Abstract:

Objective To investigate the therapeutic effect of total flavonoids of Ginkgo biloba on secretory otitis media in rats after occupational noise exposure and its influence on the toll-like receptor 9（TLR9）-erythroid cell 2-related factor 2（Nrf2） signaling pathway in the cochlea，in order to elucidate the pathological mechanism of occupational noise exposure on secretory otitis media and provide reference for the development of new drugs for the treatment of secretory otitis media after noise exposure. Methods Animal experiments were conducted from February to June 2024，with 40 Wistar rats divided into a normal control group，a model control group，and a low-dose and high-dose group of total flavonoids of Ginkgo biloba. Except for the normal control group，the rats in the other groups were exposed to 10 kHz octave noise at 100 dB sound pressure level（SPL） to establish the secretory otitis media model after noise exposure. After that，the drug groups were given corresponding drug interventions，and the normal control group and the model control group were given an equal volume of normal saline. The treatment period was 2 weeks. After the treatment，the auditory brainstem response（ABR） threshold level，interleukin-6（IL-6），tumor necrosis factor-α（TNF-α），active oxygen（ROS），and malondialdehyde（MDA） levels in the cochlear tissue of the rats were measured，and the mRNA protein levels of TLR9 and Nrf2 in the cochlear tissue were detected by real-time fluorescence reverse transcription and Western blotting. Results The levels of ABR and IL-6，TNF-α，ROS and MDA in cochlear tissue in model control group were increased to （90.04±3.23）dBSPL，（687.21±53.21）pg/mL，（459.56±40.00）pg/mL，（841.20±65.22）U/mg and （925.32±85.25）nmol/mg，respectively，which were significantly higher than those in the normal control group，and the differences were statistically significant（all P<0.05）. However，those in the high-dose group of Ginkgo flavonoids were significantly decreased to （114.53±2.18）dBSPL，（232.25±30.22） pg/mL，（208.25±23.33）pg/mL，（426.39±38.54）U/mg and（469.55±44.94）nmol/mg，the differences were statistically significant （all P<0.05），and the regulatory effect of the high-dose group was significantly better than that of the low-dose group，the differences were statistically significant（all P<0.05）. Noise exposure significantly upregulated the expression of TLR9 mRNA（3.19±0.53 vs 0.38±0.07） and protein（1.25±0.12 vs 0.12±0.02） in the cochlea，significantly higher than the normal control group；Simultaneously inhibited the levels of Nrf2 mRNA（0.47±0.09 vs 3.38±0.62） and protein（0.20±0.03 vs 1.25±0.08），significantly lower than the normal control group，with statistically significant differences（all P<0.05）. After intervention with total flavonoids from Ginkgo biloba，the mRNA and protein levels of TLR9 in the high-dose group decreased to 1.63±0.29 and 0.56±0.04，respectively，while the mRNA and protein levels of Nrf2 increased to 2.63±0.44 and 0.86±0.07，respectively，with statistically significant differences（all P<0.05）. Moreover，the regulatory effect of the high-dose group was significantly better than that of the low-dose group，and the differences were statistically significant（all P<0.05）. Conclusion Ginkgo total flavonoids can significantly improve hearing loss caused by noise exposure，reduce pathological damage to the cochlea and middle ear，inhibit inflammatory response，and enhance anti-oxidative stress ability. The mechanism is that ginkgo total flavonoids block TLR9 expression and then activate Nrf2 expression.

Key words: Ginkgo total flavonoids, Noise, Secretory otitis media, Toll-like receptor 4, Erythroid 2-related factor 2