A novel controlled local drug delivery system for inner ear disease

Dexamethasone nanocrystals-embedded hydroxypropyl methylcellulose hydrogel increases cochlear delivery and attenuates hearing loss following intratympanic injection

Herein, dexamethasone (DEX) nanocrystalline suspension (NS)-embedded hydrogel (NS-G) was constructed using a hydroxypropyl methylcellulose (HPMC) polymer to enhance cochlear delivery and attenuate hearing loss following intratympanic (IT) injection. Hydrophobic steroidal nanocrystals were prepared using a bead milling technique and incorporated into a polysaccharide hydrogel. The NS-G system with HPMC (average molecular weight, 86,000 g/mol; 15 mg/mL) was characterized as follows: rod-shaped drug crystalline; particle size <300 nm; and constant complex viscosity ≤1.17 Pa·s. Pulverization of the drug particles into submicron diameters enhanced drug dissolution, while the HPMC matrix increased the residence time in the middle ear cavity, exhibiting a controlled release profile. The IT NS-G system elicited markedly enhanced and prolonged drug delivery (> 9 h) to the cochlear tissue compared with that of DEX sodium phosphate (DEX-SP), a water-soluble prodrug. In mice with kanamycin- and furosemide-induced ototoxicity, NS-G markedly enhanced hearing preservation across all frequencies (8-32 kHz), as revealed by an auditory brainstem response test, compared with both saline and DEX-SP. Moreover, treatment with NS-G showed enhanced anti-inflammatory effects, as evidenced by decreased levels of inflammation-related cytokines. Therefore, the IT administration of DEX NS-loaded HPMC hydrogels is a promising strategy for treating hearing loss.

Complete Restoration of Hearing Loss and Cochlear Synaptopathy via Minimally Invasive, Single-Dose, and Controllable Middle Ear Delivery of Brain-Derived Neurotrophic Factor-Poly(dl-lactic acid-co-glycolic acid)-Loaded Hydrogel

Noise-induced hearing loss (NIHL) often accompanies cochlear synaptopathy, which can be potentially reversed to restore hearing. However, there has been little success in achieving complete recovery of sensorineural deafness using nearly noninvasive middle ear drug delivery before. Here, we present a study demonstrating the efficacy of a middle ear delivery system employing brain-derived neurotrophic factor (BDNF)-poly-(dl-lactic acid-co-glycolic acid) (PLGA)-loaded hydrogel in reversing synaptopathy and restoring hearing function in a mouse model with NIHL. The mouse model achieved using the single noise exposure (NE, 115 dBL, 4 h) exhibited an average 20 dBL elevation of hearing thresholds with intact cochlear hair cells but a loss of ribbon synapses as the primary cause of hearing impairment. We developed a BDNF-PLGA-loaded thermosensitive hydrogel, which was administered via a single controllable injection into the tympanic cavity of noise-exposed mice, allowing its presence in the middle ear for a duration of 2 weeks. This intervention resulted in complete restoration of NIHL at frequencies of click, 4, 8, 16, and 32 kHz. Moreover, the cochlear ribbon synapses exhibited significant recovery, whereas other cochlear components (hair cells and auditory nerves) remained unchanged. Additionally, the cochlea of NE treated mice revealed activation of tropomyosin receptor kinase B (TRKB) signaling upon exposure to BDNF. These findings demonstrate a controllable and minimally invasive therapeutic approach that utilizes a BDNF-PLGA-loaded hydrogel to restore NIHL by specifically repairing cochlear synaptopathy. This tailored middle ear delivery system holds great promise for achieving ideal clinical outcomes in the treatment of NIHL and cochlear synaptopathy.

Precision medicine: a new era for inner ear diseases

The inner ear is the organ responsible for hearing and balance. Inner ear dysfunction can be the result of infection, trauma, ototoxic drugs, genetic mutation or predisposition. Often, like for Ménière disease, the cause is unknown. Due to the complex access to the inner ear as a fluid-filled cavity within the temporal bone of the skull, effective diagnosis of inner ear pathologies and targeted drug delivery pose significant challenges. Samples of inner ear fluids can only be collected during surgery because the available procedures damage the tiny and fragile structures of the inner ear. Concerning drug administration, the final dose, kinetics, and targets cannot be controlled. Overcoming these limitations is crucial for successful inner ear precision medicine. Recently, notable advancements in microneedle technologies offer the potential for safe sampling of inner ear fluids and local treatment. Ultrasharp microneedles can reach the inner ear fluids with minimal damage to the organ, collect μl amounts of perilymph, and deliver therapeutic agents in loco. This review highlights the potential of ultrasharp microneedles, combined with nano vectors and gene therapy, to effectively treat inner ear diseases of different etiology on an individual basis. Though further research is necessary to translate these innovative approaches into clinical practice, these technologies may represent a true breakthrough in the clinical approach to inner ear diseases, ushering in a new era of personalized medicine.

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.

