Drug delivery systems for the treatment of sensorineural 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.

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.

Intratympanic steroid delivery by an indwelling catheter in refractory severe sudden sensorineural hearing loss

OBJECTIVE

Many studies over the last decade showed favorable outcomes with intratympanic (IT) steroid treatment, alone as salvage treatment or in combination with conventional systemic therapy (ST). However, in severe to profound sensorineural hearing loss resistant to ST, the optimal infusion mode, the type and concentration of the solution, the preferable drug, its total amount, and the duration and fractionation of the treatment are still debated. Aim of the study was to investigate the feasibility and the outcomes of a direct and constant IT delivery of dexamethasone (DEX) by means of a new indwelling catheter.

METHODS

A prospective case-control study in a tertiary referral university hospital. Ninety-nine subjects treated with ST only and 28 with additional IT DEX have been included in the study. A 4 Fr catheter inserted in a sub-annular fashion with a minimal postero-inferior tympanotomy through and endocanalar approach under local anesthesia. DEX 4mg/ml delivered daily, up to 7 days. Daily bone and air-conducted pure tone and speech audiometry were performed with a follow-up at 1, 3, 6 months after treatment.

RESULTS

Twenty-one out of 28 patients (75%) refractory to ST gained on average 24.0dB±20.5dB HL after IT-DEX, compared to 35.4% (average 6.7dB±16.6dB HL) of those receiving only medical ST (p<0.001). No significant side effects were noted.

CONCLUSION

In severe to profound sudden deafness refractory to conventional ST, the daily perfusion of 4mg/ml DEX through an intratympanic catheter is an easy, well accepted procedure that enables patients to receive a drug in the middle ear in a repeatable or sustained form, with minimal discomfort and a partial rescue (67.86%) and a speech recognition gain of 39%.

Successful continual intratympanic steroid injection therapy in a patient with refractory sensorineural hearing loss accompanied by relapsing polychondritis

OBJECTIVE

To report the treatment efficacy of continual intratympanic steroid injection (ITSI) therapy in a patient with refractory sensorineural hearing loss accompanied by relapsing polychondritis.

PATIENT

A 49-year-old female diagnosed with relapsing polychondritis at the age of 45 years and who had been treated with corticosteroids and immunosuppressants developed sensorineural hearing loss in the left ear.

INTERVENTION

Her unilateral hearing loss did not recover despite receiving one cyclophosphamide pulse treatment, one methylprednisolone pulse treatment, and weekly leukapheresis. Thus, we decided to initiate weekly ITSI therapy.

MAIN OUTCOME MEASURE

Pure tone audiometry.

RESULTS

A week after the first ITSI treatment, the patient's hearing improved. We continued ITSI therapy and attempted to extend the interval between treatments, but her hearing worsened when ITSI therapy was delivered at 2- to 3-week intervals. Thus, we returned ITSI therapy to once per week for 21 months (total of 71 treatments). She experienced no adverse events, like tympanic perforation, and 1 year after terminating the therapy, her hearing remained stable and did not worsen.

CONCLUSIONS

Continual, weekly ITSI therapy was effective in treating sensorineural hearing loss accompanied by relapsing polychondritis. ITSI therapy may be a promising treatment option for sensorineural hearing loss caused by autoimmune disease.

Magnetic targeted delivery of dexamethasone acetate across the round window membrane in guinea pigs

HYPOTHESIS

Magnetically susceptible PLGA nanoparticles will effectively target the round window membrane (RWM) for delivery of dexamethasone-acetate (Dex-Ac) to the scala tympani.

BACKGROUND

Targeted delivery of therapeutics to specific tissues can be accomplished using different targeting mechanisms. One technology includes iron oxide nanoparticles, susceptible to external magnetic fields. If a nanocomposite composed of biocompatible polymer (PLGA), magnetite, and Dex-Ac can be pulled into and across the mammalian RWM, drug delivery can be enhanced.

