Botulinum neurotoxins: genetic, structural and mechanistic insights

Molecular diversity of Clostridium botulinum and phenotypically similar strains

This study was undertaken to examine phenotypic and genetic features of strains preliminary classified as Clostridium botulinum species. The phenotypic characteristics were assessed with different culture media and biochemical tests. The genetic characterization included detection of botulinum toxin genes by PCR and macrorestriction analysis with SmaI, XhoI and SacII by PFGE (Pulsed-field Gel Electrophoresis). Despite similar biochemical properties of all analysed strains, only 47% of them contained genes determining toxicity specific to C. botulinum species. The most valuable differentiation of C. botulinum and C. botulinum-like strains was obtained after SmaI digestion. The highest affinity was observed among C. botulinum type B profiles which was even up to 100%. It was found 100% of affinity between C. botulinum and C. botulinum-like strains, however, the similarity among C. botulinum and C. botulinum-like was generally lower than 80%.

An Integrative Approach to Computational Modelling of the Gene Regulatory Network Controlling Clostridium botulinum Type A1 Toxin Production

Clostridium botulinum produces botulinum neurotoxins (BoNTs), highly potent substances responsible for botulism. Currently, mathematical models of C. botulinum growth and toxigenesis are largely aimed at risk assessment and do not include explicit genetic information beyond group level but integrate many component processes, such as signalling, membrane permeability and metabolic activity. In this paper we present a scheme for modelling neurotoxin production in C. botulinum Group I type A1, based on the integration of diverse information coming from experimental results available in the literature. Experiments show that production of BoNTs depends on the growth-phase and is under the control of positive and negative regulatory elements at the intracellular level. Toxins are released as large protein complexes and are associated with non-toxic components. Here, we systematically review and integrate those regulatory elements previously described in the literature for C. botulinum Group I type A1 into a population dynamics model, to build the very first computational model of toxin production at the molecular level. We conduct a validation of our model against several items of published experimental data for different wild type and mutant strains of C. botulinum Group I type A1. The result of this process underscores the potential of mathematical modelling at the cellular level, as a means of creating opportunities in developing new strategies that could be used to prevent botulism; and potentially contribute to improved methods for the production of toxin that is used for therapeutics.

Clostridium botulinum produces botulinum neurotoxins (BoNTs), highly potent substances responsible for botulism. Currently, mathematical models of C. botulinum growth and toxigenesis are largely aimed at risk assessment and do not include explicit genetic information. In this paper we present modelling based on the integration of diverse information from experimental results available in the literature. Experiments show that production of BoNTs depends on the growth-phase and is under the control of positive and negative regulatory elements at the intracellular level. Here, we integrate these regulatory elements into a combined model of population dynamics and gene regulation to build the first computational model of toxin production at the molecular level. We conduct a validation of our model against several items of published experimental data for different wild type and mutant strains of C. botulinum Group I type A1. The result of this process underscores the potential of mathematical modelling at the cellular level, as a means of creating opportunities that could be used to prevent botulism, and potentially contribute to improved methods for the production of toxin used for therapeutics.

Synaptic Vesicle Glycoprotein 2A Ligands in the Treatment of Epilepsy and Beyond

The synaptic vesicle glycoprotein SV2A belongs to the major facilitator superfamily (MFS) of transporters and is an integral constituent of synaptic vesicle membranes. SV2A has been demonstrated to be involved in vesicle trafficking and exocytosis, processes crucial for neurotransmission. The anti-seizure drug levetiracetam was the first ligand to target SV2A and displays a broad spectrum of anti-seizure activity in various preclinical models. Several lines of preclinical and clinical evidence, including genetics and protein expression changes, support an important role of SV2A in epilepsy pathophysiology. While the functional consequences of SV2A ligand binding are not fully elucidated, studies suggest that subsequent SV2A conformational changes may contribute to seizure protection. Conversely, the recently discovered negative SV2A modulators, such as UCB0255, counteract the anti-seizure effect of levetiracetam and display procognitive properties in preclinical models. More broadly, dysfunction of SV2A may also be involved in Alzheimer's disease and other types of cognitive impairment, suggesting potential novel therapies for levetiracetam and its congeners. Furthermore, emerging data indicate that there may be important roles for two other SV2 isoforms (SV2B and SV2C) in the pathogenesis of epilepsy, as well as other neurodegenerative diseases. Utilization of recently developed SV2A positron emission tomography ligands will strengthen and reinforce the pharmacological evidence that SV2A is a druggable target, and will provide a better understanding of its role in epilepsy and other neurological diseases, aiding in further defining the full therapeutic potential of SV2A modulation.

Botulinum Toxin A for Controlling Obesity

Rapid growth of the overweight population and the number of obese individuals in recent decades suggests that current strategies based on diet, exercise, and pharmacological knowledge are not sufficient to address this epidemic. Obesity is the result of a high caloric intake and energy storage, not counterbalanced by an equally important energy expense. Botulinum toxin type A (BoNT-A) use is rapidly expanding to include treatment of a variety of ophthalmological, gastrointestinal, urological, orthopedic, dermatological, secretory, painful, and cosmetic disorders. Many studies evaluating the effect of BoNT-A in gastric antrum e/o fundus for the treatment of obesity have been published. This treatment modality was based on the observation that gastric injection of BoNT-A in laparatomized rats induced a significant reduction of food intake and body weight. These studies have been published yielding debated results. Differences in the selection of patients, the doses of BoNT-A, the method of administration of the toxin, and the instruments of evaluation of some parameters among these studies may be the cause. In this review, it will study the state-of-the-art use of BoNT-A in obesity basic science models and review the clinical evidence on the therapeutic applications of BoNT-A for obesity.

Fecal-Derived Phenol Induces Egg-Laying Aversion in Drosophila

Feces is an abundant, rich source of energy, utilized by a myriad of organisms, not least by members of the order Diptera, i.e., flies. How Drosophila melanogaster reacts to fecal matter remains unclear. Here, we examined oviposition behavior toward a range of fecal samples from mammals native to the putative Southeast African homeland of the fly. We show that D. melanogaster display a strong oviposition aversion toward feces from carnivorous mammals but indifference or even attraction toward herbivore dung. We identify a set of four predictor volatiles, which can be used to differentiate fecal from non-fecal matter, as well as separate carnivore from herbivore feces. Of these volatiles, phenol-indicative of carnivore feces-confers egg-laying aversion and is detected by a single class of sensory neurons expressing Or46a. The Or46a-expressing neurons are necessary and sufficient for oviposition site aversion. We further demonstrate that carnivore feces-unlike herbivore dung-contain a high rate of pathogenic bacteria taxa. These harmful bacteria produce phenol from L-tyrosine, an amino acid specifically enriched in high protein diets, such as consumed by carnivores. Finally, we demonstrate that carnivore feces, as well as phenol, is also avoided by a ball-rolling species of dung beetle, suggesting that phenol is a widespread avoidance signal because of its association with pathogenic bacteria.

