Experimental studies on round window structure: function and permeability

Comparison of gentamicin distribution in the inner ear following administration via the endolymphatic sac or round window

OBJECTIVE/HYPOTHESIS

The distribution of gentamicin in the inner ear via the endolymphatic sac (ES) or round window (RW) routes was investigated.

STUDY DESIGN

Experimental study.

METHODS

A fluorescent gentamicin-Texas Red conjugate (GTTR) was adopted to visualize the gentamicin. Adult guinea pigs were treated with GTTR applied to the ES or RW, the animals were allowed to recover for 3 days, then confocal microscopy was used to observe and quantify GTTR distributions in cochlear and vestibular sensory epithelium.

RESULTS

When GTTR was applied via the ES, strong GTTR labeling was observed in the vestibule while little GTTR was detected in the cochlea (P < .0001). However, distinct GTTR fluorescence was observed in the cochlea and vestibule following RW application (P = .7967). There was less GTTR labeling in cochlea via ES application than through RW administration (P < .0001).

CONCLUSIONS

ES drug application may be preferable for the treatment of intractable Meniere's disease. Laryngoscope, 2010.

Potential role for lipopolysaccharide in congenital sensorineural hearing loss

Congenital sensorineural hearing loss (SNHL) is common. In the Western world, the incidence is 1-3 per 1000 live births. The aetiology encompasses genetic and non-genetic factors accounting for 55 % and 45 % of cases, respectively. Reports that describe the contribution of intrauterine infection to the occurrence of congenital SNHL are limited, and comparative analysis of the different pathogens is lacking. Lipopolysaccharide (LPS), a product of bacteriolysis, has been demonstrated to be associated with inner ear damage in experimental studies. To elucidate the potential role of this toxin in congenital SNHL and to identify the pathogenesis and transmission routes, we reviewed the literature. We speculate that different routes of exposure to LPS in utero may result in congenital inner ear damage.

Effectiveness of different approaches for establishing cisplatin-induced cochlear lesions in mice

CONCLUSIONS

Mouse cochleae are highly resistant to systemically administered cisplatin. However, cochlear lesions can be produced effectively in mice when cisplatin is applied locally through the round window niche or tympanum.

OBJECTIVE

To explore the optimal approach for creating cisplatin-induced cochlear lesions in mice.

MATERIALS AND METHODS

Cisplatin was administered to adult C57BL/6J mice via four approaches: (1) transtympanic injection, (2) round window niche injection, (3) intraperitoneal injection (i.p.) at 4 mg/kg/day for 4 consecutive days, and (4) one 15 mg/kg dose i.p. The hearing was monitored using frequency-specific auditory brainstem responses (ABRs) and distortion-product otoacoustic emissions (DPOAEs). Cochlear pathology was observed in cochleograms with Harris' hematoxylin staining.

RESULTS

Cisplatin applied systemically did not cause any significant ABR threshold elevation across the frequencies tested (2-32 kHz), whereas local application of cisplatin through the round window niche or tympanum resulted in significant ABR threshold elevations from high to medium frequencies. The functional changes were consistent with the cochlear pathology across groups.

Balance and otitis media with effusion

Dizziness can be caused by a variety of peripheral vestibular, central, and systemic disease processes. Eustachian tube dysfunction with and without middle-ear effusion has been considered one of the most common causes of balance disturbances in young children. Several studies have indicated that during an episode of otitis media the child's balance deteriorates and the child may become clumsy and fall more often. Thus, not only the adverse effect on hearing should be considered in the management of a child with otitis media, but also the child's balance.

Sensorineural hearing loss in patients with chronic otitis media

Chronic otitis media is generally associated with some degree of hearing loss, which is often the patient's chief complaint. This hearing loss is usually conductive, resulting from tympanic membrane rupture and/or changes in the ossicular chain due to fixation or erosion caused by the chronic inflammatory process. When cholesteatoma or granulation tissue is present in the middle ear cleft, the degree of ossicular destruction is even greater. An issue that has recently gained attention is additional sensorineural hearing loss due to chronic otitis media. While the conductive loss can be minimized through surgery, sensorineural hearing loss constitutes a permanent after effect, attenuated only through the use of a hearing aid. However, a few groups have reported a decrease in sensorineural function in these patients as well. This survey study performed at a referral center evaluates the occurrence of sensorineural hearing loss in ambulatory patients with this disease. We reviewed the files of patients with unilateral chronic otitis media. One hundred and fifty patients met the inclusion criteria: normal otoscopy and normal hearing in the contralateral ear.

MAIN OUTCOME MEASURE

bone-conduction threshold averages were calculated for frequencies of 500, 1,000, 2,000, 3,000 and 4,000 Hz, with comparison between the normal ear and the ear with chronic otitis media. Thresholds were examined separately for each frequency. The bone-conduction threshold averages for the normal side were lower than those for the ear with chronic otitis media. The threshold shift was statistically significant for each frequency (P<0.0001, Student's t test). There were differences between the groups when analyzed for age (500 and 1,000 Hz) or the presence of cholesteatoma (1,000 Hz). This study shows that chronic otitis media is associated with a decrease in cochlear function.

The pharmacokinetic profiles of dexamethasone and methylprednisolone concentration in perilymph and plasma following systemic and local administration

CONCLUSION

Both methylprednisolone (MTH) and dexamethasone (DEX) could successfully and effectively penetrate the round window membrane (RWM) into perilymph. RWM topical application and otocyst infusion with MTH and DEX result in high perilymph drug concentrations and low plasma levels. An intratympanic administration schedule for DEX or MTH could be carried out twice daily.

