Clostridium botulinum toxins

Recent Advances in Aptamer-Based Biosensors for Bacterial Detection

The rapid and sensitive detection of pathogenic bacteria is becoming increasingly important for the timely prevention of contamination and the treatment of infections. Biosensors based on nucleic acid aptamers, integrated with optical, electrochemical, and mass-sensitive analytical techniques, have garnered intense interest because of their versatility, cost-efficiency, and ability to exhibit high affinity and specificity in binding bacterial biomarkers, toxins, and whole cells. This review highlights the development of aptamers, their structural characterization, and the chemical modifications enabling optimized recognition properties and enhanced stability in complex biological matrices. Furthermore, recent examples of aptasensors for the detection of bacterial cells, biomarkers, and toxins are discussed. Finally, we explore the barriers to and discuss perspectives on the application of aptamer-based bacterial detection.

Critical analysis in the advancement of cell-based assays for botulinum neurotoxin

The study on botulinum neurotoxins (BoNTs) has rapidly evolved for their structure and functions as opposed to them being poisons or cures. Since their discoveries, the scientific community has come a long way in understanding BoNTs' structure and biological activity. Given its current application as a tool for understanding neurocellular activity and as a drug against over 800 neurological disorders, relevant and sensitive assays have become critical for biochemical, physiological, and pharmacological studies. The natural entry of the toxin being ingestion, it has also become important to examine its mechanism while crossing the epithelial cell barrier. Several techniques and methodologies have been developed, for its entry, pharmacokinetics, and biological activity for identification, and drug efficacy both in vivo and in vitro conditions. However, each of them presents its own challenges. The cell-based assay is a platform that exceeds the sensitivity of mouse bioassay while encompassing all the steps of intoxication including cell binding, transcytosis, endocytosis, translocation and proteolytic activity. In this article we review in detail both the neuronal and nonneuronal based cellular interaction of BoNT involving its transportation, and interaction with the targeted cells, and intracellular activities.

Molecular engineering of a minimal E-cadherin inhibitor protein derived from Clostridium botulinum hemagglutinin

Hemagglutinin (HA), a nontoxic component of the botulinum neurotoxin (BoNT) complex, binds to E-cadherin and inhibits E-cadherin-mediated cell-cell adhesion. HA is a 470 kDa protein complex comprising six HA1, three HA2, and three HA3 subcomponents. Thus, to prepare recombinant full-length HA in vitro, it is necessary to reconstitute the macromolecular complex from purified HA subcomponents, which involves multiple purification steps. In this study, we developed NanoHA, a minimal E-cadherin inhibitor protein derived from Clostridium botulinum HA with a simple purification strategy needed for production. NanoHA, containing HA2 and a truncated mutant of HA3 (amino acids 380-626; termed as HA3^mini), is a 47 kDa single polypeptide (one-tenth the molecular weight of full-length HA, 470 kDa) engineered with three types of modifications: (i) a short linker sequence between the C terminus of HA2 and N terminus of HA3; (ii) a chimeric complex composed of HA2 derived from the serotype C BoNT complex and HA3^mini from the serotype B BoNT complex; and (iii) three amino acid substitutions from hydrophobic to hydrophilic residues on the protein surface. We demonstrated that NanoHA inhibits E-cadherin-mediated cell-cell adhesion of epithelial cells (e.g., Caco-2 and Madin-Darby canine kidney cells) and disrupts their epithelial barrier. Finally, unlike full-length HA, NanoHA can be transported from the basolateral side to adherens junctions via passive diffusion. Overall, these results indicate that the rational design of NanoHA provides a minimal E-cadherin inhibitor with a wide variety of applications as a lead molecule and for further molecular engineering.

Complete subunit structure of serotype C and D botulinum progenitor toxin complex induces vacuolation in the specific epithelial cell line

Clostridium botulinum produces seven botulinum neurotoxin (BoNT) serotypes. In nature, BoNT exists as a part of the progenitor toxin complex (PTC) through associations with neurotoxin associated proteins (NAPs), including nontoxic nonhemagglutinin and hemagglutinin (HA) complex, consists of HA-70, HA-17 and HA-33. Because PTC displays higher oral toxicity than pure BoNTs, NAPs play a critical role in food poisoning. In a previous study, we demonstrated that the NAP complex in mature large-sized PTC (L-PTC) from serotypes C and D concomitantly induced cell death and cytoplasmic vacuolation in the rat intestinal epithelial cell line IEC-6. Here, we found that the serotype D NAP complex induces only cytoplasmic vacuolation in the normal rat kidney cell line NRK-52E without reducing cell viability. NAP complexes from serotype A and B L-PTCs did not affect cell viability or cytoplasmic vacuolation in IEC-6 and NRK-52E cells. Furthermore, we assessed the effect of immature L-PTCs with fewer HA-33/HA-17 trimers (two HA-33 and one HA-17) than mature L-PTCs on cell viability and cytoplasmic vacuolation in IEC-6 and NRK-52E cells. As a result, mature L-PTCs with the maximum number of HA-33/HA-17 trimers displayed the greatest potency. Consequently, the reduction in cell viability and vacuolation induction are related to the number of HA-33/HA-17 trimers in PTC. The discovery of an epithelial cell model where botulinum PTC specifically induces vacuolization may help clarify the unknown cytotoxicity of PTC, which plays an important role in the trans-epithelial transport of the toxin.

Pore Size-Dependent Stereoscopic Hydrogels Enhance the Therapeutic Efficiency of Botulinum Toxin for the Treatment of Nerve-Related Diseases

Botulinum toxin (BoNT) is a major neurotherapeutic protein that has been used at low doses for diverse pharmacological applications. However, the pleiotropic effect of BoNT depends on multiple periodic injections owing to its rapid elimination profile, short-term therapeutic effect, and high mortality rate when administered at high doses. In addition to low patient compliance, these drawbacks represent the significant challenges that limit the further clinical use of BoNT. This study developed a new hydrogel-based single dosage form of BoNT by employing a one-step cross-linking chemistry. Its controlled porous structures and composition facilitated uniform drug distribution inside the hydrogel and controllable release of BoNT mediated by slow diffusion. A single dose remained stable for at least 2.5 months and showed sustained effect for at least 20 weeks, meeting the requirements for a single-dose form of BoNT. Additionally, this dosage form was evaluated as safe from all aspects of toxicology. This delivery system resulted in a 100% survival rate after administering a BoNT dose of 30 units, while a dose of more than 5 units of naked BoNT caused a 100% mortality rate within a few days. Overall, this strategy could provide patients with the first single-dose treatment option of BoNT and improve their quality of life.

