ARL 17477, a potent and selective neuronal NOS inhibitor decreases infarct volume after transient middle cerebral artery occlusion in rats

The role of oxidative stress and neuroinflammatory mediators in the pathogenesis of high-altitude cerebral edema in rats

High-altitude environments present extreme conditions characterized by low barometric pressure and oxygen deficiency, which can disrupt brain functioning and cause edema formation. The objective of the present study is to investigate several biomolecule expressions and their role in the development of High Altitude Cerebral Edema in a rat model. Specifically, the study focuses on analyzing the changes in total arginase, nitric oxide, and lipid peroxidation (MDA) levels in the brain following acute hypobaric hypoxic exposure (7620 m, SO2=8.1 %, for 24 h) along with the histopathological assessment. The histological examination revealed increased TNF-α activity, and an elevated number of mast cells in the brain, mainly in the hippocampus and cerebral cortex. The research findings demonstrated that acute hypobaric hypoxic causes increased levels of apoptotic cells, shrinkage, and swelling of neurons, accompanied by the formation of protein aggregation in the brain parenchyma. Additionally, the level of nitric oxide and MDA was found to have increased (p<0.0001), however, the level of arginase decreased indicating active lipid peroxidation and redox imbalance in the brain. This study provides insights into the pathogenesis of HACE by evaluating some biomolecules that play a pivotal role in the inflammatory response and the redox landscape in the brain. The findings could have significant implications for understanding the neuronal dysfunction and the pathological mechanisms underlying HACE development.

ARL-17477 is a dual inhibitor of NOS1 and the autophagic-lysosomal system that prevents tumor growth in vitro and in vivo

ARL-17477 is a selective neuronal nitric oxide synthase (NOS1) inhibitor that has been used in many preclinical studies since its initial discovery in the 1990s. In the present study, we demonstrate that ARL-17477 exhibits a NOS1-independent pharmacological activity that involves inhibition of the autophagy-lysosomal system and prevents cancer growth in vitro and in vivo. Initially, we screened a chemical compound library for potential anticancer agents, and identified ARL-17477 with micromolar anticancer activity against a wide spectrum of cancers, preferentially affecting cancer stem-like cells and KRAS-mutant cancer cells. Interestingly, ARL-17477 also affected NOS1-knockout cells, suggesting the existence of a NOS1-independent anticancer mechanism. Analysis of cell signals and death markers revealed that LC3B-II, p62, and GABARAP-II protein levels were significantly increased by ARL-17477. Furthermore, ARL-17477 had a chemical structure similar to that of chloroquine, suggesting the inhibition of autophagic flux at the level of lysosomal fusion as an underlying anticancer mechanism. Consistently, ARL-17477 induced lysosomal membrane permeabilization, impaired protein aggregate clearance, and activated transcription factor EB and lysosomal biogenesis. Furthermore, in vivo ARL-17477 inhibited the tumor growth of KRAS-mutant cancer. Thus, ARL-17477 is a dual inhibitor of NOS1 and the autophagy-lysosomal system that could potentially be used as a cancer therapeutic.

Free radicals: Relationship to Human Diseases and Potential Therapeutic applications

Reactive species are highly-reactive enzymatically, or non-enzymatically produced compounds with important roles in physiological and pathophysiological cellular processes. Although reactive species represent an extensively researched topic in biomedical sciences, many aspects of their roles and functions remain unclear. This review aims to systematically summarize findings regarding the biochemical characteristics of various types of reactive species and specify the localization and mechanisms of their production in cells. In addition, we discuss the specific roles of free radicals in cellular physiology, focusing on the current lines of research that aim to identify the reactive oxygen species-initiated cascades of reactions resulting in adaptive or pathological cellular responses. Finally, we present recent findings regarding the therapeutic modulations of intracellular levels of reactive oxygen species, which may have substantial significance in developing novel agents for treating several diseases.

Extremely low frequency electromagnetic stimulation reduces ischemic stroke volume by improving cerebral collateral blood flow

Extremely low frequency electromagnetic stimulation (ELF-EMS) has been considered as a neuroprotective therapy for ischemic stroke based on its capacity to induce nitric oxide (NO) signaling. Here, we examined whether ELF-EMS reduces ischemic stroke volume by stimulating cerebral collateral perfusion. Moreover, the pathway responsible for ELF-EMS-induced NO production was investigated. ELF-EMS diminished infarct growth following experimental stroke in collateral-rich C57BL/6 mice, but not in collateral-scarce BALB/c mice, suggesting that decreased lesion sizes after ELF-EMS results from improved collateral blood flow. In vitro analysis demonstrated that ELF-EMS increased endothelial NO levels by stimulating the Akt-/eNOS pathway. Furthermore, ELF-EMS augmented perfusion in the hind limb of healthy mice, which was mediated by enhanced Akt-/eNOS signaling. In healthy C57BL/6 mouse brains, ELF-EMS treatment increased cerebral blood flow in a NOS-dependent manner, whereas no improvement in cerebrovascular perfusion was observed in collateral-sparse BALB/c mice. In addition, ELF-EMS enhanced cerebral blood flow in both the contra- and ipsilateral hemispheres of C57BL/6 mice subjected to experimental ischemic stroke. In conclusion, we showed that ELF-EMS enhances (cerebro)vascular perfusion by stimulating NO production, indicating that ELF-EMS could be an attractive therapeutic strategy for acute ischemic stroke by improving cerebral collateral blood flow.

Oxidative Stress in Ischemia/Reperfusion Injuries following Acute Ischemic Stroke

Recanalization therapy is increasingly used in the treatment of acute ischemic stroke. However, in about one third of these patients, recanalization is followed by ischemia/reperfusion injuries, and clinically to worsening of the neurological status. Much research has focused on unraveling the involved mechanisms in order to prevent or efficiently treat these injuries. What we know so far is that oxidative stress and mitochondrial dysfunction are significantly involved in the pathogenesis of ischemia/reperfusion injury. However, despite promising results obtained in experimental research, clinical studies trying to interfere with the oxidative pathways have mostly failed. The current article discusses the main mechanisms leading to ischemia/reperfusion injuries, such as mitochondrial dysfunction, excitotoxicity, and oxidative stress, and reviews the clinical trials with antioxidant molecules highlighting recent developments and future strategies.

Therapeutic time windows of compounds against NMDA receptors signaling pathways for ischemic stroke

Much evidence has proved that excitotoxicity induced by excessive release of glutamate contributes largely to damage caused by ischemia. In view of the key role played by NMDA receptors in mediating excitotoxicity, compounds against NMDA receptors signaling pathways have become the most promising type of anti-stroke candidate compounds. However, the limited therapeutic time window for neuroprotection is a key factor preventing NMDA receptor-related compounds from showing efficacy in all clinical trials for ischemic stroke. In this perspective, the determination of therapeutic time windows of these kinds of compounds is useful in ensuring a therapeutic effect and accelerating clinical application. This mini-review discussed the therapeutic time windows of compounds against NMDA receptors signaling pathways, described related influence factors and the status of clinical studies. The purpose of this review is to look for compounds with wide therapeutic time windows and better clinical application prospect.

Optogenetic Stimulation Reduces Neuronal Nitric Oxide Synthase Expression After Stroke

Post-stroke optogenetic stimulation has been shown to enhance neurovascular coupling and functional recovery. Neuronal nitric oxide synthase (nNOS) has been implicated as a key regulator of the neurovascular response in acute stroke; however, its role in subacute recovery remains unclear. We investigated the expression of nNOS in stroke mice undergoing optogenetic stimulation of the contralesional lateral cerebellar nucleus (cLCN). We also examined the effects of nNOS inhibition on functional recovery using a pharmacological inhibitor targeting nNOS. Optogenetically stimulated stroke mice demonstrated significant improvement on the horizontal rotating beam task at post-stroke days 10 and 14. nNOS mRNA and protein expression was significantly and selectively decreased in the contralesional primary motor cortex (cM1) of cLCN-stimulated mice. The nNOS expression in cM1 was negatively correlated with improved recovery. nNOS inhibitor (ARL 17477)-treated stroke mice exhibited a significant functional improvement in speed at post-stroke day 10, when compared to stroke mice receiving vehicle (saline) only. Our results show that optogenetic stimulation of cLCN and systemic nNOS inhibition both produce functional benefits after stroke, and suggest that nNOS may play a maladaptive role in post-stroke recovery.

