量研学術機関リポジトリ「QST-Repository」は、国立研究開発法人 量子科学技術研究開発機構に所属する職員等が生み出した学術成果（学会誌発表論文、学会発表、研究開発報告書、特許等）を集積しインターネット上で広く公開するサービスです。 Welcome to QST-Repository where we accumulates and discloses the academic research results(Journal Publications, Conference presentation, Research and Development Report, Patent, etc.) of the members of National Institutes for Quantum Science and Technology.
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Radioprotectors with few side effects are useful for carbon ion therapy, which directly induces clustering damage in DNA. With the aim of finding the most effective radioprotector, the authors have investigated the effects of selected amino acids which might have chemical DNA-repair functions against therapeutic carbon ions. In the present study, we employed five amino acids: tryptophan (Trp), cysteine (Cys), methionine (Met), valine (Val), and alanine (Ala). Samples of supercoiled pBR322 plasmid DNA with a 17 milli molar (mM) amino acid were prepared in TE buffer (10 mM Tris, 1 mM ethylenediaminetetraacetic acid, pH 7.5). Phosphate-buffered saline (PBS) was also used in assays of the 0.17 mM amino acid. The samples were irradiated with carbon ion beams (290 MeV/u) on 6 cm spread-out Bragg peak at the National Institute of Radiological Sciences-Heavy Ion Medial Accelerator in Chiba, Japan. Breaks in the DNA were detected as changes in the plasmids and quantified by subsequent electrophoresis on agarose gels. DNA damage yields and protection factors for each amino acid were calculated as ratios relative to reagent-free controls. Trp and Cys showed radioprotective effects against plasmid DNA damage induced by a carbon ion beams, both in PBS and TE buffer, comparable to those of Met. The double-strand break (DSB) yields and protective effects of Trp were comparable to those of Cys. The yields of both single-strand breaks and DSBs correlated with the scavenging capacity of hydroxyl radicals (rate constant for scavenging hydroxyl radicals multiplied by the amino acid concentration) in bulk solution. These data indicated that the radioprotective effects of amino acids against plasmid DNA damage induced by carbon ion irradiation could be mainly explained by the scavenging capacity of hydroxyl radicals. These findings imply that some amino acids such as Trp, Cys and Met have good potentials as radioprotectors preventing DNA damages in normal tissues in carbon ion therapy.
Protective effects of amino acids on plasmid DNA damage induced by therapeutic carbon Ions
