Appearance of inducible nitric oxide synthase in the rat central nervous system after rabies virus infection and during experimental allergic encephalomyelitis but not after peripheral administration of endotoxin

Transcriptome analysis of salivary glands of rabies-virus-infected mice

Rabies is a fatal zoonotic disease that poses a threat to public health. Rabies virus (RABV) is excreted in the saliva of infected animals, and is primarily transmitted by bite. The role of the salivary glands in virus propagation is significant, but has been less studied in the pathogenic mechanisms of RABV. To identify functionally important genes in the salivary glands, we used RNA sequencing (RNA-seq) to establish and analyze mRNA expression profiles in parotid tissue infected with two RABV strains, CVS-11 and PB4. The biological functions of differentially expressed genes (DEGs) were determined by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, which revealed 3,764 DEGs (678 up-regulated and 3,086 down-regulated) in the CVS-11 infected group and 4,557 DEGs (874 up-regulated and 3,683 down-regulated) in the PB4 infected group. Various biological processes are involved, including the salivary secretion pathway and the phosphatidylinositol 3-kinase-Akt (PI3K-Akt) signaling pathway. This study provides the first mapping of the transcriptome changes in response to RABV infection in parotid tissue, offering new insights into the study of RABV-affected salivary gland function and RABV pathogenic mechanisms in parotid tissue. The salivary gland-enriched transcripts may be potential targets of interest for rabies disease control.

Hydrogel-based 3D human iPSC-derived neuronal culture for the study of rabies virus infection

Background

Rabies is a highly fatal infectious disease that poses a significant threat to human health in developing countries. In vitro study-based understanding of pathogenesis and tropism of different strains of rabies virus (RABV) in the central nervous system (CNS) is limited due to the lack of suitable culture models that recapitulate the complex communication pathways among host cells, extracellular matrices, and viruses. Therefore, a three-dimensional (3D) cell culture that mimics cell-matrix interactions, resembling in vivo microenvironment, is necessary to discover relevant underlying mechanisms of RABV infection and host responses.

Methods

The 3D collagen-Matrigel hydrogel encapsulating hiPSC-derived neurons for RABV infection was developed and characterized based on cell viability, morphology, and gene expression analysis of neuronal markers. The replication kinetics of two different strains of RABV [wild-type Thai (TH) and Challenge Virus Standard (CVS)-11 strains] in both 2D and 3D neuronal cultures were examined. Differential gene expression analysis (DEG) of the neuropathological pathway of RABV-infected 2D and 3D models was also investigated via NanoString analysis.

Results

The 3D hiPSC-derived neurons revealed a more physiologically interconnected neuronal network as well as more robust and prolonged maturation and differentiation than the conventional 2D monolayer model. TH and CVS-11 exhibited distinct growth kinetics in 3D neuronal model. Additionally, gene expression analysis of the neuropathological pathway observed during RABV infection demonstrated a vast number of differentially expressed genes (DEGs) in 3D model. Unlike 2D neuronal model, 3D model displayed more pronounced cellular responses upon infection with CVS-11 when compared to the TH-infected group, highlighting the influence of the cell environment on RABV-host interactions. Gene ontology (GO) enrichment of DEGs in the infected 3D neuronal culture showed alterations of genes associated with the inflammatory response, apoptotic signaling pathway, glutamatergic synapse, and trans-synaptic signaling which did not significantly change in 2D culture.

Conclusion

We demonstrated the use of a hydrogel-based 3D hiPSC-derived neuronal model, a highly promising technology, to study RABV infection in a more physiological environment, which will broaden our understanding of RABV-host interactions in the CNS.

Effect of fluoxetine treatment on neurotoxicity induced by lysolecithin in male rats

Demyelination disorder is an unusual pathologic event, which occurs in the central nervous system (CNS). Multiple sclerosis (MS) is an inflammatory demyelinating disease that affects the CNS, and it is the leading cause of disability in young adults. Lysolecithin (LPC) is one of the best toxin-induced demyelination models. In this study, a suitable model is created, and the effect of fluoxetine treatment is examined on this model. In this case, it was assumed that daily fluoxetine treatment had increased the endogenous remyelination in the LPC model. This study was focused on investigating the influence of the fluoxetine dose of 5 or 10 mg/kg per day for 1 and 4 weeks on LPC-induced neurotoxicity in the corpus callosum region. It was performed as a demyelinating model in male Wistar rats. After 3 days, fluoxetine was injected intraperitoneally (5 or 10 mg/kg per day) for 1 and 4 weeks in each group. After completing the treatment course, the corpus callosum was removed to examine the gene expression and histological analysis was performed. The results of the histopathological study of hematoxylin and eosin staining of the corpus callosum showed that in 1 and 4-week treatment groups, fluoxetine has reduced the level of inflammation at the LPC injection site (5 and 10 mg/kg per day). Fluoxetine treatment in the luxol fast blue (LFB) staining of the corpus callosum has been led to an increase in myelination capacity in all doses and times. The results of the genetic study showed that the fluoxetine has significantly reduced the expression level of tumor necrosis factor-α, nuclear factor κβ, and induced nitric oxide synthase in comparison with the untreated LPC group. Also, the fluoxetine treatment has enhanced the expression level of the forkhead box P3 (FOXP3) gene in comparison with the untreated group. Fluoxetine has increased the expression level of myelination and neurotrophic genes such as myelin basic protein (MBP), oligodendrocyte transcription factor 2 (OLIG2), and brain-derived neurotrophic factor (BDNF). The outcomes demonstrated that fluoxetine reduces inflammation and strengthens the endogenous myelination in the LPC-induced demyelination model; however, supplementary studies are required for specifying the details of its mechanisms.

Lyssaviruses and the Fatal Encephalitic Disease Rabies

Lyssaviruses cause the disease rabies, which is a fatal encephalitic disease resulting in approximately 59,000 human deaths annually. The prototype species, rabies lyssavirus, is the most prevalent of all lyssaviruses and poses the greatest public health threat. In Africa, six confirmed and one putative species of lyssavirus have been identified. Rabies lyssavirus remains endemic throughout mainland Africa, where the domestic dog is the primary reservoir - resulting in the highest per capita death rate from rabies globally. Rabies is typically transmitted through the injection of virus-laden saliva through a bite or scratch from an infected animal. Due to the inhibition of specific immune responses by multifunctional viral proteins, the virus usually replicates at low levels in the muscle tissue and subsequently enters the peripheral nervous system at the neuromuscular junction. Pathogenic rabies lyssavirus strains inhibit innate immune signaling and induce cellular apoptosis as the virus progresses to the central nervous system and brain using viral protein facilitated retrograde axonal transport. Rabies manifests in two different forms - the encephalitic and the paralytic form - with differing clinical manifestations and survival times. Disease symptoms are thought to be due mitochondrial dysfunction, rather than neuronal apoptosis. While much is known about rabies, there remain many gaps in knowledge about the neuropathology of the disease. It should be emphasized however, that rabies is vaccine preventable and dog-mediated human rabies has been eliminated in various countries. The global elimination of dog-mediated human rabies in the foreseeable future is therefore an entirely feasible goal.

Subversion of the Immune Response by Rabies Virus

Rabies has affected mankind for several centuries and is one of the oldest known zoonoses. It is peculiar how little is known regarding the means by which rabies virus (RABV) evades the immune response and kills its host. This review investigates the complex interplay between RABV and the immune system, including the various means by which RABV evades, or advantageously utilizes, the host immune response in order to ensure successful replication and spread to another host. Different factors that influence immune responses—including age, sex, cerebral lateralization and temperature—are discussed, with specific reference to RABV and the effects on host morbidity and mortality. We also investigate the role of apoptosis and discuss whether it is a detrimental or beneficial mechanism of the host’s response to infection. The various RABV proteins and their roles in immune evasion are examined in depth with reference to important domains and the downstream effects of these interactions. Lastly, an overview of the means by which RABV evades important immune responses is provided. The research discussed in this review will be important in determining the roles of the immune response during RABV infections as well as to highlight important therapeutic target regions and potential strategies for rabies treatment.

