Researchers from the Keck School of Medicine of USC may have found a way to treat noise-induced hearing loss, which affects about 15 percent of Americans, the school announced Monday.
Researchers built a tool using miniature optics to image inside the cochlea, the hearing portion of the inner ear, and exposed mice to a loud noise similar to that of a roadside bomb. They discovered that after exposure to a loud noise sensory hair cells, the cells that detect sound and convert it to neural signals, die, and the inner ear fills with excess fluid, leading to the death of neurons.
“That buildup of fluid pressure in the inner ear is something you might notice if you go to a loud concert,” said Dr. John Oghalai, the study’s corresponding author and chair and professor of the USC Tina and Rick Caruso Department of Otolaryngology — Head and Neck Surgery.
“When you leave the concert, your ears might feel full and you might have ringing in your ears. We were able to see that this buildup of fluid correlates with neuron loss.”
Both neurons and sensory hair cells play critical roles in hearing.
“The death of sensory hair cells leads to hearing loss,” Oghalai said. “But even if some sensory hair cells remain and still work, if they’re not connected to a neuron, then the brain won’t hear the sound.”
The researchers found that sensory hair cell death occurred immediately after exposure to loud noise and was irreversible. However, neuron damage had a delayed onset, opening a window of opportunity for treatment.
The buildup of fluid in the inner ear occurred over a period of a few hours after loud noise exposure and contained high concentrations of potassium.
To reverse the effects of the potassium and reduce the fluid buildup, salt- and sugar-based solutions were injected into the middle ear, just through the eardrum, three hours after noise exposure. The researchers found that treatment with these solutions prevented 45-64 percent of neuron loss, suggesting that the treatment may offer a way to preserve hearing function.
The treatment could have several potential applications, Oghalai said.
“I can envision soldiers carrying a small bottle of this solution with them and using it to prevent hearing damage after exposure to blast pressure from a roadside bomb,” Oghalai said. “It might also have potential as a treatment for other diseases of the inner ear that are associated with fluid buildup, such as Meniere’s disease.”
Oghalai said he and his team plan to conduct further research on the exact sequence of steps between fluid buildup in the inner ear and neuron death, followed by clinical trials of their potential treatment for noise-induced hearing loss.