Therapeutic potential of Cuscutae Semen and Rehmanniae Radix Preparata in age-related central hearing loss associated with Gad1 regulation

초록

Ethnopharmacological relevance: Cuscutae Semen and Rehmanniae Radix Preparata have traditionally been prescribed in East Asian medicine for auditory disorders associated with aging-related kidney deficiency, as documented in classical texts including Mingyi Bielu, Bencao Gangmu, Donguibogam, and Bangyakhappyeon. However, their relevance to age-related hearing loss (ARHL) and underlying mechanisms remains unclear. Aim of the study: This study aimed to evaluate the protective effects of a combined extract of Cuscutae Semen and Rehmanniae Radix Preparata (TS) against ARHL, focusing on its effects on GABAergic signaling and central auditory gain. Materials and methods: In vivo experiments were conducted in naturally aged C57BL/6N mice, and in vitro validation was performed using HEI-OC1 auditory cells treated with 3-mercaptopropionic acid (3-MPA), a GAD inhibitor. Auditory function was assessed by auditory brainstem response (ABR) and late latency response (LLR). Molecular and biochemical analyses included Gad1 mRNA, GAD67 protein, and glutamate/GABA ratio in the auditory thalamus. Results: Aging was associated with progressive reductions in Gad1 expression, GAD67 protein, and GABA levels, accompanied by increased glutamate/GABA ratio and elevated central gain. TS administration restored GABAergic markers, normalized neurotransmitter balance, and improved ABR responses while reducing central gain. In HEI-OC1 cells, TS alleviated 3-MPA-induced cytotoxicity and preserved Gad1/GAD67 expression, and valproic acid served as a positive control confirming the GABAergic mechanism. Conclusions: TS exerted protective effects on ARHL, which were associated with restoration of GABAergic function and attenuation of central gain dysregulation. These findings support the ethnopharmacological use of Cuscutae Semen and Rehmanniae Radix Preparata in auditory disorders and highlight their therapeutic potential for age-related neurodegenerative conditions.

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