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Kedeshian K, Hong M, Hoffman L, Kita A. N-acetylcysteine microparticles reduce cisplatin-induced RSC96 Schwann cell toxicity. Laryngoscope Investig Otolaryngol 2024; 9:e1256. [PMID: 38765675 PMCID: PMC11099882 DOI: 10.1002/lio2.1256] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2023] [Revised: 12/03/2023] [Accepted: 04/16/2024] [Indexed: 05/22/2024] Open
Abstract
Objectives Cisplatin is known to cause inner ear dysfunction. There is growing evidence that cisplatin-induced demyelination of spiral or Scarpa's ganglion neurons may play an additional role in drug-induced ototoxicity alongside afferent neuron injury. As Schwann cells produce myelin, there may be an opportunity to reduce ototoxic inner ear damage by promoting Schwann cell viability. This work describes a cellular model of cisplatin-induced Schwann cell injury and investigates the ability of the antioxidant N-acetylcysteine to promote Schwann cell viability. A local delivery system of drug-eluting microparticles was then fabricated, characterized, and investigated for bioactivity. Methods RSC96 rat Schwann cells were dosed with varying concentrations of cisplatin to obtain a dose curve and identify the lethal concentration of 50% of the cells (LC50). In subsequent experiments, RSC96 cells were co-treated with cisplatin and both resuspended or eluted N-acetylcysteine. Cell viability was assessed with the CCK8 assay. Results The LC50 dose of cisplatin was determined to be 3.76 μM (p = 2.2 x 10-16). When co-dosed with cisplatin and a therapeutic concentration of resuspended or eluted N-acetylcysteine, Schwann cells had an increased viability compared to cells dosed with cisplatin alone. Conclusion RSC96 Schwann cell injury following cisplatin insult is characterized in this in vitro model. Cisplatin caused injury at physiologic concentrations and N-acetylcysteine improved cell viability and mitigated this injury. N-acetylcysteine was packaged into microparticles and eluted N-acetylcysteine retained its ability to increase cell viability, thus demonstrating promise as a therapeutic to offset cisplatin-induced ototoxicity. Level of Evidence N/A Laryngoscope, 2023.
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Affiliation(s)
- Katherine Kedeshian
- Department of Head and Neck SurgeryDavid Geffen School of Medicine at University of California Los AngelesLos AngelesCaliforniaUSA
| | - Michelle Hong
- Department of Head and Neck SurgeryDavid Geffen School of Medicine at University of California Los AngelesLos AngelesCaliforniaUSA
| | - Larry Hoffman
- Department of Head and Neck SurgeryDavid Geffen School of Medicine at University of California Los AngelesLos AngelesCaliforniaUSA
- Vestibular Neuroscience Laboratory, Brain Research InstituteDavid Geffen School of Medicine at University of California Los AngelesLos AngelesCaliforniaUSA
| | - Ashley Kita
- Department of Head and Neck SurgeryDavid Geffen School of Medicine at University of California Los AngelesLos AngelesCaliforniaUSA
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Saddler MR, McDermott JH. Models optimized for real-world tasks reveal the necessity of precise temporal coding in hearing. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.04.21.590435. [PMID: 38712054 PMCID: PMC11071365 DOI: 10.1101/2024.04.21.590435] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2024]
Abstract
Neurons encode information in the timing of their spikes in addition to their firing rates. Spike timing is particularly precise in the auditory nerve, where action potentials phase lock to sound with sub-millisecond precision, but its behavioral relevance is uncertain. To investigate the role of this temporal coding, we optimized machine learning models to perform real-world hearing tasks with simulated cochlear input. We asked how precise auditory nerve spike timing needed to be to reproduce human behavior. Models with high-fidelity phase locking exhibited more human-like sound localization and speech perception than models without, consistent with an essential role in human hearing. Degrading phase locking produced task-dependent effects, revealing how the use of fine-grained temporal information reflects both ecological task demands and neural implementation constraints. The results link neural coding to perception and clarify conditions in which prostheses that fail to restore high-fidelity temporal coding could in principle restore near-normal hearing.
