In vitro and in vivo models of drug ototoxicity: studying the mechanisms of a clinical problem

Rodent models in sensorineural hearing loss research: A comprehensive review

Sensorineural hearing loss (SNHL) constitutes a major global health challenge, affecting millions of individuals and substantially impairing social integration and quality of life. The complexity of the auditory system and the multifaceted nature of SNHL necessitate advanced methodologies to understand its etiology, progression, and potential therapeutic interventions. This review provides a comprehensive overview of the current animal models used in SNHL research, focusing on their selection based on specific characteristics and their contributions to elucidating pathophysiological mechanisms and evaluating novel treatment strategies. It discusses the most commonly used rodent models in hearing research, including mice, rats, guinea pigs, Mongolian gerbils, and chinchillas. Through a comparative analysis, this review underscores the importance of selecting models that align with specific research objectives in SNHL studies, discussing the advantages and limitations of each model. By advocating for a multidisciplinary approach that leverages the strengths of various animal models with technological advancements, this review aims to facilitate significant advancements in the prevention, diagnosis, and treatment of sensorineural hearing loss.

Ototoxicity: a high risk to auditory function that needs to be monitored in drug development

Hearing loss constitutes a major global health concern impacting approximately 1.5 billion people worldwide. Its incidence is undergoing a substantial surge with some projecting that by 2050, a quarter of the global population will experience varying degrees of hearing deficiency. Environmental factors such as aging, exposure to loud noise, and the intake of ototoxic medications are implicated in the onset of acquired hearing loss. Ototoxicity resulting in inner ear damage is a leading cause of acquired hearing loss worldwide. This could be minimized or avoided by early testing of hearing functions in the preclinical phase of drug development. While the assessment of ototoxicity is well defined for drug candidates in the hearing field - required for drugs that are administered by the otic route and expected to reach the middle or inner ear during clinical use - ototoxicity testing is not required for all other therapeutic areas. Unfortunately, this has resulted in more than 200 ototoxic marketed medications. The aim of this publication is to raise awareness of drug-induced ototoxicity and to formulate some recommendations based on available guidelines and own experience. Ototoxicity testing programs should be adapted to the type of therapy, its indication (targeting the ear or part of other medications classes being potentially ototoxic), and the number of assets to test. For multiple molecules and/or multiple doses, screening options are available: in vitro (otic cell assays), ex vivo (cochlear explant), and in vivo (in zebrafish). In assessing the ototoxicity of a candidate drug, it is good practice to compare its ototoxicity to that of a well-known control drug of a similar class. Screening assays provide a streamlined and rapid method to know whether a drug is generally safe for inner ear structures. Mammalian animal models provide a more detailed characterization of drug ototoxicity, with a possibility to localize and quantify the damage using functional, behavioral, and morphological read-outs. Complementary histological measures are routinely conducted notably to quantify hair cells loss with cochleogram. Ototoxicity studies can be performed in rodents (mice, rats), guinea pigs and large species. However, in undertaking, or at the very least attempting, all preclinical investigations within the same species, is crucial. This encompasses starting with pharmacokinetics and pharmacology efficacy studies and extending through to toxicity studies. In life read-outs include Auditory Brainstem Response (ABR) and Distortion Product OtoAcoustic Emissions (DPOAE) measurements that assess the activity and integrity of sensory cells and the auditory nerve, reflecting sensorineural hearing loss. Accurate, reproducible, and high throughput ABR measures are fundamental to the quality and success of these preclinical trials. As in humans, in vivo otoscopic evaluations are routinely carried out to observe the tympanic membrane and auditory canal. This is often done to detect signs of inflammation. The cochlea is a tonotopic structure. Hair cell responsiveness is position and frequency dependent, with hair cells located close to the cochlea apex transducing low frequencies and those at the base transducing high frequencies. The cochleogram aims to quantify hair cells all along the cochlea and consequently determine hair cell loss related to specific frequencies. This measure is then correlated with the ABR & DPOAE results. Ototoxicity assessments evaluate the impact of drug candidates on the auditory and vestibular systems, de-risk hearing loss and balance disorders, define a safe dose, and optimize therapeutic benefits. These types of studies can be initiated during early development of a therapeutic solution, with ABR and otoscopic evaluations. Depending on the mechanism of action of the compound, studies can include DPOAE and cochleogram. Later in the development, a GLP (Good Laboratory Practice) ototoxicity study may be required based on otic related route of administration, target, or known potential otic toxicity.

