Ear implant may help regrow auditory nerves: study

Electrical pulses delivered from cochlear implants, which have been commercially available since the 1970s, can be used to regrow auditory nerves in people with severe hearing loss, Australian researchers said Wednesday.

The research, published in the US journal Science Translational Medicine, may also herald a possible new way of treating a range of neurological disorders, including Parkinson's disease, and psychiatric conditions such as depression through this novel way of delivering gene therapy.

"People with cochlear implants do well with understanding speech, but their perception of pitch can be poor, so they often miss out on the joy of music," senior author Gary Housley, who is professor of the University of New South Wales, said in a statement.

"Ultimately, we hope that after further research, people who depend on cochlear implant devices will be able to enjoy a broader dynamic and tonal range of sound, which is particularly important for our sense of the auditory world around us and for music appreciation," Housley said.

The five-year research focused on regenerating surviving nerves after age-related or environmental hearing loss, using existing cochlear technology, which can partially restore hearing by providing direct electrical stimulation to auditory nerves in the inner ear. However, current cochlear implants cannot restore hearing to normal, and the electrode design has changed little in decades.

According to the researchers, auditory nerve endings can regenerate if neurotrophins, a naturally occurring family of proteins crucial for the development, function and survival of neurons, are delivered to the auditory portion of the inner ear known as the cochlea.

But until now, research has stalled because safe, localized delivery of the neurotrophins can't be achieved using drug delivery, nor by viral-based gene therapy.

In the new study involving completely deaf guinea pigs, the researchers developed a way of using electrical pulses delivered from the cochlear implant to deliver a solution of DNA containing the brain-derived neurotrophic factor (BDNF) gene to the cells close to the array of implanted electrodes.

Within a few hours, cells in the cochlea took up the DNA and started to produce neurotrophins, they said.

The researchers tested the animals' hearing using the auditory brainstem response test, a common technique used to measure hearing in newborn babies.

They found that animals that were once completely deaf had their hearing restored to almost normal levels.

"No-one had tried to use the cochlear implant itself for gene therapy," said Housley. "With our technique, the cochlear implant can be very effective for this."

First author Jeremy Pinyon of the university said it's possible that in the future this gene delivery would only add a few minutes to the implant procedure.

Integration of this technology into other "bionic" devices such as electrode arrays used in deep brain stimulation for treating diseases like depression could also afford opportunities for safe, directed gene therapy of complex neurological disorders, the researchers said.

"Our work has implications far beyond hearing disorders," said co-author Matthias Klugmann, associate professor of the university.

"Gene therapy has been suggested as a treatment concept even for devastating neurological conditions and our technology provides a novel platform for safe and efficient gene transfer into tissues as delicate as the brain."