Nitric Oxide Synthase Inhibitors into the Clinic at Last

The 1998 Nobel Prize in Medicine and Physiology for the discovery of nitric oxide, a nitrogen containing reactive oxygen species (also termed reactive nitrogen or reactive nitrogen/oxygen species) stirred great hopes. Clinical applications, however, have so far pertained exclusively to the downstream signaling of cGMP enhancing drugs such as phosphodiesterase inhibitors and soluble guanylate cyclase stimulators. All clinical attempts, so far, to inhibit NOS have failed even though preclinical models were strikingly positive and clinical biomarkers correlated perfectly. This rather casts doubt on our current way of target identification in drug discovery in general and our way of patient stratification based on correlating but not causal biomarkers or symptoms. The opposite, NO donors, nitrite and enhancing NO synthesis by eNOS/NOS3 recoupling in situations of NO deficiency, are rapidly declining in clinical relevance or hold promise but need yet to enter formal therapeutic guidelines, respectively. Nevertheless, NOS inhibition in situations of NO overproduction often jointly with enhanced superoxide (or hydrogen peroxide production) still holds promise, but most likely only in acute conditions such as neurotrauma (Stover et al., J Neurotrauma 31(19):1599-1606, 2014) and stroke (Kleinschnitz et al., J Cereb Blood Flow Metab 1508-1512, 2016; Casas et al., Proc Natl Acad Sci U S A 116(14):7129-7136, 2019). Conversely, in chronic conditions, long-term inhibition of NOS might be too risky because of off-target effects on eNOS/NOS3 in particular for patients with cardiovascular risks or metabolic and renal diseases. Nitric oxide synthases (NOS) and their role in health (green) and disease (red). Only neuronal/type 1 NOS (NOS1) has a high degree of clinical validation and is in late stage development for traumatic brain injury, followed by a phase II safety/efficacy trial in ischemic stroke. The pathophysiology of NOS1 (Kleinschnitz et al., J Cereb Blood Flow Metab 1508-1512, 2016) is likely to be related to parallel superoxide or hydrogen peroxide formation (Kleinschnitz et al., J Cereb Blood Flow Metab 1508-1512, 2016; Casas et al., Proc Natl Acad Sci U S A 114(46):12315-12320, 2017; Casas et al., Proc Natl Acad Sci U S A 116(14):7129-7136, 2019) leading to peroxynitrite and protein nitration, etc. Endothelial/type 3 NOS (NOS3) is considered protective only and its inhibition should be avoided. The preclinical evidence for a role of high-output inducible/type 2 NOS (NOS2) isoform in sepsis, asthma, rheumatic arthritis, etc. was high, but all clinical development trials in these indications were neutral despite target engagement being validated. This casts doubt on the role of NOS2 in humans in health and disease (hence the neutral, black coloring).

Antioxidant enzymes expression in lymphocytes of patients undergoing carotid endarterectomy

To remedy carotid artery stenosis and prevent stroke surgical intervention is commonly used, and the gold standard being carotid endarterectomy (CEA). During CEA cerebrovascular hemoglobin oxygen saturation decreases and when this decrease reaches critical levels it leads to cerebral hypoxia that causes neuronal damage. One of the proposed mechanism that affects changes during CEA and contribute to acute brain ischemia (ABI) is oxidative stress. The increased production of reactive oxygen species and reactive nitrogen species during ABI may cause an unregulated inflammatory response and further lead to structural and functional injury of neurons. Antioxidant activity are involved in the protection against neuronal damage after cerebral ischemia. We hypothesized that neuronal injury and poor outcomes in patients undergoing CEA may be results of oxidative stress that disturbed function of antioxidant enzymes and contributed to the DNA damage in lymphocytes.

Hypothesis related to the regulation of inducible nitric oxide synthase during carotid endarterectomy

Sudden occlusion of an artery caused by a thrombus or emboli is the most frequent cause of acute brain ischemia (ABI). Carotid endarterectomy (CEA) represents the gold standard for preventing strokes of carotid origin. However, neuronal damage caused by ischemia and/or reperfusion may contribute to a poor clinical outcome after CEA. In response to shear stress caused by hypoxic-ischemic conditions in patients undergoing CEA, stimulation of the hypothalamic-pituitaryadrenal axis leads to biological responses known as hypermetabolic stress, characterized by hemodynamic, metabolic, inflammatory and immunological changes. These changes maintain homeostasis and assist recovery, but an unregulated inflammatory response could lead to further tissue damage and death of neurons. Nitric oxide (NO) is an important signaling molecule involved in several physiological and pathological processes, including ABI. However, an excess of NO could have detrimental effects. We hypothesized that the hypoxic-ischemic state induced by carotid clamping leads to overexpression of inducible NO synthase and that uncontrolled production of NO could adversely affect outcome after CEA.

Enhanced Oxidative Stress Is Responsible for TRPV4-Induced Neurotoxicity

Transient receptor potential vanilloid 4 (TRPV4) has been reported to be responsible for neuronal injury in pathological conditions. Excessive oxidative stress can lead to neuronal damage, and activation of TRPV4 increases the production of reactive oxygen species (ROS) and nitric oxide (NO) in many types of cells. The present study explored whether TRPV4-induced neuronal injury is mediated through enhancing oxidative stress. We found that intracerebroventricular injection of the TRPV4 agonist GSK1016790A increased the content of methane dicarboxylic aldehyde (MDA) and NO in the hippocampus, which was blocked by administration of the TRPV4 specific antagonist HC-067047. The activities of catalase (CAT) and glutathione peroxidase (GSH-Px) were decreased by GSK1016790A, whereas the activity of superoxide dismutase (SOD) remained unchanged. Moreover, the protein level and activity of neuronal nitric oxide synthase (nNOS) were increased by GSK1016790A, and the GSK1016790A-induced increase in NO content was blocked by an nNOS specific antagonist ARL-17477. The GSK1016790A-induced modulations of CAT, GSH-Px and nNOS activities and the protein level of nNOS were significantly inhibited by HC-067047. Finally, GSK1016790A-induced neuronal death and apoptosis in the hippocampal CA1 area were markedly attenuated by administration of a ROS scavenger Trolox or ARL-17477. We conclude that activation of TRPV4 enhances oxidative stress by inhibiting CAT and GSH-Px and increasing nNOS, which is responsible, at least in part, for TRPV4-induced neurotoxicity.

Calpains and neuronal damage in the ischemic brain: The swiss knife in synaptic injury

The excessive extracellular accumulation of glutamate in the ischemic brain leads to an overactivation of glutamate receptors with consequent excitotoxic neuronal death. Neuronal demise is largely due to a sustained activation of NMDA receptors for glutamate, with a consequent increase in the intracellular Ca(2+) concentration and activation of calcium- dependent mechanisms. Calpains are a group of Ca(2+)-dependent proteases that truncate specific proteins, and some of the cleavage products remain in the cell, although with a distinct function. Numerous studies have shown pre- and post-synaptic effects of calpains on glutamatergic and GABAergic synapses, targeting membrane- associated proteins as well as intracellular proteins. The resulting changes in the presynaptic proteome alter neurotransmitter release, while the cleavage of postsynaptic proteins affects directly or indirectly the activity of neurotransmitter receptors and downstream mechanisms. These alterations also disturb the balance between excitatory and inhibitory neurotransmission in the brain, with an impact in neuronal demise. In this review we discuss the evidence pointing to a role for calpains in the dysregulation of excitatory and inhibitory synapses in brain ischemia, at the pre- and post-synaptic levels, as well as the functional consequences. Although targeting calpain-dependent mechanisms may constitute a good therapeutic approach for stroke, specific strategies should be developed to avoid non-specific effects given the important regulatory role played by these proteases under normal physiological conditions.

