RAT MESOTHELIAL AND TRACHEAL EPITHELIAL-CELLS SHOW EQUAL DNA SENSITIVITY TO HYDROGEN PEROXIDE-INDUCED OXIDANT INJURY

To study the relative sensitivity of rat tracheal epithelial and mesot helial cell DNA to oxidant damage, we used the comet assay, a gel micr oelectrophoresis method that allows visual determination of DNA strand breaks on a cell-by-cell basis, to evaluate damage after hydrogen per oxide exposure. By both a qualitative and a quantitative assay, trache al epithelial and mesothelial cells demonstrated a similar dose-respon se increase in the number of cells showing strand breaks and the numbe r of breaks per cell after exposure to increasing concentrations of hy drogen peroxide; but even at the highest concentration, some cells fai led to show damage. By contrast, 100% of cultured V79 lung fibroblasts showed evidence of damage. Catalase and deferoxamine largely prevente d the formation of strand breaks, while superoxide dismutase was not p rotective. To evaluate DNA repair, cells were exposed to 10 mu M hydro gen peroxide for 10 min, washed, and maintained in culture medium; by 2 h the proportion of mesothelial and epithelial cells showing comets had returned to control levels for both cell types. Both cell types al so showed a similar pattern of increasing damage after continuous expo sure to 10 mu M hydrogen peroxide for periods up to 2 h. We conclude t hat, in this system, 1) mesothelial and tracheobronchial epithelial ce lls show a similar pattern of DNA injury and repair after hydrogen per oxide exposure; 2) hydrogen peroxide damages DNA of both cell types vi a a mechanism probably related to the iron-catalyzed formation of hydr oxyl radical; and 3) both types of cells appear to be heterogeneous in their sensitivity to oxidant damage, with some cells showing extreme resistance to such damage.