OZONE-INDUCED DNA STRAND BREAKS IN GUINEA-PIG TRACHEOBRONCHIAL EPITHELIAL-CELLS

Ozone (O-3), the major oxidant of photochemical smog, is thought to be genotoxic and a potential respiratory carcinogen or promoter of carci nogenic processes. Because of oxidative reactions with the mucus in th e upper airway, O-3 reaction products are able to penetrate into the t racheobronchial epithelial (TE) cells. The carcinogenic effects of O-3 on the TE cells are especially of interest since most previous studie s have focused on the morphology or permeability changes of tracheas o nly. Therefore, the objective of this study was to examine the potenti al O-3 genotoxicity in TE cells after an in vivo exposure, using DNA s trand breaks as an index. Two-month-old male Dunkin-Hartley guinea pig s, specific pathogen free, 4 in each group, were exposed to 1.0 ppm O- 3 for 0, 12, 24, 48, 72, or 96 h. Animals exposed to filtered air with out O-3 exposure were used as controls. After O-3 exposure, the trache a with two main bronchi was removed from each animal, and TE cells wer e isolated and employed for determination of DNA strand breaks by fluo rometric analysis of DNA unwinding (FADU). The statistical significanc e level was set at alpha = .05. Compared with controls, ozone exposure did not alter the TE cell yield or viability, but caused an increase in protein content in tracheal lavage and an increase in DNA strand br eaks. The amount of DNA left in the alkali lysate of TE cells found at 72 h exposure was significantly decreased from controls for 3 differe nt alkali incubation times. An increase of the double-stranded DNA lef t in the alkali lysate of TE cells was observed at 96 h of exposure an d approached the value of 24 h of exposure. The same pattern was seen with all 3 different alkali incubation times at 15 degrees C. One Q(d) unit was estimated to correspond to 100 strand breaks per cell. The Q (d) was also used as an indicator for O-3 damage. Compared to controls , the Q(d) increases significantly after 1 ppm O-3 exposure for 72 h, regardless of the alkali incubation time at 15 degrees C.