MONDAY, April 16 (HealthScout) -- High levels of an altered form of what's commonly called the "bad" cholesterol could indicate an impending heart attack or other emergency, Japanese researchers report.
　　This altered form of low-density lipoprotein is known as oxidized LDL because it has reacted with oxygen, says lead researcher Dr. Makiko Ueda, a pathology professor at Osaka City University Medical School in Japan.

"These measurements of oxidized LDL are relatively new," says Dr. Sotirios Tsimikas, an associate professor of medicine at the University of California, San Diego. High blood levels of ordinary LDL cholesterol traditionally have been used to define cardiovascular risk. "Oxidized LDL is kind of a summation of all the cardiovascular risk factors," Tsimikas says.

Oxidized LDL is believed to play a key role in heart attacks and similar problems because it accumulates in the fatty layers of plaque that form in blood vessel walls and stimulates the process by which these plaques become inflamed and rupture.

The Japanese researchers measured oxidized LDL levels in 180 people: 45 who had just suffered heart attacks; 45 with unstable angina, or chest pain that occurs even when at rest and often is a precursor of a heart attack; 45 with less dangerous, stable angina, or chest pain that occurs during exertion; and 45 with no heart problems.

They found that oxidized LDL levels in the people who'd had heart attacks were nearly four times higher than in those with no heart problems. The levels also were double those of the people with stable angina and more than 70 percent higher than those with unstable angina, the study says.

The results "suggest a pivotal role for oxidized LDL in the genesis of coronary plaque instability and the development of acute coronary syndromes," the researchers write in tomorrow's issue of Circulation, an American Heart Association journal.

Someday, measurements of oxidized LDL could be used to measure coronary risk, but there's a ways to go first, writes Tsimikas, in an editorial that accompanies publication of the research.

"In these studies, they isolated oxidized LDL from the blood, which is not trivial," he says. "It took a couple of days to do it so they could run tests in their laboratories. Our group and others are trying to devise [methods] that will make it possible to do a simple blood test."

Dr. Donald A. Smith, director of lipid metabolism at the Cardiovascular Institute of Mount Sinai Medical Center in New York City, says such a test "could be used clinically to tell whether a patient is undergoing an acute syndrome or is at high risk of one in the near future."

But he says this type of test might not be useful for all people.

"If you look at their acute myocardial infarction [heart attack] group, you see that just a few had very high oxidized LDL levels, which brought the average up," Smith says. "So there is a tremendous overlap. Although it is possible that measuring oxidized LDL in plasma could be clinically useful, the overlap is a problem. If you are in the normal range, you could be having a heart attack or you couldn't."

The major point of the study is that "it shows that oxidized LDL is important and is associated with plaque," Smith says. "The next thing is to see whether it can be used in any practical way. Most people don't have high values even if they are having a heart attack."

The possibility of reducing risk by lowering levels of oxidized LDL has been explored in studies that have used vitamin E, an antioxidant, but the results are inconclusive, Tsimikas says. "Vitamin E may not be the perfect antioxidant," he says.
　　
　　From HealthScout