Nitric oxide within the concept of united airway disease : Exhaled and nasal nitric oxide in cystic fibrosis, asthma and upper airway inflammatory diseases

Abstract: Background: Within the concept of united airway disease, it is postulated that inflammatory disorders in the upper and lower airways are interrelated and influence each other. Fractional exhaled nitric oxide (FeNO) is an established biomarker of type-2 inflammation in the lower airways and is elevated in patients with asthma. However, the relation between nasal nitric oxide (nNO) and upper airway inflammation is less clear. Although cystic fibrosis (CF) is associated with increased airway inflammation, nitric oxide is not elevated in patients with CF.Aims: To study nNO and FeNO as biomarkers of type-2 inflammation in the upper and lower airways, respectively, in relation to symptoms, disease control and treatment of both upper and lower airway diseases, and in relation to systemic inflammation.Methods: This thesis is based on the MIDAS cohort of children and young adults with asthma (n=411) with a follow-up after 2-5 years (n=258), as well as one cohort of children and adults with CF (n=38) and one multicentre population-based cohort of middle-aged adults (n=5,824). Cross-sectional (Paper I-IV) and longitudinal (Paper III) analyses were performed. The main outcomes were nNO (Paper I-III) and FeNO (Paper II and IV) and their relations to IgE sensitisation, upper and lower airway symptoms and treatment, and systemic inflammation.Results: In subjects with asthma, nNO was associated with FeNO and increased bronchial responsiveness and nNO was higher in subjects with perennial sensitisation. In non-asthmatic middle-aged subjects with perennial sensitisation, rhinitis and rhinoconjunctivitis were associated with higher FeNO. There was also a positive interaction with perennial sensitisation for the relation between upper airway inflammatory disorders and FeNO. Treatment with nasal or inhaled corticosteroids was associated with lower nNO levels in subjects with asthma. In middle-aged subjects with asthma and perennial sensitisation, use of nasal corticosteroids related to lower FeNO, whereas use of inhaled corticosteroids related to higher FeNO levels. Patients with CF had lower levels of nNO and FeNO than controls. Moreover, lower FeNO levels were associated with lower lung function and higher blood neutrophil counts in CF.Conclusion: Within the concept of united airway disease, nNO is related to lower airway inflammation, responsiveness and treatment, and FeNO is related to upper airway inflammatory disorders, with a significant interaction with perennial sensitisation. In CF, lower FeNO is related to more severe disease with lower lung function and more systemic inflammation.