Peroxynitrite Fluxes Research Articles

Evaluation of peroxynitrite fluxes in inflammatory mice with a ratiometric fluorescence probe.

Inflammation is a critical physiological process in the human body, which is closely related to numerous disorders and cancers. ONOO- is generated and functionalized in the inflamed process, but the roles of ONOO- are still blurred. To illuminate the roles of ONOO-, we fabricated an intramolecular charge transfer (ICT)-based fluorescence probe, HDM-Cl-PN, for the ratiometric determination of ONOO- in the inflamed mouse model. The probe displayed a gradual fluorescence increase at 676nm and a fluorescence drop at 590nm toward 0-10.5μM ONOO-, and the ratio of 676nm fluorescence and 590nm fluorescence varied from 0.7 to 24.7. The significantly changed ratio and favorable selectivity ensure the sensitive detection of subtle changes in cellular ONOO-. Thanks to the excellent sensing performance, HDM-Cl-PNin vivo ratiometrically visualized ONOO- fluctuations in the LPS-triggered inflammatory process. Overall, this work not only expatiated the rational design for a ratiometric ONOO- probe but also built a bridge to investigate the connections between ONOO- and inflammation in living mice.

Highly Sensitive Near-Infrared Imaging of Peroxynitrite Fluxes in Inflammation Progress.

Inflammation is an important protection reaction in living organisms associated with many diseases. Since peroxynitrite (ONOO-) is engaged in the inflammatory processes, illustrating the key nexus between ONOO- and inflammation is significant. Due to the lack of sensitive ONOO- in vivo detection methods, the research still remains at its infancy. Herein, a highly sensitive NIR fluorescence probe DDAO-PN for in vivo detection of ONOO- in inflammation progress was reported. The probe responded to ONOO- with significant NIR fluorescence enhancement at 657 nm (84-fold) within 30 s in solution. Intracellular imaging of exogenous ONOO- with the probe demonstrated a 68-fold fluorescence increase (F/F0). Impressively, the probe can in vivo detect ONOO- fluxes in LPS-induced rear leg inflammation with a 4.0-fold fluorescence increase and LPS-induced peritonitis with an 8.0-fold fluorescence increase The remarkable fluorescence enhancement and quick response enabled real-time tracking of in vivo ONOO- with a large signal-to-noise (S/N) ratio. These results clearly denoted that DDAO-PN was able to be a NIR fluorescence probe for in vivo detection and high-fidelity imaging of ONOO- with high sensitivity and will boost the research of inflammation-related diseases.

Visualizing peroxynitrite fluxes and protective effect of endogenous hydrogen sulfide during carbonyl stress in endothelial cell

Carbonyl stress is caused by active carbonyl compounds. Abnormal metabolism will produce high concentration of active carbonyl substances, leading to carbonyl stress, thus inducing cell damage or apoptosis. It is important to find effective markers for carbonyl stress level and find therapeutic or palliative drugs. Peroxynitrite (ONOO−), as a kind of important reactive oxygen species, can be produced under a variety of pathological conditions. Hydrogen sulfide (H2S) has been known as antioxidant agent, anti-inflammatory et al. However, the protective effect of H2S and the level of ONOO− in endothelial cell apoptosis during carbonyl stress kept unknown. Herein, for address it, we reported the first single-molecule fluorescent probe (SZ) is capable of detecting ONOO− and H2S in Endothelial cell. The probe SZ shows good selectivity and low detection limit to ONOO− and H2S. More importantly, probe SZ may be a useful tool for evaluating and confirming the protective effects of endogenous H2S in Endothelial cell during carbonyl stress.

Imaging Dynamic Peroxynitrite Fluxes in Epileptic Brains with a Near-Infrared Fluorescent Probe.

