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

Mathematical and computational models of oxidative and nitrosative stress

The importance of nitric oxide (NO), superoxide (O2-), and peroxynitrite (ONOO-), interactions in physiologic functions and pathophysiological conditions such as cardiovascular disease, hypertension, and diabetes have been established extensively in in vivo and in vitro studies. Despite intense investigation of NO, O2-, and ONOO- biochemical interactions, fundamental questions regarding the role of these molecules remain unanswered. Mathematical models based on fundamental principles of mass balance and reaction kinetics have provided significant results in the case of NO. However, the models that include interaction of NO, O2-, and ONOO- have been few because of the complexity of these interactions. Not only do these mathematical and computational models provided quantitative knowledge of distributions and concentrations of NO, O2-, and ONOO- under normal physiologic and pathophysiologic conditions, they also can help to answer specific hypotheses. The focus of this review article is on the models that involve more than one of the 3 molecules (NO, O2-, and ONOO-). Specifically, kinetic models of O2- dismutase and tyrosine nitration and biotransport models in the microcirculation are reviewed. In addition, integrated experimental and computational models of dynamics of NO/O2-/ONOO- in diverse systems are reviewed.

Regulation by mitochondrial superoxide and NADPH oxidase of cellular formation of nitrated cyclic GMP: potential implications for ROS signalling

8-Nitro-cGMP (8-nitroguanosine 3',5'-cyclic monophosphate) is a nitrated derivative of cGMP, which can function as a unique electrophilic second messenger involved in regulation of an antioxidant adaptive response in cells. In the present study, we investigated chemical and biochemical regulatory mechanisms involved in 8-nitro-cGMP formation, with particular focus on the roles of ROS (reactive oxygen species). Chemical analyses demonstrated that peroxynitrite-dependent oxidation and myeloperoxidase-dependent oxidation of nitrite in the presence of H2O2 were two major pathways for guanine nucleotide nitration. Among the guanine nucleotides examined, GTP was the most sensitive to peroxynitrite-mediated nitration. Immunocytochemical and tandem mass spectrometric analyses revealed that formation of 8-nitro-cGMP in rat C6 glioma cells stimulated with lipopolysaccharide plus pro-inflammatory cytokines depended on production of both superoxide and H2O2. Using the mitochondria-targeted chemical probe MitoSOX Red, we found that mitochondria-derived superoxide can act as a direct determinant of 8-nitro-cGMP formation. Furthermore, we demonstrated that Nox2 (NADPH oxidase 2)-generated H2O2 regulated mitochondria-derived superoxide production, which suggests the importance of cross-talk between Nox2-dependent H2O2 production and mitochondrial superoxide production. The results of the present study suggest that 8-nitro-cGMP can serve as a unique second messenger that may be implicated in regulating ROS signalling in the presence of NO.

Mitochondrial oxidative stress and epilepsy in SOD2 deficient mice: attenuation by a lipophilic metalloporphyrin

Epileptic seizures are a common feature associated with inherited mitochondrial diseases. This study investigated the role of mitochondrial oxidative stress in epilepsy resulting from mitochondrial dysfunction using cross-bred mutant mice lacking mitochondrial manganese superoxide dismutase (MnSOD or SOD2) and a lipophilic metalloporphyrin catalytic antioxidant. Video-EEG monitoring revealed that in the second to third week of postnatal life (P14-P21) B6D2F2 Sod2(-/-) mice exhibited frequent spontaneous motor seizures providing evidence that oxidative stress-induced mitochondrial dysfunction may contribute to epileptic seizures. To confirm the role of mitochondrial oxidative stress in epilepsy a newly developed lipophilic metalloporphyrin, AEOL 11207, with high potency for catalytic removal of endogenously generated reactive oxygen species was utilized. AEOL 11207-treated Sod2(-/-) mice showed a significant decrease in both the frequency and duration of spontaneous seizures but no effect on seizure severity. A significant increase in the average lifespan of AEOL 11207-treated Sod2(-/-) mice compared to vehicle-treated Sod2(-/-) mice was also observed. Indices of mitochondrial oxidative stress and damage (aconitase inactivation, 3-nitrotyrosine formation, and depletion of reduced coenzyme A) and ATP levels affecting neuronal excitability were significantly attenuated in the brains of AEOL 11207-treated Sod2(-/-) mice compared to vehicle-treated Sod2(-/-) mice. The occurrence of epileptic seizures in Sod2(-/-) mice and the ability of catalytic antioxidant therapy to attenuate seizure activity, mitochondrial dysfunction, and ATP levels suggest that ongoing mitochondrial oxidative stress can contribute to epilepsy associated with mitochondrial dysfunction and disease.

HIV-1 coinfection and morphine coexposure severely dysregulate hepatitis C virus-induced hepatic proinflammatory cytokine release and free radical production: increased pathogenesis coincides with uncoordinated host defenses

Coinfection with human immunodeficiency virus type-1 (HIV-1) and hepatitis C virus (HCV) is a global problem that is more prevalent in injection drug users because they have a higher risk for acquiring both viruses. The roles of inflammatory cytokines and oxidative stress were examined in HIV-1- and HCV-coinfected human hepatic cells. Morphine (the bioactive product of heroin), HIV-1 Tat and the MN strain gp120 (gp120(MN)) proteins, and X4 HIV-1(LAI/IIIB) and R5 HIV-1(SF162) isolates were used to study the mechanisms of disease progression in HCV (JFH1)-infected Huh7.5.1 cell populations. HCV increased tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) release and augmented production of reactive oxygen species (ROS), nitric oxide (NO), and 3-nitrotyrosine (3-NT) in Huh7.5.1 cells. Morphine preferentially affected R5-tropic, but not X4-tropic, HIV-1 interactions with Huh7.5.1 cells. HIV-1 proteins or isolates increased cytokine release in HCV-infected cells, while adding morphine to coinfected cells caused complex imbalances, significantly disrupting cytokine secretion depending on the cytokine, morphine concentration, exposure duration, and particular pathogen involved. Production of ROS, NO, and 3-NT increased significantly in HCV- and HIV-1-coexposed cells while exposure to morphine further increased ROS. The proteasome inhibitor MG132 significantly decreased oxyradicals, cytokine levels, and HCV protein levels. Our findings indicate that hepatic inflammation is increased by combined exposure to HCV and HIV-1, that the ubiquitin-proteasome system and NF-κB contribute to key aspects of the response, and that morphine further exacerbates the disruption of host defenses. The results suggest that opioid abuse and HIV-1 coinfection each further accelerate HCV-mediated liver disease by dysregulating immune defenses.

