Antioxidant Therapy against Oxidative Damage of the Inner Ear: Protection and Preconditioning

Searching for LINCS to Stress: Using Text Mining to Automate Reference Chemical Curation

Adaptive stress response pathways (SRPs) restore cellular homeostasis following perturbation but may activate terminal outcomes like apoptosis, autophagy, or cellular senescence if disruption exceeds critical thresholds. Because SRPs hold the key to vital cellular tipping points, they are targeted for therapeutic interventions and assessed as biomarkers of toxicity. Hence, we are developing a public database of chemicals that perturb SRPs to enable new data-driven tools to improve public health. Here, we report on the automated text-mining pipeline we used to build and curate the first version of this database. We started with 100 reference SRP chemicals gathered from published biomarker studies to bootstrap the database. Second, we used information retrieval to find co-occurrences of reference chemicals with SRP terms in PubMed abstracts and determined pairwise mutual information thresholds to filter biologically relevant relationships. Third, we applied these thresholds to find 1206 putative SRP perturbagens within thousands of substances in the Library of Integrated Network-Based Cellular Signatures (LINCS). To assign SRP activity to LINCS chemicals, domain experts had to manually review at least three publications for each of 1206 chemicals out of 181,805 total abstracts. To accomplish this efficiently, we implemented a machine learning approach to predict SRP classifications from texts to prioritize abstracts. In 5-fold cross-validation testing with a corpus derived from the 100 reference chemicals, artificial neural networks performed the best (F1-macro = 0.678) and prioritized 2479/181,805 abstracts for expert review, which resulted in 457 chemicals annotated with SRP activities. An independent analysis of enriched mechanisms of action and chemical use class supported the text-mined chemical associations (p < 0.05): heat shock inducers were linked with HSP90 and DNA damage inducers to topoisomerase inhibition. This database will enable novel applications of LINCS data to evaluate SRP activities and to further develop tools for biomedical information extraction from the literature.

A Consolidated Understanding of the Contribution of Redox Dysregulation in the Development of Hearing Impairment

The etiology of hearing impairment is multifactorial, with contributions from both genetic and environmental factors. Although genetic studies have yielded valuable insights into the development and function of the auditory system, the contribution of gene products and their interaction with alternate environmental factors for the maintenance and development of auditory function requires further elaboration. In this review, we provide an overview of the current knowledge on the role of redox dysregulation as the converging factor between genetic and environmental factor-dependent development of hearing loss, with a focus on understanding the interaction of oxidative stress with the physical components of the peripheral auditory system in auditory disfunction. The potential involvement of molecular factors linked to auditory function in driving redox imbalance is an important promoter of the development of hearing loss over time.

A single dose of AC102 restores hearing in a guinea pig model of noise-induced hearing loss to almost prenoise levels

Although sudden sensorineural hearing loss (SSNHL) is a serious condition, there are currently no approved drugs for its treatment. Nevertheless, there is a growing understanding that the cochlear pathologies that underlie SSNHL include apoptotic death of sensory outer hair cells (OHCs) as well as loss of ribbon synapses connecting sensory inner hair cells (IHCs) and neurites of the auditory nerve, designated synaptopathy. Noise-induced hearing loss (NIHL) is a common subtype of SSNHL and is widely used to model hearing loss preclinically. Here, we demonstrate that a single interventive application of a small pyridoindole molecule (AC102) into the middle ear restored auditory function almost to prenoise levels in a guinea pig model of NIHL. AC102 prevented noise-triggered loss of OHCs and reduced IHC synaptopathy suggesting a role of AC102 in reconnecting auditory neurons to their sensory target cells. Notably, AC102 exerted its therapeutic properties over a wide frequency range. Such strong improvements in hearing have not previously been demonstrated for other therapeutic agents. In vitro experiments of a neuronal damage model revealed that AC102 protected cells from apoptosis and promoted neurite growth. These effects may be explained by increased production of adenosine triphosphate, indicating improved mitochondrial function, and reduced levels of reactive-oxygen species which prevents the apoptotic processes responsible for OHC death. This action profile of AC102 might be causal for the observed hearing recovery in in vivo models.

