Advances in research on labyrinth membranous barriers

Blood-labyrinth barrier breakdown in Meniere's disease

OBJECTIVE

We compared the signal intensity ratio (SIR) of the cochlear basal turn between Meniere's disease and healthy controls to investigate potential damage of the blood-labyrinth barrier in Meniere's disease.

METHODS

Thirty patients diagnosed with unilateral definite Meniere's disease and 24 healthy controls were enrolled. 3D-FLAIR scan was conducted to assess the grades of endolymphatic hydrops in Meniere's patients while measuring the SIR of cochlear basal turns in both groups. The differences of bilateral SIR between Meniere's disease and healthy control were compared, and the correlation between the SIR on affected ear in Meniere's disease and the grades of cochlear and vestibular hydrops were analyzed.

RESULTS

SIR of affected ear in Meniere's disease exhibited significant increase compared to that of unaffected ear. No significant difference was observed in SIR between the two ears in the healthy control. Furthermore, the SIR of unaffected side in Meniere's disease was higher than that of both ears in healthy controls. The SIR in affected ear of Meniere's disease exhibited positive correlation with hydrops in both cochlea and vestibula.

CONCLUSION

The permeability of blood-labyrinth barrier is increased in Meniere's disease, in combination with the typical criteria of Meniere's disease it may be a good biological marker. Destruction of blood-labyrinth barrier may be one of the causes of endolymphatic hydrops in Meniere's disease.

A critical evaluation of "leakage" at the cochlear blood-stria-barrier and its functional significance

The blood-labyrinth-barrier (BLB) is a semipermeable boundary between the vasculature and three separate fluid spaces of the inner ear, the perilymph, the endolymph and the intrastrial space. An important component of the BLB is the blood-stria-barrier, which shepherds the passage of ions and metabolites from strial capillaries into the intrastrial space. Some investigators have reported increased "leakage" from these capillaries following certain experimental interventions, or in the presence of inflammation or genetic variants. This leakage is generally thought to be harmful to cochlear function, principally by lowering the endocochlear potential (EP). Here, we examine evidence for this dogma. We find that strial capillaries are not exclusive, and that the asserted detrimental influence of strial capillary leakage is often confounded by hair cell damage or intrinsic dysfunction of the stria. The vast majority of previous reports speculate about the influence of strial vascular barrier function on the EP without directly measuring the EP. We argue that strial capillary leakage is common across conditions and species, and does not significantly impact the EP or hearing thresholds, either on evidentiary or theoretical grounds. Instead, strial capillary endothelial cells and pericytes are dynamic and allow permeability of varying degrees in response to specific conditions. We present observations from mice and demonstrate that the mechanisms of strial capillary transport are heterogeneous and inconsistent among inbred strains.

Macrophage Depletion Protects Against Cisplatin-Induced Ototoxicity and Nephrotoxicity

Cisplatin is a widely used and highly effective anti-cancer drug with significant side effects including ototoxicity and nephrotoxicity. Macrophages, the major resident immune cells in the cochlea and kidney, are important drivers of both inflammatory and tissue repair responses. To investigate the roles of macrophages in cisplatin-induced ototoxicity and nephrotoxicity, we used PLX3397, an FDA-approved inhibitor of the colony-stimulating factor 1 receptor (CSF1R), to eliminate tissue-resident macrophages during the course of cisplatin administration. Mice treated with cisplatin alone (cisplatin/vehicle) had significant hearing loss (ototoxicity) as well as kidney injury (nephrotoxicity). Macrophage ablation using PLX3397 resulted in significantly reduced hearing loss measured by auditory brainstem responses (ABR) and distortion-product otoacoustic emissions (DPOAE). Sensory hair cells in the cochlea were protected against cisplatin-induced death in mice treated with PLX3397. Macrophage ablation also protected against cisplatin-induced nephrotoxicity, as evidenced by markedly reduced tubular injury and fibrosis as well as reduced plasma blood urea nitrogen (BUN) and neutrophil gelatinase-associated lipocalin (NGAL) levels. Mechanistically, our data suggest that the protective effect of macrophage ablation against cisplatin-induced ototoxicity and nephrotoxicity is mediated by reduced platinum accumulation in both the inner ear and the kidney. Together our data indicate that ablation of tissue-resident macrophages represents a novel strategy for mitigating cisplatin-induced ototoxicity and nephrotoxicity.