Awareness and Attitude About Ototoxic Drugs Among Medical Doctors in Arar City, Saudi Arabia

OBJECTIVES

The purpose of this study was to assess the awareness of ototoxicity among medical doctors in Arar City, Saudi Arabia.

METHODS

This is a cross-sectional study based on a pre-formed validated questionnaire (Appendix) that included three sections covering participants' demographic data (three questions), their attitudes (five questions), and knowledge (13 questions) regarding drug-induced ototoxicity.

RESULTS

After obtaining their informed consent, 213 physicians from government and private sector health facilities in Arar were enrolled in the study. Interns and general practitioners represented 57.8% of the participants; consultants represented 17.8%. Only 71.8% of participants were interested in drug-induced ototoxicity, while 26.3% considered ototoxicity a rare complication. Approximately 90% of the participants were knowledgeable about the adverse effects of drugs on the vestibulocochlear system, and 26.7% reported having experienced cases of drug-induced ototoxicity in their practice. Participants showed an overall knowledge score about ototoxicity of 9.3±3.27 (out of 14). The knowledge score was significantly higher (p-value=0.0007) for participants with more years of clinical experience. The most widely known ototoxic drug for participants was frusemide (72.3%), followed by aminoglycoside (68.5%), while acetaminophen (44.1%) ototoxicity was the least known among participants.

CONCLUSION

Awareness of drug-induced ototoxicity is satisfactory among physicians in the Northern Borders region. However, workshops about all types of drugs with ototoxic effects and the main lines for the management of drug-induced ototoxicity are recommended to increase awareness.

What Predictability for Animal Models of Peripheral Vestibular Disorders?

The different clinical entities grouped under the term peripheral vestibulopathies (PVs) or peripheral vestibular disorders (PVDs) are distinguished mainly based on their symptoms/clinical expression. Today, there are very few commonly accepted functional and biological biomarkers that can confirm or refute whether a vestibular disorder belongs to a precise classification. Consequently, there is currently a severe lack of reliable and commonly accepted clinical endpoints, either to precisely follow the course of the vertigo syndrome of vestibular origin or to assess the benefits of therapeutic approaches, whether they are pharmacological or re-educational. Animal models of PV are a good means to identify biomarkers that could subsequently be exploited in human clinical practice. The question of their predictability is therefore crucial. Ten years ago, we had already raised this question. We revisit this concept today in order to take into account the animal models of peripheral vestibular pathology that have emerged over the last decade, and the new technological approaches available for the behavioral assessment of vestibular syndrome in animals and its progression over time. The questions we address in this review are the following: are animal models of PV predictive of the different types and stages of vestibular pathologies, and if so, to what extent? Are the benefits of the pharmacological or reeducational therapeutic approaches achieved on these different models of PV (in particular the effects of attenuation of the acute vertigo, or acceleration of central compensation) predictive of those expected in the vertiginous patient, and if so, to what extent?

Methamphetamine Exposure During Development Causes Lasting Changes to Mesolimbic Dopamine Signaling in Mice

Methamphetamine (MA) abuse remains a public health issue. Prenatal MA exposure (PME) poses a significant health problem, as we know very little about the drug's long-term physiological impact on the developing human brain. We investigated the long-term consequences of early MA exposure using a mouse model that targets the brain growth spurt, which occurs during human third-trimester. Adult mice previously subjected to acute MA during post-natal days 4-9 exhibited hyperactivity during the Open-Field Test, while exhibiting no motor coordination changes during the Rotarod Test. Neonatal MA exposure reduced basal dopamine (DA) uptake rates in adult nucleus accumbens slices compared with saline-injected controls. Although slices from neonatal MA-exposed mice showed no change in evoked DA signals in the presence of MA, they exhibited potentiated non-evoked DA release through DA efflux in response to MA. These data suggest that developmental MA exposure alters brain development to produce long-lasting physiological changes to the adult mesolimbic DA system, as well as altering responses to acute MA exposure in adulthood. This study provides new insights into an important, under-investigated area in drugs of abuse research.

