The Protective Effects Of Recombinant Human Elafin For The Newborn Mice With Chronical Hyperoxia Induced Bronchopulmonary Dysplasia

Objective: To explore the protective effects and mechanisms of recombinant human elafin for the newborn mice with chronical hyperoxia induced bronchopulmonary dysplasia(BPD).Methods: Postnatal 24 hours C57BL/6J mice were randomly divided into three groups: air-exposed control group, hyperoxia-exposed L/R-treated group(02+L/R group, Lactated-Ringer solution acted as placebo), hyperoxia-exposed Elafin-treated group(02+Elafin group). 02+L/R group and 02+Elafin group were exposed to 85% oxygen, while the air group was fed in air in the same room. Recombinant human elafin, 8ng elafin in 1μl L/R, 5μl /g body weight, was administered by intraperitoneal injection to 02+Elafin group at 30 minutes before hyperoxia exposure every day. 02+L/R group was treated with the same amount of L/R at the same time. The mice were randomly sacrificed at postnatal 1, 3, 7, 14 and 21 d for the collection of the lung tissue. Protein concentration and the number of total cells and types in BALF were determined for evaluating airway inflammation. Using hematoxylin and eosin(HE) staining, mean linear intercept(MLI), radical alveolar counts(RAC) to assess the development of newborn mice lungs. Elastic fiber staining was used to determine the expression of elastic fiber and secondary crest counts. The DQ-elastin substrate was used to test the neutrophil elastase(NE) activity. The expression and distribution of elastin were assessed by immunohistochemistry(IHC) and transmission electron microscope.The expression of mRNA and protein of NE, IL-1β, tropoelastin and fibulin-5 were detected by RT-PCR and western blot.Results: On the one hand, the lungs of newborn mice from 02+L/R group showed significant decreases in: secondary crest counts(it began to decrease at 3d, and the decreases were especially significant at 14 d and 21 d, P<0.01); radical alveolar counts(the development of alveoli was failed). On the other hand, the lungs from 02+L/R group showed significant increases in: Inflammatory infiltration and interstitial edema;Mean linear intercept; The concentration of protein, the number of total cells and neutrophil cells in BALF; The activity of neutrophil elastase(it began to increase at 1d, keeping on a higher level at other time points); The expression of elastin and fibulin-5 by IHC depositing at the alveolar septum instead of the tips of secondary crest; The expression of mRNA and protein of NE, IL-1β, tropoelastin and fibulin-5. However, recombinant human elafin treatment could improve the development of alveoli. The results showed that elafin could depress the inflammatory infiltration and interstitial edema, and inceraes the counts of secondary crest. The 02+Elafin group mice showed a significant down-regulation of: The concentration of protein, the number of total cells and neutrophil cells in BALF; The activity of neutrophil elastase(the decrease was especially s ignificant at 14 d, P<0.05); The expression of elastin and fibulin-5 by IHC(depositing at the tips of secondary crest); The expression of mRNA and protein of NE, IL-1β,tropoelastin and fibulin-5 by RT-PCR and western blot.Conclusion: The occurrence of BPD is associated with increased activity of NE. The recombinant human elafin has protective effects for the newborn mice with chronical hyperoxia induced bronchopulmonary dysplasia. And it may work by several pathways, including reducing the inflammation infiltration, inhibiting the activity of NE, down-regulating the elastin and relative protein and blocking the balance disorders of elastin system.