Topical Application of 5‐Aminolevulinic Acid Is Sufficient for Photodynamic Therapy on Vocal Folds

Abstract

Objectives To evaluate the feasibility of topical photodynamic therapy (PDT) using 5‐aminolevulinic acid (5‐ALA) for vocal fold leukoplakia. Study Design Ex vivo and in vivo. Methods 5‐ALA was applied topically as a 20% solution to ex vivo canine vocal folds. The penetration depth and concentrations of 5‐ALA in tissue were quantified using frozen sectioning and fluorescamine derivatization after 5‐ALA contact incubation or topical spraying. Then, 5‐ALA solution was sprayed on leporine vocal folds once, twice, or given systemically in vivo. Protoporphyrin IX (PPIX) location was visualized using fluorescence microscopy, and PPIX concentrations were measured using a fluorescent quantitative method. Hematoxylin and eosin (H&E) staining was performed to visualize the histological changes of vocal folds after PDT for each group. Results Topical incubation of 15 minutes with 5‐ALA achieved a penetration depth of over 2 mm and similar concentrations within the superficial 500 μm of epithelium, compared with longer incubation times. Topical spraying of 5‐ALA produced sufficient concentrations in vocal folds, but the retention time is short. An in vivo leporine model showed that laryngeal spraying of 20% 5‐ALA induced similar penetration depth and concentrations of PPIX compared to systemic administration of 5‐ALA. Two sprays of 20% 5‐ALA solution with an interval of 30 minutes are needed to produce complete exfoliation of vocal fold epithelium. Conclusion Topical PDT with laryngeal spraying of 20% 5‐ALA solution achieves sufficient therapeutic effects and is potentially applicable for the treatment of vocal fold leukoplakia. Level of Evidence NA Laryngoscope, 129:E80–E86, 2019

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