Yields of SSB and DSB induced in DNA by AlK ultrasoft X-rays and α-particles:: comparison of experimental and simulated yields

Purpose: To compare experimental yields of single strand breaks (SSB) and double strand breaks (DSB) induced in plasmid DNA in aqueous solution by alpha -particles and Al-K ultrasoft X-rays (USX) with the corresponding yields, generated via computer simulations, for a range of mean diffusion distances of the hydroxyl radical ((OH)-O-circle). Materials and methods: Aerobic, aqueous solutions of plasmid DNA were irradiated at 277K with Pu-238 alpha -particles or USX in the presence of 10(-4) to 0.33 mol dm(-3) Tris and the yields of SSB and DSB determined by gel electrophoresis. Computer simulations, using Monte Carlo track-structure codes for 1.3 keV electrons (CPA100) and 3.2 MeV alpha -particle track segments (PITS), were used to obtain yields of DNA SSB and DSB at different (OH)-O-circle scavenger conditions. Results: The experimental yield of SSB and DSB induced by AlK USX and SSB induced by alpha -particles and the dependences on the mean diffusion distance of the (OH)-O-circle are in reasonable agreement with the corresponding simulated yields and their corresponding dependences. However, for DSB induced by alpha -particles, a significant systematic difference exists between the simulated and experimental yields over the full (OH)-O-circle scavenging range, with the simulated yields being a factor of two to three greater than the experimental values. Conclusion: That the simulated yields of strand breaks are generally in reasonable agreement with those determined experimentally over a wide range of (OH)-O-circle scavenging capacities, increases confidence in the use of these simulations as a valuable source of quantitative, mechanistic information on DNA damage induced at very low radiation doses.