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

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.

Human lymphoblastoid AHH-1 cells were irradiated with 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 included cells left unirradiated or exposed to a single dose (0.02 Gy or 3 Gy). The activities of the main cellular antioxidant enzymes (AOE) - copper-zinc superoxide dismutase (SOD1), manganese superoxide dismutase (SOD2), catalase (CAT), glutathione peroxidase (GPX), glutathione-S-transferase (GST), glutathione reductase (GSR) and glucose 6-phosphate dehydrogenase (G6PD) - were evaluated at different times after treatment. The levels of SOD2 and CAT proteins were also analysed using the immuno Western blot method.

Compared with non-irradiated controls, the effect of 3 Gy alone was shown to increase GPX and CAT activities at 20 h after irradiation. Pre-exposure of cells did not change these late alterations. Soon after irradiation the activities of SOD2, GST, GPX and CAT were slightly higher in adapted than in non-adapted cells.

The data suggest that the increased activities of some AOE observed soon after the challenge dose would result in a rapid scavenging of radicals and consequently less damage in adapted cells. Due to the moderate alterations of these AOE, the activation of antioxidant defences would only partly contribute to the protective mechanism underlying the radioadaptation of AHH-1 lymphoblasts.