OBJECTIVE

To explore the pharmacokinetics of DEX and MTH in the inner ear fluids and plasma following systemic and local administration.

MATERIALS AND METHODS

Three routes of administration of steroids were used in guinea pigs: intracardial injection, otocyst infusion and RWM topical application by granule gelfoam soaked with steroids. Samples of blood or perilymph of the scala tympani were collected at 1-6 h after administration. High-performance liquid chromatography was used to assay concentrations of steroids.

RESULTS

Both the topical application and infusion administration resulted in a significantly higher concentration of steroids in perilymph than intracardial injection. The level of steroids in the perilymph reached a peak at 1-2 h after dosing, and this was maintained at a relatively high level for several hours. The intracardial injection with steroids yielded very low perilymph levels at all sampling times after administration.

Bi-phasic intensity-dependent opioid-mediated neural amplitude changes in the chinchilla cochlea: partial blockade by an N-Methyl-D-Aspartate (NMDA)-receptor antagonist

Dynorphins, glutamate, and glutamate-sensitive N-Methyl-D-Aspartate (NMDA) receptors exist in the mammalian cochlea. Dynorphins produce neural excitation and excitotoxic effects in the spinal cord through a kappa-opioid facilitation of NMDA receptor-sensitivity to glutamate. The kappa-opioid receptor drug agonists N-dimethylallyl-normetazocine [(-)-pentazocine (50 mmol)] and trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]-benzeneacetamide [U-50488H (100 mmol)] were administered across the cochlear round window membrane in the chinchilla. Each drug produced significant post-baseline amplitude changes in the click-evoked auditory nerve compound action potential. Amplitude changes at threshold amounted to increases in sensitivity that ranged from 4-8 decibels, measured in sound pressure level (dB SPL). The large neural amplitude increases at threshold were accompanied by progressively smaller amplitude changes at 5 and 10 dB above threshold (dB SL). However, at stimulus intensities > or =20 dB SL, post-baseline neural amplitudes were suppressed to levels below baseline and control values. These bi-phasic intensity-dependent neural amplitude changes have never before been observed following i.v. administered (-)-pentazocine in this species. Finally, the bi-phasic neural amplitude changes in U-50488H-treated (100 mmol) animals were partially blocked (except at 20 dB SL), following a round window pre-treatment with the NMDA receptor drug antagonist, dizocilpine hydrogen maleate [(+)-MK-801 (8 mmol)]. Our data suggests that endogenous dynorphins within lateral efferent olivocochlear neurons differentially modulate auditory neural excitation, possibly through cochlear NMDA receptors and glutamate. The role played by lateral efferent opioid neuromodulation at cochlear NMDA receptors, is discussed.

Ototoxicity of Ototopical Drops—An Update

Various topical preparations are widely used for treating external otitis, acute otitis media with perforation, post-tympanostomy tube otorrhea, and chronic suppurative otitis media. Solutions and suspensions that enter the middle ear through a perforated tympanic membrane can reach the inner ear by crossing through the round window membrane. The safety of various components of otic solutions used in this way, particularly aminoglycosides, corticosteroids, solvents, and preservatives, has been questioned in light of their ototoxic potential. The authors' objective is to review the literature discussing the safety of commonly used classes of otic preparations in settings in which the constituents can access the middle and inner ear in high concentrations and discuss their clinical experience with ototoxicity and experience with medical-legal issues.

Intratympanic Methylprednisolone for Sudden Sensorineural Hearing Loss

OBJECTIVE

Corticosteroids are commonly used for the treatment of sudden sensorineural hearing loss (SSHL). In this study, the effectiveness of intratympanic (IT) corticosteroid injection was studied and compared with a control group on patients with SSHL who failed systemic corticosteroid treatment.

MATERIALS AND METHODS

A total of 19 patients as a retreatment group (RG) and 18 patients as a control group (CG), all failed high-dose intravenous and oral corticosteroid treatments, were included in this study. These patients were invited back, and IT methylprednisolone was injected five times via 3-day intervals in RG and followed-up for a mean period of 24.9 months (range, 7-30 mo). Audiological evaluations were performed initially, a week after the completion of the injections, monthly in the following first 3 months, and at the end of follow-up period in RG. The CG was followed-up for 3 months after the completion of systemic corticosteroid treatment without any additional drug administration.

RESULTS

The mean age was 52.6 years (range, 20-79 yr) in RG and 59.9 years in CG. The mean pure-tone average for speech frequencies (500-4,000 Hz) at baseline audiogram and at the first month, at the third month, and at last controls were 65.2 (range, 43-102 dB), 45.4 (range, 23-77 dB), 43.6 (range, 30-77 dB), and 44.5 (range, 33-77 dB) dB, respectively, in RG. The mean pure-tone averages for speech frequencies (500-4,000 Hz) at the end of systemic treatment and at third-month control were 63.5 (range, 44-98 dB) and 59.0 (range, 40-100 dB) dB, respectively, in CG. The hearing gain that is equal to or more than 10 dB was achieved in 14 patients (73.6%) at the last control in RG. No hearing gain could be detected in the CG. No serious side effect was observed with IT treatment.

CONCLUSION

We conclude that IT methylprednisolone injection provides more significant hearing improvement for patients that failed with previous high-dose systemic corticosteroid administration than systemic corticosteroid treatment alone. So it may be the first-step medical treatment of idiopathic SSHL alone or at least may be combined with the systemic corticosteroid administration.

Hydrogen peroxide ototoxicity in unblocking ventilation tubes: a chinchilla pilot study

OBJECTIVE

Some clinicians use hydrogen peroxide (H2O2) to clear the lumen of ventilation tubes that become blocked postoperatively. The ototoxicity associated with H2O2 has been controversial.

