Alzheimer's centennial legacy: prospects for rational therapeutic

doi:10.1093/brain/awl251 Brain (2006), 129, 2823–2839

REV IEW ARTICLE

Alzheimer’s centennial legacy: prospects forrational therapeutic intervention targetingthe Ab amyloid pathway

Colin L. Masters1 and Konrad Beyreuther2

1Department of Pathology, The University of Melbourne and the Mental Health Research Institute of Victoria,Parkville, Victoria, Australia and 2Centre for Molecular Biology, The University of Heidelberg, Heidelberg, Germany

Correspondence to: Colin L. Masters, Department of Pathology, The University of Melbourne, 3010, Victoria, AustraliaE-mail: [email protected]

It is now 100 years since the nosological definition of Alzheimer’s disease emerged. In the first 80 years, verylittle progress wasmade in understanding themechanisms that caused the brain to degenerate in a remarkablyspecific fashion (amyloid accumulation with neurofibrillary changes). Over the past 20 years, there has been anexplosion of knowledge which continues today at an exponential rate. The molecular pathways underlying thesynaptic dysfunction in Alzheimer’s disease have delivered many validated therapeutic and diagnostic targets.A variety of therapeutic strategies aimed at disease modification are now in clinical development.

Keywords: Ab amyloid pathway; Alzheimer’s disease; amyloid beta precursor protein

Abbreviations: Ab ¼ amyloid b peptide; AChE ¼ acetylcholinesterase; AChE-I ¼ AChE inhibitors;APP ¼ amyloid beta (A4) precursor protein; MPAC ¼ metal–protein attenuating compounds;NMDA ¼ N-methyl-D-aspartate

Received July 3, 2006. Revised August 15, 2006. Accepted August 16, 2006. Advance Access publication September 29, 2006.

IntroductionAlthough Alzheimer is now credited with the elucidation

of a distinct disease entity, the record clearly shows

that others (including Bonfiglio, Fischer, Kraepelin and

Perusini) contributed substantially to the original nosolo-

gical demarcation of ‘pre-senile dementia’. Nevertheless,

we recognize today Alzheimer’s case description exactly

100 years ago as the first step in a circuitous pathway leading

to our current theories of pathogenesis based around the

molecular and genetic discoveries of the past 20 years. As

a tribute to the early pioneers who painstakingly described

the pathognomonic changes of Alzheimer’s disease. It is

worthwhile to reconsider and appreciate the images gener-

ated of the plaques and tangles with which they worked

(Fig. 1). It has long been appreciated that the plaques,

tangles, neuritic change and reactive gliosis hold the key to

understanding this disease process. In the 80 years following

Alzheimer’s descriptions, little progress was made in

unravelling the molecular and genetic basis of the disease.

Fortunately, major advances have occurred in the last

20 years.

BackgroundIn this review, we summarize our current thinking about the

biogenesis of the amyloid b peptide (Ab) from the amyloid

beta (A4) precursor protein (APP), and how this pathway

presents therapeutic and diagnostic targets that are now in

clinical development. The discoveries that have underpinned

our current theories are summarized in Table 1, and reflect

our particular interests—other researchers may see things

very differently. The pathways leading to the discovery and

characterization of the Ab amyloid peptide have been set

out in detail recently (Masters and Beyreuther, 2006). We

commenced our project to isolate and characterize the

amyloid plaques in the human brain in the late 1970s

(Masters et al., 1981; Merz et al., 1983). After the initial

sequencing of the N-terminus of Ab derived from cerebral

leptomeninges (Glenner and Wong, 1984a, b), we were able

to correct and extend the sequence of plaque-derived

amyloid, and determine the likely C-terminus (Masters et al.,

1985a,b; Kang et al., 1987). Through the discovery of the

N- and C-termini, it became apparent that the Ab peptide

was derived by proteolytic action on the APP (Kang et al.,

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1987), and that inhibition of the biogenesis of Ab could be

achieved by targeting these proteolytic events. The current

state of clinical development of this approach is discussed

below.

Very early in our research collaboration (Masters et al.,

1985b), we recognized that charge effects would have a

major contribution to aggregation of Ab, and that

protonation of the two histidine residues at position 13

and 14 could affect dimerization of Ab (which at the time

we referred to as A8) into a stable subunit, which could in

turn form the building blocks of oligomers of Ab. These

oligomers have now become the focus of an intense research

effort (Table 2), as they must represent an intermediate

species that is capable of folding into a fibril-generating

pathway leading to amorphous or compact amyloid plaques

(Davies et al., 1988). Our analysis of the amyloid plaque

cores also revealed non-proteinaceous components, includ-

ing metal ions. This was at a time when the aluminium

theory of Alzheimer’s disease was still quite strong, and we

speculated on the role of aluminium silicates in the amyloid

plaques. Subsequent work has turned our attention to other

metal ions (zinc and copper, in particular).

Independent of our work on amyloid plaques, a separate

line of enquiry revealed that the Alzheimer’s disease brain

was under oxidative stress (Martins et al., 1986). Although we

did not make the connection at the time, it now seems

clear that the toxic oligomers of Ab may be the principal

source of this oxidative damage. The first clue for this came

from the studies of Dyrks et al. (1992a,b, 1993), which

showed that aggregation/oligomerization of Ab was

mediated by metal-catalysed oxidation through the histidine,

tyrosine and methionine residues in Ab. Oxidative modifica-

tion of these residues also led to cross-link formation, and the

aggregation/oligomerization of Ab was reversible with anti-

oxidants. Around the same time, we identified metal (Zn++,

Cu++) binding sites on the ectodomain of APP (Bush et al.,

1993; Hesse et al., 1994; Multhaup et al., 1994a,b, 1995) and

in the Ab region of APP (Bush et al., 1994). Redox-active

metal ions, such as Cu++, were found to be involved in redox

chemistry (Cu++ reduced to Cu+) when in contact with

APP and Ab (Multhaup et al., 1996), and capable of

generating H2O2 and other reactive oxygen species (ROS)

(Huang et al., 1994; Multhaup et al., 1998).

Why is there now so much interest in the APP/Ab

pathway? In 2005 alone, >780 papers appeared on APP/Ab,

many of which deal with the pre-clinical and clinical

therapeutic strategies directed at the APP/Ab pathway

(Fig. 2). The theory that underlies this pathway as the

principal and proximal causal mechanism in Alzheimer’s

disease is pinned to two critical series of observations: first,

mutations in the gene encoding APP [and the presenilin

(PS) genes as components of the g-secretase machinery] are

causally linked to early onset familial Alzheimer’s disease

(Levy et al., 1990; van Broeckhoven et al., 1990; Chartier-

Harlin et al., 1991; Sherrington et al., 1995); second, gen-

etically engineered mice with these mutations (Quon et al.,

a

A

B

c

b

a

b

Fig. 1 (A) Figure 42 from Spielmeyer (1922). Silver impregnationsshowing the neurofibrillary changes in the cytoplasm of neurons.(B) Figure 201 from Spielmeyer (1922). Two senile plaques, usingBielschowsky silver impregnations, showing the central amyloidcore and associated glial cell reactions.

2824 Brain (2006), 129, 2823–2839 C. L. Masters and K. Beyreuther

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1991; Games et al., 1995) recapitulate the human disease in

that plaques, perivascular amyloid, neurofibrillary changes

and behavioural impairments are induced. More recently,

a very tight association between the mean age at onset of

pedigrees with PS mutation-related familial Alzheimer’s

disease and the ratio of secreted Ab40–Ab42 has emerged

(Duering et al., 2005; Kumar-Singh et al., 2006). This,

together with the development of a robust Ab-neuroimaging

ligand (a thioflovin T analogue), which as a biomarker

clearly differentiates Alzheimer’s disease and mild cognitive

impairment from normal controls and other neurological

diseases (Klunk et al., 2004; Mathis et al., 2005; Fagan et al.,

2006), adds much more strength to the Ab theory (Fig. 3).

But the single most important challenge to test the theory

remains as the demonstration that a drug targeting the

APP/Ab pathway actually modifies the natural history of the

disease. To this end, the criteria set out by Cummings

(2006), and listed in Table 3, have clarified the standards

to be met when we come to assessing this test of the Ab

theory of Alzheimer’s disease. The first criterion (a plausible

mechanism of action in a validated model) has been

achieved by many of the therapeutic strategies reviewed

below. But no drug has yet met any of the other four criteria,

although we remain optimistic that the current pace of

activity will deliver a result in the not too distant future.

Upstream events in the APP/Ab pathwayThe targets derived from the APP/Ab pathway outlined in

Fig. 2 are listed in more detail in Table 4. While it is not a

comprehensive or exhaustive listing, it does present a novel

and logical way of classifying the wide range of current

research activity being undertaken in this area.

Age and environmental factorsOf all the external variables that determine risk of getting

Alzheimer’s disease, age and the environment stand out

Table 1 Background leading to our current Ab theory of Alzheimer’s disease

Amyloid plaques from frozen Alzheimer’s disease brain can be isolated and characterized (Merz et al., 1983); the amyloid isolated from theAlzheimer’s disease leptomeninges is a small peptide (the b-protein) (Glenner and Wong 1984a, b)

Amyloid from the plaques (Ab) is the same peptide of �40 residues (Masters et al., 1985b) and is proteolytically derived from a neuronalprecursor, APP (Kang et al., 1987). These proteases (g- and b-secretases) have become prime therapeutic targets

Protonation of histidines (residues 6, 13, 14) may affect aggregation of Ab (Masters et al., 1985b)

Stable dimers of Ab (A8) may represent the soluble form of Ab; oligomers [tetramers (A16) or hexadecamers (A64)] may form the basic amyloidsubunit (Masters et al., 1985b)

Non-proteinaceous components of plaques include metals and other ions (silicon, aluminium, calcium) (Masters et al., 1985b)

The Alzheimer’s disease brain is under oxidative stress (Martins et al., 1986).

Amorphous plaques may represent earlier aggregates of more soluble Ab species (Davies et al., 1988; Rumble et al., 1989)

Ab is confirmed in its predicted transmembrane orientation (Dyrks et al., 1988; Weidemann et al., 1989), and shedding of APP into biologicalfluids occurs (Weidemann et al., 1989; Rumble et al., 1989)

Identification of pathogenic mutations in APP gene conclusively demonstrate that the primary pathway of Alzheimer’s disease involves APP/Ab(Levy et al., 1990; van Broeckhoven et al., 1990; Chartier-Harlin et al., 1991)

Ab in solution has a b-turn (Sorimachi et al., 1990) and has a high propensity for aggregation driven by hydrophobic residues (Hilbich et al., 1991,1992)

Soluble Ab may be produced and released by cultured cells during normal metabolism (Haas et al., 1992; Shoji et al., 1992)

Ab in membrane lipid does not aggregate or form oligomers (Dyrks et al., 1992b)

Aggregation of Ab is mediated bymetal-catalysed oxidation (Fe++/H2O2); requires oxidative modifications of histidine, tyrosine andmethionine,and protein cross-linkage; and is reversed with anti-oxidants (Dyrks et al., 1992a,b, 1993)

APP axonal trafficking has a major effect on APP processing, and can be modulated by factors such as cholesterol (Koo et al., 1990; Tiernari et al.,1996)

APP and Ab bind Zn++, Cu++ metal ions (Bush et al., 1993, 1994; Hesse et al., 1994; Multhaup et al., 1994, 1996). Redox-active metals lead toredox chemistry (Multhaup et al., 1996), Ab aggregation (dimer, oligomer) and ROS generation (Huang et al., 1999; Opazo et al., 2002)

Ab may occur in intracellular compartments (Fuller et al., 1995; Hartmann et al., 1997; Tienari et al., 1997)

Cells with APP knockout phenotype are relatively resistant to Ab toxicity (White et al., 1998)

Aggregated oligomerized Ab can be solubilized with small molecular weight compounds that have relatively low affinities for metal ions (copper,zinc) (Cherny et al., 1999). These MPAC have the capacity to ameliorate the Ab burden and toxicity in transgenic Alzheimer’s disease mousemodels (Cherny et al., 2001) and possibly in humans with Alzheimer’s disease (Ritchie et al., 2003)

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as factors that demand explanations. Yet, for all their

obviousness, no reasonable explanations have been forth-

coming. While many of the biochemical events listed in

the APP/Ab pathway are known to be developmentally

regulated, very little information is yet available on what

happens under normal ageing conditions. Partial loss of

function of a critical biochemical reaction would seem to be

a good starting point for investigation, either as an upstream

or as a downstream event; or a ‘double hit’ phenomenon

could be invoked, as seen in the early development of

ideas on oncogenesis. Whichever, the incontrovertible link

between ageing and Alzheimer’s disease remains obscure in

mechanistic terms.

