Expression of inducible nitric oxide synthase in endotoxemic rat hepatocytes is dependent on the cellular glutathione status

In-depth hepatoprotective mechanistic study of Phyllanthus niruri: In vitro and in vivo studies and its chemical characterization

Phyllanthus niruri L. is a widespread tropical plant which is used in Ayurvedic system for liver and kidney ailments. The present study aims at specifying the most active hepatoprotective extract of P. niruri and applying a bio-guided protocol to identify the active compounds responsible for this effect. P. niruri aerial parts were extracted separately with water, 50%, 70% and 80% ethanol. The cytoprotective activity of the extracts was evaluated against CCl₄-induced hepatotoxicity in clone-9 and Hepg2 cells. Bioassay-guided fractionation of the aqueous extract (AE) was accomplished for the isolation of the active compounds. Antioxidant activity was assessed using DPPH (1, 1-diphenyl-2-picrylhydrazyl) radical scavenging method and ferric reducing antioxidant power (FRAP). The in vivo hepatoprotective activity of AE was evaluated in CCl₄-induced hepatotoxicity in rats at different doses after determination of its LD₅₀. Pretreatment of clone-9 and Hepg2 with different concentrations of AE (1, 0.1, 0.01 mg/ml) had significantly reduced the levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) against CCl₄ injures, and restored the activity of the natural antioxidants; glutathione (GSH) and superoxide dismutase (SOD) towards normalization. Fractionation of AE gave four fractions (I-IV). Fractions I, II, and IV showed a significant in vitro hepatoprotective activity. Purification of I, II and IV yielded seven compounds; corilagin C1, isocorilagin C2, brevifolin C3, quercetin C4, kaempferol rhamnoside C5, gallic acid C6, and brevifolin carboxylic acid C7. Compounds C1, C2, C5, and C7 showed the highest (p< 0.001) hepatoprotective potency, while C3, C4, and C6 exhibited a moderate (p< 0.001) activity. The AE exhibited strong antioxidant DPPH (IC₅₀ 11.6 ± 2 μg/ml) and FRAP (79.352 ± 2.88 mM Ferrous equivalents) activity. In vivo administration of AE in rats (25, 50, 100 and 200 mg/kg) caused normalization of AST, ALT, alkaline phosphatase (ALP), lactate dehydrogenase (LDH), total cholesterol (TC), triglycyrides (TG), total bilirubin (TB), glucose, total proteins (TP), urea and creatinine levels which were elevated by CCl₄. AE also decreased TNF-α, NF-KB, IL-6, IL-8, IL10 and COX-2 expression, and significantly antagonizes the effect of CCl₄ on the antioxidant enzymes SOD, catalase (CAT), glutathione reductase (GR), and glutathione peroxidase (GSP). The histopathological study also supported the hepatoprotective effect of AE. P. niruri isolates exhibited a potent hepatoprotective activity against CCl₄-induced hepatotoxicity in clone-9 and Hepg2 cell lines through reduction of lipid peroxidation and maintaining glutathione in its reduced form. This is attributable to their phenolic nature and hence antioxidative potential.

Infiltration of polarized macrophages associated with liver fibrosis in infants with biliary atresia

BACKGROUND/PURPOSE

Macrophages exert critical functions in liver homeostasis and have been proposed as potential targets in combatting fibrosis. We aimed to evaluate polarized functional status of liver infiltrated macrophages in infants with biliary atresia (BA).

METHODS

Immunohistochemical staining for CD68, CD163, and IRF5 was performed in 40 BA infants. Liver biopsies were scored for fibrosis and tested for association with clinical biochemical characteristics.

RESULTS

Developing lesions in BA liver progressively accumulated both CD163⁺ macrophages (M2) and IRF5⁺ macrophages (M1), while CD163 and IRF5 staining was stronger than the control group (p<0.001). In BA, the higher staining density of CD163 and CD68 was related with elevated serum conjugated bilirubin level (p=0.014 and 0.021, respectively). The CD163/IRF5 macrophages ratio was related with liver fibrosis scores (high vs. low, p=0.004).

CONCLUSIONS

We demonstrated a strong presence of polarized macrophages in BA liver, and macrophage phenotypes were involved in disease development. The balance of different polarized macrophage subpopulations may play a key role in fibrogenesis of BA.

Ubiquitin-Conjugating Enzyme 9 Phosphorylation as a Novel Mechanism for Potentiation of the Inflammatory Response

Lipopolysaccharide (LPS), a bacterial endotoxin, induces inflammation in macrophages via activation of NF-κB signaling. Sumoylation is a post-translational modification mediated by the small ubiquitin-like modifier, SUMO. Ubiquitin-conjugating enzyme 9 (UBC9) is the only known SUMO conjugating enzyme. LPS treatment lowers SUMO-1 and UBC9 mRNA levels in primary astrocytes. UBC9 can degrade NF-κB inhibitor α (Ikbα) via a SUMO2/3-ubiquitin pathway. However, UBC9 may also promote Ikbα stability by SUMO-1 conjugation that further regulates NF-κB signaling. The role of UBC9 in liver inflammation is unknown. We reported that CDK1-mediated phosphorylation of UBC9 enhanced its stability. Herein, we describe an anti-inflammatory role of UBC9 that is lost when it is phosphorylated during inflammation. LPS exposure caused induction in UBC9 phosphorylation and CDK1 activation specifically in Kupffer cells in vivo and in RAW264.7 macrophages in vitro. Silencing or overexpression experiments in vitro and in vivo showed that UBC9 was required to blunt the proinflammatory response elicited by LPS. LPS stimulation raised the binding of phospho-UBC9 but not the unphosphorylated counterpart, to Ikbα in RAW264.7 macrophages. Hence, phospho-UBC9 may promote NF-κB signaling by regulating Ikbα and this may be a novel mechanism that deregulates liver inflammatory signaling.

Protective effect of Spirulina platensis against cell damage and apoptosis in hepatic tissue caused by high fat diet

Spirulina platensis is a microalga that may be a source of antioxidants that can reduce body fat deposition. Consumption of a high fat diet produces elevated blood lipid levels, inflammation and apoptosis. We investigated the possible effects of S. platensis on the blood lipid profile, and liver inflammation and apoptosis in rats fed a high fat diet. Sixty-four young male rats were divided into eight equal groups. The control group was fed a basic diet. The experimental groups were fed a diet for 60 days that was prepared by mixing variable amounts of 43% vegetable oil and 10% cholesterol with or without 3% S. platensis mixed with the basal diet. Blood and liver tissue samples were collected from each animal. Serum samples were used to analyze lipid parameters, total antioxidant status and total oxidant status. iNOS and eNOS were determined by immunohistochemistry. TUNEL staining was used to detect apoptosis to investigate a possible connection between inflammation and apoptosis in the liver tissue. The relations between fat deposition and liver degeneration were assessed by Sirius red staining and alpha-smooth muscle actin immunostaining. S. platensis reduced serum HDL-C, LDL-C and triglyceride, increased HDL-C levels in rats fed a high fat diet to near control levels, and reduced iNOS levels and increased eNOS levels in the liver tissue compared to vegetable oil and cholesterol treated groups. The apoptotic index was reduced in the groups that were fed a high fat or a basic diet when supplemented with S. platensis.

Liver sinusoidal endothelial dysfunction after LPS administration: a role for inducible-nitric oxide synthase

BACKGROUND & AIMS

Sepsis is associated with microvascular dysfunction, which contributes to organ failure. Intrahepatic endothelial dysfunction occurs after exposure to lipopolysaccharide (LPS). The upregulation of inducible nitric oxide synthase (iNOS) has been shown to contribute to systemic vascular dysfunction after LPS administration. However, little is known about the effects of iNOS induction on the liver microcirculation. This study aimed at exploring, in the isolated rat liver perfusion model, the role of iNOS induction in liver microvascular dysfunction associated with endotoxemia.

METHODS

All experiments were conducted in male Wistar rats, after 24 h of LPS (5 mg/kg i.p.) or saline administration in the presence or absence of the iNOS inhibitor 1400 W (3 mg/kg i.p.), administered 3 and 23 h after LPS/saline injection. Liver microvascular function was assessed by isolated liver perfusion, followed by molecular studies and liver function tests.

RESULTS

At 24 h, LPS induced liver endothelial dysfunction, as shown by a decreased vasodilatory response to acetylcholine and decreased eNOS phosphorylation at Ser(1176). This was associated with liver injury, assessed by an increase in liver transaminases and decreased indocyanin green clearance, and increased nitrooxidative stress. iNOS inhibition prevented liver endothelial dysfunction, blunted the development of liver injury and attenuated LPS-induced nitrooxidative stress.

CONCLUSIONS

iNOS upregulation contributes to liver microvascular dysfunction in endotoxemia. This suggests that this mechanism deserves further exploration in studies addressing liver protection in the context of severe acute bacterial infection.

