Use Of Nitric Oxide Synthase Inhibitors Research Articles

Agmatine as a Novel Treatment Option for Neuropathies: Experimental Evidences

N-methyl-D-aspartate receptor (NMDAR) antagonist, a subclass of glutamate receptors or nitric oxide synthase (NOS) inhibitors, prevents neuronal plasticity. However, neural plasticity plays a major role in the pain caused by inflammation and neuropathy, providing clinical opportunities for the use of NOS inhibitors and NMDAR antagonists in the treatment of chronic pain. The neuromodulator agmatine has both NOS inhibitory and NMDAR antagonistic activity, and it controls a range of neurotransmitters and signaling pathways in the brain and spinal cord. The effects of agmatine on pain modulation are described and explored in this article, along with a potential mechanism of action for these effects. We specifically offer evidence to support further clinical and pre-clinical trials looking into agmatine as a novel therapeutic agent for neuropathic pain.

Inter-Kingdom beach warfare: Microbial chemical communication activates natural chemical defences.

An inter-kingdom beach warfare between a Streptomyces sp. and Aspergillus sp. co-isolated from shallow water beach sand, collected off Heron Island, Queensland, Australia, saw the bacteriostatic Aspergillus metabolite cyclo-(L-Phe-trans-4-hydroxy-L-Pro) (3) stimulate the Streptomyces to produce nitric oxide (NO), which in turn mediated transcriptional activation of a silent biosynthetic gene cluster (BGC) for fungistatic heronapyrrole B (1). Structure activity relationship studies, coupled with the use of NO synthase inhibitors, donors and scavangers, and both genomic and transcriptomic analyses, confirmed the extraordinary chemical cue specificity of 3, and its NO-mediated mechanism of transcriptional action. Our findings reveal the importance of inter-kingdom (fungal-bacterial) chemical communication in the regulation of silent BGCs coding for chemical defenses. We propose that the detection and characterisation of NO mediated transcriptional activation (NOMETA) of silent chemical defences in the environment, may inspire broader application in the field of microbial biodiscovery.

Targeted Nitric Oxide Synthase Inhibitors for Migraine.

Nitric oxide (NO) is a small gaseous signaling molecule that has important biological effects. It has been heavily implicated in migraine; and the NO donor, nitroglycerin, has been used extensively as a human migraine trigger. Correspondingly, a number of components of the NO signaling cascade have been shown to be upregulated in migraine patients. NO is endogenously produced in the body by NO synthase (NOS), of which there are three isoforms: neuronal NOS (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS). Based on the accumulating evidence that endogenous NO regulation is altered in migraine pathogenesis, global and isoform-selective inhibitors of NOS have been targeted for migraine drug development. This review highlights the evidence for the role of NO in migraine and focuses on the use of NOS inhibitors for the treatment of this disorder. In addition, we discuss other molecules within the NO signaling pathway that may be promising therapeutic targets for migraine.

Persistent oxidative stress in human neural stem cells exposed to low fluences of charged particles

Exposure to the space radiation environment poses risks for a range of deleterious health effects due to the unique types of radiation encountered. Galactic cosmic rays are comprised of a spectrum of highly energetic nuclei that deposit densely ionizing tracks of damage along the particle trajectory. These tracks are distinct from those generated by the more sparsely ionizing terrestrial radiations, and define the geometric distribution of the complex cellular damage that results when charged particles traverse the tissues of the body. The exquisite radiosensitivity of multipotent neural stem and progenitor cells found within the neurogenic regions of the brain predispose the central nervous system to elevated risks for radiation induced sequelae. Here we show that human neural stem cells (hNSC) exposed to different charged particles at space relevant fluences exhibit significant and persistent oxidative stress. Radiation induced oxidative stress was found to be most dependent on total dose rather than on the linear energy transfer of the incident particle. The use of redox sensitive fluorogenic dyes possessing relative specificity for hydroxyl radicals, peroxynitrite, nitric oxide (NO) and mitochondrial superoxide confirmed that most irradiation paradigms elevated reactive oxygen and nitrogen species (ROS and RNS, respectively) in hNSC over a 1 week interval following exposure. Nitric oxide synthase (NOS) was not the major source of elevated nitric oxides, as the use of NOS inhibitors had little effect on NO dependent fluorescence. Our data provide extensive evidence for the capability of low doses of charged particles to elicit marked changes in the metabolic profile of irradiated hNSC. Radiation induced changes in redox state may render the brain more susceptible to the development of neurocognitive deficits that could affect an astronaut’s ability to perform complex tasks during extended missions in deep space.

