Mechanisms of inflammatory lung injury : Studies in isolated perfused rat lungs

Abstract: Isolated perfused rat lungs (IPRLs) were used to study mechanisms andmediators of lung injury due to (i) ischemia-reperfusion (IR) and (ii) endotoxin. To investigate the role of polymorphonuclear neutrophils (PMNs) in IR injury, PMNs were added to the perfusate of IPRLs subjected to IR. PMNs did not contribute to the injury as assessed by albumin leak indices. Addition of erythrocytes or catalase attenuated the injury, indicating that IR injury is dependent on a non-PMN source of toxic 02 metabolites. Moreover, increased levels of 6-keto-PGE1o: and tromboxane B2 were found in the perfusate and cyclooxygenase and thromboxane synthase inhibitors (indomethacin and U 63557A) reduced the injury, suggesting that cyclooxygenase metabolites of arachidonic acid are involved in IR lung injury.To study PMN-dependent injury in IPRLs, phorbol ester-activated PMNs were added to the perfusate in the presence of Iloprost, a long-acting prostacyclin analog. Iloprost attenuated the lung injury and decreased PMN adherence to endothelial monolayers in vitro, indicating that prostacyclin is an important regulator of PMN-dependent injury in the lung. PMN-dependent lung injury was further explored by adding calcium ionophore-activatcd PMNs prestimulated with endotoxin to the perfusate and studying the increases in pulmonary arterial pressure and capillary permeability. Both these effects were attenuated by the Ginkgo biloba-derived platelet-activating factor (PAF) antagonist, BN 52021, suggesting that endotoxin-stimulated, calcium ionophore (A 23187)activated PMNs exert important parts of their pro-inflammatory action via generation of PAF. Furthermore, addition of endotoxin to the perfusate of IPRLs caused elevated levels of group-11 phospholipase A2 (PLAz), tumor necrosis factor alpha (TNF-o:) and interleukin-1 beta (Il-1~) mRNA in the lung tissue and release of PLA2 and TNF-o: activity into the perfusate. Increased TNF-a m RNA levels and increased TNF-o: activity release were also found in alveolar macrophages exposed in vitro to asbestos as well as man made mineral fibers. In conclusion, these observations illustrate the importance of PLA2 - related mediators in inflammatory lung injury and demonstrate that neutrophils are involved in some but not necessary for all types of lung injury to occur.