OBJECTIVEBronchopulmonary dysplasia (BPD) is a multifactorial disease resulting from the impact of injury (including oxygen toxicity, barotrauma, volutrauma, and infection) on the immature lung. Oxygen toxicity is thought to be a major contributing factor in the pathogenesis in BPD. Previous animal studies have shown that exposure to hyperoxia in the neonatal period causes lung structural changes that are similar to the histology seen in human infants with BPD. Erythropoietin (EPO) has pleiotropic actions including antioxidant, anti-apoptotic, anti-inflammatory and angiogenic effects. Animal experiments reveal that EPO may have protective effects on hyperoxic lung injury, but the mechanisms remain unknown. The aim of the study was to evaluate the anti-inflammatory effects and understand mechanism of action of EPO on the hyperoxia-induced BPD in newborn rats.

METHODSeveral litters of Wistar pups were pooled together within 12 hours after birth and randomly divided into four groups: I. air-exposed control group, II. air-exposed human recombinant erythropoietin (rhEPO)-treated group, III. hyperoxia-exposed placebo group and IV. hyperoxia-exposed rhEPO-treated group . Group III and IV rats were exposed to 85% oxygen. Group II and IV rats received rhEPO (1200 IU/kg) subcutaneously on postnatal days 0 and 2. Group I and III received 0.9% saline in the same way. Pups from each group were sacrificed on days 3, 7, and 14. Blood hemoglobin concentration, hematocrit and platelet count were determined by blood cell analyzer. Total protein content in bronchoalveolar lavage fluid (BALF) and myeloperoxidase (MPO) were measured by biochemical assay. Changes of monocyte chemoattractant protein-1 (MCP-1) and cytokine-induced neutrophil chemoattractant-1 (CINC-1) mRNA expressions were measured by RT-PCR.

RESULTIn group III, there were a few inflammatory cells infiltrations in interstitium on day 3 and inflammatory response worsened on day 7. Alveolar and capillary hypoplasia and interstitial fibrosis were evident on day 14. The pathological changes were ameliorated greatly in group IV and the survival was prolonged. There were no abnormal raises of hemoglobin concentration, hematocrit and platelet count in group IV compared with group I. Total protein concentration in BALF was measured as a marker for capillary leakage. MPO is a major constituent of neutrophil cytoplasmic granules and its activity therefore is a direct measure of neutrophil presence and an indirect indicator of lung injury. Total protein concentration and MPO in BALF were greatly depressed in group IV compared with group III, P<0.05, P<0.001. The upregulation of genes of CINC-1 and MCP-1 was closely related with lung inflammation caused by oxidative stress. MCP-1 and CINC-1 mRNA expression were detected and it was found that their changes were in line with the degree of lung inflammation. MCP-1 and CINC-1 mRNA expression increased in group III compared with group I especially on day 7, P<0.01 or <0.001. The changes of MCP-1 and CINC-1 mRNA were positively correlated with changes of MPO in BALF covering all groups on days 3, 7 and 14, respectively (r = 0.391, P<0.05; r = 0.701, P<0.01; r = 0.600, P<0.01; r = 0.471, P<0.01; r = 0.789, P<0.01; r = 0.588, P<0.01).

CONCLUSIONEPO could significantly reduce the lung inflammatory cell infiltration, and capillary endothelial cell injury in hyperoxic lung injury in newborn rats. The mechanism may be related with the inhibition of MCP-1 and CINC-1 gene expression by EPO.