Fibronectin and adhesion molecules on canine scarred vocal folds

Establishing a Mouse Model of Surgical Vocal Fold Injury

OBJECTIVE

Animal models of vocal fold (VF) surgical injury and scar formation provide insight into the wound healing process. The purpose of this study was to establish an alternative model of surgical injury to the mouse VF using materials commonly available in most research laboratories or for purchase and to investigate wound healing of the epithelium (EP) and lamina propria (LP).

METHODS

Mice were anesthetized by isoflurane gas delivery and positioned on a platform so that the larynx could be observed using a laryngoscope and dissection microscope. Unilateral VF injury was created using a wire brush. Mice were euthanized and the larynx evaluated 1-, 3-, 5-, 7-, 14-, and 28-days following injury. Histological and immunofluorescent analysis was used to evaluate thickness of the EP, LP area, proliferative (Ki67+) and basal cells (p63+) in the EP, and collagen III content in the LP.

RESULTS

The depth of injury reached the superficial thyroarytenoid muscle on Day 1. The thickness of the EP of the injured VF was increased on Days 3 and 5, and the LP area was increased on Days 3, 5, and 7 as compared with the uninjured VF. Ki67+ and p63+ cells were increased on Day 3 and collagen III content was increased on Days 5 and 28 as compared with the uninjured VF.

CONCLUSION

We successfully established an alternative method of creating unilateral VF injury in the mouse. This method will be useful for future research regarding VF surgical injury and wound healing.

LEVEL OF EVIDENCE

N/A Laryngoscope, 2024.

Urinary syndecan-1 in dogs anesthetized with isoflurane or sevoflurane: A randomized, prospective study

BACKGROUND

Syndecan-1 (SDC1) is an established marker of endothelial glycocalyx shedding. Most research on SDC1 has focused on plasma or serum concentrations, and little is known about urine concentrations.

OBJECTIVES

Measure urinary SDC1 concentrations in dogs undergoing anesthesia with either sevoflurane or isoflurane and assess the effects of anesthesia duration and IV crystalloids on urinary SDC1 concentrations.

ANIMALS

Thirty-one client-owned dogs undergoing anesthesia for magnetic resonance imaging (MRI) with or without surgery for suspected intervertebral disk disease (IVDD) were used.

METHODS

Dogs with suspected IVDD were randomized to undergo anesthesia with either sevoflurane or isoflurane. Urine was collected before and immediately after anesthesia for the analysis of SDC1. Urinary creatinine concentrations also were measured, and the ratio of urinary SDC1 to urinary creatinine (USCR) was used to account for dilution.

RESULTS

Median (range) USCR was significantly higher after anesthesia compared with baseline for all groups combined (P < .05). No significant difference was found between the groups for age, sex, weight, and type of anesthesia. Multiple regression analysis of the effect of the independent variables inhalant type, age, weight, sex, anesthesia time, surgery, and quantity of IV fluids on the dependent variable SDC1 found that only the quantity of IV fluids significantly predicted a change (P < .001).

CONCLUSIONS AND CLINICAL IMPORTANCE

The total volume of lactated Ringer's solution administered to anesthetized dogs may affect USCR. Further investigations are warranted to evaluate the relationship between IV fluids and SDC1.

Anti-inflammatory and Antioxidant Effects of Japanese Herbal Medicine Kyoseihatekigan on Vocal Fold Wound Healing

OBJECTIVES

The Japanese herbal medicine kyoseihatekigan (KHG) has been used to alleviate the symptoms of croaky voice and globus hystericus, and each of its components has anti-inflammatory and antioxidant effects. However, the mechanisms underlying these beneficial actions of KHG on the vocal folds remain largely unknown. We examined the effects of KHG on rat vocal fold wound healing and assessed its anti-inflammatory and antioxidant properties.

STUDY DESIGN

Animal model.

METHODS

The vocal folds of Sprague-Dawley rats were unilaterally injured under endoscopy. Rats were divided into three groups based on KHG dosing from pre injury day 4 to post injury day 3: 0 mg/kg/day (sham group), 500 mg/kg/day (1% KHG group) and 1000 mg/kg/day (2% KHG group). Histologic changes were examined to assess the degree of inflammation and oxidative stress at day 3, and fibrosis at day 56. In addition, gene expression related to pro-inflammatory cytokines and transforming growth factor-beta1 (TGF-β1) signaling was examined by quantitative real-time polymerase chain reaction (qPCR).

RESULTS

Histologic analysis showed that the 1% and 2% KHG treatments significantly decreased cell infiltration and the 4-hydroxy-2-nonenalx-immunopositive area, and increased hyaluronic acid at day 3. Both KHG treatments significantly decreased fibrosis at day 56. qPCR revealed that mRNA of interleukin-1β and cyclooxygenase-2 were significantly suppressed at day 1 and TGF-β1 mRNA was significantly downregulated at day 5 in both KHG groups.

CONCLUSIONS

The current findings suggest that KHG has anti-inflammatory and antioxidant effects in the early phase of vocal fold wound healing, which can lead to better wound healing with less scar formation.

Effect of nodule size and stiffness on phonation threshold and collision pressures in a synthetic hemilaryngeal vocal fold model

Synthetic vocal fold (VF) replicas were used to explore the role of nodule size and stiffness on kinematic, aerodynamic, and acoustic measures of voiced speech production. Emphasis was placed on determining how changes in collision pressure may contribute to the development of phonotrauma. This was performed by adding spherical beads with different sizes and moduli of elasticity at the middle of the medial surface of synthetic silicone VF models, representing nodules of varying size and stiffness. The VF models were incorporated into a hemilaryngeal flow facility. For each case, self-sustained oscillations were investigated at the phonation threshold pressure. It was found that increasing the nodule diameter increased the open quotient, phonation threshold pressure, and phonation threshold flow rate. However, these values did not change considerably as a function of the modulus of elasticity of the nodule. Nevertheless, the ratio of collision pressure to subglottal pressure increased significantly for both increasing nodule size and stiffness. This suggests that over time, both growth in size and fibrosis of nodules will lead to an increasing cycle of compensatory vocal hyperfunction that accelerates phonotrauma.

Matrix Adhesiveness Regulates Myofibroblast Differentiation from Vocal Fold Fibroblasts in a Bio-orthogonally Cross-linked Hydrogel

Repeated mechanical and chemical insults cause an irreversible alteration of extracellular matrix (ECM) composition and properties, giving rise to vocal fold scarring that is refractory to treatment. Although it is well known that fibroblast activation to myofibroblast is the key to the development of the pathology, the lack of a physiologically relevant in vitro model of vocal folds impedes mechanistic investigations on how ECM cues promote myofibroblast differentiation. Herein, we describe a bio-orthogonally cross-linked hydrogel platform that recapitulates the alteration of matrix adhesiveness due to enhanced fibronectin deposition when vocal fold wound healing is initiated. The synthetic ECM (sECM) was established via the cycloaddition reaction of tetrazine (Tz) with slow (norbornene, Nb)- and fast (trans-cyclooctene, TCO)-reacting dienophiles. The relatively slow Tz-Nb ligation allowed the establishment of the covalent hydrogel network for 3D cell encapsulation, while the rapid and efficient Tz-TCO reaction enabled precise conjugation of the cell-adhesive RGDSP peptide in the hydrogel network. To mimic the dynamic changes of ECM composition during wound healing, RGDSP was conjugated to cell-laden hydrogel constructs via a diffusion-controlled bioorthognal ligation method 3 days post encapsulation. At a low RGDSP concentration (0.2 mM), fibroblasts residing in the hydrogel remained quiescent when maintained in transforming growth factor beta 1 (TGF-β1)-conditioned media. However, at a high concentration (2 mM), RGDSP potentiated TGF-β1-induced myofibroblast differentiation, as evidenced by the formation of an actin cytoskeleton network, including F-actin and alpha-smooth muscle actin. The RGDSP-driven fibroblast activation to myofibroblast was accompanied with an increase in the expression of wound healing-related genes, the secretion of profibrotic cytokines, and matrix contraction required for tissue remodeling. This work represents the first step toward the establishment of a 3D hydrogel-based cellular model for studying myofibroblast differentiation in a defined niche associated with vocal fold scarring.

