Compact Plaques Research Articles

CORRESPONDENCE BETWEEN [C-11]PIB PET AND POST-MORTEM MEASURES OF AMYLOID LOAD IN THE PRECUNEUS: THE ROLE OF DIFFUSE Aβ PLAQUES

gene and she was diagnosed as having FAD. Significant [C-11]PiB PET uptake was observed bilaterally in frontal, parietal, and temporal lobes, as well as in the basal ganglia, but not in the cerebellum. By histopathology, Ab immunoreactive deposits were severe in all gray matter structures of cerebrum and cerebellum. Cerebral cortical Ab deposits consisted of cored, diffuse, and cotton wool plaques (CWP). 6-CN-PiB signal was strong in cored plaques, weak-to-moderate in diffuse plaques, and absent in CWPs. In the cerebellum, Ab IHC detected a heavy burden of diffuse deposits in the parenchyma and in blood vessels, while 6-CN-PiB fluorescence was detected only in the leptomeningeal and parenchymal vessels and infrequently in small compact Ab plaques. Conclusions: As progress in imaging techniques allows us to use new tracers for misfolded proteins accumulating in neurodegenerative disease, neuropathology becomes more relevant for defining the efficiency of tracers in identifying specific lesions. The relative contribution of different Ab plaque types to [C-11]PiB PET retention in vivo is currently being investigated. Funding sources: P30AG010133, P01AG025204, U19AG032438.

Human APOE4 increases microglia reactivity at Aβ plaques in a mouse model of Aβ deposition.

BackgroundHaving the apolipoprotein E4 (APOE-ϵ4) allele is the strongest genetic risk factor for the development of Alzheimer’s disease (AD). Accumulation of amyloid beta (Aβ) in the brain is influenced by APOE genotype. Transgenic mice co-expressing five familial AD mutations (5xFAD) in the presence of human APOE alleles (ϵ2, ϵ3 or ϵ4) exhibit APOE genotype-specific differences in early Aβ accumulation, suggesting an interaction between APOE and AD pathology. Whether APOE genotype affects Aβ-plaque-associated neuroinflammation remains unclear. In the current study, we address the role of APOE genotype on Aβ-associated microglial reactivity in the EFAD transgenic mouse model.MethodsWe analyzed Aβ-induced glial activation in the brains of 6-month-old EFAD transgenic mice (E2FAD, E3FAD and E4FAD). Region-specific morphological profiles of Aβ plaques in EFAD brain sections were compared using immunofluorescence staining. We then determined the degree of glial activation in sites of Aβ deposition while comparing levels of the inflammatory cytokine Interleukin-1β (IL-1β) by ELISA. Finally, we quantified parameters of Aβ-associated microglial reactivity using double-stained EFAD brain sections.ResultsCharacterization of Aβ plaques revealed there were larger and more intensely stained plaques in E4FAD mice relative to E2FAD and E3FAD mice. E4FAD mice also had a greater percentage of compact plaques in the subiculum than E3FAD mice. Reactive microglia and dystrophic astrocytes were prominent in EFAD brains, and primarily localized to two sites of significant Aβ deposition: the subiculum and deep layers of the cortex. Cortical levels of IL-1β were nearly twofold greater in E4FAD mice relative to E3FAD mice. To control for differences in levels of Aβ in the different EFAD mice, we analyzed the microglia within domains of specific Aβ deposits. Morphometric analyses revealed increased measures of microglial reactivity in E4FAD mice, including greater dystrophy, increased fluorescence intensity and a higher density of reactive cells surrounding cortical plaques, than in E3FAD mice.ConclusionsIn addition to altering morphological profiles of Aβ deposition, APOE genotype influences Aβ-induced glial activation in the adult EFAD cortex. These data support a role for APOE in modulating Aβ-induced neuroinflammatory responses in AD progression, and support the use of EFAD mice as a suitable model for mechanistic studies of Aβ-associated neuroinflammation.

