Indirect evidence for nitric oxide involvement in multiple sclerosis by characterization of circulating antibodies directed against conjugated S-nitrosocysteine

Nitric oxide involvement in the disability and active disease of multiple sclerosis: Systematic review and meta-analysis

BACKGROUND

Multiple sclerosis (MS) is a chronic and immune-mediated disease of unknown etiology and leading to a physical and cognitive disability. Different studies suggest that nitrosative stress may play a pivotal role in the pathogenesis and disability in MS. Besides, reports evaluated NO and their metabolites, expressed by nitrite and nitrate (NOx) levels of MS patients compared with other pathologies, but did not evaluate disability and relapse/remission phases.

OBJECTIVE

Thus, this study aimed to conduct a systematic review and meta-analysis of NOx levels in MS patients in relapse/remission phases and its involvement in patient disability.

METHODS

The protocol was registered in PROSPERO (CRD42022327161). We used GRADE to estimate the articles' quality and evaluated the publication bias using Egger's and Begg's tests.

RESULTS

Here, through a search in the Pubmed, Scopus, and EMBASE databases, 5.276 studies were found, and after the selection process, 20 studies were included in this systematic review and meta-analysis. The studies included data from 1.474 MS patients and 1.717 healthy controls, 1.010 RRMS and 221 primary progressive MS (PPMS).

CONCLUSION

NOx levels are increased in relapsing-remitting MS (RRMS) patients in the relapse phase. Also, NOx levels were increased in MS patients with higher disability. However, further studies are still needed to control lifestyle habits, pain, and MS treatment effects in biased NOx levels.

In schizophrenia, psychomotor retardation is associated with executive and memory impairments, negative and psychotic symptoms, neurotoxic immune products and lower natural IgM to malondialdehyde

Objectives: Stable-phase schizophrenia comprises two distinct entities namely Major Neuro-Cognitive Psychosis (MNP) and simple NP (SNP), which are defined by neuroimmune and neurocognitive abnormalities.Methods: This study investigates associations of psychomotor retardation (PMR), clinical and biomarker characteristics of schizophrenia. We recruited 40 healthy controls and 79 schizophrenia patients and measured IgA responses to tryptophan catabolites (TRYCATs), IgM to malondialdehyde and nitroso (NO)-cysteinyl, CCL-11, an immune activation index based on cytokine levels, and motor screening task (MOT) scores.Results: PMR differentiated schizophrenia from controls and MNP from SNP. In addition, PMR was strongly associated with impairments in executive functions and episodic and semantic memory, psychotic, hostility, excitation, mannerism and negative (PHEMN) symptoms. Around 50% of the variance in PMR was predicted by the cumulative effects of the immune activation index, CCL-11, TRYCATs, NO-Cysteinyl and natural IgM. PRM can reliably be combined with PHEMN symptoms, memory and executive impairments into one latent vector reflecting overall severity of schizophrenia.Conclusions: PMR is a key psychopathological feature of schizophrenia mainly MNP. In addition, PMR may be driven by deficits in the compensatory immune-regulatory system and increased production of neurotoxic immune products, namely TRYCATs, IgM to NO-cysteinyl, and CCL-11, an endogenous cognition deteriorating chemokine.

Endothelial nitric oxide synthase (NOS3) rs2070744 polymorphism and risk for multiple sclerosis

The possible role of oxidative stress and nitric oxide (NO) in the pathogenesis of multiple sclerosis (MS) has been suggested by several neuropathological, biochemical, and experimental data. Because the single-nucleotide polymorphism (SNP) rs2070744 in the endothelial nitric oxide synthase (eNOS or NOS3) gene (chromosome 7q36.1) showed association with the risk for MS in Iranians, we attempted to replicate the possible association between this SNP and the risk for MS in the Caucasian Spanish population. The frequencies of NOS3rs2070744 genotypes and allelic variants in 300 patients diagnosed with MS and 380 healthy controls were assessed with a TaqMan-based qPCR assay. The possible influence of the genotype frequency on age at onset of MS, the severity of MS, clinical evolutive subtypes of MS, and HLA-DRB1*1501 genotype were also analyzed. The frequencies of rs2070744 genotypes and allelic variants were not associated with the risk of developing MS and were not influenced by gender, age at onset and severity of MS, the clinical subtype of MS or the HLA-DRB1*1501 genotype. This study found a lack of association between NOS3 rs2070744 SNP and the risk for MS in Caucasian Spanish people.

Upregulation of the Intestinal Paracellular Pathway with Breakdown of Tight and Adherens Junctions in Deficit Schizophrenia

In 2001, the first author of this paper reported that schizophrenia is associated with an increased frequency of the haptoglobin (Hp)-2 gene. The precursor of Hp-2 is zonulin, a molecule that affects intercellular tight junction integrity. Recently, we reported increased plasma IgA/IgM responses to Gram-negative bacteria in deficit schizophrenia indicating leaky gut and gut dysbiosis. The current study was performed to examine the integrity of the paracellular (tight and adherens junctions) and transcellular (cytoskeletal proteins) pathways in deficit versus non-deficit schizophrenia. We measured IgM responses to zonulin, occludin, E-cadherin, talin, actin, and vinculin in association with IgA responses to Gram-negative bacteria, CCL-11, IgA responses to tryptophan catabolites (TRYCATs), immune activation and IgM to malondialdehyde (MDA), and NO-cysteinyl in 78 schizophrenia patients and 40 controls. We found that the ratio of IgM to zonulin + occludin/talin + actin + viculin (PARA/TRANS) was significantly greater in deficit than those in non-deficit schizophrenia and higher in schizophrenia than those in controls and was significantly associated with increased IgA responses to Gram-negative bacteria. IgM responses to zonulin were positively associated with schizophrenia (versus controls), while IgM to occludin was significantly associated with deficit schizophrenia (versus non-deficit schizophrenia and controls). A large part of the variance (90.8%) in negative and PHEM (psychosis, hostility, excitation, and mannerism) symptoms was explained by PARA/TRANS ratio, IgA to Gram-negative bacteria, IgM to E-cadherin and MDA, and memory dysfunctions, while 53.3% of the variance in the latter was explained by PARA/TRANS ratio, IgA to Gram-negative bacteria, CCL-11, TRYCATs, and immune activation. The results show an upregulated paracellular pathway with breakdown of the tight and adherens junctions and increased bacterial translocation in deficit schizophrenia. These dysfunctions in the intestinal paracellular route together with lowered natural IgM, immune activation, and production of CCL-11 and TRYCATs contribute to the phenomenology of deficit schizophrenia.

