Botulinum toxin: Clinical use

Structural basis for botulinum neurotoxin E recognition of synaptic vesicle protein 2

Botulinum neurotoxin E (BoNT/E) is one of the major causes of human botulism and paradoxically also a promising therapeutic agent. Here we determined the co-crystal structures of the receptor-binding domain of BoNT/E (HCE) in complex with its neuronal receptor synaptic vesicle glycoprotein 2A (SV2A) and a nanobody that serves as a ganglioside surrogate. These structures reveal that the protein-protein interactions between HCE and SV2 provide the crucial location and specificity information for HCE to recognize SV2A and SV2B, but not the closely related SV2C. At the same time, HCE exploits a separated sialic acid-binding pocket to mediate recognition of an N-glycan of SV2. Structure-based mutagenesis and functional studies demonstrate that both the protein-protein and protein-glycan associations are essential for SV2A-mediated cell entry of BoNT/E and for its potent neurotoxicity. Our studies establish the structural basis to understand the receptor-specificity of BoNT/E and to engineer BoNT/E variants for new clinical applications.

Botulinum Neurotoxin Therapy in the Clinical Management of Laryngeal Dystonia

Laryngeal dystonia (LD), or spasmodic dysphonia (SD), is a chronic, task-specific, focal movement disorder affecting the larynx. It interferes primarily with the essential functions of phonation and speech. LD affects patients' ability to communicate effectively and significantly diminishes their quality of life. Botulinum neurotoxin was first used as a therapeutic agent in the treatment of LD four decades ago and remains the standard of care for the treatment of LD. This article provides an overview of the clinical application of botulinum neurotoxin in the management of LD, focusing on the classification for this disorder, its pathophysiology, clinical assessment and diagnosis, the role of laryngeal electromyography and a summary of therapeutic injection techniques, including a comprehensive description of various procedural approaches, recommendations for injection sites and dosage considerations.

Pilot Feasibility Study of a Multi-View Vision Based Scoring Method for Cervical Dystonia

Abnormal movement of the head and neck is a typical symptom of Cervical Dystonia (CD). Accurate scoring on the severity scale is of great significance for treatment planning. The traditional scoring method is to use a protractor or contact sensors to calculate the angle of the movement, but this method is time-consuming, and it will interfere with the movement of the patient. In the recent outbreak of the coronavirus disease, the need for remote diagnosis and treatment of CD has become extremely urgent for clinical practice. To solve these problems, we propose a multi-view vision based CD severity scale scoring method, which detects the keypoint positions of the patient from the frontal and lateral images, and finally scores the severity scale by calculating head and neck motion angles. We compared the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS) subscale scores calculated by our vision based method with the scores calculated by a neurologist trained in dyskinesia. An analysis of the correlation coefficient was then conducted. Intra-class correlation (ICC)(3,1) was used to measure absolute accuracy. Our multi-view vision based CD severity scale scoring method demonstrated sufficient validity and reliability. This low-cost and contactless method provides a new potential tool for remote diagnosis and treatment of CD.

Current Clinical Trials in Traumatic Brain Injury

Traumatic brain injury (TBI) is one of the leading causes of morbidity, disability and mortality across all age groups globally. Currently, only palliative treatments exist, but these are suboptimal and do little to combat the progressive damage to the brain that occurs after a TBI. However, multiple experimental treatments are currently available that target the primary and secondary biochemical and cellular changes that occur after a TBI. Some of these drugs have progressed to clinical trials and are currently being evaluated for their therapeutic benefits in TBI patients. The aim of this study was to identify which drugs are currently being evaluated in clinical trials for TBI. A search of ClinicalTrials.gov was performed on 3 December 2021 and all clinical trials that mentioned “TBI” OR “traumatic brain injury” AND “drug” were searched, revealing 362 registered trials. Of the trials, 46 were excluded due to the drug not being mentioned, leaving 138 that were completed and 116 that were withdrawn. Although the studies included 267,298 TBI patients, the average number of patients per study was 865 with a range of 5–200,000. Of the completed studies, 125 different drugs were tested in TBI patients but only 7 drugs were used in more than three studies, including amantadine, botulinum toxin A and tranexamic acid (TXA). However, previous clinical studies using these seven drugs showed variable results. The current study concludes that clinical trials in TBI have to be carefully conducted so as to reduce variability across studies, since the severity of TBI and timing of therapeutic interventions were key aspects of trial success.

Radiation of parotid or submandibular glands is effective for drooling in patients with parkinsonism; a randomised double-blind placebo-controlled trial

Background

Drooling is a common symptom in patients with parkinsonism, causing physical and emotional distress. It is unknown which major salivary glands are the best candidates for irradiation to reduce drooling with minimal adverse events. Therefore, this study assessed the efficacy and safety of submandibular and parotid salivary gland irradiation to reduce drooling.

Methods

A prospective, randomised, double-blind, placebo-controlled trial was conducted at the University Medical Center Groningen, the Netherlands. After informed consent, 31 patients with parkinsonism and severe drooling according to the Unified Parkinson Disease Rating Scale (UPDRS) were included in this study. Exclusion criteria consisted of the use of anticholinergic drugs, the existence of salivary gland diseases, and/or an history of (pre)malignancies of the salivary glands. Patients were randomized for parotid-, submandibular- or sham irradiation (2x6 Gy with one week interval). Patients were evaluated at 1, 3, 6 and 12 months after radiation. Primary outcome measure was drooling severity according to the UPDRS. Secondary outcomes measures consisted of stimulated glandular salivary secretion rates and adverse effects.

