Stem cells repair damaged hearts

WASHINGTON - Stem cells taken from cloned mice were able to regenerate mouse hearts damaged by heart attacks by forming tiny blood vessels and heart muscle cells.

The cloned cells repaired the damage more efficiently and more quickly than so-called adult stem cells taken from bone marrow, the team at Advanced Cell Technology in Massachusetts reported.

"We restored myocardial [heart muscle] function and replaced 40 per cent of the scar tissue," said Dr Robert Lanza, the company's chief medical officer.

"This is the first paper to show that cloned stem cells can repair damaged tissue in vivo [in a living animal]."

Lanza, whose team published its findings in the American Heart Association journal Circulation Research, said the cloning process seemed to have rejuvenated the cells.

Their study will add ammunition to the argument that cloning technology offers the promise of being superior to other forms of stem-cell research.

Stem cells are the body's master cells, giving rise to fresh tissue. They exist in all blood and tissue but adult stem cells are rare and difficult to redirect.

For instance, it may be possible to get a blood cell to become brain tissue, but it requires many steps and much manipulation.

Another avenue involves using embryonic stem cells, which have yet to differentiate into tissue. They can become any kind of cell, but many people object to using human embryonic stem cells because it involves using cloning techniques on human cells.

Several groups have tried to repair diseased hearts in human patients by infusing stem cells into the damaged tissue, some with remarkable results. But it is not clear how long-lived the treatment is.

Lanza's team cloned mice and removed foetal liver stem cells from the embryos.

They injected them into the hearts of mice given artificial heart attacks by blocking key arteries.

A "control" group of mice were also given similar heart attacks to see what would happen without treatment.

Within three weeks, 38 per cent of the heart tissue killed by the heart attack was alive and working again, Lanza said. In the controls, the dead tissue, called an infarct, stayed dead.

In human patients, researchers have used the patients' own bone marrow cells to repair damaged hearts but it takes time to remove the cells and get them to grow into large enough numbers to use.

Lanza said the advantage of using cloned cells was that it required about one-tenth as many cells - which meant it took less time to grow a dose.

Time was of the essence in treating heart attacks, he said. A 46 per cent infarct caused irreversible heart failure and death within days.

Plus, he said, the cloning process has been shown to regenerate cells, returning them to youthful vigour. This presumably would mean any repair using cloned cells would last longer than one using adult cells.

- REUTERS