The Biological Chemistry of Peroxynitrite

The inactivation efficacy of plasma-activated acetic acid against Salmonella Typhimurium cells and biofilm

AIM

This study aimed to examine the inactivation efficacy of plasma-activated acetic acid (PAAA) against Salmonella Typhimurium cells and biofilm and elucidate the underlying the chemical inactivation pathway.

METHODS AND RESULTS

PAAA was prepared by discharging plasma to 20 ml of 0.2% (v/v) acetic acid (AA) for 20 min (2.2 kHz and 8.4 kVpp). The count of cells and biofilms decreased by 5.71 log CFU ml^-1 and 4 log CFU/cm² after 10 min of treatment with 0.2% PAAA and 0.4% PAAA compared with control group (without any treatment), respectively. In 0.2% PAAA, the concentrations of hydrogen peroxide (H₂ O₂ ) and nitrate anions were directly proportional to the plasma discharge time, while nitrite anions (NO₂ ^- ) was not detected. However, the pH values of both 0.2% PAAA and plasma-activated water were inversely proportional to the plasma discharge time. Treatment with catalase, L-histidine, D-mannitol, and sodium azide inhibited the antibacterial activity of PAAA.

CONCLUSION

H₂ O₂ , Singlet oxygen, Hydroxyl radical, and NO₂ ^- are involved in the generation and decomposition of peroxynitrous acid generated from PAAA functioned as intermediate agent, which could diffuse through cell membranes of bacteria and induce cell injury.

SIGNIFICANCE AND IMPACT OF STUDY

This study provides the understanding of efficacy and selectivity of PAAA which could be a novel decontamination agent.

Tyrosine nitration as a key event of signal transduction that regulates functional state of the cell

This review is dedicated to the role of nitration of proteins by tyrosine residues in physiological and pathological conditions. First of all, we analyze the biochemical evidence of peroxynitrite formation and reactions that lead to its formation, types of posttranslational modifications (PTMs) induced by reactive nitrogen species, as well as three biological pathways of tyrosine nitration. Then, we describe two possible mechanisms of protein nitration that are involved in intracellular signal transduction, as well as its interconnection with phosphorylation/dephosphorylation of tyrosine. Next part of the review is dedicated to the role of proteins nitration in different pathological conditions. In this section, special attention is devoted to the role of nitration in changes of functional properties of actin-protein that undergoes PTMs both in normal and pathological conditions. Overall, this review is devoted to the main features of protein nitration by tyrosine residue and the role of this process in intracellular signal transduction in basal and pathological conditions.

Distribution and change of peroxynitrite in the guinea pig cochlea following noise exposure

Nitric oxide (NO)-mediated pathology depends on the formation of reactive intermediates, such as the peroxynitrite (ONOO⁻). ONOO⁻ can nitrate free tyrosine and tyrosine residues of proteins. Therefore, increases in tyrosine nitration reflect the amount of ONOO⁻ produced by oxidative stress. The distribution of 3-nitrotyrosine (3-NT), an ONOO⁻ marker, in the organ of corti and the cochlear lateral wall tissue from the guinea pig were examined using fluorescence immunohistochemistry. The immunoactivity of 3-NT in the normal guinea pig was compared with animals exposed to 122dBA broadband noise, 4 h/day, for 2 consecutive days. In the normal animals, 3-NT immunoreactivity was found in the outer hair cells (OHCs), inner hair cells (IHCs), pillar cells (PCs), spiral ganglion cells (SPCs) and the marginal cells of stria vascularis in the lateral wall. Sound exposure increased the 3-NT signal in all of the cells and resulted in extensive outer hair cell loss. A quantitative analysis of the 3-NT change in OHCs and marginal cells of lateral wall showed that immunolabeling was significant (P<0.01, n=10) in the noise exposure group compared with that of the control group. Anti-3-NT and propidium iodide double labeling showed that 3-NT was distributed mainly in the apical end of OHCs. In addition, 3-NT was distributed outside of the nucleus of the OHCs and marginal cells. In conclusion, the data indicate that noise exposure leads to a significant production of ONOO⁻ in the cochlear lateral wall and organ of corti. This is consistent with the known increase of NO production by loud sound stress and suggests that NO-derived free radicals participate in the cochlear pathophysiology of noise-induced hearing loss.

Impact of SIN-1-derived peroxynitrite flux on endothelial cell redox homeostasis and bioenergetics: protective role of diphenyl diselenide via induction of peroxiredoxins

Increased production of reactive nitrogen (RNS) and oxygen (ROS) species and its detrimental effect to mitochondria are associated with endothelial dysfunction. This study was designed to determine the effect of a peroxynitrite flux, promoted by 1,3-morpholinosydnonimine (SIN-1), in mitochondrial function and some redox homeostasis parameters in bovine aortic endothelial cells (BAEC). Moreover, the effect of diphenyl diselenide (PhSe)2, a simple organic selenium compound, in preventing peroxynitrite-mediated cytotoxicity was also investigated. Our results showed that overnight exposure to SIN-1 (250 μM) caused a profound impairment of oxygen consumption, energy generation and reserve capacity in mitochondria of BAEC. Mitochondrial dysfunction resulted in an additional intracellular production of peroxynitrite, amplifying the phenomenon and leading to changes in redox homeostasis. Moreover, we observed an extensive decline in mitochondrial membrane potential (ΔΨm) induced by peroxynitrite and this event was associated with apoptotic-type cell death. Alternatively, the pretreatment of BAEC with (PhSe)2, hindered peroxynitrite-mediated cell damage by preserving mitochondrial and endothelial function and consequently preventing apoptosis. The protective effect of (PhSe)2 was related to its ability to improve the intracellular redox state by increasing the expression of different isoforms of peroxiredoxins (Prx-1-3), efficient enzymes in peroxynitrite detoxification.