Natural regulatory IgM-mediated autoimmune responses directed against malondialdehyde regulate oxidative and nitrosative pathways and coupled with IgM responses to nitroso adducts attenuate depressive and physiosomatic symptoms at the end of term pregnancy

AIM

We aimed to delineate the effects of immunoglobulin (Ig)M-mediated autoimmune responses directed against malondialdehyde (MDA) and nitroso (SNO) adducts on nitro-oxidative stress and depressive and physiosomatic symptoms (DPSS) at the end of term.

METHODS

IgM responses to MDA, NO (nitroso) adducts formed by nitrosylation, and NO₂ tyrosine formed by nitration were measured as well as hydroperoxides (ferrous oxidation xylenol orange), advanced protein oxidation products (AOPP), and NO metabolite (NOx) levels in women at the end of term pregnancy and in normal controls.

RESULTS

IgM responses to MDA were significantly and inversely associated with AOPP, ferrous oxidation xylenol orange, and NOx and DPSS. IgM responses to NO adducts were significantly and inversely associated with DPSS and positively with NOx levels. There were significant associations between IgM responses to MDA, NO adducts, and NO₂ tyrosine. The DPSS score was predicted by AOPP and a lifetime history of premenstrual syndrome (both positively) and IgM responses to NO adducts (inversely). Furthermore, 71.8% of the variance in the index of nitro-oxidative stress was explained by lowered IgM responses to MDA, antioxidant levels (zinc, total radical trapping parameter), and inflammatory mediators.

CONCLUSION

Lowered levels of IgM responses to MDA during pregnancy are accompanied by a reduced regulation of nitro-oxidative processes thereby explaining increased oxidative and nitrosative stress biomarkers in association with DPSS. IgM responses to NO adducts, which reflect nitrosylation as a consequence of increased NO production, regulate DPSS symptoms at the end of term and are a trait marker of major depression. IgM responses to MDA are a key part of the compensatory anti-inflammatory responses system.

IgM-mediated autoimmune responses to oxidative specific epitopes, but not nitrosylated adducts, are significantly decreased in pregnancy: association with bacterial translocation, perinatal and lifetime major depression and the tryptophan catabolite (TRYCAT) pathway

Immunoglubulin (Ig)M responses directed to oxidative specific epitopes (OSEs) and nitric oxide (NO)-adducts are significantly associated with major depression and physio-somatic symptoms. End of term serum IgM responses to OSEs and NO-adducts were assayed in pregnant women with (n = 24) and without prenatal depression (n = 25) as well as in 24 non-pregnant women. Associations of IgM/IgA responses to Gram-negative gut commensal bacteria (leaky gut index) and IgA/IgM responses to tryptophan catabolites (TRYCATs) were analyzed. IgM responses to OSEs, but not NO-adducts, were significantly reduced at the end of term. There were no significant associations between IgM responses to OSEs and perinatal depression, whilst IgM responses to NO-adducts, especially NO-cysteinyl, were significantly associated with a lifetime major depression. IgM responses to OSEs and NO-cysteinyl were significantly associated with IgA/IgM responses to Gram-negative bacteria, especially Morganella morganii, Klebsiella pneumoniae and Citrobacter koseri. IgM responses to NO-adducts and OSEs, especially malondialdehyde and myristic acid, and C-reactive protein (CRP) were inversely associated with TRYCAT pathway activity, whilst a lifetime depression and Pseudomonas putida were positively associated. The attenuation of natural IgM-mediated responses to OSEs at the end of term may indicate lowered activity of this part of the compensatory (anti-)inflammatory reflex system and may be partly explained by lowered bacterial translocation. Increased IgM responses to NO-cysteinyl is a biomarker of lifetime depression and may be induced by bacterial translocation. Natural IgM-mediated autoimmune responses, increased nitrosylation and higher CRP levels may have negative regulatory effects on the TRYCAT pathway.

Insulin resistance, atherogenicity, and iron metabolism in multiple sclerosis with and without depression: Associations with inflammatory and oxidative stress biomarkers and uric acid

Depression is accompanied by metabolic disorders in iron metabolism, lipoproteins, and insulin resistance. We measured plasma levels of ferritin, iron, lipids, insulin, and glucose and computed the homeostasis model assessment (HOMA2IR) and atherogenic index of plasma (AIP) in MS patients with and without depression and healthy controls. Explanatory variables were serum uric acid, interleukin (IL)-6, lipid hydroperoxides (CL-LOOH), albumin, and C-reactive protein (CRP). Depression was assessed using the Hospital Anxiety and Depression Scale (HADS), neurological disability using the Expanded Disability Status Scale (EDSS), and disease progression using ∆EDSS over five years earlier. HOMA2IR and insulin were predicted by diagnosis (increased in MS), age and body mass index (BMI); AIP by diagnosis, sex, BMI, CRP, and uric acid; triglycerides by diagnosis (higher in MS without depression), age, BMI and uric acid; ferritin by diagnosis (higher in MS), sex, CRP, and albumin; and iron by albumin. The HADS score was significantly predicted by ∆EDSS, gastro-intestinal symptoms, iron (inverse), and age. MS is characterized by significantly increased insulin resistance, which is determined by increased insulin levels; and increased ferritin, a biomarker of inflammation. Depression in MS is not associated with increased insulin resistance and atherogenicity but with lowered iron.

Deficit Schizophrenia Is Characterized by Defects in IgM-Mediated Responses to Tryptophan Catabolites (TRYCATs): a Paradigm Shift Towards Defects in Natural Self-Regulatory Immune Responses Coupled with Mucosa-Derived TRYCAT Pathway Activation

Deficit schizophrenia is accompanied by mucosa-associated activation of the tryptophan catabolite (TRYCAT) pathway, as indicated by increased IgA responses to noxious (NOX) TRYCATs, but not regulatory or protective (PRO) TRYCATs, suggesting increased neurotoxic, excitotoxic, inflammatory, and oxidative potential. No previous studies examined IgM-mediated autoimmune responses to the TRYCAT pathway in deficit versus nondeficit schizophrenia. We measured IgM responses to NOX TRYCATs, namely, quinolinic acid (QA), 3-OH-kynurenine (3HK), picolinic acid (PA), and xanthurenic (XA) acid, and PRO TRYCATs, including kynurenic acid (KA) and anthranilic acid (AA), in 40 healthy controls and 40 deficit and 40 nondeficit schizophrenic patients. We computed the IgM responses to NOX (QA + PA + 3HK + XA)/PRO (AA + KA) ratio and ∆ differences in IgA - IgM TRYCAT values and NOX/PRO ratio. Deficit schizophrenia is characterized by significantly attenuated IgM responses to all TRYCATs and NOX/PRO ratio and highly increased ∆IgA - IgM NOX/PRO ratio as compared to nondeficit schizophrenia and healthy controls. The negative symptoms of schizophrenia are significantly and positively associated with increased IgM responses directed against the KA/3HK ratio and ∆IgA - IgM NOX/PRO ratio. The findings support the view that deficit schizophrenia is a distinct subtype of schizophrenia that may be significantly discriminated from nondeficit schizophrenia. Deficit schizophrenia is accompanied by a highly specific defect in IgM isotype-mediated regulatory responses directed to the TRYCAT pathway. Lowered IgM regulatory responses together with mucosa-derived activation of the TRYCAT pathway may contribute to neuroprogression, negative symptoms, and deficit schizophrenia. All in all, a highly specific defect in the compensatory (anti-)inflammatory reflex system (CIRS), namely, natural IgM-mediated regulatory responses, may underpin deficit schizophrenia.