Multi-dimensional nanoscale liquid chromatography and nano-electrospray ion-trap mass spectrometry for detection of Clostridium botulinum type C and the produced botulinum neurotoxin type C complex

Botulinum neurotoxin types C, D and their mosaic forms C/D and D/C produced mainly by Clostridium botulinum types C and D cause botulism in animals and belong to the most toxic substances for poultry and fish. In addition to intoxications, also toxoinfections with C. botulinum types C and D play a role that should not be underestimated, especially in veterinary medicine. Contrary to other botulinum neurotoxin complexes (BT x), the biosynthesis of these types is phage-encoded. Currently, the gold standard for neurotoxin detection in cases of clinical botulism is the mouse bioassay. In the last few years, alternatives for replacing this mouse bioassay have become increasingly interesting for the detection and characterisation of botulinum neurotoxins. Therefore, immunological techniques based mainly on antibodies, PCR or mass spectral methods have been developed. In this context, the most promising development is that of different endopeptidase assays. In our study, we were able to show that the 2D-nano-LC-MS/MS method presented by Klaubert et al. 2009 especially for detecting BT x A, B, E and F in complex culture media can also be used for detecting BT x C. The focus was therefore on transferring this method to detecting BT x C and pointing out necessary modifications of this current method. For method development, we used different culture preparations and sample conditions. To find out whether BT x C is just as stable against acetic peptic pretreatment as other BT x, we used sample preparations with and without peptic pretreatment. The decisive difference to previous publications is the detection of produced BT x C directly from culture supernatant of different strains of C. botulinum type C. In addition, we present a new approach of detecting protein fragments from C3 and C2 toxin and some specific host cell proteins of the bacterium Clostridium spp. in order to specify the carrier bacterium, therefore verifying the presence of an intact neurotoxin-encoding phage also without directly detecting BT x C and thus the possibility to produce neurotoxin. Herein, we describe a new method to examine environmental samples or suspected feed samples in cases of toxoinfections as well as finding out the causes of clinical botulism. This new approach is particularly interesting for veterinary medicine, especially for diseases like chronic botulism in cows or equine grass sickness.

Clostridial Neurotoxins: Structure, Function and Implications to Other Bacterial Toxins

Gram-positive bacteria are ancient organisms. Many bacteria, including Gram-positive bacteria, produce toxins to manipulate the host, leading to various diseases. While the targets of Gram-positive bacterial toxins are diverse, many of those toxins use a similar mechanism to invade host cells and exert their functions. Clostridial neurotoxins produced by Clostridial tetani and Clostridial botulinum provide a classical example to illustrate the structure-function relationship of bacterial toxins. Here, we critically review the recent progress of the structure-function relationship of clostridial neurotoxins, including the diversity of the clostridial neurotoxins, the mode of actions, and the flexible structures required for the activation of toxins. The mechanism clostridial neurotoxins use for triggering their activity is shared with many other Gram-positive bacterial toxins, especially molten globule-type structures. This review also summarizes the implications of the molten globule-type flexible structures to other Gram-positive bacterial toxins. Understanding these highly dynamic flexible structures in solution and their role in the function of bacterial toxins not only fills in the missing link of the high-resolution structures from X-ray crystallography but also provides vital information for better designing antidotes against those toxins.

Effects of antibiotics on the viability of and toxin production by Clostridium botulinum

Clostridium botulinum causes infant and adult intestinal botulism by colonizing in the intestine and producing botulinum neurotoxin (BoNT). Antimicrobial agents are not currently used for treatment due to the potential facilitation of BoNT production and bacterial cell lysis, which releases toxins into the intestinal lumen. In this study, we analyzed effects of four antibiotics on the viability of and BoNT production by four C. botulinum group I strains. Our results indicate that metronidazole rapidly reduced their viability without enhancing BoNT production. Antibiotics with these properties may promote elimination of C. botulinum from the intestines while maintaining low levels of BoNT. This article is protected by copyright. All rights reserved.

Confirmation of botulism diagnosis in Australian bird samples by ELISA and RT rtPCR

We developed a sandwich ELISA that detects Clostridium botulinum C and D toxins and reverse-transcription real-time PCRs (RT-rtPCRs) that detect botulinum C and D toxin genes, respectively, to replace the mouse bioassay. The toxin genes were closely associated with the toxin molecules and used as surrogates for the presence of toxin. Samples (638) from 103 clinical cases of birds (302) with suspected botulinum toxicity came from wild birds and poultry (9 cases). Samples tested included blood serum, other body fluids, various tissues, gut contents, maggots, water, and sediment. Botulism was diagnosed in 34 cases (all of which had positive samples in the ELISA, the C toxin gene RT-rtPCR, or both assays). Botulism was suspected in 16 cases (each of which had 1 positive sample either in the ELISA or the C toxin gene RT-rtPCR). In the remaining 53 cases, no samples were positive, but botulism could not be excluded in 32 of these cases, whereas there was no indication of botulism or another diagnosis in 21 cases. The D toxin gene was not detected in any of the clinical samples. No C or D toxin genes were detected in 71 pooled cloacal swabs from 213 healthy migratory birds. The use of an ELISA that detects botulinum C and D toxins in combination with a RT-rtPCR for the botulinum C toxin gene can help confirm the diagnosis of botulism in birds.

Potential Role of Plant Extracts and Phytochemicals Against Foodborne Pathogens

Foodborne diseases are one of the major causes of morbidity and mortality, especially in low-income countries with poor sanitation and inadequate healthcare facilities. The foremost bacterial pathogens responsible for global outbreaks include Salmonella species, Campylobacter jejuni, Escherichia coli, Shigella sp., Vibrio, Listeria monocytogenes and Clostridium botulinum. Among the viral and parasitic pathogens, norovirus, hepatitis A virus, Giardia lamblia, Trichinella spiralis, Toxoplasma and Entamoeba histolytica are commonly associated with foodborne diseases. The toxins produced by Staphylococcus aureus, Bacillus cereus and Clostridium perfringens also cause these infections. The currently available therapies for these infections are associated with various limited efficacy, high cost and side-effects. There is an urgent need for effective alternative therapies for the prevention and treatment of foodborne diseases. Several plant extracts and phytochemicals were found to be highly effective to control the growth of these pathogens causing foodborne infections in in vitro systems. The present review attempts to provide comprehensive scientific information on major foodborne pathogens and the potential role of phytochemicals in the prevention and treatment of these infections. Further detailed studies are necessary to evaluate the activities of these extracts and phytochemicals along with their mechanism of action using in vivo models.

