Botulinum neurotoxin: evolution from poison, to research tool--onto medicinal therapeutic and future pharmaceutical panacea

Therapeutic Applications of Botulinum Neurotoxins in Veterinary Medicine

Botulinum neurotoxins (BoNTs) are emerging as multipurpose therapeutic compounds for the treatment of several different syndromes involving peripheral and central nervous systems, and muscular and musculoskeletal disorders both in human and veterinary medicine. Therefore, the study of BoNTs is rapidly developing and identifying newly produced BoNT variants. Efforts should be made to clarify the biological and pharmacological characteristics of these novel BoNTs as well as the natural ones. The high potential of BoNTs as a therapeutic compound for medical syndromes lies in its ability to reach a specific cell type while bypassing other cells, thus having mild or no side effects. In this paper the recent developments in BoNTs are reviewed with the aim of analyzing the current knowledge on BoNTs' biological mechanisms of action, immunogenicity, formulations, and therapeutic applications in the veterinary field, highlighting advantages and drawbacks and identifying the gaps to be filled in order to address research priorities.

Botulinum toxin type A in the treatment of lower limb spasticity in children with cerebral palsy

BACKGROUND

Cerebral palsy (CP) is the most common cause of physical disabilities in children in high-income countries. Spasticity is the most common motor disturbance in CP. Botulinum toxin type A (BoNT-A) is considered the first-line treatment for focal spasticity in people with CP.

OBJECTIVES

To evaluate the effectiveness and safety of BoNT-A compared to other treatments used in the management of lower limb spasticity in children with CP.

SEARCH METHODS

We searched CENTRAL, PubMed, four other databases, and two trial registers in October 2018. We also searched the reference lists of relevant studies and reviews and contacted experts in the field. We did not apply any date or language restrictions.

SELECTION CRITERIA

Randomised controlled trials of children with CP, aged between birth and 19 years, treated with BoNT-A injections in the lower limb muscles compared to other interventions. The primary outcomes were gait analysis and function. The secondary outcomes were joint range of motion, quality of life, satisfaction, spasticity, and adverse events.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected studies, extracted data, assessed risk of bias, and rated the quality of the evidence using GRADE. A third review author arbitrated in case of disagreements. We conducted meta-analyses of available data whenever possible, analysing dichotomous data with risk ratios (RR), and continuous data with mean differences (MD) or standardised mean differences (SMD), with 95% confidence intervals (CI). We considered a 5% significance level for all analyses.Whenever possible, we analysed outcomes at the time points at which they were assessed: short term (2 to 8 weeks); medium term (12 to 16 weeks); and long term (> 24 weeks).

