Early effect of Botox-A injection into the masseter muscle of rats: functional and histological evaluation

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.

Repeated unilateral injections of botulinum toxin in masticatory muscles in adult rats do not amplify condylar and alveolar bone loss nor modify the volume of the hypertrophic bone proliferation at enthesis

OBJECTIVES

Botulinum toxin is used in human in repeatedly masticatory muscles injections. A single BTX injection in animal induces mandibular bone loss with a muscle enthesis hypertrophic metaplasia. Our aim was to evaluate mandibular bone changes after unilateral repeated injections of BTX in adult rats.

STUDY DESIGN

Mature male rats were randomized into 3 groups: one, two or three injections. Each rat received injections in right masseter and temporalis muscles. The left side was the control side. Microcomputed tomography was used to perform 2D and 3D analyses.

RESULTS

Bone loss was evidenced on the right sides of alveolar and condylar bone. Alveolar bone volume increased in both control left side and injected right side whereas condylar bone volume remained constant in all groups, for both sides. Enthesis bone hypertrophic metaplasias were evidenced on the BTX injected sides without any modification with the number of injections.

CONCLUSION

BTX repeated injections in masticatory muscles lead to major mandibular condylar and alveolar bone loss that does not worsen. They lead to the occurrence of an enthesis bone proliferation that is not dependent on the number of injections. These results are an argument for the safety of BTX injections in masticatory muscles in human.

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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Surgery-first approach reduces the overall treatment time without damaging long-term stability in the skeletal class III correction: a preliminary study

Background

Compared to the conventional approach, including preoperative orthodontic preparation, the so-called surgery-first approach (SFA) seems to reduce the overall treatment time in the correction of skeletal class III dentofacial deformity. However, there have been controversies about postoperative skeletal stability with SFA. Therefore, we investigated the long-term stability and the overall treatment time after maxillomandibular surgery for skeletal class III correction with or without preoperative orthodontic preparation.

Methods

This retrospective study included eight patients who underwent maxillomandibular surgery for class III correction with the SFA (SFA group) and 20 patients who underwent the conventional approach (CA group). A comparative study of the change in the maxillary and mandibular position on preoperative (T1), 1-day (T2), 6-month (T3), and 2-year (T4) postoperative lateral cephalograms. We calculated the overall treatment time for each group.

Results

At the presurgical stage (T1), there was no bias in the skeletal features between the two groups. In the surgical change from T1 to T2, the mandible (point B) of the CA group was significantly moved superiorly. Short-term changes from T2 to T3 revealed that the mandible moved forward in both groups, whereas the maxillary position showed no significant changes. Long-term changes from T3 to T4 demonstrated that none of the measured parameters showed any significant differences. Finally, the average of overall treatment time was 15.1 months in the SFA group and 26.0 months in the CA group.

Conclusions

These findings suggest that SFA in bimaxillary orthognathic surgery for skeletal class III correction leads to predictable long-term skeletal stability, similar to surgery with CA. Furthermore, SFA reduced the overall treatment time compared to CA.

Histological features of masticatory muscles after botulinum toxin A injection into the right masseter muscle of dystrophin deficient (mdx-) mice

OBJECTIVE/BACKGROUND

The most frequently used animal model for human DMD (Duchenne muscular dystrophy) research is the mdx mouse. In both species, characteristic histological changes like inflammation, muscle fiber degeneration and fibrosis are the same, but in contrast to humans, in mdx mice, phases of muscle fiber degeneration are compensated by regeneration processes.

AIM

Therefore, the interest of this study was to evaluate histological features in masticatory muscles after BTX-A injection into the right masseter muscle of wild type and dystrophic (mdx) mice, illustrating de- and regeneration processes induced by this substance.

MATERIAL AND METHODS

The right masseter muscle of 100 days old healthy and mdx mice were selectively paralyzed by a single intramuscular BTX-A injection. Masseter as well as temporal muscle of injection and non-injection side were carefully dissected 21 days and 42 days after injection, respectively, and fiber diameter, cell nuclei position, necrosis and collagen content were analyzed histomorphologically in order to evaluate de- and regeneration processes in these muscles. Statistical analysis was performed using SigmaStat Software and Mann Whitney U-test (significance level: p < 0.05).

