Botulinum neurotoxins

Disruption of layer-specific visual processing in a model of focal neocortical epilepsy

The epileptic brain is the result of a sequence of events transforming normal neuronal populations into hyperexcitable networks supporting recurrent seizure generation. These modifications are known to induce fundamental alterations of circuit function and, ultimately, of behavior. However, how hyperexcitability affects information processing in cortical sensory circuits is not yet fully understood. Here, we investigated interlaminar alterations in sensory processing of the visual cortex in a mouse model of focal epilepsy. We found three main circuit dynamics alterations in epileptic mice: (i) a spreading of visual contrast-driven gamma modulation across layers, (ii) an increase in firing rate that is layer-unspecific for excitatory units and localized in infragranular layers for inhibitory neurons, and (iii) a strong and contrast-dependent locking of firing units to network activity. Altogether, our data show that epileptic circuits display a functional disruption of layer-specific organization of visual sensory processing, which could account for visual dysfunction observed in epileptic subjects. Understanding these mechanisms paves the way to circuital therapeutic interventions for epilepsy.

Synthesis and activity evaluation of selenazole-coupled CPI-1 irreversible bifunctional inhibitors for botulinum toxin A light chain

A series of novel conjugates of benzoselenazole or selenazole and CPI-1 were designed, synthesized, and evaluated for inhibitory activities against the botulinum neurotoxin A (BoNT/A) light chain (LC) and BoNT/A in vivo. The results show that these compounds exhibit potent inhibitory activities to the LC with IC₅₀ of 0.5-4.1 µM. The reaction kinetics and the mass spectra of the reaction products of LC with benzoselenazole- or selenazole- coupled CPI-1 demonstrate that the benzoselenazole group of most inhibitors is coupled to the LC of BoNT/A. These data indicate that the CPI-1 conjugates can inhibit both the active center of BoNT/A LC as well as Cys165, therefore functioning as irreversible bifunctional inhibitors. The detoxification activities in vivo show that one of the benzoselenazole-CPI-1 compounds prolongs the survival time of mice challenged by 2 × LD₅₀ of BoNT/A. This work provides a new strategy to design potent antidotes of BoNT/A.

Botulinum Toxin A Ameliorates Neuroinflammation in the MPTP and 6-OHDA-Induced Parkinson's Disease Models

Recently, increasing evidence suggests that neuroinflammation may be a critical factor in the development of Parkinson's disease (PD) in addition to the ratio of acetylcholine/dopamine because dopaminergic neurons are particularly vulnerable to inflammatory attack. In this study, we investigated whether botulinum neurotoxin A (BoNT-A) was effective for the treatment of PD through its anti-neuroinflammatory effects and the modulation of acetylcholine and dopamine release. We found that BoNT-A ameliorated MPTP and 6-OHDA-induced PD progression, reduced acetylcholine release, levels of IL-1β, IL-6 and TNF-α as well as GFAP expression, but enhanced dopamine release and tyrosine hydroxylase expression. These results indicated that BoNT-A had beneficial effects on MPTP or 6-OHDA-induced PD-like behavior impairments via its anti-neuroinflammation properties, recovering dopamine, and reducing acetylcholine release.

Botulinum Neurotoxin-C Detection Using Nanostructured Porous Silicon Interferometer

Botulinum neurotoxins (BoNT) are the most potent toxins, which are produced by Clostridium bacteria and cause the life-threatening disease of botulism in all vertebrates. Specifically, animal botulism represents a serious environmental and economic concern in animal production due to the high mortality rates observed during outbreaks. Despite the availability of vaccines against BoNT, there are still many outbreaks of botulism worldwide. Alternative assays capable of replacing the conventional in vivo assay in terms of rapid and sensitive quantification, and the applicability for on-site analysis, have long been perused. Herein, we present a simple, highly sensitive and label-free optical biosensor for real-time detection of BoNT serotype C using a porous silicon Fabry–Pérot interferometer. A competitive immunoassay coupled to a biochemical cascade reaction was adapted for optical signal amplification. The resulting insoluble precipitates accumulated within the nanostructure changed the reflectivity spectra by alternating the averaged refractive index. The augmented optical performance allowed for a linear response within the range of 10 to 10,000 pg mL−1 while presenting a detection limit of 4.8 pg mL−1. The practical aspect of the developed assay was verified using field BoNT holotoxins to exemplify the potential use of the developed optical approach for rapid bio-diagnosis of BoNT. The specificity and selectivity of the assay were successfully validated using an adjacent holotoxin relevant for farm animals (BoNT serotype D). Overall, this work sets the foundation for implementing a miniaturized interferometer for routine on-site botulism diagnosis, thus significantly reducing the need for animal experimentation and shortening analysis turnaround for early evidence-based therapy.

