Myeloperoxidase as a Biomarker in COPD.

This is a critical review of the myeloperoxidase (MPO) biomarker in chronic obstructive pulmonary disease (COPD), covering its biological potential, methodology of analysis, and clinical use. Chronic inflammation and oxidative stress mediated by neutrophils are critical processes in COPD, wherein MPO, a heme peroxidase derived from neutrophils, functions as an effector and potentially as a biomarker. Patients with COPD and smokers have a high concentration of MPO in their biological compartments, which correlates with neutrophilic load, oxidative injury, and airflow obstruction. Analytical investigations have shown that it is possible to measure MPO levels in serum, plasma, sputum, and exhaled breath condensate (EBC). Nonetheless, there is significant preanalytical variability, particularly concerning the distinction between serum and plasma. Serum MPO levels are often elevated due to ex vivo neutrophil degranulation during the clotting process, suggesting that plasma may provide a more accurate measure of circulating MPO levels. While MPO shows promise, particularly when integrated into multi-marker panels for inflammatory endotyping and risk stratification, its clinical application remains limited due to the lack of standardized assays and inter-study harmonization of results. This review summarizes the existing evidence of MPO as a biomarker of neutrophil-mediated COPD inflammation, and it can be noted that although biologically plausible, it requires further rigorous standardization and validation of specific matrices (plasma vs. serum) and inclusion into compound biomarker approaches to be translated into clinics.