Synergism of nitric oxide and iron in killing the transformed murine oligodendrocyte cell line N20.1

An early glycolysis burst in microglia regulates mitochondrial dysfunction in oligodendrocytes under neuroinflammation

Metabolism and energy processes governing oligodendrocyte function during neuroinflammatory disease are of great interest. However, how varied cellular environments affect oligodendrocyte activity during neuroinflammation is unknown. We demonstrate that activated microglial energy metabolism controls oligodendrocyte mitochondrial respiration and activity. Lipopolysaccharide/interferon gamma promote glycolysis and decrease mitochondrial respiration and myelin protein synthesis in rat brain glial cells. Enriched microglia showed an early burst in glycolysis. In microglia-conditioned medium, oligodendrocytes did not respire and expressed less myelin. SCENITH revealed metabolic derangement in microglia and O4-positive oligodendrocytes in endotoxemia and experimental autoimmune encephalitogenic models. The early burst of glycolysis in microglia was mediated by PDPK1 and protein kinase B/AKT signaling. We found that microglia-produced NO and itaconate, a tricarboxylic acid bifurcated metabolite, reduced mitochondrial respiration in oligodendrocytes. During inflammation, we discovered a signaling pathway in microglia that could be used as a therapeutic target to restore mitochondrial function in oligodendrocytes and induce remyelination.

The Roles of Orphan G Protein-Coupled Receptors in Autoimmune Diseases

G protein-coupled receptors (GPCRs) constitute the largest family of plasma membrane receptors in nature and mediate the effects of a variety of extracellular signals, such as hormone, neurotransmitter, odor, and light signals. Due to their involvement in a broad range of physiological and pathological processes and their accessibility, GPCRs are widely used as pharmacological targets of treatment. Orphan G protein-coupled receptors (oGPCRs) are GPCRs for which no natural ligands have been found, and they not only play important roles in various physiological functions, such as sensory perception, reproduction, development, growth, metabolism, and responsiveness, but are also closely related to many major diseases, such as central nervous system (CNS) diseases, metabolic diseases, and cancer. Recently, many studies have reported that oGPCRs play increasingly important roles as key factors in the occurrence and progression of autoimmune diseases. Therefore, oGPCRs are likely to become potential therapeutic targets and may provide a breakthrough in the study of autoimmune diseases. In this article, we focus on reviewing the recent research progress and clinical treatment effects of oGPCRs in three common autoimmune diseases: multiple sclerosis (MS), rheumatoid arthritis (RA), and systemic lupus erythematosus (SLE), shedding light on novel strategies for treatments.

Total Chemical Syntheses of the GM3 and F-GM3 Ganglioside Epitopes and Comparative Pre-Clinical Evaluation for Non-Invasive Imaging of Oligodendrocyte Differentiation

Gangliosides are intimately involved in a plenum of (neuro)inflammatory processes, yet progress in establishing structure-function interplay is frequently hindered by the availability of well-defined glycostructures. Motivated by the ubiquity of the ganglioside GM₃ in chemical neurology, and in particular by its conspicuous presence in myelin, the GM₃ epitope was examined with a view to preclinical validation as a tracer. The suitability of this scaffold for the noninvasive imaging of oligodendrocyte differentiation in Multiple sclerosis is disclosed. The stereocontrolled synthesis of a site-selectively fluorinated analogue (F-GM₃) is also disclosed to enable a comparative analysis in oligodendrocyte (OL) differentiation. Whereas the native epitope caused a decrease in the viability in a dose-dependent manner, the addition of distinct F-GM₃ concentrations over 48 h had no impact on the OL viability. This is likely a consequence of the enhanced hydrolytic stability imparted by the fluorination and highlights the potential of fluorinated glycostructures in the field of molecular imaging. Given the predominant expression of GM₃ in oligodendrocytes and the capacity of GM₃ to interact with myelin-associated proteins, this preclinical evaluation has revealed F-GM₃ to be an intriguing candidate for neurological imaging.

Photosensitivity of Aqueous Sodium Nitroprusside Solutions: Nitric Oxide Release versus Cyanide Toxicity

Photolysis of the pentacyanonitrosylferrate (II) ion in sodium nitroprusside (SNP) solutions involves a competition between photosubstitution and photo-oxidation reactions, where the nitrosyl and cyanide ligands can be released as free nitric oxide (NO) or NO+ and free CN- or CN radical. We have irradiated aqueous SNP solutions at several narrow wavelength ranges in the UV/Vis region (314–576 nm), with the aim of investigating the photolability of the CN and NO ligands. Kinetics of photolysis were used to characterize the photosensitivity of SNP solutions in the range 314–576 nm. Spectral changes in the UV/Vis and IR regions upon irradiation and assays for the detection of free CN- and NO, provided additional evidences for the absence of photoprocesses leading to the release of CN- with λirr > 480 nm. In this condition, the main photoproducts were found to be the [FeIII(CN)5(H2O)]2- ion and NO, formed in a intramolecular photo-oxidative process. Irradiation with unfiltered UV/Vis light and with λirr < 480 nm, lead to the release of both CN- and NO and to a mixture of ferrocyanide and ferricyanide products. These results confirm that the exposure of SNP solutions to UV/Vis light below λirr = 480 nm can lead to cyanide poisoning and further support that above this wavelength limit, a selective NO release from SNP can be achieved, with possible implications for its biochemical action.

Peroxynitrite dominates sodium nitroprusside-induced apoptosis in human hepatocellular carcinoma cells

This study aims to explore which radicals dominate sodium nitroprusside (SNP)-induced cytotoxicity in human hepatocellular carcinoma (HCC) cells (HepG2 and Hep3B). Exposure of SNP to cell medium produced abundant nitric oxide (NO), superoxide anion (O₂^·−), hydrogen peroxide (H₂O₂) and iron ions. SNP potently induced caspases activation, mitochondrial membrane permeabilization and apoptosis in HCC cells. In Hep3B cells, pretreatment with NO scavenger (PTIO) did not prevent SNP-induced cytotoxicity. However, in HepG2 cells, SNP-induced cytotoxicity was prevented significantly by pretreatment with PTIO and O₂^·− scavenger, and especially was almost completely blocked by pretreatment with FeTPPS (peroxynitrite scavenger). In contrast, although H₂O₂ scavenger potently scavenged SNP-induced H₂O₂ production, it did not prevent SNP-induced cytotoxicity in HepG2 cells. In addition, pretreatment with DFO (iron ions chelator) and iron-saturated DFO respectively completely prevented SNP-induced cytotoxicity in HepG2 cells. Collectively, peroxynitrite from the reaction between NO and O₂^·− elicited from SNP dominates the SNP-induced apoptosis of HepG2 cells, in which both iron ions and H₂O₂ are not involved.

