Polyphenols-Based Nanosheets of Propolis Modulate Cytotoxic Amyloid Fibril Assembly of α-Synuclein

Abstract

Natural compounds with anti-aggregation capacity are increasingly recognized as viable candidates against neurodegenerative diseases. Recently, the polyphenolic fraction of propolis (PFP), a complex bee product, has been shown to inhibit amyloid aggregation of a model protein especially in the nanosheet form. Here, we examine the aggregation-modulating effects of the PFP nanosheets on α-synuclein (α-syn), an intrinsically disordered protein involved in the pathogenesis of Parkinson’s disease. Based on a range of biophysical data including intrinsic and extrinsic fluorescence, circular dichroism (CD) data, and nuclear magnetic resonance spectroscopy, we propose a model for the interaction of α-syn with PFP nanosheets, where the positively charged N-terminal and the middle non-amyloid component regions of α-syn act as the main binding sites with the negatively charged PFP nanosheets. The Thioflavin T (ThT) fluorescence, Congo red absorbance, and CD data reveal a prominent dose-dependent inhibitory effect of PFP nanosheets on α-syn amyloid aggregation, and the microscopy images and MTT assay data suggest that the PFP nanosheets redirect α-syn aggregation toward nontoxic off-pathway oligomers. When preformed α-syn amyloid fibrils are present, fluorescence images show co-localization of PFP nanosheets and ThT, further confirming the binding of PFP nanosheets with α-syn amyloid fibrils. Taken together, our results demonstrate the binding and anti-aggregation activity of PFP nanosheets in a disease-related protein system and propose them as potential nature-based tools for probing and targeting pathological protein aggregates in neurodegenerative diseases.

Neuroprotective Effect of Propolis Polyphenol-Based Nanosheets in Cellular and Animal Models of Rotenone-Induced Parkinson’s Disease

“…To demonstrate the neuroprotective effects of nanoparticles with a sheet morphology including PFP nanosheets on the brain, where protein aggregates exist, we need to examine their ability to cross the blood–brain barrier (BBB). While the ability of PFP nanosheets to cross the BBB remains to be elucidated, results reported by previous studies indicate the cellular uptake of nanoparticles with a sheet morphology and diameters ranging from 100 nm to 10 μm. , Considering the sheet morphology of PFP nanosheets with an average diameter of less than 0.7 μm, we suggest that PFP nanosheets would be able to cross biological membranes including BBB, a hypothesis that needs to be investigated in our future studies.…”

“…While the ability of PFP nanosheets to cross the BBB remains to be elucidated, results reported by previous studies indicate the cellular uptake of nanoparticles with a sheet morphology and diameters ranging from 100 nm to 10 μm. 53,54 Considering the sheet morphology of PFP nanosheets with an average diameter of less than 0.7 μm, 55 we suggest that PFP nanosheets would be able to cross biological membranes including BBB, a hypothesis that needs to be investigated in our future studies.…”

“…Extraction of the polyphenolic fraction of propolis (PFP) and preparation of the PFP nanosheets using direct oxidative pyrolysis were performed as described recently . The spectroscopic/microscopic characteristics of bulk and nano forms of PFP and information on their size distribution and surface charge are provided in our recent reports. , Stock solutions of bulk and nano forms of PFP were prepared in a final concentration of 150 mg mL –1 in dimethylsulfoxide (DMSO) and deionized water as solvent, respectively. Rotenone was dissolved in DMSO at a final concentration of 100 mM.…”

Citrus Flavonoid Hesperetin Inhibits α-Synuclein Fibrillogenesis, Disrupts Mature Fibrils, and Reduces Their Cytotoxicity: In Vitro and In Vivo Studies

“…The neurotoxic effects of the αSN aggregates play a critical role in the pathogenesis of PD, which should be focused on in the study of novel antiamyloid molecules. Therefore, the next step was to evaluate the protection of different concentrations of Hst (25, 50, and 100 μM) against αSN-mediated cytotoxicity using the MTT assay in PC12 cells suitable for PD studies .…”

Exploring the Prospective Role of Propolis in Modifying Aging Hallmarks

“…Current research has presented findings on the ability of polyphenol-based nanosheets of propolis to regulate protein aggregates implicated in neurodegenerative conditions. A study has provided evidence of the polyphenolic fraction of propolis nanosheets binding to α-synuclein fibrils while also showcasing substantial dose-dependent inhibition of α-synuclein aggregation by these nanosheets [ 290 ].…”