Ototoxicity of Chemotherapeutic Agents

Difluoromethylornithine (DFMO) and Neuroblastoma: A Review

Neuroblastoma is a type of cancer that affects the sympathetic nervous system and is the most common extracranial solid tumor in children. Difluoromethylornithine (DFMO) is a drug that has shown promise as a treatment option for high-risk neuroblastoma. This review aims to provide an overview of the current research on the use of DFMO in neuroblastoma treatment. The review includes a discussion of the mechanisms of action of DFMO, as well as its potential for use in combination with other treatments such as chemotherapy and immunotherapy. The review also examines the current clinical trials involving DFMO in high-risk neuroblastoma patients and provides insights into the challenges and future directions for the use of DFMO in neuroblastoma treatment. Overall, the review highlights the potential of DFMO as a promising therapy for neuroblastoma and highlights the need for further research to fully understand its potential benefits and limitations.

Oxidative Stress and Inflammation Caused by Cisplatin Ototoxicity

Hearing loss is a significant health problem that can result from a variety of exogenous insults that generate oxidative stress and inflammation. This can produce cellular damage and impairment of hearing. Radiation damage, ageing, damage produced by cochlear implantation, acoustic trauma and ototoxic drug exposure can all generate reactive oxygen species in the inner ear with loss of sensory cells and hearing loss. Cisplatin ototoxicity is one of the major causes of hearing loss in children and adults. This review will address cisplatin ototoxicity. It includes discussion of the mechanisms associated with cisplatin-induced hearing loss including uptake pathways for cisplatin entry, oxidative stress due to overpowering antioxidant defense mechanisms, and the recently described toxic pathways that are activated by cisplatin, including necroptosis and ferroptosis. The cochlea contains G-protein coupled receptors that can be activated to provide protection. These include adenosine A1 receptors, cannabinoid 2 receptors (CB2) and the Sphingosine 1-Phosphate Receptor 2 (S1PR2). A variety of heat shock proteins (HSPs) can be up-regulated in the cochlea. The use of exosomes offers a novel method of delivery of HSPs to provide protection. A reversible MET channel blocker that can be administered orally may block cisplatin uptake into the cochlear cells. Several protective agents in preclinical studies have been shown to not interfere with cisplatin efficacy. Statins have shown efficacy in reducing cisplatin ototoxicity without compromising patient response to treatment. Additional clinical trials could provide exciting findings in the prevention of cisplatin ototoxicity.

Vincristine exposure impairs skin keratinocytes, ionocytes, and lateral-line hair cells in developing zebrafish embryos

Environmental contamination by anticancer pharmaceuticals has been widely reported. These drugs are not readily biodegradable, and their parent compounds and/or metabolites have been detected in surface waters and groundwater throughout the world. Adverse effects of anticancer drugs occur frequently in cancer patients, and a large body of clinical knowledge has accumulated. However, the effects of these drugs on aquatic organisms have not been thoroughly studied. This study aimed to investigate the effects of acute exposure to a common anticancer drug, vincristine (VCR), on zebrafish embryonic development and skin function. After 96 h of VCR exposure (0, 1, 10, 15, and 25 mg/L), significant teratogenic effects were observed, including growth retardation, pericardial edema, spine, tail, and yolk sac malformations (VCR ≥ 15 mg/L), a decreased heart rate, and ocular malformations (VCR ≥ 10 mg/L). The value of the half lethal concentration for zebrafish embryos was 20.6 mg/L. At ≥10 mg/L VCR, systemic ion contents and acid secretion in the skin over the yolk-sac decreased, and these findings were associated with decreases in skin ionocytes (H⁺-ATPase-rich cells and Na⁺-K⁺-ATPase-rich cells). Also, the microridge-structure of skin keratinocytes was significantly damaged. The number of lateral line hair cells was reduced when VCR was ≥10 mg/L, and functional impairment was detected when VCR was as low as 1 mg/L. Results of this in vivo study in zebrafish embryos indicate that acute exposure to VCR can lead to developmental defects, impairment of skin functions, and even fish death.

A quick and reliable estimate of extended high-frequency hearing

OBJECTIVE

To encourage researchers to perform high-frequency threshold estimation using a technique outlined by Rieke and colleagues, described as fixed-level frequency threshold estimation. Their method used a Bekesy-style roving tone to estimate the highest audible frequency of a listener. The tone was fixed in its intensity (SPL) and changed in frequency as the participant indicated whether they could perceive the tone, or not. This was developed specifically for ototoxicity monitoring in the extended high-frequency region. Rieke and colleagues established that this approach to measuring hearing thresholds is both fast and reliable.

DESIGN

The current article extends this approach to using a simple PC-soundcard-transducer setup and the method of limits to rapidly establish the highest audible frequency of a listener.Study sample: 24 listeners performed standard and fixed-level audiometry in the extended high-frequency range.

RESULTS

The method described is rapid and reliable and a single summary metric is obtained for each listener.

CONCLUSIONS

The advantage of the described approach over standard pure-tone audiometry in the extended high-frequency range is the time taken, the ability to avoid missing data points and the risk of distortions or electrical noise when close to maximal system output.

Drug-Induced Ototoxicity: Diagnosis and Monitoring

Ototoxicity diagnosis and management has historically been approached using a variety of methods. However, in recent years a consensus on useful and practical approaches has been developed through clinical guidelines of the American Speech Language Hearing Association, the American Academy of Audiology, and multiple clinical trials published in peer-reviewed literature. Some of the guidelines and approaches are used to detect and monitor ototoxicity, while others are used to grade adverse events. Some of the audiologic measures are primary, while others are adjunct measures and may be tailored to the specific needs of the patient or clinical trial. For some types of monitoring, such as drug-induced tinnitus or dizziness, validated paper survey instruments can be both sensitive and easy for fragile patients. This review addresses the characteristics of some of the most common clinical ototoxins and the most common methods for detecting and monitoring ototoxicity in clinical practice and clinical trials.

