Association of increased pulmonary interleukin-6 with the priming effect of intra-amniotic lipopolysaccharide on hyperoxic lung injury in a rat model of bronchopulmonary dysplasia

Background: The authors previously demonstrated the priming effect of intra-amniotic lipopolysaccharide (LPS) on hyperoxic lung injury in a rat model of bronchopulmonary dysplasia (BPD). Objectives: To investigate the mechanism underlying this priming effect by determining biochemical profiles in a rat model of BPD. Methods: The rat model involved intra-amniotic LPS administration and postnatal hyperoxia (85%). The mRNA expressions of interleukin-6 (IL-6), vascular endothelial growth factor (VEGF), VEGF receptor-2 (VEGFR-2), basic fibroblast growth factor (bFGF), and transforming growth factor β₁ (TGF-β₁), as well as the protein levels of IL-6, VEGF, and protein carbonyl in lung tissue were compared between the LPS plus hyperoxia, the LPS only, the hyperoxia only, and the control groups. Results: Morphometric analysis of lung tissues demonstrated that alveolarization was significantly inhibited only in the LPS plus hyperoxia group. IL-6 protein levels and its mRNA expression in the lungs were significantly increased only in the LPS plus hyperoxia group. Neither LPS nor hyperoxia increased IL-6 in the lungs independently. bFGF mRNA expression was significantly decreased in the LPS-treated groups. VEGF protein levels were significantly reduced by hyperoxia, whereas protein carbonyl levels were increased by intra-amniotic LPS or hyperoxia. No additional significant change to VEGF or protein carbonyl levels was produced by intra-amniotic LPS or hyperoxia. There were no significant differences in the mRNA expressions of VEGF, VEGFR-2, and TGF- β₁. Conclusions: The priming effect of intra-amniotic LPS on hyperoxic lung injury may be associated with IL-6 elevation in the lungs.