Botulinum neurotoxin for pain management: insights from animal models

Botulinum neurotoxin serotype A inhibited ocular angiogenesis through modulating glial activation via SOCS3

BACKGROUND

Pathological angiogenesis causes significant vision loss in neovascular age-related macular degeneration and other retinopathies with neovascularization (NV). Neuronal/glial-vascular interactions influence the release of angiogenic and neurotrophic factors. We hypothesized that botulinum neurotoxin serotype A (BoNT/A) modulates pathological endothelial cell proliferation through glial cell activation and growth factor release.

METHODS

A laser-induced choroidal NV (CNV) was employed to investigate the anti-angiogenic effects of BoNT/A. Fundus fluorescence angiography, immunohistochemistry, and real-time PCR were used to assess BoNT/A efficacy in inhibiting CNV and the molecular mechanisms underlying this inhibition. Neuronal and glial suppressor of cytokine signaling 3 (SOCS3) deficient mice were used to investigate the molecular mechanisms of BoNT/A in inhibiting CNV via SOCS3.

FINDINGS

In laser-induced CNV mice with intravitreal BoNT/A treatment, CNV lesions decreased > 30%; vascular leakage and retinal glial activation were suppressed; and Socs3 mRNA expression was induced while vascular endothelial growth factor A (Vegfa) mRNA expression was suppressed. The protective effects of BoNT/A on CNV development were diminished in mice lacking neuronal/glial SOCS3.

CONCLUSION

BoNT/A suppressed laser-induced CNV and glial cell activation, in part through SOCS3 induction in neuronal/glial cells. BoNT/A treatment led to a decrease of pro-angiogenic factors, including VEGFA, highlighting the potential of BoNT/A as a therapeutic intervention for pathological angiogenesis in retinopathies.

Pain, disability, and quality of life in participants after concurrent onabotulinumtoxinA treatment of upper and lower limb spasticity: Observational results from the ASPIRE study

INTRODUCTION

Upper and lower limb spasticity is commonly associated with central nervous system disorders including stroke, traumatic brain injury, multiple sclerosis, cerebral palsy, and spinal cord injury, but little is known about the concurrent treatment of upper and lower limb spasticity with botulinum toxins.

OBJECTIVE

To evaluate onabotulinumtoxinA (onabotA) utilization and to determine if concurrent onabotA treatment of the upper and lower limbs has supported improvements in participants with spasticity.

DESIGN

Sub-analysis of a 2-year, international, prospective, observational registry (ASPIRE, NCT01930786).

SETTING

International clinic sites (54).

PARTICIPANTS

Adult spasticity participants across etiologies, who received ≥1 concurrent onabotA treatment of the upper and lower limbs during the study.

INTERVENTION

Participants were treated with onabotA at the clinician's discretion.

OUTCOMES

Baseline characteristics and outcomes of disability (Disability Assessment Scale [DAS]), pain (Numeric Pain Rating Scale [NPRS]), participant satisfaction, physician satisfaction, and quality of life (QoL; Spasticity Impact Assessment [SIA]) were evaluated. Adverse events were monitored throughout the study.

RESULTS

Of 744 participants enrolled, 730 received ≥1 dose of onabotA; 275 participants received treatment with onabotA in both upper and lower limbs during ≥1 session; 39.3% of participants were naïve to onabotA for spasticity. The mean (SD) total dose per treatment session ranged from 421.2 (195.3) to 499.6 (188.6) U. The most common baseline upper limb presentation was clenched fist (n = 194, 70.5%); lower limb was equinovarus foot (n = 219, 66.9%). High physician and participant satisfaction and improvements in pain, disability and QoL were reported after most treatments. Nine participants (3.3%) reported nine treatment-related adverse events; two participants (0.7%) reported three serious treatment-related severe adverse events. No new safety signals were identified.

CONCLUSION

More than a third of enrolled participants received at least one concurrent onabotA treatment of the upper and lower limbs, with reduced pain, disability, and improved QoL after treatment, consistent with the established safety profile of onabotA for the treatment of spasticity.

The Complex Role of Botulinum Toxin in Enhancing Goal Achievement for Post-Stroke Patients

INTRODUCTION

The rehabilitation medical team is responsible for the therapeutic management of post-stroke patients and, therefore, for the complex therapeutic approach of spasticity. Considering the generous arsenal at our disposal in terms of both pharmacological treatment, through the possibility of administering botulinum toxin to combat spasticity, and in terms of accurate assessment through developed functional scales such as the GAS (Goal Attainment Scale), one of our purposes is to monitor the parameters that influence the achievement of functional goals set by patients together with the medical team in order to render the patients as close as possible to achieving their proposed functional goals, thus enhancing their quality of life. By assessing and establishing statistical and clinical correlations between the GAS and quantifiable parameters related to the affected post-stroke upper limb, namely degree of spasticity, motor control, pain level and evolution of pain under treatment with BoNT-A (abobotulinum toxin A), and patients' overall response to BoNT-A treatment, we aim to quantify the improvement of the therapeutic management of post-stroke patients with spasticity and develop a more personalized and effective approach to their disability and impairment.

RESULTS AND DISCUSSIONS

The analysis concluded that there were two independent predictors of the Achieved GAS-T score (the study's endpoint parameter) motor control at any level of the upper limb and number of prior BoNT-A injections. The number of prior BoNT-A injections was an independent predictor of Achieved GAS-T score improvement but had no significant influence over Baseline GAS-T score. Enhancement in proximal and intermediate motor control showed a GAS score improvement of 3.3 points and a 0.93-point GAS score improvement for wrist motor control progress. From a separate viewpoint, patients with motor deficit on the left side have shown significantly greater improvement in Changed GAS-T scores by 2.5 points compared to patients with deficits on the right side; however, we note as a study limitation the fact that there was no statistical analysis over the dominant cerebral hemisphere of each patient.

CONCLUSIONS

Improvement in the Achieved GAS-T score means better achievement of patients' goals. Thus, after the BoNT- A intervention, at follow-up evaluation, GAS was found to be directly correlated with improvement in motor control of the affected upper limb. Mobility of the corresponding limb was enhanced by pain decrease during p-ROM (passive range of motion) and by amelioration of spasticity.

MATERIALS AND METHODS

We conducted an observational, non-randomized clinical study on 52 stroke patients, a representative sample of patients with post-stroke spasticity and disability from our neurological rehabilitation clinic, who have been treated and undergone a specific rehabilitation program in our tertiary diagnostic and treatment medical center, including BoNT-A focal treatment for spasticity in the affected upper limb. The primary objective of the study was to assess the influence of abobotulinum toxin A treatment on the Goal Attainment Scale. Secondary objectives of the study included the assessment of BoNT-A treatment efficacy on spasticity with the MAS (Modified Ashworth Scale), pain with the NRS (Numerical Rating Scale), and joint passive range of motion (p-ROM), identifying demographic, clinical, and pharmacological factors that influence the response to BoNT-A treatment, as well as to conduct a descriptive and exploratory analysis of the studied variables.

