A naturally occurring protein in the brain seems to curb the nerve
damage of Alzheimer's disease, Canadian researchers have found.
The discovery could eventually help lead to a better treatment for the
disease, which is the most common form of dementia and affects 10 per cent
of people over 65 – about 290,000 Canadians.
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Prof. Paul Fraser says of
the protein that his team discovered: "We might be able to
use it to create a treatment." (CBC)
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The newly found protein blocks the creation of nerve toxins in
Alzheimer's, a disease that slowly leads to memory impairment, behavioural
changes and dementia.
Supervising author Prof. Paul Fraser and his team at the Centre for
Research in Neurodegenerative Diseases at the University of Toronto
describe the discovery in Thursday's issue of the journal Nature.
They found that when the protein is taken away, there is an increase in
levels of the neurotoxin, called Abeta or beta-amyloid peptide.
"In the absence of this protein, we feel the disease would
accelerate," Fraser told CBC Newsworld. "If we can understand
how this prevents the toxic proteins, then we might be able to use it to
create a treatment."
Treatment could have fewer side effects
Other attempts to create treatments for Alzheimer's weren't specific
and resulted in inflammation in the brain, said Dr. Georges Levesque,
chair of the biomedical review panel at the Alzheimer Society of Canada.
The main advantage of the newly discovered protein, known as TPM21, is
it specifically targets Abeta – which suggests it could lead to a
treatment that has fewer, less serious side-effects.
"This one is different because it can be mimicked by a small
ligand [molecule] that can go directly in the brain," said Levesque,
who is a professor of biochemistry and human genetics at Laval University
in Quebec City.
The researchers plan to break the protein down into its components to
try to find the most active part, although they don't know how the natural
protein works.
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Alzheimer's disease
affects 10 per cent of people over 65 – about 290,000
Canadians.
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A co-author of the study, Prof. Peter St George-Hyslop of the Centre
for Research in Neurodegenerative Diseases, called the finding a
"blueprint for the development of a drug to treat the disease."
If a potential drug is designed, it would need to be tested on mice and
then in humans.
It's difficult to speculate when a drug could be on the market, but
Levesque estimated five to 10 years at the earliest.
The study was supported by the Alzheimer Society of Ontario, the
Canadian Institutes of Health Research and the Howard Hughes Medical
Institute.
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| Article |
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Published online: 11 June 2006; |
doi:10.1038/nm1423
Cyclohexanehexol inhibitors of A
aggregation prevent and reverse Alzheimer phenotype in a mouse model
JoAnne McLaurin1, 2,
Meredith E Kierstead1, 2, Mary E Brown1,
Cheryl A Hawkes1, Mark H L Lambermon1, Amie L
Phinney1, Audrey A Darabie1, Julian E Cousins1,
Janet E French1, Melissa F Lan1, Fusheng Chen1,
Sydney S N Wong1, Howard T J Mount1, 3, Paul
E Fraser1, 4, David Westaway1, 2 & Peter
St George-Hyslop1, 3
1 Centre for Research in
Neurodegenerative Diseases, 6 Queen's Park Crescent West, Toronto,
Ontario M5S 3H2 Canada.
2 Department of Laboratory Medicine
and Pathobiology, 6 Queen's Park Crescent West, Toronto, Ontario M5S 3H2
Canada.
3 Department of Medicine, and
University Health Network, Toronto Western Hospital Research Institute,
6 Queen's Park Crescent West, Toronto, Ontario M5S 3H2 Canada.
4 Department of Medical Biophysics,
University of Toronto, 6 Queen's Park Crescent West, Toronto, Ontario
M5S 3H2 Canada.
Correspondence should be addressed to JoAnne
McLaurin j.mclaurin@utoronto.ca
When
given orally to a transgenic mouse model of Alzheimer disease,
cyclohexanehexol stereoisomers inhibit aggregation of amyloid
peptide (A)
into high-molecular-weight oligomers in the brain and ameliorate several
Alzheimer disease–like phenotypes in these mice, including impaired
cognition, altered synaptic physiology, cerebral A
pathology and accelerated mortality. These therapeutic effects, which
occur regardless of whether the compounds are given before or well after
the onset of the Alzheimer disease–like phenotype, support the idea
that the accumulation of A
oligomers has a central role in the pathogenesis of Alzheimer disease.