Pathogenesis and biomarkers of carcinogenesis in ulcerative colitis

One of the most serious complications of ulcerative colitis is the development of colorectal cancer. Screening patients with ulcerative colitis by standard histological examination of random intestinal biopsy samples might be inefficient as a method of cancer surveillance. This Review focuses on the current understanding of the pathogenesis of ulcerative colitis-associated colorectal cancer and how this knowledge can be transferred into patient management to assist clinicians and pathologists in identifying patients with ulcerative colitis who have an increased risk of colorectal cancer. Inflammation-driven mechanisms of DNA damage, including the generation and effects of reactive oxygen species, microsatellite instability, telomere shortening and chromosomal instability, are reviewed, as are the molecular responses to genomic stress. We also discuss how these mechanisms can be translated into usable biomarkers. Although progress has been made in the understanding of inflammation-driven carcinogenesis, markers based on these findings possess insufficient sensitivity or specificity to be usable as reliable biomarkers for risk of colorectal cancer development in patients with ulcerative colitis. However, screening for mutations in p53 could be relevant in the surveillance of patients with ulcerative colitis. Several other new biomarkers, including senescence markers and α-methylacyl-CoA-racemase, might be future candidates for preneoplastic markers in ulcerative colitis.

Nucleotides function as endogenous chemical sensors for oxidative stress signaling

Oxidized and nitrated nucleotides including 8-oxogunanine and 8-nitroguanine derivatives such as 8-nitroguanosine 3',5'-cyclic monophosphate were generated by reactive nitrogen oxides and reactive oxygen species in cultured cells and in tissues. 8-oxoguanine and 8-nitroguanine in DNA and RNA are potentially mutagenic, and the former also induces cell death. Some derivative, 8-nitroguanosine 3',5'-cyclic monophosphate a major nitrated guanine nucleotide, was identified as a novel second messenger. Surprisingly, the amount of 8-nitroguanosine 3',5'-cyclic monophosphate generated was found to be higher than that of guanosine 3',5'-cyclic monophosphate in cells expressing inducible nitric oxide synthase. More important, 8-nitroguanosine 3',5'-cyclic monophosphate is electrophilic and reacted efficiently with sulfhydryls of proteins to produce a novel posttranslational modification (named S-guanylation) via guanosine 3',5'-cyclic monophosphate adduction. For example, 8-nitroguanosine 3',5'-cyclic monophosphate-induced S-guanylation of Kelch-like ECH-associated protein 1 led to NF-E2-related factor activation and induction of antioxidant enzymes. 8-nitroguanosine 3',5'-cyclic monophosphate may thus protect cells against oxidative stress-related cytotoxicity. Therefore, although chemically modified nucleotides produced via oxidative and nitrative stress are regarded simply as endogenous mutagens, the endogenous nucleotides stored in cells per se may serve functionally as a sensing mechanism for reactive nitrogen oxides and oxygen species to induce cellular adaptive responses to oxidative stress.

Downstream mechanisms of nitric oxide-mediated skeletal muscle glucose uptake during contraction

There is evidence that nitric oxide (NO) is required for the normal increases in skeletal muscle glucose uptake during contraction, but the mechanisms involved have not been elucidated. We examined whether NO regulates glucose uptake during skeletal muscle contractions via cGMP-dependent or cGMP-independent pathways. Isolated extensor digitorum longus (EDL) muscles from mice were stimulated to contract ex vivo, and potential NO signaling pathways were blocked by the addition of inhibitors to the incubation medium. Contraction increased (P < 0.05) NO synthase (NOS) activity (∼40%) and dichlorofluorescein (DCF) fluorescence (a marker of oxidant levels; ∼95%), which was prevented with a NOS inhibitor N(G)-monomethyl-L-arginine (L-NMMA), and antioxidants [nonspecific antioxidant, N-acetylcysteine (NAC); thiol-reducing agent, DTT], respectively. L-NMMA and NAC both attenuated glucose uptake during contraction by ∼50% (P < 0.05), and their effects were not additive. Neither the guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one, which prevents the formation of cGMP, the cGMP-dependent protein (PKG) inhibitor Rp-8-bromo-β-phenyl-1,N2-ethenoguanosine 3',5'-cyclic monophosphorothioate sodium salt nor white light, which breaks S-nitrosylated bonds, affects glucose uptake during contraction; however, DTT attenuated (P < 0.05) contraction-stimulated glucose uptake (by 70%). NOS inhibition and antioxidant treatment reduced contraction-stimulated increases in protein S-glutathionylation and tyrosine nitration (P < 0.05), without affecting AMPK or p38 MAPK phosphorylation. In conclusion, we provide evidence to suggest that NOS-derived oxidants regulate skeletal muscle glucose uptake during ex vivo contractions via a cGMP/PKG-, AMPK-, and p38 MAPK-independent pathway. In addition, it appears that NO and ROS may regulate skeletal muscle glucose uptake during contraction through a similar pathway.

Scuba diving increases erythrocyte and plasma antioxidant defenses and spares NO without oxidative damage

PURPOSE

The aim of the present work was to study the effects of a single scuba diving immersion to high depth on erythrocyte and plasma antioxidant defenses, on erythrocyte cellular damage, and on nitric oxide (NO) production.

METHODS

Seven male preprofessional divers performed an immersion at a depth of 40 m for a total time of 25 min. Blood samples were obtained before the diving session after overnight fasting, immediately after diving, and 3 h after the diving session was finished. Erythrocytes and plasma fractions were purified.

RESULTS

No significant differences were found in circulating erythrocytes, bilirubin, and hemoglobin concentration attributed to diving. Hematocrit levels were reduced after diving because of the reduction of erythrocyte size that was maintained after 3 h of recovery at the surface. Leukocyte counts significantly increased at recovery (38 +/- 4%). In erythrocytes, glutathione peroxidase activity significantly increased (18 +/- 4%) at recovery. A rise in plasma catalase activity (38 +/- 6%) immediately occurred after diving, returning to basal values after recovery. Plasma superoxide dismutase activity significantly increased (58 +/- 7%) during recovery. Markers of oxidative damage in both erythrocytes and plasma such as malondialdehyde and protein carbonyl derivates remained unchanged after diving. Nitrite levels significantly rose in plasma and erythrocytes (85 +/- 8% and 52 +/- 6%, respectively) at recovery.

CONCLUSION

Scuba diving session induced an antioxidant response in plasma and erythrocytes without the appearance of cellular damage and an increase in NO, which can be related with its vasodilator role.

Peroxynitrite is the major species formed from different flux ratios of co-generated nitric oxide and superoxide: direct reaction with boronate-based fluorescent probe

There is much interest in the nitration and oxidation reaction mechanisms initiated by superoxide radical anion (O(2)()) and nitric oxide ((*)NO). It is well known that O(2) and (*)NO rapidly react to form a potent oxidant, peroxynitrite anion (ONOO(-)). However, indirect measurements with the existing probes (e.g. dihydrorhodamine) previously revealed a bell-shaped response to co-generated (*)NO and O(2) fluxes, with the maximal yield of the oxidation or nitration product occurring at a 1:1 ratio. These results raised doubts on the formation of ONOO(-) per se at various fluxes of (*)NO and O(2). Using a novel fluorogenic probe, coumarin-7-boronic acid, that reacts stoichiometrically and rapidly with ONOO(-) (k = 1.1 x 10(6) m(-1)s(-1)), we report that ONOO(-) formation increased linearly and began to plateau after reaching a 1:1 ratio of co-generated (*)NO and O(2) fluxes. We conclude that ONOO(-) is formed as the primary intermediate during the reaction between (*)NO and O(2) co-generated at different fluxes.

