Inducible nitric oxide synthase expression is increased in the alveolar compartment of asthmatic patients

BALB/c and C57BL/6 mice differ in oxidant and antioxidant responses in innate and adaptive immune cells in an asthma model induced by cockroach allergens

Asthma is a complex and heterogenous disease affected by a multitude of factors. Several phenotypes of asthma exist which are influenced by various molecular mechanisms that include presence of antioxidant and oxidant enzymes in different immune cells such as dendritic cells (DCs), alveolar macrophages (AMs), neutrophils, and T cells. Close interaction between epithelial cells and dendritic cells initiates complex pathogenesis of asthma followed by involvement of other innate and adaptive immune cells. In chronic phase of the disease, these immune cells support each other in amplification of airway inflammation where oxidant-antioxidant balance is known to be an important contributing factor. Genetic variability in antioxidant response may influence the development of airway inflammation, however it has not been studied in mice yet. The two most studied mice strains, i.e. BALB/c and C57BL/6 are reported to have dissimilar airway responses to the same allergens due to their genetic makeup. In this investigation, we explored whether these strains had any differences in pulmonary oxidant-antioxidant system (Nrf2, SOD2, iNOS, HO-1, nitrotyrosine) in different immune cells (DCs, AMs, neutrophils, T cells), airway inflammation (presence of eosinophils and/or neutrophils) and mucus production in response to repeated cockroach allergen extract (CE) mouse model of asthma. Our data show that C57BL/6 mice had better induction of antioxidant system than BALB/c mice. Consequently, iNOS/nitrotyrosine levels were much exaggerated in BALB/c than C57BL/6 mice. As a result, BALB/c mice developed mixed granulocytic airway inflammation, whereas C57BL/6 developed mostly eosinophilic airway inflammation. Our data suggest that an exaggerated oxidant generation along with a weak antioxidant induction in response to a natural allergen on a susceptible genetic background may determine development of severe asthma phenotype such as mixed granulocyte inflammation.

Inhibition of non-receptor tyrosine kinase LCK partially mitigates mixed granulocytic airway inflammation in a murine model of asthma

Asthma affects millions of people worldwide and is one of the most common inflammatory airway diseases. Asthma phenotypes are quite complex and categorized as eosinophilic, mixed granulocytic (presence of both eosinophils and neutrophils in the airways) and neutrophilic. Mixed granulocytic asthma requires large doses of inhaled corticosteroids, which are often insufficient in controlling airway inflammation. Therefore, there is a medical need to test newer therapies to control granulocytic inflammation. Lymphocyte specific protein tyrosine kinase (LCK) signaling has gained momentum in recent years as a molecular target in inflammatory diseases such as asthma. LCK is expressed in lymphocytes and is required for inflammatory intracellular signaling in response to antigenic stimulation. Therefore, efficacy of LCK inhibitor, A770041 was tested in cockroach (CE)-induced corticosteroid insensitive murine model of asthma. The effect of LCK inhibitor was investigated on granulocytic airway inflammation, mucus production, p-LCK and downstream signaling molecules such as p-PLCγ, GATA3, p-STAT3 in CD4+ T cells. Moreover, its effects were also studied on Th2/Th17 related cytokines and oxidative stress parameters (iNOS/nitrotyrosine) in neutrophils/macrophages. Our study shows that CE-induced p-LCK levels are concomitant with increased neutrophilic/eosinophilic inflammation and mucus hypersecretion which are significantly mitigated by A770041 treatment. A770041 also caused marked attenuation of CE-induced pulmonary levels of IL-17A levels but not completely. However, A770041 in combination with dexamethasone caused complete downregulation of mixed granulocytic airway inflammation as well as Th2/Th17 related immune responses. These results suggest that combination of LCK inhibition along with corticosteroids may be pursued as an alternative strategy to completely treat mixed granulocytic asthma.

