Tyrosine nitration by peroxynitrite formed from nitric oxide and superoxide generated by xanthine oxidase

Metal ion chelating peptides with superoxide dismutase activity

The superoxide dismutase activities of two novel synthetic chelating peptides are reported. The peptides comprise a polyaminocarboxylic acid chelator (EDTA) conjugated to tyrosine (ET(1)) and phenylalanine (EP(1)). Superoxide dismutase (SOD) activity was exhibited for Cu(II) but not the Fe(III) complexes. The mimetic activities were compared to bovine erythrocyte SOD (3730 U/mg) and exhibited activities of 1119 U/mg for ET(1)-Cu(II) and 551 U/mg for EP(1)-Cu(II). Thus, small alterations in structure can have significant effects on the enzymatic activity of metallopeptides. These synthetic chelators have dual potential anti-inflammatory activity by chelating deleterious non-protein bound metal ions and concomitantly affording anti-oxidant mimetic activity.

Involvement of peroxynitrite in capsaicin-induced apoptosis of C6 glioma cells

Capsaicin induces apoptosis in some types of cells, but its mechanism remains obscure. In this study, peroxynitrite, a powerful oxidant generated from the reaction of superoxide and nitric oxide (NO) in biological system, was demonstrated to be responsible for capsaicin-mediated apoptosis in C6 glioma cells. Capsaicin-induced apoptosis was detected by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay, and also identified by Annexin V staining and comet assay. Capsazepine and ruthenium red, the vanilloid receptor 1 (VR1/TPRV1) antagonists, did not inhibit capsaicin-induced apoptosis. Exposure to capsaicin not only promoted the generation of superoxide and iNOS, but also markedly suppressed the expression of SODs. Nitrite and nitrate, the NO metabolites accumulated in the medium, and the nitrotyrosine was also increased in proteins of C6 glioma cells exposed to capsaicin. Pretreatment of cells with 4 microM ebselen (a peroxynitrite scavenger) showed effective inhibitory effect on the capsaicin-induced apoptosis. These results suggest that peroxynitrite can act as a potential mediator in the capsaicin-induced apoptosis in C6 glioma cells.

Detection of superoxide and peroxynitrite in model systems and mitochondria by the luminol analogue L-012

In the present study we investigated the specificity and sensitivity of the chemiluminescence (CL) dye and luminol analogue 8-amino-5-chloro-7-phenylpyrido[3,4-d]pyridazine-1,4-(2H,3H) dione (L-012) to detect reactive oxygen species (ROS) such as superoxide, peroxynitrite and hydrogen peroxide in cell free systems as well as in isolated mitochondria. The results obtained by L-012 were compared with other CL substances such as luminol, lucigenin, coelenterazine and the fluorescence dye dihydroethidine. The results indicate that the L-012-derived chemiluminescence induced by superoxide from hypoxanthine/xanthine oxidase (HX/XO) or by 3-morpholino sydnonimine (SIN-1)-derived peroxynitrite largely depends on the incubation time. Irrespective of the experimental conditions, L-012-derived CL in response to HX/XO and SIN-1 was 10-100 fold higher than with other CL dyes tested. In a cell-free system, authentic peroxynitrite yielded a higher L-012-enhanced CL signal than authentic superoxide and the superoxide-induced signal in cell-free as well as isolated mitochondria increased in the presence of equimolar concentrations of nitrogen monoxide (NO). The superoxide signal/background ratio detected by L-012-enhanced CL in isolated mitochondria with blocked respiration was 7 fold higher than that obtained by the superoxide sensitive fluorescence dye dihydroethidine. We conclude that L-012-derived CL may provide a sensitive and reliable tool to detect superoxide and peroxynitrite formation in mitochondrial suspensions.

Peroxynitrite delivery methods for toxicity studies

The endogenous synthesis of peroxynitrite (ONOO(-)) has been implicated in a number of diseases, but assessments of its cytotoxicity and genotoxicity have been hampered by its extremely short half-life under physiological conditions (<20 ms) and the consequent difficulty in exposing cells to known concentrations of it over at least several hours. Two methods for peroxynitrite delivery to cell cultures were investigated, one involving steady infusion of preformed ONOO(-) and the other based on the continuous in situ synthesis of ONOO(-) from NO and O(2)(-). In the latter, NO was supplied by diffusion through gas permeable tubing and O(2)(-) was generated using the hypoxanthine-xanthine oxidase reaction. The performance of both methods was assessed by measuring the rates of formation of tyrosine derivatives (dityrosine and nitrotyrosine) that are commonly employed as biomarkers for peroxynitrite. Experimental results in the absence of cells were compared in each case with predictions from kinetic models. In the infusion system, the measured dityrosine and nitrotyrosine yields were in excellent agreement with those predicted from the model. To characterize the other system, experiments were performed first to determine the kinetics of hypoxanthine oxidation by xanthine oxidase and uric acid oxidation by uricase. Simulations of the complex reaction network in the complete synthesis system suggested that dityrosine should be the major product there, that the yields of both tyrosine derivatives should be very sensitive to the relative rates of NO and O(2)(-) delivery, and that equal rates for NO and O(2)(-) should maximize those yields. Experiments performed under the predicted optimal conditions showed much lower levels of dityrosine than expected and no detectable nitrotyrosine. The unexpectedly low yields of tyrosine products could be explained largely by the partial inactivation of both xanthine oxidase and uricase by peroxynitrite-derived NO(2) and CO(3)(-) radicals. We conclude that continuous infusion of peroxynitrite is the more promising approach.

Nitric oxide as an endogenous mutagen for Sendai virus without antiviral activity

Nitric oxide (NO) may affect the genomes of various pathogens, and this mutagenesis is of particular interest for viral pathogenesis and evolution. Here, we investigated the effect of NO on viral replication and mutation. Exogenous or endogenous NO had no apparent antiviral effect on influenza A virus and Sendai virus. The mutagenic potential of NO was analyzed with Sendai virus fused to a green fluorescent protein (GFP) gene (GFP-SeV). GFP-SeV was cultured in SW480 cells transfected with a vector expressing inducible NO synthase (iNOS). The mutation frequency of GFP-SeV was examined by measuring loss of GFP fluorescence of the viral plaques. GFP-SeV mutation frequency in iNOS-SW480 cells was much higher than that in parent SW480 cells and was reduced to the level of mutation frequency in the parent cells by treatment with an NO synthase (NOS) inhibitor. Immunocytochemistry showed generation of more 8-nitroguanosine in iNOS-SW480 cells than in SW480 cells without iNOS transfection. Authentic 8-nitroguanosine added exogenously to GFP-SeV-infected CV-1 cells increased the viral mutation frequency. Profiles of the GFP gene mutations induced by 8-nitroguanosine appeared to resemble those of mutations occurring in mouse lungs in vivo. A base substitution that was characteristic of both mutants (those induced by 8-nitroguanosine and those occurring in vivo) was a C-to-U transition. NO-dependent oxidative stress in iNOS-SW480 cells was also evident. Together, the results indicate unambiguously that NO has mutagenic potential for RNA viruses such as Sendai virus without affecting viral replication, possibly via 8-nitroguanosine formation and cellular oxidative stress.

Amifostine has antiangiogenic properties in vitro by changing the redox status of human endothelial cells

Amifostine is a broad-spectrum cytoprotective agent, selective for normal tissues. It is a pro-drug metabolised to the free thiol WR-1065 that may act as a scavenger of free radicals, generated in tissues exposed to chemotherapeutic agents or radiation. WR-1065 can be further oxidized to its symmetric disulfide WR-33278 or degraded to hydrogen peroxide (H2O2). Both WR-1065 and WR-33278 resemble endogenous polyamines. Although amifostine is used in some cases in the clinic, there are only few studies concerning its actions at the cellular level. We have previously shown that amifostine inhibits angiogenesis in vivo, affecting the expression of several angiogenic genes. In the present work, we studied the effect of amifostine on human umbilical vein endothelial cell (HUVEC) functions in vitro, in order to further clarify its mechanism(s) of action. Amifostine increased HUVEC proliferation, an effect that was reversed by the intracellular H2O2 scavenger sodium pyruvate, agents that increase intracellular cAMP levels and L-valine. On the other hand, amifostine decreased HUVEC migration, an effect that was reversed by L-valine or L-arginine but not sodium pyrouvate. The decrease in migration was in line with decreased tube formation on matrigel and decreased amounts of metalloproteinase-2 released into the culture medium of HUVEC. Finally, amifostine reduced tyrosine nitration of the cytoskeletal proteins actin and alpha-tubulin in a time dependent manner. This last action could be due to the reduced production of nitric oxide (NO) or to other not yet identified mechanisms. Collectively, our results suggest that amifostine acts on endothelial cells through pathways that affect the redox status of the cells, either by producing H2O2 or by modulating NO production.

