Electrophoretic separation of amyloid β peptides in plasma

In this prospective study, for the first time we have separated and quantified amyloid β (Aβ) 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 Aβ‐sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE)/immunoblot. In addition to the Aβ 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 Aβ1–42. Since a standard peptide with the amino acid sequence Aβ2–40 migrates in the same position, we hypothesize that this plasma‐specific band may correspond to Aβ2–40. The concentration of Aβ 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., Aβ1–37/38/42) have increased significantly when the samples have been frozen at –80°C before immunoprecipitation, while the ‘middle‐length' peptides (i.e., Aβ1–39/40) have not been affected by this procedure. We have not observed significant differences of the Aβ peptides concentrations between AD and control subjects. Our method can be used to investigate the significance of plasma Aβ peptides in neurodegenerative disorders, and to monitor the efficiency of drugs with β/γ‐secretase inhibitory potency.