Inducible nitric oxide synthase appears and is co-expressed with the neuronal isoform in interneurons of the rat hippocampus after transient ischemia induced by middle cerebral artery occlusion

The potential therapeutic effect of phosphodiesterase 5 inhibitors in the acute ischemic stroke (AIS)

Acute ischemic stroke (AIS) is a focal neurological disorder that accounts for 85% of all stroke types, due to occlusion of cerebral arteries by thrombosis and emboli. AIS is also developed due to cerebral hemodynamic abnormality. AIS is associated with the development of neuroinflammation which increases the severity of AIS. Phosphodiesterase enzyme (PDEs) inhibitors have neuro-restorative and neuroprotective effects against the development of AIS through modulation of the cerebral cyclic adenosine monophosphate (cAMP)/cyclic guanosine monophosphate (cGMP)/nitric oxide (NO) pathway. PDE5 inhibitors through mitigation of neuroinflammation may decrease the risk of long-term AIS-induced complications. PDE5 inhibitors may affect the hemodynamic properties and coagulation pathway which are associated with thrombotic complications in AIS. PDE5 inhibitors reduce activation of the pro-coagulant pathway and improve the microcirculatory level in patients with hemodynamic disturbances in AIS. PDE5 inhibitors mainly tadalafil and sildenafil improve clinical outcomes in AIS patients through the regulation of cerebral perfusion and cerebral blood flow (CBF). PDE5 inhibitors reduced thrombomodulin, P-selectin, and tissue plasminogen activator. Herein, PDE5 inhibitors may reduce activation of the pro-coagulant pathway and improve the microcirculatory level in patients with hemodynamic disturbances in AIS. In conclusion, PDE5 inhibitors may have potential roles in the management of AIS through modulation of CBF, cAMP/cGMP/NO pathway, neuroinflammation, and inflammatory signaling pathways. Preclinical and clinical studies are recommended in this regard.

Investigating the Protective Effect of Gross Saponins of Tribulus terrestris Fruit against Ischemic Stroke in Rat Using Metabolomics and Network Pharmacology

Stroke is one of the leading causes of death and long-term disability worldwide. Gross saponins of Tribulus terrestris fruit (GSTTF) has been used for neuroprotective therapy on convalescents of ischemic stroke. But the related therapeutic mechanisms have not yet been well investigated. This study aimed to investigate the protective effects of GSTTF on ischemic stroke using metabolomics coupled with network pharmacology analysis. The rat urine sample was collected and profiled by an LC-MS-based metabolomics approach. The pathway analysis was performed based on the highlighted biomarkers, then the network pharmacology approach was applied to screen the potential therapeutic targets of GSTTF. Metabolomics analysis showed that a series of metabolic perturbations occurred in the middle cerebral artery occlusion (MCAO) group compared with the sham group. Gross saponins of Tribulus terrestris fruit can change the MCAO-induced urine metabolic deviations in a reverse manner via regulating multiple metabolic pathways. Two proteins, inducible nitric oxide synthase (NOS2) and glycogen synthase kinase-3 beta (GSK3B), were highlighted by the network pharmacology analysis, which may be the potential therapeutic targets for the GSTTF against ischemic stroke. This study provides an overview of the mechanism of MCAO-induced ischemic stroke and investigates the efficacy of GSTTF in the treatment of ischemic stroke. Further study is needed to reveal its underlying mechanisms more clearly.

Nitric oxide donors (nitrates), L-arginine, or nitric oxide synthase inhibitors for acute stroke

BACKGROUND

Nitric oxide (NO) has multiple effects that may be beneficial in acute stroke, including lowering blood pressure, and promoting reperfusion and cytoprotection. Some forms of nitric oxide synthase inhibition (NOS-I) may also be beneficial. However, high concentrations of NO are likely to be toxic to brain tissue. This is an update of a Cochrane review first published in 1998, and last updated in 2002.

OBJECTIVES

To assess the safety and efficacy of NO donors, L-arginine, and NOS-I in people with acute stroke.

