Tauroursodeoxycholic acid attenuates cisplatin-induced ototoxicity by inhibiting the accumulation and aggregation of unfolded or misfolded proteins in the endoplasmic reticulum.

Cisplatin-induced ototoxicity is one of the important reasons that limit the drug's clinical application, and its mechanism has not been fully elucidated so far. The aim of this study was to explore the attenuate effect of tauroursodeoxycholic acid (TUDCA), a proteostasis promoter, on cisplatin-induced ototoxicity in vivo and in vitro, and to explore its possible mechanism. Auditory brainstem response (ABR) was measured to identify the attenuate effects of TUDCA administered subcutaneously [500 mg/kg/d × 3d, cisplatin: 4.6 mg/kg/d × 3d, intraperitoneal injection (i.p.)] or trans-tympanically (0.5 mg/mL, cisplatin: 12 mg/kg, i.p. with a pump) in Sprague-Dawley (SD) rats subjected to cisplatin-induced hearing loss. The cochlear explants of neonatal rats and OC1 auditory hair cell-like cell lines cultured in vitro were used to observe the number of apoptotic cells and the endoplasmic reticulum (ER) stress in the control, cisplatin (5 μM for 48 h for cochlear explants, 10 μM for 24 h for OC1 cells), and cisplatin + TUDCA (1 mM for 24 h for cochlear explants, 1.6 mM for 24 h for OC1 cells) groups. Differences in the expression of key proteins in the ER protein quality control (ERQC) system were detected. The changes in the attenuate effect of TUDCA on cisplatin-induced ototoxicity after down-regulating calreticulin (CRT), UDP-glucose ceramide glucosyltransferase-like 1 (UGGT1), and OS9 ER lectin (OS9) were also measured. The effect of TUDCA (10 mM) on stabilizing unfolded or misfolded proteins (UFP/MFP) was analyzed in a cell-free 0.2 % bovine serum albumin (BSA) aggregation system in vitro. Both the subcutaneous and trans-tympanic TUDCA administration alleviated cisplatin-induced increase in ABR thresholds in rats. TUDCA was able to reduce cisplatin-induced apoptosis and alleviate ER stress in cochlear explants and OC1 cells. Under the cisplatin treatment, the expression levels of CRT, UGGT1, and OS9 in the auditory hair cell increased, and the expression of total ubiquitinated proteins decreased. TUDCA attenuated the effect of cisplatin on UGGT1 and OS9, and recovered the protein ubiquitination levels. After down-regulating CRT, UGGT1, or OS9, the protective effect of TUDCA decreased. In the cell-free experimental system, TUDCA inhibited the aggregation of denatured BSA molecules. In summary, TUDCA can attenuate cisplatin-induced ototoxicity, possibly by inhibiting the accumulation and aggregation of UFP/MFP and the associated ER stress.