The investigation of the effect of oleuropein on noise-induced hearing loss

Objective and Hypothesis In this study, it was aimed to investigate the possible protective effect of Oleuropein (OLE) compound, which is known to have antioxidant properties in noise induced hearing loss (NIHL) rat animal model. Materials and Methods Twenty-eight adult male albino rats included in the study were randomly assigned into four groups. Groups were designated as: Control serum physiological (SF) group (n = 7), the group which were not exposed to noise and administred equivalent volume of active substance solution 2 cc / kg / day SF. Control OLE (n = 7) group, with no noise exposure and 50 mg / kg / day OLE administration. Test SF (n = 7) group; the group that was exposed to noise and administered 2 cc / kg / day SF; and test OLE (n = 7) group, the group that was exposed to noise and OLE administered at 50 mg / kg / day. SF and OLE were administered via oral gavage to all rats. A total of 14 rats in the test group were subjected to noise at 120 dB SPL 4 kHz octave band for 4 hours. Hearing level measurements were made with auditory brainstem responses (ABR) and distortion product autoacoustic emission (DPOAE) tests at 4, 8, 12, 16 and 32 kHz frequencies. ABR and DPOAE tests were performed before the noise exposure and on the 1st, 7th and 10th days after the noise exposure. After the last hearing assesments, all rats were sacrificed on the 10th day. After sacrification, temporal bones of the rats were removed and the cochlea and spiral ganglion cells were evaluated by light microscopy using hematoxylin-eosin and TUNEL staining. 4Results ABR test revealed better hearing thresholds in the test OLE group at all frequencies compared to the test SF group. Statistical significance was observed at frequencies of 8, 12, 16 and 32 kHz (p <0.05). In the histopathological evaluations, less spiral ganglion cell damage was observed in the test OLE group compared to the test SF group. However, no statistically significant difference was found (p>0,05). Conclusion Oleuropein might be a useful antioxidant that can be used in noise induced hearing loss. However, additional research is required for confirmation of this protective effect.