Structure and function of tetanus and botulinum neurotoxins

Delivery of endolysin across outer membrane of Gram-negative bacteria using translocation domain of botulinum neurotoxin

The emergence of multidrug-resistant pathogens has outpaced the development of new antibiotics, leading to renewed interest in endolysins. Endolysins have been investigated as novel biocontrol agents for Gram-positive bacteria. However, their efficacy against Gram-negative species is limited by the barrier presented by their outer membrane, which prevents endolysin access to the peptidoglycan substrate. Here, we used the translocation domain of botulinum neurotoxin to deliver endolysin across the outer membrane of Gram-negative bacteria. The translocation domain selectively interacts with and penetrates membranes composed of anionic lipids, which have been used in nature to deliver various proteins into animal cells. In addition to the botulinum neurotoxin translocation domain, we have fused bacteriophage-derived receptor binding protein to endolysins. This allows the attached protein to efficiently bind to a broad spectrum of Gram-negative bacteria. By attaching these target-binding and translocation machineries to endolysins, we aimed to develop an engineered endolysin with broad-spectrum targeting and enhanced antibacterial activity against Gram-negative species. To validate our strategy, we designed engineered endolysins using two well-known endolysins, T5 and LysPA26, and tested them against 23 strains from six species of Gram-negative bacteria, confirming that our machinery can act broadly. In particular, we observed a 2.32 log reduction in 30 min with only 0.5 µM against an Acinetobacter baumannii isolate. We also used the SpyTag/SpyCatcher system to easily attach target-binding proteins, thereby improving its target-binding ability. Overall, our newly developed endolysin engineering strategy may be a promising approach to control multidrug-resistant Gram-negative bacterial strains.

Analgesic effect of Botulinum toxin in neuropathic pain is sodium channel independent

Botulinum neurotoxin type A BoNT/A is used off-label as a third line therapy for neuropathic pain. However, the mechanism of action remains unclear. In recent years, the role of voltage-gated sodium channels (Nav) in neuropathic pain became evident and it was suggested that block of sodium channels by BoNT/A would contribute to its analgesic effect. We assessed sodium channel function in the presence of BoNT/A in heterologously expressed Nav1.7, Nav1.3, and the neuronal cell line ND7/23 by high throughput automated and manual patch-clamp. We used both the full protein and the isolated catalytic light chain LC/A for acute or long-term extracellular or intracellular exposure. To assess the toxin's effect in a human cellular system, we differentiated induced pluripotent stem cells (iPSC) into sensory neurons from a healthy control and a patient suffering from a hereditary neuropathic pain syndrome (inherited erythromelalgia) carrying the Nav1.7/p.Q875E-mutation and carried out multielectrode-array measurements. Both BoNT/A and the isolated catalytic light chain LC/A showed limited effects in heterologous expression systems and the neuronal cell line ND7/23. Spontaneous activity in iPSC derived sensory neurons remained unaltered upon BoNT/A exposure both in neurons from the healthy control and the mutation carrying patient. BoNT/A may not specifically be beneficial in pain syndromes linked to sodium channel variants. The favorable effects of BoNT/A in neuropathic pain are likely based on mechanisms other than sodium channel blockage and new approaches to understand BoNT/A's therapeutic effects are necessary.

The Degradation of Botulinum Neurotoxin Light Chains Using PROTACs

Botulinum neurotoxins are some of the most potent natural toxins known; they cause flaccid paralysis by inhibiting synaptic vesicle release. Some serotypes, notably serotype A and B, can cause persistent paralysis lasting for several months. Because of their potency and persistence, botulinum neurotoxins are now used to manage several clinical conditions, and there is interest in expanding their clinical applications using engineered toxins with novel substrate specificities. It will also be beneficial to engineer toxins with tunable persistence. We have investigated the potential use of small-molecule proteolysis-targeting chimeras (PROTACs) to vary the persistence of modified recombinant botulinum neurotoxins. We also describe a complementary approach that has potential relevance for botulism treatment. This second approach uses a camelid heavy chain antibody directed against botulinum neurotoxin that is modified to bind the PROTAC. These strategies provide proof of principle for the use of two different approaches to fine tune the persistence of botulinum neurotoxins by selectively targeting their catalytic light chains for proteasomal degradation.

A Validation of the Equivalence of the Cell-Based Potency Assay Method with a Mouse LD50 Bioassay for the Potency Testing of OnabotulinumtoxinA

(1) Background: At present, the only potency assay approved in China for the in-country testing of botulinum toxin type A for injection products is the mouse bioassay (MBA). The Chinese market for neurotoxin products is rapidly expanding, but MBAs are subject to high variability due to individual variations in mice, as well as variations in injection sites, in addition to the limited number of batches tested for one MBA. Compared with the mLD50 method, the cell-based potency assay (CBPA) developed for the potency testing of onabotulinumtoxinA (BOTOX) by AbbVie not only does not use any experimental animals but also allows for significant time and cost savings. Due to the significant benefits conferred by the replacement of the mLD50 assay with CBPA in China, the CBPA method has been transferred, validated, and cross-validated to demonstrate the equivalence of the two potency methods. (2) Methods: The differentiated SiMa cells were treated with both BOTOX samples and the reference standard, and the cleaved SNAP25197 in the cell lysates was quantified using Chemi-ECL ELISA. A 4-PL model was used for the data fit and sample relative potency calculation. The method accuracy, linearity, repeatability, and intermediate precision were determined within the range of 50% to 200% of the labeled claim. A statistical equivalence of the two potency methods (CBPA and mLD50) was initially demonstrated by comparing the AbbVie CBPA data with NIFDC mLD50 data on a total of 167 commercial BOTOX lots (85 50U lots and 82 100U lots). In addition, six lots of onabotulinumtoxinA (three 50U and three 100U) were re-tested as cross-validation by these two methods for equivalence. (3) Results: The overall assay's accuracy and intermediate precision were determined as 104% and 9.2%, and the slope, R-square, and Y-intercept for linearity were determined as 1.071, 0.998, and 0.036, respectively. The repeatability was determined as 6.9%. The range with the acceptable criteria of accuracy, linearity, and precision was demonstrated as 50% to 200% of the labeled claim. The 95% equivalence statistic test using margins [80%, 125%] indicates that CBPA and mLD50 methods are equivalent for both BOTOX strengths (i.e., 50U and 100U). The relative potency data from cross-validation were within the range of ≥80% to ≤120%. (4) Conclusions: The CBPA meets all acceptance criteria and is equivalent to mLD50. The replacement of mLD50 with CBPA is well justified in terms of ensuring safety and efficacy, as well as for animal benefits.

