Safety and Clinical Outcomes of an Equine-derived Heptavalent Botulinum Antitoxin Treatment for Confirmed or Suspected Botulism in the United States

Aminopyridines Restore Ventilation and Reverse Respiratory Acidosis at Late Stages of Botulism in Mice

Botulinum neurotoxin (BoNT) is a potent protein toxin that causes muscle paralysis and death by asphyxiation. Treatments for symptomatic botulism are intubation and supportive care until respiratory function recovers. Aminopyridines have recently emerged as potential treatments for botulism. The clinically approved drug 3,4-diaminopyridine (3,4-DAP) rapidly reverses toxic signs of botulism and has antidotal effects when continuously administered in rodent models of lethal botulism. Although the therapeutic effects of 3,4-DAP likely result from the reversal of diaphragm paralysis, the corresponding effects on respiratory physiology are not understood. Here, we combined unrestrained whole-body plethysmography (UWBP) with arterial blood gas measurements to study the effects of 3,4-DAP, and other aminopyridines, on ventilation and respiration at terminal stages of botulism in mice. Treatment with clinically relevant doses of 3,4-DAP restored ventilation in a dose-dependent manner, producing significant improvements in ventilatory parameters within 10 minutes. Concomitant with improved ventilation, 3,4-DAP treatment reversed botulism-induced respiratory acidosis, restoring blood levels of CO2, pH, and lactate to normal physiologic levels. Having established that 3,4-DAP-mediated improvements in ventilation were directly correlated with improved respiration, we used UWBP to quantitatively evaluate nine additional aminopyridines in BoNT/A-intoxicated mice. Multiple aminopyridines were identified with comparable or enhanced therapeutic efficacies compared with 3,4-DAP, including aminopyridines that selectively improved tidal volume versus respiratory rate and vice versa. In addition to contributing to a growing body of evidence supporting the use of aminopyridines to treat clinical botulism, these data lay the groundwork for the development of aminopyridine derivatives with improved pharmacological properties. SIGNIFICANCE STATEMENT: There is a critical need for fast-acting treatments to reverse respiratory paralysis in patients with botulism. This study used unrestrained, whole-body plethysmography and arterial blood gas analysis to show that aminopyridines rapidly restore ventilation and respiration and reverse respiratory acidosis when administered to mice at terminal stages of botulism. In addition to supporting the use of aminopyridines as first-line treatments for botulism symptoms, these data are expected to contribute to the development of new aminopyridine derivatives with improved pharmacological properties.

Foodborne Botulism, Canada, 2006-20211

During 2006-2021, Canada had 55 laboratory-confirmed outbreaks of foodborne botulism, involving 67 cases. The mean annual incidence was 0.01 case/100,000 population. Foodborne botulism in Indigenous communities accounted for 46% of all cases, which is down from 85% of all cases during 1990-2005. Among all cases, 52% were caused by botulinum neurotoxin type E, but types A (24%), B (16%), F (3%), and AB (1%) also occurred; 3% were caused by undetermined serotypes. Four outbreaks resulted from commercial products, including a 2006 international outbreak caused by carrot juice. Hospital data indicated that 78% of patients were transferred to special care units and 70% required mechanical ventilation; 7 deaths were reported. Botulinum neurotoxin type A was associated with much longer hospital stays and more time spent in special care than types B or E. Foodborne botulism often is misdiagnosed. Increased clinician awareness can improve diagnosis, which can aid epidemiologic investigations and patient treatment.

Neuromuscular recovery from botulism involves multiple forms of compensatory plasticity

Introduction

Botulinum neurotoxin (BoNT) causes neuroparalytic disease and death by blocking neuromuscular transmission. There are no specific therapies for clinical botulism and the only treatment option is supportive care until neuromuscular function spontaneously recovers, which can take weeks or months after exposure. The highly specialized neuromuscular junction (NMJ) between phrenic motor neurons and diaphragm muscle fibers is the main clinical target of BoNT. Due to the difficulty in eliciting respiratory paralysis without a high mortality rate, few studies have characterized the neurophysiological mechanisms involved in diaphragm recovery from intoxication. Here, we develop a mouse model of botulism that involves partial paralysis of respiratory muscles with low mortality rates, allowing for longitudinal analysis of recovery.