Bacteriophage - A Common Divergent Therapeutic Approach for Alzheimer's Disease and Type II Diabetes Mellitus

Alzheimer's disease, the most important neurodegenerative disorder, is an irreversible, age-dependent disease of the brain characterized by problems in progressive impairments in memory, language, reasoning, behavior and visuospatial skills. It is characterized by the deposition of amyloid beta peptide, forming compact fibrillar plaques and neurofibrillary tau tangles. Another major and much more prevalent cause of morbidity and mortality in world is diabetes especially type 2 diabetes mellitus. It is caused by a combination of resistance to insulin action and an inadequate compensatory insulin secretory response. Chronic wounds caused by antibiotic resistant bacterial infections that fail to heal are a common complication of diabetes mellitus and the most frequent reason for nontraumatic lower limb amputation. Holistically, these two diseases are linked at molecular level but the exact mechanism is a topic of debate. Bacteriophages are viruses infecting bacteria and lack ability to infect mammalian cells. They are neither causative agent for Alzheimer's disease or type 2 diabetes mellitus nor involved in their pathogenicity but promises for a novel divergent therapeutic approach. The great versatility of the phage system has led to the development of improved phage delivery vectors, as well as immunomodulation of anti-amyloid beta peptide response. Phages could also constitute valuable prophylaxis against bacterial infections, especially in immunocompromised patients like in the case of diabetes. Patients having diabetes have a high risk of developing foot ulcers which are difficult to be treated by antibiotics alone due to ever increasing antibiotic resistance strains. Combination therapy based on multiple phage and broad spectrum antibiotics holds great promise. The potential therapeutic phage therapy arises from its lack of natural tropism for mammalian cells, resulting in no adverse effects.

Zinc-Triggered Induction of Tissue Plasminogen Activator and Plasminogen in Endothelial Cells and Pericytes

Cerebral amyloid angiopathy (CAA) is common in patients with Alzheimer's disease (AD) and may contribute to cerebral hemorrhage. We previously demonstrated that tissue plasminogen activator (tPA) and plasminogen (PLG) accumulated at the periphery of compact amyloid-cored plaques and in the walls of CAA-containing blood vessels in the brains of Tg2576 mice, a widely used AD mouse model. We had also observed that zinc-triggered tPA and PLG induction were observed in mouse cortical cultures. Because zinc also accumulates in amyloid plaques and blood vessel walls in AD brains, we examined whether zinc increases mRNA and protein levels of tPA and PLG in brain endothelial cells and pericytes. Four hours after the exposure of brain endothelial cells (bEnd.3) to 40 µM zinc, the mRNA and protein expressions of tPA and its substrate PLG were significantly increased. In the case of brain pericyte cultures, increases in tPA and PLG expression were also detected 2 hr after treatment. However, amyloid-β (Aβ)1-42 oligomers did not augment tPA and PLG expression in bEnd.3 cells and pericytes, suggesting that zinc but not Aβ induces tPA and PLG accumulation in CAA found in the AD brain.

Magnetization transfer contrast imaging reveals amyloid pathology in Alzheimer's disease transgenic mice

The presence of amyloid plaques in the brain is one of the pathological hallmarks of Alzheimer's disease, which might already be present in the early stage of the disease. Therefore it is important to track amyloid plaques as early as possible. In this paper, we report magnetization transfer contrast magnetic resonance imaging (MTC MRI) as a novel approach to detect amyloid plaques in vivo. Two mice models, APP/PS1 and BRI, developing amyloid pathology were investigated with MTC MRI, T2 relaxation measurements and immunohistochemistry (IHC). MT-ratios of several brain regions were compared to T2-values and correlated with quantitative IHC, revealing amyloid load and gliosis in different brain regions. APP/PS1 mice develop large compact plaques, resembling late stage Alzheimer's disease, while rather small and diffuse plaques are deposited in BRI mice, reflecting early stage of Alzheimer's disease. We found significantly higher MT-ratio's in the brain of APP/PS1 mice as compared to their controls and similar trends in BRI mice. A region based MT-ratio and IHC analysis and correlations between MT-ratios and quantitative IHC indicate amyloid plaques as the main substrate for altered MT-ratios in transgenic animals. We additionally demonstrated the improved sensitivity of MTC MRI to amyloid pathology as compared to traditional T2 relaxation measurements. Our results suggest that MTC MRI reveals extensive, and potentially even early amyloid pathology. Further unraveling the MT-effect of each pathological feature during each stage of AD might indicate MTC MRI as a useful diagnostic technique.

