Faculty Bibliography

Amyloid plaques are a characteristic feature in Alzheimer's disease (AD). A novel non-toxic contrast agent is presented, Gd-DTPA-K6Abeta1-30, which is homologous to Abeta, and allows plaque detection in vivo. muMRI was performed on AD model mice and controls prior to and following intracarotid injection with Gd-DTPA-K6Abeta1-30 in mannitol solution, to transiently open the blood-brain barrier. A gradient echo T2(*)-weighted sequence was used to provide 100mum isotropic resolution with imaging times of 115min. The scans were examined with voxel-based analysis (VBA) using statistical parametric mapping, for un-biased quantitative comparison of ligand-injected mice and controls. The results indicate that: (1) Gd-DTPA-K6Abeta1-30 is an effective, non-toxic, ligand for plaque detection when combined with VBA (p</=0.01-0.001), comparing pre and post-ligand injection scans. (2) Large plaques can be detected without the use of a contrast agent and this detection co-localizes with iron deposition. (3) Smaller, earlier plaques require contrast ligand for MRI visualization. Our ligand when combined with VBA may be useful for following therapeutic approaches targeting amyloid in transgenic mouse models

Memantine, an N-methyl-D-aspartate (NMDA) receptor antagonist, has been shown to improve learning and memory in several preclinical models of Alzheimer's disease (AD). Memantine has also been shown to reduce the levels of amyloid beta (Abeta) peptides in human neuroblastoma cells as well as to inhibit Abeta oligomer-induced synaptic loss. In this study, we assessed whether NMDA receptor inhibition by memantine in transgenic mice expressing human amyloid-beta precursor protein (APP) and presenilin 1 (PS1) is associated with cognitive benefit and amyloid burden reduction by using object recognition, micromagnetic resonance imaging (muMRI), and histology. APP/PS1 Tg mice were treated either with memantine or with vehicle for a period of 4 months starting at 3 months of age. After treatment, the mice were subjected to an object recognition test and analyzed by ex vivo muMRI, and histological examination of amyloid burden. muMRI was performed following injection with gadolinium-DTPA-Abeta(1-40). We found that memantine-treated Tg mice performed the same as wild-type control mice, whereas the performance of vehicle-treated Tg mice was significantly impaired (P = 0.0081, one-way ANOVA). Compared with vehicle-treated animals, memantine-treated Tg mice had a reduced plaque burden, as determined both histologically and by muMRI. This reduction in amyloid burden correlates with an improvement in cognitive performance. Thus, our findings provide further evidence of the potential role of NMDA receptor antagonists in ameliorating AD-related pathology. In addition, our study shows, for the first time, the utility of muMRI in conjunction with gadolinium-labeled Abeta labeling agents to monitor the therapeutic response to amyloid-reducing agents. (c) 2008 Wiley-Liss, Inc

Immunotherapies that target the amyloid-beta (Abeta) peptide in Alzheimer's disease (AD) have shown promise in animal and human studies. Although the first clinical trial was halted because of adverse reactions, this approach has been refined and additional trials are underway. Another important target in AD is the neurofibrillary tangles, composed primarily of hyperphosphorylated tau proteins, which correlate well with the degree of dementia. As Abeta and tau pathologies are likely synergistic, targeting both should be more effective and may be essential as early diagnosis prior to cognitive decline is currently not available. Also, Abeta immunotherapy only results in a very limited indirect clearance of tau aggregates in dystrophic neurites, showing the importance of developing a separate therapy that directly targets pathological tau. Our findings in two tangle mouse models indicate that immunization with a phospho-tau derivative reduces aggregated tau in the brain and slows progression of the tangle-related behavioral phenotype. These antibodies enter the brain and bind to pathological tau within neurons. We are currently clarifying further the mechanism of action of this promising therapeutic approach and determining its epitope specificity

The present invention relates to synthetic immunogenic but non-amyloidogenic peptides homologous to amyloid beta which can be used alone or conjugated to an immunostimulatory molecule in an immunizing composition for inducing an immune response to amyloid beta peptides and amyloid deposits

Significant outbreaks of prion disease linked to oral exposure of the prion agent have occurred in animal and human populations. These disorders are associated with a conformational change of a normal protein, PrP(C) (C for cellular), to a toxic and infectious form, PrP(Sc) (Sc for scrapie). None of the prionoses currently have an effective treatment. Some forms of prion disease are thought to be spread by oral ingestion of PrP(Sc), such as chronic wasting disease and variant Creutzfeldt-Jakob disease. Attempts to obtain an active immunization in wild-type animals have been hampered by auto-tolerance to PrP and potential toxicity. Previously, we demonstrated that it is possible to overcome tolerance and obtain a specific anti-PrP antibody response by oral inoculation of the PrP protein expressed in an attenuated Salmonella vector. This past study showed that 30% of vaccinated animals were free of disease more than 350 days post-challenge. In the current study we have both optimized the vaccination protocol and divided the vaccinated mice into low and high immune responder groups prior to oral challenge with PrP(Sc) scrapie strain 139A. These methodological refinements led to a significantly improved therapeutic response. 100% of mice with a high mucosal anti-PrP titer immunoglobulin (Ig) A and a high systemic IgG titer, prior to challenge, remained without symptoms of PrP infection at 400 days (log-rank test P<0.0001 versus sham controls). The brains from these surviving clinically asymptomatic mice were free of PrP(Sc) infection by Western blot and histological examination. These promising findings suggest that effective mucosal vaccination is a feasible and useful method for overcoming tolerance to PrP and preventing prion infection via an oral route

