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

Transient Receptor Potential Ankyrin 1 Channel Alters Transforming Growth Factor Beta 1/Smad Signaling in Rat Vocal Fold Fibroblasts

OBJECTIVES

Vocal fold scar remains a therapeutic challenge. Vocal fold fibroblasts (VFFs) secrete extracellular matrix (ECM), and transforming growth factor-beta 1 (TGF-β1)-mediated fibroblast to myofibroblast differentiation is central to the development of fibrosis. The transient receptor potential (TRP) channel superfamily is a group of nonselective cation channels, and activation of TRP ankyrin 1 (TRPA1) channel has been shown to have antifibrotic effects through TGF-β1/Smad signaling in various organs. This study aimed to elucidate expression of TRPA1 and the impact of TRPA1 activation on TGF-β1/Smad signaling in VFFs.

METHODS

Vocal folds were dissected from 10-week-old, male Sprague-Dawley rats and primary VFFs were established. TRPA1 was examined in VFFs and lamina propria via immunostaining. VFFs were treated with allyl isothiocyanate (AITC, TRP channel agonist, 10-5 M) ± TGF-β1 (10 ng/ml) ± A-967079 (selective TRPA1 channel antagonist, 5.0 × 10-7 M) for 4 or 24 h. Trpa1, Smad3, Smad7, Col1a1, Acta2, and Has1 mRNA expression were quantified via qPCR.

RESULTS

TRPA1 was expressed in cultured VFFs and the lamina propria. TGF-β1 administration significantly increased Trpa1 compared to control. AITC alone did not alter Smad3, Smad7, Acta2, or ECM related genes. However, the combination of AITC and TGF-β1 significantly increased Smad3 and decreased Smad7 and Acta2 compared to TGF-β1 alone; A-967079 significantly reduced this response.

CONCLUSIONS

VFFs expressed TRPA1, and the activation of TRPA1 regulated TGF-β1/Smad signaling in VFFs. These findings provide preliminary insights into potential anti-fibrotic mechanisms of TRPA1 activation through TGF-β1/Smad signaling in VFFs.

LEVEL OF EVIDENCE

NA Laryngoscope, 2024.

Factors Associated with Iatrogenic Laryngeal Injury in Recurrent Respiratory Papillomatosis

OBJECTIVE

To describe iatrogenic laryngeal injury and identify its risk factors in recurrent respiratory papillomatosis (RRP) patients receiving surgical care.

STUDY DESIGN

Case-control.

SETTING

Tertiary care academic hospital in a metropolitan area.

METHODS

Charts of patients with RRP seen at our institution from January 2002 to December 2022 were reviewed. Patients were separated into 2 cohorts based upon whether they experienced any form of iatrogenic laryngeal injury-including anterior commissure synechiae, vocal cord scar, reduced vocal fold pliability, vocal fold motion impairment, and glottic and/or subglottic stenosis. Adjusted logistic regressions were performed to identify factors associated with iatrogenic laryngeal injury.

RESULTS

Of 199 RRP patients, 133 (66.8%) had identifiable iatrogenic laryngeal injury. The most common injuries were anterior commissure synechiae (n = 67; 50.4%) and reduced vocal fold pliability (n = 54; 40.6%). On a multivariate logistic regression, patients with diabetes mellitus (adjusted odds ratio [aOR] [95% confidence interval [CI]]: 2.99 [1.02, 8.79]; P = .04) and who received at least 10 surgeries lifetime (aOR [95% CI]: 14.47 [1.70, 123.19]; P = .01) were at increased risk for iatrogenic laryngeal injury, whereas receiving less than 5 surgeries (aOR [95% CI]: 0.21 [0.09, 0.51]; P < .001) was found to be protective. When treating the lifetime number of surgeries as a continuous variable, a greater number of surgeries was a significant risk factor for iatrogenic laryngeal injury (aOR [95% CI]: 1.32 [1.14, 1.53]; P < .001).

CONCLUSION

These results suggest the importance of strict glucose control for diabetic patients receiving RRP surgical care, and emphasize the clinical need to identify medical therapies to decrease RRP surgical frequency for patients.

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.

The Effect of Oxidative Stress on the Human Voice

The vocal fold vibrates in high frequency to create voice sound. The vocal fold has a sophisticated histological "layered structure" that enables such vibration. As the vibration causes fricative damage to the mucosa, excessive voicing can cause inflammation or injury to the mucosa. Chronic inflammation or repeated injury to the vocal fold occasionally induces scar formation in the mucosa, which can result in severe dysphonia, which is difficult to treat. Oxidative stress has been proven to be an important factor in aggravating the injury, which can lead to scarring. It is important to avoid excessive oxidative stress during the wound healing period. Excessive accumulation of reactive oxygen species (ROS) has been found in the injured vocal folds of rats during the early phase of wound healing. Antioxidants proved to be useful in preventing the accumulation of ROS during the period with less scar formation in the long-term results. Oxidative stress is also revealed to contribute to aging of the vocal fold, in which the mucosa becomes thin and stiff with a reduction in vibratory capacity. The aged voice can be characterized as weak and breathy. It has been confirmed that ROS gradually increases in rat vocal fold mucosa with age, which may cause further damage to the vocal fold. Antioxidants have also proved effective in avoiding aging of the vocal fold in rat models. Recently, human trials have shown significant effects of the antioxidant Twendee X for maintaining the voice of professional opera singers. In conclusion, it is suggested that oxidative stress has a great impact on the damage or deterioration of the vocal folds, and the use of antioxidants is effective for preventing damage of the vocal fold and maintaining the voice.

Laryngeal Applications of Platelet Rich Plasma and Platelet Poor Plasma: A Systematic Review

BACKGROUND

Platelet rich plasma (PRP) and platelet poor plasma (PPP) are regenerative therapies that offer the potential for improving care for disorders of the larynx. The laryngeal applications of these substances have been examined in both animals and humans. The goal of this systematic review is to examine the various applications of PRP and PPP in laryngology, assess the protocols for preparation and application of these substances and evaluate the outcomes and complications in both humans and animals.

