Biomedical subjects

A Wendel

Publications and source records attributed to A Wendel.

At least 91 records · Page 5Linked to original sources

PubMed1994

Strong inhibition of mammalian lipoxygenases by the antiinflammatory seleno-organic compound ebselen in the absence of glutathione.

Both human recombinant 5-lipoxygenase (EC 1.13.11.34) and 15-lipoxygenase (EC 1.13.11.33, mammalian enzyme) purified from rabbit reticulocytes were inhibited in the absence of glutathione (GSH) by submicromolar concentrations of the seleno-organic compound ebselen. These concentrations were comparable to those of the enzymes. Soybean lipoxygenase-1 (EC 1.13.11.33, plant enzyme) was not inhibited, whereas prostaglandin endoperoxide synthase-1 (EC 1.14.99.1) was inhibited only at much higher concentrations of ebselen (IC50 = 37.7 +/- 4.3 microM). The action of ebselen on reticulocyte 15-lipoxygenase (IC50 = 0.17 +/- 0.01 microM) was studied in detail. Inhibition occurred instantaneously and appeared to be reversible and was largely abolished by a 20-fold molar excess of GSH over ebselen. In the presence of 1 mM GSH 50% inhibition was observed only at ebselen concentrations as high as 234 +/- 27 microM. 13S-hydroperoxy-9Z, 11E-octadecadienoic acid, the lipoxygenase product formed from linoleic acid, augmented the inhibitory effect at low concentrations and caused a partial reversal at high concentrations. A variety of derivatives or structural analogues of ebselen were also tested and proved to be either inactive or weaker inhibitors of 15-lipoxygenase. We have concluded that the potent inhibition of 15-lipoxygenase by ebselen is due neither to GSH peroxidase-like activity nor to lowering of the hydroperoxide tone. The pharmacological implications of these unique characteristics of the action of ebselen on lipoxygenases are then discussed.

Animals↗

PubMed1994

Contributions of thromboxane and leukotrienes to PAF-induced impairment of lung function in the rat.

This study was carried out to further clarify the role of eicosanoids in platelet-activating factor (PAF)-induced pulmonary vasoconstriction, bronchoconstriction, and edema formation in the isolated perfused rat lung. Infusion of PAF into the isolated perfused rat lung caused vasoconstriction [mean effective concn (EC50) = 0.88 nmol], caused bronchoconstriction (EC50 = 0.71 nmol), and increased the capillary filtration coefficient (EC50 = 1.4 nmol). Two minutes after injection of 50 nmol PAF, a high thromboxane concentration (3,000 pg/ml) and a low peptidoleukotriene concentration (150 pg/ml) were found in the effluent perfusate. PAF-induced vaso- and bronchoconstriction were unaffected by the non-redox 5-lipoxygenase inhibitor ZM-230,487 but were markedly attenuated by inhibition of cyclooxygenase with acetylsalicylic acid or thromboxane-receptor antagonism with BM-13177. Dual inhibition of cyclooxygenase and 5-lipoxygenase had the most pronounced inhibitory effect on PAF-induced vaso- and bronchoconstriction. None of the inhibitors tested prevented the increase in vascular permeability. We conclude that thromboxane is the major vasoconstrictor and bronchoconstrictor induced by PAF, whereas leukotrienes contribute a significant but minor part in this system. PAF-induced microvascular permeability was not inhibited by blockade of arachidonate metabolism and therefore seems to be mediated by a mechanism independent of eicosanoids.

Animals↗

PubMed1994

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.

Animals↗

PubMed1993

Protection by phosphodiesterase inhibitors against endotoxin-induced liver injury in galactosamine-sensitized mice.