Fully Human Monoclonal Antibodies Effectively Neutralizing Botulinum Neurotoxin Serotype B

Botulinum neurotoxin (BoNT) is the most potent natural toxin known. Of the seven BoNT serotypes (A to G), types A, B, E, and F cause human botulism. Treatment of human botulism requires the development of effective toxin-neutralizing antibodies without side effects such as serum sickness and anaphylaxis. In this study, we generated fully human monoclonal antibodies (HuMAbs) against serotype B BoNT (BoNT/B1) using a murine–human chimera fusion partner cell line named SPYMEG. Of these HuMAbs, M2, which specifically binds to the light chain of BoNT/B1, showed neutralization activity in a mouse bioassay (approximately 10 i.p. LD₅₀/100 µg of antibody), and M4, which binds to the C-terminal of heavy chain, showed partial protection. The combination of two HuMAbs, M2 (1.25 µg) and M4 (1.25 µg), was able to completely neutralize BoNT/B1 (80 i.p. LD₅₀) with a potency greater than 80 i.p. LD₅₀/2.5 µg of antibodies, and was effective both prophylactically and therapeutically in the mouse model of botulism. Moreover, this combination showed broad neutralization activity against three type B subtypes, namely BoNT/B1, BoNT/B2, and BoNT/B6. These data demonstrate that the combination of M2 and M4 is promising in terms of a foundation for new human therapeutics for BoNT/B intoxication.

Functional Analysis of Botulinum Hemagglutinin (HA)

Botulinum neurotoxin (BoNT), produced by Clostridium botulinum, is the most potent toxin and produced as a complex with non-toxic components. Food-borne botulism is caused by the ingestion of these BoNT complexes. Hemagglutinin (HA), one of the non-toxic components, is known to have lectin (carbohydrate binding) activity and E-cadherin-binding activity. These activities promote the intestinal absorption of BoNT. To elucidate the mechanism of the onset of food-borne botulism, we focused on the role of HA in the intestinal absorption of BoNT. We describe the functional analysis methods for HA, including the expression of recombinant proteins, binding to glycoproteins and epithelial cells, and localization in mouse intestinal tissue.

Botulinum Hemagglutinin: Critical Protein for Adhesion and Absorption of Neurotoxin Complex in Host Intestine

Botulinum hemagglutinin (HA) is one of the auxiliary protein components of the botulinum neurotoxin (BoNT) complex, the most lethal toxin known. HA promotes the intestinal absorption of BoNT by at least two mechanisms, resulting in high oral toxicity. One of the mechanisms is the attachment of large progenitor toxin complexes (L-PTCs) to the cell surface of the intestinal epithelium by the carbohydrate-binding activity of HA. The other is epithelial barrier disruption by the E-cadherin-binding activity of HA. The carbohydrate-binding activity of HA also promotes attachment to the basolateral cell surface, which increases the frequency of contact between HA and E-cadherin. Together, the carbohydrate-binding activity of HA is critical for the intestinal absorption of BoNTs. The trimeric triskelion-shaped structure of HA confers the multivalent binding to its ligands and increases the pathogenic biological activities of HA.

[Mechanism of intestinal absorption of botulinum neurotoxin complex]

Botulinum neurotoxins (BoNTs) produced by the anaerobic bacterium Clostridium botulinum and related species cause botulism, a neuroparalytic disease associated with a high mortality. BoNTs are always produced as large protein complexes (progenitor toxin complexes, PTCs) through association with non-toxic components (NAPs) including hemagglutinin (HA) and non-toxic non-hemagglutinin (NTNHA). Food-borne botulism is caused by the ingestion of PTCs. PTCs in the gastrointestinal tract cross the intestinal epithelial barrier, enter the blood stream, and reach the nerve endings, where BoNTs cleave the SNAREs required for vesicle fusion. Consequently, BoNTs inhibit neurotransmitter release and cause paralysis. To cause food-borne botulism, BoNTs must traverse the intestinal epithelial barrier. However, the mechanism used to cross this barrier remains unclear. Using an in vitro epithelial barrier system, we previously showed that the interaction of HA with E-cadherin results in disruption of tight junctions. Furthermore, we previously reported that microfold (M) cells in the follicle-associated epithelium (FAE) of mouse Peyer's patches (PPs) are major sites where type A1 BoNT breaches the intestinal epithelial barrier. Here, I would like to demonstrate an ingenious invasion mechanism of the BoNT complex.

Tables of Toxicity of Botulinum and Tetanus Neurotoxins

Tetanus and botulinum neurotoxins are the most poisonous substances known, so much so as to be considered for a possible terrorist use. At the same time, botulinum neurotoxin type A1 is successfully used to treat a variety of human syndromes characterized by hyperactive cholinergic nerve terminals. The extreme toxicity of these neurotoxins is due to their neurospecificity and to their metalloprotease activity, which results in the deadly paralysis of tetanus and botulism. Recently, many novel botulinum neurotoxins and some botulinum-like toxins have been discovered. This large number of toxins differs in terms of toxicity and biological activity, providing a potential goldmine for novel therapeutics and for new molecular tools to dissect vesicular trafficking, fusion, and exocytosis. The scattered data on toxicity present in the literature require a systematic organization to be usable by scientists and clinicians. We have assembled here the data available in the literature on the toxicity of these toxins in different animal species. The internal comparison of these data provides insights on the biological activity of these toxins.

Botulinum neurotoxin serotype D - A potential treatment alternative for BoNT/A and B non-responding patients

OBJECTIVES

Botulinum neurotoxin serotypes A and B (BoNT/A & B) are highly effective medicines to treat hyperactive cholinergic neurons. Due to neutralizing antibody formation, some patients may become non-responders. In these cases, the serotypes BoNT/C-G might become treatment alternatives. BoNT/D is genetically least related to BoNT/A & B and thereby circumventing neutralisation in A/B non-responders. We produced BoNT/D and compared its pharmacology with BoNT/A ex vivo in mice tissue and in vivo in human volunteers.

METHODS

BoNT/D was expressed recombinantly in E. coli, isolated by chromatography and its ex vivo potency was determined at mouse phrenic nerve hemidiaphragm preparations. Different doses of BoNT/D or incobotulinumtoxinA were injected into the extensor digitorum brevis (EDB) muscles (n = 30) of human volunteers. Their compound muscle action potentials were measured 11 times by electroneurography within 220 days.

RESULTS

Despite a 3.7-fold lower ex vivo potency in mice, a 110-fold higher dosage of BoNT/D achieved the same clinical effect as incobotulinumtoxinA while showing a 50% shortened duration of action.

CONCLUSIONS

BoNT/D blocks dose-dependently acetylcholine release in human motoneurons upon intramuscular administration, but its potency and duration of action is inferior to approved BoNT/A based drugs.

SIGNIFICANCE

BoNT/D constitutes a potential treatment alternative for BoNT/A & B non-responders.

