| Current
Alzheimer Research
ISSN: 1567-2050
Current Alzheimer Research
Volume 4, Number 4, September 2007
Contents
Advances in Alzheimer Therapy: Development
of Innovative New Strategies
Guest Editors: Nigel H. Greig, Ezio Giacobini
and Debomoy K. Lahiri
Editorial:
Advances in Alzheimer Therapy: Development of Innovative
New Strategies Pp. 336-339
Nigel H. Greig, Ezio Giacobini and Debomoy K. Lahiri
Cholinotrophic Molecular Substrates of Mild Cognitive
Impairment in the Elderly Pp. 340-350
Elliott J. Mufson, Scott E. Counts, Margaret Fahnestock
and Stephen D. Ginsberg
[Abstract]
NGF-Cholinergic Dependency in Brain Aging, MCI and
Alzheimer’s Disease Pp. 351-358
A.C. Cuello, M.A. Bruno and K.F.S. Bell
[Abstract]
Amyloid Beta Protein as a Marker or Risk Factor of
Alzheimer’s Disease Pp. 359-363
Pankaj D. Mehta
[Abstract]
Computerized Methods in the Assessment and Prediction
of Dementia Pp. 364-369
Amos D. Korczyn and Vered Aharonson
[Abstract]
Practical Issues in Stem Cell Therapy for Alzheimer’s
Disease Pp. 370-377
K. Sugaya, Y.D. Kwak, O. Ohmitsu, A. Marutle, N.H. Greig
and E. Choumrina
[Abstract]
TNF-α
Inhibition as a Treatment Strategy for Neurodegenerative Disorders:
New Drug Candidates and Targets Pp. 378-385
David Tweedie, Kumar Sambamurti and Nigel H. Greig
[Abstract]
East Meets West in the Search for Alzheimer's Therapeutics
- Novel Dimeric Inhibitors from Tacrine and Huperzine A
Pp. 386-396
W.M. Li, K.K.W. Kan, P.R. Carlier, Y.P. Pang and Y.F.
Han
[Abstract]
N-Phenylamine Derivatives as Aggregation Inhibitors
in Cell Models of Tauopathy Pp. 397-402
M. Pickhardt, J. Biernat, I. Khlistunova, Y.-P. Wang,
Z. Gazova, E.-M. Mandelkow and E. Mandelkow
[Abstract]
Neurorescue Activity, APP Regulation and Amyloid-β
Peptide Reduction by Novel Multi-Functional Brain Permeable
Iron- Chelating- Antioxidants, M-30 and Green Tea Polyphenol,
EGCG Pp. 403-411
Yael Avramovich-Tirosh, Lydia Reznichenko, Tamar Amit,
Hailin Zheng, Mati Fridkin, Orly Weinreb, Silvia Mandel and
Moussa B.H. Youdim
[Abstract]
Alpha-Secretase As a Therapeutic Target Pp.
412-417
Falk Fahrenholz
[Abstract]
Memapsin 2 (Beta-Secretase) Inhibitor Drug, between
Fantasy and Reality Pp. 418-422
Arun K. Ghosh, Geoffrey Bilcer, Lin Hong, Gerald Koelsch
and Jordan Tang
[Abstract]
The γ/ε-Secretase-Derived
APP Intracellular Domain Fragments Regulate p53 Pp.
423-426
Frédéric Checler, Claire Sunyach, Raphaelle
Pardossi-Piquard, Jean Sévalle, Bruno Vincent, Toshitaka
Kawarai, Nadège Girardot, Peter St George-Hyslop and
Cristine Alves da Costa
[Abstract]
Novel Aβ
Immunogens: Is Shorter Better? Pp. 427-436
Cynthia A. Lemere, Marcel Maier, Ying Peng, Liying Jiang
and Timothy J. Seabrook
[Abstract]
A Novel Immunotherapy for Alzheimer’s Disease:
Antibodies against the β-Secretase
Cleavage Site of APP Pp. 437-445
Michal Arbel and Beka Solomon
[Abstract]
Is alpha-Synuclein Pathology a Target for Treatment
of Neurodegenerative Disorders? Pp. 446-457
M. Windisch, H.J. Wolf, B. Hutter-Paier, A. Hofmeister
and R. Wronski
[Abstract]
Lessons from Darwin: 21st Century Designs for Clinical
Trials Pp. 458-467
Robert E. Becker
[Abstract]
Drug Trials in Dementia: Challenging Ethical Dilemmas
Pp. 468-472
Amos D. Korczyn
[Abstract]
Alzhemed: A Potential Treatment for Alzheimer's Disease
Pp. 473-478
Paul S. Aisen, Serge Gauthier, Bruno Vellas, Richard Briand,
Daniel Saumier, Julie Laurin and Denis Garceau
[Abstract]
Pharmacogenetic Aspects of Therapy with Cholinesterase
Inhibitors: The Role of CYP2D6 in Alzheimer’s Disease
Pharmacogenetics Pp. 479-500
Ramón Cacabelos, Ruth Llovo, Carmen Fraile and
Lucía Fernández-Novoa
[Abstract]
Abstracts
[Back to top]
Cholinotrophic Molecular Substrates of Mild
Cognitive Impairment in the Elderly
Elliott J. Mufson, Scott E. Counts, Margaret Fahnestock
and Stephen D. Ginsberg
Cholinergic nucleus basalis (NB) neurons provide the major
cholinergic innervation to the cortical mantle, are selectively
vulnerable in late stage Alzheimer’s disease (AD) and
require the neurotrophin, nerve growth factor (NGF) and its
receptors (TrkA and p75NTR),
