Distribution of PLGA nanoparticles in chinchilla cochleae

Probucol-bile acid nanoparticles: a novel approach and promising solution to prevent cellular oxidative stress in sensorineural hearing loss

The use of antioxidants could thus prove an effective medication to prevent or facilitate recovery from oxidative stress-induced sensorineural hearing loss (SNHL). One promising strategy to prevent SNHL is developing probucol (PB)-based nanoparticles using encapsulation technology and administering them to the inner ear via the established intratympanic route. The preclinical, clinical and epidemiological studies support that PB is a proven antioxidant that could effectively prevent oxidative stress in different study models. Such findings suggest its applicability in preventing oxidative stress within the inner ear and its associated neural cells. However, several hurdles, such as overcoming the blood-labyrinth barrier, ensuring sustained release, minimising systemic side effects and optimising targeted delivery in the intricate inner ear structures, must be overcome to efficiently deliver PB to the inner ear. This review explores the background and pathogenesis of hearing loss, the potential of PB in treating oxidative stress and its cellular mechanisms, and the obstacles linked to inner ear drug delivery for effectively introducing PB to the inner ear.

The current status of nanotechnological approaches to therapy and drug delivery in otolaryngology: A contemporary review

Objectives/Hypothesis

To summarize the current standing of nanomedicine-based technology, particularly nanoparticles (NPs), for drug delivery and diagnostic mechanisms in otolaryngology and the otolaryngology subspecialties.

Methods

Literature searches were performed using PubMed and Ovid MEDLINE from 2010 to 2022. The search focused on original articles describing developments and applications of nanotechnology and drug delivery in otology, neurotology, cranial base surgery, head and neck oncology, laryngology, bronchoesophagology, and rhinology. Keyword searches and cross-referencing were also performed. No statistical analysis was performed.

Results

The PubMed search yielded 29 articles, and two Ovid MEDLINE searches both yielded 7 and 26 articles, respectively. Cross-referencing and keyword searches in PubMed and Google Scholar yielded numerous articles. The results indicate that currently, NPs are the most thoroughly studied nanotechnology for drug delivery and therapy in otolaryngology. Organic NPs have been utilized for drug delivery in otology and head and neck oncology due to their high biocompatibility. Inorganic NPs have similarly been utilized for drug delivery. However, inorganic NPs seem to be studied less extensively in these fields, likely due to an increased risk for heavy metal toxicity. Due to their magnetic properties, inorganic NPs have been utilized for magnetic-guided delivery in otology and thermoradiation and magnetic resonance imaging in head and neck oncology. Applications of nanotechnology to the fields of laryngology, bronchoesophagology, and rhinology have been studied less compared with otology and head and neck oncology. However, researchers have primarily employed NPs and other nanotechnologies such as nanofibers and nanoclusters for drug elution at mucosal surfaces to reduce airway and nasal inflammation.

Conclusions

Nanomedicine offers potential benefits in the treatment of patients in the field of otolaryngology due to enhanced control over drug release, cell-specific targeting, and the potential to reduce drug toxicity. Future work is needed to ensure the safety of these therapies to integrate this field of research into human therapies.

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.

Topical Delivery of Elastic Liposomal Vesicles for Treatment of Middle and Inner Ear Diseases

We present a topical drug delivery mechanism through the ear canal to the middle and inner ear using liposomal nanoparticles without disrupting the integrity of the tympanic membrane. The current delivery method provides a noninvasive and safer alternative to transtympanic membrane injections, ear tubes followed by ear drops administration, and systemic drug formulations. We investigate the capability of liposomal NPs, particularly transfersomes (TLipo), used as drug delivery vesicles to penetrate the tympanic membrane (TM) and round window membrane (RWM) with high affinity, specificity, and retention time. The TLipo is applied to the ear canal and found to pass through the tympanic membrane quickly in 3 h post drug administration. They are identified in the middle ear cavity 6 h and in the inner ear 24 h after drug administration. We performed cytotoxicity in vitro and ototoxicity in vivo studies. Cell viability shows no significant difference between the applied TLipo concentration and control. Furthermore, auditory brainstem response (ABR) reveals no hearing loss in 1 week and 1 month post-administration. Immunohistochemistry results demonstrate no evidence of hair cell loss in the cochlea at 1 month following TLipo administration. Together, the data suggested that TLipo can be used as a vehicle for topical drug delivery to the middle ear and inner ear.

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.

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.

Inner Ear Drug Delivery for Sensorineural Hearing Loss: Current Challenges and Opportunities

Most therapies for treating sensorineural hearing loss are challenged by the delivery across multiple tissue barriers to the hard-to-access anatomical location of the inner ear. In this review, we will provide a recent update on various pharmacotherapy, gene therapy, and cell therapy approaches used in clinical and preclinical studies for the treatment of sensorineural hearing loss and approaches taken to overcome the drug delivery barriers in the ear. Small-molecule drugs for pharmacotherapy can be delivered via systemic or local delivery, where the blood-labyrinth barrier hinders the former and tissue barriers including the tympanic membrane, the round window membrane, and/or the oval window hinder the latter. Meanwhile, gene and cell therapies often require targeted delivery to the cochlea, which is currently achieved via intra-cochlear or intra-labyrinthine injection. To improve the stability of the biomacromolecules during treatment, e.g., RNAs, DNAs, proteins, additional packing vehicles are often required. To address the diverse range of biological barriers involved in inner ear drug delivery, each class of therapy and the intended therapeutic cargoes will be discussed in this review, in the context of delivery routes commonly used, delivery vehicles if required (e.g., viral and non-viral nanocarriers), and other strategies to improve drug permeation and sustained release (e.g., hydrogel, nanocarriers, permeation enhancers, and microfluidic systems). Overall, this review aims to capture the important advancements and key steps in the development of inner ear therapies and delivery strategies over the past two decades for the treatment and prophylaxis of sensorineural hearing loss.