Methods and results

Mice challenged by systemic administration of 0.7 LD50 BoNT/A developed physiological signs of botulism, such as respiratory depression and reduced voluntary running activity, that persisted for an average of 8-12 d. Studies in isolated hemidiaphragm preparations from intoxicated mice revealed profound reductions in nerve-elicited, tetanic and twitch muscle contraction strengths that recovered to baseline 21 d after intoxication. Despite apparent functional recovery, neurophysiological parameters remained depressed for 28 d, including end plate potential (EPP) amplitude, EPP success rate, quantal content (QC), and miniature EPP (mEPP) frequency. However, QC recovered more quickly than mEPP frequency, which could explain the discrepancy between muscle function studies and neurophysiological recordings. Hypothesizing that differential modulation of voltage-gated calcium channels (VGCC) contributed to the uncoupling of QC from mEPP frequency, pharmacological inhibition studies were used to study the contributions of different VGCCs to neurophysiological function. We found that N-type VGCC and P/Q-type VGCC partially restored QC but not mEPP frequency during recovery from paralysis, potentially explaining the accelerated recovery of evoked release versus spontaneous release. We identified additional changes that presumably compensate for reduced acetylcholine release during recovery, including increased depolarization of muscle fiber resting membrane potential and increased quantal size.

Discussion

In addition to identifying multiple forms of compensatory plasticity that occur in response to reduced NMJ function, it is expected that insights into the molecular mechanisms involved in recovery from neuromuscular paralysis will support new host-targeted treatments for multiple neuromuscular diseases.

Skin Popping for the Hand Surgeon: A Case Report and Review

INTRODUCTION

Subcutaneous injection of illicit drugs, colloquially known as skin popping, is associated with skin and soft tissue infections of the upper extremity. Sequelae of these infections often present to hand surgeons in the late stages of disease, are associated with challenging clinical scenarios, and are a significant burden to both patients and providers. The authors present an illustrative case and review the literature regarding this growing phenomenon in upper extremity surgery.

METHODS

A case report detailing the surgical reconstruction of a large forearm wound in the setting of intravenous heroin use and skin popping is presented. Search terms related to upper extremity subcutaneous drug injection were used to find relevant articles in PubMed and EMBASE. A total of 488 articles were found, with 22 studies meeting the inclusion criteria.

RESULTS

In this case report, the patient had a long history of skin popping to the forearm and presented with a chronic wound with exposed bone. The patient was treated with serial debridement, bony fixation, intravenous antibiotics, and soft tissue coverage using an arteriovenous loop and a muscle-only latissimus flap. Literature review yielded 22 studies comprising 38 patients with 55% (11/20) women and age range of 23 to 58 years. Heroin was the most commonly used drug (50.0%). The most common presentation was soft tissue infection (6/20 patients), manifestations of noninfected wounds (5/20), and wound botulism (4/20 of patients). Seventy percent of patients presented with multiple injection sites. Surgical management was described in 18% of cases, with all but one case describing drainage and debridement techniques. Only one case of formal reconstruction using a dermal template was described.

CONCLUSIONS

Skin popping infections have unique pathogenesis, presentation, and management patterns that hand surgeons must be aware of when treating these patients. A literature review revealed a relative paucity of reports regarding risk factors and surgical management of "skin popping" sequelae. If patients are reconstructive candidates, complex reconstruction requiring free tissue transfer may be warranted.

Equine Polyclonal Antibodies Prevent Acute Chikungunya Virus Infection in Mice

Chikungunya virus (CHIKV) is a mosquito-transmitted pathogen that causes chikungunya disease (CHIK); the disease is characterized by fever, muscle ache, rash, and arthralgia. This arthralgia can be debilitating and long-lasting, seriously impacting quality of life for years. Currently, there is no specific therapy available for CHIKV infection. We have developed a despeciated equine polyclonal antibody (CHIKV-EIG) treatment against CHIKV and evaluated its protective efficacy in mouse models of CHIKV infection. In immunocompromised (IFNAR^-/-) mice infected with CHIKV, daily treatment for five consecutive days with CHIKV-EIG administered at 100 mg/kg starting on the day of infection prevented mortality, reduced viremia, and improved clinical condition as measured by body weight loss. These beneficial effects were seen even when treatment was delayed to 1 day after infection. In immunocompetent mice, CHIKV-EIG treatment reduced virus induced arthritis (including footpad swelling), arthralgia-associated cytokines, viremia, and tissue virus loads in a dose-dependent fashion. Collectively, these results suggest that CHIKV-EIG is effective at preventing CHIK and could be a viable candidate for further development as a treatment for human disease.

