Peroxynitrite preferentially oxidizes the dithiol redox motifs of protein-disulfide isomerase

Protein-disulfide isomerase (PDI) is a ubiquitous dithiol-disulfide oxidoreductase that performs an array of cellular functions, such as cellular signaling and responses to cell-damaging events. PDI can become dysfunctional by post-translational modifications, including those promoted by biological oxidants, and its dysfunction has been associated with several diseases in which oxidative stress plays a role. Because the kinetics and products of the reaction of these oxidants with PDI remain incompletely characterized, we investigated the reaction of PDI with the biological oxidant peroxynitrite. First, by determining the rate constant of the oxidation of PDI's redox-active Cys residues (Cys53 and Cys397) by hydrogen peroxide (k = 17.3 ± 1.3 m-1 s-1 at pH 7.4 and 25 °C), we established that the measured decay of the intrinsic PDI fluorescence is appropriate for kinetic studies. The reaction of these PDI residues with peroxynitrite was considerably faster (k = (6.9 ± 0.2) × 104 m-1 s-1), and both Cys residues were kinetically indistinguishable. Limited proteolysis, kinetic simulations, and MS analyses confirmed that peroxynitrite preferentially oxidizes the redox-active Cys residues of PDI to the corresponding sulfenic acids, which reacted with the resolving thiols at the active sites to produce disulfides (i.e. Cys53-Cys56 and Cys397-Cys400). A fraction of peroxynitrite, however, decayed to radicals that hydroxylated and nitrated other active-site residues (Trp52, Trp396, and Tyr393). Excess peroxynitrite promoted further PDI oxidation, nitration, inactivation, and covalent oligomerization. We conclude that these PDI modifications may contribute to the pathogenic mechanism of several diseases associated with dysfunctional PDI.

A Six-Coordinate Peroxynitrite Low-Spin Iron(III) Porphyrinate Complex-The Product of the Reaction of Nitrogen Monoxide (·NO(g)) with a Ferric-Superoxide Species

Peroxynitrite (-OON═O, PN) is a reactive nitrogen species (RNS) which can effect deleterious nitrative or oxidative (bio)chemistry. It may derive from reaction of superoxide anion (O2•-) with nitric oxide (·NO) and has been suggested to form an as-yet unobserved bound heme-iron-PN intermediate in the catalytic cycle of nitric oxide dioxygenase (NOD) enzymes, which facilitate a ·NO homeostatic process, i.e., its oxidation to the nitrate anion. Here, a discrete six-coordinate low-spin porphyrinate-FeIII complex [(PIm)FeIII(-OON═O)] (3) (PIm; a porphyrin moiety with a covalently tethered imidazole axial "base" donor ligand) has been identified and characterized by various spectroscopies (UV-vis, NMR, EPR, XAS, resonance Raman) and DFT calculations, following its formation at -80 °C by addition of ·NO(g) to the heme-superoxo species, [(PIm)FeIII(O2•-)] (2). DFT calculations confirm that 3 is a six-coordinate low-spin species with the PN ligand coordinated to iron via its terminal peroxidic anionic O atom with the overall geometry being in a cis-configuration. Complex 3 thermally transforms to its isomeric low-spin nitrato form [(PIm)FeIII(NO3-)] (4a). While previous (bio)chemical studies show that phenolic substrates undergo nitration in the presence of PN or PN-metal complexes, in the present system, addition of 2,4-di-tert-butylphenol (2,4DTBP) to complex 3 does not lead to nitrated phenol; the nitrate complex 4a still forms. DFT calculations reveal that the phenolic H atom approaches the terminal PN O atom (farthest from the metal center and ring core), effecting O-O cleavage, giving nitrogen dioxide (·NO2) plus a ferryl compound [(PIm)FeIV═O] (7); this rebounds to give [(PIm)FeIII(NO3-)] (4a).The generation and characterization of the long sought after ferriheme peroxynitrite complex has been accomplished.

