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December 13, 2010

Insights Give Hope for New Attack onAlzheimers

By GINA KOLATA

Alzheimers researchers are obsessed with a small, sticky protein fragment, beta amyloid, that

clumps into barnaclelike balls in the brains of patients with this degenerative neurological disease.

It is a normal protein. Everyones brain makes it. But the problem in Alzheimers is that it starts to

accumulate into balls plaques. The first sign the disease is developing before there are any

symptoms is a buildup of amyloid. And for years, it seemed, the problem in Alzheimers was thatbrain cells were making too much of it.

But now, a surprising new studyhas found that that view appears to be wrong. It turns out that

most people with Alzheimers seem to make perfectly normal amounts of amyloid. They just cant

get rid of it. Its like an overflowing sink caused by a clogged drain instead of a faucet that does not

turn off.

That discovery is part of a wave of unexpected findings that are enriching scientists views of the

genesis of Alzheimers disease. In some cases, like the story of amyloid disposal, the work points to

new ways to understand and attack the disease. If researchers could find a way to speed up

disposal, perhaps they could slow down or halt the disease. Researchers have also found that

amyloid, in its normal small amounts, seems to have a purpose in the brain it may be acting like

a circuit breaker to prevent nerve firing from getting out of control. But too much amyloid can

shut down nerves, eventually leading to cell death. That means that if amyloid levels were reduced

early in the disease, when excess amyloid is stunning nerve cells but has not yet killed them, the

damage might be reversed.

Yet another line of research involves the brains default network: a system of cells that is alwaysturned on at some level. It includes the hippocampus, the brains memory center, but also other

areas, and is the brains mind-wandering mode the part that is active when, for instance, youre

driving in your car and you start thinking about what you will make for dinner. That brain system,

scientists find, is exactly the network that is attacked by Alzheimers, and protecting it in some way

might help keep the brain healthier longer.

For example, during nondreaming sleep, the default network is thought to be less active, like a

light bulb that has been dimmed. The network also ramps down during intense and focused

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intellectual activity, which uses different areas of the brain. One emerging theory suggests that if

the default network can be rested, amyloid production might be decreased, allowing even an

amyloid disposal system that was partly hobbled by Alzheimers to do a better job.

The result of all this work is a renewed vigor in the field. After years in which it was not clear how

to attack this devastating disease, scientists have almost an embarrassment of riches. The research

is in early stages, of course, and there are many questions about which discoveries and insights willlead to prevention or a treatment that works.

But there is a new hopefulness that, at long last, this terrible disease may eventually be conquered,

said Richard Mohs, Alzheimers group team leader at Eli Lilly.

We are much closer and quite optimistic that we will be able to do it, Dr. Mohs said.

A Key Question

When Dr. Randall Bateman first tried to get funds for an effort to answer a sort of chicken-and-eggquestion about Alzheimers, some grant reviewers turned him down, saying they doubted it would

work. But they were wrong. He got his answer, although it took much longer than he expected, and

his paper describing his results was just published online Thursday by Science.The question came

to him in 2003, when he was a neurology resident. One day he was sitting in the hospital cafeteria

atWashington Universityin St. Louis, taking advantage of free soup and rolls. Dr. David M.

Holtzman, a neurology professor, joined him, and the two began to talk about the puzzle of

Alzheimers. Why, Dr. Bateman wondered, did beta amyloid build up in patients brains? Were

people making too much? Or were they unable to dispose of what they made?

Great question, Dr. Holtzman replied, but what kind of test could you do to answer it?

Dr. Bateman pondered the issue for a year and finally figured out a method. It would not be easy

study subjects would have to sit around for 36 hours with a catheter in their spinal column

collecting cerebrospinal fluid. I said, I think I can probably develop and do this in about six

months, he told Dr. Holtzman.

Dr. Holtzman had his doubts.

I thought his idea could work conceptually, but for everything to work just right in a human being

was a long shot, he said.

Dr. Batemans plan was to put a catheter into a persons vein and infuse an ingredient, the amino

acid leucine, that cells need to make beta amyloid.

The infused leucine would be chemically modified with a form of carbon that did not affect its

function or safety but that made it easy to detect newly made amyloid as it was flushed out into the


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spinal fluid. And since he knew how much leucine he gave people, he could measure how much

amyloid they made and then see how fast it was drained.