Characterization of a novel tetravalent botulism antitoxin based on receptor-binding domain of BoNTs

Botulinum neurotoxin (BoNTs; serotypes A, B, E, and F) cause botulism disease in humans, which could be effectively treated using antitoxins. Herein, we established a novel receptor-binding domain (RBD)-based antitoxin using recombinant C terminal heavy chain (Hc) domains of BoNTs as immunogens. Immunization of horses with these recombinant Hc domains allowed the purification and digestion of IgGs from hyper-immune sera to produce high-quality and high-efficiency monovalent botulism antitoxin F(ab')₂ against each BoNT (M-BATs). However, these M-BATs could not bind or neutralize other serotypes of BoNTs, and that there were no cross-protective effects among these M-BATs. This suggested the need to prepare tetravalent antitoxins to neutralize the four BoNTs simultaneously. Thus, these M-BATs were formulated into a novel tetravalent botulism antitoxin (T-BAT), in which a 10-ml volume contained 10000 IU of BoNT/A and 5000 IU of BoNT/B, BoNT/E, and BoNT/F antitoxins. The novel antitoxin preparation could prevent and treat the four mixed botulinum neurotoxins simultaneously in vivo, representing strong efficacy in an animal poisoning model. Moreover, these antibodies in T-BAT could bind the RBD, whereas conventional antitoxins based on inactivated toxins mainly bind the light chain or heavy chain translocation domain (HN) and weakly bind the important RBD in current experimental conditions. The high levels of RBD-specific novel antitoxins can efficiently bind the RBD and neutralize natural or recombinant toxins containing this RBD. The findings of the present study experimentally support the use of RBD-specific antitoxins to treat BoNT serotype A, B, E, and F-mediated botulism. This study demonstrated the concept of developing potent novel multivalent antitoxins against all BoNTs or other toxins, using the RBD of these toxins as an alternative antigen to inactivated toxins. KEY POINTS: • Antitoxins based on the receptor-binding domains of botulinum neurotoxins were made. • Novel antitoxin binds RBD; traditional antitoxin mainly binds light chain or HN domain. • A tetravalent antitoxin could prevent and treat the four mixed neurotoxins in vivo.

Botulism in Spain: Epidemiology and Outcomes of Antitoxin Treatment, 1997-2019

BACKGROUND

Botulism is a low incidence but potentially fatal infectious disease caused by neurotoxins produced mainly by Clostridium botulinum. There are different routes of acquisition, food-borne and infant/intestinal being the most frequent presentation, and antitoxin is the treatment of choice in all cases. In Spain, botulism is under surveillance, and case reporting is mandatory.

METHODS

This retrospective study attempts to provide a more complete picture of the epidemiology of botulism in Spain from 1997 to 2019 and an assessment of the treatment, including the relationship between a delay in antitoxin administration and the length of hospitalization using the Cox proportional hazards test and Kruskal-Wallis test, and an approach to the frequency of adverse events, issues for which no previous national data have been published.

RESULTS

Eight of the 44 outbreaks were associated with contaminated commercial foods involving ≤7 cases/outbreak; preserved vegetables were the main source of infection, followed by fish products; early antitoxin administration significantly reduces the hospital stay, and adverse reactions to the antitoxin affect around 3% of treated cases.

Immunologic and Protective Properties of Subunit- vs. Whole Toxoid-Derived Anti-Botulinum Equine Antitoxin

Botulism is a paralytic disease caused by botulinum neurotoxins (BoNTs). Equine antitoxin is currently the standard therapy for botulism in human. The preparation of equine antitoxin relies on the immunization of horses with botulinum toxoid, which suffers from low yield and safety limitations. The Hc fragment of BoNTs was suggested to be a potent antibotulinum subunit vaccine. The current study presents a comparative evaluation of equine-based toxoid-derived antitoxin (TDA) and subunit-derived antitoxin (SDA). The potency of recombinant Hc/A, Hc/B, and Hc/E in mice was similar to that of toxoids of the corresponding serotypes. A single boost with Hc/E administered to a toxoid E-hyperimmune horse increased the neutralizing antibody concentration (NAC) from 250 to 850 IU/mL. Immunization of naïve horses with the recombinant subunits induced a NAC comparable to that of horses immunized with the toxoid. SDA and TDA bound common epitopes on BoNTs, as demonstrated by an in vitro competition binding assay. In vivo, SDA and TDA showed similar efficacy when administered to guinea pigs postexposure to a lethal dose of botulinum toxins. Collectively, the results of the current study suggest that recombinant BoNT subunits may replace botulinum toxoids as efficient and safe antigens for the preparation of pharmaceutical anti-botulinum equine antitoxins.

