6th Asia‐Pacific Symposium on Radiochemistry September 17 ~ 22, 2017 • ICC Jeju • Jeju Island, Korea ROLE OF LOW ENERGY ELECTRONS AND SURROUNDINGS ON DNA DAMAGE IN
RADIOBIOLOGY
Yeunsoo Park1, Hyung Ah Noh2, Hyuck Cho3
1
Plasma Technology Research Center, National Fusion Research Institute: 37 Dongjangsan-ro, Gunsan, Jeollabuk-do,
Republic of Korea, 54004, [email protected]
2
Department of Physics, Chungnam National University: 99 Daehak-ro, Yuseong-gu, Daejeon, Republic of Korea,
34134, [email protected]
3
Department of Physics, Chungnam National University: 99 Daehak-ro, Yuseong-gu, Daejeon, Republic of Korea,
34134, [email protected]
Low energy electrons (LEEs, below 10 eV) can indirectly cause DNA damages such as single-strand break (SSB),
double-strand break (DSB), base lesion, and cross-links through dissociative electron attachment (DEA) process. In this
study, we have investigated the combined effects of LEE and surrounding components (metal ions and cisplatin) on DNA
damage. We compared the yield of DNA damage with pure DNA model molecule and DNA-surrounding complexes after
LEE irradiation. In the majority cases, the damages of complex molecules were increased than that of pure DNA molecule
via elevated DEA and Fenton reaction. Interestingly, in some cases of DNA-Cu ion complex, DNA damage was similar to
that of LEE irradiation only on pure DNA. This might be related to the structural stabilization via intra- and intercrosslinks between Cu ion and guanines.
I. Introduction and Experiments
High energy ionizing radiation such as gamma- and X-rays can generate biological damage via physical, chemical and
biological reactions [1]. It can be occurred both direct ionization process and indirect reaction via the secondary specie.
Among all secondary species, LEEs of having energies not enough to ionize DNA molecules can react with DNA and their
subunits and lead to various DNA damages indirectly via DEA process: AB + e- → AB*- → A- + B [2]. It is well established
LEE-induced DNA damage during las two decades. To fully understand this kind of damage, it need to consider the effect
of surroundings in the vicinity of DNA such as water, metal ion and some proteins [3]. In this study, we have tried to find
out the combined effect of LEE irradiation and surrounding components and clarify the exact mechanisms on DNA damage.
I. A. Experimental setup
In brief, the experimental procedure consists of three steps, DNA film preparation, LEE irradiation and damage
analysis. The dried DNA films with plasmid DNA pBR322, oligonucleotide TGGT, metal ions and cisplatin were prepared
using home-made lyophilization apparatus. The prepared DNA films were irradiated by low energy electrons (below 10
eV) under ultra-high vacuum condition (~ 10-8 torr). The recovered DNA samples after LEE irradiation were analyzed with
high performance liquid chromatograph (HPLC) and gel-electrophoresis. DNA damage for all samples was quantified and
compared to find out the exact damaging mechanism.
I. B. Experimental results
DNA damage have increased through the combined effect of LEE irradiation and surrounding molecules’ action than
their single effect. LEE below 20 eV caused the untangled supercoiling structure in the plasmid DNA case and strand break
or base release in the oligomer case. The single effect of metal ions and cisplatin also occurred DNA strand breaks but the
yields were very tiny. However, the combination effect of LEE irradiation and surrounding action made considerably big
DNA damage than single effect only. Interestingly, DNA-Cu ion complex in specific concentration near 9 mM showed
protection-like phenomenon against to our expectation. This result might be related to structural stabilization via Cu ion
crosslinks neighboring Guanines on the same strand or opposite strands. The basic mechanisms of DNA damage by LEE
1
6th Asia‐Pacific Symposium on Radiochemistry September 17 ~ 22, 2017 • ICC Jeju • Jeju Island, Korea irradiation and surrounding action were regarded as DEA process and Fenton reaction. We expect these findings can use
and develop a novel cancer therapy and radioprotection agent.
Fig.1. Cu ion and Guanine interactions (left) and DNA damage by Cu ion and LEE irradiation (right).
II. CONCLUSIONS
We have investigated the roles of low energy electron and surroundings on DNA damage through the yield comparisons.
The combination effect of LEE irradiation and surrounding actions caused considerable increasing on DNA damage than
the single effect of LEE irradiation or surroundings only. Surprisingly, DNA damage in case of DNA-Cu complex with the
specific Cu ion concentration showed the different trend, protection-like effect via structure stabilization. It needs further
experimental and theoretical investigations to fully understand these phenomena
ACKNOWLEDGMENTS
This work was supported by R&D Program of ‘Plasma Convergence & Fundamental Research’ through the National
Fusion Research Institute of Korea (NFRI) funded by the Government funds and research fund of Chungnam National
University
REFERENCES
1.
2.
3.
B. Boudaiffa et al, “Resonant Formation of DNA Strand Breaks by Low-Energy (3 to 20 eV) Electrons”, Science 287,
1658 (2002).
L. Sanche, “Low Energy Electron-driven damage in biomolecules”, Eur. Phys. J. D 35, 367 (2005).
Y. Park, H. A. Noh and H. Cho, “ Effect of Low-Energy Electron Irradiation on DNA Damage by Fe3+ ion”, Radiat.
Res. 177, 775 (2012).
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