The protective effects of PBN against MPTP toxicity are independent of hydroxyl radical trapping.

To study the mechanism of the protective effect of the spin-trapping agent alpha-phenyl-N-tert-butyl nitrone (PBN) against MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) toxicity hydroxyl radicals and functional parameters of neuroprotection were determined. C57BL/6 mice received PBN (100 mg/kg IP) over a time period of 15 days and on day 8 MPTP (40 mg/kg SC). On day 15 striatal levels of dopamine, serotonin, and metabolites were analyzed. For radical determination mice received a single injection of salicylic acid (SA) (100 mg/kg IP) in the time period of 0.5 h before to 72 h after MPTP injection. In vivo maximum hydroxyl radical levels indicated by 2,3-dihydroxybenzoic acid/SA ratios were obtained 4 h after MPTP injection, and were not affected by PBN treatment. However, the MPTP-induced mortality, reduction of locomotor activity, continuous loss of body weight, and striatal dopamine depletion were significantly less pronounced in PBN-treated animals. These results elucidate the time course of hydroxyl free radical formation in MPTP toxicity. PBN improved the functional parameters of neuroprotection against MPTP toxicity, but there is no evidence for hydroxyl radical scavenging properties to this effect.