Identification of a BACE1 Binding Peptide Candidate for the Prevention of Amyloid Beta in Alzheimer's Disease.
BACKGROUND/AIMS
Amyloid plaques, generated during the progression of Alzheimer's disease, cause major neurological deficits due to substantial cell toxicity and death. The underlying cause of plaque generation stems from cleavage of the amyloid precursor protein (APP) by β-secretase (BACE1). A resulting amyloid-β (Aβ) fragment forms aggregates to produce the main constituent of a plaque.


METHODS
Phage display and biopanning techniques were used to identify a 12-mer peptide that had a natural affinity for the BACE1 enzyme. The peptide was translated from phage DNA and synthetically produced. The peptide, at concentrations of 1nM, 10nM and 100nM, was used to confirm binding by direct assay. Non-specific binding to BACE2, renin and cathepsin D was tested by direct binding assay. A BACE1 activity assay was used to determine the peptide effect on cleavage of an APP substrate. Treatment of SY5Y cells with the peptide was used to determine toxicity and prevention of Aβ40 and Aβ42 production.


RESULTS
After identification and synthetic production, the peptide exhibited a strong affinity for BACE1 at nanomolar concentrations in the direct assay. In case of non-specific binding to homologous BACE2, renin and cathepsin D, the peptide showed minor binding but was nullified when in solution with BACE1. The peptide addition to a BACE1 activity assay was able to significantly reduce the amount of substrate cleavage. SY5Y cells, when treated with the peptide, did not show any detrimental morphological changes while being able to reduce the production of natural Aβ40 and Aβ42. Even under stressed conditions (H2O2 treatment) where the Aβ production was higher, the peptide was still able to significantly reduce the effect of BACE1 while not effecting cell viability.


CONCLUSION
The identified peptide exhibited strong binding to BACE1 in vitro and was able to reduce production of Aβ, suggesting a favourable BACE1 inhibitor for future refining and characterisation.