MAIN RESULTS

We included 31 randomised controlled trials assessing 1508 participants. Most studies included ambulatory patients with more than one motor type of CP, and with a mean age of between three and seven years. There was a slight predominance of males.Studies compared BoNT-A in the lower limb muscles to usual care or physiotherapy (14 studies), placebo or sham (12 studies), serial casting (4 studies), or orthoses (1 study).We rated studies as at high or unclear risk of bias mainly due to random sequence generation, allocation concealment, blinding of participants and personnel, and blinding of outcome assessment.BoNT-A versus usual care or physiotherapyBoNT-A might improve overall gait scores at medium-term follow-up (MD 2.80, 95% CI 1.55 to 4.05; 1 study, 40 children; very low-quality evidence) and is moderately effective at improving function at short-term (SMD 0.59, 95% CI 0.23 to 0.95; 2 studies, 123 children) and medium-term (SMD 1.04, 95% CI 0.16 to 1.91; 4 studies, 191 children) follow-up (all very low-quality evidence).BoNT-A improves ankle range of motion, satisfaction, and ankle plantarflexors spasticity at one or more time points (very low-quality evidence).The proportion of adverse events in the BoNT-A group was 0.37 (95% CI 0.08 to 0.66; I² = 95%; very low-quality evidence). No adverse events were reported in the control group.BoNT-A versus placebo or shamBoNT-A improves overall gait scores at short-term (RR 1.66, 95% CI 1.16 to 2.37, P = 0.006; 4 studies, 261 assessments) and medium-term (RR 1.90, 95% CI 1.32 to 2.74, P < 0.001; 3 studies, 248 assessments) follow-up, and may improve peak ankle dorsiflexion in stance (MD 15.90 degrees, 95% CI 4.87 to 26.93, P = 0.005; 1 study, 19 children) and in swing (MD 10.20 degrees, 95% CI 4.01 to 16.39, P = 0.001; 1 study, 19 children) at short-term follow-up (all moderate-quality evidence).BoNT-A is not more effective than placebo or sham at improving function at short-term (SMD 0.24, 95% CI -0.35 to 0.83, P = 0.42; 4 studies, 305 children) or long-term (SMD -0.07, 95% CI -0.48 to 0.35, P = 0.76; 2 studies, 91 children) follow-up, but has a small positive effect at medium-term follow-up (SMD 0.28, 95% CI 0.06 to 0.49, P = 0.01; 5 studies, 327 children) (all moderate-quality evidence).BoNT-A improves passive ankle range of motion, satisfaction, and ankle plantarflexors spasticity at one or more time points (moderate-quality evidence).There was no difference between groups in the rate of adverse events at short-term follow-up (RR 1.29, 95% CI 0.87 to 1.93, P = 0.21; 12 studies, 918 children; moderate-quality evidence).BoNT-A versus serial castingThere was no difference between groups for overall gait scores at short-term (MD 0.00, 95% CI -1.66 to 1.66); medium-term (MD 0.65, 95% CI -1.21 to 2.51); or long-term (MD 0.46, 95% CI -1.33 to 2.25) follow-up in one study with 18 children (moderate-quality evidence).BoNT-A improved instrumented gait analysis only in terms of ankle dorsiflexion at initial contact (MD 6.59 degrees, 95% CI 1.39 to 11.78, P = 0.01; 2 studies, 47 children). There was no difference between groups for peak ankle dorsiflexion in stance and swing, and gait speed at any time point (moderate- and low-quality evidence).BoNT-A is not more effective than serial casting at improving function, ankle range of motion, and spasticity at any time point (moderate- and low-quality evidence).BoNT-A is not associated with a higher risk of adverse events than serial casting (RR 0.59, 95% CI 0.03 to 11.03; 3 studies, 64 children; low-quality evidence).BoNT-A versus orthosesThere was no difference between groups for function at medium-term follow-up (MD 11.14, 95% CI -0.05 to 22.33; 1 study, 43 children), but BoNT-A is more effective than orthoses at improving hip range of motion and hip adductors spasticity (all very low-quality evidence).

AUTHORS' CONCLUSIONS

The quality of the evidence was low or very low for most of the outcomes analysed. We found limited evidence that BoNT-A is more effective than placebo or a non-placebo control at improving gait, joint range of motion, satisfaction, and lower limb spasticity in children with CP, whereas the results for function were contradictory. The rate of adverse events with BoNT-A is similar to placebo. BoNT-A is not more effective than ankle serial casting to treat ankle contractures for any of the assessed outcomes, but is more effective than orthotics at improving range of motion and spasticity.

Botulinum neurotoxin: Progress in negating its neurotoxicity; and in extending its therapeutic utility via molecular engineering. MiniReview

