Passive immunotherapy against Aβ in aged APP-transgenic mice reverses cognitive deficits and depletes parenchymal amyloid deposits in spite of increased vascular amyloid and microhemorrhage

Journal of Neuroinflammation BioMed Central Research Open Access Passive immunotherapy against Aβ in aged APP-transgenic mice reverses cognitive deficits and depletes parenchymal amyloid deposits in spite of increased vascular amyloid and microhemorrhage Donna M Wilcock1, Amyn Rojiani2, Arnon Rosenthal3, Sangeetha Subbarao3, Melissa J Freeman1, Marcia N Gordon1 and Dave Morgan*1 Address: 1Alzheimer's Research Laboratory, University of South Florida, Department of Pharmacology, 12901 Bruce B Downs Blvd, Tampa, Florida 33612, USA, 2Alzheimer's Research Laboratory, University of South Florida, Department of Interdisciplinary Oncology, 12901 Bruce B Downs Blvd, Tampa, Florida 33612, USA and 3Rinat Neuroscience Corp., 3155 Porter Drive, Palo Alto, California 94304, USA Email: Donna M Wilcock - ; Amyn Rojiani - ; Arnon Rosenthal - ; Sangeetha Subbarao - ; Melissa J Freeman - ; Marcia N Gordon - ; Dave Morgan* - * Corresponding author Published: 08 December 2004 Journal of Neuroinflammation 2004, 1:24 doi:10.1186/1742-2094-1-24 Received: 10 November 2004 Accepted: 08 December 2004 This article is available from: http://www.jneuroinflammation.com/content/1/1/24 © 2004 Wilcock et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Background: Anti-Aβ immunotherapy in transgenic mice reduces both diffuse and compact amyloid deposits, improves memory function and clears early-stage phospho-tau aggregates. As most Alzheimer disease cases occur well past midlife, the current study examined adoptive transfer of anti-Aβ antibodies to 19- and 23-month old APP-transgenic mice. Methods: We investigated the effects of weekly anti-Aβ antibody treatment on radial-arm watermaze performance, parenchymal and vascular amyloid loads, and the presence of microhemorrhage in the brain. 19-month-old mice were treated for 1, 2 or 3 months while 23-month-old mice were treated for 5 months. Only the 23-month-old mice were subject to radial-arm water-maze testing. Results: After 3 months of weekly injections, this passive immunization protocol completely reversed learning and memory deficits in these mice, a benefit that was undiminished after 5 months of treatment. Dramatic reductions of diffuse Aβ immunostaining and parenchymal Congophilic amyloid deposits were observed after five months, indicating that even wellestablished amyloid deposits are susceptible to immunotherapy. However, cerebral amyloid angiopathy increased substantially with immunotherapy, and some deposits were associated with microhemorrhage. Reanalysis of results collected from an earlier time-course study demonstrated that these increases in vascular deposits were dependent on the duration of immunotherapy. Conclusions: The cognitive benefits of passive immunotherapy persist in spite of the presence of vascular amyloid and small hemorrhages. These data suggest that clinical trials evaluating such treatments will require precautions to minimize potential adverse events associated with microhemorrhage. Page 1 of 11 (page number not for citation purposes) Journal of Neuroinflammation 2004, 1:24 Background Alzheimer's disease is characterized not only by the presence of parenchymal amyloid deposits and intracellular tangles but also by the presence of amyloid deposits in the vasculature, a condition referred to as cerebral amyloid angiopathy (CAA). The CAA observed in both Alzheimer's disease patients [1] and some of the transgenic mouse models [2] is primarily composed of the shorter form of amyloid beta (Aβ), Aβ1–40, while the majority of amyloid deposits in the parenchyma are composed of Aβ1–42, although the compact amyloid deposits also contain Aβ1– 40. Anti-Aβ immunotherapy has been considered as a potential treatment for Alzheimer's disease for some time [3,4]. Active immunization with a vaccine including Aβ1–42 fibrils progressed to human clinical trials where its administration was suspended due to meningoencephalitits in a subset of patients [5]. To date there have been pathology reports on two patients who participated in the trial and subsequently died [6,7]. Both reports note that while the numbers of parenchymal amyloid deposits appeared lower than expected in these cases, the CAA in these patients did not appear outside the normal range for Alzheimer's disease. In addition, one report mentioned multiple cortical hemorrhages and the presence of hemosiderin around the CAA vessels [7]. Given the adverse reactions to the active immunization, the irreversibility of such procedures and the variable antibody response to vaccines in older individuals [8], passive immunization against the Aβ peptide emerged as an alternative immunotherapeutic strategy. Studies in young and middle aged APP-transgenic mice have reported significant amyloid reductions with passive immunization [911]. Such treatments also demonstrate rapid improvements of memory function in APP-transgenic mice, sometimes without detectable reductions in amyloid [12-14]. Most recently, intracranial administration of anti-Aβ antibodies has been shown to not only remove Aβ but also clear, early-stage, hyperphosphorylated-tau aggregates [15]. Importantly, in the only prior study evaluating adoptive antibody transfer in older APP-transgenic mice, Pfeifer et al. [16] reported a doubling of cerebral microhemorrhages associated with significant reductions in amyloid burden after administration of an N-terminal specific anti-Aβ antibody. Materials and Methods Experiment design Mice derived from APP Tg2576 mice were obtained from our breeding program at University of South Florida started in 1996 [17]. For the 5-month treatment study, 13 APP-transgenic mice, aged 23 months, were assigned to one of two groups. The first group received weekly intra- http://www.jneuroinflammation.com/content/1/1/24 peritoneal anti-Aβ antibody injections (antibody 2286; mouse-monoclonal anti-human Aβ28–40 IgG1; Rinat Neurosciences, Palo Alto, CA) for a period of 5 months (n = 6). The second group received weekly intraperitoneal antiAMN antibody (2906; mouse-monoclonal anti-Drosophila amnesiac protein IgG1; Rinat Neurosciences, Palo Alto, CA) injections for a period of 5 months (n = 7). Seven nontransgenic mice were also assigned to one of two groups. The first group received weekly intraperitoneal anti-Aβ antibody injections for a period of 5 months (n = 4). The second group received weekly intraperitoneal antiAMN antibody injections for a period of 5 months (n = 3). For the time course study of 1-, 2- or 3-month treatment, 22 APP-transgenic mice aged 19 months were assigned to one of four experimental groups, as described previously [14]. The first three groups received weekly intraperitoneal anti-Aβ antibody injections f (...truncated)