Ototoxicity of boric acid powder in a rat animal model

Abstract Introduction: Boric acid, which has antiseptic and acidic properties, is used to treat external and middle ear infections. However, we have not found any literature about the effect of boric acid powder on middle ear mucosa and inner ear. Objective: The purpose of this study is to investigate possible ototoxic effects of boric acid powder on cochlear outer hair cell function and histological changes in middle ear mucosa in a rat animal model. Methods: Twenty healthy, mature Wistar albino rats were used in this study. The rats were divided into two groups, Group A and Group B, each of which consisted of 10 rats. Initially, the animals in each group underwent distortion product otoacoustic emissions testing of their right and left ears. After the first distortion product otoacoustic emissions test, a surgical microscope was used to make a small perforation in both ears of the rats in each group, and a second distortion product otoacoustic emissions test was used to measure both ears in all of the rats. Boric acid powder was applied to the right middle ear of the rats using tympanic membrane perforation, and the distortion product otoacoustic emissions were measured immediately after the boric acid powder application. The histological changes and distortion product otoacoustic emissions were evaluated three days later in Group A and 40 days later in Group B. Results: No significant differences were found at all of the distortion product otoacoustic emissions frequencies. In Group A, mild inflammation of the middle ear mucosa was found on the third day after boric acid powder application. In Group B, boric acid powder caused mild inflammatory changes on the 40th day, which declined over time. Those changes did not lead to significant fibrosis within the mucosa. Conclusion: In rats, boric acid powder causes mild inflammation in middle ear mucosa and it has no ototoxic effects on cochlear outer hair cell function in the inner ear of rats.

摘要 引言：硼酸具有防腐与酸性特性，临床常用于治疗外耳及中耳感染。然而，目前尚无文献探讨硼酸粉剂对中耳黏膜与内耳的影响。研究目的：本研究旨在通过大鼠动物模型，探究硼酸粉剂对耳蜗外毛细胞功能及中耳黏膜组织学改变的潜在耳毒性作用。研究方法：本研究纳入20只健康成熟的Wistar白化大鼠，分为A、B两组，每组各10只。首先对两组大鼠的双耳行畸变产物耳声发射（distortion product otoacoustic emissions, DPOAE）检测。首次畸变产物耳声发射检测完成后，使用手术显微镜在各组大鼠双耳鼓膜上制作小型穿孔，随后再次对所有大鼠的双耳进行畸变产物耳声发射检测。通过鼓膜穿孔处向大鼠右侧中耳置入硼酸粉剂，并于给药后即刻检测畸变产物耳声发射。A组于给药后3天、B组于给药后40天分别评估其组织学改变与畸变产物耳声发射结果。研究结果：所有畸变产物耳声发射频率下均未观察到显著差异。A组大鼠在硼酸粉剂给药后第3天可见中耳黏膜轻度炎症反应。B组大鼠在给药后第40天出现轻度炎症改变，且随时间推移有所缓解，该改变未导致黏膜内出现显著纤维化。研究结论：在大鼠模型中，硼酸粉剂可引发中耳黏膜轻度炎症，但对大鼠内耳耳蜗外毛细胞功能无耳毒性作用。