Apoptotic action of botulinum toxin on masseter muscle in rats: early and late changes in the expression of molecular markers

Effect of botulinum toxin type A on masticatory function and musculoskeletal structure in rabbits

Botulinum toxin (BTX) injection could relieve many disorders in the maxillofacial regions. Although it could have some side effects on bones and muscles. This study investigated the effects of a single Botulinum Toxin Type A (BoNT-A) injection on masticatory function and musculoskeletal structure in rabbits. Twenty rabbits were divided into two groups: one received BoNT-A (10 units), and the other received saline. The study periodically monitored electromyography (EMG), compound action potential (CAP), food intake, and body weight, along with histological and immunohistochemical analyses after four weeks. Revealed significant reductions in body weight, EMG, and CAP in the BoNT-A group during the first two weeks, but no notable differences in the following two weeks. Histological examination showed thinning of the alveolar bone trabecula, while ultrastructural changes in the masseter muscle included swollen mitochondria, disorganized Z bands, and heterochromatic nuclei. Light microscopy revealed increased fibrous tissue, muscle fiber breakdown, and vacuolations. Desmin expression was significantly reduced in the BoNT-A group. The findings indicate that a single BoNT-A injection temporarily reduces masticatory function and causes degenerative changes in muscle tissue and bone structure, including alveolar bone resorption, lasting at least four weeks.

Effect of zinc or copper supplementation on the efficacy and sustainability of botulinum toxin A "Botox" injection in masseter muscle of albino rats

OBJECTIVES

This study aimed to evaluate whether oral zinc or copper supplementation affected the efficacy and sustainability of botulinum toxin-A (BTX-A) injection in masseter muscle of albino rats.

MATERIALS AND METHODS

32 adult male albino rats were allocated equally into four groups: group I (control), group II received 10U BTX-A injection, group III received 10U BTX-A injection + zinc (1 mg, 4 days pre-injection), and group IV received 10U BTX-A injection + copper (0.04 mg, 7 days post-injection). Rats were euthanized at 2 and 12 weeks (4 rats per subgroup) after injection. The masseter muscle was examined via histological, histochemical, histomorphometrical and real-time polymerase chain reaction (qRT-PCR) analyses.

RESULTS

The histopathological results of the BTX-A group showed atrophied muscle fibers with increased atrophy with time compared to the control group. The BTX-A + zinc group displayed more atrophy compared to BTX-A group. Conversely, the BTX-A + copper group demonstrated improved histology of muscle fibers compared to BTX-A and BTX-A + zinc groups. Histomorphometric analysis of Masson trichrome staining at 2 and 12 weeks revealed that collagen area percentage was the highest in the BTX-A + copper and control groups, followed by BTX-A and BTX-A + zinc groups. At 12 weeks, the nuclear factor kappa beta (NF-κB) mRNA expression was significantly higher in BTX-A + zinc and BTX-A groups compared to BTX-A + copper group and relative to the control group.

CONCLUSION

Zinc supplementation significantly improved the effectiveness and durability of BTX-A, whereas copper supplementation reduced its efficacy.

Influence of vitamin D on muscle strength and botulinum toxin dosage through surface electromyography

PURPOSE

To evaluate the influence of patients' serum vitamin D levels on muscle strength characteristics and whether it impacts the durability of botulinum toxin (BT) treatment.

METHODS

The muscle strength of the frontal and corrugator muscles was evaluated before and after the application of TB with pre- and post-application control measurements, and at weeks 2, 5 and 12. The effect of vitamin D on muscle strength and its interaction with BT were investigated in 20 patients. The muscle contraction force was measured by surface electromyography.

RESULTS

The results revealed statistically significant differences between the frontal measurement groups at weeks 2 and 5, as well as for the corrugator in the same weeks and at week 12. Regarding vitamin D, significant differences were observed only in the initial group with vitamin D > 30 ng/mL compared to < 30 ng/mL for the frontal muscles. Patients with higher levels of vitamin D had higher average muscle strength compared to those with lower levels in all evaluations.

CONCLUSIONS

It was observed that vitamin D influences muscle strength and the necessary dosage of BT.

