Proteolytic inactivation of MAP-kinase-kinase by anthrax lethal factor

Anthrax lethal toxin, produced by the bacterium Bacillus anthracis, is the major cause of death in animals infected with anthrax. One component of this toxin, lethal factor (LF), is suspected to be a metalloprotease, but no physiological substrates have been identified. Here it is shown that LF is a protease that cleaves the amino terminus of mitogen-activated protein kinase kinases 1 and 2 (MAPKK1 and MAPKK2) and that this cleavage inactivates MAPKK1 and inhibits the MAPK signal transduction pathway. The identification of a cleavage site for LF may facilitate the development of LF inhibitors.

Hemorrhagic metalloproteinases from snake venoms

One of the more significant consequences of crotalid envenomation is hemorrhage. Over the past 50 years of investigation, it is clear that the primary factors responsible for hemorrhage are metalloproteinases present in the venom of these snakes. The biochemical basis for their activity is the proteolytic destruction of basement membrane and extracellular matrix surrounding capillaries and small vessels. These proteinase toxins may also interfere with coagulation, thus complementing loss of blood from the vasculature. Structural studies have shown that these proteinases are synthesized as zymogens and are processed at both the amino and carboxy termini to give the mature protein. The variety of hemorrhagic toxins found in snake venoms is due to the presence of structurally related proteins composed of various domains. The type of domains found in each toxin plays an important role in the hemorrhagic potency of the protein. Recently, structural homologs to the venom hemorrhagic metalloproteinases have been identified in several mammalian reproductive systems. The functional significance of the reproductive proteins is not clear, but in light of the presence of similar domains shared with the venom metalloproteinases, their basic biochemical activities may be similar but with very different consequences. This review discusses the history of hemorrhagic toxin research with emphasis on the Crotalus atrox proteinases. The structural similarities observed among the hemorrhagic toxins are outlined, and the structural relationships of the toxins to the mammalian reproductive proteins are described.

Structure and function of tetanus and botulinum neurotoxins

Tetanus and botulinum neurotoxins are produced by Clostridia and cause the neuroparalytic syndromes of tetanus and botulism. Tetanus neurotoxin acts mainly at the CNS synapse, while the seven botulinum neurotoxins act peripherally. Clostridial neurotoxins share a similar mechanism of cell intoxication: they block the release of neurotransmitters. They are composed of two disulfide-linked polypeptide chains. The larger subunit is responsible for neurospecific binding and cell penetration. Reduction releases the smaller chain in the neuronal cytosol, where it displays its zinc-endopeptidase activity specific for protein components of the neuroexocytosis apparatus. Tetanus neurotoxin and botulinum neurotoxins B, D, F and G recognize specifically VAMP/ synaptobrevin. This integral protein of the synaptic vesicle membrane is cleaved at single peptide bonds, which differ for each neurotoxin. Botulinum A, and E neurotoxins recognize and cleave specifically SNAP-25, a protein of the presynaptic membrane, at two different sites within the carboxyl-terminus. Botulinum neurotoxin type C cleaves syntaxin, another protein of the nerve plasmalemma. These results indicate that VAMP, SNAP-25 and syntaxin play a central role in neuroexocytosis. These three proteins are conserved from yeast to humans and are essential in a variety of docking and fusion events in every cell. Tetanus and botulinum neurotoxins form a new group of zinc-endopeptidases with characteristic sequence, mode of zinc coordination, mechanism of activation and target recognition. They will be of great value in the unravelling of the mechanisms of exocytosis and endocytosis, as they are in the clinical treatment of dystonias.

A possible role of Bacteroides fragilis enterotoxin in the aetiology of colorectal cancer

The prevalence of enterotoxigenic Bacteroides fragilis (ETBF) was investigated in stool specimens from 73 patients with colorectal cancer and from 59 control patients. Stool specimens were cultured on Bacteroides Bile Esculin agar and B. fragilis was identified by conventional methods. After DNA extraction, the enterotoxin gene (bft) was detected by PCR in 38% of the isolates from colorectal cancer patients, compared with 12% of the isolates from the control group (p 0.009). This is the first study demonstrating an increased prevalence of ETBF in colorectal cancer patients.

