N-terminal heterogeneity of parenchymal and vascular amyloid-β deposits in Alzheimer's disease

Aims The deposition of amyloid-beta (A beta) peptides in the form of extracellular plaques in the brain represents one of the classical hallmarks of Alzheimer's disease (AD). In addition to 'full-length' A beta starting with aspartic acid (Asp-1), considerable amounts of various shorter, N-terminally truncated A beta peptides have been identified by mass spectrometry in autopsy samples from individuals with AD. Methods Selectivity of several antibodies detecting full-length, total or N-terminally truncated A beta species has been characterized with capillary isoelectric focusing assays using a set of synthetic A beta peptides comprising different N-termini. We further assessed the N-terminal heterogeneity of extracellular and vascular A beta peptide deposits in the human brain by performing immunohistochemical analyses using sporadic AD cases with antibodies targeting different N-terminal residues, including the biosimilar antibodies Bapineuzumab and Crenezumab. Results While antibodies selectively recognizing A beta(1-)(x)showed a much weaker staining of extracellular plaques and tended to accentuate cerebrovascular amyloid deposits, antibodies detecting A beta starting with phenylalanine at position 4 of the A beta sequence showed abundant amyloid plaque immunoreactivity in the brain parenchyma. The biosimilar antibody Bapineuzumab recognized A beta starting at Asp-1 and demonstrated abundant immunoreactivity in AD brains. Discussion In contrast to other studied A beta(1-)(x)-specific antibodies, Bapineuzumab displayed stronger immunoreactivity on fixed tissue samples than with sodium dodecyl sulfate-denatured samples on Western blots. This suggests conformational preferences of this antibody. The diverse composition of plaques and vascular deposits stresses the importance of understanding the roles of various A beta variants during disease development and progression in order to generate appropriate target-developed therapies.