Audiometry results and TEOAE and DPOAE amplitudes in men taking a phosphodiesterase type 5 inhibitor for erectile dysfunction

We conducted a prospective study of transient evoked otoacoustic emissions (TEOAEs) and distortion-product otoacoustic emissions (DPOAEs) in men who were taking an oral phosphodiesterase type 5 (PDE5) inhibitor for erectile dysfunction. Our study group was made up of 30 men (60 ears), aged 34 to 60 years (mean: 50.9). They were randomly divided into three groups; 10 men were given sildenafil (Viagra) at 50 mg twice a week, 10 were given tadalafil (Cialis) at 20 mg twice a week, and 10 were given vardenafil (Levitra) at 20 mg twice a week. All patients took their drug for 3 weeks, for a total of 6 tablets for each patient. Audiometric tests and TEOAE and DPOAE measurements were performed before and after treatment. Post-treatment audiometry demonstrated improvement in hearing in all three groups. However, post-treatment TEOAE amplitudes and DPOAE amplitudes differed among the three groups; they were significantly higher in the sildenafil group at 1.0 kHz and the same in the tadalafil group; in the vardenafil group, the DPOAE amplitude was significantly lower at 3.0 kHz while there was no change in the TEOAE amplitude. We speculate that the possible mechanism for these findings is that PDE5 inhibitors block degradation of cyclic guanosine monophosphate (cGMP) and induce dilation of the cochlear microcirculation, resulting in an increase in cochlear blood flow. We also believe that the decrease in DPOAE amplitudes at 3.0 kHz seen in the vardenafil group may be related to an accumulation of nitric oxide/cGMP complex, which is toxic to the cochlea; however, since there was no change in TEOAE amplitude in the vardenafil group, this influence may be minimal. Further studies are needed to obtain a more comprehensive assessment of the effects of PDE5 inhibitors on hearing with the use of higher doses and longer durations of therapy.

Risk of sudden sensorineural hearing loss in adults using phosphodiesterase type 5 inhibitors: Population-based cohort study

PURPOSE

The objective of the study was to determine the risk of sudden sensorineural hearing loss (SNHL) associated with use of phosphodiesterase type 5 (PDE5) inhibitors.

METHODS

We conducted a retrospective cohort study in the MarketScan Commercial Claims and Encounters Database including adult men who initiated a PDE5 inhibitor (n = 377,722) and 1,957,233 nonusers between 1998 and 2007. Periods of drug exposure were assessed on a weekly basis based on pharmacy billing records, assuming use of 1 dose per week (current use). Incident sudden SNHL was defined based on inpatient or outpatient visits with International Classification of Diseases, Ninth Revision, Clinical Modification codes 389.1x, 389.2x, or 388.2 plus ≥2 procedure codes for audiometric hearing testing within ±30 days of sudden SNHL diagnosis. We used age- and propensity score-adjusted Cox proportional hazards model to evaluate the risk of sudden SNHL during periods of current or recent use compared with that of nonuse. We conducted sensitivity analyses by varying the assumed drug utilization frequency and sudden SNHL case definition.

RESULTS

We evaluated 1233 sudden SNHL cases, resulting in an incidence of 4.35, 5.58, and 2.38 per 10,000 person-years for current, recent, and nonuse of PDE5 inhibitors, respectively. Compared with nonuse, the adjusted hazard ratio was 1.25 (1.01-1.55) for current use with a risk difference of 1.97 (1.12-2.82) per 10,000 person-years. For recent use, the adjusted hazard ratio was 1.60 (1.33-1.94) and risk difference was 3.19 (2.24-4.14). Estimates were consistent across the sensitivity analyses.

CONCLUSIONS

Use of PDE5 inhibitors is associated with a small but significantly increased risk of sudden SNHL.

Changes in Otoacoustic Emissions and Auditory Brain Stem Response after C/s-Platinum Exposure in Gerbils

Ototoxicity associated with cis-platinum administration commonly presents as hearing loss and tinnitus. The hearing loss is usually an irreversible, high-frequency sensorineural loss. Histologic studies in humans and animals suggest that the outer hair cells (OHCs) are most susceptible to cis-platinum. Evoked otoacoustic emissions (EOAE), as a measure of outer hair cell function, are potentially useful in following ototoxic insults involving OHCs. Distortion-product otoacoustic emissions (DPOAE) test frequency-specific regions of the cochlea and therefore may be particularly well suited for monitoring ototoxic injuries. We measured distortion product otoacoustic emissions, at f2 = 2, 4, 6, 8, 10, and 12 kHz, in gerbils after a single large dose of cis-platinum. Animals treated with saline served as controls. The findings were compared to auditory brain stem evoked response (ABR) thresholds, using tone pips of the same frequencies. The DPOAE and ABR thresholds were measured before treatment and again 2, 5, and 14 days after drug administration. The changes in DPOAE were compared with the changes in ABR. No treatment effect was noted in the 2-day group. Animals treated with c/s-platinum demonstrated significant elevation of DPOAE and ABR thresholds compared with control animals at 5 and 14 days. There was no significant difference between the threshold changes in the 5-and 14-day groups.

Effects of Oxaliplatin, Carboplatin, and Cisplatin Across Treatment on High-Frequency Objective and Subjective Auditory Measures in Adults

Platinum chemotherapies are often ototoxic, initially affecting the basal end of the cochlea. Thus, monitoring high-frequency auditory function is advised to reveal early damage. Objective measures of high-frequency auditory function are repeatable over time, but the sensitivity of these measures for monitoring patients receiving platinum derivatives have not been established. We monitored 13 patients across oxaliplatin, carboplatin, or cisplatin treatment using the highest frequencies with responses for each individual. Behavioral thresholds and distortion product otoacoustic emission (DPOAE) gross frequency (f2=16–2 kHz) and concentrated frequency (1/48 octave steps at the highest frequency with a present DPOAE) sweeps were monitored. DPOAE results indicated changes during treatment within individuals using absolute change criteria, as well as statistically significant differences across trial when analyzing group data. Changes varied depending on the drug administered. Behavioral thresholds changed less often than DPOAE measures and when changes were noted, they initially occurred at the highest frequencies monitored. Often, DPOAE changes occurred at frequencies which conventional equipment could not monitor (>8 kHz). Additionally, some changes were characterized by DPOAE level enhancements at conventional frequencies (<8 kHz), while levels at higher frequencies were reduced. Overall, objective high-frequency measures were sensitive to auditory changes in adults undergoing platinum chemotherapy treatment.

Modulation of vincristine and doxorubicin binding and release from silk films

Sustained release drug delivery systems remain a major clinical need for small molecule therapeutics in oncology. Here, mechanisms of small molecule interactions with silk protein films were studied with cationic oncology drugs, vincristine and doxorubicin, with a focus on hydrophobicity (non-ionic surfactant) and charge (pH and ionic strength). Interactions were primarily driven by charge interactions between the positively charged drugs and the negatively charged groups within the silk films. Exploiting chemical modifications of silk further modulated the drug interactions in a controlled fashion. Increasing anionic side groups via carboxylate- and sulfonate-modifications of tyrosine side chains in the silk protein using diazonium coupling chemistry, increased drug binding and altered drug release. The effects of silk film protein crystallinity, beta sheet content, on drug binding and release were also explored. Lower crystallinity supported more rapid drug binding when compared to higher crystalline silk films. The drug release kinetics were governed by the protonation state of vincristine and doxorubicin and were tunable based on silk crystallinity and chemistry. These studies depict an approach to characterize small molecule-silk protein interactions and methods to tune drug binding and release kinetics from this protein delivery matrix.

