Neutrophil Extracellular Traps are Increased in Severe Bronchiectasis and Reduced by Long-Term Azithromycin Treatment

Abstract

Background: Bronchiectasis is predominantly a neutrophilic inflammatory disease. There are no established therapies that directly target neutrophilic inflammation because of a lack of understanding of the underlying mechanisms leading to severe disease. Neutrophil extracellular trap (NET) formation is a mode of host defence that has been implicated in multiple inflammatory diseases. Methods: We conducted a series of UK and international studies to investigate the role of NETs in disease severity and treatment response in bronchiectasis. Nano LC/MS-MS was used to identify proteomic markers associated with disease severity, defined using the bronchiectasis severity index (BSI) (n=40). These were validated in two cohorts (n=175 and n=275) using a validated immunoassay to measure NETs. 20 patients with acute exacerbations of bronchiectasis were treated with intravenous antibiotics for 14 days and proteomics used to identify proteins associated with treatment response. Two studies of long-term macrolide treatment, one in bronchiectasis and a post-hoc analysis of the AMAZES trial in asthma, investigated the effect of macrolide treatment on NETs. Findings: 96 proteins were differentially expressed in sputum between severe and mild bronchiectasis. The most abundant and most discriminating were proteins known to be NET proteins. This was validated in two observational cohorts where sputum NETs were associated with BSI, quality of life, lung function, future risk of hospital admissions and mortality. Antibiotic treatment in 20 patients was associated with 23 significantly down-regulated and 16 up-regulated proteins, with the “neutrophil degranulation” pathway being most strongly implicated in response. Patients with Pseudomonas aeruginosa infection had a blunted proteomic and clinical response to treatment. Treatment with low dose azithromycin was associated with a significant reduction in NETs in sputum over 12 months in both bronchiectasis and asthma. Interpretation: NETs are identified as a key marker of disease severity and treatment response in bronchiectasis. Funding: Supported by the Scottish Government Chief Scientist Office (Senior Clinical Fellowship to JDC) and British Lung Foundation through the BLF Chair of Respiratory Research. Supported by the European Bronchiectasis Network (EMBARC), a European Respiratory Society Clinical Research Collaboration. Declaration of Interests: None to declare Ethics Approval Statement: The studies were approved by local research ethics committees and patients provided informed consent.