Myeloperoxidase (MPO)

Overview

Myeloperoxidase (MPO) is an enzyme predominantly found in neutrophils, a type of white blood cell, where it plays a critical role in the body"s innate immune defense by producing reactive substances that kill bacteria and fungi¹. MPO catalyzes the formation of hypochlorous acid (HOCl) from hydrogen peroxide and chloride ions, which is highly effective in microbial killing but can also contribute to tissue damage when overproduced¹. Tracking MPO levels is important because elevated MPO is linked to inflammation and oxidative stress, and it serves as a biomarker for cardiovascular diseases, autoimmune conditions, and other inflammatory disorders³⁵.

Scientific Background

MPO is a heme-containing peroxidase enzyme encoded by the MPO gene on chromosome 17⁵. It is stored in azurophilic granules of neutrophils and released during the respiratory burst, a rapid release of reactive oxygen species used to kill pathogens¹. MPO uses hydrogen peroxide (H₂O₂) to oxidize chloride ions, producing hypochlorous acid (HOCl), a potent antimicrobial agent³. Besides its antimicrobial role, MPO can oxidize low-density lipoprotein (LDL), contributing to atherosclerosis by promoting foam cell formation and endothelial dysfunction³. MPO also mediates protein modifications such as nitrosylation and chlorination, which can affect inflammation and tissue damage¹. Its activity links innate immunity with oxidative stress and chronic disease pathogenesis.

Measurement and Testing

MPO levels are commonly measured in blood serum using immunoassays that detect MPO protein or its antibodies⁴. Testing is often recommended for patients with suspected inflammatory or autoimmune diseases, such as vasculitis, or to assess cardiovascular risk^{43. Factors affecting MPO test results include acute infections, inflammatory states, and oxidative stress levels. Because MPO is released during neutrophil activation, transient elevations can occur with infections or tissue injury, so clinical context is important for interpretation.}

Reference Ranges

Standard reference ranges for MPO vary by laboratory and assay method but typically fall within low nanogram per milliliter concentrations in healthy individuals⁴. Levels may differ based on age, sex, and underlying health conditions. Elevated MPO is more common in older adults and those with chronic inflammatory or cardiovascular diseases. Interpretation of MPO levels requires consideration of demographic factors and clinical status, as mild elevations may be nonspecific, while significantly high levels often indicate active inflammation or oxidative stress.

High Values

Elevated MPO levels can result from acute or chronic inflammation, infections, autoimmune diseases (e.g., vasculitis), and cardiovascular conditions such as atherosclerosis and coronary artery disease^{35. High MPO contributes to oxidative tissue damage by producing reactive oxidants that modify lipids and proteins, promoting endothelial dysfunction and plaque formation in arteries3. Symptoms related to high MPO are often those of the underlying disease, including inflammation, fatigue, and cardiovascular events. Persistently elevated MPO is associated with increased risk of heart attacks and progression of chronic inflammatory diseases.}

Low Values

Low MPO levels are less commonly discussed but may reflect neutropenia (low neutrophil count) or impaired neutrophil function, which can reduce the body"s ability to fight infections effectively¹. Deficiency or low activity of MPO can lead to increased susceptibility to certain bacterial and fungal infections. However, low MPO is generally not a primary clinical concern unless associated with broader immune dysfunction.

Improving Biomarker Levels

To reduce elevated MPO levels and associated oxidative stress, lifestyle modifications such as adopting an anti-inflammatory diet rich in antioxidants, regular physical activity, smoking cessation, and stress management are beneficial⁵. Controlling underlying conditions like infections, autoimmune diseases, and cardiovascular risk factors (e.g., hypertension, hyperlipidemia) is critical. Some supplements with antioxidant properties may help modulate MPO activity, but clinical evidence is limited and should be guided by healthcare professionals. Targeted therapies to inhibit MPO are under research but not yet standard clinical practice.

Importance of Tracking

Monitoring MPO levels provides valuable insight into inflammatory and oxidative stress status, aiding early detection and risk stratification of cardiovascular and autoimmune diseases^{35. Tracking MPO can guide treatment decisions, evaluate disease progression, and assess response to therapy. Because MPO contributes to tissue damage, its measurement helps identify patients who may benefit from interventions to reduce inflammation and oxidative injury.}

Disclaimer

The information provided in this document is for educational purposes only and does not constitute medical advice. It is essential to consult with a qualified healthcare professional for any health concerns or before making any decisions related to your health or treatment.