Investigation of protective role of curcumin against paclitaxel-induced inner ear damage in rats

OBJECTIVES/HYPOTHESIS

The aim of this study was to investigate the potential protective effect of curcumin on paclitaxel-induced ototoxicity in rats by means of immunohistochemical and histopathological analysis and distortion product otoacoustic emissions (DPOAEs).

STUDY DESIGN

Animal study.

METHODS

Forty Sprague-Dawley rats were randomized into five groups. Group 1 was administered no paclitaxel and curcumin during the study. Groups 2, 3, 4 and 5 were administered 5 mg/kg paclitaxel; 200 mg/kg curcumin; 5 mg/kg paclitaxel, followed by 200 mg/kg curcumin; 200 mg/kg curcumin and a day later 5 mg/kg paclitaxel followed intraperitoneally by 200 mg/kg curcumin once a week for 4 consecutive weeks, respectively. After the final DPOAEs test, the animals were sacrificed and their cochlea were prepared for hematoxylin and eosin and caspase-3 staining.

RESULTS

The DPOAEs thresholds and histopathological and immunohistochemical findings were substantially correlated in all groups. The histopathologic findings in the cochlea of the paclitaxel-treated animals showed not only changes in the organ of Corti, but also damage to the stria vascularis and spiral limbus, including nuclear degeneration, cytoplasmic vacuolization, and atrophy of intermediate cells. Additionally, cochlear changes in group 2, such as intense apoptosis, were confirmed by caspase-3 immunohistochemical staining. In group 4, coreceiving curcumin could not sufficiently prevent paclitaxel-induced ototoxicity, and the results in group 5 were similar to the control group.

CONCLUSIONS

In our study, we have concluded that pre- and coreceiving curcumin can significantly protect the cochlear morphology and functions on paclitaxel-induced ototoxicity in rats. Curcumin might be considered as a potential natural product that, used as a dietary supplement, could be easily given to patients undergoing paclitaxel chemotherapy.

LEVEL OF EVIDENCE

NA

Synthesis, characterization and in vitro cytotoxicity of gold(iii) dialkyl/diaryldithiocarbamato complexes

A series of six dialkyl/diaryldithiocarbamato (dtc) gold(iii) complexes [Au(R₂dtc)₂]Cl (1,3, and5), and [Au(R₂dtc)Cl₂] (2,4, and6), (R = methyl, ethyl, and benzyl) was synthesised and evaluated for anticancer activity with promising results (EC₅₀≈ 9.5 μM).

Study of the effects of chemotherapy on auditory function

Chemotherapeutic agents are known to cause multiple toxicities such as myelotoxicity, nephrotoxicity and ototoxicity. A prospective study was carried out on 60 patients receiving Cisplatin based chemotherapy in a tertiary care centre. The effects of Cisplatin on auditory function were studied using metabolic, biochemical and audiological parameters. The auditory effects were correlated with the dose and duration of chemotherapy. The study concluded that a significant percentage (15%) of patients who were subjected to chemotherapy based on Cisplatin developed high frequency sensorineural hearing loss which was permanent and irreversible in nature.

The mechanism of guanine alkylation by nitrogen mustards: a computational study

The thermodynamics and kinetics for the monofunctional binding of nitrogen mustard class of anticancer drugs to purine bases of DNA were studied computationally using guanine and adenine as model substrates. Mechlorethamine and melphalan are used as model systems in order to better understand the difference in antitumor activity of aliphatic and aromatic mustards, respectively. In good agreement with experiments that suggested the accumulation of a reactive intermediate in the case of mechlorethamine, our model predicts a significant preference for the formation of corresponding aziridinium ion for mechlorethamine, while the formation of the aziridinium ion is not computed to be preferred when melphalan is used. Two effects are found that contribute to this difference. First, the ground state of the drug shows a highly delocalized lone pair on the amine nitrogen of the melphalan, which makes the subsequent cyclization more difficult. Second, because of the aromatic substituent connected to the amine nitrogen of melphalan, a large energy penalty has to be paid for solvation. A detailed study of energy profiles for the two-step mechanism for alkylation of guanine and adenine was performed. Alkylation of guanine is ∼6 kcal mol(-1) preferred over adenine, and the factors contributing to this preference were explained in our previous study of cisplatin binding to purine bases. A detailed analysis of energy profiles of mechlorethamine and melphalan binding to guanine and adenine are presented to provide an insight into rate limiting step and the difference in reactivity and stability of the intermediate in both nitrogen mustards, respectively.

Ultrastructural effects of cisplatin on the inner ear and lateral line system of zebrafish (Danio rerio) larvae

Zebrafish, Danio rerio, has been a prominent model vertebrate for the study of chemical toxicity and human disease. Zebrafish hair cells (HCs) show significant structural, functional and molecular similarities to the mammalian inner ear HCs. We examined the effects of cisplatin, an anti-cancer drug, on HCs of the inner ear and on HCs and support cells (SCs) of neuromasts in zebrafish using transmission and scanning electron microscopy. Forty-five zebrafish larvae, 12 days post-fertilization, were assessed: 15 unexposed controls, 15 exposed to 10 µM cisplatin solution, and 15 exposed to 50 µM cisplatin solution. Hair cells in the cristae and maculae of the inner ear and of neuromasts were extremely sensitive to cisplatin. The drug was associated with vacuolization and the presence of myelinoid bodies in HC cytoplasm and with a condensation of the nuclear chromatin. The predominant pattern of injury was widespread degeneration of mitochondria, which appeared swollen and less electron-dense with disorganized or reduced cristae. Severity of damage seemed to be concentration-dependent, and the inner ear suffered more damage than the lateral line. Alterations similar to those in HCs were also observed in SCs of the neuromasts. Scanning electron microscopy showed loss of kinocilia in neuromasts of fish exposed to the higher concentration of cisplatin.

