REACTION OF CR(VI) WITH ASCORBATE AND HYDROGEN-PEROXIDE GENERATES HYDROXYL RADICALS AND CAUSES DNA-DAMAGE - ROLE OF A CR(IV)-MEDIATED FENTON-LIKE REACTION

Incubation of Cr(VI) with ascorbate generated Cr(V), Cr(IV) and ascorbate-derived carbon-centered alkyl radicals, as well as formyl radicals. H2O2 caused generation of hydroxyl radicals ((OH)-O-.) and much higher levels of Cr(V), showing that (OH)-O-. can be generated via a Cr(IV)-mediated Fenton-like reaction (Cr(IV) + H2O2-->Cr(V) + (OH)-O-. + OH-). 1,10-Phenanthroline and deferoxamine inhibited the formation of both (OH)-O-. and Cr(V) from the reaction of Cr(VI) with ascorbate in the presence of H2O2. Electrophoretic assays showed that ascorbate-derived free radicals caused DNA double-strand breaks. (OH)-O-. radicals generated by Cr(V)- and Cr(IV)-mediated Fenton-like reactions also caused DNA double-strand breaks. HPLC measurements showed that .H-O radicals generated by Cr(IV) and Cr(V) from H2O2 caused 2'-deoxyguanine hydroxylation to form 8-hydroxy-2'-deoxyguanine.