Cisplatin Ototoxicity in the Sprague Dawley Rat Evaluated by Distortion Product Otoacoustic Emissions:Ototoxicidad por Cisplatino en la rata Sprague Dawley evaluada mediante productos de distorsión de las emisiones otoacústicas

“Spontaneous” Perilymph Fistula: A Case Report

A surgically documented case of barotrauma-induced perilymph fistula is presented in this case report. A brief review of the literature on this entity confirms the difficulty of making a definitive preoperative diagnosis in most instances. Clinical, audiometric, radiologic, and intraoperative findings are presented, and the classic presumed mechanisms for this uncommon cause of sudden sensorineural hearing loss are discussed. The presence of intact evoked otoacoustic emissions in an ear demonstrating a severe cochlear-type loss was considered helpful in narrowing the differential diagnosis in this case, and may suggest a productive avenue for future study.

Cisplatin-Induced Ototoxicity: Effects, Mechanisms and Protection Strategies

Cisplatin is a highly effective chemotherapeutic agent that is widely used to treat solid organ malignancies. However, serious side effects have been associated with its use, such as bilateral, progressive, irreversible, dose-dependent neurosensory hearing loss. Current evidence indicates that cisplatin triggers the production of reactive oxygen species in target tissues in the inner ear. A variety of agents that protect against cisplatin-induced ototoxicity have been successfully tested in cell culture and animal models. However, many of them interfere with the therapeutic effect of cisplatin, and therefore are not suitable for systemic administration in clinical practice. Consequently, local administration strategies, namely intratympanic administration, have been developed to achieve otoprotection, without reducing the antitumoral effect of cisplatin. While a considerable amount of pre-clinical information is available, clinical data on treatments to prevent cisplatin ototoxicity are only just beginning to appear. This review summarizes clinical and experimental studies of cisplatin ototoxicity, and focuses on understanding its toxicity mechanisms, clinical repercussions and prevention strategies.

Dose-dependent protection on cisplatin-induced ototoxicity - an electrophysiological study on the effect of three antioxidants in the Sprague-Dawley rat animal model

BACKGROUND

Sprague-Dawley rats were used as an acute cisplatin ototoxicity model to compare the chemo-protective efficacy of 2 sulphur-containing antioxidants (D-methionine, N-L-acetylcysteine) and 1 seleno-organic compound (ebselen). Each putative chemo-protective agent was tested at 3 different dosages in order to assess the influence of dose on auditory preservation.

MATERIAL/METHODS

A total of 40 Sprague-Dawley albino male rats were used in the study. Animals were divided into 10 groups, 3 groups of different doses for each protective agent and a cisplatin-treated control group. The animals were weight-matched before drug exposure to ensure similar weights in all groups. Auditory function was assessed with auditory brainstem responses and distortion product otoacoustic emissions at time zero and at 96 hours post-treatment.

RESULTS

At the post-treatment follow-up no significant threshold change at 8 kHz was found in the D-Met- and NAC-treated groups. All ebselen-treated animals presented significant threshold elevations. At 12 and 16 kHz, only the groups treated with 300, 450 mg/kg of D-Met and 475 mg/kg of NAC presented thresholds comparable to the pre-treatment ABR data. The ebselen-treated animals presented significant threshold shifts and showed the highest threshold elevations. The DPOAE data analysis showed that only the animals from the 350 mg/kg D-met group presented lack of statistical differences between the pre and post recordings.

CONCLUSIONS

Considering the outcome from the ABR and DPOAE analyses together, only the 350 mg/kg D-met group presented a complete auditory preservation against the 14 mg/kg cisplatin administered i.v. Data from ebselen pre-treated Sprague-Dawley albino male rats demonstrate that ebselen dosages up to 12 mg/kg given by i.p. administration lack auditory preservation in this species.

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.