SNARE-mediated Fusion of Single Proteoliposomes with Tethered Supported Bilayers in a Microfluidic Flow Cell Monitored by Polarized TIRF Microscopy

In the ubiquitous process of membrane fusion the opening of a fusion pore establishes the first connection between two formerly separate compartments. During neurotransmitter or hormone release via exocytosis, the fusion pore can transiently open and close repeatedly, regulating cargo release kinetics. Pore dynamics also determine the mode of vesicle recycling; irreversible resealing results in transient, "kiss-and-run" fusion, whereas dilation leads to full fusion. To better understand what factors govern pore dynamics, we developed an assay to monitor membrane fusion using polarized total internal reflection fluorescence (TIRF) microscopy with single molecule sensitivity and ~15 msec time resolution in a biochemically well-defined in vitro system. Fusion of fluorescently labeled small unilamellar vesicles containing v-SNARE proteins (v-SUVs) with a planar bilayer bearing t-SNAREs, supported on a soft polymer cushion (t-SBL, t-supported bilayer), is monitored. The assay uses microfluidic flow channels that ensure minimal sample consumption while supplying a constant density of SUVs. Exploiting the rapid signal enhancement upon transfer of lipid labels from the SUV to the SBL during fusion, kinetics of lipid dye transfer is monitored. The sensitivity of TIRF microscopy allows tracking single fluorescent lipid labels, from which lipid diffusivity and SUV size can be deduced for every fusion event. Lipid dye release times can be much longer than expected for unimpeded passage through permanently open pores. Using a model that assumes retardation of lipid release is due to pore flickering, a pore "openness", the fraction of time the pore remains open during fusion, can be estimated. A soluble marker can be encapsulated in the SUVs for simultaneous monitoring of lipid and soluble cargo release. Such measurements indicate some pores may reseal after losing a fraction of the soluble cargo.

"Non-Toxic" Proteins of the Botulinum Toxin Complex Exert In-vivo Toxicity

The botulinum neurotoxin (BoNT) causes muscle paralysis and is the most potent toxin in nature. BoNT is associated with a complex of auxiliary “Non-Toxic” proteins, which constitute a large-sized toxin complex (L-TC). However, here we report that the “Non-Toxic” complex of serotype D botulinum L-TC, when administered to rats, exerts in-vivo toxicity on small-intestinal villi. Moreover, Serotype C and D of the “Non-Toxic” complex, but not BoNT, induced vacuole-formation in a rat intestinal epithelial cell line (IEC-6), resulting in cell death. Our results suggest that the vacuole was formed in a manner distinct from the mechanism by which Helicobacter pylori vacuolating toxin (VacA) and Vibrio cholerae haemolysin induce vacuolation. We therefore hypothesise that the serotype C and D botulinum toxin complex is a functional hybrid of the neurotoxin and vacuolating toxin (VT) which arose from horizontal gene transfer from an ancestral BoNT-producing bacterium to a hypothetical VT-producing bacterium.

Interneuronal Transfer and Distal Action of Tetanus Toxin and Botulinum Neurotoxins A and D in Central Neurons

Recent reports suggest that botulinum neurotoxin (BoNT) A, which is widely used clinically to inhibit neurotransmission, can spread within networks of neurons to have distal effects, but this remains controversial. Moreover, it is not known whether other members of this toxin family are transferred between neurons. Here, we investigate the potential distal effects of BoNT/A, BoNT/D, and tetanus toxin (TeNT), using central neurons grown in microfluidic devices. Toxins acted upon the neurons that mediated initial entry, but all three toxins were also taken up, via an alternative pathway, into non-acidified organelles that mediated retrograde transport to the somato-dendritic compartment. Toxins were then released into the media, where they entered and exerted their effects upon upstream neurons. These findings directly demonstrate that these agents undergo transcytosis and interneuronal transfer in an active form, resulting in long-distance effects.

Impact of Clostridium botulinum genomic diversity on food safety

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C. botulinum Groups I and II form botulinum neurotoxin and cause foodborne botulism.

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Increased knowledge of C. botulinum Group I and II genomes and neurotoxin diversity.

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Impact on food safety via improved surveillance and tracing/tracking during outbreaks.

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New insights into C. botulinum biology, food chain transmission, evolution.

The deadly botulinum neurotoxin formed by Clostridium botulinum is the causative agent of foodborne botulism. The increasing availability of C. botulinum genome sequences is starting to allow the genomic diversity of C. botulinum Groups I and II and their neurotoxins to be characterised. This information will impact on microbiological food safety through improved surveillance and tracing/tracking during outbreaks, and a better characterisation of C. botulinum Groups I and II, including the risk presented, and new insights into their biology, food chain transmission, and evolution.

Coating nanoparticles with cell membranes for targeted drug delivery

Targeted delivery allows drug molecules to preferentially accumulate at the sites of action and thus holds great promise to improve therapeutic index. Among various drug-targeting approaches, nanoparticle-based delivery systems offer some unique strengths and have achieved exciting preclinical and clinical results. Herein, we aim to provide a review on the recent development of cell membrane-coated nanoparticle system, a new class of biomimetic nanoparticles that combine both the functionalities of cellular membranes and the engineering flexibility of synthetic nanomaterials for effective drug delivery and novel therapeutics. This review is particularly focused on novel designs of cell membrane-coated nanoparticles as well as their underlying principles that facilitate the purpose of drug targeting. Three specific areas are highlighted, including: (i) cell membrane coating to prolong nanoparticle circulation, (ii) cell membrane coating to achieve cell-specific targeting and (iii) cell membrane coating for immune system targeting. Overall, cell membrane-coated nanoparticles have emerged as a novel class of targeted nanotherapeutics with strong potentials to improve on drug delivery and therapeutic efficacy for treatment of various diseases.

