A potent inhibitor of inducible nitric oxide synthase, ONO-1714, a cyclic amidine derivative

Recent advances in nanotherapeutic strategies that target nitric oxide pathway for preventing cartilage degeneration

Nitric oxide (NO) is an important inflammatory mediator involved in the development and progression of osteoarthritis (OA). Increased production of NO in the affected joints promote cartilage damage. As NO synthesis is catalysed by the inducible NO synthase (iNOS) enzyme, iNOS inhibition serves as an attractive therapeutic target to prevent NO release. Despite a number of direct and indirect iNOS inhibitor molecules demonstrating chondro-protective effect, none have reached the clinic. Its limited bioavailability and adverse side effects served as a deterrent for pursuing clinical trials in OA patients. With the advent of nanotechnology, interest in targeting NO for preventing cartilage degeneration has revived. In this article, we discuss the limitations of the existing molecules and provide an insight on recent nanotechnology-based strategies that have been explored for the diagnosis and inhibition of NO in OA. These approaches hold promise in reviving the hitherto under explored potential of targeting NO to address OA.

Inducible nitric oxide synthase: Regulation, structure, and inhibition

A considerable number of human diseases have an inflammatory component, and a key mediator of immune activation and inflammation is inducible nitric oxide synthase (iNOS), which produces nitric oxide (NO) from l-arginine. Overexpressed or dysregulated iNOS has been implicated in numerous pathologies including sepsis, cancer, neurodegeneration, and various types of pain. Extensive knowledge has been accumulated about the roles iNOS plays in different tissues and organs. Additionally, X-ray crystal and cryogenic electron microscopy structures have shed new insights on the structure and regulation of this enzyme. Many potent iNOS inhibitors with high selectivity over related NOS isoforms, neuronal NOS, and endothelial NOS, have been discovered, and these drugs have shown promise in animal models of endotoxemia, inflammatory and neuropathic pain, arthritis, and other disorders. A major issue in iNOS inhibitor development is that promising results in animal studies have not translated to humans; there are no iNOS inhibitors approved for human use. In addition to assay limitations, both the dual modalities of iNOS and NO in disease states (ie, protective vs harmful effects) and the different roles and localizations of NOS isoforms create challenges for therapeutic intervention. This review summarizes the structure, function, and regulation of iNOS, with focus on the development of iNOS inhibitors (historical and recent). A better understanding of iNOS' complex functions is necessary before specific drug candidates can be identified for classical indications such as sepsis, heart failure, and pain; however, newer promising indications for iNOS inhibition, such as depression, neurodegenerative disorders, and epilepsy, have been discovered.

Changes in Cochlear Blood Flow Due to Endotoxin-Induced Otitis Media

The purpose of this study was to elucidate the influence of otitis media on blood flow in the lateral wall of the cochlea by means of a model of endotoxin-induced otitis media. The cochlear blood flow (CBF) following lipopolysaccharide inoculation into the middle ear cavities of rats was measured by laser-Doppler flowmetry and compared with that of untreated ears. After this evaluation, the influence on CBF of concomitant use of a nitric oxide synthase inhibitor was also investigated. The first day after inoculation, the CBF of treated ears decreased significantly. This decrease recovered gradually between the 7th and 14th days. With concomitant use of a nitric oxide synthase inhibitor, the decrease in CBF was prevented to some extent. The results showed a functional influence upon CBF by endotoxin-induced otitis media. The significance of prophylactic use of the drug is also discussed in regard to the effect on CBF following otitis media.

New synthesis and promising neuroprotective role in experimental ischemic stroke of ONO-1714

In an experimental permanent stroke model, we report here the contribution of ONO-1714 to brain damage prevention. Daily drug administration, twenty-one days prior to and two days after an experimental infarct, was performed by using mini-osmotic pumps (ALZET). Infarct volumes were assessed by image analysis of sequential coronal brain 1 mm(3) sections stained following the 2,3,5-triphenyltetrazolium chloride histological staining technique. Results of this study provide evidence of a significant reduction of the brain lesion size, suggesting ONO-1714 as a potential neuroprotective agent in stroke patients. ONO-1714 was prepared in our laboratory following a procedure which resulted in the supply of the desired compound in an easy and excellent yield.

Protective Effects of Total Flavones of Rhododendra on Cerebral Ischemia Reperfusion Injury

This study was to investigate the protective effects and possible mechanisms of total flavones of rhododendra (TFR) against cerebral ischemia reperfusion injury in rats and mice. Cerebral ischemia/reperfusion injury was induced by occluding the right middle cerebral artery (MCA). Infarct volume, neurological deficit, brain water content, levels of malondialdehyde (MDA), nitric oxide (NO) contents, lactate dehydrogenase (LDH) activity in plasma and brain, levels of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities and mRNA expression of inducible nitric oxide synthase (iNOS), neuronal nitric oxide synthase (nNOS) and endothelial nitric oxide synthase (eNOS) in brain were evaluated 7 or 10 days after treatment. TFR significantly reduced infarct volume, ameliorated the neurological deficit and reduced the brain water content. The activities of SOD, LDH and GPX in brain were enhanced, while the activity of LDH in plasma and the contents of MDA and NO in plasma and brain were decreased. While, the expression of iNOS and nNOS mRNA in brain were down-regulated, the expression of eNOS mRNA in the brain was up-regulated. These results suggest that TFR has protective effects for cerebral injury in rats and mice, which might be associated with its antioxidant properties and ability to regulate the expression of NOS isoforms.

Injectable Caltrop Fruit Saponin Protects Against Ischemia-Reperfusion Injury in Rat Brain

The present study aimed to investigate the protective effects of injectable caltrop fruit saponin preparation (ICFSP) on ischemia-reperfusion injury in rat brain. Rats were injected with ICFSP and then subjected to cerebral ischemia-reperfusion injury induced by middle cerebral artery occlusion. Then the neurological deficit score was evaluated by Bederson's method. The infarct size was assessed by TTC staining. The content of malondialdehyde (MDA) and nitric oxide (NO), and the activity of superoxide dismutase (SOD) in rat cerebrum were measured with kits, and the content of 6 K prostaglandin F1α (6-K-PGF 1α), thromboxane B2 (TXB2) and endothelin (ET) in blood plasma was measured by radioimmunoassay. The results demonstrated that ICFSP led to a decrease in infarct size (p < 0.01), neurological deficit score (p < 0.05) and plasma content of TXB2 and ET (p < 0.05), and an increase of the plasma level of 6-K-PGF 1α (p < 0.05) and SOD activity in cerebrum, where the MDA and NO content were decreased. The treatment improved forelimb function. ICFSP showed a similar potency compared to that of Ligustrazine hydrochloride parenteral solution (LHPS) and nimodipine (Nim). We concluded that ICFSP protects the brain damage caused by ischemia-reperfusion injury in rats, and this may be closely related to the regulation of reactive oxygen species (MDA and SOD activity) and NO levels in the rat cerebrum, as well as vasoactive factors in the plasma (6-K-PGF 1α, TXB2 and ET).