Antioxidative and antimutagenic activities of 4-vinyl-2,6-dimethoxyphenol (canolol) isolated from canola oil

A potent antioxidative compound in crude canola oil, canolol, was recently identified, and reported herein are studies of its scavenging capacity against the endogenous mutagen peroxynitrite (ONOO(-)). ONOO(-) is generated by the reaction between superoxide anion radical and nitric oxide, both of which are produced by inflammatory leukocytes. Among various antioxidative substances of natural or synthetic origin, canolol was one of the most potent antimutagenic compounds when Salmonella typhimurium TA102 was used in the modified Ames test. Its potency was higher than that of flavonoids (e.g., rutin) and alpha-tocopherol and was equivalent to that of ebselen. Canolol suppressed ONOO(-)-induced bactericidal action. It also reduced intracellular oxidative stress and apoptosis in human cancer SW480 cells when used at a concentration below 20 microM under H(2)O(2)-induced oxidative stress. In addition, canolol suppressed plasmid DNA (pUC19) strand breakage induced by ONOO(-), as revealed by agarose gel electrophoresis.

A new pitfall in detecting biological end products of nitric oxide-nitration, nitros(yl)ation and nitrite/nitrate artefacts during freezing

The present study shows that when freezing nitrite containing biological samples in the presence of sodium and phosphate, a process of tyrosine nitration and S-nitrosocysteine formation is observed. The underlying mechanism is obviously based on the already described pH decrease in sodium phosphate buffered solutions during the freezing process and probably involves nitrous acid as an intermediate. However, in pure potassium phosphate buffer freeze-artefacts were absent. The yield of 3-nitrotyrosine from albumin-bound or free tyrosine depends not only on the concentration of nitrite, tyrosine or protein, and sodium phosphate but also on the velocity of the freezing process. Nitrite and nitrate were quantified by the Griess/nitrate reductase assay. 3-nitrotyrosine formation was quantitatively measured by HPLC analysis with optical and electrochemical detection as well as qualitatively investigated by immunohistochemistry and slot blot analysis using 3-nitrotyrosine specific antibodies. The formation of S-nitrosocysteine was detected by S-nitrosothiol specific antibodies and quantified by a fluorometric assay. Irrespective of the mechanism and although the here presented results cannot be generalized, the data warrant caution for the analysis of nitration or nitros(yl)ation products following freezing of nitrite containing biological material.

The impact of metal catalysis on protein tyrosine nitration by peroxynitrite

In a series of heme and non-heme proteins the nitration of tyrosine residues was assessed by complete pronase digestion and subsequent HPLC-based separation of 3-nitrotyrosine. Bolus addition of peroxynitrite caused comparable nitration levels in all tested proteins. Nitration mainly depended on the total amount of tyrosine residues as well as on surface exposition. In contrast, when superoxide and nitrogen monoxide (NO) were generated at equal rates to yield low steady-state concentrations of peroxynitrite, metal catalysis seemed to play a dominant role in determining the sensitivity and selectivity of peroxynitrite-mediated tyrosine nitration in proteins. Especially, the heme-thiolate containing proteins cytochrome P450(BM-3) (wild type and F87Y variant) and prostacyclin synthase were nitrated with high efficacy. Nitration by co-generated NO/O(2)(-) was inhibited in the presence of superoxide dismutase. The NO source alone only yielded background nitration levels. Upon changing the NO/O(2)(-) ratio to an excess of NO, a decrease in nitration in agreement with trapping of peroxynitrite and derived radicals by NO was observed. These results clearly identify peroxynitrite as the nitrating species even at low steady-state concentrations and demonstrate that metal catalysis plays an important role in nitration of protein-bound tyrosine.

Hypoxia-induced acute lung injury in murine models of sickle cell disease

Vaso-occlusive events are the major source of morbidity and mortality in sickle cell disease (SCD); however, the pathogenic mechanisms driving these events remain unclear. Using hypoxia to induce pulmonary injury, we investigated mechanisms by which sickle hemoglobin increases susceptibility to lung injury in a murine model of SCD, where mice either exclusively express the human alpha/sickle beta-globin (halphabetaS) transgene (SCD mice) or are heterozygous for the normal murine beta-globin gene and express the halphabetaS transgene (mbeta+/-, halphabetaS+/-; heterozygote SCD mice). Under normoxia, lungs from the SCD mice contained higher levels of xanthine oxidase (XO), nitrotyrosine, and cGMP than controls (C57BL/6 mice). Hypoxia increased XO and nitrotyrosine and decreased cGMP content in the lungs of all mice. After hypoxia, vascular congestion was increased in lungs with a greater content of XO and nitrotyrosine. Under normoxia, the association of heat shock protein 90 (HSP90) with endothelial nitric oxide synthase (eNOS) in lungs of SCD and heterozygote SCD mice was decreased compared with the levels of association in lungs of controls. Hypoxia further decreased association of HSP90 with eNOS in lungs of SCD and heterozygote SCD mice, but not in the control lungs. Pretreatment of rat pulmonary microvascular endothelial cells in vitro with xanthine/XO decreased A-23187-stimulated nitrite + nitrate production and HSP90 interactions with eNOS. These data support the hypotheses that hypoxia increases XO release from ischemic tissues and that the local increase in XO-induced oxidative stress can then inhibit HSP90 interactions with eNOS, decreasing *NO generation and predisposing the lung to vaso-occlusion.

Superoxide generation mediated by 8-nitroguanosine, a highly redox-active nucleic acid derivative

Formation of 8-nitroguanosine may be characterized as nucleic acid modification induced by nitric oxide (NO). We show here that 8-nitroguanosine is a highly redox-active nucleic acid derivative that strongly stimulated superoxide generation from various NADPH-dependent reductases, including cytochrome P450 reductase and all isoforms of NO synthase. This reaction involves these reductases in a redox cycling reaction via single-electron reduction of 8-nitroguanosine to form 8-nitroguanosine anion radical. One electron is then transferred from this radical to molecular oxygen. 8-Nitroguanosine formed in vivo may function as a potent redox cofactor that intensifies oxyradical generation by various NADPH/reductase-like enzymes and thus participates in diverse physiological and pathological events.

Xanthine oxidoreductase and cardiovascular disease: molecular mechanisms and pathophysiological implications

There is substantial evidence that oxidative stress participates in the pathophysiology of cardiovascular disease. Biochemical, molecular and pharmacological studies further implicate xanthine oxidoreductase (XOR) as a source of reactive oxygen species in the cardiovascular system. XOR is a member of the molybdoenzyme family and is best known for its catalytic role in purine degradation, metabolizing hypoxanthine and xanthine to uric acid with concomitant generation of superoxide. Gene expression of XOR is regulated by oxygen tension, cytokines and glucocorticoids. XOR requires molybdopterin, iron-sulphur centres, and FAD as cofactors and has two interconvertible forms, xanthine oxidase and xanthine dehydrogenase, which transfer electrons from xanthine to oxygen and NAD(+), respectively, yielding superoxide, hydrogen peroxide and NADH. Additionally, XOR can generate superoxide via NADH oxidase activity and can produce nitric oxide via nitrate and nitrite reductase activities. While a role for XOR beyond purine metabolism was first suggested in ischaemia-reperfusion injury, there is growing awareness that it also participates in endothelial dysfunction, hypertension and heart failure. Importantly, the XOR inhibitors allopurinol and oxypurinol attenuate dysfunction caused by XOR in these disease states. Attention to the broader range of XOR bioactivity in the cardiovascular system has prompted initiation of several randomised clinical outcome trials, particularly for congestive heart failure. Here we review XOR gene structure and regulation, protein structure, enzymology, tissue distribution and pathophysiological role in cardiovascular disease with an emphasis on heart failure.

Neuroprotective effect of (-)Delta9-tetrahydrocannabinol and cannabidiol in N-methyl-D-aspartate-induced retinal neurotoxicity: involvement of peroxynitrite

In glaucoma, the increased release of glutamate is the major cause of retinal ganglion cell death. Cannabinoids have been demonstrated to protect neuron cultures from glutamate-induced death. In this study, we test the hypothesis that glutamate causes apoptosis of retinal neurons via the excessive formation of peroxynitrite, and that the neuroprotective effect of the psychotropic Delta9-tetrahydroxycannabinol (THC) or nonpsychotropic cannabidiol (CBD) is via the attenuation of this formation. Excitotoxicity of the retina was induced by intravitreal injection of N-methyl-D-aspartate (NMDA) in rats, which also received 4-hydroxy-2,2,6,6-tetramethylpiperidine-n-oxyl (TEMPOL,a superoxide dismutase-mimetic), N-omega-nitro-L-arginine methyl ester (L-NAME, a nitric oxide synthase inhibitor), THC, or CBD. Retinal neuron loss was determined by TDT-mediated dUTP nick-end labeling assay, inner retinal thickness, and quantification of the mRNAs of ganglion cell markers. NMDA induced a dose- and time-dependent accumulation of nitrite/nitrate, lipid peroxidation, and nitrotyrosine (foot print of peroxynitrite), and a dose-dependent apoptosis and loss of inner retinal neurons. Treatment with L-NAME or TEMPOL protected retinal neurons and confirmed the involvement of peroxynitrite in retinal neurotoxicity. The neuroprotection by THC and CBD was because of attenuation of peroxynitrite. The effect of THC was in part mediated by the cannabinoid receptor CB1. These results suggest the potential use of CBD as a novel topical therapy for the treatment of glaucoma.

