Presynaptic effects of botulinum toxin type A on the neuronally evoked response of albino and pigmented rabbit iris sphincter and dilator muscles

Mirror-Image Pain Update: Complex Interactions Between Central and Peripheral Mechanisms

The appearance of contralateral effects after unilateral injury has been shown in various experimental pain models, as well as in clinics. They consist of a diversity of phenomena in contralateral peripheral nerves, sensory ganglia, or spinal cord: from structural changes and altered gene or protein expression to functional consequences such as the development of mirror-image pain (MP). Although MP is a well-documented phenomenon, the exact molecular mechanism underlying the induction and maintenance of mirror-like spread of pain is still an unresolved challenge. MP has generally been explained by central sensitization mechanisms leading to facilitation of pain impulse transfer through neural connections between the two sides of the central nervous system. On the contrary, the peripheral nervous system (PNS) was usually regarded unlikely to evoke such a symmetrical phenomenon. However, recent findings provided evidence that events in the PNS could play a significant role in MP induction. This manuscript provides an updated and comprehensive synthesis of the MP phenomenon and summarizes the available data on the mechanisms. A more detailed focus is placed on reported evidence for peripheral mechanisms behind the MP phenomenon, which were not reviewed up to now.

Treatment of Acquired Deforming Hypertonia with Botulinum Toxin in Older Population: A Retrospective Study

Acquired deforming hypertonia (ADH) affects the daily care of numerous nursing home residents. The aim of this study was to analyze the practice, aims, and effectiveness of botulinum toxin injections (BTxis) in the treatment of older patients with contractures, an indication for which BTxis are still underused. Data were extracted retrospectively from medical records regarding population, contractures, and injections. A prospective analysis was conducted to evaluate treatment goals set by goal attainment scaling (GAS) at T0 and at T1, to evaluate the therapeutic effects. We also recorded the occurrence of side effects, using a telephone questionnaire. This study included 41 patients older than 70 years who had received one or more BTxis for the first time between January 2018 and December 2021. Most of the older people we included lived in an institution (66%), manifested severe dependence, and presented significant morbi-mortality (37% of the patients died in the year after the last injection). The main objectives of these injections were purely comfort, without any functional goals. The GAS scores suggested effectiveness for comfort GAS scores. No complications were recorded. This study highlights the BTxis potential to address the needs of a larger number of older patients with ADH.

Cellular and molecular mechanisms involved in the analgesic effects of botulinum neurotoxin: A literature review

Botulinum neurotoxins (BoNTs), derived from Clostridium botulinum, have been employed to treat a range of central and peripheral neurological disease. Some studies indicate that BoNT may be beneficial for pain conditions as well. It has been hypothesized that BoNTs may exert their analgesic effects by preventing the release of pain-related neurotransmitters and neuroinflammatory agents from sensory nerve endings, suppressing glial activation, and inhibiting the transmission of pain-related receptors to the neuronal cell membrane. In addition, there is evidence to suggest that the central analgesic effects of BoNTs are mediated through their retrograde axonal transport. The purpose of this review is to summarize the experimental evidence of the analgesic functions of BoNTs and discuss the cellular and molecular mechanisms by which they can act on pain conditions. Most of the studies reviewed in this article were conducted using BoNT/A. The PubMed database was searched from 1995 to December 2022 to identify relevant literature.

Prolonged Antipruritic Effect of Botulinum Toxin Type A on Cowhage-induced Itch: A Randomized, Single-blind, Placebo-controlled Trial

Botulinum toxin type A (Botox) is thought to have antipruritic effects through inhibition of pruritic factors, including acetylcholine, substance P, and glutamate. The aim of this randomized, single-blind, placebo-controlled trial was to test the effect of botulinum toxin type A on cowhage, a non-histaminergic model for chronic itch. Botulinum toxin type A was injected into the arm of 35 healthy subjects, with a saline control injected into the contralateral arm. Thermal sensory parameters (warmth and heat thresholds and heat pain intensity) and itch intensity after cowhage application were examined on test areas. Botulinum toxin type A reduced itch intensity, overall perceived itch (area under the curve (AUC); percentage change from baseline), and peak itch intensity compared with the control at 1 week, 1 month, and 3 months. Botulinum toxin type A had no effect on thermal thresholds or heat pain intensity. In conclusion, botulinum toxin type A reduced cowhage itch for at least 3 months, which suggests that botulinum toxin type A is a potential long-lasting treatment for localized, non-histaminergic itch.

Botulinum toxin A and neuropathic pain: An update

Botulinum toxin type A is a widely used neurotoxin for the treatment of muscle hyperactivity such as dystonia and spasticity. Several clinical trials have also reported an efficacy of subcutaneous or intradermal administrations of botulinum toxin A on various neuropathic pain conditions including idiopathic trigeminal neuralgia and found that specific sensory phenotypes were predictors of the response. This narrative review summarizes the potential mechanisms of action, efficacy and safety of botulinum toxin A in neuropathic pain as well as its place in the therapeutic algorithm of neuropathic pain.

Sonographically guided botulinum toxin injections in patients with neurogenic thoracic outlet syndrome: correlation with surgical outcomes

OBJECTIVE

We examined the role of botulinum toxin (BTX) injections of anterior scalene (AS) and pectoralis minor (PM) muscles in patients undergoing surgery for neurogenic thoracic outlet syndrome (NTOS). We hypothesized that symptomatic improvement from BTX injections correlates with favorable long-term response to surgery for NTOS.

MATERIALS AND METHODS

This Health Insurance Portability and Accountability Act compliant study was approved by the institutional review board and prior informed consent requirement was waived. We retrospectively analyzed prospectively acquired data in NTOS patients who underwent sonographically guided chemodenervation of AS and PM using BTX type A followed by scalenectomy and first rib resection. Overall responses to BTX injections and surgery were recorded after each procedure. Statistical analyses were performed to determine correlation between responses to BTX injections and surgery.

