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

Magnetic/Acoustic Dual-Controlled Microrobot Overcoming Oto-Biological Barrier for On-Demand Multidrug Delivery against Hearing Loss

Multidrug combination therapy in the inner ear faces diverse challenges due to the distinct physicochemical properties of drugs and the difficulties of overcoming the oto-biologic barrier. Although nanomedicine platforms offer potential solutions to multidrug delivery, the access of drugs to the inner ear remains limited. Micro/nanomachines, capable of delivering cargo actively, are promising tools for overcoming bio-barriers. Herein, a novel microrobot-based strategy to penetrate the round window membrane (RWM) is presented and multidrug in on-demand manner is delivered. The tube-type microrobot (TTMR) is constructed using the template-assisted layer-by-layer (LbL) assembly of chitosan/ferroferric oxide/silicon dioxide (CS/Fe3O4/SiO2) and loaded with anti-ototoxic drugs (curcumin, CUR and tanshinone IIA, TSA) and perfluorohexane (PFH). Fe3O4 provides magnetic actuation, while PFH ensures acoustic propulsion. Upon ultrasound stimulation, the vaporization of PFH enables a microshotgun-like behavior, propelling the drugs through barriers and driving them into the inner ear. Notably, the proportion of drugs entering the inner ear can be precisely controlled by varying the feeding ratios. Furthermore, in vivo studies demonstrate that the drug-loaded microrobot exhibits superior protective effects and excellent biosafety toward cisplatin (CDDP)-induced hearing loss. Overall, the microrobot-based strategy provides a promising direction for on-demand multidrug delivery for ear diseases.

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

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

Chitosan coated selenium: A versatile nano-delivery system for molecular cargoes

The use of nanoscale delivery platforms holds tremendous potential to overcome the current limitations associated with the conventional delivery of genetic materials and hydrophobic compounds. Therefore, there is an imperative need to develop a suitable alternative nano-enabled delivery platform to overcome these limitations. This work reports the first one-step hydrothermal synthesis of chitosan functionalized selenium nanoparticles (Selenium-chitosan, SeNP) that are capable of serving as a versatile nanodelivery platform for different types of active ingredients. The chitosan functionalization modified the surface charge to allow the loading of active ingredients and improve biocompatibility. The effective loading of the SeNP was demonstrated using genetic material, a hydrophobic small molecule, and an antibiotic. Furthermore, the loading of active ingredients showed no detrimental effect on the specific properties (fluorescence and bactericidal) of the studied active ingredients. In vitro antimicrobial inhibitory studies exhibited good compatibility between the SeNP delivery platform and Penicillin G (Pen), resulting in a reduction of the minimum inhibitory concentration (MIC) from 32 to 16 ppm. Confocal microscopy images showed the uptake of the SeNP by a macrophage cell line (J774A.1), demonstrating trackability and intracellular delivery of an active ingredient. In summary, the present work demonstrates the potential of SeNP as a suitable delivery platform for biomedical and agricultural applications.

Drug-induced hearing loss: Listening to the latest advances

Sensorineural hearing loss (SNHL) is the most common type of hearing loss. Causes include degenerative changes in the sensory hair cells, their synapses and/or the cochlear nerve. As human inner ear hair cells have no capacity for regeneration, their destruction is irreversible and leads to permanent hearing loss. SNHL can be genetically inherited or acquired through ageing, exposure to noise or ototoxic drugs. Ototoxicity generally refers to damage to the structures and functions of the inner ear following exposure to specific drugs. Ototoxicity can be multifactorial, causing damage to cochlear hair cells or cells with homeostatic functions that modulate cochlear hair cell function. Clinical strategies to limit ototoxicity include identifying patients at risk, monitoring drug concentrations, performing serial hearing assessments and switching to less ototoxic therapy. This review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, using the PubMed® database. The search terms "ototoxicity", "hearing loss" and "drugs" were combined. We included studies published between September 2013 and June 2023, and focused on medicines and drugs used in hospitals. The review highlighted a number of articles reporting the main drug classes potentially involved: namely, immunosuppressants, antimalarials, vaccines, antibiotics, antineoplastic agents, diuretics, nonsteroidal anti-inflammatory drugs and analgesics. The presumed ototoxic mechanisms were described, together with the therapeutic and preventive options developed over the last ten years.

In vivo biodistribution and ototoxicity assessment of cationic liposomal-ceftriaxone via noninvasive trans-tympanic delivery in chinchilla models: Implications for otitis media therapy

OBJECTIVES

We report the in vivo biodistribution and ototoxicity of cationic liposomal-ceftriaxone (CFX) delivered via ear drop formulation in adult chinchilla.

METHODS

CFX was encapsulated in liposomes with size of ∼100 nm and surface charge of +20 mV. 100 μl liposomes or free drug was applied twice daily in both external ear canals of adult chinchillas for either 3 or 10 days. Study groups included free ceftriaxone (CFX, Day 3: n = 4, Day 10: n = 8), liposomal ceftriaxone (CFX-Lipo, Day 3: n = 4, Day 10: n = 8), and a systemic control group (Day 3: n = 4, Day 10: n = 4). Ceftriaxone delivery to the middle ear and systemic circulation was quantified by HPLC assays. Liposome transport was visualized via confocal microscopy. Auditory brainstem response (ABR) tests and cochlear histology were used to assess ototoxicity.

RESULTS

Liposomal ceftriaxone (CFX-Lipo) displayed a ∼658-fold increase in drug delivery efficiency in the middle ear relative to the free CFX (8.548 ± 0.4638% vs. 0.013 ± 0.0009%, %Injected dose, Mean ± SEM). CFX measured in blood serum (48.2 ± 7.78 ng/ml) following CFX-Lipo treatment in ear was 41-fold lower compared to systemic free-CFX treatment (1990.7 ± 617.34 ng/ml). ABR tests and histological analysis indicated no ototoxicity due to the treatment.

CONCLUSION

Cationic liposomal encapsulation results in potent drug delivery across the tympanic membrane to the middle ear with minimal systemic exposure and no ototoxicity.

