QUANTITATION OF ALZHEIMERS AMYLOID PEPTIDE AND IDENTIFICATION OF RELATED AMYLOID PROTEINS BY DOT-BLOT IMMUNOASSAY

In Alzheimer's disease, the main component of amyloid deposits is a 39 -43 amino acid peptide referred to as amyloid peptide or A beta. A cru cial issue in the study of this disorder is to define the sequence of events that lead to amyloid deposition. In the present study, a new ap proach was developed that allows to specifically solubilize A beta pep tide trapped within amyloid deposits and to quantify its amount by dot -blot immunoassay. The present method also permits to isolate componen ts tightly bound to A beta and that are likely to catalyze its aggrega tion. Biochemical A beta quantitation was performed in 4 Brodmann area s from 17 elderly individuals exhibiting different degrees of amyloido sis. In parallel, classical neuropathology was done by histochemical a nd immunohistochemical methods. A beta amounts (pmol) were correlated to the number of amyloid deposits determined by neuropathology showing high statistical significance. Moreover, amyloid-binding proteins inc luding apolipoprotein E and heparan sulfate proteoglycans were also fo und associated to A beta in the amyloid preparation. The present bioch emical procedure is a new and reliable method to quantify amyloid depo sition in brain. Furthermore, it allows to detect amyloid-associated c omponents such as apolipoprotein E, that may be involved in the pathol ogical process of amyloidogenesis.