Regulation Of Nitric Oxide Release Research Articles

Evaluation of anti-inflammatory activity of kaurenol: Experimental evaluation and mechanistic insights.

Kaurenol, a diterpene alcohol found in Copaifera langsdorffii Desf. (known as "copaiba"), is historically used in traditional medicine for inflammatory conditions. This study aims to comprehensively assess the potential anti-inflammatory and antinociceptive properties of kaurenol. To this end, the following experiments were conducted to evaluated toxicity: locomotor performance and acute toxicity; nociception: acetic acid-induced writhing and formalin-induced antinociception; and anti-inflammatory activity: carrageenan and dextran-induced paw edema at 10, 20, and 40 mg/kg, and measurement of nitric oxide (NO), tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6), and interleukin-10 (IL-10) in macrophages at 1, 3, and 9 μg/ml. Kaurenol did not show significant locomotor changes, acute toxicity, and central analgesic activity in the first phase of formalin test at dosages tested. Kaurenol showed 53%, 64%, 64%, and 58% of inhibition in the acetic acid-induced writhing, second phase of formalin test, carrageenan and dextran-induced paw edema, respectively. The anti-inflammatory activity was associated with the regulation of NO release and probably with the regulation of mediators, such as serotonin and prostaglandin in vascular permeability, as well as by being associated with the regulation of IL-6 and IL-10. Kaurenol display anti-inflammatory activity but has no analgesic activity.

Role of the Transient Receptor Potential Vanilloid Type 1 (TRPV1) in the Regulation of Nitric Oxide Release in Wistar Rat Aorta.

The potential transient vanilloid receptor type 1 (TRPV1) plays important functional roles in the vascular system. In the present study, we explored the role of the TRPV1 in the production of nitric oxide (NO), biopterines (BH4 and BH2), cyclic guanosine monophosphate (cGMP), malondialdehyde (MDA), phosphodiesterase-3 (PDE-3), total antioxidant capacity (TAC), and calcitonin gene-related peptide (CGRP) in the rat aorta. Wistar rats were divided into four groups: (1) control, (2) capsaicin (CS, 20 mg/kg), (3) capsazepine (CZ, 24 mg/kg), and (4) CZ + CS. Treatments were applied daily for 4 days before removing the thoracic aortas for testing of aortic tissue and endothelial cells. TRPV1 activation produced increases in BH4 14%, cGMP 25%, NO 29%, and TAC 59.2% in comparison to the controls. BH2 and MDA increased with CZ. CGRP shows a tendency to decrease with CZ. The analysis by immunocytochemistry confirmed that the TRPV1 is present in aortic endothelial cells. Aortic endothelial cells were obtained from healthy rats and cultured to directly explore the effects of CS and CZ. The activation of the TRPV1 (CS 30 μM) produced increases in BH4 17%, NO 36.6%, TAC 56.3%, and CGRP 65%, when compared to controls. BH2 decreased with CZ + CS. CS effects were diminished by CZ in cells and in the tissue. We conclude that the TRPV1 is a structure present in the membrane of aortic endothelial cells and that it participates in the production of NO. The importance of the TRPV1 should be considered in vascular reactivity studies.

IL-6 promotes M2 macrophage polarization by modulating purinergic signaling and regulates the lethal release of nitric oxide during Trypanosoma cruzi infection

