After attending a concert or after spending a few hours in a place where people compete with the music to be heard by their interlocutors and the noise levels are excessively high, it is not uncommon to experience an unpleasant sensation of ringing in the ears, alterations in the perception of sound, or even a temporary hearing loss that, in severe cases, can become permanent.
A team of researchers from the University of Pittsburgh has now discovered a molecular mechanism associated with noise-induced hearing loss and has shown that it could be alleviated with drugs. Specifically, they have found that it is due to cellular damage in the inner ear associated with excess free-floating zinc, a key mineral for proper cellular function and hearing.
Tests in mice have shown that drugs that absorb excess zinc can help restore hearing loss or, if given before exposure to loud sound, can protect against hearing loss. Their findings have been published in the Proceedings of the National Academy of Sciences.
“Noise-induced hearing loss has affected millions of people, but because the biology of hearing loss is not fully understood, preventing hearing loss has been an ongoing challenge,” said lead author Thanos Tzounopoulos, director of the Pittsburgh Hearing Research Center at Pitt School of Medicine.
Tinnitus and hearing loss induced by noise exposure
Some people experience noise-induced hearing loss due to an acute traumatic injury to the ear, while others notice sudden hearing loss after being continuously exposed to loud noises, such as those produced on a battlefield or in a construction site, for example. Others notice a deterioration in their hearing after attending a loud music show.
As the authors of the research have explained, some people begin to hear sounds that do not exist, a disorder known as tinnitus and that can significantly deteriorate their quality of life. Tzounopoulos, who is also a professor and vice chair of research in the Department of Otorhinolaryngology, has focused his scientific career on researching how hearing works and developing ways to treat tinnitus and hearing loss, so he sought to determine the mechanism underlying this condition as a starting point to find effective and minimally invasive treatments.
Mice treated with a slow-release compound that absorbs excess free zinc were less likely to suffer hearing loss and were protected from noise-induced damage.
The researchers carried out experiments in mice and in cells isolated from the inner ear and found that zinc levels in the inner ear increase hours after exposure to loud noise. They found that exposure causes an intense release of zinc into the spaces within and between cells, ultimately leading to cell damage and disrupting normal cell-to-cell communication.
This discovery opens the doors to a possible solution. Experiments showed that mice treated with a slow-release compound that absorbs excess free zinc were less likely to suffer hearing loss and were protected from noise-induced damage. Researchers are now developing a treatment that will be tested for safety in preclinical studies with the goal of making it available as a simple, over-the-counter option for hearing loss prevention.
