A Sensitive and Cost-Effective Chemiluminescence ELISA for Measurement of Amyloid-β 1-42 Peptide in Human Plasma

Background: Amyloid-beta(42) (A beta(42)) is associated with plaque formation in the brain of patients with Alzheimer's disease (AD). Studies have suggested the potential utility of plasma A beta(42) levels in the diagnosis, and in longitudinal study of AD pathology. Conventional ELISAs are used to measure A beta(42) levels in plasma but are not sensitive enough to quantitate low levels. Although ultrasensitive assays like single molecule array or immunoprecipitation-mass spectrometry have been developed to quantitate plasma A beta(42) levels, the high cost of instruments and reagents limit their use. Objective: We hypothesized that a sensitive and cost-effective chemiluminescence (CL) immunoassay could be developed to detect low A beta(42) levels in human plasma. Methods: We developed a sandwich ELISA using high affinity rabbit monoclonal antibody specific to A beta(42). The sensitivity of the assay was increased using CL substrate to quantitate low levels of A beta(42) in plasma. We examined the levels in plasma from 13 AD, 25 Down syndrome (DS), and 50 elderly controls. Results: The measurement range of the assay was 0.25 to 500 pg/ml. The limit of detection was 1 pg/ml. All AD, DS, and 45 of 50 control plasma showed measurable A beta(42) levels. Conclusion: This assay detects low levels of A beta(42) in plasma and does not need any expensive equipment or reagents. It offers a preferred alternative to ultrasensitive assays. Since the antibodies, peptide, and substrate are commercially available, the assay is well suited for academic or diagnostic laboratories, and has a potential for the diagnosis of AD or in clinical trials.