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 alpha-amylase, alpha-glucosidase, acethylcholinesterase, and angiotensin-converting enzyme (ACE). Inhibition of alpha-glucosidase and acethylcholinesterase required lower leaf extract concentrations as compared with other two enzymes. The IC50 values of alpha-glucosidase and alpha-amylase inhibition were 66.08 and 438 mu g/mL, respectively, while the inhibition of ACE at 250-1250 mu g/mL was from 28.02 +/- 1.17% to 77.13 +/- 0.78%. The mode of in-hibition of alpha-glucosidase and acethylcholinesterase was evaluated by the kinetic studies. Leaf and tuber extracts displayed a mixed-type non-competitive mode of alpha-glucosidase inhibition. Phytochemical composition of ex-tracts 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.

Automated summary

This study evaluated the inhibitory activity of Dioscorea nipponica leaf and tuber extracts on important physiological enzymes. The leaf extract showed stronger enzyme inhibition than the tuber extract, which may be attributed to differences in secondary metabolite composition. The results provide valuable information for the development of functional foods and nutraceuticals with health benefits.