| Current
Alzheimer Research
ISSN: 1567-2050
Current Alzheimer Research
Volume 3, Number 3, July 2006
Contents
ISOA Special Issue
6th Annual Alzheimer’s Disease Drug Discovery
Conference
Guest Editors: Lorenzo M. Refolo and Howard M. Fillit
Sponsored by
Acumen Pharmaceuticals, Inc., Élan Pharmaceuticals,
Inc., Forest Pharmaceuticals Inc., and Neurochem. Inc.
Introduction - Partnerships Between Philanthropy, Government
and Industry are Needed to Advance Drug Discovery for Neurodegenerative
Diseases Pp. 175
Lorenzo M. Refolo and Howard M. Fillit
Treatment of Alzheimer’s Disease: The Beginning
of a New Era Dale Schenk, ISOA – October
5th-6th,
2005 Pp. 177
Dale Schenk
Fibrillar β-Amyloid
Impairs the Late Phase of Long Term Potentiation
Pp. 179-183
Daniela Puzzo and Ottavio Arancio
[Abstract]
Therapeutic Potential of Neurogenesis for Prevention
and Recovery from Alzheimer’s Disease: Allopregnanolone
as a Proof of Concept Neurogenic Agent Pp. 185-190
Roberta Diaz Brinton and Jun Ming Wang
[Abstract]
TGF-β
Pathway as a Potential Target in Neurodegeneration and Alzheimer’s
Pp. 191-195
Tony Wyss-Coray
[Abstract]
Neurotrophic Effects of the Peptide NAP: A Novel
Neuroprotective Drug Candidate Pp. 197-199
Illana Gozes and Irit Spivak-Pohis
[Abstract]
The Pharmacology of Aminoadamantane Nitrates
Pp. 201-204
Yuqiang Wang, Jerry Eu, Mark Washburn, Tong Gong, H.-S.
Vincent Chen, James W. Larrick, Stuart A. Lipton, Jonathan
S. Stamler, Gregory T. Went and Seth Porter
[Abstract]
De Novo and Molecular Target-Independent
Discovery of Orally Bioavailable Lead Compounds for Neurological
Disorders Pp. 205-214
Laura K. Wing, Heather A. Behanna, Linda J. Van Eldik,
D. Martin Watterson and Hantamalala Ralay Ranaivo
[Abstract]
Ongoing In Vivo Studies with Cytoskeletal
Drugs in Tau Transgenic Mice Pp. 215-219
Mary L. Michaelis
[Abstract]
RNA Therapeutics Directed to the Non Coding Regions
of APP mRNA, In Vivo Anti-Amyloid Efficacy of Paroxetine,
Erythromycin, and N-acetyl cysteine Pp. 221-227
Stephanie Tucker, Michelle Ahl, Hyun-Hee Cho, Sanghamitra
Bandyopadhyay, Greg Cuny, Ashley Bush, Lee Goldstein, David
Westaway, Xudong Huang and Jack T. Rogers
[Abstract]
Autoimmunity in Alzheimer’s Disease as Evidenced
by Plasma Immunoreactivity Against RAGE and Aβ42:
Complication of Diabetes Pp. 229-235
Shyamala Mruthinti, Rosann F. Schade, Dean U. Harrell,
Nidhi K. Gulati, S. Swamy-Mruthinti, Gregory P. Lee and Jerry
J. Buccafusco
[Abstract]
NO Chimeras as Therapeutic Agents in Alzheimer’s
Disease Pp. 237-245
Gregory R.J. Thatcher, Brian M. Bennett and James N. Reynolds
[Abstract]
Computational Models of the Hippocampal Region:
Implications for Prediction of Risk for Alzheimer’s
Disease in Non-demented Elderly Pp. 247-257
Mark A. Gluck, Catherine E. Myers, Michelle M. Nicolle
and Sterling Johnson
[Abstract]
Lipophilic Analogs of Thioflavin S as Novel Amyloid-Imaging
Agents Pp. 259-266
Chunying Wu, Lisheng Cai, Jingjun Wei, Victor Pike and
Yanming Wang
[Abstract]
Abstracts
[Back to top]
Fibrillar β-Amyloid
Impairs the Late Phase of Long Term Potentiation
Daniela Puzzo and Ottavio Arancio
Synaptic dysfunction is involved in early stages of Alzheimer’s
disease (AD). Amyloid-β
peptides (Aβ),
a neu-ropathologic hallmark of the disease, have been shown
to alter synaptic function. Given that Aβ
is present in different forms including monomeric, oligomeric
and fibrillar species, we have investigated whether fibrillar
Aβ
impairs synaptic function. Here we report that a synthetic
fibrillar form of Aβ
impairs the late protein-synthesis dependent phase of LTP
without affecting the early protein-synthesis independent
phase. These findings add to previous reports that Aβ
oligomers are highly toxic to cells and might cause synaptic
dysfunction, and suggest that a therapeutic intervention in
AD should include the use of drugs inhibiting and disassembling
fibril formation in addition to drugs inhibiting oligomers
formation.
