CHICAGO — Two new studies add to the rapidly growing body of evidence that inflammation can be a powerful predictor of heart disease.

The findings could help explain why people with no known risk factors such as high cholesterol or high blood pressure can still have heart attacks.

One study found that levels of an enzyme called MPO were elevated in people who had had heart attacks, heart-bypass surgery and narrowed coronary arteries. The other study linked a different substance, interleukin 6, to an increased risk of death in heart patients. Both substances are associated with inflammation. The studies were published in today's Journal of the American Medical Association.

In recent years, doctors have come to suspect that smoldering inflammation — whether triggered by an infection or some other condition — can damage the walls of heart arteries, making them more prone to the fatty buildups that can lead to heart attacks.

One of the two studies found that patients with the highest levels of MPO, or myeloperoxidase, which is normally found in infection-fighting white blood cells, had a twentyfold greater risk of heart disease than those with the lowest levels. High levels were even found in people with no significant heart disease and with no risk factors such as high cholesterol and high blood pressure.

Cleveland Clinic researchers said that may help explain why heart attacks frequently occur in people previously thought to be healthy.

It is uncertain what caused the elevated MPO levels in some of the 333 patients studied, although Dr. Stanley Hazen, who coordinated the research, said he suspects a genetic flaw.

The second study involved more than 3,000 Scandinavian patients and found that high levels of interleukin 6 increased the risk of death in patients hospitalized with chest pain and other heart-attack symptoms. Interleukin 6 is a protein linked with inflammation and heart disease.

Patients whose blood tests showed high interleukin 6 levels faced a more than threefold risk of dying within six to 12 months of initial hospitalization, compared with patients with low levels. Angioplasty or bypass surgery significantly reduced the risk of death in these patients.

Abstract of article from JAMA

Association Between Myeloperoxidase Levels and Risk of Coronary Artery Disease
Renliang Zhang, MD, PhD; Marie-Luise Brennan, PhD; Xiaoming Fu, MS; Ronnier J. Aviles, MD; Gregory L. Pearce, MS; Marc S. Penn, MD, PhD; Eric J. Topol, MD; Dennis L. Sprecher, MD; Stanley L. Hazen, MD, PhD

Context  Myeloperoxidase (MPO), a leukocyte enzyme that promotes oxidation of lipoproteins in atheroma, has been proposed as a possible mediator of atherosclerosis.

Objective  To determine the association between MPO levels and prevalence of coronary artery disease (CAD).

Design, Setting, and Patients  Case-control study conducted from July to September 2000 in a US tertiary care referral center, including 158 patients with established CAD (cases) and 175 patients without angiographically significant CAD (controls).

Main Outcome Measures  Association of MPO levels per milligram of neutrophil protein (leukocyte-MPO) and MPO levels per milliliter of blood (blood-MPO) with CAD risk.

Results  Leukocyte- and blood-MPO levels were both significantly greater in patients with CAD than in controls (P<.001). In multivariable models adjusting for traditional cardiovascular risk factors, Framingham risk score, and white blood cell counts, MPO levels were significantly associated with presence of CAD, with an OR of 11.9 (95% CI, 5.5-25.5) for the highest vs lowest quartiles of leukocyte-MPO and an OR of 20.4 (95% CI, 8.9-47.2) for the highest vs lowest quartiles of blood-MPO.

Conclusions  Elevated levels of leukocyte- and blood-MPO are associated with the presence of CAD. These findings support a potential role for MPO as an inflammatory marker in CAD and may have implications for atherosclerosis diagnosis and risk assessment.

JAMA. 2001;286:2136-2142