Midmembranous vocal fold lamina propria proteoglycans across selected species

5-Fluorouracil for Treatment of Vocal Fold Scar

BACKGROUND

Vocal fold (VF) scar can result from trauma, neoplasm, inflammatory processes, congenital causes, surgery and other etiologies. In general, once the vibratory margin of the VF has been scarred, it has not been possible to return VF function to normal; but often it can be improved. The drug 5-fluorouracil (5-FU) is a pyrimidine antimetabolic that has many clinical applications ranging from systemic chemotherapy to topical treatment of actinic keratosis and basal cell carcinoma of the skin. Local injection with 5-FU also has been used for hypertrophic scar and keloids. 5-FU was shown to have benefit in animal models of VF scar and subglottic stenosis.

OBJECTIVES

The present study aimed to evaluate the effect of 5-FU injection on VF vibratory function in patients with VF scar. Outcomes of 5-FU injection were compared to controls injected with dexamethasone.

METHODS

Adult voice center patients who had undergone VF injection with dexamethasone or a series of three 5-FU injections for treatment of VF scar were included in the study. Postoperative outcomes included percentage of subjects demonstrating improvement after injection, change in scar size, glottic closure, and VF stiffness, as well as digital image analysis measurements of mucosal wave. Outcomes were compared between subjects who received 5-FU and those who received dexamethasone.

RESULTS

There were 58 VFs injected with 5-FU and 58 historical controls injected with dexamethasone. Baseline subject characteristics and etiology of scar did not differ significantly between the 5-FU and dexamethasone cohorts, except that scar size was greater in the 5-FU group and mucosal wave was worse at baseline. After a series of three 5-FU injections, 61.22% improved, 8.16% demonstrated no change, and 30.61% worsened. In the dexamethasone cohort, 51.06% improved, 0.00% demonstrated no change, and 48.94% worsened. The response differed significantly between the 5-FU and dexamethasone cohorts, with a greater proportion of subjects who underwent 5-FU injection demonstrating improvement postoperatively. In the 5-FU cohort, 32.76% of subjects previously had undergone and failed dexamethasone injection for VF scar: and within that group 84.21% improved, 5.26% demonstrated no change, and 10.53% worsened following 5-FU injection. On digital image analysis, the percent improvement in postoperative mucosal wave was significantly greater in the 5-FU cohort compared to the dexamethasone group, which demonstrated a worsening of mucosal wave.

CONCLUSIONS

A series of three intralesional injections with 5-FU outperformed dexamethasone for improving mucosal wave in patients with VF scar. A prior failed trial of dexamethasone injection predicted a favorable response to 5-FU. Further research is encouraged to confirm or refute these findings.

A tissue-specific, injectable acellular gel for the treatment of chronic vocal fold scarring

Gel-based injectable biomaterials have significant potential for treating vocal fold defects such as scarring. An ideal injectable for vocal fold lamina propria restoration should mimic the microenvironment of the lamina propria to induce scarless wound healing and functional tissue regeneration. Most current synthetic or natural injectable biomaterials do not possess the same level of complex, tissue-specific constituents as the natural vocal fold lamina propria. In this study we present a newly-developed injectable gel fabricated from decellularized bovine vocal fold lamina propria. Blyscan assay and mass spectrometry indicated that the vocal fold-specific gel contained a large amount of sulfated glycosaminoglycans and over 250 proteins. Gene Ontology overrepresentation analysis revealed that the proteins in the gel dominantly promote antifibrotic biological process. In vivo study using a rabbit vocal fold injury model showed that the injectable gel significantly reduced collagen density and decreased tissue contraction of the lamina propria in vocal folds with chronic scarring. Furthermore, this acellular gel only elicited minimal humoral immune response after injection. Our findings suggested that the tissue-specific, injectable extracellular matrix gel could be a promising biomaterial for treating vocal fold scarring, even after the formation of mature scar. STATEMENT OF SIGNIFICANCE: Vocal fold lamina propria scarring remains among the foremost therapeutic challenges in the management of patients with voice disorders. Surgical excision of scar may cause secondary scarring and yield inconsistent results. The present study reports an extracellular matrix-derived biomaterial that demonstrated antifibrotic effect on chronic scarring in vocal fold lamina propria. Its injectability minimizes the invasiveness of the delivery procedure and the degree of mucosal violation. In this work we also describe a new methodology which can more accurately identify proteins from the complex mixture of an acellular extracellular matrix gel by excluding interfering peptides produced during the enzymatic digestion in gel fabrication.

Pathophysiology of Fibrosis in the Vocal Fold: Current Research, Future Treatment Strategies, and Obstacles to Restoring Vocal Fold Pliability

Communication by voice depends on symmetrical vibrations within the vocal folds (VFs) and is indispensable for various occupations. VF scarring is one of the main reasons for permanent dysphonia and results from injury to the unique layered structure of the VFs. The increased collagen and decreased hyaluronic acid within VF scars lead to a loss of pliability of the VFs and significantly decreases their capacity to vibrate. As there is currently no definitive treatment for VF scarring, regenerative medicine and tissue engineering have become increasingly important research areas within otolaryngology. Several recent reviews have described the problem of VF scarring and various possible solutions, including tissue engineered cells and tissues, biomaterial implants, stem cells, growth factors, anti-inflammatory cytokines antifibrotic agents. Despite considerable research progress, these technical advances have not been established as routine clinical procedures. This review focuses on emerging techniques for restoring VF pliability using various approaches. We discuss our studies on interactions among adipose-derived stem/stromal cells, antifibrotic agents, and VF fibroblasts using an in vitro model. We also identify some obstacles to advances in research.

