Peroxynitrite induces tryosine nitration and modulates tyrosine phosphorylation of synaptic proteins

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.

A Comprehensive Overview of the Complex Role of Oxidative Stress in Aging, The Contributing Environmental Stressors and Emerging Antioxidant Therapeutic Interventions

Introduction

Aging is a normal, inevitable, irreversible, and progressive process which is driven by internal and external factors. Oxidative stress, that is the imbalance between prooxidant and antioxidant molecules favoring the first, plays a key role in the pathophysiology of aging and comprises one of the molecular mechanisms underlying age-related diseases. However, the oxidative stress theory of aging has not been successfully proven in all animal models studying lifespan, meaning that altering oxidative stress/antioxidant defense systems did not always lead to a prolonged lifespan, as expected. On the other hand, animal models of age-related pathological phenotypes showed a well-correlated relationship with the levels of prooxidant molecules. Therefore, it seems that oxidative stress plays a more complicated role than the one once believed and this role might be affected by the environment of each organism. Environmental factors such as UV radiation, air pollution, and an unbalanced diet, have also been implicated in the pathophysiology of aging and seem to initiate this process more rapidly and even at younger ages.

Aim

The purpose of this review is to elucidate the role of oxidative stress in the physiology of aging and the effect of certain environmental factors in initiating and sustaining this process. Understanding the pathophysiology of aging will contribute to the development of strategies to postpone this phenomenon. In addition, recent studies investigating ways to alter the antioxidant defense mechanisms in order to prevent aging will be presented.

Conclusions

Careful exposure to harmful environmental factors and the use of antioxidant supplements could potentially affect the biological processes driving aging and slow down the development of age-related diseases. Maybe a prolonged lifespan could not be achieved by this strategy alone, but a longer healthspan could also be a favorable target.

Site-specific identification and validation of hepatic histone nitration in vivo: Implications for alcohol-induced liver injury

Oxidative and nitrative stress have been implicated in the molecular mechanisms underlying a variety of biological processes and disease states including cancer, aging, cardiovascular disease, neurological disorders, diabetes, and alcohol-induced liver injury. One marker of nitrative stress is the formation of 3-nitrotyrosine, or protein tyrosine nitration (PTN), which has been observed during inflammation and tissue injury; however, the role of PTN in the progression or possibly the pathogenesis of disease is still unclear. We show in a model of alcohol-induced liver injury that an increase in PTN occurs in hepatocyte nuclei within the liver of wild-type male C57BL/6J mice following chronic ethanol exposure (28 days). High-resolution mass spectrometric analysis of isolated hepatic nuclei revealed several novel sites of tyrosine nitration on histone proteins. Histone nitration sites were validated by tandem mass spectrometry (MS/MS) analysis of representative synthetic nitropeptides equivalent in sequence to the respective nitrotyrosine sites identified in vivo. We further investigated the potential structural impact of the novel histone H3 Tyr41 (H3Y41) nitration site identified using molecular dynamics (MD) simulations. MD simulations of the nitrated and non-nitrated forms of histone H3Y41 showed significant structural changes at the DNA interface upon H3Y41 nitration. The results from this study suggest that, in addition to other known post-translational modifications that occur on histone proteins (e.g., acetylation and methylation), PTN could induce chromatin structural changes, possibly affecting gene transcription processes associated with the development of alcohol-induced liver injury.

Activation of Tyrosine Phosphorylation Signaling in Erythrocytes of Patients with Alzheimer's Disease

Alzheimer's disease (AD) is the most prevalent type of dementia affecting older people. The identification of biomarkers is increasingly important and would be crucial for future therapy. Here, we demonstrated that in AD erythrocytes: (i) the anion transporter band3 is highly phosphorylated; (ii) the lyn kinase is phosphorylated and activated; (iii) the tyrosine phosphatase activity is downregulated, with a significant inverse correlation between band3 phosphorylation and disease progression, as revealed by Mini Mental State Examination score. Finally, we showed that in normal erythrocytes, treated in vitro with Aβ1-42 peptide, both band3 phosphorylation and lyn activation occurs. These results suggest that modulation of tyrosine phosphorylation signaling may be evaluated as a potential peripheral marker in AD.

Activation of Phosphotyrosine-Mediated Signaling Pathways in the Cortex and Spinal Cord of SOD1G93A, a Mouse Model of Familial Amyotrophic Lateral Sclerosis

Degeneration of cortical and spinal motor neurons is the typical feature of amyotrophic lateral sclerosis (ALS), a progressive neurodegenerative disease for which a pathogenetic role for the Cu/Zn superoxide dismutase (SOD1) has been demonstrated. Mice overexpressing a mutated form of the SOD1 gene (SOD1^G93A) develop a syndrome that closely resembles the human disease. The SOD1 mutations confer to this enzyme a “gain-of-function,” leading to increased production of reactive oxygen species. Several oxidants induce tyrosine phosphorylation through direct stimulation of kinases and/or phosphatases. In this study, we analyzed the activities of src and fyn tyrosine kinases and of protein tyrosine phosphatases in synaptosomal fractions prepared from the motor cortex and spinal cord of transgenic mice expressing SOD1^G93A. We found that (i) protein phosphotyrosine level is increased, (ii) src and fyn activities are upregulated, and (iii) the activity of tyrosine phosphatases, including the striatal-enriched tyrosine phosphatase (STEP), is significantly decreased. Moreover, the NMDA receptor (NMDAR) subunit GluN2B tyrosine phosphorylation was upregulated in SOD1^G93A. Tyrosine phosphorylation of GluN2B subunits regulates the NMDAR function and the recruitment of downstream signaling molecules. Indeed, we found that proline-rich tyrosine kinase 2 (Pyk2) and ERK1/2 kinase are upregulated in SOD1^G93A mice. These results point out an involvement of tyrosine kinases and phosphatases in the pathogenesis of ALS.

Mass spectrometric analysis of protein tyrosine nitration in aging and neurodegenerative diseases

This review highlights the significance of protein tyrosine nitration (PTN) in signal transduction pathways, the progress achieved in analytical methods, and the implication of nitration in the cellular pathophysiology of aging and age-related neurodegenerative diseases. Although mass spectrometry of nitrated peptides has become a powerful tool for the characterization of nitrated peptides, the low stoichiometry of this modification clearly necessitates the use of affinity chromatography to enrich modified peptides. Analysis of nitropeptides involves identification of endogenous, intact modification as well as chemical conversion of the nitro group to a chemically reactive amine group and further modifications that enable affinity capture and enhance detectability by altering molecular properties. In this review, we focus on the recent progress in chemical derivatization of nitropeptides for enrichment and mass analysis, and for detection and quantification using various analytical tools. PTN participates in physiological processes, such as aging and neurodegenerative diseases. Accumulation of 3-nitrotyrosine has been found to occur during the aging process; this was identified through mass spectrometry. Further, there are several studies implicating the presence of nitrated tyrosine in age-related diseases such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis.