Systematic review of the histological and functional effects of botulinum toxin A on masticatory muscles: Consideration in dentofacial orthopedics and orthognathic surgery

INTRODUCTION

Botulinum toxin type A causes muscle paralysis and is widely used in the masticatory muscle for stomatognathic diseases, such as temporomandibular disorder, bruxism, or masseteric hypertrophy. Nonetheless, its muscular effect remains unclear. Better understanding could aid improved use and perhaps new indications, particularly in dentofacial orthopaedics and orthognathic surgery.

METHODS

This systematic review explored the histologic and functional effects of botulinum toxin in animal and human masticatory muscles and was conducted in accordance with the recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. The MEDLINE, Web of Science, and Cochrane Library electronic databases were searched for relevant articles. The inclusion criteria were human or animal masticatory muscle analysis after botulinum toxin injection(s) AND histological structural/ultrastructural analysis by optical or electronic microscopy OR functional effect analysis by bite force evaluation (occlusal force analyzer) and muscle activity (electromyography).

RESULTS

Of an initial 1578 articles, 44 studies were eventually included. Botulinum toxin injection in the masticatory muscle altered its histological structure and functional properties. The human and animal studies revealed ultrastructural change, atrophy, and fiber type modifications of the masticatory muscles after one injection. Botulinum toxin decreased bite force and muscle activity, but recovery was uncertain.

CONCLUSIONS

Muscle forces applied on the skeleton is a key feature of facial growth. Masticatory muscle paralysis changes mechanical stress on bones, which rebalances the force applied on facial bones. This new balance could benefit dental deformity or surgical relapse. Therefore, botulinum toxin could limit the orthognathic effect of the masticatory muscles in such patients. Given the uncertain recovery, multiple injections should be avoided, and usage should not deviate from established consensus.

The Role of Botulinum Neurotoxin A in the Conservative Treatment of Fractures: An Experimental Study on Rats

This paper explores the role of botulinum neurotoxin in aiding fracture recovery through temporary muscle paralysis. Specifically, it investigates the effects of botulinum neurotoxin-induced paralysis of the sternocleidomastoid muscle on clavicle fractures in rats. The research aims to assess safety, effectiveness, and the impact on fracture healing. Healthy male Albino Wistar rats were divided into four groups: clavicle fracture, botulinum neurotoxin injection, both, and control. Surgeries were conducted under anaesthesia, and postoperatively, animals were monitored for 28 days. Euthanasia and radiological assessment followed, examining fracture healing and muscle changes, while tissues were histopathologically evaluated. The modified Lane-Sandhu scoring system was used for the radiographic evaluation of clavicle fractures, and the results varied from complete healing to nonunion. Histopathological examination at 28 days postfracture showed fibrous tissue, mesenchymal cells, and primary callus formation in all groups. Despite varied callus compositions, botulinum neurotoxin administration did not affect clavicle healing, as evidenced by similar scores to the control group. Several studies have explored botulinum neurotoxin applications in fracture recovery. Research suggests its potential to enhance functional recovery in certain types of fractures. Theoretical benefits include managing muscle spasticity, aiding reduction techniques, and preventing nonunion. However, botulinum neurotoxin's transient effect and nonuniversal applications should be considered. The present study found that botulinum toxin had no clear superiority in healing compared to controls, while histological evaluation showed potential adverse effects on muscle tissue. Further research is essential to understand its risk-benefit balance and long-term effects.

Histomorphometric Changes of the Masseter Muscle of Rats After a Single Injection of Botulinum Toxin Type A

BACKGROUND

It has been reported that botulinum toxin type A (BoNT-A) produces structural changes in masticatory muscles. However, not all histomorphometric parameters affected by BoNT-A parameters have been assessed. This study investigated the histomorphometric changes in the masseter muscle of rats after a single injection of BoNT-A.

