Originals

Inhibitory Effect of Loquat Leaf Extract on Disaccharidase, and Suppression of Postprandial Blood Glucose and Insulin in Rats

Kenichi TANABE1, 2, Chihiro USHIRODA2, 3, Sadako NAKAMURA2, 4,
Katsuhisa OMAGARI2, Tsuneyuki OKU2, 4 ＊

1Department of Food Science and Nutrition, Nagoya Women’s University
2Graduate School of Human Health Science, University of Nagasaki
3Graduate School of Medical Science, Kyoto Prefectural University of Medicine
4Institute of food, Nutrition and Health, Department of Human Domestic Science, Jumonji University

　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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