Increased plasma and salivary nitrite and decreased bronchial contribution to exhaled NO in pulmonary arterial hypertension

Fractional exhaled nitric oxide in idiopathic pulmonary arterial hypertension and mixed connective tissue disease complicating pulmonary hypertension

BACKGROUND

Fractional exhaled nitric oxide (FeNO) has been extensively studied in various causes of pulmonary hypertension (PH), but its utility as a noninvasive marker remains highly debated. The objective of our study was to assess FeNO levels in patients with idiopathic pulmonary arterial hypertension (IPAH) and mixed connective tissue disease complicating pulmonary hypertension (MCTD-PH), and to correlate them with respiratory functional data, disease severity, and cardiopulmonary function.

METHODS

We collected data from 54 patients diagnosed with IPAH and 78 patients diagnosed with MCTD-PH at the Shanghai Pulmonary Hospital Affiliated to Tongji University. Our data collection included measurements of brain natriuretic peptide (pro-BNP), cardiopulmonary exercise test (CPET), pulmonary function test (PFT), impulse oscillometry (IOS), and FeNO levels. Additionally, we assessed World Health Organization functional class (WHO-FC) of each patient.

RESULTS

(1) The fractional exhaled concentration of nitric oxide was notably higher in patients with IPAH compared to those with MCTD-PH. Furthermore, within the IPAH group, FeNO levels were found to be lower in cases of severe IPAH compared to mild IPAH (P = 0.024); (2) In severe pulmonary hypertension as per the WHO-FC classification, FeNO levels in IPAH exhibited negative correlations with FEV1/FVC (Forced Expiratory Velocity at one second /Forced Vital Capacity), MEF50% (Maximum Expiratory Flow at 50%), MEF25%, and MMEF75/25% (Maximum Mid-expiratory Flow between 75% and 25%), while in severe MCTD-PH, FeNO levels were negatively correlated with R20% (Resistance at 20 Hz); (3) ROC (Receiving operator characteristic curve) analysis indicated that the optimal cutoff value of FeNO for diagnosing severe IPAH was 23ppb; (4) While FeNO levels tend to be negatively correlated with peakPETO2(peak end-tidal partial pressure for oxygen) in severe IPAH, in mild IPAH they had a positive correlation to peakO2/Heart rate (HR). An interesting find was observed in cases of severe MCTD-PH, where FeNO levels were negatively correlated with HR and respiratory exchange ratio (RER), while positively correlated with O2/HR throughout the cardiopulmonary exercise test.

CONCLUSION

FeNO levels serve as a non-invasive measure of IPAH severity. Although FeNO levels may not assess the severity of MCTD-PH, their significant makes them a valuable tool when assessing severe MCTD-PH.

Fractional nitric oxide measurement in exhaled air (FeNO): perspectives in the management of respiratory diseases

Exhaled nitric oxide (NO) production, upregulated by inflammatory cytokines and mediators in central and peripheral airways, can be easily and non-invasively detected in exhaled air in asthma and other respiratory conditions as a promising tool for disease monitoring. The American Thoracic Society and European Respiratory Society released recommendations that standardize the measurement of the fractional exhaled NO (FeNO). In asthma, increased FeNO reflects eosinophilic-mediated inflammatory pathways and, as a biomarker of T2 inflammation can be used to identify asthma T2 phenotype. In this setting its measurement has shown to be an important tool especially in the diagnostic process, in the assessment and evaluation of poor adherence or predicting positive response to inhaled corticosteroids treatment, in phenotyping severe asthma patients and as a biomarker to predict the response to biologic treatments. The discovery of the role of NO in the pathogenesis of different diseases affecting the airways and the possibility to estimate the predominant site of increased NO production has provided new insight on its regulatory role in the airways, making it suitable for a potential extended use in clinical practice for different pulmonary diseases, even though its role remains less clear than in asthma. Monitoring FeNO in pulmonary obstructive lung diseases including chronic bronchitis and emphysema, interstitial lung diseases, obstructive sleep apnea and other pulmonary diseases is still under debate but has opened up a window to the role NO may play in the management of these diseases. The use of FeNO is reliable, cost effective and recommendable in both adults and children, and should be implemented in the management of patients with asthma and other respiratory conditions.