Botulinum toxin therapy for management of phantom and residual limb pain following amputation: A systematic review

Chronic pain following amputation is debilitating. Due to its mechanisms in modulating muscle contraction and pain, botulinum toxin has been investigated as a treatment option for phantom limb pain (PLP) and residual limb pain (RLP). The objective of this study was to determine the efficacy of botulinum toxin injection in the management of PLP and RLP following major limb amputation using a systematic review of the literature. The databases Medline, CINAHL, EMBASE, Scopus, Web of Science, and Cochrane were searched from inception through October 30, 2023. The search identified 50 articles; 37 underwent full-text review, and 11 were included in the final review. Eighty-nine individuals with pain were investigated by the included studies; 53 had RLP and 63 had PLP. There was significant variation in botulinum toxin type, injection method, and dosage. Twenty-one (53.9%) and 27 (64.3%) participants had improvement in PLP and RLP following botulinum toxin injection, respectively. Therefore, there is potential for use of botulinum toxin for the treatment of PLP and RLP. However, due to the minimal number of studies, small sample sizes, and heterogenous methodologies, our ability to conclude with certainty the efficacy of botulinum toxin injection on the treatment of PLP and RLP following amputation is limited.

Comparison of the Effects of Botulinum Toxin Doses on Nerve Regeneration in Rats with Experimentally Induced Sciatic Nerve Injury

This study was designed to compare the effects of various doses of botulinum neurotoxin A (BoNT/A) on nerve regeneration. Sixty-five six-week-old rats with sciatic nerve injury were randomly allocated to three experimental groups, a control group, and a sham group. The experimental groups received a single session of intraneural BoNT/A (3.5, 7.0, or 14 U/kg) injection immediately after nerve-crushing injury. The control group received normal intraneural saline injections after sciatic nerve injury. At three, six, and nine weeks after nerve damage, immunofluorescence staining, an ELISA, and toluidine blue staining was used to evaluate the regenerated nerves. Serial sciatic functional index analyses and electrophysiological tests were performed every week for nine weeks. A higher expression of GFAP, S100β, GAP43, NF200, BDNF, and NGF was seen in the 3.5 U/kg and 7.0 U/kg BoNT/A groups. The average area and myelin thickness were significantly greater in the 3.5 U/kg and 7.0 U/kg BoNT/A groups. The sciatic functional index and compound muscle action potential amplitudes exhibited similar trends. These findings indicate that the 3.5 U/kg and 7.0 U/kg BoNT/A groups exhibited better nerve regeneration than the 14 U/kg BoNT/A and control group. As the 3.5 U/kg and the 7.0 U/kg BoNT/A groups exhibited no statistical difference, we recommend using 3.5 U/kg BoNT/A for its cost-effectiveness.

Increasing the Passive Range of Joint Motion in Stroke Patients Using Botulinum Toxin: The Role of Pain Relief

By blocking the release of neurotransmitters, botulinum toxin A (BoNT-A) is an effective treatment for muscle over-activity and pain in stroke patients. BoNT-A has also been reported to increase passive range of motion (p-ROM), the decrease of which is mainly due to muscle shortening (i.e., muscle contracture). Although the mechanism of action of BoNT-A on p-ROM is far from understood, pain relief may be hypothesized to play a role. To test this hypothesis, a retrospective investigation of p-ROM and pain was conducted in post-stroke patients treated with BoNT-A for upper limb hypertonia. Among 70 stroke patients enrolled in the study, muscle tone (Modified Ashworth Scale), pathological postures, p-ROM, and pain during p-ROM assessment (Numeric Rating Scale, NRS) were investigated in elbow flexors (48 patients) and in finger flexors (64 patients), just before and 3-6 weeks after BoNT-A treatment. Before BoNT-A treatment, pathological postures of elbow flexion were found in all patients but one. A decreased elbow p-ROM was found in 18 patients (38%). Patients with decreased p-ROM had higher pain-NRS scores (5.08 ± 1.96, with a pain score ≥8 in 11% of cases) than patients with normal p-ROM (0.57 ± 1.36) (p < 0.001). Similarly, pathological postures of finger flexion were found in all patients but two. A decreased finger p-ROM was found in 14 patients (22%). Pain was more intense in the 14 patients with decreased p-ROM (8.43 ± 1.74, with a pain score ≥ 8 in 86% of cases) than in the 50 patients with normal p-ROM (0.98 ± 1.89) (p < 0.001). After BoNT-A treatment, muscle tone, pathological postures, and pain decreased in both elbow and finger flexors. In contrast, p-ROM increased only in finger flexors. The study discusses that pain plays a pivotal role in the increase in p-ROM observed after BoNT-A treatment.

Xeomin®, a Commercial Formulation of Botulinum Neurotoxin Type A, Promotes Regeneration in a Preclinical Model of Spinal Cord Injury

Xeomin® is a commercial formulation of botulinum neurotoxin type A (BoNT/A) clinically authorized for treating neurological disorders, such as blepharospasm, cervical dystonia, limb spasticity, and sialorrhea. We have previously demonstrated that spinal injection of laboratory purified 150 kDa BoNT/A in paraplegic mice, after undergoing traumatic spinal cord injury (SCI), was able to reduce excitotoxic phenomena, glial scar, inflammation, and the development of neuropathic pain and facilitate regeneration and motor recovery. In the present study, as proof of concept in view of a possible clinical application, we studied the efficacy of Xeomin® in the same preclinical SCI model in which we highlighted the positive effects of lab-purified BoNT/A. Data comparison shows that Xeomin® induces similar pharmacological and therapeutic effects, albeit with less efficacy, to lab-purified BoNT/A. This difference, which can be improved by adjusting the dose, can be attributable to the different formulation and pharmacodynamics. Although the mechanism by which Xeomin® and laboratory purified BoNT/A induce functional improvement in paraplegic mice is still far from being understood, these results open a possible new scenario in treatment of SCI and are a stimulus for further research.

Intraoperative abobotulinumtoxinA alleviates pain after surgery and improves general wellness in a translational animal model

Pain after surgery remains a significant healthcare challenge. Here, abobotulinumtoxinA (aboBoNT-A, DYSPORT) was assessed in a post-surgical pain model in pigs. Full-skin-muscle incision and retraction surgery on the lower back was followed by intradermal injections of either aboBoNT-A (100, 200, or 400 U/pig), vehicle (saline), or wound infiltration of extended-release bupivacaine. We assessed mechanical sensitivity, distress behaviors, latency to approach the investigator, and wound inflammation/healing for 5-6 days post-surgery. We followed with immunohistochemical analyses of total and cleaved synaptosomal-associated protein 25 kD (SNAP25), glial fibrillary acidic protein (GFAP), ionized calcium-binding adaptor protein-1(Iba1), calcitonin gene-related peptide (CGRP) and substance P (SP) in the skin, dorsal root ganglia (DRG) and the spinal cord of 400 U aboBoNT-A- and saline-treated animals. At Day 1, partial reversal of mechanical allodynia in aboBoNT-A groups was followed by a full reversal from Day 3. Reduced distress and normalized approaching responses were observed with aboBoNT-A from 6 h post-surgery. Bupivacaine reversed mechanical allodynia for 24 h after surgery but did not affect distress or approaching responses. In aboBoNT-A-treated animals cleaved SNAP25 was absent in the skin and DRG, but present in the ipsilateral dorsal horn of the spinal cord. In aboBoNT-A- versus saline-treated animals there were significant reductions in GFAP and Iba1 in the spinal cord, but no changes in CGRP and SP. Analgesic efficacy of aboBoNT-A appears to be mediated by its activity on spinal neurons, microglia and astrocytes. Clinical investigation to support the use of aboBoNT-A as an analgesic drug for post-surgical pain, is warranted.