A state-of-the-art analysis of pharmacological delivery and artificial intelligence techniques for inner ear disease treatment

Over the last several decades, both the academic and therapeutic fields have seen significant progress in the delivery of drugs to the inner ear due to recent delivery methods established for the systemic administration of drugs in inner ear treatment. Novel technologies such as nanoparticles and hydrogels are being investigated, in addition to the traditional treatment methods. Intracochlear devices, which utilize current developments in microsystems technology, are on the horizon of inner ear drug delivery methods and are designed to provide medicine directly into the inner ear. These devices are used for stem cell treatment, RNA interference, and the delivery of neurotrophic factors and steroids during cochlear implantation. An in-depth analysis of artificial neural networks (ANNs) in pharmaceutical research may be found in ANNs for Drug Delivery, Design, and Disposition. This prediction tool has a great deal of promise to assist researchers in more successfully designing, developing, and delivering successful medications because of its capacity to learn and self-correct in a very complicated environment. ANN achieved a high level of accuracy exceeding 0.90, along with a sensitivity of 95% and a specificity of 100%, in accurately distinguishing illness. Additionally, the ANN model provided nearly perfect measures of 0.99%. Nanoparticles exhibit potential as a viable therapeutic approach for bacterial infections that are challenging to manage, such as otitis media. The utilization of ANNs has the potential to enhance the effectiveness of nanoparticle therapy, particularly in the realm of automated identification of otitis media. Polymeric nanoparticles have demonstrated effectiveness in the treatment of prevalent bacterial infections in pediatric patients, suggesting significant potential for forthcoming therapeutic interventions. Finally, this study is based on a research of how inner ear diseases have been treated in the last ten years (2012-2022) using machine learning.

The biocompatibility and the metabolic impact of thermoresponsive, bile acid-based nanogels on auditory and macrophage cell lines

Deoxycholic acid (DCA), lithocholic acid (LCA), and ursodeoxycholic acid (UDCA) are bile acids that may serve as permeation enhancers when incorporated within the nanogel matrix for drug delivery in the inner ear. In this study, thermoresponsive nanogels were formulated with DCA, LCA and UDCA and their rheological properties and biocompatibility were assessed. The impact of nanogel on cellular viability was evaluated via cell viability assay, the impact of nanogels on cellular bioenergetic parameters was estimated by Seahorse mito-stress test and glycolysis-stress test, while the presence of intracellular free radicals was assessed by reactive oxygen species assay. Nanogels showed a high level of biocompatibility after 24-hour exposure to auditory and macrophage cell lines, with minimal cytotoxicity compared to untreated control. Incubation with nanogels did not alter cellular respiration and glycolysis of the auditory cell line but showed possible mitochondrial dysfunction in macrophages, suggesting tissue-dependent effects of bile acids. Bile acid-nanogels had minimal impact on intracellular reactive oxygen species, with LCA demonstrating the most pro-oxidative behaviour. This study suggests that thermoresponsive nanogels with bile acid, particularly DCA and UDCA, may be promising candidates for inner ear drug delivery.

Space Station-like Composite Nanoparticles for Co-Delivery of Multiple Natural Compounds from Chinese Medicine and Hydrogen in Combating Sensorineural Hearing Loss

Ototoxic drugs such as aminoglycoside antibiotics and cisplatin (CDDP) can cause sensorineural hearing loss (SNHL), which is closely related to oxidative stress and the acidification of the inner ear microenvironment. Effective treatment of SNHL often requires multifaceted approach due to the complex pathology, and drug combination therapy is expected to be at the forefront of modern hearing loss treatment. Here, space-station-like composite nanoparticles (CCC@mPP NPs) with pH/oxidation dual responsiveness and multidrug simultaneous delivery capability were constructed and then loaded with various drugs including panax notoginseng saponins (PNS), tanshinone IIA (TSIIA), and ammonia borane (AB) to provide robust protection against SNHL. Molecular dynamics simulation revealed that carboxymethyl chitosan/calcium carbonate-chitosan (CCC) NPs and monomethoxy poly(ethylene glycol)-PLGA (mPP) NPs can rendezvous and dock primarily by hydrogen bonding, and electrostatic forces may be involved. Moreover, CCC@mPP NPs crossed the round window membrane (RWM) and entered the inner ear through endocytosis and paracellular pathway. The docking state was basically maintained during this process, which created favorable conditions for multidrug delivery. This nanosystem was highly sensitive to pH and reactive oxygen species (ROS) changes, as evidenced by the restricted release of payload at alkaline condition (pH 7.4) without ROS, while significantly promoting the release in acidic condition (pH 5.0 and 6.0) with ROS. TSIIA/PNS/AB-loaded CCC@mPP NPs almost completely preserved the hair cells and remained the hearing threshold shift within normal limits in aminoglycoside- or CDDP-treated guinea pigs. Further experiments demonstrated that the protective mechanisms of TSIIA/PNS/AB-loaded CCC@mPP NPs involved direct and indirect scavenging of excessive ROS, and reduced release of pro-inflammatory cytokines. Both in vitro and in vivo experiments showed the high biocompatibility of the composite NPs, even after long-term administration. Collectively, this work suggests that composite NPs is an ideal multi-drug-delivery vehicle and open new avenues for inner ear disease therapies.

Neurotherapeutic efficacy of loaded sulforaphane on iron oxide nanoparticles against cuprizone-induced neurotoxicity: role of MMP-9 and S100β

Cuprizone (CUP) induces neurotoxicity and demyelination in animal models by provoking the activation of glial cells and the generation of reactive oxygen species (ROS). Sulforaphane (SF) is a phytochemical that exhibits a neuroprotective potential. In this study, we investigated the neurotherapeutic and pro-remyelinating activities of SF and SF-loaded within iron oxide nanoparticles (IONP-SF) in CUP-exposed rats. Magnetite iron oxide nanoparticles (IONPs) were prepared using the hydrothermal method that was further loaded with SF (IONP-SF). The loading of SF within the magnetite nanoparticles was assessed using FTIR, TEM, DLS, Zetasizer, and XPS. For the in vivo investigations, adult male Wistar rats (n = 40) were administrated either on a regular diet or a diet with CUP (0.2%) for 5 weeks. The rats were divided into four groups: negative control, CUP-induced, CUP + SF, and CUP + IONP-SF. CUP-exposed brains exhibited a marked elevation in lipid peroxidation, along with a significant decrease in the activities of glutathione peroxidase (GPx), and catalase (CAT). In addition, CUP intoxication downregulated the expression of myelin basic protein (MBP) and myelin proteolipid protein (PLP), upregulated the expression of Matrix metallopeptidase-9 (MMP-9) and S100β, and increased caspase-3 immunoexpression, these results were supported histopathologically in the cerebral cortexes. Treatment of CUP-rats with either SF or IONP-SF demonstrated remyelinating and neurotherapeutic activities. We could conclude that IONP-SF was more effective than free SF in mitigating the CUP-induced downregulation of MBP, upregulation of S100β, and caspase-3 immunoexpression.

