No abstract

Hemorrhage and pleural effusion are prominent pathological features of systemic anthrax infection. We examined the effect of anthrax lethal toxin (LT), a major virulence factor of Bacillus anthracis, on the barrier function of primary human lung microvascular endothelial cells. We also examined the distribution patterns of cytoskeletal actin and vascular endothelial-cadherin (VE-cadherin), both of which are involved in barrier function regulation. Endothelial monolayers cultured on porous membrane inserts were treated with the LT components lethal factor (LF) and protective antigen (PA) individually, or in combination. LT induced a concentration-and timedependent decrease in transendothelial electrical resistance that correlated with increased permeability to fluorescently labeled albumin. LT also produced a marked increase in central actin stress fibers and significantly altered VE-cadherin distribution as revealed by immunofluorescence microscopy and cell surface enzyme-linked immunosorbent assay. Bacillus anthracis, the causative agent of anthrax, is a spore-forming gram-positive bacterium. Anthrax toxin, the major virulence factor of B. anthracis, is composed of three proteins: protective antigen (PA), lethal factor (LF), and edema factor (EF). PA and LF combine to form lethal toxin (LT), and EF combines with PA to form edema toxin (ET).1-3 PA binds at least two identified cell surface receptors, tumor endothelial marker 8 and capillary morphogenesis protein 2.2,4,5 Once formed, PA-receptor complexes facilitate the endocytosis of LF and EF. Inside cells, LF acts as a metalloprotease that cleaves all of the mitogen activated protein kinase kinases (MEKs) except MEK 5, thus disrupting the activation of major mitogenactivated protein kinases (MAPKs): extracellular signalregulated kinases 1 and 2 (ERK1/2), p38 MAPK, and c-Jun NH 2 -terminal kinases (JNK).6 -8 EF acts as a Ca 2ϩ / calmodulin-dependent adenylate cyclase that causes a dramatic increase in intracellular levels of cAMP.9,10 Evidence to date suggests that LT may play a more significant role than ET in the pathogenesis of systemic anthrax. In several animal models, intravascular injections of purified LT are lethal. [11][12][13] In addition, attenuated B. anthracis strains unable to produce functional LF are 1000-fold less virulent than normal strains, whereas EFlacking strains are 10-fold less virulent.

Release of hemoglobin (Hb) into the circulation is a central pathophysiologic event that contributes to morbidity and mortality in chronic hemolytic anemias and severe malaria. These toxicities arise from Hb-mediated vasoactivity, possibly due to NO scavenging and localized tissue oxidative processes. Currently, there is no established treatment that targets circulating extracellular Hb. Here, we assessed the role of haptoglobin (Hp), the primary scavenger of Hb in the circulation, in limiting the toxicity of cell-free Hb infusion. Using a canine model, we found that glucocorticoid stimulation of endogenous Hp synthesis prevented Hb-induced hemodynamic responses. Furthermore, guinea pigs administered exogenous Hp displayed decreased Hbinduced hypertension and oxidative toxicity to extravascular environments, such as the proximal tubules of the kidney. The ability of Hp to both attenuate hypertensive responses during Hb exposure and prevent peroxidative toxicity in extravascular compartments was dependent on Hb-Hp complex formation, which likely acts through sequestration of Hb rather than modulation of its NO-and O 2 -binding characteristics. Our data therefore suggest that therapies involving supplementation of endogenous Hb scavengers may be able to treat complications of acute and chronic hemolysis, as well as counter the adverse effects associated with Hb-based oxygen therapeutics.

Lung epithelial and endothelial cell damage and defective lung tissue repair contribute to fatal COVID-19.

Polyhemoglobin-superoxide dismutase-catalase is designed to function as an oxygen carrier with antioxidant properties. This is based on cross-linking hemoglobin with superoxide dismutase and catalase (PolyHb-SOD-CAT). This study describes the structural and antioxidant properties of this solution. Our studies show that superoxide dismutase and catalase retain their enzymatic activity following glutaraldehyde polymerization with 8:1 and 16:1 glutaraldehyde:hemoglobin ratio. We have analyzed the optimal SOD/CAT ratios to prevent oxidation of hemoglobin in the presence of oxygen free radicals. The circulation half-life of crosslinked hemoglobin, SOD, and catalase in Sprague-Dawley rats correlates with the degree of polymerization as determined by high-performance molecular weight gel filtration. PolyHb-SOD-CAT decreases the formation of oxygen radicals compared with PolyHb in a rat intestinal ischemia-reperfusion model.