The production of nitric oxide (NO) is a key defense mechanism against intracellular pathogens but it must be tightly controlled in order to avoid excessive detrimental oxidative stress. In this study we described a novel mechanism through which interleukin (IL)-6 mediates the regulation of NO release induced in response to Trypanosoma cruzi infection. Using a murine model of Chagas disease, we found that, in contrast to C57BL/6 wild type (WT) mice, IL-6-deficient (IL6KO) mice exhibited a dramatic increase in plasma NO levels concomitant with a significantly higher amount of circulating IL-1β and inflammatory monocytes. Studies on mouse macrophages and human monocytes, revealed that IL-6 decreased LPS-induced NO production but this effect was abrogated in the presence of anti-IL-1β and in macrophages deficient in the NLRP3 inflammasome. In accordance, while infected WT myocardium exhibited an early shift from microbicidal/M1 to anti-inflammatory/M2 macrophage phenotype, IL6KO cardiac tissue never displayed a dominant M2 macrophage profile that correlated with decreased expression of ATP metabolic machinery and a lower cardiac parasite burden. The deleterious effects of high NO production-induced oxidative stress were evidenced by enhanced cardiac malondialdehyde levels, myocardial cell death and mortality. The survival rate was improved by the treatment of IL-6-deficient mice with a NO production-specific inhibitor. Our data revealed that IL-6 regulates the excessive release of NO through IL-1β inhibition and determines the establishment of an M2 macrophage profile within infected heart tissue.

EDF-1 contributes to the regulation of nitric oxide release in VEGF-treated human endothelial cells

Vascular endothelial growth factor (VEGF) induces nitric oxide (NO) release by triggering multiple intracellular signals, among others the calcium/calmodulin pathway and the activation of Akt, events which induce endothelial NO synthase (eNOS) activity. Because Endothelial Differentiation-related Factor (EDF)-1 is a calmodulin binding protein and plays a role in modulating endothelial functions, we evaluated whether EDF-1 is implicated in the regulation of eNOS activity in VEGF-treated human endothelial cells. While VEGF does not modulate the total amounts of EDF-1, it promotes the dissociation of calmodulin from EDF-1 which correlates with the increase of calmodulin bound to eNOS and the induction of NO release. To better characterize the contribution of EDF-1 to the regulation of VEGF-induced NO release, we stably silenced EDF-1 in endothelial cells. We here show that endothelial cells silencing EDF-1 produce more NO than controls and do not increase NO release in response to VEGF. The insensitivity to VEGF results from the incapability of cells silencing EDF-1 to phosphorylate eNOS Ser1177, even though Akt is activated. Interestingly, okadaic acid, a pharmacologic inhibitor of the serine/threonine phosphatase PP2A, which preferentially dephosphorylates eNOS Ser1177, restores NO release and eNOS Ser1177 phosphorylation in cells silencing EDF-1. Our results suggest EDF-1 as a novel contributor to the complex regulation of eNOS activity in human endothelial cells.

Phosphorylation ofN-Methyl-d-Aspartic Acid Receptor-Associated Neuronal Nitric Oxide Synthase Depends on Estrogens and Modulates Hypothalamic Nitric Oxide Production during the Ovarian Cycle

Within the preoptic region, nitric oxide (NO) production varies during the ovarian cycle and has the ability to impact hypothalamic reproductive function. One mechanism for the regulation of NO release mediated by estrogens during the estrous cycle includes physical association of the calcium-activated neuronal NO synthase (nNOS) enzyme with the glutamate N-methyl-d-aspartate (NMDA) receptor channels via the postsynaptic density 95 scaffolding protein. Here we demonstrate that endogenous variations in estrogens levels during the estrous cycle also coincide with corresponding changes in the state of nNOS Ser1412 phosphorylation, the level of association of this isoform with the NMDA receptor/postsynaptic density 95 complex at the plasma membrane, and the activity of NO synthase (NOS). Neuronal NOS Ser1412 phosphorylation is maximal on the afternoon of proestrus when both the levels of estrogens and the physical association of nNOS with NMDA receptors are highest. Estradiol mimicked these effects in ovariectomized (OVX) rats. In addition, the catalytic activity of NOS in membrane protein extracts from the preoptic region, i.e. independent of any functional protein-protein interactions or cell-cell signaling, was significantly increased in estradiol-treated OVX rats compared with OVX rats. Finally, lambda phosphatase-mediated nNOS dephosphorylation dramatically impaired NOS activity in preoptic region protein extracts, thus demonstrating the important role of phosphorylation in the regulation of NO production in the preoptic region. Taken together, these results yield new insights into the regulation of neuron-derived NO production by gonadal steroids within the preoptic region and raise the possibility that changes in nNOS phosphorylation during fluctuating physiological conditions may be involved in the hypothalamic control of key neuroendocrine functions, such as reproduction.

