(G-246) Porcine Model to the Rescue! Addressing Hearing Loss Treatment Challenges

Nearly 0.5 billion people suffer from debilitating hearing impairments. Although there are promising studies to restore hearing in rodent models, there are two major translational problems: 1) The size, ontogeny, genetics, and frequency range of hearing of most rodents’ cochlea do not match that of humans. 2) Delivery of therapeutics into the inner ear is problematic. Local delivery is more efficient, but invasive surgeries (e.g., cochleostomy), can cause damage to delicate structures in the inner ear or endolymphatic hydrops. Furthermore, these techniques are relatively easy to perform in rodents but are challenging and unreliable in bigger animal models with different anatomy. The alternative safe intratympanic method is clinically practiced but has low efficiency since drugs must permeate through the round window membrane (RWM). In this respect, rodent models also have low translational value for optimizing translational delivery techniques due to their smaller size.

Thus, our specific aims are: i) Establishing a big animal model that could bridge the gap between rodents and humans for hearing loss studies. We studied the porcine cochlea since it shares many anatomical, physiological, and genetic similarities with its human counterpart. ii) Developing a clinically relevant ex vivo model system to improve intratympanic delivery.

To address the first problem and validate a more translational animal model, we imaged the porcine inner ear in 3D using tissue-clearing and custom light-sheet microscopy. This method maintained, with high fidelity, the cochlea's 3D structure which is important to its proper function. To address the second major hurdle, we developed an ex-vivosystem for efficient testing of therapeutic delivery. We immobilized porcine RWMs, with a similar thickness to that of humans, across a 2-cavity chamber mimicking the middle and inner ear.

Using 3D imaging, we measured never-reported porcine cochlear characteristics e.g., total hair cell count and basilar membrane length. The images also revealed milestones in the ontogeny of porcine cochlear development such as cochlear turn, Reissner membrane, and Stria vascularis formations and hair cells and supporting cell organization that are remarkably like those in humans.

We validated the viability of porcine RWM explants in the ex-vivo chamber for testing drug passage. We also verified the functionality of the chamber for high and low permeability substances and tested techniques to improve the permeability of RWM.

Together with past porcine anatomical and auditory-brainstem-response studies, this work establishes the pig as an excellent large animal model for understanding hearing impairment, mapping cochlear development, and exploring regenerative medicine therapies before translation into humans. An animal model matching the human organ’s size could also guide novel treatment plans concerning therapeutic dosage, diffusion, targetability, and efficiency. The developed ex-vivo chamber is biologically functional and translational and can be used to test novel approaches for enhancing intratympanic delivery.