Involvement of nitric oxide (NO) in cough reflex sensitivity between non-sensitized and OVA-sensitized guinea pigs

Background

Exhaled nitric oxide (ENO) is elevated in bronchial asthma patients, and inhaled corticosteroid therapy lowers the elevated ENO levels in such patients. ENO appears to be an inflammatory marker, but its role in the pathophysiology of cough remains unclear. This study aimed to elucidate the relationship between NO and increased cough reflex sensitivity induced by allergic airway reactions.

Methods

Cough reflex sensitivity to inhaled capsaicin was observed under NO depletion caused by NO synthase (NOS) inhibitors in non-sensitized and ovalbumin (OVA)-sensitized guinea pigs. The bronchoalveolar lavage fluid (BALF) was analyzed in an NO depletion setting using the inducible NOS (iNOS) inhibitor ONO1714 in OVA-sensitized guinea pigs.

Results

NO depletion by the non-selective NOS inhibitor L-NAME suppressed cough reflex sensitivity in non-sensitized guinea pigs and OVA-induced increase in cough reflex sensitivity in sensitized guinea pigs; however, iNOS inhibition caused by ONO1714 partially suppressed the OVA-induced increase in cough reflex sensitivity, but not the normal cough response in non-sensitized guinea pigs. ONO1714 did not change BAL cell components in OVA-sensitized guinea pigs.

Conclusions

The results suggest that NO may be involved not only in the normal cough reflex circuit, but also in the OVA-induced increase in cough reflex sensitivity, possibly via a different mechanism of action. Further studies are needed to clarify the precise mechanism.

Novel nanomolar imidazo[4,5-b]pyridines as selective nitric oxide synthase (iNOS) inhibitors: SAR and structural insights

Inducible arginine oxidation and subsequent NO production by correspondent synthase (iNOS) are important cellular answers to proinflammatory signals. Prolonged NO production has been proved in higher organisms to cause stroke or septic shock. Several classes of potent NOS inhibitors have been reported, most of them targeting the arginine binding site of the oxygenase domain. Here we disclose the SAR and the rational design of potent and selective iNOS inhibitors which may be useful as anti-inflammatory drugs.

Relative similarity within purine nucleotide and ligand structures operating on nitric oxide synthetase, guanylyl cyclase and potassium (K ATP, BK Ca) channels

OBJECTIVES

Purine nucleotides play a central role in signal transduction events initiated at the cell membrane. The NO-cGMP-cGK pathway, in particular, mediates events involving NOS and some classes of K(+) ion channel. The aim of this study is to investigate relative molecular similarity within the ligands binding to NOS, K(ATP), BK(Ca) channels and regulatory nucleotides.

METHODS

Minimum energy conformers of the ligand structures were superimposed and fitted to L-arginine and the nucleotides of adenine and guanine using a computational program.

KEY FINDINGS

Distinctive patterns were evident in the fitting of NOS isoform antagonists to L-arginine. K(ATP) channel openers and antagonists superimposed on the glycosidic linkage and imidazole ring of the purine nucleotides, and guanidinium and ribose groups of GTP in the case of glibenclamide. The fits of BK(Ca) channel openers and antagonists to cGMP were characterized by the linear dimensions of their structures; distances between terminal oxy groups in respect of dexamethasone and aldosterone.

CONCLUSIONS

The findings provide structural evidence for the functional interaction between K(+) channel openers/antagonists and the regulatory nucleotides. Use of the purine nucleotide template systematizes the considerable heterogeneity evident within the structures of ligands operating on K(+) ion channels.

Aminoguanidine inhibition of iNOS activity ameliorates cerebral vasospasm after subarachnoid hemorrhage in rabbits via restoration of dysfunctional endothelial cells

BACKGROUND

This study was to delineate the therapeutic efficacy and potential cellular and molecular mechanisms of aminoguanidine (AG), a relatively selective inhibitor of iNOS activity, in cerebral vasospasm after subarachnoid hemorrhage (SAH) in rabbits.

METHODS

SAH was induced by a single injection of autologous arterial blood into the cisterna magna of adult male rabbits. An intravenous bolus injection of AG (150 mg/kg) was administrated 1h after SAH, and this dosage was repeated on the following day. Vasospasm was verified by computed tomography angiography (CTA) day 2 after SAH. Rabbit basilar arteries were harvested for transmission electron microscopy (TEM), immunohistochemical examination, RT-PCR, and western blot analysis.

RESULTS

CTA data revealed that cerebral vasospasm of SAH rabbits was significantly prevented via AG treatment. TEM results demonstrated the ultrastructural morphological changes of endothelial cells of SAH rabbits were ameliorated by AG treatment. In parallel, AG treatment increased eNOS mRNA and protein levels along with the reduced immunoreactivity of nitrotyrosine in rabbit basilar arteries.

CONCLUSIONS

Our discovery suggested AG inhibition of iNOS activity could significantly reverse cerebral vasospasm after SAH via restoration of dysfunctional endothelial cells by the upregulation of eNOS, indicating a regulatory cross-talk between eNOS and iNOS in the pathogenesis of SAH.

The role of nitric oxide in osteoarthritis

Elevated levels of markers of nitric oxide (NO) production are found in osteoarthritic joints suggesting that NO is involved in the pathogenesis of osteoarthritis (OA). In OA, NO mediates many of the destructive effects of interleukin-1 (IL-1) and tumour necrosis factor-alpha (TNF-alpha) in the cartilage, and inhibitors of NO synthesis have demonstrated retardation of clinical and histological signs and symptoms in experimentally induced OA and other forms of arthritis. As an important factor in cartilage, the regulation of inducible nitric oxide synthase (iNOS) expression and activity, and the effects of NO are reviewed, especially in relation to the pathogenesis of OA.