Real-Time Monitoring of a Botulinum Neurotoxin Using All-Carbon Nanotube-Based Field-Effect Transistor Devices

The possibility of exposure to botulinum neurotoxin (BoNT), a powerful and potential bioterrorism agent, is considered to be ever increasing. The current gold-standard assay, live-mouse lethality, exhibits high sensitivity but has limitations including long assay times, whereas other assays evince rapidity but lack factors such as real-time monitoring or portability. In this study, we aimed to devise a novel detection system that could detect BoNT at below-nanomolar concentrations in the form of a stretchable biosensor. We used a field-effect transistor with a p-type channel and electrodes, along with a channel comprising aligned carbon nanotube layers to detect the type E light chain of BoNT (BoNT/E-Lc). The detection of BoNT/E-Lc entailed observing the cleavage of a unique peptide and the specific bonding between BoNT/E-Lc and antibody BoNT/E-Lc (Anti-BoNT/E-Lc). The unique peptide was cleaved by 60 pM BoNT/E-Lc; notably, 52 fM BoNT/E-Lc was detected within 1 min in the device with the antibody in the bent state. These results demonstrated that an all-carbon nanotube-based device (all-CNT-based device) could be produced without a complicated fabrication process and could be used as a biosensor with high sensitivity, suggesting its potential development as a wearable BoNT biosensor.

Comparison of efficacy and toxicity between botulinum toxin subtypes A1 and A2 in cynomolgus macaques

Botulinum toxin type A (subtype A1) is used as therapeutic agent for some neurological disorders causing spasticity. The toxin products have an upper dosage limit, and their adverse events, such as side effects of diffusion following high-dose administration, have become serious issues. Therefore, a preparation with greater therapeutic efficacy at lower dosages and less diffusion in the body is desired. We have attempted to produce neurotoxin derived from subtype A2 (A2NTX), which has a different amino acid sequence from that of neurotoxin derived from subtype A1. In this study, to investigate whether A2NTX is applicable for treatment, we compared the muscle relaxation effects and the toxicity between A1LL and A2NTX in adult cynomolgus macaques. In the isometric muscle contraction test elicited by 30 Hz tetanus stimulation, the contractions observed in the 0.4 U/site A1LL-treated group were similar in value to those in the 0.13 U/site A2NTX-treated group. In the toxicity test, the 12 and 24 U/kg A1LL- and A2NTX-treated groups all exhibited similar signs of toxicity regarding symptoms, rate of weight loss, and decrease in the length of the right lower leg perimeter. Thus, A2NTX demonstrated approximately 3.0-times higher muscle relaxation activity than A1LL, and their toxicity was equivalent. This study suggested that A2NTX products are more suitable for the treatment of neurological disorders.

Development of immunodetection system for botulinum neurotoxin serotype E

Background & objectives

Botulism, a potentially fatal paralytic illness, is caused by the botulinum neurotoxins (BoNTs) secreted by Clostridium botulinum. It is an obligate anaerobic, Gram-positive, spore-forming bacterium. BoNTs are classified into seven serotypes based on the serological properties. Among these seven serotypes, A, B, E and, rarely, F are responsible for human botulism. The present study was undertaken to develop an enzyme-linked immunosorbent assay (ELISA)-based detection system for the detection of BoNT/E.

Methods

The synthetic gene coding the light chain of BoNT serotype E (BoNT/E LC) was constructed using the polymerase chain reaction primer overlapping method, cloned into pQE30UA vector and then transformed into Escherichia coli M15 host cells. Recombinant protein expression was optimized using different concentrations of isopropyl-β-D-1-thiogalactopyranoside (IPTG), different temperature and the rBoNT/E LC protein was purified in native conditions using affinity column chromatography. The purified recombinant protein was checked by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and further confirmed by western blot and matrix-assisted laser desorption ionization-tandem time-of-flight (MALDI-TOF). Polyclonal antibodies were generated against rBoNT/E LC using Freund's adjuvant in BALB/c mice and rabbit. Sandwich ELISA was optimized for the detection of rBoNT/E LC and native crude BoNT/E, and food matrix interference was tested. The developed antibodies were further evaluated for their specificity/cross-reactivity with BoNT serotypes and other bacterial toxins.

Results

BoNT/E LC was successfully cloned, and the maximum expression was achieved in 16 h of post-induction using 0.5 mM IPTG concentration at 25°C. Polyclonal antibodies were generated in BALB/c mice and rabbit and the antibody titre was raised up to 128,000 after the 2^nd booster dose. The developed polyclonal antibodies were highly specific and sensitive with a detection limit about 50 ng/ml for rBoNT/E LC and 2.5×10^[3] MLD₅₀ of native crude BoNT/E at a dilution of 1:3000 of mouse (capturing) and rabbit (revealing) antibodies. Further, different liquid, semisolid and solid food matrices were tested, and rBoNT/E LC was detected in almost all food samples, but different levels of interference were detected in different food matrices.

Interpretation & conclusions

There is no immune detection system available commercially in India to detect botulism. The developed system might be useful for the detection of botulinum toxin in food and clinical samples. Further work is in progress.

Yesterday and Today: The Impact of Research Conducted at Camp Detrick on Botulinum Toxin

Introduction

This review summarizes the research conducted on botulinum toxin (BoTx) from 1943 to 1956 by a small group of Camp Detrick investigators and their staff. A systematic, cross-disciplinary approach was used to develop effective vaccines against this biological warfare threat agent. In response to the potential need for medical countermeasures against BoTx during World War II, the refinement of isolation and purification techniques for BoTx successfully led to the large-scale production of botulinum toxoid vaccines. In addition, the work at Camp Detrick provided the foundation for the subsequent use of BoTx as a tool for studying the trophic regulation of skeletal muscle within motor neuron terminals and, more recently, for elucidation of the intricate details of neurotransmitter release at the molecular level. Indirectly, Camp Detrick investigators also played a significant role in studies that culminated in the use of BoTx as a pharmaceutical product that has been approved by the U.S. Food and Drug Administration for treating movement disorders, autonomic dysfunctions, and other conditions.

Methods

Online literature searches were performed with Google, Google Scholar, PubMed, the bibliography from the Camp Detrick technical library, and at the Defense Technical Information Center. Reference lists in some of the primary research publications and reviews also provided source material. Search terms included botulinum, botulinus, and Camp Detrick. References related to the subsequent impacts of the Camp Detrick results were selected and cited from reviews and primary references in the more recent literature. Notes on toxin nomenclature and potential sources of error in this study are presented.

Results

The literature searches returned 27 citations of Camp Detrick authors, 24 of which were articles in peer-reviewed journals. The publications by these investigators included several disciplines such as biochemistry, immunology, pharmacology, physiology, and toxicology. A fundamental finding was the identification of critical nutritional components for improved growth of Clostridium botulinum and the increased production of BoTx serotype A. The purification processes that were developed at Camp Detrick allowed for the production of crystalline material to be scaled up for the manufacture of toxoid vaccine. Based on the research by Camp Detrick scientists, a toxoid supply of over 1 million units was available to vaccinate ~300,000 troops before the large-scale operations of D-Day.

