On the Mechanism of the Ascorbic Acid-Induced Release of Nitric Oxide fromN-Nitrosated Tryptophan Derivatives: Scavenging of NO by Ascorbyl Radicals

Melatonin-Nitric Oxide Crosstalk in Plants and the Prospects of NOMela as a Nitric Oxide Donor

Melatonin regulates vital physiological processes in animals, such as the circadian cycle, sleep, locomotion, body temperature, food intake, and sexual and immune responses. In plants, melatonin modulates seed germination, longevity, circadian cycle, photoperiodicity, flowering, leaf senescence, postharvest fruit storage, and resistance against biotic and abiotic stresses. In plants, the effect of melatonin is mediated by various regulatory elements of the redox network, including RNS and ROS. Similarly, the radical gas NO mediates various physiological processes, like seed germination, flowering, leaf senescence, and stress responses. The biosynthesis of both melatonin and NO takes place in mitochondria and chloroplasts. Hence, both melatonin and nitric oxide are key signaling molecules governing their biological pathways independently. However, there are instances when these pathways cross each other and the two molecules interact with each other, resulting in the formation of N-nitrosomelatonin or NOMela, which is a nitrosated form of melatonin, discovered recently and with promising roles in plant development. The interaction between NO and melatonin is highly complex, and, although a handful of studies reporting these interactions have been published, the exact molecular mechanisms governing them and the prospects of NOMela as a NO donor have just started to be unraveled. Here, we review NO and melatonin production as well as RNS-melatonin interaction under normal and stressful conditions. Furthermore, for the first time, we provide highly sensitive, ozone-chemiluminescence-based comparative measurements of the nitric oxide content, as well as NO-release kinetics between NOMela and the commonly used NO donors CySNO and GSNO.

Nitric Oxide Acts as a Key Signaling Molecule in Plant Development under Stressful Conditions

Nitric oxide (NO), a colorless gaseous molecule, is a lipophilic free radical that easily diffuses through the plasma membrane. These characteristics make NO an ideal autocrine (i.e., within a single cell) and paracrine (i.e., between adjacent cells) signalling molecule. As a chemical messenger, NO plays a crucial role in plant growth, development, and responses to biotic and abiotic stresses. Furthermore, NO interacts with reactive oxygen species, antioxidants, melatonin, and hydrogen sulfide. It regulates gene expression, modulates phytohormones, and contributes to plant growth and defense mechanisms. In plants, NO is mainly produced via redox pathways. However, nitric oxide synthase, a key enzyme in NO production, has been poorly understood recently in both model and crop plants. In this review, we discuss the pivotal role of NO in signalling and chemical interactions as well as its involvement in the mitigation of biotic and abiotic stress conditions. In the current review, we have discussed various aspects of NO including its biosynthesis, interaction with reactive oxygen species (ROS), melatonin (MEL), hydrogen sulfide, enzymes, phytohormones, and its role in normal and stressful conditions.

Detection of nitric oxide radical and determination of its scavenging activity by antioxidants using spectrophotometric and spectrofluorometric methods

Although reactive nitrogen species (RNS) may attack biomacromolecules and cause tissue damage when unbalanced by natural antioxidant defenses of the organism, they can also take part in cell signaling under different physiological states and defend against certain pathogens. Since there is a scarcity of analytical methods to detect radicalic NO and its scavengers, a functionalized gold nanoparticle-based spectrophotometric method and a spectrofluorometric method have been separately developed to test antioxidant activity toward scavenging of NO produced from sodium nitroprusside (SNP). The spectrophotometric method involves conversion of NO to nitrite, followed by the formation of an azo dye with 4-aminothiophenol (4-ATP)-modified gold nanoparticles (AuNPs) and N-(1-naphthyl)-ethylene diamine dichloride (NED) and its absorbance measurement at 565 nm. Calibration equations were established by taking the absorbance difference in the presence and absence of antioxidants. In the spectrofluorometric method, the excess of NO radicals, after being scavenged by thiol type antioxidants, caused a decrease in resorcinol fluorescence. The developed spectrophotometric method was applied to orange juice and its trolox equivalent (TE) antioxidant activity was found. By further applying the developed methods to real samples such as bovine serum albumin (BSA), fetal bovine serum (FBS), saliva and certain biomolecules, it is envisaged that these novel methods improving the selectivity of previous methods can be useful in human health and disease research associated with nitric oxide. The developed methods were compared and validated against the conventional Griess assay with Student t-test and F tests.

Antidepressant Like Effect of Ascorbic Acid in Mice: Possible Involvement of NO-sGC-cGMP Signaling

The present study was designed to determine the antidepressant like activity of ascorbic acid (AA) in mice. Further the influence of NO-sGC-cGMP signaling in the antidepressant like effect of AA in mice was determined. Male swiss albino mice were used in the present study. Mice in the control group received saline and fluoxetine (10 mg/kg, i.p.) was used as the standard antidepressant drug. AA (50, 100 and 150 mg/kg, i.p.) was administered to the mice and depression related behavior were determined using tail suspension test (TST) and forced swim test (FST). Further the whole brain nitrite and serotonin levels were also determined. It was observed that the administration of AA (100 mg/kg, i.p.) reversed the depression like behavior in mice in TST and FST. AA (100 mg/kg, i.p.) treatment decreased the level of nitrite and increased the level of serotonin in the brain of mice significantly as compared to control. Further the behavioral and neurochemical effect of AA (50 mg/kg, i.p) was studied in NO modulator [NO donor: L-Arginine (50 mg/kg, i.p); NO-sGC inhibitor: methylene blue (1 mg/kg, i.p.) and cGMP modulator: sildenafil (1 mg/kg, i.p.)] pretreated mice. It was observed that the pretreatment of NO donor and cGMP modulator counteracted the effect conferred by AA (50 mg/kg, i.p). While the pretreatment of NO-sGC inhibitor potentiated the effect conferred by AA (50 mg/kg, i.p). The present study suggested that the AA confer antidepressant like effect in mice and NO-sGC-cGMP signaling pathway influence the antidepressant like effect of AA in mice.