Therapy for Pulmonary Arterial Hypertension: Glance on Nitric Oxide Pathway

Pulmonary arterial hypertension (PAH) is a severe disease with a resultant increase of the mean pulmonary arterial pressure, right ventricular hypertrophy and eventual death. Research in recent years has produced various therapeutic options for its clinical management but the high mortality even under treatment remains a big challenge attributed to the complex pathophysiology. Studies from clinical and non-clinical experiments have revealed that the nitric oxide (NO) pathway is one of the key pathways underlying the pathophysiology of PAH. Many of the essential drugs used in the management of PAH act on this pathway highlighting its significant role in PAH. Meanwhile, several novel compounds targeting on NO pathway exhibits great potential to become future therapy medications. Furthermore, the NO pathway is found to interact with other crucial pathways. Understanding such interactions could be helpful in the discovery of new drug that provide better clinical outcomes.

The Nitric Oxide Pathway in Pulmonary Arterial Hypertension: Pathomechanism, Biomarkers and Drug Targets

The altered Nitric Oxide (NO) pathway in the pulmonary endothelium leads to increased vascular smooth muscle tone and vascular remodelling, and thus contributes to the development and progression of pulmonary arterial hypertension (PAH). The pulmonary NO signalling is abrogated by the decreased expression and dysfunction of the endothelial NO synthase (eNOS) and the accumulation of factors blocking eNOS functionality. The NO deficiency of the pulmonary vasculature can be assessed by detecting nitric oxide in the exhaled breath or measuring the degradation products of NO (nitrite, nitrate, S-nitrosothiol) in blood or urine. These non-invasive biomarkers might show the potential to correlate with changes in pulmonary haemodynamics and predict response to therapies. Current pharmacological therapies aim to stimulate pulmonary NO signalling by suppressing the degradation of NO (phosphodiesterase- 5 inhibitors) or increasing the formation of the endothelial cyclic guanosine monophosphate, which mediates the downstream effects of the pathway (soluble guanylate cyclase sensitizers). Recent data support that nitrite compounds and dietary supplements rich in nitrate might increase pulmonary NO availability and lessen vascular resistance. This review summarizes current knowledge on the involvement of the NO pathway in the pathomechanism of PAH, explores novel and easy-to-detect biomarkers of the pulmonary NO.

Clinical Values of Nitric Oxide Parameters from the Respiratory System

BACKGROUND

Fractional exhaled nitric oxide (FENO) concentration reliably reflects central airway inflammation, but it is not sensitive to changes in the NO dynamics in the lung periphery. By measuring FENO at several different flow rates one can estimate alveolar NO concentration (C_ANO), bronchial NO flux (J_awNO), bronchial wall NO concentration (C_awNO) and the bronchial diffusivity of NO (D_awNO).

OBJECTIVE

We aimed to describe the current knowledge and clinical relevance of NO parameters in different pulmonary diseases.

METHODS

We conducted a systematic literature search to identify publications reporting NO parameters in subjects with pulmonary or systemic diseases affecting the respiratory tract. A narrative review was created for those with clinical relevance.

RESULTS

Estimation of pulmonary NO parameters allows for differentiation between central and peripheral inflammation and a more precise analysis of central airway NO output. C_ANO seems to be a promising marker of parenchymal inflammation in interstitial lung diseases and also a marker of tissue damage and altered gas diffusion in chronic obstructive pulmonary disease and systemic diseases affecting the lung. In asthma, C_ANO can detect small airway involvement left undetected by ordinary FENO measurement. Additionally, C_awNO and D_awNO can be used in asthma to assess if FENO is increased due to enhanced inflammatory activity (increased C_awNO) or tissue changes related to bronchial remodelling (altered D_awNO).

