Failure of L-NAME to cause inhibition of nitric oxide synthesis: role of inducible nitric oxide synthase

The role of nitric oxide and neuroendocrine system in pain generation

Previous studies have indicated a complex interplay between the nitric oxide (NO) pain signaling pathways and hormonal signaling pathways in the body. This article delineates the role of nitric oxide signaling in neuropathic and inflammatory pain generation and subsequently discusses how the neuroendocrine system is involved in pain generation. Hormonal systems including the hypothalamic-pituitary axis (HPA) generation of cortisol, the renin-angiotensin-aldosterone system, calcitonin, melatonin, and sex hormones could potentially contribute to the generation of nitric oxide involved in the sensation of pain. Further research is necessary to clarify this relationship and may reveal therapeutic targets involving NO signaling that alleviate neuropathic and inflammatory pain.

Impact of ovary-intact menopause in a mouse model of heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) afflicts over half of all patients with heart failure and is a debilitating and fatal syndrome affecting postmenopausal women more than any other demographic. This bias toward older females calls into question the significance of menopause in the development of HFpEF, but this question has not been probed in detail. In this study, we report the first investigation into the impact of ovary-intact menopause in the context of HFpEF. To replicate the human condition as faithfully as possible, vinylcyclohexene dioxide (VCD) was used to accelerate ovarian failure (AOF) in female mice while leaving the ovaries intact. HFpEF was established with a mouse model that involves two stressors typical in humans: a high-fat diet and hypertension induced from the nitric oxide synthase inhibitor NG-nitro-l-arginine methyl ester (l-NAME). In young female mice, AOF or HFpEF-associated stressors independently induced abnormal myocardial strain indicative of early subclinical systolic and diastolic cardiac dysfunction. HFpEF but not AOF was associated with elevations in systolic blood pressure. Increased myocyte size and reduced myocardial microvascular density were not observed in any group. Also, a broad panel of measurements that included echocardiography, invasive pressure measurements, histology, and serum hormones revealed no interaction between AOF and HFpEF. Interestingly, AOF did evoke a higher density of infiltrating cardiac immune cells in both healthy and HFpEF mice, suggestive of proinflammatory effects. In contrast to young mice, middle-aged "old" mice did not exhibit cardiac dysfunction from estrogen deprivation alone or from HFpEF-related stressors.NEW & NOTEWORTHY This is the first preclinical study to examine the impact of ovary-intact menopause [accelerated ovarian failure (AOF)] on HFpEF. Echocardiography of young female mice revealed early evidence of diastolic and systolic cardiac dysfunction apparent only on strain imaging in HFpEF only, AOF only, or the combination. Surprisingly, AOF did not exacerbate the HFpEF phenotype. Results in middle-aged "old" females also showed no interaction between HFpEF and AOF and, importantly, no cardiovascular impact from HFpEF or AOF.

Selective gene expression profiling contributes to a better understanding of the molecular pathways underlying the histological changes observed after RHMVL

Background

In previous studies, five vasoactive drugs were investigated for their effect on the recovery process after extended liver resection without observing relevant improvements. We hypothesized that an analysis of gene expression could help to identify potentially druggable pathways and could support the selection of promising drug candidates.

Methods

Liver samples obtained from rats after combined 70% partial hepatectomy and right median hepatic vein ligation (n = 6/group) sacrificed at 0 h, 24 h, 48 h, and 7days were selected for this study. Liver samples were collected from differentially perfused regions of the median lobe (obstruction-zone, border-zone, normal-zone). Gene expression profiling of marker genes regulating hepatic hemodynamics, vascular remodeling, and liver regeneration was performed with microfluidic chips. We used 3 technical replicates from each sample. Raw data were normalized using LEMming and differentially expressed genes were identified using LIMMA.

Results

The strongest differences were found in obstruction-zone at 24 h and 48 h postoperatively compared to all other groups. mRNA expression of marker genes from hepatic hemodynamics pathways (iNOS,Ptgs2,Edn1) was most upregulated.

Conclusion

These upregulated genes suggest a strong vasoconstrictive effect promoting arterial hypoperfusion in the obstruction-zone. Reducing iNOS expression using selective iNOS inhibitors seems to be a promising approach to promote vasodilation and liver regeneration.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-022-01364-z.

Modulation of peroxynitrite produced via mitochondrial nitric oxide synthesis during Ca2+ and succinate-induced oxidative stress in cardiac isolated mitochondria