Induction of persistent colitis by a human commensal, enterotoxigenic Bacteroides fragilis, in wild-type C57BL/6 mice

Enterotoxigenic Bacteroides fragilis (ETBF) causes diarrhea and is implicated in inflammatory bowel diseases and colorectal cancer. The only known ETBF virulence factor is the Bacteroides fragilis toxin (BFT), which induces E-cadherin cleavage, interleukin-8 secretion, and epithelial cell proliferation. A murine model for ETBF has not been characterized. Specific pathogen-free (SPF) C57BL/6J or germfree 129S6/SvEv mice were orally inoculated with wild-type ETBF (WT-ETBF) strains, a nontoxigenic WT strain of B. fragilis (WT-NTBF), WT-NTBF overexpressing bft (rETBF), or WT-NTBF overexpressing a biologically inactive mutated bft (rNTBF). In SPF and germfree mice, ETBF caused colitis but was lethal only in germfree mice. Colonic histopathology demonstrated mucosal thickening with inflammatory cell infiltration, crypt abscesses, and epithelial cell exfoliation, erosion, and ulceration. SPF mice colonized with rETBF mimicked WT-ETBF, whereas rNTBF caused no histopathology. Intestinal epithelial E-cadherin was rapidly cleaved in vivo in WT-ETBF-colonized mice and in vitro in intestinal tissues cultured with purified BFT. ETBF mice colonized for 16 months exhibited persistent colitis. BFT did not directly induce lymphocyte proliferation, dendritic cell stimulation, or Toll-like receptor activation. In conclusion, WT-ETBF induced acute then persistent colitis in SPF mice and rapidly lethal colitis in WT germfree mice. Our data support the hypothesis that chronic colonization with the human commensal ETBF can induce persistent, subclinical colitis in humans.

Insights into the mechanism of haemorrhage caused by snake venom metalloproteinases

Local and systemic haemorrhage are common consequences of crotaline and viperine envenoming. Several studies carried out using purified toxins have indicated that local haemorrhage can be attributed to a distinct class of venom metalloproteinases. Analyses of their cDNAs predict multi-domain enzymes, with an N-terminal metalloproteinase domain, a disintegrin-like domain and a Cys-rich C-terminus. Haemorrhagic metalloproteinases are responsible for degrading proteins of the extracellular matrix and they also have cytotoxic effects on endothelial cells. However, to date very few investigations have been carried out on the effects of venom haemorrhagic metalloproteinases on components of the haemostatic system. We describe here the effects of a high molecular weight haemorrhagic metalloproteinase, jararhagin, from the venom of a South American pit viper Bothrops jararaca, on platelet and plasma components involved in haemostasis. Jararhagin, which is not inhibited in plasma, causes the loss of the platelet collagen receptor alpha 2 beta 1 integrin (gpIa/IIa or VLA-2) and degrades the adhesive plasma protein von Willebrand factor. Alterations of these haemostatic components are known to result in bleeding. This suggests that venom haemorrhagic metalloproteinases, in addition to causing local bleeding, may also contribute to systemic haemorrhage.

Hemorrhage Caused by Snake Venom Metalloproteinases: A Journey of Discovery and Understanding

The historical development of discoveries and conceptual frames for understanding the hemorrhagic activity induced by viperid snake venoms and by hemorrhagic metalloproteinases (SVMPs) present in these venoms is reviewed. Histological and ultrastructural tools allowed the identification of the capillary network as the main site of action of SVMPs. After years of debate, biochemical developments demonstrated that all hemorrhagic toxins in viperid venoms are zinc-dependent metalloproteinases. Hemorrhagic SVMPs act by initially hydrolyzing key substrates at the basement membrane (BM) of capillaries. This degradation results in the weakening of the mechanical stability of the capillary wall, which becomes distended owing of the action of the hemodynamic biophysical forces operating in the circulation. As a consequence, the capillary wall is disrupted and extravasation occurs. SVMPs do not induce rapid toxicity to endothelial cells, and the pathological effects described in these cells in vivo result from the mechanical action of these hemodynamic forces. Experimental evidence suggests that degradation of type IV collagen, and perhaps also perlecan, is the key event in the onset of microvessel damage. It is necessary to study this phenomenon from a holistic, systemic perspective in which the action of other venom components is also taken into consideration.

