Study On The Inhibition Effect Of Natural Polyphenolic Compounds On Amyloid Protein Aggregation In Neurodegenerative Disease

Alzheimer's disease(AD)is the most common neurodegenerative diseases.The pathological features of most patients are accompanied by cerebral cortex atrophy,neuron loss,aggregation of amyloid proteins,and excessive accumulation of metal ions.As the aging of global population,the increasing incidence of AD causes heavy burden on the family and whole society.Currently,it is a major issue that how to prevent and effectively treat AD.The pathological mechanism of AD is complicated,including amyloid protein hypothesis,Tau hypothesis,neuroinflammation hypothesis and so on.The amyloid protein hypothesis proposed that the accumulation and aggregation of misfolded amyloid protein causes neuron damage,neurons apoptosis and synaptic mysfunction and neurodegeneration.Therefore,the research on AD drugs mainly focused on A?-targeting strategies.Herein,we investigated the effect of two natural polyphenols on A? aggregation.(1)Ginnalin A(GA),a polyphenolic compound isolated from the red maple(Acer rubrum),has been found to possess anticancer,anti-glycation,and anti-oxidation properties.Using thioflavin-T(ThT)fluorescence,surface plasmon resonance(SPR),and atomic force microscopy(AFM),we demonstrate that GA can also effectively inhibit A? aggregation by primarily binding to A? monomers in a dose-dependent manner.Furthermore,GA can bind to multiple sites of A? aggregates to disassemble preformed fibrils and convert them into small aggregates.Circular dichroism(CD)spectra showed that these small aggregates are much less abundant in ?-sheets,while cell viability assay confirms that they are essentially innocuous.Molecular dynamics(MD)simulations revealed that GA preferentially contacts with the Cand N-terminal ?-sheets and the U-turn region of A?(1�42)oligomers through hydrophobic interactions and hydrogen bonding.Compared with other natural compounds that have shown promise in anti-A? fibrillogenesis and ameliorating A?-induced cytotoxicity,GA is unique in that it exhibits a more efficient inhibition of A? aggregation at the very early stage through its strong interaction with A? monomers and exerts its inhibitory effect at a lower dosage.(2)Ellagic acid(EA)is a natural polyphenole rich in pomegranate.It has been found that EA has anti-mutagenic,antioxidant and anti-inflammatory abilitie.Although it has been reported that EA can alleviated the A? aggregation induced cytotoxicity,however the detailed mechanism of EA targeting A? is unclear.Our research focuses on the effect of EA on A?(1-42)aggregation.Thioflavin T fluorescence experiments showed that EA inhibited the formation of A?(1-42)fibrils.Circular dichroism showed that EA altered the content of ?-sheet structure in A?(1-42)solutions.Preliminary results of atomic force microscopy showed that EA could disaggregate pre-formed fibrils.In summary,we confirmed the inhibitory effect of GA and EA in the process of A? aggregation,indicating that these two natural polyphenols can be used as potential agents for the prevention and treatment of AD.In the future,we will further study the morphologies of aggregation products in the presence of EA and whether EA can significantly counteract the cytotoxicity induced by A?,which in turn provide supplementary data for AD therapy with EA.GA has been used as a natural sweetener and a traditional medicine for treating stomach diseases.Therefore,GA is a promising agent in delaying the onset of AD,reversing or alleviating A?-induced cytotoxicity in AD patients.