Cryotherapy Modifies Extracellular Matrix Expression of Vocal Fold in Rat Models

OBJECTIVES

Vocal fold (VF) scarring is the major cause of voice disorders. Cryotherapy is an effective anti-scarring therapy for skin lesions. The aim of this study was to explore the anti-scarring potential of cryotherapy in vocal folds.

METHODS

The extracellular matrix (ECM) mRNA expression of cryotherapy on normal VF tissue and the histologic results of cryotherapy on vocal fold healing were studied. Fifteen rats were introduced cryotherapy on the normal VF bilaterally and were harvested for real-time polymerase chain reaction (RT-PCR) analysis for collagen I, collagen III, TGFβ1, decorin, fibronectin and HAS1 at 1 day, 3 days and 7 days. Ten rats were unilaterally injured by stripping lamina propria and immediately treated with or without cryotherapy and were harvested at 2 months for histological and immunohistochemical analysis.

RESULTS

Regenerative effect of cryotherapy was validated of ECM gene expression. Histological and immunohistochemical analysis showed significantly increased hyaluronan, decreased collagen, and increased decorin deposition in injury-cryotherapy cohort compared with injury control cohort and normal control cohort.

CONCLUSIONS

Cryotherapy may provide an optimal environment for vocal fold tissue regeneration. The results of the present investigation suggest that cryotherapy has therapeutic potential in prevention and treatment of vocal fold scarring.

[Molecular laryngology : A new chapter in the understanding of laryngeal diseases]

BACKGROUND

Despite considerable advances in laryngological research, there is still a plethora of (benign) vocal fold pathologies that cannot be treated causally. This is due to the limited accessibility and sensitive microarchitecture of the vocal folds, which cannot be investigated at a cellular level. Consequently, current pathophysiological knowledge is frequently based on macroscopic findings. The impact of interventions is mainly evaluated endoscopically or via indirect diagnostic methods.

OBJECTIVE

The aim of this article is to discuss state-of-the-art biotechnological methods used in laryngological research, illustrated by practical examples.

RESULTS

In recent years, animal and in vitro experiments have significantly contributed to a continuous expansion of knowledge in this field, particularly regarding vocal fold inflammation and scar formation. Vocal fold fibroblasts, the most important cellular component of the lamina propria, can be accredited a central role in these processes.

CONCLUSION

Our knowledge regarding macroanatomy and macropathophysiology of several pathologies has increased considerably in recent years. In vitro trials have shown, e.g., that vocal fold fibroblasts in an inflammatory setting secrete less profibrotic and proinflammatory cytokines when exposed to vibration. Early vocal exercises after surgical interventions on the vocal folds may therefore promote better wound healing and consequently improved phonation. Research in molecular laryngology should create a solid basis of knowledge for subsequent clinical studies.

Hyaluronic Acid/Alginate Hydrogel Containing Hepatocyte Growth Factor and Promotion of Vocal Fold Wound Healing

BACKGROUND

Hepatocyte growth factor (HGF) has been shown to facilitate vocal fold (VF) wound healing. This study was undertaken to determine whether the therapeutic efficacy of HGF could be enhanced by applying it in hyaluronic acid and alginate (HA/ALG) composite hydrogels into VFs after injury in a rabbit model.

METHODS

HGF was loaded into HA/ALG composite hydrogel (HGF-HA/ALG) and its in vitro release profile was evaluated. In addition, HGF-HA/ALG was injected into the VFs of rabbits immediately after direct injury and HGF or PBS was injected in the same manner into control groups. Macroscopic features were observed by endoscopy at 3 months post-injury. Functional analyses including mucosal waves of VFs and viscoelastic properties were performed by kymography following high-speed digital imaging and rheometer. Histopathological and immunohistochemical evaluations were also conducted on VFs.

RESULTS

HGF release from HGF-HA/ALG was sustained for up to 3 weeks. Rabbits treated with HGF-HA/ALG showed improved mucosal vibrations and VF viscoelastic properties as compared with the PBS and HGF controls. Histopathological staining revealed HGF-HA/ALG treated VFs showed less fibrosis than PBS and HGF controls, and immunohistochemical analysis demonstrated amounts of type I collagen and fibronectin were lower in HGF-HA/ALG treated animals than in PBS and HGF controls at 3 months post-injury.

CONCLUSION

HGF containing HA/ALG hydrogel enhanced healing in our rabbit model of VF injury.

The Ability of Human Nasal Inferior Turbinate-Derived Mesenchymal Stem Cells to Repair Vocal Fold Injuries

Objective This study investigated the ability of implanted human nasal inferior turbinate-derived mesenchymal stem cells (hTMSCs) to repair injured vocal folds. To this end, we used quantitative real-time polymerase chain reaction (PCR) to analyze the early phase of wound healing and histopathological analysis to explore the late phase of wound healing in xenograft animal models. Study Design Prospective animal study. Setting Research laboratory. Subjects and Methods The right-side lamina propria of the vocal fold was injured in 20 rabbits and 30 rats. Next, hTMSCs were implanted into half of the injured vocal folds (hTMSC groups). As a control, phosphate-buffered saline (PBS) was injected into the other half of the injured vocal folds (PBS groups). Rat vocal folds were harvested for polymerase chain reaction (PCR) at 1 week after injury. Rabbit vocal folds were evaluated endoscopically and the larynges harvested for histological and immunohistochemical examination at 2 and 8 weeks after injury. Results In the hTMSC group, PCR showed that hyaluronan synthase ( HAS) 1, HAS 2, and transforming growth factor ( TGF)-β1 were significantly upregulated compared with the PBS group. Procollagen type III ( COL III) messenger RNA expression was significantly upregulated in the PBS group compared with the normal group. Histological analyses showed that hTMSC administration afforded more favorable collagen and hyaluronic acid deposition than was evident in the controls. Implanted hTMSCs were observed in injured vocal folds 2 weeks after implantation. Conclusions Our results show that hTMSCs implantation into injured vocal folds facilitated vocal fold regeneration, with presenting antifibrotic effects.

Process of tight junction recovery in the injured vocal fold epithelium: Morphological and paracellular permeability analysis

OBJECTIVES/HYPOTHESIS

The vocal fold epithelium that includes tight junction (TJ)-based barrier function protects underlying connective tissues from external insults. TJs play an important role to control paracellular permeability of not only solutes but also ions, and preserve the vocal fold homeostasis. However, the distribution of TJs and paracellular diffusion barrier across the entire vocal fold epithelium are still unknown. The aim of this study was to identify the distribution of TJs in the vocal fold epithelium and to characterize the recovery process of TJ-based paracellular diffusion barrier in a rat model of vocal fold injury.