Oxidative stress and its significant roles in neurodegenerative diseases and cancer

Reactive oxygen and nitrogen species have been implicated in diverse pathophysiological conditions, including inflammation, neurodegenerative diseases and cancer. Accumulating evidence indicates that oxidative damage to biomolecules including lipids, proteins and DNA, contributes to these diseases. Previous studies suggest roles of lipid peroxidation and oxysterols in the development of neurodegenerative diseases and inflammation-related cancer. Our recent studies identifying and characterizing carbonylated proteins reveal oxidative damage to heat shock proteins in neurodegenerative disease models and inflammation-related cancer, suggesting dysfunction in their antioxidative properties. In neurodegenerative diseases, DNA damage may not only play a role in the induction of apoptosis, but also may inhibit cellular division via telomere shortening. Immunohistochemical analyses showed co-localization of oxidative/nitrative DNA lesions and stemness markers in the cells of inflammation-related cancers. Here, we review oxidative stress and its significant roles in neurodegenerative diseases and cancer.

Oxidative and Nitrosative Stress and Immune-Inflammatory Pathways in Patients with Myalgic Encephalomyelitis (ME)/Chronic Fatigue Syndrome (CFS)

Myalgic Encephalomyelitis (ME) / Chronic Fatigue Syndrome (CFS) has been classified as a disease of the central nervous system by the WHO since 1969. Many patients carrying this diagnosis do demonstrate an almost bewildering array of biological abnormalities particularly the presence of oxidative and nitrosative stress (O&NS) and a chronically activated innate immune system. The proposal made herein is that once generated chronically activated O&NS and immune-inflammatory pathways conspire to generate a multitude of self-sustaining and self-amplifying pathological processes which are associated with the onset of ME/CFS. Sources of continuous activation of O&NS and immune-inflammatory pathways in ME/CFS are chronic, intermittent and opportunistic infections, bacterial translocation, autoimmune responses, mitochondrial dysfunctions, activation of the Toll-Like Receptor Radical Cycle, and decreased antioxidant levels. Consequences of chronically activated O&NS and immune-inflammatory pathways in ME/CFS are brain disorders, including neuroinflammation and brain hypometabolism / hypoperfusion, toxic effects of nitric oxide and peroxynitrite, lipid peroxidation and oxidative damage to DNA, secondary autoimmune responses directed against disrupted lipid membrane components and proteins, mitochondrial dysfunctions with a disruption of energy metabolism (e.g. compromised ATP production) and dysfunctional intracellular signaling pathways. The interplay between all of these factors leads to self-amplifying feed forward loops causing a chronic state of activated O&NS, immune-inflammatory and autoimmune pathways which may sustain the disease.

Association study between genes in Reelin signaling pathway and autism identifies DAB1 as a susceptibility gene in a Chinese Han population

Autism is a pervasive neurodevelopmental disorder diagnosed in early childhood. The genetic factors might play an important role in its pathogenesis. Previous studies revealed that Reelin (RELN) polymorphisms were associated with autism. However, the roles of genes in Reelin signaling pathway for autism are largely unknown. As several knockout mice models in which the Reelin pathway genes (i.e. DAB1, VLDLR/APOER2, FYN/SRC and CRK/CRKL) are deficient have the similar phenotype as the reeler mice (Reelin(-/-)), we hypothesized that the Reelin signaling pathway genes might play roles in the etiology of autism. Therefore, we conducted a family-based association study. Sixty-two tagged single nucleotide polymorphisms (SNPs) covering 15 genes in Reelin pathway were genotyped in 239 trios, and 14 significant SNPs were further investigated in the additional 188 trios. In the total 427 trios, we found significant genetic association between autism and four SNPs in DAB1 (rs12035887 G: p=0.0006; rs3738556 G: p=0.0044; rs1202773 A: p=0.0048; rs12740765 T: p=0.0196). After the Bonferroni correction, SNP rs12035887 remained significant. Furthermore, the haplotype constructed with rs1202773 and rs12023109 in DAB1 showed significant excess transmission in both individual and global haplotype analyses (p=0.0052 and 0.0279, respectively). Our findings suggested that variations in DAB1 involved in the Reelin signaling pathway might contribute to genetic susceptibility to autism with Chinese Han decent, supporting the defect in the Reelin signaling pathway as a predisposition factor for autism.

Evidence suggesting a nitric oxide-scavenging activity for traditional crude drugs, and action mechanisms of Sanguisorbae Radix against oxidative stress and aging

In this series of experiments, we found that Sanguisorbae Radix extract possesses strong free radical-scavenging activity in vitro and in vivo. This crude drug protected against renal disease, which is closely associated with excessive generation of reactive oxygen species. We also showed that Sanguisorbae Radix extract can suppress lipid peroxidation and stimulate an antioxidant defense ability in SAM, suggesting that this crude drug may be an effective agent for ameliorating the pathological conditions related to excessive generation of free radicals and oxidant damage, particularly in the aging process.

Redox proteomics in selected neurodegenerative disorders: from its infancy to future applications

Several studies demonstrated that oxidative damage is a characteristic feature of many neurodegenerative diseases. The accumulation of oxidatively modified proteins may disrupt cellular functions by affecting protein expression, protein turnover, cell signaling, and induction of apoptosis and necrosis, suggesting that protein oxidation could have both physiological and pathological significance. For nearly two decades, our laboratory focused particular attention on studying oxidative damage of proteins and how their chemical modifications induced by reactive oxygen species/reactive nitrogen species correlate with pathology, biochemical alterations, and clinical presentations of Alzheimer's disease. This comprehensive article outlines basic knowledge of oxidative modification of proteins and lipids, followed by the principles of redox proteomics analysis, which also involve recent advances of mass spectrometry technology, and its application to selected age-related neurodegenerative diseases. Redox proteomics results obtained in different diseases and animal models thereof may provide new insights into the main mechanisms involved in the pathogenesis and progression of oxidative-stress-related neurodegenerative disorders. Redox proteomics can be considered a multifaceted approach that has the potential to provide insights into the molecular mechanisms of a disease, to find disease markers, as well as to identify potential targets for drug therapy. Considering the importance of a better understanding of the cause/effect of protein dysfunction in the pathogenesis and progression of neurodegenerative disorders, this article provides an overview of the intrinsic power of the redox proteomics approach together with the most significant results obtained by our laboratory and others during almost 10 years of research on neurodegenerative disorders since we initiated the field of redox proteomics.