METHODS

Forty-four adult animals were randomly divided into control group (n = 22) and BoNT-A group (n = 22). Controls received a single dose of 0.14 mL/kg of saline in masseter muscles, and the BoNT-A group received a 7 U/Kg of BoNT-A. The groups received the same volume of injected substances. Animals were sacrificed on 7th (n = 5), 14th (n = 5), 21st (n = 5), 28th (n = 4) and 90th (n = 3) days post-treatment. Histological masseter tissue slides were obtained from hematoxylin-eosin treatment and analyzed in optical microscopy regarding muscle cross-sectional area, amount of connective tissue and quantity and diameter of myocytes. For statistical analysis, generalized linear models were used to compare the data (ANOVA). In all test, the significance level of 5% was set.

RESULTS

BoNT-A values of cross-sectional area of the masseter muscle were significantly lower than controls (p < 0.01) throughout the study. Regarding myocytes quantity, BoNT-A subgroups presented higher values than controls (p < 0.0001) since the 14th day until the end of the study; however, the diameter of myocytes was smaller in all BoNT-A subgroups (p < 0.0001) in all assessment points. The amount of connective tissue was higher in BoNT-A subgroups (p < 0.0001) throughout the study.

CONCLUSION

A single injection of BoNT-A altered the structure of masseter muscle of rats, regarding its histomorphometric parameters.

NO LEVEL ASSIGNED

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The Action of Botulinum Toxin A on the Sternocleidomastoid Muscle: An Experimental Study on Rats

In this study, we aim to investigate the effective dose of botulinum neurotoxin A that results in paralysis of the sternocleidomastoid muscle for a minimum duration of 28 days in Wistar rats. This research is the first in a series of studies to investigate the value of botulinum toxin A in the healing of clavicle fractures through the temporary paralysis of the sternocleidomastoid. A surgical incision was made under general anaesthesia, and botulinum neurotoxin A in respective doses of 4 and 6 international units (IU) or normal saline in equivalent volumes were injected directly into the exposed muscle. Electromyography was conducted on days 0, 7, and 28 following substance administration to determine the extent of muscle paralysis. Electromyography on day 0 showed no paralysis in either group. Animals injected with neurotoxin all exhibited paralysis on days 7 and 28 that was weaker in the group injected with the smaller dose of 4 IU. One death occurred in the group injected with the higher dose (6 IU), whereas in the control group, no paralysis was seen. Botulinum neurotoxin A in a dose of 6 IU resulted in complete paralysis of the sternocleidomastoid in rats for a minimum of 28 days. A dose of 4 IU resulted in less potent paralysis but was safer in our research. Botulinum neurotoxin is a substance utilised in cosmetics and therapeutics for many years, yet research shows that its use can be expanded to target a wider range of pathologies. In this series of studies, we aim to explore the neurotoxin's applications on the treatment of clavicle fractures. To investigate this, we need to first establish the duration of its action on the sternocleidomastoid muscle.

Biphasic Injection for Masseter Muscle Reduction with Botulinum Toxin

Masseter Muscle Hypertrophy (MMH) is a well-known clinical benign condition that is not gender-specific and it can be monolateral or bilateral. Botulinum Toxin type A (BoNTA) injection has been widely described for MMH treatment and non-surgical facial slimming. BoNTA masseter injections have high efficacy and safety profile, but the risks of side effects remain. Muscular bulging during mastication is a complication due to the superficial overcompensation of masseteric fibers in response to neurotoxic weakening of the deep masseter. We present a biphasic-injection technique for BoNTA administration, based following anatomical concept and developed in order to prevent paradoxical bulging. A total of 98 treatments from 2015 to 2020 were performed with this technique. No remarkable complications occurred in our study. No cases of loss of full smile, difficulty in mouth opening, dizziness, headache, neurapraxia, and xerostomia were reported. A case of asymmetric smiling was self-resolved within a week. No patient claimed transient muscle weakness as distressing. No cases of paradoxical bulging were observed. Extensive knowledge of muscular anatomy and appropriate injection technique are key factors in achieving the desired result and avoiding complications. We feel that sharing this tip could be helpful for all the physicians involved in MMH treatment with BoNTA.

