Ishikawa Akiko, Yamashita Hiromi, Hiemori Miki, Inagaki Eiko, Kimoto Masumi, Okamoto Masahiko, Tsuji Hideaki, Memon Allah Nawaz, Mohammadio Alli, Natori Yasuo
Department of Nutritional Science, Okayama Prefectural University, Soja, Okayama 719-1197, Japan.
J Nutr Sci Vitaminol (Tokyo). 2007 Apr;53(2):166-73. doi: 10.3177/jnsv.53.166.
Nerium indicum is an India-Pakistan-originated shrub belonging to the oleander family. The ingestion of leaves of N. indicum before a meal is known to effect the lowering of postprandial glucose levels in Type II diabetic patients and this plant is now used as a folk remedy for Type II diabetes in some regions of Pakistan. In the present study, the hot-water extract of N. indicum leaves was found to reduce the postprandial rise in the blood glucose when maltose or sucrose was loaded in rats. It was also found that the extract strongly inhibited alpha-glucosidase, suggesting that the suppression of the postprandial rise in the blood glucose is due to the occurrence of some inhibitors of alpha-glucosidase in the leaves. We, therefore, tried to isolate the active principles from the leaf extract, using alpha-glucosidase-inhibitory activity as the index. Employing Sephadex G-15, silica gel and reversed-phase HPLC, we isolated two active compounds. The UV, mass and NMR spectrometric analyses established that the chemical structures of these compounds are 3-O-caffeoylquinic acid (chlorogenic acid) and its structural isomer, 5-O-caffeoylquinic acid. Both compounds were shown to inhibit alpha-glucosidases in a non-competitive manner. The authentic chlorogenic acid was found to suppress the postprandial rise in the blood glucose in rats and also inhibited the absorption of the glucose moiety from maltose and glucose in the everted gut sac system prepared from rat intestine. These results demonstrate that chlorogenic acid is one of the major anti-hyperglycemic principles present in the leaves of N. indicum. Furthermore, among polyphenol compounds tested, quercetin and catechins were shown to have strong inhibitory activity against alpha-glucosidase.
夹竹桃是一种原产于印度和巴基斯坦的灌木，属于夹竹桃科。已知在餐前食用夹竹桃的叶子可降低II型糖尿病患者的餐后血糖水平，目前这种植物在巴基斯坦的一些地区被用作II型糖尿病的民间疗法。在本研究中，发现夹竹桃叶的热水提取物在给大鼠喂食麦芽糖或蔗糖时可降低餐后血糖升高。还发现该提取物强烈抑制α-葡萄糖苷酶，这表明餐后血糖升高的抑制是由于叶子中存在一些α-葡萄糖苷酶抑制剂。因此，我们试图以α-葡萄糖苷酶抑制活性为指标，从叶提取物中分离出活性成分。利用葡聚糖凝胶G-15、硅胶和反相高效液相色谱，我们分离出两种活性化合物。紫外、质谱和核磁共振光谱分析确定这些化合物的化学结构为3-O-咖啡酰奎尼酸（绿原酸）及其结构异构体5-O-咖啡酰奎尼酸。两种化合物均以非竞争性方式抑制α-葡萄糖苷酶。发现纯绿原酸可抑制大鼠餐后血糖升高，并在由大鼠肠道制备的外翻肠囊系统中抑制麦芽糖和葡萄糖中葡萄糖部分的吸收。这些结果表明绿原酸是夹竹桃叶中存在的主要降血糖成分之一。此外，在所测试的多酚化合物中，槲皮素和儿茶素对α-葡萄糖苷酶具有很强的抑制活性。