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Affiliation(s)
- Mark R Saddler
- Department of Brain and Cognitive Sciences, MIT, Cambridge, MA, USA
- McGovern Institute for Brain Research, MIT, Cambridge, MA, USA
- Center for Brains, Minds, and Machines, MIT, Cambridge, MA, USA
| | - Josh H McDermott
- Department of Brain and Cognitive Sciences, MIT, Cambridge, MA, USA
- McGovern Institute for Brain Research, MIT, Cambridge, MA, USA
- Center for Brains, Minds, and Machines, MIT, Cambridge, MA, USA
- Program in Speech and Hearing Biosciences and Technology, Harvard, Cambridge, MA, USA
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3
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Liu J, Stohl J, Overath T. Hidden hearing loss: Fifteen years at a glance. Hear Res 2024; 443:108967. [PMID: 38335624 DOI: 10.1016/j.heares.2024.108967] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/17/2023] [Revised: 01/15/2024] [Accepted: 01/29/2024] [Indexed: 02/12/2024]
Abstract
Hearing loss affects approximately 18% of the population worldwide. Hearing difficulties in noisy environments without accompanying audiometric threshold shifts likely affect an even larger percentage of the global population. One of the potential causes of hidden hearing loss is cochlear synaptopathy, the loss of synapses between inner hair cells (IHC) and auditory nerve fibers (ANF). These synapses are the most vulnerable structures in the cochlea to noise exposure or aging. The loss of synapses causes auditory deafferentation, i.e., the loss of auditory afferent information, whose downstream effect is the loss of information that is sent to higher-order auditory processing stages. Understanding the physiological and perceptual effects of this early auditory deafferentation might inform interventions to prevent later, more severe hearing loss. In the past decade, a large body of work has been devoted to better understand hidden hearing loss, including the causes of hidden hearing loss, their corresponding impact on the auditory pathway, and the use of auditory physiological measures for clinical diagnosis of auditory deafferentation. This review synthesizes the findings from studies in humans and animals to answer some of the key questions in the field, and it points to gaps in knowledge that warrant more investigation. Specifically, recent studies suggest that some electrophysiological measures have the potential to function as indicators of hidden hearing loss in humans, but more research is needed for these measures to be included as part of a clinical test battery.
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Affiliation(s)
- Jiayue Liu
- Department of Psychology and Neuroscience, Duke University, Durham, USA.
| | - Joshua Stohl
- North American Research Laboratory, MED-EL Corporation, Durham, USA
| | - Tobias Overath
- Department of Psychology and Neuroscience, Duke University, Durham, USA
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Cassinotti LR, Ji L, Yuk MC, Desai AS, Cass ND, Amir ZA, Corfas G. Hidden hearing loss in hereditary demyelinating neuropathies: insights from Charcot-Marie-Tooth mouse models. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.12.14.571732. [PMID: 38168255 PMCID: PMC10760174 DOI: 10.1101/2023.12.14.571732] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2024]
Abstract
Hidden hearing loss (HHL) is a recently described auditory neuropathy characterized by normal audiometric thresholds but reduced sound-evoked potentials. It has been proposed that HHL contributes to hearing difficulty in noisy environments in people with normal audiometric thresholds, a widespread complaint. While most studies on HHL pathogenesis have focused on inner hair cell (IHC) synaptopathy, recent research suggests that transient auditory nerve (AN) demyelination may also cause HHL. To test the impact of myelinopathy in a clinically relevant model, we studied a mouse model of Charcot-Marie-Tooth type 1A (CMT1A), the most prevalent hereditary peripheral neuropathy in humans. CMT1A mice exhibit the functional hallmarks of HHL, together with disorganization of AN heminodes near the IHCs with minor loss of AN fibers. Our results support the hypothesis that mild disruptions of AN myelination can cause HHL, and that heminodal defects contribute to the alterations in action potential amplitudes and latencies seen in these models. Also, these findings suggest that patients with CMT1A or other mild peripheral neuropathies are likely to suffer from HHL. Furthermore, these results suggest that studies of hearing in CMT1A patients might help develop robust clinical tests for HHL, which are currently lacking.