Peroxynitrite donor SIN-1 alters high-affinity choline transporter activity by modifying its intracellular trafficking

Sodium-coupled, high-affinity choline transporters (CHTs) are inhibited by 3-morpholinosydnonimine (SIN-1) [peroxynitrite (ONOO⁻) donor]; ONOO⁻ can be produced from nitric oxide and reactive oxygen species during neurodegeneration. SIN-1 rapidly increases CHT internalization from the cell surface, and this correlates with decreased choline uptake. This study addresses mechanisms by which SIN-1 inhibits CHT function in human neuronal SH-SY5Y cells. Thus, mutant L531A-CHT, which does not constitutively internalize into cells by a clathrin-mediated process, is resistant to SIN-1 effects. This suggests that CHT inhibition is not due to oxidative-nitrosative inactivation of the protein and that decreased levels of cell surface CHT in SIN-1-treated cells is related to alterations in its trafficking and subcellular disposition. Dominant-negative proteins AP180C and dynamin-K44A, which interfere with clathrin-mediated and dynamin-dependent endocytosis, respectively, attenuate CHT inhibition by SIN-1. CHT in both vehicle- and SIN-1-treated cells colocalizes with Rab7, Rab9, and Lamp-1 in late endosomes and lysosomes to a similar extent. Lysosome inhibitors increase choline uptake, suggesting that CHT proteins are normally degraded by lysosomes, and this is not altered by oxidative stress. Unexpectedly, inhibitors of proteasomes, but not lysosomes, attenuate SIN-1-mediated inhibition of choline uptake, indicating that proteasomal degradation plays a role in regulating CHT disposition in SIN-1-treated cells. SIN-1 treatment also enhances CHT ubiquitination. Thus, CHT inhibition in SIN-1-treated cells is mediated by proteasomal degradation, which differs from inhibitory mechanisms for some neurotransmitter transporters under similar conditions. Increased oxidative-nitrosative stress in the microenvironment of cholinergic nerve terminals would diminish cholinergic transmission by reducing choline availability for ACh synthesis.

Nitric oxide leads to cytoskeletal reorganization in the retinal pigment epithelium under oxidative stress

Light is a risk factor for various eye diseases, including age-related macular degeneration (AMD) and retinitis pigmentosa (RP). We aim to understand how cytoskeletal proteins in the retinal pigment epithetlium (RPE) respond to oxidative stress, including light and how these responses affect apoptotic signaling. Previously, proteomic analysis revealed that the expression levels of vimentin and serine/threonine protein phosphatase 2A (PP2A) are significantly increased when mice are exposed under continuous light for 7 days compared to a condition of 12 hrs light/dark cycling exposure using retina degeneration 1 (rd1) model. When melatonin is administered to animals while they are exposed to continuous light, the levels of vimentin and PP2A return to a normal level. Vimentin is a substrate of PP2A that directly binds to vimentin and dephosphorylates it. The current study shows that upregulation of PP2Ac (catalytic subunit) phosphorylation negatively correlates with vimentin phosphorylation under stress condition. Stabilization of vimentin appears to be achieved by decreased PP2Ac phosphorylation by nitric oxide induction. We tested our hypothesis that site-specific modifications of PP2Ac may drive cytoskeletal reorganization by vimentin dephosphorylation through nitric oxide signaling. We speculate that nitric oxide determines protein nitration under stress conditions. Our results demonstrate that PP2A and vimentin are modulated by nitric oxide as a key element involved in cytoskeletal signaling. The current study suggests that external stress enhances nitric oxide to regulate PP2Ac and vimentin phosphorylation, thereby stabilizing or destabilizing vimentin. Phosphorylation may result in depolymerization of vimentin, leading to nonfilamentous particle formation. We propose that a stabilized vimentin might act as an anti-apoptotic molecule when cells are under oxidative stress.

Targeting the progression of Parkinson's disease

By the time a patient first presents with symptoms of Parkinson's disease at the clinic, a significant proportion (50-70%) of the cells in the substantia nigra (SN) has already been destroyed. This degeneration progresses until, within a few years, most of the cells have died. Except for rare cases of familial PD, the initial trigger for cell loss is unknown. However, we do have some clues as to why the damage, once initiated, progresses unabated. It would represent a major advance in therapy to arrest cell loss at the stage when the patient first presents at the clinic. Current therapies for Parkinson's disease focus on relieving the motor symptoms of the disease, these unfortunately lose their effectiveness as the neurodegeneration and symptoms progress. Many experimental approaches are currently being investigated attempting to alter the progression of the disease. These range from replacement of the lost neurons to neuroprotective therapies; each of these will be briefly discussed in this review. The main thrust of this review is to explore the interactions between dopamine, alpha synuclein and redox-active metals. There is abundant evidence suggesting that destruction of SN cells occurs as a result of a self-propagating series of reactions involving dopamine, alpha synuclein and redox-active metals. A potent reducing agent, the neurotransmitter dopamine has a central role in this scheme, acting through redox metallo-chemistry to catalyze the formation of toxic oligomers of alpha-synuclein and neurotoxic metabolites including 6-hydroxydopamine. It has been hypothesized that these feed the cycle of neurodegeneration by generating further oxidative stress. The goal of dissecting and understanding the observed pathological changes is to identify therapeutic targets to mitigate the progression of this debilitating disease.

Age-related changes in nitric oxide synthase in the lateral geniculate nucleus of rats

Age-related changes in nitric oxide production in the visual system have not been well characterized. Therefore, we used staining and image-processing approaches to describe changes in levels of neuronal nitric oxide synthase (nNOS), the NADPH-diaphorase (NADPH-d) histochemical marker, and 3-nitrotyrosine in the lateral geniculate nucleus (LGN) of young and aged rats. The LGN plays an important role in the visual system, as it acts as a visual relay nucleus. Quantitative analysis of NADPH-d-positive and nNOS-immunoreactive neurons revealed significant optical density increases in the dorsal LGN and ventral LGN of aged rats; however, no significant changes were observed in the number of neurons with age. 3-Nitrotyrosine immunoreactivity was increased in the dorsal LGN and ventral LGN of aged rats. These results indicate that increased nitric oxide production and peroxynitrite may be associated with alterations in visual function during aging.

Age-related accumulation of 3-nitrotyrosine and nitro-A2E in human Bruch's membrane

Age-related macular degeneration (AMD) is a disease leading to severe visual loss and legal blindness in the elderly population. The pathophysiology of AMD is complex and may include genetic predispositions, accumulation of lipofuscin and drusen, local inflammation and neovascularization. Recently four independent research groups have identified a commonly inherited variant (Y402H) of the complement factor H gene in the genome from different groups of AMD patients. The Y402H variant of CFH significantly increases the risk of AMD and links the genetics of the disease with inflammation. During inflammation there is activation of inducible nitric oxide synthase and release of nitric oxide, which in principal could lead to non-enzymatic nitration within extracellular deposits and/or intrinsic extracellular matrix protein components of human Bruch's membrane. We have identified two biomarkers for non-enzymatic nitration in aged human Bruch's membrane, indicative of inflammation, that include 3-nitrotyrosine identified in Bruch's membrane preparations and nitrated A2E from the lipid soluble extract of the Bruch's membrane preparation. Approximately 30-40 times more A2E is observed in samples of the organic soluble extract of lipofuscin compared to the extract of Bruch's membrane. It is of interest to note that although A2E is a major constituent of RPE lipofuscin, nitrated A2E could not be detected in RPE extracts. We show here that nitro-A2E is a specific biomarker of nitrosative stress in Bruch's membrane and its concentration correlates directly with tissue age.