Hepatic Localization of Macrophage Phenotypes during Fibrogenesis and Resolution of Fibrosis in Mice and Humans

Macrophages have been found to both promote liver fibrosis and contribute to its resolution by acquiring different phenotypes based on signals from the micro-environment. The best-characterized phenotypes in the macrophage spectrum are labeled M1 (classically activated) and M2 (alternatively activated). Until now the in situ localization of these phenotypes in diseased livers is poorly described. In this study, we therefore aimed to localize and quantify M1- and M2-dominant macrophages in diseased mouse and human livers. The scarred collagen-rich areas in cirrhotic human livers and in CCl4-damaged mouse livers contained many macrophages. Though total numbers of macrophages were higher in fibrotic livers, the number of parenchymal CD68-positive macrophages was significantly lower as compared to normal. Scar-associated macrophages were further characterized as either M1-dominant (IRF-5 and interleukin-12) or M2-dominant (CD206, transglutaminase-2, and YM-1) and significantly higher numbers of both of these were detected in diseased livers as compared to healthy human and mouse livers. Interestingly, in mouse, livers undergoing resolution of fibrosis, the total number of CD68⁺ macrophages was significantly lower compared to their fibrotic counterparts. M2-dominant (YM-1) macrophages were almost completely gone in livers undergoing resolution, while numbers of M1-dominant (IRF-5) macrophages were almost unchanged and the proteolytic activity (MMP9) increased. In conclusion, this study shows the distribution of macrophage subsets in livers of both human and murine origin. The presence of M1- and M2-dominant macrophages side by side in fibrotic lesions suggests that both are involved in fibrotic responses, while the persistence of M1-dominant macrophages during resolution may indicate their importance in regression of fibrosis. This study emphasizes that immunohistochemical detection of M1/M2-dominant macrophages provides valuable information in addition to widely used flow cytometry and gene analysis.

Hepatic inflammation and progressive liver fibrosis in chronic liver disease

Chronic liver inflammation drives hepatic fibrosis, and current immunosuppressive, anti-inflammatory, and anti-viral therapies can weaken this driver. Hepatic fibrosis is reversed, stabilized, or prevented in 57%-79% of patients by conventional treatment regimens, mainly by their anti-inflammatory actions. Responses, however, are commonly incomplete and inconsistently achieved. The fibrotic mechanisms associated with liver inflammation have been clarified, and anti-fibrotic agents promise to improve outcomes as adjunctive therapies. Hepatitis C virus and immune-mediated responses can activate hepatic stellate cells by increasing oxidative stress within hepatocytes. Angiotensin can be synthesized by activated hepatic stellate cells and promote the production of reactive oxygen species. Anti-oxidants (N-acetylcysteine, S-adenosyl-L-methionine, and vitamin E) and angiotensin inhibitors (losartin) have had anti-fibrotic actions in preliminary human studies, and they may emerge as supplemental therapies. Anti-fibrotic agents presage a new era of supplemental treatment for chronic liver disease.

Review article: The prevention and reversal of hepatic fibrosis in autoimmune hepatitis

BACKGROUND

Immunosuppressive treatment of autoimmune hepatitis can prevent or reverse hepatic fibrosis, but these anti-fibrotic effects are inconsistent secondary gains.

AIM

To describe the anti-fibrotic effects of current therapies for autoimmune hepatitis, discuss the pathogenic mechanisms of hepatic fibrosis that might be targeted by anti-fibrotic interventions, indicate the non-invasive diagnostic tests of hepatic fibrosis that must be validated in autoimmune hepatitis and to suggest promising treatment opportunities.

METHODS

Studies cited in PubMed from 1972 to 2013 for autoimmune hepatitis, hepatic fibrosis, cirrhosis, anti-fibrotic therapy and non-invasive tests of hepatic fibrosis were selected.

RESULTS

Hepatic fibrosis improves in 53-57% of corticosteroid-treated patients with autoimmune hepatitis; progressive fibrosis slows or is prevented in 79%; and cirrhosis may be reversed. Progressive hepatic fibrosis is associated with liver inflammation, and the inability to fully suppress inflammatory activity within 12 months is associated with progression to cirrhosis (54%) and death or need for liver transplantation (15%). Liver tissue examination remains the gold standard for assessing hepatic fibrosis, but laboratory and radiological tests may be useful non-invasive methods to measure the fibrotic response. Severe liver inflammation can confound radiological assessments, and the preferred non-invasive test in autoimmune hepatitis is uncertain. Individualised treatment adjustments and adjunctive anti-fibrotic therapies are poised for study in this disease.

CONCLUSIONS

The prevention and reversal of hepatic fibrosis are achievable objectives in autoimmune hepatitis. Strategies that evaluate individualised therapies adjusted to the rapidity and completeness of the inflammatory response, and the use of adjunctive anti-fibrotic interventions, must be evaluated.

Mice lacking inducible nitric oxide synthase develop exacerbated hepatic inflammatory responses induced by Plasmodium berghei NK65 infection

Infection of mice with Plasmodium berghei NK65 represents a well-recognized malaria model in which infection is accompanied by an intense hepatic inflammatory response. Enzyme-inducible nitric oxide synthase is an important regulator of inflammation and leukocyte recruitment in microvessels, but these functions have yet to be evaluated in experimental malaria. In this study, we assessed the involvement of inducible nitric oxide synthase in inflammatory responses to murine experimental malaria induced by P. berghei NK65. We observed that wild type (WT) and nitric oxide synthase (iNOS)-deficient mice (iNOS(-/-)) mice showed similar levels of parasitemia following P. berghei NK65 infection, although infected iNOS(-/-) mice presented early mortality. Inducible nitric oxide synthase deficiency led to increased leukocyte rolling and adhesion to the liver in iNOS(-/-) mice relative to the WT animals, as observed via intravital microscopy. Infected iNOS(-/-) mice also exhibited increased hepatic leukocyte migration and subsequent liver damage, which was associated with high serum levels of the cytokines TNF-α, IL-6 and IL-10. Our data suggest potential role for the iNOS enzyme as a regulator of hepatic inflammatory response induced by P. berghei NK65-infection, and its absence leads to exacerbated inflammation and sequential associated-hepatic damage in the animals.

Biochanin A protects against acute carbon tetrachloride-induced hepatotoxicity in rats

Biochanin A (BCA) is an isoflavone found in red clover possessing multiple pharmacological activities including antimicrobial, antioxidant, and anticancer ones. The present study aimed to assess its hepatoprotective potential at different doses in a carbon tetrachloride (CCl4)-induced hepatotoxicity model in rats. The effects on hepatic injury were explored by measuring serum levels of alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase. Furthermore, the serum levels of glucose, urea, creatinine, total bilirubin, total proteins, triglycerides, and total cholesterol were determined. The metabolic capacity of the liver was assessed by measuring changes in cytochrome P450 2E1 activity. The underlying mechanisms were substantiated by measuring oxidative stress markers as catalase, superoxide dismutase, glutathione peroxidase, glutathione transferase, glutathione reductase, reduced glutathione, total antioxidant capacity, and lipid peroxidation, as well as inflammation markers such as nitric oxide, inducible nitric oxide synthase, cyclooxygenase2, tumor necrosis factor-α, and leukocyte-common antigen. The results were confirmed by histopathological examination, and the median lethal dose was determined to confirm the safety of the drug. BCA successively protected against CCl4-induced damage, normalizing many parameters to that of the control group. The study indicates that BCA possesses multimechanistic hepatoprotective activity that can be attributed to its antioxidant, anti-inflammatory, and immunomodulatory actions.

Oxidative damage in alveolar macrophages exposed to cigarette smoke extract and participation of nitric oxide in redox balance

Nitric oxide (NO) acts in both pathological and biological processes. We investigated the role of NO in the regulation of cigarette smoke-induced oxidative stress in rat alveolar macrophages (RAM). RAM collected from Wistar rats were cultured in 5% concentration cigarette smoke extract (CSE) for 1h. RAM exposed to CSE were then co-incubated with L-NAME (LN), L-arginine (LA), N-acetylcysteine (NAC) and both LN and NAC. RAM cultured only with medium was considered as control group. Biochemical analysis were performed to measure cellular metabolism (MTT), nitrite levels, superoxide dismutase (SOD) and glutathione peroxidase activities, reduced glutathione (GSH) and oxidized (GSSG), malondialdehyde and myeloperoxidase activity. During exposure to CSE, increased NO levels were not only associated with an increase of cell activation, but also affected MTT levels in RAM. CSE exposure resulted in significant redox imbalance in RAM. NAC administration affected SOD antioxidant profile regardless NO levels; however nitrite values were associated with GSH/GSSG ratio. In addition, lipid peroxidation appeared to be nitric-oxide dependent. Furthermore, the use of NAC significantly reduced the expression of NFkB normally observed in RAM exposed to CSE. The present results show that NO appeared to be involved in RAM activation, oxidative status maintenance and lipid peroxidation process during exposure to CSE.

GSH threshold requirement for NO-mediated expression of the Arabidopsis AtFer1 ferritin gene in response to iron

Iron treatment of Arabidopsis cultured cells promotes a rapid NO burst within chloroplasts, necessary for up-regulation of the AtFer1 ferritin gene expression. The same occurs in Arabidopsis leaf chloroplasts, and is dependent upon the GSH content of plants. A leaf GSH concentration threshold between 10 and 50 nmol GSHg(-1) FW is required for full induction of AtFer1 gene expression in response to iron.

3-Formylchromone interacts with cysteine 38 in p65 protein and with cysteine 179 in IκBα kinase, leading to down-regulation of nuclear factor-κB (NF-κB)-regulated gene products and sensitization of tumor cells

3-Formylchromone (3-FC) has been associated with anticancer potential through a mechanism yet to be elucidated. Because of the critical role of NF-κB in tumorigenesis, we investigated the effect of this agent on the NF-κB activation pathway. Whether activated by inflammatory agents (such as TNF-α and endotoxin) or tumor promoters (such as phorbol ester and okadaic acid), 3-FC suppressed NF-κB activation. It also inhibited constitutive NF-κB expressed by most tumor cells. This activity correlated with sequential inhibition of IκBα kinase (IKK) activation, IκBα phosphorylation, IκBα degradation, p65 phosphorylation, p65 nuclear translocation, and reporter gene expression. We found that 3-FC inhibited the direct binding of p65 to DNA, and this binding was reversed by a reducing agent, thus suggesting a role for the cysteine residue. Furthermore, mutation of Cys38 to Ser in p65 abolished this effect of the chromone. This result was confirmed by a docking study. 3-FC also inhibited IKK activation directly, and the reducing agent reversed this inhibition. Furthermore, mutation of Cys179 to Ala in IKK abolished the effect of the chromone. Suppression of NF-κB activation led to inhibition of anti-apoptotic (Bcl-2, Bcl-xL, survivin, and cIAP-1), proliferative (cyclin D1 and COX-2), invasive (MMP-9 and ICAM-1), and angiogenic (VEGF) gene products and sensitization of tumor cells to cytokines. Thus, this study shows that modification of cysteine residues in IKK and p65 by 3-FC leads to inhibition of the NF-κB activation pathway, suppression of anti-apoptotic gene products, and potentiation of apoptosis in tumor cells.