Analysis of distortion product otoacoustic emission spectra in normal-hearing adults

PURPOSE

To evaluate the ability of distortion product otoacoustic emission (DPOAE) spectral characteristics to distinguish between ears with variable hearing sensitivity within the normal range.

METHOD

Distortion product grams (DP-grams) were acquired with primary tones decremented in 1/8-octave steps and primary-tone levels presented at 65 dB SPL (L1) and 45 dB SPL (L2) across an f2 frequency range of 842-7996 Hz from 22 normal-hearing adults (44 ears). Hearing thresholds of ears classified in Group A (n = 22) were better than ears classified in Group B (n = 22). Examined parameters of the DP-grams included spectral peak occurrence, peak height, peak width, and DPOAE levels. Analyses of variance were conducted to determine whether DP-gram parameters differed between Group A and Group B.

RESULTS

For the low-resolution DP-grams examined in this study, no significant between-group differences in peak occurrence, peak height, and peak width were observed. DPOAE levels were significantly higher in ears classified in Group A compared with ears classified in Group B in individuals with symmetrical hearing.

CONCLUSIONS

Although spectral peaks are evident in DP-grams acquired with low resolution of the primary tones, DPOAE levels are more effective in distinguishing ears with greater hearing sensitivity from less sensitive ears.

Functional and morphological effects of fotemustine on the auditory system of the rat

OBJECTIVE

This study aimed to elucidate the potential inner-ear effects of fotemustine, a chemotherapeutic agent which crosses the blood-brain barrier and is used in the treatment of primary and metastatic brain tumours and metastatic melanoma.

METHODS

This study utilised distortion product otoacoustic emissions and transmission electron microscopy in order to conduct electrophysiological and morphological assessments, using a rat experimental model. Twelve ears of six male rats were examined two months following intraperitoneal slow infusion of fotemustine (100 mg/m2 or 7.4 mg/kg). Pre- and post-treatment measurements were compared. Finally, electron microscopy was performed on three rat temporal bones.

RESULTS

After infusion of fotemustine, distortion product otoacoustic emissions revealed a significant reduction in signal-to-noise ratios only at 3600 Hz (from 11.95 +/- 7.52 to -0.26 +/- 9.45 dB) and at 3961 Hz (from 18.09 +/- 7.49 to 6.74 +/- 12.11 dB) (referenced to 2f1 - f2). Transmission electron microscopy of the temporal bone revealed ultrastructural changes in the outer hair cells, stria vascularis and cochlear ganglion at the cochlear basal turn. The ganglion cell perikarya were unaffected.

CONCLUSIONS

Fotemustine was administered via intraperitoneal slow infusion in a rat experimental model. Twelve ears of six survivors, from 10 rats, were evaluated at the second month. Fotemustine was determined to have a potential for ototoxicity at 3600 and 3961 Hz. Three randomly chosen rats underwent electron microscopy for morphological analysis. Morphological effects in the cochlear basal turn were observed. Oedematous intracytoplasmic spaces and perivascular areas of the stria vascularis, as well as distorted chromatin content, were detected, thereby suggesting potential ototoxic effects for this agent. Further experimental and clinical studies are required in order to determine whether the effect seen in this pilot study is reversible, and to analyse effects in humans.

Electromagnetic Fields from Mobile Phones do not Affect the Inner Auditory System of Sprague-Dawley Rats

The auditory system is the first biological structure facing the electromagnetic fields emitted by mobile phones. The aim of this study was to evaluate the cochlear functionality of Sprague-Dawley rats exposed to electromagnetic fields at the typical frequencies of GSM mobile phones (900 and 1800 MHz) by distortion product otoacoustic emissions, which are a well-known indicator of the status of the cochlea's outer hair cells. A population of 48 rats was divided into exposed and sham-exposed groups. Three sets of four loop antennas, one for sham-exposed animals and two for exposed animals, were used for the local exposures. Rats were exposed 2 h/day, 5 days/week for 4 weeks at a local SAR of 2 W/kg in the ear. Distortion product otoacoustic emissions tests were carried out before, during and after the exposure. The analysis of the data shows no statistically significant differences between the audiological signals recorded for the different groups.

