Dose-dependent cochlear and vestibular toxicity of trans-tympanic cisplatin in the rat

Prevalence and predictors for cisplatin-induced toxicities in Zimbabwean women with cervical cancer

Aim: To describe treatment-induced toxicities (TITs) and associated factors in Zimbabwean cancer patients receiving cisplatin. Methods: In total, 252 Zimbabwean women with cervical cancer, receiving cisplatin were followed up over 12 months for TITs and disease status. Results: Peripheral neuropathy (70%) and ototoxicity (53%) were most prevalent. Advanced disease (OR = 1.3; 95% CI = 1.1-1.5; p = 0.02), pain comedications (OR = 1.3; 95% CI = 1.1-1.5; p = 0.03), alcohol (OR = 2.8; 95% CI = 1.1-7.5; p = 0.04) and comorbidities (OR = 1.2; 95% CI = 1.1-1.4; p = 0.04) increased peripheral neuropathy and ototoxicity risk. Older age increased risk of disease progression (OR = 1.9; 95% CI = 1.4-3.0; p = 0.033). Conclusion: High peripheral neuropathy and ototoxicity prevalence were observed, which are not routinely monitored in Zimbabwe. There is a need for capacity building to incorporate comprehensive TIT testing and optimize cancer care in Zimbabwe.

[Animal models of balance pathologies: New tools to study peripheral vestibulopathies]

The different types of peripheral vestibulopathies (PVs) or peripheral vestibular disorders (PVDs) are essentially diagnosed on the basis of their clinical expression. The heterogeneity of vestibular symptoms makes it difficult to stratify patients for therapeutic management. Animal models of PVs are a good mean to search for clinical evaluation criteria allowing to objectively analyze the kinetics of expression of the vertigo syndrome and to evaluate the benefits of therapeutic strategies, whether they are pharmacological or rehabilitative. The question of the predictability of these animal models is therefore crucial for the identification of behavioral and biological biomarkers that could then be used in the human clinic. In this review, we propose an overview of the different animal models of PVs, and discuss their relevance for the understanding of the underlying pathophysiological mechanisms and the development of new and more targeted therapeutic approaches.

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?

Overexpression of XIAP inhibits cisplatin-induced hair cell loss

Cisplatin is a platinum-containing drug with ototoxicity commonly used clinically and has significant efficacy against a variety of solid tumors. One of the most important mechanisms of ototoxicity is that cisplatin induces apoptosis of hair cells. According to relevant literature, X-linked inhibitor of apoptosis protein (XIAP, anti-apoptotic protein) could inhibit the apoptotic pathway. We hypothesized that this protein might protect cochlear hair cells from cisplatin-induced injury. To figure it out, we treated cochlea of normal mice with various concentrations of cisplatin to observe the response and morphology of hair cells and determine a reasonable concentration. Next, Western Blot and quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) experiments were conducted to make an investigation about the expression of XIAP protein and mRNA. In addition, we constructed and identified XIAP overexpressing mice. Finally, we treated cochlear tissues of normal and overexpressing mice with cisplatin to investigate the cyto-protection of XIAP on hair cells, respectively. It was found that 50 μmol/L cisplatin resulted in significant loss and disorganization of hair cells, while simultaneously downregulating the protein and mRNA of XIAP. In XIAP overexpressing mice, the loss and disorganization of hair cells were significantly lessened. These results showed that XIAP can lessen cisplatin-induced hair cell loss and play a role in otoprotection.

Mechanisms of Ototoxicity and Otoprotection

Ototoxicity refers to damage to the inner ear that leads to functional hearing loss or vestibular disorders by selected pharmacotherapeutics as well as a variety of environmental exposures (eg, lead, cadmium, solvents). This article reviews the fundamental mechanisms underlying ototoxicity by clinically relevant, hospital-prescribed medications (ie, aminoglycoside antibiotics or cisplatin, as illustrative examples). Also reviewed are current strategies to prevent prescribed medication-induced ototoxicity, with several clinical or candidate interventional strategies being discussed.

Mechanisms of Aminoglycoside- and Cisplatin-Induced Ototoxicity

Purpose This review article summarizes our current understanding of the mechanisms underlying acquired hearing loss from hospital-prescribed medications that affects as many as 1 million people each year in Western Europe and North America. Yet, there are currently no federally approved drugs to prevent or treat the debilitating and permanent hearing loss caused by the life-saving platinum-based anticancer drugs or the bactericidal aminoglycoside antibiotics. Hearing loss has long-term impacts on quality-of-life measures, especially in young children and older adults. This review article also highlights some of the current knowledge gaps regarding iatrogenic causes of hearing loss. Conclusion Further research is urgently needed to further refine clinical practice and better ameliorate iatrogenic drug-induced hearing loss.