RESULTS

In 157 patients, 178 BTX injections followed by surgery were identified (114 females; mean age 38 ± 13 years). Responders and non-responders to BTX injections and surgery had similar preoperative symptom duration and age (P > 0.14). Better response to BTX injections correlated positively with better response to surgery (P = 0.003), persisting after adjustment for age, gender, and symptom duration (P = 0.03). A high proportion of responders to BTX injections also responded to surgery (positive predictive value of 99%), and BTX injections showed high specificity (90%). BTX injections were moderately sensitive (66%) and accurate (67%) to determine surgical response and had low negative predictive value (14%).

CONCLUSION

Response to BTX injections correlates positively with long-term surgical outcome in subjects with NTOS, potentially playing an important role in patient management.

A Proposal for Botulinum Toxin Type A Injection Into the Temporal Region in Chronic Migraine Headache

Botulinum toxin type-A (BTX-A) injection for treating chronic migraine (CM) has developed into a new technique covering distinct injection points in the head and neck regions. The postulated analgesic mechanism implies that the injection should be administered to sensory nerves rather than to muscles. This study aimed to determine the topographical site of the auriculotemporal nerve (ATN) and to propose the effective injection points for treating CM. ATNs were investigated on 36 sides of 25 Korean cadavers. The anatomical structures of the ATN were investigated focusing on the temporal region. A right-angle ruler was positioned based on two clearly identifiable orthogonal reference lines based on the canthus and tragus as landmarks, and photographs were taken. The ATN appeared superficially in the anterosuperior region of the tragus. The nerve is located deeper than the superficial temporal artery. And it runs between the artery and the superficial temporal vein. In the superficial layer, it is divided into anterior and posterior divisions. The anterior division runs in a superior direction, while the posterior division runs in front of the ear and the several branches are distributed to the skin. We suggest that the optimal BTX-A injection points for CM are in the temporal region. The first point is about 2 cm anterior and 3 cm superior to two orthogonal reference lines defined based on the tragus and canthus, and the second point is about 4 cm superior to the first point. The third and fourth points are recommended about 2 cm superior to the first point, but respectively 1 cm anterior and posterior to it.

Efficacy of Botulinum Toxin Type A in Trigeminal Neuralgia in a South Asian Cohort

Introduction:

The antinociceptive effect of botulinum toxin-A (BTX-A) in trigeminal neuralgia (TN) has been described. We evaluated effects of BTX-A in relieving pain in patients with refractory TN at National Hospital of Sri Lanka.

Materials and Methods:

Pain in patients with TN was assessed using a visual analog from 0 to 10. Three months after commencement of drug therapy with ≥2 drugs including one first-line drug (carbamazepine/oxcarbazepine), pain scores were re-assessed. Twenty-two patients who did not report improvement of ≥50% at 90 days’ posttreatment were recruited. They were given adjunct BTX-A directly to the trigger point (if identified) or intradermal. Pain scores were assessed at 10, 20, 30, 60, and 90 days’ posttreatment.

Results:

There was a statistically significant improvement in mean pain scores at 10, 20, 30, 60, and 90 days’ posttreatment (5.59 [standard deviation (SD) = 2.7], 5.68 [SD = 2.6], 5.27 [SD = 3.2], 4.77 [SD = 3.7], and 5.32 [SD = 4.0]) compared to pre-BTX-A treatment (7.14, SD = 2.2). Percentage reduction in mean pain score ranged from 20.4% to 33.1%. Maximum response was at day 60 post-BTX-A (50% had ≥50% reduction in pain). No significant difference was found in response with higher doses and injection strategy.

Conclusion:

Consistent statistically significant reductions in pain scores at the aforesaid intervals compared to pretreatment means that there is a place for BTX in refractory TN.

Efficacy of Intra-Articular Botulinum Toxin in Osteoarticular Joint Pain: A Meta-Analysis of Randomized Controlled Trials

OBJECTIVE

This study was conducted with the aim of evaluating the efficacy of intra-articular injections of botulinum toxin type A (BT-A) into the painful joint diseases through a systematic review of the literature and a meta-analysis of controlled randomized trials. Intra-articular therapies (corticosteroids, hyaluronic acid) have limited efficacy and run a risk of toxicity in patients with joint pain. New therapeutic options are needed to treat painful osteoarticular disease.

METHODS

We searched via Pubmed, American College of Rheumatology, and European League Against Rheumatism congresses, and gray literature for the studies reported until June 2016 and addressing the issue of BT intra-articular injections in patients with refractory joint pain. Randomized trials were included. For the meta-analysis, we compared a numeric rating scale (NRS) from 0 to 10 before treatment and at 1 or 2 months and 6 months after in the BT-A and the control groups for each study. We also compared separately low dose and high dose of BT at 1 or 2 months' evaluation.

RESULTS

In a total of 269 selected articles, 8 were analyzed and 6 studies were included in the meta-analysis involving a total of 382 patients. On comparing the NRS rating for 5 trials, at 1 or 2 months irrespective of the dose of BT, 4 trials showed a positive effect of BT compared with the control on the NRS and 1 found no effect; the overall weighted mean difference [95% confidence interval (CI)] was -1.10 (-1.62, -0.58) (P<0.0001, I=63%). Among the 4 trials with a low dose of BT (100 U), comparing NRS at 1 or 2 months, 3 trials showed significant results with a positive effect of BT-A injection compared with the control on the NRS; the fourth study failed to find any effect. The overall weighted mean difference (95% CI) was -0.95 (-0.02, -1.88) (P=0.05, I=67%). In the 2 trials using a high dose of BT (200 U) comparing NRS at 1 or 2 months, there was an almost zero effect of BT, with an overall weighted mean difference (95% CI) of 0.13 (-0.55, 0.81) (P=0.71, I=0%). In the 3 trials comparing NRS at 6 months there was an overall weighted mean difference (95% CI) of -0.57 (-1.98, 0.83) (P=0.42, I=73%).

