A Sensitive Aβ Oligomer Assay Discriminates Alzheimer's and Aged Control Cerebrospinal Fluid

Ahallmark of Alzheimer's disease (AD) brain is the amyloid beta (A beta) plaque, which is comprised of A beta peptides. Multiple lines of evidence suggest that A beta oligomers are more toxic than other peptide forms. We sought to develop a robust assay to quantify oligomers from CSF. Antibody 19.3 was compared in one-site and competitive ELISAs for oligomer binding specificity. A two-site ELISA for oligomers was developed using 19.3 coupled to a sensitive, bead-based fluorescent platform able to detect single photons of emitted light. The two-site ELISA was >2500x selective for A beta oligomers over A beta monomers with a limit of detection similar to 0.09 pg/ml in human CSF. The lower limit of reliable quantification of the assay was 0.18 pg/ml and the antibody pairs recognized A beta multimers comprised of either synthetic standards, or endogenous oligomers isolated from confirmed human AD and healthy control brain. Using the assay, a significant 3- to 5-fold increase in A beta oligomers in human AD CSF compared with comparably aged controls was demonstrated. The increase was seen in three separatehumancohorts, totaling 63AD and 54 controls. CSF oligomers ranged between 0.1 and 10 pg/ml. A beta oligomer levels did not strongly associate with age or gender, but had an inverse correlation with MMSE score. The C statistic for theA beta oligomer ROC curve was 0.86, with 80% sensitivity and 88% specificity to detect AD, suggesting reasonable discriminatory power for the AD state and the potential for utility as a diagnostic marker.