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Affortit C, Coyat C, Saidia AR, Ceccato JC, Charif M, Sarzi E, Flamant F, Guyot R, Cazevieille C, Puel JL, Lenaers G, Wang J. The human OPA1 delTTAG mutation induces adult onset and progressive auditory neuropathy in mice. Cell Mol Life Sci 2024; 81:80. [PMID: 38334784 PMCID: PMC10858076 DOI: 10.1007/s00018-024-05115-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2023] [Revised: 01/05/2024] [Accepted: 01/05/2024] [Indexed: 02/10/2024]
Abstract
Dominant optic atrophy (DOA) is one of the most prevalent forms of hereditary optic neuropathies and is mainly caused by heterozygous variants in OPA1, encoding a mitochondrial dynamin-related large GTPase. The clinical spectrum of DOA has been extended to a wide variety of syndromic presentations, called DOAplus, including deafness as the main secondary symptom associated to vision impairment. To date, the pathophysiological mechanisms underlying the deafness in DOA remain unknown. To gain insights into the process leading to hearing impairment, we have analyzed the Opa1delTTAG mouse model that recapitulates the DOAplus syndrome through complementary approaches combining morpho-physiology, biochemistry, and cellular and molecular biology. We found that Opa1delTTAG mutation leads an adult-onset progressive auditory neuropathy in mice, as attested by the auditory brainstem response threshold shift over time. However, the mutant mice harbored larger otoacoustic emissions in comparison to wild-type littermates, whereas the endocochlear potential, which is a proxy for the functional state of the stria vascularis, was comparable between both genotypes. Ultrastructural examination of the mutant mice revealed a selective loss of sensory inner hair cells, together with a progressive degeneration of the axons and myelin sheaths of the afferent terminals of the spiral ganglion neurons, supporting an auditory neuropathy spectrum disorder (ANSD). Molecular assessment of cochlea demonstrated a reduction of Opa1 mRNA level by greater than 40%, supporting haploinsufficiency as the disease mechanism. In addition, we evidenced an early increase in Sirtuin 3 level and in Beclin1 activity, and subsequently an age-related mtDNA depletion, increased oxidative stress, mitophagy as well as an impaired autophagic flux. Together, these results support a novel role for OPA1 in the maintenance of inner hair cells and auditory neural structures, addressing new challenges for the exploration and treatment of OPA1-linked ANSD in patients.
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Affiliation(s)
- Corentin Affortit
- Institute for Neurosciences of Montpellier (INM), University Montpellier, INSERM, UMR 1298, 80 Rue Augustin Fliche, 34295, Montpellier, France
- Molecular Otolaryngology and Renal Research Laboratories, Department of Otolaryngology, Head and Neck Surgery, University of Iowa, Iowa City, IA, 52242, USA
| | - Carolanne Coyat
- Institute for Neurosciences of Montpellier (INM), University Montpellier, INSERM, UMR 1298, 80 Rue Augustin Fliche, 34295, Montpellier, France
| | - Anissa Rym Saidia
- Institute for Neurosciences of Montpellier (INM), University Montpellier, INSERM, UMR 1298, 80 Rue Augustin Fliche, 34295, Montpellier, France
| | - Jean-Charles Ceccato
- Institute for Neurosciences of Montpellier (INM), University Montpellier, INSERM, UMR 1298, 80 Rue Augustin Fliche, 34295, Montpellier, France
| | - Majida Charif
- Genetics, and Immuno-Cell Therapy Team, Mohamed First University, 60000, Oujda, Morocco
| | - Emmanuelle Sarzi
- Institut NeuroMyoGène, Pathophysiology and Genetics of Neuron and Muscle (INMG-PGNM) UCBL-CNRS UMR5261, Inserm U1315, Université Claude Bernard, Lyon I, Faculty of Medicine and Pharmacy, Lyon, France
| | - Frédéric Flamant
- Institut de Génomique Fonctionnelle de Lyon (IGFL), INRAE USC1370, CNRS (UMR5242), ENS Lyon, Lyon, France
| | - Romain Guyot
- Institut de Génomique Fonctionnelle de Lyon (IGFL), INRAE USC1370, CNRS (UMR5242), ENS Lyon, Lyon, France
| | - Chantal Cazevieille
- Institute for Neurosciences of Montpellier (INM), University Montpellier, INSERM, UMR 1298, 80 Rue Augustin Fliche, 34295, Montpellier, France
| | - Jean-Luc Puel
- Institute for Neurosciences of Montpellier (INM), University Montpellier, INSERM, UMR 1298, 80 Rue Augustin Fliche, 34295, Montpellier, France
| | - Guy Lenaers
- Université Angers, MitoLab Team, Unité MitoVasc, UMR CNRS 6015, INSERM U1083, SFR ICAT, Angers, France
- Service de Neurologie, CHU d'Angers, Angers, France
| | - Jing Wang
- Institute for Neurosciences of Montpellier (INM), University Montpellier, INSERM, UMR 1298, 80 Rue Augustin Fliche, 34295, Montpellier, France.
