Nitrated and Oxidized Products of a Single Tryptophan Residue in Human Cu,Zn-Superoxide Dismutase Treated with Either Peroxynitrite-Carbon Dioxide or Myeloperoxidase-Hydrogen Peroxide-Nitrite

Age-related nitration/dysfunction of myogenic stem cell activator HGF

Mechanical perturbation triggers activation of resident myogenic stem cells to enter the cell cycle through a cascade of events including hepatocyte growth factor (HGF) release from its extracellular tethering and the subsequent presentation to signaling-receptor c-met. Here, we show that with aging, extracellular HGF undergoes tyrosine-residue (Y) nitration and loses c-met binding, thereby disturbing muscle homeostasis. Biochemical studies demonstrated that nitration/dysfunction is specific to HGF among other major growth factors and is characterized by its locations at Y198 and Y250 in c-met-binding domains. Direct-immunofluorescence microscopy of lower hind limb muscles from three age groups of rat, provided direct in vivo evidence for age-related increases in nitration of ECM-bound HGF, preferentially stained for anti-nitrated Y198 and Y250-HGF mAbs (raised in-house) in fast IIa and IIx myofibers. Overall, findings highlight inhibitory impacts of HGF nitration on myogenic stem cell dynamics, pioneering a cogent discussion for better understanding age-related muscle atrophy and impaired regeneration with fibrosis (including sarcopenia and frailty).

Unveiling the human nitroproteome: Protein tyrosine nitration in cell signaling and cancer

Covalent amino acid modification significantly expands protein functional capability in regulating biological processes. Tyrosine residues can undergo phosphorylation, sulfation, adenylation, halogenation, and nitration. These posttranslational modifications (PTMs) result from the actions of specific enzymes: tyrosine kinases, tyrosyl-protein sulfotransferase(s), adenylate transferase(s), oxidoreductases, peroxidases, and metal-heme containing proteins. Whereas phosphorylation, sulfation, and adenylation modify the hydroxyl group of tyrosine, tyrosine halogenation and nitration target the adjacent carbon residues. Because aberrant tyrosine nitration has been associated with human disorders and with animal models of disease, we have created an updated and curated database of 908 human nitrated proteins. We have also analyzed this new resource to provide insight into the role of tyrosine nitration in cancer biology, an area that has not previously been considered in detail. Unexpectedly, we have found that 879 of the 1971 known sites of tyrosine nitration are also sites of phosphorylation suggesting an extensive role for nitration in cell signaling. Overall, the review offers several forward-looking opportunities for future research and new perspectives for understanding the role of tyrosine nitration in cancer biology.

Impact of Reactive Species on Amino Acids-Biological Relevance in Proteins and Induced Pathologies

This review examines the impact of reactive species RS (of oxygen ROS, nitrogen RNS and halogens RHS) on various amino acids, analyzed from a reactive point of view of how during these reactions, the molecules are hydroxylated, nitrated, or halogenated such that they can lose their capacity to form part of the proteins or peptides, and can lose their function. The reactions of the RS with several amino acids are described, and an attempt was made to review and explain the chemical mechanisms of the formation of the hydroxylated, nitrated, and halogenated derivatives. One aim of this work is to provide a theoretical analysis of the amino acids and derivatives compounds in the possible positions. Tyrosine, methionine, cysteine, and tryptophan can react with the harmful peroxynitrite or ^•OH and ^•NO₂ radicals and glycine, serine, alanine, valine, arginine, lysine, tyrosine, histidine, cysteine, methionine, cystine, tryptophan, glutamine and asparagine can react with hypochlorous acid HOCl. These theoretical results may help to explain the loss of function of proteins subjected to these three types of reactive stresses. We hope that this work can help to assess the potential damage that reactive species can cause to free amino acids or the corresponding residues when they are part of peptides and proteins.

Dynamics of nitration during dark-induced leaf senescence in Arabidopsis reveals proteins modified by tryptophan nitration

Nitric oxide (NO) is a critical molecule that links plant development with stress responses. Herein, new insights into the role of NO metabolism during leaf senescence in Arabidopsis are presented. A gradual decrease in NO emission accompanied dark-induced leaf senescence (DILS), and a transient wave of peroxynitrite (ONOO-) formation was detected by day 3 of DILS. The boosted ONOO- did not promote tryptophan (Trp) nitration, while the pool of 6-nitroTrp-containing proteins was depleted as senescence progressed. Immunoprecipitation combined with mass spectrometry was used to identify 63 and 4 characteristic 6-nitroTrp-containing proteins in control and individually darkened leaves, respectively. The potential in vivo targets of Trp nitration were mainly related to protein biosynthesis and carbohydrate metabolism. In contrast, nitration of tyrosine-containing proteins was intensified 2-fold on day 3 of DILS. Also, nitrative modification of RNA and DNA increased significantly on days 3 and 7 of DILS, respectively. Taken together, ONOO- can be considered a novel pro-senescence regulator that fine-tunes the redox environment for selective bio-target nitration. Thus, DILS-triggered nitrative changes at RNA and protein levels promote developmental shifts during the plant's lifespan and temporal adjustment in plant metabolism under suboptimal environmental conditions.

A pilot study on nitration/dysfunction of NK1 segment of myogenic stem cell activator HGF

Protein tyrosine residue (Y) nitration, a post-translational chemical-modification mode, has been associated with changes in protein activity and function; hence the accumulation of specific nitrated proteins in tissues may be used to monitor the onset and progression of pathological disorders. To verify the possible impact of nitration on postnatal muscle growth and regeneration, a pilot study was designed to examine the nitration/dysfunction of hepatocyte growth factor (HGF), a key ligand that is released from the extracellular tethering and activates myogenic stem satellite cells to enter the cell cycle upon muscle stretch and injury. Exposure of recombinant HGF (a hetero-dimer of α- and β-chains) to peroxynitrite induces Y nitration in HGF α-chain under physiological conditions. Physiological significance of this finding was emphasized by Western blotting that showed the NK1 segment of HGF (including a K1 domain critical for signaling-receptor c-met binding) undergoes nitration with a primary target of Y198. Peroxynitrite treatment abolished HGF-agonistic activity of the NK1 segment, as revealed by in vitro c-met binding and bromodeoxyuridine-incorporation assays. Importantly, direct-immunofluorescence microscopy of rat lower hind-limb muscles from two aged-groups (2-month-old “young” and 12-month-old “retired/adult”) provided in vivo evidence for age-related nitration of extracellular HGF (Y198). Overall, findings provide the insight that HGF/NK1 nitration/dysfunction perturbs myogenic stem cell dynamics and homeostasis; hence NK1 nitration may stimulate progression of muscular disorders and diseases including sarcopenia.