Blood-Labyrinth Barrier in Health and Diseases: Effect of Hormetic Nutrients

Significance: The stria vascularis, located in the inner ear, consists of three layers, one of which is the blood-labyrinth barrier (BLB). It is formed by endothelial cells, sealed together to prevent the passage of toxic substances from the blood to the inner ear, by pericytes and perivascular-resident macrophage-like melanocyte. Recent Advances: There are various causes that lead to hearing loss, and among these are noise-induced and autoimmune hearing loss, ear disorders related to ototoxic medication, Ménière's disease, and age-related hearing loss. For all of these, major therapeutic interventions include drug-loaded nanoparticles, via intratympanic or intracochlear delivery. Critical Issues: Since many pathologies associated with hearing loss are characterized by a weakening of the BLB, in this review, the molecular mechanisms underlying the response to damage of BLB cellular components have been discussed. In addition, insight into the role of hormetic nutrients against hearing loss pathology is proposed. Future Directions: BLB cellular components of neurovascular cochlear unit play important physiological roles, owing to their impermeable function against all ototoxic substances that can induce damage. Studies are needed to investigate the cross talk occurring between these cellular components to exploit their possible role as novel targets for therapeutic interventions that may unravel future path based on the use of hormetic nutrients. Antioxid. Redox Signal. 40, 542-563.

NADPH Oxidase 3: Beyond the Inner Ear

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

Sound conditioning strategy promoting paracellular permeability of the blood-labyrinth-barrier benefits inner ear drug delivery

The therapeutic effects of pharmaceuticals depend on their drug concentrations in the cochlea. Efficient drug delivery from the systemic circulation into the inner ear is limited by the blood-labyrinth-barrier (BLB). This study investigated a novel noninvasive sound conditioning (SC) strategy (90 dB SPL, 8-16 kHz, 2 h sound exposure) to temporally enhance BLB permeability in a controllable way, contributing to maximizing the penetration of pharmaceuticals from blood circulation into the cochlea. Trafficking of Fluorescein Isothiocyanate conjugated dextran and bovine serum albumin (FITC-dextran and FITC-BSA) demonstrated that paracellular leakage of BLB sustained for 6 h after SC, providing a controllable time window for systemic administration. Cochlear concentrations of dexamethasone (DEX) and dexamethasone phosphate (DEX-P), respectively transported by transcellular and paracellular pathways, showed a higher content of the latter one after SC, further confirming the key role of paracellular pathway in the SC-induced hyperpermeability. Results of high-throughput RNA-sequencing identified a series of tight junction (TJ)-associated genes after SC. The expressions of TJ (ZO-1) were reduced and irregular rearrangements of the junction were observed by transmission electron microscopy after SC. We further determined the inhibiting role of Rab13 in the recruitment of ZO-1 and later in the regulation of cellular permeability. Meanwhile, no significant change in the quantifications of endothelial caveolae vesicles after SC indicated that cellular transcytosis accounted little for the temporary hyperpermeability after SC. Based on these results, SC enhances the BLB permeability within 6 h and allows systemically applied drugs which tend to be transported by paracellular pathway to readily enter the inner ear, contributing to guiding the clinical medications on hearing loss.

The Relevance of Autophagy within Inner Ear in Baseline Conditions and Tinnitus-Related Syndromes

