Physicochemical characteristics of polysaccharide conjugates prepared from fresh tea leaves and their improving impaired glucose tolerance

Hot-water extracts were prepared from fresh tea leaves and fractionated by DEAE-cellulose DE-52 column chromatography to yield one unexplored polysaccharide-conjugate fraction TPC-L (tea polysaccharide conjugates). Chemical components, molecular weight and its distribution, water vapor sorption properties, zeta potentials and optical characteristics of TPC-L were investigated. As compared with injured cell group, the two dosages of TPC-L (150 and 300 μg/mL) were discovered to possess remarkably protective effect on human umbilical vein endothelial cells against impairments induced by high glucose in a dose-dependent manner (p < 0.05, p < 0.001, respectively). Compared with group NC (normal control), the ingestion of 40 mg/kg of TPC-L could significantly reduce blood glucose levels of normal mice ingesting starch, and significant difference of AUC (area under the curve of blood glucose) and ΔAUC (p < 0.05, p < 0.01) at the postprandial time point of 0.5 and 1.0 h were observed. The three dosages of TPC-L (10, 40 and 160 mg/kg) did not significantly lower postprandial blood glucose levels of normal mice ingesting glucose. TPC-L could improve starch tolerance to prevent impaired glucose tolerance (IGT) from developing into diabetes as well as protective effects on HUVE cells against impairments induced by high glucose It was suggested that TPC-L improved IGT through its capability of inhibition on digestive enzymes.