Epilepsy is a chronic neurodegenerative disease, and accumulating evidence suggests its pathological progression is closely associated with peroxynitrite (ONOO−). However, understanding the function remains challenging due to a lack of in vivo imaging probes for ONOO− determination in epileptic brains. Here, the first near‐infrared imaging probe (named ONP) is presented for tracking endogenous ONOO− in brains of kainate‐induced epileptic seizures with high sensitivity and selectivity. Using this probe, the dynamic changes of endogenous ONOO− fluxes in epileptic brains are effectively monitored with excellent temporal and spatial resolution. In vivo visualization and in situ imaging of hippocampal regions clearly reveal that a higher concentration of ONOO− in the epileptic brains associates with severe neuronal damage and epileptogenesis; curcumin administration can eliminate excessively increased ONOO−, further effectively protecting neuronal cells. Moreover, by combining high‐content analysis and ONP, a high‐throughput screening method for antiepileptic inhibitors is constructed, which provides a rapid imaging/screening approach for understanding epilepsy pathology and accelerating antiseizure therapeutic discovery.

P-169 - Macrophage-derived peroxynitrite at physiological O2 concentration

Cell cultures are performed at 20% O2 (95% air/5% CO2) while a range of pO2 between 2–5% is found in different tissues (20–50 µM O2 at 37 °C, pH7.4). Peroxynitrite formation may be affected by pO2 since the sources of superoxide radical (O2•−) and nitric oxide (•NO) are enzymes that utilize oxygen as substrate. Neutrophils/macrophages contain NADPH oxidase (NOX-2), activated during phagocytosis, generating O2•– in a “respiratory burst” that consumes O2 at rates greater than basal levels. The reported Km for neutrophil NOX-2 is 2–3% O2, so theoretically, it would keep 45–70% of its maximum activity at physiological pO2 (2–5%). Nitric oxide (•NO) derives from the inducible nitric oxide synthase, with a higher Km (~11% O2) being more sensitive to changes in oxygen concentration in the physiological range. Experimental results in macrophages show that O2•− generation at 2% is 64% of that obtained in cells incubated at 20% O2. Despite what was expected, •NO production was similar for both conditions. Peroxynitrite formation is being assessed using fluorescein-boronate under different oxygen tensions. The quantitative data of •NO, O2•− and peroxynitrite fluxes under physiological O2 will provide a more accurate insight into the biological interplay and role of •NO-derived oxidants.

P-82 - Peroxynitrite versus decavanadate protein oxidative modifications: the case of myosin

In many diseases as well as during biological aging peroxynitrite (ONOO-) reacts with sarcomeric proteins, such as myosin and actin, in skeletal muscle (Steinberg, Circ. Res. 2013). We have previously demonstrated that exposure of purified myosin subfragment-1 (S1) to submicromolar fluxes of peroxynitrite produces strong inhibition of the actomyosin-ATPase activity with an IC50 of inhibition of 47 µM, being the inhibition due to the oxidation of the highly-reactive Cys on myosin (Tiago et al., Biochemistry 2006; Free Radic Res. 2010). In the present communication we further explore these studies by analyzing the exposition of myosin to peroxynitrite using ADP.V analogues, as well as the exposition to decavanadate (V10), a toxic ion previously described to bind at the myosin back door. Conversely to peroxynitrite, it was observed that decavanadate exposition induces the oxidation of a core Cys on myosin and not the highly-reactive Cys, whereas a strong inhibition of the actomyosin-ATPase activity was determined (IC50=2.7 µM). It was also observed that myosin suffers modifications at Lys-84 upon peroxynitrite exposition. In sum, myosin is more sensitive to oxidative modifications mediated by decavanadate than by peroxynitrite.

Molecular visualizing and quantifying immune-associated peroxynitrite fluxes in phagocytes and mouse inflammation model

Reactions of peroxynitrite (ONOO−) with biomolecules can lead to cytotoxic and cytoprotective events. Due to the difficulty of directly and unambiguously measuring its levels, most of the beneficial effects associated with ONOO− in vivo remain controversial or poorly characterized. Recently, optical imaging has served as a powerful noninvasive approach to studying ONOO− in living systems. However, ratiometric probes for ONOO− are currently lacking. Herein, we report the design, synthesis, and biological evaluation of F482, a novel fluorescence indicator that relies on ONOO−-induced diene oxidation. The remarkable sensitivity, selectivity, and photostability of F482 enabled us to visualize basal ONOO− in immune-stimulated phagocyte cells and quantify its generation in phagosomes by high-throughput flow cytometry analysis. With the aid of in vivo ONOO− imaging in a mouse inflammation model assisted by F482, we envision that F482 will find widespread applications in the study of the ONOO− biology associated with physiological and pathological processes in vitro and in vivo.

