| Summary: | 碩士 === 東海大學 === 食品科學系 === 102 === Okra (Abelmoschus esculentus fruits) is cultivated in between warm temperature and tropical regions around the world and long been consumed as vegetable and medicine. Recent studies have demonstrated that okra may provide antioxidative, hepatoprotective, hypoglycemic and cholesterolemic effects. Nevertheless, the active components and underlying mechanisms of the antidiabetic activities in okra have not yet been fully documented. In this study, active components were isolated and identified from okra, and were tested for their antioxidative, glycosidase (α-glucosidase, α-amylase) inhibitory activities and the mechanisms of glucose homeostatic regulation in FL83B murine hepatocytes. The 50% ethanol extract of okra showed strong antioxidant activity (TEAC) and inhibitory properties against both α-amylase and α-glucosidase. The extract was further separated successively by Amberlite XAD-7 and reversed HPLC to obtain three components. MS, UV and 1H, 13C-NMR analyses identified the isolated components as uridine (1), quercetin-3-O-β-D-glucopyranosyl-(1→6)-β-D-glucopyranoside (2), quercetin-3-O-β-D-4′′-O-methyl- β-D-glucopyranoside (3). These two flavonol glycosides showed strong antioxidant activity and inhibitory activity toward α-glucosidase. For cellular analysis, FL83B cells were incubated with various concentrations of okra's 50% ethanol extract and component 2, 3 to test their viability, uptake of glucose analogue 2-NBDG, glycogen content and insulin signaling. All tested samples did not show significant inhibitory effects on the survival of FL83B cells. To further investigate the anti-hyperglycemic mechanisms of these okra derivatives, parts of FL83B were induced with high concentrations of glucose to be insulin resistant by incubation with high glucose. In the presence of samples, uptake of glucose analogue 2-NBDG was enhanced when FL83B cells were either in normal or insulin resistant state. Glycogen contents both in normal and in insulin resistant cells was also increased by adding samples in a dose-dependent manner. Okra samples showed profound effects on upregulating insulin signaling in normal and insulin resistant cells as manifested by protein expression levels of IR, IRS-1, PI3K, Akt and the phosphorylation status of Akt. Most of the gene expressions were further enhanced in the presence of insulin. In conclusion, the 50% ethanol extract and component 2, 3 of okra may provide antioxidative and glycosidases inhibitory effects in vitro, and promoting insulin signaling and insulin sensitivity, enhance glucose uptake in normal or insulin resistant cells, implying a hypoglycemic activity in vivo.
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