When the study began, Dr. Bateman was his own first subject. He then did the test on people in

their 30s and 40s, as well as healthy older people and people with Alzheimers.

He finally completed the study, getting his answer in seven years, rather than the six months he

had navely expected.

The problem in Alzheimers, he found, is disposal. Beta amyloid, he found, normally is disposed of

extremely quickly within eight hours, half the beta amyloid in the brain has been washed away,

replaced by new beta amyloid.

With Alzheimers disease, Dr. Bateman discovered, beta amyloid is made at a normal rate, but it

hangs around, draining at a rate that is 30 percent slower than in healthy people the same age.

And healthy older people, in turn, clear the substance from their brains more slowly than healthy

younger people.

That means that it might be possible to attack Alzheimers not just by getting rid of beta amyloid

but also by speeding its disposal. And, he says, there is a clear message in his results.

What we think may be happening is that a clearance mechanism is broken first, Dr. Bateman

says. Slowly, as years go by, beta amyloid starts to accumulate in the brain. If that clearance can be

fixed, or enhanced, the buildup might never occur.

Beta Amyloid as Signal Control

For years, Alzheimers researchers wondered if the brain used small molecules of beta amyloid or

if those fragments, produced when a larger protein is snipped, were more like scraps of fabric,

serving no purpose and just getting in the way.

Now, some say they may have an answer. Beta amyloid, in small quantities, seems to control

signaling between nerve cells, reducing the strength of signals when they are too strong. But when

it accumulates, the brain can have too much of a good thing. Nerve impulses can be stopped dead,

nerves can die, and the disease can take hold, according to this idea.

The work leading to this conclusion began a few years ago when Dr. Roberto Malinow of the

University of California, San Diego, decided to look at whether beta amyloid affects synapses, the

functional connections between nerve cells. Electrical signals are transmitted through synapses as

they travel from nerve cell to nerve cell. And nerve cells make beta amyloid and release it onto

their synapses. Was it doing anything there?

One way to find out, Dr. Malinow reasoned, would be to genetically engineer nerves to


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overproduce beta amyloid and determine what happened to their signaling in laboratory

experiments.

The signals, he found, were muffled.

As Dr. Malinow and his colleagues inquired further they discovered that beta amyloid seemed to

be part of a nerve cell feedback loop. A nerve will start firing, but under some conditions, the

signal can get too intense. Then the nerve releases beta amyloid, bringing the signaling down to

normal levels, at which point the nerve stops releasing beta amyloid.

The impact of beta amyloid on synapses was a very clear effect, at least in the lab, Dr. Malinow

said.

We proposed that maybe a-beta was normally part of a negative feedback system, Dr. Malinow

said, using a shorthand reference to beta amyloid.

The damage and Alzheimers disease comes in if there are too many clumps of beta amyloidin the brain. When that happens, the signals between nerve cells are reduced too much, effectively

stopping communication.

Too much of a good thing is bad, says Dr. Dennis Selkoe, a professor of neurologic diseases at

Harvard Medical School. Still, treatment at that point, before the nerves are dying, might reverse

the disease.

There may be another way to protect nerves from too much beta amyloid, and it involves a

different protein linked to Alzheimers. Problems with it show up in the brains of Alzheimerspatients later, after there has already been a buildup of beta amyloid.

The protein is tau, an integral part of normal cells. It becomes tangled and twisted in Alzheimers,

after cells are already dying, looking like strands of tangled spaghetti. For decades researchers

have argued about whether those distorted tau molecules were a cause or an effect of nerve cell

death. Now, they believe they may have an answer, which is spurring the search for drugs to

salvage tau and protect the brain from beta amyloid.

New studies by Dr. Lennart Mucke, a neurology professor at the University of California, San

Francisco, and director of the Gladstone Institute of Neurological Disease there, and others suggest

that tau facilitates beta amyloids lethal effects. In genetically engineered mice and in laboratory

experiments, the researchers found that without tau, beta amyloid cannot impair nerve cells.

If tau also plays the same role in the brains of humans, that might resolve a longstanding mystery.

