The round window as access route for agents injurious to the inner ear

Hearing loss in outbred Hartley guinea pigs experimentally infected with Pichinde virus as a surrogate model of human mammarenaviral hemorrhagic fevers

Lassa fever (LF) is a neglected tropical disease that is caused by Lassa virus (LASV), a human hemorrhagic fever-causing mammarenavirus. A notable sequela of LF is sensorineural hearing loss (SNHL) that can develop in about 33% of the patients. Animal models of LF-associated SNHL have been limited in size and scope because LASV is a biosafety level 4 (BSL4) pathogen that requires its handling in a high biocontainment laboratory. In this report, we describe the development of an alternative arenavirus hearing loss model by infecting outbred Hartley guinea pigs with a virulent strain (rP18) of the Pichinde virus (PICV), which is a guinea pig-adapted mammarenavirus that has been used as a surrogate model of mammarenaviral hemorrhagic fevers in a conventional (BSL2) laboratory. By measuring auditory brainstem response (ABR) throughout the course of the virulent rP18 PICV infection, we noticed that some of the animals experienced an acute but transient level of hearing loss. Cochleae of hearing-impaired animals, but not of controls, had demonstrable viral RNA by quantitative RT-PCR, indicating the presence of virus in the affected inner ear with no overt histopathological changes. In contrast, neither the outbred Hartley guinea pigs infected with a known avirulent strain (rP2) of PICV nor those that were mock-infected showed any evidence of hearing loss or viral infection of the inner ear. This is the first report of an immunocompetent small animal model of mammarenavirus-induced hearing loss that can be used to evaluate potential therapeutics against virus-induced hearing impairment under a conventional laboratory setting.

Does Hypochlorous Acid Cause Ototoxicity? An Experimental Study

AIM

Hypochlorous acid (HOCl) is a weak acid that ionizes in water. It is an effective antiseptic exhibiting low toxicity on living tissues. We aimed to investigate the ototoxic effects of HOCl on an animal model by using electrophysiological and histological methods.

MATERIALS AND METHODS

The study comprised 32 Sprague-Dawley rats, which were separated into four groups: control group (A), saline solution group (B), 70% isopropyl alcohol + 2% chlorhexidine group (C), and HOCl group (D). After recording the auditory brainstem response (ABR) for basal hearing thresholds (8, 16, 24, and 32 kHz), 0.03 ml of the aforementioned materials was injected intratympanically three times every 2 days in groups B, C, and D. ABR measurements were repeated on the 7th and 21st days. All animals were sacrificed, and temporal bones were prepared for examinations of cochlear histology and vascular endothelial growth factor immunohistochemistry.

RESULTS

Basal hearing levels were normal across all frequencies and groups, with no statistical differentiation. On the 7th and 21st days after the ABR test, all other groups demonstrated a significant deterioration in hearing levels compared with group A. When the results from 7th and 21st days were compared within group D, a partial recovery was observed. In histopathology, groups C and D demonstrated moderate and severe cochlear degeneration, along with decreased immunoreactivity in the organ of Corti, stria vascularis, and spiral ligament.

CONCLUSION

This is the first study to evaluate the safety of using HOCl in otology. Although HOCI is less ototoxic than the disinfectant used, it may have a toxic effect on cochlea.Level of Evidence: Animal Research.

A gold mine for drug discovery: Strategies to develop cyclic peptides into therapies

As a versatile therapeutic modality, peptides attract much attention because of their great binding affinity, low toxicity, and the capability of targeting traditionally "undruggable" protein surfaces. However, the deficiency of cell permeability and metabolic stability always limits the success of in vitro bioactive peptides as drug candidates. Peptide macrocyclization is one of the most established strategies to overcome these limitations. Over the past decades, more than 40 cyclic peptide drugs have been clinically approved, the vast majority of which are derived from natural products. The de novo discovered cyclic peptides on the basis of rational design and in vitro evolution, have also enabled the binding with targets for which nature provides no solutions. The current review summarizes different classes of cyclic peptides with diverse biological activities, and presents an overview of various approaches to develop cyclic peptide-based drug candidates, drawing upon series of examples to illustrate each strategy.

