Abatement of bleomycin-induced pulmonary injury by cell-impermeable inhibitor of phospholipase A₂

The mechanism of bleomycin (Bleo)-induced pulmonary injury is not fully understood. Elevated levels of lung phospholipase A₂ (PLA₂) have been previously reported following intratracheal (IT) instillation of Bleo, but the role of this enzyme in the pathogenesis of lung injury is not clear.In this pilot study, we have evaluated the effect of a cell impermeable inhibitor of PLA₂ (CME) on Bleo-induced pulmonary inflammation in hamsters. Pulmonary injury was induced by a single IT instillation of Bleo (1 unit/0.5 ml saline). Three groups of male Syrian hamsters were evaluated: 1) BLEO-CME animals received IT Bleo and daily intraperitoneal (IP) injections of CME (1 μmole/kg), starting 1 day before IT instillation; 2) BLEO-SAL animals-received IT Bleo and IP injections of saline and 3) SAL-SAL animals - treated with IT and IP administrations of saline. Animals were sacrificed 14 days after IT treatment and lung injury was evaluated histologically by a semiquantitative morphologic index and by a differential cell count of bronchoalveolar lavage fluid. CME treatment significantly ameliorated Bleo-induced lung injury compared to BLEO-SAL animals (P < 0.05). The percentage of neutrophiles in bronchoalveolar lavage fluid was reduced from 17.7 ± 3.2% (mean ± S.E.) in BLEO-SAL group to 7.3 ± 1.7% in BLEO-CME group (P < 0.05), achieving levels comparable to SAL-SAL control animals. These results suggest that treatment with an extracellular PLA₂ inhibitor-CME abates Bleo-induced pulmonary injury. This may indicate an active role of PLA₂ in the pathogenesis of interstitial pulmonary fibrosis.