Influence of botulinum toxin A on craniofacial morphology after injection into the right masseter muscle of dystrophin deficient (mdx-) mice

BACKGROUND

Severe craniofacial and dental abnormalities, typical for patients with progressive Duchenne muscular dystrophy (DMD), are an exellcent demonstration of Melvin L. Moss "functional matrix theory", highlighting the influence of muscle tissue on craniofacial growth and morphology. However, the currently best approved animal model for investigation of this interplay is the mdx-mouse, which offers only a limited time window for research, due to the ability of muscle regeneration, in contrast to the human course of the disease. The aim of this study was to evaluate craniofacial morphology after BTX-A induced muscle paralysis in C57Bl- and mdx-mice, to prove the suitability of BTX-A intervention to inhibit muscle regeneration in mdx-mice and thus, mimicking the human course of the DMD disease.

METHODS

Paralysis of the right masseter muscle was induced in 100 days old C57Bl- and mdx-mice by a single specific intramuscular BTX-A injection. Mice skulls were obtained at 21 days and 42 days after BTX-A injection and 3D radiological evaluation was performed in order to measure various craniofacial dimensions in the sagittal, transversal and vertical plane. Statstical analysis were performed using SigmaStat®Version 3.5. In case of normal distribution, unpaired t-test and otherwise the Mann-Whitney-U test was applied. A statistical significance was given in case of p ≤ 0.05.

RESULTS

In contrast to C57Bl-mice, in mdx-mice, three weeks after BTX-A treatment a significant decrease of skull dimensions was noted in most of the measurements followed by a significant increase at the second investigation period.

CONCLUSIONS

BTX-A can induce changes in craniofacial morphology and presumably partially inhibit muscle regeneration in mdx-mice, but cannot completely intensify craniofacial effects elicited by dystrophy. Further research is necessary in order to fully understand muscle-bone interplay after BTX-A injection into dystrophic muscles.

Ultrasound dimensional changes of the anterior belly of the digastric muscle induced by orthognathic surgery and botulinum toxin A injection in Class II malocclusion

OBJECTIVES

The aim of the study is to evaluate the ultrasonographic dimensional changes of the anterior belly of the digastric muscle (ABDM), occurring after intramuscular botulinum toxin A (BTX-A) injection during orthognathic surgery, in a series of five Class II malocclusion patients.

METHODS

All the patients received 20 units of BTX-A, into both ABDM, intraoperatively. The length, width and cross-sectional area (CSA) of the ABDM were ultrasonographically measured at three different time points: T₀ (preoperatively), T₁ (postoperatively at 2 weeks after the surgical intervention), and T₂ (postoperatively at 6-9 months).

RESULTS

A statistically significant higher length of the ABDM was noted postoperatively, at T₁ and T₂ compared to T₀. The patients showed an increased length by 12.2% at 2 weeks postoperatively and continued to increase, reaching 24.6% at 6 months. A decreased width of ABDM by 6.5% at T₁ compared with T₀ was also found.

CONCLUSIONS

Postoperative ultrasound (US) follow-up measurements in patients with Class II malocclusion, orthognathic surgery and intraoperative BTX-A injection in the ABDM, showed dimensional changes of the muscle, with elongation and thinning. The muscular modifications were more pronounced at 6 months postoperatively, indicating consistency and potential benefit of using BTX-A in reducing the risk of surgical relapse. Further data on longer-term follow-up and larger number of cases are necessary.

Efficacy of Incobotulinum toxin-A for the treatment of masseter muscle hypertrophy in Asian Indian patients: A 2-year follow-up study

BACKGROUND

With the changing trends, more and more patients are opting for nonsurgical or minimally invasive options for reshaping the face. Noninvasive treatments such as incobotulinumtoxinA (Xeomin Cosmetic^® ; Merz Pharma Canada Ltd., Burlington, ON, Canada) are a preferred modality for reducing the volume of the muscle and therefore reducing the width of masseter.

AIMS

To evaluate the efficacy of Xeomin treatment in long-term management of bilateral masseter hypertrophy in Asian Indian patients.

PATIENTS/METHODS

A total of 30 patients were enrolled in the study and were injected with 30 U Xeomin on each side of face, at baseline. Fifteen patients received a second session of Xeomin injection at 12th week, and remaining 15 patients received an additional third session, at 12th and 24th weeks post the first injection, respectively. Follow-up was done at 4th-, 12th-, 24th-, and 36th-week and at first- and second-year follow-ups.