Effect of nitric oxide to axonal degeneration in multiple sclerosis via downregulating monocarboxylate transporter 1 in oligodendrocytes

Multiple sclerosis (MS) is a neurodegenerative disease of the central nervous system (CNS). Axonal degeneration, one of the main pathological characteristics of MS, is affected by nitric oxide (NO). In turn, NO induces mitochondrial dysfunction of neurons and glial cells. Inadequate glucose causes monocarboxylate transporter 1 (MCT1) to transfer lactate from oligodendrocytes (OLs) to neurons, which decreases MCT1 and results in energy substrate deficit (mainly lactate) in axons. The condition gradually leads to axonal degeneration. This study proposes that NO-induced MCT1 down-regulation in OLs may be involved in the pathological process of axonal degeneration, which eventually leads to MS.

Dominant roles of Fenton reaction in sodium nitroprusside-induced chondrocyte apoptosis

Sodium nitroprusside (SNP) has been widely used as an exogenous nitric oxide (NO) donor to explore the molecular mechanism of NO-mediated chondrocyte apoptosis during the latest two decades. We have recently found that NO-independent ROS play a key role in SNP-induced apoptosis in rabbit chondrocytes. This study aims to investigate what kind of ROS and how the reliable ROS mediators mediate the SNP-induced apoptosis. Data shows that SNP and NO-exhausted SNP (SNPex) induced ROS production or cytotoxicity to identically degree. SNP induced a marked increase in iron ions, superoxide anion (O2(•-)), hydrogen peroxide (H2O2) and hydroxyl radical ((•)OH) level. H2O2 scavenger (CAT) and (•)OH scavenger (DMSO) significantly inhibited SNP-induced chondrocyte apoptosis. Iron ions chelator (DFO) entirely prevented SNP-induced chondrocyte apoptosis. In contrast, O2(•-) scavenger (SOD) and glutathione depletion agent (BSO) promoted SNP-induced cytotoxicity. K3[Fe(CN)6] exhibited no cytotoxicity, and H2O2 alone up to 250µM or iron ions alone up to 90µM is non-cytotoxic to chondrocytes. Combination of 25µM FeSO4 and 100µM H2O2 in the presence of BSO induced chondrocyte death similar to SNP treatment. Fetal bovine serum (FBS) enhanced iron ions release from SNP and the cytotoxicity of SNP. Our data shows that the extracellular Fenton reaction between iron ions released from SNP and H2O2 induced by SNP plays a key role in SNP-induced chondrocyte apoptosis. Overall, our results indicate that the potential of SNP to increase iron ions and ROS should be especially considered for some biological functions and, possibly, also for clinical applications of this drug.

Bio-accumulation of some heavy metals in blood serum of residents in Isfahan and Shiraz, Iran

In this study, some heavy metal (Cd, Pb, Ni, Fe, Co, Cr, Mn, Cu, and Zn) concentrations were measured in the blood serum samples of 25 patients who suffered from the multiple sclerosis (MS) disease living in two industrial regions of Isfahan, Iran, using inductively coupled plasma (ICP) instrument. Also, blood serum levels of heavy metals in 25 healthy people of Isfahan and 25 healthy people of Shiraz were analyzed as controls. In industrial regions, some of the heavy metals were also measured in the soils and food crop samples (wheat, rice, and onion). The results showed that the blood serum levels of Cd, Co, Ni, and Pb of MS patients (0.032, 0.56, 1.60, and 2.90 μg L(-1), respectively) were significantly higher than those of healthy people. These values exceeded the permissible ranges that are 0.08-0.50, 0.14-1.0, and 0.80-2.50 μg L(-1) for the Co, Ni, and Pb, respectively. The mean concentrations of Fe and Zn in the blood serum of MS patients (529 and 547 μg L(-1)) were significantly lower than those in the healthy people and also less than the acceptable ranges (700-1700 and 660-1100 μg L(-1), respectively). The target hazard quotients of Pb (2.23) and Cd (1.25) via wheat and Pb (1.34) via rice consumption were higher than one. Therefore, it is proposed that consumption of local contaminated food crops may have drastically increased the concentrations of heavy metals in the human blood serum of inhabitants of industrial regions.

OGR1/GPR68 Modulates the Severity of Experimental Autoimmune Encephalomyelitis and Regulates Nitric Oxide Production by Macrophages

Ovarian cancer G protein-coupled receptor 1 (OGR1) is a proton-sensing molecule that can detect decreases in extracellular pH that occur during inflammation. Although OGR1 has been shown to have pro-inflammatory functions in various diseases, its role in autoimmunity has not been examined. We therefore sought to determine whether OGR1 has a role in the development of T cell autoimmunity by contrasting the development of experimental autoimmune encephalomyelitis between wild type and OGR1-knockout mice. OGR1-knockout mice showed a drastically attenuated clinical course of disease that was associated with a profound reduction in the expansion of myelin oligodendrocyte glycoprotein 35-55-reactive T helper 1 (Th1) and Th17 cells in the periphery and a reduced accumulation of Th1 and Th17 effectors in the central nervous system. We determined that these impaired T cell responses in OGR1-knockout mice associated with a reduced frequency and number of dendritic cells in draining lymph nodes during EAE and a higher production of nitric oxide by macrophages. Our studies suggest that OGR1 plays a key role in regulating T cell responses during autoimmunity.

Oxidative stress and neurodegenerative disorders

Living cells continually generate reactive oxygen species (ROS) through the respiratory chain during energetic metabolism. ROS at low or moderate concentration can play important physiological roles. However, an excessive amount of ROS under oxidative stress would be extremely deleterious. The central nervous system (CNS) is particularly vulnerable to oxidative stress due to its high oxygen consumption, weakly antioxidative systems and the terminal-differentiation characteristic of neurons. Thus, oxidative stress elicits various neurodegenerative diseases. In addition, chemotherapy could result in severe side effects on the CNS and peripheral nervous system (PNS) of cancer patients, and a growing body of evidence demonstrates the involvement of ROS in drug-induced neurotoxicities as well. Therefore, development of antioxidants as neuroprotective drugs is a potentially beneficial strategy for clinical therapy. In this review, we summarize the source, balance maintenance and physiologic functions of ROS, oxidative stress and its toxic mechanisms underlying a number of neurodegenerative diseases, and the possible involvement of ROS in chemotherapy-induced toxicity to the CNS and PNS. We ultimately assess the value for antioxidants as neuroprotective drugs and provide our comments on the unmet needs.

Down-regulation of Myelin Gene Expression in Human Oligodendrocytes by Nitric Oxide: Implications for Demyelination in Multiple Sclerosis

Multiple sclerosis (MS) is a chronic autoimmune demyelinating disorder of the central nervous system (CNS) with unknown etiology. Several studies have shown that demyelination in MS is caused by proinflammatory mediators and nitric oxide (NO), which is released by perivascular infiltrates and/or activated glial cells. Both endogenous NO released by microglia and astrocytes; and NO generated from exogenous NO donors are known to induce oligodendrocytes death. However, the molecular mechanism of oligodendroglial death is poorly understood. Here we explore the role of NO in modulating the expression of myelin-specific genes that leads to oligodendroglial death. We investigated the effect of NO on the expression of myelin basic protein (MBP), 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase), myelin oligodendrocyte glycoprotein (MOG), and proteolipid protein (PLP) in human primary oligodendrocytes. Combination of IFN-γ and bacterial lipopolysaccharide (LPS) or double stranded RNA in the form of polyIC induced the production of NO and decreased the expression of myelin gene in human fetal mixed glial cultures. Either a scavenger of NO (PTIO) or an inhibitor of inducible nitric oxide synthase (L-NIL) abrogated (LPS+IFN-γ)- and polyIC-mediated suppression of myelin genes in human mixed glial cells. The role of NO was further corroborated by the inhibition of myelin gene expression in purified human oligodendroglia by several NO donors including SNP, NOC-7, SIN-1, and SNAP. This study illustrates a novel biological role of NO in down-regulating the expression of myelin genes preceding the death of oligodendrocytes.

