Prevention of impulse noise-induced hearing loss with antioxidants.
CONCLUSIONS
These findings indicate a strong protective effect of ALCAR and NAC on impulse noise-induced cochlear damage, and suggest the feasibility of using clinically available antioxidant compounds to protect the ear from acute acoustic injury.


OBJECTIVE
Reactive oxygen species have been shown to play a significant role in noise-induced hearing loss. In the current study, the protective effects of two antioxidants, acetyl-L-carnitine (ALCAR) and N-L-acetylcysteine (NAC), were investigated in a chinchilla model of hearing loss resulting from impulse noise. It was hypothesized that pre- and post-treatment with these antioxidants would ameliorate the effects of impulse noise compared to saline-treated controls.


METHODS
Eighteen animals were randomly assigned to 1 of 3 groups and exposed to impulse noise at a level of 155 dB peak SPL for 150 repetitions. ALCAR or NAC were administered twice daily (b.i.d.) for 2 days and 1 h prior to and 1 h following noise exposure, and then b.i.d. for the following 2 days. For the control group, saline was injected at the same time points. Auditory brainstem responses (ABRs) were recorded. Cochlear surface preparations were made to obtain cytocochleograms.


RESULTS
Three weeks after exposure, permanent threshold shifts for the experimental groups were significantly reduced to approximately = 10-30 dB less than that for the control group (p < 0.01). Less hair cell loss was also observed in the ALCAR and NAC groups than in the control group.
Kopke
Richard
R
Hough Ear Institute, Oklahoma City, Oklahoma 73112, USA. rickkopke@swbell.net
Bielefeld
Eric
E
Liu
Jianzhong
J
Zheng
Jiefu
J
Jackson
Ronald
R
Henderson
Donald
D
Coleman
John K M
JK
D000108:Acetylcarnitine / Q000494:pharmacology*; D000111:Acetylcysteine / Q000494:pharmacology*; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D002682:Chinchilla; D004195:Disease Models, Animal; D016057:Evoked Potentials, Auditory, Brain Stem / Q000187:drug effects; D005260:Female; D006198:Hair Cells, Auditory / Q000187:drug effects / Q000473:pathology; D006317:Hearing Loss, Noise-Induced / Q000517:prevention & control*; D020127:Recovery of Function / Q000187:drug effects
D000975:Antioxidants; D000108:Acetylcarnitine; D000111:Acetylcysteine