Anti-Diabetic Effects of Different Phenolic-Rich Fractions from Rhus Chinensis Mill. Fruits in vitro

This study investigated the inhibitory effects of the Ethanol Extract (EE), Free Phenolic (TF), Esterified Phenolic (TE) and Insoluble-bound Phenolic (TI) from Rhus chinensis Mill. fruits on α-glucosidase, Dipeptidyl Peptidase-4 (DPP-IV), and the formation of Advanced Glycation End (AGE) products. Results showed that the TF had the strongest inhibition against α-glucosidase and DPP-IV with IC50 of 0.56 ± 0.04 and 66.08 ± 1.36 μg/mL, respectively (p < 0.05). TI exhibited the strongest inhibitory effect on the formation of AGEs with IC50 of 0.43 ± 0.03 mg/mL (p < 0.05). Two major compounds (myricetin-3-O-rhamnoside and quercetin-3-O-rhamnoside) showed additive or synergistic effects on α-glucosidase inhibition, while displayed antagonistic effect on DPP-IV inhibition. Correlation analysis indicated that myricetin-3-O-(6″-galloyl) glycoside and myricetin O-gallate contributed significantly on α-glucosidase inhibition, while di-O-galloyl-glucoside and its isomer may contribute remarkably toward DPP-IV inhibition. Protocatechuic acid and myricetin-3-O-rhamnoside showed a positive correlation with the suppression of AGEs formation. Those results may provide some scientific information for exploring R. chinensis fruits as nutraceuticals and/or functional foods to prevent or improve diabetes.