METHODS

A search of PUBMED was conducted in April 2021 using combinations of keywords of "platelet rich plasma" and "platelet poor plasma" with keywords such as "larynx," "vocal folds," "laryngology," and others. Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRIMSA) guidelines were followed. Articles were reviewed by two independent coauthors and included based on selection criteria pertinent to the goals of this study. The risk of bias in the included studies was assessed by two independent co-authors using the Joanna Briggs Institute (JBI) Critical Appraisal Checklist for Randomized Controlled Trials and JBI Critical Appraisal Checklist for Quasi-Experimental Studies. Data regarding the pathologies treated using PRP and PPP, PRP, and PPP preparation protocols, application protocols, human voice outcomes, histopathological animal outcomes, and complications were extracted from each of the studies and presented in tables.

RESULTS

Seven studies were included based on the selection criteria. PRP or PPP were used for vocal fold scar, sulcus, atrophy and palsy; acute vocal fold injury; glottic insufficiency, and graft healing. PRP or PPP were derived from autologous blood in a one- or two-step centrifugation process and administered via injection, soaking of cartilage grafts or topical application. Mean and median voice handicap index-10 (VHI-10) and voice handicap index (VHI) scores decreased following PRP or PPP injections in two human studies and one human study showed a similar VHI-10 score before and after PRP treatment. Videostroboscopy showed the absence of injection site reactions and at least temporary improvement in glottic gap or vibratory function following treatment in some patients. Other objective measures of voice outcomes in human studies showed improved phonatory function in the one-to-four-month period following PRP or PPP injections, with some patients experiencing a subjective decrease or return to baseline in phonatory function following the initial improvement period. Animal studies found elevated levels of growth factors, organized collagen deposition, decreased granulation tissue, increased vascularization, and increased cartilage proliferation in PRP treated laryngeal tissue.

DISCUSSION

PRP and PPP might have the potential to be safely used in the larynx and at least temporarily influence wound healing and vocal function. Further study using comparable outcome measurement tools is required to assess their role and efficacy in treating acute vocal fold injury, chronic vocal fold pathologies, graft healing, and other laryngeal applications.

Efficacy of platelet-rich plasma (PRP) in benign vocal fold lesions: a systematic review and meta-analysis

OBJECTIVES

To evaluate the efficacy of platelet-rich plasma (PRP) in benign vocal fold lesions.

METHODS

MEDLINE, Cochrane Central, Web of Science, and Scopus databases were searched in April 2023 for relevant clinical trials. Inclusion criteria were clinical trials evaluating the efficacy of PRP in benign vocal fold lesions. We conducted a comparative double-arm analysis using the pooled mean difference (MD) and 95% confidence interval (CI). Outcomes of interest included the vocal handicap index (VHI), the Jitter and Shimmer percentages, and the noise-to-harmonic ratio (NHR).

RESULTS

Six studies matched the inclusion criteria. The pooled analysis shows that PRP was associated with significantly lower VHI scores compared with the control (MD = - 5.06, p < 0.01). Regarding the Jitter percentage, the PRP group was not superior to the control group at 2 and 4 weeks. However, the results revealed that PRP significantly reduced the Jitter percentage at 3 months (MD = - 0.61, p = 0.0008). The overall analysis favored the PRP arm significantly (p < 0.001). As for the Shimmer percentage, the combined effect estimate favored the PRP group (MD = - 1.22, p = 0.002). Subgroup analysis according to the time did not reveal any significant differences between studies at 2 weeks, 4 weeks, and 3 months. The analysis of the NHR outcome revealed a significant difference between both groups (MD = -1.09, p = 0.01). However, at 4 weeks, the treatment group had a significantly lower NHR % compared to the control group (MD = - 0.61, p = 0.02). There was no significant difference at 3 months (MD = - 2.14, p = 0.14).

CONCLUSIONS

Platelet-rich plasma is effective in reducing VHI scores, Jitter and Shimmer percentages, and NHR values. This effect is more evident after follow-up, especially 3 months.

Exploring the anti-inflammatory potential of topical hyaluronic acid for vocal fold injury in a rat model

PURPOSE

Vocal fold injuries are associated with fibrosis and dysphonia, which is a major obstacle to surgical treatment. The aim of this study is to evaluate the effect of topical hyaluronic acid with or without diclofenac on the inflammatory phase of vocal fold wound healing.

METHODS

Forty-one male Sprague-Dawley rats were randomly assigned to four groups: an uninjured control group, an injured control group without any treatment, and two intervention groups in which hyaluronic acid with or without diclofenac was applied to the injured vocal fold. Gene expression of inflammatory markers and ECM-related molecules were examined.

RESULTS

Vocal fold injury resulted in a significant upregulation of inflammatory parameters [Ptgs2, Il1b and Il10] and Has1. Tgfb1, Has3 and Eln gene expression were significantly downregulated by the topical application of hyaluronic acid. The combination of hyaluronic acid and diclofenac did not result in any significant changes.

CONCLUSIONS

Vocal fold wound healing was significantly improved by a single post-operative topical application of hyaluronic acid. The addition of diclofenac may provide no additional benefit.

Immunohistochemical localization of CD31, CD34, and periostin in vocal fold polyps

BACKGROUND

Long-term voice-abuse or sudden vocal fold microvascular disruption can lead to injury and subsequent repair/remodeling of the vocal fold mucosa. Periostin is known to be involved in airway remodeling and in various otolaryngological diseases. In ischemic heart disease, increased CD31 expression has been observed around cardiomyocytes during remodeling, and endothelial proliferation has been reported to occur at these sites.

OBJECTIVES

We investigated the expression and the roles of CD31, CD34, and periostin in the formation of vocal fold polyps.

MATERIALS AND METHODS

Fifty-seven samples of vocal fold polyps were investigate histopathologically and immunohistochemically.

RESULT

Expression of CD31 and CD34 was detected in 41 (71.9%) and 53 (93.0%) samples, respectively, obtained from patients with vocal fold polyp. Expression of periostin was detected in 41 (71.9%) samples obtained from patients with vocal polyps. The vocal polyp samples could be classified into three histological subtypes. Three patterns of CD31 and CD34 expression were observed in the vocal polyp. Four patterns of periostin expression were observed in vocal polyps. An association was observed between the CD31 expression pattern and the histological subtype of vocal fold polyps.

CONCLUSION AND SIGNIFICANCE

In vocal fold polyps, evaluation of vascular endothelial markers may be useful for staging.

