[Changes of BK(Ca) on vascular striaepericytes of D-galactose-induced aging model in guinea pigs].

Objective: The aging model of guinea pigs induced by D-galactose was set up to investigate the changes of BK(Ca) expression and function on cochlear pericytes and their relationship with age-related hearing loss. Methods: Thirty healthy 8-week-old guinea pigs were randomly divided into three groups, with 10 in each group: D-galactose aging model group, subcutaneous injection of D-galactose (500 mg/kg) daily for 6 weeks; saline control group, the same amount of saline was injected into the neck of the aging model group for 6 weeks; the blank control group, no treatment was performed. The threshold of auditory brainstem response (ABR) was detected. The content of BK(Ca) in the perivascular cells of the guinea pig cochlear cells was detected by immunofluorescence technique. The changes of peripheral current density and BK(Ca) current were detected by patch clamp technique. The data were analyzed by GraphPad Prism software. Results: Compared with the saline group and the control group, the ABR threshold and the amplitude of the wave I were significantly decreased in the aging model group, and the difference was statistically significant (P<0.01). Compared with the control group, the expression of BK(Ca) in the vascular pericytes of guinea pigs in the aging model group was significantly reduced (1.00±0.08 vs 0.27±0.03,the difference was statistically significant P<0.01), and the cell current density and BK(Ca) net current value were also significantly reduced with statistically significant (P<0.01). Conclusions: D-galactose can successfully induce guinea pig aging model, in which BK(Ca) expression decreases and net current value decreases in pericytes of cochlear striavascularis, and changes in BK(Ca) expression and function may be related to age-related hearing loss.

Chronotolerance for cisplatin ototoxicity in the rat.

Cisplatin is a potent chemotherapeutic compound for which ototoxicity is a significant side effect. Cisplatin has shown sensitivity to circadian time, in that cisplatin is most effective as an anti-tumor compound, and least nephrotoxic, when given in the active (dark) period of the light-dark cycle in rodents. The objective of the study was to determine the sensitivity of cisplatin ototoxicity to circadian time. Fifty-seven Fischer 344/NHsd rats were exposed to 12 mg/kg cisplatin by intra-peritoneal injection at one of six time points on a 12 h light-12 h dark cycle: 2, 6, or 10 h after light onset or 2, 6, or 10 h after light offset. Cochlear injury was evaluated using auditory brainstem response threshold shifts and postmortem outer hair cell counts. All animals experienced threshold shift in the highest frequencies tested (30 and 40 kHz). The animals exposed to cisplatin at 6 h after light onset (the inactive period) had significantly higher mid-frequency threshold shifts and outer hair cell losses than the groups exposed during the dark hours. The results indicate that cisplatin is less likely to cause ototoxicity in the Fischer 344/NHsd rat when given during the active period. This finding is consistent with the lower nephrotoxicity that has been detected in cisplatin-exposed animals treated during the dark hours, and the magnitude of differences in threshold shifts between the light and dark exposure indicates that circadian timing has a significant impact on susceptibility to cisplatin ototoxicity.

Comparison of Cisplatin with Lipoplatin in Terms of Ototoxicity.