RESULTS

At both investigation periods and in both mouse strains fiber diameter was significantly reduced and collagen content was significantly increased in the right injected masseter muscle whereas fiber diameters in mdx mice were much smaller, and these differences were even more apparent at the second investigation period. Necrosis and central located nuclei could generally be found in all mdx mice muscles investigated with an amount of centronucleation exceeding 60%, and a significant increase of necrosis six weeks after injection. In wild type mice central located nuclei could primarily be found in the treated masseter muscle with a portion of 2.7%, and this portion decreased after six weeks, whereas in mdx mice a decrease could also be seen in the non-injected muscles. In contrast, in wild type mice necrosis was not apparent at any time and in all muscles investigated.

CONCLUSION

From our results it can be concluded that in mdx mice masticatory muscles de- and regeneration processes were extended, triggered by a selective BTX-A injection, or mdx mice at this age, independently of BTX-A treatment, went through another cycle of de- and regeneration as a characteristic of this disease.

The effect of fixation plate use on bone healing during the reconstruction of mandibular defects

Objectives

This study sought to compare efficiency results between the use of a customized implant (CI) and a reconstruction plate (RP) in mandibular defect reconstruction in an animal model.

Materials and Methods

Fifteen rabbits underwent surgery to create a defect in the right side of the mandible and were randomly divided into two groups. For reconstruction of the mandibular defect, the RP group (n=5) received five-hole mini-plates without bone grafting and the CI group (n=10) received fabricated CIs based on the cone-beam computed tomography (CBCT) data taken preoperatively. The CI group was further divided into two subgroups depending on the time of CBCT performance preoperatively, as follows: a six-week CI (6WCI) group (n=5) and a one-week CI (1WCI) group (n=5). Daily food intake amount (DFIA) was measured to assess the recovery rate. Radiographic images were acquired to evaluate screw quantity. CBCT and histological examination were performed in the CI subgroup after sacrifice.

Results

The 1WCI group showed the highest value in peak average recovery rate and the fastest average recovery rate. In terms of reaching a 50% recovery rate, the 1WCI group required the least number of days as compared with the other groups (2.6±1.3 days), while the RP group required the least number of days to reach an 80% recovery rate (7.8±2.2 days). The 1WCI group showed the highest percentage of intact screws (94.3%). New bone formation was observed in the CI group during histological examination.

Conclusion

Rabbits with mandibular defects treated with CI showed higher and faster recovery rates and more favorable screw status as compared with those treated with a five-hole mini-plate without bone graft.

Effects of masticatory muscle function affected by BTX on maxillofacial bone growth through the sutural modification

OBJECTIVES

To evaluate the effect of botulinum toxin type A (BTX)-induced masticatory muscle hypofunction on the maxillofacial suture bone growth of growing rats.

SETTING AND SAMPLE POPULATION

Department of Orthodontics at Taipei Medical University. Forty-eight male 4-week-old Wistar rats were divided into four groups. The N group received injections of normal saline into each of the masseter and temporalis muscles. The M group received injections of normal saline into each of the temporalis muscle and injections of BTX into each of the masseter muscle. The T group received injections of normal saline into each of the masseter muscle and injections of BTX into each of the temporalis muscle. The MT group received injections of BTX into each of the masseter and temporalis muscles.

MATERIAL & METHODS

Rats were sacrificed after 42 days of growth. Changes in body and muscle weight were measured. Anthropometric measurements of the maxillary arch, sutural bone mineral density and sutural bone deposition distances were recorded. Statistical comparisons were performed using analysis of variance.

RESULTS

No significant change in body weight was found across groups. However, significant decreases were observed in muscle weight, anthropometric measurements, sutural bone mineral density and bone apposition distance in the BTX-injected group.

CONCLUSIONS

Reduced masticatory muscle function in growing rats can affect maxillofacial suture bone growth.

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.