Compound 21 is pro-angiogenic in the brain and results in sustained recovery after ischemic stroke

INTRODUCTION

Angiotensin II type 2 receptor (AT2R) stimulation is neuroprotective after experimental stroke. However, the therapeutic utility of AT2R stimulation has been hampered by the lack of a specific agonist with favourable bioavailability. Compound 21 (C21) - the first non-peptide AT2R agonist - offers a potential option to enhance stroke recovery. This study aimed to investigate the effect of C21 administration on early and late stroke outcomes, and the molecular mediators involved.

METHODS

Rats were subjected to 3 h or 90 min of middle cerebral artery occlusion (MCAO) and randomized to intraperitoneal C21 (0.03 mg/kg) or saline at reperfusion. Animals were sacrificed at 24 h or 7 days and brains were collected for molecular analysis and immunostaining, respectively. Functional outcome at days 1, 4 and 7 was assessed blindly. C21 angiogenic potential was assessed in vitro.

RESULTS

After 3 h of MCAO, C21 treatment reduced infarct size and improved behavioural outcome at 24 h without affecting blood pressure. Co-administration of the AT2R antagonist (PD123319) blocked these effects. On the molecular level, C21 decreased brain haemoglobin content, down-regulated apoptotic and oxidative markers, and increased pro-survival molecules in the brain. After 90 min of MCAO, C21 treatment resulted in sustained functional improvement at 7 days, together with increased vascular density in the ischemic penumbra. In vitro, C21 showed a pro-angiogenic effect that was blocked with brain-derived neurotrophic factor neutralization.

CONCLUSION

These findings demonstrate that a single dose of C21 is neurovascular-protective and improves stroke outcome possibly through increasing neurotrophin activity, mitigating brain inflammation, and promoting antioxidant and pro-angiogenic effects.

Modulation of the ASK1-MKK3/6-p38/MAPK signalling pathway mediates sildenafil protection against chemical hypoxia caused by malonate

BACKGROUND AND PURPOSE

PD5 inhibitors have recently been reported to exert beneficial effects against ischaemia-reperfusion injury in several organs. However, there are few studies regarding their neuroprotective effects in brain ischaemia. The present study was designed to assess the effects of sildenafil against chemical hypoxia induced by malonate. Intrastriatal injection of malonate produces energy depletion and striatal lesions similar to that seen in cerebral ischaemia through mechanisms that involve generation of reactive oxygen species (ROS).

EXPERIMENTAL APPROACH

Volume lesion was analysed by cytochrome oxidase histochemistry. Generation of reactive species was determined by in situ visualization of superoxide production and nitrotyrosine measurement. Protein levels were determined by Western blot after subcellular fractionation.

KEY RESULTS

Sildenafil, given 30 min before malonate, significantly decreased the lesion volume in the rat. This protective effect cannot be attributed to any effect on ROS production but to the inhibition of downstream pathways. Thus, malonate induced the activation of apoptosis signal-regulating kinase-1 (ASK1) and two MAPK kinases, MKK3/6 and MKK7, which lead to an increased phosphorylation of JNK and p38 MAPK, effects that were blocked by sildenafil. Selective inhibitors of p38 and JNK (SB203580 or SP600125, respectively) were used in combination with malonate in order to evaluate the plausible implication of these pathways in the protection afforded by sildenafil. While inhibition of p38 provided a significant protection against malonate-induced neurotoxicity, inhibition of JNK did not.

CONCLUSIONS AND IMPLICATIONS

Sildenafil protects against the chemical hypoxia induced by malonate through the regulation of the ASK1-MKK3/6-p38/MAPK signalling pathway.

Development of nitric oxide synthase inhibitors for neurodegeneration and neuropathic pain

Nitric oxide (NO) is an important signaling molecule in the human body, playing a crucial role in cell and neuronal communication, regulation of blood pressure, and in immune activation. However, overproduction of NO by the neuronal isoform of nitric oxide synthase (nNOS) is one of the fundamental causes underlying neurodegenerative disorders and neuropathic pain. Therefore, developing small molecules for selective inhibition of nNOS over related isoforms (eNOS and iNOS) is therapeutically desirable. The aims of this review focus on the regulation and dysregulation of NO signaling, the role of NO in neurodegeneration and pain, the structure and mechanism of nNOS, and the use of this information to design selective inhibitors of this enzyme. Structure-based drug design, the bioavailability and pharmacokinetics of these inhibitors, and extensive target validation through animal studies are addressed.

Combination of chiral linkers with thiophenecarboximidamide heads to improve the selectivity of inhibitors of neuronal nitric oxide synthase

To develop potent and selective nNOS inhibitors, a new series of double-headed molecules with chiral linkers that derive from natural amino acid derivatives have been designed and synthesized. The new structures integrate a thiophenecarboximidamide head with two types of chiral linkers, presenting easy synthesis and good inhibitory properties. Inhibitor (S)-9b exhibits a potency of 14.7 nM against nNOS and is 1134 and 322-fold more selective for nNOS over eNOS and iNOS, respectively. Crystal structures show that the additional binding between the aminomethyl moiety of 9b and propionate A on the heme and tetrahydrobiopterin (H4B) in nNOS, but not eNOS, contributes to its high selectivity. This work demonstrates the advantage of integrating known structures into structure optimization, and it should be possible to more readily develop compounds that incorporate bioavailability with these advanced features. Moreover, this integrative strategy is a general approach in new drug discovery.

Exogenous nitric oxide negatively regulates the S-nitrosylation p38 mitogen-activated protein kinase activation during cerebral ischaemia and reperfusion

AIMS

A number of studies have suggested that nitric oxide (NO) plays an important role in the reactive phosphorylation of p38MAPKα (p38). However, whether S-nitrosylation of p38 is activated by NO and the details remain unclear. The aim of the present work was to assess the activation of p38, the S-nitrosylation site and the p38 signalling pathway in rat hippocampus and in HEK293 cell induced by exogenous NO.

METHODS

Primary hippocampal cultures, HEK293 cells and rat model of cerebral ischaemia/reperfusion (brain ischaemia was induced by four-vessel occlusion procedure) were used in this study. Biotin-switch method and immunoblotting were performed to study the S-nitrosylation and phosphorylation of p38, and neuronal loss was observed by histology.

RESULTS

Endogenous NO increased p38 phosphorylation and S-nitrosylation, and the activation of p38 was dependent on the S-nitrosylation of Cys-211, which was critical for the NO-mediated activation of p38. The exogenous NO donor sodium nitroprusside, S-nitrosoglutathione, 7-nitroindazole, the inhibitor of the neuronal nitric oxide synthase, inhibited the activation of p38 signal pathway induced by cerebral ischaemia/reperfusion and attenuated the damage in rat hippocampal neurones. Moreover, the N-methyl-D-aspartate receptor (NMDAR) is probably involved in the p38 activation process of S-nitrosylation and phosphorylation.

CONCLUSION

Endogenous NO induces the S-nitrosylation and phosphorylation of p38 and mediates p38 signalling pathway by NMDAR, and as exogenous NO inhibits this process and is neuroprotective in rat cerebral ischaemia/reperfusion, it may make a contribution to stroke therapy.

