Botulinum toxin: the story of its development for the treatment of human disease

Drug Repurposing in the Chemotherapy of Infectious Diseases

Repurposing is a universal mechanism for innovation, from the evolution of feathers to the invention of Velcro tape. Repurposing is particularly attractive for drug development, given that it costs more than a billion dollars and takes longer than ten years to make a new drug from scratch. The COVID-19 pandemic has triggered a large number of drug repurposing activities. At the same time, it has highlighted potential pitfalls, in particular when concessions are made to the target product profile. Here, we discuss the pros and cons of drug repurposing for infectious diseases and analyze different ways of repurposing. We distinguish between opportunistic and rational approaches, i.e., just saving time and money by screening compounds that are already approved versus repurposing based on a particular target that is common to different pathogens. The latter can be further distinguished into divergent and convergent: points of attack that are divergent share common ancestry (e.g., prokaryotic targets in the apicoplast of malaria parasites), whereas those that are convergent arise from a shared lifestyle (e.g., the susceptibility of bacteria, parasites, and tumor cells to antifolates due to their high rate of DNA synthesis). We illustrate how such different scenarios can be capitalized on by using examples of drugs that have been repurposed to, from, or within the field of anti-infective chemotherapy.

OnabotulinumtoxinA for Pediatric Migraine

BACKGROUND

Migraine is a painful, prevalent, and problematic condition among children. Children need access to safe and effective treatment options to alleviate the impact of this chronic condition on their wellbeing.

CLINICAL IMPLICATIONS

Nurses have a crucial role in supporting patient access to BTX-A. Given the results of this and other studies demonstrating the safety and efficacy of BTX-A in children, nurses can support policy change for health plans to fund this intervention for pediatric migraineurs. Allowing children to receive the safe and effective BTX-A injections will lessen the already significant impact of chronic migraine on their physical, emotional and mental health. Nurses can also play a key role in providing education to patients regarding safe administration of BTX-A for migraine.

AIM

The objective of this study was to define the experiences, effects, and clinical response of children to onabotulinumtoxinA (BTX-A) for migraine prevention.

METHODS

Clinical documentation for patients aged 13-17 years presenting for BTX-A treatment for chronic migraine between 2016-2022 in a community-based specialty clinic within a large, urban, pediatric academic medical center were included. A series of one-way repeated measures (analysis of variance [ANOVA]) were conducted to compare headache frequency, severity, and duration at baseline, and following first and second injections of BTX-A.

RESULTS

Of 32 eligible participants, administration of BTX-A demonstrated a decrease in headache frequency and severity. Participants reported nearly seven fewer headache days per month. Participants reported neck stiffness, fever or flu-like symptoms, fatigue, and worsening pain following BTX-A administration.

CONCLUSIONS

Pediatric migraineurs need therapies that are safe, effective, and accessible. BTX-A was a safe and effective treatment for migraine among the children included in this study.

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.

Effects of Intradermal Botulinum Toxin Injections on Herpes Zoster Related Neuralgia

Background

Postherpetic neuralgia (PHN), which represents the most common chronic complication of herpes zoster, is characterized by intense pain and is difficult to treat. In fact, no treatments are currently available that can effectively reduce the pain associated with PHN. Recent evidence has been presented indicating that Botulinum toxin (BoNT-A) can serve as an effective and safe treatment for peripheral neuropathic pain.

Objective

The effects of intradermal BoNT-A injections on herpes zoster related neuralgia were investigated in this study.

Methods

Patients diagnosed with herpes zoster related acute neuralgia (N=13 - acute group) and those diagnosed with postherpetic neuralgia (N=17 - PHN group) were enrolled in this study. The two groups were treated with intradermal injections of BoNT-A at the site of their affected pain areas and were then assessed at 1 day, 1 week, 2 weeks, 1 month, 2 months and 3 months after their BoNT-A treatments.

