Temporal and anatomical distribution of nitric oxide synthase mRNA expression and nitric oxide production during central nervous system inflammation

Inhibition by Thyroid Hormones of Cell Migration Activated by IGF-1 and MCP-1 in THP-1 Monocytes: Focus on Signal Transduction Events Proximal to Integrin αvβ3

Interaction between thyroid hormones and the immune system is reported in the literature. Thyroid hormones, thyroxine, T₄, but also T₃, act non-genomically through mechanisms that involve a plasma membrane receptor αvβ3 integrin, a co-receptor for insulin-like growth factor-1 (IGF-1). Previous data from our laboratory show a crosstalk between thyroid hormones and IGF-1 because thyroid hormones inhibit the IGF-1-stimulated glucose uptake and cell proliferation in L-6 myoblasts, and the effects are mediated by integrin αvβ3. IGF-1 also behaves as a chemokine, being an important factor for tissue regeneration after damage. In the present study, using THP-1 human leukemic monocytes, expressing αvβ3 integrin in their cell membrane, we focused on the crosstalk between thyroid hormones and either IGF-1 or monocyte chemoattractant protein-1 (MCP-1), studying cell migration and proliferation stimulated by the two chemokines, and the role of αvβ3 integrin, using inhibitors of αvβ3 integrin and downstream pathways. Our results show that IGF-1 is a potent chemoattractant in THP-1 monocytes, stimulating cell migration, and thyroid hormone inhibits the effect through αvβ3 integrin. Thyroid hormone also inhibits IGF-1-stimulated cell proliferation through αvβ3 integrin, an example of a crosstalk between genomic and non-genomic effects. We also studied the effects of thyroid hormone on cell migration and proliferation induced by MCP-1, together with the pathways involved, by a pharmacological approach and docking simulation. Our findings show a different downstream signaling for IGF-1 and MCP-1 in THP-1 monocytes mediated by the plasma membrane receptor of thyroid hormones, integrin αvβ3.

Alterations in neurobehaviors and inflammation in hippocampus of rats induced by oral administration of microcystin-LR

Microcystin-LR (MC-LR) is a widely studied toxic peptide secreted by certain water blooms of cyanobacteria that exhibit hepatotoxicity and neural toxicity. This study aimed to observe the neurotoxic effects of low-dose MC-LR exposure by oral administration. Male Sprague-Dawley (SD) rats were administered orally every 2 days for 8 weeks with pure water and 0.2, 1.0, and 5.0 μg/kg MC-LR. The Morris water maze test was used to assess the spatial learning and memory capability of rats. The activation of astrocytes and nitric oxide synthase (NOS) was evaluated by immunohistochemistry, and concentrations of nitric oxide (NO) in rat hippocampus were analyzed. Slight liver dysfunction was observed in the 5.0 μg/kg MC-LR-treated rats. Impairment of spatial learning and memory was also observed in the 5.0 μg/kg MC-LR-treated rats. Astrocytes in the hippocampus of the 5.0 μg/kg MC-LR-treated rats showed enhanced activation and cell density; the inflammatory indicators, NOS and NO, increased in accordance with astrocyte activation. This study showed that oral exposure of MC-LR had adverse affects on neurobehaviors, and induced inflammation in memory-related brain regions.

Relationship between nitric oxide- and calcium-dependent signal transduction pathways in growth hormone release from dispersed goldfish pituitary cells

Nitric oxide (NO) and Ca(2+) are two of the many intracellular signal transduction pathways mediating the control of growth hormone (GH) secretion from somatotropes by neuroendocrine factors. We have previously shown that the NO donor sodium nitroprusside (SNP) elicits Ca(2+) signals in identified goldfish somatotropes. In this study, we examined the relationships between NO- and Ca(2+)-dependent signal transduction mechanisms in GH secretion from primary cultures of dispersed goldfish pituitary cells. Morphologically identified goldfish somatotropes stained positively for an NO-sensitive dye indicating they may be a source of NO production. In 2h static incubation experiments, GH release responses to the NO donor S-nitroso-N-acetyl-d,l-penicillamine (SNAP) were attenuated by CoCl2, nifedipine, verapamil, TMB-8, BHQ, and KN62. In column perifusion experiments, the ability of SNP to induce GH release was impaired in the presence of TMB-8, BHQ, caffeine, and thapsigargin, but not ryanodine. Caffeine-elicited GH secretion was not affected by the NO scavenger PTIO. These results suggest that NO-stimulated GH release is dependent on extracellular Ca(2+) availability and voltage-sensitive Ca(2+) channels, as well as intracellular Ca(2+) store(s) that possess BHQ- and/or thapsigargin-inhibited sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPases, as well as TMB-8- and/or caffeine-sensitive, but not ryanodine-sensitive, Ca(2+)-release channels. Calmodulin kinase-II also likely participates in NO-elicited GH secretion but caffeine-induced GH release is not upstream of NO production. These findings provide insights into how NO actions many integrate with Ca(2+)-dependent signalling mechanisms in goldfish somatotropes and how such interactions may participate in the GH-releasing actions of regulators that utilize both NO- and Ca(2+)-dependent transduction pathways.

