Ototoxicity of otic drops applied to the middle ear in the chinchilla

Previous studies have shown that the application of topical otic drops to the external ear canals of animals with patent tympanostomy tubes may result in hearing impairment and cochlear hair cell loss. Otic drops are used in patients with tympanostomy tubes or tympanic membrane perforations and could have deleterious effects on the human membranous labyrinth. This report describes the inner ear damage that occurred after direct application of aminoglycoside-containing otic drops to the middle ears of experimental animals. The membranous labyrinths of 25 chinchillas were studied two days to five months after application of Cortisporin otic suspension (which contains neomycin, polymyxin B, hydrocortisone, and propylene glycol) to the middle ear cavity. Application of 0.5 ml of Cortisporin resulted in degeneration of all inner and outer hair cells throughout the cochlea, as well as severe damage to the stria vascularis. Moderate to severe degeneration of the vestibular receptor organs was also observed. The endolymphatic sacs showed dark-staining endolymph, cellular debris, and macrophages in the sac lumina, as well as increased activity of the epithelial lining.     

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 24 h, 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 24 h, 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 24 h 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.     

Ototoxicity of neomycin and polymyxin B following middle ear application in the chinchilla and baboon

Previous experimental studies have demonstrated structural damage of the organ of Corti and stria vascularis following application of combination antibiotic otic drops to the middle ear. In this investigation the ototoxic effects of neomycin and polymyxin B (two antibiotics often used together in ototopical preparations) were separately evaluated after administration of each agent to the middle ear cavities of chinchillas and baboons. The antibiotics were administered in saline solution at the same concentrations used in Cortisporin Otic Suspension (3.5 mg/ml neomycin base, 10,000 units/ml polymyxin B). In both the rodent and primate, polymyxin B consistently produced greater cochlear damage than did neomycin. In fact, the extent of hair cell loss and strial injury produced by polymyxin B alone was, in many cases, comparable to that previously observed after application of Cortisporin Otic Suspension itself. Hair cell loss in the baboon was markedly less severe than in the chinchilla. It is believed that differences in position and structure of the round window membrane are important factors in the differing levels of ototoxicity observed in the rodent and primate.     

The ototoxicity of ceftazidime in the chinchilla middle ear

Ceftazidime (Tazicef) is a broad-spectrum cephalosporin antibiotic that may be useful as a topical agent in the treatment of otorrhea. To test the potential ototoxicity of the drug, 0.5 mL of a 10% solution of ceftazidime was introduced into the bullae of 22 chinchillas. The organ of Corti was normal in 20 temporal bones examined at 1 week after administration of the ceftazidime solution. Only 2 of 24 temporal bones examined after 4 weeks showed minor outer hair cell loss of the basal turn of the organ of Corti. Focal hemorrhage and occasional serous effusions were found in the middle ears of all animals after 1 week; these findings had mostly cleared after 4 weeks. Our results indicate that ceftazidime causes reversible middle ear inflammation, and may have some minor ototoxic potential under these experimental conditions.     

Ototoxicity of ear drops in patients suffering from chronic otitis media

The sensorineural hearing loss in 150 patients with chronic otitis media who were treated in the Haifa Medical Center (Rothschild) during a ten year period was studied. There were 124 patients treated with a mixture containing neomycin, polymyxin B and dexamethasone and a control group of 26 patients with dexamethasone only. All patients were followed up for a period of 1-2 years. Patients with hearing loss due to factors such as previous ear surgery, family history, exposure to noise etc., have been excluded. The conclusions reached were that there is a relationship between the period of disease and the sensorineural hearing loss and that the local treatment with a mixture containing neomycin + polymyxin B appears to contribute to the worsening of the sensorineural hearing loss in patients with chronic otitis media. Our numbers are small and further studies must be done, but the fact that currently used ear drops may produce a sensorineural hearing loss should not be ignored.     

Serial culture and characterization of the chinchilla middle ear epithelium.

We have successfully cultured a fibroblast-free chinchilla middle ear epithelium up to the 10th passage by using conditioned medium or using irradiated 3T3 cells as feeder cells. The cultured epithelial cells assumed a polygonal shape with a cobblestone appearance, indicating tight junction formation. A small number of the cells began to show abnormal morphology, such as indistinct cell boundaries, fibroid appearance, or giant cell formation, as the passage increased, particularly after the 5th passage. These morphologically transformed cells showed positive labeling with an anticytokeratin antibody, which indicated the epithelial origin of these cells. Neither ciliated nor secretory cells were observed in the serially cultured cells. The rate of cell growth slowed after the 7th passage, and after the 11th passage the cells no longer proliferated. Even with the above limitations, these cultured cells can be used for a number of in vitro experiments.     