The Ferret as a Surgical Model for Vocal Fold Scar Creation and Treatment

Objectives:

To develop a vocal fold (VF) scarring procedure in the ferret, characterize the scars histologically, and test the injectability of the lamina propria (LP). Secondarily, to compare laryngeal anatomy of the ferret with rat and rabbit.

Materials and Methods:

The larynges of 18 male ferrets were prepared by unilateral scarring, and normal larynges from 6 female Wistar rats and 5 male albino rabbits were used for comparative purposes. For scarring, the right VF were electrocauterized, ablating the entire LP. Prior to harvesting the larynges at 4 and 16 weeks, each ferret was re-anesthetized, and in 3 animals, India ink was injected into the LPs of both normal and scarred VFs.

Results:

Laryngoscopic methods and instrumentation for precise visualization, scarring, and injection were developed. The scarred VFs had reduced hyaluronic acid and increased collagen type I, III, and fibronectin compared with normal VFs. The 2 timepoints (4 and 16 weeks) differed significantly only in collagen type III level (levels were higher at 4 weeks). Injected ink migrated from scarred LP to muscle layer just beneath the scarred tissue 3 hours after injection.

Conclusion:

The ferret is a promising species for creation and experimental treatment of vocal fold scar.

A mixed-effects model approach for the statistical analysis of vocal fold viscoelastic shear properties

A mixed-effects model approach was introduced in this study for the statistical analysis of rheological data of vocal fold tissues, in order to account for the data correlation caused by multiple measurements of each tissue sample across the test frequency range. Such data correlation had often been overlooked in previous studies in the past decades. The viscoelastic shear properties of the vocal fold lamina propria of two commonly used laryngeal research animal species (i.e. rabbit, porcine) were measured by a linear, controlled-strain simple-shear rheometer. Along with published canine and human rheological data, the vocal fold viscoelastic shear moduli of these animal species were compared to those of human over a frequency range of 1-250Hz using the mixed-effects models. Our results indicated that tissues of the rabbit, canine and porcine vocal fold lamina propria were significantly stiffer and more viscous than those of human. Mixed-effects models were shown to be able to more accurately analyze rheological data generated from repeated measurements.

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.

Real-Time Agent-Based Modeling Simulation with in-situ Visualization of Complex Biological Systems: A Case Study on Vocal Fold Inflammation and Healing

We present an efficient and scalable scheme for implementing agent-based modeling (ABM) simulation with In Situ visualization of large complex systems on heterogeneous computing platforms. The scheme is designed to make optimal use of the resources available on a heterogeneous platform consisting of a multicore CPU and a GPU, resulting in minimal to no resource idle time. Furthermore, the scheme was implemented under a client-server paradigm that enables remote users to visualize and analyze simulation data as it is being generated at each time step of the model. Performance of a simulation case study of vocal fold inflammation and wound healing with 3.8 million agents shows 35× and 7× speedup in execution time over single-core and multi-core CPU respectively. Each iteration of the model took less than 200 ms to simulate, visualize and send the results to the client. This enables users to monitor the simulation in real-time and modify its course as needed.

Quantitative and Comparative Studies of the Vocal Fold Extracellular Matrix I: Elastic Fibers and Hyaluronic Acid

Objectives:

This study examines the elastic fiber and hyaluronic acid (HA) content of the midmembranous vocal fold laminae propriae (LPs) of humans, dogs, pigs, and ferrets.

Methods:

Lamina propria elastin was quantified by measuring the amino acid desmosine, and HA was measured by an enzyme-linked immunosorbent assay-based technique. Quantitative histology was used to evaluate elastin and HA levels in specific LP regions. The distributions of fibrillin-1, a primary microfibrillar component of elastic fibers, and of tropoelastin, an indicator of elastin synthesis, were immunohistochemically analyzed.

Results:

Elastin and HA constituted 8.5% ± 2.1% and 0.82% ± 0.11% of human LP, respectively, relative to tissue total protein. Although the mean LP desmosine levels were similar across species, the mean HA levels in canine (p < 3.1 × 10−5), porcine (p < 1.5 × 10−5), and ferret (p < 6.6 × 10−4) LPs were 3 to 4 times higher than that in humans. Marked interspecies differences in elastin, fibrillin-1, tropoelastin, and HA distributions were observed histologically.

Conclusions:

The elastin content of the human LP is roughly twice that of the dermis, whereas the HA content of the human LP is similar to that of the dermis. Although all species had similar levels of desmosine, histologic evaluation indicates that the porcine elastin distribution is most similar to that of the human LP. Fibrillin-1 staining suggests that stress in the human LP may be particularly high in the superior superficial layer, and tropoelastin staining indicates that the rate of LP elastin turnover may vary spatially.