Effect of General Anesthesia Maintenance with Propofol or Sevoflurane on Fractional Exhaled Nitric Oxide and Eosinophil Blood Count: A Prospective, Single Blind, Randomized, Clinical Study on Patients Undergoing Thyroidectomy

Background: Nitric oxide (NO) is considered a means of detecting airway hyperresponsiveness, since even non-asthmatic patients experiencing bronchospasm intraoperatively or postoperatively display higher levels of exhaled NO. It can also be used as a non-invasive biomarker of lung inflammation and injury. This prospective, single-blind, randomized study aimed to evaluate the impact of two different anesthesia maintenance techniques on fractional exhaled nitric oxide (FeΝO) in patients without respiratory disease undergoing total thyroidectomy under general anesthesia. Methods: Sixty patients without respiratory disease, atopy or known allergies undergoing total thyroidectomy were randomly allocated to receive either inhalational anesthesia maintenance with sevoflurane at a concentration that maintained Bispectral Index (BIS) values between 40 and 50 intraoperatively or intravenous anesthesia maintenance with propofol 1% targeting the same BIS values. FeΝO was measured immediately preoperatively (baseline), postoperatively in the Postanesthesia Care Unit and at 24 h post-extubation with a portable device. Other variables measured were eosinophil blood count preoperatively and postoperatively and respiratory parameters intraoperatively. Results: Patients in both groups presented lower than baseline values of FeΝO measurements postoperatively, which returned to baseline measurements at 24 h post-extubation. In the peripheral blood, a decrease in the percentage of eosinophils was demonstrated, which was significant only in the propofol group. Respiratory lung mechanics were better maintained in the propofol group as compared to the sevoflurane group. None of the patients suffered intraoperative bronchospasm. Conclusions: Both propofol and sevoflurane lead to the temporary inhibition of NO exhalation. They also seem to attenuate systemic hypersensitivity response by reducing the eosinophil count in the peripheral blood, with propofol displaying a more pronounced effect and ensuring a more favorable mechanical ventilation profile as compared to sevoflurane. The attenuation of NO exhalation by both agents may be one of the underlying mechanisms in the reduction in airway hyperreactivity. The clinical significance of this fluctuation remains to be studied in patients with respiratory disease.

Nitric Oxide: The Missing Factor in COVID-19 Severity?

Coronavirus disease 2019 (COVID-19) is a contagious respiratory and vascular disease that continues to spread among people around the world, mutating into new strains with increased transmission rates, such as the delta variant. The scientific community is struggling to discover the link between negative COVID-19 outcomes in patients with preexisting conditions, as well as identify the cause of the negative clinical patient outcomes (patients who need medical attention, including hospitalization) in what seems like a widespread range of COVID-19 symptoms that manifest atypically to any preexisting respiratory tract infectious diseases known so far. Having successfully developed a nutritional formulation intervention based on nitrate, a nitric oxide precursor, the authors hypothesis is that both the comorbidities associated with negative clinical patient outcomes and symptoms associated with COVID-19 sickness are linked to the depletion of a simple molecule: nitric oxide.

Comparison of fractional exhaled nitric oxide in asthmatics with and without allergic rhinitis

PURPOSE OF THE STUDY

The aim of this study was to measure the concentration of FeNO in asthmatics with and without allergic rhinitis (AR) and to determine usefulness of the test in the assessment of asthma control in the Polish population. The next objective of this study was to estimate the cut-off point of FeNO which might be a good indicator of uncontrolled asthma.

MATERIALS AND METHODS

The measurements were taken using the Hyp'Air FeNO in 303 adult patients with asthma, AR, comorbid AR and asthma, and non-diseased volunteers.

RESULTS

FeNO level in healthy adults was similar to the FeNO concentration in AR as well as controlled asthmatic patients without and with AR. Patients with partly controlled and uncontrolled asthma with and without AR had higher FeNO (>60 ppb) levels when compared to adults with controlled disease. The optimal cut-off point of FeNO > 46 ppb and FeNO > 33 ppb was estimated for identification of uncontrolled asthmatics without and with AR, respectively.

CONCLUSION

In conclusion, we found a significant correlation between the FeNO concentration and the level of asthma symptom control in asthmatic patients with and without AR.