The first non Clostridial botulinum-like toxin cleaves VAMP within the juxtamembrane domain

The genome of Weissella oryzae SG25T was recently sequenced and a botulinum neurotoxin (BoNT) like gene was identified by bioinformatics methods. The typical three-domains organization of BoNTs with a N-terminal metalloprotease domain, a translocation and a cell binding domains could be identified. The BoNT family of neurotoxins is rapidly growing, but this was the first indication of the possible expression of a BoNT toxin outside the Clostridium genus. We performed molecular modeling and dynamics simulations showing that the 50 kDa N-terminal domain folds very similarly to the metalloprotease domain of BoNT/B, whilst the binding part is different. However, neither the recombinant metalloprotease nor the binding domains showed cross-reactivity with the standard antisera that define the seven serotypes of BoNTs. We found that the purified Weissella metalloprotease cleaves VAMP at a single site untouched by the other VAMP-specific BoNTs. This site is a unique Trp-Trp peptide bond located within the juxtamembrane segment of VAMP which is essential for neurotransmitter release. Therefore, the present study identifies the first non-Clostridial BoNT-like metalloprotease that cleaves VAMP at a novel and relevant site and we propose to label it BoNT/Wo.

Identification of small molecule inhibitors of botulinum neurotoxin serotype E via footprint similarity

Botulinum neurotoxins (BoNT) are among the most poisonous substances known, and of the 7 serotypes (A-G) identified thus far at least 4 can cause death in humans. The goal of this work was identification of inhibitors that specifically target the light chain catalytic site of the highly pathogenic but lesser-studied E serotype (BoNT/E). Large-scale computational screening, employing the program DOCK, was used to perform atomic-level docking of 1.4 million small molecules to prioritize those making favorable interactions with the BoNT/E site. In particular, 'footprint similarity' (FPS) scoring was used to identify compounds that could potentially mimic features on the known substrate tetrapeptide RIME. Among 92 compounds purchased and experimentally tested, compound C562-1101 emerged as the most promising hit with an apparent IC₅₀ value three-fold more potent than that of the first reported BoNT/E small molecule inhibitor NSC-77053. Additional analysis showed the predicted binding pose of C562-1101 was geometrically and energetically stable over an ensemble of structures generated by molecular dynamic simulations and that many of the intended interactions seen with RIME were maintained. Several analogs were also computationally designed and predicted to have further molecular mimicry thereby demonstrating the potential utility of footprint-based scoring protocols to help guide hit refinement.

Apoptotic action of botulinum toxin on masseter muscle in rats: early and late changes in the expression of molecular markers

The purpose of this study was to compare the early or late expression levels of p65, Bcl-2, and type II myosin and the frequency of TUNEL-positive nuclei in the rat masseter muscle after injection of different concentrations of botulinum toxin-A (BTX-A). We injected either 5 U or 10 U of BTX-A into both masseter muscles of the rat. As a control group, the same volume of saline was injected. After 2 or 12 weeks, the animals were sacrificed. Subsequently, a biopsy and immunohistochemical staining of the samples were performed using a p65, Bcl-2, or type II myosin antibody. Additionally, a TUNEL assay and transmission electron microscopic analysis were performed. The expression of p65, Bcl-2, and type II myosin increased significantly with increasing concentrations of BTX-A at 2 weeks after BTX-A injection (P < 0.05). The number of TUNEL-positive nuclei was also significantly increased in the BTX-A-treated groups in comparison to the saline-treated control at 2 weeks after BTX-A injection (P < 0.05). Elevated expression of Bcl-2 was also observed in 10-unit BTX-A-treated group at 12 weeks after injection (P < 0.05). At 12 weeks after injection, the number of enlarged mitochondria was increased, and many mitochondria displayed aberrations in cristae morphology after BTX-A injection. In conclusion, BTX-A injection into the masseter muscle increased the expression level of p65, Bcl-2, and type II myosin at an early stage. The morphological changes of mitochondria were more evident at 12 weeks after injection.

N-linked glycosylation of SV2 is required for binding and uptake of botulinum neurotoxin A

Botulinum neurotoxin serotype A1 (BoNT/A1), a licensed drug widely used for medical and cosmetic applications, exerts its action by invading motoneurons. Here we report a 2.0-Å-resolution crystal structure of the BoNT/A1 receptor-binding domain in complex with its neuronal receptor, glycosylated human SV2C. We found that the neuronal tropism of BoNT/A1 requires recognition of both the peptide moiety and an N-linked glycan on SV2. This N-glycan-which is conserved in all SV2 isoforms across vertebrates-is essential for BoNT/A1 binding to neurons and for its potent neurotoxicity. The glycan-binding interface on SV2 is targeted by a human BoNT/A1-neutralizing antibody currently licensed as an antibotulism drug. Our studies reveal a new paradigm of host-pathogen interactions, in which pathogens exploit conserved host post-translational modifications, thereby achieving highly specific receptor binding while also tolerating genetic changes across multiple isoforms of receptors.

Detection, differentiation, and identification of botulinum neurotoxin serotypes C, CD, D, and DC by highly specific immunoassays and mass spectrometry

Botulinum neurotoxin (BoNT) serotypes C and D and their mosaic variants CD and DC cause severe cases of botulism in animal husbandry and wildlife. Epidemiological data on the exact serotype or toxin variant causing outbreaks are rarely available, mainly because of their high sequence identity and the lack of fast and specific screening tools to detect and differentiate the four similar toxins. To fill this gap, we developed four highly specific sandwich enzyme-linked immunosorbent assays (ELISAs) able to detect and differentiate botulinum neurotoxins type BoNT/C, D, CD, and DC based on four distinct combinations of specific monoclonal antibodies targeting both conserved and divergent subdomains of the four toxins. Here, highly sensitive detection with detection limits between 2 and 24 pg mL(-1) was achieved. The ELISAs were extensively validated and results were compared with data obtained by quantitative real-time PCR using a panel of Clostridium botulinum strains, real sample materials from veterinary botulism outbreaks, and non-BoNT-producing Clostridia. Additionally, in order to verify the results obtained by ELISA screening, the new monoclonal antibodies were used for BoNT enrichment and subsequent detection (i) on a functional level by endopeptidase mass spectrometry (Endopep-MS) assays and (ii) on a protein sequence level by LC-MS/MS spectrometry. Based on all technical information gathered in the validation study, the four differentiating ELISAs turned out to be highly reliable screening tools for the rapid analysis of veterinary botulism cases and should aid future field investigations of botulism outbreaks and the acquisition of epidemiological data.

