Monday, January 14, 2008

Growing New Hearts from Old

Continued from page 1

By Amanda Schaffer

Additional challenges, which might prove more difficult for larger human hearts, include loading the scaffold with the appropriate numbers of cells, keeping the cells alive with sufficient nutrients and oxygen, and having them mature properly.

Creating a heart that is electrically stable over long periods of time may also be difficult, says Richard Lee, a cardiologist at Brigham and Women's Hospital, in Boston, and a professor at Harvard Medical School.

In addition, the heart would have to be able to exist in vivo for long periods of time without causing blood clots or strokes. "There's a long way to go before you could actually feel like this is on the horizon" for treating patients, says Lee.

In recent years, research on cardiac tissue engineering has proliferated greatly. Many groups now use cells in conjunction with various kinds of scaffolding material to try to reconstruct either vascular or cardiac tissue structure.

While the heart envisioned by Taylor might be an alternative to transplant for some patients with end-stage heart disease or congestive heart failure, other work is aimed at repairing localized areas of damage, such as that caused by myocardial infarction, or heart attack.

For instance, several groups are currently working on cardiac patches, which are bands of engineered tissue that can be surgically applied over a damaged area of the heart in order to help restore its function.

Researchers working on cardiac patches face some of the same challenges that Taylor's group does: securing appropriate cells, growing them on a scaffold, and successfully integrating them into the body, says Vunjak-Novakovic. Her group is engineering patches using human adult stem cells and human embryonic stem cells, with the goal of revascularizing and rebuilding cardiac structure in an area that has been damaged by a heart attack. Cardiac patches have shown some promise in animal studies but have yet to be tested in human trials.

Taylor says that her team's decellularized heart technology might also be used to create a portion of a heart like a wall or a ventricle, or a section of tissue that could be used as a patch.

Another approach is to inject cells into damaged heart regions with the hope of rebuilding or repairing heart tissue and vasculature. Lee says that injecting bone-marrow cells into the heart's arteries has shown some success in improving ejection fraction (the percentage of blood ejected with each beat) and other measures of heart function in human clinical trials.

Given the enormous number of patients in need of new options, Lee adds, "everything should be on the table. We can't give up on any approach, no matter how wild or improbable, until we get better treatments to these people."