Brimonidine Therapy for Protection From Noise-Induced Hearing Loss.

Noise exposure is a known cause of hearing loss, and only a few effective preventive drugs are available. Therefore, in this study, we aimed to investigate the protective effects of brimonidine on noise-induced inner ear hearing impairment in mice and explore its underlying mechanisms and long-term outcomes. Mice were randomly divided into control, noise exposure, and brimonidine groups. A 62-week follow-up was conducted after noise exposure. Brimonidine inhibited the noise-induced increase in inner ear glutamate concentration and downregulated inflammatory factors and immunoglobulins. Brimonidine decreased glutaminase and VGLUT2/3 expression and reduced glutamate synthesis and vesicle transport without affecting its clearance, thereby decreasing glutamate excitotoxicity and protecting synapses and spiral ganglion neurons long term. Mice exposed to noise could temporarily restore their hearing thresholds; however, their auditory function in old age remained significantly worse than those that received brimonidine-mediated cochlear protection in youth. These findings highlight the importance of enhancing noise protection from an early age.