Abstract
Epidemiological evidence has shown that smoking is associated with an increased risk of hearing loss. However, the underlying mechanisms regarding the impact of nicotine on the cochlea remain unclear. This study aimed to investigate the cytotoxic effects of nicotine on cochlear cells using cultured cochlear basilar membranes. Cochlear basilar membranes were isolated from newborn rats, cultured, and treated with 1-100 ng/mL nicotine for 48 h. Cuticular plates and stereocilia bundle staining were used to evaluate hair cell (HC) loss. Spiral ganglion neuron and acoustic nerve fiber staining were assessed to evaluate cochlear neural injury. Scanning electron microscopy and transmission electron microscopy imaging were employed to examine cochlear ultrastructural changes. Our results showed that compared to spiral ganglia and nerve fibers, HCs are more susceptible to nicotine-induced toxicity. HC loss was more severe in the basal turn than in the middle and apical turns, while nerve fibers and spiral ganglion cells were morphologically maintained. Ultrastructural changes revealed disordered and damaged stereocilia, swelling and decreased mitochondrial density, swelling, and degranulation of the endoplasmic reticulum. Our results suggest that nicotine causes HCs' degeneration and loss and may have implications for smoking-related hearing loss.