Conclusions

BoTx research during the period 1943 to 1956 resulted in refinements in the techniques for isolating and purifying the crystalline BoTx type A. These results led to the development and manufacture of a toxoid vaccine that was available in a sufficient quantity to protect ~300,000 warfighters in a large-scale military operation. One of the most important long-term consequences derived from the knowledge gained by the efforts at Camp Detrick was the development in the 1980s of safe and effective therapeutic uses for BoTx type A, the most lethal biological substance known.

Modulation of Intestinal Paracellular Transport by Bacterial Pathogens

The passive and regulated movement of ions, solutes, and water via spaces between cells of the epithelial monolayer plays a critical role in the normal intestinal functioning. This paracellular pathway displays a high level of structural and functional specialization, with the membrane-spanning complexes of the tight junctions, adherens junctions, and desmosomes ensuring its integrity. Tight junction proteins, like occludin, tricellulin, and the claudin family isoforms, play prominent roles as barriers to unrestricted paracellular transport. The past decade has witnessed major advances in our understanding of the architecture and function of epithelial tight junctions. While it has been long appreciated that microbes, notably bacterial and viral pathogens, target and disrupt junctional complexes and alter paracellular permeability, the precise mechanisms remain to be defined. Notably, renewed efforts will be required to interpret the available data on pathogen-mediated barrier disruption in the context of the most recent findings on tight junction structure and function. While much of the focus has been on pathogen-induced dysregulation of junctional complexes, commensal microbiota and their products may influence paracellular permeability and contribute to the normal physiology of the gut. Finally, microbes and their products have become important tools in exploring host systems, including the junctional properties of epithelial cells. © 2018 American Physiological Society. Compr Physiol 8:823-842, 2018.

Molecular insights into the mechanisms of M-cell differentiation and transcytosis in the mucosa-associated lymphoid tissues

Microfold cells (M cells), which are located in the follicle-associated epithelium (FAE) covering mucosal lymphoid follicles, are specialized epithelial cells that initiate mucosal immune responses. These cells take luminal antigens and transport them via transcytosis across the FAE to the antigen-presenting cells underneath. Several intestinal pathogens exploit M cells as their portal for entry to invade the host and cause disease conditions. Recent studies have revealed that the uptake of antigens by M cells is essential for efficient antigen-specific IgA production and that this process likely maintains the homeostasis of mucosal tissues. The present article reviews recent advances in understanding the molecular mechanism of M-cell differentiation and describes the molecules expressed by M cells that are associated with antigen uptake and/or the transcytosis process. Current efforts to augment M-cell-mediated uptake for use in the development of effective mucosal vaccines are also discussed.

Translocation and dissemination of botulinum neurotoxin from the intestinal tract

Botulinum neurotoxins (BoNTs) are potent toxins which induce flaccid paralysis by inhibiting the release of acetylcholine at the neuromuscular junctions. They associate with non-toxic proteins (ANTPs or NAPs) to form complexes of various sizes which are resistant to acidic pH and protease degradation. BoNT trafficking from the digestive tract to the target neurons is still a matter of debate. BoNTs use different strategies to pass through the intestinal barrier including passage of BoNT complexes containing hemagglutinins (HAs) via M cells, HA-dependent perturbation of E-cadherin intercellular junctions between enterocytes and paracellular passage of BoNT complexes, and transcytosis of BoNT free of NAPs through certain intestinal epithelial cells. Then, BoNTs target neuronal cells, preferentially cholinergic neurons, in the intestinal mucosa and submucosa. The precise mode of BoNT dissemination until the final target neuro-muscular junctions is still elusive.

Regulation of Botulinum Neurotoxin Synthesis and Toxin Complex Formation by Arginine and Glucose in Clostridium botulinum ATCC 3502

Botulinum neurotoxin (BoNT), produced by neurotoxigenic clostridia, is the most potent biological toxin known and the causative agent of the paralytic disease botulism. The nutritional, environmental, and genetic regulation of BoNT synthesis, activation, stability, and toxin complex (TC) formation is not well studied. Previous studies indicated that growth and BoNT formation were affected by arginine and glucose in Clostridium botulinum types A and B. In the present study, C. botulinum ATCC 3502 was grown in toxin production medium (TPM) with different levels of arginine and glucose and of three products of arginine metabolism, citrulline, proline, and ornithine. Cultures were analyzed for growth (optical density at 600 nm [OD₆₀₀]), spore formation, and BoNT and TC formation by Western blotting and immunoprecipitation and for BoNT activity by mouse bioassay. A high level of arginine (20 g/liter) repressed BoNT production approximately 1,000-fold, enhanced growth, slowed lysis, and reduced endospore production by greater than 1,000-fold. Similar effects on toxin production were seen with equivalent levels of citrulline but not ornithine or proline. In TPM lacking glucose, levels of formation of BoNT/A1 and TC were significantly decreased, and extracellular BoNT and TC proteins were partially inactivated after the first day of culture. An understanding of the regulation of C. botulinum growth and BoNT and TC formation should be valuable in defining requirements for BoNT formation in foods and clinical samples, improving the quality of BoNT for pharmaceutical preparations, and elucidating the biological functions of BoNTs for the bacterium.IMPORTANCE Botulinum neurotoxin (BoNT) is a major food safety and bioterrorism concern and is also an important pharmaceutical, and yet the regulation of its synthesis, activation, and stability in culture media, foods, and clinical samples is not well understood. This paper provides insights into the effects of critical nutrients on growth, lysis, spore formation, BoNT and TC production, and stability of BoNTs of C. botulinum We show that for C. botulinum ATCC 3502 cultured in a complex medium, a high level of arginine repressed BoNT expression by ca. 1,000-fold and also strongly reduced sporulation. Arginine stimulated growth and compensated for a lack of glucose. BoNT and toxin complex proteins were partially inactivated in a complex medium lacking glucose. This work should aid in optimizing BoNT production for pharmaceutical uses, and furthermore, an understanding of the nutritional regulation of growth and BoNT formation may provide insights into growth and BoNT formation in foods and clinical samples and into the enigmatic function of BoNTs in nature.

Affinity biosensors using recombinant native membrane proteins displayed on exosomes: application to botulinum neurotoxin B receptor

The development of simple molecular assays with membrane protein receptors in a native conformation still represents a challenging task. Exosomes are extracellular vesicles which, due to their stability and small size, are suited for analysis in various assay formats. Here, we describe a novel approach to sort recombinant fully native and functional membrane proteins to exosomes using a targeting peptide. Specific binding of high affinity ligands to the potassium channel Kv1.2, the G-protein coupled receptor CXCR4, and the botulinum neurotoxin type B (BoNT/B) receptor, indicated their correct assembly and outside out orientation in exosomes. We then developed, using a label-free optical biosensor, a new method to determine the kinetic constants of BoNT/B holotoxin binding to its receptor synaptotagmin2/GT1b ganglioside (k_on = 2.3 ×10⁵ M⁻¹.s⁻¹, k_off = 1.3 10⁻⁴ s⁻¹), yielding an affinity constant (K_D = 0.6 nM) similar to values determined from native tissue. In addition, the recombinant binding domain of BoNT/B, a potential vector for neuronal delivery, bound quasi-irreversibly to synaptotagmin 2/GT1b exosomes. Engineered exosomes provide thus a novel means to study membrane proteins for biotechnology and clinical applications.

