Nitration/S-nitrosation of proteins by peroxynitrite-treatment and subsequent modification by glutathione S-transferase and glutathione peroxidase

Epigallocatechin 3-gallate ameliorates bile duct ligation induced liver injury in mice by modulation of mitochondrial oxidative stress and inflammation

Cholestatic liver fibrosis was achieved by bile duct ligation (BDL) in mice. Liver injury associated with BDL for 15 days included significant reactive oxygen/nitrogen species generation, liver inflammation, cell death and fibrosis. Administration of Epigallocatechin 3-Gallate (EGCG) in animals reduced liver fibrosis involving parenchymal cells in BDL model. EGCG attenuated BDL-induced gene expression of pro-fibrotic markers (Collagen, Fibronectin, alpha 2 smooth muscle actin or SMA and connective tissue growth factor or CTGF), mitochondrial oxidative stress, cell death marker (DNA fragmentation and PARP activity), NFκB activity and pro-inflammatory cytokines (TNFα, MIP1α, IL1β, and MIP2). EGCG also improved BDL induced damages of mitochondrial electron transport chain complexes and antioxidant defense enzymes such as glutathione peroxidase and manganese superoxide dismutase. EGCG also attenuated hydrogen peroxide induced cell death in hepatocytes in vitro and alleviate stellate cells mediated fibrosis through TIMP1, SMA, Collagen 1 and Fibronectin in vitro. In conclusion, the reactive oxygen/nitrogen species generated from mitochondria plays critical pathogenetic role in the progression of liver inflammation and fibrosis and this study indicate that EGCG might be beneficial for reducing liver inflammation and fibrosis.

Nitration of plant apoplastic proteins from cell suspension cultures

Nitric oxide causes numerous protein modifications including nitration of tyrosine residues. This modification, though one of the greatest biological importance, is poorly recognized in plants and is usually associated with stress conditions. In this study we analyzed nitrotyrosines from suspension cultures of Arabidopsis thaliana and Nicotiana tabacum, treated with NO modulators and exposed to osmotic stress, as well as of BY2 cells long-term adapted to osmotic stress conditions. Using confocal microscopy, we showed that the cell wall area is one of the compartments most enriched in nitrotyrosines within a plant cell. Subsequently, we analyzed nitration of ionically-bound cell-wall proteins and identified selected proteins with MALDI-TOF spectrometry. Proteomic analysis indicated that there was no significant increase in the amount of nitrated proteins under the influence of NO modulators, among them 3-morpholinosydnonimine (SIN-1), considered a donor of nitrating agent, peroxynitrite. Moreover, osmotic stress conditions did not increase the level of nitration in cell wall proteins isolated from suspension cells, and in cultures long-term adapted to stress conditions; that level was even reduced in comparison with control samples. Among identified nitrotyrosine-containing proteins dominated the ones associated with carbon circulation as well as the numerous proteins responding to stress conditions, mainly peroxidases.

BIOLOGICAL SIGNIFICANCE

High concentrations of nitric oxide found in the cell wall and the ability to produce large amounts of ROS make the apoplast a site highly enriched in nitrotyrosines, as presented in this paper. Analysis of ionically bound fraction of the cell wall proteins indicating generally unchanged amounts of nitrotyrosines under influence of NO modulators and osmotic stress, is noticeably different from literature data concerning, however, the total plant proteins analysis. This observation is supplemented by further nitroproteome analysis, for cells long-term adapted to stressful conditions, and results showing that such conditions did not always cause an increase in nitrotyrosine content. These findings may be interpreted as characteristic features of apoplastic protein nitration.

Interaction of inducible nitric oxide synthase with rac2 regulates reactive oxygen and nitrogen species generation in the human neutrophil phagosomes: implication in microbial killing

AIMS

Present study explores importance of inducible nitric oxide synthase (iNOS) and its interaction with Rac2 in reactive oxygen species (ROS)/reactive nitrogen species (RNS) generation, protein-nitration and in microbial killing by neutrophils.