Effect of minocycline and its nano-formulation on central auditory system in blast-induced hearing loss rat model

Blast injuries are common among the military service members and veterans. One of the devastating effects of blast wave induced TBI is either temporary or permanent hearing loss. Treating hearing loss using minocycline is restricted by optimal drug concentration, route of administration, and its half-life. Therefore, therapeutic approach using novel therapeutic delivery method is in great need. Among the different delivery methods, nanotechnology-based drug delivery is desirable, which can achieve longer systemic circulation, pass through some biological barriers and specifically targets desired sites. The current study aimed to examine therapeutic effect of minocycline and its nanoparticle formulation in moderate blast induced hearing loss rat model through central auditory system. The I.v. administered nanoparticle at reduced dose and frequency than regularly administered toxic dose. After moderate blast exposure, rats had hearing impairment as determined by ABR at 7- and 30-days post exposure. In chronic condition, free minocycline also showed the significant reduction in ABR threshold. In central auditory system, it is found in this study that minocycline nanoparticles ameliorate excitation in inferior colliculus; and astrocytes and microglia activation after the blast exposure is reduced by minocycline nanoparticles administration. The study demonstrated that in moderate blast induced hearing loss, minocycline and its nanoparticle formulation exhibited the optimal therapeutic effect on the recovery of the ABR impairment and a protective effect through central auditory system. In conclusion, targeted and non-targeted nanoparticle formulation have therapeutic effect on blast induced hearing loss.

Potential nanotechnology-based diagnostic and therapeutic approaches for Meniere's disease

Meniere's disease (MD) is a progressive inner ear disorder involving recurrent and prolonged episodes or attacks of vertigo with associated symptoms, resulting in a significantly reduced quality of life for sufferers. In most cases, MD starts in one ear; however, in one-third of patients, the disorder progresses to the other ear. Unfortunately, the etiology of the disease is unknown, making the development of effective treatments difficult. Nanomaterials, including nanoparticles (NPs) and nanocarriers, offer an array of novel diagnostic and therapeutic applications related to MD. NPs have specific features such as biocompatibility, biochemical stability, targetability, and enhanced visualization using imaging tools. This paper provides a comprehensive and critical review of recent advancements in nanotechnology-based diagnostic and therapeutic approaches for MD. Furthermore, the crucial challenges adversely affecting the use of nanoparticles to treat middle ear disorders are investigated. Finally, this paper provides recommendations and future directions for improving the performances of nanomaterials on theragnostic applications of MD.

Local Delivery of Therapeutics to the Cochlea Using Nanoparticles and Other Biomaterials

Hearing loss negatively impacts the well-being of millions of people worldwide. Systemic delivery of ototherapeutics has limited efficacy due to severe systemic side effects and the presence of the blood–labyrinth barrier that selectively limits or enables transfer of molecules between plasma and inner ear tissues and fluids. Local drug delivery into the middle and inner ear would be preferable for many newly emerging classes of drugs. Although the cochlea is a challenging target for drug delivery, recent technologies could provide a safe and efficacious delivery of ototherapeutics. Local drug delivery routes include topical delivery via the external auditory meatus, retroauricular, transtympanic, and intracochlear delivery. Many new drug delivery systems specifically for the inner ear are under development or undergoing clinical studies. Future studies into these systems may provide a means for extended delivery of drugs to preserve or restore hearing in patients with hearing disorders. This review outlines the anatomy of the (inner) ear, describes the various local delivery systems and routes, and various quantification methodologies to determine the pharmacokinetics of the drugs in the inner ear.

The Effect of Pluronic-Coated Gold Nanoparticles in Hearing Preservation Following Cochlear Implantation-Pilot Study

Introduction: During cochlear implantation, electrode insertion can cause cochlear damage, inflammation, and apoptosis, which can affect the residual hearing. Nanoparticles are increasingly studied as a way to increase the availability of inner ear protective factors. We studied the effect on rats of Pluronic-coated gold nanoparticles (Plu-AuNPs) containing dexamethasone, which were applied locally in the rat’s middle ear following the implant procedure. Methods: Seven rats were used in the study. The right ear served as a model for the Dex-Plu-AuNP group. Following the intracochlear dummy electrode insertion through the round window, Dex-Plu-AuNPs were placed in the round window niche. In the right ear, following the same insertion procedure, free dexamethasone (Dex) was placed in the same manner. Auditory brainstem response thresholds (click stimulus, pure tones at 8 kHz, 16 kHz, 24 kHz, and 32 kHz) were measured before and one week after the procedure. A two-tailed T-test was used for the variables. Statistical significance was set as p < 0.05. Results: In the Dex-Plu-AuNP group, the threshold shift was less than that in the free dexamethasone group, but no statistical significance was noted between the groups. When compared individually, only the 8 kHz frequency showed statistically significant, better results after one week, in favor of the Dex-Plu-AuNP group. The mean postoperative 8 kHz threshold in the Dex-Plu-AuNPs was significantly lower than that of the control group (p = 0.048, t-test). For the other frequencies, statistical analysis showed no significant differences between the mean threshold shifts of the two cohorts. Conclusions: The local application of Plu-AuNPs containing dexamethasone following cochlear implantation may better protect the residual hearing than dexamethasone alone, but a larger sample size is needed to reach a possible statistical significance. Dex-Plu-AuNPs do not seem to cause ototoxicity and may be used as a carrier for other agents. In a clinical setting, Dex-Plu-AuNPs may have the effect of protecting lower frequencies in patients with partial deafness who are candidates for electric acoustic stimulation (EAS). If we consider this tendency, Dex-Plu-AuNPs may also be beneficial for patients with Ménière’s disease.

Advancements in the studies of novel nanomaterials for inner ear drug delivery

Hearing loss is currently one of the most prevalent sensory disorders worldwide. Because both the blood-labyrinth barrier and the limited blood circulation in the inner ear restrain the effective delivery of most drugs to the inner ear tissues, current treatments for hearing loss are limited to mainly medication, hearing devices and cochlear surgery for therapeutic purposes, whereas treatments lack a noninvasive targeted drug-delivery system. With the continuously rapid development of new nanomaterials, the nanodelivery systems are expected to provide a potentially effective method of clinical treatment for hearing loss. This paper reviews the advantages and disadvantages of the commonly used drug-delivery methods and novel nanomaterials for inner ears as well as advancements in the targeted treatment of hearing loss.

Advances and future perspectives in epithelial drug delivery

Epithelial surfaces protect exposed tissues in the body against intrusion of foreign materials, including xenobiotics, pollen and microbiota. The relative permeability of the various epithelia reflects their extent of exposure to the external environment and is in the ranking: intestinal≈ nasal ≥ bronchial ≥ tracheal > vaginal ≥ rectal > blood-perilymph barrier (otic), corneal > buccal > skin. Each epithelium also varies in their morphology, biochemistry, physiology, immunology and external fluid in line with their function. Each epithelium is also used as drug delivery sites to treat local conditions and, in some cases, for systemic delivery. The associated delivery systems have had to evolve to enable the delivery of larger drugs and biologicals, such as peptides, proteins, antibodies and biologicals and now include a range of physical, chemical, electrical, light, sound and other enhancement technologies. In addition, the quality-by-design approach to product regulation and the growth of generic products have also fostered advancement in epithelial drug delivery systems.

