Free radical scavenging, enzyme inhibitory constituents from antidiabetic Ayurvedic medicinal plant Hydnocarpus wightiana Blume

Hydnocarpus wightiana is advocated in traditional Indian medicine to possess strong antidiabetic activity. In the course of identifying bioactive fractions from Indian medicinal plants we observed that acetone extract of the seed hulls of H. wightiana possess strong free radicals (DPPH and ABTS) scavenging, alpha-glucosidase and moderate N-acetyl-beta-D-glucosaminidase inhibitory activities. Further fractionation of the extract led to the isolation of hydnocarpin, luteolin and isohydnocarpin in substantial yields. All the compounds showed strong ABTS scavenging property. However, only luteolin could display strong DPPH scavenging activity. Furthermore, all the three compounds also showed varying degrees of alpha-glucosidase and N-acetyl-beta-D-glucosaminidase inhibitory activity, luteolin being the superior. The kinetics of alpha-glucosidase inhibition by these compounds showed that acetone extract inhibits the enzyme in competitive manner however, luteolin and isohydnocarpin showed mixed-type inhibition. This is the first report assigning hydnocarpin and isohydnocarpin free radical scavenging, alpha-glucosidase and N-acetyl-beta-D-glucosaminidase inhibitory properties and luteolin as N-acetyl-beta-D-glucosaminidase inhibitor. This study suggests that presence of amphiphilic antioxidant molecules along with enzyme inhibitory activities in the acetone extract of H. wightiana seed hulls may be responsible for the antidiabetic properties as advocated in traditional medicine.