[Back to top]
Therapeutic Potential of Neurogenesis for Prevention
and Recovery from Alzheimer’s Disease: Allopregnanolone
as a Proof of Concept Neurogenic Agent
Roberta Diaz Brinton and Jun Ming Wang
A major challenge not yet addressed by current therapeutic
interventions for Alzheimer’s disease (AD) is the regeneration
of lost neurons and neural circuitry to restore cognitive
function. Therapies that lead to cessation of the degenerative
process still leave the brain riddled with deteriorated neural
circuits and reduced neuron number. The discovery of neurogenesis
in the adult brain and the regenerative potential of neural
stem cells holds the promise for restoration of neural populations
and regeneration of neural circuits necessary for cerebral
function. While the regenerative potential of neural stem
cells is great, so too is the challenge of delivering neural
stem cells to the brain. Basic science analyses and human
trials indicate that constituents of microenvironments within
the brain determine the neurogenic potential, pheno-typic
differentiation of neural stem cells and magnitude of the
neural stem cell pool. Multiple analyses have documented that
dentate neurogenesis is regulated by multiple growth factors
which are abundant during development and which dra-matically
decline with age. While the cause(s) of age-associated decline
in neurogenesis remains to be fully determined, loss in growth
factors, FGF-2, IGF-1 and VEGF, in the microenvironment of
the subgranular zone (SGZ) are prime con-tributors to the
reduced neurogenic potential. The decline in dentate neurogenesis
can be observed as early as middle age. In the aged and AD
brain, both the pool of neural stem cells and their proliferative
potential are markedly diminished. In parallel, the level
of potential regenerative factors is diminished in the brains
of Alzheimer’s patients compared to age-matched controls.
Our efforts have been directed towards discovery and development
of small, blood brain barrier pene-trant molecules to promote
endogenous proliferation of neural stem cells within the brain.
These endeavors have led to the discovery that the neurosteroid
alloprognanolone (APα)
is a potent and highly efficacious proliferative agent in
vitro and in vivo of both rodent and human neural
stem cells. Results of our in vitro studies coupled
with our more recent analyses in the triple transgenic mouse
model of AD suggest that APα
is a promising strategy for promoting neurogenesis in the
aged brain and potentially for restoration of neuronal populations
in brains recovering from neurodegenerative disease or injury.
A brief overview of issues impacting the therapeutic potential
of neurogenesis and the factors used to promote neurogenesis
in the aging and degenerating brain is presented. Also included
is a review of our current research into the neurogenic potential
of the small molecule, blood brain bar-rier penetrating, neurosteroid
allopregnanolone (APα).
[Back to top]
TGF-β
Pathway as a Potential Target in Neurodegeneration and Alzheimer’s
Tony Wyss-Coray
Alzheimer’s disease (AD) is a fatal neurodegenerative
disease characterized by the loss of large numbers of forebrain
neurons. There are currently no effective AD treatments available
and the cause of the disease is unknown in the majority of
cases. Because normal neuronal maintenance and survival depends
on stimulation of key signaling pathways by a number of neurotrophic
factors it has been postulated that reduced signaling by or
expression of these factors may promote neurodegeneration.
Growing evidence suggests that the transforming growth factor-β
(TGF-β)
signaling pathway may be one such neurotrophic pathway that
meets important protective and survival roles in neurons.
Here I explore this evidence and discuss the pathway as a
potential target for the treatment of neurodegeneration and
AD.
[Back to top]
Neurotrophic Effects of the Peptide NAP: A Novel
Neuroprotective Drug Candidate
Illana Gozes and Irit Spivak-Pohis
This short review outlines the scientific progression from
the neuropeptide vasoactive intestinal peptide as a neuroprotective
agent that acts through glial cells to increase and modulate
the synthesis and secretion of novel neuropro-tective substances.
Recent development in the studies on activity-dependent neuroprotective
protein (ADNP) and activity-dependent neurotrophic factor
(ADNF) and short peptide derivatives of these proteins, ADNF-9
and NAP suggest that these peptides are neurotrophic and promote
neurite outgrowth. These short peptides hold promise in future
neuroprotective/neurotrophic drug development. Clinical development
of NAP is currently in progress by Allon Therapeutics, Inc.