Leukotriene D4 role in allergic asthma pathogenesis from cellular and therapeutic perspectives

Asthma is a chronic inflammatory and allergic disease that is mainly characterized by reversible airway obstruction and bronchial hyperresponsiveness. The incidence of asthma is increasing with more than 350 million people worldwide are affected. Up to now, there is no therapeutic option for asthma and most of the prescribed drugs aim to ameliorate the symptoms of the disease especially during the acute exacerbations after trigger exposure. Asthma is a heterogonous disease that involves interactions between inflammatory mediators and cellular components within the disease microenvironment including inflammatory and structural cells. Cysteinyl leukotrienes (cys-LTs) are inflammatory lipid mediators that have potent roles in asthma pathogenesis. CysLTs consisting of LTC₄, LTD₄, and LTE₄ are mainly secreted by leukocytes and act through three main G-protein coupled receptors (CysLT₁R, CysLT₂R, and CysLT₃R). LTD₄ is the most potent bronchoconstrictor which gives it the priority to be discussed in detail in this review. LTD₄ binds with high affinity to CysLT₁R and many studies showed that using CysLT₁R antagonists such as montelukast has a beneficial effect for asthmatics especially in corticosteroid refractory cases. Since asthma is a heterogeneous inflammatory disease of many cell types involved in the disease pathogenies and LTD₄ has a special role in inflammation and bronchoconstriction, this review highlights the role of LTD₄ on each cellular component in asthma and the benefits of using CysLT₁R antagonists in ameliorating LTD₄-induced effects.

A Comprehensive Evaluation of Mepolizumab Effectiveness in a Real-Life Setting

INTRODUCTION

Interleukin-5 (IL-5) is the principal cytokine regulating eosinophil growth, differentiation, activation, and expression. It is a specific target of mepolizumab, an anti-IL-5 monoclonal antibody used in the treatment of severe eosinophilic asthma. This new drug can improve symptoms, reduce asthma exacerbations and steroid use. Few data are available on its efficacy for nasal symptoms.

OBJECTIVE

To describe the all-round clinical impact of mepolizumab in a real-life setting, evaluating the efficacy and safety of the drug in severe eosinophilic asthma patients.

POPULATION AND METHODS

We retrospectively collected the clinical and functional data on 27 patients (16 males) affected with severe eosinophilic asthma, diagnosed at the Siena Regional Referral Centre and monitored for 6 months. Clinical, immunological, and functional data at baseline and follow-up were entered in a database together with comorbidities, number of exacerbations, steroid treatment, multiple-flow exhaled nitric oxide, and validated questionnaires.

RESULTS

A significant reduction in asthma exacerbations was observed in all patients after 6 months of the biological therapy (p = 0.0009), and 4/6 patients discontinued chronic oral steroids. A significant improvement in ACT, FEV1, SNOT22, and alveolar nitric oxide was observed after 1 month of mepolizumab (p = 0.003, p = 0.007, p = 0.047, and p = 0.019, respectively) and maintained after 6 months of treatment. After 6 months, FeNO 50 was reduced as well (p = 0.030). Mepolizumab was very well tolerated, and no major side effects were observed.

CONCLUSIONS

Our study suggests that mepolizumab is effective in improving control of asthma, lung function parameters, exhaled biomarkers, and nasal symptoms in patients with severe eosinophilic asthma.

Associations between source-resolved PM2.5 and airway inflammation at urban and rural locations in Beijing

BACKGROUND

A large number of research studies have explored the health effects of exposure to atmospheric particulate matter. However, limited quantitative evidence has linked specific sources of personal PM_2.5 directly to adverse health effects. This study was conducted in order to examine the association between airway inflammation and personal exposure to PM_2.5 mass, components, and sources among two healthy cohorts living in both urban and rural areas of Beijing, China.

METHODS

We conducted a follow-up study during the summer of 2016 and the winter of 2016/2017 among 92 students and 43 guards. 24-h personal and ambient exposure to PM_2.5 and fractional exhaled nitric oxide (FeNO) were measured at least twice for each participant. Chemical components of 385 personal PM_2.5 exposure samples were analyzed, and pollution sources were resolved by a positive matrix factorization (PMF) receptor model. We have constructed linear mixed effect models to evaluate the association between ambient/personal PM_2.5 mass, chemical constituents, and source specific PM_2.5 with FeNO after controlling for temperature, relative humidity, sites, season, and potential individual confounders.

RESULTS

Interquartile range (IQR) increase in household heating sources was associated with increased FeNO (2.72%; 95% CI = 1.26-4.17%) across two sites. IQR increase in roadway transport was associated with increased FeNO (9.84%; 95% CI = 2.69-17%) in urban areas; IQR increase in Secondary inorganic sources and Industrial/Combustion sources were associated with increased FeNO (7.96%; 95% CI = 1.47-14.4%% and 7.85%; 95% CI = 0.0676-15.6%, respectively) in rural areas. Personal exposure to EC, OC, and some trace elements (Se, Pb, Bi, Cs) were also estimated to be significantly associated with the increase of FeNO. In addition, there was no significant difference (P > 0.05) between the effects of ambient and personal PM_2.5 mass.

