Chromium(VI) reduction by catechol(amine)s results in DNA cleavage in vitro: Relevance to chromium genotoxicity
Catechols are found extensively in nature both as essential biomolecules and as the byproducts of normal oxidative damage of amino acids and proteins. They are also present in cigarette smoke and other atmospheric pollutants. Here, the interactions of reactive species generated in Cr(VI)/catechol(amine) mixtures with plasmid DNA have been investigated to model a potential route to Cr(VI)-induced genotoxicity. Reduction of Cr(VI) by 3,4-dihydroxyphenylalanine (DOPA) (1), dopamine (2), or adrenaline (3) produces species that cause extensive DNA damage, but the products of similar reactions with catechol (4) or 4-tert-butylcatechol (5) do not damage DNA. The Cr(VI)/catechol(amine) reactions have been studied at low added H2O2 concentrations, which lead to enhanced DNA cleavage with 1 and induce DNA cleavage with 4. The Cr(V) and organic intermediates generated by the reactions of Cr(VI) with 1 or 4 in the presence of H2O2 were characterized by EPR spectroscopy. The detected signals were assigned to Cr(V)-catechol, Cr(V)-peroxo, and mixed Cr(V)-catechol-peroxo complexes. Oxygen consumption during the reactions of Cr(VI) with 1, 2, 4, and 5 was studied, and H2O2 production was quantified. Reactions of Cr(VI) with 1 and 2, but not 4 and 5, consume considerable amounts of dissolved Oz, and give extensive H2O2 production. Extents of oxygen consumption and H2O2 production during the reaction of Cr(VI) with enzymatically generated 1 and N-acetyl-DOPA (from the reaction of Tyr and N-acetyl-Tyr with tyrosinase, respectively) were correlated with the DNA cleaving abilities of the products of these reactions. The reaction of Cr(VI) with enzymatically generated 1 produced significant amounts of H2O2 and caused significant DNA damage, but the N-acetyl-DOPA did not. The extent of in vitro DNA damage is reduced considerably by treatment of the Cr(VI)/catechol(amine) mixtures with catalase, which shows that the DNA damage is H2O2-dependent and that the major reactive intermediates are likely to be Cr(V)-peroxo and mixed Cr(V)-catechol-peroxo complexes, rather than Cr(V)-catechol intermediates.
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