Correlation of inducible nitric oxide synthase (iNOS) inhibition with TNF-α, caspase-1, FasL and TLR-3 in pathogenesis of rabies in mouse model

The role of inflammatory cytokines such as interleukin-1α/β (IL-1α/β), IL-6, IL-10, tumour necrosis factor-alpha (TNF-α), interferons, nitric oxide (NO) and inducible nitric oxide synthase (iNOS) in pathogenesis of rabies is being actively pursued. Presently, levels of certain immune molecules in pathogenesis of rabies in mice have been investigated. CVS strain of rabies infection resulted in early increase in iNOS, TNF-α, caspase-1, Fas ligand (FasL) and toll-like receptor-3 (TLR-3) mRNA levels in brain, and nitric oxide levels in serum. The severity of clinical signs and microscopic lesions largely correlated with NO levels. Aminoguanidine (AG; iNOS inhibitor) decreased NO production with delay in development of clinical signs and increase in survival time. Prolonged survival time correlated with reduced viral load evident by real-time PCR, reduced fluorescent signals of rabies antigen in brain and reduced immunohistochemistry signals in neuronal cytoplasm. These parameters suggested that nitric oxide did influence the rabies virus replication. Inhibition of iNOS by AG administration led to decreased expression of TNF-α, caspase-1, FasL and TLR-3 mRNA levels suggesting that increase in NO levels in rabies virus infection possibly contributed to development of disease through inflammation, apoptosis and immune-evasive mechanisms.

Tissue Transglutaminase contributes to experimental multiple sclerosis pathogenesis and clinical outcome by promoting macrophage migration

Multiple sclerosis is a serious neurological disorder, resulting in e.g., sensory, motor and cognitive deficits. A critical pathological aspect of multiple sclerosis (MS) is the influx of immunomodulatory cells into the central nervous system (CNS). Identification of key players that regulate cellular trafficking into the CNS may lead to the development of more selective treatment to halt this process. The multifunctional enzyme tissue Transglutaminase (TG2) can participate in various inflammation-related processes, and is known to be expressed in the CNS. In the present study, we question whether TG2 activity contributes to the pathogenesis of experimental MS, and could be a novel therapeutic target. In human post-mortem material, we showed the appearance of TG2 immunoreactivity in leukocytes in MS lesions, and particular in macrophages in rat chronic-relapsing experimental autoimmune encephalomyelitis (cr-EAE), an experimental MS model. Clinical deficits as observed in mouse EAE were reduced in TG2 knock-out mice compared to littermate wild-type mice, supporting a role of TG2 in EAE pathogenesis. To establish if the enzyme TG2 represents an attractive therapeutic target, cr-EAE rats were treated with TG2 activity inhibitors during ongoing disease. Reduction of TG2 activity in cr-EAE animals dramatically attenuated clinical deficits and demyelination. The mechanism underlying these beneficial effects pointed toward a reduction in macrophage migration into the CNS due to attenuated cytoskeletal flexibility and RhoA GTPase activity. Moreover, iNOS and TNFα levels were selectively reduced in the CNS of cr-EAE rats treated with a TG2 activity inhibitor, whereas other relevant inflammatory mediators were not affected in CNS or spleen by reducing TG2 activity. We conclude that modulating TG2 activity opens new avenues for therapeutic intervention in MS which does not affect peripheral levels of inflammatory mediators.

Oxidative tissue injury in multiple sclerosis is only partly reflected in experimental disease models

Recent data suggest that oxidative injury may play an important role in demyelination and neurodegeneration in multiple sclerosis (MS). We compared the extent of oxidative injury in MS lesions with that in experimental models driven by different inflammatory mechanisms. It was only in a model of coronavirus-induced demyelinating encephalomyelitis that we detected an accumulation of oxidised phospholipids, which was comparable in extent to that in MS. In both, MS and coronavirus-induced encephalomyelitis, this was associated with massive microglial and macrophage activation, accompanied by the expression of the NADPH oxidase subunit p22phox but only sparse expression of inducible nitric oxide synthase (iNOS). Acute and chronic CD4⁺ T cell-mediated experimental autoimmune encephalomyelitis lesions showed transient expression of p22phox and iNOS associated with inflammation. Macrophages in chronic lesions of antibody-mediated demyelinating encephalomyelitis showed lysosomal activity but very little p22phox or iNOS expressions. Active inflammatory demyelinating lesions induced by CD8⁺ T cells or by innate immunity showed macrophage and microglial activation together with the expression of p22phox, but low or absent iNOS reactivity. We corroborated the differences between acute CD4⁺ T cell-mediated experimental autoimmune encephalomyelitis and acute MS lesions via gene expression studies. Furthermore, age-dependent iron accumulation and lesion-associated iron liberation, as occurring in the human brain, were only minor in rodent brains. Our study shows that oxidative injury and its triggering mechanisms diverge in different models of rodent central nervous system inflammation. The amplification of oxidative injury, which has been suggested in MS, is only reflected to a limited degree in the studied rodent models.

Involvement of extraneural tissues and upregulation of inducible nitric oxide synthase after experimental infection with rabies virus in BALB/c mice and LEW/SsN rats

Rabies virus can cause fatal encephalomyelitis, but the involvement of extraneural organs has not been well characterized. In this study, we investigated the histopathological changes and the distribution of viral antigens in extraneural organs after pathogenic rabies virus infection in mouse and rat models. In histopathological examination, classical viral encephalitis and rabies-specific Negri body were observed in the brain. In addition to the central nervous system (CNS), inflammatory responses were found in other organs, such as the heart, kidney, liver, and lung. Similarly, immunohistochemical staining and reverse transcription-polymerase chain reaction revealed the presence of rabies virus in the CNS and extraneural tissues. Moreover, macrophages, especially in the lung and heart, were involved in the infection. Transcriptional analyses of the expression of inducible nitric oxide synthase (iNOS) demonstrated that rabies virus potentiated the gene expression of iNOS in the brain, lung, and heart. The immunoreactive iNOS-positive macrophages were detected adjacent to the infection. These results suggest that macrophages are involved in the extraneural infection and the expression of iNOS in macrophages contributes to the formation of tissue inflammation. Our study indicates the involvement of extraneural organs following rabies virus infection, which may aggravate the progression of this deadly disease.

Aminoguanidine and N-acetyl-cysteine supress oxidative and nitrosative stress in EAE rat brains

Experimental autoimmune encephalomyelitis (EAE) is a well-established animal model of human multiple sclerosis (MS). We have evaluated the role of oxidative and nitrosative stress, as the causal factors in the development of EAE, responsible for the damage of cardinal cellular components, such as lipids, proteins and nucleic acids, resulting in demyelination, axonal damage, and neuronal death. EAE was induced in female Sprague-Dawley rats, 3 months old (300±20 g), by immunization with myelin basic protein in combination with Complete Freund's adjuvant (CFA). The animals were divided into seven groups: control, EAE, CFA, EAE+aminoguanidine (AG), AG, EAE+N-acetyl-L-cysteine (NAC) and NAC. The animals were sacrificed 15 days after EAE induction, and the levels of nitrosative and oxidative stress were determined in 10% homogenate of the whole encephalitic mass. In EAE rats, brain NO production and MDA level were significantly increased (P<0.001) compared to the control values, whereas AG and NAC treatment decreased both parameters in EAE rats compared to EAE group (P<0.001). Glutathione (GSH) was reduced (P<0.001) in EAE rats in comparison with the control and CFA groups, but increased in EAE+AG and EAE+NAC group compared to the EAE group (P<0.01). Superoxide dismutase (SOD) activity was significantly decreased (P<0.001) in the EAE group compared to all other experimental groups. The clinical expression of EAE was significantly decreased (P<0.05) in the EAE groups treated with AG and NAC compared to EAE rats, during disease development. The obtained results prove an important role of oxidative and nitrosative stress in the pathogenesis of EAE, whereas AG and NAC protective effects offer new possibilities for a modified combined approach in MS therapy.

