S-Nitroglutathione, a product of the reaction between peroxynitrite and glutathione that generates nitric oxide

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

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

Heme catalyzes tyrosine 385 nitration and inactivation of prostaglandin H2 synthase-1 by peroxynitrite

The mechanism by which the inflammatory enzyme prostaglandin H(2) synthase-1 (PGHS-1) deactivates remains undefined. This study aimed to determine the stabilizing parameters of PGHS-1 and identify factors leading to deactivation by nitric oxide species (NO(x)). Purified PGHS-1 was stabilized when solubilized in beta-octylglucoside (rather than Tween-20 or CHAPS) and when reconstituted with hemin chloride (rather than hematin). Peroxynitrite (ONOO(-)) activated the peroxidase site of PGHS-1 independently of the cyclooxygenase site. After ONOO(-) exposure, holoPGHS-1 could not metabolize arachidonic acid and was structurally compromised, whereas apoPGHS-1 retained full activity once reconstituted with heme. After incubation of holoPGHS-1 with ONOO(-), heme absorbance was diminished but to a lesser extent than the loss in enzymatic function, suggesting the contribution of more than one process to enzyme inactivation. Hydroperoxide scavengers improved enzyme activity, whereas hydroxyl radical scavengers provided no protection from the effects of ONOO(-). Mass spectral analyses revealed that tyrosine 385 (Tyr 385) is a target for nitration by ONOO(-) only when heme is present. Multimer formation was also observed and required heme but could be attenuated by arachidonic acid substrate. We conclude that the heme plays a role in catalyzing Tyr 385 nitration by ONOO(-) and the demise of PGHS-1.

Carbon monoxide: endogenous production, physiological functions, and pharmacological applications

Over the last decade, studies have unraveled many aspects of endogenous production and physiological functions of carbon monoxide (CO). The majority of endogenous CO is produced in a reaction catalyzed by the enzyme heme oxygenase (HO). Inducible HO (HO-1) and constitutive HO (HO-2) are mostly recognized for their roles in the oxidation of heme and production of CO and biliverdin, whereas the biological function of the third HO isoform, HO-3, is still unclear. The tissue type-specific distribution of these HO isoforms is largely linked to the specific biological actions of CO on different systems. CO functions as a signaling molecule in the neuronal system, involving the regulation of neurotransmitters and neuropeptide release, learning and memory, and odor response adaptation and many other neuronal activities. The vasorelaxant property and cardiac protection effect of CO have been documented. A plethora of studies have also shown the importance of the roles of CO in the immune, respiratory, reproductive, gastrointestinal, kidney, and liver systems. Our understanding of the cellular and molecular mechanisms that regulate the production and mediate the physiological actions of CO has greatly advanced. Many diseases, including neurodegenerations, hypertension, heart failure, and inflammation, have been linked to the abnormality in CO metabolism and function. Enhancement of endogenous CO production and direct delivery of exogenous CO have found their applications in many health research fields and clinical settings. Future studies will further clarify the gasotransmitter role of CO, provide insight into the pathogenic mechanisms of many CO abnormality-related diseases, and pave the way for innovative preventive and therapeutic strategies based on the physiologic effects of CO.

Nitrate tolerance aggravates postischemic myocardial apoptosis and impairs cardiac functional recovery after ischemia

OBJECTIVES

This study examined the effects of nitrate tolerance (NT) on myocardial ischemia reperfusion (MI/R) injury and elucidated the potential mechanisms involved. Furthermore, the effects of GSH on postischemic myocardial apoptosis in NT rats were investigated.

METHODS AND RESULTS

Male Sprague-Dawley rats were randomized to receive nitroglycerin (60 microg/kg/h) or saline for 12 h followed by 40 min of MI and 4 h of reperfusion. Myocardial apoptosis, infarct size, nitrotyrosine formation, plasma CK and LDH activity, and cardiac function were determined. MI/R resulted in significant apoptotic cell death, which was further increased in animals with NT. In addition, NT further increased plasma CK and LDH activity, enlarged infarct size, and impaired cardiac functional recovery after ischemia. Myocardial nitrotyrosine, a footprint for cytotoxic reactive nitrogen species formation, was further enhanced in the NT heart after MI/R. Treatment of NT animals with exogenous GSH inhibited nitrotyrosine formation, reduced apoptosis, decreased infarct size, and improved cardiac functional recovery.

CONCLUSION

Our results demonstrate that nitrate tolerance markedly enhances MI/R injury and that increased peroxynitrite formation likely plays a role in this pathologic process. In addition, our results suggest that GSH could decrease peroxynitrite formation and reduce MI/R injury in nitrate tolerant hearts.

Nitrated lipids decompose to nitric oxide and lipid radicals and cause vasorelaxation

Nitric oxide-derived oxidants such as nitrogen dioxide and peroxynitrite have been receiving increasing attention as mediators of nitric oxide toxicity. Indeed, nitrated and nitrosated compounds have been detected in biological fluids and tissues of healthy subjects and in higher yields in patients under inflammatory or infectious conditions as a consequence of nitric oxide overproduction. Among them, nitrated lipids have been detected in vivo. Here, we confirmed and extended previous studies by demonstrating that nitrolinoleate, chlolesteryl nitrolinoleate, and nitrohydroxylinoleate induce vasorelaxation in a concentration-dependent manner while releasing nitric oxide that was characterized by chemiluminescence-and EPR-based methodologies. As we first show here, diffusible nitric oxide production is likely to occur by isomerization of the nitrated lipids to the corresponding nitrite derivatives that decay through homolysis and/or metal ion/ascorbate-assisted reduction. The homolytic mechanism was supported by EPR spin-trapping studies with 3,5-dibromo-4-nitrosobenzenesulfonic acid that trapped a lipid-derived radical during nitrolinoleate decomposition. In addition to provide a mechanism to explain nitric oxide production from nitrated lipids, the results support their role as endogenous sources of nitric oxide that may play a role in endothelium-independent vasorelaxation.

S-thiolation of tyrosine hydroxylase by reactive nitrogen species in the presence of cysteine or glutathione

Tyrosine hydroxylase (TH) is the initial and rate-limiting enzyme in the biosynthesis of the neurotransmitter dopamine. Peroxynitrite (ONOO-) and nitrogen dioxide (NO2) inhibit TH catalytic function and cause nitration of protein tyrosine residues. Exposure of TH to either ONOO- or NO2 in the presence of cysteine (or glutathione) prevents tyrosine nitration and results in S-thiolation instead. TH catalytic activity is suppressed by S-thiolation. Dithiothreitol prevents and reverses the modification of TH by S-thiolation, and returns enzyme activity to control levels. S-Nitrosothiols, which are known to S-thiolate proteins, can be formed in the reaction of cysteine or glutathione with reactive nitrogen species. Therefore, S-nitrosoglutathione (GSNO) was tested for its ability to modify TH. Fresh solutions of GSNO did not modify TH, whereas decomposed GSNO resulted in extensive S-thiolation of the protein. Dimedone, a sulfenic acid trap, prevents S-thiolation of TH when included with GSNO during its decomposition. Taken together, these results show that TH is S-thiolated by ONOO- or NO2 in the presence of cysteine. S-Thiolation occurs at the expense of tyrosine nitration. Glutathione disulfide S-oxide, which forms spontaneously in the decomposition of GSNO and which is found in tissue undergoing oxidative stress, may be the species that S-thiolates TH.

