Antioxidant And Hypoglycemic Effects Of Polygonatum Odoratum (Mill.) Druce Extracts In Vitro And In Vivo

Diabetes mellitus (DM) is a group of chronic metabolic disorders of carbohydrates and nowadays, the population among adults worldwide is about3%and will reach to7.7%by2030. Treatment strategies of DM mainly focus on drug therapies including insulin injection and oral hypoglycemic drugs such as glycosidase inhibitors, biguanides and sulphonylureas agents to keep the blood glucose within normal levels. Excepting high cost, many hypoglycemic agents have serious adverse effects. The rhizome of Polygonatum odoratum (Mill.) Druc, an edible medicinal herb has long been used to treat various diseases including diabetes mellitus(DM) and saponin, flavonoids and Polysaeeharides are the mian ingredients. The objectives of this study are to investigate the antioxidant and antidiabetic effect of of various extracts of P.odoratum in a-glucosidase, HepG2cell and STZ-induced diabetic rats.The dissertation is constituted by following parts:(1) In preliminary study, the hypoglycemic ability of the ethanol extract was higher than the water extract. Thus, the ethanol extract was separated and fractions with different polarity were prepared by solvent extraction and macroporous absorptive resin (D101) column and their anti-diabetic potentials were evaluated by glucose uptake in HepG2cells. The n-buthanol fraction, a saponin-rich fraction obtained by partitioning the ethanol extract with n-buthanol after petroleum ether and acetic ether showed the highest anti-diabetic potential in glucose uptake in HepG2cells followed by acetic ether fraction which was rich in flavonoids. Further fractionation the saponin-rich fraction using macroporous resin column (D101), polysaccharide, flavonoid and saponin-rich fractions were obtained by elution with water,40%and60%ethanol, respectively and their anti-diabetic potentials proved by glucose uptake test in HepG2cells. The data indicated that saponin-rich fraction had the highest ability to enhance glucose uptake in HepG2cells.(2) In addition, a-glycosidase inhibitory activities of active fractions were measured, saponin-rich fraction and flavonoid-rich fraction showeda-glycosidase inhibitory activity with IC50value of2.05±0.32and3.92±0.65mg/ml, respectively. Sugar-rich fraction had little activity.(3) saponin-rich fraction and flavonoid-rich fraction suppressed the postprandial blood glucose levels in the mild diabetic rats improved glucose tolerance significantly. Long-term therapy test (60d) in severe diabetic rats indicated that saponin-rich fraction significantly ameliorated clinical symptoms of diabetes including the elevated blood glucose, body weight loss as well as the increased food and water intake.(4) Also in long-term therapy test (60d) in severe diabetic rats, flavonoid-rich fraction was more potential than saponin-rich fraction to increase superoxide dismutase (SOD) activity and decrease malondialdehyde (MDA) level in rat plasma. Meanwhile, saponin-rich fraction inhibited aldose reductase(AR) and ameliorated kidney damage in diabetic rats.(5) Flavonoid-rich fraction had the highest intracellular antioxidant capacity in HepG2cells, saponin also had some effect.