STUDY DESIGN

We designed an experiment to test if H2O2 damages the cochlear hair cells using a Chinchilla laniger animal model.

METHODS

Nine chinchillas (18 ears) were included in this study. Each animal was used as its own control. Following the insertion of ventilation tubes in both ears and baseline recordings of the auditory brain stem responses (ABR), we instilled 2 ml of 3 percent H2O2 into their right external auditory canals (experimental ears). H2O2 was left in the external auditory canal for a total of 5 minutes and then was drained. We instilled a normal saline control solution in their left ears (control ears) in a similar fashion. ABR recordings were performed 1 day after the last instillation of H2O2 and 5 days later.

RESULTS

There was no statistically significant difference in the ABR thresholds of the experimental and control ears.

CONCLUSION

H2O2 did not appear to cause ototoxicity in chinchilla ears with tympanostomy tubes exposed to H2O2 instillation using a standard clinical protocol.

Topical antibiotic ear drops: are they safe?

A discharging ear is a very common condition for the general practitioner and the ENT surgeon. Oral and intravenous antibiotics have potential complications, are costly, and exhibit increasing resistance. This study explores the advantages and disadvantages of all common otic preparations and compares effectiveness, safety, cost and complication rates. In chronic otitis media (chronic discharging ears), topical antibiotics seem to be the treatment of choice by comparison with oral or intravenous antibiotics. Cultures and antibiograms do not correspond directly to clinical efficacy, as laboratory determination of resistance does not take into account the high concentration of antibiotics in local preparations. It is safer to use quinolone drops as a first-line treatment, but it is still possible to use short courses of other drops if quinolones are either unavailable or contraindicated (e.g. allergy), or when bacteria are resistant to them. However, in such a situation, a round window membrane involved in an established inflammatory process and therefore less permeable to the passage of topical preparations is the preferred setting, as ototoxicity is a potential complication, especially in the case of gentamicin, in which case patients should be warned accordingly.

Evaluation of the mouse model for acute otitis media

Various animal models have been employed for otitis media research. The mouse has been studied less, in spite of its many advantages. To better understand the suitability of the mouse for studies of otitis media, an evaluation was made of its middle ear inflammatory processes following inoculation with heat-killed Streptococcus pneumoniae (strain 6A), one of the three most common bacteria to cause otitis media in the human. A total of 94 BALB/c mice were injected transtympanically with three concentrations of heat-killed bacteria (10(4), 10(6), and 10(9) organisms per ml) and inflammation evaluated with both histologic examination and auditory brainstem response audiometry. Dose-related measures of the time course of inflammation showed it was maximal at 3 days. PBS-injected control mice also demonstrated some degree of middle ear inflammation. Therefore, inflammation measures from PBS injected mice were used as the threshold above which histologic inflammatory changes would be considered a response to bacteria. These quantitative comparisons of bacterial and PBS inoculations revealed the most significant middle ear measures of inflammation were amount of fluid in the middle ear, tympanic membrane thickness, and number of inflammatory cells. The induction of middle ear inflammation in the mouse demonstrated the applicability of this model for investigations of otitis media.

Transtympanic steroids as a salvage therapy in sudden hearing loss: preliminary results

PURPOSE

To understand the real efficacy of transtympanic steroid therapy for sudden sensorineural hearing loss (SSHL) in patients in whom traditional therapies have failed.

PROCEDURES

A prospective study was designed in order to evaluate hearing improvement in SSHL patients treated with transtympanic therapy. A solution of methyl-prednisolone (MP) and sodium bicarbonate was administered via a transtympanic injection to 8 patients. Hearing level was evaluated before therapy and at days 1, 7 and 30.

RESULTS

Hearing improvement was obtained in 75% of the patients. The patients in this category are usually considered untreatable.

CONCLUSION

Transtympanic steroid therapy is an efficacious solution for patients affected by SSHL in whom traditional therapies have failed. Further studies will be required to identify the most favourable dosage, route of administration and type of steroid. Transtympanic steroid application is safe, inexpensive, easy to perform and efficacious in cases of SSHL not responsive to traditional therapy.

The permeability of SPION over an artificial three-layer membrane is enhanced by external magnetic field

Background

Sensorineural hearing loss, a subset of all clinical hearing loss, may be correctable through the use of gene therapy. We are testing a delivery system of therapeutics through a 3 cell-layer round window membrane model (RWM model) that may provide an entry of drugs or genes to the inner ear. We designed an in vitro RWM model similar to the RWM (will be referred to throughout the paper as RWM model) to determine the feasibility of using superparamagnetic iron oxide (Fe₃O₄) nanoparticles (SPION) for targeted delivery of therapeutics to the inner ear.

The RWM model is a 3 cell-layer model with epithelial cells cultured on both sides of a small intestinal submucosal (SIS) matrix and fibroblasts seeded in between. Dextran encapsulated nanoparticle clusters 130 nm in diameter were pulled through the RWM model using permanent magnets with flux density 0.410 Tesla at the pole face. The SIS membranes were harvested at day 7 and then fixed in 4% paraformaldehyde. Transmission electron microscopy and fluorescence spectrophotometry were used to verify transepithelial transport of the SPION across the cell-culture model. Histological sections were examined for evidence of SPION toxicity, as well to generate a timeline of the position of the SPION at different times. SPION also were added to cells in culture to assess in vitro toxicity.

