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De-la-Torre P, Martínez-García C, Gratias P, Mun M, Santana P, Akyuz N, González W, Indzhykulian AA, Ramírez D. Identification of Druggable Binding Sites and Small Molecules as Modulators of TMC1. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.03.05.583611. [PMID: 38826329 PMCID: PMC11142246 DOI: 10.1101/2024.03.05.583611] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2024]
Abstract
Our ability to hear and maintain balance relies on the proper functioning of inner ear sensory hair cells, which translate mechanical stimuli into electrical signals via mechano-electrical transducer (MET) channels, composed of TMC1/2 proteins. However, the therapeutic use of ototoxic drugs, such as aminoglycosides and cisplatin, which can enter hair cells through MET channels, often leads to profound auditory and vestibular dysfunction. Despite extensive research on otoprotective compounds targeting MET channels, our understanding of how small molecule modulators interact with these channels remains limited, hampering the discovery of novel compounds. Here, we propose a structure-based screening approach, integrating 3D-pharmacophore modeling, molecular simulations, and experimental validation. Our pipeline successfully identified several novel compounds and FDA-approved drugs that reduced dye uptake in cultured cochlear explants, indicating MET modulation activity. Molecular docking and free-energy estimations for binding allowed us to identify three potential drug binding sites within the channel pore, phospholipids, and key amino acids involved in modulator interactions. We also identified shared ligand-binding features between TMC and structurally related TMEM16 protein families, providing novel insights into their distinct inhibition, while potentially guiding the rational design of MET-channel-specific modulators. Our pipeline offers a broad application to discover small molecule modulators for a wide spectrum of mechanosensitive ion channels.
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Affiliation(s)
- Pedro De-la-Torre
- Department of Otolaryngology - Head and Neck Surgery, Harvard Medical School and Mass Eye and Ear, Boston, MA, USA
| | | | - Paul Gratias
- Department of Otolaryngology - Head and Neck Surgery, Harvard Medical School and Mass Eye and Ear, Boston, MA, USA
| | - Matthew Mun
- Department of Otolaryngology - Head and Neck Surgery, Harvard Medical School and Mass Eye and Ear, Boston, MA, USA
| | - Paula Santana
- Facultad de Ingeniería, Instituto de Ciencias Químicas Aplicadas, Universidad Autónoma de Chile, Santiago, Chile
| | - Nurunisa Akyuz
- Department of Neurobiology, Harvard Medical School, Boston, MA, USA
| | - Wendy González
- Center for Bioinformatics and Molecular Simulations (CBSM), University of Talca, Talca 3460000, Chile
| | - Artur A. Indzhykulian
- Department of Otolaryngology - Head and Neck Surgery, Harvard Medical School and Mass Eye and Ear, Boston, MA, USA
| | - David Ramírez
- Department of Pharmacology, Faculty of Biological Sciences, University of Concepción, Chile
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Bustad E, Mudrock E, Nilles EM, Mcquate A, Bergado M, Gu A, Galitan L, Gleason N, Ou HC, Raible DW, Hernandez RE, Ma S. In vivo screening for toxicity-modulating drug interactions identifies antagonism that protects against ototoxicity in zebrafish. Front Pharmacol 2024; 15:1363545. [PMID: 38515847 PMCID: PMC10955247 DOI: 10.3389/fphar.2024.1363545] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2023] [Accepted: 02/15/2024] [Indexed: 03/23/2024] Open
Abstract
Introduction: Ototoxicity is a debilitating side effect of over 150 medications with diverse mechanisms of action, many of which could be taken concurrently to treat multiple conditions. Approaches for preclinical evaluation of drug-drug interactions that might impact ototoxicity would facilitate design of safer multi-drug regimens and mitigate unsafe polypharmacy by flagging combinations that potentially cause adverse interactions for monitoring. They may also identify protective agents that antagonize ototoxic injury. Methods: To address this need, we have developed a novel workflow that we call Parallelized Evaluation of Protection and Injury for Toxicity Assessment (PEPITA), which empowers high-throughput, semi-automated quantification of ototoxicity and otoprotection in zebrafish larvae via microscopy. We used PEPITA and confocal microscopy to characterize in vivo the consequences of drug-drug interactions on ototoxic drug uptake and cellular damage of zebrafish lateral line hair cells. Results and discussion: By applying PEPITA to measure ototoxic drug interaction outcomes, we discovered antagonistic interactions between macrolide and aminoglycoside antibiotics that confer protection against aminoglycoside-induced damage to lateral line hair cells in zebrafish larvae. Co-administration of either azithromycin or erythromycin in zebrafish protected against damage from a broad panel of aminoglycosides, at least in part via inhibiting drug uptake into hair cells via a mechanism independent from hair cell mechanotransduction. Conversely, combining macrolides with aminoglycosides in bacterial inhibition assays does not show antagonism of antimicrobial efficacy. The proof-of-concept otoprotective antagonism suggests that combinatorial interventions can potentially be developed to protect against other forms of toxicity without hindering on-target drug efficacy.
