26, Number 2, September 2011
Ian A. Clark, Lisa M. Allev, Bryce Vissel
TNF and Leptin Tell Essentially the Same Story in Alzheimer’s Disease
Abstract: Both tumor necrosis factor and leptin are, independently, under investigation as the central mechanism for Alzheimer’s disease. The wider literature provides every indication that both mediators are part of the same pathways thought to cause functional loss in this condition. This association, which has not been specifically addressed in the Alzheimer’s disease literature, may be a useful link to expedite future study into the pathogenesis of this condition.
Panagiotis Alexopoulos, Tanja Richter-Schmidinger, Marco Horn, Sebastian Maus, Martin Reichel, Christos Sidiropoulos, Cosima Rhein, Piotr Lewczuk, Arnd Doerfler, Johannes Kornhuber
Hippocampal Volume Differences Between Healthy Young Apolipoprotein E ε2 and ε4 Carriers
Abstract: The apolipoprotein E (APOE) ε4 allele is the major genetic risk factor for the development of late-onset Alzheimer’s disease (AD), whereas the presence of the APOE ε2 allele seems to confer protection. Here, we report that healthy young APOE ε4 carriers have statistically significantly smaller hippocampal volumes than APOE ε2 carriers, while no differences were detected between the two groups in memory performance. The difference in hippocampal morphology is cognitively/clinically silent in young adulthood, but could render APOE ε4 carriers more prone to the later development of AD possibly due to lower reserve cognitive capacity.
Elio Scarpini, Giuseppe Bruno, Giuseppe Zappalà, Marina Adami, Ute Richarz, Maren Gaudig, Adam Jacobs, Barbara Schäuble (Handling Associate Editor: Daniela Galimberti)
Cessation versus Continuation of Galantamine Treatment after 12 Months of Therapy in Patients with Alzheimer’s Disease: A Randomized, Double Blind, Placebo Controlled Withdrawal Trial
Abstract: Galantamine improved symptoms in Alzheimer’s disease (AD) patients after 5 to 6 months of treatment. To examine long-term outcomes, this study assessed if continuing of galantamine treatment beyond 12 months delayed further cognitive deterioration. It consisted of two phases: an open label (OL) phase (12 months), followed by a double blind, randomized, placebo controlled withdrawal phase (up to 24 months). Subjects with mild to moderate AD were included in the study and titrated up to 16 mg/day of galantamine. Subjects were eligible to enter the double blind phase if a cognitive decline of < 4 points on AD Assessment Scale-cognitive subscale (ADAS-cog)/11 was recorded at the end of the OL phase. The differences between galantamine and placebo in time to dropout were estimated using the Cox proportional hazard model. 47.4% of galantamine and 31.7% of placebo subjects completed the double blind phase. Placebo subjects were more likely to discontinue prematurely than galantamine subjects for any reason (hazard ratio [HR] 1.76, 95% confidence interval [CI] 1.10–2.81, p = 0.02), or lack of efficacy (HR 1.80, 95% CI 1.02–3.18, p = 0.04); no statistically significant difference was seen for a change in ADAS-cog ≥ 4 between treatment groups (HR 1.66, 95% CI 0.78–3.54, p = 0.19). Subjects who responded to 12 months of galantamine treatment benefited from continued drug therapy for up to 36 months. Galantamine was effective in delaying time to cognitive deterioration in subjects with mild to moderate AD. Treatment was generally safe and well tolerated.