Distortion-product otoacoustic emission test performance for ototoxicity monitoring

INTRODUCTION

A nonbehavioral method for monitoring ototoxicity in patients treated with cisplatin is needed because patients enduring chemotherapy may not be well or cooperative enough to undergo repeated hearing tests. Distortion-product otoacoustic emissions (DPOAEs) provide a nonbehavioral measure of auditory function that is sensitive to cisplatin exposure. However, interpreting DPOAE findings in the context of ototoxicity monitoring requires that their accuracy be determined in relation to a clinically accepted gold standard test.

OBJECTIVES

Among patients receiving cisplatin for the treatment of cancer, we sought to (1) identify the combination of DPOAE metrics and ototoxicity risk factors that best classified ears with and without ototoxic-induced hearing changes; and (2) evaluate the test performance achieved by the composite measure as well as by DPOAEs alone.

DESIGN

Odds of experiencing hearing changes at a given patient visit were determined using data collected prospectively from 24 Veterans receiving cisplatin. Pure-tone thresholds were examined within an octave of each subject's high-frequency hearing limit. DPOAE were collected as a set of four response growth (input/output) functions near the highest f2 frequency that yielded a robust response at L2 = L1 = 65 dB SPL. Logistic regression modeled the risk of hearing change using several DPOAE metrics, drug treatment factors, and other patient factors as independent variables. An optimal discriminant function was derived by reducing the model so that only statistically significant variables were included. Receiver operating characteristic curve analyses were used to evaluate test performance.

RESULTS

At higher cisplatin doses, ears with better hearing at baseline were more likely to exhibit ototoxic hearing changes than those with poorer hearing. Measures of pre-exposure hearing, cumulative drug dose, and DPOAEs generated a highly accurate discriminant function with a cross-validated area under the receiver operating characteristic curve of 0.9. DPOAEs alone also provided an indication of ototoxic hearing change when measured at the highest DPOAE test frequency that yielded a robust response.

CONCLUSIONS

DPOAEs alone and especially in combination with pre-exposure hearing and cisplatin dose provide an indication of whether or not hearing has changed as a result of cisplatin administration. These promising results need to be validated in a separate sample.

Distortion product otoacoustic emissions: An objective technique for the screening of hearing loss in children treated with platin derivatives

In order to develop a sensitive audiometric protocol for identifying ototoxicity in children, a retrospective study of 16 children treated with cisplatin and/or carboplatin was performed. Audiometric testing was done by means of pure-tone threshold audiometry (PTA), high-frequency audiometry (HFA), and distortion product otoacoustic emissions (DPOAEs). Cisplatin caused a sensorineural high-frequency hearing loss in the study group compared to the controls (p < 0.01). Sixty-six percent of the cisplatin patients had a grade 2 or 3 ototoxicity. However, ototoxicity was not found in the patients treated with carboplatin. An excellent correlation was found between DPOAE levels and results obtained by audiometry (r = 0.82). Patients exposed to cisplatin are at significant risk for the development of drug-induced sensorineural hearing loss. Because of the several advantages of DPOAEs (noninvasive, objective, rapid, easy to use, sensitive) this method should be added in the audiological follow-up in infants and toddlers.

Cisplatin-Induced Ototoxicity in Osteosarcoma Patients: A Report from the Late Effects Surveillance System

The aim of this study was to analyze cisplatin-induced ototoxicity in a recent study trial. Seventy-four patients who had received cisplatin for the treatment of osteosarcoma (median cumulative dose: 360 mg/m2) were investigated prospectively for ototoxicity in a multicenter trial. Hearing function was tested by audiometry. We evaluated the incidence and dependencies of hearing loss. After cessation of therapy, 51% of the patients showed a hearing loss of >20 dB in the frequency range of 4-8 kHz. Only in one patient a hearing loss was found at 2 kHz, and in none at 1 kHz. At a cumulative cisplatin dose of < or = 240 mg/m2, almost no ototoxicity was found. Incidence and magnitude of hearing loss increased significantly with a higher cumulative dose. Furthermore, hearing thresholds were significantly poorer in children <12 years. A further follow-up investigation showed only a marginal change in hearing function. We conclude that ototoxicity is moderate in our group of patients and probably irreversible.

Análise de prontuários de pacientes oncológicos quanto ao monitoramento auditivo

OBJETIVO: realizar uma análise retrospectiva dos prontuários de pacientes oncológicos quanto ao monitoramento auditivo. MÉTODOS: foram utilizados os prontuários dos pacientes em atendimento durante os meses de setembro a novembro de 2006. A amostra constituiu-se de 25 prontuários de indivíduos com idade compreendida entre um e 53 anos. Foram analisados os dados quanto aos seguintes aspectos: idade, sexo, classificação do câncer, tempo de apresentação da doença, medicamentos utilizados, tempo de tratamento quimioterápico, doenças associadas, realização de avaliação otorrinolaringológica e audiológica. RESULTADOS: verificou-se a falta de acompanhamento audiológico e otorrinolaringológico. A Vincristina foi o medicamento ototóxico mais utilizado. O tipo de câncer de maior ocorrência no setor foi a Leucemia Linfocítica aguda. O tempo que os indivíduos apresentavam o câncer foi de aproximadamente 16 meses e o tempo de tratamento quimioterápico desses pacientes foi em torno de 11 meses. Observou-se, também, a presença de doenças associadas ao câncer nos indivíduos pesquisados. CONCLUSÃO: constatou-se a necessidade de se instalar programas de monitoramento auditivo nos setores que realizam quimioterapia em pacientes oncológicos, uma vez que este tratamento utiliza medicamentos ototóxicos em diversas patologias.

Longitudinal assessment of air conduction audiograms in a phase III clinical trial of difluoromethylornithine and sulindac for prevention of sporadic colorectal adenomas

A phase III clinical trial assessed the recurrence of adenomatous polyps after treatment for 36 months with difluoromethylornithine (DFMO) plus sulindac or matched placebos. Temporary hearing loss is a known toxicity of treatment with DFMO, thus a comprehensive approach was developed to analyze serial air conduction audiograms. The generalized estimating equation method estimated the mean difference between treatment arms with regard to change in air conduction pure tone thresholds while accounting for within-subject correlation due to repeated measurements at frequencies. Based on 290 subjects, there was an average difference of 0.50 dB between subjects treated with DFMO plus sulindac compared with those treated with placebo (95% confidence interval, -0.64 to 1.63 dB; P = 0.39), adjusted for baseline values, age, and frequencies. In the normal speech range of 500 to 3,000 Hz, an estimated difference of 0.99 dB (-0.17 to 2.14 dB; P = 0.09) was detected. Dose intensity did not add information to models. There were 14 of 151 (9.3%) in the DFMO plus sulindac group and 4 of 139 (2.9%) in the placebo group who experienced at least 15 dB hearing reduction from baseline in 2 or more consecutive frequencies across the entire range tested (P = 0.02). Follow-up air conduction done at least 6 months after end of treatment showed an adjusted mean difference in hearing thresholds of 1.08 dB (-0.81 to 2.96 dB; P = 0.26) between treatment arms. There was no significant difference in the proportion of subjects in the DFMO plus sulindac group who experienced clinically significant hearing loss compared with the placebo group. The estimated attributable risk of ototoxicity from exposure to the drug is 8.4% (95% confidence interval, -2.0% to 18.8%; P = 0.12). There is a <2 dB difference in mean threshold for patients treated with DFMO plus sulindac compared with those treated with placebo.

