Nitrogen Dioxide Radical Research Articles

Wavelength-Resolved Photon Fluxes of Indoor Light Sources: Implications for HOx Production

Photochemistry is a largely unconsidered potential source of reactive species such as hydroxyl and peroxy radicals (OH and HO2, "HOx") indoors. We present measured wavelength-resolved photon fluxes and distance dependences of indoor light sources including halogen, incandescent, and compact fluorescent lights (CFL) commonly used in residential buildings; fluorescent tubes common in industrial and commercial settings; and sunlight entering buildings through windows. We use these measurements to predict indoor HOx production rates from the photolysis of nitrous acid (HONO), hydrogen peroxide (H2O2), ozone (O3), formaldehyde (HCHO), and acetaldehyde (CH3CHO). Our results suggest that while most lamps can photolyze these molecules, only sunlight and fluorescent tubes will be important to room-averaged indoor HOx levels due to the strong distance dependence of the fluxes from compact bulbs. Under ambient conditions, we predict that sunlight and fluorescent lights will photolyze HONO to form OH at rates of 106-107 molecules cm-3 s-1, and that fluorescent lights will photolyze HCHO to form HO2 at rates of ∼106 molecules cm-3 s-1; rates could be 2 orders of magnitude higher under high precursor concentrations. Ozone and H2O2 will not be important photochemical OH sources under most conditions, and CH3CHO will generally increase HO2 production rates only slightly. We also calculated photolysis rate constants for nitrogen dioxide (NO2) and nitrate radicals (NO3) in the presence of the different light sources. Photolysis is not likely an important fate for NO3 indoors, but NO2 photolysis could be an important source of indoor O3.

The role of nitrite in sulfate radical-based degradation of phenolic compounds: An unexpected nitration process relevant to groundwater remediation by in-situ chemical oxidation (ISCO)

As promising in-situ chemical oxidation (ISCO) technologies, sulfate radical-based advanced oxidation processes (SR-AOPs) are applied in wastewater treatment and groundwater remediation in recent years. In this contribution, we report for the first time that, thermally activated persulfate oxidation of phenol in the presence of nitrite (NO2−), an anion widely present in natural waters, could lead to the formation of nitrated by-products including 2-nitrophenol (2-NP), 4-nitrophenol (4-NP), 2,4-dinitrophenol (2,4-DNP), and 2,6-dinitrophenol (2,6-DNP). Nitrogen dioxide radical (NO2•), arising from SO4•− scavenging by NO2−, was proposed to be involved in the formation of nitrophenols as a nitrating agent. It was observed that nitrophenols accounted for approximately 70% of the phenol transformed under reaction conditions of [NO2−] = 200 μM, [PS] = 2 mM and temperature of 50 °C. Increasing the concentration of NO2− remarkably enhanced the formation of nitrophenols but did not affect the transformation rate of phenol significantly. The degradation of phenol and the formation of nitrophenols were significantly influenced by persulfate dosage, solution pH and natural organic matter (NOM). Further studies on the degradation of other phenolic compounds, including 4-chlorophenol (4-CP), 4-hydroxybenzoic acid (4-HBA), and acetaminophen (ATP), verified the formation of their corresponding nitrated by-products as well. Therefore, formation of nitrated by-products is probably a common but overlooked phenomenon during SO4•−-based oxidation of phenolic compounds in the presence of NO2−. Nitroaromatic compounds are well known for their carcinogenicity, mutagenicity and genotoxicity, and are potentially persistent in the environment. The formation of nitrated organic by-products in SR-AOPs should be carefully scrutinized, and risk assessment should be carried out to assess possible health and ecological impacts.

Endocrine Imbalance Associated With Proteome Changes in Diabetes.