for their survival. The molecular events underlying the demise
of these neurons in AD were investigated using tissue harvested
from participants in a longitudinal clinical pathological
study of aging and AD who agreed to an annual clinical evaluation
providing a categorization of no cognitive impairment (NCI),
mild cognitive impairment (MCI) or AD and postmortem brain
donation. Although the number of choline acetyltransferase
(ChAT)-positive neurons was unchanged, TrkA and p75NTR
receptor-containing neurons, which co-localize with ChAT,
were significantly reduced in the NB of subjects with MCI
and AD compared to those with NCI. These observations indicate
a phenotypic down-regulation rather than frank NB neuronal
degeneration in MCI. Expression profiling of single cholinergic
NB neurons revealed TrkA but not p75NTR
mRNA is reduced in MCI, suggesting that decreased neurotrophin
responsiveness may be an early biomarker for AD. The NGF precursor
molecule, proNGF, is increased in the cortex in MCI and AD.
Since proNGF accumulates in the presence of reduced cortical
TrkA and sustained levels of p75NTR,
a shift in the balance between cell survival and death molecules
may occur in prodromal AD. Coincident with these phenomena,
brain derived neurotrophic factor (BDNF) and its precursor
molecule, proBDNF, are reduced in the MCI cortex, potentially
depriving CBF neurons of additional trophic factor support.
Moreover, there is a shift in the ratio of 3 repeat tau to
4 repeat tau gene expression, whereas total tau message is
stable in NB neurons during the disease process. These data
suggest there is a shift in cholinotrophic molecular events
in MCI and early AD which may lead to cell dysfunction and
eventual cell death over the course of the disease. These
findings support the concept that from a neurotrophic pathobiologic
perspective, MCI is already early AD.
[Back to top]
NGF-Cholinergic Dependency in Brain Aging, MCI and
Alzheimer’s Disease
A.C. Cuello, M.A. Bruno and K.F.S. Bell
Forebrain cholinergic neurons are highly dependent on nerve
growth factor (NGF) for phenotype maintenance. We have established
that in addition to “target-derived” NGF neurotrophic
stimulation, cholinergic neurons also respond dose-dependently,
to intra-parenchymal NGF administration in the somato-dendritic
region of the nucleus Basalis [1], thus illustrating the potential
of alternative reparative therapies which would by-pass the
undesirable effects of diffuse neurotrophin application. Moreover,
our lab has also observed that the steady-state number of
cortical cholinergic synapses is dependent on continuous NGF
supply, as anti-NGF monoclonal antibodies and TrkA receptor
antagonists deplete pre-existing cholinergic bouton numbers
[2]. Furthermore, the application of either NGF or TrkA NGF-mimetic
agonists successfully rescues the age-dependent loss of cortical
cholinergic boutons in aged-impaired rats [3]. The vulnerability
of the cortical cholinergic system has also been demonstrated
in transgenic animal models of the Alzheimer’s disease
(AD) amyloid pathology [4-6]. It is of interest to note however,
that an up-regulation of cholinergic presynaptic boutons has
been observed in certain transgenic mouse models prior to
plaque formation [6]. This observation is similar to the visibly
increased immunoreactivity of cortical and hippocampal choline
acetyltransferase (ChAT) fibers in patients with Mild Cog-nitive
Impairment (MCI, [7]). A series of ex-vivo experiments
conducted by our group have demonstrated that contrary to
popular belief, proNGF, as opposed to mature NGF, is released
from the cerebral cortex in an activity-dependent manner.
In addition, proNGF appears to be released with a series of
pro-enzymes and enzymes, which are involved in its subsequent
maturation to NGF and degradation in the extracellular space
[8]. Given that proNGF is known to be upregulated in AD patients
[9] a dysregulation in the maturation or degradation of mature
NGF might explain the preferential vulnerability of the cholinergic
system in the AD pathology.
