Injection of autologous muscle stem cells (myoblasts) for the treatment of vocal fold paralysis: a pilot study

Scaffold-Forming Collagen and Motor-Endplate Expressing Muscle Cells for Porcine Laryngoplasty

OBJECTIVE

Vocal fold paralysis impairs quality of life, and no curative injectable therapy exists. We evaluated injection of a novel in situ polymerizing (scaffold-forming) collagen in the presence and absence of muscle-derived motor-endplate expressing cells (MEEs) to promote medialization and recurrent laryngeal nerve (RLN) regeneration in a porcine model of unilateral vocal fold paralysis.

METHODS

Twelve Yucatan minipigs underwent right RLN transection. Autologous muscle progenitor cells were isolated from muscle biopsies, differentiated, and induced to MEEs. Three weeks after RLN injury, animals received injections of collagen, collagen containing MEEs, or saline into the paralyzed right vocal fold. Stimulated laryngeal electromyography and acoustic vocalization were used for function assessments. Larynges were harvested and underwent histologic, gene expression, and further quantitative analyses.

RESULTS

Injections were well-tolerated, with the collagen scaffold showing immunotolerance and collagen-encapsulated MEEs remaining viable. Collagen-treated paralyzed vocal folds showed increased laryngeal adductor muscle volumes relative to that of the uninjured side, with those receiving MEEs and collagen showing the highest volumes. Muscles injected with MEEs and collagen demonstrated increased expression of select neurotrophic (BDNF and NTN1), motor-endplate (DOK7, CHRNA1, and MUSK), and myogenic (MYOG and MYOD) related genes relative to saline controls.

CONCLUSION

In a porcine model of unilateral vocal fold paralysis, injection of in situ polymerizing collagen in the absence and presence of MEEs enhanced laryngeal adductor muscle volume, modulated expression of neurotrophic and myogenic factors, and avoided adverse material-mediated immune responses. Further study is needed to determine long-term functional outcomes with this novel therapeutic approach.

LEVEL OF EVIDENCE

NA Laryngoscope, 2024.

Early Changes in Porcine Larynges Following Injection of Motor-Endplate Expressing Muscle Cells for the Treatment of Unilateral Vocal Fold Paralysis

OBJECTIVES

No curative injectable therapy exists for unilateral vocal fold paralysis. Herein, we explore the early implications of muscle-derived motor-endplate expressing cells (MEEs) for injectable vocal fold medialization after recurrent laryngeal nerve (RLN) injury.

METHODS

Yucatan minipigs underwent right RLN transection (without repair) and muscle biopsies. Autologous muscle progenitor cells were isolated, cultured, differentiated, and induced to form MEEs. Three weeks after the injury, MEEs or saline were injected into the paralyzed right vocal fold. Outcomes including evoked laryngeal electromyography (LEMG), laryngeal adductor pressure, and acoustic vocalization data were analyzed up to 7 weeks post-injury. Harvested porcine larynges were examined for volume, gene expression, and histology.

RESULTS

MEE injections were tolerated well, with all pigs demonstrating continued weight gain. Blinded analysis of videolaryngoscopy post-injection revealed infraglottic fullness, and no inflammatory changes. Four weeks after injection, LEMG revealed on average higher right distal RLN activity retention in MEE pigs. MEE-injected pigs on average had vocalization durations, frequencies, and intensities higher than saline pigs. Post-mortem, the MEE-injected larynges revealed statistically greater volume on quantitative 3D ultrasound, and statistically increased expression of neurotrophic factors (BDNF, NGF, NTF3, NTF4, NTN1) on quantitative PCR.

CONCLUSIONS

Minimally invasive MEE injection appears to establish an early molecular and microenvironmental framework to encourage innate RLN regeneration. Longer follow-up is needed to determine if early findings will translate into functional contraction.

LEVEL OF EVIDENCE

NA Laryngoscope, 134:272-282, 2024.

Enhanced Abductor Function in Bilateral Vocal Fold Paralysis with Muscle Stem Cells

INTRODUCTION

Patients with bilateral vocal fold paralysis (BVFP) experience airway obstruction because of loss of abductor function of posterior cricoarytenoid (PCA) muscles. We previously reported that implantation of autologous muscle progenitor (stem) cells into thyroarytenoid muscles during reinnervation resulted in improved adductor function. In this study, that same approach was applied to treating PCA muscles in a canine model of BVFP.

DESIGN

Animal study.

METHODS

Two canines underwent baseline measures of glottal resistance (GR), then complete transection and suture repair of both recurrent laryngeal nerves. Muscle stem cells were isolated from skeletal muscle and cultured. Two months later, GR was measured, and then 107 stem cells were implanted into one PCA muscle of each animal. After four more months, GR and glottal opening force (GOF) were measured and the muscles were harvested for histologic study. One control dog underwent the same procedures without stem cell implantation, for comparison.

RESULTS

GR increased by 21%-25% over baseline at 2 months, but after stem cell implantation, improved to 10%-14% over baseline at 6 months. PCA muscle strength, as determined by GOF, was 61%-65% on control sides (no stem cells), and 78%-83% on treated sides (with stem cells). Histology confirmed survival of stem cells and a 50% higher rate of innervation of motor endplates in the stem cell treated sides.

CONCLUSION

Autologous muscle progenitor (stem) cells show promise as a potential new therapy for patients with bilateral vocal fold paralysis. Additional studies are needed to determine the optimal number of cells, timing of implantation, and other variables before launching a clinical trial.

LEVEL OF EVIDENCE

NA (animal study) Laryngoscope, 134:324-328, 2024.