The dynamics of cellular metabolism involves rapid interactions between proteins and nucleic acids, proteins and proteins, and signaling. These involve the interactions with respect to the sulfur bond, noncovalent electrostatic interactions, protein structure stabilization and protein-ligand binding, weak electrostatic interactions in proteins, oxygen radicals that initiate a change in conformation and a chain of events. We review a development in molecular medicine that is a very promising work in progress. We also review the current and future research methods involving mitochondria. Long-term effects of diabetes include glycation of proteins, for example, glycohemoglobin (HbA1c), increased risk of cardiovascular diseases, atherosclerosis, retinopathy, nephropathy, and neurological dysfunctions. Tissues are exposed to significant quantities of highly reactive chemical species including nitric oxide • NO and reactive oxygen species ROS over months to years, to an extent generated by mitochondrial activities. The reactions of • NO can be broadly discussed with reference to three main processes which control their fate in biological systems: (1) diffusion and intra-cellular consumption; (2) autooxidation to form nitrous anhydride N2 O3 ; and (3) reaction with superoxide O2• - to form peroxynitrite ONOO-. Reactive nitrogen species produced by macrophages and neutrophils in the interstitial space, with emphasis on • NO, N2 O3 , ONOO-, and nitrogen dioxide radicals • NO2 generate protein and DNA damage. Serum thiol (-SH) groups act as an important extracellular scavenger of peroxides and are therefore helpful in protecting the surrounding tissues. The events described here are a homeostatic endocrine imbalance that is associated with proteostasis. The advances we have seen in untangling this web of interactions are sure to continue at a breathtaking pace. J. Cell. Biochem. 118: 3569-3576, 2017. © 2017 Wiley Periodicals, Inc.

Quantum Yield of Nitrite from the Photolysis of Aqueous Nitrate above 300 nm.

Photolysis of nitrate (NO3-) produces reactive nitrogen and oxygen species via three different channels, forming: (1) nitrogen dioxide (NO2) and hydroxyl radical (•OH), (2) nitrite (NO2-) and oxygen atom (O(3P)), and (3) peroxynitrite (ONOO-). These photoproducts are important oxidants and reactants in surface waters, atmospheric drops, and snowpacks. While the efficiency of the first channel, to form NO2, is well documented, a large range of values have been reported for the second channel, nitrite, above 300 nm. In part, this disagreement reflects secondary chemistry that can produce or destroy nitrite. In this study, we examine factors that influence nitrite production and find that pH, nitrate concentration, and the presence of an •OH scavenger can be important. We measure an average nitrite quantum yield (Φ(NO2-)) of (1.1 ± 0.2)% (313 nm, 50 μM nitrate, pH ≥ 5), which is at the upper end of past measurements and an order of magnitude above the smallest-and most commonly cited-value reported for this channel. Nitrite production is often considered a very minor channel in nitrate photolysis, but our results indicate it is as important as the NO2 channel. In contrast, at 313 nm we observe no formation of peroxynitrite, corresponding to Φ(ONOO-) < 0.26%.

A Theoretical Study on the Antioxidant Activity of Piceatannol and Isorhapontigenin Scavenging Nitric Oxide and Nitrogen Dioxide Radicals.

The antioxidant activity of naturally occurring stilbene compounds piceatannol (PIC) and isorhapontigenin (ISO) scavenging two free radicals (NO and NO2) were studied using density functional theory (DFT) method. Four reaction mechanisms have been considered: hydrogen atom transfer (HAT), radical adduct formation (RAF), single electron transfer (SET), and sequential proton loss electron transfer (SPLET). The reaction channels in water solution were traced independently, and the respective thermodynamic and kinetic parameters were obtained. We found PIC and ISO scavenge NO mainly through RAF mechanism, and scavenge NO2 through HAT mechanism. The capacity of PIC scavenging NO2 is much higher than ISO, but the reactivity of scavenging NO is lower than ISO.

The Interaction of Hypotaurine and Other Sulfinates with Reactive Oxygen and Nitrogen Species: A Survey of Reaction Mechanisms.