Novel small molecule-mediated restoration of the surface expression and anion exchange activity of mutated pendrin causing Pendred syndrome and DFNB4

Variants in SLC26A4 (pendrin) are the most common reasons for genetic hearing loss and vestibular dysfunction in East Asians. In patients with Pendred syndrome and DFNB4 (autosomal recessive type of genetic hearing loss 4), caused by variants in SLC26A4, the hearing function is residual at birth and deteriorates over several years, with no curative treatment for these disorders. In the present study, we revealed that a novel small molecule restores the expression and function of mutant pendrin. High-throughput screening of 54,000 small molecules was performed. We observed that pendrin corrector (PC2-1) increased the surface expression and anion exchange activity of p.H723R pendrin (H723R-PDS), the most prevalent genetic variant that causes Pendred syndrome and DFNB4. Furthermore, in endogenous H723R-PDS-expressing human nasal epithelial cells, PC2-1 significantly increased the surface expression of pendrin. PC2-1 exhibited high membrane permeability in vitro and high micromolar concentrations in the cochlear perilymph in vivo. In addition, neither inhibition of Kv11.1 activity in the human ether-a-go-go-related gene assay nor cell toxicity in the cell proliferation assay was observed at a high PC2-1 concentration (30 μM). These preclinical data support the hypothesis of the druggability of mutant pendrin using the novel corrector molecule PC2-1. In conclusion, PC2-1 may be a new therapeutic molecule for ameliorating hearing loss and treating vestibular disorders in patients with Pendred syndrome or DFNB4.

Overcoming barriers: a review on innovations in drug delivery to the middle and inner ear

Despite significant advances in the development of therapeutics for hearing loss, drug delivery to the middle and inner ear remains a challenge. As conventional oral or intravascular administration are ineffective due to poor bioavailability and impermeability of the blood-labyrinth-barrier, localized delivery is becoming a preferable approach for certain drugs. Even then, localized delivery to the ear precludes continual drug delivery due to the invasive and potentially traumatic procedures required to access the middle and inner ear. To address this, the preclinical development of controlled release therapeutics and drug delivery devices have greatly advanced, with some now showing promise clinically. This review will discuss the existing challenges in drug development for treating the most prevalent and damaging hearing disorders, in particular otitis media, perforation of the tympanic membrane, cholesteatoma and sensorineural hearing loss. We will then address novel developments in drug delivery that address these including novel controlled release therapeutics such as hydrogel and nanotechnology and finally, novel device delivery approaches such as microfluidic systems and cochlear prosthesis-mediated delivery. The aim of this review is to investigate how drugs can reach the middle and inner ear more efficiently and how recent innovations could be applied in aiding drug delivery in certain pathologic contexts.

Micro Injection Molding of Drug-Loaded Round Window Niche Implants for an Animal Model Using 3D-Printed Molds

A novel approach for the long-term medical treatment of the inner ear is the diffusion of drugs through the round window membrane from a patient-individualized, drug-eluting implant, which is inserted in the middle ear. In this study, drug-loaded (10 wt% Dexamethasone) guinea pig round window niche implants (GP-RNIs, ~1.30 mm × 0.95 mm × 0.60 mm) were manufactured with high precision via micro injection molding (µIM, T_mold = 160 °C, crosslinking time of 120 s). Each implant has a handle (~3.00 mm × 1.00 mm × 0.30 mm) that can be used to hold the implant. A medical-grade silicone elastomer was used as implant material. Molds for µIM were 3D printed from a commercially available resin (T_G = 84 °C) via a high-resolution DLP process (xy resolution of 32 µm, z resolution of 10 µm, 3D printing time of about 6 h). Drug release, biocompatibility, and bioefficacy of the GP-RNIs were investigated in vitro. GP-RNIs could be successfully produced. The wear of the molds due to thermal stress was observed. However, the molds are suitable for single use in the µIM process. About 10% of the drug load (8.2 ± 0.6 µg) was released after 6 weeks (medium: isotonic saline). The implants showed high biocompatibility over 28 days (lowest cell viability ~80%). Moreover, we found anti-inflammatory effects over 28 days in a TNF-α-reduction test. These results are promising for the development of long-term drug-releasing implants for human inner ear therapy.

Injectable Poloxamer Hydrogel Formulations for Intratympanic Delivery of Dexamethasone

BACKGROUND

In this study, we prepared and evaluated an injectable poloxamer (P407) hydrogel formulation for intratympanic (IT) delivery of dexamethasone (DEX).

METHODS

DEX-loaded P407 hydrogels were characterized in terms of thermogelation, drug loading capacities, particle size, and drug release. The in vivo toxicity and drug absorption of the DEX-loaded P407 formulation after IT injection were evaluated using an animal model by performing histopathological analysis and drug concentration measurements.

RESULTS

The P407 hydrogel effectively solubilized hydrophobic DEX and demonstrated a sustained release compared to the hydrophilic DEX formulation. The in vivo study showed that the hydrogel formulation delivered considerable drug concentrations to the inner ear and displayed a favorable safety profile without apparent cytotoxicity or inflammation.

CONCLUSION

P407 hydrogel can be useful as an injectable inner ear delivery formulation for hydrophobic drugs due to their biocompatibility, drug-solubilizing capacity, thermogelation, and controlled release.

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.

