Enzyme inhibitory activity of Dioscorea nipponica Makito hydroethanolic extracts of leaves and tubers in relation to their major secondary metabolites

Different anatomical parts of Dioscorea nipponica Makito have been used in foods and folk medicines for their nutritional and pharmacological properties; however, the scientific data on enzyme inhibitory activities and phytochemicals in plant extracts remain rather scarce. Such information is important for expanding possible uses of plant origin preparations in nutrition. This study, using commonly applied assays, evaluated inhibitory activity of 70% ethanol extract of D. nipponica leaves and tubers against such physiologically important enzymes as α-amylase, α-glucosidase, acethylcholinesterase, and angiotensin-converting enzyme (ACE). Inhibition of α-glucosidase and acethylcholinesterase required lower leaf extract concentrations as compared with other two enzymes. The IC50 values of α-glucosidase and α-amylase inhibition were 66.08 and 438 μg/mL, respectively, while the inhibition of ACE at 250–1250 μg/mL was from 28.02 ± 1.17% to 77.13 ± 0.78%. The mode of inhibition of α-glucosidase and acethylcholinesterase was evaluated by the kinetic studies. Leaf and tuber extracts displayed a mixed-type non-competitive mode of α-glucosidase inhibition. Phytochemical composition of extracts was determined by UPLC-QTOF/MS and HPLC-UV methods. Leaf extract was remarkably stronger enzyme inhibitor than tuber extract and it may be explained by the differences in the secondary metabolite composition. Quinic, chlorogenic acids and quercetin glycosides, which are well-known enzyme inhibitors, were the main phytochemicals in the leaf extract, while steroidal glycosides, peptides and oligomeric sugars were the major constituents in the tuber extract. It is expected that new knowledge on D. nipponica will serve for its valorisation in developing new health beneficial ingredients for functional foods and nutraceuticals. •Phytochemicals & enzyme inhibitory activity of Dioscorea nipponica extracts reported.•Quinic, chlorogenic acids & quercetin glycosides the main leaf secondary metabolites.•Phenolics-rich leaf extract was remarkably stronger inhibitor of enzymes.•Kinetics studies explain the mode of glucosidase & acethylcholinesterase inhibition.•The relation between the identified phytochemicals and enzyme inhibition is discussed.