Researchers at the University of Minnesota seeking new treatments for heart disease have grown a beating rat heart in the lab by using stem cells. VOA's Jessica Berman reports the research reported by the journal Nature Medicine is laying the groundwork for the transplant of what the scientists are calling bio-artificial organs in humans.

Experts say there are an estimated 100 million people around the world whose hearts do not work well enough to pump blood through their bodies. Many heart patients in need of a transplant will die waiting for a new organ to become available. But the researchers say if human hearts can be made from animal organs, they could save lives.

In their experiments, researchers removed the hearts of newborn lab rats and stripped them of their cells in a process called organ decellularization.

Lead researcher Doris Taylor, who heads the University of Minnesota's Center for Cardiovascular Repair, says investigators were left with a white protein matrix shaped like a heart that contained conduits where the blood vessels had been.

Dr. Taylor says these "ghost" hearts, or scaffolds, were re-populated by infusing them with progenitor cells that have a capacity for self-renewal and differentiation much like stem cells.

Within a few days, Dr. Taylor says the rat hearts began to grow cells on the outside..

"And what is really cool is that over time, our heart actually replaces that matrix that we call it," said Doris Taylor. "It is basically the cell saying 'I need something, something to hang on to,' and they build more of it over time. So, over time the human cells would replace that matrix and you would essentially have an equivalent of a human heart."

The new cells were fed nutrients and were prodded with a pacemaker. After four days, investigators noted some contractions in the rat hearts.

She says eight days later the experimental organs began pumping liquid faintly.

"What we were able to show is that we could take a previously dead heart that we removed all the cells from and really reanimate that with new cells," she said. "So, for the first time we have something that looks like a heart, that has the anatomy of a heart that we can actually begin to rebuild a whole tissue rather than just a little piece of tissue in a laboratory dish."

If perfected on larger hearts it could create a potentially unlimited supply of needed organs, and the researchers say use of a patient's own stem cells would ensure that a bio-artificial heart is compatible with his or her immune system.

The next step is to use the procedure on a pig heart to see if it will work in a larger heart.

Dr. Taylor says bio-artificial hearts for humans could be made from pig organs because the hearts are about the same size. Pig valves are already used to replace diseased heart valves in humans.

"The hope is that we have created a tool that will really make people think differently and provide an opportunity to create new options for tissue engineering and for patients who need organs," said Dr. Taylor.

Researchers in Minnesota are working with scientists in other countries to try to create other bio-artificial organs, including lungs, liver, the pancreas, and kidneys.