Investigation of Salicylanilides as Botulinum Toxin Antagonists

Botulinum neurotoxin serotype A (BoNT/A) is recognized by the Centers for Disease Control and Prevention (CDC) as the most potent toxin and as a Tier 1 biowarfare agent. The severity and longevity of botulism stemming from BoNT/A is of significant therapeutic concern, and early administration of antitoxin-antibody therapy is the only approved pharmaceutical treatment for botulism. Small molecule therapeutic strategies have targeted both the heavy chain (HC) and the light chain (LC) catalytic active site and α-/β-exosites. The LC translocation mechanism has also been studied, but an effective, nontoxic inhibitor remains underexplored. In this work, we screened a library of salicylanilides as potential translocation inhibitors. Potential leads following a primary screen were further scrutinized to identify sal30, which has a cellular minimal concentration of a drug that is required for 50% inhibition (IC50) value of 141 nM. The inquiry of salicylanilide sal30's mechanism of action was explored through a self-quenched fluorogenic substrate conjugated to bovine serum albumin (DQ-BSA) fluorescence, confocal microscopy, and vacuolar H+-ATPase (V-ATPase) inhibition assays. The summation of these findings imply that endolysosomal proton translocation through the protonophore mechanism of sal30 causes endosome pH to increase, which in turn prevents LC translocation into cytosol, a process that requires an acidic pH. Thus, the inhibition of BoNT/A activity by salicylanilides likely occurs through disruption of pH-dependent endosomal LC translocation. We further probed BoNT inhibition by sal30 using additivity analysis studies with bafilomycin A1, a known BoNT/A LC translocation inhibitor, which indicated the absence of synergy between the two ionophores.

Exposure-Response Modeling and Simulation to Support Human Dosing of Botulism Antitoxin Heptavalent Product

Botulism antitoxin heptavalent (A, B, C, D, E, F, and G – Equine; BAT) product is a sterile solution of F(ab')₂ and F(ab')₂‐related antibody fragments prepared from plasma obtained from horses that have been immunized with a specific serotype of botulinum toxoid and toxin. BAT product is indicated for the treatment of symptomatic botulism following documented or suspected exposure to botulinum neurotoxin serotypes A to G in adults and pediatric patients. Pharmacokinetic and exposure‐response models were used to explore the relationship between BAT product exposure and the probability of survival, and the occurrence of relevant moderate clinical signs observed during the preclinical development of BAT product to justify the clinical dose. The predicted probability of survival in humans for all serotypes of botulinum neurotoxin was more than 95.9% following intravenous administration of one vial of BAT product. Furthermore, this BAT product dose is expected to result in significant protection against clinical signs in human adults for all botulinum neurotoxin serotypes. Our exposure response model indicates that we have sufficient antitoxin levels to give full protection at various theoretical exposure levels and, based on neutralization capacity/potency of one dose of BAT product, it is expected to exceed the amount of circulating botulinum neurotoxin.

Antidotal treatment of botulism in rats by continuous infusion with 3,4-diaminopyridine

