Amyloid–ß peptides interaction with curcumin:AFM and electrochemical characterisation

Abstract

The naturally occurring polyphenol curcumin found in turmeric has strong affinity for binding to amyloid beta (Aβ) peptides, a key feature of Alzheimer's disease pathology. Its structure allows curcumin to interact with the hydrophobic regions of Aβ peptides, which are crucial for β-sheet formation, inhibiting Aβ aggregation and fibril formation, destabilizing existing plaques, and reducing neurotoxicity. The time-dependent structural modifications and electrochemical behaviour of human Aβ₁₋₄₀ and Aβ₁₋₄₂ peptides following their interaction with curcumin were investigated by atomic force microscopy (AFM), differential pulse (DP) voltammetry and electrochemical impedance spectroscopy (EIS). The results showed that curcumin disrupts and slows the fibrillization process by binding to specific aromatic residues of the Aβ peptides, via curcumin methoxy and hydroxy groups, hindering the conformational changes required for fibril nucleation and elongation. This targeted binding not only influences the Aβ dynamics, reducing the extent of fibrilization, but also promotes more opened configurations that enhance the electron transfer from the electroactive amino acid residues histidine H⁶, tyrosine Y¹⁰, histidines H¹³ and H¹⁴, and methionine M³⁵ to the electrode surface, due to their direct interaction with curcumin and/or their proximity to other curcumin binding sites, consistent with the curcumin inducing the formation of soluble less toxic species. This dual ability to slow fibril formation and induce the formation of unconventional Aβ_1–40 and Aβ₁₋₄₂ monomeric, oligomeric, prefibrillar, and flexible fibrillar species highlights curcumin potential as a therapeutic agent in Alzheimer's disease.