Endotoxin and pulmonary cell injury.

The physiopathologic similarity between adult respiratory distress syndrome (ARDS) secondary to sepsis and endotoxin-induced pulmonary abnormalities has provided extensive descriptive information confirming bacterial endotoxin as a factor initiating the heterogeneous pulmonary changes in ARDS. The present studies have used an established in vitro model for pulmonary cell injury to examine bacterial endotoxin 1, as a direct cytotoxic agent on the two major alveolar cell types, pulmonary endothelium and epithelium; 2, as a stimulant of neutrophil-mediated pulmonary cell injury, and 3, to examine effector mechanisms of cell-mediated damage by studying the potential effectiveness of antioxidants and antiproteolytic agents in the inhibition of this process. Endotoxin direct toxicity and stimulation of neutrophil-mediated pulmonary cell injury was observed in both pulmonary cell populations in systems free of activated serum complement. Endothelial cells were observed to be more susceptible to both the direct effect of endotoxin and to neutrophil-mediated injury when compared with epithelial cell derived monolayers. The addition of an antiprotease (soybean trypsin inhibitor [STI]) was superior to antioxidants (catalase, superoxide dismutase) in reducing the neutrophil-mediated endothelial toxicity (stimulated 51CR per cent release) observed. A 92 per cent degree of protection was observed with the highest dose of STI (5 milligrams per milliliter) used. Proteases released by activated neutrophils on endotoxin stimulation appear to be the predominant toxic species responsible for endothelial injury in this system.