Alzheimer's and prion diseases belong to a category of conformational neurodegenerative disorders [Prusiner SB (2001) N Eng J Med344, 1516-1526; Sadowski M & Wisniewski T (2007) Curr Pharm Des 13, 1943-1954; Beekes M (2007) FEBS J 274, 575]. Treatments capable of arresting or at least effectively modifying the course of disease do not yet exist for either one of these diseases. Alzheimer's disease is the major cause of dementia in the elderly and has become an ever greater problem with the aging of Western societies. Unlike Alzheimer's disease, prion diseases are relatively rare. Each year only approximately 300 people in the USA and approximately 100 people in the UK succumb to various forms of prion diseases [Beekes M (2007) FEBS J 274, 575; Sigurdsson EM & Wisniewski T (2005) Exp Rev Vaccines 4, 607-610]. Nevertheless, these disorders have received great scientific and public interest due to the fact that they can be transmissible among humans and in certain conditions from animals to humans. The emergence of variant Creutzfeld-Jakob disease demonstrated the transmissibility of the bovine spongiform encephalopathy to humans [Beekes M (2007) FEBS J 274, 575]. Therefore, the spread of bovine spongiform encephalopathy across Europe and the recently identified cases in North America have put a large human population at risk of prion infection. It is estimated that at least several thousand Britons are asymptomatic carriers of prion infections and may develop variant Creutzfeld-Jakob disease in the future [Hilton DA (2006) J Pathol 208, 134-141]. This delayed emergence of human cases following the near elimination of bovine spongiform encephalopathy in the UK may occur because prion disease have a very prolonged incubation period, ranging from months to decades, which depends on the amount of inoculum, the route of infection and the genetic predisposition of the infected subject [Hilton DA (2006) J Pathol 208, 134-141]. Therefore, there is a great need for effective therapies for both Alzheimer's disease and prion diseases.

Immunotherapies for various neurodegenerative diseases have recently emerged as a promising approach for clearing pathological protein conformers in these disorders. This type of treatment has not been assessed in models that develop neuronal tau aggregates as observed in frontotemporal dementia and Alzheimer's disease. Here, we present that active immunization with a phosphorylated tau epitope, in P301L tangle model mice, reduces aggregated tau in the brain and slows progression of the tangle-related behavioral phenotype. Females had more tau pathology than males but were also more receptive to the immunotherapy. The tau antibodies generated in these animals recognized pathological tau on brain sections. Performance on behavioral assays that require extensive motor coordination correlated with tau pathology in corresponding brain areas, and antibody levels against the immunogen correlated inversely with tau pathology. Interestingly, age-dependent autoantibodies that recognized recombinant tau protein but not the immunogen were detected in the P301L mice. To confirm that anti-tau antibodies could enter the brain and bind to pathological tau, FITC-tagged antibodies purified from a P301L mouse, with a high antibody titer against the immunogen, were injected into the carotid artery of P301L mice. These antibodies were subsequently detected within the brain and colocalized with PHF1 and MC1 antibodies that recognize pathological tau. Currently, no treatment is available for clearing tau aggregates. Our present findings may lead to a novel therapy targeting one of the major hallmarks of Alzheimer's disease and frontotemporal dementia

It was proposed that insulin-degrading enzyme (IDE) participates in the clearance of amyloid beta (Abeta) in the brain, and its low expression or activity may be relevant for the progression of Alzheimer disease. We performed a longitudinal study of brain level, activity, and distribution of IDE in transgenic mice (Tg2576) expressing the Swedish mutation in human Abeta precursor protein. At 16 months of age, Tg2576 showed a significant 2-fold increment in IDE protein level as compared with 4.5- and 11-month-old animals. The peak of IDE was in synchrony with the sharp accumulation of sodium dodecyl sulfate-soluble Abeta and massive Abeta deposition into plaques. At this stage, IDE appeared surrounding Abeta fibrillar deposits within glial fibrillar acidic protein-positive astrocytes, suggesting that it was locally overexpressed during the Abeta-mediated inflammation process. When primary astrocytes were exposed to fibrillar Abeta in vitro, IDE protein level increased as compared with control, and this effect was reduced by the addition of U0126, a specific inhibitor of the ERK1/2 mitogen-activated protein kinase cascade. We propose that in Tg2576 mice and in contrast to its behavior in Alzheimer brains, active IDE increases with age around plaques as a component of astrocyte activation as a result of Abeta-triggered inflammation