Triazole-Peptide Conjugate as a Modulator of Aβ-Aggregation, Metal-Mediated Aβ-Aggregation, and Cytotoxicity.

Abstract

Amyloid-β (Aβ) aggregation plays a key role in the pathogenesis of Alzheimer's disease (AD). Along with this, the presence of redox-active metals like Cu2+ further enhances Aβ aggregation, oxidative stress, and cellular toxicity. In this study, we have rationally designed, synthesized, and evaluated a series of triazole-peptide conjugates as potential promiscuous ligands capable of targeting different pathological factors of AD. In particular, peptidomimetic DS2 showed the best inhibitory activity against Aβ aggregation with an IC50 value of 2.43 ± 0.05 μM. In addition, DS2 disaggregates preformed Aβ42 fibrils, chelates metal ions, inhibits metal-mediated Aβ aggregation, significantly controls reactive oxygen species production, and reduces oxidative stress. DS2 exhibited very low cytotoxicity and significantly ameliorated the Aβ-induced toxicity in differentiated neuroblastoma cells, SH-SY5Y. In addition, alteration in the fibrillary architecture of Aβ42 in the absence and presence of DS2 was validated by transmission electron microscopy (TEM) images. To shed light on the inhibitory mechanism of DS2 against Aβ aggregation and disassembly of the protofibril structure, molecular dynamics (MD) simulations have been performed. DS2 binds preferentially with the central hydrophobic core (CHC) residues of Aβ42 monomer and chains D-E of Aβ42 protofibril. The dictionary of secondary structure of proteins analysis indicated a noteworthy increase in the helix content from 38.5 to 61% and, notably, a complete loss of β-sheet content of Aβ42 monomer when DS2 is added to it. DS2 suppressed Aβ42 monomer aggregation by preserving helical conformations and was able to reduce the production of aggregation-prone β-sheet structures, which are consistent with ThT, circular dichroism, and TEM assay that indicate a reduction in the formation of toxic Aβ42 aggregated species on the addition of DS2. Moreover, DS2 destabilized the Aβ42 protofibril structure by significantly reducing the binding affinity between chains D-E of protofibril, which highlighted the disruption of interchain interactions and subsequent deformation of the protofibril structure. The results of the present study demonstrate that triazole-peptide conjugates may be valuable chemotypes for the development of promising multifunctional AD therapeutic candidates.