Coating small-diameter ePTFE vascular grafts with tunable poly(diol-co-citrate-co-ascorbate) elastomers to reduce neointimal hyperplasia

Lack of long-term patency has hindered the clinical use of small-diameter prosthetic vascular grafts with the majority of these failures due to the development of neointimal hyperplasia. Previous studies by our laboratory revealed that small-diameter expanded polytetrafluoroethylene (ePTFE) grafts coated with antioxidant elastomers are a promising localized therapy to inhibit neointimal hyperplasia. This work is focused on the development of poly(diol-co-citrate-co-ascorbate) (POCA) elastomers with tunable properties for coating ePTFE vascular grafts. A bioactive POCA elastomer (@20 : 20 : 8, [citrate] : [diol] : [ascorbate]) coating was applied on a 1.5 mm diameter ePTFE vascular graft as the most promising therapeutic candidate for reducing neointimal hyperplasia. Surface ascorbate density on the POCA elastomer was increased to 67.5 ± 7.3 ng mg-1 cm-2. The mechanical, antioxidant, biodegradable, and biocompatible properties of POCA demonstrated desirable performance for in vivo use, inhibiting human aortic smooth muscle cell proliferation, while supporting human aortic endothelial cells. POCA elastomer coating number was adjusted by a modified spin-coating method to prepare small-diameter ePTFE vascular grafts similar to natural vessels. A significant reduction in neointimal hyperplasia was observed after implanting POCA-coated ePTFE vascular grafts in a guinea pig aortic interposition bypass graft model. POCA elastomer thus offers a new avenue that shows promise for use in vascular engineering to improve long-term patency rates by coating small-diameter ePTFE vascular grafts.

Enhancement of NO release from S-nitrosoalbumin by pollution derived metal ions

S-Nitrosothiols act as a comparatively long-lived reservoir of releasable nitric oxide (NO) present in vivo in a variety of body fluids. Soluble constituents of air-borne particulate matter (PM) can affect S-nitrosothiol stability and deregulate NO-based biological signaling. PM aqueous extracts of standard urban dust (SRM 1648a) were prepared, and their effect on human serum S-nitrosoalbumin (HSA-NO) stability was studied. The results indicated that PM extracts induced a release of NO from HSA-NO in a dose-dependent manner. To identify the inorganic components of urban PM responsible for HSA-NO decomposition, the effects of individual metal ions and metal ion mixtures, detected in the SRM 1648a aqueous extract, were examined. The dominant role of copper ions (specifically Cu+) was confirmed, but the results did not exclude the influence of other water-soluble PM components. Measurements with the application of several common metal ion chelators confirmed that Cu2+ may participate in NO release from HSA-NO and that reduction to monovalent Cu+ (responsible for S-NO bond breaking) may occur with the participation of S-nitrosoalbumin. The addition of ascorbic acid (AscA) significantly enhanced the effectiveness of NO release by PM extracts both kinetically and quantitatively, by inducing an increase in the reduction of Cu2+ to Cu+. These results indicate that AscA present in the respiratory tract lining fluids and plasma may amplify the activity of inorganic components of PM in S-nitrosothiol decomposition.

N-Nitrosomelatonin, an efficient nitric oxide donor and transporter in Arabidopsis seedlings

Nitric oxide (NO) produced in plant cells has the unique ability to interact with various other biomolecules, thereby facilitating its own as well as their signaling and associated actions at their sites of biosynthesis and at other sites via transcellular long distance transport of the molecular complexes. Melatonin (Mel) is one such biomolecule produced in plant cells which has fascinated plant biologists with regard to its molecular crosstalk with other molecules to serve its roles as a growth regulator. Present work reports the synthesis of N-nitrosomelatonin (NOMela) and its preferential uptake by Arabidopsis seedlings roots and long distance transport to the leaves through vascular strands. Equimolar (250 μM) concentrations of NOMela and S-nitrosoglutathione (GSNO) in aqueous solutions bring about 52.8% more release of NO from NOMela than from GSNO. Following confocal laser scanning microscopic (CLSM) imaging, Pearson's correlation coefficient analysis of the Scatter gram of endogenously taken up NOMela demonstrates significant NO signal in roots emanating from mitochondria. NOMela (250 μM) taken up by Arabidopsis seedling roots also proved more efficient as a NO transporter from primary root to leaves than 250 μM of GSNO. These novel observations on NOMela thus hold promise to decipher its crucial role as a NO carrier and reservoir in plant cells, and also as a facilitator of melatonin action in plant development.

