Induction of DNA double-strand breaks by H-1 and He-4 ions in primary human skin fibroblasts in the LET range of 8 to 124 keV/mu m

Yields of DNA double-strand breaks were determined in primary human skin fi broblasts exposed to H-1 and He-4 ions at various linear energy transfers ( LETs) and to 15 MeV electrons as the reference radiation. The values obtain ed for the relative biological effectiveness (RBE) were 2.03, 1.45 and 1.36 for H-1 ions at LETs of 35, 23 and 7.9 keV/mu m, respectively, and 1.2, 1. 18, 1.38 and 1.31 for He-4 ions at LETs of 124, 76, 35 and 27 keV/mu m, res pectively. The data were obtained using pulsed-field gel electrophoresis of DNA released from cells using the chromosomes of the yeast Saccharomyces c es cerevisiae as length markers and fitting the experimental mass distribut ions of fragmented DNA to those obtained by computer simulation of the rand om breakage of human chromosomes. The RBE values for induction of DSBs in m ammalian cells cannot be fitted to a common RBE-LET relationship for electr ons and H-1, He-4 and light ions. Comparison of the RBEs for mammalian cell s with the corresponding RBEs obtained for yeast cells shows similar RBEs o f electrons for yeast and mammalian cells; however, for He-4 and light ions in the LET range of 100 to 1000 keV/mu m, the RBEs for yeast are significa ntly higher compared with mammalian cells. These characteristics of the RBE -LET relationships for yeast and mammalian cells are attributed to the frac tion of small DNA fragments induced by particles when traversing the higher -order chromatin structures which are different to some extent in these two cell types. (C) 1999 by Radiation Research Society.