Radioprotection of Cultured Cells by Preincubation in Medium Containing Deuterium Oxide

Summary

Pretreatment with deuterium oxide (D₂O) has been shown to protect mice against lethal effects of X-rays. In contrast, X-irradiation of cultured mammalian cells in D₂O-containing medium has previously been reported to result in increased cell killing. Therefore, the effects of preincubation in medium containing 20% D₂O on radiosensitivity were tested, using cells of a heat-sensitive cell-cycle mutant (21-Tb) of the murine mastocytoma P 815-X2. The mutant cells proliferate at 33°C and are arrested in G₁ phase in a state of reversible proliferative quiescence at 39·5°C. Prior to irradiation with single X-ray doses of 0–10 Gy, the cells were cultured in normal or D₂O-containing medium, either for 96h at 33°C (‘proliferating cells’), or for 72h at 33°C followed by 24h at 39·5°C (‘arrested cells’). After X-irradiation the cells were resuspended in normal medium, and cell survival was determined by the capacity of cells to form colonies in fibrin gels. Preincubation in medium containing 20% D₂O resulted in a radioprotective effect on both proliferating and arrested cells, particularly at the higher X-ray doses. This radioprotection was manifested as a decreased slope of the semilogarithmic survival curves, whereas pretreatment with D₂O had no significant effect on postirradiation repair as judged from D_q values. These results support the interpretation that the increase in postirradiation survival may be attributed to incorporation of deuterium into cellular metabolites during the period of preincubation.