High alveolar concentration of nitric oxide is associated with alveolitis in scleroderma

Distal Lung Inflammation Assessed by Alveolar Concentration of Nitric Oxide Is an Individualised Biomarker of Severe COVID-19 Pneumonia

Pulmonary sequelae as assessed by pulmonary function tests (PFTs) are often reported in patients infected by SARS-CoV-2 during the post-COVID-19 period. Little is known, however, about the status of pulmonary inflammation during clinical recovery after patients’ discharge from the hospitals. We prospectively measured PFTs coupled with the exhaled nitric oxide (NO) stemming from the proximal airways (FeNO) and the distal lung (CaNO) in 169 consecutive patients with varying degrees of the severity of COVID-19 six weeks to one year after acute infection by SARS-CoV-2. The proportions of patients with abnormal PFTs, defined as the presence of either obstructive/restrictive patterns or impaired lung gas transfer, or both, increased with the severity of the initial lung disease (15, 30, and 52% in patients with mild, moderate, and severe COVID-19). FeNO values remained within normal ranges and did not differ between the three groups of patients. CaNO, however, was significantly higher in patients with severe or critical COVID-19, compared with patients with milder forms of the disease. There was also an inverse relationship between CaNO and DLCO. We conclude that the residual inflammation of the distal lung is still present in the post-COVID-19 follow-up period, in particular, in those patients with an initially severe form of COVID-19. This long-lasting alveolar inflammation might contribute to the long-term development of pulmonary fibrosis and warrants the regular monitoring of exhaled NO together with PFTs in patients with COVID-19.

High alveolar nitric oxide is associated with steeper lung function decline in foundry workers

Occupational dust exposure induces inflammatory responses that often precede the onset of clinical disease. Inflammation in the peripheral part of the lung can be demonstrated by measuring the alveolar NO concentration (C_ANO) in exhaled breath. The aim of the study was to assess whether cumulative dust exposure affects the change in C_ANO during follow-up and whether baseline C_ANO can predict an impairment in lung function during follow-up in foundry workers. We examined 74 dust-exposed and 42 nonexposed foundry workers and measured C_ANO and lung function at baseline and after 7 years of follow-up. An increase in C_ANO during the follow-up period was positively associated with cumulative dust exposure in foundry work (p= 0.035). Furthermore, a higher baseline C_ANO was associated with an accelerated decline in the forced vital capacity (FVC) during the follow-up period (absolute decrease in FVCp= 0.021, relative decrease in FVCp= 0.017). Higher cumulative dust exposure in foundry work is associated with a greater increase in C_ANO during follow-up, suggesting ongoing pulmonary inflammation in these subjects. Importantly, a high baseline C_ANO is associated with an accelerated decline in lung function, suggesting that C_ANO measurements might serve as a screening tool for high-risk workers.

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 in Systemic Sclerosis Lung Disease

Background. Exhaled nitric oxide (eNO) is a potential biomarker to distinguish systemic sclerosis (SSc) associated pulmonary arterial hypertension (PAH) and interstitial lung disease (ILD). We evaluated the discriminative validity, feasibility, methods of eNO measurement, and magnitude of differences across lung diseases, disease-subsets (SSc, systemic lupus erythematosus), and healthy-controls. Methods. Consecutive subjects in the UHN Pulmonary Hypertension Programme were recruited. Exhaled nitric oxide was measured at 50 mL/s intervals using chemiluminescent detection. Alveolar and conducting airway NO were partitioned using a two-compartment model of axial diffusion (CMAD) and the trumpet model of axial diffusion (TMAD). Results. Sixty subjects were evaluated. Using the CMAD model, control subjects had lower median (IQR) alveolar NO than all PAH subjects (2.0 (1.5, 2.5) versus 3.14 ppb (2.3, 4.0), p = 0.008). SSc-ILD had significantly lower median conducting airway NO compared to controls (1009.5 versus 1342.1 ml⁎ppb/s, p = 0.04). SSc-PAH had increased median (IQR) alveolar NO compared to controls (3.3 (3.0, 5.7) versus 2.0 ppb (1.5, 2.5), p = 0.01). SSc-PAH conducting airway NO inversely correlated with DLCO (r -0.88 (95% CI -0.99, -0.26)). Conclusion. We have demonstrated feasibility, identified that CMAD modeling is preferred in SSc, and reported the magnitude of differences across cases and controls. Our data supports discriminative validity of eNO in SSc lung disease.

Exhaled nitric oxide in pulmonary arterial hypertension associated with systemic sclerosis

The fractional exhaled concentration of nitric oxide (FE_NO) has been shown to be reduced in idiopathic pulmonary arterial hypertension (PAH) but has not been adequately studied in PAH associated with systemic sclerosis (SSc). We measured FE_NO at an expiratory flow rate of 50 mL/s in 21 treatment-naive patients with SSc-associated PAH (SSc-PAH), 94 subjects with SSc without pulmonary involvement, and 84 healthy volunteers. Measurements of FE_NO at additional flow rates of 100, 150, and 250 mL/s were obtained to derive the flow-independent nitric oxide exchange parameters of maximal airway flux (J'aw_NO) and steady-state alveolar concentration (CA_NO). FE_NO at 50 mL/s was similar (P = 0.22) in the SSc-PAH group (19 ± 12 parts per billion [ppb]) compared with the SSc group (17 ± 12 ppb) and healthy control group (21 ± 11 ppb). No change was observed after 4 months of targeted PAH therapy in 14 SSc-PAH group patients (P = 0.9). J'aw_NO was modestly reduced in SSc group subjects without lung disease (1.2 ± 0.5 nl/s) compared with healthy controls (1.64 ± 0.9; P < 0.05) but was similar to that in the SSc-PAH group. CA_NO was elevated in individuals with SSc-PAH (4.8 ± 2.6 ppb) compared with controls with SSc (3.3 ± 1.4 ppb) and healthy subjects (2.6 ± 1.5 ppb; P < 0.001 for both). However, after adjustment for the diffusing capacity of CO, there was no significant difference in CA_NO between individuals with SSc-PAH and controls with SSc. We conclude that FE_NO is not useful for the diagnosis of PAH in SSc. Increased alveolar nitric oxide in SSc-PAH likely represents impaired diffusion into pulmonary capillary blood.