The nitric oxide donor sodium nitroprusside requires the 18 kDa Translocator Protein to induce cell death

Various studies have shown that several lethal agents induce cell death via the mitochondrial 18 kDa Translocator Protein (TSPO). In this study we tested the possibility that nitric oxide (NO) is the signaling component inducing the TSPO to initiate cell death process. Cell viability assays included Trypan blue uptake, propidium iodide uptake, lactate dehydrogenase release, and DNA fragmentation. These assays showed that application of the specific TSPO ligand PK 11195 reduced these parameters for the lethal effects of the NO donor sodium nitroprusside (SNP) by 41, 27, 40, and 42 %, respectively. TSPO silencing by siRNA also reduced the measured lethal effects of SNP by 50 % for all of these four assays. With 2,3-bis[2-methoxy-4-nitro-5-sulphophenyl]-2H-tetrazolium-5-carboxyanilide (XTT) changes in metabolic activity were detected. PK 11195 and TSPO knockdown fully prevented the reductions in XTT signal otherwise induced by SNP. Collapse of the mitochondrial membrane potential was studied with the aid of JC-1 (5,5',6,6'-tetrachloro-1,1',3,3'-tetraethyl-benzimidazolylcarbocyanine chloride). PK 11195 and TSPO knockdown reduced, respectively by 36 and 100 %, the incidence of collapse of the mitochondrial membrane potential otherwise induced by SNP. 10-N-Nonyl-Acridine Orange (NAO) was used to detect mitochondrial reactive oxygen species generation due to SNP. PK 11195 and TSPO knockdown reduced this effect of SNP by 65 and 100 %, respectively. SNP did not affect TSPO protein expression and binding characteristics, and also did not cause TSPO S-nitrosylation. However, β-actin and various other proteins (not further defined) were S-nitrosylated. In conclusion, TSPO is required for the lethal and metabolic effects of the NO donor SNP, but TSPO itself is not S-nitrosylated.

Ferritin stimulates oligodendrocyte genesis in the adult spinal cord and can be transferred from macrophages to NG2 cells in vivo

Injured CNS tissue often contains elevated iron and its storage protein ferritin, which may exacerbate tissue damage through pro-oxidative mechanisms. Therefore, therapeutic studies often target iron reduction as a neuroprotective strategy. However, iron may be crucial for oligodendrocyte replacement and remyelination. For instance, we previously showed that intraspinal toll-like receptor 4 macrophage activation induced the generation of new ferritin-positive oligodendrocytes, and that iron chelation significantly reduced this oligodendrogenic response. Since macrophages can secrete ferritin, we hypothesize that ferritin is a macrophage-derived signal that promotes oligodendrogenesis. To test this, we microinjected ferritin into intact adult rat spinal cords. Within 6 h, NG2+ progenitor cells proliferated and accumulated ferritin. By 3 d, many of these cells had differentiated into new oligodendrocytes. However, acute neuron and oligodendrocyte toxicity occurred in gray matter. Interestingly, ferritin-positive NG2 cells and macrophages accumulated in the area of cell loss, revealing that NG2 cells thrive in an environment that is toxic to other CNS cells. To test whether ferritin can be transferred from macrophages to NG2 cells in vivo, we loaded macrophages with fluorescent ferritin then transplanted them into intact spinal white matter. Within 3-6 d, proliferating NG2 cells migrated into the macrophage transplants and accumulated fluorescently labeled ferritin. These results show that activated macrophages can be an in vivo source of ferritin for NG2 cells, which induces their proliferation and differentiation into new oligodendrocytes. This work has relevance for conditions in which iron-mediated injury and/or repair likely occur, such as hemorrhage, stroke, spinal cord injury, aging, Parkinson's disease, and Alzheimer's disease.

Glial cell lines: an overview

The importance and essential functions of glial cells in the nervous system are now beginning to be understood and appreciated. Glial cell lines have been instrumental in the elucidation of many of these properties. In this Overview, the origin and properties of most of the existing cell lines for the major glial types: oligodendroglia, astroglia, microglia and Schwann cells, are documented. Particular emphasis is given to the culture conditions for each cell line and the degree to which the line can differentiate in vitro and in vivo. The major molecular markers for each glial cell lines are indicated. Finally, methods by which the glial cell lines have been developed are noted and the future directions of glial cell line research are discussed.

Nitric oxide functions as a signal and acts upstream of AtCaM3 in thermotolerance in Arabidopsis seedlings

To characterize the role of nitric oxide (NO) in the tolerance of Arabidopsis (Arabidopsis thaliana) to heat shock (HS), we investigated the effects of heat on three types of Arabidopsis seedlings: wild type, noa1(rif1) (for nitric oxide associated1/resistant to inhibition by fosmidomycin1) and nia1nia2 (for nitrate reductase [NR]-defective double mutant), which both exhibit reduced endogenous NO levels, and a rescued line of noa1(rif1). After HS treatment, the survival ratios of the mutant seedlings were lower than those of wild type; however, they were partially restored in the rescued line. Treatment of the seedlings with sodium nitroprusside or S-nitroso-N-acetylpenicillamine revealed that internal NO affects heat sensitivity in a concentration-dependent manner. Calmodulin 3 (CaM3) is a key component of HS signaling in Arabidopsis. Real-time reverse transcription-polymerase chain reaction analysis after HS treatment revealed that the AtCaM3 mRNA level was regulated by the internal NO level. Sodium nitroprusside enhanced the survival of the wild-type and noa1(rif1) seedlings; however, no obvious effects were observed for cam3 single or cam3noa1(rif1) double mutant seedlings, suggesting that AtCaM3 is involved in NO signal transduction as a downstream factor. This point was verified by phenotypic analysis and thermotolerance testing using seedlings of three AtCaM3-overexpressing transgenic lines in an noa1(rif1) background. Electrophoretic mobility-shift and western-blot analyses demonstrated that after HS treatment, NO stimulated the DNA-binding activity of HS transcription factors and the accumulation of heat shock protein 18.2 (HSP18.2) through AtCaM3. These data indicate that NO functions in signaling and acts upstream of AtCaM3 in thermotolerance, which is dependent on increased HS transcription factor DNA-binding activity and HSP accumulation.

