Recovery of mouse neuromuscular junctions from single and repeated injections of botulinum neurotoxin A

Alteration of myoepithelial cells during botulinum toxin type A-inhibited salivary secretion

OBJECTIVE

Intraglandular injection of botulinum toxin type A (BoNT/A) effectively treats sialorrhea. Myoepithelial cells (MECs) are essential for salivary secretion. The role of MECs in BoNT/A-inhibited salivary secretion, and its underlying mechanisms remain unknown.

MATERIALS AND METHODS

BoNT/A was injected into rat submandibular glands (SMGs). At 1, 2, 4, 8, and 12 weeks postinjection, salivary flow rate of SMGs was measured. Electron microscopy, immunohistochemistry, immunofluorescence, and Western blot analysis were used to detect morphological and functional changes in MECs and chemical denervation in SMGs.

RESULTS

BoNT/A temporarily decreased salivary secretion in rat SMGs and this inhibitory effect lasted 4 weeks. During the inhibitory period, MECs atrophied and expressed reduced α-smooth muscle actin (α-SMA), vimentin, and phosphorylated myosin light chain 2 (p-MLC2), suggesting that BoNT/A attenuated MEC contractility. Furthermore, BoNT/A cleaved synaptosome-associated protein 25 (SNAP-25) and decreased the expression and activity of acetylcholinesterase (AChE), indicating that BoNT/A-induced chemical parasympathetic denervation of SMGs by cleaving SNAP-25.

CONCLUSIONS

BoNT/A temporarily caused MEC atrophy and decreased MEC contractility in rat SMGs, which contributed to reversible inhibition of salivary secretion. The underlying mechanisms involved temporary parasympathetic denervation caused by SNAP-25 cleavage. These findings provide new insights into the mechanisms of BoNT/A-inhibited salivary secretion.

The YAP1/TAZ-TEAD transcriptional network regulates gene expression at neuromuscular junctions in skeletal muscle fibers

We examined YAP1/TAZ-TEAD signaling pathway activity at neuromuscular junctions (NMJs) of skeletal muscle fibers in adult mice. Our investigations revealed that muscle-specific knockouts of Yap1 or Taz, or both, demonstrate that these transcriptional coactivators regulate synaptic gene expression, the number and morphology of NMJs, and synaptic nuclei. Yap1 or Taz single knockout mice display reduced grip strength, fragmentation of NMJs, and accumulation of synaptic nuclei. Yap1/Taz muscle-specific double knockout mice do not survive beyond birth and possess almost no NMJs, the few detectable show severely impaired morphology and are organized in widened endplate bands; and with motor nerve endings being mostly absent. Myogenic gene expression is significantly impaired in the denervated muscles of knockout mice. We found that Tead1 and Tead4 transcription rates were increased upon incubation of control primary myotubes with AGRN-conditioned medium. Reduced AGRN-dependent acetylcholine receptor clustering and synaptic gene transcription were observed in differentiated primary Tead1 and Tead4 knockout myotubes. In silico analysis of previously reported genomic occupancy sites of TEAD1/4 revealed evolutionary conserved regions of potential TEAD binding motifs in key synaptic genes, the relevance of which was functionally confirmed by reporter assays. Collectively, our data suggest a role for YAP1/TAZ-TEAD1/TEAD4 signaling, particularly through TAZ-TEAD4, in regulating synaptic gene expression and acetylcholine receptor clustering at NMJs.

Time course of surface electromyography during walking of children with spastic cerebral palsy treated with botulinum toxin type A and its rehabilitation implications

BACKGROUND

The timing of the effects of botulinum toxin A on spastic muscles is not yet fully clarified. The goal of this study was to follow the temporal changes of surface electromyographic activity of lower limb muscles during walking, after a therapeutic dose of botulinum toxin A injected into the calf muscles of children with spastic cerebral palsy.

METHODS

A group of children with spastic equinus foot was administered botulinum toxin A into the gastrocnemius medialis and lateralis muscles. Surface electromyographic activity of the tibialis anterior, gastrocnemius medialis, rectus femoris and medial hamstrings, was recorded before botulinum toxin A injections and after 4, 8, and 16 weeks. Children walked on ground and on a treadmill at an incline of 0% and 12%. The area of electromyographic activity and the index of muscle co-contraction were calculated for specific segments of gait cycle.

FINDINGS

Botulinum toxin A did not modify the speed of gait on ground. ANOVA showed significant differences in electromyography during the stance phase segments with a maximum decrease between 4 and 8 weeks' post botulinum toxin A and a full recovery at 16 weeks. A significant co-contraction of rectus femoris/gastrocnemius medialis, between 0 and 20% and 35-50% of the gait cycle, was observed from the 4th to the 8th week post- botulinum toxin A for both treadmill settings.

INTERPRETATION

The temporal identification of deterioration/recovery of electromyographic activity as well as of muscle co-contractions, could be key elements in a rehabilitation program planning combined with botulinum toxin A.

Enteric Nervous System: Identification of a Novel Neuronal Sensory Network in the Duodenal Epithelium

The communication between the intestinal epithelium and the enteric nervous system has been considered indirect. Mechanical or chemical stimuli activate enteroendocrine cells inducing hormone secretion, which act on sub-epithelial nerve ends, activating the enteric nervous system. However, we identified an epithelial cell that expresses NKAIN4, a neuronal protein associated with the β-subunit of Na+/K+-ATPase. This cell overexpresses Na+/K+-ATPase and ouabain-insensitive Na+-ATPase, enzymes involved in active sodium transport. NKAIN4-positive cells also express neuronal markers as NeuN, acetylcholine-esterase, acetylcholine-transferase, α3- and α7-subunits of ACh receptors, glutamic-decarboxylase, and serotonin-receptor-7, suggesting they are neurons. NKAIN4-positive cells show a polarized shape with an oval body, an apical process finished in a knob-like terminal in contact with the lumen, a basal cilia body at the base of the apical extension, and basal axon-like soma projections connecting sub-epithelial nerve terminals, lymphoid nodules, glial cells, and enterochromaffin cells, forming a network that reaches the epithelial surface. We also showed, using retrograde labeling and immunofluorescence, that these cells receive afferent signals from the enteric nervous system. Finally, we demonstrated that acetylcholine activates NKAIN4-positive cells inducing Ca2+ mobilization and probably serotonin secretion in enterochromaffin cells. NKAIN4-positive cells are neurons that would form a part of a duodenal sensory network for physiological or noxious luminal stimuli.

A cross-sectional study of ageing at the mouse neuromuscular junction and effects of an experimental therapeutic approach for dynapenia

Despite prior efforts to understand and target dynapenia (age-induced loss of muscle strength), this condition remains a major challenge that reduces the quality of life in the aged population. We have focused on the neuromuscular junction (NMJ) where changes in structure and function have rarely been systematically studied as a dynamic and progressive process. Our cross-sectional study found neurotransmission at the male mouse NMJ to be biphasic, displaying an early increase followed by a later decrease, and this phenotype was associated with structural changes to the NMJ. A cross-sectional characterization showed that age-induced alterations fell into four age groups: young adult (3-6 months), adult (7-18 months), early aged (19-24 months), and later aged (25-30 months). We then utilized a small molecule therapeutic candidate, GV-58, applied acutely during the later aged stage to combat age-induced reductions in transmitter release by increasing calcium influx during an action potential, which resulted in a significant increase in transmitter release. This comprehensive study of neuromuscular ageing at the NMJ will enable future research to target critical time points for therapeutic intervention. KEY POINTS: Age-induced frailty and falls are the leading causes of injury-related death and are caused by an age-induced loss of muscle strength due to a combination of neurological and muscular changes. A cross-sectional approach was used to study age-induced changes to the neuromuscular junction in a mouse model, and physiological changes that were biphasic over the ageing time course were found. Changes in physiology at the neuromuscular junction were correlated with alterations in neuromuscular junction morphology. An acutely applied positive allosteric gating modifier of presynaptic voltage-gated calcium channels was tested as a candidate therapeutic strategy that could increase transmitter release at aged neuromuscular junctions. These results provide a detailed time course of age-induced changes at the neuromuscular junction in a mouse model and test a candidate therapeutic strategy for weakness.