Brief summary

Macrophage ablation using PLX3397 was protective against cisplatin-induced ototoxicity and nephrotoxicity by limiting platinum accumulation in the inner ear and kidney.

Visualization and clinical relevance of the endolymphatic duct and sac in Ménière's disease

Background

Ménière's disease (MD) is a chronic inner ear disorder with a multifactorial etiology. Decreased visualization of the endolymphatic duct (ED) and sac (ES) is thought to be associated with MD, although controversy exists about whether this finding is specific to MD. Recent literature has revealed that two distinct ES pathologies, developmental hypoplasia and epithelial degeneration, can be distinguished in MD using the angular trajectory of the vestibular aqueduct (ATVA) or ED-ES system as a radiographic surrogate marker. It has been suggested that these two subtypes are associated with distinct phenotypical features. However, the clinical differences between the ATVA subtypes require further validation.

Research objective

The objective of this study is to investigate whether (1) non-visualization of the ED-ES system is a discriminative radiological feature for MD in a cohort of vertigo-associated pathologies (VAPs) and whether (2) different angular trajectories of the ED-ES system in MD are associated with distinguishable clinical features.

Setting

The study was conducted in the Vertigo Referral Center (Haga Teaching Hospital, The Hague, the Netherlands).

Methods

We retrospectively assessed 301 patients (187 definite MD and 114 other VAPs) that underwent 4h-delayed 3D FLAIR MRI. We evaluated (1) the visibility of the ED-ES system between MD and other VAP patients and (2) measured the angular trajectory of the ED-ES system. MD patients were stratified based on the angular measurements into αexit ≤ 120° (MD-120), αexit 120°-140° (MD-intermediate), or αexit ≥ 140° (MD-140). Correlations between ATVA subgroups and clinical parameters were evaluated.

Results

Non-visualization of the ED-ES system was more common in definite MD patients compared with other VAPs (P < 0.001). Among definite MD patients, the MD-140 subtype demonstrated a longer history of vertigo (P = 0.006), a higher prevalence of bilateral clinical disease (P = 0.005), and a trend toward a male preponderance (p = 0.053). No significant differences were found between ATVA subgroups regarding the presence or severity of auditory symptoms, or the frequency of vertigo attacks.

Conclusion

Non-visualization of the ED-ES system is significantly associated with MD. Among MD patients with a visible ED-ES system, we demonstrated that the MD-140 subtype is associated with a longer disease duration, a higher prevalence of bilateral MD, and a trend toward a male preponderance.

The Role of BDNF as a Biomarker in Cognitive and Sensory Neurodegeneration

Brain-derived neurotrophic factor (BDNF) has a crucial function in the central nervous system and in sensory structures including olfactory and auditory systems. Many studies have highlighted the protective effects of BDNF in the brain, showing how it can promote neuronal growth and survival and modulate synaptic plasticity. On the other hand, conflicting data about BDNF expression and functions in the cochlear and in olfactory structures have been reported. Several clinical and experimental research studies showed alterations in BDNF levels in neurodegenerative diseases affecting the central and peripheral nervous system, suggesting that BDNF can be a promising biomarker in most neurodegenerative conditions, including Alzheimer's disease, shearing loss, or olfactory impairment. Here, we summarize current research concerning BDNF functions in brain and in sensory domains (olfaction and hearing), focusing on the effects of the BDNF/TrkB signalling pathway activation in both physiological and pathological conditions. Finally, we review significant studies highlighting the possibility to target BDNF as a biomarker in early diagnosis of sensory and cognitive neurodegeneration, opening new opportunities to develop effective therapeutic strategies aimed to counteract neurodegeneration.

Inner Ear Drug Delivery for Sensorineural Hearing Loss: Current Challenges and Opportunities

