Chlorination of guanosine and other nucleosides by hypochlorous acid and myeloperoxidase of activated human neutrophils. Catalysis by nicotine and trimethylamine

Recent aspects of oxidative DNA damage: guanine lesions, measurement and substrate specificity of DNA repair glycosylases

This review discusses recent aspects of oxidation reactions of DNA and model compounds involving mostly OH radicals, one-electron transfer process and singlet oxygen (1O2). Emphasis is placed on the formation of double DNA lesions involving a purine base on one hand and either a pyrimidine base or a 2-deoxyribose moiety on the other hand. Structural and mechanistic information is also provided on secondary oxidation reactions of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo), a major DNA marker of oxidative stress. Another major topic which is addressed here deals with recent developments in the measurement of oxidative base damage to cellular DNA. This has been mostly achieved using the accurate and highly specific HPLC method coupled with the tandem mass spectrometry detection technique. Interestingly, optimized conditions of DNA extraction and subsequent work-up allow the accurate measurement of 11 modified nucleosides and bases within cellular DNA upon exposure to oxidizing agents, including UVA and ionizing radiations. In addition, the modified comet assay, which involves the use of bacterial DNA N-glycosylases to reveal two main classes of oxidative base damage, is applicable to isolated cells and is particularly suitable when only small amounts of biological material are available. Finally, recently available data on the substrate specificity of DNA repair enzymes belonging to the base excision pathways are briefly reviewed.

Nicotine-modulated formation of spiroiminodihydantoin nucleoside via 8-oxo-7,8-dihydro-2'-deoxyguanosine in 2'-deoxyguanosine-hypochlorous acid reaction

Hypochlorous acid (HOCl) is generated by myeloperoxidase of activated neutrophils which kill invading microorganisms, but also cause DNA damage in inflamed tissues. We report here that spiroiminodihydantoin nucleoside (dS), a further oxidized product of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG), is formed, in addition to 8-chloro-2'-deoxyguanosine and 8-oxo-dG, by reaction of 2'-deoxyguanosine with HOCl. Presence of low concentrations of nicotine significantly enhanced the yields of these HOCl-modified nucleosides. Our results imply that nicotine may enhance genotoxicity and tissue damage caused by neutrophil activation. dS may also serve as a new biomarker for oxidative DNA damage induced by oxidants such as HOCl.

Formation of 8-nitroguanosine in cellular RNA as a biomarker of exposure to reactive nitrogen species

Reactive nitrogen species, such as peroxynitrite, nitrogen oxides and nitryl chloride, have been implicated as a cause of diverse pathophysiological conditions, including inflammation, neurodegenerative and cardiovascular diseases and cancer. We previously reported that 8-nitroguanine is formed by reactions of guanine or calf-thymus DNA with peroxynitrite in vitro. In the present study, we have studied the formation of 8-nitroguanosine and 8-oxo-7,8-dihydroguanosine in reactions of calf-liver RNA with various reactive nitrogen species. 8-Nitroguanosine in RNA was found to be much more stable than 8-nitro-2' -deoxyguanosine in DNA, which rapidly depurinates to release 8-nitroguanine. Both 8-nitroguanosine and 8-oxo-7,8-dihydroguanosine were formed in calf-liver RNA following exposure to various reactive nitrogen species, such as synthetic peroxynitrite. They were also formed in RNA by reactive species formed from nitric oxide and superoxide anion generated concomitantly from 3-morpholino-sydnonimine (SIN-1) and those formed with myeloperoxidase or horseradish peroxidase in the presence of nitrite and hydrogen peroxide. 8-Nitroguanosine was detected by HPLC with an electrochemical detector in enzymatic hydrolyzates of RNA isolated from human lung carcinoma cells incubated with synthetic peroxynitrite. Our results indicate that 8-nitroguanosine in cellular RNA could be measured as a marker of damage caused by endogenous reactive nitrogen species in tissues and cells.

8-Chloro-dGTP, a hypochlorous acid-modified nucleotide, is hydrolyzed by hMTH1, the human MutT homolog

The human mutT homolog, hMTH1, suppresses spontaneous mutations by degrading the endogeneous mutagen, 8-hydroxy-dGTP. We previously reported the broad substrate specificity of hMTH1, which also degrades the oxidatively damaged purine nucleotides, 2-hydroxy-dATP, 8-hydroxy-dATP, 2-hydroxy-ATP, and 8-hydroxy-GTP, in addition to 8-hydroxy-dGTP. In this paper, we describe the hMTH1 activity for 8-chloro-dGTP, which could be formed in inflamed tissue by the reaction of dGTP with hypochlorous acid, a product of myeloperoxidase from activated human neutrophils. The hMTH1 protein was mixed with 1-20 microM of 8-chloro-dGTP and 8-hydroxy-dGTP, and the reaction products were quantified by anion-exchange HPLC to measure the pyrophosphatase reaction rate. The kinetic parameters revealed that 8-chloro-dGTP was degraded by hMTH1 with 50% efficiency as compared with that of 8-hydroxy-dGTP. This result suggests that 8-chloro-dGTP is an intrinsic substrate for hMTH1.