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NK1 segment of hepatocyte growth factor (HGF) undergoes tyrosine (Y) nitration.

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Y198 was identified as a primary target for nitration of NK1.

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NK1 nitration may abolish HGF-agonistic activity that activates myogenic stem cells.

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Nitration of extracellular HGF-Y198 was detected in vivo at early aging-phase of rat.

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Findings may provide a possible strategy to combat progressive muscle-atrophy.

Open Search-Based Proteomics Reveals Widespread Tryptophan Modifications Associated with Hypoxia in Lung Cancer

The tryptophan residue has a large hydrophobic surface that plays a unique role in the folded protein conformation and functions. Tryptophan modifications are presumably to be readily detected in proteins due to the vulnerability of the indole structure to electrophilic attacks. In this study, we report a systematic identification of sequence variations at tryptophan, termed tryptophan variants, from the proteome of patients with nonsmall cell lung cancer (NSCLC). Using shotgun proteomics and a modified open search algorithm, 25 tryptophan variants on 2481 sites in over 858 proteins were identified. Among these, 6 tryptophan variants are previously identified, 15 are newly annotated, and 4 are still unknown, most of which are involved in the cascade of oxidation in the blood microparticle. Remarkably, Trp313 of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was up-oxidized whereas Trp16 and Trp38 of hemoglobin (HBB) were down-oxidized in NCSLC tissues. The results were further supported by an independent cohort of 103 lung adenocarcinoma samples, reflecting a negative feedback and potential detoxification mechanism against tumor glycolysis and hypoxia. Overall, the study reports a quick approach to explore tryptophan variants at the proteomic scale. Our findings highlight the predominant role of tryptophan oxidation in regulating the redox balance of cancer cells and its potential role as prognostic biomarker for patients with NSCLC.

Electrochemistry for the Chemoselective Modification of Peptides and Proteins

Although electrochemical strategies for small-molecule synthesis are flourishing, this technology has yet to be fully exploited for the mild and chemoselective modification of peptides and proteins. With the growing number of diverse peptide natural products being identified and the emergence of modified proteins as therapeutic and diagnostic agents, methods for electrochemical modification stand as alluring prospects for harnessing the reactivity of polypeptides to build molecular complexity. As a mild and inherently tunable reaction platform, electrochemistry is arguably well-suited to overcome the chemo- and regioselectivity issues which limit existing bioconjugation strategies. This Perspective will showcase recently developed electrochemical approaches to peptide and protein modification. The article also highlights the wealth of untapped opportunities for the production of homogeneously modified biomolecules, with an eye toward realizing the enormous potential of electrochemistry for chemoselective bioconjugation chemistry.

Potential roles of neuronal nitric oxide synthase and the PTEN-induced kinase 1 (PINK1)/Parkin pathway for mitochondrial protein degradation in disuse-induced soleus muscle atrophy in adult rats

Excessive nitric oxide (NO) production and mitochondrial dysfunction can activate protein degradation in disuse-induced skeletal muscle atrophy. However, the increase in NO production in atrophied muscles remains controversial. In addition, although several studies have investigated the PTEN-induced kinase 1 (PINK1)/Parkin pathway, a mitophagy pathway, in atrophied muscle, the involvement of this pathway in soleus muscle atrophy is unclear. In this study, we investigated the involvement of neuronal nitric oxide synthase (nNOS) and the PINK1/Parkin pathway in soleus muscle atrophy induced by 14 days of hindlimb unloading (HU) in adult rats. HU lowered the weight of the soleus muscles. nNOS expression showed an increase in atrophied soleus muscles. Although HU increased malondialdehyde as oxidative modification of the protein, it decreased 6-nitrotryptophan, a marker of protein nitration. Additionally, the nitrosocysteine content and S-nitrosylated Parkin were not altered, suggesting the absence of excessive nitrosative stress after HU. The expression of PINK1 and Parkin was also unchanged, whereas the expression of heat shock protein 70 (HSP70), which is required for Parkin activity, was reduced in atrophied soleus muscles. Moreover, we observed accumulation and reduced ubiquitination of high molecular weight mitofusin 2, which is a target of Parkin, in atrophied soleus muscles. These results indicate that excessive NO is not produced in atrophied soleus muscles despite nNOS accumulation, suggesting that excessive NO dose not mediate in soleus muscle atrophy at least after 14 days of HU. Furthermore, the PINK1/Parkin pathway may not play a role in mitophagy at this time point. In contrast, the activity of Parkin may be downregulated because of reduced HSP70 expression, which may contribute to attenuated degradation of target proteins in the atrophied soleus muscles after 14 days of HU. The present study provides new insights into the roles of nNOS and a protein degradation pathway in soleus muscle atrophy.

Chemical modifications of tryptophan residues in peptides and proteins

Chemical protein modifications facilitate the investigation of natural posttranslational protein modifications and allow the design of proteins with new functions. Proteins can be modified at a late stage on amino acid side chains by chemical methods. The indole moiety of tryptophan residues is an emerging target of such chemical modification strategies because of its unique reactivity and low abundance. This review provides an overview of the recently developed methods of tryptophan modification at the peptide and protein levels.

Mechanisms of SOD1 regulation by post-translational modifications

SOD1 is commonly known for its ROS scavenging activity, but recent work has uncovered additional roles in modulating metabolism, maintaining redox balance, and regulating transcription. This new paradigm of expanded SOD1 function raises questions regarding the regulation of SOD1 and the cellular partitioning of its biological roles. Despite decades of research on SOD1, much of which focuses on its pathogenic role in amyotrophic lateral sclerosis, relatively little is known about its regulation by post-translational modifications (PTMs). However, over the last decade, advancements in mass spectrometry have led to a boom in PTM discovery across the proteome, which has also revealed new mechanisms of SOD1 regulation by PTMs and an array of SOD1 PTMs with high likelihood of biological function. In this review, we address emerging mechanisms of SOD1 regulation by post-translational modifications, many of which begin to shed light on how the various functions of SOD1 are regulated within the cell.

Automatic assignment of metal-containing peptides in proteomic LC-MS and MS/MS data sets

Transition metal-containing proteins and enzymes are critical for the maintenance of cellular function and metal-based (metallo)drugs are commonly used for the treatment of many diseases, such as cancer. Detection and characterisation of metallodrug targets is crucial for improving drug-design and therapeutic efficacy. Due to the unique isotopic ratios of many metal species, and the complexity of proteomic samples, standard MS data analysis of these species is unsuitable for accurate assignment. Herein a new method for differentiating metal-containing species within complex LCMS data is presented based upon the Smart Numerical Annotation Procedure (SNAP). SNAP-LC accounts for the change in isotopic envelopes for analytes containing non-standard species, such as metals, and will accurately identify, record, and display the particular spectra within extended LCMS runs that contain target species, and produce accurate lists of matched peaks, greatly assisting the identification and assignment of modified species and tailored to the metals of interest. Analysis of metallated species obtained from tryptic digests of common blood proteins after reactions with three candidate metallodrugs is presented as proof-of-concept examples and demonstrates the effectiveness of SNAP-LC for the fast and accurate elucidation of metallodrug targets.