Endothelial NOS-deficient mice reveal dual roles for nitric oxide during experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is a demyelinating autoimmune disease characterized by infiltration of T cells into the central nervous system (CNS) after compromise of the blood-brain barrier. A model used to mimic the disease in mice is experimental autoimmune encephalomyelitis (EAE). In this report, we examine the clinical and histopathological course of EAE in eNOS-deficient (eNOS-/-) mice to determine the role of nitric oxide (NO) derived from this enzyme in the disease progression. We find that eNOS-/- mice exhibit a delayed onset of EAE that correlates with delayed BBB breakdown, thus suggesting that NO production by eNOS underlies the T cell infiltration into the CNS. However, the eNOS-/- mice also eventually exhibit more severe EAE and delayed recovery, indicating that NO undertakes dual roles in MS/EAE, one proinflammatory that triggers disease onset, and the other neuroprotective that promotes recovery from disease exacerbation events.

Effects of selective iNOS inhibition on systemic hemodynamics and mortality rate on endotoxic shock in streptozotocin-induced diabetic rats

The purpose of this study was to examine whether selective iNOS inhibition can restore the hemodynamic changes and reduce the nitrotyrosine levels in the cerebral cortex of rats with streptozotocin-induced diabetes during endotoxin-induced shock. The study was designed to include three sets of experiments: (1) measurement of changes in systemic hemodynamics, (2) measurement of biochemical variables, including iNOS activity and nitrotyrosine formation in the brain, and (3) assessment of mortality rate. Rats were randomly divided into four groups: group 1, control; group 2, LPS: Escherichia coli endotoxin, 10.0 mg/kg (i.v.) bolus; group 3 (i.v.) LPS and L-N6-(1-iminoethyl)-lysine (L-NIL), 4mg/kg (i.p.); and group 4, LPS and NG-nitro-L-arginine methyl ester (L-NAME), 5 mg/kg (i.p.). In nondiabetic rats, administration of L-NIL prevented the hemodynamic and biochemical changes, and increases in plasma nitrite and cerebral nitrotyrosine levels induced by LPS. Administration of L-NAME partially prevented these LPS-induced changes. On the other hand, in diabetic rats, administration of L-NIL only partially prevented the hemodynamic and biochemical changes, and increases in plasma nitrite and cerebral nitrotyrosine levels associated with LPS. Administration of L-NAME, however, had no effects on these LPS-induced changes in diabetic rats. There was a significant difference in nitrotyrosine levels between nondiabetic and diabetic rats in groups 2, 3, and 4 at 2 and 3 h after the treatment (at 3 h; nondiabetic--control, 4.6 +/- 0.4; LPS (i.v.), 8.9 +/- 1.0, LPS (i.v.) + L-NIL, 4.7 +/- 0.5; LPS (i.v.) + L-NAME, 7.1 +/- 0.9; diabetic--control, 5.5 +/- 0.4; LPS (i.v.), 13.6 +/- 1.2; LPS (i.v.) + L-NIL, 9.0 +/- 0.9; LPS (i.v.) + L-NAME, 13.0 +/- 1.0; densitometric units). Insulin therapy resulted in a decrease in iNOS activity (at 3 h: 1.0 +/- 0.5 fmol mg min), nitrotyrosine formation (at 3 h; 5.0 +/- 0.5, densitometric units), and mortality rates (30% at 6 h, 50% at 12 h) in the LPS (i.v.) + L-NIL group of diabetic rats. Selective iNOS inhibition in diabetic rats could not improve hemodynamic instability, chemical changes, iNOS activity, and nitrotyrosine formation during septic shock compared with the improvements observed in nondiabetic rats. Tight glucose control along with administration of L-NIL can result in more effective restoration of the biochemical changes of septicemia in diabetic rats. Thus, hyperglycemia may be one of the mechanisms related to the aggravation of endotoxin-induced shock.

Different roles of nitric oxide synthase-1 and -2 between herpetic and postherpetic allodynia in mice

We investigated using the mice role of nitric oxide synthase (NOS) in the spinal dorsal horn in herpetic and postherpetic pain, especially allodynia, which was induced by transdermal inoculation of the hind paw with herpes simplex virus type-1 (HSV-1). The virus inoculation induced NOS2 expression in the lumbar dorsal horn of mice with herpetic allodynia, but not postherpetic allodynia. There were no substantial alternations in the expression level of NOS1 at the herpetic and postherpetic stages. Herpetic allodynia was significantly inhibited by i.p. administration of the selective NOS2 inhibitor S-methylisothiourea, but not the selective NOS1 inhibitor 7-nitroindazole. NOS2 expression was observed around HSV-1 antigen-immunoreactive cells. On the other hand, postherpetic allodynia was significantly inhibited by i.p. administration of 7-nitroindazole, but not S-methylisothiourea. The activity of reduced nicotinamide adenine dinucleotide phosphate diaphorase, an index of NOS1 activity, significantly increased in the laminae I and II of the lumbar dorsal horn of mice with postherpetic allodynia, but not mice without postherpetic allodynia. The expression level of NOS1 mRNA in the dorsal root ganglia was similar between mice with and without postherpetic allodynia. The results suggest that herpetic and postherpetic allodynia is mediated by nitric oxide in the dorsal horn and that NOS2 and NOS1 are responsible for herpetic and postherpetic allodynia, respectively. It may be worth testing the effects of NOS2 and NOS1 inhibitors on herpetic pain and postherpetic neuralgia in human subjects, respectively.

Evaluation of cytokines concentration and percentage of survival of rabies virus-infected mice submitted to anti-rabies Vero-cell propagated vaccine and P. acnes

Previously, survival of rabies infection was shown to correlate with low IL-6 serum concentration in mice subjected to post-exposure treatment with the Fuenzalida Palacios rabies vaccine in conjunction with the immunomodulator Propionibacterium acnes, previously Corynebacterium parvum. Considering the substitution of the Fuenzalida Palacios rabies vaccine by the Vero cell raised anti-rabies vaccine in almost all countries, the objective of this work was to evaluate the survival and cytokine serum concentration of rabies virus-infected mice treated with P. acnes in conjunction with or the anti-rabies-VERO vaccine. For this, Swiss mice were experimentally infected with street rabies virus and subjected to vaccine and/or P. acnes following infection. Animals were killed at different times and serum was collected to evaluate cytokines. The greatest survival was observed in animals given one or two does of P. acnes in the absence of vaccination. Animals given anti-rabies VERO vaccine alone or with three doses of P. acnes had the second highest survival rate. The group that had the highest percentage of mortality also had the highest IL-6 concentration on the 10th day, a time correlating with clinical symptoms of the animals. The results reinforce the inefficacy of anti-rabies vaccine in only one dose as a post-exposure treatment irrespective of the type of vaccine used, the immunomodulation activity of P. acnes in rabies post-exposure treatment and suggest a role for IL-6 in rabies virus pathogenesis.

Mechanisms of escape phenomenon of spinal cord and brainstem in human rabies

Background

Rabies virus preferentially involves brainstem, thalamus and spinal cord in human furious and paralytic rabies beginning in the early stage of illness. Nevertheless, rabies patient remains alert until the pre-terminal phase. Weakness of extremities develops only when furious rabies patient becomes comatose; whereas peripheral nerve dysfunction is responsible for weakness in paralytic rabies.

Methods

Evidence of apoptosis and mitochondrial outer membrane permeabilization in brain and spinal cord of 10 rabies patients was examined and these findings were correlated with the presence of rabies virus antigen.

Results

Although apoptosis was evident in most of the regions, cytochrome c leakage was relatively absent in spinal cord of nearly all patients despite the abundant presence of rabies virus antigen. Such finding was also noted in brainstem of 5 patients.

Conclusion

Cell death in human rabies may be delayed in spinal cord and the reticular activating system, such as brainstem, thus explaining absence of weakness due to spinal cord dysfunction and preservation of consciousness.

