betadex and Protein-Aggregation--Pathological

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; beta-Cyclodextrins; Blood-Brain Barrier; Camphanes; Cell Line, Tumor; Cells, Cultured; Delayed-Action Preparations; Drug Delivery Systems; Drug Evaluation, Preclinical; Drug Synergism; Humans; Mice; Nanoconjugates; Oxidation-Reduction; Porosity; Protein Aggregation, Pathological; Reactive Oxygen Species; Resveratrol; Selenium; Specific Pathogen-Free Organisms

Parkinson's disease is characterized by the presence of insoluble and neurotoxic aggregates (amyloid fibrils) of an intrinsically disordered protein α-synuclein. In this study we have examined the effects of four naturally occurring polyphenols in combination with β-cyclodextrin (β-CD) on the aggregation of α-synuclein in the presence of macromolecular crowding agents. Our results reveal that even at sub-stoichiometric concentrations of the individual components, the polyphenol-β-CD combination(s) not only inhibited the aggregation of the proteins but was also effective in disaggregating preformed fibrils. Curcumin was found to be the most efficient, followed by baicalein with (-)-epigallocatechin gallate and resveratrol coming in next, the latter two exhibiting very similar effects. Our results suggest that the efficiency of curcumin results from a balanced composition of the phenolic OH groups, benzene rings and flexibility. The latter ensures proper positioning of the functional groups to maximize the underlying interactions with both the monomeric form of α-synuclein and its aggregates. The uniqueness of β-CD was reinforced by the observation that none of the other cyclodextrin variants [α-CD and HP-β-CD] used was as effective, in spite of these possessing better water solubility. Moreover, the fact that the combinations remained effective under conditions of macromolecular crowding suggests that these have the potential to be developed into viable drug compositions in the near future. MTT assays on cell viability independently confirmed this hypothesis wherein these combinations (and the polyphenols alone too) appreciably impeded the toxicity of the prefibrillar α-synuclein aggregates on the mouse neuroblastoma cell lines (N2a cells).

Topics: alpha-Synuclein; Amyloid; Amyloidogenic Proteins; Animals; beta-Cyclodextrins; Catechin; Cell Line; Cell Survival; Circular Dichroism; Curcumin; Humans; Mice; Parkinson Disease; Polyphenols; Protein Aggregation, Pathological

Amyloid deposits of misfolded amyloid-β protein (Aβ) on neuronal cells are a pathological hallmark of Alzheimer's disease (AD). Prevention of the abnormal Aβ aggregation has been considered as a promising therapeutic strategy for AD treatment. To prevent reinventing the wheel, we proposed to search the existing drug database for other diseases to identify potential Aβ inhibitors. Herein, we reported the inhibitory activity of HP-β-cyclodextrin (HP-β-CD), a well-known sugar used in drug delivery, genetic vector, environmental protection and treatment of Niemann-Pick disease type C1 (NPC1), against Aβ1-42 aggregation and Aβ-induced toxicity, with the aim of adding a new function as a sugar-based Aβ inhibitor. Experimental data showed that HP-β-CD molecules were not only nontoxic to cells, but also greatly inhibited Aβ fibrillization and reduced Aβ-induced toxicity in a concentration-dependent manner. At an optimal molar ratio of Aβ : HP-β-CD = 1 : 2, HP-β-CD enabled the reduction of 60% of Aβ fibrils and increased the cell viability to 92%. Such concentration-dependent inhibitor capacity of HP-β-CD was likely attributed to several combined effects, including the enhancement of Aβ-HP-β-CD interactions, prevention of structural transition of Aβ peptides towards β-sheet structures, and reduction of self-aggregation of HP-β-CD. In parallel, molecular simulations further revealed the atomic details of HP-β-CD interacting with the Aβ oligomer, showing that HP-β-CD had a high tendency to interact with hydrophobic residues of Aβ in two β-strands and the N-terminal tail. More importantly, we identified that the inner hydrophobic cavity of HP-β-CD was a key active site for Aβ inhibition. Once the inner cavity of HP-β-CD was blocked by a small hydrophobic molecule of ferulic acid, HP-β-CD completely lost its inhibition capacity against Aβ. Given the already established pharmaceutical functions of HP-β-CD in drug delivery, our findings suggest that HP-β-CD has great potential to be designed as a sugar-based Aβ inhibitor.

Topics: Alzheimer Disease; Amyloid beta-Peptides; beta-Cyclodextrins; Humans; Hydrophobic and Hydrophilic Interactions; Protein Aggregation, Pathological