Reduced nitro-oxidative stress and neural cell death suggests a protective role for microglial cells in TNFalpha-/- mice in ischemic retinopathy

PURPOSE

Neovascularization occurs in response to tissue ischemia and growth factor stimulation. In ischemic retinopathies, however, new vessels fail to restore the hypoxic tissue; instead, they infiltrate the transparent vitreous. In a model of oxygen-induced retinopathy (OIR), TNFalpha and iNOS, upregulated in response to tissue ischemia, are cytotoxic and inhibit vascular repair. The aim of this study was to investigate the mechanism for this effect.

METHODS

Wild-type C57/BL6 (WT) and TNFalpha(-/-) mice were subjected to OIR by exposure to 75% oxygen (postnatal days 7-12). The retinas were removed during the hypoxic phase of the model. Retinal cell death was determined by TUNEL staining, and the microglial cells were quantified after Z-series capture with a confocal microscope. In situ peroxynitrite and superoxide were measured by using the fluorescent dyes DCF and DHE. iNOS, nitrotyrosine, and arginase were analyzed by real-time PCR, Western blot analysis, and activity determined by radiolabeled arginine conversion. Astrocyte coverage was examined after GFAP immunostaining.

RESULTS

The TNFalpha(-/-) animals displayed a significant reduction in TUNEL-positive apoptotic cells in the inner nuclear layer of the avascular retina compared with that in the WT control mice. The reduction coincided with enhanced astrocytic survival and an increase in microglial cells actively engaged in phagocytosing apoptotic debris that displayed low ROS, RNS, and NO production and high arginase activity.

CONCLUSIONS

Collectively, the results suggest that improved vascular recovery in the absence of TNFalpha is associated with enhanced astrocyte survival and that both phenomena are dependent on preservation of microglial cells that display an anti-inflammatory phenotype during the early ischemic phase of OIR.

4-Hydr-oxy-3-meth-oxy-5-nitro-aceto-phenone (5-nitro-apocynin)

The title mol-ecule, C(9)H(9)NO(5), is close to planar (r.m.s. deviation from the mean plane of the non-H atoms = 0.058 Å). The OH group forms a bifurcated O-H⋯(O,O) hydrogen bond, with the intra-molecular component to a nitro O atom and the inter-molecular component to a keto O atom, the latter resulting in chains along [20]. A C-H⋯O inter-action reinforces the packing.

Chemical model systems for cellular nitros(yl)ation reactions

S-nitros(yl)ation belongs to the redox-based posttranslational modifications of proteins but the underlying chemistry is controversial. In contrast to current concepts involving the autoxidation of nitric oxide ((.)NO, nitrogen monoxide), we and others have proposed the formation of peroxynitrite (oxoperoxonitrate (1(-))as an essential intermediate. This requires low cellular fluxes of (.)NO and superoxide (UO2(-)), for which model systems have been introduced. We here propose two new systems for nitros(yl)ation that avoid the shortcomings of previous models. Based on the thermal decomposition of 3-morpholinosydnonimine,equal fluxes of (.)NO and UO2(-) were generated and modulated by the addition of (.)NO donors or Cu,Zn superoxide dismutase. As reactants for S-nitros(yl)ation, NADP+-dependent isocitrate dehydrogenase and glutathione were employed, for which optimal S-nitros(yl)ation was observed at nanomolar fluxes of (.)NO and UO2(-) at a ratio of about 3:1. The previously used reactants phenol and diaminonaphthalene (C- and Nnitrosation)demonstrated potential participation of multiple pathways for nitros(yl)ation. According to our data, neither peroxynitrite nor autoxidation of UNO was as efficient as the 3 (.)NO/1 UO2(-) system in mediating S-nitros(yl)ation. In theory this could lead to an elusive nitrosonium (nitrosyl cation)-like species in the first step and to N2O3 in the subsequent reaction. Which of these two species or whether both together will participate in biological S-nitros(yl)ation remains to be elucidated. Finally, we developed several hypothetical scenarios to which the described (.)NO/UO2-flux model could apply, providing conditions that allow either direct electrophilic substitution at a thiolate or S-nitros(yl)ation via transnitrosation from S-nitrosoglutathione.

Exogenous luminal nitric oxide exacerbates esophagus tissue damage in a reflux esophagitis model of rats

OBJECTIVE

Cytotoxic concentrations of nitric oxide are generated luminally at the gastroesophageal junction through the entero-salivary recirculation of dietary nitrate in humans. The site of luminal nitric oxide generation shifts to the lower esophagus when gastric acid is refluxed into the esophagus. The aim of this study was to investigate the influence of persistent administration of exogenous nitric oxide on esophageal damage.

MATERIAL AND METHODS

0.1% sodium nitrite and/or 1% ascorbic acid was administered in an established rat acid-refluxed esophagitis model. Co-administration of both reactants in this model is thought to induce high concentrations of nitric oxide luminally in the esophagus by an acid-catalyzed chemical reaction when refluxed gastric acid is present. The tissue damage was evaluated by a macroscopic lesion index and myeloperoxidase activity. Nitrotyrosin was assessed immunohistochemically as a footprint of peroxynitrite formation.

RESULTS

Co-administration of sodium nitrite and ascorbic acid induced a 4- to 5-fold increase in the esophageal damage compared with baseline reflux esophagitis, while the damage was unchanged when either of the reagents alone was given. Nitrotyrosine was strongly stained in the tissue from the co-administration. Treatment of superoxide scavengers efficiently prevented the exacerbation of esophageal damage by exogenous nitric oxide exposure, suggesting an essential role of superoxide in esophageal damage.

CONCLUSIONS

Exogenous luminal nitric oxide greatly exacerbated the tissue damage of reflux esophagitis. Diffusion of the luminal nitric oxide into the adjacent superoxide-enriched inflamed tissue of the esophagus could lead to the production of the highly toxic agent peroxynitrite, thus causing exacerbation of the esophageal damage.