Ivan Aprahamian, José Eduardo Martinelli, Juliana Cecato, Mônica Sanches Yassuda (Handling Associate Editor: Julián Benito-León)
Screening for Alzheimer's Disease Among Illiterate Elderly: Accuracy Analysis for Multiple Instruments
Abstract: One of the challenges in screening for dementia in developing countries is related to performance differences due to educational and cultural factors. This study evaluated the accuracy of single screening tests as well as combined protocols including the Mini-Mental State Examination (MMSE), Verbal Fluency animal category (VF), Clock Drawing test (CDT), and Pfeffer Functional Activities Questionnaire (PFAQ) to discriminate illiterate elderly with and without Alzheimer’s disease (AD) in a clinical sample. Cross-sectional study with 66 illiterate outpatients diagnosed with mild and moderate AD and 40 illiterate normal controls. Diagnosis of AD was based on NINCDS-ADRDA. All patients were submitted to a diagnostic protocol including a clinical interview based on the CAMDEX sections. ROC curves area analyses were carried out to compare sensitivity and specificity for the cognitive tests to differentiate the two groups (each test separately and in two by two combinations). Scores for all cognitive (MMSE, CDT, VF) and functional assessments (PFAQ) were significantly different between the two groups (p < 0.001). The best screening instruments for this sample of illiterate elderly were the MMSE and the PFAQ. The cut-off scores for the MMSE, VF, CDT, and PFAQ were 17.5, 7.5, 2.5, and 11.5, respectively. The most sensitive combination came from the MMSE and PFAQ (94.1%), and the best specificity was observed with the combination of the MMSE and CDT (89%). Illiterate patients can be successfully screened for AD using well-known screening instruments, especially in combined protocols.
J Simon Bell, Eija Lönnroos, Anne M Koivisto, Piia Lavikainen, Marja-Liisa Laitinen, Hilkka Soininen, Sirpa Hartikainen
Use of Antiepileptic Drugs Among Community-Dwelling Persons with Alzheimer’s Disease in Finland
Abstract: Persons with Alzheimer’s disease (AD) may be particularly susceptible to the adverse drug reactions associated with anti-epileptic drugs (AEDs). The objective of this study was to investigate the national pattern of AED use among community-dwelling persons with and without AD in Finland. All persons (n= 28,093) with a diagnosis of AD in 2005 were identified by the Social Insurance Institution of Finland (SII). The SII also identified comparison persons without AD individually matched in terms of age (± one year), gender, and region. Records of all reimbursed drug purchases in 2005 were extracted from the Finnish National Prescription Register. Conditional logistic regression was used to calculate unadjusted and adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for reimbursed AED use. Persons with and without AD were aged 42 to 101 (mean 80.0) years, with men comprising 32.2% (n=9,048) of persons. Epilepsy was diagnosed for 2.1% of persons with AD compared to 1.3% of persons without AD (OR 1.66; 95% CI, 1.45 to 1.89). AEDs were used by 5.0% (n=1417) of persons with AD compared to 3.4% (n=955) persons without AD (adjusted OR 1.33; 95% CI, 1.21 to 1.46). The annual prevalence of phenytoin, clonazepam, valproic acid, and oxcarbazepine use was higher among persons with AD. In contrast, pregabalin use was lower among persons with AD (adjusted OR 0.83; 95% CI, 0.70 to 0.99). Use of older AEDs is more prevalent among persons with AD, despite persons with AD being particularly vulnerable to adverse drug reactions associated with many older AEDs.
Paul C. R. Hopkins, Ricardo Sáinz-Fuertes, Simon Lovestone (Handling Associate Editor: Toshiharu Suzuki)
The Impact of a Novel Apolipoprotein E and Amyloid-β Protein Precursor-Interacting Protein on the Production of Amyloid-β
Abstract: Alzheimer’s disease (AD) is characterized by disrupted metabolism of the amyloid-β protein precursor (AβPP) and deposition of a byproduct, the amyloid-β (Aβ) peptide, into plaques. AD is also genetically linked to the gene for apolipoprotein E (apoE). We have identified a novel apoE-binding protein (TMCC2) that also forms a complex with AβPP. TMCC2 is a neuronal, predominantly ER-localized, protein that co-migrated with AβPP during native gel electrophoresis of rat brain extracts, and co-immunoprecipitated with AβPP from transfected human cell lysates. TMCC2 bound apoE in an isoform-specific manner in vitro and co-immunoprecipitated with apoE from cell lysates. Co-expression of apoE and TMCC2 stimulated Aβ production from the “Swedish” variant of AβPP (K595M/N596L) by up to 1.5-fold (p<0.05), and also from the 99-amino acid C-terminal fragment of AβPP (AβPP-C99) that is the direct precursor to Aβ by 1.5- to 2-fold (p<0.0005), this effect was greater with apoE4 than apoE3 (p=0.02); both apoE3 and apoE4 stimulated a greater increase in Aβ1-42 than Aβ1-40 production from AβPP-C99 in the presence of TMCC2. The interaction between TMCC2 and apoE may therefore contribute to disrupted AβPP metabolism and altered Aβ production, as observed in AD.