STUDY DESIGN

Animal experiments with controls.

METHODS

Normal and vocal fold-injured rats were used. Larynges were harvested for immunohistochemical examination of TJ proteins. For functional analysis, a tracer permeability assay was performed using EZ-Link Sulfo-NHS-LC-Biotin.

RESULTS

TJ proteins occludin and zonula occludens 1 signals were localized to the junctional regions of the most luminal cell layers of the vocal fold epithelium. The injured region had been recovered with epithelium at 5 days postinjury, but the paracellular diffusion barrier assays revealed that biotinylation reagents diffused into the lamina propria at 5 days postinjury, and were blocked at the epithelium at 14 and 28 days postinjury.

CONCLUSIONS

It was strongly suggested that TJs in the vocal fold epithelium exist at the junctional regions of the first layer of stratified squamous epithelium. TJ-based paracellular diffusion barrier following vocal fold injury is recovered by 14 days postinjury, and this period corresponds with the time course of structural changes in the regenerating epithelium layer.

LEVEL OF EVIDENCE

NA. Laryngoscope, 128:E150-E156, 2018.

Macrophage Response to Allogeneic Adipose Tissue-Derived Stromal Cells in Hyaluronan-Based Hydrogel in a Porcine Vocal Fold Injury Model

OBJECTIVE

Adipose tissue-derived stromal cells (ASC) embedded in hyaluronan scaffold is a beneficial prophylactic treatment for vocal fold (VF) surgical scar. Here, we investigated the macrophage inflammatory response to allogeneic ASC-constructs and identified changes in lamina propria extracellular matrix.

METHOD

Pig ASC were characterized and transfected with GFP+ lentivirus. Thirty-three pigs underwent VF biopsies, and after 3 days, gel alone, gel+pASC, placebo, or pASC alone was injected into wound bed. Animals were sacrificed 3, 7, or 26 days post-injection. Flow cytometry; qPCR for NF-α, TGFβ, IL-10, IL-4, IFNγ, IL-12, FGF2, Col1A1, and HGF; and immunohistochemistry for collagen, elastin, HA, and fibronectin were performed to characterize macrophage phenotype, quantify cytokine transcription, analyze extracellular matrix remodeling, and track GFP+ cells.

RESULTS

No significant differences were found in SWC3+/SWC9+ phenotype or mRNA expression between cells+gel, gel, or placebo. The ASC alone exhibited significantly greater collagen, gel alone resulted in significantly less hyaluronan, and gel+pASC significantly more fibronectin (all P < .05). The pASC-GFP+ were detected 26 days post-injection.

CONCLUSIONS

The ASC-constructs were biocompatible; they did not influence the macrophage inflammatory response or provoke increases in collagen expression. Long-term engraftment was confirmed.

Evaluation of the Grafted Fascia in the Vocal Fold of Dogs: A Histologic Study

INTRODUCTION

There is no consensus on the ideal graft for medialization surgery of the vocal folds in the literature. One of the most favorable proposals is the use of autologous fascia, which seems limited by the lack of information regarding the integration of grafted tissue. Our study aims to evaluate the degree of fully engrafted fascia integration in the vocal fold lamina propria of dogs.

MATERIALS AND METHODS

Fourteen adult mongrel dogs that underwent intravenous general anesthesia were selected and kept under spontaneous ventilation. A fascia lata fragment of 4 cm² was obtained from the right leg of each dog. The dogs underwent laryngoscopy; a 3 mm incision was made in the vocal process, next to the vestibular process, and the fascia was grafted into the right vocal fold. The left vocal fold was used as a control. The animals were divided into two groups: group A, evaluated after 2 months of the procedure, and group B, evaluated after 6 months of the procedure. Histologic analysis was made semiquantitatively regarding the presence of inflammatory reaction, fibrosis, and neovascularization.

RESULTS

Our final studied group comprised 12 dogs. Microscopic examination of the larynx revealed the absence of any detectable inflammation in the incision site. The lamina propria of the grafted vocal fold showed identifiable compact, thick, and eosinophilic collagen bands. The surrounding tissue showed thin collagen bands with some organization, similar to the contralateral vocal fold.

CONCLUSION

The grafted fascia integrates into the vocal fold lamina propria and seems not to cause inflammatory reaction response.

A Review of Hyaluronic Acid and Hyaluronic Acid-based Hydrogels for Vocal Fold Tissue Engineering

Vocal fold scarring is a common cause of dysphonia. Current treatments involving vocal fold augmentation do not yield satisfactory outcomes in the long term. Tissue engineering and regenerative medicine offer an attractive treatment option for vocal fold scarring, with the aim to restore the native extracellular matrix microenvironment and biomechanical properties of the vocal folds by inhibiting progression of scarring and thus leading to restoration of normal vocal function. Hyaluronic acid is a bioactive glycosaminoglycan responsible for maintaining optimum viscoelastic properties of the vocal folds and hence is widely targeted in tissue engineering applications. This review covers advances in hyaluronic acid-based vocal fold tissue engineering and regeneration strategies.

Histologic Characterization of Rat Vocal Fold Scarring

This study aimed to clarify the characteristics of rat vocal fold scarring by examining the alteration of key components in the extracellular matrix: hyaluronic acid, collagen, and fibronectin. Under monitoring with a 1.9-mm-diameter telescope, unilateral vocal fold stripping was performed, and larynges were harvested at 2, 4, 8, and 12 weeks after operation. The vocal folds were histologically analyzed with Alcian blue stain, trichrome stain, and immunofluorescence of collagen type I, collagen type III, and fibronectin. The scarred vocal folds showed less hyaluronic acid and more collagen types I and III than did the controls at all time points. Type III was stable for 12 weeks, while type I declined until 8 weeks and thereafter remained unchanged. Fibronectin increased for 4 weeks and then decreased; it was close to the control level at 8 and 12 weeks. These results suggest that the tissue remodeling process in scarred vocal folds slows down around 2 months after wounding.

Drug Delivery System of Hepatocyte Growth Factor for the Treatment of Vocal Fold Scarring in a Canine Model

Objectives:

Vocal fold scarring remains a therapeutic challenge. Previous studies have indicated that hepatocyte growth factor (HGF), a strong antifibrotic element, has therapeutic potential for restoring scarred vocal folds. To enhance the effect of HGF in vivo, we developed a novel drug delivery system (DDS) in which HGF is embedded in gelatin hydrogel and continuously released over a period of 2 weeks. In the present study we investigated the therapeutic efficacy of the HGF DDS on vocal fold scarring by using a canine model.

Methods:

The vocal folds of 8 beagles were unilaterally scarred by stripping the entire layer of the lamina propria. The contralateral vocal folds were kept intact as normal controls. One month after the procedure, hydrogels (0.5 mL) containing 1 μg of HGF were injected into the scarred vocal folds of 4 dogs (HGF-treated group), whereas hydrogels containing saline solution were injected in the other 4 dogs (sham group). Histologic and vibratory examinations were completed for each group 6 months after the initial surgery.

Results:

The excised larynx experiments showed significantly better vibration in terms of mucosal wave amplitude and glottal closure in the HGF-treated group compared to the sham group. Histologic evaluation of the vocal folds indicated remarkable reduction in collagen deposition and tissue contraction, with favorable restoration of hyaluronic acid and elastin in the HGF-treated group.

Conclusions:

The present findings suggest that the novel HGF DDS may provide favorable effects in restoring the vibratory properties of scarred vocal folds.

