Side-by-Side Comparison of DNA Damage Induced by Low Energy Electrons and High Energy Photons with Solid TpTpT Trinucleotide

摘要

The genotoxic effects of high energy ionizing radiation have been largely attributed to the ionization of H2O leading to hydroxyl radicals (OH) and the ionization of DNA leading mostly to damage through base radical cations. However, the contribution of low energy electrons (LEEs; ≤ 10 eV), which involves sub-ionization events, has been considered to be less important than that of hydroxyl radicals and base radical cations. Here, we compare the ability of LEEs and high energy X-ray photons to induce DNA damage using dried thin films of TpTpT trinucleotide as a simple and representative model for DNA damage. The main radiation-induced damage of TpTpT as measured by HPLC-UV and LC-MS/MS analyses included thymine release (-Thy), strand breaks (pT, Tp, pTpT, TpTp and TpT), and the formation of base modifications (5,6-dihydrothymine (5,6-dhT), 5-hydroxymethyluracil (5-hmU) and 5-formyluracil (5-fU)). The global profile of products was very similar for both types of radiation indicating converging pathways of formation. The percent damage of thymine release, fragmentation and base modification was 20, 19 and 61 for high energy X-rays, respectively, compared to 35, 13 and 51 for LEEs (10 eV). Base release was significantly lower for X-rays. In both cases, phosphodiester bond cleavage gave mononucleotides (pT and Tp) and dinucleotides (pTpT and TpTp) containing a terminal phosphate as the major fragments. For base modifications, the ratio of reductive (5,6-dhT) to oxidative products (5-hmU plus 5-fU) was 0.9 for high energy X-rays compared to 1.7 for LEEs. These results indicate that LEEs give a similar profile of products compared to ionizing radiation.