Doctors may someday rejuvenate and even substantially rebuild seriously damaged hearts with just a tiny shot of bone marrow cells, according to two research reports released Friday.
In one experiment, human bone marrow cells injected into rats after a heart attack migrated to the rodents' ailing hearts and prompted the growth of new blood vessels there, suppressing scar tissue formation and boosting heart function by as much as 40 percent.
In an even more dramatic experiment, mouse bone marrow cells injected into the hearts of mice mysteriously transformed into what appear to be heart muscle cells. They settled in the heart and filled in for cells that had died in a recent heart attack.
If the approaches work as well in humans as they did in rodents, scientists said, they could usher in a new era of cardiology in which hearts with seemingly permanent damage will be remodeled without drugs or surgery and quickly regain near normal function.
"We are basically rebuilding the heart," said Piero Anversa of New York Medical College, who led the second experiment with Donald Orlic of the National Institutes of Health.
More immediately, the work is likely to intensify a simmering debate about the need to conduct research on so-called embryonic stem cells, which are derived from human embryos and fetuses and have shown promise for their ability to grow into tissues for transplantation. Like several other recent studies, the new work with hearts suggests that stem cells retrieved from adults have unexpected and perhaps equal flexibility of their own, perhaps precluding the need for the more ethically contentious cells.
Heart disease is the No. 1 killer in the United States, killing more than 40 percent of the 2.3 million Americans who die each year. Of particular relevance to the new research, more than 1 million Americans suffer heart attacks annually -- the result of a blood vessel blockage that starves crucial cardiac muscle to death.
Doctors have long accepted that tissue loss as permanent. Adult heart cells cannot multiply or replenish themselves, and it had seemed impossible to grow new ones from scratch.
But hopes that cardiac cells might be cultivated after all, and perhaps transplanted to needy patients, began to soar a few years ago with the discovery of stem cells -- primitive cells found in developing embryos and fetuses and in some parts of the adult body, which have the potential to mature into many types of cells.
Since then, researchers have made progress toward growing heart cells in laboratory dishes. But the new work suggests that if scientists could force stems cells out of a patient's marrow and into the blood, or get stem cells from a donor, then the body could turn them into heart cells itself.
Three to five hours after giving mice heart attacks by temporarily cutting off the animals' cardiac blood supply, Orlic and Anversa injected into the damaged hearts about 40,000 bone marrow stem cells from adult mice. Perhaps in response to chemical signals released by the damaged heart, the marrow cells quickly took on the key hallmarks of heart cells.
Most surprising, the researchers said, the cells invaded the dead tissue and in less than 12 days replaced about two-thirds of that scarred area with new and apparently functional heart muscle. Tests showed a significant improvement in cardiac strength.
Anversa and Orlic have yet to show that the newly transformed cells are fully functional and beating in coordination with others.
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