Results

When compared with pre-treatment values, Visual Analogue Scores (VAS) in all patients were all significantly decreased at all times tested following BoNT-A injection. Before treatment, PHN patients had significantly higher VAS than those in the acute group. However, after 1 day of treatment, there was no difference in VAS between the two groups. None of the patients in the acute phase treated with BoNT-A developed PHN.

Conclusion

BoNT-A injections significantly reduced herpetic-related pain and proved to be a more effective treatment for the PHN versus acute pain group. Moreover, an early application of BoNT-A can alleviate the probability of developing PHN.

Botulinum Toxin Use for Modulating Neuroimmune Cutaneous Activity in Psoriasis

Psoriasis is a complex immune-mediated inflammatory disorder that generates enormous interest within the scientific communities worldwide, with new therapeutic targets being constantly identified and tested. Despite the numerous topical and systemic medications available for the treatment of psoriasis, alternative therapies are still needed for the optimal management of some patients who present with localized, resistant lesions. Novel insights into the contribution of cutaneous neurogenic inflammation in the pathogenesis of psoriasis have yielded exciting new potential roles of nerve-targeting treatments, namely botulinum toxin type A (BoNT-A), for the management of this disease. This paper aims to review the existing literature on knowledge regarding the potential role of BoNT-A in psoriasis treatment, with a focus on its ability to interfere with the immunopathogenetic aspects of psoriatic disease. Furthermore, in our paper, we are also including the first report of psoriatic lesions remission following local BoNT-A injections that were administered for treating upper limb spasticity, in a patient that concomitantly suffered from psoriasis and post-stroke spasticity.

A Monoclonal Antibody Combination against both Serotypes A and B Botulinum Toxin Prevents Inhalational Botulism in a Guinea Pig Model

Botulinum neurotoxins (BoNT) are extremely potent and can induce respiratory failure, requiring long-term intensive care to prevent death. Recombinant monoclonal antibodies (mAbs) hold considerable promise as BoNT therapeutics and prophylactics. In contrast, equine antitoxin cannot be used prophylactically and has a short half-life. Two three-mAb combinations are in development that specifically neutralize BoNT serotype A (BoNT/A) and B (BoNT/B). The three-mAb combinations addressing a single serotype provided pre-exposure prophylaxis in the guinea pig inhalation model. A lyophilized co-formulation of six mAbs, designated G03-52-01, that addresses both A and B serotypes is in development. Here, we investigated the efficacy of G03-52-01 to protect guinea pigs against an aerosol exposure challenge of BoNT/A1 or BoNT/B1. Previously, it was found that each antibody demonstrated a dose-dependent exposure and reached maximum circulating concentrations within 48 h after intramuscular (IM) or intravenous (IV) injection. Here we show that G03-52-01, in a single IM injection of G03-52-01 administered 48 h pre-exposure, protected guinea pigs against an aerosol challenge of up to 238 LD₅₀s of BoNT/A1 and 191 LD₅₀s of BoNT/B1. These data suggest that a single IM administration of G03-52-01 provides pre-exposure prophylaxis against botulism from an aerosol exposure of BoNT/A1 or BoNT/B1.

Botulinum Toxin A: A Review of Potential Uses in Treatment of Female Urogenital and Pelvic Floor Disorders

Background: Botulinum toxin is an injectable neuromodulator that inhibits transmission between peripheral nerve endings and muscle fibers, resulting in muscle paralysis. Botulinum toxin type A is the most common form of botulinum toxin used in clinical practice.

Methods: In this review, we examine the mechanism of action, formulations, common clinical use in the genital-urinary tract, and potential clinical use in pelvic floor disorders of botulinum toxin type A.

Results: Several aspects of botulinum toxin A make it a favorable therapeutic tool, including its accessibility, its longevity, and its impermanence and reversibility of resultant chemodenervation in a relatively short and safe manner. Although botulinum toxin A has well-established efficacy in treating refractory overactive bladder and neurogenic detrusor overactivity, its use in pelvic floor disorders is still in its infancy.