Cytoprotective function of heme oxygenase 1 induced by a nitrated cyclic nucleotide formed during murine salmonellosis

Signaling mechanisms of NO-mediated host defense are yet to be elucidated. In this study, we report a unique signal pathway for cytoprotection during Salmonella infection that involves heme oxygenase 1 (HO-1) induced by a nitrated cyclic nucleotide, 8-nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP). Wild-type C57BL/6 mice and C57BL/6 mice lacking inducible NO synthase (iNOS) were infected with Salmonella enterica serovar Typhimurium LT2. HO-1 was markedly up-regulated during the infection, the level being significantly higher in wild-type mice than in iNOS-deficient mice. HO-1 up-regulation was associated with 8-nitro-cGMP formation detected immunohistochemically in Salmonella-infected mouse liver and peritoneal macrophages. 8-Nitro-cGMP either exogenously added or formed endogenously induced HO-1 in cultured macrophages infected with Salmonella. HO-1 inhibition by polyethylene glycol-conjugated zinc-protoporphyrin IX impaired intracellular killing of bacteria in mouse liver and in both RAW 264 cells and peritoneal macrophages. Infection-associated apoptosis was also markedly increased in polyethylene glycol-conjugated zinc-protoporphyrin IX-treated mouse liver cells and cultured macrophages. This effect of HO-1 inhibition was further confirmed by using HO-1 short interfering RNA in peritoneal macrophages. Our results suggest that HO-1 induced by NO-mediated 8-nitro-cGMP formation contributes, via its potent cytoprotective function, to host defense during murine salmonellosis.

Generation of drug-resistant mutants of Helicobacter pylori in the presence of peroxynitrite, a derivative of nitric oxide, at pathophysiological concentration

In the present study it has been shown that the reactive nitrogen species, peroxynitrite, can cause at least a 7.1-fold increase in the frequency of occurrence of drug-resistant mutants of Helicobacter pylori at a pathophysiological concentration (e.g. 1.0 microM) and in the presence of CLR. Furthermore, the CLR MIC of these resistant H. pylori strains increased by at least 250 times or higher in CLR susceptibility. In the 45 resistant strains, the modification of 23S rRNA A2142G was the predominant mutation (22/45), followed by A2143G (17/45) within the sequences of 23S rRNA. The other mutants were one each (1/45) in A2142T, and T2269G, and two each (2/45) in C2695G and T1944C, respectively. These results show that the inflammatory host reaction involving induction of reactive oxygen species (e.g. O(.-)2), and the inducible form of nitric oxide synthase, is a significant cause of mutation via peroxynitrite formation, particularly in drug-resistant bacterial strains.

Reactive oxygen species- and nitric oxide-mediated lung inflammation and mitochondrial dysfunction in wild-type and iNOS-deficient mice exposed to diesel exhaust particles

Pulmonary responses to diesel exhaust particles (DEP) exposure are mediated through enhanced production of reactive oxygen species (ROS) and nitric oxide (NO) by alveolar macrophages (AM). The current study examined the differential roles of ROS and NO in DEP-induced lung injury using C57B/6J wild-type (WT) and inducible NO synthase knockout (iNOS KO) mice. Mice exposed by pharyngeal aspiration to DEP or carbon black particles (CB) (35 mg/kg) showed an inflammatory profile that included neutrophil infiltration, increased lactate dehydrogenase (LDH) activity, and elevated albumin content in bronchoalveolar lavage fluid (BALF) at 1, 3, and 7 d postexposure. The organic extract of DEP (DEPE) did not induce an inflammatory response. Comparing WT to iNOS KO mice, the results show that NO enhanced DEP-induced neutrophils infiltration and plasma albumin content in BALF and upregulated the production of the pro-inflammatory cytokine interleukin 12 (IL-12) by AM. DEP-exposed AM from iNOS KO mice displayed diminished production of IL-12 and, in response to ex vivo lipopolysaccharide (LPS) challenge, decreased production of IL-12 but increased production of IL-10 when compared to cells from WT mice. DEP, CB, but not DEPE, induced DNA damage and mitochondria dysfunction in AM, however, that is independent of cellular production of NO. These results demonstrate that DEP-induced immune/inflammatory responses in mice are regulated by both ROS- and NO-mediated pathways. NO did not affect ROS-mediated mitochondrial dysfunction and DNA damage but upregulated IL-12 and provided a counterbalance to the ROS-mediated adaptive stress response that downregulates IL-12 and upregulates IL-10.

Induced nitric oxide synthase as a major player in the oncogenic transformation of inflamed tissue

Nitric oxide (NO) is a free radical that is involved in the inflammatory process and carcinogenesis. There are four nitric oxide synthase enzymes involved in NO production: induced nitric oxide synthase (iNOS), endothelial NO synthase (eNOS), neural NO synthase (nNOS), and mitochondrial NOS. iNOS is an inducible and key enzyme in the inflamed tissue. Recent literatures indicate that NO as well as iNOS and eNOS can modulate cancer-related events including nitro-oxidative stress, apoptosis, cell cycle, angio-genesis, invasion, and metastasis. This chapter focuses on linking NO/iNOS/eNOS to inflammation and carcinogenesis from experimental evidence to potential targets on cancer prevention and treatment.

Enhanced nitrosative stress during Trypanosoma cruzi infection causes nitrotyrosine modification of host proteins: implications in Chagas' disease

Oxidative/nitrosative stress may be important in the pathology of Chagas' disease. Experimental animals infected by Trypanosoma cruzi showed an early rise in myocardial and peripheral protein-3-nitrotyrosine (3NT) and protein-carbonyl formation that persisted during the chronic stage of disease. In comparison, experimental chronic ethanol-induced cardiomyopathy was slow to develop and presented with a moderate increase in oxidative stress and minimal to no nitrosative stress after long-term alcohol feeding of animals. The oxidative stress in both chagasic animals and animals with ethanol-induced cardiomyopathy correlated with the persistence of reactive oxygen species-producing inflammatory intermediates. Protein-3NT formation in T. cruzi-infected animals was associated with enhanced nitric oxide expression (inferred by nitrite/nitrate levels) and myeloperoxidase activity, suggesting that both peroxynitrite- and myeloperoxidase-mediated pathways contribute to increased protein nitration in Chagas' disease. We used one- and two-dimensional gel electrophoresis and Western blot analysis to identify disease-specific plasma proteins that were 3NT-modified in T. cruzi-infected animals. Nitrated protein spots (56 in total) were sequenced by matrix-assisted laser desorption ionization/time of flight mass spectrometry and liquid chromatography-tandem mass spectrometry and identified by a homology search of public databases. Clustering of 3NT-modified proteins according to their functional characteristics revealed that the nitration of immunoglobulins, apolipoprotein isoforms, and other proteins might perturb their functions and be important in the pathology of Chagas' disease. We also showed that nitrated peptides derived from titin and alpha-actin were released into the plasma of patients with Chagas' disease. Such modified proteins may be useful biomarkers of Chagas' disease.

The chemistry of peroxynitrite: implications for biological activity

In biological systems, nitric oxide (NO) combines rapidly with superoxide (O2-) to form peroxynitrite ion (ONOO-), a substance that has been implicated as a culprit in many diseases. Peroxynitrite ion is essentially stable, but its protonated form (ONOOH, pKa = 6.5 to 6.8) decomposes rapidly via homolysis of the O-O bond to form about 28% free NO2 and OH radicals. At physiological pH and in the presence of large amounts of bicarbonate, ONOO- reacts with CO2 to produce about 33% NO2 and carbonate ion radicals (CO3-) in the bulk of the solution. The quantitative role of OH/CO3(-) and NO2 radicals during the decomposition of peroxynitrite (ONOOH/ONOO-) under physiological conditions is described in detail. Specifically, the effect of the peroxynitrite dosage rate on the yield and distribution of the final products is demonstrated. By way of an example, the detailed mechanism of nitration of tyrosine, a vital aromatic amino acid, is delineated, showing the difference in the nitration yield between the addition of authentic peroxynitrite and its continuous generation by NO and O2- radicals.

