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Severity of neonatal hyperoxia determines structural and functional changes in developing mouse airway
Hua Wang1, Anjum Jafri1, Richard J Martin2
1Division of Neonatology, Rainbow Babies & Children's Hospital and Department of Pediatrics, Case Western Reserve University, Cleveland, Ohio;
Insights
Mild neonatal hyperoxia increased airway smooth muscle and reactivity in mice, while severe hyperoxia did not. This suggests oxygen exposure severity impacts long-term respiratory outcomes in developing lungs.
Area of Science:
- Neonatal physiology
- Pulmonary medicine
- Developmental biology
Background:
- Wheezing is a common respiratory issue in preterm infants.
- Bronchopulmonary dysplasia is a frequent complication.
- Neonatal hyperoxia is a potential contributing factor.
Purpose of the Study:
- To investigate the differential effects of mild versus severe neonatal hyperoxia on airway smooth muscle hypertrophy.
- To determine the impact of hyperoxia severity on airway reactivity.
- To understand the long-term respiratory consequences of neonatal oxygen exposure.
Main Methods:
- Newborn mice were exposed to mild (40% O2) or severe (70% O2) hyperoxia for 7 days.
- Respiratory system resistance (Rrs) and compliance (Crs) were measured.
- Airway reactivity was assessed via methacholine challenge.
- Airway smooth muscle thickness and lung structure were analyzed.
Main Results:
- Both mild and severe hyperoxia increased baseline Rrs and decreased Crs.
- Mild hyperoxia (40% O2) led to increased airway smooth muscle thickness and enhanced airway reactivity.
- Severe hyperoxia (70% O2) did not increase airway smooth muscle thickness but did cause lung structural changes (increased collagen, decreased alveoli).
- Airway reactivity was only significantly altered in the mild hyperoxia group.
Conclusions:
- The severity of neonatal hyperoxia exposure differentially impacts airway structural and functional development.
- Mild hyperoxia may promote airway smooth muscle hypertrophy and hyperreactivity, contributing to wheezing.
- These findings highlight the complex role of oxygen therapy in neonatal respiratory health.
Abstract:
Wheezing is a major long-term respiratory morbidity in preterm infants with and without bronchopulmonary dysplasia. We hypothesized that mild vs. severe hyperoxic exposure in neonatal mice differentially affects airway smooth muscle hypertrophy and resultant airway reactivity. Newborn mice were exposed to 7 days of mild (40% oxygen) or severe (70% oxygen) hyperoxia vs. room air controls. Respiratory system resistance (Rrs), compliance (Crs), and airway reactivity were measured 14 days after oxygen exposure ended under ketamine/xylazine anesthesia. Baseline Rrs increased and Crs decreased in both treatment groups. Methacholine challenge dose dependently increased Rrs and decreased Crs in 40% oxygen-exposed mice, whereas Rrs and Crs responses were similar between 70% oxygen-exposed and normoxic controls. Airway smooth muscle thickness was increased in 40%- but not 70%-exposed mice, whereas collagen increased and both alveolar number and radial alveolar counts decreased after 40% and 70% oxygen. These data indicate that severity of hyperoxia may differentially affect structural and functional changes in the developing mouse airway that contribute to longer-term hyperreactivity. These findings may be important to our understanding of the complex role of neonatal supplemental oxygen therapy in postnatal development of airway responsiveness.
