Overview of Noise-Induced Hearing Loss

Impact on Individuals

Noise-induced hearing loss is a significant concern for many individuals, affecting both workplace environments and recreational activities. The World Health Organization (WHO) reported in 2015 that approximately 1.1 billion teenagers and young adults, aged 12 to 35, are at risk. This increased risk is largely due to the use of personal music players at high volumes, unprotected firearm usage, and exposure to loud environments such as clubs and concerts.

Effects of Noise Exposure

The impact of noise can vary; individuals may experience no change, a temporary reduction, or a permanent loss of hearing in one or both ears. Various factors influence these effects, including the type, intensity, and duration of noise exposure, the use of protective devices, rest intervals between exposures, and pre-existing hearing conditions. Temporary hearing loss that resolves after exposure is termed a temporary threshold shift (TTS), while hearing loss that persists for weeks or months is referred to as a permanent threshold shift (PTS).

Biological Insights into Hearing Loss

Role of Glutathione Peroxidase 1

Research has extensively explored the biology of noise-induced hearing loss, particularly its effects on ear structures. Glutathione peroxidase 1 (GPx1), a substance present in high concentrations in the cochlea (part of the inner ear), is essential for maintaining normal cochlear function. Animal studies indicate that GPx1 levels decrease following acute noise exposure.

Ebselen: A Promising Investigational Drug

Mechanism of Action

Ebselen is an investigational drug that mimics the action of GPx1. It has demonstrated efficacy in reducing both temporary and permanent noise-induced hearing loss in animal studies.

Clinical Trials and Findings

The safety and effectiveness of ebselen in preventing temporary noise-induced hearing loss in healthy young adults were evaluated in a preliminary clinical trial. Results were published in The Lancet.

From January 2013 to March 2014, 83 healthy young adult participants with normal hearing were randomly assigned to one of four groups, receiving either 200 mg, 400 mg, or 600 mg of ebselen, or a placebo, orally administered twice daily for four days. On the third day of treatment, participants underwent a sound challenge test, listening to a playlist of pre-recorded music at a level known to induce TTS.

Hearing tests were conducted before and after the sound challenge, with results compared across the groups. The primary focus was on the mean TTS at 4 kHz, measured 15 minutes post-challenge. A 50% reduction in TTS in the ebselen group compared to the placebo group was deemed clinically relevant.

Results and Effectiveness

The findings revealed that the mean TTS at 4 kHz was 68% lower in the 400 mg ebselen group compared to the placebo group, indicating a significant reduction in temporary hearing loss. The 200 mg group showed a 21% reduction, while the 600 mg group experienced a 7% reduction; however, these latter two were not considered clinically significant. These results suggest that participants receiving ebselen were less likely to suffer from temporary hearing loss under the study conditions.

Tolerability and Future Research

Ebselen was well tolerated across all dosages, exhibiting few or no side effects. Researchers concluded that a dosage of 400 mg twice daily was both safe and effective in preventing noise-induced temporary hearing loss. Notably, no clear dose-response relationship was observed, echoing findings from animal studies. Further research is needed, but this preliminary investigation positions ebselen as a promising candidate for preventing noise-induced hearing loss.

Conclusion

The study contributes valuable insights into the potential of ebselen as a preventive treatment for noise-induced hearing loss, warranting further exploration in future trials.

Reference

Kil J, Labarinas E, Spankovich C, et al. Safety and efficacy of ebselen for the prevention of noise-induced hearing loss: a randomized, double-blind, placebo-controlled, phase 2 trial. The Lancet. Published online July 14, 2017. http://dx.doi.org/10.1016/S0140-6736(17)31791-9.