Increased nitric oxide production in nasal epithelial cells from allergic patients--RT-PCR analysis and direct imaging by a fluorescence indicator: DAF-2 DA

Clinical Applications of Nasal Nitric Oxide in Allergic Rhinitis: A Review of the Literature

Allergic rhinitis, a common allergic disease affecting a significant number of individuals worldwide, is observed in 25% of children and 40% of adults, with its highest occurrence between the ages of 20 and 40. Its pathogenesis, like other allergic diseases, involves innate and adaptive immune responses, characterized by immunologic hypersensitivity to environmental substances. This response is mediated by type 2 immunity. Within type 2 allergic diseases, certain molecules have been identified as clinical biomarkers that contribute to diagnosis, prognosis, and therapy monitoring. Among these biomarkers, nitric oxide has shown to play a key role in various physiological and pathological processes, including neurotransmission, immunity, inflammation, regulation of mucus and cilia, inhibition of microorganisms, and tumor cell growth. Therefore, measurement of nasal nitric oxide has been proposed as an objective method for monitoring airway obstruction and inflammation in different settings (community, hospital, rehabilitation) and in various clinical conditions, including upper airways diseases of the nose and paranasal sinuses. The purpose of this review is to analyze the potential mechanisms contributing to the production of nasal nitric oxide in allergic rhinitis and other related health issues. Additionally, this review aims to identify potential implications for future research, treatment strategies, and long-term management of symptoms.

The Functional Diversity of Nitric Oxide Synthase Isoforms in Human Nose and Paranasal Sinuses: Contrasting Pathophysiological Aspects in Nasal Allergy and Chronic Rhinosinusitis

The human paranasal sinuses are the major source of intrinsic nitric oxide (NO) production in the human airway. NO plays several roles in the maintenance of physiological homeostasis and the regulation of airway inflammation through the expression of three NO synthase (NOS) isoforms. Measuring NO levels can contribute to the diagnosis and assessment of allergic rhinitis (AR) and chronic rhinosinusitis (CRS). In symptomatic AR patients, pro-inflammatory cytokines upregulate the expression of inducible NOS (iNOS) in the inferior turbinate. Excessive amounts of NO cause oxidative damage to cellular components, leading to the deposition of cytotoxic substances. CRS phenotype and endotype classifications have provided insights into modern treatment strategies. Analyses of the production of sinus NO and its metabolites revealed pathobiological diversity that can be exploited for useful biomarkers. Measuring nasal NO based on different NOS activities is a potent tool for specific interventions targeting molecular pathways underlying CRS endotype-specific inflammation. We provide a comprehensive review of the functional diversity of NOS isoforms in the human sinonasal system in relation to these two major nasal disorders' pathologies. The regulatory mechanisms of NOS expression associated with the substrate bioavailability indicate the involvement of both type 1 and type 2 immune responses.

The Role of Nasal Nitric Oxide and Anterior Active Rhinomanometry in the Diagnosis of Allergic Rhinitis and Asthma: A Message for Pediatric Clinical Practice

Background

Allergic rhinitis (AR) and asthma are two common atopic diseases, often associated with a common ethiopathogenesis characterized by a Th2 inflammatory response with the release of many biomarkers, such as nitric oxide (NO).

Purpose

To evaluate and compare inflammatory (nFeNO and eFeNO) and functional (mNF and FEV1) parameters in AR children with or without asthma in comparison to controls. Secondly, we aimed to identify nFeNO cut-off values and verify their reliability to predict the presence of rhinitis or asthma alone or in combination.

Patients and Methods

We enrolled 160 children (6-12 years of age) with AR and/or asthma divided into four groups: controls, AR, asthma, and AR + asthma. All children underwent the following inflammatory and functional measurements: nFeNO, eFeNO, mNF and FEV1.

Results

We observed that levels of nFeNO were extremely higher in children with AR and even more in those with AR + asthma in respect to controls. Notably, all the pathological conditions, especially AR + asthma, showed significantly lower values of mNF compared to healthy children. A negative correlation linked mNF and nFeNO. Then, we found eFeNO values significantly higher in all the pathological groups compared to controls, with major values of this marker in patients affected by asthma and AR + asthma, as well as FEV1 values significantly lower in all the disease groups, especially in children with asthma and AR+ asthma. ROC curve analysis showed that nFeNO was a great predictor for rhinitis alone or with asthma, revealing an accurate cut-off of 662 ppb.

Conclusion

nFeNO measurement is non-invasive, easy to perform, economic and a valuable test in case of AR alone or in association with asthma. Thus, it should be used in patients with rhinitis, together with anterior active rhinomanometry (AAR) to diagnose and estimate the degree of nasal obstruction but also in children with asthma to assess their nasal involvement and improve the therapeutic management.

