updated 11/24/2004 1:20:48 PM ET 2004-11-24T18:20:48

Texas scientists working with mice say a single dose of a common protein appears to protect the heart muscle from extensive damage after a heart attack.

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The protein, known as thyrosin beta 4, is produced by tissues throughout the body and is already known to help heal skin wounds. The researchers now are planning a clinical trial as early as next year in which paramedics would give the protein to heart attack victims in the ambulance to provide heart cells with early protection.

Scientists who did not contribute to the experiment said the protein might work better and easier than trying to isolate and implant stem cells to repair the heart and restore its function. Thyrosin also would not create the same political controversy as stem cell research.

Details of the mouse experiment appear in Thursday’s issue of the journal Nature.

“This report provides a tantalizing clue toward a workable remedy for this prevailing cause of heart failure,” said molecular biologist Michael D. Schneider of the Baylor College of Medicine in Houston, who reviewed the study for Nature.

In the experiment, researchers at the University of Texas Southwestern Medical Center in Dallas induced heart attacks in 58 mice by constricting blood flow in a major artery leading to the left ventricle, or the heart’s primary pumping chamber.

Half of the mice were injected with a dose of thyrosin beta 4, while the rest received a placebo. Forty-five mice survived the procedure and their progress was monitored over a four-week period.

Offers early protection
After a month, the mice treated with thyrosin showed 60 percent to 100 percent improvement in their hearts’ ability to contract and pump blood. That’s at least twice the improvement of the other mice, the Texas team reported.

Heart attacksThe biggest gains in heart function occurred within one to three days of their “attacks,” they said, while the other mice tended to get worse.

The thyrosin-treated mice also showed far less scar tissue in their hearts, indicating the treatment prevented death of heart muscle cells when they were deprived of oxygen, while levels of other protective immune molecules were increased.

The heart doesn’t normally repair itself; that’s one reason why heart attack victims tend to get weaker over time. But precisely how thyrosin works remains unclear.

In large doses, it might help the damaged adult heart recognize and reactivate a biochemical pathway by which cells can survive for periods of time even without oxygen.

Researchers said other questions about thyrosin must be resolved before it could be used as a heart attack remedy. For example, the protein is known to help cancer cells spread throughout the body, and physicians would not want a medication that carries such side effects.

“But for heart attacks, it appears to offer protection early,” said the study’s senior author, Deepak Srivastava. “We probably would administer it only once. So it would be less of a concern for long-developing diseases like cancer.”

Aside from its emergency uses, Srivastava said thyrosin doses might also help prevent brain damage that sometimes occurs during surgery when patients’ circulation systems are bypassed to heart-lung machines.

“Especially with infants, their brains aren’t done forming and they are very vulnerable during surgery,” he said. “By the time they are in first or second grades, studies are beginning to show they aren’t doing as well as other children. We’re obligated to find ways to better protect their brains.”

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