Clinical Study of New Tetravalent (Type A, B, E, and F) Botulinum Toxoid Vaccine Derived from M Toxin in Japan

Botulinum toxin is the most poisonous substance known, and is believed to be a highly lethal as a biological weapon; researchers of the toxin are exposed to this hazard. Botulinum toxoid vaccines have been produced and used in Japan. However, since clinical studies involving these vaccines were conducted before establishment of the Ethical Guidelines for Clinical Research in Japan, their immunogenicity and safety were not systematically assessed. In this study, we produced a new tetravalent (type A, B, E, and F) botulinum toxoid vaccine, the first ever to be derived from M toxin, and conducted quality control tests with reference to the Minimum Requirements in Japan for adsorbed tetanus toxoid vaccine. Subsequently, a clinical study using the new vaccine in 48 healthy adult volunteers was conducted according to the guidelines in Japan. No clinically serious adverse event was noted. Neutralizing antibody titers for each type of toxin in the participants' sera, 1 month after the 4th injection were more than 0.25 IU/mL, indicating sufficient protection. This study demonstrated that the vaccine has marked immunogenicity and is safe for use in humans.

Probiotic Microorganisms Inhibit Epithelial Cell Internalization of Botulinum Neurotoxin Serotype A

Botulinum neurotoxins (BoNTs) are some of the most poisonous natural toxins known to man and are threats to public health and safety. Previous work from our laboratory showed that both BoNT serotype A complex and holotoxin can bind and transit through the intestinal epithelia to disseminate in the blood. The timing of BoNT/A toxin internalization was shown to be comparable in both the Caco-2 in vitro cell culture and in the oral mouse intoxication models. Probiotic microorganisms have been extensively studied for their beneficial effects in not only maintaining the normal gut mucosa but also protection from allergens, pathogens, and toxins. In this study, we evaluate whether probiotic microorganisms will block BoNT/A uptake in the in vitro cell culture system using Caco-2 cells. Several probiotics tested (Saccharomyces boulardii, Lactobacillus acidophilus, Lactobacillus rhamnosus LGG, and Lactobacillus reuteri) blocked BoNT/A uptake in a dose-dependent manner whereas a non-probiotic strain of Escherichia coli did not. We also showed that inhibition of BoNT/A uptake was not due to the degradation of BoNT/A nor by sequestration of toxin via binding to probiotics. These results show for the first time that probiotic treatment can inhibit BoNT/A binding and internalization in vitro and may lead to the development of new therapies.

Neutralization of Botulinum Neurotoxin Type E by a Humanized Antibody

Botulinum neurotoxins (BoNTs) cause botulism and are the deadliest naturally-occurring substances known to humans. BoNTs have been classified as one of the category A agents by the Centers for Disease Control and Prevention, indicating their potential use as bioweapons. To counter bio-threat and naturally-occurring botulism cases, well-tolerated antibodies by humans that neutralize BoNTs are relevant. In our previous work, we showed the neutralizing potential of macaque (Macaca fascicularis)-derived scFv-Fc (scFv-Fc ELC18) by in vitro endopeptidase immunoassay and ex vivo mouse phrenic nerve-hemidiaphragm assay by targeting the light chain of the botulinum neurotoxin type E (BoNT/E). In the present study, we germline-humanized scFv-Fc ELC18 into a full IgG hu8ELC18 to increase its immunotolerance by humans. We demonstrated the protection and prophylaxis capacity of hu8ELC18 against BoNT/E in a mouse model. A concentration of 2.5 ng/mouse of hu8ELC18 protected against 5 mouse lethal dose (MLD) in a mouse protection assay and complete neutralization of 1 LD50 of pure BoNT/E toxin was achieved with 8 ng of hu8ELC18 in mouse paralysis assay. Furthermore, hu8ELC18 protected mice from 5 MLD if injected up to 14 days prior to intraperitoneal BoNT/E administration. This newly-developed humanized IgG is expected to have high tolerance in humans.

[Molecular targets of bacterial effectors and toxins that underlie vulnerability to diseases]

Pathogenic bacteria produce a variety of effectors and/or toxins, which subvert target cell/tissue functions in the infected hosts. Some of those effectors/toxins also perturb host defense mechanism, thereby making up more complicated pathophysiological conditions. Such bacterial effectors/toxins may have been positively selected during evolution because they directly strike vulnerable points in the host system. In turn, this indicates that systemic exploration of molecules and signaling pathways targeted by bacterial effectors/toxins provides a powerful tool in digging up an unexpected Achilles' heel(s), malfunctioning of which gives rise to disorders not restricted to infectious diseases. Based on this viewpoint, this review shows molecular basis underlying host susceptibility and vulnerability to diseases through the studies of host molecules targeted by bacterial effectors and toxins.

Neurotoxins from Clostridium botulinum (serotype A) isolated from the soil of Mendoza (Argentina) differ from the A-Hall archetype and from that causing infant botulism

The type A of neurotoxin produced by Clostridium botulinum is the prevalent serotype in strains of Mendoza. The soil is the main reservoir for C.botulinum and is possibly one of the infection sources in infant botulism. In this study, we characterized and compared autochthonous C. botulinum strains and their neurotoxins. Bacterial samples were obtained from the soil and from fecal samples collected from children with infant botulism. We first observed differences in the appearance of the colonies between strains from each source and with the A Hall control strain. In addition, purified neurotoxins of both strains were found to be enriched in a band of 300 kDa, whereas the A-Hall strain was mainly made up of a band of ∼600 kDa. This finding is in line with the lack of hemagglutinating activity of the neurotoxins under study. Moreover, the proteolytic activity of C. botulinum neurotoxins was evaluated against SNARE (soluble N-ethylmaleimide-sensitive factor-attachment protein receptor) proteins from rat brain. It was observed that both, SNAP 25 (synaptosomal-associated protein 25) and VAMP 2 (vesicle-associated membrane protein) were cleaved by the neurotoxins isolated from the soil strains, whereas the neurotoxins from infant botulism strains only induced a partial cleavage of VAMP 2. On the other hand, the neurotoxin from the A-Hall strain was able to cleave both proteins, though at a lesser extent. Our data indicate that the C.botulinum strain isolated from the soil, and its BoNT, exhibit different properties compared to the strain obtained from infant botulism patients, and from the A-Hall archetype.

