Identification of α-glucosidase inhibitors from Cortex Lycii based on a bioactivity-labeling high-resolution mass spectrometry-metabolomics investigation

Cortex Lycii, as a kind of traditional Chinese medicines, have shown prospects in the prevention of diabetes and its complications. However, there is comparatively little information regarding the characterization of potentially hypoglycemic compounds derived from Cortex Lycii. In this study, we performed a global non-selective investigation of alpha-glucosidase inhibitors in Cortex Lycii based on a bioactivity-labeling high-resolution mass spectrometry-metabolomics method. Samples of Cortex Lycii were collected from different Chinese provinces and their ethyl acetate extracts were analyzed using an in vitro alpha-glucosidase inhibition assay for bioactivity-labeling. The ethyl acetate extracts were also subjected to liquid chromatography-mass spectrometry analysis and multivariate data analysis was subsequently conducted to identify correlations between the bioactivity measured from the enzyme-involved test and the profiles obtained based on high-resolution mass spectrometry. The variables contributing significantly to the separation of the more-active from the less-active samples were considered to indicate the potential target ions of active compounds. MS/MS fragment patterns and nuclear magnetic resonance analyses were used to identify the potential target ions. The developed platform mentioned above facilitated rapid identification of four alpha-glucosidase inhibitors, namely, N-p-trans-coumaroyltyramine (1), N-trans-caffeoyltyramine (2), (9R,10E,12Z)-9-hydroxy-10,12-octadecadienoic acid (3a), and (9S,10E,12Z)-9-hydroxy-10,12octadecadienoic acid (3b) from Cortex Lycii. The alpha-glucosidase inhibitory activities of compounds 3a and 3b with IC50 values of 1.0413 +/- 0.0551 and 1.0423 +/- 0.0049 mM, respectively, are reported here for the first time. Enzyme kinetics revealed that both 3a and 3b were non-competitive inhibitors of alpha-glucosidase, with Ki values of 2.20 and 2.24 mM, respectively. In short, the presented work identified compounds 3a and 3b as potential alpha-glucosidase inhibitors with higher inhibitory activity and a different mode of inhibition compared to the standard alpha-glucosidase inhibitor, acarbose. The integrated approach adopted in this study can be extended as a normalized procedure to rapidly identify active compounds, even from complex extracts, and can readily be adapted for the study of other natural products. (C) 2021 Elsevier B.V. All rights reserved.