Engineering an Effective Human SNAP-23 Cleaving Botulinum Neurotoxin A Variant

Botulinum neurotoxin (BoNT) serotype A inhibits neurotransmitter release by cleaving SNAP-25 and represents an established pharmaceutical for treating medical conditions caused by hyperactivity of cholinergic nerves. Oversecretion from non-neuronal cells is often also the cause of diseases. Notably, excessive release of inflammatory messengers is thought to contribute to diseases such as chronic obstructive pulmonary disease, asthma, diabetes etc. The expansion of its application to these medical conditions is prevented because the major non-neuronal SNAP-25 isoform responsible for exocytosis, SNAP-23, is, in humans, virtually resistant to BoNT/A. Based on previous structural data and mutagenesis studies of SNAP-23 we optimized substrate binding pockets of the enzymatic domain for interaction with SNAP-23. Systematic mutagenesis and rational design yielded the mutations E148Y, K166F, S254A, and G305D, each of which individually increased the activity of LC/A against SNAP-23 between 3- to 23-fold. The assembled quadruple mutant showed approximately 2000-fold increased catalytic activity against human SNAP-23 in in vitro cleavage assays. A comparable increase in activity was recorded for the full-length BoNT/A quadruple mutant tested in cultivated primary neurons transduced with a fluorescently tagged-SNAP-23 encoding gene. Equipped with a suitable targeting domain this quadruple mutant promises to complete successfully tests in cells of the immune system.

Modification and validation of the Endopep-mass spectrometry method for botulinum neurotoxin detection in liver samples with application to samples collected during animal botulism outbreaks

Botulinum neurotoxins (BoNTs) are the most potent toxins known and they cause the paralytic disease botulism in humans and animals. In order to diagnose botulism, active BoNT must be detected in biological material. Endopep-MS is a sensitive and selective method for serum samples, based on antibody capture, enzymatic cleavage of target peptides, and detection of cleavage products using matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS). In many cases of animal botulism, serum samples are not available or they do not contain detectable amounts of BoNT and liver sampling is an alternative for postmortem examinations. However, the Endopep-MS method is impaired by the inherent protease activity of liver samples. In the presented study, the Endopep-MS method has been successfully modified and validated for analysis of cattle, horse, and avian liver samples, introducing a combination of a salt washing step and a protease inhibitor cocktail. These modifications resulted in a substantial decrease in interfering signals and increase in BoNT-specific signals. This led to a substantial improvement in sensitivity for especially BoNT-C and C/D which are among the most prominent serotypes for animal botulism. Botulism was diagnosed with the new method in liver samples from dead cattle and birds from outbreaks in Sweden. Graphical Abstract.

Jitter Evaluation in Distant and Adjacent Muscles after Botulinum Neurotoxin Type A Injection in 78 Cases

To study the jitter parameters in the distant (DM) and the adjacent muscle (AM) after botulinum neurotoxin type A (BoNT/A) injection in 78 patients, jitter was measured by voluntary activation in DM (n = 43), and in AM (n = 35). Patients were receiving BoNT/A injections as a treatment for movement disorders. Mean age 65.1 years (DM) and 61.9 years (AM). The mean jitter was abnormal in 13.9% (maximum 41.4 µs) of DM, and 40% (maximum 43.7 µs) of AM. Impulse blocking was sparse. We found no correlation of the mean jitter to age, BoNT/A most recent injection (days/units), number of muscles injected, total BoNT/A units summated, number of total BoNT/A sessions, beta-blockers/calcium channel blockers use, and cases with local spread symptoms such as eyelid drop/difficulty swallowing. Maximum mean jitter (41.4/43.7 µs) for DM/AM occurred 61 and 131 days since the most recent BoNT/A, respectively. The far abnormal mean jitter (32.6/36.9 µs) occurred 229 and 313 days since the most recent BoNT/A. We suggested that jitter measurement can be done after BoNT/A in a given muscle other than the injected one, after 8 (DM) and 11 (AM) months, with reference >33 µs and >37 µs, respectively.