Foresight in Laryngology and Laryngeal Surgery: A 2020 Vision

Laryngology and laryngeal surgery have been in the vanguard of minimally invasive human procedural interventions for approximately 150 years. The natural passages through the oral cavity, nose, and pharynx have provided an accessible gateway to the larynx that has allowed for rapid translation of a variety of diagnostic and therapeutic technologies. Transoral and transcervical laryngeal surgery have been further facilitated by progressive advancements in local, topical, intravenous, and general anesthesia. With rapid developments in engineering disciplines (ie, tissue, chemical, mechanical) and voice science, there are a variety of current and near-term opportunities to advance our field. This report represents a panel at the 2005 American Broncho-Esophagological Association meeting that sought to use present perspectives, combined with cutting-edge research insights, to provide foresight into key aspects of laryngology that we believe will be developed by the year 2020. We hope that aspiring laryngeal surgeons will find elements of this discussion valuable for devising a strategic roadmap for research initiatives in laryngology and laryngeal surgery.

Sulfated glycosaminoglycans in human vocal fold lamina propria

Introduction

The distribution, concentration and function of glycosaminoglycans in the various vocal fold tissues are still unclear.

Objective

To evaluate the distribution and concentration of sulfated glycosaminoglycans in different layers of the human vocal fold according to gender and age.

Methods

We used 11 vocal folds obtained from cadavers (7 men and 4 women) with no laryngeal lesion, less than 12 h after death, and aged between 35 and 98 years. The folds underwent glycosaminoglycans extraction from the cover and ligament, and post-electrophoresis analysis. Data were compared according to the layer, age and gender.

Results

The concentration of dermatan sulfate was significantly higher in all layers. No differences were observed in the total concentrations of glycosaminoglycans in layers studied according to gender. It is significantly lower in the cover of individuals aged below 60 years.

Conclusion

Dermatan sulfate, chondroitin sulfate, and heparan sulfate were observed in the human vocal folds cover and ligament of both genders, with the concentration of dermatan sulfate being significantly higher in all layers. Glycosaminoglycans concentration on the cover is significantly lower in individuals below 60 years compared with elderly.

The histological components of the phoniatrical body-cover model in minipigs of different ages

Pigs are models in human phoniatry. However, features of maturation and ageing have not been considered with regard to the so-called body-cover model in this species. Therefore, the glottis of “young” (2–3 months; n = 6) and “old” (4–7 years; n = 6) minipigs was investigated. Their cranial (CraF) and caudal (CauF) vocal folds were histomorphometrically and stratigraphically analysed with emphasis on their amounts of collagen structures and elastic fibres. A dense subepithelial layer (SEL) was a distinct feature of CraF and CauF of both age groups; it was spread upon the underlying loose, flexible “cover” like a fibro-elastic membrane. The “cover” was characterised by the so-called superficial layer (SL), which was distinctly loose in the “young” minipigs, but had a much denser texture in the “old” minipigs. Here, the SL was dominated by elastic fibres in the CraF, but was of mixed qualities (collagenous and elastic) in the CauF. The structural requirements for the SL’s function as a loose “cover” were thus met only in the “young” animals. A clearly demarcated intermediate layer (IL)—characterised by high amounts of elastic fibres (as in humans)—was only found in the CraF of the “young” animals. In the “old” animals, it had lost its demarcation. In the depth of the CraF of the “old” animals, many thick collagen fibre bundles were detected in a location equivalent to that of the vocal muscle in the CauF. The development of their large diameters was interpreted as part of the maturation process, thereby supporting the hypothesis of their functional importance as a component of the “body.” In the CauF, the amounts of collagen structures increased throughout the entire lamina propria, resulting in a loss of demarcated stratigraphical subdivisions in the “old” minipigs. This situation resembled that described in the vocal fold of geriatric humans.

Varying RGD concentration and cell phenotype alters the expression of extracellular matrix genes in vocal fold fibroblasts

The impact of RGD integrin binding-peptide concentration and cell phenotype on directing extracellular matrix (ECM) gene expression in vocal fold fibroblasts is little understood. Less is known about cell response to RGD concentration on a biomaterial when fibroblasts are in a scar-like environment compared to a healthy environment. We investigated the effects of varying RGD integrin-binding peptide surface concentration on ECM gene expression of elastin, collagen type 3 alpha 1, decorin, fibronectin, hyaluronan synthase 2, and collagen type 1 alpha 2 in scarred and unscarred immortalized human vocal fold fibroblasts (I-HVFFs). Phenotype and RGD concentration affected ECM gene expression. Phenotype change from healthy to myofibroblast-like resulted in ECM gene up-regulation for all genes tested, except for decorin. Systematically altering RGD concentration affected the expression of elastin and collagen type 3 alpha 1 in a myofibroblast phenotype. Specifically greater up-regulation in gene expression was observed with higher RGD concentrations. This research demonstrates that controlling RGD concentration may influence ECM gene expression levels in fibroblasts. Such knowledge is critical in developing the next generation of bioactive materials that, when implanted into sites of tissue damage and scarring, will direct cells to regenerate healthy tissues with normal ECM ratios and morphologies.