Similarly, the interactions between the environment and

the risk for Alzheimer’s disease have attracted many

Table 2 Ab comes in many flavours, including soluble(toxic) Ab species: synonyms

A4 soluble dimers (A8), tetramers (A16), etc., forming oligomers(Masters et al., 1985a)Amorphous aggregates (Davies et al., 1988; Huang et al., 2000)Ab-derived diffusible ligands (ADDLs) (Lambert et al., 1998)b-Balls (Laurents et al., 2005)b-Amy balls (Westlind-Danielsson et al., 2001)Globular Ab oligomer (Barghorn et al., 2005)Paranuclei (Bitan et al., 2003)Preamyloid (Huang et al., 2000)Protofibril (Harper et al., 1997; Walsh et al., 1997)Spherocylindrical miscelles (Lomakin et al., 1997; Yong et al., 2002)Spherical particles (Gorman et al., 2003)Spherical prefibrillar aggregates (Frost et al., 2003)Toxic Ab soluble species (McLean et al., 1999)

Fig. 2 Schematic outline of the upstream and downstream events that surround the central APP/Ab pathway.


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epidemiological studies. Diet and exercise remain as the two

most interesting variables. General caloric restriction has

often been associated with longevity in rodent models of

ageing, and recent studies in transgenic models (Wang et al.,

2005) suggest an effect on Ab plaque load or a-secretase

processing of APP. The effects of exercise (Adlard et al.,

2005) and environmental enrichment (Jankowsky et al.,

2005a) have also been examined in transgenic models with

encouraging results. Lazarov et al. (2005) found a change in

a downstream event, an increase in the enzymatic activity of

neprilysin (NPE), an Ab-degrading protease, in response to

environmental enrichment. These downstream events are

discussed in more detail below.

Specific dietary intakes, especially naturally occurring

anti-oxidants or metal ions remain largely under-investigated

as risk factors. As methods for diagnosis and population-

based screening improve (using plasma biomarkers or

specific ligands of Ab for neuroimaging), it will become

more feasible to analytically examine the dietary risk profiles

of discrete populations, overcoming current limitations on

sensitivity and specificity of case ascertainment. A surprising

study has already pre-empted dietary modulation of

Alzheimer’s disease through the consumption of transgenic

Ab-expressing potatoes (Youm et al., 2005)! The proposed

mechanism involves low-level immune-mediated clearance

of Ab deposits.

The effect of modulation ofneurotransmitter systemson APP processingAcetylcholinesterase (AChE) was discovered to be present in

Alzheimer’s disease amyloid plaques 40 years ago, and the

activity of choline acetyl transferase (CAT) was found to be

decreased in the Alzheimer’s disease brain 30 years ago.

From these observations the cholinergic hypothesis/theory of

the disease arose, which led to the development of AChE

inhibitors (AChE-I) as a therapeutic strategy, with apparent

success, despite the lack of any plausible explanation for the

presence of AChE in plaques and the underlying loss of

CAT. A paradox then emerged: subjects treated with AChE-I

responded with a compensatory increase in AChE levels.

This might have been expected to negate the intended effect

of the AChE-I on the availability of ACh for cholinergic

transmission. At the same time, clinical trials of AChE-Is and

their meta-analyses continued to show favourable, albeit

mild, effects on cognitive parameters, at least during the

first 6–12 months of treatment. Against this background,

basic and clinical investigators have recently turned their

attention towards other possible mechanisms of action

of the AChE-Is, especially on the APP/Ab pathway, and

have begun to ask whether these drugs might have any

disease-modifying effects (Caccamo et al., 2006).

Various aspects of AChE-I actions on the upstream and

downstream APP/Ab pathway have been reported: attenuat-

ing the effects of Ab-induced neuronal cytoxicity (Kimura

et al., 2005), promoting a-secretase or decreasing b-secretase

activity (Caccamo et al., 2006; Zimmerman et al., 2005),

inhibiting Ab aggregation or inhibiting GSK 3b activity and

tau phosphorylation (Caccamo et al., 2006). One group

found no effect on Ab amyloid plaque load while still

improving behavioural deficits in a transgenic mouse model

(Dong et al., 2005), while another group found that

inhibitors of butyrylcholinesterase had a lowering effect on

cellular APP and Ab and brain Ab in transgenic mice (Greig

et al., 2005).

The modulation of glutamatergic transmission in

Alzheimer’s disease has also received increasing attention

with the results of the memantine clinical trials aimed

at blocking (non-competitively) the action of N-methyl-

D-aspartate (NMDA) receptors. With the growing awareness

that the toxic soluble oligomers of Ab may inhibit LTP

at the pre-synaptic level and that Ab promotes the

endocytosis of the NMDA receptor [mediated in part

through a-7 nicotinic receptor, protein phosphatase PP2B

and tyrosine phosphatase STEP (Snyder et al., 2005)],

the findings that memantine has beneficial behavioural

effects in both Ab toxicity models (Yamada et al., 2005) and

Fig. 3 Transaxial and sagittal distribution volume ratio (DVR)of Ab-ligand 11C-PIB PET images of a representative healthycontrol (HC) subject (age: 84, MMSE: 30) and an Alzheimer’sdisease patient (age: 83, MMSE: 22). Image kindly provided byDr Victor Villemagne and Associate Professor Chris Rowe,PET Centre, Austin Health, Heidelberg, Australia.

Table 3 Alzheimer’s disease modification by drugintervention: criteria

(i) Plausible mechanism of action in a validated model(ii) Clinical trial evidence based on the Lerber staggered start design(iii) Difference in survival to a meaningful clinical outcome(iv) Change in rate (slope) of decline(v) Demonstrable drug-placebo difference on an accepted

biomarker of disease progression

After Cummings (2006).


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APP transgenic mouse models (Van Dam et al., 2005)

requires further work that might tie all these obser-

vations together. NMDA receptor activation may promote

Ab production (Lesne et al., 2005) and Ab may also

modulate a-amino-5-hydroxy-3-methyl-isoxazole-propionic

acid [AMPA] receptors (Chang et al., 2006; Shemer et al.,

2006), further contributing to the impairment of synaptic

function.

Other cerebral or general systemic factorsOne suspects that there will be many other upstream

factors that play into the APP/Ab pathway, but few have

been identified to date. A particularly contentious area has

been the role of the vascular supply to the brain and the

effects of ischaemia (atherosclerosis) and hypertension.

Historically, this has deep roots, going back to the days

when ‘arteriosclerosis’ was thought to cause all forms of

dementia. Similarly, head trauma has been considered as a

risk factor for Alzheimer’s disease, and APP has been

identified as a sensitive marker of axonal damage following

traumatic brain injury. But neither hypoxia nor trauma has

yet been shown to be a major risk factor, and neither has

been shown to promote the long-term amyloidogenic

processing of APP.

Central steps in the APP/Ab pathwayTargeting the APP gene or genes withproducts interacting directly with APPWith the advent of RNA interference (RNAi) silencing, it is

to be expected that attempts at direct APP gene regulation

will emerge. As a forerunner to this, models in which the

overexpressed human APP transgene in mice can be

downregulated with doxycycline provide a proof of principle

that rapid control over Ab expression and deposition can be

obtained without gross adverse side-effects (Jankowsky et al.,

2005). Unexpectedly, Ab deposits formed before the onset

of downregulation seemed to be remarkably stable,

indicating that any treatment of this type in isolation

might have to be administered early in the natural history of

Alzheimer’s disease. Using RNAi techniques in transfected

cell lines (Xie et al., 2005), targeting the X11 gene (APAB)

successfully increased APP C-terminal fragments and lowered

Ab levels; X11 is a known interactor with the cytoplasmic

Table 4 Alzheimer’s disease therapeutic targets derived from the APP/Ab pathway

Pathway step/event Target/drug

A. Upstream eventsAgeingEnvironment Exercise, dietNeurotransmitter systems modulation Cholinergic: AChE/BuChE inhibition

Glutamatergic: NMDA antagonismSerotonergic: antidepressants

Other cerebral or general systemic factorsB. Central steps: Ab biogenesis from APP

APP gene targetAPP interactions, transport X11 gene target, growth factors, metal homeostasis, ZnT3,

oestrogen, cholesterolAPP proteolytic processing

g-Secretase (PS, Aph1, PEN-2, Nct) andassociated «- and z-cleavages

Inhibitor, modulator (NSAID), gene target

b-Secretase (BACE 1) Inhibitor, modulator/interaction (PAR 4),immunomodulations of b-cleavage site, gene target

a-Secretase Stimulation (PKC activation)Ab and its varied conformations

Monomers/dimer/trimer (A4, A8, A12)- Metal binding sites MPAC- GAG binding sites- Oxidative modifications Di-tyrosine, methionine oxidation- Ab–lipid interactions LPAC- Ab–protein interactions PPACb-Oligomers/protofibrils Anti-aggregants/disaggregantsPolymers/fibrils Anti-fibrillogenics/defibrillants

C. Downstream eventsAb-induced ‘toxicity’ through oxidative damage(protein, mitochondria, lipid, sterols, nucleic acid, etc)

Anti-oxidants, natural product screens, oestrogen

Anti-inflammatory (anti-microglia) Sigma 1 receptor, PPARg, PGE2, NSAID, iNOS inhibitionAb-tau direct/indirect interactions Microtubule stabilizers, kinase, inhibitors, anti-aggregants, etc.Ab–ApoE interactions Statins/cholesterolAb-clearance/neutralization Immunization, immunomodulationAb-degradation IDE, NPE, ACE


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domain of APP, and presents a novel method of possibly

modulating g-secretase cleavage.

APP-interacting systemsAs a presumptive cell surface receptor, APP probably has

ligands and effector mechanisms for signal transduction.

Nearly 200 proteins have been reported as having direct

interactions with APP. Suspected ligands in the extracellular

domain include growth factors [nerve growth factor (NGF)

in particular], heparin-containing extracellular matrix,

metals (through the extracellular Cu/Zn binding domain)

and APP itself through hetero- and homo-dimerization.

Small compounds such as propentofylline (Chauhan et al.,

2005) can affect NGF release, and through this modulate

the amyloidogenic pathway. Other small compounds may

bind directly to APP (Espeseth et al., 2005) and affect its

processing.

A controversial area involves the effects of hormones

(oestrogens and testosterone especially) and how they may

affect APP metabolism. Conflicting results in experimental

models have appeared, in which oestrogen deficiency

exacerbates Ab in the APP23 transgenic model (Yue et al.,

2005) and neither oestrogen deprivation nor replacement

affected Ab deposition in the PDAPP [platelet-derived

growth factor (pdgf)-b chain promoter with Indiana

mutation-V717F in APP] transgenic model (Green et al.,

2005). Further studies are clearly required for unravelling

this important area where there is an epidemiological

impression that females have a higher incidence of

Alzheimer’s disease than males (this impression does not

appear to have ever been subjected to a prospective

analytical epidemiological study). The mechanisms through

which oestrogen/testosterone might act remain obscure,

but include oestrogen-dependent regulation of metal homeo-

stasis in the brain through the expression of the neuronal

zinc transporter, ZnT3.

Cholesterol and inhibitors of cholesterol synthesis

(statins) have been shown to significantly alter APP

processing in vitro, with a reduction in b-secretase cleavage

and lessened Ab production. Cholesterol-dependent

aggregation/oligomerization has also been reported. While

some early phase clinical trials with statins have shown

encouraging results (Masse et al., 2005), others have not

(Hoglund et al., 2005). Cholesterol-independent effects have

also been noted for statins acting on isoprenyl intermediates

in the cholesterol biosynthetic pathways, with a putative

anti-inflammatory effect induced by reactive microglia (Cole

et al., 2005; Cordle et al., 2005). This might conflict with the

current theory that microglia are involved in the beneficial

process of clearing Ab deposits.

If eventually cholesterol does prove to be a risk factor,

then the observations (Papassotiropoulos et al., 2005) of an

association between the disease and the expression levels and

haplotypes of the 50 region of the cholesterol 25-hydroxylase

(CH25H) gene on chromosome 10 may provide a plausible

explanation: one in which cerebral cholesterol metabolism

(as distinct from systemic cholesterol and its association

with atherosclerosis) directly plays into the APP processing

and transport pathways.