Carola G. Schipke, Frank Jessen, Stefan Teipel, Christian Luckhaus, Jens Wiltfang, Hermann Esselmann, Lutz Frölich, Wolfgang Maier, Eckart Rüther, Frank L. Heppner, Stefan Prokop, Isabella Heuser, Oliver Peters
Long-Term Stability of Alzheimer’s Disease Biomarker Proteins in Cerebrospinal Fluid
Abstract: The quantitative analysis of peptides in human cerebrospinal fluid (CSF) has become an important step in the early diagnosis of dementia, e.g., Alzheimer’s disease. In search of new biomarkers for early detection and differential diagnosis of chronic neurodegenerative diseases, “biobanking” and long-term storage of human samples is increasingly important. The German Dementia Competence Network has accomplished one of the largest biomaterial banks in this field, comprising CSF from several hundreds of patients. Since little is known about long-term stability of biomarker proteins in frozen CSF, we investigated the reliability of quantitative analysis in a total of 56 CSF samples that had been frozen for up to six years. Here, we compare a second quantitative analysis of Aβ40, Aβ42, and the total-tau protein after several years of storage at -80°C with initial results obtained within six months after lumbar puncture. The second analysis was done using standard ELISAs or the newly developed Mesocale System. We found that regarding Aβ42 and total-tau, the results highly correlate with correlation coefficients of c=0.73 and c=0.82 respectively, while for Aβ40 the correlation coefficient was lower (c=0.53), suggesting that Aβ40 is more vulnerable to degradation. We conclude that the quantitative analysis of the concentration of Aβ42, as well as for total-tau, in CSF in samples that have been stored for years is reliable. The determination of these biomarkers and potentially new biomarkers in CSF samples stored in large biomaterial banks assembled over many years is feasible.
Supplementary Data for Schipke et al. article (PDF)
Elena L. Paley
Tryptamine-Induced Tryptophanyl-tRNAtrp Deficiency in Neurodifferentiation and Neurodegeneration Interplay: Progenitor Activation with Neurite Growth Terminated in Alzheimer’s Disease Neuronal Vesicularization and Fragmentation
Abstract: Tryptophanyl-tRNA synthetase (TrpRS) catalyzes tryptophanyl-tRNAtrp formation. At concentrations exceeding tryptophan, tryptamine inhibits TrpRS. This leads in tryptophanyl-tRNA deficiency and synthesis of aberrant proteins. Tryptamine presents in food and crosses blood-brain barrier. The purpose of this study is to test the hypothesis that tryptamine-induced changes in cell and animal models correlate with Alzheimer’s disease (AD) manifestations. Tryptamine prevented growth of human neuroblastoma. Epithelioids recovered growth in tryptamine-free medium, while neuroblasts died. Tryptamine induced epithelioid differentiation forming synaptic vesicles, neuritic contacts, and TrpRS+ axons in stable sublines. A fraction of epithelioids was adhered to satellite cells via trypsin-resistant interdigitating junctions. Tryptamine stimulated satellite division and differentiation into neurons, transitional cell variants and neuroblasts able to repopulate. Both tryptamine-inhibited and hypoxia-downregulated TrpRS translocates into cytoplasmic extensions. TrpRS is secreted into extracellular space as a free protein or within vesicles extended from cytoplasm and then pinched-off from plasma membrane of tryptamine-treated cells. Extracellular vesicles fuse incongophilic TrpRS+ plaques in tryptamine-treated culture and AD brain. TrpRS prominent immunoreactivity is associated with plasma and vesicle membranes of satellites and AD brain degenerated neurons. Tryptamine-modified mouse brain expresses amyloid and abnormal filaments in extracellular and neuronal plasma membrane vesicles. Radiolabeled tryptamine, tryptophan and serotonin uptake was 10-fold lower in tryptamine-resistant compared to tryptamine-sensitive cells. In both variants, tryptamine uptake exceeded tryptophan uptake within 2-h assuring TrpRS inhibition. Here, tryptophanyl-tRNAtrp deficiency implicates in both neurite growth and termination/collapse. Neurite growth termination prompts TrpRS+ vesicularization. TrpRS+ vesicles contribute in neuronal fragmentation and fibrillar-vesicular congophilic plaques in AD brain.
