Short interfering RNA against transient receptor potential vanilloid 1 attenuates cisplatin-induced hearing loss in the rat

Crosstalk between calcium and reactive oxygen species signaling in cancer revisited

The homeostasis of cellular reactive oxygen species (ROS) and calcium (Ca2+) are intricately linked. ROS signaling and Ca2+ signaling are reciprocally regulated within cellular microdomains and are crucial for transcription, metabolism and cell function. Tumor cells often highjack ROS and Ca2+ signaling mechanisms to ensure optimal cell survival and tumor progression. Expression and regulation of Ca2+ channels and transporters at the plasma membrane, endoplasmic reticulum, mitochondria and other endomembranes are often altered in tumor cells, and this includes their regulation by ROS and reactive nitrogen species (RNS). Likewise, alterations in cellular Ca2+ levels influence the generation and scavenging of oxidants and thus can alter the redox homeostasis of the cell. This interplay can be either beneficial or detrimental to the cell depending on the localization, duration and levels of ROS and Ca2+ signals. At one end of the spectrum, Ca2+ and ROS/RNS can function as signaling modules while at the other end, lethal surges in these species are associated with cell death. Here, we highlight the interplay between Ca2+ and ROS in cancer progression, emphasize the impact of redox regulation on Ca2+ transport mechanisms, and describe how Ca2+ signaling pathways, in turn, can regulate the cellular redox environment.

Advancing precision ear medicine: leveraging animal models for disease insights and therapeutic innovations

Gene therapy offers significant promise for treating inner ear disorders, but its clinical translation requires robust preclinical validation, often reliant on animal models. This review examines the role of these models in advancing gene therapeutics for inherited inner ear disorders, focusing on successes, challenges, and treatment solutions. By providing a precise understanding of disease mechanisms, these models offer a versatile preclinical platform that is essential for assessing and validating therapies. Successful gene supplementation and editing have shown potential in restoring hearing and balance functions and preventing their decline. However, challenges such as limitations in gene delivery methods, surgical access, immune responses, and discrepancies in disease manifestation between animal models and humans hinder clinical translation. Current efforts are dedicated to developing innovative strategies aimed at enhancing the efficiency of gene delivery, overcoming physical barriers such as the blood-labyrinth barrier, improving target specificity, and maximizing therapeutic efficacy while minimizing adverse immune responses. Diverse gene supplementation and editing strategies, along with evolving technologies, hold promise for maximizing therapeutic outcomes using disease relevant models. The future of inner ear gene therapeutics will hinge on personalized therapies and team science fueling interdisciplinary collaborations among researchers, clinicians, companies, and regulatory agencies to expedite the translation from bench to bedside and unlock the immense potential of precision medicine in the inner ear.

Cisplatin-Induced Hearing Loss, Oxidative Stress, and Antioxidants as a Therapeutic Strategy-A State-of-the-Art Review

Cisplatin is an established component of treatment protocols for various solid malignancies but carries a significant potential for serious adverse effects. Ototoxicity from cisplatin treatment is an important dose-limiting toxicity that manifests as bilateral, progressive, irreversible, dose-dependent sensorineural hearing loss, ear pain, tinnitus, and vestibular dysfunction. Despite the recent approval of sodium thiosulphate for the prevention of cisplatin-induced hearing loss (CIHL) in pediatric patients, structured prevention programs are not routinely implemented in most hospitals, and reducing platinum-induced ototoxicity in adults remains an important clinical problem without established treatment options. Cochlear oxidative stress plays a fundamental role in CIHL. Here, we review the molecular mechanisms leading to oxidative stress in CIHL and the clinical and preclinical studies testing antioxidants in CIHL to guide future clinical trials in assessing the efficacy and safety of candidate antioxidant compounds in this clinical setting.

Pharmacological Approaches to Hearing Loss

Hearing disorders pose significant challenges to individuals experiencing them and their overall quality of life, emphasizing the critical need for advanced pharmacological approaches to address these conditions. Current treatment options often focus on amplification devices, cochlear implants, or other rehabilitative therapies, leaving a substantial gap regarding effective pharmacological interventions. Advancements in our understanding of the molecular and cellular mechanisms involved in hearing disorders induced by noise, aging, and ototoxicity have opened new avenues for drug development, some of which have led to numerous clinical trials, with promising results. The development of optimal drug delivery solutions in animals and humans can also enhance the targeted delivery of medications to the ear. Moreover, large genome studies contributing to a genetic understanding of hearing loss in humans combined with advanced molecular technologies in animal studies have shown a great potential to increase our understanding of the etiologies of hearing loss. The auditory system exhibits circadian rhythms and temporal variations in its physiology, its vulnerability to auditory insults, and its responsiveness to drug treatments. The cochlear clock rhythms are under the control of the glucocorticoid system, and preclinical evidence suggests that the risk/benefit profile of hearing disorder treatments using chronopharmacological approaches would be beneficial. If translatable to the bedside, such approaches may improve the outcome of clinical trials. Ongoing research into the molecular and genetic basis of auditory disorders, coupled with advancements in drug formulation and delivery as well as optimized timing of drug administration, holds great promise of more effective treatments. SIGNIFICANCE STATEMENT: Hearing disorders pose significant challenges to individuals and their overall quality of life, emphasizing the critical need for advanced pharmacological approaches to address these conditions. Ongoing research into the molecular and genetic basis of auditory disorders, coupled with advancements in drug delivery procedures and optimized timing of drug administration, holds the promise of more effective treatments.

Microneedle-Mediated Delivery of siRNA via Liposomal-Based Transfection for Inner Ear Gene Therapy

HYPOTHESIS

Microneedle-mediated intracochlear injection of siRNA-Lipofectamine through the round window membrane (RWM) can be used to transfect cells within the cochlea.

BACKGROUND

Our laboratory has developed 100-μm diameter hollow microneedles for intracochlear injection through the guinea pig RWM. In this study, we test the feasibility of microneedle-mediated injection of siRNA and Lipofectamine, a commonly used reagent with known cellular toxicity, through the RWM for cochlear transfection.

METHODS

Fluorescently labeled scramble siRNA was diluted into Lipofectamine RNAiMax and OptiMEM. One microliter of 5 μM siRNA was injected through the RWM of Hartley guinea pigs at a rate of 1 μl/min (n = 22). In a control group, 1.0 μl of Lipofectamine, with no siRNA, was diluted into OptiMEM and injected in a similar fashion (n = 5). Hearing tests were performed before and either at 24 hours, 48 hours, or 5 days after injection. Afterward, animals were euthanized, and cochleae were harvested for imaging. Control cochleae were processed in parallel to untreated guinea pigs.

RESULTS

Fluorescence, indicating successful transfection, was observed within the basal and middle turns of the cochlea with limited distribution in the apex at 24 and 48 hours. Signal was most intense in the organ of Corti, spiral ligament, and spiral ganglion. Little to no fluorescence was observed at 5 days post-injection. No significant changes in auditory brainstem response (ABR) were noted post-perforation at 5 days, suggesting that siRNA-Lipofectamine at low doses does not cause cochlear toxicity.

CONCLUSIONS

Small volumes of siRNA and Lipofectamine can be effectively delivered to cochlear structures using microneedles, paving the way for atraumatic cochlear gene therapy.

Hearing loss during chemotherapy: prevalence, mechanisms, and protection

Ototoxicity is an often-underestimated sequela for cancer patients undergoing chemotherapy, with an incidence rate exceeding 50%, affecting approximately 4 million individuals worldwide each year. Despite the nearly 2,000 publications on chemotherapy-related ototoxicity in the past decade, the understanding of its prevalence, mechanisms, and preventative or therapeutic measures remains ambiguous and subject to debate. To date, only one drug, sodium thiosulfate, has gained FDA approval for treating ototoxicity in chemotherapy. However, its utilization is restricted. This review aims to offer clinicians and researchers a comprehensive perspective by thoroughly and carefully reviewing available data and current evidence. Chemotherapy-induced ototoxicity is characterized by four primary symptoms: hearing loss, tinnitus, vertigo, and dizziness, originating from both auditory and vestibular systems. Hearing loss is the predominant symptom. Amongst over 700 chemotherapeutic agents documented in various databases, only seven are reported to induce hearing loss. While the molecular mechanisms of the hearing loss caused by the two platinum-based drugs are extensively explored, the pathways behind the action of the other five drugs are primarily speculative, rooted in their therapeutic properties and side effects. Cisplatin attracts the majority of attention among these drugs, encompassing around two-thirds of the literature regarding ototoxicity in chemotherapy. Cisplatin ototoxicity chiefly manifests through the loss of outer hair cells, possibly resulting from damages directly by cisplatin uptake or secondary effects on the stria vascularis. Both direct and indirect influences contribute to cisplatin ototoxicity, while it is still debated which path is dominant or where the primary target of cisplatin is located. Candidates for hearing protection against cisplatin ototoxicity are also discussed, with novel strategies and methods showing promise on the horizon.