Embracing the Versatility of Botulinum Neurotoxins in Conventional and New Therapeutic Applications

Botulinum neurotoxins (BoNTs) have been used for almost half a century in the treatment of excessive muscle contractility. BoNTs are routinely used to treat movement disorders such as cervical dystonia, spastic conditions, blepharospasm, and hyperhidrosis, as well as for cosmetic purposes. In addition to the conventional indications, the use of BoNTs to reduce pain has gained increased recognition, giving rise to an increasing number of indications in disorders associated with chronic pain. Furthermore, BoNT-derived formulations are benefiting a much wider range of patients suffering from overactive bladder, erectile dysfunction, arthropathy, neuropathic pain, and cancer. BoNTs are categorised into seven toxinotypes, two of which are in clinical use, and each toxinotype is divided into multiple subtypes. With the development of bioinformatic tools, new BoNT-like toxins have been identified in non-Clostridial organisms. In addition to the expanding indications of existing formulations, the rich variety of toxinotypes or subtypes in the wild-type BoNTs associated with new BoNT-like toxins expand the BoNT superfamily, forming the basis on which to develop new BoNT-based therapeutics as well as research tools. An overview of the diversity of the BoNT family along with their conventional therapeutic uses is presented in this review followed by the engineering and formulation opportunities opening avenues in therapy.

Some Examples of Bacterial Toxins as Tools

Pathogenic bacteria produce diverse protein toxins to disturb the host's defenses. This includes the opening of epithelial barriers to establish bacterial growth in deeper tissues of the host and to modulate immune cell functions. To achieve this, many toxins share the ability to enter mammalian cells, where they catalyze the modification of cellular proteins. The enzymatic activity is diverse and ranges from ribosyl- or glycosyl-transferase activity, the deamidation of proteins, and adenylate-cyclase activity to proteolytic cleavage. Protein toxins are highly active enzymes often with tight specificity for an intracellular protein or a protein family coupled with the intrinsic capability of entering mammalian cells. A broad understanding of their molecular mechanisms established bacterial toxins as powerful tools for cell biology. Both the enzymatic part and the pore-forming/protein transport capacity are currently used as tools engineered to study signaling pathways or to transport cargo like labeled compounds, nucleic acids, peptides, or proteins directly into the cytosol. Using several representative examples, this review is intended to provide a short overview of the state of the art in the use of bacterial toxins or parts thereof as tools.

Syntaxin1A overexpression and pain insensitivity in individuals with 7q11.23 duplication syndrome

Genetic modifications leading to pain insensitivity phenotypes, while rare, provide invaluable insights into the molecular biology of pain and reveal targets for analgesic drugs. Pain insensitivity typically results from Mendelian loss-of-function mutations in genes expressed in nociceptive (pain-sensing) dorsal root ganglion (DRG) neurons that connect the body to the spinal cord. We document a pain insensitivity mechanism arising from gene overexpression in individuals with the rare 7q11.23 duplication syndrome (Dup7), who have 3 copies of the approximately 1.5-megabase Williams syndrome (WS) critical region. Based on parental accounts and pain ratings, people with Dup7, mainly children in this study, are pain insensitive following serious injury to skin, bones, teeth, or viscera. In contrast, diploid siblings (2 copies of the WS critical region) and individuals with WS (1 copy) show standard reactions to painful events. A converging series of human assessments and cross-species cell biological and transcriptomic studies identified 1 likely candidate in the WS critical region, STX1A, as underlying the pain insensitivity phenotype. STX1A codes for the synaptic vesicle fusion protein syntaxin1A. Excess syntaxin1A was demonstrated to compromise neuropeptide exocytosis from nociceptive DRG neurons. Taken together, these data indicate a mechanism for producing "genetic analgesia" in Dup7 and offer previously untargeted routes to pain control.

Pathogenicity and virulence of Clostridium botulinum

Clostridium botulinum, a polyphyletic Gram-positive taxon of bacteria, is classified purely by their ability to produce botulinum neurotoxin (BoNT). BoNT is the primary virulence factor and the causative agent of botulism. A potentially fatal disease, botulism is classically characterized by a symmetrical descending flaccid paralysis, which is left untreated can lead to respiratory failure and death. Botulism cases are classified into three main forms dependent on the nature of intoxication; foodborne, wound and infant. The BoNT, regarded as the most potent biological substance known, is a zinc metalloprotease that specifically cleaves SNARE proteins at neuromuscular junctions, preventing exocytosis of neurotransmitters, leading to muscle paralysis. The BoNT is now used to treat numerous medical conditions caused by overactive or spastic muscles and is extensively used in the cosmetic industry due to its high specificity and the exceedingly small doses needed to exert long-lasting pharmacological effects. Additionally, the ability to form endospores is critical to the pathogenicity of the bacteria. Disease transmission is often facilitated via the metabolically dormant spores that are highly resistant to environment stresses, allowing persistence in the environment in unfavourable conditions. Infant and wound botulism infections are initiated upon germination of the spores into neurotoxin producing vegetative cells, whereas foodborne botulism is attributed to ingestion of preformed BoNT. C. botulinum is a saprophytic bacterium, thought to have evolved its potent neurotoxin to establish a source of nutrients by killing its host.

Special Issue: Gram-Positive Bacterial Toxins

The Gram stain classifies most bacteria into one of two groups, Gram-negative or Gram-positive, based on the composition of their cell walls [...].

Xeomin®, a Commercial Formulation of Botulinum Neurotoxin Type A, Promotes Regeneration in a Preclinical Model of Spinal Cord Injury

Xeomin® is a commercial formulation of botulinum neurotoxin type A (BoNT/A) clinically authorized for treating neurological disorders, such as blepharospasm, cervical dystonia, limb spasticity, and sialorrhea. We have previously demonstrated that spinal injection of laboratory purified 150 kDa BoNT/A in paraplegic mice, after undergoing traumatic spinal cord injury (SCI), was able to reduce excitotoxic phenomena, glial scar, inflammation, and the development of neuropathic pain and facilitate regeneration and motor recovery. In the present study, as proof of concept in view of a possible clinical application, we studied the efficacy of Xeomin® in the same preclinical SCI model in which we highlighted the positive effects of lab-purified BoNT/A. Data comparison shows that Xeomin® induces similar pharmacological and therapeutic effects, albeit with less efficacy, to lab-purified BoNT/A. This difference, which can be improved by adjusting the dose, can be attributable to the different formulation and pharmacodynamics. Although the mechanism by which Xeomin® and laboratory purified BoNT/A induce functional improvement in paraplegic mice is still far from being understood, these results open a possible new scenario in treatment of SCI and are a stimulus for further research.

The potential role of molecular mimicry by the anaerobic microbiome in the aetiology of autoimmune disease

Autoimmune diseases are thought to develop as a consequence of various environmental and genetic factors, each of which contributes to dysfunctional immune responses and/or a breakdown in immunological tolerance towards native structures. Molecular mimicry by microbial components is among the environmental factors thought to promote a breakdown in immune tolerance, particularly through the presence of cross-reactive epitopes shared with the human host. While resident members of the microbiome are essential promoters of human health through immunomodulation, defence against pathogenic colonisation and conversion of dietary fibre into nutritional resources for host tissues, there may be an underappreciated role of these microbes in the aetiology and/or progression of autoimmune disease. An increasing number of molecular mimics are being identified amongst the anaerobic microbiota which structurally resemble endogenous components and, in some cases, for example the human ubiquitin mimic of Bacteroides fragilis and DNA methyltransferase of Roseburia intestinalis, have been associated with promoting antibody profiles characteristic of autoimmune diseases. The persistent exposure of molecular mimics from the microbiota to the human immune system is likely to be involved in autoantibody production that contributes to the pathologies associated with immune-mediated inflammatory disorders. Here-in, examples of molecular mimics that have been identified among resident members of the human microbiome and their ability to induce autoimmune disease through cross-reactive autoantibody production are discussed. Improved awareness of the molecular mimics that exist among human colonisers will help elucidate the mechanisms involved in the breakdown of immune tolerance that ultimately lead to chronic inflammation and downstream disease.