Nitric oxide modulators: an emerging class of medicinal agents

Nitric oxide, a unique messenger in biological system, is ubiquitously present virtually in all tissues revealing its versatile nature of being involved in diverse physiological functions such as vascular tone, inhibition of platelet aggregation, cell adhesion, neurotransmission and enzyme and immune regulation. The tremendous advancements made in the past few decades in this area suggests that the nitric oxide modulation either by its exogenous release through nitric oxide donors or inhibition of its synthesis by nitric oxide synthase inhibitors in physiological milieu may provide newer clinical strategies for the treatment of some diseases. In this review, an attempt is made to document and understand the biological chemistry of different classes of nitric oxide modulators that would prove to be a fruitful area in the years to come.

Cognitive function and oxidative stress after carotid endarterectomy: comparison of propofol to sevoflurane anesthesia

OBJECTIVE

To examine the antioxidant role of propofol in ischemia-reperfusion during carotid endarterectomy (CEA) and its influence on cognitive dysfunction after CEA.

DESIGN

A randomized prospective study.

SETTING

Single-center study in a university hospital.

PARTICIPANTS

Forty-four patients.

INTERVENTIONS

Patients underwent elective CEA under general anesthesia with either sevoflurane (group S, n = 21) or propofol (group P, n = 23).

MEASUREMENTS AND MAIN RESULTS

Cognitive function was assessed with the Mini-Mental State Examination (MMSE) before CEA, 1 hour after CEA, and 24 hours after CEA. Blood samples from the radial artery and the internal jugular vein were drawn before carotid clamping and 5 minutes following unclamping, and peripheral blood was obtained 24 hours postoperatively. Samples were analyzed for lactate, S100B, and P-selectin concentrations and for the antioxidative markers malondialdehyde/low-density lipoprotein ratio and nitrate + nitrite concentrations. Compared with group S, patients in group P exhibited a greater increase in their MMSE values 24 hours postoperatively. Patients who had their MMSE performance reduced at 24 hours also were significantly fewer in group P (13% v 43% in group S, p<0.05). Significantly lower levels of lactate and S100B were observed in arterial and jugular vein samples in group P. In addition, the jugular vein-arterial differences of malondialdehyde-to-low-density lipoprotein ratio and nitrates + nitrites concentrations were lower during propofol anesthesia.

CONCLUSIONS

Propofol seemed to improve cognitive performance after CEA. This improvement was associated with decreased indices of ischemic cerebral damage and seemed to be due to antioxidative effect in the ischemic cerebral circulation.

Targeting reactive nitrogen species: a promising therapeutic strategy for cerebral ischemia-reperfusion injury

Ischemic stroke accounts for nearly 80% of stroke cases. Recanalization with thrombolysis is a currently crucial therapeutic strategy for re-building blood supply, but the thrombolytic therapy often companies with cerebral ischemia-reperfusion injury, which are mediated by free radicals. As an important component of free radicals, reactive nitrogen species (RNS), including nitric oxide (NO) and peroxynitrite (ONOO(-)), play important roles in the process of cerebral ischemia-reperfusion injury. Ischemia-reperfusion results in the production of nitric oxide (NO) and peroxynitrite (ONOO(-)) in ischemic brain, which trigger numerous molecular cascades and lead to disruption of the blood brain barrier and exacerbate brain damage. There are few therapeutic strategies available for saving ischemic brains and preventing the subsequent brain damage. Recent evidence suggests that RNS could be a therapeutic target for the treatment of cerebral ischemia-reperfusion injury. Herein, we reviewed the recent progress regarding the roles of RNS in the process of cerebral ischemic-reperfusion injury and discussed the potentials of drug development that target NO and ONOO(-) to treat ischemic stroke. We conclude that modulation for RNS level could be an important therapeutic strategy for preventing cerebral ischemia-reperfusion injury.

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.

Different expressions of AQP1, AQP4, eNOS, and VEGF proteins in ischemic versus non-ischemic cerebropathy in rats: potential roles of AQP1 and eNOS in hydrocephalic and vasogenic edema formation

In this study, expressions of aquaporin (AQP) 1, AQP4, endothelial nitric oxide synthase (eNOS), and vascular endothelial growth factor in blood-cerebrospinal fluid (CSF) barrier and blood-brain barrier (BBB) are examined in rat choroid plexus and peri-infarcted hippocampal formation (HF) following systemic hyponatremia (SH) and permanent middle cerebral artery occlusion (pMCAO). These events are thought to cause the development of hydrocephalic and vasogenic edemas. The importance of CSF overproduction and intact blood-CSF barrier during hydrocephalic edema formation is demonstrated by the high expression of AQP1 (329.86±10.2%, n=4 , P<0.01) and trapped plasma immunoglobulin G (IgG) in choroid plexus epithelium after 24 hours of SH. However, the increased eNOS expression in peri-infarcted HF (130±3%, n=4, P<0.01) and extravasation of plasma IgG into the extravascular compartment after 24 hours of pMCAO suggest that increased microvascular permeability, probably due to elevated levels of nitric oxide, leads to development of vasogenic brain edema via BBB breakdown. Based on these findings, the authors suggest that modulation of different protein expression, dependent on the type of brain edema, is required for primary (pMCAO) and secondary (SH) brain injuries to attenuate brain edema and neuronal degeneration.

Design, synthesis, and biological evaluation of 3,4-dihydroquinolin-2(1H)-one and 1,2,3,4-tetrahydroquinoline-based selective human neuronal nitric oxide synthase (nNOS) inhibitors

Neuronal nitric oxide synthase (nNOS) inhibitors are effective in preclinical models of many neurological disorders. In this study, two related series of compounds, 3,4-dihydroquinolin-2(1H)-one and 1,2,3,4-tetrahydroquinoline, containing a 6-substituted thiophene amidine group were synthesized and evaluated as inhibitors of human nitric oxide synthase (NOS). A structure-activity relationship (SAR) study led to the identification of a number of potent and selective nNOS inhibitors. Furthermore, a few representative compounds were shown to possess druglike properties, features that are often difficult to achieve when designing nNOS inhibitors. Compound (S)-35, with excellent potency and selectivity for nNOS, was shown to fully reverse thermal hyperalgesia when given to rats at a dose of 30 mg/kg intraperitonieally (ip) in the L5/L6 spinal nerve ligation model of neuropathic pain (Chung model). In addition, this compound reduced tactile hyperesthesia (allodynia) after oral administration (30 mg/kg) in a rat model of dural inflammation relevant to migraine pain.

The effect of nNOS inhibitors on toxin-induced cell death in dopaminergic cell lines depends on the extent of enzyme expression

Nitric oxide is linked with neurodegeneration in Parkinson's disease (PD) through the involvement of both inducible (iNOS) and neuronal nitric oxide synthase (nNOS). While non-selective NOS inhibitors are neuroprotective, the role of nNOS has not been determined using selective NOS inhibitors. The present study investigated the neuroprotective effect of selective iNOS and nNOS inhibitors on MPP(+)- and MG-132-induced cell death in cell lines with differing levels of nNOS expression. Inhibition of endogenously expressed nNOS by 7-NI and ARR17477 enhanced the toxicity of MPP(+) and MG-132 in N1E-115 cells, whereas in transfected SH-SY5Y cells overexpressing nNOS, ARR17477 and 7-NI protected against MPP(+)- and MG-132-induced cell death. In contrast, inhibition of iNOS by 1400W was ineffective in preventing MPP(+) and MG-132 toxicity in these cell lines. These results suggest a dual role for NOS in dopaminergic cell viability. nNOS is protective against toxic insult when produced endogenously. When nNOS is overexpressed, it becomes neurotoxic to cells suggesting that inhibition of nNOS may be a promising strategy to prevent cell death in PD.

