Nitrite-induced deamination and hypochlorite-induced oxidation of DNA in intact human respiratory tract epithelial cells

No modification of purine or pyrimidine bases was observed when isolated DN A was incubated with 1 mM nitrite at pH 7.4. However, exposure of human bro nchial epithelial cells in culture medium at pH 7.4 to nitrite at concentra tions of 100 mu M or greater led to deamination of purine bases in cellular DNA. Deamination was more extensive in cells exposed to lower extracellula r pH values and higher nitrite concentrations. Significant increases in the levels of xanthine and hypoxanthine, putative deamination products of guan ine and adenine, respectively, were observed in DNA from nitrite-treated ce lls but no rise in any base oxidation products such as 8-hydroxyguanine. Th is pattern of damage suggests that exposure of cells to nitrite (even at pH 7.4) leads to intracellular generation of "reactive nitrogen species" capa ble of deaminating purines in DNA. In addition, significant DNA strand brea kage occurred in nitrite-treated cells. The time course of base damage sugg ested that the repair of deaminated purine lesions in these cells is slow. By contrast, DNA isolated from cells exposed to hypochlorous acid (HOCl) ha s significant oxidation of pyrimidine bases and chlorination of cytosine bu t little oxidation of purines. Exposure of cells to both species (NO2- plus HOCl) potentiated the oxidative DNA base damage observed but decreased the extent of deamination. Pie hypothesize that this is due to the formation o f nitryl chloride (NO2Cl) from reaction of HOCl with . NO2-. The relevance of our observations to events in the stomach and respiratory tract, at site s of inflammation, and in ischemic tissues is discussed. (C) 2000 Elsevier Science Inc.