Effect of butylated hydroxytoluene (E321) pretreatment versus L-arginine on liver injury after sub-lethal dose of endotoxin administration

Aim of this study was to compare the effects of L-arginine (L-arg) and food-antioxidant butylated hydroxytoluene (BHT) against oxidative stress of Escherichia coli endotoxin (LPS) in liver. Ninety Wistar albino rats were assigned in three groups. Rats received one of the following pre-treatment previous to 5mg/kg LPS intraperitoneally: saline, L-arg (NO donor, 100mg/kg) or BHT (250 mg/kg/day), for 3 days. At second, fourth and sixth hours, plasma nitrite-plus-nitrate, circulating liver enzymes, glutathione levels, superoxide dismutase, glutathione peroxidase activities were measured. The most remarkable liver injury was evident in BHT pre-treated animals at all time points compared to L-arg pre-treated rats. While BHT enhanced superoxide dismutase activities following LPS, glutathione decreased simultaneously compared to L-arg group. Although the risk associated with the use of BHT alone in subthreshold doses appeared to be low, higher risk of liver toxicity should be considered when over-consuming this food additive in endotoxemic settings.

Bharangin, a diterpenoid quinonemethide, abolishes constitutive and inducible nuclear factor-κB (NF-κB) activation by modifying p65 on cysteine 38 residue and reducing inhibitor of nuclear factor-κB α kinase activation, leading to suppression of NF-κB-regulated gene expression and sensitization of tumor cells to chemotherapeutic agents

Although inflammatory pathways have been linked with various chronic diseases including cancer, identification of an agent that can suppress these pathways has therapeutic potential. Herein we describe the identification of a novel compound bharangin, a diterpenoid quinonemethide that can suppress pro-inflammatory pathways specifically. We found that bharangin suppresses nuclear factor (NF)-κB activation induced by pro-inflammatory cytokine, tumor promoter, cigarette smoke, and endotoxin. Inhibition of NF-κB activation was mediated through the suppression of phosphorylation and degradation of inhibitor of nuclear factor-κB (IκBα); inhibition of IκBα kinase activation; and suppression of p65 nuclear translocation, and phosphorylation. The diterpenoid inhibited binding of p65 to DNA. A reducing agent reversed the inhibitory effect, and mutation of the Cys(38) of p65 to serine abrogated the effect of bharangin on p65-DNA binding. Molecular docking revealed strong interaction of the ligand with the p65 via two hydrogen bonds one with Lys(37) (2.204 Å) and another with Cys(38) (2.023 Å). The inhibitory effect of bharangin on NF-κB activation was specific, inasmuch as binding of activator protein-1 and octameric transcription factor 1 to DNA was not affected. Suppression of NF-κB activation by this diterpenoid caused the down-regulation of the expression of proteins involved in tumor cell survival, proliferation, invasion, and angiogenesis, leading to potentiation of apoptosis, suppression of proliferation, and invasion of tumor cells. Furthermore, the genetic deletion of p65 and mutation of p65Cys(38) residue to Ser abolished the affect of bharangin. Overall, our results demonstrate that bharangin specifically inhibits the NF-κB activation pathway by modifying p65 and inhibiting IκBα kinase activation and potentiates apoptosis in tumor cells.

LPS-induced iNOS expression in Bv-2 cells is suppressed by an oxidative mechanism acting on the JNK pathway--a potential role for neuroprotection

Activated microglia cells, observed during chronic inflammation, produce and secrete compounds that at high concentrations or during sustained production might cause neuronal cell death. Inducible nitric oxide synthase (iNOS) is expressed in response to various immunological stimuli and catalyses the formation of the free radical nitric oxide (NO), that at low and regulated levels participate in cell signaling and cytoprotective events, whereas its higher and unregulated production can promote neurotoxicity in cells or in tissues. Regulation of NO production is therefore central for maintaining NO-levels within a safe window. We have analyzed iNOS protein expression and NO production, in murine microglial Bv-2 cells after 16h treatment with the bacterial endotoxin lipopolysaccharide (LPS). We have further analyzed three MAPK pathways, by co-treating the cells with LPS and the inhibitors of ERK1/2, p38 or JNK MAPK activities. To investigate participation of an oxidative regulatory mechanism, cells were also treated with the antioxidant N-acetyl-L-cysteine (NAC). Our results show that LPS-induced iNOS expression in Bv-2 cells is mainly mediated through JNK MAPK. In addition, co-treatment of the Bv-2 cells with LPS and NAC surprisingly further increased the iNOS expression, an effect also found to be mediated through the JNK MAPK pathway. The level of phosphorylated JNK MAPK (p46) was strongly increased by LPS alone and was further increased when combined with NAC. Our data indicate that iNOS and NO production are suppressed by an oxidative mechanism acting on the JNK MAPK pathway and we speculate that it might constitute a potential regulatory mechanism controlling the NO level.

Chronic administration of ursodeoxycholic acid decreases portal pressure in rats with biliary cirrhosis

Liver cirrhosis is characterized by increased IHR (intrahepatic resistance) and lipid peroxidation, and decreased antioxidative defence. The present study investigates the effects of administration for 1 month of the antioxidant UDCA (ursodeoxycholic acid) in BDL (bile-duct-ligated) cirrhotic rats. Splanchnic haemodynamics, IHR, hepatic levels of TBARS (thiobarbituric acid-reacting substances), GSH (glutathione), SOD (superoxide dismutase) activity, nitrite, PIIINP (N-terminal propeptide of type III procollagen) and collagen deposition, histological examination of liver, mRNA expression of PIIIP-alpha1 (type III procollagen) and TGF-beta1 (transforming growth factor-beta1), protein expression of TXS (thromboxane synthase) and iNOS (inducible NO synthase), and TXA2 (thromboxane A2) production in liver perfusates were measured. The results showed that portal pressure and IHR, hepatic levels of PIIINP, hepatic collagen deposition, mRNA expression of PIIIP-alpha1 and TGF-beta1, protein expression of iNOS and TXS, and production of TXA2 in liver perfusates were significantly decreased in UDCA-treated BDL rats. The increased levels of hepatic GSH and SOD activity and decreased levels of TBARS and nitrite were also observed in UDCA-treated BDL rats. In UDCA-treated BDL rats, the reduction in portal pressure resulted from a decrease in IHR, which mostly acted through the suppression of hepatic TXA2 production and lipid peroxidation, and an increase in antioxidative defence, leading to the prevention of hepatic fibrosis.

The influence of N-acetyl-L-cysteine on oxidative stress and nitric oxide synthesis in stimulated macrophages treated with a mustard gas analogue

Background

Sulphur mustard gas, 2, 2'-dichlorodiethyl sulphide (HD), is a chemical warfare agent. Both mustard gas and its monofunctional analogue, 2-chloroethyl ethyl sulphide (CEES), are alkylating agents that react with and diminish cellular thiols and are highly toxic. Previously, we reported that lipopolysaccharide (LPS) significantly enhances the cytotoxicity of CEES in murine RAW 264.7 macrophages and that CEES transiently inhibits nitric oxide (NO) production via suppression of inducible NO synthase (iNOS) protein expression. NO generation is an important factor in wound healing. In this paper, we explored the hypotheses that LPS increases CEES toxicity by increasing oxidative stress and that treatment with N-acetyl-L-cysteine (NAC) would block LPS induced oxidative stress and protect against loss of NO production. NAC stimulates glutathione (GSH) synthesis and also acts directly as a free radical scavenger. The potential therapeutic use of the antibiotic, polymyxin B, was also evaluated since it binds to LPS and could thereby block the enhancement of CEES toxicity by LPS and also inhibit the secondary infections characteristic of HD/CEES wounds.

Results

We found that 10 mM NAC, when administered simultaneously or prior to treatment with 500 μM CEES, increased the viability of LPS stimulated macrophages. Surprisingly, NAC failed to protect LPS stimulated macrophages from CEES induced loss of NO production. Macrophages treated with both LPS and CEES show increased oxidative stress parameters (cellular thiol depletion and increased protein carbonyl levels). NAC effectively protected RAW 264.7 cells simultaneously treated with CEES and LPS from GSH loss and oxidative stress. Polymyxin B was found to partially block nitric oxide production and diminish CEES toxicity in LPS-treated macrophages.

Conclusion

The present study shows that oxidative stress is an important mechanism contributing to CEES toxicity in LPS stimulated macrophages and supports the notion that antioxidants could play a therapeutic role in preventing mustard gas toxicity. Although NAC reduced oxidative stress in LPS stimulated macrophages treated with CEES, it did not reverse CEES-induced loss of NO production. NAC and polymyxin B were found to help prevent CEES toxicity in LPS-treated macrophages.

