Binding of a beta-amyloid 1-42 peptide to human albumin grifols®

Abstract

Beta-amyloid (Aβ) deposits may be the central pathological process in Alzheimer's disease. Since there seems to be an equilibrium between brain and plasma Aβ and given that 90% of plasma Aβ may be bound to albumin (1), it might be possible to reduce plasma Aβ levels by plasma exchange with therapeutic albumin, which could in turn translate into brain amyloid burden reduction ((2), (3)). The aim of this study is to demonstrate the capacity of Human Albumin Grifols® to bind a synthetic peptide with the human amyloid beta peptide 1-42 sequence (sAβ1-42). The capacity of Human Albumin Grifols® to bind human sAβ1-42, has been measured for three different batches, using Surface Plasmon Resonance (SPR). Kinetics and equilibrium features of Human Albumin Grifols® / sAβ1-42 peptide interaction have been analyzed in a Biacore T100 by immobilizing sAβ1-42 (Biosource) on a CM5 chip. Known quantities of these samples were analyzed to obtain kinetic constants for sAβ1-42 binding and release. Moreover, a qualitative comparison of the SPR response has been established by exposing sAβ1-42 to plasma samples. Results obtained from three different lots of Human Albumin Grifols® show that the association rate constant (ka) for Human Albumin Grifols®/sAβ1-42 is (1.53 ± 0.11) x104 M−1s−1, while the corresponding dissociation rate constant (kd) is (0.026 ± 0.004) s−1. Thus, the equilibrium constant KD (concentration at which 50% of sAβ1-42 is complexed) for Human Albumin Grifols®/sAβ1-42 is on average (1.72 ± 0.24) x10−6 M, demonstrating the consistency of this interaction. Likewise, as expected according to the literature indicating that human amyloid beta appears to be able to interact with several plasma proteins, the SPR response obtained when different plasma samples were analysed was higher than for isolated albumin. These results indicate that Human Albumin Grifols® is able to bind to an Aβ1-42 peptide with the human aminoacid sequence.