Histomorphometric analysis of collagen and elastic fibres in the cranial and caudal fold of the porcine glottis

The porcine glottis differs from the human glottis in its cranial and caudal vocal folds (CraF, CauF). The fibre apparatus of these folds was studied histomorphometrically in adult minipigs. For object definition and quantification, the colour-selection tools of the Adobe-Photoshop program were used. Another key feature was the subdivision of the cross-sections of the folds into proportional subunits. This allowed a statistical analysis irrespective of differences in thickness of the folds. Both folds had a distinct, dense subepithelial layer equivalent to the basement membrane zone in humans. The subsequent, loose layer was interpreted - in principle - as being equivalent to Reinke's space of the human vocal fold. The next two layers were not clearly separated. Due to this, the concept of a true vocal ligament did not appear applicable to neither CauF nor CraF. Instead, the body-cover model was emphasized by our findings. The missing vocalis muscle in the CraF is substituted by large collagen fibre bundles in a proportional depth corresponding to the position of the muscle of the CauF. The distribution of elastic fibres made the CraF rather than the CauF more similar to the human vocal fold. We suggest that these data are useful for those wishing to use the porcine glottis as a model for studying oscillatory properties during phonation.

An in vivo study of composite microgels based on hyaluronic acid and gelatin for the reconstruction of surgically injured rat vocal folds

PURPOSE The objective of this study was to investigate local injection with a hierarchically microstructured hyaluronic acid-gelatin (HA-Ge) hydrogel for the treatment of acute vocal fold injury using a rat model. METHOD Vocal fold stripping was performed unilaterally in 108 Sprague-Dawley rats. A volume of 25 μl saline (placebo controls), HA-bulk, or HA-Ge hydrogel was injected into the lamina propria (LP) 5 days after surgery. The vocal folds were harvested at 3, 14, and 28 days after injection and analyzed using hematoxylin and eosin staining and immunohistochemistry staining for macrophages, myofibroblasts, elastin, collagen type I, and collagen type III. RESULTS The macrophage count was statistically significantly lower in the HA-Ge group than in the saline group (p < .05) at Day 28. Results suggested that the HA-Ge injection did not induce inflammatory or rejection response. Myofibroblast counts and elastin were statistically insignificant across treatment groups at all time points. Increased elastin deposition was qualitatively observed in both HA groups from Day 3 to Day 28, and not in the saline group. Significantly more elastin was observed in the HA-bulk group than in the uninjured group at Day 28. Significantly more collagen type I was observed in the HA-bulk and HA-Ge groups than in the saline group (p < .05) at Day 28. The collagen type I concentration in the HA-Ge and saline groups was found to be comparable to that in the uninjured controls at Day 28. The concentration of collagen type III in all treatment groups was similar to that in uninjured controls at Day 28. CONCLUSION Local HA-Ge and HA-bulk injections for acute injured vocal folds were biocompatible and did not induce adverse response.

Animal model for training and improvement of the surgical skills in endolaryngeal microsurgery

Animal models for training of surgical skills were widely used for a long time in the education of medical practitioners. It is recognized, however, that endolaryngeal microsurgery requires highly refined skills to handle the delicate structures of the vocal folds under the microscope. The availability of fresh human laryngeal specimens is markedly restricted by legal and hygienic issues. The aim of this work was to report on the design of a feasible and effective model to provide the much needed skills in an animal laryngeal model that is as close as possible to the human vocal fold structure. In the initial phase of the research, three animal larynges were studied: porcine/pig, bovine/calf, and ovine/sheep larynges. The pig/porcine larynx was chosen for this experimental training model because it closely resembled the human laryngeal/glottal configurations. A study was carried out on 10 porcine/pig larynges to assess the dimensions of the glottis and study the histology of the layered structure of the vocal fold. The study was pursued to confirm the resemblance of this animal specimen to the human vocal fold. A wooden box with a black finished interior was prepared with an acrylic bed at its floor. This bed allows placement of the porcine/pig larynx. The design of the box allows the endoscopic exposure of the porcine/pig larynx through a rubber diaphragm. The darkness and confinement of the box, apart from the light of the endoscope, approximates the situation in live endoscopy. The operating microscope is then used to expose the glottis. Routine fine microlaryngeal instruments were used for training in the prescribed skills.

