An efficient, high-volume technique for testing potential
drug treatments for Alzheimer's disease uncovered an organic compound that
restored motor function and longevity to fruit flies with the disease.
Princeton
University researchers report in the Journal of Biological Chemistry
that they discovered an organic compound that prevented the formation of
protein clumps, or aggregates, found on human brain cells afflicted by
Alzheimer's disease. The researchers realized the compound's potential via a
high-throughput -- meaning many materials can be examined at once -- screening
process developed at Princeton that examined the ability of 65,000 molecular
compounds to inhibit protein aggregation.
When
administered to fruit flies bred to exhibit Alzheimer's-like symptoms, the
compound -- which the researchers call D737 -- restored climbing ability and
increased the flies' lifespan by several days in comparison to flies that did
not receive the compound, the researchers reported.
The
compound worked by stopping the accumulation of a peptide known as amyloid beta
42 (Aβ42), which disrupts cell function, is found in high quantities in
Alzheimer's plaques, and is thought to initiate the disease's characteristic
neural deterioration. The fruit flies were genetically engineered at the
University of Cambridge to have human Aβ42 collect in their neurons. As in
humans, this accumulation results in memory and mobility loss, disorientation
and early death.
Senior
researcher Michael Hecht, a Princeton professor of chemistry, said the findings
demonstrate a quick and efficient screening method that could help in the
search for a medicinal defense against Alzheimer's. Currently, he said, the
disease's proliferation in an aging population has outpaced the success of
efforts to develop a treatment for it.
"As
the population ages, Alzheimer's is the big disease," Hecht said.
"There are drugs to control symptoms, but nothing to treat the disease
itself. One approach could be to control peptide aggregation as we have done,
but the compounds tested so far often fail.
"Our
technique would allow scientists to create an artificial genetic system,
examine it with a high-throughput screen and find whether it works," Hecht
said. "From that they can fish out the best results and test them in other
models."
Furthermore,
an effective compound such as D737 can reveal information about Aβ42's
structure that can be used to formulate other treatments, said lead author
Angela Fortner McKoy, a postdoctoral researcher at Rutgers University who
received her Ph.D. in chemistry from Princeton in 2011. Fortner McKoy and Hecht
worked with second author Jermont Chen, who earned his Ph.D. in chemistry from
Princeton in 2008, and Trudi Schüpbach, the Henry Fairfield Osborn Professor of
Biology.
The
Princeton researchers used a screening process developed in the Hecht lab to
specifically identify Aβ42 aggregation. First reported in the journal ACS
Chemical Biology in 2006, the technique hinges on a fusion of Aβ42 and green
fluorescent protein -- which glows under ultraviolet light and is found in
animals such as jellyfish -- that is expressed in the bacteria E. coli. The
fluorescent protein does not glow when Aβ42 is able to aggregate. When a
compound such as D737 inhibits peptide clumping, however, the E. coli bacterium
appears bright green. The efficiency of the screening system stems from the
relative simplicity of attaining and working with E. coli, a standard
laboratory bacterium, Hecht said.
For
the current research, Hecht and his co-authors examined 65,000 randomly chosen organic
compounds that Chen acquired from the Broad Institute of the Massachusetts
Institute of Technology and Harvard University. The technique revealed 269
compounds that halted the buildup of Aβ42 aggregates. Of those, Fortner McKoy
selected the eight most readily available for further testing. Fortner McKoy
found that D737 best prevented the accumulation of Aβ42 and reduced mortality
in cell cultures. In addition, the researchers found that the compound reduced
the production and accumulation of reactive oxygen species, which damage cells.
The
researchers then tested the compound on healthy fruit flies with no Aβ42
accumulation, as well as on flies with a regular human-form Aβ42 gene and flies
with a mutant gene -- which is found in some humans with Alzheimer's -- that
causes extra buildup of the peptide. For each of these three fly types, one
group of flies did not receive D737 while another group was given the compound
in concentrations of 2, 20 or 200 micromolar.
In
the flies with regular and accelerated Aβ42 buildup, those receiving D737 lived
an average of four to six days longer than similarly altered flies that were
not fed the compound. The healthy fruit flies that received D737 showed no
change in lifespan, demonstrating that the compound is non-toxic in fruit
flies, Hecht said.
To
test mobility, the researchers put 20 flies from both of the genetically
altered groups into the bottom of a vial and recorded how many had climbed to
the top. After 38 days, only 6 percent of untreated flies with normal Aβ42
accumulation could climb, as opposed to as many as 34 percent of the flies
receiving D737.
In
flies with the mutant Aβ42 gene, all those left untreated lost mobility after
27 days. Of those given the compound, however, 50 to 78 percent -- depending on
the dosage -- could still climb after the same time period.
Damian
Crowther, a group leader in the Department of Genetics at Cambridge who created
and supplied the flies used in the Princeton research but had no active role in
the work, said that D737 demonstrated a notable ability to suppress in fruit
flies the same neurological, physical and mental deficits seen in humans with
Alzheimer's.
"It's
not common to see such a strong effect in the fly model. Of the compounds that
my lab tests, which have been through rigorous in vitro screening, we see
effects as good as this in only 5 to 10 percent," Crowther said. "To
find that a compound administered orally is able to show beneficial effects on
both of these fly phenotypes indicates that the drug can access the neurons
and, once within the brain, presumably control the aggregation of amyloid beta
peptides."
Crowther
said the Princeton research further supports the approach of curbing the
buildup of Aβ42 and related variants of the amyloid beta peptide to treat
Alzheimer's. In the middle stages of accumulation, variations of the peptide
can be highly toxic to neurons and kill them, he said. But the work by Hecht
and his co-authors helps show that blocking amyloid-beta aggregation can be
safe and potent.
"There
is always a worry when looking for aggregation-blocking agents that the
aggregation process may be interrupted at the wrong point," Crowther said.
"Further
work should try to characterize in an in vivo system exactly where this
compound halts or modifies the aggregation process," he said. "For a
beneficial effect we don't need to completely block aggregation -- indeed,
amyloid formation is a thermodynamically inevitable process. It could be that
the compound simply modulates the aggregation process so that the most toxic
intermediates are less populated."
Although
the compound's success in flies would not necessarily translate to humans,
Fortner McKoy said, its effectiveness illustrates that worthwhile treatment
candidates can be uncovered with the Princeton screening method.
"It
inhibited the peptide aggregation effectively enough so that we could see an improvement
in the flies," Fortner McKoy said. "In general, a compound like this
would be further developed and changes would be made to it to test its efficacy
in humans. But the fly results show that it is worth testing this compound in
another model."
Source:
The
above story is reprinted from materials provided by Princeton
University. The original article was written by Morgan Kelly.
Note:
Materials may be edited for content and length. For further information, please
contact the source cited above.
Journal
Reference:
1.
A. F. McKoy, J. Chen, T. Schupbach,
M. H. Hecht. A Novel Inhibitor of Amyloid (A ) Peptide Aggregation:
FROM HIGH THROUGHPUT SCREENING TO EFFICACY IN AN ANIMAL MODEL OF ALZHEIMER
DISEASE. Journal of Biological Chemistry, 2012; 287 (46): 38992 DOI:
10.1074/jbc.M112.348037
Disclaimer: This article is not intended to provide medical advice,
diagnosis or treatment. Views expressed here do not necessarily reflect those
of Eagle Group or its staff.
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