Molecular Diversity of BoNT-Producing Clostridia—A Still-Emerging and Challenging Problem

The diversity of BoNT-producing Clostridia is still a worrying problem for specialists who explore the evolutionary and taxonomic diversity of C. botulinum. It is also a problem for epidemiologists and laboratory staff conducting investigations into foodborne botulism in humans and animals, because their genetic and phenotypic heterogeneity cause complications in choosing the proper analytical tools and in reliably interpreting results. Botulinum neurotoxins (BoNTs) are produced by several bacterial groups that meet all the criteria of distinct species. Despite this, the historical designation of C. botulinum as the one species that produces botulinum toxins is still exploited. New genetic tools such as whole-genome sequencing (WGS) indicate horizontal gene transfer and the occurrence of botulinum gene clusters that are not limited only to Clostridium spp., but also to Gram-negative aerobic species. The literature data regarding the mentioned heterogeneity of BoNT-producing Clostridia indicate the requirement to reclassify C. botulinum species and other microorganisms able to produce BoNTs or possessing botulinum-like gene clusters. The aim of this study was to present the problem of the diversity of BoNT-producing Clostridia over time and new trends toward obtaining a reliable classification of these microorganisms, based on a complex review of the literature.

Conservative Bladder Management and Medical Treatment in Chronic Spinal Cord Injury Patients

To review the available data on non-surgical management for neurogenic lower urinary tract dysfunction (NLUTD) in patients with chronic spinal cord injury (SCI) and provide the most updated knowledge for readers. We categorized the bladder management approaches into storage and voiding dysfunction separately; both are minimally invasive, safe, and efficacious procedures. The main goals for NLUTD management are to achieve urinary continence; improve quality of life; prevent urinary tract infections and, last but not least, preserve upper urinary tract function. Annual renal sonography workups and regular video urodynamics examinations are crucial for early detection and further urological management. Despite the extensive data on NLUTD, there are still relatively few novel publications and there is a lack of high-quality evidence. There is a paucity of new minimally invasive and prolonged efficacy treatments for NLUTD, and a partnership between urologists, nephrologists and physiatrists is required to promote and ensure the health of SCI patients in the future.

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

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

Crystal structures of OrfX1, OrfX2 and the OrfX1-OrfX3 complex from the orfX gene cluster of botulinum neurotoxin E1

Botulinum neurotoxins (BoNTs) are among the most lethal toxins known to humans, comprising seven established serotypes termed BoNT/A-G encoded in two types of gene clusters (ha and orfX) in BoNT-producing clostridia. The ha cluster encodes four non-toxic neurotoxin-associated proteins (NAPs) that assemble with BoNTs to protect and enhance their oral toxicity. However, the structure and function of the orfX-type NAPs remain largely unknown. Here, we report the crystal structures for OrfX1, OrfX2, and an OrfX1-OrfX3 complex, which are encoded in the orfX cluster of a BoNT/E1-producing Clostridium botulinum strain associated with human foodborne botulism. These structures lay the foundation for future studies on the potential roles of OrfX proteins in oral intoxication and pathogenesis of BoNTs.

Disorder-to-order transition of Synaptobrevin-2: Tracing the conformational diversity of a synaptic SNARE protein

Synaptobrevin-2 is one of the key players of neuronal exocytosis. Together with Syntaxin-1A and SNAP25, it forms the core membrane fusion machinery that is responsible for neurotransmitter release and, therefore, signal transmission between neurons. However, in the absence of interaction partners, Synaptobrevin-2 is largely unstructured and exhibits an inherent flexibility. In this graphical review, we provide an overview on the structural states of Synaptobrevin-2 in the absence and in the presence of interaction partners. For this, we first depict its natural habitat, namely the presynaptic nerve terminal, and gather biophysical properties that are likely responsible for its structural diversity. We then provide an overview on key findings describing the disorder-to-order transition of Synaptobrevin-2 from a mostly unstructured protein to a highly structured protein complex component.

Exceptionally potent human monoclonal antibodies are effective for prophylaxis and treatment of tetanus in mice

We used human monoclonal antibodies (humAbs) to study the mechanism of neuron intoxication by tetanus neurotoxin and to evaluate these antibodies as a safe preventive and therapeutic substitute for hyperimmune sera to treat tetanus in mice. By screening memory B cells from immune donors, we selected 2 tetanus neurotoxin-specific mAbs with exceptionally high neutralizing activities and extensively characterized them both structurally and functionally. We found that these antibodies interfered with the binding and translocation of the neurotoxin into neurons by interacting with 2 epitopes, whose identification pinpoints crucial events in the cellular pathogenesis of tetanus. Our observations explain the neutralization ability of these antibodies, which we found to be exceptionally potent in preventing experimental tetanus when injected into mice long before the toxin. Moreover, their Fab derivatives neutralized tetanus neurotoxin in post-exposure experiments, suggesting their potential for therapeutic use via intrathecal injection. As such, we believe these humAbs, as well as their Fab derivatives, meet the requirements to be considered for prophylactic and therapeutic use in human tetanus and are ready for clinical trials.

Therapeutic efficacy of new botulinum toxin identified in CCUG 7968 strain

Botulinum neurotoxin type A (BoNT/A) induces muscle atrophy by cleaving synaptosomal-associated protein 25. Thus, BoNT/A has been actively utilized for the treatment of masseter and gastrocnemius hypertrophy. In this study, INI101 toxin was newly identified from the CCUG 7968 strain, and its therapeutic efficacy was evaluated both in vitro and in vivo. The INI101 toxin showed identical genetic sequence, amino acid sequence, and protein subunit composition to BoNT/A produced from strain Hall A. Electromyography (EMG), and immunofluorescence staining demonstrated that INI101 (at 2 ~ 8 U/rat) effectively blocked the neuromuscular junction with no toxicity in a rat model. The EMG results showed INI101 toxin-induced weight loss and volume reduction of the gastrocnemius, similar to the effects of Botox® (BTX). Histological and immunofluorescence staining was consistent with this EMG result, showing that INI101 toxin caused muscle fiber reduction in the gastrocnemius. Notably, INI101 toxin diffused less into adjacent muscle tissue than BTX, indicating that INI101 toxin may reduce potential side effects due to diffusion into normal tissues. INI101 toxin isolated from the novel strain CCUG 7968 is a newly identified meaningful biopharmaceutical comparable to the conventional BoNT/A in the medical field. KEY POINTS: • Botulinum neurotoxin type A (BoNT/A, INI101) was identified from the CCUG 7968 strain. • INI101 toxin showed similar safety and therapeutic efficacy comparable to conventional BoNT/A both in vitro and in vivo. • INI101 toxin is a meaningful biopharmaceutical comparable to the conventional BoNT/A in the medical field.

