Atomic Force Microscopy Observation And Mechanism Investigation Of DNA Double Strand Breaks Induced By Heavy Ions

Deoxyribonucleic acid (DNA) is an important biomacromolecule. It is the carrier of biological information and the critical target for radiobiological effects. Numerous lesions that include sugar alteration, base damage, and single- and double-strand breaks together with DNA-DNA crosslinks have been identified in irradiated DNA. DNA double strand breaks (DSBs) are considered as the most important initial damage of all biological effects induced by ionizing radiation.In this experiment, DNA double strand breaks induced by heavy ions in the early period were investigated with atomic force microscopy (AFM). Because heavy ion has the characters of high-LET value and sharp Bragg peak for dose distribution. Compared with low-LET radiation, heavy ion radiation has a different structure of ionizing track through a matter. Its complex ionizing tracks lead to multiple ionization events within nanometer regions of the target, resulting in complex damage. Through studying the biological effects of heavy ion radiation, the abundant data can be offered for cancer therapy by heavy ion radiation method and the dangerous assessment of space or nuclear radiation, etc.Choosing helium nucleus (a particle, LET=101keV/ m) produced by a 241Am radioactive source, 7Li (LET=124keV/ m) and 12C (LET= 242keV/ m) heavy ions with different LET values generated by HI-13 tandem accelerator respectively, the purified plasmid DNA samples in aqueous solution were irradiated at different doses. AFM was used for nanometer-level-structure analysis of DNA damage induced by a particle and these two kinds of heavy ions. Measurement of the fragment lengths was accomplished with the use of Scion Image analyzed software, which allows a curved fragment to bemeasured in a stepwise manner at nanometer level resolution, and the change laws of three forms of DNA, supercoil, open circular and linear form as the dose increased were obtained. Distributed function of DNA fragment length was also obtained, and fitted with Tsallis entropy statistical theory. Results show that high-LET heavy ion radiation more effectively induces DNA DSBs in comparison with low-LET radiation, and produces DSBs that are distributed more locally and more densely. In addition, the DNA DSBs induced by heavy ions were also analyzed by gel electrophoresis technology, and compared with AFM results. The results indicate that AFM has become a useful tool for the analysis of the structural and functional change of DNA induced by radiation. Compared with gel electrophoresis technology, AFM can distinguish various kinds of forms of the DNA and realize the measurement of DNA short fragments induced by radiation.