Homocysteine thiolactone and H2 O2 induce amino acid modifications and alter the fibrillation propensity of the Aβ25-35 peptide

Of the proteinaceous β-sheet-rich amyloid fibrillar structures, the Aβ_25-35 peptide, a component of the full-length Aβ involved in Alzheimer's disease, has similar toxicity to the parent peptide. In this study, the effects of homocysteine thiolactone (HCTL) and hydrogen peroxide (H₂ O₂ ) on the conformation and fibrillation propensity of the Aβ_25-35 peptide were investigated. Both HCTL and H₂ O₂ induced amino acid modifications along with alteration in aggregation propensity. Methionine (Met)-35 was oxidized by H₂ O₂ and aggregation was attenuated following the increased hydrophilicity of the peptide due to sulfoxide/sulfone formation. The HCTL-modified lysine (Lys-28) residue destabilizes the structure of the peptide, which leads to fibrillation. Our studies provide important information regarding the relationship between amino acid modifications and the amyloid fibrillation process.

Detection and modulation of neurodegenerative processes using graphene-based nanomaterials: Nanoarchitectonics and applications

Neurodegenerative disorders (NDDs) are caused by progressive loss of functional neurons following the aggregation and fibrillation of proteins in the central nervous system. The incidence rate continues to rise alarmingly worldwide, particularly in aged population, and the success of treatment remains limited to symptomatic relief. Graphene nanomaterials (GNs) have attracted immense interest on the account of their unique physicochemical and optoelectronic properties. The research over the past two decades has recognized their ability to interact with aggregation-prone neuronal proteins, regulate autophagy and modulate the electrophysiology of neuronal cells. Graphene can prevent the formation of higher order protein aggregates and facilitate the clearance of such deposits. In this review, after highlighting the role of protein fibrillation in neurodegeneration, we have discussed how GN-protein interactions can be exploited for preventing neurodegeneration. A comprehensive understanding of such interactions would contribute to the exploration of novel modalities for controlling neurodegenerative processes.

Carvedilol inhibits Aβ25-35 fibrillation by intervening the early stage helical intermediate formation: A biophysical investigation

Self-assembly of disordered amyloid-beta (Aβ) peptides results in highly ordered amyloid fibrils. The structural information of the early-stage events and also in the presence of inhibitors is of great significance. It is challenging to acquire due to the nature of the amyloids and experimental constraints. Here, we demonstrate the cascade of aggregation (early to late) of the Aβ_25-35 peptide in the absence and presence of carvedilol, a nonselective β-adrenergic receptor blocker. The aggregation process of Aβ_25-35 peptide is monitored using Thioflavin T (ThT) fluorescence, dynamic light scattering (DLS), circular dichroism (CD), Raman spectroscopic techniques, and imaging experiments. We find that the Aβ_25-35 peptide undergoes an early-stage (3-6 h) helical intermediate formation across the fibrillation pathway using CD and Raman measurements. Carvedilol obstructs the helical intermediate formation of Aβ_25-35 peptide resulting in inhibition. CD spectra and deconvolution of the Raman bands suggest the β-sheet formation (24-100 h) in the absence of carvedilol. Spectroscopic results indicate a disordered structure for the peptide in the presence of carvedilol (24-100 h). Electron microscopy (EM) shows the formation of polymorphic fibrils for the peptide alone and non-amyloidal aggregates in the presence of carvedilol. Molecular docking study suggests that the plausible mode of interaction with carvedilol involves the C-terminal residues of the peptide.

Nanomaterials for Modulating the Aggregation of β-Amyloid Peptides

The aberrant aggregation of amyloid-β (Aβ) peptides in the brain has been recognized as the major hallmark of Alzheimer's disease (AD). Thus, the inhibition and dissociation of Aβ aggregation are believed to be effective therapeutic strategiesforthe prevention and treatment of AD. When integrated with traditional agents and biomolecules, nanomaterials can overcome their intrinsic shortcomings and boost their efficiency via synergistic effects. This article provides an overview of recent efforts to utilize nanomaterials with superior properties to propose effective platforms for AD treatment. The underlying mechanismsthat are involved in modulating Aβ aggregation are discussed. The summary of nanomaterials-based modulation of Aβ aggregation may help researchers to understand the critical roles in therapeutic agents and provide new insight into the exploration of more promising anti-amyloid agents and tactics in AD theranostics.