Selenium-containing indolyl compounds: Kinetics of reaction with inflammation-associated oxidants and protective effect against oxidation of extracellular matrix proteins

Activated white blood cells generate multiple oxidants in response to invading pathogens. Thus, hypochlorous acid (HOCl) is generated via the reaction of myeloperoxidase (from neutrophils and monocytes) with hydrogen peroxide, and peroxynitrous acid (ONOOH), a potent oxidizing and nitrating agent is formed from superoxide radicals and nitric oxide, generated by stimulated macrophages. Excessive or misplaced production of these oxidants has been linked to multiple human pathologies, including cardiovascular disease. Atherosclerosis is characterized by chronic inflammation and the presence of oxidized materials, including extracellular matrix (ECM) proteins, within the artery wall. Here we investigated the potential of selenium-containing indoles to afford protection against these oxidants, by determining rate constants (k) for their reaction, and quantifying the extent of damage on isolated ECM proteins and ECM generated by human coronary artery endothelial cells (HCAECs). The novel selenocompounds examined react with HOCl with k 0.2-1.0 × 10⁸M^-1s^-1, and ONOOH with k 4.5-8.6 - × 10⁵M^-1s^-1. Reaction with H₂O₂ is considerably slower (k < 0.25M^-1s^-1). The selenocompound 2-phenyl-3-(phenylselanyl)imidazo[1,2-a]pyridine provided protection to human serum albumin (HSA) against HOCl-mediated damage (as assessed by SDS-PAGE) and damage to isolated matrix proteins induced by ONOOH, with a concomitant decrease in the levels of the biomarker 3-nitrotyrosine. Structural damage and generation of 3-nitroTyr on HCAEC-ECM were also reduced. These data demonstrate that the novel selenium-containing compounds show high reactivity with oxidants and may modulate oxidative and nitrosative damage at sites of inflammation, contributing to a reduction in tissue dysfunction and atherogenesis.

Peroxynitrite-Scavenging Glycosides from the Stem Bark of Catalpa ovata

Ten new glycosides, 6,10-O-di-trans-feruloyl catalpol (1), 6,6'-O-di-trans-feruloyl catalpol (2), 3,4-dihydro-6-O-di-trans-feruloyl catalpol (10), (8R,7'S,8'R)-lariciresinol 9'-O-β-d-(6-O-trans-feruloyl)glucopyranoside (17), and ovatosides A-F (18-22, 24), were isolated from the stem bark of Catalpa ovata along with 19 known compounds. All isolates, except 6 (catalposide) and 9 (6-O-veratroyl catalpol), were found to scavenge peroxynitrite (ONOO^-) formed by 3-morpholinosydnonimine. In particular, 12 compounds showed potent activity, with IC₅₀ values in the range 0.14-2.2 μM.

Peptide-Functionalized Fluorescent Particles for In Situ Detection of Nitric Oxide via Peroxynitrite-Mediated Nitration

Nitric oxide (NO) is a free radical signaling molecule that plays a crucial role in modulating physiological homeostasis across multiple biological systems. NO dysregulation is linked to the pathogenesis of multiple diseases; therefore, its quantification is important for understanding pathophysiological processes. The detection of NO is challenging, typically limited by its reactive nature and short half-life. Additionally, the presence of interfering analytes and accessibility to biological fluids in the native tissues make the measurement technically challenging and often unreliable. Here, a bio-inspired peptide-based NO sensor is developed, which detects NO-derived oxidants, predominately peroxynitrite-mediated nitration of tyrosine residues. It is demonstrated that these peptide-based NO sensors can detect peroxynitrite-mediated nitration in response to physiological shear stress by endothelial cells in vitro. Using the peptide-conjugated fluorescent particle immunoassay, peroxynitrite-mediated nitration activity with a detection limit of ≈100 × 10-9 m is detected. This study envisions that the NO detection platform can be applied to a multitude of applications including monitoring of NO activity in healthy and diseased tissues, localized detection of NO production of specific cells, and cell-based/therapeutic screening of peroxynitrite levels to monitor pronitroxidative stress in biological samples.

Systematic in vitro assessment of responses of roGFP2-based probes to physiologically relevant oxidant species

The genetically encoded probes roGFP2-Orp1 and Grx1-roGFP2 have been designed to be selectively oxidized by hydrogen peroxide (H₂O₂) and glutathione disulfide (GSSG), respectively. Both probes have demonstrated such selectivity in a broad variety of systems and conditions. In this study, we systematically compared the in vitro response of roGFP2, roGFP2-Orp1 and Grx1-roGFP2 to increasing amounts of various oxidant species that may also occur in biological settings. We conclude that the previously established oxidant selectivity is highly robust and likely to be maintained under most physiological conditions. Yet, we also find that hypochlorous acid, known to be produced in the phagocyte respiratory burst, can lead to non-selective oxidation of roGFP2-based probes at concentrations ≥2µM, in vitro. Further, we confirm that polysulfides trigger direct roGFP2 responses. A side-by-side comparison of all three probes can be used to reveal micromolar amounts of hypochlorous acid or polysulfides.

