Associations of Sputum Biomarkers with Clinical Outcomes in People with Cystic Fibrosis

BackgroundAirway inflammation promotes bronchiectasis and lung injury in cystic fibrosis (CF). Amplification of inflammation underlies pulmonary exacerbations of disease. We asked whether sputum inflammatory biomarkers provide explanatory information on pulmonary exacerbations.Patients and MethodsWe collected sputum from randomly chosen stable adolescents and adults and prospectively observed time to next exacerbation, our primary outcome. We evaluated relationships between potential biomarkers of inflammation, clinical characteristics and outcomes and assessed clinical variables as potential confounders or mediators of explanatory models. We assessed associations between the markers and time to next exacerbation using proportional hazard models adjusting for confounders.ResultsWe enrolled 114 patients, collected data on clinical variables [December 8, 2014 to January 16, 2016; 46% male, mean age 28 years (SD 12), mean percent predicted forced expiratory volume in 1 s (FEV1%) 70 (SD 22)] and measured 24 inflammatory markers. Half of the inflammatory markers were plausibly associated with time to next exacerbation. Age and sex were confounders while we found that FEV1% was a mediator.Three potential biomarkers of RAGE axis inflammation were associated with time to next exacerbation while six potential neutrophil-associated biomarkers indicate associations between protease activity or reactive oxygen species with time to next exacerbation.ConclusionPulmonary exacerbation biomarkers are part of the RAGE proinflammatory axis or reflect neutrophil activity, specifically implicating protease and oxidative stress injury. Further investigations or development of novel anti-inflammatory agents should consider RAGE axis, protease and oxidant stress antagonists.Tweetable abstractSputum from 114 randomly chosen people with CF show RAGE axis inflammation, protease and oxidative stress injury are associated with time to next pulmonary exacerbation and may be targets for bench or factorial design interventional studies. (242 characters)