Adapted to roar: functional morphology of tiger and lion vocal folds

Vocal production requires active control of the respiratory system, larynx and vocal tract. Vocal sounds in mammals are produced by flow-induced vocal fold oscillation, which requires vocal fold tissue that can sustain the mechanical stress during phonation. Our understanding of the relationship between morphology and vocal function of vocal folds is very limited. Here we tested the hypothesis that vocal fold morphology and viscoelastic properties allow a prediction of fundamental frequency range of sounds that can be produced, and minimal lung pressure necessary to initiate phonation. We tested the hypothesis in lions and tigers who are well-known for producing low frequency and very loud roaring sounds that expose vocal folds to large stresses. In histological sections, we found that the Panthera vocal fold lamina propria consists of a lateral region with adipocytes embedded in a network of collagen and elastin fibers and hyaluronan. There is also a medial region that contains only fibrous proteins and hyaluronan but no fat cells. Young's moduli range between 10 and 2000 kPa for strains up to 60%. Shear moduli ranged between 0.1 and 2 kPa and differed between layers. Biomechanical and morphological data were used to make predictions of fundamental frequency and subglottal pressure ranges. Such predictions agreed well with measurements from natural phonation and phonation of excised larynges, respectively. We assume that fat shapes Panthera vocal folds into an advantageous geometry for phonation and it protects vocal folds. Its primary function is probably not to increase vocal fold mass as suggested previously. The large square-shaped Panthera vocal fold eases phonation onset and thereby extends the dynamic range of the voice.

Influence of glycosaminoglycan identity on vocal fold fibroblast behavior

Poly(ethylene glycol) (PEG) hydrogels have recently begun to be studied for the treatment of scarred vocal fold lamina propria due, in part, to their tunable mechanical properties, resistance to fibroblast-mediated contraction, and ability to be polymerized in situ. However, pure PEG gels lack intrinsic biochemical signals to guide cell behavior and generally fail to mimic the frequency-dependent viscoelastic response critical to normal superficial lamina propria function. Recent results suggest that incorporation of viscoelastic bioactive substances, such as glycosaminoglycans (GAGs), into PEG networks may allow these gels to more closely approach the mechanical responses of normal vocal fold lamina propria while also stimulating desired vocal fold fibroblast behaviors. Although a number of vocal fold studies have examined the influence of hyaluronan (HA) on implant mechanics and vocal fold fibroblast responses, the effects of other GAG types have been relatively unexplored. This is significant, since recent studies have suggested that chondroitin sulfate C (CSC) and heparan sulfate (HS) are substantially altered in scarred lamina propria. The present study was therefore designed to evaluate the effects of CSC and HS incorporation on the mechanical response of PEG gels and vocal fold fibroblast behavior relative to HA. As with PEG-HA, the viscoelasticity of PEG-CSC and PEG-HS gels more closely approached that of the normal vocal fold lamina propria than pure PEG hydrogels. In addition, collagen I deposition and fibronectin production were significantly higher in CSC than in HA gels, and levels of the myofibroblast marker smooth muscle α-actin (SM α-actin) were greater in CSC and HS gels than in HA gels. Since collagen I, fibronectin, and SM α-actin are generally elevated in scarred lamina propria these results suggest that CSC and HS may be undesirable for vocal fold implants relative to HA. Investigation of various signaling intermediates indicated that alterations in NFκB-p50, NFκB-p65, or pERK1/2 levels may underlie the observed differences among the PEG-GAG gels.

Experiments on Analysing Voice Production: Excised (Human, Animal) and In Vivo (Animal) Approaches

Experiments on human and on animal excised specimens as well as in vivo animal preparations are so far the most realistic approaches to simulate the in vivo process of human phonation. These experiments do not have the disadvantage of limited space within the neck and enable studies of the actual organ necessary for phonation, i.e., the larynx. The studies additionally allow the analysis of flow, vocal fold dynamics, and resulting acoustics in relation to well-defined laryngeal alterations.

PURPOSE OF REVIEW

This paper provides an overview of the applications and usefulness of excised (human/animal) specimen and in vivo animal experiments in voice research. These experiments have enabled visualization and analysis of dehydration effects, vocal fold scarring, bifurcation and chaotic vibrations, three-dimensional vibrations, aerodynamic effects, and mucosal wave propagation along the medial surface. Quantitative data will be shown to give an overview of measured laryngeal parameter values. As yet, a full understanding of all existing interactions in voice production has not been achieved, and thus, where possible, we try to indicate areas needing further study.

RECENT FINDINGS

A further motivation behind this review is to highlight recent findings and technologies related to the study of vocal fold dynamics and its applications. For example, studies of interactions between vocal tract airflow and generation of acoustics have recently shown that airflow superior to the glottis is governed by not only vocal fold dynamics but also by subglottal and supraglottal structures. In addition, promising new methods to investigate kinematics and dynamics have been reported recently, including dynamic optical coherence tomography, X-ray stroboscopy and three-dimensional reconstruction with laser projection systems. Finally, we touch on the relevance of vocal fold dynamics to clinical laryngology and to clinically-oriented research.

Characterization of vocal fold scar formation, prophylaxis, and treatment using animal models

PURPOSE OF REVIEW

To review recent literature on animal models used to study the pathogenesis, detection, prevention, and treatment of vocal fold scarring. Animal work is critical to studying vocal fold scarring because it is the only way to conduct systematic research on the biomechanical properties of the layered structure of the vocal fold lamina propria, and therefore develop reliable prevention and treatment strategies for this complex clinical problem.

RECENT FINDINGS

During the period of review, critical anatomic, physiologic, and wound healing characteristics, which may serve as the bases for selection of a certain species to help answer a specific question, have been described in mouse, rat, rabbit, ferret, and canine models. A number of different strategies for prophylaxis and chronic scar treatment in animals show promise for clinical application. The pathways of scar formation and methods for quantifying treatment-induced change have become better defined.