Inhibition of inducible nitric oxide synthase in respiratory diseases

Nitric oxide (NO) is a key physiological mediator and disturbed regulation of NO release is associated with the pathophysiology of almost all inflammatory diseases. A multitude of inhibitors of NOSs (nitric oxide synthases) have been developed, initially with low or even no selectivity against the constitutively expressed NOS isoforms, eNOS (endothelial NOS) and nNOS (neuronal NOS). In the meanwhile these efforts yielded potent and highly selective iNOS (inducible NOS) inhibitors. Moreover, iNOS inhibitors have been shown to exert beneficial anti-inflammatory effects in a wide variety of acute and chronic animal models of inflammation. In the present mini-review, we summarize some of our current knowledge of inhibitors of the iNOS isoenzyme, their biochemical properties and efficacy in animal models of pulmonary diseases and in human disease itself. Moreover, the potential benefit of iNOS inhibition in animal models of COPD (chronic obstructive pulmonary disease), such as cigarette smoke-induced pulmonary inflammation, has not been explicitly studied so far. In this context, we demonstrated recently that both a semi-selective iNOS inhibitor {L-NIL [N6-(1-iminoethyl)-L-lysine hydrochloride]} and highly selective iNOS inhibitors (GW274150 and BYK402750) potently diminished inflammation in a cigarette smoke mouse model mimicking certain aspects of human COPD. Therefore, despite the disappointing results from recent asthma trials, iNOS inhibition could still be of therapeutic utility in COPD, a concept which needs to be challenged and validated in human disease.

Somatostatin receptor subtype-dependent regulation of nitric oxide release: involvement of different intracellular pathways.

We reported previously that, in addition to direct effects, somatostatin (SST) affects tumor growth inhibiting the tumoral neoangiogenesis, via an interference with NO synthesis. Here, we analyzed the effects of SST on nitric oxide (NO) production induced by different agonists [basic fibroblast growth factor (bFGF), insulin, cholecystokinin (CCK)] and the intracellular signaling involved, using Chinese hamster ovary-k1 cells stably transfected with individual SSTR1-SSTR4. bFGF and insulin induced endothelial nitric oxide synthase activity via the generation of ceramide or the Akt-dependent phosphorylation of endothelial nitric oxide synthase, respectively. CCK regulates neuronal nitric oxide synthase activity in a Ca++-dependent manner. SST inhibited NO production stimulated by bFGF through SST receptor 1 (SSTR1), SSTR2, and SSTR3 and by CCK through SSTR2 and SSTR3. In all the cell lines, SST treatment did not modify NO synthesis induced by insulin. SSTR4 activation was not effective on any of the stimuli tested. The effects on bFGF-induced NO production were downstream from receptor phosphorylation and ceramide synthesis. SSTR2 and -3 on CCK activity were related to the inhibition of intracellular Ca++ mobilization, whereas the lack of effects on insulin was paralleled by the absence of SST activity on Akt phosphorylation. These data, identifying for the first time a selective receptor subtype-inhibitory role of SST on NO generation, may open new perspectives in the use of SST agonists to control tumoral angiogenesis.

