Modification of cellular DNA upon exposure to reactive oxygen and nitrogen species is involved in the induction of the mutagenesis, carcinogenesis and aging. The action of reactive specie hydroxyl radical with DNA generates DNA hydroperoxides. The DNA hydroperoxides and their decomposition products can be mutagenic. The decomposition of DNA hydroperoxides in the presence of metal ions generates peroxyl radicals, which can potentially generate singlet molecular oxygen (¹O₂) by the Russell mechanism. The purpose of this work was to evaluate the generation of ¹O₂ by the reaction of 5-hydroperoxymethyluracil (5-HOOMU) with cerium ions (Ce⁴⁺) and hypoclorite ions (OCl^-). 5-HOOMU was prepared using 5-hydroxymethyluracil (5-HMU) as its precursor. First, 5-HMU was synthesized by the reaction of uracil with paraformaldehyde. After that, 5-HMU was oxidized by hydrogen peroxide, producing 5-HOOMU. The formation of ¹O₂ in the reaction of 5-HOOMU with Ce⁴⁺ and OCl^- ions was characterized by chemical trapping with 9,10-diphenylanthracene (DPA), generating the corresponding endoperoxide (DPAO₂). The yield of ¹O₂ was evaluated by quantification of DPAO₂ using 9,10-dibromoanthracene as internal standard. The structures of 5-HOOMU and of DPAO₂ were confirmed by HPLC coupled to tandem mass spectrometry (HPLC/MS/MS). The generation of ¹O₂ was also demonstrated by the measurement of monomol light emission in the near-infrared region (NIR) (l = 1270nm) with a NIR photomultiplier coupled to a monochromator. These results show that ¹O₂ was generated from 5-HOOMU and Ce⁴⁺ ions by a cyclic mechanism from a linear tetraoxide intermediated proposed by Russell. The decomposition of 5-HOOMU into peroxyl radicals is a potential source of ¹O₂ in DNA, which can lead to an enhancement of DNA oxidative damage.
Financial Support: FAPESP, CNPq, CNPq, Instituto do Milênio Redoxoma, USP, Guggenheim Foundation.