Retinoic acid applied after noise exposure can recover the noise-induced hearing loss in mice

Conclusion. The early post-exposure treatment with All-trans retinoic acid (ATRA) can reduce hair cell loss and hearing deterioration in mice in which permanent threshold shift has been induced. Objective: One of the mechanism by which intense noise induces apoptosis of cochlea hair cells is the C-Jun NH2-terminal kinase (JNK) pathway. ATRA is a potent inhibitor of activator protein 1, a transcription factor of the JNK pathway. In this study we evaluated that the effect of post-exposure treatment of ATRA on noise-induced hearing loss and aimed to determine a time window for effective post-exposure treatment of ATRA. Methods. All mice were exposed to white noise for 3 h per day for three consecutive days and induced permanent threshold shift. The treatment groups fed with ATRA from 1 h, one day, two days, and three days after noise exposure for five days were compared with mice fed with same dosage of sesame oil. We measured the threshold shifts of hearing and survival rates of hair cells on the cytocochleogram. Results. Mice fed with ATRA beginning within two days after noise had less threshold shifts and more hair cell survivals than mice fed with sesame oil.