Yields of SSB and DSB induced in DNA by Al-K ultrasoft X-rays and alpha-particles: comparison of experimental and simulated yields

Purpose: To compare experimental yields of single strand breaks (SSB) and d ouble strand breaks (DSB) induced in plasmid DNA in aqueous solution by alp ha -particles and Al-K ultrasoft X-rays (USX) with the corresponding yields , generated via computer simulations, for a range of mean diffusion distanc es of the hydroxyl radical ((OH)-O-circle). Materials and methods: Aerobic, aqueous solutions of plasmid DNA were irrad iated 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 el ectrophoresis. Computer simulations, using Monte Carlo track-structure code s 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 i nduced by alpha -particles and the dependences on the mean diffusion distan ce of the (OH)-O-circle are in reasonable agreement with the corresponding simulated yields and their corresponding dependences. However, for DSB indu ced by alpha -particles, a significant systematic difference exists between the simulated and experimental yields over the full (OH)-O-circle scavengi ng 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 rea sonable agreement with those determined experimentally over a wide range of (OH)-O-circle scavenging capacities, increases confidence in the use of th ese simulations as a valuable source of quantitative, mechanistic informati on on DNA damage induced at very low radiation doses.