HUMAN ENDOTHELIAL-CELL ACTIVATION AND MEDIATOR RELEASE IN RESPONSE TOTHE BACTERIAL EXOTOXINS ESCHERICHIA-COLI HEMOLYSIN AND STAPHYLOCOCCALALPHA-TOXIN

Escherichia coli hemolysin (HlyA) and Staphylococcus aureus alpha-toxi n are membrane-perturbating bacterial exotoxins that have been implica ted as significant virulence factors in human diseases. We investigate d the capacity of these toxins to cause cell activation and mediator r elease in human endothelial cells, compared with the efficacies of thr ombin and the Ca2+ ionophore A23187. Concentration ranges tested were 1 to 1000 ng/ml (HlyA), 0.01 to 10 mu g/ml (alpha-toxin), 0.01 to 10 U /ml (thrombin), and 0.01 to 10 mu M (A23187). All stimuli caused dose- dependent generation of platelet-activating factor, nitric oxide, and prostaglandin I-2. HlyA and thrombin effected time- and dose-dependent accumulation of large quantities of inositol phosphates, with maximum effects at 100 ng/ml and 1 U/ml, respectively. Corresponding time cou rse and dose dependency were noted for HlyA-elicited diacylglycerol fo rmation. In contrast, only the highest concentrations of alpha-toxin ( 10 mu g/ml) and A23187 (10 mu M) effected some moderate inositol phosp hate accumulation, and this was suppressed in the presence of the plat elet-activating factor antagonist WEB 2086. Metabolic and secretory re sponses elicited by alpha-toxin were dependent on the presence of extr acellular Ca2+. We conclude that both HlyA and alpha-toxin are potent inductors of inflammatory and vasodilatory mediators in human endothel ial cells. HlyA-elicited effects may proceed predominantly via activat ion of the phosphatidylinositol hydrolysis-related signal transduction pathway, whereas transmembrane Ca2+ flux appears to be the major even t underlying the release of mediators in response to alpha-toxin. Thes e toxin properties may contribute to vasoregulatory and inflammatory d isturbances encountered in states of severe infection and sepsis.