An assessment of the in vitro toxicology of Clostridium perfringens type D epsilon-toxin in human and animal cells

The Molecular Architecture and Mode of Action of Clostridium perfringens ε-Toxin

Clostridium perfringens ε-toxin has long been associated with a severe enterotoxaemia of livestock animals, and more recently, was proposed to play a role in the etiology of multiple sclerosis in humans. The remarkable potency of the toxin has intrigued researchers for many decades, who suggested that this indicated an enzymatic mode of action. Recently, there have been major breakthroughs by finding that it is a pore-forming toxin which shows exquisite specificity for cells bearing the myelin and lymphocyte protein (MAL) receptor. This review details the molecular structures of the toxin, the evidence which identifies MAL as the receptor and the possible roles of other cell membrane components in toxin binding. The information on structure and mode of action has allowed the functions of individual amino acids to be investigated and has led to the creation of mutants with reduced toxicity that could serve as vaccines. In spite of this progress, there are still a number of key questions around the mode of action of the toxin which need to be further investigated.

Is Clostridium perfringens epsilon toxin associated with multiple sclerosis?

Clostridium perfringens epsilon toxin is associated with enterotoxaemia in livestock. More recently, it is proposed to play a role in multiple sclerosis (MS) in humans. Compared to matched controls, strains of C. perfringens which produce epsilon toxin are significantly more likely to be isolated from the gut of MS patients and at significantly higher levels; similarly, sera from MS patients are significantly more likely to contain antibodies to epsilon toxin. Epsilon toxin recognises the myelin and lymphocyte (MAL) protein receptor, damaging the blood-brain barrier and brain cells expressing MAL. In the experimental autoimmune encephalomyelitis model of MS, the toxin enables infiltration of immune cells into the central nervous system, inducing an MS-like disease. These studies provide evidence that epsilon toxin plays a role in MS, but do not yet fulfil Koch's postulates in proving a causal role.

Direct Visualization of the Dynamic Process of Epsilon Toxin on Hemolysis

Hemolysis is the process of rupturing erythrocytes (red blood cells) by forming nanopores on their membranes using hemolysins, which then impede membrane permeability. However, the self-assembly process before the state of transmembrane pores and underlying mechanisms of conformational change are not fully understood. In this work, theoretical and experimental evidence of the pre-pore morphology of Clostridium perfringens epsilon toxin (ETX), a typical hemolysin, is provided using in situ atomic force microscopy (AFM) complemented by molecular dynamics (MD) simulations to detect the conformational distribution of different states in Mica. The AFM suggests that the ETX pore is formed in two stages: ETX monomers first attach to the membrane and form a pre-pore in no special conditions required, which then undergo a conformational change to form a transmembrane pore at temperatures above the critical point in the presence of receptors. The authors' MD simulations reveal that initial nucleation occurs when specific amino acids adsorb to negatively charged mica cavities. This work fills the knowledge gap in understanding the early stage of hemolysis and the oligomerization of hemolysins. Moreover, the newly identified pre-pore of ETX holds promise as a candidate for nanopore applications.

Systematic evaluation of membrane-camouflaged nanoparticles in neutralizing Clostridium perfringens ε-toxin

Clostridium perfringens ε-toxin (ETX) is the main toxin leading to enterotoxemia of sheep and goats and is classified as a potential biological weapon. In addition, no effective treatment drug is currently available in clinical practice for this toxin. We developed membrane-camouflaged nanoparticles (MNPs) with different membrane origins to neutralize ETX and protect the host from fatal ETX intoxication. We evaluated the safety and therapeutic efficacy of these MNPs in vitro and in vivo. Compared with membranes from karyocytes, such as Madin-Darby canine kidney (MDCK) cells and mouse neuroblastoma N2a cells (N2a cells), membrane from erythrocytes, which do not induce any immune response, are superior in safety. The protective ability of MNPs was evaluated by intravenous injection and lung delivery. We demonstrate that nebulized inhalation is as safe as intravenous injection and that both modalities can effectively protect mice against ETX. In particular, pulmonary delivery of nanoparticles more effectively treated the challenge of inhaled toxins than intravenously injected nanoparticles. Moreover, MNPs can alter the biological distribution of ETX among different organs in the body, and ETX was captured, neutralized and slowly delivered to the liver and spleen, where nanoparticles with ETX could be phagocytized and metabolized. This demonstrates how MNPs treat toxin infections in vivo. Finally, we injected the MNPs into mice in advance to find out whether MNPs can provide preventive protection, and the results showed that the long-cycle MNPs could provide at least a 3-day protection in mice. These findings demonstrate that MNPs provide safe and effective protection against ETX intoxication, provide new insights into membrane choices and delivery routes of nanoparticles, and new evidence of the ability of nanoparticles to provide preventive protection against infections.

Statins as Potential Preventative Treatment of ETX and Multiple Pore-Forming Toxin-Induced Diseases

Epsilon toxin (ETX), produced by type B and D strains of Clostridium perfringens, can cause fatal enterotoxaemia in ruminant animals, particularly sheep, cattle, and goats. Previous studies show that the cytotoxicity of ETX is dependent on the integrity of lipid rafts, the maintenance of which is ensured by cholesterol. Zaragozic acid (ZA) is a statin drug that reduces the synthesis of squalene, which is responsible for cholesterol synthesis. In this study, ZA significantly reduced the toxicity of ETX in Madin–Darby canine kidney (MDCK) cells. We show that ZA does not affect the binding of ETX to MDCK cells, but propidium iodide staining (PI) and Western blotting confirmed that ZA significantly disrupts the ability of ETX to form pores or oligomers in MDCK cells. Additionally, ZA decreased the phosphatidylserine exposure on the plasma membrane and increased the Ca2+ influx of the cells. Results of density gradient centrifugation suggest that ZA decreased the number of lipid rafts in MDCK membranes, which probably contributed to the attenuation of pore-formation. Moreover, ZA protected mice against ETX in vivo. All mice pre-treated with ZA for 48 h before exposure to an absolute lethal dose of ETX (6400 ng/kg) survived. In summary, these findings provide an innovative method to prevent ETX intoxication. Considering many pore-forming toxins require lipid rafts, we tested and found ZA also inhibited the toxicity of other toxins such as Clostridium perfringens Net B and β-toxin (CPB) and Staphylococcus aureus α-hemolysin (Hla). We expect ZA can thus be developed as a broad-spectrum medicine for the treatment of multiple toxins. In addition, other statins, such as lovastatin (LO), also reduced the toxicity of ETX. These findings indicate that statin medicines are potential candidates for preventing and treating multiple toxin-induced diseases.