Considerable strides have been made in understanding the oxidative mechanisms involved in the final steps of the cysteine pathway leading to taurine. The oxidation of sulfinates, hypotaurine and cysteine sulfinic acid, to the respective sulfonates, taurine and cysteic acid, has never been associated with any specific enzyme. Conversely, there is strong evidence that in vivo formation of taurine and cysteic acid is the result of sulfinate interaction with a variety of biologically relevant oxidants. In the last decade, many experiments have been performed to understand whether peroxynitrite, nitrogen dioxide and carbonate radical anion could be included in the biologically relevant reactive species capable of oxidizing sulfinates. Thanks to this work, it has been possible to highlight two possible reaction mechanisms (direct and indirect reaction) of sulfinates with reactive oxygen and nitrogen species.The sulfinates oxidation, mediated by peroxynitrite, is an example of both reaction mechanisms: through a two-electron-direct-reaction with peroxynitrite or through a one-electron-indirect-transfer reaction. In the indirect mechanism, the peroxynitrite homolysis releases hydroxyl and nitrogen dioxide radical and in addition the degradation of short-lived adduct formed by peroxynitrite and CO2 can generate carbonate radical anion. The reaction of hypotaurine and cysteine sulfinic acid with peroxynitrite-derived radicals is accompanied by extensive oxygen uptake with the generation of transient intermediates, which can begin a reaction by an oxygen-dependent mechanism with the sulfonates, taurine, and cysteic acid as final products. Due to pulse radiolysis studies, it has been shown that transient sulfonyl radicals (RSO2•) have been produced during the oxidation of both sulfinates by one-electron transfer reaction.The purpose is to analyze all the aspects of the reactive mechanism in the sulfinic group oxidation of hypotaurine and cysteine sulfinic acid through the results obtained from our laboratory in recent years.

361 - Endothelial-Transcytosed Myeloperoxidase Promotes Endothelial Dysfunction in an Oxidant Specific Manner: Novel Protective Actions of Thiocyanate and Nitrite

During cardiovascular disease myeloperoxidase (MPO) released by circulating leukocytes is transcytosed into the sub-endothelial matrix of arteries. At this site, MPO catalyzes oxidative reactions that promote endothelial dysfunction. In the presence of H 2 O 2 , MPO generates several oxidants including conversion of chloride (Cl – ) into hypochlorous acid (HOCl), thiocyanate (SCN – ) into hypothiocyanous acid (HOSCN) or nitrite (NO 2 – ) into nitrogen dioxide radical ( ● NO 2 ), the latter forming 3-nitrotyrosine. Here we studied the implications of these different oxidants produced by endothelial-transcytosed MPO for endothelial function in intact arteries. Incubation of isolated aorta with MPO resulted in its accumulation into the endothelium. Exposure of MPO-containing arteries to H 2 O 2 or angiotensin II elevated aortic levels of HOCl or superoxide (O 2 ●– ) and impaired endothelial-dependent vasorelaxation in a manner restored by removal of Cl – or addition of MPO inhibitors and scavengers of HOCl or O 2 ●– . Addition of SCN – or NO 2 – to MPO-containing aortas also inhibited HOCl and O 2 ●– levels and preserved endothelial-dependent relaxation, despite NO 2 – increasing endothelial 3-nitrotyrosine levels. In an in vivo model of MPO-dependent endothelial dysfunction, LPS administration to wild-type mice induced MPO accumulation into the aortic endothelium, increased O 2 ●– and impaired endothelial-dependent relaxation, events absent or reduced in LPS-treated MPO -/- mice. Ex vivo treatment of aorta from LPS-treated mice with O 2 ●– scavengers improved endothelial function. This study supports that HOCl produced by transcytosed MPO impairs endothelial function by elevating O 2 ●–- . SCN – or NO 2 – protect against MPO-induced endothelial dysfunction by diverting MPO to produce the less damaging oxidants, HOSCN or ● NO 2 . Although 3-nitrotyrosine is considered a deleterious modification our data indicate that its formation correlates with protection in the context of endothelial dysfunction induced by MPO.

