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TUESDAY, April 13 (HealthDayNews) -- High blood levels of a recently discovered protein that is secreted by fat cells are related to a reduced risk of heart attack, a new study finds.

This is the first study to link the protein, adiponectin, to heart disease in humans, and a lot more work is needed to learn exactly where -- and whether -- it figures into cardiovascular disease, said Dr. Tobias Pischon, a research associate at the Harvard School of Public Health and lead author of a report on the protein. It appears in the April 14 issue of the Journal of the American Medical Association.

But studies since adiponectin was discovered in 1995 have shown it has some extremely interesting relationships with known risk factors and equally interesting activities, Pischon added.

"It seems that adiponectin improves lipid sensitivity and increases lipid metabolism, so there is a possibility that it can directly protect against atherosclerosis," he said. Atherosclerosis is the process by which arteries gradually become blocked by fatty deposits.

In addition, high blood levels of adiponectin are associated with low readings of such major risk factors as blood pressure and LDL cholesterol, and with high levels of HDL cholesterol, the "good" kind that carries fat out of the arteries, Pischon says.

Adiponectin is also of interest because it is one of only three proteins known to be secreted by fat cells. Leptin, one of the other two, is being studied intensively in a number of laboratories because of its possible role in obesity.

The newly reported results come from blood samples taken between 1993 and 1995 from 18,225 men in the Health Professionals Follow-Up Study. The incidence of heart attacks in of men with the highest levels of adiponectin was about 60 percent less than in men with the lowest readings, the researchers found.

That relationship held when adjustments were made for family history of heart attack, body mass index, alcohol consumption, physical activity and history of diabetes and high blood pressure, the researchers said.

"The effects of adiponectin on risk of coronary heart disease merits further study," they concluded.

Pischon and his colleagues are beginning such studies. "Right now, we want to examine what predicts adiponectin levels," he said. "For example, is it influenced by diet? Then we want to confirm this finding in women."

Further studies are needed "to put this finding into perspective," Pischon said. "Adiponectin is related to other risk factors, such as HDL cholesterol and triglyceride levels. We want to see whether there is an interaction between it and those risk factors."

It is hard to draw conclusions because "it is pretty early yet in this field," he said.

An unrelated report in the same issue of the journal looked at a life-and-death issue in patients who have coronary artery bypass surgery: What factors contribute to the risk of fatal atrial fibrillation, a heartbeat abnormality that occurs in one of every three patients in the weeks following the procedure?

A group led by Dr. Joseph Mathew, an associate professor of anesthesiology at Duke University, followed 4,657 patients treated at 70 centers in 17 countries, looking at factors related to the risk of life-threatening atrial fibrillation.

"Probably the most important finding is that patients who have more than one episode of atrial fibrillation are at greatest risk," Mathew said. "These are the patients who require the most aggressive therapy."

The team found the risk was also higher among those whose were taken off ACE inhibitors and beta blockers for the surgery.

By including a large number of factors, the study will create a risk profile that doctors can use, he said. "People taking care of these patients can use the profile to define risk and make sure the patients are treated with appropriate medications," Mathew said.

More information

The American Heart Association has a list of other risk factors for heart disease as well as information on atrial fibrillation.

(SOURCES: Joseph Mathew, M.D., associate professor, anesthesiology, Duke University, Durham, N.C.; Tobias Pischon, M.D., M.P.H., research associate, Harvard School of Public Health, Boston; April 14, 2004, Journal of the American Medical Association)

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