Phosphodiesterase inhibitors were used as a tool to manipulate cellular nucleotide levels in vitro and in vivo. The lipopolysaccharide (LPS)-induced release of tumor necrosis factor alpha (TNF-alpha) from mouse peritoneal macrophages was inhibited by prostaglandin E2 with an IC50 of 0.05 microM and by dibutyryl-cAMP with an IC50 of 180 microM. In the presence of the phosphodiesterase inhibitors zardaverine or rolipram the intracellular cAMP concentration of LPS-stimulated macrophages was significantly increased. In these cells, LPS-inducible TNF release was inhibited by zardaverine (IC50 = 1.5 microM) or by rolipram (IC50 = 0.35 microM). In a model of septic shock, i.e. LPS challenge of galactosamine-sensitized mice, a dose-dependent protection against liver injury was observed following oral application of rolipram (ED50 = 0.55 mg/kg) or of zardaverine (ED50 approximately 30 mg/kg). The adenylate cyclase activator forskolin was also protective. Rolipram also protected against TNF-induced liver injury in mice while zardaverine failed to do so. It is concluded that the intracellular cAMP level of macrophages is a critical determinant of LPS-inducible TNF release and therefore modulates the susceptibility to septic shock.

Animals↗

PubMed1993

Selenoenzymes regulate the activity of leukocyte 5-lipoxygenase via the peroxide tone.

The variation of the selenium status of leukocytes was used as a tool to investigate the influence of selenium-containing glutathione peroxidases on the formation of 5-lipoxygenase metabolites in vitro and ex vivo. Selenium-deficient rat basophilic leukemia cells had < 1% of control glutathione peroxidase activity and 35% of control phospholipid hydroperoxide-glutathione peroxidase activity. Upon stimulation, these cells released an 8-fold amount of lipoxygenase metabolites compared to controls. No (5S)-hydroperoxyeicosatetraenoic acid was detectable in whole cells; however, it was found in homogenates of selenium-deficient cells. Addition of 0.25 microgram/ml selenium to selenium-deficient cells restored control phospholipid hydroperoxide-glutathione peroxidase activity within 8 h, whereas glutathione peroxidase activity needed 7 days. 12 h after resupplementation, selenium-deficient cells had 3% glutathione peroxidase and 100% phospholipid hydroperoxide-glutathione peroxidase activity compared to controls. Resupplemented cells released control amounts of 5-lipoxygenase metabolites, indicating that restoration of phospholipid hydroperoxide-glutathione peroxidase activity is associated with a selenium-adequate leukotriene metabolism. Leukocytes that were isolated from selenium-deficient rats released a 7-fold amount of total lipoxygenase metabolites compared to cells from control animals. By injecting normally fed rats with 500 micrograms/kg selenium as Na2SeO3, leukocyte phospholipid hydroperoxide-glutathione peroxidase activity was raised 8-fold within 114 h compared to controls. Leukocytes from these animals produced significantly less lipoxygenase metabolites than controls. These findings indicate that phospholipid hydroperoxide-glutathione peroxidase activity is primarily responsible for the reduction of 5-hydroperoxyeicosate-traenoic acid and therefore governs the actual activity of leukocyte 5-lipoxygenase via regulating the tone of endogenous hydroperoxides.

Animals↗

PubMed1992

Granulocyte colony-stimulating factor treatment protects rodents against lipopolysaccharide-induced toxicity via suppression of systemic tumor necrosis factor-alpha.

Pretreatment with recombinant human granulocyte CSF (G-CSF) protected mice in two different models of septic shock. Intravenous injection of 250 micrograms/kg G-CSF to mice prevented lethality induced by 5 mg/kg LPS. Injection of 50 micrograms/kg G-CSF protected galactosamine-sensitized mice against LPS-induced hepatitis. In either case, this protection was accompanied by a suppression of LPS-induced serum TNF activity. In contrast, when galactosamine-sensitized mice were pretreated with 50 micrograms/kg murine recombinant granulocyte/macrophage CSF instead of G-CSF and subsequently challenged with LPS, serum TNF activity was significantly enhanced and mortality was increased. The suppressive effect of G-CSF on LPS-induced TNF production was also demonstrated in rats. In vivo, no TNF was detectable in the blood of LPS-treated rats, which had been pretreated with G-CSF. Ex vivo, alveolar macrophages, bone marrow macrophages, Kupffer cells, or peritoneal macrophages prepared from G-CSF-treated rats produced significantly less TNF upon stimulation with LPS than corresponding populations from control rats. However, when these macrophage populations were incubated with G-CSF in vitro, LPS-induced TNF production was unaffected. These data suggest that the G-CSF-mediated suppression of TNF production is not a direct effect of G-CSF on macrophages. To examine whether, independent of the protection against LPS, G-CSF treatment still activated neutrophils, it was demonstrated that granulocytes from G-CSF-treated rats were primed for PMA-induced oxidative burst and for ionophore/arachidonic acid-stimulated lipoxygenase product formation. The experiments of this study support the notion that G-CSF is a negative feedback signal for macrophage-derived TNF-alpha production during Gram-negative sepsis.