Tamoxifen Alters TGF-β1/Smad Signaling in Vocal Fold Injury

OBJECTIVES

Effective treatments for vocal fold fibrosis remain elusive. Tamoxifen (TAM) is a selective estrogen receptor modulator and was recently reported to have antifibrotic actions. We hypothesized that TAM inhibits vocal fold fibrosis via altered transforming growth factor beta 1 (TGF-β1) signaling. Both in vitro and in vivo approaches were employed to address this hypothesis.

METHODS

In vitro, vocal fold fibroblasts were treated with TAM (10-8 or 10-9  M) ± TGF-β1 (10 ng/ml) to quantify cell proliferation. The effects of TAM on genes related to fibrosis were quantified via quantitative real-time polymerase chain reaction. In vivo, rat vocal folds were unilaterally injured, and TAM was administered by oral gavage from pre-injury day 5 to post-injury day 7. The rats were randomized into two groups: 0 mg/kg/day (sham) and 50 mg/kg/day (TAM). Histological changes were examined on day 56 to assess tissue architecture.

RESULTS

TAM (10-8  M) did not affect Smad3, Smad7, Acta2, or genes related to extracellular matrix metabolism. TAM (10-8 or 10-9  M) + TGF-β1, however, significantly increased Smad7 and Has3 expression and decreased Col1a1 and Acta2 expression compared to TGF-β1 alone. In vivo, TAM significantly increased lamina propria area, hyaluronic acid concentration, and reduced collagen deposition compared to sham treatment.

CONCLUSIONS

TAM has antifibrotic potential via the regulation of TGF-β1/Smad signaling in vocal fold injury. These findings provide foundational data to develop innovative therapeutic options for vocal fold fibrosis.

LEVEL OF EVIDENCE

NA Laryngoscope, 133:2248-2254, 2023.

Videostroboscopy Versus High-Speed Videoendoscopy: Factors Influencing Ratings of Laryngeal Oscillation

PURPOSE

The purpose of this study was to determine whether patient voice-related diagnosis, severity of dysphonia, and rater's experience influence the relationship between laryngeal oscillation ratings made from videostroboscopic and high-speed videoendoscopic (HSV) exams.

METHOD

Stroboscopy and HSV exams from 15 patients with adductor spasmodic dysphonia (ADSD) and 15 with benign vocal fold lesions were rated for laryngeal oscillation and closure by 10 licensed speech-language pathologists (SLPs). Raters were divided into low- (< 5 years) and high-experience (> 5 years) groups. Ratings of vocal fold amplitude, mucosal wave, periodicity, phase symmetry, nonvibrating portion of the vocal fold, and glottal closure were examined using an online form adapted from the Voice Vibratory Assessment of Laryngeal Imaging (VALI).

RESULTS

Stroboscopy and HSV ratings were more strongly positively correlated for patients with benign vocal fold lesions (r between .43 and .75) than for those with ADSD (r between .40 and .68). Differences between stroboscopy and HSV exams were significantly greater for ratings of amplitude, mucosal wave, and periodicity in patients with ADSD than for patients with benign vocal fold lesions. Raters with < 5 years of experience showed significantly greater differences between stroboscopy and HSV ratings of amplitude and nonvibrating portion of the vocal fold for patients with ADSD only. Significantly greater differences between ratings of periodicity and phase symmetry were observed in patients with more severe dysphonia.

CONCLUSIONS

Differences in laryngeal ratings made between HSV and stroboscopy exams may be influenced by patient diagnosis, severity of dysphonia, and rater experience. Future study is warranted to determine how the differences observed influence clinical diagnosis and outcomes.

Safety of Platelet-Rich Plasma Subepithelial Infusion for Vocal Fold Scar, Sulcus, and Atrophy

OBJECTIVE

To demonstrate the safety profile of platelet-rich plasma (PRP) as an injectable therapeutic for the treatment of vocal fold scarring and atrophy.

METHODS

Preliminary report on a prospective clinical trial of patients with vocal fold scar or atrophy undergoing unilateral vocal fold subepithelial infusion with autologous PRP. Enrolled patients underwent four subepithelial injections spaced 1 month apart. Adverse events were assessed peri and post-injection at each session. Patient-reported outcomes were collected at every visit using the Voice Handicap Index-10 (VHI-10) and Vocal Fatigue Index (VFI) questionnaires.

RESULTS

Twelve patients underwent unilateral vocal fold injection with autologous PRP prepared according to Eclipse PRP® system protocol. Forty-three injections were performed using a peroral or percutaneous approach. An average of 1.57 ± 0.4 cc (range 0.6-2.0 cc) injectate was used. All patients tolerated the procedure without difficulty or peri-procedural complications. The average duration of follow-up was 3.6 ± 1.8 months. No significant inflammatory reactions or adverse events were seen to date. There was statistically significant improvement in patient-reported outcomes at the 3 month follow up (n = 9) follow-up (mean ΔVHI-10 = 10.8, p < 0.001, mean ΔVFI = 18.9, p = 0.01, t test, paired two sample for means, two-tail). All nine patients who completed the series of four injections subjectively (yes/no) reported they were satisfied with the results.

CONCLUSION

This prospective study cohort demonstrated a favorable safety profile, with no adverse events or peri-procedural complications. Subjective improvements in vocal quality and reduction in vocal fatigue need to be clinically correlated with further study.

LEVEL OF EVIDENCE

4 Laryngoscope, 133:647-653, 2023.

The life-cycle and restoration of the human vocal fold

Objective

To better understand the challenges of designing therapies to treat damaged vocal fold lamina propria, it is essential to understand the biophysical and pathophysiological mechanisms involved in vocal fold development, maintenance, injury, and aging. This review critically analyses these points to try and direct future efforts and new strategies toward science-based solutions.

Data Sources & Review Methods

MEDLINE, Ovid Embase, and Wed of Science databases were used to identify relevant literature. A scoping review was performed following the preferred reporting items for systematic reviews and meta-analyses extension for scoping reviews checklist.

