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

In vitro model to evaluate effect of acidic pepsin on vocal fold barrier function

The pathophysiology of laryngopharyngeal reflux (LPR) and its impact on the vocal fold is not well understood, but may involve acid damage to vocal fold barrier functions. Two different components encompass vocal fold barrier function: the mucus barrier and tight junctions. Mucus retained on epithelial microprojections protects the inside of the vocal fold by neutralizing acidic damage. Tight junctions control permeability between cells. Here we developed an in vitro experimental system to evaluate acidic injury and repair of vocal fold barrier functions. We first established an in vitro model of rat vocal fold epithelium that could survive at least one week after barrier function maturation. The model enabled repeated evaluation of the course of vocal fold repair processes. Then, an injury experiment was conducted in which vocal fold cells were exposed to a 5-min treatment with acidic pepsin that injured tight junctions and cell surface microprojections. Both of them healed within one day of injury. Comparing vocal fold cells treated with acid alone with cells treated with acidic pepsin showed that acidic pepsin had a stronger effect on intercellular permeability than acid alone, whereas pepsin had little effect on microprojections. This result suggests that the proteolytic action of pepsin has a larger effect on protein-based tight junctions than on phospholipids in microprojections. This experimental system could contribute to a better understanding of vocal fold repair processes after chemical or physical injuries, as well as voice problems due to LPR pathogenesis.

Contribution of Streptococcus pseudopneumoniae and Streptococcus salivarius to vocal fold mucosal integrity and function

Structural changes to the vocal fold (VF) epithelium, namely, loosened intercellular junctions, have been reported in VF benign lesions. The potential mechanisms responsible for the disruption of cell junctions do not address the contribution of resident microbial communities to this pathological phenomenon. In this study, we focused on determining the relationship between Streptococcus pseudopneumoniae (SP), a dominant bacterial species associated with benign lesions, and Streptococcus salivarius (SS), a commensal bacterium, with human VF epithelial cells in our three-dimensional model of the human VF mucosa. This experimental system enabled direct deposition of bacteria onto constructs at the air/liquid interface, allowing for the assessment of bacterium-host interactions at the cellular, molecular and ultrastructural levels. Our findings demonstrate that SP disrupts VF epithelial integrity and initiates inflammation via the exported products HtrA1 and pneumolysin. In contrast, SS attaches to the VF epithelium, reduces inflammation and induces Mmp2-mediated apical desquamation of infected cells to mitigate the impact of pathogens. In conclusion, this study highlights the complexity of microbial involvement in VF pathology and potential VF mucosal restoration in the presence of laryngeal commensals.

Is It Hot or Cold? Which Humid Air Is Better for Vocal Hygiene?

OBJECTIVES

The purpose of this research is to determine which type of humid air should be suggested for vocal hygiene by demonstrating the effects of hot humid air and cold humid air on the vocal cord mucosa using different histological methods.

STUDY DESIGN

Randomized controlled study.

METHODS

Cold or hot humid air was applied to the rats for 30 minutes/day for 10 days using a humid air machine placed in a closed glass cage. The control group did not receive any treatment and were kept in their cages under normal laboratory conditions. The animals were sacrificed and their larynxes were removed on the 11th day. Histologically, lamina propria (LP) thickness was measured by Crossman's three stain and the number of mast cells in 1 square millimeter of lamina propria was measured by toluidine blue. In immunohistochemical staining, the intensity of zonula occludens-1 (ZO-1) staining was measured using a rabbit polyclonal antibody and scored from 0 (no staining) to 3 (intense staining). One-way ANOVA and Kruskal-Wallis tests were used to compare groups.

RESULTS

The mean LP thickness was thinner in rats exposed to cold humid air (CHA) than in the control group (P = 0.012). In terms of LP thickness, other intergroup comparisons (cold vs hot and control vs hot) showed no statistically significant difference between groups (P > 0.05). The mean mast cell count did not differ between groups. The hot humid air (HHA) group had more intense ZO-1 staining than the other groups (P < 0.001). There was no difference in ZO-1 staining intensity between the control group and CHA group.

CONCLUSION

HHA and CHA administration had no negative effects on inflammatory findings in the vocal cords (mast cell count or LP thickness). While HHA appears to strengthen the epithelial barrier (denser ZO-1 staining), the physiologic outcomes, such as bronchoconstriction, should be cautiously assessed.

Epithelial response to vocal fold microflap injury in a preclinical model

OBJECTIVES

Functional outcomes following microflap surgery for vocal fold pathology are favorable. Although the stratified squamous epithelium appears to heal rapidly, persistent physiologic tissue alterations are likely. We sought to elucidate key biochemical processes including recruitment of immune cells, regulation of cellular junction proteins, and long-term alterations to epithelial tissue permeability following microflap with an eye toward enhanced clinical outcomes.

METHODS

Forty New Zealand rabbits were assigned to eight groups (n = 5/group): no-injury control or bilateral microflap with survival for 0 h, 12 h, 1 day, 3 days, 7 days, 30 days, and 60 days post-microflap. The epithelium was dissected from one vocal fold and transepithelial resistance was quantified. The contralateral fold was subjected to transmission electron microscopy. Images were evaluated by a blinded rater and paracellular space dilation was quantified using ImageJ. Immune cell infiltration was evaluated and recorded qualitatively.