NO-tryptophan: a new small molecule located in the rat brain

A highly specific monoclonal antibody directed against nitric oxide-tryptophan (NO-W) with good affinity (10-9 M) and specificity was developed. In the rat brain, using an indirect immunoperoxidase technique, cell bodies containing NO-W were exclusively found in the intermediate and dorsal parts of the lateral septal nucleus. No immunoreactive fibres were found in the rat brain. This work reports the first visualization and the morphological characteristics of cell bodies containing NO-W in the mammalian brain. The restricted distribution of NO-W in the rat brain suggests that this molecule could be involved in specific physiological mechanisms.

Increased S-nitrosothiols are associated with spinal cord injury in multiple sclerosis

Multiple sclerosis (MS) is an immune-mediated disorder associated with inflammation, demyelination and axonal damage. In search of potential biomarkers of spinal cord lesions in MS related to nitric oxide metabolites, we measured total nitrite and nitrate levels, and protein-bound nitrotyrosine and S-nitrosothiol concentrations in the serum of MS patients at different stages of the disease. Sixty-eight patients and 36 healthy volunteers were included in the study. Total nitrite and nitrate levels were augmented in relapsing-remitting MS, while increased S-nitrosothiol concentrations were found both in relapsing-remitting and secondary-progressive MS. Further analysis demonstrated that S-nitrosothiol levels were selectively increased in patients with spinal cord injury. The data suggest that high S-nitrosothiol concentration may be a potential serum biomarker for spinal cord injury in MS.

Genetic, Immune-Inflammatory, and Oxidative Stress Biomarkers as Predictors for Disability and Disease Progression in Multiple Sclerosis

The aim of this study was to evaluate the TNFβ NcoI polymorphism (rs909253) and immune-inflammatory, oxidative, and nitrosative stress (IO&NS) biomarkers as predictors of disease progression in multiple sclerosis (MS). We included 212 MS patients (150 female, 62 male, mean (±standard deviation (SD)) age = 42.7 ± 13.8 years) and 249 healthy controls (177 female, 72 male, 36.8 ± 11 years). The disability was measured the Expanded Disability Status Scale (EDSS) in 2006 and 2011. We determined the TNFβ NcoI polymorphism and serum levels of interleukin (IL)-6, tumor necrosis factor (TNF)-α, interferon (IFN)-γ, IL-4, IL-10, and IL-17, albumin, ferritin, and plasma levels of lipid hydroperoxides (CL-LOOH), carbonyl protein, advanced oxidation protein products (AOPPs), nitric oxide metabolites (NOx), and total radical-trapping antioxidant parameter (TRAP). The mean EDSS (±SD) in 2006 was 1.62 ± 2.01 and in 2011 3.16 ± 2.29, and disease duration was 7.34 ± 7.0 years. IL-10, TNF-α, IFN-γ, AOPP, and NOx levels were significantly higher and IL-4 lower in MS patients with a higher 2011 EDSS scores (≥3) as compared with those with EDSS < 3. The actual increases in EDSS from 2006 to 2011 were positively associated with TNF-α and IFN-γ. Increased IFN-γ values were associated with higher pyramidal symptoms and increased IL-6 with sensitive symptoms. Increased carbonyl protein and IL-10 but lowered albumin levels predicted cerebellar symptoms. The TNFB1/B2 genotype decreased risk towards progression of pyramidal symptoms. Treatments with IFN-β and glatiramer acetate significantly reduced TNF-α but did not affect the other IO&NS biomarkers or disease progression. Taken together, IO&NS biomarkers and NcoI TNFβ genotypes predict high disability in MS and are associated with different aspects of disease progression. New drugs to treat MS should also target oxidative stress pathways.

Mechanism of inducible nitric-oxide synthase dimerization inhibition by novel pyrimidine imidazoles

Overproduction of nitric oxide (NO) by inducible nitric-oxide synthase (iNOS) has been etiologically linked to several inflammatory, immunological, and neurodegenerative diseases. As dimerization of NOS is required for its activity, several dimerization inhibitors, including pyrimidine imidazoles, are being evaluated for therapeutic inhibition of iNOS. However, the precise mechanism of their action is still unclear. Here, we examined the mechanism of iNOS inhibition by a pyrimidine imidazole core compound and its derivative (PID), having low cellular toxicity and high affinity for iNOS, using rapid stopped-flow kinetic, gel filtration, and spectrophotometric analysis. PID bound to iNOS heme to generate an irreversible PID-iNOS monomer complex that could not be converted to active dimers by tetrahydrobiopterin (H4B) and l-arginine (Arg). We utilized the iNOS oxygenase domain (iNOSoxy) and two monomeric mutants whose dimerization could be induced (K82AiNOSoxy) or not induced (D92AiNOSoxy) with H4B to elucidate the kinetics of PID binding to the iNOS monomer and dimer. We observed that the apparent PID affinity for the monomer was 11 times higher than the dimer. PID binding rate was also sensitive to H4B and Arg site occupancy. PID could also interact with nascent iNOS monomers in iNOS-synthesizing RAW cells, to prevent their post-translational dimerization, and it also caused irreversible monomerization of active iNOS dimers thereby accomplishing complete physiological inhibition of iNOS. Thus, our study establishes PID as a versatile iNOS inhibitor and therefore a potential in vivo tool for examining the causal role of iNOS in diseases associated with its overexpression as well as therapeutic control of such diseases.

Methodologies for the characterization, identification and quantification of S-nitrosylated proteins

BACKGROUND

Protein S-nitrosylation plays a central role in signal transduction by nitric oxide (NO), and aberrant S-nitrosylation of specific proteins is increasingly implicated in disease.