H(2)O(2) preferentially synergizes with nitroprusside to induce apoptosis associated with superoxide dismutase dysregulation in human melanoma irrespective of p53 status: Antagonism by o-phenanthroline

The pro-oxidant hydrogen peroxide (H(2)O(2)) is converted to a reactive oxygen species by transition metals like iron. Since mutations in the p53 tumor suppressor gene contribute to drug resistance, we used genetically-matched human C8161 melanoma harbouring wt or DN-R175H mutant p53, to investigate the influence of p53 status on the potentiation of H(2)O(2) toxicity by: (a) intact sodium nitroprusside or nitroferricyanide (SNP), (b) its light-exhausted NO-depleted form (lex-SNP), (c) potassium ferricyanide, or (d) ferric ammonium sulphate. Whereas single treatments with SNP or H(2)O(2) were partly cytotoxic, preferentially potentiation of H(2)O(2) toxicity was evidenced with intact or lex-SNP. No comparable increase of H(2)O(2) toxicity was induced by ferricyanide, ferric ammonium sulphate or S-nitroso-N-acetyl penicillamine (SNAP), a known NO donor lacking iron. Immune blotting revealed apoptosis-associated PARP cleavage induced by [SNP+H(2)O(2)] irrespective of p53 status. This correlated with an eightfold induction of [Mn-SOD; SOD2] in wt p53 melanoma cells, and with a super-induction of the same enzyme reciprocal with loss of [Cu,Zn-SOD; SOD1], in mutant p53 cells. All these changes were antagonized by the anti-oxidant N-acetylcysteine or the iron chelator o-phenanthroline. We hypothesize that superoxide dismutase imbalance and iron-dependent redox changes involving OH species generated from a Fenton reaction between [SNP+H(2)O(2)], may be important in this anti-tumor activity. Although tumor drug resistance is frequently associated with DN-p53 mutations, our data shows for the first time the preferential ability of SNP to enhance H(2)O(2) toxicity, irrespective of p53 status.

Reactive oxygen species mediate p53 activation and apoptosis induced by sodium nitroprusside in SH-SY5Y cells

Sodium nitroprusside (SNP) is a water-soluble iron nitrosyl complex clinically used as a powerful vasodilator for treatment of hypertension; and, in basic research, it has been used to mainly investigate the cytotoxic effects of nitrosative stress. Although NO is considered a pharmacologically active molecule, not all of the biological effects of SNP are dependent on its NO moiety. To elucidate the molecular executioner(s) responsible for SNP cytotoxicity, this study determines the involvement of oxidative stress in p53 activation and apoptotic induction elicited by SNP in SH-SY5Y neuroblastoma cells. We demonstrate that proapoptotic activity of SNP is independent of NO production, because SNP and its 2-day light-exhausted compound SNP(ex) trigger apoptosis to the same extent. We provide evidence for the occurrence of oxidative stress and oxidative damage during both SNP and SNP(ex) exposure and demonstrate that iron-derived reactive oxygen species (ROS) are the genuine mediators of their cytotoxicity. We show that p53 is equally activated upon both SNP and SNP(ex) treatments. Moreover, as demonstrated by small interfering RNA experiments, we indicate its primary role in the induction of apoptosis, suggesting the ineffectiveness of NO in its engagement. The attenuation of p53 levels, obtained by oxy-radical scavengers, is consistent with the recovery of cell viability and ROS decrease, demonstrate that SNP-mediated p53 activation is an event triggered by ROS and/or ROS-mediated damages. Together, our results suggest that investigations of the physiopathological effects of SNP should consider the role of ROS, other than NO, particularly in some conditions such as apoptotic induction and p53 activation.

Deficient peroxide detoxification underlies the susceptibility of oligodendrocyte progenitors to dopamine toxicity

Oligodendrocyte progenitors are highly susceptible to oxidative stress due to their limited content of antioxidants and high iron levels. We previously showed that iron plays a central role in the toxicity of dopamine (DA) to oligodendrocyte progenitors. Here, we further explore the mechanisms involved in DA toxicity, specifically the role of superoxide and the glutathione system. DA induces accumulation of superoxide, membrane damage and loss in cell viability. An iron chelator, deferoxamine, reduces superoxide accumulation. However, a superoxide dismutase mimetic, MnTBAP, potentiates DA toxicity, suggesting that superoxide plays an indirect role in toxicity through dismutation to H2O2. In addition, the glutathione (GSH) analog (GME), blocks DA-induced superoxide accumulation, heme-oxygenase-1 (HO-1) expression and caspase-3 activation, and reduces cell death, while the glutathione synthetase inhibitor, buthionine sulfoximine, potentiates DA-induced HO-1 expression and cell death. Moreover, a mimetic of the peroxide-scavenging enzyme, glutathione peroxidase (GPx), ebselen, blocks caspase-3 activation induced by DA alone or in combination with iron. In conclusion, superoxide and inadequate defense by glutathione and GPx are responsible for the susceptibility of oligodendrocyte progenitors to DA toxicity. Furthermore, peroxides play a primary role in toxicity induced by DA and iron.

Nitric oxide protects against oxidative stress under heat stress in the calluses from two ecotypes of reed

Calluses from two ecotypes of reed (Phragmites communis Trin.) plant (dune reed [DR] and swamp reed [SR]), which show different sensitivity to heat stress, were used to study plant acclimations to heat stress. SR callus suffered more oxidative damage than DR callus, and DR callus maintained higher relative growth rate and cell viability and lower ion leakage than SR callus under heat stress. Application of two nitric oxide donors, sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP), dramatically alleviated heat stress induced ion leakage increase, growth suppression and cell viability decrease in both calluses under heat stress. H2O2 and MDA contents were decreased and the activities of superoxide dismutase, catalase, ascorbate peroxidase and peroxidase increased in both calluses in the presence of NO donors under heat stress. The potassium salt of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), a specific NO scavenger, arrested NO donors mediated protective effects. Moreover, measurement of the rate of NO release showed that NO production increased significantly in DR callus while kept stable in SR callus under heat stress. Pretreatment with cPTIO had no effect on SR callus under heat stress while it significantly enhanced oxidative stress in DR callus compared with that of heat stress alone. These results suggest that NO can effectively protect both calluses from oxidative stress induced by heat stress and that NO might act as a signal in activating active oxygen scavenging enzymes under heat stress and thus confer DR callus thermotolerance.

Iron contributes to dopamine-induced toxicity in oligodendrocyte progenitors

Iron is potentially toxic to oligodendrocyte progenitors due to its high intracellular levels and its ability to catalyse oxidant-producing reactions. Oxidative stress resulting from a hypoxic-ischaemic insult has been implicated in death of oligodendrocyte progenitors that occurs in the hypomyelinating disorder periventricular leucomalacia. Ischaemic insults induce the release of various neurotransmitters, including dopamine (DA), and we previously showed that DA is toxic to cultured oligodendrocytes, by inducing oxidative stress and apoptosis. Therefore, we investigated the role of iron in DA-induced cell death in oligodendrocyte progenitors. Intracellular iron levels were altered using an iron chelator, deferoxamine (DFO), and supplementation with ferrous sulphate (FeSO(4)). Addition of FeSO(4) to cultures increased DA-induced toxicity as assessed by mitochondrial dehydrogenase activity and cellular release of lactate dehydrogenase. Furthermore, FeSO(4) increased expression of the stress protein heme oxygenase-1 (HO-1), nuclear condensation and caspase-3 activation. In contrast, preincubation with DFO reduced these events as well as cleavage of alpha-spectrin, a caspase-3 substrate. In addition, FeSO(4) reversed the protective effect of DFO on DA-induced cytotoxicity, HO-1 expression and caspase-3 activation. These results indicate that elevated levels of free iron contribute to DA-induced toxicity in oligodendrocyte progenitors.

