Evaluating the ototoxicity of an anti-MRSA peptide KR-12-a2

Abstract Introduction Methicillin-resistant staphylococcus aureus is an emerging problem for the treatment of chronic suppurative otitis media, and also for pediatric tympanostomy tube otorrhea. To date, there are no effective topical antibiotic drugs to treat methicillin-resistant staphylococcus aureus otorrhea. Objective In this study, we evaluated the ototoxicity of topical KR-12-a2 solution on the cochlea when it is applied topically in the middle ear of guinea pigs. Methods The antimicrobial activity of KR-12-a2 against methicillin-resistant staphylococcus aureus strains was examined by using the inhibition zone test. Topical application of KR-12-a2 solution, gentamicin and phosphate buffered saline were applied in the middle ear of the guinea pigs after inserting ventilation tubes. Ototoxicity was assessed by auditory brainstem evoked response and scanning electron microscope examination. Results KR-12-a2 produced an inhibition zone against methicillin-resistant staphylococcus aureus from 6.25 µg. Hearing threshold in the KR-12-a2 and PBS groups were similar to that before ventilation tube insertion. However, the gentamicin group showed elevation of the hearing threshold and there were statistically significant differences compared to the phosphate buffered saline or the KR-12-a2 group. In the scanning electron microscope findings, the KR-12-a2 group showed intact outer hair cells. However, the gentamicin group showed total loss of outer hair cells. In our experiment, topically applied KR-12-a2 solution did not cause hearing loss or cochlear damage in guinea pigs. Conclusion In our experiment, topically applied KR-12-a2 solution did not cause hearing loss or cochlear damage in guinea pigs. The KR-12-a2 solution can be used as ototopical drops for treating methicillin-resistant staphylococcus aureus otorrhea; however, further evaluations, such as the definition of optimal concentration and combination, are necessary.

摘要 引言
耐甲氧西林金黄色葡萄球菌（Methicillin-resistant Staphylococcus aureus）已成为慢性化脓性中耳炎（chronic suppurative otitis media）与儿童鼓膜置管术后耳漏（pediatric tympanostomy tube otorrhea）治疗中的新兴临床难题，目前尚无有效的局部抗生素药物可用于治疗该菌引发的耳漏。
本研究旨在评估KR-12-a2溶液经豚鼠（guinea pigs）中耳局部给药后对耳蜗（cochlea）的耳毒性（ototoxicity）。
方法：采用抑菌圈试验（inhibition zone test）检测KR-12-a2对耐甲氧西林金黄色葡萄球菌菌株的抗菌活性（antimicrobial activity）。在豚鼠中耳置入鼓膜通气管（ventilation tubes）后，分别向其中耳局部滴注KR-12-a2溶液、庆大霉素（gentamicin）与磷酸盐缓冲液（phosphate buffered saline, PBS）。通过听觉脑干诱发电位（auditory brainstem evoked response）与扫描电子显微镜（scanning electron microscope）检查评估耳毒性。
结果：KR-12-a2对耐甲氧西林金黄色葡萄球菌的抑菌圈起始浓度为6.25 μg。KR-12-a2组与PBS组的听阈（hearing threshold）与鼓膜通气管置入前水平相近；而庆大霉素组的听阈出现升高，与PBS组或KR-12-a2组相比差异具有统计学意义（statistically significant differences）。扫描电子显微镜观察结果显示，KR-12-a2组的外毛细胞（outer hair cells）结构完整，而庆大霉素组的外毛细胞完全缺失。本实验中，局部应用KR-12-a2溶液未导致豚鼠出现听力损失或耳蜗损伤。
结论：本实验中，局部应用KR-12-a2溶液未导致豚鼠出现听力损失或耳蜗损伤。该KR-12-a2溶液可作为耳用滴剂（ototopical drops）用于治疗耐甲氧西林金黄色葡萄球菌耳漏；但仍需开展进一步评估，例如明确最优给药浓度与联合用药方案等。