RESULTS

Increased innate immune response was observed 12 h as well as 7 and 30 days after microflap. At 60 days following injury, decreased epithelial resistance was observed. Paracellular spaces were dilated at all time-points following injury.

CONCLUSIONS

The vocal fold epithelium was significantly altered at 60 days following microflap. The implications for this tissue phenotype are unclear. However, compromised epithelial barrier function is implicated in various diseases and may increase the risk of subsequent injury.

LEVEL OF EVIDENCE

NA Laryngoscope, 133:350-356, 2023.

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.

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.

Piezo1-expressing vocal fold epithelia modulate remodeling via effects on self-renewal and cytokeratin differentiation

Mechanoreceptors are implicated as functional afferents within mucosa of the airways and the recent discovery of mechanosensitive channels Piezo1 and Piezo2 has proved essential for cells of various mechanically sensitive tissues. However, the role for Piezo1/2 in vocal fold (VF) mucosal epithelia, a cell that withstands excessive biomechanical insult, remains unknown. The purpose of this study was to test the hypothesis that Piezo1 is required for VF mucosal repair pathways of epithelial cell injury. Utilizing a sonic hedgehog (shh) Cre line for epithelial-specific ablation of Piezo1/2 mechanoreceptors, we investigated 6wk adult VF mucosa following naphthalene exposure for repair strategies at 1, 3, 7 and 14 days post-injury (dpi). PIEZO1 localized to differentiated apical epithelia and was paramount for epithelial remodeling events. Injury to wildtype epithelium was most appreciated at 3 dpi. Shh^cre/+; Piezo1^loxP/loxP, Piezo2 ^loxP/+ mutant epithelium exhibited severe cell/nuclear defects compared to injured controls. Conditional ablation of Piezo1 and/or Piezo2 to uninjured VF epithelium did not result in abnormal phenotypes across P0, P15 and 6wk postnatal stages compared to heterozygote and control tissue. Results demonstrate a role for Piezo1-expressing VF epithelia in regulating self-renewal via effects on p63 transcription and YAP subcellular translocation-altering cytokeratin differentiation.

A Comparison of the Localization of Integral Membrane Proteins in Human and Rabbit Vocal Folds

OBJECTIVES

This study's objective was to identify and compare the localization of Aquaporin (AQP) 1, 4, 7, Na+/K + -ATPase, E-cadherin, zona occludin (ZO)-1, and occludin in human and rabbit vocal folds (VF)s to inform the design of future studies to explore the function of these proteins in the regulation of VF homeostasis.

METHODS

Four human larynges and five New Zealand white rabbit larynges were used. Samples were immunolabeled for primary antibodies against AQP1, AQP4, AQP7, the alpha subunit of Na+/K + -ATPase, E-cadherin, and ZO-1 and occludin and then captured digitally using a Nikon Eclipse 90i microscope and Hamamatsu C10600 Camera. Two raters familiar with human and rabbit VF histology identified positive labeling in tissue structures, including the apical epithelium, basal epithelium/basement membrane, and lamina propria (LP).

RESULTS

Samples from both species showed positive labeling for AQP1 in the basal epithelium/basement membrane, superficial LP, and deep/intermediate LP. Aquaporin 4, Aquaporin 7, Na+/K + -ATPase, and E-cadherin were primarily localized to the epithelium of both species. Zona occludin-1 was primarily localized apical epithelium and the superficial LP of both species. Occludin was primarily present in the apical epithelium in rabbit samples but not human.

CONCLUSION

These data provide evidence of the presence of key ion transport channels and cell adhesion proteins in human and rabbit VFs. Aquaporin 1, 4, 7, Na+/K + -ATPase, E-cadherin, and ZO-1 were similarly localized in both species. These findings will be useful to investigators interested in the exploration of VF homeostasis and barrier integrity in future studies.

LEVEL OF EVIDENCE

N/A Laryngoscope, 131:E1265-E1271, 2021.

Comparative Pharmacokinetics of Gallic Acid After Oral Administration of Gallic Acid Monohydrate in Normal and Isoproterenol-Induced Myocardial Infarcted Rats

Gallic acid (GA) is a polyphenolic natural product widely distributed in food, beverage, and traditional Chinese herbs with beneficial effects on the cardiovascular system. In this research, a comparative study was conducted to investigate the possible difference of pharmacokinetic process in normal and isoproterenol-induced myocardial infarcted rats after oral administration of GA monohydrate with the dose of 50 and 100 mg/kg, respectively. Quantification of GA in rat plasma was achieved by using a simple and rapid high-performance liquid chromatographic method. The results revealed that pharmacokinetics of GA were greatly different between normal and pathological state. GA exhibited slower absorption into the bloodstream, and yielded 1.7-fold (50 mg/kg GA) and 1.3-fold (100 mg/kg GA) less values of area under concentration-time curve as well as 2.5-fold lower of maximum blood concentration (C_max) in MI rats than those in normal rats. In addition, significant prolonged T_1/2 and MRT as well as decreased CL were also registered in MI rats. Our findings suggest that myocardial infarction could alter the pharmacokinetic process of GA, and thus the potential pharmacokinetic differences of herbal preparations (or dietary nutrition) containing GA between normal and pathological conditions should be brought to the forefront seriously in clinical practice.