Interaction and reactivity of synthetic aminoisoflavones with metal-free and metal-associated amyloid-β

Abstract

Metal ion homeostasis in conjunction with amyloid-β (Aβ) aggregation in the brain has been implicated in Alzheimer’s disease (AD) pathogenesis. To uncover the interplay between metal ions and Aβ peptides, synthetic, multifunctional small molecules have been employed to modulate Aβ aggregation in vitro. Naturally occurring flavonoids have emerged as a valuable class of compounds for this purpose due to their ability to modulate both metal-free and metal-induced Aβ aggregation. Although, flavonoids have shown anti-amyloidogenic effects, the structural moieties of flavonoids responsible for such reactivity have not been fully identified. In order to understand the structure-interaction-reactivity relationship within the flavonoid family for metal-free and metal-associated Aβ, we designed, synthesized, and characterized a set of isoflavone derivatives, aminoisoflavones (1-4), that displayed reactivity (i.e., modulation of Aβ aggregation) in vitro. NMR studies revealed a potential binding site for aminoisoflavones between the N-terminal loop and central helix on prefibrillar Aβ different from the non-specific binding observed for other flavonoids. The absence or presence of the catechol group differentiated the binding affinities and enthalpy/entropy balance between aminoisoflavones and Aβ. Furthermore, having a catechol group influenced the binding mode with fibrillar Aβ. Inclusion of additional substituents moderately tuned the impact of aminoisoflavones on Aβ aggregation. Overall, through these studies, we obtained valuable insights on the requirements for parity among metal chelation, intermolecular interactions, and substituent variation for Aβ interaction.

Influence of Aromatic Residues on the Material Characteristics of Aβ Amyloid Protofibrils at the Atomic Scale

“…DeToma investigated the instability of amyloid oligomers by addingn aturally obtainedf lavones, [40] whereas Brender et al studied the stabilization of prefibrillar oligomers by NMR spectroscopic and AFM analysis upon adding am etal ion. [41,42] In as imilar manner, otherc omputational studies have shown that (À)-epigallocatechin-3-gallate (EGCG)a gents destabilize oligomeric amyloids tructures,i ncluding prefibrillar structures.…”

Effects of hydroxyl group variations on a flavonoid backbone toward modulation of metal-free and metal-induced amyloid-β aggregation

“…The resultant Aβ species from both inhibition and disaggregation experiments were analyzed by gel electrophoresis followed by Western blotting (gel/Western blot) using an anti-Aβ antibody (6E10). [16][17][18][19][20][21][22][23][24][25][26][27] Each sample (10 μL, [Aβ] = 25 μM) was separated using a 10-20% gradient Tris-tricine gel (Invitrogen, Grand Island, NY, USA). The gel was transferred to a nitrocellulose membrane and blocked with a bovine serum albumin (BSA) solution (3% w/v; Sigma, St. Louis, MO, USA) in Trisbuffered saline (TBS; Fisher, Pittsburgh, PA, USA) containing 0.1% Tween-20 (TBS-T; Sigma-Aldrich) for 3 h at room temperature.…”

“…Samples for TEM were prepared following previously reported methods. [16][17][18][19][20][21][22][23][24][25][26][27] Glow discharged grids (Formar/Carbon 300mesh; Electron Microscopy Sciences, Hatfield, PA, USA) were treated with samples from either inhibition or disaggregation experiments (5 μL) for 2 min at room temperature. The excess sample was removed with filter paper and the grids were washed with ddH 2 O three times.…”

“…41 Previously, this has been applied to identify which chemical alterations to a framework can direct the binding of a ligand to Aβ 40 and can elucidate the structural basis for distinct reactivity. 22,23,25,26 The chemical shift perturbation (CSP) induced by the addition of flavonoids to the peptide was monitored to determine potentially preferred binding modes ( Fig. 5 and S1 in the ESI †).…”

X-Ray Crystallographic Analysis, EPR Studies, and Computational Calculations of a Cu(II) Tetramic Acid Complex

“…Clinical studies for Cu(II) complexes with a functionalized styrylpyridine group indicate binding to amyloid- β plaques and effectively crossing of the blood-brain barriers [43]. Consequently, transition metals, such as Cu and Zn, have a suggested link to AD pathology.…”