Achievements and Challenges in Transplantation of Mesenchymal Stem Cells in Otorhinolaryngology

Otorhinolaryngology enrolls head and neck surgery in various tissues such as ear, nose, and throat (ENT) that govern different activities such as hearing, breathing, smelling, production of vocal sounds, the balance, deglutition, facial animation, air filtration and humidification, and articulation during speech, while absence of these functions can lead to high morbidity and even mortality. Conventional therapies for head and neck damaged tissues include grafts, transplants, and artificial materials, but grafts have limited availability and cause morbidity in the donor site. To improve these limitations, regenerative medicine, as a novel and rapidly growing field, has opened a new therapeutic window in otorhinolaryngology by using cell transplantation to target the healing and replacement of injured tissues. There is a high risk of rejection and tumor formation for transplantation of embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs); mesenchymal stem cells (MSCs) lack these drawbacks. They have easy expansion and antiapoptotic properties with a wide range of healing and aesthetic functions that make them a novel candidate in otorhinolaryngology for craniofacial defects and diseases and hold immense promise for bone tissue healing; even the tissue sources and types of MSCs, the method of cell introduction and their preparation quality can influence the final outcome in the injured tissue. In this review, we demonstrated the anti-inflammatory and immunomodulatory properties of MSCs, from different sources, to be safely used for cell-based therapies in otorhinolaryngology, while their achievements and challenges have been described too.

Laryngeal Reconstruction Using Tissue-Engineered Implants in Pigs: A Pilot Study

OBJECTIVE/HYPOTHESIS

There are currently no treatments available that restore dynamic laryngeal function after hemilaryngectomy. We have shown that dynamic function can be restored post hemilaryngectomy in a rat model. Here, we report in a first of its kind, proof of concept study that this previously published technique is scalable to a porcine model.

STUDY DESIGN

Animal study.

METHODS

Muscle and fat biopsies were taken from three Yucatan minipigs. Muscle progenitor cells (MPCs) and adipose stem cells (ASCs) were isolated and cultured for 3 weeks. The minipigs underwent a left laterovertical partial laryngectomy sparing the left arytenoid cartilage and transecting the recurrent laryngeal nerve. Each layer was replaced with a tissue-engineered implant: 1) an acellular mucosal layer composed of densified Type I oligomeric collagen, 2) a skeletal muscle layer composed of autologous MPCs and aligned oligomeric collagen differentiated and induced to express motor endplates (MEE), and 3) a cartilage layer composed of autologous ASCs and densified oligomeric collagen differentiated to cartilage. Healing was monitored at 2 and 4 weeks post-op, and at the 8 week study endpoint.

RESULTS

Animals demonstrated appropriate weight gain, no aspiration events, and audible phonation. Video laryngoscopy showed progressive healing with vascularization and re-epithelialization present at 4 weeks. On histology, there was no immune reaction to the implants and there was complete integration into host tissue with nerve and vascular ingrowth.

CONCLUSIONS

This pilot study represents a first in which a transmural vertical partial laryngectomy was performed and successfully repaired with a customized, autologous stem cell-derived multi-layered tissue-engineered implant.

LEVEL OF EVIDENCE

NA Laryngoscope, 131:2277-2284, 2021.

Stem cell treatments for oropharyngeal dysphagia: Rationale, benefits, and challenges

Dysphagia, defined as difficulty swallowing, is a common symptom negatively impacting millions of adults annually. Estimated prevalence ranges from 14 to 33 percent in those over age 65 to over 70 percent in a nursing home setting. The elderly, those with neurodegenerative diseases, head and neck cancer patients, and those with autoimmune conditions such as Sjögren's syndrome are disproportionately affected. Oropharyngeal dysphagia refers specifically to difficulty in initiating a swallow due to dysfunction at or above the upper esophageal sphincter, and represents a large proportion of dysphagia cases. Current treatments are limited and are often ineffective. Stem cell therapy is a new and novel advancement that may fill a much-needed role in our treatment regimen. Here, we review the current literature regarding stem cell treatments for oropharyngeal dysphagia. Topics discussed include tissue regeneration advancements as a whole and translation of these principles into research surrounding tongue dysfunction, xerostomia, cricopharyngeal dysfunction, and finally an overview of the challenges and future directions for investigation. Although this field of study remains in its early stages, initial promising results show potential for the use of stem cell-based therapies to treat oropharyngeal dysphagia and warrant further research.

Safety and feasibility of fat injection therapy with adipose-derived stem cells in a rabbit hypoglossal nerve paralysis model: A pilot study

OBJECTIVE

The aim of this study is to establish a unilateral tongue atrophy model by cutting the hypoglossal nerve and to evaluate the safety and feasibility of a fat injection of adipose-derived stem cells (ADSCs) to restore swallowing function.

METHODS

A total of 12 rabbits were randomized to three groups; the ADSCs+fat group (n=4), the fat group (n=4) and the control group (n=4). All rabbits were treated with denervation of the left hypoglossal nerve and their conditions including body weight and food intake were checked during follow-up periods (8 weeks). At 4 weeks after the transection of the nerve, rabbits received the injection therapy into the denervated side of the tongue with 1.0mL fat tissue premixed with 0.5mL ADSCs in the ADSCs+fat group, 1.0mL fat tissue premixed with 0.5mL PBS in the fat group and 1.5mL PBS in the control group. Rabbits were euthanized 8 weeks post-treatment and resected tongues were collected, formalin-fixed and paraffin embedded. To evaluate the change of the intrinsic muscles of the tongue, muscle fibers around the treatment area was analyzed by evaluating 5 consecutive hematoxylin-eosin slides per rabbit.