Preferential Cochleotoxicity of Cisplatin

Cisplatin-induced ototoxicity in humans is more predominant in the cochlea than in the vestibule. Neither definite nor substantial vestibular dysfunction after cisplatin treatment has been consistently reported in the current literature. Inner ear hair cells seem to have intrinsic characteristics that make them susceptible to direct exposure to cisplatin. The existing literature suggests, however, that cisplatin might have different patterns of drug trafficking across the blood-labyrinth-barrier, or different degrees of cisplatin uptake to the hair cells in the cochlear and vestibular compartments. This review proposes an explanation for the preferential cochleotoxicity of cisplatin based on current evidence as well as the anatomy and physiology of the inner ear. The endocochlear potential, generated by the stria vascularis, acting as the driving force for hair cell mechanoelectrical transduction might also augment cisplatin entry into cochlear hair cells. Better understanding of the stria vascularis might shed new light on cochleotoxic mechanisms and inform the development of otoprotective interventions to moderate cisplatin associated ototoxicity.

Imbalance Associated With Cisplatin Chemotherapy in Adult Cancer Survivors: A Clinical Study

OBJECTIVE

This study investigated balance problems and vestibular function in adult cancer survivors who had completed cisplatin chemotherapy treatment.

STUDY DESIGN

Observational cross-sectional study.

SETTING

Tertiary care center.

PATIENTS

Adult survivors of cancer who had completed cisplatin treatment.

MAIN OUTCOME MEASURES

Patient-reported balance symptoms were evaluated by a semistructured clinical interview. Patients underwent bedside clinical tests including Dynamic Visual Acuity test, Modified Clinical Testing of Sensory Interaction and Balance (CTSIB-m), and vibration sense testing to detect peripheral neuropathy. The video Head Impulse Test (vHIT) of all semicircular canals was performed.

RESULTS

Eleven of 65 patients (17%) reported some balance symptoms after cisplatin therapy, including vertigo, dizziness, unsteadiness, and falls. Vertigo was the most common balance symptom, reported by six patients (9.2%), and the clinical histories of these patients were consistent with benign paroxysmal positional vertigo. Three patients (5%) had abnormal results of the CTSIB-m test, and they were the same patients who reported falls. There was a significant association of peripheral neuropathy detected by vibration test and balance symptoms. All patients had normal vHIT results in all semicircular canals.

CONCLUSIONS

Balance symptoms after cisplatin treatment occurred in 17% of adult cancer survivors. Patients with peripheral neuropathy were more likely to have balance symptoms. The CTSIB-m test is a useful bedside physical examination to identify patients with a high risk of fall. Though there was no vestibular dysfunction detected by the vHIT in cancer survivors after cisplatin therapy, benign paroxysmal positional vertigo was relatively prevalent in this group of patients.

Assessment of cochlear toxicity in response to chronic 3,3'-iminodipropionitrile in mice reveals early and reversible functional loss that precedes overt histopathology

The peripheral auditory and vestibular systems rely on sensorineural structures that are vulnerable to ototoxic agents that cause hearing loss and/or equilibrium deficits. Although attention has focused on hair cell loss as the primary pathology underlying ototoxicity, evidence from the peripheral vestibular system indicates that hair cell loss during chronic exposure is preceded by synaptic uncoupling from the neurons and is potentially reversible. To determine if synaptic pathology also occurs in the peripheral auditory system, we examined the extent, time course, and reversibility of functional and morphological alterations in cochleae from mice exposed to 3,3′-iminodipropionitrile (IDPN) in drinking water for 2, 4 or 6 weeks. Functionally, IDPN exposure caused progressive high- to low-frequency hearing loss assessed by measurement of auditory brainstem response wave I absolute thresholds and amplitudes. The extent of hearing loss scaled with the magnitude of vestibular dysfunction assessed behaviorally. Morphologically, IDPN exposure caused progressive loss of outer hair cells (OHCs) and synapses between the inner hair cells (IHCs) and primary auditory neurons. In contrast, IHCs were spared from ototoxic damage. Importantly, hearing loss consistent with cochlear synaptopathy preceded loss of OHCs and synapses and, moreover, recovered if IDPN exposure was stopped before morphological pathology occurred. Our observations suggest that synaptic uncoupling, perhaps as an early phase of cochlear synaptopathy, also occurs in the peripheral auditory system in response to IDPN exposure. These findings identify novel mechanisms that contribute to the earliest stages of hearing loss in response to ototoxic agents and possibly other forms of acquired hearing loss.