Treatment with 1,2,3,4-tetrahydroisoquinolone affects the levels of nitric oxide, S-nitrosothiols, glutathione and the enzymatic activity of γ-glutamyl transpeptidase in the dopaminergic structures of rat brain

Depletion of glutathione (GSH), nitrosative stress and chronic intoxication with some neurotoxins have been postulated to play a major role in the pathogenesis of Parkinson's disease. This study aimed to examine the effects of acute and chronic treatments with 1,2,3,4-tetrahydroisoquinoline (TIQ), an endo-/exogenous substance suspected of producing Parkinsonism in human, on the levels of nitric oxide (NO), S-nitrosothiols and glutathione (GSH) in the whole rat brain and in its dopaminergic structures. TIQ administered at a dose of 50 mg/kg i.p. significantly increased the tissue concentrations of NO and GSH in the substantia nigra (SN), striatum (STR) and cortex (CTX) of rats receiving this compound both acutely and chronically. Moreover, it decreased the level of oxidized glutathione (GSSG) and enhanced GSH:GSSG ratio affecting in this way the redox state of brain cells. TIQ also increased the level of S-nitrosothiols when measured in the whole rat brain and CTX, although it markedly decreased their level in the STR after both treatments. Inhibition of the constitutive NO synthase by l-NAME in the presence of TIQ caused decreases in GSH and S-nitrosothiol levels in the brain. The latter effect shows that the TIQ-mediated increases in GSH and S-nitrosothiol concentrations were dependent on the enhanced NO level. The above-described results suggest that TIQ can act as a modulator of GSH, NO and S-nitrosothiol levels but not as a parkinsonism-inducing agent in the rat brain.

Separation and detection of peroxynitrite and its metabolites by capillary electrophoresis with UV detection

A method for the separation and direct detection of peroxynitrite (ONOO(-)) and two of its degradation products, nitrite (NO(2)(-)) and nitrate (NO(3)(-)), using capillary electrophoresis with ultraviolet detection is described. The separation parameters were optimized and included electrokinetic injection, a run buffer consisting of 25 mM K(2)HPO(4) 7.5 mM DTAB, pH 12, and a field strength of -323 V/cm. A diode array UV detector was employed in these studies as it allowed the determination of all three species simultaneously. Nitrate and nitrite provided the maximum response at 214 nm while peroxynitrite generated the best response at 302 nm. All three species could be detected at 214 nm, while simultaneous detection at 214 and 302 nm positively identified each peak.

Chemical considerations and biological selectivity of protein nitrosation: implications for NO-mediated signal transduction

Nitric oxide (NO) is a diatomic free radical that plays an important role in the homeostatic regulation of the central nervous, immune, and cardiovascular systems. In addition to its interaction with guanylate cyclase, which results in the production of the second messenger cyclic GMP, there is now a large body of literature indicating that many of the effects associated with the production of NO are due to the nitrosation of cysteine residues in proteins. In this review, we outline the primary chemical pathways that may account for protein nitrosation in cells and tissues. The functional implications of protein nitrosation are discussed by using the p21(ras) subfamily of small monomeric GTPases and the cysteine-containing aspartate-specific proteases (caspases) as prototypical examples. Overall, in addition to the well characterized NO/O(2) reaction, there may exist multiple pathways accounting for protein nitrosation in cells. These include acid- and free radical-mediated mechanisms. Although protein nitrosation may not be limited to cysteine residues, there is now ample evidence that nitrosation reactions, in a fashion similar to oxidative modifications, may modulate the structure, activity, association, and localization of a specific subset of proteins in cells and tissues.

Nitrates and NO release: contemporary aspects in biological and medicinal chemistry

Nitroglycerine has been used clinically in the treatment of angina for 130 years, yet important details on the mechanism of action, biotransformation, and the associated phenomenon of nitrate tolerance remain unanswered. The biological activity of organic nitrates can be said to be nitric oxide mimetic, leading to recent, exciting progress in realizing the therapeutic potential of nitrates. Unequivocally, nitroglycerine and most other organic nitrates, including NO-NSAIDs, do not behave as NO donors in the most fundamental action: in vitro activation of sGC to produce cGMP. The question as to whether the biological activity of nitrates results primarily or exclusively from NO donation will not be satisfactorily answered until the location, the apparatus, and the mechanism of reduction of nitrates to NO are defined. Similarly, the therapeutic potential of nitrates will not be unlocked until this knowledge is attained. Aspects of the therapeutic and biological activity of nitrates are reviewed in the context of the chemistry of nitrates and the elusive efficient 3e- reduction required to generate NO.

Exogenous NADPH increases cerebral blood flow through NADPH oxidase-dependent and -independent mechanisms

OBJECTIVE

NADPH, a substrate for the superoxide-producing enzyme NADPH oxidase, produces vasodilation in the cerebral circulation. However, the mechanisms of the effect have not been fully elucidated. We used a peptide inhibitor of NADPH oxidase (gp91ds-tat) and null mice lacking the gp91phox subunit of NADPH oxidase to examine the mechanisms of the cerebrovascular effects of exogenous NADPH.

METHODS AND RESULTS

Cerebral blood flow (CBF) was assessed by laser-Doppler flowmetry in anesthetized mice equipped with a cranial window. Superfusion with NADPH increased CBF (27% at 100 micromol/L) without affecting the EEG. The CBF increase was attenuated by the free-radical scavenger MnTBAP (-54%, P<0.05) but not by the H2O2 scavenger catalase. The response was also attenuated by gp91ds-tat (-64%, P<0.05) and by the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine (-44%, P<0.05). The increase in CBF produced by NADPH was attenuated in gp91-null mice (-41%, P<0.05). NADPH increased production of reactive oxygen species, assessed by hydroethidine microfluorography, an effect blocked by MnTBAP or gp91ds-tat and not observed in gp91-null mice.

CONCLUSIONS

These data suggest that the mechanisms of the CBF increases produced by exogenous NADPH are multifactorial and include NADPH oxidase-dependent and -independent factors.

Spin trapping of glutathiyl and protein radicals produced from nitric oxide-derived oxidants

Despite the importance of protein radicals in cell homeostasis and cell injury, their formation, localization, and propagation reactions remain obscure, mainly because of the difficulties in detecting and characterizing radicals, in general, and protein radicals, in particular. New approaches based on spin trapping coupled with other methodologies are under development/testing but so far they have been applied mainly to the study of protein-tyrosyl and protein-tryptophanyl radicals. Here, our aim is to emphasize the importance of developing new methodologies for the detection of glutathyil and protein-cysteinyl radicals under physiological conditions. To this end, we summarize current EPR evidence supporting the view that glutathione and protein-cysteines are among the preferential targets of nitric oxide-derived oxidants and that they are oxidized to the glutathiyl and protein-cysteinyl radicals, respectively. The possible intermediacy of these species in the biological formation of mediators of protein-cysteine redox signaling, such as S-nitrosothiols and sulfenic acids, is also discussed.

BIOCHEMICAL MECHANISM OF NITROGLYCERIN ACTION AND TOLERANCE: Is This Old Mystery Solved?

Organic nitrates such as nitroglycerin (NTG) have been used as potent vasodilators in medicine for more than a century, but their biochemical mechanisms of action, particularly in relation to tolerance development, are still incompletely defined. Numerous candidate enzymes for NTG metabolism, as well as a multiplicity of tolerance mechanisms, have been proposed in the literature, but a consolidating hypothesis that links these phenomena together has not appeared. Here, we outline a "thionitrate oxidation hypothesis," which attempts to link nitrate bioactivation and tolerance development in an overall mechanism. We also attempt to compare and contrast the proposed mechanism against existing theories of nitrate action and tolerance. Interactions between organic nitrates, which have been thought of as endothelium-independent agents, and the vascular endothelium and endothelial nitric oxide synthase (eNOS) are also discussed.