Botulinum toxin type A counteracts neuropathic pain by countering the increase of GlyT2 expression in the spinal cord of CCI rats

Botulinum toxin type A (BoNT/A) is a potent toxin, acts by cleaving synaptosome-associated-protein-25 (SNAP-25) to regulate the release of the neural transmitter and shows analgesic effect in neuropathic pain. However, the mechanisms of BoNT/A actions involved in nociceptions remain unclear. Glycine transporter 2 (GlyT2) is an isoform of glycine transporters, which plays an important role in the regulation of glycinergic neurotransmission. Inhibition of GlyTs could decrease pain sensation in neuropathic pain, the role of GlyT2 in the analgesic effect of BoNT/A has not been studied yet. In our present study, we demonstrated that the protein levels of GlyT2 and SNAP-25 were upregulated in the spinal cord after the development of chronic constriction injury (CCI)-induced neuropathic pain. Intraplantar application of BoNT/A (20 U/kg) attenuated mechanical allodynia induced by CCI and downregulated GlyT2 expression in the spinal cord. The application of BoNT/A s also decreased the expression of GlyT2 in pheochromocytoma (PC12) cells. Moreover, intrathecal application of lentivirus-mediated GlyT2 reversed the antinociceptive effect of BoNT/A in CCI rats. These findings indicate that GlyT2 contributes to the antinociceptive effect of BoNT/A and suggest a novel mechanism underlying BoNT/A's antinociception action.

OnabotulinumtoxinA Dosing, Disease Severity, and Treatment Benefit in Patients With Cervical Dystonia: A Cohort Analysis From CD PROBE

Introduction

The Cervical Dystonia Patient Registry for Observation of OnabotulinumtoxinA Efficacy (CD PROBE) study (ClinicalTrials.gov identifier: NCT00836017), a multicenter, prospective, observational registry, was designed to identify real-world practices and outcomes for patients with cervical dystonia (CD) treated with onabotulinumtoxinA (onabotA). This secondary analysis from CD PROBE aims to determine the impact of presentation subtype on onabotA utilization and CD severity.

Materials and Methods

The study cohort includes those who completed all 3 treatments, 4 office visits, and had data recorded for all assessments. Patient outcomes were assessed with the Cervical Dystonia Impact Profile (CDIP-58), Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS), and determination of CD severity. Treatment interval, dose, and adverse events (AEs) were also recorded. Data were stratified according to prior exposure to botulinum toxins (BoNTs) and analyzed with descriptive statistics.

Results

Torticollis was the most common presentation subtype in the study cohort (N = 350); the proportion of patients with torticollis was highest in those with severe disease. At each treatment, between 40.7 and 65.2% of those categorized as severe shifted to moderate or mild severity after treatment. Sustained improvements in CDIP-58 and TWSTRS were observed regardless of prior exposure to BoNTs. Dosing of onabotA generally increased from injection 1 to injection 3 and tended to be lower for patients naïve to BoNT. Median time interval between injections for the study cohort was 94.0 to 97.5 days. The most common AEs (dysphagia, muscular weakness) and injection intervals were similar between naïve vs. non-naïve patients; there were no serious treatment-related AEs.

Conclusions

This secondary cohort analysis from CD PROBE demonstrates that three repeat treatments with onabotA at intervals consistent with labeling attenuated disease severity and neck pain, resulting in sustained improvements in physician- and patient-reported outcomes. No new safety signals were identified.

Efficacy of Botulinum Toxin Type-A I in the Improvement of Mandibular Motion and Muscle Sensibility in Myofascial Pain TMD Subjects: A Randomized Controlled Trial

This study assessed the effects of botulinum toxin type A (BoNT-A) in mandibular range of motion and muscle tenderness to palpation in persistent myofascial pain (MFP) patients (ReBEC RBR-2d4vvv). Eighty consecutive female subjects with persistent MFP, were randomly divided into four groups (n = 20): three BoNT-A groups with different doses and a saline solution group (placebo control group). Treatments were injected bilaterally in the masseter and anterior temporalis muscle in a single session. Clinical measurements of mandibular movements included: pain-free opening, maximum unassisted and assisted opening, and right and left lateral excursions. Palpation tests were performed bilaterally in the masseter and temporalis muscle. Follow-up occurred 28 and 180 days after treatment. For the statistical analysis the Mann–Whitney U-test with Bonferroni correction was used for groups comparisons. Regardless of dose, all parameters of mandibular range of motion significantly improved after 180 days in all BoNT-A groups, compared with the control group. Palpation pain over the masseter and temporalis muscles were significantly reduced in all BoNT-A groups regardless of dose, compared with the control group, after 28 and 180 days of treatment. Independent of doses, BoNT-A improved mandibular range of motion and muscle tenderness to palpation in persistent MFP patients.

The Isolated Mouse Jejunal Afferent Nerve Assay as a Tool to Assess the Effect of Botulinum Neurotoxins in Visceral Nociception

For the past two decades, botulinum neurotoxin A (BoNT/A) has been described as a strong candidate in the treatment of pain. With the production of modified toxins and the potential new applications at the visceral level, there is a real need for tools allowing the assessment of these compounds. In this study, we evaluated the jejunal mesenteric afferent nerve assay to investigate BoNT/A effects on visceral nociception. This ex vivo model allowed the continuous recording of neuronal activity in response to various stimuli. BoNT/A was applied intraluminally during three successive distensions, and the jejunum was distended every 15 min for 3 h. Finally, samples were exposed to external capsaicin. BoNT/A intoxication was validated at the molecular level with the presence of cleaved synaptosomal-associated protein of 25 (SNAP25) in nerve terminals in the mucosa and musculosa layers 3 h after treatment. BoNT/A had a progressive inhibitory effect on multiunit discharge frequency induced by jejunal distension, with a significant decrease from 1 h after application without change in jejunal compliance. The capsaicin-induced discharge was also affected by the toxin. This assay allowed the description of an inhibitory effect of BoNT/A on afferent nerve activity in response to distension and capsaicin, suggesting BoNT/A could alleviate visceral nociception.

Effectiveness of Botulinum Toxin on Pain in Stroke Patients Suffering from Upper Limb Spastic Dystonia

This observational study aimed at investigating pain in stroke patients with upper limb spastic dystonia. Forty-one consecutive patients were enrolled. A 0–10 numeric rating scale was used to evaluate pain at rest and during muscle tone assessment. Patients were asked to indicate the most painful joint at passive mobilization (shoulder, elbow, wrist-fingers). The DN4 questionnaire was administered to disclose neuropathic pain. All patients were assessed just before and 1 month after incobotulinumtoxin-A treatment. Pain was present in 22 patients, worsened or triggered by passive muscle stretching. DN4 scored < 4 in 20 patients. The most painful joints were wrist–fingers in 12 patients, elbow in 5 patients and shoulder in the remaining 5 patients. Both elbow and wrist–fingers pain correlated with muscle tone. BoNT-A treatment reduced pain in all the joints, including the shoulder. We discussed that nociceptive pain is present in a vast proportion of patients with upper limb spastic dystonia. BoNT-A treatment reduced both spastic dystonia and pain in all the joints but the shoulder, where the effect on pain could be mediated by the reduction of pathological postures involving the other joints.

