title: DNA damage induced by radiation of different linear energy transfer: initial fragmentation.
abstract: OBJECTIVE
  To investigate DNA fragmentation as a function of linear energy transfer (LET) after exposure to accelerated ions in the LET range 40-225 keV/microm.
  
  
  METHODS
  Fragmentation patterns of double-stranded DNA in the range 5 kilobasepairs (kbp) to 5.7 megabasepairs (Mbp) were analysed after irradiation of low-passage GM 5758 normal human fibroblast cells with 60Co-photons, helium ions at 40 keV/microm and high-LET nitrogen ions between 80 and 225 keV/microm. Two separate pulsed-field gel electrophoresis protocols were used, optimized for separation of 1-6 Mbp and 5 kbp to 1.5 Mbp fragments.
  
  
  RESULTS
  An increased probability of formation of short and medium-sized DNA fragments was revealed following high-LET irradiation. The DNA double-strand break (dsb) induction yields were, respectively, 5.8 and 6.9-8.8 x 10(-9) dsb bp(-1) Gy(-1) for 60Co-photons and ions. The ion yields were some 80-110% higher than those calculated according to a conventional approach, disregarding the fragment distributions. For photons, the yield was 13% higher. The corresponding relative biological effectiveness (RBE) of dsb induction was in the range 1.2-1.5.
  
  
  CONCLUSIONS
  A significant non-random contribution to the number of dsb after irradiation with high-LET was confirmed by detailed fragment analysis using pulsed-field gel electrophoresis. The LET had a strong influence on the initial DNA fragment distribution, and hence also on the induction yields measured. However, when the LET was increased to the highest values studied for nitrogen ions, the yield decreased slightly.
authors.affiliation: Division of Biomedical Radiation Sciences, Rudbeck Laboratory, Uppsala University, Sweden.
authors.forename: E
authors.initials: E
authors.lastname: Höglund
authors.forename: E
authors.initials: E
authors.lastname: Blomquist
authors.forename: J
authors.initials: J
authors.lastname: Carlsson
authors.forename: B
authors.initials: B
authors.lastname: Stenerlöw
mesh_terms: D002478:Cells, Cultured; D004247:DNA / Q000528:radiation effects*; D004249:DNA Damage; D053938:DNA Fragmentation; D006801:Humans; D018499:Linear Energy Transfer; D012062:Relative Biological Effectiveness
chemical_list: D004247:DNA