Inflammatory effects of otic drops on the middle ear

Combination topical otic preparations are used to treat many infections of the external and middle ears. Despite the presence of ototoxic drugs in a number of these drops and convincing evidence of sensorineural hearing loss in humans and animal studies (Meyerhoff et al., presented at Southern Section Triological Meeting, Jan. 1983) following use of these medications, otic drops remain the cornerstone of treatment for many infectious disorders of the ear. Twelve chinchillas underwent bilateral tympanostomy tube placement and daily instillation of Cortisporin Otic Suspension (polymyxin B, neomycin, hydrocortisone, propylene glycol) in the right external auditory canal for 7 consecutive days. The animals were sacrificed 3 days later, 10 days following initiation of the Cortisporin Otic Suspension treatment. Following routine preparation of the temporal bones for light microscopy, the tissue was evaluated for evidence of inflammatory changes. All 12 animals demonstrated granulation tissue, effusion and focal hemorrhage in the ears subjected to the Cortisporin Otic Suspension. All of the contralateral control ears were normal. The present data suggest that this inflammatory response is due to a topical irritant effect of the otic preparation.     

Biochemical study of protease inhibitors in normal chinchilla middle ear

Protein concentration and inhibitory capacity of both alpha 1-antitrypsin (alpha 1-AT) and alpha 2-macroglobulin (alpha 2-M) were measured in plasma and middle ear bulla (MEB) washings of chinchillas by use of specific antisera against chinchilla alpha 1-AT and alpha 2-M. Low molecular weight (LMW) trypsin inhibitor also was analyzed in MEB washings. Chinchilla alpha 2-M showed a common antigenicity with human alpha 2-M. The mean value of alpha 1-AT in chinchilla plasma was 412.0 +/- 87.8 and that of alpha 2-M was 435.0 +/- 117.1 mg/dL. There was a significant relationship between alpha 1-AT level and antitryptic activity, and between alpha 2-M level and trypsin binding activity in plasma. The majority of alpha 1-AT and alpha 2-M in plasma is present as free inhibitors unsaturated with proteases. The MEB washings had significant antitryptic activity, which is attributed to both alpha 1-AT and LMW trypsin inhibitors. Inhibitory functions of alpha 1-AT and LMW trypsin inhibitors appear to play an important role in the defense of the normal middle ear mucosa.     

Effect of endotoxin on cultured chinchilla middle ear epithelium.

The effect of endotoxin on the growth and morphology of cultured chinchilla middle ear epithelium was examined. Within 24 hours of culture, cells maintained in medium containing endotoxin exhibited dose-dependent morphological changes. The highest concentration of endotoxin (100 mg) resulted in cell death. The growth curve of the cells in culture demonstrated a dose-dependent, significant increase in cell number when endotoxin was added to the medium.     

Extending the chinchilla middle ear epithelial model for mucin gene investigation

Objectives

To investigate the expression of recently identified human mucin genes in an in vivo model of the chinchilla middle ear epithelium (CMEE).

Methods

CMEE was harvested, RNA was extracted and primers were designed for RT-PCR to assess for expression of mucin genes Muc6, Muc17 and Muc18. Further sequencing of these genes was also accomplished.

Results

Mucin genes Muc6, Muc17 and Muc18 was assessed and found to be identical to the expression in human and mouse MEE.

Conclusion

This study further characterizes mucin gene expression in the CMEE and provides additional sequence data for chinchilla middle ear genes. The concordance of this gene expression data to that of both the human and mouse models further demonstrates the utility of this animal model in OM investigations.     

The effect of hydrogen peroxide applied to the middle ear on inner ear function

OBJECTIVES/HYPOTHESIS: The objective was to assess the effect of hydrogen peroxide applied to the middle ear on cochlear and vestibular function. STUDY DESIGN: Prospective animal study. METHODS: Sand rats underwent a right-side total labyrinthectomy, and a polyethylene tube was inserted into the left-side middle ear. Following baseline recordings of vestibular evoked potentials in response to linear acceleration stimuli and auditory brainstem response, each experimental animal received five daily applications of hydrogen peroxide into the left-side middle ear. Two control groups received saline and gentamicin, respectively. Subsequently, recordings were repeated and compared with baseline measurements. RESULTS: Saline administration affected neither vestibular evoked potentials nor auditory brainstem response. In contrast, both responses could not be recorded following gentamicin application. After hydrogen peroxide administration, auditory brainstem response could not be recorded in 25% (3 of 12) of the animals, whereas in the remaining nine animals the average auditory brainstem response threshold was significantly elevated by 55 dB (P =.000002). Linear vestibular evoked potentials could not be recorded in 42% (5 of 12) of the animals. CONCLUSION: It appears that topical hydrogen peroxide adversely affects both cochlear and vestibular function of the sand rat. The study demonstrated the effect of a reactive oxygen species on inner ear function and may be useful in the study of mechanisms responsible for this damage and its protection. Clinically, although an animal model was used in the present study, caution should be exercised when large amounts of hydrogen peroxide are applied to a dry, perforated ear.     

Effect of Escherichia coli endotoxin on cochlear potentials following its application to the chinchilla middle ear

Summary The compound action potential (CAP) of the eighth nerve and the endocochlear potential (EP) were examined in the chinchilla as an animal model when Escherichia coli endotoxin (100g) was applied to the middle ear cavity. A significant elevation of the CAP threshold at 2, 3, and 4 kHz was observed 48h after the instillation of endotoxin, but this hearing loss was thought to be caused by a conductive component. No significant change in the CAP threshold was recognized 30 days after instillation. The EP in either period showed no significant difference. These findings indicate that the application of endotoxin at the concentration used in the present study does not cause a cochlear disturbance.Presented at the XXV Workshop on Inner Ear Biology, London, 4–7 September 1988