Ototoxicity in childhood: Recommendations of the CODEPEH (Commission for the Early Detection of Childhood Hearing Loss) for prevention and early diagnosis

Ototoxicity is defined as the damage, reversible or irreversible, produced in the inner ear by various substances that are called ototoxic and that can cause hearing loss and/or an alteration of the vestibular system. Permanent hearing loss significantly affects quality of life and is especially important in children. The lack or delay in its detection is frequent, since it often progresses in an inconspicuous manner until it affects communication and overall development. This impact can be minimized by following a strategy of audiological monitoring of ototoxicity, which allows for its early detection and treatment. This document recommends that children who are going to be treated with cisplatin or aminoglycosides be monitored. This CODEPEH review and recommendation document focuses on the early detection, prophylaxis, otoprotection, monitoring and treatment of ototoxicity caused by aminoglycosides and platinum-based antineoplastics in the paediatric population.

In silico prediction of drug-induced ototoxicity using machine learning and deep learning methods

Drug-induced ototoxicity has become a serious global problem, because of leading to deafness in hundreds of thousands of people every year. It always results from exposure to drugs or environmental chemicals that cause the impairment and degeneration of the inner ear. Herein, we focused on the in silico modeling of drug-induced ototoxicity of chemicals. We collected 1,102 ototoxic medications and 1,705 non-ototoxic drugs. Based on the data set, a series of computational models were developed with different traditional machine learning and deep learning algorithms implemented on an online chemical database and modeling environment. Six ML models performed best on 5-fold cross-validation and test set. A consensus model was developed with the best individual models. These models were further validated with an external validation. The consensus model showed best predictive ability, with high accuracy of 0.95 on test set and 0.90 on validation set. The consensus model and the data sets used for model development are available at https://ochem.eu/model/46566321. Besides, 16 structural alerts responsible for drug-induced ototoxicity were identified. We hope the results could provide meaningful knowledge and useful tools for ototoxicity evaluation in drug discovery and environmental risk assessment.

Transcriptomic characterization of dying hair cells in the avian cochlea

Sensory hair cells are prone to apoptosis caused by various drugs including aminoglycoside antibiotics. In mammals, this vulnerability results in permanent hearing loss because lost hair cells are not regenerated. Conversely, hair cells regenerate in birds, making the avian inner ear an exquisite model for studying ototoxicity and regeneration. Here, we use single-cell RNA sequencing and trajectory analysis on control and dying hair cells after aminoglycoside treatment. Interestingly, the two major subtypes of avian cochlear hair cells, tall and short hair cells, respond differently. Dying short hair cells show a noticeable transient upregulation of many more genes than tall hair cells. The most prominent gene group identified is associated with potassium ion conductances, suggesting distinct physiological differences. Moreover, the dynamic characterization of >15,000 genes expressed in tall and short avian hair cells during their apoptotic demise comprises a resource for further investigations toward mammalian hair cell protection and hair cell regeneration.

Plasticity in Limbic Regions at Early Time Points in Experimental Models of Tinnitus

Tinnitus is one of the most prevalent auditory disorders worldwide, manifesting in both chronic and acute forms. The pathology of tinnitus has been mechanistically linked to induction of harmful neural plasticity stemming from traumatic noise exposure, exposure to ototoxic medications, input deprivation from age-related hearing loss, and in response to injuries or disorders damaging the conductive apparatus of the ears, the cochlear hair cells, the ganglionic cells of the VIIIth cranial nerve, or neurons of the classical auditory pathway which link the cochlear nuclei through the inferior colliculi and medial geniculate nuclei to auditory cortices. Research attempting to more specifically characterize the neural plasticity occurring in tinnitus have used a wide range of techniques, experimental paradigms, and sampled at different windows of time to reach different conclusions about why and which specific brain regions are crucial in the induction or ongoing maintenance of tinnitus-related plasticity. Despite differences in experimental methodologies, evidence reveals similar findings that strongly suggest that immediate and prolonged activation of non-classical auditory structures (i.e., amygdala, hippocampus, and cingulate cortex) may contribute to the initiation and development of tinnitus in addition to the ongoing maintenance of this devastating condition. The overarching focus of this review, therefore, is to highlight findings from the field supporting the hypothesis that abnormal early activation of non-classical sensory limbic regions are involved in tinnitus induction, with activation of these regions continuing to occur at different temporal stages. Since initial/early stages of tinnitus are difficult to control and to quantify in human clinical populations, a number of different animal paradigms have been developed and assessed in experimental investigations. Reviews of traumatic noise exposure and ototoxic doses of sodium salicylate, the most prevalently used animal models to induce experimental tinnitus, indicate early limbic system plasticity (within hours, minutes, or days after initial insult), supports subsequent plasticity in other auditory regions, and contributes to the pathophysiology of tinnitus. Understanding this early plasticity presents additional opportunities for intervention to reduce or eliminate tinnitus from the human condition.