- Department of ENT and Head and Neck Surgery, University Hospital of Montpellier, Montpellier, France.
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Saade M, Fernandez K, Little C, Schwam ZG, Cosetti M. Utility of Extended High-Frequency Audiograms in Clinical Practice. Laryngoscope 2024; 134:907-910. [PMID: 37497866 DOI: 10.1002/lary.30890] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2023] [Revised: 05/22/2023] [Accepted: 07/01/2023] [Indexed: 07/28/2023]
Abstract
OBJECTIVES Extended high-frequency (EHF) audiometry elicits pure-tone thresholds at frequencies above 8 kHz, which are not included in routine clinical testing. This study explores the utility of EHF audiometry in patients with various audiologic symptoms despite normal-hearing thresholds at ≤8 kHz. METHODS A retrospective review was performed of all patients receiving conventional (250-8 kHz) and EHF (9-20 kHz) audiometry at a tertiary otological referral center between April 2021 and August 2022. Only patients with audiologic symptoms and pure-tone thresholds ≤25 dB HL at ≤8 kHz bilaterally on routine testing were included in subsequent analysis. EHF-PTA was defined for each ear as an average of the air conduction thresholds at 9.0, 10.0, 11.2, 12.5, 14.0, 16.0, 18.0, and 20.0 kHz. RESULTS Of the 50 patients who received EHF testing, 40 had audiologic symptoms and normal conventional audiograms at ≤8 kHz. Twenty-five of the 40 (62.5%) were found to have hearing loss in the highest frequencies. Patients with EHF hearing loss (EHF-HL) were more likely to report subjective hearing loss. Age was significantly greater in those with EHF-HL compared with those without EHF-HL, and age was positively correlated with the degree of EHF-HL. CONCLUSION EHF testing correlates with audiologic symptoms in patients with normal testing at ≤8 kHz and may be considered when standard audiometry is normal. Additional data are warranted to create an evidenced-based, clinical algorithm for EHF audiometry that can guide treatment, direct mitigation strategies, and potentially identify those at higher risk of hearing loss over time. LEVEL OF EVIDENCE 4 Laryngoscope, 134:907-910, 2024.
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Affiliation(s)
- Mia Saade
- Department of Otolaryngology-Head and Neck Surgery, Icahn School of Medicine at Mount Sinai, New York, New York, USA
| | - Karla Fernandez
- Department of Otolaryngology-Head and Neck Surgery, Icahn School of Medicine at Mount Sinai, New York, New York, USA
| | - Christine Little
- Department of Otolaryngology-Head and Neck Surgery, Icahn School of Medicine at Mount Sinai, New York, New York, USA
| | - Zachary G Schwam
- Department of Otolaryngology-Head and Neck Surgery, Icahn School of Medicine at Mount Sinai, New York, New York, USA
| | - Maura Cosetti
- Department of Otolaryngology-Head and Neck Surgery, Icahn School of Medicine at Mount Sinai, New York, New York, USA
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7
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Kurioka T, Mizutari K, Satoh Y, Kobayashi Y, Shiotani A. Blast-Induced Central Auditory Neurodegeneration Affects Tinnitus Development Regardless of Peripheral Cochlear Damage. J Neurotrauma 2024; 41:499-513. [PMID: 37795561 DOI: 10.1089/neu.2023.0259] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/06/2023] Open
Abstract
Blast exposure causes serious complications, the most common of which are ear-related symptoms such as hearing loss and tinnitus. The blast shock waves can cause neurodegeneration of the auditory pathway in the brainstem, as well as the cochlea, which is the primary receptor for hearing, leading to blast-induced tinnitus. However, it is still unclear which lesion is more dominant in triggering tinnitus, the peripheral cochlea or the brainstem lesion owing to the complex pathophysiology and the difficulty in objectively measuring tinnitus. Recently, gap detection tests have been developed and are potentially well-suited for determining the presence of tinnitus. In this study, we investigated whether the peripheral cochlea or the central nervous system has a dominant effect on the generation of tinnitus using a blast-exposed mouse model with or without earplugs, which prevent cochlear damage from a blast transmitted via the external auditory canal. The results showed that the earplug (+) group, in which the cochlea was neither physiologically nor histologically damaged, showed a similar extent of tinnitus behavior in a gap prepulse inhibition of acoustic startle reflex test as the earplug (-) group, in which the explosion caused a cochlear synaptic loss in the inner hair cells and demyelination of auditory neurons. In contrast, both excitatory synapses labeled with VGLUT-1 and inhibitory synapses labeled with GAD65 were reduced in the ventral cochlear nucleus, and demyelination in the medial nucleus of the trapezoid body was observed in both groups. These disruptions significantly correlated with the presence of tinnitus behavior regardless of cochlear damage. These results indicate that the lesion in the brainstem could be dominant to the cochlear lesion in the development of tinnitus following blast exposure.
