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

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.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.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.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.