Abstract Body (Do not enter title and authors here): Introduction: Abnormal lung development is associated with respiratory disease and pulmonary hypertension (PH) in children. PH associated with bronchopulmonary dysplasia (BPD) carries significantly morbidity and mortality due to right ventricular (RV) failure.
Aim: to develop an animal model of BPD and PH and examine the effects of chronic nitric oxide (NO) inhalation.
Methods: We exposed C57bl/6J mouse pups to 11% FiO₂ starting on post-natal day 2-4 with (11%-NO) or without (11%) continuous inhalation of 10 ppm NO for 8 weeks. Control mice breathed air (21%). At age 8 weeks we evaluated the degree of lung injury by measuring arterial PO₂ while breathing 11% FiO₂, by obtaining lung pressure-volume curves and by pathological evaluation; on transthoracic echocardiography we evaluated the degree of PH by assessing the ratio between the pulmonary artery acceleration time and the ejection time (PAAT/ET), and the RV function by assessing the tricuspid annular plane systolic excursion (TAPSE). We measured RV systolic pressure (RVSP) and RV hypertrophy with the Fulton’s ratio.
Results: 11% and 11%-NO mice compared to controls had lower PaO₂ (42.5±5.1 vs. 42.3±5.4 vs. 51.8±1.4 mmHg, p<0.01), increased lung compliance (51.3±9.6 vs. 46.9±3.2 vs. 35.0±3.3 mL/cmH₂O, p<0.001), reduced alveolarization, severe small vessel muscularization and vascular rarefaction (Fig. 1 and 2). Treatment with NO ameliorated the reduction in PAAT/ET and TAPSE that was observed in 11% mice compared to controls (11%-NO vs. 11% vs. 21%: PAAT/ET 0.27±0.03 vs. 0.22±0.04 vs. 0.32±0.04, p<0.0001, TAPSE: (0.85±0.16vs. 0.67±0.10 vs.1.1±0.2 mm, p<0.0001). Similarly, the RVSP of 11% mice was significantly elevated compared to control mice and diminished by NO treatment (11% vs. 21% vs. 11%-NO: 84±7 vs. 28±4 vs. 66±7 mmHg p<0.0001). RV hypertrophy in 11% mice was more severe than in 11%-NO mice compared to controls (Fulton’s ratio: 52±8% vs. 42±6% vs. 22±2%, p<0.0001). The median RV cardiomyocytes cross-sectional area significantly increased in both 11% and 11%-NO mice compared to controls but at a lesser extent in the 11%-NO mice (198[194-201 vs.181[178-183] vs.149[87-240] mm², p<0.0001) (Fig. 3).
Conclusions: we developed a new mouse model of BPD with associated severe PH and RV dysfunction. Continuous inhaled NO did not improve neonatal hypoxia-induced lung injury but ameliorated PH, RV hypertrophy and function. Translation of this therapy to children with BPD and PH may improve clinical outcomes.