EFFECTS OF A NEUTROPHIL ELASTASE INHIBITOR (ONO-5046) ON ACUTE PULMONARY INJURY-INDUCED BY TUMOR-NECROSIS-FACTOR-ALPHA (TNF-ALPHA) AND ACTIVATED NEUTROPHILS IN ISOLATED-PERFUSED RABBIT LUNGS

The aim of this study was to examine the effect of ONO-5046, a neutrop hil elastase (NE) inhibitor, on a model of acute lung injury induced b y tumor necrosis factor alpha (TNF alpha) and phorbol myristate acetat e (PMA)-activated neutrophils in isolated perfused rabbit lungs. 120 m in after TNF alpha (4,000 JRU/ml) was injected into the pulmonary arte ry (PA), 5 x 10(7) PMA-stimulated neutrophils were infused into the PA together with I-125-rabbit serum albumin (RSA). In the ONO-5046-treat ed group (ONO), ONO-5046 (20 mg/kg/h) was continuously infused during the experimental period from 30 min prior to neutrophil administration . Saline, the ONO-5046 vehicle, was infused instead of ONO-5046 in the positive control group (ALD) and nonactivated neutrophils were infuse d without TNF alpha in the negative control group (Cent). PA pressure was monitored over a 240 min period, and bronchoalveolar lavage (BAL) was performed at the end of the experiment. Lung tissues were examined immunohistochemically for the expression of thrombomodulin (TM). The levels of TM in the perfusate were also measured by ELISA and the radi oactivities in the BAL fluid, lung tissue and perfusate were determine d to calculate the permeability index (PI) as an indicator of alveolar septal or vascular endothelial damage. The rabbit lungs infused with ONO-5046 showed slower and less increases in PA pressure compared with ALD group. The PI was significantly higher in ALD group (PIBAL = 0.02 8 +/- 0.014, PILUNG = 0.04 +/- 0.003) than Cent (PIBAL = 0.002 +/- 0.0 01, PILUNG = 0.015 +/- 0.003) and ONO group (PIBAL = 0.004 +/- 0.003, PILUNG = 0.028 +/- 0.003 (p < 0.05). ALD group had higher TM levels in the perfusate and showed decreased expression of TM on the vascular e ndothelium compared to Cent and ONO group, suggesting that there was s hedding of TM on endothelium and ONO-5046 attenuated a shedding of TM. in conclusion, ONO-5046 attenuated acute lung injury by inhibiting th e alveolar epithelial and vascular endothelial injury triggered by act ivated neutrophils. NE appears to play an important role in the neutro phil-induced increase of pulmonary epithelial and microvascular permea bility observed in acute lung injury.