Interventions for cisplatin-induced hearing loss in children and adolescents with cancer

The identification of preventive interventions that are safe and effective for cisplatin-induced ototoxicity is important, especially in children because hearing loss can impair speech-language acquisition development. Previous randomised trials assessed systemic drugs such as amifostine, sodium diethyldithiocarbamate or disulfiram, and sodium thiosulfate. Amifostine, sodium diethyldithiocarbamate, and disulfiram did not show hearing preservation. Paediatric trials assessing sodium thiosulfate showed efficacy in terms of hearing protection. The SIOPEL 6 trial consisted solely of patients with localised hepatoblastoma and no effects on survival were shown. In the ACCL0431 trial, which included heterogeneous patients, a post-hoc analysis showed significantly worse overall survival among patients who had disseminated disease receiving sodium thiosulfate than among controls, but not among those with localised disease. Intratympanically administered drugs have mainly been assessed in adults and include N-acetylcysteine and dexamethasone. Inconsistent effects of these drugs were identified but these studies were limited by design, small sample size, and statistical approach. Future studies of systemic drugs will need to consider the measurement of disease outcomes through study design and sample size, and ototoxicity endpoints should be harmonised to enhance comparability between trials.

Ototoxicity: The Radical Drum Beat and Rhythm of Cochlear Hair Cell Life and Death

The function and structure of the auditory information processing system establishes a unique sensory environment for the "perfect storm." The battle between life and death pits the cascade of an apoptotic storm, programmed cell death cascades, against simple cell death (necrosis) pathways. Live or die, the free radical biology of oxygen and hydroxylation, and the destruction of transition metal migration through the mechanical gate sensory processes of the hair cell lead to direct access to the cytoplasm, cytoplasmic reticulum, and mitochondria of the inner workings of the hair cells. These lead to subsequent interactions with nuclear DNA resulting in permanent hearing loss. The yin and yang of pharmaceutical product development is to document what kills, why it kills, and how do we mitigate it. This review highlights the processes of cell death within the cochlea.

Safety of Extended Interval Tobramycin in Cystic Fibrosis Patients Less an 6 Years Old

OBJECTIVES

The primary objective of this study was to assess the nephrotoxicity and ototoxicity risks of extended interval tobramycin in cystic fibrosis (CF) patients who are <6 years old. A secondary objective included analyzing pharmacokinetic parameters in this age group.

METHODS

A retrospective chart review was conducted of patients with CF who were <6 years old, admitted for an acute pulmonary exacerbation from January 1, 2003, to January 1, 2014, and treated with intravenous tobramycin.

RESULTS

The median baseline serum creatinine (SCr) was 0.26 mg/dL among the 31 patients included in the study. Of the 20 patients who experienced increases in SCr, the absolute median increase was 0.065 mg/dL (0.033-0.1 mg/dL). Abnormal audiograms seen in 4 patients are attributable to middle ear effusion present on exam. The median dose of tobramycin was 11.7 mg/kg (11.3-12 mg/kg), the elimination constant was 0.4 hr^-1(0.32-0.47 hr^-1), half-life was 1.7 hr (1.5-2.1 hr), volume of distribution was 0.37 L/kg (0.31-0.47 L/kg), and median peaks and troughs fell within ranges of 20 to 30 mg/L (20.9-32.7 mg/L) and <0.01 mg/L, respectively.

CONCLUSIONS

Extended interval dosing tobramycin is safe in CF patients who are <6 years old. There was no drug-related ototoxicity, and some nephrotoxicity was observed. When dosed at 12 mg/kg, similar pharmacokinetics were seen among all age groups, and concentrations were within the desired range.