Oxidative Stress Alters the Morphology and Toxicity of Aortic Medial Amyloid

The aggregation and fibril deposition of amyloid proteins have been implicated in a range of neurodegenerative and vascular diseases, and yet the underlying molecular mechanisms are poorly understood. Here, we use a combination of cell-based assays, biophysical analysis, and atomic force microscopy to investigate the potential involvement of oxidative stress in aortic medial amyloid (AMA) pathogenesis and deposition. We show that medin, the main constituent of AMA, can induce an environment rich in oxidative species, increasing superoxide and reducing bioavailable nitric oxide in human cells. We investigate the role that this oxidative environment may play in altering the aggregation process of medin and identify potential posttranslational modification sites where site-specific modification and interaction can be unambiguously demonstrated. In an oxidizing environment, medin is nitrated at tyrosine and tryptophan residues, with resultant effects on morphology that lead to longer fibrils with increased toxicity. This provides further motivation to investigate the role of oxidative stress in AMA pathogenicity.

Vestibular end organ injury induced by middle ear treatment with ferric chloride in rats

Sensorineural hearing loss, ataxia, pyramidal signs, and vestibular deficits characterize superficial siderosis of the central nervous system. This study investigated changes in vestibular function, free radical formation, and phosphorylated cJun expression in the vestibular end organs after middle ear treatment with a ferric chloride (FeCl3) solution. A single injection of 70% FeCl3 solution into the unilateral middle ear cavity caused static vestibular symptoms, such as spontaneous nystagmus and head tilt. Asymmetric expression of c-Fos protein was observed in the bilateral vestibular nuclei and prepositus hypoglossal nuclei within 6 h after injection. Histopathologic examinations revealed partial hair cell loss, degeneration of the supporting stroma, and terminal deoxynucleotidyl transferase dUTP nick end labeling-positive cells in the neuroepithelial layer of the crista ampullaris in FeCl3-treated animals. 5-(And-6)-chloromethyl-2′,7′-dichlorodihydrofluorescein diacetate, acetyl ester and diaminofluorescein–2 diacetate fluorescence and immunoreactivity for nitrotyrosine increased markedly in the sensory neuroepithelial layer and nerve bundles of the crista ampullaris after 2 h. Strong immunoreactivity for phospho-cJun and cJun was observed in the type I hair cells of the crista ampullaris 120 h after injection. Thus, a single short-term treatment with a high concentration of FeCl3 in the unilateral middle ear cavity can induce activation of intracellular signals for cJun protein and oxidative stress through the formation of reactive oxygen species and nitric oxide in vestibular sensory receptors, resulting in vestibular dysfunction. These results suggest that activation of intracellular signals for cJun protein and oxidative stress may be a key component of the pathogenesis of vestibular deficits in patients with superficial siderosis.

ANSID: A Solid-Phase Proteomic Approach for Identification and Relative Quantification of Aromatic Nitration Sites

Nitration of tyrosine and other aromatic amino acid residues in proteins occurs in the setting of inflammatory, neurodegenerative, and cardiovascular diseases—importantly, this modification has been implicated in the pathogenesis of diverse diseases and the physiological process of aging. To understand the biological consequences of aromatic nitration in both health and disease, it is critical to molecularly identify the proteins that undergo nitration, specify their cognate modification sites and quantify their extent of nitration. To date, unbiased identification of nitrated proteins has often involved painstaking 2D-gel electrophoresis followed by Western Blotting with an anti-nitrotyrosine antibody for detection. Apart from being relatively slow and laborious, this method suffers from limited coverage, the potential for false-positive identifications, and failure to reveal specific amino acid modification sites. To overcome these shortcomings, we have developed a solid-phase, chemical-capture approach for unbiased and high-throughput discovery of nitrotyrosine and nitrotryptophan sites in proteins. Utilizing this method, we have successfully identified several endogenously nitrated proteins in rat brain and a total of 244 nitrated peptides from 145 proteins following in vitro exposure of rat brain homogenates to the nitrating agent peroxynitrite (1 mM). As expected, Tyr residues constituted the great majority of peroxynitrite-mediated protein nitration sites; however, we were surprised to discover several brain proteins that contain nitrated Trp residues. By incorporating a stable-isotope labeling step, this new Aromatic Nitration Site IDentification (ANSID) method was also adapted for relative quantification of nitration site abundances in proteins. Application of the ANSID method offers great potential to advance our understanding of the role of protein nitration in disease pathogenesis and normal physiology.

Peroxynitrous acid induces structural and functional modifications to basement membranes and its key component, laminin

Basement membranes (BM) are specialized extracellular matrices underlying endothelial cells in the artery wall. Laminin, the most abundant BM glycoprotein, is a structural and biologically active component. Peroxynitrous acid (ONOOH), a potent oxidizing and nitrating agent, is formed in vivo at sites of inflammation from superoxide and nitric oxide radicals. Considerable data supports ONOOH formation in human atherosclerotic lesions, and an involvement of this oxidant in atherosclerosis development and lesion rupture. These effects may be mediated, at least in part, via extracellular matrix damage. In this study we demonstrate co-localization of 3-nitrotyrosine (a product of tyrosine damage by ONOOH) and laminin in human atherosclerotic lesions. ONOOH-induced damage to BM was characterized for isolated murine BM, and purified murine laminin-111. Exposure of laminin-111 to ONOOH resulted in dose-dependent loss of protein tyrosine and tryptophan residues, and formation of 3-nitrotyrosine, 6-nitrotryptophan and the cross-linked material di-tyrosine, as detected by amino acid analysis and Western blotting. These changes were accompanied by protein aggregation and fragmentation as detected by SDS-PAGE. Endothelial cell adhesion to isolated laminin-111 exposed to 10 μM or higher levels of ONOOH was significantly decreased (~25%) compared to untreated controls. These data indicate that laminin is oxidized by equimolar or greater concentrations of ONOOH, with this resulting in structural and functional changes. These modifications, and resulting compromised cell-matrix interactions, may contribute to endothelial cell dysfunction, a weakening of the structure of atherosclerotic lesions, and an increased propensity to rupture.

