RORγt expression in Tregs promotes systemic lupus erythematosus via IL-17 secretion, alteration of Treg phenotype and suppression of Th2 responses.

Systemic lupus erythematosus (SLE) is a common autoimmune disorder with a complex and poorly understood immunopathogenesis. However, a pathogenic role for the T helper type 17 (Th17) axis was demonstrated by many studies, while regulatory T cells (Tregs ) were shown to mediate protection. Recently, we and others characterized a novel and independent T cell population expressing both the Treg characteristic transcription factor forkhead box protein 3 (FoxP3) and the Th17-defining retinoic acid receptor-related orphan nuclear receptor γt (RORγt). Studies in a model of acute glomerulonephritis unveiled potent regulatory, but also proinflammatory, functions of RORγt+ FoxP3+ Tregs . This bi-functional nature prompted us to suggest the name 'biTregs '. Importantly, the pathogenic biTreg effects were dependent upon expression of RORγt. We thus aimed to evaluate the contribution of RORγt+ FoxP3+ biTregs to pristane-induced SLE and explored the therapeutic potential of interference with RORγt activation. Our analyses revealed expansion of IL-17 producing biTregs in a distinctive time-course and organ-specific pattern, coincident with the development of autoimmunity and tissue injury. Importantly, specific ablation of RORγt activation in endogenous biTregs resulted in significant amelioration of pristane-induced pulmonary vasculitis and lupus nephritis. As potential mechanisms underlying the observed protection, we found that secretion of IL-17 by biTregs was abrogated completely in FoxP3Cre  × RORCfl/fl mice. Furthermore, Tregs showed a more activated phenotype after cell-specific inactivation of RORγt signalling. Finally, and remarkably, biTregs were found to potently suppress anti-inflammatory Th2 immunity in a RORγt-dependent manner. Our study thus identifies biTregs as novel players in SLE and advocates RORγt-directed interventions as promising therapeutic strategies.

The multiple functions of heme oxygenase-1 in the liver.

Heme oxygenases (HO) are essential enzymes which degrade heme into carbon monoxide (CO), biliverdin and free iron. Due to its anti-inflammatory, anti-apoptotic and, as recently described, anti-viral properties the inducible HO isoform HO-1 is an important molecule which could find its way into therapy of gastrointestinal diseases. Acute and chronic liver injuries including acute liver failure, alcoholic or viral hepatitis, chronic inflammation, fibrosis, cirrhosis, and hepatocellular carcinoma are life threatening diseases and as a consequence might result in the necessity of liver transplantation. HO-1 as well as its reaction products of heme degradation has been linked to cytoprotection. HO-1 induction in rodent models of acute and chronic hepatic inflammation resulted in improvement of liver damage and down-regulation of pro-inflammatory cytokine levels. Furthermore HO-1 induction interfered with fibrosis progression in mice and partially resolved existing fibrosis. Likewise, HO-1 induction interfered with replication of hepatitis viruses B and C, which frequently are the reason for chronic hepatitis and subsequent tumor growth. Liver transplantation is limited by ischemia/reperfusion (I/R) injury, which is characterized by hypoxia and nutrient deficiency resulting in oxidative stress, apoptosis and immune activation. Induction of HO-1 and application predominantly of CO have been shown to interfere with I/R liver injury and to improve recipient and graft survival. On the other hand HO-1 has been shown to be over-expressed in various tumors, including hepatocellular carcinoma (HCC). Due to its anti-apoptotic properties this bears the risk to promote tumor growth. Anti-apoptotic effects are predominantly mediated by CO. This review aims to summarize beneficial as well as detrimental effects of HO-1 and its products within the liver.

A novel technique for selective NF-kappaB inhibition in Kupffer cells: contrary effects in fulminant hepatitis and ischaemia-reperfusion.