Design and synthesis of 2-amino-4-methylpyridine analogues as inhibitors for inducible nitric oxide synthase and in vivo evaluation of [18F]6-(2-fluoropropyl)-4-methyl-pyridin-2-amine as a potential PET tracer for inducible nitric oxide synthase

A series of position-6 substituted 2-amino-4-methylpyridine analogues was synthesized and compounds 9, 18, and 20 were identified as the inhibitors with the greatest potential to serve as PET tracers for imaging inducible nitric oxide synthase (iNOS). [(18)F]9 was synthesized and evaluated in a mouse model of lipopolysaccharide (LPS)-induced iNOS activation. In vivo biodistribution studies of [(18)F]9 indicate higher tracer uptake in the lungs of the LPS-treated mice when compared to control mice. Tracer uptake at 60 min postinjection was reduced in a blocking study using a known inhibitor of iNOS. The expression of iNOS was confirmed by Western blot analysis of lung samples from the LPS-treated mice. MicroPET studies also demonstrated accumulation of radiotracer in the lungs of the LPS-treated mice. Taken collectively, these data suggest that [(18)F]9 shows favorable properties as a PET tracer to image iNOS activation with PET.

NO-mediated cytotoxicity contributes to multiple low-dose streptozotocin-induced diabetes but not to NOD diabetes

Type 1 diabetes (T1D) is caused mostly by autoimmune destruction of pancreatic beta-cells, the precise mechanism of which remains unclear. Two major effector mechanisms have been proposed: direct cell-mediated and indirect cytokine-mediated cytotoxicity. Cytokine-mediated beta-cell destruction is presumed mainly caused by NO production. To evaluate the role of iNOS expression in T1D, this study used a novel iNOS inhibitor ONO-1714. ONO-1714 significantly reduced cytokine-mediated cytotoxicity and NO production in both MIN6N9a cells and C57BL/6 islets in the presence of IL-1beta, TNF-alpha, and IFN-gamma. To evaluate whether NO contributes to diabetes progression in vivo, ONO-1714 was administered to four different mouse models of autoimmune diabetes: multiple low-dose STZ (MLDS)-induced C57BL/6, CY-induced, adoptive transfer and spontaneous NOD diabetes. Exposure to STZ in vitro induced NO production in MIN6N9a cells and C57BL/6 islets, and in vivo injection of ONO-1714 to MLDS-treated mice significantly reduced hyperglycemia and interestingly, led to complete suppression of cellular infiltration of pancreatic islets. In contrast, when ONO-1714 was injected into spontaneous NOD mice and CY-induced and adoptive transfer models of NOD diabetes, overt diabetes could not be inhibited in these models. These findings suggest that NO-mediated cytotoxicity significantly contributes to MLDS-induced diabetes but not to NOD diabetes.

Expert opinion on tilarginine in the treatment of shock

Tilarginine is L-N-monomethyl arginine (L-NMMA) or N(G)-monomethyl-L-arginine HCL, a non-selective inhibitor of nitric oxide synthase (NOS), which has been studied in the treatment of septic shock and cardiogenic shock complicating myocardial infarction. Despite strong evidence that excessive nitric oxide (NO) production plays a pivotal role in the pathogenesis of septic shock and may contribute to the pathogenesis of cardiogenic shock complicating myocardial infarction, outcome studies in these two disorders have proved disappointing. L-NMMA therapy was associated with an excess mortality, particularly at doses > 5 mg/(kg h), in septic shock whereas the effects of a lower dose (1 mg/(kg h)) in cardiogenic shock complicating myocardial infarction were neutral. The excess mortality in patients with septic shock was almost certainly the result of unfavourable haemodynamic changes induced by L-NMMA (decreased cardiac output, increased pulmonary vascular resistance and reduced tissue oxygen delivery) whereas the lack of benefit in patients with cardiogenic shock complicating myocardial infarction may have been because the dose of L-NMMA was too low. Further studies of L-NMMA at doses < 5 mg/(kg h) in conjunction with inotrope support may produce more beneficial results. Conversely, the use of a selective inducible NOS inhibitor to reduce the pathological effects of excessive NO production although leaving the beneficial effects of vascular NO production by endothelial NOS unaltered may prove to be of value.

Increased expression of inducible nitric oxide synthase (iNOS) in N-nitrosobis(2-oxopropyl)amine-induced hamster pancreatic carcinogenesis and prevention of cancer development by ONO-1714, an iNOS inhibitor

Elevated protein expression of inducible nitric oxide synthase (iNOS) has been observed in human pancreatic cancers and therefore, iNOS may play important roles in pancreatic carcinogenesis. This was examined in the present study, using an experimental model with N-nitrosobis(2-oxopropyl)amine (BOP)-treated hamsters. Reverse transcription-polymerase chain reaction analysis demonstrated iNOS expression in a hamster pancreatic cancer cell line as well as in human pancreatic cancer cell lines. Immunohistochemical analysis revealed increased expression of iNOS protein in atypical hyperplasia and ductal adenocarcinomas of the pancreas in BOP-treated hamsters. In addition, iNOS expression was also observed in macrophages and islet cells in pancreatic tissue surrounding tumors. In order to assess the role of iNOS expression in carcinogenesis in the pancreas, the effects of ONO-1714 [(1S, 5S, 6R, 7R)-7-chloro-3-imino-5-methyl-2-azabicyclo[4.1.0]heptane], an iNOS inhibitor, on hamster pancreatic ductal carcinogenesis were investigated. Female Syrian golden hamsters were treated with BOP at 10 mg/kg body wt, four times for 1 week, and 1 week after the last carcinogen treatment, ONO-1714 was administered at doses of 100 and 200 p.p.m. in the diet for 15 weeks. The incidences and multiplicities of atypical hyperplasia and invasive adenocarcinoma and total adenocarcinomas (non-invasive and invasive adenocarcinomas) in the pancreas were significantly lowered by treatment with 200 p.p.m. ONO-1714. Treatment with 100 p.p.m. ONO-1714 also significantly decreased the multiplicities of invasive and total adenocarcinomas. Moreover, treatment with 200 p.p.m. ONO-1714 reduced the number of BOP-induced cholangiocellular tumors. These results suggest that iNOS plays roles in promoting pancreatic carcinogenesis in both early and late stages in hamsters.

N(delta)-Methylated L-arginine derivatives and their effects on the nitric oxide generating system

So far N(delta)-methyl-l-arginine (MA) is only detected in yeast cells. Assuming that MA also exists in mammalians we examined possible physiological effects of N(delta)-methylated l-arginine derivatives on the nitric oxide generating system, that is, nitric oxide synthase (NOS), arginase and dimethylarginine dimethylaminohydrolase (DDAH). N(delta)-methyl-l-citrulline (MC) turned out to be a weak non-specific inhibitor of nitric oxide synthases. Moreover, MA is hydroxylated by all human NOS isoforms to N(omega)-hydroxy-N(delta)-methyl-l-arginine (NHAM) but not converted further. This hydroxylated intermediate, however, was detected to be a potent inhibitor of bovine liver arginase with a K(i) of 17.1+/-2.2 microM.