APP proteolytic processingAs outlined in the Background section above, the biogenesis

of Ab has been the prime validated drug target for

Alzheimer’s disease since the discovery of the proteolytic

processing of APP in 1987. Molecular details of the

C-terminal cleavage (g-secretase) were the first to emerge

(Sherrington et al., 1995), followed by the a- and b-cleavage

mechanisms (Sinha et al., 1999). Subsequent elucidation of

d-, «- and z-cleavages has added another layer of complexity.

Drug discovery programmes reflect this sequence of events:

many large pharmaceutical companies have g-secretase

inhibitors or modulators in clinical development, while

the b-secretase inhibitors are several years behind, largely in

pre-clinical discovery.

g-Secretase inhibitors and modulatorsDuring 2004, the first publications of in vivo g-secretase

inhibition/modulation of Ab42 biogenesis appeared. One of

the first inhibitors [DAPT (N-[N-(3,5–difluoorophenacetyl)-

L-alanyl]-S-phenylgylcine t-butyl ester] was shown to be

effective in acute experiments in behavioural tests (con-

textual fear conditioning) in the Tg 2576 Alzheimer’s disease

mouse model (Comery et al., 2005). Modifications to the

chemical structure of DAPT have now improved its delivery

to the brain (Quelever et al., 2005), as with other compounds

(Laras et al., 2005), in the hope of achieving lower effective

dosages minimizing the risk of adverse peripheral effects.

Many diverse classes of inhibitors and modulators are

showing very favourable acute pharmacokinetics, with rapid

lowering of plasma and CSF Ab levels (Anderson et al., 2005;

Barten et al., 2005; Lanz et al., 2004, 2005; Grimwood et al.,

2005; Peretto et al., 2005; Best et al., 2006). Importantly,

there is now strong evidence linking plasma and CSF Ab

levels, indicating that the brain/CSF pool of Ab is at least

in part a significant proportion of the plasma Ab pool.

There are still methodological issues in measuring Ab, using

either ELISA or western blotting techniques (which soluble

oligomeric species are being measured, and what forms of

Ab: total, Ab40, Ab42?). Nevertheless, these preliminary data

offer some hope that plasma Ab species may eventually

prove to be a reliable marker of cerebral Ab turnover.

Further explorations of the properties of g-secretase

inhibitors are revealing unanticipated effects on synaptic

function (Dash et al., 2005). New classes of g-secretase

inhibitors/modulators continue to be disclosed, as part of

the effort to develop compounds devoid of side-effects

(Sparey et al., 2005). The major concern is the inhibition of

signalling in the Notch pathway, which affects cellular

differentiation (Curry et al., 2005; van Es et al., 2005).

Ironically, g-secretase inhibitor compounds originally

developed for Alzheimer’s disease are now being trialled


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in Phase II studies of acute lymphoblastic leukaemia

(ClinicalTrials.gov A notch signalling pathway inhibitor for

patients with T-cell acute lymphoblastic leukaemia/

lymphoma (ALL). ClinialTrials.gov Identifier: NCT00100152.

http://www.clinicaltrials.gov/ct/show/NCT00100152?order=2.)

and advanced breast cancer (ClinicalTrials.gov A Notch

signalling pathway inhibitor for patients with advanced

breast cancer. ClinialTrials.gov Identifier: NCT00106145.

http://www.clinicaltrials.gov/ct/show/NCT00106145?order=1.).

The first in-human Phase I results to be published

(Siemers et al., 2005, 2006) have shown that the Lilly

compound LY450139 achieved a significant lowering of

plasma Ab, but not CSF Ab, in normal volunteers (up to

50 mg/day for 14 days) or subjects with Alzheimer’s disease

(up to 40 mg/day for 6 weeks). The drug was well tolerated.

Higher dosages may be required to achieve a reduction in

CSF levels. The results of Phase II studies with read-outs on

cognitive variables are eagerly awaited. In the meantime,

further research on the mechanistic operations of the

g-secretase complex (Sato et al., 2005; Fukumori et al., 2006;

Kakuda et al., 2006; Morohashi et al., 2006; Yagishita et al.,

2006) may lead to new paths of drug discovery, as might

gene targeting of presenilin, PEN-2, APH-1, nicastrin and

TMP21 lead to selective regulation of g-secretase activity

(Xie et al., 2005a; Chen et al., 2006).

b-Secretase (BACE) inhibitorsAlthough �5 years behind the development of the

g-secretase inhibitors, much progress has been made in

the discovery and design of compounds that target the active

site of BACE-1. Improved assays and structural-based

in silico designs have added to the existing pipeline of

drugs in early pre-clinical development (Kimura et al., 2005;

Kornacker et al., 2005; Lefranc-Jullien et al., 2005; Huang

et al., 2006) or early discovery programmes. Other proteins

interacting with BACE-1 may become drug targets, and

gene targeting of BACE-1 mRNA using siRNA is also

producing encouraging preliminary results (Singer et al.,

2005). As with g-secretase, unanticipated side-effects on

other BACE-1 substrates or downstream consequences of

BACE-1 inhibition may prove difficult to circumvent.

Drugs targeting Ab and its variedconformationsMonomers (A4), dimers (A8) and trimers (A12)In contrast to the inhibition of Ab biogenesis, therapeutic

strategies that directly target Ab itself should inherently have

a lower risk of throwing up unanticipated side-effects, as the

accumulated Ab molecule is restricted to Alzheimer’s

disease. If the Ab fragment (or its domain within APP)

does, however, subserve some critical normal function, then

targeting Ab itself might interfere with this function and

thereby lead to adverse side-effects, but to date, a normal

function for Ab has not been identified. APP knockout

mice are viable and healthy, providing some support for

this idea.

Current models of the physical state of Ab are evolving.

Whilst resident in the membrane, Ab is assumed to be

in an a-helical conformation. Following sequential b- and

g-cleavages, Ab as a monomer (A4), dimer (A8) [or perhaps

even as a trimer (A12)] is translocated into the extra-

cytosolic space, and may transition there into a b-strand-

enriched structure. These structures may then progress

towards b-oligomers/protofibrils through to polymers/fibrils

of amyloid filaments.

The mechanisms through which Ab causes damage to

neurons (‘the toxic gain-of-function’) are slowly emerging.

There are many theories: the two most favoured include the

ability of Ab to generate oxidative stress and the

hydrophobic interaction of Ab with lipid membranes,

particularly the synaptic plasma membrane. Our current

working model (Table 5) incorporates both theories: we

have defined a metal binding domain near the N-terminus

of Ab that is capable of binding Zn++ (which causes Ab to

precipitate) or redox-active Cu++. When Cu++ binds Ab, it

not only causes a significant increase in insolubility but also

induces a series of electron transfers that result in histidine

bridge formation, tyrosine 10 radicalization, di-tyrosine

cross-linking and oxidation of methionine 35. Ultimately, in

the presence of reductants, this results in the production of

H2O2 and hydroxyl radicals, capable of inflicting short-range

oxidative damage to proteins, lipids, sterols, nucleic acids,

Table 5 The toxic Ab oligomer pathway: the currenttheory

Ab-Cu++ facilitates intermolecular histidine bridge formation(Curtain et al., 2001; Tickler et al., 2005; Smith et al., 2006)

Membrane association of Ab monomer/dimer occurs (Curtain et al.,2003; Lau et al., 2006; G.D. Ciccotosto, unpublished data)

Exposed Met35 required to promote redox chemistry in conjunctionwith metal binding site (Barnham et al., 2003; Curtain et al., 2001,2003; Ciccotosto et al., 2004)

Tyr10 radical forms and Met35 is oxidized; one consequence isdi-tyrosine cross-linkage (Barnham et al., 2004; Smith et al., 2006),and copper induces formation of soluble oligomers (Barnham et al.,2004)

Soluble species of Ab, not plaques, are the principal determinants ofneurodegeneration (McLean et al., 1999)

ROS (H2O2) production may result in flipping of phosphatidyl serinesfrom cytoplasmic face of membrane to the exterior (White et al.,2001), which will promote further binding of Ab to the membrane

Dimeric/oligomeric soluble Ab species associate with negativelycharged head groups of phospholipids on outer surface of plasma/synaptic membrane (Smith et al., 2006; Lau et al., 2006).

Oxidation of sterols (cholestenone), lipids (4-hydroxy-2-nonenal)and proteins (carbonyls) (Smith et al., 2006)

Perturbation of plasma/synaptic membranes/proteins leads tochronic dysfunction and disease


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http://www.clinicaltrials.gov/ct/show/NCT00100152?order=2

http://www.clinicaltrials.gov/ct/show/NCT00106145?order=1

and so forth (Tabner et al., 2005). Our studies show that

toxicity to neurons in culture is associated with the ability of

Ab to associate with the lipid head group on the outer

surface of the plasma membrane (Lau et al., 2006).

If this schema is only partially correct, then it is clear that

any therapeutic strategy targeting Ab directly might have

multiple routes, many intersecting and overlapping. Thus,

targeting the metal binding site of Ab might relate to Ab in

one or more of its varied conformations (a-helix, b-strand,

b-sheet; A4, A8, A16 versus higher-order oligomers versus

polymerized fibril) or whilst interacting with other proteins

or lipids.

In consideration of targeting the metal binding site on Ab,

we have developed the concept of an MPAC—a metal–

protein attenuating compound—in distinction to the more

widely known term of metal chelator. The MPAC has

relatively weak binding constants for metals, and is able

to compete with the target site for the metal ion. As a

consequence, an MPAC should not alter the general

homeostasis of metal ions in the whole animal. In contrast,

a metal chelator has high, effectively irreversible, binding

constants for metal ions. A chelator might affect the metal

binding to Ab through deletion of the total pool of

bioavailable metal, but is not expected necessarily to interact

with the Ab metal binding site itself.

The study of MPACs in Alzheimer’s disease has been

initiated with studies of clioquinol, an 8-OH quinoline, with

encouraging pre-clinical (Cherny et al., 2001) and early

Phase II clinical results (Ritchie et al., 2003). The next-

generation MPAC has progressed to a new chemical entity

based around the 8-OH quinoline structure. This compound

(PBT2-Prana Biotechnology) has passed Phase I and will

soon commence Phase II clinical development.

Additional binding sites on Ab, such as the glycosami-

noglycan (GAG) site [HHQK (13–16)], have been targeted

with compounds such as 3-amino-1-propanesulphonic acid

[3-APS (Alzhemed); Neurochem]. The results of early

clinical trials have been released by the company, with

some effects seen on CSF Ab42, but none on ADAS-cog or

Mini-Mental State Examination (MMSE). A large Phase III

study is under way, coupled to an open-label extension

study. The double-blind study results are expected in

January 2007.

We have identified other structural changes or mechan-

isms of toxicity for Ab that include the oxidative

modifications of Tyr10 and Met35, the interaction of Ab

with the polar head groups of the lipid bilayer or the

interaction of Ab with other proteins. These areas remain

very much in the early discovery phase and may deliver

LPACs—lipid–protein attenuating compounds, or PPACs—

protein–protein attenuating compounds.

b-Oligomers/protofibrils and polymers/fibrils of AbThe pharmaceutical industry has for a long time interro-

gated its libraries for compounds that are anti-aggregants

and/or anti-fibrillogenic. Many hits with compounds that

look similar to Congo Red have never been developed.

Similarly, compounds capable of disaggregating or defibri-

llating Ab have been sought, but not with the intensity of the

search for anti-aggregants. While many peptidyl/protein-like

designs have been examined, other small molecules have

been discovered that hold some promise (Kanapathipillai

et al., 2005; Lin et al., 2005; Wang et al., 2005; McLaurin

et al., 2006). Most interesting, however, is the development

of assays specifically designed to examine the effects of

soluble b-oligomers of Ab (possibly the trimeric form A12)

and to use these assays in a discovery process of small

compounds capable of inhibiting b-oligomer formation

(Walsh et al., 2005).

Targeting the downstream effects of AbThere are many productive lines of enquiry being applied to

the downstream effects of Ab, beginning with the direct

consequences of Ab toxicity and oxidative damage through

to the promotion of Ab clearance/degradation. Big questions

remain on the role of the innate immune system and the

value of targeting neurofibrillary tangle formation.