Nitric oxide synthase expression and nitric oxide toxicity in oligodendrocytes

Oligodendrocytes (OLG) have more complex interactions with nitric oxide (NO) than initially suspected. Historically, OLG were seen only as targets of high NO levels released from other cells. Expression of nitric oxide synthase type II (NOS-2) in primary cultures of OLGs stimulated by cytokines led to controversy due to the presence of small numbers of microglia, cells also inducible for NOS-2 expression. The present review summarizes the findings that immature OLG express NOS-2, but that they do not in their most mature stage in culture as membrane sheet-bearing cells. This raises questions about the regulation of NOS-2 expression in OLG. Additionally, novel data are presented on NOS-3 expression in cultured OLG. If confirmed in vivo, this finding suggests that constitutive NOS-3 expression may play a key role in OLG injury due to its activation by calcium, in interaction with pathways mediating glutamate toxicity. The authors discuss in vivo NO levels to place in vitro findings in context, and compare OLG sensitivity to NO with that of other brain cells. Lastly, the multiple interactions of NO are considered with regard to glutamate cytotoxicity, the antioxidant glutathione, mitochondrial function, and myelin architecture.

Sodium nitroprusside, cyanide, nitrite, and nitrate break Arabidopsis seed dormancy in a nitric oxide-dependent manner

The seeds of many plant species are dormant at maturity and dormancy loss is a prerequisite for germination. Numerous environmental and chemical treatments are known to lessen or remove seed dormancy, but the biochemical changes that occur during this change of state are poorly understood. Several lines of research have implicated nitric oxide (NO) as a participant in this process. Here, we show that dormant seeds of Arabidopsis thaliana (L.) Heynh. will germinate following treatment with the NO donor sodium nitroprusside (SNP), cyanide (CN), nitrite or nitrate. In all cases, the NO scavenger c-PTIO effectively promotes the maintenance of seed dormancy. c-PTIO does not, however, inhibit germination of fully after-ripened seeds, and c-PTIO does not interact directly with nitrite, nitrate or CN. We also show that volatile CN effectively breaks dormancy of Arabidopsis seeds, and that CN is the volatile compound in SNP that promotes dormancy loss. Our data support the hypothesis that NO is a signaling molecule that plays an important role in the loss of seed dormancy.

Nitric oxide gas stimulates germination of dormant Arabidopsis seeds: use of a flow-through apparatus for delivery of nitric oxide

Nitric oxide (NO) is a gaseous free radical that reacts with O(2) in air and aqueous solution. NO donors have been widely used to circumvent the difficulties inherent in working with a reactive gas, but NO donors do not deliver NO at a constant rate for prolonged periods of time. Furthermore, some of the most commonly used NO donors produce additional, bioactive decomposition products. We designed and built an apparatus that allowed for the precise mixing of gaseous NO with air and the delivery of gas through sample vials at fixed rates. This experimental setup has the added advantage that continuous flow of gas over the sample reduces the buildup of volatile breakdown products. To show that this experimental setup was suitable for studies on the dormancy and germination of Arabidopsis thaliana seeds, we introduced vapors from water or sodium nitroprusside (SNP) into the gas stream. Seeds remained dormant when treated with water vapor, but gases generated by SNP increased germination to 90%. When pure NO was mixed with air and passed over dormant seeds, approximately approximately 30% of the seeds germinated. Because nitrite accumulates in aqueous solutions exposed to NO gas, we measured the accumulation of nitrite under our experimental conditions and found that it did not exceed 100 microM. Nitrite or nitrate at concentrations of up to 500 microM did not increase germination of C24 ecotype Arabidopsis seeds to more than 10%. These data support the hypothesis that NO participates in the loss of Arabidopsis seed dormancy, and they show that for some dormant seeds, exposure to exogenous NO is sufficient to trigger germination.

Signaling pathways in the nitric oxide and iron-induced dopamine release in the striatum of freely moving rats: Role of extracellular Ca2+ and L-type Ca2+ channels

We showed previously that exogenous iron potentiated nitric oxide (NO) donor-induced release of striatal dopamine (DA) in freely moving rats, using microdialysis. In this study, the increase in dialysate DA induced by intrastriatal infusion of the NO-donor 3-morpholinosydnonimine (SIN-1, 1.0 mM for 180 min) was scarcely affected by Ca2+ omission. N-methyl-d-glucamine dithiocarbamate (MGD) is a thiol compound whose NO trapping activity is potentiated by iron(II). Intrastriatal co-infusion of MGD either alone or associated with iron(II), however, potentiated SIN-1-induced increases in dialysate DA. In contrast, co-infusion of the NO trapper 4-(carboxyphenyl)-4,4,5,5-tetramethylimidazole-1-oxyl 3-oxide (carboxy-PTIO) significantly attenuated the increase in dialysate DA induced by SIN-1 (5.0 mM for 180 min). SIN-1+MGD+iron(II)-induced increases in dialysate DA were inhibited by Ca2+ omission or co-infusion of either deferoxamine or the L-type (Ca(v) 1.1-1.3) Ca2+ channel inhibitor nifedipine; in contrast, the increase was scarcely affected by co-infusion of the N-type (Ca(v) 2.2) Ca2+ channel inhibitor omega-conotoxin GVIA. These results demonstrate that exogenous NO-induced release of striatal DA is independent on extracellular Ca2+; however, in presence of the NO trapper MGD, NO may preferentially react with either endogenous or exogenous iron to form a complex which releases striatal DA with an extracellular Ca2+-dependent and nifedipine-sensitive mechanism.

Cytokines induce nitric oxide-mediated mtDNA damage and apoptosis in oligodendrocytes. Protective role of targeting 8-oxoguanine glycosylase to mitochondria

Nitric oxide (NO) that is produced by inducible NO synthase (iNOS) in glial cells is thought to contribute significantly to the pathogenesis of multiple sclerosis. Oligodendrocytes can be stimulated to express iNOS by inflammatory cytokines, which are known to accumulate in the multiple sclerotic brain. The potentially pathological levels of NO produced under these circumstances can target a wide spectrum of intracellular components. We hypothesized that one of the critical targets for damage that leads to disease is mtDNA. In this study, we found that cytokines, in particular a combination of tumor necrosis factor-alpha (50 ng/ml) and IFNgamma (25 ng/ml), cause elevated NO production in primary cultures of rat oligodendrocytes. Western blot analysis revealed a strong enhancement of iNOS expression 48 h after cytokine treatment. Within the same time period, NO-mediated mtDNA damage was shown by Southern blot analysis and by ligation-mediated PCR. Targeting the DNA repair enzyme human 8-oxoguanine DNA glycosylase (hOGG1) to the mitochondria of oligodendrocytes had a protective effect against this cytokine-mediated mtDNA damage. Moreover, it was shown that mitochondrial transport sequence hOGG1-transfected oligodendrocytes had fewer apoptotic cells compared with cells containing vector only following treatment with the cytokines. Subsequent experiments revealed that targeting hOGG1 to mitochondria reduces the activation of caspase-9, showing that this recombinant protein works to reduce apoptosis that is occurring through a mitochondria-based pathway.

