A Diruthenium Metallodrug as a Potent Inhibitor of Amyloid-β Aggregation: Synergism of Mechanisms of Action

Abstract

The physical and chemical properties of paddlewheel diruthenium compounds are highly dependent on the nature of the ligands surrounding the bimetallic core. Herein, we compare the ability of two diruthenium compounds, [Ru 2 Cl(D-p-FPhF)- 2), to act as inhibitors of amyloid aggregation of the Aβ 1−42 peptide and its peculiar fragments, Aβ 1−16 and Aβ 21−40 . A wide range of biophysical techniques has been used to determine the inhibition capacity against aggregation and the possible mechanism of action of these compounds (Thioflavin T fluorescence and autofluorescence assays, UV−vis absorption spectroscopy, circular dichroism, nuclear magnetic resonance, mass spectrometry, and electron scanning microscopy). Data show that the most effective inhibitory effect is shown for compound 1. This compound inhibits fiber formation and completely abolishes the cytotoxicity of Aβ 1−42 . The antiaggregatory capacity of this complex can be explained by a binding mechanism of the dimetallic units to the peptide chain along with π−π interactions between the formamidinate ligand and the aromatic side chains. The results suggest the potential use of paddlewheel diruthenium complexes as neurodrugs and confirm the importance of the steric and charge effects on the properties of diruthenium compounds.

Comparative Analysis of the Inhibitory Mechanism of Aβ1–42 Aggregation by Diruthenium Complexes

“…This latter observation was made in the context of the inability of sample Aβ 1–42+ complex 1 to develop fibrils and the lack of cytotoxicity in SH-SY5 cells. This analysis is consistent with our previous investigation of the analogous compound [Ru 2 Cl­(D- p -FPhF)­(O 2 CCH 3 ) 3 ]·H 2 O . Complex 2 exhibits a similar behavior to complex 1 : for both complexes, the ligand exchange associated with the interaction with the Aβ peptide could be assisted by π–π aromatic interactions due to the presence of formamidinate ligands (two in the case of complex 2 ), as also suggested by the analysis of aromatic emission.…”

“…In order to evaluate the formation of direct Ru 2‑ Aβ adducts, first Aβ 1–42 peptide was initially incubated with each Ru 2 complex. As reported for similar systems, , the presence of peaks due to the formation of direct adducts between the whole peptide and metal complexes cannot be observed in the mass spectra of Aβ 1–42 with Ru 2 complexes (Figure S3). In detail, the spectrum of Aβ 1–42 alone exhibits multicharged peaks: the quadruple ( m / z 1129.17 a.m.u.)…”

“…DLS was employed to evaluate the effects of the bimetallic complexes on the size of the Aβ 1–42 aggregates (Figure ). The correct autocorrelation of the native Aβ 1–42 is achieved after 24 h with a diameter of ∼195 nm (Figure a). ,, The presence of complex 1 (1:1 molar ratio) anticipates the autocorrelation at t = 0 h of aggregation, likely through the stabilization of greater oligomers centered at ∼730, 760, and 800 nm, with increasing intensities, at t = 0, 2, and 4 h of analysis, respectively (Figure b and Table S1). Additionally, smaller diameters, compatible with the peptide alone, are also observed (Table S1).…”

“…With the aim to observe direct interactions between the amyloid peptide and the investigated bimetallic complexes, we performed a similar ESI-MS analysis employing the N-terminal Aβ 1–42 fragment, Aβ 1–16 , which is often used as a model to mime the binding abilities of the entire Aβ 1–42 . It is noteworthy that the Aβ 1–16 peptide (sequence DAEFRHDSGYEVHHQK) contains His residues at positions 6, 13, and 14, and Asp and Glu residues that could coordinate the diruthenium centers . The results indicate that the Aβ 1–16 peptide forms different adducts with complexes 1 and 2 (Figure ): this process involves the loss of several acetate groups from the metal complexes.…”

“…The applicability of two diruthenium compounds, [Ru 2 Cl­(D- p -FPhF)­(O 2 CCH 3 ) 3 ]·H 2 O [D- p -FPhF – = N , N′ -bis­(4-fluorophenyl)­formamidinate] and K 3 [Ru 2 (CO 3 ) 4 ]·3H 2 O, in AD has been newly investigated for the first time by our research groups . Data revealed that the most effective complex was [Ru 2 Cl­(D- p -FPhF)­(O 2 CCH 3 ) 3 ]·H 2 O since it was able to inhibit Aβ aggregation and avoid Aβ-induced toxicity at very early stages.…”