An ultrasensitive method for the detection of aggregated Beta-amyloid

There is strong evidence that the over-production and aggregation of Beta-amyloid (Abeta) in the form of amyloid plaques is a hallmark of Alzheimer's disease (AD). Histopathology is the current standard used to monitor the accumulation of amyloid plaques in animal models of AD. Cognitive defects arise prior to the detection of Abeta in the form of plaques, but it is nearly impossible to detect the presence of amyloid plaques in the brain of transgenic mice such as the APP/PS1 prior to 6 months of age. This technological hurdle lengthens the time required to perform pre clinical trials of candidate therapeutic compounds. Objective: Develop an ultrasensitive assay which can detect the presence of aggregated Abeta and evaluate plasma, CSF, and tissue homogenates from AD mouse models and patients. 10% brain homogenates were prepared using frozen brain tissue. Aggregated Abeta was isolated from brain homogenates using a proprietary enrichment method. Monomeric Abeta was released with disaggregants and detected using an ultra-sensitive immunoassay. This assay can routinely detect a 1/400,000-fold dilution of 10% human AD brain homogenate whereas the signal from normal human brain is undetectable. We have detected aggregated Abeta in the brains of APP/PS1 mice as young as 3 months of age. A series of blinded samples from APP/PS1 mice and non-transgenic littermates were evaluated. We correctly identified samples from 14-month old and 3 month old APP/PS1 mice and non-transgenic littermates. The level of aggregated Abeta was 5000-fold higher in older mice compared to the younger mice. Attempts to detect aggregated Abeta in a limited number of clinical plasma and CSF samples from human AD patients and age-matched controls were unsuccessful. These results suggest that the concentration of aggregated Abeta in human plasma and CSF is below the limit of detection of this assay. The Amorfix assay provides a method to rapidly detect the presence of aggregated Beta-amyloid in transgenic mice at a stage in disease progression previously undetected using conventional methods. The ability to detect aggregated Abeta at earlier stages of disease could be used to accelerate the drug development process for AD therapeutic candidates.