Reactive nitrogen species in cellular signaling

The transduction of cellular signals occurs through the modification of target molecules. Most of these modifications are transitory, thus the signal transduction pathways can be tightly regulated. Reactive nitrogen species are a group of compounds with different properties and reactivity. Some reactive nitrogen species are highly reactive and their interaction with macromolecules can lead to permanent modifications, which suggested they were lacking the specificity needed to participate in cell signaling events. However, the perception of reactive nitrogen species as oxidizers of macromolecules leading to general oxidative damage has recently evolved. The concept of redox signaling is now well established for a number of reactive oxygen and nitrogen species. In this context, the post-translational modifications introduced by reactive nitrogen species can be very specific and are active participants in signal transduction pathways. This review addresses the role of these oxidative modifications in the regulation of cell signaling events.

Protein oxidation: identification and utilisation of molecular markers to differentiate singlet oxygen and hydroxyl radical-mediated oxidative pathways

The effect of reactive oxidation species (ROS) on tryptophan or tyrosine was investigated by qualitatively determining the major detectable oxidation products generated by hydroxyl radicals, produced by the Fenton process, or singlet oxygen, generated by exposure to green light in the presence of Rose Bengal, on these photosensitive amino acids in synthetic pentapeptides. Based on mass spectrometric analysis it would appear that the hydroxyl radical favours a pathway leading to the formation of tryptophandione-based products from tryptophan. In contrast singlet oxygen attack appears to favour the formation of kynurenine-type products from tryptophan. Specific oxidative products observed proteomically are therefore potentially able to discriminate between predominant ROS-mediated pathways. To validate these findings, a keratin-enriched extract was exposed to UVB light under aqueous conditions. The observation of the conversion of tryptophan to hydroxytryptophan in marker peptides, and the absence of singlet-oxygen specific modifications, suggested that under these conditions oxidative degradation occurred primarily via hydroxyl radical attack. These observations provide the first direct proteomic evidence of the dominant photodegradation pathways in wet wool.

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.

Effect of chronic treatment with conventional and organic purple grape juices (Vitis labrusca) on rats fed with high-fat diet

Serra Gaucha is described as the most important wine region of Brazil. Regarding cultivars widespread in the Serra Gaucha, about 90 % of the area is occupied by vines of Vitis labrusca that is the most important specie used in grape juice production. The objective of this study was to investigate the antioxidant and neuroprotective effect of chronic intake of purple grape juice (organic and conventional) from Bordo variety (V. labrusca) on oxidative stress in different brain regions of rats supplemented with high-fat diet (HFD) for 3 months. A total of 40 male rats were randomly divided into 4 groups. Group 1 received a standard diet and water, group 2 HFD and water, group 3 HFD and conventional grape juice (CGJ), and group 4 HFD and organic grape juice (OGJ). All groups had free access to food and drink and after 3 months of treatment the rats were euthanized by decapitation and the cerebral cortex, hippocampus and cerebellum isolated and homogenized on ice for oxidative stress analysis. We observed that the consumption of calories in HFD and control groups, were higher than the groups supplemented with HFD and grape juices and that HFD diet group gain more weight than the other animals. Our results also demonstrated that HDF enhanced lipid peroxidation (TBARS) and protein damage (carbonyl) in cerebral cortex and hippocampus, reduced the non-enzymatic antioxidants defenses (sulfhydryl) in cerebral cortex and cerebellum, reduced catalase and superoxide dismutase activities in all brain tissues and enhanced nitric oxide production in all cerebral tissues. CGJ and OGJ were able to ameliorate these oxidative alterations, being OGJ more effective in this protection. Therefore, grape juices could be useful in the treatment of some neurodegenerative diseases associated with oxidative damage.

Proteomic analysis of endogenous nitrotryptophan-containing proteins in rat hippocampus and cerebellum

Nitration of tryptophan residues is a novel post-translational modification. In the present study, we examined whether NO2Trp (nitrotryptophan)-containing proteins are produced in the hippocampus and cerebellum of the adult rat under physiological conditions in vivo. Using Western blot analysis with anti-6-NO2Trp-specific antibody, we found many similar immunoreactive spots in the protein extracts from both regions. These spots were subsequently subjected to trypsin digestion and LC-ESI-MS/MS (LC-electrospray ionization-tandem MS) analysis. We identified several cytoskeletal proteins and glycolytic enzymes as NO2Trp-containing proteins and determined the position of nitrated tryptophan residues with significant ion score levels (P<0.05) in several proteins in both regions. We also observed that the total amount of NO2Trp-containing proteins in the cerebellum was significantly greater than that in the hippocampus (P<0.05). Moreover, IP (immunoprecipitation) assays using anti-aldolase C antibody showed that the relative intensity of immunostaining for NO2Trp over aldolase C was much higher in cerebellum than in hippocampus. The amounts of nNOS (neuronal nitric oxide synthase) and eNOS (endothelial nitric oxide synthase) were much greater in cerebellum than in hippocampus. This is the first evidence of several specific sites of nitrated tryptophan in proteins under physiological conditions in vivo.

Disulfide bond as a switch for copper-zinc superoxide dismutase activity in asthma

AIM

Loss of superoxide dismutase (SOD) activity is a defining biochemical feature of asthma. However, mechanisms for the reduced activity are unknown. We hypothesized that loss of asthmatic SOD activity is due to greater susceptibility to oxidative inactivation.

RESULT

Activity assays of blood samples from asthmatics and healthy controls revealed impaired dismutase activity of copper-zinc SOD (CuZnSOD) in asthma. CuZnSOD purified from erythrocytes or airway epithelial cells from asthmatic was highly susceptible to oxidative inactivation. Proteomic analyses identified that inactivation was related to oxidation of cysteine 146 (C146), which is usually disulfide bonded to C57. The susceptibility of cysteines pointed to an alteration in protein structure, which is likely related to the loss of disulfide bond. We speculated that a shift to greater intracellular reducing potential might account for the change. Strikingly, measures of reduced and oxidized glutathione confirmed greater reducing intracellular state in asthma, compared with controls. Similarly, greater free thiol in CuZnSOD was confirmed by ~2-fold greater N-ethylmaleimide binding to C146 in asthma as compared with controls.

INNOVATION

Greater reducing potential under a chronic inflammatory state of asthma, thus, leads to susceptibility of CuZnSOD to oxidative inactivation due to cleavage of C57-C146 disulfide bond and exposure of usually unavailable cysteines.

CONCLUSION

Vulnerability of CuZnSOD influenced by redox likely amplifies injury and inflammation during acute asthma attacks when reactive oxygen species are explosively generated. Overall, this study identifies a new paradigm for understanding the chemical basis of inflammation, in which redox regulation of thiol availability dictates protein susceptibility to environmental and endogenously generated reactive species.