Animals↗

PubMed1992

A link between extracellular reactive oxygen and endotoxin-induced release of tumour necrosis factor alpha in vivo.

Pretreatment with the reactive oxygen species scavengers superoxide dismutase (SOD) and catalase or with the xanthine oxidase inhibitor allopurinol protected mice against hepatitis induced by the combined administration of lipopolysaccharide (endotoxin) and D-galactosamine. In the sera of protected animals no tumor necrosis factor (TNF alpha) was detectable in contrast to abundant amounts in the sera of injured control animals. A similar protection by the suppression of systemic TNF alpha was observed following the pretreatment of mice with polystyrene-coupled SOD prior to endotoxic challenge. Both pretreatments were ineffective when hepatitis was evoked by administration of the mediator TNF alpha instead of endotoxin. These findings indicate that the formation of extracellular reactive oxygen species is a condition needed to induce the release of TNF alpha and thus to mediate endotoxin-induced toxicity.

Alanine Transaminase↗

PubMed1992

Endotoxin-inducible cytotoxicity in liver cell cultures--II. Demonstration of endotoxin-tolerance.

Endotoxins from gram negative bacteria, central mediators of septic shock, share the characteristic property of inducing tolerance against their own action. This work investigates whether a corresponding ex-vivo tolerance can be observed in a cellular system with endotoxin-inducible hepatocytoxicity. The following experimental approaches were chosen in order to induce an endotoxin-unresponsive state prior to cell preparation: (1) pretreatment of rats with endotoxin, (2) partial hepatectomy, (3) use of neonatal rats and (4) pretreatment of rats with silica. An in-vivo protection against endotoxin-induced liver injury was obtained by all of these four measures: cells prepared from these groups of animals showed greatly diminished sensitivity towards endotoxin-induced hepatocytotoxicity in vitro. The suppressed endotoxin sensitivity after silica pretreatment was partially restored in vitro by the addition of native Kupffer cells (KC). Isolated KC of all but the endotoxin-pretreated animals secreted tumor necrosis factor-alpha in response to endotoxin. It is concluded that different types of tolerance can be distinguished: (a) impairment of macrophage functions (silica pretreatment), (b) hepatocyte unresponsiveness (neonatal rats and hepatectomy) and (c) impaired macrophage function combined with hepatocyte unresponsiveness (endotoxin-pretreated rats).

Animals↗

PubMed1992

NADH-dependent reductive stress and ferritin-bound iron in allyl alcohol-induced lipid peroxidation in vivo: the protective effect of vitamin E.

The role of iron in allyl alcohol-induced lipid peroxidation and hepatic necrosis was investigated in male NMRI mice in vivo. Ferrous sulfate (0.36 mmol/kg) or a low dose of ally alcohol (0.6 mmol/kg) itself caused only minor lipid peroxidation and injury to the liver within 1 h. When FeSO4 was administered before allyl alcohol, lipid peroxidation and liver injury were potentiated 50-100-fold. Pretreatment with DL-tocopherol acetate 5 h before allyl alcohol protected dose-dependently against allyl alcohol-induced lipid peroxidation and liver injury in vivo. Products of allyl alcohol metabolism, i.e. NADH and acrolein, both mobilized trace amounts of iron from ferritin in vitro. Catalytic concentrations of FMN greatly facilitated the NADH-induced reductive release of ferritin-bound iron. NADH effectively reduced ferric iron in solution. Consequently, a mixture of NADH and Fe3+ or NADH and ferritin induced lipid peroxidation in mouse liver microsomes in vitro. Our results suggest that the reductive stress (excessive NADH formation) during allyl alcohol metabolism can release ferrous iron from ferritin and can reduce chelated ferric iron. These findings provide a rationale for the strict iron-dependency of allyl alcohol-induced lipid peroxidation and hepatotoxicity in mice in vivo and document iron mobilization and reduction as one of several essential steps in the pathogenesis.

1-Propanol↗

PubMed1992

The physiological consequences of glutathione variations.