Findings

Overall 31 parkinsonian patients were included. Initially 11 patients were radiated on the parotid glands, 10 patients on the submandibular glands and 10 patients were sham-radiated. After 6 months, the sham-radiated patients were actively treated after a second randomisation. One patient in the parotid radiation group discontinued his participation after three months due to physical deterioration. Radiation of parotid or submandibular glands significantly improved the existing drooling, as compared to placebo radiation. Parotid- and submandibular radiation was equally effective, but more patients in the submandibular radiated group reported sticky saliva vs. patients treated by parotid radiation (33∙33% vs. 13∙33%).

Interpretation

Major salivary gland radiation significantly improves drooling in parkinsonian patients with few adverse effects. However, parotid gland radiation is accompanied by fewer side effects and therefore is the preferred mode of radiation in this patient population.

Patient perspectives on the therapeutic profile of botulinum neurotoxin type A in cervical dystonia

BACKGROUND

Botulinum neurotoxin type A (BoNT-A) is an effective pharmacological treatment for the management of cervical dystonia (CD) that requires repeated administration at variable intervals. We explored patient perceptions of the impact of CD and the waning of BoNT-A therapeutic effects.

METHODS

An internet-based survey was conducted through Carenity, a global online patient community, from May to September 2019. Eligible respondents were adults with CD who had ≥ 2 previous BoNT-A injections.

RESULTS

209 respondents (81% females; mean age of 49.7 years) met the screening criteria. The mean BoNT-A injection frequency was 3.9 injections/year. The mean reported onset of BoNT-A therapeutic effect was 11.7 days and the time to peak effect was 4.5 weeks. Symptom re-emergence between injections was common (88%); the time from injection to symptom re-emergence was 73.6 days (~ 10.5 weeks). Treatment was not reported to completely abolish symptoms, even at peak effect. However, symptom severity was rated (0 = no symptoms; 10 = very strong symptoms) as lowest at the peak of treatment effects (mean scores ~ 3/10), increasing as the effects of treatment start waning (~ 5.5/10) and was strongest one day before the next session (~ 7-8/10). The impact of CD on quality of life followed the same 'rollercoaster' pattern.

CONCLUSIONS

This survey highlights the burden of CD symptoms, even in patients undergoing regular treatment. Symptom re-emergence is common and has significant impact on daily activities and quality of life. Greater awareness of the therapeutic profile of BoNT-A treatment should lead to better informed therapeutic discussions and planning.

A novel compound heterozygous mutation in the arginase-1 gene identified in a Chinese patient with argininemia: A case report

INTRODUCTION

Arginineemia, also known as arginase deficiency, is a rare autosomal recessive metabolic disease. The diagnosis sometimes may be delayed due to atypical clinical manifestations. Confirmation of arginineemia depends on genetic testing.

PATIENT CONCERNS

We reported a Chinese male child presenting with hyperargininemia and progressive spastic diplegia, who has a novel compound heterozygous mutation in the arginase-1 (ARG1) gene (c.263-266delAGAA, p.K88Rfs45;c.674T>C,p.L216P), respectively, coming from his mother and father.

DIAGNOSIS

The patient was diagnosed with argininemia with a novel compound homozygous mutation of the ARG1 gene at the age of 12 years.

INTERVENTIONS

The patient had a low-protein diet (0.8 g/kg/day). Baclofen, eperisone hydrochloride, botulinum toxin, and rehabilitation training were used to improve his spastic diplegia symptoms for 3 months.

OUTCOMES

The patient's blood arginine was still high after 3 months' low-protein diet. His spastic diplegia symptoms had not aggravated after 3 months' treatment.

CONCLUSIONS

Argininemia should be considered in a patient with slowly progressive neurologic manifestations, especially spastic diplegia. This case also suggests that tandem mass spectrometry should be used as an effective tool in the validity of neonatal screening for early diagnosis.

Patient Perspectives on the Therapeutic Profile of Botulinum Neurotoxin Type A in Spasticity

Background: Botulinum toxin-A (BoNT-A) injections are first-line treatment for adult spasticity. Prior patient surveys have reported that BoNT-A treatment improves quality of life but that symptoms usually recur before the next injection. We aimed to explore, in-depth, patient perceptions of the impact of spasticity and the waning of BoNT-A therapeutic effects. Methods: An internet-based survey was conducted through Carenity, an online patient community, from May to September 2019 in France, Germany, Italy, UK and USA. Eligible respondents were adult patients with spasticity due to stroke, traumatic brain injury (TBI) or spinal cord injury (SCI) who had ≥2 previous BoNT-A injections. Results: Two hundred and ten respondents (mean 47.2 years) met screening criteria and had their responses analyzed. Overall, 43% of respondents had spasticity due to stroke, 30% due to TBI and 27% due to SCI. The mean [95% CI] injection frequency for spasticity management was 3.6 [3.4-3.7] injections/year. Respondents described the time profile of their response to BoNT-A. The mean reported onset of therapeutic effect was 12.9 [12.1-13.7] days and the mean time to peak effect was 5.0 [4.7-5.4] weeks. Symptom re-emergence between injections was common (83%); the time from injection to symptom re-emergence was 89.4 [86.3-92.4] days. Muscle spasms usually re-emerge first (64%), followed by muscle stiffness or rigidity (40%), and limb pain (20%). Over half (52%) of respondents said they had lost their self-confidence, 46% experienced depression and 41% experienced a lack of sleep due to their spasticity symptoms in the past 12 months. Following a report of symptom re-emergence, the most common management approaches were to add adjunctive treatments (36%), increase the BoNT-A dose (28%), and wait for the next injection (26%). Seventy two percentage of respondents said they would like a longer lasting BoNT-A treatment. Conclusions: Patients with spasticity can expect a characteristic profile of BoNT-A effects, namely time lag to onset and peak effect followed by a gradual decline in the symptomatic benefits. Symptom re-emergence is common and has significant impact on quality of life. Greater patient/clinician awareness of this therapeutic profile should lead to better level of overall satisfaction with treatment, informed therapeutic discussions and treatment schedule planning.