The evaluation of nitric oxide involvement in Metrazol induced status epilepticus using multiparametric monitoring

Nitric oxide (NO) has been implicated in the neuronal hyperexcitability hence its involvement in the pathophysiology of epilepsy is clear. However, some studies indicate that NO has anticonvulsant effects while others present its convulsive effects. In the present study we tested the involvement of NO in pentylenetetrazol (Metrazol) induced Status Epilepticus (SE) rats, using the nonspecific inhibitor, N-omega-nitro- l-arginine methyl ester ( l-NAME) and the neuronal-specific inhibitor, 7-nitroindazole (7N1). The effects of NOS (NO synthase) inhibitors were tested, within the seizures and between them, using the Multiparametric Assembly (MPA) which continuously monitored Cerebral Blood Flow (CBF) by Laser Doppler flowmetry, mitochondrial NADH redox state by the fluorometric technique, extracellular K + and H + levels using selective mini-electrodes and electrical activity (DC potential and ECoG) using special electrodes. Between seizures a trend of increase in CBF with oxidation of NADH was seen, with no change in K + and H + extracellular levels. Pre-treatment with l-NAME prevented this trend of increase in CBF whereas the injection of 7NI even decreased CBF between seizures. Within seizures, CBF increased and mitochondrial NADH was oxidized at the first seizures, while in the last seizure NADH was reduced. The use of NOS inhibitors significantly increased the degree of NADH oxidation at the latest convulsions. In conclusion our results demonstrated beneficial effect of NOS inhibitors on the brain cortex under SE induced by Metrazol, implying that they may serve as anticonvulsant drugs.

Elastokine-mediated up-regulation of MT1-MMP is triggered by nitric oxide in endothelial cells

Membrane-type I matrix metalloproteinase (MT1-MMP) has been previously reported to be up-regulated in human microvascular endothelial cell-1 line (HMEC) by elastin-derived peptides (elastokines). The aim of the present study was to identify the signaling pathways responsible for this effect. We showed that elastokines such as (VGVAPG) 3 peptide and kappa elastin induced nitric oxide (NO) production in a time-, concentration- and receptor-dependent manner as it could be abolished by lactose and a receptor-derived competitive peptide. As evidenced by the use of NO synthase inhibitors, elastokine-mediated up-regulation of MT1-MMP and pseudotube formation on Matrigel required NO production through activation of the PI 3-kinase/Akt/NO synthase and NO/cGMP/Erk1/2 pathways. Elastokines induced both PI 3-kinase p110γ sub-unit, Akt and Erk1/2 activation, as shown by a transient increase in phospho-Akt and phospho-Erk1/2, reaching a maximum after 5 and 15 min incubation, respectively. Inhibitors of PI 3-kinase and MEK1/2 suppressed elastokine-mediated MT1-MMP expression at both the mRNA and protein levels, and decreased the ability of elastokines to accelerate pseudotube formation. Besides, elastokines mediated a time- and concentration-dependent increase of cGMP, suggesting a link between NO and MT1-MMP expression. This was validated by the use of a guanylyl cyclase inhibitor, a NO donor and a cGMP analog. The guanylyl cyclase inhibitor abolished the stimulatory effect of elastokines on MT1-MMP expression. Inversely, the cGMP analog, mimicked the effect of both elastokines and NO donor in a concentration- and time-dependent manner. Overall, our results demonstrated that such elastokine properties through NO and MT1-MMP may be of importance in the context of tumour progression.

Effects of nitric oxide synthase inhibitors in attenuating nicotine withdrawal in rats

This study evaluates the effects of three nitric oxide synthase (NOS) inhibitors (L-NNA, L-NAME, L-NMMA) in attenuating the precipitated nicotine withdrawal syndrome in rats. Male albino Wistar rats were made dependent on nicotine by subcutaneous infusion of nicotine (9.0 mg/kg/day) via a 7 day osmotic pump, whereas control rats received saline via osmotic pumps. Test doses of each NOS inhibitor were administered 30 min prior to mecamylamine (1 mg/kg) challenge in control and test rats on the 7th day. Somatic signs of withdrawal were scored for 15 min by using the global Gellert–Holtzman rating scale followed by a measurement of motor activity. A comparison of NOS inhibitors treated rats with the mecamylamine-precipitated nicotine rats showed that at highest dose L-NNA appears to produce a more complete attenuation of all aspects of withdrawal syndrome. On the other hand, L-NAME appears to do so both at moderate and highest doses. This could be due to an incomplete reversal of some signs of withdrawals by L-NMMA. However, motor activity increased in nicotine dependent rats with the administration of NOS inhibitors. This study demonstrates that NO plays an important role in the expression of behavioral signs of nicotine withdrawal syndrome and suggests a potential use of NOS inhibitors as an aid in tobacco smoking cessation.