BACKGROUND AND AIMS: The transcription factor nuclear factor kappa B (NF-kappaB) has risen as a promising target for anti-inflammatory therapeutics. In the liver, however, NF-kappaB inhibition mediates both damaging and protective effects. The outcome is deemed to depend on the liver cell type addressed. Recent gene knock-out studies focused on the role of NF-kappaB in hepatocytes, whereas the role of NF-kappaB in Kupffer cells has not yet been investigated in vivo. Here we present a novel approach, which may be suitable for clinical application, to selectively target NF-kappaB in Kupffer cells and analyse the effects in experimental models of liver injury. METHODS: NF-kappaB inhibiting decoy oligodeoxynucleotides were loaded upon gelatin nanoparticles (D-NPs) and their in vivo distribution was determined by confocal microscopy. Liver damage, NF-kappaB activity, cytokine levels and apoptotic protein expression were evaluated after lipopolysaccharide (LPS), d-galactosamine (GalN)/LPS, or concanavalin A (ConA) challenge and partial warm ischaemia and subsequent reperfusion, respectively. RESULTS: D-NPs were selectively taken up by Kupffer cells and inhibited NF-kappaB activation. Inhibition of NF-kappaB in Kupffer cells improved survival and reduced liver injury after GalN/LPS as well as after ConA challenge. While anti-apoptotic protein expression in liver tissue was not reduced, pro-apoptotic players such as cJun N-terminal kinase (JNK) were inhibited. In contrast, selective inhibition of NF-kappaB augmented reperfusion injury. CONCLUSIONS: NF-kappaB inhibiting decoy oligodeoxynucleotide-loaded gelatin nanoparticles is a novel tool to selectively inhibit NF-kappaB activation in Kupffer cells in vivo. Thus, liver injury can be reduced in experimental fulminant hepatitis, but increased at ischaemia-reperfusion.

A T cell-dependent experimental liver injury in mice inducible by concanavalin A.

Male NMRI or BALB/c mice developed severe liver injury as assessed by transaminase release within 8 h when an intravenous dose greater than 1.5 mg/kg concanavalin A (Con A) was given. Histopathologically, only the liver was affected. Electron micrographs revealed leukocyte sticking to endothelial cells and bleb formation of hepatocytes. The hepatotoxicity of the lectin correlated neither with its agglutination activity nor with its sugar specificity. Administration of 0.5 mg/kg dexamethasone or 50 mg/kg cyclosporine A or 50 mg/kg FK 506 (Fujimycin) resulted in protection of the animals whereas indomethacin pretreatment failed to protect. Con A hepatitis was accompanied by the release of IL-2 into the serum of the animals. Mice with severe combined immunodeficiency syndrome lacking B as well as T lymphocytes were resistant against Con A. Athymic nude mice with immature T lymphocytes were also resistant. Pretreatment of mice with an antibody against T lymphocytes fully protected against Con A as did monoclonal anti-mouse CD4. Monoclonal anti-mouse CD8 failed to protect. Pretreatment of mice with silica particles, i.e., deletion of macrophages, prevented the induction of hepatitis. These findings provide evidence that Con A-induced liver injury depends on the activation of T lymphocytes by macrophages in the presence of Con A. The model might allow the study of the pathophysiology of immunologically mediated hepatic disorders such as autoimmune chronic active hepatitis.

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.

Potentiation by granulocyte macrophage colony-stimulating factor of lipopolysaccharide toxicity in mice.

GM-CSF is known to prime leukocytes for inflammatory stimuli in vitro. The objective of this study was to investigate the role of GM-CSF in vivo in a systemic inflammatory reaction syndrome. The results demonstrate a potentiation of LPS toxicity by GM-CSF in a mortality model as well as in a septic liver failure model in mice. Pretreatment of animals with 50 micrograms/kg GM-CSF induced lethality within 24 h in mice challenged with a subtoxic dose of LPS while controls survived > 72 h. A monoclonal anti-GM-CSF antibody significantly protected against a lethal LPS dose. Serum GM-CSF was inducible by LPS and peaked at 2 h. GM-CSF pretreatment dramatically potentiated systemic TNF release and hepatotoxicity induced by a subtoxic dose of LPS in galactosamine-sensitized mice. Potentiation of LPS hepatotoxicity was possible until 30 min after LPS challenge. Polyclonal anti-GM-CSF IgG protected against septic liver failure in this model and attenuated serum TNF concentrations. In vitro an ex vivo experiments revealed that after GM-CSF pretreatment LPS-induced IL-1 release from bone marrow or spleen cells was also enhanced. These findings suggest that GM-CSF represents an endogenous enhancer of LPS-induced organ injury, possibly by potentiating the release of proinflammatory cytokines such as TNF and IL-1.

Concanavalin A-induced liver injury triggers hepatocyte proliferation.