A novel inhibitor of inducible nitric oxide synthase, ONO-1714, does not ameliorate hypoxia-induced pulmonary hypertension in rats

A recent study showed that long-term administration of the inducible nitric oxide synthase (iNOS) inhibitor L-NIL reduced the development of pulmonary hypertension. The purpose of the present study was to identify the effect of an another iNOS inhibitor, ONO-1714, on the development of pulmonary hypertensive vascular changes in chronic hypoxic pulmonary hypertension in rats. ONO-1714 was administered to rats exposed to hypobaric hypoxia (air at 380 mmHg) for 10 days. Muscularization of normally nonmuscular peripheral arteries and medial hypertrophy of normally muscular arteries were assessed by light microscopy. iNOS mRNA and protein levels of the lung were assessed in normal and hypoxic rats. Chronic hypoxia induced pulmonary hypertension, right ventricular hypertrophy, and hypertensive pulmonary vascular changes. Although an acute single injection of ONO-1714 induced a significant increase in mean pulmonary artery pressure in chronic hypoxic pulmonary hypertensive rats, the increase was slight and transient. There were no significant differences among rats with and without long-term administration of ONO-1714 in pulmonary artery pressure, right ventricular hypertrophy, medial wall thickness of muscular arteries, and the percentage of muscularized arteries at the alveolar wall and duct levels. Although there was a significantly increased expression of iNOS as assessed with the reverse-transcription polymerase chain reaction in rats that were exposed to 10 days of hypobaric hypoxia, we could not detect a significant level of iNOS protein by Western blotting. ONO-1714 does not have a therapeutic role in preventing the development of chronic hypoxic pulmonary hypertension.

A specific inducible nitric oxide synthase inhibitor, ONO-1714 attenuates inflammation-related large bowel carcinogenesis in male Apc(Min/+) mice

It is generally assumed that inflammation influences carcinogenesis. We previously reported that dextran sodium sulfate (DSS) strongly enhances colon carcinogenesis in the Apc(Min/+) mice and the over-expression of inducible nitric oxide synthase (iNOS) contributes to this enhancement. In the current study, we investigated the effect of a selective iNOS inhibitor, ONO-1714 on colitis-related colon carcinogenesis in the Apc(Min/+) mouse treated with DSS. Male C57BL/6J Apc(Min/+) and Apc(+/+) mice were exposed to 1% DSS in their drinking water for 7 days. ONO-1714 was given to the mice at a dose level of 50 or 100 ppm in diet for 5 weeks (during the administration of DSS). The tumor inhibitory effects by ONO-1714 were assessed at week 5 by counting the incidence and multiplicity of colonic neoplasms. Additionally, we assessed serum lipid levels and colonic mRNA expression for cyclooxygenase (COX)-2, iNOS, tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta. Feeding with ONO-1714 significantly inhibited the occurrence of colonic adenocarcinoma in a dose-dependent manner in the Apc(Min/+) mice. In addition, the treatment with ONO-1714 significantly lowered the serum triglyceride levels and mRNA expression levels of COX-2, TNFalpha and IL-1beta of colonic mucosa in the DSS-treated Apc(Min/+) mice. Neither ONO-1714 nor DSS affected the colonic pathology in the Apc(+/+) mice. Our findings may suggest that ONO-1714 could therefore serve as an effective agent for suppression of colitis-related colon cancer development in the Apc(Min/+) mice.

New therapeutic targets in atrophic age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness in developed countries. There is no effective treatment for the most prevalent atrophic (dry) form of AMD. Atrophic AMD is triggered by abnormalities in the retinal pigment epithelium (RPE) that lies beneath the photoreceptor cells and normally provides critical metabolic support to these light-sensing cells. Secondary to RPE dysfunction, macular rods and cones degenerate leading to the irreversible loss of vision. Oxidative stress, formation of drusen, accumulation of lipofuscin, local inflammation and reactive gliosis represent the pathologic processes implicated in pathogenesis of atrophic AMD. This review discusses potential target areas for small-molecule and biologic intervention, which may lead to development of new therapeutic treatments for atrophic AMD.

A novel potent inhibitor of inducible nitric oxide synthase, ONO-1714, reduces hyperoxic lung injury in mice

STUDY OBJECTIVES

High-concentration oxygen therapy is used to treat tissue hypoxia, but hyperoxia causes lung injury. Overproduction of nitric oxide by nitric oxide synthase (NOS) is thought to promote hyperoxic lung injury. The present study was conducted to examine the role of inducible nitric oxide synthase (iNOS) in hyperoxic lung injury in mice.

MEASUREMENTS AND RESULTS

Mice were exposed to >98% oxygen for 72 h, and ONO-1714 (0.05 mg/kg) (ONO) was subcutaneously administered to block iNOS. Hyperoxia significantly increased total cell count, protein concentration, and nitrites/nitrates in the bronchoalveolar lavage fluid and proinflammatory cytokines in the lung tissue. ONO significantly prevented the increases in all of these variables. ONO suppressed histologic evidence of lung injury. ONO markedly inhibited iNOS protein expression and nitrotyrosine production in lung homogenates. After exposure to hyperoxia, alveolar epithelial cells stained positively for 8-hydroxy-2'-deoxyguanosine, a proper marker of oxidative DNA damage by reactive oxygen species. ONO attenuated this finding.

CONCLUSIONS

NOS play important roles in the pathogenesis of hyperoxic lung injury. Selective iNOS inhibitors may be useful for the treatment of hyperoxic lung injury.

