Effects of vitamin A deficiency on age-related and noise-induced sensorineural hearing loss in mice

Abstract

Vitamin A deficiency (VAD) causes a variety of pathologic phenotypes such as skin differentiation, spermatogenesis, and immune system function in human and animal subjects. VAD has also been reported to induce hearing impairment, yet its underlying mechanism is still unclear. In the present study, I evaluated the effect of VAD on hearing function using a mouse model of VAD. The hearing ability was evaluated with auditory brainstem responses (ABR) in two mouse strains: ICR (albino type) and C57BL/6 (pigmented type). For each strain, mice were divided into two groups as follows: group 1 (VAD group) was fed a purified vitamin A-free diet from 7 days after pregnancy and group 2 (control group) was fed a normal diet. Hearing thresholds was measured by ABR from 3 weeks until 20 weeks after birth. After serum levels of retinoic acid in VAD group reached less than a half of those in control group, only albino VAD group showed significant increase in hearing thresholds, compared to those of other groups (albino control group and both groups of pigmented mice) (p<.05). When identifying the histopathology in albino mice, the results were closely correlated with the changes in hearing thresholds with aging. However, when noise was applied to the pigmented strain, pigmented VAD mice showed poorer recovery of auditory thresholds after noise exposure than pigmented control mice. In conclusion, hearing thresholds of VAD mice were impaired by aging and noise insult when compared to other groups, although cochlear melanocytes might play some protective roles in pigmented VAD mice. These results suggest that VAD may cause age-related hearing loss and also affect the recovery of noise-induced hearing loss in mice.