SEARCH METHODS

We searched the Cochrane Stroke Group Trials Register (last searched 6 February 2017), MEDLINE (1966 to June 2016), Embase (1980 to June 2016), ISI Science Citation Indexes (1981 to June 2016), Stroke Trials Registry (searched June 2016), International Standard Randomised Controlled Trial Number (ISRCTN) (searched June 2016), Clinical Trials registry (searched June 2016), and International Clinical Trials Registry Platform (ICTRP) (searched June 2016). Previously, we had contacted drug companies and researchers in the field.

SELECTION CRITERIA

Randomised controlled trials comparing nitric oxide donors, L-arginine, or NOS-I versus placebo or open control in people within one week of onset of confirmed stroke.

DATA COLLECTION AND ANALYSIS

Two review authors independently applied the inclusion criteria, assessed trial quality and risk of bias, and extracted data. The review authors cross-checked data and resolved issues through discussion. We obtained published and unpublished data, as available. Data were reported as mean difference (MD) or odds ratio (OR) with 95% confidence intervals (CI).

MAIN RESULTS

We included five completed trials, involving 4197 participants; all tested transdermal glyceryl trinitrate (GTN), an NO donor. The assessed risk of bias was low across the included studies; one study was double-blind, one open-label and three were single-blind. All included studies had blinded outcome assessment. Overall, GTN did not improve the primary outcome of death or dependency at the end of trial (modified Rankin Scale (mRS) > 2, OR 0.97, 95% CI 0.86 to 1.10, 4195 participants, high-quality evidence). GTN did not improve secondary outcomes, including death (OR 0.78, 95% CI 0.40 to 1.50) and quality of life (MD -0.01, 95% CI -0.17 to 0.15) at the end of trial overall (high-quality evidence). Systolic/diastolic blood pressure (BP) was lower in people treated with GTN (MD -7.2 mmHg (95% CI -8.6 to -5.9) and MD -3.3 (95% CI -4.2 to -2.5) respectively) and heart rate was higher (MD 2.0 beats per minute (95% CI 1.1 to 2.9)). Headache was more common in those randomised to GTN (OR 2.37, 95% CI 1.55 to 3.62). We did not find any trials assessing other nitrates, L-arginine, or NOS-I.

AUTHORS' CONCLUSIONS

There is currently insufficient evidence to recommend the use of NO donors, L-arginine or NOS-I in acute stroke, and only one drug (GTN) has been assessed. In people with acute stroke, GTN reduces blood pressure, increases heart rate and headache, but does not alter clinical outcome (all based on high-quality evidence).

The role of nitric oxide in pre-synaptic plasticity and homeostasis

Since the observation that nitric oxide (NO) can act as an intercellular messenger in the brain, the past 25 years have witnessed the steady accumulation of evidence that it acts pre-synaptically at both glutamatergic and GABAergic synapses to alter release-probability in synaptic plasticity. NO does so by acting on the synaptic machinery involved in transmitter release and, in a coordinated fashion, on vesicular recycling mechanisms. In this review, we examine the body of evidence for NO acting as a retrograde factor at synapses, and the evidence from in vivo and in vitro studies that specifically establish NOS1 (neuronal nitric oxide synthase) as the important isoform of NO synthase in this process. The NOS1 isoform is found at two very different locations and at two different spatial scales both in the cortex and hippocampus. On the one hand it is located diffusely in the cytoplasm of a small population of GABAergic neurons and on the other hand the alpha isoform is located discretely at the post-synaptic density (PSD) in spines of pyramidal cells. The present evidence is that the number of NOS1 molecules that exist at the PSD are so low that a spine can only give rise to modest concentrations of NO and therefore only exert a very local action. The NO receptor guanylate cyclase is located both pre- and post-synaptically and this suggests a role for NO in the coordination of local pre- and post-synaptic function during plasticity at individual synapses. Recent evidence shows that NOS1 is also located post-synaptic to GABAergic synapses and plays a pre-synaptic role in GABAergic plasticity as well as glutamatergic plasticity. Studies on the function of NO in plasticity at the cellular level are corroborated by evidence that NO is also involved in experience-dependent plasticity in the cerebral cortex.

