Efficiency of resveratrol in the prevention and treatment of age-related hearing loss
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Age-related hearing loss (ARHL) is a major public health concern, which is characterized by gradual, progressive sensorineural hearing loss and deterioration of sound localization, with no effective treatment available to date. The aim of the present study was to evaluate the efficacy of resveratrol to prevent and treat ARHL. For this purpose, 32 male C57BL/6 mice were assigned to four groups: Early treatment, late treatment, control and sham control. The experiment lasted for 15 months. Treatment was started at three months of age in the early treatment group and at sixth months in the late treatment group. The auditory brainstem response test was performed once every three months. At the end of the study period, inducible nitric oxide synthase (iNOS), cyclooxygenase (COX)-2, NF-kappa B, Bcl-2, Bcl-xL, Bax, Bcl-2 homologous antagonist/killer (Bak), caspase-3 and caspase-9 levels in the cochlear tissues of the animals were analyzed by reverse transcription-quantitative PCR. Hearing thresholds of the mice in the early treatment group were better than those in the other groups (P<0.001) at the end of the study. However, hearing levels in the late treatment group were not significantly different from those in the control groups (P>0.05), although mean thresholds were lower. The threshold shift in the early treatment group was significantly lower at all frequencies when compared with those in the control groups (P<0.001). The mRNA expression levels of pro-apoptotic genes Bax and Bak were lower (P<0.05), anti-apoptotic genes Bcl-2 and Bcl-xL were higher (P<0.05), NF-kappa B, COX-2 and iNOS as genes that have a role in inflammation and caspase-3 and caspase-9 as genes with a vital role in apoptosis were lower (P<0.05) in the early treatment group when compared with the late treatment and control groups. These results suggested that resveratrol is effective in the prevention of ARHL, particularly when started prior to the beginning of hearing loss.