Abstract
Recently, we identified novel saponins from edible seeds of Japanese horse chestnuts (Aesculus turbinata BL.) obtained during processing of the seeds with wooden ashes which was intended to remove harshness. In the present study, we isolated saponins and related compounds from natural and edible seeds, and examined the attenuating effect on increasing levels of blood glucose using male ICR mice. All of the deacetylescins Ia, IIa, Ib, and IIb were similarly effective in attenuating glucose levels and were less potent than the natural escins. Experiments on escins and related derivatives revealed that the potency of the compounds in the attenuation was in the order of escins>deacetylescins>desacylescins. The findings suggest that the acyl moiety at C-21 and the acetyl moiety at C-22 are important in attenuating increasing levels of blood glucose. Escin and related substances exhibited much weaker inhibitory activities on α-amylases as compared with (-)-epigallocatechin gallate. In addition, those compounds showed almost no inhibition of intestinal α-glucosidase activity. The results indicate that escins and their derivatives have little ability to inhibit the digestive enzymes for saccharides. The saponin fraction which includes deacetylescins and desacylescins as major components obtained from edible seeds was much less bitter taste than escins from natural seeds at the same concentrations. Taken together, deacetylescins and desacylescins from edible seeds seem to be useful as sources of nutraceutical foods because of their activity in attenuating increasing levels of blood glucose as well reducing the bitter taste.