A kinase inhibitor library screen identifies novel enzymes involved in ototoxic damage to the murine organ of Corti

Ototoxicity is a significant side effect of a number of drugs, including the aminoglycoside antibiotics and platinum-based chemotherapeutic agents that are used to treat life-threatening illnesses. Although much progress has been made, the mechanisms that lead to ototoxic loss of inner ear sensory hair cells (HCs) remains incompletely understood. Given the critical role of protein phosphorylation in intracellular processes, including both damage and survival signaling, we screened a library of kinase inhibitors targeting members of all the major families in the kinome. Micro-explants from the organ of Corti of mice in which only the sensory cells express GFP were exposed to 200 μM of the ototoxic aminoglycoside gentamicin with or without three dosages of each kinase inhibitor. The loss of sensory cells was compared to that seen with gentamicin alone, or without treatment. Of the 160 inhibitors, 15 exhibited a statistically significant protective effect, while 3 significantly enhanced HC loss. The results confirm some previous studies of kinase involvement in HC damage and survival, and also highlight several novel potential kinase pathway contributions to ototoxicity.

Resolution of Cochlear Inflammation: Novel Target for Preventing or Ameliorating Drug-, Noise- and Age-related Hearing Loss

A significant number of studies support the idea that inflammatory responses are intimately associated with drug-, noise- and age-related hearing loss (DRHL, NRHL and ARHL). Consequently, several clinical strategies aimed at reducing auditory dysfunction by preventing inflammation are currently under intense scrutiny. Inflammation, however, is a normal adaptive response aimed at restoring tissue functionality and homeostasis after infection, tissue injury and even stress under sterile conditions, and suppressing it could have unintended negative consequences. Therefore, an appropriate approach to prevent or ameliorate DRHL, NRHL and ARHL should involve improving the resolution of the inflammatory process in the cochlea rather than inhibiting this phenomenon. The resolution of inflammation is not a passive response but rather an active, highly controlled and coordinated process. Inflammation by itself produces specialized pro-resolving mediators with critical functions, including essential fatty acid derivatives (lipoxins, resolvins, protectins and maresins), proteins and peptides such as annexin A1 and galectins, purines (adenosine), gaseous mediators (NO, H₂S and CO), as well as neuromodulators like acetylcholine and netrin-1. In this review article, we describe recent advances in the understanding of the resolution phase of inflammation and highlight therapeutic strategies that might be useful in preventing inflammation-induced cochlear damage. In particular, we emphasize beneficial approaches that have been tested in pre-clinical models of inflammatory responses induced by recognized ototoxic drugs such as cisplatin and aminoglycoside antibiotics. Since these studies suggest that improving the resolution process could be useful for the prevention of inflammation-associated diseases in humans, we discuss the potential application of similar strategies to prevent or mitigate DRHL, NRHL and ARHL.

Hypertension is associated with dysfunction of both peripheral and central auditory system

OBJECTIVES

Arterial hypertension negatively influences the peripheral auditory system, causing sensorineural hearing loss. Much less is known about the detrimental effects of hypertension on the central auditory functions.

METHODS

We tested 32 arterial hypertension patients and 32 age and sex-matched healthy volunteers with the expanded tonal audiometry (0.125-12.5 kHz), distortion product otoacoustic emissions (0.75-8 kHz), horizontal minimum audible angle test for eight azimuths with binaural stimulation and the random gap detection test.

RESULTS

Peripheral hearing of the hypertensive patients was impaired in comparison with the controls within all audiometric frequencies (0.125-12.5 kHz) and within specific groups of frequencies. Distortion product otoacoustic emission results were significantly lower for frequencies 4 (P = 0.04) and 6 kHz (P < 0.001). The sound localization ability in the horizontal minimum audible angle test was significantly worse in the hypertensive patients in the 0°, 45°, 90°, 135°, and 270° azimuth when the interaural pure tone average (0.5-1-2 kHz) was set less than 20 dB hearing level (P < 0.05), and in the 0°, 90°, 225°, and 270°azimuth when the binaural pure tone average (0.5-1-2 kHz) was set 20 dB or less hearing level (P < 0.05). Gap detection thresholds in the random gap detection test did not differ between the two groups.

CONCLUSION

Arterial hypertension is independently related to the damage of the peripheral part of the auditory system resulting in high-frequency hearing loss. Hypertensive disturbances of central auditory processing are more discrete and concern the spatial hearing resolution.

