Kinetics of double strand breaks of DNA in tritiated water evaluated using single molecule observation method

Damages of DNA in tritiated water

Tritium is a radioisotope of hydrogen emitting low energy β-rays in disintegration to ³He. DNA molecules are damaged mainly by β-ray irradiation, and additional damages can be induced by break of chemical bond by nuclear transmutation to inert ³He. Deep knowledges of the mechanisms underlying DNA damages lead to better understanding of biological effects of tritium. This chapter reviews recent experimental and computer simulation activities on quantitative evaluation of damage rates by β-ray irradiation and nuclear transmutation. The rate of DNA double-strand breaks in tritiated water has been examined using a single molecule observation method. The effects of β-ray irradiation were not noticeable at the level of tritium concentration of ∼kBq/cm³, while the irradiation effects were clear at tritium concentrations of ∼MBq/cm³. The factors affecting on the DSB rate are discussed. A new image processing method for the automatic measurement of DNA length using OpenCV and deep learning is also introduced. The effects of tritium transmutation on hydrogen bonds acting between the two main strands of DNA have been examined using molecular dynamics simulations. The study showed that the collapsing of DNA structure by the transmutation can be quantitatively evaluated using the root mean square deviation of atomic positions.

Quantitative evaluation of DNA double-strand breaks (DSBs) through single-molecule observation

By adapting the method of single molecular observation for individual DNAs, it will be shown that reliable analysis of double-strand breaks, DSBs, becomes possible for various kinds of damage sources. Single DNA above the size of several-tens kilo base-pairs exhibits the length scale above several μm, indicating that their whole conformation is visible with fluorescence microscopy by adding suitable fluoresce dye to the solution. Various examples of the quantitative evaluation on DSBs are described, together with the evaluation of the protective effects of anti-oxidants.