Carbon monoxide blocks oxidative stress-induced hepatocyte apoptosis via inhibition of the p54 JNK isoform

Most chronic liver diseases are accompanied by oxidative stress, which may induce apoptosis in hepatocytes and liver injury. Oxidative stress induces heme oxygenase-1 (HO-1) expression. This stress-responsive cytoprotective protein is responsible for heme degradation into carbon monoxide (CO), free iron, and biliverdin. CO is an important intracellular messenger; however, the exact mechanisms responsible for its cytoprotective effect are not yet elucidated. Thus, we investigated whether HO-1 and CO protect primary hepatocytes against oxidative-stress-induced apoptosis. In vivo, bile duct ligation was used as model of chronic liver disease. In vitro, primary hepatocytes were exposed to the superoxide anion donor menadione in a normal and in a CO-- containing atmosphere. Apoptosis was determined by measuring caspase-9, -6, -3 activity and poly(ADP-ribose) polymerase cleavage, and necrosis was determined by Sytox green staining. The results showed that (1) HO-1 is induced in chronic cholestatic liver disease, (2) superoxide anions time- and dose-dependently induce HO-1 activity, (3) HO-1 overexpression inhibits superoxide-anions-induced apoptosis, and (4) CO blocks superoxide-anions-induced JNK phosphorylation and caspase-9, -6, -3 activation and abolishes apoptosis but does not increase necrosis. We conclude that HO-1 and CO protect primary hepatocytes against superoxide-anions-induced apoptosis partially via inhibition of JNK activity. CO could represent an important candidate for the treatment of liver diseases.

Nitric oxide-deficiency regulates hepatic heme oxygenase-1

Nitric oxide plays a crucial role in the maintenance of liver function and integrity. During stress, the inducible heme oxygenase-1 protein and its reaction products, including carbon monoxide, also exert potent hepatoprotective effects. We investigated a potential relationship between endogenous nitric oxide synthesis and the hepatic regulation of heme oxygenase-1. Inhibition of nitric oxide synthesis in vivo by injection of l-NAME led to a dose-dependent induction of heme oxygenase-1 mRNA, protein and activity in the rat liver, whereas did not affect the expression of other heat shock proteins. The effect of l-NAME was demonstrated by hemodynamic changes within the liver circulation as measured by ultrasonic flow probes. Inhibition of nitric oxide synthase led to a decline in hepatic arterial and portal venous blood flow, and subsequently caused liver cell damage. In contrast, the combined administration of l-NAME and the nitric oxide-independent intestinal vasodilator dihydralazine completely restored portal venous flow, abolished the liver cell damage, and prevented the upregulation of heme oxygenase-1, despite inhibition of nitric oxide production. In conclusion, nitric oxide deficiency upregulates hepatic heme oxygenase-1, which is reversible by maintaining hepatic blood flow. This interdependence has important implications for the development of therapeutic strategies aimed at modulating the activity of these hepatoprotective mediator systems.

Discrepant effects of inducible nitric oxide synthase modulation on systemic and splanchnic endothelial nitric oxide synthase activity and expression in cirrhotic rats

BACKGROUND

Arterial vasodilatation, which is a major factor in the pathogenesis of the hyperkinetic circulatory state and portal hypertension in cirrhosis, is due to arterial nitric oxide (NO) overproduction secondary to endothelial NO synthase (eNOS) and inducible NOS (iNOS) upregulation. However, in cirrhosis, the respective roles of eNOS and iNOS isoforms in NO overproduction are still unknown and the effect of iNOS modulation on eNOS activity and expression has not been evaluated in the systemic or splanchnic vessels. The aim of this study was to evaluate the effects of modulating aortic and superior mesenteric arteries (SMA) iNOS on arterial eNOS activity and expression in rats with cirrhosis.

METHODS

eNOS and iNOS protein expression and eNOS activity (assessed by its phosphorylation at serine 1177) were measured in the aortas and SMA in untreated and treated cirrhotic rats with lipopolysaccharide (LPS), N-iminoethyl-L-lysine (L-NIL), a selective iNOS inhibitor, and LPS plus L-NIL.

RESULTS

LPS administration significantly increased eNOS and iNOS protein expression and eNOS activity in the aortas of both sham-operated and cirrhotic rats. However, in SMA, LPS administration induced a decrease in eNOS protein expression and activity and an increase in iNOS protein expression.

CONCLUSION

The results of this study may explain the worsening of the hyperdynamic state in cirrhosis during septic shock by direct LPS-induced eNOS activation in large systemic vessels, and its inhibition in concomitant small splanchnic vasculature by iNOS synthesized NO.

Inhibition of inducible Nitric Oxide Synthase by a mustard gas analog in murine macrophages

BACKGROUND

2-Chloroethyl ethyl sulphide (CEES) is a sulphur vesicating agent and an analogue of the chemical warfare agent 2,2'-dichlorodiethyl sulphide, or sulphur mustard gas (HD). Both CEES and HD are alkylating agents that influence cellular thiols and are highly toxic. In a previous publication, we reported that lipopolysaccharide (LPS) enhances the cytotoxicity of CEES in murine RAW264.7 macrophages. In the present investigation, we studied the influence of CEES on nitric oxide (NO) production in LPS stimulated RAW264.7 cells since NO signalling affects inflammation, cell death, and wound healing. Murine macrophages stimulated with LPS produce NO almost exclusively via inducible nitric oxide synthase (iNOS) activity. We suggest that the influence of CEES or HD on the cellular production of NO could play an important role in the pathophysiological responses of tissues to these toxicants. In particular, it is known that macrophage generated NO synthesised by iNOS plays a critical role in wound healing.

RESULTS

We initially confirmed that in LPS stimulated RAW264.7 macrophages NO is exclusively generated by the iNOS form of nitric oxide synthase. CEES treatment inhibited the synthesis of NO (after 24 hours) in viable LPS-stimulated RAW264.7 macrophages as measured by either nitrite secretion into the culture medium or the intracellular conversion of 4,5-diaminofluorescein diacetate (DAF-2DA) or dichlorofluorescin diacetate (DCFH-DA). Western blots showed that CEES transiently decreased the expression of iNOS protein; however, treatment of active iNOS with CEES in vitro did not inhibit its enzymatic activity

CONCLUSION

CEES inhibits NO production in LPS stimulated macrophages by decreasing iNOS protein expression. Decreased iNOS expression is likely the result of CEES induced alteration in the nuclear factor kappa B (NF-kappaB) signalling pathway. Since NO can act as an antioxidant, the CEES induced down-regulation of iNOS in LPS-stimulated macrophages could elevate oxidative stress. Since macrophage generated NO is known to play a key role in cutaneous wound healing, it is possible that this work has physiological relevance with respect to the healing of HD induced skin blisters.

Nitrotyrosine formation and heme oxygenase-1 expression in endotoxemic cirrhotic rats

BACKGROUND

Endotoxemia increases hepatic toxicity and mortality in cirrhosis. Because the mechanism of augmented hepatotoxicity in endotoxemic cirrhotic rats is still unclear, we wanted to investigate whether oxidative and nitrosative stress play a causative role in lipopolysaccharide (LPS)-treated cirrhotic rats.

METHODS

Liver cirrhosis was produced by the administration of thioacetamide (0.3 g/L of tap water) for a period of 3 months in rats. At the end of this period, cirrhotic rats were sacrificed 6 h after LPS injection (5 mg/kg, intraperitoneally). Serum transaminase activities, plasma total nitrite and nitrotyrosine (NT) levels as well as hepatic lipid peroxides, NT formation and heme oxygenase 1 (HO-1) expression were determined.

RESULTS

LPS administration to cirrhotic rats caused further increases in serum transaminase activities, and plasma total nitrite and NT levels as well as hepatic lipid peroxide levels as compared to cirrhotic rats. Hepatic NT formation and HO-1 expression were also found to be increased in LPS-injected cirrhotic rats.

CONCLUSIONS

Our results indicate that increased oxidative and nitrosative stress may have a synergistic effect in LPS-augmented hepatotoxicity in cirrhotic rats.

Kinetic Modeling of Nitric-Oxide-Associated Reaction Network

PURPOSE

Nitric oxide and superoxide are the two important free radicals in the biological system. The coexistence of both free radicals in the physiological milieu gives rise to intricate oxidative and nitrosative reactions, which have been implicated in many physiological and/or pathophysiological conditions, such as vasodilatation and inflammation. It is difficult, if not impossible, to study the complexity of the nitric oxide/superoxide system using current experimental approaches. Computational modeling thus offers an alternative way for studying the problem.

METHODS

In this present study, key reaction pathways related to the generation, reaction and scavenging of both nitric oxide and superoxide were integrated into a reaction network. The network dynamics was investigated by numerical simulations to a set of coupled differential equations and by dynamical analysis. Two specific questions pertaining to the reaction kinetics of the reactive chemical species in the nitric oxide/superoxide system were studied: (1) how does the system respond dynamically when the generation rate of nitric oxide and superoxide varies? (2) how would antioxidants such as glutathione modulate the system dynamics?

RESULTS

While changing basal GSH levels does not alter the kinetics of nitric oxide, superoxide, and peroxynitrite, the kinetic profiles of N203, GSNO and GSH are sensitive to the variation of basal GSH levels. The kinetics of the potential nitrosative species, N203, is switch like, which is dependent on the level of GSH.

CONCLUSIONS

The model predicts that concurrent high nitric oxide and superoxide generation--such as in the inflammatory conditions--may result in nonlinear system dynamics, and glutathione may serve as a dynamic switch of N203 mediated nitrosation reaction.

EFFECT OF NITRIC OXIDE ON THE HYPOGLYCAEMIC PHASE OF ENDOTOXAEMIA

BACKGROUND

Depletion of liver glycogen stores and subsequent hypoglycaemia is one of the unresolved features in endotoxaemia. The aim of this study was to elucidate the effect of L-arginine treatment on the glucose requirement and impending liver damage during the hypoglycaemic period of endotoxaemia.

