Protection against acoustic trauma by direct application of D-methionine to the inner ear

Abstract

Conclusion: The findings from this study extend the use of the local application of D-methionine (D-met) to protect against acoustic trauma and demonstrate that D-met slowly diffuses from the perilymph. Objectives: The objectives of the study were to determine the effect of D-met on auditory function and morphology after acoustic trauma and to measure the concentration of D-met in perilymph. Methods: Auditory thresholds were determine before, immediately after, and 24 h after acoustic trauma. Cochleae were analyzed using immunocytochemistry for c-Fos, TUJI, and cytochrome c. The concentration of D-met was determined from perilymph. Results: Protection against acoustic trauma (immediately and 24 h post trauma) on auditory brainstem thresholds was found at a time when the concentration of D-met in perilymph showed a fivefold increase above basal levels. The local application of D-met to the guinea pig cochlea results in elevated D-met concentrations that are maintained in the perilymph for at least 24 h.

Keywords::

• Amino acids
• auditory
• cochlea
• HPLC
• hearing loss
• noise trauma
• perilymph

Acknowledgments

This work was supported by grants from the Swedish Research Council, Tysta Skolan, Hörselforskingsfonden, Karolinska Institutet, and the Knut and Alice Wallenberg Foundation (KAW2008.0149). The authors would like to thank Agneta Viberg for her expert technical help in this project.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.