Reactivity of Metal-Free and Metal-Associated Amyloid-?? with Glycosylated Polyphenols and Their Esterified Derivatives

Both amyloid-?? (A??) and transition metal ions are shown to be involved in the pathogenesis of Alzheimer???s disease (AD), though the importance of their interactions remains unclear. Multifunctional molecules, which can target metal-free and metal-bound A?? and modulate their reactivity (e.g., A?? aggregation), have been developed as chemical tools to investigate their function in AD pathology; however, these compounds generally lack specificity or have undesirable chemical and biological properties, reducing their functionality. We have evaluated whether multiple polyphenolic glycosides and their esterified derivatives can serve as specific, multifunctional probes to better understand AD. The ability of these compounds to interact with metal ions and metal-free/-associated A??, and further control both metal-free and metal-induced A?? aggregation was investigated through gel electrophoresis with Western blotting, transmission electron microscopy, UV-Vis spectroscopy, fluorescence spectroscopy, and NMR spectroscopy. We also examined the cytotoxicity of the compounds and their ability to mitigate the toxicity induced by both metal-free and metal-bound A??. Of the polyphenols investigated, the natural product (Verbascoside) and its esterified derivative (VPP) regulate the aggregation and cytotoxicity of metal-free and/or metal-associated A?? to different extents. Our studies indicate Verbascoside represents a promising structure for further multifunctional tool development against both metal-free A?? and metal-A??.open0

Self-assembly and anti-amyloid cytotoxicity activity of amyloid beta peptide derivatives

The self-assembly of two derivatives of KLVFF, a fragment Abeta(16-20) of the amyloid beta (Abeta) peptide, is investigated and recovery of viability of neuroblastoma cells exposed to Abeta is observed at sub-stoichiometric peptide concentrations. Fluorescence assays show that NH2-KLVFF-CONH2 undergoes hydrophobic collapse and amyloid formation at the same critical aggregation concentration (cac). In contrast, NH2-K(Boc)LVFF-CONH2 undergoes hydrophobic collapse at a low concentration, followed by amyloid formation at a higher cac. These findings are supported by the beta-sheet features observed by FTIR. Electrospray ionization mass spectrometry indicates that NH2-K(Boc)LVFF-CONH2 forms a significant population of oligomeric species above the cac. Cryo-TEM, used together with SAXS to determine fibril dimensions, shows that the length and degree of twisting of peptide fibrils seem to be influenced by the net peptide charge. Grazing incidence X-ray scattering from thin peptide films shows features of beta-sheet ordering for both peptides, along with evidence for lamellar ordering of NH2-KLVFF-CONH2. This work provides a comprehensive picture of the aggregation properties of these two KLVFF derivatives and show their utility, in unaggregated form, in restoring the viability of neuroblastoma cells against Abeta-induced toxicity

Interaction and reactivity of synthetic aminoisoflavones with metal-free and metalassociated amyloid-beta

Metal ion homeostasis in conjunction with amyloid-b (Ab) aggregation in the brain has been implicated in Alzheimer’s disease (AD) pathogenesis. To uncover the interplay between metal ions and Ab peptides, synthetic, multifunctional small molecules have been employed to modulate Ab 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 Ab 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 Ab, we designed, synthesized, and characterized a set of isoflavone derivatives, aminoisoflavones (1–4), that displayed reactivity (i.e., modulation of Ab aggregation) in vitro. NMR studies revealed a potential binding site for aminoisoflavones between the N-terminal loop and central helix of prefibrillar Ab, which is 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 Ab. Furthermore, having a catechol group influenced the binding mode with fibrillar Ab. Inclusion of additional substituents moderately tuned the impact of aminoisoflavones on Ab aggregation. Overall, through these studies, we obtained valuable insights into the requirements for parity among metal chelation, intermolecular interactions, and substituent variation for Ab interaction