Immunological characterisation and immunoprotective efficacy of functional domain antigens of botulinum neurotoxin serotype A

Botulinum neurotoxins (BoNTs) are highly toxic proteins that mediate their effects by binding to neuronal receptors and block the neutralizing ability of therapeutic antibodies. Vaccination is currently the most effective strategy to prevent botulism. In this study, a series of recombinant functional domain antigens of BoNT/A were prepared and identified, and their immunoprotective efficacies were explored and compared. Our results showed that all antigens produced strong humoral immune responses, although their protective effects against the toxin were different. Only the Hc and HN-L antigens produced strong protective effects and afforded complete immunoprotection. In addition, the combined vaccine groups showed that there was no synergistic effect on immune responses after antigen combination, suggesting that the integrity of the toxin antigen or domain is crucial to the immune effects. Studies of the dose-dependent immunoprotective effects further confirmed that the Hc domain antigen afforded more effective protective potency than the HN-L antigen, equivalent to the immune effect of the full-length toxin (Hc + HN-L combination group). Overall, our results demonstrated that the Hc domain elicited a strong protective immune response and also provided basic data and theoretical support for the development of Hc-based BoNT/A subunit vaccine. Therefore, the receptor binding domain Hc is implicated as a promising target antigen of the BoNT/A recombinant subunit vaccine as an alternative to the toxoid vaccine.

Structural and biochemical characterization of the protease domain of the mosaic botulinum neurotoxin type HA

The extreme toxicity of botulinum neurotoxins (BoNTs) relies on their specific cleavage of SNARE proteins, which eventually leads to muscle paralysis. One newly identified mosaic toxin, BoNT/HA (aka H or FA), cleaves VAMP-2 at a unique position between residues L54 and E55, but the molecular basis underlying VAMP-2 recognition of BoNT/HA remains poorly characterized. Here, we report a ∼2.09 Å resolution crystal structure of the light chain protease domain of BoNT/HA (LC/HA). Structural comparison between LC/HA and LC of BoNT/F1 (LC/F1) reveals distinctive hydrophobic and electrostatic features near the active sites, which may explain their different VAMP-2 cleavage sites. When compared to BoNT/F5 that cleaves VAMP-2 at the same site as BoNT/HA, LC/HA displays higher affinity for VAMP-2, which could be caused by their different surface charge properties surrounding a VAMP-2 exosite-binding cleft. Furthermore, systematic mutagenesis studies on VAMP-2 and structural modeling demonstrate that residues R47 to K59 spanning the cleavage site in VAMP-2 may adopt a novel extended conformation when interacting with LC/HA and LC/F5. Taken together, our structure provides new insights into substrate recognition of BoNT/HA and paves the way for rational design of small molecule or peptide inhibitors against LC/HA.

Clinical analysis of 86 botulism cases caused by cosmetic injection of botulinum toxin (BoNT)

This study was conducted to analyze the clinical characteristics of and treatment strategies for botulism among patients receiving cosmetic injection of botulinum toxin (BoNT).A total of 86 botulism patients caused by cosmetic injection of BoNT were enrolled in our study. All of the patients were diagnosed according to their history of cosmetic BoNT injection, clinical symptoms and signs, and other auxiliary examinations (including those on renal and liver functions, blood index detection, and chest X-ray). All of the patients received comprehensive treatments and botulinum antitoxin serum injection.The main symptoms of botulism patients included headache, dizziness, insomnia, fatigue, blurred vision, eye opening difficulty, slurred speech, dysphagia, bucking, constipation, and anxiety. These clinical symptoms occurred 0∼36 days after BoNT injection, especially from 2nd to 6th day after the operation. Furthermore, the usage dose of BoNT was negatively related to latent period. Finally, patients all discharged from our hospital 1∼20 days after treatments, and their symptoms relieved or disappeared.Botulism is a severe side effect for BoNT injection. Injecting botulinum antitoxin serum may be an effective approach to improve clinical outcomes of botulism cases.

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.

