Searching for a Better Parkinson's Drug
By Fran Berger - HealthScout Reporter
MONDAY, Oct. 16, 2000 (HealthScout) -- A group of researchers in
Arizona thinks it may have found an answer to why medications for
Parkinson's disease often stop working.
A previously unsuspected brain molecule may be to blame for the loss of
effectiveness of the drug now used to treat the disease, say researchers
at the Thomas H. Christopher Center for Parkinson's Disease Research at
the Sun Health
Research Institute in Sun City, Arizona. They say the drug -- levodopa,
or L-dopa -- generally becomes ineffective after a few years.
Other experts, however, are quick to say "proceed with caution."
Parkinson's disease is caused by the progressive death of nerve cells in
the region of the brain that produces dopamine, a chemical that helps
direct normal movement and activity. L-dopa acts through receptor cells
that convert it to dopamine.
"Dopamine is a sort of key, with receptors [the lock]," says lead
researcher Jeffrey N. Joyce, head of the Christopher Center. "The key
has to fit in the lock, the gates open and movement occurs."
"We know that anti-Parkinsonian drugs act through what we call the D2
family of receptors," Joyce says. "The prevailing hypothesis was [that
reduced effectiveness] had to be a reaction to the number of D2
receptors," which is greatly reduced
in many Parkinson's patients.
But that's not what the research team found.
After examining brain tissue from two groups of people with Parkinson's
disease who had died, the researchers say that those who had lost their
response to L-dopa did not have a decreased level of receptor D2 after
all, but rather a decrease
in another receptor, D3. Results of the research are being presented at
the American Neurological Association meeting this week in Boston.
"Many Parkinson's disease patients, after anywhere from five to 10 years
of the illness, begin to lose real effective clinical response" to their
treatments, Joyce says. Although drugs cannot be used to replace brain
cells lost to the disease, he
says, the team hopes the discovery will lead to new treatments with
extended effectiveness.
But, Dr. Robert G. Feldman, director of the American Parkinson Disease
Association Center for Advanced Research at Boston University, thinks
that making this research information public may be dangerous because it
will cause people to
rush to their doctors, demanding new treatment.
"It's dangerous to make a blanket statement that L-dopa is losing its
effectiveness," Feldman says. "It totally ignores the usefulness of
levodopa to an individual patient, who will benefit or not depending on
that person's response to given doses, the frequency of dopamine and the
duration of having received levodopa."
"Dopamine replacement is only one small part of the picture," he says.
Other research indicates that the medial spiny neurons, where many
different receptors are operating, "may in fact be where fluctuations
and responses to dopamine
replacement therapy … take place," Feldman says.
People need to exercise caution, he says. "They should understand there
are many factors that contribute," Feldman says. "Such information
should be for internal consumption only."
"Every patient should be aware of what medications are available and
talk with their clinician about what is the best treatment for them,"
Joyce says.
But he believes the battle needs to be fought outside the doctor's
office as well.
"Parkinson disease support groups must continue to advise congressmen
that they want research money for Parkinson's disease," he says. "There
is a new initiative through the National Institutes of Health, which
includes funding for Parkinson's disease, that has to get through
Congress next year."
To learn more about how Parkinson's develops and inhibits normal
activity of the brain, visit the Society for Neuroscience. For
information on the disease, including symptoms and treatments, check out
the Web site of the Parkinsons Center of Oregon.
Or, you may want to read previous HealthScout articles on
http://rd.yahoo.com/Dailynews/inlinks/hsn/*http://www.healthscout.com/cgi-bin/WebObjects/Af.woa?search=Parkinson"s
%20disease"> Parkinson's disease.
Copyright © 2000 Yahoo! Inc./Copyright © 2000 Healthscout.com
--
Judith Richards, London, Ontario, Canada
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