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 investigated the role of nitric oxide (NO) in the induction of injury to human pulmonary artery endothelial cells. NO has been a putative source of cytotoxic reactive oxygen species in some settings. Incubation of endothelial cells with neutrophils increased the release of lactate dehydrogenase activity and preloaded fura-2 from endothelial cells, indicating that neutrophils induce endothelial cell injury. This effect was augmented by treatment with carboxy-PTIO, which traps NO in the medium, or with L-NAME, an inhibitor of NO synthase. When endothelial cells were incubated with neutrophils stimulated by phorbol myristate acetate, an activator of protein kinase C, endothelial cell damage was further enhanced and the amount of NO in the medium was decreased. Dibutyryl cyclic AMP, a cell-permeable analogue of cyclic AMP, protected against neutrophil-induced endothelial cell injury and increased NO release into the medium. The effects of dibutyryl cyclic AMP were abrogated by treatment with H-89, a potent inhibitor of cyclic AMP-dependent protein kinase. The protective effect on neutrophil-induced endothelial cell injury by dibutyryl cyclic AMP was abolished by addition of carboxy-PTIO or L-NAME. Thus, our studies suggest that NO, presumably released from endothelial cells, protects against endothelial injury by activated neutrophils and the protective effect by cyclic AMP during coculture with activated neutrophils is mediated through the action of NO. However, when monocytes activated by lipopolysaccharide and IFN-gamma were used instead of neutrophils, endothelial cells were likewise injured, but a much higher level of NO was detected and injury was diminished by addition of carboxy-PTIO to the medium. These observations suggest that the high levels of NO released by activated monocytes contribute to endothelial injury, whereas low levels of NO protect endothelial cells against injury by neutrophils.