Daniel Llano, an associate professor in the Department of Molecular and Integrative Physiology at the University of Illinois Urbana-Champaign, is the corresponding author on the paper.
Key points:
- Researchers have found a possible connection between PCB exposure in utero and later hearing loss.
- The findings center around a surplus of oxidative stress, which suppresses the auditory system’s ability to recover from acoustic trauma.
Polychlorinated biphenyls, or PCBs, have been banned in the U.S. since 1979, but that hasn’t completely stopped human exposure. Now, researchers have linked the environmental chemical to another health trauma—hearing loss.
A team at the Beckman Institute for Advanced Science and Technology found that early exposure PCBs made it more difficult for mice to recover from sound-related trauma sustained later in life. In particular, exposure to PCBs can be harmful to a developing fetus.
“The most sensitive period in pregnancy for these types of developmental exposures is typically early in the pregnancy, in the first trimester,” said Daniel Llano, corresponding author and associate professor at the University of Illinois Urbana-Champaign. “But PCBs as chemical entities are very permeant to all sorts of membranes. They can cross the placenta and they can get into the brain. That makes them particularly dangerous throughout all phases of pregnancy.”
Initial research by Susan Schantz, a professor emerita, found that rats treated with PCBs experienced seizures in response to certain levels of sound. The researchers suspected that if an individual who was exposed to PCBs in utero sustained acoustic trauma later in life—for example, from an occupation associated with high noise levels or even a recreational activity like a rock concert—their hearing might not recover as would typically be expected.
For the new study, published in JNeurosci, the researchers focused on a lower brain region known as the inferior colliculus. There, they used multiphoton imaging to identify damage resulting from the combination of PCBs and noise. They also observed the neurons to become hypo-excitable—a brand new finding.
The researchers used chemical analysis to further understand the mechanisms behind the changes. Their findings centered around a common cellular process called oxidative stress that automatically releases oxygen radicals when cells are sick or exposed to toxins. Oxygen radicals are eliminated by an intrinsic system within the body. Mice with higher levels of the intrinsic protective system suffered less damage to the inferior colliculus, suggesting that PCBs and noise could cause a surplus of oxidative stress in the inferior colliculus, suppressing the auditory system’s ability to recover from acoustic trauma.
“On its own, PCB exposure in utero may cause only a moderate degree of hearing loss,” Llano said. “But that PCB exposure creates a particular vulnerability to later hearing loss. And so someone who is exposed to PCBs during development and has a significant occupational or recreational exposure to sound later in life may suffer greater-than-expected consequences when it comes to hearing.”
While oxidative stress appears to be a key mediator of the effect, investigators have yet to measure oxygen radicals in the tissues to confirm this. The team says they will continue to investigative the connections among PCB exposure, noise exposure and hearing loss.