Botulinum toxin type A and acupuncture for masticatory myofascial pain: a randomized clinical trial

BoNT-A has been widely used for TMD therapy. However, the potential benefits compared to dry needling techniques are not clear.

Revealing the Therapeutic Potential of Botulinum Neurotoxin Type A in Counteracting Paralysis and Neuropathic Pain in Spinally Injured Mice

Botulinum neurotoxin type A (BoNT/A) is a major therapeutic agent that has been proven to be a successful treatment for different neurological disorders, with emerging novel therapeutic indications each year. BoNT/A exerts its action by blocking SNARE complex formation and vesicle release through the specific cleavage of SNAP-25 protein; the toxin is able to block the release of pro-inflammatory molecules for months after its administration. Here we demonstrate the extraordinary capacity of BoNT/A to neutralize the complete paralysis and pain insensitivity induced in a murine model of severe spinal cord injury (SCI). We show that the toxin, spinally administered within one hour from spinal trauma, exerts a long-lasting proteolytic action, up to 60 days after its administration, and induces a complete recovery of muscle and motor function. BoNT/A modulates SCI-induced neuroglia hyperreactivity, facilitating axonal restoration, and preventing secondary cells death and damage. Moreover, we demonstrate that BoNT/A affects SCI-induced neuropathic pain after moderate spinal contusion, confirming its anti-nociceptive action in this kind of pain, as well. Our results provide the intriguing and real possibility to identify in BoNT/A a therapeutic tool in counteracting SCI-induced detrimental effects. Because of the well-documented BoNT/A pharmacology, safety, and toxicity, these findings strongly encourage clinical translation.

Botulinum Toxin and Neuronal Regeneration after Traumatic Injury of Central and Peripheral Nervous System

Botulinum neurotoxins (BoNTs) are toxins produced by the bacteria Clostridiumbotulinum, the causing agent for botulism, in different serotypes, seven of which (A–G) are well characterized, while others, such as H or FA, are still debated. BoNTs exert their action by blocking SNARE (soluble N-ethylmale-imide-sensitive factor-attachment protein receptors) complex formation and vesicle release from the neuronal terminal through the specific cleavage of SNARE proteins. The action of BoNTs at the neuromuscular junction has been extensively investigated and knowledge gained in this field has set the foundation for the use of these toxins in a variety of human pathologies characterized by excessive muscle contractions. In parallel, BoNTs became a cosmetic drug due to its power to ward off facial wrinkles following the activity of the mimic muscles. Successively, BoNTs became therapeutic agents that have proven to be successful in the treatment of different neurological disorders, with new indications emerging or being approved each year. In particular, BoNT/A became the treatment of excellence not only for muscle hyperactivity conditions, such as dystonia and spasticity, but also to reduce pain in a series of painful states, such as neuropathic pain, lumbar and myofascial pain, and to treat various dysfunctions of the urinary bladder. This review summarizes recent experimental findings on the potential efficacy of BoNTs in favoring nerve regeneration after traumatic injury in the peripheral nervous system, such as the injury of peripheral nerves, like sciatic nerve, and in the central nervous system, such as spinal cord injury.

Effect of Botulinum Toxin A on Bladder Pain-Molecular Evidence and Animal Studies

Botulinum toxin A (BTX-A) is a powerful neurotoxin with long-lasting activity that blocks muscle contractions. In addition to effects on neuromuscular junctions, BTX-A also plays a role in sensory feedback loops, suggesting the potentiality for pain relief. Although the only approved indications for BTX-A in the bladder are neurogenic detrusor overactivity and refractory overactive bladder, BTX-A injections to treat bladder pain refractory to conventional therapies are also recommended. The mechanism of BTX-A activity in bladder pain is complex, with several hypotheses proposed in recent studies. Here we comprehensively reviewed properties of BTX-A in peripheral afferent and efferent nerves, the inhibition of nociceptive neurotransmitter release, the reduction of stretch-related visceral pain, and its anti-inflammatory effects on the bladder urothelium. Studies have also revealed possible effects of BTX-A in the human brain. However, further basic and clinical studies are warranted to provide solid evidence-based support in using BTX-A to treat bladder pain.

SNAP-25 Contributes to Neuropathic Pain by Regulation of VGLuT2 Expression in Rats

Synaptosomal-associated protein 25 (SNAP-25) plays an important role in neuropathic pain. However, the underlying mechanism is largely unknown. Vesicular glutamate transporter 2 (VGluT2) is an isoform of vesicular glutamate transporters that controls the storage and release of glutamate. In the present study, we found the expression levels of VGluT2 correlated with the upregulation of SNAP-25 in the spinal cord of rats following chronic constriction injury (CCI)-induced neuropathic pain. Cleavage of SNAP-25 by Botulinum toxin A (BoNT/A) attenuated mechanical allodynia, downregulated the expression of VGluT2 and reduced glutamate release. Overexpression of VGluT2 abolished the antinociceptive effect of BoNT/A. Upregulation of SNAP-25 in naive rats increased VGluT2 expression and induced pain-responsive behaviors. In pheochromocytoma (PC12) cells, the expression of VGluT2 was also depended on SNAP-25 dysregulation. Moreover, we found VGluT2 was involved in SNAP-25-mediated regulation of astrocyte expression and activation of the PKA/p-CREB pathway mediated the upregulation of SNAP-25 in neuropathic pain. The findings of our study indicate that VGluT2 contributes to the effect of SNAP-25 in maintaining the development of neuropathic pain and suggests a novel mechanism underlying SNAP-25 regulation of neuropathic pain.

The effects of botulinum toxin type A injection on pain symptoms, quality of life, and sleep quality of patients with diabetic neuropathy: A randomized double-blind clinical trial

Background: Neuropathic pain is one of the most common problems in patients with diabetes mellitus (DM). In this study, the effect of botulinum toxin type A (BTX-A) on neuropathic pain, quality of sleep, and quality of life of diabetic patients with sensorimotor polyneuropathy was studied. Methods: This randomized placebo-controlled trial study was carried out in a double-blind (patient-researcher) method. The study was performed on 32 patients with type 2 DM. Neuropathy was confirmed by Douleur Neuropathique 4 (DN4) Questionnaire and nerve conduction study (NCS). The patients were randomly assigned to two intervention and control groups based on the random numbers table. After selecting the subjects, we used 36-Item Short Form Health Survey (SF-36), Neuropathic Pain Scale (NPS), Visual Analogue Scale (VAS), and Pittsburgh Sleep Quality Index (PSQI) questionnaires before and after 3 months of 100 units BTX-A injection (as intervention group) or same amount of chloride sodium (as control group) to the subjects' feet. The data were analyzed by SPSS software using independent two-sample t-test, chi-square test, and one-way repeated measures analysis of variance (ANOVA). Results: 12 male and 20 female patients participated in this study. There was a significant difference in the mean VAS, PSQI, physical dimension of the SF-36, and some NPS indices over time (12 weeks) (P < 0.001). Conclusion: The results of this study showed that BTX-A reduced neuropathic pain and improved the quality of life and sleep in people with diabetic neuropathy.

