Itaru Sakai1, Shun-ichiro Izumi2,*, Takayo Murano2,
Shinji Okuwaki2, Tsunehisa Makino2 and Takashi Suzuki1
1Bio-Team, Applied Technology Research Center, NKK Corporation, Kawasaki 210-0855, Japan
2Department of Obstetrics and Gynecology, Tokai University School of Medicine, Bohsei-dai, Isehara 259-1193, Japan
*Corresponding author. FAX: +81-463-91-4343
Abstract: Water extract from commercial English tea has a potent inhibitory activity against human placenta aldose reductase (NADPH oxidoreductase, E.C.184.108.40.206.). Inhibitory activity was separated into five major fractions by one-step chromatography with a C-18 reverse phase column. The most active fraction was further subjected to reverse phase column chromatography. As a result, a well-known flavone-glycoside, isoquercitrin, was isolated as the most potent chemical. The inhibitory character of isoquercitrin for aldose reductase was a mix of uncompetitive and noncompetitive inhibitions, and its IC50 was 1«10-6 M. In rat sciatic nerve tissue preparations, sorbitol accumulation in the presence of high concentrations of glucose (30 mM) was inhibited by 38% at 5«10-4 M of isoquercitrin. The flavone-glycoside isoquercitrin is the active inhibitor of aldose reductase inhibitor present in English tea. Given the ability of aldose reductase inhibitors to prevent diabetic complications, an epidemiological study of the effect of tea consumption on the pathogenesis and progression of diabetic complications would be interesting.
Keywords: Aldose reductase, Enzyme inhibitor, Tea leaf, Human placenta, Diabetes
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