Botulinum neurotoxin-encoding plasmids can be conjugatively transferred to diverse clostridial strains

Most Group I Clostridium botulinum strains harbor botulinum neurotoxin (bont) genes on their chromosome, while some carry these genes (including bont/a, bont/b, and bont/f) on large plasmids. Prior work in our laboratory demonstrated that Group I BoNT plasmids were mobilized to C. botulinum recipient strains containing the Tn916 transposon. Here, we show that Tn916 is nonessential for plasmid transfer. Relying on an auxotrophic donor phenotype and a plasmid-borne selectable marker, we observed the transfer of pCLJ, a 270 kb plasmid harboring two bont genes, from its host strain to various clostridia. Transfer frequency was greatest to other Group I C. botulinum strains, but the plasmid was also transferred into traditionally nontoxigenic species, namely C. sporogenes and C. butyricum. Expression and toxicity of BoNT/A4 was confirmed in transconjugants by immunoblot and mouse bioassay. These data indicate that conjugation within the genus Clostridium can occur across physiological Groups of C. botulinum, supporting horizontal gene transfer via bont-bearing plasmids. The transfer of plasmids possessing bont genes to resistant Clostridium spp. such as C. sporogenes could impact biological safety for animals and humans. These plasmids may play an environmental role in initiating death in vertebrates, leading to decomposition and nutrient recycling of animal biomass.

Novel Distinctive Roles of Docking Proteins in Short-term Synaptic Plasticity of Frog Neuromuscular Transmission Revealed by Botulinum Neurotoxins

Short-term synaptic plasticity (SSP) is a basic mechanism for temporal processing of neural information in synaptic transmission. Facilitation, the fastest component of SSP, has been extensively investigated with regard to Ca²⁺ signaling and other relevant substances. However, systematic analyses on the slower components of SSP, originated by Magleby and Zengel, have remained stagnant for decades, as few chemicals directly modifying these slower components have been identified. In combination with refined experimental protocols designed to study the stimulation frequency-dependence of SSP and botulinum neurotoxins A and C (BoNT-A and BoNT-C), we investigated SSP of frog neuromuscular transmission to clarify the roles of synaptosomal-associated protein of 25 kDa (SNAP-25) and syntaxin, SNARE proteins exclusively participating in vesicular events including docking, priming and exocytosis. We found that BoNT-A treatment eliminated slow potentiation, and BoNT-C poisoning abolished intermediate augmentation, two components of SSP. Fast facilitation was maintained after double poisoning with BoNT-A and -C, but the postsynaptic response became biphasic. A novel depression, termed repression, emerged by double poisoning. Repression was different from depletion because it developed even at a low-frequency stimulation of 1 Hz. We conclude that SNAP-25 and syntaxin not only play roles as cooperative exocytotic machinery, but also have roles in SSP.

An Ultrasensitive Gold Nanoparticle-based Lateral Flow Test for the Detection of Active Botulinum Neurotoxin Type A

Botulism is a severe and potentially lethal paralytic disease caused by several botulinum neurotoxin-producing Clostridia spp. In China, the majority of the cases caused by botulism were from less-developed rural areas. Here, we designed specific substrate peptides and reconfigured gold nanoparticle-based lateral flow test strip (LFTS) to develop an endopeptidase-based lateral flow assay for the diagnosis of botulism. We performed this lateral flow assay on botulinum neurotoxin-spiked human serum samples. The as-prepared LFTS had excellent performance in the detection of botulinum neurotoxin using only 1 μL of simulated serum, and its sensitivity and specificity were comparable to that of mouse lethality assay. Moreover, the assay takes only half a day and does not require highly trained laboratory staff, specialized facility, or equipment. Finally, our LFTS can be potentially extended to other serotypes of BoNTs by designing specific substrate peptides against the different types of BoNTs. Overall, we demonstrate a strategy by which LFTS and endopeptidase activity assays can be integrated to achieve facile and economic diagnosis of botulism in resource-limited settings.

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.

Infection, Pain, and Itch

Pain and itch are unpleasant sensations that often accompany infections caused by viral, bacterial, parasitic, and fungal pathogens. Recent studies show that sensory neurons are able to directly detect pathogens to mediate pain and itch. Nociceptor and pruriceptor neurons respond to pathogen-associated molecular patterns, including Toll-like receptor ligands, N-formyl peptides, and bacterial toxins. Other pathogens are able to silence neuronal activity to produce analgesia during infection. Pain and itch could lead to neuronal modulation of the immune system or behavioral avoidance of future pathogen exposure. Conversely, pathogens could modulate neuronal signaling to potentiate their pathogenesis and facilitate their spread to other hosts. Defining how pathogens modulate pain and itch has critical implications for sensory neurobiology and our understanding of host-microbe interactions.