Concanavalin A (Con A) injection into mice leads to immune-mediated liver injury. We studied whether after Con A-induced liver injury, TNF- and IL-6-dependent signaling pathways known to be related to hepatocyte proliferation are activated. 2 h after Con A injection, maximum TNF-alpha, and after 4-8 h, maximum IL-6 serum levels were found. The rise in aminotransferases and DNA fragmentation started after 4 h; maximum levels were evident after 8 h. 5-Bromo-2'-deoxyuridine staining and nuclear cyclin A expression as markers of the S-phase were first detected in hepatocyte nuclei after 24 h, peaking after 48 h. An increase in TNF-dependent nuclear expression of CCAAT/enhancer-binding protein-beta (C/EBP-beta)/liver-enriched activating protein (LAP) was detected after 1 h, whereas an increase in RNA expression was evident only after 4 h. C/EBP-beta/LAP expression returned to normal values before progression into the S-phase. DNA binding of signal transducer and activator of transcription (STAT) 3/acute phase response factor (APRF) increased for up to 8 h. As found by supershift experiments, in addition to STAT3/APRF, STAT1 also binds to the same sequence. During the course of time gel shift experiments, DNA binding of the apoptosis-related STAT1 started earlier than DNA binding of STAT3/APRF, which regulates hepatocyte proliferation. However, the subsequent decrease in DNA binding of both factors was comparable. This study demonstrates that after Con A injection, TNF- and IL-6- dependent signals trigger nuclear events regulating hepatocyte apoptosis and proliferation during liver injury.

Acetaminophen/paracetamol: A history of errors, failures and false decisions.

Acetaminophen/paracetamol is the most widely used drug of the world. At the same time, it is probably one of the most dangerous compounds in medical use, causing hundreds of deaths in all industrialized countries due to acute liver failure (ALF). Publications of the last 130 years found in the usual databases were analyzed. Personal contacts existed to renowned researchers having contributed to the medical use of paracetamol and its precursors as H.U. Zollinger, S. Moeschlin, U. Dubach, J. Axelrod and others. Further information is found in earlier reviews by Eichengrün, Rodnan and Benedek, Sneader, Brune; comp. references. The history of the discovery of paracetamol starts with an error (active against worms), continues with a false assumption (paracetamol is safer than phenacetin), describes the first side-effect 'epidemy' (phenacetin nephropathy, drug-induced interstitial nephritis) and ends with the discovery of second-generation problems due to the unavoidable production of a highly toxic metabolite of paracetamol N-acetyl-p-benzoquinone imine (NAPQI) that may cause not only ALF and kidney damage but also impaired development of the fetus and the newborn child. It appears timely to reassess the risk/benefit ratio of this compound.

Requirement of peptidergic sensory innervation for disease activity in murine models of immune hepatitis and protection by beta-adrenergic stimulation.

To investigate the interaction between the peripheral nervous and the immune system in vivo, we used two mouse models of T cell and TNF-alpha dependent liver injury inducible by either concanavalin A or a combination of D-galactosamine and staphylococcal enterotoxin B. Mice depleted of peptidergic sensory nerve fibres by capsaicin were protected from liver injury. Moreover, TNF-alpha production was significantly reduced. Examination of the effect of catecholamines on liver injury showed that the beta2-adrenergic agonist salbutamol prevented, whereas chemical sympathectomy by 6-hydroxydopamine, deteriorated the disease. Hence, strategies reducing the activity of peptidergic sensory nerve fibres or stimulating beta2-adrenoreceptors, may be of benefit in immune-mediated liver disease.

Pre-apoptotic alterations in hepatocytes of TNFalpha-treated galactosamine-sensitized mice.

Tumor necrosis factor (TNF) induces apoptotic death of hepatocytes in the galactosamine (GalN)-sensitized mouse liver after 5 hr. In our study, the most remarkable sign of the early stage of apoptosis was the focal rupture of the outer mitochondrial membrane. Parts of the inner membrane extended through the gap of the outer membrane, whereas the rest of the inner membrane still formed the cristae. This feature appeared in hepatocytes before chromatin condensation. With the diaminobenzidine technique for localization of cytochrome oxidase activity, the reaction product was detectable by light and electron microscopy. Ten percent of the hepatocytes were apoptotic, with condensed chromatin and high enzyme activity, 37% were pre-apoptotic, without chromatin condensation but high enzyme activity, and 53% had neither condensed chromatin nor a remarkable reaction product of cytochrome oxidase activity. Fas (APO-1, CD95) molecules on the plasma membrane of hepatocytes increased and were represented immunohistochemically in cells without chromatin condensation. DNA strand breaks were also detectable before chromatin aggregation. The results of this study indicate that mitochondria play a pivotal role in pre-apoptotic hepatocytes, together with an increase of the Fas molecule on the plasma membrane and with the occurrence of DNA strand breaks in the nucleus.

Synergism of Pseudomonas aeruginosa exotoxin A with endotoxin, superantigen, or TNF results in TNFR1- and TNFR2-dependent liver toxicity in mice.