Tinnitus is the perception of noise in the absence of acoustic stimulation (phantom noise). In most patients suffering from chronic peripheral tinnitus, an alteration of outer hair cells (OHC) starting from the stereocilia (SC) occurs. This is common following ototoxic drugs, sound-induced ototoxicity, and acoustic degeneration. In all these conditions, altered coupling between the tectorial membrane (TM) and OHC SC is described. The present review analyzes the complex interactions involving OHC and TM. These need to be clarified to understand which mechanisms may underlie the onset of tinnitus and why the neuropathology of chronic degenerative tinnitus is similar, independent of early triggers. In fact, the fine neuropathology of tinnitus features altered mechanisms of mechanic-electrical transduction (MET) at the level of OHC SC. The appropriate coupling between OHC SC and TM strongly depends on autophagy. The involvement of autophagy may encompass degenerative and genetic tinnitus, as well as ototoxic drugs and acoustic trauma. Defective autophagy explains mitochondrial alterations and altered protein handling within OHC and TM. This is relevant for developing novel treatments that stimulate autophagy without carrying the burden of severe side effects. Specific phytochemicals, such as curcumin and berberin, acting as autophagy activators, may mitigate the neuropathology of tinnitus.

Otoprotective Effects of Quercetin Against Oxidative Damage in the Rat's Cochlea Induced by Noise and Silver Nanoparticles

The aim of this study was to investigate the otoprotective effects of Quercetin (Que) against both noise-induced hearing loss (NIHL) and the ototoxicity of silver nanoparticles (SNPs) in rats. Forty-two male Wistar rats were divided into seven groups (n = 6): control, SNPs, Que (100 mg/kg) plus SNPs (100 mg/kg), noise (104 dB), Que plus noise, noise plus SNPs, and noise plus Que plus SNPs. In the weight change results, there was no significant difference between the groups exposed to noise plus SNPs and SNPs compared to the control group. However, animals had significant changes in DPOAE amplitude at 1 and 3 days post-exposure when compared to baseline. Additionally, the DPOAE value of rats administered with Que plus SNPs was higher than in all other groups. Que also decreased the levels of TACT, MDA, IL-6, TNF-α, and NOX3 in the groups exposed to noise and SNPs and increased the SOD level and expression of myosin heavy chain VII (MYH7) and β-tubulin III (TUBB3) proteins. Furthermore, Que decreased structural changes in the animals' cochlea. Our findings indicate that pretreatment with Que efficiently counteracted the adverse effects of noise and SNPs on inner hair cell, outer hair cell, and nerve cells, which are responsible for high-frequency perception.

Protective effects of alpha lipoic acid (ALA) are mediated by hormetic mechanisms

The endogenous and dietary agent, alpha lipoic acid (ALA) is evaluated for its capacity to induce a broad spectrum of adaptive responses via hormetic dose responses and their underlying mechanisms. ALA was shown to induce hormetic effects in a wide range of experimental models within in vitro and in vivo experimental settings which included direct exposure and pre- and post-conditioning experimental protocols. The hormetic effects occur in a broad range of organ systems, including the brain, heart, kidney and other tissues, with possible public health and clinical/therapeutic applications linked to reducing the onset and progression of neurogenerative diseases and also in the preservation of sperm health and functionality during cryopreservation. This paper provides the first integrated assessment of ALA-induced hormetic dose responses. Underlying mechanisms that mediated the occurrence of ALA-induced hormetic effects involved the induction of low levels of ROS that activate key cell signaling antioxidant (e.g. Nrf2) pathways.

Rhodiola rosea and Salidroside commonly induce hormesis, with particular focus on longevity and neuroprotection

The biological effects of Rhodiola rosea extracts and one of its major constituents, Salidroside, were evaluated for their capacity to induce hormesis/hormetic effects. The findings indicate that the Rhodiola rosea extracts and Salidroside commonly induce hormetic dose responses within a broad range of biological models, cell types and across a broad range of endpoints, with particular emphasis on longevity and neuroprotective endpoints. This paper represents the first integrative documentation and assessment of Rhodiola rosea extracts and Salidroside induction of hormetic effects. These findings have important biomedical applications and should have an important impact with respect to critical study design, dose selection and other experimental features.