Reactive oxygen and nitrogen species in steatotic hepatocytes: a molecular perspective on the pathophysiology of ischemia-reperfusion injury in the fatty liver

SIGNIFICANCE

Hepatic ischemia-reperfusion (IR) injury results from the temporary deprivation of hepatic blood supply and is a common side effect of major liver surgery (i.e., transplantation or resection). IR injury, which in most severe cases culminates in acute liver failure, is particularly pronounced in livers that are affected by non-alcoholic fatty liver disease (NAFLD). In NAFLD, fat-laden hepatocytes are damaged by chronic oxidative/nitrosative stress (ONS), a state that is acutely exacerbated during IR, leading to extensive parenchymal damage.

RECENT ADVANCES

NAFLD triggers ONS via increased (extra)mitochondrial fatty acid oxidation and activation of the unfolded protein response. ONS is associated with widespread protein and lipid (per)oxidation, which reduces the hepatic antioxidative capacity and shifts the intracellular redox status toward an oxidized state. Moreover, activation of the transcription factor peroxisome proliferator-activated receptor α induces expression of mitochondrial uncoupling protein 2, resulting in depletion of cellular energy (ATP) reserves. The reduction in intracellular antioxidants and ATP in fatty livers consequently gives rise to severe ONS and necrotic cell death during IR.

CRITICAL ISSUES

Despite the fact that ONS mediates both NAFLD and IR injury, the interplay between the two conditions has never been described in detail. An integrative overview of the pathophysiology of NAFLD that renders steatotic hepatocytes more vulnerable to IR injury is therefore presented in the context of ONS.

FUTURE DIRECTIONS

Effective methods should be devised to alleviate ONS and the consequences thereof in NAFLD before surgery in order to improve resilience of fatty livers to IR injury.

Nitro-fatty acids: formation, redox signaling, and therapeutic potential

SIGNIFICANCE

Nitrated derivatives of unsaturated fatty acids (nitro-fatty acids) are being formed and detected in human plasma, cell membranes, and tissue, triggering signaling cascades via covalent and reversible post-translational modifications of susceptible nucleophilic amino acids in transcriptional regulatory proteins and enzymes.

RECENT ADVANCES

Nitro-fatty acids modulate metabolic as well as inflammatory signaling pathways, including the p65 subunit of nuclear factor κB and the transcription factor peroxisome proliferator-activated receptor-γ. Moreover, nitro-fatty acids can activate heat shock as well as phase II antioxidant responses. As electrophiles, they also activate the Nuclear factor erythroid 2-related factor 2 pathway.

CRITICAL ISSUES

We first discuss the mechanisms of nitro-fatty acid formation as well as their key chemical and biochemical properties, including their capacity to release nitric oxide and exert antioxidant actions. The electrophilic properties of nitro-fatty acids to activate anti-inflammatory signaling pathways are discussed in detail. A critical issue is the influence of nitroarachidonic acid on prostaglandin endoperoxide H synthases, modulating inflammatory processes through redirection of arachidonic acid metabolism and signaling.

FUTURE DIRECTIONS

Based on this information, we analyze in vivo data supporting nitro-fatty acids as promising pharmacological tools to prevent inflammatory diseases associated with oxidative and nitrative stress conditions. A key future issue is to evaluate whether nitro-fatty acid supplementation would be useful for human diseases linked to inflammation as well as their potential toxicity when administered by long periods of time.

Nitro-fatty acids: novel anti-inflammatory lipid mediators

Nitro-fatty acids are formed and detected in human plasma, cell membranes, and tissue, modulating metabolic as well as inflammatory signaling pathways. Here we discuss the mechanisms of nitro-fatty acid formation as well as their key chemical and biochemical properties. The electrophilic properties of nitro-fatty acids to activate anti-inflammatory signaling pathways are discussed in detail. A critical issue is the influence of nitroarachidonic acid on prostaglandin endoperoxide H synthases, redirecting arachidonic acid metabolism and signaling. We also analyze in vivo data supporting nitro-fatty acids as promising pharmacological tools to prevent inflammatory diseases.

Degradation of palm oil refinery wastewaters by non-thermal gliding arc discharge at atmospheric pressure

The gliding electric discharge in humid air is a source of activated species forming (e.g. (•)OH, (•)NO and their derivatives H2O2, ONO2H and NO3H) which are present in a non-thermal plasma at atmospheric pressure. These species are able to degrade organic pollutants in palm oil refinery wastewaters (PORW). The increase in acidity (pH decrease), conductivity and total dissolved solids (TDS) and the decrease in the total organic carbon (TOC) of PORW samples exposed to the discharge are reported. More than 50% TOC abatement is obtained for 15 min treatment in batch conditions with a laboratory reactor. The organic pollutants of PORW, i.e. mainly fatty acids are degraded according to a pseudo first-order reaction (k* = 0.06 min(-1)). Post discharge reactions are also observed after having switched off the discharge, which suggests that the pseudo first-order (k ≈ 0.05 min(-1)) degradation reactions should be attributed to the diffusion of soluble reactive species, e.g. H2O2 and ONOOH in the liquid target.