Conclusion: The efficacy of botulinum toxin A for treating pelvic pain, voiding dysfunction, muscle pain and dysfunction, and certain colorectal-related pain issues shows promise but requires additional rigorous evaluation.

An Update on Botulinum Toxin in Neurology

Botulinum neurotoxin (BoNT) is an effective treatment for many neurologic disorders. This article gives a comprehensive overview of the clinical applications of BoNT across the field of neurology.

Manufacturing and Clinical Formulations of Botulinum Neurotoxins

Botulinum Neurotoxins have always existed in nature, but its paralytic effect on humans due to the consumption of poorly preserved food was not recognized until 18th century. There are 8 serotypes of botulinum neurotoxins (A, B, C, D, E, F, G, H). Serotype A have been the most recognized one and was initially developed for large scale production in 1940's. The first batch for clinical use was produced by Edward Schantz, who collaborated with Dr. Alan Scott, an ophthalmologist, evaluating botulinum neurotoxin to treat strabismus. The process Schantz used had variability and led to inconsistent batch production. However, this process is still used by various manufacturers of commercial botulinum neurotoxin products as the foundation. These manufacturers have refined the manufacturing of botulinum neurotoxins by implementing new advanced techniques, including better potency assays. Despite the improvements in the manufacturing process, botulinum neurotoxins are still one of the most potent molecules and therefore, require special handing and additional safety/security measurements during production.

Application of botulinum toxin in maxillofacial field: Part III. Ancillary treatment for maxillofacial surgery and summary

Botulinum toxin (BTX) has various therapeutic indications: bruxism, square jaw, facial wrinkle, oral ulcer and maxillofacial pain, etc. In this paper, we will discuss the effectiveness of using BTX in dental implant surgery and orthognathic and orthodontic treatment. We summarized the clinical application of botulinum toxin in the maxillofacial field at the finale.

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

Introduction

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

Methods

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

Results

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

Conclusions

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

New therapeutics from Nature: The odd case of the bacterial cytotoxic necrotizing factor 1

Natural products may represent a rich source of new drugs. The enthusiasm toward this topic has recently been fueled by the 2015 Nobel Prize in Physiology or Medicine, awarded for the discovery of avermectin and artemisinin, natural products from Bacteria and Plantae, respectively, which have targeted one of the major global health issues, the parasitic diseases. Specifically, bacteria either living in the environment or colonizing our body may produce compounds of unexpected biomedical value with the potentiality to be employed as therapeutic drugs. In this review, the fascinating history of CNF1, a protein toxin produced by pathogenic strains of Escherichia coli, is divulged. Even if produced by bacteria responsible for a variety of diseases, CNF1 can behave as a promising benefactor to mankind. By modulating the Rho GTPases, this bacterial product plays a key role in organizing the actin cytoskeleton, enhancing synaptic plasticity and brain energy level, rescuing cognitive deficits, reducing glioma growth in experimental animals. These abilities strongly suggest the need to proceed with the studies on this odd drug in order to pave the way toward clinical trials.

Evidence and experience with onabotulinumtoxinA in chronic migraine: Recommendations for daily clinical practice

OnabotulinumtoxinA has been demonstrated to be effective as a preventive treatment in patients with chronic migraine (CM). Five years after the approval of onabotulinumtoxinA in Spain, the Headache Study Group of the Spanish Society of Neurology considered it worthwhile to gather a group of experts in treating patients with CM in order to draw up, based on current evidence and our own experience, a series of guidelines aimed at facilitating the use of the drug in daily clinical practice. For this purpose, we posed 12 questions that we ask ourselves as doctors, and which we are also asked by our patients. Each author responded to one question, and the document was then reviewed by everyone. We hope that this review will constitute a practical tool to help neurologists treating patients with CM.