[Back to top]
Amyloid Beta Protein as a Marker or Risk Factor of
Alzheimer’s Disease
Pankaj D. Mehta
Alzheimer disease (AD) is a neurodegenerative disease that
affects cognition, behavior and function. The etiology of
the disease is unknown, however, the Primary Risk Factors
for AD are aging, and family history. Neurofibrillary tangles
(NFT) and amyloid-bearing neuritic plaques in the limbic and
cerebral cortices are the characteristic neuropathologic lesions
in brains of patients with AD. The NFT is mainly composed
of hyprephosphorylated tau, whereas the major component of
the neuritic plaques is the amyloid beta (Aβ)
protein. The clinical diagnosis of probable AD is based on
history, physical examination, neuropsychological testing,
laboratory studies and neuroimaging techniques. However, there
is no specific laboratory marker to support the diagnosis
of definite AD or monitoring the progression of the disease.
Several biochemical markers related to neuropathology have
been identified in cerebrospinal fluid (CSF). We describe
the studies of CSF or blood levels of amyloid β
protein in patients with AD and age-matched nondemented controls.
Due to the heterogeneity and complex nature of the disease,
it is highly unlikely that that a single marker specific for
AD will be found.
[Back to top]
Computerized Methods in the Assessment and Prediction
of Dementia
Amos D. Korczyn and Vered Aharonson
Computerized administration of neuropsychological tests can
be an objective, sensitive and efficient way to screen for
and monitor cognitive changes in the elderly. However, current
computer software still suffers from limitations in both the
administration of those tests and the interpretation of their
results, which might severely hamper their usability. In this
paper qualitative aspects of current methods and their use
in the prediction of dementia are discussed, guidelines for
correct design and usage of computerized methods are suggested
and a solution that overcomes several of the methodological
limitations is proposed.
[Back to top]
Practical Issues in Stem Cell Therapy for Alzheimer’s
Disease
K. Sugaya, Y.D. Kwak, O. Ohmitsu, A. Marutle, N.H. Greig
and E. Choumrina
We have demonstrated that aged animals show significant improvements
in cognitive function and neurogenesis after brain transplantation
of human neural stem cells or of human adult mesenchymal stem
cells that have been dedif-ferentiated by transfection of
the embryonic stem cell gene. We have also demonstrated that
peripheral administration of a pyrimidine derivative increased
cognition, endogenous brain stem cell proliferation and neurogenesis.
These results indi-cate a bright future for stem cell therapies
in Alzheimer’s disease (AD). Before this is realized,
however, we need to con-sider the affect of AD pathology on
stem cell biology to establish an effective stem cell therapy
for this disease. Although amyloid-β
(Aβ)
deposition is a hallmark of AD, an absence of a phenotype
in the β-amyloid
precursor protein (APP) knockout mouse, might lead one to
underestimate the potential physiological functions of APP
and suggest that it is unes-sential or can be compensated
for. We have found, however, that APP is needed for differentiation
of neural stem cells (NSCs) in vitro, and that NSCs transplanted
into a APP-knockout mouse did not migrate or differentiate
- indicating that APP plays an important role in differentiation
or migration process of NSCs in the brain. Then again, treatment
with high a concentration of APP or its over-expression increased
glial differentiation of NSCs. Human NSCs transplanted into
APP-transgenic mouse brain exhibited less neurogenesis and
active gliosis around the plaque like formations. Treatment
of such animals with the compound, (+)-phenserine, that is
known to reduce APP protein levels, increased neurogenesis
and suppressed gliosis. These results suggest APP levels can
regulate NSC biology in the adult brain, that altered APP
metabolism in Down syndrome or AD may have implications for
the pathophysiology of these diseases, and that a combination
of stem cell therapy and regulation of APP levels could provide
a treatment strategy for these disorders.
[Back to top]
TNF-α
Inhibition as a Treatment Strategy for Neurodegenerative Disorders:
New Drug Candidates and Targets
David Tweedie, Kumar Sambamurti and Nigel H. Greig
As the average ages of North Americans and Europeans continue
to rise; similarly the incidence of “old age”
associated illnesses likewise increases. Most notably among
these ailments are conditions linked to dementia-related neu-rodegenerative
disorders, such as Alzheimer’s disease (AD), Parkinson’s
disease (PD) and stroke. While in the early stages, these
conditions are associated with cellular dysfunction in distinctly
different brain regions, thus affecting different neuronal
cell types; it is most likely that the final stages share
similar cellular and molecular processes leading to neuronal
death and ultimately overt clinical symptoms. In this regard,
different environmental and genetic triggers ranging from
head trauma to protein mutations and toxicological exposure
may instigate a cascade of intracellular events that ul-timately
lead to neuronal death. One strong candidate trigger protein,
and thus a potential target for therapeutic manipulation is
the potent pro-inflammatory / pro-apoptotic cytokine, tumor
necrosis factor-α
(TNF-α).
TNF-α
is secreted by the brain resident marcophage (the microglial
cell) in response to various stimuli. It has been demonstrated
to play a major role in central nervous system (CNS) neuroinflammation-mediated
cell death in AD, PD and amyotrophic lateral sclerosis (ALS)
as well as several other CNS complications.