Nanodelivery of antioxidant Agents: A promising strategy for preventing sensorineural hearing loss

Sensorineural hearing loss (SNHL), often stemming from reactive oxygen species (ROS) generation due to various factors such as ototoxic drugs, acoustic trauma, and aging, remains a significant health concern. Oxidative stress-induced damage to the sensory cells of the inner ear, particularly the non-regenerating hair cells, is a critical pathologic mechanism leading to SNHL. Despite the proven efficacy of antioxidants in mitigating oxidative stress, their clinical application for otoprotection is hindered by the limitations of conventional drug delivery methods. This review highlights the challenges associated with systemic and intratympanic administration of antioxidants, including the blood-labyrinthine barrier, restricted permeability of the round window membrane, and inadequate blood flow to the inner ear. To overcome these hurdles, the application of nanoparticles as a delivery platform for antioxidants emerges as a promising solution. Nanocarriers facilitate indirect drug delivery to the cochlea through the round and oval window membrane, optimising drug absorption while reducing dosage, Eustachian tube clearance, and associated side effects. Furthermore, the development of nanoparticles carrying antioxidants tailored to the intracochlear environment holds immense potential. This literature research aimed to critically examine the root causes of SNHL and ROS overproduction in the inner ear, offering insights into the application of nanoparticle-based drug delivery systems for safeguarding sensorineural hair cells. By focusing on the intricate interplay between oxidative stress and hearing loss, this research aims to contribute to the advancement of innovative therapeutic strategies for the prevention of SNHL.

A novel cell-free therapy using exosomes in the inner ear regeneration

Cellular and molecular alterations associated with hearing loss are now better understood with advances in molecular biology. These changes indicate the participation of distinct damage and stress pathways that are unlikely to be fully addressed by conventional pharmaceutical treatment. Sensorineural hearing loss is a common and debilitating condition for which comprehensive pharmacologic intervention is not available. The complex and diverse molecular pathology that underlies hearing loss currently limits our ability to intervene with small molecules. The present review focuses on the potential for the use of extracellular vesicles in otology. It examines a variety of inner ear diseases and hearing loss that may be treatable using exosomes (EXOs). The role of EXOs as carriers for the treatment of diseases related to the inner ear as well as EXOs as biomarkers for the recognition of diseases related to the ear is discussed.

Inhibition of Gpx4-mediated ferroptosis alleviates cisplatin-induced hearing loss in C57BL/6 mice

Cisplatin-induced hearing loss is a common side effect of cancer chemotherapy in clinics; however, the mechanism of cisplatin-induced ototoxicity is still not completely clarified. Cisplatin-induced ototoxicity is mainly associated with the production of reactive oxygen species, activation of apoptosis, and accumulation of intracellular lipid peroxidation, which also is involved in ferroptosis induction. In this study, the expression of TfR1, a ferroptosis biomarker, was upregulated in the outer hair cells of cisplatin-treated mice. Moreover, several key ferroptosis regulator genes were altered in cisplatin-damaged cochlear explants based on RNA sequencing, implying the induction of ferroptosis. Ferroptosis-related Gpx4 and Fsp1 knockout mice were established to investigate the specific mechanisms associated with ferroptosis in cochleae. Severe outer hair cell loss and progressive damage of synapses in inner hair cells were observed in Atoh1-Gpx4-/- mice. However, Fsp1-/- mice showed no significant hearing phenotype, demonstrating that Gpx4, but not Fsp1, may play an important role in the functional maintenance of HCs. Moreover, findings showed that FDA-approved luteolin could specifically inhibit ferroptosis and alleviate cisplatin-induced ototoxicity through decreased expression of transferrin and intracellular concentration of ferrous ions. This study indicated that ferroptosis inhibition through the reduction of intracellular ferrous ions might be a potential strategy to prevent cisplatin-induced hearing loss.

NADPH Oxidase 3: Beyond the Inner Ear

Reactive oxygen species (ROS) were formerly known as mere byproducts of metabolism with damaging effects on cellular structures. The discovery and description of NADPH oxidases (Nox) as a whole enzyme family that only produce this harmful group of molecules was surprising. After intensive research, seven Nox isoforms were discovered, described and extensively studied. Among them, the NADPH oxidase 3 is the perhaps most underrated Nox isoform, since it was firstly discovered in the inner ear. This stigma of Nox3 as "being only expressed in the inner ear" was also used by me several times. Therefore, the question arose whether this sentence is still valid or even usable. To this end, this review solely focuses on Nox3 and summarizes its discovery, the structural components, the activating and regulating factors, the expression in cells, tissues and organs, as well as the beneficial and detrimental effects of Nox3-mediated ROS production on body functions. Furthermore, the involvement of Nox3-derived ROS in diseases progression and, accordingly, as a potential target for disease treatment, will be discussed.

Puerarin inhibits cisplatin-induced ototoxicity in mice through regulation of TRPV1-dependent calcium overload

Puerarin (PUE), a flavonoid derivative with vasodilatory effects found in the traditional Chinese medicine kudzu, has anti-sensorineural hearing loss properties. However, the mechanism of its protective effect against ototoxicity is not well understood. In this study, we used in vitro and in vivo methods to investigate the protective mechanism of puerarin against cisplatin (CDDP)-induced ototoxicity. We established an ototoxicity model of CDDP in BALB/c mice and assessed the degree of hearing loss and cochlear cell damage. We used bioinformatics analysis, molecular docking, histological analysis, and biochemical and molecular biology to detect the expression of relevant factors. Our results show that puerarin improved CDDP-induced hearing loss and reduced hair cell loss. It also blocked CDDP-induced activation of TRPV1 and inhibited activation of IP3R1 to prevent intracellular calcium overload. Additionally, puerarin blocked CDDP-stimulated p65 activation, reduced excessive ROS production, and alleviated cochlear cell apoptosis. Our study provides new evidence and potential targets for the protective effect of puerarin against drug-induced hearing loss. Puerarin ameliorates cisplatin-induced ototoxicity and blocks cellular apoptosis by inhibiting CDDP activated TRPV1/IP3R1/p65 pathway, blocking induction of calcium overload and excessive ROS expression.

A journey from molecule to physiology and in silico tools for drug discovery targeting the transient receptor potential vanilloid type 1 (TRPV1) channel

The heat and capsaicin receptor TRPV1 channel is widely expressed in nerve terminals of dorsal root ganglia (DRGs) and trigeminal ganglia innervating the body and face, respectively, as well as in other tissues and organs including central nervous system. The TRPV1 channel is a versatile receptor that detects harmful heat, pain, and various internal and external ligands. Hence, it operates as a polymodal sensory channel. Many pathological conditions including neuroinflammation, cancer, psychiatric disorders, and pathological pain, are linked to the abnormal functioning of the TRPV1 in peripheral tissues. Intense biomedical research is underway to discover compounds that can modulate the channel and provide pain relief. The molecular mechanisms underlying temperature sensing remain largely unknown, although they are closely linked to pain transduction. Prolonged exposure to capsaicin generates analgesia, hence numerous capsaicin analogs have been developed to discover efficient analgesics for pain relief. The emergence of in silico tools offered significant techniques for molecular modeling and machine learning algorithms to indentify druggable sites in the channel and for repositioning of current drugs aimed at TRPV1. Here we recapitulate the physiological and pathophysiological functions of the TRPV1 channel, including structural models obtained through cryo-EM, pharmacological compounds tested on TRPV1, and the in silico tools for drug discovery and repositioning.