Superoxide: a key player in hypertension

Superoxide is increased in the vessel wall of spontaneously hypertensive rats (SHR) where, if "blocked," potentiates endothelium-dependent vasodilation. The purpose of this study was to determine the role of superoxide anion in hypertension and its interaction with nitric oxide (NO). For this purpose we used a low molecular weight synthetic superoxide dismutase mimetic (M40403), known to remove selectively superoxide anion. Baseline mean arterial pressure (MAP) was significantly elevated in the SHR compared with its normal counterpart, Wistar Kyoto (WKY). M40403 at a dose (2 mg x kg(-1) x h(-1)), which had no effect in the WKY, significantly decreased MAP in SHR rats. To determine whether superoxide anion increases MAP by inactivating NO, NO synthesis was blocked with N(G) nitro-arginine methyl ester (L-NAME, 3 mg/kg i.v.), a nonselective nitric oxide synthase inhibitor. L-NAME (3 mg/kg, i.v) blocked the anti-hypertensive effect of M40403 (2 mg/kg over 30 min). When used at a dose that yielded similar increases in MAP, norepinephrine (2.1 microg/kg) failed to alter the anti-hypertensive effects of M40403 in the SHR. To investigate whether the anti-hypertensive effect of M40403 was associated with an improvement of the alterations in vascular reactivity, a separate group of experiments was carried out ex vivo. Endothelium-dependent vasorelaxation to acetylcholine (10 nM-10 microM), an index of endothelial function, was reduced in aortic rings taken from SHR rats when compared with WKY rats. In vivo treatment with M40403 caused an improvement of the degree of the endothelial dysfunction in SHR rats. Furthermore, immunohistochemical analysis for nitrotyrosine (the product formed from the interaction of nitric oxide with superoxide) revealed a positive staining in aorta from SHR rats. The degree of staining for nitrotyrosine was markedly reduced in tissue sections obtained from SHR rats treated with M40403. Our data suggest that overt production of superoxide in SHR couples with nitric oxide, reducing its function and leading to a loss of blood vessel tone and hypertension. Another important effect appears to be at the level of endothelial cellular integrity, where by interacting with nitric oxide, superoxide anion forms peroxynitrite and subsequent endothelial cell dysfunction. By removing superoxide, M40403 restores blood pressure to near-to-normal values.

Formation and stability of S-nitrosothiols in RAW 264.7 cells

S-Nitrosothiols have been suggested to be mediators of many nitric oxide-dependent processes, including apoptosis and vascular relaxation. Thiol nitrosation is a poorly understood process in vivo, and the mechanisms by which nitric oxide can be converted into a nitrosating agent have not been established. There is a discrepancy between the suggested biological roles of nitric oxide and its known chemical and physical properties. In this study, we have examined the formation of S-nitrosothiols in lipopolysaccharide-treated RAW 264.7 cells. This treatment generated 17.4 +/- 1.0 pmol/mg of protein (means +/- SE, n =27) of intracellular S-nitrosothiol that slowly decayed over several hours. S-Nitrosothiol formation depended on the formation of nitric oxide and not on the presence of nitrite. Extracellular thiols were nitrosated by cell-generated nitric oxide. Oxygenated ferrous hemoglobin inhibited the formation of S-nitrosothiol, indicating the nitrosation occurred more slowly than diffusion. We discuss several mechanisms for S-nitrosothiol formation and conclude that the nitrosation propensity of nitric oxide is a freely diffusible element that is not constrained within an individual cell and that both nitric oxide per se and nitric oxide-derived nitrosating agents are able to diffuse across cell membranes. To achieve intracellular localization of the nitrosation reaction, mechanisms must be invoked that do not involve the formation of nitric oxide as an intermediate.

Inhibitors of nitric oxide synthase block carbon monoxide-induced increases in cGMP in retina

Previous studies indicate that the gaseous messengers carbon monoxide (CO) and nitric oxide (NO) can interact to cause robust increases in intracellular cGMP levels in the retina. The purpose of the present study was to investigate the biochemical basis of the interactions between NO and CO for these increases. Turtle retinas were incubated in vitro with CO to stimulate cGMP production in the presence or absence of the nitric oxide synthase inhibitors N-omega-nitro-L-arginine methyl ester and S-methyl-thiocitrulline. Cyclic GMP immunocytochemistry was then used to evaluate the changes in cGMP levels in response to these stimuli. The results indicated that CO itself stimulated increases in cGMP in bipolar and amacrine cells, and that the increases were completely blocked by SMTC and L-NAME. We postulate that the increases of cGMP in response to CO might be mediated, at least partly, by CO displacing and releasing NO from its intracellular storage pool(s).

Increased oxidative stress with aging reduces chondrocyte survival: Correlation with intracellular glutathione levels

OBJECTIVE

To examine the role of oxidative stress in mediating cell death in chondrocytes isolated from the articular cartilage of young and old adult human tissue donors.

METHODS

Cell death induced by the oxidant SIN-1 was evaluated in the alginate bead culture system using fluorescent probes to assess membrane integrity. Generation of peroxynitrite by the decomposition of SIN-1 was confirmed by positive immunostaining of treated cells for 3-nitrotyrosine. Determinations of oxidized glutathione (GSSG) and reduced glutathione (GSH) were performed in monolayer cultures using an enzyme- recycling assay. Cells were depleted of intracellular glutathione either by the addition of DL-buthionine-(S,R)-sulfoximine or by removal of L-cystine from the culture media. The activity of cellular antioxidant enzymes was determined spectrophotometrically by the decay of substrate from the reaction mixture.

RESULTS

More chondrocytes (>2-fold) from old donors (>/=50 years) died after exposure to 1 mM SIN-1 relative to those derived from young donors (18-49 years). Although autocrine production of insulin-like growth factor 1 (IGF-1) promotes chondrocyte survival, pretreatment with IGF-1 could not prevent the cell death induced by SIN-1 exposure. Cells isolated from old donors had a higher ratio of GSSG to GSH. Glutathione reductase is the principal enzyme involved in the regeneration of GSH from GSSG. Treatment of chondrocytes with SIN-1 to induce oxidative stress in vitro resulted in the decreased activity of glutathione reductase and thioredoxin reductase, but not catalase. Cells depleted of intracellular glutathione were more susceptible to cell death induced by SIN-1.

CONCLUSION

These results provide evidence that increased oxidative stress with aging makes chondrocytes more susceptible to oxidant-mediated cell death through the dysregulation of the glutathione antioxidant system. This may represent an important contributing factor to the development of osteoarthritis in older adults.