Sensitive detection and estimation of cell-derived peroxynitrite fluxes using fluorescein-boronate

The specific and sensitive detection of peroxynitrite (ONOO−/ONOOH) in biological systems is a great challenge due to its high reactivity towards several biomolecules. Herein, we validated the advantages of using fluorescein-boronate (Fl-B) as a highly sensitive fluorescent probe for the direct detection of peroxynitrite under biologically-relevant conditions in two different cell models. The synthesis of Fl-B was achieved by a very simply two-step conversion synthetic route with high purity (>99%) and overall yield (∼42%). Reactivity analysis of Fl-B with relevant biological oxidants including hydrogen peroxide (H2O2), hypochlorous acid (HOCl) and peroxynitrite were performed. The rate constant for the reaction of peroxynitrite with Fl-B was 1.7×106M−1s−1, a million times faster than the rate constant measured for H2O2 (k=1.7M−1s−1) and 2,700 faster than HOCl (6.2×102M−1s−1) at 37°C and pH 7.4. The reaction of Fl-B with peroxynitrite was significant even in the presence of physiological concentrations of CO2, a well-known peroxynitrite reactant. Experimental and simulated kinetic analyses confirm that the main oxidation process of Fl-B takes place with peroxynitrite itself via a direct bimolecular reaction and not with peroxynitrite-derived radicals. Fl-B was successfully applied for the detection of endogenously-generated peroxynitrite by endothelial cells and in macrophage-phagocyted parasites. Moreover, the generated data allowed estimating the actual intracellular flux of peroxynitrite. For instance, ionomycin-stimulated endothelial cells generated peroxynitrite at a rate of ∼ 0.1μMs−1, while immunostimulated macrophages do so in the order of ∼1μMs−1 inside T. cruzi-infected phagosomes. Fl-B revealed not to be toxic in concentrations up to 1mM for 24h. Cellular peroxynitrite detection was achieved by conventional laboratory fluorescence-based methods including flow cytometry and epi-fluorescence microscopy. Fl-B was shown to be more sensitive than the coumarin boronate due to a higher molar absorption coefficient and quantum yield. Overall, our results show that Fl-B is a kinetically selective and highly sensitive probe for the direct detection of cell-derived peroxynitrite.

Formation of 2-nitrophenol from salicylaldehyde as a suitable test for low peroxynitrite fluxes

There has been some dispute regarding reaction products formed at physiological peroxynitrite fluxes in the nanomolar range with phenolic molecules, when used to predict the behavior of protein-bound aromatic amino acids like tyrosine. Previous data showed that at nanomolar fluxes of peroxynitrite, nitration of these phenolic compounds was outcompeted by dimerization (e.g. biphenols or dityrosine). Using 3-morpholino sydnonimine (Sin-1), we created low fluxes of peroxynitrite in our reaction set-up to demonstrate that salicylaldehyde displays unique features in the detection of physiological fluxes of peroxynitrite, yielding detectable nitration but only minor dimerization products.By means of HPLC analysis and detection at 380nm we could identify the expected nitration products 3- and 5-nitrosalicylaldehyde, but also novel nitrated products. Using mass spectrometry, we also identified 2-nitrophenol and a not fully characterized nitrated dimerization product. The formation of 2-nitrophenol could proceed either by primary generation of a phenoxy radical, followed by addition of the NO2-radical to the various resonance structures, or by addition of the peroxynitrite anion to the polarized carbonyl group with subsequent fragmentation of the adduct (as seen with carbon dioxide). Interestingly, we observed almost no 3- and 5-nitrosalicylic acid products and only minor dimerization reaction.Our results disagree with the previous general assumption that nitration of low molecular weight phenolic compounds is always outcompeted by dimerization at nanomolar peroxynitrite fluxes and highlight unique features of salicylaldehyde as a probe for physiological concentrations of peroxynitrite.