Differences in the Vulnerability of Waterbird Species to Botulism Outbreaks in Mediterranean Wetlands: an Assessment of Ecological and Physiological Factors

Avian botulism kills thousands of waterbirds every year, including endangered species, but information about the differences between species in vulnerability to botulism outbreaks and the capacity to act as carriers of Clostridium botulinum is still poorly known. Here, we estimated the vulnerability to botulism of 11 waterbird species from Mediterranean wetlands by comparing the number of affected birds with the census of individuals at risk. The capacity of different species to act as carriers was studied by detecting the presence of the C. botulinum type C/D botulinum neurotoxin (BoNT) gene in fecal samples and prey items of waterbirds in the wild and by the serial sampling of cloacal swabs of birds affected by botulism. We found differences among species in their vulnerabilities to botulism, probably related to feeding habits, season of arrival, turnover, and, possibly, phylogenetic resilience. The globally endangered white-headed duck (Oxyura leucocephala) showed mortality rates in the studied outbreaks of 7% and 17% of the maximum census, which highlights botulism as a risk factor for the conservation of the species. Invasive water snails, such as Physa acuta, may be important drivers in botulism epidemiology, because 30% of samples tested positive for the BoNT gene during outbreaks. Finally, our results show that birds may excrete the pathogen for up to 7 days, and some individuals can do it for longer periods. Rails and ducks excreted C. botulinum more often and for longer times than gulls, which could be related to their digestive physiology (i.e., cecum development).

IMPORTANCE

Botulism is an important cause of mortality in waterbirds, including some endangered species. The global climate change may have consequences in the ecology of wetlands that favor the occurrence of botulism outbreaks. Here, we offer some information to understand the ecology of this disease that can be useful to cope with these global changes in the future. We have found that some species (i.e., coots and dabbling ducks) are more vulnerable to botulism and have a more relevant role in the onset and amplification of the outbreaks than other species (i.e., flamingos and grebes). Feeding habits can explain these differences in part; in addition to the well-known role of necrophagous fly maggots, we found here that water snails are frequent carriers of Clostridium botulinum This is relevant, because these water snails can thrive in eutrophic and polluted wetlands, exacerbating other changes driven by climate change in wetlands.

Intracellular trafficking of bacterial toxins

Bacterial toxins often translocate across a cellular membrane to gain access into the host cytosol, modifying cellular components in order to exert their toxic effects. To accomplish this feat, these toxins traffic to a membrane penetration site where they undergo conformational changes essential to eject the toxin's catalytic subunit into the cytosol. In this brief review, we highlight recent findings that elucidate both the trafficking pathways and membrane translocation mechanisms of toxins that cross the plasma, endosomal, or endoplasmic reticulum (ER) membrane. These findings not only illuminate the specific nature of the host-toxin interactions during entry, but should also provide additional therapeutic strategies to prevent or alleviate the bacterial toxin-induced diseases.

Detection of Clostridium botulinum neurotoxin genes (A-F) in dairy farms from Northern Germany using PCR: A case-control study

Classical botulism in cattle mainly occurs after ingestion of feed contaminated with preformed toxin. In 2001 a form of botulism ("visceral botulism") was postulated to occur after ingestion of Clostridium (C.) botulinum cells or spores, followed by colonization of the intestine, and local production of botulinum neurotoxin (BoNT) causing chronic generalized disease. To verify the potential role of C. botulinum in the described syndrome, a case-control study was conducted, including 139 farms. Fecal samples, rumen content, water and silage samples were collected on each farm. Real time BoNT gene PCR assays were conducted after enrichment in RCM (Reinforced Clostridial Medium) at 37 °C and conventional PCRs after enrichment in MCM (Modified Cooked Meat Medium) at 30 °C. Furthermore, a direct detection of BoNT genes without prior enrichment was attempted. BoNT A, B, C, D, E and F genes were detected in animal samples from 25 (17.99%), 3 (2.16%), 0 (0.0%), 2 (1.44%), 1 (0.72%), and 3 (2.16%) farms, respectively. Eleven feed samples were positive for BoNT A gene. By enrichment a significant increase in sensitivity was achieved. Therefore, this should be an essential part of any protocol. No significant differences regarding BoNT gene occurrence could be observed between Case and Control farms or chronically diseased and clinically healthy animals within the particular category. Thus, the postulated form of chronic botulism in cows could not be confirmed. This study supports the general opinion that C. botulinum can occasionally be found in the rumen and intestine of cows without causing disease.

Effects of Megaplasmid Loss on Growth of Neurotoxigenic Clostridium butyricum Strains and Botulinum Neurotoxin Type E Expression

Clostridium butyricum strains that atypically produce the botulinum neurotoxin type E (BoNT/E) possess a megaplasmid of unknown functions in their genome. In this study, we cured two botulinum neurotoxigenic C. butyricum type E strains of their megaplasmids, and compared the obtained megaplasmid-cured strains to their respective wild-type parental strains. Our results showed that the megaplasmids do not confer beta-lactam resistance on the neurotoxigenic C. butyricum type E strains, although they carry several putative beta-lactamase genes. Instead, we found that the megaplasmids are essential for growth of the neurotoxigenic C. butyricum type E strains at the relatively low temperature of 15°C, and are also relevant for growth of strains under limiting pH and salinity conditions, as well as under favorable environmental conditions. Moreover, the presence of the megaplasmids was associated with increased transcript levels of the gene encoding BoNT/E in the C. butyricum type E strains, indicating that the megaplasmids likely contain transcriptional regulators. However, the levels of BoNT/E in the supernatants of the cured and uncured strains were similar after 24 and 48 h culture, suggesting that expression of BoNT/E in the C. butyricum type E strains is not ultimately controlled by the megaplasmids. Together, our results reveal that the C. butyricum type E megaplasmids exert pleiotropic effects on the growth of their microbial hosts under optimal and limiting environmental conditions, and also highlight the possibility of original regulatory mechanisms controlling the expression of BoNT/E.

