Mending a Damaged Heart with Stem Cells

Scientists experimenting on rats have found that it is possible to repair damaged heart muscle through treatment with human embryonic cells. The researchers also found that the treatment improves heart function and slows down progression of heart failure.

Researchers have been trying to find a method of treating damaged hearts with stem cells and there have been some promising results. However, they have not yet been able to develop a method that is completely successful.

It has been proven without doubt that it is possible to create heart cells from embryonic cells. However, research has also found that most of these cells do not convert into heart muscles cells; and many of them fail to survive after they are transplanted into a damaged heart.

Now researchers led by Dr. Charles Murry at the Centre for Cardiovascular Biology and Regenerative Medicine at the University of Washington in Seattle have found a method of increasing the survival rates of these cells.

The research team developed a cocktail that allowed the stem cells to survive. Cells treated with this special “survival” mixture were then injected into laboratory rats that had had their hearts damaged in a manner similar to that from a heart attack.

“If we prepared our cells in this cocktail and transplanted them, we could get virtually 100% of the rats to have human heart muscle grafts in them,” Dr. Murry said. To further confirm their finding, the researchers created three other groups of rats and administered different concoctions to them.

One group of rats was given only injections of water; another group received just the survival cocktail without any cells while the third group was administered non-cardiac cells. The effects on these rats were then compared with the first group of rats. It was observed that rats in all the three groups that did not receive the human heart cells developed heart failure.

“In contrast, the animals that got the human heart muscle grafts implanted in them had a complete reversal of the progression of heart failure,” Dr. Murry said and noted that their study shows it is possible to grow heart muscle even in an injured heart.

“In patients who had suffered a heart attack, if we were able to re-muscularise 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.”

Dr. Murry finds their finding promising but also feels that studies should be carried out in larger animals such as sheep or pigs before it can be confirmed. The hearts of larger animals beat slower than rats – 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.

In the opinion of Dr. Kenneth R. Chien, there are several issues that still need to be addressed before it would be possible to treat humans with stem cells following 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. Chien, a member of the Harvard Stem Cell Institute.

According to Dr. Chien, embryonic heart cells are different from adult stem cells in the sense that they appear to actually become heart muscle. Studies have found that adult stem cells create blood vessels to improve heart function, he explained.

Dr. Chien also noted that doctors need to ensure that the heart muscle continues to function after the stem cell transplantation by following up over an extended period. Care especially needs to be taken to check that some of the cells do not turn into cancer cells as has been found to happen 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 neighbouring cells,” Dr. 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,” Dr. Chien said. “But this is an important step.”

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