CONCLUSIONS

BT-A intra-articular injections have short-term benefits with a statistically significant decrease in the NRS pain score of around 1 point in patients with refractory joint pain. A decrease in the pain score was also observed at 6 months but with a nonsignificant result.

Botulinum toxin to improve vessel graft patency in cerebral revascularization surgery: report of 3 cases

Surgical revascularization continues to play an important role in the management of complex intracranial aneurysms and ischemic cerebrovascular disease. Graft spasm is a common complication of bypass procedures and can result in ischemia or graft thrombosis. The authors here report on the first clinical use of botulinum toxin to prevent graft spasm following extracranial-intracranial (EC-IC) bypass. This technique was used in 3 EC-IC bypass surgeries, 2 for symptomatic carotid artery occlusions and 1 for a ruptured basilar tip aneurysm. In all 3 cases, the harvested graft was treated ex vivo with botulinum toxin before the anastomosis was performed. Post-bypass vascular imaging demonstrated patency and the absence of spasm in all grafts. Histopathological analyses of treated vessels did not show any immediate endothelial or vessel wall damage. Postoperative angiograms were without graft spasm in all cases. Botulinum toxin may be a reasonable option for preventing graft spasm and maintaining patency in cerebral revascularization procedures.

Antioxidant effect of human placenta hydrolysate against oxidative stress on muscle atrophy

Sarcopenia, which refers to the muscle loss that accompanies aging, is a complex neuromuscular disorder with a clinically high prevalence and mortality. Despite many efforts to protect against muscle weakness and muscle atrophy, the incidence of sarcopenia and its related permanent disabilities continue to increase. In this study, we found that treatment with human placental hydrolysate (hPH) significantly increased the viability (approximately 15%) of H₂ O₂ -stimulated C2C12 cells. Additionally, while H₂ O₂ -stimulated cells showed irregular morphology, hPH treatment restored their morphology to that of cells cultured under normal conditions. We further showed that hPH treatment effectively inhibited H₂ O₂ -induced cell death. Reactive oxygen species (ROS) generation and Mstn expression induced by oxidative stress are closely associated with muscular dysfunction followed by atrophy. Exposure of C2C12 cells to H₂ O₂ induced abundant production of intracellular ROS, mitochondrial superoxide, and mitochondrial dysfunction as well as myostatin expression via nuclear factor-κB (NF-κB) signaling; these effects were attenuated by hPH. Additionally, hPH decreased mitochondria fission-related gene expression (Drp1 and BNIP3) and increased mitochondria biogenesis via the Sirt1/AMPK/PGC-1α pathway and autophagy regulation. In vivo studies revealed that hPH-mediated prevention of atrophy was achieved predominantly through regulation of myostatin and PGC-1α expression and autophagy. Taken together, our findings indicate that hPH is potentially protective against muscle atrophy and oxidative cell death.

Assessing adverse effects of intra-articular botulinum toxin A in healthy Beagle dogs: A placebo-controlled, blinded, randomized trial

OBJECTIVE

To investigate the clinical, cytological, and histopathological adverse effects of intra-articularly injected botulinum toxin A in dogs and to study whether the toxin spreads from the joint after the injection.

METHODS

A longitudinal, placebo-controlled, randomized clinical trial was conducted with six healthy laboratory Beagle dogs. Stifle joints were randomized to receive either 30 IU of onabotulinum toxin A or placebo in a 1:1 ratio. Adverse effects and spread of the toxin were examined by evaluating dynamic and static weight-bearing of the injected limbs, by assessing painless range of motion and pain on palpation of joints, and by performing synovial fluid analysis, neurological examination, and electrophysiological recordings at different examination time-points in a 12-week period after the injections. The dogs were then euthanized and autopsy and histopathological examination of joint structures and adjacent muscles and nerves were performed.

RESULTS

Intra-articular botulinum toxin A did not cause local weakness or injection site pain. Instead, static weight-bearing and painless range of motion of stifle joints decreased in the placebo limbs. No clinically significant abnormalities associated with intra-articular botulinum toxin A were detected in the neurological examinations. Electrophysiological recordings showed low compound muscle action potentials in two dogs in the botulinum toxin A-injected limb. No significant changes were detected in the synovial fluid. Autopsy and histopathological examination of the joint and adjacent muscles and nerves did not reveal histopathological adverse effects of the toxin.

CONCLUSION

Intra-articular botulinum toxin A does not produce significant clinical, cytological, or histopathological adverse effects in healthy dogs. Based on the electrophysiological recordings, the toxin may spread from the joint, but its clinical impact seems to be low.

Botulinum Toxin in the Field of Dermatology: Novel Indications

Since its approval by the US Food and Drug Administration in 2002 for glabellar wrinkles, botulinum toxin (BTX) has been widely used to correct facial wrinkles. As a result, many consider BTX synonymous with cosmetic dermatology. Recent studies indicate that BTX elicits biological effects on various skin cell types via the modulation of neurotransmitter release, and it seems that BTX has a wider zone of dermatologic influence than originally understood. Clinicians and researchers are now beginning to explore the potential of BTX beyond the amelioration of facial lines and encouraging results are seen with BTX in a variety of skin conditions. In this paper, we review novel dermatological indications of BTX which includes (but not limited to) scar prevention, facial flushing, post-herpetic neuralgia and itch. These areas show great promise, but there is definite need for larger, double-blinded, randomized control trials against established treatments before BTX becomes a clinical reality.

