Cell killing and chromatid damage in primary human bronchial epithelial cells irradiated with accelerated Fe-56 ions

We examined cell killing and chromatid damage in primary human bronchial ep ithelial cells irradiated with high-energy Fe-56 ions. Cells were irradiate d with graded doses of Fe-56 ions (1 GeV/nucleon) accelerated with the Alte rnating Gradient Synchrotron at Brookhaven National Laboratory, The surviva l curves for cells plated 1 h after irradiation (immediate plating) showed little or no shoulder. However, the survival curves for cells plated 24 h a fter irradiation (delayed plating) had a small initial shoulder. The RBE fo r Fe-56 ions compared to Cs-137 gamma rays was 1.99 for immediate plating a nd 2.73 for delayed plating at the D-10. The repair ratio (delayed plating/ immediate plating) was 1.67 for Cs-137 y rays and 1.22 for Fe-56 ions. The dose-response curves for initially measured and residual chromatid fragmen ts detected by the Calyculin A-mediated premature chromosome condensation t echnique showed a linear response. The results indicated that the induction frequency for initially measured fragments was the same for Cs-137 gamma r ays and Fe-56 ions. On the other hand, similar to 85% of the fragments indu ced by Cs-137 y rays had rejoined after 24 h of postirradiation incubation; the corresponding amount for Fe-56 ions was 37%. Furthermore, the frequenc y of chromatid exchanges induced by gamma rays measured 24 h after irradiat ion was higher than that induced by Fe-56 ions. No difference in the amount of chromatid damage induced by the two types of radiations was detected wh en assayed 1 h after irradiation. The results suggest that high-energy Fe-5 6 ions induce a higher frequency of complex, unrepairable damage at both th e cellular and chromosomal levels than Cs-137 y rays in the target cells fo r radiation-induced lung cancers. (C) 2001 by Radiation Research Society.