Peroxynitrite induces tyrosine residue modifications in synaptophysin C-terminal domain, affecting its interaction with src

Peroxynitrite is a potent oxidant that contributes to tissue damage in neurodegenerative disorders. We have previously reported that treatment of rat brain synaptosomes with peroxynitrite induced post-translational modifications in pre- and post-synaptic proteins and stimulated soluble N-ethylmaleimide sensitive fusion proteins attachment receptor complex formation and endogenous glutamate release. In this study we show that, following peroxynitrite treatment, the synaptic vesicle protein synaptophysin (SYP) can be both phosphorylated and nitrated in a dose-dependent manner. We found that tyrosine-phosphorylated, but not tyrosine-nitrated, SYP bound to the src tyrosine kinase and enhanced its catalytic activity. These effects were mediated by direct and specific binding of the SYP cytoplasmic C-terminal tail with the src homology 2 domain. Using mass spectrometry analysis, we mapped the SYP C-terminal tail tyrosine residues modified by peroxynitrite and found one nitration site at Tyr250 and two phosphorylation sites at Tyr263 and Tyr273. We suggest that peroxynitrite-mediated modifications of SYP may be relevant in modulating src signalling of synaptic terminal in pathophysiological conditions.

Effect of nitric oxide donor and gamma irradiation on modifications of ERK and JNK in murine peritoneal macrophages

Mitogen activated protein kinases (MAPKs) play an important role in activation, differentiation and proliferation of macrophages. Macrophages, upon activation, produce large amounts of nitric oxide that inhibit the growth of variety of microorganisms and tumor cells. This nitric oxide which is known to interfere with tyrosine phosphorylation may result in changes in the pattern of activation of MAPKs. In a previous study we have found that tyrosine phosphorylation of MAPKs was completely abolished in the presence of nitric oxide donor and radiation but this did not affect the function of macrophages. In this study the other post translational modifications namely nitration and ubiquitination of JNK and ERK have been looked at. Both ERK and JNK were found to be nitrated. However, there was no increase in ubiquitination of ERK and JNK, indicating that ubiquitination, in this case was not a natural consequence of nitration and may serve in signaling. Additionally, when the nitration was extensive, phosphorylation was also inhibited. The activation of substrates of ERK and JNK were looked at to determine the consequences of such modifications. Inhibition of phosphorylation and extensive nitration of JNK did not prevent activation of its substrate, c-jun. This study indicates that ERK and JNK may be under regulation by different type of modifications in macrophages.

Effect of nitric oxide donor and gamma irradiation on MAPK signaling in murine peritoneal macrophages

Irradiation (IR) of cells is known to activate enzymes of mitogen activated protein kinase (MAPK) family. These are known to be involved in cellular response to stress and are determinants of cell death or survival. When radiotherapy is delivered to malignant cells, macrophages, being radioresistant, survive, get activated, and produce large amounts of nitric oxide. As a result of activation they recognize and phagocytose tumor and normal cell apoptotic bodies leading to tumor regression. In this study, the MAPK signaling in peritoneal macrophages was investigated which plays an important role in its various functions, in an environment which is predominantly nitric oxide, as is after IR. The behavior of macrophages in such an environment was also looked at. The three MAPK (ERK1/2, p38, and JNK) respond differently to Sodium nitroprusside (SNP) alone or IR alone. All the three were activated following IR but only JNK was activated following SNP treatment. Surprisingly, when both the stresses were given simultaneously or one after the other, this differential response was lost and there was a complete inhibition of phosphorylation of all the three MAPKs, irrespective of the order of the two insults (IR and SNP). The noteworthy observation was that despite the complete inhibition of MAPK signaling there was no effect on either the viability or the phagocytic efficiency of peritoneal macrophages.

Exercise and immobilization in aging animals: the involvement of oxidative stress and NF-kappaB activation

In the early 1980s, the concept of threshold of age in exercise and aging was proposed. In several studies it was shown that subjecting young animals to short periods of moderate to intense exercise improved the biochemical and morphological status of their skeletal muscles. This was not the case for old animals subjected to the same exercise regimens. Thus, by measuring several muscle energy-providing enzymes as well as antioxidant enzymes it was demonstrated that their levels and activities increased in young animals postexercise, while in old animals reduced activity of these enzymes was found on completion of the training. However, old animals that started training in young and middle age were still capable of improving their muscle condition as a result of exercise, as long as the onset of training was below a specific age threshold. In the following years, it was shown that intense physical exercise in young humans and animals is accompanied by elevation of oxidative stress parameters in muscles and other organs. Specifically, strenuous training of animals led to increased protein oxidation as measured by protein carbonyl accumulation in muscles, which could be attenuated by the administration of vitamin E. Nuclear factor kappaB (NF-kappaB) is a redox-sensitive transcription factor responsive to closely related reactive oxygen species (ROS) and reactive nitrogen species (RNS) redox cascades. Its involvement in exercise and immobilization has been demonstrated in several studies, indicating that these conditions may lead to inflammatory responses and to oxidative damage to tissues. Indeed, recent studies have revealed that NF-kappaB is involved in inflammatory responses that may result in muscle protein degradation. Additional studies have also demonstrated that the pattern and type of the NF-kappaB activation pathway vary between muscles of young and old animals subjected to limb immobilization for several weeks. This indicates that NF-kappaB may play a crucial role in the regulation of both inflammatory processes and protein turnover and degradation in muscles of old animals. Thus, the modulation of NF-kappaB activity in muscles of old animals by specific inhibitors may provide a means to retard muscle damage and protein degradation under conditions of immobilization.

Identification of 3-nitrotyrosine-modified brain proteins by redox proteomics

Two-dimensional (2D) gel electrophoresis allows separation of complex mixtures of proteins based on isoelectric points and relative mobility. This method has not changed much fundamentally since their original description in the late 1970s. Despite several limitations, such as solubilization of membrane proteins and separation of highly basic proteins, this method has been used successfully in many laboratories as part of proteomics protocols. Our laboratory coupled 2D-PAGE with 2D Western blot analysis to identify brain proteins modified oxidatively with excess carbonylation, bound 4-hydroxy-2-nonenal, or 3-nitrotyrosine (3-NT) in various diseases and animal models of these disorders. This chapter describes in detail the protocol used for the identification of 3-NT-modified proteins in biological samples that may help in delineating the role of protein nitration in the progression or pathogenesis of various diseases.

Tau is Endogenously Nitrated in Mouse Brain: Identification of a Tyrosine Residue Modified In vivo by NO

Nitration of tau protein is normally linked to neurodegeneration but, until now, no comprehensive information is available regarding tau nitration in healthy subjects. It has been previously reported that in differentiated PC12 cells, tau co-immunoprecipitated with alpha-tubulin is nitrated at tyrosine residues and that this post-translation modification doesn't impair the association of tau with the cytoskeleton. The present paper is focused on the identification of tyrosine residues endogenously modified in tau from PC12 cells and reports for the first time that tau is also nitrated in vivo in normal mouse brain and that one tyrosine is endogenously modified.