Ameliorating the toxic gain-of-function ofAb: anti-oxidants, neuroprotectants andother products of natural originExisting knowledge and screens of natural product libraries

have thrown up a wide variety of anti-oxidants and

‘neuroprotectants’ that have an effect on the actions of Ab

in experimental assays of its toxicity. Many of these assays

are difficult to control, and there is little agreement in the

field as to their validity. Nevertheless, an increasing number

of papers are appearing reporting efficacy of compounds

derived from plants [ferulic acid (Sultana et al., 2005), green

tea extracts (Rezai-Zadeh et al., 2005), curcumin (Yang et al.,

2005) and resveratol (Marambaud et al., 2005)], and other

natural products [docosahexaenoic acid (Lim et al., 2005),

vitamin E (Quintanilla et al., 2005), oestrogens (Coma et al.,

2005) and glutathione (Woltjer et al., 2005)]. From these

investigations, a common theme emerges: that a wide variety

of anti-oxidants can ameliorate the toxic gain of function of

Ab. This is consistent with our argument that Ab itself is the

principal pro-oxidant in Alzheimer’s disease. Other lines of

evidence are emerging that contribute to an understanding

of the oxidative stress (Nathan et al., 2005) or form a feed-

forward mechanism (Tong et al., 2005) to account for the

progressive nature of the disease.

Suppressing brain ‘inflammation’There is considerable controversy around the concept that

the Alzheimer’s disease brain is undergoing inflammation.

As usually understood, inflammatory changes are not visible.

What Alzheimer, Cajal (1928) and their contemporaries


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recognized was that microglia were increased in number,

activated and, together with astrocytes, were reacting to

some underlying factor, possibly the amyloid within the

plaque. They also recognized that the dystrophic neurites

and drusige Entartung associated with the perivascular

amyloid deposits could represent the reactive and regen-

erative response of neurons to the same injurious process. It

is surprising, therefore, in recent times for the idea of

‘inflammation’ in Alzheimer’s disease to have gained such

ground. In this scenario, the microglia are seen as

inflammatory invaders causing damage through their release

of cytokines and other powerful destructive molecules

designed to respond to injury. This innate immune reaction

would therefore exacerbate the clinical expression of

Alzheimer’s disease and lead to its progression towards

neuronal dysfunction and death. From this, trials of anti-

inflammatories have been conducted, and considerable

research efforts undertaken to examine the effects of anti-

inflammatories in a variety of experimental models. These

include the non-steroidal anti-inflammatories (Morihara

et al., 2005), peroxisome proliferator-activated receptor-g

agonists (Echeverria et al., 2005; Heneka et al., 2005;

Sastre et al., 2006) and cannabinoids (Ramırez et al.,

2005). To date, no prospective clinical trial with an anti-

inflammatory has shown a convincing beneficial outcome.

In the light of the data emerging around the immunization/

immunomodulation strategies against Ab (see below), the

counter-hypothesis that microglia are actually beneficial

could prove to be correct.

Targeting tau aggregation in theAb pathwayWhile Ab has captured the imagination of most Alzheimer’s

disease researchers, studies of the neurofibrillary tangle

and its constituent, the tau microtubule-associated protein,

have progressed to a point where clear therapeutic strategies

are emerging. The exact form of tau that causes neuronal

degeneration is now being re-examined (Duff and Planel,

2005), with data emerging that the soluble aggregated

species, akin to soluble b-oligomers of Ab, might represent

the best target. The binding sites on tau (Mukrasch et al.,

2005) for a variety of interactors are potential targets.

Downregulation of expression of the tau gene (Santacruz

et al., 2005) or altering the alternative splicing (Rodriguez-

Martin et al., 2005) also offer some new strategies.

As the molecular basis for the accumulation of tau in

the diseased brain becomes clearer, so will the precise

therapeutic target. If tau accumulation is closely linked to

Ab toxicity, then oxidative modifications of tau become

understandable (Santa-Maria et al., 2005; Zhang et al.,

2005; Reynolds et al., 2005a, b, 2006) and subject to anti-

oxidative classes of drugs. Looking at the normal function

and processing of tau has raised the possibility of using

microtubule-stabilizing agents such as paclitaxel (Taxol)

(Michaelis et al., 2005). Great controversy still persists on

the role of normal and abnormal phosphorylation of tau

in its passage from a highly soluble cytoskeletal-associated

protein into an aggregated neurofibrillary tangle. If

phosphorylation of specific amino acids by specific kinases

such as c-Abl, Cdk5, GSK-3, ERK2 or MAPK proves to be

pathogenic, then specific kinase inhibitors [including novel

compounds (le Corre et al., 2006) or well-recognized drugs

such as lithium (Noble et al., 2005)] might be developed for

Alzheimer’s disease—indeed, a trial with lithium is currently

in progress in the United Kingdom. However, if phosphor-

ylation proves to be a secondary event, following aggregation

and accumulation of intracellular tau, then this approach

would not be expected to be useful. Other post-translational

modifications including proteolytic cleavages have been

proposed (Cotman et al., 2005)—all amenable to therapeutic

drug discoveries. As with Ab, small compounds capable of

inhibiting aggregation and fibrillization of tau are now being

examined in vitro (Necula et al., 2005; Taniguchi et al.,

2005), but require much more work in animal models.

How does ApoE fit within the Ab pathway?As the major (if not the sole) genetic risk factor for

determining the age at onset, it is surprising that we still do

not have a definitive explanation on its mechanism of

action. Targeting the ApoE gene directly, or aiming for the

delivery of the protective ApoE isoform (Dodart et al.,

2005), offers some prospect of therapeutic intervention.

However, understanding the precise interaction between

ApoE and the processing of APP/Ab is likely to yield more

amenable therapeutic strategies. At this time, it appears most

likely that ApoE acts through the clearance mechanisms

governing Ab metabolism.

Using immunization andimmunomodulation of Ab to promoteclearance and inhibit toxicity(neutralization)Since 1999, increasing evidence has accumulated to make a

compelling antibody-mediated Ab clearance/neutralization

strategy. Experiments in mouse models continue to demon-

strate efficacy (Banks et al., 2005; Brendza et al., 2005;

Buttini et al., 2005; Klyubin et al., 2005; Rowan et al., 2005;

Bales et al., 2006; Levites et al., 2006; Ma et al., 2006; Maier

et al., 2006). The aborted clinical trial with the Elan

Ab42 antigen (AN1792) has provided a wealth of clinical

information (Gilman et al., 2005; Lee et al., 2005a), which

will assist further development of strategies designed to

avoid the auto-immune adverse events (Lee et al., 2005b;

Racke et al., 2005). Chief among these will be avoidance of

T-cell-mediated responses and the development of passive

immunization protocols (Hartman et al., 2005). The results

of the current clinical trials by Elan using passive

immunization are awaited with great interest (see below).

In the meantime, novel methods of antigen presentation


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(Okura et al., 2006; Qu et al., 2006) and the use of neo-

epitopes (Arbel et al., 2005) are under investigation. Neo-

epitopes generated post-transationally by modification of Ab

(through oxidative mechanisms, as discussed above) should

have inherently less potential to generate an auto-immune

adverse reaction (Lee et al., 2006).

A startling process of lateral thinking has emerged with

the report (Alvarez et al., 2006) of the use of Cerebrolysin in

a successful Phase II study of Alzheimer’s disease in Spain

and Romania. The product is a proteolytic extract of pig

brain and is administered by multiple intravenous infusions

over an 8 week period. Putting aside the possibility of

transmitting a porcine form of prion disease, the method

raises interesting regulatory and religious issues.

Modulating the Ab degradation pathwayThe re-uptake, clearance and degradation of Ab is still

subject to considerable uncertainties. If sporadic Alzheimer’s

disease is the result of a low-level shift (<10%, for example)

in the efficiency in any of these mechanisms, then a

therapeutic strategy aimed at restoring or by-passing this

faulty mechanism could be very useful. Each of the different

pools of Ab probably has slightly different mechanisms of

elimination, varying with the cellular compartment in

which Ab resides over the course of its catabolic cycle.

Several pieces of evidence point towards the enzymes NPE

and insulin degrading enzyme as key players (Farris et al.,

2005; Saito et al., 2005; Saido et al., 2006), but the highly

sought evidence from gene linkage studies remains

elusive (Eckman and Eckman, 2005). A new candidate,

angiotensin-converting enzyme (ACE), has emerged

(Hemming and Selkoe, 2005), and it will be of great interest

to learn whether the ACE inhibitors could be having an

adverse influence over the natural history of the disease.

The futureThe clinical development of drugs directly targeting the

Ab pathway is at an early stage of evolution. In Table 6

we list the publicly disclosed trials that are in progress or

which have completed/discontinued with drugs that

have been developed specifically to target the Ab pathway.

The g-secretase inhibitors trials are of immense theoretical

interest, as they are likely to provide the most compelling

support for the Ab theory of Alzheimer’s disease. The trials

around the Ab metal binding or CAG binding sites also have

the potential to address this aspect. Early clinical develop-

ment of Ab aggregation inhibitors has been reported

(McLaurin et al., 2006). Immunization/immunomodulation

of Ab holds great promise for elucidating the Ab clearance/

neutralization strategies in which there is currently a dearth

of information. A variety of prospective statin-mediated

approaches will also test the hypothesis that cholesterol has

an important role in the biogenesis of Alzheimer’s disease.

The anti-oxidant trials have the disadvantage of lacking

specificity for Ab, but nonetheless will continue to provide

much needed guidance for the general theory of the diseased

brain being under oxidative stress.

It is extremely unlikely that a single class of compound or

targeting a single mechanism of action will be sufficient to

treat this illness. For this complex disease, it is far more

Table 6 Drugs in clinical development directly targeting the Ab pathway

Target Drug Company Status Clinical trials.gov identifier

g-Secretase inhibition R-flurbiprofen (Flurizan)MCP-7869

Myriad genetics Phase 3(in progress)

NCT00105547

LY-450139 Eli Lilly & Co Phase 2 NCT00244322MK 0752 Merck Inc Phase 2

Ab monomer/oligomerMetal binding site PBT2(PBT1) Prana biotechnology Phase 2GAG binding site 3APS (Alzhemed) Neurochem Inc Phase 3 NCT00217769

Disaggregation of AbOligomerization site? Scyllo-cyclohexanehexol AZD-103 Transition Phase 1

TherapeuticsAb clearance/neutralization

Immunomodulation AN-1792 (acute immunizationsynthetic Ab42)

Elan/Wyeth Phase 3(discontinued)

AAB-001 (passive immunotherapy) Elan/Wyeth Phase 2 NCT00112073ACC-001 (immunization) Elan/Wyeth Phase 1CAD 106 (Ab N-terminus 1–6) Novartis Phase 1

RAGE receptor inhibitor TTP 488 TransTech Pharma Phase 2APP/Ab processing

Cholesterol synthesis Statins Merck/Pfizer Phase 2Anti-oxidants

Curcumin French Foundation Phase 2 NCT00099710VitE/VitC/a-lipoic acid. Coenzyme Q NIH Phase 1 NCT00117403


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likely that a combination of drugs targeting various aspects

of the greater APP/Ab pathway will evolve into some form

of rational therapy. Trials now in progress should represent

the very beginning of the enlightenments required to find the

right combinations—all predicated on the assumption that

the APP/Ab pathway underlies the cause of the disease.

Acknowledgements and disclosuresSome of the work described in this article is supported by

research grants from the National Health and Medical

Research Council of Australia (to C.L.M.) and the Deutsche

Forschungsgemeinschaft and the Bundesministerium fur

Forschung und Technologie (to K.B.). We thank

Kevin Barnham and Ashley Bush for discussions around

Table 5.

Conflict of interest statement: C.L.M. discloses an interest in

Prana Biotechnology

References

Adlard PA, Perreau VM, Pop V, Cotman CW. Voluntary exercise decreases

amyloid load in a transgenic model of Alzheimer’s disease. J Neurosci 2005;

25: 4217–21.

Alvarez XA, Cacabelos R, Laredo M, Couceiro V, Sampedro C, Varela M, et al.

A 24-week, double-blind, placebo-controlled study of three dosages of

Cerebrolysin in patients with mild to moderate Alzheimer’s disease. Eur J

Neurol 2006; 13: 43–54.

Anderson JJ, Holtz G, Baskin PP, Turner M, Rowe B, Wang B, et al.

