Drugs could prevent hearing loss

Three chemicals have the potential to protect the ears of those exposed to hazardous levels of noise

August 02, 2007|By Kendall Powell | Kendall Powell,Los Angeles Times

Ted Ax knows he should wear earplugs when he leans into the noisy engine compartment of an MG sports car. He's been working among clanging metal and whirring power tools in garages for the past 15 years and has already developed tinnitus, a ringing in the ears that is one of the most common symptoms of hearing loss caused by excessive noise.

But between the need to pinpoint troubled engine sounds and listen for the phone -- and with his fingers forever covered in grease -- the Denver man's earplugs go unused.

"I have yet to come up with a real-world scenario where I can have hearing protection and do my job," says the 42-year-old foreign-car mechanic.

Ax might soon have a more amenable option -- a pill he could take before work that would help protect his ears from noise.

Ax is one of an estimated 30 million Americans who are exposed to hazardous levels of noise daily at work or at leisure, be it from the buzz of leaf-blowers and landscape equipment, the jangling of construction tools, the cacophony of a concert or the roar of a motorcycle engine. Until now, hearing protection for such people has consisted of using barrier devices such as earplugs or earmuffs and limiting the time a worker spends exposed to loud noises.

Recently, however, several groups have started testing various chemicals for their safety and effectiveness at preventing noise-induced hearing loss in people. If the tests go well and the drugs are approved by the Food and Drug Administration, they would be the first of their kind.

Noise damages hearing by stressing out the inner-ear cells that convert sound waves into electrical signals that travel to the brain. These hair cells vibrate in response to sound and can be both physically and chemically destroyed by noise.

Most commonly, noise causes levels of toxic chemicals called free radicals inside the hair cell to rise beyond manageable levels, and the cell dies. Once a hair cell dies, the body cannot replace it.

Damage can occur from repeated exposure to noise at or above 85 decibels -- the loudness of a busy city street or a vacuum cleaner -- or from a short burst of a very intense noise such as gunfire.

If too many hair cells die, the inner ear can no longer detect sounds from certain frequencies -- particularly, high-pitched sounds. Eventually, that hearing loss obscures conversation, dropping out sounds such as "ess" and "ch."

"I compare it sometimes to playing Wheel of Fortune, when the vowels are up and you have to guess the word without the consonant sounds," says Kathleen Campbell, director of audiology research at Southern Illinois University in Springfield.

So too can come an aggravating tinnitus, in which a person experiences a ringing, hissing or roaring in the ears, even when no external sound is present.

About 10 million Americans suffer from noise-induced hearing loss, according to the National Institute for Occupational Safety and Health. The problem is particularly rampant in the military: In 2006, the Department of Veteran Affairs paid $1 billion in compensation to veterans for service-related hearing disabilities, the vast majority of which are noise-related.

"The military is really loud, for long periods of time," says Cmdr. Ben Balough, chairman of otolaryngology at the Navy Medical Center in San Diego. Explosions and jet engine noise are so jarring that even wearing hearing protection is not always enough.

So it's not surprising that three of the potentially protective chemicals -- D-methionine, ebselen and N-acetylcysteine (NAC) -- will be tested on military personnel first. All three give a boost to a natural antioxidant, glutathione, that's found in hair cells and battles chemical stress. All three can be taken orally as pills or dissolved in water. And each has been shown to be relatively safe in preliminary human studies.

The developers of these drugs say a drug for noise-induced hearing loss will likely be approved in the next five to 10 years.

Whether these drugs will be picked up by other occupations or for recreational noise exposures such as hunting and concerts remains up in the air.

"Clearly there's a tremendous need in the military, but I really doubt people are going to be swigging this stuff before going to a nightclub," says William Martin, a hearing scientist at Oregon Health & Science University in Portland. Drugs, he says, usually come with expensive price tags and possible side effects.

But Jonathan Kil, chief executive of Seattle-based Sound Pharmaceuticals, which is developing ebselen, predicts that people would take a pill before mowing the lawn or heading out for a night on the town if it were available as a safe and effective way to save their hearing.

Ax, the Colorado mechanic, says he would have taken a drug if it could have safely prevented his hearing loss and the ringing sensation he now lives with daily.

"That," he says, "would have been a no-brainer."

Kendall Powell wrote this article for the Los Angeles Times.

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