Recently, agents that modulate the levels of circulating peripheral
TNF-α
protein have been shown to be worthwhile therapeutic agents
with the use of Enbrel (Etanercept) and Remicade (Infliximab),
both of which display beneficial properties against rheumatoid
arthritis and other peripheral inflammatory diseases. Unfortunately,
these agents are largely unable to penetrate the blood-brain
barrier, which severely limits their use in the setting of
neuroinflammation in the CNS. However, thalidomide, a small
molecule drug, can inhibit TNF-α
protein synthesis and, unlike larger molecules, is readily
capable of crossing the blood-brain barrier. Thus thalidomide
and its analogs are excellent candidate agents for use in
determining the potential value of anti-TNF-α
therapies in a variety of diseases underpinned by inflammation
within the nervous system. Consequently, we have chosen to
discuss the relevance of unregulated TNF-α
expression in illnesses of the CNS and, to an extent, the
peripheral nervous system. Additionally, we consider the utilization
of thalidomide-derived agents as anti-TNF-α
therapeutics in the setting of neuroinflammation.
[Back to top]
East Meets West in the Search for Alzheimer's Therapeutics
- Novel Dimeric Inhibitors from Tacrine and Huperzine A
W.M. Li, K.K.W. Kan, P.R. Carlier, Y.P. Pang and Y.F.
Han
Alzheimer’s disease (AD) is linked to cholinergic deficiency
and the overactivation of glutamate receptors. The acetylcholinesterase
(AChE) inhibition treatment approach has produced the most
encouraging results in clinical practice, and memantine, a
moderate antagonist of N-methyl-D-aspartate (NMDA) receptors,
has been approved for treating AD. However, AChE inhibitors
have limited success as they only improve memory in mild dementia
but cannot stop the process of neurodegeneration; while memantine
possesses neuroprotective effects only with a little ability
in memory enhancement. There has been a major rush among neuroscience
research institutions and pharmaceutical firms worldwide to
search for safer and more effective therapeutic agents for
AD. The novel dimers, derived from tacrine and the fragment
of huperzine A (HA’), have been demonstrated to be potent
and selective reversible inhibitors of AChE. Bis(7)-tacrine,
bis(12)-hupyridone (E12E) and HA’(10)-tacrine, are representatives
of three series of novel dimers. According to the pre-clinical
studies, these compounds have been shown to have low toxicity
and high efficacy for improving cognitive deficits in several
animal models. More interestingly, bis(7)-tacrine, similar
to memantine, prevents glutamate-induced neurotoxicity by
moderately blocking glutamate receptor NMDA subtype. Furthermore,
bis(7)-tacrine, as well as E12E, possesses multiple neuroprotective
effects in vitro and in vivo. Taking together,
these dimeric AChE inhibitors, especially bis(7)-tacrine,
E12E and HA’(10)-tacrine, may provide beneficial effects
in AD and other neurodegenerative diseases.
[Back to top]
N-Phenylamine Derivatives as Aggregation Inhibitors
in Cell Models of Tauopathy
M. Pickhardt, J. Biernat, I. Khlistunova, Y.-P. Wang,
Z. Gazova, E.-M. Mandelkow and E. Mandelkow
Cell models of tauopathy were generated in order to study
mechanisms of neurodegeneration involving abnormal changes
of tau. They are based on neuroblastoma cell lines (N2a) that
inducibly express different forms of the repeat domain of
tau (tauRD), e.g. the 4-repeat
domain of tau with the wild-type sequence, the repeat domain
with the ΔK280
mutation ("pro-aggregation mutant"), or the repeat
domain with ΔK280
and two proline point mutations ("anti-aggregation mutant").
The data indicate that the aggregation of tauRD is toxic,
and that aggregation and toxicity can be prevented by low
molecular weight compounds, notably compounds based on the
N-phenylamine core. Thus the cell models are suitable for
developing aggregation inhibitor drugs.
[Back to top]
Neurorescue Activity, APP Regulation and Amyloid-β
Peptide Reduction by Novel Multi-Functional Brain Permeable
Iron- Chelating- Antioxidants, M-30 and Green Tea Polyphenol,
EGCG
Yael Avramovich-Tirosh, Lydia Reznichenko, Tamar Amit,
Hailin Zheng, Mati Fridkin, Orly Weinreb, Silvia Mandel and
Moussa B.H. Youdim
Accumulation of iron at sites where neurons degenerate in
Parkinson’s disease (PD) and Alzheimer’s disease
(AD) is thought to have a major role in oxidative stress induced
process of neurodegeneration. The novel non-toxic lipophilic
brain- permeable iron chelators, VK-28 (5- [4- (2- hydroxyethyl)
piperazine- 1- ylmethyl]- quinoline- 8- ol) and its multi-functional
derivative, M-30 (5-[N-methyl-N-propargylaminomethyl]-8-hydroxyquinoline),
as well as the main polyphenol constituent of green tea (-)-epigallocatechin-3-gallate
(EGCG), which possesses iron metal chelating, radical scavenging
and neuroprotective properties, offer potential therapeutic
benefits for these diseases. M-30 and EGCG decreased apoptosis
of human SH-SY5Y neuroblastoma cells in a neurorescue, serum
deprivation model, via multiple protection mechanisms including:
reduction of the pro-apoptotic proteins, Bad and Bax, reduction
of apoptosis-associated Ser139 phosphorylated H2A.X and inhibition
of the cleavage and activation of caspase-3. M-30 and EGCG
also promoted morphological changes, resulting in axonal growth-associated
protein-43 (GAP-43) implicating neuronal differentiation.