Results

The layered arrangement of the vocal fold, develops during early childhood and is maintained during adulthood unless injury occurs. The stellate cells of the macular flava are likely to be important in this process. The capacity for vocal fold regeneration and growth is lost during adulthood and repair results in the deposition of fibrous tissue from resident fibroblasts. With advancing age, viscoelastic tissue declines, possibly due to cell senescence. Strategies aimed at replacing fibrous tissue within the vocal folds must either stimulate resident cells or implant new cells to secrete healthy extracellular protein. Injection of basic fibroblast growth factor is the most widely reported therapy that aims to achieve this.

Conclusions

The pathways involved in vocal fold development, maintenance and aging are incompletely understood. Improved understanding has the potential to identify new treatment targets that could potentially overcome loss of vocal fold vibratory tissue.

Antifibrotic effects of Quercetin on TGF-β1-induced vocal fold fibroblasts

OBJECTIVE

To investigate the effects of Quercetin on vocal fold fibroblasts induced by TGF-β1 and vocal fold injury.

METHODS

The effects of Quercetin on collagen type I (COL-I), collagen type III (COL-III), and fibronectin (FN) expressions in transforming growth factor-β1 (TGF-β1)-induced human vocal fold fibroblasts were examined by the quantitative reverse transcription-polymerase chain reaction and the enzyme-linked immunosorbent assay. The Cell Counting Kit-8 was used to assess the influence of Quercetin on cell proliferation. A rat vocal fold injury model was developed. These rats were divided into a control group, a model group, and a Quercetin group. Pathorphological observations from Hematoxylin-eosin staining, the density of fibroblasts, and hypertrophic index were compared among the three groups.

RESULTS

Compared with cells untreated with TGF-β1, the mRNA and protein expression levels of COL-I, COL-II, and FN and proliferation ability in TGF-β1-induced human vocal fold fibroblasts were increased (all P<0.05). Compared with human vocal fold fibroblasts induced by TGF-β1, the mRNA and protein expression levels of COL-I, COL-II, and FN and proliferation ability in TGF-β1-induced human vocal fold fibroblasts following Quercetin stimulation were decreased (all P<0.05). There were no statistical differences between human vocal fold fibroblasts treated with or without Quercetin regarding cell proliferation and COL-I, COL-II, and FN expressions. Compared with the model group, Quercetin suppressed the fibrosis of the vocal fold following injury and the protein levels of COL-I, COL-II, and FN in tissue samples (all P<0.001). The density of fibroblasts and hypertrophic index in the vocal fold scar from the Quercetin group were lower than those in the model group (all P<0.05).

CONCLUSIONS

Quercetin inhibited TGF-β1-induced fibrotic changes and proliferation in human vocal fold fibroblasts and had an antifibrotic effect in vocal fold after injuries.

Tissue Engineering as a Promising Treatment for Glottic Insufficiency: A Review on Biomolecules and Cell-Laden Hydrogel

Glottic insufficiency is widespread in the elderly population and occurs as a result of secondary damage or systemic disease. Tissue engineering is a viable treatment for glottic insufficiency since it aims to restore damaged nerve tissue and revitalize aging muscle. After injection into the biological system, injectable biomaterial delivers cost- and time-effectiveness while acting as a protective shield for cells and biomolecules. This article focuses on injectable biomaterials that transport cells and biomolecules in regenerated tissue, particularly adipose, muscle, and nerve tissue. We propose Wharton's Jelly mesenchymal stem cells (WJMSCs), induced pluripotent stem cells (IP-SCs), basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), hepatocyte growth factor (HGF), insulin growth factor-1 (IGF-1) and extracellular vesicle (EV) as potential cells and macromolecules to be included into biomaterials, with some particular testing to support them as a promising translational medicine for vocal fold regeneration.

The role of systemic dehydration in vocal fold healing: Preliminary findings

Rationale

Systemic dehydration negatively alters the expression of vocal fold inflammatory and cell junction markers. These biological changes can have downstream effects on the healing processes of injured vocal folds. In the dermis, reduced hydration prolongs inflammation and delays healing. It is unknown whether this biological effect is observed in vocal fold tissue.

Objective

To investigate the effects of systemic dehydration on vocal fold healing outcomes following acute, bilateral vocal fold injury in a rodent model.

Methods

Eighteen systemic dehydrated and 18 euhydrated adult male Sprague Dawley rats experienced bilateral vocal fold injuries or no injury (N = 9/group). Vocal fold gene expression levels of inflammatory mediators and epithelial cell junction markers were measured 24 h post-injury.

Results

Pro-inflammatory gene markers (IL-1β; TNF-α) were differentially expressed in response to systemic dehydration with vocal fold injury compared to non-injury. Epithelial cell junction markers (Cadherin-3, Desmoglein-1) also exhibited divergent trends following systemic dehydration, but these data were not statistically significant.

Conclusions

Systemic dehydration may affect cellular vocal fold healing processes within 24 h. These findings lay the groundwork for further investigation of how hydration status can affect vocal fold tissue recovery and influence clinical care.

The potential of functionalized dressing releasing flavonoids facilitates scar-free healing

Scars are pathological marks left after an injury heals that inflict physical and psychological harm, especially the great threat to development and aesthetics posed by oral and maxillofacial scars. The differential expression of genes such as transforming growth factor-β, local adherent plaque kinase, and yes-related transcriptional regulators at infancy or the oral mucosa is thought to be the reason of scarless regenerative capacity after tissue defects. Currently, tissue engineering products for defect repair frequently overlook the management of postoperative scars, and inhibitors of important genes alone have negative consequences for the organism. Natural flavonoids have hemostatic, anti-inflammatory, antioxidant, and antibacterial properties, which promote wound healing and have anti-scar properties by interfering with the transmission of key signaling pathways involved in scar formation. The combination of flavonoid-rich drug dressings provides a platform for clinical translation of compounds that aid in drug disintegration, prolonged release, and targeted delivery. Therefore, we present a review of the mechanisms and effects of flavonoids in promoting scar-free regeneration and the application of flavonoid-laden dressings.

