Therapeutic albumin binding to remove amyloid-β.

Clearance of plasma amyloid-β (Aβ) through plasma exchange and replacement with therapeutic albumin to facilitate net Aβ efflux from the brain to plasma is a novel approach for the treatment of Alzheimer's disease. Therefore, thorough characterization of the capacity of therapeutic albumin to bind Aβ is warranted. In this study, Aβ40 and Aβ42 were quantified by commercial ELISA or Araclon ABtest® in samples of Grifols' therapeutic albumin (Albutein®) 5%, 20%, and 25%. The capacity of Albutein® to bind Aβ was assessed by: a) ELISA in serially diluted therapeutic albumin (0-45 mg/ml protein concentration) to which 80 pg/ml of synthetic Aβ peptide (sAβ40 or sAβ42) were added; b) ELISA in samples of the therapeutic albumin containing serially diluted sAβ40 or sAβ42 (60-400 pg/ml); and c) surface plasmon resonance (SPR) for sAβ42 binding. The Aβ content in Albutein® was below the quantification threshold of the ELISA tests (<25 to <62.5 pg/ml) and ABtest® (<3.125 pg/ml). Quantification of exogenously added sAβ42 decreased in parallel with increasing protein concentration (59-78% at 45 mg/ml albumin). Recovery of sAβ serially diluted in Albutein® was ∼60% for sAβ40 and ∼70% for sAβ42, but was ∼100% in control samples without albumin. The KD by SPR analysis for sAβ42 interaction with Albutein® was 1.72 ± 0.24 × 10-6 M. In conclusion, Grifols' therapeutic albumin has undetectable content of Aβ40 and Aβ42. Moreover, Grifols' therapeutic albumin consistently binds peptides containing the primary sequence of human Aβ.