Inner Ear Diagnostics and Drug Delivery via Microneedles

Objectives: Precision medicine for inner ear disorders has seen significant advances in recent years. However, unreliable access to the inner ear has impeded diagnostics and therapeutic delivery. The purpose of this review is to describe the development, production, and utility of novel microneedles for intracochlear access. Methods: We summarize the current work on microneedles developed using two-photon polymerization (2PP) lithography for perforation of the round window membrane (RWM). We contextualize our findings with the existing literature in intracochlear diagnostics and delivery. Results: Two-photon polymerization lithography produces microneedles capable of perforating human and guinea pig RWMs without structural or functional damage. Solid microneedles may be used to perforate guinea pig RWMs in vivo with full reconstitution of the membrane in 48–72 h, and hollow microneedles may be used to aspirate perilymph or inject therapeutics into the inner ear. Microneedles produced with two-photon templated electrodeposition (2PTE) have greater strength and biocompatibility and may be used to perforate human RWMs. Conclusions: Microneedles produced with 2PP lithography and 2PTE can safely and reliably perforate the RWM for intracochlear access. This technology is groundbreaking and enabling in the field of inner ear precision medicine.

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.

Dual Viscosity Mixture Vehicle for Intratympanic Dexamethasone Delivery Can Block Ototoxic Hearing Loss

Clinically there is no effective method to prevent drug induced hearing loss in patients undergoing chemotherapy and anti-tuberculosis therapy. In this study, we developed an intratympanic (IT) local drug delivery vehicle featuring hyaluronic acid-based dual viscosity mixture encapsulation of dexamethasone (D), named dual-vehicle + D, and assessed its protective effect in ototoxic hearing loss. We assessed the residence time, biocompatibility, and treatment outcome of the novel vehicle compared with the current standard of care vehicle (saline) and control conditions. The hearing threshold and hair cell count were significantly better in the dual-vehicle + D group compared to the other two groups. The final hearing benefit in the dual-vehicle group was approximately 25–35 dB, which is significant from a clinical point of view. Morphologic evaluation of the cochlear hair cells also supported this finding. Due to the high viscosity and adhesive property of the vehicle, the residence time of the vehicle was 49 days in the dual-vehicle + D group, whereas it was less than 24 h in the saline + D group. There was no sign of inflammation or infection in all the animals. From this study we were able to confirm that dual viscosity mixture vehicle for IT D delivery can effectively block ototoxic hearing loss.

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.

High-Molecular-Weight Hyaluronic Acid Vehicle Can Deliver Gadolinium Into the Cochlea at a Higher Concentration for a Longer Duration: A 9.4-T Magnetic Resonance Imaging Study

Intratympanic (IT) gadolinium (Gd) injection is one method of delivering Gd into the inner ear to evaluate the amount of endolymphatic hydrops (EH) using magnetic resonance imaging (MRI). As Gd is usually prepared in a fluid form mixed with saline, Gd injected into the middle ear drains easily through the Eustachian tube within several hours. High-molecular-weight (hMW) hyaluronic acid (HA) is an ideal vehicle for IT Gd due to its viscous and adhesive properties. The present study was performed to elucidate whether novel hMW HA is superior to conventional HA in delivering Gd into the inner ear in the short term. The second aim was to verify the long-term Gd delivery efficiency of hMW HA compared to the standard-of-care vehicle (saline). IT Gd injection and 3D T1-weighted MRI were performed in 13 rats. For the short-term study (imaging after 1, 2, and 3 h), the left ear was treated with hMW HA+Gd and the right ear with conventional HA+Gd. For the long-term study (imaging after 1, 2, 3, and 4 h, 1 – 3 days, and 7 – 10 days), the left ear was treated with hMW HA+Gd and the right ear with saline+Gd. Signal intensities (SIs) in the scala tympani (ST) and scala vestibuli (SV) were quantified. Compared to conventional HA, signal enhancement was 2.3 – 2.4 times greater in the apical and middle turns after hMW HA+Gd injection (SV at 1 h). In comparison to the standard-of-care procedure, the SI was not only greater in the short term but the higher SI also lasted for a longer duration. On days 7 – 10 after IT Gd delivery, the SI in the basal turn was 1.9 – 2.1 times greater in hMW HA+Gd-treated ears than in saline IT Gd-treated ears. Overall, hMW HA may be a useful vehicle for more efficient IT Gd delivery. Gd enhancement in the cochlea improved approximately two-fold when hMW HA was used. In addition, this greater enhancement lasted for up to 7 – 10 days. Repeated MRI of EH may be possible for several days with a single IT hMW HA+Gd delivery.

Determination of the Round Window Niche Anatomy Using Cone Beam Computed Tomography Imaging as Preparatory Work for Individualized Drug-Releasing Implants

Modern therapy of inner ear disorders is increasingly shifting to local drug delivery using a growing number of pharmaceuticals. Access to the inner ear is usually made via the round window membrane (RWM), located in the bony round window niche (RWN). We hypothesize that the individual shape and size of the RWN have to be taken into account for safe reliable and controlled drug delivery. Therefore, we investigated the anatomy and its variations. Cone beam computed tomography (CBCT) images of 50 patients were analyzed. Based on the reconstructed 3D volumes, individual anatomies of the RWN, RWM, and bony overhang were determined by segmentation using 3D Slicer^TM with a custom build plug-in. A large individual anatomical variability of the RWN with a mean volume of 4.54 mm³ (min 2.28 mm³, max 6.64 mm³) was measured. The area of the RWM ranged from 1.30 to 4.39 mm² (mean: 2.93 mm²). The bony overhang had a mean length of 0.56 mm (min 0.04 mm, max 1.24 mm) and the shape was individually very different. Our data suggest that there is a potential for individually designed and additively manufactured RWN implants due to large differences in the volume and shape of the RWN.

