title: DNA strand break dependence on Tris and arginine scavenger concentrations under ultra-soft X-ray irradiation: the contribution of secondary arginine radicals.
abstract: In this study, we used a bench-top cold-cathode ultra-soft X-ray (USX) generator to expose aqueous DNA plasmid solutions to low-LET radiation under various scavenging conditions. Single- and double-strand breaks were assessed using classic gel electrophoresis quantification of linear, circular and supercoiled plasmid DNA topologies. With their very low penetration range in water, USX can only interact with matter up to short distances, of the order of 50 μm. We validated a stirring procedure which makes it possible to expose 100 µL of aqueous samples (2 mm thick). The scavenging of OH radicals by Tris buffer was studied at ambient temperature under aerobic conditions and compared to data gathered in the literature. A very good agreement was found with the rare data dealing with DNA plasmid exposed to Al Kα photons at low temperature (T ≤ 277 K), which therefore validated the experimental procedure. The yields for DNA single-strand breaks determined during this study enabled the ratio of indirect to direct effects to be determined at 96.2%, in good agreement with the value of 97.7% stemming from a study based on γ-ray irradiation of frozen solutions of plasmid DNA. Then, arginine was used both to create a "biological-like" chemical environment around the DNA plasmids and as an OH radical scavenger, in vitro. Although arginine has a greater scavenging (protecting) power than Tris, surprisingly, it led to higher rates of strand breakage. Based on the specific binding modes of arginine to DNA, we suggest that the side effects observed are due to the presence of arginine near to, but also inside, the DNA double helix.
authors.affiliation: UMR CNRS 6249 Chrono-Environnement, Université de Bourgogne Franche-Comté, 16 route de Gray, 25030, Besançon Cedex, France.|Laboratoire de Physique des Rayonnements et Applications, Université de Jijel, B.P. 98, 18000, Ouled Aissa, Jijel, Algeria.
authors.forename: Mounir
authors.initials: M
authors.lastname: Souici
authors.affiliation: UMR CNRS 6249 Chrono-Environnement, Université de Bourgogne Franche-Comté, 16 route de Gray, 25030, Besançon Cedex, France.
authors.forename: Talat Tariq
authors.initials: TT
authors.lastname: Khalil
authors.affiliation: UMR CNRS 6249 Chrono-Environnement, Université de Bourgogne Franche-Comté, 16 route de Gray, 25030, Besançon Cedex, France.
authors.forename: Omar
authors.initials: O
authors.lastname: Boulanouar
authors.affiliation: Laboratoire de Physique des Rayonnements et Applications, Université de Jijel, B.P. 98, 18000, Ouled Aissa, Jijel, Algeria.
authors.forename: Abdelfettah
authors.initials: A
authors.lastname: Belafrites
authors.affiliation: UMR CNRS 6249 Chrono-Environnement, Université de Bourgogne Franche-Comté, 16 route de Gray, 25030, Besançon Cedex, France.
authors.forename: Christophe
authors.initials: C
authors.lastname: Mavon
authors.affiliation: UMR CNRS 6249 Chrono-Environnement, Université de Bourgogne Franche-Comté, 16 route de Gray, 25030, Besançon Cedex, France. michel.fromm@univ-fcomte.fr.
authors.forename: Michel
authors.initials: M
authors.lastname: Fromm
mesh_terms: D001120:Arginine / Q000378:metabolism*; D053960:DNA Breaks / Q000187:drug effects* / Q000528:radiation effects*; D004305:Dose-Response Relationship, Drug; D016166:Free Radical Scavengers / Q000494:pharmacology*; D005609:Free Radicals / Q000378:metabolism; D010957:Plasmids / Q000235:genetics; D014325:Tromethamine / Q000494:pharmacology*; D014965:X-Rays / Q000009:adverse effects
chemical_list: D016166:Free Radical Scavengers; D005609:Free Radicals; D014325:Tromethamine; D001120:Arginine
keywords: Arginine; DNA damage; Plasmid DNA; Ultra-soft X-rays