Correlation between nasal nitric oxide and its metabolites, RANTES, IL-5 in allergic rhinitis

There have been two measurement methods for nasal nitric oxide (nNO): direct measurement of nNO and indirect measurement of NO metabolites or the NO synthase enzyme. The aim of this study is to investigate the difference in nNO between allergic rhinitis (AR) patients and the correlation of the direct measurement of nNO and indirect measurement of nNO metabolites, RANTES, and IL-5. Fifteen patients with AR, 15 patients with septal deviation as a control group were enrolled. We measured the nNO level using a chemiluminescence analyzer and the amount of NO metabolites, RANTES, and IL-5 in nasal lavage fluid using the ELISA method. Nasal NO levels were significantly higher in AR than the control (195.7 ± 39.6 vs 159.4 ± 25.8 ppb, P = 0.027). NO metabolites, IL-5, and RANTES levels were higher in AR, but there was no statistically significant difference. There was no significant correlation between nNO and nNO metabolites, RANTES, IL-5, and clinical parameters except for the olfactory test score in AR. There was a negative correlation between nNO and the olfactory test score in AR ( r = −0.590, P = 0.034). Nasal NO concentration increased in AR. However, nNO metabolites and IL-5, RANTES in nasal secretion did not show any correlation with nNO. Direct measurement of nNO could be a potentially useful biomarker of AR compared to indirect measurement of NO metabolites, cytokines, and chemokines in nasal secretion.

Clinical application of nasal nitric oxide measurement in allergic rhinitis: A systematic review and meta-analysis

BACKGROUND

Nasal nitric oxide (nNO) is considered a biomarker of nasal inflammation.

OBJECTIVE

To perform a systematic review with meta-analysis and meta-regressions on the association between nNO levels and allergic rhinitis (AR).

METHODS

PubMed, Web of Science, Scopus, and EMBASE databases were systematically searched. Differences between cases and controls were expressed as standardized mean differences (SMD) with 95% confidence intervals (CI).

RESULTS

Overall, 39 articles were included: 30 containing data on nNO measured by nasal aspiration (1881 patients with AR and 1337 controls) and 12 assessing nNO by nasal exhalation (525 patients with AR and 350 controls). Compared with controls, AR presented significantly higher nNO values both during nasal aspiration (SMD, 1.309; 95% CI, 0.841-1.777; P < .001) and nasal exhalation (SMD, 0.708; 95% CI, 0.303-1.114; P = .001). Sensitivity and subgroup analyses confirmed that the results for the evaluated outcomes were not affected by the presence of clinical confounding factors (asthma, nasal polyps, inhaled corticosteroids, smoking history), this being valid for both perennial and seasonal diseases during exposure to allergens. For the aspiration method, meta-regressions indicated that older age and a better pulmonary function were associated with a lower difference in nNO levels between patients with AR and controls, whereas an increasing aspiration flow was associated with a high effect size.

CONCLUSION

nNO levels are higher in AR, particularly when using high aspiration flows and in younger patients, who often perceive this condition as a source of disability. Further studies are needed to evaluate the usefulness of this biomarker for monitoring airway disorders and optimizing strategies in different settings (community, hospital, rehabilitation).

Nasal Nitric Oxide Is Correlated With Nasal Patency and Nasal Symptoms

PURPOSE

Nitric oxide (NO) is an important endogenous mediator in both upper and lower respiratory systems. The purpose of the present study was to extract nasal NO (nNO) normal range of Chinese adults and the internal influencing factors. The differences in nNO levels between rhinitis and asymptomatic atopic subjects, and the diagnostic value of nNO in allergic rhinitis (AR) were further investigated.

METHODS

One thousand adults were recruited from the general public. Participants were divided into different subgroups according to the questionnaires and skin prick tests. In all of these subjects, nNO, fractional exhaled NO (FeNO) and nasal airflow resistance were measured. The normal ranges of nNO and FeNO, the differences between subgroups, and the correlations between NO (nNO and FeNO) and other internal factors were analyzed.

RESULTS

Both nNO and FeNO levels were significantly higher in AR patients than in healthy and asymptomatic atopic subjects. The nNO levels were significantly lower in asymptomatic atopic subjects than in normal adults. FeNO levels were significantly higher in non-AR patients than in the healthy and asymptomatic atopic adults. The cutoff value of nNO for the diagnosis of AR was 117.5 ppb (sensitivity, 50.9%; specificity, 63.9%). The nNO levels were correlated with FeNO levels, total nasal resistance measured at 75Pa, nasal volume within 0-7 cm from the anterior nares (V_0-7cm) and nasal symptom visual analogue scale (VAS) scores, while the FeNO levels were correlated with age, height, weight, body surface area, nasal volume of V_0-7cm and the nasal symptom VAS score.