Otoprotection against aminoglycoside- and cisplatin-induced ototoxicity focusing on the upstream drug uptake pathway

Aminoglycoside- and cisplatin-induced ototoxicity, which is a significant issue owing to the widespread use of these drugs in clinical practice, involves the entry of aminoglycosides and cisplatin into the endolymph and hair cells via specific channels or transporters, followed by reactive oxygen species (ROS) generation and hair cells apoptosis. Current strategies focalize primarily on interference with downstream ROS effects; however, recent evidence has demonstrated that inhibiting the uptake of aminoglycosides and cisplatin by hair cells is another promising strategy for tackling the upstream drug uptake pathway. With advances in structural biology, the conformations of certain aminoglycoside and cisplatin channels and transporters, such as the mechanoelectrical transduction channel and organic cation transporter-2, have been largely elucidated. These channels and transporters may become potential targets for the introduction of new otoprotective strategies. This review focuses on the strategies for inhibiting ototoxic drugs uptake by auditory hair cells and provides potential targets for recent developments in the field of otoprotection. Molecular dynamics (MD) simulations of these proteins could help identify the molecules that inhibit the uptake of aminoglycosides and cisplatin by hair cells. Integrating upstream drug uptake pathway targets and MD simulations may help dissect molecular mechanisms and develop novel otoprotective strategies for aminoglycoside- and cisplatin-induced ototoxicity.

The Chemoprotective Potentials of Alpha-lipoic Acid against Cisplatin-induced Ototoxicity: A Systematic Review

PURPOSE

Ototoxicity is one of the major adverse effects of cisplatin therapy which restrict its clinical application. Alpha-lipoic acid administration may mitigate cisplatin-induced ototoxicity. In the present study, we reviewed the protective potentials of alpha-lipoic acid against the cisplatin-mediated ototoxic adverse effects.

METHODS

Based on the PRISMA guideline, we performed a systematic search for the identification of all relevant studies in various electronic databases up to June 2022. According to the inclusion and exclusion criteria, the obtained articles (n=59) were screened and 13 eligible articles were finally included in the present study.

RESULTS

The findings of in-vitro experiments showed that cisplatin treatment significantly reduced the auditory cell viability in comparison with the control group; nevertheless, the alpha-lipoic acid co-administration protected the cells against the reduction of cell viability induced by cisplatin treatment. Moreover, the in-vivo results of the auditory brainstem response (ABR) and distortion product otoacoustic emission (DPOAE) tests revealed a decrease in DPOAE and an increase in ABR threshold of cisplatin-injected animals; however, it was shown that alpha-lipoic acid co-treatment had an opposite pattern on the evaluated parameters. Other findings demonstrated that cisplatin treatment could significantly induce the biochemical and histopathological alterations in inner ear cells/tissue; in contrast, alpha-lipoic acid co-treatment ameliorated the cisplatin-mediated biochemical and histological changes.

CONCLUSION

The findings of audiometry, biochemical parameters, and histological evaluation showed that alpha-lipoic acid co-administration alleviates the cisplatin-induced ototoxicity. The protective role of alpha-lipoic acid against the cisplatin-induced ototoxicity can be due to different mechanisms of anti-oxidant, anti-apoptotic, anti-inflammatory activities, and regulation of cell cycle progression.

Susceptibility of immature spiral ganglion neurons to aminoglycoside-induced ototoxicity is mediated by the TRPV1 channel in mice

Aminoglycoside antibiotics are among the most common agents that can cause sensorineural hearing loss. From clinical experience, premature babies, whose inner ear is still developing, are more susceptible to aminoglycoside-induced ototoxicity, which is echoed by our previous study carried out in organotypic cultures. This study aimed to investigate whether a nonselective cation channel, TRPV1, contributes to the susceptibility of immature spiral ganglion neurons (SGNs) to the damage caused by aminoglycosides. Through western blotting and immunofluorescence, we found that the TRPV1 expression levels were much higher in immature SGNs than in their mature counterparts. In postnatal day 7 cochlear organotypic cultures, AMG-517 reduced reactive oxygen species generation and inhibited SGN apoptosis under aminoglycoside challenge. However, in adult mice, AMG-517 did not ameliorate the ABR threshold increase at high frequencies (16 kHz and 32 kHz) after aminoglycoside administration, and the SGNs within the cochleae had no morphological changes. By further regulating the function of TRPV1 in primary cultured SGNs with its inhibitor AMG-517 and agonist capsaicin, we demonstrated that TRPV1 is a major channel for aminoglycoside uptake: AMG-517 can significantly reduce, while capsaicin can significantly increase, the uptake of GTTR. In addition, TRPV1 knockdown in SGNs can also significantly reduce the uptake of GTTR. Taken together, our results demonstrated that aminoglycosides can directly enter immature SGNs through the TRPV1 channel. High expression of TRPV1 contributes to the susceptibility of immature SGNs to aminoglycoside-induced damage. The TRPV1 inhibitor AMG-517 has the potential to be a therapeutic agent for preventing aminoglycoside-induced ototoxicity in immature SGNs.

Aminoglycosides-Related Ototoxicity: Mechanisms, Risk Factors, and Prevention in Pediatric Patients

Aminoglycosides are broad-spectrum antibiotics largely used in children, but they have potential toxic side effects, including ototoxicity. Ototoxicity from aminoglycosides is permanent and is a consequence of its action on the inner ear cells via multiple mechanisms. Both uncontrollable risk factors and controllable risk factors are involved in the pathogenesis of aminoglycoside-related ototoxicity and, because of the irreversibility of ototoxicity, an important undertaking for preventing ototoxicity includes antibiotic stewardship to limit the use of aminoglycosides. Aminoglycosides are fundamental in the treatment of numerous infectious conditions at neonatal and pediatric age. In childhood, normal auditory function ensures adequate neurocognitive and social development. Hearing damage from aminoglycosides can therefore strongly affect the normal growth of the child. This review describes the molecular mechanisms of aminoglycoside-related ototoxicity and analyzes the risk factors and the potential otoprotective strategies in pediatric patients.

Effects of natural products on cisplatin ototoxicity and chemotherapeutic efficacy

INTRODUCTION

Cisplatin is a very effective chemotherapeutic agent against a variety of solid tumors. Unfortunately, cisplatin causes permanent sensorineural hearing loss in at least two-thirds of patients treated. There are no FDA approved drugs to prevent this serious side effect.

AREAS COVERED

This paper reviews various natural products that ameliorate cisplatin ototoxicity. These compounds are strong antioxidants and anti-inflammatory agents. This review includes mostly preclinical studies but also discusses a few small clinical trials with natural products to minimize hearing loss from cisplatin chemotherapy in patients. The interactions of natural products with cisplatin in tumor-bearing animal models are highlighted. A number of natural products did not interfere with cisplatin anti-tumor efficacy and some agents actually potentiated cisplatin anti-tumor activity.

EXPERT OPINION

There are a number of natural products or their derivatives that show excellent protection against cisplatin ototoxicity in preclinical studies. There is a need to insure uniform standards for purity of drugs derived from natural sources and to ensure adequate pharmacokinetics and safety of these products. Natural products that protect against cisplatin ototoxicity and augment cisplatin's anti-tumor effects in multiple studies of tumor-bearing animals are most promising for advancement to clinical trials. The most promising natural products include honokiol, sulforaphane, and thymoquinone.

Alpha-lipoic acid modulates the diabetes mellitus-mediated neuropathic pain via inhibition of the TRPV1 channel, apoptosis, and oxidative stress in rats

Diabetes mellitus (DM) is a chronic syndrome involving neuropathic pain. Increased oxidative stress in DM is assumed to increase free reactive oxygen radicals (ROS) and causes diabetic damage. The sciatic nerve (ScN) and dorsal root ganglion (DRG) both contain high levels of the TRPV1 channel, which is triggered by capsaicin and ROSs and results in increased Ca²⁺ entry into the neurons. Alpha-lipoic acid (ALA) is considered an important part of the antioxidant system. To better characterize the protective effects of ALA on the DM-induced neuronal through TRPV1 modulation, we investigated the role of ALA on DM-induced neuropathic pain, oxidative ScN, and DRG damage in diabetic rats. Forty adult Wistar albino female rats were divided into four groups as control, ALA (50 mg/kg for 14 days), streptozotocin (STZ and 45 mg/kg and single dose), and STZ + ALA. Rats were used for the pain tests. After obtaining the DRGs and ScN, they were used for plate reader, patch-clamp, and laser confocal microscope analyses. We observed the modulator role of ALA on the thresholds of mechanical withdrawal pain (von Frey test) and hot sensitivity pain (hot plate test) in the STZ + ALA group. The treatment of ALA decreased STZ-induced increase of TRPV1 current densities, intracellular free Ca²⁺ concentrations (Fura-2 and Fluo - 3/AM), ROS, caspase 3, caspase 9, mitochondrial membrane potential, and apoptosis values in the ScN and DRG neurons, although its treatment induced the increase of cell viability and body weight gain. The treatment of ALA acted a neuroprotective role on the TRPV1 channel stimulation-mediated Ca²⁺ influx, neuropathic pain, and neuronal damage in diabetic rats. The neuroprotective role of ALA treatment can be explained by its modulating the TRPV1 channel activity, intracellular Ca²⁺ increase-induced oxidative stress, and apoptosis.