CONCLUSION

NO parameters may be useful for diagnosis, prediction of disease progression and prediction of treatment responses in different parenchymal lung and airway diseases. Formal trials to test the added clinical value of NO parameters are needed.

Exhaled nitric oxide is not a biomarker for idiopathic pulmonary arterial hypertension or for treatment efficacy

BACKGROUND

Idiopathic pulmonary arterial hypertension (IPAH) is a fatal illness. Despite many improvements in the treatment of these patients, there is no unique prognostic variable available to track these patients. The aim of this study was to evaluate the association between fractional exhaled nitric oxide (FeNO) levels, as a noninvasive biomarker, with disease severity and treatment outcome.

METHODS

Thirty-six patients (29 women and 7 men, mean age 38.4 ± 11.3 years) with IPAH referred to the outpatient's clinic of Masih Daneshvari Hospital, Tehran, Iran, were enrolled into this pilot observational study. Echocardiography, six-minute walking test (6MWT), FeNO, brain natriuretic peptide (BNP) levels and the functional class of patients was assessed before patients started treatment. Assessments were repeated after three months. 30 healthy non-IPAH subjects were recruited as control subjects.

RESULTS

There was no significant difference in FeNO levels at baseline between patients with IPAH and subjects in the control group. There was also no significant increase in FeNO levels during the three months of treatment and levels did not correlate with other disease measures. In contrast, other markers of disease severity were correlated with treatment effect over the three months.

CONCLUSION

FeNO levels are a poor non-invasive measure of IPAH severity and of treatment response in patients in this pilot study.

Effects of Oral Supplementation With Nitrate-Rich Beetroot Juice in Patients With Pulmonary Arterial Hypertension-Results From BEET-PAH, an Exploratory Randomized, Double-Blind, Placebo-Controlled, Crossover Study

BACKGROUND

The nitrate-nitrite-nitric oxide (NO) pathway may represent a potential therapeutic target in patients with pulmonary arterial hypertension (PAH). We explored the effects of dietary nitrate supplementation, with the use of nitrate-rich beetroot juice (BRJ), in patients with PAH.

METHODS AND RESULTS

We prospectively studied 15 patients with PAH in an exploratory randomized, double-blind, placebo-controlled, crossover trial. The patients received nitrate-rich beetroot juice (∼16 mmol nitrate per day) and placebo in 2 treatment periods of 7 days each. The assessments included; exhaled NO and NO flow-independent parameters (alveolar NO and bronchial NO flux), plasma and salivary nitrate and nitrite, biomarkers and metabolites of the NO-system, N-terminal pro-B-type natriuretic peptide, echocardiography, ergospirometry, diffusing capacity of the lung for carbon monoxide, and the 6-minute walk test. Compared with placebo ingestion of BRJ resulted in increases in; fractional exhaled NO at all flow-rates, alveolar NO concentrations and bronchial NO flux, and plasma and salivary levels of nitrate and nitrite. Plasma ornithine levels decreased and indices of relative arginine availability increased after BRJ compared to placebo. A decrease in breathing frequency was observed during ergospirometry after BRJ. A tendency for an improvement in right ventricular function was observed after ingestion of BRJ. In addition a tendency for an increase in the peak power output to peak oxygen consumption ratio (W peak/VO₂ peak) was observed, which became significant in patients reaching an increase of plasma nitrite >30% (responders).

CONCLUSIONS

BRJ administered for 1 week increases pulmonary NO production and the relative arginine bioavailability in patients with PAH, compared with placebo. An increase in the W peak/VO₂ peak ratio was observed after BRJ ingestion in plasma nitrite responders. These findings indicate that supplementation with inorganic nitrate increase NO synthase-independent NO production from the nitrate-nitrite-NO pathway.

Exhaled Nitric Oxide and Exhaled Breath Temperature as Potential Biomarkers in Patients with Pulmonary Hypertension

BACKGROUND

Pulmonary hypertension (PH) is a progressive fatal disease thus, noninvasive prognostic tools are needed to follow these patients. The aim of our study was to evaluate fractional exhaled nitric oxide (FeNO) and exhaled breath temperature (EBT) values in patients with PH from different causes and to correlate them with respiratory functional data.