OBJECTIVE: Cisplatin (CDDP) is an anti-neoplastic agent that has been used in treatments of both pediatric and adult cancers. It has many side effects, such as ototoxicity, nephrotoxicity, and neurotoxicity. Lipoplatin (LIPO) is a nanomolecule with 110 nm diameter and composed of lipids and CDDP. In this study, we aimed to compare the toxic effects of LIPO with CDDP in the cochlear cells with anti-tumoral doses determined in neuroblastoma cells. MATERIALS AND METHODS: House Ear Institute Organ Corti 1 (HEI-OC1), MYC-N amplified KELLY, and MYC-N non-amplified SH-SY5Y human neuroblastoma cells were used in this study. Firstly, anti-tumoral lethal dose 50 (LD50) of LIPO and CDDP were determined using the WST-1 assay in both neuroblastoma cells. Then anti-tumoral doses of CDDP and LIPO were applied on HEI-OC1 cells for evaluating the toxic effects. The apoptotic cell death was measured using flow cytometric analysis of annexin-V/7-amino-actinomycin (7-AAD) and cell cycle tests. RESULTS: LIPO or CDDP inhibited cell viability in a dose- and time-dependent manner in both neuroblastoma and HEI-OC1 cells. LD50 values were selected as 20 mM for CDDP and 750 mM for LIPO in neuroblastoma cells. After the 48-hour incubation, KELLY cells treated with 20 mM CDDP and 750 mM LIPO had a 53% viability; SH-SY5Y cells treated 20 mM CDDP and 750 mM LIPO had a 45% and 58% viability, respectively; and HEI-OC1 cells treated with 20 mM CDDP and 750 mM LIPO had a 65% and 82% viability, respectively. CONCLUSION: LIPO showed less toxic effects in the HEI-OC1 cells compared to CDDP at anti-tumoral doses.

Cochleotoxicity monitoring protocol.

INTRODUCTION: Cochlear damage is frequent in long-term aminoglycosides therapy or chemotherapeutic treatments with platinum-based agents. Despite its prevalence, it is currently underestimated and underdiagnosed. A monitoring protocol is vital to the early detection of cochleotoxicity and its implementation is widely encouraged in every hospital unit. Our aim was to elaborate a cochleotoxicity monitoring protocol for patients treated with platinum compounds or aminoglycosides antibiotics. METHODS: PubMed® database was searched using terms relevant to drug cochleotoxicity in order to identify the most adequate protocol. Several articles and guidelines influenced our decision. RESULTS: There is no consensus on a universal monitoring protocol. Its formulation and application rely heavily on available resources and personnel. High-frequency audiometry and otoacoustic emissions play an important role on early detection of cochleotoxicity caused by aminoglycoside antibiotics and platinum compounds. CONCLUSION: A cochleotoxicity monitoring protocol consisting on an initial evaluation, treatment follow-up and post-treatment evaluation is proposed.

Self-protection of type III fibrocytes against severe 3-nitropropionic-acid-induced cochlear damage in mice.

After intense sound exposure, the lack of obvious degeneration in type III fibrocytes suggests that they might protect themselves against acoustic trauma. However, it is unknown whether and how type III fibrocytes play this role in other cochlear damage models. In this study, we investigated the self-protection of type III fibrocytes against severe cochlear energy failure induced by local administration of 3-nitropropionic acid to the inner ear. We detected that the type III fibrocytes did not degenerate significantly after 500 mM 3-nitropropionic acid application, and showed increased expression of proliferation marker Ki67. Moreover, low immunoreactivity for inducible nitric oxide synthase and cleaved caspase-3 was observed in type III fibrocytes 2 days after damage. These results indicate that after severe cochlear energy failure type III fibrocytes possess obvious proliferation activity, as well as strong antioxidant and antiapoptotic capacity, which can protect them from degeneration.

Protective role of misoprostol in prevention of gentamicin ototoxicity.

OBJECTIVES: To demonstrate potential protective effect of misoprostol on cochlear toxicity caused by gentamicin with electrophysiological tests and histopathological studies. MATERIALS AND METHODS: The study included 80 ears of 40 rats with normal hearing threshold and DPOAE value in both ears. Animals were assigned into 4 groups. The rats were randomized into 4 groups. Group I (n = 10): Gentamicin, Group II (n = 10): Gentamicin plus misoprostol, Group III (n = 10): Saline; Group IV (n = 10): Misoprostol. All drugs used in the study were given once daily for 15 days. DPOAE and ABR measurements were repeated after drug administration. Subsequently, the rats' cochleae were examined histopathologically. Baseline DPOAE and ABR values were compared to those obtained after drug exposure and cochlear toxicity was evaluated in electrophysiological manner. RESULTS: When At baseline, there were no significant differences in DPOAE responses at frequencies of 1001, 1501, 2002, 3003, 4004, 6006 and 7996 Hz among groups. However In DPOAE test, statistically significant difference was observed between the pre-study basal values and post-study results in groups other than gentamicin + misoprostol group. Additionally, It was found that there was a significant difference in DPOAE response at frequency of 4004 Hz obtained at baseline and after drug exposure according to measurements of epithelial vacuolization in stria vascularis. While ABR threshold values were compared at baseline, there were no significant difference in ABR threshold values of left and right ear between groups. Histopathologically it was also found that there were significant differences measurements of epithelial vacuolization in stria vascularis and inflammation among groups (p < 0.05). CONCLUSION: By these results, misoprostol, a potent antioxidant, has protective effect against cochlear damage, and that may be a safe alternative.