Novel nitric oxide synthase inhibitors: a patent review

INTRODUCTION

Knowledge of NO and its function in cell signaling has rapidly developed since its biological effects were first described in 1977. It is formed from L-arginine by NOS isoforms (nNOS, iNOS and eNOS). These enzymes are products of separate genes, encoded on three different chromosomes and responsible for regulating a variety of functions within cells and tissues. NOS isoforms are currently under investigation as targets for novel therapeutics in especially neurodegenerative disorders, inflammation and pain. Many important questions regarding these messengers and signaling molecules remain to be answered.

AREAS COVERED

This review gives an overview of patents covering drug-like inhibitors for the NOS isoforms filed and published within the last 6 years, up to September 2010, as well as insight into recent highlights in this area.

EXPERT OPINION

The NOS isoforms are attractive targets in drug design for various pathological conditions and have received considerable interest over recent years. With the advances in molecular biology, modeling software, synthesis, bioassays, and our understanding of the NOS enzymes and the function of NO, novel bioavailable and highly selective drug therapies utilizing this mode of action may soon see the light.

The contribution of L-arginine to the neurotoxicity of recombinant tissue plasminogen activator following cerebral ischemia: a review of rtPA neurotoxicity

Alteplase is the only drug licensed for acute ischemic stroke, and in this formulation, the thrombolytic agent recombinant tissue plasminogen activator (rtPA) is stabilized in a solution of L-arginine. Improved functional outcomes after alteplase administration have been shown in clinical trials, along with improved histological and behavioral measures in experimental models of embolic stroke. However, in animal models of mechanically induced ischemia, alteplase can exacerbate ischemic damage. We have systematically reviewed the literature of both rtPA and L-arginine administration in mechanical focal ischemia. The rtPA worsens ischemic damage under certain conditions, whereas L-arginine can have both beneficial and deleterious effects dependent on the time of administration. The interaction between rtPA and L-arginine may be leading to the production of nitric oxide, which can cause direct neurotoxicity, altered cerebral blood flow, and disruption of the neurovascular unit. We suggest that alternative formulations of rtPA, in the absence of L-arginine, would provide new insight into rtPA neurotoxicity, and have the potential to offer more efficacious thrombolytic therapy for ischemic stroke patients.

Normobaric hyperoxia delays and attenuates early nitric oxide production in focal cerebral ischemic rats

Overproduction of neuronal nitric oxide synthase (nNOS)-derived NO is detrimental during cerebral ischemia. Normobaric hyperoxia (NBO) has been shown to be neuroprotective, extending the therapeutic time window for ischemic stroke, but the mechanism is not fully understood. In the present study, using a rat model of ischemic stroke, we investigated the effect of early NBO treatment on neuronal NO production. Male Sprague-Dawley rats were given normoxia (30% O(2)) or NBO (95% O(2)) during 10, 30, 60 or 90min filament occlusion of the middle cerebral artery. NO(x)(-) (nitrite plus nitrate) and 3-nitrotyrosine were measured in the ischemic cortex. Ischemia caused a rapid increase in the production of NO(x)(-), with a peak at 10min after ischemia onset, then gradually declining to the baseline level at 60min. NBO treatment delayed the NO(x)(-) production peak to 30min and attenuated the total amount of NO(x)(-). Ischemia also increased 3-nitrotyrosine formation, which was significantly reduced by NBO treatment. Inhibition of nNOS by pre-treatment with 7-nitroindazole had similar effect as NBO treatment on NO(x)(-) and 3-nitrotyrosine production, and when combined with NBO, no further reduction in NO production was observed. Furthermore, NBO treatment significantly decreased brain infarct volume. Taken together, our findings demonstrate that delaying and attenuating the early NO release from nNOS may be an important mechanism accounting for NBO's neuroprotection.

Naphthoquinones and bioactive compounds from tobacco as modulators of neuronal nitric oxide synthase activity

Studies were conducted with extracts of several varieties of tobacco in search of neuronal nitric oxide synthase (nNOS) inhibitors which may be of value in the treatment of stroke. Current therapies do not directly exploit modulation of nNOS activity due to poor selectivity of the currently available nNOS inhibitors. The properties of a potentially novel nNOS inhibitor(s) derived from tobacco extracts, and the concentration-dependent, modulatory effects of the tobacco-derived naphthoquinone compound, 2,3,6-trimethyl-1,4-naphthoquinone (TMN), on nNOS activity were investigated, using 2-methyl-1,4-naphthoquinone (menadione) as a control. Up to 31 microM, both TMN and menadione stimulated nNOS-catalysed L-citrulline production. However, at higher concentrations of TMN (62.5-500 microM), the stimulation was lost in a concentration-dependent manner. With TMN, the loss of stimulation did not decrease beyond the control activity. With menadione (62.5-500 microM), the loss of stimulation surpassed that of the control (78+/-0.01% of control activity), indicating a true inhibition of nNOS activity. This study suggests that potential nNOS inhibitors are present in tobacco, most of which remain to be identified.

Effects of Pretreatment with a Xanthine Oxidase Inhibitor on Free Radical Levels during Carotid Endarterectomy

OBJECTIVE

Free radicals contribute to the tissue damage caused by ischaemia-reperfusion. The aim of the present study was to investigate whether preoperative antioxidant therapy (allopurinol) affects free radical levels in cerebral venous blood in connection with surgery for carotid artery stenosis.

MATERIALS AND METHODS

Twenty-five patients were randomised into the study. Thirteen were controls and 12 were pretreated with allopurinol the day before surgery. Before, during and after surgery, blood samples were drawn from the ipsilateral jugular vein. Radical levels were measured using the spin trap technique ex vivo using OXANOH as the spin trap. Multivariate statistics were used with Principal Component Analysis and Partial Least Square regression analysis.

RESULTS

Radical levels increased with diabetes, high leukocyte count, high creatinine and a high degree of contralateral stenosis. Radical levels decreased with high age, blood pressure, collateral circulation as well as operation for left-side carotid artery stenosis. After pretreatment with allopurinol, several of the relationships noted in the control group were eliminated, i.e. leukocyte count, side of operation, Betapred pretreatment and collateral circulation.

CONCLUSIONS

Radical levels can be determined in connection with surgery for carotid artery stenosis using an ex vivo spin trap method. With preoperative antioxidant therapy the relationships between enhanced radical levels and clinical data, as seen in control subjects, disappeared. This might indicate a beneficial effect of preoperative pretreatment with antioxidants.

Neuronal nitric oxide synthase: structure, subcellular localization, regulation, and clinical implications

Nitric oxide (NO), a free gaseous signaling molecule, is involved in the regulation of the cardiovascular, nervous and immune system. The neurotransmitter function of nitric oxide is dependent on dynamic regulation of its biosynthetic enzyme, nitric oxide synthase (NOS). There are three types of NOS, neuronal nitric oxide synthase (nNOS), endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS). Of the three NOS, we focus on nNOS in the present review. Brain nNOS exists in particulate and soluble forms and the differential subcellular localization of nNOS may contribute to its diverse functions. Proteins bearing PDZ domains can interact directly with the PDZ domain of nNOS, influencing the subcellular distribution and/or activity of the enzyme. During the past several years, an increasing number of reports have demonstrated the importance of nNOS in a variety of synaptic signaling events. nNOS has been implicated in modulating physiological functions such as learning, memory, and neurogenesis, as well as being involved in a number of human diseases. In this review we concentrate on recent findings regarding the structural features, subcellular localization and factors regulating nNOS function. In particular, we conclude with a section discussing the role of nNOS in a wide range of physiological and pathological conditions.

