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BACKGROUND: To investigate the possible protective activity of oleuropein compound on noise-induced hearing loss in rats.METHODS: 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. RESULTS: Better hearing thresholds were achieved in the experimental oleuropein group compared to the experimental normal saline groupat 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.CONCLUSION: 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.KEYWORDS: Acoustic trauma, animal models, antioxidant, oleuropein, noise-induced hearing loss

Amaç ve HipotezBu çalışmamızda antioksidan özellikleri olduğu bilinen Oleuropein (OLE)bileşiğinin sıçanlarda oluşturulan gürültüye bağlı işitme kaybı (GBİK) modelindekiolası koruyucu etkinliğinin araştırılması amaçlandı.Gereç ve YöntemAraştırmaya dahil edilen 28 erişkin erkek albino sıçan rastgele dört grubaayrıldı. Kontrol serum fizyolojik (SF) (n=7) grubu; gürültü verilmeyen ve etkenmadde çözeltisi ile eş hacimde olacak şekilde 2 cc/kg/gün SF uygulanan grup,kontrol OLE (n=7) grubu; gürültü verilmeyen ve 50 mg/kg/gün OLE uygulanan grupolarak düzenlendi. Deney SF (n=7) grubu; gürültü verilen ve 2 cc/kg/gün SFuygulanan grup, deney OLE (n=7) grubu; gürültü verilen ve 50 mg/kg/gün OLEuygulanan grup olarak düzenlendi. Tüm sıçanlara SF ve OLE oral gavaj yoluylauygulandı.Deney grubundaki toplam 14 sıçana 120 dB SPL şiddetinde, 4 kHz oktavbantta 4 saat süre ile gürültü verildi. İşitme düzeyi ölçümleri 4, 8, 12, 16 ve 32 kHzfrekanslarında işitsel uyarılmış beyinsapı potansiyelleri (İUBP) ve distorsiyon ürünüotoakustik emisyon (DPOAE) testleri ile yapıldı. İUBP ve DPOAE testleri gürültüverilmesi öncesinde ve gürültü verilmesi sonrası 1, 7 ve 10. günde yapıldı.Son testler sonrası 10. günde tüm sıçanlar sakrifiye edildi. Sakrifikasyonunardından sıçanların temporal kemikleri çıkarılarak koklea ve spiral ganglion hücreleriışık mikroskobunda hematoksilen-eozin ve TUNEL boyama yöntemiyledeğerlendirildi.BulgularİUBP testi sonuçlarına göre deney OLE grubunda, deney SF grubuna kıyaslatüm frekanslarda daha iyi işitme eşikleri elde edildi. İstatistiksel anlamlılık ise 8, 12,16 ve 32 kHz frekanslarda görüldü (p0,05).SonuçElde edilen bulgulara göre OLE gürültüye bağlı işitme kaybındakullanılabilecek faydalı bir antioksidan olabilir. Ancak bu koruyucu etkininkanıtlanmasına yönelik ek araştırmalara ihtiyaç bulunmaktadır. Objective and HypothesisIn this study, it was aimed to investigate the possible protective effect ofOleuropein (OLE) compound, which is known to have antioxidant properties in noiseinduced hearing loss (NIHL) rat animal model.Materials and MethodsTwenty-eight adult male albino rats included in the study were randomlyassigned into four groups. Groups were designated as: Control serum physiological(SF) group (n = 7), the group which were not exposed to noise and administredequivalent 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 / daySF; and test OLE (n = 7) group, the group that was exposed to noise and OLEadministered at 50 mg / kg / day. SF and OLE were administered via oral gavage toall rats.A total of 14 rats in the test group were subjected to noise at 120 dB SPL4 kHz octave band for 4 hours. Hearing level measurements were made withauditory brainstem responses (ABR) and distortion product autoacoustic emission(DPOAE) tests at 4, 8, 12, 16 and 32 kHz frequencies. ABR and DPOAE tests wereperformed before the noise exposure and on the 1st, 7th and 10th days after thenoise 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 andspiral ganglion cells were evaluated by light microscopy using hematoxylin-eosinand TUNEL staining.4ResultsABR test revealed better hearing thresholds in the test OLE group at allfrequencies compared to the test SF group. Statistical significance was observed atfrequencies of 8, 12, 16 and 32 kHz (p 0,05).ConclusionOleuropein might be a useful antioxidant that can be used in noise inducedhearing loss. However, additional research is required for confirmation of thisprotective effect. 104