The effects of the antioxidant α-tocopherol succinate on cisplatin-induced ototoxicity in HEI-OC1 auditory cells

Conclusion: D-α-tocopherol succinate significantly reduced a cisplatin-induced hair cell loss in HEI-OC1 cell lines. These effects were mediated by its scavenging activity against Reactive Oxygen Species (ROS) and inhibition of Apoptosis.

Objectives: Alpha-tocopherol is a class of methylated Phenols, known as fat-soluble Antioxidants, and is a different form of vitamin E, which reduces free radicals and acts as an antioxidant. We hypothesized that the antioxidative effect of α-tocopherol could protect against cisplastin-induced cytotoxicity, and thus evaluated its effects on cisplatin-induced ototoxicity in HEI-OC1 auditory cells.

Methods: HEI-OC1 cells were pretreated with D-α-tocopherol succinate at a concentration of 10 µM for 24 h, and then exposed to 15 µM cisplatin for 48 h. The cellular viability was measured by using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. The intracellular ROS level was measured by using a Fluorescent Dye, 2',7'-dichlorofluorescein diacetate (DCFH-DA). Both Annexin V-FITC and propidium iodide (PI) staining were performed to analyze the pattern of Apoptosis. The enzymatic activity of Caspase-3 was assayed with caspase3/CPP32 fluorometric assay kit. Also, it was assessed by immunoblotting technique of poly-ADP-ribose polymerase (PARP).

Results: Pretreatment with 10 µM D-α-tocopherol succinate protected HEI-OC1 auditory cells against cisplatin-induced cytotoxicity. D-α-tocopherol succinate significantly reduced the cisplatin-induced increase in ROS. D-α-tocopherol succinate treatment induced a 15% reduction of ROS and 50% decrease in necrosis and late Apoptosis as compared to cisplatin treatment. D-α-tocopherol succinate also decreased the activation of Caspase-3 and reduced levels of cleaved poly-ADP-ribose polymerase (PARP).