Multi-target inhibition ability of neohesperidin dictates its neuroprotective activity: Implication in Alzheimer's disease therapeutics

The polygenic nature of Alzheimer's disease (AD) and cross-talk between several signaling cascades make it harder to decode the disease pathogenesis. β-secretase (BACE1) works upstream in the amyloidogenic processing of amyloid precursor protein (APP) to generate Aβ that rapidly aggregates to form fibrils, the most abundant component of plaques observed in AD brains. Here, we report dual inhibition of BACE1 and Aβ aggregation by neohesperidin, a flavonoid glycoconjugate, using multi-spectroscopic approaches, force microscopy, molecular modeling, and validated the potency in SH-SY5Y neuroblastoma cell lines. Steady-state and time-resolved fluorescence reveal that neohesperidin binds close to the catalytic aspartate dyad. This binding conformationally restricts the protein in closed form which possibly precludes APP recognition and thereby inhibits BACE1 activity. Neohesperidin also dose-dependently inhibits the amyloid fibril formation, as evident from ANS, ThT assay, and AFM. Neohesperidin ameliorates aggregated Aβ_25-35 induced ROS generation and mitochondrial dysfunction in the SH-SY5Y cell line. As a result, the amyloid induced apoptosis is significantly prohibited and normal neuronal morphology is rescued. These findings suggest neohesperidin as an inhibitor of the pathogenic conversion of Aβ to fibrillar amyloid assembly. Neohesperidin thus emerges as a non-toxic multi-potent scaffold for the development of AD therapeutics.

Graphene oxide sheets and quantum dots inhibit α-synuclein amyloid formation by different mechanisms

Aggregation and amyloid formation of the 140-residue presynaptic and intrinsically disordered protein α-synuclein (α-syn) is a pathological hallmark of Parkinson's disease (PD). Understanding how α-syn forms amyloid fibrils, and investigations of agents that can prevent their formation is therefore important. We demonstrate herein that two types of graphene oxide nanoparticles (sheets and quantum dots) inhibit α-syn amyloid formation by different mechanisms mediated via differential interactions with both monomers and fibrils. We have used thioflavin-T fluorescence assays and kinetic analysis, circular dichroism, dynamic light scattering, fluorescence spectroscopy and atomic force microscopy to asses the kinetic nature and efficiency of this inhibitory effect. We show that the two types of graphene oxide nanoparticles alter the morphology of α-syn fibrils, disrupting their interfilament assembly and the resulting aggregates therefore consist of single protofilaments. Our results further show that graphene oxide sheets reduce the aggregation rate of α-syn primarily by sequestering of monomers, thereby preventing primary nucleation and elongation. Graphene quantum dots, on the other hand, interact less avidly with both monomers and fibrils. Their aggregation inhibitory effect is primarily related to adsorption of aggregated species and reduction of secondary processes, and they can thus not fully prevent aggregation. This fine-tuned and differential effect of graphene nanoparticles on amyloid formation shows that rational design of these nanomaterials has great potential in engineering materials that interact with specific molecular events in the amyloid fibril formation process. The findings also provide new insight into the molecular interplay between amyloidogenic proteins and graphene-based nanomaterials in general, and opens up their potential use as agents to manipulate fibril formation.

Multi-functional neuroprotective activity of neohesperidin dihydrochalcone: a novel scaffold for Alzheimer's disease therapeutics identified via drug repurposing screening

Multi-target screening identifies neohesperidin dihydrochalcone for Alzheimer's disease therapeutics, which exhibits strong BACE1 and amyloid aggregation inhibition along with antioxidant activity.