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

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

Engineering Botulinum Neurotoxins for Enhanced Therapeutic Applications and Vaccine Development

Botulinum neurotoxins (BoNTs) show increasing therapeutic applications ranging from treatment of locally paralyzed muscles to cosmetic benefits. At first, in the 1970s, BoNT was used for the treatment of strabismus, however, nowadays, BoNT has multiple medical applications including the treatment of muscle hyperactivity such as strabismus, dystonia, movement disorders, hemifacial spasm, essential tremor, tics, cervical dystonia, cerebral palsy, as well as secretory disorders (hyperhidrosis, sialorrhea) and pain syndromes such as chronic migraine. This review summarizes current knowledge related to engineering of botulinum toxins, with particular emphasis on their potential therapeutic applications for pain management and for retargeting to non-neuronal tissues. Advances in molecular biology have resulted in generating modified BoNTs with the potential to act in a variety of disorders, however, in addition to the modifications of well characterized toxinotypes, the diversity of the wild type BoNT toxinotypes or subtypes, provides the basis for innovative BoNT-based therapeutics and research tools. This expanding BoNT superfamily forms the foundation for new toxins candidates in a wider range of therapeutic options.

Expression, Purification, and Verification of Recombinant Botulinum Neurotoxin Type A Binding Domain: A Comparison Between X33 and PichiaPink Strains of Pichia pastoris

Background: An effective method to develop a safe vaccine against botulism is to utilize molecular biology techniques to produce recombinant antigens, which provoke the immune response in the recipient organism. A suggested antigen is a specific recombinant fragment of the botulinum neurotoxin (BoNT), which elicits the predictable immune response and does not have any toxic effects. In this study, the binding domain of the heavy chain of BoNT serotype A, which is the responsible subunit for binding to the receptor(s) of presynaptic membranes in neuromuscular junctions, is the selected fragment of this toxin to be recombinantly produced. Objectives: In order to prevent a severe syndrome such as Botulism, developing efficient vaccines against it is a necessity. Efforts have been made to accomplish this throughout time; however, some have discontinued due to the risks and unreliability of their production and usage. Methods: The encoding gene of BoNT/A-Hc was cloned into two different strains of Pichia pastoris, which were compared to each other based on the yield of the recombinant product. Results: The results demonstrated that the expression of recombinant BoNT/A-Hc by PichiaPink strain was successful, and the achieved recombinant BoNT/A-Hc was subsequently purified and then verified by using the specific antibody and analytical methods. Conclusions: In contrast, the expression results from the X-33 strain were not significant.

Will repeated botulinum toxin A improve detrusor overactivity and bladder compliance in patients with chronic spinal cord injury?

Chronic spinal cord injury (SCI) can induce neurogenic detrusor overactivity (NDO), leading to urinary incontinence and renal damage due to low bladder compliance and high detrusor pressure during the storage and voiding of urine. In 2011, Botox^® (onabotulinumtoxinA, botulinum neurotoxin serotype A [BoNT-A]) was approved by the Food and Drug Administration for the treatment of NDO. Intradetrusor injection of BoNT-A has been shown to have clinical utility for the treatment of urinary incontinence, with consequent improvements in quality of life for patients. In the past 20 years, this treatment has been shown to be an effective treatment for patients with SCI refractory to antimuscarinic medication. The present review focused on publications in MEDLINE/PubMed relating to botulinum toxin to evaluate the treatment outcomes of repeated injection of BoNT-A, the mechanisms of action, results of clinical and urodynamic studies, and adverse effects.

Repeated intrastriatal application of botulinum neurotoxin-A did not influence choline acetyltransferase-immunoreactive interneurons in hemiparkinsonian rat brain - A histological, stereological and correlational analysis

In Parkinson's disease, dopamine depletion leads to hyperactivity of cholinergic interneurons in the caudate-putamen (CPu). Botulinum neurotoxin-A (BoNT-A) inhibits the release of acetylcholine in the peripheral nervous system and is also thought to act as a local anticholinergic drug when injected intrastriatally. In hemiparkinsonian (hemi-PD) rats, a unilateral intrastriatal injection of 1 ng BoNT-A significantly diminished apomorphine-induced rotation behavior for at least 3 months, the effect fading thereafter. A second intrastriatal BoNT-A application, 6 months after the first one, led to a stronger and longer-lasting, beneficial behavioral reaction. As a single BoNT-A injection was not cytotoxic in the rat striatum and resembled BoNT-A treatment in clinical practice, here, we investigated the structural outcome of repeated intrastriatal BoNT-A injections with respect to striatal volume, the number of choline acetyltransferase-immunoreactive (ChAT-ir) interneurons and of the length of their dendritic arbors, and the numeric density of ChAT-ir BoNT-A-induced varicosities (BiVs). Repeated unilateral intrastriatal BoNT-A application decreased the volume of the injected CPu, but did not significantly change the number of striatal ChAT-ir interneurons. Also, the total dendrite length of ChAT-ir interneurons after repeated BoNT-A application resembled the values in double vehicle-injected hemi-PD rats. In repeatedly BoNT-A-injected hemi-PD rats, the numeric density of ChAT-ir BiVs in the CPu was increased compared with rats only intrastriatally injected once with BoNT-A. Even repeated BoNT-A injections in rat striata did not cause substantial morphological changes in ChAT-ir neuron, except for the increased numeric density of ChAT-ir BiVs.

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.

The role of the single interchains disulfide bond in tetanus and botulinum neurotoxins and the development of antitetanus and antibotulism drugs

A large number of bacterial toxins consist of active and cell binding protomers linked by an interchain disulfide bridge. The largest family of such disulfide-bridged exotoxins is that of the clostridial neurotoxins that consist of two chains and comprise the tetanus neurotoxins causing tetanus and the botulinum neurotoxins causing botulism. Reduction of the interchain disulfide abolishes toxicity, and we discuss the experiments that revealed the role of this structural element in neuronal intoxication. The redox couple thioredoxin reductase-thioredoxin (TrxR-Trx) was identified as the responsible for reduction of this disulfide occurring on the cytosolic surface of synaptic vesicles. We then discuss the very relevant finding that drugs that inhibit TrxR-Trx also prevent botulism. On this basis, we propose that ebselen and PX-12, two TrxR-Trx specific drugs previously used in clinical trials in humans, satisfy all the requirements for clinical tests aiming at evaluating their capacity to effectively counteract human and animal botulism arising from intestinal toxaemias such as infant botulism.