Local drug delivery using poly(lactic-co-glycolic acid) nanoparticles in thermosensitive gels for inner ear disease treatment

Intratympanic (IT) therapies have been explored to address several side effects that could be caused by systemic administration of steroids to treat inner ear diseases. For effective drug delivery to the inner ear, an IT delivery system was developed using poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) and thermosensitive gels to maintain sustained release. Dexamethasone (DEX) was used as a model drug. The size and zeta potential of PLGA NPs and the gelation time of the thermosensitive gel were measured. In vitro drug release was studied using a Franz diffusion cell. Cytotoxicity of the formulations was investigated using SK-MEL-31 cells. Inflammatory responses were evaluated by histological observation of spiral ganglion cells and stria vascularis in the mouse cochlea 24 h after IT administration. In addition, the biodistribution of the formulations in mouse ears was observed by fluorescence imaging using coumarin-6. DEX-NPs showed a particle size of 150.0 ± 3.2 nm in diameter and a zeta potential of −18.7 ± 0.6. The DEX-NP-gel showed a gelation time of approximately 64 s at 37 °C and presented a similar release profile and cytotoxicity as that for DEX-NP. Furthermore, no significant inflammatory response was observed after IT administration. Fluorescence imaging results suggested that DEX-NP-gel sustained release compared to the other formulations. In conclusion, the PLGA NP-loaded thermosensitive gel may be a potential drug delivery system for the inner ear.

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.

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.

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.

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.

Opportunities and challenging issues of nanomaterials in otological fields: an occupational health perspective

Nanotechnology may offer innovative solutions to overcome the physiological and anatomical barriers that make the diagnosis and treatment of ear diseases an extremely challenging issue. However, despite the solutions provided by nano-applications, the still little-known toxicological behavior of nanomaterials raised scientific concerns regarding their biosafety for treated patients and exposed workers. Therefore, this review provides an overview on recent developments and upcoming opportunities in nanoscale otological applications, and critically assesses possible adverse effects of nanosized compounds on ear structures and hearing functionality. Although such preliminary data do not allow to draw definite strategies for the evaluation of nanomaterial ototoxicity, they can still be useful to improve scientific community and workforce awareness regarding possible nanomaterial adverse effects on ear.

A 3D Microscaffold Cochlear Electrode Array for Steroid Elution

In cochlear implants, the electrode insertion trauma during surgery can cause damage residual hearing. Preserving the residual hearing is an important challenge and the localized administration of drugs, such as steroids, is one of the most promising ways, but remains a challenge. Here, a microscaffold cochlear electrode array (MiSCEA) consisting of a microfabricated flexible electrode array and a 3D microscaffold for steroid reservoir is reported. The MiSCEA without loaded drug is tested by measuring the electrically evoked auditory brainstem response of the cochlea in guinea pigs (n = 4). The scaffold is then coated with steroid (dexamethasone) encapsulated in polylactic-co-glycolic acid and the continuous release of the steroid into artificial perilymph during six weeks is monitored. The steroid-containing scaffolds are then implanted into guinea pigs (n = 4) and threshold shifts are analyzed for four weeks by measuring the acoustically evoked auditory brainstem response. The threshold shifts tend to be lower in the group implanted with the steroid-containing MiSCEAs. The feasibility of 3D MiSCEA opens up the development of potential next-generation cochlear electrode with improved steroid release dynamics into cochlea.

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

Hearing loss is the most common neurosensory impairment worldwide. While conductive hearing loss can be managed by surgery, the management of sensorineural hearing loss (SNHL), related to the damage of sensory cells of the inner ear is more challenging to manage medically. Many causes of SNHL such as sudden idiopathic SNHL, Meniere's disease, noise-induced hearing loss, autoimmune hearing loss or hearing loss from exposure to ototoxic substances can benefit from delivery of otoprotective drugs to the inner ear. However, systemic drug delivery through oral, intravenous and intramuscular methods leads to undesirable side effects due to the inner ear's limited blood supply and the relatively poor penetration of the blood-inner ear barrier (BLB). Therefore, there has been an increased interest for the targeted drug delivery to the inner ear using nanoparticles. Drug delivery through nanoparticles offers several advantages including drug stabilization for controlled release and surface modification for specific targeting. Understanding the biocompatibility of nanoparticles with cochlea and developing novel non-invasive delivery methods will promote the translation of nanoparticle-mediated drug delivery for auditory disorders from bench to bedside.

Toward the Optical Cochlear Implant

When hearing fails, cochlear implants (CIs) provide open speech perception to most of the currently half a million CI users. CIs bypass the defective sensory organ and stimulate the auditory nerve electrically. The major bottleneck of current CIs is the poor coding of spectral information, which results from wide current spread from each electrode contact. As light can be more conveniently confined, optical stimulation of the auditory nerve presents a promising perspective for a fundamental advance of CIs. Moreover, given the improved frequency resolution of optical excitation and its versatility for arbitrary stimulation patterns the approach also bears potential for auditory research. Here, we review the current state of the art focusing on the emerging concept of optogenetic stimulation of the auditory pathway. Developing optogenetic stimulation for auditory research and future CIs requires efforts toward viral gene transfer to the neurons, design and characterization of appropriate optogenetic actuators, as well as engineering of multichannel optical implants.

Inner Ear Therapeutics: An Overview of Middle Ear Delivery

There are a variety of methods to access the inner ear and many of these methods depend on utilizing the middle ear as a portal. In this approach the middle ear can be used as a passive receptacle, as part of an active drug delivery system, or simply as the most convenient way to access the inner ear directly in human subjects. The purpose of this volume is to examine some of the more cutting-edge approaches to treating the middle ear. Before considering these therapies, this manuscript provides an overview of some therapies that have been delivered through the middle ear both in the past and at the current time. This manuscript also serves as a review of many of the methods for accessing the inner ear that directly utilize or pass though the middle ear. This manuscript provides the reader a basis for understanding middle ear delivery, the basis of delivery of medicines via cochlear implants, and examines the novel approach of using hypothermia as a method of altering the responses of the inner ear to damage.

