Researchers at Harvard Medical School (HMS) have developed what they believe to be a game-changing cure for hearing loss: a new combination of drug-like molecules that can rebuild the hair cells in the inner ear that permit hearing.

Reprogramming genetic pathways in the inner ear allowed the hair cells to regrow in mice, as explained in a new paper published in the Proceedings of the National Academy of Sciences.

Now, researchers are hoping that this study may pave the way for human clinical trials that will one day result in a treatment for hearing loss. It’s a huge “if,” to be sure, but for those who have had trouble hearing, it’s also a fascinating possibility.

“These findings are extremely exciting because throughout the history of the hearing loss field, the ability to regenerate hair cells in an inner ear has been the holy grail,” said Zheng-Yi Chen, the HMS associate professor who led the study. As the authors put it, “we now have a drug-like cocktail that shows the feasibility of an approach that we can explore for future clinical applications.”

What’s up with human hair cells?

Hair cells are like biological microphones and transmit sound information from the inner ear to the brain, but unlike some fish, birds, and reptiles, humans do not have the ability to replace hair cells.

Chen’s team was able to induce the division and differentiation into hair cells of other cell types in an earlier work, also in mice.

This new study expands upon those findings by using newly discovered chemical compounds to activate the same pathways.

The team was able to eliminate genes that inhibited the activation of a genetic pathway necessary for hair cell proliferation in the inner ear by employing molecules called “small interfering RNAs” (siRNAs).

Releasing the brake

To illustrate his point, Chen used the analogy of a car’s brake, saying that “if the break is always engaged, you can’t drive.” According to Chen, he and the team identified a small interfering RNA (siRNA) that can ease the brake off of this genetic route.

They observed that adult mice could grow new hair cells that appear to be fully functional by injecting their newly created drug cocktail directly into the inner ear.

The researchers intend to test the treatment on larger animals prior to using it on humans.

However, if the study turns out to be successful, it could have a significant effect on people who have experienced partial hearing loss.

“My colleagues and I frequently are contacted by people with hearing loss who are desperate for effective treatments,” Chen added. They believe that introducing a new treatment into clinical practice will be possible if they can combine a surgical procedure with a better, more refined iteration of the gene therapy they are currently developing.

Source study: Proceedings of the National Academy of Sciences— Reprogramming by drug-like molecules leads to regeneration of cochlear hair cell-like cells in adult mice