History of Botulinum Toxin Treatment in Movement Disorders

BACKGROUND

The frontiers of clinical medicine constantly expand as a result of the innovative efforts of visionary researchers and keen observations of seasoned clinicians. In medicine, rarely has a therapeutic agent been found efficacious in the management of so many symptoms and in such a relatively short time as botulinum toxin. One of the most notable contributions of botulinum toxin therapy in clinical medicine is in the field of movement disorders.

METHODS

The English literature was searched using the Yale search engine including but not limited to PubMed and Ovid. The search includes articles from January 1 1980 to March 1 2016.

RESULTS

A total of 2055 articles were identified. Of these, 132 met the criteria for this review.

DISCUSSION

This historical review highlights early and seminal contributions that have introduced the application of botulinum toxins in the field of movement disorders and provides evidence-based contributions that have established botulinum toxin as an effective treatment for abnormal movements.

An optical biosensor assay for rapid dual detection of Botulinum neurotoxins A and E

The enzymatic activity of the pathogenic botulinum neurotoxins type A and E (BoNT/A and E) leads to potentially lethal paralytic symptoms in humans and their prompt detection is of crucial importance. A chip assay based on Surface Plasmon Resonance monitoring of the cleavage products is a simple method that we have previously established to detect BoNT/A activity. We have now developed a similar format assay to measure BoNT/E activity. A monoclonal antibody specifically recognizing SNAP25 cleaved by BoNT/E was generated and used to measure the appearance of the neo-epitope following injection of BoNT/E over SNAP-25 immobilized on a chip. This assay detects BoNT/E activity at 1 LD₅₀/ml within minutes and linear dose-responses curves were obtained using a multiplexed biosensor. A threshold of 0.01 LD₅₀/ml was achieved after 5 h of cleavage. This assay is 10-fold more sensitive than the in vivo assay for direct detection of BoNT/E in serum samples. The SNAP25 chip assay is able to discriminate in an automated manner the presence of BoNT/E, BoNT/A or a combination of both toxins.

Identification and Characterization of Botulinum Neurotoxin A Substrate Binding Pockets and Their Re-Engineering for Human SNAP-23

Botulinum neurotoxins (BoNTs) are highly potent bacterial proteins that block neurotransmitter release at the neuromuscular junction by cleaving SNAREs (soluble N-ethyl maleimide sensitive factor attachment protein receptors). However, their serotype A (BoNT/A) that cleaves SNAP-25 (synaptosomal-associated protein of 25 kDa) has also been an established pharmaceutical for treatment of medical conditions that rely on hyperactivity of cholinergic nerve terminals for 25 years. The expansion of its use to a variety of further medical conditions associated with hypersecretion components is prevented partly because the involved SNARE isoforms are not cleaved. Therefore, we examined by mutational analyses the reason for the resistance of human SNAP-23, an isoform of SNAP-25. We show that replacement of 10 SNAP-23 residues with their SNAP-25 counterparts effects SNAP-25-like cleavability. Conversely, transfer of each of the replaced SNAP-23 residues to SNAP-25 drastically decreased the cleavability of SNAP-25. By means of the existing SNAP-25-toxin co-crystal structure, molecular dynamics simulations, and corroborative mutagenesis studies, the appropriate binding pockets for these residues in BoNT/A were characterized. Systematic mutagenesis of two major BoNT/A binding pockets was conducted in order to adapt these pockets to corresponding amino acids of human SNAP-23. Human SNAP-23 cleaving mutants were isolated using a newly established yeast-based screening system. This method may be useful for engineering novel BoNT/A pharmaceuticals for the treatment of diseases that rely on SNAP-23-mediated hypersecretion.

Botulinum toxin in the management of blepharospasm: current evidence and recent developments

Blepharospasm is a focal (although usually bilateral) dystonia of the orbicularis oculi muscles, producing excessive eye closure. This produces significant disability through functional blindness. Botulinum neurotoxins (BoNT) have become the treatment of choice for blepharospasm; the impressive response rate and the tolerable safety profile have been proven through multiple clinical studies. There are currently four BoNT approved in the United States for different indications - we review the data on blepharospasm for each of these drugs. Currently, incobotulinumtoxinA and onabotulinumtoxinA have the most evidence of benefit for patients with blepharospasm. Current evidence, recent development and future directions are discussed.