Updating NO•/HNO interconversion under physiological conditions: A biological implication overview

Azanone (HNO/NO^-), also called nitroxyl, is a highly reactive compound whose biological role is still a matter of debate. A key issue that remains to be clarified regarding HNO and its biological activity is that of its endogenous formation. Given the overlap of the molecular targets and reactivity of nitric oxide (NO•) and HNO, its chemical biology was perceived to be similar to that of NO• as a biological signaling agent. However, despite their closely related reactivity, NO• and HNO's biochemical pathways are quite different. Moreover, the reduction of nitric oxide to azanone is possible but necessarily coupled to other reactions, which drive the reaction forward, overcoming the unfavorable thermodynamic barrier. The mechanism of this NO•/HNO interplay and its downstream effects in different contexts were studied recently, showing that more than fifteen moderate reducing agents react with NO• producing HNO. Particularly, it is known that the reaction between nitric oxide and hydrogen sulfide (H₂S) produces HNO. However, this rate constant was not reported yet. In this work, firstly the NO•/H₂S effective rate constant was measured as a function of the pH. Then, the implications of these chemical (non-enzymatic), biologically compatible, routes to endogenous HNO formation was discussed. There is no doubt that HNO could be (is?) a new endogenously produced messenger that mediates specific physiological responses, many of which were attributed yet to direct NO• effects.

Signaling pathway played by salicylic acid, gentisic acid, nitric oxide, polyamines and non-enzymatic antioxidants in compatible and incompatible Solanum-tomato mottle mosaic virus interactions

Plants are exposed to a vast array of pathogens. The interaction between them may be classified in compatible and incompatible. Polyamines (PAs) are involved in defense responses, as well as salicylic acid (SA), gentisic acid (GA) and nitric oxide (NO), which can increase the content of reactive oxygen species (ROS), creating a harsh environment to the pathogen. ROS can also damage the host cell and they can be controlled by ascorbate and glutathione. Among phytopathogens, one of the major threats to tomato crops is tomato mottle mosaic virus (ToMMV). Resistance against this virus probably involves the Tm-2² gene. This work aimed to analyze signaling and antioxidant molecules in the defense response against ToMMV in Solanum pimpinellifolium and in S. lycopersicum 'VFNT'. In S. pimpinellifolium plants inoculated with ToMMV, an increase in NO, SA, GA, ascorbate and oxidized glutathione and a decrease in the content of PAs were observed. Characteristic symptoms of diseased plants and high absorbance values in PTA-ELISA indicated a compatible interaction. In VFNT-inoculated plants, less significant differences were noticed. Symptoms and viral concentration were not detected, indicating an incompatible interaction, possibly associated with the effector-triggered immunity (ETI) response.

Cytoskeletal stability and metabolic alterations in primary human macrophages in long-term microgravity

The immune system is one of the most affected systems of the human body during space flight. The cells of the immune system are exceptionally sensitive to microgravity. Thus, serious concerns arise, whether space flight associated weakening of the immune system ultimately precludes the expansion of human presence beyond the Earth's orbit. For human space flight, it is an urgent need to understand the cellular and molecular mechanisms by which altered gravity influences and changes the functions of immune cells. The CELLBOX-PRIME (= CellBox-Primary Human Macrophages in Microgravity Environment) experiment investigated for the first time microgravity-associated long-term alterations in primary human macrophages, one of the most important effector cells of the immune system. The experiment was conducted in the U.S. National Laboratory on board of the International Space Station ISS using the NanoRacks laboratory and Biorack type I standard CELLBOX EUE type IV containers. Upload and download were performed with the SpaceX CRS-3 and the Dragon spaceship on April 18th, 2014 / May 18th, 2014. Surprisingly, primary human macrophages exhibited neither quantitative nor structural changes of the actin and vimentin cytoskeleton after 11 days in microgravity when compared to 1g controls. Neither CD18 or CD14 surface expression were altered in microgravity, however ICAM-1 expression was reduced. The analysis of 74 metabolites in the cell culture supernatant by GC-TOF-MS, revealed eight metabolites with significantly different quantities when compared to 1g controls. In particular, the significant increase of free fucose in the cell culture supernatant was associated with a significant decrease of cell surface-bound fucose. The reduced ICAM-1 expression and the loss of cell surface-bound fucose may contribute to functional impairments, e.g. the activation of T cells, migration and activation of the innate immune response. We assume that the surprisingly small and non-significant cytoskeletal alterations represent a stable "steady state" after adaptive processes are initiated in the new microgravity environment. Due to the utmost importance of the human macrophage system for the elimination of pathogens and the clearance of apoptotic cells, its apparent robustness to a low gravity environment is crucial for human health and performance during long-term space missions.

Solid-phase synthesis provides a modular, lysine-based platform for fluorescent discrimination of nitroxyl and biological thiols

A synthetically facile solid-phase approach yields fluorescent Cu(ii)-based lysine conjugates which selectively detect nitroxyl and thiols in live cells.

We describe a modular, synthetically facile solid-phase approach aimed at separating the fluorescent reporter and binding unit of small-molecule metal-based sensors. The first representatives contain a lysine backbone functionalized with a tetramethylrhodamine fluorophore, and they operate by modulating the oxidation state of a copper ion ligated to an [N₄] (cyclam) or an [N₂O] (quinoline-phenolate) moiety. We demonstrate the selectivity of their Cu(ii) complexes for sensing nitroxyl (HNO) and thiols (RSH), respectively, and investigate the mechanism responsible for the observed reactivity in each case. The two lysine conjugates are cell permeable in the active, Cu(ii)-bound forms and retain their analyte selectivity intracellularly, even in the presence of interfering species such as nitric oxide, nitrosothiols, and hydrogen sulfide. Moreover, we apply the new probes to discriminate between distinct levels of intracellular HNO and RSH generated upon stimulation of live HeLa cells with ascorbate and hydrogen sulfide, respectively. The successful implementation of the lysine-based sensors to gain insight into biosynthetic pathways validates the method as a versatile tool for producing libraries of analogues with minimal synthetic effort.

