deficient mice were not protected after direct administration of recombinant TNF-alpha to GalN-treated mice. Accordingly, pretreatment of wild-type mice with a potent and specific inhibitor of iNOS significantly reduced transaminase release after Con A or GalN/LPS, but not after GalN/TNF-alpha treatment. Furthermore, the amount of plasma TNF-alpha and of intrahepatic TNF-alpha mRNA and protein was significantly reduced in iNOS-/- mice. Our results demonstrate that iNOS-derived NO regulates proinflammatory genes in vivo, thereby contributing to inflammatory liver injury in mice by stimulation of TNF-alpha production.

Silibinin protects mice from T cell-dependent liver injury.

BACKGROUND/AIMS Silibinin is the major pharmacologically active compound of the Silybum marianum fruit extract silymarin. Its well-known hepatoprotective activities are mostly explained by antioxidative properties, inhibition of phosphatidylcholine synthesis or stimulation of hepatic RNA and protein synthesis. Here, we characterized the hepatoprotective potential of silibinin as an immune-response modifier in T cell-dependent hepatitis in vivo. METHODS Silibinin was tested in the mouse model of concanavalin A (ConA)-induced, T cell-dependent hepatitis. Liver injury was assessed by quantification of plasma transaminase activities and intrahepatic DNA fragmentation. Plasma cytokine concentrations were determined by enzyme-linked immunosorbent assay (ELISA), intrahepatic cytokine and inducible NO synthase (iNOS) mRNA levels by reverse transcriptase polymerase chain reaction, intrahepatic iNOS expression by immunofluorescent staining, and intrahepatic nuclear factor kappa B (NF-kappaB) activation by electrophoretic mobility shift assay. RESULTS Silibinin significantly inhibited ConA-induced liver disease. Silibinin proved to be an immune-response modifier in vivo, inhibiting intrahepatic expression of tumor necrosis factor, interferon-gamma, interleukin (IL)-4, IL-2, and iNOS, and augmenting synthesis of IL-10. In addition, silibinin inhibited intrahepatic activation of NF-kappaB. CONCLUSIONS Silibinin, suppressing T cell-dependent liver injury as an immune-response modifier, might be a valuable drug in therapeutic situations in which intrahepatic immunosuppression is required.

Concanavalin A—induced liver cell damage: Activation of intracellular pathways triggered by tumor necrosis factor in mice

BACKGROUND & AIMS Concanavalin A (con A) induces tumor necrosis factor (TNF)-dependent hepatocyte apoptosis resembling immune-mediated fulminant hepatic failure in humans. Intracellular pathways originating at the TNF receptor are either linked to apoptosis, nuclear factor (NF)-kappaB translocation, or Jun kinase (JNK) activation. The aim of this study was to study TNF-dependent pathways after con A injection in vivo. METHODS Con A, con A plus anti-TNF, and control buffer were injected into BALB/c mice. Immunofluorescence, Western blot, Northern blot, gel shift, Erk, and JNK activity and DNA fragmentation experiments were performed at different time points after injection. RESULTS DNA fragmentation in hepatocytes was increased 4-24 hours after con A injection. JNK was activated maximally (>20-fold) directly after con A injection, whereas binding and nuclear translocation of NF-kappaB was maximal after 4 hours. All pathways were blocked by anti-TNF. JNK activation was specific because related ERK 1 + 2 were not activated after con A. High nuclear expression of c-Jun was already evident 1 hour after con A injection; however, in contrast to JNK, anti-TNF treatment did not block c-Jun nuclear expression and DNA binding. CONCLUSIONS In the con A model, activation of TNF-dependent pathways is associated with apoptosis of hepatocytes. Their modulation in vivo may have implications to develop new therapeutic strategies to prevent apoptosis.

α-Galactosylceramide-Induced Liver Injury in Mice Is Mediated by TNF-α but Independent of Kupffer Cells

NKT cells expressing phenotypic markers of both T and NK cells seem to be pivotal in murine models of immune-mediated liver injury, e.g., in Con A-induced hepatitis. Also α-galactosylceramide (α-GalCer), a specific ligand for invariant Vα14 NKT cells, induces hepatic injury. To improve the comprehension of NKT-cell mediated liver injury, we investigated concomitants and prerequisites of α-GalCer-induced hepatitis in mice. Liver injury induced by α-GalCer injection into C57BL/6 mice was accompanied by intrahepatic caspase-3 activity but appeared independent thereof. α-GalCer injection also induces pronounced cytokine responses, including TNF-α, IFN-γ, IL-2, IL-4, and IL-6. We provide a detailed time course for the expression of these cytokines, both in liver and plasma. Cytokine neutralization revealed that, unlike Con A-induced hepatitis, IFN-γ is not only dispensable for α-GalCer-induced hepatotoxicity but even appears to exert protective effects. In contrast, TNF-α was clearly identified as an important mediator for hepatic injury in this model that increased Fas ligand expression on NKT cells. Whereas intrahepatic Kupffer cells are known as a pivotal source for TNF-α in Con A-induced hepatitis, they were nonessential for α-GalCer-mediated hepatotoxicity. In α-GalCer-treated mice, TNF-α was produced by intrahepatic lymphocytes, in particular NKT cells. BALB/c mice were significantly less susceptible to α-GalCer-induced liver injury than C57BL/6 mice, in particular upon pretreatment with d-galactosamine, a hepatocyte-specific sensitizer to TNF-α-mediated injury. Finally, we demonstrate resemblance of murine α-GalCer-induced hepatitis to human autoimmune-like liver disorders. The particular features of this model compared with other immune-mediated hepatitis models may enhance comprehension of basic mechanisms in the etiopathogenesis of NKT cell-comprising liver disorders.

Leukotriene-mediated liver injury

The pathogenic mechanism of fulminant hepatitis induced by 700 mg/kg D-galactosamine plus 33 micrograms/kg endotoxin was investigated in male NMRI mice. The extent of liver injury was assessed by measurement of serum transaminases and sorbitol dehydrogenase activities 9 hr after intoxication, as well as by histopathological evaluation. When the hepatic glutathione content of galactosamine endotoxin-treated animals had been decreased by more than 90% following administration of 250 mg/kg phorone or 400 mg/kg diethyl maleate given three times, no signs of liver injury were observed. Since different agents interfering with the leukotriene synthesis pathway also prevented galactosamine/endotoxin-induced hepatitis, we suspected that a glutathione-derived peptidoleukotriene may be the pathogenic metabolite. In vivo inhibition of the catabolism of leukotriene C4 by administration of 50 mg/kg of the glutamyl transpeptidase inhibitor AT 125 (Acivicin) also protected the animals against liver injury. In order to elucidate which metabolite of leukotriene C4 was responsible for the observed hepatotoxicity we intravenously injected leukotrienes into animals that had received only galactosamine. Injection of 50 micrograms/kg leukotriene E4 1 hr after galactosamine had no effect. The same dose of leukotriene D4 led to a fulminant hepatitis which was prevented when the leukotriene D4 antagonist FPL 55712 had been given before. In contrast, lipoxygenase inhibitors or AT 125 did not protect against galactosamine + LTD4. Galactosamine/endotoxin-induced and galactosamine/leukotriene D4-induced hepatitis resulted in similarly localized histopathological changes, i.e. diffuse necrosis in the organ. We conclude from our results that galactosamine/endotoxin-induced hepatitis is mediated by a leukotriene D4-dependent mechanism.