RESULTS

Food intake did not decrease upon nerve denervation, and none of the rabbits displayed adverse effect such as aspiration, surgical wound dehiscence or infection. No significant body weight changes were found between the three groups at 4 and 8 weeks after nerve transection (p>0.05). In the control group, the denervated side of tongue had significantly smaller muscle fiber areas and diameters compared to the non-denervated side (p<0.05). The ADSCs+fat group demonstrated a larger area of inferior longitudinal muscle fibers compared to the control and the fat groups (582±312µm² vs. 405±220µm² and 413±226µm²; p<0.05). A significant thicker lesser diameter of inferior longitudinal muscle fibers was found in the ADSCs+fat group compared to the control and the fat groups (24±8µm vs. 20±6µm and 20±7µm; p<0.05).

CONCLUSION

The rabbit tongue atrophy model was found suitable for the assessment of muscle change after nerve transection. Fat injection therapy with ADSCs demonstrated great potential to prevent the muscle atrophy after denervation and to promote the muscle regeneration around the injection area.

Skeletal Muscle Regeneration in Advanced Diabetic Peripheral Neuropathy

BACKGROUND

Decreased lean muscle mass in the lower extremity in diabetic peripheral neuropathy (DPN) is thought to contribute to altered joint loading, immobility, and disability. However, the mechanism behind this loss is unknown and could derive from a reduction in size of myofibers (atrophy), destruction of myofibers (degeneration), or both. Degenerative changes require participation of muscle stem (satellite) cells to regenerate lost myofibers and restore lean mass. Determining the degenerative state and residual regenerative capacity of DPN muscle will inform the utility of regeneration-targeted therapeutic strategies.

METHODS

Biopsies were acquired from 2 muscles in 12 individuals with and without diabetic neuropathy undergoing below-knee amputation surgery. Biopsies were subdivided for histological analysis, transcriptional profiling, and satellite cell isolation and culture.

RESULTS

Histological analysis revealed evidence of ongoing degeneration and regeneration in DPN muscles. Transcriptional profiling supports these findings, indicating significant upregulation of regeneration-related pathways. However, regeneration appeared to be limited in samples exhibiting the most severe structural pathology as only extremely small, immature regenerated myofibers were found. Immunostaining for satellite cells revealed a significant decrease in their relative frequency only in the subset with severe pathology. Similarly, a reduction in fusion in cultured satellite cells in this group suggests impairment in regenerative capacity in severe DPN pathology.

CONCLUSION

DPN muscle exhibited features of degeneration with attempted regeneration. In the most severely pathological muscle samples, regeneration appeared to be stymied and our data suggest that this may be partly due to intrinsic dysfunction of the satellite cell pool in addition to extrinsic structural pathology (eg, nerve damage).

CLINICAL RELEVANCE

Restoration of DPN muscle function for improved mobility and physical activity is a goal of surgical and rehabilitation clinicians. Identifying myofiber degeneration and compromised regeneration as contributors to dysfunction suggests that adjuvant cell-based therapies may improve clinical outcomes.

Surgical Options for Pediatric Bilateral Vocal Cord Palsy: State of the Art

Management of pediatric bilateral vocal cord palsy (BVCP) is a controversial and challenging topic. It may represent a severe obstructive condition usually associated with respiratory distress, and, in such condition, tracheostomy has been considered the gold standard for a long time. Many surgical options have been described and used to increase the glottic space in BVCP (1), with ongoing research of less invasive techniques. The challenge and current trend in our department and in many major pediatric centers is to avoid tracheotomy through an early treatment. Many techniques introduced in the last decade reduced the number of tracheotomies and increased the decannulation rate. Furthermore, we observed a recent increase in attention to preserve the quality of the voice with new techniques, such as endoscopic arytenoid abduction lateropexy which is in our opinion an important innovation to improve glottic space with satisfactory voice results. We present a review of the literature about the evolution of the treatment options for pediatric BVCP during the years.

The Clinical Course of Idiopathic Bilateral Vocal Fold Motion Impairment in Adults: Case Series and Review of the Literature

AIM

Steps for assessment and successful management of bilateral vocal fold motion impairment (VFMI) are (1) recognition of its presence, (2) identifying the etiology and factors restricting vocal fold motion, (3) evaluation of airway patency, and (4) establishing a management plan. No large series documenting the course and outcome of adult idiopathic bilateral VFMI has been published within the past 15 years.

METHODS

Retrospective chart review of adult patients with idiopathic bilateral VFMI at a tertiary academic center. A diagnosis was established if history, physical examination with laryngoscopy, and initial imaging excluded a cause. Records were reviewed for demographics, clinical characteristics, surgical intervention details, and length of follow-up.

RESULTS

Nine adult patients with idiopathic bilateral VFMI were identified. There were five males and four females with a mean age of 59.6 years. The mean follow-up period was 54.4 months (range, 6-111 months). Upon presentation to our laryngology service, three patients were advised observation, three patients were advised to undergo urgent tracheostomy, and three patients were advised to undergo elective surgery for airway management. By the end of the follow-up period, only four patients (4/9, 44.4%) were tracheostomy dependent, one of them was lost to follow-up after tracheostomy tub downsizing for decannulation.

CONCLUSIONS

To our best knowledge, this is the largest series so far of adult patients with idiopathic bilateral VFMI. Conservative treatment can be considered as an alternative to surgery in select cases.

