Oleuropein Effect on Noise-Induced Hearing Loss

To investigate the possible protective activity of oleuropein compound on noise-induced hearing loss in rats.

Twenty-eight adult male albino rats were divided into 4 groups. Control normal saline (n=7) group was kept noise-free. Control oleuropein group (n=7) group was kept noise-free and was administered with 50 mg/kg/day oleuropein. The experimental normal saline (n=7) group was subjected to noise. The experimental oleuropein (n=7) group was subjected to noise and was administered with 50 mg/kg/day oleuropein. The experimental groups were subjected to 4 kHz octave noise with a frequency of 120 dB Sound Pressure Level (SPL) for 4 hours. Hearing level measurements were performed with auditory brainstem response and distortion-product otoacoustic emission tests before and after the 1st, 7th, and 10th day of the noise exposure. On the 10th day, rats were sacrificed. The temporal bones of the rats were removed and the cochlea and spiral ganglion cells were evaluated using hematoxylin-eosin staining under light microscopy.

Better hearing thresholds were achieved in the experimental oleuropein group compared to the experimental normal saline group at 8 kHz, 12 kHz, 16 kHz, and 32 kHz frequencies (P < .05). Although no statistically significant difference was found between the groups, in the experimental normal saline group, the percentage of damaged spiral ganglion cells was higher than the experimental oleuropein group.

Our findings suggest that oleuropein may have a partial protective effect against noise-related hearing loss. However, further research with higher doses is needed to justify this protective effect.