Scarless Healing of Injured Vocal Folds Using an Injectable Hyaluronic Acid-Waterborne Polyurethane Hybrid Hydrogel to Tune Inflammation and Collagen Deposition

Vocal fold (VF) scarring results from injury to the unique layered structure and is one of the main reasons for long-lasting dysphonia. A minimally invasive procedure with injectable hydrogels is a promising method for therapy. However, current surgical techniques or standard injectable fillers do not yield satisfactory outcomes. In this work, an injectable hybrid hydrogel consisting of oxide hyaluronic acid and hydrazide-modified waterborne polyurethane emulsion was injected precisely into the injury site and cross-linked in situ by a dynamic hydrazone bond. The prepared hydrogel displays excellent injectability and self-healing ability, showing favorable biocompatibility and biodegradability to facilitate endogenous newborn cell migration and growth for tissue regeneration. With the aim of evaluating the antifibrosis and regeneration capacity of the hybrid hydrogel in the VF scarring model, the morphology and vibration characteristics of VFs, inflammatory response, and healing status were collected. The hybrid hydrogel can decrease the inflammation and increase the ratio of collagen III/collagen I to heal damaged scar-free tissue. Fascinatingly, the mucosal wave oscillations of healing VF by injecting the hybrid hydrogel were vibrated like the normal VF, achieving functional restoration. This work highlights the utility of hybrid hydrogels consisting of synthetic biodegradable waterborne polyurethane emulsions and natural hyaluronic acid as promising biomaterials for scarless healing of damaged VFs.

Larynx proteomics after jellyfish collagen IL : Increased ECM /collagen and suppressed inflammation

Objectives/Hypothesis

Compare proteomic profiles of rabbit vocal folds (VFs) injected with micronized cross‐linked jellyfish collagen “collagen Type 0” (MX‐JC) against two clinical products for injection medialization laryngoplasty (IL).

Study Design

Animal model.

Methods

Left recurrent laryngeal nerve sectioning and IL were performed in New Zealand White rabbits (N = 6/group). Group 1 received (MX‐JC) and adipose‐derived stem cells (ADSCs), Group 2, MX‐JC alone; Group 3, cross‐linked hyaluronic acid; and Group 4, micronized acellular dermis. Animals were sacrificed at 4 and 12 weeks. Proteomic profiling of injected versus noninjected VFs by nano‐liquid chromatography, tandem mass spectrometry, and reactome gene ontology analysis was performed.

Results

Overall, 37–61 proteins were found to be upregulated and 60–284 downregulated in injected versus non‐injected VFs (>1.5 fold, false discovery rate‐adjusted p < .05). Over‐representation analysis (% of total) revealed top up‐regulated pathways at 4 and 12 weeks, respectively: Group 1, keratan sulfate metabolism (46%) and cellular processes (29%); Group 2, extracellular matrix (ECM)/collagen processes (33%) and beta oxidation (39%); Group 3, cellular processes (50%) and energy metabolism (100%); and Group 4, keratan sulfate metabolism (31%) and inflammation (50%). Top downregulated pathways were: Group 1, Inflammation (36%) and glucose/citric acid metabolism (42%); Group 2, cell signaling (38%) and glucose/citric acid metabolism (35%); Group 3, keratan sulfate metabolism (31%) and ECM/collagen processes (48%); and Group 4, glucose/citric acid metabolism (33%) and ECM/collagen processes (43%).

Conclusions

MX‐JC “collagen Type 0” upregulates pathways related to ECM/collagen formation and downregulates pathways related to inflammation suggesting that it is promising biomaterial for IL.

Level of Evidence

NA

The Effect of Platelet-Rich Plasma Injection on Short Term Vocal Outcomes Following Phonosurgery-A Pilot Study

Background and Objectives: The efficiency and optimal voice rest period following phonosurgery remains debatable. Platelet-rich plasma (PRP) is a safe and cheap alternative to many bioactive agents being studied on animal models, and is already in use in many medical areas. We investigate the short-term effects of PRP and voice rest on voice outcomes following phonosurgery as an alternative to voice rest alone. Materials and Methods: A prospective single-blinded pilot study was conducted. Sixteen patients with a diagnosis of vocal fold cyst and polyps were included, forming equal groups (PRP and voice rest vs. voice rest alone). Voice analysis was carried out on the preoperative day, day three, and week three following surgery. The measured parameters were fundamental frequency (F0), noise–signal ratio (NSR), harmonic poverty (HP), attack alteration (AL), pitch instability (PI), and amplitude instability (AI).VHI(Voice Handicap Index)-30 questionnaires were carried out before surgery and three weeks following surgery to assess the impact of subjective voice change on quality of life. PRP was obtained using commercial kits with separator gel. Results: An average 3.68-fold increase in platelets was obtained with PRP. No side effects were noted after injection. All voice parameters improved on day three and week three following surgery. Statistical significance was noted only in the fundamental frequency of male patients (p = 0.048) in favor of the PRP-voice rest group. In addition, the VHI- 30 questionnaire results between preoperative and postoperative assessments showed statistically significant differences in total VHI score (p = 0.02) as well as the physical (p = 0.05) and emotional (p = 0.02) scale in favor of the PRP-voice rest group. Conclusions: PRP presents short term safety in patients who undergo phonosurgery, although long-term outcomes are unknown. PRP and voice rest are superior to voice rest alone when considering subjective assessment of the voice. When analyzing acoustic parameters, PRP and voice rest are not superior to voice rest alone.

Stem cell therapy for vocal fold regeneration after scarring: a review of experimental approaches

This review aims at becoming a guide which will help to plan the experimental design and to choose adequate methods to assess the outcomes when testing cell-based products in the treatment of the damaged vocal folds. The requirements to preclinical trials of cell-based products remain rather hazy and dictated by the country regulations. Most parameters like the way the cells are administered, selection of the cell source, selection of a carrier, and design of in vivo studies are decided upon by each research team and may differ essentially between studies. The review covers the methodological aspects of preclinical studies such as experimental models, characterization of cell products, assessment of the study outcome using molecular, morphological and immunohistochemical analyses, as well as measuring the tissue physical properties. The unified recommendations to perform preclinical trials could significantly facilitate the translation of cell-based products into the clinical practice.

