Effect of temperature during irradiation on the level of micronuclei in human peripheral blood lymphocytes exposed to X-rays and neutrons.

It has been reported that the level of cytogenetic damage in human peripheral blood lymphocytes (PBL) is higher following irradiation at 37 degrees C than at 0-4 degrees C. The mechanisms of this cytogenetic temperature effect are not fully known. The aim of our study was to check whether the effect was related to the indirect or direct action of radiation. PBL were kept at 37 degrees C and 0 degree C for 20 min and exposed to 2 Gy of X-rays. In some experiments PBL were isolated and 0.5 M dimethyl sulfoxide (DMSO) was added for 5 min before exposure. PBL were also irradiated at 37 degrees C and 0 degree C with 1 Gy of 6 MeV neutrons. Micronuclei were scored as the endpoint. Following exposure to X-rays the level of initial DNA damage was also measured by the alkaline and neutral comet assay. The frequency of micronuclei in cells exposed at 37 degrees C to X-rays or neutrons was higher than that after exposure at 0 degree C. No effect of temperature was seen when PBL were exposed to X-rays in the presence of DMSO. No effect of temperature was observed on the level of DNA damage measured with the alkaline or neutral comet assay. The results of experiments with DMSO indicate that the temperature effect is due to the indirect action of radiation, i.e., via reactive oxygen species. However, this is not supported by the results with neutrons and the comet assay. Possible reasons for the discrepancies are discussed.