Effect of human recombinant erythropoietin on inflammation of hyperoxic lung injury in neonatal rats

Objective To explore the effects of human recombinant erythropoietin (rhEPO) on inflammation of hyperoxic lung injury in neonatal rats. Methods Seventy-two neonatal rats were randomly divided into 4 groups: control group, BPD group, hyperoxia + low-dose recombinant erythropoietin [EPO(L)]group, and hyperoxia + high-dose recombinant erythropoietin [EPO(H)]group.The neonatal rats in BPD group, hyperoxia + EPO(L)group and hyperoxia + EPO(H)group were exposed to 850 mL/L oxygen.Then the neonatal rats in hyperoxia + EPO(L)group and hyperoxia + EPO(H)group were given 800 IU/kg and 2 000 IU/kg rhEPO by subcutaneous injection respectively at 1 d, 3 d and 7 d, while the control group and BPD group were given the same amount of 9 g/L saline water.Initially, the body weight of each group was recorded at 3 d, 7 d and 14 d. The morphological structure changes of lung tissues were observed by HE staining under light microscope, and the radial alveolar count(RAC) in lung tissues were detected.The expression of nuclear factor kappa B(NF-κB) was detected by immunofluorescence staining; Western blot was applied to determine the protein expression of phosphorylated NF-κB(pNF-κB), inhibitor protein(IκB) and Caspase-3 in lung tissues; and the expression of interleukin-1β(IL-1β) in bronchoalveolar lavage fluid was determined using enzyme linked immunosorbent assay (ELISA). Results (1) On the 14th day, the body weight of neonatal rats in the BPD group was lower than that in the control group [(18.97±3.21) g vs.(27.97±2.30) g], and the difference was statistically significant(P<0.01); however, the body weights of neonatal rats in the hyperoxia+ EPO(L)group and hyperoxia+ EPO(H)group[(24.16±2.15) g, (26.04±1.97) g] was much heavier than that in the BPD group, and the differences was statistically significant(all P<0.05). (2) The morphological structure of lung tissues which was observed by HE staining showed that in the BPD group, there were a few inflammatory cells infiltration in alveolar septum on the 3rd day, the inflammatory response was more evident on the 7th day, when exudation could be seen in the alveolar cavity; and on the 14th day, the number of pulmonary alveoli decreased, pulmonary bulla formed, and septa were thickened.Besides, it was also observed that compared with control group, RAC was significantly decreased in BPD group on the 14th day(5.50±1.29 vs.14.33±2.80), and the difference was statistically significant(P<0.01). Pathological changes were ameliorated and the infiltration of inflammatory reaction cells was reduced in the hyperoxia+ EPO(L)group and hyperoxia + EPO(H)group.RAC was remarkably higher in the hyperoxia+ EPO(L)group and hyperoxia+ EPO(H)group than that in the BPD group on the 14th day, and the differences were statistically significant (all P<0.05). (3)Immunofluorescence results showed that: the number of NF-κB p65 positive cells increased significantly and fluorescence intensity increased in the BPD group, while EPO could greatly reduce the number of NF-κB p65 positive cells and lower the fluorescence intensity.(4)Western blot results indicated that compared with the control group, the expressions of pNF-κB p65 and Cleaved Caspase-3 was significantly increased, and the differences were statistically significant (all P<0.05); and IκB was significantly lower, and the difference was statistically significant (P<0.05). The expression of NF-κB p65 and Cleaved Caspase-3 was significantly lower, but IκB was significantly higher in the hyperoxia+ EPO(L)group and the hyperoxia+ EPO(H)group than those in the BPD group, and the differences were statistically significant (all P<0.05). (5) ELISA results revealed that the expression of IL-1β in the BPD group was significantly higher than that in the control group, and the difference was statistically significant (P<0.05); Compared with BPD group, the expression of IL-1β was significantly lower in the hyperoxia+ EPO(L)group and hyperoxia+ EPO(H)group, and the differences were statistically significant (all P<0.05). Conclusions EPO can reduce hyperoxia-induced lung tissue apoptosis and protect newborn rats against hyperoxic lung injury by decreasing the inflammatory response of cells through the NF-κB pathway on BPD. Key words: Bronchopulmonary dysplasia; Human recombinant erythropoietin; Hyperoxia; Inflammatory reaction; Nuclear transcription factor kappa B