Purification and Characterization of Botulinum Neurotoxin FA from a Genetically Modified Clostridium botulinum Strain

Botulinum neurotoxins (BoNTs), produced by neurotoxigenic clostridial species, are the cause of the severe disease botulism in humans and animals. Early research on BoNTs has led to their classification into seven serotypes (serotypes A to G) based upon the selective neutralization of their toxicity in mice by homologous antibodies. Recently, a report of a potential eighth serotype of BoNT, designated "type H," has been controversial. This novel BoNT was produced together with BoNT/B2 in a dual-toxin-producing Clostridium botulinum strain. The data used to designate this novel toxin as a new serotype were derived from culture supernatant containing both BoNT/B2 and novel toxin and from sequence information, although data from two independent laboratories indicated neutralization by antibodies raised against BoNT/A1, and classification as BoNT/FA was proposed. The sequence data indicate a chimeric structure consisting of a BoNT/A1 receptor binding domain, a BoNT/F5 light-chain domain, and a novel translocation domain most closely related to BoNT/F1. Here, we describe characterization of this toxin purified from the native strain in which expression of the second BoNT (BoNT/B) has been eliminated. Mass spectrometry analysis indicated that the toxin preparation contained only BoNT/FA and confirmed catalytic activity analogous to that of BoNT/F5. The in vivo mouse bioassay indicated a specific activity of this toxin of 3.8 × 10(7) mouse 50% lethal dose (mLD50) units/mg, whereas activity in cultured human neurons was very high (50% effective concentration [EC50] = 0.02 mLD50/well). Neutralization assays in cells and mice both indicated full neutralization by various antibodies raised against BoNT/A1, although at 16- to 20-fold-lower efficiency than for BoNT/A1. IMPORTANCE Botulinum neurotoxins (BoNTs), produced by anaerobic bacteria, are the cause of the potentially deadly, neuroparalytic disease botulism. BoNTs have been classified into seven serotypes, serotypes A to G, based upon their selective neutralization by homologous antiserum, which is relevant for clinical and diagnostic purposes. Even though supportive care dramatically reduces the death rate of botulism, the only pharmaceutical intervention to reduce symptom severity and recovery time is early administration of antitoxin (antiserum raised against BoNTs). A recent report of a novel BoNT serotype, serotype H, raised concern of a "treatment-resistant" and highly potent toxin. However, the toxin's chimeric structure and characteristics indicate a chimeric BoNT/FA. Here we describe the first characterization of this novel toxin in purified form. BoNT/FA was neutralized by available antitoxins, supporting classification as BoNT/FA. BoNT/FA required proteolytic activation to achieve full toxicity and had relatively low potency in mice compared to BoNT/A1 but surprisingly high activity in cultured neurons.

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 Rho Termination Factor of Clostridium botulinum Contains a Prion-Like Domain with a Highly Amyloidogenic Core

Prion-like proteins can switch between a soluble intrinsically disordered conformation and a highly ordered amyloid assembly. This conformational promiscuity is encoded in specific sequence regions, known as prion domains (PrDs). Prions are best known as the causative factors of neurological diseases in mammals. However, bioinformatics analyses reveal that proteins bearing PrDs are present in all kingdoms of life, including bacteria, thus supporting the idea that they serve conserved beneficial cellular functions. Despite the proportion of predicted prion-like proteins in bacterial proteomes is generally low, pathogenic species seem to have a higher prionic load, suggesting that these malleable proteins may favor pathogenic traits. In the present work, we performed a stringent computational analysis of the Clostridium botulinum pathogen proteome in the search for prion-like proteins. A total of 54 candidates were predicted for this anaerobic bacterium, including the transcription termination Rho factor. This RNA-binding protein has been shown to play a crucial role in bacterial adaptation to changing environments. We show here that the predicted disordered PrD domain of this RNA-binding protein contains an inner, highly polar, asparagine-rich short sequence able to spontaneously self-assemble into amyloid-like structures, bearing thus the potential to induce a Rho factor conformational switch that might rewire gene expression in response to environmental conditions.

Rapid Microfluidic Assay for the Detection of Botulinum Neurotoxin in Animal Sera

Potent Botulinum neurotoxins (BoNTs) represent a threat to public health and safety. Botulism is a disease caused by BoNT intoxication that results in muscle paralysis that can be fatal. Sensitive assays capable of detecting BoNTs from different substrates and settings are essential to limit foodborne contamination and morbidity. In this report, we describe a rapid 96-well microfluidic double sandwich immunoassay for the sensitive detection of BoNT-A from animal sera. This BoNT microfluidic assay requires only 5 μL of serum, provides results in 75 min using a standard fluorescence microplate reader and generates minimal hazardous waste. The assay has a <30 pg·mL⁻¹ limit of detection (LOD) of BoNT-A from spiked human serum. This sensitive microfluidic BoNT-A assay offers a fast and simplified workflow suitable for the detection of BoNT-A from serum samples of limited volume in most laboratory settings.

Recombinant Botulinum Toxoids: A Practical Guide for Production

Clostridium botulinum is a Gram-positive, spore-forming, anaerobic bacillus that produces a potent neurotoxin. Botulinum neurotoxins (BoNTs) are classified from serotypes A to H, and even though they have similar mechanisms of action, they show preferential hosts. In veterinary medicine, BoNT serotypes C and D are the most important, once several animal species are susceptible to them. Since BoNTs are the most potent toxins known in nature, the best way to control botulism in animals is through vaccination. However, current commercial vaccines are based on inactivated toxins (toxoids) and cells (bacterins) and present many drawbacks, such as a time-consuming production with variable antigen yield and biosafety risks. Recombinant vaccines, especially those produced by Escherichia coli expression system, have proved to be an interesting alternative to overcome these problems. E. coli is a very well-known microorganism that allows the production of large amounts of nontoxic recombinant antigens in a short period using simple culture medium reducing the production complexity and decreasing most of the biosafety risks involved in the process. We describe herein a method for the production of recombinant vaccines for veterinary medicine application, involving initial steps of gene design up to vaccine formulation and evaluation itself.

A Novel Inhibitor Prevents the Peripheral Neuroparalysis of Botulinum Neurotoxins

Botulinum neurotoxins (BoNTs) form a large class of potent and deadly neurotoxins. Given their growing number, it is of paramount importance to discover novel inhibitors targeting common steps of their intoxication process. Recently, EGA was shown to inhibit the action of bacterial toxins and viruses exhibiting a pH-dependent translocation step in mammalian cells, by interfering with their entry route. As BoNTs act in the cytosol of nerve terminals, the entry into an appropriate compartment wherefrom they translocate the catalytic moiety is essential for toxicity. Herein we propose an optimized procedure to synthesize EGA and we show that, in vitro, it prevents the neurotoxicity of different BoNT serotypes by interfering with their trafficking. Furthermore, in mice, EGA mitigates botulism symptoms induced by BoNT/A and significantly decreases the lethality of BoNT/B and BoNT/D. This opens the possibility of using EGA as a lead compound to develop novel inhibitors of botulinum neurotoxins.

