Bacillus anthracis lethal toxin, but not edema toxin, increases pulmonary artery pressure and permeability in isolated perfused rat lungs

Abstract

Although lethal toxin (LT) and edema toxin (ET) contribute to lethality during Bacillus anthracis infection, whether they increase vascular permeability and the extravascular fluid accumulation characterizing this infection is unclear. We employed an isolated perfused Sprague-Dawley rat lung model to investigate LT and ET effects on pulmonary vascular permeability. Lungs ( n ≥ 6 per experimental group) were isolated, ventilated, suspended from a force transducer, and perfused. Lung weight and pulmonary artery (Ppa) and left atrial pressures were measured over 4 h, after which pulmonary capillary filtration coefficients (Kf.c) and lung wet-to-dry weight ratios (W/D) were determined. When compared with controls, LT increased Ppa over 4 h and Kf.c and W/D at 4 h ( P < 0.0001). ET decreased Ppa in a significant trend ( P = 0.09) but did not significantly alter Kf.c or W/D ( P ≥ 0.29). Edema toxin actually blocked LT increases in Ppa but not LT increases in Kf.c and W/D. When Ppa was maintained at control levels, LT still increased Kf.c and W/D ( P ≤ 0.004). Increasing the dose of each toxin five times significantly increased and a toxin-directed monoclonal antibody decreased the effects of each toxin ( P ≤ 0.05). Two rho-kinase inhibitors (GSK269962 and Y27632) decreased LT increases in Ppa ( P ≤ 0.02) but actually increased Kf.c and W/D in LT and control lungs ( P ≤ 0.05). A vascular endothelial growth factor receptor inhibitor (ZM323881) had no significant effect ( P ≥ 0.63) with LT. Thus, LT but not ET can increase pulmonary vascular permeability independent of increased Ppa and could contribute to pulmonary fluid accumulation during anthrax infection. However, pulmonary vascular dilation with ET could disrupt protective hypoxic vasoconstriction. NEW & NOTEWORTHY The most important findings from the present study are that Bacillus anthracis lethal toxin increases pulmonary artery pressure and pulmonary permeability independently in the isolated rat lung, whereas edema toxin decreases the former and does not increase permeability. Each effect could be a basis for organ dysfunction in patients with this lethal infection. These findings further support the need for adjunctive therapies that limit the effects of both toxins during infection.

Hydrocortisone decreases lethality and inflammatory cytokine and nitric oxide production in rats challenged with B. anthracis cell wall peptidoglycan

“…Patients progressing to severe anthrax infection have extensive extravascular fluid accumulation manifested as pleural and peritoneal effusions and tissue edema [4,17,46,47]. Even though evidence suggests that lethal toxin disrupts endothelial barrier function, PGN-stimulated intravascular inflammation and coagulopathy could also contribute to this endothelial dysfunction [46,48,49]. Such inflammation is known to disrupt endothelial gap junction function and allows extravasation of protein and fluid [50,51].…”

Impact of Bacterial Toxins in the Lungs

“…To review the pathogenicity of anthrax toxins to lungs at the cellular level, it may be more appropriate to discuss each of the toxins (LeTx and EdTx) separately. Accordingly, it has been shown in a model of isolated perfused rat lungs that they have different impacts on pulmonary vascular pressures and permeability [288]. However, in vivo studies revealed that these toxin components may cooperate synergistically to cause edema formation and cell death.…”

“…Thus, the concerted action of the two should not be overlooked in practice [289]. It has been shown in vitro and in vivo that LeTx creates most characteristics of an anthrax infection including cytokine-independent vascular dysregulation and collapse, pulmonary vascular constriction, disruption of the rat pulmonary microvascular endothelial barrier integrity leading to severe blood vessel leakage, pulmonary edema, and disrupted gas exchange that clinically leads to ALI/ARDS [275,288,[290][291][292][293][294].…”