Protective role of edaravone against neomycin‐induced ototoxicity in zebrafish

Abstract

Aminoglycosides such as neomycin are one of the most commonly prescribed types of antibiotics worldwide. However, these drugs appear to generate free radicals within the inner ear, which can result in permanent hearing loss. We evaluated the effects of edaravone, a neuroprotective agent, on neomycin-induced ototoxicity in transgenic zebrafish. The 5-day post fertilization (dpf) zebrafish larvae were exposed to 125 μM neomycin and various concentrations of edaravone for 1 h. Hair cell survival was calculated as average numbers of the hair cells in the control group, which was not exposed to neomycin. Ultrastructural changes were evaluated using a scanning electron microscope (SEM) and transmission electron microscope (TEM). Edaravone protected against neomycin-induced hair cell loss in the neuromasts (1000 μM: 11.6 ± 1.1 cells, neomycin only: 5.5 ± 0.5 cells; n = 10, P<0.05) and decreased the TUNEL reaction for detecting apoptosis. In ultrastructural analysis, structures of mitochondria and hair cells within neuromasts were preserved in zebrafish exposed to 125 μM neomycin and 1000 μM edaravone for 1 h. Edaravone protected against neomycin-induced hair cell loss by preventing apoptosis.

Sodium Selenite Acts as an Otoprotectant against Neomycin-Induced Hair Cell Damage in a Zebrafish Model

“…Sodium selenite (Selenase; sodium selenite pentahydrate 1.66 mg/10 ml) was purchased from Biosyn Arzneimittel GmbH (Fellbach, Stuttgart, Germany). We previously reported that neuromasts treated with 125 μM neomycin for 1 h exhibited a viability of 50%, thus a dose of 125 μM neomycin was chosen as an adequate experimental concentration for the current study [ 28 ].…”

“…The larvae were then washed with the embryo medium three times. Zebrafish larvae were anesthetized using tricaine (3-aminobenzoic acid 0.4 g/ethyl ester; 100 mL; pH 7, adjusted using Tris buffer) for 5 min as described elsewhere [ 28 , 29 ]. The zebrafish were mounted using methylcellulose on a depression slide for evaluation under a fluorescence microscope.…”

“…Hair cells within neuromasts of the supraorbital (SO1 and SO2), otic (O1) and occipital (OC1) were examined [ 28 , 29 , 31 ]. The total numbers of hair cells of four neuromasts (SO1, SO2, O1, and OC1) were counted in each zebrafish under all experimental and control conditions (n = 10 fish per treatment) by using a fluorescence microscope (LSM5 PASCAL; Carl Zeiss, Germany).…”

“…Thereafter, they were incubated with 50 μL of TUNEL reaction mixture (TdT and fluorescein–dUTP) at 37°C for 60 min in a humid atmosphere. The TUNEL intensity within four neuromasts (SO1, SO2, O1, and OC1) of the transgenic zebrafish was examined under a fluorescence microscope (AxioCam MRc5, Carl Zeiss) [ 28 , 32 ]. The TUNEL-positive cells were counted per each neuromast and the average number was compared among positive (125 μM neomycin) control group, co-treated group with 125 μM neomycin 500 μM sodium selenite, and negative control group (n = 10 fish per treatment).…”

Survival of auditory hair cells

“…Zebrafish are a robust model for investigating ototoxicity and regenerative mechanisms. In this model, edaravone, a potent free radical scavenger, attenuates apoptosis and approximately doubled the number of surviving hair cells when administered concurrently with ototoxic levels of neomycin or cisplatin (Hong et al, 2013; Choi et al, 2014b). Similarly, trimetazidine, an anti- ischemic agent typically used to treat angina pectoris, is also known to reduce oxygen-derived free radicals and exhibited a three-fold attenuation of neomycin-induced hair cell loss in zebrafish (Chang et al, 2013).…”