Clostridial gas gangrene. I. Cellular and molecular mechanisms of microvascular dysfunction induced by exotoxins of Clostridium perfringens

Effects of Clostridium perfringens phospholipase C in mammalian cells

Clostridium perfringens phospholipase C (Cp-PLC), the major virulence factor in the pathogenesis of gas gangrene, is a Zn(2+) metalloenzyme with lecithinase and sphingomyelinase activities. Its structure shows an N-terminal domain containing the active site, and a C-terminal Ca(2+) binding domain required for membrane interaction. Although the knowledge of the structure of Cp-PLC and its interaction with aggregated phospholipids has advanced significantly, an understanding of the effects of Cp-PLC in mammalian cells is still incomplete. Cp-PLC binds to artificial bilayers containing cholesterol and sphingomyelin or phosphatidylcholine (PC) and degrades them, but glycoconjugates present in biological membranes influence its binding or positioning toward its substrates. Studies with Cp-PLC variants harboring single amino-acid substitutions have revealed that the active site, the Ca(2+) binding region, and the membrane interacting surface are required for cytotoxic and haemolytic activity. Cp-PLC causes plasma membrane disruption at high concentrations, whereas at low concentrations it perturbs phospholipid metabolism, induces DAG generation, PKC activation, Ca(2+) mobilization, and activates arachidonic acid metabolism. The cellular susceptibility to Cp-PLC depends on the composition of the plasma membrane and the capacity to up-regulate PC synthesis. The composition of the plasma membrane determines whether Cp-PLC can bind and acquire its active conformation, and thus the extent of phospholipid degradation. The capacity of PC synthesis and the availability of precursors determine whether the cell can replace the degraded phospholipids. Whether the perturbations of signal transduction processes caused by Cp-PLC play a role in cytotoxicity is not clear. However, these perturbations in endothelial cells, platelets and neutrophils lead to the uncontrolled production of intercellular mediators and adhesion molecules, which inhibits bacterial clearance and induces thrombotic events, thus favouring bacterial growth and spread in the host tissues.

Biology and pathogenesis of thrombosis and procoagulant activity in invasive infections caused by group A streptococci and Clostridium perfringens

Group A streptococcal necrotizing fasciitis/myonecrosis and Clostridium perfringens gas gangrene are two of the most fulminant gram-positive infections in humans. Tissue destruction associated with these infections progresses rapidly to involve an entire extremity. Multiple-organ failure is common, and morbidity and mortality remain high. Systemic activation of coagulation and dysregulation of the anticoagulation pathways contribute to the pathogenesis of many diverse disease entities of infectious etiology, and it has been our hypothesis that microvascular thrombosis contributes to reduced tissue perfusion, hypoxia, and subsequent regional tissue necrosis and organ failure in these invasive gram-positive infections. This article reviews the coagulation, anticoagulation, and fibrinolytic systems from cellular players to cytokines to novel antithrombotic therapies and discusses the mechanisms contributing to occlusive microvascular thrombosis and tissue destruction in invasive group A streptococcal and C. perfringens infections. A thorough understanding of these mechanisms may suggest novel therapeutic targets for patients with these devastating infections.

Clostridium sordellii phospholipase C: gene cloning and comparison of enzymatic and biological activities with those of Clostridium perfringens and Clostridium bifermentans phospholipase C

The gene encoding Clostridium sordellii phospholipase C (Csp) was cloned and expressed as a histidine-tagged (His-tag) protein, and the protein was purified to compare its enzymatic and biological activities with those of Clostridium perfringens phospholipase C (Cpa) and Clostridium bifermentans phospholipase C (Cbp). Csp was found to consist of 371 amino acid residues in the mature form and to be more homologous to Cbp than to Cpa. The egg yolk phospholipid hydrolysis activity of the His-tag Csp was about one-third of that of His-tag Cpa, but the hemolytic activity was less than 1% of that of His-tag Cpa. His-tag Csp was nontoxic to mice. Immunization of mice with His-tag Cbp or His-tag Csp did not provide effective protection against the lethal activity of His-tag Cpa. These results indicate that Csp possesses similar molecular properties to Cbp and suggest that comparative analysis of toxic and nontoxic clostridial phospholipases is helpful for characterization of the toxic properties of clostridial phospholipases.

The role of clostridial toxins in the pathogenesis of gas gangrene

Clostridium perfringens gas gangrene is, without a doubt, the most fulminant necrotizing infection that affects humans. In victims of traumatic injury, the infection can become well established in as little as 6-8 h, and the destruction of adjacent healthy muscle can progress several inches per hour despite appropriate antibiotic coverage. Shock and organ failure are present in 50% of patients and, among these, 40% die. Despite modern medical advances and intensive-care regimens, radical amputation remains the single best life-saving treatment. Over the past century, much has been learned about the pathogenesis of this disease, and novel therapies are on the horizon for patients with this devastating infection.

