[Preliminary observation on the differential expression of metformin in preventing noise-induced hearing loss in inner ear protein group of rats]

Objective: To study the protective effects of metformin on noise-induced hearing loss (NIHL) and its differential protein omics expression profile. Methods: In January 2021, 39 male Wistar rats were randomly divided into control group, noise exposure group and metformin+noise exposure group, with 13 rats in each group. Rats in the noise exposure group and metformin+noise exposure group were continuously exposed to octave noise with sound pressure level of 120 dB (A) and center frequency of 8 kHz for 4 h. Rats in the metformin+noise exposure group were treated with 200 mg/kg/d metformin 3 d before noise exposure for a total of 7 d. Auditory brainstem response (ABR) was used to test the changes of hearing thresholds before noise exposure and 1, 4, 7 d after noise exposure in the right ear of rats in each group. Tandem mass tag (TMT) quantitative proteomics was used to identify and analyze the differentially expressed protein in the inner ear of rats in each group, and it was verified by immunofluorescence staining with frozen sections. Results: The click-ABR thresholds of right ear in the noise exposure group and metformin+noise exposure group were significantly higher than those in the control group 1, 4, 7 d after noise exposure (P<0.05) . The click-ABR threshold of right ear in the metformin+noise exposure group were significantly lower than that in the noise exposure group (P<0.05) . Compared with the noise exposure group, 1035 up-regulated proteins and 1145 down-regulated proteins were differentially expressed in the metformin+noise exposure group. GO enrichment analysis showed that the significantly differentially expressed proteins were mainly involved in binding, molecular function regulation, signal transduction, and other functions. Enrichment analysis of KEGG pathway revealed that the pathways for significant enrichment of differentially expressed proteins included phosphatidylinositol 3-kinase-protein kinase B (PI3K-Akt) signaling pathway, focal adhesion, diabetic cardiomyopathy, mitogen, and mitogen-activated protein kinase (MAPK) signaling pathway. Immunofluorescence experiments showed that compared with the noise exposure group, the fluorescence intensity of insulin-like growth factor 1 receptor (IGF1R) in the metformin+noise exposure group was increased, and the fluorescence intensity of eukaryotic translation initiation factor 4E binding protein 1 (eIF4EBP1) was decreased. Conclusion: Noise exposure can lead to an increase in rat hearing threshold, and metformin can improve noise-induced hearing threshold abnormalities through multiple pathways and biological processes.