Restoring cochlear hair cells: regeneration, technology and health
The inner ear holds about 16.000 "hair" cells that in simple are responsible to transform waves (sound) into a coded electric signal for our brain to interpret sound. Those "hair" cells are quite fragile and we must take care of them.
"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. Nevertheless he adds that there are a number of other factors that also have a strong impact in the inner ear: Drugs, antibiotics, stress and many other things can be a contributor to hearing loss.
Regeneration of the cochlear hair cells is slow (not to say nonexistent) compared to other cells in the human body. Damage to them is essentially permanent. Researchers are developing a technique to stimulate progenitor hair cells in the inner ear that allows them to grow 2,000 times faster than previously possible.
For Karp, their research originates from the desire of applying natural characteristics of other animals to humans. "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."
"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."
Frequency Therapeutics is readying the technique for clinical use on humans. Karp says they hope to begin human clinical trials by mid-late 2018 and eventually deliver the treatment as an outpatient procedure for hearing loss. Given the nature of the procedure, Karp believes that the technology might advance to become 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."