Sulfenic acid formation in human serum albumin by hydrogen peroxide and peroxynitrite

Human serum albumin (HSA), the most abundant protein in plasma, has been proposed to have an antioxidant role. The main feature responsible for this property is its only thiol, Cys34, which comprises approximately 80% of the total free thiols in plasma and reacts preferentially with reactive oxygen and nitrogen species. Herein, we show that the thiol in HSA reacted with hydrogen peroxide with a second-order rate constant of 2.26 M(-1) s(-1) at pH 7.4 and 37 degrees C and a 1:1 stoichiometry. The formation of intermolecular disulfide dimers was not observed, suggesting that the thiol was being oxidized beyond the disulfide. With the reagent 7-chloro-4-nitrobenzo-2-oxa-1,3-diazol (NBD-Cl), we were able to detect the formation of sulfenic acid (HSA-SOH) from the UV-vis spectra of its adduct. The formation of sulfenic acid in Cys34 was confirmed by mass spectrometry using 5,5-dimethyl-1,3-cyclohexanedione (dimedone). Sulfenic acid was also formed from exposure of HSA to peroxynitrite, the product of the reaction between nitric oxide and superoxide radicals, in the absence or in the presence of carbon dioxide. The latter suggests that sulfenic acid can also be formed through free radical pathways since following reaction with carbon dioxide, peroxynitrite yields carbonate radical anion and nitrogen dioxide. Sulfenic acid in HSA was remarkably stable, with approximately 15% decaying after 2 h at 37 degrees C under aerobic conditions. The formation of glutathione disulfide and mixed HSA-glutathione disulfide was determined upon reaction of hydrogen peroxide-treated HSA with glutathione. Thus, HSA-SOH is proposed to serve as an intermediate in the formation of low molecular weight disulfides, which are the predominant plasma form of low molecular weight thiols, and in the formation of mixed HSA disulfides, which are present in approximately 25% of circulating HSA.

Oxidation and nitrosation of thiols at low micromolar exposure to nitric oxide. Evidence for a free radical mechanism

Although the nitric oxide (.NO)-mediated nitrosation of thiol-containing molecules is increasingly recognized as an important post-translational modification in cell signaling and pathology, little is known about the factors that govern this process in vivo. In the present study, we examined the chemical pathways of nitrosothiol (RSNO) production at low micromolar concentrations of .NO. Our results indicate that, in addition to nitrosation by the .NO derivative dinitrogen trioxide (N2O3), RSNOs may be formed via intermediate one-electron oxidation of thiols, possibly mediated by nitrogen dioxide (.NO2), and the subsequent reaction of thiyl radicals with .NO. In vitro, the formation of S-nitrosoglutathione (GSNO) from .NO and excess glutathione (GSH) was accompanied by the formation of glutathione disulfide, which could not be ascribed to the secondary reaction of GSH with GSNO. Superoxide dismutase significantly increased GSNO yields and the thiyl radical trap, 5,5-dimethyl-1-pyrroline N-oxide (DMPO), inhibited by 45 and 98% the formation of GSNO and GSSG, respectively. Maximum nitrosation yields were obtained at an oxygen concentration of 3%, whereas higher oxygen tensions decreased GSNO and increased GSSG formation. When murine fibroblasts were exposed to exogenous .NO, RSNO formation was sensitive to DMPO and oxygen tension in a manner similar to that observed with GSH alone. Our data indicate that RSNO formation is favored at oxygen concentrations that typically occur in tissues. Nitrosothiol formation in vivo depends not only on the availability of .NO and O2 but also on the degree of oxidative stress by affecting the steady-state concentration of thiyl radicals.

Role of glutathione in macrophage control of mycobacteria

Reactive oxygen and nitrogen intermediates are important antimicrobial defense mechanisms of macrophages and other phagocytic cells. While reactive nitrogen intermediates have been shown to play an important role in tuberculosis control in the murine system, their role in human disease is not clearly established. Glutathione, a tripeptide and antioxidant, is synthesized at high levels by cells during reactive oxygen intermediate and nitrogen intermediate production. Glutathione has been recently shown to play an important role in apoptosis and to regulate antigen-presenting-cell functions. Glutathione also serves as a carrier molecule for nitric oxide, in the form of S-nitrosoglutathione. Previous work from this laboratory has shown that glutathione and S-nitrosoglutathione are directly toxic to mycobacteria. A mutant strain of Mycobacterium bovis BCG, defective in the transport of small peptides such as glutathione, is resistant to the toxic effect of glutathione and S-nitrosoglutathione. Using the peptide transport mutant as a tool, we investigated the role of glutathione and S-nitrosoglutathione in animal and human macrophages in controlling intracellular mycobacterial growth.

Mechanism-based partial inactivation of glutathione S-transferases by nitroglycerin: tyrosine nitration vs sulfhydryl oxidation

Liver glutathione-S-transferases (GSTs) are responsible for the detoxification of electrophiles, and specifically for the metabolism of orally administered organic nitrates such as nitroglycerin (NTG). Recent studies showed that reactive nitrogen species produced by tetranitromethane (TNM), peroxynitrite, or the myeloperoxidase/H2O2/nitrite system can inactivate GST. It is not known whether NTG can similarly inactivate liver GSTs, and if shown, by what mechanism(s). We incubated purified GSTs with NTG, S-nitroso-N-acetylpenicillamine (SNAP), TNM, or vehicle (5% dextrose, D5W), followed by determination of GST activity. Incubation of GST with NTG and TNM caused significant decreases in GST activity whereas no changes were observed with SNAP or D5W. The relative GST activity (vs preincubation) was 73+/-14% for NTG, 37+/-8% for TNM, 98+/-13% for SNAP, and 98+/-9% for D5W, respectively. Exogenous glutathione (GSH) prevented both NTG- and TNM-induced changes in GST activity, consistent with the observed oxidative modification of GST, such as -SH oxidation and dimerization of oxidized GST. In contrast, NTG and TNM exhibited substantial differences in their ability to nitrate tyrosine (TYR) sites in GST. These results demonstrated that NTG can reduce the activity of its own metabolizing enzyme such as GST and this inhibitory effect of NTG was unlikely to be mediated through NO, as such, since SNAP had no effect on GST activity. The partial inactivation of GST by NTG appeared to involve -SH oxidation, but not TYR nitration. These findings provided the first evidence of mechanism-based protein inactivation by NTG, and may lend insight into the hepatic metabolism of NTG and other organic nitrates after repeated oral exposure.

Interactions of peroxynitrite and other nitrating substances with human platelets: the role of glutathione and peroxynitrite permeability

Platelets labeled with 2',7'-dihydrodichlorofluorescein diacetate (DCF-DA) and stimulated with 50-400nM peroxynitrite (ONOO(-)) produced a rapid increase of the fluorescence signal at 523nm with good linearity and reproducibility. Platelet fluorescence was inhibited by 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), suggesting that HCO(3)(-)/Cl(-) transporter mediated ONOO(-) transport into the platelets. Exposure of platelets to potassium superoxide, hydrogen peroxide, and sodium nitroprusside at concentrations of up to 100 microM did not generate a fluorescence signal. We also studied other nitrating compounds to establish the specificity of the DCF-DA-labeled platelet ONOO(-) assay. A rapid increase of fluorescence was observed when sodium hypochlorite (0.15 to 0.75mM) was added to platelets suspended in a buffered nitrite solution. Exposure of platelets to NO(2), nitroglycerin, and tetranitromethane produced a slow sustained increase of fluorescence. Endogenous glutathione appeared to be an essential factor in the generation of fluorescence by ONOO(-) and other nitrating compounds. We further studied other conditions that increased platelet fluorescence. Stimulation of platelets with thrombin (1U/mL) produced a rapid increase in fluorescence that corresponded to the formation of 20.5nmol ONOO(-) per 10(7) cells, whereas stimulation with collagen and arachidonic acid was without effect. Hypoxia of platelets for 20 and 40min followed by 5min of reoxygenation doubled the fluorescence from these platelets compared with control platelets. Thus, thrombin produced an effect that was likely due to the formation of ONOO(-) in platelets, whereas hypoxia-reoxygenation was likely to cause the formation of an active nitroglutathione-like molecule.