RESULTS

The iNOS transcript and protein were constitutively present in human as well as in mice neutrophils. iNOS protein was found in cytosol, granules containing elastase and gelatinase, and in other subcellular organelles in resting human neutrophils. After phagocytosis of bovine serum albumin (BSA) coated beads, both human and mice neutrophils showed significant elevation in superoxide radicals, nitric oxide (NO), ROS/RNS and consequent BSA nitration. These responses were significantly reduced in presence of iNOS, NADPH oxidase (NOX), myeloperoxidase or Rac inhibitors, as well as in iNOS, Nox2 and Rac2 silenced human or iNOS-knockout mice neutrophils. Complex formed on interaction of iNOS with Rac2 coprecipitated with anti-Rac2, predominantly in cytosol in resting human neutrophils, while iNOS-Rac2 complex translocated to phagosomes after phagocytosis. This was accompanied by generation of superoxide radicals, NO, ROS/RNS and consequent BSA-nitration. Importance of Rac2 in iNOS mediated NO formation and microbial killing was confirmed by pretreatment of mice with Rac inhibitor, NSC23766 that significantly abrogated NO release and microbial killing in vivo.

INNOVATION

Present study highlights previously undefined role of Rac2-iNOS interaction, in translocation of iNOS to phagosomal compartment and consequent NO, superoxide radicals, ROS/RNS generation, BSA nitration and microbial killing.

CONCLUSIONS

Altogether results obtained demonstrate the role of iNOS in NO and ROS/RNS generation, after phagocytosis of coated latex beads by human polymorphonuclear neutrophils. These studies imply functional importance of iNOS and its interaction with Rac2 in pathogen killing by the neutrophils.

S100A8 and S100A9-oxidant scavengers in inflammation

S100A8 and S100A9 are generally considered proinflammatory. Hypohalous acids generated by activated phagocytes promote novel modifications in murine S100A8 but modifications to human S100A8 are undefined and there is no evidence that these proteins scavenge oxidants in human disease. Recombinant S100A8 was exquisitely sensitive to equimolar ratios of HOCl, which generated sulfinic and sulfonic acid intermediates and novel oxathiazolidine oxide/dioxide forms (mass additions, m/z +30 and +46) on the single Cys42 residue. Met78(O) and Trp54(+16) were also present. HOBr generated sulfonic acid intermediates and oxidized Trp54(+16). Evidence for oxidation of the single Cys3 residue in recS100A9 HOCl was weak; Met63, Met81, Met83, and Met94 were converted to Met(O) in vitro. Oxidized S100A8 was prominent in lungs from patients with asthma and significantly elevated in sputum compared to controls, whereas S100A8 and S100A9 were not significantly increased. Oxidized monomeric S100A8 was the major component in asthmatic sputum, and modifications, including the oxathiazolidine adducts, were similar to those generated by HOCl in vitro. Oxidized Met63, Met81, and Met94 were variously present in S100A9 from asthmatic sputum. Results have broad implications for conditions under which hypohalous acid oxidants are generated by activated phagocytes. Identification in human disease of the novel S100A8 Cys derivatives typical of those generated in vitro strongly supports the notion that S100A8 contributes to antioxidant defense during oxidative stress.

A rapid approach for the detection, quantification, and discovery of novel sulfenic acid or S-nitrosothiol modified proteins using a biotin-switch method

The recent development of robust methods for the detection of proteins susceptible to S-nitrosylation (RSNO) and sulfenation (RSOH) has provided greater insight into the role of these oxidative modifications in cell signaling. These techniques, which have been termed "biotin-switch" methods, essentially use selective chemical reduction to swap an oxidative modification for a stable easily detectable biotin-tag. This allows for the rapid purification and subsequent detection of modified proteins using mass spectrometry. This chapter provides an overview of these biotin-switch methods, and explores its impact on the field of redox biology, including recent advances as well as limitations associated with this technique.