Supplementary Data for Paley et al. article (PDF)
Yang Hui, Dayong Wang, Wenjing Li, Lina Zhang, Jianfeng Jin, Ning Ma, Lingyun Zhou, Osamu Nakajima, Weiming Zhao, Xu Gao (Handling Associate Editor: Wolff Kirsch)
Long-Term Overexpression of Heme Oxygenase 1 Promotes Tau Aggregation in Mouse Brain by Inducing Tau Phosphorylation
Abstract: Intracellular tau aggregates composed of neurofibrillary tangles (NFTs) are a defining feature of Alzheimer’s disease (AD). Increased expression of heme oxygenase-1 (HO-1) is a common phenomenon in AD. Interestingly, the spatial distribution of HO-1 expression is essentially identical to that of pathological accumulation of tau in AD. In this study, we developed a new transgenic mouse overexpressing HO-1, called CAG-HO-1 Tg mice, to explore the relationship between HO-1 and tau aggregation. In this model, we found that long-term overexpression of HO-1 significantly promoted tau aggregation in brain, by analyzing changes in morphology and insoluble tau expression levels. Moreover, our research provides the first in vivo evidence that HO-1 can enhance iron loading and tau (Ser199/202/396) phosphorylation in brains of transgenic mice. Cellular evidence indicates that HO-1 can induce the phosphorylation of tau through iron accumulation in Neuro2a cells stably transfected with HO-1. Our data suggest that long-term overexpression of HO-1 can promote tau aggregation. This mechanism involves excessive iron production mediated by HO-1 overexpression, which induces tau phosphorylation. Our results provide a potential pathway for the pathogenesis of tauopathies, which remains largely unknown.
Cristina Ploia*, Xanthi Antoniou*, Alessandra Sclip, Valentina Grande, Daniele Cardinetti, Alessio Colombo, Nadia Canu, Luisa Benussi, Roberta Ghidoni, Gianluigi Forloni, Tiziana Borsello *These two authors contributed equally to this work.
JNK Plays a Key Role in Tau Hyperphosphorylation in Alzheimer’s Disease Models
Abstract: Alzheimer’s disease (AD) is a major clinical concern, and the search for new molecules to combat disease progression remains important. One of the major hallmarks in AD pathogenesis is the hyperphosphorylation of tau and subsequent formation of neurofibrillary tangles. Several kinases are involved in this process. Amongst them, c-Jun N-terminal kinases (JNKs) are activated in AD brains and are also associated with the development of amyloid plaques. This study was designed to investigate the contribution of JNK in tau hyperphosphorylation and whether it may represent a potential therapeutic target for the fight against AD. The specific inhibition of JNK by the cell permeable peptide D-JNKI-1 led to a reduction of p-tau at S202/T205 and S422, two established target sites of JNK, in rat neuronal cultures and in human AD fibroblasts cultures. Similarly, D-JNKI-1 reduced p-tau at S202/T205 in an in vivo model of AD (TgCRND8 mice). Our findings support the fundamental role of JNK in the regulation of tau hyperphosphorylation and subsequently in AD pathogenesis.