Mechanism and regulation of peroxidase-catalyzed nitric oxide consumption in physiological fluids: critical protective actions of ascorbate and thiocyanate

Catalytic consumption of nitric oxide (NO) by myeloperoxidase and related peroxidases is implicated as playing a key role in impairing NO bioavailability during inflammatory conditions. However, there are major gaps in our understanding of how peroxidases consume NO in physiological fluids, in which multiple reactive enzyme substrates and antioxidants are present. Notably, ascorbate has been proposed to enhance myeloperoxidase-catalyzed NO consumption by forming NO-consuming substrate radicals. However, we show that in complex biological fluids ascorbate instead plays a critical role in inhibiting NO consumption by myeloperoxidase and related peroxidases (lactoperoxidase, horseradish peroxidase) by acting as a competitive substrate for protein-bound redox intermediates and by efficiently scavenging peroxidase-derived radicals (e.g., urate radicals), yielding ascorbyl radicals that fail to consume NO. These data identify a novel mechanistic basis for how ascorbate preserves NO bioavailability during inflammation. We show that NO consumption by myeloperoxidase Compound I is significant in substrate-rich fluids and is resistant to competitive inhibition by ascorbate. However, thiocyanate effectively inhibits this process and yields hypothiocyanite at the expense of NO consumption. Hypothiocyanite can in turn form NO-consuming radicals, but thiols (albumin, glutathione) readily prevent this. Conversely, where ascorbate is absent, glutathione enhances NO consumption by urate radicals via pathways that yield S-nitrosoglutathione. Theoretical kinetic analyses provide detailed insights into the mechanisms by which ascorbate and thiocyanate exert their protective actions. We conclude that the local depletion of ascorbate and thiocyanate in inflammatory microenvironments (e.g., due to increased metabolism or dysregulated transport) will impair NO bioavailability by exacerbating peroxidase-catalyzed NO consumption.

Oxidative and nitrosative stress induced in myofibrillar proteins by a hydroxyl-radical-generating system: impact of nitrite and ascorbate

Understanding the chemistry behind the redox properties of nitrite and ascorbate is essential to identify the impact of curing agents on food quality and optimize the formulation of cured meat products. This study was designed to gain insight into the interactions between curing agents and myofibrillar proteins (MPs) during in vitro oxidation by a hydroxyl-radical-generating system. MPs (4 mg/mL) were oxidized for 4 days at 37 °C under constant stirring with 25 μM iron(III) and 2.5 mM hydrogen peroxide. Dependent upon the addition of nitrite (0, 75, and 150 mg/L) and ascorbate (0, 250, and 500 mg/L), nine different reaction units were prepared in triplicate (n = 3) according to a total factorial design. Upon completion of the oxidation assay, samples were analyzed for the concentration of tryptophan (TRP), α-aminoadipic semialdehyde (AAS), Schiff bases (SBs), and 3-nitrotyrosine (3NT). Ascorbate at 250 mg/L significantly inhibited the depletion of TRP (∼20% inhibition) and the formation of AAS and SBs (>90% inhibition) in MP suspensions. Nitrite, alone, had a negligible effect on protein oxidation but induced the formation of a specific marker of nitrosative stress, namely, 3NT. Ascorbate was also efficient at inhibiting the formation of 3NT by a dose-dependent anti-nitrosative effect and enabled the antioxidant action of nitrite.

Nitric oxide in plants: the roles of ascorbate and hemoglobin

Ascorbic acid and hemoglobins have been linked to nitric oxide metabolism in plants. It has been hypothesized that ascorbic acid directly reduces plant hemoglobin in support of NO scavenging, producing nitrate and monodehydroascorbate. In this scenario, monodehydroascorbate reductase uses NADH to reduce monodehydroascorbate back to ascorbate to sustain the cycle. To test this hypothesis, rates of rice nonsymbiotic hemoglobin reduction by ascorbate were measured directly, in the presence and absence of purified rice monodehydroascorbate reductase and NADH. Solution NO scavenging was also measured methodically in the presence and absence of rice nonsymbiotic hemoglobin and monodehydroascorbate reductase, under hypoxic and normoxic conditions, in an effort to gauge the likelihood of these proteins affecting NO metabolism in plant tissues. Our results indicate that ascorbic acid slowly reduces rice nonsymbiotic hemoglobin at a rate identical to myoglobin reduction. The product of the reaction is monodehydroascorbate, which can be efficiently reduced back to ascorbate in the presence of monodehydroascorbate reductase and NADH. However, our NO scavenging results suggest that the direct reduction of plant hemoglobin by ascorbic acid is unlikely to serve as a significant factor in NO metabolism, even in the presence of monodehydroascorbate reductase. Finally, the possibility that the direct reaction of nitrite/nitrous acid and ascorbic acid produces NO was measured at various pH values mimicking hypoxic plant cells. Our results suggest that this reaction is a likely source of NO as the plant cell pH drops below 7, and as nitrite concentrations rise to mM levels during hypoxia.