Masticatory hypofunction effects induced by BTXA injection of hippocampal neurons in developing rats

BACKGROUND AND OBJECTIVE

In clinical practice, malocclusion is often encountered during the period of growth and development of individuals. In addition to nutritional imbalance, some studies have found that mastication affects learning and memory ability. Tooth loss and masticatory hypofunction have been suggested as risk factors of Alzheimer disease. However, relatively little research has been done in developing animals. The present study evaluated the relationship between masticatory hypofunction and neuropathological changes of the hippocampus in developing rats.

DESIGN

Four-week-old Wistar rats were randomly divided into saline-injected and botulinum toxin type A (BTXA)-injected groups. After an experiment period of 4 weeks, the rats were sacrificed for evaluation of neuropathological changes in the hippocampus through Nissl staining and phosphorylated cyclic AMP (cAMP) response element binding protein (CREB) immunohistochemistry.

RESULTS

Nissl staining revealed a significant reduction in the density of neurons in the BTXA-injected rats. The BTXA-injected rats exhibited a decreased level of CREB phosphorylation. The degree of p-CREB immunoreactivity differed significantly between the two groups.

CONCLUSION

The BTXA-injected rats exhibited a reduction in neuron density and phosphorylated CREB, indicating that mastication might influence the learning and memory ability during the growth period. Therefore, it is strongly suggested that malocclusion be corrected as soon as possible during growth and development.

Custom Implant for Reconstruction of Mandibular Continuity Defect

PURPOSE

The purpose of this study was to compare the daily food intake rate and the rate of screw loosening between 2 groups of rabbits with mandibular continuity defects: custom implant (CI) group and 5-hole mini-plate group.

MATERIALS AND METHODS

Two types of cylindrical implants were printed, and their physical strength was compared. In this study using rabbits, 1 group (n = 5) received a CI for the reconstruction of a mandibular continuity defect (CI group) and the other group (n = 5) received a 5-hole mini-plate without a bone graft (reconstruction plate [RP] group). After reconstruction, the daily food intake rate and the rate of screw loosening were examined postoperatively. Histologic examination in the CI group was performed 3 months after the operation.

RESULTS

The design that mimicked the mandible showed greater physical strength. The amount of time required to achieve 50% recovery was shorter in the CI group than in the RP group (P = .011). The total number of loosened screws in the CI group was lower than that in the RP group at 3 months postoperatively (P = .008). New bone formation in the porous CI was evident in the CI group.

CONCLUSIONS

Rabbits with mandibular continuity defects treated with CIs for reconstruction showed faster recovery of the daily food intake rate and fewer loosened screws than those treated with a 5-hole mini-plate without bone graft.

Non-invasive different modalities of treatment for temporomandibular disorders: review of literature

Temporomandibular disorders (TMDs) are diseases that affect the temporomandibular joint and supporting structures. The goal of treatment for TMDs is elimination or reduction of pain and return to normal temporomandibular joint function. Initial treatment for TMDs is non-invasive and conservative, not surgical. Oral and maxillofacial surgeons should fully understand and actively care about non-invasive treatments for TMDs. The purpose of this study is to review the validity and outcomes of non-invasive and surgical treatment modalities for TMDs.

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.

Early molecular response and microanatomical changes in the masseter muscle and mandibular head after botulinum toxin intervention in adult mice

BACKGROUND

Masseter muscle paralysis induced by botulinum toxin type A (BoNTA) evokes subchondral bone loss in mandibular heads of adult rats and growing mice after 4 weeks. However, the primary cellular and molecular events leading to altered bone remodeling remain unexplored. Thus, the aim of the current work has been to assess the molecular response that precedes the early microanatomical changes in the masseter muscle and subchondral bone of the mandibular head in adult mice after BoNTA intervention.

METHODS

A pre-clinical in vivo study was performed by a single intramuscular injection of 0.2 U BoNTA in the right masseter (experimental) of adult BALB/c mice. The contralateral masseter was injected with vehicle (control). Changes in mRNA levels of molecular markers of bone loss or muscle atrophy/regeneration were addressed by qPCR at day 2 or 7, respectively. mRNA levels of receptor activator of nuclear factor-κB ligand (RANKL) was assessed in mandibular heads, whilst mRNA levels of Atrogin-1/MAFbx, MuRF-1 and Myogenin were addressed in masseter muscles. In order to identify the early microanatomical changes at day 14, fiber diameters in transversal sections of masseter muscles were quantified, and histomorphometric analysis was used to determine the bone per tissue area and the trabecular thickness of subchondral bone of the mandibular heads.

