Inhibition Effect and Molecular Mechanisms of Quercetin on the Aβ42 Dimer: A Molecular Dynamics Simulation Study

Protective effect of flavonoids on oxidative stress injury in Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disease, which is mainly caused by the damage of the structure and function of the central nervous system. At present, there are many adverse reactions in market-available drugs, which can't significantly inhibit the occurrence of AD. Therefore, the current focus of research is to find safe and effective therapeutic drugs to improve the clinical treatment of AD. Oxidative stress bridges different mechanism hypotheses of AD and plays a key role in AD. Numerous studies have shown that natural flavonoids have good antioxidant effects. They can directly or indirectly resist -oxidative stress, inhibit Aβ aggregation and Tau protein hyperphosphorylation by activating Nrf2 and other oxidation-antioxidation-related signals, regulating synaptic function-related pathways, promoting mitochondrial autophagy, etc., and play a neuroprotective role in AD. In this review, we summarised the mechanism of flavonoids inhibiting oxidative stress injury in AD in recent years. Moreover, because of the shortcomings of poor biofilm permeability and low bioavailability of flavonoids, the advantages and recent research progress of nano-drug delivery systems such as liposomes and solid lipid nanoparticles were highlighted. We hope this review provides a useful way to explore safe and effective AD treatments.

Insights into the baicalein-induced destabilization of LS-shaped Aβ42 protofibrils using computer simulations

Amyloid-β (Aβ) peptides aggregate spontaneously into various aggregating species comprising oligomers, protofibrils, and mature fibrils in Alzheimer's disease (AD). Disrupting β-sheet rich neurotoxic smaller soluble Aβ42 oligomers formed at early stages is considered a potent strategy to interfere with AD pathology. Previous experiments have demonstrated the inhibition of the early stages of Aβ aggregation by baicalein; however, the molecular mechanism behind inhibition remains largely unknown. Thus, in this work, molecular dynamics (MD) simulations have been employed to illuminate the molecular mechanism of baicalein-induced destabilization of preformed Aβ42 protofibrils. Baicalein binds to chain A of the Aβ42 protofibril through hydrogen bonds, π-π interactions, and hydrophobic contacts with the central hydrophobic core (CHC) residues of the Aβ42 protofibril. The binding of baicalein to the CHC region of the Aβ42 protofibril resulted in the elongation of the kink angle and disruption of K28-A42 salt bridges, which resulted in the distortion of the protofibril structure. Importantly, the β-sheet content was notably reduced in Aβ42 protofibrils upon incorporation of baicalein with a concomitant increase in the coil content, which is consistent with ThT fluorescence and AFM images depicting disaggregation of pre-existing Aβ42 fibrils on the incorporation of baicalein. Remarkably, the interchain binding affinity in Aβ42 protofibrils was notably reduced in the presence of baicalein leading to distortion in the overall structure, which agrees with the structural stability analyses and conformational snapshots. This work sheds light on the molecular mechanism of baicalein in disrupting the Aβ42 protofibril structure, which will be beneficial to the design of therapeutic candidates against disrupting β-sheet rich neurotoxic Aβ42 oligomers in AD.

Perspective for Molecular Dynamics Simulation Studies of Amyloid-β Aggregates

The cause of Alzheimer's disease is related to aggregates such as oligomers and amyloid fibrils consisting of amyloid-β (Aβ) peptides. Molecular dynamics (MD) simulation studies have been conducted to understand the molecular mechanism of the formation and disruption of Aβ aggregates. In this Perspective, the MD simulation studies are classified into four categories, focusing on the target systems: aggregation of Aβ peptides in bulk solution, Aβ aggregation at the interface, aggregation inhibitor against Aβ peptides, and nonequilibrium MD simulation of Aβ aggregates. MD simulation studies in these categories are first reviewed. Future perspectives in each category are then presented. Finally, the overall perspective is presented on how MD simulations of Aβ aggregates can be utilized for developing Alzheimer's disease treatment.