THE ROLE OF NITRIC-OXIDE IN HUMAN PULMONARY-ARTERY ENDOTHELIAL-CELL INJURY MEDIATED BY NEUTROPHILS

Human endothelial cells are injured by the action of leukocytes. We in vestigated the role of nitric oxide (NO) in the induction of injury to human pulmonary artery endothelial cells. NO has been a putative sour ce of cytotoxic reactive oxygen species in some settings. Incubation o f endothelial cells with neutrophils increased the release of lactate dehydrogenase activity and preloaded fura-2 from endothelial cells, in dicating that neutrophils induce endothelial cell injury. This effect was augmented by treatment with carboxy-PTIO, which traps NO in the me dium, or with L-NAME, an inhibitor of NO synthase. When endothelial ce lls were incubated with neutrophils stimulated by phorbol myristate ac etate, an activator of protein kinase C, endothelial cell damage was f urther enhanced and the amount of NO in the medium was decreased. Dibu tyryl cyclic AMP, a cell-permeable analogue of cyclic AMP, protected a gainst neutrophil-induced endothelial cell injury and increased NO rel ease into the medium. The effects of dibutyryl cyclic AMP were abrogat ed by treatment with H-89, a potent inhibitor of cyclic AMP-dependent protein kinase. The protective effect on neutrophil-induced endothelia l cell injury by dibutyryl cyclic AMP was abolished by addition of car boxy-PTIO or L-NAME. Thus, our studies suggest that NO, presumably rel eased from endothelial cells, protects against endothelial injury by a ctivated neutrophils and the protective effect by cyclic AMP during co culture with activated neutrophils is mediated through the action of N O. However when monocytes activated by lipopolysaccharide and IFN-gamm a were used instead of neutrophils, endothelial cells were likewise in jured, but a much higher level of NO was detected and injury was dimin ished by addition of carboxy-PTIO to the medium. These observations su ggest that the high levels of NO released by activated monocytes contr ibute to endothelial injury, whereas low levels of NO protect endothel ial cells against injury by neutrophils.