Disruption of tracheobronchial airway growth following postnatal exposure to ozone and ultrafine particles.

This study examined airway structure changes in adult rats after a long recovery period due to sub-chronic juvenile exposure to ozone and ultrafine particles that have a high organic fraction. Neonatal male Sprague-Dawley rats were exposed during lung development to 3 cycles of 0.5 ppm ozone from postnatal day 7 through 25. Two different exposure patterns were used: 5-day exposure per week (Ozone52) or 2-day exposure per week (Ozone25) with or without co-exposure to ultrafine particles (OPFP5252, OPFP5225). Airway architecture was evaluated at 81 days of age, after 56 days of continued development beyond the exposure period in filtered air (FA). By analyzing CT images from lung airway casts, we determined airway diameter, length, branching angle, and rotation angle for most conducting airways. Compared with the FA control group, the Ozone52 group showed significant decreases in airway diameter in generations larger than 10 especially in the right diaphragmatic lobe and in airway length in distal generations, while changes in airway structure due to the Ozone25 exposure were not appreciable. Interaction effects of ozone and ultrafine particle exposures were not significant. These results suggest that airway alterations due to postnatal ozone exposure are not limited to the distal region but occur extensively from the middle to distal conducting airways. Further, alterations due to early ozone exposure do not recover nearly 2 months after exposure has ceased demonstrating a persistent airway structural change following an early life exposure to ozone.