Local Drug Delivery for the Treatment of Neurotology Disorders

Neurotology disorders such as vertigo, tinnitus, and hearing loss affect a significant proportion of the population (estimated 39 million in the United States with moderate to severe symptoms). Yet no pharmacological treatments have been developed, in part due to limitations in effective drug delivery to the anatomically protected inner ear compartment. Intratympanic delivery, a minimally invasive injection performed in the office setting, offers a potential direct route of administration. Currently, off-label use of therapeutics approved to treat disorders via systemic administration are being injected intratympanically, mostly in the form of aqueous solutions, but provide variable levels of drug exposure for a limited time requiring repeated injections. Hence, current drug delivery approaches for neurotology disorders are sub-optimal. This review, following a description of pharmacokinetic considerations of the inner ear, explores the merits of novel delivery approaches toward the treatment of neurotology disorders. Methodologies employing local delivery to the inner ear are described, including direct intracochlear delivery as well as intratympanic methods of infusion and injection. Intratympanic injection delivery formulation strategies including hydrogels, polymers and nanoparticulate systems are explored. These approaches represent progress toward more effective delivery options for the clinical treatment of a variety of neurotology disorders.

Innovative pharmaceutical approaches for the management of inner ear disorders

The sense of hearing is essential for permitting human beings to interact with the environment, and its dysfunctions can strongly impact on the quality of life. In this context, the cochlea plays a fundamental role in the transformation of the airborne sound waves into electrical signals, which can be processed by the brain. However, several diseases and external stimuli (e.g., noise, drugs) can damage the sensorineural structures of cochlea, inducing progressive hearing dysfunctions until deafness. In clinical practice, the current pharmacological approaches to treat cochlear diseases are based on the almost exclusive use of systemic steroids. In the last decades, the efficacy of novel therapeutic molecules has been proven, taking advantage from a better comprehension of the pathological mechanisms underlying many cochlear diseases. In addition, the feasibility of intratympanic administration of drugs also permitted to overcome the pharmacokinetic limitations of the systemic drug administration, opening new frontiers in drug delivery to cochlea. Several innovative drug delivery systems, such as in situ gelling systems or nanocarriers, were designed, and their efficacy has been proven in vitro and in vivo in cochlear models. The current review aims to describe the art of state in the cochlear drug delivery, highlighting lights and shadows and discussing the most critical aspects still pending in the field.

Regeneration of Cochlear Hair Cells and Hearing Recovery through Hes1 Modulation with siRNA Nanoparticles in Adult Guinea Pigs

Deafness is commonly caused by the irreversible loss of mammalian cochlear hair cells (HCs) due to noise trauma, toxins, or infections. We previously demonstrated that small interfering RNAs (siRNAs) directed against the Notch pathway gene, hairy and enhancer of split 1 (Hes1), encapsulated within biocompatible poly(lactic-co-glycolic acid) nanoparticles (PLGA NPs) could regenerate HCs within ototoxin-ablated murine organotypic cultures. In the present study, we delivered this sustained-release formulation of Hes1 siRNA (siHes1) into the cochleae of noise-injured adult guinea pigs. Auditory functional recovery was measured by serial auditory brainstem responses over a nine-week follow-up period, and HC regeneration was evaluated by immunohistological evaluations and scanning electron microscopy. Significant HC restoration and hearing recovery were observed across a broad tonotopic range in ears treated with siHes1 NPs, beginning at three weeks and extending out to nine weeks post-treatment. Moreover, both ectopic and immature HCs were uniquely observed in noise-injured cochleae treated with siHes1 NPs, consistent with de novo HC production. Our results indicate that durable cochlear HCs were regenerated and promoted significant hearing recovery in adult guinea pigs through reversible modulation of Hes1 expression. Therefore, PLGA-NP-mediated delivery of siHes1 to the cochlea represents a promising pharmacologic approach to regenerate functional and sustainable mammalian HCs in vivo.

Understanding the translocation mechanism of PLGA nanoparticles across round window membrane into the inner ear: a guideline for inner ear drug delivery based on nanomedicine

Background

The round window membrane (RWM) functions as the primary biological barrier for therapeutic agents in the inner ear via local application. Previous studies on inner ear nano-drug delivery systems mostly focused on their pharmacokinetics and distribution in the inner ear, but seldom on the interaction with the RWM. Clarifying the transport mechanism of nanoparticulate carriers across RWM will shed more light on the optimum design of nano-drug delivery systems intended for meeting demands for their clinical application.

Methods

The poly (lactic-co-glycolic acid) nanoparticles (PLGA NPs) encapsulating coumarin-6 were prepared by emulsifying solvent evaporation method. We utilized confocal laser scanning microscope (CLSM) in combination with transmission electron microscope to investigate the transport pathway of PLGA NPs in the RWM. Simultaneously, the concentration and time dependence of NPs across the RWM were also determined. The endocytic mechanism of NPs through this membrane interface was classically analyzed by means of various endocytic inhibitors. The intracellular location of NPs into lysosomes was evaluated using CLSM scanning microscope colocalization analysis. The Golgi-related inhibitors were employed to probe into the function of Golgi and endoplasmic reticulum (ER) in the discharge of NPs out of cells.

Results

PLGA NPs were herein transported through the RWM of a sandwich-like structure into the perilymph via the transcellular pathway. NPs were internalized predominantly via macropinocytosis and caveolin-mediated endocytic pathways. After being internalized, the endocytosed cargos were entrapped within the lysosomal compartments and/or the endoplasmic reticulum/Golgi apparatus which mediated the exocytotic release of NPs.

Conclusion

For the first time, we showed the translocation itinerary of NPs in RWM, providing a guideline for the rational fabrication of inner ear nanoparticulate carriers with better therapeutic effects.