Results

Transepithelial electrical resistance measurements confirmed epithelial confluence, as SPION crossed a membrane consisting of three co-cultured layers of cells, under the influence of a magnetic field. Micrographs showed SPION distributed throughout the membrane model, in between cell layers, and sometimes on the surface of cells. TEM verified that the SPION were pulled through the membrane into the culture well below. Fluorescence spectrophotometry quantified the number of SPION that went through the SIS membrane. SPION showed no toxicity to cells in culture.

Conclusion

A three-cell layer model of the human round window membrane has been constructed. SPION have been magnetically transported through this model, allowing quantitative evaluation of prospective targeted drug or gene delivery through the RWM. Putative in vivo carrier superparamagnetic nanoparticles may be evaluated using this model.

The biology of intratympanic drug administration and pharmacodynamics of round window drug absorption

The application of therapeutic agents to the round window holds great promise in the treatment of inner ear disease. The primary benefit of this route of administration is the ability to achieve high inner ear concentrations of drugs without systemic side effects. Recent research has elucidated the anatomy and physiology of the round window and provided important information on the inner ear pharmacokinetics and the pharmacodynamics of drugs administered intratympanically. Although amino-glycosides and steroids have been most thoroughly studied, many other classes of pharmaceuticals, including otoprotective agents, other antibiotics,and topical anesthetics, have therapeutic potential in the inner ear and will probably be the subject of future studies. The authors believe that direct delivery approaches other than through the round window, perhaps with slow or sustained release formulations, may hold the key to the future treatment of inner ear disorders.

Round window pH manipulation alters the ototoxicity of systemic cisplatin

The effect of manipulation of pH on the ototoxicity of systemic cisplatin was studied in Wistar rats. After control auditory brainstem responses (ABR) were performed, the auditory bullae were opened and acidic (pH 6.0), neutral (pH 7.4) or basic (pH 9.0) phosphate-buffered saline (PBS) was applied to fill the round window niche (RWN). After 30 min, 13 mg/kg cisplatin solution or saline was administered intraperitoneally. After 3 days, follow-up ABRs were performed and cochleae were processed for morphological analysis. Animals that received basic PBS on the RWN and cisplatin intraperitoneally had significantly smaller ABR threshold shifts compared to rats pretreated with neutral pH buffer (P<0.05). Animals that received acidic PBS on the RWN and systemic cisplatin showed significantly greater ABR threshold shifts compared to those pretreated with neutral pH buffer (P<0.05). No significant threshold changes were observed in animals that received buffer of any pH on the RWN, followed by saline intraperitoneally. Semiquantitative analysis of hair cell survival confirmed a protective effect by basic PBS against cisplatin and a synergistic effect by acidic PBS on cisplatin ototoxicity (P<0.05). It appears that changes in cochlear pH can modulate the ototoxic effects of systemically applied cisplatin.

Ototoxic protection of sodium thiosulfate: daily vs constant infusion

OBJECTIVE

Compare the effect of a daily dose of sodium thiosulfate (STS) to continuous infusion of STS on Hartley albino guinea pig (HAGP) on cisplatin (CP)-induced sensorineural hearing loss. Study design Prospective randomized pilot study comparing a single daily dose of STS to a constant controlled infusion of STS given the middle ear space (MES) with an ototoxic regimen of CP. The hearing thresholds will be obtained by auditory brainstem response (ABR) 1 week before and after treatment. Treatment effects on responses at 2, 8, and 16 kHz signals will be investigated by an analysis of variance with one between subjects' condition and two within subjects' conditions.

SETTING

Basic science laboratory.

RESULTS

STS protection resulted in significantly less hearing loss post-treatment for the protected ears. Guinea pigs with continuous infusion of STS demonstrated less loss in the protected ear than those who received the single daily dose. As expected, hearing loss at 2 kHz was less than that at 8 and 16 kHz.

CONCLUSION

A continuous infusion of STS directly to the MES is better than a single daily dose of STS to the MES in reducing the ototoxicity of CP.

SIGNIFICANCE

Any targeted protection, whether by continuous infusion or daily dose, is better than no protection against the sensorineural hearing loss of CP.

The effect of otitis media with effusions on balance in children

There is increasing interest in the effect, otitis media with effusions (OME) has on the balance in children. The aim of our investigation was to determine whether a universal effect on balance could be demonstrated in children with OME by using sway posturography. Assessment was made in 20 children with proven OME before and after the insertion of bilateral ventilation tubes. Sway posturography was performed on each occasion in each of the four recording conditions in the presence and absence of both reduced optic fixation and reduced proprioception. The pathlength traversed during the recording interval was measured and analysed by a split-unit anova. The results demonstrate an overall improvement in mean pathlength of 20% following treatment of the effusions (P < 0.001) (95% CI 14-25%). The effect of reduced optic fixation and of reduced proprioception were similar when increasing the mean pathlength by 22% (P < 0.001). These results demonstrate that OME has a universal effect on balance in all recording conditions.

Adenoviral vector gene delivery via the round window membrane in guinea pigs

We have found that damage from a local anesthetic solution containing phenol permitted beta-galactosidase (beta-gal) gene delivery to the guinea pig inner ear via the round window membrane (RWM). RWM damage was evident as degeneration of the outer epithelium. After adenovirus lacZ vector was applied to the damaged RWM, immunohistochemistry showed strong beta-gal expression in the RWM, mesothelial cells, organ of Corti, spiral limbus, spiral ligament and spiral ganglion. In the vestibular labyrinth, expression was seen in the sensory and supporting cells, transitional cells, and the dark-cell area. Thus, adenovirus can transfect a variety of inner ear cells in the guinea pig through a damaged RWM.