Intratympanic Diltiazem-Chitosan Hydrogel as an Otoprotectant Against Cisplatin-Induced Ototoxicity in a Mouse Model

HYPOTHESIS

Local administration of the calcium-channel blocker (CCB), diltiazem, via intratympanic (IT) chitosan-glycerophosphate (CGP) hydrogel will protect against cisplatin-induced ototoxicity.

BACKGROUND

Cisplatin induces calcium-mediated apoptosis of cochlear outer hair cells (OHCs). Previous work demonstrated otoprotection and reduced auditory brainstem response (ABR) threshold shifts in a cisplatin-induced ototoxicity mouse model treated with multiple doses of IT diltiazem given in solution. Here, we evaluated the role of a single dose of IT CGP-diltiazem as a novel otoprotectant against cisplatin-induced ototoxicity.

METHODS

Baseline pure-tone and click-evoked ABRs were performed in control (IT CGP-saline, n = 13) and treatment (IT CGP-diltiazem 2 mg/kg, n = 9) groups of female CBA/J mice. A single dose of IT CGP hydrogel was administered just before intraperitoneal injection of cisplatin (14 mg/kg). On Day 7 posttreatment, ABRs were performed and cochleae were harvested. Hair cells were quantified using anti-myosin VIIa immunostaining and inner hair cell ribbon synapses were quantified using Ctbp2 immunostaining.

RESULTS

There was a statistically significant effect of treatment on click- and tone-evoked ABRs between groups. The mean threshold shifts were significantly reduced in both click- and tone-evoked ABRs on Day 7 in IT CGP-diltiazem treated mice compared with CGP-saline control mice. There were no significant differences in OHC counting between groups, but there appears to be an otoprotection against loss of synapses in the apical turn from IT CGP-diltiazem treated mice (p < 0.05).

CONCLUSIONS

This preliminary work suggests that IT CGP-diltiazem reduces ABR threshold shifts with possible mechanisms of protecting ribbon synapses in the setting of cisplatin-induced ototoxicity. More work is necessary to determine the mechanism underlying this otoprotection.

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.

Implantable Drug Reservoir Devices for Inner Ear Delivery of Pharmacotherapeutics

Objective

Cisplatin is a platinum-based chemotherapeutic drug that secondarily induces toxicity in inner ear sensory epithelia, contributing to auditory and vestibular dysfunction. We describe the creation of a drug reservoir device (DRD) to combat this ototoxicity for the duration of chemotherapy. As ototoxic side effects of chemotherapy may limit an oncologist’s ability to prescribe first-line agents such as cisplatin, mitigating such devastating effects through prolonged topical therapy would be tremendously valuable.

Study Design

We investigated (1) the ability of an electrospun polylactic acid DRD to provide prolonged delivery of the posited otoprotectant metformin and (2) the development of an in vitro model utilizing Sh-Sy5y human neuroblastoma cells to assess the efficacy of metformin in reducing cisplatin-induced toxicity.

Setting

Neurophysiology laboratory.

Methods

Basic science experiments were performed to assess DRD properties and metformin’s effects on cisplatin toxicity in culture.

Results

We found that DRDs with increasing polylactic acid concentrations exhibited metformin release for up to 8 weeks. In modeling elution across the round window in vitro, continued elution of metformin was observed for at least 6 weeks, as quantified by spectrophotometry. Unfortunately, metformin did not exhibit protective efficacy in this model using Sh-Sy5y cells.

Conclusion

While metformin was not found to be protective in Sh-Sy5y cells, these results suggest that an electrospun DRD can provide a tailorable drug delivery system providing medication for the duration of chemotherapy treatment. This represents a novel drug delivery system and efficacy screening assay with broad clinical applications in personalized delivery of inner ear therapies.

Poly-Lactic Acid-Based Biopolymer Formulations Are Safe for Sustained Intratympanic Dexamethasone Delivery

HYPOTHESIS AND BACKGROUND

The clinical treatment of sudden sensorineural hearing loss currently relies on the administration of steroids, either systemically or via intratympanic injections. Intratympanic injections bypass the hemato-cochlear barrier, reducing its systemic side effects. The efficacy of the injections is limited through rapid drug clearance via the Eustachian tube, and through nonoptimal properties of slow-release drug carriers. A new slow-release drug delivery vehicle based on hexyl-substituted-poly-lactic-acid (HexPLA), with the highest possible safety profile and complete bio-degradability, has been evaluated for safety and efficacy in a standardized guinea pig model of intratympanic injection.

METHODS

A total of 83 animals received through retrobullar injection either empty Nile-red-colored HexPLA vehicle, 5%-dexamethasone-HexPLA, 5%-dexamethasone suspension, or a sham operation. Long-term residence time of vehicle, biocompatibility, click- and pure-tone hearing thresholds, and dexamethasone levels in the perilymph were prospectively assessed.

RESULTS

At 1 week after injection, HexPLA vehicle was morphologically present in the middle ear and perilymph levels in the 5%-dexamethasone-HexPLA were on average 2 to 3 μg/ml and one order of magnitude higher compared with those of the 5%-dexamethasone suspension group. No significant postoperative morphological or functional changes were observed up to 3 months postdelivery.