Isolation and characterization of a metalloproteinase with weak hemorrhagic activity from the venom of the snake Bothrops asper (terciopelo)

A metalloproteinase, named BaP1, was purified to homogeneity from the venom of Bothrops asper (Pacific region) of Costa Rica by ion-exchange chromatography on CM-Sephadex and gel filtration on Sephacryl S-200. The enzyme has a mol. wt of 24,000 and contains few Cys and high numbers of Asp, Leu, Ser and Glu. BaP1 hydrolyzes casein, hide powder azure and fibrinogen, having an optimal pH of 8.0. It rapidly digests the A alpha-chain of fibrinogen and, later on, the B beta-chain, leaving the gamma-chain unaffected. Chelating agents (EDTA and 1,10-phenanthroline) inhibited proteolytic activity, whereas 2-mercaptoethanol and soybean trypsin inhibitor did not affect this activity. BaP1 has a weak hemorrhagic activity, with a minimum hemorrhagic dose of 20 micrograms; this activity was inhibited by EDTA and was abolished after incubation at 60 degrees C. In addition, BaP1 induces edema and a mild myotoxic effect, lacking coagulant, defibrinating and lethal effects.

Tetanus and botulinum neurotoxins are zinc proteases specific for components of the neuroexocytosis apparatus

Tetanus and botulinum neurotoxins bind to nerve cells, penetrate the cytosol, and block neurotransmitter release. Comparison of their amino-acid sequences shows the presence of the highly conserved His-Glu-x-x-His zinc-binding motif of zinc-endopeptidases (HExxH). Atomic absorption measurements of clostridial neurotoxins show the presence of one atom of zinc/toxin molecule bound to the light chain. The toxin-bound zinc ion is essential for the neurotoxins inhibition of neurotransmitter release in Aplysia neurons injected with the toxins. Phosphoramidon, a very specific inhibitor of zinc-endopeptidases, blocks the intracellular activity of the clostridial neurotoxins. Highly purified preparations of the light chain of tetanus and botulinum B and F neurotoxins cleaved specifically VAMP/synaptobrevin, an integral membrane protein of small synaptic vesicles, both in vivo and in vitro. From these studies, it can be concluded that the clostridial neurotoxins responsible for tetanus and botulism block neuroexocytosis via the proteolytic cleavage of specific components of the neuroexocytotic machinery.

Mechanisms of vascular damage by hemorrhagic snake venom metalloproteinases: tissue distribution and in situ hydrolysis

BACKGROUND

Envenoming by viper snakes constitutes an important public health problem in Brazil and other developing countries. Local hemorrhage is an important symptom of these accidents and is correlated with the action of snake venom metalloproteinases (SVMPs). The degradation of vascular basement membrane has been proposed as a key event for the capillary vessel disruption. However, SVMPs that present similar catalytic activity towards extracellular matrix proteins differ in their hemorrhagic activity, suggesting that other mechanisms might be contributing to the accumulation of SVMPs at the snakebite area allowing capillary disruption.

METHODOLOGY/PRINCIPAL FINDINGS

In this work, we compared the tissue distribution and degradation of extracellular matrix proteins induced by jararhagin (highly hemorrhagic SVMP) and BnP1 (weakly hemorrhagic SVMP) using the mouse skin as experimental model. Jararhagin induced strong hemorrhage accompanied by hydrolysis of collagen fibers in the hypodermis and a marked degradation of type IV collagen at the vascular basement membrane. In contrast, BnP1 induced only a mild hemorrhage and did not disrupt collagen fibers or type IV collagen. Injection of Alexa488-labeled jararhagin revealed fluorescent staining around capillary vessels and co-localization with basement membrane type IV collagen. The same distribution pattern was detected with jararhagin-C (disintegrin-like/cysteine-rich domains of jararhagin). In opposition, BnP1 did not accumulate in the tissues.

CONCLUSIONS/SIGNIFICANCE

These results show a particular tissue distribution of hemorrhagic toxins accumulating at the basement membrane. This probably occurs through binding to collagens, which are drastically hydrolyzed at the sites of hemorrhagic lesions. Toxin accumulation near blood vessels explains enhanced catalysis of basement membrane components, resulting in the strong hemorrhagic activity of SVMPs. This is a novel mechanism that underlies the difference between hemorrhagic and non-hemorrhagic SVMPs, improving the understanding of snakebite pathology.

