Staphylococcal alpha-toxin elicits hypertension in isolated rabbit lungs. Evidence for thromboxane formation and the role of extracellular calcium.

Abstract

Astract. Staphylococcal a-toxin is known to damage mammalian cell membranes. Studies of erythrocytes indicate that the native toxin generates a discrete transmembrane channel with an effective diameter of 2-3 nm. (Fiissle, R., S. Bhakdi, A. Szeigoleit, J. TranumJensen, T. Kranz, and H. J. Wellensiek. 1981. J. Cell BioL 91:83-94.) In isolated rabbit lungs, perfused with recirculating blood-and plasma-free perfusion fluid, the mediation of a toxin-provoked vascular pressor response by the triggering of the arachidonic acid cascade and its dependence on extracellular calcium were investigated. Dose-dependent pulmonary artery pressor responses were elicited by the injection of 0.5-5 jg staphylococcal a-toxin into the pulmonary artery. The pressor responses were completely abolished by preincubation of the toxin with neutralizing antibodies or by preformation of atoxin hexamers in vitro. They were accompanied by the release of the arachidonic acid metabolites thromboxane B2 and 6-keto-prostaglandin Fl, ( release of potassium, but not lactatedehydrogenase into the medium. Calcium depletion of the intravascular space did not suppress the toxin-dependent potassium release but did abrogate the pressor response and the release of the arachidonic acid metabolites. When calcium was reintroduced into the circulation without the application of a second toxin stimulus, marked pressor responses paralleled by the release of arachidonic acid metabolites occurred.The conclusion drawn from these studies is that staphylococcal a-toxin provokes pulmonary vascular hypertension which is apparently mediated by thromboxane A2 formation, which surpasses the biological effect of the simultaneously formed prostaglandin 12. The triggering of the arachidonic acid cascade is strictly dependent on extracellular calcium and may be mediated by a nonphysiological calcium bypass through transmembrane toxin channels with subsequent stimulation of phospholipase activity.

Human Endothelial Cell Activation and Mediator Release in Response toListeria monocytogenesVirulence Factors

“…Strict dependency on extracellular Ca 2ϩ was noted. This finding is reminiscent of previous studies of the pore-forming agent staphylococcal alpha-toxin, which was found to be operative by an extra-intracellular Ca 2ϩ shift (presumably via the hydrophilic channels within the toxin-created transmembrane pore), thereby elicit- ing Ca 2ϩ -dependent intracellular events (13,34,35,(41)(42)(43)(44)47). Interestingly, and again in line with previous studies of alphatoxin-elicited cellular responses, the optimum concentration of LLO ranged below the highest concentration employed, indicating that substantial pore-formation, but not overt cell lysis, in still-viable cells represents the precondition for maximum NO provocation by LLO.…”

Thromboxane-mediated hypertension and vascular leakage evoked by low doses of Escherichia coli hemolysin in rabbit lungs.

“…The time course and magnitude of the hemolysin-induced pressor response were reminiscent of the acute pulmonary hypertension induced by Staphylococcus aureus alpha toxin (34). The latter generates transmembrane pores of similar dimensions to those produced by E. coli (53,54).…”

“…The model of isolated rabbit lungs, originating from animals with a body weight between 2.2 and 2.8 kg, has been previously described (34)(35)(36). Briefly, the lungs were ventilated with 4% C02, 17% 02, and 79% N2 (frequency, 45 strokes/min; tidal volume, 30 ml), and the endexpiratory pressure was set zero.…”

“…TXA2 and PGI2 were assayed by RIA from the recirculating buffer fluid and the bronchoalveolar lavage fluid as their stable hydrolysis products TXB2 and 6-keto-PGF, aph. as described (34,40). Lactatedehydrogenase and potassium in the perfusion fluid were measured according to standard techniques.…”

Prevention and Treatment ofStaphylococcus aureusPneumonia with a β-Cyclodextrin Derivative

“…Hla displays a detrimental effect on the lung epithelium, resulting in cellular injury and death as well as the generation of proinflammatory mediators (23,29). The toxin also has the capacity to target the pulmonary vascular endothelium, as treatment of isolated pulmonary arteries ex vivo results in increased vascular resistance and vascular leakage (31,32). In addition to its role in the lung, this toxin plays a critical role in S. aureus pathogenesis in intraperitoneal, intramammary, and corneal models of infection (3,7,27).…”