Phosphorylation of neuronal nitric oxide synthase at Ser1412 in the dentate gyrus of rat brain after transient forebrain ischemia

We previously demonstrated that calmodulin-dependent protein kinase IIα (CaM-KIIα) phosphorylates nNOS at Ser(847) in the hippocampus after forebrain ischemia; this phosphorylation attenuates NOS activity and might contribute to resistance to post-ischemic damage. We also revealed that cyclic AMP-dependent protein kinase (PKA) could phosphorylate nNOS at Ser(1412)in vitro. In this study, we focused on chronological and topographical changes in the phosphorylation of nNOS at Ser(1412) after rat forebrain ischemia. The hippocampus and adjacent cortex were collected at different times, up to 24h, after 15min of forebrain ischemia. NOS was partially purified from crude samples using ADP agarose gel. Neuronal NOS, phosphorylated (p)-nNOS at Ser(1412), PKA, and p-PKA at Thr(197) were studied in the rat hippocampus and cortex using Western blot analysis and immunohistochemistry. Western blot analysis revealed that p-nNOS at Ser(1412) significantly increased between 1 and 6h after reperfusion in the hippocampus, but not in the cortex. PKA was cosedimented with nNOS by ADP agarose gel. Immunohistochemistry revealed that phosphorylation of nNOS at Ser(1412) and PKA at Thr(197) occurred in the subgranular layer of the dentate gyrus. Forebrain ischemia might thereby induce temporary activation of PKA at Thr(197), which then phosphorylates nNOS at Ser(1412) in the subgranular layer of the dentate gyrus.

Effects of subacute exposure to 1,2-dichloroethane on mouse behavior and the related mechanisms

The aim of this study was to explore the effects of subacute exposure to 1,2-dichloroethane (1,2-DCE) on mouse behavior and the related mechanisms focusing on alteration of oxidative stress and amino acid neurotransmitters in the brain. Mouse behavior was examined by open field test. Levels of nitric oxide (NO), malondialdehyde (MDA) and nonprotein sulfhydryl (NPSH) and activity of inducible nitric oxide synthase (iNOS) and superoxide dismutase (SOD) were determined by colorimetric method. Contents of glutamate (Glu), aspartate (Asp) and gamma-aminobutyric acid (GABA) were evaluated by high-performance liquid chromatography. Reduced locomotor and exploratory activities and increased anxiety were found in 0.45 and 0.9 g/m3 1,2-DCE-treated mice. In contrast, increased excitability was found in 0.225 g/m3 1,2-DCE-treated mice. Compensatory antioxidant status and increased NOS activity and NO level in the brain were found in 1,2-DCE-treated mice. Moreover, Glu contents in 1,2-DCE-treated mice and GABA contents in 0.9 g/m3 1,2-DCE-treated mice increased, whereas GABA contents in 0.225 g/m3 1,2-DCE-treated mice decreased significantly compared with control. Taken together, our results suggested that mouse behavior could be disturbed by subacute exposure to 1,2-DCE, and the changes of amino acid neurotransmitter in the brain might be related to the behavioral effects.

Relaxin exerts two opposite effects on mechanical activity and nitric oxide synthase expression in the mouse colon

