In vitro antioxidant and antidiabetic activities of Rehmannia glutinosa tuberous root extracts

To analyse the antioxidant and antidiabetic activities of Rehmannia glutinosa tuberous roots, extracts with nine different solvents were investigated. Antioxidant activity was measured with two methods, 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging and reducing power. Each extract exhibited a dose-dependent free radical scavenging action against DPPH and a reducing power, but diverse antioxidant activities. To determine the antidiabetic activity, we measured the alpha-glucosidase inhibitory capacity of each extract. We found that 10 mu g/ml of 60% MeOH or 80% of MeOH extract inhibited more than 90% of alpha-glucosidase activity, and this inhibitory activity was not mediated by catalpol, a major iridoid constituent of R. glutinosa tuberous roots. Overall, the data suggested that the tuberous roots of R. glutinosa have potential as natural antioxidants and antidiabetics.