Role of antioxidant supplementation in preventing noise induced hearing loss

Abstract

Objective: Oxidative stress plays a significant role in noise induced hearing loss (NIHL) as it largely participates in the mechanisms that underlie cell death after noise exposure and leads to sensorineural hearing loss. Many antioxidant drugs have been tested to prevent NIHL. Study design: We compared the protective effects of five molecules having antioxidant properties (vitamin E, ferulic acid, active CoQ10, its synthetic analogue – idebenone, and the soluble formulation CoQter) tested in our laboratory. This study has been conducted in a model of acoustic trauma in rats in which the molecules were given intraperitoneally 1 h before and once daily for three days after pure tone noise exposure (10 kHz for 1 h at 100dB SPL).We evaluated their hearing function via electrophysiological measurements at 2, 7 and 21 days and performed morphological studies with scanning electron microscopy and TUNEL assay as a parameter of apoptotic activation. Results: All molecules decreased threshold shift, reaching almost a complete recovery starting from day 7 with a further light recovery at day 21. At this time-point all treatments reached almost 80–90% of protection; however, CoQter and vitamin E were the most effective treatments. A decreasing number of TUNEL-positive nuclei for each treatment were observed two days after noise exposure. The cochleogram and morphological observations were consistent with the protective effects measured by ABR, 21 days after trauma. Conclusion: These results indicate that the best protection can be achieved by using antioxidant molecules acting against mitochondrial induced oxidative stress, such as vitamin E and CoQter and the degree of protection depends on the pharmacological properties of the molecules.