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Drug provides key to halting Alzheimer's disease in mice
Clinical trials on humans beginning in June 2006
Jun 12/06
by Elizabeth Monier-Williams (about)
(email)
Researchers at the University of Toronto are one step closer to slowing
or stopping the progression of Alzheimer’s disease. In a study published
online in Nature Medicine, Professor JoAnne McLaurin and her
colleagues David Westaway, Howard Mount, Paul Fraser and Peter St George-Hyslop
at the Centre for Research in Neurodegenerative Diseases have identified a
drug that stops the amyloid β peptide — which causes toxic neural
damage in brains affected by Alzheimer’s disease — from accumulating.
When the researchers orally administered a small molecule known as
scyllo-cyclohexanehexol (AZD-103) to mice that had been genetically altered
to have Alzheimer’s disease, they found that the drug prevents aggregates
of the amyloid β peptides from forming, thereby reducing the toxicity
in the brain and preventing additional cognitive damage or memory loss.
These benefits were apparent when the drug was administered to mice before
they began to exhibit Alzheimer’s-like symptoms and after the symptoms had
begun.
“This is a significant breakthrough in drug development for
Alzheimer’s disease,” says McLaurin. “We have effectively demonstrated
improvement in memory and pathology among mice and are cautiously optimistic
that the same may hold true for human patients after formal clinical trials
have been conducted.”
Based on the study’s results, Health Canada has approved the drug for
Phase 1 Clinical Trials. Funded by the Ontario Research and Development
Challenge Fund and administered by Transition Therapeutics Inc., the trials
will determine whether the drug produces side effects in healthy humans.
“The study’s results are promising, but we must be aware of the fact
that AZD-103 must be formally tested in humans to ensure that it is safe and
effective,” says University Professor Peter St George-Hyslop, director of
the Centre for Research in Neurodegenerative Diseases. “This is a
long-term collaboration involving the University of Toronto and the
Alzheimer Society of Ontario, supported by both federal and provincial
research funding organizations; if successful, it will be an example of
basic science being funded from the initial discovery through to a
translational product that can be used by a Canadian company to improve the
quality of life for people with Alzheimer’s.”
AZD-103 should not be confused with the health food substance
myo-inositol or inositol, which the researchers have previously shown to be
ineffective in treating Alzhiemer’s disease.
Since 1990, the Centre for Research in Neurodegenerative Diseases has
made several fundamental discoveries that have had significant impact on our
understanding of Alzheimer’s and other neurodegenerative diseases. The
centre’s researchers were the first to show that Alzheimer’s is a
complex disorder with many causes, some of which are genetic; they have
identified several genes associated with Alzheimer’s, including Presenilin
1 and Presenilin 2, which cause aggressive early-onset forms of
Alzheimer’s. Most recently they discovered two other genes, Nicastrin and
TMP21 that are also involved in the biochemical processes of amyloid ß-peptide
production.
The study was funded by the Alzheimer Society of Ontario, the Canadian
Institutes of Health Research, the Natural Sciences and Engineering Research
Council of Canada, the Canada Foundation for Innovation, the Ontario
Research and Development Challenge Fund, the Howard Hughes Medical Institute
and the Scottish Rite and Cryptic Foundations.
Contact:
JoAnne McLaurin, Center for Research in Neurodegenerative Diseases, U of
T Faculty of Medicine, Office: 416-978-1035 ; e-mail: j.mclaurin@utoronto.ca
http://www.nature.com/nm/journal/vaop/ncurrent/extref/nm1423-S7.pdf
Supplementary methods:
Mice.
Experimental groups
of TgCRND8 mice on a C3H/B6 outbred background were
initially treated with either epi- or scyllo-cyclohexanehexol
30 mg/day. This initial
dosage was chosen based upon the dosage of
myo-cyclohexanehexol (6-18
grams/day/adult or 86 – 257 mg/kg/day) that is typically
administered to human patients
for various psychiatric disorders
40.
In these dosages, myo-cyclohexanehexol had no
toxicity in humans or animals. We have also repeated the
studies described here, using
doses of 5 mg/kg/day – 30 mg/day. Two cohorts (n=10 mice in
each treatment arm)
entered the study at six weeks of age and outcomes were
analyzed at four and six months
of age. A third cohort of animals (n=10 mice per treatment
arm) entered the study at five
months of age, and outcomes were then analyzed after one month
of treatment. The body
weight, coat characteristics and in-cage behaviour was
monitored. Mannitol was used as
a negative control for potential alterations in caloric
intake. All experiments were
performed according to the Canadian Council on Animal Care
guidelines and approved
by the Animal Care Committee, University of Toronto.
