MMP9 and chronic obstructive pulmonary disease: In our study, MMP-9 increased significantly with the severity of airway obstruction, and TIMP-1 changed slightly, suggesting an imbalance between proteases and protease inhibitors culminating in enhanced proteolytic activity and indicating the importance of the MMP-9/TIMP-1 ratio as a potential biomarker in airway remodeling and COPD development.