Poly(4-styrenesulfonate) as an Inhibitor of Aβ40 Amyloid Fibril Formation

The formation of amyloid, a cross-β-sheet fibrillar aggregate of proteins, is associated with a variety of neurodegenerative diseases. Amyloidogenic proteins such as β-amyloid (Aβ) are known to exist with a large amount of polyelectrolyte macromolecules in vivo. The exact nature of Aβ–polyelectrolyte interactions and their roles in Aβ-aggregation are largely unknown. In this regard, we report the inhibiting effect of an anionic polyelectrolyte poly­(4-styrenesulfonate) (PSS) on the aggregation of Aβ40 peptide. The results demonstrate the strong inhibition potential of PSS on the aggregation of Aβ40 and imply the dominant role of hydrophobicity of the polyelectrolyte in reducing the propensity of Aβ40 amyloid formation. Additional studies with poly­(vinyl sulfate) (PVS) and <i>p</i>-toluenesulfonate (PTS), which share similar charge density with PSS except the former lacking the nonpolar aromatic side chain and the latter the aliphatic hydrocarbon backbone, reveal that the presence of both aliphatic backbone and aromatic side chain group in PSS is essential for its Aβ-aggregation inhibition activity. The interactions involved in the Aβ40–PSS complex were further investigated using molecular dynamics (MD) simulation. Our results provide new insights into the structural interplay between polyelectrolytes and Aβ peptide, facilitating the ultimate understanding of amyloid formation in Alzheimer’s disease. The results should assist in developing novel polyelectrolytes as potential chemical tools to study amyloid aggregation

Positively Charged Chitosan and <i>N</i>‑Trimethyl Chitosan Inhibit Aβ40 Fibrillogenesis

Amyloid fibrils, formed by aggregation of improperly folded or intrinsically disordered proteins, are closely related with the pathology of a wide range of neurodegenerative diseases. Hence, there is a great deal of interest in developing molecules that can bind and inhibit amyloid formation. In this regard, we have investigated the effect of two positively charged polysaccharides, chitosan (CHT) and its quarternary derivative <i>N</i>-trimethyl chitosan chloride (TMC), on the aggregation of Aβ40 peptide. Our aggregation kinetics and atomic force microscopy (AFM) studies show that both CHT and TMC exhibit a concentration-dependent inhibiting activity on Aβ40 fibrillogenesis. Systematic pH-dependent studies demonstrate that the attractive electrostatic interactions between the positively charged moieties in CHT/TMC and the negatively charged residues in Aβ40 play a key role in this inhibiting activity. The stronger inhibiting activity of TMC than CHT further suggests the importance of charge density of the polymer chain in interacting with Aβ40 and blocking the fibril formation. The possible interactions between CHT/TMC and Aβ40 are also revealed at the atomic level by molecular docking simulation, showing that the Aβ40 monomer could be primarily stabilized by electrostatic interactions with charged amines of CHT and quaternary amines of TMC, respectively. Binding of CHT/TMC on the central hydrophobic core region of Aβ40 peptide may be responsible for blocking the propagation of the nucleus to form fibrillar structures. These results suggest that incorporation of sugar units such as d-glucosamine and <i>N</i>-trimethyl-d-glucosamine into polymer structural template may serve as a new strategy for designing novel antiamyloid molecules

Gold Nanoparticles as a Probe for Amyloid‑β Oligomer and Amyloid Formation

The process of amyloid-β (Aβ) amyloid formation is pathologically linked to Alzheimer’s disease (AD). The identification of Aβ amyloids and intermediates that are crucial players in the pathology of AD is critical for exploring the underlying mechanism of Aβ aggregation and the diagnosis of the disease. Herein, we performed a gold nanoparticle (AuNP)-based study to detect the formation of Aβ amyloid fibrils and oligomers. Our results demonstrate that the intensity of the surface plasmon resonance (SPR) absorption band of the AuNPs is sensitive to the quantity of Aβ40 amyloids. This allows the SPR assay to be used for detection and semiquantification of Aβ40 amyloids and characterization of the kinetics of Aβ amyloid formation. Furthermore, our study demonstrates that the SPR band intensity of the AuNPs is sensitive to the presence of oligomers of Aβ40, and an Aβ40 mutant which forms more stable oligomers. The kinetics of the stable oligomer formation of the Aβ40 mutant can also be monitored following the SPR band intensity change of AuNPs. Our results indicate that this nanoparticle-based method can be used for mechanistic studies of early protein self-assembly and fibrillogenesis