Structural and mechanistic insights into modulation of α-Synuclein fibril formation by aloin and emodin.

α-Synuclein (α-Syn) aggregation/fibrillation is a leading cause of neuronal death and is one of the major pathogenic factors involved in the progression of Parkinson's' disease (PD). Against this backdrop, discovering new molecules as inhibitors or modulators of α-Syn aggregation/fibrillation is a subject of enormous research. In this study, we have shown modulation, disaggregation, and neuroprotective potential of aloin and emodin against α-Syn aggregation/fibrillation. Thioflavin T (ThT) fluorescence assay showed an increase in lag phase from (51.14 ± 2) h to (68.58 ± 2) h and (74.14 ± 3) h in the presence of aloin and emodin respectively. ANS binding assay represents a modulatory effect of these molecules on hydrophobicity which is crucial for aggregates/fibril formation. NMR spectroscopy and tyrosine quenching studies reveal the binding of aloin/emodin with monomeric α-Syn. TEM and DLS micrographs illustrate the attenuating effect of aloin/emodin against the development of large aggregates/fibrils. Our seeding experiments suggest aloin/emodin generate seeding incompetent oligomers that direct the off-pathway aggregation/fibrillation. Also, aloin/emodin capably reduces the fibrils-induced cytotoxicity and disassembles the preexisting amyloid fibrils. These findings provide deep insight into the modulatory mechanism of α-Syn aggregation/fibrillation in the presence of aloin and emodin, thereby suggesting their potential roles as promising therapeutic molecules against aggregation/fibrillation related disorders.

Ellagic Acid Modulates Uninduced as well as Mutation and Metal-Induced Aggregation of α-Synuclein: Implications for Parkinson's Disease.

α-Synuclein (αS) is an intrinsically disordered protein whose aggregation and deposition in Lewy bodies is involved in the progression of Parkinson's disease (PD) and other related disorders. The aggregation process of αS is also triggered by mutations like A53T and E46K in the SNCA gene and disruption in metal-ion homeostasis. Currently, there is no obviating therapy available in the market that could effectively prevent the progression of the disease. In this backdrop, there exists an emerging need to consider naturally occurring polyphenols and flavonoids as potential therapeutic agents against PD. In this study, we demonstrate the modulatory effect of ellagic acid (EA) against wild-type as well as mutation and metal-induced aggregation of αS. Thioflavin T (ThT) fluorescence assay suggests that EA acts on the nucleation phase of αS fibrillization, thereby increasing the lag phase from 21.33 ± 3.01 to 48.20 ± 5.05 h and reducing the fibrils growth rate from 4.60 ± 2.06 to 0.890 ± 0.36 h-1. 8-Anilino-1-naphthalene sulfonic acid (ANS), Congo red (CR), and intrinsic fluorescence studies indicate that the interaction of EA with αS facilitates the structural changes in the protein that lead to inhibition of fibril formation. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) images illustrate that the size of fibrils diminishes up to 100 nm in the presence of EA. Dot blot and seeding experiments put forward that EA directs the αS aggregation toward off-pathway fibrillization. Our 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay deciphers the role of EA in minimizing the αS fibril-induced toxicity, thereupon leading to an increase in cell viability. Also, EA attenuates both mutations as well as metal-induced αS fibrillization and disaggregates the preexisting fibrils. Additionally, computational studies elucidate that EA preferentially interacts with the N-terminal and NAC domain of αS. Hence, this work reveals the aggregation inhibition mechanism of EA and provides considerable therapeutic interventions against PD and related disorders.