CONCLUSIONS

The nNO level can be significantly different between healthy and AR patients and may be significantly correlated with nasal symptoms and nasal patency of rhinitis patients. However, the clinical value of nNO is still in the exploration stage.

Interleukin-13 stimulates production of nitric oxide in cultured human nasal epithelium

The diversity and extent of signaling functions of nitric oxide (NO) in cell physiology as well as its presence and influence as a common component of ambient air pollution and tobacco smoke are gaining increasing research attention relative to both health and disease. While cellular NO production is typically associated with inflammatory cells and processes, the airway epithelium particularly of the paranasal sinuses, has been documented to be a rich source of excreted NO. Inasmuch as excreted NO derives from both mucosal and inflammatory cell sources, distinguishing the individual contribution of these compartments to total excreted cellular NO is potentially problematic. We simulated an inflammatory mucosal environment by stimulating human nasal epithelial cultures with interleukin-13 (IL-13), a mediator produced by eosinophils in asthma, allergic rhinitis, and sinusitis. While a consistent baseline of NO excretion in control cultures was documented, widely variable individual responses to IL-13 exposure were observed in companion cultures maintained under identical conditions and tested at the same time. These studies suggest that cellular NO excretion by the healthy epithelial mucosa is subject to considerable individual variability and may be significantly elevated among some individuals in the presence of IL-13 stimulation.

Rhinovirus Delays Cell Repolarization in a Model of Injured/Regenerating Human Airway Epithelium

Rhinovirus (RV), which causes exacerbation in patients with chronic airway diseases, readily infects injured airway epithelium and has been reported to delay wound closure. In this study, we examined the effects of RV on cell repolarization and differentiation in a model of injured/regenerating airway epithelium (polarized, undifferentiated cells). RV causes only a transient barrier disruption in a model of normal (mucociliary-differentiated) airway epithelium. However, in the injury/regeneration model, RV prolongs barrier dysfunction and alters the differentiation of cells. The prolonged barrier dysfunction caused by RV was not a result of excessive cell death but was instead associated with epithelial-to-mesenchymal transition (EMT)-like features, such as reduced expression of the apicolateral junction and polarity complex proteins, E-cadherin, occludin, ZO-1, claudins 1 and 4, and Crumbs3 and increased expression of vimentin, a mesenchymal cell marker. The expression of Snail, a transcriptional repressor of tight and adherence junctions, was also up-regulated in RV-infected injured/regenerating airway epithelium, and inhibition of Snail reversed RV-induced EMT-like features. In addition, compared with sham-infected cells, the RV-infected injured/regenerating airway epithelium showed more goblet cells and fewer ciliated cells. Inhibition of epithelial growth factor receptor promoted repolarization of cells by inhibiting Snail and enhancing expression of E-cadherin, occludin, and Crumbs3 proteins, reduced the number of goblet cells, and increased the number of ciliated cells. Together, these results suggest that RV not only disrupts barrier function, but also interferes with normal renewal of injured/regenerating airway epithelium by inducing EMT-like features and subsequent goblet cell hyperplasia.

The role of nasal fractional exhaled nitric oxide as an objective parameter independent of nasal airflow resistance in the diagnosis of allergic rhinitis

OBJECTIVE

Patients with allergic rhinitis (AR) show augmented activity of nitric oxide (NO) metabolism, similar to those in bronchial asthma (BA). We hypothesized that measurements of nasal fractional exhaled NO (FeNO) could be used as an objective marker to detect the presence of AR. Our objective was to clarify the influence of nasal airflow resistance (NAR) on nasal FeNO levels through an exhalation maneuver in symptomatic AR patients. We also examined the diagnostic test validity of the mean nasal FeNO level for disease discrimination by means of a receiver operating characteristic (ROC) curve analysis.

METHODS

Fifty-nine untreated perennial AR patients without BA and 60 healthy controls were enrolled in this retrospective cross-sectional study. The subjective symptoms were recorded and the disease severity was classified according to the Japanese guideline for AR. The oral and nasal FeNO measurements were carried out using a handheld electrochemical analyzer according to the ATS/ERS guidelines. NAR was measured using a rhinomanometer by the anterior method.

RESULTS

The patients in the moderate-to-most severe AR group showed significantly higher levels of oral FeNO compared to the controls. The AR patients in both the mild (n=25) and the moderate-to-most severe (n=34) groups showed significantly higher levels of nasal FeNO compared to the controls (44.1ppb, 54.5ppb, and 26.5ppb, respectively). There was no significant difference in total NAR between the AR patients and the controls. The results of our comparison of nasal FeNO and NAR values of the ipsilateral nasal cavity for each individual indicated no significant correlation between the two-paired parameters. The optimal cut-off point of the mean nasal FeNO level was calculated as 38.5ppb (with 71% sensitivity and 86% specificity) to discriminate the presence of AR.

