Isoliquiritigenin attenuates cisplatin-induced hearing loss and ototoxicity by activating the Keap1-Nrf2-ARE pathway

Cisplatin-induced hearing loss (CIHL), a major dose-limiting toxicity of cisplatin, is primarily caused by oxidative stress and apoptosis in cochlear hair cells. This study aims to investigate the otoprotective effects of Isoliquiritigenin (ISL, a natural Nrf2 agonist) on CIHL and to elucidate the underlying anti-CIHL mechanism(s) of ISL. Initially, ISL was identified as a natural Nrf2 agonist from a phytochemical library using a luciferase reporter gene system. The otoprotective effects of ISL were then investigated in HEI-OC1 cells, cochlear explants, and in cisplatin-induced ototoxicity murine models. In cisplatin-induced ototoxicity mice, ISL markedly restored full-frequency auditory brainstem response (ABR) thresholds and attenuated cisplatin-induced hair cell loss in the cochlea. In HEI-OC1 cells and cochlear explants, ISL significantly attenuated cisplatin-triggered reactive oxygen species (ROS) overproduction, mitochondrial dysfunction, and hair cell apoptosis. Mechanistically, ISL covalently modify two critical cysteine residues (Cys226 and Cys288) of KEAP1, which subsequently stabilized Nrf2 and upregulated the expression of downstream antioxidant proteins including NAD(P)H quinone oxidoreductase 1 (NQO1), heme oxygenase-1 (HO-1) and superoxide Dismutase (SOD). Collectively, our findings clearly demonstrate that ISL significantly attenuates cisplatin-induced hearing loss (CIHL) by activating the Keap1-Nrf2-ARE signaling via covalent modifying two key cysteine residues on KEAP1.