Antioxidant and Radioprotective Effects of Ocimum Flavonoids Orientin and Vicenin in Escherichia coli

摘要

Antioxidant effect of the Ocimum flavonoids, orientin and vicenin (25-500 μM), was evaluated by the kat-sod assay in Escherichia coli mutants (DSH56, superoxide dismutase-deficient and DSH19, catalase-deficient) treated with 50 mM menadione or H_2O_2 (1mM). Protection by orientin (200 μM) and vicenin (200 μM) against H_2O_2-induced DNA damage in DSH19 cells (β-galactosidase test) and against radiation lethality in wild-type (DSH7) and DSH19 cells exposed to 0-150 Gy gamma radiation was also studied. Menadione and H_2O_2 reduced the surviving fraction to 0.2 and 0.4 in DSH56 and DSH19 cells, respectively. Even 25 μM of either flavonoid significantly increased the surviving fraction, with maximum protection at 200 μM. H_2O_2 increased the β-galactosidase activity in a concentration-dependent manner, which was significantly (P < 0.050-0.001) reduced by orientin and vicenin (200 μM). Radiation produced a dose-dependent decrease in the surviving fraction of both DSH7 and DSH19 cells. Pretreatment with 200 μM orientin or vicenin significantly increased the survival (DRF: DSH7 = 2.2; DSH19 = 1.8). Both compounds were equally effective in reducing the cytotoxicity of radiation and the chemical oxidants. The cytoprotective action of these plant flavonoids could be ascribed to their free radical scavenging activity.