Induction and processing of oxidative clustered DNA lesions in 56Fe-Ion-irradiated human monocytes

Space and cosmic radiation is characterized by energetic heavy ions of high linear energy transfer (LET). Although both low- and high-LET radiations can create oxidative clustered DNA lesions and double-strand breaks (DSBs), the local complexity of oxidative clustered DNA lesions tends to increase with increasing LET. We irradiated 28SC human monocytes with doses from 0-10 Gy of Fe-56 ions (1.046 GeV/nucleon, LET = 148 keV/mu m) and determined the induction and processing of prompt DSBs and oxidative clustered DNA lesions using pulsed-field gel electrophoresis (PFGE) and Number Average Length Analysis (NALA). The Fe-56 ions produced decreased yields of DSBs (10.9 DSB Gy(-1) Gbp(-1)) and clusters (1 DSB: similar to 0.8 Fpg clusters: similar to 0.7 Endo III clusters: similar to 0.5 Endo IV clusters) compared to previous results with Cs-137 gamma rays. The difference in the relative biological effectiveness (RBE) of the measured and predicted DSB yields may be due to the formation of spatially correlated DSBs (regionally multiply damaged sites) which result in small DNA fragments that are difficult to detect with the PFGE assay. The processing data suggest enhanced difficulty compared with gamma rays in the processing of DSBs but not clusters. At the same time, apoptosis is increased compared to that seen with gamma rays. The enhanced levels of apoptosis observed after exposure to Fe-56 ions may be due to the elimination of cells carrying high levels of persistent DNA clusters that are removed only by cell death and/or splitting during DNA replication. (c) 2007 by Radiation Research Society.