Local tissue damage induced by BaP1, a metalloproteinase isolated from Bothrops asper (Terciopelo) snake venom

The pathogenesis of hemorrhage and other local effects induced by the metalloproteinase BaP1, isolated from Bothrops asper venom, was investigated using various in vivo and in vitro models. Upon intramuscular injection in mice BaP1 caused rapid hemorrhage in muscular and adipose tissues. Vital microscopy using mouse cremaster muscle evidenced the formation of multiple hemorrhagic foci of an explosive character, originating from capillaries and small venules. In contrast to crude B. asper venom, which besides hemorrhage also induced myonecrosis and thrombosis, vital microscopy detected only hemorrhage after application of BaP1, during the 40-min observation period. However, histological observation in mouse gastrocnemius muscle evidenced a few areas of limited myonecrosis was followed by an incomplete regenerative response, since regenerating muscle fibers were interspersed with fibrosis in some areas. Metalloproteinase BaP1 was not cytotoxic to human and murine endothelial cells in culture, causing only a mild detachment from the culture plate. BaP1 hydrolyzed types I and IV collagen, fibronectin, and laminin upon incubation with these extracellular matrix proteins in vitro. These results suggest that hemorrhage induced by BaP1 is due primarily to the proteolytic degradation to basement membrane components of microvessels and that endothelial cell disruption may be a secondary event. It is concluded that, in addition to hemorrhage, BaP1 contributes to the local tissue damage caused by the venom by inducing myonecrosis, inflammation, and extracellular matrix alterations.

Bacterial infection of a model insect: Photorhabdus luminescens and Manduca sexta

Invertebrates, including insects, are being developed as model systems for the study of bacterial virulence. However, we understand little of the interaction between bacteria and specific invertebrate tissues or the immune system. To establish an infection model for Photorhabdus, which is released directly into the insect blood system by its nematode symbiont, we document the number and location of recoverable bacteria found during infection of Manduca sexta. After injection into the insect larva, P. luminescens multiplies in both the midgut and haemolymph, only later colonizing the fat body and the remaining tissues of the cadaver. Bacteria persist by suppressing haemocyte-mediated phagocytosis and culture supernatants grown in vitro, as well as plasma from infected insects, suppress phagocytosis of P. luminescens. Using GFP-labelled bacteria, we show that colonization of the gut begins at the anterior of the midgut and proceeds posteriorly. Within the midgut, P. luminescens occupies a specific niche between the extracellular matrix and basal membrane (lamina) of the folded midgut epithelium. Here, the bacteria express the gut-active Toxin complex A (Tca) and an RTX-like metalloprotease PrtA. This close association of the bacteria with the gut, and the production of toxins and protease, triggers a massive programmed cell death of the midgut epithelium.

The toxins of Bacteroides fragilis

Bacteroides fragilis are both key commensals and important human pathogens. Particular strains of B. fragilis, termed enterotoxigenic B. fragilis (ETBF), are recently identified enteric pathogens of children and adults. These strains are distinguished by secretion of a 20kDa metalloprotease toxin (B. fragilis toxin or BFT), the first recognized and only established toxin to date for B. fragilis. Three isotypes of BFT are encoded by distinct bft loci contained within a 6kb chromosomal region unique to ETBF strains termed the B. fragilis pathogenicity island (BfPAI). Experimental studies have suggested that the cellular target for BFT is E-cadherin, the primary protein of the zonula adherens. It is postulated that BFT cleavage of E-cadherin is critical in precipitating the intracellular events culminating in the two established activities for BFT; namely, stimulation of secretion in ligated intestinal segments in several animal species and alteration of cellular morphology only in epithelial cells that retain the ability to polarize and form a tight junctional complex. Future studies will be directed to characterizing in greater detail both the molecular genetics of the BFT toxin and the precise steps in its cellular mechanism of action.

