Antioxidant capacity and radioprotective properties of the flavonoids galangin and kaempferide isolated from Alpinia galanga L. (Zingiberaceae) against radiation induced cellular DNA damage

Alpinia galanga L. belonging to the family Zingiberaceae is widely grown in the state of Kerala, India. They are effective antioxidant and free radical scavenger under both in vitro and in vivo condition. The efficacy of the isolated flavonoids in conferring protection from radiation induced damages to genomic DNA was studied. The bioflavonoids, galangin and kaempferide were isolated from the AE fractions Alpinia galanga. The isolated flavanoids - galangin and kaempferide, and the crude extracts (AE and EE) were assayed for their various free radical scavenging activities like DPPH (1,1-diphenyl-2-picryl-hydrazyl), hydroxyl and superoxide radical scavenging activities. The in vitro DNA damage was monitored by assessing the radiation induced relaxation of supercoiled plasmid DNA (pBR 322). Damage to cellular DNA of human peripheral blood leukocytes induced by γ-radiation (4 Gy) was monitored by alkaline single cell gel electrophoresis or comet assay. The extracts and pure compounds scavenged hydroxyl radicals in a concentration dependent manner. The compounds demonstrated a concentration dependent scavenging capacity by neutralizing the superoxide radicals. A considerably lower concentration (400-1000 ppm) of the pure flavonoids showed good antioxidant capacity. The presence of 10 mM kaempferide helped in reducing the extent of DNA damage following 4 Gy gamma irradiation (P<0.001). Galangin (10 mM) also facilitated in reduction of comet parameters. The extracts of Alpinia galanga or the isolated bioflavonoids - galangin and kaempferide can protect DNA from radiation induced lesions resulting from radiation exposures under in vitro and ex vivo conditions.