CONCLUSIONS

Although personal PM_2.5 mass was not significantly associated with the health effects, airway inflammation can be linked to source-resolved exposures.

Baicalein attenuates OVA-induced allergic airway inflammation through the inhibition of the NF-κB signaling pathway

Asthma is a type of chronic lung inflammation with restrictions in effective therapy. NF-κB pathway activation has been suggested to play an important role in the pathogenesis of asthma. Baicalein, one of the major active flavonoids found in Scutellaria baicalensis, exhibits potent anti-inflammatory properties by inhibiting NF-κB activity. Herein, we report that Baicalein significantly reduces OVA-induced airway hyperresponsiveness (AHR), airway inflammation, serum IgE levels, mucus production, and collagen deposition around the airway. Additionally, western blot analysis and immunofluorescence assay showed that Baicalein attenuates the activation of NF-κB, which was mainly reflected by IκBα phosphorylation and degradation, p65 nuclear translocation and downstream iNOS expression. Furthermore, in human epithelial cells, Baicalein blocked TNF-α-induced NF-κB activation. Our study provides evidence that Baicalein administration alleviates the pathological changes in asthma through inactivating the NF-κB/iNOS pathway. Baicalein might be a promising potential therapy agent for patients with allergic asthma in the future.

Exhaled nitric oxide in pediatric patients with respiratory disease

Measurement of nitric oxide (NO) levels in exhaled air from the upper and lower airways is currently used as a non-invasive marker of inflammation in respiratory diseases. Assessment of NO exhaled from the lower air respiratory tract is considered to be a quick method for confirmation and control of asthma in patients as well as an estimation of treatment efficiency. The main aim of this study was to determine differences between levels of exhaled nitric oxide (fractional exhaled NO; FeNO) in patients with respiratory disease as measured by an electrochemical analyzer. Measurements were taken in 352 pediatric patients aged 4-17 with cystic fibrosis (CF) (n = 43), asthma (n = 69), allergic rhinitis (AR) (n = 70), asthma and AR (n = 128) and non-diseased children (n = 42) recruited from the Allergology Outpatient Department, Provincial Hospital No 2, Rzeszów. The second objective of this study was to assess any correlations between FeNO and clinical parameters of patients. The level of FeNO in patients with CF was normal when compared with control subjects (10.8 ± 2.9 versus 11.4 ± 6 ppb). We found significantly higher FeNO in patients with asthma (26.6 ± 15.3 ppb, p < 0.001), AR (18.4 ± 9.6 ppb, p < 0.01) as well as in patients with both asthma and AR (43.3 ± 31.1 ppb, p < 0.001) when compared to healthy children. Statistical analysis revealed a positive correlation between FeNO and age, height and weight of control subjects, and height in children with AR. FeNO was independent of sex, BMI, spirometry and blood results as well as the type of residence in control children and subjects with CF, asthma, AR and combined asthma and AR. In conclusion, we found normal levels of FeNO in children with CF and elevated levels in patients with asthma, AR and combined asthma and AR as compared to control subjects. Due to conflicting data, there is still a need for additional research, especially related to regarding factors that affect FeNO levels in respiratory disease.

Flow-independent nitric oxide parameters in asthma: a systematic review and meta-analysis

INTRODUCTION

Fractional exhaled nitric oxide (F_ENO) has been proposed as a non-invasive marker of inflammation in the lungs. Measuring F_ENO at several flow rates enables the calculation of flow independent NO-parameters that describe the NO-exchange dynamics of the lungs more precisely. The purpose of this study was to compare the NO-parameters between asthmatics and healthy subjects in a systematic review and meta-analysis.

METHODS

A systematic search was performed in Ovid Medline, Web of Science, Scopus and Cochrane Library databases. All studies with asthmatic and healthy control groups with at least one NO-parameter calculated were included.

RESULTS

From 1137 identified studies, 33 were included in the meta-analysis. All NO-parameters (alveolar NO concentration (C_ANO), bronchial flux of NO (J_awNO), bronchial mucosal NO concentration (C_awNO) and bronchial wall NO diffusion capacity (D_awNO)) were found increased in glucocorticoid-treated and glucocorticoid-naïve asthma. J_awNO and C_ANO were most notably increased in both study groups. Elevation of D_awNO and C_awNO seemed less prominent in both asthma groups.