Alterations in hearing function of patients with glucose disorders

OBJECTIVE

To study the prevalence of hearing impairment in patients with various glucose disorders.

PATIENTS AND METHODS

A total of 499 individuals were studied, 51 patients with type 1 (TIDM), 188 patients with type 2 diabetes mellitus (T2DM), 39 patients with impaired fasting glucose (IFG), and 221 controls. Measurements were performed, blood was drawn, and a relevant questionnaire was completed. Ηearing function was assessed by pure-tone audiometry (PTA) and distortion product otoacustic emissions (DPOAEs).

RESULTS

Patients with impaired glucose metabolism (IGM: T2DM or IFG) compared to controls had a higher percentage of abnormal PTA and DPOAEs for both the right (70.2 vs. 56.9% and 40.4 vs. 24.2%, respectively, p < 0.001) and the left (74.1 vs. 59.3% and 47.5 vs. 25.4%, respectively, p < 0.001) ear. Patients with TIDM had similar levels for the left ear (54.9 vs. 59.3% and 27.5 vs. 25.4%, respectively, p > 0.05) and lower levels for the right ear (35.3 vs. 56.9% and 13.7 vs. 24.2%, respectively, p < 0.001 and p = 0.044) percentages of abnormal PTA and DPOAEs compared to controls. Logistic regression analysis indicated that independent parameters for abnormal DPOAEs in one or both ears are age, male gender, exposure to noisy environments, and the presence of IGM.

CONCLUSIONS

Hearing impairment was more prevalent in patients with IGM compared to healthy controls, as assessed by PTA and DPOAEs. Age, male gender, and exposure to noise are other factors that can independently affect hearing ability. Physicians should bear in mind possible defects in hearing ability when dealing with such patients.

Otomycosis With Tympanic Membrane Perforation: A Review of the Literature

OBJECTIVE

The purpose of the present study was to assess the rate of tympanic membrane perforation in patients with otomycosis and to discuss the literature regarding the difficulties in managing this condition.

DATA SOURCES

Literature review from 1999 to 2019, Web of Science, PubMed, and Medline.

STUDY SELECTION

We searched for eligible articles concerning the clinical entity of tympanic membrane perforation secondary to otomycosis. Case series and clinical trials were the types of articles included for this review.

DATA EXTRACTION

All the articles described in the study selection were used for this review.

DATA SYNTHESIS

Statistical techniques were not used.

CONCLUSION

Based on the available literature, it seems that tympanic membrane perforation secondary to otomycosis is not uncommon. The presence of this complication is associated with 2 problems: Antimycotic solutions are irritant to middle ear and may be ototoxic to the cochlea. Although most cases of fungus caused tympanic membrane (TM) perforation resolve with proper medical treatment, in a few patients a tympanoplasty may be required.

Evaluation of Ototoxicity of an Antifog Agent and the Suspected Underlying Mechanisms: An Animal Study

Use of rigid endoscopes has become widespread in middle ear surgeries, thereby attracting attention to the safety of antifog agents. However, few studies on the ototoxicity of antifog agents have been conducted. The purpose of this study was to evaluate hair cell damage and the underlying mechanisms caused by antifog agents using zebrafish larvae. We exposed zebrafish larvae at 3 days postfertilization to various concentrations of the antifog agent, Ultrastop (0.01, 0.02, 0.04, and 0.08%) for 72 hours. The average number of hair cells within 4 neuromasts of larvae, including supraorbital (SO1 and SO2), otic (O1), and occipital (OC1), in the control group were compared to those in the exposure groups. Significant hair cell loss was observed in the experimental groups compared to that in the control group (P < .01; control: 53.88 ± 4.85, 0.01%: 45.08 ± 11.70, 0.02%: 41.36 ± 12.00, 0.04%: 35.36 ± 16.18, and 0.08%: 15.60 ± 7.53 cells). Concentration-dependent increase in hair cell apoptosis by terminal deoxynucleotidyltransferase (TDT)-mediated dUTP-biotin nick end labeling assay (control: 0.00 ± 0.00, 0.01%: 3.48 ± 2.18, 0.02%: 9.64 ± 5.75, 0.04%: 17.72 ± 6.26, and 0.08%: 14.60 ± 8.18 cells) and decrease in the viability of hair cell mitochondria by 2-(4-[dimethylamino] styryl)-N-ethylpyridinium iodide assay (control: 9.61 ± 1.47, 0.01%: 8.28 ± 2.22, 0.02%: 8.45 ± 2.72, 0.04%: 7.25 ± 2.44, and 0.08%: 6.77 ± 3.26 percentage of total area) were observed. Antifog agent exposure can cause hair cell damage in zebrafish larvae, possibly by induction of mitochondrial damage with subsequent apoptosis of hair cells.

