Study Using PET Brain Imaging Shows Ropinirole Slows the Loss of Dopamine
Function in Parkinson's Disease, According to Emory 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
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.