RESULTS

For the patients who received two injections, the maximum reduction of 26.85% was observed at 24th week, which was maintained as 20.04% reduction until second follow-up year. The patients who received three injections exhibited very high reduction of 43.12% of masseter volume at 36th week, which was maintained at 38.72 % until the second follow-up year. Three sessions of Xeomin injections were proved to be more effective in long-term maintenance of reduced masseter volume than 2 sessions of injections.

CONCLUSIONS

Xeomin injections were found to be effective in long-term management of bilateral masseter hypertrophy. This is the first of its kind paper, which evaluates the long-term effects of Xeomin injections for the treatment of masseter hypertrophy.

Botulinum toxin A injection into the anterior belly of the digastric muscle increased the posterior width of the maxillary arch in developing rats

Background

The purpose of this study was to evaluate the effects of botulinum toxin A (BTX) injection into the anterior belly of the digastric muscle on a growing rat.

Methods

Ten Sprague Dawley rats were used in this study. When the rats were 13 days old, 0.5 units of BTX was injected into the anterior belly of the digastric muscle for the experimental group (n = 5). For the control, the same volume of normal saline was injected (n = 5). The rats were sacrificed at 60 days old, and the skulls were harvested for micro-computed tomography (μCT) analysis.

Results

In anthropometric analysis, the zygomatic arch and mandibular bi-condylar width were significantly lower in the experimental group than those in the control group (P = 0.025 and 0.027, respectively). The maxillary point width was significantly higher in the experimental group than that in the control group (P = 0.020).

Conclusion

BTX injection into the anterior belly of the digastric muscle had effects on the maxillofacial bony width in growing rats.

Masseter muscle atrophy impairs bone quality of the mandibular condyle but not the alveolar process early after induction

BACKGROUND

Masseter muscle function influences mandibular bone homeostasis. As previously reported, bone resorption markers increased in the mouse mandibular condyle two days after masseter paralysis induced with botulinum toxin type A (BoNTA), followed by local bone loss.

OBJECTIVE

This study aimed to evaluate the bone quality of both the mandibular condyle and alveolar process in the mandible of adult mice during the early stage of a BoNTA-induced masseter muscle atrophy, using a combined 3D histomorphometrics and shape analysis approach.

METHODS

Adult BALB/c mice were divided into an untreated control group and an experimental group; the latter received one single BoNTA injection in the right masseter (BoNTA-right) and saline in the left masseter (Saline-left). 3D bone microstructural changes in the mandibular condyle and alveolar process were determined with high-resolution microtomography. Additionally, landmark-based geometric morphometrics was implemented to assess external shape changes.

RESULTS

After 2 weeks, masseter mass was significantly reduced (P-value <0.001). When compared to Saline-left and untreated condyles, BoNTA-right condyles showed significant bone loss (P-value <0.001) and shape changes. No significant bone loss was observed in the alveolar processes of any of the groups (P-value >0.05).

CONCLUSION

Condyle bone quality deteriorates at an early stage of BoNTA-induced masseter muscle atrophy, and before the alveolar process is affected. Since the observed bone microstructural changes resemble those in human temporomandibular joint degenerative disorders, the clinical safety of BoNTA intervention in the masticatory apparatus remains to be clarified.

The effect of botulinum toxin-A injection into the masseter muscles on prevention of plate fracture and post-operative relapse in patients receiving orthognathic surgery

Background

Botulinum toxin-A (BTX-A) injection into muscle reduces muscular power and may prevent post-operative complication after orthognathic surgery. The purpose of this study was (1) to evaluate BTX-A injection into the masseter muscle on the prevention of plate fracture and (2) to compare post-operative relapse between the BTX-A injection group and the no injection group.

Methods

Sixteen patients were included in this study. Eight patients received BTX-A injection bilaterally, and eight patients served as control. All patients received bilateral sagittal split ramus osteotomy for the mandibular setback and additional surgery, such as LeFort I osteotomy or genioplasty. Post-operative plate fracture was recorded. SNB angle, mandibular plane angle, and gonial angle were used for post-operative relapse.

