Positively Charged Chitosan and N-Trimethyl Chitosan Inhibit Aβ40 Fibrillogenesis

Abstract

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 N-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 N-trimethyl-d-glucosamine into polymer structural template may serve as a new strategy for designing novel antiamyloid molecules.

Biocompatible Inhibitor Based on Chitosan and Amphiphilic Peptide against Mutant Huntingtin Toxicity

“…Chitosan‐decorated nanomaterials have currently been applied to the delivery of peptides, proteins, small molecules, genes, and multitheranostics drugs for satisfactory biodegradability, biocompatibility, and non‐immunogenicity in chitosan . Earlier studies also reported that chitosan and its derivative could inhibit the fibrillogenesis of amyloid β‐protein Aβ‐40 and/or age‐related diseases . Based on these properties, we tried to incorporate chitosan oligosaccharide lactate with E 6 Q 10 to increase interactions with the cell membrane and facilitate cell delivery.…”

Estimation of the lag time in a subsequent monomer addition model for fibril elongation

“…Eqn (29) allows us to test the validity of the lag time expression under different conditions of the ratio of reactant in excess to limiting reactant (m 0 to f 0 *), given that the conditions, eqn (26) and (28), for the reactant stationary approximation are met. With m 0 fixed to one and the length n fixed, for large values of f 0 *, such that a o 10, the percentage of the maximum product reached at the lag time increases very rapidly and the excess monomer condition is unstable.…”

“…Eqn (1) and variations thereof are often used to estimate the empirical parameters for progress curves of protein aggregation experiments. [24][25][26] The lag time (t lag ) is typically estimated by extending the tangent at t m to the initial baseline. The lag time is then given in terms of the empirical parameters:…”

Interaction of polymers with amyloidogenic peptides

“…The interaction of cationic biopolymers such as chitosan (CHT) and N-trimethyl chitosan (TMC, quaternary derivative) with A (1 − 40) has been reported. 54 The charge density of CHT is dependent on solution pH, while TMC always holds a positive charge irrespective of changes in pH. At neutral pH (7.4), the inhibitory activity of CHT and TMC on A (1 − 40) fibrillogenesis is driven by electrostatic interaction between the CHT holding positive charges and the negatively charged aspartic acid and glutamic acid.…”

“…The interaction of cationic biopolymers such as chitosan (CHT) and N ‐trimethyl chitosan (TMC, quaternary derivative) with Aβ(1 − 40) has been reported . The charge density of CHT is dependent on solution pH, while TMC always holds a positive charge irrespective of changes in pH.…”