Botulinum toxin in the treatment of trigeminal neuralgia: 6-Month follow-up

BACKGROUND

Botulinum toxin type-A (BTX-A) has been successfully utilized to treat trigeminal neuralgia. In this study, through the use of a new technique, the efficacy of the injection of BTX-A to the maxillary and mandibular nerves was evaluated.

METHODS

A total of 27 patients were injected with 100 Units of BTX-A to the maxillary and mandibular nerves. Visual analogue scale score and pain frequency were assessed before treatment and at the first week, second month, and sixth month after treatment. Patients with ≥50% reduction in mean pain score at the second and sixth month were defined as responders.

RESULTS

A total of 27 patients were included in the study. BTX-A significantly reduced pain intensity and pain attack frequency at the first week, second month, and sixth month after treatment. At the second month, 74.1% of patients, at the sixth month, 88.9% of patients responded to treatment. Forty-four percent of patients did not experience any pain at the sixth month. The mean recurrence period was 87.7 ± 20.4. BTX-A was well tolerated and showed few treatment-related adverse events.

CONCLUSION

Injection to the maxillary and mandibular roots seems to be a highly effective method. In the event of recurrence, after each injection, the pain severity and attack frequency decreased.

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.

The effect of intra-articular botulinum toxin A on substance P, prostaglandin E2, and tumor necrosis factor alpha in the canine osteoarthritic joint

Background

Recently, intra-articular botulinum toxin A (IA BoNT A) has been shown to reduce joint pain in osteoarthritic dogs. Similar results have been reported in human patients with arthritis. However, the mechanism of the antinociceptive action of IA BoNT A is currently not known. The aim of this study was to explore this mechanism of action by investigating the effect of IA BoNT A on synovial fluid (SF) and serum substance P (SP), prostaglandin E₂ (PGE₂), and tumor necrosis factor alpha (TNF-α) in osteoarthritic dogs. Additionally, the aim was to compare SF SP and PGE₂ between osteoarthritic and non-osteoarthritic joints, and investigate associations between SP, PGE₂, osteoarthritic pain, and the signalment of dogs. Thirty-five dogs with chronic naturally occurring osteoarthritis and 13 non-osteoarthritic control dogs were included in the study. Osteoarthritic dogs received either IA BoNT A (n = 19) or IA placebo (n = 16). Serum and SF samples were collected and osteoarthritic pain was evaluated before (baseline) and 2 and 8 weeks after treatment. Osteoarthritic pain was assessed with force platform, Helsinki Chronic Pain Index, and joint palpation. Synovial fluid samples were obtained from control dogs after euthanasia. The change from baseline in SP and PGE₂ concentration was compared between the IA BoNT A and placebo groups. The synovial fluid SP and PGE₂ concentration was compared between osteoarthritic and control joints. Associations between SP, PGE₂, osteoarthritic pain, and the signalment of dogs were evaluated.

Results

There was no significant change from baseline in SP or PGE₂ after IA BoNT A. Synovial fluid PGE₂ was significantly higher in osteoarthritic compared to control joints. Synovial fluid PGE₂ correlated with osteoarthritic pain. No associations were found between SP or PGE₂ and the signalment of dogs. The concentration of TNF-α remained under the detection limit of the assay in all samples.

Conclusions

The results suggest that the antinociceptive effect of IA BoNT A in the joint might not be related to the inhibition of SP nor PGE₂. Synovial fluid PGE₂, but not SP, could be a marker for chronic osteoarthritis and pain in dogs.

Botulinum toxin type A reduces inflammatory hypernociception induced by arthritis in the temporomadibular joint of rats

OBJECTIVE

This study aimed to investigate the antinociceptive effects of Botulinum toxin type A (BoNT-A) on persistent inflammatory hypernociception induced by arthritis in the temporomandibular joint (TMJ) of rats.

MATERIAL AND METHODS

Wistar rats were induced to persistent inflammatory hypernociception in the left TMJ. Then, animals were treated with intra-TMJ injections of BoNT-A, using doses of 3.5, 7 and 14 U/kg. Saline was used as control group. Behavioral tests were applied to evaluated the effect of BoNT-A in the inflammatory hypernociception. After that, animals were euthanized and samples from peri-articular tissues and trigeminal ganglia were obtained for further analyses.

RESULTS

BoNT-A reduced the persistent inflammatory hypernociception induced by arthritis in the TMJ of rats. BoNT-A significantly reduced the peripheral release of the neurotransmitters Substance P and Calcitonin gene related peptide; and the pro-inflammatory cytokine IL-1β. Otherwise, BoNT-A had no effect in the peripheral release of glutamate and the cytokine TNF-α.

CONCLUSION

These results demonstrate that intra-articular injection of BoNT-A reduces the albumin-induced arthritis persistent hypernociception in TMJ of rats by peripheral inhibition of neuropeptides release.

Effect of Onabotulinum Toxin A on Substance P and Receptor Neurokinin 1 in the Rat Ventral Prostate

INTRODUCTION

The objective of this work is to examine if sensory innervation impacts lower urinary tract symptoms (LUTS). Onabotulinum toxin A (BoNTA) has been used for the treatment of overactive and neurogenic bladder and as a treatment for LUTS secondary to benign prostatic hyperplasia (BPH). The mechanism of how BoNTA impacts LUTS/BPH is unclear. In rats, BoNTA injection causes prostate denervation, apoptosis and atrophy. In clinical trials reduced prostate size and LUTS are observed inconsistently, suggesting a neurologic component. We will examine if BoNTA treatment inhibits substance P production in sensory nerve fibers in the rat prostate.

METHODS

Twenty Sprague Dawley rats were divided into four groups including 1X PBS (control, n=6), 2.5 units Onabotulinum toxin A (BoNTA, n=6), 5 units BoNTA (n=6) injected into both lobes of the ventral prostate (VP) and sham surgery (n=2). Rats were Euthanized after one week. Substance P and its receptor neurokinin 1 localization and quantification were performed by counting the number of stained neurons and nerve bundles, by semi-quantitative immunohistochemical analysis and by western analysis.

