2′-Deoxyguanosine as a surrogate trapping agent for DNA reactive drug metabolites

Formation of Bulky DNA Adducts by Non-Enzymatic Production of 1,2-Naphthoquinone-Epoxide from 1,2-Naphthoquinone under Physiological Conditions

Quinones may be formed metabolically or abiotically from environmental pollutants and polycyclic aromatic hydrocarbons (PAHs); many are recognized as toxicological intermediates that cause a variety of deleterious cellular effects including mutagenicity. The PAH-o-quinone, 1,2-naphthoquinone (1,2-NQ), may exert its genotoxic effects through interactions with cellular nucleophiles such as DNA, however, the mechanisms of 1,2-NQ adduct formation are still under investigation. With the aim to further understand these mechanisms, the chemical structures of adducts formed from the reaction of 2'-deoxyguanosine (dG) with 1,2-NQ under physiological conditions were investigated by liquid chromatography electrospray ionization tandem mass spectrometry and ¹H NMR analyses. Results showed that 1,2-NQ underwent non-enzymatic oxidation to form a 1,2-NQ-epoxide which in turn formed at least four bulky adducts with dG, and these adducts were more likely to be formed under physiological conditions. A mechanism was proposed whereby hydration of 1,2-NQ to form unstable naphthohydroquinones and 2-hydroxy-1,4-naphthoquinone resulted in formation of hydrogen peroxide that oxidized 1,2-NQ. These results suggest that the genotoxicity of 1,2-NQ may not only be caused through oxidative DNA damage and adduct formation through Michael addition but also through non-enzymatic oxidative transformation of 1,2-NQ itself to form an intermediate PAH-epoxide which covalently binds to DNA.

Mass spectrometry analysis of nucleosides and nucleotides

Mass spectrometry has been widely utilised in the study of nucleobases, nucleosides and nucleotides as components of nucleic acids and as bioactive metabolites in their own right. In this review, the application of mass spectrometry to such analysis is overviewed in relation to various aspects regarding the analytical mass spectrometric and chromatographic techniques applied and also the various applications of such analysis.

Chloropicrin-induced toxic responses in human lung epithelial cells

Chloropicrin is a slowly evaporating toxic irritant that is known to cause damage in the respiratory system. Here we used a lung epithelial cell line (A549) to study the molecular responses underlying chloropicrin toxicity. Glutathione (GSH), synthetic peptide and 2'-deoxyguanosine were used as in vitro trapping agents to identify early markers of chloropicrin toxicity. Microscopy of the cells revealed massive vacuolization by chloropicrin exposure (80-100μM). The number of apoptotic cells increased with the chloropicrin concentration as assessed by flow cytometry. Immunoblotting analysis revealed increases in the amount of four proteins (p53, p21, p27 and phospho-Erk1/2) that are involved in DNA-damage, cell cycle regulation and apoptosis. Chloropicrin evoked a dose-dependent increase in levels of reactive oxygen species within one hour of exposure. The treatment triggered also the formation of disulphide bonds between the model thiol-containing peptides as analysed by LC/MS. Chloropicrin did not form stable adducts with the model peptides or 2'-deoxyguanosine. N-acetyl-cysteine (1mM NAC) fully prevented the vacuoles and chloropicrin-induced cytotoxicity. The results suggest that an oxidative insult, particularly modification of free sulfhydryl groups in proteins is involved in the acute toxicity evoked by chloropicrin in airway epithelial cells. The protective effect of NAC as a potential antidote in chloropicrin intoxication will require further investigation.