Potentiation of Otoprotective Effect of Hydrocortisone Immobilized on Povidone Nanoparticles under Conditions of Intravenous Injection

The otoprotective effect of immobilized hydrocortisone was studied on the model of acute acoustic injury to the auditory analyzer in male Wistar rats. The effects of true solution and suspension where polyvinylpyrrolidone particles (100-500 nm) served as dispersed phase (hydrocortisone concentration 5 mg/kg). The agents were administered immediately after continuous acoustic stimulation: 5 kHz tone, 110 dB for 2 h. The hearing status was evaluated by the amplitude of otoacoustic emission at the distortion product frequency (4-6.4 kHz) 1 and 24 h and 7 days after acoustic stimulation. Single injection of hydrocortisone suspension caused a more pronounced therapeutic effect within 1 day after acoustic stimulation.

Challenges and opportunities in developing targeted molecular imaging to determine inner ear defects of sensorineural hearing loss

The development of inner ear gene carriers and delivery systems has enabled genetic defects to be repaired and hearing to be restored in mouse models. Today, promising advances in translational therapies provide confidence that targeted molecular therapy for inner ear diseases will be developed. Unfortunately, the currently available non-invasive modalities, such as Computerized Tomography scan or Magnetic Resonance Imaging provide insufficient resolution to identify most pathologies of the human inner ear, even when the current generation of contrast agents is utilized. The development of targeted contrast agents may play a critical role in determining the cause of, and treatment for, sensorineural hearing loss. Such agents should be able to pass through the cochlea barriers, possess minimal cytotoxicity, and easily conjugate to a targeting agent, without distorting the anatomic details. This review focuses on a series of contrast agents which may fit these criteria for potential clinical application.

A novel vehicle for local protein delivery to the inner ear: injectable and biodegradable thermosensitive hydrogel loaded with PLGA nanoparticles

Delivery of biomacromolecular drugs into the inner ear is challenging, mainly because of their inherent instability as well as physiological and anatomical barriers. Therefore, protein-friendly, hydrogel-based delivery systems following local administration are being developed for inner ear therapy. Herein, biodegradable poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) containing interferon α-2 b (IFN α-2 b) were loaded in chitosan/glycerophosphate (CS/GP)-based thermosensitive hydrogel for IFN delivery by intratympanic injection. The injectable hydrogel possessed a physiological pH and formed semi-solid gel at 37 °C, with good swelling and deswelling properties. The CS/GP hydrogel could slowly degrade as visualized by scanning electron microscopy (SEM). The presence of NPs in CS/GP gel largely influenced in vitro drug release. In the guinea pig cochlea, a 1.5- to 3-fold increase in the drug exposure time of NPs-CS/GP was found than those of the solution, NPs and IFN-loaded hydrogel. Most importantly, a prolonged residence time was attained without obvious histological changes in the inner ear. This biodegradable, injectable, and thermosensitive NPs-CS/GP system may allow longer delivery of protein drugs to the inner ear, thus may be a potential novel vehicle for inner ear therapy.

Engineering PLGA nano-based systems through understanding the influence of nanoparticle properties and cell-penetrating peptides for cochlear drug delivery

The properties of poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) and penetration enhancers play a deciding role in the inner ear drug delivery of NPs across the round window membrane (RWM). Thus, PLGA nano-based systems with a variety of particle sizes and surface chemistries and those combined with cell-penetrating peptides (CPPs) as penetration enhancers were devised to explore their impact on the cochlear drug delivery in vivo. First, we demonstrated that the properties of NPs dictated the extent of NP cochlear entry by near-infrared fluorescence imaging. NPs with the sizes of 150 and 300nm had faster entry than that of 80nm NPs. At 0.5h, among the NPs unmodified and modified with chitosan (CS), poloxamer 407 (P407) and methoxy polyethylene glycol, CS-PLGA-NPs (positive surface charge) carried payload to the cochlea fastest, whereas P407-PLGA-NPs (surface hydrophilicity) showed the greatest distribution in the cochlea at 24h. Compared to other CPPs (TAT, penetratin and poly(arginine)₈), low molecular weight protamine (LMWP) performed an outstanding enhanced NP cellular uptake in HEI-OC1 cells and cochlear entry. More importantly, NPs with optimized properties and CPPs may be combined to improve RWM penetration. For the first time, we confirmed that the combination of P407-PLGA-NPs (mean diameter: 100-200nm) and LMWP provided a synergistic enhancement in NP entry to the organ of Corti and stria vascularis without inducing pathological alteration of cochlear tissues and RWM. Taken together, we propose an effective PLGA nano-based strategy for enhanced drug delivery to the inner ear tissues that combines hydrophilic molecule-modified NPs and CPPs, ultimately opening an avenue for superior inner ear therapy.

siRNA-loaded biodegradable nanocarriers for therapeutic MAPK1 silencing against cisplatin-induced ototoxicity

Ototoxicity represents a major adverse side-effect of cis-diamminedichloroplatinum-II (cisplatin, CDDP). The mitogen-activated protein kinase (MAPK) pathway is thought to play a central role in potentiating the apoptotic effect of CDDP within the cochlea. We hypothesized that prophylactic inhibition of MAPK signaling, using small interfering RNA (siRNA), might confer a protective effect against CDDP-induced apoptosis within the auditory sensory epithelia. To enhance the therapeutic utility of this approach, we synthesized biocompatible siMAPK1-loaded nanoparticles (NPs) and performed physicochemical characterizations for size, morphology, drug loading and release kinetics, using dynamic light scattering, electron microscopy and spectrophotometric analyses, respectively. Our findings show 183.88±6.26 nm-sized spherical siMAPK1-loaded NPs with -27.12±6.65mV zeta potential and 112.78±0.24pmol/mg of siMAPK1 loading that exhibit a sustained release profile for prolonged therapeutic efficacy. Synthesized NPs were validated for biocompatibility and prophylactically protected against CDDP-induced cytotoxicity in HEI-OC1 cells and hair cell loss in murine organotypic cochlear explants. Our study confirms a pivotal role for MAPK1 signaling as a potentiating factor for CDDP-induced apoptosis and cochlear hair cell loss, and highlights siMAPK1 NP treatment as a therapeutic strategy for limiting the ototoxic side-effects associated with systemic CDDP administration.

