Comparative analysis of 1-deoxynojirimycin contribution degree to α-glucosidase inhibitory activity and physiological distribution in Morus alba L

Abstract

Natural α-glucosidase inhibitors offer an attractive strategy to manage postprandial hyperglycemia in patients with type 2 diabetes. 1-Deoxynojirimycin (DNJ), the main hypoglycemic constituents in Morus alba L., has been extensively researched. Here, for different parts of the mulberry tree, the DNJ content and the IC50 values of DNJ and ethanol extracts have been determined and compared. Possible metabolic pathways and storage sites for DNJ in mulberry trees have been investigated, and the kinetics of inhibition of α-glucosidase by DNJ and ethanol extracts of different parts of the mulberry tree have been measured. DNJ content was found to be highest in trunk bark, whereas α-glucosidase inhibitory activity was highest in both twig and trunk bark. Buds and roots are likely to be the topmost and bottommost sites of DNJ biosynthesis. DNJ is an insect antifeedant (not including silkworms) and may itself have antiviral activity, or be the precursor to a compound with antiviral activity. Ethanol extracts of twig, trunk and root bark are mixed-type inhibitors of α-glucosidase; extracts from other parts of the tree are competitive inhibitors. The study provides useful information about the physiological distribution of important active components, especially DNJ, in the mulberry tree and suggests how best to develop and use the crude drug resources provided by the tree.