APOE4-specific Changes in Aβ Accumulation in a New Transgenic Mouse Model of Alzheimer Disease

APOE4 is the greatest risk factor for Alzheimer disease (AD) and synergistic effects with amyloid-β peptide (Aβ) suggest interactions among apoE isoforms and different forms of Aβ accumulation. However, it remains unclear how the APOE genotype affects plaque morphology, intraneuronal Aβ, soluble Aβ42, and oligomeric Aβ (oAβ), particularly in vivo. As the introduction of human APOE significantly delays amyloid deposition in transgenic mice expressing familial AD (FAD) mutations (FAD-Tg), 5xFAD-Tg mice, which exhibit amyloid deposition by age 2 months, were crossed with apoE-targeted replacement mice to produce the new EFAD-Tg mice. Compared with 5xFAD mice, Aβ deposition was delayed by ∼4 months in the EFAD mice, allowing detection of early changes in Aβ accumulation from 2-6 months. Although plaque deposition is generally greater in E4FAD mice, E2/E3FAD mice have significantly more diffuse and E4FAD more compact plaques. As a first report in FAD-Tg mice, the APOE genotypes had no effect on intraneuronal Aβ accumulation in EFAD mice. In E4FAD mice, total apoE levels were lower and total Aβ levels higher than in E2FAD and E3FAD mice. Profiles from sequential three-step extractions (TBS, detergent, and formic acid) demonstrated that the lower level of total apoE4 is reflected only in the detergent-soluble fraction, indicating that less apoE4 is lipoprotein-associated, and perhaps less lipidated, compared with apoE2 and apoE3. Soluble Aβ42 and oAβ levels were highest in E4FAD mice, although soluble apoE2, apoE3, and apoE4 levels were comparable, suggesting that the differences in soluble Aβ42 and oAβ result from functional differences among the apoE isoforms. Thus, APOE differentially regulates multiple aspects of Aβ accumulation.

Alteration of the Cerebral Zinc Pool in a Mouse Model of Alzheimer Disease

Synaptic vesicle Zn is regulated by zinc transporter 3 (ZnT3) and is involved in neurotransmission and synaptic plasticity. Here, we describe extensive alterations of ZnT3-regulated Zn pools in the brains of human amyloid precursor protein-transgenic (Tg2576) mice. In contrast to wild-type littermates in which ZnT3 expression and synaptic Zn increased with age, there were age-dependent reductions in ZnT3 expression and synaptic Zn levels in the hippocampal mossy fiber area of Tg2576 mice. In these mice, a novel Zn pool and ZnT3 expression were colocalized and appeared along dystrophic neurites surrounding compact amyloid plaques that were identified by in situ blue fluorescence, congophilic birefringence, and Aβ42 immunoreactivity. Zn-specific histofluorescence and ZnT3 immunofluorescence in dystrophic neurites were also colocalized with the δ-subunit of adaptor protein complex 3, lysosome-associated membrane protein, cathepsin D, and neurofilament-containing hyperphosphorylated paired helical filaments. The synaptic vesicle marker protein synaptophysin and vesicle-associated membrane protein were not found in these neurites, suggesting a role of ZnT3 distinct from itsnormal role in synaptic Zn. ZnT3 immunoreactivity and Zn histofluorescence were also evident in activated astrocytes. These datasuggest that extensive modifications of the cerebral Zn pool, particularly synaptic Zn, may underlie neuronal dysfunction characteristic of Alzheimer disease.

BACE1 Elevation is Involved in Amyloid Plaque Development in the Triple Transgenic Model of Alzheimer’s Disease: Differential Aβ Antibody Labeling of Early-Onset Axon Terminal Pathology