CONCLUSION

Nasal FeNO measurements can be an objective parameter for the diagnosis and classification of perennial AR in Japanese individuals. Nasal FeNO and NAR appear to be two independent measures that can be used to objectively evaluate nasal functions.

Comparison of nasal nitric oxide levels between the inferior turbinate surface and the middle meatus in patients with symptomatic allergic rhinitis

BACKGROUND

Because of the anatomical complexity and the high output of the human nose, it has been unclear whether nasal nitric oxide (NO) serves as a reliable marker of allergic rhinitis (AR). We examined whether nasal NO levels in the inferior turbinate (IT) surface and the middle meatus (MM) differ in symptomatic AR patients.

METHODS

We measured fractional exhaled NO (FeNO) and nasal NO in normal subjects (n = 50) and AR patients with mild symptoms (n = 16) or moderate or severe symptoms (n = 27). Nasal NO measurements were obtained using an electrochemical analyzer connected to a catheter and an air-suction pump (flow rate 50mL/sec).

RESULTS

Compared to the normal subjects, the AR patients showed significantly higher nasal FeNO and nasal NO levels in the IT area. No significant difference in the MM area was observed among the three groups. The MM area showed higher NO levels than the IT area in all three groups. The ratio of nasal NO levels of the MM area to the IT area (MM/IT ratio) was significantly lower in the AR groups. The moderate/severe AR patients showed significantly higher nasal NO in the IT area (104.4 vs. 66.2ppb) and lower MM/IT ratios than those in the mild AR patients. The analysis of nasal brushing cells revealed significantly higher eosinophil cationic protein and nitrotyrosine levels in the AR groups.

CONCLUSIONS

Nasal NO assessment in the IT area directly reflects persistent eosinophilic inflammation and may be a valid marker to estimate the severity of AR.

Evaluation of oxidative DNA damage and antioxidant defense in patients with nasal polyps

OBJECTIVES

The presence of inflammatory cells indicates the development of epithelial cell injury in nasal polyposis (NP) and the potential for production of high levels of reactive oxygen and nitrogen species. The aim of our study was to clarify the role of oxidative stress and antioxidant status in the deterioration accompanying NP.

METHODS

Twenty patients (11 men) aged 47.2 ± 17.0 years with nasal polyps were included in the study. Twenty healthy subjects (7 men) aged 48.2 ± 15.3 years formed the control group. The erythrocyte activities of antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx), and plasma nitric oxide (NO) concentrations were measured. An alkaline comet assay was used to determine the extent of blood lymphocyte DNA damage of oxidized purines as glicosylo-formamidoglicosylase (Fpg) sites, and oxidized pyrimidines as endonuclease III (Nth) sites.

RESULTS

A significant increase of NO (P < 0.05) and non-significant decreases of SOD (P > 0.05), CAT (P > 0.05), and GPx (P > 0.05) were seen in NP patients compared to healthy controls. The level of blood lymphocyte oxidative DNA damage in NP patients was significantly higher compared to the control group (P = 0.01).

DISCUSSION

The blood lymphocyte DNA damage level increased in patients with NP. Elevated DNA damage may be related to overproduction of reactive oxygen and nitrogen species and/or decreased antioxidant protection.

Measurements of nasal fractional exhaled nitric oxide with a hand-held device in patients with allergic rhinitis: relation to cedar pollen dispersion and laser surgery

BACKGROUND

There has been an increasing interest in monitoring the fractional concentrations of exhaled NO (FeNO) levels in allergic rhinitis (AR) patients. In the present study, we examined whether the nasal FeNO measurement might reflect the degree of local allergic inflammation as well as subjective symptoms.

METHODS

The FeNO measurement was performed using a handheld electrochemical analyzer (NObreath®) with a nose adaptor. In the cross-sectional study, 56 patients with perennial AR patients, 18 AR patients with bronchial asthma (BA), 12 patients with vasomotor rhinitis, and 30 normal subjects were enrolled. For the follow-up study, 12 seasonal allergic rhinitis (SAR) patients against Japanese cedar and 10 perennial AR patients who underwent laser surgery were examined.

RESULTS

The AR patients and vasomotor rhinitis patients showed significantly higher oral FeNO levels as compared with the normal subjects. The nasal FeNO levels were significantly higher in the perennial AR patients with or without BA than in the normal subjects and vasomotor rhinitis patients. There were positive correlations between the nasal symptom scores and FeNO levels. The SAR patients showed a significant decrease in the nasal FeNO level after the pollen dispersion season. In addition, the therapeutic effects of laser surgery in the AR patients accompanied a significant reduction in the nasal FeNO levels one month after treatment.