Nitric Oxide in Neurodegeneration

Nitric oxide NO is an atypical neurotransmitter and is formed from L-arginine by the enzyme nitric oxide synthase (NOS), which is of three types, namely neuronal NOS (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS). nNOS and eNOS are constitutive, calcium-calmodulin dependent and release NO from neurons and endothelium, while iNOS is inducible, calcium independent and formed in activated immune cells. NO plays a modulatory role in brain, controlling release of neurotransmitters and is involved in synaptogenesis, synaptic plasticity, memory function and neuroendocrine secretion. Availability of animal models, use of NOS inhibitors and mutant mice lacking each NOS isoforms have provided evidence for the injurious effects of NO. NADPH-diaphorase staining is used to localise NOS containing neurons and 3-NT staining gives an idea of generation of NO. NO may also have some neuroprotective effects as NOS (NADPH-diaphorase positive) neurons are selectively resistant to NMDA mediated toxicity, ischaemic hypoxic insults and the degenerative processes of HD, AD, PD and ALS. Use of selective NOS inhibitors is beneficial in animal models, but has met with little or no success in the clinical treatment of neurodegenerative diseases perse. doi: 10.5214/ans.0972.7531.2007.140104

Sustained, long-lasting inhibition of nitric oxide synthase aggravates the neural damage in some models of excitotoxic brain injury

Brain nitric oxide (NO) can be a mediator of physiological and neuroprotective actions and an effector of neural damage. The effectiveness of acute or chronic inhibition of NO production in in vivo experiments of neurotoxicity/neuroprotection is controversial. We report here on the effects of a chronic, sustained inhibition of nitric oxide synthase (NOS) on the neurodegenerative damage caused by three different excitotoxic lesions. The damage caused by intrastriatal injection of ibotenic or kainic acid was aggravated in rats subjected to chronic NOS inhibition. On the contrary, the drop of cortical cholinergic input consequent to ibotenic acid-mediated degeneration of basal forebrain neurons was not altered by chronic NOS inhibition. The worsening of the damage was not related to any overt differential sensitivity to excitotoxicity of NOS-containing striatal neurons under conditions of NOS inhibition. These results suggest that, contrary to what has been often reported for short-term, mild inhibition of NO production, chronic and sustained NOS inhibition may exacerbate neuropathology. Thus, long-lasting shortage of NO may be detrimental when neuroprotective mechanisms related to the physiological action of this free radical are severely impaired. Although we cannot exclude that inhibition of the endothelial NOS isoform could have contributed to the worsening of neuropathology, differences among the paradigms of neurotoxicity used in the present study suggest a primary involvement of the neuronal NOS isoform. In view of the potential therapeutic use of NOS inhibitors, the effects of a too drastic alteration of the balance between neuroprotective and neurodegenerative actions of NO should be carefully considered.

Nitric oxide synthase inhibitors for septic shock

The physiologic role of nitric oxide (NO) in the maintenance of vasomotor tone is firmly established in both humans and animals. Evidence that excessive NO production plays a key role in the cardiovascular manifestations of septic shock also exists. Nitric oxide synthase (NOS) inhibitors have been used in both experimental and human sepsis as a means of raising blood pressure and restoring vasomotor tone. The use of NOS inhibitors in the treatment of septic shock is based on the following: the cardiovascular manifestations seen in septic shock are caused by an overproduction of NO, the increase in NO contributes to mortality, and NOS inhibitors are safe. This article discusses the evidence to support the use of NOS inhibitors in septic shock. Copyright © 2001 by W.B. Saunders Company

Antidystonic efficacy of nitric oxide synthase inhibitors in a rodent model of primary paroxysmal dystonia.