SUMMARY

Recent animal vocal fold scarring studies have enriched and confirmed earlier work indicating that restoring pliability to the scarred vocal fold mucosa is challenging but achievable. Differences between animal models and differences in outcome measurements across studies necessitate considering each study individually to obtain guidance for future research. With increased standardization of measurement techniques it may be possible to make more inter-study comparisons.

Cross-sample validation provides enhanced proteome coverage in rat vocal fold mucosa

The vocal fold mucosa is a biomechanically unique tissue comprised of a densely cellular epithelium, superficial to an extracellular matrix (ECM)-rich lamina propria. Such ECM-rich tissues are challenging to analyze using proteomic assays, primarily due to extensive crosslinking and glycosylation of the majority of high M_r ECM proteins. In this study, we implemented an LC-MS/MS-based strategy to characterize the rat vocal fold mucosa proteome. Our sample preparation protocol successfully solubilized both proteins and certain high M_r glycoconjugates and resulted in the identification of hundreds of mucosal proteins. A straightforward approach to the treatment of protein identifications attributed to single peptide hits allowed the retention of potentially important low abundance identifications (validated by a cross-sample match and de novo interpretation of relevant spectra) while still eliminating potentially spurious identifications (global single peptide hits with no cross-sample match). The resulting vocal fold mucosa proteome was characterized by a wide range of cellular and extracellular proteins spanning 12 functional categories.

Injectable hyaluronic acid-dextran hydrogels and effects of implantation in ferret vocal fold

Injectable hydrogels may potentially be used for augmentation/regeneration of the lamina propria of vocal fold tissue. In this study, hyaluronic acid (HA) and dextran were chemically modified and subsequently crosslinked via formation of hydrazone bonds in phosphate buffer. Swelling ratios, degradation, and compressive moduli of the resulting hydrogels were investigated. It was found that the properties of HA-dextran hydrogels were variable and the trend of variation could be correlated with the hydrogel composition. The biocompatibility of three injectable HA-dextran hydrogels with different crosslinking density was assessed in the vocal fold region using a ferret model. It was found that HA-dextran hydrogels implanted for three weeks stimulated mild foreign-body reactions. Distinct tissue-material interactions were also observed for hydrogels made from different formulations: the hydrogel with the lowest crosslinking density was completely degraded in vivo; while material residues were visible for other types of hydrogel injections, with or without cell penetration into the implantation depending on the hydrogel composition. The in vivo results suggest that the HA-dextran hydrogel matrices can be further developed for applications of vocal fold tissue restoration.

Vibration stimulates vocal mucosa-like matrix expression by hydrogel-encapsulated fibroblasts

The composition and organization of the vocal fold extracellular matrix (ECM) provide the viscoelastic mechanical properties that are required to sustain high-frequency vibration during voice production. Although vocal injury and pathology are known to produce alterations in matrix physiology, the mechanisms responsible for the development and maintenance of vocal fold ECM are poorly understood. The objective of this study was to investigate the effect of physiologically relevant vibratory stimulation on ECM gene expression and synthesis by fibroblasts encapsulated within hyaluronic acid hydrogels that approximate the viscoelastic properties of vocal mucosa. Relative to static controls, samples exposed to vibration exhibited significant increases in mRNA expression levels of HA synthase 2, decorin, fibromodulin and MMP-1, while collagen and elastin expression were relatively unchanged. Expression levels exhibited a temporal response, with maximum increases observed after 3 and 5 days of vibratory stimulation and significant downregulation observed at 10 days. Quantitative assays of matrix accumulation confirmed significant increases in sulphated glycosaminoglycans and significant decreases in collagen after 5 and 10 days of vibratory culture, relative to static controls. Cellular remodelling and hydrogel viscosity were affected by vibratory stimulation and were influenced by varying the encapsulated cell density. These results indicate that vibration is a critical epigenetic factor regulating vocal fold ECM and suggest that rapid restoration of the phonatory microenvironment may provide a basis for reducing vocal scarring, restoring native matrix composition and improving vocal quality.

A bovine acellular scaffold for vocal fold reconstruction in a rat model

With a rat model of vocal fold injury, this study examined the in vivo host response to an acellular xenogeneic scaffold derived from the bovine vocal fold lamina propria, and the potential of the scaffold for constructive tissue remodeling. Bilateral wounds were created in the posterior vocal folds of 20 rats, and bovine acellular scaffolds were implanted into the wounds unilaterally, with the contralateral vocal folds as control. The rats were humanely sacrificed after 3 days, 7 days, 1 month, and 3 months, and the coronal sections of their larynges were examined histologically. Expressions of key matrix proteins including collagen I, collagen III, elastin, fibronectin, hyaluronic acid, and glycosaminoglycans (GAGs) were quantified with digital image analysis. Significant infiltration of host inflammatory cells and host fibroblasts in the scaffold implant was observed in the acute stage of wound repair (3 days and 7 days postsurgery). The mean relative densities of collagen I, collagen III, and GAGs in the implanted vocal folds were significantly higher than those in the control after 3 days, followed by gradual decreases over 3 months. Histological results showed that the scaffolds were apparently degraded by 3 months, with no fibrotic tissue formation or calcification. These preliminary findings suggested that the bovine acellular scaffold could be a potential xenograft for vocal fold regeneration.