Relationships between neurons expressing neuronal nitric oxide synthase, degree of microglia activation and animal survival. A study in the rat cortex after transient ischemia

The focal ischemia obtained in an animal model of middle cerebral artery occlusion (MCAo) causes the "core" of damage in the striatum and the "penumbra" of damage in the fronto-parietal cortex. The latter is mainly functionally affected and shows changes in nNOS and iNOS expression during the acute phase of ischemia. With the aim to study possible relationships between these changes and the affection entity during the animal recovery, we investigated from 24 up to 144 h after reperfusion the expression and content of these two NOS isoforms in the neurons and microglia and the degree of microglia reactivity in the fronto-parietal cortices of rats undertaken to transient MCAo. Evaluation of motor-sensory performances and survival allowed dividing the animals into two groups. Immunohistochemistry, western blot and quantitative analysis demonstrated, both in the ischemic and contralateral cortex of the rats with longer survival, wellness and significantly increased number of the nNOS-IR neurons at 24 h and moderately activated microglia up to 144 h. In the rats not recovering, injured and significantly decreased nNOS-IR neurons, intensely activated microglia and appearance of iNOS-IR were seen at all time points. In conclusion, since the recovery occurs when nNOS-IR neurons are greatly increased, we presume nNOS protect the tissue likely controlling the passage from the state of reactive to that of activated microglia. Moreover, the morphological signs of wellness and the two-fold increase in number of the nNOS-IR neurons appear to be characteristic of the "penumbra" area and could explain why this region is mainly functionally affected.

Molecular targets in cerebral ischemia for developing novel therapeutics

Cerebral ischemia (stroke) triggers a complex series of biochemical and molecular mechanisms that impairs the neurologic functions through breakdown of cellular integrity mediated by excitotoxic glutamatergic signalling, ionic imbalance, free-radical reactions, etc. These intricate processes lead to activation of signalling mechanisms involving calcium/calmodulin-dependent kinases (CaMKs) and mitogen-activated protein kinases (MAPKs) such as extracellular signal-regulated kinase (ERK), p38, and c-Jun N-terminal kinase (JNK). The distribution of these transducers bring them in contact with appropriate molecular targets leading to altered gene expression, e.g. ERK and JNK mediated early gene induction, responsible for activation of cell survival/damaging mechanisms. Moreover, inflammatory reactions initiated at the neurovascular interface and alterations in the dynamic communication between the endothelial cells, astrocytes and neurons are thought to substantially contribute to the pathogenesis of the disease. The damaging mechanisms may proceed through rapid nonspecific cell lysis (necrosis) or by active form of cell demise (apoptosis or necroptosis), depending upon the severity and duration of the ischemic insult. A systematic understanding of these molecular mechanisms with prospect of modulating the chain of events leading to cellular survival/damage may help to generate the potential strategies for neuroprotection. This review briefly covers the current status on the molecular mechanisms of stroke pathophysiology with an endeavour to identify potential molecular targets such as targeting postsynaptic density-95 (PSD-95)/N-methyl-d-aspartate (NMDA) receptor interaction, certain key proteins involved in oxidative stress, CaMKs and MAPKs (ERK, p38 and JNK) signalling, inflammation (cytokines, adhesion molecules, etc.) and cell death pathways (caspases, Bcl-2 family proteins, poly (ADP-ribose) polymerase-1 (PARP-1), apoptosis-inducing factor (AIF), inhibitors of apoptosis proteins (IAPs), heat shock protein 70 (HSP70), receptor interacting protein (RIP), etc., besides targeting directly the genes itself. However, selecting promising targets from various signalling cascades, for drug discovery and development is very challenging, nevertheless such novel approaches may lead to the emergence of new avenues for therapeutic intervention in cerebral ischemia.

Nitric oxide and peroxynitrite in health and disease

The discovery that mammalian cells have the ability to synthesize the free radical nitric oxide (NO) has stimulated an extraordinary impetus for scientific research in all the fields of biology and medicine. Since its early description as an endothelial-derived relaxing factor, NO has emerged as a fundamental signaling device regulating virtually every critical cellular function, as well as a potent mediator of cellular damage in a wide range of conditions. Recent evidence indicates that most of the cytotoxicity attributed to NO is rather due to peroxynitrite, produced from the diffusion-controlled reaction between NO and another free radical, the superoxide anion. Peroxynitrite interacts with lipids, DNA, and proteins via direct oxidative reactions or via indirect, radical-mediated mechanisms. These reactions trigger cellular responses ranging from subtle modulations of cell signaling to overwhelming oxidative injury, committing cells to necrosis or apoptosis. In vivo, peroxynitrite generation represents a crucial pathogenic mechanism in conditions such as stroke, myocardial infarction, chronic heart failure, diabetes, circulatory shock, chronic inflammatory diseases, cancer, and neurodegenerative disorders. Hence, novel pharmacological strategies aimed at removing peroxynitrite might represent powerful therapeutic tools in the future. Evidence supporting these novel roles of NO and peroxynitrite is presented in detail in this review.

Vasorelaxing effect of BAY 41-2272 in rat basilar artery: involvement of cGMP-dependent and independent mechanisms

Decreases in intrinsic NO cause cerebral vasospasms because of the dysregulation of cGMP formation by NO-mediated pathways. Because 5-cyclopropyl-2-{1-(2-fluorobenzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl}pyrimidin-4-ylamine (BAY 41-2272) is a potent soluble guanylyl cyclase (sGC) stimulator in an NO-independent manner, this study aimed to investigate the mechanisms underlying the relaxant effects of BAY 41-2272 in the rat basilar artery. BAY 41-2272 (0.0001 to 1 micromol/L) induced relaxations in a concentration-dependent manner, with pEC50 values of 8.13+/-0.03 and 7.63+/-0.05 in intact and denuded rings, respectively. The sGC inhibitor 1H-[1,2,4] oxadiazolo [4,3,-a]quinoxalin-1-one (ODQ) markedly displaced the curve for BAY 41-2272 to the right in intact or denuded rings (&10-fold). The NO synthesis inhibitor NG-nitro-L-arginine methyl ester caused a rightward shift in the curve for BAY 41-2272 (4-fold), whereas the phosphodiesterase type 5 inhibitor sildenafil enhanced BAY 41-2272-induced relaxations (3- to 4-fold). The Na+-K+-ATPase inhibitor ouabain caused 3-fold rightward shifts in the curves for BAY 41-2272. Ca2+-induced contractions in K+ depolarized rings were significantly attenuated by BAY 41-2272 in an ODQ-insensitive manner. The NO donor glyceryl trinitrate and BAY 41-2272 caused rightward shifts in the contractile responses to serotonin. Their coincubation caused a synergistic inhibition of serotonin-induced contractions. BAY 41-2272 and glyceryl trinitrate increased cGMP levels (but not cAMP) by 10-fold and 4-fold above baseline, respectively, in an ODQ-sensitive manner. cGMP levels increased by 50-fold after coincubation. BAY 41-2272 potently relaxes the rat basilar artery in a synergistic fashion with NO. Targeting the sGC with selective activators, such as BAY 41-2272, may represent a new therapy to treat cerebrovascular disease.

Influence of the selective neuronal NO synthase inhibitor ARL 17477 on nitrergic neurotransmission in porcine stomach

Selective neuronal NOS (nNOS) inhibitors have been developed for possible application in cerebral ischemia and neurodegenerative disorders. To investigate the degree of interference with peripheral nNOS, the influence of the selective nNOS inhibitor ARL 17477 was studied on electrically induced nitrergic relaxations in pig gastric fundus strips and on gastric fundic compliance in conscious pig. Circular muscle strips of porcine gastric fundus were electrically stimulated (10 s trains at 4 Hz, 0.1 ms and 40 V). ARL 17477 inhibited the electrically induced relaxations in a concentration-dependent way (3x10(-6) M-10(-4) M). The inhibitory effect of ARL 17477 developed more progressively than that of N(G)-nitro-L-arginine methyl ester (L-NAME; 3x10(-4) M). In conscious pigs, instrumented with a fundic cannula, L-NAME (20 mg/kg i.v.) significantly increased mean arterial blood pressure and decreased fundic compliance in the fasted state (71+/-13 ml/mm Hg versus 185+/-37 ml/mm Hg after saline; P<0.05). ARL 17477 (3 mg/kg, i.v.) did not influence blood pressure but influenced gastric fundic volume-pressure curves in a similar way as L-NAME. Plasma concentration analysis of ARL 17477 indicated a half-life of less than 30 min in pig. ARL 17477 thus inhibits the effect of nitrergic neurons in the pig gastric fundus in vitro, leading to inhibited gastric compliance in the conscious pig. The study indicates that selective nNOS inhibitors, applied for cerebral disorders, might also interfere with neuronal nitrergic regulation of gastrointestinal motility.