Advances in nano-based inner ear delivery systems for the treatment of sensorineural hearing loss

Sensorineural hearing loss (SNHL) is one of the most common diseases, accounting for about 90% of all hearing loss. Leading causes of SNHL include advanced age, ototoxic medications, noise exposure, inherited and autoimmune disorders. Most of SNHL is irreversible and managed with hearing aids or cochlear implants. Although there is increased understanding of the molecular pathophysiology of SNHL, biologic treatment options are limited due to lack of noninvasive targeted delivery systems. Obstacles of targeted inner ear delivery include anatomic inaccessibility, biotherapeutic instability, and nonspecific delivery. Advances in nanotechnology may provide a solution to these barriers. Nanoparticles can stabilize and carry biomaterials across the round window membrane into the inner ear, and ligand bioconjugation onto nanoparticle surfaces allows for specific targeting. A newer technology, nanohydrogel, may offer noninvasive and sustained biotherapeutic delivery into specific inner ear cells. Nanohydrogel may be used for inner ear dialysis, a potential treatment for ototoxicity-induced SNHL.

Label-Free Ferrocene-Loaded Nanocarrier Engineering for In Vivo Cochlear Drug Delivery and Imaging

It is hypothesized that ferrocene (FC)-loaded nanocarriers (FC-NCs) are safe label-free contrast agents for cochlear biodistribution study by transmission electron microscopy (TEM). To test this hypothesis, after engineering, the poly(epsilon-caprolactone)/polyglycolide NCs are tested for stability with various types and ratios of sugar cryoprotectants during freeze-drying. Their physicochemical properties are characterized by UV-visible spectroscopy, dynamic light scattering, Fourier transform infrared spectroscopy, and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDS). The biodistribution of the FC-NCs in the cochlear tissue after intratympanic injection in guinea pigs is visualized by TEM. Auditory brainstem responses are measured before and after 4-day treatments. These FC-NCs have 153.4 ± 8.7 nm, 85.5 ± 11.2%, and -22.1 ± 1.1 mV as mean diameters, percent drug association efficiency, and zeta potential, respectively (n = 3). The incorporation of FC into the NCs is confirmed by Fourier transform infrared spectroscopy and SEM/EDS spectra. Lactose (3:1 ratio, v/v) is the most effective stabilizer after a 12-day study. The administered NCs are visible by TEM in the scala media cells of the cochlea. Based on auditory brainstem response data, FC-NCs do not adversely affect hearing. Considering the electrondense, radioactive, and magnetic properties of iron inside FC, FC-NCs are promising nanotemplate for future inner ear theranostics.

Superparamagnetic nanoparticles as vectors for inner ear treatments: driving and toxicity evaluation

Conclusion Super paramagnetic nanoparticles (MNP) are a promising vector to achieve controlled drug delivery into the cochlea. Objective The goal of the study was to evaluate the toxicological risk of MNP upon the inner ear. Methods Fe3O4-MNP displacement was studied in various catheter materials, shape, and solvent with a local magnetic field. EC5V cells (derived from the inner ear) were cultured with MNP (100 and 500 nm) at various concentrations or without MNP. Cell survival was assessed with a flow cytometry analysis. Localization of MNP within the cells was studied with confocal microscopy. In vivo, a single intra-cochlear administration of 200 nm MNP (3 × 10(10)MNP/mL, n = 8; 1.5 × 10(12) MNP/mL, n = 6) or saline (n = 14) was performed in guinea pigs. Hearing thresholds were assessed with auditory brainstem responses at Day 7. Results MNP could be concentrated at different locations of the catheter with sequential activation of solenoids. MNP were internalized in the cytoplasm, but not in the nuclei nor in endosomes at 48 h. After 48 h of incubation, no difference for cell survival between the groups was observed, whatever the MNP concentration. A size effect was observed with less survival in the 100 nm group. In guinea pigs at day 7, hearing threshold shift was not different in the three groups.

A novel chitosan-hydrogel-based nanoparticle delivery system for local inner ear application

HYPOTHESIS

A chitosan-hydrogel-based nanoparticle (nanohydrogel) delivery system can be used to deliver therapeutic biomaterials across the round window membrane (RWM) into the inner ear in a mouse model.

BACKGROUND

Delivering therapies to the inner ear has always been a challenge for the otolaryngologist. Advances in biomedical nanotechnology, increased understanding of the RWM diffusion properties, and discovery of novel therapeutic targets and agents, have all sparked interest in the controlled local delivery of drugs and biomaterials to the inner ear using nanoparticles (NPs).

METHODS

Fluorescently-labeled liposomal NPs were constructed and loaded into a chitosan-based hydrogel to form a nanohydrogel, and in vitro studies were performed to evaluate its properties and release kinetics. Furthermore, the nanohydrogel was applied to the RWM of mice, and perilymph and morphologic analysis were performed to assess the NP delivery and distribution within the inner ear.

RESULTS

NPs with an average diameter of 160 nm were obtained. In vitro experiments showed that liposomal NPs can persist under physiologic conditions for at least two weeks without significant degradation and that the nanohydrogel can carry and release these NPs in a controlled and sustained manner. In vivo findings demonstrated that the nanohydrogel can deliver intact nanoparticles into the perilymphatic system and reach cellular structures in the scala media of the inner ear of our mouse model.

CONCLUSION

Our study suggests that the nanohydrogel system has great potential to deliver therapeutics in a controlled and sustained manner from the middle ear to the inner ear without altering inner ear structures.

