Responsiveness to methacholine, but not leukotriene D4, correlates with fractional exhaled nitric oxide in asthma

Background and Aims Correlation between fractional exhaled nitric oxide (FeNO) and responsiveness to inhaled leukotriene D4 (LTD4) and methacholine (MCh) might be different. This study aims to determine the correlation between FeNO and airway responsiveness to LTD4 and MCh, and to compare the airway responsiveness to inhaled LTD4 and MCh and FeNO in non-smokers, patients without rhinitis and non-smokers without rhinitis. Methods In this cross-over study, asthmatic patients and healthy subjects underwent LTD4 and MCh inhalation challenge at a 2- to 14-day interval. The FeNO was measured by using NIOX MINO, a portable instrument, at the initial visit, before spirometry and inhalation challenge tests. Subgroup analyses were performed in asthmatic patients based on the categorisation of never-smoker group, non-rhinitis group and never-smoker without rhinitis group. Results Of 62 asthmatic patients enrolled, 43 did not have self-reported rhinitis (asthmatic patients without rhinitis), 56 were never-smokers (asthmatic non-smokers), giving rise to 37 non-smokers who did not have rhinitis (asthmatic non-smokers without rhinitis). Twenty-one healthy subjects were enrolled. Overall, Log10FeNO correlated with Log10PD20FEV1-MCh but not Log10PD20FEV1-LTD4 or Log10(LTD4/MCh potency ratio). Reduced FeNO was associated with significantly higher Log10PD20FEV1-MCh but not Log10PD20FEV1-LTD4, except for non-smokers. Compared with all asthmatic patients, asthmatic non-smokers without rhinitis were characterised by markedly reduced levels of Log10PD20FEV1-MCh but not Log10PD20FEV1-LTD4. The difference in all parameters did not reach statistical significance among asthmatic patients without rhinitis, asthmatic non-smokers and asthmatic non-smokers without rhinitis. Conclusion FeNO correlates with airway responsiveness to inhaled MCh but not LTD4, in asthmatic patients, particularly in asthmatic non-smokers without rhinitis.