Nitric oxide, antioxidants and prooxidants in plant defence responses

In plant cells the free radical nitric oxide (NO) interacts both with anti- as well as prooxidants. This review provides a short survey of the central roles of ascorbate and glutathione-the latter alone or in conjunction with S-nitrosoglutathione reductase-in controlling NO bioavailability. Other major topics include the regulation of antioxidant enzymes by NO and the interplay between NO and reactive oxygen species (ROS). Under stress conditions NO regulates antioxidant enzymes at the level of activity and gene expression, which can cause either enhancement or reduction of the cellular redox status. For instance chronic NO production during salt stress induced the antioxidant system thereby increasing salt tolerance in various plants. In contrast, rapid NO accumulation in response to strong stress stimuli was occasionally linked to inhibition of antioxidant enzymes and a subsequent rise in hydrogen peroxide levels. Moreover, during incompatible Arabidopsis thaliana-Pseudomonas syringae interactions ROS burst and cell death progression were shown to be terminated by S-nitrosylation-triggered inhibition of NADPH oxidases, further highlighting the multiple roles of NO during redox-signaling. In chemical reactions between NO and ROS reactive nitrogen species (RNS) arise with characteristics different from their precursors. Recently, peroxynitrite formed by the reaction of NO with superoxide has attracted much attention. We will describe putative functions of this molecule and other NO derivatives in plant cells. Non-symbiotic hemoglobins (nsHb) were proposed to act in NO degradation. Additionally, like other oxidases nsHb is also capable of catalyzing protein nitration through a nitrite- and hydrogen peroxide-dependent process. The physiological significance of the described findings under abiotic and biotic stress conditions will be discussed with a special emphasis on pathogen-induced programmed cell death (PCD).

Xanthine oxidase-mediated denitrosation of N-nitroso-tryptophan by superoxide and uric acid

Recent studies indicate the formation of protein nitrosamines in vivo and tryptophan residues in proteins might represent important targets of nitrosative and oxidative stress. In the present work, we examined the mechanism by which xanthine oxidase (XO) denitrosates N-nitroso Trp residues and determined the applicability of the reactions involved to the detection of nitrosated Trp residues by tri-iodide-based chemiluminescence. We found that - in addition to superoxide - denitrosation of N-acetyl-nitroso Trp (NANT) by hypoxanthine and XO occurred via the intermediacy of uric acid. Zero-order dependence of NANT decay rate with uric acid was achieved with increasing concentrations of uric acid (k(0)∼6.0×10(-4)s(-1)) and generated nitric oxide. In contrast, S-nitrosoglutathione and nitrosyl-myoglobin were stable in the presence of uric acid. NANT decomposition by uric acid could be reproducibly measured using the tri-iodide-based chemiluminescence assay in the presence of excess nitrite upon pre-treatment with acidified sulfanilamide. N-nitrosated albumin was sensitive to uric acid-induced decomposition only after proteolytic degradation. In conclusion, XO decomposes nitrosated Trp through superoxide and uric acid pathways and in the case of uric acid generates free nitric oxide. Site-specificity of this reaction may possibly be used in combination with the tri-iodide-based chemiluminescence assay to discern between nitrosated Trp, S-nitrosothiols, and nitrosylated heme proteins.

Regulation of Influenza Virus-Caused Oxidative Stress by Kegan Liyan Oral Prescription, as Monitored by Ascorbyl Radical ESR Signals

To study the oxidative stress level of the influenza virus A FM1 subset-infected mouse in intranasal inhalation as a model, we employ an ascorbyl radical's ESR (electron spin resonance) spectrum as an oxidative stress biomarker. These infected mice were pretreated with Ribavirin, ascorbic acid, superoxide dismutase (SOD) or Kegan Liyan oral prescription (KGLY, proprietary Chinese medicine for influenza and common cold) in the stomach tube for 3 days, and then followed by the virus-infecting for 4 days. On the 4th day, samples were collected. It is recognized the strength of ascorbyl radical's ESR signal ( A -.) (a H4 = 0.177 Gauss, g = 2.00517) denotes oxidative stress level in vivo and in vitro. The magnitude of ESR spectrum (28.65 ± 10.71 AU) in mice infected with influenza virus was significantly higher than those of healthy control mice (19.10 ± 3.61 AU). Serum A -. in mice treated with Ribavirin, ascorbic acid, SOD and KGLY declined to 19.70 ± 6.05, 18.50 ± 2.93 and 16.25 ± 3.59, 18.40 ± 2.14 AU respectively. It is close to A -. signal height in healthy controls via down-regulation of the influenza virus-caused oxidative stress level getting decline in the lung index of pneumonia as compare to those of untreated healthy and the influenza virus infected mice pneumonia. It is well known that SOD can prevent the influenza virus pneumonia enhancing mouse survival rate; Ribavirin can treat viral diseases. Data from this study suggested that KGLY may indirectly relieve influenza virus-infected pneumonia via down- regulation of virus caused oxidative stress coupled with a redox reaction cascade as ribavirin, ascorbic acid and SOD.

What are the differences between ascorbic acid and NADH as hydride and electron sources in vivo on thermodynamics, kinetics, and mechanism?