Interaction of Clostridium perfringens Epsilon Toxin with the Plasma Membrane: The Role of Amino Acids Y42, Y43 and H162

Clostridium perfringens epsilon toxin (Etx) is a pore forming toxin that causes enterotoxaemia in ruminants and may be a cause of multiple sclerosis in humans. To date, most in vitro studies of Etx have used the Madin-Darby canine kidney (MDCK) cell line. However, studies using Chinese hamster ovary (CHO) cells engineered to express the putative Etx receptor, myelin and lymphocyte protein (MAL), suggest that amino acids important for Etx activity differ between species. In this study, we investigated the role of amino acids Y42, Y43 and H162, previously identified as important in Etx activity towards MDCK cells, in Etx activity towards CHO-human MAL (CHO-hMAL) cells, human red blood cells (hRBCs) and synthetic bilayers using site-directed mutants of Etx. We show that in CHO-hMAL cells Y42 is critical for Etx binding and not Y43 as in MDCK cells, indicating that surface exposed tyrosine residues in the receptor binding domain of Etx impact efficiency of cell binding to MAL-expressing cells in a species-specific manner. We also show that Etx mutant H162A was unable to lyse CHO-hMAL cells, lysed hRBCs, whilst it was able to form pores in synthetic bilayers, providing evidence of the complexity of Etx pore formation in different lipid environments.

Investigation of genetic toxicity and oxidative stress of Clostridium perfringens epsilon toxin type D on human peripheral blood lymphocytes

Epsilon toxin (Etx) is an enormously potent pore-forming toxin and a category B biological agent. Etx is the main virulence determinant of Clostridiumperfringens types B and D toxin. It has a cytotoxic effect on distal and collecting kidney tubules. Also, Etx crosses the blood-brain barrier, binds to myelin structures, and destroys oligodendrocytes. The main purpose of this study was to investigate the toxic effects of Etx on human blood lymphocytes, which we examined for the first time for the genetic toxicity of this bacterial toxin. In this study, after taking blood and dividing into nine groups and putting in contact with different dilutions of Etx (1,5,10,25,50,100 and 200 μM), methotrexate (750 μM), and normal saline by Cytokinesis blocked micronucleus (CBMN) assay, we looked at genetic toxicity and the level of oxidative stress created in the under study lymphocytes. The results of this study showed that Etx has significant oxidative stress effects on human lymphocytes at doses above 25 μM, and also this bacterial toxin significantly increases the number of micronuclei formed in lymphocytes. The results of this study indicate that Etx has toxic effects it is genetic and interferes with cell division processes. Thus, human lymphocytes can be used extensively in future studies on Etx.

Central residues of the amphipathic β-hairpin loop control the properties of Clostridium perfringens epsilon-toxin channel

Clostridium perfringens epsilon toxin (ETX) is a heptameric pore-forming toxin of the aerolysin toxin family. ETX is the most potent toxin of this toxin family and the third most potent bacterial toxin with high cytotoxic and lethal activities in animals. In addition, ETX shows a demyelinating activity in nervous tissue leading to devastating multifocal central nervous system white matter disease in ruminant animals. Pore formation in target cell membrane is most likely the initial critical step in ETX biological activity. Eight single to quadruple ETX mutants were generated by replacement of polar residues (serine, threonine, glutamine) in middle positions of the β-strands forming the β-barrel and facing the channel lumen with charged glutamic residues. Channel activity and ion selectivity were monitored in artificial lipid monolayer membranes and cytotoxicity was investigated in MDCK cells by the viability MTT test and propidium iodide entry. All the mutants formed channels with similar conductance in artificial lipid membranes and increasing cation selectivity for increasing number of mutations. Here, we show that residues in the central position of each β-strand of the amphipathic β-hairpin loop that forms the transmembrane pore, control the size and ion selectivity of the channel. While the highest cationic ETX mutants were not cytotoxic, no strict correlation was observed between ion selectivity and cytotoxicity.

In vivo Blood-brain Barrier Permeability Assays Using Clostridium perfringens Epsilon Toxin

In order for the brain to function properly, a carefully orchestrated homeostasis must be maintained. To help regulate this delicate balance, the brain has developed a highly selective blood-brain barrier (BBB). Under normal conditions, the BBB excludes harmful blood-borne material from the brain parenchyma. However, numerous neuropathological conditions can disrupt this barrier, causing BBB permeability and subsequent CNS dysfunction. Understanding the mechanisms involved in BBB permeability are essential to elucidating the pathology of various neurological disorders as well as identifying methods for drug delivery to the CNS. Here, we describe several in vivo methods to measure BBB permeability in mice using an array of diverse sized tracers including exogenous 376 Da fluorescein salt, 66.5 kDa bovine serum albumin, and 70 kDa dextran as well as endogenous 160 kDa mouse IgG. When administered intravenously, these substances are excluded from a healthy brain by the BBB. However, BBB dysfunction can allow entry of these tracers into the brain and this accumulation can be measured using spectrophotometry, fluorescent microscopy, and immunohistochemistry. We also describe a method to induce BBB permeability using Clostridium perfringens epsilon toxin. Finally, we include a short discussion about the advantages and disadvantages of each method and their appropriate downstream applications.

A small bioactive glycoside inhibits epsilon toxin and prevents cell death

Clostridium perfringens epsilon toxin (Etx) is categorized as the third most lethal bioterrorism agent by the Centers for Disease Control and Prevention (CDC), with no therapeutic counter measures available for humans. Here, we have developed a high-affinity inhibitory compound by synthesizing and evaluating the structure activity relationship (SAR) of a library of diverse glycosides (numbered 1-12). SAR of glycoside-Etx heptamers revealed exceptionally strong H-bond interactions of glycoside-4 with a druggable pocket in the oligomerization and β-hairpin region of Etx. Analysis of its structure suggested that glycoside-4 might self-aggregate to form a robust micelle-like supra-molecular complex due to its linear side-chain architecture, which was authenticated by fluorescence spectroscopy. Further, this micelle hinders the Etx monomer-monomer interaction required for oligomerization, validated by both surface plasmon resonance (SPR) and immunoblotting. This phenomenon in turn leads to blockage of pore formation. Downstream evaluation revealed that glycoside-4 effectively blocked cell death of Etx-treated cultured primary cells and maintained cellular homeostasis via disrupting oligomerization, blocking pore formation, restoring calcium homeostasis, stabilizing the mitochondrial membrane and impairing high mobility group box 1 (HMGB1) translocation from nucleus to cytoplasm. Furthermore, a single dosage of glycoside-4 protected the Etx-challenged mice and restored normal function to multiple organs. This work reports for the first time a potent, nontoxic glycoside with strong ability to occlude toxin lethality, representing it as a bio-arm therapeutic against Etx-based biological threat.

