Cytotonic effect ofClostridium difficileenterotoxin on Chinese hamster ovary cells

Recombinant Mucin-Type Fusion Proteins with a Galα1,3Gal Substitution as Clostridium difficile Toxin A Inhibitors

The capability of a recombinant mucin-like fusion protein, P-selectin glycoprotein ligand-1/mouse IgG2b (PSGL-1/mIgG2b), carrying Galα1,3Galβ1,4GlcNAc determinants to bind and inhibit Clostridium difficile toxin A (TcdA) was investigated. The fusion protein, produced by a glyco-engineered stable CHO-K1 cell line and designated C-PGC2, was purified by affinity and gel filtration chromatography from large-scale cultures. Liquid chromatography-mass spectrometry was used to characterize O-glycans released by reductive β-elimination, and new diagnostic ions to distinguish Galα1,3Gal- from Galα1,4Gal-terminated O-glycans were identified. The C-PGC2 cell line, which was 20-fold more sensitive to TcdA than the wild-type CHO-K1, is proposed as a novel cell-based model for TcdA cytotoxicity and neutralization assays. The C-PGC2-produced fusion protein could competitively inhibit TcdA binding to rabbit erythrocytes, making it a high-efficiency inhibitor of the hemagglutination property of TcdA. The fusion protein also exhibited a moderate capability for neutralization of TcdA cytotoxicity in both C-PGC2 and CHO-K1 cells, the former with and the latter without cell surface Galα1,3Galβ1,4GlcNAc sequences. Future studies in animal models of C. difficile infection will reveal its TcdA-inhibitory effect and therapeutic potential in C. difficile-associated diseases.

Local and systemic neutralizing antibody responses induced by intranasal immunization with the nontoxic binding domain of toxin A from Clostridium difficile

Fourteen of the 38 C-terminal repeats from Clostridium difficile toxin A (14CDTA) were cloned and expressed either with an N-terminal polyhistidine tag (14CDTA-HIS) or fused to the nontoxic binding domain from tetanus toxin (14CDTA-TETC). The recombinant proteins were successfully purified by bovine thyroglobulin affinity chromatography. Both C. difficile toxin A fusion proteins bound to known toxin A ligands present on the surface of rabbit erythrocytes. Intranasal immunization of BALB/c mice with three separate 10-microg doses of 14CDTA-HIS or -TETC generated significant levels of anti-toxin A serum antibodies compared to control animals. The coadministration of the mucosal adjuvant heat labile toxin (LT) from Escherichia coli (1 microg) significantly increased the anti-toxin A response in the serum and at the mucosal surface. Importantly, the local and systemic antibodies generated neutralized toxin A cytotoxicity. Impressive systemic and mucosal anti-toxin A responses were also seen following coadministration of 14CDTA-TETC with LTR72, an LT derivative with reduced toxicity which shows potential as a mucosal adjuvant for humans.

Toxins A and B of Clostridium difficile

The toxins produced by Clostridium difficile share several functional properties with other bacterial toxins, like the heat-labile enterotoxin of Escherichia coli and cholera toxin. However, functional and structural differences also exist. Like cholera toxin, their main target is the disruption of the microfilaments in the cell. However, since these effects are not reversible, as found with cholera toxin, additional mechanisms add to the cytotoxic potential of these toxins. Unlike most bacterial toxins, which are built from two structurally and functionally different small polypeptide chains, the functional and binding properties of the toxins of C. difficile are confined within one large polypeptide chain, making them the largest bacterial toxins known so far.

Clostridium difficile toxin A and its effects on cells

Clostridium difficile toxin A in its native form is a high molecular weight (520-540 K) aggregate with five major biological activities. It is lethal, enterotoxic, cytotoxic and cytotonic, and induces hemagglutination of rabbit red blood cells. Possibly these activities are contained in separate components. A major subunit of c. 230-310 K has been defined but lower molecular weight components cannot be excluded. The major component has been cloned, and sequence analysis indicated a complicated pattern of repeating sequences in the C-terminal third of the molecule. This review deals mainly with the effects of toxin A on cultured cells. Most mammalian cells are sensitive to toxin A whose major effect is to stop cell division irreversibly. The toxin binds via its repeat sequences to a trisaccharide receptor expressed on rabbit red cells and on brush border membranes from hamster intestine. This receptor seems to be functional in the hemagglutination reaction and the enterotoxicity. Its role in the cytotoxic effect of the toxin is not clear, but no other receptor structure has as yet been identified. In order to exert its cytotoxic (antiproliferative) effect toxin A must first be internalized by endocytosis. Thus a latency period of at least 30 min after toxin binding to cells is consistently observed, and all cytotoxic effects can be prevented by blocking the endocytosis pathway. The first microscopically visible signs of cytotoxicity consist in retraction and rounding of intoxicated cells. In addition the nucleus becomes polarized to one side of the cell while other cell organelles are not significantly affected. These morphological changes seem to be the consequence of a cytoskeletal rearrangement, mainly involving some components of the microfilament system. Inhibition of macromolecular syntheses as well as permeabilization of the plasma membrane may follow the early cytoskeletal effects and finally lead to cell death. Attempts to identify metabolic pathways of significance in the cytotoxicity suggest that the cytosolic level of Ca2+ is not important, thus excluding certain mechanisms for cell killing. In this respect the cytotoxic mode of action of toxin A clearly differs from that of toxin B. However, the biochemical basis for the antiproliferative effect of toxin A remains unknown.