METHODS

Twenty-four PH patients underwent spirometry, carbon monoxide diffusion (DLCO) test, transthoracic echocardiography, right-heart catheterization, and FeNO and EBT measurements.

RESULTS

We studied 3 groups according to the type of PH: 10 patients with pulmonary arterial hypertension (PAH) (group A), 11 patients with PH due to chronic obstructive pulmonary disease (COPD) (group B), and 3 patients with PH associated with left heart disease (group C). Mean FeNO values tend to be higher in group B (15.0 ± 9.3ppb) compared with other groups (respectively, 9.9 ± 5.7 and 8.5 ± 5.2 ppb in groups A and C; p = 0.271) but no statistical significance has been reached. Mean values of alveolar NO concentration (CANO) were higher in groups A and B compared to group C (respectively, 16.9 ± 12.6; 13.9 ± 6.8; and 6.7 ± 2.0 ppb) (p = 0.045). EBT mean values were significantly lower in group C when compared with other groups (group C: 29.0 +- 1.3°C, groups A and B: 30.9 ± 1.3 and 31.2 ± 1.2°C, respectively: p = 0.041). EBT levels were inversely correlated to mean pulmonary artery pressure (PAPm) levels (Spearman coefficient -0.481; p = 0.017).

CONCLUSIONS

eNO, CANO, and EBT have been evaluated in three groups of PH patients. Interestingly EBT reduction was correlated with PAPm increase, whereas FeNO was higher in COPD patients and CANO in PAH and COPD groups. Further studies are needed to clarify EBT, FeNO, and CANO roles as biomarkers in the monitoring of patients with PH.

Fractional Exhaled Nitric Oxide Measurement in Pulmonary Hypertension: A Follow-Up Study

Pulmonary hypertension (PH) is a fatal disease although significant improvements in treatment are achieved. Easily implemented and noninvasive prognostic techniques are needed while following-up these patients. The aim was to investigate the role of fractional exhaled nitric oxide (FeNO) in follow-up for patients with PH. In this longitudinal study, patients with pulmonary arterial hypertension (PAH) and chronic thromboembolic PH (CTEPH) who were seen in PH Outpatient Clinic, Istanbul Faculty of Medicine, Istanbul University, were enrolled in the study. Echocardiography, 6-minute walking test, brain natriuretic peptide, and FeNO measurements were performed, and World Health Organization functional class was evaluated to all patients at baseline, and third, and sixth months. Right-heart catheterization and pulmonary function tests at the time of diagnosis were recorded. The study comprised 31 patients (23 women, 8 men; mean age: 53.4 ± 17.1 years) with PAH (n = 19) and CTEPH (n = 12) and 80 healthy controls. Patients with PH had lower FeNO values than the control group (16.5 ppb vs 19.8 ppb; P < .05). Fractional exhaled nitric oxide values did not change during follow-up and did not correlate with other follow-up measures except tricuspid annular plane systolic excursion values. Fractional exhaled nitric oxide was higher in the idiopathic PAH subgroup at baseline and at third month than patients with PAH associated with other diseases. Fractional exhaled nitric oxide did not change in patients who had clinical deterioration. As a conclusion; Patients with PH had lower FeNO values than healthy controls, but FeNO did not change significantly during follow-up. Large-scale studies with prolonged follow-up periods are needed to understand the role of FeNO in the follow-up of the patients with PH.

Profiling nitric oxide metabolites in patients with idiopathic pulmonary arterial hypertension

Intact nitric oxide (NO) signalling is critical to maintaining appropriate pulmonary vascular tone. NO bioavailability is reduced in patients with pulmonary arterial hypertension. This study aimed to examine the impact of NO plasma metabolites (NOx) relative to haemodynamic dysfunction and mortality in patients with idiopathic pulmonary arterial hypertension (IPAH).