Rapid analytical methods for on-site triage for traumatic brain injury

Traumatic brain injury (TBI) results from an event that causes rapid acceleration and deceleration of the brain or penetration of the skull with an object. Responses to stimuli and questions, loss of consciousness, and altered behavior are symptoms currently used to justify brain imaging for diagnosis and therapeutic guidance. Tests based on such symptoms are susceptible to false-positive and false-negative results due to stress, fatigue, and medications. Biochemical markers of neuronal damage and the physiological response to that damage are being identified. Biosensors capable of rapid measurement of such markers in the circulation offer a solution for on-site triage, as long as three criteria are met: (a) Recognition reagents can be identified that are sufficiently sensitive and specific, (b) the biosensor can provide quantitative assessment of multiple markers rapidly and simultaneously, and (c) both the sensor and reagents are designed for use outside the laboratory.

Protein nitration, PARP activation and NAD+ depletion may play a critical role in the pathogenesis of cyclophosphamide-induced hemorrhagic cystitis in the rat

OBJECTIVES

Hemorrhagic cystitis (HC) is a major dose-limiting side effect of cyclophosphamide (CP). The mechanism by which CP induces cystitis is not clear. Recent studies demonstrate that nitric oxide; (peroxynitrite) is involved in bladder damage caused by CP. However, the molecular targets of peroxynitrite are not known. The present study is aimed at investigating whether proteins and DNA are molecular targets of peroxynitrite using a rat model.

METHODS

The experimental rats received a single i.p. injection of 150 mg kg(-1) body weight CP in saline and killed 6 or 16 h later. The control rats received saline. The bladders were used for histological and biochemical analysis. Nitrotyrosine and poly-(ADP-ribose) polymerase (PARP) were localized immunohistochemically as indicators of protein nitration and DNA damage, respectively. Nitrite, malondialdehyde, protein thiol and superoxide dismutase (SOD) activity were assayed in the bladder.

RESULTS

Hematuria and urinary bladder edema was observed in the CP-treated rats and histologically, moderate to severe damage to the urinary bladder was observed. The bladders of CP-treated rats stained strongly for nitrotyrosine as well as for PARP. Significant decrease in oxidized NAD levels was observed in the bladders of CP-treated rats 16 h following treatment with CP. Protein thiol was depleted and the activity of the peroxynitrite sensitive enzyme SOD was significantly reduced in the bladders of CP-treated rats.

CONCLUSION

The results of the present study reveal that protein nitration, PARP activation and NAD+ depletion may play a critical role in the pathogenesis of CP-induced hemorrhagic cystitis. Based on the results we propose a mechanism for CP-induced cystitis.

Effects of long-term exposure of extremely low frequency magnetic field on oxidative/nitrosative stress in rat liver

Thirty-two adult Wistar-Albino female and male rats were used to investigate the long-term (45 days) effects of extremely low frequency magnetic field (ELF-MF; 50Hz, 1mT, 4h/day) exposure on oxidative/nitrosative stress in liver tissues of rats. The rats were divided randomly into four groups: female control (FC; n = 8) and MF-exposed female rats (F-MF; n = 8); male control (MC; n = 8) and MF-exposed male rats (M-MF; n = 8). Liver tissue from each animal was harvested and utilized for malondialdehyde (MDA) and 3-nitrotyrosine (3-NT) detection. MDA levels were measured by MDA-TBA method, while the 3-NT levels were determined by the HPLC-UV system. There were no significant differences between the MDA levels of the control (FC; MC) and MF-exposed (F-MF; M-MF) rats (P > 0.05). In the F-MF rats, 3-NT levels were significantly increased when compared to those of the FC rats (P < 0.05). There were no significant differences between the 3-NT levels of the MC and M-MF rats. In conclusion, our study suggests that the long-term ELF-MF exposure may enhance the oxidative/nitrosative stress in liver tissue of the female rats and could have a deteriorative effect on cellular proteins rather than lipids by enhancing 3-NT formation.

Peroxynitrite: biochemistry, pathophysiology and development of therapeutics

Peroxynitrite--the product of the diffusion-controlled reaction of nitric oxide with superoxide radical--is a short-lived oxidant species that is a potent inducer of cell death. Conditions in which the reaction products of peroxynitrite have been detected and in which pharmacological inhibition of its formation or its decomposition have been shown to be of benefit include vascular diseases, ischaemia-reperfusion injury, circulatory shock, inflammation, pain and neurodegeneration. In this Review, we first discuss the biochemistry and pathophysiology of peroxynitrite and then focus on pharmacological strategies to attenuate the toxic effects of peroxynitrite. These include its catalytic reduction to nitrite and its isomerization to nitrate by metalloporphyrins, which have led to potential candidates for drug development for cardiovascular, inflammatory and neurodegenerative diseases.

Dynamics of nitric oxide and peroxynitrite during global brain ischemia/reperfusion in rat hippocampus: NO-sensor measurement and modeling study

The dynamics of nitric oxide (NO) and peroxynitrite concentration changes during brain ischemia/reperfusion are poorly understood. In this paper, a NO-selective sensor was used to measure NO concentration changes in the rat brain hippocampus during global brain ischemia/reperfusion. Four-vessel occlusion model of transient global brain ischemia was used. Global cerebral ischemia was induced by occluding both common carotid arteries with artery nips (for 20 min) and reperfusion was induced by loosening the artery nips. Results showed that the changes of NO concentration during global brain ischemia/reperfusion could be divided into different stages. Together with the effects of O2 tension changes and NO synthase (NOS) on nitric oxide levels, we determined five stages in the NO concentration profile: (1) acute O2-limited decrease stage; (2) O2-limited steady stage; (3) neuronal NOS activation stage; (4) acute O2-recovery elevation stage; and (5) O2-recovery steady stage. In addition, a chemical reaction network model was constructed to simulate the dynamics of peroxynitrite during the reperfusion stage, and the effects of a change in the NO formation rate on the dynamics of peroxynitrite were investigated specifically. Results show the rate of NO formation has a great influence on peroxynitrite dynamics.