Vocal fold injury models in rats: a literature review on techniques and methodology

This study reviewed the current literature on technical aspects regarding controlled vocal fold injuries in the rat model. Data from PubMed, Embase, and Scopus database for English language literature was collected to identify methodological steps leading to a controlled surgical injury of the rat vocal fold. Inclusion criteria: full disclosure of anesthesia protocol, positioning of the rat for surgery, vocal fold visualization method, instrumentation for vocal fold injury, vocal fold injury type. Articles with partial contribution were evaluated and separately included due to the limited number of original methodologies. 724 articles were screened, and eleven articles were included in the analysis. Anesthesia: ketamine hydrochloride and xylazine hydrochloride varied in dose from 45 mg/kg and 4.5 mg/kg to 100 mg/kg and 10 mg/kg. Visualization: The preferred method was the 1.9 mm, 25-30 degree endoscopes. The widest diameter endoscope used was 2.7 mm with a 0 or 30 degree angle of view. Instruments for lesion induction range from 18 to 31G needles, microscissors, micro forceps to potassium titanyl phosphate, and blue light lasers. Injury types: vocal fold stripping was the main injury type, followed by vocal fold scarring and charring. One article describes scaffold implantation with injury to the superior aspect of the vocal fold. Rats are good candidates for in vivo larynx and vocal folds research. A more standardized approach should be considered regarding the type of vocal fold injury to ease data comparison.

Progress in Vocal Fold Regenerative Biomaterials: An Immunological Perspective

Vocal folds, housed in the upper respiratory tract, are important to daily breathing, speech and swallowing functions. Irreversible changes to the vocal fold mucosae, such as scarring and atrophy, require a regenerative medicine approach to promote a controlled regrowth of the extracellular matrix (ECM)-rich mucosa. Various biomaterial systems have been engineered with an emphasis on stimulating local vocal fold fibroblasts to produce new ECM. At the same time, it is imperative to limit the foreign body reaction and associated immune components that can hinder the integration of the biomaterial into the host tissue. Modern biomaterial designs have become increasingly focused on actively harnessing the immune system to accelerate and optimize the process of tissue regeneration. An array of physical and chemical biomaterial parameters have been reported to effectively modulate local immune cells, such as macrophages, to initiate tissue repair, stimulate ECM production, promote biomaterial-tissue integration, and restore the function of the vocal folds. In this perspective paper, the unique immunological profile of the vocal folds will first be reviewed. Key physical and chemical biomaterial properties relevant to immunomodulation will then be highlighted and discussed. A further examination of the physicochemical properties of recent vocal fold biomaterials will follow to generate deeper insights into corresponding immune-related outcomes. Lastly, a perspective will be offered on the opportunity of integrating material-led immunomodulatory strategies into future vocal fold tissue engineering therapies.

Human amniotic epithelial cell transplantation improves scar remodeling in a rabbit model of acute vocal fold injury: a pilot study

Objective

To gain insight into the molecular mechanisms underlying the early stages of vocal fold extracellular matrix (ECM) remodeling after a mid-membranous injury resulting from the use of human amniotic epithelial cells (hAEC), as a novel regenerative medicine cell-based therapy.

Methods

Vocal folds of six female, New Zealand White rabbits were bilaterally injured. Three rabbits had immediate bilateral direct injection of 1 × 10⁶ hAEC in 100 µl of saline solution (hAEC) and three with 100 µl of saline solution (controls, CTR). Rabbits were euthanized 6 weeks after injury. Proteomic analyses (in-gel trypsin protein digestion, LC–MS/MS, protein identification using Proteome Discoverer and the Uniprot Oryctolagus cuniculus (Rabbit) proteome) and histological analyses were performed.

Results

hAEC treatment significantly increased the expression of ECM proteins, elastin microfibril interface-located protein 1 (EMILIN-1) and myocilin that are primarily involved in elastogenesis of blood vessels and granulation tissue. A reactome pathway analysis showed increased activity of the anchoring fibril formation by collagen I and laminin, providing mechanical stability and activation of cell signaling pathways regulating cell function. hAEC increased the abundance of keratin 1 indicating accelerated induction of the differentiation programming of the basal epithelial cells and, thereby, improved barrier function. Lastly, upregulation of Rab GDP dissociation inhibitor indicates that hAEC activate the vesicle endocytic and exocytic pathways, supporting the exosome-mediated activation of cell–matrix and cell-to-cell interactions.

Conclusions

This pilot study suggests that injection of hAEC into an injured rabbit vocal fold favorably alters ECM composition creating a microenvironment that accelerates differentiation of regenerated epithelium and promotes stabilization of new blood vessels indicative of accelerated and improved repair.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02701-w.

Current approaches to management of vocal fold scar

PURPOSE OF REVIEW

Vocal fold (VF) fibrosis remains an insoluble problem in most cases, with a severe impact on vocal quality and effort. This review examines current investigations and research strands that explore the understanding of VF wound healing and applied treatments for the management of VF scar.

RECENT FINDINGS

Recent work focused on VF fibrosis has examined wound healing in the glottis, fibrosis-modifying medication, and tissue engineering approaches that span cytokine and growth factor therapy, scaffold and cell delivery platforms, seeded scaffolds, conditioned media and stem cell therapy. Many show promise and may deliver improvements in the wound bed favouring less fibrogenic healing patterns, ultimately with the goal of preserving or restoring VF vibration. Further collaborative research is required that examines combined approaches, long term outcomes, better three-dimensional modelling of cell-cell interactions and delivery modalities for molecular therapies.

SUMMARY

VF fibrosis research continues to expand and explore a variety of mechanistic pathways in order to understand VF healing and identify novel and complementary targets for manipulation. Many different approaches show promise and may also offer synergistic benefits. Research continues to strive for healing that more closely resembles true VF architecture and function.

Asiatic Acid Improves Extracellular Matrix Remodeling in Vocal Fold Scarring Via SMAD7 Activation

OBJECTIVES/HYPOTHESIS

Vocal fold (VF) fibroblasts are the central target for developing new strategies for the treatment of VF scarring and fibrosis. Asiatic acid (AA) is a triterpenoid derivate with antifibrotic properties. However, the effect of AA in VF scarring is poorly understood. The objective of this study was to investigate the potential application of AA as a therapeutic treatment in VF scarring.

STUDY DESIGN

Xxxxx.

METHODS

The functional expression of SMAD7 was knocked down with recombinant adenoviruses and adeno-associated viruses carrying shRNAs in the in vitro and in vivo models, which were constructed to investigate AA's antifibrotic function. The expression of collagens and SMADs in cultured human and rabbit cell lines and animal models was evaluated with quantitative reverse transcription polymerase chain reaction and immunohistochemistry labeling, respectively. Cell migration capacity and contraction in VF fibroblast cell lines were also evaluated.