CONCLUSIONS

HexPLA is safe, fully biocompatible, and efficient for sustained high-dose, intratympanic delivery of dexamethasone at least for 1 week and therefore of high interest for the treatment of sudden sensorineural hearing loss and other acute inner ear diseases. Due to the favorable chemical properties, a wide range of other drugs can be loaded into the vehicle further increasing its potential value for otological applications.

Developments in Bio-Inspired Nanomaterials for Therapeutic Delivery to Treat Hearing Loss

Sensorineural hearing loss affects millions of people worldwide and is a growing concern in the aging population. Treatment using aminoglycoside antibiotics for infection and exposure to loud sounds contribute to the degeneration of cochlear hair cells and spiral ganglion neurons. Cell loss impacts cochlear function and causes hearing loss in ∼ 15% of adult Americans (∼36 million). The number of individuals with hearing loss will likely grow with increasing lifespans. Current prosthesis such as hearing aids and cochlear implants can ameliorate hearing loss. However, hearing aids are ineffective if hair cells or spiral ganglion neurons are severely damaged, and cochlear implants are ineffective without properly functioning spiral ganglion neurons. As such, strategies that alleviate hearing loss by preventing degeneration or promoting cell replacement are urgently needed. Despite showing great promise from in vitro studies, the complexity and delicate nature of the inner ear poses a huge challenge for delivering therapeutics. To mitigate risks and complications associated with surgery, new technologies and methodologies have emerged for efficient delivery of therapeutics. We will focus on biomaterials that allow controlled and local drug delivery into the inner ear. The rapid development of microsurgical techniques in conjunction with novel bio- and nanomaterials for sustained drug delivery appears bright for hearing loss treatment.

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.

Dexamethasone-loaded chitosan-based genipin-cross-linked hydrogel for prevention of cisplatin induced ototoxicity in Guinea pig model

OBJECTIVES

The aim of this study was to investigate the protective effects of a sustained release form of dexamethasone (dex) loaded chitosan-based genipin-cross-linked hydrogel (CBGCH) in a guinea pig model of cisplatin (CP) induced hearing loss.

METHODS

Implantation of CBGCH was made by intratympanic (IT) injection. Ototoxicity was produced by intraperitoneal (IP) single dose of 14 mg/kg CP. Animals were randomly divided into four groups with 6 guinea pigs in each. Group 1 received only IP CP; group 2 received only IT dex-loaded CBGCH injections. Group 3 and group 4 received IP CP, plus IT nondrug CBGCH and IT dex-loaded CBGCH respectively 24 h prior to IP CP injections. Distortion product otoacoustic emissions (DPOAEs) and auditory brainstem response (ABR) measurements were obtained before the treatments and solely ABR measurements were done after 3 and 10 days. The ultrastructural effects were investigated by scanning electron microscopy (SEM) analysis.

RESULTS

The postCP ABR thresholds at 4, 8, 12, 16, 32 kHz frequencies were significantly better in group 4 than groups 1 and 3 (p < 0.05). The comparison of time effective ABR thresholds between groups 1 and 4 and between groups 3 and 4 showed significantly lower ABR thresholds in group 4 (p < 0.05). The SEM analysis showed that stereocilia of inner and outer hair cells were preserved in group 4, almost like group 2, whereas cytotoxic degenerations were noted in groups 1 and 3.

CONCLUSIONS

Intratympanic administration of dex-loaded CBGCH has been shown to provide functional and structural protection against CP-induced ototoxicity.

Advances and Challenges in Pharmaceutical Therapies to Prevent and Repair Cochlear Injuries From Noise

Noise induces a broad spectrum of pathological injuries to the cochlea, reflecting both mechanical damage to the delicate architecture of the structures of the organ of Corti and metabolic damage within the organ of Corti and lateral wall tissues. Unlike ototoxic medications, the blood-labyrinth barrier does not offer protection against noise injury. The blood-labyrinth barrier is a target of noise injury, and can be weakened as part of the metabolic pathologies in the cochlea. However, it also offers a potential for therapeutic intervention with oto-protective compounds. Because the blood-labyrinth barrier is weakened by noise, penetration of blood-borne oto-protective compounds could be higher. However, systemic dosing for cochlear protection from noise offers other significant challenges. An alternative option to systemic dosing is local administration to the cochlea through the round window membrane using a variety of drug delivery techniques. The review will discuss noise-induced cochlear pathology, including alterations to the blood-labyrinth barrier, and then transition into discussing approaches for delivery of oto-protective compounds to reduce cochlear injury from noise.

Middle Ear Administration of a Particulate Chitosan Gel in an in vivo Model of Cisplatin Ototoxicity

Background

Middle ear (intratympanic, IT) administration is a promising therapeutic method as it offers the possibility of achieving high inner ear drug concentrations with low systemic levels, thus minimizing the risk of systemic side effects and drug-drug interactions. Premature elimination through the Eustachian tube may be reduced by stabilizing drug solutions with a hydrogel, but this raises the secondary issue of conductive hearing loss.

Aim

This study aimed to investigate the properties of a chitosan-based particulate hydrogel formulation when used as a drug carrier for IT administration in an in vivo model of ototoxicity.