Synthetic pyrethroid increases lipid and protein oxidation and induces glutathione depletion in the cerebellum of adult rats: ameliorative effect of vitamin C

The wide use and wide-spectrum toxicity of synthetic pyrethroid (SP) insecticides make them an emerging ecotoxicological concern. The objective of the current study was aimed to investigate the involvement of oxidative stress in lambda-cyhalothrin (LTC)-induced cerebellum damages in adult rats and to evaluate the possible protective effect of vitamin C (vit C) as antioxidant. Exposure of rats to LTC during 3 weeks caused a significant (p < 0.05) increase in the levels of lipid peroxidation (LPO), nitric oxide (NO) and protein carbonyls (PCO) along with a significant (p < 0.05) decrease in the levels of reduced glutathione (GSH) and the activities of acetylcholinesterase, superoxide dismutase, catalase, glutathione peroxidase and gluthione-S-transferase (p < 0.05) when compared with the control group. The oral administration of vit C (200 mg/kg per d) to LTC-treated rats significantly (p < 0.05) diminished the levels of LPO, NO and PCO and significantly (p < 0.05) increased the activities of GSH and antioxidant enzymes. Our results showed that the administration of vit C could ameliorate some of the oxidative damage in the cerebellum induced by SPs exposure, suggesting that the ascorbic acid could exhibit a potential antioxidant activity against neurotoxicity induced by pesticides exposure.

Age-related modification of antioxidant enzyme activities in relation to cardiovascular risk factors

BACKGROUND

Since oxidative stress might cause and promote cardiovascular risk factors such as oxidized low-density lipoproteins (oxLDL), apolipoprotein(a) [apo(a)], asymmetric dimethylarginine (ADMA) and fetuin A, we investigated antioxidant enzyme activities in relation to the vascular redox balance and these risk factors in elderly people.

MATERIALS AND METHODS

For this observational study, a total of 102 subjects were recruited and divided into three groups: A (70-74 years/n = 48), B (75-79 years/n = 35) and C (≥ 80 years/n = 19). Activities of the erythrocyte antioxidant enzymes superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (CAT) were determined photometrically oxLDL, apo(a), ADMA and fetuin A by ELISA. Plasma concentrations of the lipid peroxidation products malondialdehyde (MDA) and conjugated dienes (CD) were analysed with HPLC.

RESULTS

There were no significant age-associated alterations in apo(a) levels, but there was a significant age-related decrease in activities of SOD (A>C, B>C: P < 0·01), CAT (A>C: P < 0·05) and GSH-Px (A>C: P < 0·05), accompanied by a significant increase in oxLDL (A<C: P < 0·001; B<C: P < 0·05), ADMA (A<B: P < 0·05; A<C: P < 0·001), MDA (A<C, B<C: P < 0·01) and CD (A<C, B<C: P < 0·01), and a significant decrease in fetuin A (A>C: P < 0·01; B>C: P < 0·05). Consequently, all groups showed significant negative age-associated correlations between CAT and MDA (A, B, C: P < 0·05), GSH-Px and CD (A, C: P < 0·01; B: P < 0·05), SOD and oxLDL (A, B: P < 0·05; C: P < 0·01), and fetuin A and MDA (A: P < 0·01; B, C: P < 0·05), and a significant positive correlation between oxLDL and ADMA (A, B: P < 0·05; C: P < 0·01).

CONCLUSIONS

This study indicates a significant age-related decrease in antioxidant enzyme activities accompanied by significantly increased systemic oxidative stress, which promotes the cardiovascular risk factors oxLDL, ADMA and fetuin A in elderly people.

Protein nitrotryptophan: formation, significance and identification

Reactive nitrogen species are formed during a variety of disease states and have been shown to modify several amino acids on proteins. To date, the majority of research in this area has focused on the nitration of tyrosine residues to form 3-nitrotyrosine. However, emerging evidence suggests that another modification, nitration of tryptophan residues, to form nitrotryptophan (NO(2)-Trp), may also play a significant role in the biology of nitrosative stress. This review takes an in-depth look at NO(2)-Trp, presenting the current research about its formation, prevalence and biological significance, as well as the methods used to identify NO(2)-Trp-modified proteins. Although more research is needed to understand the full biological role of NO(2)-Trp, the data presented herein suggest a contribution to nitrosative stress-induced cell dysregulation and perhaps even in physiological cell processes.

Nitration of tryptophan in ribosomal proteins is a novel post-translational modification of differentiated and naïve PC12 cells

Neuron growth factor (NGF) signaling in PC12 cell, which is derived from pheochromocytoma of rat adrenal medulla, induces expression of neuronal nitric oxide synthase (nNOS) and nitric oxide (NO) production. Subsequently, NO causes differentiation of PC12 cell to neuronal cell with morphological changes, such as neurite extension. In this study, we showed that 6-nitrotryptophan-containing proteins were produced in PC12 cell (naïve PC12 cell) and/or NGF-induced PC12 cell (differentiated PC12 cell). Western blot analysis of the protein extract of naïve PC12 cell and differentiated PC12 cell using anti 6-nitrotryptophan antibody showed several immunoreactive bands, which were subsequently subjected to trypsin digestion and LC-ESI-MS-MS analysis. The peptides from five ribosomal proteins, namely, 60S ribosomal protein L7 (Trp154), 60S acidic ribosomal protein P1 (Trp43), 40S ribosomal protein S2 (Trp60), 40S ribosomal protein S6 (Trp45), and 40S ribosomal protein S19 (Trp52), were identified as nitrotryptophan residue-containing proteins with significant ion score levels (p<0.05). Among these, tryptophan nitration was observed only in differentiated PC12 cell for S19 protein, and only in naïve PC12 cell for L7 protein. Tryptophan nitration of the other ribosomal proteins P1, S2, and S6 was observed in both naive and differentiated PC12 cells. The positive signal of nitrotryptophan-containing proteins in the Western blotting around 16 kDa (Band 1), which includes 40S ribosomal protein S19, was suppressed by treatment with NOS inhibitor, L-NAME. The tryptophan nitration of 40S ribosomal protein was not observed by LC-ESI-MS-MS analysis of this sample. This is the first study to identify several specific sites of nitrated tryptophan on proteins not only in viable culture cells but also in a physiological process: cell differentiation.