Botulinum neurotoxins (BoNTs) are highly potent, select agent toxins that inhibit neurotransmitter release at motor nerve terminals, causing muscle paralysis and death by asphyxiation. Other than post-exposure prophylaxis with antitoxin, the only treatment option for symptomatic botulism is intubation and supportive care until recovery, which can require weeks or longer. In previous studies, we reported the FDA-approved drug 3,4-diaminopyridine (3,4-DAP) reverses early botulism symptoms and prolongs survival in lethally intoxicated mice. However, the symptomatic benefits of 3,4-DAP are limited by its rapid clearance. Here we investigated whether 3,4-DAP could sustain symptomatic benefits throughout the full course of respiratory paralysis in lethally intoxicated rats. First, we confirmed serial injections of 3,4-DAP stabilized toxic signs and prolonged survival in rats challenged with 2.5 LD50 BoNT/A. Rebound of toxic signs and death occurred within hours after the final 3,4-DAP treatment, consistent with the short half-life of 3,4-DAP in rats. Based on these data, we next investigated whether the therapeutic benefits of 3,4-DAP could be sustained throughout the course of botulism by continuous infusion. To ensure administration of 3,4-DAP at clinically relevant doses, three infusion dose rates (0.5, 1.0 and 1.5 mg/kg∙h) were identified that produced steady-state serum levels of 3,4-DAP consistent with clinical dosing. We then compared dose-dependent effects of 3,4-DAP on toxic signs and survival in rats intoxicated with 2.5 LD50 BoNT/A. In contrast to saline vehicle, which resulted in 100% mortality, infusion of 3,4-DAP at ≥ 1.0 mg/kg∙h from 1 to 14 d after intoxication produced 94.4% survival and full resolution of toxic signs, without rebound of toxic signs after infusion was stopped. In contrast, withdrawal of 3,4-DAP infusion at 5 d resulted in re-emergence of toxic sign and death within 12 h, confirming antidotal outcomes require sustained 3,4-DAP treatment for longer than 5 d after intoxication. We exploited this novel survival model of lethal botulism to explore neurophysiological parameters of diaphragm paralysis and recovery. While neurotransmission was nearly eliminated at 5 d, neurotransmission was significantly improved at 21 d in 3,4-DAP-infused survivors, although still depressed compared to naïve rats. 3,4-DAP is the first small molecule to reverse systemic paralysis and promote survival in animal models of botulism, thereby meeting a critical treatment need that is not addressed by post-exposure prophylaxis with conventional antitoxin. These data contribute to a growing body of evidence supporting the use of 3,4-DAP to treat clinical botulism.

Polyclonal hyper immunoglobulin: A proven treatment and prophylaxis platform for passive immunization to address existing and emerging diseases

Passive immunization with polyclonal hyper immunoglobulin (HIG) therapy represents a proven strategy by transferring immunoglobulins to patients to confer immediate protection against a range of pathogens including infectious agents and toxins. Distinct from active immunization, the protection is passive and the immunoglobulins will clear from the system; therefore, administration of an effective dose must be maintained for prophylaxis or treatment until a natural adaptive immune response is mounted or the pathogen/agent is cleared. The current review provides an overview of this technology, key considerations to address different pathogens, and suggested improvements. The review will reflect on key learnings from development of HIGs in the response to public health threats due to Zika, influenza, and severe acute respiratory syndrome coronavirus 2.

Exotoxin-Targeted Drug Modalities as Antibiotic Alternatives

The paradigm of antivirulence therapy dictates that bacterial pathogens are specifically disarmed but not killed by neutralizing their virulence factors. Clearance of the invading pathogen by the immune system is promoted. As compared to antibiotics, the pathogen-selective antivirulence drugs hold promise to minimize collateral damage to the beneficial microbiome. Also, selective pressure for resistance is expected to be lower because bacterial viability is not directly affected. Antivirulence drugs are being developed for stand-alone prophylactic and therapeutic treatments but also for combinatorial use with antibiotics. This Review focuses on drug modalities that target bacterial exotoxins after the secretion or release-upon-lysis. Exotoxins have a significant and sometimes the primary role as the disease-causing virulence factor, and thereby they are attractive targets for drug development. We describe the key pre-clinical and clinical trial data that have led to the approval of currently used exotoxin-targeted drugs, namely the monoclonal antibodies bezlotoxumab (toxin B/TcdB, Clostridioides difficile), raxibacumab (anthrax toxin, Bacillus anthracis), and obiltoxaximab (anthrax toxin, Bacillus anthracis), but also to challenges with some of the promising leads. We also highlight the recent developments in pre-clinical research sector to develop exotoxin-targeted drug modalities, i.e., monoclonal antibodies, antibody fragments, antibody mimetics, receptor analogs, neutralizing scaffolds, dominant-negative mutants, and small molecules. We describe how these exotoxin-targeted drug modalities work with high-resolution structural knowledge and highlight their advantages and disadvantages as antibiotic alternatives.

