MPO IN DEPTH

The enzyme myeloperoxidase, (MPO), in our bodies played a role in the past as a defense. But in modern civilization it causes our demise. This intra White Cell enzyme generates reactive oxidants that kills invading microbes. In modern times it hastens plaque build up inside our blood vessel walls. Three mechanisms have been elucidated by the scientists. The MPO oxidizes the LDL cholesterol, modifying it so it is atherogenic. This now bad, bad cholesterol is rapidly ingested by the macrophages that reside within the inside wall (endothelium) of our arteries. These ingest the LDL particles, get sick, die and spill their fatty guts thus enlarging the existing fatty streaks to form an inflammatory plaque. The second mechanism is it oxidizes the endothelial Nitric Oxide that normally keeps these cells healthy. Then this nefarious enzyme weakens the fibrous cover of the plaque, which makes it rupture. There, along with the platelets already in the blood and another enzyme, Plaq2, a micro-clot forms to patch the weak spot. If that clot does not spontaneously dissolve, it blocks blood flow to the heart or brain, a heart attack or stroke usually occurs.

The increased amounts of MPO can be measured in the blood. If greater than 723 pmol/L, there is a 5-fold increase of a catastrophic event even in the absence of other cardiovascular risk factors. But if other risk factors are present a high value makes it much more dangerous. MPO is also used clinically in the Emergency Room to determine if the acute chest pain that the patient is having is a heart attack or not. Another emerging use is that it predicts the severity of heart failure (inability of the heart to pump enough blood) and the prognosis. It is also used to determine the rate of narrowing of the carotid arteries.

Statins decrease MPO levels and Acetaminophen blocks its activity, which stops the transformation of the bad cholesterol (LDL) that is available for the macrophages to ingest. This important test can be done by the Cleveland Clinic, through Cleveland Heart Lab by a special arrangement with a local physician. Blood samples, are overnighted to them for MPO and four other valuable markers. They include urinary Isoprostain and Microalbumin; a pro-oxidant and an arterial disrupter, HsCRP; indicating lining damage, and Plac2; a predictor of plaque rupture. Many insurance companies and Medicare now cover the test. And for those who don't have coverage, the cost is relatively inexpensive: $189 for MPO and the other tests conducted with it.