Compounds Effective in Preventing Hearing Loss and Tinnitus

Editor: We've been reporting on the work of a company called American Biohealth Group, which is using technology licensed from the Navy to prevent and treat hearing loss. They have just presented their most recent results at a meeting of the Association for Research in Otolaryngology, and the results look very promising! This technology is probably not applicable to people who currently have hearing loss, but it may be very effective in preventing future cases of noise induced hearing loss. Here are portions of the press release. For additional information, including the complete text of the press release, please point your browser to www.abgpharma.com.

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American BioHealth Group LLC (ABG), a privately held San Diego-based company developing hearing loss prevention and treatment technology licensed exclusively from the U.S. Navy, announced today that positive pre-clinical data on that technology were presented in a poster at the Association for Research in Otolaryngology (ARO) Meeting held in Daytona Beach, Florida February 23 -27, 2003.

In the poster presentation, submitted by Army Colonel Richard D. Kopke, MD, and other researchers at DOD Spatial Orientation Center, Naval Medical Center, San Diego and the Center for Hearing and Deafness, State University of New York at Buffalo, pre-clinical data were presented demonstrating that administration of the antioxidant N-acetylcysteine (NAC) decreased acute noise-induced hearing loss (NIHL) due to loud impulse noise exposure. This new data extends previous research indicating that NAC is protective against loud continuous noise such as jet engine noise.

In the reported study, NAC, given in a basic science model before and after simulated M-16 rifle fire consisting of 150 shots over 75 seconds, reduced permanent hearing loss by over 70%. A similar reduction in damage to the cochlear hair cells was also noted. In other related research presented by the Naval Medical Center group at ARO, data were reported indicating that two key mechanisms of inner ear injury were depletion of inner ear glutathione and damage to mitochondria. Glutathione is a key inner ear antioxidant and NAC replenishes the inner ear glutathione depleted by loud noise.

Also reported by Dr. Kopke in a related presentation at the annual meeting of the National Hearing Conservation Association in Dallas, Texas just prior to the ARO meeting, the Navy group determined that a mitochondrial protectant known as acetyl-L-carnitine (ALCAR), also licensed by ABG from the U.S. Navy, effectively reduced permanent hearing loss due to acute trauma from continuous noise, both when given as prevention before the noise and when given hours later as treatment.

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Noise-induced hearing loss is a significant unmet socioeconomic problem in industrial societies. It is estimated that 30 million individuals are exposed to injurious levels of noise each day, contributing significantly to the overall cost of hearing loss in the nation of $56B per year. In addition to loud noise of various types, many pathological conditions affecting the inner ear, such as traumatic injury, toxins, aging, infection, and some genetic conditions may be associated with the excessive production of reactive oxygen species (ROS) leading to oxidative stress. If the inner ear's own antioxidant defenses are overwhelmed injury or even death and permanent loss of the sensory cells of the inner ear occurs. This leads to permanent hearing loss and often also tinnitus, or the sensation of ringing in the ear. The technology licensed by ABG from the Navy boosts the inner ear antioxidant defenses to prevent or treat the damage caused by the toxic ROS. Preventing and treating acute injury to the cochlea or hearing organ in the inner ear may also reduce tinnitus in the acute setting. This approach has been validated in a number of other laboratories worldwide in a number of different models for hearing loss. These findings demonstrated the feasibility of reducing noise-induced hearing loss using clinically available antioxidant compounds. The recently reported research at ARO extends earlier studies to examine the capacity of the agent NAC to protect subjects in a model of impulse noise, as this stimulus simulates noise exposure in military operational environments. Clinical trials using NAC to counter noise-induced hearing loss and tinnitus are planned for the coming year in a military setting.

NAC is the active ingredient in a formulation known as Mucamist, an oral agent given to counteract liver damage in cases of acetaminophen overdose. NAC is a free radical scavenger and is a precursor to glutathione (GSH). NAC is well-absorbed and subsequently broken down into cysteine, which is taken up into cells and converted to GSH. At therapeutic doses it has few side effects. NAC is a currently FDA-approved compound, has been in clinical use over three decades with safety established through high-dose use over extended periods.