8-Nitroxanthine, a product of myeloperoxidase, peroxynitrite, and activated human neutrophils, enhances generation of superoxide by xanthine oxidase

Reactive nitrogen and oxygen species are implicated in the damage of ischemic tissue that is reperfused. One important pathway may involve xanthine oxidase. Xanthine oxidase uses xanthine, a product of ATP degradation in ischemic tissue, to produce superoxide and hydrogen peroxide. Superoxide reacts rapidly with nitric oxide to form peroxynitrite, a powerful oxidant. Another potential source of reactive nitrogen species is the myeloperoxidase-hydrogen peroxide-nitrite system of activated phagocytes. We demonstrate that peroxynitrite and myeloperoxidase nitrate xanthine in vitro. Through 13C NMR spectroscopy, UV/visible spectroscopy, and mass spectrometry, the major product was identified as 8-nitroxanthine. Xanthine nitration by peroxynitrite was optimal at neutral pH and was markedly stimulated by physiological concentrations of bicarbonate. Xanthine nitration by myeloperoxidase required hydrogen peroxide and nitrite. However, it was independent of chloride ion and little affected by scavengers of hypochlorous acid, suggesting that the reactive agent is a nitrogen dioxide-like species. 8-Nitroxanthine was generated by a low, steady flux of peroxynitrite, and also by the myeloperoxidase-hydrogen peroxide-nitrite system of activated human neutrophils, suggesting that the reactions may be physiologically relevant. 8-Nitroxanthine may exert biological effects because it markedly increased the production of superoxide by the xanthine oxidase-xanthine system. Our observations suggest a mechanism for the enhanced formation of superoxide in reperfused tissue, which might increase the production of peroxynitrite and 8-nitroxanthine. Generation of 8-nitroxanthine by peroxynitrite and myeloperoxidase could represent a positive feedback mechanism that enhances further the production of both reactive oxygen and nitrogen species in ischemic tissue that is reperfused.

Inhibitory activity of flavonoids fromPrunus davidiana and other flavonoids on total ROS and hydroxyl radical generation

Since reactive oxygen species (ROS) and hydroxyl radicals (*OH) play an important role in the pathogenesis of many human degenerative diseases, much attention has focused on the development of safe and effective antioxidants. Preliminary experiments have revealed that the methanol (MeOH) extract of the stem of Prunus davidiana exerts inhibitory/scavenging activities on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals, total ROS and peroxynitrites (ONOO-). In the present study, the antioxidant activities of this MeOH extract and the organic solvent-soluble fractions, dichloromethane (CH2Cl2), ethyl acetate (EtOAc), and n-butanol (n-BuOH), and the water layer of P. davidiana stem were evaluated for the potential to inhibit *OH and total ROS generation in kidney homogenates using 2',7'-dichlorodihydrofluorescein diacetate (DCHF-DA), and for the potential to scavenge authentic ONOO-. We also evaluated the inhibitory activity of seven flavonoids isolated from P. davidiana stem, kaempferol, kaempferol 7-O-beta-D-glucoside, (+)-catechin, dihydrokaempferol, hesperetin 5-O-beta-D-glucoside, naringenin and its 7-O-beta-D-glucoside, on the total ROS, *OH and ONOO- systems. For the further elucidation of the structure-inhibitory activity relationship of flavonoids on total ROS and *OH generation, we measured the antioxidant activity of sixteen flavonoids available, including three active flavonoids isolated from P. davidiana, on the total ROS and *OH systems. We found that the inhibitory activity on total ROS generation increases in strength with more numerous hydroxyl groups on their structures. Also, the presence of an ortho-hydroxyl group, whether on the A-ring or B-ring, and a 3-hydroxyl group on the C-ring increased the inhibitory activity on both total ROS and *OH generation.

Mononuclear phagocyte xanthine oxidoreductase contributes to cytokine-induced acute lung injury

Acute lung injury (ALI) is characterized by increased alveolar cytokines, inflammatory cell infiltration, oxidative stress, and alveolar cell apoptosis. Previous work suggested that xanthine oxidoreductase (XOR) may contribute to oxidative stress in ALI as a product of the vascular endothelial cell. We present evidence that cytokine induced lung inflammation and injury involves activation of XOR in the newly recruited mononuclear phagocytes (MNP). We found that XOR was increased predominantly in the MNP that increase rapidly in the lungs of rats that develop ALI following intratracheal cytokine insufflation. XOR was recovered from the MNP largely converted to its oxygen radical generating, reversible O-form, and alveolar MNP exhibited increased oxidative stress as evidenced by increased nitrotyrosine staining. Cytokine insufflation also increased alveolar cell apoptosis. A functional role for XOR in cytokine-induced inflammation was demonstrated when feeding rats two different XOR inhibitors, tungsten and allopurinol, decreased MNP XOR induction, nitrotyrosine staining, inflammatory cell infiltration, and alveolar cell apoptosis. Transfer of control or allopurinol treated MNP into rat lungs confirmed a specific role for MNP XOR in promoting lung inflammation. These data indicate that XOR can contribute to lung inflammation by its expression and conversion in a highly mobile inflammatory cell population.

Hyperoxia induces retinal vascular endothelial cell apoptosis through formation of peroxynitrite

Hyperoxia exposure induces capillary endothelial cell apoptosis in the developing retina, leading to vaso-obliteration followed by proliferative retinopathy. Previous in vivo studies have shown that endothelial nitric oxide synthase (NOS3) and peroxynitrite are important mediators of the vaso-obliteration. Now we have investigated the relationship between hyperoxia, NOS3, peroxynitrite, and endothelial cell apoptosis by in vitro experiments using bovine retinal endothelial cells (BREC). We found that BREC exposed to 40% oxygen (hyperoxia) for 48 h underwent apoptosis associated with activation of caspase-3 and cleavage of the caspase substrate poly(ADP-ribose) polymerase. Hyperoxia-induced apoptosis was associated with increased formation of nitric oxide, peroxynitrite, and superoxide anion and was blocked by treatment with uric acid, nitro-L-arginine methyl ester, or superoxide dismutase. Analyses of the phosphatidylinositol 3-kinase/Akt kinase survival pathway in cells directly treated with peroxynitrite revealed inhibition of VEGF- and basic FGF-induced activation of Akt kinase. These results suggest that hyperoxia-induced formation of peroxynitrite induces BREC apoptosis by crippling key survival pathways and that blocking peroxynitrite formation prevents apoptosis. These data may have important clinical implications for infants at risk of retinopathy of prematurity.

Aberrant utilization of nitric oxide and regulation of soluble guanylate cyclase in rat diabetic retinopathy

Although nitric oxide (NO) was shown not only to exert biological activities through activation of soluble guanylate cyclase (sGC), but also to cause oxidative stress, mechanisms for switching these pathways are unknown. This study aimed to examine aberrant utilization of NO under disease conditions such as diabetes mellitus. Diabetes was induced in male Wistar rats by injecting streptozotocin (STZ; 50 mg/kg body weight, i.p.). Retina was perfusion-fixed for immunohistochemistry to detect the gas-mediated activation of sGC by anti-sGC antibodies that are function-sensitive [monoclonal antibody (MoAb) 3221] and -insensitive (MoAb28131). Regional lipid peroxidation was also examined by an anti-acrolein MoAb. At 6 weeks after STZ injection, inducible NO synthase induction became evident, coinciding with the overproduction of nitrotyrosine, followed by that of acrolein. Despite such NO overproduction, sGC did not exhibit any notable activation. When STZ-treated animals were posttreated with a derivative of superoxide dismutase that stays in circulation without undergoing renal ultrafiltration, immunoreactivities to MoAb3221 but not to MoAb28131 increased markedly in diabetic retina, suggesting that superoxide cancels free NO for local sGC activation. These results provide evidence of aberrant utilization of NO and suggest that superoxide plays a role in interfering with NO-mediated sGC activation for phototransducing events in this neural tissue.

Experimental diabetes causes breakdown of the blood-retina barrier by a mechanism involving tyrosine nitration and increases in expression of vascular endothelial growth factor and urokinase plasminogen activator receptor

The purpose of these experiments was to determine the specific role of reactive oxygen species (ROS) in the blood-retinal barrier (BRB) breakdown that characterizes the early stages of vascular dysfunction in diabetes. Based on our data showing that high glucose increases nitric oxide, superoxide, and nitrotyrosine formation in retinal endothelial cells, we hypothesized that excess formation of ROS causes BRB breakdown in diabetes. Because ROS are known to induce increases in expression of the well-known endothelial mitogen and permeability factor vascular endothelial growth factor (VEGF) we also examined their influence on the expression of VEGF and its downstream target urokinase plasminogen activator receptor (uPAR). After 2 weeks of streptozotocin-induced diabetes, analysis of albumin leakage confirmed a prominent breakdown of the BRB. This permeability defect was correlated with significant increases in the formation of nitric oxide, lipid peroxides, and the peroxynitrite biomarker nitrotyrosine as well as with increases in the expression of VEGF and uPAR. Treatment with a nitric oxide synthase inhibitor (N-omega-nitro-L-arginine methyl ester, 50 mg/kg/day) or peroxynitrite scavenger (uric acid, 160 mg/kg/day) blocked the breakdown in the BRB and prevented the increases in formation of lipid peroxides and tyrosine nitration as well as the increases in expression of VEGF and uPAR. Taken together, these data indicate that early diabetes causes breakdown of the BRB by a mechanism involving the action of reactive nitrogen species in promoting expression of VEGF and uPAR.