Reductions in b-amyloid concentrations in vivo by the g-secretase

inhibitors BMS-289948 and BMS-299897. Biochem Pharmacol 2005;

69: 689–98.

Arbel M, Yacoby I, Solomon B. Inhibition of amyloid precursor protein

processing by b-secretase through site-directed antibodies. Proc Natl Acad

Sci USA 2005; 102: 7718–23.

Bales KR, Tzavara ET, Wu S, Wade MR, Bymaster FP, Paul SM, et al.

Cholinergic dysfunction in a mouse model of Alzheimer disease is reversed

by an anti-Ab antibody. J Clin Invest 2006; 116: 825–32.

Banks WA, Pagliari P, Nakaoke R, Morley JE. Effects of a behaviorally active

antibody on the brain uptake and clearance of amyloid beta proteins.

Peptides 2005; 26: 287–94.

Barghorn S, Nimmrich V, Striebinger A, Krantz C, Keller P, Janson B, et al.

Globular amyloid b-peptide1–42 oligomer—a homogenous and stable

neuropathological protein in Alzheimer’s disease. J Neurochem 2005;

95: 834–47.

Barnham KJ, Ciccotosto GD, Tickler AK, Ali FE, Smith DG, Williamson NA,

et al. Neurotoxic, redox-competent Alzheimer’s b-amyloid is released from

lipid membrane by methionine oxidation. J Biol Chem 2003;

278: 42959–65.

Barnham KJ, Haeffner F, Ciccotosto GD, Curtain CC, Tew D, Mavros C, et al.

Tyrosine gated electron transfer is key to the toxic mechanism of

Alzheimer’s disease b-amyloid. FASEB J FJ Express 2004; 18: 1427–9.

Barnham KJ, Cappai R, Beyreuther K, Masters CL, Hill AF. Delineating

common molecular mechanisms in Alzheimer’s and prion diseases. Trends

Biochem Sci 2006; 31: 465–72.

Barten DM, Guss VL, Corsa JA, Loo A, Hansel SB, Zheng M, et al. Dynamics

of b-amyloid reductions in brain, cerebrospinal fluid, and plasma of

b-amyloid precursor protein transgenic mice treated with a g-secretase

inhibitor. J Pharmacol Exp Ther 2005; 312: 635–43.

Best JD, Jay MT, Otu F, Churcher I, Reilly M, Morentin-Gutierrez P, et al.

In vivo characterisation of Ab(40) changes in brain and CSF using the novel

g-secretase inhibitor MRK-560 (N-[cis-4-[(4-chlorophenyl)sulfonyl]-4-

(2,5 difluorophenyl)cyclohexyl]-1,1,1-trifluoromethanesulfonamide) in

the rat. J Pharmacol Exp Ther 2006; 317: 786–90.

Bitan G, Kirkitadze MD, Lomakin A, Vollers SS, Benedek GB, Teplow DB.

Amyloid b-protein (Ab) assembly: Ab40 and Ab42 oligomerize through

distinct pathways. Proc Natl Acad Sci USA 2003; 100: 330–5.

Brendza RP, Bacskai BJ, Cirrito JR, Simmons KA, Skoch JM, Klunk WE, et al.

Anti-Ab antibody treatment promotes the rapid recovery of amyloid-

associated neuritic dystrophy in PDAPP transgenic mice. J Clin Invest 2005;

115: 428–33.

Bush AI, Multhaup G, Moir RD, Williamson TG, Small DH, Rumble B, et al.

A novel zinc (II) binding site modulates the function of the bA4

amyloid protein precursor of Alzheimer’s disease. J Biol Chem 1993;

268: 16109–12.

Bush AI, Pettingell WH, Multhaup G, d Paradis M, Vonsattel J-P, Gusella JF,

et al. Rapid induction of Alzheimer Ab amyloid formation by zinc. Science

1994; 265: 1464–7.

Buttini M, Masliah E, Barbour R, Grajeda H, Motter R, Johnson-Wood K,

et al. b-amyloid immunotherapy prevents synaptic degeneration in a

mouse model of Alzheimer’s disease. J Neurosci 2005; 25: 9096–101.

Caccamo A, Oddo S, Billings LM, Green KN, Martinez-Coria H, Fisher A, et al.

M1 receptors play a central role in modulating AD-like pathology in

transgenic mice. Neuron 2006; 49: 671–82.

Cajal S [Ramon y]. Study of regenerative processes of the cerebrum

(continued). In: Degeneration and Regeneration of the Nervous System.

[Translated and edited by RM May]. Volume II. Fourth Part. VII. London:

Oxford University Press; 1928. p. 734–60.

Chang EH, Savage MJ, Flood DG, Thomas JM, Levy RB, Mahadomrongkul V,

et al. AMPA receptor downscaling at the onset of Alzheimer’s disease

pathology in double knockin mice. Prot Natl Acad Sci USA 2006;

103: 3410–5.

Chartier-Harlin M, Crawford F, Houlden H, Warren A, Hughes D, Fidani L,

et al. Early-onset Alzheimer’s disease caused by mutations at codon 717 of

the b-amyloid precursor protein gene. Nature 1991; 353: 844–6.

Chauhan NB, Siegel GJ, Feinstein DL. Propentofylline attenuates tau

hyperphosphorylation in Alzheimer’s Swedish mutant model Tg2576.

Neuropharmacology 2005; 48: 93–104.

Chen F, Hasegawa H, Schmitt-Ulms G, Kawarai T, Bohm C, Katayama T, et al.

TMP21 is a presenilin complex component that modulates g-secretase but

not «-secretase activity. Nature 2006; 440: 1208–12.

Cherny RA, Legg JT, McLean CA, Fairlie DP, Huang X, Atwood CS, et al.

Aqueous dissolution of Alzheimer’s disease Ab amyloid deposits by

biometal depletion. J Biol Chem 1999; 274: 23223–8.

Cherny RA, Atwood CS, Xilinas ME, Gray DN, Jones WD, McLean CA, et al.

Treatment with a copper-zinc chelator markedly and rapidly inhibits

b-amyloid accumulation in Alzheimer’s disease transgenic mice. Neuron

2001; 30: 665–76.

Ciccotosto GD, Tew D, Curtain CC, Smith D, Carrington D, Masters CL, et al.

Enhanced toxicity and cellular binding of a modified amyloid b peptide

with a methionine to valine substitution. J Biol Chem 2004; 279:

42528–34.

Cole SL, Grudzien A, Manhart IO, Kelly BL, Oakley H, Vassar R. Statins cause

intracellular accumulation of amyloid precursor protein, b-secretase-

cleaved fragments, and amyloid b-peptide via an isoprenoid-dependent

mechanism. J Biol Chem 2005; 280: 18755–70.

Coma M, Guix FX, Uribesalgo I, Espuna G, Sole M, Andreu D, et al. Lack of

oestrogen protection in amyloid-mediated endothelial damage due to

protein nitrotyrosination. Brain 2005; 128: 1613–21.

Comery TA, Martone RL, Aschmies S, Atchison KP, Diamantidis G, Gong X,

et al. Acute g-secretase inhibition improves contextual fear conditioning in

the Tg2576 mouse model of Alzheimer’s disease. J Neurosci 2005;

25: 8898–902.

Cordle A, Landreth G. 3-Hydroxy-3-methylglutaryl-coenzyme a reductase

inhibitors attenuate b-amyloid-induced microglial inflammatory

responses. J Neurosci 2005; 25: 299–307.

Cotman CW, Poon WW, Rissman RA, Blurton-Jones M. The role of caspase

cleavage of tau in Alzheimer disease neuropathology. J Neuropathol Exp

Neurol 2005; 64: 104–12.

Cummings JL. What we can learn from open-label extensions of randomized

clinical trials. Arch Neurol 2006; 63: 18–9.


Dow



ecember 2021

Curry CL, Reed LL, Golde TE, Miele L, Nickoloff BJ, Foreman KE. Gamma

secretase inhibitor blocks notch activation and induces apoptosis in

Kaposi’s sarcoma tumor cells. Oncogene 2005; 24: 6333–44.

Curtain CC, Ali F, Volitakis I, Cherny RA, Norton RS, Beyreuther K, et al.

Alzheimer’s disease amyloid-b binds copper and zinc to generate an

allosterically ordered membrane-penetrating structure containing super-

oxide dismutase-like subunits. J Biol Chem 2001; 276: 20466–73.

Curtain CC, Ali FE, Smith DG, Bush AI, Masters CL, Barnham KJ. Metal

ions, pH and cholesterol regulate the interactions of Alzheimer’s

disease amyloid-b peptide with membrane lipid. J Biol Chem 2003;

278: 2977–82.

Dash PK, Moore AN, Orsi SA. Blockade of g-secretase activity within the

hippocampus enhances long-term memory. Biochem Biophys Res

Commun 2005; 338: 777–82.

Davies L, Wolska B, Hilbich C, Multhaup G, Martins R, Simms G, et al. A4

amyloid protein deposition and the diagnosis of Alzheimer’s disease:

prevalence in aged brains determined by immunocytochemistry compared

with conventional neuropathlogic techniques. Neurology 1988;

38: 1688–93.

Dodart JC, Marr RA, Koistinaho M, Gregersen BM, Malkani S, Verma IM,

et al. Gene delivery of human apolipoprotein E alters brain Ab burden in a

mouse model of Alzheimer’s disease. Proc Natl Acad Sci USA 2005;

102: 1211–6.

Dong H, Csernansky CA, Martin MV, Bertchume A, Vallera D, Csernansky JG.

Acetylcholinesterase inhibitors ameliorate behavioral deficits in the Tg2576

mouse model of Alzheimer’s disease. Psychopharmacology (Berl) 2005;

181: 145–52.

Duering M, Grimm M, Grimm HS, Schroder J, Hartmann T. Mean age of

onset in familial Alzheimer’s disease is determined by amyloid beta 42.

Neurobiol Aging 2005; 26: 785–8.

Duff K, Planel E. Untangling memory deficits. Nat Med 2005; 11: 826–7.

Dyrks T, Weidemann A, Multhaup G, Salbaum JM, Lemaire HG, Kang J, et al.

Identification, transmembrane orientation and biogenesis of the amyloid

A4 precursor of Alzheimer’s disease. EMBO J 1988; 7: 949–57.

Dyrks T, Dyrks E, Hartmann T, Masters C, Beyreuther K. Amyloidogenicity of

bA4 and bA4-bearing APP fragments by metal catalysed oxidation. J Biol

Chem 1992a; 267: 18210–7.

Dyrks T, Dyrks E, Masters C, Beyreuther K. Membrane inserted APP

fragments containing the bA4 sequence of Alzheimer’s disease do not

aggregate. FEBS Lett 1992b; 309: 20–4.

Dyrks T, Dyrks E, Masters CL, Beyreuther K. Amyloidogenicity of rodent and

human bA4 sequences. FEBS Lett 1993; 324: 231–6.

Echeverria V, Clerman A, Dore S. Stimulation of PGE2 receptors EP2 and EP4

protects cultured neurons against oxidative stress and cell death following

b-amyloid exposure. Eur J Neurosci 2005; 22: 2199–206.

Eckman EA, Eckman CB. Ab-degrading enzymes: modulators of Alzheimer’s

disease pathogenesis and targets for therapeutic intervention. Biochem Soc

Trans 2005; 33: 1101–5.

Espeseth AS, Xu M, Huang Q, Coburn CA, Jones KL, Ferrer M, et al.

Compounds that bind APP and inhibit Ab processing in vitro suggest a

novel approach to Alzheimer disease therapeutics. J Biol Chem 2005;

280: 17792–7.

Fagan AM, Mintun MA, Mach RH, Lee S-Y, Dence CS, Shah AR, et al. Inverse

relation between in vivo amyloid imaging load and cerebrospinal fluid Ab42

in humans. Ann Neurol 2006; 59: 512–9.

Farris W, Leissring MA, Hemming ML, Chang AY, Selkoe DJ. Alternative

splicing of human insulin-degrading enzyme yields a novel isoform with a

decreased ability to degrade insulin and amyloid b-protein. Biochem 2005;

44: 6513–25.

Frost D, Gorman PM, Yip CM, Chakrabartty A. Co-incorporation of Ab40

and Ab42 to form mixed pre-fibrillar aggregates. Eur J Biochem 2003;

270: 654–63.

Fukumori A, Okochi M, Tagami S, Jiang J, Itoh N, Nakayama T, et al.