β-amyloid precursor protein (APP) and presenilins mutations cause early-onset familial Alzheimer's disease (FAD). Some FAD-based mouse models produce amyloid plaques, others do not. β-Amyloid (Aβ) deposition can manifest as compact and diffuse plaques; it is unclear why the same Aβ molecules aggregate in different patterns. Is there a basic cellular process governing Aβ plaque pathogenesis? We showed in some FAD mouse models that compact plaque formation is associated with a progressive axonal pathology inherent with increased expression of β-secretase (BACE1), the enzyme initiating the amyloidogenic processing of APP. A monoclonal Aβ antibody, 3D6, visualized distinct axon terminal labeling before plaque onset. The present study was set to understand BACE1 and axonal changes relative to diffuse plaque development and to further characterize the novel axonal Aβ antibody immunoreactivity (IR), using triple transgenic AD (3xTg-AD) mice as experimental model. Diffuse-like plaques existed in the forebrain in aged transgenics and were regionally associated with increased BACE1 labeled swollen/sprouting axon terminals. Increased BACE1/3D6 IR at axon terminals occurred in young animals before plaque onset. These axonal elements were also co-labeled by other antibodies targeting the N-terminal and mid-region of Aβ domain and the C-terminal of APP, but not co-labeled by antibodies against the Aβ C-terminal and APP N-terminal. The results suggest that amyloidogenic axonal pathology precedes diffuse plaque formation in the 3xTg-AD mice, and that the early-onset axonal Aβ antibody IR in transgenic models of AD might relate to a cross-reactivity of putative APP β-carboxyl terminal fragments.

Amyloid-β Annular Protofibrils Evade Fibrillar Fate in Alzheimer Disease Brain

Annular protofibrils (APFs) represent a new and distinct class of amyloid structures formed by disease-associated proteins. In vitro, these pore-like structures have been implicated in membrane permeabilization and ion homeostasis via pore formation. Still, evidence for their formation and relevance in vivo is lacking. Herein, we report that APFs are in a distinct pathway from fibril formation in vitro and in vivo. In human Alzheimer disease brain samples, amyloid-β APFs were associated with diffuse plaques, but not compact plaques; moreover, we show the formation of intracellular APFs. Our results together with previous studies suggest that the prevention of amyloid-β annular protofibril formation could be a relevant target for the prevention of amyloid-β toxicity in Alzheimer disease.

Observations in APP Bitransgenic Mice Suggest that Diffuse and Compact Plaques Form via Independent Processes in Alzheimer's Disease

Studies of familial Alzheimer's disease suggest that misfolding and aggregation of amyloid-β (Aβ) peptides initiate the pathogenesis. The Arctic mutation of Aβ precursor protein (APP) results in AD, and Arctic Aβ is more prone to form Aβ protofibrils and extracellular deposits. Herein is demonstrated that the burden of diffuse Aβ deposits but not compact plaques is increased when tg-Swe mice are crossed with tg-ArcSwe mice synthesizing low levels of Arctic Aβ. The diffuse deposits in bitransgenic mice, which contain primarily wild-type Aβ42, accumulate in regions both with and without transgene expression. However, APP processing, when compared with tg-Swe, remains unchanged in young bitransgenic mice, whereas wild-type Aβ42 aggregation is accelerated and fibril architecture is altered in vitro and in vivo when a low level of Arctic Aβ42 is introduced. Thus, the increased number of diffuse deposits is likely due to physical interactions between Arctic Aβ and wild-type Aβ42. The selective increase of a single type of parenchymal Aβ deposit suggests that different pathways lead to formation of diffuse and compact plaques. These findings could have general implications for Alzheimer's disease pathogenesis and particular relevance to patients heterozygous for the Arctic APP mutation. Moreover, it further illustrates how Aβ neuropathologic features can be manipulated in vivo by mechanisms similar to those originally conceptualized in prion research.

Neuronal and Axonal Loss Are Selectively Linked to Fibrillar Amyloid-β within Plaques of the Aged Primate Cerebral Cortex

The amyloid-beta peptide (Abeta) deposited in plaques in Alzheimer's disease has been shown to cause degeneration of neurons in experimental paradigms in vivo and in vitro. However, it has been difficult to convincingly demonstrate toxicity of native amyloid deposits in the aged and Alzheimer brains. Here we provide evidence that the fibrillar conformation of Abeta (fAbeta) deposited in compact plaques is associated with the pathologies observed in Alzheimer brains. fAbeta containing compact but not diffuse plaques in the aged rhesus cortex contained activated microglia and clusters of phosphorylated tau-positive swollen neurites. Scholl's quantitative analysis revealed that the area adjacent to fAbeta, containing compact but not diffuse plaques in aged rhesus, aged human, and Alzheimer's disease cortex, displays significant loss of neurons and small but statistically significant reduction in the density of cholinergic axons. These observations suggest that fAbeta toxicity may not be restricted to cultured cells and animal injection models. Rather, fAbeta deposited in native compact plaques in aged and AD brains may exert selective toxic effects on its surrounding neural environment.

