d-Methionine attenuated cisplatin-induced vestibulotoxicity through altering ATPase activities and oxidative stress in guinea pigs

Cisplatin has been used as a chemotherapeutic agent to treat many kinds of malignancies. Its damage to the vestibulo-ocular reflex (VOR) system has been reported. However, the underlying biochemical change in the inner ear or central vestibular nervous system is not fully understood. In this study, we attempted to examine whether cisplatin-induced vestibulotoxicity and d-methionine protection were correlated with the changes of ATPase activities and oxidative stress of ampullary tissue of vestibules as well as cerebellar cortex (the inhibitory center of VOR system) of guinea pigs. By means of a caloric test coupled with electronystagmographic recordings, we found that cisplatin exposure caused a dose-dependent (1, 3, or 5 mg/kg) vestibular dysfunction as revealed by a decrease of slow phase velocity (SPV). In addition, cisplatin significantly inhibited the Na+, K+-ATPase and Ca2+-ATPase activities in the ampullary tissue with a good dose-response relationship but not those of cerebellar cortex. Regression analysis indicated that a decrease of SPV was well correlated with the reduction of Na+, K+-ATPase and Ca2+-ATPase activities of the ampullary tissue. d-Methionine (300 mg/kg) reduced both abnormalities of SPV and ATPase activities in a correlated manner. Moreover, cisplatin exposure led to a significant dose-dependent increase of lipid peroxidation and nitric oxide concentrations of the vestibules, which could be significantly suppressed by d-methionine. However, cisplatin did not alter the levels of lipid peroxidation and nitric oxide of the cerebellum. In conclusion, cisplatin inhibited ATPase activities and increased oxidative stress in guinea pig vestibular labyrinths. d-Methionine attenuated cisplatin-induced vestibulotoxicity associated with ionic disturbance through its antioxidative property.