Recent advances in local drug delivery to the inner ear

Inner ear diseases are not adequately treated by systemic drug administration mainly because of the blood-perilymph barrier that reduces exchanges between plasma and inner ear fluids. Local drug delivery methods including intratympanic and intracochlear administrations are currently developed to treat inner ear disorders more efficiently. Intratympanic administration is minimally invasive but relies on diffusion through middle ear barriers for drug entry into the cochlea, whereas intracochlear administration offers direct access to the colchlea but is rather invasive. A wide range of drug delivery systems or devices were evaluated in research and clinic over the last decade for inner ear applications. In this review, different strategies including medical devices, hydrogels and nanoparticulate systems for intratympanic administration, and cochlear implant coating or advanced medical devices for intracoclear administration were explored with special attention to in vivo studies. This review highlights the promising systems for future clinical applications as well as the current hurdles that remain to be overcome for efficient inner ear therapy.

Nanoparticle mediated drug delivery of rolipram to tyrosine kinase B positive cells in the inner ear with targeting peptides and agonistic antibodies

Aim: Systemic pharmacotherapies have limitation due to blood-labyrinth barrier, so local delivery via the round window membrane opens a path for effective treatment. Multifunctional nanoparticle (NP)-mediated cell specific drug delivery may enhance efficacy and reduce side effects. Different NPs with ligands to target TrkB receptor were tested. Distribution, uptake mechanisms, trafficking, and bioefficacy of drug release of rolipram loaded NPs were evaluated.

Methods: We tested lipid based nanocapsules (LNCs), Quantum Dot, silica NPs with surface modification by peptides mimicking TrkB or TrkB activating antibodies. Bioefficacy of drug release was tested with rolipram loaded LNCs to prevent cisplatin-induced apoptosis. We established different cell culture models with SH-SY-5Y and inner ear derived cell lines and used neonatal and adult mouse explants. Uptake and trafficking was evaluated with FACS and confocal as well as transmission electron microscopy.

Results: Plain NPs show some selectivity in uptake related to the in vitro system properties, carrier material, and NP size. Some peptide ligands provide enhanced targeted uptake to neuronal cells but failed to show this in cell cultures. Agonistic antibodies linked to silica NPs showed TrkB activation and enhanced binding to inner ear derived cells. Rolipram loaded LNCs proved as effective carriers to prevent cisplatin-induced apoptosis.

Discussion: Most NPs with targeting ligands showed limited effects to enhance uptake. NP aggregation and unspecific binding may change uptake mechanisms and impair endocytosis by an overload of NPs. This may affect survival signaling. NPs with antibodies activate survival signaling and show effective binding to TrkB positive cells but needs further optimization for specific internalization. Bioefficiacy of rolipram release confirms LNCs as encouraging vectors for drug delivery of lipophilic agents to the inner ear with ideal release characteristics independent of endocytosis.

Targeted delivery of brain-derived neurotrophic factor for the treatment of blindness and deafness

Neurodegenerative causes of blindness and deafness possess a major challenge in their clinical management as proper treatment guidelines have not yet been found. Brain-derived neurotrophic factor (BDNF) has been established as a promising therapy against neurodegenerative disorders including hearing and visual loss. Unfortunately, the blood–retinal barrier and blood–cochlear barrier, which have a comparable structure to the blood–brain barrier prevent molecules of larger sizes (such as BDNF) from exiting the circulation and reaching the targeted cells. Anatomical features of the eye and ear allow use of local administration, bypassing histo-hematic barriers. This paper focuses on highlighting a variety of strategies proposed for the local administration of the BDNF, like direct delivery, viral gene therapy, and cell-based therapy, which have been shown to successfully improve development, survival, and function of spiral and retinal ganglion cells. The similarities and controversies for BDNF treatment of posterior eye diseases and inner ear diseases have been analyzed and compared. In this review, we also focus on the possibility of translation of this knowledge into clinical practice. And finally, we suggest that using nanoparticulate drug-delivery systems may substantially contribute to the development of clinically viable techniques for BDNF delivery into the cochlea or posterior eye segment, which, ultimately, can lead to a long-term or permanent rescue of auditory and optic neurons from degeneration.

Enhanced local bioavailability of single or compound drugs delivery to the inner ear through application of PLGA nanoparticles via round window administration

In this paper, the potential of poly(D,L-lactide-co-glycolide acid) (PLGA) nanoparticles (NPs) for carrying single or compound drugs traversing the round window membrane (RWM) was examined after the round window (RW) administration of different NPs to guinea pigs. First, coumarin-6 was incorporated into PLGA NPs as a fluorescent probe to investigate its ability to cross the RWM. Then, PLGA NPs with salvianolic acid B (Sal B), tanshinone IIA (TS IIA), and total panax notoginsenoside (PNS) including notoginsenoside R1 (R1), ginsenoside Rg1 (Rg1), and ginsenoside Rb1 (Rb1) were developed to evaluate whether NPs loaded with compound drugs would pass through the RWM and improve the local bioavailability of these agents. PLGA NPs loaded with single or compound drugs were prepared by the emulsification solvent evaporation method, and their particle size distribution, particle morphology, and encapsulation efficiency were characterized. In vitro release study showed sustained-release profiles of Sal B, TS IIA, and PNS from the NPs. The pharmacokinetic results showed that NPs applied to the RWM significantly improved drug distribution within the inner ear. The AUC0-t of coumarin-6 in the perilymph (PL) following RW administration of NPs was 4.7-fold higher than that of coumarin-6 solution, and the Cmax was 10.9-fold higher. Furthermore, the AUC(0-t) of R1, Rg1, and Rb1 were 4.0-, 3.1-, and 7.1-fold greater, respectively, after the application of NPs compared to the compound solution, and the Cmax were, respectively, 14.4-, 10.0-, and 16.7-fold higher. These findings suggest that PLGA NPs with unique properties at the nanoscale dimensions have a powerful ability to transport single or compound drugs into the PL through the RWM and remarkably enhance the local bioavailability of the encapsulated drugs in the inner ear. The use of PLGA NPs as nanoscale delivery vehicles to carry drugs across the RWM may be a promising strategy for the treatment of inner ear diseases.