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

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

Intratympanic microcrystals of dexamethasone and lipoic acid for the treatment of cisplatin-induced inner ear injury

Steroids (anti-inflammatory drugs) combined with antioxidants are frequently prescribed to treat cisplatin (CP)-induced hearing loss in the clinic. Compared to systemic administration of free drugs, local drug delivery systems offer better therapeutic qualities and patient compliance since they not only can bypass the blood-labyrinth barrier but also can perform sustained release. In this work, dexamethasone (DEX) and lipoic acid (LA) non-spherical microcrystals (MCs) were prepared without complicated chemical modification. Following a series of physical characterizations, including morphology, stability and injectability, dissolution and round window membrane distribution of MCs, DEX MCs, LA MCs and the simple mixture of DEX MCs + LA MCs (combination group) were administered in guinea pigs by intratympanic injection. We found that LA MCs enabled improvement of DEX absorption in the combination group compared to a single dose. In addition, no significant morphological changes or inflammatory responses were observed in cochlear tissue, indicating good biocompatibility. Finally, the combination group also demonstrated synergistic therapeutic effect for protecting hair cells against CP-induced damage. The local co delivery of DEX MCs and LA MCs offers a new strategy for the treatment of CP-induced inner ear injury since they provide sustained anti-inflammatory and antioxidant effects simultaneously.

Prevention of Noise-Induced Hearing Loss In Vivo: Continuous Application of Insulin-like Growth Factor 1 and Its Effect on Inner Ear Synapses, Auditory Function and Perilymph Proteins

As noise-induced hearing loss (NIHL) is a leading cause of occupational diseases, there is an urgent need for the development of preventive and therapeutic interventions. To avoid user-compliance-based problems occurring with conventional protection devices, the pharmacological prevention is currently in the focus of hearing research. Noise exposure leads to an increase in reactive oxygen species (ROS) in the cochlea. This way antioxidant agents are a promising option for pharmacological interventions. Previous animal studies reported preventive as well as therapeutic effects of Insulin-like growth factor 1 (IGF-1) in the context of NIHL. Unfortunately, in patients the time point of the noise trauma cannot always be predicted, and additive effects may occur. Therefore, continuous prevention seems to be beneficial. The present study aimed to investigate the preventive potential of continuous administration of low concentrations of IGF-1 to the inner ear in an animal model of NIHL. Guinea pigs were unilaterally implanted with an osmotic minipump. One week after surgery they received noise trauma, inducing a temporary threshold shift. Continuous IGF-1 delivery lasted for seven more days. It did not lead to significantly improved hearing thresholds compared to control animals. Quite the contrary, there is a hint for a higher noise susceptibility. Nevertheless, changes in the perilymph proteome indicate a reduced damage and better repair mechanisms through the IGF-1 treatment. Thus, future studies should investigate delivery methods enabling continuous prevention but reducing the risk of an overdosage.

Network pharmacology and experimental evidence reveal the protective mechanism of Yi-Qi Cong-Ming decoction on age-related hearing loss

CONTEXT

Yi-Qi Cong-Ming (YQCM) decoction has been widely used to prevent age-related hearing loss (ARHL), the most prevalent neurodegenerative disease in the elderly.

OBJECTIVE

To explore the mechanism of YQCM decoction in the treatment of ARHL.

MATERIALS AND METHODS

The chemical constituents of YQCM were screened from the Traditional Chinese Medicine Systems Pharmacology Database. Potential targets of YQCM against ARHL were predicted by DrugBank, GeneCards, and OMIM database. Protein-protein network and enrichment analysis were used for exploring possible molecular mechanisms. Molecular docking and an in vitro model of ARHL by exposing auditory cells with 100 μM H₂O₂ for 3 h were applied. Cell viability and mitochondrial membrane potential (ΔΨM) were detected by CCK-8 and high-content analysis. γH2AX and cleaved caspase-3 were detected by Western blot.

RESULTS

The main compounds have good affinities with hub targets, especially AKT1, PTGS2, and CASP3. GO and KEGG analysis showed that the main biological process and key targets were related to negative regulation of the apoptotic process. H₂O₂ treatment could reduce the cell viability by 68% and impaired ΔΨM, while 90 μg/mL YQCM pre-treatment could restore the cell viability by 97.45% and increase ΔΨM (2-fold higher). YQCM pre-treatment also reduced γH2AX and cleaved caspase-3 protein levels.