NADPH oxidase-dependent degradation of single-walled carbon nanotubes in macrophages

Previous studies have shown that carboxylated single-walled carbon nanotubes (SWCNTs) could be oxidatively biodegraded by neutrophil myeloperoxidase (MPO) and peroxynitrite (ONOO^-). However, the biodegradation mechanism of nanotubes in macrophages has not been explored enough. Here, we showed that both MPO and ONOO^- could effectively oxidize SWCNTs to generate shorter and oxidative nanotubes in vitro. SWCNTs were significantly degraded in zymosan-stimulated macrophages, and the degradation mechanism was dependent on MPO and ONOO^--driven oxidative pathways of activated macrophages, where NADPH oxidase was found to be a major determinant of the biodegradation process. Moreover, the functionalization of IgG to SWCNTs could stimulate MPO release and ONOO^- formation in macrophages, thereby creating the conditions favorable for degradation of nanotubes and subsequently contributing to the higher degradation degree of IgG-coated SWCNTs. Therefore, our discovery of NADPH oxidase-dependent SWCNTs degradation in activated macrophages will open new opportunities for the regulation of SWCNTs fate in vivo.

[Research on the Reaction Dynamics between Peroxynitrite and Tyrosine Catalyzed with Mimic Enzyme through Flow Injection Analyzer]

As a highly active free radical in vivo, peroxynitrite can damage various biological macromolecules and cause a series of major diseases, which is of great significance to determine its content and reactive mechanism. It is very difficult to capture the dynamic process of peroxynitrite due to its active property and fast reacted rate. In this paper, we firstly explored the kinetic characteristics of peroxynitrite and tyrosine with the presence of Hemoglobin and Hemin by using flow injection analyzer. The results showed that the oxidation processes of peroxynitrite and tyrosine catalyzed with hemoglobin and hemin were in accordance with Michaelis-Menten’s dynamics law; Based on the Michaelis constant (K(m)) and the maximum initial rate (V(max)), we deduced the reaction mechanism that peroxynitrite, catalyzed by mimic enzymes, directly oxidized tyrosine combined with mimic enzymes, rather than decomposed to · OH and O(-₂)·; In addition, we detected the rate constant of the reaction catalyzed by these two kinds of enzymes at different temperature and pH, resulting that the optimum conditions of hemoglobin to catalyze this system were 25 ℃ and pH 8, the rate constant was 1.035×10(6) mol·L(-1) · s(-1), while hemin was 37 ℃ and pH 9.5, the rate constant was 6.842×10(5) mol·L(-1) · s(-1); Comparing the kinetic parameters, K(m)Hb(4.46 μmol·L(-1))<K(Hemin)(m)(4.90 μmol · L-1), V(Hb)(max)(0.072 ΔIF/s)>V(Hemin)(max)(0.026 ΔIF/s), we discovered that the rate constant of hemoglobin in optimum condition was greater than that in hemin, and the catalytic activity of hemoglobin was higher than that of hemin. All these results have provided kinetic parameters for the study of determining the content of peroxynitrite and exploring its reaction mechanism with enzymatic method. It also laid a theoretical foundation for developing new diagnosis technology to prevent and cure diseases caused by free radicals in vivo.

Comprehensive analysis of the formation and stability of peroxynitrite-derived 8-nitroguanine by LC-MS/MS: Strategy for the quantitative analysis of cellular 8-nitroguanine

Peroxynitrite is a major oxidizing and nitrating biological agent formed at sites of inflammation. Peroxynitrite can cause DNA damage and is thought to contribute to inflammation-related carcinogenesis. This study describes a sensitive and reliable liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the direct determination of peroxynitrite-derived 8-nitroguanine (8-nitroGua) in DNA hydrolysates. This method exhibited a sensitive detection limit of 3 fmol and inter- and intraday imprecision of <10% and was applied to systemically examine the formation and stability of peroxynitrite-derived 8-nitroGua in different DNA substrates under various conditions. The 8-nitroGua formation was maximal at pH 8. The formation rate of 8-nitroGua in different DNA substrates decreased in the order of monodeoxynucleoside>single-stranded DNA>double-stranded DNA. A stability test revealed that the half-life for the depurination of 8-nitroGua from DNA was short and affected by both the temperature and DNA structure. When present in monodeoxynucleoside, the half-life of 8-nitroGua was estimated to be ~6min at 25°C and 2.3h at ~0°C. In single-stranded DNA, the half-life varied from 1.6h at 37°C to 533h at -20°C, whereas the half-life increased from 2.4h at 37°C to 1115h at -20°C in double-stranded DNA. We demonstrated that the measurement of 8-nitroGua in isolated DNA is not practicable because 8-nitroGua is unstable and lost during DNA extraction from cell. Therefore, we suggest that directly detecting cellular 8-nitroGua following nuclear membrane lysis is an alternative measure of the nitrative damage of nucleic acids, accounting for both DNA and RNA lesions within cells.

