Protective effect of idebenone on ethambutol-induced optic neuropathy in R28 cells and mice

Abstract

Ethambutol is an anti-tuberculosis medication that induces retinal ganglion cell injury in the visual system. Oxidative stress and mitochondrial dysfunction are widely accepted as possible pathogenic mechanisms of ethambutol-induced optic neuropathy. Idebenone, a Coenzyme Q-10 derivate, is a potent free radical scavenger with demonstrated neuroprotective effect in experimental models of Leber’s hereditary optic neuropathy, which shares common clinical features with ethambutol-induced optic neuropathy. The present study was designed to investigate whether idebenone could provide protective effect against ethambutol-induced optic neuropathy in R28 cell line and mice. The cultured R28 cell lines were pretreated with different dose of idebenone for 24h, followed by the challenge with 3mM ethambutol for 24h. Exposure of ethambutol caused the loss of cell viability and the ATP content with dose-dependent manner in R28 cell. Idebenone pretreatment had protective effect on cell survival and ATP contents in ethambutol induced neuronal death of R28 cells. However, we demonstrated that ethambutol exposure did not significantly elevate intracellular reactive oxygen species generation and mitochondria-derived superoxide production, and it had no effect on mitochondrial membrane potential. However, zinc accumulation in lysosome and microtubule associated protein 1 light chain 3 were increased with ethambutol treatment, which were efficiently attenuated by idebenone pretreatment. In mouse model, 200mg/kg ethambutol was injected intraperitoneally alternate day for 6 weeks and 200mg/kg idebenone was introduced with oral gavage. Idebenone had a slight protective effect of visual function in mouse model, which was tested by optomotor test. However, it failed to demonstrate a beneficial effect on ganglion cell structure by optical coherence tomography, and photopic negative response was not differ among groups. In conclusion, these results suggest that idebenone has a mild protective effect against ethambutol-induced neurotoxicity, and these beneficial effects of idebenone may be attributable to its roles on lysosomal zinc accumulation, not directly in preventing reactive oxygen species.