Persistent Thalamic Sound Processing Despite Profound Cochlear Denervation.

Neurons at higher stages of sensory processing can partially compensate for a sudden drop in peripheral input through a homeostatic plasticity process that increases the gain on weak afferent inputs. Even after a profound unilateral auditory neuropathy where >95% of afferent synapses between auditory nerve fibers and inner hair cells have been eliminated with ouabain, central gain can restore cortical processing and perceptual detection of basic sounds delivered to the denervated ear. In this model of profound auditory neuropathy, auditory cortex (ACtx) processing and perception recover despite the absence of an auditory brainstem response (ABR) or brainstem acoustic reflexes, and only a partial recovery of sound processing at the level of the inferior colliculus (IC), an auditory midbrain nucleus. In this study, we induced a profound cochlear neuropathy with ouabain and asked whether central gain enabled a compensatory plasticity in the auditory thalamus comparable to the full recovery of function previously observed in the ACtx, the partial recovery observed in the IC, or something different entirely. Unilateral ouabain treatment in adult mice effectively eliminated the ABR, yet robust sound-evoked activity persisted in a minority of units recorded from the contralateral medial geniculate body (MGB) of awake mice. Sound driven MGB units could decode moderate and high-intensity sounds with accuracies comparable to sham-treated control mice, but low-intensity classification was near chance. Pure tone receptive fields and synchronization to broadband pulse trains also persisted, albeit with significantly reduced quality and precision, respectively. MGB decoding of temporally modulated pulse trains and speech tokens were both greatly impaired in ouabain-treated mice. Taken together, the absence of an ABR belied a persistent auditory processing at the level of the MGB that was likely enabled through increased central gain. Compensatory plasticity at the level of the auditory thalamus was less robust overall than previous observations in cortex or midbrain. Hierarchical differences in compensatory plasticity following sensorineural hearing loss may reflect differences in GABA circuit organization within the MGB, as compared to the ACtx or IC.

Recovery of endocochlear potential after severe damage to lateral wall fibrocytes following acute cochlear energy failure.

Reduction of endocochlear potential (EP) is one of the main causes of sensorineural hearing loss. In this study, we investigated changes in the EP using a mouse model of acute cochlear energy failure, which comprised severe cochlear lateral wall damage induced by the local administration of 3-nitropropionic acid to the inner ear. We also analyzed the correlation between EP changes and histological findings in the cochlear lateral wall. We detected the recovery of the EP and hearing function at lower frequencies after severe damage of the cochlear lateral wall fibrocytes at the corresponding region. Remodeling of the cochlear lateral wall was associated with EP recovery, including the re-expression of ion transporters or gap junctions (i.e. Na/K/ATPase-ß1 and connexin 26). These results indicate a mechanism for late-phase hearing recovery after severe deafness, which is frequently observed in clinical settings.

Ginkgolide B protects against cisplatin-induced ototoxicity: enhancement of Akt-Nrf2-HO-1 signaling and reduction of NADPH oxidase.