Cell Production in Injured Vocal Folds: A Rat Study

Objectives:

Fibroblasts are reported to play an important role in producing the extracellular matrix of the vocal fold. However, no reports have focused on how and where these cells are generated in the vocal fold after injury. To reveal the characteristics of vocal fold cell production, we investigated cell proliferation in the acute phase of wound healing.

Methods:

Using a telescope for guidance, we made an incision in the middle region of the vocal fold tissue in 24 rats and performed immunohistochemical staining for vimentin, α-smooth muscle actin, and 5-bromo-2-deoxyuridine.

Results:

After injury, epithelialization occurred with a peak at day 1, and fibroblasts proliferated in the lamina propria with a peak at day 3, whereas those in the macula flava did not show any increased proliferation.

Conclusions:

It is suggested that the fibroblasts in the macula flava have functions different from those of fibroblasts in the lamina propria and that the macula flava does not serve as a cell source for the vocal fold in response to injury.

Growth Factor Therapy for Vocal Fold Scarring in a Canine Model

Vocal fold scarring remains a therapeutic challenge. Hepatocyte growth factor (HGF) has strong antifibrotic activity and has proved to have therapeutic potential in restoration of scar tissues such as liver cirrhosis and lung fibrosis. The present study aimed to clarify the effects of HGF injection into scarred vocal folds in a canine model. Canine vocal folds were stripped unilaterally and treated with intracordal injection of saline solution (sham group), HGF (HGF group), or HGF with cultured autologous normal vocal fold fibroblasts (Fb/HGF group) 1 month after injury. The larynges were harvested 6 months after the initial injury and then subjected to vibratory and histologic examination. The results of vibratory examinations in the excised larynx setup revealed that phonation threshold pressure significantly increased and vocal efficiency was significantly reduced in all treated groups as compared to normal data obtained from normal canine larynges. However, the HGF group presented much better results than both the sham and Fb/HGF groups in terms of mucosal wave amplitude and incidence of vocal fold bowing, glottal incompetence, and phase asymmetry. The histologic data indicated a significant increase of collagen in both the sham and Fb/HGF groups, while normal levels of collagen were found in the HGF group. Tissue contraction of the lamina propria was also observed in both the sham and Fb/HGF groups, but was barely detectable in the HGF group. Although the HGF-treated vocal folds appeared to require more driving forces for vibration, HGF might prevent excessive collagen deposition and tissue contraction and thus reduce the effects of scarring on the vibratory properties of the vocal folds. From these data it is concluded that HGF has considerable potential in the treatment of vocal fold scarring.

MERS versus Standard Surgical Approaches for Porcine Vocal Fold Scarring with Adipose Stem Cell Constructs

OBJECTIVE

Cells, scaffold, and surgical approaches are important for regeneration of the lamina propria of the scarred vocal fold (VF). Microendoscopy of Reinke's space (MERS) is a surgical approach used to access the lamina propria. The present study evaluated MERS in the treatment of VF scarring as compared with standardized approaches for the treatment of VF scarring with adipose stem cell constructs.

STUDY DESIGN

Animal study.

SETTING

Academic center.

SUBJECTS AND METHODS

VF injury was performed bilaterally to induce scarring in 20 pigs. Eight weeks after injury, pigs were classified into no treatment, minithyrotomy, VF injection, VF incision/dissection, and MERS. All groups (except control) were implanted with adipose stem cell and hyaluronan. Four weeks after treatment, histology for collagen, hyaluronan, and fibronectin; mRNA expression for α-smooth muscle actin, tumor growth factor β1, collagen 1α1, collagen 3α1, matrix metalloproteinase 2, basic fibroblast growth factor, and hepatocyte growth factor; and tissue rheology were evaluated.

RESULTS

Differences were measured among surgical approaches for protein levels of collagen, hyaluronan, and fibronectin (P = .0133, P < .0001, and P = .0025, respectively). Fibroblast growth factor, collagen 1α1, and matrix metalloproteinase 2 transcript levels were different among treatment groups (P = .003, P = .0086, and P = .014, respectively), while no differences were measured for α-smooth muscle actin, tumor growth factor β1, hepatocyte growth factor, and collagen 3α1. Rheologically, significant differences were not measured between groups.

CONCLUSION

MERS is a promising surgical approach for the treatment of VF scarring, optimizing the placement of implanted biomaterials.

Comparison of ASCs and BMSCs combined with atelocollagen for vocal fold scar regeneration

OBJECTIVES/HYPOTHESIS

Vocal fold scar remains a therapeutic challenge. Mesenchymal stromal cells (MSCs) are promising tools for regenerative medicine. Nevertheless, few in vivo studies have directly compared various sources of MSCs. The aim of this study was to investigate the therapeutic potential of adipose-derived stromal cells (ASCs) in comparison with bone marrow-derived stromal cells (BMSCs) for vocal fold regeneration.

STUDY DESIGN

Prospective animal experiments with controls.

METHODS

Two months after stripping of the lamina propria, 18 beagles were divided into four implantation groups: atelocollagen alone (collagen group), atelocollagen with BMSCs (BMSC-collagen), atelocollagen with ASCs (ASC-collagen), or a sham-treated group. One or 6 months after implantation, vibratory and histological examinations were performed.

RESULTS

Mucosal vibration was significantly improved in both of the MSC-implanted groups compared with the sham-treated group, whereas only the ASC-collagen group showed a significantly smaller glottal gap than the collagen group. Moreover, in the ASC-collagen group, a significant reduction of collagen density was observed compared to the sham-treated group, and there was a trend for better restoration of hyaluronic acid (HA). Implanted MSCs were detected 1 month postimplantation; however, none survived 6 months postimplantation.

CONCLUSIONS

Although implantation of an atelocollagen sponge and ASCs into vocal fold scars induced vibratory recovery comparable to that of BMSCs, ASCs might have more potential in terms of restoration of HA and suppression of excessive collagen deposition.

LEVEL OF EVIDENCE

NA Laryngoscope, 126:1143-1150, 2016.

Biomechanical Screening of Cell Therapies for Vocal Fold Scar

Candidate cell sources for vocal fold scar treatment include mesenchymal stromal cells from bone marrow (BM-MSC) and adipose tissue (AT-MSC). Mechanosensitivity of MSC can alter highly relevant aspects of their behavior, yet virtually nothing is known about how MSC might respond to the dynamic mechanical environment of the larynx. Our objective was to evaluate MSC as a potential cell source for vocal fold tissue engineering in a mechanically relevant context. A vibratory strain bioreactor and cDNA microarray were used to evaluate the similarity of AT-MSC and BM-MSC to the native cell source, vocal fold fibroblasts (VFF). Posterior probabilities for each of the microarray transcripts fitting into specific expression patterns were calculated, and the data were analyzed for Gene Ontology (GO) enrichment. Significant wound healing and cell differentiation GO terms are reported. In addition, proliferation and apoptosis were evaluated with immunohistochemistry. Results revealed that VFF shared more GO terms related to epithelial development, extracellular matrix (ECM) remodeling, growth factor activity, and immune response with BM-MSC than with AT-MSC. Similarity in glycosaminoglycan and proteoglycan activity dominated the ECM analysis. Analysis of GO terms relating to MSC differentiation toward osteogenic, adipogenic, and chondrogenic lineages revealed that BM-MSC expressed fewer osteogenesis GO terms in the vibrated and scaffold-only conditions compared to polystyrene. We did not evaluate if vibrated BM-MSC recover osteogenic expression markers when returned to polystyrene culture. Immunostaining for Ki67 and cleaved caspase 3 did not vary with cell type or mechanical condition. We conclude that VFF may have a more similar wound healing capacity to BM-MSC than to AT-MSC in response to short-term vibratory strain. Furthermore, BM-MSC appear to lose osteogenic potential in the vibrated and scaffold-only conditions compared to polystyrene, potentially attenuating the risk of osteogenesis for in vivo applications.