Injection into the Longus Colli Muscle via the Thyroid Gland

Background

Anterior forms of cervical dystonia are considered to be the most difficult to treat because of the deep cervical muscles that can be involved.

Case Report

We report the case of a woman with cervical dystonia who presented with anterior sagittal shift, which required injections through the longus colli muscle to obtain a satisfactory outcome. The approach via the thyroid gland was chosen.

Discussion

The longus colli muscle can be injected under electromyography (EMG), computed tomography (CT), ultrasonography (US), or endoscopy guidance. We recommend using both ultrasonography and electromyography guidance as excellent complementary techniques for injection at the C5-C6 level.

Efficacy and Safety of Long-Term Therapy with Type A Botulinum Toxin in Patients with Blepharospasm

Blepharospasm (BPS) is one of the most frequent types of facial dystonia and, at the same time, one of the most disabling, being able to trigger functional blindness if not treated. Our aim with this work was to evaluate the efficacy and safety of long-term onabotulinum A toxin (BAT) treatment in a cohort of patients with BPS. The retrospective study was conducted on consecutive patients with BPS treated with subcutaneous BAT. The selection of muscles and dose was made based on each patient's needs. The clinical and demographic characteristics, number of sessions, dose, duration and effectiveness of treatment, and adverse events were analysed. 130 patients were included in the study. The median (95% confidence interval) length of follow-up was 14 (13-15.6) years with an average of 20.5 sessions (range from 10 to 57). Regarding the efficacy of the treatment, 114 (87.7%) experienced satisfactory results with functional and aesthetics recovery. Patient evaluation of global response suggested a clear improvement without adverse events in 72 (55.4%) patients. Adverse events developed at least once during the treatment in 39% of patients, with transient ptosis and haematoma the most common reported both by physician and patient. The results of our study suggest that botulin toxin A is a safe and effective long-term treatment for blepharospasm with mild, transient and well-tolerated side effects when they appear.

Botulinum toxin in movement disorders

Botulinum toxin has gained immense popularity since its introduction for therapeutic use. It is used in a variety of movement disorders like hemi-facial spasm, focal dystonias like blepharospasm, cervical dystonia, oromandibular dystonia, limb dystonias. It is also being used in patients with tremors, tics and for a variety of indications in Parkinson's disease as well. There are eight subtypes of toxins available, but type A and B are the ones used in movement disorder clinics. The toxin mainly acts by inhibiting the release of acetylcholine at the neuromuscular junction and causing weakness. Type B toxin has more effect over the autonomic nervous system and hence is preferred for hyper-secretory disorders. The use of electromyography and ultrasound further improve the accuracy of the procedure. It is a relatively safe therapeutic option with its effect lasting for around three months. It has very few side effects. The key is to start with the lowest possible dose and then gradually increase the dose depending upon the patient's response. Selecting the right muscles for injection is of utmost importance and is guided by the knowledge of anatomy of the muscles.

Botulinum toxin type A enhances the inhibitory spontaneous postsynaptic currents on the substantia gelatinosa neurons of the subnucleus caudalis in immature mice

Botulinum toxin type A (BoNT/A) has been used therapeutically for various conditions including dystonia, cerebral palsy, wrinkle, hyperhidrosis and pain control. The substantia gelatinosa (SG) neurons of the trigeminal subnucleus caudalis (Vc) receive orofacial nociceptive information from primary afferents and transmit the information to higher brain center. Although many studies have shown the analgesic effects of BoNT/A, the effects of BoNT/A at the central nervous system and the action mechanism are not well understood. Therefore, the effects of BoNT/A on the spontaneous postsynaptic currents (sPSCs) in the SG neurons were investigated. In whole cell voltage clamp mode, the frequency of sPSCs was increased in 18 (37.5%) neurons, decreased in 5 (10.4%) neurons and not affected in 25 (52.1%) of 48 neurons tested by BoNT/A (3 nM). Similar proportions of frequency variation of sPSCs were observed in 1 and 10 nM BoNT/A and no significant differences were observed in the relative mean frequencies of sPSCs among 1-10 nM BoNT/A. BoNT/A-induced frequency increase of sPSCs was not affected by pretreated tetrodotoxin (0.5 µM). In addition, the frequency of sIPSCs in the presence of CNQX (10 µM) and AP5 (20 µM) was increased in 10 (53%) neurons, decreased in 1 (5%) neuron and not affected in 8 (42%) of 19 neurons tested by BoNT/A (3 nM). These results demonstrate that BoNT/A increases the frequency of sIPSCs on SG neurons of the Vc at least partly and can provide an evidence for rapid action of BoNT/A at the central nervous system.