The Use of Nanoparticles in Otoprotection

The inner ear can be insulted by various noxious stimuli, including drugs (cisplatin and aminoglycosides) and over-acoustic stimulation. These stimuli damage the hair cells giving rise to progressive hearing loss. Systemic drugs have attempted protection from ototoxicity. Most of these drugs poorly reach the inner ear with consequent ineffective action on hearing. The reason for these failures resides in the poor inner ear blood supply, the presence of the blood-labyrinthine barrier, and the low permeability of the round window membrane (RWM). This article presents a review of the use of nanoparticles (NPs) in otoprotection. NPs were recently used in many fields of medicine because of their ability to deliver drugs to the target organs or cells. The studies included in the review regarded the biocompatibility of the used NPs by in vitro and in vivo experiments. In most studies, NPs proved safe without a significant decrease in cell viability or signs of ototoxicity. Many nano-techniques were used to improve the drugs' kinetics and efficiency. These techniques included encapsulation, polymerization, surface functionalization, and enhanced drug release. In such a way, it improved drug transmission through the RWM with increased and prolonged intra-cochlear drug concentrations. In all studies, the fabricated drug-NPs effectively preserved the hair cells and the functioning hearing from exposure to different ototoxic stimuli, simulating the actual clinical circumstances. Most of these studies regarded cisplatin ototoxicity due to the wide use of this drug in clinical oncology. Dexamethasone (DEX) and antioxidants represent the most used drugs in most studies. These drugs effectively prevented apoptosis and reactive oxygen species (ROS) production caused by ototoxic stimuli. These various successful experiments confirmed the biocompatibility of different NPs and made it successfully to human clinical trials.

An enhanced antioxidant strategy of astaxanthin encapsulated in ROS-responsive nanoparticles for combating cisplatin-induced ototoxicity

Background

Excessive accumulation of reactive oxygen species (ROS) has been documented as the crucial cellular mechanism of cisplatin-induced ototoxicity. However, numerous antioxidants have failed in clinical studies partly due to inefficient drug delivery to the cochlea. A drug delivery system is an attractive strategy to overcome this drawback.

Methods and results

In the present study, we proposed the combination of antioxidant astaxanthin (ATX) and ROS-responsive/consuming nanoparticles (PPS-NP) to combat cisplatin-induced ototoxicity. ATX-PPS-NP were constructed by the self-assembly of an amphiphilic hyperbranched polyphosphoester containing thioketal units, which scavenged ROS and disintegrate to release the encapsulated ATX. The ROS-sensitivity was confirmed by ¹H nuclear magnetic resonance spectroscopy, transmission electron microscopy and an H₂O₂ ON/OFF stimulated model. Enhanced release profiles stimulated by H₂O₂ were verified in artificial perilymph, the HEI-OC1 cell line and guinea pigs. In addition, ATX-PPS-NP efficiently inhibited cisplatin-induced HEI-OC1 cell cytotoxicity and apoptosis compared with ATX or PPS-NP alone, suggesting an enhanced effect of the combination of the natural active compound ATX and ROS-consuming PPS-NP. Moreover, ATX-PPS-NP attenuated outer hair cell losses in cultured organ of Corti. In guinea pigs, NiRe-PPS-NP verified a quick penetration across the round window membrane and ATX-PPS-NP showed protective effect on spiral ganglion neurons, which further attenuated cisplatin-induced moderate hearing loss. Further studies revealed that the protective mechanisms involved decreasing excessive ROS generation, reducing inflammatory chemokine (interleukin-6) release, increasing antioxidant glutathione expression and inhibiting the mitochondrial apoptotic pathway.

Conclusions

Thus, this ROS-responsive nanoparticle encapsulating ATX has favorable potential in the prevention of cisplatin-induced hearing loss.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01485-8.

Epigallocatechin gallate-loaded tetrahedral DNA nanostructures as a novel inner ear drug delivery system

The study of drug delivery systems to the inner ear is a crucial but challenging field. The sensory organ (in the inner ear) is protected by the petrous bone labyrinth and the membranous labyrinth, both of which need to be overcome during the drug delivery process. The requirements for such a delivery system include small size, appropriate flexibility and biodegradability. DNA nanostructures, biomaterials that can arrange multiple functional components with nanometer precision, exhibit characteristics that are compatible with the requirements for inner ear drug delivery. Herein, we report the development of a novel inner ear drug delivery system based on epigallocatechin gallate (EGCG)-loaded tetrahedral DNA nanostructures (TDNs, EGCG@TDNs). The TDNs self-assembled via base-pairing of four single-stranded DNA constructs and EGCG was loaded into the TDNs through non-covalent interactions. Cy5-labeled TDNs (Cy5-TDNs) were significantly internalized by the House Ear Institute-Organ of Corti 1 cell line, and this endocytosis was energy-, clathrin-, and micropinocytosis-dependent. Cy5-TDNs penetrated the round window membrane (RWM) rapidly in vivo. Local application of EGCG@TDNs onto the RWM of guinea pigs in a single dose continuously released EGCG over 4 hours. Drug concentrations in the perilymph were significantly elevated compared with the administration of free EGCG at the same dose. EGCG@TDNs were found to have favorable biocompatibility and strongly affected the RSL3-induced down-regulation of GPX4 and the generation of reactive oxygen species, on the basis of 2',7'-dichlorodihydrofluorescein diacetate staining. JC-1 staining suggested that EGCG@TDNs successfully reversed the decrease in mitochondrial membrane potential induced by RSL-3 in vitro and rescued cells from apoptosis, as demonstrated by the analysis of Annexin V-FITC/PI staining. Further functional studies showed that a locally administered single-dose of EGCG@TDNs effectively preserved spiral ganglion cells in C57/BL6 mice after noise-induced hearing loss. Hearing loss at 5.6 and 8 kHz frequencies was significantly attenuated when compared with the control EGCG formulation. Histological analyses indicated that the administration of TDNs and EGCG@TDNs did not induce local inflammatory responses. These favorable histological and functional effects resulting from the delivery of EGCG by TDNs through a local intratympanic injection suggest potential for therapeutic benefit in clinical applications.

