Alzheimer's Cure Elusive Despite Progress
Ronald Reagan's struggle shows how far we've come, how far we have to go.
Tomorrow's Plaque Fighters continued...
This isn't science fiction any more. Several companies are
racing to develop this strategy, known as passive immunization or passive
"It works in the mouse model," Gandy says. "It
should be effective."
The second idea is to keep plaque from forming clumps. Amyloid
gets particularly sticky when it combined with two substances: sugars and
metals (especially zinc). Drugs that block both of these combinations are in
the pipeline. And they work in mice, Gandy says.
The third idea -- and the one closest to reality -- involves
new uses for existing drugs. Amyloid doesn't just happen. It's the result of a
complex biochemical process. The process stops without a key set of
It's recently become clear that some of the
cholesterol-fighting drugs called statins block these enzymes. Data from trials
of one of these drugs -- Lipitor -- suggest that people taking the drug to
treat high cholesterol have a lower risk of Alzheimer's disease. The National
Institute on Aging (NIA) is conducting a large clinical trial to see whether
another of these drugs, Zocor, actually prevents Alzheimer's.
The NIA is also looking at another class of drugs capable of
blocking amyloid production. It's the NSAIDs or nonsteroidal anti-inflammatory
drugs -- the same class to which aspirin and ibuprofen belong. One of these
drugs, Ansaid, may be particularly effective against amyloid, Gandy says.
If these drugs already exist, why aren't they being used? The
reason is that amyloid plaques are notoriously hard to detect until Alzheimer's
disease is well under way.
That, too, is changing. Gandy says that new imaging techniques
called PET scans will allow doctors to see tiny spots of amyloid.
"This might be useful for very early diagnosis of people
getting Alzheimer's disease, decades before symptoms show up," Gandy says.
"And it will help with developing prevention drugs, because it will let you
see what is going on."
Many people who don't think plaque is the No. 1 bad guy have
another villain in mind. These are the tangled fibers in the brains of
Alzheimer's patients. It's been hard to work on anti-tangle drugs, because
there's no good animal model. But progress is being made, Gandy says.
Today's Alzheimer's Disease Treatments
While waiting for tomorrow, a lot of exciting Alzheimer's
treatments are available today.
Currently available drugs slow Alzheimer's process. Patients
who were on a sharp decline often stabilize. Today, there are several ways to
treat Alzheimer's disease:
Aricept, Exelon, and Reminyl. These are the
cholinesterase inhibitors. Cholinesterase breaks down an important brain
chemical called acetylcholine. These drugs keep this from happening.
Unfortunately, this doesn't stop brain cells from dying. About half of the
patients who take these drugs see a modest improvement in mental function.
(Tacrine, the first member of this class of drugs, now rarely is used because
it sometimes causes liver damage.) In April 2005, Reminyl's label
was changed to include information about the deaths of 13 elderly patients who
were taking the drug during a study. The deaths were due to various causes,
including heart attack and stroke.
Namenda, approved in October 2003, is the newest kind of
Alzheimer's drug. It's called an NMDA receptor antagonist. The NMDA receptor is
a kind of dimmer switch that controls the actions of a brain chemical called
glutamate. Glutamate plays a major role in learning and memory. Too much of it
kills brain cells. Too little makes them grind to a halt. Namenda helps balance
Vitamin E. Everybody's brain is under constant attack
from destructive oxygen molecules called free radicals. We've evolved effective
ways to fend off these attacks. But Alzheimer's disease and the normal aging
process seems to lower these defenses. Antioxidant compounds -- especially
vitamin E -- may reinforce this crumbling line of defense.