Expression of inducible nitric-oxide synthase and intracellular protein tyrosine nitration in vascular smooth muscle cells: role of reactive oxygen species

A significant increase in the induction of inducible nitric-oxide synthase (iNOS) protein expression and in the levels of nitrite plus nitrate was observed in rat aortic smooth muscle cells (RASMCs) stably transfected with catalase (RASMC-2C2) as compared with empty vector-transfected RASMC-V4 cells after exposure to cytokines and lipopolysaccharide. The increased expression of iNOS protein in the RASMC-2C2 cells was associated with a significant activation of nuclear transcription factor kappaB, one of the transcriptional regulators of iNOS expression. The induction of iNOS was also accompanied by increased protein tyrosine nitration in both cell types as revealed by immunocytochemical staining and high pressure liquid chromatography with on-line electrospray ionization tandem mass spectrometry. Nitrotyrosine formation was inhibited by 1400W, an iNOS inhibitor, by 4-(2-aminoethyl) benzenesulfonyl fluoride, an inhibitor of NADPH oxidase, and by the superoxide dismutase mimetic M40403, but not by the peroxidase inhibitor 4-aminobenzoic hydrazide. Electron microscopy using affinity-purified anti-nitrotyrosine antibodies revealed labeling at the cytosolic side of the rough endoplasmic reticulum membranes, in the nucleus, occasionally in mitochondria, and consistently within the fibrillar layer underneath the plasma membrane. Collectively, the data in this model system indicate that hydrogen peroxide, by inhibiting the activation of nuclear transcription factor kappaB, prevents iNOS expression, whereas superoxide contributes in a precise pattern of intracellular protein tyrosine nitration.

Effects of peroxynitrite on isolated cardiac trabeculae: selective impact on myofibrillar energetic controllers

Formation of peroxynitrite and cardiac protein nitration have been implicated in multiple cardiac disease states, but their contributions to disease initiation remain undefined. We have previously observed nitration of myofibrillar regions of cardiac myocytes in several experimental and clinical settings of cardiac myocyte dysfunction and postulated that oxidative insult to key components of the contractile apparatus may be initiating events. Here we tested the hypothesis that peroxynitrite alters myofibrillar contractile function, and investigated a mechanistic role for nitration in this process. Isolated rat ventricular trabeculae were exposed to physiologically relevant concentrations of peroxynitrite and ATP-dependent contractile responses were measured. Maximal trabecular force generation was significantly impaired following 300 nM peroxynitrite exposures. Several myofibrillar proteins demonstrated increased tyrosine nitration, the most significant increases occurred in the myosin heavy chain and the myofibrillar isoform of creatine kinase. Additional functional experiments were conducted using phosphocreatine (high energy phosphate substrate for myofibrillar creatine kinase) as the primary energy substrate. Myofibrillar creatine kinase-dependent force generation was impaired at peroxynitrite concentrations as low as 50 nM, suggesting potent inactivation of the enzyme. Extent of tyrosine nitration of myofibrillar creatine kinase was negatively correlated to myofibrillar creatine kinase-dependent force generation. These data demonstrate that the cardiac contractile apparatus is highly sensitive to peroxynitrite, and that MM-CK may be a uniquely vulnerable target.

Experimental diabetes causes breakdown of the blood-retina barrier by a mechanism involving tyrosine nitration and increases in expression of vascular endothelial growth factor and urokinase plasminogen activator receptor

The purpose of these experiments was to determine the specific role of reactive oxygen species (ROS) in the blood-retinal barrier (BRB) breakdown that characterizes the early stages of vascular dysfunction in diabetes. Based on our data showing that high glucose increases nitric oxide, superoxide, and nitrotyrosine formation in retinal endothelial cells, we hypothesized that excess formation of ROS causes BRB breakdown in diabetes. Because ROS are known to induce increases in expression of the well-known endothelial mitogen and permeability factor vascular endothelial growth factor (VEGF) we also examined their influence on the expression of VEGF and its downstream target urokinase plasminogen activator receptor (uPAR). After 2 weeks of streptozotocin-induced diabetes, analysis of albumin leakage confirmed a prominent breakdown of the BRB. This permeability defect was correlated with significant increases in the formation of nitric oxide, lipid peroxides, and the peroxynitrite biomarker nitrotyrosine as well as with increases in the expression of VEGF and uPAR. Treatment with a nitric oxide synthase inhibitor (N-omega-nitro-L-arginine methyl ester, 50 mg/kg/day) or peroxynitrite scavenger (uric acid, 160 mg/kg/day) blocked the breakdown in the BRB and prevented the increases in formation of lipid peroxides and tyrosine nitration as well as the increases in expression of VEGF and uPAR. Taken together, these data indicate that early diabetes causes breakdown of the BRB by a mechanism involving the action of reactive nitrogen species in promoting expression of VEGF and uPAR.

Tyrosine-nitration of caspase 3 and cytochrome c does not suppress apoptosis induction in squamous cell carcinoma cells

The influence of tyrosine nitration of cytochrome c and caspase 3 on apoptosis induction was investigated in an established squamous carcinoma cell line, OSC-4. The intracellular NO and O2(-) levels were increased up to about 110-120% and 140-180% of the control levels, respectively, after the treatment of OSC-4 cells with 5-FU (100 microg/ml), PLM (10 microg/ml), CDDP (10 microg/ml), or gamma-rays (20 Gy). The treatment of OSC-4 cells with ONOO(-) (1 mM) and the above anticancer agents induced tyrosine nitration of 14, 32 kDa protein among others and nitration of tyrosine residues of cytochrome c and caspase 3 was identified by the Western blotting of immunoprecipitates obtained by antibodies to these proapoptotic proteins. When cytochrome c and procaspase 3 were treated with ONOO(-), tyrosine nitration was increased in a ONOO(-)-dose dependent manner. Tyrosine nitration of cleaved (17 kDa) caspase 3, however, was not induced by ONOO(-). Procaspase 3 in the cytosol of HeLa cells was activated by the addition of ONOO(-)-treated as well as ONOO(-)-untreated cytochrome c. In addition, cleavage of ICAD and PARP were not suppressed in OSC-4 cells by pretreatment with ONOO(-). Activity of cleaved caspase 3 was not suppressed at low concentrations or by treatment with ONOO(-) or NO donors, SIN-1 and SNP. Furthermore, apoptosis of OSC-4 cells by the anticancer agents was not suppressed by ONOO(-). In conclusion, these results suggest that nitration of tyrosine residues of cytochrome c and procaspase 3 is induced by chemoradiotherapy but their nitration does not suppress cancer cell apoptosis.

Mutation of tyrosine 190 to alanine eliminates the inactivation of cytochrome P450 2B1 by peroxynitrite

We have previously reported that cytochrome P450 2B1 was inactivated by peroxynitrite and that the decrease in the catalytic activity correlated with an increase in the nitration of tyrosine. Digestion of the peroxynitrite-treated P450 2B1 with Lys C followed by amino acid sequencing of the major nitrotyrosine-containing peptide demonstrated that it spanned residues 160-225. This peptide contains two tyrosine residues at positions 190 and 203. In this study, we mutated Tyr 190 to Ala (Y190A) and Tyr 203 to Ala (Y203A) in wild-type recombinant P450 2B1 (WT) in order to identify the specific residue(s) that is nitrated and to determine whether nitrotyrosine formation is reponsible for the peroxynitrite-mediated inactivation of P450 2B1. All three P450s were expressed in Escherichia coli, purified to homogeneity, and characterized. The catalytic activities for four different substrates of P450 2B1 increased approximately 2-fold for the Y203A mutant, but decreased by about 60% for the Y190A mutant when compared to WT. The addition of peroxynitrite to the P450s resulted in concentration-dependent decreases in the catalytic activities of WT and Y203A, but no loss of the catalytic activities of Y190A. The extent of tyrosine nitration of Y190A by peroxynitrite decreased by approximately 75% as compared with WT or the Y203A protein. Following digestion of the peroxynitrite-modified proteins with Lys C, a major nitrotyrosine-containing peptide was detected from WT and Y203A, but not from Y190A. Collectively, these results indicate that Tyr 190 is the target residue for peroxynitrite-mediated nitration and that nitration of this tyrosine is a responsible for the inactivation of P450 2B1. Modeling studies suggest that Tyr 190 may play a structural role in maintaining the integrity of the protein for maximal activity through hydrogen bonding with Glu 149.