The unsolved chapter of vocal fold scars and how tissue engineering could help us solve the problem

Vocal fold scarring is a relatively small field in scar research with prerequisites found nowhere else. The deterioration of the delicate tri-layered micro-structure of the epithelium of the vocal folds leads to impaired vibration characteristics resulting in a permanent hoarse and breathy voice. Tissue engineering approaches could help to restore the pre-injury status. Despite a considerable progress in this field during the last years, routine clinical applications are not available so far. One reason might be that vocal fold fibroblasts, as the responsible cell type for fibrogenesis, have very particular properties that are only poorly characterized. Moreover, in vivo trials are costly and time consuming and a representative in vitro model does not exist so far. These particular circumstances lead to innovative in vitro strategies and concepts such as macro-molecular crowding that can also be applied in adjacent fields.

Vocal fold epithelial barrier in health and injury: a research review

PURPOSE

Vocal fold epithelium is composed of layers of individual epithelial cells joined by junctional complexes constituting a unique interface with the external environment. This barrier provides structural stability to the vocal folds and protects underlying connective tissue from injury while being nearly continuously exposed to potentially hazardous insults, including environmental or systemic-based irritants such as pollutants and reflux, surgical procedures, and vibratory trauma. Small disruptions in the epithelial barrier may have a large impact on susceptibility to injury and overall vocal health. The purpose of this article is to provide a broad-based review of current knowledge of the vocal fold epithelial barrier.

METHOD

A comprehensive review of the literature was conducted. Details of the structure of the vocal fold epithelial barrier are presented and evaluated in the context of function in injury and pathology. The importance of the epithelial-associated vocal fold mucus barrier is also introduced.

RESULTS/CONCLUSIONS

Information presented in this review is valuable for clinicians and researchers as it highlights the importance of this understudied portion of the vocal folds to overall vocal health and disease. Prevention and treatment of injury to the epithelial barrier is a significant area awaiting further investigation.

Classification for animal vocal fold surgery: resection margins impact histological outcomes of vocal fold injury

OBJECTIVES/HYPOTHESIS

Extent of vocal fold injury impacts the nature and timing of wound healing and voice outcomes. However, depth and extent of the lesion created to study wound healing in animal models vary across studies, likely contributing to different outcomes. Our goal was to create a surgery classification system to enable comparison of postoperative outcomes across animal vocal fold wound-healing studies.

STUDY DESIGN

Prospective, controlled animal study.

METHODS

Rats underwent one of three types of unilateral vocal fold surgeries classified by depth and length of resection. The surgeries were: for subepithelial injury, resection of epithelium and superficial layer of the lamina propria at the midmembranous portion of the vocal fold; for transmucosal injury, resection of epithelium and lamina propria; and for transmuscular injury, resection of epithelium, lamina propria, and superficial portion of the vocalis muscle. Wound healing was evaluated histologically at various time points up to 35 days postinjury.

RESULTS

Complete healing occurred by 14 days postsurgery for subepithelial injury, and by day 35 for transmucosal injury. Injury remained present at day 35 for transmuscular injury.

CONCLUSIONS

Timing and completeness of healing varied by extent and depth of resection. Scarless healing occurred rapidly following subepithelial injury, whereas scarring was observed at 5 weeks after transmuscular injury. The proposed classification system may facilitate comparison of surgical outcomes across vocal fold wound-healing studies.

LEVELS OF EVIDENCE

N/A.

Restoration of scarred vocal folds using 5 amino acid-deleted type hepatocyte growth factor

OBJECTIVES/HYPOTHESIS

Our previous studies demonstrated a regenerative effect of recombinant human hepatocyte growth factor (HGF) on vocal fold scarring using full-length HGF. However, clinical application has not yet been achieved because of the lack of a good manufacturing practice (GMP) for full-length HGF. Another natural form of human HGF, 5 amino acid-deleted type HGF (dHGF), has been newly produced under a GMP procedure. In the current study, we investigated the effect of dHGF in comparison with full-length HGF for the treatment of vocal fold scars using a canine model.

STUDY DESIGN

Prospective animal experiment.

METHODS

The vocal folds of nine beagles were unilaterally injured. Four weeks after injury, the vocal folds were treated with an intracordal injection of full-length HGF (full HGF group), dHGF (dHGF group), or phosphate-buffered saline (sham group). Vibratory and histological examinations were performed for each group 6 months after injury.

RESULTS

Vibratory examinations demonstrated significantly lower phonation threshold pressure and a higher ratio of normalized mucosal wave amplitude in both the full HGF and dHGF groups as compared to the sham group. Histological examination showed restoration of hyaluronic acid in both the full HGF and dHGF groups as compared to the sham group. No significant differences were observed for each parameter between the full HGF group and the dHGF group.

CONCLUSIONS

dHGF showed the same potential for regenerative effects on vocal fold scars as full-length HGF. dHGF should be applicable for human clinical trials in patients with vocal fold scars.

Clinical practice: vocal nodules in dysphonic children

Common among children, vocal symptoms are a cause of concern for parents who seek elucidation of their diagnosis and treatment. Vocal nodules are the major cause of dysphonias in children and are related to vocal abuse. We conducted a literature review considering clinical, physiopathological, epidemiological, and histological aspects of vocal nodules, as well as diagnostic methods, highlighting the main studies addressing this issue. The controversial points of treatments were also discussed.

Bone marrow-derived clonal mesenchymal stem cells as a source of cell therapy for promoting vocal fold wound healing

OBJECTIVES

We investigated whether mouse bone marrow-derived clonal mesenchymal stem cells (BM-cMSCs) could promote vocal fold (VF) wound healing by using a xenograft animal model.

METHODS

Homogeneous BM-cMSCs isolated by a subfractionation culturing method from the bone marrow aspirates of green fluorescent protein transgenic mice were injected into the VFs of rabbits immediately after direct mechanical injury. Macroscopic, biomechanical (rheometric), histologic, immunohistochemical, and transcriptional evaluations were performed on the scarred VFs 1 to 3 months after injury. Engraftment of the implanted BM-cMSCs was determined by detection of green fluorescent protein cells in the recipient VF by confocal microscopy.

RESULTS

The BM-cMSC-treated VFs showed improved morphological properties and viscoelasticity as compared to control VFs injected with phosphate-buffered saline solution. Histologic and immunohistochemical evaluations showed less excessive collagen deposition and increased density of glycosaminoglycans in the BM-cMSC-treated VFs as compared to the control VFs at 3 months after injury (p = 0.003 and p = 0.037, respectively). BM-cMSC transplantation led to a significant attenuation of fibronectin (p = 0.036) and transforming growth factor beta1 (p = 0.042) messenger RNA expression at 1 month after injury. Green fluorescent protein-expressing BM-cMSCs engrafted in recipient VFs were found at 1 month after implantation.

