Human stem cells could soon improve heart function in people if injected following a heart attack, a new study suggests.

In studies on rats, U.S. scientists showed that transplanting human cardiac cells derived from stem cells (cardiomyocytes) regenerated damaged heart muscles in the weeks following a heart attack.

When they were injected into the ventricular wall of the hearts of rats, the human cardiac cells derived from stem cells decreased the diameter of the left ventricle and rebuilt the heart's muscle wall.
(CBC)

The embryonic cells, genetically manufactured to become cardiac cells, were grown in a "cocktail" of substances meant to extend their lifespan post-injection.

Embryonic cells are harvested from three-day-old embryos donated for research by women undergoing IVF treatments, Thomas Okarma, president and chief executive officer of Geron Corp., a biotechnology firm that conducted the study along with researchers at the University of Washington, told CBCnews.ca.

"We're injecting cells into necrosing [dying] muscle tissue, which is an extremely hostile environment to expect a fresh, live new heart muscle to be happy in," Okarma said. "We had to inject it with a bunch of factors that prevent the heart muscles cells from being killed."

Cells repair heart structure, function

During a heart attack, the heart muscle dies within days and the scar doesn't contract, Okarma said. So, over time, the heart enlarges, increasing the diameter of its chambers.

However, in the study, cardiac cells injected into the ventricular wall of the heart decreased the diameter of the left ventricle, rebuilt the heart muscle wall and improved the strength of the contracting heart muscles, according to Okarma.

"The animals that got our cells, four days after the infarction [heart attack], didn't enlarge — the heart stayed small because the heart muscle cells we put in are functional. They prevented the onset of heart failure.

"Our cardiomyocytes are the first human cardiac cells shown to survive after injection into an infarcted ventricle and to produce significant improvement in heart function," Okarma said.

The results were compared with control groups of rats that did not receive transplanted stem cells.

Four weeks after the transplant, the hearts of the rats that received the cardiac cells were scanned with an MRI to assess the growth of new tissue and to determine whether the injected stem cells had migrated to other organs.

The scientists discovered that the newly introduced cells remained solely in the heart and that no tumours or cysts developed — a common occurrence when foreign cells are transplanted into the heart.

"This will become the treatment of choice for patients who suffer a heart attack because no pill fixes a broken heart."
— Thomas Okarma

The findings are published Monday in Nature Biotechnology.

The scientists believe the study shows that transplantation of human stem cells into human hearts is possible, although further studies on larger animals are needed.

Okarma said studies on sheep are currently underway. He predicts human trials will occur in two to three years.

"This will become the treatment of choice for patients who suffer a heart attack," Okarma predicted, "because no pill fixes a broken heart."