Electrophoretic separation of amyloid β peptides in plasma

Abstract

In this prospective study, for the first time we have separated and quantified amyloid beta (Abeta) peptides in the plasma of patients with Alzheimer's disease (AD, n = 8) and age- and environment-matched healthy controls (n = 9) with urea-based Abeta-sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE)/immunoblot. In addition to the Abeta peptides 1-37/38/39/40/42, which we recently identified as regular constituents of human cerebrospinal fluid (CSF), we have observed a novel electrophoretic band migrating slightly cathodically to Abeta1-42. Since a standard peptide with the amino acid sequence Abeta2-40 migrates in the same position, we hypothesize that this plasma-specific band may correspond to Abeta2-40. The concentration of Abeta peptides in the plasma has been approximately 100-fold lower compared to the CSF. Interestingly, the concentration of the two shortest peptides and the longest one of these considered here (i.e., Abeta1-37/38/42) have increased significantly when the samples have been frozen at -80 degrees C before immunoprecipitation, while the 'middle-length' peptides (i.e., Abeta1-39/40) have not been affected by this procedure. We have not observed significant differences of the Abeta peptides concentrations between AD and control subjects. Our method can be used to investigate the significance of plasma Abeta peptides in neurodegenerative disorders, and to monitor the efficiency of drugs with beta/gamma-secretase inhibitory potency.

β-Amyloid Peptide Variants in Brains and Cerebrospinal Fluid from Amyloid Precursor Protein (APP) Transgenic Mice

“…In line with this hypothesis, in a human control brain sample devoid of amyloid plaques (amyloid stage 0), we observed a substantially different pattern of A␤ peptides than in the human brain samples classified as amyloid stages B or C. In the sample without plaques, the total amount of A␤ was comparatively small and presumably represented soluble A␤. The predominant A␤ variant was A␤ , which is consistent with A␤(1-40) representing the main soluble A␤ species in cell culture supernatants (9) and biological fluids (10,11). Thus, the soluble A␤ species appear similar in humans and transgenic mice.…”

“…The resulting A␤ peptides represent a heterogeneous group of peptides with different lengths. A␤ is the predominant form released from cultured cells (9) and in biological fluids, such as blood (10) and cerebrospinal fluid (CSF) (11). Longer forms ending at amino acid 42 are believed to be particularly important in the pathogenesis of AD due to a higher propensity to aggregate (12).…”

Soluble amyloid precursor proteins in the cerebrospinal fluid as novel potential biomarkers of Alzheimer's disease: a multicenter study

“…[28][29][30] In case of both candidate biomarkers in this study, no difference was observed between the results from samples stored at þ 4 1C and room temperature, and between samples constantly kept frozen (at À80 1C) or exposed for refreezing, respectively. This could mean that CSF samples may be sent between laboratories via regular mail without necessity of cooling, and that precious aliquots of experimental study samples can be thawed and refrozen.…”

Stability of amyloid‐β peptides in plasma and serum

“…For example, it has been reported that CSF Ab peptide levels may be diminished by freezing or the use of specific sampling tube types, such as polystyrene [14,15]. With respect to plasma Ab peptides, freezing of samples resulted in a significant increase in Ab1-37, Ab1-38 and Ab1-42, but unchanged concentrations for Ab1-39 and Ab1-40 [2]. Otherwise, storage of CSF for up to 48 h has not been reported to be problematic [11], but this has not yet been investigated for blood.…”

“…Ab1-37/38/39/40/42, which our group had characterised as regular constituents of human CSF [1], to also occur in plasma [2]. However, plasma Ab peptides were characterised by the additional amino-terminally truncated species Ab2-40.…”