RNAi-mediated silencing of nuclear factor erythroid-2-related factor 2 gene expression in non-small cell lung cancer inhibits tumor growth and increases efficacy of chemotherapy

Nuclear factor erythroid-2-related factor 2 (Nrf2) is a redox-sensitive transcription factor that regulates the expression of electrophile and xenobiotic detoxification enzymes and efflux proteins, which confer cytoprotection against oxidative stress and apoptosis in normal cells. Loss of function mutations in the Nrf2 inhibitor, Kelch-like ECH-associated protein (Keap1), results in constitutive activation of Nrf2 function in non-small cell lung cancer. In this study, we show that constitutive activation of Nrf2 in lung cancer cells promotes tumorigenicity and contributes to chemoresistance by up-regulation of glutathione, thioredoxin, and the drug efflux pathways involved in detoxification of electrophiles and broad spectrum of drugs. RNAi-mediated reduction of Nrf2 expression in lung cancer cells induces generation of reactive oxygen species, suppresses tumor growth, and results in increased sensitivity to chemotherapeutic drug-induced cell death in vitro and in vivo. Inhibiting Nrf2 expression using naked siRNA duplexes in combination with carboplatin significantly inhibits tumor growth in a subcutaneous model of lung cancer. Thus, targeting Nrf2 activity in lung cancers, particularly those with Keap1 mutations, could be a promising strategy to inhibit tumor growth and circumvent chemoresistance.

Cochlear implantation in a previously irradiated temporal bone--a case report

A case of successful cochlear implantation following irradiation of the temporal bone is presented. Loss of cochlear architecture is demonstrated and is attributable to previous radiation. Viability of cochlear nerve and spiral ganglion following radiation is questioned. To date there has been only one previously published report on the subject.

Effects of extremely low frequency electromagnetic fields on distortion product otoacoustic emissions in rabbits

OBJECTIVE

Humans are continuously exposed to extremely low frequency (ELF), electromagnetic fields (EMF), transmitted from the common sources like power stations, electric transmission lines, communication and radio-television signal transmission units. The present study aimed to assess the effects of 50 Hz ELF-EMF of 5.068 and 10.182 kV/m electric fields, which refer to the lower and upper intensity limits beyond which hazardous effects can be observed, on the auditory functions of rabbits via Distortion Product Otoacoustic Emission (DPOAE) recordings.

METHODS

The study was performed on 20 healthy adult female New Zealand White rabbits randomly divided into two groups and applied 50 Hz ELF-EMF with either 5.068 kV/m (Group 1) or 10.182 kV/m (Group 2) of electric field for 3h/day during 14 days. DPOAE responses recorded on the 0th day before exposure (B-EMF) and on the 6th (A-EMF-6th) and 14th (A-EMF-14th) days after exposure (AE). Mean stimulus intensity and emission amplitudes at 1.0-8.0 kHz were analyzed.

RESULTS

In Group 2 rabbits, on 6th and 14th days, the DPOAE amplitudes were observed as increased at 1.5-4.0 kHz (at 2.0 and 4.0 kHz significantly) than B-EMF values. At 6.0 kHz, A-EMF-14th amplitudes were significantly lower than A-EMF values.

CONCLUSION

These results suggest that ELF EMFs might affect hearing functions by frequency dependent manner. Higher ELF EMFs exposure caused increase of cochlear activity. Ototoxic effect of 10.182 kV/m ELF EMFs may begin at the basal turn of the cochlea by reducing DPOAEs at high frequencies.

Cisplatininduzierte Hörstörungen bei Kindern in Abhängigkeit von der Pigmentierung der Iris

BACKGROUND

Cisplatin is commonly used as a chemotherapeutic agent in the treatment of solid tumors. Ototoxicity is an important side-effect. Melanin in the inner ear either plays an otoprotective role or has a negative influence on hearing. The concentration of cochlear melanin correlates with its concentration in the iris.

PATIENTS AND METHODS

We retrospectively examined 65 children (37 males, 28 females, average age 7.5 years) treated with cisplatin at the University Clinic of Muenster, Germany. We checked whether their eye color could be inferred from the prevalence and extent of cisplatin-induced hearing loss.

RESULTS

We found a hearing loss of >20 dB in 29 light-eyed and in 21 dark-eyed patients. Seven light-eyed and eight dark-eyed patients did not suffer from hearing impairment. Using the chi(2)-test on these four parameters, we found no significant connection between iris pigmentation and the prevalence or extent of hearing loss, although light-eyed children (80.6%) suffered more from hearing loss than dark-eyed children (72.4%). After the end of therapy with cisplatin, the prevalence of hearing loss was 83.3% in children up to 6 years and 71.4% in children older than 6 years. The average cumulative dose of cisplatin was 372 mg/m(2) of body surface in children with hearing loss, compared to 390 mg/m(2) in children without hearing loss.

CONCLUSION

We found no significant correlation between iris pigmentation (eye color) and hearing loss. Cisplatin-induced hearing loss occurs frequently and requires repeated monitoring.

The effect of treatment with vincristine on transient evoked and distortion product otoacoustic emissions

OBJECTIVE

Vincristine chemotherapy is mainly associated with neurotoxic effects. The ototoxicity of vincristine has been related to high dosage, while low and moderate doses do not seem to induce significant hearing impairment when measured by pure tone or speech audiometry. Otoacoustic emissions have been reported to be more sensitive in early detection of ototoxicity than conventional pure tone audiometry. The present study was directed at determining whether vincristine treatment interferes with outer hair cell function in the absence of measurable changes in pure tone audiometry.