Both compounds significantly reduced the levels of cellular
holo-amyloid precursor protein (APP) in SH-SY5Y cells. The
ability of theses novel iron chelators and EGCG to regulate
APP are in line with the presence of an iron-responsive element
(IRE) in the 5’-untranslated region (5’UTR) of
APP. Also, EGCG reduced the levels of toxic amyloid-beta peptides
in CHO cells over-expressing the APP “Swedish”
mutation. The diverse molecular mechanisms and cell signaling
path-ways participating in the neuroprotective/neurorescue
and APP regulation/processing actions of M-30 and EGCG, make
these multifunctional compounds potential neuroprotective
drugs for the treatment of neurodegenerative diseases, such
as PD, AD, Huntington’s disease and amyotrophic lateral
sclerosis.
[Back to top]
Alpha-Secretase As a Therapeutic Target
Falk Fahrenholz
In the non-amyloidogenic pathway the α-secretase
cleaves the amyloid precursor protein (APP) within the sequence
of Aβ-peptides
and precludes their formation. In addition, α-secretase
cleavage releases an N-terminal extracellular domain with
neurotrophic and neuroprotective properties. The disintegrin
metalloproteinase ADAM10 has been shown to act as α-secretase
in vivo, to prevent amyloid plaque formation and
hippocampal defects in an Alzheimer disease mouse model. An
increase in α-secretase
activity therefore is an attractive strategy for treatment
of AD and may be achieved by modulating selective signalling
pathways. Functional characterization of the human ADAM10
promoter showed that it contains several binding elements
for transcription factors which are regulated by extracellular
ligands. Retinoic acid (RA) was identified as an inducer of
human ADAM10 promoter activity. In human neuroblastoma cell
lines RA treatment upregulated the expression of both the
α-secretase
ADAM10 and its substrates APP and the related APP-like-protein
2 (APLP2), and led to an enhanced secretion of their extracellular
domains. Furthermore, G protein-coupled receptors (GPCRs)
localized in brain areas affected by AD were investigated.
Activation of the PAC1 receptor by the neuropeptide PACAP
was identified as an approach for upregulation of the α-secretase
pathway.
[Back to top]
Memapsin 2 (Beta-Secretase) Inhibitor Drug, between
Fantasy and Reality
Arun K. Ghosh, Geoffrey Bilcer, Lin Hong, Gerald Koelsch
and Jordan Tang
A major strategy for the development of a disease-modifying
therapy against Alzheimer’s disease is pharmacological
intervention designed to reduce levels of β-amyloid
in the brain. Among various ways of reducing β-amyloid
production, the inhibition of β-secretase
(memapsin 2, BACE) is particularly attractive. Not only does
β-secretase
initiates the amyloid cascade, it also is an aspartic protease,
a class of proteases for which successful inhibitor drugs
have been developed to treat AIDS patients. Extensive efforts
in research and development of a β-secretase
inhibitor drug have taken place in many laboratories during
the past few years. However, no drug candidate is currently
in clinical trials. In spite of the lack of obvious success,
much progress has been made to incorporate the drug-like properties
in the evolution of better inhibitors. The inhibitors from
more recent generations are indeed similar in characteristics
to other protease inhibitor drugs. This progress permits optimism
that development of clinical candidates of β-secretase
inhibitor drugs is a realistic goal.
[Back to top]
The γ/ε-Secretase-Derived
APP Intracellular Domain Fragments Regulate p53
Frédéric Checler, Claire Sunyach, Raphaelle
Pardossi-Piquard, Jean Sévalle, Bruno Vincent, Toshitaka
Kawarai, Nadège Girardot, Peter St George-Hyslop and
Cristine Alves da Costa
Amyloid β-peptide
(Aβ),
which plays a central role in Alzheimer Disease, is generated
by presenilin-dependent and presenilin-independent γ-secretase
cleavages of β-amyloid
precursor protein (βAPP).