Applications of botulinum toxin in dentistry: A comprehensive review

The horizons of treatment options in dentistry are broadening rapidly. In this scenario, applications of unconventional treatment options like use of botulinum toxin (BT) are gaining momentum. The use of BT has been popularly accepted in esthetic procedures like management of facial wrinkles; however, it has been documented to be successful in a variety of conditions. Of particular interest to this paper are applications of BT in the maxillofacial region, concerned to dentistry. BT offers a transient, reversible, relatively safe treatment option to many conditions of interest to a dental practitioner. Dental surgeons by their virtue of being extensively aware of the anatomy of faciomaxillary region are a potential pool of operators who can use BT in their armamentarium with minor skill enhancement and thus widen the perspective of alternative, minimally invasive options to refractory conditions or invasive protocols.

Temporomandibular joint dislocation

Temporomandibular joint (TMJ) dislocation is an uncommon but debilitating condition of the facial skeleton. The condition may be acute or chronic. Acute TMJ dislocation is common in clinical practice and can be managed easily with manual reduction. Chronic recurrent TMJ dislocation is a challenging situation to manage. In this article, we discuss the comprehensive review of the different treatment modalities in managing TMJ dislocation.

Relevance of sonography for botulinum toxin treatment of cervical dystonia: an expert statement

Botulinum neurotoxin A (BoNT A) is the first-line treatment for cervical dystonia. However, although BoNT A has a favorable safety profile and is effective in the majority of patients, in some cases the treatment outcome is disappointing or side effects occur when higher doses are used. It is likely that in such cases either the target muscles were not injected accurately or unintended weakness of non-target muscles occurred. It has been demonstrated in clinical trials for spastic movement disorders that sonography-guided BoNT A injections could improve treatment outcome. As the published evidence for a benefit of sonography-guided BoNT injection in patients with cervical dystonia is scarce, it is the aim of this review to discuss the relevance of sonography in this indication and provide a statement from clinical experts for its use. The clear advantage of sonography-guided injections is non-invasive, real-time visualization of the targeted muscle, thus improving the precision of injections and potentially the treatment outcomes as well as avoiding adverse effects. Other imaging techniques are of limited value due to high costs, radiation exposure or non-availability in clinical routine. In the hands of a trained injector, sonography is a quick and non-invasive imaging technique. Novel treatment concepts of cervical dystonia considering the differential contributions of distinct cranial and cervical muscles can reliably be implemented only by use of imaging-guided injection protocols.

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

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

Comparison of Systemic Toxicity between Botulinum Toxin Subtypes A1 and A2 in Mice and Rats

The adverse events caused by botulinum toxin type A (subtype A1) product, thought to be after-effects of toxin diffusion after high-dose administration, have become serious issues. A preparation showing less diffusion in the body than existing drugs has been sought. We have attempted to produce neurotoxin derived from subtype A2 (A2NTX) with an amino acid sequence different from that of neurotoxin derived from subtype A1 (A1NTX). In this study, to investigate whether A2NTX has the potential to resolve these issues, we compared the safety of A2NTX, a progenitor toxin derived from subtype A1 (A1 progenitor toxin) and A1NTX employing the intramuscular lethal dose 50% (im LD50) in mice and rats and the compound muscle action potential (CMAP) in rats. Mouse im LD50 values for A1 progenitor toxin and A2NTX were 93 and 166 U/kg, respectively, and the rat im LD50 values were 117 and 153 U/kg, respectively. In the rat CMAP test, the dose on the contralateral side, which caused a 50% reduction in the CMAP amplitude, that is, CMAP-TD50 , was calculated as 19.0, 16.6 and 28.7 U/kg for A1 progenitor toxin, A1NTX and A2NTX, respectively. The results indicate that A2NTX is safer than A1 progenitor toxin and A1NTX.

Comparable Botulinum Toxin Outcomes between Primary and Secondary Blepharospasm: A Retrospective Analysis

Background

Blepharospasm is a focal cranial dystonia, which could be idiopathic in origin or secondary to an underlying disorder that commonly impairs quality of life. Botulinum toxin (BoNT) injections have become the treatment of choice; however, a less favorable response to BoNT is expected in secondary blepharospasm. No studies have been conducted comparing outcomes between blepharospasm cohorts. We therefore aim to compare BoNT outcomes in primary and secondary blepharospasm subjects.

Methods

A retrospective review of 64 blepharospasm subjects receiving BoNT therapy was conducted. Demographics, BoNT treatment schedules, duration of BoNT therapy, and side effects were recorded. Outcome measures were duration of benefit, peak-dose benefit recorded with the Clinical Global Impressions Scale (CGIS), and related side effects.

Results

No difference was found between the two cohorts regarding duration of benefit from treatment (primary 9.47 weeks vs. secondary 9.63 weeks, p = 0.88). Perceived peak-dose benefit was more commonly reported as “very much improved” in secondary patients, but this was not significant (p = 0.13). Higher BoNT dosages were required in both groups over time, with a mean increase of 20.5% in primary and 26.5% in secondary blepharospasm. Ptosis (8%) and diplopia (6%) were the most common reported side effects. Mean follow-up in years was similar between groups, 3.6 years for primary vs. 2.4 years for secondary blepharospasm (p = 0.17).

Discussion

BoNT injections were effective with comparable benefits seen in both primary and secondary blepharospasm populations. Clinicians should be aware of the similar benefit from BoNT reported in secondary blepharospasm patients. The average duration of benefit in this cohort was comparable with previous reports.