The major low molecular weight thiol inside cells, the tripeptide glutathione (GSH), is of importance for protection of the cell against oxidative challenge, for thiol homeostasis required to guarantee basic functions, and for defence mechanisms against xenobiotics. Since the pathophysiological significance of a perturbed GSH status in human disease is less clear, this review evaluates the consequences of in vivo variations of GSH. Owing to intracellular GSH concentrations above 2 mM depletion of GSH as such has little metabolic consequences unless an additional stress is superimposed. The kinetic properties of GSH-dependent enzymes imply that loss of up to 90% of intracellular GSH may still be compatible with cellular integrity. Mitochondrial GSH, which accounts for about 10% of total cellular GSH, may define the threshold beyond that toxicity commences. Thus, in cases of severe GSH-depletion a substitution of GSH as a therapeutic measure seems justified. Such a severe depletion of GSH has been described for some diseases such as liver dysfunction, AIDS or pulmonary fibrosis.

Animals↗

PubMed1992

Colchicine prevents tumor necrosis factor-induced toxicity in vivo.

Tumor necrosis factor (TNF) toxicity was induced in vivo by intravenous administration of 15 micrograms of recombinant murine TNF-alpha per kg to galactosamine-sensitized mice. Within 8 h, the animals developed a fulminant hepatitis. Intravenous administration of 0.5 mg of colchicine per kg at 19 and 4 h prior to TNF challenge protected the animals against hepatitis. Lipopolysaccharide (LPS)-stimulated, bone marrow-derived macrophages from C3H/HeN mice released significant amounts of TNF in vitro. When such macrophages were intravenously given to LPS-resistant galactosamine-sensitized C3H/HeJ mice, these animals died within 24 h. Preincubation of these transferred macrophages with colchicine did not suppress the LPS-inducible TNF release from these cells. Concordantly, administration of macrophages exposed to colchicine in vitro resulted in full lethality. However, in vivo pretreatment of C3H/HeJ mice with colchicine 19 and 4 h prior to the transfer of LPS-stimulated macrophages prevented lethality. In LPS-responsive NMRI mice which had been protected against galactosamine-LPS-induced hepatitis by pretreatment with colchicine, TNF was still released into the blood. We conclude from our findings that the in vivo protection by colchicine is mediated by blocking TNF action on target cells while the effector cells of LPS toxicity, i.e., the macrophages, remain responsive.

Animals↗

PubMed1992

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.

Animals↗

PubMed1992

A novel xanthine derivative counteracting in vivo tumor necrosis factor alpha toxicity in mice.

The xanthine derivative A 802715 (1-(5-hydroxy-5-methyl)hexyl-3-methyl-7- propyl-xanthine, Hoechst AG) caused dose-dependent protection against lipopolysaccharide (LPS)-induced lethal shock in mice. In animals which had received the compound, the LPS-induced increase of serum tumor necrosis factor (TNF alpha) levels was not significantly affected. Protection against LPS-induced lethality was observed not only when A 802715 was given 1 hr before or simultaneously with LPS but also when administered 1 hr after LPS challenge. Administration of 200 mg/kg of the compound 1 hr before challenge also fully protected against lethal shock induced by intravenous administration of recombinant murine TNF alpha. It is concluded that A 802715 counteracts TNF alpha toxicity and that the drug bears the potential of therapeutic intervention in septic shock.

Animals↗

PubMed1992

The role of leukotriene D4 in septic shock models.

Septic shock is a major complication during the treatment of intense care patients. A similar pathologic state can be experimentally induced in rodents by application of endotoxins. There is circumstantial as well as direct evidence for a participation of leukotriene D4 in this experimental multiorgan failure. Due to liver-specific sensitivation by galactosamine endotoxin-induced multiorgan failure can be experimentally transposed to a single organ, i.e. hepatic failure. Data presented here show a participation of the eicosanoid leukotriene D4 in either model of sepsis. We have recently described a cellular system modelling endotoxin-induced hepatic failure. In this system based on the coculture of hepatocytes and nonparenchymal liver cells leukotriene D4 is required for the development of cytotoxicity. It is concluded that the three models share pivotal mechanistic principles and might be used complementary to each other in order to study underlying molecular events.

Animals↗

PubMed1991

Reactive oxygen species, antiproteases, and cytokines in sepsis.

