Resveratrol is a naturally occurring polyphenol that is synthesized by a variety of plant species. It is abundant in grapes and grape products (e.g., red wine). Resveratrol has demonstrated reactive oxygen species (ROS) scavenger activity, and it has been linked to nuclear factor-kappa B (NF-kappaB) activity. We recently demonstrated that NF-kappaB is important to the survival of immature mammalian hair cells. Therefore, we undertook an in vitro experiment to determine if resveratrol is able to exert some protective influence against gentamicin-induced damage to and death of auditory hair cells. To accomplish this, we dissected the organ of Corti (OC) from newborn Sprague-Dawley rats and cultured the OCs in medium overnight for recovery. We treated two groups of OC explants with different concentrations of resveratrol plus gentamicin for 24 hours; for comparison and control purposes, we also treated a group of explants with gentamicin only and we left a group untreated. We found that resveratrol in both concentrations had a moderate but statistically significant protective effect against gentamicin-induced toxicity in vitro.
Hair cells are the most vulnerable elements in the inner ear and their degeneration is the most common cause of hearing loss. In the last few years progress has been made in uncovering the molecular mechanisms involved in hair cell damage and death. However, little is known about factors important for hair cell survival. Recently, it has been demonstrated that the transcription factor NF-kappaB is required for survival of immature auditory hair cells in vitro. Here we used DNA microarray technology to explore NF-kappaB downstream events in organ of Corti explants of postnatal day-5 Sprague-Dawley rats which were exposed to a cell-permeable NF-kappaB-inhibitory peptide. Gene expression was analyzed using DNA microarray technology. Genes were selected on the basis of comparative analysis, which reliably distinguished the NF-kappaB inhibitor-treated samples from control samples. Interestingly, among the up-regulated genes was the gene coding for the regulatory subunit of phosphatidylinositol 3-kinase. Moreover, inhibition of the phosphatidylinositol 3-kinase signaling pathway in organ of Corti explants exposed to the NF-kappaB inhibitor reduced caspase-3 activation. These data link NF-kappaB-dependent hair cell death to phosphatidylinositol 3-kinase signaling.
Abstract Objective/Hypothesis: Mammalian auditory hair cells that are unable to regenerate and various agents, including gentamicin, can irreversibly damage the hair cells. Erythropoietin, known as the primary regulator of erythropoiesis, exerts also neuroprotective effects by binding to its receptor. We tested whether erythropoietin can protect the hair cells from gentamicin‐induced damage. Study Design: This study localized the erythropoietin receptor in the cochlea and analyzed the effect of erythropoietin on gentamicin‐damaged hair cells in vitro. Methods: Expression of erythropoietin receptor in the rat cochlea was analyzed by reverse transcriptase–polymerase chain reaction (RT‐PCR) and immunohistochemistry. Protection of auditory hair cells from gentamicin was tested in vitro by exposing cultured rat organs of Corti with increasing concentrations of erythropoietin (0.1 U/mL, 1 U/mL, and 10 U/mL). Results: We detected erythropoietin and erythropoietin receptor mRNA expression in the organ of Corti, spiral ganglion, and stria vascularis by RT‐PCR. Immunohistochemistry revealed that the erythropoietin receptor localizes to the outer and inner hair cells and supporting cells of the organ of Corti, as well as to the spiral ganglion cells and the stria vascularis. Significantly less hair cell loss occurred in the organs of Corti that were pretreated with 0.1 U/mL erythropoietin as compared with samples treated with gentamicin only. Conclusion: Decreased hair cell loss in erythropoietin‐treated organs of Corti that had been exposed to gentamicin provides evidence for a protective effect of erythropoietin in aminoglycoside‐induced hair cell death.
Background: With the use of standard electrodes in cochlear implantation, residual acoustic hearing is markedly reduced or even lost. Possible reasons for this loss are direct implantation trauma to the inner ear, reaction of the cochlea triggered by the implantation, and change of cochlear mechanics due to the electrode. Hypothesis: The introduction of a cochlear implant electrode does not alter the global mechanical behavior of the cochlear fluid as recorded at the stapes and the round window (RW) to the point of clinical relevance. Objectives: 1) To assess RW motion in response to acoustic stimulation in live human subjects for the first time and to compare findings with the published data on similar measurements in human temporal bones; 2) to test the hypothesis by comparing intraoperative measurements of the stapes with the RW before and after cochlear implant. Patients and Methods: The study included 18 adult patients with profound bilateral hearing loss. A scanning laser Doppler interferometer system measuring through the facial recess and a calibrated multi-sinewave acoustic stimulation tone in the ear canal were used. Changes in cochlear mechanics were assessed by comparing intraoperative measurements of stapes with RW membrane responses to acoustic signals before and after cochlear implantation. Results: Vibration amplitudes and phase at the stapes and RW were not different in our patient group from published results from temporal bones. No significant changes in amplitude and phase were seen at the stapes and RW after cochlear implantation. Conclusion: It was possible to assess RW motion in live human subjects. Our results provide evidence that even a standard electrode does not alter cochlear mechanics to the point of clinical relevance.
