MPO and rheumatoid arthritis: Myeloperoxidase also plays a role in the chemical modifications of different lipoproteins, protein nitrosylation, tyrosyl radical formation, and dityrosine crosslinking, etc. Myeloperoxidase gained special importance as a well-known biomarker due to its role in a number of inflammatory diseases including rheumatoid arthritis, cardiovascular diseases, neurodegenerative diseases, diabetic retinopathy, liver diseases, cancer, and transplant rejection.