MIAMI – Adult stem cells might help repair hearts damaged by heart attack _ in part by becoming heart cells themselves.

That was the finding of a new study, released Monday, that points to a promising new treatment for heart-attack patients that could reduce mortality and lessen the need for heart transplants.

Adult stem cells also could help heal livers, kidneys, pancreases and other organs. If confirmed by further trials, the new therapy could be in general use within five years, estimates Dr. Joshua Hare, a University of Miami cardiologist and lead author of the 10-university study.

“This clearly did help heal the human heart,” Hare said.Though the study only involved 53 patients, it’s the first time adult stem cells have been shown to help repair heart damage.

Previous heart-attack treatments, such as angioplasty, have restored blood flow, but did not heal heart tissue.

“This is a pretty big deal. Echocardiograms showed improved heart function, particularly in those patients with large amounts of cardiac damage,” said Hare, who also is director of the UM Medical School’s Interdisciplinary Stem Cell Institute.

“They also had improvements in lung function.”

The study will appear in the Dec. 8 issue of the peer-reviewed Journal of the American College of Cardiology.

Researchers say it’s the strongest evidence so far that adult stem cells can actually differentiate, or turn into heart cells, to repair damage.

Until now, some researchers had believed only controversial embryonic stem cells could differentiate into heart or other organ cells.

The study suggests adult stem cells derived from bone marrow are more flexible than previously thought.

“This is an exciting first step in a direction many thought cell therapy couldn’t go,” said Dr. Robert Simari, a cardiologist at the Mayo Clinic in Rochester who was not involved in the trial.

“It has demonstrated safety and good changes.”

In the trial, 53 patients who had had heart attacks in the previous 10 days were injected with “mesenchymal,” or adult stem cells, then kept under close study for six months.

The stem cells, injected into a vein in the arm or leg, automatically gravitated to the damaged heart, drawn by chemical signals from the injured cells, Hare said.

Other researchers are looking at whether the same injected stem cells might be drawn to the liver, kidney or other organs if they are damaged.

Mesenchymal stem cells have the advantage that they can be taken from the bone marrow of an unrelated donor without needing to be matched by blood type.

In the future, Hare said, hospitals might keep stores of frozen stem cells on hand for speedy “off-the-shelf” use in treating heart attacks.

In earlier studies with other kinds of adult stem cells, the cells had to be drawn from the patient’s own bone marrow, which would be done only after the heart attack.

Also, other kinds of adult stem cells had to be injected directly into the heart by a catheter via a slit in the groin, or applied during open-heart surgery, while mesenchymal stem cells can be injected into any appropriate vein in arm or leg.

In the current study, the stem cells were extracted and purified and supplied by Osiris Therapeutics of Columbia, Md., which sponsored the study.

Patients who received the stem cells were compared to similar patients who received placebo injections. Both were followed by MRI and echocardiogram.

After six months, treated patients:  Were four times as likely to have improved overall condition.  Were able to pump more blood with each heartbeat than untreated patients. Had only one-quarter as many dangerous heart arrhythmias. Suffered no toxicity or other serious adverse side effects.

The way in which mesenchymal stem cells help repair a damaged heart is more complicated than the cells simply becoming heart cells, said Dr. Alan Heldman, a UM cardiologist who has worked on the project with Hare for 10 years at Johns Hopkins University and UM.

“The stem cells take part in the growth of new blood vessels to bring more oxygen to the heart. They help modulate the scarring from the heart attack. They fight inflammation.

There’s a lot going on,” he said. Hoping to speed the new stem-cell therapy into general use, UM researchers already are enrolling patients for the next phase of the trial.

In it, 220 patients will be treated at hospitals and universities in a dozen or more cities, Heldman said.

It should take less than two years. FDA approval of the procedure could clear it for general use within five years, Hare said. In an editorial accompanying the new study in the medical journal, cardiologist Dr. Marc Penn calls the study “an important step.”

“There is excitement in what the future holds with regard to advances in this field,” Penn writes.

• Fred Takser