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.

Glycosaminoglycan composition of the vocal fold lamina propria in relation to function

OBJECTIVES

This study was designed to quantify the specific glycosaminoglycans (GAGs) in the midmembranous vocal fold (VF) lamina propria (LP) and to interpret their presence in relation to the known stresses borne by each LP layer.

METHODS

GAGs from normal human LP and from both normal and scarred canine LPs were analyzed by fluorophore-assisted carbohydrate electrophoresis (FACE). Immunostaining was conducted to give insight into the spatial distribution of each GAG type.

RESULTS

Hyaluronan composes roughly 0.64% +/- 0.41% of the human LP as measured relative to tissue total protein. Chondroitin sulfate and/or dermatan sulfate (CS/DS), keratan sulfate, and heparan sulfate chains constitute approximately 23.9% +/- 12.1%, 14.7% +/- 6.1%, and 61.4% +/- 13.6%, respectively, of human LP sulfated GAGs.

CONCLUSIONS

Observed CS/DS sulfation patterns imply that versican is a major contributor to human LP CS levels. In addition, examination of LP GAG with respect to gender revealed a significant variation in total levels of CS/DS and a potential difference in the levels of versican relative to decorin and biglycan. In dogs, LP scarring appeared to result in a reduction in hyaluronan and CS/DS. These FACE results were combined with histologic data to update current descriptive models linking LP microstructure with the regional variations in LP loading.

Phonatory characteristics of excised pig, sheep, and cow larynges

The purpose of this study was to examine the phonatory characteristics of pig, sheep, and cow excised larynges and to find out which of these animal species is the best model for human phonation. Excised pig, sheep, and cow larynges were prepared and mounted over a tapered tube on the excised bench that supplied pressurized, heated, and humidified air in a manner similar to that for excised canine models. Each excised larynx was subjected to a series of pressure-flow experiments with adduction as major control parameter. The subglottal pressure, electroglottograph (EGG), mean flow rate, audio signal, and sound pressure level were recorded during each experiment. EGG signal was used to extract the fundamental frequency. It was found that pressure-frequency relations were nonlinear for these species with large rate of frequency changes for the pig. The average oscillation frequencies for these species were 220+/-57 Hz for the pig, 102+/-33 Hz for the sheep, and 73+/-10 Hz for the cow. The average phonation threshold pressure for the pig was 7.4+/-2.0 cm H(2)O, 6.9+/-2.9 cm H(2)O for the sheep, and 4.4+/-2.3 cm H(2)O for the cow.

Collagen fiber and versican distribution within the lamina propria of fetal vocal folds

OBJECTIVES

To analyze the presence and distribution of collagen fibers and versican in human vocal fold lamina propria of fetal larynges.

STUDY DESIGN

Cross sectional analysis of cadaveric vocal folds of human fetuses.

METHODS

Seven fetal larynges obtained from 28- to 36-week-old fetuses were analyzed with the Picrosirius-polarization method, immunohistochemistry, and image analysis.

RESULTS

Collagen fibers within the lamina propria exhibited a monolaminar distribution pattern and spatial arrangement in "wicker basket." Versican distribution was larger in the superficial and intermediate layers when compared to the deep layer.

CONCLUSION

Our findings suggest that collagen and versican distribution and arrangement within the lamina propria in the developing fetus are important for vocalization at birth.

Foresight in laryngology and laryngeal surgery: a 2020 vision

Laryngology and laryngeal surgery have been in the vanguard of minimally invasive human procedural interventions for approximately 150 years. The natural passages through the oral cavity, nose, and pharynx have provided an accessible gateway to the larynx that has allowed for rapid translation of a variety of diagnostic and therapeutic technologies. Transoral and transcervical laryngeal surgery have been further facilitated by progressive advancements in local, topical, intravenous, and general anesthesia. With rapid developments in engineering disciplines (ie, tissue, chemical, mechanical) and voice science, there are a variety of current and near-term opportunities to advance our field. This report represents a panel at the 2005 American Broncho-Esophagological Association meeting that sought to use present perspectives, combined with cutting-edge research insights, to provide foresight into key aspects of laryngology that we believe will be developed by the year 2020. We hope that aspiring laryngeal surgeons will find elements of this discussion valuable for devising a strategic roadmap for research initiatives in laryngology and laryngeal surgery.