Peroxynitrite in myocardial ischemia-reperfusion injury

Peroxynitrite is a highly reactive oxidant which is produced during reperfusion of the ischemic heart. The role that this molecule plays in reperfusion injury has been controversial. Many investigations have demonstrated toxic effects of peroxynitrite, whereas others have found it to be protective during reperfusion. This review surveys evidence supporting both sides and proposes that peroxynitrite is a dichotomous molecule with beneficial and detrimental effects on the reperfused heart. Its toxic effects are mediated by modification and activation of a variety of targets (including poly (ADP) ribose synthetase and matrix metalloproteinases) while its beneficial effects are primarily mediated through its reaction with thiols, resulting in the formation of NO donor compounds (S-nitrosothiols).

Activation of constitutive nitric-oxide synthase activity is an early signaling event induced by ionizing radiation

Ionizing radiation at clinical dose levels activates both pro- and anti-proliferative signal transduction pathways, the balance of which determines cell fate. The initiating and amplifying mechanisms involved in the activation are poorly understood. We demonstrate that one mechanism involves stimulation of constitutive nitric-oxide synthase (NOS) activity. NOS activity of Chinese hamster ovary cells was measured by the arginine --> citrulline conversion assay. Irradiation stimulated a transient activation of NOS with maximal activity at 5 min of post-irradiation. Western blot analysis and genetic manipulation by overexpression of wild type or dominant negative NOS mutant identify the radiation-induced isoform as NOS-1. Further evidence that NOS-1 is activated by radiation was the demonstration of radiation-induced cGMP formation in cells transiently transfected with the NO-dependent soluble guanylate cyclase. Protein Tyr nitration, a footprint of peroxynitrite formation, followed radiation exposure and was inhibited by expression of a dominant negative NOS-1 mutant. Radiation-induced ERK1/2 kinase activity, a cytoprotective response to radiation, was also blocked by inhibiting NOS activity. These experiments establish NO-dependent signal transduction pathways as being radio-responsive. Given the lipophilic and relatively stable properties of NO, these results also suggest a possible mechanism by which ionization events in one cell may activate signaling processes in adjacent cells.

Artifactual-free analysis of S-nitrosoglutathione and S-nitroglutathione by neutral-pH, anion-pairing, high-performance liquid chromatography. Study on peroxynitrite-mediated S-nitration of glutathione to S-nitroglutathione under physiological conditions

The endogenous potent vasodilators and inhibitors of platelet aggregation S-nitrosoglutathione (GSNO) and S-nitroglutathione (GSNO2) are frequently analyzed by high-performance liquid chromatography (HPLC) using mobile phases of acidic pH. These systems are associated with problems stemming from rapid and considerable artifactual formation of GSNO from glutathione (GSH) and ubiquitous nitrite. We describe a novel ion-pairing HPLC method with UV absorbance detection at 334 nm for the highly specific and interference-free analysis of GSNO and GSNO2 in the presence of high GSH and nitrite concentrations. Complete avoidance of artifactual formation of GSNO was accomplished by using the anion-pairing agent tetrabutylammoniumhydrogen sulphate in the mobile phase that enables analysis of GSNO at neutral pH, at which GSH and nitrite do not react to form GSNO. This HPLC system was used to study formation of GSNO2 from GSH and peroxynitrite under physiological conditions. We found by this HPLC system that peroxynitrite (0-300 microM) reacts with GSH (0-5 mM) to form GSNO2 at a mean yield of 2%. Analysis of the same samples by a cation-pairing HPLC system with acidic mobile phase (pH 2.0) revealed, however, GSNO plus GSNO2 formation of the order of 20% due to on column reaction of GSH with peroxynitrite-derived nitrite to form GSNO. Ammonium sulfamate is frequently used to remove nitrite from thiol-containing solutions under acidic conditions. By means of the anion-pairing HPLC system it is demonstrated that nitrite removal by this method is incomplete even when ammonium sulfamate is used at high concentrations. These findings underscore the absolute requirement of neutral pH conditions for the analysis of GSNO. The novel anion-pairing HPLC method should be useful to provide reliable data on formation, reaction and metabolism of GSNO and GSNO2 in biological fluids using various detectors including mass spectrometers.

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.

Inhibition of peroxynitrite-induced nitration of tyrosine by glutathione in the presence of carbon dioxide through both radical repair and peroxynitrate formation

Peroxynitrite (ONOO-/ONOOH) is assumed to react preferentially with carbon dioxide in vivo to produce nitrogen dioxide (NO2*) and trioxocarbonate(1-) (CO3*-) radicals. We have studied the mechanism by which glutathione (GSH) inhibits the NO2*/CO3*--mediated formation of 3-nitrotyrosine. We found that even low concentrations of GSH strongly inhibit peroxynitrite-dependent tyrosine consumption (IC50 = 660 microM) as well as 3-nitrotyrosine formation (IC50) = 265 microM). From the determination of the level of oxygen produced or consumed under various initial conditions, it is inferred that GSH inhibits peroxynitrite-induced tyrosine consumption by re-reducing (repairing) the intermediate tyrosyl radicals. An additional protective pathway is mediated by the glutathiyl radical (GS*) through reduction of dioxygen to superoxide (O2*-) and reaction with NO2* to form peroxynitrate (O2NOOH/O2NOO-), which is largely unreactive towards tyrosine. Thus, GSH is highly effective in protecting tyrosine against an attack by peroxynitrite in the presence of CO2. Consequently, formation of 3-nitrotyrosine by freely diffusing NO2* radicals is highly unlikely at physiological levels of GSH.

Nitric oxide chemistry and cellular signaling

Nitric oxide (NO) has been shown to mediate a number of different physiological functions within every major organ system. This wide variety of functional roles is made all the more remarkable when one considers that NO is a simple diatomic molecule. However, despite the simplicity of the molecule, NO possesses a wide range of chemical reactivity and multiple potential reactive targets. It is the variability of NO reactivity, which leads to its capability to control such a vast range of biological functions. In essence the functionality of NO is controlled by its chemical reactivity. In order to understand this possibility further it is necessary to consider the biologically relevant reactions of nitric oxide.

Carbon dioxide stimulates the production of thiyl, sulfinyl, and disulfide radical anion from thiol oxidation by peroxynitrite

Reaction of peroxynitrite with the biological ubiquitous CO(2) produces about 35% yields of two relatively strong one-electron oxidants, CO(3) and ( small middle dot)NO(2), but the remaining of peroxynitrite is isomerized to the innocuous nitrate. Partial oxidant deactivation may confound interpretation of the effects of HCO3-/CO(2) on the oxidation of targets that react with peroxynitrite by both one- and two-electron mechanisms. Thiols are example of such targets, and previous studies have reported that HCO3-/CO(2) partially inhibits GSH oxidation by peroxynitrite at pH 7.4. To differentiate the effects of HCO3-/CO(2) on two- and one-electron thiol oxidation, we monitored GSH, cysteine, and albumin oxidation by peroxynitrite at pH 5.4 and 7.4 by thiol disappearance, oxygen consumption, fast flow EPR, and EPR spin trapping. Our results demonstrate that HCO3-/CO(2) diverts thiol oxidation by peroxynitrite from two- to one-electron mechanisms particularly at neutral pH. At acid pH values, thiol oxidation to free radicals predominates even in the absence of HCO3-/CO(2). In addition to the previously characterized thiyl radicals (RS.), we also characterized radicals derived from them such as the corresponding sulfinyl (RSO.) and disulfide anion radical (RSSR.-) of both GSH and cysteine. Thiyl, RSO. and RSSR.- are reactive radicals that may contribute to the biodamaging and bioregulatory actions of peroxynitrite.