Neuromuscular recovery from botulism involves multiple forms of compensatory plasticity

Introduction

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

Methods and results

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

Discussion

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

An evaluation of onobotulinumtoxinA as a therapeutic option for pediatric neurogenic detrusor overactivity

INTRODUCTION

Neurogenic detrusor overactivity (NDO) results in involuntary detrusor contractions during bladder filling or storage risking transmission of pressure to the upper urinary tracts and/or significant incontinence. The goals of bladder management in children with NDO prioritize the preservation of renal function, prevention of UTIs, and optimizing quality of life. First-line measures include intermittent catheterization and anticholinergic medication. However, when conservative measures fail, surgical intervention may be indicated. Historically, the next step was major reconstructive surgery to create a low-pressure urinary reservoir. The introduction of intravesical botulinum neurotoxin A (BoNT/A) for use in children in 2002 offered a less invasive option for management. However, its exact role is still evolving.

AREAS COVERED

This article summarizes the mechanism of action of BoNT/A for management of NDO and evaluates the current literature defining common practice and clinical efficacy in children with NDO. The findings of the recently completed phase III trial for intravesical onabotulinumtoxinA in children are discussed in detail.

EXPERT OPINION

As the first BoNT/A approved for use in children with NDO, onabotulinumtoxinA appears to be a safe and less invasive alternative to major reconstructive surgery. However, data defining appropriate patient selection and its role as a long-term treatment option continue to develop.

Older mice show decreased regeneration of neuromuscular junctions following lengthening contraction-induced injury

Progressive muscle atrophy and loss of muscle strength associated with old age have been well documented. Although age-associated impairments in skeletal muscle regeneration following injury have been demonstrated, less is known about whether aging impacts the regenerative response of neuromuscular junctions (NMJ) following contraction-induced injury. Reduced ability of NMJs to regenerate could lead to increased numbers of denervated muscle fibers and therefore play a contributing role to age-related sarcopenia. To investigate the relationship between age and NMJ regeneration following injury, extensor digitorum longus (EDL) muscles of middle-aged (18-19 months) and old mice (27-28 months) were subjected to a protocol of lengthening contractions (LC) that resulted in an acute force deficit of ~55% as well as functional and histological evidence of a similar magnitude of injury 3 days post LCs that was not different between age groups. After 28 days, the architecture and innervation of the NMJs were evaluated. The numbers of fragmented endplates increased and of fully innervated NMJs decreased post-injury for the muscle of both middle-aged and old mice and for contralateral uninjured muscles of old compared with uninjured muscles of middle-aged controls. Thus, the diminished ability of the skeletal muscle of old mice to recover following injury may be due in part to an age-related decrease in the ability to regenerate NMJs in injured muscles. The impaired ability to regenerate NMJs may be a triggering factor for degenerative changes at the NMJ contributing to muscle fiber weakness and loss in old age.

Potentiation of neuromuscular transmission by a small molecule calcium channel gating modifier improves motor function in a severe spinal muscular atrophy mouse model

Spinal muscular atrophy (SMA) is a monogenic disease that clinically manifests as severe muscle weakness owing to neurotransmission defects and motoneuron degeneration. Individuals affected by SMA experience neuromuscular weakness that impacts functional activities of daily living. We have used a mouse model of severe SMA (SMNΔ7) to test whether a calcium channel gating modifier (GV-58), alone or in combination with a potassium channel antagonist (3,4-diaminopyridine; 3,4-DAP), can improve neuromuscular function in this mouse model. Bath application of GV-58 alone or in combination with 3,4-DAP significantly restored neuromuscular transmission to control levels in both a mildly vulnerable forearm muscle and a strongly vulnerable trunk muscle in SMNΔ7 mice at postnatal days 10-12. Similarly, acute subcutaneous administration of GV-58 to postnatal day 10 SMNΔ7 mice, alone or in combination with 3,4-DAP, significantly increased a behavioral measure of muscle strength. These data suggest that GV-58 may be a promising treatment candidate that could address deficits in neuromuscular function and strength and that the addition of 3,4-DAP to GV-58 treatment could aid in restoring function in SMA.

Improvement of Pain and Function by Using Botulinum Toxin Type A Injection in Patients with an Osteoarthritic Knee with Patellar Malalignment: An Electromyographic Study

Objective: To determine the pain and electromyographic (EMG) amplitude ratio of the vastus medialis oblique (VMO) to the vastus lateralis (VL) after botulinum toxin type A (BTA) was injected in the bilateral osteoarthritic knee of patients with patellar malalignment for analysis. Material and methods: A total of fifteen patients were recruited; the more symptomatic knee of each patient received a BTA injection (BTA side). The other set of patients were left untreated. In all, fifteen healthy participants comprised the control group. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and numeric rating scale (NRS) for pain were assessed. The EMG amplitude of VL and VMO activity was recorded using an isokinetic dynamometer and synchronized using the BIOPAC MP100. The data were collected before and at 4, 8, and 12 weeks post−BTA injection. Results: The EMG ratios of the patient group were lower than those of the control group at all testing velocities (p < 0.05). The VMO/VL ratio improved significantly on the BTA side only. The VMO/VL ratios on the BTA side were higher than those on the untreated side (p < 0.05). Knee pain decreased significantly after the BTA injection. The EMG ratios were negatively correlated with the NRS and WOMAC scores. Conclusion: BTA injection effectively reduces knee pain and restores the EMG ratio between the VMO and VL.

In Adult Skeletal Muscles, the Co-Receptors of Canonical Wnt Signaling, Lrp5 and Lrp6, Determine the Distribution and Size of Fiber Types, and Structure and Function of Neuromuscular Junctions

Canonical Wnt signaling is involved in skeletal muscle cell biology. The exact way in which this pathway exerts its contribution to myogenesis or neuromuscular junctions (NMJ) is a matter of debate. Next to the common co-receptors of canonical Wnt signaling, Lrp5 and Lrp6, the receptor tyrosine kinase MuSK was reported to bind at NMJs WNT glycoproteins by its extracellular cysteine-rich domain. Previously, we reported canonical Wnt signaling being active in fast muscle fiber types. Here, we used conditional Lrp5 or Lrp6 knockout mice to investigate the role of these receptors in muscle cells. Conditional double knockout mice died around E13 likely due to ectopic expression of the Cre recombinase. Phenotypes of single conditional knockout mice point to a very divergent role for the two receptors. First, muscle fiber type distribution and size were changed. Second, canonical Wnt signaling reporter mice suggested less signaling activity in the absence of Lrps. Third, expression of several myogenic marker genes was changed. Fourth, NMJs were of fragmented phenotype. Fifth, recordings revealed impaired neuromuscular transmission. In sum, our data show fundamental differences in absence of each of the Lrp co-receptors and suggest a differentiated view of canonical Wnt signaling pathway involvement in adult skeletal muscle cells.

