Presence of aldose reductase inhibitors in tea leaves

Water extract from commercial English tea has a potent inhibitory activity against human placenta aldose reductase (NADPH oxidoreductase, E.C.1.1.1.21 .). 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 pot ent chemical. The inhibitory character of isoquercitrin for aldose reductas e was a mix of uncompetitive and noncompetitive inhibitions, and its IC50 w as 1 x 10(-6) M. In rat sciatic nerve tissue preparations, sorbitol accumul ation in the presence of high concentrations of glucose (30 mM) was inhibit ed by 38% at 5 x 10(-4) M of isoquercitrin. The flavone-glycoside isoquerci trin is the active inhibitor of aldose reductase inhibitor present in Engli sh tea. Given the ability of aldose reductase inhibitors to prevent diabeti c complications, an epidemiological study of the effect of tea consumption on the pathogenesis and progression of diabetic complications would be inte resting.