Protein S-guanylation by the biological signal 8-nitroguanosine 3',5'-cyclic monophosphate

The signaling pathway of nitric oxide (NO) depends mainly on guanosine 3',5'-cyclic monophosphate (cGMP). Here we report the formation and chemical biology of a nitrated derivative of cGMP, 8-nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP), in NO-mediated signal transduction. Immunocytochemistry demonstrated marked 8-nitro-cGMP production in various cultured cells in an NO-dependent manner. This finding was confirmed by HPLC plus electrochemical detection and tandem mass spectrometry. 8-Nitro-cGMP activated cGMP-dependent protein kinase and showed unique redox-active properties independent of cGMP activity. Formation of protein Cys-cGMP adducts by 8-nitro-cGMP was identified as a new post-translational modification, which we call protein S-guanylation. 8-Nitro-cGMP seems to regulate the redox-sensor signaling protein Keap1, via S-guanylation of the highly nucleophilic cysteine sulfhydryls of Keap1. This study reveals 8-nitro-cGMP to be a second messenger of NO and sheds light on new areas of the physiology and chemical biology of signal transduction by NO.

Octopamine-mediated neuronal plasticity in honeybees: implications for olfactory dysfunction in humans

Biogenic amines, such as norepinephrine (in vertebrates) and octopamine (in invertebrates), have structural and functional similarities. These amines play crucial roles in animal behavior by modifying the synaptic output of relevant neurons. Increased levels of norepinephrine in the olfactory bulb preferentially increase mitral cell excitatory responses to olfactory nerve inputs, suggesting its critical role in modulating olfactory function including memory formation and/or recall of specific olfactory memories. Increased levels of octopamine in the antennal lobe play an important role in a reinforcement pathway involved in olfactory learning and memory in honeybees. Similar to adrenergic receptors in the human brain, activation of octopaminergic receptors in the honeybee brain induces specific second messenger pathways that change protein phosphorylation and/or gene expression, altering the activity and/or abundance of proteins responsible for neuronal signaling leading to changes in olfactory behavior. The author's studies in honeybees Apis mellifera indicate that oxidative stress plays a major role in olfactory dysfunction. A similar mechanism has been proposed for olfactory abnormalities in patients of Alzheimer disease and Parkinson disease. Due to similarities in cellular and molecular processes, which govern neuronal plasticity in humans and honeybees, the author proposes that the honeybee can be used as a potential and relatively simple model system for understanding human olfactory dysfunction during aging and in neurodegenerative diseases.

Bilirubin oxidation provoked by nitric oxide radicals predicts the progression of acute cardiac allograft rejection

Bilirubin, a strong intrinsic antioxidant, quenches free radicals produced under inflammatory conditions. The oxidized bilirubin metabolites, i.e. biopyrrins, are immediately excreted into urine and can indicate the intensity of oxidation in vivo. Our preliminary studies suggested the involvement of reactive nitrogen species (RNS) in generation of biopyrrins. However, little is known about biological significance of bilirubin oxidation by RNS. Here, we analyzed the correlation between bilirubin oxidation and nitric oxide (NO) radicals during rat acute cardiac allograft rejection. In allograft recipients, urinary biopyrrins steeply increased on day 3 prior to the increase in myocardial tissue damage marker, serum troponin-T. In contrast, no significant changes in urinary biopyrrins were evident in recipients of isografts or cyclosporine-A treated allografts. Urinary nitrotyrosine, a marker of oxidation by NO radicals also increased on day 3, while administration of a NO synthase inhibitor, N(G)-monomethyl-L-arginine apparently diminished the elevation of urinary biopyrrins as well as nitrotyrosine. Immunohistochemistry revealed enhanced local expression of heme oxygenase-1, biopyrrins and nitrotyrosine in allografts in accordance with the cellular infiltrates, suggesting that changes in urinary biopyrrins reflect the bilirubin oxidation in grafts undergoing rejection. These results indicate that locally evoked bilirubin oxidation by NO radicals can predict the progression of rejection.

Enhanced Superoxide Production in Renal Outer Medulla of Dahl Salt-Sensitive Rats Reduces Nitric Oxide Tubular-Vascular Cross-Talk

Studies were conducted to determine whether the diffusion of NO from the renal medullary thick ascending limb (mTAL) to the contractile pericytes of surrounding vasa recta was reduced and, conversely, whether diffusion of oxygen free radicals was enhanced in the salt-sensitive Dahl S rat (SS/Mcwi). Angiotensin II ([Ang II] 1 μmol/L)–stimulated NO and superoxide (O 2 ·− ) production were imaged by fluorescence microscopy in thin tissue strips from the inner stripe of the outer medulla. In prehypertensive SS/Mcwi rats and a genetically designed salt-resistant control strain (consomic SS-13 BN ), Ang II failed to increase either NO or O 2 ·− in pericytes of isolated vasa recta. Ang II stimulation resulted in production of NO in epithelial cells of the mTAL that diffused to vasa recta pericytes of SS-13 BN rats but not in SS/Mcwi rats except when tissues were preincubated with the superoxide scavenger TIRON (1 mmol/L). Ang II resulted in a greater increase of O 2 ·− in the mTAL of SS/Mcwi compared with SS.13 BN mTAL. The O 2 ·− diffused to adjoining pericytes in tissue strips only in SS/Mcwi rats but not in control SS-13 BN rats. Diffusion of Ang II-stimulated O 2 ·− from mTAL to vasa recta pericytes was absent when tissue strips from SS/Mcwi rats were treated with the NO donor DETA-NONOate (20 μmol/L). We conclude that the SS/Mcwi rat exhibits increased production of O 2 ·− in mTAL that diffuses to surrounding vasa recta and attenuates NO cross-talk. Diffusion of O 2 ·− from mTAL to surrounding tissue could contribute to reduced bioavailability of NO, reductions of medullary blood flow, and interstitial fibrosis in the outer medulla of SS/Mcwi rats.