Isolation and functional characterization of the novel Clostridium botulinum neurotoxin A8 subtype

Botulism is a severe neurological disease caused by the complex family of botulinum neurotoxins (BoNT). Based on the different serotypes known today, a classification of serotype variants termed subtypes has been proposed according to sequence diversity and immunological properties. However, the relevance of BoNT subtypes is currently not well understood. Here we describe the isolation of a novel Clostridium botulinum strain from a food-borne botulism outbreak near Chemnitz, Germany. Comparison of its botulinum neurotoxin gene sequence with published sequences identified it to be a novel subtype within the BoNT/A serotype designated BoNT/A8. The neurotoxin gene is located within an ha-orfX+ cluster and showed highest homology to BoNT/A1, A2, A5, and A6. Unexpectedly, we found an arginine insertion located in the HC domain of the heavy chain, which is unique compared to all other BoNT/A subtypes known so far. Functional characterization revealed that the binding characteristics to its main neuronal protein receptor SV2C seemed unaffected, whereas binding to membrane-incorporated gangliosides was reduced in comparison to BoNT/A1. Moreover, we found significantly lower enzymatic activity of the natural, full-length neurotoxin and the recombinant light chain of BoNT/A8 compared to BoNT/A1 in different endopeptidase assays. Both reduced ganglioside binding and enzymatic activity may contribute to the considerably lower biological activity of BoNT/A8 as measured in a mouse phrenic nerve hemidiaphragm assay. Despite its reduced activity the novel BoNT/A8 subtype caused severe botulism in a 63-year-old male. To our knowledge, this is the first description and a comprehensive characterization of a novel BoNT/A subtype which combines genetic information on the neurotoxin gene cluster with an in-depth functional analysis using different technical approaches. Our results show that subtyping of BoNT is highly relevant and that understanding of the detailed toxin function might pave the way for the development of novel therapeutics and tailor-made antitoxins.

Development of an ELISA microarray assay for the sensitive and simultaneous detection of ten biodefense toxins

Plant and microbial toxins are considered bioterrorism threat agents because of their extreme toxicity and/or ease of availability. Additionally, some of these toxins are increasingly responsible for accidental food poisonings. The current study utilized an ELISA-based protein antibody microarray for the multiplexed detection of ten biothreat toxins, botulinum neurotoxins (BoNT) A, B, C, D, E, F, ricin, shiga toxins 1 and 2 (Stx), and staphylococcus enterotoxin B (SEB), in buffer and complex biological matrices. The multiplexed assay displayed a sensitivity of 1.3 pg mL(-1) (BoNT/A, BoNT/B, SEB, Stx-1 and Stx-2), 3.3 pg mL(-1) (BoNT/C, BoNT/E, BoNT/F) and 8.2 pg mL(-1) (BoNT/D, ricin). All assays demonstrated high accuracy (75-120 percent recovery) and reproducibility (most coefficients of variation <20%). Quantification curves for the ten toxins were also evaluated in clinical samples (serum, plasma, nasal fluid, saliva, stool, and urine) and environmental samples (apple juice, milk and baby food) with overall minimal matrix effects. The multiplex assays were highly specific, with little cross-reactivity observed between the selected toxin antibodies. The results demonstrate a multiplex microarray that improves current immunoassay sensitivity for biological warfare agents in buffer, clinical, and environmental samples.

Two novel toxin variants revealed by whole-genome sequencing of 175 Clostridium botulinum type E strains

We sequenced 175 Clostridium botulinum type E strains isolated from food, clinical, and environmental sources from northern Canada and analyzed their botulinum neurotoxin (bont) coding sequences (CDSs). In addition to bont/E1 and bont/E3 variant types, neurotoxin sequence analysis identified two novel BoNT type E variants termed E10 and E11. Strains producing type E10 were found along the eastern coastlines of Hudson Bay and the shores of Ungava Bay, while strains producing type E11 were only found in the Koksoak River region of Nunavik. Strains producing BoNT/E3 were widespread throughout northern Canada, with the exception of the coast of eastern Hudson Bay.

New targets in the search for preventive and therapeutic agents for botulism

Botulism is a severe neuroparalytic disease resulting from exposure to one of the most poisonous toxins to humans. Because of this high potency and the use of toxins as biological weapons, botulism is a public health concern and each case represents an emergency. Current therapy involves respiratory supportive care and anti-toxins administration. As a preventive measure, vaccination against toxins represents an effective strategy but is undesirable due the rarity of botulism and the effectiveness of toxins in treating several neuromuscular disorders. This paper summarizes the current issues in botulism treatment and prevention, highlighting the challenge for future researches.

