Monitoring of reactive oxygen species production after traumatic brain injury in rats with microdialysis and the 4-hydroxybenzoic acid trapping method

The detection of reactive oxygen species (ROS) after traumatic brain injury (TBI) is based on indirect methods due to the high reactivity and short ha lf-life of ROS in biological tissue. The commonly used salicylate trapping method has several disadvantages making it unsuitable for human use. We hav e evaluated 4-hydroxybenzoic acid (4-HBA) together with microdialysis (MD) in the rat as an alternative method. 4-HBA forms one stable adduct, 3,4-dih ydroxybenzoic acid (3,4-DHBA), when reacting with ROS and has not previousl y been used together with MD after TBI. Twenty-seven rats were used for the assessment of 3,4-DHBA production as an indicator of ROS formation in a co ntrolled contusion injury model using intracerebral MD with 3 mM 4-HBA in t he perfusate. For comparison, salicylate trapping was used in eight rats. T BI caused a 250 % increase of 3,4-DHBA that peaked at 30 min after injury i n severely injured rats and remained significantly elevated as compared to baseline for 90 min after trauma. The mild injury level caused a 100% incre ase in 3,4-DHBA formation at 30 min after the injury. When the MD probe was placed in the perimeter of the injury site, no significant increase in ROS formation occurred. Salicylate trapping showed a similar increase in adduc t formation after severe injury. In addition, high cortical concentrations of 4-HBA and salicylate were found. It is concluded that microdialysis with 4-HBA as a trapping agent appears to be a useful method for ROS detection in the rat with a potential clinical utility.