Dose and time-dependent protection of the antioxidant N-L-acetylcysteine against impulse noise trauma.

Noise-induced hearing loss is one of the most common causes of hearing disability, and at present there is no effective biological protection or cure. Firearms and some industrial equipment can generate very high levels of impulse noise, which is known to cause sensorineural hearing loss. It has been shown that antioxidants such as N-L-acetylcysteine (NAC) can protect the inner ear from oxidative damage. The present study investigates whether NAC (i.p.) can protect the cochlea from impulse noise trauma. Rats were exposed to 50 noise pulses at 160 dB SPL peak value. Electrophysiological hearing thresholds were assessed with auditory brainstem response (ABR) up to 4 weeks after noise exposure. Animals exposed to impulse noise, without treatment of NAC, had larger threshold shifts in the frequency range 4-40 kHz than animals injected with NAC. Hair cell loss was significantly reduced using a schedule of three NAC injections in the rats. These results suggest that NAC can partially protect the cochlea against impulse noise trauma.