Phenolic profiles and screening of potential α-glucosidase inhibitors from Polygonum aviculare L. leaves using ultra-filtration combined with HPLC-ESI-qTOF-MS/MS and molecular docking analysis

Polygonum aviculare L. leaves (PALs), as an important medicinal crop product, have been reported to have a strong alpha-glucosidase inhibitory effect. However, it is unclear which exact active compositions are primary responsible for the beneficial effects. This study showed that PALs extracted with 70 % ethanol as solvent had significantly higher total phenolic/flavonoid contents and alpha-glucosidase inhibitory activity than PALs extracted with other solvents. The PALs ethanol extracts showed excellent alpha-glucosidase inhibitory activity (IC50 = 21.42 +/- 1.37 mu g/mL), which was significantly higher than that of anti-diabetes drug acarbose (IC50 = 176.79 +/- 1.72 mu g/mL). The phenolic compositions of the PALs extracts were identified by high performance liquid chromatography and quadrupole-time-of-flight-mass spectrometry (HPLC-ESI-qTOF-MS/MS) method. In order to discriminate the specific alpha-glucosidase inhibitors from the PALs extract, an combined strategy integrating affinity ultrafiltration and HPLC-ESI-qTOF-MS/MS was developed. Seven potential alpha-glucosidase inhibitors with high affinity ability including orientin, myricitrin, hyperoside, isoquercitrin, o-coumaric acid, polydatin and quercetin from PALs extract were screened. The alpha-glucosidase inhibitory activity assay confirmed that myricitrin (IC50 = 8.65 +/- 1.48 mu g/mL), quercetin (IC50 = 15.17 +/- 3.25 mu g/mL), and polydatin (IC50 = 35.15 +/- 3.25 mu g/mL) were primarily responsible for the alpha-glucosidase inhibitory activity of the PALs extract. Then, structure-activity relationships of these potential inhibitors were also discussed. More importantly, the possible inhibitory mechanisms of the identified inhibitors toward alpha-glucosidase were further clarified by molecular docking analysis. In conclusion, the proposed method can be used to effectively recognize the potential alpha-glucosidase inhibitors from complex extracts system in natural products.