Identification, cloning, expression and functional characterization of an astacin-like metalloprotease toxin from Loxosceles intermedia (brown spider) venom

Injuries caused by brown spiders (Loxosceles genus) are associated with dermonecrotic lesions with gravitational spreading and systemic manifestations. The venom has a complex composition containing many different toxins, of which metalloproteases have been described in many different species of this genus. These toxins may degrade extracellular matrix constituents acting as a spreading factor. By using a cDNA library from an Loxosceles intermedia venom gland, we cloned and expressed a 900 bp cDNA, which encoded a signal peptide and a propeptide, which corresponded to a 30 kDa metalloprotease, now named LALP (Loxosceles astacin-like protease). Recombinant LALP was refolded and used to produce a polyclonal antiserum, which showed cross-reactivity with a 29 kDa native venom protein. CD analysis provided evidence that the recombinant LALP toxin was folded correctly, was still in a native conformation and had not aggregated. LALP addition to endothelial cell cultures resulted in de-adhesion of the cells, and also in the degradation of fibronectin and fibrinogen (this could be inhibited by the presence of the bivalent chelator 1,10-phenanthroline) and of gelatin in vitro. Sequence comparison (nucleotide and deduced amino acid), phylogenetic analysis and analysis of the functional recombinant toxin revealed that LALP is related in both structure and function to the astacin family of metalloproteases. This suggests that an astacin-like toxin is present in a animal venom secretion and indicates that recombinant LALP will be a useful tool for future structural and functional studies on venom and the astacin family.

The Bacteroides fragilis toxin fragilysin disrupts the paracellular barrier of epithelial cells

Bacteroides fragilis is a member of the normal colonic microflora of most mammals and is the most commonly isolated anaerobe from human clinical specimens. Some strains produce a toxin (fragilysin, a zinc-metalloproteinase) implicated as a cause of diarrheal disease in farm animals and humans. Studies in our laboratory confirm that the proteolytic activity of this toxin is responsible for the fluid secretion and tissue damage observed in vivo. In this study, we investigated the effects of fragilysin on the paracellular barrier of epithelial cells. Researchers suggest that, since the toxin rapidly intoxicates HT-29 cells, it may be internalized. However, we could not prevent cell rounding by using inhibitors of receptor-mediated endocytosis, which indicates that the toxin may act outside the cell. Based on these observations, we studied the effects of the highly purified B. fragilis fragilysin on the barrier function of cultured epithelial cells. Fragilysin rapidly increased the permeability of the paracellular barrier of epithelial cells to ions (decrease in electrical resistance across monolayers) and to larger molecules (increase in mannitol flux across monolayers). We tested a human colon cell line and cell lines from the lung and the kidney; the human colon cell line was most sensitive, but all three were affected in the same manner. Our studies show that B. fragilis fragilysin alters the barrier function of the epithelial lining, possibly by degrading the tight junction proteins, such as ZO-1. The proteolytic activity is required to cause this effect. The toxin's action has been assumed to be limited to the intestine; however, our studies show that fragilysin could also contribute to the pathogenesis of B. fragilis in extraintestinal infections.

Effectiveness of batimastat, a synthetic inhibitor of matrix metalloproteinases, in neutralizing local tissue damage induced by BaP1, a hemorrhagic metalloproteinase from the venom of the snake bothrops asper

Batimastat (BB-94), a synthetic hydroxamate peptidomimetic matrix metalloproteinase inhibitor, was tested for its ability to inhibit proteolytic and toxic effects induced by BaP1, a 24-kDa hemorrhagic metalloproteinase isolated from the venom of Bothrops asper, the medically most important snake species in Central America and southern Mexico. Batimastat inhibited proteolytic activity on biotinylated casein, with anIC(50) of 80 nM. In addition, batimastat was effective in inhibiting hemorrhagic, dermonecrotic, and edema-forming activities of this metalloproteinase if incubated with the enzyme prior to the assays. When the inhibitor was administered i.m. at the site of the toxin injection without preincubation, rapidly after metalloproteinase administration, it totally abrogated the hemorrhagic and dermonecrotic effects of BaP1. Inhibition was less effective as the time lapse between toxin and batimastat injection increased, due to the extremely rapid development of BaP1-induced local tissue damage in this experimental model. On the other hand, batimastat was ineffective if administered by the i.p. route immediately after toxin injection. It is concluded that batimastat, and probably other synthetic metalloproteinase inhibitors, may become useful therapeutic tools aimed at the in situ inhibition of venom metalloproteinases, when injected at the site of the bite rapidly after envenomation.