Tyrosine nitration is a novel post-translational modification occurring on the neural intermediate filament protein peripherin

The biological implication of protein tyrosine nitration in signaling pathways triggered by nitric oxide is recently emerging. Here we report for the first time that nitrotyrosination occurs in the neural intermediate filament protein peripherin. In neuron-like PC12 cells, nitrated peripherin is associated with the cytoskeleton fraction, its level increases during the progression of NGF-induced differentiation and the nitrated protein remains closely associated with stable microtubules. Tyr 17 and Tyr 376 were identified by MALDI-TOF analyses as two specific residues endogenously nitrated. Finally, peripherin nitration is not restricted to PC12 cells but it is also present in vivo in rat brain.

Regulation of cGMP-dependent protein kinase-mediated vasodilation by hypoxia-induced reactive species in ovine fetal pulmonary veins

We previously reported that hypoxia attenuates cGMP-dependent protein kinase (PKG)-mediated relaxation in pulmonary vessels (Am J Physiol Lung Cell Mol Physiol 279: L611-L618, 2003). To determine whether hypoxia-induced reactive oxygen and nitrogen species (ROS and RNS, respectively) may be involved in the downregulation of PKG-mediated relaxation, ovine fetal intrapulmonary veins were exposed to 4 h of normoxia or hypoxia, with or without scavengers of ROS [N-acetylcysteine (NAC)] or peroxynitrite (quercetin and Trolox) and preconstricted with endothelin-1. Hypoxia decreased the relaxation response to 8-bromo-cGMP, PKG protein expression, and kinase activity and increased tyrosine nitration in PKG. However, ROS and RNS scavengers prevented these changes. To determine whether increased PKG nitration diminishes PKG activity, pulmonary vein smooth muscle cells (PVSMC) were exposed to shorter-term (30 min) hypoxia, which increased PKG nitration and decreased PKG activity but did not alter PKG protein expression. Increased dihydro-2,7-dichlorofluorescein diacetate (DCFH(2)-DA) fluorescence in PVSMC after 4 h or 30 min of hypoxia was not observed in the presence of NAC, quercetin, or Trolox, suggesting increased ROS and RNS production. Increased PKG nitration and the associated decrease in PKG activity in PVSMC after 30 min of hypoxia were also reversed on reoxygenation. The consequences of PKG nitration were assessed by exposure of purified PKG-Ialpha to peroxynitrite, which caused increased 3-nitrotyrosine immunoreactivity and inhibition of kinase activity. Our data suggest that, after 30 min of hypoxia, reversible covalent modification of PKG by hypoxia-induced reactive species may be an important mechanism by which the relaxation response to cGMP is regulated. However, after 4 h of hypoxia, PKG nitration and decreased PKG expression are involved.

Inhibition of nitric oxide synthase increases synaptophysin mRNA expression in the hippocampal formation of rats

Synaptophysin is a protein involved in the biogenesis of synaptic vesicles and budding. It has been used as an important tool to investigate plastic effects on synaptic transmission. Nitric oxide (NO) can influence plastic changes in specific brain regions related to cognition and emotion. Experimental evidence suggests that NO and synaptophysin are co-localized in several brain regions and that NO may change synaptophysin expression. Therefore, the aim of the present work was to investigate if inhibition of NO formation would change synaptophysin mRNA expression in the hippocampal formation. Male Wistar rats received single or repeated (once a day for 4 days) i.p. injections of saline or l-nitro-arginine (l-NOARG, 40mg/kg), a non-selective inhibitor of nitric oxide synthase (NOS). Twenty-four hours after the last injection the animals were sacrificed and their brains removed for 'in situ' hybridization study using (35)S-labeled oligonucleotide probe complementary to synaptophysin mRNA. The results were analyzed by computerized densitometry. Acute administration of l-NOARG induced a significant (p<0.05, ANOVA) increase in synaptophysin mRNA expression in the dentate gyrus, CA1 and CA3. The effect disappeared after repeated drug administration. No change was found in the striatum, cingulated cortex, substantia nigra or nucleus accumbens. These results reinforce the proposal that nitric oxide is involved in plastic events in the hippocampus.

Chromatographic and mass spectrometric methods for quantitative determination of 3-nitrotyrosine in biological samples and their application to human samples

The permanent modification of soluble and protein-associated tyrosine by nitration results in the formation of 3-nitrotyrosine, which can be used as a marker of "nitro-oxidative" damage to proteins. Based on the analysis of patient materials, over 40 different diseases and/or conditions have been linked to increased nitration of tyrosine. They include many cardiovascular diseases, conditions associated with immunological reactions and neurological diseases. In this article we review the existing chromatographic and mass spectrometric methods for quantitative measurements of 3-nitrotyrosine in different human biological samples including plasma, either from the free amino acid pool or from hydrolyzed proteins from different matrices.

Nitric oxide and peroxynitrite in health and disease

The discovery that mammalian cells have the ability to synthesize the free radical nitric oxide (NO) has stimulated an extraordinary impetus for scientific research in all the fields of biology and medicine. Since its early description as an endothelial-derived relaxing factor, NO has emerged as a fundamental signaling device regulating virtually every critical cellular function, as well as a potent mediator of cellular damage in a wide range of conditions. Recent evidence indicates that most of the cytotoxicity attributed to NO is rather due to peroxynitrite, produced from the diffusion-controlled reaction between NO and another free radical, the superoxide anion. Peroxynitrite interacts with lipids, DNA, and proteins via direct oxidative reactions or via indirect, radical-mediated mechanisms. These reactions trigger cellular responses ranging from subtle modulations of cell signaling to overwhelming oxidative injury, committing cells to necrosis or apoptosis. In vivo, peroxynitrite generation represents a crucial pathogenic mechanism in conditions such as stroke, myocardial infarction, chronic heart failure, diabetes, circulatory shock, chronic inflammatory diseases, cancer, and neurodegenerative disorders. Hence, novel pharmacological strategies aimed at removing peroxynitrite might represent powerful therapeutic tools in the future. Evidence supporting these novel roles of NO and peroxynitrite is presented in detail in this review.

Endocannabinoids and reactive nitrogen and oxygen species in neuropathologies

Neuropathologies that affect our population include ischemic stroke and neurodegenerative diseases of immune origin, including multiple sclerosis. The endocannabinoid system in the brain, including agonists anandamide (arachidonyl ethanolamide) and 2-arachidonoylglycerol, and the CB1 and CB2 cannabinoid receptors, has been implicated in the pathophysiology of these disease states, and can be a target for therapeutic interventions. This review concentrates on cellular signal transduction pathways believed to be involved in the cellular damage.