Visualizing Peroxynitrite Fluxes in Endothelial Cells Reveals the Dynamic Progression of Brain Vascular Injury

Accumulating evidence suggests that formation of peroxynitrite (ONOO(-)) in the cerebral vasculature contributes to the progression of ischemic damage, while the underlying molecular mechanisms remain elusive. To fully understand ONOO(-) biology, efficient tools that can realize the real-time tracing of endogenous ONOO(-) fluxes are indispensable. While a few ONOO(-) fluorescent probes have been reported, direct visualization of ONOO(-) fluxes in the cerebral vasculature of live mice remains a challenge. Herein, we present a fluorescent switch-on probe (NP3) for ONOO(-) imaging. NP3 exhibits good specificity, fast response, and high sensitivity toward ONOO(-) both in vitro and in vivo. Moreover, NP3 is two-photon excitable and readily blood-brain barrier penetrable. These desired photophysical and pharmacokinetic properties endow NP3 with the capability to monitor brain vascular ONOO(-) generation after injury with excellent temporal and spatial resolution. As a proof of concept, NP3 has enabled the direct visualization of neurovascular ONOO(-) formation in ischemia progression in live mouse brain by use of two-photon laser scanning microscopy. Due to these favorable properties, NP3 holds great promise for visualizing endogenous peroxynitrite fluxes in a variety of pathophysiological progressions in vitro and in vivo.

Tyrosine nitration in peptides by peroxynitrite generated in situ in a light-controlled platform: Effects of pH and thiols

Peroxynitrite has been shown to play a critical role in inflammation and affords 3-nitrotyrosine as the hallmark product. The reported methods of generating this reactive nitrogen species in situ often fails to provide a high and steady flux of peroxynitrite resulting in poor yields of 3-nitrotyrosine. Herein we report a two-component peroxynitrite-generating platform in which this anion is produced in a biomimetic fashion and under the control of visible light. Incorporation of the nitric oxide- and superoxide-generating components in polymer matrices allows easy alterations of pH in the reaction wells of this platform. We have demonstrated very efficient nitration of tyrosine by peroxynitrite at different pH values and with varying concentrations of carbonate. In addition to tyrosine, a set of tyrosine-containing peptides was also studied. Presence of glutathione in the reaction wells increases the extent of tyrosine nitration in such peptide substrates presumably by raising the lifetime of nitric oxide in the reaction medium. When a cysteine residue was included in the sequence of the peptide, the extent of nitration of the tyrosine residue was found to depend on the position of the cysteine residue with respect to tyrosine. The extent of tyrosine nitration is strongly attenuated when the cysteine residue is directly adjacent to the tyrosine. This effect has been attributed to an intramolecular radical transfer mechanism. Taken together, results of this study demonstrate the potential of this light-controlled platform as a convenient bioanalytical tool in studying the reactions of peroxynitrite under widely varying conditions.

Unique Features of the Low Molecular Weight Probe Salicylaldehyde in the Detection of Nanomolar Peroxynitrite Fluxes

Unique Features of the Low Molecular Weight Probe Salicylaldehyde in the Detection of Nanomolar Peroxynitrite Fluxes

Early disruption of the actin cytoskeleton in cultured cerebellar granule neurons exposed to 3-morpholinosydnonimine-oxidative stress is linked to alterations of the cytosolic calcium concentration

Cytoskeleton damage is a frequent feature in neuronal cell death and one of the early events in oxidant-induced cell injury. This work addresses whether actin cytoskeleton reorganization is an early event of SIN-1-induced extracellular nitrosative/oxidative stress in cultured cerebellar granule neurons (CGN). The actin polymerization state, i.e. the relative levels of G-/F-actin, was quantitatively assessed by the ratio of the fluorescence intensities of microscopy images obtained from CGN double-labelled with Alexa594-DNase-I (for actin monomers) and Bodipy-FL-phallacidin (for actin filaments). Exposure of CGN to a flux of peroxynitrite as low as 0.5–1 μM/min during 30 min (achieved with 0.1 mM SIN-1) was found to promote alterations of the actin cytoskeleton dynamics as it increases the G-actin/F-actin ratio. Because L-type voltage-operated Ca 2+ channels (L-VOCC) are primary targets in CGN exposed to SIN-1, the possible role of Ca 2+ dynamics on the perturbation of the actin cytoskeleton was also assessed from the cytosolic Ca 2+ concentration response to the L-VOCC's agonist FPL-64176 and to the L-VOCC's blocker nifedipine. The results showed that SIN-1 induced changes in the actin polymerization state correlated with its ability to decrease Ca 2+ influx through L-VOCC. Combined analysis of cytosolic Ca 2+ concentration and G-actin/F-actin ratio alterations by SIN-1, cytochalasin D, latrunculin B and jasplakinolide support that disruption of the actin cytoskeleton is linked to cytosolic calcium concentration changes.