8-nitroguanosine formation in viral pneumonia and its implication for pathogenesis

For many diseases, mediation of pathogenesis by nitric oxide (NO) has been suggested. In this study, we explored NO-induced viral pathogenesis with a focus on nucleic acid damage as evidenced by 8-nitroguanosine formation in vivo. Wild-type mice and littermate mice deficient in inducible NO synthase (iNOS) were infected with influenza or Sendai virus. Formation of 8-nitroguanosine in virus-infected lungs was assessed immunohistochemically with an antibody specific for 8-nitroguanosine. Extensive nitration of RNA either treated with peroxynitrite or obtained from cultured RAW 264 cells expressing iNOS was readily detected by this antibody. Strong 8-nitroguanosine immunostaining was evident primarily in the cytosol of bronchial and bronchiolar epithelial cells of virus-infected wild-type mice but not iNOS-deficient mice. This staining colocalized with iNOS immunostaining in the lung. 8- Nitroguanosine staining disappeared after addition of exogenous authentic 8-nitroguanosine during the antibody reaction and after pretreatment of tissues with sodium hydrosulfite, which reduces 8-nitroguanosine to 8-aminoguanosine. NO was generated in excess in lungs of wild-type mice but was eliminated in iNOS-deficient mice after virus infection; this result also correlated well with formation of 8-nitroguanosine and 3-nitrotyrosine. One consequence of the lack of iNOS expression was marked improvement in histopathological changes in the lung and the lethality of the infection without effects on cytokine responses and viral clearance. It is intriguing that 8-nitroguanosine markedly stimulated superoxide generation from cytochrome P450 reductase and iNOS in vitro. The present data constitute a demonstration of 8-nitroguanosine formation in vivo and suggest a potential role for NO-induced nitrative stress in viral pathogenesis.

In vitro antioxidant activity of some selected Prunus species in Korea

In the course of the investigations of natural antioxidants, we examined the antioxidant activities of the methanol (MeOH) extracts of some selected Prunus species, including P buergeriana, P davidiana, P padus, P pendula for. ascendens, P. sargentii, P. serrulata var. spontanea and P. yedoensis by three methods as represented by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, total ROS (reactive oxygen species) and the peroxynitrite (ONOO-) scavenging activity tests. We also evaluated the activities of the organic solvent-soluble fractions, including the dichloromethane (CH2Cl2), ethyl acetate (EtOAc), n-butanol (n-BuOH) fractions and the water (H2O) layer of P serrulata var. spontanea leaves. By means of bioassay-directed fractionation, we isolated eleven known flavonoids (1-11) from the EtOAc soluble fraction of the MeOH extract of the Prunus serrulata var. spontanea leaves, exhibiting strong antioxidant activity and characterized as prunetin (1), genistein (2), quercetin (3), prunetin 4'-O-beta-glucopyranoside (4), kaempferol 3-O-alpha-arabinofuranoside (5), prunetin 5-O-beta-glucopyranoside (6), kaempferol 3-O-beta-xylopyranoside (7), genistin (8), kaempferol 3-O-beta-glucopyranoside (9), quercetin 3-O-beta-glucopyranoside (10) and kaempferol 3-O-beta-xylopyranosyl-(1-->2)-beta-glucopyranoside (11). Compounds 3 and 10 showed good activities in all tested model systems. Compounds 2 and 8 showed scavenging activities in the DPPH and ONOO- tests, while compounds 5, 7, 9 and 11 were active in the ONOO- and ROS tests. On the other hand, compounds 1, 4 and 6 did not show any activities in the tested model systems.

Protein nitration is mediated by heme and free metals through Fenton-type chemistry: an alternative to the NO/O2- reaction

The chemical origins of nitrated tyrosine residues (NT) formed in proteins during a variety of pathophysiological conditions remain controversial. Although numerous studies have concluded that NT is a signature for peroxynitrite (ONOO(-)) formation, other works suggest the primary involvement of peroxidases. Because metal homeostasis is often disrupted in conditions bearing NT, the role of metals as catalysts for protein nitration was examined. Cogeneration of nitric oxide (NO) and superoxide (O(2)(-)), from spermine/NO (2.7 microM/min) and xanthine oxidase (1-28 microM O(2)(-)/min), respectively, resulted in protein nitration only when these species were produced at approximately equivalent rates. Addition of ferriprotoporphyrin IX (hemin) to this system increased nitration over a broad range of O(2)(-) concentrations with respect to NO. Nitration in the presence of superoxide dismutase but not catalase suggested that ONOO(-) might not be obligatory to this process. Hemin-mediated NT formation required only the presence of NO(2)(-) and H(2)O(2), which are stable end-products of NO and O(2)(-) degradation. Ferrous, ferric, and cupric ions were also effective catalysts, indicating that nitration is mediated by species capable of Fenton-type chemistry. Although ONOO(-) can nitrate proteins, there are severe spatial and temporal constraints on this reaction. In contrast, accumulation of metals and NO(2)(-) subsequent to NO synthase activity can result in far less discriminate nitration in the presence of an H(2)O(2) source. Metal catalyzed nitration may account for the observed specificity of protein nitration seen under pathological conditions, suggesting a major role for translocated metals and the labilization of heme in NT formation.

Peroxynitrite triggers a delayed resistance of coronary endothelial cells against ischemia-reperfusion injury

Experiments were designed to test whether nitric oxide (NO) and peroxynitrite trigger delayed coronary endothelial protection induced by preconditioning (PC) in rats. Prolonged ischemia reperfusion markedly reduced the response of isolated coronary arteries to acetylcholine, and this was prevented by PC performed 24 h earlier. The NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) administered during PC abolished its delayed endothelial protective effect, whereas the inducible NOS inhibitor N-(3(aminomethyl)benzyl)acetaminide had no effect. Delayed endothelial PC was also abolished by the peroxynitrite scavengers selenomethionine or uric acid given during PC. In parallel, the NO/peroxynitrite donor S-morpholinosydnonimine and authentic peroxynitrite, administered 24 h before prolonged ischemia-reperfusion mimicked endothelial PC, whereas the NO donor S-nitroso-N-acetylpencillamine had no effect. This suggests that peroxynitrite is an essential trigger of the delayed coronary endothelial protection induced by PC in rat hearts.

Role of nitric oxide in host defense in murine salmonellosis as a function of its antibacterial and antiapoptotic activities

Host defense functions of nitric oxide (NO) are known for many bacterial infections. In this study, we investigated the antimicrobial effect of NO in murine salmonellosis by using inducible NO synthase (iNOS)-deficient mice infected with an avirulent or virulent Salmonella enterica serovar Typhimurium strain. All iNOS-deficient mice died of severe septicemia within 6 days after intraperitoneal injection with an avirulent strain (LT2) to which wild-type mice were highly resistant; 50% lethal doses (LD(50)s) of the LT2 strain for iNOS-deficient and wild-type mice were 30 CFU and 7 x 10(4) CFU, respectively. Lack of NO production in iNOS-deficient mice was verified directly by electron spin resonance spectroscopy. Bacterial yields in liver and blood were much higher in iNOS-deficient mice than in wild-type mice throughout the course of infection. Very small amounts of a virulent strain of serovar Typhimurium (a clinical isolate, strain Gifu 12142; LD(50), 50 CFU) given orally caused severe septicemia in iNOS-deficient animals; wild-type mice tolerated higher doses (LD(50), 6 x 10(2) CFU). Histopathology of livers from infected iNOS-deficient mice revealed extensive damage, such as diffuse hepatocellular apoptosis and increased neutrophil infiltration, but livers from infected wild-type mice showed a limited number of microabscesses, consisting of polymorphonuclear cells and macrophages and low levels of apoptotic change. The LT2 strain was much more susceptible to the bactericidal effect of peroxynitrite than the Gifu strain, suggesting that peroxynitrite resistance may contribute to Salmonella pathogenicity. These results indicate that NO has significant host defense functions in Salmonella infections not only because of its direct antimicrobial effect but also via cytoprotective actions for infected host cells, possibly through its antiapoptotic effect.

Oxidation and nitrosation in the nitrogen monoxide/superoxide system

Based on the previous report of McCord and co-workers (Crow, J. P., Beckman, J. S., and McCord, J. M. (1995) Biochemistry 34, 3544-3552), the zinc dithiolate active site of alcohol dehydrogenase (ADH) has been studied as a target for cellular oxidants. In the nitrogen monoxide ((*NO)/superoxide (O(2)) system, an equimolar generation of both radicals under peroxynitrite (PN) formation led to rapid inactivation of ADH activity, whereas hydrogen peroxide and ( small middle dot)NO alone reacted too slowly to be of physiological significance. 3-Morpholino sydnonimine inactivated the enzyme with an IC(50) value of 250 nm; the corresponding values for PN, hydrogen peroxide, and (*NO) were 500 nm, 50 microm, and 200 microm. When superoxide was generated at low fluxes by xanthine oxidase, it was quite effective in ADH inactivation (IC(50) (XO) approximately 1 milliunit/ml). All inactivations were accompanied by zinc release and disulfide formation, although no strict correlation was observed. From the two zinc thiolate centers, only the zinc Cys(2)His center released the metal by oxidants. The zinc Cys(4) center was also oxidized, but no second zinc atom could be found with 4-(2-pyridylazo)resorcinol (PAR) as a chelating agent except under denaturing conditions. Surprisingly, the oxidative actions of PN were abolished by a 2-3-fold excess of (*)NO under generation of a nitrosating species, probably dinitrogen trioxide. We conclude that in cellular systems, low fluxes of (*)NO and O(2) generate peroxynitrite at levels effective for zinc thiolate oxidations, facilitated by the nucleophilic nature of the complexed thiolate group. With an excess of (*)NO, the PN actions are blocked, which may explain the antioxidant properties of (*)NO and the mechanism of cellular S-nitrosations.

