Alzheimer’s Disease (AD) is a neurodegenerative disorder characterized by progressive impairment in memory. One of the main hallmarks of AD is the presence of senile plaques in the brain, i.e. extracellular deposits of amyloid-beta nanofibrils, and the presence of neurofibrillary tangles composed of tau.  The amyloid-beta nanofibrils are generated by the self-assembling of the monomers into supramolecular assemblies linked together by beta-sheet structures. Another known feature of AD is the impairment of the redox status of the cell that leads to an oxidative environment that induces cell apoptosis. In the AD context natural polyphenols (presenting pyrogallol and galloyl moieties) are multifunctional compounds able to act both as: 1) inhibitors of the amyloid-beta self-assembling process (due to their beta-sheet breaking capacity); and 2) modulators of the cellular redox status reducing the cellular oxidative stress through their antioxidant activity. Thus, natural polyphenols are promising compounds that may protect the AD patients’ against neuronal loss . In this work, we extracted and purified castalagin and vescalagin from cork powder and we tested them for their capacity to inhibit the fibrillization of amyloid-beta and their antioxidant activity. We confirmed their capacity of maintain SH-SY5Y cell viability under oxidative environment (i.e. hydrogen peroxide); in addition, the polyphenols were also able to block the self-assembling process that generates the amyloid-beta nanofibrils. Instead of nanofibrils, the system amyloid-beta:polyphenols generated spherical aggregates (confirmed by atomic force microscopy, AFM). The addition of polyphenol also reduced the capacity of amyloid-beta to form the stable beta-sheet structures (confirmed by circular dichroism, CD); we also confirmed that this interaction reduces the entropy of the system (observed by isothermal calorimetry, ITC)) leading to stable amyloid-beta:polyphenol complexes. Finally, as expected, polyphenols were also able to protect SH-SY5Y cells from the cytotoxicity of amyloid-beta, retaining cellular activity due to the reduced formation of nanofibers and increased deposition of the peptide into non-toxic aggregates. In general, our results demonstrate that castalagin and vescalagin (present in cork) are multifunctional promising candidates for the treatment of neurodegenerative disorders, in particular AD.
Acknowledgements: Authors acknowledge the financial support from Project “NORTE-08-5369-FSE-000037”, financed by “Programa Operacional Norte 2020”. This work was also supported by the European Union H2020 programme under grant agreement numbers: H2020-TWINN-2015-692333 – CHEM2NATURE; and H2020-WIDESPREAD-2014-2-668983 – FORECAST.
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