Influence of pH on the ototoxicity of cisplatin: a round window application study

Cisplatin is an antineoplastic agent that produces a number of dose-limiting side effects, including ototoxicity. We investigated the effect of pH on cisplatin ototoxicity. Auditory brainstem responses (ABR) were recorded in chinchillas. Then the auditory bullae were opened and acidic (pH=6.5), neutral (pH=7.4) or alkaline (pH=10.2) phosphate-buffered saline (PBS) was applied to the round window membrane. After 30 min, any remaining solution was removed and cisplatin solution was applied to the round window membrane. After 3 days, follow-up ABRs were performed and the cochleae were processed for morphological analysis. Neutral PBS+cisplatin administration resulted in profound threshold changes at all frequencies. Acidic PBS+cisplatin administration showed had a trend of increased threshold changes, but the change did not reach statistical significance. However, the degree of hair cell loss was significantly higher than that of the neutral PBS-cisplatin group. Alkaline PBS significantly reduced cisplatin-induced threshold changes (P<0.05) compared to the neutral PBS group. Because the pH of cisplatin solution was 6.0, pH 6.0 PBS was applied to round window membrane. This acidic PBS solution did not cause any hearing impairment. These results demonstrate that pH can modulate the ototoxic effects of cisplatin.

Round window membrane in young and aged C57BL/6 mice

Although there have been many studies on the round window membrane (RWM), little information has been reported about changes in the membrane associated with aging. We have undertaken morphological studies of RWMs using young (7-8 weeks old) and aged (27-29 months old) C57BL/6 mice. The RWM was thinner in mice from the aged group compared with that of the young group. The cell density in the epithelial and inner layers was also reduced in the aged group. In the middle layer of the RWM in aged mice, transmission electron microscopy revealed many degenerated short and thick elastic fibers. Confocal laser microscopy using fluorescein isothiocyanate(FITC)-wheat germ agglutinin (WGA) staining was used to identify WGA-positive fibers in the middle layer of the RWM, which changed in a similar manner to the fibers in aging skin.

Round window membrane delivery of L-methionine provides protection from cisplatin ototoxicity without compromising chemotherapeutic efficacy

Cisplatin (cis-diamminedichloroplatinum(II) (CDDP)) is a widely used, highly effective, oncolytic agent that has serious ototoxic side-effects. To test the effectiveness of local delivery, of L-methionine (L-Met) as an otoprotective agent against CDDP ototoxicity, we used a rat model of a highly metastatic breast cancer tumor, i.e. Fisher 344 rats implanted with MTLn3 breast cancer cells. Four experimental groups were evaluated--I: untreated; II: CDDP-treated (three dosages); III: systemically-delivered L-Met + CDDP-treated; IV: locally delivered L-Met + CDDP-treated. The integrity of the outer hair cells (OHCs) was determined using scanning electron microscopy (SEM); hearing was assessed by recording auditory brainstem responses (ABRs) at multiple frequencies. The chemotherapeutic effectiveness of CDDP was quantified by measuring changes in tumor mass and the presence of tumor metastasis. L-Met provided otoprotection of the OHCs against CDDP toxicity in the cochleae of rats following either systemic (III) or local (IV) administration. The ABRs were unchanged in each of the L-Met protection Groups (III and IV) and in the untreated animals of Group I. Treatment with CDDP only (II) induced significant hearing losses at both 16 and 18 kHz when compared to ABRs of untreated rats(I). CDDP was effective in controlling the MTLn3 initiated breast cancer tumors in the CDDP-treated (II) and the local L-Met protection, CDDP-treated (IV) Groups. In contrast, the tumors in the systemic L-Met protection, CDDP-treated Group (III) were not controlled by the CDDP treatment regime. This study demonstrates that local delivery of L-Met to the scala tympani of the cochlea via the round window membrane (IV) provides effective protection against CDDP ototoxicity without compromising its ability to control a highly metastatic form of cancer.

Intratympanic dexamethasone for sudden sensorineural hearing loss: clinical and laboratory evaluation

OBJECTIVE

To discuss the value of intratympanic dexamethasone (IT-DEX) perfusion for sudden sensorineural hearing loss (SSNHL), clinically and in an animal model.

STUDY DESIGN

Retrospective case review of 10 patients with SSNHL treated with IT-DEX. The findings are correlated with this institution's previous findings from a study of IT-DEX in guinea pigs.

SETTING

Ambulatory tertiary otologic referral center.

PATIENTS

Sequential patients with SSNHL who chose IT-DEX treatment.

INTERVENTIONS

Dexamethasone 0.5 mg was injected transtympanically and bathed the round window for 20 minutes. Animal study: 79 ears were randomized into five groups: control, IT-DEX versus intravenous (IV)-DEX, IT-DEX with histamine, IT-DEX with hyaluronic acid, and IT-DEX with dimethylsulfoxide.

MAIN OUTCOME MEASURES

Clinical study: postprocedure audiometry. Animal study: perilymph steroid concentration.

RESULTS

IT-DEX results in significant hearing improvement and in significantly higher perilymph concentration of steroid than IV-DEX.

CONCLUSIONS

IT-DEX is an appropriate treatment option for the treatment of SSNHL. Further study of dosages and frequency of administration is warranted.