Clostridium perfringens alpha-toxin induces rabbit neutrophil adhesion

Clostridium perfringens alpha-toxin, which is one of the main agents involved in the development of gas gangrene, stimulates O(2)(-)production in neutrophils. Exposure of rabbit neutrophils to the alpha-toxin induced firm adhesion of the cells to fibrinogen and fibronectin. Incubation of rabbit neutrophils and neutrophil lysates with alpha-toxin led to the production of diacylglycerol (DG) and L-alpha-phosphatidic acid (PA), respectively. The toxin-induced DG and PA formation preceded the toxin-induced adhesion of the neutrophils to fibrinogen and fibronectin, and the production of O(2)(-). Pertussis toxin inhibited the alpha-toxin-induced formation of PA, the adhesion of the neutrophils to fibrinogen and production. GTP gamma S stimulated the events induced by the alpha-toxin, whereas GDP beta S inhibited them. The alpha-toxin stimulated phosphorylation of a protein with a molecular mass of about 40 kDa. In addition, treatment of the cells with 1-oleoyl-2-acetyl-sn-glycerol (OAG) and phorbol-12,13-dibutyrate (PDBu) stimulated cell adhesion, production of and phosphorylation of the 40 kDa protein, but had no effect on the formation of PA. The events induced by the presence of OAG and PDBu were not inhibited by pertussis toxin. Protein kinase C inhibitors, H-7, staurosporine and chelerythrine, blocked alpha-toxin-induced adhesion, production of O(2)(-)and phosphorylation of the 40 kDa protein. These observations suggested that alpha-toxin-stimulated adhesion to the matrix and production were due to the formation of DG, through activation of phospholipid metabolism by a pertussis-toxin-sensitive GTP-binding protein, followed by activation of protein kinase C by DG.

Combination bacteriolytic therapy for the treatment of experimental tumors

Current chemotherapeutic approaches for cancer are in part limited by the inability of drugs to destroy neoplastic cells within poorly vascularized compartments of tumors. We have here systematically assessed anaerobic bacteria for their capacity to grow expansively within avascular compartments of transplanted tumors. Among 26 different strains tested, one (Clostridium novyi) appeared particularly promising. We created a strain of C. novyi devoid of its lethal toxin (C. novyi-NT) and showed that intravenously injected C. novyi-NT spores germinated within the avascular regions of tumors in mice and destroyed surrounding viable tumor cells. When C. novyi-NT spores were administered together with conventional chemotherapeutic drugs, extensive hemorrhagic necrosis of tumors often developed within 24 h, resulting in significant and prolonged antitumor effects. This strategy, called combination bacteriolytic therapy (COBALT), has the potential to add a new dimension to the treatment of cancer.

Synergistic effects of alpha-toxin and perfringolysin O in Clostridium perfringens-mediated gas gangrene

To examine the synergistic effects of alpha-toxin and perfringolysin O in clostridial myonecrosis, homologous recombination was used to construct an alpha-toxin deficient derivative of a perfringolysin O mutant of Clostridium perfringens. The subsequent strain was complemented with separate plasmids that carried the alpha-toxin structural gene (plc), the perfringolysin O gene (pfoA), or both toxin genes, and the resultant isogenic strains were examined in a mouse myonecrosis model. Synergistic effects were clearly observed in these experiments. Infection with the control strain, which did not produce either toxin, resulted in very minimal gross pathological changes, whereas the isogenic strain that was reconstituted for both toxins produced a pathology that was clearly more severe than when alpha-toxin alone was reconstituted. These changes were most apparent in the rapid spread of the disease, the gross pathology of the footpad and in the rate at which the mice had to be euthanatized for ethical reasons. Elimination of both alpha-toxin and perfringolysin O production removed most of the histopathological features typical of clostridial myonecrosis. These effects were restored when the mutant was complemented with the alpha-toxin structural gene, but reconstituting only perfringolysin O activity produced vastly different results, with regions of coagulative necrosis, apparently enhanced by vascular disruption, being observed. Reconstitution of both alpha-toxin and perfringolysin O activity produced histopathology most similar to that observed with the alpha-toxin reconstituted strain. The spreading of myonecrosis was very rapid in these tissues, and coagulative necrosis appeared to be restricted to the lumen of the blood vessels. The results of these virulence experiments clearly support the hypothesis that alpha-toxin and perfringolysin O have a synergistic effect in the pathology of gas gangrene.