Hemodynamics influences vascular peroxynitrite formation: Implication for low-density lipoprotein apo-B-100 nitration

Hemodynamics, specifically, fluid shear stress, modulates the focal nature of atherogenesis. Superoxide anion (O2(-.)) reacts with nitric oxide (.NO) at a rapid diffusion-limited rate to form peroxynitrite (O2(-.) + .NO-->ONOO(-)). Immunohistostaining of human coronary arterial bifurcations or curvatures, where OSS develops, revealed the presence of nitrotyrosine staining, a fingerprint of peroxynitrite; whereas in straight segments, where PSS occurs, nitrotyrosine was absent. We examined vascular nitrative stress in models of oscillatory (OSS) and pulsatile shear stress (PSS). Bovine aortic endothelial cells (BAEC) were exposed to fluid shear stress that simulates arterial blood flow: (1) PSS at a mean shear stress (tau(ave)) of 23 dyn cm(-2) and a temporal gradient (partial differential(tau)/partial differential(t)) at 71 dyn cm(-2) s(-1), and (2) OSS at tau(ave) = 0.02 dyn cm(- 2) and partial differential(tau)/partial differential(t) = +/- 3.0 dyn cm(-2) s(-1) at a frequency of 1 Hz. OSS significantly up-regulated one of the NADPH oxidase subunits (NOx4) expression accompanied with an increase in O2(-.) production. In contrast, PSS up-regulated eNOS expression accompanied with .NO production (total NO(2)(-) and NO(3)(-)). To demonstrate that O2(-.) and .NO are implicated in ONOO(-) formation, we added low-density lipoprotein cholesterol (LDL) to the medium in which BAEC were exposed to the above flow conditions. The medium was analyzed for LDL apo-B-100 nitrotyrosine by liquid chromatography electrospray ionization tandem mass spectrometry (LC/ESI/MS/MS). OSS induced higher levels of 3-nitrotyrosine, dityrosine, and o-hydroxyphenylalanine compared with PSS. In the presence of ONOO(-), specific apo-B-100 tyrosine residues underwent nitration in the alpha and beta helices: alpha-1 (Tyr(144)), alpha-2 (Tyr(2524)), beta-2 (Tyr(3295)), alpha-3 (Tyr(4116)), and beta-2 (Tyr(4211)). Hence, the characteristics of shear stress in the arterial bifurcations influenced the relative production of O2(-.) and .NO with an implication for ONOO(-) formation as evidenced by LDL protein nitration.

Reduced hyperpolarization in endothelial cells of rabbit aortic valve following chronic nitroglycerine administration

This study was undertaken to determine whether long-term in vivo administration of nitroglycerine (NTG) downregulates the hyperpolarization induced by acetylcholine (ACh) in aortic valve endothelial cells (AVECs) of the rabbit and, if so, whether antioxidant agents can normalize this downregulated hyperpolarization. ACh (0.03-3 microM) induced a hyperpolarization through activations of both apamin- and charybdotoxin-sensitive Ca2+-activated K+ channels (K(Ca)) in rabbit AVECs. The intermediate-conductance K(Ca) channel (IK(Ca)) activator 1-ethyl-2-benzimidazolinone (1-EBIO, 0.3 mM) induced a hyperpolarization of the same magnitude as ACh (3 microM). The ACh-induced hyperpolarization was significantly weaker, although the ACh-induced [Ca2+]i increase was unchanged, in NTG-treated rabbits (versus NTG-untreated control rabbits). The hyperpolarization induced by 1-EBIO was also weaker in NTG-treated rabbits. The reduced ACh-induced hyperpolarization seen in NTG-treated rabbits was not modified by in vitro application of the superoxide scavengers Mn-TBAP, tiron or ascorbate, but it was normalized when ascorbate was coadministered with NTG in vivo. Superoxide production within the endothelial cell (estimated by ethidium fluorescence) was increased in NTG-treated rabbits and this increased production was normalized by in vivo coadministration of ascorbate with the NTG. It is suggested that long-term in vivo administration of NTG downregulates the ACh-induced hyperpolarization in rabbit AVECs, possibly through chronic actions mediated by superoxide.

Red blood cells in the metabolism of nitric oxide-derived peroxynitrite

In this review we have analyzed the reactions of nitric oxide (.NO) with superoxide radical (O(2).-) at the vascular compartment which results in limitation of the bioavailability of .NO and the formation of peroxynitrite (ONOO-), a strong oxidant species. The intravascular formation of peroxynitrite can result in oxidative modifications of plasma and vessel wall proteins including the formation of protein-3-nitrotyrosine. The role of red blood cells (RBC) and oxyhemoglobin in the metabolism of intravascular peroxynitrite will be discussed. While RBC constitute an important 'sink' of both .NO and peroxynitrite, redox reactions of these species with oxyhemoglobin may in part contribute to erythrocyte aging. The intravascular formation, reactions and detoxification of peroxynitrite are revealed as important factors controlling vascular dysfunction and degeneration in a variety of pathophysiologically-relevant conditions.

Superoxide fluxes limit nitric oxide-induced signaling

Independently, superoxide (O2-) and nitric oxide (NO) are biologically important signaling molecules. When co-generated, these radicals react rapidly to form powerful oxidizing and nitrating intermediates. Although this reaction was once thought to be solely cytotoxic, herein we demonstrate using MCF7, macrophage, and endothelial cells that when nanomolar levels of NO and O2- were produced concomitantly, the effective NO concentration was established by the relative fluxes of these two radicals. Differential regulation of sGC, pERK, HIF-1alpha, and p53 were used as biological dosimeters for NO concentration. Introduction of intracellular- or extracellular-generated O2- during NO generation resulted in a concomitant increase in oxidative intermediates with a decrease in steady-state NO concentrations and a proportional reduction in the levels of sGC, ERK, HIF-1alpha, and p53 regulation. NO responses were restored by addition of SOD. The intermediates formed from the reactions of NO with O2- were non-toxic, did not form 3-nitrotyrosine, nor did they elicit any signal transduction responses. H2O2 in bolus or generated from the dismutation of O2- by SOD, was cytotoxic at high concentrations and activated p53 independent of NO. This effect was completely inhibited by catalase, suppressed by NO, and exacerbated by intracellular catalase inhibition. We conclude that the reaction of O2- with NO is an important regulatory mechanism, which modulates signaling pathways by limiting steady-state levels of NO and preventing H2O2 formation from O2-.

Modification of tryptophan and tryptophan residues in proteins by reactive nitrogen species

Formation of 3-nitrotyrosine by the reaction between reactive nitrogen species (RNS) and tyrosine residues in proteins has been analyzed extensively and it is used widely as a biomarker of pathophysiological and physiological conditions mediated by RNS. In contrast, few studies on the nitration of tryptophan have been reported. This review provides an overview of the studies on tryptophan modifications by RNS and points out the possible importance of its modification in pathophysiological and physiological conditions. Free tryptophan can be modified to several nitrated products (1-, 4-, 5-, 6-, and 7-), 1-N-nitroso product, and several oxidized products by reaction with various RNS, depending on the conditions used. Among them, 1-N-nitrosotryptophan and 6-nitrotryptophan (6-NO(2)Trp) have been found as the abundant products in the reaction with peroxynitrite, and 6-NO(2)Trp has been the most abundant product in the reaction with the peroxidase/hydrogen peroxide/nitrite systems. 6-NO(2)Trp has also been observed as the most abundant nitrated product of the reactions between peroxynitrite or myeloperoxidase/hydrogen peroxide/nitrite and tryptophan residues both in human Cu,Zn-superoxide dismutase and in bovine serum albumin, as well as the reaction of peroxynitrite with myoglobin and hemoglobin. Several oxidized products have also been identified in the modified Cu,Zn-SOD. However, no 1-N-nitrosotryptophan and 1-N-nitrotryptophan has been observed in the proteins reacted with peroxynitrite or the myeloperoxidase/H(2)O(2)/nitrite system. The modification of tryptophan residues in proteins may occur at a more limited number of sites in vivo than that of tyrosine residues, since tryptophan residues are more buried inside proteins and exist less frequently in proteins, generally. However, surface-exposed tryptophan residues tend to participate in the interaction with the other molecules, therefore the modification of those tryptophans may result in modulation of the specific interaction of proteins and enzymes with other molecules.