Presenilin-dependent g-secretase on plasma membrane and endosomes is

functionally distinct. Biochemistry 2006; 45: 4907–14.

Fuller SJ, Storey E, Li Q-X, Smith AI, Beyreuther K, Masters CL.

Intracellular production of bA4 amyloid of Alzheimer’s disease:

modulation by phosphoramidon and lack of coupling to the secretion

of the amyloid precursor protein. Biochemistry 1995; 34: 8091–8.

Games D, Adams D, Alessandrini R, Barbour R, Berthelette P, Blackwell C,

et al. Alzheimer-type neuropathology in transgenic mice overexpressing

V717V b-amyloid precursor protein. Nature 1995; 373: 523–7.

Gilman S, Koller M, Black RS, Jenkins L, Griffith SG, Fox NC, et al. Clinical

effects of Ab immunization (AN1792) in patients with AD in an

interrupted trial. Neurol 2005; 64: 1553–62.

Glenner GG, Wong CW. Alzheimer’s disease: initial report of the purification

and characterization of a novel cerebrovascular amyloid protein. Biochem

Biophys Res Commun 1984a; 120: 885–90.

Glenner GG, Wong CW. Alzheimer’s disease and Down’s syndrome: sharing

of a unique cerebrovascular amyloid fibril protein. Biochem Biophys Res

Commun 1984b; 122: 1131–5.

Gorman PM, Yip CM, Fraser PE, Chakrabartty A. Alternate aggregation

pathways of the Alzheimer b-amyloid peptide: Ab association kinetics at

endosomal pH. J Mol Biol 2003; 325: 743–57.

Green PS, Bales K, Paul S, Bu G. Estrogen therapy fails to alter amyloid

deposition in the PDAPP model of Alzheimer’s disease. Endocrinology

2005; 146: 2774–81.

Greig NH, Utsuki T, Ingram DK, Wang Y, Pepeu G, Scali C, et al. Selective

butyrylcholinesterase inhibition elevates brain acetylcholine, augments

learning and lowers Alzheimer b-amyloid peptide in rodent. Proc Natl

Acad Sci USA 2005; 102: 17213–8.

Grimwood S, Hogg J, Jay MT, Lad AM, Lee V, Murray F, et al. Determination

of guinea-pig cortical g-secretase activity ex vivo following the systemic

administration of a g-secretase inhibitor. Neuropharmacology 2005;

48: 1002–11.

Haass C, Schlossmacher MG, Hung AY, Vigo-Pelfrey C, Mellon A,

Ostaszewski BL, et al. Amyloid b-peptide is produced by cultured cells

during normal metabolism. Nature 1992; 359: 322–5.

Harper JD, Lieber CM, Lansbury PT. Atomic force microscopic imaging of

seeded fibril formation and fibril branching by the Alzheimer’s disease

amyloid-b protein. Chem Biol 1997; 4: 951–9.

Hartman RE, Izumi Y, Bales KR, Paul SM, Wozniak DF, Holtzman DM.

Treatment with an Amyloid-b antibody ameliorates plaque load, learning

deficits, and hippocampal long-term potentiation in a mouse model of

Alzheimer’s disease. J Neurosci 2005; 25: 6213–20.

Hartmann T, Bieger SC, Bruhl B, Tienari PJ, Ida N, Allsop D, et al. Distinct

sites of intracellular production for Alzheimer’s disease Ab40/42 amyloid

peptides. Nat Med 1997; 3: 1016–20.

Hemming ML, Selkoe DJ. Amyloid b-protein is degraded by cellular

angiotensin-converting enzyme (ACE) and elevated by an ACE inhibitor.

J Biol Chem 2005; 280: 37644–50.

Heneka MT, Sastre M, Dumitrescu-Ozimek L, Hanke A, Dewachter I,

Kuiperi C, et al. Acute treatment with the PPARg agonist pioglitazone and

ibuprofen reduces glial inflammation and Ab1-42 levels in APPV717I

transgenic mice. Brain 2005; 128: 1442–53.

Hesse L, Beher D, Masters CL, Multhaup G. The bA4 amyloid precursor

protein binding to copper. FEBS Lett 1994; 349: 109–16.

Hilbich C, Kisters-Woike B, Reed J, Masters CL, Beyreuther K. Aggregation

and secondary structure of amyloid bA4 peptides of Alzheimer’s disease.

J Mol Biol 1991; 218: 149–63.

Hilbich C, Kisters-Woike B, Reed J, Masters CL, Beyreuther K. Substitutions

of hydrophobic amino acids reduce the amyloidogenicity of Alzheimer’s

disease bA4 peptides. J Mol Biol 1992; 228: 460–73.

Hoglund K, Thelen KM, Syversen S, Sjogren M, von Bergmann K, Wallin A,

et al. The effect of simvastatin treatment on the amyloid precursor protein

and brain cholesterol metabolism in patients with Alzheimer’s disease.

Dement Geriatr Cogn Disord 2005; 19: 256–65.

Huang X, Cuajungco MP, Atwood CS, Hartshorn MA, Tyndall JD,

Hanson GR, et al. Cu(II) potentiation of Alzheimer Ab neurotoxicity.

Correlation with cell-free hydrogen peroxide production and metal

reduction. J Biol Chem 1999; 274: 37111–6.

Huang TH, Yang DS, Fraser PE, Chakrabartty A. Alternate aggregation

pathways of the Alzheimer b-amyloid peptide. An in vitro model of

preamyloid. J Biol Chem 2000; 275: 36436–40.


Dow



ecember 2021

Huang D, Luthi U, Kolb P, Cecchini M, Barberis A, Caflisch A. In silico

discovery of b-secretase inhibitors. J Am Chem Soc 2006; 128: 5436–43.

Jankowsky JL, Melnikova T, Fadale DJ, Xu GM, Slunt HH, Gonzales V, et al.

Environmental enrichment mitigates cognitive deficits in a mouse model of

Alzheimer’s disease. J Neurosci 2005a; 25: 5217–24.

Jankowsky JL, Slunt HH, Gonzales V, Savonenko AV, Wen JC,

Jenkins NA, et al. Persistent amyloidosis following suppression of Ab

production in a transgenic model of Alzheimer disease. PLoS Med 2005b;

2: e355.

Kakuda N, Funamoto S, Yagishita S, Takami M, Osawa S, Dohmae N, et al.

Equimolar production of amyloid b-protein and amyloid precursor

protein intracellular domain from b-carboxyl-terminal fragment by

g-secretase. J Biol Chem 2006; 281: 14776–86.

Kanapathipillai M, Lentzen G, Sierks M, Park CB. Ectoine and hydroxyectoine

inhibit aggregation and neurotoxicity of Alzheimer’s b-amyloid. FEBS Lett

2005; 579: 4775–80.

Kang J, Lemaire H-G, Unterbeck A, Salbaum JM, Masters CL, Grzeschik KH,

et al. The precursor of Alzheimer’s disease amyloid A4 protein resembles a

cell surface receptor. Nature 1987; 325: 733–6.

Kimura M, Akasofu S, Ogura H, Sawada K. Protective effect of donepezil

against Ab(1–40) neurotoxicity in rat septal neurons. Brain Res 2005;

1047: 72–84.

Kimura T, Shuto D, Hamada Y, Igawa N, Kasai S, Liu P, et al. Design and

synthesis of highly active Alzheimer’s b-secretase (BACE1) inhibitors,

KMI-420 and KMI-429, with enhanced chemical stability. Bioorg Med

Chem Lett 2005; 15: 211–5.

Klunk WE, Engler H, Nordberg A, Wang Y, Blomquist G, Holt DP, et al.

Imaging brain amyloid in Alzheimer’s disease with Pittsburgh

compound-B. Ann Neurol 2004; 55: 306–19.

Klyubin I, Walsh DM, Lemere CA, Cullen WK, Shankar GM, Betts V, et al.

Amyloid b protein immunotherapy neutralizes Ab oligomers that disrupt

synaptic plasticity in vivo. Nat Med 2005; 11: 556–61.

Koo EH, Sisodia SS, Archer DR, Martin LJ, Weidemann A, Beyreuther K, et al.

Precursor of amyloid protein Alzheimer disease undergoes fast anterograde

axonal transport. Proc Natl Acad Sci USA 1990; 87: 1561–5.

Kornacker MG, Lai Z, Witmer M, Ma J, Hendrick J, Lee VG, et al. An inhibitor

binding pocket distinct from the catalytic active site on human b-APP

cleaving enzyme. Biochemistry 2005; 44: 11567–73.

Kumar-Singh S, Theuns J, Van Broeck B, Pirici D, Vennekens K, Corsmit E,

et al. Mean age-of-onset of familial Alzheimer disease caused by presenilin

mutations correlates with both increased Ab42 and decreased Ab40. Hum

Mutat 2006; 27: 686–95.

Lambert MP, Barlow AK, Chromy BA, Edwards C, Freed R, Liosatos M, et al.

Diffusible, nonfibrillar ligands derived from Ab1–42 are potent central

nervous system neurotoxins. Proc Natl Acad Sci USA 1998; 95:

6448–53.

Laras Y, Quelever G, Garino C, Pietrancosta N, Sheha M, Bihel F, et al.

Substituted thiazolamide coupled to a redox delivery system: a new

g-secretase inhibitor with enhanced pharmacokinetic profile. Org Biomol

Chem 2005; 3: 612–8.

Lanz TA, Hosley JD, Adams WJ, Merchant KM. Studies of Ab

pharmacodynamics in the brain, cerebrospinal fluid, and plasma in

young (plaque-free) Tg2576 mice using the g-secretase inhibitor N2-[(2S)-

2-(3,5–difluorophenyl)-2-hydroxyethanoyl]-N1-[(7S)-5-methyl-6-oxo-

6,7–dihydro-5H-dibenzo[b,d]azepin-7-yl]-L-alaninamide (LY-411575).

J Pharmacol Exp Ther 2004; 309: 49–55.

Lanz TA, Fici GJ, Merchant KM. Lack of specific amyloid-b(1-42)

suppression by nonsteroidal anti-inflammatory drugs in young, plaque-

free Tg2576 mice and in guinea pig neuronal cultures. J Pharmacol Exp

Ther 2005; 312: 399–406.

Lau T-L, Ambroggio EE, Tew DJ, Cappai R, Masters CL, Fidelio GD, et al.

Amyloid-b peptide disruption of lipid membranes and the effect of metal

ions. J Mol Biol 2006; 356: 759–70.

Laurents DV, Gorman PM, Guo M, Rico M, Chakrabartty A,

Bruix M. Alzheimer’s Ab40 studies by NMR at low pH reveals that

sodium 4,4–dimethyl-4-silapentane-1-sulfonate (DSS) binds and promotes

b-cell oligomerization. J Biol Chem 2005; 280: 3675–85.

Lazarov O, Robinson J, Tang YP, Hairston IS, Korade-Mirnics Z, Lee VM,

et al. Environmental enrichment reduces Ab levels and amyloid deposition

in transgenic mice. Cell 2005; 120: 701–13.

Le Corre S, Klafki HW, Plesnila N, Hubinger G, Obermeier A, Sahagun H. An

inhibitor of tau hyperphosphorylation prevents severe motor impairments

in tau transgenic mice. Proc Natl Acad Sci USA 2006; 103: 9673–8.

Lee EB, Leng LZ, Lee VM, Trojanowski JQ. Meningoencephalitis associated

with passive immunization of a transgenic murine model of Alzheimer’s

amyloidosis. FEBS Lett 2005; 579: 2564–8.

Lee M, Bard F, Johnson-Wood K, Lee C, Hu K, Griffith SG, et al. Ab42

immunization in Alzheimer’s disease generates Ab N-terminal antibodies.

Ann Neurol 2005; 58: 430–5.

Lee EB, Leng LZ, Zhang B, Kwong L, Trojanowski JQ, Abel T, et al. Targeting

amyloid-b peptide (Ab) oligomers by passive immunization with a

conformation-selective monoclonal antibody improves learning and

memory in Ab precursor protein (APP) transgenic mice. J Biol Chem

2006; 281: 4292–9.

Lefranc-Jullien S, Lisowski V, Hernandez JF, Martinez J, Checler F. Design

and characterization of a new cell-permeant inhibitor of the b-secretase

BACE1. Br J Pharmacol 2005; 145: 228–35.