METHODS

Sixty-three of 98 male Wistar rats were assigned equally to one of three groups and received saline as control, L-arginine as selective nitric oxide donor or N(G)-nitro-L-arginine methyl ester for non-selective inhibition of nitric oxide production 1 h before endotoxin injection. At 2, 4 and 6 h following endotoxin, blood and liver samples were collected. Plasma nitrite plus nitrate, glucose, insulin and glucagon concentrations and total liver-reduced glutathione were measured. Hepatocellular glycogen content and liver damage were assessed simultaneously by histological quantification. An additional seven rats were allocated to each group and subjected to i.v. glucose tolerance test during the hypoglycaemic period.

RESULTS

Increased levels of endogenousglutathione (P = 0.003) and excess nitric oxide (P = 0.002) apparently protected the liver from endotoxin-induced injury by preserving the optimum glucose consumption rate, insulin/glucagon ratio and liver glycogen in L-arginine-plus-endotoxin-treated group. Furthermore, expected hypoglycaemic period was not observed in these animals.

CONCLUSION

Exogenous L-arginine prevented the excessive liver glycogen release without inhibiting glucose consumption while decreasing hepatic injury during the expected hypoglycaemic phase of endotoxaemia.

Superoxide anions and hydrogen peroxide induce hepatocyte death by different mechanisms: involvement of JNK and ERK MAP kinases

BACKGROUND/AIMS

In liver diseases, reactive oxygen species (ROS) are involved in cell death and liver injury, but the mechanisms are not completely elucidated. To elucidate the mechanisms of hepatocyte cell death induced by the ROS superoxide anions and hydrogen peroxide, primary cultures of hepatocytes were exposed to the superoxide anion donor menadione (10-50 micromol/L) or H2O2 (1-5 mmol/L). Hepatocytes were also treated with caspases and MAPKs inhibitors, superoxide dismutase (PEG-SOD) and SNAP, a nitric oxide donor. Apoptosis was determined by measuring caspase-9, -6, -3 activation and cleaved PARP, and necrotic cell death by Sytox Green staining.

RESULTS

(1) Menadione (50 micromol/L) induces JNK phosphorylation, caspase-9, -6, -3 activation, PARP cleavage and apoptosis. Superoxide anions-induced apoptosis is dependent on JNK activity. Menadione (50 micromol/L) induces the phosphorylation of ERK1/2 and this attenuates cell death. (2) H2O2 increases necrotic cell death at high concentration or when H2O2 detoxification is impaired. H2O2 does not activate MAPKs signalling. (3) PEG-SOD prevents ERK1/2-, JNK- phosphorylation, caspase activation and apoptosis induced by menadione. Glutathione depletion increases menadione-induced apoptosis. (4) SNAP abolishes menadione-induced apoptosis but increases necrotic cell death.

CONCLUSIONS

In normal hepatocytes, superoxide anions-induced caspase activation and apoptosis is dependent on JNK activity and totally abolished by superoxide scavengers.

Antioxidant and anti-inflammatory efficacy of NAC in the treatment of COPD: discordant in vitro and in vivo dose-effects: a review

In order to develop efficient therapeutic regimes for chronic obstructive pulmonary disease (COPD), N-acetylcysteine (NAC) has been tested as a medication which can suppress various pathogenic processes in this disease. Besides its well-known and efficient mucolytic action, NAC meets these needs by virtue of its antioxidant and anti-inflammatory modes of action. NAC is a thiol compound which by providing sulfhydryl groups, can act both as a precursor of reduced glutathione and as a direct ROS scavenger, hence regulating the redox status in the cells. In this way it can interfere with several signaling pathways that play a role in regulating apoptosis, angiogenesis, cell growth and arrest and inflammatory response. Overall, the antioxidant effects of NAC are well documented in in vivo and in vitro studies. It successfully inhibits oxidative stress at both high and low concentrations, under acute (in vitro) and chronic administration (in vivo). With regard to its anti-inflammatory action, in contrast, the effects of NAC differ in vivo and in vitro and are highly dose-dependent. In the in vitro settings anti-inflammatory effects are seen at high but not at low concentrations. On the other hand, some long-term effectiveness is reported in several in vivo studies even at low dosages. Increasing the dose seems to improve NAC bioavailability and may also consolidate some of its effects. In this way, the effects that are observed in the clinical and in vivo studies do not always reflect the success of the in vitro experiments. Furthermore, the results obtained with healthy volunteers do not always provide incontrovertible proof of its usefulness in COPD especially when number of exacerbations and changes in lung function are chosen as the primary outcomes. Despite these considerations and in view of the present lack of effective therapies to inhibit disease progression in COPD, NAC and its derivatives, because of their multiple molecular modes of action, remain promising medication once doses and route of administration are optimized.

3H-1,2-dithiole-3-thione targets nuclear factor kappaB to block expression of inducible nitric-oxide synthase, prevents hypotension, and improves survival in endotoxemic rats

Septicemia is a major cause of death associated with noncoronary intensive care. Systemic production of nitric oxide (NO) by inducible nitric-oxide synthase (iNOS) is a major cause of hypotension and poor organ perfusion seen in septic shock. Here, we show that pretreatment of F344 rats with the cancer chemoprotective agent 3H-1,2-dithiole-3-thione (D3T) blocks lipopolysaccharide (LPS)-mediated induction of hepatic iNOS and significantly reduces the associated serum levels of NO metabolites and enzyme markers of toxicity provoked by treatment with LPS. Immunohistochemical analysis shows that this protective effect is largely due to suppression of iNOS expression in hepatocytes. Importantly, pretreatment of animals with D3T blunts LPS-mediated hypotension and dramatically increases their survival. Inasmuch as iNOS expression can be regulated by nuclear factor (NF) kappaB, mechanistic studies show that D3T blocks NFkappaB nuclear translocation and DNA binding and that these effects are accompanied by changes in the levels of phospho-inhibitor of NFkappaB. In conclusion, this study identifies new drug classes and targets that may improve the prevention and treatment of septic shock, as well as chronic diseases associated with the NFkappaB and iNOS pathways.

Quercetin attenuates nuclear factor-kappaB activation and nitric oxide production in interleukin-1beta-activated rat hepatocytes

We investigated whether different concentrations of the flavonoid quercetin ameliorate nitric oxide production and nuclear factor (NF)-kappaB activation in interleukin (IL)-1beta-activated rat hepatocytes. Primary cultures of rat hepatocytes were treated with IL-1beta alone or with quercetin in concentrations ranging from 5 to 100 micromol/L. The generation of reactive oxygen species, assessed by flow cytometry using dichlorodihydrofluorescein diacetate, was significantly reduced, and the oxidized:reduced glutathione ratio decreased in cultures treated with 50 and 100 micromol/L of quercetin. Quercetin at 100 micromol/L significantly prevented the IL-1beta-induced release of nitrite into the culture medium. Western blot and reverse transcription-PCR analyses demonstrated that increased levels of inducible nitric oxide synthase (iNOS) protein and mRNA in hepatocytes stimulated by IL-1beta were prevented by 50 micromol/L and 100 micromol/L of quercetin. Electrophoretic mobility shift assay experiments and Western blots indicated that quercetin blocked the activation of NF-kappaB and decreased the inhibitor kappaB protein levels induced by IL-1beta. In summary, quercetin, a natural flavonol widely distributed in the human diet, inhibits NO production in IL-1beta-stimulated hepatocytes through the inhibition of iNOS expression. Although the mode of action remains to be clarified, our findings support the view that the mechanism of action is via inhibition of IL-1beta-induced NF-kappaB activation.

A Pilot Study of the Effect of Inhaled Buffered Reduced Glutathione on the Clinical Status of Patients With Cystic Fibrosis

STUDY OBJECTIVES

To assess the impact of inhaled, buffered reduced glutathione (GSH) on clinical indicators of cystic fibrosis (CF) pathophysiology.

DESIGN AND PATIENTS

A randomized, double-blind, placebo-controlled pilot study was conducted over an 8-week period. Nineteen subjects, age 6 to 19 years, with CF status documented by positive sweat chloride test results (> 60 mEq/L) were recruited for the trial. After matching on age and sex, 10 patients were randomly assigned to the treatment group and 9 patients to the placebo group. Primary outcomes were FEV1, FVC, forced expiratory flow at 25 to 75% of vital capacity, and peak flow; secondary outcomes were body mass index, 6-min walk distance, and self-reported cough frequency, mucus production/viscosity/color, wellness, improvement, and stamina. INTERVENTIONS AND ANALYSIS: Treatment was buffered GSH, and placebo was sodium chloride with a hint of quinine. The total daily dose of buffered GSH was approximately 66 mg/kg of body weight, and the total daily dose of placebo was approximately 15 mg/kg of body weight (quinine, 25 to 30 microg/kg). Doses were distributed across four inhalation sessions per day and spaced 3- to 4-h apart. General linear mixed models were used to analyze the data. The final sample size was nine subjects in the treatment group and seven subjects in the placebo group.

RESULTS

Mean change for peak flow was -6.5 L/min for the placebo group and +33.7 L/min for the GSH group (p = 0.04), and self-reported average improvement on a scale from 1 to 5 (1 being much worse and 5 being much better) was 2.8 for placebo and 4.7 for GSH (p = 0.004). Of the 13 primary and secondary outcomes examined, 11 outcomes favored the treatment group over the placebo group (p = 0.002), indicating a general tendency of improvement in the GSH group. No adverse events in the treatment group were noted.

CONCLUSION

This pilot study indicates the promise of nebulized buffered GSH to ameliorate CF disease, and longer, larger, and improved studies of inhaled GSH are warranted.