Most therapies for treating sensorineural hearing loss are challenged by the delivery across multiple tissue barriers to the hard-to-access anatomical location of the inner ear. In this review, we will provide a recent update on various pharmacotherapy, gene therapy, and cell therapy approaches used in clinical and preclinical studies for the treatment of sensorineural hearing loss and approaches taken to overcome the drug delivery barriers in the ear. Small-molecule drugs for pharmacotherapy can be delivered via systemic or local delivery, where the blood-labyrinth barrier hinders the former and tissue barriers including the tympanic membrane, the round window membrane, and/or the oval window hinder the latter. Meanwhile, gene and cell therapies often require targeted delivery to the cochlea, which is currently achieved via intra-cochlear or intra-labyrinthine injection. To improve the stability of the biomacromolecules during treatment, e.g., RNAs, DNAs, proteins, additional packing vehicles are often required. To address the diverse range of biological barriers involved in inner ear drug delivery, each class of therapy and the intended therapeutic cargoes will be discussed in this review, in the context of delivery routes commonly used, delivery vehicles if required (e.g., viral and non-viral nanocarriers), and other strategies to improve drug permeation and sustained release (e.g., hydrogel, nanocarriers, permeation enhancers, and microfluidic systems). Overall, this review aims to capture the important advancements and key steps in the development of inner ear therapies and delivery strategies over the past two decades for the treatment and prophylaxis of sensorineural hearing loss.

Age-Related Hearing Loss Is Accompanied by Chronic Inflammation in the Cochlea and the Cochlear Nucleus

Age-related hearing loss (ARHL) is a major hearing impairment characterized by pathological changes in both the peripheral and central auditory systems. Low-grade inflammation was observed in the cochlea of deceased human subjects with ARHL and animal models of early onset ARHL, which suggests that inflammation contributes to the development of ARHL. However, it remains elusive how chronic inflammation progresses during normal aging in the cochlea, and especially the accompanying changes of neuroinflammation in the central auditory system. To address this, we investigated chronic inflammation in both the cochlea and the cochlear nucleus (CN) of CBA/CaJ mice, an inbred mouse strain that undergoes normal aging and develops human, like-late-onset ARHL. Using immunohistochemistry, confocal microscopy, and quantitative image processing, we measured the accumulation and activation of macrophages in the cochlea and microglia in the CN using their shared markers: ionized calcium binding adaptor molecule 1 (Iba1) and CD68—a marker of phagocytic activity. We found progressive increases in the area covered by Iba1-labeled macrophages and enhanced CD68 staining in the osseous spiral lamina of the cochlea that correlated with elevated ABR threshold across the lifespan. During the process, we further identified significant increases in microglial activation and C1q deposition in the CN, indicating increased neuroinflammation and complement activation in the central auditory system. Our study suggests that during normal aging, chronic inflammation occurs in both the peripheral and the central auditory system, which may contribute in coordination to the development of ARHL.

Three-Dimensional Analysis of Round Window Membrane in the Chinchilla Model with Acute Otitis Media Induced with Streptococcus Pneumoniae 7F

Objective:

The purpose of this study was to investigate the morphological changes of round window membrane (RWM) in chinchillas with Streptococcus pneumoniae (S. pneumoniae) serotype 7F induced acute otitis media (AOM) by two dimensional (2D) and three dimensional (3D) measurements.

Methods:

Temporal bone specimens taken from 12 chinchillas were divided into two groups. The control group consisted of healthy animals that were injected with intrabullar saline. The subjects in the experimental group were induced with AOM by intrabullar injection of S. pneumoniae 7F. The 2D and 3D measurements of RWM were compared between the groups.

Results:

Dramatic changes were noted in the RWM of the experimental group compared to the control group. The thickness [mean ± standard deviation (SD)] of the RWM was significantly (p<0.05) increased in the experimental group compared to the control group by 2D measurements taken at three different points of RWM. Moreover, 3D measurements revealed that the volume (mean ± SD) of RWM was significantly (p=0.009) increased in the experimental group.

Conclusion:

The results of our study, which indicated significant change in RWM in both 2D and 3D measurements, may shed light on the relationship between AOM and inner ear diseases. Based on our results, we recommend evaluating 3D analyses of RWM, which provide useful data, to better understand the changes in the membrane.

Pathophysiological mechanisms at the sources of the endolymphatic hydrops, and possible consequences

The mechanisms of ion exchanges and water fluxes underlying the endolymphatic hydrops phenomenon, remain indeterminate so far. This review intends to reposition the physical environment of the endolymphatic compartment within the inner ear, as well as to recall the molecular effectors present in the membranous labyrinth and that could be at the source of the hydrops.