Cisplatin is a widely used chemotherapeutic drug for the treatment of various cancers. However, the ototoxicity severely limited its maximum dose. The present study was designed to evaluate the effect of Ginkgolide B (GB), a major component of Ginkgo biloba extracts, on cisplatin-induced ototoxicity and to elucidate the molecular mechanism in vitro and in vivo. In HEI-OC1 auditory cells, GB concentration-dependently inhibited the reduction of cell viability and increase in apoptosis exerted by cisplatin. Cisplatin-activated mitochondrial apoptotic molecular events were significantly inhibited by GB. In addition, GB notably suppressed the increase in NOX2 and p47(phox) expression and the decrease in nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) expression in cisplatin-exposed cells. Inhibition of Nrf2 using SiRNA and blockage of HO-1 by zinc protoporphyrin IX (ZnPP) suppressed the protective effects of GB. Moreover, GB prevented cisplatin-induced reduction of Akt phosphorylation and LY294002, an inhibitor of PI3 K/Akt signaling, blocked the anti-apoptotic effect of GB in cisplatin-treated cells. Furthermore, the protective effect of GB was tested in cisplatin-exposed rats. GB treatment markedly protected animals against cisplatin-induced hearing loss and vestibular dysfunction. Inhibition of Akt and HO-1 significantly suppressed the improvement in hearing loss and vestibular dysfunction in GB-treated rats. We demonstrate that GB decreases ROS generation through reducing NOX2 expression and enhancing activity through Akt-Nrf2-HO-1 pathway, resulting in inhibition of mitochondrial apoptosis and final reduction of cisplatin-induced ototoxicity in vitro and in vivo. Our findings have gained an insight into the mechanism of GB-exerted protective effect against cisplatin-induced ototoxicity.

Loss of auditory activity modifies the location of potassium channel KCNQ5 in auditory brainstem neurons.

KCNQ5/Kv7.5, a low-threshold noninactivating voltage-gated potassium channel, is preferentially targeted to excitatory endings of auditory neurons in the adult rat brainstem. Endbulds of Held from auditory nerve axons on the bushy cells of the ventral cochlear nucleus (VCN) and calyces of Held around the principal neurons in the medial nucleus of the trapezoid body (MNTB) are rich in KCNQ5 immunoreactivity. We have previously shown that this synaptic distribution occurs at about the time of hearing onset. The current study tests whether this localization in excitatory endings depends on the peripheral activity carried by the auditory nerve. Auditory nerve activity was abolished by cochlear removal or intracochlear injection of tetrodotoxin (TTX). Presence of KCNQ5 was analyzed by immunocytochemistry, Western blotting, and quantitative reverse transcription polymerase chain reaction. After cochlear removal, KCNQ5 immunoreactivity was virtually undetectable at its usual location in endbulbs and calyces of Held in the anteroventral CN and in the MNTB, respectively, although it was found in cell bodies in the VCN. The results were comparable after intracochlear TTX injection, which drastically reduced KCNQ5 immunostaining in MNTB calyces and increased immunolabeling in VCN cell bodies. Endbulbs of Held in the VCN also showed diminished KCNQ5 labeling after intracochlear TTX injection. These results show that peripheral activity from auditory nerve afferents is necessary to maintain the subcellular distribution of KCNQ5 in synaptic endings of the auditory brainstem. This may contribute to adaptations in the excitability and neurotransmitter release properties of these presynaptic endings under altered input conditions.

Hydrogen protects auditory hair cells from cisplatin-induced free radicals.

Cisplatin is a widely used chemotherapeutic agent for the treatment of various malignancies. However, its maximum dose is often limited by severe ototoxicity. Cisplatin ototoxicity may require the production of reactive oxygen species (ROS) in the inner ear by activating enzymes specific to the cochlea. Molecular hydrogen was recently established as an antioxidant that selectively reduces ROS, and has been reported to protect the central nervous system, liver, kidney and cochlea from oxidative stress. The purpose of this study was to evaluate the potential of molecular hydrogen to protect cochleae against cisplatin. We cultured mouse cochlear explants in medium containing various concentrations of cisplatin and examined the effects of hydrogen gas dissolved directly into the media. Following 48-h incubation, the presence of intact auditory hair cells was assayed by phalloidin staining. Cisplatin caused hair cell loss in a dose-dependent manner, whereas the addition of hydrogen gas significantly increased the numbers of remaining auditory hair cells. Additionally, hydroxyphenyl fluorescein (HPF) staining of the spiral ganglion showed that formation of hydroxyl radicals was successfully reduced in hydrogen-treated cochleae. These data suggest that molecular hydrogen can protect auditory tissues against cisplatin toxicity, thus providing an additional strategy to protect against drug-induced inner ear damage.