METHODS

We studied prospectively a cohort of ten children suffering from leukemia. All children were subjected to tympanogram, stapedial muscle reflex, pure tone audiometry, transient evoked (TEOAEs) and distortion product (DPOAEs) otoacoustic emissions on day 1 and on day 22 of treatment with vincristine. TEOAEs were analyzed in terms of emission level and reproducibility as a function of frequency. DPOAEs were obtained as DP-grams and were analyzed in terms of amplitude.

RESULTS

The analyzed parameters of TEOAEs and DPOAEs revealed a declining tendency, although changes did not reach statistical significance. Pure tone audiometry and stapedial reflex thresholds were not altered.

CONCLUSION

For the population of this study, vincristine did not seem to cause significant alterations of otoacoustic emissions' recordings and consequently significant outer hair cell damage.

Protection against Cisplatin-Induced Toxicities byN-Acetylcysteine and Sodium Thiosulfate as Assessed at the Molecular, Cellular, and in Vivo Levels

Cisplatin (CDDP) is a common, highly toxic chemotherapeutic agent. This study investigates chemoprotective effects of N-acetylcysteine (NAC) and sodium thiosulfate (STS) on in vitro and in vivo CDDP toxicities. For ototoxicity studies, CDDP (6 mg/kg) was administered to rats via a retrograde carotid artery infusion. Auditory brainstem response thresholds at 4 to 20 kHz were tested before and 7 days post-treatment. STS (8 g/m(2) i.v.) was administered at 4, 8, or 12 h after CDDP. For nephrotoxicity studies, rats were treated with CDDP intraperitoneally (10 mg/kg) before or after NAC (400 mg/kg) or STS (8 g/m(2)), and blood urea nitrogen (BUN) and creatinine concentrations were measured after 3 days. In vitro cytotoxicity and chemoprotection in human tumor cell lines were assessed by cell viability and immunoblotting assays. Rats treated with STS 4 h after CDDP exhibited no hearing change. The STS 8-h group had less otoprotection, whereas 12-h rats had ototoxicity. CDDP induced high BUN and creatinine, corresponding to renal tubule toxicities. All NAC-treated animals showed normal BUN and reduced creatinine levels compared with CDDP alone and no histopathological evidence of nephrotoxicity. Delayed STS treatment was not consistently protective against nephrotoxicity. STS administration fully protected against the in vitro cytotoxic and apoptotic effects of CDDP if added within 2 h of CDDP, but chemoprotection decreased if STS administration was 4 h, and was minimal by 6 h, after CDDP. Thus, the chemoprotection route and timing of administration can be manipulated to maintain CDDP antitumor efficacy while protecting against toxicities.

Acceleration of cisplatin ototoxicity by perilymphatic application of 4-methylthiobenzoic acid

The antitumor agent cisplatin has dose-limiting side effects such as ototoxicity. Systemical co-treatment with anti-oxidants like 4-methylthiobenzoic acid (MTBA) and sodium thiosulfate (STS) provides protection against cisplatin ototoxicity. However, systemically administered protective agents may reduce the chemotherapeutic effect of cisplatin. Local application of the protective agents could avoid this undesirable effect. In the present study, we aimed at suppressing cisplatin-induced ototoxicity in guinea pigs by administering MTBA or STS perilymphatically through cochlear perfusion. Guinea pig cochleas were perfused for 10 min with artificial perilymph (ArtP) containing cisplatin at 0.3 mg/ml, either alone, or in combination with MTBA (0.1 or 1.0 mg/ml) or STS (0.75 or 3.0 mg/ml). The compound action potential (CAP) and the summating potential (SP), evoked by 8 kHz tone bursts, and the endocochlear potential (EP; MTBA only) were measured just before and 1, 2, 3 and 4 h after perfusion. Cisplatin gradually reduced the CAP amplitude in time. Adding MTBA only accelerated this ototoxic effect. After cisplatin treatment a decline was found in the EP, irrespective of co-treatment, i.e., addition of MTBA did not accelerate the EP decrease. In contrast to MTBA, STS ameliorated the ototoxic effect of cisplatin. In conclusion, local application of anti-oxidants can ameliorate cisplatin ototoxicity but this is not a feature of all anti-oxidants.

Treatment of peripheral sensorineural hearing loss: gene therapy

Noise, chemicals and genetic defects are all common causes of irreversible hearing loss, which at present have no cure. Gene therapy may soon be utilized in both the protection and the treatment of these exogenous and endogenous sources of hearing loss. Gene therapy technology is rapidly developing and the inner ear is a particularly feasible model for gene therapy. This review outlines our current understanding of the mechanisms behind deafness and prospects for treatment, discusses the inner ear model in detail and reviews the efforts that have been made in inner ear gene therapy. Finally, the proposed next steps will be discussed. The viral mediated delivery of neurotrophins and antioxidants offers imminent promise in preventing and treating exogenous hearing loss and improving cochlear implant therapy.

Cochlear implantation for treatment-induced ototoxic deafness in Langerhans cell histiocytosis. A case report

A case is presented where the authors carried out a cochlear implantation on a girl whose deafness was induced by cytostatic agents. The normally hearing child was diagnosed with Langerhans cell histiocytosis at the age of 3 years and received polychemotherapy for almost 2 years. By her 5th year, she started to develop a bilateral, progressive sensorineural hearing loss, necessitating a hearing aid in both ears. While her histiocytosis was cured, her hearing ultimately deteriorated to total deafness on the right and profound hearing loss on the left ear. After 3 years, her hearing aids no longer provided adequate hearing for the postlingually deafened girl. At the age of 14, a cochlear implantation was performed on her right ear with excellent results.

Irreversible Ototoxicity Associated with Difluoromethylornithine

Difluoromethylornithine (DFMO) is a potent, irreversible inhibitor of ornithine decarboxylase, the rate-limiting enzyme in the synthesis of polyamines that promote cellular proliferation. DFMO has been tested as a potential cancer therapeutic and chemopreventive agent in clinical trials. Reversible hearing loss is a recognized toxicity of DFMO that usually occurs at doses above 2 g/m2/d, and generally when the cumulative dose exceeds 250 g/m2. In a recently completed Barrett's esophagus chemoprevention trial, a participant developed a 15-dB decrease in hearing at frequencies of 250, 2,000, and 3,000 Hz in the right ear and a ≥20-dB decrease in hearing at 4,000 to 6,000 Hz in the left ear after taking 0.5 g/m2/d DFMO for approximately 13 weeks (cumulative dose of 45 g/m2). The threshold shifts persisted 7 months after DFMO was discontinued. There was no obvious impact on the participant's clinical hearing, but these findings were consistent with irreversible hearing loss. This is the first case reported of irreversible ototoxicity in a clinical trial participant receiving DFMO and, thus, trial participants should be made aware of this small but important risk.

