Pathogenic events in Alzheimer's disease are believed to involve an imbalance between the production and clearance of the neurotoxic 42 amino acid form of the beta-amyloid peptide (Abeta1-42). Although much is known about the production of Abeta1-42, many questions remain about its degradation. Here, we describe an optimized automated immunoprecipitation mass spectrometry method that enables accurate and rapid monitoring of the major Abeta isoforms in cerebrospinal fluid. Furthermore, we describe a technique of antibody immobilization, minimizing background signals. The identities of these Abeta products were confirmed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and nanoflow liquid chromatography and tandem mass spectrometry with a hybrid linear trap Fourier transform ion cyclotron resonance mass spectrometer. Finally, we report the finding of two novel Abeta peptides (Abeta2-17 and Abeta3-17).

The neurodegenerative disorder Alzheimer's disease (AD) is the most common cause of dementia in the elderly. The presence of neurofibrillary tangles, consisting of hyperphosphorylated tau protein, is one of the major neuropathologic characteristics of the disease, making this protein an attractive biomarker for AD and a possible target for therapy. Here, we describe an optimized immunoprecipitation mass spectrometry method that enables, for the first time, detailed characterization of tau in human cerebrospinal fluid. The identities of putative tau fragments were confirmed using nanoflow liquid chromatography and tandem mass spectrometry. Nineteen tryptic fragments of tau were detected, of which 16 are found in all tau isoforms while 3 represented unique tau isoforms. These results pave the way for clinical CSF studies on the tauopathies.

Background: Aggregation of β-amyloid (Aβ) into oligomers and plaques is the central pathogenic mechanism in Alzheimer’s disease (AD). Aβ is produced from the amyloid precursor protein (APP) by β- and γ-secretases, whereas, in the nonamyloidogenic pathway, α-secretase cleaves within the Aβ sequence, and thus precludes Aβ formation. A lot of research has focused on Aβ production and the neurotoxic 42-amino-acid form of Aβ (Aβ1–42), while less is known about the nonamyloidogenic pathway and how Aβ is degraded. Objective: To study the Aβ metabolism in man by searching for novel Aβ peptides in cerebrospinal fluid (CSF). Methods: Immunoprecipitation, using an anti-Aβ antibody, 6E10, was combined with either matrix-assisted laser desorption/ionization time-of-flight mass spectrometry or nanoflow liquid chromatography and tandem mass spectrometry. Results: We identified 12 truncated APP/Aβ peptides in the CSF, all of which end at amino acid 15 in the Aβ sequence, i.e. 1 amino acid before the proposed α-secretase site. Of these 12 APP/Aβ peptides, 11 are novel peptides and start N-terminally of the β-secretase site. The most abundant APP/Aβ peptide starts 25 amino acids before the β-secretase site, APP/Aβ (–25 to 15), and had a concentration of approximately 80 pg/ml. The identity of all the APP/Aβ peptides was verified in a cohort of AD patients and controls. A first pilot study also showed that the intensity of several APP/Aβ peaks in CSF was higher in AD cases than in controls. Conclusion: These data suggest an enzymatic activity that cleaves the precursor protein in a specific manner that may reflect a novel metabolic pathway for APP and Aβ.