DNA strand breaks caused by exposure to ozone and nitrogen dioxide

The present study demonstrates that exposure to ozone (O3) and nitrogen dioxide (NO2) can cause DNA single-strand breaks in alveolar macrophages. Three-month-old male Sprague-Dawley rats, specific pathogen free, were exposed to either 1.2 ppm NO2 or 0.3 ppm O3 alone or a combination of these two oxidants continuously for 3 days. The control group was exposed to filtered room air. The oxidant effects were substantiated by determining total and differential cell counts, lactate dehydrogenase activity, and total soluble protein in bronchoalveolar lavage. DNA damage was measured as single-strand breaks by alkaline elution assay. The results showed that, relative to control, NO2 exposure did not cause any significant change in the parameters studied. Exposure to O3 and combined exposure to NO2 and O3 caused significant changes in all parameters studied except cell viability. The rates of elution (Kc) of single-strand DNA from polycarbonate filter for O3 exposure and combined exposure were 73 and 79% faster than that of the control, respectively. The amounts of DNA single-strand breaks caused by O3 and combined exposure were significantly greater than the amounts detected for the NO2-exposed and control groups.