Pseudomonas aeruginosa is a potentially dangerous Gram-negative nosocomial pathogen, causing bacteremia in debilitated patients, and a prominent cause of bacterial cholangitis. Opportunistic infections with other nosocomial pathogens, e.g. Staphylococcus aureus, are common. Hence, multi-intoxication with P. aeruginosa exotoxin A (PEA) and other bacterial toxins, including endotoxin (LPS) and the superantigen S. aureus enterotoxin B (SEB), is very likely. Here we show that PEA synergistically interacted with LPS, SEB, or recombinant murine tumor necrosis factor alpha (rmuTNF) in mice, resulting in severe liver injury. Enhanced and prolonged circulation of cytokines, including TNF, which depended on the presence of T cells, was a remarkable feature of synergistic PEA/LPS- or PEA/SEB-induced hepatotoxicity. PEA/LPS-, PEA/SEB- or PEA/rmuTNF-induced liver injury was mediated by both TNF receptors (TNFRs), i.e. TNFR1 and TNFR2. In view of the fact that TNFR1, but not TNFR2, signaling is unequivocally required for host defense, our results suggest that anti-TNFR2 strategies might be beneficial to protect the liver from inflammatory damage caused by synergistic interactions of PEA with other TNF-inducing bacterial toxins.

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.

A novel biologically active seleno-organic compound--VI. Protection by ebselen (PZ 51) against galactosamine/endotoxin-induced hepatitis in mice.

Male albino NMRI mice were given 700 mg/kg galactosamine and 33 micrograms/kg salmonella endotoxin intraperitoneally. After 9 hr, serum sorbitol dehydrogenase activity had risen from 60 to 7320 U/l, SGOT from 90 to 5580, and SGPT from 70 to 10,440. When a similar dose of galactosamine alone or endotoxin alone was given, no significant liver injury was found. Animals pre-treated with an oral dose of ebselen (600 mg/kg 1-3 hr before galactosamine/endotoxin administration) were fully protected against this type of hepatitis. When pretreated 1 hr before intoxication with different doses of ebselen, significant dose-dependent reduction of serum enzyme activities was observed at doses higher than 1 mg/kg. After pre-treatment with 6 mg/kg ebselen, no biochemical or histological signs of liver lesions were detectable 36 hr after intoxication. In order to comparatively evaluate the model used, several established anti-inflammatory drugs were administered at doses which showed 50% effectiveness in preventing carageenan paw edema. A dose of 200 micrograms/kg dexamethasone, or 9 mg/kg indomethacin abolished galactosamine/endotoxin-induced enzyme release in our animals, as did the lipoxygenase pathway inhibitor diethylcarbamazine (78 mg/kg). In contrast, administration of cyclooxygenase pathway inhibitors such as aspirin (220 mg/kg) or ibuprofen (45 mg/kg) failed to prevent hepatitis. The effect of ebselen was also investigated in four different models of acute drug-induced liver damage. A dose of 600 mg/kg of the organic selenium compound was ineffective or weakly active in benzo(alpha)pyrene- or phenobarbital-treated mice which were intoxicated by intraperitoneal administration of 350 or 400 mg/kg body weight of paracetamol. Similarly negative results were obtained against bromobenzene-induced hepatotoxicity (520 mg/kg bromobenzene i.p.), carbon tetrachloride intoxication (3.2 g/kg), or allyl alcohol-induced liver damage (60 mg/kg). The selective efficacy of ebselen against galactosamine/endotoxin induced liver damage is interpreted in terms of its recently recognized ability to inhibit the formation of leukotrienes.

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.

Evidence for the involvement of a reperfusion injury in galactosamine/endotoxin-induced hepatitis in mice.

Simultaneous intraperitoneal administration of 700 mg/kg galactosamine and 33 micrograms/kg Salmonella abortus equi endotoxin to male NMRI albino mice resulted in fulminant hepatitis as assessed after nine hours by measurement of serum transaminases as well as sorbitol dehydrogenase activities. Intraperitoneal pretreatment of animals with 2 X 100 mg/kg allopurinol, or intravenous pretreatment with 33 kU superoxide dismutase or 1 MU catalase fully prevented hepatitis. Administration of 10 micrograms/kg of the prostacyclin analogue iloprost antagonized liver injury when given simultaneously with galactosamine/endotoxin but did not protect when given 90 min later. Tocopherol or desferal pretreatment of the animals had no significant protective effect. Together with our recent finding that hepatic leukotriene D4 production is likely to be responsible for galactosamine/endotoxin-induced hepatitis we interpret these results as evidence for a leukotriene-induced hepatic ischemia followed by a reperfusion syndrome.

