Xanthine oxidase-inhibitory activity and antioxidant properties of the methanol extract and flavonoids of Artemisia Asiatica

The MeOH extract of the aerial parts of Artemisia asiatica significantly inhibited the xanthine oxidase (XO) induced uric acid production. Flavonoids were isolated from the active extract and identified as eupatilin (1), hispidulin (2), jaceosidin (3), cirsilineol (4), 5,7,4', 5'-tetrahydroxy-6,3'-dimethoxyflavone (5), 6-methoxytricin (6) and chrysosplenetin (7). With the exception of cirsilineol and chrysoplenetin, all these flavonoids exerted marked XO-inhibitory effects, with IC50 values in the range 1.33-6.13 mu M. The degree of XO inhibition by 1-3, 5 and 6 suggests the importance of the free OH group on C-7. Evaluation of the isolated compounds 1-7 for their free radical scavenging activity in DPPH tests, revealed the substantial antioxidant activity of 5,7,4', 5'-tetrahydroxy-6,3'-dimethoxy-flavone (5), which contains ortho-dihydroxy and 5-hydroxy groups. In summary, the flavonoid-containing MeOH extract of A. asiatica exhibits dual action, inhibiting XO (1-3, 5, 6) and resulting in a reduced generation of reactive oxygen species, and additionally scavenging free radicals (5).