Effects of 900 MHz electromagnetic fields exposure on cochlear cells' functionality in rats: Evaluation of distortion product otoacoustic emissions

In recent years, the widespread use of mobile phones has been accompanied by public debate about possible adverse consequences on human health. The auditory system is a major target of exposure to electromagnetic fields (EMF) emitted by cellular telephones; the aim of this study was the evaluation of possible effects of cellular phone-like emissions on the functionality of rat's cochlea. Distortion Products OtoAcoustic Emission (DPOAE) amplitude was selected as cochlea's outer hair cells (OHC) status indicator. A number of protocols, including different frequencies (the lower ones in rat's cochlea sensitivity spectrum), intensities and periods of exposure, were used; tests were carried out before, during and after the period of treatment. No significant variation due to exposure to microwaves has been evidenced.

Ultrastructural and electrophysiologic changes of rat cochlea after irradiation

OBJECTIVE/HYPOTHESIS

To determine the acute and subacute cochlear effects of sublethal total body irradiation.

STUDY DESIGN

The study was designed prospectively as a Sprague-Dawley (SD) rat model with otoacoustic emission measurement.

METHODS AND MATERIALS

Ten rats and 20 ears were included in the study. Distortion product otoacoustic emission (DPOAE) measurements were performed under ketamine anesthesia before and 1 to 8 weeks after sublethal dose total body irradiation. Eight and six rats survived at the first and eighth week measurements, respectively. The frequency bandwidth was set to 1,067 Hz (referenced to f1) - 9,512 Hz (referenced to f2) (2f1 - f2 = 832 - 6,076 Hz) and eight points were sampled per octave, but low-frequency (<2,549 Hz [referenced to 2f1 - f2]) results were not included in the analysis. Averages were obtained at each frequency, and statistical analysis was performed to compare the pre-and postradiation values. Then, three of the rats were killed for transient electron microscopy (TEM) of the temporal bones.

RESULTS

The posttreatment DPOAEs at almost all frequencies showed a trend toward decline at both the first and eighth weeks, but significant reduction was only detected at 3,600 and 3,961 Hz (referenced to 2f1 - f2) in the first week. TEM of the cochlea revealed ultrastructural changes in the outer hair cells (OHCs) and stria vascularis of the basal turn. The cochlear ganglion nuclei and cochlear nerve axons were unaffected.

CONCLUSION

Radiation can affect the cochlea in the acute phase at the mid to high frequencies; further prediction for long-term effects requires longer follow-ups.

Evaluation of anesthesia effects in a rat animal model using otoacoustic emission protocols

Anesthesia effects on otoacoustic emission (OAE) recordings were evaluated in a group of 72 Sprague-Dawley rats (mean weight 225+/-20 gr). Two anesthesia dosages (high and normal) and two anesthetic protocols (ketamine-xylazine, ketamine-xylazine-atropine) were tested. Transient evoked OAE (TEOAE) and distortion product OAE (DPOAE) responses were recorded in 10 min intervals, for a total period of 60 min. Analyses of the data with repeated measure models indicated the following: (1) The animals receiving a high dose of anesthesia (cumulative dose 66.6 mg of ketamine and 13.2 mg of xylazine/kg of body weight) presented significant alterations of the TEOAE response level and the signal to noise ratio at 3.0 kHz; (2) the animals receiving a normal dose of ketamine-xylazine anesthesia (cumulative dose 50 mg of ketamine and 10 mg of xylazine/kg of body weight) presented TEOAE and DPOAE responses invariant in terms of time; (3) significant differences were observed in the DPOAE responses from animals anesthetized with ketamine-xylazine and ketamine-xylazine-atropine. The data support the hypothesis that the ketamine anesthesia OAE suppressing mechanism is related to middle-ear mechanics.