The seeds of the tea plant [Camellia sinensis (L.) O. KUNTZE (Theaceae)] are known to contain saponin constituents with an insectifuge activity and its crude saponin fraction has been used as a surface-active agent.2) Previously, we reported the structure elucidation and anti-sweet activity of two acylated polyhydroxyoleane-12-ene oligoglycosides, theasaponins E 1 (6) and E 2 (7), from the seeds of C. sinensis cultivated in Japan.2) In addition, from the seeds and leaves of C. sinensis var. assamica PIERRE cultivated in Sri Lanka, we isolated assamsaponins A (8), B (9), C (10), D (11), E, F (12), G, H, and I (13) with gastric emptying activity and an accelerating effect on gastrointestinal transit.3,4) Recently, we characterized floratheasaponins A (14), B, and C with antihyperlipidemic activity from the flowers of C. sinensis.1) As a continuing study on the bioactivity of saponin constituents from the tea plant, we found that the saponin fraction of the methanolic extract from the seeds of C. sinensis showed protective effects on ethanol-and indomethacin-induced gastric The saponin fraction from the seeds of the tea plant [Camellia sinensis (L.) O. KUNTZE (Theaceae)] was found to exhibit potent protective effects on ethanol-and indomethacin-induced gastric mucosal lesions in rats. Five new triterpene saponins, theasaponins E 3 (1), E 4 (2), E 5 (3), E 6 (4), and E 7 (5), were isolated together with 11 known saponins from the saponin fraction. The chemical structures of 1-5 were elucidated on the basis of chemical and physicochemical evidence. Among the isolated saponins, theasaponins E 1 (6), E 2 (7), and E 5 (3) and assamsaponin C (10) showed an inhibitory effect on ethanol-induced gastric mucosal lesions at a dose of 5.0 mg/kg, p.o. and their activities were stronger than that of omeplazole. With regard to the structure-activity relationships of theasaponins, the following structural requirements for a protective effect on ethanol-induced gastric lesions were suggested; 1) the 21-and/or 22-acyl groups are essential for the activity, 2) acetylation of the 16-hydroxyl group reduce the activity.
Six new triterpene saponins, theasaponins A(1) (1), A(2) (2), A(3) (3), F(1) (4), F(2) (5), and F(3) (6), were isolated from the saponin fraction of the seeds of Camellia sinensis. The stereostructures of 1-6 were elucidated on the basis of chemical and physicochemical evidence. Theasaponin A(2) (2) showed an inhibitory effect on ethanol-induced gastric mucosal lesions in rats at a dose of 5.0 mg/kg, p.o., and its activity was more potent than that of omeplazole. Structure-activity relationships for theasaponins on ethanol-induced gastroprotective activities may be suggested as follows: (1) the 28-acetyl moiety enhances activity; (2) theasaponins having a 23-aldehyde group exhibit more potent activities than those with a 23-hydroxymethyl group or a 23-methoxycarbonyl group.
Scope: Recent studies have reported that tiliroside, a glycosidic flavonoid, possesses antidiabetic activities. In the present study, we investigated the effects of tiliroside on carbohydrate digestion and absorption in the gastrointestinal tract. Methods and results: This study showed that tiliroside inhibits pancreatic a-amylase (IC 50 5 0.28 mM) in vitro. Tiliroside was found as a noncompetitive inhibitor of a-amylase with K i values of 84.2 mM. In male ICR mice, the increase in postprandial plasma glucose levels was significantly suppressed in the tiliroside-administered group. Tiliroside treatment also suppressed hyperinsulinemia after starch administration. Tiliroside administration inhibited the increase of plasma glucose levels in an oral glucose tolerance test, but not in an intraperitoneal glucose tolerance test. In human intestinal Caco-2 cells, the addition of tiliroside caused a significant dose-dependent inhibition of glucose uptake. The inhibitory effects of both sodium-dependent glucose transporter 1 (SGLT1) and glucose transporter 2 (GLUT2) inhibitors (phlorizin and phloretin, respectively) on glucose uptake were significantly inhibited in the presence of tiliroside, suggesting that tiliroside inhibited glucose uptake mediated by both SGLT1 and GLUT2. Conclusions: These findings indicate that the anti-diabetic effects of tiliroside are at least partially mediated through inhibitory effects on carbohydrate digestion and glucose uptake in the gastrointestinal tract.
As a part of our characterization studies on the bioactive saponin constituents of tea ‰owers (Camellia sinensis, ‰ower buds), the methanolic extract and 1-butanol-soluble portion (the saponin fraction) from the ‰ower buds were found to exhibit potent inhibitory eŠects on ethanol-and indomethacin-induced gastric mucosal lesions in rats and on serum glucose elevation in sucrose-loaded rats. Among the constituents of the 1-butanol-soluble portion, ‰oratheasapo-nins A, B, and C showed gastroprotective and hypoglycemic activities. Furthermore, we have developed qualitative and quantitative methods using HPLC for the principle saponins, ‰oratheasaponins A F, in tea ‰owers, which were previously found to show antiallergic and antiobesity eŠects. Using those methods, the saponin composition of Indian tea ‰owers were found to be similar to those of Chinese (Anhui) but not of Japanese tea ‰owers. On the other hand, it was found that the ‰oratheasaponin contents in tea ‰owers varied markedly during the blooming period, and they were abundant at half-bloom. Additionally, the contents of caŠeine in the tea ‰owers were examined using HPLC.
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