Extracellular Vesicles in Inner Ear Therapies-Pathophysiological, Manufacturing, and Clinical Considerations

Intratympanic injection of MSC-derived small extracellular vesicles protects spiral ganglion neurons from degeneration

Sensorineural hearing loss is one of the most prevalent sensory deficits. Spiral ganglion neurons (SGNs) exhibit very limited regeneration capacity and their degeneration leads to profound hearing loss. Mesenchymal stem cell-derived small extracellular vesicles (MSC-sEV) have been demonstrated to repair tissue damage in various degenerative diseases. However, the effects of MSC-sEV on SGN degeneration remain unclear. In this study, we investigated the efficacy of MSC-sEV for protection against ouabain-induced SGN degeneration. MSC-sEV were derived from rat bone marrow and their components related to neuron growth were determined by proteomic analysis. In primary culture SGNs, MSC-sEV significantly promoted neurite growth and growth cone development. The RNA-Seq analysis of SGNs showed that enriched pathways include neuron development and axon regeneration, consistent with proteomics. In ouabain induced SGN degeneration rat model, MSC-sEV administration via intratympanic injection significantly enhanced SGN survival and mitigated hearing loss. Furthermore, after ouabain treatment, SGNs displayed evident signs of apoptosis, including nuclei condensation and fragmentation, with numerous cells exhibiting TUNEL-positive. However, administration of MSC-sEV effectively decreased the number of TUNEL-positive cells and reduced caspase-3 activation. In conclusion, our findings demonstrate the potential of MSC-sEV in preventing SGN degeneration and promoting neural growth, suggesting intratympanic injection of MSC-sEV is a specific and efficient strategy for neural hearing loss.

A novel cell-free therapy using exosomes in the inner ear regeneration

Cellular and molecular alterations associated with hearing loss are now better understood with advances in molecular biology. These changes indicate the participation of distinct damage and stress pathways that are unlikely to be fully addressed by conventional pharmaceutical treatment. Sensorineural hearing loss is a common and debilitating condition for which comprehensive pharmacologic intervention is not available. The complex and diverse molecular pathology that underlies hearing loss currently limits our ability to intervene with small molecules. The present review focuses on the potential for the use of extracellular vesicles in otology. It examines a variety of inner ear diseases and hearing loss that may be treatable using exosomes (EXOs). The role of EXOs as carriers for the treatment of diseases related to the inner ear as well as EXOs as biomarkers for the recognition of diseases related to the ear is discussed.

MSC-derived exosomes protect auditory hair cells from neomycin-induced damage via autophagy regulation

BACKGROUND

Sensorineural hearing loss (SNHL) poses a major threat to both physical and mental health; however, there is still a lack of effective drugs to treat the disease. Recently, novel biological therapies, such as mesenchymal stem cells (MSCs) and their products, namely, exosomes, are showing promising therapeutic potential due to their low immunogenicity, few ethical concerns, and easy accessibility. Nevertheless, the precise mechanisms underlying the therapeutic effects of MSC-derived exosomes remain unclear.

RESULTS

Exosomes derived from MSCs reduced hearing and hair cell loss caused by neomycin-induced damage in models in vivo and in vitro. In addition, MSC-derived exosomes modulated autophagy in hair cells to exert a protective effect. Mechanistically, exogenously administered exosomes were internalized by hair cells and subsequently upregulated endocytic gene expression and endosome formation, ultimately leading to autophagy activation. This increased autophagic activity promoted cell survival, decreased the mitochondrial oxidative stress level and the apoptosis rate in hair cells, and ameliorated neomycin-induced ototoxicity.

CONCLUSIONS

In summary, our findings reveal the otoprotective capacity of exogenous exosome-mediated autophagy activation in hair cells in an endocytosis-dependent manner, suggesting possibilities for deafness treatment.

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.

Deep intracochlear injection of triamcinolone-acetonide with an inner ear catheter in patients with residual hearing

Introduction

In a previous study, an inner ear catheter was used to deliver low- and high-dose steroids into the cochlea prior to cochlear implant electrode insertion. With this approach, more apical regions of the cochlea could be reached and a reduction of electrode impedances in the short term was achieved in cochlear implant recipients. Whether intracochlear application of drugs via the catheter is a safe method also for patients with residual hearing has not been investigated hitherto. The aim of the present study was therefore to investigate the effect of intracochlear triamcinolone application in cochlear implant recipients with residual hearing.

Patients and methods

Patients with residual hearing were administered triamcinolone-acetonide (4 mg/ml; n = 10) via an inner ear catheter just prior to insertion of a MED-EL FLEX28 electrode. Impedances were measured at defined time points (intra-operatively, post-operatively and at first fitting) and retrospectively compared with a control group (no steroid application) and low- and high-dose group. Hearing thresholds were measured preoperatively, 3 days after surgery and at first fitting by pure tone audiometry. Pre- to postoperative hearing loss was determined at first fitting and compared to results from a previous study.

Results

The median hearing loss after implantation (125-1,500 Hz) was 20.6 dB. Four patients (40%) showed a median hearing loss of less than 15 dB, three patients (30%) between 15 and 30 dB and three patients (30%) more than 30 dB. The median hearing loss was similar to the results obtained from our previous study showing a median hearing loss of 24 dB when using FLEX28 electrode arrays.

Conclusion

No difference in residual hearing loss was found when comparing application of triamcinolone-acetonide using an inner ear catheter prior to the insertion of a FLEX28 electrode array to the use of the FLEX28 electrode array without the catheter. Thus, we conclude that application of drugs to the cochlea with an inner ear catheter could be a feasible approach in patients with residual hearing.