Expression of neuronal and inducible nitric oxide synthase in neuronal and glial cells after transient occlusion of the middle cerebral artery

We presently investigated the time-course of neuronal nitric oxide synthase and inducible nitric oxide synthase expression and content in the rat striatum up to 6 days after ischemia induced by transient middle cerebral artery occlusion, a condition that potentially allows functional recovery, with the aim to identify the cell types expressing these two enzymes and to correlate neuronal nitric oxide synthase and inducible nitric oxide synthase changes in order to verify whether and how these changes are related to tissue damage, motor-sensory performances and survival. Before and after surgery, the animals underwent neurological evaluation. The results demonstrated that the rats with a score > or = 12 at the neurological evaluation 24 h after ischemia showed a significant increase in neuronal nitric oxide synthase-immunoreactive neurones and absence of inducible nitric oxide synthase-immunoreactive cells and survived up to the sixth day; conversely, the rats with a score < 12 at the neurological evaluation 24 h after ischemia showed a progressive significant decrease in neuronal nitric oxide synthase-immunoreactive neurones and appearance of inducible nitric oxide synthase-immunoreactive cells and none of the rats survived up to the sixth day. Microglia cells were activated in both groups but only in the latter did these cells express inducible nitric oxide synthase. Measurement of the infarct area demonstrated that it occupied a similar territory in both groups of rats but in those with a score < 12 the edema was more extended. In conclusion, we demonstrated that a neurotoxic insult such as ischemia can induce neuronal nitric oxide synthase expression in the neurones and that when neuronal nitric oxide synthase-immunoreactive neurones increase in number, microglia activation is less extended, inducible nitric oxide synthase-immunoreactive cells are absent, tissue damage reduced and the rats survive longer. Conversely, when there is a significant decrease of neuronal nitric oxide synthase-immunoreactive neurones, microglia cells are intensely activated, inducible nitric oxide synthase-immunoreactive cells appear and the animal survival is shortened.

Ischemic damage increases nitric oxide production via inducible nitric oxide synthase in the cochlea

The present study was designed to elucidate the dynamic changes of nitric oxide (NO) production in the perilymph and to investigate the immunostaining for inducible nitric oxide synthase (iNOS) in the cochlea for 7 days after transient cochlear ischemia. Moreover, aminoguanidine, which is a selective iNOS inhibitor, was administrated immediately following ischemia and every 24h thereafter for 7 days to investigate whether the production of NO is dependent on the iNOS pathway. Significant increases in the oxidative NO metabolites, nitrite (NO(2)(-)) and nitrate (NO(3)(-)), were measured on day 1 using an in vivo microdialysis and on-line high performance liquid chromatography (HPLC) system. The immunostaining for iNOS was strongly expressed on days 1 and 4 and returned to normal on day 7 after the ischemia. The administration of aminoguanidine reduced the oxidative NO metabolites on day 1 and suppressed the expression of iNOS. These findings suggest that transient ischemia causes a remarkable increase in NO production in the perilymph, which might be attributable to the iNOS pathway.

Lack of iNOS induction in a severe model of transient focal cerebral ischemia in rats

Calcium-independent nitric oxide synthase (NOS) activity has been reported in ischemic brains and usually attributed to the inducible isoform, iNOS. Because calcium-independent mechanisms have recently been shown to regulate the constitutive calcium-dependent NOS, we proposed to confirm the presence of iNOS activity in our model of transient focal cerebral ischemia in rats. Our initial results showed that, in our model, ischemia induced an important increase in brain calcium concentration. Consequently, the determination of calcium-independent NOS activity required a higher concentration of calcium chelator than classically used in the NOS assay. In these conditions, calcium-independent NOS activity was not observed after ischemia. Moreover, our ischemia was associated with neither iNOS protein expression, measured by Western blotting, nor increased NO production, evaluated by its metabolites (nitrate/nitrite). Our results demonstrate that iNOS activity may be overestimated due to increased brain calcium concentration in ischemic conditions and also that iNOS is not systematically induced after cerebral ischemia.

Modulation of prostaglandin biosynthesis by nitric oxide and nitric oxide donors

The biosynthesis and release of nitric oxide (NO) and prostaglandins (PGs) share a number of similarities. Two major forms of nitric-oxide synthase (NOS) and cyclooxygenase (COX) enzymes have been identified to date. Under normal circumstances, the constitutive isoforms of these enzymes (constitutive NOS and COX-1) are found in virtually all organs. Their presence accounts for the regulation of several important physiological effects (e.g. antiplatelet activity, vasodilation, and cytoprotection). On the other hand, in inflammatory setting, the inducible isoforms of these enzymes (inducible NOS and COX-2) are detected in a variety of cells, resulting in the production of large amounts of proinflammatory and cytotoxic NO and PGs. The release of NO and PGs by the inducible isoforms of NOS and COX has been associated with the pathological roles of these mediators in disease states as evidenced by the use of selective inhibitors. An important link between the NOS and COX pathways was made in 1993 by Salvemini and coworkers when they demonstrated that the enhanced release of PGs, which follows inflammatory mechanisms, was nearly entirely driven by NO. Such studies raised the possibility that COX enzymes represent important endogenous "receptor" targets for modulating the multifaceted roles of NO. Since then, numerous papers have been published extending the observation across various cellular systems and animal models of disease. Furthermore, other studies have highlighted the importance of such interaction in physiology as well as in the mechanism of action of drugs such as organic nitrates. More importantly, mechanistic studies of how NO switches on/off the PG/COX pathway have been undertaken and additional pathways through which NO modulates prostaglandin production unraveled. On the other hand, NO donors conjugated with COX inhibitors have recently found new interest in the understanding of NO/COX reciprocal interaction and potential clinical use. The purpose of this article is to cover the advances which have occurred over the years, and in particular, to summarize experimental data that outline how the discovery that NO modulates prostaglandin production has impacted and extended our understanding of these two systems in physiopathological events.

Nitric oxide synthase inhibitors in experimental ischemic stroke and their effects on infarct size and cerebral blood flow: a systematic review

Nitric oxide produced by the neuronal or inducible isoform of nitric oxide synthase (nNOS, iNOS) is detrimental in acute ischemic stroke (IS), whereas that derived from the endothelial isoform is beneficial. However, experimental studies with nitric oxide synthase inhibitors have given conflicting results. Relevant studies were found from searches of EMBASE, PubMed, and reference lists; of 456 references found, 73 studies involving 2321 animals were included. Data on the effects of NOS inhibition on lesion volume (mm3, %) and cerebral blood flow (CBF; %, ml * min(-1) * g(-1)) were analyzed using the Cochrane Review Manager software. NOS inhibitors reduced total infarct volume in models of permanent (standardized mean difference (SMD) -0.56, 95% confidence interval (95% CI) -0.86, -0.26) and transient (SMD -0.99, 95% CI -1.25, -0.72) ischemia. Cortical CBF was reduced in models of permanent but not transient ischemia. When assessed by type of inhibitor, total lesion volume was reduced in permanent models by nNOS and iNOS inhibitors, but not by nonselective inhibitors. All types of NOS inhibitors reduced infarct volume in transient models. NOS inhibition may have negative effects on CBF but further studies are required. Selective nNOS and iNOS inhibitors are candidate treatments for acute IS.

