Urea-based two-dimensional electrophoresis of beta-amyloid peptides in human plasma:: Evidence for novel Aβ species

The detailed analysis of beta-amyloid (A beta) peptides in human plasma is still hampered by the limited sensitivity of available mass spectrometric methods and the lack of appropiate ELISAs to measure A beta peptides other than A beta(1-38), A beta(1-40), and A beta(1-42). By combining high-yield A beta immuno-precipitation (IP), IEF, and urea-based A beta-SDS-PAGE-immunoblot, at least 30 A beta-immuno-reactive spots were detected in human plasma samples as small as 1.6 mL. This approach clearly resolved A beta peptides A beta(1-40), A beta(1-42), A beta(1-37), A beta(1-38), A beta(1-39), the N-truncated A beta(2-40), A beta(2-42), and, for the first time, also A beta(1-41). Relative quantification indicated that A beta(1-40) and A beta(1-42) accounted for less than 60% of the total amount of A beta peptides in plasma. All other A beta peptides appear to be either C-terminally or N-terminally truncated forms or as yet uncharacterized A beta species which migrated as trains of spots with distinct pIs. The AD pattern found in cerebrospinal fluid (CSF) was substantially less complex. This sensitive method (2-D A beta-WIB) might help clarifying the origin of distinct AD species from different tissues, cell types, or intracellular pools as well as their amyloidogenicity. It might further help identifying plasma AD species suitable as biomarkers for the diagnosis of Alzheimer's disease (AD).