In Skeletal Muscle Fibers, Protein Kinase Subunit CSNK2A1/CK2α Is Required for Proper Muscle Homeostasis and Structure and Function of Neuromuscular Junctions

CSNK2 tetrameric holoenzyme is composed of two subunits with catalytic activity (CSNK2A1 and/or CSNK2A2) and two regulatory subunits (CSNK2B) and is involved in skeletal muscle homeostasis. Up-to-date, constitutive Csnk2a2 knockout mice demonstrated mild regenerative impairments in skeletal muscles, while conditional Csnk2b mice were linked to muscle weakness, impaired neuromuscular transmission, and metabolic and autophagic compromises. Here, for the first time, skeletal muscle-specific conditional Csnk2a1 mice were generated and characterized. The ablation of Csnk2a1 expression was ensured using a human skeletal actin-driven Cre reporter. In comparison with control mice, first, conditional knockout of CSNK2A1 resulted in age-dependent reduced grip strength. Muscle weakness was accompanied by impaired neuromuscular transmission. Second, the protein amount of other CSNK2 subunits was aberrantly changed. Third, the number of central nuclei in muscle fibers indicative of regeneration increased. Fourth, oxidative metabolism was impaired, reflected by an increase in cytochrome oxidase and accumulation of mitochondrial enzyme activity underneath the sarcolemma. Fifth, autophagic processes were stimulated. Sixth, NMJs were fragmented and accompanied by increased synaptic gene expression levels. Altogether, knockout of Csnk2a1 or Csnk2b results in diverse impairments of skeletal muscle biology.

Lasting Peripheral and Central Effects of Botulinum Toxin Type A on Experimental Muscle Hypertonia in Rats

Recent animal experiments suggested that centrally transported botulinum toxin type A (BoNT-A) might reduce an abnormal muscle tone, though with an unknown contribution to the dominant peripheral muscular effect observed clinically. Herein, we examined if late BoNT-A antispastic actions persist due to possible central toxin actions in rats. The early effect of intramuscular (i.m.) BoNT-A (5, 2 and 1 U/kg) on a reversible tetanus toxin (TeNT)-induced calf muscle spasm was examined 7 d post-TeNT and later during recovery from flaccid paralysis (TeNT reinjected on day 49 post-BoNT-A). Lumbar intrathecal (i.t.) BoNT-A-neutralizing antiserum was used to discriminate the transcytosis-dependent central toxin action of 5 U/kg BoNT-A. BoNT-A-truncated synaptosomal-associated protein 25 immunoreactivity was examined in the muscles and spinal cord at day 71 post-BoNT-A. All doses (5, 2 and 1 U/kg) induced similar antispastic actions in the early period (days 1-14) post-BoNT-A. After repeated TeNT, only the higher two doses prevented the muscle spasm and associated locomotor deficit. Central trans-synaptic activity contributed to the late antispastic effect of 5 U/kg BoNT-A. Ongoing BoNT-A enzymatic activity was present in both injected muscle and the spinal cord. These observations suggest that the treatment duration in sustained or intermittent muscular hyperactivity might be maintained by higher doses and combined peripheral and central BoNT-A action.

Causes of Botulinum Toxin Treatment Failure

Purpose

The purpose of this article is to review the cause of botulinum toxin (BT) failure and determine the ways to minimize the risks of its occurrence.

Methods

A PubMed and Google Scholar literature search was conducted with the search terms botulinum toxin, treatment, failure, causes, and prevention. Fifteen relevant articles were found and used as the scientific base for this article.

Results

The failure of BT therapy is associated with immunogenic and non-immunogenic causes and the formation of neutralizing antibodies toward the active components of BT or the complexing proteins. Enzyme-linked immunosorbent assay (ELISA) testing and mouse hemidiaphragm assay (MHA) can diagnose the failure. The risk of developing treatment failure can be minimized by using complexing protein-free formulations, selecting a treatment regimen with the least immunogenicity, proper injection technique, and gentle product handling.

Conclusion

The treatment failure can compromise the success of BT treatment. Current medical literature shows controversial evidence for and against BT immunogenicity. Therefore, the cause of BT failure is likely to be multifactorial.

Comparative Pharmacodynamics of Three Different Botulinum Toxin Type A Preparations following Repeated Intramuscular Administration in Mice

Botulinum neurotoxin type A (BoNT/A) causes muscle paralysis by blocking cholinergic signaling at neuromuscular junctions and is widely used to temporarily correct spasticity-related disorders and deformities. The paralytic effects of BoNT/A are time-limited and require repeated injections at regular intervals to achieve long-term therapeutic benefits. Differences in the level and duration of effectivity among various BoNT/A products can be attributed to their unique manufacturing processes, formulation, and noninterchangeable potency units. Herein, we compared the pharmacodynamics of three BoNT/A formulations, i.e., Botox^® (onabotulinumtoxinA), Xeomin^® (incobotulinumtoxinA), and Coretox^®, following repeated intramuscular (IM) injections in mice. Three IM injections of BoNT/A formulations (12 U/kg per dose), 12-weeks apart, were administered at the right gastrocnemius. Local paresis and chemodenervation efficacy were evaluated over 36 weeks using the digit abduction score (DAS) and compound muscle action potential (CMAP), respectively. One week after administration, all three BoNT/A formulations induced peak DAS and maximal reduction of CMAP amplitudes. Among the three BoNT/A formulations, only Coretox^® afforded a significant increase in paretic effects and chemodenervation with a prolonged duration of action after repeated injections. These findings suggest that Coretox^® may offer a better overall therapeutic performance in clinical settings.

Plasma Metabolomic Changes in Children with Cerebral Palsy Exposed to Botulinum Neurotoxin

The long-term effect of botulinum neurotoxin A (BoNT-A) on children with cerebral palsy (CP) is unclear, and how the dynamic changes of metabolites impact the duration of effect remains unknown. To tackle this, we collected 120 plasma samples from 91 children with spastic CP for analysis, with 30 samples in each time point: prior to injection and 1, 3, and 6 months after injection. A total of 354 metabolites were identified across all the time points, 39 of which exhibited significant changes (with tentative IDs) (p values <0.05, VIP > 1). Principal component analysis and partial least-squares discriminant analysis disclosed a clear separation between different groups (p values <0.05). Network analysis revealed the coordinated changes of functional metabolites. Pathway analysis highlighted the metabolic pathways associated with energy consumption and glycine, serine, and threonine metabolism and cysteine and methionine metabolism. Collectively, our results identified the significant dynamic changes of plasma metabolite after BoNT-A injections on children with CP. Metabolic pathways associated with energy expenditure might provide a new perspective for the effect of BoNT-A in children with CP. Glycine, serine, and threonine metabolism and cysteine and methionine metabolism might be related to the duration of effect of BoNT-A.

Botulinum toxin injections as salvage therapy is beneficial for management of patellofemoral pain syndrome

PURPOSE

Patellofemoral pain syndrome (PFPS) is a common pathology usually presenting with anterior or retropatellar pain. It is associated with a relative imbalance between the vastus medialis oblique (VMO) and the vastus lateralis (VL) muscles. This can lead to considerable morbidity and reduced quality of life (QOL). This study aims to assess the long-term functional outcome of PFPS treated with VL muscle botulinum toxin A (BoNT-A) injection.

MATERIALS AND METHODS

A retrospective review was performed on 26 consecutive patients (31 knees) with a mean age of 50.1 years (± 19.7 years) who were treated with BoNT-A injections to the VL muscle followed by physiotherapy between 2008 and 2015. Pre- and post-treatment pain levels (numerical rating scale, NRS), QOL (SF-6D), and functional scores (Kujala and Lysholm questionnaires) were measured. Demographics, physical therapy compliance, previous surgeries, perioperative complications, and patient satisfaction levels were collected.

RESULTS

The mean follow-up time was 58.8 ± 36.4 months. There were significant improvements in all the examined domains. The average pain score (NRS) decreased from 7.6 to 3.2 (P < 0.01), and the Kujala, Lysholm, and SF-6D scores improved from 58.9 to 82.7 (P < 0.001), 56.2 to 83.2 (P < 0.001), and 0.6 to 0.8 (P < 0.001), respectively. Similar delta improvement was achieved irrespective of gender, age, compliance to post-treatment physical therapy, or coexisting osteoarthritis. Patients who presented with a worse pre-treatment clinical status achieved greater improvement. Prior to BoNT-A intervention, 16 patients (18 knees) were scheduled for surgery, of whom 12 (75%, 13 knees) did not require further surgical intervention at the last follow-up.