Mitochondrial redox system: A key target of antioxidant therapy to prevent acquired sensorineural hearing loss

Noise (noise-induced hearing loss), and ototoxic drugs (drug-induced ototoxicity), and aging (age-related hearing loss) are the major environmental factors that lead to acquired sensorineural hearing loss. So far, there have been numerous efforts to develop protective or therapeutic agents for acquired hearing loss by investigating the pathological mechanisms of each types of hearing loss, especially in cochlear hair cells and auditory nerves. Although there is still a lack of information on the underlying mechanisms of redox homeostasis and molecular redox networks in hair cells, an imbalance in mitochondrial reactive oxygen species (ROS) levels that enhance oxidative stress has been suggested as a key pathological factor eventually causing acquired sensorineural hearing loss. Thus, various types of antioxidants have been investigated for their abilities to support auditory cells in maintenance of the hearing function against ototoxic stimuli. In this review, we will discuss the scientific possibility of developing drugs that target particular key elements of the mitochondrial redox network in prevention or treatment of noise- and ototoxic drug-induced hearing loss.

Otoprotective Effects of Fucoidan Reduce Cisplatin-Induced Ototoxicity in Mouse Cochlear UB/OC-2 Cells

Cisplatin is a widely used standard chemotherapy for various cancers. However, cisplatin treatment is associated with severe ototoxicity. Fucoidan is a complex sulfated polysaccharide mainly derived from brown seaweeds, and it shows multiple bioactivities such as antimicrobial, anti-inflammatory, anticancer, and antioxidant activities. Despite evidence of the antioxidant effects of fucoidan, research on its otoprotective effects remains limited. Therefore, the present study investigated the otoprotective effects of fucoidan in vitro using the mouse cochlear cell line UB/OC-2 to develop new strategies to attenuate cisplatin-induced ototoxicity. We quantified the cell membrane potential and analyzed regulators and cascade proteins in the apoptotic pathway. Mouse cochlear UB/OC-2 cells were pre-treated with fucoidan before cisplatin exposure. The effects on cochlear hair cell viability, mitochondrial function, and apoptosis-related proteins were determined via flow cytometry, Western blot analysis, and fluorescence staining. Fucoidan treatment reduced cisplatin-induced intracellular reactive oxygen species production, stabilized mitochondrial membrane potential, inhibited mitochondrial dysfunction, and successfully protected hair cells from apoptosis. Furthermore, fucoidan exerted antioxidant effects against oxidative stress by regulating the Nrf2 pathway. Therefore, we suggest that fucoidan may represent a potential therapeutic agent for developing a new otoprotective strategy.

Protective Effect of Avenanthramide-C on Auditory Hair Cells against Oxidative Stress, Inflammatory Cytokines, and DNA Damage in Cisplatin-Induced Ototoxicity

Cisplatin-induced ototoxicity leads to hearing impairment, possibly through reactive oxygen species (ROS) production and DNA damage in cochlear hair cells (HC), although the exact mechanism is unknown. Avenanthramide-C (AVN-C), a natural, potent antioxidant, was evaluated in three study groups of normal adult C57Bl/6 mice (control, cisplatin, and AVN-C+cisplatin) for the prevention of cisplatin-induced hearing loss. Auditory brainstem responses and immunohistochemistry of outer hair cells (OHCs) were ascertained. Cell survival, ROS production, Phospho-H2AX-enabled tracking of DNA damage-repair kinetics, and expression levels of inflammatory cytokines (TNF-α, IL-1β, IL6, iNOS, and COX2) were assessed using House Ear Institute-Organ of Corti 1 (HEI-OC1 Cells). In the in vivo mouse model, following cisplatin-induced damage, AVN-C decreased the hearing thresholds and sheltered all cochlear turns' OHCs. In HEI-OC1 cells, AVN-C preserved cell viability and decreased ROS production, whereas cisplatin enhanced both ROS levels and cell viability. In HEI-OC1 cells, AVN-C downregulated IL6, IL-1β, TNF-α, iNOS, and COX2 production that was upregulated by cisplatin treatment. AVN-C attenuated the cisplatin-enhanced nuclear H2AX activation. AVN-C had a strong protective effect against cisplatin-induced ototoxicity through inhibition of ROS and inflammatory cytokine production and DNA damage and is thus a promising candidate for preventing cisplatin-induced sensorineural hearing loss.

Emerging and established therapies for chemotherapy-induced ototoxicity

PURPOSE

Ototoxicity is considered a dose-limiting side effect of some chemotherapies. Hearing loss, in particular, can have significant implications for the quality of life for cancer survivors. Here, we review therapeutic approaches to mitigating ototoxicity related to chemotherapy.

METHODS

Literature review.

CONCLUSIONS

Numerous otoprotection strategies are undergoing active investigation. However, numerous challenges exist to confer adequate protection while retaining the anti-cancer efficacy of the chemotherapy.

IMPLICATIONS FOR CANCER SURVIVORS

Ototoxicity can have significant implications for cancer survivors, notably those receiving cisplatin. Clinical translation of multiple otoprotection approaches will aid in limiting these consequences.

Cisplatin-induced ototoxicity: From signaling network to therapeutic targets

Administration of cisplatin, a common chemotherapeutic drug, has an inevitable side effect of sensorineural hearing loss. The main etiologies are stria vascularis injury, spiral ganglion degeneration, and hair cell death. Over several decades, the research scope of cisplatin-induced ototoxicity has expanded with the discovery of the molecular mechanism mediating inner ear cell death, highlighting the roles of reactive oxygen species and transport channels for cisplatin uptake into inner ear cells. Upon entering hair cells, cisplatin disrupts organelle metabolism, induces oxidative stress, and targets DNA to cause intracellular damage. Recent studies have also reported the role of inflammation in cisplatin-induced ototoxicity. In this article, we preform a narrative review of the latest reported molecular mechanisms of cisplatin-induced ototoxicity, from extracellular to intracellular. We build up a signaling network starting with cisplatin entering into the inner ear through the blood labyrinth barrier, disrupting cochlear endolymph homeostasis, and activating inflammatory responses of the outer hair cells. After entering the hair cells, cisplatin causes hair cell death via DNA damage, redox system imbalance, and mitochondrial and endoplasmic reticulum dysfunction, culminating in programmed cell death including apoptosis, necroptosis, autophagic death, pyroptosis, and ferroptosis. Based on the mentioned mechanisms, prominent therapeutic targets, such as channel-blocking drugs of cisplatin transporter, construction of cisplatin structural analogues, anti-inflammatory drugs, antioxidants, cell death inhibitors, and others, were collated. Considering the recent research efforts, we have analyzed the feasibility of the aforementioned therapeutic strategies and proposed our otoprotective approaches to overcome cisplatin-induced ototoxicity.

Altering gene expression using antisense oligonucleotide therapy for hearing loss

Hearing loss affects more than 430 million people, worldwide, and is the third most common chronic physical condition in the United States and Europe (GBD Hearing Loss Collaborators, 2021; NIOSH, 2021; WHO, 2021). The loss of hearing significantly impacts motor and cognitive development, communication, education, employment, and overall quality of life. The inner ear houses the sensory organs for both hearing and balance and provides an accessible target for therapeutic delivery. Antisense oligonucleotides (ASOs) use various mechanisms to manipulate gene expression and can be tailor-made to treat disorders with defined genetic targets. In this review, we discuss the preclinical advancements within the field of the highly promising ASO-based therapies for hereditary hearing loss disorders. Particular focus is on ASO mechanisms of action, preclinical studies on ASO treatments of hearing loss, timing of therapeutic intervention, and delivery routes to the inner ear.