Vitreous mediators in retinal hypoxic diseases

The causes of retinal hypoxia are many and varied. Under hypoxic conditions, a variety of soluble factors are secreted into the vitreous cavity including growth factors, cytokines, and chemokines. Cytokines, which usually serve as signals between neighboring cells, are involved in essentially every important biological process, including cell proliferation, inflammation, immunity, migration, fibrosis, tissue repair, and angiogenesis. Cytokines and chemokines are multifunctional mediators that can direct the recruitment of leukocytes to sites of inflammation, promote the process, enhance immune responses, and promote stem cell survival, development, and homeostasis. The modern particle-based flow cytometric analysis is more direct, stable and sensitive than the colorimetric readout of the conventional ELISA but, similar to ELISA, is influenced by vitreous hemorrhage, disruption of the blood-retina barrier, and high serum levels of a specific protein. Finding patterns in the expression of inflammatory cytokines specific to a particular disease can substantially contribute to the understanding of its basic mechanism and to the development of a targeted therapy.

SOD1 aggregation in astrocytes following ischemia/reperfusion injury: a role of NO-mediated S-nitrosylation of protein disulfide isomerase (PDI)

Background

Ubiquitinated-protein aggregates are implicated in cerebral ischemia/reperfusion injury. The very presence of these ubiquitinated-protein aggregates is abnormal and seems to be disease-related. However, it is not clear what leads to aggregate formation and whether the aggregations represent a reaction to aggregate-mediated neurodegeneration.

Methods

To study the nitrosative stress-induced protein aggregation in cerebral ischemia/reperfusion injury, we used primary astrocyte cultures as a cell model, and systematically examined their iNOS expression and consequent NO generation following oxygen glucose deprivation and reperfusion. The expression of protein disulfide isomerase (PDI) and copper-zinc superoxide dismutase (SOD1) were also examined, and the biochemical interaction between PDI and SOD1 was determined by immunoprecipitation. In addition, the levels of S-nitrosylated PDI in cultured astrocytes after oxygen glucose deprivation and reperfusion treatment were measured using the biotin-switch assay. The formation of ubiquitinated-protein aggregates was detected by immunoblot and immunofluorescence staining.

Results

Our data showed that the up-regulation of iNOS expression after oxygen glucose deprivation and reperfusion treatment led to excessive NO generation. Up-regulation of PDI and SOD1 was also identified in cultured astrocytes following oxygen glucose deprivation and reperfusion, and these two proteins were found to bind to each other. Furthermore, the increased nitrosative stress due to ischemia/reperfusion injury was highly associated with NO-induced S-nitrosylation of PDI, and this S-nitrosylation of PDI was correlated with the formation of ubiquitinated-protein aggregates; the levels of S-nitrosylated PDI increased in parallel with the formation of aggregates. When NO generation was pharmacologically inhibited by iNOS specific inhibitor 1400W, S-nitrosylation of PDI was significantly blocked. In addition, the formation of ubiquitinated-protein aggregates in cultured astrocytes following oxygen glucose deprivation and reperfusion was also suppressed by 1400W. Interestingly, these aggregates were colocalized with SOD1, which was found to co-immunoprecipitate with PDI.

Conclusions

NO-mediated S-nitrosylation of PDI may be involved in the formation of the SOD1-linked ubiquitinated-protein aggregates in cerebral ischemia/reperfusion injury.

Roles of activated microglia in hypoxia induced neuroinflammation in the developing brain and the retina

Amoeboid microglial cells (AMCs) in the developing brain display surface receptors and antigens shared by the monocyte-derived tissue macrophages. Activation of AMCs in the perinatal brain has been associated with periventricular white matter damage in hypoxic-ischemic conditions. The periventricular white matter, where the AMCs preponderate, is selectively vulnerable to hypoxia as manifested by death of premyelinating oligodendrocytes and degeneration of axons leading to neonatal mortality and long-term neurodevelopmental deficits. AMCs respond vigorously to hypoxia by producing excess amounts of inflammatory cytokines e.g. the tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) along with glutamate, nitric oxide (NO) and reactive oxygen species which collectively cause oligodendrocyte death, axonal degeneration as well as disruption of the immature blood brain barrier. A similar phenomenon is observed in the hypoxic developing cerebellum in which activated AMCs induced Purkinje neuronal death through production of TNF-α and IL-1β via their respective receptors. Hypoxia is also implicated in retinopathy of prematurity in which activation of AMCs has been shown to cause retinal ganglion cell death through production of TNF-α and IL-1β and NO. Because AMCs play a pivotal role in hypoxic injuries in the developing brain affecting both neurons and oligodendrocytes, a fuller understanding of the underlying molecular mechanisms of microglial activation under such conditions would be desirable for designing of a novel therapeutic strategy for management of hypoxic damage.

