Activities of antioxidants, α-Glucosidase inhibitors and aldose reductase inhibitors of the aqueous extracts of four Flemingia species in Taiwan

The aim of this study was to examine the possible antioxidant and antidiabetic effects of the aqueous extracts of four Flemingia species in Taiwan. A number of methods were employed for this investigation, including ABTS radical monocation scavenging, FRAP (ferric reducing antioxidant power) method, DPPH (1, 1-diphenyl-2-picrylhydrazyl) radical scavenging, total polyphenol content, total flavonoid content, total flavonol content, and inhibition of α-glucosidase and aldose reductase methods. The results showed that the aqueous extract of Flemingia macrophylla (WFM) had the strongest antioxidant activity in comparison with the other extracts. We also found that WFM had higher contents of polyphenol compounds, flavonoids and flavonols than the other extracts. The correlation coefficient (R) values of TEAC (trolox equivalent antioxidant capacity) and FRAP showed high correlations (R=0.83). The R values of TEAC and total polyphenol content showed a higher correlation (R=0.66). The R values of TEAC and total flavonoid content for the aqueous extracts was 0.94. The antidiabetic activities of the four Flemingia species were studied in vitro using α-glucosidase and aldose reductase (AR) inhibitory methods. WFM had the highest inhibitory activities on α-glucosidase and aldose reductase, with IC50 (concentration with 50% inhibition) of 153.92 ± 0.20 μg/mL and 79.36 ± 3.20 μg/mL respectively. The positive control (genistein) had higher inhibitory activities on α-glucosidase and aldose reductase (IC50 16.65 ± 0.92 μg/mL and 45.62 ± 2.16 μg/ mL) respectively. In LC-MS-MS analyses, the chromatograms of WFM with the highest antioxidant and antidiabetic activity were established. Genistein might be an important bioactive compound in WFM extract. This experiment suggests that WFM might serve as a good resource for future development of antioxidant and antidiabetic drugs.