Ascorbic acid (AscH(2)) and dihydronicotinamide adenine dinucleotide (NADH) are two very important natural redox cofactors, which can be used as hydride, electron, and hydrogen atom sources to take part in many important bioreduction processes in vivo. The differences of the two natural reducing agents as hydride, hydrogen atom, and electron donors in thermodynamics, kinetics, and mechanisms were examined by using 5,6-isopropylidene ascorbate (iAscH(-)) and β-D-glucopyranosyl-1,4-dihydronicotinamide acetate (GluNAH) as their models, respectively. The results show that the hydride-donating ability of iAscH(-) is smaller than that of GluNAH by 6.0 kcal/mol, but the electron-donating ability and hydrogen-donating ability of iAscH(-) are larger than those of GluNAH by 20.8 and 8.4 kcal/mol, respectively, which indicates that iAscH(-) is a good electron donor and a good hydrogen atom donor, but GluNAH is a good hydride donor. The kinetic intrinsic barrier energy of iAscH(-) to release hydride anion in acetonitrile is larger than that of GluNAH to release hydride anion in acetonitrile by 6.9 kcal/mol. The mechanisms of hydride transfer from iAscH(-) and GluNAH to phenylxanthium perchlorate (PhXn(+)), a well-known hydride acceptor, were examined, and the results show that hydride transfer from GluNAH adopted a one-step mechanism, but the hydride transfer from iAscH(-) adopted a two-step mechanism (e-H(•)). The thermodynamic relation charts (TRC) of the iAscH(-) family (including iAscH(-), iAscH(•), iAsc(•-), and iAsc) and of the GluNAH family (including GluNAH, GluNAH(•+), GluNA(•), and GluNA(+)) in acetonitrile were constructed as Molecule ID Cards of iAscH(-) and of GluNAH in acetonitrile. By using the Molecule ID Cards of iAscH(-) and GluNAH, the character chemical properties not only of iAscH(-) and GluNAH but also of the various reaction intermediates of iAscH(-) and GluNAH all have been quantitatively diagnosed and compared. It is clear that these comparisons of the thermodynamics, kinetics, and mechanisms between iAscH(-) and GluNAH as hydride and electron donors in acetonitrile should be quite important and valuable to diagnose and understand the different roles and functions of ascorbic acid and NADH as hydride, hydrogen atom, and electron sources in vivo.

Redox-sensitivity and site-specificity of S- and N- denitrosation in proteins

BACKGROUND

S-nitrosation--the formation of S-nitrosothiols (RSNOs) at cysteine residues in proteins--is a posttranslational modification involved in signal transduction and nitric oxide (NO) transport. Recent studies would also suggest the formation of N-nitrosamines (RNNOs) in proteins in vivo, although their biological significance remains obscure. In this study, we characterized a redox-based mechanism by which N-nitroso-tryptophan residues in proteins may be denitrosated.

METHODOLOGY/PRINCIPAL FINDINGS

The denitrosation of N-acetyl-nitroso Trp (NANT) by glutathione (GSH) required molecular oxygen and was inhibited by superoxide dismutase (SOD). Transnitrosation to form S-nitrosoglutathione (GSNO) was observed only in the absence of oxygen or presence of SOD. Protein denitrosation by GSH was studied using a set of mutant recombinant human serum albumin (HSA). Trp-214 and Cys-37 were the only two residues nitrosated by NO under aerobic conditions. Nitroso-Trp-214 in HSA was insensitive to denitrosation by GSH or ascorbate while denitrosation at Cys-37 was evident in the presence of GSH but not ascorbate. GSH-dependent denitrosation of Trp-214 was restored in a peptide fragment of helix II containing Trp-214. Finally, incubation of cell lysates with NANT revealed a pattern of protein nitrosation distinct from that observed with GSNO.

CONCLUSIONS

We propose that the denitrosation of nitrosated Trp by GSH occurs through homolytic cleavage of nitroso Trp to NO and a Trp aminyl radical, driven by the formation of superoxide derived from the oxidation of GSH to GSSG. Overall, the accessibility of Trp residues to redox-active biomolecules determines the stability of protein-associated nitroso species such that in the case of HSA, N-nitroso-Trp-214 is insensitive to denitrosation by low-molecular-weight antioxidants. Moreover, RNNOs can generate free NO and transfer their NO moiety in an oxygen-dependent fashion, albeit site-specificities appear to differ markedly from that of RSNOs.

Reactive oxygen species and nitric oxide in plant mitochondria: origin and redundant regulatory systems

Plant mitochondria differ from their mammalian counterparts in many respects, which are due to the unique and variable surroundings of plant mitochondria. In green leaves, plant mitochondria are surrounded by ample respiratory substrates and abundant molecular oxygen, both resulting from active photosynthesis, while in roots and bulky rhizomes and fruit carbohydrates may be plenty, whereas oxygen levels are falling. Several enzymatic complexes in mitochondrial electron transport chain (ETC) are capable of reactive oxygen species (ROS) formation under physiological and pathological conditions. Inherently connected parameters such as the redox state of electron carriers in the ETC, ATP synthase activity and inner mitochondrial membrane potential, when affected by external stimuli, can give rise to ROS formation via complexes I and III, and by reverse electron transport (RET) from complex II. Superoxide radicals produced are quickly scavenged by superoxide dismutase (MnSOD), and the resulting H(2)O(2) is detoxified by peroxiredoxin-thioredoxin system or by the enzymes of ascorbate-glutathione cycle, found in the mitochondrial matrix. Arginine-dependent nitric oxide (NO)-releasing activity of enzymatic origin has been detected in plant mitochondria. The molecular identity of the enzyme is not clear but the involvement of mitochondria-localized enzymes responsible for arginine catabolism, arginase and ornithine aminotransferase has been shown in the regulation of NO efflux. Besides direct control by antioxidants, mitochondrial ROS production is tightly controlled by multiple redundant systems affecting inner membrane potential: NAD(P)H-dependent dehydrogenases, alternative oxidase (AOX), uncoupling proteins, ATP-sensitive K(+) channel and a number of matrix and intermembrane enzymes capable of direct electron donation to ETC. NO removal, on the other hand, takes place either by reactions with molecular oxygen or superoxide resulting in peroxynitrite, nitrite or nitrate ions or through interaction with non-symbiotic hemoglobins or glutathione. Mitochondrial ROS and NO production is tightly controlled by multiple redundant systems providing the regulatory mechanism for redox homeostasis and specific ROS/NO signaling.