Snake and Spider Toxins Induce a Rapid Recovery of Function of Botulinum Neurotoxin Paralysed Neuromuscular Junction

Botulinum neurotoxins (BoNTs) and some animal neurotoxins (β-Bungarotoxin, β-Btx, from elapid snakes and α-Latrotoxin, α-Ltx, from black widow spiders) are pre-synaptic neurotoxins that paralyse motor axon terminals with similar clinical outcomes in patients. However, their mechanism of action is different, leading to a largely-different duration of neuromuscular junction (NMJ) blockade. BoNTs induce a long-lasting paralysis without nerve terminal degeneration acting via proteolytic cleavage of SNARE proteins, whereas animal neurotoxins cause an acute and complete degeneration of motor axon terminals, followed by a rapid recovery. In this study, the injection of animal neurotoxins in mice muscles previously paralyzed by BoNT/A or /B accelerates the recovery of neurotransmission, as assessed by electrophysiology and morphological analysis. This result provides a proof of principle that, by causing the complete degeneration, reabsorption, and regeneration of a paralysed nerve terminal, one could favour the recovery of function of a biochemically- or genetically-altered motor axon terminal. These observations might be relevant to dying-back neuropathies, where pathological changes first occur at the neuromuscular junction and then progress proximally toward the cell body.

The pattern of growth observed for Clostridium botulinum type A1 strain ATCC 19397 is influenced by nutritional status and quorum sensing: a modelling perspective

Botulinum neurotoxins (BoNTs) produced by the anaerobic bacterium Clostridium botulinum are the most poisonous substances known to mankind. However, toxin regulation and signals triggering synthesis as well as the regulatory network and actors controlling toxin production are unknown. Experiments show that the neurotoxin gene is growth phase dependent for C. botulinum type A1 strain ATCC 19397, and toxin production is influenced both by culture conditions and nutritional status of the medium. Building mathematical models to describe the genetic and molecular machinery that drives the synthesis and release of BoNT requires a simultaneous description of the growth of the bacterium in culture. Here, we show four plausible modelling options which could be considered when constructing models describing the pattern of growth observed in a botulinum growth medium. Commonly used bacterial growth models are unsuitable to fit the pattern of growth observed, since they only include monotonic growth behaviour. We find that a model that includes both the nutritional status and the ability of the cells to sense their surroundings in a quorum-sensing manner is most successful at explaining the pattern of growth obtained for C. botulinum type A1 strain ATCC 19397.

Use of Monoclonal Antibodies in the Sensitive Detection and Neutralization of Botulinum Neurotoxin Serotype B

Botulinum neurotoxins (BoNT) are some of nature’s most potent toxins. Due to potential food contamination, and bioterrorism concerns, the development of detection reagents, therapeutics and countermeasures are of urgent interest. Recently, we have developed a sensitive electrochemiluminescent (ECL) immunoassay for BoNT/B, using monoclonal antibodies (mAbs) MCS6-27 and anti-BoNT/B rabbit polyclonal antibodies as the capture and detector. The ECL assay detected as little as 1 pg/mL BoNT/B in the buffer matrix, surpassing the detection sensitivities of the gold standard mouse bioassays. The ECL assay also allowed detection of BoNT/B in sera matrices of up to 100% sera with negligible matrix effects. This highly-sensitive assay allowed the determination of the biological half-lives of BoNT/B holotoxin in vivo. We further tested the toxin neutralization potential of our monoclonal antibodies using the mouse systemic and oral intoxication models. A combination of mAbs protected mice in both pre- and post-exposure models to lethal doses of BoNT/B. MAbs were capable of increasing survival of animals when administered even 10 h post-intoxication in an oral model, suggesting a likely time for BoNT/B complexes to reach the blood stream. More sensitive detection assays and treatments against BoNT intoxication will greatly enhance efforts to combat botulism.

Qualitative and Quantitative Detection of Botulinum Neurotoxins from Complex Matrices: Results of the First International Proficiency Test

In the framework of the EU project EQuATox, a first international proficiency test (PT) on the detection and quantification of botulinum neurotoxins (BoNT) was conducted. Sample materials included BoNT serotypes A, B and E spiked into buffer, milk, meat extract and serum. Different methods were applied by the participants combining different principles of detection, identification and quantification. Based on qualitative assays, 95% of all results reported were correct. Successful strategies for BoNT detection were based on a combination of complementary immunological, MS-based and functional methods or on suitable functional in vivo/in vitro approaches (mouse bioassay, hemidiaphragm assay and Endopep-MS assay). Quantification of BoNT/A, BoNT/B and BoNT/E was performed by 48% of participating laboratories. It turned out that precise quantification of BoNT was difficult, resulting in a substantial scatter of quantitative data. This was especially true for results obtained by the mouse bioassay which is currently considered as "gold standard" for BoNT detection. The results clearly demonstrate the urgent need for certified BoNT reference materials and the development of methods replacing animal testing. In this context, the BoNT PT provided the valuable information that both the Endopep-MS assay and the hemidiaphragm assay delivered quantitative results superior to the mouse bioassay.

Recommended Immunological Strategies to Screen for Botulinum Neurotoxin-Containing Samples

Botulinum neurotoxins (BoNTs) cause the life-threatening neurological illness botulism in humans and animals and are divided into seven serotypes (BoNT/A–G), of which serotypes A, B, E, and F cause the disease in humans. BoNTs are classified as “category A” bioterrorism threat agents and are relevant in the context of the Biological Weapons Convention. An international proficiency test (PT) was conducted to evaluate detection, quantification and discrimination capabilities of 23 expert laboratories from the health, food and security areas. Here we describe three immunological strategies that proved to be successful for the detection and quantification of BoNT/A, B, and E considering the restricted sample volume (1 mL) distributed. To analyze the samples qualitatively and quantitatively, the first strategy was based on sensitive immunoenzymatic and immunochromatographic assays for fast qualitative and quantitative analyses. In the second approach, a bead-based suspension array was used for screening followed by conventional ELISA for quantification. In the third approach, an ELISA plate format assay was used for serotype specific immunodetection of BoNT-cleaved substrates, detecting the activity of the light chain, rather than the toxin protein. The results provide guidance for further steps in quality assurance and highlight problems to address in the future.