SCOPE OF REVIEW

Here, methodologies for the characterization, identification and quantification of SNO-proteins are reviewed, focusing on techniques suitable for the structural characterization and absolute quantification of isolated SNO-proteins, the identification and relative quantification of SNO-proteins from complex mixtures as well as the mass spectrometry-based identification and relative quantification of sites of S-nitrosylation (SNO-sites) in proteins.

MAJOR CONCLUSIONS

Structural characterization of SNO-proteins by X-ray crystallography is increasingly being utilized to understand both the relationships between protein structure and Cys thiol reactivity as well as the consequences of S-nitrosylation on protein structure and function. New methods for the proteomic identification and quantification of SNO-proteins and SNO-sites have greatly impacted the ability to study protein S-nitrosylation in complex biological systems.

GENERAL SIGNIFICANCE

The ability to identify and quantify SNO-proteins has long been rate-determining for scientific advances in the field of protein S-nitrosylation. Therefore, it is critical that investigators in the field have a good understand the utility and limitations of modern analytical techniques for SNO-protein analysis. This article is part of a Special Issue entitled: Regulation of cellular processes by S-nitrosylation.

Mechanisms of oxidative damage in multiple sclerosis and a cell therapy approach to treatment

Although significant advances have recently been made in the understanding and treatment of multiple sclerosis, reduction of long-term disability remains a key goal. Evidence suggests that inflammation and oxidative stress within the central nervous system are major causes of ongoing tissue damage in the disease. Invading inflammatory cells, as well as resident central nervous system cells, release a number of reactive oxygen and nitrogen species which cause demyelination and axonal destruction, the pathological hallmarks of multiple sclerosis. Reduction in oxidative damage is an important therapeutic strategy to slow or halt disease processes. Many drugs in clinical practice or currently in trial target this mechanism. Cell-based therapies offer an alternative source of antioxidant capability. Classically thought of as being important for myelin or cell replacement in multiple sclerosis, stem cells may, however, have a more important role as providers of supporting factors or direct attenuators of the disease. In this paper we focus on the antioxidant properties of mesenchymal stem cells and discuss their potential importance as a cell-based therapy for multiple sclerosis.

Inflammation induced neurological handicap processes in multiple sclerosis: new insights from preclinical studies

Multiple sclerosis (MS) is described as originating from incompletely explained neuroinflammatory processes, dysfunction of neuronal repair mechanisms and chronicity of inflammation events. Blood-borne immune cell infiltration and microglia activation are causing both neuronal destruction and myelin loss, which are responsible for progressive motor deficiencies, organic and cognitive dysfunctions. MRI as a non-invasive imaging method offers various ways to visualise de- and remyelination, neuronal loss, leukocyte infiltration, blood-brain barrier modification and new sensors are emerging to detect inflammatory lesions at an early stage. We describe studies performed on experimental autoimmune encephalomyelitis (EAE) animal models of MS that shed new light on mechanisms of functional impairments to understand the neurological handicap in MS. We focus on examples of neuroinflammation-mediated inhibition of CNS repair involving adult neurogenesis in the sub-ventricular zone and hippocampus and such experimentally observed inhibitions could reflect deficient plasticity and activation of compensatory mechanisms in MS. In parallel with cognitive decline, organic deficits such as bladder dysfunction are described in most of MS patients. Neuropharmacological interventions, electrical stimulation of nerves, MRI and histopathology follow-up studies helped in understanding the operating events to remodel the neurological networks and to compensate the inflammatory lesions both in spinal cord and in cortical regions. At the molecular level, the local production of reactive products is a well-described phenomenon: oxidative species disturb cellular physiology and generate new molecular epitopes that could further promote immune reactions. The translational research from EAE animal models to MS patient cohorts helps in understanding the mechanisms of the neurological handicap and in development of new therapeutic concepts in MS.

Identification of major S-nitrosylated proteins in murine experimental autoimmune encephalomyelitis

Nitrosative stress has been implicated in the pathophysiology of several CNS disorders, including multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE). We have recently shown that protein nitrosothiols (PrSNOs) accumulate in the brain of MS patients, and there is indirect evidence that PrSNO levels are also increased in EAE. In this study we sought to identify the major PrSNOs in the spinal cord of EAE animals prepared by active immunization of C57/BL6 mice with MOG(35-55) peptide. For this purpose, PrSNOs from control and EAE mice at various disease stages were derivatized with HPDP-biotin, and the biotinylated proteins were isolated with streptavidin-agarose. Proteins from total and streptavidin-bound fractions were then analyzed by Western blotting using antibodies against the major S-nitrosylated substrates of CNS tissue. With this approach we found that the proportion of S-nitrosylated neurofilament proteins, NMDA receptors, alpha/beta-tubulin, beta-actin, and GAPDH is increased in EAE. Other potential substrates either were not S-nitrosylated in vivo (HCN3, HSP-72, CRMP-2, gamma-actin, calbindin) or their S-nitrosylation levels were unaltered in EAE (Na/K ATPase, hexokinase, glycogen phosphorylase). We also discovered that neuronal specific enolase is the major S-nitrosylated protein in acute EAE. Given that S-nitrosylation affects protein function, it is likely that the observed changes are significant to the pathophysiology of inflammatory demyelination.

Circulating antibodies to cysteinyl catecholamines in amyotrophic lateral sclerosis and Parkinson's disease patients

Amyotrophic lateral sclerosis (ALS) is a degenerative disease of unknown aetiology, affecting motor neurons. Many radical species, such as O(2)(-) NO, and ONOO(-), and lipoperoxidative products are involved, but not all processes have yet been identified. It is known that the oxidation of catecholamines leads to quinone formation. These orthoquinones react with the sulphhydril group of cysteine to produce neurotoxic cysteinyl catecholamine (Cyst-CA) neo-compounds. We synthesised Cyst-CA in order to mimic their endogenous formation. Using the ELISA method, circulating antibodies to Cyst-CA were found in sporadic ALS sera. First, the antibody titres were compared to those of controls and patients with other neurodegenerative diseases. Significant antibody levels were found for Cyst-CA. The G and A isotypes were found but not the M isotype. A second series of experiments showed that A and G titres were elevated, depending on the type of Cyst-CA and the onset of the disease. IgG to Cyst-3,4-dihydroxyphenylalanine (L-DOPA) were present in cases of bulbar and upper limb onsets. IgA to Cyst-homovanillic acid (HVA), Cyst-adrenaline (A), and Cyst-dopamine (DA) were found in lower limb onset. These results indirectly show that: 1) the oxidation of CA and the formation of Cyst-CA may be involved in ALS; 2) these radical processes have different targets depending on the onset of the disease.