Botulinum neurotoxin type A subtype 2 confers greater safety than subtype 1 in a rat Parkinson's disease model

Botulinum neurotoxin type A (BoNT/A) cleaves SNAP-25 and interrupts the release of acetylcholine. We previously reported that BoNT/A subtype 2 (BoNT/A2) ameliorates pathologic behavior more effectively than subtype 1 (BoNT/A1) in a rat Parkinson's disease model. Here, we further show BoNT/A2 has fewer adverse effects than BoNT/A1. We first confirmed that intrastriatal treatments of both BoNT/As had no-effect on dopaminergic terminals in the striatum. SNAP-25 cleaved by BoNT/A2 was strictly localized to the striatum on the injected side; however, SNAP-25 cleaved by BoNT/A1 diffused contralaterally. Furthermore, treatment with BoNT/A1 caused a significant reduction in body weight, while BoNT/A2 treatment did not. These results suggest that BoNT/A2 is more beneficial for clinical application against Parkinson's disease than BoNT/A1.

Botulinum neurotoxin A subtype 2 reduces pathological behaviors more effectively than subtype 1 in a rat Parkinson's disease model

Recent reports indicate that interruption of acetylcholine release by intrastriatal injection of botulinum neurotoxin type A (BoNT/A) in a rat Parkinson's disease model reduces pathogenic behavior without adverse side effects such as memory dysfunction. Current knowledge suggests that BoNT/A subtype 1 (BoNT/A1) and BoNT/A subtype 2 (BoNT/A2) exert different effects. In the present study, we compared the effects of BoNT/A1 and BoNT/A2 on rotation behavior and in vivo cleavage of presynaptic protein SNAP-25 in a rat unilateral 6-hydroxydopamine-induced Parkinson's disease model. BoNT/A2 more effectively reduced pathogenic behavior by efficiently cleaving SNAP-25 in the striatum compared with that of BoNT/A1. Our results suggest that BoNT/A2 has greater clinical therapeutic value for treating subjects with Parkinson's disease compared to that of BoNT/A1.

Botulinum neurotoxin A2 reduces incidence of seizures in mouse models of temporal lobe epilepsy

Temporal lobe epilepsy often shows pharmacoresistance, and well-known anti-convulsants sometimes are not effective for blocking chronic seizures. Botulinum neurotoxins are metalloproteases that act on presynaptic proteins and inhibit neurotransmitter release in both the peripheral and central nerve systems. That is why neurotoxins may elicit an effect for the restraint of the seizures. Meanwhile, it has been suggested that a property and the stability of neurotoxin activities differ among the types A-G, in which type A neurotoxin (ANTX) is, especially, the most stable and can continue having activity for a long term. The present study therefore investigated the effects of hippocampal injections of A2NTX on seizures derived in TLE model mice, received repeated kindling stimulations in the amygdala. The injections induced complete disappearance of grand mal seizures in half of the population of amygdala kindled mice for 4 days. The injections also induced reduction of the evoked seizure level significantly for at least 18 days after injections. Taken together, these results suggest that A2NTX prevents from epileptic seizures, proposing that A2NTX is available as a new antiepileptic reagent.

A substrate sensor chip to assay the enzymatic activity of Botulinum neurotoxin A

Botulinum neurotoxin A (BoNT/A) induces muscle paralysis by enzymatically cleaving the presynaptic SNARE protein SNAP-25, which results in lasting inhibition of acetylcholine release at the neuromuscular junction. A rapid and sensitive in vitro assay for BoNT/A is required to replace the mouse lethality assay (LD50) in current use. We have developed a fully automated sensor to assay the endoprotease activity of BoNT/A. We produced monoclonal antibodies (mAbs) that recognize SNAP-25 neo-epitopes specifically generated by BoNT/A action. Recombinant SNAP-25 was coupled to the sensor surface of a surface plasmon resonance (SPR) system and samples containing BoNT/A were injected over the substrate sensor. Online substrate cleavage was monitored by measuring binding of mAb10F12 to a SNAP-25 neo-epitope. The SNAP-25-chip assay was toxin serotype-specific and detected 55 fM BoNT/A (1 LD50/ml) in 5 min and 0.4 fM (0.01 LD50/ml) in 5h. Time-course and dose-response curves were linear, yielding a limit of quantification of 0.03 LD50/ml. This label-free method is 100 times more sensitive than the mouse assay, potentially providing rapid read-out of small amounts of toxin for environmental surveillance and the quality control of pharmaceutical preparations.