November 12, 2007

Two Stem cells advances: one for vascular treatment another for controlled release of cells

South Korean scientists said Monday they used human embryonic stem cells to treat mice suffering from a vascular disease, in an experiment that could lead to cures for strokes and other ailments.

The stem cells were differentiated into blood vessels that were grafted onto the animals afflicted with ischemia. Ischemia is caused by a shortage of blood to a part of the body, stemming from the constriction of blood vessels. Of the 11 mice treated, four developed new vascular cells that fully revived the damaged limb, while four suffered from a relatively mild case of necrosis. Three lost their legs due to the cut-off of blood flow. 10 other mice given alternative treatment failed to recover.

Engineers at Rensselaer Polytechnic Institute have transformed a polymer found in common brown seaweed into a device that can support the growth and release of stem cells at the sight of a bodily injury or at the source of a disease.

“We have developed a scaffold for stem cell culture that can degrade in the body at a controlled rate,” said lead researcher Ravi Kane, professor of chemical and biological engineering. “With this level of control we can foster the growth of stem cells in the scaffold and direct how, when, and where we want them to be released in the body.”

Kane and his collaborators, which include the author of the paper and former Rensselaer graduate student Randolph Ashton, created the device from a material known as alginate. Alginate is a complex carbohydrate found naturally in brown seaweed. When mixed with calcium, alginate gels into a rigid, three-dimensional mesh.

The device could have wide-ranging potential for use in regenerative medicine, Kane explains. For example, the scaffolds could one day be used in the human body to release stem cells directly into injured tissue. Kane and his colleagues hope that the scaffold could eventually be used for medical therapies such as releasing healthy bone stem cells right at the site of a broken bone, or releasing neural stem cells in the brain where cells have been killed by diseases such as Alzheimer’s.

In order to control the degradation of the alginate scaffold, the researchers encapsulated varying amounts of alginate lyase into microscale beads, called microspheres. The microspheres containing the alginate lyase were then encapsulated into the larger alginate scaffolds along with the stem cells. As the microspheres degraded, the alginate lyase enzyme was released into the larger alginate scaffold and slowly began to eat away at its surface, releasing the healthy stem cells in a controlled fashion.