Protective Effect Of Melatonin Against Radiation-induced Cochlear Damage In Balb/c Mice

Background and purposeThe nasopharyngeal carcinoma(NPC)is one of the most common malignant tumors in China,especially in Guangdong.Most of them are low differentiated squamous cell carcinoma.Radiotherapy is a use of ionizing radiation and biological interactions,produce free radicals,and against all kinds of cells that lead to lipid peroxidation damage of the cell membrane,promote a treatment of tissue damage,it has no obvious targeted therapeutic target,exposure were not spared.Radiation field radiotherapy includes the middle and inner ear and the auditory nerve and brainstem tissues,can occur with varying degrees of damage.In animal experiments,it was found that the inner ear tissues,especially the outer hair cells of the cochlea,were obviously damaged after irradiation.Melatonin is an endogenous compound the pineal gland,In 1993,it was identified as a free radical scavenger,has potent antioxidant effect and has protective effect on radiation important free radicals caused by multiple organ damage in this study through the preparation of radiation induced sensorineural hearing loss and radiation before intraperitoneal injection melatonin pretreatment mice model,and set two time,three expression changes were observed on the morphology and function of mouse cochlear outer hair cells of prestin protein and mRNA,melatonin on whether prevention of radioactive sensorineural hearing loss,hope hearing system for the prevention and treatment of complications caused by radiotherapy of nasopharyngeal carcinoma and provide the basis.Methods4-week-old male Balb/c mice were randomly divided into 6 groups,as follows:the control group;the 5mg/kg melatonin group received melatonin(5mg/kg i.p.);the 50mg/kg melatonin group received melatonin(50mg/kg i.p.);a 5mg/kg melatonin+radiotherapy group received 16Gy irradiation and melatonin(5mg/kg i.p.)30 min later;a 50mg/kg melatonin+radiotherapy group received 16 Gy irradiation and melatonin(50mg/kg i.p.)30 min later;and the radiotherapy group received 16 Gy irradiation only.Each test group was randomly divided into two groups,and auditory brainstem response(ABR)?distortion product otoacoustic emissions(DPOAEs)?histopathologic studies(HE)?prestin protein immunostained?prestin mRNA qPCR?western blot were performed on the 3rd and 7th days after exposure to 16 Gy radiation.All statistical tests and graphics were created using SPSS 19.0.Comparisons of groups used a one-way Kruskal-Wallis analysis of variance(ANOVA)and the post-ANOVA Tukey-B test.A P<0.05 was the criterion for statistical significance.Results1.ABR showed that response thresholds were significantly increased and wave I latencies were extended after radiotherapy,different doses of melatonin+ radiotherapy group were also affected by the changes,but the range of increased and extended were lower and the difference was statistically significantthe(P<0.05).2.DPOAE showed that the radiotherapy-induced hearing loss occurred at frequencies of 8-12kHz.The injury was aggravated with the extension of time,and the hearing loss was significantly reduced in the melatonin+radiotherapy groups compared with the radiotherapy group(P<0.05).There were significant differences between the two melatonin+radiotherapy groups(P<0.05).3.Based on histopathologic studies,the basement membrane of the cochlea was distorted and broken,the outer hair cytoplasm was swollen with nuclear condensation or loss,and the structure of the vascular stria was occasionally destroyed in the radiotherapy group.The pathologic changes of the inner ear cells were markedly reduced in both melatonin+radiotherapy groups.4.QPCR showed that the expression of prestin protein mRNA was up-regulated after radiotherapy(P<0.05),while the expression of prestin protein mRNA was significantly decreased in the melatonin+radiotherapy groups(P<0.05);there were significant differences between the two pre-treatment groups(P<0.05).5.Immunostained and WB showed that prestin protein mainly distributed in lateral membrane above the outer hair cell nucleus.Compared with control group,the expression of prestin protein in the inner ear was up-regulated in radiotherapy group,the difference was statistically significant(P<0.05),however,different doses of melatonin+radiotherapy can reduce the abnormal expression of prestin after radiotherapy(P<0.05),and large dose melatonin+radiotherapy was more significant than little,the difference was statistically significant(P<0.05).Conclusions1.Melatonin is protective against radiation-induced cochlear damage by reducing damage to outer hair cells and decreasing the abnormal expression of prestin protein mRNA.2.The prestin protein of cochlea is mainly distributed in the lateral membrane above the outer hair cell nucleus,and melatonin can control the abnormal expression of prestin protein induced by radiotherapy,which is related to dose.