While the poisonous effects of botulinum neurotoxin (BoNT) have been recognized since antiquity, the overall actions and mechanisms of effects of BoNT have been elucidated primarily over the past several decades. The general utility of BoNT is described in the paper, but the focus is mainly on the approaches towards negating the toxic effects of BoNT, and on the projection of an engineered BoNT molecule serving as a Trojan Horse to deliver a therapeutic load for treatment of a host of medical disorders. The BoNT molecule is configured with a binding domain, a zinc-dependent protease with specificity primarily for vesicular proteins, and a translocation domain for delivery of the metalloprotease into the cytoplasm. The anti-toxin approaches for BoNT include the use of vaccines, antibodies, block of BoNT binding or translocation, inhibition of metalloprotease activity, impeded translocation of the protease/catalytic domain, and inhibition of the downstream Src signaling pathway. Projections of BoNT as a therapeutic include its targeting to non-cholinergic nerves, also targeting to non-neuronal cells for treatment of hypersecretory disorders (e.g., cystic fibrosis), and treatment of hormonal disorders (e.g., acromegaly). Still in the exploratory phase, there is the expectation of major advances in BoNT neuroprotective strategies and burgeoning utility of engineered BoNTs as therapeutics.

OnabotulinumtoxinA for chronic migraine: a critical appraisal

Chronic migraine (CM) is a severe disabling condition with a few available evidence-based management options. OnabotulinumtoxinA (onaBoNTA) is approved for use in a number of disorders. Its benefits and potential use in migraine were observed incidentally while treating patients cosmetically for wrinkles. The mechanism of action of onaBoNTA in CM is not fully understood, but there is evidence that this involves axonal transport via sensory fibers. The Phase III REsearch Evaluating Migraine Prophylaxis Therapy trials have established the efficacy as well as the long-term safety and tolerability of onaBoNTA in CM. This review will discuss the evidence behind its use in this setting.

SRC family kinase inhibitors antagonize the toxicity of multiple serotypes of botulinum neurotoxin in human embryonic stem cell-derived motor neurons

Botulinum neurotoxins (BoNTs), the causative agents of botulism, are potent inhibitors of neurotransmitter release from motor neurons. There are currently no drugs to treat BoNT intoxication after the onset of the disease symptoms. In this study, we explored how modulation of key host pathways affects the process of BoNT intoxication in human motor neurons, focusing on Src family kinase (SFK) signaling. Motor neurons derived from human embryonic stem (hES) cells were treated with a panel of SFK inhibitors and intoxicated with BoNT serotypes A, B, or E (which are responsible for >95 % of human botulism cases). Subsequently, it was found that bosutinib, dasatinib, KX2-391, PP1, PP2, Src inhibitor-1, and SU6656 significantly antagonized all three of the serotypes. Furthermore, the data indicated that the treatment of hES-derived motor neurons with multiple SFK inhibitors increased the antagonistic effect synergistically. Mechanistically, the small molecules appear to inhibit BoNTs by targeting host pathways necessary for intoxication and not by directly inhibiting the toxins' proteolytic activity. Importantly, the identified inhibitors are all well-studied with some in clinical trials while others are FDA-approved drugs. Overall, this study emphasizes the importance of targeting host neuronal pathways, rather than the toxin's enzymatic components, to antagonize multiple BoNT serotypes in motor neurons.

Safety of botulinum toxin A in aesthetic treatments: a systematic review of clinical studies

BACKGROUND

The use of botulinum toxin A (BoNT-A) for aesthetic treatments is growing steadily, and new safety data have been reported in recently published studies.

OBJECTIVE

To investigate the safety data on the use of the three BoNT-A formulations approved for facial aesthetics from recent studies and to confirm their safety profiles.

METHODS

The literature search was conducted using three online databases restricted to the timeframe from January 2000 to June 2012. Only clinical trials, randomized or open label, with safety as the primary or secondary endpoint, were included.

RESULTS

Thirty-five papers were selected, with a total of subjects 8,787 studied. OnabotulinumtoxinA was used in 60.0% of the studies, abobotulinumtoxinA in 37.1%, and incobotulinumtoxinA in 2.8%. The glabella was the most investigated area (51.4%), followed by the upper face (25.7%), crow's feet (11.4%), and lower face (11.4%). Treatment-related adverse events were blepharoptosis (2.5%), brow ptosis (3.1%), and eye sensory disorders (3%) in the upper face and lip asymmetries and imbalances in the lower face (6.9%). All of these events resolved spontaneously.