Protection against cisplatin-induced ototoxicity by N-acetylcysteine in a rat model

Cisplatin (CDDP) is a widely used chemotherapeutic agent that is highly ototoxic. Animal studies and clinical trials have shown that thiosulfates can protect against platinum-induced ototoxicity. This study investigated a new model for CDDP ototoxicity in the rat, and tested the potential chemoprotective effect of administering N-acetylcysteine (NAC) before giving CDDP. Long Evans rats were treated with CDDP 6 mg/kg delivered to the aorta via a retrograde right external carotid artery infusion, 15 min after intravenous (IV) infusion of saline (n=8) or NAC 400 mg/kg (n=8), such that the vertebral arteries were perfused. Subsequent groups were similarly treated with NAC 30 min before (n=7) and 4 h after (n=7) CDDP. Auditory brainstem response (ABR) thresholds were tested at 4-20 kHz, 7 days after treatment and compared to baseline ABR values. The NAC-treated rats exhibited no significant change from baseline values at all time intervals, while the saline-treated rats showed marked ototoxicity, especially at higher frequencies. Furthermore, the rats treated with NAC 15 min before CDDP exhibited less overall toxicity to CDDP, as evidenced in weight loss 7 days post-treatment (mean for saline=-39.63 g; mean for NAC=-21.13 g; p=0.0084). These data show that treatment with NAC can prevent CDDP-induced ototoxicity in rats.

Carboplatin-induced oxidative injury in rat inferior colliculus

Carboplatin is currently being used as an anticancer drug against human cancers. However, high dose of carboplatin chemotherapy resulted in ototoxicity in cancer patients. Carboplatin-induced ototoxicity was related to oxidative stress to the cochlea and inner hair cell loss in animals. It is likely that initial oxidative injury spreads throughout the neuroaxis of the auditory system later. The study aim was to evaluate carboplatin-induced hearing loss and oxidative injury to the central auditory system (inferior colliculus) of the rat. Male Wistar rats were divided into two groups of seven animals each and treated as follows: (1) control (normal saline, intraperitoneal [i.p.]) and (2) carboplatin (256 mg/kg, i.p.). Auditory brain-evoked responses (ABRs) were recorded before and 4 days after treatments. The animals were sacrificed on the 4th day and inferior colliculus from brain stem and cerebellum were isolated and analyzed. Carboplatin significantly elevated the hearing threshold shifts at clicks, 2-, 4-, 8-, 16-, and 32-kHz tone burst stimuli. Carboplatin significantly increased nitric oxide and lipid peroxidation, xanthine oxidase, and manganese superoxide dismutase activities in the inferior colliculus, but not in the cerebellum, indicating an enhanced flux of free radicals in the central auditory system. Carboplatin significantly depressed the reduced to oxidized glutathione ratio, antioxidant enzyme activities, such as copper-zinc superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, and glutathione S-transferase, and enzyme protein expressions in the inferior colliculus, but not in the cerebellum, 4 days after treatment. The data suggest that carboplatin induced oxidative injury specifically in the inferior colliculus of the rat leading to hearing loss.

Supporting cells as a target of cisplatin-induced inner ear damage: therapeutic implications

OBJECTIVES/HYPOTHESIS

Cisplatin induces adverse effects such as ototoxicity and nephrotoxicity. Unexplained hearing improvement in sudden deafness and fluctuating hearing loss suggests the presence of some mechanisms other than the primary lesion of the outer hair cell. The authors' aim was to study the functional and morphological lesions induced in the cochlea of the rat after cisplatin injection.

STUDY DESIGN

Prospective experimental morphological and functional study.

METHODS

Forty-eight Wistar rats were given intraperitoneal injections of 5 mg/kg cisplatin. After short-, medium-, and long-term survival, animals were studied by means of auditory brainstem response testing and scanning electronic microscopy.

RESULTS

An increased hearing loss was observed in animals with long-term survival compared with animals with short-term survival after a single dose of cisplatin. These findings correlated with a more intense injury of the supporting cells, continuing with the late deterioration of the hair cells.

CONCLUSION

The study suggested that the initial damage of the supporting cells could be responsible for the late injury of the hair cells. This hypothesis was supported by the late increase in hearing loss after a single dose of cisplatin, emphasizing the role of the supporting cells in the cochlear changes induced by cisplatin.

Late effects surveillance system for sarcoma patients

BACKGROUND

In 1998, a prospective multicenter pilot study of the 'Late Effects Surveillance System' (LESS) was started to investigate late effects of patients with Ewing, osteo- or soft-tissue sarcoma.

PROCEDURE

Two hundred thirty patients were included in this pilot study. The patients were treated between 1/1/1998 and 6/30/1999 according to the sarcoma protocols COSS-96, CWS-96, and EICESS-92, the median cumulative doses of the focussed drugs were for cisplatin: 360 mg/m(2), for doxorubicin: 270 mg/m(2), and for ifosfamide: 24 g/m(2). The patients were investigated using an organ related standardized screening methodology. We report on toxicities in the first year after cessation of therapy-the beginning of the patient follow-up-and the feasibility of LESS.

RESULTS

Cardiotoxicity: 16/129 (12%) patients treated with doxorubicin exhibited a reduced systolic heart function (fractional shortening (FS) <29%). Altogether three patients required cardiac drug therapy. Ototoxicity: In 5/73 (7%) patients treated with cisplatin a hearing deficit <4 kHz (>20 dB) was found. One patient needed a hearing aid. Nephrotoxicity: 2 of 214 (1%) patients treated with ifosfamide suffered from a tubulopathy, which required supplementation therapy. 10/50 (20%) showed a reduced fractional phosphate reabsorption. Incidence of hypomagnesemia was significantly increased in patients additionally treated with cisplatin.

CONCLUSIONS

Some relevant impairments are noted in the first year after antineoplastic therapy. We expect to detect more major late sequelae in our prospective study during the increasing posttherapeutic interval. Our pilot study shows the feasibility of the methodology.