Nitrosative stress inhibits the aminophospholipid translocase resulting in phosphatidylserine externalization and macrophage engulfment: implications for the resolution of inflammation

Macrophage recognition of apoptotic cells depends on externalization of phosphatidylserine (PS), which is normally maintained within the cytosolic leaflet of the plasma membrane by aminophospholipid translocase (APLT). APLT is sensitive to redox modifications of its -SH groups. Because activated macrophages produce reactive oxygen and nitrogen species, we hypothesized that macrophages can directly participate in apoptotic cell clearance by S-nitrosylation/oxidation and inhibition of APLT causing PS externalization. Here we report that exposure of target HL-60 cells to nitrosative stress inhibited APLT, induced PS externalization, and enhanced recognition and elimination of "nitrosatively" modified cells by RAW 264.7 macrophages. Using S-nitroso-L-cysteine-ethyl ester (SNCEE) and S-nitrosoglutathione (GSNO) that cause intracellular and extracellular trans-nitrosylation of proteins, respectively, we found that SNCEE (but not GSNO) caused significant S-nitrosylation/oxidation of thiols in HL-60 cells. SNCEE also strongly inhibited APLT, activated scramblase, and caused PS externalization. However, SNCEE did not induce caspase activation or nuclear condensation/fragmentation suggesting that PS externalization was dissociated from the common apoptotic pathway. Dithiothreitol reversed SNCEE-induced S-nitrosylation, APLT inhibition, and PS externalization. SNCEE but not GSNO stimulated phagocytosis of HL-60 cells. Moreover, phagocytosis of target cells by lipopolysaccharide-stimulated macrophages was significantly suppressed by an NO. scavenger, DAF-2. Thus, macrophage-induced nitrosylation/oxidation plays an important role in cell clearance, and hence in the resolution of inflammation.

Kinetics of peroxiredoxins and their role in the decomposition of peroxynitrite

Methodologies and results of studies on the kinetics of peroxiredoxins (Prx) are reviewed. Peroxiredoxins are broad-spectrum peroxidases that catalyze the reduction of H2O2, organic hydroperoxides and peroxynitrite by thiols. Their catalytic cycle starts with the oxidation of a particularly reactive cysteine residue (C(P)) to a sulfenic acid derivative by the peroxide substrate, the sulfenic acid then reacts with a thiol to form a disulfide, and the cycle is completed by thiol/disulfide exchange reactions that regenerate the ground-state enzyme. Depending on the subtype of peroxiredoxin, the thiol reacting with the primary oxidation product (E-SOH) may be a cysteine residue of a second subunit (typical 2-Cys Prx), a cysteine residue of the same subunit (atypical 2-Cys Prx) or reducing substrate (1-Cys Prx and at least one example of an atypical 2-Cys Prx). In a typical 2-Cys Prx the intra-subunit disulfide formation with the second "resolving" cysteine (C(R)) is mandatory for the reduction by the specific substrate, which is a protein characterized by a CXXC motif such as thioredoxin, tryparedoxin or AhpF. These consecutive redox reactions define the catalysis as an enzyme substitution mechanism, which is corroborated by a ping-pong pattern that is commonly observed in steady-state analyses, chemical identification of catalytic intermediates and stopped-flow analyses of partial reactions. More complex kinetic patterns are discussed in terms of cooperativity between the subunits of the oligomeric enzymes, generation of different oxidized intermediates or partial over-oxidation of C(P) to a sulfinic acid. Saturation kinetics is often not observed indicating that a typical complex between reduced enzyme and hydroperoxide is not formed and that, in these cases, formation of the complex between the oxidized enzyme and its reducing substrate is slower than the reaction within this complex. Working with sulphur catalysis, Prxs are usually less efficient than the heme- or selenium-containing peroxidases, but in some cases the k(+1) values (bimolecular rate constant for oxidation of reduced E by ROOH) are comparable, the overall range being 2 x 10(3)-4 x 10(7) M(-1)s(-1) depending on the hydroperoxide and the individual Prx. For the reduction of peroxynitrite k(+1) values of 1 x 10(6) up to 7 x 10(7) M(-1)s(-1) have been measured. The net forward rate constants k'(+2) for the reductive part of the cycle range between 2 x 10(4)-1 x 10(7) M(-1)s(-1). These kinetic characteristics qualify the peroxiredoxins as moderately efficient devices to detoxify hydroperoxides, which is pivotal to organisms devoid of more efficient peroxidases, and as most relevant to the detoxification of peroxynitrite. In higher organisms, their specific role is seen in the regulation of signalling cascades that are modulated by H2O2, lipid hydroperoxides or peroxynitrite.

Bio imaging of intracellular NO production in single bone cells after mechanical stimulation

We show the intracellular upregulation of NO production after mechanical stimulation, an essential chemical signal in bone remodeling. This is done in real time using the fluorescent chromophore DAR-4M AM. Differences in cellular response to mechanical stimulation of different regions of a single cell were observed.