CONCLUSIONS

BM-cMSCs appeared to survive in the injured xenogeneic VFs after transplantation for up to 1 month and favorably enhanced the wound healing of VFs after injury. We conclude that BM-cMSCs are a possible source of cell therapy for vocal fold regeneration.

Vocal fold scars: current concepts and future directions. Consensus report of the Phonosurgery Committee of the European Laryngological Society

Scarring of the vocal folds leads to a deterioration of the highly complex micro-structure with consecutively impaired vibratory pattern and glottic insufficiency. The resulting dysphonia is predominantly characterized by a reduced vocal capacity. Despite the considerable progress in understanding of the underlying pathophysiology, the treatment of scarred vocal folds is still an unresolved chapter in laryngology and phonosurgery. Essential for a successful treatment is an individual, multi-dimensional concept that comprises the whole armamentarium of surgical and non-surgical (i.p. voice therapy) modalities. An ideal approach would be to soften the scar, because the reduced pliability and consequently the increased vibratory rigidity impede the easiness of vibration. The chosen phonosurgical method is determined by the main clinical feature: Medialization techniques for the treatment of glottic gap, or epithelium freeing techniques for improvement of vibration characteristics often combined with injection augmentation or implantation. In severe cases, buccal mucosa grafting can be an option. New developments, include treatment with anxiolytic lasers, laser technology with ultrafine excision/ablation properties avoiding coagulation (Picosecond infrared laser, PIRL), or techniques of tissue engineering. However, despite the promising results by in vitro experiments, animal studies and first clinical trials, the step into clinical routine application has yet to be taken.

Response of fibroblasts to transforming growth factor-β1 on two-dimensional and in three-dimensional hyaluronan hydrogels

Transforming growth factor-β1 (TGF-β1), an important cytokine with multiple functions, is secreted during wound healing. Previous studies have utilized two-dimensional (2D) cell culture to elucidate the functions of TGF-β1; however, 2D culture does not represent the complex three-dimensional (3D) in vivo environment. Using a synthetic hyaluronan (HA) extracellular matrix (ECM) hydrogel, we investigated the effect of TGF-β1 on fibroblasts cultured in three conditions--on tissue culture polystyrene (TCP), on HA (2D), and in HA (3D). After TGF-β1 treatment (0.1 to 20 ng/mL), morphological features and ECM regulation were analyzed by immunocytochemistry, Western blot, quantitative polymerase chain reaction, and zymogram assays. On TCP, cells showed the typical spindle shape with strong alpha smooth muscle actin (α-SMA) staining of cytoplasmic myofilaments along the cell axes after TGF-β1 treatment; on HA (2D), spindle-shape cells showed little α-SMA staining; in HA (3D), cells were smaller and rounded with less α-SMA deposition. The α-SMA gene and protein expression on TCP were significantly upregulated by TGF-β1, but TGF-β1 did not induce α-SMA expression in the presence of HA (both 2D and 3D). 3D HA culture significantly downregulated collagen I, III, and fibronectin expression, increased matrix metalloproteinase 1 and 2 (MMP1/MMP2) activity, upregulated MMP1 mRNA and downregulated TIMP3 mRNA expression. This study suggested that exogenous HA, particularly in 3D culture, appears to suppress ECM production, enhances ECM degradation and remodeling, and inhibits myofibroblast differentiation without decreasing TGF-β receptor expression.

Implantation of an atelocollagen sponge with autologous bone marrow-derived mesenchymal stromal cells for treatment of vocal fold scarring in a canine model

OBJECTIVES

Vocal fold scarring remains a therapeutic challenge. A new regenerative approach is needed to restore disorganized extracellular matrix. Tissue regeneration requires appropriate cells and a scaffold. Bone marrow-derived mesenchymal stromal cells (BMSCs) are multipotent and secrete many kinds of growth factors to regenerate tissues. Atelocollagen sponges have many large pores that permit cell entry. The present study was performed to evaluate whether implantation of an atelocollagen sponge plus BMSCs is effective for the treatment of vocal fold scarring.

METHODS

Twelve beagles underwent implantation of an atelocollagen sponge or of an atelocollagen sponge with autologous BMSCs (1.0 x 10(6) cells) in the subepithelial pockets of scarred vocal folds. Six months after the operation, vibratory examinations and histologic examinations were performed.

RESULTS

Mucosal vibrations improved significantly for the atelocollagen sponge-implanted vocal folds. Histologic analyses revealed favorable restoration of the extracellular matrix in the lamina propria. Increased distribution of hyaluronic acid and decreased dense collagen deposition were also noted. These improvements were enhanced by implantation of BMSCs.

CONCLUSIONS

Implantation of atelocollagen sponges with autologous BMSCs into scarred vocal folds significantly increased hyaluronic acid distribution and decreased dense collagen deposition in the lamina propria, leading to better mucosal vibration.

Effects of basic fibroblast growth factor on rat vocal fold fibroblasts

OBJECTIVES

The overarching goal of this line of research is to translate basic fibroblast growth factor (bFGF) treatment for vocal fold scarring into practical clinical use. In a previous canine investigation, we demonstrated that bFGF improves phonation threshold pressure, mucosal wave amplitude, and histologic measures in vocal folds treated after injury. In the present study, we studied the effects of bFGF on gene expression of the extracellular matrix and growth factors in rat vocal fold fibroblasts.

METHODS

Fibroblasts harvested from the vocal folds of 5 rats were treated with 3 concentrations of bFGF (0, 10, and 100 ng/mL). The fibroblasts were collected at 24 hours and 72 hours after bFGF administration. Quantitative polymerase chain reaction was then used to investigate the gene expression of the investigated growth factors and extracellular matrices.

RESULTS

The results revealed significantly down-regulated expression of procollagen I and significantly up-regulated expression of hyaluronic acid synthase (HAS) 2 and fibronectin in fibroblasts treated with bFGF. The administration of bFGF also resulted in the up-regulation of bFGF and hepatocyte growth factor (HGF). No changes in the expression of HAS-1, tropoelastin, or procollagen III were observed between the treatment and control conditions.

CONCLUSIONS

Treatment with bFGF induces the down-regulation of procollagen I and the up-regulation of HAS-2 in vocal fold fibroblast cell cultures. These gene expression alterations to key mediators of the wound healing process may translate into potential benefits in the remediation of vocal fold injury. The up-regulation of HGF, an antifibrotic effector molecule, may demonstrate additional benefits by optimizing the wound healing environment and by accelerating the wound repair cascade. These findings may provide fuel for additional discoveries into the development of growth factor therapy for the treatment of vocal fold scar.

Biosimulation of inflammation and healing in surgically injured vocal folds

OBJECTIVES

The pathogenesis of vocal fold scarring is complex and remains to be deciphered. The current study is part of research endeavors aimed at applying systems biology approaches to address the complex biological processes involved in the pathogenesis of vocal fold scarring and other lesions affecting the larynx.

METHODS

We developed a computational agent-based model (ABM) to quantitatively characterize multiple cellular and molecular interactions involved in inflammation and healing in vocal fold mucosa after surgical trauma. The ABM was calibrated with empirical data on inflammatory mediators (eg, tumor necrosis factor) and extracellular matrix components (eg, hyaluronan) from published studies on surgical vocal fold injury in the rat population.

RESULTS

The simulation results reproduced and predicted trajectories seen in the empirical data from the animals. Moreover, the ABM studies suggested that hyaluronan fragments might be the clinical surrogate of tissue damage, a key variable that in these simulations both is enhanced by and further induces inflammation.

