Stannous chloride mediates single strand breaks in plasmid DNA through reactive oxygen species formation

Stannous ion (Sn) has been employed in nuclear medicine and in food industr y. We described that Stannous Chloride (SnCl2) inactivation effect in Esche richia coli is mediated by a Fenton-like reaction. The effect of SnCl2 was studied through: (i) the alteration of plasmid topology in neutral and acid ic pH by gel electrophoresis; and (ii) the transformation efficiency of an wild type E. coli strain. Treatment of plasmid DNA pUC 9.1 with SnCl2, at p H 7.4, results in DNA single-strand breaks (SSB), in a dose-dependent manne r. Addition of sodium benzoate partly inhibited the DNA damage, while EDTA completely abolishes DNA-SSB. Furthermore, the ability of the plasmid to tr ansform E. coli was reduced. At pH 1.3, SnCl2 exerts a protective effect on plasmid against HCl depurination. Our results suggest the generation of RO S, such as (OH)-O-. by a Fenton-like reaction, close to the site of the les ions due to a possible complexation of stannous ion to DNA. (C) 1999 Elsevi er Science Ireland Ltd. All rights reserved.