We hypothesized that NO^• is generated in isolated cardiac mitochondria as the source for ONOO^- production during oxidative stress. We monitored generation of ONOO^- from guinea pig isolated cardiac mitochondria subjected to excess Ca²⁺ uptake before adding succinate and determined if ONOO^- production was dependent on a nitric oxide synthase (NOS) located in cardiac mitochondria (mtNOS). Mitochondria were suspended in experimental buffer at pH 7.15, and treated with CaCl₂ and then the complex II substrate Na-succinate, followed by menadione, a quinone redox cycler, to generate O₂^•-. L-tyrosine was added to the mitochondrial suspension where it is oxidized by ONOO^- to form dityrosine (diTyr) in proportion to the ONOO^- present. We found that exposing mitochondria to excess CaCl₂ before succinate resulted in an increase in diTyr and amplex red fluorescence (H₂O₂) signals, indicating that mitochondrial oxidant stress, induced by elevated mtCa²⁺ and succinate, increased mitochondrial ONOO^- production via NO^• and O₂^•-. Changes in mitochondrial ONOO^- production dependent on NOS were evidenced by using NOS inhibitors L-NAME/L-NNA, TEMPOL, a superoxide dismutase (SOD) mimetic, and PTIO, a potent global NO^• scavenger. L-NAME and L-NNA decreased succinate and menadione-mediated ONOO^- production, PTIO decreased production of ONOO^-, and TEMPOL decreased ONOO^- levels by converting more O₂^•- to H₂O₂. Electron microscopy showed immuno-gold labeled iNOS and nNOS in mitochondria isolated from cardiomyocytes and heart tissue. Western blots demonstrated iNOS and nNOS bands in total heart tissue, bands for both iNOS and nNOS in β-tubulin-free non-purified (crude) mitochondrial preparations, and a prominent iNOS band, but no nNOS band, in purified (Golgi and ER-free) mitochondria. Prior treatment of guinea pigs with lipopolysacharride (LPS) enhanced expression of iNOS in liver mitochondria but not in heart mitochondria. Our results indicate that release of ONOO^- into the buffer is dependent both on O₂^•- released from mitochondria and NO^• derived from a mtCa²⁺-inducible nNOS isoform, possibly attached to mitochondria, and a mtNOS isoform like iNOS that is non-inducible.

Calmodulin inhibition as a mode of action of antifungal imidazole pharmaceuticals in non-target organisms

To improve assessment of risks associated with pharmaceutical contamination of the environment, it is crucial to understand effects and mode of action of drugs in non-target species. The evidence is accumulating that species with well-conserved drug targets are prone to be at risk when exposed to pharmaceuticals. An interesting group of pharmaceuticals released into the environment is imidazoles, antifungal agents with inhibition of ergosterol synthesis as a primary mode of action in fungi. However, imidazoles have also been identified as competitive antagonists of calmodulin (CaM), a calcium-binding protein with phylogenetically conserved structure and function. Therefore, imidazoles would act as CaM inhibitors in various organisms, including those with limited capacity to synthesize sterols, such as arthropods. We hypothesized that effects observed in crustaceans exposed to imidazoles are related to the CaM inhibition and CaM-dependent nitric oxide (NO) synthesis. To test this hypothesis, we measured (i) CaM levels and its gene expression, (ii) NO accumulation and (iii) gene expression of NO synthase (NOS1 and NOS2), in the cladoceran Daphnia magna exposed to miconazole, a model imidazole drug. Whereas significantly increased CaM gene expression and its cellular allocation were observed, supporting the hypothesized mode of action, no changes occurred in either NO synthase expression or NO levels in the exposed animals. These findings suggest that CaM inhibition by miconazole leads to protein overexpression that compensates for the loss in the protein activity, with no measurable downstream effects on NO pathways. The inhibition of CaM in D. magna may have implications for effect assessment of exposure to mixtures of imidazoles in aquatic non-target species.

Affective dimensions of pain and region -specific involvement of nitric oxide in the development of empathic hyperalgesia

Empathy for pain depends on the ability to feel, recognize, comprehend and share painful emotional conditions of others. In this study, we investigated the role of NO in a rat model of empathic pain. Pain was socially transferred from the sibling demonstrator (SD) who experienced five formalin injection to the naïve sibling observer (SO) through observation. SO rats received L-NAME (a nonspecific NO synthase inhibitor) or L-arginine (a precursor of NO) prior to observing the SD. Nociception, and concentrations of NO metabolites (NOx) in the serum, left and right hippocampus, prefrontal cortex, and cerebellum were evaluated. Nociceptive responses were significantly increased in the pain-observing groups. NOx levels measured 24 h after the last pain observation using the Griess method, were indicative of NOx concentration decreases and increases in the left hippocampus and cerebellum, respectively. There was an increase in tissue concentration of NOx in cerebellum and prefrontal cortex in both pain and observer groups 7 days after the fifth formalin injection. Our results suggest that NO is involved in development of empathic hyperalgesia, and observation of sibling’s pain can change NO metabolites in different brain regions in observer rats.

End o' the line revisited: moving on from nitric oxide to CGRP

When endothelin-1(ET-1) was discovered it was hailed as the prototypical endothelium-derived contracting factor (EDCF). However, over the years little evidence emerged convincingly demonstrating that the peptide actually contributes to moment-to-moment changes in vascular tone elicited by endothelial cells. This has been attributed to the profound inhibitory effect of nitric oxide (NO) on both the production (by the endothelium) and the action (on vascular smooth muscle) of ET-1. Hence, the peptide is likely to initiate acute changes in vascular diameter only under extreme conditions of endothelial dysfunction when the NO bioavailability is considerably reduced if not absent. The present essay discusses whether or not this concept should be revised, in particular in view of the potent inhibitory effect exerted by calcitonin gene related peptide (CGRP) released from sensorimotor nerves on vasoconstrictor responses to ET-1.