Systemic lipopolysaccharide induces cochlear inflammation and exacerbates the synergistic ototoxicity of kanamycin and furosemide.

Aminoglycoside antibiotics are highly effective agents against gram-negative bacterial infections, but they cause adverse effects on hearing and balance dysfunction as a result of toxicity to hair cells of the cochlea and vestibular organs. While ototoxicity has been comprehensively studied, the contributions of the immune system, which controls the host response to infection, have not been studied in antibiotic ototoxicity. Recently, it has been shown that an inflammatory response is induced by hair cell injury. In this study, we found that lipopolysaccharide (LPS), an important component of bacterial endotoxin, when given in combination with kanamycin and furosemide, augmented the inflammatory response to hair cell injury and exacerbated hearing loss and hair cell injury. LPS injected into the peritoneum of experimental mice induced a brisk cochlear inflammatory response with recruitment of mononuclear phagocytes into the spiral ligament, even in the absence of ototoxic agents. While LPS alone did not affect hearing, animals that received LPS prior to ototoxic agents had worse hearing loss compared to those that did not receive LPS pretreatment. The poorer hearing outcome in LPS-treated mice did not correlate to changes in endocochlear potential. However, LPS-treated mice demonstrated an increased number of CCR2(+) inflammatory monocytes in the inner ear when compared with mice treated with ototoxic agents alone. We conclude that LPS and its associated inflammatory response are harmful to the inner ear when coupled with ototoxic medications and that the immune system may contribute to the final hearing outcome in subjects treated with ototoxic agents.

Ototoxicity of gentian violet on the guinea pig cochlea.

PURPOSE: Gentian violet (GV) is an antimicrobial and antifungal agent that has been used widely to treat intractable discharge in the ear. The purpose of this report is to warn clinicians about the ototoxic effect of GV in the middle ear. MATERIALS AND METHODS: GV ototoxicity was evaluated by measuring compound action potentials (CAPs) in the VIIIth nerve in adult Hartley guinea pigs. The middle ear cavities of the animals were filled with GV solution (0.5% or 0.13%), and CAPs were measured after intervals of 5 and 30 minutes and 1, 2, 6, and 24 hours. After all measurements were completed, the temporal bones were harvested for histopathologic evaluation. Celloidin-embedded specimens were cut into 20-µm slices and examined using light microscopy. The bacteriostatic activity of GV was evaluated using a disk-diffusion assay. RESULTS: A 0.5% GV solution produced a mild elevation in the CAP threshold at 30 minutes, a greater reduction at 1 hour, and complete abolishment of CAP at 24 hours. A 0.13% GV solution caused mild elevation in the CAP threshold at 2 hours and severe elevation at 6 hours. Massive new bone formation was found in the middle ear cavity at 6 weeks. GV concentrations of 0.13% and 0.06% were effective against all bacteria tested, with the exception of Pseudomonas aeruginosa. CONCLUSIONS: Although GV has marked antibacterial and antifungal activities, its use should be limited to the external ear canal. GV exerts an ototoxic effect in a concentration- and time-dependent manner, and so the use of this drug in the middle ear cavity is not recommended.

Mitochondria-targeted antioxidant MitoQ reduces gentamicin-induced ototoxicity.

