Differential protein expression profiles in salicylate ototoxicity of the mouse cochlea

The purpose of this study was to investigate protein expression profiles of salicylate ototoxicity using proteomic analysis, and to identify whether salicylates induce apoptosis in organotypic culture of mouse cochlear cells. The adult mice were injected intraperitoneally with 400 mg/kg of sodium salicylate. Approximately 30 dB threshold shift was observed 3 h after the injection, and the hearing threshold returned to normal range within 3 days. Proteomic analysis of mouse cochlea was performed 3 h after salicylate injection, because this was the time to show maximal ototoxic effect in salicylate intoxication. Expression pattern of proteomic analysis at 3 h was compared with those of normal cochlea and cochlea 3 days after salicylate injection. Sixteen proteins were transiently up-regulated threefolds or more at 3 h after the injection compared with normal cochlea, and three proteins were down-regulated at 3 h. Similar protein expression profiles were also observed between normal and 3 days group. These up-regulated and down-regulated proteins at 3 h were analyzed by MALDI-TOF MS. The mRNA expressions of nine selected genes from 16 up-regulated protein profiles were also investigated by RT-PCR, and their expression levels at 3 h were found to be higher than those of normal cochlea. We also confirmed the ototoxicity of salicylate in organotypic culture of cochlear cells using MTT assay, Hoechst staining and DNA laddering assay in vitro, and found that salicylate decreased the viability of cells in a time and dose-dependent manner, and that induced apoptosis in organotypic culture of cochlear cells. This study demonstrated that some proteins can be related to salicylate ototoxicity, and provides basic information about candidate proteins which are related to pathologic changes in salicylate-induced ototoxicity.