Peroxynitrite-mediated oxidation of plasma fibronectin

Fibronectin is a large dimeric glycoprotein present in both human plasma and in basement membranes. The latter are specialized extracellular matrices underlying endothelial cells in the artery wall. Peroxynitrous acid (ONOOH) a potent oxidizing and nitrating agent, is formed in vivo from superoxide and nitric oxide radicals by stimulated macrophages and other cells. Considerable evidence supports ONOOH involvement in human atherosclerotic lesion development and rupture, possibly via extracellular matrix damage. Here we demonstrate that Tyr and Trp residues on human plasma fibronectin are highly sensitive to ONOOH with this resulting in the formation of 3-nitrotyrosine, 6-nitrotryptophan and dityrosine as well as protein aggregation and fragmentation. This occurs with equimolar or greater levels of oxidant, and in a dose-dependent manner. Modification of Tyr was quantitatively more significant than Trp (9.1% versus 1.5% conversion with 500μM ONOOH) after accounting for parent amino acid abundance, but only accounts for a small percentage of the total oxidant added. LC-MS studies identified 28 nitration sites (24 Tyr, 4 Trp) with many of these present within domains critical to protein function, including the cell-binding and anastellin domains. Human coronary artery endothelial cells showed decreased adherence and cell-spreading on ONOOH-modified fibronectin compared to control, consistent with cellular dysfunction induced by the modified matrix. Studies on human atherosclerotic lesions have provided evidence for co-localization of 3-nitrotyrosine and fibronectin. ONOOH-mediated fibronectin modification and compromised cell-matrix interactions, may contribute to endothelial cell dysfunction, a weakening of the fibrous cap of atherosclerotic lesions, and an increased propensity to rupture.

Chemical excitation of electrons: A dark path to melanoma

Sunlight's ultraviolet wavelengths induce cyclobutane pyrimidine dimers (CPDs), which then cause mutations that lead to melanoma or to cancers of skin keratinocytes. In pigmented melanocytes, we found that CPDs arise both instantaneously and for hours after UV exposure ends. Remarkably, the CPDs arising in the dark originate by a novel pathway that resembles bioluminescence but does not end in light: First, UV activates the enzymes nitric oxide synthase (NOS) and NADPH oxidase (NOX), which generate the radicals nitric oxide (NO) and superoxide (O2(-)); these combine to form the powerful oxidant peroxynitrite (ONOO(-)). A fragment of the skin pigment melanin is then oxidized, exciting an electron to an energy level so high that it is rarely seen in biology. This process of chemically exciting electrons, termed "chemiexcitation", is used by fireflies to generate light but it had never been seen in mammalian cells. In melanocytes, the energy transfers radiationlessly to DNA, inducing CPDs. Chemiexcitation is a new source of genome instability, and it calls attention to endogenous mechanisms of genome maintenance that prevent electronic excitation or dissipate the energy of excited states. Chemiexcitation may also trigger pathogenesis in internal tissues because the same chemistry should arise wherever superoxide and nitric oxide arise near cells that contain melanin.

Electrochemical detection of peroxynitrite using hemin-PEDOT functionalized boron-doped diamond microelectrode

Peroxynitrite is a potent nitroxidation agent and highly reactive metabolite, clinically correlated with a rich pathophysiology. Its sensitive and selective detection is challenging due to its high reactivity and short sub-second lifetime. Boron-doped diamond (BDD) microelectrodes have attracted interest because of their outstanding electroanalytical properties that include a wide working potential window and enhanced signal-to-noise ratio. Herein, we report on the modification of a BDD microelectrode with an electro-polymerized film of hemin and polyethylenedioxythiophene (PEDOT) for the purpose of selectively quantifying peroxynitrite. The nanostructured modified polymer layer was characterized by Raman spectroscopy and scanning electron microscopy (SEM). The electrochemical response to peroxynitrite was studied by voltammetry and time-based amperometry. The measured detection limit was 10 ± 0.5 nM (S/N = 3), the sensitivity was 4.5 ± 0.5 nA nM(-1) and the response time was 3.5 ± 1 s. The hemin-PEDOT BDD sensors exhibited a response variability of 5% or less (RSD). The stability of the sensors after a 20-day storage in 0.1 M PB (pH 7.4) at 4 °C was excellent as at least 93% of the initial response to 50 nM PON was maintained. The presence of PEDOT was correlated with a sensitivity increase.