Regurgitation of bile acids from leaky bile ducts causes sclerosing cholangitis in Mdr2 (Abcb4) knockout mice

BACKGROUND & AIMS

Because the mechanisms leading to bile duct damage in sclerosing cholangitis are unknown, we aimed to determine the pathogenesis of bile duct injury in multidrug resistance gene (Mdr2) (Abcb4) knockout mice (Mdr2(-/-)) as a novel model of the disease.

METHODS

Mdr2(-/-) and wild-type controls (Mdr2(+/+)) were studied at 2, 4, and 8 weeks of age. Liver histology, ultrastructure, immunofluorescence microscopy (to study inflammatory cells, tight junction protein ZO-1, basement membrane protein laminin, fluorescence-labeled ursodeoxycholic acid), immunohistochemistry (for alpha-smooth muscle actin, nitrotyrosine), sirius red staining, bacterial cultures of intra-abdominal organs, and polymerase chain reaction (PCR) for Helicobacter bilis DNA were compared between both genotypes. Hepatic cytokine expression was determined by reverse-transcription PCR.

RESULTS

Bile ducts of Mdr2(-/-) showed disrupted tight junctions and basement membranes, bile acid leakage into portal tracts, induction of a portal inflammatory (CD11b, CD4-positive) infiltrate, and activation of proinflammatory (tumor necrosis factor [TNF]-alpha, interleukin [IL]-1beta) and profibrogenic cytokines (transforming growth factor [TGF]-beta1). This resulted in activation of periductal myofibroblasts, leading to periductal fibrosis, separating the peribiliary plexus from bile duct epithelial cells and, finally, causing atrophy and death of the bile duct epithelium. Bacterial translocation was not increased and H. bilis was not detectable in Mdr2(-/-).

CONCLUSIONS

Sclerosing cholangitis in Mdr2(-/-) mice is a multistep process with regurgitation of bile from leaky ducts into the portal tracts, leading to induction of periductal inflammation, followed by activation of periductal fibrogenesis, finally causing obliterative cholangitis owing to atrophy and death of bile duct epithelial cells.

Defying death: the hepatocyte's survival kit

Acute liver injury can develop as a consequence of viral hepatitis, drug- or toxin-induced toxicity or rejection after liver transplantation, whereas chronic liver injury can be due to long-term exposure to alcohol, chemicals, chronic viral hepatitis, metabolic or cholestatic disorders. During liver injury, liver cells are exposed to increased levels of cytokines, bile acids and oxidative stress. This results in death of hepatocytes. In contrast, stellate cells become active and are resistant against cell death. Eventually, acute and chronic liver injury is followed by loss of liver function for which no effective therapies are available. Hepatocytes are well equipped with protective mechanisms to prevent cell death. As long as these protective mechanisms can be activated, the balance will be in favour of cell survival. However, the balance between cell survival and cell death is delicate and can be easily tipped towards cell death during liver injury. Therefore understanding the cellular mechanisms controlling death of liver cells is of clinical and scientific importance and can lead to the identification of novel intervention targets. This review describes some of the mechanisms that determine the balance between cell death and cell survival during liver diseases. The strict regulation of apoptotic cell death allows therapeutic intervention strategies. In this light, receptor-mediated apoptosis and mitochondria-mediated cell death are discussed and strategies are provided to selectively interfere with these processes.

Interleukin-1beta represses MRP2 gene expression through inactivation of interferon regulatory factor 3 in HepG2 cells

The human multidrug resistance protein 2 (MRP2/ABCC2), expressed on the bile canalicular membrane, mediates the multispecific efflux of several organic anions, including conjugates of glucuronate, sulfate, and glutathione. Expression of MRP2 can be altered in response to environmental stimuli such as cholestasis and jaundice. We previously reported that MRP2 mRNA expression levels are decreased in the nontumorous part of hepatitis C virus-infected human liver tissues, and that inflammatory cytokines inhibit MRP2 expression in human hepatic (HepG2) cells. We investigated the molecular mechanisms by which inflammatory cytokines modulate MRP2 gene expression in hepatic cells. Treatment of human hepatic cells with interleukin-1beta (IL-1beta) or tumor necrosis factor alpha resulted in a decrease in the protein and mRNA levels of MRP2. IL-1beta inhibited the transcriptional activity of MRP2 promoter constructs by 40%, and this inhibition of MRP2 promoter activity was mediated through the interferon stimulatory response element (ISRE). Electrophoretic mobility shift assays with IL-1beta-treated nuclear extracts showed a decrease in the formation of DNA protein complexes, specifically those including interferon regulatory factor 3 (IRF3). Expression of recombinant human IRF3 increased MRP2 promoter activity. Treatment with a specific extracellular signal-regulated kinase inhibitor relieved IL-1beta-induced MRP2 mRNA downregulation and abrogated the binding of IRF3 to the ISRE element. In conclusion, IL-1beta induces downregulation of the MRP2 gene by inactivating IRF3 binding to ISRE on the MRP2 promoter in human hepatic cells; this inactivation is accomplished via interference with the extracellular signal-regulated kinase pathway.

Systemic, pulmonary, and hepatosplanchnic effects of N-acetylcysteine during long-term porcine endotoxemia

OBJECTIVE

Controversial data have been reported on the effects of N-acetylcysteine in patients with septic shock. We therefore investigated the systemic, pulmonary, and hepatosplanchnic hemodynamic, gas exchange, and metabolic effects of N-acetylcysteine during long-term, volume-resuscitated, hyperdynamic porcine endotoxemia, which mimics the features of hyperdynamic human sepsis.

DESIGN

Prospective, randomized, controlled experimental study.

SETTING

Investigational animal laboratory.

SUBJECTS

Eighteen pigs were randomized to receive endotoxin alone (controls, n = 9) or endotoxin plus N-acetylcysteine (n = 9).

INTERVENTIONS

Anesthetized, mechanically ventilated, and instrumented animals received continuous intravenous endotoxin and were resuscitated with hydroxyethylstarch to keep mean arterial pressure >60 mm Hg. After 12 hrs of endotoxemia, they were randomized to receive either placebo or N-acetylcysteine (150 mg/kg loading dose over 1 hr followed by 20 mg.kg-1.hr-1 for 11 hrs).

MEASUREMENTS AND MAIN RESULTS

Before as well as 12, 18, and 24 hrs after starting the endotoxin infusion, systemic, pulmonary, and hepatosplanchnic hemodynamics, oxygen exchange, and metabolism as well as nitric oxide, glutathione, and 8-isoprostane concentrations were assessed. N-acetylcysteine failed to improve any of the variables of the systemic, pulmonary, or hepatosplanchnic hemodynamics, gas exchange, and metabolism. Although N-acetylcysteine significantly elevated glutathione concentration, it did not influence the 8-isoprostane concentrations and even further reduced hepatic venous pH.

CONCLUSIONS

Despite the increased glutathione concentration, N-acetylcysteine did not improve systemic, pulmonary, and hepatosplanchnic hemodynamics, oxygen exchange, and metabolism. When compared with previous reports in the literature, a different timing of N-acetylcysteine administration and/or an ongoing or even N-acetylcysteine-induced aggravation of oxidative stress may account for this result.

Ischemia and hepatic reperfusion: is it possible to reduce hepatic alterations?

Our aim was to evaluate liver damage after ischemia and reperfusion, and at the same time test the effectiveness of some drugs in preventing these alterations. For this study, we utilized 50 rats divided into four groups: three underwent hepatic ischemia through occlusion of the portal vein and hepatic artery for 30 min, and one underwent a sham operation. In all groups, hepatic enzymes and bilirubine were tested at 2 h, 3 h, 4 h, 24 h, and 30 h. The drugs utilized were: L-arginine, donor of nitric oxide, and L-canavanine, inhibitor of nitric oxide synthase (NOS). Our data showed that the drugs tested could make an improvement in hepatic function after ischemia/reperfusion, preventing its damage. These preliminary results could suggest a clinical application in order to prolong ischemic period during liver transplantation or liver resection in cirrhotic patients.

Effect of a potent iNOS inhibitor (ONO-1714) on acetaminophen-induced hepatotoxicity in the rat

Overproduction of nitric oxide (NO) in the liver has been implicated as an important event in endotoxin shock and in other models of hepatic inflammation and injury. The present study was undertaken to evaluate the effect of ONO-1714, a potent and specific inhibitor of inducible NO synthase (iNOS), on acetaminophen-induced hepatotoxicity in the rats. Oral administration of ONO-1714 dose-dependently inhibited NOx (NO2- and NO3-) accumulation in rat plasma after lipopolysaccharide (LPS) treatment. Intraperitoneal acetaminophen at 1 g/kg caused damage to the centrilobular regions of the liver and increase in serum alanine and aspartate transaminase (ALT and AST, respectively) levels accompanied by elevated plasma NOx levels after 24 h. Oral administration of ONO-1714 at 10 and 100 microg/kg dose-dependently reduced the acetaminophen-induced hepatic tissue damage and the increases in serum ALT and AST levels. ONO-1714 also blocked the increase in plasma NOx concentrations. These findings demonstrate that oral ONO-1714, an iNOS inhibitor, protects against acetaminophen-evoked hepatic inflammation/injury, strongly suggesting that NO produced by iNOS plays a key role in the pathogenesis of this drug-induced hepatotoxicity.