Strategies for Targeted Delivery to the Peripheral Nerve

Delivery of compounds to the peripheral nervous system has the potential to be used as a treatment for a broad range of conditions and applications, including neuropathic pain, regional anesthesia, traumatic nerve injury, and inherited and inflammatory neuropathies. However, efficient delivery of therapeutic doses can be difficult to achieve due to peripheral neuroanatomy and the restrictiveness of the blood-nerve barrier. Depending on the underlying integrity of the blood-nerve barrier in the application at hand, several strategies can be employed to navigate the peripheral nerve architecture and facilitate targeted delivery to the peripheral nerve. This review describes different applications where targeted delivery to the peripheral nervous system is desired, the challenges that the blood-nerve barrier poses in each application, and bioengineering strategies that can facilitate delivery in each application.

Efficacy of Botulinum Toxin A for Treating Cramps in Diabetic Neuropathy

OBJECTIVE

Muscle cramps occur in >50% of diabetic patients and reduce the quality of life. No effective treatment is available. We evaluated the clinical effectiveness of botulinum toxin A (BTX-A) injections for treating cramps in diabetic patients with neuropathy.

METHODS

This single-center, double-blind, placebo-controlled perspective study investigated the efficacy and safety of BTX-A intramuscular injection for treating calf or foot cramps refractory to common pharmacological drugs. Fifty diabetic patients with peripheral neuropathy and cramps were randomly assigned to 2 matched groups. BTX-A (100 or 30 units) or saline was injected on each side into the gastrocnemius or the small flexor foot muscles. Changes in pain intensity (primary outcome) and cramp frequency were evaluated over the course of 20 weeks after BTX-A administration. Cramp interference in daily life and the electrophysiological cramp threshold frequency were also measured. The treatment was repeated 5 months after first injection in 19 responders.

RESULTS

All outcome measures improved significantly after BTX-A compared with placebo. The changes with respect to baseline were already significant after 1 week and persisted up to week 14. Only 5 of 25 (20%) patients were nonresponders (<50% decrease of the primary outcome). The responses to a second BTX-A injection provided results similar to the first administration. Mild pain at the injection site (4/25 cases) was the only adverse event, and it disappeared within 2 to 3 days.

INTERPRETATION

Local BTX-A infiltration is an efficacious and safe procedure for obtaining a sustained amelioration of muscle cramps associated with diabetic neuropathy. Ann Neurol 2018;84:682-690.

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.

Botulinum Toxin B Affects Neuropathic Pain but Not Functional Recovery after Peripheral Nerve Injury in a Mouse Model

Clinical use of neurotoxins from Clostridium botulinum is well established and is continuously expanding, including in treatment of pain conditions. Background: The serotype A (BoNT/A) has been widely investigated, and current data demonstrate that it induces analgesia and modulates nociceptive processing initiated by inflammation or nerve injury. Given that data concerning the serotype B (BoNT/B) are limited, the aim of the present study was to verify if also BoNT/B is able not only to counteract neuropathic pain, but also to interfere with inflammatory and regenerative processes associated with the nerve injury. Methods: As model of neuropathic pain, chronic constriction injury (CCI) of the sciatic nerve was performed in CD1 male mice. Mice were intraplantarly injected with saline (control) or BoNT/B (5 or 7.5 pg/mouse) into the injured hindpaw. For comparison, another mouse group was injected with BoNT/A (15 pg/mouse). Mechanical allodynia and functional recovery of the injured paw was followed for 101 days. Spinal cords and sciatic nerves were collected at day 7 for immunohistochemistry. Results and Conclusions: The results of this study show that BoNT/B is a powerful biological molecule that, similarly to BoNT/A, can reduce neuropathic pain over a long period of time. However, the analgesic effects are not associated with an improvement in functional recovery, clearly highlighting an important difference between the two serotypes for the treatment of this chronic pain state.

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 toxin type A in motor nervous system: unexplained observations and new challenges

In the motor system, botulinum toxin type A (BoNT/A) actions were classically attributed to its well-known peripheral anticholinergic actions in neuromuscular junctions. However, the enzymatic activity of BoNT/A, assessed by the detection of cleaved synaptosomal-associated protein 25 (SNAP-25), was recently detected in motor and sensory regions of the brainstem and spinal cord after toxin peripheral injection in rodents. In sensory regions, the function of BoNT/A activity is associated with its antinociceptive effects, while in motor regions we only know that BoNT/A activity is present. Is it possible that BoNT/A presence in central motor nuclei is without any function? In this brief review, we analyze this question. Limited data available in the literature warrant further investigations of BoNT/A actions in motor nervous system.

OnabotulinumtoxinA Improves Pain in Patients With Post-Stroke Spasticity: Findings From a Randomized, Double-Blind, Placebo-Controlled Trial

CONTEXT

Patients with post-stroke spasticity (PSS) commonly experience pain in affected limbs, which may impact quality of life.

OBJECTIVES

To assess onabotulinumtoxinA for pain in patients with PSS from the BOTOX(®) Economic Spasticity Trial, a multicenter, randomized, double-blind, placebo-controlled trial.

METHODS

Patients with PSS (N = 273) were randomized to 22- to 34-week double-blind treatment with onabotulinumtoxinA + standard care (SC) or placebo injection + SC and were eligible to receive open-label onabotulinumtoxinA up to 52 weeks. Assessments included change from baseline on the 11-point pain numeric rating scale, proportion of patients with baseline pain ≥4 achieving ≥30% and ≥50% improvement in pain, and pain interference with work at Week 12, end of double-blind treatment, and Week 52.

RESULTS

At baseline, most patients (74.3%) experienced pain and 47.4% had pain ≥4 (pain subgroup). Mean pain reduction from baseline at Week 12 was significantly greater with onabotulinumtoxinA + SC (-0.77, 95% CI -1.14 to -0.40) than placebo + SC (-0.13, 95% CI -0.51 to 0.24; P < 0.05). Higher proportions of patients in the pain subgroup achieved ≥30% and ≥50% reductions in pain at Week 12 with onabotulinumtoxinA + SC (53.7% and 37.0%, respectively) compared with placebo (28.8% and 18.6%, respectively; P < 0.05). Reductions in pain were sustained through Week 52. Compared with placebo + SC, onabotulinumtoxinA consistently reduced pain interference with work.

CONCLUSION

This is the first randomized, placebo-controlled trial demonstrating statistically significant and clinically meaningful reductions in pain and pain interference with work with onabotulinumtoxinA in patients with PSS.

Neck Pain and Cervical Dystonia: Treatment Outcomes from CD PROBE (Cervical Dystonia Patient Registry for Observation of OnabotulinumtoxinA Efficacy)

BACKGROUND

Pain is a prevailing feature of cervical dystonia (CD), the most common form of focal dystonia. This analysis examined pain relief after onabotulinumtoxinA treatment in CD subjects with moderate/severe pain from the Cervical Dystonia Patient Registry for Observation of OnabotulinumtoxinA Efficacy (CD PROBE).