CONCLUSIONS

Our study suggested that YQCM prevents ARHL by modulating the apoptosis process in auditory hair cells. Moreover, this study proved that bioinformatics analysis combined with molecular docking and cell model is a promising method to explore other possible pharmacological interventions of ARHL.

Exosomes Derived from Bone Marrow-Mesenchymal Stem Cells Attenuates Cisplatin-Induced Ototoxicity in a Mouse Model

Background: Both hypoxia preconditioning and exosomes derived from bone marrow mesenchymal stem cells (BMSC-Exo) have been adopted to alleviate hair-loss-related ototoxicity. Whether hypoxic BMSCs-derived exosomes (hypBMSC-Exo) could alleviate cisplatin-induced ototoxicity is investigated in this study. Methods: Cisplatin intraperitoneally injected C57BL/6 mice were trans-tympanically administered BMSC-Exo or hypBMSC-Exo in the left ear. Myosin 7a staining was utilized to detect mature hair cells. Auditory brainstem response (ABR) was assessed to indicate auditory sensitivity at 8, 16, 24, and 32 kHz. The relative expressions of hypoxia-inducible factor-1α (HIF-1α), superoxide dismutase 1 (SOD1), and SOD2 were determined with RT-PCR and Western blot. The content of hydrogen peroxide (H₂O₂), malondialdehyde (MDA), SOD, and glutathione (GSH) in the middle turns of the cochlea were measured. Results: Up-regulated HIF-1α expression was observed in hypBMSC-Exo compared with BMSC-Exo. Diminished auditory sensitivity and increased hair cell loss was observed in the cisplatin-exposed mice with increased content of H₂O₂ and MDA and decreased content of SOD and GSH, which could be reversed by hypBMSC-Exo or BMSC-Exo administration. It is worth noting that hypBMSC-Exo demonstrated more treatment benefits than BMSC-Exo with up-regulated SOD1 and SOD2 expression in the middle turns of the cochlea tissues. Conclusions: Hypoxic preconditioning may provide a new therapeutic option in regenerative medicine, and hypBMSC-Exo could be utilized to alleviate cisplatin-induced ototoxicity.

Safety and Efficacy of Intratympanic Alpha-Lipoic Acid Injection in a Mouse Model of Noise-Induced Hearing Loss

Alpha-lipoic acid (ALA) is an antioxidant with oto-protective effects. In the present study, the safety and effectiveness of ALA therapy after noise-induced hearing loss was confirmed based on the administration method. The safety of intratympanic ALA (IT-ALA) was evaluated with oto-endoscopy and middle ear mucosa morphologic study. Perilymph ALA concentrations according to the administration routes were compared, and the efficacy of ALA was investigated through hearing tests and cochlear histological studies. The middle ear mucosa was swollen 1 week after IT-ALA but completely recovered within 3 weeks. ALA concentration in the perilymph was significantly higher in the IT-ALA group. Recovery of organ of Corti morphology and hearing levels were predominant in the IT-ALA group compared with the intraperitoneal injection group (IP-ALA) and showed similar rescue effects in the IT-dexamethasone group (IT-DEX). Interleukin-1 beta and nuclear factor-kappa B expression was significantly downregulated in the IT-ALA group. IT-ALA showed better cochlear recovery from acoustic trauma with higher inner ear penetration rate than IP-ALA. The rescue effect of IT-ALA after noise-induced hearing loss was similar to IT-DEX; however, the ALA and DEX mechanisms are different. IT-ALA appears to be another safe and effective treatment modality after acoustic trauma and comparable to IT-DEX.

