Use this URL to cite or link to this record in EThOS: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367943
Title: Biological and phytochemical studies on some traditional anti-diabetic plants
Author: Srijayanta, Sairavee
ISNI:       0000 0001 3475 9603
Awarding Body: University of London
Current Institution: King's College London (University of London)
Date of Award: 2000
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Abstract:
This current study aims to investigate the effect of selected medicinal plants on anti-diabetic activity, focusing on potential inhibitory effects on intestinal glucose absorption and a stimulatory effect on insulin secretion from pancreatic β-cells using two different in vitro models, brush border membrane vesicles (BBMV) and an insulin secreting cell line - RINm5F cells. Plants used in the studies were selected based on their reputations as anti-diabetic remedies in some countries with varying degrees of scientific evidence to support their traditional use. Investigation of the effect of the aqueous extracts of the selected plants revealed four plants which were capable of causing marked inhibition of glucose uptake into BBMV. These plants were Lycium chinensis (Solanaceae), Piper longum (Piperaceae), Pterocarpus marsupium (Leguminosae) and Salacia reticulata (Celastraceae). The results suggested that the inhibition observed in these cases was not associated with glucose in the extracts which could interfere with the assay, as the extracts appeared to contain negligible amount of glucose. There was a possibility that these plants contained active constituents that were capable of inhibiting a transport activity of SGLT1, a transporter of glucose across the brush border. This is the first study to report the effect of these plants on this model. Bioassay-guided fractionation of L. chinensis afforded the isolation of a pure compound which, by means of NMR and Mass spectrometry, was identified as sitosterol glucoside. Investigation of the effect of aqueous extracts of the selected plants on RINm5F cells revealed two plants which were capable of stimulating insulin secretion. These plants were Anemarrhena asphodeloides (Liliaceae) and a member of the genus Parvatia (Lardizabalaceae). The effect of these plants did not appear to be associated with cell membrane damage as judged by lack of appreciable LDH leakage from the cells after exposure to the extracts. However, no further study was conducted on Parvatia spp., since the identity of this plant was ambiguous. Bioassay guided fractionation of A. asphodeloides methanolic extract which was found to have the most potent activity resulted in the isolation of 4 compounds i.e. mangiferin, mangiferin glucoside, timosaponin AIII and timosaponin BI. Of these, mangiferin was able to stimulate the secretion of insulin from both RINm5F cells and rat islets. The effect of mangiferin was found to be potentiated by the presence of nutrient, suggesting that the compound may have potential advantages for use in the treatment of NIDDM as it would cause greater insulin release following a meal than in basal conditions. It appeared that the stimulation of insulin release caused by mangiferin was associated neither to PKA nor PKC pathway in the secretory response. Mangiferin glucoside was found to cause a significant secretion of insulin from RINm5F cells but not in rat islets. Unlike mangiferin, the effect of mangiferin glucoside did not appear to be potentiated by the presence of nutrient. Timosaponin AIII was found to be a very potent insulin secretagogue, the compound as low as 1-8 μg/ml was found to cause a significant release of insulin from RINm5F cells without damaging cell membranes. In contrast to timosaponin AIII, timosaponin BI was found to have no effect on insulin secretion from RINm5F cells. Besides these four compounds, two other compounds were also isolated from non active fraction of methanolic A. asphodeloides extract, i.e. cis hinokiresinol and 4'-methyl-cis-hinokiresinol.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.367943  DOI: Not available
Keywords: Medicinal; Glucose uptake
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