Anthrolysin O and fermentation products mediate the toxicity of Bacillus anthracis to lung epithelial cells under microaerobic conditions.
Bottom Line: Human small airway epithelial, umbilical vein endothelial, Caco-2, and Hep-G2 cells were found to be susceptible.Its effect was found to be synergistic with a metabolic product of B. anthracis, succinic acid.Cell death appears to be caused by an acute primary membrane permeabilization by ALO, followed by a burst of reactive radicals from the mitochondria fuelled by the succinate, which is generated by bacteria in the hypoxic environment.
Affiliation: National Center for Biodefense and Infectious Diseases, George Mason University, Manassas, VA, USA.Show MeSH
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Mentions: SA is a substrate of succinate dehydrogenase (or Complex II of the mitochondrial electron transport chain), which converts succinate to fumarate. Under some pathophysiological conditions such as hypoxia, the SA-supported mitochondrial respiration could lead to the formation of damaging ROS (Schonfeld & Wojtczak, 2008). Taking into account that the Alamar Blue dye used in our cell viability test largely reflects the redox activity of the mitochondria, we hypothesized that the mitochondria were the likely targets of the Sup-induced respiratory burst, resulting in the release of ROS and consequent self-intoxication. In agreement with this suggestion, a conventional specific inhibitor of Complex II, thenoyltrifluoroacetone, demonstrated protection of cells from the toxicity of Sups (Fig. 3c). Using MitoSox Red, a peroxide-sensitive probe designed for the detection of mitochondrial ROS production (Fauconnier et al., 2007), we observed a faster accumulation of the dye fluorescence in the presence of Sups, compared with the cells incubated in CSFM at pH 5.3 (Fig. 5a). This finding was further supported in the experiments with dehydrorhodamine 123-loaded HSAECs. The cells treated with Sups showed increased oxidation of this dye to the fluorescent rhodamine in the cytoplasm compared with the pH 5.3-titrated CSFM (not shown). Cell death was accompanied by the quick dissipation of the mitochondrial membrane potential detected with the specific dye, JC-1 (Fig. 5b). This observation is consistent with the mitochondrial damage by ROS (Pacher et al., 2007; Schonfeld & Wojtczak, 2008;) and the reduced ATP content of treated cells (Fig. 1a).
Affiliation: National Center for Biodefense and Infectious Diseases, George Mason University, Manassas, VA, USA.