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 mesothelial cell DNA to oxidant damage, we used the comet assay, a gel microelectrophoresis method that allows visual determination of DNA strand breaks on a cell-by-cell basis, to evaluate damage after hydrogen peroxide exposure. By both a qualitative and a quantitative assay, tracheal epithelial mesothelial cells demonstrated a similar dose-response increase in the number of cells showing strand breaks and the number of breaks per cell after exposure to increasing concentrations of hydrogen peroxide; but even at the highest concentration, some cells failed to show damage. By contrast, 100% of cultured V79 lung fibroblasts showed evidence of damage. Catalase and deferoxamine largely prevented the formation of strand breaks, while superoxide dismutase was not protective. To evaluate DNA repair, cells were exposed to 10 microM hydrogen 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 also showed a similar pattern of increasing damage after continuous exposure to 10 microM hydrogen peroxide for periods up to 2 h. We conclude that, in this system, 1) mesothelial and tracheobronchial epithelial cells show a similar pattern of DNA injury and repair after hydrogen peroxide exposure; 2) hydrogen peroxide damages DNA of both cell types via a mechanism probably related to the iron-catalyzed formation of hydroxyl 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.