The possibility of using stem cells to rebuild tissue of patients with heart attacks and heart failure has revived hopes. But clinical trials have produced only modest results – and not in the way clinicians expected.Now the early results are pointing researchers toward other types of stem cells that may be better suited to repair cardiac muscle.
With over 5 million Americans now suffering from heart failure, the number is sure to rise as 76 million Baby Boomers grow older. Cardiologists, however, are expecting breakthroughs in stem cell therapy.
“We’re trying to tear pages out of
nature’s playbook,” says Dr. Douglas Losordo, director of the Program in Cardiovascular Regenerative Medicine at Northwestern Memorial Hospital in Chicago.Initially, stem
cells found in bone marrow were particularly tantalizing for heart repair.These stem cells were successfully used to rebuild the immune systems of cancer patients, and scientists discovered the cells have the capacity to grow into heart muscle, blood vessels, and other tissues.
In just a few minutes, a heart blockage can kill at least a billion cells because of a lack of oxygen. These cells don’t grow back, scar tissue remains, and a weakened circulatory system results.
Patients experiencing
heart failure have an average life expectancy of less than five years, according to Dr. Chuck Murry, director of the Center for Cardiovascular Biology at the University of Washington in Seattle. “It’s deadlier than breast cancer,” Dr. Murry says.
New Study Paths
From 2002 to 2006, there were at least 18 randomized controlled studies involving nearly 1,000 patients.
“Everyone started putting
bone marrow into the heart,” according to Dr. Christine Mummery, a researcher at Leiden University Medical Center in the Netherlands. She is responsible for studying how to turn stem cells into heart muscle cells known as cardiomyocytes.The therapy produced only marginal results, according to Dr. Mummery. But researchers found stem cells which don’t grow into new heart cells seem to help patients in other ways, and that’s what they’re analyzing.
“It’s a little
bit mysterious,” says Dr. Eduardo Marban, director of the Cedar-Sinai Heart Institute in Los Angeles.Dr. Marban believes
transplanted cells secrete chemicals which boost heart function, not because of new tissue growth. The “stem cells are raising an alarm to resident cardiac stem cells. They seem to work indirectly,” he says.Consequently, Dr. Marban started to study stem cells from the heart instead of bone marrow.
Unfortunately, the
so-called cardiac progenitor cells naturally repair heart muscle but far too slowly to cope with catastrophic injury. These cells are rare and account for about one in 40,000 working heart cells.But generated in larger concentrations researchers think cardiac progenitor cells might promote healing and reverse heart scarring.
“Let’s just say we’re extremely encouraged,” Dr. Marban says.
Multipurpose Helpers
In other labs, researchers are focused on more powerful, pluripotent stem cells which have the potential to grow into any type of tissue in the body.
Some labs are
using embryonic stem cells, and others are studying induced pluripotent stem cells derived from adult tissues and rewound to an embryonic state.At the Harvard Stem Cell Institute, Dr. Kenneth Chien has
grown mouse embryonic stem cells into a strip of mature cardiac tissue. According to the journal Science, the patch was only six or seven cell layers thick, similar to a heart “Band-Aid.”Further, embryonic stem cells run the risk of rejection and are still a long way from being tested in humans. These cells also can form into tumors and not beat in sync with surrounding heart tissue.
Some of the most promising work with pluripotent stem cells is about ramping up the heart’s own healing abilities.
WMB believes stem cell research holds promise for improving life expectancy, especially for those with severe heart problems. More and varied research in stem cell uses should be encouraged.
TechMan
