WEDNESDAY, Sept. 7, 2005 (HealthDay News) -- A German study points to another major risk factor for heart attacks and other cardiovascular problems -- low levels of the cells that repair damage to the lining of arteries.
People with the lowest blood levels of these endothelial progenitor cells had a substantially increased risk of a major incident such as a heart attack and of dying.
The findings, by cardiologists at the University of Saarland, appear in the Sept. 8 issue of the New England Journal of Medicine.
Endothelial progenitor cells are made in the bone marrow and migrate to the arteries, where they are used to repair the damage caused by diabetes, high cholesterol levels and inflammation, said Dr. Anthony Rosenzweig, who has done extensive work on the cells and wrote an editorial accompanying the report.
"There has been a lot of literature about the association between low levels of progenitor cells and cardiovascular risk," said Rosenzweig, who is leader of the cardiovascular program at the Harvard Stem Cell Institute. "This is the first study that links the number of these cells to cardiovascular events. It is a larger study and a longer study than any done before, and it is linked to hard clinical endpoints such as death."
The German researchers followed 519 patients with known coronary artery disease, using sophisticated tests such as flow cytometry to determine blood levels of the cells. In the year after the first measurements were made, 214 participants had major cardiovascular events, and 43 of them died.
The risk of death from cardiovascular disease was two-thirds lower for people with the highest progenitor cell levels, compared with those who had the lowest levels, the study found.
One possible explanation for the findings is that "people with low levels of the cells are less able to respond to noxious stimuli in the environment, such as high cholesterol levels," Rosenzweig said.
There are different theories about the cause of low levels of the cells, said Dr. Brian H. Annex, director of vascular medicine at Duke University Medical Center, and a member of a team that has done extensive research in the field.
"You could imagine a group of patients who are somehow predisposed to have less of these progenitor cells and so are at increased risk of cardiovascular events because of a reduced repair capacity," he said. "Or it could be that the disease of atherosclerosis consumes these cells, until you reach the point where you can no longer generate enough cells to repair arterial damage."
The German study "does open up a number of interesting questions that we will be exploring," Annex said. "This is certainly a major step in understanding the relationship, but there are a lot of unknowns -- why are the values low in some people, what are the mechanisms of damage, what therapies can be used to increase the numbers of cells?"
Tests for progenitor cells are not likely to be widely used in the near future, Rosenzweig said, because "these are not things that are easy to do routinely in most hospitals in the United States."
Laboratory studies of therapies to increase progenitor cell levels have begun, he said, but the immediate lesson is to reinforce the standard methods of reducing the risk of cardiovascular disease.
Diabetes, high cholesterol and smoking reduce progenitor cell levels, while exercise and cholesterol-reducing statin drugs increases them, Rosenzweig said. "In some ways, this report reinforces the advice to stick with established therapies," he said.
Learn more about the known risk factors for heart disease from the American Heart Association.