CONCLUSIONS

A single intervention of BoNT-A injections to the VL muscle combined with physiotherapy is beneficial for the treatment of patients with persistent PFPS.

LEVEL III EVIDENCE

Retrospective cohort study.

OnabotulinumtoxinA for the prophylactic treatment of headaches in adult patients with chronic migraine: a safety evaluation

Introduction: Existing oral prophylaxis for chronic migraine (CM) are often ineffective or poorly tolerated. OnabotulinumtoxinA (onabotA) is approved for headache prophylaxis in CM and ameliorates headaches in patients refractory to multiple preventatives.Areas covered: We appraise evidence regarding action mechanisms, pharmacodynamics, and pharmacokinetics of onabotA in CM prophylaxis. We critically evaluate salient clinical and real-world studies demonstrating its efficacy in improving multiple aspects of CM. We discuss onabotA safety, tolerability, and adverse events (AEs) for CM prophylaxis from clinical trials, post-authorization studies and meta-analyses, including novel pregnancy safety data and comparisons with oral prophylactics. We explore areas of future interest, particularly onabotA safety and efficacy in the context of novel antibody-based prophylaxis.Expert opinion: Clinical and real-world evidence demonstrate onabotA safety, tolerability and efficacy for CM prophylaxis. Most AEs are mild/moderate and self-limiting, with few serious AEs and no treatment-related deaths. Common AEs include neck pain, ptosis, muscle weakness, and stiffness. Modifying existing responder-criteria enables more patients to benefit from onabotA. OnabotA shows superior safety and efficacy to oral preventatives, and appears safe in pregnancy. Future pregnancy-risk register will clarify pregnancy and lactation safety further. Future research comparing onabotA safety and efficacy with newly emergent antibody-based prophylaxis is keenly awaited.

Dissection, in vivo imaging and analysis of the mouse epitrochleoanconeus muscle

Analysis of rodent muscles affords an opportunity to glean key insights into neuromuscular development and the detrimental impact of disease‐causing genetic mutations. Muscles of the distal leg, for instance the gastrocnemius and tibialis anterior, are commonly used in such studies with mice and rats. However, thin and flat muscles, which can be dissected, processed and imaged without major disruption to muscle fibres and nerve‐muscle contacts, are more suitable for accurate and detailed analyses of the peripheral motor nervous system. One such wholemount muscle is the predominantly fast twitch epitrochleoanconeus (ETA), which is located in the upper forelimb, innervated by the radial nerve, and contains relatively large and uniformly flat neuromuscular junctions (NMJs). To facilitate incorporation of the ETA into the experimental toolkit of the neuromuscular disease field, here, we describe a simple method for its rapid isolation (<5 min), supported by high‐resolution videos and step‐by‐step images. Furthermore, we outline how the ETA can be imaged in live, anaesthetised mice, to enable examination of dynamic cellular processes occurring at the NMJ and within intramuscular axons, including transport of organelles, such as mitochondria and signalling endosomes. Finally, we present reference data on wild‐type ETA fibre‐type composition in young adult, male C57BL6/J mice. Comparative neuroanatomical studies of different muscles in rodent models of disease can generate critical insights into pathogenesis and pathology; dissection of the wholemount ETA provides the possibility to diversify the repertoire of muscles analysed for this endeavour.

Botulinum Toxin in Movement Disorders: An Update

Since its initial approval in 1989 by the US Food and Drug Administration for the treatment of blepharospasm and other facial spasms, botulinum toxin (BoNT) has evolved into a therapeutic modality for a variety of neurological and non-neurological disorders. With respect to neurologic movement disorders, BoNT has been reported to be effective for the treatment of dystonia, bruxism, tremors, tics, myoclonus, restless legs syndrome, tardive dyskinesia, and a variety of symptoms associated with Parkinson's disease. More recently, research with BoNT has expanded beyond its use as a powerful muscle relaxant and a peripherally active drug to its potential central nervous system applications in the treatment of neurodegenerative disorders. Although BoNT is the most potent biologic toxin, when it is administered by knowledgeable and experienced clinicians, it is one of the safest therapeutic agents in clinical use. The primary aim of this article is to provide an update on recent advances in BoNT research with a focus on novel applications in the treatment of movement disorders. This comprehensive review of the literature provides a critical review of evidence-based clinical trials and highlights recent innovative pilot studies.

Methocarbamol blocks muscular Nav 1.4 channels and decreases isometric force of mouse muscles

BACKGROUND

The muscle relaxant methocarbamol is widely used for the treatment of muscle spasms and pain syndromes. To elucidate molecular mechanisms of its action, we studied its influence on neuromuscular transmission, on isometric muscle force, and on voltage-gated Na+ channels.

METHODS

Neuromuscular transmission was investigated in murine diaphragm-phrenic nerve preparations and muscle force studied on mouse soleus muscles. Nav 1.4 channels and Nav 1.7 channels were functionally expressed in eukaryotic cell lines.

RESULTS

Methocarbamol, at 2 mM, decreased the decay of endplate currents, slowed the decay of endplate potentials and reduced tetanic force of soleus muscles. The drug reversibly inhibited current flow through muscular Nav 1.4 channels, while neuronal Nav 1.7 channels were unaffected.

CONCLUSIONS

The study provides evidence for peripheral actions of methocarbamol on skeletal muscle. Muscular Na+ channels are a molecular target of methocarbamol. Since Nav 1.7 currents were unaffected, methocarbamol is unlikely to exert its analgesic effect by directly blocking Nav 1.7 channels.

Diaphragm neuromuscular transmission failure in a mouse model of an early-onset neuromotor disorder

The spa transgenic mouse displays spasticity and hypertonia that develops during the early postnatal period, with motor impairments that are remarkably similar to symptoms of human cerebral palsy. Previously, we observed that spa mice have fewer phrenic motor neurons innervating the diaphragm muscle (DIAm). We hypothesize that spa mice exhibit increased susceptibility to neuromuscular transmission failure (NMTF) due to an expanded innervation ratio. We retrogradely labeled phrenic motor neurons with rhodamine and imaged them in horizontal sections (70 µm) using confocal microscopy. Phrenic nerve-DIAm strip preparations from wild type and spa mice were stretched to optimal length, and force was evoked by phrenic nerve stimulation at 10, 40, or 75 Hz in 330-ms duration trains repeated each second (33% duty cycle) across a 120-s period. To assess NMTF, force evoked by phrenic nerve stimulation was compared to force evoked by direct DIAm stimulation superimposed every 15 s. Total DIAm fiber number was estimated in hematoxylin and eosin-stained strips. Compared to wild type, spa mice had over twofold greater NMTF during the first stimulus train that persisted throughout the 120 s period of repetitive activation. In both wild type and spa mice, NMTF was stimulation-frequency dependent. There was no difference in neuromuscular junction morphology or the total number of DIAm fibers between wild type and spa mice, however, there was an increase innervation ratio (39%) in spa mice. We conclude that early-onset developmental neuromotor disorders impair the efficacy of DIAm neuromuscular transmission, likely to contribute to respiratory complications.NEW & NOTEWORTHY Individuals with motor control deficits, including cerebral palsy (CP) often have respiratory impairments. Glycine-receptor mutant spa mice have early-onset hypertonia, and limb motor impairments, similar to individuals with CP. We hypothesized that in the diaphragm of spa mice, disruption of glycinergic inputs to MNs would result in increased phrenic-DIAm neuromuscular transmission failure. Pathophysiologic abnormalities in neuromuscular transmission may contribute to respiratory dysfunction in conditions where early developmental MN loss or motor control deficits are apparent.

