Characterization of inhibitors of postprandial hyperglycemia from the leaves of Nerium indicum
Characterization of inhibitors of postprandial hyperglycemia from the leaves of Nerium indicum
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DOI：
10.3177/jnsv.53.166
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发表时间：
2007-04-01
影响因子：
1.6
通讯作者：
Natori, Yasuo
中科院分区：
文献类型：
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作者：
Ishikawa, Akiko;Yamashita, Hiromi;Natori, Yasuo
夹竹桃是一种起源于印度-巴基斯坦的灌木，属于夹竹桃科。众所周知，饭前摄入籼稻叶子可以降低II型糖尿病患者餐后葡萄糖水平，现在在巴基斯坦的一些地区，这种植物被用作治疗II型糖尿病的民间疗法。本研究发现，大鼠在摄入麦芽糖或蔗糖时，籼稻叶热水提取物可降低餐后血糖升高。还发现提取物对a-葡萄糖苷酶有较强的抑制作用，提示其对餐后血糖升高的抑制作用是由于叶片中存在一些抑制e-葡萄糖苷酶的抑制剂。因此，我们以a-葡萄糖苷酶抑制活性为指标，试图从叶提取物中分离出活性成分。采用Sephadex G-15、硅胶和反相高效液相色谱分离得到两种活性化合物。紫外光谱、质谱和核磁共振谱分析证实，这些化合物的化学结构为3- o -咖啡酰奎宁酸（绿原酸）及其结构异构体5- o -咖啡酰奎宁酸。两种化合物均以非竞争性方式抑制α -葡萄糖苷酶。研究发现，绿原酸能抑制大鼠餐后血糖升高，并能抑制麦芽糖中葡萄糖部分的吸收，也能抑制大鼠肠外翻肠囊系统对葡萄糖的吸收。这些结果表明绿原酸是籼稻叶片中存在的主要抗高血糖成分之一。此外，槲皮素和儿茶素对葡萄糖苷酶具有较强的抑制活性。
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 a-glucosidase, suggesting that the suppression of the postprandial rise in the blood glucose is due to the occurrence of some inhibitors of ce-glucosidase in the leaves. We, therefore, tried to isolate the active principles from the leaf extract, using a-glucosidase-inhibitory activity as the index. Employing Sephadex G-15, silicagel 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 a-glucosidase.