[Back to top]
The Pharmacology of Aminoadamantane Nitrates
Yuqiang Wang, Jerry Eu, Mark Washburn, Tong Gong, H.-S.
Vincent Chen, James W. Larrick, Stuart A. Lipton, Jonathan
S. Stamler, Gregory T. Went and Seth Porter
Memantine, an aminodamantane, has recently been approved to
treat moderate-to-severe Alzheimer’s disease in the
US after over 20 years on the market in Europe for treatment
of Parkinson’s disease. The unique properties of Memantine
allow for its selective inhibition of abnormally active NMDA
receptor channels while preserving normal glutamate activity
and healthy neuronal function. Recently, it has been shown
that compounds such as nitroglycerin, used for years for ischemic
coronary disease, can also regulate the NMDA receptor channel.
Novel compounds have been synthesized in an attempt to combine
these activities, in an attempt to synergistically improve
upon the activities of both nitrates and aminoadamantanes.
We have subjected these compounds to several laboratory tests
to compare their ability to affect the function of the NMDA
receptor and to dilate blood vessels. These tests provide
an initial indication of which of the compounds may have enhanced
activity relative to memantine. The results also provide guidance
for the synthesis of additional compounds that are likely
to have the properties that are being sought.
[Back to top]
De Novo and Molecular Target-Independent
Discovery of Orally Bioavailable Lead Compounds for Neurological
Disorders
Laura K. Wing, Heather A. Behanna, Linda J. Van Eldik,
D. Martin Watterson and Hantamalala Ralay Ranaivo
There is immediate potential to enhance success and innovation
in drug development by pairing newly emerging approaches in
medicinal chemistry and computational biology with knowledge
gained from the recent era of high throughput screens and
the early years of modern drug discovery when in vivo
efficacy was an early “Go/No Go” project management
decision. Focused, in-parallel synthetic chemistry platforms,
combined with computational analyses serving as decision aids
in planning, minimize the total number of compounds synthesized
while maximizing the probability of creating bioavailable
compounds that sample diverse chemical space. Incorporating
a hierarchal strategy that emphasizes early selection of synthesized
compounds based on biological or biophysical endpoints presents
fewer and more relevant compounds for secondary evaluation
of in vivo efficacy using animal screens with disease
relevant or clinically translatable endpoints. We summarize
here an interdisciplinary approach at the chemistry-biology
interface that is used for the rapid discovery of novel lead
compounds for neurodegenerative disorders, such as Alzheimer’s
disease (AD). The chemistry platform uses established chemistries
amenable to in-parallel strategies to create synthetic diversifications
of the privileged pyridazine chemotype that sample a restricted
chemical space. The hierarchal biology platform uses primary
screens for in vitro activity and selectivity with
the target cell type, and rapid secondary screens for in
vivo efficacy and toxicity in animal models with good
phenotypic penetrance for disease relevant pathophysiological
endpoints or clinically translatable surrogate endpoints.
For the AD case study, novel lead compounds were developed
in less than two years by a small academic group, and corporate
sponsored clinical trials are planned.
[Back to top]
Ongoing In Vivo Studies with Cytoskeletal
Drugs in Tau Transgenic Mice
Mary L. Michaelis
Most drug discovery efforts for Alzheimer’s disease
(AD) have focused on prevention or clearance of β-amyloid
(Aβ)
fibrils or oligomers, with far less attention to prevention
of 
abnormalities that lead to neurofibrillary tangles (NFTs).
Much evidence now indicates that Aβ
multimers can trigger neurodegenerative changes that involve
formation of dystrophic neurites and cytoskeletal collapse,
possibly due loss of microtubule (MT) stabilization by the
protein. We have found that several MT-stabilizing agents
such as Taxol significantly enhanced neuronal survival in
the presence of Aβ
and identified agents that enter the brain, a necessity for
in vivo testing in animal models of
pathology. Studies were designed to test two agents in the
mutant (JNPL3) mouse that develops severe motor deficits at
about seven months of age, accompanied by neuropathological
markers of
pathology. In addition to using motor performance tests through
the planned period of drug administration, we designed a simple
appetitive memory test that required a reduction in ad
lib food intake. Although the neurochemical data are
still being analyzed, we were surprised to find that all of
the JNPL3 mice, whether receiving the drug or not, developed
no signs of motor impairment up to 10 months of age. This
is considerably beyond the age at which free-fed mice survived
and suggests that the food restriction alone may have delayed
the pathological process. A study is ongoing with free-fed
mice to determine if the drug interventions do have any beneficial
effects in these mutant mice.
