Myeloperoxidase (MPO) is a heme-containing enzyme predominantly found in polymorphonuclear leukocytes (neutrophils) and monocytes. It plays a critical role in innate immunity by catalyzing the formation of reactive oxidants, chiefly hypochlorous acid (HOCl), from hydrogen peroxide and chloride ions. This enzymatic activity is central to the microbicidal function of immune cells and influences various metabolic and inflammatory pathways.

Role of MPO in Metabolism

• MPO catalyzes the conversion of hydrogen peroxide (H₂O₂) and chloride ions (Cl⁻) into hypochlorous acid (HOCl): a potent oxidant that contributes to pathogen killing.
• Beyond host defense: MPO-mediated oxidation modifies biomolecules such as low-density lipoproteins (LDL), forming MPO-oxidized LDL (Mox-LDL), which is implicated in vascular inflammation and atherosclerosis.
• MPO activity influences oxidative stress and inflammatory signaling: linking it to metabolic diseases and vascular damage.

Principle of MPO Activity Assay Kits

MPO assay kits provide quantitative measurement of MPO enzymatic activity in biological samples such as cell lysates, tissue extracts, serum, plasma, and body fluids. Two common detection methods are used:

• Colorimetric Assays: These rely on MPO catalyzing the oxidation of substrates (e.g., o-dianisidine or chromogenic probes) in the presence of H₂O₂, producing a colored product measurable by absorbance. The intensity of the color correlates with MPO activity.
• Fluorometric Assays: These detect MPO activity through fluorescent substrates that emit light upon MPO-catalyzed oxidation, offering enhanced sensitivity and suitability for high-throughput screening.

Key Features of MPO Assay Kits

• High sensitivity: detection limits as low as 0.05 mU per well.
• Versatility: applicable to various sample types including human serum, plasma, tissue homogenates, and cell lysates.
• Quantitative: allows determination of MPO activity units, facilitating comparisons across samples.
• Used extensively: in research on inflammation, oxidative stress, cardiovascular diseases, and immune response.

Biological and Clinical Relevance

MPO-generated HOCl and related reactive species contribute to pathogen clearance but also cause oxidative modifications in host tissues. MPO activity is associated with:

• Inflammatory diseases: such as atherosclerosis, where MPO-modified LDL promotes endothelial dysfunction and plaque formation.
• Oxidative stress-related tissue damage.
• Potential biomarker: for cardiovascular risk and therapeutic target.

Myeloperoxidase assay kits enable precise quantification of MPO activity, a pivotal enzyme linking immune metabolism and oxidative stress. Their application advances understanding of MPO’s role in health and disease, particularly in inflammation and vascular pathology.