RESULTS

Substance P was localized in neuronal axons and bundles in the stroma of the VP but not in the epithelium. Receptor neurokinin 1 was identified in neuronal bundles of the stroma and in columnar epithelium of the VP ducts. Substance P decreased ~90% after BoNTA treatment (p=0.0001) while receptor neurokinin 1 did not change by IHC (p=0.213) or Western (p=0.3675).

CONCLUSIONS

BoNTA treatment decreases substance P in the rat VP.

The Inhibitory Effect of Botulinum Toxin Type A on Rat Pyloric Smooth Muscle Contractile Response to Substance P In Vitro

A decrease in pyloric myoelectrical activity and pyloric substance P (SP) content following intrasphincteric injection of botulinum toxin type A (BTX-A) in free move rats have been demonstrated in our previous studies. The aim of the present study was to investigate the inhibitory effect of BTX-A on rat pyloric muscle contractile response to SP in vitro and the distributions of SP and neurokinin 1 receptor (NK1R) immunoreactive (IR) cells and fibers within pylorus. After treatment with atropine, BTX-A (10 U/mL), similar to [D-Arg¹, D-Phe⁵, D-Trp^7,9, Leu¹¹]-SP (APTL-SP, 1 μmol/L) which is an NK1R antagonist, decreased electric field stimulation (EFS)-induced contractile tension and frequency, whereas, subsequent administration of APTL-SP did not act on contractility. Incubation with BTX-A at 4 and 10 U/mL for 4 h respectively decreased SP (1 μmol/L)-induced contractions by 26.64% ± 5.12% and 74.92% ± 3.62%. SP-IR fibers and NK1R-IR cells both located within pylorus including mucosa and circular muscle layer. However, fewer SP-fibers were observed in pylorus treated with BTX-A (10 U/mL). In conclusion, BTX-A inhibits SP release from enteric terminals in pylorus and EFS-induced contractile responses when muscarinic cholinergic receptors are blocked by atropine. In addition, BTX-A concentration- and time-dependently directly inhibits SP-induced pyloric smooth muscle contractility.

Botulinum toxin type A as an adjunct in postoperative pain management in dogs undergoing radical mastectomy

The aim of this randomised placebo-controlled, observer-blinded study was to evaluate the analgesic effects of botulinum toxin type A (BoNT-A) as an adjunct for postoperative pain control in dogs. Sixteen dogs undergoing bilateral radical mastectomy for treatment of mammary tumours were enrolled. Twenty-four hours before surgery, the subjects were distributed into two groups of eight dogs each: 7 iu/kg BoNT-A (BoNT-A) or saline (Control) was administered subcutaneously in each mammary gland. Following sedation with intramuscular 0.03 mg/kg acepromazine and 0.3 mg/kg morphine, anaesthesia was induced intravenously with 4 mg/kg propofol and maintained with isoflurane/O2. Postoperative analgesia was evaluated for 72 hours after extubation using the Visual Analogue Scale (VAS) and modified Glasgow Composite Measure Pain Scale (modified-GCMPS). Rescue analgesia was provided with intramuscular morphine (0.5 mg/kg). Data were analysed using analysis of variance, Tukey's test, Mann-Whitney U test and Friedman test (P<0.05). The pain scores were significantly lower in the BoNT-A than in the Control from 8 hours to 60 hours and from 12 hours to 60 hours after extubation, based on the VAS and modified-GCMPS, respectively. Rescue analgesia was required by significantly more dogs in the Control (7/8) compared with the BoNT-A (2/8) (P=0.022). Pre-emptive BoNT-A appears to be effective as an adjuvant for postoperative pain management in dogs undergoing bilateral radical mastectomy.

OnabotulinumtoxinA for trigeminal neuralgia: a review of the available data

Trigeminal neuralgia (TN) patients may develop side effects from centrally acting drugs, have contraindications for neurosurgical procedures, or experience relapse during conventional therapies. OnabotulinumtoxinA (BoNT/A) has been reported to be effective for TN, although this finding has been challenged. An overview of the available evidence based on a narrative/qualitative analysis of the literature is presented. About 90% of patients who receive BoNT/A show an improvement, a higher figure than that reported for the placebo effect of BoNT/A for other headaches. Tolerability of BoNT/A is good, and its few side-effects are transient. The articles reviewed were mainly case reports, case series and open-label trials; however, randomized controlled trials have endorsed the efficacy of BoNT/A for TN. This evidence, together with a better understanding of the analgesic mechanisms of BoNT/A and its proven efficacy in treating other pain syndromes, supports the use of this toxin as a therapeutic option for TN.

Cross-Excitation in Peripheral Sensory Ganglia Associated with Pain Transmission

Despite the absence of synaptic contacts, cross-excitation of neurons in sensory ganglia during signal transmission is considered to be chemically mediated and appears increased in chronic pain states. In this study, we modulated neurotransmitter release in sensory neurons by direct application of type A botulinum neurotoxin (BoNT/A) to sensory ganglia in an animal model of neuropathic pain and evaluated the effect of this treatment on nocifensive. Unilateral sciatic nerve entrapment (SNE) reduced the ipsilateral hindpaw withdrawal threshold to mechanical stimulation and reduced hindpaw withdrawal latency to thermal stimulation. Direct application of BoNT/A to the ipsilateral L4 dorsal root ganglion (DRG) was localized in the cell bodies of the DRG and reversed the SNE-induced decreases in withdrawal thresholds within 2 days of BoNT/A administration. Results from this study suggest that neurotransmitter release within sensory ganglia is involved in the regulation of pain-related signal transmission.

