Drat those free radicals! These atoms or groups of atoms that contain odd or unpaired electrons are toxic and can weaken and destroy healthy cells throughout the body. They wreak havoc on our body’s cells, protein and DNA, causing everything from wrinkles and dry skin to cancer and sensorineural hearing loss. The best defense against free radicals is antioxdants, so it's no wonder we're encouraged to eat foods rich in antioxidants and stay out of the sun. Someday, we may also be advised to take a supplement called ebselen, currently being studied for it’s ability to prevent hearing loss caused by exposure to excessive noise.
According to the National Institute on Deafness and Other Communication Disorders (NIDCD), nearly one in four Americans between the ages of 20 to 69, or ten million adults, exhibit some symptoms of noise-induced hearing loss (NIHL) in one or both ears. NIHL is one of the most common occupational illnesses in the United States and accounts for the majority of hearing loss we experience in old age. And, until recently, nothing besides living in a quiet environment and diligently protecting ears from excessive noise has been identified as a way to prevent it.
Ebselen is a synthetic drug with anti-inflammatory and antioxidant properties. Researchers from Sound Pharmaceuticals discovered that ebselen acts much like glutathione, a naturally-occurring enzyme in our bodies known to block the oxidation process responsible for destroying the delicate hair cells of the inner ear. These hair cells are responsible for translating the noise our ears collect into electrical impulses, then sending them along the auditory pathway for the brain to interpret as sound. They do not regenerate, so when they die or are damaged, we lose the ability to hear the frequency and tone they were responsible for translating.
Healthy Hearing has been following the progress of ebselen trials since 2015, when we first reported about it. Since that time, Sound Pharmaceuticals has completed its phase 2 clinical trials.
New drug approval process
The Food and Drug Administration (FDA) process to test and market new drugs in the U.S. is a long and expensive one. Testing on humans does not begin until after a compound has been tested on animals and an Investigational New Drug (IND) application that includes a plan for testing efficacy and safety are submitted. Human studies consist of three phases.
- Phase 1 studies focus on the safety of the compound and include 20-80 human subjects.
- Phase 2 studies can include hundreds of subjects. These trials are to determine how well the drug works (efficacy) compared to comparable compounds or placebo. Safety and short-term side effects are also studied.
- Phase 3 studies determine how well the drug works for different patient types, possible interactions with other drugs and the effects of different dosages.
In 2006, in order to understand the relationship between glutathione and noise-induced hearing loss (NIHL), Sound Pharmaceuticals researchers first examined the prevalence of glutathione in the cochleas of lab rats before and after exposure to excessive sound, and then again after dosing them with ebselen. Results from this first phase indicated that the drug, administered before and immediately after exposure to sound, reduced swelling in the inner ear as well as the loss of outer hair cells typically associated with exposure to excessive noise.
In Phase 2 completed this year, Sound Pharmaceuticals used a double-blind, placebo-controlled trial using adults between the ages of 18-31. During this phase, each participant was randomly given a 200 mg, 400 mg, 600 mg dose of ebselen or placebo twice a day for four days, beginning two days before they were exposed to a calibrated sound challenge. After the sound challenge, each participant was measured for any temporary hearing loss, known as temporary threshold shift (TTS), which often occurs with exposure to high levels of noise. The trials concluded those taking 400 mg of ebselen realized a 68% reduction in TTS associated with noise-induced hearing loss.
Although preliminary indications from Phase 2 research indicates ebselen is effective in preventing noise-induced hearing loss, the drug has a long way to go before it reaches the pharmacy shelves of your local drugstore. For the time being, the best way to prevent NIHL is by turning down the volume on your personal electronic devices, wearing ear protection whenever your work or hobbies put you in a noisy environment and scheduling annual hearing evaluations with a hearing healthcare professional you can trust.
If it's too late for prevention, and you know you already have a hearing loss, the best treatment is hearing aids. Don't put it off any longer - these marvels of technology are available now and accommodate most any hearing loss, preference and budget.