Quinolinic acid modulates the activity of src family kinases in rat striatum: in vivo and in vitro studies

Quinolinic acid (QA) has been shown to evoke neurotoxic events via NMDA receptor (NMDAR) overactivation and oxidative stress. NMDARs are particularly vulnerable to free radicals, which can modulate protein tyrosine kinase (PTK) and phosphotyrosine phosphatase (PTP) activities. The src family of tyrosine kinases are associated with the NMDAR complex and regulate NMDA channel function. Because QA is an NMDAR agonist as well as a pro-oxidant agent, we investigated whether it may affect the activity of PTKs and PTPs in vivo and in vitro. In synaptosomes prepared from striata dissected 15 min, 30 min or 15 days after bilateral injection of QA we observed modulation of the phosphotyrosine pattern; a significant decrease in PTP activity; and a sustained increase in c-src and lyn activity at 15 and 30 min after treatment with QA, followed by a decrease 2 weeks later. Striatal synaptosomes treated in vitro with QA showed time- and dose-dependent modulation of c-src and lyn kinase activities. Moreover, the nitric oxide synthase inhibitor NG-nitro-L-arginine-methyl ester, the NMDAR antagonist d-2-amino-5-phosphonovaleric acid and pyruvate suppressed the QA-induced modulation of c-src activity. These findings suggest a novel feature of QA in regulating src kinase activity through the formation of reactive radical species and/or NMDAR overactivation.

Aging influences multiple incidices of oxidative stress in the aortic media of the Fischer 344/NNiaxBrown Norway/BiNia rat

Here, we determine the influence of aging on multiple markers of oxidative stress in the aorta of adult (6-month), aged (30-month) and very aged (36-month) Fischer 344/NNiaHSdxBrown Norway/BiNia (F344/NxBN) rats. Compared to adults, increases in as determined by oxidation of hydroethidine (HE) to ethidium (Et) were increased 79.7+/-7.0% in 36-month aortae and this finding was highly correlated with increases in medal thickness (r=0.773, p<0.01) and total protein nitration (r=0.706, p<0.01) but not Ki67, a marker for cell proliferation. Regression analysis showed that increases in aortic superoxide anion (O.-2) with aging were significantly correlated with changes in the expression and/or regulation of proteins involved in metabolic (AMPK-alpha), signaling (mitogen activated protein kinases (MAPKs) along with c-Src), apoptotic (Bax, Bcl-2, Traf-2) and transcriptional (NF-kappaB) activities. These results suggest that the aging F344/NxBN aorta may be highly suited for unraveling the molecular events that lead to age-associated alterations in aortic oxidative stress.

Mechanism of 1-methyl-4-phenylpyridinium-induced dopamine release from PC12 cells

The molecular mechanism of 1-methyl-4-phenylpyridinium (MPP+), a Parkinsonism-inducing neurotoxin, has been studied in PC12 cells. The cells treated with MPP+ (100 microM) induced a rapid increase in phosphorylation of tyrosine residues of several proteins, including synaptophysin, a major 38 kDa synaptic vesicle protein implicated in exocytosis. An accelerated release of dopamine by MPP+ correlated with phosphorylation of synaptophysin. Exposing the cells to MPP+ triggered reactive oxygen species (ROS) generation within 60 min of treatment and the said effect was blocked by mazindol, a dopamine uptake blocker. In addition, pretreatment with 50-100 microM of selegiline, a selective MAO-B inhibitor, significantly suppressed MPP+-mediated ROS generation. These effects of MPP+ result in the generation of ROS, which may be involved in neuronal degeneration seen in Parkinson's disease.

Peroxynitrite Generated at the Level Produced by Spinal Cord Injury Induces Peroxidation of Membrane Phospholipids in Normal Rat Cord: Reduction by a Metalloporphyrin

The goal of the present study was to determine in vivo whether peroxynitrite, at the concentration and duration produced by SCI, contributes to membrane lipid peroxidation (MLP) after traumatic spinal cord injury (SCI) and the capability of a broad spectrum scavenger of reactive species, Mn (III) tetrakis (4-benzoic acid) porphyrin (MnTBAP), to reduce MLP. This was accomplished by administering a peroxynitrite donor 3-morpholinosydnonimine (SIN-1) into the gray matter of an uninjured rat spinal cord through a microdialysis fiber to generate ONOO at the SCI-elevated levels. The resulting MLP was characterized by measuring the productions of extracellular malondialdehyde and of intracellular 4-hydroxynonenal. We demonstrated that extracellular SIN- 1 administration significantly increased the concentration of malondialdehyde (p < 0.001) and the numbers of hydroxynonenal-positive cells (p < 0.001) as compared to a control group in which ACSF was administered. Simultaneous administration of MnTBAP through a second microdialysis fiber significantly reduced SIN-1-induced malondialdehyde production (p < 0.001) and the numbers of HNE-positive cells (p < 0.001). There was no significant difference between MnTBAP-treated and ACSF-controls (p = 0.3). These results demonstrate in vivo that (1) SCI-produced levels of peroxynitrite sufficient to cause MLP, and therefore that peroxynitrite is an agent of secondary damage after acute SCI; (2) MnTBAP can efficiently reduce SIN-1-induced MLP.

Protein phosphatase 1alpha is tyrosine-phosphorylated and inactivated by peroxynitrite in erythrocytes through the src family kinase fgr

Protein serine/threonine phosphorylation is a significant component of the intracellular signal that together with tyrosine phosphorylation regulates several processes, including cell-cycle progression, muscle contraction, transcription, and neuronal signaling. Cross-talk between phosphoserine/threonine- and phosphotyrosine-mediated pathways is not yet well understood. In this study we found that peroxynitrite, a physiological oxidant formed by the fast radical-radical reaction between the nitric oxide and the superoxide anion, induced tyrosine phosphorylation of the serine/threonine protein phosphatase 1alpha (PP1alpha) in human erythrocytes through activation of src family kinases. We have previously shown in mouse red cells that upregulation of the src kinase fgr phosphorylates PP1alpha, acting as an upstream negative regulator of PP1alpha, and downregulates K-Cl cotransport. Here we found that PP1alpha is a selective substrate of peroxynitrite-activated fgr and that tyrosine phosphorylation of PP1alpha corresponds to an inhibition of its enzymatic activity. Despite fgr activation and PP1alpha downregulation, peroxynitrite stimulated in a dose-dependent fashion the function of the K-Cl cotransporter. In an attempt to understand the mechanism of K-Cl cotransport activation, we found that the effect of peroxynitrite is completely reversed by dithriothreitol, suggesting that peroxynitrite acts as an oxidizing agent by an SH-dependent and PP1alpha-independent mechanism. These findings highlight a novel function of peroxynitrite in regulating the intracellular signal transduction pathways involving serine/threonine phosphorylation and the functional role of proteins that are targets of these phosphatases.

