Protective Effects Of Epigallocatechin-3-gallate Against Noise Trauma On Cochlea

Noise can cause hearing loss, which is irreversible.After noise exposure, a large amount of free radicals exists in the cochlea. As a result, excessive free radicals bring damage to the inner ear hair cells to undergo death. NO can be oxidized as peroxynitrite, and through further nitro, generating 3-nitrotyrosine.Green tea contains a large number of polyphenolic compounds, which has a strong antioxidant activity, and among them, Epigallocatechin gallate (EGCG) is the strongest one. With a powerful function of anti-inflammatory, anti-aging, anti-mutagenic, anti-cancer, clearing pharmacological effects of free radicals and nerve protection, it’s attracting more and more attentions from researchers. In this study, we injected EGCG in guinea pigs intraperitoneally before the noise exposure to study its protective effect on noise-induced hearing loss.1. Noise induced hearing loss and the protective effect of EGCGThe aim of this study was to assess EGCG protecting 120 dB SPL white noise-induced hearing loss.45 Guinea pigs were divided into three groups: EGCG+noise exposure group; normal saline+noise exposure group; and control group. For EGCG administration, the guinea pigs were given abdominal injection (25mg/1000g) 1 day before and 1 hour before noise exposure (120 dB SPL,4 h). For the control group, the guinea pigs received no noise exposure. The hearing function was detected by the auditory brainstem response (ABR) recording after noise exposure. We found that the ABR threshold of Normal control group was 22±2.74 dB SPL, while EGCG+noise exposure group was 52.00±9.03 dB SPL, and NS+noise exposure group was 71.00±4.18 dB SPL, and the two groups had statistical difference (P<0.01). 1,3,7 and 14 days after noise exposure, EGCG+noise exposure group and the saline+ noise exposure group had some degree of recovery, but the former had lower ABR thresholds (P<0.01). Using short pure tone (Tone burst) for stimulus, two groups were statistically different in 2k,4k,8k,16k frequency. This part suggests that pre-treatment with EGCG significantly reduced noise-induced hearing loss.2. Noise induced morphological changes of cochlea and the protective effect of EGCGThe aim of this study was to observe the noise-induced morphological changes of cochlea, explore the protective effect of EGCG. Guinea pigs were also divided into three groups. Using DAPI to staine nuclei, and phalloidin to staine cytoskeleton, Accounting outer hair cells,3-nitrotyrosine (3-NT) staining, outer hair cell motility protein (Prestin) staining, we show that counting the outer hair cells in 60 times confocal imaging microscope, the normal control group was 60.1±0.71, NS±noise exposure group was 43.5±2.39, EGCG±noise exposure group was 53.9±1.63. Differences between the two groups was statistically significant (P<0.05). IHC staining showed that, compared with the saline+noise exposure group, EGCG+noise exposure group’s outer hair cells are in better shape, and the quantity and morphology is better. Prestin is dyeing clear, 3-nitrotyrosine (3-NT) staining light. This part showed that preventive intraperitoneal injection of EGCG can reduce nitric oxide radicals within the cochlea, reducing the outer hair cell damage caused by noise.