CTSG and chronic obstructive pulmonary disease: Their activation can release specific inflammatory mediators that cause irreversible airway damage, such as neutrophil elastase, matrix metalloproteinase-9 (MMP-9), cathepsin G, matrix metalloproteinase-48 (MMP-48), and myeloperoxidase (MPO), These substances can contribute to the pathophysiological mechanisms [35] of COPD.