Involvement of inducible nitric oxide synthase in radiation-induced vascular endothelial damage

The use of radiation therapy has been linked to an increased risk of cardiovascular disease. To understand the mechanisms underlying radiation-induced vascular dysfunction, we employed two models. First, we examined the effect of X-ray irradiation on vasodilation in rabbit carotid arteries. Carotid arterial rings were irradiated with 8 or 16 Gy using in vivo and ex vivo methods. We measured the effect of acetylcholine-induced relaxation after phenylephrine-induced contraction on the rings. In irradiated carotid arteries, vasodilation was significantly attenuated by both irradiation methods. The relaxation response was completely blocked by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, a potent inhibitor of soluble guanylate cyclase. Residual relaxation persisted after treatment with L-N(ω)-nitroarginine (L-NA), a non-specific inhibitor of nitric oxide synthase (NOS), but disappeared following the addition of aminoguanidine (AG), a selective inhibitor of inducible NOS (iNOS). The relaxation response was also affected by tetraethylammonium, an inhibitor of endothelium-derived hyperpolarizing factor activity. In the second model, we investigated the biochemical events of nitrosative stress in human umbilical-vein endothelial cells (HUVECs). We measured iNOS and nitrotyrosine expression in HUVECs exposed to a dose of 4 Gy. The expression of iNOS and nitrotyrosine was greater in irradiated HUVECs than in untreated controls. Pretreatment with AG, L-N(6)-(1-iminoethyl) lysine hydrochloride (a selective inhibitor of iNOS), and L-NA attenuated nitrosative stress. While a selective target of radiation-induced vascular endothelial damage was not definitely determined, these results suggest that NO generated from iNOS could contribute to vasorelaxation. These studies highlight a potential role of iNOS inhibitors in ameliorating radiation-induced vascular endothelial damage.

Late-life enalapril administration induces nitric oxide-dependent and independent metabolic adaptations in the rat skeletal muscle

Recently, we showed that administration of the angiotensin-converting enzyme inhibitor enalapril to aged rats attenuated muscle strength decline and mitigated apoptosis in the gastrocnemius muscle. The aim of the present study was to investigate possible mechanisms underlying the muscle-protective effects of enalapril. We also sought to discern the effects of enalapril mediated by nitric oxide (NO) from those independent of this signaling molecule. Eighty-seven male Fischer 344 × Brown Norway rats were randomly assigned to receive enalapril (n = 23), the NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME; n = 22), enalapril + L-NAME (n = 19), or placebo (n = 23) from 24 to 27 months of age. Experiments were performed on the tibialis anterior muscle. Total NOS activity and the expression of neuronal, endothelial, and inducible NOS isoforms (nNOS, eNOS, and iNOS) were determined to investigate the effects of enalapril on NO signaling. Transcript levels of tumor necrosis factor-alpha (TNF-α) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) were assessed to explore actions of enalapril on inflammation and mitochondrial biogenesis, respectively. Protein expression of energy-sensing and insulin signaling mediators, including protein kinase B (Akt-1), phosphorylated Akt-1 (pAkt-1), mammalian target of rapamycin (mTOR), AMP-activated protein kinase subunit alpha (AMPKα), phosphorylated AMPKα (pAMPKα), and the glucose transporter GLUT-4, was also determined. Finally, the generation of hydrogen peroxide (H2O2) was quantified in subsarcolemmal (SSM) and intermyofibrillar (IFM) mitochondria. Enalapril increased total NOS activity, which was prevented by L-NAME co-administration. eNOS protein content was enhanced by enalapril, but not by enalapril + L-NAME. Gene expression of iNOS was down-regulated by enalapril either alone or in combination with L-NAME. In contrast, protein levels of nNOS were unaltered by treatments. The mRNA abundance of TNF-α was reduced by enalapril relative to placebo, with no differences among any other group. PCG-1α gene expression was unaffected by enalapril and lowered by enalapril + L-NAME. No differences in protein expression of Akt-1, pAkt-1, AMPKα, pAMPKα, or GLUT-4 were detected among groups. However, mTOR protein levels were increased by enalapril compared with placebo. Finally, all treatment groups displayed reduced SSM, but not IFM H2O2 production relative to placebo. Our data indicate that enalapril induces a number of metabolic adaptations in aged skeletal muscle. These effects result from the concerted modulation of NO and angiotensin II signaling, rather than from a dichotomous action of enalapril on the two pathways. Muscle protection by enalapril administered late in life appears to be primarily mediated by mitigation of oxidative stress and pro-inflammatory signaling.

Chronic inhibition of nitric oxide synthase activity by NG-nitro-L-arginine induces nitric oxide synthase expression in the developing rat cerebellum

Studies on chronic inhibition of nitric oxide synthase (NOS) in the CNS suggest a plastic change in nitric oxide (NO) synthesis in areas related to motor control, which might protect the animal from the functional and behavioral consequences of NO deficiency. In the present study, the acute and chronic effect of the substrate analogue inhibitor N(G)-nitro-l-arginine (l-NNA) was examined on NO production, NO-sensitive cyclic guanosine monophosphate (cGMP) levels and the expression of NOS isoforms in the developing rat cerebellum. Acute intraperitoneal administration of the inhibitor (5-200mg/kg) to 21-day-old rats reduced NOS activity and NO concentration dose dependently by 70-90% and the tissue cGMP level by 60-80%. By contrast, chronic application of l-NNA between postnatal days 4-21 diminished the total NOS activity and NO concentration only by 30%, and the tissue cGMP level by 10-50%. Chronic treatment of 10mg/kg l-NNA induced neuronal (n)NOS expression in granule cells, as revealed by in situ hybridization, NADPH-diaphorase histochemistry and Western-blot, but it had no significant influence on tissue cGMP level or on layer formation of the cerebellum. However, a higher concentration (50mg/kg) of l-NNA decreased the intensity of the NADPH-diaphorase reaction in granule cells, significantly reduced cGMP production, and retarded layer formation and induced inducible (i)NOS expression & activity in glial cells. Treatments did not affect endothelial (e)NOS expression. The administration of the biologically inactive isomer D-NNA (50mg/kg) or saline was ineffective. The present findings suggest the existence of a concentration-dependent compensatory mechanism against experimentally-induced cronich inhibition of NOS, including nNOS or iNOS up-regulation, which might maintain a steady-state NO level in the developing cerebellum.

