Setting-Up of a Novel Long-Term Multiple-Hit Preterm Rabbit Bronchopulmonary Dysplasia Model

Background: Bronchopulmonary dysplasia (BPD) is a chronic lung disease that affects preemies. The BPD development process includes several factors leading to the disruption of alveolar growth and pulmonary vascular development. In the hyperoxia-exposed BPD preterm rabbit model, pups are delivered on the day 28 of gesta¬tion and exposed to 7 days of hyperoxia (95%). This provides the combination of 2 etiological factors of human BPD, i.e., prematurity and hyperoxia. Objective: The study aims to extend this animal BPD model up to 14 days, after preterm delivery, combining a lower oxy¬gen concentration with an additional postnatal insult, i.e., the infec¬tion-induced inflammation, in order to mimic a more clinically rel¬evant condition that may be more suitable for drug candidate testing. Methods: Preterm rabbits were delivered in the saccular stage of lung development and exposed to different oxygen concentrations (21 or 50%) for 14 days. After preterm birth, rabbits exposed to the hyper¬oxic condition were intratracheally injected with a single (on day 0) or multiple (on days 0 and 5) doses of 5 mg/kg lipopolysaccharide (LPS) to induce a local inflammatory injury. Age-matched rabbits, born at term and left with their mothers, were used as physiological controls. Growth, survival, pulmonary function, and histological outcomes, such as acute lung injury (ALI) and radial alveolar count, were assessed. Results: Preterm pups exposed to both normoxia and hyperoxia for 14 days showed good survival rates. Single or repeated LPS administrations did not worsen pulmonary function compared to the untreated normoxia or 50% hyperoxia groups. On the con¬trary, the ALI score highlighted an increase in lung inflammation in preterm pups treated with LPS. Compared to term controls, all pre¬term groups showed a reduction in lung function and alveolariza¬tion. Conclusion: Rearing preterm rabbits in normoxic and hyper¬oxic (50%) conditions for 14 days is feasible. The normoxic group appeared to trigger a mild/moderate BPD phenotype compared to the term controls. Exposure to 50% oxygen combined or not with LPS intratracheal injections was well tolerated, but it did not lead to the development of a more severe BPD-like phenotype compared to the normoxic group. Thus, different oxygen concentrations and oth¬er proinflammatory stimuli need to be further evaluated.