HYPOTHESIS: Oral supplementation with mitoquinone (MitoQ) prevents gentamicin-induced ototoxicity in guinea pigs. BACKGROUND: Antioxidants have been shown to protect against aminoglycoside (AG)-induced ototoxicity. MitoQ, a mitochondria-targeted derivative of the antioxidant ubiquinone, is attached to a lipophilic triphenylphosphonium (TPP) cation, which enables its accumulation inside the mitochondria several hundred-fold over the untargeted antioxidant. MitoQ has improved bioavailability and can reach most tissues and has been used in Parkinson's disease and hepatitis C human trials, which demonstrated that MitoQ can be safely used in humans. Thus, MitoQ is a promising novel therapeutic approach for protecting against AG-induced ototoxicity. METHODS: Gentamicin-treated guinea pigs were supplied with water alone (control), decyl-TPP (positive control), or MitoQ-supplemented drinking water. Auditory function was assessed by auditory brainstem response. Cochlear damage was assessed using scanning electron microscopy. Western blotting was performed to evaluate changes in proteins related to apoptosis and oxidative damage in the cochlea. RESULTS: Threshold shifts at 4 and 8 kHz at 4 and 7 weeks after gentamicin treatment were smaller in animals treated with MitoQ compared with those in the control- and decyl-TPP-treated animals (p < 0.05). Protein carbonyls and levels of the proapoptotic protein Bak were lower (p < 0.05 and p = 0.008, respectively), whereas the level of the antioxidant enzyme manganese superoxide dismutase was higher (p = 0.01) in the cochlea of MitoQ-treated animals. The expression of 3-nitrotyrosine and Hrk were not different between groups (p > 0.05). CONCLUSION: Oral supplementation with MitoQ attenuated gentamicin-induced cochlear damage and hearing loss in guinea pigs. MitoQ holds promise as a means for protecting against AG ototoxicity.

Kanamycin-furosemide ototoxicity in the mouse cochlea: a 3-dimensional analysis.

OBJECTIVE: Administration of an aminoglycoside antibiotic and loop diuretic causes damage to hair cells in the organ of Corti, resulting in their death and the death of their corresponding spiral ganglion neurons. While this phenomenon has been studied previously, analysis of its effects in the whole cochlea has not been reported. The authors sought to evaluate the effects of a combination dose of kanamycin and furosemide in mice cochlea using an imaging system and computer analysis that allowed for nondestructive, whole-cochlea visualization. STUDY DESIGN: Study using an animal model. SETTING: Cochlear analysis laboratory. SUBJECTS AND METHODS: Five mice received kanamycin and furosemide and 3 mice received saline. Cochleas were harvested and imaged with scanning thin-sheet laser imaging microscopy (sTSLIM) to analyze sensory cells and cochlea structures. RESULTS: The drug-treated animals showed substantial loss of inner hair cells and complete outer hair cell loss. All treated mice showed spiral ganglion neuron loss with fewer neurons than control animals and decreased cell density in the middle turn of the cochlea. The spiral ligament and spiral limbus in the treated animals also showed a decrease in fibrocyte cell density in the middle to apical portion of the cochlea. The stria vascularis appeared normal in all animals. CONCLUSION: Imaging methods that allow for whole-cochlea analysis provide insight into changes that occur in the cochlea after ototoxic insult. Trends that may not be apparent in cross-section samples of the cochlea can be observed. Computer analysis of these trends allows them to be assessed accurately.

Effect of systemic lipopolysaccharide-induced inflammation on cytokine levels in the murine cochlea: a pilot study.

The objective was to detect changes in cytokine expression within cochleae in a murine model of systemic inflammation, with or without aminoglycoside exposure. Four groups of mice received 1 of the following: saline only, systemic bacterial lipopolysaccharides (LPS) for 6 hours to induce endotoxemia and inflammatory responses, systemic gentamicin for 3 hours, or both treatments. After exsanguination, pooled cochleae (4/group) were processed for enzyme-linked immunosorbent assay (ELISA) for 16 cytokines. Gentamicin alone did not change cochlear cytokine levels, while LPS (± gentamicin) substantially elevated cochlear expression of several cytokines, particularly interleukin-1α, interleukin-6, monocyte chemotactic protein-1, macrophage inflammatory protein-1α, and RANTES. Since cytokines increase blood-brain barrier permeability, we hypothesize that cytokine-enhanced permeability of the blood-labyrinth barrier (BLB) could potentiate aminoglycoside-induced ototoxicity. This pilot study demonstrated the feasibility of detecting cytokine expression in murine cochleae using ELISA and facilitates future studies investigating BLB permeability in animal models of systemic inflammation.

