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Polyphenol extracts from Croatian autochthonous grape varieties Plavac mali and Babić:Physical properties and anti-amyloid activity

Amyloid fibril formation is related to a large number of highly debilitating diseases including Alzheimer and Creutzfeldt-Jakob diseases [1]. Recent discovery of strong anti-amyloid inhibitors among the small polyphenols [2] opens wide perspectives of application of natural polyphenolic extracts for health issues. We report a study of the physical properties and the antiamyloidogeneic activities of the polyphenol extracts of Croatian autochthonous grapevine varieties Plavac Mali and Babić. Plavac Mali and Babić were collected at Institute for Adriatic Crops and Karst Reclamation, Split, central Dalmatia, 2011 grape harvest. From grape variety, four polyphenolic fractions were obtained: skins-methanol (SkMet), skin-acetone (SkAc), seed-methanol (SeMet) and seed-acetone (SeAc). The solubility, the size, the shape and the structure of polyphenol molecules in phosphate buffer (50 mM, pH7.2) of all fractions were studied by the small-angle X-ray scattering (SAXS), following the methods reported in [3]. The SeMet fractions are soluble in water and contained branched poly-catechins with a typical degree of polymerization (DP) between 13 and 20. The SkMet extracts are only partially soluble in water (50-80% soluble). The Plavac Mali SkMet extract contained surprisingly long tannin macromolecules with a DP between 60 and 160, while the Babić SkMet tannins were considerably shorter (DP 16-20). The extracts SeAc and SkAc were poorly soluble and less aboundant by a factor of approximately 50 comparing to the Met extracts. The ability of the four Met extracts to inhibit amyloidogenesis was tested on the reduced carboxymethylated -casein (RCMK), which is known to be a convenient tool for the identification of polyphenolic inhibitors of amyloid fibril formation [4]. The kinetics of RCMK fibril formation alone and in the presence of 0.1 g/L of polyphenol fractions were followed in situ by the dynamical light scattering (DLS) over typically 200 minutes at 45°C. The scattering intensity and the effective hydrodynamic diameters were monitored. Fibril inhibition abilities of our polyphenol fractions were evaluated by comparison with the result for the EGCG, to our knowledge the best amyloid inhibitor known today. The antiamyloid activity of skin extracts is comparable to the activity of the EGCG. On the contrary, the seed extracts show only moderate amyloid inhibiting properties.

polyphenols; anti-amyloid activity; grape extracts; Plavac mali; Babić

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