Lesne S, Ali C, Gabriel C, Croci N, MacKenzie ET, Glabe CG, et al. NMDA

receptor activation inhibits a-secretase and promotes neuronal amyloid-b

production. J Neurosci 2005; 25: 9367–77.

Levites Y, Das P, Price RW, Rochette MJ, Kostura LA, McGowan EM, et al.

Anti-Ab42- and anti-Ab40-specific mAbs attenuate amyloid deposition

in an Alzheimer disease mouse model. J Clin Invest 2006; 116:

193–201.

Levy E, Carman MD, Fernandez-Madrid IJ, Power MD, Lieberburg I,

van Duinen SG, et al. Mutation of the Alzheimer’s disease amyloid gene

in hereditary cerebral hemorrhage, Dutch type. Science 1990; 248:

1124–6.

Lim GP, Calon F, Morihara T, Yang F, Teter B, Ubeda O, et al. A diet enriched

with the omega-3 fatty acid docosahexaenoic acid reduces amyloid burden

in an aged Alzheimer mouse model. J Neurosci 2005; 25: 3032–40.

Liu R, Barkhordarian H, Emadi S, Park CB, Sierks MR. Trehalose

differentially inhibits aggregation and neurotoxicity of beta-amyloid 40

and 42. Neurobiol Dis 2005; 20: 74–81.

Lomakin A, Teplow DB, Kirschner DA, Benedek GB. Kinetic theory of

fibrillogenesis of amyloid b-protein. Proc Natl Acad Sci USA 1997;

94: 7942–7.

Ma Q-L, Lim GP, Harris-White ME, Yang F, Ambegaokar SS, Ubeda OJ, et al.

Antibodies against b-amyloid reduce Ab oligomers, glycogen synthase

kinase-3b activation and t phosphorylation in vivo and in vitro. J Neurosci

Res 2006; 83: 374–84.

Maier M, Seabrook TJ, Lazo ND, Jiang L, Das P, Janus C, et al. Short

amyloid-b (Ab) immunogens reduce cerebral Ab load and learning deficits

in an Alzheimer’s disease mouse model in the absence of an Ab-specific

cellular immune response. J Neurosci 26: 4717–28.

Marambaud P, Zhao H, Davies P. Resveratrol promotes clearance of

Alzheimer’s disease amyloid-b peptides. J Biol Chem 2005; 280: 37377–82.

Martins RN, Harper CG, Stokes GG, Masters CL. Increased cerebral glucose

6-phosphate dehydrogenase in Alzheimer’s disease may reflect oxidative

stress. J Neurochem 1986; 46: 1042–5.

Masse I, Bordet R, Deplanque D, Al Khedr A, Richard F, Libersa C, et al.

Lipid lowering agents are associated with a slower cognitive

decline in Alzheimer’s disease. J Neurol Neurosurg Psychiatry 2005;

76: 1624–9.

Masters CL, Beyreuther K. Pathways to the discovery of the Ab amyloid of

Alzheimer’s disease. In: Alzheimer disease. A century of scientific and

clinical research. J Alz Dis (Suppl) 2006; 9: 155–161.

Masters CL, Gajdusek DC, Gibbs CJ Jr. Creutzfeldt-Jakob disease virus

isolations from the Gerstmann-Straussler syndrome. With an analysis of

the various forms of amyloid plaque deposition in the virus-induced

spongiform encephalopathies. Brain 1981; 104: 559–87.

Masters CL, Simms G, Weinman NA, Multhaup G, McDonald BL,

Beyreuther K. Amyloid plaque core protein in Alzheimer disease and

Down syndrome. Proc Natl Acad Sci USA 1985a; 82: 4245–9.


Dow



ecember 2021

Masters CL, Multhaup G, Simms G, Pottgiesser J, Martins RN, Beyreuther K.

Neuronal origin of a cerebral amyloid: neuro-fibrillary tangles of

Alzheimer’s disease contain the same protein as the amyloid of plaque

cores and blood vessels. EMBO J 1985b; 4: 2757–63.

Mathis CA, Klunk WE, Price JC, DeKosky ST. Imaging technology for

neurodegenerative diseases. Arch Neurol 2005; 62: 196–200.

McLaurin J, Kierstead ME, Brown ME, Hawkes CA, Lambermon MHL,

Phinney AL, et al. Cyclohexanehexol inhibitors of Ab aggregation prevent

and reverse Alzheimer phenotype in a mouse model. Nat Med 2006;

12: 801–9.

McLean CA, Cherny RA, Fraser FW, Fuller SJ, Smith MJ, Beyreuther K, et al.

Soluble pool of Ab as a determinant of severity of neurodegeration in

Alzheimer’s disease. Ann Neurol 1999; 46: 860–6.

Merz PA, Wisniewski HM, Somerville RA, Bobin SA, Masters CL, Iqbal K.

Ultrastructural morphology of amyloid fibrils from neuritic and amyloid

plaques. Acta Neuropathol 1983; 60: 113–24.

Michaelis ML, Ansar S, Chen Y, Reiff ER, Seyb KI, Himes RH, et al.

b-amyloid-induced neurodegeneration and protection by structurally

diverse microtubule-stabilizing agents. J Pharmacol Exp Ther 2005;

312: 659–68.

Morihara T, Teter B, Yang F, Lim GP, Boudinot S, Boudinot FD, et al.

Ibuprofen suppresses interleukin-1b induction of pro-amyloidogenic

a1-antichymotrypsin to ameliorate b-amyloid (Ab) pathology in

Alzheimer’s models. Neuropsychopharmacology 2005; 30: 1111–20.

Morohashi Y, Kan T, Tominari Y, Fuwa H, Okamura Y, Watanabe N, et al.

C-terminal fragment of presenilin is the molecular target of a dipeptidic

g-secretase-specific inhibitor DAPT (N-[N-(3,5–difluorophenacetyl)-

L-alanyl]-S-phenylgylcine t-butyl ester). J Biol Chem 2006; 281:

14670–6.

Multhaup G, Bush AI, Pollwein P, Masters CL. Interaction between the zinc

(II) and the heparin binding site of the Alzheimer’s disease bA4 amyloid

precursor protein (APP). FEBS Lett 1994; 355: 151–4.

Multhaup G, Mechler H, Masters CL. Characterization of the high affinity

heparin binding site of the Alzheimer’s disease bA4 amyloid precursor

protein (APP) and its enhancement by zinc (II). J Mol Recognit 1995;

8: 247–57.

Multhaup G, Schlicksupp A, Hesse L, Beher D, Ruppert T, Masters CL, et al.

The amyloid precursor protein of Alzheimer’s disease in the reduction of

copper (II) to copper (I). Science 1996; 271: 1406–9.

Multhaup G, Ruppert T, Schlicksupp A, Hesse L, Bill E, Pipkorn R, et al.

Copper-binding amyloid precursor protein undergoes a site-specific

fragmentation in the reduction of hydrogen peroxide. Biochemistry 1998;

37: 7224–30.

Mukrasch MD, Biernat J, von Bergen M, Griesinger C, Mandelkow E,

Zweckstetter M. Sites of tau important for aggregation populate

b-structure and bind to microtubules and polyanions. J Biol Chem

2005; 280: 24978–86.

Nathan C, Calingasan N, Nezezon J, Ding A, Lucia MS, La Perle K, et al.

Protection from Alzheimer’s-like disease in the mouse by genetic ablation

of inducible nitric oxide synthase. J Exp Med 2005; 202: 1163–9.

Necula M, Chirita CN, Kuret J. Cyanine dye N744 inhibits tau fibrillization by

blocking filament extension: implications for the treatment of tauopathic

neurodegenerative diseases. Biochemistry 2005; 44: 10227–37.

Noble W, Planel E, Zehr C, Olm V, Meyerson J, Suleman F, et al. Inhibition of

glycogen synthase kinase-3 by lithium correlates with reduced tauopathy

and degeneration in vivo. Proc Natl Acad Sci USA 2005; 102: 6990–5.

Okura Y, Miyakoshi A, Kohyama K, Park I-K, Staufenbiel M, Matsumoto Y.

Nonviral Ab DNA vaccine therapy against Alzheimer’s disease: long-term

effects and safety. Proc Natl Acad Sci USA 2006; 103: 9619–24.

Opazo C, Huang XD, Cherny RA, Moir RD, Roher AE, White AR, et al.

Metalloenzyme-like activity of Alzheimer’s disease b-amyloid:

Cu-dependent catalytic conversion of dopamine, cholesterol and biological

reducing agents to neurotoxic H2O2. J Biol Chem 2002; 277: 40302–8.

Papassotiropoulos A, Lambert JC, Wavrant-De Vrieze F, Wollmer MA,

van der Kammer H, Streffer JR, et al. Cholesterol 25-hydroxylase on

chromosome 10q is a susceptibility gene for sporadic Alzheimer’s disease.

Neurodegener Dis 2005; 2: 233–41.

Peretto I, Radaelli S, Parini C, Zandi M, Raveglia LF, Dondio G, et al.

Synthesis and biological activity of flurbiprofen analogues as selective

inhibitors of b-amyloid1–42 secretion. J Med Chem 2005; 48: 5705–20.

Qu B, Boyer PJ, Johnston SA, Hynan LS, Rosenberg RN. Ab42 gene

vaccination reduces brain amyloid plaque burden in transgenic mice.

J Neurol Sci 2006; 244: 151–8.

Quelever G, Kachidian P, Melon C, Garino C, Laras Y, Pietrancosta N, et al.

Enhanced delivery of g-secretase inhibitor DAPT into the brain via an

ascorbic acid mediated strategy. Org Biomol Chem 2005; 3:

2450–7.

Quintanilla RA, Munoz FJ, Metcalfe MJ, Hitschfeld M, Olivares G, Godoy JA,

et al. Trolox and 17b-estradiol protect against amyloid b-peptide

neurotoxicity by a mechanism that involves modulation of the Wnt

signaling pathway. J Biol Chem 2005; 280: 11615–25.

Quon D, Wang Y, Catalano R, Marian Scardina J, Murakami K, Cordell B.

Formation of b-amyloid protein deposits in brains of transgenic mice.

Nature 1991; 352: 239–41.

Racke MM, Boone LI, Hepburn DL, Parsadainian M, Bryan MT, Ness DK,

et al. Exacerbation of cerebral amyloid angiopathy-associated microhe-

morrhage in amyloid precursor protein transgenic mice by immunother-

apy is dependent on antibody recognition of deposited forms of amyloid b.

J Neurosci 2005; 25: 629–36.

Ramırez BG, Blazquez C, Gomez del Pulgar T, Guzman M, de Ceballos ML.

Prevention of Alzheimer’s disease pathology by cannabinoids:

neuroprotection mediated by blockade of microglial activation. J Neurosci

2005; 25: 1904–13.

Reynolds MR, Berry RW, Binder LI. Site-specific nitration and oxidative

dityrosine bridging of the t protein by peroxynitrite: implications for

Alzheimer’s disease. Biochemistry 2005a; 44: 1690–700.

Reynolds MR, Berry RW, Binder LI. Site-specific nitration dif-

ferentially influences t assembly in vitro. Biochemistry 2005b;

44: 13997–4009.

Reynolds MR, Lukas TJ, Berry RW, Binder LI. Peroxynitrite-mediated t

modifications stabilize preformed filaments and destabilize

microtubules through distinct mechanisms. Biochemistry 2006;

45: 4314–26.

Rezai-Zadeh K, Shytle D, Sun N, Mori T, Hou H, Jeanniton D, et al. Green tea

epigallocatechin-3-gallate (EGCG) modulates amyloid precursor protein

cleavage and reduces cerebral amyloidosis in Alzheimer transgenic mice.

J Neurosci 2005; 25: 8807–14.

Ritchie CW, Bush AI, Mackinnon A, Macfarlane S, Mastwyk M, MacGregor L,

et al. Metal-protein attenuation with iodochlorydroxyquin clioquinol)

targeting Ab amyloid deposition and toxicity in Alzheimer disease: a pilot

phase 2 clinical trial. Arch Neurol 2003; 60: 1685–91.

Rodriguez-Martin T, Garcia-Blanco MA, Mansfield SG, Grover AC,

Hutton M, Yu Q, et al. Reprogramming of tau alternative splicing by

spliceosome-mediated RNA trans-splicing: implications for tauopathies.

Proc Natl Acad Sci USA 2005; 102: 15659–64.

