Levels and fluxes in enzymatic antioxidants following gamma irradiation are inadequate to confer radiation resistance in Drosophila melanogaster

Abstract

Ionizing radiation (IR) causes biological effects either by directly damaging the molecules or by generating free radicals. Antioxidant mechanisms are believed to be involved in neutralising free radicals. Levels of antioxidants therefore assume significance in determining the extent of radiation damage. The fruit fly Drosophila melanogaster (D. melanogaster) exhibits remarkable IR tolerance compared to mammals. Present study addresses the questions (1) Whether levels of antioxidants are high in radio-tolerant fruit fly D. melanogaster compared to mammals? (2) Does the antioxidant activity enhance adequately enough post-irradiation? We analysed enzymatic antioxidant profiles and their fluxes prior to and 60min post-irradiation (50Gy). Enzymatic antioxidants were analysed in all the developmental stages of D. melanogaster as the fruit fly shows dramatic changes in radiation resistance during development. Activity of superoxide dismutase (SOD) in Drosophila (pre-irradiation) was comparable to that of mammals. Catalase activity was lower than mammals while glutathione peroxidise (DmGPx) activity was significantly higher. Following irradiation SOD showed changes ranging from 1.40 to 1.62 folds only in larval stages. Catalase activity showed positive change of 1.25 folds only in adults. Activity of DmGPx was largely unaffected. Early pupae showed increased (3.67 fold) glutathione S-transferase activity post-irradiation. Non-enzymatic antioxidants such as total antioxidant capacity showed significant whereas reduced glutathione showed insignificant flux. In conclusion, the levels of enzymatic antioxidants in Drosophila compared to IR sensitive mammals and post-irradiation fluxes in antioxidant enzyme levels appear inadequate to explicate the dramatic radiation resistance observed in Drosophila. The observations are in agreement with the recent findings refuting the role of enzymatic antioxidants in radiation resistance.