Structural changes upon peroxynitrite-mediated nitration of peroxiredoxin 2; nitrated Prx2 resembles its disulfide-oxidized form

Peroxiredoxins are cys-based peroxidases that function in peroxide detoxification and H2O2-induced signaling. Human Prx2 is a typical 2-Cys Prx arranged as pentamers of head-to-tail homodimers. During the catalytic mechanism, the active-site cysteine (CP) cycles between reduced, sulfenic and disulfide state involving conformational as well as oligomeric changes. Several post-translational modifications were shown to affect Prx activity, in particular CP overoxidation which leads to inactivation. We have recently reported that nitration of Prx2, a post-translational modification on non-catalytic tyrosines, unexpectedly increases its peroxidase activity and resistance to overoxidation. To elucidate the cross-talk between this post-translational modification and the enzyme catalysis, we investigated the structural changes of Prx2 after nitration. Analytical ultracentrifugation, UV absorption, circular dichroism, steady-state and time-resolved fluorescence were used to connect catalytically relevant redox changes with tyrosine nitration. Our results show that the reduced nitrated Prx2 structurally resembles the disulfide-oxidized native form of the enzyme favoring a locally unfolded conformation that facilitates disulfide formation. These results provide structural basis for the kinetic analysis previously reported, the observed increase in activity and the resistance to overoxidation of the peroxynitrite-treated enzyme.

Screening of peroxynitrite scavengers in Flos Lonicerae by using two new methods, an HPLC-DAD-CL technique and a peroxynitrite spiking test followed by HPLC-DAD analysis

INTRODUCTION

Peroxynitrite is involved in the pathogenesis of a number of significant diseases. Peroxynitrite scavengers thus have potential application in understanding and treating these diseases. It is, therefore, important to establish screening methods able to rapidly identify peroxynitrite scavengers from herbal plants.

OBJECTIVE

To develop effective and easily operable screening methods for identifying peroxynitrite scavengers in complex matrices, including Chinese herbal medicines.

METHODS

Two simple and efficient screening methods have been developed for the identification of natural peroxynitrite scavengers in Flos Lonicerae Japonicae (FLJ). Method I used HPLC-DAD-(luminol-peroxynitrite)-CL techniques combined with Q-TOF MS/MS analysis, while Method II used pre-column reaction of the sample with peroxynitrite, followed by HPLC separation and Q-TOF MS/MS analysis.

RESULTS

Five peroxynitrite scavengers (neochlorogenic acid, chlorogenic acid, 3,4-O-dicaffeoyl quinic acid, 3,5-O-dicaffeoyl quinic acid and 4,5-O-dicaffeoyl quinic acid) were identified in FLJ using Method I. Besides the compounds identified using Method I, three additional peroxynitrite scavengers (rutin, isoquercitrin and luteoloside) were identified using Method II.

CONCLUSION

The two new methods proved to be complementary and the use of these methods should allow rapid detection of peroxynitrite-scavenging natural products from FLJ and other complex matrices.

Kinetics of reaction of peroxynitrite with selenium- and sulfur-containing compounds: Absolute rate constants and assessment of biological significance

