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Oligomer-based Diagnostics of Alzheimer's Disease

Biomarkers reflecting basic pathological processes of Alzheimer’s disease (AD) are of utmost importance regarding early diagnostics and therapy development. Formation of amyloid β (Aβ) and Tau aggregates is the major pathological hallmark of AD. Therefore Aβ and Tau aggregates and oligomers are promising biomarker candidates.

Quantitation of oligomers in body fluids like blood plasma is technically challenging as titers are expected in the femtomolar range, and the oligomeric species must be differentiated from omnipresent monomers. Additionally, the dynamic nature of oligomers and monomers renders them unstable towards harsh chemical and physical treatments allowing only mild washing conditions. To overcome these issues, we developed the surface-based fluorescence intensity distribution analysis (sFIDA) assay. sFIDA is an immune-based method with single particle sensitivity that is highly specific towards oligomers and insensitive towards monomers.

In sFIDA, monoclonal antibodies (mAbs) are used as capture molecules that immobilize the target proteins on a glass surface. For the fluorescent stain of captured protein oligomers, mAbs are used that bind to the same or an overlapping epitope region on the target protein. By this configuration, staining of monomers is avoided and only oligomers are detected. We obtain single particle sensitivity by imaging the samples with multicolor laser scanning and evaluating the number of pixel exceeding a background signal.
sFIDA works with tissue homogenates and body liquids, like blood and spinal fluid. The technology can be used for direct measures of target engagement both in pre-clinical and clinical studies.