Oxidative injury by peroxynitrite in neural and vascular tissue of the lateral geniculate nucleus in experimental glaucoma

In glaucoma, recent studies show that neural degeneration extends beyond the retinal ganglion cells to include target neurons in the lateral geniculate nucleus of the brain. The pathobiology of LGN degeneration in glaucoma is as yet unknown. We investigated whether peroxynitrite-mediated oxidative stress plays a role in glaucomatous degeneration of the LGN. Nitrotyrosine (NT), a marker for peroxynitrite-mediated oxidative injury, was studied in right LGN sections from monkeys with experimental unilateral glaucoma in the right eye and from normal controls. Immunoreactivity for NT was analyzed using bright-field microscopy. The density of NT profiles localized in neural tissue was determined for LGN layers (2,3,5) connected to the glaucoma eye and LGN layers (1,4,6) connected to the non-glaucoma eye. Density was calculated for each LGN layer by dividing the number of NT profiles by the cross-sectional area of each LGN layer. Blood vessels in each LGN were examined for NT formation. NT formation was detected in LGN layers of all monkeys with glaucoma. Quantitative analysis revealed that compared to controls, the density of NT profiles was increased in monkeys with glaucoma in LGN layers connected to glaucoma and non-glaucoma eyes. The mean density of NT profiles (+/-SEM) in neural tissue was significantly increased in glaucoma LGN layers compared to those of controls (2.30+/-0.56 vs. 0.29+/-0.12; P=0.016). Nitrotyrosine was readily apparent in LGN blood vessel endothelium in glaucoma, and not detected in blood vessels of control LGNs. The presence of NT in neural and vascular tissue of the glaucomatous LGN implicates peroxynitrite-mediated oxidative cell injury in the pathobiology of central neural degeneration in glaucoma.

Nitric Oxide Reverts the Resistance to Doxorubicin in Human Colon Cancer Cells by Inhibiting the Drug Efflux

Multidrug resistance (MDR) is a phenomenon by which cancer cells evade the cytotoxic effects of chemotherapeutic agents. It may occur through different mechanisms, but it often correlates with the overexpression of integral membrane transporters, such as P-glycoprotein (Pgp) and MDR-associated proteins (MRPs), with resulting decrease of drug accumulation and cellular death. Doxorubicin is a substrate of Pgp; it has been suggested that its ability to induce synthesis of nitric oxide (NO) could explain, at least in part, its cytotoxic effects. Culturing the human epithelial colon cell line HT29 in the presence of doxorubicin, we obtained a doxorubicin-resistant (HT29-dx) cell population: these cells accumulated less intracellular doxorubicin, were less sensitive to the cytotoxic effects of doxorubicin and cisplatin, overexpressed Pgp and MRP3, and exhibited a lower NO production (both under basal conditions and after doxorubicin stimulation). The resistance to doxorubicin could be reversed when HT29-dx cells were incubated with inducers of NO synthesis (cytokines mix, atorvastatin). Some NO donors increased the drug accumulation in HT29-dx cells in a guarosine-3′:5′-cyclic monophosphate–independent way; this effect was associated with a marked reduction of doxorubicin efflux rate in HT29 and HT29-dx cells, and tyrosine nitration in the MRP3 protein. Our results suggest that onset of MDR and impairment of NO synthesis are related; this finding could point to a new strategy to reverse doxorubicin resistance in human cancer.

Peroxynitrite-Dependent Upregulation of Src Kinases in Red Blood Cells: Strategies to Study the Activation Mechanisms

Several studies have demonstrated that treatment of cells with oxidants, and in particular with peroxynitrite, may cause the upregulation of tyrosine phosphorylation signaling. In erythrocytes, peroxynitrite induces tyrosine phosphorylation of the major intrinsic membrane protein, band 3. A closer look at the enzymes involved revealed that the effect of peroxynitrite was due to the inhibition of phosphotyrosine phosphatases and/or to the activation of src kinases. The activity of src kinases is modulated not only by phosphatases and other kinases but also through redox modification of cysteine residues: Peroxynitrite can, thus, affect src kinase activity by means of direct and indirect mechanisms. In this chapter, we describe the different pathways leading to src kinase activation and the experimental procedures that can be performed to reveal the activation mechanism. The aim is to provide a more general strategy adaptable to different cell types and different oxidants.

The nitration of tau protein in neurone-like PC12 cells

Tyrosine nitration of proteins is emerging as a post-translational modification playing a role in physiological conditions. Looking for the molecular events triggered by nitric oxide in nerve growth factor-induced neuronal differentiation, we now find that nitration occurs on the microtubule-associated protein tau. In differentiated PC12 cells, we have identified as tau a nitrated protein that co-immunoprecipitates with alpha-tubulin and indicated that the modified protein is associated with the cytoskeleton but it is confined to a restricted cell region. This paper supplies the first evidence that nitration of tau occurs in a physiological process and suggests that it could play a role in neuronal differentiation.

Free radical-dependent nuclear localization of Bcl-2 in the central nervous system of aged rats is not associated with Bcl-2-mediated protection from apoptosis

We have previously reported that Bcl-2 is up-regulated in the CNS of aged F344 rats as a consequence of oxidative stress. In addition to increased levels of expression, we now report that there is a subcellular redistribution of Bcl-2 in the CNS of aged F344 rats. Using western blotting, we found Bcl-2 predominantly located in the cytosol of young rats. However, in aged rats Bcl-2 was found primarily in the nucleus. This distribution, in the hippocampus and cerebellum, was reversed by treatment with the nitrone spin trap N-tert-butyl-alpha-phenylnitrone (PBN). Paradoxically, PBN treatment in young rats had the opposite effect, changing Bcl-2 from predominantly cytosolic to nuclear. We also detected an increase in Bax in aged hippocampal samples (both nuclear and cytosolic), which was reversed by treatment with PBN. The distribution of Bcl-2 and Bax in the cytosol of aged rats dramatically decreased the Bcl-2/Bax ratio, a probable indicator of neuronal vulnerability, which was restored upon treatment with PBN. In order to assess the effect of nuclear association of Bcl-2 we used PC12 cells stably transfected with a Bcl-2 construct to which we added the nuclear localization sequence of the SV40 large T antigen to the N-terminus which resulted in nuclear targeting of Bcl-2. Measurement of cell death using lactate dehydrogenase assays showed that, contrary to wild-type Bcl-2, Bcl-2 localized to the nucleus was not effective in protecting cells from treatment with 250 microm H2O2. These results suggest that nuclear localization of Bcl-2 observed in the aged CNS may not reflect a protective mechanism against oxidative stress, a major component of age-associated CNS impairments.

Combined pharmacological preconditioning with a G-protein-coupled receptor agonist, a mitochondrial KATP channel opener and a nitric oxide donor mimics ischaemic preconditioning