RESULTS

AA downregulated the downstream fibrotic activation in a dose-dependent manner. Meanwhile, AA attenuated VF scarring/fibrosis by reducing collagen deposition. Furthermore, the antifibrotic effects of AA were associated with the upregulation of SMAD7. In contrast, knockdown of SMAD7 inhibited the effect of AA on transforming growth factor-beta-1 (TGF-β1) stimulation, which suggests a central role for SMAD7 in AA-induced antifibrotic activities during VF fibrosis.

CONCLUSION

We concluded that AA, which is a novel therapeutic candidate for preventing VF scarring/fibrosis, might exert its antifibrotic effect via the TGF-β1/SMAD signaling pathway.

LEVEL OF EVIDENCE

N/A Laryngoscope, 2021.

In Vitro Evaluation of Biomaterials for Vocal Fold Injection: A Systematic Review

Vocal fold injection is a preferred treatment in glottic insufficiency because it is relatively quick and cost-saving. However, researchers have yet to discover the ideal biomaterial with properties suitable for human vocal fold application. The current systematic review employing PRISMA guidelines summarizes and discusses the available evidence related to outcome measures used to characterize novel biomaterials in the development phase. The literature search of related articles published within January 2010 to March 2021 was conducted using Scopus, Web of Science (WoS), Google Scholar and PubMed databases. The search identified 6240 potentially relevant records, which were screened and appraised to include 15 relevant articles based on the inclusion and exclusion criteria. The current study highlights that the characterization methods were inconsistent throughout the different studies. While rheologic outcome measures (viscosity, elasticity and shear) were most widely utilized, there appear to be no target or reference values. Outcome measures such as cellular response and biodegradation should be prioritized as they could mitigate the clinical drawbacks of currently available biomaterials. The review suggests future studies to prioritize characterization of the viscoelasticity (to improve voice outcomes), inflammatory response (to reduce side effects) and biodegradation (to improve longevity) profiles of newly developed biomaterials.

Regenerative medicine for end-stage fibrosis and tissue loss in the upper aerodigestive tract: a twenty-first century review

OBJECTIVE

This review assesses regenerative medicine of the upper aerodigestive tract during the first two decades of the twenty-first century, focusing on end-stage fibrosis and tissue loss in the upper airways, salivary system, oropharynx and tongue.

METHOD

PubMed, Embase, Google Scholar, Cochrane Library, Medline and clinicaltrials.org were searched from 2000 to 2019. The keywords used were: bioengineering, regenerative medicine, tissue engineering, cell therapy, regenerative surgery, upper aerodigestive tract, pharynx, oropharynx, larynx, trachea, vocal cord, tongue and salivary glands. Original studies were subcategorised by anatomical region. Original human reports were further analysed. Articles on periodontology, ear, nose and maxillofacial disorders, and cancer immunotherapy were excluded.

RESULTS

Of 716 relevant publications, 471 were original studies. There were 18 human studies included, within which 8 reported airway replacements, 5 concerned vocal fold regeneration and 3 concerned salivary gland regeneration. Techniques included cell transplantation, injection of biofactors, bioscaffolding and bioengineered laryngeal structures.

CONCLUSION

Moderate experimental success was identified in the restoration of upper airway, vocal fold and salivary gland function. This review suggests that a shift in regenerative medicine research focus is required toward pathology with a higher disease burden.

Cigarette smoke-induced changes in the murine vocal folds: a Raman spectroscopic observation

Raman spectroscopic methods are being projected as novel tools to study the early invisible molecular level changes in a label-free manner. In the present study, we have used Raman spectroscopy to explore the earliest biochemical changes in murine vocal folds in response to time-bound cigarette smoke exposure. Mice were exposed to cigarette smoke for 2 or 4-weeks through a customized smoke inhalation system. The larynx was collected and initial evaluations using standard methods of analysis such as histopathology and immunofluorescence was performed. Concurrent unstained sections were used for Raman imaging. Two common pathological features of vocal fold disorders including alterations in collagen content and epithelial hypercellularity, or hyperplasia, were observed. The mean spectra, principal component analysis, and Raman mapping also revealed differences in the collagen content and hypercellularity in the smoke exposed tissues. The differences in 2-week exposed tissues were found to be more prominent as compared to 4-week. This was attributed to adaptive responses and the already reported biphasic effects, which suggest that collagen synthesis is significantly reduced at higher cigarette smoke concentrations. Overall findings of the study are supportive of the prospective application of Raman imaging in monitoring changes due to cigarette smoke in the vocal folds.

Mycoplasma affects baseline gene expression and the response to glucocorticoids in vocal fold fibroblasts

Introduction. In vitro experimentation is intentionally contrived to isolate specific phenomena in the context of profound biological complexity. Mycoplasmas in the upper airway likely contribute to this complexity and play a largely unknown role in both health and disease. Similarly, the presence and role of mycoplasma in in vitro investigation are largely unknown.Hypothesis. We hypothesize mycoplasma in human vocal fold fibroblasts (VFF) will affect both basal gene-expression patterns as well as the cell response to exogenous stimuli.Aim. We sought to determine mycoplasma presence across vocal fold fibroblast cultures, basal transcriptional changes as a function of mycoplasma, and responsiveness to exogenous glucocorticoids in mycoplasma-positive and -negative VFF.Methodology. PCR-based mycoplasma detection was performed in an immortalized human VFF line as well as rat and rabbit primary VFF cultures and extracted rat laryngeal tissue. RNA sequencing was performed in mycoplasma-positive and -negative human cells at baseline and in response to dexamethasone.Results. Mycoplasma was identified in the human cell line as well as primary culture from rabbits. Mycoplasma was not detected in tissue or primary culture from rat vocal folds. Basal mRNA expression in human VFF differed significantly following mycoplasma treatment. In addition, differential responses to dexamethasone were observed across multiple pathways as a function of mycoplasma presence in these cells. Pathways including apoptosis, DNA damage repair, and G1 to S cell cycle signalling were significantly enriched in mycoplasma-positive cells.Conclusion. Variability of mycoplasma presence across culture conditions and differential responses to exogenous stimuli as a function of mycoplasma presence are potentially problematic for the translation of in vitro experimentation in the upper aerodigestive tract. It remains unclear if these findings represent contamination or the baseline state of this specialized tissue.