Nitric oxide in asthma physiopathology

Asthma is a chronic inflammatory airway disease characterized by allergen-induced airway hyperresponsiveness, airway inflammation, and remodeling. Nitric oxide (NO) derived from constitutive and inducible enzymes affects many aspects of asthma physiopathology. Animal in vivo studies have indicated that inhibition of iNOS may play a central role in the modulation of these features, particularly extracellular matrix remodeling. Additionally, increases in iNOS-derived NO, observed in asthmatic patients, may lead to an increase in peroxynitrite and an imbalance of oxidant and antioxidant pathways. In addition, endogenous nitric oxide produced by constitutive enzymes may protect against the remodeling of the lung. Therefore, nitric oxide donors and/or iNOS inhibitors may have therapeutic potential in asthma treatment and can also be used with corticosteroids to counteract airway remodeling. This paper focuses on the pathophysiological role of nitric oxide, mainly derived from inducible isoforms, in the various pathologic mechanisms of allergic asthma and the importance of nitric oxide and/or arginase inhibitors in asthma treatment.

Expression patterns of endothelial and inducible nitric oxide isoforms in the porcine umbilical cord

Stable fetal-placental blood pressure and flow are extremely important in fetal growth and development. Uncontrolled and long-standing increased or decreased vascular blood pressure in the umbilical cord (UC) affects hyperaemia or ischaemia and consequently causes fetal death. Nitric oxide (NO) is one of the most active factors controlling blood flow through relaxation of the vascular smooth muscle. In this study, we investigated endothelial (eNOS) and inducible (iNOS) nitric oxide synthase expression and NADPH-diaphorase activity (NADPH-d) in the porcine UC at various stages of pregnancy. The UCs were collected from pigs on days 40, 60, 75 and 90 of pregnancy and postpartum. Western blot analysis as well as immunohistochemical staining revealed protein presence for eNOS and iNOS in the UC of the pig. The eNOS expression was maintained at a significantly higher level in all analysed days of pregnancy when compared with postnatal stage. Additionally, a significant protein increase for eNOS was observed in a periplacental part of UC on day 90. There were no obvious differences in iNOS protein level in UC samples derived from different stages of pregnancy. NADPH-diaphorase histochemical activity was correlated with NOS immunoreactivity during all analysed days of pregnancy. These results suggest that NOS isoforms are responsible for regulation of blood circulation in UC and immune responses.

Guinea pig model of Mycobacterium tuberculosis latent/dormant infection

Although guinea pigs are considered one of the best animal models of tuberculosis, little data exist describing latent or dormant tuberculosis infection in these animals. Here we address this issue using a streptomycin auxotrophic mutant of Mycobacterium tuberculosis. This mutant grows unimpaired in the presence of streptomycin but in its absence shifts to latency/dormancy (lack growth and over-expression of alpha-crystallin). To establish infection animals are inoculated with the mutant followed by daily administration of streptomycin (three weeks), which allows initial microbial multiplication in the animal's tissues. Withdrawal of streptomycin establishes latency/dormancy and few viable organisms are recovered from the animals' lungs and spleen six months later. During the infectious process guinea pigs steadily gained weight and presented no clinical signs (scuff fur and lethargy) of disease. Histopathology of organs mimicked tuberculous lesions in humans and PBMC from infected animals strongly responded to stimulation with PPD. Finally, tuberculin skin test (a hallmark of latent infection diagnosis) performed in infected animals was strongly positive (>or=15 mm induration). These results point to an interesting and reliable model of latent/dormant tuberculosis infection in guinea pigs.

The estrogen effects on endothelial repair and mitogen-activated protein kinase activation are abolished in endothelial nitric-oxide (NO) synthase knockout mice, but not by NO synthase inhibition by N-nitro-L-arginine methyl ester

We have previously shown that estrogen exerts a vasoprotective effect by accelerating reendothelialization after perivascular artery injury through activation of the estrogen receptor alpha. Because 17beta-estradiol (E2) is known to increase the bioavailability of nitric oxide, in this study, we used the same perivascular model to characterize the role of the endothelial nitric oxide synthase (eNOS) pathway in reendothelialization. Surprisingly, we found that the stimulatory effect of E2 on reendothelialization was not altered following pharmacological inhibition of nitric-oxide synthase enzymatic activity by N-nitro-L-arginine methyl ester, whereas it was abolished in eNOS-deficient (eNOS-/-) mice. This discrepancy between eNOS gene inactivation and the pharmacological inhibition of eNOS was confirmed in a classical model of endovascular injury. When assessing the involvement of eNOS in short-term membrane-associated signaling events induced by E2, we found that E2 stimulated phosphorylation of extracellular signal-regulated kinase 1/2 in isolated perfused carotid arteries from wild-type mice in the absence or presence of N-nitro-l-arginine methyl ester, whereas this stimulation was abolished in carotid arteries from eNOS-/- mice. Similar results were obtained in primary cultures of mouse aortic endothelial cells. These data reveal an original and unexpected role of eNOS, in which its presence but not its enzymatic activity appears to be a determinant for estrogen signaling in the endothelium. The consequences of this novel function of eNOS with respect to vascular diseases should be explored.