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Affiliation(s)
- Takaomi Kurioka
- Department of Otolaryngology, Head, and Neck Surgery, National Defense Medical College, Saitama, Japan
| | - Kunio Mizutari
- Department of Otolaryngology, Head, and Neck Surgery, National Defense Medical College, Saitama, Japan
| | - Yasushi Satoh
- Department of Biochemistry, National Defense Medical College, Saitama, Japan
| | - Yasushi Kobayashi
- Department of Anatomy, National Defense Medical College, Saitama, Japan
| | - Akihiro Shiotani
- Department of Otolaryngology, Head, and Neck Surgery, National Defense Medical College, Saitama, Japan
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8
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Kedeshian K, Hong M, Hoffman L, Kita A. N-acetylcysteine Microparticles Reduce Cisplatin-induced RSC96 Schwann Cell Toxicity. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.10.31.564430. [PMID: 37961184 PMCID: PMC10635004 DOI: 10.1101/2023.10.31.564430] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2023]
Abstract
Objectives Cisplatin is known to cause inner ear dysfunction. There is growing evidence that cisplatin-induced demyelination of spiral or Scarpa's ganglion neurons may play an additional role in drug-induced ototoxicity alongside afferent neuron injury. As Schwann cells produce myelin, there may be an opportunity to reduce ototoxic inner ear damage by promoting Schwann cell viability. This work describes a cellular model of cisplatin-induced Schwann cell injury and investigates the ability of the antioxidant N-acetylcysteine to promote Schwann cell viability. A local delivery system of drug-eluting microparticles was then fabricated, characterized, and investigated for bioactivity. Methods RSC96 rat Schwann cells were dosed with varying concentrations of cisplatin to obtain a dose curve and identify the lethal concentration of 50% of the cells (LC 50 ). In subsequent experiments, RSC96 cells were co-treated with cisplatin and both resuspended or eluted N-acetylcysteine. Cell viability was assessed with the CCK8 assay. Results The LC 50 dose of cisplatin was determined to be 3.76 μM (p=2.2 × 10 -16 ). When co-dosed with cisplatin and therapeutic concentration of resuspended or eluted N-acetylcysteine, Schwann cells had an increased viability compared to cells dosed with cisplatin alone. Conclusion RSC96 Schwann cell injury following cisplatin insult is characterized in this in vitro model. Cisplatin caused injury at physiologic concentrations and N-acetylcysteine improved cell viability and mitigated this injury. N-acetylcysteine was packaged into microparticles and eluted N-acetylcysteine retained its ability to increase cell viability, thus demonstrating promise as a therapeutic to offset cisplatin-induced ototoxicity. Lay Summary Cisplatin is a chemotherapeutic agent known to cause balance and hearing problems through damage to the inner ear. This project explored cisplatin injury in a Schwann cell culture model and packaged an antioxidant into microparticles suitable for future drug delivery applications.
