Brimonidine Protects Auditory Hair Cells from in vitro-Induced Toxicity of Gentamicin

Brimonidine, an alpha-2 adrenergic receptor (α 2 -AR) agonist, has neuroprotective effects in the visual system and in spiral ganglion neurons. Auditory hair cells (HCs) express all 3 α 2 -AR subtypes, but their roles in HCs remain unknown. This study investigated the effects of brimonidine on auditory HCs that were also exposed to gentamicin, which is toxic to HCs. Organ of Corti explants were exposed to gentamicin in the presence or absence of brimonidine, and the α 2 -AR protein expression levels and Erk1/2 and Akt phosphorylation levels were determined. Brimonidine had a protective effect on auditory HCs against gentamicin-induced toxicity that was blocked by yohimbine. This suggested that the protective effect of brimonidine on HCs was mediated by the α 2 -AR. None of the treatments altered α 2 -AR protein expression levels, and brimonidine did not significantly change the activation levels of the Erk1/2 and Akt proteins. These observations indicated that brimonidine, acting directly via α 2 -AR, protects HCs from gentamicin-induced toxicity. Therefore, brimonidine shows potential for preventing or treating sensorineural hearing loss.