Clostridium perfringens Epsilon Toxin Compromises the Blood-Brain Barrier in a Humanized Zebrafish Model

Clostridium perfringens epsilon toxin (ETX) is hypothesized to mediate blood-brain barrier (BBB) permeability by binding to the myelin and lymphocyte protein (MAL) on the luminal surface of endothelial cells (ECs). However, the kinetics of this interaction and a general understanding of ETX's behavior in a live organism have yet to be appreciated. Here we investigate ETX binding and BBB breakdown in living Danio rerio (zebrafish). Wild-type zebrafish ECs do not bind ETX. When zebrafish ECs are engineered to express human MAL (hMAL), proETX binding occurs in a time-dependent manner. Injection of activated toxin in hMAL zebrafish initiates BBB leakage, hMAL downregulation, blood vessel stenosis, perivascular edema, and blood stasis. We propose a kinetic model of MAL-dependent ETX binding and neurovascular pathology. By generating a humanized zebrafish BBB model, this study contributes to our understanding of ETX-induced BBB permeability and strengthens the proposal that MAL is the ETX receptor.

Research articleHemolysis in human erythrocytes by Clostridium perfringens epsilon toxin requires activation of P2 receptors

Epsilon-toxin (ETX) is produced by types B and D strains of Clostridium perfringens, which cause fatal enterotoxaemia in sheep, goats and cattle. Previous studies showed that only a restricted number of cell lines are sensitive to ETX and ETX-induced hemolysis has not previously been reported. In this study, the hemolytic ability of ETX was examined using erythrocytes from 10 species including murine, rabbit, sheep, monkey and human. We found that ETX caused hemolysis in human erythrocytes (HC₅₀ = 0.2 μM) but not erythrocytes from the other test species. Moreover, the mechanism of ETX-induced hemolysis was further explored. Recent studies showed that some bacterial toxins induce hemolysis through purinergic receptor (P2) activation. Hence, the function of purinergic receptors in ETX-induced hemolysis was tested, and we found that the non-selective P2 receptor antagonists PPADS inhibited ETX-induced lysis of human erythrocytes in a concentration-dependent manner, indicating that ETX-induced hemolysis requires activation of purinergic receptors. P2 receptors comprise seven P2X (P2X1-7) and eight P2Y (P2Y1, P2Y2, P2Y4, P2Y6, and P2Y11-P2Y14) receptor subtypes. The pattern of responsiveness to more selective P2-antagonists implies that both P2Y13 and P2X7 receptors are involved in ETX-induced hemolysis in human species. Furthermore, we demonstrated that extracellular ATP is likely not involved in ETX-induced hemolysis and the activation of P2 receptors. These findings clarified the mechanism of ETX-induced hemolysis and provided new insight into the activities and ETX mode of action.

A Novel Panel of Rabbit Monoclonal Antibodies and Their Diverse Applications Including Inhibition of Clostridium perfringens Epsilon Toxin Oligomerization

The pore-forming epsilon toxin (ETX) produced by Clostridium perfringens is among the most lethal bacterial toxins known. Sensitive antibody-based reagents are needed to detect toxin, distinguish mechanisms of cell death, and prevent ETX toxicity. Using B-cell immuno-panning and cloning techniques, seven ETX-specific monoclonal antibodies were generated from immunized rabbits. ETX specificity and sensitivity were evaluated via western blot, ELISA, immunocytochemistry (ICC), and flow cytometry. ETX-neutralizing function was evaluated both in vitro and in vivo. All antibodies recognized both purified ETX and epsilon protoxin via western blot with two capable of detecting the ETX-oligomer complex. Four antibodies detected ETX via ELISA and three detected ETX bound to cells via ICC or flow cytometry. Several antibodies prevented ETX-induced cell death by either preventing ETX binding or by blocking ETX oligomerization. Antibodies that blocked ETX oligomerization inhibited ETX endocytosis and cellular vacuolation. Importantly, one of the oligomerization-blocking antibodies was able to protect against ETX-induced death post-ETX exposure in vitro and in vivo. Here we describe the production of a panel of rabbit monoclonal anti-ETX antibodies and their use in various biological assays. Antibodies possessing differential specificity to ETX in particular conformations will aid in the mechanistic studies of ETX cytotoxicity, while those with ETX-neutralizing function may be useful in preventing ETX-mediated mortality.

The Cytotoxicity of Epsilon Toxin from Clostridium perfringens on Lymphocytes Is Mediated by MAL Protein Expression

Epsilon toxin (Etx) from Clostridium perfringens is a pore-forming protein that crosses the blood-brain barrier, binds to myelin, and, hence, has been suggested to be a putative agent for the onset of multiple sclerosis, a demyelinating neuroinflammatory disease. Recently, myelin and lymphocyte (MAL) protein has been identified to be a key protein in the cytotoxic effect of Etx; however, the association of Etx with the immune system remains a central question. Here, we show that Etx selectively recognizes and kills only human cell lines expressing MAL protein through a direct Etx-MAL protein interaction. Experiments on lymphocytic cell lines revealed that MAL protein-expressing T cells, but not B cells, are sensitive to Etx and reveal that the toxin may be used as a molecular tool to distinguish subpopulations of lymphocytes. The overall results open the door to investigation of the role of Etx and Clostridium perfringens on inflammatory and autoimmune diseases like multiple sclerosis.

The development of tolerance to Clostridium perfringens type D o-toxin in MDCK and G-402 cells

The epithelial Madin Darby canine kidney (MDCK) cell line, Caucasian renal leiomyoblastoma (G-402) cells, human small airways epithelial (HSAE) cells, human bronchial epithelial (HBE) cells and human renal proximal tubule (HRPT) epithelial cells were examined for sensitivity to Clostridium perfringens biotype D o-toxin. MDCK and G-402 cells were confirmed as being the only established cell lines that are sensitive to the toxin. HSAE, HBE and HRPT epithelial cells were only found to be sensitive to the toxin at concentrations of -1 mg/ mL. Cultures of MDCK and G-402 cells, with increased resistance (tolerance) to the cytotoxic effects of o-toxin, were developed by exposing these cultures to progressively higher concentrations of toxin. The greatest relative increase in tolerance to o-toxin was developed in MDCK cells, in which the LC50 in control cultures was 2mg/mL as determined by the MTS/PMS assay system; after selection for tolerance, this was raised to 100 mg/mL. This represents a 50-fold increase in tolerance as measured by this index. Using G-402 cells, it was possible to increase the LC50 by twofold from 290 to 590 mg/mL.