Results

Total number of fractured plates in patients was 2 out of 16 plates in the BTX-A injection group and that was 8 out of 16 plates in the no treatment group (P = 0.031). However, there were no significant differences in post-operative changes in SNB angle, mandibular plane angle, and gonial angle between groups (P > 0.05).

Conclusions

BTX-A injection into the masseter muscle could reduce the incidence of plate fracture.

Botulinum Toxin Induced Atrophy: An Uncharted Territory

Botulinum neurotoxins (BoNTs) produce local chemo-denervation by cleaving soluble N-ethylmaleimide-sensitive factor activating protein receptor (SNARE) proteins. Botulinum neurotoxins are therapeutically indicated in several neurological disorders and have been in use for three decades. The long-term efficacy, safety, and side effects of BoNTs have been well documented in the literature. However, the development of muscle atrophy following chronic exposure to BoNTs has not received sufficient attention. Muscle atrophy is not only cosmetically distressing, but also has an impact on future injections. An extensive literature search was conducted on atrophy and mechanisms of atrophy. Five hundred and four relevant articles in the English language were reviewed. This review revealed the surprising lack of documentation of atrophy within the literature. In addition, as demonstrated in this review, the mechanisms and the clinical factors that may lead to atrophy have also been poorly studied. However, even with this limited information it is possible to indicate factors that could modify the clinical approach to botulinum toxin injections. This review highlights the need for further study of atrophy following BoNT injections.

Effect of the masseter muscle injection of botulinum toxin A on the mandibular bone growth of developmental rats

Background

The objective of this study was to evaluate the influence of masticatory muscle injection of botulinum toxin type A (BTX-A) on the growth of the mandibular bone in vivo.

Methods

Eleven Sprague-Dawley rats were used, and BTX-A (n = 6) or saline (n = 5) was injected at 13 days of age. All injections were given to the right masseter muscle, and the BTX-A dose was 0.5 units. All of the rats were euthanized at 60 days of age. The skulls of the rats were separated and fixed with 10% formalin for micro-computed tomography (micro-CT) analysis.

Results

The anthropometric analysis found that the ramus heights and bigonial widths of the BTX-A-injected group were significantly smaller than those of the saline-injected group (P < 0.05), and the mandibular plane angle of the BTX-A-injected group was significantly greater than in the saline-injected group (P < 0.001). In the BTX-A-injected group, the ramus heights II and III and the mandibular plane angles I and II showed significant differences between the injected and non-injected sides (P < 0.05). The BTX-A-injected side of the mandible in the masseter group showed significantly lower mandibular bone growth compared with the non-injected side.

Conclusion

BTX-A injection into the masseter muscle influences mandibular bone growth.

Correction of Malocclusion by Botulinum Neurotoxin Injection into Masticatory Muscles

Botulinum toxin (BTX) is a neurotoxin, and its injection in masticatory muscles induces muscle weakness and paralysis. This paralytic effect of BTX induces growth retardation of the maxillofacial bones, changes in dental eruption and occlusion state, and facial asymmetry. Using masticatory muscle paralysis and its effect via BTX, BTX can be used for the correction of malocclusion after orthognathic surgery and mandible fracture. The paralysis of specific masticatory muscles by BTX injection reduces the tensional force to the mandible and prevents relapse and changes in dental occlusion. BTX injection in the anterior belly of digastric and mylohyoid muscle prevents the open-bite and deep bite of dental occlusion and contributes to mandible stability after orthognathic surgery. The effect of BTX injection in masticatory muscles for maxillofacial bone growth and dental occlusion is reviewed in this article. The clinical application of BTX is also discussed for the correction of dental malocclusion and suppression of post-operative relapse after mandibular surgery.

Botulinum Toxin Conjugated With Silk Fibroin and 4-Hexylresorcinol

PURPOSE

The objective of this study was to evaluate whether silk fibroin (SF) incorporated into 4-hexylresorcinol (4HR) could increase botulinum toxin-A (BTX-A) activity.

MATERIAL AND METHODS

In total, 30 rats were used for this study. The animals were divided into 6 groups according to the injected materials (SA: saline only; SF; 4HR; B2: 2 units of BTX-A; B2 + SF + 4HR: combination of B2, SF, and 4HR; B5: 5 units of BTX-A). Serial sonography was used for the evaluation of muscle thickness after injection. Immunohistochemical staining was used for the evaluation of myosin type II (myo2) and Bcl-2 protein expression.