Pharmacological modulation of the endocannabinoid system in a viral model of multiple sclerosis

Theiler's virus infection of the central nervous system (CNS) induces an immune-mediated demyelinating disease in susceptible mouse strains and serves as a relevant infection model for human multiple sclerosis (MS). Cannabinoids have been shown to exert beneficial effects on animal models of MS and evidence suggests that the endocannabinoid system plays a role in the tonic control of spasticity. In this study we show that OMDM1 [(R)-N-oleoyl-(1'-hydroxybenzyl)-2'-ethanolamine] and OMDM2 [(S)-N-oleoyl-(1'-hydroxybenzyl)-2'-ethanolamine], two selective inhibitors of the putative endocannabinoid transporter and hence of endocannabinoid inactivation, provide an effective therapy for Theiler murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD). Treatment of TMEV-infected mice with OMDM1 and OMDM2 enhanced anandamide levels in the spinal cord and ameliorated motor symptoms. This was associated with a down-regulation of inflammatory responses in the spinal cord. In addition we show that OMDM1 and OMDM2 down-regulate macrophage function by (i) decreasing the surface expression of major histocompatibility complex (MHC) class II molecules, (ii) inhibiting nitric oxide synthase-2 (NOS-2) expression and (iii) reducing the production of the pro-inflammatory cytokines interleukin-1beta (IL-1beta) and interleukin-12 (IL-12p40). Taken together, these results point to the manipulation of the endocannabinoid system as a possible strategy to develop future MS therapeutic drugs.

Emerging concepts in periventricular white matter injury

Approximately 10% of newborns are born prematurely. Of these children, more than 10% will sustain neurological injuries leading to significant learning disabilities, cerebral palsy, or mental retardation, with very low birth weight infants having an even higher incidence of brain injury. Whereas intraventricular hemorrhage was the most common form of serious neurological injury a decade ago, periventricular white matter injury (PWMI) is now the most common cause of brain injury in preterm infants. The spectrum of chronic PWMI includes focal cystic necrotic lesions (periventricular leukomalacia; PVL) and diffuse myelination disturbances. Recent neuroimaging studies support that the incidence of PVL is declining, whereas diffuse cerebral white matter injury is emerging as the predominant lesion. Factors that predispose to PVL include prematurity, hypoxia, ischemia, and inflammation. It is believed that injury to oligodendrocyte (OL) progenitors contributes to the pathogenesis of myelination disturbances in PWMI by disrupting the maturation of myelin-myelin-forming oligodendrocytes. Other potential mechanisms of injury include activation of microglia and axonal damage. Chemical mediators that may contribute to white matter injury include reactive oxygen (ROS) and nitrogen species (RNS), glutamate, cytokines, and adenosine. As our understanding of the pathogenesis of PWMI improves, it is anticipated that new strategies for directly preventing brain injury in premature infants will evolve.

Uncoupling of flow and metabolism induced by sodium nitroprusside in rat cerebral cortex

The effects of sodium nitroprusside (SNP) on cerebral blood flow and glucose metabolism were investigated by the microinfusion of SNP into rat cerebral cortex. A significant enhancement in glucose metabolism, as measured using [14C]deoxyglucose (DG), was observed throughout widespread areas of the cerebral cortex within 1 h of microinjection of 50 nmol/microl SNP. Using a kinetic analysis, the increase in glucose metabolism was found to be due to an increase in the phosphorylation of [14C]DG in the brain. On the other hand, regional cerebral blood flow, as measured using [14C]iodoantypirine, was not significantly altered by the SNP infusion. No significant cell death was detected by 2,3,5-triphenyltetrazolium chloride (TTC) staining 1 h after the SNP infusion. The uncoupling of flow and metabolism was almost completely prevented by pretreatment with an NMDA antagonist, MK-801. However, pretreatment with MK-801 did not prevent the SNP-induced neural cell death detected 6 h after the SNP infusion. These results suggest that the SNP-induced uncoupling of flow and metabolism was not directly related to neural cell death in the cerebral cortex.

Chronic exposure to nitric oxide alters the free iron pool in endothelial cells: role of mitochondrial respiratory complexes and heat shock proteins

The mechanisms of nitric oxide (NO) signaling include binding to the iron centers in soluble guanylate cyclase and cytochrome c oxidase and posttranslational modification of proteins by S-nitrosation. Low levels of NO control mitochondrial number in cells, but little is known of the impact of chronic exposure to high levels of NO on mitochondrial function in endothelial cells. The focus of this study is the interaction of NO with mitochondrial respiratory complexes in cell culture and the effect this has on iron homeostasis. We demonstrate that chronic exposure of endothelial cells to NO decreased activity and protein levels of complexes I, II, and IV, whereas citrate synthase and ATP synthase were unaffected. Inhibition of these respiratory complexes was accompanied by an increase in cellular S-nitrosothiol levels, modification of cysteines residues, and an increase in the labile iron pool. The NO-dependent increase in the free iron pool and inhibition of complex II was prevented by inhibition of mitochondrial protein synthesis, consistent with a major contribution of the organelle to iron homeostasis. In addition, inhibition of mitochondrial protein synthesis was associated with an increase in heat shock protein 60 levels, which may be an additional mechanism leading to preservation of complex II activity.

Intrastriatal microinjection of sodium nitroprusside induces cell death and reduces binding of dopaminergic receptors

Rat striatum was microinjected with 50 nmol sodium nitroprusside (SNP) and neural cell death as well as the binding of dopaminergic receptors were followed for 24 h after the infusion using TTC staining, cresyl violet staining, and quantitative autoradiography. Striatal cell death was observed 3 h after the infusion of SNP. A widespread area of cell death, including part of the cerebral cortex, was seen at 24 h after the infusion. A decrease of more than 80% in dopamine D1 receptor binding was seen in rat brain slices prepared 2 h after the infusion of SNP, whereas only a slight decrease in dopamine D2 receptor binding and almost no changes in dopamine transporter binding were observed. One day after the infusion, less than 10% of the binding of all three types of dopaminergic receptors remained in a widespread area in the infused side of the striatum and part of the cerebral cortex. Microinjection of either NOC-18 (50 nmol), another type of NO donor, or sodium cyanide (50 nmol) did not caused cell death. In addition, microinjection of FeCl2 (50 nmol) into the striatum caused cell death and reduction in dopamine D() receptor binding. These results suggest that iron-related radical reactions, but not NO itself, might have important roles on SNP-caused cell death. The current receptor binding study also indicated that dopamine D1 receptor binding is the most sensitive indicator for detection of cell death or cell damage induced by radical reactions in the rat striatum.