Subsequent 2-D electrophoresis of membrane preparations from tolerant and control MDCK cells revealed that the expression of a discrete group of proteins found in control cells with a range of molecular weights from 32–36 kDa, all with acidic isoelectric points (IEPs), were either not expressed in o-toxin tolerant cells or had undergone a shift in IEP to a more alkaline pH in tolerant cells. This suggests that o-toxin lethality in MDCK cells may be mediated by membrane-located proteins. Their absence or alteration in toxin-resistant cells would, at least partly, explain the failure of most cell lines to demonstrate sensitivity to this toxin, despite being derived from tissues that are damaged by o-toxin. This approach may have utility in the study of other toxin / cell interactions and could be used in the development of novel medical countermeasures by identifying cellular targets which mediate toxin lethality.

Clostridium Perfringens Epsilon Toxin Binds to Membrane Lipids and Its Cytotoxic Action Depends on Sulfatide

Epsilon toxin (Etx) is one of the major lethal toxins produced by Clostridium perfringens types B and D, being the causal agent of fatal enterotoxemia in animals, mainly sheep and goats. Etx is synthesized as a non-active prototoxin form (proEtx) that becomes active upon proteolytic activation. Etx exhibits a cytotoxic effect through the formation of a pore in the plasma membrane of selected cell targets where Etx specifically binds due to the presence of specific receptors. However, the identity and nature of host receptors of Etx remain a matter of controversy. In the present study, the interactions between Etx and membrane lipids from the synaptosome-enriched fraction from rat brain (P2 fraction) and MDCK cell plasma membrane preparations were analyzed. Our findings show that both Etx and proEtx bind to lipids extracted from lipid rafts from the two different models as assessed by protein-lipid overlay assay. Lipid rafts are membrane microdomains enriched in cholesterol and sphingolipids. Binding of proEtx to sulfatide, phosphatidylserine, phosphatidylinositol (3)-phosphate and phosphatidylinositol (5)-phosphate was detected. Removal of the sulphate groups via sulfatase treatment led to a dramatic decrease in Etx-induced cytotoxicity, but not in proEtx-GFP binding to MDCK cells or a significant shift in oligomer formation, pointing to a role of sulfatide in pore formation in rafts but not in toxin binding to the target cell membrane. These results show for the first time the interaction between Etx and membrane lipids from host tissue and point to a major role for sulfatides in C. perfringens epsilon toxin pathophysiology.

Clostridium perfringens epsilon toxin: the third most potent bacterial toxin known

Epsilon toxin (ETX) is produced by Clostridium perfringens type B and D strains and causes enterotoxemia, a highly lethal disease with major impacts on the farming of domestic ruminants, particularly sheep. ETX belongs to the aerolysin-like pore-forming toxin family. Although ETX has striking similarities to other toxins in this family, ETX is often more potent, with an LD50 of 100 ng/kg in mice. Due to this high potency, ETX is considered as a potential bioterrorism agent and has been classified as a category B biological agent by the Centers for Disease Control and Prevention (CDC) of the United States. The protoxin is converted to an active toxin through proteolytic cleavage performed by specific proteases. ETX is absorbed and acts locally in the intestines then subsequently binds to and causes lesions in other organs, including the kidneys, lungs and brain. The importance of this toxin for veterinary medicine and its possible use as a biological weapon have drawn the attention of researchers and have led to a large number of studies investigating ETX. The aim of the present work is to review the existing knowledge on ETX from C. perfringens type B and D.

Correlation between in vitro cytotoxicity and in vivo lethal activity in mice of epsilon toxin mutants from Clostridium perfringens

Epsilon toxin (Etx) from Clostridium perfringens is a pore-forming protein with a lethal effect on livestock, producing severe enterotoxemia characterized by general edema and neurological alterations. Site-specific mutations of the toxin are valuable tools to study the cellular and molecular mechanism of the toxin activity. In particular, mutants with paired cysteine substitutions that affect the membrane insertion domain behaved as dominant-negative inhibitors of toxin activity in MDCK cells. We produced similar mutants, together with a well-known non-toxic mutant (Etx-H106P), as green fluorescent protein (GFP) fusion proteins to perform in vivo studies in an acutely intoxicated mouse model. The mutant (GFP-Etx-I51C/A114C) had a lethal effect with generalized edema, and accumulated in the brain parenchyma due to its ability to cross the blood-brain barrier (BBB). In the renal system, this mutant had a cytotoxic effect on distal tubule epithelial cells. The other mutants studied (GFP-Etx-V56C/F118C and GFP-Etx-H106P) did not have a lethal effect or cross the BBB, and failed to induce a cytotoxic effect on renal epithelial cells. These data suggest a direct correlation between the lethal effect of the toxin, with its cytotoxic effect on the kidney distal tubule cells, and the ability to cross the BBB.

Toxin plasmids of Clostridium perfringens

In both humans and animals, Clostridium perfringens is an important cause of histotoxic infections and diseases originating in the intestines, such as enteritis and enterotoxemia. The virulence of this Gram-positive, anaerobic bacterium is heavily dependent upon its prolific toxin-producing ability. Many of the ∼16 toxins produced by C. perfringens are encoded by large plasmids that range in size from ∼45 kb to ∼140 kb. These plasmid-encoded toxins are often closely associated with mobile elements. A C. perfringens strain can carry up to three different toxin plasmids, with a single plasmid carrying up to three distinct toxin genes. Molecular Koch's postulate analyses have established the importance of several plasmid-encoded toxins when C. perfringens disease strains cause enteritis or enterotoxemias. Many toxin plasmids are closely related, suggesting a common evolutionary origin. In particular, most toxin plasmids and some antibiotic resistance plasmids of C. perfringens share an ∼35-kb region containing a Tn916-related conjugation locus named tcp (transfer of clostridial plasmids). This tcp locus can mediate highly efficient conjugative transfer of these toxin or resistance plasmids. For example, conjugative transfer of a toxin plasmid from an infecting strain to C. perfringens normal intestinal flora strains may help to amplify and prolong an infection. Therefore, the presence of toxin genes on conjugative plasmids, particularly in association with insertion sequences that may mobilize these toxin genes, likely provides C. perfringens with considerable virulence plasticity and adaptability when it causes diseases originating in the gastrointestinal tract.

