The role of neutrophil collagenase in acute lung injury induced by endotoxin

Objective In the LPS-induced acute lung injury (ALI) there is massive accumulation of neutrophils in the lung. The effect of neutrophil collagenase on the degradation of lung matrix collagen ig still unknown. The aim of this study was to investigate the role of neutrophil collagenase in LPS-induced ALI.Methods Thirty SD rats of either sex weighing 190 ± 40 g were randomly divided into five groups of 6 animals : group 1 control and group 2-5 LPS. In LPS groups animals were anesthetized with intraperitoneal 3% pentobarbital 30 mg·kg-1. Right jugular vein was cannulated. LPS (O55: B5 Sigma USA) 5 mg·kg-1 was injected iv. The animals were sacrificed at 2 h (group 2), 4 h (group 3), 6 h( group 4) and 8 h( group 5) after iv LPS administration. Bronchoalveolar lavage was performed immediately with 3 ml of normal saline. The fluid washed out was collected and subjected to hypothermic centrifugation (3000 r·min-1, 10 min 4℃) . The supernatant was collected for determination of its protein content. Lung tissue was obtained for determination of myeloperoxidase (MPO) activity, expression of matrix metallo-proteinase-8 (MMP-8) , CrossLaps protein content (the degradation product of type Ⅰ collagen) and wet/dry lung weight ratio(W/D), and microscopic examination. Pulmonary permeability index was calculated (protein content in bronchoalveolar wash-out fluid / plasma protein concentration) .Results At 4, 6 and 8 h after iv LPS administration (in group 3-5) the MMP-8 expression, crosslaps protein content, MPO activity, W/D and lung permeability index were significantly increased as compared with those in control group ( P 0.01) Microscopic examination showed massive neutrophil infiltration in lung parenchyma and alveoli. Conclusion The typeⅠ collagen degradation induced by neutrophils is through MMP-8 which may play an important role in the process of LPS-induced ALI.