Noise-induced hearing loss (NIHL) is defined as a reduction in auditory acuity (hearing ability) associated with long term exposure to loud sounds. It is the second most common form of a sensorineural hearing deficit, after presbycusis (age-related hearing loss).
There can be two types of hearing loss due to exposure to loud sounds. The first one is a temporary threshold shift /TTS. Hearing impairment due to TTS will be a temporary one, from which the patient recovers gradually. Depending on the duration of exposure, the recovery period may last from minutes to hours or days.
The second type of hearing loss due to noise exposure is the permanent threshold shift / PTS, where elevation in hearing thresholds is a permanent one. This usually occurs following repeated temporary threshold shifts. In some cases, it can happen following a single episode of noise exposure also.
Permanent threshold shift is traditionally divided into two types –
- Acoustic trauma – Situation where a single exposure to an intense sound leads to an immediate hearing loss.
- Noise-induced hearing loss (NIHL) –PTS due to long term exposure to low-intensity levels of sounds.
The diagnosis of noise-induced hearing loss is usually a delayed one until the loss became severe enough for patients to volunteer for a hearing exam. The importance of awareness of NIHL is that it is a type of hearing loss that can be completely preventable.
Prestin and Otolin 1 biomarkers
According to Webster’s Dictionary, a biomarker is “a distinct biochemical, genetic, or molecular characteristic or substance that is an indicator of a particular biological condition or process. Biomarkers are routinely utilized in the clinical practice as they are powerful indicators of normal and pathological biological processes. They help in making a diagnosis, getting information on the progression of the disease, to find a response to therapy and for the development of new pharmaceuticals.
The inner ear of humans has been found to possess a number of unique proteins, measurement of which can be considered to understand the inner ear functional status. Connexin 26/30 and Pendrin are the currently known biomarkers for evaluating hearing loss.
In the 53rd American Neurotology Society (ANS) Annual Spring Meeting, results of collaborative research by Sensorion and UConn Health were jointly presented. The oral presentation, titled “Noise-Induced Trauma Produces a Temporal Pattern of Change in Serum Levels of the Outer Hair Cell Biomarker Prestin” is the first of its type because it identified a potential biomarker for noise-induced hearing loss.
Prestin is a protein found in the outer hair cells of the cochlea. These outer hair cells are the earliest cells to get damaged due to long term noise exposure. Researchers analyzed the blood samples of a preclinical model with noise-induced hearing loss for the amount of circulating blood prestin levels. They were able to prove that changes in levels of prestin circulating within patients’ blood correlated with their degree of hearing loss and these changes happen at a time before the hearing loss can be measured by hearing tests.
Another independent research by two Egyptian doctors Hana RS and Bawi B in 2018 observed that, in addition to Prestin levels, Otolin-1 levels were also found to be significantly higher in patients with NIHL than that of control levels.
Much work lies ahead before we can reliably utilize these novel biomarkers in the clinical setting. But as with most diseases or conditions, the earlier hearing loss can be identified, the better the chances for appropriate and effective intervention. This new biomarker may help in diagnosing hearing loss at the earliest possible stages. Researchers also hope that the new biomarker may help us gain insights into other mysterious ear disorders such as Meniere’s disease and sudden sensorineural hearing loss.
References
- Hana RS, Bawi BL. Prestin, otolin-1 regulation, and human 8-oxoG DNA glycosylase 1 gene polymorphisms in noise-induced hearing loss. Ibnosina Journal of Medicine and Biomedical Sciences. 2018 Mar 1;10(2):60.
- Parham K. Ushering in the era of circulatory otologic biomarkers. Ibnosina Journal of Medicine and Biomedical Sciences. 2018 Mar 1;10(2):37.