199 - Oxygen Effect on Protection of Human Lymphoid Cells Against Free Radicals by the Carotenoid Lycopene

Carotenoids are known to act as dietary antioxidants and so are of wide interest for their health benefits. Dietary lycopene, the carotenoid pigment in tomatoes, has been shown to protect against human lymphoid cell membrane damage from free radicals produced by gamma radiation and also by the nitrogen dioxide radical, generated photolytically. This protective effect is dramatically reduced as the oxygen concentration increases, particularly for damage due to gamma radiolysis – becoming near zero at 100% oxygen from 5-fold protection at 20% oxygen and 50-fold protection at zero per-cent oxygen. The effect is less pronounced for nitrogen dioxide-induced cell killing falling from 17-fold protection in the absence of oxygen to 9-fold at 100% oxygen. Non-cellular gamma radiation and laser studies were also carried out to support the molecular mechanisms suggested for the effect of oxygen. The remarkable reduction in protection by lycopene against gamma radiation at high oxygen concentrations could be exploited to enhance radiation procedures for therapy and preliminary studies have also been undertaken for irradiations with high energy protons.

Tryptophan versus nitric oxide, nitrogen dioxide and carbonate radicals: differences in reactivity and implications for oxidative damage to proteins

The reactions of carbonate (CO 3 ·− ), nitric oxide (NO·) and nitrogen dioxide (NO 2 · ) radicals with free zwitterionic tryptophan and N-formyl-tryptophanamide (a model for tryptophan as a protein residue) have been studied using density functional theory and transition state theory. All possible reactions mechanisms have been analyzed. They are single electron transfer (SET), radical adduct formation and formal hydrogen transfer. The aqueous solution has been mimicked at physiological pH. Thermochemical and kinetic data are reported for both tryptophan models. We find that the reaction rate constants for CO 3 ·− with both tryptophan models are limited by diffusion, while for reaction with NO 2 · they are approximately 3.00 × 106 M−1 s−1, and NO· does not react at all. The overall rate constants of free zwitterionic tryptophan with NO 2 · and CO 3 ·− are 1.11 and 1.29 times larger than those of the N-formyl-tryptophanamide model, respectively. Therefore, it seems that the free amino acid and the residue in the protein have similar reactivities. While CO 3 ·− reacts via all three studied mechanisms at similar rates, NO 2 · reacts exclusively via SET. Our work suggests that free tryptophan has some scavenging activity and protective effect, but that bonded tryptophan could be a target for oxidative stress.

Role of nitrite, urate and pepsin in the gastroprotective effects of saliva

Dietary nitrate is now recognized as an alternative substrate for nitric oxide (•NO) production in the gut. This novel pathway implies the sequential reduction of nitrate to nitrite, •NO and other bioactive nitrogen oxides but the physiological relevance of these oxidants has remained elusive. We have previously shown that dietary nitrite fuels an hitherto unrecognized nitrating pathway at acidic gastric pH, through which pepsinogen is nitrated in the gastric mucosa, yielding a less active form of pepsin in vitro. Here, we demonstrate that pepsin is nitrated in vivo and explore the functional impact of protein nitration by means of peptic ulcer development. Upon administration of pentagastrin and human nitrite-rich saliva or sodium nitrite to rats, nitrated pepsin was detected in the animal's stomach by immunoprecipitation. •NO was measured in the gastric headspace before and after nitrite instillation by chemiluminescence. At the end of each procedure, the stomach's lesions, ranging from gastric erosions to haemorrhagic ulcers, were scored. Nitrite increased gastric •NO by 200-fold (p<0.05) and nitrated pepsin was detected both in the gastric juice and the mucosa (p<0.05). Exogenous urate, a scavenger of nitrogen dioxide radical, blunted •NO detection and inhibited pepsin nitration, suggesting an underlining free radical-dependent mechanism for nitration. Functionally, pepsin nitration prevented the development of gastric ulcers, as the lesions were only apparent when pepsin nitration was inhibited by urate. In sum, this work unravels a novel dietary-dependent nitrating pathway in which pepsin is nitrated and inactivated in the stomach, preventing the progression of gastric ulcers.

Cold atmospheric plasma jet-generated RONS and their selective effects on normal and carcinoma cells.