Glutathione reverses peroxynitrite-mediated deleterious effects of nitroglycerin on ischemic rat hearts

This study examined the potential deleterious effect of high-dose nitroglycerin (NTG) on cardiac function and cellular injury after ischemia (30 min) and reperfusion (120 min) in isolated perfused rat hearts. Low-dose (0.75 microg/h), medium-dose (3.75 microg/h), high-dose (15 microg/h) NTG or high-dose NTG plus glutathione (GSH, 1 mmol/L) was administrated at the time of reperfusion. Administration of high-dose NTG significantly exacerbated cardiac reperfusion injury as evidenced by increased creatine kinase and lactate dehydrogenase activity in coronary effluent, increased cardiomyocyte apoptosis and necrosis, and decreased cardiac function recovery after reperfusion. Compared with the vehicle group, formation of nitrotyrosine, a footprint for peroxynitrite (ONOO) production, was markedly increased in the hearts treated with medium-dose or high-dose NTG. Most interestingly, cotreatment with GSH blocked high-dose NTG-induced ONOO formation and attenuated myocardial ischemia/reperfusion injury. Taken together, our present results demonstrated that administration of high-dose NTG aggravated, rather than attenuated myocardial ischemia/reperfusion injury likely via increasing ONOO formation. Coadministration of GSH may reverse the advert action of high-dose NTG.

Reactive nitrogen species derived activation of rat liver microsomal glutathione S-transferase

The effect of reactive nitrogen species on rat liver microsomal glutathione S-transferase (MGST1) was investigated using microsomes and purified MGST1. When microsomes or the purified enzyme were incubated with peroxynitrite (ONOO(-)), the GST activity was increased to 2.5-6.5 fold in concentration-dependent manner and a small amount of the MGST1 dimer was detected. MGST1 activity was increased by ONOO(-) in the presence of high amounts of reducing agents including glutathione (GSH) and the activities increased by ONOO(-) or ONOO(-) plus GSH treatment were decreased by 30-40% by further incubation with dithiothreitol (DTT, reducing disulfide) or by sodium arsenite (reducing sulfenic acid). Furthermore, GSH was detected by HPLC from the MGST1 which was incubated with ONOO(-) plus GSH or S-nitrosoglutathione followed by DTT treatment. In addition, the MGST1 activity increased by nitric oxide (NO) donors such as S-nitrosoglutathione, S-nitrosocysteine or the non-thiol NO donor 1-hydroxy-2-oxo-3 (3-aminopropyl)-3-isopropyl was restored by the DTT treatment. Since DTT can reduce S-nitrosothiol and disulfide bond to thiol, S-nitrosylation and a mixed disulfide bond formation of MGST1 were suggested. Thus, it was demonstrated that MGST1 is activated by reactive nitrogen species through a forming dimeric protein, mixed disulfide bond, nitrosylation and sulfenic acid.

Nitric oxide and posttranslational modification of the vascular proteome: S-nitrosation of reactive thiols

Nitric oxide (NO*) is known to exert its effects via guanylyl cyclase and cyclic GMP-dependent pathways and by cyclic GMP-independent pathways, including the posttranslational modification of proteins. Much ongoing research is focused on defining the mechanisms of NO*-mediated protein modification, the identity and function of the modified proteins, and the significance of these changes in health and disease. S-nitrosation or thionitrite formation has only been found on a limited number of residues in a subset of proteins in in vitro and in vivo studies. Protein S-nitrosation also appears to be reversible. There are several theories about the in vivo S-nitrosating agent, and most suggest a role for oxidation products of NO* in this process. Flux in cellular S-nitrosoprotein pools appears to be regulated by NO* availability and is redox-sensitive. An analysis of S-nitrosation in candidate proteins has clarified the mechanism by which NO* regulates enzymatic and cellular functions. These findings suggest the utility of using proteomic methods to identify unique targets for protein S-nitrosation to understand further the molecular mechanisms of the effects of NO*.

Mechanisms underlying resistance of pancreatic islets from ALR/Lt mice to cytokine-induced destruction