Improved adductor function after canine recurrent laryngeal nerve injury and repair using muscle progenitor cells

OBJECTIVE

Muscle progenitor cells (MPCs) can be isolated from muscle samples and grown to a critical mass in culture. They have been shown to survive and integrate when implanted into rat laryngeal muscles. In this study, the ability of MPC implants to enhance adductor function of reinnervated thyroarytenoid muscles was tested in a canine model.

STUDY DESIGN

Animal study.

METHODS

Sternocleidomastoid muscle samples were harvested from three canines. Muscle progenitor cells were isolated and cultured to 10⁷ cells over 4 to 5 weeks, then implanted into right thyroarytenoid muscles after ipsilateral recurrent laryngeal nerve transection and repair. The left sides underwent the same nerve injury, but no cells were implanted. Laryngeal adductor force was measured pretreatment and again 6 months later, and the muscles were harvested for histology.

RESULTS

Muscle progenitor cells were successfully cultured from all dogs. Laryngeal adductor force measurements averaged 60% of their baseline pretreatment values in nonimplanted controls, 98% after implantation with MPCs, and 128% after implantation with motor endplate-enhanced MPCs. Histology confirmed that the implanted MPCs survived, became integrated into thyroarytenoid muscle fibers, and were in close contact with nerve endings, suggesting functional innervation.

CONCLUSION

Muscle progenitor cells were shown to significantly enhance adductor function in this pilot canine study. Patient-specific MPC implantation could potentially be used to improve laryngeal function in patients with vocal fold paresis/paralysis, atrophy, and other conditions. Further experiments are planned.

LEVEL OF EVIDENCE

NA. Laryngoscope, 2017.

Current Treatment Options for Bilateral Vocal Fold Paralysis: A State-of-the-Art Review

Vocal fold paralysis (VFP) refers to neurological causes of reduced or absent movement of one or both vocal folds. Bilateral VFP (BVFP) is characterized by inspiratory dyspnea due to narrowing of the airway at the glottic level with both vocal folds assuming a paramedian position. The primary objective of intervention for BVFP is to relieve patients’ dyspnea. Common clinical options for management include tracheostomy, arytenoidectomy and cordotomy. Other options that have been used with varying success include reinnervation techniques and botulinum toxin (Botox) injections into the vocal fold adductors. More recently, research has focused on neuromodulation, laryngeal pacing, gene therapy, and stem cell therapy. These newer approaches have the potential advantage of avoiding damage to the voicing mechanism of the larynx with an added goal of restoring some physiologic movement of the affected vocal folds. However, clinical data are scarce for these new treatment options (i.e., reinnervation and pacing), so more investigative work is needed. These areas of research are expected to provide dramatic improvements in the treatment of BVFP.

Novel murine xenograft model for the evaluation of stem cell therapy for profound dysphagia

OBJECTIVES/HYPOTHESIS

Dysphagia is common and costly. Treatments are limited and innovative therapies are required. The tongue is essential for safe, effective swallowing and is a natural target for regenerative therapy. Muscle-derived stem cells (MDSCs) hold potential to restore dynamic function, and their application in the damaged tongue is appealing. We examined the safety and efficacy of human MDSC implantation into a novel mouse tongue model.

STUDY DESIGN

Animal study.

METHODS

Adult immune-deficient mice were randomized to surgical (hemiglossectomy) and nonsurgical groups. Animals underwent lingual injection of human MDSCs or saline (control). Groups were followed for 12 weeks. The primary outcome was MDSC survival measured by an in vivo imaging system (IVIS). Secondary outcomes included animal survival and weight. Comparisons were made using a Mann-Whitney U test with an α of .05.

RESULTS

Human MDSCs survived to the endpoint demonstrating 132% ± 465% and 15% ± 11% bioluminescence by IVIS at 12 weeks in hemiglossectomy and nonsurgical groups, respectively. All but one animal (hemiglossectomy with saline injection) survived to the study endpoint. Mean weight increased from baseline in all groups, with the greatest change observed in hemiglossectomy mice with MDSC injection (baseline 24.5 g ± 3.9 g; delta 5.9 g ± 4.6 g), exceeding the weight gain seen in surgical control mice (baseline 24.9 g ± 4.2 g, delta 2.7 g ± 1.4 g) (P = .04).

CONCLUSIONS

MDSCs exhibited over 100% survival at 3 months when injected into an immune-deficient hemiglossectomy mouse model. Tongue-injured animals injected with MDSCs exhibited superior weight gain after hemiglossectomy than control animals (P < .05). These data support further investigation into the use of autologous MDSCs as a potential treatment for dysphagia secondary to tongue weakness and fibrosis LEVEL OF EVIDENCE: NA Laryngoscope, 127:E359-E363, 2017.

Human Muscle Precursor Cells Overexpressing PGC-1α Enhance Early Skeletal Muscle Tissue Formation

Muscle precursor cells (MPCs) are activated satellite cells capable of muscle fiber reconstruction. Therefore, autologous MPC transplantation is envisioned for the treatment of muscle diseases. However, the density of MPCs, as well as their proliferation and differentiation potential, gradually declines with age. The goals of this research were to genetically modify human MPCs (hMPCs) to overexpress the peroxisome proliferator-activated receptor γ coactivator (PGC-1α), a key regulator of exercise-mediated adaptation, and thereby to enhance early skeletal muscle formation and quality. We were able to confirm the sustained myogenic phenotype of the genetically modified hMPCs. While maintaining their viability and proliferation potential, PGC-1α-modified hMPCs showed an enhanced myofiber formation capacity in vitro. Engineered muscle tissues were harvested 1, 2, and 4 weeks after subcutaneous injection of cell-collagen suspensions, and histological analysis confirmed the earlier myotube formation in PGC-1α-modified samples, predominantly of slow-twitch myofibers. Increased contractile protein levels were detected by Western blot. In summary, by genetically modifying hMPCs to overexpress PGC-1α, we were able to promote early muscle fiber formation in vitro and in vivo, with an initial switch to slow-type myofibers. Therefore, overexpressing PGC-1α is a novel strategy to further enhance skeletal muscle tissue engineering.