CONCLUSIONS

The nasal FeNO measurement by NObreath® is easy to perform and suitable for monitoring AR patients in various treatment modalities. Furthermore, it may have potential usefulness as a tool to improve daily clinical care.

The association of oxidative stress and nasal polyposis

Many diseases are linked to damage from reactive oxygen species that occurs from an imbalance between reactive oxygen species and antioxidants, a condition called oxidative stress. Nasal polyposis is considered to be an inflammatory condition in nasal and paranasal sinus cavities and its aetiology is still unclear. There are very few data on epithelial changes in nasal polyposis and their relationship with free radical damage. Malondialdehyde as a major end-product of lipid peroxidation, and superoxide dismutase and nitric oxide as antioxidants play important roles in oxidative stress. In this study, the concentrations of malondialdehyde, superoxide dismutase and nitric oxide were compared in normal and nasal polyposis-affected tissue samples. Malondialdehyde levels were significantly higher, and superoxide dismutase and nitric oxide levels were significantly lower in patients with nasal polyposis compared with the control group. This study demonstrates that there is a strong relationship between oxidative stress and the pathogenesis of nasal polyposis.

Effect of carbon dioxide on calcitonin gene-related peptide secretion from trigeminal neurons

OBJECTIVE

The goal of this study was to determine whether the physiological effects of carbon dioxide (CO(2)) involve regulation of CGRP secretion from trigeminal sensory neurons.

BACKGROUND

The neuropeptide calcitonin gene-related peptide (CGRP) is implicated in the pathophysiology of allergic rhinosinusitis and migraine. Recent clinical evidence supports the use of noninhaled intranasal delivery of 100% CO(2) for treatment of these diseases. Patients report 2 distinct physiological events: first, a short duration stinging or burning sensation within the nasal mucosa, and second, alleviation of primary symptoms.

METHODS

Primary cultures of rat trigeminal ganglia were utilized to investigate the effects of CO(2) on CGRP release stimulated by a depolarizing stimulus (KCl), capsaicin, nitric oxide, and/or protons. The amount of CGRP secreted into the culture media was determined using a CGRP-specific radioimmunoassay. Intracellular pH and calcium levels were measured in cultured trigeminal neurons in response to CO(2) and stimulatory agents using fluorescent imaging techniques.

RESULTS

Incubation of primary trigeminal ganglia cultures at pH 6.0 or 5.5 was shown to significantly stimulate CGRP release. Similarly, CO(2) treatment of cultures caused a time-dependent acidification of the media, achieving pH values of 5.5-6 that stimulated CGRP secretion. In addition, KCl, capsaicin, and a nitric oxide donor also caused a significant increase in CGRP release. Interestingly, CO(2) treatment of cultures under isohydric conditions, which prevents extracellular acidification while allowing changes in PCO(2) values, significantly repressed the stimulatory effects of KCl, capsaicin, and nitric oxide on CGRP secretion. We found that CO(2) treatment under isohydric conditions resulted in a decrease in intracellular pH and inhibition of the KCl- and capsaicin-mediated increases in intracellular calcium.

CONCLUSIONS

Results from this study provide the first evidence of a unique regulatory mechanism by which CO(2) inhibits sensory nerve activation, and subsequent neuropeptide release. Furthermore, the observed inhibitory effect of CO(2) on CGRP secretion likely involves modulation of calcium channel activity and changes in intracellular pH.

The impact of nitrite and antioxidants on ultraviolet-A-induced cell death of human skin fibroblasts

Nitrite (NO(2)(-)) occurs ubiquitously in biological fluids such as blood and sweat. Ultraviolet A-induced nitric oxide formation via decomposition of cutaneous nitrite, accompanied by the production of reactive oxygen (ROS) or nitrogen species (RNS), represents an important source for NO in human skin physiology. Examining the impact of nitrite and the antioxidants glutathione (GSH), Trolox (TRL), and ascorbic acid (ASC) on UVA-induced toxicity of human skin fibroblasts (FB) we found that NO(2)(-) concentration-dependently enhances the susceptibility of FB to the toxic effects of UVA by a mechanism comprising enhanced induction of lipid peroxidation. While ASC completely protects FB cultures from UVA/NO(2)(-)-induced cell damage, GSH or TRL excessively enhances UVA/NO(2)(-)-induced cell death by a mechanism comprising nitrite concentration-dependent TRL radical formation or GSH-derived oxidative stress. Simultaneously, in the presence of GSH or TRL the mode of UVA/NO(2)(-)-induced cell death changes from apoptosis to necrosis. In summary, during photodecomposition of nitrite, ROS or RNS formation may act as strong toxic insults. Although inhibition of oxidative stress by NO and other antioxidants represents a successful strategy for protection from UVA/NO(2)(-)-induced injuries, GSH and TRL may nitrite-dependently aggravate the injurious impact by TRL or GSH radical formation, respectively.

