Pseudomonas aeruginosa exotoxin A induces pulmonary endothelial cytotoxicity: protection by dibutyryl-cAMP

In pseudomonal septicaemia, serum levels of antibody to exotoxin A have been demonstrated to be an important independent predictor of survival. Previously, we have demonstrated that exotoxin A directly injures pulmonary endothelial cells, and that dibutyryl-cyclic adenosine monophosphate (Db-cAMP) can attenuate this injury. The object of this study was to examine the mechanisms of this pulmonary endothelial cell injury and the mechanism of Db-cAMP protection. The effects of differing duration of exposure to exotoxin A and a reduction in temperature on endothelial cell injury were examined. In addition, the effect of post-treatment with Db-cAMP on exotoxin A-induced endothelial cell injury was studied. A brief, 5 min, exposure to exotoxin resulted in maximum injury comparable to that produced by 18 h exposure. This injury did not occur at low temperatures, which would inhibit receptor-mediated endocytosis. Db-cAMP protected endothelial cells, even when added up to one hour after exotoxin exposure. These results suggest that, in this model, exotoxin A-induced injury of endothelial cells is receptor-mediated. Furthermore, this injury may be attenuated even after exotoxin A internalization has taken place.