The Antioxidant Flavonoids, Orientin and Vicenin Enhance Repair of Radiation-Induced Damage

Orientin (Ot) and vicenin (Vc), two water soluble flavonoids isolated from the Indian Holy Basil, are potent radioprotectants, but the mechanisms of protection are not fully understood. In the present study, we investigated the effects of these flavonoids as antioxidants in chemical systems and plasmid DNA and radioprotectants in bacterial and mammalian cells. The radical scavenging activities of Ot and Vc were assessed in two chemical systems, dipehnylpicrylhydrazyl (DPPH) and 2,2´-azino-bis(3-thylbenz-thiazoline-6-sulfonic acid) (ABTS) by estimating absorbance at 517 and 734 nm, respectively. Protection by the flavonoids against H2O2 (30 mM) damage to plasmid pGEM-7Zf was assessed by DNA electrophoresis. Effect of flavonoid pre-treatment on survival of irradiated (30-150 Gy γ-rays) repair proficient (AB1157) and repair deficient (MD2130) E.coli cells was assayed. Furthermore, induction and repair of DNA damage to 4 Gy irradiated mouse splenocytes was analyzed using the comet assay. Ot and Vc significantly scavenged DPPH and ABTS. Both flavonoids protected plasmid pGEM-7Zf in the nicked circular form following H2O2 treatment. Pretreatment with 200 μM of either flavonoid significantly increased clonogenic survival of repair proficient cells at all radiation (RT) doses; in repair deficient strain, protection was significant at the lower RT doses (30 and 50 Gy, p<0.01). Ot and Vc significantly reduced 4 Gy-induced DNA damage and allowed for faster repair of ex-vivo irradiated mouse splenocytes.