Therapeutic effects of xanthine oxidase inhibitors: renaissance half a century after the discovery of allopurinol

The prototypical xanthine oxidase (XO) inhibitor allopurinol, has been the cornerstone of the clinical management of gout and conditions associated with hyperuricemia for several decades. More recent data indicate that XO also plays an important role in various forms of ischemic and other types of tissue and vascular injuries, inflammatory diseases, and chronic heart failure. Allopurinol and its active metabolite oxypurinol showed considerable promise in the treatment of these conditions both in experimental animals and in small-scale human clinical trials. Although some of the beneficial effects of these compounds may be unrelated to the inhibition of the XO, the encouraging findings rekindled significant interest in the development of additional, novel series of XO inhibitors for various therapeutic indications. Here we present a critical overview of the effects of XO inhibitors in various pathophysiological conditions and also review the various emerging therapeutic strategies offered by this approach.

Involvement of Salmonella enterica serovar Typhi RpoS in resistance to NO-mediated host defense against serovar Typhi infection

The involvement of nitric oxide (NO) in host defense and cytoprotective functions in murine salmonellosis has been reported. Salmonella mutants with the altered sigma factor RpoS (sigmaS) are less virulent and are susceptible to various stresses. This study investigated the role of the rpoS gene of Salmonella enterica serovar Typhi in NO-dependent host defense in vitro and in vivo. Wild-type mice and mice deficient in inducible NO synthase (iNOS) were infected intraperitoneally or orally with serovar Typhi strains. iNOS-deficient mice were more susceptible to infection by both wild-type and rpoS mutant strains of serovar Typhi and showed extensive apoptotic liver damage compared with wild-type mice. Intracellular killing of Salmonella was analyzed with RAW 264 macrophage-like cells and primary peritoneal macrophages from wild-type and iNOS-deficient mice after cells were infected with the serovar Typhi parent or rpoS mutant strain. The rpoS mutant was more susceptible to killing by macrophages than was the wild-type strain. Also, the wild-type strain produced more extensive apoptotic changes in macrophages than did rpoS mutant. These effects were nullified in RAW 264 cells treated with an NOS inhibitor and in iNOS-deficient primary macrophages. Peroxynitrite susceptibility assays of these strains were also performed. The rpoS mutant Typhi strain was more sensitive to in vitro peroxynitrite treatment than was the parent strain. Together these data show that NO has a significant host defense function during serovar Typhi infection, and that Salmonella RpoS, because it reacts to the presence of NO or its reactive derivatives, is thought to have a role in the pathogenicity of serovar Typhi.

Immunological detection of nitrosative stress-mediated modified Tamm-Horsfall glycoprotein (THP) in calcium oxalate stone formers

The generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in hyperoxaluric condition has been proved experimentally. This may result in the formation of the cytotoxic metabolite peroxynitrite, which is capable of causing lipid peroxidation and protein modification. The presence of nitrotyrosine in proteins has been associated with several pathological conditions. The present study investigated the presence of nitrotyrosine in the stone formers Tamm-Horsfall glycoprotein (THP). In vitro nitration of control THP was carried out using peroxynitrite. New Zealand white rabbits were immunized with peroxynitrated THP at 15-day intervals. Antisera collected following the third immunization were assayed for antibody titres using solid-phase ELISA. Antibodies were purified by affinity chromatography. The carbonyl content of control, stone formers and nitrated THP were determined. Western blotting was carried with control, stone formers and nitrated THPs. Immunodiffusion studies demonstrated cross-reaction with nitrated bovine serum albumin. Significant amounts (p < 0.001) of carbonyl content were present in both stone formers and nitrated THPs. Western blot analysis confirmed the presence of nitrated amino acid 3-nitrotyrosine in stone formers, which could bring about structural and functional modifications of THP in hyperoxaluric patients. A cross-reaction with nitrated bovine serum albumin confirms that the raised antibody has certain paratopes similar to the epitope of nitrated protein molecules. Detection of 3-nitrotyrosine in stone formers THP indicates that it is one of the key factors influencing the conversion of THP to a structurally and immunologically altered form during calcium oxalate stone formation.

Inorganic nitric oxide metabolites participating in no-dependent modifications of biopolymers

Biogenous nitric(II) oxide (NO), the higher nitrogen oxides (NO2, isomeric N2O3 and N2O4, ONOO-, etc.) that are NO-derived in vivo, and the products of their transformations are active compounds capable of reactions with biopolymers and low-molecular metabolites. The products of these reactions are often considered to be various NO-dependent modifications (NODMs). The nitrated, nitrosylated, nitrosated, and other NODMs play key roles in the regulation of the most important biochemical processes. In this review, we briefly discuss the metabolic reactions of nitrogen oxides that supply active intermediates for NODMs, the NODM reaction products, and some mechanisms of NODM reparation that allow the recovery of chemically intact biopolymer molecule from a modified (chemically damaged) NODM. For example, residues of 3-nitrotyrosine arising due to the NODM reactions of proteins can be reduced to unsubstituted Tyr residues as a result of alternative NODM reactions through intermediate diazotyrosine derivatives. The heterogeneity of a medium in vivo is an important factor controlling the proceeding of NODM reactions. We showed that many processes determining NODM efficiency proceed differently in the heterogeneous media of organisms and in homogeneous aqueous solutions.

Interleukin-1beta induces death in chondrocyte-like ATDC5 cells through mitochondrial dysfunction and energy depletion in a reactive nitrogen and oxygen species-dependent manner

IL-1 (interleukin-1) acts as a key mediator of the degeneration of articular cartilage in RA (rheumatoid arthritis) and OA (osteoarthritis),where chondrocyte death is observed. It is still controversial, however, whether IL-1 induces chondrocyte death. In the present study, the viability of mouse chondrocyte-like ATDC5 cells was reduced by the treatment with IL-1beta for 48 h or longer. IL-1beta augmented the expression of the catalytic gp91 subunit of NADPH oxidase, gp91phox, as well as inducible NO synthase in ATDC5 cells. Generation of nitrated guanosine and tyrosine suggested the formation of reactive nitrogen species including ONOO- (peroxynitrite), a reaction product of NO and O2-, in ATDC5 cells and rat primary chondrocytes treated with IL-1beta. Death of ATDC5 cells after IL-1beta treatment was prevented by an NADPH-oxidase inhibitor, AEBSF[4-(2-aminoethyl)benzene-sulphonyl fluoride], an NO synthase inhibitor, L-NAME (NG-nitro-L-arginine methyl ester), and a ONOO- scavenger, uric acid. The viability of ATDC5 cells was reduced by the ONOO(-)-generator 3-(4-morpholinyl)sydnonimine hydrochloride, but not by either the NO-donor 1-hydroxy-2-oxo-3-(N-methyl-2-aminopropyl)-3-methyl-1-triazene or S-nitrosoglutathione. Disruption of mitochondrial membrane potential and ATP deprivation were observed in IL-1beta-treated ATDC5 cells, both of which were restored by L-NAME, AEBSF or uric acid. On the other hand, no morphological or biochemical signs indicating apoptosis were observed in these cells. These results suggest that the death of chondrocyte-like ATDC5 cells was mediated at least in part by mitochondrial dysfunction and energy depletion through ONOO- formation after IL-1beta treatment.

