Abstract
BACKGROUND: Asthma in people who are obese is often more difficult to manage and is associated with worse lung function and increased symptoms compared with asthma in non-obese people. This may involve airway neutrophilia, as neutrophilic airway inflammation is associated with more severe, steroid-resistant asthma. Neutrophil extracellular traps (NETs) are released from activated neutrophils and the level of NETs in airways disease has been associated with poor lung function. The aim of this study was to examine the presence of airway NETs in obese people with asthma. METHODS: Sputum samples from obese (n=63) and non-obese (n=61) subjects with asthma were analysed for NET content by measuring extracellular DNA (eDNA) by PicoGreen and DNA-elastase complexes by ELISA. Lung function was assessed by spirometry and asthma control was assessed by the Asthma Control Questionnaire-6 (ACQ6). RESULTS: DNA-elastase complexes were significantly increased in obese people with asthma (64.3 µg·mL(-1) (17.6-200.6) versus 30.8 µg·mL(-1) (11.8-96.1); p=0.032); however, sputum eDNA (8.2 µg·mL(-1) (3.9-21.1) versus 7.3 µg·mL(-1) (4.2-17.2); p=0.890) was similar between obese and non-obese people with asthma. Obese people with asthma with high sputum eDNA (eDNA >20 µg·mL(-1)) had lower lung function compared with non-obese and obese people with asthma with low sputum eDNA (eDNA ≤20 µg·mL(-1)) shown by decreased forced expiratory volume in 1 s (FEV(1)) % predicted (p<0.01) and forced vital capacity (FVC) % predicted (p<0.01). Sputum eDNA negatively correlated with FEV(1) % predicted (r= -0.374, p<0.001) and FVC %predicted (r= -0.293, p=0.001). CONCLUSION: NETs are increased in obese individuals with asthma and are associated with body mass index. Sputum eDNA is associated with poorer lung function and is also associated with sputum NETs. Hence, NETs may be a potential therapeutic target for obese asthmatic patients.