Cytotoxic component(s) of Klebsiella oxytoca on HEp-2 cells

A cytotoxic component(s) was detected in culture filtrates of Klebsiella oxytoca isolated from patients with antibiotic-associated hemorrhagic colitis. Eleven of 12 isolates exhibited cytotoxicity on HEp-2 cells. The cytotoxic activity of K. oxytoca strain MH43-1 was stable for the treatment of 60 C for 30 min, but inactivated by the treatment of 100 C for 15 min. This cytotoxicity was not destroyed by the treatment with trypsin or pronase, and the component was filtrable through a membrane filter which cut off molecular weight 5,000.

Production, purification and characterization of Clostridium difficile toxic proteins different from toxin A and from toxin B

The purification and characterization of three new proteins called C1, C2, and C3 from Clostridium difficile are described. Their estimated molecular mass were about 350 (C1), 270 (C2) and 140 (C3) kDa, consisting of subunits of 39 (C1), 43 (C2) and 41 (C3) kDa, respectively. Immunodiffusion revealed that the three proteins contained similar but not identical antigenic determinants to toxin A. Each protein induced a cytotonic effect on hamster ovaric cells; the combined proteins, had a specific activity on cells 5-times higher than that of toxin A. In rat intestinal loops, they induced a clear fluid secretion, while toxin A elicited a haemorrhagic fluid response. The cytotonic activities of all three proteins were abolished by antiserum against toxin A, while antiserum against toxin B inhibited only the activity of the 270 kDa protein. In contrast to toxin A, the cytotoxicity of the three proteins was inactivated by trypsin. Thus, the chemical, antigenic and biological properties of these proteins differed from those of toxin A and toxin B.

Purification and some properties of cytotoxin produced by Clostridium difficile

The cytotoxin produced by Clostridium difficile was highly purified by using ammonium sulfate fractionation and successive column chromatographies of DEAE-Sephadex A-25, hydroxyapatite, Bio-Gel A-0.5m, Phenyl-Sepharose CL-4B, and Mono Q. The purified cytotoxin gave a single band on conventional and sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the presence of dithiothreitol. Its molecular weight was estimated to be 260,000 and 50,000 by gel filtration and sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis in the presence of dithiothreitol, respectively. Thus it was supposed that the toxin consists of 5 subunits having molecular weight of approximately 50,000. It had an isoelectric point of 6.6. The toxin was heat-labile (60 C for 10 min) and inactivated by treatment with trypsin and pronase, or at pH below 4 or over 10. The minimum cytotoxic dose of the cytotoxin against Chinese hamster ovary cells was 3 ng. It was also demonstrated that the toxin is antigenically different from enterotoxin of C. difficile.

Molecular cloning and expression of Clostridium difficile toxin A in Escherichia coli K12

Clostridium difficile toxin A was purified to homogeneity and was used to raise monospecific antiserum in rabbits. A gene bank of C. difficile DNA in Escherichia coli was constructed by cloning Sau3A-cleaved clostridial DNA fragments into the bacteriophage vector lambda EMBL3. Out of 4500 plaques screened with antitoxin A, 9 clones were positively identified. One of these clones lambda tA5 expressed a 235 kDa protein which exhibited a cytotonic effect on Chinese hamster ovary cells, and had the ability to haemagglutinate rabbit erythrocytes, both properties characteristic of toxin A. The size of the lambda tA5 insert DNA was 14.3 kb.

Purification of two high molecular weight toxins of Clostridium difficile which are antigenically related

Two Cl. difficile toxins were isolated from cultures of Cl. difficile strain VPI 10463. A purification procedure to prepare homogenous Cl. difficile toxins is given. This procedure allows purification of high molecular weight toxins A and B without using immunaffinity chromatography. The main step of the purification is the separation of a partially purified toxin preparation over a FPLC-Mono Q column by anion exchange chromatography. The experimental conditions for a rechromatography were determined to prepare the two major toxic activities as homogenous high molecular weight proteins. Our toxin A has a molecular weight (Mr) of ca. 300 kDa and an IP of 4.7. The Mr of our toxin B is ca. 250 kDa, the isoelectric focusing gives rise to two bands one at 4.7 and the other at 4.8. The two bands represent charge isomers as have been described for other bacterial toxins. Both toxins differ in cytotoxicity testing by a factor of 1000 but have the same activity when tested in vivo. Toxin specific monoclonal antibodies (mabs) were elicited by separate immunization of mice either with toxin A or toxin B, respectively. All of our mabs cross react with pure toxin A and toxin B when tested by ELISA or Western Blotting. Some mabs strongly cross react indicating that both toxins have major epitopes in common. A hypothesis for the structural and possible functional relatedness between the two toxins is discussed.