The hormone relaxin exerts a variety of functions on the smooth muscle of reproductive and nonreproductive organs, most of which occur through a nitric oxide (NO)-mediated mechanism. In the stomach and ileum, relaxin causes muscle relaxation by modulating the activity and expression of different nitric oxide synthase (NOS) isoforms region-dependently. Nothing is known on the effects of relaxin in the colon, the gut region expressing the highest number of neuronal (n) NOSβ-immunoreactive neurons and mainly involved in motor symptoms of pregnancy and menstrual cycle. Therefore, we studied the effects of relaxin exposure in the mouse proximal colon in vitro evaluating muscle mechanical activity and NOS isoform expression. The functional experiments showed that relaxin decreases muscle tone and increases amplitude of spontaneous contractions; the immunohistochemical results showed that relaxin increases nNOSβ and endothelial (e) NOS expression in the neurons and decreases nNOSα and eNOS expression in the smooth muscle cells (SMC). We hypothesized that, in the colon, relaxin primarily increases the activity and expression of nNOSβ and eNOS in the neurons, causing a reduction of the muscle tone. The downregulation of nNOSα and eNOS expression in the SMC associated with increased muscle contractility could be the consequence of continuous exposue of these cells to the NO of neuronal origin. These findings may help to better understand the physiology of NO in the gastrointestinal tract and the role that the "relaxin-NO" system plays in motor disorders such as functional bowel disease.

Leukaemia inhibitory factor stimulates proliferation of olfactory neuronal progenitors via inducible nitric oxide synthase

Neurogenesis continues in the adult brain and in the adult olfactory epithelium. The cytokine, leukaemia inhibitory factor and nitric oxide are both known to stimulate neuronal progenitor cell proliferation in the olfactory epithelium after injury. Our aim here was to determine whether these observations are independent, specifically, whether leukaemia inhibitory factor triggers neural precursor proliferation via the inducible nitric oxide synthase pathway. We evaluated the effects of leukaemia inhibitory factor on inducible form of nitric oxide synthase (iNOS) expression, and cell proliferation in olfactory epithelial cell cultures and olfactory neurosphere-derived cells. Leukaemia inhibitory factor induced expression of iNOS and increased cell proliferation. An iNOS inhibitor and an anti-leukaemia inhibitory factor receptor blocking antibody inhibited leukaemia inhibitory factor-induced cell proliferation, an effect that was reversed by a NO donor. Altogether, the results strongly suggest that leukaemia inhibitory factor induces iNOS expression, increasing nitric oxide levels, to stimulate proliferation of olfactory neural precursor cells. This finding sheds light on neuronal regeneration occurring after injury of the olfactory epithelium.

Regulation of injury-induced neurogenesis by nitric oxide

The finding that neural stem cells (NSCs) are able to divide, migrate, and differentiate into several cellular types in the adult brain raised a new hope for restorative neurology. Nitric oxide (NO), a pleiotropic signaling molecule in the central nervous system (CNS), has been described to be able to modulate neurogenesis, acting as a pro- or antineurogenic agent. Some authors suggest that NO is a physiological inhibitor of neurogenesis, while others described NO to favor neurogenesis, particularly under inflammatory conditions. Thus, targeting the NO system may be a powerful strategy to control the formation of new neurons. However, the exact mechanisms by which NO regulates neural proliferation and differentiation are not yet completely clarified. In this paper we will discuss the potential interest of the modulation of the NO system for the treatment of neurodegenerative diseases or other pathological conditions that may affect the CNS.

Nitric oxide: considerations for the treatment of ischemic stroke

Some 40 years ago it was recognized by Furchgott and colleagues that the endothelium releases a vasodilator, endothelium-derived relaxing factor (EDRF). Later on, several groups identified EDRF to be a gas, nitric oxide (NO). Since then, NO was identified as one of the most versatile and unique molecules in animal and human biology. Nitric oxide mediates a plethora of physiological functions, for example, maintenance of vascular tone and inflammation. Apart from these physiological functions, NO is also involved in the pathophysiology of various disorders, specifically those in which regulation of blood flow and inflammation has a key role. The aim of the current review is to summarize the role of NO in cerebral ischemia, the most common cause of stroke.