New Elements To Consider When Modeling the Hazards Associated with Botulinum Neurotoxin in Food

Botulinum neurotoxins (BoNTs) produced by the anaerobic bacterium Clostridium botulinum are the most potent biological substances known to mankind. BoNTs are the agents responsible for botulism, a rare condition affecting the neuromuscular junction and causing a spectrum of diseases ranging from mild cranial nerve palsies to acute respiratory failure and death. BoNTs are a potential biowarfare threat and a public health hazard, since outbreaks of foodborne botulism are caused by the ingestion of preformed BoNTs in food. Currently, mathematical models relating to the hazards associated with C. botulinum, which are largely empirical, make major contributions to botulinum risk assessment. Evaluated using statistical techniques, these models simulate the response of the bacterium to environmental conditions. Though empirical models have been successfully incorporated into risk assessments to support food safety decision making, this process includes significant uncertainties so that relevant decision making is frequently conservative and inflexible. Progression involves encoding into the models cellular processes at a molecular level, especially the details of the genetic and molecular machinery. This addition drives the connection between biological mechanisms and botulism risk assessment and hazard management strategies. This review brings together elements currently described in the literature that will be useful in building quantitative models of C. botulinum neurotoxin production. Subsequently, it outlines how the established form of modeling could be extended to include these new elements. Ultimately, this can offer further contributions to risk assessments to support food safety decision making.

The Influence of Safety, Efficacy, and Medical Condition Severity on Natural versus Synthetic Drug Preference

Research indicates that there is a preference for natural v. synthetic products, but the influence of this preference on drug choice in the medical domain is largely unknown. We present 5 studies in which participants were asked to consider a hypothetical situation in which they had a medical issue requiring pharmacological therapy. Participants ( N = 1223) were asked to select a natural, plant-derived, or synthetic drug. In studies 1a and 1b, approximately 79% of participants selected the natural v. synthetic drug, even though the safety and efficacy of the drugs were identical. Furthermore, participants rated the natural drug as safer than the synthetic drug, and as that difference increased, the odds of choosing the natural over synthetic drug increased. In studies 2 and 3, approximately 20% of participants selected the natural drug even when they were informed that it was less safe (study 2) or less effective (study 3) than the synthetic drug. Finally, in study 4, approximately 65% of participants chose a natural over synthetic drug regardless of the severity of a specific medical condition (mild v. severe hypertension), and this choice was predicted by perceived safety and efficacy differences. Overall, these data indicate that there is a bias for natural over synthetic drugs. This bias could have implications for drug choice and usage.

Generation and Characterization of Six Recombinant Botulinum Neurotoxins as Reference Material to Serve in an International Proficiency Test

The detection and identification of botulinum neurotoxins (BoNT) is complex due to the existence of seven serotypes, derived mosaic toxins and more than 40 subtypes. Expert laboratories currently use different technical approaches to detect, identify and quantify BoNT, but due to the lack of (certified) reference materials, analytical results can hardly be compared. In this study, the six BoNT/A1–F1 prototypes were successfully produced by recombinant techniques, facilitating handling, as well as improving purity, yield, reproducibility and biosafety. All six BoNTs were quantitatively nicked into active di-chain toxins linked by a disulfide bridge. The materials were thoroughly characterized with respect to purity, identity, protein concentration, catalytic and biological activities. For BoNT/A₁, B₁ and E₁, serotypes pathogenic to humans, the catalytic activity and the precise protein concentration were determined by Endopep-mass spectrometry and validated amino acid analysis, respectively. In addition, BoNT/A₁, B₁, E₁ and F₁ were successfully detected by immunological assays, unambiguously identified by mass spectrometric-based methods, and their specific activities were assigned by the mouse LD₅₀ bioassay. The potencies of all six BoNT/A1–F1 were quantified by the ex vivo mouse phrenic nerve hemidiaphragm assay, allowing a direct comparison. In conclusion, highly pure recombinant BoNT reference materials were produced, thoroughly characterized and employed as spiking material in a worldwide BoNT proficiency test organized by the EQuATox consortium.

The long journey of botulinum neurotoxins into the synapse

Botulinum neurotoxins (BoNT) cause the disease botulism, a flaccid paralysis of the muscle. They are also very effective, widely used medicines applied locally in sub-nanogram quantities. BoNTs are released together with several non-toxic, associated proteins as progenitor toxin complexes (PCT) by Clostridium botulinum to become highly potent oral poisons ingested via contaminated food. They block the neurotransmission in susceptible animals and humans already in nanogram quantities due to their specific ability to enter motoneurons and to cleave only selected neuronal proteins involved in neuroexocytosis. BoNTs have developed a sophisticated strategy to passage the gastrointestinal tract and to be absorbed in the intestine of the host to finally attack neurons. A non-toxic non-hemagglutinin (NTNHA) forms a binary complex with BoNT to protect it from gastrointestinal degradation. This binary M-PTC is one component of the bi-modular 14-subunit ∼760 kDa large progenitor toxin complex. The other component is the structurally and functionally independent dodecameric hemagglutinin (HA) complex which facilitates the absorption on the intestinal epithelium by glycan binding. Subsequent to its transcytosis the HA complex disrupts the tight junction of the intestinal barrier from the basolateral side by binding to E-cadherin. Now, the L-PTC can also enter the circulation by paracellular routes in much larger quantities. From here, the dissociated BoNTs reach the neuromuscular junction and accumulate via interaction with polysialo gangliosides, complex glycolipids, on motoneurons at the neuromuscular junction. Subsequently, additional specific binding to luminal segments of synaptic vesicles proteins like SV2 and synaptotagmin leads to their uptake. Finally, the neurotoxins shut down the synaptic vesicle cycle, which they had exploited before to enter their target cells, via specific cleavage of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins, which constitute the core components of the cellular membrane fusion machinery.

Clostridium botulinum type C hemagglutinin affects the morphology and viability of cultured mammalian cells via binding to the ganglioside GM3

Botulinum neurotoxin is conventionally divided into seven serotypes, designated A-G, and is produced as large protein complexes through associations with non-toxic components, such as hemagglutinin (HA) and non-toxic non-HA. These non-toxic proteins dramatically enhance the oral toxicity of the toxin complex. HA is considered to have a role in toxin transport through the intestinal epithelium by carbohydrate binding and epithelial barrier-disrupting activity. Type A and B HAs disrupt E-cadherin-mediated cell adhesion, and, in turn, the intercellular epithelial barrier. Type C HA (HA/C) disrupts the barrier function by affecting cell morphology and viability, the mechanism of which remains unknown. In this study, we identified GM3 as the target molecule of HA/C. We found that sialic acid binding of HA is essential for the activity. It was abolished when cells were pre-treated with an inhibitor of ganglioside synthesis. Consistent with this, HA/C bound to a-series gangliosides in a glycan array. In parallel, we isolated clones resistant to HA/C activity from a susceptible mouse fibroblast strain. These cells lacked expression of ST-I, the enzyme that transfers sialic acid to lactosylceramide to yield GM3. These clones became sensitive to HA/C activity when GM3 was expressed by transfection with the ST-I gene. The sensitivity of fibroblasts to HA/C was reduced by expressing ganglioside synthesis genes whose products utilize GM3 as a substrate and consequently generate other a-series gangliosides, suggesting a GM3-specific mechanism. Our results demonstrate that HA/C affects cells in a GM3-dependent manner.

