In vitro inhibition of α-glucosidases and glycogen phosphorylase by catechin gallates in green tea

• Published in: Food chemistry 2010-10, Vol.122 (4), p.1061-1066
• Main Authors: Kamiyama, Ogusa, Sanae, Fujiko, Ikeda, Kyoko, Higashi, Yasuhiko, Minami, Yasuhiro, Asano, Naoki, Adachi, Isao, Kato, Atsushi
• Format: Article
• Language: English
• Subjects: alpha-glucosidase; Anti-diabetic effect; Biological and medical sciences; catechin; cell culture; Coffee, tea and other stimulative beverage industries; enzyme inhibition; enzyme inhibitors; epigallocatechin; food analysis; food composition; Food industries; functional foods; Fundamental and applied biological sciences. Psychology; Gallated catechins; glycemic effect; glycogen; Glycogen phosphorylase inhibition; green tea; Green tea extract; human cell lines; in vitro studies; noninsulin-dependent diabetes mellitus; phosphorylase; α-Glucosidase inhibition
• ISSN: 0308-8146; 1873-7072
• DOI: 10.1016/j.foodchem.2010.03.075

We investigated in vitro inhibition of mammalian carbohydrate-degrading enzymes by green tea extract and the component catechins, and further evaluated their inhibitory activities in cell cultures. The extract showed good inhibition toward rat intestinal maltase and rabbit glycogen phosphorylase (GP) b, with IC 50 values of 45 and 7.4 μg/ml, respectively. The polyphenol components, catechin 3-gallate (CG), gallocatechin 3-gallate (GCG), epicatechin 3-gallate (ECG), and epigallocatechin 3-gallate (EGCG), were good inhibitors of maltase, with IC 50 values of 62, 67, 40, and 16 μM, respectively, and EGCG also showed good inhibition toward maltase expressed on Caco-2 cells, with an IC 50 value of 27 μM. The ungallated catechins, such as catechin, gallocatechin (GC), epicatechin (EC), and epigallocatechin (EGC), showed no significant inhibition toward GP b, whereas the gallated catechins CG, GCG, ECG, and EGCG inhibited the enzyme, with IC 50 values of 35, 6.3, 27, and 34 μM. From multiple inhibition studies by Dixon plots, GCG appears to bind a new allostelic site, the indole inhibitor site. These gallated catechins also inhibited glucagon-stimulated glucose production dose-dependently, with IC 50 values ranging from 33 to 55 μM. Dietary supplementation with these gallated catechins or the green tea extract containing them, which inhibits both α-glucosidases and GP in vitro and in cell culture, would contribute to the protection or improvement of type 2 diabetes.