Matrix metalloproteinase 9 in exhaled breath condensate in patients with stable chronic obstructive pulmonary disease: an observational study

INTRODUCTION Data on the measurement of matrix metalloproteinase 9 (MMP-9) in exhaled breath condensate (EBC) from patients with chronic obstructive pulmonary disease (COPD) are scarce and inconsistent. OBJECTIVES We aimed to assess the usefulness of enzyme-linked immunosorbent assay (ELISA) and immunoenzymatic assay (IEA) for the measurement of MMP-9 in EBC, the agreement between the results of both methods, and the relationships between total and active MMP-9 in EBC and clinical and functional COPD characteristics. PATIENTS AND METHODS Total (ELISA and IEA) and active (IEA) MMP-9 levels were assessed in EBC from 70 patients with stable COPD and 21 controls and correlated with pulmonary function and COPD symptom severity. RESULTS MMP-9 levels did not reach the sensitivity threshold of the ELISA kit in any of the COPD patients and in 11 controls. Total and active MMP-9 (IEA) levels did not differ between COPD patients and controls. In COPD patients, total MMP-9 levels correlated positively with forced expiratory volume in 1 second (FEV1) and FEV1 to forced vital capacity ratio and inversely with residual volume to total lung capacity ratio. A weak positive correlation between active MMP-9 concentrations and COPD Assessment Test (CAT) score was found (r = 0.31, P = 0.01). CONCLUSIONS The utility of ELISA in MMP-9 assessment in EBC is limited in COPD patients, while MMP-9 measurement in EBC by IEA is feasible. The positive correlation between active MMP-9 and CAT score in our patients and the inverse relationship between total MMP-9 concentration and the degree of airway obstruction reflect the complex role of MMP-9 in COPD.