METHODS

CD PROBE was a prospective, multicenter, observational registry of CD subjects who were naïve to botulinum toxin (BoNT), new to physician, or had not received BoNT within ≥ 16 weeks if in a clinical trial. Subjects were eligible for 3 treatments, with variable session intervals. Descriptive and inferential statistics were utilized to evaluate the change in pain scores in the population with moderate/severe neck pain at baseline (Pain Numeric Rating Scale [PNRS] score 4 to 10).

RESULTS

Of 1046 enrolled, 733 (70.7%) had moderate/severe neck pain at baseline. Postinjection pain questionnaire responses 4 to 6 weeks after each of the 3 treatments revealed that a majority of subjects (67.1%, 72.4%, and 76.4%) reported pain relief; mean time to pain relief was 7.1, 7.4, and 7.6 days. All pain scales showed significant improvements from baseline to final visit (all P < 0.0001): PNRS, mean 6.6 to 3.8; CD Impact Profile-58 Pain and Discomfort subscale, mean 78.7 to 56.5; and Toronto Western Spasmodic Torticollis Rating Scale Pain subscale, mean 12.6 to 8.5. Multivariable regression models showed that initial pain score significantly contributed to the final pain score for all scales.

CONCLUSION

Results from this real-world clinical registry indicate that a majority of CD subjects with moderate/severe neck pain experience significant relief following onabotulinumtoxinA treatment.

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.

Chapter 3: Molecular basis for the therapeutic effectiveness of botulinum neurotoxin type A

The utility of botulinum neurotoxin type A (BoNT/A) for treating overactive muscles and endocrine glands is attributable to a unique conflation of properties honed to exploit and inactivate synaptic transmission. Specific, high-affinity coincident binding to gangliosides plus an intraluminal loop of synaptic vesicle protein 2 (SV2) by the heavy chain (HC) of BoNT/A confers selectivity for presynaptic nerve terminals and subsequent uptake by endocytosis. Upon vesicle acidification, the HC forms a channel for transmembrane transfer of the light chain to the cytosol, as observed by single channel recordings. The light chain is a Zn(2+) -dependent endoprotease that cleaves and inactivates SNAP-25, thereby blocking exocytotic release of transmitters, a discovery that revealed the pivotal role of the latter in synaptic vesicle fusion. A di-leucine motif in BoNT/A light chain stabilizes this protease, contributing to its longevity inside nerves. The ubiquity of SV2 and SNAP-25 has prompted re-evaluation of the nerve types susceptible to BoNT/A. In urology, there is emerging evidence that BoNT/A blocks neuropeptide release from afferent nerves, exocytosis of acetylcholine and purines from efferent nerves, and possibly ATP release from the urothelium. Suppression by BoNT/A of the surface expression of nociceptor channels on bladder afferents might also contribute to its improvement of urological sensory symptoms.

Botulinum Toxin-A for Painful Diabetic Neuropathy: A Meta-Analysis

OBJECTIVES

Painful diabetic neuropathy (PDN) is a debilitating complication of diabetes that greatly affects the quality of life of those afflicted. There are many treatment options for neuropathic pain. Recent studies show a promising analgesic effect using botulinum toxin-A (BTX-A) for neuropathic pain.

METHODS

This article is a meta-analysis of two studies using BTX-A in the treatment of neuropathic pain. Electronic searches of MEDLINE/PubMed, EMBASE, and Cochrane Libraries using the terms "botulinum neurotoxin" and "neuropathic pain" were conducted. Only class I and class II therapeutic trials, as classified by the American Academy of Neurology were included. The primary outcome measured was the difference in visual analogue scale (VAS) from pre-intervention and post-intervention after 1 month. Data were analyzed for biases and heterogeneity following Cochrane and PRISMA guidelines.

RESULTS

Two studies on PDN were analyzed in the meta-analysis showing improvement of 1.96 VAS points (95% CI, -3.09 to -0.84; Z score = 3.43, P < 0.001) following treatment with BTX-A. This corresponds to clinically significant improvement of "minimum change in pain." The adverse effects of infection at injection site was not statistically significant (P = 0.49). BTX-A may be effective for PDN.

CONCLUSION

Tests for significance, low overall risk of bias, and almost no statistical heterogeneity suggests that there is a correlation between BTX-A and improvement of pain scores in PDN. Further large-scale controlled trials are needed.

Analgesic effects of botulinum neurotoxin type A in a model of allyl isothiocyanate- and capsaicin-induced pain in mice

We evaluate analgesic effects of BoNT/A in relation to the two main transient receptor potentials (TRP), the vanilloid 1 (TRPV1) and the ankyrin 1 (TRPA1), having a role in migraine pain. BoNT/A (15 pg/mouse) was injected in the inner side of the medial part of hindlimb thigh of mice, where the superficial branch of femoral artery is located. We chosen this vascular structure because it is similar to other vascular structures, such as the temporal superficial artery, whose perivascular nociceptive fibres probably contributes to migraine pain. After an interval, ranging from 7 to 30 days, capsaicin (agonist of TRPV1) or allyl isothiocyanate (AITC; agonist of TRPA1) were injected in the same region previously treated with BoNT/A and nocifensive response to chemicals-induced pain was recorded. In absence of BoNT/A, capsaicin and AITC induced extensive nocifensive response, with a markedly different temporal profile: capsaicin induced maximal pain during the first 5 min, while AITC induced maximal pain at 15-30 min after injection. Pretreatment with BoNT/A markedly reduced both the capsaicin- and AITC-induced pain for at least 21 days. These data suggest a long lasting analgesic effect of BoNT/A exerted via prevention of responsiveness of TRPV1 and TRPA1 toward their respective agonists.

Botulinum toxin for neuropathic pain and spasticity: an overview

In recent years, a large body of data has surfaced reporting the therapeutic benefit of botulinum toxin injection in multiple conditions. The aim of this review is: to summarize the highest quality literature pertaining to clinical application of botulinum toxin in neuropathic pain conditions including postherpetic neuralgia, trigeminal neuralgia, diabetic polyneuropathy, post-traumatic neuralgia, carpal tunnel syndrome, complex regional pain syndrome, phantom limb and stump pain, and occipital neuralgia; to provide an overview of the clinical trials using botulinum toxin in adult spasticity; and to assign levels of evidence according to the American Academy of Neurology guidelines. In summary, there is level A evidence for established efficacy in postherpetic neuralgia and adult spasticity; level B evidence for probable efficacy in trigeminal neuralgia and post-traumatic neuralgia; level B evidence for probable lack of efficacy in carpal tunnel syndrome; level C evidence for possible efficacy in diabetic polyneuropathy; and level U (insufficient) evidence in complex regional pain syndrome, phantom limb and stump pain, and occipital neuralgia.

