Bile acids in the lower airways is associated with airway microbiota changes in chronic obstructive pulmonary disease: an observational study

BACKGROUND: Chronic obstructive pulmonary disease (COPD) is a complex disorder with a high degree of interindividual variability. Gastrointestinal dysfunction is common in patients with COPD and has been proposed to influence the clinical progression of the disease. Using the presence of bile acid(s) (BA) in bronchoalveolar lavage (BAL) fluid as a marker of gastric aspiration, we evaluated the relationships between BAs, clinical outcomes and bacterial lung colonisation. METHODS: We used BAL specimens from a cohort of patients with COPD and healthy controls. BAs were profiled and quantified in BAL supernatants using mass spectrometry. Microbial DNA was extracted from BAL pellets and quantified using quantitative PCR. We profiled the BAL microbiota using an amplicon sequencing approach targeting the V3-V4 region of the 16S rRNA gene. RESULTS: Detection of BAs in BAL was more likely at the earliest clinical stages of COPD and was independent of the degree of airway obstruction. BAL specimens with BAs demonstrated higher bacterial biomass and lower diversity. Likewise, the odds of recovering bacterial cultures from BAL were higher if BAs were also detected. Detection of BAs in BAL was not associated with either inflammatory markers or clinical outcomes. We also observed different bacterial community types in BAL, which were associated with different clinical groups, levels of inflammatory markers and the degree of airway obstruction. CONCLUSION: Detection of BAs in BAL was associated with alterations in the airway bacterial communities. Further studies are needed to evaluate whether BAs in BAL can be used to stratify patients and predict disease progression trajectories.