Botulinum toxin suppression of CNS network activity in vitro

The botulinum toxins are potent agents which disrupt synaptic transmission. While the standard method for BoNT detection and quantification is based on the mouse lethality assay, we have examined whether alterations in cultured neuronal network activity can be used to detect the functional effects of BoNT. Murine spinal cord and frontal cortex networks cultured on substrate integrated microelectrode arrays allowed monitoring of spontaneous spike and burst activity with exposure to BoNT serotype A (BoNT-A). Exposure to BoNT-A inhibited spike activity in cultured neuronal networks where, after a delay due to toxin internalization, the rate of activity loss depended on toxin concentration. Over a 30 hr exposure to BoNT-A, the minimum concentration detected was 2 ng/mL, a level consistent with mouse lethality studies. A small proportion of spinal cord networks, but not frontal cortex networks, showed a transient increase in spike and burst activity with exposure to BoNT-A, an effect likely due to preferential inhibition of inhibitory synapses expressed in this tissue. Lastly, prior exposure to human-derived antisera containing neutralizing antibodies prevented BoNT-A induced inhibition of network spike activity. These observations suggest that the extracellular recording from cultured neuronal networks can be used to detect and quantify functional BoNT effects.

Structure of dual receptor binding to botulinum neurotoxin B

Botulinum neurotoxins are highly toxic, and bind two receptors to achieve their high affinity and specificity for neurons. Here we present the first structure of a botulinum neurotoxin bound to both its receptors. We determine the 2.3-Å structure of a ternary complex of botulinum neurotoxin type B bound to both its protein receptor synaptotagmin II and its ganglioside receptor GD1a. We show that there is no direct contact between the two receptors, and that the binding affinity towards synaptotagmin II is not influenced by the presence of GD1a. The interactions of botulinum neurotoxin type B with the sialic acid 5 moiety of GD1a are important for the ganglioside selectivity. The structure demonstrates that the protein receptor and the ganglioside receptor occupy nearby but separate binding sites, thus providing two independent anchoring points.

Synthesis/biological evaluation of hydroxamic acids and their prodrugs as inhibitors for Botulinum neurotoxin A light chain

Botulinum neurotoxin A (BoNT/A) is the most potent toxin known. Unfortunately, it is also a potential bioweapon in terrorism, which is without an approved therapeutic treatment once cellular intoxication takes place. Previously, we reported how hydroxamic acid prodrug carbamates increased cellular uptake, which translated to successful inhibition of this neurotoxin. Building upon this research, we detail BoNT/A protease molecular modeling studies accompanied by the construction of small library of hydroxamic acids based on 2,4-dichlorocinnamic hydroxamic acid scaffold and their carbamate prodrug derivatization along with the evaluation of these molecules in both enzymatic and cellular models.

Comparison of the immunogenicity of botulinum toxin type A and the efficacy of A1 and A2 neurotoxins in animals with A1 toxin antibodies

One issue with botulinum toxin type A products is a reduced therapeutic response in patients that have been injected with frequent dosing over a prolonged period. A possible cause of this is hemagglutinin, found in progenitor toxins, displaying adjuvant activity, enhancing antibody production against the toxin. We investigated whether there is any difference in immunogenicity between the LL toxin-derived subtype A1 (A1LL) and the neurotoxin-derived subtypes A1 and A2 (A1NTX and A2NTX, respectively), and investigated whether A2NTX is effective in animals which produce antibodies against A1LL. Neutralizing antibodies were detected in the A1LL-administered group; however, they were not detected in swine and rabbits administered multiple doses of A2NTX. These results indicate that A2NTX has a lower immunogenicity than A1LL. In rats with neutralizing antibodies, produced by the administration of A1LL, that were administered either A1NTX or A2NTX, A2NTX showed more potent inhibitory neuromuscular transmission than A1NTX. In human sera immunized with the botulinum toxoid vaccine (containing LL, L, and M toxoid derived subtype A1) reacted with either A1NTX or A2NTX, A2NTX showed more potent inhibitory neuromuscular transmission than A1NTX. This suggests that A2NTX has a greater therapeutic value in humans who have neutralizing antibodies against the A1 toxin.

Botulinum toxin type A: implications in wound healing, facial cutaneous scarring, and cleft lip repair

Botulinum toxin is a neurotoxin that has been utilized to induce chemo-denervation of muscles. Cutaneous wounds represent a special situation in which the tensile forces applied by these muscles on wound edges might have deleterious effects on the healing process. The aim of this review was to investigate such an effect and to review other mechanisms this toxin might have on the healing process. We also reviewed the role of botulinum toxin in the management of hypertrophic scars and cleft lip repair.

Sustained efficacy and safety of repeated incobotulinumtoxinA (Xeomin(®)) injections in blepharospasm

IncobotulinumtoxinA (Xeomin(®), NT 201) is a purified botulinum toxin type A free from accessory (complexing) proteins. Previous studies evaluated single sets of incobotulinumtoxinA injections for the treatment of blepharospasm. Individualized injection intervals and other potential determinants of efficacy and safety need to be evaluated in a prospective, longitudinal study. Subjects with blepharospasm who completed a ≤ 20 weeks double-blind, placebo-controlled main period entered a ≤ 69 weeks open-label extension period (OLEX) and received ≤ 5 additional incobotulinumtoxinA treatments at flexible doses (≤ 50 U per eye) and flexible injection intervals (minimum of 6 weeks). Outcome measures included Jankovic Rating Scale (JRS) (sumscore, severity subscore and frequency subscore), Blepharospasm Disability Index, and adverse events. All 102 subjects who completed the main period entered the OLEX; 82 subjects completed the study, 56 received the maximum five injections. From each injection visit to a control visit 6 weeks later, investigator-rated JRS sumscores and subscores, and patient-rated Blepharospasm Disability Index were significantly improved (p ≤ 0.001 for all). All scores were still significantly improved at trial termination compared with the first injection visit (p < 0.05 for all). The most frequently reported adverse events were eyelid ptosis (31.4 %) and dry eye symptoms (17.6 %). The injection interval had no impact on the incidence of adverse events (post hoc analysis). No subject developed neutralizing antibodies during the study. Repeated incobotulinumtoxinA injections, administered at flexible doses and injection intervals from 6 to 20 weeks according to subjects' needs, provide sustained efficacy in the treatment of blepharospasm with no new or unexpected safety risks.