Antibodies and Vaccines against Botulinum Toxins: Available Measures and Novel Approaches

Botulinum neurotoxin (BoNT) is produced by the anaerobic, Gram-positive bacterium Clostridium botulinum. As one of the most poisonous toxins known and a potential bioterrosism agent, BoNT is characterized by a complex mode of action comprising: internalization, translocation and proteolytic cleavage of a substrate, which inhibits synaptic exocytotic transmitter release at neuro-muscular nerve endings leading to peripheral neuroparalysis of the skeletal and autonomic nervous systems. There are seven major serologically distinct toxinotypes (A-G) of BoNT which act on different substrates. Human botulism is generally caused by BoNT/A, B and E. Due to its extreme lethality and potential use as biological weapon, botulism remains a global public health concern. Vaccination against BoNT, although an effective strategy, remains undesirable due to the growing expectation around therapeutic use of BoNTs in various pathological conditions. This review focuses on the current approaches for botulism control by immunotherapy, highlighting the future challenges while the molecular underpinnings among subtypes variants and BoNT sequences found in non-clostridial species remain to be elucidated.

The role of human serum albumin and neurotoxin associated proteins in the formulation of BoNT/A products

Botulinum neurotoxin (BoNT) is synthesized as a progenitor toxin complex (PTC) by Clostridium botulinum. This PTC comprises, in addition to the neurotoxin itself, neurotoxin associated proteins (NAPs) which are composed of three hemagglutinins and one non-toxic, non-hemagglutinin protein. After oral ingestion, these NAPs protect the neurotoxin from the low pH and proteases in the gastrointestinal tract and play a role in the entry via the intestinal barrier. Two of the three therapeutically used botulinum neurotoxin serotype A (BoNT/A) products (onabotulinumtoxinA and abobotulinumtoxinA) contain different amounts of NAPs, while incobotulinumtoxinA, lacks these proteins. In addition, human serum albumin (HSA) that is supposed to stabilize BoNT/A is added at different concentrations. Up to now, the function of the NAPs and HSA after parenteral therapeutic application is not completely understood. To investigate the influence of NAPs and HSA on potency of BoNT/A, we used the ex vivo mouse phrenic nerve hemidiaphragm assay. Increasing doses of HSA resulted dose-dependently in a more pronounced effect of BoNT/A. Though, a plateau was reached with concentrations of 0.8 mg/ml HSA and higher, the accessory addition of NAPs in a relevant amount (4 ng/ml) did not further enhance the effect of BoNT/A. In conclusion, in our ex vivo assay an adequate concentration of HSA prevented BoNT/A from loss of effect and supplementary NAPs did not alter this effect. A confirmation of these data in an in vivo assay is still lacking. However, it might be supposed that even in clinically applied BoNT/A products an increase of HSA accompanied by the avoidance of NAPs could potentially reduce the injected dose and, thus, the risk of unwanted side effects, the treatment costs as well as the risk of a secondary therapy failure due to BoNT/A neutralizing antibodies.

Tetanus

Tetanus is a vaccine-preventable disease that still commonly occurs in many low-income and middle-income countries, although it is rare in high-income countries. The disease is caused by the toxin of the bacterium Clostridium tetani and is characterised by muscle spasms and autonomic nervous system dysfunction. Global vaccination initiatives have had considerable success but they continue to face many challenges. Treatment for tetanus aims to control spasms and reduce cardiovascular instability, and consists of wound debridement, antitoxin, antibiotics, and supportive care. Recent research has focused on intravenous magnesium sulphate and intrathecal antitoxin administration as methods of spasm control that can avoid the need for ventilatory support. Nevertheless, without access to mechanical ventilation, mortality from tetanus remains high. Even with such care, patients require several weeks of hospitalisation and are vulnerable to secondary problems, such as hospital-acquired infections.

AbobotulinumtoxinA: A New Therapy for Hip Osteoarthritis. A Prospective Randomized Double-Blind Multicenter Study

Background: Hip Osteoarthritis (OA) causes pain and disability. Here we evaluate abobotulinumtoxinA (Dysport®) (AboBoNT-A) injections versus placebo as a novel treatment option to improve hip range of motion, pain and quality of life. Methods: This prospective randomized double-blind multicenter study (EudraCT # 2012-004890-25) recruited 46 outpatients with hip OA who were randomized 2:1 to the Treatment Group (TG; 31 subjects), or the Placebo Group (PG; 15 subjects). The TG received 400 U of AboBoNT-A injected into the adductor muscles, and the PG received placebo solution. The primary endpoints were the difference in Harris Hip Score (HHS) and Visual Analogic Scale for pain (VAS) at Week 4 between groups (TG vs. PG). Secondary endpoints were the change from baseline in HHS, VAS pain, Medical Research Council scale for muscle strength (MRC) and Short Form scale (SF-36) scores. Results: In TG at Week 4, the HHS and VAS score were significantly improved compared to PG, and pairwise assessments showed significant improvements in HSS and VAS pain at each time point compared to baseline for TG. No significant changes were observed in MRC and SF-36 over time, though SF-36 showed a positive trend. There were no significant differences from baseline in the PG. No adverse events were detected in either treatment group. Conclusions: AboBoNT-A injections in hip OA improve range of motion and pain without any significant side effects.

Repeated Intrastriatal Botulinum Neurotoxin-A Injection in Hemiparkinsonian Rats Increased the Beneficial Effect on Rotational Behavior

Injection of botulinum neurotoxin-A (BoNT-A) into the striatum of hemiparkinsonian (hemi-PD) rats reduced apomorphine-induced rotation behavior significantly, for at least 3 months. Thereafter, rotation behavior increased again. We injected hemi-PD rats with 1 ng BoNT-A twice, the second injection following 6 months after the first one and tested the rats for apomorphine-induced rotations and spontaneous motor behaviors, i.e., corridor task and stepping test. To test the hypothesis that BoNT-A reduced striatal hypercholinism in hemi-PD rats, the acetylcholinesterase inhibitor donepezil was injected prior to separate apomorphine-induced rotation tests. In hemi-PD rats, the first BoNT-A injection led to a clear reduction of the apomorphine-induced rotations, and the second BoNT-A injection to a more massive and prolonged reaction. In hemi-PD rats whose apomorphine-induced rotation behavior was strongly reduced by an intrastriatal BoNT-A, subsequent donepezil injections led to significant increases of the rotation rate. Concerning corridor task and stepping test, neither first nor second BoNT-A injections changed hemi-PD rats' behavior significantly. The data give evidence for the possibility of repeated intrastriatal administrations of BoNT-A, for treatment of motor symptoms in experimental hemi-PD over a longer time.