DISCUSSION

We found that all the NO-parameters are elevated in asthma as compared to healthy subjects. However, results were highly heterogenous and the evidence on C_awNO and D_awNO is still quite feeble due to only few studies reporting them. To gain more knowledge on the NO-parameters in asthma, nonlinear methods and standardized study protocols should be used in future studies.

Comparison of inducible nitric oxide synthase mRNA expression in different airway portions and association with nitric oxide parameters from patients with asthma

Background

Fractional exhaled nitric oxide concentration (FeNO) is widely used to support diagnosis and monitoring of bronchial asthma (BA). Tsoukias and George proposed a two‐compartment model (2CM) for assessing the alveolar concentration of NO, referred to as CANO(2CM), while Condorelli et al proposed a model based on the trumpet shape of the airway tree and axial diffusion (TMAD), referred to as CANO(TMAD). In addition, Högman et al proposed non‐linear model, referred to as CANO(non‐linear).

Objective

We examined associations between the expression of inducible nitric oxide synthase (iNOS) mRNA in airway cells (ACs) by bronchoscopy and NO‐parameters calculated by the three methods and identified which of them accurately reflected expression of iNOSmRNA from different airway portions.

Methods

We retrospectively analysed data of 18 patients with stable, mild‐moderate asthma, including 10 steroid‐naïve BA (snBA) patients. Samples were obtained from airway brushings and bronchoalveolar lavage (BAL). Expressions of iNOS protein in tissue samples were evaluated by immunostaining. The iNOSmRNA in ACs was measured by qPCR. NO‐parameters calculated by the three methods above and evaluated whether they were associated with iNOSmRNA in ACs derived from proximal (2nd carina), distal (10‐15th) airways and alveolar regions.

Results

Immunostaining revealed expression of iNOS proteins mainly in epithelial cells in the airways, while it was mainly expressed in macrophages in the alveolar region in the snBA group. The iNOSmRNA expression was increased in both proximal and distal ACs in the snBA group compared with steroid‐treated BA group (stBA). CANO(2CM) negatively associated with FEV₁ (%predicted) and also associated with iNOSmRNA in distal ACs significantly. However, CANO(TMAD) and CANO(non‐linear) showed no correlation with lung function nor iNOSmRNA expression in any portions of ACs.

Conclusions

These results suggested that CANO(2CM) reflected distal airway inflammation in steroid‐naïve asthma.

Aloperine suppresses allergic airway inflammation through NF-κB, MAPK, and Nrf2/HO-1 signaling pathways in mice

To explore the effects of aloperine (ALO) on allergic airway inflammation, we investigated whether its mechanism is related with NF-κB, MAPK, and Nrf2/HO-1 signaling pathways. Histochemical staining and inflammatory cell count were used to observe lung histopathological changes in mice. ELISA was used to detect the content of inflammatory cytokines and IgE in the mouse bronchoalveolar lavage fluid (BALF). Airway hyperresponsiveness (AHR) to inhale methacholine was measured by the plethysmography in conscious mice. Immunohistochemical method was used to detect the expression levels of Nrf2 and HO-1 in lung tissues. The key proteins of MAPK, NF-κB, and Nrf2/HO-1 in lung tissues were quantitatively analyzed by Western blot. Finally, the in vitro effect of ALO on the production of pro-inflammatory mediators and cytokines by lipopolysaccharide-stimulated RAW 264.7 cells was also evaluated. In the ovalbumin (OVA)-induced asthma mouse model, ALO reduced the exudation and infiltration of inflammatory cells and suppressed goblet cell hyperplasia. ALO-treated asthmatic mice also decreased the protein levels of interleukin (IL)-4, IL-5, IL-13, IFN-γ, and IgE in BALF and attenuated AHR. Furthermore, ALO inhibited the expression of key proteins of MAPK and NF-κB pathways, and increased the expression of Nrf2/HO-1 in OVA-challenged mice. Additional in vitro study has shown that ALO abrogates the macrophage production of inducible nitric oxide synthase, cyclooxygenase-2, tumor necrosis factor-α, IL-6, and IL-1β. Taken together, ALO attenuated allergic airway inflammation through regulating NF-κB, MAPK, and Nrf2/HO-1 signaling pathways. The results suggest the utility of ALO as an anti-inflammatory agent for the treatment of asthma.