Blockade of glutamate release by botulinum neurotoxin type A in humans: a dermal microdialysis study

BACKGROUND

The analgesic action of botulinum neurotoxin type A (BoNTA) has been linked to the blockade of peripheral release of neuropeptides and neurotransmitters in animal models; however, there is no direct evidence of this in humans.

OBJECTIVES

To investigate the effect of BoNTA on glutamate release in humans, using an experimental model of pain and sensitization provoked by capsaicin plus mild heat.

METHODS

Twelve healthy volunteers (six men, six women) were pretreated with BoNTA (10 U) on the volar forearm and with a saline control on the contralateral side. Dermal microdialysis was applied one week later to collect interstitial samples before and after the application of a capsaicin patch (8%) plus mild heat (40°C⁄60 min) to provoke glutamate release, pain and vasodilation. Samples were collected every hour for 3 h using linear microdialysis probes (10 mm, 100 kD). Dialysate was analyzed for glutamate concentration. Pain intensity and skin vasomotor reactions (temperature and blood flow changes) were also recorded.

RESULTS

BoNTA significantly reduced glutamate release compared with saline (P<0.05). The provoked pain intensity was lower in the BoNTA-pretreated arm (P<0.01). The reduction in pain scores was not correlated with glutamate level. Cutaneous blood flow (P<0.05), but not cutaneous temperature (P≥0.05), was significantly reduced by BoNTA. There was a correlation between glutamate level and skin blood flow (r=0.58⁄P<0.05) but not skin temperature (P≥0.05). No differences according to sex were observed in any response.

CONCLUSIONS

The present study provided the first direct evidence supporting the inhibitory effect of BoNTA on glutamate release in human skin, which is potentially responsible for some of the analgesic action of BoNTA.

Two doses of botulinum toxin type A for the treatment of trigeminal neuralgia: observation of therapeutic effect from a randomized, double-blind, placebo-controlled trial

BACKGROUND

In the majority of cases, trigeminal neuralgia (TN) is a unilateral condition with ultra-short stabbing pain located along one or more branches of the trigeminal nerve. Although prophylactic pharmacological treatment is first choise, considering of insufficient effect or unacceptable side effects, neurosurgical treatment or lesion treatment should be considered. In addition to all these procedures mentioned above, one approach has been based on local intradermal and/or submucosal injections of Botulinum Toxin Type A (BTX-A).

METHODS

We conducted a randomized, double-blind, placebo-controlled since November 2012, and adopted local multi-point injection in 84 cases of classical TN with different doses of BTX-A. Eighty four patients were randomized into following groups: placebo (n = 28); BTX-A 25U (n = 27); BTX-A 75U (n = 29). Follow-up visits were conducted every week after the injection, and the overall duration of the study for each patient were 8 weeks to observe the pain severity, efficacy and adverse reactions at endpoint.

RESULTS

The visual analogue scale (VAS) scores of 25U and 75U groups reduced significantly compared to placebo as early as week 1, and sustained until week 8 throughout the study. There was no significant difference in VAS between 25U and 75U groups throughout the study. The response rates of 25U group (70.4%) and 75U group (86.2%) were significantly higher than placebo group (32.1%) at week 8, and there was no significant difference between 25U and 75U groups. Evaluation of the Patient Global Impression of Change (PGIC) demonstrated that 66.7% (25U group) and 75.9% (75U group) of the patients reported that their pain symptoms were 'much improved' or 'very much improved' versus 32.1% of the placebo group, and there was also no significant difference between 25U and 75U groups. All adverse reactions were graded as mild or moderate.

CONCLUSIONS

BTX-A injection in TN is safe and efficient. It is a useful treatment for refractory TN. Lower dose (25U) and high dose (75U) were similar in efficacy in short-term.

The effect of botulinum toxin B pretreatment to the blood flow in the microvascular anastomosis

BACKGROUND

Although multiple factors can lead to free flap failure, vessel-related accidents are the most important. Many methods have been developed (both intraoperative and postoperative) to prevent vessel-related complications. In this article, we study the effects of a "preoperative treatment" using botulinum toxin B that could enhance the velocity and blood flow of vascular pedicles and decrease vascular accidents.

METHODS

Ten Sprague-Dawley rats were pretreated with botulinum toxin type B at the perivascular area of the femoral vessel. Ten other rats were injected with saline as a control group. After 3 days, pedicle diameter and the peak mean frequency of blood in the pedicle were measured using laser Doppler flowmetry, and the peak mean blood velocity was calculated. We performed a "pedicle division and reanastomosis" operation to compare changes in vessel diameter and peak mean blood velocity.

RESULTS

Vessel diameter was significantly increased in the botox-pretreated group for both veins and arteries. A comparison of the deep femoral vein and artery blood velocities showed that the peak mean velocity was significantly higher in the botox group. The average increase in blood velocity was significantly larger in the botox group.

CONCLUSIONS

Botulinum toxin B is helpful by influencing the microvascular environment through an increase in the blood velocity of the pedicle.

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.

Botulinum toxin type A selectivity for certain types of pain is associated with capsaicin-sensitive neurons