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Hong MK, Echanique KA, Hoffman LF, Kita AE. Designing a Prolonged Method of Therapeutic Delivery to Support Rehabilitation From Ototoxic Damage in a Schwann Cell Model. Otol Neurotol 2023; 44:373-381. [PMID: 36791364 PMCID: PMC10038897 DOI: 10.1097/mao.0000000000003839] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2023]
Abstract
HYPOTHESIS The ototoxicity of gentamicin and cisplatin can be evaluated with a Schwann cell model to screen for otoprotective agents that can be encapsulated into poly (lactic-co-glycolic acid) (PLGA) microparticles for drug delivery to the inner ear. BACKGROUND Aminoglycosides and cisplatin are widely prescribed but known to cause ototoxicity. There is strong evidence that compromise to Schwann cells ensheathing inner ear afferent neurons results in inner ear dysfunction mimicking drug-induced ototoxicity. There is a need for a model for ototoxic demyelination to screen medications for protective potential and to subsequently target and tune the delivery of any promising agents. METHODS RT4-D6P2T rat schwannoma cells were used as a Schwann cell model to assess gentamicin and cisplatin toxicity and to screen for protective agents. Cell viability was evaluated with the MTT cell proliferation assay. N -acetylcysteine (NAC) was encapsulated into a PLGA microparticle, and its elution profile was determined. RESULTS The estimated 50% lethal concentration dose for gentamicin was 805.6 μM, which was 46-fold higher than that for cisplatin (17.5 μM). In several trials, cells dosed with NAC and cisplatin demonstrated a 22.6% ( p < 0.001) increase in cell viability when compared with cisplatin alone. However, this protective effect was not consistent across all trials. NAC was encapsulated into a PLGA microparticle and elution plateaued at 5 days. CONCLUSION When dosed at their respective therapeutic ranges, cisplatin is more likely than gentamicin to induce damage to the Schwann cell model. Although NAC demonstrates an uncertain role in protecting against cisplatin-induced Schwann cell cytotoxicity, this study establishes a method to screen for other otoprotective medications to encapsulate into a tunable microparticle for localized drug delivery.
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Affiliation(s)
- Michelle K Hong
- Department of Head and Neck Surgery, David Geffen School of Medicine at UCLA, Los Angeles, California
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10
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Hidden hearing loss: current concepts. Curr Opin Otolaryngol Head Neck Surg 2022; 30:321-325. [PMID: 36004790 DOI: 10.1097/moo.0000000000000824] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
PURPOSE OF REVIEW The purpose of this review is to offer a concise summary of current knowledge regarding hidden hearing loss (HHL) and to describe the variety of mechanisms that contribute to its development. We will also discuss the various diagnostic tools that are available as well as future directions. RECENT FINDINGS Hidden hearing loss often also called cochlear synaptopathy affects afferent synapses of the inner hair cells. This description is in contrast to traditional models of hearing loss, which predominantly affects auditory hair cells. In HHL, the synapses of nerve fibres with a slow spontaneous firing rate, which are crucial for locating sound in background noise, are severely impaired. In addition, recent research suggests that HHL may also be related to cochlear nerve demyelination. Noise exposure causes loss of myelin sheath thickness. Auditory brainstem response, envelope-following response and middle-ear muscle reflex are promising diagnostic tests, but they have yet to be validated in humans. SUMMARY Establishing diagnostic tools for cochlear synaptopathy in humans is important to better understand this patient population, predict the long-term outcomes and allow patients to take the necessary protective precautions.
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Valderrama JT, de la Torre A, McAlpine D. The hunt for hidden hearing loss in humans: From preclinical studies to effective interventions. Front Neurosci 2022; 16:1000304. [PMID: 36188462 PMCID: PMC9519997 DOI: 10.3389/fnins.2022.1000304] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2022] [Accepted: 08/29/2022] [Indexed: 11/30/2022] Open
Abstract
Many individuals experience hearing problems that are hidden under a normal audiogram. This not only impacts on individual sufferers, but also on clinicians who can offer little in the way of support. Animal studies using invasive methodologies have developed solid evidence for a range of pathologies underlying this hidden hearing loss (HHL), including cochlear synaptopathy, auditory nerve demyelination, elevated central gain, and neural mal-adaptation. Despite progress in pre-clinical models, evidence supporting the existence of HHL in humans remains inconclusive, and clinicians lack any non-invasive biomarkers sensitive to HHL, as well as a standardized protocol to manage hearing problems in the absence of elevated hearing thresholds. Here, we review animal models of HHL as well as the ongoing research for tools with which to diagnose and manage hearing difficulties associated with HHL. We also discuss new research opportunities facilitated by recent methodological tools that may overcome a series of barriers that have hampered meaningful progress in diagnosing and treating of HHL.