Mass spectrometric identification of tryptophan nitration sites on proteins in peroxynitrite-treated lysates from PC12 cells

One of the important sites of peroxynitrite action that affects cellular function is known to be nitration of tyrosine residues. However, tryptophan residues could be another target of peroxynitrite-dependent modification of protein function, as we have shown previously using a model protein (F. Yamakura et al., J. Biochem. 138:57-69; 2005). Here, we report the identification of several proteins that allowed us to determine the position of nitrotryptophan in their amino acid sequences in a more complex system. We modified lysates from PC12 cells with and without nerve growth factor (NGF) by treatment with peroxynitrite (0.98 or 4.9 mM). Western blot analyses using anti-6-nitrotryptophan antibody showed several immunoreactive bands and spots, which were subsequently subjected to trypsin digestion and LC-ESI-MS-MS analysis. We identified several tryptic peptides including nitrotryptophan residues, which were derived from L-lactate dehydrogenase A, malate dehydrogenase 1, M2 pyruvate kinase, and heat-shock protein 90 α, in peroxynitrite-treated lysates from PC12 cells, and l-lactate dehydrogenase A, malate dehydrogenase 1, transaldorase, and lactoylglutathione lyase, in peroxynitrite-treated lysates from NGF/PC12 cells. The molar ratio of 3-nitrotyrosine to 6-nitrotryptophan in protease-digested PC12 cell lysates treated with peroxynitrite was determined to be 5.8 to 1 by using an HPLC-CoulArray system. This is the first report to identify several specific sites of nitrated tryptophan on proteins in a complex system treated with peroxynitrite and to compare the susceptibility of nitration between tryptophan and tyrosine residues of the proteins.

Peroxynitrite mediates active site tyrosine nitration in manganese superoxide dismutase. Evidence of a role for the carbonate radical anion

Protein tyrosine nitration has been observed in a variety of human diseases associated with oxidative stress, such as inflammatory, neurodegenerative, and cardiovascular conditions. However, the pathways leading to nitration of tyrosine residues are still unclear. Recent studies have shown that peroxynitrite (PN), produced by the reaction of superoxide and nitric oxide, can lead to protein nitration and inactivation. Tyrosine nitration may also be mediated by nitrogen dioxide produced by the oxidation of nitrite by peroxidases. Manganese superoxide dismutase (MnSOD), which plays a critical role in cellular defense against oxidative stress by decomposing superoxide within mitochondria, is nitrated and inactivated under pathological conditions. In this study, MnSOD is shown to catalyze PN-mediated self-nitration. Direct, spectroscopic observation of the kinetics of PN decay and nitrotyrosine formation (k(cat) = 9.3 × 10(2) M(-1) s(-1)) indicates that the mechanism involves redox cycling between Mn(2+) and Mn(3+), similar to that observed with superoxide. Distinctive patterns of tyrosine nitration within MnSOD by various reagents were revealed and quantified by MS/MS analysis of MnSOD trypsin digest peptides. These analyses showed that three of the seven tyrosine residues of MnSOD (Tyr34, Tyr9, and Tyr11) were the most susceptible to nitration and that the relative amounts of nitration of these residues varied widely depending upon the nature of the nitrating agent. Notably, nitration mediated by PN, in both the presence and absence of CO2, resulted in nitration of the active site tyrosine, Tyr34, while nitration by freely diffusing nitrogen dioxide led to surface nitration at Tyr9 and Tyr11. Flux analysis of the nitration of Tyr34 by PN-CO2 showed that the nitration rate coincided with the kinetics of the reaction of PN with CO2. These kinetics and the 20-fold increase in the efficiency of tyrosine nitration in the presence of CO2 suggest a specific role for the carbonate radical anion (•CO3(-)) in MnSOD nitration by PN. We also observed that the nitration of Tyr34 caused inactivation of the enzyme, while nitration of Tyr9 and Tyr11 did not interfere with the superoxide dismutase activity. The loss of MnSOD activity upon Tyr34 nitration implies that the responsible reagent in vivo is peroxynitrite, acting either directly or through the action of •CO3(-).

Effect of acute administration of 3-butyl-1-phenyl-2-(phenyltelluro)oct-en-1-one on oxidative stress in cerebral cortex, hippocampus, and cerebellum of rats

Organotellurium compounds have been synthesized since 1840, but pharmacological and toxicological studies about them are still incipient. Therefore, the objective of this study was to verify the effect of acute administration of the organochalcogen 3-butyl-1-phenyl-2-(phenyltelluro)oct-en-1-one on some parameters of oxidative stress in the brain of 30-day-old rats. Animals were treated intraperitoneally with a single dose of the organotellurium (125, 250, or 500 μg/kg body weight) and sacrificed 60 min after the injection. The cerebral cortex, the hippocampus, and the cerebellum were dissected and homogenized in KCl. Afterward, thiobarbituric acid reactive substances (TBARS), carbonyl, sulfhydryl, catalase (CAT), superoxide dismutase (SOD), nitric oxide (NO) formation, and hydroxyl radical production were measured in the brain. The organotellurium enhanced TBARS in the cerebral cortex and the hippocampus, and increased protein damage (carbonyl) in the cerebral cortex and the cerebellum. In contrast, the compound provoked a reduced loss of thiol groups measured by the sulfhydryl assay in all the tissues studied. Furthermore, the activity of the antioxidant enzyme CAT was reduced by the organochalcogen in the cerebral cortex and the cerebellum, and the activity of SOD was inhibited in all the brain tissues. Moreover, NO production was increased in the cerebral cortex and the cerebellum by this organochalcogen, and hydroxyl radical formation was also enhanced in the cerebral cortex. Our findings indicate that this organotellurium compound induces oxidative stress in the brain of rats, corroborating that this tissue is a potential target for organochalcogen action.

A ditryptophan cross-link is responsible for the covalent dimerization of human superoxide dismutase 1 during its bicarbonate-dependent peroxidase activity

Unlike intermolecular disulfide bonds, other protein cross-links arising from oxidative modifications cannot be reversed and are presumably more toxic to cells because they may accumulate and induce protein aggregation. However, most of these irreversible protein cross-links remain poorly characterized. For instance, the antioxidant enzyme human superoxide dismutase 1 (hSod1) has been reported to undergo non-disulfide covalent dimerization and further oligomerization during its bicarbonate-dependent peroxidase activity. The dimerization was shown to be dependent on the oxidation of the single, solvent-exposed Trp(32) residue of hSod1, but the covalent dimer was not isolated nor was its structure determined. In this work, the hSod1 covalent dimer was isolated, digested with trypsin in H(2)O and H(2)(18)O, and analyzed by UV-Vis spectroscopy and mass spectrometry (MS). The results demonstrate that the covalent dimer consists of two hSod1 subunits cross-linked by a ditryptophan, which contains a bond between C3 and N1 of the respective Trp(32) residues. We further demonstrate that the cross-link cleaves under usual MS/MS conditions leading to apparently unmodified Trp(32), partially hinders proteolysis, and provides a mechanism to explain the formation of hSod1 covalent trimers and tetramers. This characterization of the covalent hSod1 dimer identifies a novel oxidative modification of protein Trp residues and provides clues for studying its occurrence in vivo.

Mass spectrometric identification of oxidative modifications of tryptophan residues in proteins: chemical artifact or post-translational modification?