A new approach to geometrical measurements in an animal model of vocal fold scar

A standard method for quantifying the geometric properties of vocal folds has not been widely adopted. An ideal method of geometrical measurement should effectively quantify the dimensions of the medial vibratory portion of the vocal fold, should be easily performed, should yield consistent results, and should be readily available at little to no cost. We have developed a new approach for geometrical measurements to meet these goals. The objective of this study is to describe this new approach and to assess its effectiveness in a canine model of vocal fold scar. One hundred thirty-five mid-membranous coronal sections of vocal folds from 10 canines (five with unilateral surgical scarring) were examined by light microscopy; digital images were captured. ImageJ was used to measure a variety of described parameters. Comparison between scarred vocal folds and control vocal folds was made. At least 20% of the slides for each vocal fold were randomly selected (n=42) for repeat measurements of interrater and intrarater reliability. A statistically significant difference between scarred and control vocal folds was obtained for horizontal distance (P<0.001), vertical distance (P=0.005), area (P<0.001), mean optical density (OD) (P<0.001), and OD at defined points along the length of the vocal fold (P< or =0.009). Reliability calculations for intrarater and interrater measurements ranged from r=0.845 to r=0.994 and from r=0.734 to r=0.976, respectively. The proposed approach for geometrical measurements meets the intended objectives in a canine model of vocal fold scar. Future work is needed to apply this approach to other model systems.

A Biodegradable, Acellular Xenogeneic Scaffold for Regeneration of the Vocal Fold Lamina Propria

A novel method for preparing an acellular xenogeneic extracellular matrix scaffold for tissue engineering was developed. Bovine vocal fold lamina propria specimens were treated with high-concentration sodium chloride, nucleic acid digestion, and ethanol dehydration for decellularization and removal of immunogenic foreign epitopes. Human vocal fold fibroblasts from primary culture were seeded onto the acellular scaffolds and cultured for 21 days. The decellularized and the recellularized scaffolds were examined by light microscopy, fluorescent microscopy, and scanning electron microscopy. Collagen synthesis and release by fibroblasts were quantified by the Sircol assay, whereas the synthesis and release of hyaluronic acid, decorin, and fibronectin were assessed by enzyme-linked immunosorbent assays. Viscoelastic shear properties of the scaffolds were quantified by a simple-shear rheometer at frequencies of up to 250 Hz. Preliminary results showed that a biodegradable, acellular extracellular matrix scaffold with an intact basement membrane and 3-dimensional structure of the matrix proteins was engineered. Vocal fold fibroblasts readily attached to and infiltrated the scaffold with high viability and active protein synthesis, demonstrating the biocompatibility. The elastic shear modulus and dynamic viscosity of the acellular scaffold and the fibroblast-repopulated scaffold were comparable to those of the human vocal fold cover. These findings support the potential of the scaffold as a xenograft for vocal fold reconstruction and regeneration.

Effects of Growth Factors on Extracellular Matrix Production by Vocal Fold Fibroblasts in 3-Dimensional Culture

Culturing cells in 3-dimensional (3D) systems is important in tissue engineering and in fundamental studies of cellular mechanisms that are sensitive or specific to the 3D environment. To guide the engineering of artificial vocal fold lamina propria tissue, we developed 3D cultures containing human vocal fold fibroblasts (hVFFs) dispersed in a synthetic peptide hydrogel matrix. Growth factors were added to the culture to examine their influence on extracellular matrix (ECM) synthesis, cell proliferation, and matrix contraction. The hVFF-hydrogel constructs were treated with transforming growth factor-beta 1 (TGF-beta1), basic fibroblast growth factor (bFGF), or hepatocyte growth factor (HGF), and the culture was maintained for 21 days. TGF-beta1 induced matrix contraction and enhanced collagen and sulfated glycosaminoglycan production, bFGF effectively increased cell proliferation, and HGF stimulated synthesis of hyaluronic acid and elastin with less collagen accumulation than other conditions. Of the growth factors tested, HGF appears to be most useful for stimulating essential tissue components for restoring vocal fold pliability. The results also suggest that multiple growth factors might be employed sequentially or in combination to program the makeup of cell-hydrogel constructs for vocal fold tissue repair.

Quantitative and comparative studies of the vocal fold extracellular matrix II: collagen

OBJECTIVES

This study examines the collagen content and turnover in the midmembranous vocal fold laminae propriae (LPs) of humans, dogs, pigs, and ferrets.

METHODS

The LP collagen levels were assessed by quantifying tissue hydroxyproline. Quantitative histology allowed evaluation of the collagen content in specific LP regions. Several collagen types and two markers of collagen turnover were examined immunohistochemically.

RESULTS

Collagen made up 43.4% +/- 2.6% of human LP total protein (TP), with men having approximately 30% higher collagen content than women (p < .024). The collagen levels in pigs (52.6% +/- 1.9% of TP) and ferrets (29.8% +/- 3.7% of TP), but not that in dogs (45.3% +/- 1.2% of TP), varied significantly from that in humans (pigs, p < .016; ferrets, p < .011). Quantitative histology indicated marked interspecies differences in total collagen distribution. Collagen types I, III, and IV were detected in the LP, and spatially complex staining patterns were observed for the two markers of collagen turnover studied.

CONCLUSIONS

The collagen content of the human LP is approximately 60% to 70% of that of human dermis. Although canine LP collagen levels are most similar to those of humans, quantitative histology indicates that the collagen distribution of the human LP is best matched by the porcine LP. Collagen types I and III seem to be the dominant LP collagens. Spatial variations in collagen turnover appear to exist that may contribute to normal LP physiology.