Claudio Babiloni, Roberta Lizio, Filippo Carducci, Fabrizio Vecchio, Alberto Redolfi, Silvia Marino, Gioacchino Tedeschi, Patrizia Montella, Antonio Guizzaro, Fabrizio Esposito, Alessandro Bozzao, Franco Giubilei, Francesco Orzi, Carlo C. Quattrocchi, Andrea Soricelli, Elena Salvatore, Annalisa Baglieri, Placido Bramanti, Marina Boccardi, Raffaele Ferri, Filomena Cosentino, Michelangelo Ferrara, Ciro Mundi, Gianpaolo Grilli, Silvia Pugliese, Gianluca Gerardi, Laura Parisi, Fabrizio Vernieri, Antonio I. Triggiani, Jan T. Pedersen, Hans-Göran Hårdemark, Paolo M.Rossini, Giovanni B. Frisoni
Resting State Cortical Electroencephalographic Rhythms and White Matter Vascular Lesions in Subjects with Alzheimer’s Disease: An Italian Multicenter Study
Abstract: Resting state electroencephalographic (EEG) rhythms do not deteriorate with the increase of white matter vascular lesion in amnesic mild cognitive impairment (MCI) subjects , although white matter is impaired along Alzheimer’s disease (AD). Here we tested whether this is true even in AD subjects. Closed-eye resting state EEG data were recorded in 40 healthy elderly (Nold), 96 amnesic MCI, and 83 AD subjects. White matter vascular lesions were indexed by magnetic resonance imaging recorded in the MCI and AD subjects (about 42% of cases following ADNI standards). The MCI subjects were divided into two sub-groups based on the median of the white matter lesion, namely MCI+ (people with highest vascular load; n=48) and MCI- (people with lowest vascular load; n=48). The same was true for the AD subjects (AD+, n=42; AD-, n=41). EEG rhythms of interest were delta (2-4Hz), theta (4-8Hz), alpha1 (8-10.5Hz), alpha2 (10.5-13Hz), beta1 (13-20Hz), beta2 (20-30Hz), and gamma (30-40Hz). LORETA software estimated cortical EEG sources. When compared to Nold group, MCI and AD groups showed well known abnormalities of delta and alpha sources. Furthermore, amplitude of occipital, temporal, and limbic alpha 1 sources were higher in MCI+ than MCI- group. As a novelty, amplitude of occipital delta sources was lower in AD+ than AD- group. Furthermore, central, parietal, occipital, temporal, and limbic alpha sources were higher in amplitude in AD+ than AD- group. Amplitude of these sources was correlated to global cognitive status (i.e., Mini Mental State Evaluation score). These results suggest that in amnesic MCI and AD subjects, resting state posterior delta and alpha EEG rhythms do not deteriorate with the increase of white-matter vascular lesion. These rhythms might be more sensitive to AD neurodegenerative processes and cognitive status rather than to concomitant lesions to white matter.
Ianessa A. Humbert, Donald G. McLaren, Georgia Malandraki, Sterling C. Johnson, JoAnne Robbins
Swallowing Intentional Off-State in Aging and Alzheimer’s Disease: Preliminary Study
Abstract: Frontal cortical activation is elicited when subjects have been instructed not to initiate a sensorimotor task. The goal of this preliminary fMRI study was to examine BOLD response to a ”Do Not Swallow” instruction (an intentional “off-state”) in the context of other swallowing tasks in 3 groups of participants (healthy young, healthy old, and early Alzheimer’s disease(AD)). Overall, the older group had larger, bilaterally active clusters in the cortex, including the dorsomedial prefrontal cortex during the intentional swallowing off-state; this region is commonly active in response inhibition studies. Disease-related differences were evident where the AD group had significantly greater BOLD response in the insula/operculum than the old. These findings have significant clinical implications for control of swallowing across the age span and in neurodegenerative disease. Greater activation in the insula/operculum for the AD group supports previous studies where this region is associated with initiating swallowing. The AD group may have required more effort to “turn off” swallowing centers to reach the intentional swallowing off-state.