Unraveling peroxynitrite formation in biological systems

Peroxynitrite promotes oxidative damage and is implicated in the pathophysiology of various diseases that involve accelerated rates of nitric oxide and superoxide formation. The unambiguous detection of peroxynitrite in biological systems is, however, difficult due to the combination of a short biological half-life, limited diffusion, multiple target molecule reactions, and participation of alternative oxidation/nitration pathways. In this review, we provide the conceptual framework and a comprehensive analysis of the current experimental strategies that can serve to unequivocally define the existence and quantitation of peroxynitrite in biological systems of different levels of organization and complexity.

Microscopic modeling of NO and S-nitrosoglutathione kinetics and transport in human airways

Nitric oxide (NO) appears in the exhaled breath and is elevated in inflammatory diseases. We developed a steady-state mathematical model of the bronchial mucosa for normal small and large airways to understand NO and S-nitrosoglutathione (GSNO) kinetics and transport using data from the existing literature. Our model predicts that mean steady-state NO and GSNO concentrations for large airways (generation 1) are 2.68 nM and 113 pM, respectively, in the epithelial cells and 0.11 nM (approximately 66 ppb) and 507 nM in the mucus. For small airways (generation 15), the mean concentrations of NO and GSNO, respectively, are 0.26 nM and 21 pM in the epithelial cells and 0.02 nM (approximately 12 ppb) and 132 nM in the mucus. The concentrations in the mucus compare favorably to experimentally measured values. We conclude that 1) the majority of free NO in the mucus, and thus exhaled NO, is due to diffusion of free NO from the epithelial cell and 2) the heterogeneous airway contribution to exhaled NO is due to heterogeneous airway geometries, such as epithelium and mucus thickness.

Adventitia-derived nitric oxide in rat aortas exposed to endotoxin: cell origin and functional consequences

The role of adventitial cells in bacterial lipopolysaccharide (LPS)-induced vascular nitric oxide (NO) overproduction has been largely ignored. In rat aortas exposed to LPS in vitro or in vivo, it was found that adventitia contained the major part of NO synthase (NOS)-2 protein (Western blot and immunohistochemistry) and generated the largest amount of NO (electron paramagnetic resonance spin trapping). NOS-2 immunoreactive cells were mainly resident macrophages at an early stage (5 h, in vitro or in vivo) and fibroblasts at a later stage (20 h, in vitro). Adventitial NOS-2 activity largely accounted for 1) the relaxing effect of L-arginine in rings exposed to LPS in vivo, 2) generation of an "NO store" revealed by N-acetylcysteine-induced relaxation, and 3) formation of protein-bound dinitrosyl iron complexes in the medial layer of aortic rings exposed to LPS in vitro. In conclusion, the adventitia is a powerful source of NO triggered by LPS in the rat aorta. This novel source of NO has an important impact on smooth muscle function and might be implicated in various inflammatory diseases.

Glutathione Reverses Endothelial Damage From Peroxynitrite, the Byproduct of Nitric Oxide Degradation, in Crystalloid Cardioplegia

Background —NO has been advocated as an adjunct to cardioplegia solutions. However, NO undergoes a rapid biradical reaction with superoxide anions to produce peroxynitrite (ONOO − ). ONOO − in crystalloid cardioplegia solution induces injury to coronary endothelium and to systolic function after cardioplegia and reperfusion. However, ONOO − may be degraded to less lethal or cardioprotective intermediates with glutathione (GSH) in reactions separate from its well known antioxidant effects. We hypothesized that GSH detoxifies ONOO − and reverses defects in endothelial function and systolic function when present in crystalloid cardioplegia.

Methods and Results —In anesthetized dogs on cardiopulmonary bypass, a 45-minute period of global normothermic ischemia was followed by 60 minutes of intermittent cold crystalloid cardioplegia (Plegisol) and 2 hours of reperfusion. The cardioplegia solution contained 5 μmol/L authentic ONOO − ; catalase was included to attenuate the potential antioxidant effects of GSH and to unmask the effects on ONOO − . In 1 group (CP+GSH, n=5), the cardioplegia contained 500 μmol/L GSH, whereas 1 group received crystalloid cardioplegia without GSH (CCP, n=6). There were no group differences in postcardioplegia left ventricular systolic function (end-systolic pressure-volume relation, impedance catheter: CCP 10.0±2.4 versus CP+GSH 10.6±1.3 mm Hg/mL) or diastolic chamber stiffness (β-coefficient: CCP 0.35±0.2 versus CP+GSH 0.31±0.18). Myocardial neutrophil accumulation (myeloperoxidase activity) was attenuated in CP+GSH versus CCP (2.2±0.7 versus 5.4±1.2, P <0.05). In postexperimental coronary arteries, maximal endothelium-dependent relaxation was greater in CP+GSH than in CCP (118±6% versus 92±5%, P <0.05), with a smaller EC 50 value (−7.10±0.05 versus −6.98±0.03, respectively, P <0.05). Smooth muscle relaxation was complete in both groups. The adherence of neutrophils to postexperimental coronary arteries as a measure of endothelial function was less in CP+GSH than in CCP (98±18 versus 234±36 neutrophils/mm 2 , P <0.05). Nitrosoglutathione, a byproduct of the reaction between ONOO − and GSH, was greater in CP+GSH than in CCP (4.1±2.3 versus 0.4±0.2 μg/mL, P <0.05).

Conclusions —GSH in crystalloid cardioplegia detoxifies ONOO − and forms cardioprotective nitrosoglutathione, resulting in attenuated neutrophil adherence and selective endothelial protection through the inhibition of neutrophil-mediated damage.

Novel mode of nitric oxide neurotransmission mediated via S-nitroso-cysteinyl-glycine

S-nitroso-cysteinyl-glycine, a novel nitric oxide-adduct thiol compound, can be detected in the brain (2.3+/-0.6 pmol/mg protein), and released following stimulation of sensory afferents to the rat ventrobasal thalamus in vivo (resting conditions 17 nM; stimulation: 186 nM). Iontophoretic application of CysNOGly (20-80 nA) onto thalamic neurons in vivo resulted in enhancements of excitatory responses to either NMDA or AMPA (182+/-13.6% and 244+/-27.8% of control values, n = 15). CysNOGly enhanced responses to stimulation of vibrissal afferents to 132+/-2.2% (n = 7) of control values. In contrast, the dipeptide CysGly reduced responses of ventrobasal neurons to NMDA and AMPA (54+/-8.4% and 55+/-10.8% of control, n = 5). CysNOGly was also a potent activator of soluble guanylate cyclase in vitro. Moreover, we found that NMDA elevated CysNOGly levels in vitro and this stimulatory effect was reduced by inhibitors of the neuronal NO synthase and of the gamma-glutamyl transpeptidase, suggesting that production of NO and CysGly is a prelude to CysNOGly synthesis. These findings suggest that the nitrosothiol CysNOGly plays a role in synaptic transmission in the ventrobasal thalamus. We propose a novel synaptic buffering mechanism where S-nitroso-cysteinyl-glycine serves to restrict the locus of action of nitric oxide and so increase its local availability for target delivery. This could lead to a change in neuronal responses favouring sensory transmission similar to that seen in wakefulness or arousal in order to locally enhance transmission of persistent sensory stimuli.