Botulinum toxin for the treatment of refractory erythema and flushing of rosacea

BACKGROUND

Persistent erythema and severe rosacea flushing can cause significant physical discomfort and emotional stress to patients. Currently, no satisfactory treatments are available.

METHODS

We report two cases of refractory flushing and erythema of rosacea that were successfully treated with intradermal botulinum toxin injections.

RESULTS

Good cosmetic results were achieved for both patients. The side effects during and after treatment were mild pain and localized bruising; these symptoms resolved within several days without further treatment.

CONCLUSION

Intradermal botulinum toxin injection may be an effective treatment for refractory erythema and rosacea flushing that deserves further study in a larger patient population.

Botulinum toxin type A products are not interchangeable: a review of the evidence

Botulinum toxin type A (BoNTA) products are injectable biologic medications derived from Clostridium botulinum bacteria. Several different BoNTA products are marketed in various countries, and they are not interchangeable. Differences between products include manufacturing processes, formulations, and the assay methods used to determine units of biological activity. These differences result in a specific set of interactions between each BoNTA product and the tissue injected. Consequently, the products show differences in their in vivo profiles, including preclinical dose response curves and clinical dosing, efficacy, duration, and safety/adverse events. Most, but not all, published studies document these differences, suggesting that individual BoNTA products act differently depending on experimental and clinical conditions, and these differences may not always be predictable. Differentiation through regulatory approvals provides a measure of confidence in safety and efficacy at the specified doses for each approved indication. Moreover, the products differ in the amount of study to which they have been subjected, as evidenced by the number of publications in the peer-reviewed literature and the quantity and quality of clinical studies. Given that BoNTAs are potent biological products that meet important clinical needs, it is critical to recognize that their dosing and product performance are not interchangeable and each product should be used according to manufacturer guidelines.

[Applications of botulinum toxin in Neurology]

At present, botulinum toxin (BT) is one of the most fundamental available drugs in Neurology, only comparable with levodopa. BT is currently used in those entities characterized by excessive muscle contraction, including dystonia and spasticity. In addition, BT has been used to control pain associated with increased muscle contraction in dystonia and spasticity, but also is useful to control chronic pain not associated with muscle contraction, such as chronic daily headache. Finally, BT is useful in sialorrhoea and bruxism. The mechanism of action is complex, mainly acting on terminal neuromuscular junction, but also exhibiting analgesic properties, probably through inhibition of pain neurotransmitters release.

Modulation of botulinum toxin-induced changes in neuromuscular function with antibodies directed against recombinant polypeptides or fragments

Botulinum toxin is an agent that is typically encountered in two settings: as an agent that can cause disease (e.g. botulism), and as an agent that can be used to treat disease (i.e., a variety of neurologic disorders). In both cases it would be advantageous to develop a sound understanding of the mechanisms by which antibodies neutralize the toxin. In the present study, recombinant antigens were used to generate antibodies against the carboxyterminal half of the toxin heavy chain (HC50), the entire toxin light chain (LC), and the HA17, HA35 and HA70 components of the progenitor toxin complex. These antibodies were then evaluated for their respective abilities to alter botulinum toxin-induced changes in locomotor behavior in mice. The botulinum toxin type A complex was shown to produce dose-dependent depression of locomotor behavior within the dose range of 0.3-0.7 mouse LD50 units. At a dose of 0.5 LD50, the toxin typically reduced running behavior by 90% or more, and full recovery was not observed for approximately 4 weeks. Mice that were actively or passively vaccinated against the HC50 polypeptide were resistant to toxin action, presumably because the antibodies occluded the toxin binding domain. Interestingly, mice that were actively or passively vaccinated against LC were also resistant to toxin action. This effect may have been due to steric hindrance of the binding process. There was no scenario in which anti-HA antibodies altered the effects of toxin on locomotor behavior. This absence of effect was likely due to the fact that HAs and neurotoxin in the progenitor toxin complex spontaneously dissociate in physiologic media.

