Small doses of high-linear energy transfer radiation increase the radioresistance of Chinese hamster V79 cells to subsequent X irradiation.
Chinese hamster V79 cells show a complex X-ray survival response which is characterized by hypersensitivity followed by increased resistance as the dose increases to 1 Gy. This hypersensitivity can be eliminated by pretreating cells with X rays or hydrogen peroxide. Accordingly, the protective effect that results from the priming treatments could be considered analogous to the "adaptive response" induced by low-linear energy transfer (LET) radiation and some chemical agents in human lymphocytes. Indeed, no hyper-radiosensitive response after single treatments in V79 cells or adaptive response in human lymphocytes has been reported after exposure to high-LET radiation. To investigate this further, we measured the survival after X irradiation of V79-379A cells previously irradiated with small priming doses of high-LET radiation. After a 0.2-Gy priming dose of neutrons followed by a 1-Gy 250 kVp X-ray dose given 4 h later, survival was 1.08 +/- 0.04 compared to 0.73 +/- 0.03 when the doses were given concurrently. Increases in survival were also observed from 0.80 +/- 0.03 to 0.96 +/- 0.05 after a 0.2-Gy priming treatment with 250 kVp X rays and from 0.78 +/- 0.03 to 0.84 +/- 0.03 with a priming dose of Bragg-peak negative pi mesons. The results indicate that a protective effect, as measured by an increase in radioresistance, is induced by high-LET neutrons, as well as by Bragg-peak pi mesons and X rays, and that a threshold level of damage is required for adaptation to occur.
Marples
B
B
Medical Biophysics, British Columbia Cancer Research Centre, Vancouver, Canada.
Skov
K A
KA
D000222:Adaptation, Physiological; D000818:Animals; D002460:Cell Line; D002470:Cell Survival / Q000528:radiation effects; D006224:Cricetinae; D003412:Cricetulus; D004249:DNA Damage; D004307:Dose-Response Relationship, Radiation; D005214:Fast Neutrons; D006801:Humans; D018499:Linear Energy Transfer; D008651:Mesons; D011836:Radiation Tolerance / Q000502:physiology*; D011853:Radiobiology