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Affiliation(s)
- Joaquin T. Valderrama
- National Acoustic Laboratories, Sydney, NSW, Australia
- Department of Linguistics, Macquarie University Hearing, Macquarie University, Sydney, NSW, Australia
- *Correspondence: Joaquin T. Valderrama, ;
| | - Angel de la Torre
- Department of Signal Theory, Telematics and Communications, University of Granada, Granada, Spain
- Research Centre for Information and Communications Technologies (CITIC-UGR), University of Granada, Granada, Spain
| | - David McAlpine
- Department of Linguistics, Macquarie University Hearing, Macquarie University, Sydney, NSW, Australia
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Budak M, Roberts MT, Grosh K, Corfas G, Booth V, Zochowski M. Binaural Processing Deficits Due to Synaptopathy and Myelin Defects. Front Neural Circuits 2022; 16:856926. [PMID: 35498371 PMCID: PMC9050145 DOI: 10.3389/fncir.2022.856926] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2022] [Accepted: 03/23/2022] [Indexed: 11/13/2022] Open
Abstract
Hidden hearing loss (HHL) is a deficit in auditory perception and speech intelligibility that occurs despite normal audiometric thresholds and results from noise exposure, aging, or myelin defects. While mechanisms causing perceptual deficits in HHL patients are still unknown, results from animal models indicate a role for peripheral auditory neuropathies in HHL. In humans, sound localization is particularly important for comprehending speech, especially in noisy environments, and its disruption may contribute to HHL. In this study, we hypothesized that neuropathies of cochlear spiral ganglion neurons (SGNs) that are observed in animal models of HHL disrupt the activity of neurons in the medial superior olive (MSO), a nucleus in the brainstem responsible for locating low-frequency sound in the horizontal plane using binaural temporal cues, leading to sound localization deficits. To test our hypothesis, we constructed a network model of the auditory processing system that simulates peripheral responses to sound stimuli and propagation of responses via SGNs to cochlear nuclei and MSO populations. To simulate peripheral auditory neuropathies, we used a previously developed biophysical SGN model with myelin defects at SGN heminodes (myelinopathy) and with loss of inner hair cell-SGN synapses (synaptopathy). Model results indicate that myelinopathy and synaptopathy in SGNs give rise to decreased interaural time difference (ITD) sensitivity of MSO cells, suggesting a possible mechanism for perceptual deficits in HHL patients. This model may be useful to understand downstream impacts of SGN-mediated disruptions on auditory processing and to eventually discover possible treatments for various mechanisms of HHL.
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Affiliation(s)
- Maral Budak
- Biophysics Program, University of Michigan, Ann Arbor, MI, United States
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI, United States
| | - Michael T. Roberts
- Department of Otolaryngology Head and Neck Surgery, University of Michigan, Ann Arbor, MI, United States
- Kresge Hearing Research Institute, University of Michigan, Ann Arbor, MI, United States
| | - Karl Grosh
- Kresge Hearing Research Institute, University of Michigan, Ann Arbor, MI, United States
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, United States
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States
| | - Gabriel Corfas
- Department of Otolaryngology Head and Neck Surgery, University of Michigan, Ann Arbor, MI, United States
- Kresge Hearing Research Institute, University of Michigan, Ann Arbor, MI, United States
- *Correspondence: Gabriel Corfas,
| | - Victoria Booth
- Department of Mathematics and Anesthesiology, University of Michigan, Ann Arbor, MI, United States
- Victoria Booth,
| | - Michal Zochowski
- Biophysics Program, University of Michigan, Ann Arbor, MI, United States
- Department of Physics, University of Michigan, Ann Arbor, MI, United States
- Michal Zochowski,
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Goupell MJ, Best V, Colburn HS. Intracranial lateralization bias observed in the presence of symmetrical hearing thresholds. JASA EXPRESS LETTERS 2021; 1:104401. [PMID: 34708221 PMCID: PMC8521647 DOI: 10.1121/10.0006720] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/11/2021] [Accepted: 09/20/2021] [Indexed: 06/13/2023]
Abstract
It is generally assumed that listeners with normal audiograms have relatively symmetric hearing, and more specifically that diotic stimuli (having zero interaural differences) are heard as centered in the head. While measuring intracranial lateralization with a visual pointing task for tones and 50-Hz-wide narrowband noises from 300 to 700 Hz, examples of systematic and large (>50% from midline to the ear) lateralization biases were found. In a group of ten listeners, five showed consistent lateralization bias to the right or left side at all or a subset of frequencies. Asymmetries in hearing, not apparent in audiometric thresholds, may explain these lateralization biases.