Nitration of Solvent-exposed Tyrosine 74 on Cytochrome c Triggers Heme Iron-Methionine 80 Bond Disruption: NUCLEAR MAGNETIC RESONANCE AND OPTICAL SPECTROSCOPY STUDIES

Cytochrome c, a mitochondrial electron transfer protein containing a hexacoordinated heme, is involved in other physiologically relevant events, such as the triggering of apoptosis, and the activation of a peroxidatic activity. The latter occurs secondary to interactions with cardiolipin and/or post-translational modifications, including tyrosine nitration by peroxynitrite and other nitric oxide-derived oxidants. The gain of peroxidatic activity in nitrated cytochrome c has been related to a heme site transition in the physiological pH region, which normally occurs at alkaline pH in the native protein. Herein, we report a spectroscopic characterization of two nitrated variants of horse heart cytochrome c by using optical spectroscopy studies and NMR. Highly pure nitrated cytochrome c species modified at solvent-exposed Tyr-74 or Tyr-97 were generated after treatment with a flux of peroxynitrite, separated, purified by preparative high pressure liquid chromatography, and characterized by mass spectrometry-based peptide mapping. It is shown that nitration of Tyr-74 elicits an early alkaline transition with a pKa = 7.2, resulting in the displacement of the sixth and axial iron ligand Met-80 and replacement by a weaker Lys ligand to yield an alternative low spin conformation. Based on the study of site-specific Tyr to Phe mutants in the four conserved Tyr residues, we also show that this transition is not due to deprotonation of nitro-Tyr-74, but instead we propose a destabilizing steric effect of the nitro group in the mobile Omega-loop of cytochrome c, which is transmitted to the iron center via the nearby Tyr-67. The key role of Tyr-67 in promoting the transition through interactions with Met-80 was further substantiated in the Y67F mutant. These results therefore provide new insights into how a remote post-translational modification in cytochrome c such as tyrosine nitration triggers profound structural changes in the heme ligation and microenvironment and impacts in protein function.

Chemical–Biological Fingerprinting: Probing the Properties of DNA Lesions Formed by Peroxynitrite

DNA-damaging agents usually produce a vast collection of lesions within the genome. Analysis of these lesions from the structural and biological viewpoints is often complicated by the reality that some of the lesions are chemically fragile, leading to an even larger set of secondary and tertiary products. In an effort to deconvolute complex DNA-damage spectra, a strategy is presented whereby an oligonucleotide containing a specific target for chemical reaction is allowed to react with a DNA-damaging agent. A large collection of HPLC-resolvable modified oligonucleotides is generated, and chromatographically distinct members of the set are then individually characterized using chemical, spectroscopic, biochemical, and genetic probes. The biological component of this "chemical-biological fingerprinting" tool is the use of polymerase bypass in vivo in cells having defined replication status and quantitative and qualitative patterns of lesion-directed mutagenesis, as key properties that complement physical analysis of modified DNA. This approach was applied to the complex product spectrum generated by peroxynitrite in the presence of CO2; peroxynitrite is a powerful oxidizing and nitrating agent generated as part of immune response. An oligonucleotide containing the primary oxidation product, 7,8-dihydro-8-oxoguanine (8-oxoGua), which is highly susceptible to further oxidation and/or nitration, was treated with peroxynitrite. Using mass spectrometry, coelution with authentic standards, sensitivity to piperidine, recognition and strand cleavage by the DNA repair enzyme MutM, and mutagenicity and genotoxicity in vivo, a matrix was created that defined the properties of the secondary DNA lesions formed when 3-morpholinosydnonimine (SIN-1) delivered a low, constant flux of peroxynitrite to an oligonucleotide containing 8-oxoGua. Two lesions were identified as the diastereomers of spiroiminodihydantoin (Sp), which had been observed previously in nucleoside-based experiments employing SIN-1. A third lesion, triazine, was tentatively identified. However, in addition to these lesions, a number of secondary lesions were generated that had chemical-biological fingerprints inconsistent with that of any known 8-oxoGua-derived lesion described to date. In vitro experiments showed that while some of these newly characterized secondary lesions were removed from DNA by MutM, others were in fact very poor substrates for this repair enzyme. These 8-oxoGua-derived lesions also showed varying degrees of sensitivity to piperidine. Furthermore, all of the secondary lesions observed in this work were potently mutagenic and genotoxic in Escherichia coli. Therefore, while 8-oxoGua itself is nontoxic and only mildly mutagenic in repair-proficient cells, peroxynitrite reveals the promutagenic potential and triggers the covert nature of this DNA lesion.

