Mass spectrometric quantification of amyloid-beta in cerebrospinal fluid and plasma

Alzheimer’s disease (AD) is the most common neurodegenerative disease among the elderly and accounts for 60-80% of all cases of dementia. Currently, the diagnosis of AD is based on cognitive tests and mental state exams, but the peptide amyloid-beta (Aβ) in cerebrospinal fluid (CSF) is increasingly used in clinical trials and settings. As for most protein and peptide biomarkers, quantification is performed using antibody-based techniques such as enzyme-linked immunosorbent assay (ELISA). However these immunoassays suffer from high variability in measurements of Aβ concentrations, hampering its use as a diagnostic marker. The aim of this thesis was to develop an antibody independent method for absolute quantification of Aβ in human CSF, free of the specificity and reproducibility issues associated with antibody-based quantification. The method was based on solid-phase extraction (SPE) and liquid chromatography (LC)-tandem mass spectrometry (MS/MS). Stable isotope labeled Aβ peptides were used as internal standards, enabling absolute quantification. The method was first tested in a pilot study with CSF samples from AD patients and controls. As expected, the level of the 42 amino acid variant of Aβ (Aβ1-42) was decreased in AD CSF as compared to controls (p