The C-terminus of Botulinum A Protease Has Profound and Unanticipated Kinetic Consequences Upon the Catalytic Cleft

Botulinum neurotoxins (BoNTs) are among the most deadly poisons known though ironically, they also are of great therapeutic utility. A number of research programs have been initiated to discover small molecule inhibitors of BoNTs metalloprotease activity. Many, though not all of these programs have screened against a truncated and more stable form of the enzyme, that possess comparable catalytic properties to the full length enzyme. Interestingly, several classes of inhibitors notably the hydroxamates, display a large shift in potency between the two enzyme forms. In this report we compare the kinetics of active-site, alpha-exosite and beta-exosite inhibitors versus truncated and full length enzyme. Molecular dynamics simulations conducted with the truncated and homology models of the fully length BoNT LC/A indicate the flexibility of the C-terminus of the full length enzyme is responsible for the potency shifts of active-site proximally binding inhibitors while distal binding (alpha-exosite) inhibitors remain equipotent.

Antinociceptive effects of A1 and A2 type botulinum toxins on carrageenan-induced hyperalgesia in rat

We performed a study on the antinociceptive effects of A1 and A2 type (A1LL and A2NTX, respectively) botulinum toxin on carrageenan-induced hyperalgesia in the rat. Both A1LL and A2NTX had antinociceptive effects in the carrageenan-induced inflammatory pain model, reducing the mechanical and thermal hyperalgesia. A2NTX also reduced the increase in c-fos immunoreactivity in L4-L5 spinal segments induced by carrageenan, suggesting that A2NTX inhibits the activation of spinal nociceptive afferent fibers that project to the CNS. Our results indicate that A2NTX may offer a new therapeutic tool to treat inflammatory pain.

Evaluation of adamantane hydroxamates as botulinum neurotoxin inhibitors: synthesis, crystallography, modeling, kinetic and cellular based studies

Botulinum neurotoxins (BoNTs) are the most lethal biotoxins known to mankind and are responsible for the neuroparalytic disease botulism. Current treatments for botulinum poisoning are all protein based and thus have a limited window of treatment opportunity. Inhibition of the BoNT light chain protease (LC) has emerged as a therapeutic strategy for the treatment of botulism as it may provide an effective post exposure remedy. Using a combination of crystallographic and modeling studies a series of hydroxamates derived from 1-adamantylacetohydroxamic acid (3a) were prepared. From this group of compounds, an improved potency of about 17-fold was observed for two derivatives. Detailed mechanistic studies on these structures revealed a competitive inhibition model, with a K(i)=27 nM, which makes these compounds some of the most potent small molecule, non-peptidic BoNT/A LC inhibitors reported to date.

A direct inhibitory effect of botulinum toxin type A on antral circular muscle contractility of guinea pig

PURPOSE

Recent studies suggest new mechanisms of Botulinum toxin (BoNT) other than inhibiting acetylcholine (ACh) release from nerve terminals. The aim of this study was to determine whether other mechanisms for BoNT exist, so that it directly inhibits smooth muscle contraction.

MATERIALS AND METHODS

Guinea pig antral muscle strips were studied in vitro after 2 hours of exposure to Botulinum toxin type A (BoNT/A). Contractile responses to electric field stimulation (EFS), high K(+) (60 mM) and ACh (100 μM) were evaluated 24 and 48 hours after antral intramuscular injection of BoNT/A or vehicle.

RESULTS

BoNT/A inhibited muscular contraction caused by high K(+) and ACh. Contractile responses to low (1 and 4 Hz) and high (8 and 20 Hz) frequency EFS of antral muscle strips 24 and 48 hours after antral intramuscular injection of BoNT/A were significantly inhibited.

CONCLUSION

The ability of BoNT/A to directly inhibit antral muscular contractility suggests a new mechanism for the pharmacologic actions of BoNT-direct inhibition of muscular contraction.

Rating scales for cervical dystonia: a critical evaluation of tools for outcome assessment of botulinum toxin therapy

Botulinum neurotoxin is the therapy of choice for all forms of cervical dystonia (CD), but treatment regimens still vary considerably. The interpretation of treatment outcome is mainly based on the clinical experience and on the scientific value of the rating scales applied. The aim of this review is to describe the historical development of rating scales for the assessment of CD and to provide an appraisal of their advantages and drawbacks. The Tsui score and the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS) have been widely employed in numerous clinical studies as specific instruments for CD. The obvious advantage of the Tsui score is its simplicity so that it can be easily implemented in clinical routine. The TWSTRS allows a more sophisticated assessment of functional features of CD, but only the Tsui score includes a rating for tremor. Other benefits of the TWSTRS are the disability and pain subscales, but despite its value in clinical trials, it might be too complex for routine clinical practice. None of the rating scales used at present has been rigorously tested for responsiveness to detect significant changes in clinical status after therapeutic interventions. Moreover, clinical data support a new classification of CD leading to a differentiation between head and neck subtypes. As the current rating scales are not able to cover all these aspects of the disorder, further research is needed to develop a valid and reliable instrument which considers the most current classification of CD.