The Mycobacterial Thioredoxin Peroxidase Can Act as a One-cysteine Peroxiredoxin

Thioredoxin peroxidase (TPx) has been reported to dominate the defense against H(2)O(2), other hydroperoxides, and peroxynitrite at the expense of thioredoxin (Trx) B and C in Mycobacterium tuberculosis (Mt). By homology, the enzyme has been classified as an atypical 2-C-peroxiredoxin (Prx), with Cys(60) as the "peroxidatic" cysteine (C(P)) forming a complex catalytic center with Cys(93) as the "resolving" cysteine (C(R)). Site-directed mutagenesis confirms Cys(60) to be C(P) and Cys(80) to be catalytically irrelevant. Replacing Cys(93) with serine leads to fast inactivation as seen by conventional activity determination, which is associated with oxidation of Cys(60) to a sulfinic acid derivative. However, in comparative stopped-flow analysis, WT-MtTPx and MtTPx C93S reduce peroxynitrite and react with TrxB and -C similarly fast. Reduction of pre-oxidized WT-MtTPx and MtTPx C93S by MtTrxB is demonstrated by monitoring the redox-dependent tryptophan fluorescence of MtTrxB. Furthermore, MtTPx C93S remains stable for 10 min at a morpholinosydnonimine hydrochloride-generated low flux of peroxynitrite and excess MtTrxB in a dihydrorhodamine oxidation model. Liquid chromatography-tandem mass spectrometry analysis revealed disulfide bridges between Cys(60) and Cys(93) and between Cys(60) and Cys(80) in oxidized WT-MtTPx. Reaction of pre-oxidized WT-MtTPx and MtTPx C93S with MtTrxB C34S or MtTrxC C40S yielded dead-end intermediates in which the Trx mutants are preferentially linked via disulfide bonds to Cys(60) and never to Cys(93) of the TPx. It is concluded that neither Cys(80) nor Cys(93) is required for the catalytic cycle of the peroxidase. Instead, MtTPx can react as a 1-C-Prx with Cys(60) being the site of attack for both the oxidizing and the reducing substrate. The role of Cys(93) is likely to conserve the oxidation equivalents of the sulfenic acid state of C(P) as a disulfide bond to prevent overoxidation of Cys(60) under a restricted supply of reducing substrate.