Hypoxia-ischemia and retinal ganglion cell damage

Retinal hypoxia is the potentially blinding mechanism underlying a number of sight-threatening disorders including central retinal artery occlusion, ischemic central retinal vein thrombosis, complications of diabetic eye disease and some types of glaucoma. Hypoxia is implicated in loss of retinal ganglion cells (RGCs) occurring in such conditions. RGC death occurs by apoptosis or necrosis. Hypoxia-ischemia induces the expression of hypoxia inducible factor-1α and its target genes such as vascular endothelial growth factor (VEGF) and nitric oxide synthase (NOS). Increased production of VEGF results in disruption of the blood retinal barrier leading to retinal edema. Enhanced expression of NOS results in increased production of nitric oxide which may be toxic to the cells resulting in their death. Excess glutamate release in hypoxic-ischemic conditions causes excitotoxic damage to the RGCs through activation of ionotropic and metabotropic glutamate receptors. Activation of glutamate receptors is thought to initiate damage in the retina by a cascade of biochemical effects such as neuronal NOS activation and increase in intracellular Ca²⁺ which has been described as a major contributing factor to RGC loss. Excess production of proinflammatory cytokines also mediates cell damage. Besides the above, free-radicals generated in hypoxic-ischemic conditions result in RGC loss because of an imbalance between antioxidant- and oxidant-generating systems. Although many advances have been made in understanding the mediators and mechanisms of injury, strategies to improve the damage are lacking. Measures to prevent neuronal injury have to be developed.

Nitric oxide, ischaemia and brain inflammation

Cerebral ischaemia results in the activation of three isoforms of NOS (nitric oxide synthase) that contribute to the development of and recovery from stroke pathology. This review discusses, in particular, the role of the transcriptionally activated NOS-2 (inducible NOS) isoform and summarizes the outcomes of experimental stroke studies with regard to the therapeutic utility of nitric oxide donors and NOS inhibitors.

Enhanced astrocytic nitric oxide production and neuronal modifications in the neocortex of a NOS2 mutant mouse

Background

It has been well accepted that glial cells in the central nervous system (CNS) produce nitric oxide (NO) through the induction of a nitric oxide synthase isoform (NOS2) only in response to various insults. Recently we described rapid astroglial, NOS2-dependent, NO production in the neocortex of healthy mice on a time scale relevant to neuronal activity. To explore a possible role for astroglial NOS2 in normal brain function we investigated a NOS2 knockout mouse (B6;129P2-Nos2^tm1Lau/J, Jackson Laboratory). Previous studies of this mouse strain revealed mainly altered immune responses, but no compensatory pathways and no CNS abnormalities have been reported.

Methodology/Principal Findings

To our surprise, using NO imaging in brain slices in combination with biochemical methods we uncovered robust NO production by neocortical astrocytes of the NOS2 mutant. These findings indicate the existence of an alternative pathway that increases basal NOS activity. In addition, the astroglial mutation instigated modifications of neuronal attributes, shown by changes in the membrane properties of pyramidal neurons, and revealed in distinct behavioral abnormalities characterized by an increase in stress-related parameters.

Conclusions/Significance

The results strongly indicate the involvement of astrocytic-derived NO in modifying the activity of neuronal networks. In addition, the findings corroborate data linking NO signaling with stress-related behavior, and highlight the potential use of this genetic model for studies of stress-susceptibility. Lastly, our results beg re-examination of previous studies that used this mouse strain to examine the pathophysiology of brain insults, assuming lack of astrocytic nitrosative reaction.

From blood to brain: amoeboid microglial cell, a nascent macrophage and its functions in developing brain

Amoeboid microglial cells (AMC) in the developing brain are active macrophages. The macrophagic nature of these cells has been demonstrated by many methods, such as the localization of various hydrolytic enzymes and the presence of complement type 3 surface receptors in them. More importantly is the direct visualization of these cells engaged in the phagocytosis of degenerating cells at the ultrastructural level. Further evidence of them being active macrophages is the avid internalization of tracers administered by the intravenous or intraperitoneal routes in developing rats. The potential involvement of AMC in immune functions is supported by the induced expression of major histocompatibility complex class I and II antigens on them when challenged by lipopolysaccharide or interferon-gamma. Immunosuppressive drugs, such as glucocorticoids and immune function-enhancing drugs like melatonin, affect the expression of surface receptors and antigens and the release of cytokines by AMC. Recent studies in our laboratory have shown the expression of insulin-like growth factors, endothelins, 2',3'-cyclic nucleotide 3'-phosphodiesterase, and N-methyl-D-asparate receptors. This along with the release of chemokines, such as stromal derived factor-1a and monocyte chemoattractant protein-1, suggests multiple functional roles of AMC in early brain development.