Role of endoplasmic reticulum stress in drug-induced toxicity

Drug‐induced toxicity is a key issue for public health because some side effects can be severe and life‐threatening. These adverse effects can also be a major concern for the pharmaceutical companies since significant toxicity can lead to the interruption of clinical trials, or the withdrawal of the incriminated drugs from the market. Recent studies suggested that endoplasmic reticulum (ER) stress could be an important event involved in drug liability, in addition to other key mechanisms such as mitochondrial dysfunction and oxidative stress. Indeed, drug‐induced ER stress could lead to several deleterious effects within cells and tissues including accumulation of lipids, cell death, cytolysis, and inflammation. After recalling important information regarding drug‐induced adverse reactions and ER stress in diverse pathophysiological situations, this review summarizes the main data pertaining to drug‐induced ER stress and its potential involvement in different adverse effects. Drugs presented in this review are for instance acetaminophen (APAP), arsenic trioxide and other anticancer drugs, diclofenac, and different antiretroviral compounds. We also included data on tunicamycin (an antibiotic not used in human medicine because of its toxicity) and thapsigargin (a toxic compound of the Mediterranean plant Thapsia garganica) since both molecules are commonly used as prototypical toxins to induce ER stress in cellular and animal models.

Differences in perilymphatic space enhancement and adverse inflammatory reaction after intratympanic injection of two different gadolinium agents: A 9.4-T magnetic resonance imaging study

PURPOSE

To compare the inner ear enhancement after intratympanic injection of two widely used gadolinium (Gd) agents by 9.4 T micro-magnetic resonance imaging (MRI) and to investigate the effects of Gd on the inner ear.

METHODS

Twelve ears of six rats received intratympanic administration of 1/5 diluted Gd agents: gadoterate meglumine (Gd-DTPA) for the left ear and gadodiamide (Gd-DTPA-BMA) for the right ear. MRI was performed every 30 min from 1 to 4 h after administration. The normalized signal intensity was evaluated by quantitative analysis at each cochlear fluid compartment. Eight, six, and seven ears treated with Gd-DTPA, Gd-DPTA-BMA, and nothing as controls, respectively, were processed for histological evaluation after MRI. After hematoxylin & eosin staining, adverse inflammatory reactions were evaluated for turbid aggregation and lymphocytes.

RESULTS

The perilymphatic enhancement of Gd-DTPA was superior to that of Gd-DTPA-BMA regardless of cochlear turn, compartment, and time point. Inflammatory reactions were found in 4/8 (50.0%) and 4/6 (66.6%) ears administered Gd-DTPA and Gd-DTPA-BMA, respectively. Regardless of the contrast agent used, inflammatory reactions were most definite in the scala tympani of the basal turn, i.e., near the round window. Slightly greater inflammatory reactions were observed in ears injected with Gd-DTPA-BMA compared to Gd-DTPA although the difference was not statistically significant. No inflammatory reaction was observed in any of the seven controls. The auditory brainstem response threshold was 11.8 ± 2.5 dB SPL before IT Gd injection and it did not change for up to 5 days (15.4 ± 6.6 dB SPL) post-injection.

CONCLUSIONS

Gd-DTPA was superior to Gd-DTPA-BMA for visualization of the inner ear. Administration of diluted Gd agents intratympanically may induce considerable inflammatory reactions in the inner ear.

Future opportunities in preventing ototoxicity: Caffeic acid phenethyl ester may be a candidate (Review)

Caffeic acid phenethyl ester (CAPE) is an important active component of propolis, which is derived from honeybee hives. It has received increasing attention in a variety of medical and pharmaceutical research, due to its anti‑oxidant, antiproliferative, anti‑inflammatory, antiviral and antifungal activity, in addition to its antineoplastic properties. Besides the use of CAPE as an antioxidant and anti‑inflammatory agent in a number of in vivo studies of ear disease, its beneficial effects have been reported in the treatment of cancer, arthritis, allergies, heart disease, diabetes, kidney disease, liver disease and neurological disease. CAPE influences a number of biochemical pathways, as well as several targets involved in ear diseases, in particular, in ototoxicity. The protective effects of CAPE in ototoxicity, which may be induced by a number factors, including lipopolysaccharides, hydrogen peroxide and streptomycin, are evaluated and discussed in the present review.

