Synthesis and mechanistic investigation of short peptides as Aβ aggregation inhibitors

Neurotoxic oligomers of amyloid-beta (Aβ) peptide build up in the cortical region of the brain of people with Alzheimer's disease (AD). The lipophilic C-terminus region of Aβ plays a pivotal role in neurotoxic oligomer formation. Studies have confirmed that a modified fragment of the Aβ₄₂ peptide prevents its aggregation. Our research on the C-terminus fragment shows it can effectively stop the parent peptide (Aβ₄₂) from killing PC-12 cells at concentrations between 2 and 10 μM. We have synthesized peptides applying a solid phase synthesis strategy involving an eco-friendly microwave (MW)-assisted protocol. The lead peptide Gly-Cle-Val-Ile-Ala-NH₂ (20) showed a 100 % anti-aggregation effect against Aβ₄₂ at 2 μM. The Th-T fluorescence assays showed 100 % inhibition of the amyloid species in all tested concentrations; even a 0.5 μM dose of the peptide could inhibit Aβ₄₂ aggregations at 24 and 48 h of incubation. Also, 96.8 % deformation was found at 10 μM at 72 h of incubation. In the ANS fluorescence assays, 59 % and 41.7 % inhibition of the amyloid species and 34.4 % deformation results were obtained. The Th-T and ANS fluorescence assays supported the results. In the CD spectroscopy investigation, peptide 20 curbed β-sheet conformations. The fact that Aβ₄₂ fibrillary networks were not visible in HRTEM and STEM images showed evidence that Aβ₄₂ had not aggregated in the presence of peptide 20. DLS study provided a further mechanistic understanding of the effectiveness of peptide 20. We conclude that peptide 20 diminishes the Aβ peptide aggregation process at low μM concentrations and is non-cytotoxic.