Materials and Methods

Two particulate chitosan-based IT delivery systems, Thio-25 and Thio-40, were investigated in albino guinea pigs (n = 94). Both contained the hearing protecting drug candidate sodium thiosulfate with different concentrations of chitosan gel particles (25% vs. 40%). The safety of the two systems was explored in vivo. The most promising system was then tested in guinea pigs subjected to a single intravenous injection with the anticancer drug cisplatin (8 mg/kg b.w.), which has ototoxic side effects. Hearing status was evaluated with acoustically evoked frequency-specific auditory brainstem response (ABR) and hair cell counting. Finally, in vivo magnetic resonance imaging was used to study the distribution and elimination of the chitosan-based system from the middle ear cavity in comparison to a hyaluronan-based system.

Results

Both chitosan-based IT delivery systems caused ABR threshold elevations (p < 0.05) that remained after 10 days (p < 0.05) without evidence of hair cell loss, although the elevation induced by Thio-25 was significantly lower than for Thio-40 (p < 0.05). Thio-25 significantly reduced cisplatin-induced ABR threshold elevations (p < 0.05) and outer hair cell loss (p < 0.05). IT injection of the chitosan- and hyaluronan-based systems filled up most of the middle ear space. There were no significant differences between the systems in terms of distribution and elimination.

Conclusion

Particulate chitosan is a promising drug carrier for IT administration. Future studies should assess whether the physical properties of this technique allow for a smaller injection volume that would reduce conductive hearing loss.

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.

A novel nanoparticle delivery system for targeted therapy of noise-induced hearing loss

Hearing loss is the most prevalent sensory disability worldwide and may be caused by age, drugs or exposure to excessive noise. We have previously developed a minimally-invasive nanohydrogel drug delivery system that successfully delivers nanoparticles into the inner ear. We have substantially extended this technique by functionalizing the nanoparticles and introducing a targeting peptide which recognizes prestin, a transmembrane electromotile protein uniquely expressed in outer hair cells (OHCs) of the inner ear. We demonstrate the successful delivery of molecules and plasmids specifically to OHCs. When compared to untargeted nanoparticles, the delivery of a c-Jun N-terminal kinase (JNK) inhibitor, D-JNKi-1, to OHCs by targeted nanoparticles improved protection from noise induced hearing loss (NIHL). This is the first demonstration of a protection from NIHL using a novel safe and controllable delivery system which is minimally-invasive to the inner ear and, as such, is an extremely appealing technique for use in many clinical applications.

Otic drug delivery systems: formulation principles and recent developments

Disorders of the ear severely impact the quality of life of millions of people, but the treatment of these disorders is an ongoing, but often overlooked challenge particularly in terms of formulation design and product development. The prevalence of ear disorders has spurred significant efforts to develop new therapeutic agents, but perhaps less innovation has been applied to new drug delivery systems to improve the efficacy of ear disease treatments. This review provides a brief overview of physiology, major diseases, and current therapies used via the otic route of administration. The primary focuses are on the various administration routes and their formulation principles. The article also presents recent advances in otic drug deliveries as well as potential limitations. Otic drug delivery technology will likely evolve in the next decade and more efficient or specific treatments for ear disease will arise from the development of less invasive drug delivery methods, safe and highly controlled drug delivery systems, and biotechnology targeting therapies.

Preservation of Hearing Following Cochlear Implantation Using Different Steroid Therapy Regimens: A Prospective Clinical Study

Background

A prospective clinical study was conducted to assess different regimens of steroid therapy and preservation of hearing following cochlear implantation.

Material/Methods

Study participants were ≥18 years-of-age, with a cochlear duct length ≥27.1 mm measured by computed tomography (CT), with hearing sound levels in the range of 10–120 decibels (dB) and sound frequencies of 125–250 hertz (Hz); sound levels of 35–120 dB and frequencies of 500–1,000 Hz; sound levels of 75–120 dB and frequencies of 2,000–8,000 Hz. Study exclusion criteria included diseases with contraindications for steroid therapy or medications that increased the effects of steroids. Patients had cochlear implantation and were divided into three treatment groups: intravenous (IV) steroid therapy (standard steroid therapy): combined oral and IV steroid therapy (prolonged steroid therapy); and a control group (cochlear implantation without steroid therapy). Hearing preservation was established by pure tone audiometry based on the pre-operative and postoperative average hearing thresholds according to the formula developed by the HEARRING Network.

Results

There were 36 patients included in the study. In all cases, the cochlear implant electrode was inserted via the round window approach with a straight electrode length of 28 mm. Patients with combined oral and IV steroid therapy (prolonged steroid therapy) had better results when compared with patients with intravenous (IV) steroid therapy (standard steroid therapy) and the control group.

Conclusions

Prolonged steroid therapy using combined oral and IV steroids stabilized hearing thresholds and preserved hearing in adult patients following cochlear implantation.

Is oval window transport a royal gate for nanoparticle delivery to vestibule in the inner ear?