TRPV1 channel in spermatozoa is a molecular target for ROS-mediated sperm dysfunction and differentially expressed in both natural and ART pregnancy failure

Bi-directional crosstalk between Ca2+ signaling and ROS modulates physiological processes as a part of a regulatory circuit including sperm function. The role of transient receptor potential vanilloid 1 (TRPV1) in this regard cannot be undermined. This is the first report demonstrating the Ca2+-sensitive TRPV1 channel to be under-expressed in spermatozoa of subfertile men, idiopathic infertile men, and normozoospermic infertile males with high ROS (idiopathic infertility and unilateral varicocele). To study the effect of TRPV1 in determining the fertility outcome, we compared the expression profile of TRPV1 in spermatozoa of male partners who achieved pregnancy by natural conception (NC+, n = 10), IVF (IVF+, n = 23), or ICSI (ICSI +, n = 9) and their respective counterparts with failed pregnancy NC (n = 7), IVF (n = 23), or ICSI (n = 10), by both immunocytochemistry and flow-cytometry. Reduced expression of TRPV1 in sperm of IVF ± and ICSI ± men with respect to that NC+ men imply its role in mediating successful fertilization. Unsuccessful pregnancy outcome with an underexpression of TRPV1 in sperm of NC-/IVF-/ICSI-men suggests its role in conception and maintenance of pregnancy. Since ROS is regarded as one of the major contributors to sperm dysfunction, the effect of H2O2 +/- TRPV1 modulators (RTX/iRTX) on acrosomal reaction and calcium influx was evaluated to confirm TRPV1 as a redox sensor in human sperm. A significant increment in the percentage of acrosome reacted spermatozoa along with augmented Ca2+-influx was observed after H2O2 treatment, both in the presence or absence of TRPV1 agonist resiniferatoxin (RTX). The effect was attenuated by the TRPV1 antagonist iodoresiniferatoxin (iRTX), indicating the involvement of TRPV1 in mediating H2O2 response. Enhancement of motility and triggering of acrosomal reaction post TRPV1 activation suggested that disruption of these signaling cascades in vivo, possibly due to down-regulation of TRPV1 in these subfertile males. Bioinformatic analysis of the crosstalk between TRPV1 with fertility candidate proteins (reported to influence IVF outcome) revealed cell death and survival, cellular compromise, and embryonic development to be the primary networks affected by anomalous TRPV1 expression. We therefore postulate that TRPV1 can act as a redox sensor, and its expression in spermatozoa may serve as a fertility marker.

Transient Receptor Potential Channels and Auditory Functions

Significance: Transient receptor potential (TRP) channels are cation-gated channels that serve as detectors of various sensory modalities, such as pain, heat, cold, and taste. These channels are expressed in the inner ear, suggesting that they could also contribute to the perception of sound. This review provides more details on the different types of TRP channels that have been identified in the cochlea to date, focusing on their cochlear distribution, regulation, and potential contributions to auditory functions. Recent Advances: To date, the effect of TRP channels on normal cochlear physiology in mammals is still unclear. These channels contribute, to a limited extent, to normal cochlear physiology such as the hair cell mechanoelectrical transduction channel and strial functions. More detailed information on a number of these channels in the cochlea awaits future studies. Several laboratories focusing on TRPV1 channels have shown that they are responsive to cochlear stressors, such as ototoxic drugs and noise, and regulate cytoprotective and/or cell death pathways. TRPV1 expression in the cochlea is under control of oxidative stress (produced primarily by NOX3 NADPH oxidase) as well as STAT1 and STAT3 transcription factors, which differentially modulate inflammatory and apoptotic signals in the cochlea. Inhibition of oxidative stress or inflammation reduces the expression of TRPV1 channels and protects against cochlear damage and hearing loss. Critical Issues: TRPV1 channels are activated by both capsaicin and cisplatin, which produce differential effects on the inner ear. How these differential actions are produced is yet to be determined. It is clear that TRPV1 is an essential component of cisplatin ototoxicity as knockdown of these channels protects against hearing loss. In contrast, activation of TRPV1 by capsaicin protected against subsequent hearing loss induced by cisplatin. The cellular targets that are influenced by these two drugs to account for their differential profiles need to be fully elucidated. Furthermore, the potential involvement of different TRP channels present in the cochlea in regulating cisplatin ototoxicity needs to be determined. Future Directions: TRPV1 has been shown to mediate the entry of aminoglycosides into the hair cells. Thus, novel otoprotective strategies could involve designing drugs to inhibit entry of aminoglycosides and possibly other ototoxins into cochlear hair cells. TRP channels, including TRPV1, are expressed on circulating and resident immune cells. These receptors modulate immune cell functions. However, whether they are activated by cochlear stressors to initiate cochlear inflammation and ototoxicity needs to be determined. A better understanding of the function and regulation of these TRP channels in the cochlea could enable development of novel treatments for treating hearing loss. Antioxid. Redox Signal. 36, 1158-1170.

Gstm1/Gstt1 is essential for reducing cisplatin ototoxicity in CBA/CaJ mice

Cisplatin is a widely used chemotherapeutic agent. However, its clinical utility is limited because of cisplatin-induced ototoxicity. Glutathione S-transferase (GST) was found to play a vital role in reducing cisplatin ototoxicity in mice. Deletion polymorphisms of GSTM1 and GSTT1, members of the GST family, are common in humans and are presumed to be associated with cisplatin-induced hearing impairment. However, the specific roles of GSTM1 and GSTT1 in cisplatin ototoxicity are not completely clear. Here, under cisplatin treatment, simultaneous deletion of Gstm1 and Gstt1 lead to a more profound hearing loss in CBA/CaJ mice (Gstm1/Gstt1-DKO) than in wild-type mice. The Gstm1/Gstt1-DKO mice, in which phase II detoxification genes were upregulated, exhibited more severe oxidative stress and higher outer hair cell apoptosis in the cochleae than the control mice. Thus, our study revealed that Gstm1 and Gstt1 protect auditory hair cells from cisplatin-induced ototoxicity in the CBA/CaJ mice, and genetic screening for GSTM1 and GSTT1 polymorphisms could help determine a standard cisplatin dose for cancer patients undergoing chemotherapy.

Conversations in Cochlear Implantation: The Inner Ear Therapy of Today

As biomolecular approaches for hearing restoration in profound sensorineural hearing loss evolve, they will be applied in conjunction with or instead of cochlear implants. An understanding of the current state-of-the-art of this technology, including its advantages, disadvantages, and its potential for delivering and interacting with biomolecular hearing restoration approaches, is helpful for designing modern hearing-restoration strategies. Cochlear implants (CI) have evolved over the last four decades to restore hearing more effectively, in more people, with diverse indications. This evolution has been driven by advances in technology, surgery, and healthcare delivery. Here, we offer a practical treatise on the state of cochlear implantation directed towards developing the next generation of inner ear therapeutics. We aim to capture and distill conversations ongoing in CI research, development, and clinical management. In this review, we discuss successes and physiological constraints of hearing with an implant, common surgical approaches and electrode arrays, new indications and outcome measures for implantation, and barriers to CI utilization. Additionally, we compare cochlear implantation with biomolecular and pharmacological approaches, consider strategies to combine these approaches, and identify unmet medical needs with cochlear implants. The strengths and weaknesses of modern implantation highlighted here can mark opportunities for continued progress or improvement in the design and delivery of the next generation of inner ear therapeutics.

Oxidative Stress and Inflammation Caused by Cisplatin Ototoxicity

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

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.

Detecting Novel Ototoxins and Potentiation of Ototoxicity by Disease Settings

Over 100 drugs and chemicals are associated with permanent hearing loss, tinnitus, and vestibular deficits, collectively known as ototoxicity. The ototoxic potential of drugs is rarely assessed in pre-clinical drug development or during clinical trials, so this debilitating side-effect is often discovered as patients begin to report hearing loss. Furthermore, drug-induced ototoxicity in adults, and particularly in elderly patients, may go unrecognized due to hearing loss from a variety of etiologies because of a lack of baseline assessments immediately prior to novel therapeutic treatment. During the current pandemic, there is an intense effort to identify new drugs or repurpose FDA-approved drugs to treat COVID-19. Several potential COVID-19 therapeutics are known ototoxins, including chloroquine (CQ) and lopinavir-ritonavir, demonstrating the necessity to identify ototoxic potential in existing and novel medicines. Furthermore, several factors are emerging as potentiators of ototoxicity, such as inflammation (a hallmark of COVID-19), genetic polymorphisms, and ototoxic synergy with co-therapeutics, increasing the necessity to evaluate a drug's potential to induce ototoxicity under varying conditions. Here, we review the potential of COVID-19 therapies to induce ototoxicity and factors that may compound their ototoxic effects. We then discuss two models for rapidly detecting the potential for ototoxicity: mammalian auditory cell lines and the larval zebrafish lateral line. These models offer considerable value for pre-clinical drug development, including development of COVID-19 therapies. Finally, we show the validity of in silico screening for ototoxic potential using a computational model that compares structural similarity of compounds of interest with a database of known ototoxins and non-ototoxins. Preclinical screening at in silico, in vitro, and in vivo levels can provide an earlier indication of the potential for ototoxicity and identify the subset of candidate therapeutics for treating COVID-19 that need to be monitored for ototoxicity as for other widely-used clinical therapeutics, like aminoglycosides and cisplatin.