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

In various peroxynitrite (PN)-treated proteins, the formations of stable 3-nitrotyrosine (nitration) and labile S-nitrosocysteine (S-nitrosation) were observed by employing rapid Western blot in 6 h. The steps of SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and membrane-blotting were performed at 4 degrees C. It was noted that the intensity of immunoreactive bands specific for anti-nitrotyrosine was stronger than that specific for anti-S-nitrosocysteine. Additionally, the intensity was in the manner of a dose-dependency of PN. Nitration/S-nitrosation were formed in the following treated proteins, including bovine serum albumin (BSA), DNase-1, ceruloplasmin, catalase and hemoglobin (Hb). The incubation of PN-pretreated hemoglobin with 1 mM reduced glutathione (GSH) did not change immunoreactivity significantly. However, the addition of glutathione S-transferase (GST) or glutathione peroxidase (GPX) to the above incubation mixture, resulted in decreased immunoreactivity, suggesting GSH may form a transition complex with PN-pretreated hemoglobin and/or partially reduce/modify the treated hemoglobin, thereby increasing the accessibility for the subsequent modification by GST or GPX. Such decreased immunoreactivity indicates that nitrotyrosine and S-nitrosocysteine of treated hemoglobin was, indeed, further modified via (a) converting -NO2 to -NH2 in tyrosine residues, (b) denitrating -NO2 directly/indirectly in tyrosine residues, and/or (c) changing -S-NO to -SH in cysteine residues, or denitrosation. The findings imply similar enzymatic modifications of proteins may also occur in vivo, and therefore play a pivotal role in the NO-related cellular signaling cascade(s).

Direct real-time evaluation of nitration with green fluorescent protein in solution and within human cells reveals the impact of nitrogen dioxide vs. peroxynitrite mechanisms

3-Nitrotyrosyl adducts in proteins have been detected in a wide range of diseases. The mechanisms by which reactive nitrogen oxide species may impede protein function through nitration were examined by using a unique model system, which exploits a critical tyrosyl residue in the fluorophoric pocket of recombinant green fluorescent protein (GFP). Exposure of purified GFP suspended in phosphate buffer to synthetic peroxynitrite in either 0.5 or 5 microM steps resulted in progressively increased 3-nitrotyrosyl immunoreactivity concomitant with disappearance of intrinsic fluorescence (IC(50) approximately 20 microM). Fluorescence from an equivalent amount of GFP expressed within intact MCF-7 tumor cells was largely resistant to this bolus treatment (IC(50) > 250 microM). The more physiologically relevant conditions of either peroxynitrite infusion (1 microM/min) or de novo formation by simultaneous, equimolar generation of nitric oxide (NO) and superoxide (e.g., 3-morpholinosydnonimine; NONOates plus xanthine oxidase/hypoxanthine, menadione, or mitomycin C) were examined. Despite robust oxidation of dihydrorhodamine under each of these conditions, fluorescence decrease of both purified and intracellular GFP was not evident regardless of carbon dioxide presence, suggesting that oxidation and nitration are not necessarily coupled. Alternatively, both extra- and intracellular GFP fluorescence was exquisitely sensitive to nitration produced by heme-peroxidase/hydrogen peroxide-catalyzed oxidation of nitrite. Formation of nitrogen dioxide (NO(2)) during the reaction between NO and the nitroxide 2-phenyl-4,4,5,5-tetramethylimidazole-1-oxyl 3-oxide indicated that NO(2) can enter cells and alter peptide function through tyrosyl nitration. Taken together, these findings exemplified that heme-peroxidase-catalyzed formation of NO(2) may play a pivotal role in inflammatory and chronic disease settings while calling into question the significance of nitration by peroxynitrite.

Comparison of the effect of adenoviral delivery of three superoxide dismutase genes against hepatic ischemia-reperfusion injury

The purpose of this study was to investigate the effectiveness of superoxide dismutase (SOD) overexpression in an acute model of hepatic oxidative stress. Oxidative stress was established using a warm ischemia-reperfusion model, where nearly 70% of the liver was made hypoxic by clamping the hepatic artery and a branch of the portal vein for 1 hr followed by restoration of blood flow. Animals were infected i.v. with 1 x 10(9) plaque-forming units (PFU) of adenovirus containing the transgene for cytosolic Cu/Zn-SOD (Ad.SOD1), mitochondrial Mn-SOD (Ad.SOD2), extracellular Cu/Zn-SOD (Ad.SOD3), or the bacterial reporter gene for beta-galactosidase (Ad.lacZ) 3 days prior to experiments. Ad.SOD1 and Ad.SOD2 caused a three-fold increase in SOD expression and activity in liver compared to Ad.lacZ-treated control animals. Intravenous administration of Ad.SOD3 increased SOD activity slightly in serum but not in liver. Increases in serum transaminases and pathology due to ischemia-reperfusion were blunted by Ad.SOD1 and Ad.SOD2; however, extracellular SOD had no significant effect. Moreover, lipid-derived free radical adducts (a(N) = 15.65 G and a(H)(beta) = 2.78 G) were increased by ischemia-reperfusion. This effect was blunted by about 60% in Ad.SOD1- and Ad.SOD2-infected animals, but was unaffected by Ad.SOD3. However, when high doses of Ad.SOD3 (3 x 10(10) PFU) were administered. serum SOD activity was elevated three-fold and was protective against hepatic ischemia-reperfusion injury under these conditions. These data demonstrate that adenoviral delivery of superoxide dismutase can effectively reduce hepatic oxidative stress.

Protein tyrosine nitration in mouse peritoneal macrophages activated in vitro and in vivo: evidence against an essential role of peroxynitrite

Tyrosine nitration is considered a key reaction of peroxynitrite-triggered tissue injury in inflammatory diseases. We investigated the potential involvement of peroxynitrite in protein tyrosine nitration in isolated murine peritoneal macrophages activated either in vitro with interferon-gamma/lipopolysaccharide or in vivo by priming mice with Corynebacterium parvum (10 mgxkg-1). Both protocols led to release of NO and accumulation of nitrite accompanied by formation of protein-bound 3-nitrotyrosine. Oxidation of dihydrorhodamine 123, a measure of peroxynitrite release, remained close to basal levels upon in vitro activation of the macrophages but was increased approximately twofold in vivo. Tyrosine nitration in macrophages activated in vitro was inhibited by catalase and the time course of nitration correlated with nitrite accumulation, whereas superoxide (O2*-) and H2O2 release occurred at much earlier times. To address the contribution of O2*- and peroxynitrite to in vivo nitration, a O2*- scavenger (MnTBAP; 1 mgxkg-1) was given to C. parvum-primed mice. MnTBAP led to almost complete inhibition of C. parvum-triggered O2*- and peroxynitrite release, whereas nitrite accumulation and formation of 3-nitrotyrosine were less affected ( approximately 50% of controls). These results argue against an essential role of peroxynitrite in protein tyrosine nitration in vivo.

Peroxidases inhibit nitric oxide (NO) dependent bronchodilation: development of a model describing NO-peroxidase interactions

Recent studies demonstrate that nitric oxide (NO) serves as a physiological substrate for mammalian peroxidases [(2000) J. Biol. Chem. 275, 37524]. We now show that eosinophil peroxidase (EPO) and lactoperoxidase (LPO), peroxidases known to be enriched in airways of asthmatic subjects, function as a catalytic sink for NO, modulating its bioavailability and function. Using NO-selective electrodes and direct spectroscopic and rapid kinetic methods, we examined the interactions of NO with EPO and LPO compounds I and II and ferric forms and compared the results to those reported for myeloperoxidase. A unified kinetic model for NO interactions with intermediates of mammalian peroxidases during steady-state catalysis is presented that accommodates unique features observed with each member of the mammalian peroxidase superfamily. Potential functional consequences of peroxidase-NO interactions in asthma are investigated by utilizing organ chamber studies with tracheal rings. In the presence of pathophysiologically relevant levels of peroxidases and H(2)O(2), NO-dependent bronchodilation of preconstricted tracheal rings was reversibly inhibited. Thus, NO interaction with mammalian peroxidases may serve as a potential mechanism for modulating their catalytic activities, influencing the regulation of local inflammatory and infectious events in vivo.

