Influences of Glycosidic Bonds in Flavonoids from Tartary Buckwheat on Glucose Uptake in C2C12 Myotubes

Tartary buckwheat has highest content of rutin in grains. Rutin can be degraded to isoquercetin and quercetin during processing, which may change its biological activities. This study compared the glucose uptake and mechanisms in C2C12 myotubes of rutin, quercetin and isoquecetin, which had different glycosidic bonds. Results showed that contact of water during processing led to degradation of rutin, which was the key flavonoid in tartary buckwheat. Rutin and its degraded products(quercetin and isoquercetin) effectively stimulated glucose uptake in C2C12 myotubes in the order: quercetin>isoquercetin>rutin. Therefore, substitution of sugar moiety to hydroxyl group in quercetin led to decrease of glucose uptake in C2C12 myotubes. Rutin and isoquercetin did not stimulate the expression of IRS-1 and p-AKT in the insulin-dependent pathway. At high concentration(400 μmol/L), rutin and isoquercetin stimulated glucose uptake and promoted the expression of phosphorylation of AMP-activated protein kinase(AMPK)/ acetyl-CoA carboxylase(ACC) in insulin-independent pathway in the order: isoquercetin>rutin. Quercetin inhibited expression of insulin receptor substract-1(IRS-1) and phosphorylation of AKT. However, quercetin significantly promoted expression of phosphorylation of AMPK/ACC, thus significantly increased the glucose uptake in C2C12 myotubes. Comparison of hypoglycemic effects and mechanisms among rutin and its degraded products were beneficial to reveal hypoglycemic effects of flavonoids from tartary buckwheat.