The mechanisms of action and use of botulinum neurotoxin type A in aesthetics: Key Clinical Postulates II

BACKGROUND

The literature on botulinum neurotoxin type A (BoNT-A) is extensive, often contradictory, and confounded by a competitive market of products and research attempting to distinguish brand individuality.

METHODS

A comprehensive review of literature on the principles of BoNT-A in aesthetics as well as clinical examples.

RESULTS

In 2017, the Eight Key Clinical Postulates were formulated as a guide for the aesthetic practitioner in understanding BoNT-A pharmacodynamics and to compare different toxins. These are now updated to include (a) All type A toxins act identically; (b) The mathematical relationship between toxin and receptor is the basis of efficacy, and clinical efficacy is influenced by molecular potency and patient attributes including muscle mass, gender, age, and ethnicity; (c) Efficacy, onset, and duration are functions of "molecular potency" defined as the number of active 150 kDa molecules available for binding; (d) "Molecular potency" is difficult to objectively quantify for commercially available toxins; (e) Up to a point, increased molecular potency decreases time to onset and increases duration of effect, and the "Molecular Potency Quotient" is a construct for comparing molecular potency commercial cost; (f) The area of effect of a toxin injection is dependent upon molecular potency, diffusion (passive), and spread (active); (g) Differing reconstitution volumes; and (h) Increased number of injection sites can affect spread, onset, and duration of effect.

CONCLUSIONS

The principles of BoNT-A use in aesthetics are complex yet understandable as outlined in the framework of the updated Eight Key Clinical Postulates and serves as a useful tool for providing the most effective treatment and interpreting research on present and future toxin formulations.

Lack of Desmin in Mice Causes Structural and Functional Disorders of Neuromuscular Junctions

Desmin, the major intermediate filament (IF) protein in muscle cells, interlinks neighboring myofibrils and connects the whole myofibrillar apparatus to myonuclei, mitochondria, and the sarcolemma. However, desmin is also known to be enriched at postsynaptic membranes of neuromuscular junctions (NMJs). The pivotal role of the desmin IF cytoskeletal network is underscored by the fact that over 120 mutations of the human DES gene cause hereditary and sporadic myopathies and cardiomyopathies. A subgroup of human desminopathies comprises autosomal recessive cases resulting in the complete abolition of desmin protein. In these patients, who display a more severe phenotype than the autosomal dominant cases, it has been reported that some individuals also suffer from a myasthenic syndrome in addition to the classical occurrence of myopathy and cardiomyopathy. Since further studies on the NMJ pathology are hampered by the lack of available human striated muscle biopsy specimens, we exploited homozygous desmin knock-out mice which closely mirror the striated muscle pathology of human patients lacking desmin protein. Here, we report on the impact of the lack of desmin on the structure and function of NMJs and the transcription of genes coding for postsynaptic proteins. Desmin knock-out mice display a fragmentation of NMJs in soleus, but not in the extensor digitorum longus muscle. Moreover, soleus muscle fibers show larger NMJs. Further, transcription levels of acetylcholine receptor (AChR) genes are increased in muscles from desmin knock-out mice, especially of the AChRγ subunit, which is known as a marker of muscle fiber regeneration. Electrophysiological recordings depicted a pathological decrement of nerve-dependent endplate potentials and an increased rise time of the nerve-independent miniature endplate potentials. The latter appears related to the fragmentation of NMJs in desmin knockout mice. Our study highlights the essential role of desmin for the structural and functional integrity of mammalian NMJs.

Characterization of Differences in the Time Course of Reflex and Voluntary Responses Following Botulinum Toxin Injections in Chronic Stroke Survivors

Spasticity is a major impairment that can occur following a hemispheric stroke and is often treated with injections of botulinum toxin, a neurotoxin that impairs transmission at the neuromuscular junction. Hyperreflexia is a defining feature of spasticity. Our main objective here was to quantify the time course of changes in the deep tendon reflex (DTR) responses and voluntary activation capacity following BT injection as well as to track changes in a clinical assessment of spasticity. Four chronic stroke survivors, scheduled to receive BT in their Biceps Brachii(BB) as part of their clinical care plan, were recruited for repeated testing sessions over the course of 4 months post injection. Both surface BB EMG reflex response to bicipital tendon taps as well as signals of applied tendon tap forces were recorded before and up to 18 weeks post-BT. Voluntary force and biceps EMG signals were also recorded during maximum voluntary (isometric) contractions (MVC) at each testing session. Our results show major reductions (up to 75%) in voluntary sEMG and force arising between 11 to 35 days post-BT-injection. The stretch reflex gain declined two weeks after the maximal reductions in voluntary EMG and force. Paradoxically, there was a short-term increase in stretch reflex gain, in three out of four participants, approximately 11-35 days post BT. The time course of recovery of voluntary MVC and reflex responses varied considerably with a longer recovery time for the reflex responses.

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

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

Pharyngeal Motility Before and After Thyroarytenoid Muscle Botulinum Toxin Injection

Botulinum toxin type A (BTA) injection in intrinsic laryngeal musculature may result in dysphagia and consequent loss of quality of life (QOL) in a percentage of patients. This study aims to evaluate pharyngeal motility as a putative cause for this change in swallow quality in light of high-resolution manometry (HRM). Twenty patients (95% females, median age 66 years) underwent high-resolution manometry before and after BTA injection. Dysphagia was evaluated based on a QOL dedicated questionnaire (SWAL-QOL) before and after BTA injection. Pharyngeal motility at the topography of the vellum, epiglottis, and upper esophageal sphincter (UES) were recorded. Eleven (55%) subjects had worsened QOL after BTA injection. In patients with worsened QOL, UES extension decreased (p = 0.005), UES residual pressure increased (p = 0.02), UES basal pressure decreased (p = 0.04), and velopharynx contraction duration decreased (p = 0.04). UES residual pressure increased (p = 0.01), velopharynx peak pressure (p = 0.04) and upstroke (p = 0.007) decreased in patients with maintained QOL. There was no difference between groups when comparing pre-injection values. UES extension (p = 0.01) and UES maximum relaxation time (p = 0.03) was lower in the group with worsened QOL after BTA as compared to no change in QOL. Pharyngeal motility as measured by HRM was not a predictor for post procedure dysphagia and the changes in motility after BTA injection does not seem to be a strong contributor to dysphagia.

The Botulinum Treatment of Neurogenic Detrusor Overactivity: The Double-Face of the Neurotoxin

Botulinum neurotoxin (BoNT) can counteract the highly frequent involuntary muscle contractions and the uncontrolled micturition events that characterize the neurogenic detrusor overactivity (NDO) due to supra-sacral spinal cord lesions. The ability of the toxin to block the neurotransmitter vesicular release causes the reduction of contractions and improves the compliance of the muscle and the bladder filling. BoNT is the second-choice treatment for NDO once the anti-muscarinic drugs have lost their effects. However, the toxin shows a time-dependent efficacy reduction up to a complete loss of activity. The cellular mechanisms responsible for BoNT effects exhaustion are not yet completely defined. Similarly, also the sites of its action are still under identification. A growing amount of data suggest that BoNT, beyond the effects on the efferent terminals, would act on the sensory system recently described in the bladder mucosa. The specimens from NDO patients no longer responding to BoNT treatment displayed a significant increase of the afferent terminals, likely excitatory, and signs of a chronic neurogenic inflammation in the mucosa. In summary, beyond the undoubted benefits in ameliorating the NDO symptomatology, BoNT treatment might bring to alterations in the bladder sensory system able to shorten its own effectiveness.