Antinociceptive effect of botulinum toxin type A on experimental abdominal pain

Visceral pain, especially in the abdominal region, represents one of the most common types of pain. Its chronic form is usually very hard to treat by conventional analgesic agents and adjuvants. We investigated the antinociceptive effect of botulinum toxin type A (BTX-A) in male Wistar rats in two models of visceral pain: peritonitis induced by intraperitoneal injection of 1% acetic acid and colitis induced by intracolonic instillation of 0.1% capsaicin. Pain was measured as the number of abdominal writhes. Additionally, referred mechanical sensitivity in the ventral abdominal area was evaluated by von Frey test and the extent of spinal c-Fos expression was immunohistochemically examined. BTX-A significantly reduced the number of abdominal writhes in both models of visceral pain after intrathecal application in a dose of 2 U/kg. In the experimental colitis model, BTX-A (2 U/kg) reduced both referred mechanical allodynia and c-Fos expression in the dorsal horn of the spinal cord (S2/S3 segments). In contrast to intrathecal administration, BTX-A (2 U/kg) administered into the cisterna magna had no effect on pain suggesting that the primary site of its action is a spinal cord.

Botulinum toxin A, brain and pain

Botulinum neurotoxin type A (BoNT/A) is one of the most potent toxins known and a potential biological threat. At the same time, it is among the most widely used therapeutic proteins used yearly by millions of people, especially for cosmetic purposes. Currently, its clinical use in certain types of pain is increasing, and its long-term duration of effects represents a special clinical value. Efficacy of BoNT/A in different types of pain has been found in numerous clinical trials and case reports, as well as in animal pain models. However, sites and mechanisms of BoNT/A actions involved in nociception are a matter of controversy. In analogy with well known neuroparalytic effects in peripheral cholinergic synapses, presently dominant opinion is that BoNT/A exerts pain reduction by inhibiting peripheral neurotransmitter/inflammatory mediator release from sensory nerves. On the other hand, growing number of behavioral and immunohistochemical studies demonstrated the requirement of axonal transport for BoNT/A's antinociceptive action. In addition, toxin's enzymatic activity in central sensory regions was clearly identified after its peripheral application. Apart from general pharmacology, this review summarizes the clinical and experimental evidence for BoNT/A antinociceptive activity and compares the data in favor of peripheral vs. central site and mechanism of action. Based on literature review and published results from our laboratory we propose that the hypothesis of peripheral site of BoNT/A action is not sufficient to explain the experimental data collected up to now.

The effects of intradermal botulinum toxin type a injections on pain symptoms of patients with diabetic neuropathy

BACKGROUND

Considering the dramatic increasing rate of diabetes and consequently its related complications, most importantly diabetic peripheral neuropathy (DPN), challenges regarding proper treatment of DPN and its effect on the quality-of-life and care of diabetic patients, the aim of this current study is to evaluate the effect of intradermal botulinum toxin type A (BTX-A) injections on pain symptoms of patients with diabetic neuropathic pain.

MATERIALS AND METHODS

In this randomized double-blind placebo-controlled clinical trial study, diabetic patients aged <70 years with neuropathic pain in both feet were enrolled. Diabetic neuropathy (DN) in selected patients was diagnosed using DN4 questionnaire and nerve conduction velocity examinations. They randomized in two intervention (BTX-A injection/100 unit, N = 20) and placebo groups (normal saline injection, N = 20). The outcome of injection on diabetic neuropathic pain was assessed using neuropathy pain scale (NPS) and visual analog scale (VAS) score and compared in two studied groups.

RESULTS

There was no significant difference in DN4, NPS and VAS scales of studied population after intervention in the placebo group. Intradermal injection of BTX-A reduced NPS scores for all items except cold sensation (P = 0.05). It reduced DN4 scores for electric shocks, burning, pins and needles and brushing (P < 0.05). According to VAS scale 30% and 0% of patients in intervention and placebo groups have no pain after intervention (P = 0.01).

CONCLUSION

Intradermal injection of BTX-A is a well-tolerated agent that has a significant effect on DPN pain.

Anti-inflammatory effects of botulinum toxin type a in a complete Freund's adjuvant-induced arthritic knee joint of hind leg on rat model

The objective of the study is to verify histopathologically the anti-inflammatory effect of botulinum toxin type A (BoNT-A) in a Complete Freund's Adjuvant (CFA)-induced arthritic knee joint of hind leg on rat model using immunofluorescent staining of anti-ionized calcium-binding adaptor molecule 1 (Iba-1) and interleukin-1β (IL-1β) antibody. Twenty-eight experimental rats were injected with 0.1 ml of CFA solution in the knee joint of the hind leg bilaterally. Three weeks after CFA injection, the BoNT-A group (N = 14) was injected with 20 IU (0.1 ml) of BoNT-A bilaterally while the saline group (N = 14) was injected with 0.1 ml of saline in the knee joint of the hind leg bilaterally. One and two weeks after BoNT-A or saline injection, joint inflammation was investigated in seven rats from each group using histopathological and immune-fluorescent staining of Iba-1 and IL-1β antibody. The number of Iba-1 and IL-1β immune-reactive (IR) cells was counted in the BoNT-A and saline groups for comparison. There was a significant reduction in joint inflammation and destruction in the BoNT-A group at 1 and 2 weeks after BoNT-A injection compared with the saline group. The binding of Iba-1 and IL-1β antibody was significantly lower in the BoNT-A group than the saline group at 1 and 2 weeks after BoNT-A injection. The number of Iba-1 and IL-1β-IR cells at 1 and 2 weeks after the injection of BoNT-A were significantly different from the corresponding number of Iba-1 and IL-1β-IR cells in the saline group. To conclude, BoNT-A had an anti-inflammatory effect in a CFA-induced arthritic rat model, indicating that BoNT-A could potentially be used to treat inflammatory joint pain.

A critical evaluation of migraine trigger site deactivation surgery

Migraine headache trigger site deactivation surgery is a term that encompasses 4 different surgical procedures that are performed based on headache onset location for the preventative treatment of migraine headaches. Multiple studies have demonstrated some efficacy of these procedures, but closer evaluation of the methodology of these studies reveals major flaws in study design. In this article, the author provides an overview of the procedures and presurgical screening tools, as well as a critical evaluation of 2 of the major studies that have been published. In addition, the author provides his opinion on future study designs that may help to better determine the potential efficacy of these experimental procedures and potential headache subtypes (contact point headache, supraorbital neuralgia, and occipital neuralgia) that may respond to peripheral decompression surgery.

Botulinum toxin A increases analgesic effects of morphine, counters development of morphine tolerance and modulates glia activation and μ opioid receptor expression in neuropathic mice

The use of botulinum neurotoxin type A (BoNT/A) against pain, with emphasis for its possible use in alleviating chronic pain, still represents an outstanding challenge for experimental research. In this study, we examined the effects of BoNT/A on morphine-induced tolerance during chronic morphine treatment in neuropathic CD1 mice subjected to sciatic nerve lesion according to the Chronic Constriction Injury (CCI) model of neuropathic pain. We measured the effects of BoNT/A on CCI-induced allodynia and hyperalgesia and on the expression of glial fibrillary acidic protein (GFAP, marker of astrocytes), complement receptor 3/cluster of differentiation 11b (CD11b, marker of microglia), and neuronal nuclei (NeuN) at the spinal cord level. We also analyzed the colocalized expression of GFAP, CD11b and NeuN with phosphorylated p-38 mitogen-activated protein kinase and with μ-opioid receptor (MOR). A single intraplantar injection of BoNT/A (15 pg/paw) into the injured hindpaw, the day before the beginning of chronic morphine treatment (9 days of twice daily injections of 40 mg/kg morphine), was able to counteract allodynia and enhancement of astrocytes expression/activation induced by CCI. In addition, BoNT/A increased the analgesic effect of morphine and countered morphine-induced tolerance during chronic morphine treatment. These effects were accompanied, in neurons, by re-expression of MORs that had been reduced by repeated morphine administration. The combinatory effects of BoNT/A and morphine could have relevant therapeutic implications for sufferers of chronic pain who could benefit of pain relief reducing tolerance due to repeated treatment with opiates.