Inhibition of inducible nitric oxide synthase enhances anti-tumour immune responses in rats immunized with IFN-gamma-secreting glioma cells

Interferon gamma (IFN-gamma) has successfully been used in immunotherapy of different experimental tumours. Mechanistically, IFN-gamma has extensive effects on the immune system including release of nitric oxide (NO) by upregulation of the inducible nitric oxide synthase (iNOS). NO has putative immunosuppressive effects but could also play a role in killing of tumour cells. Therefore, the aim of the present study was to clarify whether inhibition of iNOS in rats immunized with glioma cells (N32) producing IFN-gamma (N32-IFN-gamma), could enhance the anti-tumour immune response. Initially, both a selective iNOS, l-N(6)-(1-Iminoethyl)-l-lysine (l-NIL), and non-selective, N-nitro-l-arginine methyl ester (l-NAME), inhibitor of NOS were tested in vitro. After polyclonal stimulation with LPS and SEA, both l-NIL and l-NAME enhanced proliferation and production of IFN-gamma from activated rat splenocytes and this effect was inversely correlated to the production of NO. However, l-NIL had a broader window of efficacy and a lower minimal effective dose. When rats were immunized with N32-IFN-gamma, and administered NOS inhibitors by intraperitoneal (i.p.) mini-osmotic pumps, only splenocytes of rats treated with l-NIL, but not l-NAME, displayed an enhanced proliferation and production of IFN-gamma when re-stimulated with N32 tumour cells. Based on these findings, l-NIL was administered concurrently with N32-IFN-gamma cells to rats with intracerebral (i.c.) tumours resulting in a prolonged survival. These results show that inhibition of iNOS can enhance an IFN-gamma-based immunotherapy of experimental i.c. tumours implying that NO released after immunization has mainly immunosuppressive net effects.

Endostatin/Collagen XVIII Accumulates in Patients with Traumatic Brain Injury

In patients with traumatic brain injury (TBI), hypoperfusion contributes to ongoing and expanding areas of neuronal damage long after the initial trauma has ceased. In order to evaluate whether the antiangiogenic protein endostatin may play a role in this process, we analyzed its spatial distribution in brains of 18 patients with TBI. We observed an increase of endostatin/collagen XVIII(+) macrophages/microglial cells but not astrocytes up to day 14 and a consequent decrease to day 16 post-TBI. In addition, paracellular endostatin/collagen XVIII deposits were detected. In vitro experiments revealed that microglial endostatin release is induced predominantly by hypoxia and, to a lesser extent, by reactive oxygen intermediates. Common NO synthase inhibitor pharmacotherapy with aminoguanidine and L-NAME completely abolished endostatin release from microglial cells, raising hopes of altering endostatin release in vivo.

Effects of nitric oxide synthases in chronic allergic airway inflammation and remodeling

The precise role of each nitric oxide (NO) synthase (NOS) isoform in the pathobiology of asthma is not well established. Our objective was to investigate the contribution of constitutive NO synthase (cNOS) and inducible NOS (iNOS) isoforms to lung mechanics and inflammatory and remodeling responses in an experimental model of chronic allergic pulmonary inflammation. Guinea pigs were submitted to seven ovalbumin exposures with increasing doses (1 approximately 5 mg/ml) for 4 wk. The animals received either chronic L-NAME (N-nitro-L-arginine methyl ester, in drinking water) or 1,400 W (iNOS-specific inhibitor, intraperitoneal) treatments. At 72 h after the seventh inhalation of ovalbumin solution, animals were anesthetized, mechanically ventilated, exhaled NO was collected, and lung mechanical responses were evaluated before and after antigen challenge. Both L-NAME and 1,400 W treatments increased baseline resistance and decreased elastance of the respiratory system in nonsensitized animals. After challenge, L-NAME increased resistance of the respiratory system and collagen deposition on airways, and decreased peribronchial edema and mononuclear cell recruitment. Administration of 1,400 W reduced resistance of the respiratory system response, eosinophilic and mononuclear cell recruitment, and collagen and elastic fibers content in airways. L-NAME treatment reduced both iNOS- and neuronal NOS-positive eosinophils, and 1,400 W diminished only the number of eosinophils expressing iNOS. In this experimental model, inhibition of NOS-derived NO by L-NAME treatment amplifies bronchoconstriction and increases collagen deposition. However, blockage of only iNOS attenuates bronchoconstriction and inflammatory and remodeling processes.