Dexamethasone pharmacokinetics in the inner ear: comparison of route of administration and use of facilitating agents

There is growing otologic interest in treating inner ear disorders, such as sudden sensorineural hearing loss and acute or unremitting Meniere's disease, with intratympanic dexamethasone (IT-DEX). Although anecdotally reported, there are no scientific clinical papers and few prior laboratory research publications on the subject. This study compares perilymph dexamethasone concentrations after systemic and intratympanic administration and assesses the role of 3 potential transport facilitators of IT-DEX into perilymph. Forty guinea pigs (79 ears) were randomly separated into 5 groups. Dexamethasone levels were measured by radioimmunoassay. IT-DEX resulted in higher perilymph steroid levels than intravenous dexamethasone (P < 0.05). Histamine facilitator resulted in significantly higher perilymph steroid levels than IT-DEX alone (P < 0.05). Neither hyaluronic acid nor dimethylsulfoxide was a potent facilitator. This study demonstrates that IT-DEX administration results in superior perilymph levels within 1 hour of administration and does not result in systemic absorption. Histamine is a potent facilitating agent. The clinical implications are considerable.

Ototoxicity of common topical antimycotic preparations

OBJECTIVE

To determine the ototoxic effects of five commonly used topical antimycotic agents-clotrimazole, miconazole, nystatin, tolnaftate, and gentian violet-in the guinea pig.

DESIGN

A controlled animal study in which the ototoxicity of commonly used topical antifungal agents was investigated by measurement of hair cell loss.

METHODS

Several readily available topical antimycotic preparations were instilled into the middle ears of female Hartley guinea pigs over a 1-week period. Two weeks after the last instillation, the animals were euthanized. An active control group was treated with neomycin to confirm the adequacy of the treatment in delivering a known ototoxin; an untreated control group defined the normal distribution of hair cells. The temporal bones were removed, and the cochleas were fixed and dissected. The basilar membranes were examined under the scanning electron microscope. A map of hair cell survival was made for each row in segments of each turn.

RESULTS

The untreated control animals had no discernible hair cell loss in the two lower turns. In the apical turn and sometimes the third turn, loss of hair cells was a common finding, this is a known effect of aging in this species. The animals treated with neomycin had damage consistently in the basal turn, sometimes extending into the second turn, as well as the expected hair cell loss in the apical turn. Clotrimazole, miconazole, or tolnaftate did not cause any hair cell loss in the first two turns. Hair cell loss in the third and fourth turns was similar to that of the untreated control group. Likewise, nystatin exhibited no evidence of ototoxicity. Of note, however, the preparation used in this study left a persistent residue in the round window niche. Of the first four animals treated with gentian violet, three developed pronounced behavioral signs of vestibular damage, and three demonstrated extensive middle ear inflammation and extensive new bone growth. Hair cell counts were not attempted because the extreme bone growth interfered with successful perfusion and dissection.

CONCLUSIONS

Extrapolating from guinea pigs to humans requires caution. However, it is likely that guinea pigs are, if anything, more susceptible to topical ototoxins than are humans. The specific antimycotics clotrimazole, miconazole, and tolnaftate appear to be safe. Gentian violet has the potential for severe damage. The persistent residue left by the nystatin preparation is cause for concern and is a reminder that both the active ingredient and vehicle must be considered in evaluation of safety.

Presumed reduction of vestibular function in unilateral Menière's disease with aminoglycoside eardrops

We report the first case in the world literature of deliberate ablation of vestibular function in unilateral Menière's disease with aminoglycoside eardrops (Garasone). These findings give conclusive proof that Garasone eardrops, and by implication, all topical aminoglycoside ear drops can be vestibulotoxic in the presence of a tympanic membrane defect. The lower concentration of gentamicin in Garasone, in comparison to the standard intratympanic preparations for chemical ablation of vestibular function, may also offer a reduction in the potential risk of cochleotoxocity.

Ototoxicity of topical gentamicin preparations

OBJECTIVE

To document that commercially available topical gentamicin-containing eardrops carry a risk of ototoxicity if they reach the middle ear through a tympanic membrane defect.

STUDY DESIGN

Clinical study, retrospective case-note review.

SETTING

Department of Otolaryngology, The Toronto Hospital, University of Toronto.

PATIENTS

Sixteen patients were identified with well-documented histories, physical findings and laboratory investigations consistent with topical gentamicin-induced ototoxicity. One patient with incapacitating unilateral Meniere's disease underwent successful intentional vestibular ablation using topical gentamicin/steroid drops.

RESULTS

In all cases of inadvertent ototoxicity, patients had used the drops for longer than 7 days (average 20.7 d) prior to symptoms developing. All patients developed vestibulotoxicity that was confirmed on ENG testing. Only 1 patient had a noticeable worsening of cochlear reserve. Deliberate and successful therapeutic ablation of vestibular function in a patient with unilateral Meniere's disease confirms the vestibulotoxic nature of commercially available topical gentamicin preparations.

CONCLUSIONS

Physicians should consider the potential for ototoxicity if gentamicin-containing eardrops (and by extrapolation all topical aminoglycoside drops) are used for longer than 7 days in patients with a tympanic membrane defect. These preparations should not be used in the presence of healthy middle ear mucosa and should be discontinued shortly after the discharge has stopped. It is important to recognize that toxicity is primarily vestibular rather than cochlear.

Effects of otitis media with effusion on the vestibular system in children

Middle ear effusion has been considered the most common cause of vestibular disturbance in children. However, there have been only a few studies on vestibular disturbance in children with otitis media with effusion. We studied the vestibular systems of 30 children with otitis media with effusion aged 8 to 13 years and compared the results with 15 age- and sex-matched controls. A questionnaire relating to vestibular disturbance was given to patients and their parents. Spontaneous nystagmus and positional nystagmus were recorded by electronystagmography as diagnostic tests of the vestibular system. Romberg's and past-pointing tests were performed on children with otitis media with effusion and controls. After vestibular tests were completed, myringotomy was performed, and a ventilation tube was inserted. The questionnaire and the vestibular tests were repeated after the operation and during the first month after surgery. Our study showed that there was a history of vestibular disturbance in 33% of children with otitis media with effusion. Electronystagmography and Romberg's test findings demonstrated that 33% of the children had vestibular dysfunction (p < 0.05). After myringotomy with ventilation tube insertion, vestibular test results returned to normal, and symptoms related to vestibular disturbance improved. These findings confirm the assumption that middle ear effusion may affect the vestibular system, which can be resolved after myringotomy with ventilation tube insertion.

