MONDAY, Aug. 27, 2007 (HealthDay News) -- Experiments in rats show that human embryonic stem cells can repair damaged heart muscle, improve heart function and slow the progression of heart failure.
Using stem cells to repair damaged hearts is something that appears promising, but so far it has been fraught with problems.
Previous experiments have shown that it is possible to create heart cells from embryonic stem cells. However, most of these cells do not become heart muscle cells, and many don't survive once transplanted into a damaged heart.
"We found a way to increase the survival of these cells," said lead researcher Dr. Charles Murry, director of the Center for Cardiovascular Biology and Regenerative Medicine at the University of Washington, in Seattle.
Murry's team created a "survival" cocktail that prevented the cells from dying. The treated cells were then implanted in rats that had had their hearts damaged to simulate a heart attack.
"If we prepared our cells in this cocktail and transplanted them, we could get virtually 100 percent of the rats to have human heart muscle grafts in them," Murry said.
The researchers compared the rats receiving the cells with three other groups of rats. One group received only injections of water, and another group was given the survival cocktail without cells. The third group was given non-cardiac cells.
The researchers found that the rats that didn't receive the human heart cells all developed heart failure, according to the report in the Aug. 27 online issue of Nature Biotechnology.
"In contrast, the animals that got the human heart muscle grafts implanted in them had a complete reversal of the progression of heart failure," Murry said.
The study shows that growing heart muscle in an injured heart is possible, Murry noted. "In patients who had suffered a heart attack, if we were able to re-muscularize their heart with stem cell-derived heart muscle cells, this should prevent them from developing heart failure," he said. "The rub is that the rat is not a person."
Murry thinks that while the finding is promising, it needs to be confirmed in larger animals such as sheep or pigs, because their hearts beat slower. Rat hearts beat 450 times a minute, while the human heart beats about 70 times a minute. "So, there may be problems that were not predicted with the rat model," he acknowledged.
One expert thinks that while the results of this study are promising, there are still many problems to be overcome before stem cells can be used to treat humans after a heart attack.
"This study makes the case that you can use embryonic stem cells after a heart attack, and shows that there is an improvement in cardiac function," said Dr. Kenneth R. Chien, a member of the Harvard Stem Cell Institute.
In contrast to adult stem cells, these embryonic heart cells appear to actually be heart muscle. Experiments with adult stem cells seem to show improved heart function by creating blood vessels, Chien explained.
Chien noted that long-term follow-up is needed to be sure the heart muscle continues to function and that some of these cells don't become cancer cells, as has been the case with adult stem cells.
"The other issue is whether these cells will survive over a long time and how efficiently are they grafted in with the neighboring cells," Chien said. "In addition, because rat hearts beat so fast, they are resistant to arrhythmias. When you put this into an animal with a slower heart rate, would there be arrhythmias over the long term?"
"Clinical applications are many years away," Chien said. "But this is an important step."
More information
For more information on stem cells and heart attack, visit the U.S. National Institutes of Health.