Prestin as a biochemical marker for early detection of acquired sensorineural hearing loss

Acquired sensorineural hearing loss and tinnitus can come about through various etiologies such as exposure to excessively loud noise or drugs with ototoxic properties. As such, acquired hearing loss is a common source of morbidity which deleteriously affects the ability to communicate. At present our ability to detect acquired hearing loss and tinnitus at its earliest stages is limited and there are no adjuncts to audiometric evaluation. The earliest cellular targets of noise and ototoxins in the cochlea are the outer hair cells (OHC). I hypothesize that serum assays of OHC specific protein, prestin, will allow detection and quantification of OHC damage before audiometric testing can identify presence of hearing loss. At present, there are no data available to evaluate this hypothesis, but initial evaluation can readily be carried out using existing experimental animal models of ototoxicity and noise-induced hearing loss. Early detection of OHC damage is critical to adoption of measures aimed at ameliorating hearing loss and tinnitus, thus reducing permanent deficits and disability.

Impact of nonaspirin nonsteroidal anti-inflammatory agents and acetaminophen on sensorineural hearing loss: a systematic review

OBJECTIVE

To perform a systematic review evaluating the association between sensorineural hearing loss and (1) nonsteroidal anti-inflammatory drugs (NSAIDs) as a class, (2) NSAIDs available over the counter, (3) NSAIDs in short intravenous courses, (4) prescription NSAIDs utilized by patients without systemic inflammatory conditions, (5) prescription NSAIDs in patients with arthritides, and (6) acetaminophen with and without concomitant narcotic usage.

DATA SOURCES

Computerized searches of PubMed, EMBASE, and the Cochrane Library were updated through May 2014, along with manual searches and inquiries to topic experts.

REVIEW METHODS

The systematic review was performed according to an a priori protocol. Data extraction was performed by 2 independent investigators, and it focused on relevant audiologic measurements, methodological elements related to risk of bias, and potential confounders.

RESULTS

The 23 criterion-meeting studies included a total of 92,532 participants, with mixed results. Sulindac was the only specific agent to have been studied with formal audiometry in a randomized double-blind placebo-controlled trial in which hearing was the reported primary outcome: Although an effect was seen in the unadjusted analysis (pure tone threshold>15 dB, 9.3% vs 2.9%; relative risk [RR], 3.2; confidence interval [CI], 1.09-9.55; P=.02), the effect dissipated in the adjusted analysis (P=.09). There was a significant effect on self-reported hearing loss from NSAIDs as a class (RR, 1.21; CI, 1.11-1.33), ibuprofen (RR, 1.13; CI, 1.06-1.19), and acetaminophen (RR, 1.21; CI, 1.11-1.33), but no formal audiometric data confirm or refute this suggested effect. Audiometry has demonstrated profound loss in some instances of acetaminophen-narcotic combination ingestions.

CONCLUSIONS

Data are varied regarding the impact of NSAIDs and acetaminophen on population hearing health.

A prediction model of drug-induced ototoxicity developed by an optimal support vector machine (SVM) method

Drug-induced ototoxicity, as a toxic side effect, is an important issue needed to be considered in drug discovery. Nevertheless, current experimental methods used to evaluate drug-induced ototoxicity are often time-consuming and expensive, indicating that they are not suitable for a large-scale evaluation of drug-induced ototoxicity in the early stage of drug discovery. We thus, in this investigation, established an effective computational prediction model of drug-induced ototoxicity using an optimal support vector machine (SVM) method, GA-CG-SVM. Three GA-CG-SVM models were developed based on three training sets containing agents bearing different risk levels of drug-induced ototoxicity. For comparison, models based on naïve Bayesian (NB) and recursive partitioning (RP) methods were also used on the same training sets. Among all the prediction models, the GA-CG-SVM model II showed the best performance, which offered prediction accuracies of 85.33% and 83.05% for two independent test sets, respectively. Overall, the good performance of the GA-CG-SVM model II indicates that it could be used for the prediction of drug-induced ototoxicity in the early stage of drug discovery.

Prevention of Cisplatin-Induced Hearing Loss by Intratympanic Dexamethasone

Objective

To examine the role of intratympanic Dexamethasone (ITD) in the prevention of Cisplatin-induced hearing loss.

Study Design

Prospective randomized controlled clinical trial.

Setting

Tertiary referral center.