Hair Cell Protection from Ototoxic Drugs

Hearing loss is often caused by death of sensory hair cells (HCs) in the inner ear. HCs are vulnerable to some ototoxic drugs, such as aminoglycosides(AGs) and the cisplatin.The most predominant form of drug-induced cell death is apoptosis. Many efforts have been made to protect HCs from cell death after ototoxic drug exposure. These mechanisms and potential targets of HCs protection will be discussed in this review.And we also propose further investigation in the field of HCs necrosis and regeneration, as well as future clinical utilization.

Nox3-Derived Superoxide in Cochleae Induces Sensorineural Hearing Loss

Reactive oxygen species (ROS) produced by NADPH oxidases (Nox) contribute to the development of different types of sensorineural hearing loss (SNHL), a common impairment in humans with no established treatment. Although the essential role of Nox3 in otoconia biosynthesis and its possible involvement in hearing have been reported in rodents, immunohistological methods targeted at detecting Nox3 expression in inner ear cells reveal ambiguous results. Therefore, the mechanism underlying Nox3-dependent SNHL remains unclear and warrants further investigation. We generated Nox3-Cre knock-in mice, in which Nox3 was replaced with Cre recombinase (Cre). Using Nox3-Cre;tdTomato mice of either sex, in which tdTomato is expressed under the control of the Nox3 promoter, we determined Nox3-expressing regions and cell types in the inner ear. Nox3-expressing cells in the cochlea included various types of supporting cells, outer hair cells, inner hair cells, and spiral ganglion neurons. Nox3 expression increased with cisplatin, age, and noise insults. Moreover, increased Nox3 expression in supporting cells and outer hair cells, especially at the basal turn of the cochlea, played essential roles in ROS-related SNHL. The extent of Nox3 involvement in SNHL follows the following order: cisplatin-induced hearing loss > age-related hearing loss > noise-induced hearing loss. Here, on the basis of Nox3-Cre;tdTomato, which can be used as a reporter system (Nox3-Cre+/-;tdTomato+/+ and Nox3-Cre+/+;tdTomato+/+), and Nox3-KO (Nox3-Cre+/+;tdTomato+/+) mice, we demonstrate that Nox3 inhibition in the cochlea is a promising strategy for ROS-related SNHL, such as cisplatin-induced HL, age-related HL, and noise-induced HL.SIGNIFICANCE STATEMENT We found Nox3-expressing regions and cell types in the inner ear, especially in the cochlea, using Nox3-Cre;tdTomato mice, a reporter system generated in this study. Nox3 expression increased with cisplatin, age, and noise insults in specific cell types in the cochlea and resulted in the loss (apoptosis) of outer hair cells. Thus, Nox3 might serve as a molecular target for the development of therapeutics for sensorineural hearing loss, particularly cisplatin-induced, age-related, and noise-induced hearing loss.

Cannabinoid Signaling in Auditory Function and Development

Plants of the genus Cannabis have been used by humans for millennia for a variety of purposes. Perhaps most notable is the use of certain Cannabis strains for their psychoactive effects. More recently, several biologically active molecules within the plants of these Cannabis strains, called phytocannabinoids or simply cannabinoids, have been identified. Furthermore, within human cells, endogenous cannabinoids, or endocannabinoids, as well as the receptors and secondary messengers that give rise to their neuromodulatory effects, have also been characterized. This endocannabinoid system (ECS) is composed of two primary ligands-anandamide and 2-arachidonyl glycerol; two primary receptors-cannabinoid receptors 1 and 2; and several enzymes involved in biosynthesis and degradation of endocannabinoid ligands including diacylglycerol lipase (DAGL) and monoacylglycerol lipase (MAGL). Here we briefly summarize cannabinoid signaling and review what has been discerned to date with regard to cannabinoid signaling in the auditory system and its roles in normal physiological function as well as pathological conditions. While much has been uncovered regarding cannabinoid signaling in the central nervous system, less attention has been paid to the auditory system specifically. Still, evidence is emerging to suggest that cannabinoid signaling is critical for the development, maturation, function, and survival of cochlear hair cells (HCs) and spiral ganglion neurons (SGNs). Furthermore, cannabinoid signaling can have profound effects on synaptic connectivity in CNS structures related to auditory processing. While clinical cases demonstrate that endogenous and exogenous cannabinoids impact auditory function, this review highlights several areas, such as SGN development, where more research is warranted.

Cisplatin-induced ototoxicity: Updates on molecular mechanisms and otoprotective strategies

Cisplatin is a highly effective antitumor drug generally used in the treatment of solid malignant tumors. However, cisplatin causes severe side effects such as bone marrow depression, nephrotoxicity, and ototoxicity, thus limiting its clinical application. The incidence of ototoxicity induced by cisplatin ranges from 20% to 70%, and it usually manifests as a progressive, bilateral and irreversible hearing loss. Although the etiology of cisplatin-induced ototoxicity remains unclear, an increasing body of evidence suggests that the ototoxicity of cisplatin is mainly related to the production of reactive oxygen species and activation of apoptotic pathway in cochlear tissues. Many drugs have been well proved to protect cisplatin-induced hearing loss in vitro and in vivo. However, the anti-tumor effect of cisplatin is also weakened by systemic administration of those drugs for hearing protection, especially antioxidants. Therefore, establishing a local administration strategy contributes to the otoprotection without affecting the effect of cisplatin. This review introduces the pathology of ototoxicity caused by cisplatin, and focuses on recent developments in the mechanisms and protective strategies of cisplatin-induced ototoxicity.

The Two-Way Relationship Between Calcium and Metabolism in Cancer

Calcium ion (Ca²⁺) signaling is critical to many physiological processes, and its kinetics and subcellular localization are tightly regulated in all cell types. All Ca²⁺ flux perturbations impact cell function and may contribute to various diseases, including cancer. Several modulators of Ca²⁺ signaling are attractive pharmacological targets due to their accessibility at the plasma membrane. Despite this, the number of specific inhibitors is still limited, and to date there are no anticancer drugs in the clinic that target Ca²⁺ signaling. Ca²⁺ dynamics are impacted, in part, by modifications of cellular metabolic pathways. Conversely, it is well established that Ca²⁺ regulates cellular bioenergetics by allosterically activating key metabolic enzymes and metabolite shuttles or indirectly by modulating signaling cascades. A coordinated interplay between Ca²⁺ and metabolism is essential in maintaining cellular homeostasis. In this review, we provide a snapshot of the reciprocal interaction between Ca²⁺ and metabolism and discuss the potential consequences of this interplay in cancer cells. We highlight the contribution of Ca²⁺ to the metabolic reprogramming observed in cancer. We also describe how the metabolic adaptation of cancer cells influences this crosstalk to regulate protumorigenic signaling pathways. We suggest that the dual targeting of these processes might provide unprecedented opportunities for anticancer strategies. Interestingly, promising evidence for the synergistic effects of antimetabolites and Ca²⁺-modulating agents is emerging.

Strategies to reduce the risk of platinum containing antineoplastic drug-induced ototoxicity

INTRODUCTION

Cisplatin is a highly effective chemotherapeutic agent against a variety of solid tumors in adults and in children. Unfortunately, a large percentage of patients suffer permanent sensorineural hearing loss. Up to 60% of children and at least 50% of adults suffer this complication that seriously compromises their quality of life. Hearing loss is due to damage to the sensory cells in the inner ear. The mechanisms of cochlear damage are still being investigated. However, it appears that inner ear damage is triggered by reactive oxygen species (ROS) formation and inflammation 34.

AREAS COVERED

We discuss a number of potential therapeutic targets that can be addressed to provide hearing protection. These strategies include enhancing the endogenous antioxidant pathways, heat shock proteins, G protein coupled receptors and counteracting ROS and reactive nitrogen species, and blocking pathways that produce inflammation, including TRPV1 and STAT1 36.