INTRODUCTION

Osteocytes are the most abundant bone cells that are believed to be the mechanosensors of bone, responding to mechanical stresses in interstitial fluid flow through the canaliculi. Under mechanical load, chemical signals such as NO play a key role in the activity of osteoblasts/osteoclasts that regulate bone remodeling. Despite the importance of NO in signaling, its real-time detection has proved challenging. This is largely because of the short NO half-life (typically approximately 0.1-5 s). Here, we show the upregulation of intracellular NO production in single osteocytes under localized mechanical stimulation.

MATERIALS AND METHODS

We used the chromophore DAR-4M AM for NO detection. This is loaded into surface-attached MLO-Y4 osteocyte-like and MC3T3-E1 osteoblast-like cells that are subjected to a localized mechanical stimulation using optical tweezers or a microneedle tip. DAR-4M AM is membrane-permeable and chelates NO, forming a stable, fluorescent compound, which is visible with a rhodamine filter.

RESULTS

Nonstimulated MLO-Y4 and MC3T3-E1 cells showed basal NO production levels, as indicated by a gradual increase in their fluorescence intensity. Localized mechanical stimulation of single MC3T3-E1 cells and MLO-Y4 cells by optical tweezers (150-550 pN, 0.5-3 Hz, 1 minute) showed a nearly 15-30% increase, whereas MLO-Y4 cells stimulated by a microneedle (10-20 nN, 1 minute) showed nearly 15-16% increase relative to their nonstimulated state. Furthermore, stimulation of a single cell process by a microneedle resulted in a 2-10% increase in the fluorescence intensity.

CONCLUSIONS

NO is essential for mechanically induced bone remodeling and is a meaningful parameter for measuring bone cell activation after mechanical loading. Here we show NO upregulation in individual bone cells after a localized mechanical stimulation. We also show that both the cell body and the cell processes might be involved in mechanosensing. This technique allows characterization of the mechanosensitivity of different parts of a single osteocyte. This opens up the possibility to uncover the complexities and function of single osteocytes in the dynamic process of bone remodeling.

Lipid nitration and formation of lipid-protein adducts: biological insights

Lipid-protein adducts are formed during oxidative and nitrative stress conditions associated with increasing lipid and protein oxidation and nitration. The focus of this review is the analysis of interactions between oxidative-modified lipids and proteins and how lipid nitration can modulate lipid-protein adducts formation. For this, two biologically-relevant models will be analysed: a) human low density lipoprotein, whose oxidation is involved in the early steps of atherogenesis, and b) alpha-synuclein/lipid membranes system, where lipid-protein adducts are being associated with the develop of Parkinson disease and other synucleinopathies.

EPR spin-trapping of protein radicals to investigate biological oxidative mechanisms

Presently, free radicals and oxidants are considered to mediate from signaling circuits involved in physiology and pathology to cell and tissue injury. The elucidation of these many inter-related processes requires a better understanding of cellular oxidative mechanisms many of which are mediated by protein radicals. Here, we will discuss the potentialities of EPR spin-trapping of protein radicals to unravel oxidative mechanisms. An overview of the methodology and its application to identify protein residues that are the target of specific oxidants, characterize emerging oxidants, and discriminate radical from non radical mechanisms will be presented. The examples are based on work developed in our laboratories but will be discussed in a broad scenario to emphasize that simple experiments can provide relevant insights into the biological reactivity of known and emerging biological oxidants and into signaling mechanisms.

Kinetic Modeling of Nitric-Oxide-Associated Reaction Network

PURPOSE

Nitric oxide and superoxide are the two important free radicals in the biological system. The coexistence of both free radicals in the physiological milieu gives rise to intricate oxidative and nitrosative reactions, which have been implicated in many physiological and/or pathophysiological conditions, such as vasodilatation and inflammation. It is difficult, if not impossible, to study the complexity of the nitric oxide/superoxide system using current experimental approaches. Computational modeling thus offers an alternative way for studying the problem.

METHODS

In this present study, key reaction pathways related to the generation, reaction and scavenging of both nitric oxide and superoxide were integrated into a reaction network. The network dynamics was investigated by numerical simulations to a set of coupled differential equations and by dynamical analysis. Two specific questions pertaining to the reaction kinetics of the reactive chemical species in the nitric oxide/superoxide system were studied: (1) how does the system respond dynamically when the generation rate of nitric oxide and superoxide varies? (2) how would antioxidants such as glutathione modulate the system dynamics?

RESULTS

While changing basal GSH levels does not alter the kinetics of nitric oxide, superoxide, and peroxynitrite, the kinetic profiles of N203, GSNO and GSH are sensitive to the variation of basal GSH levels. The kinetics of the potential nitrosative species, N203, is switch like, which is dependent on the level of GSH.

CONCLUSIONS

The model predicts that concurrent high nitric oxide and superoxide generation--such as in the inflammatory conditions--may result in nonlinear system dynamics, and glutathione may serve as a dynamic switch of N203 mediated nitrosation reaction.

Nitric oxide and cnidarian bleaching: an eviction notice mediates breakdown of a symbiosis

Nitric oxide (NO) is a free radical implicated in numerous cell signaling,physiological and pathophysiological processes of eukaryotic cells. Here, we describe the production of NO as part of the cellular stress response of the symbiotic sea anemone Aiptasia pallida, which hosts dinoflagellates from the genus Symbiodinium. We show that exposure to elevated temperatures induces symbiotic anemones to produce high levels of NO, leading to the collapse of the symbiosis. These results shed light on the poorly understood cellular mechanism through which elevated seawater temperature causes the release of symbiotic algae from symbiotic cnidarians, a detrimental process known as coral (cnidarian) bleaching. The results presented here show that the host cell is a major source of NO during exposure to elevated temperatures and that this constitutes a cytotoxic response leading to bleaching. These results have important evolutionary implications as the observed NO production in these basal metazoans displays many parallels to the cytotoxic inflammatory response to pathogens, a well-understood process in mammalian model systems.

