Ozone exposure during the early postnatal period alters the timing and pattern of alveolar growth and development in nonhuman primates

Abstract

Exposure to oxidant air pollutants in early childhood, with ozone as the key oxidant, has been linked to significant decrements in pulmonary function in young adults and exacerbation of airway remodeling in asthma. Development of lung parenchyma in rhesus monkeys is rapid during the first 2 years of life (comparable to the first 6 years in humans). Our hypothesis is that ozone inhalation during infancy alters alveolar morphogenesis. We exposed infant rhesus monkeys biweekly to 5, 8 hr/day, cycles of 0.5 ppm ozone with or without house dust mite allergen from 1 to 3 or 1 to 6 months of age. Monkeys were necropsied at 3 and 6 months of age. A morphometric approach was used to quantify changes in alveolar volume and number, the distribution of alveolar size, and capillary surface density per alveolar septa. Quantitative real time PCR was used to measure the relative difference in gene expression over time. Monkeys exposed to ozone alone or ozone combined with allergen had statistically larger alveoli that were less in number at 3 months of age. Alveolar capillary surface density was also decreased in the ozone exposed groups at 3 months of age. At 6 months of age, the alveolar number was similar between treatment groups and was associated with a significant rise in alveolar number from 3 to 6 months of age in the ozone exposed groups. This increase in alveolar number was not associated with any significant increase in microvascular growth as measured by morphometry or changes in angiogenic gene expression. Inhalation of ozone during infancy alters the appearance and timing of alveolar growth and maturation. Understanding the mechanism involved with this altered alveolar growth may provide insight into the parenchymal injury and repair process that is involved with chronic lung diseases such as severe asthma and COPD.

Fig. 1

Exposure diagram. Timing of HDMA and Ozone exposure in a typical 14-day cycle.

Fig. 2

Alveolar counting method. Counting of alveolar bridges (B) in serial sections where connecting bridges (B) between serial sections are demonstrated.

Fig. 3

Representative images from each exposure cohort. (A) FA (B) HDMA (C) Ozone (D) Ozone + HDMA

Fig. 4

Lung volume. The volume of the right middle lung lobe for four treatment groups at 3 and 6 months is represented. There was a significant increase (*) (P ≤ 0.05) between the O₃ + HDMA and FA groups at 6 months of age. Volume significantly increased from 3 to 6 months within the HDMA, O₃, and HDMA + O₃ groups (**) (P ≤ 0.05).

Fig. 5

Alveolar number. The number of alveoli in the right middle lung lobe for four treatment groups at 3 and 6 months is represented. There was a significant decrease (*) (P ≤ 0.05) between the O₃ and O₃ + HDMA compared to the FA groups at 3 months of age. From 3 to 6 months alveolar number increased significantly within the HDMA, O₃, and O₃ + HDMA groups.

Fig. 6

Alveolar volume. The number-weighted alveolar volume in the right middle lung lobe for four treatment groups at 3 and 6 months is represented. There was a significant increase (*) (P ≤ 0.05) between the O₃ and O₃ + HDMA compared to the FA groups at 3 months of age. From 3 to 6 months the alveolar volume decreased in the O₃ + HDMA only (**) (P ≤ 0.05).

Fig. 7

Distribution of alveolar volume. The coefficient of variation of the distribution of number-weighted alveolar volumes (CVn alv) in the right middle lung lobe for four treatment groups at 3 and 6 months is represented. There was a significant decrease (*) (P ≤ 0.05) between the O₃ and O₃ + HDMA compared to the FA groups at 3 and 6 months of age.

Fig. 8

Capillary surface density. The ratio of the pulmonary capillary to interalveolar septal surface (Ss cap, IAS) in the right middle lung lobe for four treatment groups at 3 and 6 months is represented. There was a significant decrease (*) (P ≤ 0.05) between the O₃and O₃ + HDMA compared to the FA groups at 3 months. From 3 to 6 months there was a significant decrease in capillary surface density in the FA and HDMA groups (**) (P ≤ 0.05) and a significant increase within the O₃ group. (†) (P ≤ 0.05).