N-Terminally Truncated And Pyroglutamate-Modified A Beta Forms Are Measurable In Human Cerebrospinal Fluid And Are Potential Markers Of Disease Progression In Alzheimer'S Disease

Alzheimer's disease (AD) is a pathology characterized by the accumulation in the brain of intracellular and extracellular amyloid-beta (A beta) aggregates, especially of A beta 1-40 and A beta 1-42 peptides. It is known that N-terminally truncated or modified A beta forms also exist in AD brains and cerebrospinal fluid (CSF), and they play a key role in the pathogenesis of the disease. Herein, we developed an antibody-free method based on Solid-Phase Extraction and Electrospray Ionization Liquid Chromatography Mass Spectrometry for the identification and quantitation in human CSF of A beta isoforms. In human CSF, we could detect and quantify a panel of 19 A beta isoforms, including N-terminally truncated and pyroglutamate-modified forms, never quantified before in CSF. Among these, we identified novel N-terminally truncated A beta species: four bound to copper and two phosphorylated forms, which were found to be the most common proteoforms in human CSF along with A beta 1-40, A beta 3-40, and A beta pE11-42. We tested the newly developed and validated method in a pilot study on CSF from elderly individuals with subjective memory complaints (SMCs, n = 9), mild cognitive impairment (MCI, n = 18), and AD (n = 15); along with A beta 1-42, five N-terminally truncated forms (A beta 11-40, A beta 3-42, A beta pE11-42, A beta pE3-40, and A beta 4-40 Cu2+) are altered in AD/MCI. Thus, we demonstrated that N-terminally truncated and pyroglutamate-modified A beta can be quantified in human CSF, and five of them, along with A beta 1-42, are potential markers of AD progression. The described method could represent a useful tool for patients' stratification and monitoring. Moreover, the newly identified A beta CSF species might represent new potential therapeutic targets.