Increased plasma levels of TNF-α but not of IL1-β in MPTP-treated monkeys one year after the MPTP administration

The cause of Parkinson's disease remains unknown although some evidence suggests that an inflammatory reaction, mediated by cytokines such as TNF-alpha and IL-1beta, is related with dopaminergic degeneration in the brain. In the present work we measured the plasma levels of TNF-alpha and IL-1beta in parkinsonian monkeys one year after MPTP administration. TNF-alpha levels were seen to have increased in parkinsonian monkeys reflecting the clinical symptoms observed, while IL-1beta levels remained unchanged. These results suggest that TNF-alpha plays a role in sustaining of dopaminergic degeneration in chronic parkinsonism.

Modulation of the immune response in the nervous system by rabies virus

Rabies virus (RABV) is a pathogen well-adapted to the nervous system, where it infects neurons. RABV is transmitted by the bite of an infected animal. It enters the nervous system via a motor neuron through the neuromuscular junction, or via a sensory nerve through nerve spindles. It then travels from one neuron to the next, along the spinal cord to the brain and the salivary glands. The virions are then excreted in the saliva of the animal and can be transmitted to another host by bite. Thus preservation of neuronal network integrity is crucial for the virus to be transmitted. Successful invasion of the nervous system by RABV seems to be the result of a subversive strategy based on the survival of infected neurons. This strategy includes protection against virus-mediated apoptosis and destruction of T cells that invade the CNS in response to infection.

Neuronal dysfunction and death in rabies virus infection

Because morphologic changes in natural rabies are usually relatively mild, it is thought that the severe clinical disease with a fatal outcome must be due to neuronal dysfunction of rabies virus-infected neurons. The precise bases of this functional impairment are unknown, and current knowledge on electro-physiological alterations, effects on ion channels and neurotransmission, and neurotoxicity are reviewed. Rabies virus may induce neuronal death, possibly through apoptotic mechanisms. Neuronal apoptosis has been observed in vitro and also in vivo under particular experimental conditions. The relevance of neuronal apoptosis in these situations to natural rabies has not yet been fully elucidated.

Brain microglia and blood-derived macrophages: molecular profiles and functional roles in multiple sclerosis and animal models of autoimmune demyelinating disease

Microglia and macrophages, one a brain-resident, the other a mostly hematogenous cell type, represent two related cell types involved in the brain pathology in multiple sclerosis and its autoimmune animal model, the experimental allergic encephalomyelitis. Together, they perform a variety of different functions: they are the primary sensors of brain pathology, they are rapidly recruited to sites of infection, trauma or autoimmune inflammation in experimental allergic encephalomyelitis and multiple sclerosis and they are competent presenters of antigen and interact with T cells recruited to the inflamed CNS. They also synthesise a variety of molecules, such as cytokines (TNF, interleukins), chemokines, accessory molecules (B7, CD40), complement, cell adhesion glycoproteins (integrins, selectins), reactive oxygen radicals and neurotrophins, that could exert a damaging or a protective effect on adjacent axons, myelin and oligodendrocytes. The current review will give a detailed summary on their cellular response, describe the different classes of molecules expressed and their attribution to the blood derived or brain-resident macrophages and then discuss how these molecules contribute to the neuropathology. Recent advances using chimaeric and genetically modified mice have been particularly telling about the specific, overlapping and nonoverlapping roles of macrophages and microglia in the demyelinating disease. Interestingly, they point to a crucial role of hematogenous macrophages in initiating inflammation and myelin removal, and that of microglia in checking excessive response and in the induction and maintenance of remission.

Role of Microglia and Macrophages in Eae

Microglia and macrophages are related cell types that play an important role in the pathogenesis of MS and EAE. This chapters reviews the role of these cells in the normal brain and their contribution to inflammatory demyelinating disease, including their role in antigen presentation, co-stimulation, and production of cytokines and other inflammatory mediators

Cytokines, nitric oxide, and cGMP modulate the permeability of an in vitro model of the human blood-brain barrier

The endothelial cells (EC) of the microvasculature in the brain form the anatomical basis of the blood-brain barrier (BBB). In the present study, the effects of agents that modify the permeability of a well-established in vitro model of the human BBB were studied. The monolayers formed by confluent human brain microvessel endothelial cell (HBMEC) cultures are impermeable to the macromolecule tracer horseradish peroxidase (HRP) and have high electrical resistance. Exposure of HBMEC to various cytokines including TNF-alpha, IL-1beta, interferon gamma (IFN-gamma), or lipopolysaccharide (LPS) decreased transendothelial electrical resistance (TEER) mainly by increasing the permeability of the tight junctions. Primary cultures of HBMEC express endothelial nitric oxide synthase (eNOS) and produce low levels of NO. Treatment with the NO donors sodium nitroprusside (SNP) and DETA NONOate or the cGMP agonist 8-Br-cGMP significantly increased monolayer resistance. Conversely, inhibition of soluble guanylyl cyclase with ODQ rapidly decreased the resistance, and pretreatment of HBMEC with Rp-8-CPT-cGMPS, an inhibitor of cGMP-dependent protein kinase, partially prevented the 8-Br-cGMP-induced increase in resistance. Furthermore, NO donors and 8-Br-cGMP could also reverse the increased permeability of the monolayers induced by IL-1beta, IFN-gamma, and LPS. These results indicate that NO can decrease the permeability of the human BBB through a mechanism at least partly dependent on cGMP production and cGMP-dependent protein kinase activation.

Increased interleukin-10 associated with low IL-6 concentration correlated with greater survival rates in mice infected by rabies virus vaccinated against it and immunomodulated with P. acnes

Macrophage activity, cytokines serum concentration, serum neutralizing antibodies and lethality by rabies were evaluated in swiss mice experimentally infected with street rabies virus and submitted or not to antirabies vaccination and immunomodulation with P. acnes. Animals were killed at different times and serum was collected in order to evaluate cytokines concentration; peritonial and splenic macrophages were collected for macrophage activity evaluation. Greater survival rates higher IL-10 and low IL-6 serum concentration were observed in vaccinated animals treated using P. acnes.

Immunohistochemical localization of endothelial and inducible nitric oxide synthase within neurons of cattle with rabies

The expression of constitutive endothelial nitric oxide synthase (eNOS) and inducible NOS (iNOS) in the brains of cattle with natural rabies was studied. Increased expression of eNOS was detected in neurons of the brain stem and Purkinje cells of cerebellum. By contrast, iNOS was diffusely localized in the cytoplasm of affected neurons, and some inflammatory cells were positive. eNOS and rabies antigen were co-localized in inclusion bodies (Negri bodies) in neurons. The specific localization of eNOS, but not iNOS, in the Negri bodies suggests that eNOS is involved in the formation of rabies virus inclusion bodies.

Selective inducible nitric oxide inhibition can restore hemodynamics, but does not improve neurological dysfunction in experimentally-induced septic shock in rats

In this study, we evaluated the time course of changes in inducible nitric oxide synthase (iNOS) in the brain by using the rat model of sepsis induced by cecal ligation and puncture (CLP) and examined whether selective iNOS inhibition can prevent the hemodynamic and neurological changes induced by sepsis. Male Wistar rats were randomly divided into four groups: control, sham, CLP, and CLP + the selective iNOS inhibitor L-N6-(1-iminoethyl)-lysine (L-NIL). Septic shock was induced in the rats by CLP under pentobarbital anesthesia, and then we measured hemodynamic variables, neurological indicators, blood gases, plasma levels of nitrate/nitrite (an indicator of the biosynthesis of NO), and brain iNOS activity and nitrotyrosine levels after 1, 6, 12, and 24 h. Plasma nitrite was increased at 12 and 24 h in the CLP group. The activity of iNOS in the brain was increased at 12 and 24 h after CLP (at 12 h: control, 0.3 +/- 0.05; sham, 0.3 +/- 0.1; CLP, 1.3 +/- 0.08*; CLP + L-NIL, 0.33 +/- 0.1 fmol x mg(-1) x min(-1); at 24 h: control, 0.27 +/- 0.08; sham, 0.31 +/- 0.1; CLP, 1.0 +/- 0.3*; CLP + L-NIL, 0.34 +/- 0.1 fmol x mg(-1) x min(-1); mean +/- SD; *P < 0.05). Brain nitrotyrosine was increased at 24 h after CLP (at 24 h: control, 6.7 +/- 0.4; sham, 6.7 +/- 0.5; CLP, 11.2 +/- 2.8*; CLP + L-NIL, 7.52 +/- 0.5 densitometric units; means +/- SD; *P < 0.01). In contrast, in both the CLP and CLP + L-NIL groups, the consciousness reflex was significantly decreased at 24 h after CLP. Selective iNOS inhibition restored the hemodynamic changes induced by sepsis but could not improve neurological dysfunction.