Protein tyrosine nitration in cytokine-activated murine macrophages. Involvement of a peroxidase/nitrite pathway rather than peroxynitrite

Peroxynitrite, formed in a rapid reaction of nitric oxide (NO) and superoxide anion radical (O(2)), is thought to mediate protein tyrosine nitration in various inflammatory and infectious diseases. However, a recent in vitro study indicated that peroxynitrite exhibits poor nitrating efficiency at biologically relevant steady-state concentrations (Pfeiffer, S., Schmidt, K., and Mayer, B. (2000) J. Biol. Chem. 275, 6346-6352). To investigate the molecular mechanism of protein tyrosine nitration in intact cells, murine RAW 264.7 macrophages were activated with immunological stimuli, causing inducible NO synthase expression (interferon-gamma in combination with either lipopolysaccharide or zymosan A), followed by the determination of protein-bound 3-nitrotyrosine levels and release of potential triggers of nitration (NO, O(2)*, H(2)O(2), peroxynitrite, and nitrite). Levels of 3-nitrotyrosine started to increase at 16-18 h and exhibited a maximum at 20-24 h post-stimulation. Formation of O(2) was maximal at 1-5 h and decreased to base line 5 h after stimulation. Release of NO peaked at approximately 6 and approximately 9 h after stimulation with interferon-gamma/lipopolysaccharide and interferon-gamma/zymosan A, respectively, followed by a rapid decline to base line within the next 4 h. NO formation resulted in accumulation of nitrite, which leveled off at about 50 microm 15 h post-stimulation. Significant release of peroxynitrite was detectable only upon treatment of cytokine-activated cells with phorbol 12-myristate-13-acetate, which led to a 2.2-fold increase in dihydrorhodamine oxidation without significantly increasing the levels of 3-nitrotyrosine. Tyrosine nitration was inhibited by azide and catalase and mimicked by incubation of unstimulated cells with nitrite. Together with the striking discrepancy in the time course of NO/O(2) release versus 3-nitrotyrosine formation, these results suggest that protein tyrosine nitration in activated macrophages is caused by a nitrite-dependent peroxidase reaction rather than peroxynitrite.

L-tyrosine and nitric oxide synergize to prevent cytotoxic effects of superoxide

We found previously that the nitric oxide donor DEA/NO enhanced lipid peroxidation, DNA fragmentation, and cytotoxicity in human bronchial epithelial cells (BEAS-2B) when they were cultured in LHC-8 medium containing the superoxide-generating system hypoxanthine/xanthine oxidase (HX/XO). We have now discovered that DEA/NO's prooxidant action can be reversed by raising the L-tyrosine concentration from 30 to 400 microM. DEA/NO also protected the cells when they were cultured in Dulbecco's Modified Eagle's Medium (DMEM), whose standard concentration of L-tyrosine is 400 microM. Similar trends were seen with the colon adenoma cell line CaCo-2. Since HPLC analysis of cell-free DMEM or LHC-8 containing 400 microM L-tyrosine, DEA/NO, and HX/XO revealed no evidence of L-tyrosine nitration, our data suggest the existence of an as-yet uncharacterized mechanism by which L-tyrosine can influence the biochemical and toxicological effects of reactive nitrogen species.

Activation of matrix metalloproteinases by peroxynitrite-induced protein S-glutathiolation via disulfide S-oxide formation

Oxidative stress may cause tissue injury through activation of the precursors of matrix metalloproteinase (proMMPs). In this study, we observed glutathione (GSH)-dependent proMMP activation induced by peroxynitrite, a potent oxidizing agent formed during inflammatory processes. Peroxynitrite strongly activated all three types of purified human proMMPs (proMMP-1, -8, and -9) in the presence of similar concentrations of GSH. Of the potential reaction products between peroxynitrite and GSH, only S-nitroglutathione (GSNO(2)) caused proMMP activation. Extensive S-glutathiolation of the proMMP protein occurred during activation of proMMP by peroxynitrite and GSH, as shown by radiolabeling studies with [(35)S]GSH or [(3)H]GSH. Evidence of appreciable S-glutathiolation persisted even after dithiothreitol and protein-denaturing treatment, however, suggesting that some S-glutathiolation did not occur through formation of simple mixed disulfide. Matrix-assisted laser-desorption ionization-time-of-flight mass spectrometry indicated that not only peroxynitrite plus GSH but also synthetic GSNO(2) produced dithiothreitol-resistant S-glutathiolation of the synthetic peptide PRCGVPD, which is a well conserved Cys-containing sequence of the propeptide autoinhibitory domain of proMMPs. PRCGVPD S-glutathiolation is presumed to be formed through glutathione disulfide S-oxide (GS(O)SR), based on the m/z 1064. Our results illustrate a unique mechanism of oxidative proMMP activation and oxidative tissue injury during inflammation.

Nitration and oxidation of a hydrophobic tyrosine probe by peroxynitrite in membranes: comparison with nitration and oxidation of tyrosine by peroxynitrite in aqueous solution

It has been reported that peroxynitrite will initiate both oxidation and nitration of tyrosine, forming dityrosine and nitrotyrosine, respectively. We compared peroxynitrite-dependent oxidation and nitration of a hydrophobic tyrosine analogue in membranes and tyrosine in aqueous solution. Reactions were carried out in the presence of either bolus addition or slow infusion of peroxynitrite, and also using the simultaneous generation of superoxide and nitric oxide. Results indicate that the level of nitration of the hydrophobic tyrosyl probe located in a lipid bilayer was significantly greater than its level of oxidation to the corresponding dimer. During slow infusion of peroxynitrite, the level of nitration of the membrane-incorporated tyrosyl probe was greater than that of tyrosine in aqueous solution. Evidence for hydroxyl radical formation from decomposition of peroxynitrite in a dimethylformamide/water mixture was obtained by electron spin resonance spin trapping. Mechanisms for nitration of the tyrosyl probe in the membrane are discussed. We conclude that nitration but not oxidation of a tyrosyl probe by peroxynitrite is a predominant reaction in the membrane. Thus, the local environment of target tyrosine residues is an important factor governing its propensity to undergo nitration in the presence of peroxynitrite. This work provides a new perspective on selective nitration of membrane-incorporated tyrosine analogues.

Novel effects of nitric oxide

Nitric oxide (NO), a simple free radical gas, elicits a surprisingly wide range of physiological and pathophysiological effects. NO interacts with soluble guanylate cyclase to evoke many of these effects. However, NO can also interact with molecular oxygen and superoxide radicals to produce reactive nitrogen species that can modify a number of macromolecules including proteins, lipids, and nucleic acids. NO can also interact directly with transition metals. Here, we have reviewed the non--3',5'-cyclic-guanosine-monophosphate-mediated effects of NO including modifications of proteins, lipids, and nucleic acids.

Tyrosine nitration: localisation, quantification, consequences for protein function and signal transduction

The nitration of free tyrosine or protein tyrosine residues generates 3-nitrotyrosine the detection of which has been utilised as a footprint for the in vivo formation of peroxynitrite and other reactive nitrogen species. The detection of 3-nitrotyrosine by analytical and immunological techniques has established that tyrosine nitration occurs under physiological conditions and levels increase in most disease states. This review provides an updated, comprehensive and detailed summary of the tissue, cellular and specific protein localisation of 3-nitrotyrosine and its quantification. The potential consequences of nitration to protein function and the pathogenesis of disease are also examined together with the possible effects of protein nitration on signal transduction pathways and on the metabolism of proteins.

Reaction of superoxide and nitric oxide with peroxynitrite. Implications for peroxynitrite-mediated oxidation reactions in vivo

Peroxynitrite (ONOO(-)/ONOOH), the product of the diffusion-limited reaction of nitric oxide (*NO) with superoxide (O(-*)(2)), has been implicated as an important mediator of tissue injury during conditions associated with enhanced *NO and O(-*)(2) production. Although several groups of investigators have demonstrated substantial oxidizing and cytotoxic activities of chemically synthesized peroxynitrite, others have proposed that the relative rates of *NO and production may be critical in determining the reactivity of peroxynitrite formed in situ (Miles, A. M., Bohle, D. S., Glassbrenner, P. A., Hansert, B., Wink, D. A., and Grisham, M. B. (1996) J. Biol. Chem. 271, 40-47). In the present study, we examined the mechanisms by which excess O(-*)(2) or *NO production inhibits peroxynitrite-mediated oxidation reactions. Peroxynitrite was generated in situ by the co-addition of a chemical source of *NO, spermineNONOate, and an enzymatic source of O(-*)(2), xanthine oxidase, with either hypoxanthine or lumazine as a substrate. We found that the oxidation of the model compound dihydrorhodamine by peroxynitrite occurred via the free radical intermediates OH and NO(2), formed during the spontaneous decomposition of peroxynitrite and not via direct reaction with peroxynitrite. The inhibitory effect of excess O(-*)(2) on the oxidation of dihydrorhodamine could not be ascribed to the accumulation of the peroxynitrite scavenger urate produced from the oxidation of hypoxanthine by xanthine oxidase. A biphasic oxidation profile was also observed upon oxidation of NADH by the simultaneous generation of *NO and O(-*)(2). Conversely, the oxidation of glutathione, which occurs via direct reaction with peroxynitrite, was not affected by excess production of *NO. We conclude that the oxidative processes initiated by the free radical intermediates formed from the decomposition of peroxynitrite are inhibited by excess production of *NO or O(-*)(2), whereas oxidative pathways involving a direct reaction with peroxynitrite are not altered. The physiological implications of these findings are discussed.