Formation mechanism of silver nanoparticle 1D microstructures and their hierarchical assembly into 3D superstructures

Flower-like silver nanoparticle superstructures are prepared by the reaction of silver nitrate and ascorbic acid in an acidic aqueous solution of a polynaphthalene system. The three-dimensional flower-like structure has a purely hierarchic arrangement, wherein each petal is composed of bundles of silver particle chains, each enclosed in a polymer sheath. The ordering arises from strong adsorption of silver ions onto the polymer and by the interplay of the redox properties of nitric and ascorbic acid. As a result, linear silver cyanide, formed on the polymer, probably due to intrinsic electric dipole fields, organizes the silver particle chains in dumbbell-like structures, resembling buds and flower-like structures. By dilution and heating of the mother liquors, it is also possible to obtain single petals, i.e. micrometer sized bundles of linearly aggregated silver nanoparticle chains, each enclosed in a polymer sheath.The comprehension of the hierarchic assembly of silver nanoparticles, paves the way to a facile general method to prepare polymer-metal nanoparticle chains and flower-like superstructures.The results of this study improve both the understanding of the formation mechanism of hierarchic structures at mild temperatures and our ability to tailor them to sizes and shapes appropriate for technological purposes.

Comparing the chemical biology of NO and HNO

For the past couple of decades nitric oxide (NO) and nitroxyl (HNO) have been extensively studied due to the important role they play in many physiological and/or pharmacological processes. Many researchers have reported important signaling pathways as well as mechanisms of action of these species, showing direct and indirect effects depending on the environment. Both NO and HNO can react with, among others, metals, proteins, thiols and heme proteins via unique and distinct chemistry leading to improvement of some clinical conditions. Understanding the basic chemistry of NO and HNO and distinguishing their mechanisms of action as well as methods of detection are crucial for understanding the current and potential clinical applications. In this review, we summarize some of the most important findings regarding NO and HNO chemistry, revealing some of the possible mechanisms of their beneficial actions.

N-nitrosomelatonin: synthesis, chemical properties, potential prodrug

Melatonin is easily nitrosated via various mechanisms at the nitrogen atom of the indole ring to give N-nitrosomelatonin (NOMela). This mini-review provides a comprehensive view of this N-nitroso compound. With an improved procedure NOMela can now economically synthesized with low laboratory expenditure. The major chemical property of NOMela, i.e. the (formally) transfer of the NO+ function to its target nucleophile, is explained in detail and a variety of detection methods using this reaction are suggested. As the suspected carcinogenical potential of NOMela is clearly overruled it seems attractive to apply this nitroso compound for endogenous generation of S-nitrosothiols that act as nitric oxide donors in vivo.

The impact of N-nitrosomelatonin as nitric oxide donor in cell culture experiments

N-nitrosomelatonin (NOMela) is well-known for its capabilities of transnitrosating nucleophiles such as thiols and ascorbate, thereby generating nitric oxide (NO)-releasing compounds. It is unknown, however, whether NOMela can be successfully applied as a precursor of NO in a complex biological environment like a cell culture system. NO donors may be useful to induce the transcription factor hypoxia inducible factor 1 (HIF-1), which coordinates the protection of cells and tissues from the lack of oxygen (hypoxia). In this study, the effects of NOMela in an in vitro cell-free assay [NO-release, inhibition of prolylhydroxylase1 (PHD1)] and in living cells (upregulation of HIF-1, reduction of HIF-1 hydroxylation, upregulation of the HIF-1-target gene PHD2) were compared with those of the frequently applied NO donor S-nitrosoglutathione (GSNO) under normoxic and hypoxic conditions. In contrast to GSNO, NOMela released NO in a predictable manner and this release in vitro was found to be independent of the composition of the buffer system. The NOMela-mediated effects in oxygenated cells were in all cases comparable to the hypoxic response, whereas unphysiological strong effects were observed with GSNO. Probably, because of the antioxidative power of the NOMela-dependent formation of melatonin, cells were completely protected against the attack of reactive nitrogen oxygen species, which are generated by autoxidation of NO. In conclusion, NOMela had to be an excellent NO precursor for cells in culture and potentially tissues.

Potential role of tryptophan derivatives in stress responses characterized by the generation of reactive oxygen and nitrogen species

To face physicochemical and biological stresses, living organisms evolved endogenous chemical responses based on gas exchange with the atmosphere and on formation of nitric oxide (NO(*)) and oxygen derivatives. The combination of these species generates a complex network of variable extension in space and time, characterized by the nature and level of the reactive oxygen (ROS) and nitrogen species (RNS) and of their organic and inorganic scavengers. Among the latter, this review focusses on natural 3-substituted indolic structures. Tryptophan-derived indoles are unsensitive to NO(*), oxygen and superoxide anion (O(2)(*-)), but react directly with other ROS/RNS giving various derivatives, most of which have been characterized. Though the detection of some products like kynurenine and nitroderivatives can be performed in vitro and in vivo, it is more difficult for others, e.g., 1-nitroso-indolic compounds. In vitro chemical studies only reveal the strong likelihood of their in vivo generation and biological effects can be a sign of their transient formation. Knowing that 1-nitrosoindoles are NO donors and nitrosating agents indicating they can thus act both as mutagens and protectors, the necessity for a thorough evaluation of indole-containing drugs in accordance with the level of the oxidative stress in a given pathology is highlighted.