METHOD

In vitro targeting and release kinetics of PLGA-magnetite-Dex-Ac nanoparticles first were measured using a RWM model. Next, these optimized nanocomposites were targeted to the RWM by filling the niche in anesthetized guinea pigs. A permanent magnet was placed opposite the RWM for 1 hour. Cochlear soft tissues, perilymph, and RWM were harvested after euthanasia and steroid levels were measured using HPLC.

RESULTS

Membrane transport, in vitro, proved optimal targeting using a lower particle magnetite concentration (1 versus 5 or 10 mg/ml). In vivo targeted PLGA-magnetite-Dex-Ac particles had an average size of 482.8 ± 158 nm (DLS) and an average zeta potential -19.9 ± 3.3 mV. In 1 hour, there was significantly increased cochlear targeted delivery of Dex or Dex-Ac, compared with diffusion alone.

CONCLUSION

Superparamagnetic PLGA-magnetite-Dex-Ac nanoparticles under an external magnetic field (0.26 mT) for 1 hour significantly increased Dex-Ac delivery to the inner ear. The RWM was not completely permeated and also became loaded with nanocomposites, indicating that delivery to the cochlea would continue for weeks by PLGA degradation and passive diffusion.

A novel aerosol-mediated drug delivery system for inner ear therapy: intratympanic aerosol methylprednisolone can attenuate acoustic trauma

We developed a novel aerosol-mediated drug delivery system for inner ear therapy by using a silicon-based multiple-Fourier horn nozzle. Intratympanic aerosol (ITA) methylprednisolone (MP) delivery can protect hearing after acoustic trauma. The highest concentration of MP (38.9 ± 5.47 ppm) appeared at 2 h and declined rapidly within 10 h. The concentrations of MP remained at a relatively low level for more than 10 h. Compared to the baseline, the auditory brainstem response (ABR) thresholds shifted markedly at 1 h after noise exposure in all groups (p < 0.05). From the cochleograms, it can be noted that the main lesions encompassed the 2-20 kHz frequency range. Significant differences ( ) were observed for the range between 5 and 8 kHz in the cell loss of outer hair cells (OHCs). The losses for IHCs were lower than for OHCs. The MP movement in the middle ear was simulated by a convection diffusion equation with a relaxation time. The relaxation time was 0.5 h, and the concentration threshold of MP on the round window membrane (RWM) in the middle ear (C T) was 8900 ppm. Using the unit hydrograph (UH) method, we obtained a proper boundary concentration on the RWM at the cochlea, which resulted in a well-fit concentration. Finally, a linking mechanism between the middle ear and the cochlea was established by the RWM. The adjustable permeability and concentration threshold provide the flexibility to match the peak times and peak values of the concentration on the RWM in the middle ear and the cochlea.

Strategies for drug delivery to the human inner ear by multifunctional nanoparticles

Hearing loss is a very significant health problem. The methods currently available for inner ear drug delivery are limited and a noninvasive cell-specific drug delivery strategy needs to be found.

AIM

In this study we investigated the ability of polymersomes, lipid core nanocapsules and hyperbranched poly-L-lysine to cross the round window membrane.

MATERIALS & METHODS

Nanoparticles (NPs) used in this study have different size and chemical compositions. Freshly frozen human temporal bones were used for this investigation. Intact human round window membrane within the freshly frozen human temporal bone served as an excellent model to test the membrane permeation and distribution within the tissues.

RESULTS

In this investigation we were able to visualize the NPs across the round window membrane. The NPs were subsequently found to be distributed in the sensory hair cells, nerve fibers and to other cells of the cochlea.

CONCLUSION

This finding raises hope in terms of future multifunctional NP-based drug delivery strategy to the human inner ear.

Drug delivery for treatment of inner ear disease: current state of knowledge

Delivery of medications to the inner ear has been an area of considerable growth in both the research and clinical realms during the past several decades. Systemic delivery of medication destined for treatment of the inner ear is the foundation on which newer delivery techniques have been developed. Because of systemic side effects, investigators and clinicians have begun developing and using techniques to deliver therapeutic agents locally. Alongside the now commonplace use of intratympanic gentamicin for Meniere's disease and the emerging use of intratympanic steroids for sudden sensorineural hearing loss, novel technologies, such as hydrogels and nanoparticles, are being explored. At the horizon of inner ear drug-delivery techniques, intracochlear devices that leverage recent advances in microsystems technology are being developed to apply medications directly into the inner ear. Potential uses for such devices include neurotrophic factor and steroid delivery with cochlear implantation, RNA interference technologies, and stem-cell therapy. The historical, current, and future delivery techniques and uses of drug delivery for treatment of inner ear disease serve as the basis for this review.