We report that the presenilins (PS1 and PS2) also regulate
p53-associated cell death? Thus, we established that PS deficiency,
catalytically inactive PS mutants, γ-secretase
inhibitors and βAPP
or APLP2 depletion reduced the expression and activity of
p53, and lowered the transactivation of its promoter and mRNA
levels. p53 expression was also reduced in the brains or βAPP-deficient
mice or in brains where both PS had been invalidated by double
conditional knock out. AICDC59 and AICDC50, the γ-
and ε-secretase-derived
C-terminal fragments of βAPP,
respectively, trigger the activation of caspase-3, p53-dependent
cell death, and increase p53 activity and mRNA. Finally, HEK293
cells expressing PS1 harboring familial AD (FAD) mutations
or FAD-affected brains, all display enhanced p53 activity
and p53 expression. Our studies demonstrate that AICDs control
p53 at a transcriptional level, in vitro and in
vivo and unravel a still unknown function for presenilins.
[Back to top]
Novel Aβ
Immunogens: Is Shorter Better?
Cynthia A. Lemere, Marcel Maier, Ying Peng, Liying Jiang
and Timothy J. Seabrook
Active and passive Aβ
immunotherapy in Alzheimer’s disease (AD)-like mouse
models lowers cerebral amyloid-β
protein (Aβ)
levels, especially if given early in the disease process,
and improves cognitive deficits. In 2002, a Phase IIa clinical
trial was halted due to meningoencephalitis in ~6% of the
AD patients. It is hypothesized that the immunogen, full-length
Aβ1-42,
may have led to an autoimmune response. Currently, we are
developing novel Aβ
peptide immunogens for active immunization in amyloid precursor
protein transgenic mice (APP Tg) to target Aβ
B cell epitopes (within Aβ1-15)
and avoid Aβ-specific
T cell epitopes (Aβ16-42)
so as to generate a safe and effective AD vaccine. Intranasal
immunization with dendrimeric Aβ1-15
(16 copies of Aβ1-15
on a lysine core) or a tandem repeat of Aβ1-15
joined by 2 lysines and conjugated to an RGD motif with a
mutated form of an E. coli-derived adjuvant generated robust
Aβ
titers in both wildtype and APP Tg mice. The Aβ
antibodies recognized a B cell epitope within Aβ1-7,
were mostly T-helper 2 associated immunoglobulin isotypes,
bound human AD and APP Tg plaques, and detected Aβ
oligomers. Splenic T cells reacted to the immunogens but not
full-length Aβ.
Six months of intranasal immunization (from 6-to-12 months
of age) of J20 mice with each immunogen lowered insoluble
Aβ42
by 50%, reduced plaque burden and gliosis, and increased Aβ
in plasma. Interestingly, Aβ
antibody generation was influenced by route of immunization.
Transcutaneous immunization with dβ1-15,
but not full-length Abeta, led to high Aβ
titers. In summary, our short Aβ
immunogens induced robust titers of predominantly Th2 antibodies
that were able to clear cerebral Aβ
in the absence of Aβ-specific
T cell reactivity, indicating the potential for a safer vaccine.
We remain optimistic about the potential of such a vaccine
for prevention and treatment of AD.
[Back to top]
A Novel Immunotherapy for Alzheimer’s Disease:
Antibodies against the β-Secretase
Cleavage Site of APP
Michal Arbel and Beka Solomon
One of the main neuropathological lesions observed at brain
autopsy of Alzheimer’s disease (AD) patients are the
extracellular senile plaques mainly composed of amyloid-β
(Aβ)
peptides. Aβ
is generated by proteolytic processing of amyloid precursor
protein (APP) via β
and γ-secretases.
The β-secretase
APP cleaving enzyme 1 (BACE1) has become a target of intense
research aimed at blocking the enzyme activity. Recent studies
showed that BACE1 is involved in processing other non-APP
substrates, and that other proteases are involved in APP processing.
We have recently established a novel approach to inhibit Aβ
production via antibodies against the β-secretase
cleavage site of APP. These antibodies bind wild type and
Swedish mutated APP expressed in transgenic mice brain tissues.
The isolated antibodies do not bind any form of Aβ
peptides. Antibody up-take experiments, using Chinese hamster
ovary cells expressing wild-type APP, suggest that antibody
internalization and trafficking are mediated via the endocytic
pathway. Administration of antibodies to the cells growing
media resulted in a considerable decrease in intracellular
Aβ
levels, as well as in the levels of the corre-sponding C-terminal
fragment (C99). The relevance of intra-neuronal accumulation
of mainly Aβ42
as an early event in AD pathogenesis suggests that this approach
may be applicable as a novel therapeutic strategy in AD treatment.
[Back to top]
Is alpha-Synuclein Pathology a Target for Treatment
of Neurodegenerative Disorders?
M. Windisch, H.J. Wolf, B. Hutter-Paier, A. Hofmeister
and R. Wronski
Alpha-synuclein is the main constituent of intra-neuronal
Lewy bodies, which are characteristic of Parkinson’s
disease, but aggregates are also found as axonal inclusions.