Course of Self-Reported Dysphagia, Voice Impairment and Pain in Head and Neck Cancer Survivors

BACKGROUND

Head and neck cancer (HNC)-specific symptoms have a substantial impact on health-related quality of life. The aim of this study was to determine whether self-reported dysphagia, voice problems and pain of HNC patients changed over time and whether specific clinical or sociodemographic variables were associated with these symptoms.

METHODS

HNC patients (n = 299) in an outpatient setting answered questionnaires (Eating Assessment Tool-10; questions from the EORTC QLQ-C30 and EORTC H&N35) on dysphagia, voice problems and pain, collected with the software "OncoFunction" at three different timepoints (t1-t3) after diagnosis. The mean score changes from t1 to t3 were expressed in terms of effect sizes d. The impact of sociodemographic and clinical factors on the course of the variables was tested with multivariate analyses of variance.

RESULTS

Dysphagia, voice impairment and pain in HNC survivors significantly improved over a period of approximately 14 months after diagnosis. Tumor site, stage, treatment modality, occupational state and ECOG state were significantly correlated with self-reported functional outcome. The pain level of the HNC patients was rather low.

CONCLUSIONS

Patients suffer from functional impairments after HNC treatment, but an improvement in self-reported symptoms could be demonstrated within this time period.

Mechanisms Underlying the Antifibrotic Potential of Estradiol for Vocal Fold Fibrosis

OBJECTIVES/HYPOTHESIS

Vocal fold fibrosis remains a significant clinical challenge. Estrogens, steroid hormones predominantly responsible for secondary sexual characteristics in women, have been shown to alter wound healing and limit fibrosis, but the effects on vocal fold fibrosis are unknown. We sought to elucidate the expression of estrogen receptors and the effects of estrogens on TGF-β1 signaling in rat vocal fold fibroblasts (VFFs).

STUDY DESIGN

In vitro.

METHODS

VFFs were isolated from 10-week-old, male Sprague-Dawley rats, and estrogen receptor alpha (ERα) and G protein-coupled receptor 30 (GPR30) were examined via immunostaining and quantitative polymerase chain reaction (qPCR). VFFs were treated with estradiol (E2, 10^-7 , 10^-8 or 10^-9  M) ± transforming growth factor beta 1 (TGF-β1, 10 ng/mL). ICI 182,780 (ICI, 10^-7  M) or G36 (10^-7  M) were employed as antagonists of ERα or GPR30, respectively. qPCR was employed to determine estrogen receptor-mediated effects of E2 on genes related to fibrosis.

RESULTS

ERα and GPR30 were expressed in VFFs at both the protein and the mRNA levels. E2 (10^-7  M) did not alter Smad3, Smad7, Acta2 mRNA, or extracellular matrix related genes. However, the combination of E2 (10^-8  M) and TGF-β1 significantly increased Smad7 (P = .03) and decreased Col1a1 (P = .04) compared to TGF-β1 alone; this response was negated by the combination of ICI and G36 (P = .009).

CONCLUSIONS

E2 regulated TGF-β1/Smad signaling via estrogen receptors in VFFs. These findings provide insight into potential mechanisms of estrogens on vocal fold injury with the goal of enhanced therapeutics for vocal fold fibrosis.

LEVEL OF EVIDENCE

NA Laryngoscope, 131:2285-2291, 2021.

Phlorotannins ameliorate extracellular matrix production in human vocal fold fibroblasts and prevent vocal fold fibrosis via aerosol inhalation in a laser-induced fibrosis model

Vocal fold fibrosis is an abnormal condition characterized by unfavorable changes in the organization of the extracellular matrix in vocal fold lamina propria. To prevent and treat vocal fold fibrosis, a number of synthetic drugs, such as mitomycin C and the glucocorticoid family, are used after surgery, but these are known to have some side effects. Therefore, using both in vitro and in vivo studies, this study investigated whether phlorotannins extracted from Ecklonia cava have the potential to prevent vocal fold fibrosis with minimal side effects. The results show that phlorotannins suppressed both the expression of the fibrotic phenotypic marker and cell migration by inhibiting the activation of the mitogen-activated protein kinase (MAPK) and Smad2/3 signaling pathways in human vocal fold fibroblasts stimulated by transforming growth factor-β. Additionally, phlorotannins exhibited antifibrotic efficacy without an excessive inflammatory response in a laser-induced fibrosis rabbit model when delivered as an aerosol via inhalation. Based on these results, phlorotannins should be considered a promising candidate for use in the prevention of vocal fold fibrosis.

Mechanisms of larynx and vocal fold development and pathogenesis

The larynx and vocal folds sit at the crossroad between digestive and respiratory tracts and fulfill multiple functions related to breathing, protection and phonation. They develop at the head and trunk interface through a sequence of morphogenetic events that require precise temporo-spatial coordination. We are beginning to understand some of the molecular and cellular mechanisms that underlie critical processes such as specification of the laryngeal field, epithelial lamina formation and recanalization as well as the development and differentiation of mesenchymal cell populations. Nevertheless, many gaps remain in our knowledge, the filling of which is essential for understanding congenital laryngeal disorders and the evaluation and treatment approaches in human patients. This review highlights recent advances in our understanding of the laryngeal embryogenesis. Proposed genes and signaling pathways that are critical for the laryngeal development have a potential to be harnessed in the field of regenerative medicine.

Human pluripotent stem cell-derived cardiac stromal cells and their applications in regenerative medicine

Coronary heart disease is one of the leading causes of death in the United States. Recent advances in stem cell biology have led to the development and engineering of human pluripotent stem cell (hPSC)-derived cardiac cells and tissues for application in cellular therapy and cardiotoxicity studies. Initial studies in this area have largely focused on improving differentiation efficiency and maturation states of cardiomyocytes. However, other cell types in the heart, including endothelial and stromal cells, play crucial roles in cardiac development, injury response, and cardiomyocyte function. This review discusses recent advances in differentiation of hPSCs to cardiac stromal cells, identification and classification of cardiac stromal cell types, and application of hPSC-derived cardiac stromal cells and tissues containing these cells in regenerative and drug development applications.