Potential of laryngeal muscle regeneration using induced pluripotent stem cell-derived skeletal muscle cells

Conclusion Induced pluripotent stem (iPS) cells may be a new potential cell source for laryngeal muscle regeneration in the treatment of vocal fold atrophy after recurrent laryngeal nerve paralysis. Objectives Unilateral vocal fold paralysis can lead to degeneration, atrophy, and loss of force of the thyroarytenoid muscle. At present, there are some treatments such as thyroplasty, arytenoid adduction, and vocal fold injection. However, such treatments cannot restore reduced mass of the thyroarytenoid muscle. iPS cells have been recognized as supplying a potential resource for cell transplantation. The aim of this study was to assess the effectiveness of the use of iPS cells for the regeneration of laryngeal muscle through the evaluation of both in vitro and in vivo experiments. Methods Skeletal muscle cells were generated from tdTomato-labeled iPS cells using embryoid body formation. Differentiation into skeletal muscle cells was analyzed by gene expression and immunocytochemistry. The tdTomato-labeled iPS cell-derived skeletal muscle cells were transplanted into the left atrophied thyroarytenoid muscle. To evaluate the engraftment of these cells after transplantation, immunohistochemistry was performed. Results The tdTomato-labeled iPS cells were successfully differentiated into skeletal muscle cells through an in vitro experiment. These cells survived in the atrophied thyroarytenoid muscle after transplantation.

Stem cell approaches for vocal fold regeneration

OBJECTIVES/HYPOTHESIS

Current interventions in the management of vocal fold (VF) dysfunction focus on conservative and surgical approaches. However, the complex structure and precise biomechanical properties of the human VF mean that these strategies have their limitations in clinical practice and in some cases offer inadequate levels of success. Regenerative medicine is an exciting development in this field and has the potential to further enhance VF recovery beyond conventional treatments. Our aim in this review is to discuss advances in the field of regenerative medicine; that is, advances in the process of replacing, engineering, or regenerating the VF through utilization of stem cells, with the intention of restoring normal VF structure and function.

DATA SOURCES

English literature (1946-2015) review.

METHODS

We conducted a systematic review of MEDLINE for cases and studies of VF tissue engineering utilizing stem cells.

RESULTS

The three main approaches by which regenerative medicine is currently applied to VF regeneration include cell therapy, scaffold development, and utilization of growth factors.

CONCLUSION

Exciting advances have been made in stem cell biology in recent years, including use of induced pluripotent stem cells. We expect such advances to be translated into the field in the forthcoming years. Laryngoscope, 126:1865-1870, 2016.

Peripheral nerve regeneration: experimental strategies and future perspectives

Peripheral nerve injuries represent a substantial clinical problem with insufficient or unsatisfactory treatment options. This review summarises all the events occurring after nerve damage at the level of the cell body, the site of injury and the target organ. Various experimental strategies to improve neuronal survival, axonal regeneration and target reinnervation are described including pharmacological approaches and cell-based therapies. Given the complexity of nerve regeneration, further studies are needed to address the biology of nerve injury, to improve the interaction with implantable scaffolds, and to implement cell-based therapies in nerve tissue engineering.

Stem cell-derived tissue-engineered constructs for hemilaryngeal reconstruction

OBJECTIVES

As an initial step toward our goal of developing a completely tissue-engineered larynx, the aim of this study was to describe and compare three strategies of creating tissue-engineered muscle-polymer constructs for hemilaryngeal reconstruction.

METHODS

Cartilage-mimicking polymer was developed from electrospun poly(D,L-lactide-co-ε-caprolactone) (PCL). Primary muscle progenitor cell cultures were derived from syngeneic F344 rat skeletal muscle biopsies. Twenty F344 rats underwent resection of the outer hemilaryngeal cartilage with the underlying laryngeal adductor muscle. The defects were repaired with muscle stem cell-derived muscle-PCL constructs (5 animals), myotube-derived muscle-PCL constructs (5 animals), motor end plate-expressing muscle-PCL constructs (5 animals), or PCL alone (controls; 5 animals). The outcome measures at 1 month included animal survival, muscle thickness, and innervation status as determined by electromyography and immunohistochemistry.

RESULTS

All of the animals survived the 1-month implant period and had appropriate weight gain. The group that received motor end plate-expressing muscle-PCL constructs demonstrated the greatest muscle thickness and the strongest innervation, according to electromyographic activity and the percentage of motor end plates that had nerve contact.

CONCLUSIONS

Although all of the tissue-engineered constructs provided effective reconstruction, those that expressed motor end plates before implantation yielded muscle that was more strongly innervated and viable. This finding suggests that this novel approach may be useful in the development of a tissue-engineered laryngeal replacement.

Autologous myoblasts attenuate atrophy and improve tongue force in a denervated tongue model: a pilot study

OBJECTIVES/HYPOTHESIS

Autologous muscle-derived stem cell (MdSC) therapy is a promising treatment to restore function. No group has evaluated MdSC therapy in a denervated tongue model. The purpose of this pilot investigation was to determine the extent of autologous MdSC survival, effects on tongue muscle atrophy, maximal contractile force, and lingual pressure in a denervated ovine tongue model.

