Zinc deficiency triggers hearing loss by reducing ribbon synapses of inner hair cells in CBA/N mice.

Zinc plays a vital role in our metabolism, encompassing antioxidant regulation, immune response, and auditory function. Several studies have reported that zinc levels correlate with hearing loss. We have previously demonstrated that the auditory brainstem response (ABR) threshold increased in mice fed a zinc-deficient diet. However, the effects of zinc deficiency on hearing were not fully elucidated. The present study investigated whether zinc deficiency affects hearing in association with neuronal components or cochlear structures. CBA/N mice were fed a normal or zinc-deficient diet for 8 weeks and assessed for ABR and distortion product otoacoustic emissions (DPOAE). The cochlear sections were stained with hematoxylin and eosin solution. Also, we observed the expression of synaptic ribbons, neurofilaments, and alpha-synuclein (α-Syn). The 8-week zinc-deficient diet mice had an elevated ABR threshold but no changed DPOAE threshold or cochlear structures. A reduced number of synaptic ribbons of inner hair cells (IHCs) and impaired efferent nerve fibers were observed in the zinc-deficient diet mice. The number of outer hair cells (OHCs) and expression of α-Syn remained unchanged. Our results suggest that zinc-mediated hearing loss is associated with the loss of neuronal components of IHCs.

Prognostic Factors for Recovery from Sudden Sensorineural Hearing Loss: A Retrospective Study.

BACKGROUND AND OBJECTIVES: This study aimed to investigate prognostic factors in patients with idiopathic sudden sensorineural hearing loss (ISSNHL). SUBJECTS AND METHODS: From January 2007 to December 2011, a retrospective chart review identified 494 consecutive patients with ISSNHL. Demographic, audiometric, and clinical data were analyzed using a logistic regression test. RESULTS: Hearing recovery from ISSNHL was significantly associated with factors such as age, duration from onset of symptoms to commencement of treatment, severity of the initial pure tone threshold, and the treatment method. Intratympanic (IT) steroid administration alone showed a comparable efficiency to oral steroid administration with or without IT steroid injection. In patients who received IT steroid injection, the duration from onset to treatment, severity of initial hearing loss, and sequential IT steroid injection following systemic steroid administration were statistically associated with hearing improvement. CONCLUSIONS: Age, severity of initial pure tone threshold, duration from onset to treatment, initial speech discrimination, and initial pure tone threshold are statistically significant prognostic factors related to hearing improvement in ISSNHL. IT steroid injection as an initial single treatment is comparable to systemic oral steroid administration.