Quantitative analysis of amyloid-β peptides in cerebrospinal fluid using immunoprecipitation and MALDI-Tof mass spectrometry

Immunoprecipitation (IP) combined with matrix-assisted laser desorption ionization (MALDI) time of flight (Tof) mass spectrometry has been used to develop quantitative assays for amyloid-b (Ab) peptides in cerebrospinal fluid (CSF). Inclusion of 15 N labelled standard peptides allows for absolute quantification of multiple Ab isoforms in individual samples. Characterization of variability associated with all steps of the assay indicated that the IP step is the single largest contributor to overall variability. Optimization of the assay resulted in overall coefficient of variation � 8% with high agreement to an Ab1-40 and Ab1-42 ELISA assay. Application of the MALDI-Tof assay to CSF obtained from healthy volunteers and Alzheimer’s disease patients indicated statistically significant 43% lower levels of Ab1-42 in the AD group (P ¼ 0.0025).