The nitric oxide-cGMP signaling pathway differentially regulates presynaptic structural plasticity in cone and rod cells

Although abundant structural plasticity in the form of axonal retraction, neurite extension, and formation of presynaptic varicosities is displayed by photoreceptors after retinal detachment and during genetic and age-related retinal degeneration, the mechanisms involved are mostly unknown. We demonstrated recently that Ca(2+) influx through cGMP-gated channels in cones and voltage-gated L-type channels in rods is required for neurite extension in vitro (Zhang and Townes-Anderson, 2002). Here, we report that the nitric oxide (NO)-cGMP signaling pathway is active in photoreceptors and that its manipulation differentially regulates the structural plasticity of cone and rod cells. The NO receptor soluble guanylyl cyclase (sGC) was detected immunocytochemically in both cone and rod cells. Stimulation of sGC increased cGMP production in retinal cultures. In cone cells, quantitative analysis showed that NO or cGMP stimulated neuritic sprouting; this stimulatory effect was dependent on both Ca2+ influx through cGMP-gated channels and phosphorylation by protein kinase G (PKG). At the highest levels of cGMP, however, cone outgrowth was no longer increased. In rod photoreceptors, NO or cGMP consistently inhibited neuritic growth in a dose-dependent manner; this inhibitory effect required PKG. When NO-cGMP signaling was inhibited, changes in the neuritic development of cone and rod cells were also observed but in the opposite direction. These results expand the role of cGMP in axonal activity to adult neuritogenesis and suggest an explanation for the neurite sprouting observed in an autosomal recessive form of retinitis pigmentosa that is characterized by high cGMP levels in photoreceptor layers.

Endothelial endostatin release is induced by general cell stress and modulated by the nitric oxide/cGMP pathway

Endostatin is a 20 kDa carboxyl-terminal fragment of collagen XVIII that, when added exogenously, inhibits endothelial proliferation and migration in vitro and angiogenesis and tumor growth in vivo. Previous results showed endostatin/collagen XVIII labeling in few endothelial cells in human glioblastoma multiforme. We have now observed constitutive release of endostatin from one of four endothelial cell lines. Induction of endostatin release was observed after H2O2, an in vitro model of cell stress, CoCl2, a model of hypoxia, and by IFN-gamma challenge. Endostatin expression and release was reduced by the nitric oxide synthase inhibitors aminoguanidine and L-NAME and induced by the NO synthase-independent NO donors sodium nitroprusside (SNP) and spermine-NONO-ate. SNP-mediated endostatin induction was abrogated by the soluble guanylate cyclase inhibitor 1H-(1.2.4) oxadiazolo (4,3-A) quinoxalin-1-one. Adenoviral endostatin transduction resulted in the release of endostatin from endothelial cells and in down-regulation of iNOS (NOS2) and eNOS (NOS3), and surprisingly in a 10% induction of PCNA. These results describe the modulation of endostatin release by the NO signaling cascade and provide important new pharmacological information for the systemic induction of endogenous endostatin release by common NO donor pharmacotherapy.

Nitric oxide mediates apoptosis through formation of peroxynitrite and Fas/Fas-ligand interactions in experimental autoimmune uveitis

Conflicting reports have led to the description of nitric oxide as a "double-edged sword" in animal models of autoimmunity. In this study we show that tissue damage within the eye during experimental autoimmune uveoretinitis correlates with peroxynitrite formation in infiltrating monocytes/macrophages within the outer retina together with extensive photoreceptor apoptosis and apoptosis of Fas(+) T cells within the retina. Inducible nitric oxide synthase (NOS2) expression was primarily restricted to infiltrating monocytes/macrophages in the outer retina and photoreceptor rod outer segments (target tissue), but despite showing evidence of lipid peroxidation, myeloid cells remained resistant to apoptosis. The protective effect of the NOS inhibitor N(G)-nitro-L-arginine methyl ester could be attributed to dramatically reduced photoreceptor apoptosis, absence of nitrotyrosine formation, and reduced NOS2 protein expression. However, inhibition of NOS by N(G)-nitro-L-arginine methyl ester was accompanied by a sparing of CD3(+) and CD2(+) T cells despite continued expression of Fas and Fas ligand, thus compromising functional inactivation of T cells in the target tissue. These data suggests that in addition to contributing to tissue damage in the retina through generation of reactive oxygen species, nitric oxide also seems to be required for activation-induced cell death and elimination of T cells in the retina.

Dexamethasone worsens nitric oxide inhibition-induced hypertension and renal dysfunction

Chronic nitric oxide (NO) inhibition with Nomega-nitro-L-arginine methyl ester (L-NAME) has previously been reported to produce systemic hypertension, renal vasoconstriction, and renal damage. In this study we investigated whether a compensatory restoration of NO synthesis occurs in chronic L-NAME hypertension and whether chronic treatment with dexamethasone (Dex) (which inhibits inducible NO synthase [iNOS]) can influence the course of the hypertension. We found that in the conscious chronically L-NAME-treated (approximately =10 mg/kg/24 h) hypertensive rats, acute systemic NOS inhibition elicited a further increase in blood pressure (BP), indicating partial restoration of NO production. Chronic Dex in a dose previously reported to inhibit iNOS (5 microg/24 h), amplified the hypertension (within 2 days), renal vasoconstriction, and reduction in glomerular filtration rate because of L-NAME. In contrast, chronic Dex alone had no effects on renal hemodynamics or BP during the first week, although by the end of week 2 a small increase in BP (approximately =10 mm Hg) was evident. These results show that BP continues to increase with chronic L-NAME despite partial restoration of NO production. An iNOS, which might be stimulated and escaped inhibition by L-NAME, may be responsible for the compensatory restoration of NO synthesis, serving to attenuate the development of hypertension and renal dysfunction.