CONCLUSION

The short-term safety profile of BoNT-A in cosmetic nonsurgical procedures was confirmed for all the three commercial formulations.

Neurotransmitter vesicle release from human model neurons (NT2) is sensitive to botulinum toxin A

Botulinum neurotoxins (BoNTs) internalize into nerve terminals and block the release of neurotransmitters into the synapse. BoNTs are widely used as a therapeutic agent for treatment of movement disorders and recently gained more attention as a biological weapon. Consequently, there is strong interest to develop a cell-based assay platform to screen the toxicity and bioactivity of the BoNTs. In this study, we present an in vitro screening assay for BoNT/A based on differentiated human embryonal carcinoma stem (NT2) cells. The human NT2 cells fully differentiated into mature neurons that display immunoreactivity to cytoskeletal markers (βIII-tubulin and MAP2) and presynaptic proteins (synapsin and synaptotagmin I). We showed that the human NT2 cells undergo a process of exo-endocytotic synaptic vesicle recycling upon depolarization with high K(+) buffer. By employing an antibody directed against light chain of BoNT/A, we detected internalized toxin as a punctate staining along the neurites of the NT2 neurons. Using well-established methods of synaptic vesicle exocytosis assay (luminal synaptotagmin I and FM1-43 imaging) we show that pre-incubation with BoNT/A resulted in a blockade of vesicle release from human NT2 neurons in a dose-dependent manner. Moreover, this blocking effect of BoNT/A was abolished by pre-adsorbing the toxin with neutralizing antibody. In a proof of principle, we demonstrate that our cell culture assay for vesicle release is sensitive to BoNT/A and the activity of BoNT/A can be blocked by specific neutralizing antibodies. Overall our data suggest that human NT2 neurons are suitable for large scale screening of botulinum bioactivity.

Botulinum neurotoxin: where are we with detection technologies?

Because of its high toxicity, botulinum neurotoxin (BoNT) poses a significant risk to humans and it represents a possible biological warfare agent. Nevertheless, BoNT serotypes A and B are considered an effective treatment for a variety of neurological disorders. The growing applicability of BoNT as a drug, and its potential use as a biological threat agent, highlight the urgent need to develop sensitive detection assays and therapeutic counter measures. In the last decade, significant progress has been made in BoNT detection technologies but none have fully replaced the mouse lethality assay, the current "gold standard". Recently, new advances in robotics and the availability of new reagents have allowed development of methods for rapid toxin analysis. These technologies while promising need further refinement.

Rapidly optimizing an aptamer based BoNT sensor by feedback system control (FSC) scheme

The sensitivity and detection time of an aptamer based biosensor for detecting botulinum neurotoxin (BoNT) depend upon the formation of proper tertiary architecture of aptamer, which closely correlates with the combinatorial effects of multiple types of ions and their concentrations presented in the buffer. Finding the optimal conditions for four different ions at 12 different concentrations, 20,736 possible combinations, by brute force is an extremely laborious and time-consuming task. Here, we introduce a feedback system control (FSC) scheme that can rapidly identify the best combination of components to form the optimal aptamer structure binding to a target molecule. In this study, rapid identification of optimized ionic combinations for electrochemical aptasensor of BoNT type A (BoNT/A) detection has been achieved. Only about 10 iterations with about 50 tests in each iteration are needed to identify the optimal ionic concentration out of the 20,736 possibilities. The most exciting finding was that a very short detection time and high sensitivity could be achieved with the optimized combinational ion buffer. Only a 5-min detection time, compared with hours or even days, was needed for aptamer-based BoNT/A detection with a limit of detection of 40 pg/ml. The methodologies described here can be applied to other multi-parameter chemical systems, which should significantly improve the rate of parameter optimization.