Mechanisms of biological S-nitrosation and its measurement

Nitric oxide (NO) exhibits multiple biological actions through formation of various oxidized intermediates derived from NO. Among them, nitrosothiol adducts (RS-NOs) with the sulfhydryl moiety of proteins and amino acids appears to be an important species in view of its unique chemical reactivity. Understanding of the biologically relevant S-nitrosation mechanism is essential because RS-NOs seem to be critically involved in modulation of intracellular and intercellular signal transduction, including gene transcription, cell apoptosis, and oxidative stress. RS-NOs have been recently found to be formed efficiently via one-electron oxidation of NO catalyzed by ceruloplasmin, a major copper-containing protein in mammalian plasma. Ceruloplasmin is synthesized mainly by hepatocytes, but it is also expressed by other cells such as macrophages and astrocytes. Once RS-NOs are formed, they function as NO transporters in biological systems, the NO being transferred to different sulfhydryls of various biomolecules. This transfer may be mediated by transnitrosation reactions occurring chemically or enzymatically by a means of specific enzymes such as protein disulfide isomerase. The molecular mechanism of biological S-nitrosation is discussed as related to the important physiological and pathophysiological functions of RS-NOs. Also, RS-NO assays that are being successfully used for detection of biological S-nitrosation are briefly reviewed.

Adaptive responses to peroxynitrite: increased glutathione levels and cystine uptake in vascular cells

We and others recently demonstrated increased glutathione levels, stimulated cystine uptake, and induced gamma-glutamylcysteinyl synthase (gamma-GCS) in vascular cells exposed to nitric oxide donors. Here we report the effects of peroxynitrite on glutathione levels and cystine uptake. Treatment of bovine aortic endothelial and smooth muscle cells with 3-morpholinosydnonimine (SIN-1), a peroxynitrite donor, resulted in transient depletion of glutathione followed by a prolonged increase beginning at 8-9 h. Concentration-dependent increases in glutathione of up to sixfold occurred 16-18 h after 0.05-2.5 mM SIN-1. Responses to SIN-1 were inhibited by copper-zinc superoxide dismutases and manganese(III)tetrakis(1-methyl-4-pyridyl)porphyrin pentachloride, providing evidence for peroxynitrite involvement. Because glutathione synthesis is regulated by amino acid availability, we also studied cystine uptake. SIN-1 treatment resulted in a prolonged increase in cystine uptake beginning at 6-9 h. Increases in cystine uptake after SIN-1 were blocked by inhibitors of protein and RNA synthesis, by extracellular glutamate but not by extracellular sodium. These studies suggest induction of the x(c)(-) pathway of amino acid uptake. A close correlation over time was observed for increases in cystine uptake and glutathione levels. In summary, vascular cells respond to chronic peroxynitrite exposure with adaptive increases in cellular glutathione and cystine transport.

Depletion of intracellular glutathione reduces mutations by nitric oxide-donating drugs

The Mutatect system is a mouse tumor line in which mutations at the hypoxanthine phosphoribosyltransferase (Hprt) locus can be readily detected both in vitro and in vivo. We have previously shown that the nitric oxide-generating drugs, glyceryl trinitrate (GTN) and sodium nitroprusside (SNP), can induce mutations that are readily detected in these cells. In the present report, we have tested the effect of glutathione depletion by buthionine sulfoximine (BSO) on cytotoxicity and mutagenicity by these two drugs. Exposure for 24 h to either drug (123 microM GTN; 500 microM SNP) induced mutations with relatively little cytotoxicity. Pretreatment with 50 microM BSO for 24 h, and then removal at the time of GTN or SNP addition, enhanced cytotoxicity to a modest extent. However, mutagenicity induced by both GTN and SNP was largely abolished. BSO did not affect nitrite accumulation in the medium over a 24-h period, indicating no inhibition of bioactivation of GTN or SNP. Maintaining BSO in the medium for 24 h prior and throughout the period of exposure to GTN or SNP produced a similar effect on mutations. N-Acetylcysteine and oxothiazolidine-4-carboxylate, drugs that are used to increase intracellular glutathione, also blocked mutations. We postulate that a product of the reaction between nitric oxide and intracellular glutathione, such as GSNO or some species derived from it, is promutagenic.

Glutathione protects against myocardial ischemia-reperfusion injury by detoxifying peroxynitrite

Peroxynitrite (ONOO(-)) formation during acute reperfusion of the ischemic heart contributes to the poor recovery of mechanical function. As glutathione (GSH) detoxifies ONOO(-), we studied whether it could protect isolated rat hearts subjected to exogenous ONOO(-)or to ischemia-reperfusion. We showed that GSH (300 microm, n=5) abolished the detrimental effect of ONOO(-)(80 microm, n=5) on mechanical function of aerobically perfused hearts. Hearts were subjected to 25 min aerobic perfusion, 20 min global, no-flow ischemia and 30 min reperfusion. GSH (3-300 microm, n=7-12) or saline vehicle (control, n=22) were infused for 10 min prior to ischemia and throughout reperfusion. During reperfusion, GSH caused a concentration-dependent improvement in the recovery of mechanical function, which was not associated with significant changes in the intracellular concentration of GSH. The concentration of dityrosine (a marker of ONOO(-) formation) in the coronary effluent during reperfusion was significantly reduced in GSH-treated hearts. The concentration of myocardial cGMP was significantly elevated by GSH during ischemia and early reperfusion. GSH improves the recovery of myocardial mechanical function after ischemia-reperfusion, an effect which may be related to the detoxification of ONOO(-)by GSH and the stimulation of soluble guanylate cyclase.

Simultaneous derivatization and quantification of the nitric oxide metabolites nitrite and nitrate in biological fluids by gas chromatography/mass spectrometry

Simultaneous quantification of nitrite and nitrate, the major oxidative metabolites of L-arginine-derived nitric oxide (NO), in biological fluids by GC or GC/MS methods is currently impossible. The separate analysis of these anions is associated with severe methodological problems. Therefore, a GC/MS method was developed which allows, for the first time, simultaneous quantification of nitrite and nitrate in various biological fluids. The method involves a single derivatization procedure, by which endogenous nitrite and nitrate and their externally added 15N-labeled analogues are simultaneously converted in aqueous acetone by pentafluorobenzyl bromide to the nitro and nitric acid ester pentafluorobenzyl derivatives, respectively, and a single GC/MS analysis. Nitrite and nitrate concentrations measured in plasma and urine of humans by this method correlated excellently with those from quantification of nitrite and nitrate in these matrixes using a previously reported GC/MS method that, however, requires reduction of nitrate to nitrite. Also, the present method enables discrimination between S-nitro- and S-nitroso-glutathione, which have identical chromatographic and spectrophotometric properties. The method is very useful to routinely study metabolism and reactions of NO and its metabolites in vitro and in vivo. It is accurate, interference-free, sensitive-50 fmol of [15N]-nitrite and [15N]nitrate were detected at signal-to-noise ratios of 870:1 and 95:1, respectively-and should be a reference method for nitrite and nitrate measurements.

Cell signaling by reactive nitrogen and oxygen species in atherosclerosis

The production of reactive oxygen and nitrogen species has been implicated in atherosclerosis principally as means of damaging low-density lipoprotein that in turn initiates the accumulation of cholesterol in macrophages. The diversity of novel oxidative modifications to lipids and proteins recently identified in atherosclerotic lesions has revealed surprising complexity in the mechanisms of oxidative damage and their potential role in atherosclerosis. Oxidative or nitrosative stress does not completely consume intracellular antioxidants leading to cell death as previously thought. Rather, oxidative and nitrosative stress have a more subtle impact on the atherogenic process by modulating intracellular signaling pathways in vascular tissues to affect inflammatory cell adhesion, migration, proliferation, and differentiation. Furthermore, cellular responses can affect the production of nitric oxide, which in turn can strongly influence the nature of oxidative modifications occurring in atherosclerosis. The dynamic interactions between endogenous low concentrations of oxidants or reactive nitrogen species with intracellular signaling pathways may have a general role in processes affecting wound healing to apoptosis, which can provide novel insights into the pathogenesis of atherosclerosis.