Application of botulinum toxin to clinical therapy: advances and cautions

The therapeutic use of botulinum toxin Type A has followed a novel and unanticipated pathway of applications, from its initial application by Scott to paralyze the extraocular muscles of the eyes to correct strabismus. In the late 1970s, Scott formed a company, called Oculinum Inc, to make botulinum toxin Type A available for this ophthalmic application. From this modest and limited beginning, it has found use for treatment of a plethora of cosmetic, neuromuscular, and skeletal disabilities, including cervical dystonia, blepharospasm, and temporary improvement in the appearance of moderate to severe glabellar lines. Botulinum toxin Type A is now being used as therapy in voiding disorders, migraine and tension-type headache, writer's cramp, and laryngeal muscle hyperactivity syndromes. It has reduced the spasm and pain associated with perianal fissures. It has found application in the reduction of glandular function in severe primary axillary hyperhidrosis and sialorrhea. Additional applications are being studied in the area of pain management based on its apparent ability to inhibit neuropeptide release from nociceptors.

Botulinum toxin decreases hyperalgesia and inhibits P2X3 receptor over-expression in sensory neurons induced by ventral root transection in rats

OBJECTIVES

We aim to determine the effects of Botulinum toxin type A (BTX-A) on neuropathic pain behavior and the expression of P2X(3) receptor in dorsal root ganglion (DRG) in rats with neuropathic pain induced by L5 ventral root transection (L5 VRT).

METHODS

Neuropathic pain was induced by L5 VRT in male Sprague-Dawley rats. Either saline or BTX-A was administered to the plantar surface. Behavioral tests were conducted preoperatively and at predefined postoperative days. The expression of P2X(3) receptors in DRG neurons was detected by immunoreactivity at postoperative days 3, 7, 14, and 21.

RESULTS

The number of positive P2X(3) neurons in the ipsilateral L5 DRG increased significantly after L5 VRT (P<0.001). This increase persisted for at least 3 weeks after the operation. No significant changes in P2X(3) expression were detected in the contralateral L5, or in the L4 DRGs bilaterally. Subcutaneous administration of BTX-A, performed on the left hindpaw at days 4, 8, or 16 post VRT surgery, significantly reduced mechanical allodynia bilaterally and inhibited P2X(3) over-expression induced by L5 VRT.

CONCLUSIONS

L5 VRT led to over-expression of P2X(3) receptors in the L5 DRG and bilateral mechanical allodynia in rats. Subcutaneous injection of BTX-A significantly reversed the neuropathic pain behavior and the over-expression of P2X(3) receptor in nociceptive neurons. These data not only show over-expression of purinergic receptors in the VRT model of neuropathic pain but also reveal a novel mechanism of botulinum toxin action on nociceptive neurons.

Synthesis and evaluation of library of betulin derivatives against the botulinum neurotoxin A protease

Botulinum neurotoxins (BoNTs) are the most toxic proteins currently known. Current treatments for botulinum poisoning are all protein based with a limited window of opportunity. Inhibition of the BoNT light chain protease (LC) has emerged as a new therapeutic strategy for the treatment of botulism as it may provide an effective post-exposure remedy. As such, a small library of 40 betulin derivatives was synthesized and screened against the light chain of BoNT serotype A (LC/A); five positive hits (IC(50) <100 μM) were uncovered. Detailed evaluation of inhibition mechanism of three most active compounds revealed a competitive model, with sub-micromolar K(i) value for the best inhibitor (7). Unfortunately, an in vitro cell-based assay did not show any protection of rat cerebellar neurons against BoNT/A intoxication by 7.

Botulinum toxin has an increased effect when targeted toward the muscle's endplate zone: a high-density surface EMG guided study

OBJECTIVES

To compare the effect of endplate-targeted injections of a low Botulinum neurotoxin type A (BoNT-A) dose with that of injections at defined distances from the motor endplate zone.

METHODS

In eight healthy volunteers, the main endplate zones of the right and left extensor digitorum brevis (EDB) muscles were localized using high-density surface EMG. On the study side BoNT-A was injected at fixed distances from the endplate zone. On the control side, BoNT-A was administered into the endplate zone. Compound muscle action potential (CMAP) prior to the injection and 2, 12, and 24 weeks later were recorded.

RESULTS

On the control side, the mean CMAP reduction 2 weeks after BoNT-A injection was 79.3%. The difference in CMAP reduction between both EDB muscles was significantly related to the injection distance from the endplate zone. Increasing the injection distance by 1cm reduced the effect of BoNT-A by 46%.

CONCLUSIONS

Guided injection of a reduced BoNT-A dose into the muscle's endplate zone(s) is a promising strategy for optimizing the therapeutic effectiveness of BoNT-A and for minimizing side-effects such as unwanted weakness of adjacent muscles.

SIGNIFICANCE

Precise endplate-targeted injections increase the effect of BoNT-A and may thus prove to reduce required dosage and treatment costs.

Botulinum neurotoxin for pain management: insights from animal models

The action of botulinum neurotoxins (BoNTs) at the neuromuscular junction has been extensively investigated and knowledge gained in this field laid the foundation for the use of BoNTs in human pathologies characterized by excessive muscle contractions. Although much more is known about the action of BoNTs on the peripheral system, growing evidence has demonstrated several effects also at the central level. Pain conditions, with special regard to neuropathic and intractable pain, are some of the pathological states that have been recently treated with BoNTs with beneficial effects. The knowledge of the action and potentiality of BoNTs utilization against pain, with emphasis for its possible use in modulation and alleviation of chronic pain, still represents an outstanding challenge for experimental research. This review highlights recent findings on the effects of BoNTs in animal pain models.