Loss of Protein Kinase Csnk2b/CK2β at Neuromuscular Junctions Affects Morphology and Dynamics of Aggregated Nicotinic Acetylcholine Receptors, Neuromuscular Transmission, and Synaptic Gene Expression

The protein kinase Csnk2/CK2 is important for cell proliferation, differentiation, and survival. Previously, we showed that CK2 binds distinctive proteins at neuromuscular junctions (NMJs) of mice and phosphorylates some of them. CK2 likely stabilizes clustered nicotinic acetylcholine receptors (AChRs). In the absence of the β-subunit of CK2 in skeletal muscle fibers, mice develop an age-dependent decrease of grip strength accompanied by NMJ fragmentation and impairments of neuromuscular transmission. However, the precise role of CK2β regarding the clustering of AChRs and downstream signaling at NMJs is unknown. Here, we compared conditional CK2β-deficient mice with controls and found in the mutants (1) a lower decrement of endplate potentials after repetitive stimulation and decrements of nerve-evoked compound muscle action potentials decayed more rapidly after synaptic transmission was partially blocked, (2) that their muscle weakness was partially rescued by administration of an acetylcholine esterase inhibitor, (3) fragmented NMJs and impaired AChR clustering was detected in muscles and cultured muscle cells, (4) enlarged myonuclei, (5) impaired synaptic gene expression, and (6) a high turnover rate of their AChR clusters in vivo. Altogether, our data demonstrate a role for CK2 at the NMJ by maintaining a high density of AChRs and ensuring physiological synaptic gene expression.

'Fragmentation' of NMJs: a sign of degeneration or regeneration? A long journey with many junctions

Mammalian neuromuscular junctions (NMJs) often consist of curved bands of synaptic contact, about 3-6 μm wide, which resemble pretzels. This contrasts with the NMJs of most animal species which consist of a cluster of separate synaptic spots, each of which is also about 3-6 μm across. In a number of situations, including a variety of disease states as well as normal ageing, mammalian NMJs acquire a more 'fragmented' appearance that resembles somewhat that of other species. This 'fragmentation' of the NMJ has sometimes been interpreted as a 'disintegration' or 'degeneration', with the suggestion that it might be associated with impaired neuromuscular transmission. An alternative view is that NMJ fragmentation is the outcome of a normal process by which the NMJ is maintained in an effective state. In this highly personal commentary, I cite a number of examples of this and point out that although the 'pretzel' form arises during normal development as a result of the sculpting of an immature synaptic 'plaque', in virtually all situations where new synaptic contact is established in adult mammals this occurs by the addition of new synaptic 'spots' rather than by the extension, or neoformation, of 'pretzels'. Further, where appropriate studies have been performed, no evidence of a correlation between the degree of fragmentation and the efficacy of transmission has emerged. It may therefore be more appropriate to consider NMJ 'fragmentation' as a form of regeneration, rather than of degeneration. This article is part of a Special Issue entitled: Honoring Ricardo Miledi - outstanding neuroscientist of XX-XXI centuries.

Effects of Repeated Eyelid Injections with Botulinum Toxin A on Innervation of Treated Muscles in Patients with Blepharospasm

PURPOSE

To assess changes in innervation and muscle morphology after repeated botulinum toxin A injections in subjects with benign essential blepharospasm.

METHODS

Surgical waste specimens were processed for histologic examination of nerve fibers, neuromuscular junctions, fiber size, and central nucleation and compared to age matched controls and to two subjects with blepharospasm that had not received botulinum toxin A injections.

RESULTS

There was a significant increase in amount of nerve fibers and numbers of neuromuscular junctions in the orbicularis oculi muscles from subjects with blepharospasm treated repetitively with botulinum toxin A. In addition there was a significant decrease in mean muscle fiber cross-sectional area and an increase in central nucleation. The specimens from the subjects with only blepharospasm had the same density of nerves but had intermediate levels of neuromuscular junctions.

CONCLUSIONS

These data suggest that repeated injections of botulinum toxin A has an effect on nerve and neuromuscular junction numbers, which are partly mirrored in orbicularis oculi muscle from subjects with blepharospasm only. These studies suggest the potential for modulating these changes in order to extend the duration of effectiveness of botulinum toxin.

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

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

Collagen VI is required for the structural and functional integrity of the neuromuscular junction

The synaptic cleft of the neuromuscular junction (NMJ) consists of a highly specialized extracellular matrix (ECM) involved in synapse maturation, in the juxtaposition of pre- to post-synaptic areas, and in ensuring proper synaptic transmission. Key components of synaptic ECM, such as collagen IV, perlecan and biglycan, are binding partners of one of the most abundant ECM protein of skeletal muscle, collagen VI (ColVI), previously never linked to NMJ. Here, we demonstrate that ColVI is itself a component of this specialized ECM and that it is required for the structural and functional integrity of NMJs. In vivo, ColVI deficiency causes fragmentation of acetylcholine receptor (AChR) clusters, with abnormal expression of NMJ-enriched proteins and re-expression of fetal AChRγ subunit, both in Col6a1 null mice and in patients affected by Ullrich congenital muscular dystrophy (UCMD), the most severe form of ColVI-related myopathies. Ex vivo muscle preparations from ColVI null mice revealed altered neuromuscular transmission, with electrophysiological defects and decreased safety factor (i.e., the excess current generated in response to a nerve impulse over that required to reach the action potential threshold). Moreover, in vitro studies in differentiated C2C12 myotubes showed the ability of ColVI to induce AChR clustering and synaptic gene expression. These findings reveal a novel role for ColVI at the NMJ and point to the involvement of NMJ defects in the etiopathology of ColVI-related myopathies.

Motoneuron Wnts regulate neuromuscular junction development

The neuromuscular junction (NMJ) is a synapse between motoneurons and skeletal muscles to control motor behavior. Unlike extensively investigated postsynaptic differentiation, less is known about mechanisms of presynaptic assembly. Genetic evidence of Wnt in mammalian NMJ development was missing due to the existence of multiple Wnts and their receptors. We show when Wnt secretion is abolished from motoneurons by mutating the Wnt ligand secretion mediator (Wls) gene, mutant mice showed muscle weakness and neurotransmission impairment. NMJs were unstable with reduced synaptic junctional folds and fragmented AChR clusters. Nerve terminals were swollen; synaptic vesicles were fewer and mislocated. The presynaptic deficits occurred earlier than postsynaptic deficits. Intriguingly, these phenotypes were not observed when deleting Wls in muscles or Schwann cells. We identified Wnt7A and Wnt7B as major Wnts for nerve terminal development in rescue experiments. These observations demonstrate a necessary role of motoneuron Wnts in NMJ development, in particular presynaptic differentiation.

Botulinum neurotoxin formulations: overcoming the confusion

Botulinum toxin A is produced by anaerobic spore-forming bacteria and is used for various therapeutic and cosmetic purposes. Botulinum toxin A injections are the most popular nonsurgical procedure worldwide. Despite an increased demand for botulinum toxin A injections, the clinical pharmacology and differences in formulation of commonly available products are poorly understood. The various products available in the market are unique and vary in terms of units, chemical properties, biological activities, and weight, and are therefore not interchangeable. For safe clinical practice and to achieve optimal results, the practitioners need to understand the clinical issues of potency, conversion ratio, and safety issues (toxin spread and immunogenicity). In this paper, the basic clinical pharmacology of botulinum toxin A and differences between onabotulinum toxin A, abobotulinum toxin A, and incobotulinum toxin A are discussed.

