The effect of the duration of treatment with antioxidants on age-related hearing loss

Background and aims: The effect of antioxidants depends on several factors, including the type, dose, timing, and treatment duration. Several studies have demonstrated that antioxidants can prevent age-related hearing loss (ARHL), however, a few studies have focussed on the role of factors influencing the effects of antioxidant therapy. This study aimed to investigate the effect of duration of treatment on ARHL using an herbal antioxidant, silymarin, in a D-galactose-induced ageing rat model. Method: 40 three-months-old Wistar rats were divided into four groups: a short-term silymarin-treated group that received 500 mg/kg/day D-galactose (8 consecutive weeks) +200 mg/kg/day silymarin (4 consecutive weeks), long-term silymarin-treated group received 500 mg/kg/day D-galactose (8 consecutive weeks)+ 200 mg/kg/day silymarin (8 consecutive weeks), placebo group received 500 mg/kg/day D-galactose + placebo (propylene glycol; 8 consecutive weeks), and control group received normal saline (8 consecutive weeks). Auditory Brainstem Response (ABR) was measured at 4, 8, 12, and 16 kHz frequencies before and after the intervention. Results: No significant differences were found in ABR absolute and inter-peak latencies between groups. In contrast, there was a significant difference in ABR threshold shift between the placebo and the long-term silymarin-treated groups at 4 and 16 kHz frequencies (p <= .05), but without a similar difference through comparison with the short-term silymarin-treated group (p > .05). Additionally, a significant decrease in ABR amplitude of PI and PII was observed in the placebo group at 4 kHz frequency compared to the long-term silymarin-treated group (p <= .05), but not to the short-term silymarin-treated group (p > .05). Conclusion: The present study results indicate that the duration of treatment with antioxidants influences the successful prevention and treatment of ARHL. Consequently, this factor must be considered in the antioxidant therapy of ARHL. However, further studies are required to fully evaluate the effects of optimal treatment duration with antioxidants on ARHL along with the other influencing factors.