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Alzheimer's, Dementia & Mental Health
New Finding Indicates Alzheimer’s Caused by Peptide
Imbalance
Yin and Yang effect challenges existing theories on
cause of AD
May 30, 2007 – A challenge to the popular theories
on the causes and prevention of Alzheimer’s disease has emerged from
researchers at Rensselaer Polytechnic Institute. A specific imbalance
between two peptides may be the cause of the fatal neurological disease
that affects more than five million people in the United States They say
their new hypothesis could be a key to preventing this form of dementia.
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"We have found that two peptides, AB42 and AB40,
must be in balance for normal function," said Chunyu Wang, lead
researcher and assistant professor of biology at Rensselaer.
"They are like the Yin and Yang in Taiji, an
ancient Chinese philosophy. When the peptides are produced in the
correct proportions, the brain is healthy; but when that delicate
balance is changed, pathological changes will occur in the brain and the
person’s memories become hazy, leading to eventual dementia."
Wang expects that this imbalance could be the main
factor in the progression of Alzheimer’s disease. If correct, the
addition of AB40 may stop the disease’s development. Wang notes that
further research is needed, but his preliminary results challenge the
current mode of thinking about how these peptides contribute to the
progression of the disease.
The research will be published in the June edition
of the Journal of Molecular Biology.
Peptides are formed by the linking of different
amino acids. The two peptides that Wang investigated were both Amyloid
B-peptides (AB) — specifically those composed of 40 and 42 amino acids,
called AB40 and AB42. These two peptides have been previously found in
deposits, called senile plaques or amyloid plaques, in brains afflicted
with Alzheimer’s disease. These plaques, mainly composed of AB42
fibrils, are a hallmark of Alzheimer’s disease.
Prior research has uncovered that increased levels
of AB42 become toxic to brain cells when individual molecules of AB42,
or monomers, combine to form oligomer or fibril chains. This process is
called aggregation. But the role of AB40, which is also found in senile
plaques and generated from the same protein as AB42, has not been
clearly established. Wang set out to determine what role this peptide
played in the generation of AB42 aggregates.
Wang used the advanced Nuclear Magnetic Resonance (NMR)
machines within Rensselaer’s Center for Biotechnology and
Interdisciplinary Studies to monitor the formation of harmful AB42
fibrils in the presence of different levels of AB40. NMR is an extremely
powerful research tool capable of characterizing the three-dimensional
structure and dynamics of biological molecules.
Using NMR data, Wang found that as AB40 levels
increased, the aggregation of AB42 fibrils sharply decreased, protecting
benign AB42 monomers.
"We have found that the ratio of AB40 to AB42 plays
a key role in AB42 aggregation," Wang said. "The current mode of
thinking in Alzheimer’s emphasizes the toxic role of AB42 but neglects
the protective role of AB40. Combined with previous work on AB40 by many
other groups, our data suggest that AB40 has an equally important,
protective role in Alzheimer’s. Thus AB42, the bad molecule, and AB40,
the good molecule, are like Yin and Yang in Taiji. The brain can only
function normally when they are in balance."
Wang’s experiments show that when there is 15 times
more AB40 than AB42, the formation of AB42 fibrils is almost completely
stopped. "This means that the introduction of AB40 to tip the peptide
balance toward AB40 could potentially halt or slow down the progression
of the Alzheimer’s in the human brain," Wang said.
Wang plans to continue investigating how AB40 halts
the formation of AB42 fibrils, and he already sees vast implications for
this change in thinking about the progression of the disease.
"This has the potential to become a simple therapy
to prevent the formation of toxic AB42 species," he said. "I plan to
continue my research on the role of AB40 and hope that we can test this
theory on human neurons, animal models, and someday in clinical trials.
One critical advantage of using AB40 for the prevention or therapy for
Alzheimer’s is that AB40 is already known to be largely free of side
effects at near physiological concentration."
Editor’s Notes:
The research was funded by the Alzheimer’s
Association and a New York State Office of Science, Technology, and
Academic Research (NYSTAR) James D. Watson Investigator Program Award.
Rensselaer graduate student Yilin Yan worked with
Wang on the research project.
About Rensselaer
Rensselaer Polytechnic Institute, founded in
1824, is the nation’s oldest technological university. The university
offers bachelor’s, master’s, and doctoral degrees in engineering, the
sciences, information technology, architecture, management, and the
humanities and social sciences. Institute programs serve undergraduates,
graduate students, and working professionals around the world.
Rensselaer faculty are known for pre-eminence in research conducted in a
wide range of fields, with particular emphasis in biotechnology,
nanotechnology, information technology, and the media arts and
technology. The Institute is well known for its success in the transfer
of technology from the laboratory to the marketplace so that new
discoveries and inventions benefit human life, protect the environment,
and strengthen economic development.
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