Behavioural tests:
Morris
Water Maze testing was performed as previously described 23.
After non-spatial pre-training, mice underwent place
discrimination training for 5 days
with 4-trials per day, followed by a cued visible platform to
rule out general motivational,
learning deficits and motor problems, and a probe trial to
evaluate memory. The probe
trial was conducted at 72 h after the last testing, and used
an annulus-crossing index to
assess spatial recall. The annulus-crossing index measures the
number of passes over the
original platform position relative to passes over the other
three quadrants. Data were
subjected to a repeated measures analysis of variance (ANOVA)
with treatment
(untreated, epi- or scyllo-cyclohexanehexol) and genotype
(TgCRND8 versus non-Tg) as
‘between-subject’ factors. Open field test for motor
activity was preformed as described
previously
44.
Duration of walking, pausing and grooming were analyzed as indices of
spontaneous locomotor activity. Sensorimotor function was
examined with an
EconomexTM accelerating rotarod (Columbus Instruments,
Columbus, OH), as described
elsewhere
45.
The rod was set to accelerate at a rate of 0.2 r.p.m./s, from an initial,
constant speed of 5 r.p.m. Latency to fall was recorded in
four daily trials, conducted at
30 min intervals. All mice were trained for seven days before
testing. The test day
performance score for each animal was obtained by summing its
latency to fall over the
four trials.
Cerebral A
β burden.
Brains were removed and one hemisphere was
fixed in
4%
[ (R) should be 'B' (Beta)]
paraformaldehyde and embedded in paraffin wax in the mid
sagittal plane. To generate
sets of systematic uniform random sections, 5 μm serial
sections were collected across
the entire hemisphere. Sets of sections at 50 m intervals were
used for analyses (10-14
sections/set). Plaques were identified after antigen retrieval
with formic acid, and
incubation with primary anti-A
β
antibody (Dako M-0872), followed by secondary
antibody (Dako StreptABCcomplex/horseradish kit). End products
were visualized with
DAB and were counter-stained with luxol fast blue. A
β
plaque burden was assessed with
Leco IA-3001 image analysis software interfaced with Leica
microscope and Hitachi KPM1U
CCD video camera. Openlab imaging software (Improvision,
Lexington, MA) was
then used to convert micrographs to binary images for plaque
number and plaque area
determinations. Vascular A
β burden
was defined as Aβ plaques
originating from or
surrounding blood vessels and was analysed similarly.
Soluble A
β oligomer
Analyses. The levels of soluble Aβ
oligomers were measured by a
dot blot assay with anti-oligomer specific antibodies on all
brain homogenates from all
experimental groups
25.
Briefly, oligomers were solubilised from one hemi-brain in PBS
in the presence of protease inhibitor cocktail (Sigma). After
centrifugation at 78,500 x g
for 1 h at 4 °C, the supernatants were analysed. Protein
content was determined by the
BCA protein assay (Pierce). Two g of total protein was spotted
onto nitrocellulose,
blocked with 10 % non-fat milk in TBS before incubation with
the biotinylated
oligomeric specific antibody (generous gift of C. Glabe).
Blots were incubated with
streptavidin-HRP and ECL chemiluminescence kit. Soluble and
fibrillar A
β42
were used
as negative controls and synthetic oligomeric A
β42
was used as a positive control.
Control samples were re-identified after oligomeric antibody
was stripped and re-probing
with the anti-A
β antibody
6E10.
Right hemispheres from 4 month old CRND8 Tg mice treated or
untreated with
scyllo-cyclohexanehexol were sonicated in 10 vol/wet weight
Tris buffered saline (TBS;
20 mM Tris [pH 7.3], 140 mM NaCl containing a protease
inhibitor cocktail). Samples
were centrifuged (100, 000g, 20 min, 4°C), supernatant
collected and frozen at -80°C
until use. Proteins (20 g) were separated by SDS-PAGE on a
10-20 % Tris-Tricine gel,
transferred to a nitrocellulose membrane, blocked for 1 h at
room temp with 8 % non-fat
milk and incubated overnight with anti-A
β
(6E10; 1:2,500). Membranes were rinsed
with TBST, exposed to anti-mouse (1:5,000) for 1 h at room
temperature, washed with
TBST (6 x 10 min) and developed using enhanced
chemiluminescence. Blots were
stripped and re-probed with either anti-APP (22C11; 1:1,000)
or anti-GAPDH (1:10, 000)
to confirm equal protein loading.
