Drug may help troops battle combat-related hearing loss
City scientists say pill could benefit others
Drug may help troops battle combat-related hearing loss
By Brian Kimball
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Published: July 6, 2008
Two Oklahoma City scientists believe they are on a track that will lead to a significant reduction in combat-related hearing loss suffered by troops.
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From left, Robert Floyd and Dr. Richard Kopke in the lab at Hough Ear Institute in Oklahoma City. They are working on a pill that helps prevent hearing loss after traumatic noise exposure. By CHRIS LANDSBERGER, THE OKLAHOMAN
Did you know?
Noise level
Below are some common sources of noise measured in decibels:
•Zero: The faintest sounds heard by ear
•30: A whisper or quiet library
•60: A normal conversation or a keyboard
•90: A lawn mower, shop tools or truck traffic
•100: A chain saw, pneumatic drill or snowmobile
•115: Sandblasting, a loud rock concert or an automobile horn
•140: A gun muzzle blast, jet engine or other noise that causes pain and injures unprotected ears after exposure
The physiology
Triggered by ...
Prolonged exposure to excessively loud noise, such as rock concerts or power tools, or exposure to traumatic levels of noise for a short period of time, such as gunshots or airplane noise.
Results ...
Hair cells become damaged and, over time, destroy themselves after a traumatic noise event. Total destruction of the affected hair cells usually occurs within a three-week period after the traumatic noise event.
If hair cells die, the ear registers less sound, which means fewer signals are sent to the brain, resulting in hearing loss.
What the two-drug mixture does ...
It produces antioxidants that stimulate hair cells to repair themselves after a traumatic noise event rather than allowing the hair cells to destroy themselves. This allows the ear to remain close to the same level of hearing as it did before the traumatic noise event.
Sources: Hough Ear Institute and Oklahoma Medical Research Foundation. McClatchy-Tribune Information Services
About the drugs
n-acetyl-cysteine: NAC
NAC has been used for years to combat Tylenol overdoses because it helps stop liver cells from dying by producing glutathione, an antioxidant. The antioxidant restores the liver cells rather than letting them die.
The same thing happens with hair cells in the ear, Kopke said. NAC helps the body produce more glutathione, which keeps hair cells in the ear from dying and retains hearing after exposure to traumatic noise.
4-OHPBN nitrone
Although Floyd and Kopke are unsure what role the nitrone plays in hearing loss prevention, Kopke said the results of the two-drug combination are far better than the results of administering NAC alone.
It is thought the nitrone deals more with nitrogen-related toxins, but both drugs could "work on several other things that could be playing a role,” Kopke said.
The physiology
Triggered by ...
Prolonged exposure to excessively loud noise, such as rock concerts or power tools, or exposure to traumatic levels of noise for a short period of time, such as gunshots or airplane noise.
Results ...
Hair cells become damaged and, over time, destroy themselves after a traumatic noise event.
Total destruction of the affected hair cells usually occurs within a three-week period after the traumatic noise event.
If hair cells die, the ear registers less sound, which means fewer signals are sent to the brain, resulting in hearing loss.
What the two-drug mixture does ...
It produces antioxidants that stimulate hair cells to repair themselves after a traumatic noise event rather than allowing the hair cells to destroy themselves.
This allows the ear to remain close to the same level of hearing as it did before the traumatic noise event.
Sources: Hough Ear Institute and Oklahoma Medical Research Foundation. McClatchy-Tribune Information Services
About the drugs
n-acetyl-cysteine
NAC has been used for years to combat Tylenol overdoses because it helps stop liver cells from dying by producing glutathione, an antioxidant.
The antioxidant restores the liver cells rather than letting them die.
The same thing happens with hair cells in the ear, Kopke said. NAC helps the body produce more glutathione, which keeps hair cells in the ear from dying and retains hearing after exposure to traumatic noise.
4-OHPBN nitrone
Although Floyd and Kopke are unsure what role the nitrone plays in hearing loss prevention, Kopke said the results of the two-drug combination are far better than the results of administering NAC alone.
Combining cancer drug
Now Kopke is teaming with Floyd to combine NAC with a drug used in cancer research and age-related diseases to create a mixture that prevents hair cells in the ear from dying after exposure to loud noises.
Their study focuses on administering the two-drug combination of NAC and 4-OHPBN nitrone after a traumatic noise event because "it may not be advantageous to give it to 1,000 people when only maybe 100 are going to experience hearing loss,” Kopke said.
What studies found
Floyd and Kopke are conducting trials of the drug on chinchillas, an animal that has a hearing range and ear structure similar to humans. The findings have yielded results better than expected, Floyd said.
After exposing the chinchillas to 105 decibel noise for six hours — roughly the equivalent of being in the front row at a rock concert — the animals are injected with the drug under their skin.
Without the medication, hair cells in the ear died, resulting in hearing loss.
The scientists have seen a retention rate of 90 percent of the animals' hearing for those that received the drug four hours after traumatic noise exposure.
Animals given the drug 12 hours after noise exposure retained 80 percent of their hearing. If given the drug 24 hours later they showed a 50 percent retention rate, Kopke said.
The chinchillas' hearing levels are measured by putting a sensor in their ears that picks up electrical activity in their brains.
Floyd and Kopke also are checking for adverse effects the drug might have.
While NAC and the nitrone by themselves have been deemed safe by the FDA, it is unclear whether they are completely safe together.
The side effects discovered from Kopke's earlier trial on Marines using only NAC were minimal (headaches and upset stomach), he said.
The scientists hope clinical trials on humans are a possibility in one or two years, Kopke said.
Related Topics:
Science and Technology, Technology, Health and Fitness, Sciences, Medical Technology, Hearing Loss and Deafness
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