Guinea Pig Hearts Repaired By Human Stem Cells, Human Hearts Next Say Researchers

By Mo Mozuch on August 6, 2012 8:43 PM EDT

photo:yeepet.com
photo:yeepet.com

The heart is the strongest muscle in the body, but it also one of the weakest when it comes to repairing itself. Damage done to heart tissue after heart attacks often leads to more medical problems, and researchers have been looking for ways to increase the healing power of heart tissue cells so that, like skin cells, they can repair themselves quickly. A University of Washington study published in the journal Nature details an experiment in which heart muscle cells created from human stem cells repaired heart-attack damage in guinea pigs.

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"What we have done is prove that these cells do what working heart muscles do, which is beat in sync with the rest of the heart," said Chuck Murry, a cardiovascular biologist at the University of Washington in Seattle, who co-led the research.

The initial challenge for researchers was to find a laboratory animal with the right kind of heart. Cardiomyocytes, muscle cells, derived from human embryonic stem cells typically beat fewer than 150 times a minute. Electrical stimulation can increase the cardiomyocytes beat rate to a maximum of about 240 beats per minute. Rats and mice have a heart rate of  400 and 600 beats a minute, too fast for researchers. Guinea pigs, however, have a heart rate of about 200-250 beats per minute. After devising a system to suppress the guinea pigs' immune systems so that they would accept human cells, researchers began transplantation experiments.

To track the progress of the cells in the guinea pig hearts, the researchers used a new genetic engineering technology to insert a sensor gene into the cells that would fluoresce when contracted.  Michael LaFlamme, a cardiovascular biologist at the University of Washington, said that they could tell from the first transplant that the cells, and the experiment, worked. When he looked into the chest cavity the heart was "flashing back at us," he told Nature.

The long-term success of the experiment was seen four weeks later. When the guinea pigs were re-examined, researchers saw that the ones with the cardiomyocytes were stronger and healthier than hearts receiving other treatments.  Not everyone is optimistic that the findings represent a breakthrough in heart disease treatments, however.

Glenn Fishman, a cardiologist at New York University Langone School of Medicine, told Nature that "the conclusion that the human cells can connect with the guinea pig tissue is true, but the clinical implications are a bit of a stretch." Cardiomyocytes only engrafted in a small percentage of the scar tissue, he explains, and the increased health is due to the paracrine effect. The paracrine effect occurs when transplanted tissue rejuvenates neighboring host tissue. Fishman said that the paracrine effect itself is being studied as a treatment for heart disease.

LaFlamme remains optimistic that the experiment can lead to significant breakthroughs. It's exciting "to see that the cells can couple electrically", he says. "Now we can test new strategies to make more couple." And although cell transplants to humans might be a long way off, he adds, "I think it's a nut we can crack."

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