In mammalian skeletal muscle, phosphorylation of TOMM22 by protein kinase CSNK2/CK2 controls mitophagy

In yeast, Tom22, the central component of the TOMM (translocase of outer mitochondrial membrane) receptor complex, is responsible for the recognition and translocation of synthesized mitochondrial precursor proteins, and its protein kinase CK2-dependent phosphorylation is mandatory for TOMM complex biogenesis and proper mitochondrial protein import. In mammals, the biological function of protein kinase CSNK2/CK2 remains vastly elusive and it is unknown whether CSNK2-dependent phosphorylation of TOMM protein subunits has a similar role as that in yeast. To address this issue, we used a skeletal muscle-specific Csnk2b/Ck2β-conditional knockout (cKO) mouse model. Phenotypically, these skeletal muscle Csnk2b cKO mice showed reduced muscle strength and abnormal metabolic activity of mainly oxidative muscle fibers, which point towards mitochondrial dysfunction. Enzymatically, active muscle lysates from skeletal muscle Csnk2b cKO mice phosphorylate murine TOMM22, the mammalian ortholog of yeast Tom22, to a lower extent than lysates prepared from controls. Mechanistically, CSNK2-mediated phosphorylation of TOMM22 changes its binding affinity for mitochondrial precursor proteins. However, in contrast to yeast, mitochondrial protein import seems not to be affected in vitro using mitochondria isolated from muscles of skeletal muscle Csnk2b cKO mice. PINK1, a mitochondrial health sensor that undergoes constitutive import under physiological conditions, accumulates within skeletal muscle Csnk2b cKO fibers and labels abnormal mitochondria for removal by mitophagy as demonstrated by the appearance of mitochondria-containing autophagosomes through electron microscopy. Mitophagy can be normalized by either introduction of a phosphomimetic TOMM22 mutant in cultured myotubes, or by in vivo electroporation of phosphomimetic Tomm22 into muscles of mice. Importantly, transfection of the phosphomimetic Tomm22 mutant in muscle cells with ablated Csnk2b restored their oxygen consumption rate comparable to wild-type levels. In sum, our data show that mammalian CSNK2-dependent phosphorylation of TOMM22 is a critical switch for mitophagy and reveal CSNK2-dependent physiological implications on metabolism, muscle integrity and behavior.

Age-related changes in the structure and function of mammalian neuromuscular junctions

As mammals age, their neuromuscular junctions (NMJs) change their form, with an increasingly complex system of axonal branches innervating increasingly fragmented regions of postsynaptic differentiation. It has been suggested that this remodeling is associated with impairment of neuromuscular transmission and that this contributes to age-related muscle weakness in mammals, including humans. Here, we review previous work on NMJ aging, most of which has focused on either structure or function, as well as a new study aimed at seeking correlation between the structure and function of individual NMJs. While it is clear that extensive structural changes occur as part of the aging process, it is much less certain how, if at all, these are correlated with an impairment of function. This leaves open the question of whether loss of NMJ function is a significant cause of age-related muscle weakness.

The Use of Botulinum Neurotoxin Type A in Aesthetics: Key Clinical Postulates

BACKGROUND

The most common aesthetic procedure performed worldwide is the injection of botulinum neurotoxin Type A (BoNT-A). Aesthetic providers must fully comprehend the objective scientific data, theoretical mechanisms of action, and differences between brands of BoNT-A.

OBJECTIVE

To determine and review the relevant clinical postulates for the use of botulinum toxin in aesthetics.

MATERIALS AND METHODS

The BoNT-A clinical postulates presented here discuss how each brand of BoNT-A acts identically, how the molecular potency may vary between the different products, how patient age, gender, genetics, and muscle mass cause variation in toxin receptor number and density, and how both practitioner and patient can affect toxin distribution.

RESULTS

A total of 8 clinical postulates have been identified that are key to understanding the use of botulinum toxin in aesthetics and to obtaining the best clinical results.

CONCLUSION

All of these factors affect the potential efficacy of the injected toxin and hence the aesthetic results obtained.

The Structure of Human Neuromuscular Junctions: Some Unanswered Molecular Questions

The commands that control animal movement are transmitted from motor neurons to their target muscle cells at the neuromuscular junctions (NMJs). The NMJs contain many protein species whose role in transmission depends not only on their inherent properties, but also on how they are distributed within the complex structure of the motor nerve terminal and the postsynaptic muscle membrane. These molecules mediate evoked chemical transmitter release from the nerve and the action of that transmitter on the muscle. Human NMJs are among the smallest known and release the smallest number of transmitter "quanta". By contrast, they have the most deeply infolded postsynaptic membranes, which help to amplify transmitter action. The same structural features that distinguish human NMJs make them particularly susceptible to pathological processes. While much has been learned about the molecules which mediate transmitter release and action, little is known about the molecular processes that control the growth of the cellular and subcellular components of the NMJ so as to give rise to its mature form. A major challenge for molecular biologists is to understand the molecular basis for the development and maintenance of functionally important aspects of NMJ structure, and thereby to point to new directions for treatment of diseases in which neuromuscular transmission is impaired.

The binding of botulinum neurotoxins to different peripheral neurons

Botulinum neurotoxins are the most potent toxins known. The double receptor binding modality represents one of the most significant properties of botulinum neurotoxins and largely accounts for their incredible potency and lethality. Despite the high affinity and the very specific binding, botulinum neurotoxins are versatile and multi-tasking toxins. Indeed they are able to act both at the somatic and at the autonomic nervous system. In spite of the preference for cholinergic nerve terminals botulinum neurotoxins have been shown to inhibit to some extent also the noradrenergic postganglionic sympathetic nerve terminals and the afferent nerve terminals of the sensory neurons inhibiting the release of neuropeptides and glutamate, which are responsible of nociception. Therefore, there is increasing evidence that the therapeutic effect in both motor and autonomic disorders is based on a complex mode of botulinum neurotoxin action modulating the activity of efferent as well as afferent nerve fibres.

Botulinum neurotoxin A promotes functional recovery after peripheral nerve injury by increasing regeneration of myelinated fibers

The injection of safe doses of botulinum neurotoxin A (BoNT/A) have been reported to be useful for the treatment of neuropathic pain, but it is still unknown how functional recovery is induced after peripheral nerve injury. We evaluated the effects of intranerve application of BoNT/A, on regeneration and sensorimotor functional recovery in partial and complete peripheral nerve injuries in the mouse. After sciatic nerve crush (SNC) and intranerve delivery of BoNT/A (15pg), axonal regeneration was measured by nerve pinch test at different days. Regeneration of myelinated and unmyelinated fibers was assessed by immunohistochemical double labeling for NF200/GAP43 and CGRP/GAP43. S100 was used as Schwann cells marker. Medial footpad skin reinnervation was assessed by PGP staining. Motor functions were assessed by means of nerve conduction tests. In other mice groups, nerve conduction tests were performed also after chronic constriction injury (CCI) of the sciatic nerve and intraplantar injection of BoNT/A (15pg). In SNC mice, BoNT/A increased the rate of axonal regeneration. The advantage of regrowing myelinated axons after BoNT/A injection was evidenced by longer NF200+ nerve profiles and confirmed by nerve histology. We observed also a higher expression of S100 in the distal portion of BoNT/A-injected regenerated nerves. In CCI mice, BoNT/A induced an increase in reinnervation of gastrocnemius and plantar muscles. These results show that a low dose of BoNT/A, insufficient to produce muscular dysfunction, conversely speeds up sensorimotor recovery by stimulating myelinated axonal regeneration, and points out its application as a multipotent treatment for peripheral neuropathies.