Role of the nitric-oxide synthase isoforms during morphine-induced hyperthermia in rats

Recently, we demonstrated that the diffusible messenger molecule nitric oxide (NO) is involved in the hyperthermic response induced by morphine by using a nonselective nitric-oxide synthase inhibitor, N-nitro-L-arginine methyl ester. The present work extended these studies to include 7-nitroindazole (7-NI), an inhibitor specific for neuronal nitric-oxide synthase (nNOS), N(5)-(-iminoethyl)-L-ornithine (L-NIO), an inhibitor of endothelial NOS (eNOS), and aminoguanidine (AG), a potent inhibitor of inducible NOS (iNOS). A biotelemetry system was used in this study to measure the body temperature (Tb). A dose of 7-NI (5 or 10 mg/kg), which did not affect Tb by itself, blocked the hyperthermia induced by morphine in a dose-dependent manner (15 mg/kg i.p.). However, pretreatment with L-NIO (10-20 mg/kg) or with AG (50 mg/kg) failed to alter the hyperthermia induced by morphine. L-NIO (10-20 mg/kg) or AG (50 mg/kg) had no effect on Tb. These results suggest the involvement of nNOS in morphine-induced hyperthermia.

Genetic Models in Applied Physiology. Differential role of nitric oxide synthase isoforms in fever of different etiologies: studies using Nos gene-deficient mice

Male C57BL/6J mice deficient in nitric oxide synthase (NOS) genes (knockout) and control (wild-type) mice were implanted intra-abdominally with battery-operated miniature biotelemeters (model VMFH MiniMitter, Sunriver, OR) to monitor changes in body temperature. Intravenous injection of lipopolysaccharide (LPS; 50 microg/kg) was used to trigger fever in response to systemic inflammation in mice. To induce a febrile response to localized inflammation, the mice were injected subcutaneously with pure turpentine oil (30 microl/animal) into the left hindlimb. Oral administration (gavage) of N(G)-monomethyl-l-arginine (l-NMMA) for 3 days (80 mg. kg(-1). day(-1) in corn oil) before injection of pyrogens was used to inhibit all three NOSs (N(G)-monomethyl-d-arginine acetate salt and corn oil were used as control). In normal male C57BL/6J mice, l-NMMA inhibited the LPS-induced fever by approximately 60%, whereas it augmented fever by approximately 65% in mice injected with turpentine. Challenging the respective NOS knockout mice with LPS and with l-NMMA revealed that inducible NOS and neuronal NOS isoforms are responsible for the induction of fever to LPS, whereas endothelial NOS (eNOS) is not involved. In contrast, none of the NOS isoforms appeared to trigger fever to turpentine. Inhibition of eNOS, however, exacerbates fever in mice treated with l-NMMA and turpentine, indicating that eNOS participates in the antipyretic mechanism. These data support the hypothesis that nitric oxide is a regulator of fever. Its action differs, however, depending on the pyrogen used and the NOS isoform.

Erythropoietin exerts an anti-inflammatory effect on the CNS in a model of experimental autoimmune encephalomyelitis

In recent work we reported that systemically administered erythropoietin (EPO) crosses the blood-brain barrier and has protective effects in animal models of cerebral ischemia, brain trauma and in a rat model of experimental autoimmune encephalomyelitis (EAE). Here we characterize the effect of systemic EPO on the inflammatory component of actively induced, acute EAE in Lewis rats. Administration of EPO at doses of 500-5000 U/kg bw i.p., daily from day 3 after immunization with myelin basic protein (MBP), delayed the onset of EAE and decreased its clinical score at peak time (days 12-13). Immunohistochemical analysis of the spinal cord using anti-glial fibrillary acidic protein (GFAP) and anti-CD11b antibodies showed that EPO markedly diminished inflammation and glial activation/proliferation. EAE induced significant levels of TNF and IL-6 in the spinal cord, where IL-6 was maximum at the onset of the disease (day 10) and TNF at its peak (day 12). EPO delayed the increase of TNF levels, without altering their peak levels, and markedly reduced those of IL-6 suggesting that the decreased inflammation and clinical score may be in part upon attenuation of IL-6. On the other hand, EPO was without effect in a model of adjuvant-induced arthritis in Lewis rats, suggesting a specificity towards autoimmune demyelinating diseases. These data suggest that EPO might act as a protective cytokine in inflammatory pathologies of the CNS.

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.

Altered inflammatory response and increased neurodegeneration in metallothionein I+II deficient mice during experimental autoimmune encephalomyelitis

Metallothionein-I+II (MT-I+II) are antioxidant, neuroprotective proteins, and in this report we have examined their roles during experimental autoimmune encephalomyelitis (EAE) by comparing MT-I+II-knock-out (MTKO) and wild-type mice. We herewith show that EAE susceptibility is higher in MTKO mice relatively to wild-type mice, and that the inflammatory responses elicited by EAE in the central nervous system (CNS) are significantly altered by MT-I+II deficiency. Thus, during EAE the MTKO mice showed increased macrophage and T-lymphocytes infiltration in the CNS, while their reactive astrogliosis was significantly decreased. In addition, the expression of the proinflammatory cytokines interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha elicited by EAE was further increased in the MTKO mice, and oxidative stress and apoptosis were also significantly increased in MTKO mice compared to normal mice. The present results strongly suggest that MT-I+II are major factors involved in the inflammatory response of the CNS during EAE and that they play a neuroprotective role in this scenario.

Estrogen prevents the lipopolysaccharide-induced inflammatory response in microglia

After neuronal injury and in several neurodegenerative diseases, activated microglia secrete proinflammatory molecules that can contribute to the progressive neural damage. The recent demonstration of a protective role of estrogen in neurodegenerative disorders in humans and experimental animal models led us to investigate whether this hormone regulates the inflammatory response in the CNS. We here show that estrogen exerts an anti-inflammatory activity on primary cultures of rat microglia, as suggested by the blockage of the phenotypic conversion associated with activation and by the prevention of lipopolysaccharide-induced production of inflammatory mediators: inducible form of NO synthase (iNOS), prostaglandin-E(2) (PGE(2)), and metalloproteinase-9 (MMP-9). These effects are dose-dependent, maximal at 1 nm 17beta-estradiol, and can be blocked by the estrogen receptor (ER) antagonist ICI 182,780. The demonstration of ERalpha and ERbeta expression in microglia and macrophages and the observation of estrogen blockade of MMP-9 mRNA accumulation and MMP-9 promoter induction further support the hypothesis of a genomic activity of estrogen via intracellular receptors. This is the first report showing an anti-inflammatory activity of estrogen in microglia. Our study proposes a novel explanation for the protective effects of estrogen in neurodegenerative and inflammatory diseases and provides new molecular and cellular targets for the screening of ER ligands acting in the CNS.

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.