RhoA/Rho-kinase activation promotes lung fibrosis in an animal model of systemic sclerosis

BACKGROUND

Systemic sclerosis (SSc) is a connective-tissue disease characterized by vascular injury, immune-system disorders, and excessive fibrosis of the skin and multiple internal organs. Recent reports found that RhoA/Rho-kinase (ROCK) pathway is implicated in various fibrogenic diseases. Intradermal injection of hypochlorous acid (HOCl)-generating solution induced inflammation, autoimmune activation, and fibrosis, mimicking the cutaneous diffuse form of SSc in humans. Our study aimed firstly to describe pulmonary inflammation and fibrosis induced by HOCl in mice, and secondly to determine whether fasudil, a selective inhibitor of ROCK, could prevent lung and skin fibroses in HOCl-injected mice.

METHODS

Female C57BL/6 mice received daily intradermal injection of hypochlorous acid (HOCl) for 6 weeks to induce SSc, with and without daily treatment with fasudil (30 mg·kg(-1)·day(-1)) by oral gavage.

RESULTS

HOCl intoxication induced significant lung inflammation (macrophages and neutrophils infiltration), and fibrosis. These modifications were prevented by fasudil treatment. Simultaneously, HOCl enhanced ROCK activity in lung and skin tissues. Inhibition of ROCK reduced skin fibrosis, expression of α-smooth-muscle actin and 3-nitrotyrosine, as well as the activity of ROCK in the fibrotic skin of HOCl-treated mice, through inhibition of phosphorylation of Smad2/3 and ERK1/2. Fasudil significantly decreased the serum levels of anti-DNA-topoisomerase-1 antibodies in mice with HOCl-induced SSc.

CONCLUSIONS

Our findings confirm HOCl-induced pulmonary inflammation and fibrosis in mice, and provide further evidence for a key role of RhoA/ROCK pathway in several pathological processes of experimental SSc. Fasudil could be a promising therapeutic approach for the treatment of SSc.

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.

Increased exhaled nitric oxide precedes lung fibrosis in two murine models of systemic sclerosis

Exhaled nitric oxide (NO) is increased as a result of lung inflammation, which in turn causes subsequent interstitial lung disease in patients with systemic sclerosis (SSc). However, the exact time course of inflammatory and fibrotic changes in the SSc lung has not yet been described. Our objective was to assess the chronological evolution of lung inflammatory and fibrotic processes in mice pre-treated with hypochlorous acid (HOCl) or bleomycin. C57BL/6 mice were randomized into three groups receiving subcutaneous injections of HOCl, bleomycin, or PBS for 2, 4 or 6 weeks. Exhaled NO (eNO) was measured at the end of each injection period and after 2 resting weeks without injection (8 week group). Mice were then sacrificed to obtain skin and lung tissues to measure fibrotic changes and NO synthases (NOS) expression. Increased eNO, inducible NOS and nitrotyrosine expression in bronchial epithelium, lung neutrophils and macrophages were observed at early phases in both HOCl- and bleomycin-treated mice. Conversely, lung vascular endothelial NOS expression decreased significantly at 6th and 8th weeks. Skin fibrosis was significantly increased from the 4th week and lung fibrosis from 6th week. We conclude that lung inflammation occurs early after injury as reflected by increased exhaled NO and inducible NOS expression, and precedes fibrotic changes in skin and lungs of mice pre-treated with bleomycin and HOCl. Early detection and treatment of pulmonary inflammation might be useful in preventing subsequent occurrence of lung fibrosis in SSc patients.

[Use of pulmonary function tests and biomarkers studies to diagnose and follow-up interstitial lung disease in systemic sclerosis]

Interstitial lung disease (ILD) is becoming one of the main causes of death of patients with systemic sclerosis (SSc). The prevalence of ILD associated with SSc (SSc-ILD) varies from 33% to 100% according to diagnostic methods. Clinical features such as dyspnea on exertion, dry cough, and chest pains are not specific and usually late-appearing, implying more specific tests in the diagnostic, prognosis, and follow-up of ILD in patients with SSc. High resolution thoracic CT scanner (HRCT) is more sensitive than chest X-ray in the detection of SSc-ILD. Pulmonary function tests (PFT) are non-invasive and periodically used to assess the impacts of SSc on respiratory function. Diagnostic values of bronchoalveolar lavage and histological examination on lung biopsy are controversial. However, these techniques are essential for studying cellular and molecular mechanisms underlying the pathophysiology of SSc-ILD. Several biomarkers such as surfactant-A (SP-A), -D (SP-D), mucin-like high molecular weight glycoprotein (KL-6), and chemokine CCL-18 have been implicated in SSc-PID. Serum levels of these proteins are correlated with the severity of SSc-ILD, as assessed by HRCT and/or PFT. Finally, alveolar concentration of exhaled nitric oxide can be used to screen SSc patients with high risk of deterioration of respiratory function, in whom immunosuppressant treatment could be useful in preventing the evolution to irreversible lung fibrosis.