Neutralizing antibodies and secondary therapy failure after treatment with botulinum toxin type A: much ado about nothing?

OBJECTIVES

As the indications and duration of treatment of botulinum toxin type A (BoNT-A) increase, so do reports of patients who fail therapy after initially responding well. Although a loss of efficacy is commonly thought to be associated with neutralizing antibodies (NAbs), this relationship is not strongly correlated, and other factors may play a significant role. To explore this issue, we evaluated levels of NAbs in a large selected cohort of secondary nonresponders to BoNT-A using the highly sensitive mouse phrenic nerve-hemidiaphragm assay.

METHODS

Serum samples from 503 patients treated with BoNT-A who had a variety of diagnoses were tested for the presence of NAbs.

RESULTS

Fewer than half of the patients (n = 224, 44.5%) were found to be NAb-positive, indicating that in more than half of the secondary nonresponders, lack of efficacy is not due to NAb formation. The proportion of secondary nonresponders with NAbs was greater for higher dose indications (focal spasticity and spasmodic torticollis) than for lower dose indications (blepharospasm and hemifacial spasm) and increased with shorter injection intervals. Neutralizing antibody development was independent of the commercial preparation used.

CONCLUSIONS

Our results indicate that although NAb formation does play a role in secondary treatment failure with BoNT-A, this is not the cause in all patients, and the influence of other factors needs to be investigated. Gaining a better understanding of the underlying mechanisms for secondary treatment failure may help in the prediction, diagnosis, management, and prevention of this problem.

The evolution of botulinum neurotoxin type A for cosmetic applications

Very few pharmaceutical preparations share an evolutionary history as remarkable as that of botulinum neurotoxin (BoNT). The exotoxin of the organism Clostridium botulinum, once feared as a terrible poison, has been reborn as a highly regarded and widely used therapeutic and aesthetic agent. In less than two decades since the report of the success of BoNT type A (BoNTA) in reducing glabellar lines, injection of this product has become the most common non-surgical cosmetic procedure performed in the USA and worldwide. In addition to temporarily eliminating rhytids by muscle weakening, other dermatologic applications of BoNTA include correcting facial asymmetries and treating hyperhidrosis. Although BOTOX is the most clinically substantiated and published of the BoNTA preparations, other BoNTA products, as well as a BoNT type B product, are available in some parts of the world, and others are in development.

Use of botulinum toxin A in adult neurological disorders: efficacy, tolerability and safety

The protein botulinum neurotoxin A (BoNT/A) is one of seven distinct neurotoxins produced by Clostridium botulinum. BoNT/A blocks cholinergic synapses with an extremely high specificity and potency. Appropriately purified and diluted, BoNT/A serves as a reliable and well tolerated drug that is applied by local injection.The efficacy of BoNT/A is evident in the symptomatic therapy of disorders in which muscular hyperactivity plays a prominent role, such as focal dystonias and hemifacial spasm; in these disorders, BoNT/A is considered first-line therapy. BoNT/A is also beneficial in the treatment of both adults and children with spasticity of various causes. The pain that frequently accompanies these conditions is effectively reduced by BoNT/A. A genuine analgesic effect for BoNT/A unrelated to skeletal muscle spasmolysis has been suggested on the basis of in vitro and in vivo (animal) data. However, studies in humans designed to detect such an effect were negative, as were controlled studies of BoNT/A in patients with primary headache disorders.BoNT/A also acts on cholinergic synapses of the autonomic nervous system, and injection of BoNT/A into salivary glands significantly decreases the production of saliva. This may be beneficial for patients with Parkinson's disease, in whom the excessive production of saliva may be problematic.Overall, BoNT/A has been confirmed as an efficacious, predictable and well tolerated drug in an ever-increasing number of neurological disorders.