Nuclear and mitochondrial genomes combine in ALR/Lt mice to produce systemically elevated defenses against free radical damage, rendering these mice resistant to immune-mediated pancreatic islet destruction. We analyzed the mechanism whereby isolated islets from ALR mice resisted proinflammatory stress mediated by combined cytokines (IL-1beta, TNF-alpha, and IFN-gamma) in vitro. Such damage entails both superoxide and NO radical generation, as well as peroxynitrite, resulting from their combination. In contrast to islets from other mouse strains, ALR islets expressed constitutively higher glutathione reductase, glutathione peroxidase, and higher ratios of reduced to oxidized glutathione. Following incubation with combined cytokines, islets from control strains produced significantly higher levels of hydrogen peroxide and NO than islets from ALR mice. Nitrotyrosine was generated in NOD and C3H/HeJ islets but not by ALR islets. Western blot analysis showed that combined cytokines up-regulated the NF-kappaB inducible NO synthase in NOD-Rag and C3H/HeJ islets but not in ALR islets. This inability of cytokine-treated ALR islets to up-regulate inducible NO synthase and produce NO correlated both with reduced kinetics of IkappaB degradation and with markedly suppressed NF-kappaB p65 nuclear translocation. Hence, ALR/Lt islets resist cytokine-induced diabetogenic stress through enhanced dissipation and/or suppressed formation of reactive oxygen and nitrogen species, impaired IkappaB degradation, and blunted NF-kappaB activation. Nitrotyrosylation of beta cell proteins may generate neoantigens; therefore, resistance of ALR islets to nitrotyrosine formation may, in part, explain why ALR mice are resistant to type 1 diabetes when reconstituted with a NOD immune system.

Hierarchical change in antioxidant enzyme gene expression and activity in acute cardiac rejection: Role of inducible nitric oxide synthase

Reactive oxygen and nitrogen may mediate inflammation injury, but the status of the antioxidant defense system that might influence this process is unknown. In the present study, we examined the expression profile of the antioxidant enzymes, manganese superoxide dismutase (MnSOD), catalase and glutathione peroxidase (GPX) in acutely rejecting cardiac allografts and the potential role of inducible nitric oxide synthase (iNOS) in modulating antioxidant gene expression and activity. Donor hearts from Lewis (isograft) or Wistar-Furth (allograft) rats were transplanted into Lewis recipient rats. A subset of the allografts received L-N6-(1-imino-ethyl) lysine (L-NIL), a specific iNOS inhibitor, beginning the day of surgery until the day of harvesting. Catalase and glutathione peroxidase (GPX) protein levels were significantly decreased by postoperative day 4 (POD4) and postoperative day 5 (POD5), respectively, in allografts compared to isografts. While CuZn superoxide dismutase (CuZn SOD) levels were unchanged, there was a 50% decrease in MnSOD protein in allografts at postoperative day 6 (POD6). The sequential loss in antioxidant protein levels was not due to transcriptional regulation since there was no change in RNA levels for any of the genes tested. L-NIL did not alter catalase protein; however, the loss of MnSOD protein at POD6 was prevented by L-NIL. Consistent with a decrease in antioxidant protein levels, there was a sequential loss in enzyme activity for MnSOD, catalase and GPX. L-NIL however, restored MnSOD and GPX activities but not catalase activity. Treatment with CsA restored both protein and enzyme activities of GPX and MnSOD but not catalase. These results indicate that the loss in MnSOD and GPX protein and activity in allografts occurs via an iNOS-dependent mechanism whereas the decrease in catalase appears to be iNOS-independent. This suggests a differential role for iNOS in regulating post-translational modification of individual antioxidant enzymes in acute cardiac transplantation.

GEA 3162 decomposes to co-generate nitric oxide and superoxide and induces apoptosis in human neutrophils via a peroxynitrite-dependent mechanism

1. GEA 3162 (1,2,3,4,-oxatriazolium, 5-amino-3-(3,4-dichlorophenyl)-chloride), has powerful effects on neutrophil function and apoptosis, but the underlying mechanisms are unclear, particularly with respect to the possible roles of nitric oxide (NO) and/or peroxynitrite (ONOO(-)). 2. Our hypothesis was that GEA 3162 is a generator of ONOO(-) and that its biological effects on neutrophil apoptosis differ from those of a conventional NO donor. The effects of GEA 3162 were compared to those of the established ONOO(-) donor, 3-morpholinosydnonimine (SIN-1), and the NO donor, diethylamine diazeniumdiolate (DEA/NO) in neutrophils from healthy volunteers. Electrochemical detection and electron paramagnetic resonance were used to define the NO-related species generated from these agents. 3. GEA 3162 and SIN-1 influence neutrophil apoptosis differently from DEA/NO. All three compounds induced morphological neutrophil apoptosis. However, both GEA 3162 and SIN-1 paradoxically inhibited internucleosomal DNA fragmentation, whereas DEA/NO induced fragmentation compared to control. 4. In contrast to DEA/NO, generation of free NO was not detectable in solutions of GEA 3162 or SIN-1 (100 microm). However, Cu/Zn superoxide dismutase (SOD; 50-750 U ml(-1)) unmasked NO generated from these compounds in a concentration-dependent manner. GEA 3162 and SIN-1 oxidised the O(2)(-)- and ONOO(-)-sensitive dye, dihydrorhodamine 123 (DHR 123; 1 microm), suggesting that ONOO(-) released from these compounds is responsible for oxidation of DHR 123. 5. We conclude that GEA 3162 is an ONOO(-) donor with pro-apoptotic properties that more closely resemble SIN-1 than the NO donor, DEA/NO. Moreover, unlike NO, ONOO(-) induces apoptosis in neutrophils via a mechanism that does not require DNA fragmentation.