Botulinum Neurotoxins: Qualitative and Quantitative Analysis Using the Mouse Phrenic Nerve Hemidiaphragm Assay (MPN)

The historical method for the detection of botulinum neurotoxin (BoNT) is represented by the mouse bioassay (MBA) measuring the animal survival rate. Since the endpoint of the MBA is the death of the mice due to paralysis of the respiratory muscle, an ex vivo animal replacement method, called mouse phrenic nerve (MPN) assay, employs the isolated N. phrenicus-hemidiaphragm tissue. Here, BoNT causes a dose-dependent characteristic decrease of the contraction amplitude of the indirectly stimulated muscle. Within the EQuATox BoNT proficiency 13 test samples were analysed using the MPN assay by serial dilution to a bath concentration resulting in a paralysis time within the range of calibration curves generated with BoNT/A, B and E standards, respectively. For serotype identification the diluted samples were pre-incubated with polyclonal anti-BoNT/A, B or E antitoxin or a combination of each. All 13 samples were qualitatively correctly identified thereby delivering superior results compared to single in vitro methods like LFA, ELISA and LC-MS/MS. Having characterized the BoNT serotype, the final bath concentrations were calculated using the calibration curves and then multiplied by the respective dilution factor to obtain the sample concentration. Depending on the source of the BoNT standards used, the quantitation of ten BoNT/A containing samples delivered a mean z-score of 7 and of three BoNT/B or BoNT/E containing samples z-scores <2, respectively.

Current status and future directions of botulinum neurotoxins for targeting pain processing

Current evidence suggests that botulinum neurotoxins (BoNTs) A1 and B1, given locally into peripheral tissues such as skin, muscles, and joints, alter nociceptive processing otherwise initiated by inflammation or nerve injury in animal models and humans. Recent data indicate that such locally delivered BoNTs exert not only local action on sensory afferent terminals but undergo transport to central afferent cell bodies (dorsal root ganglia) and spinal dorsal horn terminals, where they cleave SNAREs and block transmitter release. Increasing evidence supports the possibility of a trans-synaptic movement to alter postsynaptic function in neuronal and possibly non-neuronal (glial) cells. The vast majority of these studies have been conducted on BoNT/A1 and BoNT/B1, the only two pharmaceutically developed variants. However, now over 40 different subtypes of botulinum neurotoxins (BoNTs) have been identified. By combining our existing and rapidly growing understanding of BoNT/A1 and /B1 in altering nociceptive processing with explorations of the specific characteristics of the various toxins from this family, we may be able to discover or design novel, effective, and long-lasting pain therapeutics. This review will focus on our current understanding of the molecular mechanisms whereby BoNTs alter pain processing, and future directions in the development of these agents as pain therapeutics.

Interactions of a potent cyclic peptide inhibitor with the light chain of botulinum neurotoxin A: Insights from X-ray crystallography

The seven antigenically distinct serotypes (A-G) of botulinum neurotoxin (BoNT) are responsible for the deadly disease botulism. BoNT serotype A (BoNT/A) exerts its lethal action by cleaving the SNARE protein SNAP-25, leading to inhibition of neurotransmitter release, flaccid paralysis and autonomic dysfunction. BoNTs are dichain proteins consisting of a ∼ 100 kDa heavy chain and a ∼ 50 kDa light chain; the former is responsible for neurospecific binding, internalization and translocation, and the latter for cleavage of neuronal SNARE proteins. Because of their extreme toxicity and history of weaponization, the BoNTs are regarded as potential biowarfare/bioterrorism agents. No post-symptomatic therapeutic interventions are available for BoNT intoxication other than intensive care; therefore it is imperative to develop specific antidotes against this neurotoxin. To this end, a cyclic peptide inhibitor (CPI-1) was evaluated in a FRET assay for its ability to inhibit BoNT/A light chain (Balc). CPI was found to be highly potent, exhibiting a Ki of 12.3 nM with full-length Balc448 and 39.2 nM using a truncated crystallizable form of the light chain (Balc424). Cocrystallization studies revealed that in the Balc424-CPI-1 complex, the inhibitor adopts a helical conformation, occupies a high percentage of the active site cavity and interacts in an amphipathic manner with critical active site residues. The data suggest that CPI-1 prevents SNAP-25 from accessing the Balc active site by blocking both the substrate binding path at the surface and the Zn(2+) binding region involved in catalysis. This differs from linear peptide inhibitors described to date which block only the latter.

Inhibition of botulinum neurotoxins interchain disulfide bond reduction prevents the peripheral neuroparalysis of botulism

Botulinum neurotoxins (BoNTs) form a growing family of metalloproteases with a unique specificity either for VAMP, SNAP25 or syntaxin. The BoNTs are grouped in seven different serotypes indicated by letters from A to G. These neurotoxins enter the cytosol of nerve terminals via a 100 kDa chain which binds to the presynaptic membrane and assists the translocation of a 50 kDa metalloprotease chain. These two chains are linked by a single disulfide bridge which plays an essential role during the entry of the metalloprotease chain in the cytosol, but thereafter it has to be reduced to free the proteolytic activity. Its reduction is mediated by thioredoxin which is continuously regenerated by its reductase. Here we show that inhibitors of thioredoxin reductase or of thioredoxin prevent the specific proteolysis of VAMP by the four VAMP-specific BoNTs: type B, D, F and G. These compounds are effective not only in primary cultures of neurons, but also in preventing the in vivo mouse limb neuroparalysis. In addition, one of these inhibitors, Ebselen, largely protects mice from the death caused by a systemic injection. Together with recent results obtained with BoNTs specific for SNAP25 and syntaxin, the present data demonstrate the essential role of the thioredoxin-thioredoxin reductase system in reducing the interchain disulfide during the nerve intoxication mechanism of all serotypes. Therefore its inhibitors should be considered for a possible use to prevent botulism and for treating infant botulism.

Laboratory Investigation of the First Case of Botulism Caused by Clostridium butyricum Type E Toxin in the United States

We report here the laboratory investigation of the first known case of botulism in the United States caused by Clostridium butyricum type E. This investigation demonstrates the importance of extensive microbiological examination of specimens, which resulted in the isolation of this organism.