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Affiliation(s)
- Ethan Bustad
- Center for Global Infectious Disease Research, Seattle Children’s Research Institute, Seattle, WA, United States
| | - Emma Mudrock
- Center for Global Infectious Disease Research, Seattle Children’s Research Institute, Seattle, WA, United States
| | - Elizabeth M. Nilles
- Center for Global Infectious Disease Research, Seattle Children’s Research Institute, Seattle, WA, United States
| | - Andrea Mcquate
- Department of Otolaryngology-HNS, University of Washington, Seattle, WA, United States
- Department of Biological Structure, University of Washington, Seattle, WA, United States
- Department of Biology, University of New Mexico, Albuquerque, NM, United States
| | - Monica Bergado
- Center for Global Infectious Disease Research, Seattle Children’s Research Institute, Seattle, WA, United States
| | - Alden Gu
- Center for Global Infectious Disease Research, Seattle Children’s Research Institute, Seattle, WA, United States
| | - Louie Galitan
- Center for Global Infectious Disease Research, Seattle Children’s Research Institute, Seattle, WA, United States
| | - Natalie Gleason
- Center for Global Infectious Disease Research, Seattle Children’s Research Institute, Seattle, WA, United States
| | - Henry C. Ou
- Department of Otolaryngology-HNS, University of Washington, Seattle, WA, United States
- Department of Pediatrics, Seattle Children’s Hospital, Seattle, WA, United States
| | - David W. Raible
- Department of Otolaryngology-HNS, University of Washington, Seattle, WA, United States
- Department of Biological Structure, University of Washington, Seattle, WA, United States
- VM Bloedel Hearing Research Center, University of Washington, Seattle, WA, United States
| | - Rafael E. Hernandez
- Center for Global Infectious Disease Research, Seattle Children’s Research Institute, Seattle, WA, United States
- Department of Pediatrics, University of Washington, Seattle, WA, United States
| | - Shuyi Ma
- Center for Global Infectious Disease Research, Seattle Children’s Research Institute, Seattle, WA, United States
- Department of Pediatrics, University of Washington, Seattle, WA, United States
- Department of Chemical Engineering, University of Washington, Seattle, WA, United States
- Pathobiology Graduate Program, Department of Global Health, University of Washington, Seattle, WA, United States
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Hsieh CY, Tsai CY, Chou YF, Hsu CJ, Wu HP, Wu CC. Otoprotection against aminoglycoside- and cisplatin-induced ototoxicity focusing on the upstream drug uptake pathway. J Chin Med Assoc 2024; 87:17-24. [PMID: 37962398 DOI: 10.1097/jcma.0000000000001023] [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] [Indexed: 11/15/2023] Open
Abstract
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.
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Affiliation(s)
- Cheng-Yu Hsieh
- Department of Otolaryngology Head and Neck Surgery, Taichung Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, Taichung, Taiwan, ROC
- Institute of Clinical Medicine, National Taiwan University College of Medicine, Taipei, Taiwan, ROC
| | - Cheng-Yu Tsai
- Graduate Institute of Medical Genomics and Proteomics, National Taiwan University College of Medicine, Taipei, Taiwan, ROC
- Department of Otolaryngology, National Taiwan University Hospital, Taipei, Taiwan, ROC
| | - Yi-Fan Chou
- Department of Otolaryngology Head and Neck Surgery, Taichung Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, Taichung, Taiwan, ROC
- School of Medicine, Tzu Chi University, Hualien, Taiwan, ROC
| | - Chuan-Jen Hsu
- Department of Otolaryngology Head and Neck Surgery, Taichung Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, Taichung, Taiwan, ROC
- Department of Otolaryngology, National Taiwan University Hospital, Taipei, Taiwan, ROC
| | - Hung-Pin Wu
- Department of Otolaryngology Head and Neck Surgery, Taichung Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, Taichung, Taiwan, ROC
- School of Medicine, Tzu Chi University, Hualien, Taiwan, ROC
| | - Chen-Chi Wu
- Department of Otolaryngology, National Taiwan University Hospital, Taipei, Taiwan, ROC
- Graduate Institute of Clinical Medicine, National Taiwan University College of Medicine, Taipei, Taiwan, ROC
- Department of Medical Research, National Taiwan University Hospital Hsin-Chu Branch, Hsinchu, Taiwan, ROC
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Villarino NW, Hamed YMF, Ghosh B, Dubin AE, Lewis AH, Odem MA, Loud MC, Wang Y, Servin-Vences MR, Patapoutian A, Marshall KL. Labeling PIEZO2 activity in the peripheral nervous system. Neuron 2023; 111:2488-2501.e8. [PMID: 37321223 PMCID: PMC10527906 DOI: 10.1016/j.neuron.2023.05.015] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2022] [Revised: 03/24/2023] [Accepted: 05/17/2023] [Indexed: 06/17/2023]
Abstract
Sensory neurons detect mechanical forces from both the environment and internal organs to regulate physiology. PIEZO2 is a mechanosensory ion channel critical for touch, proprioception, and bladder stretch sensation, yet its broad expression in sensory neurons suggests it has undiscovered physiological roles. To fully understand mechanosensory physiology, we must know where and when PIEZO2-expressing neurons detect force. The fluorescent styryl dye FM 1-43 was previously shown to label sensory neurons. Surprisingly, we find that the vast majority of FM 1-43 somatosensory neuron labeling in mice in vivo is dependent on PIEZO2 activity within the peripheral nerve endings. We illustrate the potential of FM 1-43 by using it to identify novel PIEZO2-expressing urethral neurons that are engaged by urination. These data reveal that FM 1-43 is a functional probe for mechanosensitivity via PIEZO2 activation in vivo and will facilitate the characterization of known and novel mechanosensory processes in multiple organ systems.