Architecture of the botulinum neurotoxin complex: a molecular machine for protection and delivery

Botulinum neurotoxins (BoNTs) are extremely poisonous protein toxins that cause the fatal paralytic disease botulism. They are naturally produced in bacteria with several nontoxic neurotoxin-associated proteins (NAPs) and together they form a progenitor toxin complex (PTC), the largest bacterial toxin complex known. In foodborne botulism, the PTC functions as a molecular machine that helps BoNT breach the host defense in the gut. Here, we discuss the substantial recent advance in elucidating the atomic structures and assembly of the 14-subunit PTC, including structures of BoNT and four NAPs. These structural studies shed light on the molecular mechanisms by which BoNT is protected against the acidic environment and proteolytic destruction in the gastrointestinal tract, and how it is delivered across the intestinal epithelial barrier.

Botulinum toxin A complex exploits intestinal M cells to enter the host and exert neurotoxicity

To cause food-borne botulism, botulinum neurotoxin (BoNT) in the gastrointestinal lumen must traverse the intestinal epithelial barrier. However, the mechanism by which BoNT crosses the intestinal epithelial barrier remains unclear. BoNTs are produced along with one or more non-toxic components, with which they form progenitor toxin complexes (PTCs). Here we show that serotype A1 L-PTC, which has high oral toxicity and makes the predominant contribution to causing illness, breaches the intestinal epithelial barrier from microfold (M) cells via an interaction between haemagglutinin (HA), one of the non-toxic components, and glycoprotein 2 (GP2). HA strongly binds to GP2 expressed on M cells, which do not have thick mucus layers. Susceptibility to orally administered L-PTC is dramatically reduced in M-cell-depleted mice and GP2-deficient (Gp2^−/−) mice. Our finding provides the basis for the development of novel antitoxin therapeutics and delivery systems for oral biologics.

It is unclear how ingested botulinum neurotoxin invades the host to cause illness. Here, the authors show that the toxin complex containing neurotoxin, hemagglutinin (HA), and NTNHA proteins traverses the epithelial barrier via HA-glycoprotein 2 interaction and endocytosis by Peyer’s patch microfold cells.

Translocation of botulinum neurotoxin serotype A and associated proteins across the intestinal epithelia

Botulinum neurotoxins (BoNTs) are some of the most poisonous natural toxins. Botulinum neurotoxins associate with neurotoxin-associated proteins (NAPs) forming large complexes that are protected from the harsh environment of the gastrointestinal tract. However, it is still unclear how BoNT complexes as large as 900 kDa traverse the epithelial barrier and what role NAPs play in toxin translocation. In this study, we examined the transit of BoNT serotype A (BoNT/A) holotoxin, complex and recombinantly purified NAP complex through cultured and polarized Caco-2 cells and, for the first time, in the small mouse intestine. Botulinum neurotoxin serotype A and NAPs in the toxin complex were detectable inside intestinal cells beginning at 2 h post intoxication. Appearance of the BoNT/A holotoxin signal was slower, with detection starting at 4-6 h. This indicated that the holotoxin alone was sufficient for entry but the presence of NAPs enhanced the rate of entry. Botulinum neurotoxin serotype A detection peaked at approximately 6 and 8 h for complex and holotoxin, respectively, and thereafter began to disperse with some toxin remaining in the epithelia after 24 h. Purified HA complexes alone were also internalized and followed a similar time course to that of BoNT/A complex internalization. However, recombinant HA complexes did not enhance BoNT/A holotoxin entry in the absence of a physical link with BoNT/A. We propose a model for BoNT/A toxin complex translocation whereby toxin complex entry is facilitated by NAPs in a receptor-mediated mechanism. Understanding the intestinal uptake of BoNT complexes will aid the development of new measures to prevent or treat oral intoxications.

Comparison of Systemic Toxicity between Botulinum Toxin Subtypes A1 and A2 in Mice and Rats

The adverse events caused by botulinum toxin type A (subtype A1) product, thought to be after-effects of toxin diffusion after high-dose administration, have become serious issues. A preparation showing less diffusion in the body than existing drugs has been sought. We have attempted to produce neurotoxin derived from subtype A2 (A2NTX) with an amino acid sequence different from that of neurotoxin derived from subtype A1 (A1NTX). In this study, to investigate whether A2NTX has the potential to resolve these issues, we compared the safety of A2NTX, a progenitor toxin derived from subtype A1 (A1 progenitor toxin) and A1NTX employing the intramuscular lethal dose 50% (im LD50) in mice and rats and the compound muscle action potential (CMAP) in rats. Mouse im LD50 values for A1 progenitor toxin and A2NTX were 93 and 166 U/kg, respectively, and the rat im LD50 values were 117 and 153 U/kg, respectively. In the rat CMAP test, the dose on the contralateral side, which caused a 50% reduction in the CMAP amplitude, that is, CMAP-TD50 , was calculated as 19.0, 16.6 and 28.7 U/kg for A1 progenitor toxin, A1NTX and A2NTX, respectively. The results indicate that A2NTX is safer than A1 progenitor toxin and A1NTX.

Role of neurotoxin associated proteins in the low pH induced structural changes in the botulinum neurotoxin complex

Botulinum Neurotoxin (BoNT) produced by the bacterium Clostridium botulinum as a complex with NAPs causes botulism. It has been known that the NAPs protect the toxin from both extremes of pHs and proteases of the GI tract. In an attempt to emulate the physiological conditions encountered by the toxin, we examined BoNT/A, BoNT/A complex, and NAPs under different pH conditions and monitored their structural characteristics by far-UV CD and thermal denaturation analysis. BoNT/A complex showed the maximum CD signal with a mean residue weight ellipticity of -1.8 × 10(5)° cm(2)/dmol at 222 nm at both acidic and neutral pHs. Thermal denaturation analysis revealed NAPs to be the most stable amongst the three protein samples examined. Interestingly and quite uniquely, at pH 2.5, there was an increase in CD signal for BoNT complex as a function of temperature, which correlated with the NAPs profile, indicating a shielding effect of NAPs on BoNT complex at low pH. Calculation of the weighted mean of the ellipticities at the Tm for thermal unfolding of toxin and NAPs at neutral and acidic pHs showed variation with that of BoNT complex, suggesting structural reorganization in BoNT complex upon the association of NAPs and BoNT. In conclusion, this study reveals the structural behavior of BoNT complex and NAPs with pH changes substantially, which could be quite relevant for BoNT survival under extreme pH conditions in vivo.