Hemolysin and the multifunctional autoprocessing RTX toxin are virulence factors during intestinal infection of mice with Vibrio cholerae El Tor O1 strains

The seventh cholera pandemic that started in 1961 was caused by Vibrio cholerae O1 strains of the El Tor biotype. These strains produce the pore-forming toxin hemolysin, a characteristic used clinically to distinguish classical and El Tor biotypes. Even though extensive in vitro data on the cytolytic activities of hemolysin exist, the connection of hemolysin to virulence in vivo is not well characterized. To study the contribution of hemolysin and other accessory toxins to pathogenesis, we utilized the model of intestinal infection in adult mice sensitive to the actions of accessory toxins. In this study, we showed that 4- to 6-week-old streptomycin-fed C57BL/6 mice were susceptible to intestinal infection with El Tor strains, which caused rapid death at high doses. Hemolysin had the predominant role in lethality, with a secondary contribution by the multifunctional autoprocessing RTX (MARTX) toxin. Cholera toxin and hemagglutinin/protease did not contribute to lethality in this model. Rapid death was not caused by increased dissemination due to a damaged epithelium since the numbers of CFU recovered from spleens and livers 6 h after infection did not differ between mice inoculated with hemolysin-expressing strains and those infected with non-hemolysin-expressing strains. Although accessory toxins were linked to virulence, a strain defective in the production of accessory toxins was still immunogenic since mice immunized with a multitoxin-deficient strain were protected from a subsequent lethal challenge with the wild type. These data suggest that hemolysin and MARTX toxin contribute to vaccine reactogenicity but that the genes for these toxins can be deleted from vaccine strains without affecting vaccine efficacy.

Prolonged colonization of mice by Vibrio cholerae El Tor O1 depends on accessory toxins

Cholera epidemics caused by Vibrio cholerae El Tor O1 strains are typified by a large number of asymptomatic carriers who excrete vibrios but do not develop diarrhea. This carriage state was important for the spread of the seventh cholera pandemic as the bacterium was mobilized geographically, allowing the global dispersion of this less virulent strain. Virulence factors associated with the development of the carriage state have not been previously identified. We have developed an animal model of cholera in adult C57BL/6 mice wherein V. cholerae colonizes the mucus layer and forms microcolonies in the crypts of the distal small bowel. Colonization occurred 1 to 3 h after oral inoculation and peaked at 10 to 12 h, when bacterial loads exceeded the inoculum by 10- to 200-fold, indicating bacterial growth within the small intestine. After a clearance phase, the number of bacteria within the small intestine, but not those in the cecum or colon, stabilized and persisted for at least 72 h. The ability of V. cholerae to prevent clearance and establish this prolonged colonization was associated with the accessory toxins hemolysin, the multifunctional autoprocessing RTX toxin, and hemagglutinin/protease and did not require cholera toxin or toxin-coregulated pili. The defect in colonization attributed to the loss of the accessory toxins may be extracellularly complemented by inoculation of the defective strain with an isogenic colonization-proficient V. cholerae strain. This work thus demonstrates that secreted accessory toxins modify the host environment to enable prolonged colonization of the small intestine in the absence of overt disease symptoms and thereby contribute to disease dissemination via asymptomatic carriers.

Proteolytic activity of the Bacteroides fragilis enterotoxin causes fluid secretion and intestinal damage in vivo

Strains of Bacteroides fragilis that produce an enterotoxin have been implicated in diarrheal disease in farm animals and humans during the past decade. Our laboratory has purified and characterized this enterotoxin as a single polypeptide (M(r), approximately 20,000). Recently, we used PCR to clone and sequence the enterotoxin gene from B. fragilis and showed that it exhibits significant homology with extracellular metalloproteases. Further studies showed that the purified enterotoxin has protease activity. To further characterize the role of this enterotoxin in diarrheal disease, we studied the histological and pathological effects of highly purified B. fragilis enterotoxin in lamb, rabbit, and rat ligated intestinal loops. When the enterotoxin was injected into ligated ileal and colonic loops, there was significant tissue damage and subsequent fluid accumulation. The fluid response in the ileum was greater in lambs than in rabbits and rats, whereas the fluid response in the colon was greater in rabbits than in lambs and rats. Analysis of the intestinal fluid elicited by the enterotoxin revealed an accumulation of chloride and sodium as well as albumin and total protein. Histological examination revealed mild necrosis of epithelial cells, crypt elongation, villus attenuation, and hyperplasia. There was extensive detachment and rounding of surface epithelial cells and an infiltration of neutrophils. Enterotoxic activity was inhibited by the metal chelators EDTA and 1,10-phenanthroline; to some degree, the enterotoxic activity could be reconstituted by the addition of zinc to the chelated enterotoxin. Our results indicate that the enterotoxin elicits a significant fluid response subsequent to tissue damage in the small and large intestine. These data further support the idea that this enterotoxin is an important virulence factor in B. fragilis-associated diarrhea.