CONCLUSIONS

A relatively simple ABM such as the one reported in this study can provide new understanding of laryngeal wound healing and generate working hypotheses for further wet-lab studies.

Treatment of acute vocal fold scar with local injection of basic fibroblast growth factor: a canine study

CONCLUSIONS

Results of the current study revealed improved phonation threshold pressure (PTP), normalized mucosal wave amplitude (NMWA), and less contraction of the lamina propria in injured larynges treated with basic fibroblast growth factor (bFGF).

OBJECTIVES

We investigated the effects of local injection of bFGF for treatment of acute vocal fold injury in a canine model.

METHODS

Vocal folds of eight beagles were unilaterally injured by removal of the mucosa under direct laryngoscopy. Four beagles received local injections of bFGF delivered to the scarred vocal fold at 1 month after injury. The remaining four beagles received local injections of saline and served as a sham-treatment group. Larynges were harvested 5 months after treatment and excised larynx experiments were performed to measure PTP, NMWA, and normalized glottal gap (NGG). Histologic staining was performed to evaluate structural changes of the extracellular matrix.

RESULTS

Excised larynx measurements revealed significantly lower PTP and increased NMWA in bFGF-treated vocal fold. Elastica Van Gieson staining revealed less contraction of the bFGF-treated vocal fold. Histologic measurements revealed that the thickness of the lamina propria was significantly greater in the bFGF-treated vocal fold. Alcian blue staining revealed improved restoration of hyaluronic acid in the bFGF-treated vocal fold.

Voice rest versus exercise: a review of the literature

Voice rest is commonly prescribed after vocal fold surgery to promote wound healing of the vocal fold. Currently, there is no standard protocol that is established based on biological evidence. In orthopedic rehabilitation, long-term rest is found to be less effective for connective tissue healing than exercise. Connective tissue healing is also an important factor for successful voice rehabilitation; however, whether this concept can be extrapolated to voice rehabilitation is unknown. The purpose of this article is to review current clinical and basic science literature to examine the effect of voice rest in postsurgical rehabilitation. First, we present a summary of clinical literature that pertains to voice rest. Second, we present description of connective tissues that are involved in orthopedic and voice rehabilitation, specifically, ligament and lamina propria, respectively, and their wound healing process. Third, a summary of the literature from orthopedic research on the effect of rest versus exercise is presented. Lastly, it summarizes in vitro and in vivo studies that examined the effect of mechanical stress on vocal fold tissue. Current literature suggests that there is a lack of clinical evidence that supports a specific type and duration of voice rest, and extrapolation of the findings from orthopedic research may be unreasonable due to the morphological and biochemical difference between the tissues. To determine the effect of voice rest, further elucidation of vocal fold wound healing process and the effect of mechanical stress on vocal fold tissue remodeling are needed.

Surgical method to create vocal fold injuries in mice

OBJECTIVES

The goal of this study was to develop a surgical method for the creation of vocal fold injuries in mice, as a precursor to the use of genetically engineered mouse models in the study of vocal fold wound healing and scar formation.

METHODS

Seven FVB strain mice were used in this study. A laryngoscope and 3 micro-instruments were designed and fabricated to facilitate endoscopic vocal fold visualization and the creation of vocal fold surgical injuries. The larynges were harvested 1 and 7 days after surgery, and the vocal fold injury sites were evaluated by routine hematoxylin and eosin staining. Additional immunohistochemical analysis of collagen type I and elastin distribution in the lamina propria was performed for an uninjured control larynx.

RESULTS

Endoscopic visualization and vocal fold stripping resulting in thyroarytenoid muscle exposure were successful in all animals. Histologic and immunohistochemical analyses revealed a simple lamina propria structure with relatively even collagen type I and elastin distribution in the control vocal fold, obliteration of vocal fold mucosa 1 day after surgery, and complete reepithelialization by 7 days.

CONCLUSIONS

These results demonstrate the feasibility of creating reproducible vocal fold injuries via an endoscopic approach in mice. The observation that the mouse lamina propria may have a relatively simple histologic structure indicates that additional characterization should be performed and caution used in translating findings between this and other model systems.

[Postoperative care in operative laryngology]

The postoperative care after phonosurgery and laryngologic procedures from the physician's view comprises control of wound healing and confirmation of restitution of the vocal folds or the larynx. The physician manages the patient's behaviour, prescribes medication if necessary and provides advice on measures to promote healing, such as voice rest and work incapacity. Basic knowledge on wound healing is an aid for deciding at which point in time voice rest and work incapacity can be ended. Professional voice users need a specifically tailored line of conduct during the period of voice rehabilitation. The documentation includes the organic findings and the vocal function.

Extracellular matrix gene expression after vocal fold injury in a rabbit model

OBJECTIVES

We determined the expression of matrix metalloproteinase (MMP)-1, MMP-9, collagen types I and III, and fibronectin from rabbit vocal folds after injury.

METHODS

Thirty rabbits were involved in this study. Five animals were assigned to each time period. Noninjured vocal fold specimens were collected as a control. Gene expression was analyzed at 2, 4, 8, 24, 48, and 72 hours after injury by use of real-time polymerase chain reaction.

RESULTS

Compared to 2 hours after injury, MMP-1 expression was increased at 4, 8, 24, 48, and 72 hours. Compared to 4 hours, MMP-1 expression was increased at 8, 24, 48, and 72 hours. Compared to the control specimens, MMP-9 expression was increased at 4, 8, 24, 48, and 72 hours. Compared to 2 hours, MMP-9 expression was increased at 4, 8, 24, 48, and 72 hours. Compared to 2 and 4 hours, collagen type I expression was increased at 72 hours. Collagen type III expression was increased at 72 hours compared to 2, 4, and 8 hours. Compared to 2 hours, fibronectin expression was increased at 24, 48, and 72 hours.

CONCLUSIONS

Results revealed time-dependent changes in expression of MMP-1, MMP-9, collagen types I and III, and fibronectin from rabbit vocal folds after injury. Future experiments are planned to investigate the effects of phonation on expression of these genes after injury.

Characteristics of age-related changes in cultured human vocal fold fibroblasts

OBJECTIVES/HYPOTHESIS

Normal human vocal fold fibroblast (hVFF) primary cell lines are unavailable commercially and are very difficult to acquire, subsequently little is known about their characteristics. The purpose of this study was to compare the morphological and proliferation characteristics and gene expression of hVFFs from different aged donors.

STUDY DESIGN

In vitro.

METHODS

We developed three normal hVFF primary cell lines from donors aged 21 (21T), 59 (59T) and 79 (79T) years. We characterized their morphological features, proliferative abilities, telomere lengths, and their functional gene expression by quantitative real-time PCR.

RESULTS

The 21T line maintained a typical spindle shape until passage 14 whereas 59T and 79T changed morphology to wider, shorter cells at passage 7. Proliferation rates were constant for the 21T through passage 14; 59T's proliferative half-life was passage 9, whereas 79T maintained lower proliferation rates from passage 4. Gene expression levels for fibronectin, collagen I, collagen VI, procollagen I and elastin demonstrated similar patterns for all lines, however, relative amounts decreased with the age of donor. Telomere lengths did not show differences related with donor age.

CONCLUSIONS

hVFF primary cultures have limited proliferative capacity. The morphology, proliferation, differentiation, and gene expression levels of VFF can be affected by age, but senescence patterns were similar across the ages.