Botulinum Toxin Type a as a Therapeutic Agent against Headache and Related Disorders

Botulinum neurotoxin A (BoNT/A) is a toxin produced by the naturally-occurring Clostridium botulinum that causes botulism. The potential of BoNT/A as a useful medical intervention was discovered by scientists developing a vaccine to protect against botulism. They found that, when injected into a muscle, BoNT/A causes a flaccid paralysis. Following this discovery, BoNT/A has been used for many years in the treatment of conditions of pathological muscle hyperactivity, like dystonias and spasticities. In parallel, the toxin has become a “glamour” drug due to its power to ward off facial wrinkles, particularly frontal, due to the activity of the mimic muscles. After the discovery that the drug also appeared to have a preventive effect on headache, scientists spent many efforts to study the potentially-therapeutic action of BoNT/A against pain. BoNT/A is effective at reducing pain in a number of disease states, including cervical dystonia, neuropathic pain, lower back pain, spasticity, myofascial pain and bladder pain. In 2010, regulatory approval for the treatment of chronic migraine with BoNT/A was given, notwithstanding the fact that the mechanism of action is still not completely elucidated. In the present review, we summarize experimental evidence that may help to clarify the mechanisms of action of BoNT/A in relation to the alleviation of headache pain, with particular emphasis on preclinical studies, both in animals and humans. Moreover, we summarize the latest clinical trials that show evidence on headache conditions that may obtain benefits from therapy with BoNT/A.

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.

On the translocation of botulinum and tetanus neurotoxins across the membrane of acidic intracellular compartments

Tetanus and botulinum neurotoxins are produced by anaerobic bacteria of the genus Clostridium and are the most poisonous toxins known, with 50% mouse lethal dose comprised within the range of 0.1-few nanograms per Kg, depending on the individual toxin. Botulinum neurotoxins are similarly toxic to humans and can therefore be considered for potential use in bioterrorism. At the same time, their neurospecificity and reversibility of action make them excellent therapeutics for a growing and heterogeneous number of human diseases that are characterized by a hyperactivity of peripheral nerve terminals. The complete crystallographic structure is available for some botulinum toxins, and reveals that they consist of four domains functionally related to the four steps of their mechanism of neuron intoxication: 1) binding to specific receptors of the presynaptic membrane; 2) internalization via endocytic vesicles; 3) translocation across the membrane of endocytic vesicles into the neuronal cytosol; 4) catalytic activity of the enzymatic moiety directed towards the SNARE proteins. Despite the many advances in understanding the structure-mechanism relationship of tetanus and botulinum neurotoxins, the molecular events involved in the translocation step have been only partially elucidated. Here we will review recent advances that have provided relevant insights on the process and discuss possible models that can be experimentally tested. This article is part of a Special Issue entitled: Pore-Forming Toxins edited by Mauro Dalla Serra and Franco Gambale.

Current and potential urological applications of botulinum toxin A

Botulinum toxin subtype A (BoNT-A) is a potent neurotoxin that can selectively modulate neurotransmitter release from nerve endings, resulting in muscular paralysis. BoNT-A might also act on sensory nerves, and have an anti-inflammatory effect. In the first urological use of BoNT-A, injection into the urethral sphincters of patients with detrusor-sphincter dyssynergia resulted in a reduction of urethral resistance and improved voiding efficiency. Subsequently, intravesical BoNT-A injections have received regulatory approval for treatment of neurogenic detrusor overactivity owing to spinal cord lesions or multiple sclerosis, and idiopathic overactive bladder in adults. BoNT-A has also been widely used to treat patients with the off-label indications of neurogenic or non-neurogenic voiding dysfunction and male lower urinary tract symptoms owing to BPH and bladder-neck dysfunction. Other indications for which urologists have applied BoNT-A injections include interstitial cystitis/bladder pain syndrome, bladder oversensitivity and chronic pelvic pain syndrome. BoNT-A is currently delivered as an intravesical injection; however, use of liposome encapsulated formulations is also beginning to show some therapeutic potential.

Inhibiting oral intoxication of botulinum neurotoxin A complex by carbohydrate receptor mimics

Botulinum neurotoxins (BoNTs) cause the disease botulism manifested by flaccid paralysis that could be fatal to humans and animals. Oral ingestion of the toxin with contaminated food is one of the most common routes for botulism. BoNT assembles with several auxiliary proteins to survive in the gastrointestinal tract and is subsequently transported through the intestinal epithelium into the general circulation. Several hemagglutinin proteins form a multi-protein complex (HA complex) that recognizes host glycans on the intestinal epithelial cell surface to facilitate BoNT absorption. Blocking carbohydrate binding to the HA complex could significantly inhibit the oral toxicity of BoNT. Here, we identify lactulose, a galactose-containing non-digestible sugar commonly used to treat constipation, as a prototype inhibitor against oral BoNT/A intoxication. As revealed by a crystal structure, lactulose binds to the HA complex at the same site where the host galactose-containing carbohydrate receptors bind. In vitro assays using intestinal Caco-2 cells demonstrated that lactulose inhibits HA from compromising the integrity of the epithelial cell monolayers and blocks the internalization of HA. Furthermore, co-administration of lactulose significantly protected mice against BoNT/A oral intoxication in vivo. Taken together, these data encourage the development of carbohydrate receptor mimics as a therapeutic intervention to prevent BoNT oral intoxication.

Structure of the BoNT/A1--receptor complex

Botulinum neurotoxin A causes botulism but is also used for medical and cosmetic applications. A detailed molecular understanding of BoNT/A--host receptor interactions is therefore fundamental for improving current clinical applications and for developing new medical strategies targeting human disorders. Towards this end, we recently solved an X-ray crystal structure of BoNT/A1 in complex with its neuronal protein receptor SV2C. Based on our findings, we discuss the potential implications for BoNT/A function.

Inhibiting Microbial Toxins Using Plant-Derived Compounds and Plant Extracts

Many pathogenic bacteria and fungi produce potentially lethal toxins that cause cytotoxicity or impaired cellular function either at the site of colonization or other locations in the body through receptor-mediated interactions. Various factors, including biotic and abiotic environments, competing microbes, and chemical cues affect toxin expression in these pathogens. Recent work suggests that several natural compounds can modulate toxin production in pathogenic microbes. However, studies explaining the mechanistic basis for their effect are scanty. This review discusses the potential of various plant-derived compounds for reducing toxin production in foodborne and other microbes. In addition, studies highlighting their anti-toxigenic mechanism(s) are discussed.