Recent insights into Pasteurella multocida toxin and other G-protein-modulating bacterial toxins

Over the past few decades, our understanding of the bacterial protein toxins that modulate G proteins has advanced tremendously through extensive biochemical and structural analyses. This article provides an updated survey of the various toxins that target G proteins, ending with a focus on recent mechanistic insights in our understanding of the deamidating toxin family. The dermonecrotic toxin from Pasteurella multocida (PMT) was recently added to the list of toxins that disrupt G-protein signal transduction through selective deamidation of their targets. The C3 deamidase domain of PMT has no sequence similarity to the deamidase domains of the dermonecrotic toxins from Escherichia coli (cytotoxic necrotizing factor [CNF]1-3), Yersinia (CNFY) and Bordetella (dermonecrotic toxin). The structure of PMT-C3 belongs to a family of transglutaminase-like proteins, with active site Cys-His-Asp catalytic triads distinct from E. coli CNF1.

Toxin-based therapeutic approaches

Protein toxins confer a defense against predation/grazing or a superior pathogenic competence upon the producing organism. Such toxins have been perfected through evolution in poisonous animals/plants and pathogenic bacteria. Over the past five decades, a lot of effort has been invested in studying their mechanism of action, the way they contribute to pathogenicity and in the development of antidotes that neutralize their action. In parallel, many research groups turned to explore the pharmaceutical potential of such toxins when they are used to efficiently impair essential cellular processes and/or damage the integrity of their target cells. The following review summarizes major advances in the field of toxin based therapeutics and offers a comprehensive description of the mode of action of each applied toxin.

Sensing the deadliest toxin: technologies for botulinum neurotoxin detection

Sensitive and rapid detection of botulinum neurotoxins (BoNTs), the most poisonous substances known to date, is essential for studies of medical applications of BoNTs and detection of poisoned food, as well as for response to potential bioterrorist threats. Currently, the most common method of BoNT detection is the mouse bioassay. While this assay is sensitive, it is slow, quite expensive, has limited throughput and requires sacrificing animals. Herein, we discuss and compare recently developed alternative in vitro detection methods and assess their ability to supplement or replace the mouse bioassay in the analysis of complex matrix samples.

Sensing the deadliest toxin: technologies for botulinum neurotoxin detection

Sensitive and rapid detection of botulinum neurotoxins (BoNTs), the most poisonous substances known to date, is essential for studies of medical applications of BoNTs and detection of poisoned food, as well as for response to potential bioterrorist threats. Currently, the most common method of BoNT detection is the mouse bioassay. While this assay is sensitive, it is slow, quite expensive, has limited throughput and requires sacrificing animals. Herein, we discuss and compare recently developed alternative in vitro detection methods and assess their ability to supplement or replace the mouse bioassay in the analysis of complex matrix samples.

Plumbagin, a novel Nrf2/ARE activator, protects against cerebral ischemia

Many phytochemicals function as noxious agents that protect plants against insects and other damaging organisms. However, at subtoxic doses, the same phytochemicals may activate adaptive cellular stress response pathways that can protect cells against a variety of adverse conditions. We screened a panel of botanical pesticides using cultured human and rodent neuronal cell models, and identified plumbagin as a novel potent activator of the nuclear factor E2-related factor 2 (Nrf2)/antioxidant response element (ARE) pathway. In vitro, plumbagin increases nuclear localization and transcriptional activity of Nrf2, and induces the expression of the Nrf2/ARE-dependent genes, such as heme oxygenase 1 in human neuroblastoma cells. Plumbagin specifically activates the Nrf2/ARE pathway in primary mixed cultures from ARE-human placental alkaline phosphatase reporter mice. Exposure of neuroblastoma cells and primary cortical neurons to plumbagin provides protection against subsequent oxidative and metabolic insults. The neuroprotective effects of plumbagin are abolished by RNA interference-mediated knockdown of Nrf2 expression. In vivo, administration of plumbagin significantly reduces the amount of brain damage and ameliorates-associated neurological deficits in a mouse model of focal ischemic stroke. Our findings establish precedence for the identification and characterization of neuroprotective phytochemicals based upon their ability to activate adaptive cellular stress response pathways.