Metallothionein I+II expression and their role in experimental autoimmune encephalomyelitis

We examined the expression and roles of neuroprotective metallothionein-I+II (MT-I+II) in the rat CNS in experimental autoimmune encephalomyelitis (EAE), an animal model for the human autoimmune disease, multiple sclerosis (MS). EAE caused significant macrophage activation, T-lymphocyte infiltration, and astrogliosis in spinal cord, brain stem, and cerebellum, which peaked 14-18 days after immunization. The remission of symptoms and histopathological changes began at days 19-21 and were completed by days 30-40. MT-I+II expression was increased significantly in EAE infiltrates. In order to study the effects of increased MT levels, we administered Zn-MT-II intraperitoneally (i.p.) to rats during EAE. Clinically, Zn-MT-II treatment reduced the severity of EAE symptoms and mortality in a time- and dose-dependent manner. Histopathologically, Zn-MT-II increased reactive astrogliosis and decreased macrophages and T lymphocytes significantly in the CNS. In spleen sections, the number of macrophages both in control and EAE-sensitized rats was reduced by Zn-MT-II, while the number of lymphocytes remained unaltered by Zn-MT-II. Therefore, we suggest that MT-II has peripheral mechanisms of action on macrophages, while T lymphocytes are affected locally in the CNS. During EAE, oxidative stress was decreased by Zn-MT-II, which could contribute to the diminished clinical scores observed. None of the effects caused by Zn-MT-II could be attributable to the zinc content. These results suggest MT-I+II as potentially useful factors for the treatment of EAE/MS.

Differential role of nitric oxide pathway and heat shock protein in preconditioning and lipopolysaccharide-induced brain ischemic tolerance

The purposes of this study were to investigate the role of nitric oxide (NO), nitric oxide synthase (NOS), and 70 kDa heat shock protein in brain ischemic tolerance induced by ischemic preconditioning and lipopolysaccharide. Focal cerebral ischemia was induced in rats by intraluminal middle cerebral artery occlusion. Infarct volume was significantly reduced (1) in rats subjected to 3 min ischemia 72 h prior to 60 min ischemia; (2) in rats administered lipopolysaccharide (0.5 mg/kg; i.p.) 72 h prior to 60 min ischemia compared with controls. The beneficial effect of ischemic preconditioning was unchanged despite prior administration of nitro-L-arginine methyl ester (L-NAME), a NOS inhibitor. Conversely, the protective effect of lipopolysaccharide was nullified by L-NAME. Using immunohistochemical techniques, we observed that (1) ischemic preconditioning but not lipopolysaccharide induces the expression of 70 kDa heat shock protein in cerebral cortex and (2) lipopolysaccharide induces early increased expression of endothelial NOS in cerebral blood vessels. The results suggest that (1) endothelium-derived NO plays a role of a trigger in the brain tolerance induced by lipopolysaccharide, and (2) 70 kDa heat shock protein is involved in the protection afforded by ischemic preconditioning but not by lipopolysaccharide.

Constitutive and inducible nitric oxide synthases after dynorphin-induced spinal cord injury

It has recently been demonstrated that selective inhibition of both neuronal constitutive and inducible nitric oxide synthases (ncNOS and iNOS) is neuroprotective in a model of dynorphin (Dyn) A(1-17)-induced spinal cord injury. In the present study, various methods including the conversion of 3H-L-arginine to 3H-citrulline, immunohistochemistry and in situ hybridization are employed to determine the temporal profiles of the enzymatic activities, immunoreactivities, and mRNA expression for both ncNOS and iNOS after intrathecal injection of a neurotoxic dose (20 nmol) of Dyn A(1-17). The expression of ncNOS immunoreactivity and mRNA increased as early as 30 min after injection and persisted for 1-4 h. At 24-48 h, the number of ncNOS positive cells remained elevated while most neurons died. The cNOS enzymatic activity in the ventral spinal cord also significantly increased at 30 min 48 h, but no significant changes in the dorsal spinal cord were observed. However, iNOS mRNA expression increased later at 2 h, iNOS immunoreactivity and enzymatic activity increased later at 4 h and persisted for 24-48 h after injection of 20 nmol Dyn A(1-17). These results indicate that both ncNOS and iNOS are associated with Dyn-induced spinal cord injury, with ncNOS predominantly involved at an early stage and iNOS at a later stage.

Our shifting understanding of the role of nitric oxide in autoimmune encephalomyelitis: a review

Nitric oxide was first described being produced in inflammatory cells involved in experimental autoimmune encephalomyelitis in 1992. Since then some 45 papers have appeared examining the role of NO in this central nervous system autoimmune inflammatory disease. Of the first 10 papers published all resulted in the interpretation that NO was a pathologic or "bad" molecule in the context of EAE. A few papers then began to appear suggesting that NO may not in fact always be a harmful molecule and by the end of 1997 early 1998, 22 papers suggested a destructive role for the molecule while three suggested it was protective. The past two years have seen a significant increase in reports supporting a protective mechanism for NO in EAE such that as of July 1999, 27 papers suggest a destructive and 15 a protective role for NO with a few uncommitted. This review sets out in a more or less chronological order the studies examining the role of NO in EAE and maps our changing understanding of the molecules role in this CNS inflammatory disease and by inference perhaps multiple sclerosis.

Dose-dependent attenuation of lipopolysaccharide-fever by inhibitors of inducible nitric oxide-synthase in guinea pigs

Different doses of aminoguanidine or S-methylisothiourea, both predominantly inhibitors of the inducible form of nitric oxide (NO)-synthase, were injected into the arterial circulation of guinea pigs alone or along with 10 microg/kg bacterial lipopolysaccharide. Doses of 10 mg/kg, 50 mg/kg or 250 mg/kg aminoguanidine per se had no influence on abdominal temperature of guinea pigs. Only the highest dose of aminoguanidine (250 mg/kg) completely suppressed the first phase of the biphasic febrile response to lipopolysaccharide-injections. Lipopolysaccharide-fever was not modulated by administration of 10 mg/kg or 50 mg/kg aminoguanidine, when compared to fever in response to injections of lipopolysaccharide along with solvent. Doses of 10 mg/kg or 50 mg/kg S-methylisothiourea did not alter abdominal temperature while a dose of 250 mg/kg S-methylisothiourea had a lethal effect in guinea pigs. The febrile response to lipopolysaccharide was unimpaired by administration of 10 mg/kg S-methylisothiourea, while a dose of 50 mg/kg again attenuated fever predominantly by a suppression of the first fever phase. None of the applied doses of aminoguanidine or S-methylisothiourea resulted in a significant attenuation of the lipopolysaccharide-induced circulating cytokines tumor necrosis factor-alpha (TNF-alpha) and interleukin-6. The drugs themselves, without lipopolysaccharide-injections, did not enhance or reduce circulating levels of the investigated cytokines. The results indicate that endogenous NO may participate in the induction of lipopolysaccharide-fever and that fever suppression by systemic administration of NO-synthase inhibitors occurs independently from the lipopolysaccharide-induced circulating cytokines.

Increased urinary nitric oxide metabolites in patients with multiple sclerosis correlates with early and relapsing disease

Nitric oxide (NO) has been implicated in the immunopathogenesis of MS as a potential mediator of neuronal loss. To investigate the role of.NO in the development of progressive disease we measured the NO metabolites (nitrate and nitrite) and neopterin, in the urine of 129 patients with demyelinating disease (DD): 23 with clinically isolated syndromes compatible with demyelination and in 46 relapsing remitting (RR) and 60 patients with progressive MS. Eighty-nine of these 129 patients underwent Gd-enhanced MRI. In addition 58 normal control subjects (NC), 19 AIDS and 35 rheumatoid arthritis (RA) patients were studied. Patients with DD, AIDS and RA had significantly elevated urinary nitrate plus nitrite (nit : creat. urine) and neopterin (neopt : creat.urine) to creatinine ratios compared to NC subjects. (Median[25th - 75th%] nit : creat.urine: NC=1183[962 - 1365] vs DD=1245[875 - 2403], AIDS=1686[1231 - 2531], and RA=1950[1214 - 2726] mumol/mol, P<0.001 and median[25th - 75th%] neopt : creat.urine: NC=99[76 - 151] vs DD=163[119 - 266], AIDS=972[653 - 1456], and RA=389[257 - 623] mu mol/mol, P<0.001). Patients with early DD and RR MS had significantly elevated nit : creat.urine compared to patients with progressive MS (nit : creat. urine: 1612[1020 - 2733] vs 1159[790 - 1641] mu mol/mol, P=0.006). The nit : creat.urine and neopt : creat.urine did not correlate with clinical relapse or MRI activity. Excretion of.NO metabolites is increased in patients with early or relapsing-remitting disease.NO appears to be a double-edged sword, mediating tissue damage and modulating complex immunological functions which may be protective in MS.

