Researchers at Emory University and a group of international collaborators, using positron emission tomography (PET) brain imaging, have determined that a relatively new drug slows the loss of dopamine function in early stages of Parkinson's disease (PD) compared with an older, more commonly used drug.
Investigators say the drug ropinirole (brand name ReQuip ®) slows the loss of dopamine, a neurotransmitter produced by neurons in the brain that is found in steadily decreasing amounts as the disease progresses, in a more effective manner than levodopa (brand name Sinemet ®).
In this trial, the progression of the loss of dopamine function was slowed by over 30 percent in participants taking ropinirole as compared with participants in a comparable stage of the disease taking levodopa.
Three-dimensional PET scans were taken before and after the study to show the level of dopamine loss in the brain, which can be inferred from a radioactive marker whose uptake by neurons is measured in PET imaging.
This multi-site, international trial is called "Requip as EArly therapy versus L-dopa", or the REAL-PET study. Emory University, under the guidance of Ray Watts, M.D., professor of neurology, Emory University School of Medicine, led the American sites, recruiting the most patients worldwide in the study.
Dr. Watts and collaborators will present their findings at the American Academy of Neurology 54th Annual Meeting in Denver, Colo., on Tuesday, April 16.
"We are really pleased with the outcome of this trial because it is one of the first of its kind to demonstrate slowing of the rate of loss of dopamine function in PD patients," Dr. Watts says. "It is also one of the first studies designed to use PET imaging in PD patients to differentiate how two different therapies (ropinirole vs. levodopa) affect progression of the loss of dopamine function."
Participants in this double-blind, two-year study had been diagnosed within the past two years with PD, a progressive movement disorder affecting the central nervous system.
Researchers wanted to try ropinirole on the early stages of PD and in participants who had not begun taking levodopa, often called L-dopa. L-dopa, which helps the remaining cells make dopamine in the brain to restore dopamine deficiency, has been the gold standard for treating Parkinson's disease for some 30 years.
Participants underwent a PET scan at the beginning the trial to determine the loss of dopamine in the brain, particularly in the substantia nigra and putamen. When the radioactive tracer 18fluorodopa or 18F-dopa (a positron emitter) is injected, the 3D PET scanner highlights these losses or changes in the brain. The 18F-dopa uptake marks the quantity of functioning dopamine-producing brain cells remaining.
Participants were then randomized to take ropinirole, a dopamine agonist, (93 participants) or L-dopa (93 participants) three times a day for two years. At the end of the trial, another PET scan was taken and compared to the previous scan two years earlier. Investigators found clear evidence, with the use of a PET scan, that progression of the loss of dopamine function was significantly slowed by over 30 percent in participants taking ropinirole.
"These findings could certainly mean a better quality of life for a longer period of time in PD patients," Dr. Watts explains. "Progression of the loss of dopamine function over 10 years can now possibly be stretched to 13 years by starting and maintaining treatment with ropinirole. These findings will help guide the treatment of early PD and could be an important factor in changing the treatment methods of PD."
Investigators also determined the incidence of dyskinesia, involuntary movements (fragmented or jerky motions) that can result from dopaminergic therapy, was greatly reduced in participants taking ropinirole.
Ropinirole has been approved for use by the Food and Drug Administration (FDA). GlaxoSmithKline, the maker of ropinirole, funded this study.
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