Efficacy of common reagents for killing ticks in the ear canal

Objective

To determine if widely available solutions can effectively kill ticks that may be found in the human ear canal.

Methods

This study was prospective, controlled and blinded animal study. Lone star ticks (Amblyomma americanum), both nymphal and adult, were submerged in one of four preparations (acetone, isopropyl alcohol 70%, ethanol 95%, or 4% lidocaine) in test tubes (n = 20 per group) for 20 minutes. Ticks were agitated by intermittent probing. Activity of the nymphal ticks was directly observed while those of the adult ticks was video‐recorded during the exposure period. Two blinded investigators viewed the videos of adult ticks and during the exposure period to determine the time until death (ie, movement cessation). Mortality was assessed immediately after exposure, and confirmed 24 and 48 hours after exposure.

Results

Acetone killed ticks most rapidly (nymph mean time = 185.1 s; adult mean time = 562.9 s). Isopropyl alcohol 70% (nymphs, 328.9 s; adults, 1128.4 s) and ethanol 95% (nymphs, 294 s; adults, 1129.4 s) took longer to kill the ticks. All ticks treated with 4% lidocaine survived. These differences were significant (nymphs, P < .0001; adults, P < .0001).

Conclusions

Acetone was the fastest acting and most effective reagent, followed by ethanol and isopropyl alcohol. These solutions may prove useful in otoacariasis with an intact tympanic membrane.

Level of Evidence

N/A

Animal Model of Sensorineural Hearing Loss Associated with Lassa Virus Infection

Approximately one-third of Lassa virus (LASV)-infected patients develop sensorineural hearing loss (SNHL) in the late stages of acute disease or in early convalescence. With 500,000 annual cases of Lassa fever (LF), LASV is a major cause of hearing loss in regions of West Africa where LF is endemic. To date, no animal models exist that depict the human pathology of LF with associated hearing loss. Here, we aimed to develop an animal model to study LASV-induced hearing loss using human isolates from a 2012 Sierra Leone outbreak. We have recently established a murine model for LF that closely mimics many features of human disease. In this model, LASV isolated from a lethal human case was highly virulent, while the virus isolated from a nonlethal case elicited mostly mild disease with moderate mortality. More importantly, both viruses were able to induce SNHL in surviving animals. However, utilization of the nonlethal, human LASV isolate allowed us to consistently produce large numbers of survivors with hearing loss. Surviving mice developed permanent hearing loss associated with mild damage to the cochlear hair cells and, strikingly, significant degeneration of the spiral ganglion cells of the auditory nerve. Therefore, the pathological changes in the inner ear of the mice with SNHL supported the phenotypic loss of hearing and provided further insights into the mechanistic cause of LF-associated hearing loss.

IMPORTANCE

Sensorineural hearing loss is a major complication for LF survivors. The development of a small-animal model of LASV infection that replicates hearing loss and the clinical and pathological features of LF will significantly increase knowledge of pathogenesis and vaccine studies. In addition, such a model will permit detailed characterization of the hearing loss mechanism and allow for the development of appropriate diagnostic approaches and medical care for LF patients with hearing impairment.

A comparison of Locacorten-Vioform and clotrimazole in otomycosis: A systematic review and one-way meta-analysis

OBJECTIVES/HYPOTHESIS

The goal of this systematic review was to compare the efficacy and ototoxicity of Locacorten-Vioform (Paladin Labs Inc., Montreal, Quebec, Canada) and clotrimazole in the treatment of patients with otomycosis.