Subjects and Methods

Twenty-six patients suffering from a neoplastic disease for which the treatment protocol included Cisplatin were recruited. Prior to each Cisplatin treatment session ITD was injected to the baseline randomly assigned ear while the other ear of the same patient served as the control. Audiometry and Distortion Product Otoacoustic Emissions (DPOAEs) test results of the baseline and follow-up examinations were compared within and between the study and control ears.

Results

The cumulative dose of Cisplatin was greater than 400 mg for the 15 subjects who completed the study. The pure tone threshold at 8000 Hz and pure tone average threshold at 4000 to 8000 Hz significantly increased in both the study ( P < .005, P < .03, respectively) and control ears ( P < .01, P < .005, respectively). Significant increase in the pure tone threshold for 6000 Hz was observed in the control ( P < .02) but not in the study group. Within the groups comparison also revealed significant decrease in the DPOAE average signal-to-noise ratio (SNR) for the f2 frequencies 7031 ( P < .04) and 8391 Hz ( P < .04) and SNR average for 4000 to 8000 Hz in the control ( P < .04) but not in the study ears.

Conclusions

ITD significantly attenuated hearing loss at 6000 Hz and decreased the outer hair dysfunction in the DPOAE f2 range of 4000 to 8000 Hz. ITD might have potential in the reduction of Cisplatin-induced hearing loss.

Vestibular damage in chronic ototoxicity: a mini-review

Ototoxicity is a major cause of the loss of hearing and balance in humans. Ototoxic compounds include pharmaceuticals such as aminoglycoside antibiotics, anti-malarial drugs, loop diuretics and chemotherapeutic platinum agents, and industrial chemicals including several solvents and nitriles. Human and rodent data indicate that the main target of toxicity is hair cells (HCs), which are the mechanosensory cells responsible for sensory transduction in both the auditory and the vestibular system. Nevertheless, the compounds may also affect the auditory and vestibular ganglion neurons. Exposure to ototoxic compounds has been found to cause HC apoptosis, HC necrosis, and damage to the afferent terminals, of differing severity depending on the ototoxicity model. One major pathway frequently involved in HC apoptosis is the c-jun N-terminal kinase (JNK) signaling pathway activated by reactive oxygen species, but other apoptotic pathways can also play a role in ototoxicity. Moreover, little is known about the effects of chronic low-dose exposure. In rodent vestibular epithelia, extrusion of live HCs from the sensory epithelium may be the predominant form of cell demise during chronic ototoxicity. In addition, greater involvement of the afferent terminals may occur, particularly the calyx units contacting type I vestibular HCs. As glutamate is the neurotransmitter in this synapse, excitotoxic phenomena may participate in afferent and ganglion neuron damage. Better knowledge of the events that take place in chronic ototoxicity is of great interest, as it will increase understanding of the sensory loss associated with chronic exposure and aging.

Gentamicin rapidly inhibits mitochondrial metabolism in high-frequency cochlear outer hair cells

Aminoglycosides (AG), including gentamicin (GM), are the most frequently used antibiotics in the world and are proposed to cause irreversible cochlear damage and hearing loss (HL) in 1/4 of the patients receiving these life-saving drugs. Akin to the results of AG ototoxicity studies, high-frequency, basal turn outer hair cells (OHCs) preferentially succumb to multiple HL pathologies while inner hair cells (IHCs) are much more resilient. To determine if endogenous differences in IHC and OHC mitochondrial metabolism dictate differential sensitivities to AG-induced HL, IHC- and OHC-specific changes in mitochondrial reduced nicotinamide adenine dinucleotide (NADH) fluorescence during acute (1 h) GM treatment were compared. GM-mediated decreases in NADH fluorescence and succinate dehydrogenase activity were observed shortly after GM application. High-frequency basal turn OHCs were found to be metabolically biased to rapidly respond to alterations in their microenvironment including GM and elevated glucose exposures. These metabolic biases may predispose high-frequency OHCs to preferentially produce cell-damaging reactive oxygen species during traumatic challenge. Noise-induced and age-related HL pathologies share key characteristics with AG ototoxicity, including preferential OHC loss and reactive oxygen species production. Data from this report highlight the need to address the role of mitochondrial metabolism in regulating AG ototoxicity and the need to illuminate how fundamental differences in IHC and OHC metabolism may dictate differences in HC fate during multiple HL pathologies.