Rapid and reactive nitric oxide production by astrocytes in mouse neocortical slices

Nitric oxide (NO), a cellular signaling molecule, is produced in the brain by both neurons and astrocytes. While neurons are capable of rapid release of small amounts of NO serving as neurotransmitter, astrocytic NO production has been demonstrated mainly as a slow reaction to various stress stimuli. Little is known about the role of astrocyte-produced NO. Using the NO indicator 4,5-diaminofluorescein-2 diacetate (DAF-2DA) and acute slices from mouse brain, we distinguished neurons from astrocytes based on their different fluorescence kinetics and pattern, cellular morphology, electrophysiology, and responses to selective nitric oxide synthase (NOS) inhibitors. Typically, astrocytic fluorescence followed neuronal fluorescence with a delay of 1-2 min and was dependent on the inducible NOS isoform (iNOS) activity. Western blot analysis established the presence of functional iNOS in the neocortex. An assay for cell death revealed that most DAF-2DA-positive neurons, but not astrocytes, were damaged. Whole cell recordings from astrocytes confirmed that these cells maintained their membrane potential and passive properties during illumination and afterward. Induction of excitotoxicity by brief application of glutamate triggered an immediate and intense astrocytic response, while high-frequency electrical stimulation failed to do so. The present study demonstrates, for the first time, rapid and massive iNOS-dependent NO production by astrocytes in situ, which appears to be triggered by acute neuronal death. These data may bear important implications for our theoretical understanding and practical management of acute brain insults.

Leukocyte mitochondrial alterations after cardiac surgery involving cardiopulmonary bypass: clinical correlations

Cardiac surgery with the use of cardiopulmonary bypass (CPB) is known to initiate systemic inflammatory responses that are associated with immune dysregulations, but the pathomechanisms underlying these changes remain elusive. Mitochondrial transmembrane potential (MTP) is an important determinant of leukocytic functions and viability, and may be altered as a part of the cellular responses to systemic inflammatory insults. Therefore, we examined MTP in three subsets of peripheral leukocytes in 18 patients receiving uncomplicated cardiac surgery involving CPB. The MTP of neutrophils and lymphocytes significantly increased, whereas that of monocytes significantly declined, after the surgery. The alterations in leukocytic MTP were transient, normalizing 3 days to 1 week after the surgery, and were accompanied by transient overproduction of intracellular oxidants, including nitric oxide and superoxide. Despite these perturbations, the viability status of leukocytes remained unaltered. Positive correlations were found between the changes of leukocyte MTP and various clinical parameters, implying that leukocyte mitochondrial alterations are parts of the systemic immune perturbations induced by the bypass surgery.

Antagonism of the interleukin-1 receptor following traumatic brain injury in the mouse reduces the number of nitric oxide synthase-2-positive cells and improves anatomical and functional outcomes

Interleukin (IL)-1beta plays an important role in the inflammatory response that results from traumatic brain injury and antagonism of the actions of this cytokine can affect outcome. We subjected male mice to aseptic cryogenic injury and assessed recovery through anatomical, histological and functional measures following treatment with recombinant mouse IL-1 receptor antagonist (IL-1ra). A single dose (1 microg, i.c.v.) at the time of injury reduced lesion volume 3 days later, as assessed by Nissl staining, and also the number (30%) of FluoroJade-positive degenerating neurones. Mice treated with IL-1ra performed better on the beam balance and in the grid test as compared with vehicle-treated animals. Furthermore, IL-1ra-treated animals showed fewer (40%) nitric oxide synthase-2-positive cells in and around the lesion. These data suggest that activation of the IL-1 receptor following trauma contributes to the pathology and that antagonism can reduce both anatomical and functional consequences of neuroinflammation.

Glial nitric oxide and ischemia

One of the responses to cerebral ischemia is an increase in the production of nitric oxide, catalyzed by enzymes expressed in both resident and infiltrating cells. The nitric oxide that is generated does contribute to the ensuing pathology, but it can also be beneficial. The effects of nitric oxide depend on the cell site of production, the amount generated, and the chemical nature of the products of further oxidation. Understanding how nitric oxide production from microglia and astrocytes contributes to ischemic pathology is important for the development and application of future therapeutics based on inhibiting or amplifying its production in the injured brain.