Peroxynitrite (the physiological mixture of ONOOH and its anion, ONOO(-)) is a powerful biologically-relevant oxidant capable of oxidizing and damaging a range of important targets including sulfides, thiols, lipids, proteins, carbohydrates and nucleic acids. Excessive production of peroxynitrite is associated with several human pathologies including cardiovascular disease, ischemic-reperfusion injury, circulatory shock, inflammation and neurodegeneration. This study demonstrates that low-molecular-mass selenols (RSeH), selenides (RSeR') and to a lesser extent diselenides (RSeSeR') react with peroxynitrite with high rate constants. Low molecular mass selenols react particularly rapidly with peroxynitrite, with second order rate constants k2 in the range 5.1 × 10(5)-1.9 × 10(6)M(-1)s(-1), and 250-830 fold faster than the corresponding thiols (RSH) and many other endogenous biological targets. Reactions of peroxynitrite with selenides, including selenosugars are approximately 15-fold faster than their sulfur homologs with k2 approximately 2.5 × 10(3)M(-1)s(-1). The rate constants for diselenides and sulfides were slower with k2 0.72-1.3 × 10(3)M(-1)s(-1) and approximately 2.1 × 10(2)M(-1)s(-1) respectively. These studies demonstrate that both endogenous and exogenous selenium-containing compounds may modulate peroxynitrite-mediated damage at sites of acute and chronic inflammation, with this being of particular relevance at extracellular sites where the thiol pool is limited.

Substituent effects on the stability and antioxidant activity of spirodiazaselenuranes

Spirodiazaselenuranes are structurally interesting compounds and the stability of these compounds depends highly on the nature of the substituents attached to the nitrogen atoms. Aromatic substituents are known to play important roles in stabilizing the Se-N bonds in spiro compounds. In this study, several spirodiazaselenuranes are synthesized by introducing benzylic and aliphatic substituents to understand their effect on the stability of the Se-N bonds and the antioxidant activity. Replacement of phenyl substituent by benzyl/alkyl groups significantly reduces the stability of the spirodiazaselenuranes and slows down the oxidative cyclization process. The selenium centre in the spiro compounds undergoes further oxidation to produce the corresponding selenurane oxides, which are stable at room temperature. Comparison of the glutathione peroxidase (GPx) mimetic activity of the compounds showed that the diaryl selenides having heterocyclic rings are significantly more active due to the facile oxidation of the selenium centre. However, the activity is reduced significantly for compounds having aliphatic substituents. In addition to GPx activity, the compounds also inhibit peroxynitrite-mediated nitration and oxidation reaction of protein and small molecules, respectively. The experimental observations suggest that the antioxidant activity is increased considerably upon substitution of the aromatic group with the benzylic/aliphatic substituents on the nitrogen atoms.

Payload drug vs. nanocarrier biodegradation by myeloperoxidase- and peroxynitrite-mediated oxidations: pharmacokinetic implications

With the advancement of nanocarriers for drug delivery into biomedical practice, assessments of drug susceptibility to oxidative degradation by enzymatic mechanisms of inflammatory cells become important. Here, we investigate oxidative degradation of a carbon nanotube-based drug carrier loaded with Doxorubicin. We employed myeloperoxidase-catalysed and peroxynitrite-mediated oxidative conditions to mimic the respiratory burst of neutrophils and macrophages, respectively. In addition, we revealed that the cytostatic and cytotoxic effects of free Doxorubicin, but not nanotube-carried drug, on melanoma and lung carcinoma cell lines were abolished in the presence of tumor-activated myeloid regulatory cells that create unique myeloperoxidase- and peroxynitrite-induced oxidative conditions. Both ex vivo and in vitro studies demonstrate that the nanocarrier protects the drug against oxidative biodegradation.

Simultaneous quantification and validation of new peroxynitrite scavengers from Artemisia iwayomogi

CONTEXT

Artemisia iwayomogi Kitamura (Compositae) has been very widely used for the treatment of acute or chronic hepatitis, jaundice, and gastritis. In the course of our continuing efforts to identify and quantify peroxynitrite scavengers from Compositae plants, A. iwayomogi was used in this study.

OBJECTIVE

The present study was aimed to identify and quantify the peroxynitrite scavengers of A. iwayomogi.

MATERIALS AND METHODS

Silica gel and ODS were used for column chromatography. The isolated compounds were quantified using an HPLC equipped with a Capcell Pak C18 column (5 μm, 250 mm × 4.6 mm i.d.), and the method was validated for the quality control. Peroxynitrite (ONOO(-))-scavenging activities of the compounds and extracts were evaluated on the measurement of highly fluorescent rhodamine 123 converted from non-fluorescent dihydrorhodamine (DHR)-123 under the presence of peroxynitrite.

RESULTS

Based on the spectroscopic evidences, a new compound, 2"-O-caffeoylrutin (2"-O-trans-caffeic acid ester of quercetin 3-O-α-L-rhamnopyranosyl(1 → 6)-β-D-glucopyranoside) was isolated and determined together with patuletin 3-O-glucoside, scopolin, scopoletin, rutin, 3,4-dicaffeoylquinic acid, and chlorogenic acid. All of them were potent peroxynitrite scavengers (IC50 ≤ 1.88 μg/mL).