Use of Botulism Antitoxin Heptavalent (A, B, C, D, E, F, G)-(Equine) (BAT®) in Clinical Study Subjects and Patients: A 15-Year Systematic Safety Review

Botulism is a rare, sometimes fatal paralytic illness caused by botulinum neurotoxins. BAT^® (Botulism Antitoxin Heptavalent (A, B, C, D, E, F, G)—(Equine)) is an equine-derived heptavalent botulinum antitoxin indicated for the treatment of symptomatic botulism in adult and pediatric patients. This review assesses the cumulative safety profile for BAT product from 2006 to 2020, using data received from clinical studies, an expanded-access program, a post-licensure registry, spontaneous and literature reports. The adverse event (AE) incidence rate for BAT product was calculated conservatively using only BAT product exposures for individuals with a record (512) and was alternatively estimated using all BAT product exposure data, including post-licensure deployment information (1128). The most frequently reported BAT product-related AEs occurring in greater than 1% of the 512–1128 BAT product-exposed individuals were hypersensitivity, pyrexia, tachycardia, bradycardia, anaphylaxis, and blood pressure increase reported in 2.3–5.1%, 1.8–3.9%, 1.0–2.2%, 0.89–2.0%, 0.62–1.4%, and 0.62–1.4%, respectively. For patients properly managed in an intensive care setting, the advantages of BAT product appear to outweigh potential risks in patients due to morbidity and mortality of botulism. AEs of special interest, including bradycardia, hemodynamic instability, hypersensitivity, serum sickness, and febrile reactions in the registry, were specifically solicited.

Outbreak of foodborne botulism in Alexandria, Egypt: modulating indications for administration of heptavalent botulinum antitoxin

In October 2019, ninety-four patients were admitted into Alexandria Poison Center (APC) with a history of ingestion of Feseekh (salted fish). In an attempt to allocate the resources, not all patients were given HBAT (botulism antitoxin heptavalent (A, B, C, D, E, F, G) equine immediately. The current study aimed to portray the clinical characteristics of the cases, explore the possible relation between these characteristics and necessity of HBAT administration, explore the reliability of mouse lethal test, and establish a clinical guide for management including preservation of resources. The current prospective study included 94 patients who were admitted to Alexandria Poison Center (APC) in the period from the 29^th of September to the 27^th of October 2019. The patients' data were recorded using a checklist that includes: personal data, past medical history, clinical assessment, investigations, treatment, and the outcome. The checklist was carried out to assess and follow up each patient. Hospitalized patients were categorized according to symptoms consistent with botulism. The equine HBAT, made by Emergent BioSolutions Canada Inc. (formerly Cangene Corporation), was used in the treatment. HBAT was given to thirty-four patients (36.2%) only out of the total admission. However, eighty-two (87.2%) of patients were completely cured, whereas ten patients (10.6%) were discharged with mild neurological sequels and death occurred only in two cases (2.2%). Sixty cases (63.8%) with suspected foodborne botulism could be managed by supportive treatment only with no need for HBAT, while patients with evident neurological signs received HBAT immediately.

Discovery of Dipeptides as Potent Botulinum Neurotoxin A Light-Chain Inhibitors

The botulinum neurotoxin, the caustic agent that causes botulism, is the most lethal toxin known to man. The neurotoxin composed of a heavy chain (HC) and a light chain (LC) enters neurons and cleaves SNARE proteins, leading to flaccid paralysis, which, in severe occurrences, can result in death. A therapeutic target for botulinum neurotoxin (BoNT) intoxication is the LC, a zinc metalloprotease that directly cleaves SNARE proteins. Herein we report dipeptides containing an aromatic connected to the N-terminus via a sulfonamide and a hydroxamic acid at the C-terminus as BoNT/A LC inhibitors. On the basis of a structure-activity relationship study, 33 was discovered to inhibit the BoNT/A LC with an IC₅₀ of 21 nM. X-ray crystallography analysis of 30 and 33 revealed that the dipeptides inhibit through a competitive mechanism and identified several key intermolecular interactions.