DATA SOURCES

Embase, Cumulative Index to Nursing and Allied Health Literature, MEDLINE, World Health Organization International Clinical Trials Registry Platform, European Union Clinical Trials Register, Cochrane Library databases of clinical trials, and ClinicalTrials.gov.

METHODS

We included any randomized controlled trials or nonrandomized studies (case-control, cohort, and case series) assessing the topical use of Locacorten-Vioform (Paladin Labs Inc.) and/or clotrimazole in adult and/or pediatric immunocompetent patient population with otomycosis. DerSimonian and Laird's random effects approach was used for meta-analysis, followed by an assessment of heterogeneity and subgroup analysis.

RESULTS

Of 226 reviewed articles, 14 were retained. Clotrimazole efficacy rate was 85% (95% confidence interval [CI]: 79.7-89.0%), whereas Locacorten-Vioform (Paladin Labs Inc.) was 73% (95% CI: 56.0-84.5%). Overall, study quality was low. There was high heterogeneity in both groups (I(2) of 47 and 49). There were only three studies assessing Locacorten-Vioform (Paladin Labs Inc.); therefore, comparative assessment was not possible. A one-way meta-analysis involving 13 clotrimazole studies was performed. Heterogeneity across studies was high; however, studies using objective analysis assessing treatment efficacy, randomized controlled trials, studies using drops, studies performed in Asia, and studies where Candida was the major fungus at diagnosis demonstrated low heterogeneity.

CONCLUSION

Although both are safe and effective, there is insufficient evidence supporting increased efficacy of either clotrimazole or Locacorten-Vioform (Paladin Labs Inc.) for the treatment of otomycosis. High-quality comparative studies are required.

LEVEL OF EVIDENCE

N/A. Laryngoscope, 126:1411-1419, 2016.

Ototoxic Effect of Ultrastop Antifog Solution Applied to the Guinea Pig Middle Ear

Objectives

Recent advances in endoscopic technology have allowed its application to middle ear surgery. An antifog agent is necessary for endoscopy because moisture and blood may obscure visibility. Ultrastop is one of the most commonly used antifog agents. The current study examined the ototoxic effect of topical application of Ultrastop in the guinea pig ear.

Study Design

A preliminary experimental animal study.

Setting

University hospital.

Subjects and Methods

Eighteen male Hartley guinea pigs (weight, 480-620 g) were divided into 3 groups to be treated with Ultrastop, gentamicin (50 mg/mL, positive control), or saline solution (negative control). After auditory brainstem responses were measured, topical solutions of 0.2 mL were applied through a small hole made at the tympanic bulla. Posttreatment auditory brainstem responses were obtained 14 days after the treatment. The extent of middle ear damage was investigated and scored.

Results

The saline-treated group showed no deterioration in auditory brainstem response threshold. The Ultrastop-treated and gentamicin-treated groups showed severe deterioration in auditory brainstem response threshold. Middle ear examination revealed extensive changes in the Ultrastop-treated group and medium changes in the gentamicin-treated group.

Conclusion

Ultrastop applied topically to the guinea pig middle ear caused significant middle ear inflammation and hearing impairment.

Noise-induced hearing loss in Korean workers: co-exposure to organic solvents and heavy metals in nationwide industries

Background

Noise exposure is a well-known contributor to work-related hearing loss. Recent biological evidence suggests that exposure to ototoxic chemicals such as organic solvents and heavy metals may be additional contributors to hearing loss. However, in industrial settings, it is difficult to determine the risks of hearing loss due to these chemicals in workplaces accompanied by excessive noise exposure. A few studies suggest that the effect of noise may be enhanced by ototoxic chemicals. Therefore, this study investigated whether co-exposure to organic solvents and/or heavy metals in the workplace modifies the risk of noise exposure on hearing loss in a background of excessive noise.