DISCUSSION AND CONCLUSION

The peroxynitrite scavengers were mainly distributed in the EtOAc fraction rather than the ether and BuOH fractions. The 70% MeOH extract exhibited a high peroxynitrite-scavenging activity. Through the validation, the present HPLC method was verified to be sufficiently sensitive, accurate, precise, and stable. Therefore, this method can be used for the quality control of A. iwayomogi.

Insights into the mechanism of the reaction between hydrogen sulfide and peroxynitrite

Hydrogen sulfide and peroxynitrite are endogenously generated molecules that participate in biologically relevant pathways. A revision of the kinetic features of the reaction between peroxynitrite and hydrogen sulfide revealed a complex process. The rate constant of peroxynitrite decay, (6.65 ± 0.08) × 10(3) M(-1) s(-1) in 0.05 M sodium phosphate buffer (pH 7.4, 37°C), was affected by the concentration of buffer. Theoretical modeling suggested that, as in the case of thiols, the reaction is initiated by the nucleophilic attack of HS(-) on the peroxide group of ONOOH by a typical bimolecular nucleophilic substitution, yielding HSOH and NO2(-). In contrast to thiols, the reaction then proceeds to the formation of distinct products that absorb near 408 nm. Experiments in the presence of scavengers and carbon dioxide showed that free radicals are unlikely to be involved in the formation of these products. The results are consistent with product formation involving the reactive intermediate HSSH and its fast reaction with a second peroxynitrite molecule. Mass spectrometry and UV-Vis absorption spectra predictions suggest that at least one of the products is HSNO2 or its isomer HSONO.

Tyrosine nitration as mediator of cell death

Nitrotyrosine is used as a marker for the production of peroxynitrite and other reactive nitrogen species. For over 20 years the presence of nitrotyrosine was associated with cell death in multiple pathologies. Filling the gap between correlation and causality has proven to be a difficult task. Here, we discuss the evidence supporting tyrosine nitration as a specific posttranslational modification participating in the induction of cell death signaling pathways.

ONOOH does not react with H2: Potential beneficial effects of H2 as an antioxidant by selective reaction with hydroxyl radicals and peroxynitrite

H2 has been suggested to act as an antioxidant when administered just before the reperfusion phase of induced oxidative stress. These effects have been reported, for example, for the heart, brain, and liver. It is hypothesized that this beneficial effect may be due to selective scavenging of HO(⋅) and ONOOH by H2. The reaction of H2 with HO(⋅) has been studied by pulse radiolysis in the past and is too slow to be physiologically relevant, not to mention that the reaction yields the reactive H(⋅) radical. We therefore investigated whether H2 reacts with ONOOH and whether the presence of H2 influences the yield of nitration of tyrosine by ONOOH. With only negative results, we entertained the notion that H2 may possibly exert its beneficial effects by reducing Fe(III) centers, oxidized during oxidative stress. However, neither hemes nor iron-sulfur clusters were reduced.

Evaluation of the anti-nitrative effect of plant antioxidants using a cowpea Fe-superoxide dismutase as a target

Nitric oxide cytotoxicity arises from its rapid conversion to peroxynitrite (ONOO(-)) in the presence of superoxide, provoking functional changes in proteins by nitration of tyrosine residues. The physiological significance of this post-translational modification is associated to tissue injury in animals, but has not been yet clarified in plants. The objective of this study was to establish new approaches that could help to understand ONOO(-) reactivity in plants. A recombinant Fe-superoxide dismutase from cowpea (Vigna unguiculata (L.) Walp.), rVuFeSOD, was the target of the ONOO(-)-generator SIN-1, and the anti-nitrative effect of plant antioxidants and haemoglobins was tested in vitro. Nitration on rVuFeSOD was evaluated immunochemically or as the loss of its enzymatic activity. This assay proved to be useful to test a variety of plant compounds for anti-nitrative capacity. Experimental data confirmed that rice (Oryza sativa L.) haemoglobin-1 (rOsHbI) and cowpea leghaemoglobin-2 exerted a protective function against ONOO(-) by diminishing nitration on rVuFeSOD. Both plant haemoglobins were nitrated by SIN-1. The chelator desferrioxamine suppressed nitration in rOsHbI, indicating that Fe plays a key role in the reaction. The removal of the haem moiety in rOsHbI importantly suppressed nitration, evidencing that this reaction may be self-catalyzed. Among small antioxidants, ascorbate remarkably decreased nitration in all tests. The phenolic compounds caffeic acid, gallic acid, pyrogallol, 4-hydroxybenzoic acid and the flavonoid gossypin also diminished tyrosine nitration and protected rVuFeSOD to different extents. It is concluded that small plant antioxidants, especially ascorbate, and haemoglobins may well play key roles in ONOO(-) homeostasis in vivo.