Oxidative modification of tryptophan to kynurenine (KYN) and N-formyl kynurenine (NFK) has been described in mitochondrial proteins associated with redox metabolism, and in human cataract lenses. To a large extent, however, previously reported identifications of these modifications were performed using peptide mass fingerprinting and/or tandem-MS data of proteins separated by gel electrophoresis. To date, it is uncertain whether NFK and KYN may represent sample handling artifacts or exclusively post-translational events. To address the problem of the origin of tryptophan oxidation, we characterized several antibodies by liquid chromatography-tandem mass spectrometry, with and without the use of electrophoretic separation of heavy and light chains. Antibodies are not normally expected to undergo oxidative modifications, however, several tryptophan (Trp) residues on both heavy and light chains were found extensively modified to both doubly oxidized Trp and KYN following SDS-PAGE separation and in-gel digestion. In contrast, those residues were observed as non-modified upon in-solution digestion. These results indicate that Trp oxidation may occur as an artifact in proteins separated by SDS-PAGE, and their presence should be carefully interpreted, especially when gel electrophoretic separation methods are employed.

Protein cysteine S-guanylation and electrophilic signal transduction by endogenous nitro-nucleotides

Nitric oxide (NO), a gaseous free radical that is synthesized in organisms by nitric oxide synthases, participates in a critical fashion in the regulation of diverse physiological functions such as vascular and neuronal signal transduction, host defense, and cell death regulation. Two major pathways of NO signaling involve production of the second messenger guanosine 3',5'-cyclic monophosphate (cGMP) and posttranslational modification (PTM) of redox-sensitive cysteine thiols of proteins. We recently clarified the physiological formation of 8-nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP) as the first demonstration, since the discovery of cGMP more than 40 years ago, of a new second messenger derived from cGMP in mammals. 8-Nitro-cGMP is electrophilic and reacts efficiently with sulfhydryls of proteins to produce a novel PTM via cGMP adduction, a process that we named protein S-guanylation. 8-Nitro-cGMP may regulate electrophilic signaling on the basis of its electrophilicity through induction of S-guanylation of redox sensor proteins. Examples include S-guanylation of the redox sensor protein Kelch-like ECH-associated protein 1 (Keap1), which leads to activation of NF-E2-related factor 2 (Nrf2)-dependent expression of antioxidant and cytoprotective genes. This S-guanylation-mediated activation of an antioxidant adaptive response may play an important role in cytoprotection during bacterial infections and oxidative stress. Identification of new redox-sensitive proteins as targets for S-guanylation may help development of novel therapeutics for oxidative stress- and inflammation-related disorders and vascular diseases as well as understanding of cellular protection against oxidative stress.

A new assignment technique of 2D-NMR spectra by spin-lock sequence to a tripeptide containing tryptophan in water

We developed a new assignment technique of tryptophan residues using pulsed field gradient TOCSY-ROESY (PFG-TORO) and pulsed field gradient TOCSY-ROESY-TOCSY (PFG-TOROTO) techniques in water. Connectivity from betaH to zeta2H (H-7) via epsilon1H (H-1) and delta1H (H-2) in the TORO spectrum and from betaH to zeta3H (H-5) and eta2H (H-6) via epsilon1H (H-1) and delta1H (H-2) in the TOROTO spectrum could be able to assign each of the protons of the indole rings.

Profiling of residue-level photo-oxidative damage in peptides

Protein and peptide oxidation is a key feature in the progression of a variety of disease states and in the poor performance of protein-based products. The present work demonstrates a mass spectrometry-based approach to profiling degradation at the amino acid residue level. Synthetic peptides containing the photosensitive residues, tryptophan and tyrosine, were used as models for protein-bound residue photodegradation. Electrospray ionisation tandem mass spectrometry (ESI-MS/MS) was utilised to characterise and provide relative quantitative information on the formation of photoproducts localised to specific residues, including the characterisation of low abundance photomodifications not previously reported, including W + 4O modification, hydroxy-bis-tryptophandione and topaquinone. Other photoproducts observed were consistent with the formation of tyrosine-derived dihydroxyphenylalanine (dopa), trihydroxyphenylalanine, dopa-quinone and nitrotyrosine, and tryptophan-derived hydroxytryptophan, dihydroxytryptophan/N-formylkynurenine, kynurenine, hydroxyformylkynurenine, tryptophandiones, tetrahydro-beta-carboline and nitrotryptophan. This approach combined product identification and abundance tracking to generate a photodegradation profile of the model system. The profile of products formed yields information on formative mechanisms. Profiling of product formation offers new routes to identify damage markers for use in tracking and controlling oxidative damage to polypeptides.

Oxidative risk for atherothrombotic cardiovascular disease

In the vasculature, reactive oxidant species, including reactive oxygen, nitrogen, or halogenating species, and thiyl, tyrosyl, or protein radicals may oxidatively modify lipids and proteins with deleterious consequences for vascular function. These biologically active free radical and nonradical species may be produced by increased activation of oxidant-generating sources and/or decreased cellular antioxidant capacity. Once formed, these species may engage in reactions to yield more potent oxidants that promote transition of the homeostatic vascular phenotype to a pathobiological state that is permissive for atherothrombogenesis. This dysfunctional vasculature is characterized by lipid peroxidation and aberrant lipid deposition, inflammation, immune cell activation, platelet activation, thrombus formation, and disturbed hemodynamic flow. Each of these pathobiological states is associated with an increase in the vascular burden of free radical species-derived oxidation products and, thereby, implicates increased oxidant stress in the pathogenesis of atherothrombotic vascular disease.

Post-translational modifications of superoxide dismutase

Post-translational modifications of proteins control many biological processes through the activation, inactivation, or gain-of-function of the proteins. Recent developments in mass spectrometry have enabled detailed structural analyses of covalent modifications of proteins and also have shed light on the post-translational modification of superoxide dismutase. In this review, we introduce some covalent modifications of superoxide dismutase, nitration, phosphorylation, glutathionylaion, and glycation. Nitration has been the most extensively analyzed modification both in vitro and in vivo. Reaction of human Cu,Zn superoxide dismutase (SOD) with reactive nitrogen species resulted in nitration of a single tryptophan residue to 6-nitrotryptophan, which could be a new biomarker of a formation of reactive nitrogen species. On the other hand, tyrosine 34 of human MnSOD was exclusively nitrated to 3-nitrotyrosine and almost completely inactivated by the reaction with peroxynitrite. The nitrated MnSOD has been found in many diseases caused by ischemia/reperfusion, inflammation, and others and may have a pivotal role in the pathology of the diseases. Most of the post-translational modifications have given rise to a reduced activity of SOD. Since phosphorylation and nitration of SOD have been shown to have a possible reversible process, these modifications may be related to a redox signaling process in cells. Finally we briefly introduce a metal insertion system of SOD, focusing particularly on the iron misincorporation of nSOD, as a part of post-translational modifications.

