Therapeutic and protective effects of autologous serum in amikacin-induced ototoxicity

Objective:Possible therapeutic and protective benefits of intratympanic autologous serum application in amikacin-induced ototoxicity were investigated.Methods:Twenty-four guinea pigs were separated equally into two groups: therapeutic (group A) and protective (group B). Transient evoked otoacoustic emissions were recorded before and after autologous serum application. Apoptotic cells were identified in the organ of Corti, spiral limbus and spiral ganglion by the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (‘TUNEL’) method.Results:Transient evoked otoacoustic emission responses at 1, 1.4 and 2.8 kHz improved without significance after autologous serum application in group A (p> 0.05). A significantly protective effect of autologous serum was determined at 4 kHz in group B (p< 0.05). There were significantly fewer apoptotic cells at the spiral limbus in the therapeutic and protective groups compared to the control group (p< 0.05).Conclusion:Autologous serum may offer protection against ototoxicity-induced hearing loss, but it cannot restore hearing. Immunohistochemically, autologous serum significantly decreases activation of the intrinsic pathway of pro-apoptotic signalling in mesenchymal cells compared to neurons and neurosensory cells.

Location and function of the epithelial Na channel in the cochlea

In the cochlea, endolymph is a K-rich and Na-poor fluid. The purpose of the present study was to check the presence and to assess the role of epithelial Na channel (ENaC) in this organ. α-, β-, and γ-ENaC subunit mRNA, and proteins were detected in rat cochlea by RT-PCR and Western blot. α-ENaC subunit mRNA was localized by in situ hybridization in both epithelial (stria vascularis, spiral prominence, spiral limbus) and nonepithelial structures (spiral ligament, spiral ganglion). The α-ENaC-positive tissues were also positive for β-subunit mRNA (except spiral ganglion) or for γ-subunit mRNA (spiral limbus, spiral ligament, and spiral ganglion), but the signals of β- and γ-subunits were weaker than those observed for α-subunit. In vivo, the endocochlear potential was recorded in guinea pigs under normoxic and hypoxic conditions after endolymphatic perfusion of ENaC inhibitors (amiloride, benzamil) dissolved either in K-rich or Na-rich solutions. ENaC inhibitors altered the endocochlear potential when Na-rich but not when K-rich solutions were perfused. In conclusion, ENaC subunits are expressed in epithelial and nonepithelial cochlear structures. One of its functions is probably to maintain the low concentration of Na in endolymph.