[Back to top]
RNA Therapeutics Directed to the Non
Coding Regions of APP mRNA, In Vivo Anti-Amyloid
Efficacy of Paroxetine, Erythromycin, and N-acetyl cysteine
Stephanie Tucker, Michelle Ahl, Hyun-Hee Cho, Sanghamitra
Bandyopadhyay, Greg Cuny, Ashley Bush, Lee Goldstein, David
Westaway, Xudong Huang and Jack T. Rogers
Lead compounds directed to the 5’ leader of the
Amyloid Precursor Protein transcript (i.e., paroxetine (SSRI),
N-acetyl cysteine (antioxidant), and erythromycin (macrolide
antibiotic)) were employed in a pilot study to evaluate their
anti-amyloid efficacy in the TgCRND8 transgenic mouse model
for Alzheimer’s Disease (AD). The relative levels of
Aβ
peptide were reduced after exposure of mice to paroxetine
(N=5), NAC (N=7), and erythromycin (N=7) relative to matched
placebo counterparts. Paroxetine limited the levels of APP
holoprotein and total Aβ
peptide levels (measure-ments of Aβ
were performed at two separate sites by quantitative western
blotting and ELISA assay). The paroxetine data provided proof-of-concept
for our strategy for further screening the APP 5’UTR
target to identify novel drugs that exhibit anti-amyloid efficacy
in vivo. Erythromycin and azithromycin were macrolide
antibiotics that markedly changed the cleavage of the APP
C-Terminal Fragment (CTF) in SH-SY5Y cells. Erythromycin provided
orally to TgCRND8 mice consistently (100%) reduced brain Aβ(1-42)
levels. These data demonstrated a highly statistically significant
anti-amyloid trend for paroxetine, NAC and erythromycin. The
potential for conducting further studies with these compounds
using larger cohorts of TgCRND8 mice is discussed, particularly
since erythromycin has recently been exposed to mice for a
further 6 months (N=6). It will be possible to employ the
chemical structures of paroxetine and erythromycin as starting
points for drug design and development for AD therapeutics.
[Back to top]
Autoimmunity in Alzheimer’s Disease as Evidenced
by Plasma Immunoreactivity Against RAGE and Aβ42:
Complication of Diabetes
Shyamala Mruthinti, Rosann F. Schade, Dean U. Harrell,
Nidhi K. Gulati, S. Swamy-Mruthinti, Gregory P. Lee and Jerry
J. Buccafusco
Features of autoimmunity have been associated with both
Alzheimer’s disease (AD) and with diabetes. In both
diseases high levels of advanced glycation end products (AGEs)
and their receptor (RAGE) have been detected in tissues and
in the circulation. In addition high titers of antibodies
directed against a RAGE-like peptide occur in the circulation.
In this study we report the presence of auto-antibodies directed
against RAGE and the cytotoxic amyloid peptide Aβ42
in plasma samples derived from four study groups. Anti-RAGE
IgG titers were greatest in the AD-diabetic cohort. They were
followed in decreasing order by the AD-non-diabetic cohort,
the elderly diabetic cohort, and lastly by the control non-diabetic
elderly cohort. The same profile of IgG differences was evident
for the anti-Aβ42
titers. When all of the data were combined, there was a strong
linear correlation between the RAGE and Aβ42
titers suggesting that the two peptides exist as a tight complex
in plasma. Plasma IgG titers were not correlated with cognitive
status except that AD and AD-diabetic participants were significantly
cognitively impaired relative to the two non-AD groups. There
also was no significant correlation between IgG titers and
subject age, except that there was a trend for a negative
slope for the AD participants and a positive slope for the
control participants. In keeping with the human data, we also
report that chemically-induced diabetes in rats was associated
with high levels of AGEs, anti-RAGE-like IgGs, and anti-Aβ42-like
IgGs. For non-diabetic rats, there was a clear age-dependency
regarding the magnitude of the IgG levels. These data support
the concept of an interrelationship between diabetes and AD.
For both diseases one underlying contributing factor to cytotoxicity
could be the development of an autoimmune response triggered
by the presence of AGEs and amyloid peptides.
[Back to top]
NO Chimeras as Therapeutic Agents in Alzheimer’s
Disease
Gregory R.J. Thatcher, Brian M. Bennett and James N. Reynolds
NO is an important messenger molecule in the brain, playing
an important role in learning and memory, in particular via
the ERK/CREB signaling pathway. NO is also a neuroprotective
agent; multiple mechanisms having been demonstrated that can
contribute to cell survival as levels of antioxidants and
trophic factors are reduced with aging. Small molecules that
mimic the biological activity of NO, including NO donors,
may thus ameliorate cognition and provide neuroprotection.