Alpha-synuclein pathology is found together with beta-amyloid
plaques and neurofibrillary tangles in Alzheimer’s disease
and other neurodegenerative disorders. In spite of the fact
that the biological function of this synaptic protein is not
known so far, there is an increasing body of evidence indicating
an interaction with amyloid peptides, but also with tau-hyperphosphorylation.
A high proportion of alpha-synuclein purified from Lewy bodies
is phosphorylated on Ser129. There are still different opinions
about the toxicity of the alpha-synuclein aggregates. Alpha-synuclein
seems to influence different intracellular signaling pathways
which are in direct relation to defense mechanisms against
reactive oxygen species or apoptosis. It is obvious that overproduction
of alpha-synuclein, but also different mutations, are inducing
the formation of aggregates. Because of the possible link
to neurodegeneration, different attempts have been made to
counteract alpha-synuclein aggregation. An interesting approach
is utilizing beta-synuclein, a biological factor, with an
aminoacid sequence closely resembling that of alpha-synuclein.
Proof of concept studies indicated that overexpression of
beta-synuclein is able to counteract alpha-synuclein aggregation
in a transgenic animal model, while also ameliorating functional
deficits. As an alternative approach, the use of low molecular
beta-synuclein N-terminal peptide derivatives has been considered.
Several of these structures displayed clear neuroprotective
activities in tissue culture models of neurodegeneration,
including beta-amyloid toxicity. Therefore it has been speculated
that these compounds might have a broad therapeutic efficacy
in different neurodegenerative disorders. A proof of concept
study in hAPP-transgenic animals resulted in a highly significant
decrease in beta-amyloid plaque load, an increase in soluble
beta-amyloid peptides and a decrease in insoluble forms. There
was also significant improvement of cognitive deficits in
this APP transgenic mouse model following intranasal but also
peripheral treatment with three of these compounds. From this
study it is concluded that the observed effects of the peptides
derived from beta-synuclein N-terminus are depending on both,
a direct interaction with aggregation of proteins, but also
with stimulation of anti-apoptotic and anti-oxidative intracellular
signaling pathways.
[Back to top]
Lessons from Darwin: 21st Century Designs for Clinical
Trials
Robert E. Becker
What are the resources needed by clinical pharmacology to
test drugs in ways that model how the practitioner achieves
optimal effectiveness and safety with each patient? I describe
the applications of test-retest standard error of measurement,
clinical decision rules, means or other statistical summaries
of observations, clinical trial designs that use each patient
as her own control, and methods to control observer and site
variance as steps for developing a CT tested model for optimal
clinical uses of an Alzheimer’s drug by a practitioner.
Many investigators and clinicians have been concerned with
clinical judgments being scientifically uncontrolled and unsystematic.
The methods I describe demonstrate how clinical trials can
be used to overcome these limitations in current patient care.
“Darwin showed that one simply could not understand
evolution as long as one accepted essentialism. Species and
populations are not types, they are not essentialistically
defined classes, but rather are biopopulations composed of
genetically unique individuals” E. Mayr [1].
[Back to top]
Drug Trials in Dementia: Challenging Ethical Dilemmas
Amos D. Korczyn
Advances in the treatment of demented individuals is critically
dependent upon experimental administration of new drugs to
such people, who, by definition, frequently cannot provide
informed consent. Ethical problems associated with studies
on demented individuals are therefore of great importance.
While there is some similarity to other groups (children,
psychotic individuals and patients in coma) there also exist
several differences.
Obtaining an informed consent from a dementing individual
is always problematic. Advance directives are helpful to caregivers
and patients should be encouraged, at early stages of the
disease, to provide them.
Participation in drug studies carries inherent benefits to
patients, but at the same time exposes them to risks and discomforts
which should be monitored and reviewed more intensively than
in studies on cognitively intact individuals. The vulnerability
of demented people and their dependence requires special attention
by the institutional review board (IRB), unique items to be
included in the study protocols and consent forms, etc.
Representatives of patients’ advocacy groups can make
important contributions to the IRB, to serve the best interests
of the patient and prevent exploitation by the industry as
well as by researchers, and honoring the autonomy of the patients.
It would be helpful and justified to enable subjects to continue
in the study in an open-label design in this situation, once
they sign a suitable informed consent. A no-fault insurance
could be provided to the patient in this situation.
