MPO and chronic obstructive pulmonary disease: MPO plays a very crucial role in the progression of inflammatory conditions including COPD, such as protein and lipid oxidation (Hazen et al., 1999); NF-κB activation (Van der Veen et al., 2009); release of RNS and inflammatory cytokines, namely, TNF-α, IL-6, and IL-8; and neutrophil activation in autocrine manner, ultimately resulting in increased neutrophil infiltration, and it is also involved in advanced glycation end product (AGE) formation, leading to proinflammatory and profibrotic mediator release (Anderson et al., 1999; Reynolds et al., 2008).