Bovine serum albumin nanoparticles as controlled release carrier for local drug delivery to the inner ear

Nanoparticles have attracted increasing attention for local drug delivery to the inner ear recently. Bovine serum albumin (BSA) nanoparticles were prepared by desolvation method followed by glutaraldehyde fixation or heat denaturation. The nanoparticles were spherical in shape with an average diameter of 492 nm. The heat-denatured nanoparticles had good cytocompatibility. The nanoparticles could adhere on and penetrate through the round window membrane of guinea pigs. The nanoparticles were analyzed as drug carriers to investigate the loading capacity and release behaviors. Rhodamine B was used as a model drug in this paper. Rhodamine B-loaded nanoparticles showed a controlled release profile and could be deposited on the osseous spiral lamina. We considered that the bovine serum albumin nanoparticles may have potential applications in the field of local drug delivery in the treatment of inner ear disorders.

A microfluidic reciprocating intracochlear drug delivery system with reservoir and active dose control

Reciprocating microfluidic drug delivery, as compared to steady or pulsed infusion, has unique features which may be advantageous in many therapeutic applications. We have previously described a device, designed for wearable use in small animal models, that periodically infuses and then withdraws a sub-microliter volume of drug solution to and from the endogenous fluid of the inner ear. This delivery approach results in zero net volume of liquid transfer while enabling mass transport of compounds to the cochlea by means of diffusion and mixing. We report here on an advanced wearable delivery system aimed at further miniaturization and complex dosing protocols. Enhancements to the system include the incorporation of a planar micropump to generate reciprocating flow and a novel drug reservoir that maintains zero net volume delivery and permits programmable modulation of the drug concentration in the infused bolus. The reciprocating pump is fabricated from laminated polymer films and employs a miniature electromagnetic actuator to meet the size and weight requirements of a head-mounted in vivo guinea pig testing system. The reservoir comprises a long microchannel in series with a micropump, connected in parallel with the reciprocating flow network. We characterized in vitro the response and repeatability of the planar pump and compared the results with a lumped element simulation. We also characterized the performance of the reservoir, including repeatability of dosing and range of dose modulation. Acute in vivo experiments were performed in which the reciprocating pump was used to deliver a test compound to the cochlea of anesthetized guinea pigs to evaluate short-term safety and efficacy of the system. These advances are key steps toward realization of an implantable device for long-term therapeutic applications in humans.

Nanomedicine strategies for drug delivery to the ear

The highly compartmentalized anatomy of the ear aggravates drug delivery, which is used to combat hearing-related diseases. Novel nanosized drug vehicles are thought to overcome the limitations of classic approaches. In this article, we summarize the nanotechnology-based efforts involving nano-objects, such as liposomes, polymersomes, lipidic nanocapsules and poly(lactic-co-glycolic acid) nanoparticles, as well as nanocoatings of implants to provide an efficient means for drug transfer in the ear. Modern strategies do not only enhance drug delivery efficiency, in the inner ear these vector systems also aim for specific uptake into hair cells and spiral ganglion neurons. These novel peptide-mediated strategies for specific delivery are reviewed in this article. Finally, the biosafety of these vector systems is still an outstanding issue, since long-term application to the ear has not yet been assessed.

Inner ear symptoms and disease: pathophysiological understanding and therapeutic options

In recent years, huge advances have taken place in understanding of inner ear pathophysiology causing sensorineural hearing loss, tinnitus, and vertigo. Advances in understanding comprise biochemical and physiological research of stimulus perception and conduction, inner ear homeostasis, and hereditary diseases with underlying genetics. This review describes and tabulates the various causes of inner ear disease and defines inner ear and non-inner ear causes of hearing loss, tinnitus, and vertigo. The aim of this review was to comprehensively breakdown this field of otorhinolaryngology for specialists and non-specialists and to discuss current therapeutic options in distinct diseases and promising research for future therapies, especially pharmaceutic, genetic, or stem cell therapy.

Gene therapy for deafness

Hearing loss is the most common sensory deficit in humans and can result from genetic, environmental or combined etiologies that prevent normal function of the cochlea, the peripheral sensory organ. Recent advances in understanding the genetic pathways that are critical for the development and maintenance of cochlear function, as well as the molecular mechanisms that underlie cell trauma and death, have provided exciting opportunities for modulating these pathways to correct genetic mutations, to enhance the endogenous protective pathways for hearing preservation and to regenerate lost sensory cells with the possibility of ameliorating hearing loss. A number of recent animal studies have used gene-based therapies in innovative ways toward realizing these goals. With further refinement, some of the protective and regenerative approaches reviewed here may become clinically applicable.

Regeneration of mammalian cochlear and vestibular hair cells through Hes1/Hes5 modulation with siRNA

The Notch pathway is a cell signaling pathway determining initial specification and subsequent cell fate in the inner ear. Previous studies have suggested that new hair cells (HCs) can be regenerated in the inner ear by manipulating the Notch pathway. In the present study, delivery of siRNA to Hes1 and Hes5 using a transfection reagent or siRNA to Hes1 encapsulated within poly(lactide-co-glycolide acid) (PLGA) nanoparticles increased HC numbers in non-toxin treated organotypic cultures of cochleae and maculae of postnatal day 3 mouse pups. An increase in HCs was also observed in cultured cochleae and maculae of mouse pups pre-conditioned with a HC toxin (4-hydroxy-2-nonenal or neomycin) and then treated with the various siRNA formulations. Treating cochleae with siRNA to Hes1 associated with a transfection reagent or siRNA to Hes1 delivered by PLGA nanoparticles decreased Hes1 mRNA and up-regulated Atoh1 mRNA expression allowing supporting cells (SCs) to acquire a HC fate. Experiments using cochleae and maculae of p27(kip1)/-GFP transgenic mouse pups demonstrated that newly generated HCs trans-differentiated from SCs. Furthermore, PLGA nanoparticles are non-toxic to inner ear tissue, readily taken up by cells within the tissue of interest, and present a synthetic delivery system that is a safe alternative to viral vectors. These results indicate that when delivered using a suitable vehicle, Hes siRNAs are potential therapeutic molecules that may have the capacity to regenerate new HCs in the inner ear and possibly restore human hearing and balance function.