Neuropeptide Y and its receptor analogs differentially modulate the immunoreactivity for neuronal or endothelial nitric oxide synthase in the rat brain following focal ischemia with reperfusion

An intracerebroventricular (i.c.v.) injection of neuropeptide Y (NPY) or [Leu31, Pro34]-NPY (non-Y2 receptor agonist) given during middle cerebral artery occlusion (MCAO) increases the infarct volume and nitric oxide (NO) overproduction in the rat brain. An i.c.v. injection of NPY3-36 (non-Y1 receptor agonist) has no effects, while BIBP3226 (selective Y1 receptor antagonist) reduces the infarct volume and NO overproduction. This study examined the effects of NPY or its receptor analog on the immunoreactivity (ir) for three isoforms of NO synthase (NOS) following 1 h of MCAO and 3 h of reperfusion. Focal ischemia/reperfusion led to increased ir for neuronal NOS (nNOS) within the ipsilateral caudate putamen and insular cortex. NPY or [Leu31, Pro34]-NPY enhanced but BIBP3226 suppressed such increase in the nNOS-ir. Focal ischemia/reperfusion also led to an ipsilateral increase in extent and/or intensity of the ir for endothelial NOS (eNOS) in the caudate putamen and/or parietal cortex. NPY or [Leu31, Pro34]-NPY suppressed but BIBP3226 enhanced such change in the eNOS-ir. NPY3-36 did not consistently influence the nNOS-ir or eNOS-ir following MCAO. Specific ir for inducible NOS was undetectable. These opposing effects of NPY-Y1 receptor activation or inhibition on nNOS and eNOS may lead to harmful or beneficial consequences following ischemia/reperfusion.

Inducible form of nitric oxide synthase expression in rat cortical neuronal cells in vitro

The inducible form of nitric oxide synthase (iNOS) is an essential element of the immune response, which is expressed primarily in microglial cells within the CNS. Exposure of rat cortical neuronal cells to the pro-inflammatory bacterial endotoxin lipopolysaccharide (LPS) resulted in a significant increase in the expression of the cellular iNOS protein expression and NO generation (which serves as an indirect measure of NOS catalytic activity). These effects were potentiated by costimulation with interferon-gamma (IFNgamma) and the increase in NO generation was abolished by the iNOS selective inhibitor 1400W, although this did not attenuate the toxin-induced increase in the enzyme expression. As the cortex is one of the principal areas to be targeted in Alzheimer's disease (AD), the present findings may help to further our understanding of the biochemical events associated with the neurodegenerative process.

Direct evidence that induced nitric oxide production in hepatocytes prevents liver damage during lipopolysaccharide tolerance in rats

BACKGROUND

The role of nitric oxide (NO) in lipopolysaccharide (LPS) tolerance in the liver has been investigated in a number of previous studies, but it is still not clear whether NO is cytotoxic or cytoprotective. The aims of this study were to investigate whether low-dose LPS (LLPS)-induced hepatic production of NO is beneficial and to clarify the origins of cytoprotective NO-producing cells in the liver during LPS tolerance.

MATERIALS AND METHODS

Male Wistar rats received saline or LLPS intraperitoneally (i.p.; 0.01-1000 microg/kg) followed by a high dose of LPS (HLPS, 5 mg/kg) at various time intervals (4-16 h). NG-nitro-L-arginine methyl ester (L-NAME) was used to investigate the effects of inhibition of NOS. 4,5-Diaminofluorescein (DAF-2) was used to identify NO-producing cells in isolated liver cells in vitro. At various time points (4-16 h) after saline or LLPS (1 microg/kg, i.p.) injection, hepatocytes and Kupffer cells were isolated, incubated in 7 microm DAF-2 diacetate, and perfused with Krebs solution. Illumination at 495 nm revealed DAF-fluorescence (515 nm) in isolated cells under confocal laser fluorescence microscopy. The NO production in hepatocytes and Kupffer cells was assessed by the number of labeled cells per 1000 cells or per 100 cells, respectively.

RESULTS

Pretreatment with LLPS (0.1-100 microg/kg) resulted in a significant reduction (maximal at 8 h) of the HLPS-induced liver damage. L-NAME abolished the LLPS-induced protection. The NO production in hepatocytes was significantly increased and reached a maximum of 84% of all cells 8 h after LLPS administration. By contrast, the NO production in Kupffer cells remained constant at 95%, even following preinjection of LLPS.

CONCLUSION

LLPS-induced NO in hepatocytes, but not in Kupffer cells, exhibits cytoprotective effects on HLPS-induced liver damage, suggesting that NO has a beneficial role in the induction of the early phase of LPS tolerance.

Impaired nitric oxide production of the myenteric plexus in colitis detected by a new bioimaging system

Direct measurement of the release of nitric oxide (NO) from the myenteric plexus has been extremely difficult to date, due to the lack of suitable methodologies. We have developed a new bioimaging system to visualize the nitrergic neurons of the myenteric plexus and investigated whether NO production is impaired in dextran sulfate sodium (DSS)-induced colitis. Longitudinal muscle layers with the myenteric plexus intact were obtained from the rat colon and were incubated with 4,5-diaminofluorescein-2-diacetate (DAF-2DA) (7 microm) for 30 min. Illumination at 450-490 nm revealed the fluorescence in the myenteric plexus. Confocal laser microscopy and three-dimensional reconstruction techniques were used to quantify the changes in the amount of NO production by the myenteric plexus. Fluorescent double-labeled immunostaining for nNOS was performed to confirm the colocalization of nNOS in 4,5-diaminofluorescein (DAF-2)-positive cells. DAF-2 fluorescence was abolished by pretreatment with N(G)-nitro-l-arginine methyl ester (l-NAME; a nonselective NOS inhibitor), 1-(2-trifluoromethylphenyl) imidazole (TRIM; a selective neuronal NOS inhibitor), and omega-conotoxin GVIA (an N-type Ca(2+) channel blocker), but not by nifedipine (an l-type Ca(2+) channel blocker). Fluorescent double-labeled immunostaining showed that DAF-2-positive cells colocalized with nNOS-positive cells. Oral administration of 5% DSS for 7 days induced distal colitis and the number of DAF-2-positive neurons were significantly reduced to 55 +/- 17% of control. DAF-2 offers a sensitive indicator for visualizing production of NO with high spatial resolution. This new system may contribute to the study of the pathophysiological role of the nitrergic pathway in the gastrointestinal tract.