Targeting Tau Protein in Alzheimerʼs Disease

Alzheimer's disease (AD) is characterized histopathologically by numerous neurons with neurofibrillary tangles and neuritic (senile) amyloid-beta (Abeta) plaques, and clinically by progressive dementia. Although Abeta is the primary trigger of AD according to the amyloid cascade hypothesis, neurofibrillary degeneration of abnormally hyperphosphorylated tau is apparently required for the clinical expression of this disease. Furthermore, while approximately 30% of normal aged individuals have as much compact plaque burden in the neocortex as is seen in typical cases of AD, in several tauopathies, such as cortical basal degeneration and Pick's disease, neurofibrillary degeneration of abnormally hyperphosphorylated tau in the absence of Abeta plaques is associated with dementia. To date, all AD clinical trials based on Abeta as a therapeutic target have failed. In addition to the clinical pathological correlation of neurofibrillary degeneration with dementia in AD and related tauopathies, increasing evidence from in vitro and in vivo studies in experimental animal models provides a compelling case for this lesion as a promising therapeutic target. A number of rational approaches to inhibiting neurofibrillary degeneration include inhibition of one or more tau protein kinases, such as glycogen synthase kinase-3beta and cyclin-dependent protein kinase 5, activation of the major tau phosphatase protein phosphatase-2A, elevation of beta-N-acetylglucosamine modification of tau through inhibition of beta-N-acetylglucosaminidase or increase in brain glucose uptake, and promotion of the clearance of the abnormally hyperphosphorylated tau by autophagy or the ubiquitin proteasome system.

Aβ Immunotherapy Protects Morphology and Survival of Adult-Born Neurons in Doubly Transgenic APP/PS1 Mice

The hippocampus is heavily affected by progressive neurodegeneration and beta-amyloid pathology in Alzheimer's disease (AD). The hippocampus is also one of the few brain regions that generate new neurons throughout adulthood. Because hippocampal neurogenesis is regulated by both endogenous and environmental factors, we determined whether it benefits from therapeutic reduction of beta-amyloid peptide (Abeta)-related toxicity induced by passive Abeta immunotherapy. Abeta immunotherapy of 8-9-month-old mice expressing familial AD-causing mutations in the amyloid precursor protein and presenilin-1 genes with an antibody against Abeta decreased compact beta-amyloid plaque burden and promoted survival of newly born neurons in the hippocampal dentate gyrus. As these neurons matured, they exhibited longer dendrites with more complex arborization compared with newly born neurons in control-treated transgenic littermates. The newly born neurons showed signs of functional integration indicated by expression of the immediate-early gene Zif268 in response to exposure to a novel object. Abeta immunotherapy was associated with higher numbers of synaptophysin-positive synaptic boutons. Labeling dividing progenitor cells with a retroviral vector encoding green fluorescent protein (GFP) showed that Abeta immunotherapy restored the impaired dendritic branching, as well as the density of dendritic spines in new mature neurons. The presence of cellular prion protein (PrP(c)) on the dendrites of the GFP(+) newly born neurons is compatible with a putative role of PrP(c) in mediating Abeta-related toxicity in these cells. In addition, passive Abeta immunotherapy was accompanied by increased angiogenesis. Our data establish that passive Abeta immunotherapy can restore the morphological maturation of the newly formed neurons in the adult hippocampus and promote angiogenesis. These findings provide evidence for a role of Abeta immunotherapy in stimulating neurogenesis and angiogenesis in transgenic mouse models of AD, and they suggest the possibility that Abeta immunotherapy can recover neuronal and vascular functions in brains with beta-amyloidosis.

