Rapid Screening of Nonalkaloid α-Glucosidase Inhibitors from a Mulberry Twig Extract Using Enzyme-Functionalized Magnetic Nanoparticles Coupled with UPLC-MS/MS

Mulberry twigs are an important source of alpha-glucosidase inhibitors. To date, research studies on alpha-glucosidase in mulberry twigs have mainly focused on alkaloids such as 1-deoxynojirimycin (DNJ). Preliminary studies have shown that there may be more active nonalkaloid alpha-glucosidase inhibitors in mulberry twigs. In this study, we immobilized alpha-glucosidase on Fe3O4@SiO2 for the first time and rapidly screened four nonalkaloid alpha-glucosidase inhibitors (kuwanon G, kuwanon C, kuwanon H, and morusin) using ligand fishing technology with ultrahigh-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) from the mulberry twig extract of Jialing 20, the excellent artificial triploid variety of mulberry cultivated extensively in Southwest China. The half maximal inhibitory concentrations (IC50) of kuwanon H and kuwanon G were 2.82 +/- 0.68 and 2.83 +/- 0.31 mu M, respectively, with better inhibition activity than that of DNJ (with an IC50 of 7.04 +/- 0.82 mu M). Meanwhile, the molecular docking results showed that the action sites of these two isopentenyl flavonoids on alpha-glucosidase were different from that of DNJ. In brief, this work is beneficial to discovering new alpha-glucosidase inhibitors from mulberry twigs quickly and accurately and provides a theoretical basis for the mulberry twig extract as a functional food or a natural hypoglycemic drug source, as well as a reference for directional breeding of mulberry, which greatly improves the exploitation and utilization value of mulberry twigs as an agricultural byproduct in the fields of agricultural production, functional food, and natural medicine.