U74500A inhibition of oxidant-mediated lung injury.

Toxic oxygen species are thought to play a primary role in the pathophysiological mechanisms responsible for a diverse group of lung diseases. In this study, isolated perfused rat lungs were subjected to oxidant injury induced by ischemia-reperfusion (IR) and t-butyl hydroperoxide (t-buOOH) challenge. Both forms of injury caused large increases in capillary permeability as assessed by the capillary filtration coefficient (Kfc). IR and t-buOOH challenge caused increases in the Kfc of 0.95 +/- 0.22 and 0.30 +/- 0.06 ml.min-1.cmH2O-1.100 g lung tissue-1, respectively. U74500A, a potent inhibitor of iron-mediated lipid peroxidation, significantly attenuated the endothelial damage seen in both forms of injury. In lungs pretreated with U74500A, the Kfc increased 0.01 +/- 0.02 and 0.11 +/- 0.03 ml.min-1.cmH2O-1.100 g lung tissue-1 following IR and t-buOOH challenge, respectively. In lungs pretreated with the iron binding protein transferrin the Kfc increased 0.31 +/- 0.11 and 0.19 +/- 0.03 ml.min-1.cmH2O-1.100 g lung tissue-1 following IR and t-buOOH challenge, respectively. In these studies, transferrin significantly attenuated permeability in the IR group only. However, the attenuation of injury in IR due to U74500A was significantly greater (P less than 0.05) than the attenuation provided by transferrin. Both forms of injury also caused small but statistically significant increases in pulmonary artery pressure. These results suggest that the increase in capillary permeability seen after IR and t-buOOH is in part mediated by iron-dependent mechanisms.