Human embryonic stem cells transplanted into the brains of people with Parkinson’s disease survive and grow better in patients under age 60 than in older patients, researchers report. Physicians have been transplanting the cells as a new source of dopamine–a brain chemical necessary for muscle movement that’s in short supply in Parkinson’s patients.
However, side effects seen in some of the patients suggest the cells might be overproducing dopamine. These transplant patients exhibit jerky movements similar to those often seen after long-term use of the dopamine-replacement drug levodopa, says study coauthor Curt R. Freed, a neuroscientist at the University of Colorado School of Medicine in Denver. This drug typically works initially but can eventually cause side effects.
A team led by Freed transplanted stem cells into 20 patients with advanced Parkinson’s disease by drilling holes in each person’s skull and injecting the cells into the brain. These patients had ceased responding well to medication and were plagued by uncontrolled movements, rigidity, and tremors.
Twenty other patients with similarly disabling Parkinson’s underwent a sham procedure in which surgeons drilled holes in the patients’ skulls but didn’t inject anything.
All patients were tested on and off medication. Over the next year, patients getting the sham surgery didn’t improve significantly. In contrast, 10 of the transplant recipients who were under age 60 regained some movement control and shed some rigidity while not taking medication, say Freed and his colleagues in the March 8 New England Journal of Medicine. Tremors didn’t improve for these patients.
The 10 older patients receiving the transplants didn’t show improvements in the first year, Freed reports. Up to 3 years after the surgery, however, these older patients improved by 14 percent in standard tests of movement control when off medication, while the under-60 patients improved by 38 percent.
Patients in the study weren’t told for 1 year whether they had received a transplant. Then, sham-surgery recipients were given the option of getting a transplant, and 14 did, Freed says.
The study is the first of its size to use sham surgery on Parkinson’s patients, providing an important comparison group, says Jeffrey L. Platt, a transplant immunologist at the Mayo Clinic in Rochester, Minn.
Five transplant recipients developed jerking motions that indicate an excess of dopamine. This could have arisen from too many cells being transplanted, Freed says. As a result, the researchers counseled the remaining six patients not to get transplants while the scientists observe the long-term effects of the transplants.