Serotonin 5-HT1A, 5-HT1B, and 5-HT2A receptor mRNA expression in subjects with major depression, bipolar disorder, and schizophrenia

BACKGROUND

Alterations of serotonin neurotransmission are implicated in both mood disorders and schizophrenia. Specific serotonin-receptor-based abnormalities in these psychiatric illnesses have been intensively studied; however, it has been difficult to draw any conclusions because of a lack of consensus. These inconsistencies have most likely arisen from the unavailability of selective ligands.

METHODS

Our study used in situ hybridization to quantify 5-HT(1A), 5-HT(1B), and 5-HT(2A) mRNA levels in the hippocampus (HC) and 5-HT(1A) and 5-HT(2A) mRNA levels in the dorsolateral prefrontal cortex (DLPFC) of subjects with a history of major depression disorder (MDD), bipolar disorder (BPD), schizophrenia, and a normal comparison group (15 subjects per group).

RESULTS

In the DLPFC, there is a significant decrease in 5-HT(1A) mRNA of subjects with MDD and in 5-HT(2A) mRNA of subjects with BPD. Subjects with MDD have a significant decrease in 5-HT(1A) mRNA in the HC; subjects with BPD and schizophrenia had increased 5-HT(1B) mRNA levels and a significant decrease in 5-HT(2A) mRNA levels in the hippocampal formation.

CONCLUSIONS

Alterations in 5-HT(1A,) 5-HT(1B), and 5-HT(2A) mRNA levels in the brains of subjects with both mood disorders and schizophrenia add further support for hypothesis of dysregulation of the serotonergic system in these psychiatric disorders.

Downregulation of nitric oxide formation by cytosolic phospholipase A2-released arachidonic acid

Exposure of PC12 cells to A23187 or thapsigargin caused a concentration-dependent release of arachidonic acid (AA) mediated by cytosolic phospholipase A2 (PLA2). Under the same conditions, however, analysis of nitric oxide (NO) formation revealed that activation of NO synthase (NOS) is best described by a bell-shaped curve. Reduced detection of NO observed at increasing A23187 or thapsigargin concentrations was not due to formation of peroxynitrite or to activation of NO-consuming processes, but rather to AA-dependent inhibition of NOS activity. Furthermore, NO formation observed under optimal conditions for NOS activity was suppressed by AA as well as by the PLA2 activator melittin. Finally, the effects of AA were not the consequence of direct enzyme inhibition, because this lipid messenger failed to inhibit formation of NO by purified neuronal NOS, but were mediated by an AA-dependent signaling and not by downstream products of the cyclooxygenase and lipoxygenase pathways. In conclusion, the present study underscores a novel mechanism whereby endogenous, or exogenous, AA promotes inhibition of NOS activity. Because AA is generated in response to various agonists acting on membrane receptors and extensively released in inflammatory conditions, these findings have important physiopathological implications.

Intracellular release of nitric oxide by NCX 972, an NO-releasing metronidazole, enhances in vitro killing of Entamoeba histolytica

The activity of NCX 972, a new molecule obtained by adding a nitric oxide (NO) moiety to metronidazole, was tested against six isolates of Entamoeba histolytica in xenic cultures. NCX 972 released NO into trophozoite cells and enhanced killing of amoebas in a dose- and time-dependent manner compared to metronidazole.

Interfering with nitric oxide measurements. 4,5-diaminofluorescein reacts with dehydroascorbic acid and ascorbic acid

4,5-Diaminofluorescein (DAF-2) is widely used for detection and imaging of NO based on its sensitivity, noncytotoxicity, and specificity. In the presence of oxygen, NO and NO-related reactive nitrogen species nitrosate 4,5-diaminofluorescein to yield the highly fluorescent DAF-2 triazole (DAF-2T). However, as reported here, the DAF-2 reaction to form a fluorescent product is not specific to NO because it reacts with dehydroascorbic acid (DHA) and ascorbic acid (AA) to generate new compounds that have fluorescence emission profiles similar to that of DAF-2T. When DHA is present, the formation of DAF-2T is attenuated because the DHA competes for DAF-2, whereas AA decreases the nitrosation of DAF-2 to a larger extent, possibly because of additional reducing activity that affects the amount of available N(2)O(3) from the NO. The reaction products of DAF-2 with DHA and AA have been characterized using capillary electrophoresis with laser-induced fluorescence detection and electrospray mass spectrometry. The reactions of DAF-2 with DHA and AA are particularly significant because DHA and AA often colocalize with nitric-oxide synthase in the central nervous, cardiovascular, and immune systems, indicating the importance of understanding this chemistry.