Maintaining the redox-balance intact: gosha-jinki-gan but not insulin activates retinal soluble guanylate cyclase in diabetic rats

Strategies to prevent hyperglycemia-induced cytotoxic reactive oxygen species in the retina include the prevention of free radical production, activation of radical-scavenging capacities and inhibition of aldose reductase. This study examined the effect of the standardized Japanese herbal extract product gosha-jinki-gan (GJG) in comparison to insulin treatment in the rat retina. Diabetes was induced in male Wistar rats by single injection of streptozotocin (50 mg/kg i.p.). At 6 and 12 weeks, eye-cups were removed for immunohistochemistry. At 12 weeks, lipid peroxidation (tested with the antiacrolein antibody, Ab5F6) was enhanced significantly in the untreated diabetic group. This effect was absent in both treatment groups, notably in the outer retina. A similar result was obtained for nitrotyrosine overproduction. As an early treatment effect, GJG -- but not insulin -- enhanced soluble guanylate cyclase (sGC) activation (using the function-sensing antibody, MoAb 3221). GJG not only reduces nitroxidative stress and lipid peroxidation in the retina, it also ameliorates glucose metabolism within the cells. We propose that the high glucose turnover in the insulin-treated model disturbs the intracellular redox equilibrium, one result of which might be the impaired sGC activation.

The highly conserved Glu149 and Tyr190 residues contribute to peroxynitrite-mediated nitrotyrosine formation and the catalytic activity of cytochrome P450 2B1

Tyr190 in cytochrome P450 2B1 has previously been shown to be a prime target for nitration by peroxynitrite (PN) resulting in nitrotyrosine formation and the inactivation of this enzyme. Modeling studies have suggested that Tyr190 may play a structural role in maintaining the integrity of the protein for maximal activity through hydrogen bonding with Glu149. To elucidate the roles of Tyr190 and Glu149 hydrogen-bonding in maintaining the catalytically competent structure of P450 2B1, we have mutated Tyr190 to Phe or Ala and Glu149 to Gln or Ala to characterize the catalytic activities and the structural stabilities of mutated proteins. The results demonstrate that (a) the catalytic activities of all four mutants were decreased significantly compared to wild-type (WT); (b) nitration of Tyr190 by PN or mutation of Tyr190 to Phe did not alter the Km of the reductase for P450; (c) PN decreases the catalytic activity of the heat-treated Y190A, E149Q, and E149A mutants to a much greater extent than the WT and Y190F; and (d) after exposure of the P450s to PN, the extent of nitrotyrosine formation and the inactivation of the catalytic activity of the E149Q and E149A mutants were markedly decreased when compared to WT. These findings suggest that (1) the hydrogen bond between Tyr190 and Glu149 stabilizes the protein for maximal activity; (2) the benzyl ring and hydroxyl groups of Tyr190 stabilize the protein structure when P450 is exposed to the temperatures higher than 45 degrees C; and (3) Glu149 may be critical in directing the site of nitration by PN. Since Glu149 and Tyr190 are both highly conserved in the P450 2 family, they may play an important role in the tertiary structure and functional properties of these P450s.

Tyrosine nitration by superoxide and nitric oxide fluxes in biological systems: modeling the impact of superoxide dismutase and nitric oxide diffusion

Tyrosine nitration is a posttranslational modification observed in many pathologic states that can be associated with peroxynitrite (ONOO(-)) formation. However, in vitro, peroxynitrite-dependent tyrosine nitration is inhibited when its precursors, superoxide (O(2)*(-)) and nitric oxide ((*)NO), are formed at ratios (O(2)*(-)/(*)NO) different from one, severely questioning the use of 3-nitrotyrosine as a biomarker of peroxynitrite-mediated oxidations. We herein hypothesize that in biological systems the presence of superoxide dismutase (SOD) and the facile transmembrane diffusion of (*)NO preclude accumulation of O(2)*(-) and (*)NO radicals under flux ratios different from one, preventing the secondary reactions that result in the inhibition of 3-nitrotyrosine formation. Using an array of reactions and kinetic constants, computer-assisted simulations were performed in order to assess the flux of 3-nitrotyrosine formation (J(NO(2(-))Y)) during exposure to simultaneous fluxes of superoxide (J(O(2)*(-))) and nitric oxide (J((*)NO)), varying the radical flux ratios (J(O(2)*(-))/ J((*)NO)), in the presence of carbon dioxide. With a basic set of reactions, J(NO(2(-))Y) as a function of radical flux ratios rendered a bell-shape profile, in complete agreement with previous reports. However, when superoxide dismutation by SOD and (*)NO decay due to diffusion out of the compartment were incorporated in the model, a quite different profile of J(NO(2(-))Y) as a function of the radical flux ratio was obtained: despite the fact that nitration yields were much lower, the bell-shape profile was lost and the extent of tyrosine nitration was responsive to increases in either O(2)*(-) or (*)NO, in agreement with in vivo observations. Thus, the model presented herein serves to reconcile the in vitro and in vivo evidence on the role of peroxynitrite in promoting tyrosine nitration.

Nitrative DNA damage in inflammation and its possible role in carcinogenesis

Chronic inflammation has long been recognized as a risk factor for human cancer at various sites. Examples include Helicobacter pylori-induced gastritis for gastric cancer, inflammatory bowel disease (ulcerative colitis and Crohn's disease) for colorectal cancer and chronic viral hepatitis for liver cancer. Here we review the role in carcinogenesis of nitrative damage to nucleic acids, DNA and RNA, which occurs during inflammation through the generation of reactive nitrogen species, such as peroxynitrite, nitroxyl, and nitrogen dioxide. Enhanced formation of 8-nitroguanine, representative of nitrative damage to nucleobases, has been detected in various inflammatory conditions. The biochemical nature of DNA damage mediated by reactive nitrogen species is discussed in relation to its possible involvement in mutations, genetic instability, and cell death. Better understanding of the mechanisms and role of such nitrative damage in chronic inflammation-associated human cancer is a necessary basis to develop new strategies for cancer prevention by modulating the process of inflammation.