OZONE-INDUCED DNA SINGLE STRAND BREAKS IN HUMAN AND GUINEA PIG LUNG CELLS IN VIVO

Abstract

Ozone O3 has been postulated to induce DNA damage and has been shown to be mildly tumorigenic in some studies utilizing long-term rodent exposures. We investigated lung DNA damage induced by controlled O3 exposure in vivo in guinea pigs and human subjects. We specifically examined DNA single-strand breaks SSB using the single-cell gel electrophoresis assay. Guinea pigs were exposed for 2 h to air, 0.4 ppm O3, or 1.0 ppm O3, and lung cells were collected by bronchoalveolar lavage BAL and bronchial scraping within 1 h after exposure. Both the 0.4 and 1.0 ppm O3 exposures induced significant increases in SSB in both the BAL cells and tracheal cells as indicated by an increased cell DNA length in electrophoresized agarose gel. The increase in DNA SSB was a more sensitive biomarker of exposure compared to more traditional biomarkers BAL total protein and lactate dehydrogenase, alterations in BAL cell differential, which changed only at the 1.0 ppm exposure. In an initial study with human volunteers, BAL and bronchial epithelial cells were collected from human volunteers 1-2 h after an air or 0.4 ppm O3 exposure in vivo without exercise. BAL cells primarily macrophages and bronchial epithelial cells showed no change in DNA SSB compared to the air-exposed controls. In a second study, DNA SSB in bronchial epithelial cells and BAL cells collected from exercising subjects exposed to 0.4 ppm O3 were not altered by steroid prednisone, beclomethasone pre- treatment compared to placebo treatment. However the bronchial epithelial cell DNA SSB values in the O3-exposed, placebo-pretreated group were significantly increased compared to values air or O3 exposed, no exercise in the first study. The dosimetry of O3 deposi- tion in the guinea pig and human subjects appeared similar based on the amount of 18O derived from 18O-labeled O3 found in the BAL cell fraction. These data suggest that O3 exposure at 0.4 ppm induces DNA SSB in rodent and human lung cells, although the effect of exercise on the increase of human lung cell SSB is unclear. Formation of DNA SSB may be an indicator of the tumorigenic potential of O3. Additionally, DNA SSB can potentially be a good biomarker of O3 exposure in humans and animal model systems. 3