Unlocking the Power of Exosomes for Crossing Biological Barriers in Drug Delivery

Since the 2013 Nobel Prize was awarded for the discovery of vesicle trafficking, a subgroup of nanovesicles called exosomes has been driving the research field to a new regime for understanding cellular communication. This exosome-dominated traffic control system has increased understanding of many diseases, including cancer metastasis, diabetes, and HIV. In addition to the important diagnostic role, exosomes are particularly attractive for drug delivery, due to their distinctive properties in cellular information transfer and uptake. Compared to viral and non-viral synthetic systems, the natural, cell-derived exosomes exhibit intrinsic payload and bioavailability. Most importantly, exosomes easily cross biological barriers, obstacles that continue to challenge other drug delivery nanoparticle systems. Recent emerging studies have shown numerous critical roles of exosomes in many biological barriers, including the blood–brain barrier (BBB), blood–cerebrospinal fluid barrier (BCSFB), blood–lymph barrier (BlyB), blood–air barrier (BAB), stromal barrier (SB), blood–labyrinth barrier (BLaB), blood–retinal barrier (BRB), and placental barrier (PB), which opens exciting new possibilities for using exosomes as the delivery platform. However, the systematic reviews summarizing such discoveries are still limited. This review covers state-of-the-art exosome research on crossing several important biological barriers with a focus on the current, accepted models used to explain the mechanisms of barrier crossing, including tight junctions. The potential to design and engineer exosomes to enhance delivery efficacy, leading to future applications in precision medicine and immunotherapy, is discussed.

The Correlation Between Endolymphatic Hydrops and blood-labyrinth barrier Permeability of Meniere Disease

OBJECTIVES

This study was designed to assess the correlation between the grades of endolymphatic hydrops and the blood-labyrinth barrier permeability in the affected ear in Meniere's disease, following the administration of intravenous gadolinium contrast.

STUDY DESIGN

Prospective study.

METHODS

The quantitative values of endolymphatic hydrops were determined after intravenous injection of a double-dose of gadobutrol in 39 patients with unilateral definite Meniere's disease. Additionally, the signal intensity ratio of bilateral cochlear basal turns was evaluated and analyzed; The correlation between the grades of the endolymphatic hydrops and the signal intensity ratio of the cochlear basal turns in the affected ear was examined.

RESULTS

The grades of the endolymphatic hydrops can be quantitatively evaluated using magnetic resonance imaging (MRI). The signal intensity ratio of the cochlear basal turns in the affected ear was significantly higher than in the unaffected ear (P = .001); there was a positive correlation between the signal intensity ratio of the cochlear basal turn and the grades of cochlear (r = 0.634, P = 0.000) and vestibular(r = 0.559, P = .000) hydrops in the affected ear.

CONCLUSIONS

The increased permeability of the blood-labyrinth barrier may play a role in the process of endolymphatic hydrops in Meniere's disease.

Clinical and radiological characteristics of patients with collapse or fistula of the saccule as evaluated by inner ear MRI

Background: Delayed 3D-FLAIR sequences enable the distinction between the utricle and the saccule.Aims/objectives: We sought to evaluate the clinical and radiological findings in patients with no visible saccule (NVS) on 4-hour post-contrast MRI.Material and Methods: We retrospectively assessed the presence of NVS signs in 400 patients who underwent delayed inner ear MRI.Results: We reported on 28 patients with NVS. Among this group, on the NVS affected side: 14 had isolated sensorineural hearing loss (SNHL); 4 had fluctuating cochleo-vestibular disease; 3 had definite Menière's disease; 3 had Minor syndrome; 2 had delayed endolymphatic hydrops (EH); 2 had inner ear malformations; 1 had sudden cochleo-vestibular deficit following stapes surgery; 1 had a perilymphatic fistula and 1 had a contralateral fluctuating SNHL. Sixteen out of these 28 patients (57.1%) had cochlear hydrops on the same side as the NVS, while 10 patients (35.7%) had saccular hydrops on the contralateral side. Moreover, isolated blood labyrinth barrier (BLB) impairment on the NVS side was observed in 7 patients. Two patients (7.1%) had large vestibular aqueduct and NVS on the same side and one patient had perilymphatic fistula.Conclusions and significance: NVS seems to be multifactorial and could be linked to hydropic ear disease, third-mobile window pathologies and congenital malformation.

