Immunization with Small Amyloid-beta-derived Cyclopeptide Conjugates Diminishes Amyloid-beta-Induced Neurodegeneration in Mice

Background: Soluble oligomeric (misfolded) species of amyloid-beta (A beta) are the main mediators of toxicity in Alzheimer's disease (AD). These oligomers subsequently form aggregates of insoluble fibrils that precipitate as extracellular and perivascular plaques in the brain. Active immunization against A beta is a promising disease modifying strategy. However, eliciting an immune response against A beta in general may interfere with its biological function and was shown to cause unwanted side-effects. Therefore, we have developed a novel experimental vaccine based on conformational neo-epitopes that are exposed in the misfolded oligomeric A beta, inducing a specific antibody response. Objective: Here we investigate the protective effects of the experimental vaccine against oligomeric A beta(1-42)-induced neuronal fiber loss in vivo. Methods: C57BL/6 mice were immunized or mock-immunized. Antibody responses were measured by enzyme-linked immunosorbent assay. Next, mice received a stereotactic injection of oligomeric A beta(1-42) into the nucleus basalis of Meynert (NBM) on one side of the brain (lesion side), and scrambled A beta(1-42) peptide in the contralateral NBM (control side). The densities of choline acetyltransferase-stained cholinergic fibers origination from the NBM were measured in the parietal neocortex postmortem. The percentage of fiber loss in the lesion side was determined relative to the control side of the brain. Results: Immunized responders (79%) showed 23% less cholinergic fiber loss (p = 0.01) relative to mock-immunized mice. Moreover, fiber loss in immunized responders correlated negatively with the measured antibody responses (R-2 = 0.29, p = 0.02). Conclusion: These results may provide a lead towards a (prophylactic) vaccine to prevent or at least attenuate (early onset) AD symptoms.