SAN FRANCISCO - Scientists may be on the brink of curing Parkinson's disease using transplanted embryonic stem cells, but where and when that new treatment is tested in humans depends on unresolved political decisions, researchers suggested Friday.
Dr. Ole Isacson of Harvard Medical School and Dr. Ronald McKay of the National Institutes of Health said Friday they have both "cured" Parkinson's in mice and rats, using stem cells removed from embryos of laboratory animals.
In a report at the national meeting of the American Association for the Advancement of Science, Isacson said mouse and rat embryonic cells, after careful processing, can be grafted into the animal brains where they transform into replacements for cells killed by Parkinson's.
"In mouse models (laboratory tests) these cells have restored function," said Isacson.
Using a slightly different technique, McKay said his NIH lab has also prompted mouse embryonic stem cells to convert into cells that are lacking in Parkinson's.
McKay and Isacson said researchers are almost ready to test the technique in humans, but social and political issues must be resolved in the United States before that step can be taken in this country.
At the same time, McKay said it may happen soon in Britain, France or the Netherlands, as those countries are adopting policies to advance embryonic stem cell research.
"It's going to happen, but just where may depend on social and political issues," McKay said. "There is a great sense of optimism shared by many people in the field right now."
In the United States, some groups, including some members of Congress, oppose the use of embryonic stem cells in research because gathering the cells requires the death of a human embryo.
New NIH guidelines permit federal funding of such stem cell research, but only if the cells are extracted from embryos in labs not receiving federal funding.
Tommy Thompson, the new secretary of Health and Human Services that oversees NIH, said he is reviewing the policy on embryonic stem cells research.
Some researchers have sought NIH funds to conduct embryonic stem cell studies, but no grants have been issued, said McKay.
More than 1 million Americans have been diagnosed with Parkinson's, a disease caused by the death of brain cells that produce dopamine, a key nerve chemical. When patients lose about 80 percent of these cells, they develop the classic Parkinson's symptoms: tremors and rigidity.
Parkinson's can be treated with L-dopa, a drug that makes dopamine in the brain. But L-dopa is effective for only a short time and after that the disease progresses.
Limited experiments using brain cells from aborted fetuses have stabilized patients for up to 12 years, Isacson said. The transplanted cells convert to dopamine-producing cells, replacing those lacking in patients with Parkinson's.
But using tissue from aborted fetuses in research also is opposed by many groups. And because of limited availability and for technical reasons, fetal tissue is not considered ideal for treating Parkinson's.
The best hope, said the researchers, are the embryonic stem cells. These are master cells that can be coaxed to transform into virtually any type of tissue in the body.
Embryonic stem cells can be grown in great numbers, making them available for treating thousands of patients, the researchers said.
"You can generate embryonic stem cells with huge efficiencies," said McKay.