Neuronal delivery of antibodies has therapeutic effects in animal models of botulism

Botulism is caused by a potent neurotoxin that blocks neuromuscular transmission, resulting in death by asphyxiation. Currently, the therapeutic options are limited and there is no antidote. Here, we harness the structural and trafficking properties of an atoxic derivative of botulinum neurotoxin (BoNT) to transport a function-blocking single-domain antibody into the neuronal cytosol where it can inhibit BoNT serotype A (BoNT/A1) molecular toxicity. Post-symptomatic treatment relieved toxic signs of botulism and rescued mice, guinea pigs, and nonhuman primates after lethal BoNT/A1 challenge. These data demonstrate that atoxic BoNT derivatives can be harnessed to deliver therapeutic protein moieties to the neuronal cytoplasm where they bind and neutralize intracellular targets in experimental models. The generalizability of this platform might enable delivery of antibodies and other protein-based therapeutics to previously inaccessible intraneuronal targets.

Early recovery of botulism: one decade of experience

BACKGROUND

Botulism is a rare but serious disease, which appears in different forms. In this study, we reviewed the clinical features, laboratory data, and outcomes of patients who referred to our tertiary center.

MATERIALS AND METHODS

All confirmed cases of botulism referred to an academic referral center and a teaching hospital during 2009-2019, were retrospectively reviewed.

RESULTS

Fifty-three cases of clinical or laboratory-confirmed botulism were examined in this study. Nineteen patients were confirmed by laboratory data (serotype A (89.5%) and serotype E (10.5%)). In seven cases, the cause of botulism was unclear. In two patients, systemic symptoms emerged after the therapeutic injection of botulinum neurotoxin. The majority of cases (83%) were caused by an obvious food source. In 66% of cases, the initial symptoms emerged within less than 36 h, while in 20.8% of cases, the symptoms developed within or after 36 h; however, in seven patients that their botulism sources were unclear, the onset could not be estimated. All patients showed cranial involvement and generalized manifestation, and 49.1% had gastrointestinal symptoms. Except for two patients who were not treated due to immediate drug reactions who manifested severe hemodynamic instability, the rest of the patients were treated with trivalent antitoxin (A, B, and E). The complete resolution of the symptoms during hospitalization was documented in 50.9% of the patients. About 17% of the patients were intubated. Two patients died due to massive bilateral pulmonary thromboembolism and cardiac asystole following respiratory failure.

CONCLUSIONS

Although the complete resolution of the symptoms usually takes several weeks, in our experience, most patients showed at least partial resolution upon discharge. Early treatment results in better outcomes.

Botulinum Toxin as a Biological Warfare Agent: Poisoning, Diagnosis and Countermeasures

Botulinum toxin is a neurotoxin produced by Clostridium botulinum and some other relative species. It causes a lethal disease called botulism. It can enter the body via infections by Clostridium (e.g. wound and children botulism) or by direct contact with the toxin or eating contaminated food (food-borne botulism). Botulinum toxin is also considered as a relevant biological warfare agent with an expected high number of causalities when misused for bioterrorist or military purposes. The current paper surveys the actual knowledge about botulinum toxin pathogenesis, the manifestation of poisoning, and current trends in diagnostics and therapeutics. Relevant and recent literature is summarized in this paper.

Symptomatic treatment of botulism with a clinically approved small molecule

Botulinum neurotoxins (BoNTs) are potent neuroparalytic toxins that cause mortality through respiratory paralysis. The approved medical countermeasure for BoNT poisoning is infusion of antitoxin immunoglobulins. However, antitoxins have poor therapeutic efficacy in symptomatic patients; thus, there is an urgent need for treatments that reduce the need for artificial ventilation. We report that the US Food and Drug Administration-approved potassium channel blocker 3,4-diaminopyridine (3,4-DAP) reverses respiratory depression and neuromuscular weakness in murine models of acute and chronic botulism. In ex vivo studies, 3,4-DAP restored end-plate potentials and twitch contractions of diaphragms isolated from mice at terminal stages of BoNT serotype A (BoNT/A) botulism. In vivo, human-equivalent doses of 3,4-DAP reversed signs of severe respiratory depression and restored mobility in BoNT/A-intoxicated mice at terminal stages of respiratory collapse. Multiple-dosing administration of 3,4-DAP improved respiration and extended survival at up to 5 LD50 BoNT/A. Finally, 3,4-DAP reduced gastrocnemius muscle paralysis and reversed respiratory depression in sublethal models of serotype A-, B-, and E-induced botulism. These findings make a compelling argument for repurposing 3,4-DAP to symptomatically treat symptoms of muscle paralysis caused by botulism, independent of serotype. Furthermore, they suggest that 3,4-DAP is effective for a range of botulism symptoms at clinically relevant time points.