Chronic blockade of NO synthase paradoxically increases islet NO production and modulates islet hormone release

Islet production of nitric oxide (NO) and CO in relation to islet hormone secretion was investigated in mice given the NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) in their drinking water. In these mice, the total islet NO production was paradoxically increased, reflecting induction of inducible NOS (iNOS) in background of reduced activity and immunoreactivity of constitutive NOS (cNOS). Unexpectedly, normal mice fasted for 24 h also displayed iNOS activity, which was further increased in L-NAME-drinking mice. Glucose-stimulated insulin secretion in vitro and in vivo was increased in fasted but unaffected in fed mice after L-NAME drinking. Glucagon secretion was increased in vitro. Control islets incubated with different NOS inhibitors at 20 mM glucose displayed increased insulin release and decreased cNOS activity. These NOS inhibitors potentiated glucose-stimulated insulin release also from islets of L-NAME-drinking mice. In contrast, glucagon release was suppressed. In islets from L-NAME-drinking mice, cyclic nucleotides were upregulated, and forskolin-stimulated hormone release, CO production, and heme oxygenase (HO)-2 expression increased. In conclusion, chronic NOS blockade evoked iNOS-derived NO production in pancreatic islets and elicited compensatory mechanisms against the inhibitory action of NO on glucose-stimulated insulin release by inducing upregulation of the islet cAMP and HO-CO systems.

Distinct regulation of nitric oxide and cyclic guanosine monophosphate production by steroid hormones in the rat uterus

It has previously been reported that uterine nitric oxide (NO) production is enhanced during rat pregnancy compared to non-pregnant, labouring or postpartum states. The present hypothesis is that these changes in uterine NO production during pregnancy are caused by the interplay of oestrogen and progesterone. It is further postulated that changes in cyclic guanosine monophosphate (cGMP) production closely follow the changes in uterine NO synthesis. To test these hypotheses a variety of hormonal regimens (17beta-oestradiol, progesterone and combinations) were applied to different rat models (prepubertal, non-pregnant intact and ovariectomized as well as pregnant rats). The production of nitric oxide (NO) as well as basal and in-vitro NO-stimulated cGMP tissue content were measured in parallel. NO production was measured by the accumulation of nitrites and nitrates in a 24 h incubation medium as analysed by Greiss reaction. cGMP content was measured by radioimmunoassay. Diethylenetriamine/NO (DETA/NO) was used as NO donor. NO production in the rat uterus was markedly increased by pregnancy compared to other physiological (prepubertal, or cycling dioestrus) and experimentally induced (OVX) states. In contrast, uterine cGMP was significantly decreased in pregnancy. Pregnancy also inhibited the elevation in uterine cGMP after in-vitro NO challenge. Chronic 17beta-oestradiol treatment in prepubertal and/or OVX models increased NO production and also mimicked the effect of pregnancy on cGMP. Administration of progesterone in prepubertal rats induced a parallel decrease in both uterine NO and cGMP. In conclusion, sex steroid hormones distinctly regulate uterine NO and cGMP production depending upon the dose and regimen used, as well as the animal's reproductive state.

L-NAME causes antinociception by stimulation of the arginine-NO-cGMP pathway

NG-nitro-L-arginine methyl ester (L-NAME) has been used extensively as a paradigmatic inhibitor of NO synthase and has been shown to cause antinociception in several experimental models. We describe here how L-NAME produced a dose-dependent antinociceptive effect when injected intraperitoneally in the mouse after acetic acid induced writhings, or intraplantarly in the rat paw pressure hyperalgesia induced by carrageenin or prostaglandin E2. In contrast another NO synthase inhibitor, NG-monomethyl-L-arginine (L-NMMA), had no significant effect per se but inhibited L-NAME systemic induced antinociception in mice and local induced antinociception in the rat paw hyperalgesia test. D-NAME had no antinociceptive effect upon carrageenin-induced hyperalgesia. Pretreatment of the paws with two inhibitors of guanylate cyclase, methylene blue (MB) and 1H-:[1,2,4]-oxadiazolo-:[4,3-a] quinoxalin-1-one (ODQ) abolished the antinociceptive effect of L-NAME. L-Arginine and the cGMP phosphodiesterase inhibitor, MY 5445 significantly enhanced the L-NAME antinociceptive effect. The central antinociceptive effect of L-NAME was blocked by co-administration of L-NMMA, ODQ and MB. The present series of experiments shows that L-NAME, but not L-NMMA, has an antinociceptive effect. It can be suggested that L-NAME causes the antinociceptive effect by stimulation of the arginine/ NO/ cGMP pathway, since the antinociceptive effect of L-NAME can be antagonized by L-NMMA and abolished by the guanylate cyclase inhibitors (MB and ODQ). In addition, the NO synthase substrate, L-arginine and the cGMP phosphodiesterase inhibitor, MY5445 were seen to potentiate the effects of L-NAME. Thus, L-NAME used alone, has limitations as a specific inhibitor of the arginine-NO-cGMP pathway and may therefore be a poor pharmacological tool for use in characterising participation in pathophysiological processes.

Expression of inducible nitric oxide synthase in tumors in relation with their regression induced by lipid A in rats

It is well documented that nitric oxide (NO) is an effector molecule of macrophage-mediated tumor cell toxicity in vitro; however, little is known about the role of NO in the antitumor immune response in vivo. We have developed a treatment protocol using lipid A. We have investigated the effects of lipid A on inducible NO synthase (NOS II) expression and evolution inside tumors during the course of treatment. Lipid A (OM-174) treatment induced tumor regression in rats bearing established colon tumors. Furthermore, NO was synthesized and secreted inside the tumors of lipid A-treated rats, as demonstrated by the increase of NOS II mRNA and NOS II content in the tumors, as well as of NOS II activity and NO production. During treatment, NOS II was localized in tumor cells only. Lipid A had no direct effect on tumor cells in vitro, while the combination of interferon gamma (IFN-gamma) plus interleukin-1 beta (IL-1beta) induced production of NO by tumor cells which was cytostatic. The content of IFN-gamma and IL-1beta in tumors was enhanced during lipid A treatment; this is in agreement with an indirect effect of lipid A in vivo via the IFN-gamma and IL-1beta pathways.

