Effect Of Sivelestat Sodium On The Progression Of Radiation-induced Lung Injury And Its Mechanism

OBJECTIVE Radiotherapy is an effective treatment strategy for thoracic malignancies,but a significant proportion of patients experience radiation-induced lung injury(RILI)after therapeutic irradiation.The mechanisms regulating this event remain elusive.The aim of this study was to investigate the protective effect of neutrophil elastase inhibitor sivelestat on radiation-induced lung injury during the course of radiotherapy and evaluate whether sivelestat influences the outcome of radiotherapy in murine Lewis lung carcinoma model.METHODS Lewis lung carcinoma(LLC)cells(1×10~6)were inoculated into the right flank of the male mice.After 8 days,the mice were randomly divided into 4treatment groups(10 mice/group):tumor model(control),radiotherapy,radiotherapy+sivelestat(50 mg/kg),radiotherapy+sivelestat(100 mg/kg).The mice were locally irradiated at the tumor and thorax with a single dose of 20 Gy.After irradiation,the mice were treated with sivelestat(50 mg/kg,100 mg/kg)via intraperitoneal injection once a day for 27 days.Twenty-seven days after thoracic irradiation,the tumors were collected and weighted.Blood was collected by cardiac puncture.Serum was collected and the activity of neutrophil elastase from serum was evaluated.The lungs were collected,fixed with formaldehyde,embedded in paraffin,cut,and stained with haematoxylin and eosin(HE).Total protein concentration and nucleated cells of bronchoalveolar lavage fluid(BALF)were determined.Lung-infiltrating neutrophils were analyzed by flow cytometry using CD11b and Ly6G double staining.RESULTS After irradiation,the LLC tumor-bearing mice showed pulmonary inflammation.The relative activity of neutrophil elastase in BALF of radiotherapy+50 mg/kg sivelestat group(1.91±0.21)and radiotherapy+100 mg/kg sivelestat group(1.39±0.18)were significantly lower than that of radiotherapy group(2.97±0.39)(F=31.844,P<0.001).The relative activity of neutrophil elastase in serum of radiotherapy+50 mg/kg sivelestat group(1.93±0.15)and radiotherapy+100 mg/kg sivelestat group(1.31±0.19)were significantly lower than that of radiotherapy group(2.65±0.36)(F=25.580,P<0.001).HE-stained histopathologic sections of lung tissue showed that sivelestat(50,100mg/kg)protected the alveolar structure in tumor-bearing mice with radiotherapy.BALF protein of radiotherapy+50 mg/kg sivelestat group(0.61±0.09)mg/mL and radiotherapy+100 mg/kg sivelestat group(0.41±0.05)mg/mL were considerably lower than that of radiotherapy group(0.96±0.20)mg/mL(F=18.465,P=0.001).BALF nucleated cell counts of radiotherapy+50 mg/kg sivelestat group(2.63±0.32)×10~5/mL and radiotherapy+100 mg/kg sivelestat group(1.57±0.25)×10~5/mL were considerably lower than that of radiotherapy group(3.70±0.36)×10~5/mL(F=53.210,P<0.001).Neutrophil infiltration in lung tissues of radiotherapy+50 mg/kg sivelestat group(4.50±0.51)%and radiotherapy+100 mg/kg sivelestat group(3.71±0.69)%were significantly lower than that of mice with radiotherapy(6.52±1.01)%(F=14.589,P=0.001).The tumor weights were(7.9±1.0)g,(2.3±0.6)g,(2.2±0.4)g and(2.3±0.3)g respectively in control mice,radiotherapy group,radiotherapy+50 mg/kg sivelestat group and radiotherapy+100 mg/kg sivelestat group.LLC tumor growth was inhibited after radiotherapy(F=206.162,P<0.001).Sivelestat treatment did not affect the tumor weights as compared to the radiotherapy group(P=0.829,P=0.949).CONCLUSION Neutrophil elastase inhibitor sivelestat ameliorates radiation-induced lung injury while preserving the therapeutic effect of radiotherapy in murine Lewis lung carcinoma model.