Current Strategies to Combat Cisplatin-Induced Ototoxicity

Cisplatin is widely used for the treatment of a number of solid malignant tumors. However, ototoxicity induced by cisplatin is an obstacle to effective treatment of tumors. The basis for this toxicity has not been fully elucidated. It is generally accepted that hearing loss is due to excessive production of reactive oxygen species by cells of the cochlea. In addition, recent data suggest that inflammation may trigger inner ear cell death through endoplasmic reticulum stress, autophagy, and necroptosis, which induce apoptosis. Strategies have been extensively explored by which to prevent, alleviate, and treat cisplatin-induced ototoxicity, which minimize interference with antitumor activity. Of these strategies, none have been approved by the Federal Drug Administration, although several preclinical studies have been promising. This review highlights recent strategies that reduce cisplatin-induced ototoxicity. The focus of this review is to identify candidate agents as novel molecular targets, drug administration routes, delivery systems, and dosage schedules. Animal models of cisplatin ototoxicity are described that have been used to evaluate drug efficacy and side effect prevention. Finally, clinical reports of otoprotection in patients treated with cisplatin are highlighted. For the future, high-quality studies are required to provide reliable data regarding the safety and effectiveness of pharmacological interventions that reduce cisplatin-induced ototoxicity.

Styrene alters potassium endolymphatic concentration in a model of cultured utricle explants

Despite well-documented neurotoxic and ototoxic properties, styrene remains commonly used in industry. Its effects on the cochlea have been extensively studied in animals, and epidemiological and animal evidence indicates an impact on balance. However, its influence on the peripheral vestibular receptor has yet to be investigated. Here, we assessed the vestibulotoxicity of styrene using an in vitro model, consisting of three-dimensional cultured newborn rat utricles filled with a high‑potassium (K⁺) endolymph-like fluid, called "cysts". K⁺ entry in the cyst ("influx") and its exit ("efflux") are controlled by secretory cells and hair cells, respectively. The vestibular epithelium's functionality is thus linked to K⁺ concentration, measured using a microelectrode. Known inhibitors of K⁺ efflux and influx validated the model. Cysts were subsequently exposed to styrene (0.25; 0.5; 0.75 and 1 mM) for 2 h or 72 h. The decrease in K⁺ concentration measured after both exposure durations was dose-dependent, and significant from 0.75 mM styrene. Vacuoles were visible in the cytoplasm of epithelial cells from 0.5 mM after 2 h and from 0.25 mM after 72 h. The results presented here are the first evidence that styrene may deregulate K⁺ homeostasis in the endolymphatic space, thereby altering the functionality of the vestibular receptor.

Aminoglycoside- and Cisplatin-Induced Ototoxicity: Mechanisms and Otoprotective Strategies

Ototoxicity refers to damage of inner ear structures (i.e., the cochlea and vestibule) and their function (hearing and balance) following exposure to specific in-hospital medications (i.e., aminoglycoside antibiotics, platinum-based drugs), as well as a variety of environmental or occupational exposures (e.g., metals and solvents). This review provides a narrative derived from relevant papers describing factors contributing to (or increasing the risk of) aminoglycoside and cisplatin-induced ototoxicity. We also review current strategies to protect against ototoxicity induced by these indispensable pharmacotherapeutic treatments for life-threatening infections and solid tumors. We end by highlighting several interventional strategies that are currently in development, as well as the diverse challenges that still need to be overcome to prevent drug-induced hearing loss.

An optimized, clinically relevant mouse model of cisplatin-induced ototoxicity

Cisplatin-induced ototoxicity results in significant, permanent hearing loss in pediatric and adult cancer survivors. Elucidating the mechanisms underlying cisplatin-induced hearing loss as well as the development of therapies to reduce and/or reverse cisplatin ototoxicity have been impeded by suboptimal animal models. Clinically, cisplatin is most commonly administered in multi-dose, multi-cycle protocols. However, many animal studies are conducted using single injections of high-dose cisplatin, which is not reflective of clinical cisplatin administration protocols. Significant limitations of both high-dose, single-injection protocols and previous multi-dose protocols in rodent models include high mortality rates and relatively small changes in hearing sensitivity. These limitations restrict assessment of both long-term changes in hearing sensitivity and effects of potential protective therapies. Here, we present a detailed method for an optimized mouse model of cisplatin ototoxicity that utilizes a multi-cycle administration protocol that better approximates the type and degree of hearing loss observed clinically. This protocol results in significant hearing loss with very low mortality. This mouse model of cisplatin ototoxicity provides a platform for examining mechanisms of cisplatin-induced hearing loss as well as developing therapies to protect the hearing of cancer patients receiving cisplatin therapy.

