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.