Analysis of heterogeneous A4 peptides in human cerebrospinal fluid and blood by a newly developed sensitive Western blot assay

• Published in: The Journal of biological chemistry 1996-09, Vol.271 (37), p.22908-22914
• Main Authors: Ida, N, Hartmann, T, Pantel, J, Schröder, J, Zerfass, R, Förstl, H, Sandbrink, R, Masters, C L, Beyreuther, K
• Format: Article
• Language: English
• Subjects: Aged; Aged, 80 and over; Amyloid beta-Protein Precursor - analysis; Amyloid beta-Protein Precursor - blood; Amyloid beta-Protein Precursor - cerebrospinal fluid; Antibodies, Monoclonal; Blotting, Western - methods; Enzyme-Linked Immunosorbent Assay; Female; Humans; Male; Peptide Fragments - analysis
• ISSN: 0021-9258

The betaA4 peptide, a major component of senile plaques in Alzheimer's disease (AD) brain, has been found in cerebrospinal fluid (CSF) and blood of both AD patients and normal subjects. Although betaA4 1-40 is the major form produced by cell metabolism and found in CSF, recent observations suggest that the long-tailed betaA4 1-42 plays a more crucial role in AD pathogenesis. Here, we established new monoclonal antibodies against the C-terminal end of betaA4 1-40 and 1-42, and used them for the specific Western blot detection. After optimizing the assay conditions, these antibodies detected low picogram amount of betaA4, and both betaA4 1-40 and 1-42 levels in CSF could be determined by direct loading of the samples. Blood levels of betaA4 1-40 and 1-42 were also determined by specific immunoprecipitation followed by Western blot detection. We found that CSF betaA4 1-42 level is lower in AD patients compared with non-demented controls, although there was a significant overlap between the groups. The level of betaA4 1-40 in CSF, and of betaA4 1-40 as well as betaA4 1-42 in plasma, were not different between AD patients and controls. Besides the 4-kDa full-length betaA4 band, we could also detect several N-terminal variants of betaA4 in CSF and plasma of both AD patients and controls. Two N-terminally truncated betaA4 species migrating at the position of 3.3 and 3.7 kDa were found in CSF, while 3.7- and 5-kDa forms were found in plasma. The relative abundance of these various species were considerably different in the CSF and plasma, suggesting that the cellular source and/or clearance of betaA4 is different in these two compartments.