A forskolin-loaded nanodelivery system prevents noise-induced hearing loss

Hearing loss is the most common sensory disorder worldwide and may result from age, drugs, or exposure to excessive noise. Crossing the blood-labyrinth barrier to achieve targeted drug delivery to the inner ear is key to the treatment of hearing loss. We designed a nanoparticle (NP)-based system for targeted drug delivery of forskolin (FSK) to the inner ear, driven by the prestin-targeting peptide LS19 ("ligand-receptor type interaction"). In vivo experiments in developing zebrafish embryos (4-96 h past fertilization) and mice confirmed that LS19-FSK specifically targeted and accumulated in zebrafish lateral line neuromasts and mouse outer hair cells (OHCs). LS19 peptide modification enabled LS19-FSK-NPs to rapidly target OHCs with high specificity. Furthermore, the multifunctional LS19-FSK-NPs were successfully delivered to the OHCs via the round window membrane route and exhibited slow-release properties. The sustained release and intracellular accumulation of FSK inhibited apoptosis of OHCs. Compared with LS19-NPs and FSK-NPs, LS19-FSK-NPs provided significantly stronger protection against noise-induced hearing damage, based on auditory brainstem responses at 4, 8, 16, and 32 kHz. Thus, our specially designed targeted nano-delivery system may serve as a basis for future clinical applications and treatment platforms and has the potential to significantly improve the treatment results of many inner ear diseases.

Computational methodology for drug delivery to the inner ear using magnetic nanoparticle aggregates

BACKGROUND AND OBJECTIVE

The main goal of the proposed study is to improve the efficiency of the ear treatment via targeted drug delivery to the inner ear, i.e. the cochlea. Although pharmacotherapy has been proposed as a solution to prevent damage or restore functionality to hair cells, the main challenge in such treatments is ensuring adequate drug delivery to the cells. To this end, we present a methodology for the evaluation of the magnetic forces needed to move magnetic particle nanorobots (abbreviated as MNP) and their aggregates through the cochlea round window membrane (RWM).

METHODS

The FEM - Lagrangian-Eulerian approach (Abaqus software) was used to determine the specific parameters of movement of the nanoparticles crossing the RWM. This method results in a high consistency of FEM simulations and in-vivo experimental results in regards to the required magnetic force during the movement of spherical nanoparticles with a given viscosity η_ave. Based on the analysis of the experimental studies found in subject literature, the sizes of the MNPs and their aggregates able to cross RWM with and without the application of magnetic force F_M have been determined.

RESULTS

The present work accounts for both the experimental and theoretical aspects of these investigations. Presented research confirms the definite usability of the Lagrange-Euler method for the precise determination of the required magnetic force value FM to control the accelerated motion of MNP aggregates of complex shapes through RWM. It is possible to determine the predominant parameters with a precision of less than 5% for single-layer aggregates and spatial aggregates crossing the RWM. It can be concluded that the MNPs and their aggregates should not be larger than 500-750 nm to cross the RWM with high velocities of penetration close to 800 nm/s for magnetic forces of hundreds 10^-14 Newtons.

CONCLUSIONS

The proposed Lagrangian-Eulerian approach is capable of accurately predicting the movement parameters of MNP aggregates of irregular shape that are close to the experimental test cases. The presented method can serve as a supplementary tool for the design of drug delivery systems to the inner ear using MNPs.

Nanomaterials for Inner Ear Diseases: Challenges, Limitations and Opportunities

The inner ear is located deep in the temporal bone and has a complex anatomy. It is difficult to observe and obtain pathological tissues directly. Therefore, the diagnosis and treatment of inner ear diseases have always been a major clinical problem. The onset of inner ear disease can be accompanied by symptoms such as hearing loss, dizziness and tinnitus, which seriously affect people’s lives. Nanoparticles have the characteristics of small size, high bioavailability and strong plasticity. With the development of related research on nanoparticles in inner ear diseases, nanoparticles have gradually become a research hotspot in inner ear diseases. This review briefly summarizes the research progress, opportunities and challenges of the application of nanoparticles in inner ear diseases.

Surface Modification of Lipid-Based Nanoparticles

There is a growing interest in the development of lipid-based nanocarriers for multiple purposes, including the recent increase of these nanocarriers as vaccine components during the COVID-19 pandemic. The number of studies that involve the surface modification of nanocarriers to improve their performance (increase the delivery of a therapeutic to its target site with less off-site accumulation) is enormous. The present review aims to provide an overview of various methods associated with lipid nanoparticle grafting, including techniques used to separate grafted nanoparticles from unbound ligands or to characterize grafted nanoparticles. We also provide a critical perspective on the usefulness and true impact of these modifications on overcoming different biological barriers, with our prediction on what to expect in the near future in this field.

Novel insights and perspectives for the diagnosis and treatment of hearing loss through the implementation of magnetic nanotheranostics

Hearing loss (HL) is a sensory disability that affects 5% of the world's population. HL predominantly involves damage and death to the cochlear cells. Currently, there is no cure or specific medications for HL. Furthermore, the arrival of therapeutic molecules to the inner ear represents a challenge due to the limited blood supply to the sensory cells and the poor penetration of the blood-cochlear barrier. Superparamagnetic iron oxide nanoparticles (SPIONs) perfectly coordinate with the requirements for controlled drug delivery along with magnetic resonance imaging (MRI) diagnostic and monitoring capabilities. Besides, they are suitable tools to be applied to HL, expecting to be more effective and non-invasive. So far, the published literature only refers to some preclinical studies of SPIONs for HL management. This contribution aims to provide an integrated view of the best options and strategies that can be considered for future research punctually in the field of magnetic nanotechnology applied to HL.

Nanocarriers for Inner Ear Disease Therapy

Hearing loss is a common disease due to sensory loss caused by the diseases in the inner ear. The development of delivery systems for inner ear disease therapy is important to achieve high efficiency and reduce side effects. Currently, traditional drug delivery systems exhibit the potential to be used for inner ear disease therapy, but there are still some drawbacks. As nanotechnology is developing these years, one of the solutions is to develop nanoparticle-based delivery systems for inner ear disease therapy. Various nanoparticles, such as soft material and inorganic-based nanoparticles, have been designed, tested, and showed controlled delivery of drugs, improved targeting property to specific cells, and reduced systemic side effects. In this review, we summarized recent progress in nanocarriers for inner ear disease therapy. This review provides useful information on developing promising nanocarriers for the efficient treatment of inner ear diseases and for further clinical applications for inner ear disease therapy.

