Peanut sprout extract attenuates cisplatin-induced ototoxicity by induction of the Akt/Nrf2-mediated redox pathway.

OBJECTIVE: Cisplatin is commonly used to treat solid tumors. However, permanent hearing loss is a major side effect of cisplatin chemotherapy and often results in dose reduction of the cisplatin chemotherapy. Peanut sprouts show cytoprotective properties owing to their antioxidant activities. This study was designed to investigate the effect of peanut sprout extract (PSE) on cisplatin-induced ototoxicity in an auditory cell line, HEI-OC1 cells. METHODS: Cells were exposed to cisplatin for 24 h, with or without pre-treatment with PSE, cell viability was examined using the MTT assay. Apoptotic cells were identified by double staining with Hoechst 33258 and propidium iodide. Western blot analysis was performed to examine apoptotic proteins including C-PARP and C-caspase, anti-apoptotic protein Bcl-2, and Nrf2 redox system activation. Mitochondrial reactive oxygen species (ROS) were investigated to examine whether PSE could scavenge cisplatin-induced ROS. Real-time PCR analyses were performed to investigate the mRNA levels of antioxidant enzymes including NQO1, HO-1, GPx2, Gclc, and catalase. RESULTS: The cisplatin-treated group showed reduced cell viability, increased apoptotic properties and markers, and increased ROS levels. PSE pre-treatment before cisplatin exposure significantly increased cell viability and reduced apoptotic properties and ROS production. These effects resulted from the up-regulation of antioxidant genes, including NQO1, HO-1, GPx2, Gclc, and catalase through Akt phosphorylation and Nrf2 activation. CONCLUSION: Our results demonstrate that PSE protects from cisplatin-induced cytotoxicity by activating the antioxidant effects via the Akt/Nrf-2 pathway in this auditory cell line, and indicate that PSE may provide novel treatment to prevent cisplatin-induced ototoxicity.

Supporting cell characteristics in long-deafened aged mouse ears.

Significant sensory hair cell loss leads to irreversible hearing and balance deficits in humans and other mammals. Future therapeutic strategies to repair damaged mammalian auditory epithelium may involve inserting stem cells into the damaged epithelium, inducing non-sensory cells remaining in the epithelium to transdifferentiate into replacement hair cells via gene therapy, or applying growth factors. Little is currently known regarding the status and characteristics of the non-sensory cells that remain in the deafened auditory epithelium, yet this information is integral to the development of therapeutic treatments. A single high-dose injection of the aminoglycoside kanamycin coupled with a single injection of the loop diuretic furosemide was used to kill hair cells in adult mice, and the mice were examined 1 year after the drug insult. Outer hair cells are lost throughout the entire length of the cochlea and less than a third of the inner hair cells remain in the apical turn. Over 20% and 55% of apical organ of Corti support cells and spiral ganglion cells are lost, respectively. We examined the expression of several known support cell markers to investigate for possible support cell dedifferentiation in the damaged ears. The support cell markers investigated included the microtubule protein acetylated tubulin, the transcription factor Sox2, and the Notch signaling ligand Jagged1. Non-sensory epithelial cells remaining in the organ of Corti retain acetylated tubulin, Sox2 and Jagged1 expression, even when the epithelium has a monolayer-like appearance. These results suggest a lack of marked SC dedifferentiation in these aged and badly damaged ears.