In a hamster model (genetic symbol dt(sz)) of primary paroxysmal non-kinesiogenic dystonic choreoathetosis, recent studies have shown beneficial effects of glutamate and dopamine receptor antagonists. Nitric oxide (NO), synthesized from L-arginine by NO synthase in response to glutamate receptor activation, elicits cyclic GMP and modulates glutamate-mediated processes and striatal dopamine release. Therefore, the effects of NO synthase inhibitors and of L-arginine on severity of dystonia were investigated in dt(sz) hamsters in which dystonic attacks, characterized by twisting movements and postures, can be induced by stress. The NO synthase inhibitors N(G)-nitro-L-arginine (L-NNA), N(G)-nitro-L-arginine methyl ester (L-NAME) and 7-nitroindazole significantly reduced the severity of dystonia. At antidystonic effective doses neither L-NNA nor L-NAME caused observable side effects, whereas 7-nitroindazole exerted moderate reduction of locomotor activity. The antidystonic effect of L-NAME was reversed by co-administration of the NO precursor L-arginine. However, L-arginine administered alone did not exert any effect on severity of dystonia. Cerebellar cyclic GMP levels in brains of mutant hamsters in comparison to non-dystonic control hamsters did not significantly differ, but the cerebellar cyclic GMP levels tended to be increased in dt(sz) hamsters during a dystonic attack. L-NAME significantly decreased the cerebellar cyclic GMP levels in both dt(sz) and control hamsters. Although an overproduction of NO is probably not critically involved in the pathogenesis of paroxysmal dystonia, it may contribute to the manifestation of dystonic attacks, as indicated by the antidystonic effects of NO synthase inhibitors. Peripheral side effects may limit the clinical use of NO synthase inhibitors, but more selective inhibitors of the neuronal NO synthase should be considered as interesting candidates for the treatment of paroxysmal dystonia.

Nitric Oxide and Septic Vascular Dysfunction

Nitric Oxide and Septic Vascular Dysfunction

Correlation between brain nitric oxide synthase activity and opiate withdrawal.

The opiate withdrawal induced by administration of naloxone to morphine-dependent mice correlates with an increment of calcium- dependent nitric oxide synthase (NOS) activity in the cerebellum. L-NAME, an irreversible competitive inhibitor of NOS (0.5, 5, 25, 50 mg/kg) injected sc. 45 min. prior to naloxone significantly reduced the number of escape jumps and other motor symptoms of abstinence. In addition, L-NAME also decreased NOS activity in cerebellum. L-arginine, but not D-arginine, when coadministered with L-NAME, prevented both the inhibition of NOS activity and the reduction of withdrawal symptoms induced by L-NAME in morphine-withdrawn animals. These results demonstrate a hyperactivity of the L-arginine: NO pathway in opiate withdrawal and suggests the possibility of a therapeutic use of NOS inhibitors in this state.

Effects of nitric oxide synthase inhibitor on hemodynamic change and O2 delivery in septic dogs.

To elucidate the role of nitric oxide (NO) in septic shock, we measured hemodynamic and pulmonary gas changes in anesthetized dogs after intravenous administration of bacterial lipopolysaccharide (LPS) with or without NO synthase inhibitor, NG-nitro-L-arginine (L-NNA). Infusion of LPS (250 ng.kg-1.min-1) for 2 h decreased mean arterial pressure over 1-4 h. Although L-NNA (10 mg/kg) blocked LPS-induced hypotension, it decreased cardiac index, oxygen delivery index, arterial pH, and arterial PO2 and increased systemic vascular resistance index in the presence or absence of LPS. Administration of NG-nitro-D-arginine (D-NNA, 10 mg/kg) alone caused fewer hemodynamic effects (increased systemic vascular resistance index and decreased cardiac index) than L-NNA alone. Our study provides evidence that L-NNA prevents endotoxin-induced hypotension but decreases cardiac output and oxygen delivery, effects that may, in part, be due to a nonspecific NO synthase-independent event. Thus clinical use of NO synthase inhibitors for the treatment of septic shock should be cautiously considered.

Administration of a nitric oxide synthase inhibitor does not suppress low-dose streptozotocin-induced diabetes in mice

Nitric oxide (NO) has been reported as being a key mediator of the autoimmune destruction of B-cells in type I diabetes, and studies have described a suppression of low-dose streptozotocin-induced (LDS) diabetes in mice after the use of NO synthase inhibitors. However, these studies disagree with regard to the outcome of hyperglycemia and insulitis after treatment with these L-arginine analogs. The present study tries to clarify this topic by administering N-nitro-L-arginine-methylester (NAME) (15 mg/d/mouse/15 d) after an LDS treatment in 108 male C57BL6/J mice. Glycemia measured at the end of the NAME treatment did show a slight, but significant, reduction when compared to LDS control animals (p < 0.001), but values returned to diabetic levels 2 wk after withdrawal of NAME. Morphological observations demonstrated that the degree of infiltration and islet B-cell damage was absolutely not inhibited by NAME. In conclusion, treatment with L-arginine analogs is not capable of protecting mice from LDS-induced diabetes.