Viscoelastic measurements after vocal fold scarring in rabbits--short-term results after hyaluronan injection

CONCLUSIONS

The scarring model resulted in significant damage and elevated viscoelasticity of the lamina propria. Hyaluronan preparations may alter viscoelasticity in scarred rabbit vocal folds.

OBJECTIVES

Vocal fold scarring results in stiffness of the lamina propria and severe voice problems. The aims of this study were to examine the degree of scarring achieved in the experiment and to measure the viscoelastic properties after injection of hyaluronan in rabbit vocal folds.

MATERIALS AND METHODS

Twenty-two vocal folds from 15 New Zealand rabbits were scarred, 8 vocal folds were controls. After 8 weeks 12 of the scarred vocal folds received injections with 2 types of cross-linked hyaluronan products and 10 scarred folds were injected with saline. After 11 more weeks the animals were sacrificed. After dissection, 15 vocal folds were frozen for viscoelastic measurements, whereas 14 vocal folds were prepared and stained. Measurements were made of the lamina propria thickness. Viscoelasticity was measured on intact vocal folds with a linear skin rheometer (LSR) adapted to laryngeal measurements.

RESULTS

Measurements on the digitized slides showed a thickened lamina propria in the scarred samples as compared with the normal vocal folds (p<0.05). The viscoelastic analysis showed a tendency to stiffening of the scarred vocal folds as compared with the normal controls (p=0.05). There was large variation in stiffness between the two injected hyaluronan products.

Current treatment of vocal fold scarring

PURPOSE OF REVIEW

Vocal fold scarring still remains a therapeutic challenge, with the most problematic issue being the histologic changes that are primarily responsible for altering the viscoelasticity of the vocal fold mucosa. Optimal treatment for vocal fold scarring has not yet been established. To restore or regenerate damaged vocal folds, it is important to investigate the changes to the layer structure of the lamina propria. Tissue engineering and regenerative medicine may provide new strategies for the prevention and treatment of vocal fold scarring. Recent developments in this field are reviewed in the present article.

RECENT FINDINGS

Histologic studies have revealed that hyaluronic acid, fibronectin, decorin, and various other extracellular matrix components, as well as collagen, may contribute to determining the vibratory properties of the vocal fold mucosa. Changes of these molecules are thought to affect the viscoelasticity of the scarred vocal folds. Based on such histologic findings, innovative approaches have been developed, including administration of hyaluronic acid into injured or scarred vocal folds. Other strategies that have recently shown advances include growth factor therapy and cell therapy using stem cells or mature fibroblasts. The effects of these new treatments have not fully been confirmed clinically, but there seems to be great therapeutic potential in such regenerative medical strategies.

SUMMARY

Recent research has revealed the detailed histologic and rheologic changes related to vocal fold scarring. Based on these findings, various new therapeutic strategies have been developed in animal models using tissue engineering and regenerative medicine. However, no clinical trials have been performed, and more studies are necessary to establish the optimum modality.

Implantation of Esterified Hyaluronic Acid in Microdissected Reinke??s Space after Vocal Fold Microsurgery: First Clinical Experiences

OBJECTIVE

In this pilot study are presented the first clinical experiences of the use of a resorbable bioimplant made of esterified hyaluronic acid inserted in the microdissected superficial layer of the lamina propria (SLLP), also called Reinke's space, after a flap excision procedure for a benign vocal fold lesion. Laryngeal and vocal evolution of implanted patients are depicted and discussed.

STUDY DESIGN

Eleven bio-implants have been inserted in microdissected SLLP of 11 cases presenting with benign vocal fold lesions. The surgical procedure consisted of the excision of primary lesion by a microflap technique immediately followed by implantation of esterified hyaluronic acid in Reinke's space.

METHODS

All patients underwent rigid laryngoscopy and a microsurgical procedure under general anesthesia. The cordal lesion was treated with cold instrumentation of Bouchayer (7 cases) or with a mixed technique using CO(2) laser (4 cases). After the classical freeing-up of Reinke's space and the creation of a mucosal flap, a few fibers of esterified hyaluronic bioimplant are gently arranged in Reinke's space before redraping the ligament and closing the cordal incision with a few drops of fibrin glue. Laryngeal and vocal assessments were performed pre- and postoperatively in all patients using videostroboscopy as well as perceptual and objective voice evaluation. All patients were followed in a longitudinal manner: between two and five postoperative evaluations were performed. The longest follow-up was 19 months and the shortest 2 months.

RESULTS

All cases exhibited postsurgical improvement of the pliability of the SLLP. None of them developed an adverse scarring process. Improvement of SLLP's pliability was maintained in time in all cases. Vocal improvement was observed in all. Temporary inflammation was noted in one case. There were no serious adverse effects apparent during the follow-up period.

CONCLUSION

Bio-implantation of esterified hyaluronic acid in Reinke's space is technically easy and well tolerated. All treated cases exhibited postoperative good pliability of the SLLP compared with their preoperative evaluation.

Current understanding and review of the literature: vocal fold scarring

Vocal fold scarring is the greatest cause of poor voice after vocal fold injury. Scarring causes a disruption of the viscoelastic layered structure of the lamina propria, an increase in stiffness of the vibratory structure, and glottic incompetence. Current treatments for this complex condition are inconsistent and often produce suboptimal results. Research investigating this condition has dramatically increased over the last several years. The literature has been directed toward understanding vocal fold scarring at the biological level and translating this to the clinical forum. We present an up-to-date, thorough, and scholarly review of the literature in vocal fold scarring since 1996.

Acute histologic effects of extraesophageal reflux on vocal fold healing

This study evaluates how extraesophageal reflux affects membranous vocal fold healing in a canine model. We created membranous vocal fold injuries in the animals and randomly assigned them to topical application of acid and pepsin at pH 2 or pH 6 or of normal saline solution every other day for 12 days. The experimental vocal folds were compared to uninjured, control vocal folds from animals painlessly sacrificed for other reasons. Hematoxylin and eosin, fibronectin, and procollagen I staining were performed for histologic analysis. The injured specimens had three times greater cellular infiltrate (p < or = .001, analysis of variance) and twice as much fibronectin and procollagen I (p < or = .001, analysis of variance) as did the specimens from the control animals. No significant differences or trends were identified for cellular infiltrate, fibronectin, or procollagen I within the injured groups (p > .05, Bonferroni t-test). Acute wound healing did not appear to be influenced by the presence of acid and pepsin at pH 2 or 6 as compared to saline solution.

Functional outcomes of reduced hyaluronan in acute vocal fold scar

To examine the functional effects of hyaluronan and collagen alterations in acute vocal fold scar, we injured 15 pig larynges by vocal fold mucosa stripping. At 3, 10, and 15 days after operation, we performed excised larynx experiments to measure phonation threshold pressure (PTP) and vocal economy (an acoustic output-cost ratio; OCR), and then performed hyaluronan and collagen assays. Five uninjured larynges were used as excised controls. Hyaluronan was reduced in the scarred vocal folds through 15 days of wound healing. Collagen was increased at day 15. The PTP was increased and OCR was decreased in scarred larynges, indicating decreased vocal efficiency and ease of phonation. Thus, PTP and OCR were sensitive to the biomolecular changes in acute vocal fold scar. Hyaluronan was more susceptible than collagen to acute tissue ultrastructural alterations. These findings may provide a rationale for increasing hyaluronan in acute vocal fold scar to improve postoperative vocal outcomes.