Comparing the otoprotective effects of two polyphenols, ferulic acid and caffeic acid, in the experimental model of noise-induced hearing loss

Noise-induced hearing loss is one of the most common acquired sensorineural hearing loss, and it is due to metabolic damage in cochlear structures, leading to increased oxidative stress and cell death with permanent loss of function. Thus, addressing the possibility to counteract redox imbalance by using exogenous antioxidant, such as dietary polyphenols, is challenging. In this study we compared the otoprotective effect of two polyphenol compounds, caffeic acid and ferulic acid, against noise-induced hearing loss cochlear damage. Thus, we used an experimental model of acoustic trauma by exposing Wistar rats to acute noise. Animals were treated with 30 mg/kg of CA and 300 mg/kg of FA in a peri-traumatic window before and after noise exposure. Electrophysiological recording of auditory brainstem nuclei was used to evaluate hearing sensitivity. Morphological and immunofluorescence analyses were used to study the effect of antioxidant supplementation in cochlear structures. Our data demonstrated that both caffeic acid and ferulic acid showed a similar otoprotective effect at functional and morphological level, by attenuating threshold shift values and reducing hair cell death after noise exposure. However, analyses of lipid peroxidation in cochlear specimens indicate a best neuroprotective effect of ferulic acid against lipid peroxidation induced by noise, especially in spiral ganglion neurons. Collectively, our data suggest that antioxidant supplementation with polyphenols can be effective against noise and that comparing caffeic acid and ferulic acid, the last molecule can be more efficient in counteracting neuronal damage, with the possibility to prevent synaptopathy or neuropathy consequences of noise-induced hearing loss.