Altering the Process of Aß-Plaque Formation: Effect of Monoclonal Antibodies

Amyloid diseases are a steadily expanding group of debilitating human disorders, including Alzheimer's disease and Parkinson's disease, which are characterized by deposits of insoluble protein fibrils in various tissues. High-visibility studies have found that amyloid mature fibrils are one of the main pathogenic agents in Alzheimer's, resulting in the deposition of extracellular Amyloid beta (As) plaques. Hence, determining the kinetics of amyloid fibril formation, characterizing the morphology of intermediate aggregates and relating them to underlying changes in protein structure are essential for their prevention and removal. Equally important, experimental techniques to provide in-situ characterization of amyloid-s aggregation, aggregate structures and associated changes in protein structure are critical for testing drug targets for their ability to disrupt fibril formation. We have used atomic force microscopy (AFM), transmission electron microscopy (TEM), and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy to monitor the time course of changes in topology and conformation of the peptide aggregates. These measurements allow us to detect changes in intra and intermolecular beta sheets, beta turns, and alpha helix conformational rearrangements and relate them to topography conformations. We have tested the effects of different monoclonal antibodies (anti-As mAbs), both N-terminus and C-terminus, on preformed fibrils. We found that for molar ratios of 10:1 to 50:1 (amyloid:antibody), the dissolution process proceeds to completion within 144 hours. We determined that lower stoichiometric molar ratios of antibodies (1000:1) in preincubated solutions of As peptides also promoted defibrillization, but the time to achieve complete removal is more than 6 days. The outcomes of this study provide an in-vitro quantitative model to understand the potentially catalytic capacity of anti-As mAbs to monomerize assemblies of As and instruct the design and interpretation of ongoing clinical trials of these therapeutics in Alzheimer' disease patients.