1. Although pharmacological preconditioning (PPC) has emerged as an alternative to ischaemic preconditioning (IPC) in cardioprotection, the efficacy of PPC compared with IPC has not been investigated. Because IPC is mediated by complex signalling cascades arising from multiple triggers, we have hypothesized that combined PPC is necessary to mimic IPC. 2. Isolated and perfused rat hearts underwent IPC by three cycles of 5 min ischaemia and 5 min reperfusion before 30 min global ischaemia followed by 120 min reperfusion. Adenosine (30 micromol/L), diazoxide (50 micromol/L) and s-nitroso-N-acetylpenicillamine (SNAP; 50 micromol/L) were added for 25 min just before (pretreatment modality) or 45 min before (PPC modality) the index ischaemia. 3. Ischaemic preconditioning significantly improved isovolumic left ventricular (LV) function and reduced infarct size. Although pretreatment with adenosine, diazoxide or SNAP alone was capable of reducing infarct size, PPC with each drug alone or in a combination of two drugs except for diazoxide plus SNAP failed to reduce infarct size. In contrast, PPC in combination with adenosine, diazoxide and SNAP (triple combination PPC) conferred significant improvement of LV function and reduction of infarct size that was as effective as IPC. 4. Cardioprotection afforded by triple combination PPC was abolished by the Gi/o-protein inhibitor pertussis toxin, the mitochondiral KATP channel inhibitor 5-hydroxydecanoate or the nitric oxide (NO) scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl imidazoline-1-oxyl 3-oxide (carboxy-PTIO). 5. Protein kinase C (PKC)-epsilon in the particulate fraction was activated throughout preconditioning ischaemia and reperfusion. Although PKC-epsilon was activated during treatment with adenosine, diazoxide or SNAP alone, it was inactivated after washout. In contrast, PKC-epsilon remained activated after triple combination PPC. The PKC inhibitor chelerythrine abolished activation of PKC-epsilon and cardioprotection afforded by IPC and triple combination PPC. 6. These results demonstrate that combined PPC with a G-protein-coupled receptor agonist, a mitochondrial KATP channel opener and an NO donor is necessary to mimic IPC and such synergistic cardioprotection is associated with enhanced and sustained activation of PKC-epsilon.

Expression of inducible nitric oxide synthase and elevation of tyrosine nitration of a 32-kilodalton cellular protein in brain capillary endothelial cells from rats infected with a neuropathogenic murine leukemia virus

PVC-211 murine leukemia virus (MuLV) is a neuropathogenic variant of Friend MuLV (F-MuLV) which causes a rapidly progressive spongiform neurodegenerative disease in rodents. The primary target of PVC-211 MuLV infection in the brain is the brain capillary endothelial cell (BCEC), which is resistant to F-MuLV infection. Previous studies have shown that changes in the envelope gene of PVC-211 MuLV confer BCEC tropism to the virus. However, little is known about how infection of BCECs by PVC-211 MuLV induces neurological disease. Previous results suggest that nitric oxide (NO), which has been implicated as a potential neurotoxin, is involved in PVC-211 MuLV-induced neurodegeneration. In this study, we show that expression of inducible nitric oxide synthase (iNOS), which produces NO from L-arginine, is induced in BCECs from PVC-211 MuLV-infected rats. Furthermore, elevated levels of a 32-kDa cellular protein modified by 3-nitrotyrosine, which is a hallmark of NO production, were observed in virus-infected BCECs. BCECs from rats infected with BCEC-tropic but nonneuropathogenic PVF-e5 MuLV, which is a chimeric virus between PVC-211 MuLV and F-MuLV, fail to induce either iNOS expression or elevation of tyrosine nitration of a 32-kDa protein. These results suggest that expression of iNOS and nitration of tyrosine residues of a 32-kDa protein in PVC-211 MuLV-infected BCECs may play an important role in neurological disease induction.

Tyrosine nitration of a synaptic protein synaptophysin contributes to amyloid beta-peptide-induced cholinergic dysfunction

Amyloid beta (Abeta) is a critical factor involved in the pathogenesis of Alzheimer's disease (AD). We have previously demonstrated that continuous intracerebroventricular infusion of Abeta1-40 induced a time-dependent expression of the inducible nitric oxide (NO) synthase (iNOS) and an overproduction of NO in the rat hippocampus. The pathophysiological significance of the overproduction of NO on brain function was manifested by an impairment of nicotine-evoked acetylcholine(ACh) release and memory deficits.(4) Molecular mechanisms by which NO participates in the Abeta-induced brain dysfunction, however, remain to be determined. Here we show that chronic Abeta1-40 infusion caused a robust peroxynitrite formation and subsequent tyrosine nitration of proteins in the hippocampus. Immunoprecipitation and Western blot analyses further revealed that synaptophysin, a synaptic protein, was a main target of tyrosine nitration. Chronic infusion of Abeta1-40 resulted in an impairment of nicotine-evoked ACh release as analyzed by microdialysis. Daily treatment with the iNOS inhibitor aminoguanidine (AG) or the peroxynitrite scavenger uric acid (UA) prevented the tyrosine nitration of synaptophysin as well as the impairment of nicotine-evoked ACh release induced by Abeta. Our findings suggest that the tyrosine nitration of synaptophysin is related to Abeta-induced impairment of ACh release.

Peroxynitrite generated in the rat spinal cord induces oxidation and nitration of proteins: reduction by Mn (III) tetrakis (4-benzoic acid) porphyrin

To determine whether peroxynitrite at the concentration and duration present after spinal cord injury induces protein oxidation and nitration in vivo, the peroxynitrite donor 3-morpholinosydnonimine (SIN-1) was administered into the gray matter of the rat spinal cord for 5 hr. The cords were removed at 6, 12, 24, and 48 hr after SIN-1 exposure, immunohistochemically stained with antibodies to dinitrophenyl (DNP) and nitrotyrosine (Ntyr), markers of protein oxidation and nitration, respectively, and the immunostained neurons were counted. The percentages of DNP-positive (P = 0.023-0.002) and Ntyr-positive (P < 0.001 for all) neurons were significantly higher in the SIN-1-exposed groups than in the ACSF controls at each time, suggesting that peroxynitrite induced intracellular oxidation and nitration of proteins. The percentages of DNP- and Ntyr-positive neurons were not significantly different over time in either SIN-1- or ACSF-exposed groups (P = 0.20-1.00). The percentage of DNP-positive neurons was 7.6 +/- 3% to 12 +/- 4.2% at 6-24 hr, and it was 14 +/- 2% to 19 +/- 2% at 6-24 hr for Ntyr-positive neurons after SIN-1-exposure, whereas both ranged over 2-3% in ACSF controls. Mn (III) tetrakis (4-benzoic acid) porphyrin (MnTBAP, a broad-spectrum scavenger of reactive species) significantly reduced the percentages of DNP- and Ntyr-positive neurons (P = 0.04 and 0.002, respectively) compared to a SIN-1-exposed, untreated group at 24 hr after SIN-1 exposure. There were no significant differences between MnTBAP-treated and ACSF controls (P = 0.7 for DNP and 0.2 for Ntyr). These results further demonstrate peroxynitrite-induced protein oxidation and nitration and the efficiency of MnTBAP in scavenging peroxynitrite.

Peroxynitrite activates kinases of the src family and upregulates tyrosine phosphorylation signaling

The hypothesis that peroxynitrite may act as a signaling molecule able to upregulate protein tyrosine phosphorylation is discussed. This article focuses on the mechanisms for activating kinases of the src family, an important class of nonreceptor tyrosine kinases implicated in the regulation of cell communication, proliferation, migration, differentiation, and survival. Recent in vitro findings show that in erythrocytes, synaptosomes, and cerebellar primary culture cells peroxynitrite is able to inhibit phosphatases and to activate different members of the src kinase family through different mechanisms involving cysteine-dependent and -independent processes. The ability of nitrotyrosine-containing peptides with SH2 binding affinity to activate src kinases is also discussed.