Bicarbonate availability for vocal fold epithelial defense to acidic challenge

Influence of age on voice quality after transoral CO2 laser microsurgery

OBJECTIVE

To study the post-operative evolution of voice quality of patients treated by transoral CO2 laser microsurgery (TLM) according to the age.

METHODS

Patients treated by type I to VI TLM and post-operative speech therapy were prospectively recruited from our hospital. The voice quality was assessed pre-, 1-, 3- 6- and 12-month posttreatment with voice handicap index (VHI), dysphonia, roughness, breathiness, asthenia, strain (GRBAS), maximal phonation time (MPT), F0, F0 standard deviation (STD), percent jitter, percent shimmer, noise-to-harmonic ratio (NHR), vocal fold vibration assessment and speech fluency. Evolution of voice outcomes was analyzed considering age of patients (< 60 vs. ≥ 60 years).

RESULTS

Seventy-five patients completed the evaluations. Thirty-four and forty-one patients were < 60 or ≥ 60 yo, respectively. Subjective and objective voice parameters (VHI, G, R, B), jitter and fluency significantly improved from 1- to 6-month post-TLM in < 60 yo individuals. The voice parameters improved 12-month post-TLM in the ≥ 60 yo group at the exception of VHI that improved 3-month post-TLM. There were positive associations between age and 12-month NHR, G and A parameters.

CONCLUSION

The post-operative evolution of voice quality parameters may vary between patients according to the age. Preoperative VHI is predictive of 12-month subjective and objective voice outcomes.

Methodology for the establishment of primary porcine vocal fold epithelial cell cultures

OBJECTIVE

A current lack of methods for epithelial cell culture significantly hinders our understanding of the role of the epithelial and mucus barriers in vocal fold health and disease. Our first objective was to establish reproducible techniques for the isolation and culture of primary porcine vocal fold epithelial cells. Our second objective was to evaluate the functional significance of cell cultures using an in vitro exposure to an inflammatory cytokine.

METHODS

Epithelial cells were isolated from porcine vocal folds and expanded in culture. Characterization of cultures was completed by immunostaining with markers for pan-cytokeratin (epithelial cells), vimentin (stromal cells), von Willebrand factor (endothelial cell), and MUC1 and MUC4 (mucin) glycoproteins. Established epithelial cell cultures were then exposed to the inflammatory cytokine tumor necrosis factor alpha (TNF-α) for 24-hours, and transcript expression of MUC1 and MUC4 was evaluated.

RESULTS

Reproducible, porcine vocal fold epithelial cell cultures, demonstrating cobblestone appearance characteristic of the typical morphology of epithelial cell cultures were created. Cells showed positive staining for pan-cytokeratin with limited expression of vimentin and von Willebrand factor. Epithelial cells also expressed MUC1 and MUC4. TNF-α significantly increased transcript expression of MUC4.

CONCLUSION

Here, we present the first report of successful culture of primary porcine vocal fold epithelial cells. Cultures will provide researchers with a valuable new in vitro tool to investigate vocal fold epithelium and mucus as well as the effects of common challenges, including inflammatory cytokines, on these barriers.

LEVEL OF EVIDENCE

NA Laryngoscope, 129:E355-E364, 2019.

Acute Acrolein Exposure Induces Impairment of Vocal Fold Epithelial Barrier Function

Acrolein is a ubiquitous pollutant abundant in cigarette smoke, mobile exhaust, and industrial waste. There is limited literature on the effects of acrolein on vocal fold tissue, although there are clinical reports of voice changes after pollutant exposures. Vocal folds are responsible for voice production. The overall objective of this study was to investigate the effects of acrolein exposure on viable, excised vocal fold epithelial tissue and to characterize the mechanism underlying acrolein toxicity. Vocal fold epithelia were studied because they form the outermost layer of the vocal folds and are a primary recipient of inhaled pollutants. Porcine vocal fold epithelia were exposed to 0, 50, 100, 500, 900 or 1300 μM of acrolein for 3 hours; the metabolic activity, epithelial resistance, epithelial permeability, tight junction protein (occludin and claudin 3) expression, cell membrane integrity and lipid peroxidation were investigated. The data demonstrated that acrolein exposure at 500 μM significantly reduced vocal fold epithelial metabolic activity by 27.2% (p≤0.001). Incubation with 100 μM acrolein caused a marked increase in epithelial permeability by 130.5% (p<0.05) and a reduction in transepithelial electrical resistance (TEER) by 180.0% (p<0.001). While the expression of tight junctional protein did not change in acrolein-treated samples, the cell membrane integrity was significantly damaged with a 45.6% increase of lipid peroxidation as compared to controls (p<0.05). Taken together, these data provide evidence that acute acrolein exposure impairs vocal fold epithelial barrier integrity. Lipid peroxidation-induced cell membrane damage may play an important role in reducing the barrier function of the epithelium.

Utility of cell viability assays for use with ex vivo vocal fold epithelial tissue

OBJECTIVES/HYPOTHESIS

Ex vivo models are routinely used to investigate the barrier function of the vocal fold epithelium. However, there are limited reports on assays that can be used to investigate the effect of clinically relevant challenges on vocal fold epithelial tissue viability. Our objective was to determine the utility of two assays routinely used in cell culture-a cellular metabolic activity assay and a cell membrane integrity assay-to investigate the viability of ex vivo porcine vocal fold epithelium.

STUDY DESIGN

Prospective, ex vivo animal study.

METHODS

Porcine vocal folds were exposed to acrolein, hydrochloric acid, or hydrogen peroxide challenge. An untreated, sham challenge was included as a control. Assays including metabolic activity, cell membrane integrity, and histology were used to determine whether challenges reduced epithelial viability as compared to sham.

RESULTS

Cell membrane integrity and metabolic activity assays detected reductions in viability following hydrochloric acid and hydrogen peroxide challenges but not acrolein challenge as compared to sham. No challenge produced significant changes in epithelial appearance as evidenced by light microscopy.

CONCLUSIONS

Metabolic activity and cell membrane integrity assays are valuable tools that can be used to evaluate the viability of ex vivo vocal fold epithelial tissue following clinically relevant challenges. As viability is reduced, the ability of epithelial tissue to maintain its barrier function is compromised. Accurate assessment of viability may provide us clues into understanding mechanisms underlying vocal fold epithelial injury and disease.

LEVEL OF EVIDENCE

NA Laryngoscope, 125:E180-E185, 2015.