Australian researchers found that the electrical pulses from cochlear implants can regrow auditory nerves to improve hearing among people with severe hearing loss.
Previous studies have established that auditory nerve endings could regenerate if a family of nerve-nourishing proteins called neurotrophins function properly and surviving neurons are transmitted to the cochlea, the inner ear's auditory part. However, neurotrophins cannot be locally delivered safely using drug delivery or gene therapy based on virus so research has been stalled for a long time.
The inner ear has microscopic hair cells called the cochlea which detects and converts vibrations to electrical impulses that we recognize as sound. When these hair cells are lost due to aging, loud noises or other causes, hearing loss occurs. There are different types of hearing loss and it depends on which part of the path between the brain and the ear is damaged. People with cochlear implants have the damage in the cochlea.
University of New South Wales researchers in Australia found a remarkable breakthrough in delivering one of the nerves' hairy endings that regrow when exposed to neurotrophins. The research team injected a growth factor-producing gene to the ears of deaf guinea pigs. These animals are commonly used to test for human hearing. The team adapted a cochlear implant electrode to beam a couple of strong electrical pulses.
"No-one had tried to use the cochlear implant itself for gene therapy," senior author of the study Gary Housley said. "With our technique, the cochlear implant can be very effective for this." Housley is a professor at the University of New South Wales.
This technology was integrated into other devices such as those used in deep brain stimulation used for treating depression to direct safe gene therapy of complex neurological conditions. The researchers used the electrical pulses from the cochlear implant to deliver a DNA solution with BDNF (brain-derived neurotrophic factor) gene to the cells near the implanted electrode arrays.
The cells in the cochlea took the DNA in a couple of hours and produced neurotrophins. When the researchers tested the guinea pigs' hearing with a widely used technique in measuring hearing in infants called the auditory brainstem response test, they found that the animals' hearing was restored from completely deaf to almost normal levels.
"That is a really clever way of delivering the nerve booster," Stanford University otolaryngology professor Stefan Heller said. "This is a promising approach." Heller was not part of the research.
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