Progress in Gene Editing Tools and Their Potential for Correcting Mutations Underlying Hearing and Vision Loss

Blindness and deafness are the most frequent sensory disorders in humans. Whatever their cause - genetic, environmental, or due to toxic agents, or aging - the deterioration of these senses is often linked to irreversible damage to the light-sensing photoreceptor cells (blindness) and/or the mechanosensitive hair cells (deafness). Efforts are increasingly focused on preventing disease progression by correcting or replacing the blindness and deafness-causal pathogenic alleles. In recent years, gene replacement therapies for rare monogenic disorders of the retina have given positive results, leading to the marketing of the first gene therapy product for a form of childhood hereditary blindness. Promising results, with a partial restoration of auditory function, have also been reported in preclinical models of human deafness. Silencing approaches, including antisense oligonucleotides, adeno-associated virus (AAV)-mediated microRNA delivery, and genome-editing approaches have also been applied to various genetic forms of blindness and deafness The discovery of new DNA- and RNA-based CRISPR/Cas nucleases, and the new generations of base, prime, and RNA editors offers new possibilities for directly repairing point mutations and therapeutically restoring gene function. Thanks to easy access and immune-privilege status of self-contained compartments, the eye and the ear continue to be at the forefront of developing therapies for genetic diseases. Here, we review the ongoing applications and achievements of this new class of emerging therapeutics in the sensory organs of vision and hearing, highlighting the challenges ahead and the solutions to be overcome for their successful therapeutic application in vivo.

Bile acid-permeation enhancement for inner ear cochlear drug - pharmacological uptake: bio-nanotechnologies in chemotherapy-induced hearing loss

Ototoxicity is the damage to inner ear sensory epithelia due to exposure to certain medications and chemicals. This occurs when toxins enter the tightly controlled inner ear environment inducing hair cell death, resulting in hearing loss. Recent studies have explored hydrogel-based bio-nanotechnologies and new drug delivery formulations to prevent drug-induced hearing loss, with much attention given to administration of antioxidant drugs. Bile acids have been recognized as promising excipients due to their biocompatibility and unique physiochemical properties. As yet bile acids have not been explored in improving drug delivery to the inner ear despite improving drug stability and delivery in other systems and demonstrating positive biological effects in their own right.

The impact of calcium phosphate on FITC-BSA loading of sonochemically prepared PLGA nanoparticles for inner ear drug delivery elucidated by two different fluorimetric quantification methods

Although therapeutically active proteins are highly efficacious, their content in protective nanoparticles is often too low to elicit adequate plasma levels. A strategy to increase protein loading is the in-situ generation of calcium phosphate as a protein adsorbent. To verify this approach, a highly sensitive and reliable fluorimetric method for quantification of incorporated fluorescein-labelled bovine serum albumin (FITC-BSA) as a model protein drug was developed. Dequenching the fluorescein label by pronase E, which digests the protein backbone, and dissolving the nanoparticle matrix in acetonitrile enabled FITC-BSA quantification in the nanogram per milliliter range. This test was confirmed by a second assay involving alkaline hydrolysis of FITC-BSA and the matrix. Nanoparticles prepared with calcium phosphate contained 40 µg FITC-BSA/mg and nanoparticles without calcium phosphate only 15 µg FITC-BSA/mg, representing a 2.7-fold increase in model protein loading. In this work the nanoparticle preparation procedure was optimized in terms of size for administration in the inner ear, but the range of applications is not limited.

Drug Delivery across Barriers to the Middle and Inner Ear

The prevalence of ear disorders has spurred efforts to develop drug delivery systems to treat these conditions. Here, recent advances in drug delivery systems that access the ear through the tympanic membrane (TM) are reviewed. Such methods are either non-invasive (placed on the surface of the TM), or invasive (placed in the middle ear, ideally on the round window [RW]). The major hurdles to otic drug delivery are identified and highlighted the representative examples of drug delivery systems used for drug delivery across the TM to the middle and (crossing the RW also) inner ear.

The Expression and Roles of the Super Elongation Complex in Mouse Cochlear Lgr5+ Progenitor Cells

The super elongation complex (SEC) has been reported to play a key role in the proliferation and differentiation of mouse embryonic stem cells. However, the expression pattern and function of the SEC in the inner ear has not been investigated. Here, we studied the inner ear expression pattern of three key SEC components, AFF1, AFF4, and ELL3, and found that these three proteins are all expressed in both cochlear hair cells (HCs)and supporting cells (SCs). We also cultured Lgr5+ inner ear progenitors in vitro for sphere-forming assays and differentiation assays in the presence of the SEC inhibitor flavopiridol. We found that flavopiridol treatment decreased the proliferation ability of Lgr5+ progenitors, while the differentiation ability of Lgr5+ progenitors was not affected. Our results suggest that the SEC might play important roles in regulating inner ear progenitors and thus regulating HC regeneration. Therefore, it will be very meaningful to further investigate the detailed roles of the SEC signaling pathway in the inner ear in vivo in order to develop effective treatments for sensorineural hearing loss.

Approaches for ear-targeted delivery systems in neurosensory disorders to avoid chronic hearing loss mediated neurological diseases

BACKGROUND & OBJECTIVE

Hearing loss is a common audio-vestibular-related neurosensory disability of inner ears, in which patients exhibit clinical symptoms of dizziness, gait unsteadiness, and oscillopsia, at an initial stage. While, if such disorders are untreated for a prolonged duration then the progression of disease into a chronic state significantly decreases GABA level as well as an alteration in the neurotransmission of CNS systems. Hence, to control the progression of disease into a chronic state, timely and targeted delivery of the drug into the site of action in the ear is now attracting the interest of neurologists for effective and safe treatment of such disorders. Among delivery systems, owing to small dimension, better penetration, rate-controlled release, higher bioavailability; nanocarriers are preferred to overcome delivery barriers, improvement in residence time, and enhanced the performance of loaded drugs. Subsequently, these carriers also stabilize encapsulated drugs while the opportunity to modify the surface of carriers favors guided direction for site-specific targeting. Conventional routes of drug delivery such as oral. intravenous, and intramuscular are poorer in performance because of inadequate blood supply to the inner ear and limited penetration of blood-inner ear barrier.

CONCLUSION

This review summarized novel aspects of non-invasive and biocompatible nanoparticles-based approaches for targeted delivery of drugs into the cochlea of the ear to reduce the rate, and extent of the emergence of any hearing loss mediated neurological disorders.

Dual Strategy for Improving the Oral Bioavailability of Resveratrol: Enhancing Water Solubility and Inhibiting Glucuronidation

Resveratrol (RES) suffers from poor water solubility and extensive metabolism, which lead to low bioavailability. A phospholipid complex (PC) containing RES and a UDP-glucuronosyltransferase (UGT) inhibitor was prepared to address these two limiting factors, thereby improving RES bioavailability. First, 11 natural active ingredients metabolized by similar enzyme subtypes to RES were screened in a glucuronidation assay in liver microsomes. Then, glycyrrhetinic acid (GA), the strongest inhibitor, was prepared with RES in a PC. RES-PC was prepared as a control. As expected, the water solubility and the cumulative dissolution of RES were significantly enhanced by RES-PC and RES/GA-PC. Compared with the RES group, the AUC_0-10 of RES and resveratrol-3-glucuronide (R-3-G) in the RES/GA-PC group showed increases of 2.49- and 1.70-fold, respectively, with the proportion of RES absorption to total absorption increasing 1.45 times. These results demonstrated that RES/GA-PC could improve the bioavailability of RES by increasing its water solubility and inhibiting its glucuronidation.