STUDY DESIGN

Pilot animal experiment.

METHODS

Bilateral implantable cuff electrodes were placed around the hypoglossal nerves in two Dorper cross ewes. Tensometer and high-resolution manometry (HRM) testing were performed during supermaximum hypoglossal nerve stimulation to assess baseline tongue strength. Sternocleidomastoid muscle biopsies were acquired to create autologous MdSC cultures. At 1 month, 5 × 10(8) green fluorescent protein (GFP)-labeled autologous MdSCs were injected into the partially denervated tongue. Two-months postinjection, lingual tensometer testing, HRM, and postmortem histological assessment were performed.

RESULTS

GFP+ myofibers were identified in denervated tongue specimens indicating MdSC survival. Muscle fiber diameter was larger in GFP+ fibers for both tongue specimens, suggesting attenuation of muscle atrophy. Myofiber diameter was larger in GFP+ myofibers than preinjury diameters, providing evidence of new muscle formation. These myogenic changes led to a 27% increase in maximal tongue contractile force and a 54% increase in maximum base of tongue pressure in one animal.

CONCLUSIONS

Autologous MdSC therapy may be a viable treatment for the partially denervated tongue, with current findings demonstrating that injected MdSCs survived and fused with tongue myofibers, with a resultant increase in myofiber diameter and an increase in tongue strength.

LEVEL OF EVIDENCE

N/A.

The use of laryngeal mucosa mesenchymal stem cells for the repair the vocal fold injury

Stem cell transplantation is a kind of attractive and new approach that complements traditional restorative or surgical techniques for the regeneration of injured or pathologically damaged laryngeal tissues. However, the best cell delivery strategy remains to be identified. The objective of this study was to establish a new strategy to the healing of injured vocal fold, using laryngeal mucosa mesenchymal stem cells differentiating into myofibroblasts or fibroblasts and improving the reconstruction microenvironment in the vocal fold injury as a new alternative as seed cells for laryngeal tissue engineering. After isolation and expansion, cells were identified as adherent mesenchymal cells with substantial proliferation potential in vitro, and were also characterized by flow cytometry. The differentiation potential of mesenchymal cells was maintained during proliferation as confirmed by culturing for adipogenesis, osteogenesis and chondrocyte. When LM-MSC was transplanted into the injured vocal fold, it has the potent differentiated into myofibroblasts and fibroblasts, which could regulate extracellular matrix, block collagen and the fibronectin rapid increased, inhibit the rapidly decrease of elastic fiber and HA, decrease the microenvironment inflammatory reaction, and prevent the formation of vocal fold scar.

Cell-cell interaction between vocal fold fibroblasts and bone marrow mesenchymal stromal cells in three-dimensional hyaluronan hydrogel

Mesenchymal stromal cells (MSCs) are multipotential adult cells present in all tissues. Paracrine effects and differentiating ability make MSCs an ideal cell source for tissue regeneration. However, little is known about how interactions between implanted MSCs and native cells influence cellular growth, proliferation, and behaviour. By using an in vitro three-dimensional (3D) co-culture assay of normal or scarred human vocal fold fibroblasts (VFFs) and bone marrow-derived MSCs (BM-MSCs) in a uniquely suited hyaluronan hydrogel (HyStem-VF), we investigated cell morphology, survival rate, proliferation and protein and gene expression of VFFs and BM-MSCs. BM-MSCs inhibited cell proliferation of both normal and scarred VFFs without changes in VFF morphology or viability. BM-MSCs demonstrated decreased proliferation and survival rate after 7 days of co-culture with VFFs. Interactions between BM-MSCs and VFFs led to a significant increase in protein secretion of collagen I and hepatocyte growth factor (HGF) and a decrease of vascular endothelial growth factor (VEGF), monocyte chemotactic protein-1 (MCP-1) and interleukin-6 (IL-6). In particular, BM-MSCs significantly upregulated matrix metalloproteinase 1 (MMP1) and HGF gene expression for scarred VFFs compared to normal VFFs, indicating the potential for increases in extracellular matrix remodelling and tissue regeneration. Application of BM-MSCs-hydrogels may play a significant role in tissue regeneration, providing a therapeutic approach for vocal fold scarring. Copyright © 2013 John Wiley & Sons, Ltd.

Influence of Different Growth Factors on Chondrogenic Differentiation of Adipose-Derived Stem Cells in Polyurethane-Fibrin Composites

Introduction

Chondrogenic differentiation of adipose-derived stem cells (ASCs) has proven to be feasible. To compensate for laryngeal palsy or cartilage defects after surgery or trauma using tissue engineering, a formable and stable scaffold material is mandatory.

Methods

ASCs were seeded in fibrin-polyurethane scaffolds and cultured in chondrogenic differentiation medium adding the growth factors TGF-□1, TGF-□3, and BMP-2 for up to 35 days.

Results

Histological examination showed acid glycosaminoglycans in the extracellular matrix in all groups. Immunofluorescence presented positive staining for collagen II, aggrecan, and SOX-9 in the TGF-□1–, TGF-□3–, and BMP-2-group. With Real-time PCR analyses, chondrogenic differentiation became apparent by the expression of the specific genes COL2A1 (collagen II), AGC 1 (aggrecan), and SOX-9, whereas collagen II expression was low in all groups compared to bone marrow-derived stem cells (BMSC) due to reduced chondrogenic ability.