EXPERT OPINION

Numerous potential protective agents show promise in animal models by systemic or local administration. However, clinical trials have not shown much efficacy to date with the exception of sodium thiosulfate. There is an urgent need to discover safe and effective protective agents that do not interfere with the efficacy of cisplatin against tumors yet preserve hearing 151.

Effect of myricetin on the gene expressions of NOX3, TGF-β1, prestin, and HSP-70 and anti-oxidant activity in the cochlea of noise-exposed rats

Objective(s):

Noise-induced hearing loss is one of the most common occupational diseases in industrialized countries and can be affected by various environmental and genetic factors. This study was designed to examine the effect of myricetin in preventing this disorder.

Materials and Methods:

Twenty-one Wistar rats were randomly divided into five groups: Non-exposed, noise exposure only, noise exposure with vehicle, noise exposure with myricetin 5 mg/Kg, and noise exposure with myricetin 10 mg/kg. All animals were sacrificed after last noise exposure. The left cochlea was dissected from each rat. It was used for mRNA expression analysis (NOX3, TGF-β1, prestin, and HSP-70). Blood samples were collected to assess superoxide dismutase (SOD) activity, 1, 1 diphenyl picrylhydrazyl (DPPH), and malondialdehyde (MDA) measurements.

Results:

Real time-PCR assay revealed that noise decreased NOX3 and increased TGF-β1, prestin, and HSP-70 gene expressions. Administration of myricetin at the dose of 5 mg/kg, but not at 10 mg/kg, significantly reversed these changes. Noise also increased MDA levels and decreased SOD and DPPH scavenging activities. Myricetin at the doses of 5 and 10 mg/kg also reversed these changes.

Conclusion:

The findings of this study showed that myricetin at the dose of 5 mg/Kg was able to reverse noise-induced abnormalities in gene expression and oxidant/anti-oxidant balance. It is a possibility that myricetin via enhancement of anti-oxidant activity induced these effects.

Protective Effects of Glucose-Related Protein 78 and 94 on Cisplatin-Mediated Ototoxicity

Cisplatin is a widely used chemotherapeutic drug for treating various solid tumors. Ototoxicity is a major dose-limiting side effect of cisplatin, which causes progressive and irreversible sensorineural hearing loss. Here, we examined the protective effects of glucose-related protein (GRP) 78 and 94, also identified as endoplasmic reticulum (ER) chaperone proteins, on cisplatin-induced ototoxicity. Treating murine auditory cells (HEI-OC1) with 25 μM cisplatin for 24 h increased cell death resulting from excessive intracellular reactive oxygen species (ROS) accumulation and caspase-involved apoptotic signaling pathway activation with subsequent DNA fragmentation. GRP78 and GRP94 expression was increased in cells treated with 3 nM thapsigargin or 0.1 μg/mL tunicamycin for 24 h, referred to as mild ER stress condition. This condition, prior to cisplatin exposure, attenuated cisplatin-induced ototoxicity. The involvement of GRP78 and GRP94 induction was demonstrated by the knockdown of GRP78 or GRP94 expression using small interfering RNAs, which abolished the protective effect of mild ER stress condition on cisplatin-induced cytotoxicity. These results indicated that GRP78 and GRP94 induction plays a protective role in remediating cisplatin-ototoxicity.

Ursolic acid protects against cisplatin‑induced ototoxicity by inhibiting oxidative stress and TRPV1‑mediated Ca2+‑signaling

Cisplatin (CDDP) is widely used in clinical settings for the treatment of various cancers. However, ototoxicity is a major side effect of CDDP, and there is an associated risk of irreversible hearing loss. We previously demonstrated that CDDP could induce ototoxicity via activation of the transient receptor potential vanilloid receptor 1 (TRPV1) pathway and subsequent induction of oxidative stress. The present study investigated whether ursolic acid (UA) treatment could protect against CDDP‑induced ototoxicity. UA is a triterpenoid with strong antioxidant activity widely used in China for the treatment of liver diseases. This traditional Chinese medicine is mainly isolated from bearberry, a Chinese herb. The present results showed that CDDP increased auditory brainstem response threshold shifts in frequencies associated with observed damage to the outer hair cells. Moreover, CDDP increased the expression of TRPV1, calpain 2 and caspase‑3 in the cochlea, and the levels of Ca2+ and 4‑hydroxynonenal. UA co‑treatment significantly attenuated CDDP‑induced hearing loss and inhibited TRPV1 pathway activation. In addition, UA enhanced CDDP‑induced growth inhibition in the human ovarian cancer cell line SKOV3, suggesting that UA synergizes with CDDP in vitro. Collectively, the present data suggested that UA could effectively attenuate CDDP‑induced hearing loss by inhibiting the TRPV1/Ca²+/calpain‑oxidative stress pathway without impairing the antitumor effects of CDDP.

2-Hydroxypropyl-β-cyclodextrin Ototoxicity in Adult Rats: Rapid Onset and Massive Destruction of Both Inner and Outer Hair Cells Above a Critical Dose

2-Hydroxypropyl-β-cyclodextrin (HPβCD), a cholesterol chelator, is being used to treat diseases associated with abnormal cholesterol metabolism such as Niemann-Pick C1 (NPC1). However, the high doses of HPβCD needed to slow disease progression may cause hearing loss. Previous studies in mice have suggested that HPβCD ototoxicity results from selective outer hair cell (OHC) damage. However, it is unclear if HPβCD causes the same type of damage or is more or less toxic to other species such as rats, which are widely used in toxicity research. To address these issues, rats were given a subcutaneous injection of HPβCD between 500 and 4000 mg/kg. Distortion product otoacoustic emissions (DPOAE), the cochlear summating potential (SP), and compound action potential (CAP) were used to assess cochlear function followed by quantitative analysis of OHC and inner hair cell (IHC) loss. The 3000- and 4000-mg/kg doses abolished DPOAE and greatly reduced SP and CAP amplitudes. These functional deficits were associated with nearly complete loss of OHC as well as ~ 80% IHC loss over the basal two thirds of the cochlea. The 2000-mg/kg dose abolished DPOAE and significantly reduced SP and CAP amplitudes at the high frequencies. These deficits were linked to OHC and IHC losses in the high-frequency region of the cochlea. Little or no damage occurred with 500 or 1000 mg/kg of HPβCD. The HPβCD-induced functional and structural deficits in rats occurred suddenly, involved damage to both IHC and OHC, and were more severe than those reported in mice.

Otoprotective Effects of Zingerone on Cisplatin-Induced Ototoxicity

Previous studies have described the effects of zingerone (ZO) on cisplatin (CXP)-induced injury to the kidneys, liver, and other organs but not to the cochlea. This study aimed to investigate the effects of ZO on CXP-induced ototoxicity. Eight-week-old Sprague-Dawley rats were used and divided into a control group, a CXP group, and a CXP + ZO group. Rats in the CXP group received 5 mg/kg/day CXP intraperitoneally for five days. Rats in the CXP + ZO group received 5 mg/kg/day CXP intraperitoneally for five days and 50 mg/kg/day ZO intraperitoneally for seven days. Auditory brainstem response thresholds (ABRTs) were measured before (day 0) and after (day 10) drug administration. Cochlear histology was examined using hematoxylin and eosin (H&E) staining and cochlear whole mounts. The expression levels of cytochrome P450 (CYP)1A1, CYP1B1, inducible nitric oxide synthase (iNOS), nuclear factor kappa B (NFκB), tumor necrosis factor alpha (TNFα), and interleukin 6 (IL6) were estimated using quantitative reverse transcription-polymerase chain reaction. The expression levels of heme oxygenase 1 (HO1) and caspase 3 were analyzed via Western blotting. The auditory thresholds at 4, 8, and 16 kHz were attenuated in the CXP + ZO group compared with the CXP group. The mRNA expression levels of CYP1A1, CYP1B1, iNOS, NFκB, TNFα, and IL6 were lower in the CXP + ZO group than in the CXP group. The protein expression levels of HO1 and caspase 3 were lower in the CXP + ZO group than in the CXP group. Cotreatment with ZO exerted otoprotective effects against CXP-induced cochlear injury via antioxidative and anti-inflammatory activities involving CYPs, iNOS, NFκB, and TNFα.

