Contribution of antioxidant enzymes to the adaptive response to ionizing radiation of human lymphoblasts

Purpose: To investigate whether the adaptive response to ionizing radiation triggered by a low-dose pre-exposure could be due to the activation of the antioxidant defence system. Materials and methods: Human lymphoblastoid AHH-1 cells were irradiated wit h a 0.02 Gy gamma-radiation and 6 h later were exposed to a 3 Gy challenge dose according to a protocol allowing mutagenic adaptation. Controls includ ed cells left unirradiated or exposed to a single dose (0.02 Gy or 3 Gy). T he activities of the main cellular antioxidant enzymes (AOE) - copper-zinc superoxide dismutase (SOD1), manganese superoxide dismutase (SOD2), catalas e (CAT), glutathione peroxidase (GPX), glutathione-S-transferase (GST), glu tathione reductase (GSR) and glucose 6-phosphate dehydrogenase (G6PD)- were evaluated at different times after treatment. The levels of SOD2 and CAT p roteins were also analysed using the immune Western blot method. Results: Compared with non-irradiated controls, the effect of 3 Gy alone wa s shown to increase GPX and CAT activities at 20 h after irradiation. Pre-e xposure of cells did not change these late alterations. Soon after irradiat ion the activities of SOD2, CST, GPX and CAT were slightly higher in adapte d than in nonadapted cells. Conclusion: The data suggest that the increased activities of some AOE obse rved soon after the challenge dose would result in a rapid scavenging of ra dicals and consequently less damage in adapted cells. Due to the moderate a lterations of these AGE, the activation of antioxidant defences would only partly contribute to the protective mechanism underlying the radioadaptatio n of AHH-1 lymphoblasts.