TORONTO - Researchers have restored the ability to hear in deaf gerbils using implanted human embryonic stem cells, achieving what they call a first step in potentially overcoming some causes of hearing loss in people.
While more study is needed to ensure the technique is safe for humans, principal researcher Dr. Marcelo Rivolta of the University of Sheffield said the work shows that stem cells can indeed regenerate nerve cells needed for hearing.
"It is early days, but we believe this is a substantial step forward because what we have here is the proof of concept that we can use human stem cells derived from human embryonic stem cells to repair the ear," Rivolta said from Sheffield, England.
The researchers describe their work in a paper published Wednesday in the journal Nature.
The "progenitor" cells implanted in the gerbils were produced in the lab from a line of human embryonic stem cells approved for use in research.
Embryonic stem cells give rise to virtually all tissue types in the body, from the various organs to neurons to skin. Progenitor cells generated from the stem cells have been manipulated to produce only certain kinds of cells.
These "otic progenitors" differentiate into cells with the same properties as hair cells and auditory neurons, which are critical for sensing sound.
Hair cells, located in the spiral-shaped cochlea in the inner ear, amplify and transform sound vibrations into electrical signals, which are then relayed via the auditory nerve to the brain stem.
While the researchers were able to use neurons to repair the auditory nerve in the gerbils, hair cells are more challenging to deal with, said Rivolta. "We don't have a very good surgical technique to deliver the cells into the specific place that we need to."
Damage to the hair cells — which can be caused by genetic disorders, prolonged exposure to high-decibel noise and infections like bacterial meningitis — can lead to partial or profound hearing loss.
Such hearing loss can be partially overcome by a cochlear implant, a small electronic device that bypasses damaged portions of the ear and transfers sound signals by directly stimulating the auditory nerve.
"You can replace the hair cells with the cochlear implant, but the cochlear implant will work very poorly or not work at all if you don't have the nerve," said Rivolta, explaining that the idea would be to regenerate the auditory nerve with stem cells — combined with cochlear implants.
However, trials to test the stem cell therapy in people is at least a few years off.
While researchers kept track of the gerbils' progress for about 10 weeks after treatment, Rivolta said the next studies would follow the animals for up to 15 weeks to see if any adverse effects show up.
That's because embryonic stem cells — which by their very nature are genetically programmed to give rise to many kinds of cells — have been known to produce tumours in experimental animal models.
Although Rivolta believes tumour formation won't be an issue with the otic progenitor cells, he said safety has to be the first priority before human trials could begin.
"In the current experiments, we haven't seen any problems. But it's not enough. We need to follow it for longer."
© The Canadian Press, 2013