Effect of Quercetin on Recovery of Hearing Threshold in Noise-Induced HSP72 Model

Kim, Young Ho; Lim, Hyun Ho

Abstract

BACKGROUND AND OBJECTIVES
Heat shock proteins (HSPs) are a group of proteins that are preferentially expressed in many cell types when cells and organisms are exposed to various stresses. Their functions are not being fully clarified though HSPs are known to have a protective role against cellular injury. Quercetin, a bioflavonoid distributed widely in plants, has been reported to inhibit the stress response in heat-shocked cells. This study was undertaken to investigate the inhibitory effect of quercetin on HSP72 synthesis in rat cochlea and functional auditory threshold change after the intense noise overstimulation. MATERIALS AND METHOD: Sprague-Dawley rats treated with flavonoid were exposed to the intense broad band noise for three hours. Control animals were exposed to the same noise level. Immunocytochemistry of cochlear tissues was performed to detect HSP72 expression six hours after noise exposure. Also, auditory brainstem responses (ABRs) were recorded before and after noise exposure in each group.
RESULTS
In animals exposed to noise for 3 hours without injection of quercetin, most of the outer hair cells (OHCs) of the cochlear second turn showed HSP72 immunoreactivity. However, animals exposed to noise for 3 hours with injection of quercetin revealed minimal HSP72 immunoreactivity in the OHCs. Results of ABRs of all groups showed about 40 dB threshold shifts immediately after the noise exposure. While control animals showed rapid recovery of the auditory threshold shifts after the ending of noise exposure and returned to the preexposure level by 24 hours, animals treated with quercetin showed delayed onset of recovery in the auditory threshold shifts after the ending of noise exposure and returned to the preexposure level by 48 hours.
CONCLUSION
Quercetin may have an inhibitory effect on the HSP synthesis and expression of HSP72 and the outer hair cells may play a role in the protection of auditory function against acoustic trauma and rapid functional restoration of hearing.