Bilirubin is cytotoxic to rat oligodendrocytes in vitro

High levels of unconjugated bilirubin can be neurotoxic and gliotoxic. However, the effect of bilirubin on oligodendrocyte viability has never been investigated. In the present study, we searched the possible toxic effect of bilirubin on differentiated rat oligodendrocytes. Bilirubin was added to oligodendrocyte cultures at different concentrations varied between 10 and 100 microM, and cultures were incubated for different times (24, 48 and 72 h). Cell viability was evaluated by trypan blue exclusion. The results showed that bilirubin decreased oligodendroglial cell viability in a concentration and time-dependent manner. Bilirubin induced apoptotic cell death as revealed by TUNEL staining and poly(ADP-ribose) polymerase cleavage. We found that bilirubin induced inducible nitric oxide synthase (NOS) mRNA expression in rat oligodendrocytes. Bilirubin also increased oligodendroglial nitrite production in a concentration-dependent manner and NOS inhibitor partly blocked bilirubin-induced cytotoxicity. These results suggest that bilirubin induces cytotoxicity, at least partly, via the induction of nitric oxide production in oligodendrocytes.

Sensitivities of benzodiazepine receptor binding and muscarinic acetylcholine receptor binding for the detection of neural cell death caused by sodium nitroprusside microinjection in rat brain

Sodium nitroprusside (SNP) was microinjected into rat cerebral cortex and changes in muscarinic acetylcholine receptor (mAChR) binding and benzodiazepine receptor (BZR) binding were followed for 24 h after the infusion using [(3)H]-N-methyl-4-piperidyl benzilate ([(3)H]-NMPB) and [(3)H]-flumazenil, respectively, as a radioligand. The microinjection of SNP dose-dependently caused significant neural cell death 3 h after infusion, with the area of cell death becoming extensive 24 h after infusion. Neither SIN-1 nor NOC-18, other types of NO donors, caused neural cell death. Together with the result that deferoxamine, an iron-chelating agent, protected SNP-induced brain injury indicated important roles of iron-related radicals in SNP cytotoxicity in rat brain. In vitro [(3)H]-NMPB binding was significantly reduced in parallel with the time course of neural cell death detected by TTC staining and Nissl staining. In contrast, [(3)H]-flumazenil binding was essentially unaltered during the 24-h period after the SNP infusion. Similar results were observed in in vivo binding experiments. In vivo [(3)H]-NMPB binding was found to be much more sensitive at detecting cell death caused by SNP. On the other hand, [(3)H]-flumazenil binding in vivo was relatively insensitive to SNP-induced cell death. These results indicate that mAChR binding may be superior to BZR binding for detecting cell death in brain tissue, in contrast to what was previously thought.

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.

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.

Cyclic AMP differentiation of the oligodendroglial cell line N20.1 switches staurosporine-induced cell death from necrosis to apoptosis

Understanding the regulation of cell death pathways is critical for protecting myelin-producing cells and their associated axons during injury resulting from multiple sclerosis and other degenerative diseases. The immortalized N20.1 oligodendroglial cell line provides a useful model for identifying mechanisms that can be exploited to attenuate cell death in myelin-producing cells and their precursors. In our hands, the N20.1 cell line exhibits different characteristics and morphology depending on temperature (permissive or non-permissive) and the presence of cAMP-elevating agents (Studzinski et al. [1998] Neurochem. Res. 23:435-441; Boullerne et al. [1999] J. Neurochem. 72:1050-1060; Studzinski et al. [1999] J. Neurosci. Res. 57:633-642). Our laboratory previously observed that NO donors cause primarily necrotic death in N20.1 cells grown at permissive temperature, but the NO donor SNP switched a portion of cell death to the apoptic pathway. We have continued our study of apoptotic death in these cells by comparing the effects of staurosporine, a known apoptotic agent, on cells grown at the permissive temperature ("undifferentiated") vs. the non-permissive temperature in the presence of forskolin ("differentiated"). Undifferentiated N20.1 cells exhibit maximal cell death after 24 hr of exposure to 50 nM staurosporine, whereas differentiated cells show delayed cell death, with maximal death seen after 48 hr. Pyknotic nuclei were observed in both growth conditions; however, differentiated cells were protected by caspase inhibitors, whereas undifferentiated cells were not. Increased ssDNA staining and DNA laddering were found following 24-hr staurosporine treatment in the differentiated cells only. These results support the conclusion that N20.1 cells can switch from necrotic to apoptotic cell death when cell division is slowed and cyclic AMP is elevated.

Two temporal stages of oligodendroglial response to excitotoxic lesion in the gray matter of the adult rat brain

Excitotoxic lesions in the gray matter induce profuse demyelination of passage and afferent fibers in areas of neuronal loss, independent of Wallerian degeneration. The time course of this phenomenon, which extends over weeks after the excitotoxin injection, suggests that demyelination is not related only to a direct effect of the toxin. In order to define mechanisms at work, a parallel study of myelin and oligodendrocytes was carried out following kainate injections into the adult rat thalamus. Within the 1st day postlesion, myelin alteration appeared throughout the area exhibiting neuronal loss, while the number of oligodendrocytes fell by 45%. No apoptotic oligodendrocytes were identified at that time. Over the following 2 days, there was no further loss of myelin and oligodendrocytes, but there was an increase in the number of oligodendrocytes displaying typical signs of apoptosis as revealed with TUNEL-end-labeled nuclei, Hoechst-labeled condensed chromatin bodies, or bax immunoreactivity. This resulted in a second, progressive loss of both myelin and oligodendrocytes leading to their almost complete disappearance 2 weeks postlesion. These results demonstrate two temporal stages of oligodendroglial cell death. The excitotoxin injection resulted in the rapid destruction of a first oligodendroglial population, most probably by necrosis. A second population died in a delayed manner from apoptosis. This second wave of death coincided with an activated microglia/macrophage invasion of the lesion, suggesting that delayed oligodendroglial death results from toxic microglia/macrophage effects. In addition, the longest surviving oligodendrocytes were located next to reactive astrocytes, suggesting the existence of trophic interactions between these two glial populations.

Nitric oxide reduces the palmitoylation of rat myelin proteolipid protein by an indirect mechanism

Brain slices from 20-day-old rats were incubated with [3H]palmitate for 2 hours in the absence or presence of the NO-donors S-nitroso-N-acetyl-penicillamine (SNAP), ethyl-2-[hydroxyimino]-5-nitro-3-hexeneamide (NOR-3), 4-phenyl-3-furoxan carbonitrile (PFC) and sodium nitroprusside (SNP). Each of these drugs reduced the incorporation of [3H]palmitate into myelin proteolipid protein (PLP) in a concentration-dependent manner, SNP being the most active. The effect of SNAP was prevented by the NO-scavenger PTIO (2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide). Furthermore, decayed-SNAP, sodium nitrite and N- nitrosopyrrolidine were inactive, suggesting that free NO and/or some of its direct oxidation products are the active molecular species. The amount of fatty acids bound to PLP and the rate of deacylation were unaffected by NO. Although NO diminished the number of thiols in brain and myelin proteins, with the formation of both nitrosothiols and disulfides, these changes did not parallel those in PLP acylation. In contrast, NO was effective at reducing the palmitoylation of brain and myelin lipids, and this effect along with that of PLP, was ascribed to a decrease in palmitoyl-CoA levels. The NO-induced reduction in acyl-CoA concentration was due to the decline in ATP levels, while the amount of [3H]palmitate incorporated into the tissue, the activity of palmitoyl-CoA ligase and palmitoyl-CoA hydrolase, and the concentration of CoASH were unaltered by the drugs. Experiments with endogenously-synthesized [18O]fatty acids confirmed that NO affects predominantly the ATP-dependent palmitoylation of PLP. In conclusion, the inhibitory action of NO on the fatty acylation of PLP is indirect and caused by energy depletion.