A low-toxic site-directed mutant of Clostridium perfringens ε-toxin as a potential candidate vaccine against enterotoxemia

Clostridium perfringens epsilon toxin (ETX), one of the most potent toxins known, is a potential biological weapon; therefore, the development of an effective vaccine is important for preventing intoxication or disease by ETX. In this study, genetically detoxified epsilon toxin mutants were developed as candidate vaccines. We used site-directed mutagenesis to mutate the essential amino acid residues (His106, Ser111 and Phe199). Six site-directed mutants of ETX (mETX (H106P) , mETX (S111H) , mETX (S111Y) , mETX (F199H) , mETX (F199E) , mETX (S111YF199E) ) were generated and then expressed in Escherichia coli. Both mETX (F199E) and mETX (H106P) with low or non-cytotoxicity that retained their immunogenicity were selected to immunize mice 3 times, and the mouse survival data were recorded after challenging with recombinant wild-type ETX. mETX (F199E) induces the same protection as mETX (H106P) , which was reported previously as a promising toxin mutant for vaccine, and both of them could protect immunized mice against a 100× LD₅₀ dose of active wild-type recombinant ETX. This work showed that mETX (F199E) is another promising candidate vaccine against enterotoxemia and other diseases caused by ETX.

Oligomerization of Clostridium perfringens epsilon toxin is dependent upon caveolins 1 and 2

Evidence from multiple studies suggests that Clostridium perfringens ε-toxin is a pore-forming toxin, assembling into oligomeric complexes in the plasma membrane of sensitive cells. In a previous study, we used gene-trap mutagenesis to identify mammalian factors contributing to toxin activity, including caveolin-2 (CAV2). In this study, we demonstrate the importance of caveolin-2 and its interaction partner, caveolin-1 (CAV1), in ε-toxin-induced cytotoxicity. Using CAV2-specific shRNA in a toxin-sensitive human kidney cell line, ACHN, we confirmed that cells deficient in CAV2 exhibit increased resistance to ε-toxin. Similarly, using CAV1-specific shRNA, we demonstrate that cells deficient in CAV1 also exhibit increased resistance to the toxin. Immunoprecipitation of CAV1 and CAV2 from ε-toxin-treated ACHN cells demonstrated interaction of both CAV1 and -2 with the toxin. Furthermore, blue-native PAGE indicated that the toxin and caveolins were components of a 670 kDa protein complex. Although ε-toxin binding was only slightly perturbed in caveolin-deficient cells, oligomerization of the toxin was dramatically reduced in both CAV1- and CAV2-deficient cells. These results indicate that CAV1 and -2 potentiate ε-toxin induced cytotoxicity by promoting toxin oligomerization – an event which is requisite for pore formation and, by extension, cell death.

Multifaceted interactions of bacterial toxins with the gastrointestinal mucosa

The digestive tract is one of the ecosystems that harbors the largest number and greatest variety of bacteria. Among them, certain bacteria have developed various strategies, including the synthesis of virulence factors such as toxins, to interact with the intestinal mucosa, and are responsible for various pathologies. A large variety of bacterial toxins of different sizes, structures and modes of action are able to interact with the gastrointestinal mucosa. Some toxins, termed enterotoxins, directly stimulate fluid secretion in enterocytes or cause their death, whereas other toxins pass through the intestinal barrier and disseminate by the general circulation to remote organs or tissues, where they are active. After recognition of a membrane receptor on target cells, toxins can act at the cell membrane by transducing a signal across the membrane in a hormone-like manner, by pore formation or by damaging membrane compounds. Other toxins can enter the cells and modify an intracellular target leading to a disregulation of certain physiological processes or disorganization of some structural architectures and cell death. Toxins are fascinating molecules, which mimic or interfere with eukaryotic physiological processes. Thereby, they have permitted the identification and characterization of new natural hormones or regulatory pathways. Besides use as protective antigens in vaccines, toxins offer multiple possibilities in pharmacology, such as immune modulation or specific delivery of a protein of interest into target cells.

Evidence for a prepore stage in the action of Clostridium perfringens epsilon toxin

Clostridium perfringens epsilon toxin (ETX) rapidly kills MDCK II cells at 37°C, but not 4°C. The current study shows that, in MDCK II cells, ETX binds and forms an oligomeric complex equally well at 37°C and 4°C but only forms a pore at 37°C. However, the complex formed in MDCK cells treated with ETX at 4°C has the potential to form an active pore, since shifting those cells to 37°C results in rapid cytotoxicity. Those results suggested that the block in pore formation at 4°C involves temperature-related trapping of ETX in a prepore intermediate on the MDCK II cell plasma membrane surface. Evidence supporting this hypothesis was obtained when the ETX complex in MDCK II cells was shown to be more susceptible to pronase degradation when formed at 4°C vs. 37°C; this result is consistent with ETX complex formed at 4°C remaining present in an exposed prepore on the membrane surface, while the ETX prepore complex formed at 37°C is unaccessible to pronase because it has inserted into the plasma membrane to form an active pore. In addition, the ETX complex rapidly dissociated from MDCK II cells at 4°C, but not 37°C; this result is consistent with the ETX complex being resistant to dissociation at 37°C because it has inserted into membranes, while the ETX prepore readily dissociates from cells at 4°C because it remains on the membrane surface. These results support the identification of a prepore stage in ETX action and suggest a revised model for ETX cytotoxicity, i) ETX binds to an unidentified receptor, ii) ETX oligomerizes into a prepore on the membrane surface, and iii) the prepore inserts into membranes, in a temperature-sensitive manner, to form an active pore.

Molecular basis of toxicity of Clostridium perfringens epsilon toxin

Clostridium perfringens ε-toxin is produced by toxinotypes B and D strains. The toxin is the aetiological agent of dysentery in newborn lambs but is also associated with enteritis and enterotoxaemia in goats, calves and foals. It is considered to be a potential biowarfare or bioterrorism agent by the US Government Centers for Disease Control and Prevention. The relatively inactive 32.9 kDa prototoxin is converted to active mature toxin by proteolytic cleavage, either by digestive proteases of the host, such as trypsin and chymotrypsin, or by C. perfringens λ-protease. In vivo, the toxin appears to target the brain and kidneys, but relatively few cell lines are susceptible to the toxin, and most work has been carried out using Madin-Darby canine kidney (MDCK) cells. The binding of ε-toxin to MDCK cells and rat synaptosomal membranes is associated with the formation of a stable, high molecular weight complex. The crystal structure of ε-toxin reveals similarity to aerolysin from Aeromonas hydrophila, parasporin-2 from Bacillus thuringiensis and a lectin from Laetiporus sulphureus. Like these toxins, ε-toxin appears to form heptameric pores in target cell membranes. The exquisite specificity of the toxin for specific cell types suggests that it binds to a receptor found only on these cells.