Inhibition of Skeletal Muscle S1-Myosin ATPase by Peroxynitrite

Exposure of myosin subfragment 1 (S1) to 3-morpholinosydnonimine (SIN-1) produced a time-dependent inhibition of the F-actin-stimulated S1 Mg(2+)-ATPase activity, reaching 50% inhibition with 46.7 +/- 8.3 microM SIN-1 for 8.7 microM S1, that is, at a SIN-1/S1 molar ratio of approximately 5.5. The inhibition was due to the peroxynitrite produced by SIN-1 decomposition because (1) decomposed SIN-1 was found to have no effect on S1 ATPase activity, (2) addition of SIN-1 in the presence of superoxide dismutase and catalase fully prevented inhibition by SIN-1, and (3) micromolar pulses of chemically synthesized peroxynitrite produced inhibition of F-actin-stimulated S1 Mg(2+)-ATPase activity. In parallel, SIN-1 produced the inhibition of the nonphysiological Ca(2+)-dependent and K(+)/EDTA-dependent S1 ATPase activity of S1 and, therefore, suggested that the inhibition of F-actin-stimulated S1 Mg(2+)-ATPase activity is produced by the oxidation of highly reactive cysteines of S1 (Cys(707) and Cys(697)), located close to the catalytic center. This point was further confirmed by the titration of S1 cysteines with 5,5'-dithiobis(2-nitrobenzoic acid) and by the parallel decrease of Cys(707) labeling by 5-(iodoacetamido)fluorescein, and it was reinforced by the fact that other common protein modifications produced by peroxynitrite, for example, protein carbonyl and nitrotyrosine formation, were barely detected at the concentrations of SIN-1 that produced more than 50% inhibition of the F-actin-stimulated S1 Mg(2+)-ATPase activity. Differential scanning calorimetry of S1 (untreated and treated with different SIN-1 concentrations) pointed out that SIN-1, at concentrations that generate micromolar peroxynitrite fluxes, impaired the ability of ADP.V(1) to induce the intermediate catalytic transition state and also produced the partial unfolding of S1 that leads to an enhanced susceptibility of S1 to trypsin digestion, which can be fully protected by 2 mM GSH.

Peroxynitrite induces F-actin depolymerization and blockade of myosin ATPase stimulation

Treatment of F-actin with the peroxynitrite-releasing agent 3-morpholinosydnonimine (SIN-1) produced a dose-dependent F-actin depolymerization. This is due to released peroxynitrite because it is not produced by ‘decomposed SIN-1’, and it is prevented by superoxide dismutase concentrations efficiently preventing peroxynitrite formation. F-actin depolymerization has been found to be very sensitive to peroxynitrite, as exposure to fluxes as low as 50–100nM peroxynitrite leads to nearly 50% depolymerization in about 1h. G-actin polymerization is also impaired by peroxynitrite although with nearly 2-fold lower sensitivity. Exposure of F-actin to submicromolar fluxes of peroxynitrite produced cysteine oxidation and also a blockade of the ability of actin to stimulate myosin ATPase activity. Our results suggest that an imbalance of the F-actin/G-actin equilibrium can account for the observed structural and functional impairment of myofibrils under the peroxynitrite-mediated oxidative stress reported for some pathophysiological conditions.

Peroxynitrite-induced oxidation and nitration products of guanine and 8-oxoguanine: Structures and mechanisms of product formation

Peroxynitrite induces DNA base damage predominantly at guanine (G) and 8-oxoguanine (8-oxoG) nucleobases via oxidation reactions. Nitration products are also observed, consistent with the generation of radical intermediates that can recombine with the (.)NO(2) formed during peroxynitrite degradation. The neutral G radical, G(.), reacts with (.)NO(2) to yield 8-nitroguanine (8-nitroG) and 5-nitro-4-guanidinohydantoin (NI), while for 8-oxoG we have proposed a reactive guanidinylidene radical intermediate. The products generated during peroxynitrite-mediated 8-oxoG oxidation depend on oxidant flux, with dehydroguanidinohydantoin (DGh), 2,4,6-trioxo-[1,3,5]triazinane-1-carboxamidine (CAC) and NO(2)-DGh predominating at high fluxes and spiroiminodihydantoin (Sp), guanidinohydantoin (Gh) and 4-hydroxy-2,5-dioxo-imidazolidine-4-carboxylic acid (HICA) predominating at low fluxes. Both product sets are observed at intermediate fluxes. It is therefore important in model systems to ensure that the relative concentrations are well controlled to minimize competing reactions that may not be relevant in vivo. Increasingly sophisticated systems for modeling peroxynitrite production in vivo are being developed and these should help with predicting the products most likely to be formed in vivo. Together with the emerging information on the genotoxic and mutational characteristics of the individual oxidation products, it may be found that the extent of tissue damage, mutational spectra and, hence, cancer risk may change as a function of peroxynitrite fluxes as different product combinations predominate.

Interaction with phospholipids modulates α-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.