Now, drug to reverse 'permanent' deafness
London: Harvard scientists have developed a drug which they claim can cure permanent deafness by stimulating the inner ear.
The drug, codenamed LY411575, works by triggering the regeneration of sensory hair cells.
Until now it has not been possible to restore the cells once they have been lost due to factors such as loud noise exposure, infection and toxic drugs, the `Daily Mail` reported.
This type of deafness, often suffered by rock musicians and DJs, is generally assumed to be irreversible.
Scientists succeeded in partially restoring hearing to mice that had been deafened by loud noise and believe the research could lead to effective treatments for acute noise-induced deafness in humans.
The tiny sensory hairs in the cochlea are vital to hearing. Sound vibrations transferred from the eardrum shake the hairs, causing nerve messages to be fired to the brain.
Without the hairs, the hearing pathway is blocked and no signals are received by the brain`s auditory centre.
While birds and fish are capable of regenerating sound-sensing hair cells, mammals are not.
The new approach involves reprogramming inner ear cells by inhibiting a protein called Notch.
Previous laboratory research had shown that Notch signals help prevent stem cells in the cochlea transforming themselves into new sensory hair cells.
The new drug suppresses Notch. Mice with noise-induced hearing loss generated functioning sensory hair cells after the drug was injected into their damaged cochleas.
"We show that hair cells can be regenerated from the surrounding cells in the cochlea," lead researcher Dr Albert Edge, from Harvard Medical School in the US, said.
"These cells, called supporting cells, transdifferentiate into hair cells after inhibition of the Notch signalling pathway, and the new hair cell generation results in a recovery of hearing in the region of the cochlea where the new hair cells appear," Edge said.
"The significance of this study is that hearing loss is a huge problem affecting 250 million worldwide," Edge added.
A green fluorescent protein was used to label the newly generated hair cells. Electronic measurements of auditory brainstem responses confirmed that three months after treatment, lost hair cells had been replaced and were working.
Improvement in hearing was seen over a wide range of frequencies.
"The missing hair cells had been replaced by new hair cells after the drug treatment, and analysis of their location allowed us to correlate the improvement in hearing to the areas where the hair cells were replaced," Edge added.
The study was published in the journal Neuron.