Intracellular glutathione mediates the denitrosylation of protein nitrosothiols in the rat spinal cord

Protein S-nitrosothiols (PrSNOs) have been implicated in the pathophysiology of neuroinflammatory and neurodegenerative disorders. Although the metabolically instability of PrSNOs is well known, there is little understanding of the factors involved in the cleavage of S-NO linkage in intact cells. To address this issue, we conducted chase experiments in spinal cord slices incubated with S-nitrosoglutathione (GSNO). The results show that removal of GSNO leads to a rapid disappearance of PrSNOs (t(1/2) approximately 2 hr), which is greatly accelerated when glutathione (GSH) levels are raised with the permeable analogue GSH ethyl ester. Moreover, PrSNOs are stable in the presence of the GSH depletor diethyl maleate, indicating that GSH is critical for protein denitrosylation. Inhibition of GSH-dependent enzymes (glutathione S-transferase, glutathione peroxidase, and glutaredoxin) and enzymes that could mediate denitrosylation (alcohol dehydrogense-III, thioredoxin and protein disulfide isomerase) do not alter the rate of PrSNO decomposition. These findings and the lack of protein glutathionylation during the chase indicate that most proteins are denitrosylated via rapid transnitrosylation with GSH. The differences in the denitrosylation rate of individual proteins suggest the existence of additional structural factors in this process. This study is relevant to our recent discovery that PrSNOs accumulate in the central nervous system of patients with multiple sclerosis.

Role of arginine metabolism in immunity and immunopathology

A heterogeneous set of cells that are commonly grouped as "myeloid cells", interacts in a complex landscape of physiological and pathological situations. In this review we attempt to trace a profile of the "myeloid connection" through different normal and pathological states, by analyzing common metabolic pathways of the amino acid l-arginine. Myeloid cells exert various, often divergent, actions on the immune response through mechanisms that exploit mediators of this peculiar metabolic pathway, ranging from l-arginine itself to its downstream metabolites, like nitric oxide and polyamines. Various pathological situations, including neoplastic and autoimmune diseases, as well as injury repair and infections are discussed here, showing how l-arginine metabolism is able to play a dual role, both as an active protector and a possible threat to the organism.

Contrasting potential of nitric oxide and peroxynitrite to mediate oligodendrocyte injury in multiple sclerosis

Nitric oxide (NO) and peroxynitrite (ONOO(-)) are potential mediators of the injury and cytotoxicity occurring over time to oligodendrocytes in multiple sclerosis (MS) lesions. Our in vitro results indicate that human adult CNS-derived oligodendrocytes are relatively resistant to NO-mediated damage. In contrast, human oligodendrocytes are highly susceptible to peroxynitrite-mediated injury. In situ, we found that inducible nitric oxide synthase (iNOS) was expressed in astrocytes and macrophages in all active demyelinating and remyelinating MS lesions examined, yet no correlation was found between numbers of glial cells expressing iNOS and the extent of oligodendrocyte cell death. Nitrotyrosine groups, indicative of the presence of peroxynitrite in vivo, could be detected on astrocytes, macrophages, and oligodendrocytes in MS lesions. High numbers of nitrotyrosine-positive oligodendrocytes were found in one MS case that featured extensive oligodendrocyte cell death. Our results indicate that NO alone is unlikely to induce oligodendrocyte injury, whereas its more potent byproduct peroxynitrite is a potential mediator of injury to oligodendrocytes in MS.

Effectors of demyelination and remyelination in the CNS: implications for multiple sclerosis

Most of the research on multiple sclerosis (MS) has focused on the early events that trigger demyelination and subsequent remyelination. Less attention has been given to the factors that directly mediate the demyelination that is the hallmark of the disease. Effector cells or molecules are those factors directly responsible for mediating the damage in the disease. Similarly, there are effector molecules that are critical for remyelination in the central nervous system (CNS). By understanding those effector molecules in demyelination and remyelination that directly influence the pathologic process, we should be able to generate specific therapies with the greatest potential for benefiting MS patients. This review focuses on effector cells and molecules that are critical for demyelination and remyelination in MS but also in experimental models of the disease including experimental autoimmune encephalomyelitis (EAE), virus-induced models of demyelination (Theiler's virus, murine hepatitis virus), and toxic models of demyelination (lysolecithin, ethidium bromide, and cuprizone). These are models in which the effector molecules for demyelination and remyelination have been most precisely evaluated.

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.

Extracellular S-nitrosoglutathione, but not S-nitrosocysteine or N(2)O(3), mediates protein S-nitrosation in rat spinal cord slices

There is evidence that protein S-nitrosothiols (PrSNOs) accumulate in inflammatory demyelinating disorders like multiple sclerosis and experimental allergic encephalomyelitis. However, very little is known regarding the mechanism by which PrSNOs are formed in target cells. The present study compares the ability of potential intercellular mediators of nitrosative damage including S-nitrosoglutathione (GSNO), S-nitrosocysteine and N(2)O(3) to induce protein S-nitros(yl)ation in the spinal cord, a CNS region that is commonly affected in multiple sclerosis and experimental allergic encephalomyelitis. The results clearly demonstrate that while all three NO-donors cause S-nitrosation of proteins in cell-free systems, only GSNO is a viable S-nitrosating agent in rat spinal cord slices. Generation of PrSNOs with GSNO occurs by S-transnitrosation as the process was not inhibited by either the NO-scavenger rutin or the N(2)O(3)-scavenger azide. Contrary to other cell types, nerve cells incorporate intact GSNO and neither functional l-amino acid transporters nor cell-surface thiols are required. We also found that there is a restricted number of proteins available for S-nitrosation, even at high, non-physiological concentrations of GSNO. These proteins are highly concentrated in mitochondria and mitochondria-rich subcellular compartments. This study is relevant to those CNS disorders characterized by excessive nitric oxide production.

Production of nitric oxide and self-nitration of proteins during monocyte differentiation to dendritic cells

Nitric oxide (NO) can stimulate dendritic cells to a more activated state. However, nitric oxide and peroxynitrites production by dendritic cells has been usually associated with pathological situations such as autoimmunity or inflammatory diseases. This study was designed to determine if dendritic cells obtained from healthy volunteers produce nitric oxide and peroxynitrites, which results in protein nitration. The expression of arginase II, but not arginase I, isoform was detected in monocytes and dendritic cells. There was higher inducible nitric oxide synthase (iNOS) protein expression and lower arginase activity both in immature and mature dendritic cells, compared to monocytes. This caused nitric oxide production, and maturation of dendritic cells which provoked a significative increase of nitrites and nitrates compared to immature dendritic cells. There was also peroxynitrites synthesis during monocyte differentiation as shown by the nitration of proteins. Immunoblot revealed a pattern of nitrated proteins in cell extracts obtained from monocytes and dendritic cells, however there were bands that appeared only in human dendritic cells, in particular an intense 90 kDa band. Nitric oxide production and nitrotyrosine formation could affect the antigen presentation and modify the immune response.

