ABSTRACT
BACKGROUND AND OBJECTIVES: The study was designed to investigate the changes in the expression of hypoxia inducible factor-1alpha (HIF-1alpha) according to time after being exposed to noise trauma and find out the effect of HIF-1 alpha in the prevention of noiseinduced hearing loss by pre-treatment with cobalt chloride (CoCl2). SUBJECTS AND METHOD: BALB/c hybrid mice with 25 dB HL or less ABR were used in this study. In the study group, subjects were exposed to 120 dB SPL broad white band noise for 3 hours per day for 3 days. The changes in their hearing were documented before and after 1, 2, 3, 4, and 9 days of the first noise exposure. CoCl2 was injected into the peritoneum 2 hours prior to each noise exposure to see the effect of induced HIF-1alpha on noise-induced hearing loss. For the control, injection with distilled water was performed and hearing thresholds were measured in the same manner. Cochlea from each group was obtained in order to observe the morphological changes in the inner ear and the expression of the HIF-1alpha using immunohistochemial staining and immuno-fluorescein staining along with quantification of the hair cell loss. RESULTS: Mice exposed to the noise for 3 days, showed permanent threshold shift and the expression of HIF-1alpha was increased. When HIF-1alpha was induced by pre-treatment of CoCl2 prior to the noise exposure, however, hearing recovery was observed to some degree. And hair cell survival rate was also higher when treated with CoCl2 compared to the distilled water treated group. CONCLUSION: When pre-treated with CoCl2, inducing HIF-1alpha before the noise trauma, it allowed for a less stereocilia loss in the hair cells in the organ of Corti. HIF-1alpha may play an important role in the prevention of noise-induced hearing loss.