Evaluation of the Potential Protective Effect of 21-Aminosteroid U-74389G on Liver Injury Induced by Reduced and Prolonged Partial Hepatic Ischaemia Reperfusion in Rats

The protective effect of the 21-aminosteroid U-74389G was studied in an experimental model of partial ischaemia reperfusion liver injury. Previous studies have proven the remarkable potency of 21-aminosteroids to prevent oxidant-induced cell injury in vitro and in vivo. However, the capability of these compounds to limit oxidative injury in clinical trials has been considered to be less certain. The potential protective effect exerted by U-74389G on reduced and prolonged models of ischaemia reperfusion liver injury was studied in male rats subjected to 75 min. of segmentary hepatic ischaemia followed by 1 or 24 hr of reperfusion. Liver injury was evaluated by measuring serum levels of liver enzymes and by histopathological studies. The oxidative status of liver cells was measured by evaluating the levels of liver lipid peroxidation products such as malondialdehyde and the levels of reduced glutathione. Our results lead us to think that treatment with U-74389G (6 mg/kg) does not bring about any protective effect neither in the levels of transaminases nor in the percentage of hepatocellular necrosis and cellular infiltration observed in any reperfusion-period groups. In fact and in contrast with our expectations, U-74389G seemed to increase enzyme release. Furthermore, at the dose used, this 21-aminosteroid is not capable of inhibiting the lipoperoxidation processes, although it induced an important increase of GSH levels at any time-period of reperfusion. This last finding seem to suggest that U-74389G could increase the resistance to oxidant-induced liver tissue damage. However, our results show that, at the dose used, this compound did not exert any protective effect on liver tissue, thus explaining, at least partially, the absence of beneficial effects on the part of these compounds in clinical trials carried out to limit organ injury in transplants.

Resistance of rat hepatocytes against bile acid-induced apoptosis in cholestatic liver injury is due to nuclear factor-kappa B activation

BACKGROUND/AIMS

To examine the extent and mechanisms of apoptosis in cholestatic liver injury and to explore the role of the transcription factor nuclear factor-kappa B in protection against bile acid-induced apoptosis.

METHODS

Cholestatic liver injury was induced by bile duct ligation in Wistar rats. Furthermore, primary cultures of rat hepatocytes were exposed to glycochenodeoxycholic acid (GCDCA), tauroursodeoxycholic acid (TUDCA), taurochenodeoxycholic acid (TCDCA) and to cytokines. Apoptosis was determined by TUNEL-staining, active caspase-3 staining, activation of caspase-8, -9 and -3.

RESULTS

Limited hepatocyte apoptosis and an increased expression of NF-kappaB-regulated anti-apoptotic genes A1 and cIAP2 were detected in cholestatic rat livers. Bcl-2 expression was restricted to bile duct epithelium. In contrast to TCDCA and TUDCA, GCDCA induced apoptosis in a Fas-associated protein with death domain (FADD)-independent pathway in hepatocytes. Although bile acids do not activate NF-kappaB, NF-kappaB activation by cytokines (induced during cholestasis) protected against GCDCA-induced apoptosis in vitro by upregulating A1 and cIAP2.

CONCLUSIONS

GCDCA induces apoptosis in a mitochondria-controlled pathway in which caspase-8 is activated in a FADD-independent manner. However, bile acid-induced apoptosis in cholestasis is limited. This could be explained by cytokine-induced activation of NF-kappaB-regulated anti-apoptotic genes like A1 and cIAP2.

Glutathione depletion increases nitric oxide-induced oxidative stress in primary rat hepatocyte cultures: involvement of low-molecular-weight iron

Various drugs and chemicals can cause a glutathione (GSH) depletion in the liver. Moreover, nitric oxide (NO) can be generated in response to physiological and pathological situations such as inflammation. The aim of this study was to estimate oxidative stress when primary rat hepatocytes were exposed to GSH depletion after NO production. For this purpose, cells were preincubated with lipopolysaccharide (LPS) and gamma-interferon (IFN) for 18 h in order to induce NO production by NO synthase and then L-buthionine sulfoximine (BSO), an inhibitor of GSH synthesis, was added for 5 h. In hepatocyte cultures preincubated with LPS and IFN before BSO addition, an increase in lipid peroxidation was noted. In those cells, an elevation of iron-bound NO and a decrease in free NO led us to suggest the involvement of low-molecular-weight iron (LMW iron) in the enhancement of oxidative stress. Indeed, addition of deferiprone, a chelator of LMW iron, reduced iron-bound NO levels and the extent of oxidative stress. Moreover, an important elevation of LMW iron levels was also observed. As both, N-acetylcysteine, a GSH precursor, and N(G)-monomethyl-L-arginine, a NO synthase inhibitor, totally inhibited the elevation of LMW iron and oxidative stress, a cooperative role could be attributed to NO production and GSH depletion.

Protective mechanism of salvia miltiorrhiza on carbon tetrachloride-induced acute hepatotoxicity in rats

The purpose of this study was to investigate the possible mechanisms of Salvia miltiorrhiza (Sm) in carbon tetrachloride (CCl(4))-induced acute hepatotoxicity in rats. Male Wistar rats received a single dose of CCl(4) (2 ml/kg in corn oil, intraperitoneally). Three hours after CCl(4) intoxication, rats received either Sm (100 mg/kg) or silymarin (100 mg/kg) by gastrogavage twice a day for 2 consecutive days. CCl(4)-induced liver damage was shown by significant elevation of serum aminotransferase levels. Additionally, a significant decrease was observed in hepatic microsomal P450 2E1 protein content and hepatic concentrations of antioxidant enzymes. In contrast, rats given both Sm and silymarin supplement had less elevation of serum aminotransferase concentrations associated with less severe lobular damage of hepatocytes than rats receiving CCl(4) alone. Sm administration restored the reduction of hepatic microsomal P450 2E1 protein content as well as inducing an increase in hepatic glutathione concentration. On the other hand, administration of silymarin resulted in an elevation of hepatic superoxide dismutase levels. Moreover, both Sm and silymarin treatment inhibited the elevation of hepatic inducible nitric oxide (iNOS) protein content and nitrite concentration in liver homogenate 24 h after CCl(4) intoxication. We concluded that administration of Sm is effective in amelioration of CCl(4)-induced hepatotoxicity. This effect may be due to its ability to decrease the metabolic activation of CCl(4) by an increase in P450 2E1 protein content and its antioxidant activity associated with less increase in hepatic iNOS protein content.

Aminoguanidine, an inducible nitric oxide synthase inhibitor, plus N-acetylcysteine treatment reduce the lipopolysaccharide-augmented hepatotoxicity in rats with cirrhosis

Hepatic cirrhosis is produced in rats by administration of thioacetamide (TAA) (0.3 g/L tap water for a period of three months). This treatment caused an increase in oxidative stress in the liver. Lipopolysaccharide (LPS) administration (5 mg/kg) to rats with cirrhosis was observed to increase hepatotoxicity as well as oxidative stress according to biochemical and histopathological findings. However, aminoguanidine (AG), an inducible nitric oxide synthase (iNOS) inhibitor, plus N-acetylcysteine (NAC) treatment reduced the LPS-augmented hepatotoxicity in rats with cirrhosis without making any changes in oxidative stress in the liver.

Low NO bioavailability in CCl4 cirrhotic rat livers might result from low NO synthesis combined with decreased superoxide dismutase activity allowing superoxide-mediated NO breakdown: A comparison of two portal hypertensive rat models with healthy controls

BACKGROUND: In cirrhotic livers, the balance of vasoactive substances is in favour of vasoconstrictors with relatively insufficient nitric oxide. Endothelial dysfunction has been documented in cirrhotic rat livers leading to a lower activity of endothelial nitric oxide synthase but this might not be sufficient to explain the low nitric oxide presence. We compared the amount of all nitric oxide synthase isoforms and other factors that influence nitric oxide bioavailability in livers of two portal hypertensive rat models: prehepatic portal hypertension and carbon tetrachloride induced cirrhosis, in comparison with healthy controls. RESULTS: Endothelial nitric oxide synthase was the solely detected isoform by Western blotting in all livers. In cirrhotic livers, the amount of endothelial nitric oxide synthase protein was lower than in healthy controls, although an overlap existed. Levels of caveolin-1 messenger RNA were within the normal range but endothelin-1 messenger RNA levels were significantly higher in cirrhotic livers (p < 0.05). A markedly lower superoxide dismutase activity was observed in cirrhotic livers as compared to healthy controls (p < 0.05). CONCLUSIONS: In contrast to prehepatic portal hypertension, cirrhotic livers had decreased endothelial nitric oxide synthase protein and enhanced endothelin-1 messenger RNA amount. We hypothesise that a vasodilator/vasoconstrictor imbalance may be further aggravated by the reduced activity of superoxide dismutase. Decreased activity allows enhanced superoxide action, which may lead to breakdown of nitric oxide in liver sinusoids.

Oxidative stress in viral and alcoholic hepatitis

Liver damage ranges from acute hepatitis to hepatocellular carcinoma, through apoptosis, necrosis, inflammation, immune response, fibrosis, ischemia, altered gene expression and regeneration, all processes that involve hepatocyte, Kupffer, stellate, and endothelial cells. Reactive oxygen and nitrogen species (ROS, RNS) play a crucial role in the induction and in the progression of liver disease, independently from its etiology. They are involved in the transcription and activation of a large series of cytokines and growth factors that, in turn, can contribute to further production of ROS and RNS. The main sources of free radicals are represented by hepatocyte mitochondria and cytochrome p450 enzymes, by endotoxin-activated macrophages (Kupffer cells), and by neutrophils. The consequent alteration of cellular redox state is potentiated by the correlated decrease of antioxidant and energetic reserves. Indices of free radical-mediated damage, such as the increase of malondialdehyde, 4-hydroxynonenal, protein-adducts, peroxynitrite, nitrotyrosine, etc., and/or decrease of glutathione, vitamin E, vitamin C, selenium, etc., have been documented in patients with viral or alcoholic liver disease. These markers may contribute to the monitoring the degree of liver damage, the response to antiviral therapies and to the design of new therapeutic strategies. In fact, increasing attention is now paid to a possible "redox gene therapy." By enhancing the antioxidant ability of hepatocytes, through transgene vectors, one could counteract oxidative/nitrosative stress and, in this way, contribute to blocking the progression of liver disease.