Botulinum Neurotoxins: Biology, Pharmacology, and Toxicology

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

Key Parameters for the Use of AbobotulinumtoxinA in Aesthetics: Onset and Duration

Time to onset of response and duration of response are key measures of botulinum toxin efficacy that have a considerable influence on patient satisfaction with aesthetic treatment. However, there is no overall accepted definition of efficacy for aesthetic uses of botulinumtoxinA (BoNT-A). Mechanical methods of assessment do not lend themselves to clinical practice and clinicians rely instead on assessment scales such as the Frontalis Activity Measurement Standard, Frontalis Rating Scale, Wrinkle Severity Scale, and Subject Global Assessment Scale, but not all of these have been fully validated. Onset of activity is typically seen within 5 days of injection, but has also been recorded within 12 hours with abobotulinumtoxinA. Duration of effect is more variable, and is influenced by parameters such as muscle mass (including the effects of age and sex) and type of product used. Even when larger muscles are treated with higher doses of BoNT-A, the duration of effect is still shorter than that for smaller muscles. Muscle injection technique, including dilution of the toxin, the volume of solution injected, and the positioning of the injections, can also have an important influence on onset and duration of activity. Comparison of the efficacy of different forms of BoNT-A must be made with the full understanding that the dosing units are not equivalent. Range of equivalence studies for abobotulinumtoxinA (Azzalure; Ipsen Limited, Slough UK/Galderma, Lausanne CH/Dysport, Ipsen Biopharm Limited, Wrexham UK/Galderma LP, Fort Worth, TX) and onabotulinumtoxinA (Botox; Allergan, Parsippany, NJ) have been conducted, and results indicate that the number of units of abobotulinumtoxinA needs to be approximately twice as high as that of onabotulinumtoxinA to achieve the same effect. An appreciation of the potential influence of all of the parameters that influence onset and duration of activity of BoNT-A, along with a thorough understanding of the anatomy of the face and potency of doses, are essential to tailoring treatment to individual patient needs and expectations.

Expression of a Mutant SEMA3A Protein with Diminished Signalling Capacity Does Not Alter ALS-Related Motor Decline, or Confer Changes in NMJ Plasticity after BotoxA-Induced Paralysis of Male Gastrocnemic Muscle

Terminal Schwann cells (TSCs) are specialized cells that envelop the motor nerve terminal, and play a role in the maintenance and regeneration of neuromuscular junctions (NMJs). The chemorepulsive protein semaphorin 3A (SEMA3A) is selectively up-regulated in TSCs on fast-fatigable muscle fibers following experimental denervation of the muscle (BotoxA-induced paralysis or crush injury to the sciatic nerve) or in the motor neuron disease amyotrophic lateral sclerosis (ALS). Re-expression of SEMA3A in this subset of TSCs is thought to play a role in the selective plasticity of nerve terminals as observed in ALS and following BotoxA-induced paralysis. Using a mouse model expressing a mutant SEMA3A with diminished signaling capacity, we studied the influence of SEMA3A signaling at the NMJ with two denervation paradigms; a motor neuron disease model (the G93A-hSOD1 ALS mouse line) and an injury model (BotoxA-induced paralysis). ALS mice that either expressed 1 or 2 mutant SEMA3A alleles demonstrated no difference in ALS-induced decline in motor behavior. We also investigated the effects of BotoxA-induced paralysis on the sprouting capacity of NMJs in the K108N-SEMA3A mutant mouse, and observed no change in the differential neuronal plasticity found at NMJs on fast-fatigable or slow muscle fibers due to the presence of the SEMA3A mutant protein. Our data may be explained by the residual repulsive activity of the mutant SEMA3A, or it may imply that SEMA3A alone is not a key component of the molecular signature affecting NMJ plasticity in ALS or BotoxA-induced paralysis. Interestingly, we did observe a sex difference in motor neuron sprouting behavior after BotoxA-induced paralysis in WT mice which we speculate may be an important factor in the sex dimorphic differences seen in ALS.

LAP proteins are localized at the post-synaptic membrane of neuromuscular junctions and appear to modulate synaptic morphology and transmission

Erbin, Lano, Scribble, and Densin-180 belong to LAP (leucine-rich repeats and PDZ domain) adaptor proteins involved in cell signaling pathways. Previously, we identified Erbin, Lano, and Scribble, but not Densin-180, in muscle cells, where they are involved in regulating the aggregation of nicotinic acetylcholine receptors in vitro. Here, we analyzed their cellular localization at the neuromuscular junction (NMJ) in skeletal muscles of mice. Erbin, Lano, and Scribble were significantly accumulated at NMJs and localized in different synaptic cells. Moreover, we used mouse mutants to analyze the role of Erbin at the NMJ. We used two Erbin mutant mouse strains that either completely lack Erbin protein (Erbin^null/null ) or express a truncated Erbin mutant where the carboxy-terminal PDZ domain is replaced by β-galactosidase (Erbin^ΔC/ΔC ) thereby abolishing its interaction with ErbB receptor tyrosine kinases. Neither the lack of the PDZ domain of Erbin, nor its complete absence interfered with the general localization of LAP proteins at NMJs, but Lano and Scribble transcript levels were up-regulated in homozygous Erbin-null muscles. Furthermore, grip strength was reduced and neural transmission impaired in homozygous aged Erbin-null but not Erbin-ΔC mice. Erbin-null skeletal muscles did not reveal any conspicuous impairment of the muscle fiber. Localization of other NMJ marker proteins was not affected either. Quantitative 3D morphometry showed that NMJs of Erbin-null muscles were significantly smaller and fragmented in the soleus. We speculate that Erbin, Lano, and Scribble act at the post-synaptic membrane of NMJs in a concerted fashion to regulate nicotinic acetylcholine receptors cluster morphology and neural transmission. Cover Image for this issue: doi: 10.1111/jnc.13340.

Age-related fragmentation of the motor endplate is not associated with impaired neuromuscular transmission in the mouse diaphragm

As mammals age, their neuromuscular junctions (NMJs) gradually change their form, acquiring an increasingly fragmented appearance consisting of numerous isolated regions of synaptic differentiation. It has been suggested that this remodelling is associated with impairment of neuromuscular transmission, and that this contributes to age-related muscle weakness in mammals, including humans. The underlying hypothesis, that increasing NMJ fragmentation is associated with impaired transmission, has never been directly tested. Here, by comparing the structure and function of individual NMJs, we show that neuromuscular transmission at the most highly fragmented NMJs in the diaphragms of old (26-28 months) mice is, if anything, stronger than in middle-aged (12-14 months) mice. We suggest that NMJ fragmentation per se is not a reliable indicator of impaired neuromuscular transmission.

Altered short-term synaptic plasticity and reduced muscle strength in mice with impaired regulation of presynaptic CaV2.1 Ca2+ channels

Facilitation and inactivation of P/Q-type calcium (Ca(2+)) currents through the regulation of voltage-gated Ca(2+) (CaV) 2.1 channels by Ca(2+) sensor (CaS) proteins contributes to the facilitation and rapid depression of synaptic transmission in cultured neurons that transiently express CaV2.1 channels. To examine the modulation of endogenous CaV2.1 channels by CaS proteins in native synapses, we introduced a mutation (IM-AA) into the CaS protein-binding site in the C-terminal domain of CaV2.1 channels in mice, and tested synaptic facilitation and depression in neuromuscular junction synapses that use exclusively CaV2.1 channels for Ca(2+) entry that triggers synaptic transmission. Even though basal synaptic transmission was unaltered in the neuromuscular synapses in IM-AA mice, we found reduced short-term facilitation in response to paired stimuli at short interstimulus intervals in IM-AA synapses. In response to trains of action potentials, we found increased facilitation at lower frequencies (10-30 Hz) in IM-AA synapses accompanied by slowed synaptic depression, whereas synaptic facilitation was reduced at high stimulus frequencies (50-100 Hz) that would induce strong muscle contraction. As a consequence of altered regulation of CaV2.1 channels, the hindlimb tibialis anterior muscle in IM-AA mice exhibited reduced peak force in response to 50 Hz stimulation and increased muscle fatigue. The IM-AA mice also had impaired motor control, exercise capacity, and grip strength. Taken together, our results indicate that regulation of CaV2.1 channels by CaS proteins is essential for normal synaptic plasticity at the neuromuscular junction and for muscle strength, endurance, and motor coordination in mice in vivo.