| Cisplatin (cis-diamrninedichoroplatinum, CDDP) is currently being used clinically as an effective antitumour agent against a variety of neoplasms, especially the cancer in the field of head and neck surgery. However, the use of higher dose of CDDP to affect greater antitumour activity is limited by the onset of side-effect, especially ototoxicity and nephrotoxicity. It is reported that the mechanisms of ototoxicity of CDDP are related to the drug accumulation in cochlear endolymph, imbalance of chemical composition in endolymph, Ca2+ disorder, disorder of energy metabolism, free radical damage and cells apoptosis. The prevention of CDDP-induced ototoxicity has become an important topic in clinical and basic research, but it has not introduced any simple and effective measures.The hearing trauma caused by high intensity noise is similar to ototoxicity of CDDP in hearing physiology, morphology and traumatic mechanism. It is reported that sound conditioning can reduce hearing damage morphologically and functionally in acoustic trauma, and the proposed mechanisms include the upregulation of endogenous antioxidants, increase of the number of NMDA receptors, changes of the expression of heat shock proteins (HSPs), calcium buffering systems and neurotrophic factors. In addition, it is reported that sound conditioning could suppress the apoptosis caused by high intensity noise. Because of the similarity between the hearing trauma caused by high intensity noise and ototoxicity of CDDP, we proposed that sound conditioning can provide protective effects against ototoxicity induced by CDDP. But there are no related reports yet. This experiment investigated the effect of sound conditioning on CDDP-induced ototoxicity in hearing electrophysiology, function and morphology, and studied the effects of reactive oxygen species(ROS), nitric oxide(NO) and cells apoptosis in this effect in order to provide pragmatic measures to prevent CDDP-induced ototoxicity and introduce some theoretical and experimentalevidences to prevent ototoxicity induced by CDDP. Statistical analysis was performed using ANOVA and Mann-Whitney U, depending on the type of data. P values below 0.05 were considered significant. Methods and Results:1. Experimental grouping and treatment of animalsHealthy male albino guinea pigs(weight 250g~350g), were divided randomly into four groups: (l)control group, the animals were administrated with saline only (8ml/kg b.w., iv); (2)sound conditioning group(SOU group), the animals were exposed to white noise at 85dB SPL, 5h/d, for 10 days, 3 days after the exposure, the animals were injected with saline (8ml/kg b.w., iv); (3) cisplatin group(CDDP group), the animals were injected with CDDP intravenously 8mg/kg b.w.(lmg/ml in saline); (4)sound conditioning +cisplatin group(SOU+CDDP group), the animals were exposed to white noise at 85dB SPL, 5h/d, for 10 days first, 3 days after the exposure, the animals were administrated with CDDP (8mg/kg b.w., iv). 3 days after administrating with CDDP or saline, animals of every group were euthanized by decapitation and their cochlear were quickly removed.2. The effect of sound conditioning against ototoxicity induced by CDDP in electrophysiologyHearing thresholds of auditory brainstem responses (ABRs) of all animals were measured before and after each treatment to evaluate hearing function. The hearing thresholds of guinea pigs in control group were stable. The thresholds (click and tone burst) of animals in SOU group changed little after treatment. The animals in CDDP group showed elevated ABRs thresholds, especially in click and high frequency tone burst(4 6 8kHz), compared with the thresholds in control animals (p<0.05). The thresholds (click and high frequency tone burst) of animals in SOU+CDDP group elevated a little but in no statistical significance (P>0.05), and their thresholds were lower significantly than the thresholds of animals in CDDP group (p<0.05).3. The effect of sound conditioning on hair cells trauma caused by CDDP Immediately after the animals were sacrificed, the cochlear were removed andprocessed for morphological examination of the sensorineural epithelium. Count thehair cells (HCs) and calculate the loss ratio in the basal turn. There was no significant cochlear HCs loss in control group and SOU group. The cochlea of the animals in CDDP group, however, showed obviously loss of the OHCs, especially in the third row of the basal turn. In SOU+CDDP group the loss of HCs was sporadic and mainly in the third row of the basal turn, but less markedly than loss of HCs in CDDP group.4. The effect of sound conditioning on cells apoptosis caused by CDDPThe apoptotic cell death in cochlea of guinea pigs in every group was detected via TUNEL method. In control group, the apoptotic labeling by TUNEL in spiral ganglion (SG) and organ of Corti was almost negative. There was sporadic positive TUNEL labeling in organ of Corti, and no positive labeling in SG The TUNEL labeling of cochlea in CDDP group, however, was much more than that of control group, especially in organ of Corti and sporadic positive labeling in SG There was a little positive labeling in SG and organ of Corti in SOU+CDDP group. The apoptotic labeling in SOU+CDDP group was more than that of control group but less than that of CDDP group. According to the localization and morphological character, the positive TUNEL cells in organ of Corti of the animals in every group were mainly outer hair cells and supporting cells, and little were inner hair cells.5. The effect of sound conditioning on changes in activity of SOD and content of MDA caused by CDDPImmediately after the animals were sacrificed, the cochlear were removed and made into tissue homogenate for examining the activity of SOD and the content of MDA. The activity of SOD of SOU group (212.83 ±20.79U/mgprot) was lower than that of control group(263.85±44.33U/mgprot, p<0.05), but the content of MDA (19.22 ± 1.79nmol/mgprot) of it was higher than control(12.57 + 1.45nmol/mgprot, p<0.05). Compared with control group and SOU group, the activity of SOD of CDDP group(169.18±33.82 U/mgprot, p<0.05) was markedly decreased and the content of MDA(35.85±3.70 nmol/mgprot, p<0.05) was significantly increased. The activity of SOD of SOU+CDDP group(218.17±29.55 U/mgprot) was evidently higher than that of CDDP group, but the content of MDA(19.06±1.98 nmol/mgprot) was lower than that of CDDP group(p<0.05); Compared with control, the activity of SOD decreased... |
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