Nitric oxide, cell bioenergetics and neurodegeneration

Following stimulation of NMDA receptors, neurons transiently synthesize nitric oxide (NO) in a calcium/calmodulin-dependent manner through the activation of neuronal NO synthase. Nitric oxide acts as a messenger, activating soluble guanylyl cyclase and participating in the transduction signalling pathways involving cyclic GMP. Nitric oxide also binds to cytochrome c oxidase, and is able to inhibit cell respiration in a process that is reversible and in competition with oxygen. This action can also lead to the release of superoxide anion from the mitochondrial respiratory chain. Here, we discuss recent evidence that this mitochondrial interaction represents a molecular switch for cell signalling pathways involved in the control of physiological functions. These include superoxide- or oxygen-dependent modulation of gene transcription, calcium-dependent cell signalling responses, changes in the mitochondrial membrane potential or AMP-activated protein kinase-dependent control of glycolysis. In pathophysiological conditions, such as brain ischaemia or neurological disorders, NO is formed excessively by NMDA receptor over-activation in neurons, or by inducible NO synthase from neighbouring glia (microglial cells and astrocytes). Elevated NO concentrations can then interact with superoxide anion, generated by the mitochondria or by other mechanisms, leading to the formation of the powerful oxidant species peroxynitrite. During pathological conditions activation of the NAD(+)-consuming enzyme poly(APD-ribose) polymerase-1 (PARP-1) is also a likely mechanism for NO-mediated energy failure and neurotoxicity. Activation of PARP-1 is, however, a repair process, which in milder forms of oxidative stress protects neurons from death. Thus, whilst NO plays a physiological role in neuronal cell signalling, its over-production may cause neuronal energy compromise leading to neurodegeneration.

Nitric oxide and multiple sclerosis

Nitric oxide (NO) is a free radical signaling molecule with remarkably complex biochemistry. Its involvement in multiple sclerosis (MS) had been postulated soon after the discovery of the critical role NO plays in inflammation. However, the extent of NO's contribution to MS is not yet understood, party due to the often opposing roles that NO can play in cellular processes. This review briefly covers new developments in the area of NO that may be relevant to MS. It also describes recent progress in understanding the role of NO in MS, new potential targets of the action of NO in the cell, and prospects for NO-based therapies.

Evidence of Nitrosative Damage in the Brain White Matter of Patients with Multiple Sclerosis

Nitric oxide (NO) has been implicated in the pathophysiology of both experimental autoimmune encephalomyelitis and multiple sclerosis (MS). NO-mediated protein damage in MS appears to be confined to large plaques where 3-nitrotyrosine has been detected. To determine whether nitrosative damage takes place beyond visible MS plaques, the occurrence of various NO-triggered protein modifications in normal-appearing white matter (NAWM) of eight MS brains was assessed and compared to that in white matter (WM) of four control brains. As determined by amino acid analysis and western blotting, no evidence of tyrosine nitration was found in the MS samples studied, suggesting that they did not contain appreciable amounts of plaque-derived material. The amino acid composition of total myelin proteins and proteolipid protein (PLP) was also unaltered in the diseased tissue, as was the fatty acid composition of PLP. In addition, we detected no changes in the number of protein free thiols suggesting that oxidation do not occur to any appreciable extent. However, the levels of nitrite in MS-NAWM were higher than those in control WM, while in the MS-gray matter (GM) the concentration of this ion was unaltered. Furthermore, five of the MS samples analyzed, and the same as those with high levels of glial fibrilary acidic protein, showed increased amounts of protein nitrosothiols as determined by the "biotin switch" method. S-nitrosation of GM proteins was again normal. There was no indication of N-nitrosation of tryptophan and N-terminal amino groups in both control and MS tissue. Overall, the data suggests that WM, but not GM, from MS brains is subjected to considerable nitrosative stress. This is the first report to present direct evidence of increased protein S-nitrosation and nitrite content in the brain parenchyma of MS patients.

Antibodies directed against nitrosylated neoepitopes in sera of patients with human African trypanosomiasis

Antibodies directed against nitrosylated epitopes have been found in sera from patients suffering from human African trypanosomiasis (HAT) but not in sera from control subjects living in the same endemic area or African control subjects living in France. We conjugated amino acids to albumin by glutaraldehyde (conjugates) and then nitrosylated the conjugates. Both conjugates and nitrosylated conjugates were analysed by enzyme-linked immunosorbent assay (ELISA). We detected antibodies directed against nitrosylated L-cysteine and L-tyrosine conjugates; antibody levels were higher in stage II patients than in stage I. Patients with severe clinical signs had higher antibody levels, and antibody levels were highest in patients with major neurological signs. Antibody response was only associated with the IgM isotype. We evaluated antibody specificity and avidity by competition experiments using conjugates and nitrosylated conjugates. Avidity was around 2 x10(-6) m for the S-nitroso-cysteine epitope and 2 x 10(-8) m for the S-nitroso-tyrosine epitope. Detection of circulating antibodies to S-nitroso-cysteine and S-nitroso-tyrosine epitopes provides indirect evidence for nitric oxide (NO) involvement in HAT and their levels are correlated with disease severity.

Investigation of an inducible nitric oxide synthase gene (NOS2A) polymorphism in a multiple sclerosis population

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) affecting most commonly the Caucasian population. Nitric oxide (NO) is a biological signaling and effector molecule and is especially important during inflammation. Inducible nitric oxide synthase (iNOS) is one of the three enzymes responsible for generating NO. It has been reported that there is an excessive production of NO in MS concordant with an increased expression of iNOS in MS lesions. This study investigated the role of a bi-allelic tetranucleotide polymorphism located in the promoter region of the human iNOS (NOS2A) gene in MS susceptibility. A group of MS patients (n = 101) were genotyped and compared to an age- and sex-matched group of healthy controls (n = 101). The MS group was subdivided into three subtypes, namely relapsing-remitting MS (RR-MS), secondary-progressive MS (SP-MS) and primary-progressive MS (PP-MS). Results of a chi-squared analysis and a Fisher's exact test revealed that allele and genotype distributions between cases and controls were not significantly different for the total population (chi(2) = 3.4, P(genotype) = 0.15; chi(2) = 3.4, P(allele) = 0.082) and for each subtype of MS (P > 0.05). This suggests that there is no direct association of this iNOS gene variant with MS susceptibility.