Endoplasmic reticulum, Golgi, and lysosomes are disorganized in lung fibroblasts from chronic obstructive pulmonary disease patients

Chronic Obstructive Pulmonary Disease (COPD) is often caused by smoking and other stressors. This causes oxidative stress, which induces numerous changes on both the transcriptome and proteome of the cell. We aimed to examine if the endomembrane pathway, including the endoplasmic reticulum (ER), Golgi, and lysosomes, was disrupted in fibroblasts from COPD patients as opposed to healthy ever-smokers or never-smokers, and if the response to stress differed. Different cellular compartments involved in the endomembrane pathway, as well as mRNA expression and apoptosis, were examined before and after the addition of stress in lung fibroblasts from never-smokers, ever-smokers, and patients with COPD. We found that the ER, Golgi, and lysosomes were disorganized in fibroblasts from COPD patients under baseline conditions. After a time course with ER stress inducing chemicals, changes to the phenotypes of cellular compartments in COPD patient fibroblasts were observed, and the expression of the ER stress-induced gene ERP72 was upregulated more in the COPD patient's cells compared to ever-smokers or never-smokers. Lastly, a tendency of increased active Caspase-3 was observed in COPD fibroblasts. Our results show that COPD patients have phenotypic changes in the lung fibroblasts endomembrane pathway, and respond differently to stress. Furthermore, these fibroblasts were cultured for several weeks outside the body, but they were not able to regain proper ER structure, indicating that the internal changes to the endomembrane system are permanent in smokers. This vulnerability to cellular stress might be a cause as to why some smokers develop COPD.

Club cell protein (CC16) in plasma, bronchial brushes, BAL and urine following an inhaled allergen challenge in allergic asthmatics

BACKGROUND

Club cell protein (CC16) is a pneumoprotein secreted by epithelial club cells. CC16 possesses anti-inflammatory properties and is a potential biomarker for airway epithelial damage. We studied the effect of inhaled allergen on pulmonary and systemic CC16 levels.

METHODS

Thirty-four subjects with allergic asthma underwent an inhaled allergen challenge. Bronchoscopy with bronchoalveolar lavage (BAL) and brushings was performed before and 24 h after the challenge. CC16 was quantified in BAL and CC16 positive cells and CC16 mRNA in bronchial brushings. CC16 was measured in plasma and urine before and repeatedly after the challenge. Thirty subjects performed a mannitol inhalation challenge prior to the allergen challenge.

RESULTS

Compared to baseline, CC16 in plasma was significantly increased in all subjects 0-1 h after the allergen challenge, while CC16 in BAL was only increased in subjects without a late allergic response. Levels of CC16 in plasma and in the alveolar fraction of BAL correlated significantly after the challenge. There was no increase in urinary levels of CC16 post-challenge. Mannitol responsiveness was greater in subjects with lower baseline levels of CC16 in plasma.

CONCLUSIONS

The increase in plasma CC16 following inhaled allergen supports the notion of CC16 as a biomarker of epithelial dysfunction.

Effects of growth and aging on the reference values of pulmonary nitric oxide dynamics in healthy subjects

The lung just like all other organs is affected by age. The lung matures by the age of 20 and age-related changes start around middle age, at 40-50 years. Exhaled nitric oxide (F_ENO) has been shown to be age, height and gender dependent. We hypothesize that the nitric oxide (NO) parameters alveolar NO (C_ANO), airway flux (J_awNO), airway diffusing capacity (D_awNO) and airway wall content (C_awNO) will also demonstrate this dependence. Data from healthy subjects were gathered by the current authors from their earlier publications in which healthy individuals were included as control subjects. Healthy subjects (n = 433) ranged in age from 7 to 78 years. Age-stratified reference values of the NO parameters were significantly different. Gender differences were only observed in the 20-49 age group. The results from the multiple regression models in subjects older than 20 years revealed that age, height and gender interaction together explained 6% of variation in F_ENO at 50 ml s^-1 (F_ENO₅₀), 4% in J_awNO, 16% in C_awNO, 8% in D_awNO and 12% in C_ANO. In conclusion, in this study we have generated reference values for NO parameters from an extended NO analysis of healthy subjects. This is important in order to be able to use these parameters in clinical practice.