Cold atmospheric helium plasma jets were fabricated and utilized for plasma–cell interactions. The effect of operating parameters and jet design on the generation of specific reactive oxygen and nitrogen species (RONS) within cells and cellular response were investigated. It was found that plasma treatment induced the overproduction of RONS in various cancer cell lines selectively. The plasma under a relatively low applied voltage induced the detachment of cells, a reduction in cell viability, and apoptosis, while the plasma under higher applied voltage led to cellular necrosis in our case. To determine whether plasma-induced reactive oxygen species (ROS) generation occurs through interfering with mitochondria-related cellular response, we examined the plasma effects on ROS generation in both parental A549 cells and A549 ρ0 cells. It was observed that cancer cells were more susceptible to plasma-induced RONS (especially nitric oxide (NO) and nitrogen dioxide (NO2−) radicals) than normal cells, and consequently, plasma induced apoptotic cell responses mainly in cancer cells.

Mutagenic effects induced by the attack of NO2 radical to the guanine-cytosine base pair.

We investigate the attack of the nitrogen dioxide radical (NO•2) to the guanine—cytosine (GC) base pair and the subsequent tautomeric reactions able to induce mutations, by means of density functional theory (DFT) calculations. The conducted simulations allow us to identify the most reactive sites of the GC base pair. Indeed, the computed relative energies demonstrate that the addition of the NO•2 radical to the C8 position of the guanine base forms to the most stable adduct. Although the initial adducts might evolve to non-canonical structures via inter-base hydrogen bonds rearrangements, the probability for the proton exchange to occur lies in the same range as that observed for undamaged DNA. As a result, tautomeric errors in NO2-attacked DNA arises at the same rate as in canonical DNA, with no macroscopic impact on the overall stability of DNA. The potential mutagenic effects of the GC–NO•2 radical adducts likely involve side reactions, e.g., the GC deprotonation to the solvent, rather than proton exchange between guanine and cytosine basis.

Leghemoglobin is nitrated in functional legume nodules in a tyrosine residue within the heme cavity by a nitrite/peroxide-dependent mechanism.

Protein tyrosine (Tyr) nitration is a post-translational modification yielding 3-nitrotyrosine (NO2 -Tyr). Formation of NO2 -Tyr is generally considered as a marker of nitro-oxidative stress and is involved in some human pathophysiological disorders, but has been poorly studied in plants. Leghemoglobin (Lb) is an abundant hemeprotein of legume nodules that plays an essential role as an O2 transporter. Liquid chromatography coupled to tandem mass spectrometry was used for a targeted search and quantification of NO2 -Tyr in Lb. For all Lbs examined, Tyr30, located in the distal heme pocket, is the major target of nitration. Lower amounts were found for NO2 -Tyr25 and NO2 -Tyr133. Nitrated Lb and other as yet unidentified nitrated proteins were also detected in nodules of plants not receiving NO3- and were found to decrease during senescence. This demonstrates formation of nitric oxide (˙NO) and NO2- by alternative means to nitrate reductase, probably via a ˙NO synthase-like enzyme, and strongly suggests that nitrated proteins perform biological functions and are not merely metabolic byproducts. In vitro assays with purified Lb revealed that Tyr nitration requires NO2-+H2 O2 and that peroxynitrite is not an efficient inducer of nitration, probably because Lb isomerizes it to NO3-. Nitrated Lb is formed via oxoferryl Lb, which generates nitrogen dioxide and tyrosyl radicals. This mechanism is distinctly different from that involved in heme nitration. Formation of NO2 -Tyr in Lb is a consequence of active metabolism in functional nodules, where Lb may act as a sink of toxic peroxynitrite and may play a protective role in the symbiosis.

Photolysis of chloropicrin by simulated sunlight

The rate of chloropicrin removal and product formation when chloropicrin is exposed to simulated sunlight were determined in the absence and presence of oxygen. We observed phosgene and nitrosyl chloride as the products, which are produced after chloropicrin undergoes cleavage of the C–N bond to form carbon trichloride and nitrogen dioxide radicals. The observed rates are not strongly dependent on chloropicrin pressure but do vary with oxygen pressure, and the presence of oxygen clearly changed the mechanism of the reaction of the radical products. Under near-environmental pressures of oxygen, we estimate the environmental half-life of chloropicrin at 5.9 ± 1.5 h.

Photodegradation of veterinary ionophore antibiotics under UV and solar irradiation.