Development and Characterization of a Topically Deliverable Prophylactic Against Oxidative Damage in Cochlear Cells

Hearing loss affects roughly 466 million people worldwide. While the causes of hearing loss are diverse, mechanistically, inflammation and oxidative stress have been identified as major players in hearing loss regardless of pathogenesis. Treatment options remain extremely limited and there is currently no FDA approved drug therapy. Studies indicate that antioxidants such as d-Methionine have shown some protective effects; however, these studies involved systemic or invasive localized delivery methods and highlighted the need for the development of minimally invasive localized therapeutic approaches. Described herein is the development of an antioxidant-conjugated system that shows prophylactic potential against oxidative damage and appears suitable for topical delivery. Specifically, our covalent conjugate of hyaluronan with d-Methionine shows cytocompatibility and protection from oxidative stress in two mouse cochlear cell lines (HEI-OC1 and SV-k1). Mechanistically, the data indicate that the protective effects of the conjugate are due to the hyaluronan-mediated cellular internalization of the antioxidant. Most notably, the conjugate can efficiently permeate through an in vitro round window membrane model without the loss of the attached antioxidant, for subsequent delivery of the therapeutic cargo to the hearing sensory cells. Collectively these findings show that the novel conjugate could be a potential topical preventive agent against hearing loss.

mito-TEMPO Attenuates Oxidative Stress and Mitochondrial Dysfunction in Noise-Induced Hearing Loss via Maintaining TFAM-mtDNA Interaction and Mitochondrial Biogenesis

The excessive generation of reactive oxygen species (ROS) and mitochondrial damage have been widely reported in noise-induced hearing loss (NIHL). However, the specific mechanism of noise-induced mitochondrial damage remains largely unclear. In this study, we showed that acoustic trauma caused oxidative damage to mitochondrial DNA (mtDNA), leading to the reduction of mtDNA content, mitochondrial gene expression and ATP level in rat cochleae. The expression level and mtDNA-binding function of mitochondrial transcription factor A (TFAM) were impaired following acoustic trauma without affecting the upstream PGC-1α and NRF-1. The mitochondria-target antioxidant mito-TEMPO (MT) was demonstrated to enter the inner ear after the systemic administration. MT treatment significantly alleviated noise-induced auditory threshold shifts 3d and 14d after noise exposure. Furthermore, MT significantly reduced outer hair cell (OHC) loss, cochlear ribbon synapse loss, and auditory nerve fiber (ANF) degeneration after the noise exposure. In addition, we found that MT treatment effectively attenuated noise-induced cochlear oxidative stress and mtDNA damage, as indicated by DHE, 4-HNE, and 8-OHdG. MT treatment also improved mitochondrial biogenesis, ATP generation, and TFAM-mtDNA interaction in the cochlea. These findings suggest that MT has protective effects against NIHL via maintaining TFAM-mtDNA interaction and mitochondrial biogenesis based on its ROS scavenging capacity.

LncRNA H19 inhibits oxidative stress injury of cochlear hair cells by regulating miR-653-5p/SIRT1 axis

Oxidative stress is one of the important mechanisms of inner ear cell damage, which can lead to age-related hearing loss (ARHL). LncRNA H19 is significantly downregulated in the cochlea of old mouse, however, the role of H19 in the development of ARHL remains unclear. In this study, we aim to investigate the expression and function of H19 in oxidative stress injury of cochlear hair cells induced by HO. RT-qPCR and western blot analysis confirms that HEI-OC1 cells stimulated with HO decreases the expressions of H19 and SIRT1, but increases the expression of miR-653-5p. Overexpression of H19 could increase cell viability, ATP level and mitochondrial membrane potential, but reduce mitochondrial ROS generation and cell apoptosis ratio in HO-stimulated HEI-OC1 cells. MiR-653-5p is a target of H19, which can bind to the 3'-UTR of SIRT1. H19 is found to regulate the expression of SIRT1 through miR-653-5p. Further experiments demonstrates that H19 regulates HEI-OC1 cell viability, ATP level, mitochondrial membrane potential, mitochondrial ROS generation, and cell apoptosis ratio via the miR-653-5p/SIRT1 axis. In conclusion, lncRNA H19 inhibits oxidative stress injury of cochlear hair cells via the miR-653-5p/SIRT1 axis.