Microtechnologies for inner ear drug delivery

PURPOSE OF REVIEW

Treatment of auditory dysfunction is dependent on inner ear drug delivery, with microtechnologies playing an increasingly important role in cochlear access and pharmacokinetic profile control. This review examines recent developments in the field for clinical and animal research environments.

RECENT FINDINGS

Micropump technologies are being developed for dynamic control of flow rates with refillable reservoirs enabling timed delivery of multiple agents for protection or regeneration therapies. These micropumps can be combined with cochlear implants with integral catheters or used independently with cochleostomy or round window membrane (RWM) delivery modalities for therapy development in animal models. Sustained release of steroids with coated cochlear implants remains an active research area with first-time-in-human demonstration of reduced electrode impedances. Advanced coatings containing neurotrophin producing cells have enhanced spiral ganglion neuron survival in animal models, and have proven safe in a human study. Microneedles have emerged for controlled microperforation of the RWM for significant enhancement in permeability, combinable with emerging matrix formulations that optimize biological interaction and drug release kinetics.

SUMMARY

Microsystem technologies are providing enhanced and more controlled access to the inner ear for advanced drug delivery approaches, alone and in conjunction with cochlear implants.

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.

Ultrasound Microbubble-Facilitated Inner Ear Delivery of Gold Nanoparticles Involves Transient Disruption of the Tight Junction Barrier in the Round Window Membrane

The application of ultrasound microbubbles (USMBs) enhances the permeability of the round window membrane (RWM) and improves drug delivery to the inner ear. In this study, we investigated the efficiency of USMB-aided delivery of chitosan-coated gold nanoparticles (CS-AuNPs) and the mechanism of USMB-mediated enhancement of RMW permeability. We exposed mouse inner ears to USMBs at an intensity of 2 W/cm² and then filled the tympanic bulla with CS-AuNPs or fluorescein isothiocyanate-decorated CS-AuNPs (FITC-CS-AuNPs). The membrane uptake of FITC-CS-AuNPs and their depth of permeation into the three-layer structure of the RWM, with or without prior USMB treatment, were visualized by z-stack confocal laser scanning microscopy. Ultrastructural changes in the RWM due to USMB-mediated cavitation appeared as sunburn-like peeling and various degrees of depression in the RWM surface, with pore-like openings forming in the outer epithelium. This disruption of the outer epithelium was paralleled by a transient reduction in tight junction (TJ)-associated protein levels in the RWM and an enhanced delivery of FITC-CS-AuNPs into the RWM. Without prior USMB exposure, the treatment with CS-AuNPs also caused a noticeable reduction in TJ proteins of the RWM. Our findings indicated that the combined treatment with USMBs and CS-AuNPs represents a promising and efficient drug and gene delivery vehicle for a trans-RWM approach for inner ear therapy. The outer epithelial layer of the RWM plays a decisive role in controlling the transmembrane transport of substances such as CS-AuNPs following the administration of USMBs. Most importantly, the enhanced permeation of AuNPs involved the transient disruption of the TJ-created paracellular barrier in the outer epithelium of the RWM.

Nanoparticles for the Treatment of Inner Ear Infections

The inner ear is sensitive to various infections of viral, bacterial, or fungal origin, which, if left untreated, may lead to hearing loss or progress through the temporal bone and cause intracranial infectious complications. Due to its isolated location, the inner ear is difficult to treat, imposing an acute need for improving current therapeutic approaches. A solution for enhancing antimicrobial treatment performance is the use of nanoparticles. Different inorganic, lipidic, and polymeric-based such particles have been designed, tested, and proven successful in the controlled delivery of medication, improving drug internalization by the targeted cells while reducing the systemic side effects. This paper makes a general presentation of common inner ear infections and therapeutics administration routes, further focusing on newly developed nanoparticle-mediated treatments.

Use of Super Paramagnetic Iron Oxide Nanoparticles as Drug Carriers in Brain and Ear: State of the Art and Challenges

Drug delivery and distribution in the central nervous system (CNS) and the inner ear represent a challenge for the medical and scientific world, especially because of the blood-brain and the blood-perilymph barriers. Solutions are being studied to circumvent or to facilitate drug diffusion across these structures. Using superparamagnetic iron oxide nanoparticles (SPIONs), which can be coated to change their properties and ensure biocompatibility, represents a promising tool as a drug carrier. They can act as nanocarriers and can be driven with precision by magnetic forces. The aim of this study was to systematically review the use of SPIONs in the CNS and the inner ear. A systematic PubMed search between 1999 and 2019 yielded 97 studies. In this review, we describe the applications of the SPIONS, their design, their administration, their pharmacokinetic, their toxicity and the methods used for targeted delivery of drugs into the ear and the CNS.

Base editing: advances and therapeutic opportunities

Base editing - the introduction of single-nucleotide variants (SNVs) into DNA or RNA in living cells - is one of the most recent advances in the field of genome editing. As around half of known pathogenic genetic variants are due to SNVs, base editing holds great potential for the treatment of numerous genetic diseases, through either temporary RNA or permanent DNA base alterations. Recent advances in the specificity, efficiency, precision and delivery of DNA and RNA base editors are revealing exciting therapeutic opportunities for these technologies. We expect the correction of single point mutations will be a major focus of future precision medicine.

Nanocarriers for drug delivery to the inner ear: Physicochemical key parameters, biodistribution, safety and efficacy

Despite the high incidence of inner ear disorders, there are still no dedicated medications on the market. Drugs are currently administered by the intratympanic route, the safest way to maximize drug concentration in the inner ear. Nevertheless, therapeutic doses are ensured for only a few minutes/hours using drug solutions or suspensions. The passage through the middle ear barrier strongly depends on drug physicochemical characteristics. For the past 15 years, drug encapsulation into nanocarriers has been developed to overcome this drawback. Nanocarriers are well known to sustain drug release and protect it from degradation. In this review, in vivo studies are detailed concerning nanocarrier biodistribution, their pathway mechanisms in the inner ear and the resulting drug pharmacokinetics. Key parameters influencing nanocarrier biodistribution are identified and discussed: nanocarrier size, concentration, surface composition and shape. Recent advanced strategies that combine nanocarriers with hydrogels, specific tissue targeting or modification of the round window permeability (cell-penetrating peptide, magnetic delivery) are explored. Most of the nanocarriers appear to be safe for the inner ear and provide a significant efficacy over classic formulations in animal models. However, many challenges remain to be overcome for future clinical applications.