Importance of tryptophan nitration of carbonic anhydrase III for the morbidity of atopic dermatitis

The nitration of proteins results from the vigorous production of reactive nitrogen species in inflammatory disease. We previously reported the proteomic analysis of nitrated tryptophan residues in in vitro model cells for inflammatory diseases using a 6-nitrotryptophan-specific antibody. In this paper, we applied this method to the analysis of a disease model animal and identified the 6-nitrotryptophan-containing proteins in the skin of atopic dermatitis model mice (AD-NC/Nga mice). We found three nitrotryptophan-containing proteins, namely, carbonic anhydrase III (CAIII), α-enolase (α-ENO), and cytoskeletal keratin type II (KTII), and identified the positions of the nitrotryptophan residues in their amino acid sequences: Trp47 and Trp123 in CAIII, Trp365 in α-ENO, and Trp221 in KTII. Among these, the nitration of CAIII was increased not only in the lesional skin of AD-NC/Nga mice but also in the mice that did not present any symptoms. The in vitro nitration of purified CAIII by peroxynitrite reduced its CO2 hydratase activity in a dose-dependent manner. In addition, we found that CAIII was induced during the differentiation of normal human epidermal keratinocytes. Furthermore, we found the presence of CAIII and the formation of 6-nitrotryptophan-containing proteins in both the lesional and the nonlesional sections of the skin of patients with atopic dermatitis through immunohistochemical staining. This study provides the first demonstration of the formation of 6-nitrotryptophan in human tissues and disease.

Metal-catalyzed protein tyrosine nitration in biological systems

Protein tyrosine nitration is an oxidative postranslational modification that can affect protein structure and function. It is mediated in vivo by the production of nitric oxide-derived reactive nitrogen species (RNS), including peroxynitrite (ONOO(-)) and nitrogen dioxide ((•)NO₂). Redox-active transition metals such as iron (Fe), copper (Cu), and manganese (Mn) can actively participate in the processes of tyrosine nitration in biological systems, as they catalyze the production of both reactive oxygen species and RNS, enhance nitration yields and provide site-specificity to this process. Early after the discovery that protein tyrosine nitration can occur under biologically relevant conditions, it was shown that some low molecular weight transition-metal centers and metalloproteins could promote peroxynitrite-dependent nitration. Later studies showed that nitration could be achieved by peroxynitrite-independent routes as well, depending on the transition metal-catalyzed oxidation of nitrite (NO₂(-)) to (•)NO₂ in the presence of hydrogen peroxide. Processes like these can be achieved either by hemeperoxidase-dependent reactions or by ferrous and cuprous ions through Fenton-type chemistry. Besides the in vitro evidence, there are now several in vivo studies that support the close relationship between transition metal levels and protein tyrosine nitration. So, the contribution of transition metals to the levels of tyrosine nitrated proteins observed under basal conditions and, specially, in disease states related with high levels of these metal ions, seems to be quite clear. Altogether, current evidence unambiguously supports a central role of transition metals in determining the extent and selectivity of protein tyrosine nitration mediated both by peroxynitrite-dependent and independent mechanisms.

Croix CM, Watkins SC, Kisin ER, Kotchey GP, Balasubramanian K, Vlasova II, Yu J, Kim K, Seo W, Mallampalli RK, Star A, Shvedova AA. Lung macrophages "digest" carbon nanotubes using a superoxide/peroxynitrite oxidative pathway

In contrast to short-lived neutrophils, macrophages display persistent presence in the lung of animals after pulmonary exposure to carbon nanotubes. While effective in the clearance of bacterial pathogens and injured host cells, the ability of macrophages to "digest" carbonaceous nanoparticles has not been documented. Here, we used chemical, biochemical, and cell and animal models and demonstrated oxidative biodegradation of oxidatively functionalized single-walled carbon nanotubes via superoxide/NO* → peroxynitrite-driven oxidative pathways of activated macrophages facilitating clearance of nanoparticles from the lung.