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Another Step Closer to Growing New Brain Cells for Parkinson's Patients

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Feb. 16, 2001 (San Francisco) -- Scientists announced Friday that they were able to use cells from mouse embryos to replace lost brain cells in mice with symptoms of Parkinson's disease.

The results represent a significant step toward using cells cultured from very early human embryos in therapies for people with Parkinson's disease, and they offer a proof of principle that premature cells from embryos can be directed to develop into cells that can be used as replacement tissue for other diseases.

The embryonic cells in the mice make the same proteins as normal brain cells, especially an important brain chemical called dopamine, just like the brain cells that die off in animals with Parkinson's disease.

"They look exactly and work exactly like normal dopamine cells," says Ole Isacson, PhD, director of the Neuroregeneration Laboratories and associate professor of neuroscience at Harvard Medical School. He presented his research here at the annual meeting of the American Association for the Advancement of Science.

Patients with Parkinson's disease develop tremors and have trouble moving after they lose about 80% of a specialized set of cells in a brain region, called the substantia nigra, that secretes dopamine. But the first symptoms appear earlier, so a treatment that kept the brain from getting worse would keep patients relatively healthy.

The drug L-dopa restores dopamine to the brain and eases Parkinson's symptoms. But the positive effects don't last forever, and patients develop side effects, including excessive movement, Isacson says.

So more than a decade ago, scientists looked at how to generate a more permanent replacement -- new, normally functioning brain cells. A variety of methods have been tried: In animals and then in people, they've tried transplanting brain cells from fetuses to the substantia nigra, with mixed results. In early transplant patients from Sweden, for example, the replacement cells are still working more than 11 years after they were transplanted, Isacson says.

But this treatment can't work for everyone because there are not enough fetal brain cells to go around, and the treatment is too expensive. To come up with a more reliable source of cells for transplants, researchers turned to immature human cells, called stem cells, that can be coaxed into mature brain cells.

Three types of stem cells exist, which come from three different sources: adult tissue such as bone marrow, fetal tissue, and very early embryos. Some right-to-life groups object to using human stem cells that came from tissue from aborted fetuses, or those from very early embryos, which are generally created for use in fertility clinics and would otherwise be discarded.

Researchers are testing all three types of stem cells as replacement cells for Parkinson's and other diseases, but they don't know yet which one will work best, says Ronald McKay of the National Institutes of Health. One problem has been getting stem cells to mature into specialized cells, such as dopamine-producing neurons.

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