Conclusions

These findings demonstrate the general ability of ASCs to differentiate into matrix-producing chondrocytes in fibrin-polyurethane scaffolds. However, further experiments are necessary to enhance this chondrogenic potential of ASCs seeded in fibrin-polyurethane scaffolds in order to produce a suitable regeneration method for treating cartilage defects or an implantable medialization material for vocal cord palsy.

Ciliary neurotrophic factor (CNTF) promotes skeletal muscle progenitor cell (MPC) viability via the phosphatidylinositol 3-kinase-Akt pathway

Muscle progenitor cells (MPCs) are currently being investigated as cellular vectors to deliver neurotrophic factor (NF) for the promotion of re-innervation after axonal injury. Ideally NF delivery in such a model would enhance axonal regeneration while simultaneously promoting MPC viability. To date, insulin-like growth factor 1 (IGF-1) is one of the few NFs known to promote both re-innervation and MPC viability. We herein identify ciliary neurotrophic factor (CNTF) as a factor that promotes MPC viability in culture, and demonstrate CNTF to impart greater viability effects on MPCs than IGF-1. We demonstrate that pharmacological inhibition via LY294002 results in abrogation of CNTF-mediated viability, suggesting that the CNTF-mediated MPC viability benefit occurs via the PI3-Akt pathway. Finally, we employ a genetic model, establishing MPC cultures from mice deficient in class IA PI-3 K (p85α(-/-) ) mice, and demonstrate that the viability benefit imparted by CNTF is completely abrogated in PI-3 K-deficient MPCs compared to wild-type controls. In summary, our investigations define CNTF as a promoter of MPC viability beyond IGF-1, and reveal that the CNTF-mediated MPC viability effects occur via the PI3-Akt pathway.

Neurotrophic factor-secreting autologous muscle stem cell therapy for the treatment of laryngeal denervation injury

OBJECTIVES/HYPOTHESIS

To determine if the spontaneous reinnervation that characteristically ensues after recurrent laryngeal nerve (RLN) injury could be selectively promoted and directed to certain laryngeal muscles with the use of neurotrophic factor (NF)-secreting muscle stem cell (MSC) vectors while antagonistic reinnervation is inhibited with vincristine (VNC).

STUDY DESIGN

Basic science investigation involving primary cell cultures, gene cloning/transfer, and animal experiments.

METHODS

MSC survival assays were used to test multiple individual NFs in vitro. Motoneuron outgrowth assays assessed the trophic effects of identified NF on cranial nerve X (CNX)-derived motoneurons in vitro. Therapeutic NF was cloned into a lentiviral vector, and MSCs were transduced to secrete NF. Sixty rats underwent left RLN transection injury, and at 3 weeks received injections of either MSCs (n = 24), MSCs secreting NF (n = 24), or saline (n = 12) into the left thyroarytenoid muscle complex; half of the animals in the MSC groups simultaneously received left posterior cricoarytenoid injections of VNC, whereas half of the animals received saline.

RESULTS

Ciliary neurotrophic factor (CNTF) had the greatest survival-promoting effect on MSCs in culture. The addition of CNTF (50 ng/mL) to CNX motoneuron cultures resulted in enhanced neurite outgrowth and branching. In the animal model, the injected MSCs fused with the denervated myofibers, immunohistochemistry demonstrated enhanced reinnervation based on motor endplate to nerve contact, and reverse transcriptase-polymerase chain reaction confirmed stable CNTF expression at longest follow-up (4 months) in the CNTF-secreting MSC treated groups.

CONCLUSIONS

MSC therapy may have a future role in selectively promoting and directing laryngeal reinnervation after RLN injury.

Local neurotoxins for prevention of laryngeal synkinesis after recurrent laryngeal nerve injury

OBJECTIVES

Persistent vocal fold motion impairment after recurrent laryngeal nerve (RLN) injury is not characteristically due to absent reinnervation, but often results from spontaneous aberrant reinnervation (synkinesis). We administered local neurotoxins to selected laryngeal muscles after RLN injury to determine whether aberrant reinnervation could be selectively inhibited.

METHODS

Unilateral RLN transection was performed in 24 male rats. Three weeks later, the denervated laryngeal adductor complex was injected with phenol, high- or low-dose vincristine sulfate (VNC), or saline solution. One month later, rat larynges were evaluated via videolaryngoscopy and laryngeal electromyography (LEMG). Larynges from euthanized animals were analyzed via immunofluorescent staining for the presence of reinnervation.

RESULTS

One animal that received phenol and 3 animals that received high-dose VNC died of toxicity-related complications. In the surviving neurotoxin-treated animals, videolaryngoscopy showed increased lateralization of the immobile vocal fold. Only 1 phenol-injected rat had adductor complex motor recruitment (score of 3+) with LEMG. The other neurotoxin-treated animals demonstrated an absence of adductor complex reinnervation, with only insertional activity and fibrillations (no motor units/recruitment). Spontaneous ipsilateral abductor reinnervation was not affected by the adductor injections.

CONCLUSIONS

Low-dose VNC injections appear to be relatively safe and effective in selectively inhibiting spontaneous aberrant reinnervation after RLN injury in an animal model.

Palliative treatment of dysphonia and dysarthria

The focus of this article is the palliative treatment of a variety of dysphonic conditions. Symptomatic relief of hoarseness can be achieved by voice therapy, augmentative alternative communication modalities, and surgery. The causes of dysphonia addressed herein include amyotrophic lateral sclerosis, Parkinson's disease, multiple sclerosis, stroke, head and neck cancers requiring glossectomy or laryngectomy, unilateral vocal fold paralysis, and presbyphonia. Palliative treatment of dysphonia and voice disorders provides symptomatic relief but not a cure of the underlying disease state. For these patients there are a number of palliative interventions that can greatly improve their quality of life.

