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.

Keywords: Aplicação tópica; KR-12-a2; Ototoxicidade; Ototoxicity; Peptídeo Anti-MRSA; Topical application; anti-MRSA peptide.

Figure 1

(A) The α-helical wheel diagrams for KR-12-a2. The positively charged and hydrophobic amino acids are represented using red and blue color, respectively. The line indicates the interface between the hydrophobic and the positively charged face. (B) Circular Dichroism (CD) spectra of the peptides in 10 mM sodium phosphate buffer, pH 7.2, and 30 mM Sodium Dodecyl Sulfate (SDS) micelles.

Figure 1

(A) The α-helical wheel diagrams for KR-12-a2. The positively charged and hydrophobic amino acids are represented using red and blue color, respectively. The line indicates the interface between the hydrophobic and the positively charged face. (B) Circular Dichroism (CD) spectra of the peptides in 10 mM sodium phosphate buffer, pH 7.2, and 30 mM Sodium Dodecyl Sulfate (SDS) micelles.

Figure 2

Inhibition zone test showing the antibacterial effect against MRSA. The size of the inhibition zone was dose-dependent.

Figure 3

Hearing is preserved after topical application of KR-12-a2 as well as PBS, but shows deterioration after GM application. The GM group shows significant differences compared to the PBS or the KR-12-a2 group. Click (p = 0.014), 4 kHz (p = 0.011), 8 kHz (p = 0.009), 16 kHz (p = 0.003), 32 kHz (p = 0.002). There are no significant differences among preoperative, PBS and KR-12-a2 groups.

Figure 4

(A) Scanning electron microscopic findings showing well-preserved hair cells in the KR-12-a2 group; total hair cell loss is observed in the GM group. (B) There are no differences between the PBS and KR-12-a2 groups except with respect to the gentamicin results.

Figure 4

(A) Scanning electron microscopic findings showing well-preserved hair cells in the KR-12-a2 group; total hair cell loss is observed in the GM group. (B) There are no differences between the PBS and KR-12-a2 groups except with respect to the gentamicin results.