Drug delivery to the inner ear by nanomedicine strategies has emerged as an effective therapeutic approach for the management of inner ear diseases including hearing and balance disorders. It is well accepted that substance enters the perilymph from the middle ear through the round window membrane (RWM), but the passage through the oval window (OW) has long been neglected. Up to now, researchers still know little about the pathway via which nanoparticles (NPs) enter the inner ear or how they reach the inner ear following local applications. Herein, we engineered fluorescence traceable chitosan (CS) NPs, investigated the NP distribution within cochlear and vestibular organs, and assessed the availability of RWM and OW pathways to NP transport. Intriguingly, there were high levels of CS NPs in vestibular hair cells, dark cells and supporting cells, but negligible ones in cochlear hair cells and epithelial cells after intratympanic administration. However, the NPs were visualized in two cell models, L929 and HEI-OC1 cell lines, and in the hair cells of cochlear explants after co-incubation in vitro. These combined studies implied that CS NPs might enter the vestibule directly through the OW and then preferentially accumulated in the cells of vestibular organs. Thus, in vivo studies were carried out and clearly revealed that CS NPs entered the inner ear through both the RWM and OW, but the latter played a governing role in delivering NPs to the vestibule with vivid fluorescence signals in the thin bone of the stapes footplate. Overall, these findings firstly suggested that the OW, as a royal gate, afforded a convenient access to facilitate CS NPs transport into inner ear, casting a new light on future clinical applications of NPs in the effective treatment of vestibular disorders by minimizing the risk of hearing loss associated with cochlear hair cell pathology.

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.

A Comparative Study of Drug Delivery Methods Targeted to the Mouse Inner Ear: Bullostomy Versus Transtympanic Injection

We present two minimally invasive microsurgical techniques in rodents for specific drug delivery into the middle ear so that it may reach the inner ear. The first procedure consists of perforation of the tympanic bulla, termed bullostomy; the second one is a transtympanic injection. Both emulate human clinical intratympanic procedures. Chitosan-glycerophosphate (CGP) and Ringer´s Lactate buffer (RL) were used as biocompatible vehicles for local drug delivery. CGP is a nontoxic biodegradable polymer widely used in pharmaceutical applications. It is a viscous liquid at RT but it congeals to a semi solid phase at body temperature. RL is an isotonic solution used for intravenous administrations in humans. A small volume of this vehicle is precisely placed on the Round Window (RW) niche by means of a bullostomy. A transtympanic injection fills the middle ear and allows less control but broader access to the inner ear. The safety profiles of both techniques were studied and compared by using functional and morphological tests. Hearing was evaluated by registering the Auditory Brainstem Response (ABR) before and several times after microsurgery. The cytoarchitecture and preservation level of cochlear structures were studied by conventional histological techniques in paraformaldehyde-fixed and decalcified cochlear samples. In parallel, unfixed cochlear samples were taken and immediately frozen to analyze gene expression profiles of inflammatory markers by quantitative Reverse Transcriptase Polymerase Chain Reaction (qRT-PCR). Both procedures are suitable as drug delivery methods into the mouse middle ear, although transtympanic injection proved to be less invasive compared to bullostomy.

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.

The effect of dexamethasone/cell-penetrating peptide nanoparticles on gene delivery for inner ear therapy

Dexamethasone (Dex)-loaded PHEA-g-C18-Arg8 (PCA) nanoparticles (PCA/Dex) were developed for the delivery of genes to determine the synergistic effect of Dex on gene expression. The cationic PCA nanoparticles were self-assembled to create cationic micelles containing an octadecylamine (C18) core with Dex and an arginine 8 (Arg8) peptide shell for electrostatic complexation with nucleic acids (connexin 26 [Cx26] siRNA, green fluorescent protein [GFP] DNA or brain-derived neurotrophic factor [BDNF] pDNA). The PCA/Dex nanoparticles conjugated with Arg8, a cell-penetrating peptide that enhances permeability through a round window membrane in the inner ear for gene delivery, exhibited high uptake efficiency in HEI-OC1 cells. This potential carrier co-delivering Dex and the gene into inner ear cells has a diameter of 120-140 nm and a zeta potential of 20-25 mV. Different types of genes were complexed with the Dex-loaded PCA nanoparticle (PCA/Dex/gene) for gene expression to induce additional anti-inflammatory effects. PCA/Dex showed mildly increased expression of GFP and lower mRNA expression of inflammatory cytokines (IL1b, IL12, and INFr) than did Dex-free PCA nanoparticles and Lipofectamine^® reagent in HEI-OC1 cells. In addition, after loading Cx26 siRNA onto the surface of PCA/Dex, Cx26 gene expression was downregulated according to real-time polymerase chain reaction for 24 h, compared with that using Lipofectamine reagent. After loading BDNF DNA into PCA/Dex, increased expression of BDNF was observed for 30 h, and its signaling pathway resulted in an increase in phosphorylation of Akt, observed by Western blotting. Thus, Dex within PCA/Dex/gene nanoparticles created an anti-inflammatory effect and enhanced gene expression.

Trans-Oval-Window Implants, A New Approach for Drug Delivery to the Inner Ear: Extended Dexamethasone Release From Silicone-based Implants

HYPOTHESIS

The purpose of this study was to develop a new strategy to deliver drugs to the inner ear from dexamethasone (DXM)-loaded silicone implants and to evaluate the distribution of the drug in the cochlea with confocal microscopy.

BACKGROUND

Systemic drug administration for the treatment of inner ear disorders is tricky because of the blood-cochlear barrier, a difficult anatomical access, the small size of the cochlea, and can cause significant adverse effects. An effective way to overcome these obstacles is to administer drugs locally.

