Peroxynitrite generated in the rat spinal cord induces oxidation and nitration of proteins: Reduction by MN (III) tetrakis (4-benzoic acid) porphyrin

To determine whether peroxynitrite at the concentration and duration present after spinal cord injury induces protein oxidation and nitration in vivo, the peroxynitrite donor 3-morpholinosydnonimine (SIN-1) was administered into the gray matter of the rat spinal cord for 5 hr. The cords were removed at 6, 12, 24, and 48 hr after SIN-1 exposure, immunohistochemically stained with antibodies to dinitrophenyl (DNP) and nitrotyrosine (Ntyr), markers of protein oxidation and nitration, respectively, and the immunostained neurons were counted. The percentages of DNP-positive (P = 0.023-0.002) and Ntyr-positive (P < 0.001 for all) neurons were significantly higher in the SIN-1-exposed groups than in the ACSF controls at each time, suggesting that peroxynitrite induced intracellular oxidation and nitration of proteins. The percentages of DNP- and Ntyr-positive neurons were not significantly different over time in either SIN-1- or ACSF-exposed groups (P = 0.20-1.00). The percentage of DNP-positive neurons was 7.6 ± 3% to 12 ± 4.2% at 6-24 hr, and it was 14 ± 2% to 19 ± 2% at 6-24 hr for Ntyr-positive neurons after SIN-1-exposure, whereas both ranged over 2-3% in ACSF controls. Mn (III) tetrakis (4-benzoic acid) porphyrin (MnTBAP, a broad-spectrum scavenger of reactive species) significantly reduced the percentages of DNP- and Ntyr-positive neurons (P = 0.04 and 0.002, respectively) compared to a SIN-1-exposed, untreated group at 24 hr after SIN-1 exposure. There were no significant differences between MnTBAP-treated and ACSF controls (P = 0.7 for DNP and 0.2 for Ntyr). These results further demonstrate peroxynitrite-induced protein oxidation and nitration and the efficiency of MnTBAP in scavenging peroxynitrite.