Many protein misfolding diseases, for example, Alzheimer's, Parkinson's and Huntington's, are characterised by the accumulation of protein aggregates in an amyloid fibrillar form. Natural products which inhibit fibril formation are a promising avenue to explore as therapeutics for the treatment of these diseases. In this study we have shown, using in vitro thioflavin T assays and transmission electron microscopy, that grape seed extract inhibits fibril formation of kappa-casein (κ-CN), a milk protein which forms amyloid fibrils spontaneously under physiological conditions. Among the components of grape seed extract, gallic acid was the most active component at inhibiting κ-CN fibril formation, by stabilizing κ-CN to prevent its aggregation. Concomitantly, gallic acid significantly reduced the toxicity of κ-CN to pheochromocytoma12 cells. Furthermore, gallic acid effectively inhibited fibril formation by the amyloid-beta peptide, the putative causative agent in Alzheimer's disease. It is concluded that the gallate moiety has the fibril-inhibitory activity.
Keywords: 1,4-dithiothreitol; 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide; AD; Alzheimer’s disease; Amyloid fibril; Amyloid-beta peptide; Aβ; DTT; EGCG; GA; GSE; Gallic acid; Grape seed extract; HD; Huntington’s disease; Kappa-casein; MTT; PC12; PD; Parkinson’s disease; Protein aggregation; RCM-κ-CN; TEM; ThT; Thioflavin T; amyloid-beta peptide; epigallocatechin-3-gallate; gallic acid; grape seed extract; pheochromocytoma12; reduced and carboxymethylated kappa-casein; transmission electron microscopy.
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