RESULTS

An increase of up to 4-fold in RANKL mRNA levels were detected in mandibular heads of the BoNTA-injected sides as early as 2 days after intervention. Moreover, a 4-6 fold increase in Atrogin-1/MAFbx and MuRF-1 and an up to 25 fold increase in Myogenin mRNA level were detected in masseter muscles 7 days after BoNTA injections. Masseter muscle mass, as well as individual muscle fiber diameter, were significantly reduced in BoNTA-injected side after 14 days post-intervention. At the same time, in the mandibular heads from the treated side, the subchondral bone loss was evinced by a significant reduction in bone per tissue area (-40%) and trabecular thickness (-55%).

CONCLUSIONS

Our results show that masseter muscle paralysis induced by BoNTA leads to significant microanatomical changes by day 14, preceded by molecular changes as early as 2 days in bone, and 7 days in muscle. Therefore, masseter muscle atrophy and subchondral bone loss detected at 14 days are preceded by molecular responses that occur during the first week after BoNTA intervention.

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.

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

The purpose of this study was to compare the early or late expression levels of p65, Bcl-2, and type II myosin and the frequency of TUNEL-positive nuclei in the rat masseter muscle after injection of different concentrations of botulinum toxin-A (BTX-A). We injected either 5 U or 10 U of BTX-A into both masseter muscles of the rat. As a control group, the same volume of saline was injected. After 2 or 12 weeks, the animals were sacrificed. Subsequently, a biopsy and immunohistochemical staining of the samples were performed using a p65, Bcl-2, or type II myosin antibody. Additionally, a TUNEL assay and transmission electron microscopic analysis were performed. The expression of p65, Bcl-2, and type II myosin increased significantly with increasing concentrations of BTX-A at 2 weeks after BTX-A injection (P < 0.05). The number of TUNEL-positive nuclei was also significantly increased in the BTX-A-treated groups in comparison to the saline-treated control at 2 weeks after BTX-A injection (P < 0.05). Elevated expression of Bcl-2 was also observed in 10-unit BTX-A-treated group at 12 weeks after injection (P < 0.05). At 12 weeks after injection, the number of enlarged mitochondria was increased, and many mitochondria displayed aberrations in cristae morphology after BTX-A injection. In conclusion, BTX-A injection into the masseter muscle increased the expression level of p65, Bcl-2, and type II myosin at an early stage. The morphological changes of mitochondria were more evident at 12 weeks after injection.

Topical delivery of 4-hexylresorcinol promotes wound healing via tumor necrosis factor-α suppression

OBJECTIVE

The objective of this study was to evaluate (1) the effect of 4-hexylresorcinol (4HR) application on TNF-α expression in RAW264.7 cells and (2) the effect of 4HR ointment on burn wound healing in a rat burn wound model.

MATERIALS AND METHODS

RAW264.7 cells were cultured in the presence of different concentrations of 4HR, and the attached cells were sampled for western blot analysis at each time point. Animal studies were conducted on male Wistar rats (n=24). Three treatment groups were evaluated in this study: (1) treatment with ointment alone (negative control), (2) treatment with ointment containing 0.2wt% 4HR, and (3) treatment with ointment containing 2wt% 4HR. For the assessment of wound healing, digital photographs were taken at 1, 5, and 14 days. Animals were sacrificed at 1, 5, and 14 days for histological examination or ELISA analysis.

RESULTS

Western blot analysis showed that TNF-α protein levels were reduced following treatment with 4HR at concentrations between 1 and 10μg/mL. In animal studies, the average denuded area 14 days after burn was smaller in the 2wt% 4HR treatment group compared with the control group (P=0.022). Immunohistochemical analysis revealed lower TNF-α expression in the 2wt% 4HR treatment group compared with the control group 14 days after burn (P=0.027).

CONCLUSION

4HR reduced TNF-α expression in RAW264.7 cells and in the burn wounds of rats. Burn wounds dressed with ointment containing 4HR also exhibited rapid epithelization and collagen regeneration.