A metal-organic framework based inner ear delivery system for the treatment of noise-induced hearing loss

Noise-induced hearing loss (NIHL) is associated with both acute and chronic noise exposure. The application of steroid hormones is the first-line treatment for NIHL. However, a high dose of steroid hormone in the body is necessary to maintain its efficacy and causes side effects, such as headache and osteoporosis. In this work, we prepared a zeolitic imidazolate framework (ZIF)-based system for steroid hormone delivery in the inner ear. Methylprednisolone (MP), a typical steroid hormone, was encapsulated into ZIF-90 nanoparticles (NPs) using one-pot synthesis method. The obtained MP@ZIF-90 NPs are negatively charged and 120 nm in size and showed good biocompatibility and stability at a pH value of 7.4. After intraperitoneal injection, ZIF-90 could efficiently protect drugs during peripheral blood circulation, enter the inner ear via the blood labyrinthine barrier (BLB) and slowly release the drugs. Auditory brainstem response (ABR) tests indicated that MP@ZIF-90 exhibits better protection of mice from noise than those using the free MP and ZIF-8 with encapsulated MP (MP@ZIF-8). More importantly, MP@ZIF-90 showed no defects to the inner ear after being treated for noise and low nephrotoxicity during therapy, which demonstrates the biocompatibility of this material. We believe the ZIF-90 based delivery system is an efficient strategy for inner ear therapy of NIHL.

Development of nanoparticle drug-delivery systems for the inner ear

Hearing loss has become the most common sensory nerve disorder worldwide, with no effective treatment strategy. Low-permeability and limited blood supply to the blood-labyrinth barrier limit the effective delivery and efficacy of therapeutic drugs in the inner ear. Nanoparticle (NP)-based drugs have shown benefits of stable controlled release and functional surface modification, and NP-based delivery systems have become a research hotspot. In this review, we discuss the development of new targeted drug-delivery systems based on the biocompatibility and safety of different NPs in the cochlea, as well as the advantages and disadvantages of their prescription methods and approaches. We believe that targeted NP-based drug-delivery systems will be effective treatments for hearing loss.

Lithium niobate nanoparticles as biofunctional interface material for inner ear devices

Sensorineural hearing loss (SNHL) affects the inner ear compartment and can be caused by different factors. Usually, the lack, death, or malfunction of sensory cells deputed to transduction of mechanic-into-electric signals leads to SNHL. To date, the therapeutic option for patients impaired by severe or profound SNHL is the cochlear implant (CI), a high-tech electronic device replacing the entire cochlear function. Piezoelectric materials have catalyzed attention to stimulate the auditory neurons by simply mimicking the function of the cochlear sensory epithelium. In this study, the authors investigated lithium niobate (LiNbO₃) as a potential candidate material for next generation CIs. LiNbO₃ nanoparticles resulted otocompatible with inner ear cells in vitro, had a pronounced immunomodulatory activity, enhanced human beta-defensin in epithelial cells, and showed direct antibacterial activity against P. aeruginosa. Moreover, LiNbO₃ nanoparticles were incorporated into poly(vinylidene fluoride-trifluoro ethylene) fibers via electrospinning, which enhanced the piezoelectric response. Finally, the resulting fibrous composite structures support human neural-like cell growth in vitro, thus showing promising features to be used in new inner ear devices.

Inner ear delivery: Challenges and opportunities

OBJECTIVES

The treatment of inner ear disorders remains challenging due to anatomic barriers intrinsic to the bony labyrinth. The purpose of this review is to highlight recent advances and strategies for overcoming these barriers and to discuss promising future avenues for investigation.

DATA SOURCES

The databases used were PubMed, EMBASE, and Web of Science.

RESULTS

Although some studies aimed to improve systemic delivery using nanoparticle systems, the majority enhanced local delivery using hydrogels, nanoparticles, and microneedles. Developments in direct intracochlear delivery include intracochlear injection and intracochlear implants.

CONCLUSIONS

In the absence of a systemic drug that targets only the inner ear, the best alternative is local delivery that harnesses a combination of new strategies to overcome anatomic barriers. The combination of microneedle technology with hydrogel and nanoparticle delivery is a promising area for future investigation.

LEVEL OF EVIDENCE

NA.

Delivering Therapeutics to the Cochlea: The Importance of the Patient's Perspective

Hearing loss represents a major sensory impairment in humans with a strong impact on quality of life. The current standard of care for chronic sensorineural hearing loss is limited to hearing aids and implantable devices like cochlear implants. Treatments for acute hearing loss consist of systemic or intratympanic corticosteroids. Emerging therapies are being developed to prevent hearing loss or to restore it at the cellular level. Many challenges and questions remain as to the delivery of these therapeutics into the inner ear. Scientists, clinicians, and industry stakeholders should always consider the treatment burden from the patient's perspective when designing new drug delivery approaches. This article highlights key issues to consider.

Effect of TiO2 and Fe doped TiO2 nanoparticles on mitochondrial membrane potential in HBL-100 cells

Titanium dioxide (TiO₂) nanoparticles (NPs) have made unbelievable progress in the field of nanotechnology and biomedical research. The proper toxicological assessment of TiO₂ NPs and the reduction of its cytotoxicity need to be addressed. Fe doping in TiO₂ has been investigated to reduce the toxic effects of TiO₂ NPs. Fe doped TiO₂ powder samples were synthesized by sol-gel methods. The prepared samples were characterized by x-ray diffractometer (XRD), transmission electron microscope (TEM), and Raman spectroscopy to study their structure, morphology, and molecular conformation. XRD results revealed the coexistence of anatase (A) and rutile (R) phases of TiO₂. The A-R transformation was observed with an increase in Fe doping along with the formation of α-Fe₂O₃ phase. TEM showed changes in morphology from spherical nanoparticles to elongated rod-shaped nanostructures with increasing Fe content. Shape variation of TiO₂ nanoparticles after incorporation of Fe is a key reason behind the toxicity reduction. The authors observed that the toxicity of TiO₂ nanoparticles was rescued upon Fe incorporation. The effect of NPs on the mitochondrial membrane potential (MMP) was assessed using flow cytometry. The MMP (%) decreased in TiO₂ treated cells and increased by 1% Fe doped TiO₂ NPs treated cells. Confocal imaging revealed the presence of functional mitochondria upon the exposure of Fe doped TiO₂ NPs. The goal of the present study was to decrease the toxic effects induced by TiO₂ NPs on mitochondrial potential and its prevention by Fe doping.