Washington: Researchers at the Brigham and Women's Hospital in Boston have found that injections of hardy stem cells can help recover rats from a heart attack. However, they are still doubtful whether such cell therapy can help human patients.

According to a report in 'Nature', hopes for the stem-cell treatment had been raised in 2001 when two reports revealed that mouse bone-marrow stem cells, which normally make blood, had patched up damaged heart tissue. But later, in many ensuing studies, more than 90 per cent of cells pumped into the heart died within two days.

In the latest study, Victor Dzau and his colleagues at the Brigham and Women's Hospital inserted a cell- survival gene called Akt 1 into a type of bone-marrow stem cell one. They injected the cells into rats whose hearts had been starved of oxygen as happens when blocked arteries cause a heart attack.

It was observed that more than 60 per cent of the modified cells survived for 48 hours. They even halted the heart's subsequent decline towards failure.

"It's pretty amazing," says Stanton Gerson, who studies blood stem cells at Case Western Reserve University in Cleveland, Ohio.

The result bolsters the idea that stem cells could mend human hearts after an attack, according to researchers. Proponents also point to positive results from first-stage clinical trials in which heart-attack patients are injected with their own blood cells. However, the question raised is, are these stem cells safe or effective for human beings?

The researchers also say that it is not yet clear how stem cells heal the heart. They may spawn new muscle cells, fuse with existing cells or simply prompt the cells to repair and grow themselves.

"It's an intellectual question that will take years to sort out," says Gerson. Nonetheless, advocates argue that preliminary human trials on the safety of stem-cell therapy should continue because the need is so great. An estimated 23 million people worldwide are affected by heart failure today.

Wary researchers, however, warn that a single incident, in which stem cells may trigger a heart tumour, can condemn the field. "I think we need to be really careful," says Charles Murry, who studies heart failure at the University of Washington in Seattle.

ANI