June 14, 2005 Feature

A Magic Pill?

Compound Could Mediate Noise-Induced Hearing Loss

In a country that is often said to look for magic pills as health solutions, a new treatment for hearing loss could be on the horizon: a hearing pill.

A recently concluded double-blinded, placebo-controlled clinical trial reviewed use of a commonly available nutritional supplement, N-acetylcysteine or NAC. The study by the Naval Medical Center San Diego at the Marine Corp Recruit Depot in Camp Pendleton, CA, used a special formulation of NAC to determine its prophylactic qualities to prevent hearing loss.

The clinical trial found that when compared to the placebo, NAC reduced permanent hearing loss in the ear closest to the source of acoustic trauma. NAC also shows potential in healing symptoms of acoustic trauma, such as tinnitus and balance disorders. Another study will tackle those issues.

Ben J. Balough, a Navy commander and otolaryngologist who directed the study, cautioned against thinking of NAC as a one-a-day brand just yet. "Optimal dosing for a given patient and particular noise exposure is unknown at this point. Our goal is to provide something akin to a nutritional supplement to provide additional hearing protection for noise exposure over and above that from standard ear plugs," he said.

Nearly 1,000 Marine recruits participated in the study, which lasted about six months and ended in October 2004. Doctors requested volunteers, who then received hearing screenings. Those who met hearing requirements were enrolled in the study for approximately one month during their routine recruit training. Their noise exposure was 300 rounds of M-16 fire over one week.

In addition to the standard ear plug protection that all recruits use, nearly 600 of the participants took 900 mg of NAC three times a day while the rest were given a placebo. Balough said the study was ideal because noise conditions were tightly controlled. "We knew they weren't going off to the disco at night; they weren't listening to their Walkmans. And we knew when they were getting their [NAC] doses," he said.

Research assistants (RAs) gave the recruits the pharmaceutical grade formulation, a fizzy tablet that dissolved in water. Participants received their final hearing tests 10 days after the noise exposure was completed.

No significant differences between placebos and active agents were present in the reported side effects of gas and bloating. Balough noted these effects could have been due to the fizzy tablet formulation. "You had green recruits in a hurry. Some of them were swallowing it before it completely dissolved. When our RAs noted this and we made sure the tabs were fully dissolved, the number of these effects declined."

The next study will focus on two already approved protocols examining the effects of higher doses of NAC for more severe noise exposures as well as tinnitus and balance problems. Balough said the group wants to conduct another controlled trial to further examine NAC's prophylactic qualities in noise injury. "It would be at a much higher dose, by a factor of about 10. We want to see if we can reverse or lessen an injury," he said. The higher dose is for treatment of noise injury. Further prophylactic trials will use a low dose but add other agents to the mix.

Finding a Gold Standard

Work on the hearing pill started about 10 years ago, Balough said. He named a group of fellow military researchers and doctors who worked on the project: Mike Hoffer, Ronald Jackson, and Rick Kopke. Basic science shows that the ear has its own protective mechanism against noise. The group discovered that protective mechanisms in the ear are mediated by glutamate.

"For the neurotransmitters in the ear, glutathione reductase is one of the key enzymatic pathways that helps detoxify free radicals," he said. "The gold standard was NAC." Research and experiments with animals and cells revealed that NAC mediated noise injuries. The next step was the study with the Marine recruits.

Although the Navy has the patent on the NAC formulation used in the study, the government requires that such work be made available to the public. American BioHealth Group (ABG) bought the license from the government and is marketing it as the "hearing pill." The Navy has a cooperative research and development agreement with ABG. The government will make money from the patent if ABG is successful.

It is not considered a medication at this point. Balough said the FDA considers it a "nutriceutical" at the lower dose. While NAC is available at health food stores, products in such settings are not regulated, making efficacy and dosage inconsistent.

Balough said the goal is to make the pill available for the military, but results are premature as yet. It is the line commander's decision whether soldiers must take it, he said. "They decide whether it's worth enough to augment things on the field. They haven't asked for our official opinion yet."

The Navy will continue to pursue military applications for NAC. The substance is ripe for other areas of research though, Balough noted. Researchers at the University of California, San Diego, are considering a study of NAC applications in the geriatric population.

The complete study will be published in several peer-reviewed publications in the coming months. 

Dee Naquin Shafer,  an assistant managing editor of The ASHA Leader, can be reached at dshafer@asha.org. 

cite as: Shafer, D. N. (2005, June 14). A Magic Pill? : Compound Could Mediate Noise-Induced Hearing Loss. The ASHA Leader.

  

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