The veterinary ionophore antibiotics (IPAs) are extensively used as coccidiostats and growth promoters and are released to the environment via land application of animal waste. Due to their propensity to be transported with runoff, IPAs likely end up in surface waters where they are subject to photodegradation. This study is among the first to investigate the photodegradation of three commonly used IPAs, monensin (MON), salinomycin (SAL) and narasin (NAR), under UV and solar irradiation. Results showed that MON was persistent in a deionized (DI) water matrix when exposed to UV and sunlight, whereas SAL and NAR could undergo direct photolysis with a high quantum yield. Water components including nitrate and dissolved organic matter had a great impact on the photodegradation of IPAs. A pseudosteady state kinetic model was successfully applied to predict IPAs' photodegradation rates in real water matrices. Applying LC/MS/MS, multiple photolytic transformation products of IPAs were observed and their structures were proposed. The direct photolysis of SAL and NAR occurred via cleavage on the ketone moiety and self-sensitized photolysis. With the presence of nitrate, MON was primarily degraded by hydroxyl radicals, whereas SAL showed reactivity toward both hydroxyl and nitrogen-dioxide radicals. Additionally, toxicity tests showed that photodegradation of SAL eliminated its antibiotic properties against Bacillus subtilis.

Reactivity of hypotaurine and cysteine sulfinic acid toward carbonate radical anion and nitrogen dioxide as explored by the peroxidase activity of Cu,Zn superoxide dismutase and by pulse radiolysis

Hypotaurine and cysteine sulfinic acid are known to be readily oxidized to the respective sulfonates, taurine and cysteic acid, by several oxidative agents that may be present in biological systems. In this work, the relevance of both the carbonate anion and nitrogen dioxide radicals in the oxidation of hypotaurine and cysteine sulfinic acid has been explored by the peroxidase activity of Cu,Zn superoxide dismutase (SOD) and by pulse radiolysis. The extent of sulfinate oxidation induced by the system SOD/H2O2 in the presence of bicarbonate (CO3•– generation), or nitrite (•NO2 generation) has been evaluated. Hypotaurine is efficiently oxidized by the carbonate radical anion generated by the peroxidase activity of Cu,Zn SOD. Pulse radiolysis studies have shown that the carbonate radical anion reacts with hypotaurine more rapidly (k = 1.1 × 109 M−1s−1) than nitrogen dioxide (k = 1.6 × 107 M−1s−1). Regarding cysteine sulfinic acid, it is less reactive with the carbonate radical anion (k = 5.5 × 107 M−1s−1) than hypotaurine. It has also been observed that the one-electron transfer oxidation of both sulfinates by the radicals is accompanied by the generation of transient sulfonyl radicals (RSO2•). Considering that the carbonate radical anion could be formed in vivo at high level from bicarbonate, this radical can be included in the oxidants capable of performing the last metabolic step of taurine biosynthesis. Moreover, the protective effect exerted by hypotaurine and cysteine sulfinate on the carbonate radical anion-mediated tyrosine dimerization indicates that both sulfinates have scavenging activity towards the carbonate radical anion. However, the formation of transient reactive intermediates during sulfinate oxidation by carbonate anion and nitrogen dioxide radical may at the same time promote oxidative reactions.

Comparative theoretical synthesis of high-energy density materials 2,4,6-trinitro-1,3,5-triazine

In this study, the optimal synthetic route for 2,4,6-trinitro-1,3,5-triazine (TNTA) was investigated. The synthesis of TNTA was performed using cyanamide (H2NCN) as a starting material. In the first stage, a radical addition reaction was used to generate melamine, which is the precursor of TNTA. In addition, a gaseous nitration reaction using nitrogen dioxide radicals (•NO2) as the nitration agent was used to gradually induce radical substitutions to convert dicyandiamide (H2NCN)2 to melamine (H2NCN)3. Additional nitration steps lead to triaminocyanide and, ultimately, TNTA. In addition, nitryl cyanide (O2NCN) was also tested as a starting material for radical addition to generate dinitryl cyanide (O2NCN)2, trinitryl cyanide (O2NCN)3, and, finally, TNTA. The activation energy barrier in each of the reaction steps as well as the various synthetic routes were compared to provide insight into the design of more feasible routes for the synthesis of TNTA. © 2014 Wiley Periodicals, Inc.