Local application of hepatocyte growth factor using gelatin hydrogels attenuates noise-induced hearing loss in guinea pigs

CONCLUSION

Local application of hepatocyte growth factor using biodegradable gelatin hydrogels attenuates noise-induced hearing loss in guinea pigs.

OBJECTIVES

To develop an inner ear drug delivery system using gelatin hydrogels that is capable of a sustained delivery of growth factors to the cochlea. We examined the efficacy of the local application of gelatin hydrogels containing hepatocyte growth factor (HGF) in protecting cochlear hair cells from noise-induced damage.

MATERIALS AND METHODS

A piece of gelatin hydrogel previously immersed in either HGF or saline was placed on the round window membrane of a guinea pig 1 h after noise exposure (4 kHz octave band noise at 120 dB sound pressure level for 3 h). Auditory function was monitored using auditory brainstem responses (ABRs), and the loss of hair cells was evaluated quantitatively.

RESULTS

Local HGF treatment significantly reduced the noise exposure-caused ABR threshold shifts and the loss of outer hair cells in the basal portion of the cochleae.

State-of-the-art mechanisms of intracochlear drug delivery

PURPOSE OF REVIEW

Treatment of auditory and vestibular dysfunction has become increasingly dependent on inner ear drug delivery. Recent advances in molecular therapy and nanotechnology have pushed development of alternate delivery methodologies involving both transtympanic and direct intracochlear infusions. This review examines recent developments in the field relevant to both clinical and animal research environments.

RECENT FINDINGS

Transtympanic delivery of gentamicin and corticosteroids for the treatment of Meniere's disease and sudden sensorineural hearing loss continues to be clinically relevant, with understanding of pharmacokinetics becoming more closely studied. Stabilizing matrices placed on the round window membrane for sustained passive delivery of compounds offer more controlled dosing profiles than transtympanic injections. Nanoparticles are capable of traversing the round window membrane and cochlear membranous partitions, and may become useful gene delivery platforms. Cochlear and vestibular hair cell regeneration has been demonstrated by vector delivery to the inner ear, offering promise for future advanced therapies.

SUMMARY

Optimal methods of inner ear drug delivery will depend on toxicity, therapeutic dose range, and characteristics of the agent to be delivered. Advanced therapy development will likely require direct intracochlear delivery with detailed understanding of associated pharmacokinetics.

Novel Therapy for Hearing Loss

HYPOTHESIS

Local application of recombinant human insulin-like growth factor 1 (rhIGF-1) via a biodegradable hydrogel after onset of noise-induced hearing loss (NIHL) can attenuate functional and histologic damage.

BACKGROUND

The biodegradable gelatin hydrogel makes a complex with drugs by static electric charges and releases drugs by degradation of gelatin polymers. We previously demonstrated the efficacy of local rhIGF-1 application via hydrogels before noise exposure for prevention of NIHL.

METHODS

First, we used an enzyme-linked immunosorbent assay to measure human IGF-1 concentrations in the cochlear fluid after placing a hydrogel containing rhIGF-1 onto the round window membrane of guinea pigs. Second, the functionality and the histology of guinea pig cochleae treated with local rhIGF-1 application at different concentrations after noise exposure were examined. Control animals were treated with a hydrogel immersed in physiologic saline alone.

RESULTS

The results revealed sustained delivery of rhIGF-1 into the cochlear fluid via the hydrogel. The measurement of auditory brainstem responses demonstrated that local rhIGF-1 treatment significantly reduced the threshold elevation from noise. Histologic analysis exhibited increased survival of outer hair cells by local rhIGF-1 application through the hydrogel.

CONCLUSION

These findings indicate that local rhIGF-1 treatment via gelatin hydrogels is effective for treatment of NIHL.