Reversal of biochemical and behavioral parameters of brain aging by melatonin and acetyl L-carnitine

The potential utility of dietary supplementation in order to prevent some of the oxidative and inflammatory changes occurring in the brain with age, has been studied. The cerebral cortex of 27-month-old male B6C3F1 mice had elevated levels of nitric oxide synthase 1 (EC 1.14.13.39) (nNOS) and peptide nitrotyrosine relative to cortices of younger (4-month-old) animals. After 25-month-old mice received basal diet together with 300 mg/l acetyl L-carnitine in the drinking water for 8 weeks, these levels were fully restored to those found in younger animals. A partial restoration was found when old animals received basal diet supplemented with 200 ppm melatonin in the diet. Levels of mRNA (messenger RNA) for nNOS were unchanged following these treatments implying translational regulation of nNOS activity. Behavioral indices indicative of exploratory behavior were also depressed in aged animals. Dietary supplementation with melatonin or acetyl L-carnitine partially reversed these changes. These findings suggest that dietary supplementation cannot merely arrest but indeed reverse some age-related increases in markers of oxidative and inflammatory events occurring with the cortex.

Beta-amyloid inhibits NOS activity by subtracting NADPH availability

The amyloid peptides Abeta1-42 and Abeta25-35 strongly inhibited the activity of constitutive neuronal and endothelial nitric oxide synthases (i.e., NOS-I and NOS-III, respectively) in cell-free assays. The molecular mechanism of NOS inhibition by Ab fragments was studied in detail with Abeta25-35. The inhibitory ability was mostly NADPH-dependent and specific for the soluble form of Abeta25-35. Optical, fluorescence, and NMR spectroscopy showed that the soluble, but not aggregated, Abeta25-35 interacted with NADPH, thus suggesting that a direct recruitment of NADPH may result in diminished availability of the redox cofactor for NOS functioning. To assess the physiological relevance of our findings, rat neuronal-like PC12 and glioma C6 cell lines were used as cellular models. After Abeta25-35 internalization into cells was verified, the activity of constitutive NOS was measured using the DAF-2DA detection system and found to be severely impaired upon Abeta25-35 uptake. Consistent with previous results on the molecular cross-talk between NOS isoforms, repression of constitutive NOS by Abeta25-35 resulted in enhanced expression of inducible NOS (NOS-II) mRNA in C6 cells. Our results represent the first evidence that amyloid fragments impair constitutive NOS activity in cell-free and cellular systems, providing a possible molecular mechanism for the onset and/or maintenance of Alzheimer's disease.

Inhibition of mitochondrial respiration by endogenous nitric oxide: a critical step in Fas signaling

We have found that activation of human adult T cell leukemia (Jurkat) cells with anti-Fas Ab leads, in a concentration-dependent manner, to an early burst of production of nitric oxide (NO), which inhibits cell respiration. This results in mitochondrial hyperpolarization, dependent on the hydrolysis of glycolytic ATP by the F1F(o)-ATPase acting in reverse mode. During this early phase of activation, there is a transient release of superoxide anion. All these processes can be prevented by an inhibitor of NO synthase. Approximately 2 h after stimulation with anti-Fas Ab, a distinct second phase can be detected. This comprises a concentration-dependent collapse in mitochondrial membrane potential, a second wave of free radical production, and activation of caspase-8 leading to apoptosis. This second phase is abolished by an inhibitor of caspase activation. In contrast, inhibition of NO synthesis leads to an enhancement and acceleration of these latter processes, suggesting that the early NO-dependent phase represents a protective mechanism. The significance of the two phases in relation to cell survival and death remains to be studied.

A fluorescence-based method for measuring nitric oxide in extracts of skeletal muscle

We describe here a fluorescence assay for nitric oxide synthase activity in skeletal muscle based on a new indicator, 4,5-diaminofluorescein (DAF-2). The rapid and irreversible binding of DAF-2 to oxidized NO allows real-time measurement of NO production. The method is safer and more convenient than the usual citrulline radioassay and can be used with crude muscle extracts. Rabbit fast tibialis anterior (TA) muscle had a nitric oxide synthase (NOS) activity of 44.3 +/- 3.5 pmol/min/mg muscle. Addition of NOS blocker N(G)-allyl-L-arginine reduced this activity by 43%. Slow soleus muscle displayed NOS activity of 7.3 +/- 2.5 pmol/min/mg muscle, 16% that of the TA muscle. Continuous stimulation of TA muscle at 10 Hz for 3 weeks reduced NOS activity by 47% to an intermediate value consistent with the associated conversion of the muscle phenotype from fast to slow.