Enhancement of Nitric Oxide Production by Corticotropin-releasing Hormone (CRH) in Murine Microglial Cells, BV2

Background: Microglial cells, major immune effector cells in the central nervous system, become activated in neurodegenerative disorders. Activated microglial cells produce proinflammatory mediators such as nitric oxide (NO), tumor necrosis factor- and interleukin-(IL-). These proinflammatory mediators have been shown to be significantly increased in the neurodegenerative disorders such as Alzhimer's disease and Pakinson's disease. It was known that one of the neurodegeneration source is stress and it is important to elucidate mechanisms of the stress response for understanding the stress-related disorders and developing improved treatments. Because one of the neuropeptide which plays a main role in regulating the stress response is corticotropin-releasing hormone (CRH), we analyzed the regulation of NO release by CRH in BV2 murine microglial cell as macrophage in the brain. Methods: First, we tested the CRH receptor expression in the mRNA levels by RT-PCR. To test the regulation of NO release by CRH, cells were treated with CRH and then NO release was measured by Griess reagent assay. Results: Our study demonstrated that CRH receptor 1 was expressed in BV2 murine microglial cells and CRH treatment enhanced NO production. Furthermore, additive effects of lipopolysaccaride (LPS) and CRH were confirmed in NO production time dependantly. Conclusion: Taken together, these data indicated that CRH is an important mediator to regulate NO release on microglial cells in the brain during stress.

Paracrine factors in tubuloglomerular feedback: adenosine, ATP, and nitric oxide.

The tubuloglomerular feedback response, the change in afferent arteriolar tone caused by a change in NaCl concentration at the macula densa, is likely initiated by the generation of a vasoactive mediator within the confines of the juxtaglomerular apparatus. Substantial progress has been made in identifying the nature of this mediator and the factors that modulate its effect on vascular tone. In support of earlier studies using P1 purinergic antagonists, the application of the knockout technique has shown that adenosine 1 receptors are absolutely required for eliciting TGF responses. The background level of angiotensin II appears to be an important cofactor determining the efficiency of A1AR-induced vasoconstriction, probably through a synergistic interaction at the level of the G protein-dependent transduction mechanism. The source of the adenosine is still unclear, but it is conceivable that adenosine is generated extracellularly from released ATP through a cascade of ecto-nucleotidases. There is also evidence that ATP may activate P2 receptors in preglomerular vessels, which may contribute to autoregulation of renal vascular resistance. Nitric oxide (NO), generated by the neuronal isoform of nitric oxide synthase in macula densa cells, reduces the constrictor effect of adenosine, but the regulation of NO release and its exact role in states of TGF-induced hyperfiltration are still unclear.

Role of Ca2+-Independent Phospholipase A2 and Cyclooxygenase/Lipoxygenase Pathways in the Nitric Oxide Production by Murine Macrophages Stimulated by Lipopolysaccharides

There is evidence of molecular cross talk between inflammatory mediators such as nitric oxide (NO) and prostaglandins (PG), which may regulate tissue homeostasis and contribute to pathophysiological processes. Here we examine the role of endogenous arachidonic acid (AA) and its AA metabolites in the regulation of NO release by lipopolysaccharide (LPS)-stimulated macrophages RAW 264.7. Our results suggest that bromoenol lactone-sensitive phospholipase A2 is involved in AA release and the subsequent PG and leukotriene (LT) production. The cyclooxygenase inhibitor, indomethacin, and lipoxygenase inhibitors such as baicalein and zileuton blocked the dose-dependent PGE2 or LTB4 and nitrite (NO−2) production induced by LPS. Furthermore, the effects of indomethacin were reverted by exogenous PGE2 and forskolin, whereas AH23848B, an EP4 PGE2 subtype receptor antagonist, decreased NO−2 release. On the other hand, the effect of baicalein on NO−2 production was reverted by exogenous LTB4 and the fibrate WY 14,643, a natural and a synthetic peroxisome proliferator-activated receptor α (PPARα), respectively. Thus, PGE2 via EP4 receptor/cAMP and LTB4 via PPARα may be involved in the control of NO synthesis by LPS in macrophage RAW 264.7 cultures.

Luminal calcium in regulation of nitric oxide release and acid secretion in rat stomachs after damage.