Cytokine regulation of pro- and anti-apoptotic genes in rat hepatocytes: NF-kappaB-regulated inhibitor of apoptosis protein 2 (cIAP2) prevents apoptosis

BACKGROUND/AIMS

In acute liver failure, hepatocytes are exposed to various cytokines that activate both cell survival and apoptotic pathways. NF-kappaB is a central transcription factor in these responses. Recent studies indicate that blocking NF-kappaB causes apoptosis, indicating the existence of NF-kappaB-regulated anti-apoptotic genes. In the present study the relationship between NF-kappaB activation and apoptosis has been investigated in hepatocytes.

METHODS

Primary rat hepatocytes were exposed to a cytokine mixture of tumor necrosis factor alpha, interleukin-1beta, interferon-gamma and lipopolysaccharide. Modulation of signalling pathways was performed by using dominant negative adenoviral constructs. Apoptosis and NF-kappaB activation were determined by caspase-3 activity, Hoechst staining and electrophoretic mobility shift assay, respectively. Furthermore, expression and regulation of apoptosis-related genes were investigated.

RESULTS

(1) Inhibition of NF-kappaB activation results in apoptosis. (2) Inhibitor of apoptosis protein (IAP) family members, inhibitor of apoptosis protein1 (cIAP1), and X-chromosome-linked IAP, are expressed in rat hepatocytes. cIAP2 is induced by cytokines in an NF-kappaB-dependent manner and overexpression of cIAP2 inhibits apoptosis. (3) The anti-apoptotic Bcl-2 family member A1/Bfl-1 and the pro-apoptotic members Bak and Bid are induced by cytokines and NF-kappaB-dependent. (4) Nitric oxide inhibits caspase-3 activity in hepatocytes.

CONCLUSIONS

In inflammatory conditions, hepatocyte survival is dependent on NF-kappaB activation and cIAP2 contributes significantly to this protection.

A novel inhibitor of inducible nitric oxide synthase (ONO-1714) prevents critical warm ischemia-reperfusion injury in the pig liver

BACKGROUND

Recently, a novel inhibitor of inducible nitric oxide synthase, ONO-1714, was developed. We evaluated the effect of ONO-1714 on a critical warm I/R model of the pig liver.

METHODS

Pigs were subjected to 180 min of hepatic warm I/R under the extracorporeal circulation. We investigated the time course of changes in the serum NO2- + NO3- (NOx), the cellular distribution of endothelial and inducible nitric oxide synthase, thrombocyte-thrombi, and nitrotyrosine by immunohistochemistry. The hepatic tissue blood flow (HTBF) was measured continuously using a laser-Doppler blood flowmeter.

RESULTS

ONO-1714 at 0.05 mg/kg improved the survival rate from 54 (control group) to 100%. The serum NOx levels in the ONO-1714 group were significantly lower than those in the control group at 1, 1.5, 2, 3, and 6 hr after reperfusion. The serum aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) levels of the ONO-1714 group were significantly lower than the control group, and the HTBF of the ONO-1714 group was significantly higher than the control group. The formation of thrombocyte-thrombi and nitrotyrosine after reperfusion was significantly lower in the ONO-1714 group.

CONCLUSIONS

These results indicated that ONO-1714 improved the survival rates and attenuated I/R injury in a critical hepatic warm I/R model of the pig. ONO-1714 will be beneficial for hepatectomy or liver transplantation in the clinical field.

Cytochrome P450 and antioxidant activity in interleukin-6 knockout mice after induction of the acute-phase response

Hepatic cytochrome P450 (CYP) expression and antioxidant activity have been shown to decrease following endotoxin (lipopolysaccharide [LPS]) or proinflammatory cytokine administration. Using mice deficient in interleukin-6 (IL-6), the role of IL-6 in the regulation of hepatic CYP activity, glutathione (GSH) metabolism, and catalase (CAT) activity was analyzed after LPS administration. Administration of LPS produced comparable decreases in hepatic CYP3A activity in WT B6x129 (WT) mice and IL-6 knockout mice. No decrease was observed for CYP2D9 activity after LPS administration in either WT or IL-6 knockout mice. LPS administration significantly increased hepatic and renal CYP2E1 and CYP4A activity in WT mice, with no effect in IL-6 knockout mice. CYP2A12 activity increased in IL-6 knockout, mice with no change in WT mice after LPS administration. LPS administration had no significant effect on hepatic GSH reductase, GST peroxidase, GSH-S-transferase (GST), or total GSH in either WT or IL-6 knockout. However, hepatic CAT activity was significantly reduced in WT mice after LPS administration, with no effect in IL-6 knockout mice. These results support IL-6 as a critical mediator of the effects of LPS on specific hepatic and renal CYP activities and hepatic CAT activity.

Rat liver slices as a tool to study LPS-induced inflammatory response in the liver

BACKGROUND/AIMS

Inflammation in the liver is a complex interaction between parenchymal and non-parenchymal cells, and therefore can not be studied in vitro in pure cultures of these cells.

METHODS

We investigated whether Kupffer cells in the liver slice are still responsive to an inflammatory stimulus of lipopolysaccharide (LPS), and evoke an inflammatory response in the hepatocytes.

RESULTS

TNFalpha, IL-1beta and IL-10 were significantly elevated in culture medium of LPS-stimulated rat liver slices. Nitric oxide (NO) production of LPS-treated slices gradually increased from 5 to 24 h (24 h: 81+/-5 microM vs. 14+/-2 microM in control P < 0.05), paralleled by inducible nitric oxide synthase (iNOS) in the hepatocytes, iNOS mRNA was induced after 3 h. NO production but not iNOS induction was significantly inhibited by NOS inhibitors S-methylisothiourea and N(G)-nitro-L-arginine methylester. Both pentoxifylline and dexamethasone inhibited TNFalpha and IL-1beta production, albeit to a different extent, iNOS induction and, as a result thereof, NO production.

CONCLUSIONS

These results imply that non-parenchymal cells in liver slices are viable and can be activated by LPS. In addition, it is concluded that the upregulation of iNOS in hepatocytes by LPS is caused by cytokines produced by Kupffer cells because inhibition of TNFalpha and IL-1beta production attenuated iNOS induction.

Rethinking cystic fibrosis pathology: the critical role of abnormal reduced glutathione (GSH) transport caused by CFTR mutation

Though the cause of cystic fibrosis (CF) pathology is understood to be the mutation of the CFTR protein, it has been difficult to trace the exact mechanisms by which the pathology arises and progresses from the mutation. Recent research findings have noted that the CFTR channel is not only permeant to chloride anions, but other, larger organic anions, including reduced glutathione (GSH). This explains the longstanding finding of extracellular GSH deficit and dramatically reduced extracellular GSH:GSSG (glutathione disulfide) ratio found to be chronic and progressive in CF patients. Given the vital role of GSH as an antioxidant, a mucolytic, and a regulator of inflammation, immune response, and cell viability via its redox status in the human body, it is reasonable to hypothesize that this condition plays some role in the pathogenesis of CF. This hypothesis is advanced by comparing the literature on pathological phenomena associated with GSH deficiency to the literature documenting CF pathology, with striking similarities noted. Several puzzling hallmarks of CF pathology, including reduced exhaled NO, exaggerated inflammation with decreased immunocompetence, increased mucus viscoelasticity, and lack of appropriate apoptosis by infected epithelial cells, are better understood when abnormal GSH transport from epithelia (those without anion channels redundant to the CFTR at the apical surface) is added as an additional explanatory factor. Such epithelia should have normal levels of total glutathione (though perhaps with diminished GSH:GSSG ratio in the cytosol), but impaired GSH transport due to CFTR mutation should lead to progressive extracellular deficit of both total glutathione and GSH, and, hypothetically, GSH:GSSG ratio alteration or even total glutathione deficit in cells with redundant anion channels, such as leukocytes, lymphocytes, erythrocytes, and hepatocytes. Therapeutic implications, including alternative methods of GSH augmentation, are discussed.

Gamma interferon prevents the inhibitory effects of oxidative stress on host responses to Escherichia coli infection

Oxidative stress occurs in animals challenged with bacterial endotoxin and can affect the expression of important host inflammatory genes. However, much less is known about the effects of oxidative stress on responses to gram-negative bacteria. The current study compared the effects of redox imbalance on hepatic responses of mice to Escherichia coli bacteria versus purified endotoxic lipopolysaccharide (LPS). Oxidative stress induced by glutathione depletion virtually eliminated hepatic tumor necrosis factor alpha responses to both E. coli and LPS. Inducible NO synthase (iNOS) and intercellular adhesion molecule-1 (ICAM-1) expression was also markedly inhibited by glutathione depletion in LPS-challenged mice, but was unaffected in E. coli-infected animals. Three findings suggested that gamma interferon (IFN-gamma) production explained the differences between LPS and bacterial challenge. Glutathione depletion completely inhibited the IFN-gamma response to LPS, but only partially inhibited IFN-gamma production in infected mice. Exogenous IFN-gamma restored iNOS and ICAM-1 responses to LPS in stressed mice. Conversely, IFN-gamma-deficient, glutathione-depleted mice showed a marked decrease in iNOS and ICAM-1 expression when challenged with E. coli. These findings indicate that both the nature of the microbial challenge and the production of IFN-gamma can be important in determining the effects of redox imbalance during gram-negative bacterial infections.