RESULTS

The relative thickness of the masseter muscle in B2 group was 66.14% ± 4.55% to the preinjection level; in B2 + SF + 4HR group was 54.59% ± 4.83%, and in B5 group was 56.19% ± 8.28%. Any BTX-injected group showed significantly lower value of the relative muscle thickness compared to SA, SF, or 4HR group (P < 0.001 for all). The difference of relative muscle thickness between B2 group and B2 + SF + 4HR group was statistically significant (P < 0.001). The intensity of myo2 immunostaining in B5, B2, and B2 + SF + 4HR group was significantly higher than those in the other groups (P < 0.05).

CONCLUSIONS

When 2 units of BTX was incorporated to SF and 4HR, combination formula showed similar activity to those of 5 units of BTX.

Ultrastructural evaluation of intramuscular applied botulinum toxin type A in striated muscles of rats

BACKGROUND

Botulinum toxin type A (BTX-A) is clinically utilized for therapeutic and cosmetic purposes in maxillofacial surgery as well as many other medical specialties. There is no sufficient ultrastructural research about BTX and it is controversial whether BTX-A causes muscle degeneration to some extent, in the course of therapy. The aim of this study was to evaluate the histological effects of BTX-A when injected into masseter and gluteal muscles.

MATERIALS AND METHODS

A total of 30 male Sprague-Dawley rats were used and randomly divided into experimental (n =15) and control groups (n =15). Masseter and gluteal muscles were injected with a single dose of BTX-A in normal saline (0.5 U/0.1 ml), or 0.1 ml of normal saline, in the experimental and control groups, respectively. After 12 weeks all the rats were sacrificed. Gluteal, masseter muscles, and the sciatic nerves of the rats were prepared and electron microscopic, and light microscopic evaluation was performed on semi-thin sections cut from Epon embedded tissues and stained with toluidine blue. Quantitative parameters such as muscle fiber thickness and qualitative assessments including sarcosomal (striated muscle mitochondria) deformation, glycogen content, features of the triad structures and the intensity of connective tissue around the muscle fibers, and endoneurial and perineural tissue around nerve fibers were evaluated microscopically. We paired BTX- A (+) and BTX-A (-) samples statistically. Independent Samples t-test was used for the statistical analysis.

RESULTS

Muscle fiber's diameter was significantly decreased in BTX-A (+) group (p <0,001). Atrophic changes in the myofibrils were characterized by a decrease in the myofibrillar diameter and changes in the sarcomere structure, and were prominent in the BTX-A (+) group. Also, some other changes like dilatation in the sarcoplasmic reticulum cisternae, mitochondrial swelling, and clearing of mitochondrial cristae associated with degeneration, were detected. No morphologic difference in the sciatic nerve fibers was detected, and myelin sheaths of axon structures were intact in both groups.

CONCLUSION

BTX-A-induced muscular changes that are predominantly related to atrophy instead of degeneration. Although predominantly related to atrophy, our degeneration related findings suggest that further studies are needed focusing on detecting BTX-A effects on a cellular level. Hippokratia 2016, 20(4): 292-298.

S100 and p65 expression are increased in the masseter muscle after botulinum toxin-A injection

Background

The purpose of this study was to compare the expression levels of p65 and S100 in the rat masseter muscle after the injection of different concentrations of botulinum toxin-A (BTX-A).

Methods

We injected either 5 or 10 U of BTX-A into both masseter muscle of rats. As a control group, the same volume of saline was injected. After 14 days, the animals were sacrificed. Subsequently, a biopsy and immunohistochemical staining of the samples were performed using a p65 or S100 antibody.

Results

The cross-sectional area of each myofibril was significantly reduced by BTX-A injection (P < 0.001). The expression of p65 and S100 increased significantly with increasing concentrations of BTX-A (P < 0.001).

Conclusions

The injection of BTX-A into the masseter muscle induced muscle atrophy. Subsequently, p65 and S100 expression in myoblasts were increased for the protection of muscle cells.