Methods

We examined 30,072 workers nationwide in a wide range of industries from the Korea National Occupational Health Surveillance 2009. Data on industry-based exposure (e.g., occupational noise, heavy metals, and organic solvents) and subject-specific health outcomes (e.g., audiometric examination) were collected. Noise was measured as the daily 8-h time-weighted average level. Air conduction hearing thresholds were measured from 0.5 to 6 kHz, and pure-tone averages (PTA) (i.e., means of 2, 3, and 4 kHz) were computed.

Results

In the multivariate linear model, PTA increment with occupational noise were 1.64-fold and 2.15-fold higher in individuals exposed to heavy metals and organic solvents than in unexposed individuals, respectively.

Conclusion

This study provides nationwide evidence that co-exposure to heavy metals and/or organic solvents may exacerbate the effect of noise exposure on hearing loss in workplaces. These findings suggest that workers in industries dealing with heavy metals or organic solvents are susceptible to such risks.

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.

Effects of topical oxiconazole and boric acid in alcohol solutions to rat inner ears

OBJECTIVE

The aim of this study is to evaluate the ototoxicity of topical oxiconazole and boric acid in alcohol solutions.

STUDY DESIGN

Prospective controlled animal study.

SETTING

Research laboratory.

METHOD

Fifty adult Wistar albino rats were divided into 5 groups consisting of 10 animals each. The right tympanic membranes were perforated, and baseline and posttreatment distortion product otoacoustic emission (DPOAE) measurements were performed.

RESULTS

The solutions were applied through the external ear canal to the middle ear twice a day for 14 days. The rats in group I and group II received 0.1 mL of oxiconazole-containing solution drops and 4% boric acid in alcohol solution drops, respectively. Group III received gentamicin solution (40 mg/mL) (ototoxic control), group IV received saline solution, and group V was followed without any medication. The baseline DPOAE results of the right ears of all animals tested were normal. Animals in groups I, II, IV, and V showed no statistically significant change in the DPOAE amplitudes. The rats in the gentamicin group showed a significant decrease.

CONCLUSION

This study demonstrates that topically used oxiconazole and boric acid in alcohol solutions to the middle ear appear to be safe on the inner ear of rats. The safety of these drugs has not yet been confirmed in humans. Caution should be taken when prescribing these drugs, especially to patients who had tympanic membrane perforation. Ear drops should be chosen more carefully in an external ear infection for patients with tympanic membrane perforation to avoid ototoxicity.

Ototoxicity of Povidone-Iodine applied to the middle ear cavity of guinea pigs

OBJECTIVE

Povidone-Iodine preparation is used as a disinfectant in otological surgeries. The ototoxicity of Povidone-Iodine preparation was evaluated using infant, young and adult guinea pigs. The effects of different concentrations and of different exposure durations on compound action potentials were also studied.

MATERIALS & METHODS

Povidone-Iodine was used to fill one middle ear cavity of the guinea pig, and the compound action potential (CAP) was measured from the round window membrane at 24h, 7 days, and 28 days. The contralateral side was filled with saline as control. Test sounds used were clicks and tone bursts of 2, 4, and 8 kHz.

RESULTS

At 24h, Povidone-Iodine solution showed a significant toxic effect in the infant group. In the young animal group, no toxic effect was seen. In the adult group, a mild degree of deafness for 2 kHz was found. At 7 days, the young group showed significant hearing loss for all frequencies, but the adult group did not show any hearing loss. With a half strength solution, both young and adult group did not show hearing loss. At 28 days, with a full strength solution, hearing loss became prominent for all sound stimulation. With 1/8th dilution, the young group showed a moderate hearing loss, but the adult group did not.

CONCLUSION

The thicker round window membrane in human is expected to provide more protection to the human cochlea than in the guinea pig model that we have studied. Mild hearing loss at 24h and 7 days using 10% solution, but no hearing loss with 5% solution at 7 days may indicate that rinsing of the middle ear cavity with saline during surgery should minimize the ototoxic effect of this product. The age of the animals does influence the outcome of the ototoxicity experiment. From this experiment, Povidone-Iodine preparations in the infant should be used with caution. Povidone scrub should not be used for otologic surgery.

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.

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.