Inflammatory pathogenesis of snake venom metalloproteinase-induced skin necrosis

Local tissue damage, characterized by edema, hemorrhage and necrosis, is a common consequence of envenoming by many vipers. We have investigated the contribution of inflammatory responses induced by the venom metalloproteinase jararhagin (isolated from Bothrops jararaca venom) in the development of these lesions. Local venom effects (edema, hemorrhage and necrosis) were induced experimentally in knockout mice deficient in the TNF receptors TNFR1 or TNFR2, IL-1betaR, IL-6 and iNOS. Jararhagin-induced dermal necrosis was abolished in mice deficient in the TNF receptors TNFR1 and TNFR2, and the same activity was significantly reduced in IL-6(-/-) mice. There was no significant difference in edema and hemorrhage activities following jararhagin insult between knockout and WT strains, indicating that these local venom metalloproteinase-induced effects are independent of these pro-inflammatory mediators. The contribution of both TNF receptors and IL-6 in local tissue necrosis raises important therapeutic issues regarding the treatment of local envenoming.

Purification and characterization of an extracellular protease from Pseudomonas cepacia

An extracellular proteinase (PSCP) produced by Pseudomonas cepacia was purified from culture supernatants by ammonium sulfate precipitation, anion exchange chromatography on DEAE-Sephacel, and G200 gel filtration chromatography. The protease has an apparent Mr of 34,000 by electrophoresis. Substrates cleaved by the protease include gelatin, hide powder, and collagen but not human immunoglobulin G (IgG), IgM, secretory IgA, or IgA. The enzyme had the characteristics of a metalloprotease, a pH optimum of 6, and a temperature optimum of 45 degrees C. Intratracheal instillation of purified PSCP into rat lungs produced a bronchopneumonia characterized by polymorphonuclear cell infiltration and proteinaceous exudation into large airways. Rats responded immunologically to active immunization with PSCP, but this response was not protective against subsequent lung infection with P. cepacia. PSCP was shown to have antigenic similarity with Pseudomonas aeruginosa elastase by an immunoblotting technique. Sera from 10 cystic fibrosis patients, with and without a previous history of P. cepacia colonization, were shown to possess antibody reactive against PSCP.

Botulinum neurotoxin serotypes A and B preparations have different safety margins in preclinical models of muscle weakening efficacy and systemic safety

This preclinical study compared the muscle weakening efficacy, duration, and safety margin of the recently approved botulinum toxin type B (BTX-B; Myobloc/Neurobloc) to botulinum toxin type A (BTX-A; BOTOX((R))). Mice received a single hind limb intramuscular injection of BTX-B (1-150U/kg) or BTX-A (1-120U/kg). An observer who was masked to treatment assessed the magnitude and duration of muscle weakening efficacy on a 0-4 scale using the digit abduction scoring assay. Safety margins were determined as the ratio of the IM median lethal dose to the IM dose that produced half-maximal muscle weakness in the DAS. BTX-A produced muscle weakness at lower doses than BTX-B (IM ED(50): 6.2+/-0.6 vs. 20.8+/-1.4U/kg, respectively) (p<0.0001). BTX-A at 29U/kg and BTX-B at 67U/kg produced comparable peak DAS scores of approximately 4 indicating maximal muscle weakness. At these doses, the duration of BTX-A was longer, with a return to baseline by day 36 compared to a return to baseline by day 14 with BTX-B. The mean dose that was lethal in 50% of mice was lower for BTX-A than BTX-B (81.4+/-3.5 vs. 104.6+/-1.9U/kg, respectively) (p<0.001) and the safety margin was higher (13.9+/-1.7 vs. 5.4+/-0.3, respectively (p<0.001). These results indicate that the BTX-A:BTX-B dose ratio for muscle weakening efficacy is different from the ratio for systemic effects following IM injections and suggest that no single dose ratio is adequate to compare these preparations. The in vivo differences found are consistent with the different clinical profiles reported for these two products.