Ultrasound-aided microbubbles facilitate the delivery of drugs to the inner ear via the round window membrane

The round window membrane (RWM) acts as a barrier between the middle ear and cochlea and can serve as a crucial route for therapeutic medications entering the inner ear via middle ear applications. In this study, we targeted the practical application of microbubbles (MBs) ultrasound on increasing the RWM permeability for facilitating drug or medication delivery to the inner ear. Using biotin-fluorescein isothiocyanate conjugates (biotin-FITC) as delivery agents and guinea pig animal models, we showed that MB ultrasound exposure can improve the inner ear system use of biotin-FITC delivery via the RWM by approximately 3.5 to 38 times that of solely soaking biotin-FITC around the RWM for spontaneous diffusion. We also showed that there was significant enhancement of hair cell uptake of gentamicin in animals whose tympanic bullas were soaked with MB-mixed gentamicin-Texas Red or gentamicin and exposed to ultrasound. Furthermore, increased permeability of the RWM from acoustic cavitation of MBs could also be visualized immediately following ultrasound exposure by using Alexa Fluor 488-conjugated phalloidin as a tracer. Most importantly, such applications had no resulting damage to the integrity of the RWM or deterioration of the hearing thresholds assessed by auditory brainstem responses. We herein provide a basis for MB ultrasound-mediated techniques with therapeutic medication delivery to the inner ear for future application in humans.

Novel multiple agents loaded PLGA nanoparticles for brain delivery via inner ear administration: in vitro and in vivo evaluation

The aim of this study was to develop novel multiple agents loaded poly (D,L-lactide-co-glycolide acid) (PLGA) nanoparticles (NPs) and evaluate their potential for brain delivery via inner ear administration. PLGA NPs loaded with salvianolic acid B (Sal B), tanshinone IIA (TS IIA) and panax notoginsenoside (PNS) were prepared by double emulsion/solvent evaporation method. It was observed that optimized NPs displayed satisfactory encapsulation efficiency and desired sustained-release characteristics. NPs following intratympanic administration (IT) in guinea pigs greatly improved drug distribution within the inner ear, cerebrospinal fluid (CSF) and brain tissues compared with intravenous administration (IV). Pharmacodynamic studies demonstrated that NPs following IT markedly inhibited oxidizing reactions and protected the brain from cerebral ischemia reperfusion (I/R) injury by upregulating superoxide dismutase (SOD) activity both in serum and brain tissues, simultaneously significantly reducing the levels of malondialdehyde (MDA) and nitric oxide synthase (NOS). Moreover intratympanic delivery did not cause injury of cochlear function by preliminary study on the toxicity. These findings suggested that PLGA NPs-based delivery system via inner ear administration was a promising candidate to brain delivery for the treatment of brain diseases.

Gene therapy for the inner ear

Animal studies on inner ear development, repair and regeneration provide understanding of molecular pathways that can be harnessed for treating inner ear disease. Use of transgenic mouse technology, in particular, has contributed knowledge of genes that regulate development of hair cells and innervation, and of molecular players that can induce regeneration, but this technology is not applicable for human treatment, for practical and ethical reasons. Therefore other means for influencing gene expression in the inner ear are needed. We describe several gene vectors useful for inner ear gene therapy and the practical aspects of introducing these vectors into the ear. We then review the progress toward using gene transfer for therapies in both auditory and balance systems, and discuss the technological milestones needed to advance to clinical application of these methods.

Minimally invasive drug delivery to the cochlea through application of nanoparticles to the round window membrane

Direct drug delivery to the cochlea is associated with the risk of irreversible damage to the ear. In this study, liposome and polymersome nanoparticles (NPs), both formed from amphiphilic molecules (lipids in liposomes and block copolymers in polymersomes), were tested as potential tools for drug delivery to the cochlea via application onto the round window membrane in adult mice (strain C3H). One day after round window membrane application, both types of NPs labeled with fluorescent markers were identified in the spiral ganglion in all cochlear turns without producing any distinct morphological or functional damage to the inner ear. NPs were detected, although to a lesser extent, in the organ of Corti and the lateral wall. The potential of liposome and polymersome NPs as therapeutic delivery systems into the cochlea via the round window membrane was evaluated using disulfiram, a neurotoxic agent, as a model payload. Disulfiram-loaded NP delivery resulted in a significant decrease in the number of spiral ganglion cells starting 2 days postapplication, with associated pronounced hearing loss reaching 20-35 dB 2 weeks postapplication as assessed through auditory brainstem responses. No changes in hair cell morphology and function (as assessed by recording otoacoustic emissions) were detected after disulfiram-loaded NP application. No effects were observed in controls where solution of free disulfiram was similarly administered. The results demonstrate that liposome and polymersome NPs are capable of carrying a payload into the inner ear that elicits a biological effect, with consequences measurable by a functional readout.

Intratympanic injection of shRNA-expressing lentivirus causes gene silencing in the inner ear in chicken

The hair cells and their neural innervation in the avian inner ear can regenerate after injury. Identifying the genes involved in the regeneration and neuroplasticity of avian hair cell will enable us to experimentally induce new hair cell production and potentially harness this process for therapeutic replacement of hair cells in mammals and ultimately in humans suffering from sensorineural hearing loss. In this study, we developed a method for suppressing the expression level of genes in avian inner ear by intratympanic injection of shRNA-expressing lentivirus. The intratympanic injection approach is more convenient and presumably of less implication when compared with two existing methods, in which a nano-particles or gelfoam containing a recombinant virus is placed in the middle ear by surgery, or a recombinant virus is directly injected into the inner ear. Thus, we developed an easier method for identifying and characterizing molecules involved in the process of avian hair cell regeneration and re-innervation.