Cerebrovascular hemodynamics and ischemic tolerance: lipopolysaccharide-induced resistance to focal cerebral ischemia is not due to changes in severity of the initial ischemic insult, but is associated with preservation of microvascular perfusion

Lipopolysaccharide (LPS), administered 72 hours before middle cerebral artery (MCA) occlusion, confers significant protection against ischemic injury. For example, in the present study, LPS (0.9 mg/kg intravenously) induced a 31% reduction in infarct volume (compared with saline control) assessed 24 hours after permanent MCA occlusion. To determine whether LPS induces true tolerance to ischemia, or merely attenuates initial ischemic severity by augmenting collateral blood flow, local CBF was measured autoradiographically 15 minutes after MCA occlusion. Local CBF did not differ significantly between LPS- and saline-pretreated rats (e.g., 34 +/- 10 and 29 +/- 15 mL x 100 g(-1) x min(-1) for saline and LPS pretreatment in a representative region of ischemic cortex), indicating that the neuroprotective action of LPS is not attributable to an immediate reduction in the degree of ischemia induced by MCA occlusion, and that LPS does indeed induce a state of ischemic tolerance. In contrast to the similarity of the initial ischemic insult between tolerant (LPS-pretreated) and nontolerant (saline-pretreated) rats, microvascular perfusion assessed either 4 hours or 24 hours after MCA occlusion was preserved at significantly higher levels in the LPS-pretreated rats than in controls. Furthermore, the regions of preserved perfusion in tolerant animals were associated with regions of tissue sparing. These results suggest that LPS-induced tolerance to focal ischemia is at least partly dependent on the active maintenance of microvascular patency and hence the prevention of secondary ischemic injury.

Systemic administration of lipopolysaccharide induces release of nitric oxide and glutamate and c-fos expression in the nucleus tractus solitarii of rats

There is increasing recognition that communication pathways exist between the immune system and brain, which allows bidirectional regulation of immune and brain responses to infection. The endotoxin lipopolysaccharide (LPS) has been reported to elicit release of cytokines and expression of inducible nitric oxide synthase (iNOS) in peripheral organs. Whereas LPS given systemically causes endotoxic shock, little is known about its central nervous system action, particularly the induction of iNOS. Nitric oxide (NO) and glutamate in the nucleus tractus solitarii (NTS) are important mediators of central cardiovascular regulation. We have previously demonstrated that intravenous injections of LPS increased the NO precursor L-arginine-induced depressor effect in the NTS. The present study investigated further the effects of LPS on the release of NO and glutamate in the NTS and the expression of c-fos, an immediate early response gene product, in neural substrates for central cardiovascular control. In vivo microdialysis coupled with chemiluminescence and electrochemical detection techniques were used to measure extracellular levels of NO and glutamate in the rat NTS. Immunohistochemistry was used for the examination of c-fos protein expression. We found that intravenous infusion of LPS (10 mg/kg) produced a biphasic depressor effect, with an early, sharp hypotension that partially recovered in 15 minutes and a secondary, more prolonged hypotension. In the NTS, a progressive increase of extracellular glutamate and NO levels occurred 3 and 4 hours after LPS was given, respectively. The effects of LPS on the induction of delayed hypotension and NO formation in the NTS were abolished by pretreatment with the iNOS inhibitor aminoguanidine. Finally, c-fos protein expression in the NTS and related structures for cardiovascular regulation was observed after LPS challenge. Taken together, these data suggest that an endotoxin given systemically can elicit delayed increases of glutamate release and iNOS-dependent NO production in the NTS and activate the central neural pathway for modulating cardiovascular function.

Inducible nitric oxide synthase expression in cultures enriched for mature oligodendrocytes is due to microglia

Expression of inducible nitric oxide (NO) synthase (NOS-2) occurs during inflammation in the central nervous system (CNS) and has been linked to demyelination accompanying certain CNS inflammatory diseases. Although astrocytes and microglia are thought to be the major sources of NOS-2 expression in the CNS in vivo, recent evidence suggested that the myelin-producing oligodendrocytes (OLs) themselves can express NOS-2 in culture. Given the potentially important pathological implications of this finding, the purpose of this study was to examine further the expression of NOS-2 by OLs in vitro. After exposure to lipopolysaccharide (LPS) and interferon-gamma (IFNgamma), primary cultures enriched for mature OLs released NO in a time-dependent manner, although the amount varied considerably between different culture preparations. Increased NO production was accompanied by expression of NOS-2 mRNA and protein, as determined by reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot analysis, respectively. Immunofluorescence analysis revealed that the cell-type expressing NOS-2 in these cultures was galactocerebroside (Gal C)-negative but CD11b-positive. Further, NO production could be attenuated in cultures treated with the microglial/macrophage toxin, leucine methyl ester, prior to LPS/IFNgamma stimulation. Thus, microglia were the source of NOS-2 catalytic activity in these cultures. The present results indicate that LPS and IFNgamma are not effective stimuli for induction of NOS-2 in OLs in primary cell culture.

Down-regulation of microglial cyclo-oxygenase-2 and inducible nitric oxide synthase expression by lipocortin 1

1. Activated microglial cells are believed to play an active role in most brain pathologies, during which they can contribute to host defence and repair but also to the establishment of tissue damage. These actions are largely mediated by microglial secretory products, among which are prostaglandins (PGs) and nitric oxide (NO). 2. The anti-inflammatory protein, lipocortin 1 (LC1) was reported to have neuroprotective action and to be induced by glucocorticoids in several brain structures, with a preferential expression in microglia. In this paper we tested whether the neuroprotective effect of LC1 could be explained by an inhibitory effect on microglial activation. 3. We have previously shown that bacterial endotoxin (LPS) strongly stimulates PGE2 and NO production in rat primary microglial cultures, by inducing the expression of the key enzymes cyclo-oxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS), respectively. 4. Dexamethasone (DEX, 1-100 nM) and LC1-derived N-terminus peptide (peptide Ac2-26, 1-100 microg ml(-1)) dose-dependently inhibited the production of both PGE2 and NO from LPS-stimulated microglia. The inhibitory effects of DEX on NO and of the peptide on NO and PGE2 synthesis were partially abrogated by a specific antiserum, raised against the N-terminus of human LC1. The peptide Ac2-26 did not affect arachidonic acid release from control and LPS-stimulated microglial cultures. 5. Western blot experiments showed that the LPS-induced expression of COX-2 and iNOS was effectively down-regulated by DEX (100 nM) and peptide Ac2-26 (100 microg ml(-1)). 6. In conclusion, our findings support the hypothesis that LC1 may foster neuroprotection by limiting microglial activation, through autocrine and paracrine mechanisms.

Nitric oxide synthase expression and apoptotic cell death in brains of AIDS and AIDS dementia patients

OBJECTIVES

To determine the occurrence and cellular localization of inducible nitric oxide synthase (iNOS), NOS activity and its association with cell death in brains of AIDS and AIDS dementia complex (ADC) patients.

DESIGN AND METHODS

Post-mortem cerebral cortex tissue of eight AIDS patients, eight ADC patients and eight control subjects was processed for iNOS immunocytochemistry, NADPH-diaphorase activity staining as an index of NOS activity, and in situ end-labelling to detect cell death.

RESULTS

iNOS-positive cells were present in the white matter of 14 out of 16 AIDS and ADC patients, whereas two out of eight control subjects showed iNOS-positive cells. iNOS immunoreactivity was exclusively localized in activated macrophages and microglial cells that both showed NADPH-diaphorase activity. In addition, NADPH-diaphorase activity, not related to iNOS immunoreactivity, was observed in astrocytes in both white and grey matter of AIDS and ADC patients. All AIDS and ADC patients, and only one control subject showed characteristic features of apoptotic cell death.