An inhaled inducible nitric oxide synthase inhibitor reduces damage of Candida-induced acute lung injury

Excessive nitric oxide (NO) generated by inducible nitric oxide synthase (iNOS) aggravates acute lung injury (ALI) by producing peroxynitrite. We previously showed by immunostaining that the expression of iNOS was suppressed by inhalation of N(G)-nitro-L-arginine methyl ester in mice with Candida-induced ALI. This study tested the hypothesis that a novel iNOS inhibitor suppresses not only iNOS expression, but also iNOS messenger RNA (mRNA) production by interrupting a positive feedback loop at the time of NO production in Candida-induced ALI. Mice were pretreated by inhalation of saline or ONO-1714, a selective iNOS inhibitor, and were given an intravenous injection of Candida albicans to induce ALI. After inhalation of 1 mM aerosolized ONO-1714, the nitrite-nitrate concentration in bronchoalveolar lavage fluid (BALF) at 24 h was significantly lower than that after inhalation of saline. Tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) levels and neutrophils in BALF were decreased by inhalation of ONO-1714. Inhalation of ONO-1714 markedly suppressed nitrotyrosine production and inhibited the expression of iNOS mRNA as well as proteins in the lung. Survival was prolonged by inhalation of ONO-1714. We conclude that pretreatment with inhaled ONO-1714 suppresses the production of peroxinitrite and decreases oxidative stress associated with peroxinitrite in Candida-induced ALI.

Cardiovascular responses and neurotransmitter changes during static muscle contraction following blockade of inducible nitric oxide synthase (iNOS) within the ventrolateral medulla

The enzyme nitric oxide synthase (NOS) which is necessary for the production of nitric oxide from L-arginine exists in three isoforms: neuronal NOS (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS). Our previous studies have demonstrated the roles of nNOS and eNOS within the rostral (RVLM) and caudal ventrolateral medulla (CVLM) in modulating cardiovascular responses during static skeletal muscle contraction via altering localized glutamate and GABA levels (Brain Res. 977 (2003) 80-89; Neuroscience Res. 52 (2005) 21-30). In this study, we investigated the role of iNOS within the RVLM and CVLM on cardiovascular responses and glutamatergic/GABAergic neurotransmission during the exercise pressor reflex. Bilateral microdialysis of a selective iNOS antagonist, aminoguanidine (AGN; 1.0 microM), for 60 min into the RVLM attenuated increases in mean arterial pressure (MAP), heart rate (HR), and extracellular glutamate levels during a static muscle contraction. Levels of GABA within the RVLM were increased. After 120 min of discontinuation of the drug, MAP and HR responses and glutamate/GABA concentrations recovered to baseline values during a subsequent muscle contraction. In contrast, bilateral application of AGN (1.0 microM) into CVLM potentiated cardiovascular responses and glutamate concentration while attenuating levels of GABA during a static muscle contraction. All values recovered after 120 min of discontinuation of the drug. These results demonstrate that iNOS within the ventrolateral medulla plays an important role in modulating cardiovascular responses and glutamatergic/GABAergic neurotransmission that regulates the exercise pressor reflex.

Effects of inducible nitric oxide synthase inhibitors on asthma depending on administration schedule

The effectiveness of two inducible nitric oxide synthase (iNOS) inhibitors on allergic airway inflammation was investigated under different administration schedules. Rats sensitized to ovalbumin (OVA) were exposed to OVA for 3 consecutive days. Both iNOS inhibitors showed markedly different effects between two pretreatment schedules: pretreatment before each of three OVA exposures S1 and before the third exposure alone S2. S1 pretreatment resulted in higher pulmonary resistance than triple OVA alone. This potentiation was associated with increased eosinophil infiltration and malondialdehyde levels in the lungs, which were suppressed by superoxide dismutases (SODs) but not by methylprednisolone. However, the S2 administration of both iNOS inhibitors completely suppressed the airway response. Administration by schedule S1 completely suppressed plasma nitrite and nitrate levels, but that by S2 caused only a slight suppression. The triple OVA exposures resulted in the upregulation of iNOS in alveolar macrophages and arginase activity, Mn- and Cu/Zn-SOD expression, and nitrotyrosine and lipid peroxide deposition in the airway. However, inhibitors administered by schedule S1 suppressed this upregulation, but further potentiated nitrotyrosine, which in turn was inhibited by SOD. Although iNOS inhibitors may be beneficial for asthma, repeated administration may be detrimental because of extensive reduction of NO and downregulation of SOD.

Suppressive effect of an inducible nitric oxide inhibitor, ONO-1714, on AOM-induced rat colon carcinogenesis

The expression of inducible nitric oxide synthase (iNOS) is markedly elevated in rat colon cancers induced by azoxymethane (AOM). In addition, iNOS can be detected in most adenomas and dysplastic aberrant crypt foci (ACF), suggesting that iNOS plays an important role in colon carcinogenesis. In the present study, the effect of an iNOS inhibitor, ONO-1714 ((1S,5S,6R,7R)-7-chloro-3-imino-5-methyl-2-azabicyclo[4.1.0] heptane hydrochloride), on AOM-induced rat colon carcinogenesis was investigated. Male F344 rats were treated with 15 mg/kg body weight of AOM once a week, for 2 weeks. ONO-1714 was given to the rats at doses of 10, 20, 50, and 100 ppm in diet for 4 weeks from the day before the first carcinogen treatment. The number of AOM-induced ACF in the rats receiving 10, 20, 50 and 100 ppm ONO-1714 were 94, 73 (P < 0.05), 71 (P < 0.005), and 53% (P < 0.0005), respectively, of the control value. Moreover, the mean number of aberrant crypts per focus was significantly lowered in 100 ppm ONO-1714 group (P < 0.05). Then, the effects of long-term treatment (32 weeks) with 50 and 100 ppm ONO-1714 on AOM-induced colorectal tumor development were examined. Although incidences and multiplicities of colon tumors did not significantly differ among the groups, number of tumors developing in the middle part of colon were reduced with both 50 and 100 ppm doses (P < 0.05). Furthermore, colon tumor volume tended to be decreased by ONO-1714 treatment, and the number of colon tumors more than 3mm in diameter was significantly lowered in the 100 ppm ONO-1714 group (P < 0.01). These results suggest that iNOS plays roles in both early and late stages of colon carcinogenesis.

Inhibition of inducible nitric oxide synthase prevents hepatic, but not pulmonary, injury following ischemia-reperfusion of rat liver

The aim of this study was to investigate the contribution of inducible nitric oxide synthase (iNOS)-derived nitric oxide on the liver and lung injury following hepatic ischemia-reperfusion (I/R) using a novel and potent iNOS inhibitor, ONO-1714. Rats were subjected to 90 min of partial hepatic ischemia followed by 3, 6, 12, and 24 hr of reperfusion. Expression of iNOS mRNA peaked at 3 hr of reperfusion in the liver and lung. Plasma nitric oxide levels were increased fourfold at 24 hr of reperfusion and plasma ALT was increased, reaching a peak at 12 hr of reperfusion; both were significantly inhibited by ONO-1714. Histological examination revealed extensive liver damage, whereas this was not seen in the ONO-1714 group. Lung injury was not significantly changed in groups with versus without ONO-1714. Nitrotyrosine expression was seen in regions similar to those of the histological injuries of the liver, while this staining was absent in the ONO-1714 group. These data show that generation of peroxynitrite could be involved in the pathogenesis of liver injury but not lung injury after hepatic I/R. Inhibition of iNOS could be applied for attenuation of liver injury following hepatic I/R.