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Affiliation(s)
- Nicholas W Villarino
- Department of Neuroscience, Dorris Neuroscience Center, The Scripps Research Institute, La Jolla, CA 92037, USA; Howard Hughes Medical Institute, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Yasmeen M F Hamed
- Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA; Graduate Program in Development, Disease Models, and Therapeutics, Baylor College of Medicine, Houston, TX 77030
| | - Britya Ghosh
- Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA
| | - Adrienne E Dubin
- Department of Neuroscience, Dorris Neuroscience Center, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Amanda H Lewis
- Department of Neurobiology, Duke University Medical Center, Durham, NC 27710, USA
| | - Max A Odem
- Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA
| | - Meaghan C Loud
- Department of Neuroscience, Dorris Neuroscience Center, The Scripps Research Institute, La Jolla, CA 92037, USA; Howard Hughes Medical Institute, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Yu Wang
- Department of Neuroscience, Dorris Neuroscience Center, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - M Rocio Servin-Vences
- Department of Neuroscience, Dorris Neuroscience Center, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Ardem Patapoutian
- Department of Neuroscience, Dorris Neuroscience Center, The Scripps Research Institute, La Jolla, CA 92037, USA; Howard Hughes Medical Institute, The Scripps Research Institute, La Jolla, CA 92037, USA.
| | - Kara L Marshall
- Department of Neuroscience, Dorris Neuroscience Center, The Scripps Research Institute, La Jolla, CA 92037, USA; Howard Hughes Medical Institute, The Scripps Research Institute, La Jolla, CA 92037, USA; Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030, USA; Jan and Dan Duncan Neurological Research Institute at Texas Children's Hospital, Houston, TX 77030, USA.
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Cheng HL, Lee SC, Chang-Chien J, Su TR, Yang JJ, Su CC. Protective mechanism of ferulic acid against neomycin-induced ototoxicity in zebrafish. ENVIRONMENTAL TOXICOLOGY 2023; 38:604-614. [PMID: 36367326 DOI: 10.1002/tox.23707] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2022] [Revised: 10/27/2022] [Accepted: 10/28/2022] [Indexed: 06/16/2023]
Abstract
Ototoxicity refers to damage of sensory hair cells and functional hearing impairment following aminoglycosides exposure. Previously, we have determined that ferulic acid (FA) protected hair cells against serial concentrations of neomycin-induced ototoxic damage. The aim of the present study is to assess the mechanism and effects of FA on neomycin-induced hair cells loss and impact on mechanosensory-mediated behaviors alteration using transgenic zebrafish (pvalb3b: TagGFP). We first identified the optimal protective condition as pre/co-treatment method in early fish development. Pretreatment of the larvae with FA significantly protected against neomycin-induced hair cells loss through preventing neomycin passed through the cytoplasm of hair cells, and subsequently decreased reactive oxygen species production and TUNEL signals in 4 day post-fertilization (dpf) transgenic zebrafish larvae. Moreover, preservation of functional hair cells correlated directly with rescue of the altered swimming behavior, indicates FA pretreatment protects against neomycin ototoxic damage in 7-dpf transgenic zebrafish larvae. Together, our findings unravel the otoprotective role of FA as an effective agent against neomycin-induced ototoxic effects and offering the theoretical foundation for discovering novel candidates for hearing protection.
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Affiliation(s)
- Hsin-Lin Cheng
- Department of Biomedical Sciences, Chung Shan Medical University, Taichung, Taiwan
- Department of Medical Research, Chung Shan Medical University Hospital, Taichung, Taiwan
| | - Shan-Chih Lee
- Department of Medical Research, Chung Shan Medical University Hospital, Taichung, Taiwan
- Department of Medical Imaging and Radiological Sciences, Chung Shan Medical University, Taichung, Taiwan
| | - Ju Chang-Chien
- Department of Biomedical Sciences, Chung Shan Medical University, Taichung, Taiwan
| | - Tzu-Rong Su
- Dean chamber, Antai Medical Care Corporation Antai Tian-Sheng Memorial Hospital, Pingtung, Taiwan
- Department of Beauty Science, Meiho University, Pingtung, Taiwan
| | - Jiann-Jou Yang
- Department of Biomedical Sciences, Chung Shan Medical University, Taichung, Taiwan
- Department of Medical Research, Chung Shan Medical University Hospital, Taichung, Taiwan
| | - Ching-Chyuan Su
- Dean chamber, Antai Medical Care Corporation Antai Tian-Sheng Memorial Hospital, Pingtung, Taiwan
- Department of Beauty Science, Meiho University, Pingtung, Taiwan
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Ballesteros A, Swartz KJ. Regulation of membrane homeostasis by TMC1 mechanoelectrical transduction channels is essential for hearing. SCIENCE ADVANCES 2022; 8:eabm5550. [PMID: 35921424 PMCID: PMC9348795 DOI: 10.1126/sciadv.abm5550] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
The mechanoelectrical transduction (MET) channel in auditory hair cells converts sound into electrical signals, enabling hearing. Transmembrane-like channel 1 and 2 (TMC1 and TMC2) are implicated in forming the pore of the MET channel. Here, we demonstrate that inhibition of MET channels, breakage of the tip links required for MET, or buffering of intracellular Ca... induces pronounced phosphatidylserine externalization, membrane blebbing, and ectosome release at the hair cell sensory organelle, culminating in the loss of TMC1. Membrane homeostasis triggered by MET channel inhibition requires Tmc1 but not Tmc2, and three deafness-causing mutations in Tmc1 cause constitutive phosphatidylserine externalization that correlates with deafness phenotype. Our results suggest that, in addition to forming the pore of the MET channel, TMC1 is a critical regulator of membrane homeostasis in hair cells, and that Tmc1-related hearing loss may involve alterations in membrane homeostasis.