Investigation of a neuronal nitric oxide synthase gene (NOS1) polymorphism in a multiple sclerosis population

Multiple Sclerosis (MS) is a chronic neurological disease characterized by demyelination associated with infiltrating white blood cells in the central nervous system (CNS). Nitric oxide synthases (NOS) are a family of enzymes that control the production of nitric oxide. It is possible that neuronal NOS could be involved in MS pathophysiology and hence the nNOS gene is a potential candidate for involvement in disease susceptibility. The aim of this study was to determine whether allelic variation at the nNOS gene locus is associated with MS in an Australian cohort. DNA samples obtained from a Caucasian Australian population affected with MS and an unaffected control population, matched for gender, age and ethnicity, were genotyped for a microsatellite polymorphism in the promoter region of the nNOS gene. Allele frequencies were compared using chi-squared based statistical analyses with significance tested by Monte Carlo simulation. Allelic analysis of MS cases and controls produced a chi-squared value of 5.63 with simulated P = 0.96 (OR(max) = 1.41, 95% CI: 0.926-2.15). Similarly, a Mann-Whitney U analysis gave a non-significant P-value of 0.377 for allele distribution. No differences in allele frequencies were observed for gender or clinical course subtype (P > 0.05). Statistical analysis indicated that there is no association of this nNOS variant and MS and hence the gene does not appear to play a genetically significant role in disease susceptibility.

Circulating antibodies directed against nitrosylated antigens in trypanosome-infected mice

Nitric oxide has been implicated as an effector cytotoxic molecule in trypanosomiasis. In this work, we investigated the presence of circulating antibodies directed against nitrosylated epitopes as biological indicators for nitric oxide (NO) production in the sera of trypanosome-infected mice. We tested these sera with synthetic antigens, such as S-nitrosated protein or nitrosylated conjugates of amino acids that possess a high affinity to NO, by an immunoenzymatic assay. We detected antibodies directed against nitroso epitopes in the sera of infected mice, as compared to non-infected control mice. The antibody response was linked to the IgM isotype. Our results indicate the production of NO and its derivatives in trypanosomiasis. This production may potentially induce the synthesis of nitroso epitopes in vivo and favor the development of a humoral immune response.

Interleukin-12 induces mild experimental allergic encephalomyelitis following local central nervous system injury in the Lewis rat

The major pathological feature in the central nervous system (CNS) following traumatic brain injury is activation of microglia both around and distant from the injury site. Intraperitoneal administration of interleukin-12 (IL-12) after brain injury resulted in a 7% weight loss, clinical signs of mild EAE and significant myelin basic protein (MBP)-specific splenic cell proliferation. The extent of pathology, in terms of the number of inflammatory perivascular cuffs and activation of microglia was greatest if IL-12 was administered immediately compared to a week following brain injury, whether at one or two sites. Specifically immunostaining for MHC class II and iNOS on macrophages and microglia, ICAM-1 on endothelial cells and macrophages was observed around the site of injury. A degree of myelin processing was apparent from immunostaining of MBP in inflammatory cells distant from the lesion. Inflammatory cuffs comprising macrophages, activated microglia, CD4(+) T cells and iNOS(+) cells were also detected distant to the injury site in the medulla and spinal cord of animals treated with IL-12. These results suggest that immune-mediated events in which IL-12 production is stimulated as for example viral infection, superimposed on a brain injury, could provide a trigger for a MS-like pathology.

Role of S-nitrosation of cysteine residues in long-lasting inhibitory effect of nitric oxide on arterial tone

S-Nitrosation of cysteine residues plays an important role in nitric oxide (NO) signaling and transport. The aim of the present study was to investigate the role of S-nitrosothiols as a storage form of NO, which may account for the long-lasting effects in the vasculature. Rat aorta exposed to S-nitrosoglutathione (GSNO) displayed, even after washout of the drug, a persistent increase in cysteine-NO residues (detected by immunostaining using an antiserum that selectively recognized S-nitrosoproteins) and in NO content (detected by NO spin-trapping), a persistent attenuation of the effect of vasoconstrictors, and a relaxant response upon addition of low molecular weight (LMW) thiols. Rat mesenteric and porcine coronary artery exposed in vitro to GSNO, as well as aorta and mesenteric arteries removed from rats treated in vivo with GSNO, displayed similar modifications of contraction. In isolated aorta exposed to GSNO, the decrease of the contractile response and the relaxant effect of LMW thiols were both blunted by NO scavengers (oxyhemoglobin or 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) or by a cyclic GMP-dependent protein kinase inhibitor (Rp-8-bromoguanosine-3',5'-cyclic monophosphorothioate). In these arteries, mercuric chloride (which cleaves the cysteine-NO bond) exerted a transient relaxation, completely abolished the one of LMW thiols, and blunted the increase in cysteine-NO residues and NO content. Together, these data support the idea that S-nitrosation of cysteine residues is involved in long-lasting effects of NO on arterial tone. They suggest that S-nitrosation of tissue thiols is a mechanism of formation of local NO stores from which biologically active NO can subsequently be released.

S-nitrosylation in health and disease

S-nitrosylation is a ubiquitous redox-related modification of cysteine thiol by nitric oxide (NO), which transduces NO bioactivity. Accumulating evidence suggests that the products of S-nitrosylation, S-nitrosothiols (SNOs), play key roles in human health and disease. In this review, we focus on the reaction mechanisms underlying the biological responses mediated by SNOs. We emphasize reactions that can be identified with complex (patho)physiological responses, and that best rationalize the observed increase or decrease in specific classes of SNOs across a spectrum of disease states. Thus, changes in the levels of various SNOs depend on specific defects in both enzymatic and non-enzymatic mechanisms of nitrosothiol formation, processing and degradation. An understanding of these mechanisms is crucial for the development of an integrated model of NO biology, and for effective treatment of diseases associated with dysregulation of NO homeostasis.

Serum nitric oxide metabolites in patients with multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system characterized by myelin breakdown. The free radical nitric oxide (NO), which is considered to be a major metabolite in immune function and in autoimmune disorders, is among the possible mediators causing the inflammatory reactions in MS. Consequently, NO has been implicated in the pathogenesis of MS and its animal model experimental allergic encephalomyelitis (EAE). In this study, stable metabolites of NO (NO(2-)+NO(3-)) levels were determined in sera of MS patients (n=23) and control subjects (n=16). NO(2-)+NO(3-) levels were higher in MS patients when compared to control subjects. However, there was not any correlation with serum NO(2-)+NO(3-) values and clinical features of the disease such as duration of sickness, the time elapsed from the last attack and EDSS values. Our results imply that nitric oxide may be involved in the pathogenesis of MS although further studies are required to elucidate underlying mechanisms.