Occasionally, in autopsies pathologists find that people who had normal memories had lots of

plaques in their brains. Perhaps those people, for some reason, made very little tau or were

naturally resistant to the injurious interaction between tau and beta amyloid. Could that be why


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they somehow endured a buildup of beta amyloid?

Thats a very interesting question, Dr. Mucke said. We dont know the answer. But, he adds,

researchers should try to learn from such cases how to better fight the disease.

Early Detection Crucial

In order to treat Alzheimers before it is too late, scientists now believe they have to detect it muchearlier, before there are symptoms. To do that, they have developed several new methods,

including brain scans that can show amyloid plaques in living patients. And for Dr. Marcus E.

Raichle, a neurologist at Washington University, what the scans showed was a revelation.

I was absolutely struck by where this stuff was accumulating in the brain, he said.

Amyloid was in exactly the areas he was studying, the default network. It is used not only in

daydreaming but in memory and in the sense of self. For example, if a man is shown a list of

adjectives honest, kind, thoughtful and asked if they reflect the way he thinks of himself, theman will use his default network.

It seems to be a target of Alzheimers disease, which I found stunning, Dr. Raichle said.

The entire default network, and only the default network, was under attack.

The default network is costly for the brain to run, using huge amounts of glucose, Dr. Raichle said.

And one indication that a person is getting Alzheimers is that in scans, the brains glucose use is

markedly lower. The observation that Alzheimers attacks the default network, then, explains the

observation that a low use of glucose by the brain is associated with Alzheimers disease.

The default network has a unique metabolic profile, Dr. Raichle said. That opens up a whole set

of biological questions about how these synapses are operating.

Why does Alzheimers attack that region? he asked. The simple answer is, we dont know.

Meanwhile, Dr. Holtzman was doing a different sort of experiment that turned out to bear directly

on what Dr. Raichle was finding.

He found a way to measure amyloid levels in the brains of living mice. He would drill a small hole

in each ones skull and insert a probe that allowed beta amyloid to be collected.

Dr. Holtzman kept the probes in while the animals were eating and running around their cages

and when they were sleeping. Beta amyloid synthesis increased when they were awake, when the

default network is most active, and decreased when they slept.

His colleagues, Dr. David Brody at Washington University and Dr. Sandra Magnoni of Milan


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University, then devised an experiment in people. Their subjects were in comas followinghead

trauma or strokes. Often, doctors drill a small hole in these patients skulls and insert a catheter to

monitor fluids in the brain. Dr. Brody and Dr. Magnoni asked if they could also measure beta

amyloid.

They found that the less active the persons brain, the less beta amyloid it made. That made the

researchers ask whether something similar was happening during sleep the default network wasless active, so perhaps less beta amyloid was being made. If so, the implication, which Dr.

Holtzman is studying, is that people who are sleep-deprived might be at greater risk of

Alzheimers.

Another question is whether, as observations have suggested, people with more education are less

prone to develop Alzheimers disease. Dr. Holtzmans hypothesis is that education, by encouraging

more deliberate problem-solving and thought, decreases the activity of the default network, which

is not highly engaged with such focused activity.

At this point, with so many threads of research pointing to so many ideas about Alzheimers,

everything is a target for treatments to prevent or slow the disease enhancing the brains beta

amyloid disposal system, interfering with nerve cells feedback loops, blocking tau, protecting the

brains default network by focusing on its unique metabolic properties.

But researchers say the best hope for the immediate future is with experimental drugs, now being

tested, that slow beta amyloid production. The hope is that if the flow of amyloid into the brain is

slowed, levels can go down even if the amyloid drain is slightly clogged. The drugs might work

even if the problem is with the drain, not the faucet.

The trick in Alzheimers, though, might be to start treatment before too much damage is done.

And, said Dr. Samuel E. Gandy, a neurology professor at Mount Sinai School of Medicine, there

are some big questions that will have to be answered soon.

The question for the amyloid folks is, How early is early enough to start treatment? How long is

long enough to treat? And what are the other targets we should be attacking?

But for now, Dr. Holtzman says, the new findings are offering hope.

We have a richer view of the genesis of Alzheimers disease as well as new directions for research,

prevention and treatment, he said.


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