Gene-trap mutagenesis identifies mammalian genes contributing to intoxication by Clostridium perfringens ε-toxin

The Clostridium perfringens ε-toxin is an extremely potent toxin associated with lethal toxemias in domesticated ruminants and may be toxic to humans. Intoxication results in fluid accumulation in various tissues, most notably in the brain and kidneys. Previous studies suggest that the toxin is a pore-forming toxin, leading to dysregulated ion homeostasis and ultimately cell death. However, mammalian host factors that likely contribute to ε-toxin-induced cytotoxicity are poorly understood. A library of insertional mutant Madin Darby canine kidney (MDCK) cells, which are highly susceptible to the lethal affects of ε-toxin, was used to select clones of cells resistant to ε-toxin-induced cytotoxicity. The genes mutated in 9 surviving resistant cell clones were identified. We focused additional experiments on one of the identified genes as a means of validating the experimental approach. Gene expression microarray analysis revealed that one of the identified genes, hepatitis A virus cellular receptor 1 (HAVCR1, KIM-1, TIM1), is more abundantly expressed in human kidney cell lines than it is expressed in human cells known to be resistant to ε-toxin. One human kidney cell line, ACHN, was found to be sensitive to the toxin and expresses a larger isoform of the HAVCR1 protein than the HAVCR1 protein expressed by other, toxin-resistant human kidney cell lines. RNA interference studies in MDCK and in ACHN cells confirmed that HAVCR1 contributes to ε-toxin-induced cytotoxicity. Additionally, ε-toxin was shown to bind to HAVCR1 in vitro. The results of this study indicate that HAVCR1 and the other genes identified through the use of gene-trap mutagenesis and RNA interference strategies represent important targets for investigation of the process by which ε-toxin induces cell death and new targets for potential therapeutic intervention.

Clostridium perfringens epsilon toxin is cytotoxic for human renal tubular epithelial cells

Clostridium perfringens epsilon toxin (ETX) is responsible for a fatal enterotoxemia in different animal species, producing extensive renal damage, neurological disturbance and edema of lungs, heart and kidneys. However, there is no information about the susceptibility of humans to ETX. Here, we report that primary cultures of human renal tubular epithelial cells (HRTEC) exposed to ETX showed a marked swelling with subsequent large blebs surrounding most cells. The incubation of HRTEC with ETX produced a reduction of cell viability in a dose- and time-dependent manner. The CD(50) after 1-hour and 24-hour incubation were 3 µg/mL and 0.5 µg/mL, respectively. The pulse with ETX for 3 min was enough to produce a significant cytotoxic effect on HRTEC after 1-hour incubation. ETX binds to HRTEC forming a large complex of about 160 kDa similar to what was found in the Madin-Darby canine kidney (MDCK) cell line. The HRTEC could be a useful cell model to improve the understanding of the mechanisms involved on the cell damage mediated by ETX.

Clostridial toxins

Clostridia produce the highest number of toxins of any type of bacteria and are involved in severe diseases in humans and other animals. Most of the clostridial toxins are pore-forming toxins responsible for gangrenes and gastrointestinal diseases. Among them, perfringolysin has been extensively studied and it is the paradigm of the cholesterol-dependent cytolysins, whereas Clostridium perfringens epsilon-toxin and Clostridium septicum alpha-toxin, which are related to aerolysin, are the prototypes of clostridial toxins that form small pores. Other toxins active on the cell surface possess an enzymatic activity, such as phospholipase C and collagenase, and are involved in the degradation of specific cell-membrane or extracellular-matrix components. Three groups of clostridial toxins have the ability to enter cells: large clostridial glucosylating toxins, binary toxins and neurotoxins. The binary and large clostridial glucosylating toxins alter the actin cytoskeleton by enzymatically modifying the actin monomers and the regulatory proteins from the Rho family, respectively. Clostridial neurotoxins proteolyse key components of neuroexocytosis. Botulinum neurotoxins inhibit neurotransmission at neuromuscular junctions, whereas tetanus toxin targets the inhibitory interneurons of the CNS. The high potency of clostridial toxins results from their specific targets, which have an essential cellular function, and from the type of modification that they induce. In addition, clostridial toxins are useful pharmacological and biological tools.

In vitro effects of Clostridium perfringens type D epsilon toxin on water and ion transport in ovine and caprine intestine

Clostridium perfringens type D produces enterotoxaemia in sheep, goats and other animals. The disease is caused by C. perfringens epsilon toxin, and while enterotoxaemia in goats is usually characterized by enterocolitis, the disease in sheep is characterized by systemic lesions (such as lung and brain oedema) with minor and inconsistent changes observed in the intestine. A possible explanation for these differences is that epsilon toxin is more promptly absorbed by sheep than goat intestine. In an attempt to clarify this, we examined the in vitro effects of epsilon toxin on sheep and goat intestine. Pieces of intestinal mucosa from recently slaughtered animals were mounted in a modified Ussing-type chamber where net water flux (J(w)), short-circuit current (I(sc)) and tissue conductance (G(t)) were simultaneously recorded. After 70 min of incubation with epsilon toxin a reduction in absorptive J(w) and an increase in I(sc) and G(t) were observed in colonic tissues of both sheep and goats, but no alterations were registered in the ileum of either species. These in vitro results show that epsilon toxin affects the transport function of the colonic mucosa but it does not seem to produce any transport alteration in the ileum mucosa.

Distribution of Clostridium perfringens epsilon toxin in the brains of acutely intoxicated mice and its effect upon glial cells

Epsilon toxin (epsilon-toxin), produced by Clostridium perfringens types B and D, causes fatal enterotoxaemia in livestock. The disease is principally manifested as severe and often fatal neurological disturbance. Oedema of several organs, including the brain, is also a clinical sign related to microvascular damage. Recombinant epsilon-toxin-green fluorescence protein (epsilon-toxin-GFP) and epsilon-prototoxin-GFP have already been characterised as useful tools to track their distribution in intravenously injected mice, by means of direct fluorescence microscopy detection. The results shown here, using an acutely intoxicated mouse model, strongly suggest that epsilon-toxin-GFP, but not epsilon-prototoxin-GFP, not only causes oedema but is also able to cross the blood-brain barrier and accumulate in brain tissue. In some brain areas, epsilon-toxin-GFP is found bound to glial cells, both astrocytes and microglia. Moreover, cytotoxicity assays, performed with mixed glial primary cultures, demonstrate the cytotoxic effect of epsilon-toxin upon both astrocytes and microglial cells.