The genetic vulnerability to cisplatin ototoxicity: a systematic review

Ototoxicity is one of the major side-effects of platinum-based chemotherapy, in particular cisplatin (cis-diammine dichloroplatinum II). To our knowledge, no systematic review has previously provided a quantitative summary estimate of the impact of genetics upon the risk of developing hearing loss. We searched Embase, Medline, ASSIA, Pubmed, Scopus, and Web of Science, for studies documenting the genetic risk of ototoxicity in patients with cancer treated with cisplatin. Titles/abstracts and full texts were reviewed for inclusion. Meta-analytic estimates of risk (Odds Ratio) from the pooled data were calculated for studies that have been repeated twice or more. The search identified 3891 papers, of which 30 were included. The majority were retrospective (44%), ranging from n = 39 to n = 317, some including only patients younger than 25 years of age (33%), and some on both genders (80%). The most common cancers involved were osteosarcoma (53%), neuroblastoma (37%), prostate (17%) and reproductive (10%). Most studies performed genotyping, though only 5 studies performed genome-wide association studies. Nineteen single-nucleotide polymorphisms (SNPs) from 15 genes were repeated more than twice. Meta-analysis of group data indicated that rs1872328 on ACYP2, which plays a role in calcium homeostasis, increases the risk of ototoxicity by 4.61 (95% CI: 3.04-7.02; N = 696, p < 0.0001) as well as LRP2 rs4668123 shows a cumulated Odds Ratio of 3.53 (95% CI: 1.48-8.45; N = 118, p = 0.0059), which could not be evidenced in individual studies. Despite the evidence of heterogeneity across studies, these meta-analytic results from 30 studies are consistent with a view of a genetic predisposition to platinum-based chemotherapy mediated ototoxicity. These new findings are informative and encourage the genetic screening of cancer patients in order to identify patients with greater vulnerability of developing hearing loss, a condition having a potentially large impact on quality of life. More studies are needed, with larger sample size, in order to identify additional markers of ototoxic risk associated with platinum-based chemotherapy and investigate polygenic risks, where multiple markers may exacerbate the side-effects.

Characterization of spatial and temporal development of Type I and Type II hair cells in the mouse utricle using new cell-type-specific markers

The utricle of the inner ear, a vestibular sensory structure that mediates perception of linear acceleration, is comprised of two morphologically and physiologically distinct types of mechanosensory hair cells, referred to as Type Is and Type IIs. While these cell types are easily discriminated in an adult utricle, understanding their development has been hampered by a lack of molecular markers that can be used to identify each cell type prior to maturity. Therefore, we collected single hair cells at three different ages and used single cell RNAseq to characterize the transcriptomes of those cells. Analysis of differential gene expression identified Spp1 as a specific marker for Type I hair cells and Mapt and Anxa4 as specific markers for Type II hair cells. Antibody labeling confirmed the specificity of these markers which were then used to examine the temporal and spatial development of utricular hair cells. While Type I hair cells develop in a gradient that extends across the utricle from posterior-medial to anterior-lateral, Type II hair cells initially develop in the central striolar region and then extend uniformly towards the periphery. Finally, by combining these markers with genetic fate mapping, we demonstrate that over 98% of all Type I hair cells develop prior to birth while over 98% of Type II hair cells develop post-natally. These results are consistent with previous findings suggesting that Type I hair cells develop first and refute the hypothesis that Type II hair cells represent a transitional form between immature and Type I hair cells.