Supplementary Data for Humbert et al. article (PDF)
Sangmook Lee, Garth F. Hall and Thomas B. Shea
Potentiation of Tau Aggregation by cdk5 and GSK3β
Abstract: Hyperphosphorylation of tau is closely associated with its aggregation by as yet undefined mechanisms. We attempted herein to further investigate the interrelationships between tau aggregation and phosphorylation by inhibition and activation of cdk5 and GSK3β in cells expressing normal tau and a mutant form of tau (3PO-tau), which generates intracellular aggregates while retaining microtubule-binding capacity). Aggregates were routinely observed in cells expressing 3PO-tau, but never in cells expressing normal tau, whether or not cdk5 or GSK3β was overexpressed. In addition, in cells expressing 3PO-tau, both the percentage of cells with aggregates, as well as the size of aggregates, was increased following overexpression of cdk5 or GSK3β, decreased following treatment with pharmacological agents (roscovitine and lithium) active against these kinases, and increased following treatment with the phosphatase inhibitor okadaic acid. These findings collectively indicate that phosphorylation potentiates aggregation in the presence of one or more key tau mutations. These findings confirm and extend prior studies in which overexpression of the cdk5 activator p35, or GSK3β, induced phosphorylation, mislocalization and/or aggregation of tau.
Fei Song, Anne Poljak, Michael Valenzuela, Richard Mayeux, George A. Smythe, Perminder S. Sachdev
Meta-Analysis of Plasma Amyloid-βlevels in Alzheimer’s Disease
Abstract: Plasma amyloid-β (Aβ) levels have been proposed as biomarkers of Alzheimer’s disease (AD), but studies have produced inconsistent results. We present a meta-analytic review of cross-sectional studies that examined plasma Aβ levels in AD and cognitively normal subjects, and longitudinal studies that used baseline plasma Aβ levels to predict conversion from normal cognition to AD. Medline and EMBASE databases were searched to generate an initial list of relevant studies, and selected authors approached for additional data. Twelve cross- sectional studies (n=1483) and seven longitudinal (n=3920) met the inclusion criteria for meta-analysis. Random effects model was used tocalculate the weighted mean difference (WMD) by Review Manager Version 4.2. In longitudinal studies, cognitively normal individuals who converted to AD had higher baseline Aβ1-40 and Aβ1-42 levels (WMD: 10.29, z=3.80, p=0.0001 and WMD: 8.01, z=2.76, p=0.006, respectively), and non-significantly increased Aβ1-42/ Aβ1-40 ratio (WMD: 0.03, z=1.65, p=0.10). In cross sectional studies, compared to cognitively normal individuals, AD patients had marginally but non-significantly lower Aβ1-42 levels (WMD:-2.84, z=1.73, p=0.08), but Aβ1-40 levels were not significantly different (WMD: 3.43, z=0.40, p=0.69). Our systematic review suggests a model of differential longitudinal changes in plasma Aβ levels in cognitively stable individuals versus those who go on to develop AD dementia. Baseline Aβ1-40 and Aβ1-42 levels in cognitively normal elderly individuals might be predictors of higher rates of progression to AD, and should be further explored as potential biomarkers.
