報 文

ビワ葉抽出物の二糖類水解酵素阻害作用ならびにラットにおけるグルコースの腸管吸収抑制を介した血糖上昇抑制作用

田辺賢一1, 2,後田ちひろ2, 3,中村禎子2, 4,大曲勝久2,奥 恒行2, 4 *

1名古屋女子大学家政学部
2長崎県立大学大学院人間健康科学研究科
3京都府立医科大学大学院医学研究科
4十文字学園女子大学食・栄養・健康研究所

 Loquat (Eriobotrya japonica Lindley) leaf has been used in traditional medicine for its anti-inflammatory, narcotic, diuretic, and antitussive effects, and has been reported to be effective for treating gastrointestinal diseases and diabetes mellitus. Loquat contains many biologically active compounds such as polyphenols and triterpenoids. The objective of the present study was to investigate the inhibitory effect of loquat leaf extract (LLE) with 50% methanol on disaccharidases and suppression of increases in blood glucose and insulin. The LLE powder contained 10% of polyphenols and 35% sugars and others, and was dissolved in distilled water (8,000 μg/mL). LLE clearly inhibited disaccharidases in the rat small intestine, with particularly strong inhibition of maltase. The inhibitory mode of LLE was non-competitive for sucrase, maltase, trehalase, and lactase. In addition, LLE decreased glucose uptake significantly via SGLT1 using the everted gut sac. Therefore, LLE clearly inhibited absorption of glucose in the small intestine. Furthermore, when sucrose (150 mg) or glucose (150 mg) solutions were mixed with LLE (60 mg) and administered orally to rats, the resulting increases in blood glucose and insulin levels were suppressed significantly (p<0.05). These results demonstrate that suppression of increases in blood glucose and insulin levels by LLE is caused by inhibition of both disaccharidase activity and glucose transport in rats. LLE could therefore be used as an ingredient of functional food that prevents diabetes mellitus and the metabolic syndrome.
Keywords: loquat leaf extract, inhibitory effect, suppressive effect, postprandial blood glucose, disaccharidase

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