Reduction of noise-induced hearing loss using L-NAC and salicylate in the chinchilla

The effects of a combination of two antioxidant compounds were studied in a chinchilla model of noise-induced hearing loss. After obtaining baseline threshold using inferior colliculus evoked potentials, chinchillas were exposed for 6 h to octave band noise centered at 4 kHz (105 dB SPL). Post-noise thresholds were obtained h after the noise exposure, and then animals received either saline or salicylate and N-L-acetylcysteine combination. Another group received antioxidant treatment 1 h prior to noise. Rearing was tested at 1, 2 and 3 weeks post-noise. Subsequently, the cochleae were harvested, and cytocochleograms were prepared. There was a 20-40 dB SPL threshold shift at 3 weeks for tested controls. Permanent threshold shifts (PTS) were significantly reduced similar to the pre-treatment group at 1 and 2 kHz (0-10 dB) but was intermediate between the control and pre-treatment groups at 4 and 8 kHz (23 dB). Animals pre-treated with antioxidant had a significant reduction in hair cell loss but those post-treated with antioxidant had no protection from hair cell loss. These findings demonstrate the feasibility of reduction of noise-induced hearing loss using clinically available antioxidant compounds. (C) 2000 Elsevier Science B.V. All rights reserved