Application of Nanomedicine in Inner Ear Diseases

The treatment of inner ear disorders always remains a challenge for researchers. The presence of various physiological barriers, primarily the blood–labyrinth barrier (BLB), limits the accessibility of the inner ear and hinders the efficacy of various drug therapies. Yet despite recent advances in the cochlea for repair and regeneration, there are currently no pharmacological or biological interventions for hearing loss. Current research focuses on the localized drug-, gene-, and cell-based therapies. Drug delivery based on nanotechnology represents an innovative strategy to improve inner ear treatments. Materials with specific nanostructures not only exhibit a unique ability to encapsulate and transport therapeutics to the inner ear but also endow specific targeting properties to auditory hair cells as well as the stabilization and sustained drug release. Along with this, some alternative routes, like intratympanic drug delivery, can also offer a better means to access the inner ear without exposure to the BLB. This review discusses a variety of nano-based drug delivery systems to the ear for treating inner ear diseases. The main factors affecting the curative efficacy of nanomaterials are also discussed. With a deeper understanding of the link between these crucial factors and the clinical effect of nanomaterials, it paves the way for the optimization of the therapeutic activity of nanocarriers.

Dual-Specificity Phosphatase 1 (DUSP1) Has a Central Role in Redox Homeostasis and Inflammation in the Mouse Cochlea

Stress-activated protein kinases (SAPK) are associated with sensorineural hearing loss (SNHL) of multiple etiologies. Their activity is tightly regulated by dual-specificity phosphatase 1 (DUSP1), whose loss of function leads to sustained SAPK activation. Dusp1 gene knockout in mice accelerates SNHL progression and triggers inflammation, redox imbalance and hair cell (HC) death. To better understand the link between inflammation and redox imbalance, we analyzed the cochlear transcriptome in Dusp1-/- mice. RNA sequencing analysis (GSE176114) indicated that Dusp1-/- cochleae can be defined by a distinct profile of key cellular expression programs, including genes of the inflammatory response and glutathione (GSH) metabolism. To dissociate the two components, we treated Dusp1-/- mice with N-acetylcysteine, and hearing was followed-up longitudinally by auditory brainstem response recordings. A combination of immunofluorescence, Western blotting, enzymatic activity, GSH levels measurements and RT-qPCR techniques were used. N-acetylcysteine treatment delayed the onset of SNHL and mitigated cochlear damage, with fewer TUNEL+ HC and lower numbers of spiral ganglion neurons with p-H2AX foci. N-acetylcysteine not only improved the redox balance in Dusp1-/- mice but also inhibited cytokine production and reduced macrophage recruitment. Our data point to a critical role for DUSP1 in controlling the cross-talk between oxidative stress and inflammation.

A Review on Recent Advancement on Age-Related Hearing Loss: The Applications of Nanotechnology, Drug Pharmacology, and Biotechnology

Aging is considered a contributing factor to many diseases such as cardiovascular disease, Alzheimer’s disease, and hearing loss. Age-related hearing loss, also termed presbycusis, is one of the most common sensory impairments worldwide, affecting one in five people over 50 years of age, and this prevalence is growing annually. Associations have emerged between presbycusis and detrimental health outcomes, including social isolation and mental health. It remains largely untreatable apart from hearing aids, and with no globally established prevention strategies in the clinical setting. Hence, this review aims to explore the pathophysiology of presbycusis and potential therapies, based on a recent advancement in bile acid-based bio-nanotechnologies. A comprehensive online search was carried out using the following keywords: presbycusis, drugs, hearing loss, bile acids, nanotechnology, and more than 150 publications were considered directly relevant. Evidence of the multifaceted oxidative stress and chronic inflammation involvement in cellular damage and apoptosis that is associated with a loss of hair cells, damaged and inflamed stria vascularis, and neuronal signalling loss and apoptosis continues to emerge. New robust and effective therapies require drug delivery deeper into the various layers of the cochlea. Bile acid-based nanotechnology has gained wide interest in its permeation-enhancing ability and potential for numerous applications in treating presbycusis.