Neutrophil elastase and oxygen radicals: Synergism in lung injury after hindlimb ischemia

Hindlimb ischemia and reperfusion lead to lung injury dependent on activated polymorphonuclear neutrophils (PMN) adherence. This study tests whether elastase and oxygen radicals participate in PMN-induced injury once they have become sequestered in lungs. Anesthetized rats treated with saline (n = 9) or the specific elastase inhibitor methoxysuccinyl-L-Ala-L-Ala-L-Pro-L-Val-chloromethylketone (MAAPV, n = 6) underwent 4 h of bilateral hindlimb tourniquet ischemia followed by 4 h of reperfusion. At this time, in saline-treated rats, PMN were sequestered in lungs as assayed by myeloperoxidase activity [(MPO) 51 ± 5 U/g tissue], higher than MPO in saline-treated sham rats (n = 9; 18 ± 3 U/g MPO; P < 0.01); bronchoalveolar lavage (BAL) fluid leukotriene (LT) B₄ levels increased to 594 ± 46 relative to 200 ± 38 pg/ml in shams (P < 0.01); increased permeability was documented by BAL fluid protein content of 599 ± 91 compared with 214 ± 35 μg/ml in sham animals (P < 0.01); and edema was shown by increase in lung wet-to-dry weight ratio of 4.77 ± 0.14 relative to 4.00 ± 0.09 in sham rats (P < 0.01). In MAAPV-treated animals, lung neutrophil sequestration (62 ± 9 U/g MPO) and rise of LTB₄ in BAL fluid (780 ± 244 pg/ml) were not affected, but both BAL fluid protein (335 ± 32 μg/ml) and lung wet-to-dry weight ratio (4.21 ± 0.17) were reduced (both P < 0.05). Another group of rats (n = 7) was treated with the oxygen radical scavengers superoxide dismutase and catalase 2 h after removal of tourniquets. This did not affect lung neutrophil sequestration (58 ± 8 U MPO/g) but prevented the rise of LTB₄ in BAL fluid (167 ± 44 pg/ml) as well as BAL fluid protein (245 ± 95 μg/ml) and lung wet-to-dry weight ratio (4.02±0.11) (all P<0.05). Infusion of MAAPV or oxygen radical scavengers into sham animals was without effect on neutrophil-endothelial interactions (23 ± 4 and 16 ± 1 U/g MPO, respectively). These data indicate that neutrophils sequestered in lungs after remote ischemia probably mediate permeability edema via release of both elastase and oxygen radicals.