The role of cytokines in the depression of CYP1A activity using cultured astrocytes as an in vitro model of inflammation in the central nervous system

The interaction and modulation of hepatic cytochrome P450 enzymes by infection and inflammation has been well described both in clinical settings and in animal models. Recent evidence found that inflammation in the central nervous system (CNS) leads to alterations in cytochrome P450 activity in both brain and liver. The bacterial endotoxin lipopolysaccharide (LPS) was used to induce an inflammatory response in cultured astrocytes as a model of CNS inflammation. This inflammatory response involves a range of immune mediators, such as acute phase cytokines, nitric oxide, prostanoid products, and reactive oxygen species. It is hypothesized that cytokines, released during inflammation, act to modulate the expression of specific isoforms of cytochrome P450 resulting in altered activity levels. High levels of the cytokines tumor necrosis factor-alpha and interleukin-1beta were released into culture medium after the addition of LPS to astrocyte cultures. When these same cytokines were added directly to the cultures, they also were able to modulate levels of CYP1A activity. The concurrent addition of dexamethasone to astrocytes blocked both the cytokine release and the alteration of CYP1A activity, thus supporting a role for these cytokines in this response. These results provide evidence suggesting an involvement of acute phase cytokines in mediating the LPS-induced depression of CYP1A activity in cultured astrocytes.

Characterization of basal nitric oxide production in living cells

Nitric oxide (NO) is an important modulator of immune, endocrine and neuronal functions; however, measuring physiological levels of NO in cell cultures is generally difficult because of the lack of suitable methodologies. We have selected three cell lines from different origins: the neuroblastoma-derived Neuro2A (N2A), the cholinergic SN56 and the non-neuronal COS-1. We first demonstrated the presence of NADPH-diaphoretic activity, a potential marker of the NO-synthesizing (NOS) enzyme. By immunocytochemistry, using specific antibodies for each NOS subtype, we observed that subtype I was present in all cell lines and that subtype II was present in COS-1 and N2A cell lines. The presence of these NOS subtypes was further verified by Western blot analysis. Control cells treated with DAF-2 DA exhibited significant fluorescent levels corresponding to basal NO production. The subcellular distribution of the synthesizing enzyme was consistent with the NO-fluorescence signal; whereas, fixation affected the subcellular pattern of NO fluorescence signal. Addition of NOS inhibitors or NO scavengers to the incubation medium reduced the intensity of the NO fluorescence signal in a concentration-dependent manner. Conversely, increasing concentrations of a NO donor, or incident light, increased the fluorescence intensity. Our observation of NO production and distribution using the DAF-2 method has a direct impact on studies using these cell lines.

Relative importance of nitric oxide and carbon monoxide in regulating the ACTH response to immune and non-immune signals

The present work investigated the effect of nitric oxide (NO) or carbon monoxide (CO) in the ACTH response to an immune signal [the intravenous injection of interleukin-1 β (IL-1β)] or to a neurogenic stressor (mild intermittent inescapable foot shocks). The arginine derivative N(ω)-L-arginine methylester (L-NAME), which non-specifically inhibits NO formation induced by all constitutive forms of NO synthase (NOS), significantly augmented the effect of IL-1P,but blockade of CO formation with metalloporphyrins was without effect. On the other hand, L-NAME blunted the effect of shocks on the early phase of ACTH release, while we had reported earlier that metalloporphyrins exerted a similar effect. This effect was mimicked by blockade of neuronal (n) NOS by N(ω)-Propyl-L-arginine (PA), although the resulting decrease in hormone levels was less than that induced by L-NAME. These results indicate that endogenous NO, but not CO, interferes with ACTH released by a peripheral immune signal. In contrast, NO formed by nNOS enhances the ability of shocks to induce ACTH secretion.

Direct evidence of nitric oxide presence within mitochondria

Nitric oxide (NO) has been implicated in the modulation of mitochondrial respiration, membrane potential, and subsequently in apoptosis. Although the presence of a mitochondrial NO synthase (mtNOS) has been described, there is no direct evidence in vivo of the presence of NO within mitochondria. It was the aim of this study to demonstrate the in vivo production of NO within mitochondria. Using the novel fluorometric NO detection system, 4,5-diaminofluorescein diacetate (DAF-2/DA), we observed the presence of NO production in PC12 and COS-1 cells by conventional and confocal fluorescence microscopy. Part of the overall NO signal was colocalized within a subpopulation of mitochondria, labeled with the potential-dependent probe MitoTracker red. These findings demonstrate for the first time that the subcellular distribution of NO production is consistent with the presence of a mitochondrial NOS. Our results provide a new tool to directly study the modulatory role of NO in mitochondrial respiration and membrane potential, in vivo.