Although the shock syndrome is recognized as a form of "mediator poisoning", a plethora of details is hardly converging into a coherent concept of chronological and molecular order. As a model for organ failure in septic shock, three alternative experimental approaches with a common pathology are presented: When galactosamine-sensitized mice receive either lipopolysaccharide or leukotriene D4 or tumor necrosis factor alpha they develop fulminant hepatitis within few hours with a lethal outcome within one day. Detailed pharmacological intervention studies allow to conclude that endotoxin-induced leukotriene D4 release induces a transient ischemia by the known vasoconstrictive action of this eicosanoid. A following reperfusion/reoxygenation phase gives rise to superoxide formation which inactivates alpha 1 proteinase inhibitor. Thus a serine protease becomes active which is responsible for the processing of a monocytic tumor necrosis factor alpha precursor to be released into the circulation after proteolytic cleavage. By this sequence the final central mediator of shock and sepsis becomes systematically abundant. The concept arising from these studies reconciles previously known findings and provides a link between the role of reactive oxygen species in inflammation, the balance of proteases and antiproteases in the extracellular space and the release of the cytokine tumor necrosis factor in sepsis and shock.

Animals↗

PubMed1991

GSH rescue by N-acetylcysteine.

Reduced glutathione (GSH) is the main intracellular low molecular weight thiol. GSH acts as a nucleophilic scavenger and as an enzyme-catalyzed antioxidant in the event of electrophilic/oxidative tissue injury. Therefore, GSH has a major role as a protector of biological structures and functions. GSH depletion has been recognized as a hazardous condition during paracetamol intoxication. Conversely, GSH rescue, meaning recovery of the protective potential of GSH by early administration of N-acetylcysteine (NAC), has been found to be life-saving. Lack of GSH and electrophilic/oxidative injury have been identified among the causes of the adult respiratory distress syndrome (ARDS), idiopathic pulmonary fibrosis (IPF), and the acquired immunodeficiency syndrome (AIDS). Experimental and early clinical data (in ARDS) point to the role of NAC in the treatment of these conditions. Recently, orally given NAC has been shown to enhance the levels of GSH in the liver, in plasma, and notably in the bronchoalveolar lavage fluid. Rescue of GSH through NAC needs to be appreciated as an independent treatment modality for an array of different disease, all of which have one feature in common: pathogenetically relevant loss of GSH.

Acetylcysteine↗

PubMed1991

Endotoxin-inducible cytotoxicity in liver cell cultures--I.

It is known that rodents challenged with a combination of galactosamine and endotoxin develop a fulminant hepatitis within several hours. Until now, no in-vitro correlate for this organ-specific lesion has been described. Here, in-vitro conditions have been developed which allow examination of lipopolysaccharide (endotoxin)-inducible cell injury to hepatocytes. Under these in-vitro conditions (RPMI 1640 supplemented with 10% calf serum, 40% oxygen tension) which require the presence of functionally intact Kupffer cells, a concentration-dependent lactate dehydrogenase release is inducible by different lipopolysaccharides in hepatocyte cultures from Fischer rats. It can be abrogated by polymyxin B. These co-cultures secreted tumor necrosis factor-alpha into the medium upon a lipopolysaccharide stimulus. The presence of a tumor necrosis factor-alpha antiserum reduced the major part of the endotoxin-inducible cytotoxicity. Similarities in vitro and in vivo of the cytotoxic potency of various endotoxin species and the different responsiveness of hepatocytes from two different rat strains support that this co-culture system might be useful for studying endotoxin-inducible lesions in vitro.

Animals↗

PubMed1991

Time course of IL-6 and TNF alpha release during endotoxin-induced endotoxin tolerance in rats.

Development of endotoxin tolerance in rats induced by repeated application of low dosages of endotoxin is associated with repeatable IL-6 formation, reversible drop in white blood cells, pronounced consumption of platelets, gradual formation of alpha 2M as an example of acute phase proteins, and flattening TNF alpha formation. In the status of full tolerance the TNF alpha release is completely eliminated. Inhibition of TNF alpha biosynthesis and induction of acute phase protein formation by IL-6 are discussed as possible factors in the development of endotoxin tolerance.

Acute-Phase Proteins↗