The effect of endogenous nitric oxide on mechanical ciliostimulation of human nasal mucosa

BACKGROUND

Endogenous nitric oxide (NO) production by the inducible NO-synthase is enhanced in the nasal respiratory epithelium of patients with allergic rhinitis. Recent experimental data suggest endogenous NO to be strongly involved in the regulation of ciliary activity, the driving force of the mucociliary transport system.

OBJECTIVE

In this study, we investigated the effect of endogenous NO on mechanical stimulation of ciliary activity in a nasal mucosa explant model.

METHODS

Cultures of nasal mucosa explants were incubated with TNF-alpha and bacterial lipopolysaccharides (LPS) to enhance endogenous NO production. Direct in vitro NO imaging was performed by the fluorescent NO-indicator DAF-2 DA and laser scanning confocal microscopy. Ciliary beat frequency (CBF) was determined using a photoelectric technique. Mechanical stimulation was performed by two consecutive flow increments in a closed perfusion chamber. Endogenous NO-synthesis was blocked by l-NAME before the second flow stimulation.

RESULTS

Under control conditions the mean rise of CBF relative to baseline was 30.2% during the first flow increment and 30.7% during the second flow increment. Blocking of the endogenous NO synthesis in TNF-alpha/LPS-stimulated cultures reduced baseline CBF by 10.6+/-2.1% (P<0.05) but the effect of mechanical ciliostimulation on CBF remained unchanged (36.0% vs. 38.2%).

CONCLUSION

In conclusion, endogenous NO- and Ca(2+)-dependent mechanical stimulation of ciliary activity probably use independent intracellular signalling pathways. The combination of both effects on ciliary activity is likely to improve the local defence against inhaled allergens in patients with nasal allergies.

Nasal nitric oxide and nasal allergy

Measurements of nasal nitric oxide (nNO) are attractive because they are completely noninvasive and can easily be performed. The measurements may be useful in the early diagnosis of patients with chronic airway disorders such as Kartager's syndrome and cystic fibrosis. The possible use of nNO measurements in the diagnosis and treatment of allergic rhinitis still needs to be further evaluated because of the variable and also contradicting findings of nNO concentrations in this disease. In this review we will discuss the origin, production and measurement of nNO as well as the effect of allergic rhinitis, nasal allergen challenge and medication on nNO. Subsequently, we examine published data on allergic rhinitis and nNO, and summarize the effect of treatment of rhinitis on nNO. Finally, we discuss the potential future role for nNO in the diagnosis and management of allergic rhinitis.

Effects of cigarette smoke on degranulation and NO production by mast cells and epithelial cells

Exhaled nitric oxide (eNO) is decreased by cigarette smoking. The hypothesis that oxides of nitrogen (NO_X) in cigarette smoke solution (CSS) may exert a negative feedback mechanism upon NO release from epithelial (AEC, A549, and NHTBE) and basophilic cells (RBL-2H3) was tested in vitro. CSS inhibited both NO production and degranulation (measured as release of beta-hexosaminidase) in a dose-dependent manner from RBL-2H3 cells. Inhibition of NO production by CSS in AEC, A549, and NHTBE cells was also dose-dependent. In addition, CSS decreased expression of NOS mRNA and protein expression. The addition of NO inhibitors and scavengers did not, however, reverse the effects of CSS, nor did a NO donor (SNP) or nicotine mimic CSS. N-acetyl-cysteine, partially reversed the inhibition of beta-hexosaminidase release suggesting CSS may act via oxidative free radicals. Thus, some of the inhibitory effects of CSS appear to be via oxidative free radicals rather than a NO_X -related negative feedback.