Unlike most classical analgesics, botulinum toxin type A (BoNT/A) does not alter acute nociceptive thresholds, and shows selectivity primarily for allodynic and hyperalgesic responses in certain pain conditions. We hypothesized that this phenomenon might be explained by characterizing the sensory neurons targeted by BoNT/A in the central nervous system after its axonal transport. BoNT/A's central antinociceptive activity following its application into the rat whisker pad was examined in trigeminal nucleus caudalis (TNC) and higher-level nociceptive brain areas using BoNT/A-cleaved synaptosomal-associated protein 25 (SNAP-25) and c-Fos immunohistochemistry. Occurrence of cleaved SNAP-25 in TNC was examined after nonselective ganglion ablation with formalin or selective denervation of capsaicin-sensitive (vanilloid receptor-1 or TRPV1-expressing) neurons, and in relation to different cellular and neuronal markers. Regional c-Fos activation and effect of TRPV1-expressing afferent denervation on toxin's antinociceptive action were studied in formalin-induced orofacial pain. BoNT/A-cleaved SNAP-25 was observed in TNC, but not in higher-level nociceptive nuclei. Cleaved SNAP-25 in TNC disappeared after formalin-induced trigeminal ganglion ablation or capsaicin-induced sensory denervation. Occurrence of cleaved SNAP-25 in TNC and BoNT/A antinociceptive activity in formalin-induced orofacial pain were prevented by denervation with capsaicin. Cleaved SNAP-25 localization demonstrated toxin's presynaptic activity in TRPV1-expressing neurons. BoNT/A reduced the c-Fos activation in TNC, locus coeruleus, and periaqueductal gray. Present experiments suggest that BoNT/A alters the nociceptive transmission at the central synapse of primary afferents. Targeting of TRPV1-expressing neurons might be associated with observed selectivity of BoNT/A action only in certain types of pain.

Effects of intrabursal administration of botulinum toxin type B on lameness in horses with degenerative injury to the podotrochlear apparatus

OBJECTIVE

To determine the safety and short-term efficacy of intrabursal administration of botulinum toxin type B (BTXB) to alleviate lameness in horses with degenerative injury to the podotrochlear apparatus (PA).

ANIMALS

10 Quarter Horses with degenerative injury to the PA.

PROCEDURES

Degenerative injury to the PA was confirmed with diagnostic analgesia and imaging. Then, BTXB (3.8 to 4.5 U/kg) was injected into the podotrochlear (navicular) bursa of each horse. Three horses were used in a safety evaluation. Subsequently, video recordings of lameness evaluations were obtained for 7 client-owned horses 5 days before (baseline) and 7 and 14 days after BTXB treatment and used to determine the effect of BTXB injection on lameness; 1 horse was removed from the study 8 days after BTXB treatment. Three investigators who were unaware of the treated forelimbs or time points separately reviewed the recordings and graded the lameness of both forelimbs of the horses.

RESULTS

Improvement in lameness of the treated forelimbs was detected at 1 or both time points after BTXB administration in all horses. However, all horses had some degree of lameness at the end of the study. Two horses developed transient increases in lameness 48 to 72 hours after treatment; lameness resolved uneventfully.

CONCLUSIONS AND CLINICAL RELEVANCE

Intrabursal injection of BTXB temporarily alleviated chronic lameness in horses with degenerative injury to the PA, without causing serious short-term adverse effects. Further investigation into the potential use of BTXB in horses affected by degenerative injury to the PA is warranted.

Intra-articular botulinum toxin A for the treatment of osteoarthritic joint pain in dogs: a randomized, double-blinded, placebo-controlled clinical trial

The aim of this study was to investigate the efficacy of intra-articular (IA) botulinum toxin A (IA BoNT A) for the treatment of osteoarthritic joint pain in dogs. The study was a placebo-controlled, randomized, double-blinded clinical trial with parallel group design and 12-week follow-up. Thirty-six dogs with chronic lameness due to stifle, hip or elbow osteoarthritis were randomized to receive an IA injection of 30IU of BoNT A or placebo. The main outcome variables were vertical impulse (VI) and peak vertical force (PVF) measured with a force platform, and Helsinki chronic pain index (HCPI). Subjective pain score and the need for rescue analgesics were secondary variables. The response to treatment was assessed as the change from baseline to each examination week. The variables were analyzed by ANOVA with repeated measurements and results were considered statistically significant if P ⩽ 0.05. The improvement from baseline to 12 weeks after baseline was statistically significant in VI, PVF and HCPI in the treatment group (P=0.001, P=0.054 and P=0.053, respectively). Additionally, there were statistically significant improvements in VI in the treatment group at 2, 4 and 8 weeks after baseline (P=0.037, P=0.016 and P=0.016, respectively). The difference between groups in improvement in VI was statistically significant at 12weeks after baseline (P=0.005). There was no significant change in the subjective pain score or in the requirement for rescue analgesics in either group. No major adverse events thought to be related to trial protocol were detected. These results suggest that IA BoNT A has some efficacy in reducing osteoarthritic pain in dogs.

Botulinum toxin type A in chronic migraine

The use of botulinum toxin type A continues to be investigated by the US FDA for potential use in the treatment of headache. As part of this process there has been extensive research conducted by individual study sites as well as multicenter trials. To date, the majority of the focus has been on migraine headache as well as on tension-type headache. The results of these studies have been mixed. A variety of issues may contribute to the mixed results, including difference in the dose of toxin used, the number of injection sites utilized, the treatment paradigm itself, confounding medications, high and prolonged placebo response, as well as patient selection issues. Currently, the focus on botulinum toxin type A is on those patients who have chronic daily headache with a migraine component to their clinical picture. The results of two large trials in this population produced positive findings, especially when consideration is given to the a priori additional analyses of this complex patient population. The results of these studies have allowed a more focused program to be undertaken in the Phase III evaluation. At the same time, additional work has been performed to understand the mechanism by which botulinum toxin type A may work to alleviate migraine. This work may contribute substantially to improving outcomes with botulinum toxin type A. Characterization of the mechanism of action in pain may be crucial to outcomes because many issues are related to central sensitization.

A closer look to botulinum neurotoxin type A-induced analgesia

Chronic pain indicates a type of pain that lasts over time and is accompanied by diagnostic and therapeutic difficulties. It follows that treatment failures are common and patients roam from doctor to doctor in search of an effective care program. So there is an urgent need for long-acting and effective therapeutics to alleviate symptoms of the varied forms of chronic pain. During the past few years, a good success has been achieved with a derivative of a neurotoxin. It has been shown that administration of this toxin can block the release of neurotransmitters and pain mediators. Botulinum neurotoxin type A (BoNT/A) is well known as a treatment for neuromuscular conditions such as dystonia and spasticity. However, the clinical application for BoNT/A has continued to expand. Its analgesic effect has been used in clinical practice with satisfactory results. This review provides an introduction of a hypothesis for the mechanism by which BoNT/A eases chronic pain. It also summarizes the clinical therapeutic effects of BoNT/A in different types of chronic pain and its potential prospects.