Cisplatin ototoxicity in the guinea pig: vestibular and cochlear damage

The aim of the present study was to investigate both vestibular and cochlear cisplatin toxicity. Twelve albino guinea pigs were divided into an experimental (n=8) and a control saline group (n=4) and were treated with cisplatin at a daily dose of 2.5 mg/kg for 6 consecutive days. Vestibular dysfunction was evaluated by computing the gain of the vestibular ocular reflex (VOR) evoked by stimulation in the horizontal (HVOR) and vertical (VVOR) planes. Changes in cochlear function were characterised as compound action potential threshold shifts. After the functional testing, tympanic bullae were removed and processed for morphological examination of the sensorineural epithelium. The onset of vestibular functional impairment was observed on the third day, although the VOR gain decrease was not significant. The impairment of the vestibular function progressed until the sixth day becoming statistically significant particularly at VVOR mid frequencies of stimulation. At these frequencies both macula and crista ampullaris functions are involved. Concomitantly a progressive auditory threshold shift was observed at all stimulus frequencies. The decline of the auditory function was statistically significant from the third day of treatment and it was more evident at high frequencies. Morphological observations showed a massive loss of outer hair cells and a degeneration of the organ of Corti in the basal/middle turns and only a slight loss of hair cells of the cristae ampullares and maculae. In conclusion, functional and morphological data provide evidence that the toxic effect of cisplatin is more pronounced in the organ of Corti than in the vestibular epithelium.

Barrett's esophagus: chemoprevention

The clinical applicability of the experimental data discussed previously remains questionable, and results of clinical studies on chemoprevention in Barrett's esophagus are needed. The utility of selectively targeting acid exposure, ODC, and COX-2 is not clear, and elucidation of that role will be facilitated by a better understanding of the contribution of these factors in the development of Barrett's cancers. The insights already gained into the basic mechanisms of acid exposure, ODC, and COX-2 in the pathogenesis of Barrett's esophagus and esophageal adenocarcinoma hold promise for the development of future therapies aimed at these molecular targets and their signaling pathways. In preclinical studies, the ability of COX-2 selective NSAIDs and DFMO to inhibit carcinogenesis is encouraging. Results of well-designed, prospective clinical studies, however, are still needed to establish the efficacy of potent acid suppression, COX-2 inhibitors, and DFMO in the prevention of this malignancy.

Bilateral hearing loss during vincristine therapy: a case report

Vincristine sulfate is a chemotherapeutic agent used in different cancer therapies. It is also the first choice of treatment for peripheral T-cell lymphoma with cyclophosphamide and adriamycin. Sudden hearing loss during vincristine therapy is a very rare event. This is a case of a 16-year old girl who developed sudden bilateral hearing loss related to vincristine therapy.

Distortion product otoacoustic emissions test is useful in children undergoing cisplatin treatment

BACKGROUND

Cisplatin is a widely used chemotherapy agent that has several adverse effects, such as ototoxicity. Evaluation of hearing loss due to cisplatin therapy in children is difficult. The purpose of this study was to compare the validity of distortion product otoacoustic emissions (DPOAEs) with pure tone audiometry (PTA) in assessing hearing loss in children under cisplatin therapy.

METHODS

We reviewed the files of 26 children aged between 2 and 15 years; 14 were girls. All were under treatment with cisplatin for malignancy. PTA and DPOAEs were obtained at the same session. Three subjects were studied twice; thus, there were 29 sets of studies.

RESULTS

Determining a cut-off point at 45 dB HL for PTA and 4 dB SPL difference for DPOAEs, diagnostic specificity for the latter was 0.97 while sensitivity was 0.57.

CONCLUSIONS

DPOAEs represent a highly valuable test for evaluating hearing loss due to cisplatin treatment. DPOAEs is a quick and objective hearing assessment method not requiring much cooperation from children.

Monitoramento da audição de pacientes expostos à cisplatina

A cisplatina é um agente quimioterápico que apresenta dentre seus efeitos colaterais a ototoxicidade. Este estudo teve como objetivos avaliar a audição de pacientes portadores de osteossarcoma expostos à cisplatina e verificar qual o método de investigação mais adequado para identificar precocemente as alterações auditivas induzidas por drogas ototóxicas. FORMA DE ESTUDO: Clínico prospectivo. MATERIAL E MÉTODO: 13 indivíduos portadores de osteossarcoma que receberam quatro ciclos de cisplatina de 120 mg/m²/ciclo, fracionados em dois dias de aplicação (60 mg/m²/dia), foram submetidos à avaliação audiológica - audiometria tonal liminar (250 a 18000 Hz) e emissões otoacústicas transitórias (EOAT) e por produto de distorção (EOAPD) - antes do início do tratamento e após cada ciclo de cisplatina. RESULTADOS: Observou-se, nos valores médios, perda auditiva após a dose cumulativa de 480 mg/m² a partir de 8 kHz. Quanto aos valores individuais, 15,3% dos pacientes apresentaram perda auditiva de grau leve a moderado a partir de 3 kHz, 15,3% a partir de 4 kHz, 15,3% a partir de 6 kHz e 15,3% a partir de 8 kHz. Não foi observada redução na amplitude das EOAT precocemente à alteração dos limiares nas altas freqüências. Houve redução da amplitude das EOAPD concomitante ao aumento do limiar de audibilidade. CONCLUSÃO: A audiometria de altas freqüências é mais efetiva na detecção precoce da perda auditiva induzida por cisplatina. As EOAT e EOAPD podem ser usadas como complemento à avaliação audiométrica. Todos os pacientes expostos à cisplatina têm perda auditiva nas altas freqüências, e destes, 30,6% tem perda auditiva a partir das freqüências de 3 e 4 kHz consideradas importantes para a compreensão da fala.

Effects of topical mitomycin on inner ear: a light and electron microscopic study

Providing maintenance of myringotomy patency without use of ventilation tubes in the treatment of secretory otitis media has been one of the important study areas. For this reason, laser and Mitomycin C (MMC) are used together in experimental studies. But there has been no ultrastructural studies concerning whether leakage of MMC to middle ear during application of this procedure has an ototoxic effect or not and if so, to what extent. In this study, we searched the ultrastructural changes which occurred in the middle ear by direct applications of MMC to the middle ear for different time durations. The study was carried out over thirty adult guinea pigs without ear diseases. Bilateral myringotomy was performed and MMC was applied only to the right middle ear of each guinea pig. The first group received MMC once for 10 minutes, the second group received it once for 20 minutes, and the third group took it each day for 10 minutes during a one week period. The left ears of the samples were accepted as the control group. On the 8th day, sacrification was carried out. After electron and light microscopy examination, significant changes in the inner ear were observed in the third group though no significant change was observed for the first and the second groups. As a result it was concluded that the application of MMC to the middle ear once for a short duration causes no toxic effect on the inner ear.