Rowan MJ, Klyubin I, Wang Q, Anwyl R. Synaptic plasticity disruption by

amyloid b protein: modulation by potential Alzheimer’s disease modifying

therapies. Biochem Soc Trans 2005; 33: 563–7.

Rumble B, Retallack R, Hilbich C, Simms G, Multhaup G, Martins R, et al.

Amyloid A4 protein and its precursor in Down’s syndrome and Alzheimer’s

disease. N Eng J Med 1989; 320: 1446–52.

Saido TC, Iwata N. Metabolism of amyloid b peptide and pathogenesis of

Alzheimer’s disease: towards presymptomatic diagnosis, prevention and

therapy. Neurosci Res 2006; 54: 235–53.

Saito T, Iwata N, Tsubuki S, Takaki Y, Takano J, Huang SM, et al.

Somatostatin regulates brain amyloid b peptide Ab42 through modulation

of proteolytic degradation. Nat Med 2005; 11: 434–9.

Santa-Maria I, Hernandez F, Smith MA, Perry G, Avila J, Moreno FJ.

Neurotoxic dopamine quinone facilitates the assembly of tau into fibrillar

polymers. Mol Cell Biochem 2005; 278: 203–12.

Sastre M, Dewachter I, Rossner S, Bogdanovic N, Rosen E, Borghgraef P, et al.

Nonsteroidal anti-inflammatory drugs repress b-secretase gene promoter

activity by the activation of PPARg. Proc Natl Acad Sci USA 2006;

103: 443–8.


Dow



ecember 2021

Santacruz K, Lewis J, Spires T, Paulson J, Kotilinek L, Ingelsson M, et al. Tau

suppression in a neurodegenerative mouse model improves memory

function. Science 2005; 309: 476–81.

Sato T, Tanimura Y, Hirotani N, Saido TC, Morishima-Kawashima M,

Ihara Y. Blocking the cleavage at midportion between g- and «-sites

remarkably suppresses the generation of amyloid b-protein. FEBS Lett

2005; 579: 2907–12.

Schneider A, Schulz-Schaeffer W, Hartmann T, Schulz JB, Simons M.

Cholesterol depletion reduces aggregation of amyloid-beta peptide in

hippocampal neurons. Neurobiol Dis 2006; 23: 573–7.

Shemer I, Holmgren C, Min R, Fulop L, Zilberter M, Sousa KM, et al. Non-

fibrillar b-amyloid abates spike-timing-dependent synaptic potentiation at

excitatory synapses in layer 2/3 of the neocortex by targeting postsynaptic

AMPA receptors. Eur J Neurosci 2006; 23: 2035–47.

Sherrington R, Liang Y, Rogaeva EA, Levesque G, Ikeda M, Chi H, et al.

Cloning of a gene bearing missense mutations in early-onset familial

Alzheimer’s disease. Nature 1995; 375: 754–60.

Shoji M, Golde TE, Ghiso J, Cheung TT, Estus S, Shaffer LM, et al. Production

of the Alzheimer amyloid b protein by normal proteolytic processing.

Science 1992; 258: 126–9.

Siemers E, Skinner M, Dean RA, Gonzales C, Satterwhite J, Farlow M, et al.

Safety, tolerability, and changes in amyloid b concentrations after

administration of a g-secretase inhibitor in volunteers. Clin Neurophar-

macol 2005; 28: 126–32.

Siemers ER, Quinn JF, Kaye J, Farlow MR, Porsteinsson A, Tariot P, et al.

Effects of a g-secretase inhibitor in a randomized study of patients with

Alzheimer disease. Neurol 2006; 66: 602–4.

Sinha S, Anderson JP, Barbour R, Basi GS, Caccavello R, Davis D, et al.

Purification and cloning of amyloid precursor protein b-secretase from

human brain. Nature 1999; 402: 537–40.

Singer O, Marr RA, Rockenstein E, Crews L, Coufal NG, Gage FH, et al.

Targeting BACE1 with siRNAs ameliorates Alzheimer disease neuropatho-

logy in a transgenic model. Nat Neurosci 2005; 8: 1343–9.

Smith DP, Smith DG, Curtain CC, Boas JF, Pilbrow JR, Ciccotosto GD, et al.

Cu2+ mediated amyloid b toxicity with an intermolecular histidine bridge.

J Biol Chem 2006; 281: 15145–54.

Snyder EM, Nong Y, Almeida CG, Paul S, Moran T, Choi EY, et al. Regulation

of NMDA receptor trafficking by amyloid-b. Nat Neurosci 2005; 8: 1051–8.

Sorimachi K, Craik DJ, Lloyd EJ, Beyreuther K, Masters CL. Identification of a

b-turn in the tertiary structure of a peptide fragment of the Alzheimer

amyloid protein. Biochem Internat 1990; 22: 447–54.

Sparey T, Beher D, Best J, Biba M, Castro JL, Clarke E, et al. Cyclic sulfamide

g secretase inhibitiors. Bioorg Med Chem Lett 2005; 15: 4212–6.

Spielmeyer W. Histopathologie des Nervensystems. Berlin: Julius Springer,

1992. p. 493.

Sultana R, Ravagna A, Mohmmad-Abdul H, Calabrese V, Butterfield DA.

Ferulic acid ethyl ester protects neurons against amyloid b-peptide(1–42)-

induced oxidative stress and neurotoxicity: relationship to antioxidant

activity. J Neurochem 2005; 92: 749–58.

Tabner BJ, El-Agnaf OMA, Turnbull S, German MJ, Paleologou KE,

Hayashi Y, et al. Hydrogen peroxide is generated during the very early

stages of aggregation of the amyloid peptides implicated in Alzheimer

disease and familial British dementia. J Biol Chem 2005; 280:

35789–92.

Taniguchi S, Suzuki N, Masuda M, Hisanaga S, Iwatsubo T, Goedert M, et al.

Inhibition of heparin-induced tau filament formation by phenothiazines,

polyphenols, and porphyrins. J Biol Chem 2005; 280: 7614–23.

Tickler AK, Smith DG, Ciccotosto GD, Tew DJ, Curtain CC, Carrington D,

et al. Methylation of the imidazole side chains of the Alzheimer’s disease

amyloid-b peptide results in abolition of SOD-like structures and

inhibition of neurotoxicity. J Biol Chem 2005; 280: 13355–63.

Tienari PJ, De Strooper B, Ikonen E, Simons M, Weidemann A, Czech C, et al.

The b-amyloid domain is essential for axonal sorting of amyloid precursor

protein. EMBO J 1996; 15: 5218–29.

Tienari PJ, Ida N, Ikonen E, Simons M, Weidemann A, Multhaup G, et al.

Intracellular and secreted Alzheimer b-amyloid species are generated by

distinct mechanisms in cultured hippocampal neurons. Proc Natl Acad Sci

USA 1997; 94: 4125–30.

Tong Y, Zhou W, Fung V, Christensen MA, Qing H, Sun X, et al. Oxidative

stress potentiates BACE1 gene expression and Ab generation. J Neural

Transm 2005; 112: 455–69.

van Broeckhoven C, Haan J, Bakker E, Hardy JA, van Hul W, Wehnert A, et al.

Amyloidb protein precursor gene and hereditary cerebral hemorrhage with

amyloidosis (Dutch). Science 1990; 248: 1120–2.

Van Dam D, Abramowski D, Staufenbiel M, De Deyn PP. Symptomatic

effect of donepezil, rivastigmine, galantamine and memantine on

cognitive deficits in the APP23 model. Psychopharmacology (Berl)

2005; 180: 177–90.

van Es JH, van Gijn ME, Riccio O, van den Born M, Vooijs M, Begthel H, et al.

Notch/g-secretase inhibition turns proliferative cells in intestinal crypts

and adenomas into goblet cells. Nature 2005; 435: 959–63.

Walsh DM, Lomakin A, Benedek GB, Condron MM, Teplow DB. Amyloid

b-protein fibrillogenesis—detection of a protofibrillar intermediate. J Biol

Chem 1997; 272: 22364–72.

Walsh DM, Townsend M, Podlisny MB, Shankar GM, Fadeeva JV, Agnaf OE,

et al. Certain inhibitors of synthetic amyloid b-peptide (Ab) fibrillogenesis

block oligomerization of natural Ab and thereby rescue long-term

potentiation. J Neurosci 2005; 25: 2455–62.

Wang J, Ho L, Qin W, Rocher AB, Seror I, Humala N, et al. Caloric restriction

attenuates b-amyloid neuropathology in a mouse model of Alzheimer’s

disease. FASEB J 2005; 19: 659–61.

Wang SS, Chen YT, Chou SW. Inhibition of amyloid fibril formation of

b-amyloid peptides via the amphiphilic surfactants. Biochim Biophys Acta

2005; 1741: 307–13.

Weidemann A, Konig G, Bunke D, Fischer P, Salbaum JM, Masters CL, et al.

Identification, biogenesis and localization of precursors of Alzheimer’s

disease A4 amyloid protein. Cell 1989; 57: 115–26.

Westlind-Danielsson A, Arnerup G. Spontaneous in vitro formation of

supramolecular b-amyloid structures, ‘bamy balls’, by b-amyloid 1-40

peptide. Biochem 2001; 40: 14736–43.

White AR, Zheng H, Galatis D, Maher F, Hesse L, Multhaup G, et al. Survival

of cultured neurons from amyloid precursor protein knock-out mice

against Alzheimer’s amyloid-b toxicity and oxidative stress. J Neurosci

1998; 18: 6207–17.

White AR, Guirguis R, Brazier MW, Jobling MF, Hill AF, Beyreuther K, et al.

Sublethal concentrations of prion peptide PrP106-126 or the

amyloid beta peptide of Alzheimer’s disease activates expression of

pro-apoptotic markers in primary cortical neurons. Neurobiol Dis 2001;

8: 299–316.

Xie Z, Romano DM, Tanzi RE. Effects of RNAi-mediated silencing of PEN-2,

APH–1a, and Nicas wild-type vs FAD mutant forms of presenilin 1. J Mol

Neurosci 2005a; 25: 67–77.

Xie Z, Romano DM, Tanzi RE. RNA interference-mediated silencing of

X11a and X11b attenuates amyloid b-protein levels via differential effects

on b-amyloid precursor protein processing. J Biol Chem 2005b;

280: 15413–21.

Yagashita S, Morishima-Kawashima M, Tanimura Y, Ishiura S, Ihara Y.

DAPT-induced intracellular accumulations of longer amyloid b-proteins:

further implications for the mechanism of intramembrane cleavage by

g-secretase. Biochemistry 2006; 45: 3952–60.

Yamada K, Takayanagi M, Kamei H, Nagai T, Dohniwa M, Kobayashi K, et al.

Effects of memantine and donepezil on amyloid b-induced memory

impairment in a delayed-matching to position task in rats. Behav Brain Res

2005; 162: 191–99.

Yang F, Lim GP, Begum AN, Ubeda OJ, Simmons MR, Ambegaokar SS,

et al. Curcumin inhibits formation of amyloid b oligomers and fibrils,

binds plaques, and reduces amyloid in vivo. J Biol Chem 2005;

280: 5892–901.

Yong W, Lomakin A, Kirkitadze MD, Teplow DB, Chen SH, Benedek GB.

Structure determination of micelle-like intermediates in amyloid b-protein

fibril assembly by using small angle neutron scattering. Proc Natl Acad Sci

USA 2002; 99: 150–4.


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ecember 2021

Youm JW, Kim H, Han JH, Jang CH, Ha HJ, Mook-Jung I, et al. Transgenic

potato expressing Ab reduce Ab burden in Alzheimer’s disease mouse

model. FEBS Lett 2005; 579: 6737–44.

Yue X, Lu M, Lancaster T, Cao P, Honda S, Staufenbiel M, et al. Brain estrogen

deficiency accelerates Ab plaque formation in an Alzheimer’s disease

animal model. Proc Natl Acad Sci USA 2005; 102: 19198–203.

Zhang YJ, Xu YF, Chen XQ, Wang XC, Wang JZ. Nitration and

oligomerization of tau induced by peroxynitrite inhibit its microtubule-

binding activity. FEBS Lett 2005; 579: 2421–7.

Zimmermann M, Borroni B, Cattabeni F, Padovani A, Di Luca M.

Cholinesterase inhibitors influence APP metabolism in Alzheimer disease

patients. Neurobiol Dis 2005; 19: 237–42.


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Alzheimer's centennial legacy: prospects for rational therapeutic

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