Exhaled matrix metalloproteinase-9 (MMP-9) in different biological phenotypes of asthma

BACKGROUND AND OBJECTIVES: Airway remodeling is a main feature of asthma. Different biological phenotypes of severe asthma have been recently recognized by the ENFUMOSA study group and among these one is characterized by neutrophilic airway inflammation. Concentrations of MMP-9 in airways have been suggested as a marker to monitor airway remodeling in asthma. OBJECTIVE: The aim of the present study was to explore airway remodeling in different biological phenotypes of asthma by measuring MMP-9 in EBC and correlating these with other variables. METHODS: Sixty consecutive subjects with asthma and 20 healthy controls were enrolled in the study. Exhaled MMP-9, pH and NO levels and inflammatory cells in sputum were measured in all subjects enrolled. RESULTS: We observed an increase of exhaled MMP-9 in asthmatic subjects compared to controls. Higher exhaled MMP-9 concentrations were described in severe asthmatics compared to mild to moderate especially in those with neutrophilic airway inflammation. We further found a correlation between exhaled MMP-9 and percentage of neutrophils in sputum, FEV1, exhaled NO and pH. CONCLUSION: Our results seem to substantiate the feasibility of measuring exhaled MMP-9 in the breath of asthmatic patients. MMP-9 may be considered a proxy of the amount of the ongoing airway remodeling in asthma. MMP-9 has been shown to be differentially released in different phenotypes of asthma. The measure of exhaled MMP-9 could help to monitor the ongoing airway remodeling, recognize severe stages of asthma, and possibly help determine the appropriate choice of therapy.