METHODS

In vitro, the drug release from DXM-loaded silicone-based thin films and tiny implants into artificial perilymph was thoroughly analyzed by high-performance liquid chromatography. In vivo, a silicone implant loaded with 10% DXM and 5% polyethylene glycol 400 was implanted next to the stapes's footplate of gerbils. Delivery of DXM into the inner ear was proved by confocal microscopy imaging of the whole cochlea and the organ of Corti.

RESULTS

The study showed a continuous and prolonged release during 90 days in vitro. This was confirmed by confocal microscopy that allowed detection of DXM by fluorescence labeling in the cell body of the hair cells for at least 30 days. Interestingly, fluorescence was already observed after 20 minutes of implantation, reached a climax at day 7, and could still be detected 30 days after implantation.

CONCLUSIONS

Thus, we developed a new device for local corticosteroids delivery into the oval window with an extended drug release of DXM to the inner ear.

Inner ear delivery of dexamethasone using injectable silk-polyethylene glycol (PEG) hydrogel

Minimally invasive delivery and sustained release of therapeutics to the inner ear are of importance to the medical treatment of inner ear disease. In this study, the injectable silk fibroin-polyethylene glycol (Silk-PEG) hydrogel was investigated as a drug delivery carrier to deliver poorly soluble micronized dexamethasone (mDEX) to the inner ear of guinea pigs. Encapsulation of mDEX with a loading up to 5% (w/v) did not significantly change the silk gelation time, and mDEX were evenly distributed in the PEG-Silk hydrogel as visualized by SEM. The loading of mDEX in Silk-PEG hydrogel largely influenced in vitro drug release kinetics. The optimized Silk-PEG-mDEX hydrogel (2.5% w/v loading, in situ-forming, 10 μl) was administered directly onto the round window membrane of guinea pigs. The DEX concentration in perilymph maintained above 100 ng/ml for at least 10 days for the Silk-PEG formulation while less than 12h for the control sample of free mDEX. Minimal systemic exposure was achieved with low DEX concentrations (<0.2 μg/ml) in cerebrospinal fluid (CSF) and plasma in the first 2h after the local application of the Silk-PEG-mDEX hydrogel. A transient hearing threshold shift was found but then resolved after 14 days as revealed by auditory brainstem response (ABR), showing minimal inflammatory responses on the round window membrane and scala taympani. The Silk-PEG hydrogel completely degraded in 21 days. Thus, the injectable PEG-Silk hydrogel is an effective and safe vehicle for inner ear delivery and sustained release of glucocorticoid.

Otoprotective properties of 6α-methylprednisolone-loaded nanoparticles against cisplatin: In vitro and in vivo correlation

6α-Methylprednisolone-loaded surfactant-free nanoparticles have been developed to palliate cisplatin ototoxicity. Nanoparticles were based on two different amphiphilic pseudo-block copolymers obtained by free radical polymerization and based on N-vinyl pyrrolidone and a methacrylic derivative of α-tocopheryl succinate or α-tocopherol. Copolymers formed spherical nanoparticles by nanoprecipitation in aqueous media that were able to encapsulate 6α-methylprednisolone in their inner core. The obtained nanovehicles were tested in vitro using HEI-OC1 cells and in vivo in a murine model. Unloaded nanoparticles were not able to significantly reduce the cisplatin ototoxicity. Loaded nanoparticles reduced cisplatin-ototoxicity in vitro being more active those based on the methacrylic derivative of vitamin E, due to their higher encapsulation efficiency. This formulation was able to protect hair cells in the base of the cochlea, having a positive effect in the highest frequencies tested in a murine model. A good correlation between the in vitro and the in vivo experiments was found.

FROM THE CLINICAL EDITOR

Cisplatin is a commonly used chemotherapeutic agent against many cancers clinically. However, one of the significant side-effects remains ototoxicity. Here, the authors presented their data on using 6α-methylprednisolone-loaded nanoparticles in the reduction of ototoxicity in in-vitro and in-vivo experiments. Early promising results should enable further refinement of adopting this new approach in future experiments.

In vitro analysis of a novel controlled release system designed for intratympanic administration of N-acetylcysteine: a preliminary report

The aim of this in-vitro experimental study was to design a novel drug delivery system that may permit controlled release of N-acetylcysteine (NAC) following intratympanic administration. The system was composed of two different solutions that attained a hydrogel form within seconds after getting into contact with each other. The authors performed swelling, pH and temperature tests and analysis of controlled release of NAC from this novel controlled release system. For the structure and porosity analysis of the hydrogel, an environmental scanning electron microscope (SEM) was used. The diameter of designed hydrogel showed an increase when pH was increased. In addition, in comparison to acidic values, the pore diameter of the hydrogel increased significantly especially in physiological level. The increase in the pore diameter was also directly proportional to the increase in temperature. Spectrophotometric analysis showed that the amount of NAC released into the medium was statistically significant (p=0.038, t=-2.18, 95% CI; DF: 27). SEM analysis of the samples revealed a smooth surface topography and numerous porous structures. The authors are of the opinion that the designed hydrogel may be used as an alternative method for intratympanic delivery of NAC for otoprotective purposes. The disadvantages of intratympanic injection of the drug in its liquid form, including leakage through eustachian tube, restraining the patient in an uncomfortable position, necessity for repetitive injections and dose dependent inflammation of the middle ear epithelium, may also be avoided. Further in vivo studies should be conducted to assess its tolerability and effectivity.

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.