The Protective Effect of Epigallocatechin-3-Gallate Against Gentamicin Vestibular Ototoxicity in Type I Vestibular Hair Cell of Guinea Pig / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: Gentamicin (GM) is well known for its vestibulotoxicity. There have been many reports about vestibulotoxicity, however, its mechanism is still unclear. So far, it is known that GM affects the voltage-dependent K+ current and nitric oxide (NO) production. Epigallocatechin-3-gallate (EGCG) is the major component of green tea and is known to have anti-oxidative and anti-toxic effect. This study was undertaken to investigate the protective effect of EGCG against gentamicin on vestibular hair cell (VHC). MATERIALS AND METHOD: White guinea pigs (200-250 g) were rapidly decapitated and the temporal bones were immediately removed. Under a dissecting microscope, the crista ampullaris was obtained. The dissociated VHCs were transferred into a recording chamber mounted onto an inverted microscope. Whole-cell membrane currents and potentials were recorded using standard patch-clamp techniques. In addition, measurements of NO production were obtained using the NO-sensitive dye, 4,5-diamino-fluorescein diacetate (DAF-2DA). RESULTS: Type I VHCs Voltage-dependent K+ current was activated from low depolarizing stimulation. As the stimulation increased, higher current was detected. Voltage-dependent K+ current in type I VHCs was decreased when GM (200 microM) was administrated and GM effects of K+ current inhibition was significantly blocked by EGCG. Extracellular GM-induced an increase in DAF-2DA fluorescence, which thus indicates NO production in VHCs. Also, the GMinduced NO production was inhibited by EGCG. CONCLUSION: GM inhibits voltage-dependent K+ current by releasing NO in isolated type I VHCs. EGCG blocks this inhibitory effects, suggesting a protective role on GM vestibulotoxicity.

Vestibular Hair Cell Regeneration in Guinea Pig after Gentamicin Damage / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: The recovery of the vestibular sensory epithelia of guinea pigs after gentamicin (GM) induced hair cell injury was assessed both quantitatively and qualitatively with a functional study of the vestibular system using animal rotatory chair. MATERIALS AND METHOD: Evaluations were made via calculating the number of utricle cells bearing hair bundles using scanning electron microscopy (SEM). The number of ampullar hair cells and supporting cells were calculated by toluidine blue staining. Animal rotatory chair test was performed for the evaluation of functional recovery of vestibular system after gentamicin damage in guinea pigs. RESULTS: The initial loss of hair cells in utricle and ampulla were followed by the recovery of hair cell number. The quantitative analyses indicated that the lost hair cells were replaced or regenerated after the end of GM administration, or at 3 months. SEM revealed the morphological recovery of the damaged hair cells and new hair cell regeneration in utricle. In animal rotatory chair test, the gain in slow harmonic acceleration were decreased immediate after GM application, and the gain increased over 3 months. The value of bias off the vertical axis rotation also decreased immediatly after the GM application, and the decreased value of bias were partially recovered. CONCLUSION: We find guinea pig vestibular hair cell regeneration after gentamicin damage with morphologic and functional study.