Giving heart attack survivors stem cells from their own bone marrow did little to repair their damaged hearts, according to the three most comprehensive studies to date of this controversial therapy.
The modest results suggest more study is needed and, some scientists say, demonstrate the need to lift federal funding restrictions on using stem cells from embryos, which offer more promise for turning into heart-repairing tissue.
``The optimal cell type has not been discovered yet," said Dr. Kenneth Chien, director of Massachusetts General Hospital Cardiovascular Research Center, who had no role in the studies.
Chien said experiments over the past 15 years suggest embryonic stem cells can turn into beating cardiac muscle, though it has not been tried in human patients. ``This is an area worthy of further pursuit," he said.
The three new studies, reported in today's New England Journal of Medicine, are the largest and most scientific tests yet of whether stem cells derived from adult patients can improve heart function.
Stem cells are blank slates that have the potential to become heart cells or other types of specialized cells. Scientists do not know whether those found in adults have the same potential to specialize as those from embryos.
The studies focused on damage caused by heart attacks, which weaken the heart muscle and reduce its ability to pump blood. Researchers looked at whether stem cells could remedy damage to the main pumping chamber.
In each study, stem cells were infused into the heart through cardiac catheterization. A tiny balloon momentarily blocked regular blood flow into the heart, and stem cells were injected in an attempt to give them a couple of minutes to try to take root. Success was measured by changes in the amount of blood pumped out.
In a commentary in the journal, Dr. Robert Schwartz, a deputy editor, said dozens of companies promise cures that involve adult or cord-blood stem cells, though there's no clear proof that this works. ``These three clinical trials probably will not stop the exploitation of patients," he wrote.