Treatment Of Vocal Fold Scarring Research Articles

The Prevention of Vocal Fold Scarring Using Autologous Adipose Tissue-Derived Stromal Cells

Prevention and treatment of vocal fold scarring and atrophy remain challenging. The aim of this study was to treat injured vocal folds using autologous adipose tissue-derived stromal cells (ADSCs) and evaluate the ability to prevent vocal fold scarring and atrophy by ADSCs in a canine animal model. Ten adult dogs were used for this experiment. ADSCs from the adipose tissue from the inguinal area were isolated and cultured in all dogs. Immediately after being mixed with atelocollagen, the ADSCs (1–3 × 10⁶) were injected into the right vocal fold of each animal, using a syringe with a 23-gauge needle. As a control, atelocollagen was injected into the left vocal fold of the same dog. The effects of the prevention of vocal fold scarring and atrophy were measured by morphological and histological assessment. At 8 weeks, there was a difference in granuloma and atrophic changes between the ADSC-injected and control sides in the majority of the dogs. This difference continued to be present at the 24 weeks’ follow-up. On histopathologic examination, a large number of cells labeled with a fluorochrome were observed in ADSC-injected vocal folds 8 weeks after the initial treatment. This study demonstrates the multipotential ability of ADSCs in the regeneration of injured vocal folds. Injecting ADSCs into a damaged vocal fold appears to be useful in preventing vocal fold scarring and atrophy 24 weeks after initial damage.

Hyaluronic Acid-Based Microgels and Microgel Networks for Vocal Fold Regeneration

Vocal fold scarring disrupts the viscoelastic properties of the lamina propria that are critical for normal phonation. There is a clinical need for the development of advanced biomaterials that approximate the mechanical properties of the lamina propria for in vivo vocal fold regeneration. We have developed hyaluronic acid (HA)-based microgels and cross-linked microgel networks with tunable degradation and mechanical properties. HA microgels were prepared by cross-linking HA derivatives carrying hydrazide (HAADH) and aldehyde (HAALD) functionalities within the inverse emulsion droplets. Alternatively, poly(ethylene glycol) dialdehyde (PEGDiALD) was employed in place of HAALD. Microgels based on HAADH/HAALD are more resistant to enzymatic degradation than those generated from HAADH/PEGDiALD. In vitro cytotoxicity studies using vocal fold fibroblasts indicate that microgels synthesized from HAADH/HAALD are essentially nontoxic, whereas microgels derived from HAADH/PEGDiALD exhibit certain adverse effects on the cultured cells at high concentration (> or =2 mg/mL). These microgels exhibit residual functional groups that can be used as reactive handles for covalent conjugation of therapeutic molecules. The presence of residual functional groups also allows for subsequent cross-linking of the microgels with other reactive polymers, giving rise to doubly cross-linked networks (DXNs) with tunable viscoelasticity. Mechanical measurements using a torsional wave apparatus indicate that HA-based DXNs exhibit elastic moduli that are similar to those of vocal fold lamina propria at frequencies close to the range of human phonation. These HA-based microgel systems are promising candidates for the treatment of vocal fold scarring, not just as biocompatible filler materials, but as smart entities that can repair focal defects, smooth the vocal fold margin, and potentially soften and dissolve scar tissue.

Current treatment of vocal fold scarring

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. 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. 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.

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.

Treatment of vocal fold scar with an auto-crosslinked polysaccharide hyaluronan-based gel

Problem: To examine the effectiveness of an auto-crosslinked polysaccharide (ACP) hyaluronan-based gel for the treatment of acute vocal fold scar in a canine animal model. Methods: Twelve canine larynges were injured by unilateral stripping of the vocal fold mucosa, from the epithelium down to the thyroarytenoid muscle. Six of these animals were treated with a transcutaneous injection of ACP gel (30 mg) into the thyroarytenoid muscle and remaining lamina propria at the time of injury, and again at 7 and 14 days postoperatively. The remaining animals were treated with an injection of sodium chloride to serve as sham controls. All animals were euthanized 2 months following the initial treatment. Excised larynx experiments were completed to obtain phonation threshold pressure (PTP) and vocal economy an acoustic output cost ratio (OCR), followed by histologic analysis for hyaluronan and collagen between the scarred and control vocal fold. Results: Dense, thick bundle collagen was observed on the injured side of sham-treated larynges. Minimal collagen deposition was observed on the injured side of ACP-treated larynges. PTP was lower and OCR was higher in the ACP-treated animals. Conclusion: ACP-treated larynges revealed greater ease of phonation and better vocal economy than sham-treated larynges. Collagen deposition was less dense in ACP-treated larynges. ACP gel provided sufficient bulk to the scarred vocal fold. Significance: ACP gel may provide a useful bio-injectable substance for improving rheologic tissue and aerodynamic properties for phonation in the scarred larynx. Support: None reported.

Morphological and functional changes of human vocal fold fibroblasts with hepatocyte growth factor.

Fibroblasts produce extracellular matrix and play an important role in wound healing and scarring. Hepatocyte growth factor (HGF) has strong antifibrotic activity, and has been suggested to have therapeutic potential for treatment of fibrotic diseases. In the present in vitro study, morphological and functional changes of human vocal fold fibroblasts with HGF were examined by transmission electron microscopy and enzyme-linked immunosorbent assay to help clarify the potential use of HGF in the prevention or treatment of vocal fold scarring. The HGF stimulated the production of hyaluronic acid (HA) and decreased the production of collagen type I from the fibroblasts in Reinke's space (FbRS), whereas fibronectin production was not affected. The HGF also changed the shape of the FbRS from an oval shape toward a spindle and stellate shape, and developed Golgi apparatus (GA) and rough endoplasmic reticulum (rER) in the FbRS. The fibroblasts in the macula flava (FbMF) presented with much more production of HA and collagen type I than did FbRS, and were more frequently formed in a stellate shape with well-developed GA and rER. The HGF decreased the production of collagen type I from the FbMF, but barely affected the FbMF in terms of the shape of the cells, the development of GA and rER, or the production of HA. These results were interpreted to suggest that the FbMF are not as susceptible to HGF as are FbRS. On the contrary, HGF appeared to activate the FbRS and modify the function. The increased HA and decreased collagen type I production from the FbRS suggest that HGF may be useful in the prevention or treatment of fibrotic vocal fold scarring.