[Back to top]
Alzhemed: A Potential Treatment for Alzheimer's Disease
Paul S. Aisen, Serge Gauthier, Bruno Vellas, Richard Briand,
Daniel Saumier, Julie Laurin and Denis Garceau
As a potential disease-modifying treatment for AD, Alzhemed
(tramiprosate) is a compound that binds to soluble amyloid-beta
peptide (Aβ)
and inhibits the formation of neurotoxic aggregates that lead
to amyloid plaque deposition in the brain. The safety, tolerability,
and pharmacodynamic effects of Alzhemed were assessed in a
double-blind study in which 58 individuals with mild-to-moderate
AD (MMSE 13-25) were randomized to receive placebo or Alzhemed
50, 100 or 150 mg BID for 3 months. At the end of the double-blind
phase, 42 of these subjects entered a 36-month open-label
(OL) phase in which they received Alzhemed 150 mg BID. Assessments
included plasma and cerebrospinal fluid (CSF) Alzhemed concentrations,
CSF levels of Aβ,
as well as cognitive (Alzheimer’s Disease Assessment
Scale-cognitive sub-scale, Mini-Mental State Examination)
and clinical performance (Clinical Dementia Rating scale,
Sum-of-Boxes) measures. Alzhemed was safe and well tolerated,
crossed the blood-brain barrier, and dose-dependently reduced
CSF Aβ42
levels after 3 months of treatment. Mild AD subjects (MMSE
19-25 at entry) displayed greater reduction of CSF Aβ42
levels than moderate AD participants (MMSE 13-18 at entry).
There was no effect of Alzhemed on the cognitive or clinical
measures after 3 months of treatment. The OL follow-up suggested
a stabilization of cognitive function especially in mild AD
subjects over the 36-month study period. Alzhemed thus appears
to be well tolerated with long-term exposure and reduces CSF
Aβ42
levels in mild-to-moderate AD subjects. These findings will
be discussed in the context of two large-scale randomized,
double-blind, placebo-controlled Phase III clinical trials
that are currently being conducted to test the long-term safety
and efficacy of Alzhemed.
[Back to top]
Pharmacogenetic Aspects of Therapy with Cholinesterase
Inhibitors: The Role of CYP2D6 in Alzheimer’s Disease
Pharmacogenetics
Ramón Cacabelos, Ruth Llovo, Carmen Fraile and
Lucía Fernández-Novoa
Recent studies demonstrate that the therapeutic response in
Alzheimer’s disease (AD) is genotype-specific. More
than 200 genes are potentially associated with AD pathogenesis
and neurodegeneration, and approximately 1,400 genes distributed
across the human genome account for 20 to 95% of variability
in drug disposition and pharmacodynamics. Cytochrome P450
enzymes encoded by genes of the CYP superfamily, such as CYP1A1
(15q22-q24), CYP2A6 (19q13.2), CYP2C8 (10q24), CYP2C9 (10q24),
CYP2C19 (10q24.1-q24.3), CYP2D6 (22q13.1), CYP2E1 (10q24.3-qter),
and CYP3A5 (7q22.1), acting as terminal oxidases in multicomponent
electron transfer chains which are called P450-containing
monooxygenase systems, metabolize more than 90% of drugs.
Some of the enzymatic products of the CYP gene superfamily
can share substrates, inhibitors and inducers whereas others
are quite specific for their substrates and interacting drugs.
Some cholinesterase inhibitors (tacrine, donepezil, galantamine)
are metabolized via CYP-related enzymes, especially CYP2D6,
CYP3A4, and CYP1A2. The distribution of CYP2D6 genotypes in
the Spanish population is the following: (a) Extensive Metabolizers
(EM)(51.61%): *1/*1, 47.10%; and *1/*10, 4.52%; (b) Intermediate
Metaboliz-ers (IM)(32.26%): *1/*3, 1.95%; *1/*4, 17.42%; *1/*5,
3.87%; *1/*6, 2.58%; *1/*7, 0.75%; *10/*10, 1.30%; *4/*10,
3.23%; *6/*10, 0.65%; and *7/*10, 0.65%; (b) Poor Metabolizers
(PM)(9.03%): *4/*4, 8.37%; and *5/*5, 0.65%; and (c) Ultrarapid
Metabolizers (UM)(7.10%): *1xN/*1, 4.52%; *1xN/*4, 1.95%;
and CYP2D6 gene duplications, 0.65%. PMs and UMs also accumulate
genotypes of risk associated with APOE-, PS-, ACE-, and PRNP-related
genes. Approximately, 15% of the AD population may exhibit
an abnormal metabolism of cholinesterase inhibitors; about
50% of this population cluster would show an ultrarapid metabolism,
requiring higher doses of cholinesterase inhibitors to reach
a therapeutic threshold, whereas the other 50% of the cluster
would exhibit a poor metabolism, displaying potential adverse
events at low doses. In AD patients treated with a multifactorial
therapy, including cholinesterase inhibitors (e.g., donepezil),
the best responders are the CYP2D6-related EMs and IMs, and
the worst responders are PMs and UMs. In addition, the presence
of the APOE-4 allele in genetic clusters integrating CYP2D6
and APOE genotypes contributes to deteriorate the therapeutic
outcome. From these data, it can be postulated that pharmacogenetic
and pharmacogenomic factors are responsible for 75-85% of
the therapeutic response in AD patients treated with conventional
drugs.
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