Solid-phase extraction enhances detection of beta-amyloid peptides in plasma and enables Aβ quantification following passive immunization with Aβ antibodies

We have previously developed a solid-phase extraction (SPE) procedure to enable the detection of beta-amyloid (A beta) peptides in brain tissue from non-transgenic animals. We have now adapted these methods to enrich the A beta fraction in cerebrospinal fluid (CSF) and plasma. Human CSF and plasma and Tg2576 mouse plasma were subjected to guanidine denaturation followed by SPE in 96-well cassettes. The resulting eluates could be concentrated significantly to enhance detection of low-abundance A beta peptides by immunoassay. The concentrated eluates diluted in a linear fashion with consistent recovery between SPE columns. This technique was therefore used to facilitate quantification of A beta 1-X, 1-40, 1-42, and 1-38 peptides in normal human CSF and plasma samples. SPE sample preparation was also applied to the plasma of mice dosed peripherally with a monoclonal antibody raised against A beta. When such samples were assayed directly, the presence of the systemically administered antibody interfered with the subsequent immunoassay, by preventing detection of antibody-bound A beta. After subjecting plasma from antibody-treated animals to denaturation and SPE, the antibody-antigen complex was disrupted, and the A beta fraction could be isolated from the antibody-containing fraction. Application of this method allowed for detection of a 100-fold increase in plasma A beta 1-40 following treatment of Tg2576 mice or wild type littermate control mice with A beta 40-specific monoclonal antibody 9TL. Given the availability of a variety of SPE matrices, we hypothesize that these methods could facilitate plasma antigen retrieval using multiple therapeutic antibody approaches. (c) 2007 Elsevier B.V. All rights reserved.