Calcium-sensing receptor activation induces nitric oxide production in H-500 Leydig cancer cells

Nitric oxide (NO) is a versatile second messenger. NO is produced by Leydig cells, where NO is a negative regulator of steroidogenesis. In cancer cells, NO is thought to have mutagenic and proliferative effects. We have previously shown that the calcium-sensing receptor (CaR) has promalignant effects in rat H-500 Leydig cancer cells, a model for humoral hypercalcemia of malignancy. Calcium, the major physiological ligand of the CaR, is a recognized intracellular cofactor in the process of NO production by virtue of its positive modulation of neuronal and endothelial nitric oxide synthase (NOS), but importantly, not of inducible (i) NOS activity. iNOS activity is regulated by changes in its expression level. Therefore, we investigated whether CaR activation changes iNOS expression. We found that high extracellular calcium (Cao2+) upregulates the level of mRNA for iNOS, whereas no change was seen in neuronal or endothelial NOS, as assessed by microarray and real-time PCR, respectively. The high Cao2+-induced iNOS upregulation was also detected by Northern and Western blotting. By quantitative real-time PCR, we showed that calcium maximally upregulates iNOS at 18 h. The effect of calcium was abolished by overexpression of a dominant-negative CaR (R185Q), confirming that the effect of Cao2+ was mediated by the CaR. Cells treated with high calcium had higher NO production than those treated with low calcium, as detected with the NO-specific DAF2-AM dye. This was confirmed in single-cell fluorescence determinations using confocal microscopy. In conclusion, high calcium upregulates the levels of iNOS mRNA and protein as well as NO production in H-500 cells, and the effect of Cao2+ on iNOS expression is mediated by the CaR.

Performance of diamino fluorophores for the localization of sources and targets of nitric oxide

An emergent approach to the detection of nitric oxide (NO) in tissues relies on the use of fluorescence probes that are activated by products of NO autoxidation. Here we explore the performance of the widely used NO probe 4,5-diaminofluorescein diacetate (DAF-2 DA) for the localization of sources of NO in rat aortic tissue, either from endogenous NO synthesis or from chemically or photolytically released NO from targets of nitrosation/nitrosylation. Of importance toward understanding the performance of this probe in tissues is the finding that, with incubation conditions commonly used in the literature (10 microM DAF-2 DA), intracellular DAF-2 accumulates to concentrations that approach the millimolar range. Whereas such high probe concentrations do not interfere with NO release or signaling, they help to clarify why DAF-2 nitrosation is possible in the presence of endogenous nitrosation scavengers (e.g., ascorbate and glutathione). The gain attained with such elevated concentrations is, however, mitigated by associated high levels of background autofluorescence from the probe. This, together with tissue autofluorescence, limits the sensitivity of the probe to low-micromolar levels of accumulated DAF-2 triazole (DAF-2 T), the activated form of the probe, which is higher than the concentrations of most endogenous nitrosation/nitrosylation products found in tissues. We further show that the compartmentalization of DAF-2 around elastic fibers further limits its potential to characterize the site of NO production at the subcellular level. Moreover, we find that reaction of DAF-2 with HgCl(2) and other commonly employed reagents is associated with spectral changes that may be misinterpreted as NO signals. Finally, UV illumination can lead to high levels of nitrosating species that interfere with NO detection from enzymatic sources. These findings indicate that while DAF-2 may still represent an important tool for the localization of NO synthesis, provided important pitfalls and limitations are taken into consideration, it is not suited for the detection of basally generated nitrosation/nitrosylation products.

Enhancement of apoptosis by nitric oxide released from α-phenyl-tert-butyl nitrone under hyperthermic conditions

The aim of this study was to examine whether a neuroprotector, PBN (alpha-phenyl-tert-butyl nitrone), enhances apoptosis induced by hyperthermia, which generates superoxide (O2-) intracellularly, since the release of nitric oxide (NO) from PBN under oxidative stress has been reported. When human myelomonocytic lymphoma U937 cells were treated with hyperthermia (44 degrees C, 10 min) and PBN, an increase in the concentration of nitrite in the culture medium, and a decrease in the hyperthermia-induced production of O2- was observed. Imaging using a fluorescence dye for intracellular NO, diaminofluorescein-2 diacetate (DAF-2 DA), revealed the formation of NO in the apoptotic cells treated with hyperthermia and PBN combined. Apoptotic endpoints were significantly enhanced by the combined treatment: a decrease in mitochondrial trans-membrane potential, cleavage of Bid, release of cytochrome c, and activation of caspase-8 and -3. An increase in the intracellular Ca2+ concentration ([Ca2+]i), externalization of Fas, and decrease in Hsp70 and phosphorylated HSF1 were observed following the combined treatment. Furthermore, scavengers of NO an d ONOO- significantly inhibited the enhancement of apoptosis, the externalization of Fas and the increase in [Ca2+]i. These results suggest that, (1) NO is released from PBN by hyperthermia, and subsequently reacts with O2- to form ONOO-, (2) NO and ONOO- are involved in the enhancement of apoptosis through Fas-mitochondria-caspase and [Ca2+]i-dependent pathways, and (3) a decrease in Hsp70 and phosphorylated HSF1 also contributed to the enhancement of apoptosis.