Nanoparticle-based drug delivery in the inner ear: current challenges, limitations and opportunities

Hearing loss is the most common neurosensory impairment worldwide. While conductive hearing loss can be managed by surgery, the management of sensorineural hearing loss (SNHL), related to the damage of sensory cells of the inner ear is more challenging to manage medically. Many causes of SNHL such as sudden idiopathic SNHL, Meniere's disease, noise-induced hearing loss, autoimmune hearing loss or hearing loss from exposure to ototoxic substances can benefit from delivery of otoprotective drugs to the inner ear. However, systemic drug delivery through oral, intravenous and intramuscular methods leads to undesirable side effects due to the inner ear's limited blood supply and the relatively poor penetration of the blood-inner ear barrier (BLB). Therefore, there has been an increased interest for the targeted drug delivery to the inner ear using nanoparticles. Drug delivery through nanoparticles offers several advantages including drug stabilization for controlled release and surface modification for specific targeting. Understanding the biocompatibility of nanoparticles with cochlea and developing novel non-invasive delivery methods will promote the translation of nanoparticle-mediated drug delivery for auditory disorders from bench to bedside.

Quantitative analysis of cochlear signal intensity on three-dimensional and contrast-enhanced fluid-attenuated inversion recovery images in patients with Meniere's disease: Correlation with the pure tone audiometry test

PURPOSE

The purpose of this study was to correlate the quantitative analysis of cochlear signal intensity (SI) on 3-dimensional fluid-attenuated inversion recovery (3D-FLAIR) and contrast-enhanced (CE) 3D-FLAIR images with results of the pure tone audiometry (PTA) test in patients with Meniere's disease (MD).

MATERIALS AND METHODS

Over a 3-year period, 123 patients with MD underwent 3-Tesla (3 T) temporal magnetic resonance imaging (MRI), including 3D-FLAIR and CE-FLAIR sequences. The SI of membranous labyrinth of the cochlea in both ears of each patient was measured by drawing a region of interest (ROI) with a seed growing technique. The correlation between measured cochlear SIs on 3D-FLAIR and CE-FLAIR images, contrast enhancement index (CEI), and contrast enhancement ratio (CER) and clinical findings and pre- and post-treatment PTA results were assessed.

RESULTS

Cochlear signal ratios of symptomatic ears on 3D-FLAIR and CE-FLAIR images were significantly higher than those of asymptomatic ears (P < 0.001). The area under the curve, from the receiver operating characteristic curve of cochlear SIs on 3D-FLAIR and CE-FLAIR images for discrimination between symptomatic and asymptomatic ears, was 0.729 and 0.728, respectively. Cochlear SIs on 3D-FLAIR and CE-FLAIR images were significantly correlated with patients' sex (P < 0.05 and P < 0.01, respectively), symptomatic ear (both P < 0.0001), and pre-treatment PTA (P < 0.0001 and P < 0.005, respectively), but were not significantly correlated with patients' age, post-treatment PTA or hearing threshold level at 0.5, 1.0, 2.0, or 4.0 kHz.

CONCLUSION

Quantitative analysis of cochlear SI on 3D-FLAIR and CE-FLAIR images may be a helpful diagnostic adjunct for MD, but may be of little value in predicting the prognosis of MD.

Semicircular canal biomechanics in health and disease

The semicircular canals are responsible for sensing angular head motion in three-dimensional space and for providing neural inputs to the central nervous system (CNS) essential for agile mobility, stable vision, and autonomic control of the cardiovascular and other gravity-sensitive systems. Sensation relies on fluid mechanics within the labyrinth to selectively convert angular head acceleration into sensory hair bundle displacements in each of three inner ear sensory organs. Canal afferent neurons encode the direction and time course of head movements over a broad range of movement frequencies and amplitudes. Disorders altering canal mechanics result in pathological inputs to the CNS, often leading to debilitating symptoms. Vestibular disorders and conditions with mechanical substrates include benign paroxysmal positional nystagmus, direction-changing positional nystagmus, alcohol positional nystagmus, caloric nystagmus, Tullio phenomena, and others. Here, the mechanics of angular motion transduction and how it contributes to neural encoding by the semicircular canals is reviewed in both health and disease.

Dose-Dependent Tissue Distribution of K117, a Bis-pyridinium Aldoxime, in Rats

Background:

Bis-pyridinium aldoximes are reactivators of the paraoxon-inhibited butyrylcholinesterase enzyme. Paraoxon is the active product of parathion, a widely used insecticide.

Objective:

The objective of this study is to examine the dose-dependent distribution of K117, a bis-pyridinium aldoxime in rat tissues.

