Cytotoxicity of Vibrio vulnificus cytolysin on rat peritoneal mast cells

Vibrio vulnificus cytolysin induces apoptosis in HUVEC, SGC-7901 and SMMC-7721 cells via caspase-9/3-dependent pathway

Vibrio vulnificus cytolysin (VVC) is known to be a pore-forming toxin which shows cytotoxicity for mammalian cells in culture and induces apoptosis in endothelial cells. In order to determine whether VVC induces apoptosis in vascular endothelial cells and tumor cells, the cytotoxicity induced by recombinant VVC (rVVC) and its potential mechanism in HUVEC, SGC-7901 and SMMC-7721 cells were investigated. Our study demonstrated that rVVC induced the release of intracellular K(+) from all the target cells, yet lactate dehydrogenase was not released by rVVC. It indicates that osmotic lysis might not contribute to the cytolysin-induced cytotoxicity. The study also demonstrated that rVVC induced apoptosis in HUVEC, SGC-7901 and SMMC-7721 cells in time- and dosage-dependent manners, which was associated with the activation of caspase-9 and -3, but not caspase-8. During the apoptotic process of the target cells, rVVC labeled with FITC was monitored to attach initially to the surface of the cells and entered the cytoplasma subsequently. These findings suggest that VVC may be not only a pore-forming toxin, but also a transmembrane toxin with powerful ability to induce apoptosis in human vascular endothelial cells and tumor cells.

Depletion of lymphocytes, but not neutrophils, via apoptosis in a murine model of Vibrio vulnificus infection

Vibrio vulnificus causes severe sepsis in humans. There are several reports about the relationship between host immunity and bacterial growth in V. vulnificus infection. However, the effect on leukocytes of V. vulnificus infection in vivo has not been elucidated. A murine model of V. vulnificus infection was used to investigate its effects on leukocytes in this study. Bacteria were recovered from the blood of mice 3 h after subcutaneous injection in the right lower flank. They were detected in 87.5 % (n = 7/8) of mice at 6 h, but this value decreased to 12.5 % (n = 1/8) at 12 h. In contrast, the number of lymphocytes in peripheral blood had already started to decrease at 3 h, and reached a minimum at 6-9 h post-inoculation. Typical DNA laddering, a hallmark of apoptosis, was also detected in thymocytes and splenocytes at 6 and 9 h, and showed a tendency to disappear by 12 h. Although the number of lymphocytes decreased in the model, the numbers of neutrophils did not. These results suggested that V. vulnificus has selective cytotoxicity for lymphocytes in peripheral blood in vivo, and the lymphocyte depletion was probably associated with apoptosis in vivo.

Induction of nitric oxide synthase expression by Vibrio vulnificus cytolysin

The pore-forming cytolysin of Vibrio vulnificus (VVC) causes severe hypotension and vasodilatation in vivo. Under the condition of bacterial sepsis, large amounts of nitric oxide (NO) produced by inducible NO synthase (iNOS) can contribute to host-induced tissue damage causing hypotension and septic shock. In this study, we investigated the effect of purified VVC on NO production in mouse peritoneal macrophages. VVC induced NO production in the presence of interferon-gamma. Increased NO production was not affected by polymyxin B, and heat inactivation of cytolysin abolished the NO-inducing capability. NO production was induced at the same concentration range of cytolysin for pore formation, as evidenced by the release of preloaded 2-deoxy-d-[(3)H]glucose. At the higher concentrations of cytolysin causing the depletion of cellular ATP, no NO production was observed. Increased expression of iNOS and activation of NFkappaB by VVC were confirmed by Western blotting and gel shift assay, respectively. These results suggest the role of cytolysin as an inducer of iNOS and NO production in macrophage and as a possible virulence determinant in V. vulnificus infection.

Vibrio vulnificus cytolysin induces superoxide anion-initiated apoptotic signaling pathway in human ECV304 cells

Previous studies showed that exposure to Vibrio vulnificus cytolysin (VVC) caused characteristic morphologic changes and dysfunction of vascular structures in lung. VVC showed cytotoxicity for mammalian cells in culture and acted as a vascular permeability factor. In this study, the underlying mechanisms of VVC-induced cytotoxicity was investigated on ECV304 cell, a human vascular endothelial cell line. When cells were exposed to 0.4 hemolytic units (HU) of VVC, consecutive apoptotic events were observed; the elevation of superoxide anion (O (-.)(2)), the release of cytochrome c, the activation of caspase-3, the cleavage of poly(ADP-ribose) polymerase, and the DNA fragmentation. The pretreatment with 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), O(-.) 2) scavenger, completely abolished O(-.)(2) levels and downstream apoptotic events. Moreover, pretreatment with cyclosporin A (CsA), a mitochondrial permeability transition inhibitor, was capable of attenuating O(-.)(2)-mediated cytochrome c release and caspase-3 activation, and consequent apoptosis. Apoptosis, as demonstrated by oligonucleosomal DNA fragmentation and fluorescence microscopy, was induced 24 h after VVC treatment, which was also prevented by caspase-3 inhibitor, Ac-DEVD-CHO. Caspase-1 inhibitor, Ac-YVAD-CHO, did not protect ECV 304 cells from apoptosis. These results suggest a scenario where VVC-induced apoptosis is triggered by the generation of O(-.)(2), release of cytochrome c from mitochondria, activation of caspase-3, degradation of poly(ADP-ribose) polymerase, and DNA fragmentation. The induction of apoptosis in endothelial cells by VVC may provide a pivotal mechanism for understanding the pathophysiology of septicemia.