Toll‐like receptor 4 antagonist protects neonatal mice from hyperoxia‐induced alveolar simplification

Abstract

Bronchopulmonary dysplasia (BPD) is the most common co‐morbidity following preterm birth. The characteristic lung phenotype of BPD is impaired alveolarization due at least in part to inflammation caused by exposure to hyperoxia. Clinical studies have suggested that interruption of the inflammatory response in preterm infants could result in amelioration and potential reversal of the deleterious effects of hyperoxic exposure on lung development that lead to the BPD phenotype. Neonatal mice placed in hyperoxia (85% oxygen) on post‐natal day 1 (P1) over a week develop histological evidence of lung injury and abnormal lung development manifest by fewer and larger alveoli, otherwise termed alveolar simplification, that is reminiscent of BPD in humans. In fetal mice administration of LPS altered lung development by impairing alveolarization leading to pathological changes resembling BPD, while these changes did not occur in toll‐like receptor 4 (TLR‐4) knock‐out mice. In adult mice with influenza, treatment with a TLR4 antagonist protected the mice from developing lung injury and mortality. We tested the hypothesis that neonatal mice treated with a TLR4 antagonist would be protected from hyperoxia‐induced alveolar simplification. C57BL/6 mice were used in these studies. Neonatal mice on post‐natal day 1 (P1) were placed in either room air (normoxia) or 85% oxygen (hyperoxia) by placing their cages in a Plexiglas chamber and flowing either room air or 85% oxygen through the chamber at 10 lpm. Dams were rotated daily between a normoxic litter and a hyperoxic litter to prevent oxygen toxicity in the dam. Mice were either given vehicle (DMSO) or a TLR4 antagonist, TAK242, 2 mg/kg IM daily during the exposure. After 7 days the neonatal animals were euthanized and the lungs were inflation‐fixed for H&E staining and determination of alveolar area, perimeter, and number using automated software. The vehicle‐treated mice exposed to hyperoxia had significantly greater alveolar area and perimeter than did vehicle‐treated mice exposed to normoxia, while vehicle‐treated, hyperoxia‐exposed mice had significantly fewer alveoli than did vehicle‐treated, normoxia‐exposed mice. The vehicle‐treated, hyperoxia‐exposed mice had substantially greater mean alveolar area than did TAK242‐treated, hyperoxia‐exposed mice (1381±61 μm2 vs 1036±52 μm2, p<0.001). Alveolar perimeter was greater in vehicle‐treated, hyperoxia‐exposed mice (213±6 μm) than in TAK242‐treated, hyperoxia‐exposed mice (184±6 μm, p<0.001). Furthermore, in hyperoxia, vehicle‐treated mice had substantially lower mean alveolar numbers than did TAK242‐treated mice (29±2 vs 42±3, p<0.005); whereas in normoxia, there was no difference in alveolar area, perimeter or number between vehicle‐treated mice and TAK242‐treated mice. Taken together these data demonstrate that a TLR4 antagonist attenuates the lung histopathologic changes reminiscent of BPD in a hyperoxic neonatal mouse model.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.