Ototopical antifungals and otomycosis: a review

There has been an increase in the prevalence of otomycosis in recent years. This has been linked to the extensive use of antibiotic eardrops. Treatment of otomycosis is challenging, and requires a close follow-up. We present a review of the literature on otomycosis, the topical antifungals most commonly used, and discuss their ototoxic potential. Candida albicans and Aspergillus are the most commonly identified organisms. Antifungals from the Azole class seem to be the most effective, followed by Nystatin and Tolnaftate.

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.

Round window gentamicin absorption: an in vivo human model

OBJECTIVE/HYPOTHESIS

Using a novel human labyrinthine sampling model, in vivo gentamicin absorption through the round window can be measured.

STUDY DESIGN

A prospective study.

METHODS

Gentamicin was delivered either transtympanically (preoperative) or through a facial recess approach (intraoperative). The lateral semicircular canal and vestibule were opened, and by means of a microsyringe, labyrinthine fluid was aspirated. A sample of serum was also drawn. In all patients cerebrospinal fluid was also drawn. The samples were analyzed using a standard chemistry analyzer.

RESULTS

Intratympanic gentamicin diffused through the round window membrane and achieved concentrations in the labyrinthine fluid ranging from 0 to 16 mg/L. Intratympanic gentamicin was absorbed into the systemic circulation in 4 of 11 patients with serum levels ranging from 0.3 to 0.4 mg/L. No gentamicin was detected in the cerebrospinal fluid.

CONCLUSIONS

Intratympanic gentamicin diffuses rapidly through the round window membrane and achieves significant levels in the inner ear. Thus, this new model can be used to assess round window permeability to clinically relevant medications such as steroids and ototopical antibiotics.

Intratympanic ciprofloxacin and the human labyrinthine sampling model

OBJECTIVE

The aim of the study was to investigate the potential absorption of intratympanic ciprofloxacin through the human round window membrane.

STUDY DESIGN

A prospective study.

METHODS

Ciprofloxacin was instilled into the middle ear of 10 patients undergoing acoustic tumor removal. The lateral semicircular canal and vestibule were subsequently opened and, using a microsyringe, labyrinthine fluid was aspirated. A sample each of serum and cerebrospinal fluid was also drawn.

RESULTS

Into each middle ear, 0.5 mL ciprofloxacin (0.3%) was instilled. The time interval between the ciprofloxacin application to the round window membrane and sampling of labyrinthine fluid and plasma ranged from 9 to 120 minutes. There was no measurable ciprofloxacin in the labyrinthine fluid, cerebrospinal fluid, or serum of 10 patients.

CONCLUSION

The lack of measurable absorption of intratympanic ciprofloxacin into the inner ear indicates that the chance of ototoxicity when ciprofloxacin is used clinically, even in the presence of a tympanic membrane perforation, is low.

Effects of gentamicin and pH on [Ca2+]i in apical and basal outer hair cells from guinea pigs

Aminoglycosides are widely used antibiotics and frequently produce acute ototoxicity. In this study we attempted to comparatively investigate the effects of gentamicin on Ca2+ influx of apical and basal outer hair cells (OHCs) isolated from guinea-pig cochlea. Since the solution of gentamicin sulfate salt is acidic (pH 3.1-3.3), we also explored the effect of external acidification on Ca2+ influx. By means of fura-2 microspectrofluorimetry, we measured the intracellular calcium concentration ([Ca2+]i) of OHCs bathed in Hanks' balanced salt solution (pH 7.40) during either a resting state or high K+-induced depolarization. Our results show that at the resting state, the baseline [Ca2+]i in apical OHCs (94+/-2.0 nM) was slightly lower than that in basal OHCs (101.1+/-2.4 nM). By contrast, the increase in [Ca2+]i evoked by high K+ depolarization in apical OHCs was about two-fold greater than that in basal OHCs. Nifedipine (30 microM) abolished the increased [Ca2+]i in both types of OHCs, suggesting that Ca2+ influx was mainly through L-type Ca2+ channels of OHCs. While gentamicin and extracellular acidification (pH 7.14) can separately attenuate this increase in [Ca2+]i in both types of OHCs, their suppressive effects are additive in basal OHCs, but not in apical OHCs. The implications of these findings are that: (1) apical and basal OHCs behave differently in response to depolarization-increased [Ca2+]i, and (2) basal OHCs are more vulnerable to the impairment of Ca2+ entry during depolarization by a combination of gentamicin and extracellular acidification, which is correlated with the clinical observation that ototoxicity of aminoglycosides at the basal coil of OHCs is more severe than that at the apical coils. Moreover, the possibility that extracellular acidification may enhance the acute ototoxic effects of aminoglycosides should be considered especially in topical applications.

