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

Effects of different electrodes used in bone-guided extracochlear implants on electrical stimulation of auditory nerves in guinea pigs

Objective:

Conventional cochlear implants provide patients who are deaf with hearing via electrical intracochlear stimulations. Stimulation electrodes are inserted into the cochlea through a cochleostomy or round window membrane (RWM) approach. However, these methods might induce cochlear ossificans and loss of residual hearing by damaging inner ear structures. To avoid an invasive electrode insertion, we developed a novel bone-guided extracochlear implant that stimulated the auditory nerves between the cochlear bones and the RWM to prevent cochlea damage. Power consumption plays an important role in wireless implantable electronic devices. Therefore, we aimed to investigate the effects of different electrodes on the stimulating threshold currents of the auditory nerve and the power consumption of bone-guided extracochlear implants using a commercial stimulator.

Materials and Methods:

Inert aurum (Au) electrodes were compared with biocompatible platinum (Pt) and iridium oxide (IrO_x) electrodes in practical implantable applications. IrO_x electrodes were used for their high-charge storage capacity, low impedance, and biocompatibility. The electrodes were fabricated via sputtering and were experimentally characterized with cyclic voltammetry and then examined using in vivo tests.

Results:

Based on electrical auditory brainstem responses, IrO_x electrodes yielded lower acoustic nerve-stimulating threshold currents (132 μA) compared with Au electrodes (204 μA). IrO_x electrodes also had a lower acoustic nerve stimulating threshold current (132 μA) compared with Pt electrodes (168 μA).

Conclusion:

As expected, IrO_x electrodes were beneficial in the development of multielectrode bone-guided extracochlear implants, with the lowest acoustic nerve-stimulating threshold and current consumptions compared with Au and Pt electrodes.

Histone acetylation in refractory sudden sensorineural hearing loss patients after intratympanic methylprednisolone perfusion

OBJECTIVE

To examine the relationship between the therapeutic effect of intratympanic methylprednisolone perfusion and histone acetylation in refractory sudden sensorineural hearing loss.

METHODS

Thirty-four refractory sudden sensorineural hearing loss patients were enrolled and treated with intratympanic methylprednisolone perfusion. Pure tone average, acetylated histone H3, acetylated histone H4 and histone deacetylase 2 (HDAC2) were measured in peripheral blood mononuclear cells before and after intratympanic methylprednisolone perfusion. Sixteen healthy volunteers were recruited to obtain normal reference values.

RESULTS

Pure tone average in sudden sensorineural hearing loss patients improved from 84.14 ± 13.54 dB to 73.56 ± 18.45 dB after intratympanic methylprednisolone perfusion. Up-regulations in HDAC2 protein level, and down-regulations in histone H3 and H4 acetylation were observed in the intratympanic methylprednisolone perfusion sensitive group (pure tone average gain of 15 dB or more), while no significant changes were observed in the intratympanic methylprednisolone perfusion insensitive group (pure tone average gain of less than 15 dB).

CONCLUSION

Intratympanic methylprednisolone perfusion can improve hearing in a considerable number of refractory sudden sensorineural hearing loss patients. The therapeutic effect is closely related to reduced histone acetylation.

Toxicology study for magnetic injection of prednisolone into the rat cochlea

This paper investigates the safety of a novel 'magnetic injection' method of delivering therapy to the cochlea, in a rodent model. In this method of administration, a magnetic field is employed to actively transport drug-eluting superparamagnetic iron-oxide core nanoparticles into the cochlea, where they then release their drug payload (we delivered the steroid prednisolone). Our study design and selection of control groups was based on published regulatory guidance for safety studies that involve local drug delivery. We tested for both single and multiple delivery doses to the cochlea, and found that magnetic delivery did not harm hearing. There was no statistical difference in hearing between magnetically treated ears versus ears that received intra-tympanic steroid (a mimic of a standard-of-care for sudden sensorineural hearing loss), both 2 and 30 days after treatment. Since our treatment is local to the ear, the levels of steroid and iron circulating systemically after our treatment were low, below mass-spectrometry detection limits for the steroid and no different from normal for iron. No adverse findings were observed in ear tissue histopathology or in animal gross behavior. At 2 and 30 days after treatment, inflammatory changes examined in the ear were limited to the middle ear, were very mild in severity, and by day 90 there was ongoing and almost complete reversibility of these changes. There were no ear tissue scarring or hemorrhage trends associated with magnetic delivery. In summary, after conducting a pre-clinical safety study, no adverse safety issues were observed.

Animal model studies yield translational solutions for cochlear drug delivery

The field of hearing and deafness research is about to enter an era where new cochlear drug delivery methodologies will become more innovative and plentiful. The present report provides a representative review of previous studies where efficacious results have been obtained with animal models, primarily rodents, for protection against acute hearing loss such as acoustic trauma due to noise overexposure, antibiotic use and cancer chemotherapies. These approaches were initiated using systemic injections or oral administrations of otoprotectants. Now, exciting new options for local drug delivery, which opens up the possibilities for utilization of novel otoprotective drugs or compounds that might not be suitable for systemic use, or might interfere with the efficacious actions of chemotherapeutic agents or antibiotics, are being developed. These include interesting use of nanoparticles (with or without magnetic field supplementation), hydrogels, cochlear micropumps, and new transtympanic injectable compounds, sometimes in combination with cochlear implants.

Assessment of the efficacy of a local steroid rescue treatment administered 2 days after a moderate noise-induced trauma in guinea pig

OBJECTIVES

Intratympanic injection of corticosteroids membrane after noise-induced hearing loss is an accepted alternative to general administration. We investigated the effect on hearing of a hyaluronic acid gel with liposomes loaded with dexamethasone (DexP) administered into the middle ear.

METHODS

An acute acoustic trauma was performed to 13 guinea pigs for a period of 1 h on Day -2. Two 2 days after the noise trauma, the animals were then assigned randomly to four experimental groups: control without gel, gel injection, gel-containing free DexP, gel-containing DexP loaded into liposomes. Auditory thresholds were measured with Auditory Brainstem Response before Day -2 and at Day 0, Day 7 and Day 30 after noise trauma.

RESULTS

Seven days after, a complete hearing recovery was observed in the control group at all frequencies apart from 8 kHz, and no recovery was observed in the three groups receiving a gel injection. Thirty days after trauma, all of the animals had recovered normal hearing, apart from at the 8-kHz frequency, with similar auditory thresholds.

CONCLUSIONS

Local DexP administration 48 h after a mild acoustic trauma did not improve hearing recovery, even with a sustained release in a specific gel formulation designed for inner ear therapy.