This new treatment could combat hearing loss by regenerating hair cells in the inner ear

A human ear.

Here’s an unexpected story: Scientists are working on a drug to stimulate ear hair growth.

In this case, the ear hairs in question are actually tiny, sensory hair cells in our cochlea. We have about 15,000 of them in each ear, and they’re crucial to helping us detect sound waves. But the little cells are also very fragile.

“There's so many ways that these hair cells can be damaged from loud noises, and it really doesn't take a long exposure,” says Jeffrey Karp, an associate professor of medicine at Brigham and Women's Hospital. Noise isn’t the only culprit, he adds. Age, some antibiotics and chemotherapy drugs and even heavy aspirin use are thought to contribute to hair cell damage, as well.

The cochlear hair cells don’t regenerate, so right now, damage to them is permanent — and common among people with some types of hearing loss. But that may not always be the case. A team of Boston-area researchers, including Karp, have developed a technique to stimulate progenitor hair cells in the inner ear — growing 2,000 times more hair cells than previously possible.

For Karp and his team, their research grew from a simple question: If some animals can regenerate limbs and teeth, why can’t we? “We were kind of envious of creatures like sharks that can regrow their teeth throughout life,” he says. “We were envious of salamanders, where you can cut off an entire limb and it regrows, or a tail. And we said, you know, why have humans been left out of this regenerative process?”

“And when we take a close look, we actually haven't been left out of this completely,” he says. Specifically, the lining of our intestines regenerates quickly, every four to five days. “It's really the most regenerative tissue in our entire body, so it was really a great place for us to start our work.”

Researchers isolated the stem cell in our intestinal lining that’s responsible for the snappy regeneration. “And so through trying to really understand the cues of how that cell is regulated, we were able to come up with small molecules … that could regulate that stem cell, and grow it in almost unlimited quantities in pure form,” Karp explains.

In the laboratory, the team applied the molecules to progenitor hair cells from the inner ear — to great effect. “We were able to obtain very large populations of hair cells,” Karp says. “We demonstrated that they had functionality — you know, really bona fide hair cells. And we demonstrated this for tissue from mice, nonhuman primates and even human tissue.”

Now, a company formed by members of the team, Frequency Therapeutics, is readying the technique for clinical use. Karp says they hope to begin human clinical trials within about 18 months and eventually deliver the treatment as an outpatient procedure for hearing loss. He thinks the treatment could someday be as mundane as a simple injection.

“A lot of people have middle ear infections, and it's a very standard procedure for people to get antibiotics injected into the middle ear,” Karp explains. “And so we envision really just kind of piggybacking on that type of infrastructure that's already available.

“Really, the goal here is to get the molecules into the inner ear. So, we would just inject them into the middle ear, and allow them to diffuse across and it should be a relatively quick procedure.”

This article is based on an interview that aired on PRI's Science Friday

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