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Ramkumar V, Sheth S, Dhukhwa A, Al Aameri R, Rybak L, Mukherjea D. Transient Receptor Potential Channels and Auditory Functions. Antioxid Redox Signal 2022; 36:1158-1170. [PMID: 34465184 PMCID: PMC9221156 DOI: 10.1089/ars.2021.0191] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
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.
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Affiliation(s)
- Vickram Ramkumar
- Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, Illinois, USA
| | - Sandeep Sheth
- Department of Pharmaceutical Sciences, Larkin University College of Pharmacy, Miami, Florida, USA
| | - Asmita Dhukhwa
- Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, Illinois, USA
| | - Raheem Al Aameri
- Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, Illinois, USA
| | - Leonard Rybak
- Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, Illinois, USA.,Department of Otolaryngology, Southern Illinois University School of Medicine, Springfield, Illinois, USA
| | - Debashree Mukherjea
- Department of Otolaryngology, Southern Illinois University School of Medicine, Springfield, Illinois, USA
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Kim J, Hemachandran S, Cheng AG, Ricci AJ. Identifying targets to prevent aminoglycoside ototoxicity. Mol Cell Neurosci 2022; 120:103722. [PMID: 35341941 PMCID: PMC9177639 DOI: 10.1016/j.mcn.2022.103722] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2021] [Revised: 03/14/2022] [Accepted: 03/19/2022] [Indexed: 12/21/2022] Open
Abstract
Aminoglycosides are potent antibiotics that are commonly prescribed worldwide. Their use carries significant risks of ototoxicity by directly causing inner ear hair cell degeneration. Despite their ototoxic side effects, there are currently no approved antidotes. Here we review recent advances in our understanding of aminoglycoside ototoxicity, mechanisms of drug transport, and promising sites for intervention to prevent ototoxicity.
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Affiliation(s)
- Jinkyung Kim
- Department of Otolaryngology-Head and Neck Surgery, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Sriram Hemachandran
- Department of Otolaryngology-Head and Neck Surgery, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Alan G Cheng
- Department of Otolaryngology-Head and Neck Surgery, Stanford University School of Medicine, Stanford, CA 94305, USA.
| | - Anthony J Ricci
- Department of Otolaryngology-Head and Neck Surgery, Stanford University School of Medicine, Stanford, CA 94305, USA; Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA.
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Hu Z, Komal F, Singh A, Deng M. Generation of a Spiral Ganglion Neuron Degeneration Mouse Model. Front Cell Dev Biol 2021; 9:761847. [PMID: 34778272 PMCID: PMC8578993 DOI: 10.3389/fcell.2021.761847] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2021] [Accepted: 09/29/2021] [Indexed: 11/27/2022] Open
Abstract
Spiral ganglion neurons (SGNs) can be injured by a wide variety of insults. However, there still is a lack of degeneration models to specifically damage the SGNs without disturbing other types of cells in the inner ear. This study aims to generate an SGN-specific damage model using the Cre-LoxP transgenic mouse strains. The Cre-inducible diphtheria toxin receptor (iDTR+/+) knock-in mouse strain was crossed with a mouse strain with Cre activity specific to neurons (NeflCreER/CreER). Expression of the Cre-recombinase activity was evaluated using the reporter mouse strain Ai9 at pre-hearing, hearing onset, and post-hearing stages. Accordingly, heterozygous NeflCreER/+;iDTR+/– mice were treated with tamoxifen on postnatal days 1–5 (P1–5), followed by diphtheria toxin (DT) or vehicle injection on P7, P14, and P21 to evaluate the SGN loss. Robust tamoxifen-induced Cre-mediated Ai9 tdTomato fluorescence was observed in the SGN area of heterozygous NeflCreER/+;Ai9+/– mice treated with tamoxifen, whereas vehicle-treated heterozygote mice did not show tdTomato fluorescence. Compared to vehicle-treated NeflCreER/+;iDTR+/– mice, DT-treated NeflCreER/+;iDTR+/– mice showed significant auditory brainstem response (ABR) threshold shifts and SGN cell loss. Hair cell count and functional study did not show significant changes. These results demonstrate that the NeflCreER/CreER mouse strain exhibits inducible SGN-specific Cre activity in the inner ear, which may serve as a valuable SGN damage model for regeneration research of the inner ear.