Microglia Activated with the Toll-Like Receptor 9 Ligand CpG Attenuate Oligomeric Amyloid β Neurotoxicity in in Vitro and in Vivo Models of Alzheimer’s Disease

Soluble oligomeric amyloid beta (oAbeta) 1-42 causes synaptic dysfunction and neuronal injury in Alzheimer's disease (AD). Although accumulation of microglia around senile plaques is a hallmark of AD pathology, the role of microglia in oAbeta1-42 neurotoxicity is not fully understood. Here, we showed that oAbeta but not fibrillar Abeta was neurotoxic, and microglia activated with unmethylated DNA CpG motif (CpG), a ligand for Toll-like receptor 9, attenuated oAbeta1-42 neurotoxicity in primary neuron-microglia co-cultures. CpG enhanced microglial clearance of oAbeta1-42 and induced higher levels of the antioxidant enzyme heme oxygenase-1 in microglia without producing neurotoxic molecules such as nitric oxide and glutamate. Among subclasses of CpGs, class B and class C activated microglia to promote neuroprotection. Moreover, intracerebroventricular administration of CpG ameliorated both the cognitive impairments induced by oAbeta1-42 and the impairment of associative learning in Tg2576 mouse model of AD. We propose that CpG may be an effective therapeutic strategy for limiting oAbeta1-42 neurotoxicity in AD.

Familial prion disease with a novel serine to isoleucine mutation at codon 132 of prion protein gene (PRNP)

Familial prion disease with a novel serine to isoleucine mutation at codon 132 of prion protein gene (<i>PRNP</i>)

The Neurovascular Unit in Health and Disease

Over the past 10 years, study of the blood vessel in cerebrovascular disease has expanded from consideration of only endothelial cells to include interactions with neurons, astrocytes, pericytes, and extracellular matrix. The role of other cells in the pathobiology of cerebral blood vessels has been encompassed under the term “neurovascular unit (NVU).” This session brings together a series of papers on the role of the NVU in stroke and neurodegenerative diseases. The endothelial cell remains central to the NVU, but its function is regulated by input from adjacent pericytes, astrocytes, and neurons.1 The extracellular matrix and the matrix-degrading enzymes and inhibitors play a key role at the basal lamina and the cell surface in the regulation of cell signaling.2 Much has been learned about the function of astrocytes, which rapidly transduce information between the microenvironment and other brain cells and the macrophage-like pericytes in effecting changes at the cerebral capillary level. The presentations were arranged to emphasize recent advances in our understanding of the anatomy and physiology of the NVU (Lo), recent studies on the astrocytes (Nedergaard), and pericytes (Fisher). The final 2 presentations describe the role of extracellular matrix enzymes in amyloid metabolism as it relates to Alzheimer disease (Lee) and vascular cognitive impairment (Rosenberg). The goal of the session was to provide an overview on the role of the separate cell types composing the NVU and to show how they interact in acute and chronic cerebrovascular diseases. Transgenic …

P1-404: Neuronal and axonal damage are selectively observed in association with fibrillar amyloid-β deposits in the aged rhesus and human cortex

Compact plaques containing the fibrillar form of the amyloid-β (fAβ) peptide are abundant in the cerebral cortex of Alzheimer's disease (AD) patients. While we have shown selective toxicity of fAβ in the aged primate brain, toxicity of plaque-associated fAβ has been difficult to demonstrate in the AD brain. In the present set of experiments we investigated pathology associated with single fAβ deposits in the cerebral cortex of the aged rhesus, aged human and AD cortex. We performed an analysis of the loss of neurons and acetylcholinesterase (AChE)-positive cholinergic axons around compact plaques using concentric circles 20 μm apart. The plaque was placed in the center circle and the number of neurons in between circles and intersection of axons with circles were determined in sections double stained for Aβ and Nissl or Aβ and AChE. Compact plaques with fAβ in the rhesus cortex contained activated microglia as indicated by the presence of HLA-DR and CD68 immunoreactivity. Compact plaques were also associated with swollen neurites containing epitopes of phosphorylated tau observed in tangles in the AD brain, in association with fAβ. The number of neurons per mm2 in the first 20 μm area around rhesus compact plaques was significantly lower than the number in each of the next four areas and this number displayed a progressive increase in each of these four areas. A similar pattern was noted with cholinergic fibers where the number of cholinergic axon intersects per mm was significantly lower near compact plaques when compared with areas away from the plaques. We also observed significant neuronal loss associated with single compact plaques in the human aged and AD cortex. Presence of pathology in the rhesus and human cortex was a nearly exclusive property of fAβ containing plaques as demonstrated with thioflavin-S staining. These observations indicate that fAβ in native deposits exerts toxic effects on the surrounding environment. While the precise mechanisms of these toxic effects are undetermined, it is likely that microglia activation and accumulation of phosphorylated tau in neurites make a significant contribution to this process.