A total of 104 consecutive adult IPAH patients who had undergone genetic counselling when first diagnosed were enrolled in this prospective study.

The median concentration of NOx (μmol·L−1) was significantly lower in IPAH patients compared with healthy subjects, and was decreased further in 19 carriers of the bone morphogenetic protein-receptor type-2 (BMPR2) mutation compared to non-carriers. Reduced concentrations of NOx were correlated with mean pulmonary arterial pressure (mPAP), pulmonary vascular resistance (PVR) and cardiac output. Compared with higher baseline NOx concentrations, patients with a NOx concentration of ≤10 μmol·L−1 had a markedly worse survival. After adjustment for clinical features, a BMPR2 mutation and haemodynamics, a lower NOx level remained an increased risk of mortality.

Patients with IPAH had lower levels of plasma NOx, which correlated inversely with mPAP, PVR and survival. Plasma NOx may be an important biomarker and prognostic indicator, suggesting that reduced NO synthesis contributes to the pathogenesis of IPAH.

Application of nitric oxide measurements in clinical conditions beyond asthma

Fractional exhaled nitric oxide (FeNO) is a convenient, non-invasive method for the assessment of active, mainly Th2-driven, airway inflammation, which is sensitive to treatment with standard anti-inflammatory therapy. Consequently, FeNO serves as a valued tool to aid diagnosis and monitoring in several asthma phenotypes. More recently, FeNO has been evaluated in several other respiratory, infectious, and/or immunological conditions. In this short review, we provide an overview of several clinical studies and discuss the status of potential applications of NO measurements in clinical conditions beyond asthma.

The fraction of NO in exhaled air and estimates of alveolar NO in adolescents with asthma: methodological aspects

RATIONALE

This study investigated the oral contribution to exhaled NO in young people with asthma and its potential effects on estimated alveolar NO (Calv(NO) ), a proposed marker of inflammation in peripheral airways. Secondary aims were to investigate the effects of various exhalation flow-rates and the feasibility of different proposed adjustments of (Calv(NO) ) for trumpet model and axial diffusion (TMAD).

METHODS

Exhaled NO at flow rates of 50-300 ml/sec, and salivary nitrite was measured before and after antibacterial mouthwash in 29 healthy young people (10-20 years) and 29 with asthma (10-19 years). Calv(NO) was calculated using the slope-intercept model with and without TMAD adjustment.

RESULTS

Exhaled NO at 50 ml/sec decreased significantly after mouthwash, to a similar degree in asthmatic and healthy subjects (8.8% vs. 9.8%, P = 0.49). The two groups had similar salivary nitrite levels (56.4 vs. 78.4 µM, P = 0.25). Calv(NO) was not significantly decreased by mouthwash. Calv(NO) levels were similar when flow-rates between 50-200 or 100-300 ml/sec were used (P = 0.34 in asthmatics and P = 0.90 in healthy subjects). A positive association was found between bronchial and alveolar NO in asthmatic subjects and this disappeared after the TMAD-adjustment. Negative TMAD-adjusted Calv(NO) values were found in a minority of the subjects.

CONCLUSIONS

Young people with and without asthma have similar salivary nitrite levels and oral contributions to exhaled NO and therefore no antibacterial mouthwash is necessary in routine use. TMAD corrections of alveolar NO could be successfully applied in young people with asthma and yielded negative results only in a minority of subjects.

Exhaled nitric oxide (FENO) in non-pulmonary diseases

Exhaled nitric oxide (F(E)NO) represents the only exhaled biomarker that has reached clinical practice even in primary care settings, due to the non-invasiveness of its assessment and ease of repeat measurements, even in patients with severe airflow obstruction. While F(E)NO has been suggested as a readily determined biomarker that can aid in the diagnosis and management of asthma, its potential role in pathophysiology of non-pulmonary diseases is less clear and therefore remains to be established. The purpose of the present review is to highlight the current literature investigating the use of F(E)NO in the diagnosis and management of non-pulmonary diseases.