Aerobic fitness is associated with extracellular DNA levels in the sputum of patients with cystic fibrosis

Abstract

Aims: Patients with cystic fibrosis (CF) develop with progressive loss of lung function and aerobic fitness. However, the precise mechanisms of exercise intolerance are still controversial and appear to be influenced by several factors. This study aimed to evaluate the association of aerobic fitness with free DNA levels in the sputum of patients with CF.

Methods: This cross-sectional study included patients with CF older than 6 years, free from active exacerbations, but who were able to produce spontaneously expectorated sputum. Extracellular DNA in the sputum was quantified. Lung function (spirometry) and aerobic fitness (cardiopulmonary exercise testing [CPET]) were performed. In addition, demographic, anthropometric and clinical data were collected.

Results: Sixteen patients with a mean age of 19.4 ± 6.9 years and mean forced expiratory volume in the first second (FEV₁ ) of 51.8 ± 28.1 (% of predicted) were included. Mean peak oxygen consumption (VO₂ peak) was 32.8 ± 5.2 mL• kg^-1 • min^-1 , oxygen saturation at the end of the test was 90.6% ± 6.3% and mean extracellular DNA levels was 305.3 ± 153.6 μg/mL. Individuals with a VO₂ peak ≤ 30 mL• kg^-1 • min^-1 (P = .03) and a SpO₂ ≤ 90% at the end of the test (P = .03) had a greater amount of extracellular DNA in the sputum. The proportion of patients with reduced VO₂ peak in the group of patients with the lowest concentration of DNA in the sputum (<243 μg/mL) was significantly lower (0% vs 100%; P = .04).

Conclusion: There is an association between the presence of free DNA in sputum and aerobic fitness in patients with CF.