We investigated the role of luminal Ca2+ in the regulation of nitric oxide (NO) release and acid secretion in the rat stomach following damage by sodium taurocholate (TC). Under urethane anesthesia, a rat stomach was mounted in an ex vivo chamber, perfused with saline, and transmucosal potential difference (PD), luminal pH, acid secretion, and luminal contents of Ca2+ and NO were measured before and after exposure to 20 mM TC for 30 min, with or without coapplication of EGTA (5 mM) and/or CaCl2 (10 mM). Mucosal exposure to TC caused a reduction in PD and a decrease of acid secretion, with a concomitant increase of NO as well as Ca2+ content in the gastric lumen. The increase of NO release as well as the reduced acid response were attenuated by pretreatment with L-NAME or coapplication of EGTA, and the latter inhibited the luminal increase of Ca2+. The changes caused by L-NAME were antagonized by coadministration of L-arginine, while those induced by EGTA were partially antagonized by coinstillation of CaCl2. Neither treatment tested had any effect on gastric PD responses to TC. These results suggest that: (1) damage in the stomach increases the release of Ca2+ as well as NO in the lumen; (2) acid secretion decreases in response to damage by both an NO- and Ca2+-dependent mechanism; and (3) the increase of luminal Ca2+ is an adaptive response of the stomach to damage and may play an important role in increasing NO production and hence in regulating acid secretion.

NMDAR1 Glutamate Receptor Subunit Isoforms in Neostriatal, Neocortical, and Hippocampal Nitric Oxide Synthase Neurons

Nitric oxide (NO), an unconventional and diffusible neurotransmitter, is synthesized by nitric oxide synthase (NOS). NMDA glutamate receptors are potent regulators of NO synthesis. We have used dual-label immunofluorescence and confocal microscopy to examine forebrain neurons in the rat that contain high levels of neuronal NOS (nNOS) for the presence of the NMDAR1 receptor subunit protein and regions of this protein encoded by three alternative spliced segments of the NMDAR1 mRNA: N1, C1, and C2. In the neostriatum, neocortex, and hippocampus, nNOS-labeled neurons exhibit strong NMDAR1 immunoreactivity (-ir). In all three of these regions, nNOS-positive neurons are characterized by the absence of immunoreactivity for the C1 segment of NMDAR1, whereas C1-ir is abundant in most nNOS-negative neurons. In addition, nNOS-ir neurons exhibit selective staining for the alternative C2' terminus of NMDAR1 that is produced when the C2 segment is absent. These results demonstrate directly that neurons with abundant nNOS-ir contain NMDAR1 receptor subunit proteins and that the NMDAR1 isoforms present in these cells differ from those of most other neurons in these regions. The distinct NMDA receptor phenotype of these nNOS-positive neurons is likely to contribute to both the physiological regulation of NO release by glutamate as well as to NO-mediated excitotoxic injury.

Regulation of nitric oxide production in human coronary microvessels and the contribution of local kinin formation.

The goal of this study was to define the regulation of nitric oxide release by coronary microvessels from the failing and nonfailing human heart and to determine the role of local kinin production in the elaboration of nitric oxide by human coronary microvascular endothelium. Ten hearts from humans with end-stage heart failure and two hearts from patients without heart failure were harvested at the time of orthotopic cardiac transplantation. Microvessels were sieved and the production of nitrite was determined by the Griess reaction. Microvessels were incubated in the presence of agonists for nitric oxide production (acetylcholine and bradykinin), which caused dose-dependent increases in nitrite, a response that was blocked by NG-nitro-L-arginine methyl ester and receptor-specific antagonists (atropine and HOE 140, respectively). In addition, the production of nitrite by microvessels from the failing heart appeared to be less than that produced by microvessels from the nonfailing heart. Incubation with norepinephrine or the alpha2-adrenergic agonist BHT 920 also caused dose-dependent increases in nitrite production, which were blocked by the B2-receptor antagonist HOE 140. This implicated local kinin synthesis as an intermediate step in the production of nitric oxide in response to alpha2-adrenoceptor stimulation. The production of nitric oxide was also prevented by the addition of serine protease inhibitors, which blocked the action of local kallikrein, again suggesting a role for local kinin synthesis. Our results indicate that nitric oxide is produced by human coronary microvessels, that nitric oxide production may be reduced but certainly not increased in microvessels from the failing human heart, and that there is active local kinin generation in these blood vessels.