Functional analysis of neutralizing antibodies against Clostridium perfringens epsilon-toxin

The Clostridium perfringens epsilon-toxin causes a severe, often fatal illness (enterotoxemia) characterized by cardiac, pulmonary, kidney, and brain edema. In this study, we examined the activities of two neutralizing monoclonal antibodies against the C. perfringens epsilon-toxin. Both antibodies inhibited epsilon-toxin cytotoxicity towards cultured MDCK cells and inhibited the ability of the toxin to form pores in the plasma membranes of cells, as shown by staining cells with the membrane-impermeant dye 7-aminoactinomycin D. Using an antibody competition enzyme-linked immunosorbent assay (ELISA), a peptide array, and analysis of mutant toxins, we mapped the epitope recognized by one of the neutralizing monoclonal antibodies to amino acids 134 to 145. The antibody competition ELISA and analysis of mutant toxins suggest that the second neutralizing monoclonal antibody also recognizes an epitope in close proximity to this region. The region comprised of amino acids 134 to 145 overlaps an amphipathic loop corresponding to the putative membrane insertion domain of the toxin. Identifying the epitopes recognized by these neutralizing antibodies constitutes an important first step in the development of therapeutic agents that could be used to counter the effects of the epsilon-toxin.

Development of a cell culture assay for the quantitative determination of vaccination-induced antibodies in rabbit sera against Clostridium perfringens epsilon toxin and Clostridium novyi alpha toxin

Cell culture assays are possible alternatives to replace in vivo neutralization tests currently required for potency testing of clostridial vaccines. Cell culture assays based on the MDCK cell line and the Vero cell line which are sensitive to the Clostridium (C.) perfringens type D epsilon toxin and Clostridium novyi type B alpha toxin, respectively, were developed, and the test conditions were standardized. The antibody titres of vaccinated rabbits measured in vitro were compared with the results of current test procedures recommended by European Pharmacopoeia. The correlation coefficients calculated were significant for all sera tested. The cell culture assays proved to be sensitive, specific, reproducible and reliable. Therefore, these cell culture assays could be suitable in vitro alternatives to the in vivo mouse neutralization experiments required for potency tests of clostridial vaccines, but further validation studies are necessary.

Vaccines against the category B toxins: Staphylococcal enterotoxin B, epsilon toxin and ricin

The threat of bioterrorism worldwide has accelerated the demand for the development of therapies and vaccines against the Category B toxins: staphylococcal enterotoxin B (SEB), epsilon toxin (ETX) produced by Clostridium perfringens types B and D, and ricin, a natural product of the castor bean. The diverse and unique nature of these toxins poses a challenge to vaccinologists. While formalin-inactivated toxins can successfully induce antibody-mediated protection in animals, their usefulness in humans is limited because of potential safety concerns. For this reason, research is now aimed at developing recombinant, attenuated vaccines based on a detailed understanding of the molecular mechanisms by which these toxins function. Vaccine development is further complicated by the fact that as bioterrorism agents, SEB, ETX and ricin would most likely be disseminated as aerosols or in food/water supplies. Our understanding of the mechanisms by which these toxins cross mucosal surfaces, and importance of mucosal immunity in preventing toxin uptake is only rudimentary.

Changes in ganglioside content affect the binding of Clostridium perfringens epsilon-toxin to detergent-resistant membranes of Madin-Darby canine kidney cells

Epsilon-toxin (ET) of Clostridium perfringens, which causes fatal enterotoxemia in ungulates, was previously shown to bind to and form a heptameric pore within the detergent-resistant membranes (DRMs) of MDCK cells. Depletion of cholesterol has also been shown to decrease the cytotoxicity of ET and its heptamerization. In this study, we investigated the effects of changes in sphingolipids, other DRM components of MDCK cells, on the cells' susceptibility to ET. Treatment with fumonisin B1 and PDMP, inhibitors of sphingolipid and glycosphingolipid syntheses, respectively, increased the susceptibility, while D609, a sphingomyelin synthesis inhibitor, had the opposite effect. The exogenous addition of ganglioside G(M1) dramatically decreased the ET binding, heptamerization and cytotoxicity. These effects were shown not to be due to ET binding to G(M1) or to denaturation of ET. We also found that the ET cytotoxicity towards MDCK cells decreased with an increase in culture time. In accordance with the resistance observed for prolonged cultured cells, G(M3), a major ganglioside component, increased and sialidase treatment increased their susceptibility. These results suggest that membrane-anchored sialic acid of G(M3) within DRMs inhibits ET binding, leading to prevention of the heptamerization of ET and cell death. It is also suggested that sialidase produced by this organism aids the targeting of ET to MDCK cells.

Effect of epsilon toxin-GFP on MDCK cells and renal tubules in vivo

Epsilon toxin (epsilon-toxin), produced by Clostridium perfringens types B and D, causes fatal enterotoxemia, also known as pulpy kidney disease, in livestock. Recombinant epsilon-toxin-green fluorescence protein (epsilon-toxin-GFP) and epsilon-prototoxin-GFP were successfully expressed in Escherichia coli. MTT assays on MDCK cells confirmed that recombinant epsilon-toxin-GFP retained the cytotoxicity of the native toxin. Direct fluorescence analysis of MDCK cells revealed a homogeneous peripheral pattern that was temperature sensitive and susceptible to detergent. epsilon-Toxin-GFP and epsilon-prototoxin-GFP bound to endothelia in various organs of injected mice, especially the brain. However, fluorescence mainly accumulated in kidneys. Mice injected with epsilon-toxin-GFP showed severe kidney alterations, including hemorrhagic medullae and selective degeneration of distal tubules. Moreover, experiments on kidney cryoslices demonstrated specific binding to distal tubule cells of a range of species. We demonstrate with new recombinant fluorescence tools that epsilon-toxin binds in vivo to endothelial cells and renal tubules, where it has a strong cytotoxic effect. Our binding experiments indicate that an epsilon-toxin receptor is expressed on renal distal tubules of mammalian species, including human.

Accumulation of Clostridium perfringens epsilon-toxin in the mouse kidney and its possible biological significance

In this paper we show that Clostridium perfringens epsilon-toxin accumulates predominantly in the mouse kidney, where it is distributed mainly in glomeruli, capillaries, and collecting ducts. Although some pycnotic and exfoliated epithelial cells were observed in distal tubuli and collecting ducts, there were no findings indicative of severe renal injury. Bilateral nephrectomy increased the mouse lethality of the toxin, suggesting that the kidney contributes to the host defense against the lethal toxicity of epsilon-toxin.

