BETA-AMYLOID PROTEIN IS HIGHER IN ALZHEIMERS-DISEASE BRAINS - DESCRIPTION OF A QUANTITATIVE BIOCHEMICAL ASSAY

Deposition of beta-amyloid protein (Abeta) in senile plaques and in th e walls of cerebral vessels is a pathologic hallmark of Alzheimer's di sease (AD). The current diagnostic criteria for AD requires the presen ce of neurofibrillary tangles and a minimum number of senile plaques i n cortex. Senile plaques are readily visualized by silver staining or immunocytochemistry using antibodies raised to Abeta. Available histoc hemical and immunocytochemical methods are sensitive but the results m ay occasionally be variable and sampling from many brain regions is di fficult and impractical. This study describes a simple biochemical met hod for quantifying the Abeta load in unfixed brain homogenates. The i mmunoassay recognizes all forms of Abeta deposits (neuritic and diffus e plaques, and cerebrovascular amyloid) and has a sensitivity and spec ificity comparable to immunocytochemistry. In direct comparisons, resu lts from the dot blot method correspond well with both Western blot an alysis of partially purified Abeta and plaque counting by immunocytoch emistry. In a retrospective series of 39 postmortem AD and control cas es, the amount of Abeta in brain by dot blot immunoreactivity effectiv ely separated the two groups. Therefore, this method provides a rapid, sensitive, and accurate quantitation of Abeta in postmortem brain tis sue and represents an alternative approach for studying Abeta depositi on in aging and AD.