Protein tyrosine nitration: selectivity, physicochemical and biological consequences, denitration, and proteomics methods for the identification of tyrosine-nitrated proteins

Protein tyrosine nitration (PTN) is a post-translational modification occurring under the action of a nitrating agent. Tyrosine is modified in the 3-position of the phenolic ring through the addition of a nitro group (NO2). In the present article, we review the main nitration reactions and elucidate why nitration is not a random chemical process. The particular physical and chemical properties of 3-nitrotyrosine (e.g., pKa, spectrophotometric properties, reduction to aminotyrosine) will be discussed, and the biological consequences of PTN (e.g., modification of enzymatic activity, sensitivity to proteolytic degradation, impact on protein phosphorylation, immunogenicity and implication in disease) will be reviewed. Recent data indicate the possibility of an in vivo denitration process, which will be discussed with respect to the different reaction mechanisms that have been proposed. The second part of this review article focuses on analytical methods to determine this post-translational modification in complex proteomes, which remains a major challenge.

Effect of in vitro exposure of human serum to 3-butyl-1-phenyl-2-(phenyltelluro)oct-en-1-one on oxidative stress

The objective of this study was to verify the effect of the organochalcogen 3-butyl-1-phenyl-2-(phenyltelluro)oct-en-1-one on some parameters of oxidative stress in human serum. Serum of volunteers were incubated for 30 min in the presence or absence of 1, 10, or 30 microM of 3-butyl-1-phenyl-2-(phenyltelluro)oct-en-1-one and oxidative stress was measured. First, we tested the influence of the compound on 1,1-diphenyl-2-picrylhydrazyl (DPPH(*)) radical-scavenging and verified that the organotellurium did not have any antioxidant properties. The organochalcogen was capable to enhance TBARS but the compound was not able to alter carbonyl assay. Furthermore, the organochalcogen provoked a reduction of protein thiol groups measured by the sulfhydryl assay. Moreover, the organotellurium enhanced the activity of catalase and superoxide dismutase, inhibited the activity of glutathione peroxidase and did not modify the glutathione S-transferase activity. Furthermore, nitric oxide production and hydroxyl radical activity were not affected by the compound. Our findings showed that this organochalcogen induces oxidative stress in human serum, indicating that this compound is potentially toxic to human beings.

Synthesis and NMR characteristics of N-acetyl-4-nitro, N-acetyl-5-nitro, N-acetyl-6-nitro and N-acetyl-7-nitrotryptophan methyl esters

N-acetyl-4-nitrotryptophan methyl ester (2), N-acetyl-5-nitrotryptophan methyl ester (3), N-acetyl-6-nitrotryptophan methyl ester (4) and N-acetyl-7-nitrotryptophan methyl ester (5) were synthesized through a modified malonic ester reaction of the appropriate nitrogramine analogs followed by methylation with BF(3)-methanol. Assignments of the (1)H and (13)C NMR chemical shifts were made using a combination of (1)H-(1)H COSY, (1)H-(13)C HETCOR and (1)H-(13)C selective INEPT experiments.

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

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

Amyotrophic lateral sclerosis: Protein chaperone dysfunction revealed by proteomic studies of animal models

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that affects motor neurons and causes progressive muscle weakness and atrophy. The etiology and pathogenesis of ALS are largely unknown and no effective treatment is presently available. About 10% of patients have the familial or inherited form of the disease (fALS), among which 20% is linked to mutations with Cu(2+)/Zn(2+) superoxide dismutase (mSOD1). Transgenic animals expressing human mSOD1 are excellent models for understanding not only fALS but sporadic ALS as well. Pathological features in both ALS patients and mSOD1 transgenic animals' spinal cords share commonalties including the accumulation of misfolded protein inclusions. Recent proteomic investigations on ALS animal models have discovered alterations in protein expression, protein-protein interactions and post-translational modifications. These efforts have revealed aspects of potential pathogenic mechanisms and identified probable therapeutic targets. The present review summarizes the major findings of proteomics studies performed on the mSOD1 mice with particular emphasis on the spinal cord proteome. These results are compared with those reported using cell cultures or specimens obtained from ALS patients. The convergence of pathogenic processes on protein chaperone function, and its relationship to protein degradation, metabolic dysfunction and oxidative signaling events is discussed.

Detection and characterization of peroxynitrite-induced modifications of tyrosine, tryptophan, and methionine residues by tandem mass spectrometry

Nitration and oxidation of tyrosine, tryptophan, and methionine residues in proteins are potential markers of their interaction with peroxynitrite. This chapter describes the procedure for the detection of these nitro-oxidative modifications by tandem mass spectrometry. The peptide YGDLANWMIPGK, shown to contain a nitrohydroxytryptophan in the mitochondrial enzyme succinyl-CoA:3-ketoacid coenzyme A transferase (SCOT) in vivo, was synthesized and exposed to peroxynitrite in order to test whether an identical tryptophan derivative could be generated in vitro. Data show that the occurrence of specific fragmented ions corresponding to the oxidation of methionine, nitration of tyrosine, and nitration/oxidation of tryptophan residues can be used to identify the sites of the nitration and oxidation of proteins in vitro and in vivo. It is also demonstrated that a nitrohydroxy addition to the tryptophan, similar to that present in SCOT in vivo, can be produced in vitro.

Nitration of tryptophan 372 in succinyl-CoA:3-ketoacid CoA transferase during aging in rat heart mitochondria

The main objective of this study was to test the hypothesis that in vivo post-translational modifications in proteins, induced by the endogenously generated reactive oxygen and nitrogen molecules, can alter protein function and thereby have an effect on metabolic pathways during the aging process. Succinyl-CoA:3-ketoacid coenzyme A transferase (SCOT), the mitochondrial enzyme involved in the breakdown of ketone bodies in the extrahepatic tissues, was identified in rat heart to undergo age-associated increase in a novel, nitro-hydroxy, addition to tryptophan 372, located in close proximity ( approximately 10 A) of the enzyme active site. Between 4 and 24 months of age, the molar content of nitration was more than doubled while specific enzyme activity increased significantly. The amount of SCOT protein, however, remained unchanged. In vitro treatment of heart mitochondrial soluble proteins with relatively low concentrations of peroxynitrite enhanced the nitration as well as specific activity of SCOT. Results of this study identify tryptophan to be a specific target of nitration in vivo, for the first time. We hypothesize that increases in tryptophan nitration of SCOT and catalytic activity constitute a plausible mechanism for the age-related metabolic shift toward enhanced ketone body consumption as an alternative source of energy supply in the heart.