Diaphorase activity in sebaceous glands and related structures of the male red deer

The localisation of diaphorase was visualised by light microscopy using the dye nitro blue tetrazolium and NADPH as substrates. Under appropriate conditions, diaphorase reduces this dye to a dark blue insoluble formazan. The enzyme was located at very low activity in many tissue and glandular structures of the deer, but at very much higher activity in sebaceous glands in the dermal velvet of the antler and skin, and in additional sebaceous gland-related structures in the ear canal, prepuce and tail (scent) gland. Within sebaceous glands, activity was greatest in the outermost layers of the acini, but decreased as the cells progressed and differentiated centripetally. There was little or no difference between the staining observed when NADH was used as a substrate, compared to NADPH. There was generalised staining (usually light) for glucose-6-phosphate dehydrogenase, lactate dehydrogenase, and glycerol-3-phosphate dehydrogenase. However, this staining was not specifically localised to sebaceous glands and related structures, showing that the observed activity in these structures was due to a diaphorase that was distinct from any of the dehydrogenase activities tested. The possible role of diaphorase in sebaceous development and secretion is discussed.

Nitric oxide synthase inhibitor attenuates intestinal damage induced by zinc deficiency in rats

A nitric oxide synthase (NOS) inhibitor, NG-nitro-L -arginine methyl ester (L-NAME), was given to zinc-deficient (ZD) rats to determine whether it prevents the intestinal damage usually observed under these conditions. Weanling male rats were given free access to a ZD diet (2 mg zinc/kg), whereas control rats including pair-fed (PF) and ad libitum consumption (AL) groups were given a zinc-supplemented (50.8 mg zinc/kg) diet for 4 wk. Half of the ZD rats received L-NAME (0.3 g/L in drinking water) for 3 wk starting at the wk 2 of the deficient period. Plasma zinc concentration in ZD rats was significantly lower (P < 0.05) than that of AL and PF rats. Administration of L-NAME did not alter this concentration. Intestinal zinc concentration did not differ among groups. However, metallothionein-1 (MT-1) mRNA level was significantly lower in the intestine of ZD rats than in AL or PF rats. Treatment of ZD rats with L-NAME did not affect this level. Intestinal microvascular permeability evaluated by Evans blue showed significantly higher extravasation in ZD rats than in AL rats, whereas L-NAME administration inhibited the extravasation. Expression of inducible NOS mRNA was observed in intestine of ZD but not of AL or PF rats, and there was no significant difference between ZD rats, regardless of L-NAME treatment. The activity ratio of inducible NOS to total NOS in ZD rats not receiving L-NAME was significantly higher than that in AL rats or ZD rats treated with L-NAME (P < 0.05). The number of apoptotic-positive and goblet cells in intestinal villi was significantly higher in ZD rats compared with AL or PF rats. L-NAME administration in ZD rats reversed this effect. These results indicate that inhibition of NOS ameliorates zinc deficiency-induced intestinal damage in rats.

Evidence for the involvement of the nitric oxide-cGMP pathway in the antinociception of morphine in the formalin test

The effect of inhibition of nitric oxide synthesis and guanylate cyclase on the peripheral antinociceptive effect of morphine was assessed by using the formalin test in the rat. Saline, N(G)-monomethyl-L-arginine, a nitric oxide synthesis inhibitor (50 microg) and methylene blue, a guanylate cyclase inhibitor (500 microg), did not exhibit any antinociceptive activity. However, morphine (10 microg) produced a significant antinociceptive effect in phases 2a and 2b, which was reduced by pretreatment with either N(G)-monomethyl-L-arginine or methylene blue. These results suggest that the local administration of morphine induces antinociception by the activation of the L-arginine-nitric oxide-cGMP pathway.

Nitric oxide production by endothelial cells: comparison of three methods of quantification

Vascular endothelial cells have been found to produce a relaxant mediator, identified as nitric oxide (NO) and implicated in numerous physiological functions. Subsequently, there has been an intensive search for accurate and specific detection methods to measure biological NO production. In the present study, we compared three approaches to evaluate NO production, based respectively on the Griess reaction (that quantifies nitrites and nitrates after their reduction), on the hemoglobin reaction (that quantifies oxyhemoglobin to methemoglobin transformation by NO), and on the electrochemical NO detection with a porphyrinic micro-probe. Comparison was made both under standard conditions and biological conditions, through calibration curves and measurements of histamine-induced NO production by cultured human endothelial cells and its modulation by L-arginine and N(omega)-monomethyl-L-arginine. We demonstrated that these three methods differ in terms of sensitivity and selectivity. The hemoglobin reaction and nitrate measurements suffer from a lack of specificity. Nitrite determination by the Griess reaction was hardly suitable for kinetic studies but it remains useful for the evaluation of basal NO production. The electrochemical technique, although it does not allow measurement of basal NO production, is the only one to exhibit great sensitivity and specificity and to allow instantaneous and non destructive measurements. This study brings up the potential hazards and pitfalls that may be associated with the various methods.