Immunization reverses memory deficits without reducing brain Aβ burden in Alzheimer's disease model

Abstract

We have previously shown that chronic treatment with the monoclonal antibody m266, which is specific for amyloid beta-peptide (Abeta), increases plasma concentrations of Abeta and reduces Abeta burden in the PDAPP transgenic mouse model of Alzheimer's disease (AD). We now report that administration of m266 to PDAPP mice can rapidly reverse memory deficits in both an object recognition task and a holeboard learning and memory task, but without altering brain Abeta burden. We also found that an Abeta/antibody complex was present in both the plasma and the cerebrospinal fluid of m266-treated mice. Our data indicate that passive immunization with this anti-Abeta monoclonal antibody can very rapidly reverse memory impairment in certain learning and memory tasks in the PDAPP mouse model of AD, owing perhaps to enhanced peripheral clearance and (or) sequestration of a soluble brain Abeta species.

Probing the origins, diagnosis and treatment of amyloid diseases using antibodies

“…Finally, in some transgenic mice, vaccination with Ab has prevented the age dependent memory loss characteristic of such animals while only modestly decreasing the amyloid plaque burden, suggesting that the antibodies produced following the vaccination could specifically target the oligomeric species responsible for memory loss [79]. Even more remarkably, a single administration of a monoclonal antibody to Ab has recently been shown rapidly (within hours) to reverse memory impairment in certain learning and memory tasks in transgenic mouse models of Alzheimer's disease without any detectable alteration in the Ab burden, suggesting that this antibody also targets soluble Ab species that are particularly toxic [80].…”

“…Recent studies report the success of both active and passive vaccination approaches to slowing and/or reversing the aggregation process, and its pathological consequences, in mouse models of light chain amyloidosis [71], Alzheimer's disease [77,79,80,[86][87][88][89][90] and mammalian prion diseases [76,[91][92][93]. The molecular mechanisms by which antibodies act in a therapeutic manner are just beginning to be understood (for recent reviews see [94][95][96][97][98][99]) (Textbox 3).…”

Impact of amyloid imaging on drug development in Alzheimer's disease

“…These results were interpreted to imply that insoluble Aβ is a surrogate marker for "small assemblies" of Aβ that disrupt cognition and occur as intermediates during the formation of insoluble Aβ. This finding was extended to the PDAPP strain of mice by Dodart and colleagues [50]. This group previously reported that chronic treatment of PDAPP mice with the m266 anti-Aβ antibody (every 2 weeks from 4 to 9 months of age) reduced Aβ burden at least in part by increasing peripheral clearance [55].…”

“…This group previously reported that chronic treatment of PDAPP mice with the m266 anti-Aβ antibody (every 2 weeks from 4 to 9 months of age) reduced Aβ burden at least in part by increasing peripheral clearance [55]. In the subsequent study in 24 month-old PDAPP mice [50], they found that a "subchronic" six-week course of m266 immunotherapy reversed the cognitive deficits measured, but did not decrease the Aβ immunohistochemical burden (brain Aβ levels were not determined by ELISA). More surprisingly, they found that the cognitive deficits measured in 11 month-old PDAPP mice could be reversed within days of a single dose of the m266 anti-Aβ antibody.…”

“…In summary, the evidence that oligomeric Aβ42 is the most toxic species of Aβ is convincing. Studies strongly support the following: 1) all else being equal, enriched oligomeric preparations of Aβ42 appear to be the most toxic species [38,39]; 2) oligomeric species of Aβ42 can inhibit long term potentiation (LTP) and lead to synaptic dysfunction [48,49]; 3) memory loss occurs prior to extensive deposition of fibrillar Aβ42 in transgenic mice and can be reversed by targeting soluble species of Aβ42 [50,51,52,53]; and 4) oligomeric Aβ42 species exist in AD brain [54]. However, it is important to appreciate that the removal or reduction of the soluble, toxic oligomeric forms of Aβ42 from brain parenchyma will require the concomitant reduction and removal of the insoluble (fibrillar) Aβ42 pool as well.…”