New Insights on the Effect of TNF Alpha Blockade by Gene Silencing in Noise-Induced Hearing Loss

Noise exposure represents the second most common cause of acquired sensorineural hearing loss and we observed that tumor necrosis factor α (TNFα) was involved in this context. The effect of Tnfα gene silencing on the expression profile related to the TNFα metabolic pathway in an experimental model of noise-induced hearing loss had not previously been studied. Methods: Single ears of Wistar rats were pretreated with Tnfα small interfering RNA (siRNA) by trans-tympanic administration 24 h before they were exposed to white noise (120 dBSPL for three hours). After 24 h of noise exposure, we analyzed the electrophysiological threshold and the amplitude of waves I, II, III, and IV in the auditory brain response click. In addition, qRT-PCR was performed to evaluate the TNFα metabolic pathway in the ears submitted or not to gene silencing. Results: Preservation of the electrophysiological threshold and the amplitude of waves was observed in the ears submitted to gene silencing compared to the ears not treated. Increased anti-apoptotic gene expression and decreased pro-apoptotic gene expression were found in the treated ears. Conclusion: Our results allow us to suggest that the blockade of TNFα by gene silencing was useful to prevent noise-induced hearing loss.

The Role of the Reactive Oxygen Species Scavenger Agent, Astaxanthin, in the Protection of Cisplatin-Treated Patients Against Hearing Loss

Emerging evidence of significant hearing loss occurring shortly after cisplatin administration in cancer patients has stimulated research into the causes and treatment of this side effect. Although the aetiology of cisplatin-induced hearing loss (CIHL) remains unknown, an increasing body of research suggests that it is associated with excessive generation of intracellular reactive oxygen species (ROS) in the cochlea. Astaxanthin, a xanthophyll carotenoid, has powerful anti-oxidant, anti-inflammatory, and anti-apoptotic properties based on its unique cell membrane function, diverse biological activities, and ability to permeate the blood-brain barrier. In this review, we summarize the role of ROS in CIHL and the effect of astaxanthin on inhibiting ROS production. We focus on investigating the mechanism of action of astaxanthin in suppressing excessive production of ROS.

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.

Targeting Inflammatory Processes Mediated by TRPVI and TNF-α for Treating Noise-Induced Hearing Loss

Noise trauma is the most common cause of hearing loss in adults. There are no known FDA approved drugs for prevention or rescue of noise-induced hearing loss (NIHL). In this study, we provide evidence that implicates stress signaling molecules (TRPV1, NOX3, and TNF-α) in NIHL. Furthermore, we provide evidence that inhibiting any one of these moieties can prevent and treat NIHL when administered within a window period. Hearing loss induced by loud noise is associated with the generation of reactive oxygen species (ROS), increased calcium (Ca²⁺) in the endolymph and hair cells, and increased inflammation in the cochlea. Increased (Ca²⁺) and ROS activity persists for several days after traumatic noise exposure (NE). Chronic increases in (Ca²⁺) and ROS have been shown to increase inflammation and apoptosis in various tissue. However, the precise role of Ca²⁺ up-regulation and the resulting inflammation causing a positive feedback loop in the noise-exposed cochlea to generate sustained toxic amounts of Ca²⁺ are unknown. Here we show cochlear TRPV1 dysregulation is a key step in NIHL, and that inflammatory TNF-α cytokine-mediated potentiation of TRPV1 induced Ca²⁺ entry is an essential mechanism of NIHL. In the Wistar rat model, noise produces an acute (within 48 h) and a chronic (within 21 days) increase in cochlear gene expression of TRPV1, NADPH oxidase 3 (NOX3) and pro-inflammatory mediators such as tumor necrosis factor-α (TNF-α) and cyclooxygenase-2 (COX2). Additionally, we also show that H₂O₂ (100 μM) produces a robust increase in Ca²⁺ entry in cell cultures which is enhanced by TNF-α via the TRPV1 channel and which involves ERK1/2 phosphorylation. Mitigation of NIHL could be achieved by using capsaicin (TRPV1 agonist that rapidly desensitizes TRPV1. This mechanism is used in the treatment of pain in diabetic peripheral neuropathy) pretreatment or by inhibition of TNF-α with Etanercept (ETA), administered up to 7 days prior to NE or within 24 h of noise. Our results demonstrate the importance of the synergistic interaction between TNF-α and TRPV1 in the cochlea and suggest that these are important therapeutic targets for treating NIHL.

Local Drug Delivery for Prevention of Hearing Loss

Systemic delivery of therapeutics for targeting the cochlea to prevent or treat hearing loss is challenging. Systemic drugs have to cross the blood-labyrinth barrier (BLB). BLB can significantly prevent effective penetration of drugs in appropriate concentrations to protect against hearing loss caused by inflammation, ototoxic drugs, or acoustic trauma. This obstacle may be obviated by local administration of protective agents. This route can deliver higher concentration of drug compared to systemic application and preclude systemic side effects. Protective agents have been administered by intra-tympanic injection in numerous preclinical studies. Drugs such as steroids, etanercept, D and L-methionine, pifithrin-alpha, adenosine agonists, melatonin, kenpaullone (a cyclin-dependent kinase 2 (CDK2) inhibitor) have been reported to show efficacy against cisplatin ototoxicity in animal models. Several siRNAs have been shown to ameliorate cisplatin ototoxicity when administered by intra-tympanic injection. The application of corticosteroids and a number of other drugs with adjuvants appears to enhance efficacy. Administration of siRNAs to knock down AMPK kinase, liver kinase B1 (LKB1) or G9a in the cochlea have been found to ameliorate noise-induced hearing loss. The local administration of these compounds appears to be effective in protecting the cochlea against damage from cisplatin or noise trauma. Furthermore the intra-tympanic route yields maximum protection in the basal turn of the cochlea which is most vulnerable to cisplatin ototoxicity and noise trauma. There appears to be very little transfer of these agents to the systemic circulation. This would avoid potential side effects including interference with anti-tumor efficacy of cisplatin. Nanotechnology offers strategies to effectively deliver protective agents to the cochlea. This review summarizes the pharmacology of local drug delivery by intra-tympanic injection to prevent hearing loss caused by cisplatin and noise exposure in animals. Future refinements in local protective agents provide exciting prospects for amelioration of hearing loss resulting from cisplatin or noise exposure.

Inflammation up-regulates cochlear expression of TRPV1 to potentiate drug-induced hearing loss

Aminoglycoside antibiotics are essential for treating life-threatening bacterial infections, despite the risk of lifelong hearing loss. Infections induce inflammation and up-regulate expression of candidate aminoglycoside-permeant cation channels, including transient receptor potential vanilloid-1 (TRPV1). Heterologous expression of TRPV1 facilitated cellular uptake of (fluorescently tagged) gentamicin that was enhanced by agonists, and diminished by antagonists, of TRPV1. Cochlear TRPV1 was immunolocalized near the apical membranes of sensory hair cells, adjacent supporting cells, and marginal cells in the stria vascularis. Exposure to immunostimulatory lipopolysaccharides, to simulate of bacterial infections, increased cochlear expression of TRPV1 and hair cell uptake of gentamicin. Lipopolysaccharide exposure exacerbated aminoglycoside-induced auditory threshold shifts and loss of cochlear hair cells in wild-type, but not in heterozygous Trpv1+/- or Trpv1 knockout, mice. Thus, TRPV1 facilitates cochlear uptake of aminoglycosides, and bacteriogenic stimulation upregulates TRPV1 expression to exacerbate cochleotoxicity. Furthermore, loss-of-function polymorphisms in Trpv1 can protect against immunogenic exacerbation of aminoglycoside-induced cochleotoxicity.

Predicting the Need for a Tier II Ototoxicity Study From Early Renal Function Data

History has established that many drugs, such as the antibiotics, chemotherapies, and loop diuretics, are capable of inducing both nephrotoxicity and ototoxicity. The exact mechanisms by which cellular damage occurs remain to be fully elucidated. Monitoring the indices of renal function conducted in the Food and Drug Administration's prescribed set of early investigational new drug (IND)-enabling studies may be the first signs of ototoxicity properties of the new drug candidate. In developing improved and efficacious new molecular entities, it is critically necessary to understand the cellular and molecular mechanisms underlying the potential ototoxic effects as early in the drug development program as possible. Elucidation of these mechanisms will facilitate the development of safe and effective clinical approaches for the prevention and amelioration of drug-induced ototoxicity prior to the first dose in man. Biomarkers for nephrotoxicity in early tier I or tier II nonclinical IND-enabling studies should raise an inquiry as to the need to conduct a full auditory function assay early in the game to clear the pipeline with a safer candidate that has a higher probability of continued therapeutic compliance once approved for distribution.