Selective inhibition of inducible nitric oxide synthase reduces neurological deficit but not cerebral edema following traumatic brain injury

The role of inducible nitric oxide synthase (iNOS) in cerebral edema and neurological deficit following traumatic brain injury (TBI) is not yet clear-cut. Therefore, the aim of this study was to investigate the effect of three different iNOS inhibitors on cerebral edema and functional outcome after TBI. First, the time courses of blood--brain barrier (BBB) breakdown, cerebral edema, and neurological deficit were studied in a rat model of fluid percussion-induced TBI. The permeability of BBB to Evans blue was increased from 1 h to 24 h after TBI. Consistently, a significant increase in brain water content (BWC) was observed at 6 and 24 h post-TBI. A deficit in sensorimotor neurological functions was also observed from 6 h to 7 days with a maximum 24 h after TBI. Second, a single dose of aminoguanidine (AG; 100 mg/kg, i.p.), L-N-iminoethyl-lysine (L-NIL; 20 mg/kg, i.p.), or N-[3-(aminomethyl)benzyl]acetamide (1400W; 20 mg/kg, s.c.) was administered at 6 h post-TBI. Treatment with AG reduced by 71% the increase in BWC evaluated at 24 h, while L-NIL and 1400W had no effect. In contrast, the three iNOS inhibitors reduced the neurological deficit from 30% to 40%. Third, 1400W (20 mg/kg, s.c.) was administered at 5 min, 8 and 16 h post-TBI. Although this treatment paradigm had no effect on cerebral edema evaluated at 24 h, it significantly reduced the neurological deficit and iNOS activity. In conclusion, iNOS contributes to post-TBI neurological deficit but not to cerebral edema. The beneficial effect of iNOS inhibitors is not due to their anti-edematous effect, and the reduction of cerebral edema by AG is unlikely related to iNOS inhibition. The 6 h therapeutic window of iNOS inhibitors could allow their use in the treatment of functional deficit at the acute phase of TBI.

Neuroprotective effects of scutellarin on rat neuronal damage induced by cerebral ischemia/reperfusion

AIM

To investigate the neuroprotective effect and mechanisms of scutellarin, a flavonoid extracted from Erigeron breviscapus Hand Mazz, against neuronal damage following cerebral ischemia/reperfusion.

METHODS

Rats were pretreated ig with scutellarin for 7 d and then subjected to cerebral ischemia/reperfusion (I/R) injury induced by a middle cerebral artery occlusion (MCAO). The infarct volume and neurological deficit were determined by TTC staining and Longa's score. The permeability of the blood-brain barrier was evaluated by measurement of the Evans blue (EB) content in the brain with a spectrophotometer. The total NOx content was determined. Nitric oxide synthase (NOS) isoforms (iNOS, eNOS, nNOS) and the key angiogenic molecules, vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF), were detected by Western blotting.

RESULTS

Scutellarin significantly reduced infarct volume (P<0.05 or P<0.01), ameliorated the neurological deficit and reduced the permeability of the blood-brain barrier (BBB) (P<0.05). When rats were pretreated with scutellarin (50 or 75 mg/kg), upregulation of eNOS expression and downregulation of VEGF, bFGF, and iNOS expression was observed, whereas scutellarin had no effect on nNOS expression.

CONCLUSION

Scutellarin has protective effects for cerebral injury through regulating the expression of NOS isoforms and angiogenic molecules.

Selective iNOS inhibitor, ONO1714 successfully retards the development of high-cholesterol diet induced atherosclerosis by novel mechanism

OBJECTIVE

We have reported that inducible nitric oxide synthase (iNOS) is present only in deep areas of plaque in atherosclerosis. However, the role of iNOS in the development of atherosclerosis is not well known. We therefore investigated the relevance of iNOS inhibition.

METHODS AND RESULTS

Seven groups of male rabbits were fed a 0.5% high-cholesterol diet (HCD) for 8 weeks. Gp1-HCD was fed HCD only; Gp2-O17 was fed HCD with ONO1714, an iNOS inhibitor; Gp3-AG was fed HCD with amino-guanidine (AG), an iNOS inhibitor; Gp4-AR was fed HCD with l-arginine; Gp5-AR-O17 was fed HCD with l-arginine with ONO1714; Gp6-LNA was fed HCD with l-NAME (a NOS inhibitor); and Gp7-LN-O17 was fed HCD with l-NAME plus ONO1714. ONO1714 decreased atherosclerosis by about 70% (area occupied by lesions: 3.0+/-0.4% in Gp2-O17 versus 10.3+/-1.6% in Gp1-HCD) and also decreased atherosclerosis in Gp7-LN-O17. The ONO compound enhanced the atheroprotective effect of l-arginine. Amino-guanidine also showed an anti-atherosclerotic effect. Tone-related basal NO release and acetylcholine-induced NO-dependent relaxation were improved in Gp2-O17 and Gp5-AR-O17. O(2)(-) release was decreased in Gp2-O17 and Gp7-LN-O17.

CONCLUSION

ONO1714 retards the progression of atherosclerosis in rabbits. Although the up-regulation of endothelial nitric oxide synthase (eNOS) and the decrease of O(2)(-) may play roles in this retardation, the inhibition of iNOS may be the principal factor, alone was not sufficient.

Application of electron spin resonance spin-trapping technique for evaluation of substrates and inhibitors of nitric oxide synthase

The electron spin resonance (ESR) spin-trapping technique coupled with iron-dithiocarbamate complexes is one of the most specific methods for nitric oxide (NO) detection. In this study, we applied this method for the evaluation of the substrate and the inhibitors of NO synthase (NOS). A three-line ESR signal was detected from the mixture of inducible NOS (iNOS), l-arginine (Arg), nicotinamide adenine dinucleotide phosphate (NADPH), tetrahydrobiopterin, dithiothreitol, and Fe(2+)-N-(dithiocarboxy) sarcosine (DTCS-Fe), and the signal intensity increased time-dependently. The signal was not observed by excluding either Arg or NADPH, and it was decreased by the addition of hemoglobin, which is an NO scavenger, and N(G)-monomethyl-l-arginine (l-NMMA), N(G)-nitro-l-arginine (l-NAME), and aminoguanidine (AG), which are NOS inhibitors, depending on the concentration. In comparison with l-NAME and AG, l-NMMA strongly inhibited iNOS activity. By using this method, the K(m) value of Arg and the K(i) value of l-NMMA for iNOS were determined to be 12.6 and 6.1muM, respectively. These values are consistent with the reported values measured by the oxyhemoglobin and citrulline assays. These results suggest that the ESR spin-trapping technique coupled with the iron-dithiocarbamate complex can be applied for the evaluation of substrates and inhibitors of NOS, and it would be a powerful tool due to its simplicity and high specificity to NO.