S2-02-05: Anti-abeta antibodies in Alzheimer's disease mouse models

The pioneering work of Schenk and colleagues demonstrated the therapeutic potential of generating an antibody response capable of recognizing Abeta and Abeta amyloid. Indeed, dozens of studies now show that in mouse models of AD antibodies to Abeta can attenuate Abeta deposition and plaque associated pathologies (e.g. gliosis) and reverse behavioral deficits in these mice. Despite initial setbacks multiple active and passive Abeta immunotherapy trials are now being tested humans. Both active immunizations with fibrillar or Abeta or fragments of Abeta and passive immunization with anti-Abeta antibodies have been evaluated in mouse models of AD. Endpoints have included Abeta deposition, gliosis, behavioral alterations, and levels of Abeta and antibody in various brain, CSF and plasma. Numerous studies consistently demonstrate that active or passive immunotherapy suppresses Abeta deposition in mouse models of AD. Though diffuse plaques may be cleared by immunotherapy, it is controversial as to whether compact plaques are cleared. In mice only rare side effects have been reported. To date there is no consensus as to mechanisms of action, ideal target epitope, or whether an antibody is truly needed. Our work suggests that efficacy is related to target epitope, is dependent on the levels of Abeta deposition at the time of initiation of therapy, and cannot be easily explained by most of the postulated mechanisms. Novel strategies targetting amyloid versus Abeta will be presented. Abeta immunotherapy remains a promising approach for the treatment of AD. Late stage trials of passive immunotherapy are underway in humans. Though mouse models may be helpful in evaluating the potential efficacy of a given Abeta immunotherapy, they may not be useful in predicting possible side effects. Even in mice the efficacy of immunotherapy is limited with respect to certain endpoints when treatment is initiated in mice with AD like amyloid loads. Further understanding of the mechanisms underlying efficacy are likely to be needed in order to develop an optimized immunologic approach to targeting Abeta in AD.

O1-03-05: Dynamics of compact plaque growth in APP/PS1 mice

O1-03-05: Dynamics of compact plaque growth in APP/PS1 mice

Contrasting In Vivo Effects of Two Peptide-Based Amyloid-β Protein Aggregation Inhibitors in a Transgenic Mouse Model of Amyloid Deposition

Previous studies have shown that 17,19,21-tri-N-methyl-Abeta16-22 peptide (Abeta16-22m), and a peptide analogue containing alpha,alpha-disubstituted amino acids (alphaalpha AA) in the hydrophobic core domain of Abeta, termed AMY-1, effectively inhibited full-length Abeta aggregation in vitro. To investigate the amyloid-modifying effects of these agents in vivo, we injected these compounds into the hippocampus of 13-month-old amyloid precursor protein (APP) transgenic mice, a model of amyloid deposition. After 7 days, brain tissues were stained for immunohistochemistry to detect total Abeta and thioflavine-S (THIO-S) to measure Abeta compact plaques. Both diffuse Abeta deposits and compact amyloid plaques were significantly increased when injecting 0.3 nmol Abeta16-22m compared to the PBS vehicle. The amyloid aggregation-modifying peptide AMY-1 showed a slight reduction of Abeta deposition in the injection area at a dose of 0.3 nmol, but neuronal toxicity, measured by Fluoro-Jade and Nissl stains, appeared when higher doses (3 nmol) were tested. Our data indicate that, unlike observations reported in vitro, the Abeta16-22m increased deposition of Abeta in the brain of APP transgenic mice in vivo. Possible explanations for this outcome include unique influences of the brain environment and/or modification of Abeta production or clearance by the administered agent. The AMY-1 peptide showed a trend for reducing Abeta deposits, but led to toxicity at higher doses. These data emphasize the need for evaluating potential Abeta aggregation inhibitors with in vivo models of amyloid deposition before assuming they will have benefit in treating Alzheimer's disease patients.