Insecticidal activity of common reagents for insect foreign bodies of the ear

OBJECTIVE

Insects commonly present as painful and distressing foreign bodies of the external ear canal. Removing live insects can be challenging, especially for primary care physicians who have limited equipment. The purpose of this study is to compare the insecticidal activity of commonly available preparations for insects that are most frequently recovered from ear canals: cockroaches (German and American), ticks, beetles, and honeybees.

STUDY DESIGN

Prospective, blinded.

METHODS

One hundred seventy insects of each species were placed in test tubes and submerged in 17 test preparations (10 tubes per preparation, 1 insect per test tube). Insect activity was stimulated by agitation of the test tube. Responses were monitored, and the time until death was measured.

RESULTS

Most test preparations exhibited some insecticidal activity against most insect species. Ticks were completely resistant to all of the test reagents. Ethanol killed the American cockroaches (mean time, 32.6 s), German cockroaches (mean time, 29.6 s), and honeybees (mean time, 19.6 s) the most rapidly.

CONCLUSION

Many commonly available reagents may be used to kill or immobilize insect foreign bodies of the ear.

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.

Experimental model of cisplatin ototoxicity in chinchillas

Cisplatin is an important antineoplastic agent. Its ototoxicity has been well defined, both in human and animal studies. However, animal models of systemic cisplatin administration have been complicated by multiple toxic effects. We studied cisplatin ototoxicity in an animal model involving topical application of cisplatin to the round-window membrane. Adult chinchillas were anesthetized with ketamine and pentobarbital, and auditory function was tested with the use of auditory brain-stem responses to various stimuli (clicks and 8-and 16-kHz tone bursts). Each animal was used as its own control. The middle-ear cavity was exposed through the bulla. In the experimental ear, a 25-microl solution of 0.25 mg cisplatin/1.0 ml normal saline solution was applied to the round-window membrane. In the control ear, 25 microl normal saline solution was applied to the round-window membrane. Follow-up auditory brain-stem response testing was conducted 7 days after treatment. A significant increase in threshold in the experimental ears was seen on comparison with the control ears. This finding suggests that application of cisplatin to the round-window membrane is a useful animal model in which to study cisplatin ototoxicity.

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.

Auditory brain stem response changes after application of endotoxin to the round window membrane in experimental otitis media

The effects of endotoxin (purified Escherichia coli lipopolysaccharide 0111:B4) on cochlear function in normal and otitis media animals were evaluated. Two types of experimental otitis media models were developed in guinea pigs: eustachian tube obstruction and intratympanic injection of endotoxin. In normal animals, three different concentrations (0.01, 0.1, or 1.0 mg/ml) of endotoxin were applied onto the round window membrane, and auditory brain stem responses were recorded at 1, 3, 6, and 12 hours and 1, 2, 3, and 14 days after the application of endotoxin. Concentrations of 0.01 and 0.1 mg/ml of endotoxin did not affect the auditory brain stem response thresholds, whereas a concentration of 1.0 mg/ml resulted in elevation of the auditory brain stem response thresholds. Alteration of the auditory brain stem response threshold began at 3 hours, reached a peak at 24 or 48 hours, and returned to a normal level 2 weeks after the application of endotoxin. However, when the same concentration (1.0 mg/ml) of endotoxin was applied to the round window membranes of animals that underwent eustachian tube obstruction or intratympanic injection of endotoxin, the endotoxin did not cause any alteration of the auditory brain stem response threshold compared with normal animals.