The role of systemic handling in the pathophysiologic actions of botulinum toxin

The ability of botulinum toxin to poison cholinergic nerve transmission is a dynamic phenomenon that involves not only the actions of the toxin on the body but also the actions of the body on the toxin. The former has been the subject of intense research, whereas the latter has received almost no attention. Therefore, a series of studies were performed to characterize systemic handling of botulinum toxin. The results indicated that the toxin reaches the general circulation (transcytosis across epithelial cells) without obvious changes in structure or biological activity. The general circulation acts as a holding compartment until there is adequate fractional distribution to neuromuscular junctions to produce blockade of transmission. During its transit through this compartment, the toxin 1) undergoes little biotransformation, 2) does not accumulate significantly in circulating cells, and 3) remains largely in the free state. In naive animals, the t(1/2) for toxin in the general circulation is approximately 10 h, and at any given point in time, there is little uptake in nontarget organs (liver, kidney, heart, and lung). In immunized animals, toxin clearance from the general circulation is rapid, and there is substantial accumulation of antibody-antigen complexes in liver. Thus, enhanced clearance from the circulation is a major mechanism by which active immunization can protect against poisoning.

Presynaptic neurotoxins with enzymatic activities

Toxins that alter neurotransmitter release from nerve terminals are of considerable scientific and clinical importance. Many advances were recently made in the understanding of their molecular mechanisms of action and use in human therapy. Here, we focus on presynaptic neurotoxins, which are very potent inhibitors of the neurotransmitter release because they are endowed with specific enzymatic activities: (1) clostridial neurotoxins with a metallo-proteolytic activity and (2) snake presynaptic neurotoxins with a phospholipase A2 activity.

Neurologic uses of botulinum neurotoxin type A

This article reviews the current and most neurologic uses of botulinum neurotoxin type A (BoNT-A), beginning with relevant historical data, neurochemical mechanism at the neuromuscular junction. Current commercial preparations of BoNT-A are reviewed, as are immunologic issues relating to secondary failure of BoNT-A therapy. Clinical uses are summarized with an emphasis on controlled clinical trials (as appropriate), including facial movement disorders, focal neck and limb dystonias, spasticity, hypersecretory syndromes, and pain.

Botulinum neurotoxins: fundamentals for the facial plastic surgeon

The most commonly performed nonsurgical cosmetic procedure in the facial plastic surgery armamentarium involves the various commercial preparations of botulinum neurotoxins. These drugs have undergone a transformation from public health scourge to near ubiquitous therapeutic modality across the entire medical spectrum. Herein, the history of botulinum neurotoxins is reviewed, including an exploration of their pharmacology, neuromuscular junction physiology, a description of the commercially available preparations, and the recent research concerning the practicalities of their clinical use.

From poison to remedy: the chequered history of botulinum toxin

Botulinum toxin poisoning has afflicted mankind through the mists of time. However, the first incident of food-borne botulism was documented as late as the 18th century, when the consumption of meat and blood sausages gave rise to many deaths throughout the kingdom of Württemberg in South Western Germany. The district medical officer Justinus Kerner (1786--1862), who was also a well-known German poet, published the first accurate and complete descriptions of the symptoms of food-borne botulism between 1817 and 1822 and attributed the intoxication to a biological poison. Kerner also postulated that the toxin might be used for treatment purposes. In 1895, an outbreak of botulism in the small Belgian village of Ellezelles led to the discovery of the pathogen "Clostridium botulinum" by Emile Pierre van Ermengem. Modern botulinum toxin treatment was pioneered by Alan B. Scott and Edward J. Schantz in the early 1970s, when the type-A serotype was used in medicine to correct strabismus. Other preparations of the type-A toxin were developed and manufactured in the United Kingdom, Germany, and China, whereas a therapeutic type-B toxin was prepared in the United States. To date, the toxin has been used to treat a wide variety of conditions associated with muscular hyperactivity, glandular hypersecretions and pain.