Botulinum A like type B and tetanus toxins fulfils criteria for being a zinc-dependent protease

Although botulinum neurotoxin (BoNT) types A and B and tetanus toxin (TeTx) are specific inhibitors of transmitter release whose light chains contain a zinc-binding motif characteristic of metalloendoproteases, only the latter two proteolyse synaptobrevin. Chelation of zinc or its readdition at high concentration hindered blockade of neuromuscular transmission by BoNT/A and B, indicating that type A also acts via a zinc-dependent mechanism. Such treatments prevented proteolysis of synaptobrevin II in rat brain synaptic vesicles by BoNT/B and TeTx but only the activity of the latter was antagonised appreciably by ASQFETS, a peptide spanning their cleavage site. The toxin's neuroparalytic activities were attenuated by phosphoramidon or captopril, inhibitors of certain zinc requiring proteases. However, these agents were ineffective in reducing the toxins' degradation of synaptobrevin except that a high concentration of captopril partially blocked the activity of TeTx but not BoNT/B, as also found for these drugs when tested on synaptosomal noradrenaline release. These various criteria establish that a zinc-dependent protease activity underlies the neurotoxicity of BoNT/A, a finding confirmed at motor nerve endings for type B and TeTx. Moreover, the low potencies of captopril and phosphoramidon in counteracting the toxins' effects necessitate the design of improved inhibitors for possible use in the clinical treatment of tetanus or botulism.

Purification and characterization of BaH4, a hemorrhagic metalloproteinase from the venom of the snake Bothrops asper

A hemorrhagic metalloproteinase, named BaH4, was isolated from the venom of the snake Bothrops asper by a combination of ion-exchange chromatography on DEAE-Sepharose and gel filtration on Sephacryl S-200. BaH4 is a 69 kDa protein with a pI of 5.3. It was recognized by antibodies raised against hemorrhagic metalloproteinase BaH1 isolated from B. asper venom, with a reaction of partial immunologic identity. BaH4 shows proteolytic activity on biotinylated casein, hide powder azure and fibrin, although having lower activity than crude B. asper venom and metalloproteinase BaP1 isolated from the same venom. BaH4 hydrolyzed fibronectin, laminin and type IV collagen in vitro, albeit at a relatively high enzyme:substrate ratio. Proteolytic activity was inhibited by chelating agents and 2-mercaptoethanol, but not by soybean trypsin inhibitor. Prominent hemorrhage developed in gastrocnemius and cremaster muscles after administration of BaH4. Moreover, it induced lethality in mice after intravenous injection, with an LD50 of 0.37 microg/g. Histological observations showed conspicuous pulmonary hemorrhage when the enzyme was injected intravenously. BaH4 is a hemorrhagic metalloproteinase which may play a relevant role in local and systemic bleeding characteristic of B. asper envenomations.

Vibrio cholerae hemagglutinin/protease (HA/protease) causes morphological changes in cultured epithelial cells and perturbs their paracellular barrier function

In this report, we describe the cytotoxic activity of the cholera hemagglutinin/protease (HA/protease). A concentrated protein sample from the 37 degrees C overnight culture supernatant of CVD110, a delta ctxA, delta zot, delta Ace and hlyA::(ctxB mer) mutant of El Tor biotype Ogawa serotype strain E7946 caused morphological changes in cultured MDCK-I epithelial cells and altered their arrangement of filamentous actin (F-actin) and Zonula occludens-associated protein ZO-1. The drastic morphological changes can be inhibited by Zincov, a specific bacterial metalloprotease inhibitor. The cytotoxic fractions of the sample after FPLC gelfiltration fractionation showed two visible protein bands with molecular weights of approximately 34- and 32 kDa. Microsequencing of these two proteins revealed that they were the cholera HA/protease.