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Affiliation(s)
- Zhengqing Hu
- John D. Dingell VA Medical Center, Detroit, MI, United States.,Department of Otolaryngology-HNS, Wayne State University School of Medicine, Detroit, MI, United States
| | - Fnu Komal
- Department of Otolaryngology-HNS, Wayne State University School of Medicine, Detroit, MI, United States
| | - Aditi Singh
- Department of Otolaryngology-HNS, Wayne State University School of Medicine, Detroit, MI, United States
| | - Meng Deng
- Department of Otolaryngology-HNS, Wayne State University School of Medicine, Detroit, MI, United States
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Does Calcium Dobesilate Have Therapeutic Effect on Gentamicin-induced Cochlear Nerve Ototoxicity? An Experimental Study. Otol Neurotol 2020; 41:e1185-e1192. [PMID: 32976341 DOI: 10.1097/mao.0000000000002820] [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
HYPOTHESIS The ototoxic effects of aminoglycosides are well known. Gentamicin carries a substantial risk of hearing loss. Gentamicin is widely used to combat life-threatening infections, despite its ototoxic effects. Calcium dobesilate is a pharmacologically active agent used to treat many disorders due to its vasoprotective and antioxidant effects. We investigated the therapeutic role of calcium dobesilate against gentamicin-induced cochlear nerve ototoxicity in an animal model. METHODS Thirty-two Sprague Dawley rats were divided into four groups: Gentamicin, Gentamicin + Calcium Dobesilate, Calcium Dobesilate, and Control. Preoperative and postoperative hearing thresholds were determined using auditory brainstem response thresholds with click and 16-kHz tone-burst stimuli. Histological analysis of the tympanic bulla specimens was performed under light and transmission electron microscopy. The histological findings were subjected to semiquantitative grading, of which the results were compared between the groups. RESULTS Gentamicin + Calcium Dobesilate group had, on average, 27 dB better click-evoked hearing than Gentamicin group (p < 0.01), whereas the difference was not significant with 16-kHz tone-burst stimuli (p > 0.01). Histologically examining the Control and Calcium Dobesilate groups revealed normal ultrastructural appearances. The Gentamicin group showed the most severe histological alterations including myelin destruction, total axonal degeneration, and edema. The histological evidence of damage was significantly reduced in the Gentamicin + Calcium Dobesilate group compared with the Gentamicin group. CONCLUSION Adding oral calcium dobesilate to systemic gentamicin was demonstrated to exert beneficial effects on click-evoked hearing thresholds, as supported by the histological findings.
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Hudson AM, Lockard GM, Namjoshi OA, Wilson JW, Kindt KS, Blough BE, Coffin AB. Berbamine Analogs Exhibit Differential Protective Effects From Aminoglycoside-Induced Hair Cell Death. Front Cell Neurosci 2020; 14:234. [PMID: 32848624 PMCID: PMC7403526 DOI: 10.3389/fncel.2020.00234] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2020] [Accepted: 07/02/2020] [Indexed: 12/17/2022] Open
Abstract
Hearing loss is the third most common chronic health condition in the United States and largely results from damage to sensory hair cells. Major causes of hair cell damage include aging, noise exposure, and medications such as aminoglycoside antibiotics. Due to their potent antibacterial properties and low cost, aminoglycosides are often used for the treatment of gram-negative bacterial infections, surpassing expensive antibiotics with fewer harmful side effects. However, their use is coupled with permanent hearing loss in over 20% of patients requiring these life-sustaining antibiotics. There are currently no FDA-approved drugs that prevent hearing loss from aminoglycosides. A previous study by our group identified the plant alkaloid berbamine as a strong protectant of zebrafish lateral line hair cells from aminoglycoside damage. This effect is likely due to a block of the mechanotransduction channel, thereby reducing aminoglycoside entry into hair cells. The present study builds on this previous work, investigating 16 synthetic berbamine analogs to determine the core structure underlying their protective mechanisms. We demonstrate that nearly all of these berbamine analogs robustly protect lateral line hair cells from ototoxic damage, with ED50 values nearing 20 nM for the most potent analogs. Of the 16 analogs tested, nine strongly protected hair cells from both neomycin and gentamicin damage, while one conferred strong protection only from gentamicin. These data are consistent with prior research demonstrating that different aminoglycosides activate somewhat distinct mechanisms of damage. Regardless of the mechanism, protection required the entire berbamine scaffold. Phenolic alkylation or acylation with lipophilic groups appeared to improve protection compared to berbamine, implying that these structures may be responsible for mitigating damage. While the majority of analogs confer protection by blocking aminoglycoside uptake, 18% of our analogs also confer protection via an uptake-independent mechanism; these analogs exhibited protection when delivered after aminoglycoside removal. Based on our studies, berbamine analogs represent a promising tool to further understand the pathology of aminoglycoside-induced hearing loss and can serve as lead compounds to develop otoprotective drugs.
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Affiliation(s)
- Alexandria M Hudson
- Integrative Physiology and Neuroscience, Washington State University, Vancouver, WA, United States
| | - Gavin M Lockard
- College of Arts and Sciences, Washington State University, Vancouver, WA, United States
| | - Ojas A Namjoshi
- RTI International, Research Triangle Park, NC, United States
| | - Joseph W Wilson
- RTI International, Research Triangle Park, NC, United States
| | - Katie S Kindt
- National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, United States
| | - Bruce E Blough
- RTI International, Research Triangle Park, NC, United States
| | - Allison B Coffin
- Integrative Physiology and Neuroscience, Washington State University, Vancouver, WA, United States.,College of Arts and Sciences, Washington State University, Vancouver, WA, United States
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12
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Majumder P, Blacker TS, Nolan LS, Duchen MR, Gale JE. Multiphoton NAD(P)H FLIM reveals metabolic changes in individual cell types of the intact cochlea upon sensorineural hearing loss. Sci Rep 2019; 9:18907. [PMID: 31827194 PMCID: PMC6906381 DOI: 10.1038/s41598-019-55329-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2019] [Accepted: 11/27/2019] [Indexed: 12/17/2022] Open
Abstract
An increasing volume of data suggests that changes in cellular metabolism have a major impact on the health of tissues and organs, including in the auditory system where metabolic alterations are implicated in both age-related and noise-induced hearing loss. However, the difficulty of access and the complex cyto-architecture of the organ of Corti has made interrogating the individual metabolic states of the diverse cell types present a major challenge. Multiphoton fluorescence lifetime imaging microscopy (FLIM) allows label-free measurements of the biochemical status of the intrinsically fluorescent metabolic cofactors NADH and NADPH with subcellular spatial resolution. However, the interpretation of NAD(P)H FLIM measurements in terms of the metabolic state of the sample are not completely understood. We have used this technique to explore changes in metabolism associated with hearing onset and with acquired (age-related and noise-induced) hearing loss. We show that these conditions are associated with altered NAD(P)H fluorescence lifetimes, use a simple cell model to confirm an inverse relationship between τbound and oxidative stress, and propose such changes as a potential index of oxidative stress applicable to all mammalian cell types.