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Affiliation(s)
- Matthew J Goupell
- Department of Biomedical Engineering, Boston University, Boston, Massachusetts 02215, USA
| | - Virginia Best
- Department of Speech, Language, and Hearing Sciences, Boston University, Boston, Massachusetts 02215, USA , ,
| | - H Steven Colburn
- Department of Biomedical Engineering, Boston University, Boston, Massachusetts 02215, USA
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14
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Correction: Contrasting mechanisms for hidden hearing loss: Synaptopathy vs myelin defects. PLoS Comput Biol 2021; 17:e1008910. [PMID: 33826606 PMCID: PMC8026032 DOI: 10.1371/journal.pcbi.1008910] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
[This corrects the article DOI: 10.1371/journal.pcbi.1008499.].
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Budak M, Grosh K, Sasmal A, Corfas G, Zochowski M, Booth V. Contrasting mechanisms for hidden hearing loss: Synaptopathy vs myelin defects. PLoS Comput Biol 2021; 17:e1008499. [PMID: 33481777 PMCID: PMC7857583 DOI: 10.1371/journal.pcbi.1008499] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2020] [Revised: 02/03/2021] [Accepted: 11/06/2020] [Indexed: 11/18/2022] Open
Abstract
Hidden hearing loss (HHL) is an auditory neuropathy characterized by normal hearing thresholds but reduced amplitudes of the sound-evoked auditory nerve compound action potential (CAP). In animal models, HHL can be caused by moderate noise exposure or aging, which induces loss of inner hair cell (IHC) synapses. In contrast, recent evidence has shown that transient loss of cochlear Schwann cells also causes permanent auditory deficits in mice with similarities to HHL. Histological analysis of the cochlea after auditory nerve remyelination showed a permanent disruption of the myelination patterns at the heminode of type I spiral ganglion neuron (SGN) peripheral terminals, suggesting that this defect could be contributing to HHL. To shed light on the mechanisms of different HHL scenarios observed in animals and to test their impact on type I SGN activity, we constructed a reduced biophysical model for a population of SGN peripheral axons whose activity is driven by a well-accepted model of cochlear sound processing. We found that the amplitudes of simulated sound-evoked SGN CAPs are lower and have greater latencies when heminodes are disorganized, i.e. they occur at different distances from the hair cell rather than at the same distance as in the normal cochlea. These results confirm that disruption of heminode positions causes desynchronization of SGN spikes leading to a loss of temporal resolution and reduction of the sound-evoked SGN CAP. Another mechanism resulting in HHL is loss of IHC synapses, i.e., synaptopathy. For comparison, we simulated synaptopathy by removing high threshold IHC-SGN synapses and found that the amplitude of simulated sound-evoked SGN CAPs decreases while latencies remain unchanged, as has been observed in noise exposed animals. Thus, model results illuminate diverse disruptions caused by synaptopathy and demyelination on neural activity in auditory processing that contribute to HHL as observed in animal models and that can contribute to perceptual deficits induced by nerve damage in humans.
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Affiliation(s)
- Maral Budak
- Biophysics Program, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Karl Grosh
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States of America
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan, United States of America
- Kresge Hearing Research Institute, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Aritra Sasmal
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Gabriel Corfas
- Kresge Hearing Research Institute, University of Michigan, Ann Arbor, Michigan, United States of America
- Department of Otolaryngology Head and Neck Surgery, University of Michigan, Ann Arbor, Michigan, United States of America
- * E-mail: (GC); (MZ); (VB)
| | - Michal Zochowski
- Biophysics Program, University of Michigan, Ann Arbor, Michigan, United States of America
- Department of Physics, University of Michigan, Ann Arbor, Michigan, United States of America
- * E-mail: (GC); (MZ); (VB)
| | - Victoria Booth
- Departments of Mathematics & Anesthesiology, University of Michigan, Ann Arbor, Michigan, United States of America
- * E-mail: (GC); (MZ); (VB)
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