Facial aesthetics: is botulinum toxin treatment effective and safe? A systematic review of randomised controlled trials

BACKGROUND

The use of botulinum toxin type A (BTA) in facial aesthetics for the treatment of wrinkles has recently become more popular as an alternative to surgical techniques. However, its true efficacy and potential adverse effects are still unclear.

OBJECTIVES

The primary objective of this study was to review the efficacy of BTA in facial aesthetics. A secondary objective was to determine whether there are any adverse effects associated with the procedure of using BTA in facial aesthetics.

SEARCH STRATEGY

We conducted literature searches on Medline (1977 to January 2009), Cochrane Controlled Trials Register (CENTRAL), EMBASE (1977 to January 2009) and CINAHL (1977 to January 2009). The search strategy also included reference lists of located articles and hand searching for randomised controlled trials (RCTs). We contacted authors of studies for further information where required.

SELECTION CRITERIA

Randomised studies comparing BTA with placebo in facial aesthetics in a double-blind and crossover or parallel group design.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed trial quality and extracted data. The area of face injected, assessment methods, outcome measures, duration of action of BTA and associated adverse effects were reviewed.

RESULTS AND DISCUSSION

A total of eleven RCTs involving 1,603 subjects were found, of which 1,203 were enrolled for treatment with BTA. The 11 trials were not directly comparable to each other due to differences in the areas of the face injected with BTA, length of study period, concentration of BTA used and outcome measures. The studies showed similar trends. The use of BTA showed improvements in facial wrinkles over placebo, with a peak effect reported at around one month and the effects lasting between 4-6 months. No studies reported any severe adverse effects. The incidence of blepharoptosis in glabellar lines treated with BTA was reported to be between 0-5.4%, and may be related to the technique of injection into the muscles. The incidence of other side-effects such as headache, pain at injection site and mild bruising was similar in both the BTA and placebo groups.

AUTHORS' CONCLUSIONS

The use of BTA in facial aesthetics is more effective than placebo. The incidence of adverse effects associated with BTA is similar to placebo, with the exception of blepharoptosis which is reported to be 0-5.4% after treatment of glabellar lines with BTA.

Evolution of neurotoxins: from research modalities to clinical realities

In the 1950s, the discovery of anti-nerve growth factor, an immunotoxin stunting sympathetic neural development, signaled the advent of neurotoxins as research modalities. Other selective neurotoxins were discovered in rapid succession. In the 1960s, 6-hydroxydopamine and 6-hydroxydopa were shown to destroy noradrenergic and dopaminergic nerves. Excitotoxins (glutamate, aspartate, and analogs) were discovered in the 1970s. DSP-4 [N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine] proved to be selective for noradrenergic destruction, while 5,6- and 5,7-dihydroxytryptamines were relatively selective for serotonin neurons. Additional neurotoxins were discovered, but it was MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) that predominated neurotoxicity research in the 1980s. Eventually, Clostridium botulinum neurotoxin (BoNT), discovered as a "poisonous" principle in the late 1800s, resurfaced in purified and standardized forms as a clinically useful drug. Neurotoxins represent chemical tools, useful not only for discerning neuronal mechanisms and animal modeling of neurological disorders, but also for their use in medicine and potential as treatments for medical disorders. This unit reviews the early discovery of neurotoxins, describes categories of neurotoxins, and finally characterizes their usefulness--first as research tools, and eventually as clinical therapeutic agents.

Aptamer-based electrochemical biosensor for Botulinum neurotoxin

We have developed an aptamer-based electrochemical sensor for detection of Botulinum neurotoxin, where steric hindrance is applied to achieve specific signal amplification via conformational change of the aptamer. The incubation time and potassium concentration of the reaction buffer were found to be key parameters affecting the sensitivity of detection of the recognition of Botulinum neurotoxin by the aptamer. Under optimized experimental conditions, a high signal-to-noise ratio was obtained within 24 h with a limit of detection (LOD) of 40 pg/ml by two standard deviation cutoffs above the noise level.