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Affiliation(s)
- Paromita Majumder
- UCL Ear Institute, University College London, Grays Inn Road, London, WC1X 8EE, UK.
| | - Thomas S Blacker
- Research Department of Cell & Developmental Biology, University College London, Gower Street, London, WC1E 6BT, UK. .,Department of Physics & Astronomy, University College London, Gower Street, London, WC1E 6BT, UK. .,Centre for Mathematics and Physics in the Life Sciences and Experimental Biology, University College London, Gower Street, London, WC1E 6BT, UK.
| | - Lisa S Nolan
- UCL Ear Institute, University College London, Grays Inn Road, London, WC1X 8EE, UK
| | - Michael R Duchen
- Research Department of Cell & Developmental Biology, University College London, Gower Street, London, WC1E 6BT, UK
| | - Jonathan E Gale
- UCL Ear Institute, University College London, Grays Inn Road, London, WC1X 8EE, UK.,Research Department of Cell & Developmental Biology, University College London, Gower Street, London, WC1E 6BT, UK
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13
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Kros CJ, Steyger PS. Aminoglycoside- and Cisplatin-Induced Ototoxicity: Mechanisms and Otoprotective Strategies. Cold Spring Harb Perspect Med 2019; 9:cshperspect.a033548. [PMID: 30559254 DOI: 10.1101/cshperspect.a033548] [Citation(s) in RCA: 98] [Impact Index Per Article: 19.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
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.
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Affiliation(s)
- Corné J Kros
- Sussex Neuroscience, School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QG, United Kingdom
| | - Peter S Steyger
- Oregon Hearing Research Center, Oregon Health & Science University, Portland, Oregon 97239.,National Center for Rehabilitative Auditory Research, VA Portland Health Care System, Portland, Oregon 97239
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14
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Kitcher SR, Kirkwood NK, Camci ED, Wu P, Gibson RM, Redila VA, Simon JA, Rubel EW, Raible DW, Richardson GP, Kros CJ. ORC-13661 protects sensory hair cells from aminoglycoside and cisplatin ototoxicity. JCI Insight 2019; 4:126764. [PMID: 31391343 PMCID: PMC6693895 DOI: 10.1172/jci.insight.126764] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2018] [Accepted: 07/09/2019] [Indexed: 12/14/2022] Open
Abstract
Aminoglycoside (AG) antibiotics are widely used to prevent life-threatening infections, and cisplatin is used in the treatment of various cancers, but both are ototoxic and result in loss of sensory hair cells from the inner ear. ORC-13661 is a new drug that was derived from PROTO-1, a compound first identified as protective in a large-scale screen utilizing hair cells in the lateral line organs of zebrafish larvae. Here, we demonstrate, in zebrafish larvae and in mouse cochlear cultures, that ORC-13661 provides robust protection of hair cells against both ototoxins, the AGs and cisplatin. ORC-13661 also prevents both hearing loss in a dose-dependent manner in rats treated with amikacin and the loading of neomycin-Texas Red into lateral line hair cells. In addition, patch-clamp recordings in mouse cochlear cultures reveal that ORC-13661 is a high-affinity permeant blocker of the mechanoelectrical transducer (MET) channel in outer hair cells, suggesting that it may reduce the toxicity of AGs by directly competing for entry at the level of the MET channel and of cisplatin by a MET-dependent mechanism. ORC-13661 is therefore a promising and versatile protectant that reversibly blocks the hair cell MET channel and operates across multiple species and toxins. Candidate drug ORC-13661 robustly protects against ototoxicity by aminoglycoside antibiotics and cisplatin by reversibly blocking mechanotransduction of sensory hair cells.
