CUHK electronic theses & dissertations collection

alpha-Glucosidase from yeast was used to screen for alpha-glucosidase inhibitory activities in Chinese herbal medicines. Seventy crude extracts were studied. The extracts of Semen Fagopyri Esculenti, Herba Euphorbiae Humifusae, Radix Polygoni Multiflori, Cortex Cinnamomi, Radix Paeoniae Rubra, and Radix Paeoniae Alba exhibited alpha-glucosidase inhibitory activities. These herbs have high potential for finding active compounds to develop into new antidiabetic drugs.In this study, an assay technique involving brush border membrane vesicles was developed to screen for glucose uptake inhibitory actions in sixteen compounds from natural sources. Two compounds, namely naringenin and desoxyrhaponticin, were demonstrated to exhibit moderate inhibitory action on glucose uptake in rabbit intestinal brush border membrane vesicles, and showed very strong inhibitory action in rat everted intestinal sleeves. The kinetics study indicated that they behave as competitive inhibitors on glucose uptake. Moreover, they could reduce the level of the glucose uptake in the diabetic rat intestinal and renal membrane vesicles. In vivo study further demonstrated that desoxyrhaponticin could significantly reduce the glucose levels after a single oral administration of glucose in neonatal streptozotocin-induced diabetic rats, but not naringenin. These results suggest that naringenin and desoxyrhaponticin may be useful in the control of hyperglycemia. They act by inhibiting glucose uptake in the intestine and glucose reabsorption in the renal proximal tubules.On the other hand, several synthetic compounds based on the structure of valienamine were found to show strong inhibition on intestinal alpha-glucosidases such as sucrase, glucoamylase and maltase. The strongest inhibitor was further studied. It could reduce the postprandial plasma glucose level of neonatal streptozotocin-induced diabetic rats. These results demonstrated that it has the potential to develop inter an oral antihyperglycemic agent.The objective of this study is to improve the postprandial hyperglycemic conditions of diabetes by two approaches: (1) inhibiting the digestive enzymes (alpha-glucosidases), and (2) inhibiting active glucose transport in the small intestine. We have screened for new inhibitors of alpha-glucosidase and monosaccharide cotransporters from natural products and their derivatives. These compounds may be useful in the management of type 2 diabetes and diabetic complications.Type 2 diabetes mellitus accounts for 90-95% of all diabetic cases and has become a major health concern over the world. There is increasing evidence that postprandial hyperglycemia, a hallmark of diabetes, plays a critical role in the development of type 2 diabetes and cardiovascular complications. Therefore the early identification of postprandial hyperglycemia and its effective control can offer the potential for early intervention and prevention of diabetic complications.Li Jianmei."August 2006."Adviser: Christopher H. K. Cheng.Source: Dissertation Abstracts International, Volume: 68-03, Section: B, page: 1592.Thesis (Ph.D.)--Chinese University of Hong Kong, 2006.Includes bibliographical references (p. 161-180).Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web.Abstracts in English and Chinese.School code: 1307