Ototoxicity and topical eardrops

Topical aminoglycoside ear drops are theoretically acknowledged to be potentially ototoxic when administered in the presence of a tympanic membrane perforation. Although the development of clinical ototoxicity appears to be rare, nine well-documented and incontrovertible cases (12 ears in total) of iatrogenic topical vestibulotoxicity are presented, representing the largest series in the English language world literature to date. All patients were treated with the topical gentamicin-containing ear drops Garasone, (betamethasone sodium phosphate and gentamicin sulphate) for prolonged periods. Toxicity was found to be primarily vestibular rather than cochlear. Further review of five previously reported cases in addition to the findings from another four patients identified with topical ototoxicity are described. Although compensation occurred in unilateral cases the disability in bilateral cases was typically severe and often resulted in litigation.

Visual-induced postural sway in children with and without otitis media

Children with otitis media with effusion (OME) have been shown to have a significantly higher velocity of sway than normal children. To further evaluate the effect of OME on balance, we studied visual dependency for balance by investigating the influence of optic flow on postural sway. The results of this preliminary study suggest that children with OME may be more visually dependent for balance than healthy age-matched controls. This was particularly evident for higher-frequency stimulus conditions (0.25 Hz) as opposed to lower-frequency stimulus conditions (0.10 Hz). These findings indicate that OME may affect vestibular function in children, thereby causing excessive reliance on other, nonvestibular sensory cues to maintain balance. Further studies are needed to define the role of vestibular function in the management of children with OME.

Electrophysiological effects of multiple instillation of Haemophilus influenzae type b endotoxin on the inner ear

An analysis of auditory brainstem response (ABR) thresholds and ABR-based frequency tuning curves was performed in 15 Sprague-Dawley rats exposed to Haemophilus influenzae type b endotoxin; 5 microg/50 microl toxin was instilled every second day, altogether five times, into the middle ear cavity through a small perforation in the tympanic membrane. ABR was measured 48 h after the second application and 24 h, 48 h, 5 days and 10 days after the fifth instillation. Five applications of toxin had no statistical effect on ABR thresholds and no changes in TC configuration were observed. It is concluded that Haemophilus influenzae type b endotoxin, instilled repeatedly through the tympanic membrane into the middle ear, does not affect cochlear electrophysiology.

Round window membrane. Structure function and permeability: a review

The ultrastructure of the round window membrane of humans, monkeys, felines, and rodents discloses three basic layers: an outer epithelium, a middle core of connective tissue, and an inner epithelium. Interspecies variations are mainly in terms of thickness, being thinnest in rodents and thicker in humans. Morphologic evidence suggests that the layers of the round window participate in absorption and secretion of substances to and from the inner ear, and that the entire membrane could play a role in the defense system of the ear. Different substances, including antibiotics, local anesthetics, and tracers such as cationic ferritin, horseradish peroxidase, and 1 mu latex microspheres, are placed in the middle ear side traverse the membrane. Cationic ferritin and 1 micron microspheres placed in perilymph become incorporated by the inner epithelial cells of the membrane. Permeability is selective; factors include size, concentration, liposolubility, electrical charge, and thickness of the membrane. Passage of substances through the round window membrane is by different pathways, the nature of which is seemingly decided at the outer epithelium of the round window membrane.

Effect of Pseudomonas aeruginosa exotoxin A on inner ear function

Electrophysiological changes were studied in the albino rat following instillation of Pseudomonas aeruginosa exotoxin A into the middle ear cavity through the tympanic membrane. Hearing threshold was measured by a burst-elicited, frequency-specific auditory brainstem response (ABR) technique prior to exposure, then 24 and 48 h, 5 days, 2 and 4 weeks after the toxin instillation. A single dose (1 microgram/20 microliters) of Pseudomonas aeruginosa exotoxin A raised the ABR threshold over the whole frequency range, by 5-25 dB, particularly in the high tones. All threshold shifts were of combined conductive and cochlear type, reversible, with deterioration starting at 24-48 h and recovery at 2-4 weeks. Effusion of serous fluid occurred at 24 or 48 h, resulting in conductive hearing loss. Latency/intensity curves revealed a cochlear component in addition to conductive hearing loss. Morphological examination by SEM showed slight and inconsistent derangement of OHCs. It is concluded that Pseudomonas aeruginosa exotoxin A causes middle ear inflammation, facilitating penetration to the inner ear and that this toxin also reversibly affects cochlear function.

Oval and round window membrane changes in otitis media in the human. An ultrastructural study

An ultrastructural study of oval and round window changes in otitis media in humans was done. Ten cases were evaluated. In this first ultrastructural study of oval and round windows in otitis media, done at different stages of the disease, the round window membrane changes were similar to those of the mucoperiostium. Morphologic evidence suggests that the round window membrane layers participate in absorption and secretion of substances to and from the inner ear, such that the entire membrane could play a role in a middle and inner ear "defense system." Although the middle ear side of the footplate of the stapes had histopathological changes, the vestibular side remained essentially unchanged.