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Affiliation(s)
- Siân R Kitcher
- Sussex Neuroscience, School of Life Sciences, University of Sussex, Brighton, United Kingdom
| | - Nerissa K Kirkwood
- Sussex Neuroscience, School of Life Sciences, University of Sussex, Brighton, United Kingdom
| | - Esra D Camci
- Virginia Merrill Bloedel Hearing Research Center, University of Washington, Seattle, Washington, USA
| | - Patricia Wu
- Virginia Merrill Bloedel Hearing Research Center, University of Washington, Seattle, Washington, USA.,Department of Biological Structure, University of Washington, Seattle, Washington, USA
| | - Robin M Gibson
- Virginia Merrill Bloedel Hearing Research Center, University of Washington, Seattle, Washington, USA
| | - Van A Redila
- Virginia Merrill Bloedel Hearing Research Center, University of Washington, Seattle, Washington, USA
| | - Julian A Simon
- Fred Hutchinson Cancer Research Center, Seattle, Washington, USA
| | - Edwin W Rubel
- Virginia Merrill Bloedel Hearing Research Center, University of Washington, Seattle, Washington, USA
| | - David W Raible
- Virginia Merrill Bloedel Hearing Research Center, University of Washington, Seattle, Washington, USA.,Department of Biological Structure, University of Washington, Seattle, Washington, USA
| | - Guy P Richardson
- Sussex Neuroscience, School of Life Sciences, University of Sussex, Brighton, United Kingdom
| | - Corné J Kros
- Sussex Neuroscience, School of Life Sciences, University of Sussex, Brighton, United Kingdom
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15
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O'Reilly M, Kirkwood NK, Kenyon EJ, Huckvale R, Cantillon DM, Waddell SJ, Ward SE, Richardson GP, Kros CJ, Derudas M. Design, Synthesis, and Biological Evaluation of a New Series of Carvedilol Derivatives That Protect Sensory Hair Cells from Aminoglycoside-Induced Damage by Blocking the Mechanoelectrical Transducer Channel. J Med Chem 2019; 62:5312-5329. [PMID: 31083995 DOI: 10.1021/acs.jmedchem.8b01325] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Aminoglycosides (AGs) are broad-spectrum antibiotics used for the treatment of serious bacterial infections but have use-limiting side effects including irreversible hearing loss. Here, we assessed the otoprotective profile of carvedilol in mouse cochlear cultures and in vivo zebrafish assays and investigated its mechanism of protection which, we found, may be mediated by a block of the hair cell's mechanoelectrical transducer (MET) channel, the major entry route for the AGs. To understand the full otoprotective potential of carvedilol, a series of 18 analogues were prepared and evaluated for their effect against AG-induced damage as well as their affinity for the MET channel. One derivative was found to confer greater protection than carvedilol itself in cochlear cultures and also to bind more tightly to the MET channel. At higher concentrations, both carvedilol and this derivative were toxic in cochlear cultures but not in zebrafish, suggesting a good therapeutic window under in vivo conditions.
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Affiliation(s)
| | | | | | | | - Daire M Cantillon
- Wellcome Trust Centre for Global Health Research, Brighton and Sussex Medical School , University of Sussex , Falmer , Brighton BN1 9PX , U.K
| | - Simon J Waddell
- Wellcome Trust Centre for Global Health Research, Brighton and Sussex Medical School , University of Sussex , Falmer , Brighton BN1 9PX , U.K
| | - Simon E Ward
- Medicines Discovery Institute , Cardiff University , Park Place , Cardiff CF10 3AT , U.K
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16
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Kenyon EJ, Kirkwood NK, Kitcher SR, O'Reilly M, Derudas M, Cantillon DM, Goodyear RJ, Secker A, Baxendale S, Bull JC, Waddell SJ, Whitfield TT, Ward SE, Kros CJ, Richardson GP. Identification of ion-channel modulators that protect against aminoglycoside-induced hair cell death. JCI Insight 2017; 2:96773. [PMID: 29263311 DOI: 10.1172/jci.insight.96773] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Accepted: 11/15/2017] [Indexed: 12/22/2022] Open
Abstract
Aminoglycoside antibiotics are used to treat life-threatening bacterial infections but can cause deafness due to hair cell death in the inner ear. Compounds have been described that protect zebrafish lateral line hair cells from aminoglycosides, but few are effective in the cochlea. As the aminoglycosides interact with several ion channels, including the mechanoelectrical transducer (MET) channels by which they can enter hair cells, we screened 160 ion-channel modulators, seeking compounds that protect cochlear outer hair cells (OHCs) from aminoglycoside-induced death in vitro. Using zebrafish, 72 compounds were identified that either reduced loading of the MET-channel blocker FM 1-43FX, decreased Texas red-conjugated neomycin labeling, or reduced neomycin-induced hair cell death. After testing these 72 compounds, and 6 structurally similar compounds that failed in zebrafish, 13 were found that protected against gentamicin-induced death of OHCs in mouse cochlear cultures, 6 of which are permeant blockers of the hair cell MET channel. None of these compounds abrogated aminoglycoside antibacterial efficacy. By selecting those without adverse effects at high concentrations, 5 emerged as leads for developing pharmaceutical otoprotectants to alleviate an increasing clinical problem.
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Affiliation(s)
| | | | | | | | - Marco Derudas
- Sussex Drug Discovery Centre, School of Life Sciences, and
| | - Daire M Cantillon
- Wellcome Trust Centre for Global Health Research, Brighton and Sussex Medical School, University of Sussex, Brighton, United Kingdom
| | | | | | - Sarah Baxendale
- Bateson Centre and Department of Biomedical Science, University of Sheffield, Sheffield, United Kingdom
| | - James C Bull
- Department of Biosciences, College of Science, Swansea University, Swansea, United Kingdom
| | - Simon J Waddell
- Wellcome Trust Centre for Global Health Research, Brighton and Sussex Medical School, University of Sussex, Brighton, United Kingdom
| | - Tanya T Whitfield
- Bateson Centre and Department of Biomedical Science, University of Sheffield, Sheffield, United Kingdom
| | - Simon E Ward
- Sussex Drug Discovery Centre, School of Life Sciences, and.,Medicines Discovery Institute, Cardiff University, Cardiff, United Kingdom
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17
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Jiang M, Karasawa T, Steyger PS. Aminoglycoside-Induced Cochleotoxicity: A Review. Front Cell Neurosci 2017; 11:308. [PMID: 29062271 PMCID: PMC5640705 DOI: 10.3389/fncel.2017.00308] [Citation(s) in RCA: 163] [Impact Index Per Article: 23.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2017] [Accepted: 09/15/2017] [Indexed: 12/20/2022] Open
Abstract
Aminoglycoside antibiotics are used as prophylaxis, or urgent treatment, for many life-threatening bacterial infections, including tuberculosis, sepsis, respiratory infections in cystic fibrosis, complex urinary tract infections and endocarditis. Although aminoglycosides are clinically-essential antibiotics, the mechanisms underlying their selective toxicity to the kidney and inner ear continue to be unraveled despite more than 70 years of investigation. The following mechanisms each contribute to aminoglycoside-induced toxicity after systemic administration: (1) drug trafficking across endothelial and epithelial barrier layers; (2) sensory cell uptake of these drugs; and (3) disruption of intracellular physiological pathways. Specific factors can increase the risk of drug-induced toxicity, including sustained exposure to higher levels of ambient sound, and selected therapeutic agents such as loop diuretics and glycopeptides. Serious bacterial infections (requiring life-saving aminoglycoside treatment) induce systemic inflammatory responses that also potentiate the degree of ototoxicity and permanent hearing loss. We discuss prospective clinical strategies to protect auditory and vestibular function from aminoglycoside ototoxicity, including reduced cochlear or sensory cell uptake of aminoglycosides, and otoprotection by ameliorating intracellular cytotoxicity.