Atmospheric reactions of 9,10-anthraquinone

The probably carcinogenic compound 9,10-anthraquinone is mainly existing in the atmosphere in the particulate phase and is often detected and measured among other oxygenated PAHs in atmospheric samples. Its fate, once released or formed in the atmosphere, still remains unknown. In this work, heterogeneous chemical oxidation processes of 9,10-anthraquinone were investigated with ozone (O3), nitrogen dioxide (NO2) and hydroxyl radical (OH). The study of 9,10-anthraquinone adsorbed on silica particles showed no reactivity with O3 and NO2. On the other hand, the reaction with OH radicals was observed and led to the formation of 1-hydroxy-9,10-anthraquinone, another oxidation product recognized as possibly carcinogenic to humans. This study showed that reactions with ozone and nitrogen dioxide are unlikely to contribute to atmospheric degradation of 9,10-anthraquinone, whereas reactions with OH radicals could be involved in 9,10-anthraquinone degradation processes, even if such reaction is probably very slow under ambient conditions.

An airway epithelial iNOS-DUOX2-thyroid peroxidase metabolome drives Th1/Th2 nitrative stress in human severe asthma.

Severe refractory asthma is associated with enhanced nitrative stress. To determine the mechanisms for high nitrative stress in human severe asthma, 3-nitrotyrosine (3NT) was compared with Th1 and Th2 cytokine expression. In severe asthma, high 3NT levels were associated with high IFN-γ and low IL-13 expression, both of which have been reported to increase inducible nitric oxide synthase (iNOS) in human airway epithelial cells (HAEC). We found IL-13 and IFN-γ synergistically enhanced iNOS, nitrite and 3NT, corresponding with increased H2O2. Catalase inhibited while superoxide dismutase enhanced 3NT formation, supporting a critical role for H2O2 but not peroxynitrite, in 3NT generation. Dual oxidase-2 (DUOX2), central to H2O2 formation, was also synergistically induced by IL-13 and IFN-γ. The catalysis of nitrite and H2O2 to nitrogen dioxide radical (NO2•) requires an endogenous peroxidase in this epithelial cell system. Thyroid peroxidase (TPO) was identified by microarray analysis ex vivo as a gene distinguishing HAEC of severe asthma from controls. IFN-γ induced TPO in HAEC and siRNA knockdown decreased nitrated tyrosine residues. Ex vivo, DUOX2, TPO and iNOS were higher in severe asthma and correlated with 3NT. Thus a novel iNOS-DUOX2-TPO-NO2• metabolome drives nitrative stress in HAEC and likely in severe asthma.

Arylnitroalkenes as scavengers of macrophage-generated oxidants

Oxygen and nitrogen derived molecules mediated oxidation and nitration have been involved in several pathological conditions. Conversely, nitric oxide and hydrogen peroxide are important signalization intermediates, whose concentrations are tightly regulated by specialized enzyme repertoires and should remain undisturbed by the addition of exogenous antioxidant molecules, as already demonstrated by intervention studies with antioxidant vitamins. Our goal was to develop specific antioxidants able to scavenge peroxynitrite anion, as well the radicals derived from the homolytic decomposition of its conjugated acid, nitrogen dioxide and hydroxyl radical. Fourteen substituted nitroalkenes, seven 4-substituted 1-(2-nitro-1Z-ethenyl)benzene, and seven 4-substituted (2-nitro-1Z-propenyl)benzene, with different stereochemical and electronic characteristics were synthesized and tested. Compounds with the electron donor group N,N-dimethylamino showed the highest reaction rates against peroxynitrite, and also reacted with its homolytic decomposition products, OH and NO2. While 1,1-dimethylamino-4-(2-nitro-1Z-ethenyl)benzene came up as a lead for future developments without the risk of interfering with signalization pathways, since it was highly specific for peroxynitrite and peroxynitrite derived radicals, its methylated analogous 1,1-dimethylamino-4-(2-nitro-1Z-propenyl)benzene was less specific and also reacted with NO and O2−, the biological precursor of H2O2.