Interaction with phospholipids modulates alpha-synuclein nitration and lipid-protein adduct formation

Intracellular aggregates of alpha-syn (alpha-synuclein) represent pathoanatomical hallmarks of neurodegenerative disorders (synucleinopathies). The molecular mechanisms underlying alpha-syn aggregation into filamentous inclusions may involve oxidation and nitration of the protein. Whereas the effects of oxidants and nitrating species on soluble alpha-syn have been studied in detail, the effect of these reactive species on alpha-syn associated with lipids is still unknown. In the present paper, we report that alpha-syn bound to small unilamellar liposomes composed of phosphatidylcholine/phosphatidic acid is resistant to oxidation and nitration when compared with soluble alpha-syn. Additionally, increasing concentrations of unsaturated fatty acids diminished the oxidation and nitration of alpha-syn upon exposure to fluxes of peroxynitrite (8-20 microM x min(-1)). To investigate the effect of oxidized lipids on alpha-syn, the protein was incubated with the bifunctional electrophile 4-HNE [4-hydroxy-2(E)-nonenal]. MS analysis showed the formation of three major products corresponding to the native protein and alpha-syn plus one or two 4-HNE molecules. Trypsin digestion of the modified protein followed by peptide 'finger-printing' revealed that 4-HNE modified the peptide E46GVVHGVATVAEK58. Further analysis of the peptides with liquid chromatography-tandem MS identified the modified residue as His50. The data indicate that the association of alpha-syn with biological membranes protects the protein from oxidation and nitration and thus diminishes the formation of protein molecules capable of forming aggregates. However, products of lipid peroxidation can also modify alpha-syn, generating novel protein adducts that could serve as biomarkers for documenting oxidative processes in human as well as animal and cellular models of alpha-syn aggregation and pathology.

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

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

Reactivity of Peroxynitrite and Nitric Oxide with LDL

Low density lipoprotein (LDL) oxidation by peroxynitrite is a complex process, finely modulated by control of peroxynitrite formation, LDL availability and free-radical scavenging by nitric oxide (*NO), ascorbate and alpha-tocopherol (alpha -TOH). In the presence of CO2, lipid targets are spared at the expense of surface constituents. Since surface damage may lead to oxidation-induced LDL aggregation and particle recognition by scavenger receptors, CO2 cannot be considered an inhibitor of peroxynitrite-dependent LDL modifications. Chromanols, urate and ascorbate cannot scavenge peroxynitrite in the vasculature, although intermediates of urate oxidation and high ascorbate concentrations may do soin vitro. Most if not all of the protection against peroxynitrite-induced LDL oxidation afforded by urate, ascorbate, chromanols and also*NO should be considered to depend on their free radical scavenging abilities, including inactivation of lipid peroxyl radicals (LOO),*NO2, and CO3*-; as well as their capacity to reduce high oxidation states of metal centers. Peroxynitrite direct interception by reduced manganese (II) porphyrins is possibly the most powerful although unspecific strategy to inhibit peroxynitrite reactions. In light of the recent demonstration of nitrated bioactive lipids in vivo, renewed interest in the mechanisms of peroxynitrite- and nitric oxide-mediated lipid nitration and nitrosation is guaranteed.

Septic diaphragmatic dysfunction is prevented by Mn(III)porphyrin therapy and inducible nitric oxide synthase inhibition

OBJECTIVE

Decreased diaphragmatic contractility and organ failure observed during sepsis is mediated by an overproduction of nitric oxide ((.)NO)-derived species, mitochondria being a major target of oxidative and nitrative stress. We tested the potential protective effects of (a) a novel synthetic antioxidant, the manganese(III) 5,10,15,20-tetrakis(N-ethylpyridinium-2-yl) porphyrin (MnTE-2-PyP(5+)) and (b) the inducible (.)NO synthase inhibitor aminoguanidine (AG) on a rat model of sepsis.

SETTING

University research laboratories.

SUBJECTS AND INTERVENTIONS

Sepsis was induced by cecal ligation and perforation in rats.

MEASUREMENTS AND RESULTS

Systemic hemodynamics, pulmonary gas exchange, in vitro diaphragmatic function and mitochondrial respiration were evaluated. Moreover, plasma and mitochondrial oxidative and nitrative stress parameters were investigated. Sepsis determined diaphragmatic dysfunction and a significant decrease in mitochondrial coupling and respiration. Oxidative stress was evidenced by decreased plasma antioxidants and increased lipid oxidation. Tyrosine nitration was increased in the plasma and mitochondria of the septic animals. These alterations were ameliorated or prevented by either MnTE-2-PyP(5+) or AG.

CONCLUSIONS

Our results demonstrate that overproduction of (.)NO and (.)NO-derived reactive species play a critical role in mitochondrial impairment and diaphragmatic function during sepsis. More importantly, AG but mainly the novel metalloporphyrin MnTE-2-PyP(5+) were able to ameliorate diaphragmatic and mitochondrial dysfunction and could contribute to preventing organ failure during severe sepsis.

