Yamashita Hiroshi

This study investigated the potential of adalimumab (ADA), a monoclonal antibody targeting TNF-alfa, to protect the inner ear from intense sound exposure, given that inflammatory cytokines, including TNF-alfa, are linked to hearing loss in acoustic disorders. In this study, adalimumab was administered to mice, and its effect on the inner ear was assessed. We examined the translocation of ADA to the inner ear and its ototoxicity and impact on acoustic exposure. The results showed that adalimumab partially reached the cochlea after administration but increased the susceptibility to acoustic exposure, resulting in higher hair cell loss in the inner ear. While TNF-alfa had been considered a potential therapeutic target, the results suggested that excessive TNF-alfa suppression could harm the inner ear. We acknowledged some limitations, such as the use of adalimumab instead of an anti-mouse TNF-alfa antibody and the need to explore the suppression of other cytokines for better inner ear protection. In conclusion, adalimumab administration was found to increase the inner earʼs susceptibility to acoustic exposure, potentially leading to more significant hair cell damage, possibly due to excessive TNF-alfa suppression

Vestibular hair cells are susceptible to damage from various stimuli such as infections, ischemia, and certain therapeutic drugs, including aminoglycoside antibiotics and the antineoplastic agent cisplatin. In mammals, damage to the vestibular hair cells is permanent. This study aimed to evaluate the protective effects of nobiletin (NOB) against aminoglycoside-induced hair cell death using utricles collected from adult mice. The utricles removed from CBA/N mice were assigned to eight groups according to the dose of NOB and the administration or not of neomycin. Hair cells in the utricles were counted by double labeling with calmodulin and calbindin. NOB inhibited hair cell death in utricles exposed to neomycin. The protective effect of NOB on hair cells in the utricles was also suggested to have resulted from the inhibition of the production and accumulation of 4-hydroxy-2-nonenal, the final product of lipid peroxide aldehyde. NOB suppressed neomycin-induced hair cell death. The principle of hair cell protection from aminoglycoside-induced hair cell death suggests that NOB inhibits reactive oxygen species formation in the utricles exposed to neomycin.

Benign paroxysmal positional vertigo (BPPV) is the most common vertigo disease and is more likely to occur in perimenopausal women, suggesting an association with osteoporosis. Since otoconia are primarily composed of calcium carbonate, abnormal calcium metabolism may lead to otoconia dislocation. However, the detailed mechanism is currently unknown. In this study, we investigated the effects of drugs (cadmium and dexamethasone) that cause abnormal calcium metabolism on otolith formation in zebrafish larvae. Here, otolith size was clearly reduced in the cadmium group, and the calcium content of the larvae was also markedly reduced. In contrast, in the dexamethasone group, which also had a lower calcium content than the control group, otolith size increased. Our results suggest that, as in bone, calcium metabolism influences the repeated dissolution and recrystallization of otoliths and maintains homeostasis in response to calcium concentrations in the endolymphatic fluid.