MPO Levels: What High Results Mean for Your Heart Health

Myeloperoxidase (MPO) is an enzyme produced by white blood cells called neutrophils as part of the body’s response to inflammation. It helps defend the body against pathogens, making its presence a normal part of immune function.

The Biological Function of Myeloperoxidase

Myeloperoxidase is stored within neutrophils, the most common type of white blood cell in humans. When these neutrophils are recruited to a site of infection or tissue injury, they can release their contents, including MPO, to combat invading threats. This release is part of the immune system’s first line of defense against pathogens such as bacteria and fungi.

The primary function of MPO is to participate in a process known as the “oxidative burst.” During this event, MPO uses hydrogen peroxide and chloride ions to produce a potent antimicrobial substance called hypochlorous acid. This substance, which is the active component in household bleach, is highly effective at killing a wide range of microorganisms. The production of hypochlorous acid is a major part of the neutrophil’s ability to destroy foreign invaders.

This mechanism is a fundamental aspect of the innate immune system, the body’s non-specific defense network. By generating these powerful oxidants, MPO helps neutrophils efficiently clear infections and remove cellular debris from sites of injury.

MPO as a Clinical Health Marker

While the acute production of MPO is beneficial for fighting infections, its role in chronic conditions has drawn clinical attention. Persistent inflammation can cause neutrophils to continuously release MPO into the bloodstream and tissues. This sustained elevation means the powerful substances MPO produces can begin to inflict damage on the body’s own cells, which is why healthcare providers measure MPO levels as a marker for certain health risks.

Of particular concern is the effect of chronically high MPO on the cardiovascular system. The enzyme and its reactive products can damage the endothelium, the thin layer of cells lining the blood vessels. This damage contributes directly to the process of atherosclerosis, the hardening and narrowing of arteries. MPO promotes atherosclerosis by oxidizing low-density lipoprotein (LDL) cholesterol, leading to the formation of “foam cells,” a component of arterial plaque.

MPO activity can also make existing atherosclerotic plaques less stable. The enzyme can degrade the structural cap of the plaque, making it more prone to rupture. When a plaque ruptures, it can trigger the formation of a blood clot that blocks blood flow, potentially leading to a heart attack or stroke. For these reasons, a blood test for MPO is used to assess vascular inflammation.

Interpreting MPO Level Results

MPO levels are measured with a simple blood test, and the results help healthcare providers gauge a person’s risk for near-term cardiovascular events. While specific reference ranges can differ slightly between laboratories, results are categorized into levels of risk. These values are measured in picomoles per liter (pmol/L).

A low or normal MPO level is considered to be less than 420 pmol/L. Individuals with results in this range are thought to have a lower short-term risk of experiencing a heart attack or stroke. This suggests a minimal amount of vascular inflammation.

Borderline or intermediate MPO levels may indicate a moderate degree of vascular inflammation and a corresponding moderate risk of a cardiovascular event. A high MPO level, which some laboratories consider greater than 539 pmol/L, signifies substantial inflammation and a heightened risk for a heart attack or stroke in the near future. This risk is independent, meaning it provides information beyond what is learned from cholesterol panels or blood pressure readings.

Factors That Influence MPO Levels

Several health conditions and lifestyle choices can influence MPO levels. As a marker of inflammation, any condition characterized by chronic inflammation can lead to its elevation. Factors that can increase MPO levels include:

• Autoimmune diseases like rheumatoid arthritis and lupus
• Chronic infections
• Smoking
• Obesity

Conversely, certain strategies may help manage and potentially lower MPO levels. Adopting an anti-inflammatory diet, such as the Mediterranean diet, which is rich in fruits, vegetables, and antioxidants, may be beneficial. Regular physical exercise and quitting smoking are other direct actions that can reduce the inflammatory burden on the body.

Certain medications have also been shown to affect MPO. Statins, commonly prescribed to lower cholesterol, can also reduce MPO levels, adding to their protective cardiovascular effects. Any plan to manage MPO levels, whether through lifestyle changes or medication, should be developed and monitored in consultation with a healthcare provider.