Interactions of oxidants with vascular signaling systems

Individual reactive oxygen species (ROS) and oxidation products of NO interact with vascular signaling mechanisms in ways that appear to have fundamental roles in the control of vascular physiological and pathophysiological function. The activities of ROS-producing systems (including various NADPH and NADH oxidases, xanthine oxidase, and NO synthase) in endothelium and/or vascular smooth muscle are controlled by receptor activation, oxygen tension, metabolic processes, and physiological forces associated with blood pressure and flow. This review focuses on how the chemical properties and metabolic sensing interactions of individual ROS (including superoxide anion, hydrogen peroxide, and peroxynitrite) interact with cellular regulatory systems to produce vascular responses. These species appear to often function through producing selective alterations in individual heme or thiol redox-regulated systems (including guanylate cyclase, cyclooxygenase, mitochondrial electron transport, and tyrosine phosphatases) to initiate physiological responses through signaling pathways that control phospholipases, protein kinases, ion channels, contractile proteins, and gene expression.

Electrospray ionization mass spectrometry of low-molecular-mass S-nitroso compounds and their thiols

Low-molecular-mass S-nitroso compounds (R-S-N=O) are potent vasodilators and inhibitors of platelet aggregation. This work describes the electrospray ionization mass spectrometric (ESI-MS) analysis of physiological and synthetic low-molecular-mass S-nitroso compounds and their thiols including S-nitrosoglutathione, S-nitrosocysteine, glutathione and cysteine. Mass spectra of the unlabeled and S-15N-labeled low-molecular-mass S-nitroso compounds investigated are characterized by abundant cations due to [M+H]+, [M+Na]+, [(M+H)-NO]+, [2 M+H]+, and [(2 M+H)-2NO]+. Mass spectra of low-molecular-mass thiols are characterized by abundant cations due to [M+H]+, [M+Na]+ and [2M+H]+. Using off-line electrospray ionization tandem mass spectrometry we unequivocally identified S-[15N]nitrosoglutathione in human red blood cells formed after their incubation with S-[15N]nitrosocysteine. These results suggest that ESI-MS in combination with an appropriate liquid chromatographic system should be a useful analytical approach for the on-line quantitative determination of low-molecular-mass S-nitroso compounds in biological fluids in the presence of their thiols and nitrite. Considerations were made about on-line ESI-MS and quantitative measurements.

Evidence for the involvement of peroxynitrite in ischaemic preconditioning in rat isolated hearts

1. The aim of this study was to investigate the involvement of peroxynitrite, reactive metabolite originating from nitric oxide and superoxide, in preconditioning of the ischaemic myocardium in rat isolated hearts. 2. Isolated hearts perfused with Krebs-Henseleit solution were preconditioned either by 3 min of coronary artery occlusion (CAO) or by peroxynitrite administration at three different concentrations (0.1, 1, 10 microM) for 3 min, followed by 10 min reperfusion and 30 min of CAO. Peroxynitrite, at 1 microM concentration, decreased the incidence of VT from 100% (n=14) to 62% (n=13) and abolished the occurrence of VF (50% in the control group). 3. N-2-mercaptopropionylglycine (MPG, 1 microM - 10 mM) produced a concentration-dependent inhibition of peroxynitrite signals in luminol chemiluminescence and 67+/-1% inhibition was observed at 100 microM (n=7). MPG (at 300 microM, n=7) added to the perfusate 10 min prior to ischaemic preconditioning or peroxynitrite infusion and maintained until CAO, significantly reversed the beneficial effects of the ischaemic and peroxynitrite-treated groups. MPG administration in the peroxynitrite-treated group increased the incidence of VT from 62% (n=13) to 100% (n=10) and total VF from 0% (n=0) to 67% (n=10). Similarly, MPG elevated the incidence of VT from 50% (n=10) to 100% (n=8) in the ischaemic preconditioned group. On its own, MPG did not affect the severity of cardiac arrhythmias. 4. These results suggest that endogenously produced peroxynitrite plays a significant role in the antiarrhythmic effect of ischaemic preconditioning in the rat isolated hearts.

Decreased aortic glutathione levels may contribute to impaired nitric oxide-induced relaxation in hypercholesterolaemia

The aim of this study was to determine if the decrease in aortic total glutathione (GSH) levels in hypercholesterolaemia is related to the impairment of relaxation to acetylcholine (ACh) and exogenous nitric oxide (NO). Isometric tension and vascular GSH levels were measured in thoracic aortic rings from rabbits fed for 12 weeks with 0.5% cholesterol diet. Hypercholesterolaemia decreased aortic GSH levels and impaired relaxation to ACh and NO. To determine if GSH depletion impaired the response to NO, normal rabbit thoracic aorta was incubated with 1,3-bis [2-chloroethyl]-1-nitrosourea (BCNU; 0.2 mmol L(-1)), a GSH reductase inhibitor, or diazine-dicarboxylic acid bis [N, N dimethylamide] (diamide; 1 mmol L(-1)), a thiol oxidizing agent. BCNU or diamide decreased aortic GSH levels and impaired ACh and NO-induced relaxation. The effects of diamide on GSH levels and relaxation were partially prevented by co-incubation with GSH ester (GSE; 2 mmol L(-1)). Increasing GSH with GSE significantly enhanced NO-induced relaxation in aorta from both hypercholesterolaemic and normal rabbits, however relaxation of hypercholesterolaemic rabbit aorta was not restored to normal. These data suggest that other factors, perhaps related to the long-term decrease in GSH levels, are responsible for reduced NO bioactivity in hypercholesterolaemia.

Reactive oxygen species and reactive nitrogen species: relevance to cyto(neuro)toxic events and neurologic disorders. An overview

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are formed under physiological conditions in the human body and are removed by cellular antioxidant defense system. During oxidative stress their increased formation leads to tissue damage and cell death. This process may be especially important in the central nervous system (CNS) which is vulnerable to ROS and RNS damage as the result of the brain high O(2) consumption, high lipid content and the relatively low antioxidant defenses in brain, compared with other tissues. Recently there has been an increased number of reports suggesting the involvement of free radicals and their non-radical derivatives in a variety of pathological events and multistage disorders including neurotoxicity, apoptotic death of neurons and neural disorders: Alzheimer's (AD), Parkinson's disease (PD) and schizophrenia. Taking into consideration the basic molecular chemistry of ROS and RNS, their overall generation and location, in order to control or suppress their action it is essential to understand the fundamental aspects of this problem. In this presentation we review and summarize the basics of all the recently known and important properties, mechanisms, molecular targets, possible involvement in cellular (neural) degeneration and apoptotic death and in pathogenesis of AD, PD and schizophrenia. The aim of this article is to provide an overview of our current knowledge of this problem and to inspire experimental strategies for the evaluation of optimum innovative therapeutic trials. Another purpose of this work is to shed some light on one of the most exciting recent advances in our understanding of the CNS: the realisation that RNS pathway is highly relevant to normal brain metabolism and to neurologic disorders as well. The interactions of RNS and ROS, their interconversions and the ratio of RNS/ROS could be an important neural tissue injury mechanism(s) involved into etiology and pathogenesis of AD, PD and schizophrenia. It might be possible to direct therapeutic efforts at oxidative events in the pathway of neuron degeneration and apoptotic death. From reviewed data, no single substance can be recommended for use in human studies. Some of the recent therapeutic strategies and neuroprotective trials need further development particularly those of antioxidants enhancement. Such an approach should also consider using combinations of radical(s) scavengers rather than a single substance.