[Treatment of laryngeal movement disorders with botulinum toxins: part 1: History and mode of action]

Laryngeal dystonia (spasmodic dysphonia) is a movement disorder characterised by involuntary contractions of the laryngeal muscles involved in vocalisation. The introduction of botulinum toxin (BTX) in the treatment of laryngeal dystonia had a major clinical impact due to the striking improvement of symptoms. Most patients with severe types of spasmodic dysphonia are treated with injections of botulinum toxin type A. For patients with a resistance against type A toxin there is a new hypercleaned type A toxin or type B available. Research on type F toxin is also underway. In this article, the history of botulinum toxin, its therapeutic activity and possibilities for its use are described.

Botulinum Neurotoxins and Injectable Fillers: Minimally Invasive Management of the Aging Upper Face

Attitudes on the use of injectable agents for rejuvenation of the face have changed dramatically over the last decade. This is particularly true for the upper third of the face, where the impact of the use of Botox had its first application. In the author's opinion, no technique, device, or pharmaceutical has had a greater impact on the aesthetic surgery than the now widely used botulinum toxin as an injectable agent.

The structure and mode of action of different botulinum toxins

The seven serotypes (A-G) of botulinum neurotoxin (BoNT) are proteins produced by Clostridium botulinum and have multifunctional abilities: (i) they target cholinergic nerve endings via binding to ecto-acceptors (ii) they undergo endocytosis/translocation and (iii) their light chains act intraneuronally to block acetylcholine release. The fundamental process of quantal transmitter release occurs by Ca2+-regulated exocytosis involving sensitive factor attachment protein-25 (SNAP-25), syntaxin and synaptobrevin. Proteolytic cleavage by BoNT-A of nine amino acids from the C-terminal of SNAP-25 disables its function, causing prolonged muscle weakness. This unique combination of activities underlies the effectiveness of BoNT-A haemagglutinin complex in treating human conditions resulting from hyperactivity at peripheral cholinergic nerve endings. In vivo imaging and immunomicroscopy of murine muscles injected with type A toxin revealed that the extended duration of action results from the longevity of its protease, persistence of the cleaved SNAP-25 and a protracted time course for the remodelling of treated nerve-muscle synapses. In addition, an application in pain management has been indicated by the ability of BoNT to inhibit neuropeptide release from nociceptors, thereby blocking central and peripheral pain sensitization processes. The widespread cellular distribution of SNAP-25 and the diversity of the toxin's neuronal acceptors are being exploited for other therapeutic applications.

An Initial Assessment of the Systemic Pharmacokinetics of Botulinum Toxin

Botulinum toxin is an extraordinarily potent molecule that has an unusually long duration of action. Despite this, there is little information available on natural mechanisms for metabolism or elimination and virtually no information on pharmacologically induced mechanisms for metabolism and elimination. Therefore, a number of experiments were performed on laboratory animals that addressed two major issues: 1) the effect of blood on the structure, function, and biologic half-life of the toxin, and 2) the effect of neutralizing antibodies on half-life and elimination of circulating toxin. In the first series of studies, the metabolic transformation of toxin was assessed by incubating it in blood for varying lengths of time. At each time point, aliquots were examined to determine the amount of toxin, the structure of toxin, the catalytic activity of toxin, and the neuromuscular blocking activity of toxin. This work demonstrated that blood did not alter any characteristic of the toxin molecule. Experiments were also done in which toxin was administered to mice and rats at doses that produced clinical poisoning. The results demonstrated that the elimination half-life for native (nonmetabolized) toxin in blood and serum was 230 to 260 min. During the second series of studies, the rate of elimination of circulating toxin was studied in the presence of antibodies directed against the carboxyl-terminal half of the toxin molecule. This work demonstrated that neutralizing antibodies 1) enhanced clearance of toxin from the circulation and 2) enhanced tissue accumulation of toxin, particularly in liver and spleen.