Cytokine-induced cell death in immortalized Schwann cells: roles of nitric oxide and cyclic AMP

Tumor necrosis factor-alpha and interferon-gamma are pleiotropic cytokines that regulate Schwann cell responses during injury and inflammatory demyelination. We have previously shown that cyclic AMP (cAMP)-elevating agents decrease the demyelination and Wallerian degeneration in experimental allergic neuritis. In this study, we examined the role of cAMP in cytokine-mediated signaling in a spontaneously immortal Schwann cell clone (iSC). We found that tumor necrosis factor-alpha and interferon-gamma exert synergistic inhibitory action on Schwann cell viability via the production of nitric oxide (NO) and ceramide (cer). Furthermore, we found that: (i) NO synthase inhibitors attenuate the cytokine-induced cer accumulation and cell death indicating that NO acts upstream of cer; and (ii) cytokine-induced cell death is decreased in iSCs pretreated continuously for 48-72 h with forskolin, an activator of adenylate cyclase. Although forskolin modulates the phosphorylation of ERKs and Akt, it decreases the susceptibility of iSC to cytokines via a separate mechanism operating after NO induction and before cer accumulation. We propose that the protective effect of cAMP-elevating agents in experimental allergic neuritis may be mediated in part via modulation of Schwann cell responses to cytokines.

LPS/IFN-gamma cytotoxicity in oligodendroglial cells: role of nitric oxide and protection by the anti-inflammatory cytokine IL-10

Proinflammatory mediators have been implicated in demyelinating disorders, including multiple sclerosis, whereas it has been proposed that the anti-inflammatory cytokines interleukin- (IL-) 4 and IL-10 participate in disease recovery. The present study analysed the effect of interferon-gamma (IFN-gamma) and bacterial endotoxin (lipopolysaccharide, LPS) on proliferation and survival of progenitors and differentiated oligodendrocytes. We also investigated the presence of receptors for IL-4 and IL-10 in oligodendroglial cells and explored a possible protective action of IL-4 and IL-10 in cultures following LPS/IFN-gamma. Finally, the role of endogenous nitric oxide (NO) on cell viability and the modulatory action of IL-4 and IL-10 on inducible nitric oxide synthase (iNOS) expression were also analysed. We report that LPS and/or IFN-gamma reduced proliferation and viability of oligodendroglial cells. Cell death, presumably by apoptosis as evidence by TUNEL and Annexin V binding, was observed following LPS/IFN-gamma, progenitors being more sensitive than differentiated cells. At both developmental stages, LPS/IFN-gamma-treated cultures expressed iNOS protein and released micromolar concentrations of NO. In progenitors, LPS/IFN-gamma-mediated cell damage was partially dependent on endogenous NO production, whereas NO was fundamental for cytotoxicity of differentiated oligodendrocytes. Both cell types expressed mRNA for IL-4 and IL-10 receptors and expression of IL-10 receptors at the protein level was also demonstrated. Treatment with either cytokine inhibited the expression of iNOS resulting from the proinflammatory stimulation. IL-10 was more effective than IL-4 in suppressing iNOS expression and, interestingly, IL-10 conferred protection against oligodendroglial death evoked by LPS/IFN-gamma. Our data raise the question of whether IL-10 may play a protective role in demyelinating diseases, not only downregulating the function of inflammatory cells but also promoting survival of progenitors and differentiated oligodendrocytes.

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.

The possible role of gradual accumulation of copper, cadmium, lead and iron and gradual depletion of zinc, magnesium, selenium, vitamins B2, B6, D, and E and essential fatty acids in multiple sclerosis

Multiple sclerosis (MS) has a much higher incidence among caucasians that in any other race. Furthermore: females are much more susceptible than males and white females living in colder, wetter areas are much more susceptible than those living in warmer areas. On the other hand, menstruating women have increased copper (Cu) absorption and half-life, so they tend to accumulate more Cu than males. Moreover, rapidly growing girls have an increased demand for zinc (Zn), but their rapidly decreasing production of melatonin results in impaired Zn absorption, which is exacerbated by the high Cu levels. The low Zn levels result in deficient CuZnSuperoxide dismutase (CuZnSOD), which in turn leads to increased levels of superoxide. Menstruating females also often present with low magnesium (Mg) and vitamin B6 levels. Vitamin B6 moderates intracellular nitric oxide (NO) production and extracellular Mg is required for NO release from the cell, so that a deficiency of these nutrients results in increased NO production in the cell and reduced release from the cell. The trapped NO combines with superoxide to form peroxinitrite, an extremely powerful free radical that leads to the myelin damage of MS. Iron (Fe), molybdenum (Mo) and cadmium (Cd) accumulation also increase superoxide production. Which explains MS in males, who tend to accumulate Fe much faster and Cu much less rapidly than females. Since vitamin D is paramount for Mg absorption, the much reduced exposure to sunlight in the higher latitudes may account for the higher incidence in these areas. Moreover, vitamin B2 is a cofactor for xanthine oxidase, and its deficiency exacerbates the low levels of uric acid caused by high Cu levels, resulting in myelin degeneration. Finally Selenium (Se) and vitamin E prevent lipid peroxidation and EPA and DHA upregulate CuZnSOD. Therefore, supplementation with 100 mg MG, 25 mg vit B6, 10 mg vit B2, 15 mg Zn and 400 IU vit D and E, 100 microg Se, 180 mg EPA and 120 mg DHA per day between 14 and 16 years of age may prevent MS.

Cell death in the oligodendrocyte lineage: a molecular perspective of life/death decisions in development and disease

Cell death in the oligodendrocyte lineage occurs during development and in pathological conditions as the result of a balance between opposing molecular signals. This review focuses on the molecular mechanisms of activation of signal transduction pathways affecting life/death decisions in progenitor cells and in mature oligodendrocytes. Loss of trophic support, cytokine receptor activation, and oxidative stress may differentially contribute to the induction of cell death at specific stages of development and to the pathogenesis of demyelinating disorders. The execution of the death program leading to the morphological changes of apoptosis and/or necrosis is then determined by the generation of reactive oxygen species and the level of impairment of mitochondrial function. The final decision of a cell to die or survive is determined by a competition between survival and death signals. Depending on ligand availability, type, and levels of receptor expression and downstream cross-talks between distinct signaling pathways, the cell may activate a death execution program that will be affected by its stage of differentiation and its energetic metabolism.