Comparison of effects of nitric oxide synthase (NOS) inhibitors on plasma nitrite/nitrate levels and tissue NOS activity in septic organs

An excessive production of nitric oxide (NO) by NO synthase (NOS) is considered to contribute to circulatory disturbance, tissue damage, and refractory hypotention, which are often observed in septic disorders. It is anticipated that a selective inducible NOS (iNOS) inhibitor with excellent pharmacokinetics may be potentially effective as a novel and potent therapeutic intervention in sepsis. We examined whether or not a selective iNOS inhibitor shows iNOS selectivity at the tissue level, when administered systemically. The effects of four NOS inhibitors on plasma nitrite/nitrate (NOx) and tissue NOS levels were compared in major organs (lungs, liver, heart, kidneys, and brain) 6 hr after the injection of E. coli lipopolysaccharide (LPS) into male Wistar-King rats. The rats treated with the three iNOS inhibitors (N-(3-(aminomethyl)benzyl)acetamidine (1400W), (1 S, 5 S, 6 R, 7 R )-2-aza-7-chloro-3-imino-5-methylbicyclo [4.1.0] heptane hydrochloride (ONO-1714), and aminoguanidine) administered 1 hr after LPS injection, showed dose-dependent decreases in plasma NOx levels and NOS activity in the lungs. The non-selective NOS inhibitor (N(G)-methyl-L-arginine (L-NMMA)) had an effect only at the maximum dose. The differences in in vitro iNOS selectivity among these drugs did not correlate with iNOS selectivity at the tissue level. The relationship between plasma NOx levels and NOS activity in the lungs showed a linear relationship with or without the NOS inhibitors. In conclusion, the iNOS selectivity of these drugs does not seem to differ at the tissue level. Plasma NOx levels may be a useful indicator of lung NOS activity.

Effects of nitric oxide synthase inhibitor on acid aspiration-induced lung injury in rats

The current study was designed to determine the effects of nitric oxide synthase (NOS) in the development of acid aspiration-induced lung injury in rats. Hydrochloric acid (HCl, 0.1 N; 2 ml/kg) or normal saline (NS, 2 ml/kg) was instilled into the lung of anesthetized, ventilated Sprague-Dawley rats. NG-monomethyl-L-arginine (L-NMMA, 20 mg kg(-1)) and a selective inducible nitric oxide synthase (iNOS) inhibitor, ONO-1714 (0.1 and 0.3 mg kg(-1)), were used to block NOS. Bronchoalveolar lavage fluid (BALF) and wet and dry measurements of lung (W/D) were obtained 5h after HCl or NS instillation. Unlike the control group, rats instilled with HCl showed significant increases in total nuclear cell counts (NCC), neutrophil counts, concentrations of albumin, tumor necrosis factor-alpha (TNF-alpha), interleukine-6 (IL-6) and nitrites/nitrates (NO(x)) in BALF. These parameters were associated with the significantly increased W/D in the HCl group compared with the NS group. ONO-1714 (0.1 mg kg(-1)) significantly prevented the increases in all these parameters. Its inhibitory effects were superior to those of L-NMMA and 0.3 mg kg(-1) of ONO-1714. NOS plays an important role in the pathogenesis of acid aspiration-induced lung injury. Furthermore, selective iNOS inhibition at the optimal dose was most effective in improving lung injury induced by acid aspiration in rats.

Expression of GDNF in spinal cord injury and its repression by ONO-1714

ONO-1714 is a newly developed specific inhibitor for inducible nitric oxide synthase (iNOS). We have shown that ONO-1714 has some neuroprotective effects. In this report, we investigated the effects of ONO-1714 in injured spinal cords, and analyzed the expression of glial cell-line-derived neurotrophic factor (GDNF) after injury. Male Sprague-Dawley rats were subjected to contusive spinal cord injury and administrated 0.1 mg/kg ONO-1714. The injured spinal cords were isolated at appropriate time points and GDNF mRNA was determined by semi-quantitative RT-PCR. GDNF-positive cells were also counted after immunohistochemical stainings. ONO-1714 diminished the early stage production of GDNF after injury as well as it reduced the production of nitric oxide produced by iNOS and apoptotic cells.

Novel and orally bioavailable inducible nitric oxide synthase inhibitors: synthesis and evaluation of optically active 4,5-dialkyl-2-iminoselenazolidine derivatives

We have previously reported that (4R,5R)-5-ethyl-2-imino-4-methylthiazolidine (3) strongly inhibits inducible nitric oxide synthase (iNOS). In a successive search for strong and selective iNOS inhibitors, we, herein, describe the synthesis of the selenium analogue of 3 (4: ES-2133) and its related optically active compounds and examine their in vitro and in vivo inhibitory activity against iNOS. In addition, an alternative synthetic method to the selected compound 4 and its pharmacokinetic profile is also reported.

Effects of MPSS and a potent iNOS inhibitor on traumatic spinal cord injury

ONO-1714, a selective inhibitor of inducible nitric oxide synthetase (iNOS) attenuated the increase of apoptosis and improved the functional outcome of urinary bladder after traumatic spinal cord injury. These findings suggest that iNOS plays a role in the process of SCI. Early treatment with 30 mg/kg methylprednisolone sodium succinate (MPSS) could also inhibit the expression of iNOS gene, apoptosis and the loss of urinary bladder function. We confirmed that early MPSS treatment may prevent injury associated with apoptosis and urinary bladder disability by reducing iNOS mRNA. However, delayed single MPSS treatment 8 h after spinal cord injury was not effective. Early repeated MPSS treatment might allow greater recovery from acute spinal cord injury.