Several lines of evidence have linked the neurodegeneration
and dementia characteristic of Alzheimer’s disease with
the action of β-amyloid
protein at the α
7-nicotinic acetylcholine receptor. The interplay of
Aβ
with α 7-nicotinic
ACh receptors operating via the ERK signaling cascade links
the amyloid cascade and the cholinergic hypothesis in pathways
that impact synaptic plasticity and memory. This interplay
also provides linkages to disruption of NO/cGMP signaling
in AD, and in addition, recent direct evidence has been found
demonstrating that Aβ
downregulates the NO/cGMP/CREB pathway. Activation of soluble
guanylyl cyclase elevating cGMP in the brain represents the
central element of a therapeutic approach to the treatment
of AD and other neurodegenerative diseases, furthermore, evidence
suggests that NO may display cGMP-independent activity and
may operate via multiple biochemical signaling pathways to
ensure the survival of neurons subjected to stress. GT 1061
is an NO chimera, an NO mimetic compound that contains an
ancillary, synergistic pharmacophore, currently in clinical
trials for Alzheimer’s. NO chimeras and hybrid nitrates
hold promise as therapeutics for AD with multiple sites of
action.
[Back to top]
Computational Models of the Hippocampal Region:
Implications for Prediction of Risk for Alzheimer’s
Disease in Non-demented Elderly
Mark A. Gluck, Catherine E. Myers, Michelle M. Nicolle
and Sterling Johnson
We have pursued an interdisciplinary research program
to develop novel behavioral assessment tools for evaluating
specific memory impairments following damage to the medial
temporal lobe, including the hippocampus and associated structures
that show pathology early in the course of Alzheimer’s
disease (AD). Our approach uses computational models to identify
the functional consequences of hippocampal-region damage,
leading to testable predictions in both rodents and humans.
Our modeling argues that hippocampal-region dysfunction may
selectively impair the ability to generalize when familiar
information is presented in novel recombinations. Previous
research has shown that specific reductions in hippocampal
volume in non-demented elderly individuals correlate with
future development of AD. In two previous studies, we tested
non-demented elderly with and without mild hippocampal atrophy
(HA) on stimulus-response learning tasks. Individuals with
and without HA could learn the initial information, but the
HA group was selectively impaired on transfer tests where
familiar features and objects were recombined. This suggests
that such generalization deficits may be behavioral markers
of HA, and an early indicator of risk for subsequent cognitive
decline. Converging support for the relevance of these tasks
to aging and Alzheimer’s disease comes from our recent
fMRI studies of individuals with mild cognitive impairment
(MCI). Activity in the hippocampus declines with progressive
training on these tasks, suggesting that the hippocampus is
important for learning new stimulus representations that support
subsequent transfer. Individuals with HA may be able to learn,
but in a more hippocampal-independent fashion that does not
support later transfer. Ultimately, this line of research
could lead to a novel battery of behavioral tests sensitive
to very mild hippocampal atrophy and risk for decline to AD,
allowing early diagnosis and also allowing researchers to
test new Alzheimer’s drugs that target individuals in
the earliest stages of the disease – before significant
cognitive decline. A new mouse version of one of our tasks
shows promise for translating these paradigms into rodents,
allowing for future studies of therapeutic interventions in
transgenic mouse models of AD.
[Back to top]
Lipophilic Analogs of Thioflavin S as Novel Amyloid-Imaging
Agents
Chunying Wu, Lisheng Cai, Jingjun Wei, Victor Pike and
Yanming Wang
Lipophilic analogs of thioflavin S were synthesized and radiolabeled
with positron or single photon emitting radionuclides. The
binding affinity for Aβ
was evaluated using isolated amyloid fibrils from human brain
tissue. Binding specificity was assessed using fluorescent
tissue staining. In vivo brain uptake was evaluated
in mice. Following synthesis, neutral analogs of thioflavin
S capable of radiolabeling with 11C
or 125I,
were found to bind isolated human Aβ
with affinities in the nanomolar range. Fluorescent tissue
staining showed selective binding to Aβ
deposits in vitro. Biodistribution of selected compounds
displayed high brain permeability at early time points. At
later points, the compounds were cleared from the normal brain,
indicating low non-specific binding in vivo. These
studies indicated that novel amyloid imaging probes can be
developed based on thioflavin S that readily entered the brain
and selectively bound to Aβ
deposits and neurofibrilary tangles. Potential applications
of these amyloid binding agents include facilitating drug
screening in animal models and use as in vivo markers
of early and definitive diagnosis of AD.
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