Nitric oxide, oxidants, and protein tyrosine nitration

The occurrence of protein tyrosine nitration under disease conditions is now firmly established and represents a shift from the signal transducing physiological actions of (.)NO to oxidative and potentially pathogenic pathways. Tyrosine nitration is mediated by reactive nitrogen species such as peroxynitrite anion (ONOO(-)) and nitrogen dioxide ((.)NO2), formed as secondary products of (.)NO metabolism in the presence of oxidants including superoxide radicals (O2(.-)), hydrogen peroxide (H2O2), and transition metal centers. The precise interplay between (.)NO and oxidants and the identification of the proximal intermediate(s) responsible for nitration in vivo have been under controversy. Despite the capacity of peroxynitrite to mediate tyrosine nitration in vitro, its role on nitration in vivo has been questioned, and alternative pathways, including the nitrite/H2O2/hemeperoxidase and transition metal-dependent mechanisms, have been proposed. A balanced analysis of existing evidence indicates that (i) different nitration pathways can contribute to tyrosine nitration in vivo, and (ii) most, if not all, nitration pathways involve free radical biochemistry with carbonate radicals (CO3(.-)) and/or oxo-metal complexes oxidizing tyrosine to tyrosyl radical followed by the diffusion-controlled reaction with (.)NO2 to yield 3-nitrotyrosine. Although protein tyrosine nitration is a low-yield process in vivo, 3-nitrotyrosine has been revealed as a relevant biomarker of (.)NO-dependent oxidative stress; additionally, site-specific nitration focused on particular protein tyrosines may result in modification of function and promote a biological effect. Tissue distribution and quantitation of protein 3-nitrotyrosine, recognition of the predominant nitration pathways and individual identification of nitrated proteins in disease states open new avenues for the understanding and treatment of human pathologies.

Biological chemistry of reactive oxygen and nitrogen and radiation-induced signal transduction mechanisms

In the past few years, nuclear DNA damage-sensing mechanisms activated by ionizing radiation have been identified, including ATM/ATR and the DNA-dependent protein kinase. Less is known about sensing mechanisms for cytoplasmic ionization events and how these events influence nuclear processes. Several studies have demonstrated the importance of cytoplasmic signaling pathways in cytoprotection and mutagenesis. For cytoplasmic signaling, radiation-stimulated reactive oxygen species (ROS) and reactive nitrogen species (RNS) are essential activators of these pathways. This review summarizes recent studies on the chemistry of radiation-induced ROS/RNS generation and emphasizes interactions between ROS and RNS and the relative roles of cellular ROS/RNS generators as amplifiers of the initial ionization events. Cellular mechanisms for regulating ROS/RNS levels are discussed. The mechanisms by which cells sense ROS/RNS are examined in terms of how ROS/RNS modify protein structure and function, for example, interactions with metal-thiol clusters, protein tyrosine nitration, protein cysteine oxidation, S-thiolation and S-nitrosylation. We propose that radiation-induced ROS are the initiators and that nitric oxide (NO*) or derivatives are the effectors activating these signal transduction pathways. In responding to cellular ionization events, the cell converts an oxidative signal to a nitrosative one because ROS are too reactive and unspecific in their reactions for regulatory purposes and the cell is equipped to precisely modulate NO* levels.

Evidence of an electron-transfer mechanism in the peroxynitrite-mediated oxidation of 4-alkylphenols and tyrosine

The mechanism of interaction of the peroxynitrite with some 4-alkylphenols and tyrosine was mainly studied by means of ESR spectroscopy and product analysis. The radical intermediates, detected as spin adducts to the 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO), were identified as carbon-centered radicals to the benzene ring. The reaction seems to proceed via an electron transfer process (ET), most likely mediated by a NOx derivative, leading to the intermediacy of a phenoxyl-type radical as proved by the detection of the corresponding Pummerer-type ketone. No evidence of the formation of hydroxyl radicals, due to the homolytic cleavage of the peroxynitrite at physiological pH was obtained, even though DEPMPO hydroxyl spin adducts were detected: the latter most likely arises from the direct attack of the spin trap by the oxidant species. The possible involvement of HCO(3)(-)/CO(2), i.e., the formation of the nitrosoperoxycarbonate, ONOOCO(2)(*)(-), was also investigated.

Nitric Oxide System and Protein Nitration are Modified by an Acute Hypobaric Hypoxia in the Adult Rat Hippocampus

Changes in the nitric oxide system of the hippocampus from rats submitted to hypobaric hypoxia were investigated. Adult rats were exposed to a simulated altitude of 8,325 m (27,000 ft) for 7 h and killed after 0 h, 1, 3, 5, 10 and 20 days of reoxygenation. The number of neuronal nitric oxide synthase immunoreactive neurons and their dendritic plexus, as well as neuronal nitric oxide synthase immunoblotting densitometry and calcium-dependent activity increased from 0 h to 3 days of reoxygenation. In addition, endothelial nitric oxide synthase immunoreactivity peaked after 7 h of hypobaric hypoxia. Nitrotyrosine immunoreactivity showed an increase in the pyramidal cells of CA2-CA3 and in glial cells surrounding the blood vessels after 0 h, 1 and 3 days of reoxygenation. Immunoblotting densitometry of 1 of the 2 nitrotyrosine-immunoreactive bands detected also increased after 0 h and 1 day of reoxygenation. Inducible nitric oxide synthase immunoreactivity was found only in some blood vessels after 0 h, 1 and 3 days of reoxygenation, but no changes in inducible nitric oxide synthase activity or immunoblotting were detected. We conclude that transient activation of the nitric oxide system constitutes a hippocampal response to hypobaric hypoxia.