A novel potent inhibitor of inducible nitric oxide inhibitor, ONO-1714, reduces intestinal ischemia-reperfusion injury in rats

The overproduction of nitric oxide (NO) by inducible nitric oxide synthase (iNOS) may contribute to the pathophysiology of intestinal injury induced by ischemia-reperfusion. The aim of the present study was to examine the effect of selective iNOS inhibition by a cyclic amidine analogue, ONO-1714, on reperfusion-induced small intestinal injury and inflammation in rats. Intestinal damage was induced in male Sprague-Dawley rats by clamping both the superior mesenteric artery and the celiac trunk for 30 min, followed by reperfusion. The luminal nitrite concentration in the small intestine was measured by Griess reaction and the iNOS mRNA expression by RT-PCR. The severity of the intestinal mucosal injury and inflammation were evaluated by several biochemical markers and by the histological findings. The rats which were killed after ischemia-reperfusion had increased luminal concentrations of nitrite and iNOS mRNA expression, in addition to severe intestinal inflammation characterized by significant increases in myeloperoxidase activity, a marker of neutrophil infiltration, and by the mucosal content of CINC-1 cytokine, a neutrophil chemotactic cytokine. Administration with ONO-1714 significantly inhibited the luminal NO production. Reperfusion after 30-min ischemia resulted in an increase in luminal protein and hemoglobin concentrations, with levels reaching a maximum after 60 min of reperfusion. In contrast, pre-treatment with ONO-1714 2h before the ischemia inhibited the increases in luminal protein and hemoglobin concentration in a dose-dependent manner (0.001-0.1mg/kg). The contents of the thiobarbituric acid-reactive substances (a marker of oxidative lipid peroxidation) were significantly increased by ischemia-reperfusion, and this increase was reduced by ONO-1714. After reperfusion, the increase in tissue-associated myeloperoxidase activity, an index of neutrophil infiltration, was significantly inhibited by pre-treatment with ONO-1714. ONO-1714 also inhibited increases in intestinal CINC-1 protein and mRNA expression, as determined by ELISA and RT-PCR, respectively. In conclusion, the improvement of reperfusion-induced intestinal injury by ONO-1714 suggested that an excess of NO, produced by iNOS, may have contributed to the initiation/amplification of intestinal inflammatory injury by various mechanisms, including nitrosative and oxidative damage as well as the enhancement of inflammatory cytokine release.

4,5-Disubstituted-1,3-oxazolidin-2-imine derivatives: a new class of orally bioavailable nitric oxide synthase inhibitor

In our search for a novel class of inducible nitric oxide synthase (iNOS) inhibitors, 1,3-oxazolidin-2-imine was found to weakly inhibit iNOS. Further modifications of this compound resulted in a remarkable increase in both the in vivo and in vitro inhibitory activity and selectivity for iNOS.

A comparative study of intratympanic steroid and NO synthase inhibitor for treatment of cochlear lateral wall damage due to acute otitis media

We studied the damage to the cochlear lateral wall induced by otitis media and the therapeutic effects of intratympanic administration of steroid and nitric oxide (NO) synthase inhibitor. In Sprague-Dawley rats, right middle ear cavities were inoculated with lipopolysaccharide, followed after 30 min by intratympanic administration of dexamethasone, NOS-inhibitor or PBS. Twenty-four hours after lipopolysaccharide inoculation, cochlear blood flow was measured by laser-Doppler flowmetry. Prostaglandin E(1) was topically applied to the round window membrane of the right ear and changes in cochlear blood flow were calculated. Changes of cochlear blood flow were significantly different among the three groups. Increases in cochlear blood flow following PGE(1) application were higher in the group that received NOS-inhibitor. Electron microscopic examination revealed that changes in the stria vascularis were less severe in rats treated with dexamethasone or NOS-inhibitor. Our results show the effectiveness of intratympanic dexamethasone or NOS-inhibitor in treating cochlear lateral wall damage caused by otitis media.

Endogenous nitric oxide and pulmonary circulation response to hypoxia in high-altitude adapted Tibetan sheep

Nitric oxide (NO) is important for the pulmonary circulation response to acute and chronic hypoxia. We examined effects of endogenous nitric oxide synthase (NOS) inhibition on pulmonary vascular tone in response to hypoxia in Tibetan sheep dwelling at 3,000 m above sea level using a pressure chamber. Unanaesthetized male sheep living at 2,300 m above sea level ( n=7) were prepared for vascular monitoring. Pulmonary artery ( P(pa)), pulmonary artery wedge ( P(cwp)) and systemic artery pressures together with cardiac output (CO) were measured, and pulmonary vascular resistance (PVR) was calculated as ( P(pa)- P(cwp))/CO. A non-selective NOS inhibitor, N(omega)-nitro- l-arginine (NLA; 20 mg kg(-1)), and a selective NOS inhibitor, ONO-1714 (0.1 mg kg(-1)), were used and measurements were made at 0 m, 2,300 m, and 4,500 m, with and without the NOS inhibitors. After NLA, P(pa) increased slightly and CO decreased in animals at baseline (2,300 m). The increased PVR after NLA at 4,500 m was greater than that at 2,300 m ( P<0.05). Selective NOS inhibition increased PVR at baseline, but not at 4,500 m. The enhanced pulmonary vasoconstriction after NO inhibition at basal and hypoxic conditions suggests a modulating role of NOS bioactivity in the pulmonary circulation and that augmented endothelial NOS plays a counterregulatory role in the pulmonary vasoconstrictor response to acute hypoxia in high-altitude adapted Tibetan sheep.

The potent inducible nitric oxide synthase inhibitor ONO-1714 inhibits neuronal NOS and exerts antinociception in rats

We evaluated if ONO-1714, known as an inducible nitric oxide synthase (iNOS) inhibitor, could inhibit neuronal NOS (nNOS) and exert antinociception. ONO-1714 potently inhibited both crude rat cerebellar NOS and recombinant human nNOS in vitro. Systemic ONO-1714 at 1-10 mg/kg suppressed carrageenan-induced thermal hyperalgesia in rats, an effect being equivalent to the antinociception caused by L-NAME or 7-nitroindazole at 25 mg/kg. The same doses of ONO-1714 also caused hypertension. Intrathecal (i.t.) ONO-1714 potently reduced the hyperalgesia, the effective dose range (0.2-0.6 microg/rat) being much lower than the antinociceptive dose (150 microg/rat) of i.t. L-NAME. Thus, ONO-1714 is considered a potent inhibitor of nNOS in addition to iNOS. The distinct relative antinociceptive activities of systemic and i.t. ONO-1714 are attributable to its possible poor blood-brain barrier permeability.