Studies On Biological Activities Of Ellagitannins From UBurs Of Castanea Mollissima, And Their Metabolic Products Ellagic Acid And Urolithins

The spiny burs of Chinese chestnut (Castanea mollissima Blume) are usually discarded as waste during post-harvesting processing, although abundant ellagitannins and significant antioxidant activities have been reported in previous reports. Many health benefits of the chestnut and other ellagitannins-containing fruits and nuts such as strawberry, raspberry, blackberry have been attributed to the ellagitannins among them. However, the bioavailability of ellagitannins is extremely poor after oral administration and part of them was transformed to ellagic acid in the intestinal tract, after which both the ellagitannins and ellagic acid suffer extensive metabolism by the gut microbiota to produce urolithins. These urolithin metabolites, such as urolithin A, urolithin B and urolithin C were much easier to be absorbed. The poor bioavailability and the extensive gut metabolism of ellagitanins and ellagic acid suggest that urolithins rather than ellagitannins or ellagic acid may be the actual bioactive molecules responsible for the health benefits of them. Therefore, it is crucial to compare the bioactivities of these metabolites in order to elucidate the influence of gut microbiota metabolism on the bioactivities of ellagitannins and ellagic acd.In this paper, the total ellagitannins extracts were extracted and purified at first, and three major metabolites including urolithin A, urolithin B and urolithin C were chemically synthesized, respectively. Accordingly, the antioxidant activities of these metabolites and ellagic aid, including the DPPH and ABTS radical scavenging activities, reducing power, cellular antioxidant activities, and polyethelene polyprolene (PP) processing antioxidant activities were assessed. The major results of these assays were listed as following.(1) The optimal extraction and enrichment procedure were established on based on the ellagitannins extraction yields and antioxidant activities.50%(v/v) ethanol aqueous solution was optimized as the extraction solution, and HPD100 macroporous resin absorption with gradient ethanol aqueous chromatography elution was used for enrichment of ellagitannins.(2) The chemically synthetic schemes for urolithin A, urolithin B and urolithin C were established, and about 10 grams of each were synthesized. The structures of them were confirmed based on the 1H and 13CNMR data.(3) All the metabolites and ellagic acid showed antioxidant activities in DPPH and ABTS radical scavenging assays, as well as the reducing power assay. Ellagic acid exhibited the highest antioxidant activities, followed by urolithin A, urolithin B and urolithin C subsequently. The antioxidant activities of these components were highly correlated with the amounts of phenolic hydroxy substituents, which indicated that the radical scavenging activities significantly decreased with the removal of phenolic hydroxy substituents in the process of metabolism of ellagic acid in the intestinal tracts.(4) MTT assay based on HepG2 cell lines showed that ellagitannins extracts from chestnut burs, ellagic acid and urolithins exhibited significantly different effects on the proliferation of HepG2 cells. Both the ellagitannins and ellagic acid exhibited proliferation-promotion effects and no anti-proliferation effects were observed even at high concentrations. While the urolithins, including urolithin A, urolithin B and urolithin C exhibited dose-dependent anti-proliferation effects. These results indicated that the gut metabolism altered the bioactivities of ellagitannins and ellagic acid.(5) The results of MFR during the melt extrusion showed that fullerene possessed excellent stability effect on PP, and antioxidant 168 showed great synergistic effects. However, the effect of ellagitannins extracts from chesnut spiny burs, ellagic acid and urolithins are not significant.