Comparison of effects of botulinum toxin subtype A1 and A2 using twitch tension assay and rat grip strength test

Botulinum toxin type A is used as a therapeutic agent for some spastic neurological disorders. Type A organisms have been classified into four subtypes (A1 to A4) based on the amino acid sequence variability of the produced neurotoxin. At present, commercially available preparations of the toxin belong to subtype A1. To date, no study has compared the characteristics of the biological activity of toxins from different subtypes. We compared the efficacy of A1 toxin (LL toxin or neurotoxin: NTX) with that of A2 toxin (NTX) employing the twitch tension assay using the mouse phrenic nerve hemidiaphragm and grip strength test in rats. The inhibitory effects on neuromuscular transmission of A2NTX at pH 7.4 and pH 6.8 were 1.95 and 3.73 times more potent than those of A1LL, respectively. The 50% effective doses for the administered limb, the dose which caused a 50% reduction in grip strength, i.e. ED(50), of A1LL, A1NTX, and A2NTX were calculated as 0.087, 0.060, and 0.040 U/head, respectively. These doses for the contralateral limb, i.e. TD(50), of A1LL, A1NTX, and A2NTX were calculated as 6.35, 7.54, and 15.62 U/head, respectively. In addition, the time required for A2NTX-injected rats to recover the grip strength of the contralateral limb was 17 days, while that for rats injected with A1LL was 35 days. The results indicated that A2NTX is a more potent neuromuscular blocker than A1 toxins, and suggested that A2NTX will provide a preferentical therapeutic agent for neurological disorders.

Gastrointestinal dysfunction in Parkinson's disease

In recent years, an increasingly detailed picture of gastrointestinal dysfunction in the setting of Parkinson's disease has emerged. Abnormalities of function may occur at virtually all levels of the gastrointestinal tract. Weight loss, dental deterioration, salivary excess, dysphagia, gastroparesis, decreased bowel movement frequency, and anorectal dysfunction all may occur. The pathophysiologic basis for this dysfunction entails both central and enteric nervous system involvement.

Identification of a Natural Product Antagonist against the Botulinum Neurotoxin Light Chain Protease

Botulinum neurotoxins (BoNTs) are the etiological agents responsible for botulism, a disease characterized by peripheral neuromuscular blockade and a characteristic flaccid paralysis of humans. BoNTs are the most lethal known poisons affecting humans and has been recognized as a potential bioterrorist threat. Current treatments for botulinum poisoning are predominately prophylactic in nature relying on passive immunization with antitoxins. Inhibition of the BoNT light chain metalloprotease (LC) has emerged as a new therapeutic strategy for the treatment of botulism that may provide an effective post-exposure remedy. A high-throughput screening effort against the light chain of BoNT serotype A (LC/A) was conducted with the John Hopkins Clinical Compound Library comprised of over 1,500 existing drugs. Lomofungin, a natural product first isolated in the late 1960's, was identified as an inhibitor of LC/A, displaying classical noncompetitive inhibition kinetics with a K(i) of 6.7 ± 0.7 µM. Inhibitor combination studies reveal that lomofungin binding is nonmutually exclusive (synergistic). The inhibition profile of lomofungin has been delineated by the use of both an active site inhibitor, 2,4-dichlorocinnamic hydroxamate, and a noncompetitive inhibitor d-chicoric acid; the mechanistic implications of these observations are discussed. Lastly, cellular efficacy was investigated using a rat primary cell model which demonstrated that lomofungin can protect against SNAP-25 cleavage, the intracellular protein target of LC/A.

Botulinum toxin type A reduces pain supersensitivity in experimental diabetic neuropathy: bilateral effect after unilateral injection

We investigated antinociceptive activity of botulinum toxin type A (BTX-A) in a model of diabetic neuropathic pain in rats. Male Wistar rats were made diabetic by a single intraperitoneal injection of streptozotocin (80mg/kg). Sensitivity to mechanical and thermal stimuli was measured with the paw-pressure and hot-plate test, respectively. The formalin test was used to measure sensitivity to chemical stimuli. Diabetic animals with pain thresholds lower for at least 25% compared to the non-diabetic group were considered neuropathic and were injected with BTX-A either subcutaneously (3, 5 and 7U/kg) or intrathecally (1U/kg). Mechanical and thermal sensitivity was measured at several time-points. After peripheral application, BTX-A (5 and 7U/kg) reduced mechanical and thermal hypersensitivity not only on ipsilateral, but on contralateral side, too. The antinociceptive effect started 5days following BTX-A injection and lasted at least 15days. Formalin-induced hypersensitivity in diabetic animals was abolished as well. When applied intrathecally, BTX-A (1U/kg) reduced diabetic hyperalgesia within 24h supporting the assumption of retrograde axonal transport of BTX-A from the peripheral site of injection to central nervous system. The results presented here demonstrate the long-lasting pain reduction after single BTX-A injection in the animals with diabetic neuropathy. The bilateral pain reduction after unilateral toxin application and the effectiveness of lower dose with the faster onset after the intrathecal injection suggest the involvement of the central nervous system in the antinociceptive action of BTX-A in painful diabetic neuropathy.

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.