Enhanced S -Nitroso-Albumin Formation From Inhaled NO During Ischemia/Reperfusion

In the present study, we investigated whether inhaled nitric oxide (NO) was transported by plasma proteins, such as S -nitroso-albumin (SNO-Alb), in the feline circulation and whether this molecule delivers NO to the periphery under conditions of stress, specifically ischemia/reperfusion (I/R). A flow probe was interposed between the femoral and superior mesenteric artery for blood flow measurements, and a branch of the superior mesenteric vein was cannulated for arterial-venous sampling. In animals breathing room air, SNO-Alb was below detection level in arterial or venous blood. NO inhalation resulted in a significant arterial-venous gradient for SNO-Alb. Concomitant with this loss of SNO-Alb across the intestinal vasculature was an increase in nitrite (NO 2 − ). However, this release of NO was not sufficient to alter intestinal blood flow. I/R during NO inhalation caused a very large increase in arterial SNO-Alb that permitted a 5-fold increase in SNO-Alb consumption and significant generation of NO 2 − within the postischemic intestinal vasculature. The increased SNO-Alb consumption was sufficient to dramatically improve intestinal blood flow. The very large burst of arterial SNO-Alb during I/R was completely blocked by the administration of superoxide dismutase, suggesting that oxidative stress contributed to the increased SNO-Alb formation. Our data suggest that inhaled NO can increase nitrosothiol production and these molecules may be a functional NO delivery system during cardiovascular disease.

Nitric oxide, nitrotyrosine, and nitric oxide modulators in asthma and chronic obstructive pulmonary disease

Nitric oxide (NO), a simple free-radical gas, elicits a diverse range of physiologic and pathophysiologic effects, and plays an important role in pulmonary diseases. Nitrosative stress and nitration of proteins in airway epithelium may be responsible for steroid resistance in asthma and their ineffectiveness in chronic obstructive pulmonary disease (COPD), supporting the potential role of future therapeutic strategies aimed at regulating NO synthesis in asthma and COPD. In this article, we review the potential role of NO modulators (NO synthase inhibitors and NO donors), which, if given on a regular basis, may have clinical benefit in asthma and COPD.

Regulation of aldose reductase and the polyol pathway activity by nitric oxide

Increased flux of glucose through the polyol pathway has been implicated in the pathophysiology of secondary diabetic complications. The first step of this pathway, which generates sorbitol from glucose, is catalyzed by aldose reductase (AR) (AKR1B). In vitro, the binding of substrates and inhibitors to AR is highly sensitive to the oxidation state of the enzyme due to the presence of a hyper-reactive cysteine residue at the active site of the enzyme. This residue (Cys-298) can be readily modified in air or, by thiol-modifying reagents, nitric oxide (NO) donors and nitrosothiols. We show that exposure of rat erythrocytes to NO donors inhibits AR activity and AR mediated accumulation of sorbitol, possibly by S-glutathiolation of Cys-298. Both glutathiolation and inhibition of AR are reversible upon subsequent incubation of the cells with fresh media without NO donors. These observations suggest that NO regulates the cellular activity of AR and in turn the flux of glucose via the polyol pathway. The inhibition of AR by exogenous or endogenous NO appears to be related to reversible S-glutathiolation of the AR protein. Because hyperglycemic states are associated with a decrease in NO generation, the loss of NO-mediated repression of AR may be a significant factor in the activation of the polyol pathway and the development of secondary diabetic complications.