BioEd Online

Embryonic stem cells from mice can help mend the broken hearts of sheep. This cross-species experiment is one more step in finding out whether human embryonic stem cells can mend the damage done by heart attacks.

A heart attack damages the muscle and blood vessels that allow a heart to pump blood around the body. Doctors have long sought a way to repair this damage, and some experts say that embryonic stem cells hold the answer. These cells have the potential to turn into any type of cell needed, such as heart-muscle cells.

Studies have already shown that embryonic stem cells can improve blood flow after an attack in small animals, such as rodents¹. But in people, ethical controversies have slowed research into the benefits of embryonic stem cells for ailing hearts.

In human trials scientists have used stem cells from a patient's bone marrow to help the healing. These cells are not as flexible as embryonic ones, but can sometimes be persuaded to turn into the desired cell types. Patients treated this way are able to pump more blood after a heart attack than those who don't get the treatment. But researchers hope that embryonic stem cells might have a greater effect.

Sheep well

Michel Pucéat of the French National Centre for Scientific Research in Montpellier and his colleagues decided to test embryonic stem cells in sheep to see how well they work in large mammals. Because there is not much call for sheep embryonic stem cells, they are hard to source, so the team used mouse cells instead.

The researchers injected about 30 million cells into the hearts of nine sheep that had suffered heart attacks. They found that the sheep pumped blood through their hearts 15% more efficiently than the untreated sheep a month after the injections. Distinctive markers from the stem cells were found inside the sheep hearts, proving that the stem cells had gone to work and replaced some of the damaged tissue. The team reports its results in the Lancet².

"I think it's very exciting," says Joshua Hare, an expert in cardiac transplantation at the Johns Hopkins University School of Medicine in Baltimore, Maryland.

For the moment, the improvement is of the same order of magnitude as that achieved in humans with bone marrow transplants. But Hare says that the healing should increase over time: other studies have shown the biggest benefit from stem cells two months after injections.

Pucéat says that this form of cardiac therapy holds much future promise. He and his colleagues are currently conducting tests to assess the healing power of human embryonic stem cells in baboons.