Inhalation of Molecular Hydrogen, a Rescue Treatment for Noise-Induced Hearing Loss.

Abstract

Noise-induced hearing loss is closely linked to reactive oxygen species generation in the cochlea, yet effective systemic drug delivery to the inner ear remains clinically challenging. This animal study investigated whether a single 1-hour inhalation of 2% molecular hydrogen (H2), administered immediately after 2 hours of broadband noise exposure, could protect cochlear structures in guinea pigs. Animals were assigned to six groups and assessed immediately, at 1 week, or at 2 weeks post-exposure using frequency-specific auditory brainstem response (ABR) measurements. At the 2-week time point, H2-treated animals showed significantly lower ABR thresholds compared with air-treated controls, along with marked preservation of outer hair cells throughout the cochlea. Quantification of synaptophysin immunoreactivity indicated that H2 inhalation also protected synaptic structures of inner hair cells. Conversely, an elevated Iba1 signal in the stria vascularis suggested a heightened local inflammatory response in H2-treated animals. The authors note that repeated H2 inhalation sessions may yield greater benefit, and that translation to human clinical conditions requires further investigation.

Mechanism

H2 inhalation is proposed to selectively scavenge cochlear reactive oxygen species generated by noise exposure, thereby reducing oxidative damage to outer hair cells and inner hair cell synaptic structures and limiting auditory threshold shifts.