Unilateral Botulinum Neurotoxin-A Injection into the Striatum of C57BL/6 Mice Leads to a Different Motor Behavior Compared with Rats

Different morphological changes in the caudate-putamen (CPu) of naïve rats and mice were observed after intrastriatal botulinum neurotoxin-A (BoNT-A) injection. For this purpose we here studied various motor behaviors in mice (n = 46) longitudinally up to 9 months after intrastriatal BoNT-A administration as previously reported for rats, and compared both outcomes. Apomorphine- and amphetamine-induced rotational behavior, spontaneous motor behavior, as well as lateralized neglect were studied in mice after the injection of single doses of BoNT-A into the right CPu, comparing them with sham-injected animals. Unilateral intrastriatal injection of BoNT-A in mice induced significantly increased contralateral apomorphine-induced rotations for 1 to 3 months, as well as significantly increased contralateral amphetamine-induced rotations 1 to 9 months after injection. In rats (n = 28), unilateral BoNT-A injection also induced significantly increased contralateral apomorphine-induced rotations 3 months after injection, but did not provoke amphetamine-induced rotations at all. Lateralized sensorimotor integration, forelimb preference, and forelimb stepping were significantly impaired on the left side. The differences in motor behaviors between rats and mice may be caused by different BoNT-A effects on cholinergic and catecholaminergic fibers in rat and mouse striata, interspecies differences in striatal receptor densities, and different connectomes of the basal ganglia.

The fusion pore, 60 years after the first cartoon

Neurotransmitter release occurs in the form of quantal events by fusion of secretory vesicles with the plasma membrane, and begins with the formation of a fusion pore that has a conductance similar to that of a large ion channel or gap junction. In this review, we propose mechanisms of fusion pore formation and discuss their implications for fusion pore structure and function. Accumulating evidence indicates a direct role of soluble N-ethylmaleimide-sensitive-factor attachment receptor proteins in the opening of fusion pores. Fusion pores are likely neither protein channels nor purely lipid, but are of proteolipidic composition. Future perspectives to gain better insight into the molecular structure of fusion pores are discussed.

Light Chain Diversity among the Botulinum Neurotoxins

Botulinum neurotoxins (BoNT) are produced by several species of clostridium. There are seven immunologically unique BoNT serotypes (A⁻G). The Centers for Disease Control classifies BoNTs as 'Category A' select agents and are the most lethal protein toxins for humans. Recently, BoNT-like proteins have also been identified in several non-clostridia. BoNTs are di-chain proteins comprised of an N-terminal zinc metalloprotease Light Chain (LC) and a C-terminal Heavy Chain (HC) which includes the translocation and receptor binding domains. The two chains are held together by a disulfide bond. The LC cleaves Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs). The cleavage of SNAREs inhibits the fusion of synaptic vesicles to the cell membrane and the subsequent release of acetylcholine, which results in flaccid paralysis. The LC controls the catalytic properties and the duration of BoNT action. This review discusses the mechanism for LC catalysis, LC translocation, and the basis for the duration of LC action. Understanding these properties of the LC may expand the applications of BoNT as human therapies.

Detection of Clostridium tetani Neurotoxins Inhibited In Vivo by Botulinum Antitoxin B: Potential for Misleading Mouse Test Results in Food Controls

The presence of botulinum neurotoxin-producing Clostridia (BPC) in food sources is a public health concern. In favorable environmental conditions, BPC can produce botulinum neurotoxins (BoNTs) outside or inside the vertebrate host, leading to intoxications or toxico-infectious forms of botulism, respectively. BPC in food are almost invariably detected either by PCR protocols targeted at the known neurotoxin-encoding genes, or by the mouse test to assay for the presence of BoNTs in the supernatants of enrichment broths inoculated with the tested food sample. The sample is considered positive for BPC when the supernatant contains toxic substances that are lethal to mice, heat-labile and neutralized in vivo by appropriate polyclonal antibodies raised against purified BoNTs of different serotypes. Here, we report the detection in a food sample of a Clostridium tetani strain that produces tetanus neurotoxins (TeNTs) with the above-mentioned characteristics: lethal for mice, heat-labile and neutralized by botulinum antitoxin type B. Notably, neutralization occurred with two different commercially available type B antitoxins, but not with type A, C, D, E and F antitoxins. Although TeNT and BoNT fold very similarly, evidence that antitoxin B antiserum can neutralize the neurotoxic effect of TeNT in vivo has not been documented before. The presence of C. tetani strains in food can produce misleading results in BPC detection using the mouse test.

Experimental Intrastriatal Applications of Botulinum Neurotoxin-A: A Review

Parkinson’s disease (PD) is one of the most frequent neurodegenerative disorders. Its main pathophysiological characteristic is the loss of dopaminergic neurons in the substantia nigra pars compacta followed by a lack of striatal dopaminergic input and a consequent disinhibition of tonically active cholinergic interneurons. The resulting striatal hypercholinism causes major motor symptoms in PD. Anticholinergic pharmacotherapies have antiparkinsonian effects on motor symptoms, but, due to systemic actions, also numerous severe side effects occur on a regular basis. To circumvent these side effects, a local anticholinergic therapy acting exclusively in the striatum would be reasonable. Botulinum neurotoxin-A (BoNT-A) is synthesized by Clostridium botulinum and blocks the release of acetylcholine from the presynaptic bouton. For several decades, BoNT-A has been used successfully for medical and cosmetic purposes to induce controlled paralyses of single muscles. Our group and others investigated the experimental treatment of striatal hypercholinism by the direct injection of BoNT-A into the striatum of rats and mice as well as of hemiparkinsonian animal models. This review gives an overview of the most important results of the experimental intrastriatal BoNT-A application, with a focus on hemiparkinsonian rats.

Early experimental results of using a novel delivery carrier, hyaluronan-phosphatidylethanolamine (HA-PE), which may allow simple bladder instillation of botulinum toxin A as effectively as direct detrusor muscle injection

INTRODUCTION

Botulinum toxin A (BTX-A) is a neurotoxin that inhibits acetylcholine release by cleaving cytosolic synaptosome-associated protein 25 (SNAP-25) and results in bladder relaxation. A BTX-A intravesical injection has been established as an effective option for treating detrusor overactivity.

STUDY DESIGN

Sixty female Sprague Dawley rats were equally divided into control and experimental groups. Control Groups 1 to 3 received: BTX-A 10 units + saline instillation; hyaluronan-phosphatidylethanolamine (HA-PE) 0.5 g + saline instillation; and BTX-A 5 Uintra-detrusor injections, respectively. Treatment Groups 4 to 6 received: Alexa^®594-labeled BTX-A 10 U + HA-PE 0.5 g + saline instillation; BTX-A 5 U + HA-PE 0.2-0.5 g instilled for 60 min; and BTX-A 10 U + HA-PE 0.2-0.5 g instilled for 30 min, respectively. All procedures were performed under isoflurane general anesthesia. The primary outcome of this study was the degree of SNAP-25 staining in control and experimental groups compared to Group 3 (detrusor muscle injection). Urodynamic studies were performed at baseline and at day 14 after 1% acetic acid (AA) instillation, to evaluate the maximum pressure during filling (MP) and inter-contraction intervals (ICI). Group 4 rats were examined for Alexa^®594 fluorescence to demonstrate physical translocation of BTX-A-HA-PE complex. Standard histology was performed to assess the effect of HA-PE on bladder mucosa and detrusor muscle.