Cost savings associated with timely treatment of botulism with botulism antitoxin heptavalent product

Background

Botulism is a rare, serious, and sometimes fatal paralytic illness caused by exposure to neurotoxins produced by Clostridium botulinum bacteria. Patients with documented or suspected exposure to botulinum toxin serotypes A-G can be treated with BAT^® [Botulism Antitoxin Heptavalent (A, B, C, D, E, F, G)–(Equine)] product, which was approved in 2013 in the United States (US). Patients with botulism have demonstrated greater clinical benefit with early BAT product treatment (≤2 days from symptom onset) versus late treatment (>2 days).

Objective

Economic outcomes associated with improved clinical outcome benefits of BAT product treatment have not yet been reported. This ad hoc analysis aimed to estimate and compare costs associated with hospitalization, intensive care unit stay, and mechanical ventilation for patients with botulism administered BAT product treatment early or late.

Methods

Clinical outcomes data for early and late BAT product treatment were obtained from a patient registry conducted between October 2014 and July 2017. Total per patient mean daily costs were estimated based on information from published literature. Total population costs per group were calculated by multiplying estimated mean cost per patient by the average annual number of non-infant botulism cases in the US.

Results

Mean per patient costs were 2.5 times lower for patients treated with BAT product early versus late. On average in the US, early BAT product treatment could save greater than $3.9 million per year versus late treatment.

Conclusion

Substantial economic savings can be achieved with early BAT product treatment. The findings support the recommendation for public health authorities to ensure antitoxin treatment is readily available in sufficient quantities to manage botulism cases, including sporadic outbreaks and potential mass exposure biological attacks.

Safety and Pharmacokinetics of a Four Monoclonal Antibody Combination Against Botulinum C and D Neurotoxins

Botulism is caused by botulinum neurotoxin (BoNT), the most poisonous substance known. BoNTs are also classified as Tier 1 biothreat agents due to their high potency and lethality. The existence of seven BoNT serotypes (A-G), which differ between 35% to 68% in amino acid sequence, necessitates the development of serotype specific countermeasures. We present results of a Phase 1 clinical study of an anti-toxin to BoNT serotypes C and D, NTM-1634, which consists of an equimolar mixture of four fully human IgG1 monoclonal antibodies (mAbs), each binding to non-overlapping epitopes on BoNT serotypes C and D resulting in potent toxin neutralization in rodents. This first-in-human study evaluated the safety and pharmacokinetics of escalating doses of NTM-1634 administered intravenously to healthy adults (NCT03046550). Three cohorts of eight healthy subjects received a single intravenous dose of NTM-1634 or placebo at 0.33 mg/kg, 0.66 mg/kg or 1 mg/kg. Follow-up examinations and pharmacokinetic evaluations were continued up to 121 days post-infusion. Subjects were monitored using physical examinations, hematology and chemistry blood tests, and electrocardiograms. Pharmacokinetic parameters were estimated using noncompartmental methods. The results demonstrated that the materials were safe and well-tolerated with the expected half-lives for human mAbs and with minimal anti-drug antibodies detected over the dose ranges and duration of the study.

Therapeutic efficacy of equine botulism heptavalent antitoxin against all seven botulinum neurotoxins in symptomatic guinea pigs

Botulism neurotoxins are highly toxic and are potential agents for bioterrorism. The development of effective therapy is essential to counter the possible use of these toxins in military and bioterrorism scenarios, and to provide treatment in cases of natural intoxication. Guinea pigs were intoxicated with a lethal dose of botulinum neurotoxin serotypes A, B, C, D, E, F or G, and at onset of the clinical disease intoxicated animals were treated with either BAT^® [Botulism Antitoxin Heptavalent (A, B, C, D, E, F, G)–(Equine)] or placebo. BAT product treatment significantly (p<0.0001) enhanced survival compared to placebo for all botulinum neurotoxin serotypes and arrested or mitigated the progression of clinical signs of botulism intoxication. These results demonstrated the therapeutic efficacy of BAT product in guinea pigs and provided supporting evidence of effectiveness for licensure of BAT product under FDA 21 CFR Part 601 (Subpart H Animal Rule) as a therapeutic for botulism intoxication to serotypes A, B, C, D, E, F or G in adults and pediatric patients.