Mechanisms of cisplatin ototoxicity: theoretical review.

INTRODUCTION: Cisplatin is an effective chemotherapeutic agent commonly used in the treatment of malignant tumours, but ototoxicity is a significant side effect. OBJECTIVES: To discuss the mechanisms of cisplatin ototoxicity and subsequent cell death, and to present the results of experimental studies. MATERIAL AND METHODS: We conducted a systematic search for data published in national and international journals and books, using the Medline, SciELO, Bireme, LILACS and PubMed databases. RESULTS: The nicotinamide adenine dinucleotide phosphate oxidase 3 isoform (also termed NOX3) seems to be the main source of reactive oxygen species in the cochlea. These reactive oxygen species react with other molecules and trigger processes such as lipid peroxidation of the plasma membrane and increases in expression of the transient vanilloid receptor potential 1 ion channel. CONCLUSION: Cisplatin ototoxicity proceeds via the formation of reactive oxygen species in cochlear tissue, with apoptotic cell death as a consequence.

Oto-toxic effect of gastric reflux.

The reflux of gastric content from the nasopharynx into the middle ear via the Eustachian tube may disrupt inner ear functions. The purpose of this study was to investigate the effect of experimental gastric reflux on the cochlear function of rats. Twelve rats were included in this study. Acidified gastric pepsin was prepared by the addition of HCl and deionized water to pepsinogen from porcine stomach. The left ears were designated as the experimental ears, and the solution was delivered daily for 30 days. The control ears received an equal amount of a saline solution. Distortion product otoacoustic emissions were recorded at baseline (before the injection) and on days 3, 10, and 30. When the mean baseline distortion product otoacoustic emission measurements were compared with the final mean measurements on day 30, the acidified gastric pepsin caused statistically significant (P < 0.05) hearing loss in the experimental ears. There was no significant change in the hearing of the control ears. This is the first study on the ototoxicity of acidified gastric pepsin. Our results demonstrate that acidified gastric pepsin causes hearing loss due to inner ear ototoxicity in a rat animal model.

Atoh1 induces auditory hair cell recovery in mice after ototoxic injury.

OBJECTIVES/HYPOTHESIS: To evaluate the ability of the Ad28.gfap.atoh1 to promote hair cell regeneration and hearing recovery in cochlea injured with kanamycin and furosemide. STUDY DESIGN: In vivo model of hair cell ablation and subsequent treatment with Atoh1. METHODS: The hair cells of C57BL/6 mice were ablated with systemic administration of kanamycin and furosemide. The left ears were treated with Ad28.gfap.atoh1. The right ears were not treated. Preablation audiograms and distortion product otoacoustic emissions (DPOAEs) were compared to 1- or 2-month postablation studies. Harvested cochleae were examined for histologic evidence of hair cell regeneration and spiral ganglion cell survival. RESULTS: Delivery of Ad28.gfap.atoh1 results in development of auditory hair cells. There was no recovery of DPOAEs at 1 or 2 months post-treatment. Two months after delivery of Ad28.gfap.atoh1, the left ear exhibited a moderate recovery of hearing at 4 and 8 kHz (P < .01). There was no significant difference at 16 or 32 kHz. One month after treatment, myosin VII-positive immunohistochemical staining can be seen in both the inner and outer hair cells of the treated ear. In the untreated ear, minimal myosin VII-positive debris is seen, with no indication of normal hair cells. Two months after ablation, there is evidence of hair cell recovery on the treated side, whereas the untreated cochlea demonstrates a flattened epithelium. Untreated ears showed decreased spiral ganglion cell density at the basal turn compared to treated ears. CONCLUSIONS: Ad28.gfap.atoh1 promotes hair cell regeneration in cochlea ablated with kanamycin and furosemide resulting in moderate hearing recovery.