Therapy and prophylaxis of inhaled biological toxins

This review highlights the current lack of therapeutic and prophylactic treatments for use against inhaled biological toxins, especially those considered as potential biological warfare (BW) or terrorist threats. Although vaccine development remains a priority, the use of rapidly deployable adjunctive therapeutic or prophylactic drugs could be life-saving in severe cases of intoxication or where vaccination has not been possible or immunity not established. The current lack of such drugs is due to many factors. Thus, methods involving molecular modelling are limited by the extent to which the cellular receptor sites and mode of action and structure of a toxin need to be known. There is also our general lack of knowledge of what effect individual toxins will have when inhaled into the lungs - whether and to what extent the action will be cell specific and cytotoxic or rather an acute inflammatory response requiring the use of immunomodulators. Possible sources of specific high-affinity toxin antagonists being investigated include monoclonal antibodies, selected oligonucleotides (aptamers) and derivatized dendritic polymers (dendrimers). The initial selection of suitable agents of these kinds can be made using cytotoxicity assays involving cultured normal human lung cells and a range of suitable indicators. The possibility that a mixture of selected antibody, aptamer or dendrimer-based materials for one or more toxins could be delivered simultaneously as injections or as inhaled aerosol sprays should be investigated.

Clostridium perfringens epsilon toxin rapidly decreases membrane barrier permeability of polarized MDCK cells

Epsilon toxin is produced by Clostridium perfringens types B and D which are responsible for fatal intestinal diseases in animals. The main biological activity of epsilon toxin is the production of oedema in various organs. We have previously found that epsilon toxin forms a large membrane complex in MDCK cells which is not internalized into cell, and induces cell volume enlargement and loss of cell viability (Petit, L., Gibert, M., Gillet, D., Laurent-Winter, C., Boquet, P., Popoff, M. R. (1997) J Bacteriol 179, 6480-6487). Here, we show that epsilon toxin is very potent to decrease the trans-epithelial electrical resistance of polarized MDCK cells grown on filters without altering the organization of the junctional complexes. The dose-dependent decrease in trans-epithelial electrical resistance, more marked when the toxin was applied to the apical side than to the basal side of MDCK cells, was associated with a moderate increase of the paracellular permeability to low-molecular-weight compounds but not to macromolecules. Epsilon toxin probably acts by forming large membrane pores which permit the flux of ions and other molecules such as the entry of propidium iodide and finally to the loss of cell viability.

Clostridium perfringens epsilon-toxin forms a heptameric pore within the detergent-insoluble microdomains of Madin-Darby canine kidney cells and rat synaptosomes

Clostridium perfringens epsilon-toxin, which is responsible for enterotoxaemia in ungulates, forms a heptamer in rat synaptosomal and Madin-Darby canine kidney (MDCK) cell membranes, leading to membrane permealization. Thus, the toxin may target the detergent-resistant membrane domains (DRMs) of these membranes, in analogy to aerolysin, a heptameric pore-forming toxin that associates with DRMs. To test this idea, we examined the distribution of radiolabeled epsilon-toxin in DRM and detergent-soluble membrane fractions of MDCK cells and rat synaptosomal membranes. When MDCK cells and synaptosomal membranes were incubated with the toxin and then fractionated by cold Triton X-100 extraction and flotation on sucrose gradients, the heptameric toxin was detected almost exclusively in DRMs. The results of a toxin overlay assay revealed that the toxin preferentially bound to and heptamerized in the isolated DRMs. Furthermore, cholesterol depletion by methyl-beta-cyclodextrin abrogated their association and lowered the cytotoxicity of the toxin toward MDCK cells. When epsilon-protoxin, an inactive precursor able to bind to but unable to heptamerize in the membrane, was incubated with MDCK cell membranes, it was detected mainly in their DRMs. These results suggest that the toxin is concentrated and induced to heptamerize on binding to a putative receptor located preferentially in DRMs, with all steps from initial binding through pore formation completed within the same DRMs.

Microbiological, biological, and chemical weapons of warfare and terrorism

Microbiological, biological, and chemical toxins have been employed in warfare and in terrorist attacks. In this era, it is imperative that health care providers are familiar with illnesses caused by these agents. Botulinum toxin produces a descending flaccid paralysis. Staphylococcal enterotoxin B produces a syndrome of fever, nausea, and diarrhea and may produce a pulmonary syndrome if aerosolized. Clostridium perfringens epsilon-toxin could possibly be aerosolized to produce acute pulmonary edema. Ricin intoxication can manifest as gastrointestinal hemorrhage after ingestion, severe muscle necrosis after intramuscular injection, and acute pulmonary disease after inhalation. Nerve agents inhibit acetylcholinesterase and thus produce symptoms of increased cholinergic activity. Ammonia, chlorine, vinyl chloride, phosgene, sulfur dioxide, and nitrogen dioxide, tear gas, and zinc chloride primarily injure the upper respiratory tract and the lungs. Sulfur mustard (and nitrogen mustard) are vesicant and alkylating agents. Cyanide poisoning ranges from sudden-onset headache and drowsiness to severe hypoxemia, cardiovascular collapse, and death. Health care providers should be familiar with the medical consequences of toxin exposure, and understand the pathophysiology and management of resulting illness.

Clostridium perfringens epsilon toxin induces a rapid change of cell membrane permeability to ions and forms channels in artificial lipid bilayers

Epsilon toxin is a potent toxin produced by Clostridium perfringens types B and D, which are responsible for a rapidly fatal enterotoxemia in animals. One of the main properties of epsilon toxin is the production of edema. We have previously found that epsilon toxin causes a rapid swelling of Madin-Darby canine kidney cells and that the toxin does not enter the cytosol and remains associated with the cell membrane by forming a large complex (Petit, L., Gibert, M., Gillet, D., Laurent-Winter, C., Boquet, P., and Popoff, M. R. (1997) J. Bacteriol. 179, 6480-6487). Here, we report that epsilon toxin induced in Madin-Darby canine kidney cells a rapid decrease of intracellular K(+), and an increase of Cl(-) and Na(+), whereas the increase of Ca(2+) occurred later. The entry of propidium iodide that was correlated with the loss of cell viability monitored by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test indicates that epsilon toxin formed large pores. In artificial lipid bilayers, epsilon toxin caused current steps with a single-channel conductance of 60 pS in 100 mm KCl, which represented general diffusion pores. The channels were slightly selective for anions, but cations could also penetrate. Epsilon toxin formed wide and water-filled channels permeable to hydrophilic solutes up to a molecular mass of at least 1 kDa, which probably represents the basic mechanism of toxin action on target cells.