Azurocidin-1 as a mediator of bronchiectasis severity, epithelial defence, and target of dipeptidyl peptidase-1 inhibition: an international, multicohort study

Background: Dipeptidyl peptidase-1 (DPP1) inhibitors prevent the activation of neutrophil serine proteases and reduce exacerbations in people with bronchiectasis. We previously identified a novel effect of DPP1 inhibitors in reducing the neutrophil pseudoenzyme azurocidin-1 (AZU1). The aim of this study was to investigate the role of AZU1 in the pathophysiology of bronchiectasis. Methods: Sputum AZU1 concentrations were analysed in multiple cohorts. These consisted of two observational cohorts of patients with bronchiectasis (EMBARC BRIDGE cohort 1 and cohort 2) and a cohort of patients with chronic obstructive pulmonary disease (COPD; TARDIS COPD cohort) to correlate AZU1 with disease severity and exacerbations. A rhinovirus challenge study was used to investigate AZU1 concentrations during experimental exacerbation in COPD, people who smoke, and controls. A post-hoc analysis of the phase 2 WILLOW trial of brensocatib versus placebo was used to assess the effect of DPP1 inhibition on airway AZU1. Findings: Higher AZU1 sputum concentration was associated with increased bronchiectasis disease severity index (p<0·0001), decreased percentage predicted forced expiratory volume in 1 second (r=–0·4662, p<0·001), and increased exacerbation frequency (p<0·0019; EMBARC cohort 1, n=197). AZU1 was associated with radiological severity (Reiff score), symptoms (quality of life bronchiectasis respiratory symptom score), and bacterial infection (sputum microbiology and 16S microbiome alpha diversity; highest levels of AZU1 were found in airway samples with Pseudomonas aeruginosa; p<0·0001; EMBARC cohort 2, n=144). Bronchiectasis patients with bacterial and viral exacerbations had increased concentrations of AZU1 (p=0·0003; n=96). These findings were extended to COPD, in which AZU1 was related to COPD severity (COPD cohort, n=101), and in patients with COPD challenged with rhinovirus A16, AZU1 was increased at day 9 post-challenge (p<0·001; n=9). In-vitro AZU1 impaired ciliary function and epithelial integrity, suggesting a mechanism by which AZU1 drives disease pathogenesis. In a post-hoc analysis of the WILLOW trial, AZU1 was the most downregulated protein with brensocatib treatment (brensocatib 10 mg, n=71; brensocatib 25 mg, n=73; and placebo, n=71). Over 24 weeks, AZU1 was significantly reduced by DPP1 inhibition (p<0·0001). Interpretation: AZU1 was identified as a novel marker of disease severity in bronchiectasis, associated with bacterial infection and exacerbation, and targeted by DPP1 inhibition. Funding: EMBARC3 and Insmed.