Manipulating gene expression in the mature inner ear

An Overview of Nanoparticle Based Delivery for Treatment of Inner Ear Disorders

Nanoparticles offer new possibilities for inner ear treatment as they can carry a variety of drugs, protein, and nucleic acids to inner ear. Nanoparticles are equipped with several functions such as targetability, immuno-transparency, biochemical stability, and ability to be visualized in vivo and in vitro. A group of novel peptides can be attached to the surface of nanoparticles that will enhance the cell entry, endosomal escape, and nuclear targeting. Eight different types of nanoparticles with different payload carrying strategies are available now. The transtympanic delivery of nanoparticles indicates that, depending on the type of nanoparticle, different migration pathways into the inner ear can be employed, and that optimal carriers can be designed according to the intended cargo. The use of nanoparticles as drug/gene carriers is especially attractive in conjunction with cochlear implantation or even as an inclusion in the implant as a drug/gene reservoir.

Localized cell and drug delivery for auditory prostheses

Localized cell and drug delivery to the cochlea and central auditory pathway can improve the safety and performance of implanted auditory prostheses (APs). While generally successful, these devices have a number of limitations and adverse effects including limited tonal and dynamic ranges, channel interactions, unwanted stimulation of non-auditory nerves, immune rejection, and infections including meningitis. Many of these limitations are associated with the tissue reactions to implanted auditory prosthetic devices and the gradual degeneration of the auditory system following deafness. Strategies to reduce the insertion trauma, degeneration of target neurons, fibrous and bony tissue encapsulation, and immune activation can improve the viability of tissue required for AP function as well as improve the resolution of stimulation for reduced channel interaction and improved place-pitch and level discrimination. Many pharmaceutical compounds have been identified that promote the viability of auditory tissue and prevent inflammation and infection. Cell delivery and gene therapy have provided promising results for treating hearing loss and reversing degeneration. Currently, many clinical and experimental methods can produce extremely localized and sustained drug delivery to address AP limitations. These methods provide better control over drug concentrations while eliminating the adverse effects of systemic delivery. Many of these drug delivery techniques can be integrated into modern auditory prosthetic devices to optimize the tissue response to the implanted device and reduce the risk of infection or rejection. Together, these methods and pharmaceutical agents can be used to optimize the tissue-device interface for improved AP safety and effectiveness.

A method for introducing non-silencing siRNA into the guinea pig cochlea in vivo

The aim of this preliminary study was to establish the methodology by which siRNA can be introduced into the adult guinea pig cochlea in vivo whilst preserving auditory function with a view to using targeted siRNAs to knockdown genes essential for auditory transduction. Initially a fluorescently tagged non-silencing siRNA complexed with a lipid-based transfection reagent was introduced into the perilymphatic compartment of the cochlea. Although auditory function was fully preserved, siRNA uptake was only observed in cells lining the perilymphatic space that are not critically involved in auditory transduction and therefore of little interest. Another approach was therefore adopted, in which siRNA was introduced directly into the scala media (endolymphatic compartment) of the apical (fourth) cochlear turn by slow pressure injection. During endolymphatic perfusion, the endocochlear potential (EP) and compound action potential (CAP) thresholds for basal turn frequencies from 6 to 20 kHz could be preserved, while CAP thresholds for 1-4 kHz were often elevated by 10-20 dB. CAP thresholds and EP were preserved 24 and 48 h after perfusion in some animals but reduced in others. siRNA uptake was observed predominantly in marginal and intermediate cells of the stria vascularis in all cochlear turns but not in cells of the organ of Corti.