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 A₄ would prevent lung injury in a murine model of BPD.

Objective

To determine the effect of Resolvin D1 and/or Lipoxin A4 on hyperoxia-induced lung injury.

Methods

C57/BL6 pups were randomized at birth to Room Air, Hyperoxia (>90% oxygen), Hyperoxia + Resolvin D1, Hyperoxia + Lipoxin A₄, or Hyperoxia + Resolvin D1/Lipoxin A₄. Resolvin D1 and/or Lipoxin A₄ (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 TGFβ₁ and TGFβ₂.

Result

The increased ST observed with hyperoxia exposure was normalized by both Resolvin D1 and Lipoxin A₄; while, hyperoxia-induced alveolar simplification was attenuated by Lipoxin A₄. Relative to hyperoxia, Resolvin D1 reduced the gene expression of CXCL2 (2.9 fold), TIMP1 (6.7 fold), and PPARγ (4.8 fold). Treatment with Lipoxin A₄ also led to a reduction of CXCL2 (2.4 fold) while selectively increasing TGFβ₂ (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.