Background: Ionizing radiation is one of the environmental stresses which can be originated from the ground (radon at home) or from the space (cosmic radiation, long distance air travelling). The radiation-induced cellular effects (sister-chromatid exchanges, chromosome aberrations, apoptosis, micronucleation, transformation, mutations and changes of gene expression) can cause cell death or can be carried through generations causing cancer. The adaptation of the cells can be triggered by a low dose of radiation, which defend the cell from a higher dose. It takes some time and its mechanism is not known yet. Cells can be damaged not only by direct-hit but also the non-targeted bystander effect.

Purpose: Our main objective was to study radioadaptive response in mammalian cells induced by high-LET (neutron, alpha-particles)low dose irradiation. We examined the role of antioxidant system in the radiosensitivity and radioadaptation of cells. We measured the newly synthetized proteins, heat shock proteins (HSPs)which can have a role in the adapting response.

Methods: We exposed mammalian cells to neutron (in biological channel of AERI research reactor) and alpha-particles (source: ²¹⁰Po) and determined the number of irradiation induced mutants on HPRT-gene. The cells were exposed to 0.5-2-10 mGy adapting dose and after 3, 5, 24 and 48 hours (adaptation times) to 2 Gy gamma challenge dose respectively. The repair mechanism was examined by the Comet-assay. Antioxidant enzimes as superoxide-dismutase (SOD), glutathione reductase (GR) and glutathione-peroxidase (GPx) were measured at different timepoints respectively. Heat shock protein expression was determined with SDS-PAGE electrophoresis.

Results: Our results indicated that the mutation frequency (MF) of cells exposed to an adapting dose prior to a higher challenge dose were 58-65 % lower than MF of cells irradiated just with 2 Gy. The maximum adaptation were achieved after 5 hours adaptation time. We observed that the non-irradiated cells have shown a higher MF than the control groups if they were grown in medium from irradiated cells. Antioxidant activity decreased when the challenge dose was applied after 1 hour and increased after when was applied after 3 or 5 hours. Radiation caused a decrease in normal protein synthesis and expression of some newly synthetized proteins with molecular weight between 18 and 109 kDa.