Neurogliaform and Ivy Cells: A Major Family of nNOS Expressing GABAergic Neurons

Neurogliaform and Ivy cells are members of an abundant family of neuronal nitric oxide synthase (nNOS) expressing GABAergic interneurons found in diverse brain regions. These cells have a defining dense local axonal plexus, and display unique synaptic properties including a biphasic postsynaptic response with both a slow GABA(A) component and a GABA(B) component following even a single action potential. The type of transmission displayed by these cells has been termed "volume transmission," distinct from both tonic and classical synaptic transmission. Electrical connections are also notable in that, unlike other GABAergic cell types, neurogliaform family cells will form gap junctions not only with other neurogliaform cells, but also with non-neurogliaform family GABAergic cells. In this review, we focus on neurogliaform and Ivy cells throughout the hippocampal formation, where recent studies highlight their role in feedforward inhibition, uncover their ability to display a phenomenon called persistent firing, and reveal their modulation by opioids. The unique properties of this family of cells, their abundance, rich connectivity, and modulation by clinically relevant drugs make them an attractive target for future studies in vivo during different behavioral and pharmacological conditions.

Aminoguanidine administration ameliorates hippocampal damage after middle cerebral artery occlusion in rat

The effects of a selective inducible nitric oxide synthase inhibitor aminoguanidine (AG) on neuronal cells survival in hippocampal CA1 region after middle cerebral artery occlusion (MCAO) were examined. Transient focal cerebral ischemia was induced in rats by 60 or 90 min of MCAO, followed by 7 days of reperfusion. AG treatment (150 mg/kg i.p.) significantly reduced total infarct volumes: by 70% after 90 min MCAO and by 95% after 60 min MCAO, compared with saline-treated ischemic group. The number of degenerating neurons in hippocampal CA1 region was also markedly lower in aminoguanidine-treated ischemic groups compared to ischemic groups without AG-treatment. The number of iNOS-positive cells significantly increased in the hippocampal CA1 region of ischemic animals, whereas it was reduced in AG-treated rats. Our findings demonstrate that aminoguanidine decreases ischemic brain damage and improves neurological recovery after transient focal ischemia induced by MCAO.

Direct protection of cultured neurons from ischemia-like injury by minocycline

Minocycline, a tetracycline antibiotic, is now known to protect cells via an anti-inflammatory mechanism. We further explored this effect using an in vitro model of ischemia-like injury to neurons. Coculturing neurons with microglia, the brain's resident immune cell, modestly increased cell death due to oxygen and glucose deprivation (OGD), compared to neurons alone. Treatment of cocultures with minocycline decreased cell death to a level significantly lower than that of neurons alone. Treatment of cocultures with minocycline or inhibitors of various immune mediators, also led to decreased cell death. Importantly, treatment of neuron cultures without added microglia with these same inhibitors of tissue plasminogen activator, matrix metalloproteinases, TNF-alpha and inducible nitric oxide synthase as well as minocycline also led to decreased cell death. Thus, anti-inflammatory treatments appear to be directly protective of neurons from in vitro ischemia.

Inflammation mediates varying effects in neurogenesis: relevance to the pathogenesis of brain injury and neurodegenerative disorders

Brain inflammation is a complex cellular and molecular response to stress, injury or infection of the CNS in attempt to defend against insults, clear dead and damaged neurons and return the CNS to a normal state. Inflammation in the CNS is driven by the activation of resident microglia, astrocytes and infiltrating peripheral macrophages, which release a plethora of anti- and pro-inflammatory cytokines, chemokines, neurotransmitters and reactive oxygen species. This inflammatory state inadvertently causes further bystander damage to neurons and produces both detrimental and favorable conditions for neurogenesis. Inflammatory factors have varying effects on neural progenitor cell proliferation, migration, differentiation, survival and incorporation of newly born neurons into the CNS circuitry. The unique profile of inflammatory factors, which depends on the severity of inflammation, can have varying consequences on neurogenesis. Inflammatory factors released during mild acute inflammation usually stimulate neurogenesis; where as the factors released by uncontrolled inflammation create an environment that is detrimental to neurogenesis. This review will provide a summary of current progress in this emerging field and examine the potential mechanisms through which inflammation affects neurogenesis during neurological complications.