Researchers from United States have successfully healed the scars caused by a heart attack using stem cells gathered from the patient's own heart. The amount of scar tissue was halved in the small safety trial reported in the Lancet medical journal. The authors said there was also an “unprecedented” increase in new heart muscle.
A heart attack happens when the organ is starved of oxygen, such as a clot blocking the flow of blood to the heart. As the heart heals, the dead muscle is replaced with scar tissue, but because this does not beat like heart muscle the ability to pump blood around the body is reduced. About 1.3 million Americans have a heart attack each year. Doctors around the world are looking at ways of “regenerating” the heart to replace the scar tissue with beating muscle. Stem cells, which can transform into any other type of specialized cell, figure prominently in their plans.
For the new study the researchers conducted a trial at the Cedars-Sinai Heart Institute. It was designed to test the safety of using stem cells taken from a heart attack patient's own heart. Within a month of a heart attack, a tube was inserted into a vein in the patient's neck and was pushed down towards the heart. A sample of heart tissue, about “half the size of a raisin”, was taken. This was taken to the laboratory where the stem cells were isolated and grown. Up to 25 million of these stem cells were then put into the arteries surrounding the heart.
Twenty five patients took part in the trial. Before the treatment, scar tissue accounted for an average of 24% of their left ventricle, a major chamber of the heart. It went down to 16% after six months and 12% after a year. Healthy heart muscle appeared to take its place. The study said the cells, “have an unprecedented ability to reduce scar and simultaneously stimulate the regrowth of healthy [heart] tissue”.
One of the researchers Dr Eduardo Marban said, “While the primary goal of our study was to verify safety, we also looked for evidence that the treatment might dissolve scar and regrow lost heart muscle. This has never been accomplished before, despite a decade of cell therapy trials for patients with heart attacks. Now we have done it. The effects are substantial, and surprisingly larger in humans than they were in animal tests.”
“If we can regenerate the whole heart, then the patient would be completely normal,” Marban said. “We haven’t fulfilled that yet, but we’ve gotten rid of half of the injury, and that’s a good start.”
However, there was no increase in a significant measure of the heart's ability to pump - the left ventricle ejection fraction: the percentage of blood pumped out of the left ventricle. Prof Anthony Mathur, who is co-ordinating a stem cell trial involving 3,000 heart attack patients, said that even if the study found an increase in ejection fraction then it would be the source of much debate. He argued that as it was a proof-of-concept study, with a small group of patients, “proving it is safe and feasible is all you can ask”. “The findings would be very interesting, but obviously they need further clarification and evidence,” he added.
“The findings in this paper are encouraging,” Deepak Srivastava, director of the San Francisco-based Gladstone Institute of Cardiovascular Disease, said in an interview. “There’s a dire need for new therapies for people with heart failure, it’s still the No. 1 cause of death in men and women.”
Prof Jeremy Pearson, associate medical director at the British Heart Foundation, said, “It's the first time these scientists' potentially exciting work has been carried out in humans, and the results are very encouraging. These cells have been proven to form heart muscle in a petri dish but now they seem to be doing the same thing when injected back into the heart as part of an apparently safe procedure. It's early days, and this research will certainly need following up, but it could be great news for heart attack patients who face the debilitating symptoms of heart failure.”
Warren Sherman, director of stem cell research and regenerative medicine at Columbia University Medical Center in New York, said the study was an important proof of the potential of stem cells — harvested from patients, grown in the lab, then injected back into patients' hearts.
Doctors don't yet know exactly how the stem cells reduce the size of the dead zone of scar tissue, said Kenneth Margulies, director of heart failure and transplant research at the University of Pennsylvania. And while the shrinking suggests that the stem cells are replacing dead cells with living ones, doctors can't definitely prove that without doing a biopsy of the actual cells, he said.
The technology is being developed by closely held Capricor Inc., which will further test it in 200 patients for the second of three trials typically required for regulatory approval. Marban is a founder of the Los Angeles-based company and chairman of its scientific advisory board. His wife, Linda Marban, is also a founder and chief executive officer. “We’d like to study patients who are much sicker and see if we can actually spare them early death, or the need for a heart transplant, or a device,” Eduardo Marban said.
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