Resolvin D1 and Lipoxin A4 Improve Alveolarization and Normalize Septal Wall Thickness in a Neonatal Murine Model of Hyperoxia-Induced Lung Injury

Background: The critical fatty acids Docosahexaenoic Acid (DHA) and Arachidonic Acid (AA) decline in preterm infants within the first postnatal week and are associated with neonatal morbidities, including bronchopulmonary dysplasia (BPD). DHA and AA are precursors to downstream metabolites that terminate the inflammatory response. We hypothesized that treatment with Resolvin D1 and/or Lipoxin A(4) would prevent lung injury in a murine model of BPD. Objective: To determine the effect of Resolvin D1 and/or Lipoxin A(4) on hyperoxia-induced lung injury. Methods: C57/BL6 pups were randomized at birth to Room Air, Hyperoxia (>90% oxygen), Hyperoxia + Resolvin D1, Hyperoxia + Lipoxin A(4), or Hyperoxia + Resolvin D1/Lipoxin A(4). Resolvin D1 and/or Lipoxin A(4) (2 ng/g) were given IP on days 0, 3, 6, and 9. On day 10, mice were sacrificed and lungs collected for morphometric analyses including Mean Linear Intercept (MLI), Radial Alveolar Count (RAC), and Septal Thickness (ST); RT-PCR analyses of biomarkers of lung development and inflammation; and ELISA for TGF beta(1) and TGF beta(2). Result: The increased ST observed with hyperoxia exposure was normalized by both Resolvin D1 and Lipoxin A(4); while, hyperoxia-induced alveolar simplification was attenuated by Lipoxin A(4). Relative to hyperoxia, Resolvin D1 reduced the gene expression of CXCL2 (2.9 fold), TIMP1 (6.7 fold), and PPAR gamma (4.8 fold). Treatment with Lipoxin A(4) also led to a reduction of CXCL2 (2.4 fold) while selectively increasing TGF beta(2) (2.1 fold) and Smad3 (1.58 fold). Conclusion: The histologic and biochemical changes seen in hyperoxia-induced lung injury in this murine model can be reversed by the addition of DHA and AA fatty acid downstream metabolites that terminate the inflammatory pathways and modulate growth factors. These fatty acids or their metabolites may be novel therapies to prevent or treat lung injury in preterm infants.