RESULTS

Group 3 showed the least SNAP-25 staining (7.3 ± 5.0%) compared with all groups except Group 5A (12.4 ± 12.27%, P = 1.0). Group 6A, which had high HA-PE dose but a shorter instillation time, showed fairly extensive SNAP-25 staining (22.9 ± 10%). Confocal microscopy of Group 4 confirmed the presence of Alexa^®594 fluorescence across the urothelium. Urodynamic parameters were not significantly different at baseline (P = 1.0). After acetic acid instillation, Group 5A showed minimal change in ICI, which was comparable to ICI in Group 3 rats.

DISCUSSION

SNAP-25 staining in Group 5A was comparable to Group 3, suggesting that adequate HA-PE and instillation time allows the efficacy of this carrier mechanism to be comparable to standard intra-detrusor injections. All other groups showed significantly higher SNAP-25 staining compared to Group 3. A dose response effect was demonstrated; higher dose of HA-PE (Group 5A vs Group 5B) and longer instillation time (Group 5 vs Group 6) led to lower SNAP-25 staining.

CONCLUSION

This novel method of BTX-A delivery to the bladder using a carrier (HA-PE) is promising and requires further investigation. Using a larger animal model, identifying an optimal dose of HA-PE and instillation time, and reproducing the current results are further required to validate this carrier.

Discovery of novel bacterial toxins by genomics and computational biology

Hundreds and hundreds of bacterial protein toxins are presently known. Traditionally, toxin identification begins with pathological studies of bacterial infectious disease. Following identification and cultivation of a bacterial pathogen, the protein toxin is purified from the culture medium and its pathogenic activity is studied using the methods of biochemistry and structural biology, cell biology, tissue and organ biology, and appropriate animal models, supplemented by bioimaging techniques. The ongoing and explosive development of high-throughput DNA sequencing and bioinformatic approaches have set in motion a revolution in many fields of biology, including microbiology. One consequence is that genes encoding novel bacterial toxins can be identified by bioinformatic and computational methods based on previous knowledge accumulated from studies of the biology and pathology of thousands of known bacterial protein toxins. Starting from the paradigmatic cases of diphtheria toxin, tetanus and botulinum neurotoxins, this review discusses traditional experimental approaches as well as bioinformatics and genomics-driven approaches that facilitate the discovery of novel bacterial toxins. We discuss recent work on the identification of novel botulinum-like toxins from genera such as Weissella, Chryseobacterium, and Enteroccocus, and the implications of these computationally identified toxins in the field. Finally, we discuss the promise of metagenomics in the discovery of novel toxins and their ecological niches, and present data suggesting the existence of uncharacterized, botulinum-like toxin genes in insect gut metagenomes.

A mutated recombinant subunit vaccine protects mice and guinea pigs against botulinum type A intoxication

Botulinum neurotoxins (BoNTs) are the most potent toxins to mammals. A toxoid vaccine was previously used for prevention of botulinum intoxication; however, this vaccine is no longer available. Currently, no approved botulinum vaccines are available from the Food and Drug Administration (FDA). Recently, a recombinant host cell receptor-binding subunit created for use as a potential vaccine completed phase 2 clinical trials. The current study designed a vaccine candidate against BoNT type A (BoNT/A) using a structural design. Our vaccine candidate was the BoNT/A heavy chain C-terminal region (HCR) that contained the point mutation BA15 (R1269A) within the ganglioside-binding site. A Biacore affinity test showed that the affinity of BA15 for ganglioside GT1b was 100 times lower than that of the HCR. A SNAP25 cleavage assay revealed that immunized sera blocked SNAP25 cleavage of the BoNT/A toxin via BA15. In an in vivo experiment, mice and guinea pigs immunized with BA15 produced neutralizing antibodies that protected against 3,000 LD50 of BoNT/A. In conclusion, the results of both in vitro and in vivo assays showed that our BA15 vaccine candidate was similar to the recombinant host cell receptor-binding subunit vaccine. The inability of BA15to bind ganglioside shows that BA15 is a potential safe vaccine candidate.

Hsp90 and Thioredoxin-Thioredoxin Reductase enable the catalytic activity of Clostridial neurotoxins inside nerve terminals

Botulinum (BoNTs) and tetanus (TeNT) neurotoxins are the most toxic substances known and form the growing family of Clostridial neurotoxins (CNT), the etiologic agents of botulism and tetanus. CNT are composed of a metalloprotease light chain (L), linked via a disulfide bond to a heavy chain (H). H mediates the binding to nerve terminals and the membrane translocation of L into the cytosol, where its substrates, the three SNARE proteins, are localized. L translocation is accompanied by unfolding and, once delivered on the cytosolic side of the endosome membrane, it has to be reduced and reacquire the native fold to be active. The Thioredoxin-Thioredoxin Reductase system (Trx-TrxR) specifically reduces the interchain disulfide bond while the cytosolic chaperone protein Hsp90 mediates L refolding. Both steps are essential for CNT activity and their inhibition efficiently blocks the neurotoxicity in cultured neurons and mice. Trx and its reductase physically interact with Hsp90 and are loosely bound to the cytosolic side of synaptic vesicles, the organelle exploited by CNT to enter nerve terminals and wherefrom L is translocated into the cytosol. Therefore, Trx, TrxR and Hsp90 orchestrate a chaperone-redox molecular machinery that enables the catalytic activity of the L inside nerve terminals. Given the fundamental role of L reduction and refolding, this machinery represents a rational target for the development of mechanism-based antitoxins.

Exocytotic fusion pores as a target for therapy

Regulated exocytosis can be split into a sequence of steps ending with the formation and the dilation of a fusion pore, a neck-like connection between the vesicle and the plasma membrane. Each of these steps is precisely controlled to achieve the optimal spatial and temporal profile of the release of signalling molecules. At the level of the fusion pore, tuning of the exocytosis can be achieved by preventing its formation, by stabilizing the unproductive narrow fusion pore, by altering the speed of fusion pore expansion and by completely closing the fusion pore. The molecular structure and dynamics of fusion pores have become a major focus of cell research, especially as a promising target for therapeutic strategies. Electrophysiological, optical and electrochemical methods have been used extensively to illuminate how cells regulate secretion at the level of a single fusion pore. Here, we describe recent advances in the structure and mechanisms of the initial fusion pore formation and the progress in therapeutic strategies with the focus on exocytosis.

Deubiquitinating enzyme VCIP135 dictates the duration of botulinum neurotoxin type A intoxication

Botulism is characterized by flaccid paralysis, which can be caused by intoxication with any of the seven known serotypes of botulinum neurotoxin (BoNT), all of which disrupt synaptic transmission by endoproteolytic cleavage of SNARE proteins. BoNT serotype A (BoNT/A) has the most prolonged or persistent effects, which can last several months, and exerts its effects by specifically cleaving and inactivating SNAP25. A major factor contributing to the persistence of intoxication is the long half-life of the catalytic light chain, which remains enzymatically active months after entry into cells. Here we report that BoNT/A catalytic light chain binds to, and is a substrate for, the ubiquitin ligase HECTD2. However, the light chain evades proteasomal degradation by the dominant effect of a deubiquitinating enzyme, VCIP135/VCPIP1. This deubiquitinating enzyme binds BoNT/A light chain directly, with the two associating in cells through the C-terminal 77 amino acids of the light chain protease. The development of specific DUB inhibitors, together with inhibitors of BoNT/A proteolytic activity, may be useful for reducing the morbidity and public health costs associated with BoNT/A intoxication and could have potential biodefense implications.