Post-ischemic inflammation: molecular mechanisms and therapeutic implications

Ischemic stroke is characterized by the disruption of cerebral blood flow (CBF). This reduction of CBF results in energy failure and secondary biochemical disturbances, eliciting a robust in situ inflammatory response. Post-ischemic inflammation is a dynamic process involving a complicated set of interactions among various inflammatory cells and molecules. The resident inflammatory brain cells, microglia, are especially activated in response to ischemic insults, many of which are regulated by nuclear transcription factor, kappa B (NF-kappaB). As a result, several inflammatory genes are expressed, leading to local generation of various cytokines, which in turn promulgate inflammatory signals. Meanwhile, endothelial cells lining the local cerebral blood vessels are stimulated to produce adhesion molecules, causing the migration of peripheral circulating leukocytes into the compromised brain tissue, an event that amplifies inflammatory signaling cascades. Post-ischemic inflammation appears to serve multiple purposes, depending on its timing and magnitude, as well as the topographic distribution of various inflammatory molecules. Data from experimental manipulations of some inflammatory molecules are yielding insight into therapeutic strategies for ischemic stroke. This review focuses on some recent advances regarding the regulation of inflammatory signaling pathways, the detrimental effects of post-ischemic inflammation and the potential molecular targets for ischemic stroke therapy.

Involvement of NO in the convulsive behavior and oxidative damage induced by the intrastriatal injection of methylmalonate

Acute intrastriatal administration of methylmalonic acid (MMA) induces convulsions through NMDA receptor-mediated mechanisms and increases production of end products of oxidative damage. Although it has been demonstrated that nitric oxide (NO) production increases with NMDA receptor stimulation and contributes to the oxidative damage observed in several neurodegenerative disorders, the role of NO in MMA-induced convulsions has not been investigated to date. In the present study we investigated the effects of the intrastriatal injection of N(omega)-nitro-L-arginine methyl ester (L-NAME: 10(-4) to 10(0) nmol/0.5 microl) on the convulsions and striatal protein carbonylation induced by the intrastriatal injection of MMA (4.5 micromol/1.5 microl). l-NAME (10(-3) to 10(-1)nmol) protected against MMA-induced convulsions and protein carbonylation ex vivo. These results suggest the involvement of NO in the convulsive behavior and protein carbonylation elicited by MMA.

Mechanisms of ischemic brain injury

Stroke is the third leading cause of death and the leading cause of long-term disability in the United States. Approximately 80% of all strokes are ischemic and there are limited therapies approved for the treatment of acute ischemic stroke. Understanding the mechanisms of ischemic brain damage is necessary for the development of innovative treatment strategies. In this review, we discuss the hemodynamic and molecular mechanisms of ischemic brain damage and the potential therapeutic strategies, including reperfusion and primary and secondary neuroprotection, and strategies for recovery of function, such as neural plasticity and stem cell transplantation. The effective treatment of ischemic stroke is likely to result from a combination of therapeutic modalities aimed at different mechanisms of ischemic brain damage and delivered at specific times after acute cerebral ischemia.

The neuronal nitric oxide synthase inhibitor, TRIM, as a neuroprotective agent: effects in models of cerebral ischaemia using histological and magnetic resonance imaging techniques

Most neuroprotective compounds that appear promising in the pre-clinical phase of testing are subsequently dismissed as relatively ineffective when entered into large-scale clinical trials. Many pre-clinical studies of potential neuroprotective candidates evaluate efficacy in only one or possibly two different models of ischaemia. In this study we examined the effects of 1,2-trifluoromethylphenyl imidazole (TRIM), a novel neuronal nitric oxide synthase (nNOS) inhibitor, in three models of cerebral ischaemia (global gerbil, global rat and focal rat). In addition, to follow the progression of the pathology, we also compared traditional histology methods with more advanced magnetic resonance imaging (MRI) as endpoint measures for neurological damage and neuroprotection. TRIM (50 mg/kg i.p.) prevented ischaemia-induced hippocampal damage following global ischaemia in gerbils when administered before or immediately post-occlusion, but failed to protect when administration was delayed until 30 min post-occlusion. Further studies indicated that the compound (administered at 50 mg/kg, i.p., immediately after occlusion) also protected in a rat four-vessel occlusion (4-VO) model using both histological and diffusion-weighted (DW) imaging techniques. In a final study, TRIM (50 mg/kg i.p. 30 min after occlusion) provided a significant reduction in infarct volume at 4 and 24 h as measured using diffusion-weighted (DW) and proton density (PD)-weighted magnetic resonance imaging (MRI). This was confirmed using histological techniques. These studies confirm that nNOS inhibitors may have utility in stroke and provide evidence that combined magnetic resonance and histological methods can provide a powerful method of assessing neuronal damage in rodent models of cerebral ischaemia.

Dihydroquinolines with amine-containing side chains as potent n-NOS inhibitors

Dihydroquinolines with aminoalkyl side chains have been synthesized and have been shown to be potent n-NOS inhibitors. A marked selectivity versus e-NOS of up to approximately 300-fold was observed, whereas i-NOS was moderately inhibited.

Anti-epileptic drugs as possible neuroprotectants in cerebral ischemia

Many similarities exist between cerebral ischemia and epilepsy regarding brain-damaging and auto-protective mechanisms that are activated following the injurious insult. Therefore, drugs that are effective in minimizing seizure-induced brain damage may also be useful in minimizing ischemic injury. Use of such drugs in stroke victims may have important clinical and financial advantages. Therefore, the authors conducted a Medline search of studies involving the use of anti-epileptic drugs (AEDs) as possible neuroprotectants and summarize the data. Most AEDs have been tested in animal models of focal or global ischemia and some were already tested in humans, for a possible neuroprotective effect. The existing data is rather scant and insufficient but it appears that only drugs that have multiple mechanisms of action seem to have some potential in conferring a degree of neuroprotection that could be clinically applicable to stroke patients. In conclusion, some of the newer AEDs show promise as possible neuroprotectants in the setup of acute ischemic stroke but more studies are needed before clinical trials in humans could be undertaken.

Post-ischemic administration [correction of administeration] but not pre-ischemic administration [correction of administeration] of NG-nitro-L-arginine prevents spatial memory impairments and apoptosis by an inhibition of a delayed increase in NOx- in the hippocampus following repeated cerebral ischemia

In the present study, we investigated the effects of N(G)-nitro-L-arginine (L-NAME), an inhibitor of nitric oxide synthase, on repeated cerebral ischemia-induced impairment of spatial memory of the 8-arm radial maze in rats. Repeated ischemia (10 min ischemia x 2 times with 1 h interval) impaired the spatial memory in the 8-arm radial maze test and produced apoptosis in the hippocampus 7 days after final occlusion, and gradually increased the NO(x)(-) levels approximately 30-180 min after the second reperfusion. Post-ischemic administration of L-NAME at a dose of 50 mg/kg, i.p. 30 min following the second occlusion, significantly attenuated the repeated ischemia-induced impairment of spatial memory in the 8-arm radial maze test and suppressed apoptosis in the hippocampus, and also significantly suppressed a delayed increase in the NO(x)(-) levels induced by repeated ischemia. However, pre-ischemic administration of L-NAME at a dose of 50 mg/kg, i.p. 30 min before the first occlusion, caused about 90% mortality (the mortality rate of vehicle-treated group was 10%). These results suggest that the delayed generation of NO(x)(-) may cause spatial memory impairment and induction of apoptosis in the hippocampus in rats subjected to repeated ischemia.