N-nitrosomelatonin outcompetes S-nitrosocysteine in inhibiting glyceraldehyde 3-phosphate dehydrogenase: first evidence that N-nitrosomelatonin can modify protein function

Low-molecular-weight S-nitrosothiols (RSNOs) are well known for their capability to transnitrosate cysteine residues of enzymes thereby altering their catalytic activity. It is unknown, however, whether N-nitrosomelatonin (NOMela) which is highly effective in transnitrosating low-molecular-weight thiols (RSHs) can also alter protein function. In the present study, we report on such a capability with glyceraldehyde 3-phosphate dehydrogenase (GAPDH) as a target enzyme. Reaction of NOMela with GAPDH resulted in an increase of RSNOs at the expense of RSHs. Somewhat surprisingly, NOMela was about 10-fold more effective than S-nitrosocysteine in inhibiting GAPDH. Vitamin C and glutathione increased the NOMela-dependent inhibition of the enzyme by accelerating the intermediacy of nitroxyl which is also highly effective in nitrosating RSHs. The occurrence of this intermediate during the NOMela-vitamin C reaction was verified by using Mn(III)-tetrakis(1-methyl-4-pyridyl)porphorin pentachloride as nitroxyl scavenger. The NOMela-dependent inactivation of GAPDH was so effective that this reaction can be used to quantify NOMela with high sensitivity.

N-nitroso-melatonin releases nitric oxide in the presence of serotonin and its derivatives

A novel reaction was observed between 5-hydroxytryptophan derivatives like serotonin and N-nitroso-melatonin (NOMela). This reaction decreased the concentration of serotonin by about 50% and generated initially as detectable products nitric oxide and melatonin with stoichiometrical yields. The other expected product, a serotonin-derived radical, could not be detected by electron spin resonance (ESR) spectrometry, probably because the self-decay of phenoxyl type radicals proceed at the diffusion-controlled limit. From the facts that the decay rate of NOMela corresponded very well with the nitric oxide releasing rate and that nitrite was the only thermodynamically stable nitrogen oxide-containing product, it is concluded that the NOMela-serotonin reaction proceeded quantitatively. The observed reaction might be a possibility to counteract a pharmacologically abnormal high serotonin concentration in various diseases.

Generation, basic chemistry, and detection of N-nitrosotryptophan derivatives

N-Terminal blocked tryptophan derivatives like melatonin or tryptophan residues in peptides are easily nitrosated at the nitrogen atom of the indole ring to give the corresponding N-nitrosotryptophan derivatives. This article provides a comprehensive view of the synthesis, chemical properties, and detection methods of this class of N-nitroso compounds of potential importance in biological systems.

Reaction of Vitamin E Compounds withN-Nitrosated Tryptophan Derivatives and Its Analytical Use

We recently showed that nitrosated tryptophan residues may act as endogenous nitric oxide storage compounds. Here, a novel reaction of nitrosotryptophan derivatives is described, in the form of the release of nitric oxide from N-nitrosotryptophan derivatives initiated either by alpha-tocopherol or by its water-soluble form trolox. Alpha-tocopherol and trolox were found to release stoichiometric amounts of nitric oxide from N-acetyl-N-nitrosotryptophan as well as from the nitrosotryptophan residue in albumin. The reaction proceeds both in water and in lipophilic solution and reconstitutes the indole moiety of the tryptophan molecule quantitatively. During this reaction, alpha-tocopherol- and trolox-derived phenoxyl-type radicals were identified as intermediates by ESR spectrometry. The chemical mechanism of the NO-releasing process was established. Since S-nitrosothiols do not react under the applied conditions, it is suggested that the trolox-dependent release of nitric oxide may be utilizable for the detection of N-nitrosotryptophan residues in biological samples. Furthermore, as N-nitrosotryptophan derivatives do not undergo spontaneous decay in lipophilic environments, vitamin E may have the so far unrecognized function of preventing the accumulation of N-nitrosotryptophan residues to toxic concentrations in biological systems.

Effects of Endogenous Ascorbate on Oxidation, Oxygenation, and Toxicokinetics of Cell-Free Modified Hemoglobin after Exchange Transfusion in Rat and Guinea Pig

Chemically modified hemoglobin (Hb) solutions are promising oxygen therapeutics; however, these agents are prone to intravascular oxidation. Using a 50% exchange transfusion (ET) model with bovine polymerized hemoglobin (PolyHbBv), we examined heme oxidation, oxygenation markers, and toxicokinetics in rats, an ascorbic acid (AA)-producing species, and in guinea pigs, a non-AA-producing species. Plasma AA decreased by 50% in guinea pigs after ET, but it was unchanged in rats for the first 20 h post-ET. Both species cleared PolyHbBv from the circulation at similar rates. However, exposure to ferric PolyHbBv over time was 5-fold greater in the guinea pig. Mass spectrometry analysis of plasma revealed oxidative modifications within the tetrameric fraction of PolyHbBv in guinea pig. Oxygen equilibrium curves of PolyHbBv measured in plasma after ET were more left-shifted in guinea pigs compared with rats, consistent with increased ferric PolyHbBv formation. Renal hypoxia-inducible factor (HIF)-1alpha, whose activity strictly depends on the partial pressure of oxygen increased over time, and it correlated inversely with circulating ferrous PolyHbBv in both species. Interestingly, HIF-1alpha activity was greater in guinea pigs compared with rats at 72 h post-ET. Mean arterial pressure increases were also greater in guinea pigs; however, minimal differences in cardiac and renal pathology were observed in either species. The present findings suggest the importance of plasma AA in maintaining the stability of acellular Hb susceptible to oxidation, and they may be relevant to humans, which display a similar plasma/tissue antioxidant status to guinea pig.