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Affiliation(s)
- Meiyan Jiang
- Oregon Hearing Research Center, Oregon Health & Science University, Portland, OR, United States
| | - Takatoshi Karasawa
- Oregon Hearing Research Center, Oregon Health & Science University, Portland, OR, United States
| | - Peter S Steyger
- Oregon Hearing Research Center, Oregon Health & Science University, Portland, OR, United States.,National Center for Rehabilitative Auditory Research, Portland VA Medical Center (VHA), Portland, OR, United States
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18
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Kirkwood NK, O'Reilly M, Derudas M, Kenyon EJ, Huckvale R, van Netten SM, Ward SE, Richardson GP, Kros CJ. d-Tubocurarine and Berbamine: Alkaloids That Are Permeant Blockers of the Hair Cell's Mechano-Electrical Transducer Channel and Protect from Aminoglycoside Toxicity. Front Cell Neurosci 2017; 11:262. [PMID: 28928635 PMCID: PMC5591855 DOI: 10.3389/fncel.2017.00262] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2017] [Accepted: 08/14/2017] [Indexed: 12/03/2022] Open
Abstract
Aminoglycoside antibiotics are widely used for the treatment of life-threatening bacterial infections, but cause permanent hearing loss in a substantial proportion of treated patients. The sensory hair cells of the inner ear are damaged following entry of these antibiotics via the mechano-electrical transducer (MET) channels located at the tips of the hair cell's stereocilia. d-Tubocurarine (dTC) is a MET channel blocker that reduces the loading of gentamicin-Texas Red (GTTR) into rat cochlear hair cells and protects them from gentamicin treatment. Berbamine is a structurally related alkaloid that reduces GTTR labeling of zebrafish lateral-line hair cells and protects them from aminoglycoside-induced cell death. Both compounds are thought to reduce aminoglycoside entry into hair cells through the MET channels. Here we show that dTC (≥6.25 μM) or berbamine (≥1.55 μM) protect zebrafish hair cells in vivo from neomycin (6.25 μM, 1 h). Protection of zebrafish hair cells against gentamicin (10 μM, 6 h) was provided by ≥25 μM dTC or ≥12.5 μM berbamine. Hair cells in mouse cochlear cultures are protected from longer-term exposure to gentamicin (5 μM, 48 h) by 20 μM berbamine or 25 μM dTC. Berbamine is, however, highly toxic to mouse cochlear hair cells at higher concentrations (≥30 μM) whilst dTC is not. The absence of toxicity in the zebrafish assays prompts caution in extrapolating results from zebrafish neuromasts to mammalian cochlear hair cells. MET current recordings from mouse outer hair cells (OHCs) show that both compounds are permeant open-channel blockers, rapidly and reversibly blocking the MET channel with half-blocking concentrations of 2.2 μM (dTC) and 2.8 μM (berbamine) in the presence of 1.3 mM Ca2+ at −104 mV. Berbamine, but not dTC, also blocks the hair cell's basolateral K+ current, IK,neo, and modeling studies indicate that berbamine permeates the MET channel more readily than dTC. These studies reveal key properties of MET-channel blockers required for the future design of successful otoprotectants.
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Affiliation(s)
- Nerissa K Kirkwood
- Sussex Neuroscience, School of Life Sciences, University of SussexBrighton, United Kingdom
| | - Molly O'Reilly
- Sussex Neuroscience, School of Life Sciences, University of SussexBrighton, United Kingdom
| | - Marco Derudas
- Sussex Drug Discovery Centre, School of Life Sciences, University of SussexBrighton, United Kingdom
| | - Emma J Kenyon
- Sussex Neuroscience, School of Life Sciences, University of SussexBrighton, United Kingdom
| | - Rosemary Huckvale
- Sussex Drug Discovery Centre, School of Life Sciences, University of SussexBrighton, United Kingdom
| | - Sietse M van Netten
- Institute of Artificial Intelligence and Cognitive Engineering, University of GroningenGroningen, Netherlands
| | - Simon E Ward
- Sussex Drug Discovery Centre, School of Life Sciences, University of SussexBrighton, United Kingdom
| | - Guy P Richardson
- Sussex Neuroscience, School of Life Sciences, University of SussexBrighton, United Kingdom
| | - Corné J Kros
- Sussex Neuroscience, School of Life Sciences, University of SussexBrighton, United Kingdom
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