Preemptive Strike: Protecting Service Members from Inner-ear Injury

Hearing loss can make functioning in a normal environment incredibly difficult. For military personnel, it can be even more devastating—impacting life both in service and at home. Baylor University researcher Dwayne Simmons, Ph.D., Cornelia Marschall Smith Endowed Professor and department chair of biology, is studying how to restore hearing and balance function after exposure to either loud noises and/or blasts that are typically encountered by soldiers in combat or on patrol.

Simmons’ research focuses on the dual sensory systems of the inner ear: the cochlea, which is responsible for hearing and the vestibular organs, which are responsible for equilibrium and balance. Both loud noises and blasts can significantly damage the inner ear, making individuals very vulnerable and disoriented.

“Hearing allows you to understand commands, make sense of the world about you, and react accordingly. You need to be able to understand when you're in danger,” Simmons said. “The inner ear also has a vestibular or balance aspect. When you are disoriented in terms of your ability to balance, that can be hugely debilitating.”

Preventing the Irreversible

To determine the mechanisms behind issues of hearing loss, Simmons is studying the role of inflammation and calcium regulation in damage to sensory hair cells. Repeated trauma — repetitive instances of excessive noise or low-level blasts not only damages the sensory hair cells in the inner ear, but also disrupts the the connection between the sensory cells and neurons within the inner ear. These repetitive exposures can lead to temporary dysfunction, but also lead to permanent damage.

“We're looking at ways to ameliorate short-term damage to the inner ear — if we can tackle that, then that will obviously and ultimately help with the longer-term repetitive exposures,” Simmons said. “If we can lessen the injury that occurs at a cellular molecular level with great precision, and target reducing trauma to specific sensory cells — which is kind of unique in terms of our approach — then we think that we will be able to not only help minimize the insult from a large acoustic blast, but also from the repetitive kinds of trauma that occur on a more routine level that wind up causing significant hearing and balance problems down the road.”

Because the inner ear is a sensitive and complex system, Simmons is targeting very specific cells within the ear that seem to be hypersensitive to trauma. He sees an opportunity, through a targeted therapeutic treatment, to prevent these cells from undergoing injury, thus preventing longer-term consequences.

Unfortunately, most inner ear injuries lead to hearing loss that is irreversible. Current treatments and therapies have variable outcomes, and have not been very successful at restoring hearing. Severe hearing loss often leads to the use of cochlear implants or hearing aids. The best option of treatment would be to prevent injury from ever becoming severe enough to permanently damage sensory cells or neurons.

“We want something that can actually help to reduce the injury to those really sensitive sensory cells, with the hope to minimize the overall kind of injury that occurs. We're looking at prophylactic protection, as well as treatment after the fact,” he said.

A therapeutic treatment could be given in the form of an injection, ahead of anticipated blasts or injury-inducing noise, that would provide a window of protection. The treatment would bolster the resiliency of the inner ear against injury for a limited period of time, decreasing the frequency of short-term damage and repetitive injury.

“We’re developing our experiments for prophylactic treatment, before someone actually experiences the trauma — giving this drug 24 or 48 and having that protection last for that time period. That, then, would allow your inner ear to be more resilient to these insults,” Simmons said.

A Prevalent DoD Concern

Hearing loss happens to be the most prevalent Department of Defense (DoD) disability. About 2% of the service force population develop permanent hearing loss, and about 14% develop temporary hearing loss. While temporary hearing loss was previously thought to have minimal consequences, it has been shown to be a potential predictor for future, more permanent issues. Altogether, service-related hearing loss costs the DoD at least $1 billion annually.

Applying his research to DoD problems, Simmons has been able to merge theory with practical intervention strategies. He considers the ways in which targeting an inflammatory pathway related to inner ear injuries could have direct application to humans in real-time.

“Working through and with the DoD is an amazing opportunity for us to take something that could stay at a theoretical level and actually make that translation to something that can be applied to human beings in real time,” Simmons said. “Working to protect our service women and men who are out there risking their lives also makes me feel extremely patriotic.

“If we can protect their hearing and balance, then they come back as healthy as possible and they're able to perform their jobs in real-time. Once we have something that works for the military, the application to the civilian is just right around the corner.”