The time course of hydroxyl radical formation following spinal cord injury: The possible role of the iron-catalyzed Haber-Weiss reaction

This study explores whether the hydroxyl radical ((OH)-O-.)-one of the most destructive reactive oxygen species-plays a role in secondary spinal cord injury (SCI). First, we measured the time course of (OH)-O-. formation in rat spinal tissue after impact SCI by administering salicylate as a trapping agent into the intrathecal space of the cord and measuring the hydroxylation products of salicylate, 2,3- and 2,5-dihydroxybenzoic acid (2,3- and 2,5-DHBA) by HPLC. The 2,3-DHBA concentration was significantly higher in injured spinal tissue than in sham controls at 5 min, 1 and 3 h, but not at 5 h post-injury. Second, we generated (OH)-O-. by administering H2O2 and FeCl2/EDTA (Fenton's reagents) at the concentrations produced by SCI into the gray matter of the cord for 4 h and found that it induced significant cell loss at 24 h post-(OH)-O-. exposure. Mn (III) tetrakis (4-benzoic acid) porphyrin(MnTBAP)-a broad spectrum reactive species scavenger-significantly reduced (OH)-O-.-induced cell death. Finally, we generated superoxide and administered FeCl3/EDTA in the intrathecal space of the cord at the concentration produced by SCI and measured extracellular (OH)-O-. formation in the gray matter of the cord by microdialysis sampling. We found that the levels of (OH)-O-. significantly increased compared to the pre-administration level, indicating that (OH)-O-. can be produced in vivo by the iron-catalyzed Haber-Weiss reaction. All together, we demonstrated that (OH)-O-. is an endogenous secondary damaging agent following SCI and the metal-catalyzed Haber-Weiss reaction may contribute to early (OH)-O-. formation after SCI.