The role of reactive oxygen species in traumatic brain injury : Experimental studies in the rat

Sammanfattning: Traumatic brain injury (TBI) is a major cause of mortality and disability. As common sequelae in survivors of TBI are disabling functional, emotional and cognitive disturbances, improved treatment of TBI patients is urgently needed. At present, no neuroprotective pharmacological treatment exists. The formation of oxygen-centered free radicals, reactive oxygen species (ROS), is considered an important event in the pathophysiology of TBI. In the present thesis, the fluid percussion (FPI) and controlled cortical contusion injury models of TBI in rats were used. Two nitrone radical scavengers, α-Phenyl-N-tert -butyl nitrone (PBN) and the sulfonated analogue of PBN, 2-sulfophenyl-N-tert-butyl nitrone (S-PBN), were used as tools to study the role of ROS in TBI. Pre-treatment with PBN (30 mg/kg) improved morphological and cognitive outcome after severe controlled cortical contusion injury. Treatment with equimolar doses of PBN and S-PBN administered 30 min after FPI followed by a 24 h intravenous infusion improved morphological outcome. Only S-PBN improved cognitive outcome as assessed in the Morris Water Maze. Surprisingly, pre-treatment with PBN increased the number of apoptotic neurons at 24 hours after injury despite a reduced lesion volume. FPI resulted in an early increase in glucose uptake and a reduction in regional cerebral blood flow (rCBF) assessed by fluoro-2-deoxyglucose (FDG) and hexamethylpropylene amine oxime (HMPAO) autoradiography. At 12 h, a marked reduction in glucose uptake and rCBF ensued. These TBI-induced changes were attenuated by PBN and S-PBN pre-treatment. A method for ROS detection using 4-hydroxybenzoate in conjunction with microdialysis was evaluated. The results showed a marked increase in ROS formation as assessed by an increase in the single adduct 3,4-DHBA, lasting 90 min after injury. In a separate study, PBN and S-PBN equally reduced 3,4-DHBA formation despite no detectable brain concentrations of S-PBN at 30 or 60 min post-injury. In conclusion, ROS play an important role in the injury process after TBI. We report a method for ROS detection with potential clinical utility. Nitrones increased ROS elimination and improved functional and morphological outcome. Nitrone treatment may have a clinical potential as a neuroprotective concept in TBI.