Botulinum toxins: mechanisms of action, antinociception and clinical applications

Botulinum toxin (BoNT) is a potent neurotoxin that is produced by the gram-positive, spore-forming, anaerobic bacterium, Clostridum botulinum. There are 7 known immunologically distinct serotypes of BoNT: types A, B, C1, D, E, F, and G. Clostridum neurotoxins are produced as a single inactive polypeptide chain of 150kDa, which is cleaved by tissue proteinases into an active di-chain molecule: a heavy chain (H) of ∼100 kDa and a light chain (L) of ∼50 kDa held together by a single disulfide bond. Each serotype demonstrates its own varied mechanisms of action and duration of effect. The heavy chain of each BoNT serotype binds to its specific neuronal ecto-acceptor, whereby, membrane translocation and endocytosis by intracellular synaptic vesicles occurs. The light chain acts to cleave SNAP-25, which inhibits synaptic exocytosis, and therefore, disables neural transmission. The action of BoNT to block the release of acetylcholine botulinum toxin at the neuromuscular junction is best understood, however, most experts acknowledge that this effect alone appears inadequate to explain the entirety of the neurotoxin's apparent analgesic activity. Consequently, scientific and clinical evidence has emerged that suggests multiple antinociceptive mechanisms for botulinum toxins in a variety of painful disorders, including: chronic musculoskeletal, neurological, pelvic, perineal, osteoarticular, and some headache conditions.

Botulinum toxin injections for simple partial motor seizures associated with pain

Intractable epilepsy with painful partial motor seizures is a relatively rare and difficult disorder to treat. We evaluated the usefulness of botulinum toxin to reduce ictal pain. Two patients received two or four botulinum toxin (BTX) injections at one-to-two-month intervals. Patient 1 had painful seizures of the right arm and hand. Patient 2 had painful seizures involving the left foot and leg. Injections were discontinued after improved seizure control following resective surgery. Both patients received significant pain relief from the injections with analgesia lasting at least two months. Seizure severity was reduced, but seizure frequency and duration were unaffected. For these patients, BTX was effective in temporarily relieving pain associated with muscle contraction in simple partial motor seizures. Our findings do not support the hypothesis that modulation of motor end-organ feedback affects focal seizure generation. BTX is a safe and reversible treatment that should be considered as part of adjunctive therapy after failure to achieve control of painful partial motor seizures.

Inhibitory effect of botulinum toxin type A on the NANC system in rat respiratory models of neurogenic inflammation

This study investigated whether botulinum toxin type A (BTX-A) inhibits respiratory neurogenic inflammation in the non-adrenergic, non-cholinergic (NANC) transmitter system in rats. Neurogenic inflammation models were induced in Sprague Dawley (SD) rats through bilateral cerebral artery occlusion (BCAO) for different times (0, 30 and 60 min) or by stimulation with capsaicin at different doses (5 or 15 g/kg). Pre-Bötzinger Complex-Spikes and the expression of substance P, synaptosomal-associated protein-25 (SNAP-25), and reactive oxygen species (ROS) were detected with or without pretreatment of rats with BTX-A (15 or 30 U/kg). BCAO reduced pre-Bot C spike activity (spike/s) and increased the breath rate (breaths/s) in an unstable pattern in comparison to controls, while pretreatment with BTX-A slightly reduced this phenomenon. Pretreatment with BTX-A inhibited BCAO- or capsaicin-induced increases in expression of SNAP-25, substance P, and ROS in a dose-dependent manner in brainstem and lung tissue. BTX-A exerts a suppressive effect on neurogenic inflammation via non-adrenergic, non-cholinergic transmitters. These results add to the body of evidence elucidating the non-cholinergic effects of BTX-A in the context of neurogenic inflammation.

Central action of peripherally applied botulinum toxin type A on pain and dural protein extravasation in rat model of trigeminal neuropathy

BACKGROUND

Infraorbital nerve constriction (IoNC) is an experimental model of trigeminal neuropathy. We investigated if IoNC is accompanied by dural extravasation and if botulinum toxin type A (BoNT/A) can reduce pain and dural extravasation in this model.

METHODOLOGY/PRINCIPAL FINDINGS

Rats which developed mechanical allodynia 14 days after the IoNC were injected with BoNT/A (3.5 U/kg) into vibrissal pad. Allodynia was tested by von Frey filaments and dural extravasation was measured as colorimetric absorbance of Evans blue-plasma protein complexes. Presence of dural extravasation was also examined in orofacial formalin-induced pain. Unilateral IoNC, as well as formalin injection, produced bilateral dural extravasation. Single unilateral BoNT/A injection bilaterally reduced IoNC induced dural extravasation, as well as allodynia (lasting more than 2 weeks). Similarly, BoNT/A reduced formalin-induced pain and dural extravasation. Effects of BoNT/A on pain and dural extravasation in IoNC model were dependent on axonal transport through sensory neurons, as evidenced by colchicine injections (5 mM, 2 µl) into the trigeminal ganglion completely preventing BoNT/A effects.

CONCLUSIONS/SIGNIFICANCE

Two different types of pain, IoNC and formalin, are accompanied by dural extravasation. The lasting effect of a unilateral injection of BoNT/A in experimental animals suggests that BoNT/A might have a long-term beneficial effect in craniofacial pain associated with dural neurogenic inflammation. Bilateral effects of BoNT/A and dependence on retrograde axonal transport suggest a central site of its action.