RESUMO
AIMS: The deposition of amyloid-ß (Aß) 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' Aß starting with aspartic acid (Asp-1), considerable amounts of various shorter, N-terminally truncated Aß 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 Aß species has been characterized with capillary isoelectric focusing assays using a set of synthetic Aß peptides comprising different N-termini. We further assessed the N-terminal heterogeneity of extracellular and vascular Aß 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 Aß1-x showed a much weaker staining of extracellular plaques and tended to accentuate cerebrovascular amyloid deposits, antibodies detecting Aß starting with phenylalanine at position 4 of the Aß sequence showed abundant amyloid plaque immunoreactivity in the brain parenchyma. The biosimilar antibody Bapineuzumab recognized Aß starting at Asp-1 and demonstrated abundant immunoreactivity in AD brains. DISCUSSION: In contrast to other studied Aß1-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 Aß variants during disease development and progression in order to generate appropriate target-developed therapies.