CONCLUSIONS

Different forms of NOS are present in microglial cells and astrocytes of AIDS and ADC patients but are largely absent in control subjects. Although more NOS-expressing cells occur in ADC than in AIDS patients, apoptotic cell death was found in both patient groups to the same extent. We postulate that NO production in brains of AIDS patients results in cumulative cortical cell loss, which becomes neurologically evident at later stages of disease and is expressed as ADC.

Nitric oxide in neurodegeneration

Nitric oxide (NO) is a unique biological messenger molecule which mediates diverse physiologic roles. NO mediates blood vessel relaxation by endothelium, immune activity of macrophages and neurotransmission of central and peripheral neurons. NO is produced from three NO Synthase (NOS) isoforms: Neuronal NOS (nNOS), endothelial NOS, and inducible NOS (iNOS). In the central nervous system, NO may play important roles in neurotransmitter release, neurotransmitter reuptake, neurodevelopment, synaptic plasticity, and regulation of gene expression. However, excessive production of NO following a pathologic insult can lead to neurotoxicity. NO plays a role in mediating neurotoxicity associated with a variety of neurologic disorders, including stroke, Parkinson's Disease, and HIV dementia.

An antiviral mechanism of nitric oxide: inhibition of a viral protease

Although nitric oxide (NO) kills or inhibits the replication of a variety of intracellular pathogens, the antimicrobial mechanisms of NO are unknown. Here, we identify a viral protease as a target of NO. The life cycle of many viruses depends upon viral proteases that cleave viral polyproteins into individual polypeptides. NO inactivates the Coxsackievirus protease 3C, an enzyme necessary for the replication of Coxsackievirus. NO S-nitrosylates the cysteine residue in the active site of protease 3C, inhibiting protease activity and interrupting the viral life cycle. Substituting a serine residue for the active site cysteine renders protease 3C resistant to NO inhibition. Since cysteine proteases are critical for virulence or replication of many viruses, bacteria, and parasites, S-nitrosylation of pathogen cysteine proteases may be a general mechanism of antimicrobial host defenses.

N-Acetyl-cysteine inhibition of encephalomyelitis Theiler's virus-induced nitric oxide and tumour necrosis factor-alpha production by murine astrocyte cultures

The pathological mechanisms that cause central nervous system (CNS) dysfunction in most neurological diseases are not well established. Theiler's murine encephalomyelitis virus (TMEV) is known to interact with cells of the CNS and its intracerebral inoculation to susceptible mice strains causes neurological disorders resembling multiple sclerosis (MS). In this study, we reported that primary astrocyte cultures from SJL/J susceptible mice when infected with TMEV released important amounts of nitrites (NO2-) to the culture medium, as measured in the supernatants 24 hours after infection. In addition, we observed an increment in the production of tumour necrosis factor alpha (TNF-alpha) by susceptible SJL/J strain derived astrocytes infected with TMEV. The treatment with the thiolic antioxidant N-acetyl-cysteine partially suppressed the virus-stimulated production of nitric oxide and TNF-alpha, in a dose response fashion. These results indicate that during viral infection astrocytes are an important cellular source of nitric oxide and TNF-alpha, substances which play important roles during CNS inflammatory events. The effects of the antioxidant N-acetyl-cysteine, modulating the production of the above compounds by TMEV-infected astrocytes may be a significant factor in preventing CNS demyelination.

An inhibitor of inducible nitric oxide synthase ameliorates experimental autoimmune myocarditis in Lewis rats

We studied the effect of nitric oxide (NO) on experimental autoimmune myocarditis (EAC) in rats. We examined the role of inducible nitric oxide synthase (iNOS), an enzyme that produces NO, on hearts affected with EAC, by testing the effects of aminoguanidine (AG), a selective iNOS inhibitor, on the course of EAC. Western blotting detected iNOS in the affected cardiac tissues, but not in CFA immunized cases. Immunohistochemically, the majority of ED1+ macrophages in the EAC lesions were positive for iNOS and nitrotyrosine. A high dose of AG (200 mg/kg/day) significantly reduced the incidence of EAC (p < 0.05) and ameliorated the histological score for the cardiac inflammation (p < 0.01) compared with the low dose AG (100 mg/kg/day) and vehicle treated groups. The immunoblot analysis showed that a high dose of AG effectively suppressed iNOS in hearts affected with EAC. An iNOS band was barely detected in the high dose AG (200 mg/kg) treated group, while it was distinctively visualized in the vehicle and low dose AG (100 mg/kg) treated groups. These results suggest that iNOS is upregulated in EAC lesions and increased NO production plays an important role in the development of EAC. In addition, selective iNOS inhibitors may have a therapeutic role in treating certain autoimmune diseases including EAC.

Inducible nitric oxide synthase and nitrotyrosine are found in monocytes/macrophages and/or astrocytes in acute, but not in chronic, multiple sclerosis

We have examined the localization of inducible nitric oxide synthase (iNOS) and nitrotyrosine (the product of nitration of tyrosine by peroxynitrite, a highly reactive derivative of nitric oxide [NO]) in demyelinating lesions from (i) two young adult patients with acute multiple sclerosis (MS), (ii) a child with MS (consistent with diffuse sclerosis), and (iii) five adult patients with chronic MS. Previous reports have suggested a possible correlation between iNOS, peroxynitrite, related nitrogen-derived oxidants, and the demyelinating processes in MS. We have demonstrated iNOS-immunoreactive cells in both acute-MS and diffuse-sclerosis-type lesions. In acute-MS lesions, iNOS was localized in both monocytes/macrophages and reactive astrocytes. However, foamy (myelin-laden) macrophages and the majority of reactive astrocytes were iNOS negative. In specimens from the childhood MS patient, iNOS protein was present only in a subpopulation of reactive or hypertrophic astrocytes. In contrast, no iNOS staining was detected in chronic-MS lesions. Immunohistochemical staining of acute-MS lesions with an antibody to nitrotyrosine revealed codistribution of iNOS- and nitrotyrosine-positive cells, although nitrotyrosine staining was more widespread in cells of the monocyte/macrophage lineage. In diffuse-sclerosis-type lesions, nitrotyrosine staining was present in hypertrophic astrocytes, whereas it was absent in chronic-MS lesions. These results suggest that NO and nitrogen-derived oxidants may play a role in the initiation of demyelination in acute-MS lesions but not in the later phase of the disease.

The potential role of nitric oxide in multiple sclerosis

Nitric oxide (.NO) and its reactive derivative peroxynitrite (ONOO-) have been implicated in the pathogenesis of multiple sclerosis (MS). They are cytotoxic to oligodendrocytes and neurones in culture by inhibiting the mitochondrial respiratory chain (complexes II/III and IV) and inhibiting certain key intracellular enzymes. Recently .NO has been implicated as a possible aetiological factor in reversible conduction block in demyelinated axons. Inducible nitric oxide synthase (iNOS) is upregulated in the central nervous system of animals with experimental allergic encephalomyelitis (EAE) and in patients with MS. In some EAE models inhibiting iNOS activity decreases disease severity whilst in other models disease activity is exacerbated. Raised levels of nitrate and nitrite, stable end-products of .NO/ONOO-, are found in the cerebrospinal fluid, serum and urine of patients with MS. CSF levels of nitrate and nitrite correlate with blood-brain-barrier dysfunction, which suggests that .NO may play a role in inflammatory blood-brain-barrier dysfunction. In a longitudinal study on 24 patients with relapsing remitting and secondary progressive MS, raised serum nitrate and nitrite levels correlated with a relapsing course and infrequent relapses. However, no correlation was found between raised serum levels of nitrate and nitrite and MRI activity, disease progression, or the development of cerebral atrophy. In autoimmune mediated CNS demyelinating disease .NO may be a double-edged sword, mediating tissue damage on the one hand and on the other hand modulating complex immunological functions which may be protective.