Enhanced vascular permeability in solid tumor involving peroxynitrite and matrix metalloproteinases

Peroxynitrite (ONOO(-)), which is generated from nitric oxide (NO) and superoxide anion (O(2)(.-)) under pathological conditions, plays an important role in pathophysiological processes. Activation of matrix metalloproteinases (MMPs) contributes to tumor angiogenesis and metastasis. NO mediates the enhanced vascular permeability and retention (EPR) effect in solid tumors, and ONOO(-)activates proMMP to MMP in vitro. In this study, we examined the role of ONOO(-)in the EPR effect in solid tumors and normal tissues as related to MMP activation. Authentic ONOO(-), at 50 nmol or higher concentrations, induced the enhanced vascular permeability in normal dorsal skin of mice. ONOO(-)scavengers ebselen and uric acid significantly suppressed the EPR effect in mouse sarcoma 180 (S-180) tumors. Indirect evidence for formation of ONOO(-)in S-180 and mouse colon adenocarcinoma (C-38) tumors included strong immunostaining for nitrotyrosine in the tumor tissue, predominantly surrounding the tumor vessels. MMP inhibitor BE16627B (66.6 mg / kg i.v., given 2 times) or SI-27 (10 mg / kg i.p., given 2 times) significantly suppressed the ONOO(-)-induced EPR effect in S-180 tumors and in normal skin. Soybean trypsin inhibitor (Kunitz type), broad-spectrum proteinase inhibitor ovomacroglobulin, and bradykinin receptor antagonist HOE 140 also significantly suppressed the ONOO(-)-induced EPR effect in normal skin tissues. These data suggest that ONOO(-)may be involved in and promote the EPR effect in tumors, which could be mediated partly through activation of MMPs and a subsequent proteinase cascade to generate potent vasoactive mediators such as bradykinin.

Role of free radicals in viral pathogenesis and mutation

Oxygen radicals and nitric oxide (NO) are generated in excess in a diverse array of microbial infections. Emerging concepts in free radical biology are now shedding light on the pathogenesis of various diseases. Free-radical induced pathogenicity in virus infections is of great importance, because evidence suggests that NO and oxygen radicals such as superoxide are key molecules in the pathogenesis of various infectious diseases. Although oxygen radicals and NO have an antimicrobial effect on bacteria and protozoa, they have opposing effects in virus infections such as influenza virus pneumonia and several other neurotropic virus infections. A high output of NO from inducible NO synthase, occurring in a variety of virus infections, produces highly reactive nitrogen oxide species, such as peroxynitrite, via interaction with oxygen radicals and reactive oxygen intermediates. The production of these various reactive species confers the diverse biological functions of NO. The reactive nitrogen species cause oxidative tissue injury and mutagenesis through oxidation and nitration of various biomolecules. The unique biological properties of free radicals are further illustrated by recent evidence showing accelerated viral mutation by NO-induced oxidative stress. NO appears to affect a host's immune response, with immunopathological consequences. For example, NO is reported to suppress type 1 helper T cell-dependent immune responses during infections, leading to type 2 helper T cell-biased immunological host responses. NO-induced immunosuppression may thus contribute to the pathogenesis of virus infections and help expansion of quasispecies population of viral pathogens. This review describes the pathophysiological roles of free radicals in the pathogenesis of viral disease and in viral mutation as related to both nonspecific inflammatory responses and immunological host reactions modulated by NO.

Nitric oxide and the regulation of gene expression

During the past 15 years, nitric oxide (NO) and NO synthases have become an important research topic in cellular and molecular biology. NO is produced by many if not all mammalian cells and fulfils a broad spectrum of signaling functions in physiological and pathophysiological processes. In this review, recent advances in our understanding of the mechanisms by which NO regulates the expression of eukaryotic genes will be summarized. The currently available data illustrate that NO has multiple molecular targets: it can not only directly influence the activity of transcription factors but also modulates upstream signaling cascades, mRNA stability and translation, as well as the processing of the primary gene products.

Role of nitric oxide and superoxide in acute cardiac allograft rejection in rats

The role of NO and superoxide (O(2)(-)) in tissue injury during cardiac allograft rejection was investigated by using a rat ex vivo organ perfusion system. Excessive NO production and inducible NO synthase (iNOS) expression were observed in cardiac allografts at 5 days after cardiac transplantation, but not in cardiac isografts, as identified by electron spin resonance spectroscopy and Northern blotting. Cardiac isografts or allografts obtained on Day 5 after transplantation were perfused with Krebs bicarbonate buffer with or without various antidotes for NO or O(2)-, including N(omega)-monomethyl-L-arginine (L-NMMA; 1 mM), 2-phenyl-4,4,5, 5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO; 100 microM), 4-amino-6-hydroxypyrazolo[3,4-d]pyrimidine (AHPP; a xanthine oxidase inhibitor; 100 microM), and superoxide dismutase (SOD; 100 units/ml). Treatment of the cardiac allografts with PTIO showed most remarkable improvement of the cardiac injury as revealed by significant reduction in aspartate transaminase, lactate dehydrogenase, and creatine phosphokinase concentrations in the perfusate. Similar but less potent protective effect on the allograft injury was observed by treatment with L-NMMA, AHPP, and SOD. Immunohistochemical analyses for iNOS and nitrotyrosine indicated that iNOS is mainly expressed by macrophages infiltrating the allograft tissues, and nitrotyrosine formation was demonstrated not only in macrophages but also in cardiac myocytes of the allografts, providing indirect evidence for the generation of peroxynitrite during allograft rejection. Our results suggest that tissue injury in rat cardiac allografts during acute rejection is mediated by both NO and O(2)(-), possibly through peroxynitrite formation.

Nitric oxide and virus infection

Nitric oxide (NO) has complex and diverse functions in physiological and pathophysiological phenomena. The mechanisms of many events induced by NO are now well defined, so that a fundamental understanding of NO biology is almost established. Accumulated evidence suggests that NO and oxygen radicals such as superoxide are key molecules in the pathogenesis of various infectious diseases. NO biosynthesis, particularly through expression of an inducible NO synthase (iNOS), occurs in a variety of microbial infections. Although antimicrobial activity of NO is appreciated for bacteria and protozoa, NO has opposing effects in virus infections such as influenza virus pneumonia and certain other neurotropic virus infections. iNOS produces an excessive amount of NO for long periods, which allows generation of a highly reactive nitrogen oxide species, peroxynitrite, via a radical coupling reaction of NO with superoxide. Thus, peroxynitrite causes oxidative tissue injury through potent oxidation and nitration reactions of various biomolecules. NO also appears to affect a host's immune response, with immunopathological consequences. For example, overproduction of NO in virus infections in mice is reported to suppress type 1 helper T-cell-dependent immune responses, leading to type 2 helper T-cell-biased immunological host responses. Thus, NO may be a host response modulator rather than a simple antiviral agent. The unique biological properties of NO are further illustrated by our recent data suggesting that viral mutation and evolution may be accelerated by NO-induced oxidative stress. Here, we discuss these multiple roles of NO in pathogenesis of virus infections as related to both non-specific inflammatory responses and immunological host reactions modulated by NO during infections in vivo.

Superoxide reacts with nitric oxide to nitrate tyrosine at physiological pH via peroxynitrite

Tyrosine nitration is a widely used marker of peroxynitrite (ONOO(-)) produced from the reaction of nitric oxide with superoxide. Pfeiffer and Mayer (Pfeiffer, S., and Mayer, B. (1998) J. Biol. Chem. 273, 27280-27285) reported that superoxide produced from hypoxanthine plus xanthine oxidase in combination with nitric oxide produced from spermine NONOate did not nitrate tyrosine at neutral pH. They suggested that nitric oxide and superoxide at neutral pH form a less reactive intermediate distinct from preformed alkaline peroxynitrite that does not nitrate tyrosine. Using a stopped-flow spectrophotometer to rapidly mix potassium superoxide with nitric oxide at pH 7.4, we report that an intermediate spectrally and kinetically identical to preformed alkaline cis-peroxynitrite was formed in 100% yield. Furthermore, this intermediate nitrated tyrosine in the same yield and at the same rate as preformed peroxynitrite. Equivalent concentrations of nitric oxide under aerobic conditions in the absence of superoxide did not produce detectable concentrations of nitrotyrosine. Carbon dioxide increased the efficiency of nitration by nitric oxide plus superoxide to the same extent as peroxynitrite. In experiments using xanthine oxidase as a source of superoxide, tyrosine nitration was substantially inhibited by urate formed from hypoxanthine oxidation, which was sufficient to account for the lack of tyrosine nitration previously reported. We conclude that peroxynitrite formed from the reaction of nitric oxide with superoxide at physiological pH remains an important species responsible for tyrosine nitration in vivo.