Abstract
OBJECTIVES: Local administration of 3-nitropropionic acid (3-NP) to the inner ear induces sensorineural hearing loss. Several studies have shown the otoprotective effects of ginkgo biloba extract EGb 761. Moreover, EGb 761 has been reported to activate Sirtuin 1 (SIRT1). The present study was designed to investigate whether EGb 761 prevents 3-NP-induced sensorineural hearing loss and determine its effects on the expression of SIRT1. METHODS: Sprague Dawley rats were divided into four experimental groups: control group receiving vehicle of 3-NP, EGb group receiving EGb 761, 3-NP group receiving 3-NP, and EGb+3-NP group receiving EGb 761 and 3-NP. EGb 761 was given orally for 5 days. The 3-NP solution was injected into the tympanum 3 days after the start of EGb 761 administration. The auditory brainstem response was recorded before and after the injection. At 4 weeks after the administration of 3-NP or vehicle of 3-NP, cochleae were harvested, and hematoxylin and eosin staining and immunohistochemistry for SIRT1 antibody were performed. RESULTS: EGb+3-NP group showed significantly lower threshold shifts than 3-NP group. There was a significant preservation of type II fibrocytes and spiral ganglion cells in EGb+3-NP group than in 3-NP group. In EGb+3-NP group, there was a significantly greater number of SIRT1 immunopositive type II fibrocytes and spiral ganglion cells than in 3-NP group. Calculating the percentage of SIRT1 immunoreactive type II fibrocytes and spiral ganglion cells in viable type II fibrocytes and spiral ganglion cells, respectively, EGb+3-NP group showed significantly higher SIRT1 immunoreactive cells than 3-NP group. CONCLUSION: These results suggest that EGb 761 may prevent hearing loss induced by 3-NP in an acute ototoxic animal model, which appears to be related with SIRT1 expression.