The role of nitric oxide in multiple sclerosis

Nitric oxide (NO) is a free radical found at higher than normal concentrations within inflammatory multiple sclerosis (MS) lesions. These high concentrations are due to the appearance of the inducible form of nitric oxide synthase (iNOS) in cells such as macrophages and astrocytes. Indeed, the concentrations of markers of NO production (eg, nitrate and nitrite) are raised in the CSF, blood, and urine of patients with MS. Circumstantial evidence suggests that NO has a role in several features of the disease, including disruption of the blood-brain barrier, oligodendrocyte injury and demyelination, axonal degeneration, and that it contributes to the loss of function by impairment of axonal conduction. However, despite these considerations, the net effect of NO production in MS is not necessarily deleterious because it also has several beneficial immunomodulatory effects. These dual effects may help to explain why iNOS inhibition has not provided reliable and encouraging results in animal models of MS, but alternative approaches based on the inhibition of superoxide production, partial sodium-channel blockade, or the replacement of lost immunomodulatory function, may prove beneficial.

Anti-S-nitrosocysteine antibodies are a predictive marker for demyelination in experimental autoimmune encephalomyelitis: implications for multiple sclerosis

Multiple sclerosis (MS) is characterized by inflammation within the CNS. This inflammatory response is associated with production of nitric oxide (NO) and NO-related species that nitrosylate thiols. We postulated that MS patients would exhibit an antibody (Ab) response directed against proteins containing S-nitrosocysteine (SNO-cysteine) and showed that anti-NO-cysteine Abs of the IgM isotype are in fact present in the sera of some MS patients (Boullerne et al., 1995). We report here the presence of a seemingly identical Ab response directed against SNO-cysteine in an acute model of MS, experimental autoimmune encephalomyelitis (EAE) induced in Lewis rats with the 68-84 peptide of guinea pig myelin basic protein (MBP(68-84)). Serum levels of anti-SNO-cysteine Abs peaked 1 week before the onset of clinical signs and well before the appearance of anti-MBP(68-84) Abs. The anti-SNO-cysteine Ab peak titer correlated with the extent of subsequent CNS demyelination, suggesting a link between Ab level and CNS lesion formation. In relapsing-remitting MS patients, we found elevated anti-SNO-cysteine Ab at times of relapse and normal values in most patients judged to be in remission. Two-thirds of patients with secondary progressive MS had elevated anti-SNO-cysteine Ab levels, including those receiving interferon beta-1b. The data show that a rise in circulating anti-SNO-cysteine Ab levels precedes onset of EAE. Anti-SNO-cysteine Abs are also elevated at times of MS attacks and in progressive disease, suggesting a possible role for these Abs, measurable in blood, as a biological marker for clinical activity.

In vivo damage of CNS myelin and axons induced by peroxynitrite

In multiple sclerosis (MS) the mechanisms of injury caused by peroxynitrite remain uncertain. To study histological, ultra structural and molecular alterations caused by peroxynitrite in brain, the peroxynitrite donor 3-morpholinosydnonimine was injected in rat corpus callosum. Peroxynitrite induces strong primary axonal damage with characteristics of primary acute axonopathy, together with severe myelin alteration, myelin vacuolation and demyelination, and nitrotyrosine formation as confirmed by detection of nitrosated target proteins. Administration of the peroxynitrite scavenger uric acid inhibited these effects. In vivo, peroxynitrite leads to a disorganisation of myelin and to axonal damage presenting some similarities to the formation of MS lesions. Understanding the action of peroxynitrite in this process will open new therapeutic strategies by specific inhibition of peroxynitrite formation and action.

Myelin/axonal pathology in interleukin-12 induced serial relapses of experimental allergic encephalomyelitis in the Lewis rat

Lewis rats, on recovery from monophasic clinical experimental allergic encephalomyelitis (EAE), can be induced to develop repeated paralytic relapses with a graded reduction in clinical severity following intraperitoneal administration of IL-12. By the time of the third relapse, the number and size of inflammatory cuffs in the spinal cord were reduced with the makeup of the cellular infiltrate shifting to a significantly increased number of B cells. Serum levels of myelin basic protein (MBP)-specific IgG1 and IgG2b were found to rise over time while MBP and MBP peptide-positive macrophages and microglia became evident in perivascular cuffs and in spinal cord parenchyma, indicative of myelin phagocytosis. Axonal death was observed in semithin and EM sections of spinal cord in third relapse animals in association with iNOS and tPA immunostaining throughout gray and white matter. These neurotoxic or excitotoxic agents may contribute to axonal damage directly or indirectly by activated microglia and macrophages, leading to limited damage of the axonal-myelin unit.

Role of calcium in nitric oxide-induced cytotoxicity: EGTA protects mouse oligodendrocytes

Active nitrogen species are overproduced in inflammatory brain lesions in multiple sclerosis (MS) and experimental allergic encephalomyelitis (EAE). NO has been shown to mediate the death of oligodendrocytes (OLs), a primary target of damage in MS. To develop strategies to protect OLs, we examined the mechanisms of cytotoxicity of two NO donors, S-nitroso-N-acetyl-penicillamine (SNAP) and sodium nitroprusside (SNP) on mature mouse OLs. Nitrosonium ion (NO+) rather than NO. mediates damage with both SNAP and SNP, as shown by significant protection with hemoglobin (HbO2), but not with the NO. scavenger PTIO. SNAP and SNP differ in time course and mechanisms of killing OLs. With SNAP, OL death is delayed for at least 6 hr, but with SNP, OL death is continuous over 18 hr with no delay. Relative to NO release, SNP is more toxic than SNAP, due to synergism of NO with cyanide released by SNP. SNAP elicits a Ca2+ influx in over half of the OLs within min. Further, OL death due to NO release from SNAP is Ca2+-dependent, because the Ca2+ chelator EGTA protects OLs from killing by SNAP, and also from killing by the NONOates NOC-9 and NOC-18, which spontaneously release NO. SNP does not elicit a Ca2+ influx, and EGTA is not protective. In comparison to the N20.1 OL cell line (Boullerne et al., [1999] J. Neurochem. 72:1050-1060), mature OLs are (1) more sensitive to SNAP, (2) much more resistant to SNP, (3) sensitive to cyanide, but not iron, and (4) exhibit a Ca2+ influx and EGTA protection in response to NO generated by SNAP.