Endolymphatic sac morphology after instillation of hyperosmolar hyaluronan in the round window niche

One hundred and sixty-eight mice were injected with hyaluronan (HA) of varying tonicity in the middle ear and compared with 81 control animals to study the effects of hypertonic solutions in the middle ear on inner ear fluid homeostasis and endolymphatic sac (ES) response. Six hours after 1.9% HA and 4, 6 and 8 h after 4% HA deposition there was a significant increase in the proportion of granule-containing light epithelial cells in the ES as compared with controls indicating an enhanced secretory activity from the epithelial lining. Six, 8 and 10 h after deposition of 4% HA, the ES volume was significantly reduced. The secretory activity and the ability of the ES to vary its volume could be specific responses to dehydration of the inner ear resulting from the high colloid osmotic pressure exerted by concentrated HA. The secretion of high-molecular substances into the ES may serve to keep the ES lumen patent and thus ensure a proper ES function and/or to regulate the intralabyrinthine volume and fluid pressure. Whether the findings may have clinical relevance for Ménière's patients remains to be elucidated.

Is the vestibular system affected by middle ear effusion?

The association between middle ear effusion (MEE) and vestibular pathology is controversial. To investigate this point, 50 children with MEE scheduled for myringotomy and grommet, and 20 normal hearing children without MEE scheduled for adenotonsillectomy, underwent vestibular investigations by craniocorpography and rotatory chair, preoperatively and postoperatively. Most of the correlations, preoperative vs. postoperative, and study vs. control groups, were nonsignificant. Assuming that serous labyrinthitis is responsible for vestibular involvement in MEE, the lack of significant vestibular pathology in our study could probably be explained by the fact that no children with acute otitis media episodes or otalgia were included.

Round window membrane in serous and purulent otitis media. Structural study in the rat

The rat was used as an animal model to reveal structural alterations in the round window membrane (RWM) during serous otitis media (SOM) and purulent otitis media (POM) over a 6-week period. Comparison of POM animals and control animals showed that the RWM in the former became almost six times as thick as that in controls, whereas that of SOM animals was twice as thick. The structural changes in the RWM in POM animals were confined mainly to the epithelium facing the middle ear cavity and the subepithelial space, which was invaded by inflammatory cells and exhibited dilated vessels. The normal flat epithelium was transformed via cuboidal cells to a cylindric epithelium containing both ciliated and goblet cells. In SOM animals, light microscopy revealed only minor changes in the RWM structure. Ultrastructurally, however, the connective tissue layer exhibited dense aggregations of collagen, increased numbers of fibroblasts, and, in one case, elastic fibers. This last phenomenon was not observed in either POM ears or normal ears. The study showed that various inflammatory conditions of the middle ear, both noninfectious (SOM) and infectious (POM), can cause different structural alterations of the RWM. These structural changes may influence passage through the RWM differently.

Inner ear damage and passage through the round window membrane of Pseudomonas aeruginosa exotoxin A in a chinchilla model

By the use of computer-assisted morphometric analysis of the organ of Corti and/or measurements of action potential threshold changes, inner ear changes in chinchillas were evaluated 4 weeks after application on the round window membrane of a Pseudomonas aeruginosa exotoxin A solution. Severe inner ear damage was detected after application of 50 ng (5 microL at a concentration of 10 micrograms/mL) exotoxin A, whereas application of 5 ng exotoxin did not cause measurable inner ear damage. Perilymph concentrations of exotoxin A were measured with an enzyme-linked immunosorbent assay 1.5 to 19 hours after 50 ng, 0.5 micrograms, or 5 micrograms of exotoxin A was applied on the round window membrane. Only the highest concentration produced measurable levels of exotoxin in the inner ear fluids. It is concluded that exotoxin A present on the round window membrane of the chinchilla has the ability to penetrate into the inner ear and cause irreversible inner ear changes.

Permeability of the normal round window membrane to Haemophilus influenzae type b endotoxin

Sensorineural hearing loss associated with otitis media may be due to passage of ototoxic substances such as bacterial toxins and antibiotics, from the middle ear into the inner ear. The round window membrane is the most likely route for such transport. The aim of this study was to analyze the extent of endotoxin passage through the normal round window membrane. The round window membranes of 19 chinchillas were exposed in vivo to Gelfoam soaked in purified Haemophilus influenzae type b endotoxin at a concentration of 45,000 endotoxin units per ml (EU/ml) during 3 to 24 h. Endotoxin levels in the perilymph were measured with Limulus Amaebocyte Lysate or Quantitative Chromogenic Limulus Amaebocyte Lysate. Endotoxin was detected in half of the inner ears at concentrations close to the detection limit (approximately 4 EU/ml). The results suggest that the normal round window membrane efficiently protects the inner ear against the passage of bacterial endotoxins from the middle ear cavity. It is unlikely that endotoxin at concentrations found in the middle ear secretion during otitis media can traverse the round window membrane in sufficient amount to cause inner ear deterioration.

Gentamicin ototoxicity: histological and ultrastructural alterations after transtympanic administration

The histological and ultrastructural appearances of the inner ear vestibulum were studied after transtympanic administration of gentamicin in guinea-pigs. The animals were treated with a single transtympanic dose (0.2 cm3) of 4% gentamicin sulphate solution in the right ear; the left one was considered as control. After 7 days they were sacrificed and the vestibula of both inner ears were removed to be examined both by light and electron microscopy. In the treated inner ear damage was not always evident at light microscopical level, even if a case of complete disepithelialization of cristae ampullares was found. The examination by TEM revealed evident damage in the vestibular non-sensorial cells, such as severe cellular vacuolation, whereas sensorial elements presented heterochromatinic thickenings and cytoplasmic wrinkling, as compared to controls. The tunica fibrosa presented an irregular fibrillar plot, as well as that of the myelinic lamellae in the vestibular nerve fibres.