Reactive oxygen species in human inner ear perilymph

Conclusions: The results reported here provide the first evidence of the production of superoxide, a biologically relevant reactive oxygen species (ROS), in human inner ear perilymph (hIP) in pathological conditions, by the activity of the xanthine dehydrogenase/xanthine oxidase (XA/XO) enzyme system. Objective: To investigate the presence of ROS in hIP. Methods: Since damage and apoptosis of inner ear hair cells may occur as a result of ROS-mediated injury, we investigated the presence and production of ROS in 105 hIP samples; 98 collected from patients affected by profound sensorineural hearing loss, during surgery for cochlear implantation, and 7 controls, collected from patients affected by otosclerosis, in case of spontaneous leakage after stapedotomy. ROS production was investigated by spectrophotometric analysis and polyacrylamide gel electrophoresis (SDS-PAGE). Results: In hIP samples tested by cytochrome c reduction kinetics, the average superoxide production was 27.34 mmoles per mg of total protein, against 0.36 in controls. Some of these hIP samples, analyzed by cytochrome c reduction kinetics in the presence of xanthine, were found to be positive for ROS-producing XA/XO enzyme. These results were supported by SDS-PAGE analysis.