Autoinhibitory domain fragment of endothelial NOS enhances pulmonary artery vasorelaxation by the NO-cGMP pathway

Catalytic activity of eNOS is regulated by multiple posttranscriptional mechanisms, including a 40-amino acid (604-643) autoinhibitory domain (AID) located in the reductase domain of the eNOS protein. We examined whether an exogenous synthetic AID, an 11-amino acid (626-636) fragment of AID (AAF), or scrambled AAF (AAF-SR), enhanced eNOS activity and NO-cGMP-mediated vasorelaxation using pulmonary artery (PA) endothelial/smooth muscle cell (PAEC/PASM) coculture, isolated PA segment, and isolated lung perfusion models. Incubation of isolated total membrane fraction of PAEC with AID or AAF resulted in concentration-dependent loss of eNOS activity. In contrast, incubation of intact PAEC with AID or AAF but not AAF-SR caused concentration- and time-dependent activation of eNOS. Because AID and AAF had similar effects on activation of eNOS, AAF and AAF-SR were used for further evaluation. Although AAF stimulation increased catalytic activity of PKC-alpha in PAEC, AAF-mediated activation of eNOS was independent of phosphorylation of Ser1177 or Thr495 and/or expression of eNOS protein. AAF stimulation of PAEC increased NO and cGMP production, which were attenuated by pretreatment with the eNOS inhibitor l-NAME. AAF caused time-dependent vasodilation of U-46619-precontracted endothelium-intact but not endothelium-denuded PA segments, and this response was attenuated by l-NAME. AAF, but not AAF-SR, also caused vasorelaxation in an ex vivo isolated mouse lung perfusion model precontracted with U-46619. Incubation with fluorescence-labeled AAF demonstrated translocation of AAF in PAEC in culture, isolated PA, and isolated intact lungs. These results demonstrate that AAF-stimulated vasodilation is mediated via activation of eNOS and enhanced NO-cGMP production in PA and intact lung.

Expression of nitric oxide synthases in nasal mucosa from a mouse model of allergic rhinitis

Nitric oxide (NO), which is produced by nitric oxide synthase (NOS), has been recently identified as a multifunctional mediator. As for nasal tissue, however, the distribution and expression patterns of 3 isoforms of NOS, including neuronal NOS (nNOS, type I NOS), inducible NOS (iNOS, type II NOS), and endothelial NOS (eNOS, type III NOS), are still unclear. To evaluate the function of NO in the pathophysiology of nasal allergy, we investigated the distribution of NOSs in the nasal mucosa of C57BL/6 mice with allergic rhinitis to the house dust mite, Dermatophagoides farinae. Immunoreactivity to each isoform of NOS was immunohistochemically observed. In the allergic nasal mucosa, many eosinophils had infiltrated. Immunoreactivity to NOS types I and III was localized to the surface epithelial and vascular endothelial cells in both allergic and control groups without a statistically significant difference. In contrast, the type II NOS immunoreactivity was weak in normal mice and increased after allergic sensitization. The type II NOS expression of the surface epithelial and vascular endothelial cells was significantly elevated in the allergic group as compared with the control group. These findings suggest that a large amount of NO may be produced in the nasal mucosa of mice by type II NOS after allergic sensitization and that type II NOS may play an important role in the pathogenesis of allergic rhinitis.

Characterization of airway nitric oxide in allergic rhinitis: the effect of intranasal administration of L-NAME

BACKGROUND

Several studies have attempted to assess nasal nitric oxide (NO) levels in allergic rhinitis (AR). However, there seem to be differences in the results obtained. We therefore wanted to investigate this further by studying airway NO in AR and controls at several modalities, and also the effect of intranasal administration of the nitric oxide synthase (NOS) inhibitor NG-nitro-L-arginine-methyl ester.HCl (L-NAME).

METHODS

Airway NO was determined through repeated measurements at three flow rates of air (0.5, 3, and 9 l/min), using a single-breath method and a method of nasal aspiration, in 18 patients with birch pollen AR during season and in 18 controls.

RESULTS

Patients with AR were characterized by no difference in nasal but higher orally exhaled NO and a larger interindividual spread in nasal and orally exhaled NO compared to controls. We also found a greater reduction in nasal NO after L-NAME in patients compared to controls.

DISCUSSION

These results indicate that several factors determine the levels of nasal NO in rhinitis. NO production in the nasal mucosa of patients with AR may be upregulated. On the other hand, this increase could be counteracted by swelling of the mucosa and secretions resulting in impaired NO diffusion from, for example, the paranasal sinuses, where particularly high levels of NO have been found. Also, the high background levels of NO from constitutive sources in the nose may blunt smaller increases in mucosal NO output.

CONCLUSION

It seems that the methods for measurement of nasal NO need to be improved and standardized before we can consider to use this test in monitoring inflammation in AR.