Leukocyte alterations do not account for hepatitis induced by endotoxin or TNF alpha in galactosamine-sensitized mice.

Subtoxic doses of endotoxin (salmonella abortus equi lipopolysaccharide, LPS) (5 micrograms/kg i.p.) or tumor necrosis factor alpha (TNF alpha) (15 micrograms/kg i.v.) induced fulminant hepatitis within 8 hr, when mice had been sensitized by a subtoxic dose of D-galactosamine (700 mg/kg i.p.). LPS-treatment led to the release of TNF into the circulation, independently of the presence of D-galactosamine. The TNF-dependent development of hepatitis was accompanied by a severe lymphopenia and neutrophilia as assessed by leukocyte differential count. The total leukocyte count was not significantly affected. Lymphopenia and neutrophilia were induced by LPS or TNF alpha alone; however, the differential count was not influenced by D-galactosamine. A quantity of 260 micrograms/kg phorbol myristate acetate (PMA) i.p. or 5 micrograms/kg platelet activating factor (PAF) i.v. or 3.3 mg/kg N-formyl-methionyl-leucyl-phenylalanine methylester (FMLP) i.v. or 167 mg/kg zymosan i.v. also caused lymphopenia and neutrophilia in mice. However, none of these agents induced the production of systemic TNF and therefore failed to induce hepatitis in D-galactosamine-sensitized mice. In LPS-insensitive C3H/HeJ mice administration of LPS produced neither differential count changes nor hepatitis while both events were observed when TNF alpha was given. This shows that TNF alpha alone gives rise to lymphopenia/neutrophilia as well as hepatitis independent of LPS. When the action of TNF alpha was blocked by anti TNF alpha antiserum pretreatment of LPS-sensitive mice, the animals were protected against LPS-induced hepatitis. However, lymphopenia and neutrophilia still occurred to a similar extent. The involvement of a putative additional mediator of LPS-induced leukocyte alterations was checked. The findings suggest that this mediator, if present, is different from IL-1, IL-2, eicosanoids or superoxide. We conclude from our findings that changes in leukocyte numbers and composition following D-galactosamine LPS or D-galactosamine/TNF alpha administration is an epiphenomenon rather than a causal event of leukocyte stimulation in the process of inducing a fulminant hepatitis in mice.

A novel biologically active seleno-organic compound--V. Inhibition by ebselen (PZ 51) of rat peritoneal neutrophil lipoxygenase.

Suspensions of rat peritoneal PMNLs elicited with glycogen were stimulated by calcium and an ionophore to produce leukotrienes from endogenous arachidonic acid. We investigated the effect of the non-toxic, anti-inflammatory seleno-organic compound, ebselen (PZ 51). When ethanolic extracts of the medium of stimulated cells were analysed by HPLC, a dose-dependent inhibition by ebselen of LTB4 formation with a concomitant decrease of 5-HETE production was found. Half-maximum inhibition was observed at 20 mumoles/l ebselen. Similar findings were obtained after analysis of chloroform extracts of both cells and medium using a different HPLC system. Under these conditions, enhanced 5-HETE formation was associated with reduced production of LTB4 and other di-HETE isomers, when purified glutathione peroxidase + GSH were present. We conclude that the reported GSH peroxidase-like activity of ebselen, catalysing the reduction of 5-HPETE to 5-HETE, can not account for our findings. Therefore, the lipoxygenase reaction itself apparently represents the site of inhibition of LTB4 formation by ebselen.

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.

In vivo evidence for protease-catalysed mechanism providing bioactive tumor necrosis factor alpha.

Mice pretreated by intravenous injection of 42 mg/kg of the serine protease inhibitor alpha 1-antitrypsin prior to a hepatotoxic dose of D-galactosamine/lipopolysaccharide (GalN/LPS) were fully protected against hepatitis. Pretreatment with alpha 1-antitrypsin with doses up to 300 mg/kg at different times failed to protect galactosamine sensitized animals against tumor necrosis factor alpha (TNF alpha)-induced hepatitis. No bioactive TNF alpha was detectable in serum of mice protected against GalN/LPS-induced hepatitis by pretreatment with alpha 1-antitrypsin. In contrast, abundant amounts of TNF were found in sera of GalN/LPS-treated control animals. It is concluded that a serine protease sensitive to alpha 1-antitrypsin provides bioactive TNF alpha by proteolytic cleavage of a TNF alpha precursor.