The Price of Immune Responses and the Role of Vitamin D in the Inner Ear

Abstract

Objective: In this review the authors discuss evidence from the literature concerning vitamin D and temporal bone diseases (benign paroxysmal positional vertigo [BPPV], Menière's disease [MD], vestibular neuritis, idiopathic facial paralysis, idiopathic acute hearing loss). Common features shared by Menière's disease, glaucoma, and the possible influence by vitamin D are briefly discussed.

Data sources, study selection: Publications from 1970 until recent times have been reviewed according to a keyword search (see above) in PubMed.

Conclusions: MD, BPPV, vestibular neuritis, idiopathic facial paralysis, idiopathic acute hearing loss may all have several etiological factors, but a common feature of the current theories is that an initial viral infection and a subsequent autoimmune/autoinflammatory reaction might be involved. Additionally, in some of these entities varying degrees of demyelination have been documented. Given the immunomodulatory effect of vitamin D, we postulate that it may play a role in suppressing an eventual postviral autoimmune reaction. This beneficial effect may be enhanced by the antioxidative activity of vitamin D and its potential in stabilizing endothelial cells. The association of vitamin D deficiency with demyelination has already been established in other entities such as multiple sclerosis and experimental autoimmune encephalitis. Mice without vitamin D receptor show degenerative features in inner ear ganglia, hair cells, as well as otoconia. The authors suggest further studies concerning the role of vitamin D deficiency in diseases of the temporal bone. Additionally, the possible presence and degree of demyelination in these entities will have to be elucidated more systematically in the future.

Figure 1.

Phenotype of vitamin D receptor knockout mouse (KO) compared to wildtype littermate (WT: wild type at the age of 4.5 (top) and 8.5 (bottom) months. (Reprinted from (77) with permission from Elsevier).

Figure 2.

Effects of vitamin D receptor (Vdr) deletion in the vestibule. A-D: tissue sections were stained with an antibody against calretinin (green). Nuclei of cells were stained with DAPI (blue). The intensity of calretinin signals is reduced in the ganglion (B) and hair cells (D) of Vdr null mice as compared with age-matched wildtype controls (C57Bl/6J, labelled as C57) in A and C, respectively. Arrowheads in C-D denote hair cells, and arrows point to supporting cells. E-H: scanning electron micrographs of otoconia in C57 (E, G) and Vdr null mice (F, H) show degenerative features of otoconia in both the utricle and saccule of the Vdr null mice, such as fissure (arrows in F), fusion (arrowhead in H) and smaller particles (hollow arrowhead in H).

Figure 3.

Abnormal formation and/or loss of hair cells in the cochlea of Vdr null mice.

Figure 4.

Hypothetical mechanisms underlying the effects of vitamin D in the inner ear.