Regulation of nitric oxide release by macrophages after intratracheal lipopolysaccharide.

We investigated the effect of intratracheal (i.t.) lipopolysaccharide (LPS) on alveolar macrophage release of nitric oxide. Mice received i.t. LPS at doses ranging from 1 to 100 micrograms/100 g body weight and were killed at serial intervals for bronchoalveolar lavage. Control mice received i.t. phosphate-buffered saline. We found that after i.t. LPS, there was an early (1 to 3 days) influx of neutrophils followed by a later (5 to 7 days) influx of macrophages into the lungs. Alveolar macrophages lavaged from mice given i.t. LPS did not spontaneously release nitric oxide (measured as nitrite), but the capacity of these cells to release nitric oxide in vitro in response to interferon-gamma (IFN-gamma) or LPS was markedly upregulated. Alveolar macrophages lavaged from mice given i.t. LPS but not i.t. phosphate-buffered saline also expressed mRNA for inducible nitric oxide synthase as measured by semiquantitative reverse-transcription polymerase chain reaction. To investigate possible mechanisms for cellular priming for increased nitric oxide release after i.t. LPS, mice were depleted of CD4+ lymphocytes with an anti-CD4 antibody. Alveolar macrophages from CD4-depleted mice given i.t. LPS released significantly less nitric oxide in vitro in comparison to macrophages from nondepleted mice. Additional mice were treated with neutralizing doses of anti-tumor necrosis factor or anti-IFN-gamma antibody before i.t. LPS. Pretreatment with each cytokine antibody decreased but did not eliminate macrophage priming for nitric oxide release after i.t. LPS. We conclude that intratracheal LPS induces mRNA for nitric oxide synthase in alveolar macrophages, priming the cells for increased release of nitric oxide in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

Alpha 2-adrenoceptor-mediated modulation of the nitrergic innervation of the canine isolated ileocolonic junction.

1. The effects of specific alpha-adrenoceptor agonists and antagonists on electrically-evoked non-adrenergic non-cholinergic (NANC) relaxations, previously demonstrated as nitrergic, were investigated in isolated circular muscle strips of the canine ileocolonic junction. 2. During a substance P-induced contraction and in the presence of atropine and guanethidine, the specific alpha 1-adrenoceptor agonist, phenylephrine and antagonist, prazosin, as well as the specific alpha 2-adrenoceptor antagonist, yohimbine, had no effect on the NANC relaxations evoked by electrical field stimulation. In contrast, clonidine and the more specific alpha 2-adrenoceptor agonist, UK-14,304, significantly reduced the electrically-induced relaxations, preferentially those in response to low frequency stimulation. The inhibitory effect of UK-14,304 on these relaxations was antagonized by yohimbine. 3. During a noradrenaline-induced contraction, clonidine, but not UK-14,304 significantly augmented the relaxations to electrical stimulation. 4. The adrenoceptor agonists and antagonists used had no effect on concentration-response curves to NO or on the relaxation induced by nitroglycerin. 5. These results indicate that stimulation of prejunctional alpha 2-adrenoceptors inhibits the nitrergic NANC relaxations induced by field stimulation and thus suggest prejunctional regulation of nitric oxide release via alpha 2-adrenoceptors in the canine ileocolonic junction.

S-1-3 - Regulation of nitric oxide release from vascular endothelial cells

S-1-3 - Regulation of nitric oxide release from vascular endothelial cells