title: Quantitative assessment of the contribution of clustered damage to DNA double-strand breaks induced by 60Co gamma rays and fission neutrons.
abstract: The induction of DNA strand breaks by fission neutrons was studied in aqueous plasmid (pBR322) DNA under aerobic conditions for a wide range of hydroxyl radical (*OH) scavenger concentrations and was compared to the induction of strand breaks by 6OCo gamma rays. Strand breaks were measured using agarose gel electrophoresis coupled with sensitive 32P-based phosphor imaging. Yields are reported for DNA single-strand breaks (SSBs) and double-strand breaks formed linearly with dose (alphaDSBs). The fraction of alphaDSBs that were dependent on the multiply damaged site (MDS) or clustered damage mechanism was also calculated using a model. G values for SSBs and alphaDSBs declined with increasing *OH scavenging capacity. However, with increasing *OH scavenging capacities, the decrease in yields of strand breaks for fission neutrons was not as pronounced as for gamma rays. The percentage of alphaDSBs for gamma rays was dependent on *OH scavenging capacity, appearing negligible at low scavenging capacities but increasing at higher scavenging capacities. In contrast, fission neutrons induced high percentages of alphaDSBs that were approximately independent of *OH scavenging capacity. The levels of alphaDSBs formed by the MDS mechanism after exposure to fission neutrons are consistent with the expected distinctive features of high-LET energy deposition events and track structure. The results also confirm observations made by others that even for low-LET radiation, the MDS mechanism contributes significantly to DNA damage at cell-like scavenging conditions.
authors: Radiation Effects Branch, Naval Research Laboratory, Washington, DC 20375, USA.
authors: W K
authors: WK
authors: Pogozelski
authors: M A
authors: MA
authors: Xapsos
authors: W F
authors: WF
authors: Blakely
mesh_terms: D003037:Cobalt Radioisotopes; D004247:DNA / Q000528:radiation effects*; D004249:DNA Damage; D004307:Dose-Response Relationship, Radiation; D016166:Free Radical Scavengers / Q000494:pharmacology; D005720:Gamma Rays; D018499:Linear Energy Transfer; D009502:Neutrons
chemical_list: D003037:Cobalt Radioisotopes; D016166:Free Radical Scavengers; D004247:DNA