Direct evidence of singlet molecular oxygen [O2(1Deltag)] production in the reaction of linoleic acid hydroperoxide with peroxynitrite

Peroxynitrite (ONOO-), a biologically active species, can induce lipid peroxidation in biological membranes, thereby leading to the formation of various hydroperoxides. We report herein on the formation of singlet molecular oxygen [O(2) ((1)Delta(g))] in the reaction of peroxynitrite with linoleic acid hydroperoxide (LAOOH) or (18)O-labeled LAOOH. The formation of O(2) ((1)Delta(g)) was characterized by (i) dimol light emission in the red spectral region (lambda > 570 nm) using a red-sensitive photomultiplier; (ii) monomol light emission in the near-infrared region (lambda = 1270 nm) with a liquid nitrogen-cooled germanium diode or a photomultiplier coupled to a monochromator; (iii) the enhacing effect of deuterium oxide on chemiluminescence intensity, as well as the quenching effect of sodium azide; and (iv) chemical trapping of O(2) ((1)Delta(g)) or (18)O-labeled O(2) ((1)Delta(g)) with the 9,10-diphenylanthracene (DPA) and detection of the corresponding DPAO(2) or (18)O-labeled DPA endoperoxide by HPLC coupled to tandem mass spectrometry. Moreover, the presence of O(2) ((1)Delta(g)) was unequivocally demonstrated by a direct spectral characterization of the near-infrared light emission attributed to the transition of O(2) ((1)Delta(g)) to the triplet ground state. For the sake of comparison, O(2) ((1)Delta(g)) deriving from the thermolysis of the endoperoxide of 1,4-dimethylnaphthalene or from the H(2)O(2)/hypochlorite and H(2)O(2)/molybdate systems were also monitored. These novel observations identified the generation of O(2) ((1)Delta(g)) in the reaction of LAOOH with peroxynitrite, suggesting a potential O(2) ((1)Delta(g))-dependent mechanism that contributes to cytotoxicity mediated by lipid hydroperoxides and peroxynitrite reactions in biological systems.

Nitrolinoleate, a nitric oxide-derived mediator of cell function: synthesis, characterization, and vasomotor activity

Nitric oxide (*NO) and *NO-derived reactive species rapidly react with lipids during both autocatalytic and enzymatic oxidation reactions to yield nitrated derivatives that serve as cell signaling molecules. Herein we report the synthesis, purification, characterization, and bioactivity of nitrolinoleate (LNO2). Nitroselenylation of linoleic acid yielded LNO2 that was purified by solvent extraction, silicic acid chromatography, and reverse-phase HPLC. Structural characterization was performed by IR spectroscopy, 15N-NMR, LC-negative ion electrospray mass spectroscopy (MS), and chemiluminescent nitrogen analysis. Quantitative MS analysis of cell and vessel LNO2 metabolism, using L[15N]O2 as an internal standard, revealed that LNO2 is rapidly metabolized by rat aortic smooth muscle (RASM) monolayers and rat thoracic aorta, resulting in nitrite production and up to 3-fold increases in cGMP (ED50 = 30 microM for RASM, 50 microM for aorta). LNO2 induced endothelium-independent relaxation of preconstricted rat aortic rings, which was unaffected by L(G)-nitro-l-arginine methyl ester addition and inhibited by the guanylate cyclase inhibitor 1H-[1,2,4] oxadiazole[4,3-a]quinoxalin-1-one and the *NO scavenger HbO2. These results reveal that synthetic LNO2, identical to lipid derivatives produced biologically by the reaction of *NO and *NO-derived species with oxidizing unsaturated fatty acids (e.g., linoleate), can transduce vascular signaling actions of *NO.

A chemical perspective on the interplay between NO, reactive oxygen species, and reactive nitrogen oxide species

Nitric oxide (nitrogen monoxide, NO) plays a veritable cornucopia of regulatory roles in normal physiology. In contrast, NO has also been implicated in the etiology and sequela of numerous neurodegenerative diseases that involve reactive oxygen species (ROS) and nitrogen oxide species (RNOS). In this setting, NO is often viewed solely as pathogenic; however, the chemistry of NO can also be a significant factor in lessening injury mediated by both ROS and RNOS. The relationship between NO and oxidation, nitrosation, and nitration reactions is summarized. The salient factors that determine whether NO promotes, abates, or interconnects these chemistries are emphasized. From this perspective of NO chemistry, the type, magnitude, location, and duration of either ROS or RNOS reactions may be predicted.

Polyphenols and red wine as peroxynitrite scavengers: a chemiluminescent assay

A novel chemiluminescent assay for evaluating peroxynitrite (ONOO(-))-scavenging capacity was developed. The experimental protocol ensures sensitivity and reproducibility of measurements. The addition of 0-500 microM ONOO(-) to rat liver homogenate generated a luminous signal that was analyzed by chemiluminescence in a LKB Wallac liquid scintillation counter. The obtained optimal conditions were: 1-2 mg/mL of homogenate protein in 120 mM KCl, 30 mM phosphate buffer (pH 7.4), and 220 microM ONOO(-) at 30 degrees C. As polyphenols we used (+)-catechin, (-)-epicatechin, and myricetin. The most efficient of the compounds tested was myricetin with an IC(50) of 20 microM. The effectiveness of this method was verified by evaluating the antioxidant ability of three red wine samples to decrease peroxynitrite-initiated chemiluminescence. The ONOO(-)-scavenging activity of wines measured by this assay was related to the phenolic level of the samples. The quickness and reliability of this assay makes it particularly suitable for a large-scale screening of watery food extracts.

Unraveling peroxynitrite formation in biological systems

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