Alzheimer's clue found in specific plaque

WASHINGTON (AP) --
Researchers have
uncovered a new clue
to the cause of
Alzheimer's disease.

The brains of people
with the memory-
robbing form of
dementia are
cluttered with a
plaque made up of
beta-amyloid, a sticky
protein. But there
long has been a
question whether this
is a cause of the
disease or a side
effect. Also involved
are tangles of a
protein called tau;
some scientists
suspect this is the
cause.

Now, researchers
have caused
Alzheimer's symptoms
in rats by injecting
them with one
particular form of
beta-amyloid.
Injections with other
forms of beta-amyloid
did not cause illness,
which may explain why
some people have
beta-amyloid plaque in
their brains but do
not show disease
symptoms.

The findings by a
team led by Dr.
Ganesh M. Shankar
and Dr. Dennis J.
Selkoe of Harvard
Medical School are
reported in the
current online edition
of the journal Nature
Medicine.

The researchers used
extracts from the
brains of people who
donated their bodies
to medicine.

Forms of soluble beta-
amyloid containing
different numbers of
molecules, as well as
insoluble cores of the
brain plaque, were
injected into the
brains of mice. There
was no detectable
effect from the
insoluble plaque or the
soluble one-molecule
or three-molecule
forms, the
researchers found.But the two-molecule
form of soluble beta-
amyloid produced
characteristics of
Alzheimer's in the
rats, they reported.

Those rats had
impaired memory
function, especially
for newly learned
behaviors. Studies
were also done on
mice and when their
brains were
inspected, the density
brain cells were
reduced by 47
percent. The beta-
amyloid seemed to
affect synapses, the
connections between
cells that are
essential for
communication
between them.

The research, for the
first time, showed the
effect of a particular
type of beta-amyloid
in the brain, said Dr.
Marcelle Morrison-
Bogorad, director of
the division of
neuroscience at the
National Institute on
Aging, which helped
fund the research.

It was surprising that
only one of the three
types had an effect,
she said in a
telephone interview.

Morrison-Bogorad said
the findings may help
explain the discovery
of plaque in the brains
of people who do not
develop dementia. For
some time, doctors
have wondered why
they find some brains
in autopsy that are
heavily coated with
beta-amyloid, but the
person did not have
Alzheimer's.The answer may lie in
the two types of beta-
amyloid that did not
cause symptoms.

Now, the question is
why one has the
damaging effect and
not others.

"A lot of work needs
to be done," Morrison-
Bogorad said. "Nature
keeps sending us
down paths that look
straight at the
beginning, but there
are a lot of curves
before we get to the
end."

Dr. Richard J. Hodes,
director of the
National Institute on
Aging, said that "while
more research is
needed to replicate
and extend these
findings, this study
has put yet one more
piece into place in the
puzzle that is
Alzheimer's."

In addition to the
Institute on Aging, the
research was funded
by Science Foundation
Ireland, Wellcome
Trust, the McKnight
and Ellison
foundations and the
Lefler Small Grant
Fund.

SOURCE: AP via CNN

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