Materials and Methods:

White male Wistar rats were intramuscularly injected with various doses of K117; the animals were sacrificed 30 minutes after injections. The dose-dependent body distribution of K117 was determined using reversed-phase HPLC.

Results:

Dose-dependent distribution of K117 in body tissues was linear in the serum and other body tissues throughout the whole range of the concentrations studied. However, the of distribution was not observed in the brain and cerebrospinal fluid, especially with high doses.

Conclusion:

The body distribution of K117 significantly depends on doses used, the p-value is: 500 nmol, i.m., when applied in the range of 100 to 10,000 nmol.

The clinical value of 4-hour delayed-enhanced 3D-FLAIR MR images in sudden hearing loss

OBJECTIVE

The aim of this study was to investigate the clinical significance of 4-hour delayed-enhanced 3.0 Tesla (3T) 3D-fluid-attenuated inversion recovery (FLAIR) MR imaging in sudden sensorineural hearing loss (SSNHL).

STUDY DESIGN

Case series with comparisons.

SETTING

Tertiary referral centre.

PARTICIPANTS

Eighty-seven idiopathic SSNHL patients were enrolled between January 2015 and December 2016 and received high dose steroid therapy and intratympanic steroid injections as salvage treatment.

INTERVENTION

Pre-contrast, 10-minute and 4-hour delayed-enhanced 3D-FLAIR MR images were obtained using double-dose IV gadolinium.

MAIN OUTCOME MEASURES

The results of treatment were evaluated according to Siegel's criteria 3 months after the start of treatment. Where possible lesion-side laterality of the inner ear was identified based on the MR images, the associations between MR findings and other clinical parameters were analysed, and the relationships between hearing recovery and MR image findings were assessed.

RESULTS

Lesion-side laterality was identified on MRI in 52 (59.7%), 18 (20.1%) and 8 (9.2%) patients, based on 4-hour delayed, 10-minute delayed, and pre-contrast images, respectively. The hearing recovery rate was significantly lower in the patients with lesion-side laterality on 4-hour delayed images (P < 0.001). In a multivariate analysis, lesion-side laterality on 4-hour delayed images was associated with poor prognosis (OR = 5.6) after adjusting other prognostic factors including initial hearing level, lesion-side laterality on 10-min delayed images and presence of vertigo. In addition, as the extent of enhancement in the inner ear increased the probability of hearing recover decreased (P = 0.001).

CONCLUSIONS

Contrast enhancement of inner ear structures can be seen on 4-hour delayed-enhanced 3T 3D-FLAIR MR images in idiopathic SSNHL. Asymmetric lesion-side enhancement of the inner ear may be associated with a poor prognosis.

Purinergic signaling in the organ of Corti: Potential therapeutic targets of sensorineural hearing losses

Purinergic signaling is deeply involved in the development, functions and protective mechanisms of the cochlea. Release of ATP and activation of purinergic receptors on sensory and supporting/epithelial cells play a substantial role in cochlear (patho)physiology. Both the ionotropic P2X and the metabotropic P2Y receptors are widely distributed on the inner and outer hair cells as well as on the different supporting cells in the organ of Corti and on other epithelial cells in the scala media. Among others, they are implicated in the sensitivity adjustment of the receptor cells by a K⁺ shunt and can attenuate the cochlear amplification by modifying cochlear micromechanics acting on outer hair cells and supporting cells. Cochlear blood flow is also regulated by purines. Sensorineural hearing losses currently lack any specific or efficient pharmacotherapy. Decreasing hearing sensitivity and increasing cochlear blood supply by pharmacological targeting of purinergic signaling in the cochlea are potential new therapeutic approaches in these hearing disabilities, especially in the noise-induced ones.

Progress in the Development of Preventative Drugs for Cisplatin-Induced Hearing Loss

Cisplatin is a highly effective treatment for malignant cancers and has become a cornerstone in chemotherapeutic regimens. Unfortunately, its use in the clinic is often coupled with a high incidence of severe hearing loss. Over the past few decades, enormous effort has been put forth to find protective agents that selectively protect against the ototoxic side effects of cisplatin and do not interfere with its antitumoral activity. Many therapies have been successful in preclinical work, but only a few have shown any protection in the clinic, and none have been approved by the FDA. This review summarizes the clinical and preclinical studies of the most effective small-molecule candidates currently in clinical trials, while also detailing their molecular mechanisms of action, to gain insight for future drug development in the field.