Researchers from the National Institute of Deafness and Other Communication Disorders have discovered that exposure to specific sounds can safely condition mice to preemptively combat drug-induced hearing loss.
Drug-Induced Hearing Loss: An Unlikely Consequence
Researchers at the National Institute of Deafness and Other Communication Disorders (NIDCD) wanted to know how to combat the hearing loss associated with many therapeutic drugs. Drug-induced hearing loss impacts thousands of patients every year, and the dilemma is especially problematic for patients that need specific treatment with the medicines producing these side effects.
They hypothesized that exposing the inner ear to a limited range of sounds would stimulate the production of certain proteins in the part of the inner ear called the cochlea, and such priming would prevent drug-induced hearing loss in the form of damage to the hair cells necessary for detecting sound vibrations. Mice have receptor hairs in their inner ear that allow them to hear sound, just as humans do, and to conduct this experiment researchers tested the effects of these harmful drugs on two groups of mice. One group of mice was exposed to a sound vaccine of 90.1 decibels, which is about the same level of sound produced by truck traffic, while another group was not given the vaccine.
The two major groups of drugs that affect hearing are cisplatin and aminoglycoside antibiotics. These drugs are ototoxic, or harmful to the inner ear. Scientists exposed the mice to relatively low doses of cisplatin for 4 days, followed by a 10-day resting period, or relatively high doses of cisplatin for 2 days, followed by a 10-day resting period.
After applying the dose for 3 cycles they observed that mice without the sound vaccine displayed significant hearing loss, whereas mice that did receive the sound vaccine displayed relatively little change to their hearing. The scientists conducted similar trials with kanamycin, another ototoxic drug, and found that the sound vaccine played a significant role in preventing hearing loss.
How It Works and What It Means: Preventing Drug-Induced Hearing Loss
In both mice and men, sounds stimulate the ear to produce certain proteins called heat shock proteins, which help prevent the sensory hairs from being damaged. Heat shock proteins serve many functions in the human body and can be triggered by many different kinds of stimuli, including exercise, starvation, infection, and inflammation. In mice there are two specific heat shock proteins that help protect against hearing loss, Hsp32 and Hsp70.
The sounds used in the conditioning therapy are loud enough to spark the production of heat shock protein but are too weak to cause any permanent hearing damage themselves. The mice were exposed to the sounds at 2-hour intervals, and although they experienced slight hearing loss 24 hours after sound therapy, their hearing was back to normal a week later.
This new mode of sound prepping has the potential to be used against a wide variety of ear-damaging threats in addition to cisplatin and aminoglycoside antibiotics. This is because the heat shock protein response can be elicited from such a large range of sound stimuli. Sound therapy is also used to help prevent noise trauma as well as age-related hearing loss, two very common incidents that affect hearing-impaired individuals. With further research into sound therapy and its potential benefits, as well as research in specific heat shock proteins and their effectiveness, scientists will be able to develop new methods to more efficiently prevent hearing loss.