NRH attenuates age-related hearing loss by suppressing cochlear ferroptosis and cellular senescence via Sirt3 activation

BACKGROUND: Age-related hearing loss (ARHL) is a prevalent sensory disorder with significant clinical and social burdens, yet no FDA-approved pharmacological treatments are currently available. Emerging evidence implicates declined cellular NAD⁺ levels in the pathogenesis of age-related diseases, suggesting NAD⁺ metabolism as a potential therapeutic target. PURPOSE: In this study, we investigate the efficacy of Dihydronicotinamide riboside (NRH), a highly bioavailable NAD⁺ precursor, in mitigating ARHL. METHODS: C57BL/6 mice were used as animal model of ARHL and received oral administration of NRH (125 mg/kg) every other day. Then hearing thresholds were assessed and cochlear structure was evaluated. D-galactose (D-gal)-induced aging models were generated using organ explants and HEI-OC1 cells to investigate the protective effects of NRH treatment. Transcriptomic profiling and molecular docking characterized NRH's mechanism of action, while H&E staining confirmed its safety profile. Temporal NRH metabolism in organ explants was tracked using fluorophore-conjugated NRH. RESULTS: NRH administration ameliorated ARHL in C57BL/6 mice, as evidenced by improved auditory thresholds and elevated cochlear NAD⁺ levels. Treatment preserved cochlear hair cells, synapses, and auditory neurons. Mechanistically, NRH activated Sirt3, thereby inhibiting oxidative stress and lipid peroxidation via modulation of ferroptosis-related pathways, ultimately mitigating cochlear cellular senescence. NRH demonstrated a favorable safety profile and exhibited temporal distribution across distinct cochlear cell types. CONCLUSION: Our findings demonstrate that NRH mitigates ARHL in C57BL/6 mice, holding significant translational potential for ARHL treatment.