Calyx junction dismantlement and synaptic uncoupling precede hair cell extrusion in the vestibular sensory epithelium during sub-chronic 3,3'-iminodipropionitrile ototoxicity in the mouse

The cellular and molecular events that precede hair cell (HC) loss in the vestibular epithelium during chronic ototoxic exposure have not been widely studied. To select a study model, we compared the effects of sub-chronic exposure to different concentrations of 3,3'-iminodipropionitrile (IDPN) in the drinking water of two strains of mice and of both sexes. In subsequent experiments, male 129S1/SvImJ mice were exposed to 30 mM IDPN for 5 or 8 weeks; animals were euthanized at the end of the exposure or after a washout period of 13 weeks. In behavioral tests, IDPN mice showed progressive vestibular dysfunction followed by recovery during washout. In severely affected animals, light and electron microscopy observations of the vestibular epithelia revealed HC extrusion towards the endolymphatic cavity. Comparison of functional and ultrastructural data indicated that animals with fully reversible dysfunction did not have significant HC loss or stereociliary damage, but reversible dismantlement of the calyceal junctions that characterize the contact between type I HCs (HCI) and their calyx afferents. Immunofluorescent analysis revealed the loss of calyx junction proteins, Caspr1 and Tenascin-C, during exposure and their recovery during washout. Synaptic uncoupling was also recorded, with loss of pre-synaptic Ribeye and post-synaptic GluA2 puncta, and differential reversibility among the three different kinds of synaptic contacts existing in the epithelium. qRT-PCR analyses demonstrated that some of these changes are at least in part explained by gene expression modifications. We concluded that calyx junction dismantlement and synaptic uncoupling are early events in the mouse vestibular sensory epithelium during sub-chronic IDPN ototoxicity.

Physiological assesment of vestibular function and toxicity in humans and animals

Physiological methods that can be similarly recorded in humans and animals have a major role in sensory toxicology, as they provide a bridge between human sensory perception data and the molecular and cellular data obtained in animal studies. Vestibular toxicity research lags well behind other sensory systems in many aspects, including the availability of methods for functional assessment in animals that could be robustly translated to human significance. Here we review the methods available for the assessment of vestibular function in both humans and laboratory animals, with an emphasis on their similarity or divergence, to highlight their potential utility for the predictive assessment of vestibular toxicity.

Postural Control in Bilateral Vestibular Failure: Its Relation to Visual, Proprioceptive, Vestibular, and Cognitive Input

Patients with bilateral vestibular failure (BVF) suffer from postural and gait unsteadiness with an increased risk of falls. The aim of this study was to elucidate the differential role of otolith, semicircular canal (SSC), visual, proprioceptive, and cognitive influences on the postural stability of BVF patients. Center-of-pressure displacements were recorded by posturography under six conditions: target visibility; tonic head positions in the pitch plane; horizontal head shaking; sensory deprivation; dual task; and tandem stance. Between-group analysis revealed larger postural sway in BVF patients on eye closure; but with the eyes open, BVF did not differ from healthy controls (HCs). Head tilts and horizontal head shaking increased sway but did not differ between groups. In the dual task condition, BVF patients maintained posture indistinguishable from controls. On foam and tandem stance, postural sway was larger in BVF, even with the eyes open. The best predictor for the severity of bilateral vestibulopathy was standing on foam with eyes closed. Postural control of our BVF was indistinguishable from HCs once visual and proprioceptive feedback is provided. This distinguishes them from patients with vestibulo-cerebellar disorders or functional dizziness. It confirms previous reports and explains that postural unsteadiness of BVF patients can be missed easily if not examined by conditions of visual and/or proprioceptive deprivation. In fact, the best predictor for vestibular hypofunction (VOR gain) was examining patients standing on foam with the eyes closed. Postural sway in that condition increased with the severity of vestibular impairment but not with disease duration. In the absence of visual control, impaired otolith input destabilizes BVF with head retroflexion. Stimulating deficient SSC does not distinguish patients from controls possibly reflecting a shift of intersensory weighing toward proprioceptive-guided postural control. Accordingly, proprioceptive deprivation heavily destabilizes BVF, even when visual control is provided.

Apoptosis in inner ear sensory hair cells

Apoptosis, or controlled cell death, is a normal part of cellular lifespan. Cell death of cochlear hair cells causes deafness; an apoptotic process that is not well understood. Worldwide, 1.3 billion humans suffer some form of hearing loss, while 360 million suffer debilitating hearing loss as a direct result of the absence of these cochlear hair cells (Worldwide Hearing, 2014). Much is known about apoptosis in other systems and in other cell types thanks to studies done since the mid-20th century. Here we review current literature on apoptosis in general, and causes of deafness and cochlear hair cells loss as a result of apoptosis. The family of B-cell lymphoma (Bcl) proteins are among the most studied and characterized. We will review current literature on the Bcl2 and Bcl6 protein interactions in relation to apoptosis and their possible roles in vulnerability and survival of cochlear hair cells.