Botulinum Neurotoxins: Biology, Pharmacology, and Toxicology

The study of botulinum neurotoxins (BoNT) is rapidly progressing in many aspects. Novel BoNTs are being discovered owing to next generation sequencing, but their biologic and pharmacological properties remain largely unknown. The molecular structure of the large protein complexes that the toxin forms with accessory proteins, which are included in some BoNT type A1 and B1 pharmacological preparations, have been determined. By far the largest effort has been dedicated to the testing and validation of BoNTs as therapeutic agents in an ever increasing number of applications, including pain therapy. BoNT type A1 has been also exploited in a variety of cosmetic treatments, alone or in combination with other agents, and this specific market has reached the size of the one dedicated to the treatment of medical syndromes. The pharmacological properties and mode of action of BoNTs have shed light on general principles of neuronal transport and protein-protein interactions and are stimulating basic science studies. Moreover, the wide array of BoNTs discovered and to be discovered and the production of recombinant BoNTs endowed with specific properties suggest novel uses in therapeutics with increasing disease/symptom specifity. These recent developments are reviewed here to provide an updated picture of the biologic mechanism of action of BoNTs, of their increasing use in pharmacology and in cosmetics, and of their toxicology.

Implementing the Bruker MALDI Biotyper in the Public Health Laboratory for C. botulinum Neurotoxin Detection

Currently, the gold standard method for active botulinum neurotoxin (BoNT) detection is the mouse bioassay (MBA). A Centers for Disease Control and Prevention-developed mass spectrometry (MS)-based assay that detects active BoNT was successfully validated and implemented in a public health laboratory in clinical matrices using the Bruker MALDI-TOF MS (Matrix-assisted laser desorption ionization–time of flight mass spectrometry) Biotyper. For the first time, a direct comparison with the MBA was performed to determine MS-based assay sensitivity using the Bruker MALDI Biotyper. Mice were injected with BoNT/A, /B, /E, and /F at concentrations surrounding the established MS assay limit of detection (LOD) and analyzed simultaneously. For BoNT/B, /E, and /F, MS assay sensitivity was equivalent or better than the MBA at 25, 0.3, and 8.8 mLD₅₀, respectively. BoNT/A was detected by the MBA between 1.8 and 18 mLD₅₀, somewhat more sensitive than the MS method of 18 mLD₅₀. Studies were performed to compare assay performance in clinical specimens. For all tested specimens, the MS method rapidly detected BoNT activity and serotype in agreement with, or in the absence of, results from the MBA. We demonstrate that the MS assay can generate reliable, rapid results while eliminating the need for animal testing.

Tetanus: A Potential Public Health Threat in Times of Disaster

BACKGROUND

Tetanus is a potentially fatal condition that is rare in urban environments but is seen in developing countries and post-natural-disaster. Therefore, the purpose of this report was to review the epidemiology, pathogenesis, and management of tetanus in the trauma patient.

METHODS

A thorough literature review was conducted to look for the most current and thorough guidelines on the prophylaxis and treatment of tetanus. PUBMED (National Center for Biotechnology Information, National Institutes of Health; Bethesda, Maryland USA), MEDLINE (US National Library of Medicine, National Institutes of Health; Bethesda, Maryland USA), and Cochrane Library (The Cochrane Collaboration; Oxford, United Kingdom) databases were searched for articles in English, published from 2005 to 2015, using the keywords "Tetanus," "Trauma/Surgery," and "Disaster." Controlled trials, randomized controlled trials, trials of adult patients, published guidelines, expert opinions, and review articles were selected and extracted.

RESULTS

Current vaccination schedules in developed countries provide prophylaxis for tetanus. However, when severe natural disasters occur, many patients may not be able to provide a reliable vaccination history. In these situations, tetanus immune globulin (TIG) is indicated; if resources are not limited, both tetanus toxoid and TIG should be given to those with high-risk wounds. If resources are limited, TIG should be reserved for those that would benefit most or those least likely to have the protective antibodies.

CONCLUSIONS

Although tetanus is a disease that has a low incidence in the developed world due to high rates of immunization, during large-scale natural disasters, compounding factors like the types of injuries, lack of medical services and supplies, and the delay in treatment associated with an already low immunization rate result in an increased incidence and outbreaks of the disease that has higher mortality in an underdeveloped society. It is important for the urban physician that cares for trauma and critical patients to become familiar with the protocols for treatment and immunization of patients that have tetanus-prone wounds, as well as recognize the potential for outbreaks in the settings of major natural disasters. Finkelstein P , Teisch L , Allen CJ , Ruiz G . Tetanus: a potential public health threat in times of disaster. Prehosp Disaster Med. 2017;32(3):339-342.

Botulinum toxin in spinal cord injury patients with neurogenic detrusor overactivity

Evidence for the efficacy and safety of intravesical onabotulinum toxin A (onabotA) injections has led to them being licensed in many countries, including Korea, for the treatment of patients with urinary incontinence due to neurogenic detrusor overactivity (NDO) resulting from spinal cord injury or multiple sclerosis who are refractory or intolerant to anticholinergic medications. OnabotA injections have an inhibitory effect on acetylcholine release for up to 10 months, with a recommended dose of 200 U. OnabotA treatment has a beneficial effect not only on urinary symptoms, but also on quality of life. Several clinical studies have shown onabotA to have better effects than placebo in achieving continence, reducing incontinence episodes, improving urodynamic parameters, and improving health-related quality of life. Urinary tract infections and postvoid residual volume are the most prevalent side effects. In patients with residual volume, clean intermittent catheterization may be necessary. In patients with spinal cord injury or multiple sclerosis, it is recommended to evaluate physical and cognitive function before intravesical onabotA injection to ensure that the patient and caregiver are able to perform catheterization if necessary. Further controlled trials should assess the optimal dose, injection technique, long-term safety of repeated injections, and optimal timing of onabotA treatment in the treatment of NDO.

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.

A matrix-focused structure-activity and binding site flexibility study of quinolinol inhibitors of botulinum neurotoxin serotype A

Our initial discovery of 8-hydroxyquinoline inhibitors of BoNT/A and separation/testing of enantiomers of one of the more active leads indicated considerable flexibility in the binding site. We designed a limited study to investigate this flexibility and probe structure-activity relationships; utilizing the Betti reaction, a 36 compound matrix of quinolinol BoNT/A LC inhibitors was developed using three 8-hydroxyquinolines, three heteroaromatic amines, and four substituted benzaldehydes. This study has revealed some of the most effective quinolinol-based BoNT/A inhibitors to date, with 7 compounds displaying IC₅₀ values ⩽1μM and 11 effective at ⩽2μM in an ex vivo assay.