Terhi Peuralinna, Maarit Tanskanen, Mira Mäkelä, Tuomo Polvikoski, Anders Paetau, Hannu Kalimo, Raimo Sulkava, John Hardy, Shiao-Lin Lai, Sampath Arepalli, Dena Hernandez, Bryan J. Traynor, Andrew Singleton, Pentti J. Tienari, Liisa Myllykangas (Handling Associate Editor: Carol Brayne)
APOE and AβPP Gene Variation in Cortical and Cerebrovascular Amyloid-β Pathology and Alzheimer’s Disease: A Population-Based Analysis
Abstract: Cortical and cerebrovascular amyloid-β (Aβ) deposition is a hallmark of Alzheimer’s disease (AD), but also occurs in elderly people not affected by dementia. The apolipoprotein E (APOE) ε4 is a major genetic modulator of Aβ deposition and AD risk. Variants of the amyloid-β protein precursor (AβPP) gene have been reported to contribute to AD and cerebral amyloid angiopathy (CAA). We analyzed the role of APOE and AβPP variants in cortical and cerebrovascular Aβ deposition, and neuropathologically verified AD (based on modified NIA-RI criteria) in a population-based autopsy sample of Finns aged ≥85 years (Vantaa85+ Study; n=282). Our updated analysis of APOE showed strong associations of the ε4 allele with cortical (p=4.91*10-17) and cerebrovascular (p=9.87*10-11) Aβ deposition as well as with NIA-RI AD (p=1.62*10-8). We also analyzed 60 single nucleotide polymorphisms (SNPs) at the AβPP locus. In single SNP or haplotype analyses there were no statistically significant AβPP locus associations with cortical or cerebrovascular Aβ deposition or with NIA-RI AD. We sequenced the promoter of the AβPP gene in 40 subjects with very high Aβ deposition, but none of these subjects had any of the previously reported or novel AD-associated mutations. These results suggest that cortical and cerebrovascular Aβ depositions are useful quantitative traits for genetic studies, as highlighted by the strong associations with the APOE e4 variant. Promoter mutations or common allelic variation in the AβPP gene do not have a major contribution to cortical or cerebrovascular Aβ deposition, or very late-onset AD in this Finnish population based study.
Gregory Hook, Vivian Hook, Mark Kindy (Handling Associate Editor: Ottavio Arancio)
The Cysteine Protease Inhibitor, E64d, Reduces Brain Amyloid-β and Improves Memory Deficits in Alzheimer’s Disease Animal Models by Inhibiting Cathepsin B, but not BACE1, β-Secretase Activity
Abstract: The cysteine protease cathepsin B is a potential drug target for reducing brain amyloid-β (Ab) and improving memory in Alzheimer’s disease (AD), as reduction of cathepsin B in transgenic mice expressing human wild-type amyloid-b protein precursor (AbPP) results in significantly decreased brain Ab. Cathepsin B cleaves the wild-type β-secretase site sequence in AβPP to produce Aβ, and cathepsin B inhibitors administered to animal models expressing AβPP containing the wild-type β-secretase site sequence reduce brain β in a manner consistent with β-secretase inhibition. But such inhibitors could act either by direct inhibition of cathepsin B β-secretase activity or by off-target inhibition of the other b-secretase, the aspartyl protease BACE1. To evaluate that issue, we orally administered a cysteine protease inhibitor, E64d, to normal guinea pigs or transgenic mice expressing human AbPP, both of which express the human wild-type β-secretase site sequence. In guinea pigs, oral E64d administration caused a dose-dependent reduction of up to 92% in brain, CSF, and plasma of Ab40 and Ab42, a reduction of up to 50% in the C-terminal b-secretase fragment (CTFb), and a 91% reduction in brain cathepsin B activity, but increased brain BACE1 activity by 20%. In transgenic AD mice, oral E64d administration improved memory deficits and reduced brain Ab40 and Ab42, amyloid plaque, brain CTFb, and brain cathepsin B activity, but increased brain BACE1 activity. We conclude that E64d likely reduces brain Ab by inhibiting cathepsin B and not BACE1 b-secretase activity and that E64d therefore may have potential for treating AD patients.