Optimization of autologous muscle stem cell survival in the denervated hemilarynx

OBJECTIVE

Current treatments for vocal fold paralysis are suboptimal in that they fail to restore dynamic function. Autologous muscle stem cell (MSC) therapy is a promising potential therapy for vocal fold paralysis in that it can attenuate denervation-induced muscle atrophy and provide a vehicle for delivery of neurotrophic factors, thereby potentially selectively guiding reinnervation. The goal of this project was to characterize optimal conditions for injected autologous MSC survival in the thyroarytenoid (TA) muscle following recurrent laryngeal nerve (RLN) injury by local administration of adjuvant factors.

STUDY DESIGN

Animal experiment.

METHODS

Unilateral RLN transection and sternocleidomastoid muscle (approximately 1 g) biopsies were performed in 20 male Wistar rats. One month later, 10 autologous MSCs labeled via retroviral-enhanced green fluorescent protein (EGFP) transduction were injected into the denervated hemilarynx of each animal with one of four adjuvant therapies: cardiotoxin [(CTX) 10 M], insulin-like growth factor-1 [(IGF- 1) 100 microg/mL], ciliary neurotrophic factor [(CNTF) 50 microg/mL], or saline. Animals were euthanized 1 month later and larynges harvested, sectioned, and analyzed for MSC survival.

RESULTS

All specimens demonstrate extensive MSC survival, with fusion of the MSCs with the denervated myofibers. Based on mean fluorescent intensity of the laryngeal specimens, IGF-1 and CNTF had the greatest positive influence on MSC survival. Myofiber diameters demonstrated myofiber atrophy to be inversely related to MSC survival, with the least atrophy in the groups having the greatest MSC survival.

CONCLUSIONS

Autologous MSC therapy may be a future treatment for vocal fold paralysis. These findings support a model whereby MSCs genetically engineered to secrete CNTF and/or IGF-1 may not only promote neural regeneration, but also enhance MSC survival in an autocrine fashion.

Cavernous nerve regeneration using acellular nerve grafts

INTRODUCTION

The restoration of erectile function following complete transection of nerve tissue during surgery remains challenging. Recently, graft procedures using sural nerve grafts during radical prostatectomy have had favorable outcomes, and this has rekindled interest in the applications of neural repair in a urologic setting. Although nerve repair using autologous donor graft is the gold standard of treatment currently, donor nerve availability and the associated donor site morbidity remain a problem. In this study, we investigated whether an "off-the-shelf" acellular nerve graft would serve as a viable substitute. We examined the capacity of acellular nerve scaffolds to facilitate the regeneration of cavernous nerve in a rodent model.

MATERIALS AND METHODS

Acellular nerve matrices, processed from donor rat corporal nerves, were interposed across nerve gaps. A total of 80 adult male Sprague-Dawley rats were divided into four groups. A 0.5-cm segment of cavernosal nerve was excised bilaterally in three of the four groups. In the first group, acellular nerve segments were inserted bilaterally at the defect site. The second group underwent autologous genitofemoral nerve grafts at the same site, and the third group had no repair. The fourth group underwent a sham procedure. Serial cavernosal nerve function assessment was performed using electromyography (EMG) at 1 and 3 months following initial surgery. Histological and immunocytochemical analyses were performed to identify the extent of nerve regeneration.

RESULTS

Animals implanted with acellular nerve grafts demonstrated a significant recovery in erectile function when compared with the group that received no repair, both at 1 and 3 months. EMG of the acellular nerve grafts demonstrated adequate intracavernosal pressures by 3 months (87.6% of the normal non-injured nerves). Histologically, the retrieved regenerated nerve grafts demonstrated the presence of host cell infiltration within the nerve sheaths. Immunohistochemically, antibodies specific to axons and Schwann cells demonstrated an increase in nerve regeneration across the grafts over time. No organized nerve regeneration was observed when the cavernous nerve was not repaired.

CONCLUSION

These findings show that the use of nerve guidance channel systems allow for accelerated and precise cavernosal nerve regeneration. Acellular nerve grafts represent a viable alternative to fresh autologous grafts in a rodent model of erectile dysfunction.

The thyrohyoid approach to in-office injection augmentation of the vocal fold

PURPOSE OF REVIEW

The purpose of this article is to review the history of vocal fold injection augmentation and provide a thorough description of the percutaneous thyrohyoid approach to office-based vocal fold injection augmentation for the management of glottic incompetence.

RECENT FINDINGS

A number of techniques for vocal fold injection augmentation have been developed since the first procedure was performed. Since vocal fold injection augmentation is performed without an open surgical approach, morbidity is reduced and the technique can be done in the outpatient setting. Accordingly, over the past decade there has been an effort to perfect techniques and to develop new materials and methods to make the procedure more effective and comfortable for the patient.

SUMMARY

Recently, office-based vocal fold injection augmentation has gained significant popularity among laryngologists. While there are a variety of in-office injection techniques, the thyrohyoid approach, in the authors' opinion, is the simplest and best tolerated. This technique is effective and eliminates many of the shortcomings of the other approaches. This approach continues to be the 'workhorse' for in-office vocal fold injection augmentation in the senior author's practice. It is important, however, for any practitioner to be familiar with the other approaches, as this technique is not universally effective for all patients.