The rat Digit Abduction Score (DAS) assay: a physiological model for assessing botulinum neurotoxin-induced skeletal muscle paralysis

Botulinum neurotoxins (BoNT) are approved for a number of therapeutic indications, including blepharospasm, cervical dystonia and hyperhidrosis, and have also shown efficacy in a variety of pain disorders. The potency of any given BoNT preparation can be routinely assessed by using the Digit Abduction Score (DAS) assay, which measures the local muscle weakening efficacy of BoNT following injection into mouse hindlimb muscle. While most studies have employed mice to assess BoNT efficacy in the DAS, few have utilized rats. In this study, we applied the DAS assay to a rat model and compared the potency of IM-BOTOX(®) (onabotulinumtoxinA) injections between two separate hind limb muscles, gastrocnemius and tibialis anterior (TA). The results demonstrated that the DAS assay can be performed on rats with similar criteria and parameters as for mice. Moreover in the rat, BoNT can be injected into either the gastrocnemius or TA muscle to elicit similar DAS scoring responses. Interestingly, onabotulinumtoxinA potency in the rat DAS was ∼3-fold higher following TA injections than gastrocnemius injections. Additionally, our data showed that the durational kinetics of onabotulinumtoxinA in the rat DAS are approximately twice as long as in the mouse DAS. These results position the rat DAS as a more flexible model for examining the mechanisms of BoNT diffusion and muscle paralysis, while mouse DAS can be used for physiological screening of BoNT because of the potential for higher throughput. Overall, these data confirm the utility of the DAS assay for characterizing the physiological potency of BoNT and related compounds.

Involvement of μ-opioid receptors in antinociceptive action of botulinum toxin type A

Botulinum toxin A (BTX-A) is approved for treatment of chronic migraine and has been investigated in various other painful conditions. Recent evidence demonstrated retrograde axonal transport and suggested the involvement of CNS in antinociceptive effect of BTX-A. However, the mechanism of BTX-A central antinociceptive action is unknown. In this study we investigated the potential role of opioid receptors in BTX-A's antinociceptive activity. In formalin-induced inflammatory pain we assessed the effect of opioid antagonists on antinociceptive activity of BTX-A. Naltrexone was injected subcutaneously (0.02-2 mg/kg) or intrathecally (0.07 μg/10 μl-350 μg/10 μl), while selective μ-antagonist naloxonazine was administered intraperitoneally (5 mg/kg) prior to nociceptive testing. The influence of naltrexone (2 mg/kg s.c.) on BTX-A antinociceptive activity was examined additionally in an experimental neuropathy induced by partial sciatic nerve transection. To investigate the effects of naltrexone and BTX-A on neuronal activation in spinal cord, c-Fos expression was immunohistochemically examined in a model of formalin-induced pain. Antinociceptive effects of BTX-A in formalin and sciatic nerve transection-induced pain were prevented by non-selective opioid antagonist naltrexone. Similarly, BTX-A-induced pain reduction was abolished by low dose of intrathecal naltrexone and by selective μ-antagonist naloxonazine. BTX-A-induced decrease in dorsal horn c-Fos expression was prevented by naltrexone. Prevention of BTX-A effects on pain and c-Fos expression by opioid antagonists suggest that the central antinociceptive action of BTX-A might be associated with the activity of endogenous opioid system (involving μ-opioid receptor). These results provide first insights into the mechanism of BTX-A's central antinociceptive activity.

The analgesic effect on neuropathic pain of retrogradely transported botulinum neurotoxin A involves Schwann cells and astrocytes

In recent years a growing debate is about whether botulinum neurotoxins are retrogradely transported from the site of injection. Immunodetection of cleaved SNAP-25 (cl-SNAP-25), the protein of the SNARE complex targeted by botulinum neurotoxin serotype A (BoNT/A), could represent an excellent approach to investigate the mechanism of action on the nociceptive pathways at peripheral and/or central level. After peripheral administration of BoNT/A, we analyzed the expression of cl-SNAP-25, from the hindpaw's nerve endings to the spinal cord, together with the behavioral effects on neuropathic pain. We used the chronic constriction injury of the sciatic nerve in CD1 mice as animal model of neuropathic pain. We evaluated immunostaining of cl-SNAP-25 in the peripheral nerve endings, along the sciatic nerve, in dorsal root ganglia and in spinal dorsal horns after intraplantar injection of saline or BoNT/A, alone or colocalized with either glial fibrillar acidic protein, GFAP, or complement receptor 3/cluster of differentiation 11b, CD11b, or neuronal nuclei, NeuN, depending on the area investigated. Immunofluorescence analysis shows the presence of the cl-SNAP-25 in all tissues examined, from the peripheral endings to the spinal cord, suggesting a retrograde transport of BoNT/A. Moreover, we performed in vitro experiments to ascertain if BoNT/A was able to interact with the proliferative state of Schwann cells (SC). We found that BoNT/A modulates the proliferation of SC and inhibits the acetylcholine release from SC, evidencing a new biological effect of the toxin and further supporting the retrograde transport of the toxin along the nerve and its ability to influence regenerative processes. The present results strongly sustain a combinatorial action at peripheral and central neural levels and encourage the use of BoNT/A for the pathological pain conditions difficult to treat in clinical practice and dramatically impairing patients' quality of life.

Beyond muscular effects: depression of spinal recurrent inhibition after botulinum neurotoxin A

The natural target of the botulinum neurototoxin type A (BoNT-A) is the neuromuscular junction. When injected into a muscle, BoNT-A is internalized by motoneurone terminals where it functions as an endopeptidase, cleaving protein components of the synaptic machinery responsible for vesicle docking and exocytosis. As a result, BoNT-A induces a characteristic flaccid paralysis of the affected muscle. In animal models, BoNT-A applied in the periphery can also influence central activity via retrograde transport and transcytosis. An analogous direct central effect in humans is still debated. The present study was designed to address whether BoNT-A modifies the activity of the spinal recurrent inhibitory pathways, when injected at muscular level, in humans. To avoid methodological bias, the recurrent inhibition from an injected muscle (soleus) was investigated on an untreated muscle (quadriceps), and stimulation parameters (producing recurrent inhibition) were monitored on a third non-injected muscle but innervated by the same nerve as the soleus (flexor digitorum brevis). The experiments were performed on 14 post-stroke patients exhibiting spasticity in ankle plantarflexors, candidates for BoNT-A. One month after BoNT-A, the level of recurrent inhibition was depressed. It is suggested that the depression of recurrent inhibition was induced by BoNT-A, injected peripherally, through axonal transport and blockade of the cholinergic synapse between motoneurone recurrent collaterals and Renshaw cells.