One of the sometimes frustrating things about being a hearing specialist is that a lot of the situations we deal with which have caused our patients to lose their hearing cannot be reversed. Damage to the very tiny, sensitive hair cells of the inner ear is among the more common reasons for hearing loss. The work of these hair cells is to vibrate in response to sound waves. These vibrations are then interpreted by the brain into what we think of as hearing.
The sensitivity of these tiny hair cells enables them to vibrate in such a manner, and thus enables us to hear, but their very sensitivity makes them extremely fragile, and susceptible to damage. Aging, infections, certain medications or prolonged exposure to high-volume sounds (resulting in noise-induced hearing loss/NIHL) are all potential sources of damage. Once these hair cells have been damaged in human ears, science has to date not found a way to repair or “fix” them. Instead, hearing professionals and audiologists must use technologies such as hearing aids or cochlear implants to make up for hearing loss that is in essence irreversible.
This would not be the case if humans were more like fish and chickens. Though this may seem odd, it’s true, because unlike humans, some species of birds and fish have the ability to regenerate their inner ear hair cells if they become damaged, and thus get back their normal hearing. Chickens and zebra fish are just two examples of species that have the ability to automatically replicate and replace their damaged inner ear hair cells, thus allowing them to fully recover from hearing loss.
Bearing in mind that this research is preliminary and has to date produced no proven benefits for humans, some hope for the treatment of hearing loss comes from research called the Hearing Restoration Project (HRP). The nonprofit organization, Hearing Health Foundation, is currently funding research at laboratories in Canada and the US Scientists involved in the HRP are trying to isolate the molecules that allow the inner ear hair cells in some animals to replicate themselves, with the ultimate goal of finding some way to enable human inner ear hair cells to do the same.
This research is painstaking and challenging. Researchers need to sift through the many compounds involved in the regeneration process – some of which support replication while others inhibit it. But their hope is that if they can isolate the compounds that stimulate this regeneration process to happen in fish and avian cochlea, they can find a way to enable it to happen in human cochlea. A few of the HRP researchers are working on gene therapies as a way to promote such regrowth, while others are working on stem cell-based approaches.
Although this research is still in it’s early stages, our team wishes them swift success so that their findings can be extended to humans. Almost nothing would be more satisfying than to be able to provide our hearing loss patients a true cure.