Free 3-nitrotyrosine causes striatal neurodegeneration in vivo.
Peroxynitrite formation has been demonstrated in several neurodegenerative disorders; thus far, protein nitration and consequent alterations in protein function are implicated as mechanistic events. Free 3-nitrotyrosine (free-3NT) is also elevated in these settings; a neurotoxic role for this modified amino acid has not been investigated. We tested the hypothesis that free-3NT is neurotoxic in vivo, using a mouse model of striatal degeneration. The neurodegenerative effects of the dopaminergic neurotoxin 6-hydroxydopamine (6-OHDA) (unilateral intrastriatal injection, 64 nmol) were compared with free-3NT (32 nmol) or free-tyrosine (free-TYR) (32 nmol). 6-OHDA-treated mice exhibited significant ipsilateral turning behavior after d-amphetamine challenge, indicative of unilateral striatal injury (ipsilateral-contralateral turning differential, 21.1 +/- 6.8). Significant turning behavior was also observed in free-3NT-treated mice but not in free-tyrosine-treated mice (free-3NT, 16.0 +/- 3.9; free-TYR, 1 +/- 2.7; p < 0.01). Immunohistochemistry was used to evaluate striatal tyrosine hydroxylase (TH) content. 6-OHDA or free-3NT treatment caused severe reductions in TH immunoreactivity in injected striata compared with the contralateral hemisphere (injected/contralateral immunoreactivity ratio: 6-OHDA, 0.23 +/- 0.07; free-3NT, 0.49 +/- 0.02). Free-tyrosine treatment had no effect (1.03 +/- 0.09). Turning behavior was correlated with striatal TH ratio (p < 0.01). Furthermore, we observed a striking unilateral reduction in TH-positive cell body counts in the substantia nigra pars compacta of 6-OHDA- and free-3NT-treated mice (injected/contralateral cell count ratio: 6-OHDA, 0.40 +/- 0.04; free-3NT, 0.59 +/- 0.02). Free-tyrosine treatment had no effect (1.05 +/- 0.04). No evidence for increased striatal protein incorporation of 3NT was observed in any treatment group. These data represent the first evidence that free-3NT can elicit neurodegenerative effects in vivo; free-3NT may have a causal role in neurodegenerative conditions.
Mihm
M J
MJ
Division of Pharmacology, College of Pharmacy, The Ohio State University, Columbus, Ohio 43210, USA.
Schanbacher
B L
BL
Wallace
B L
BL
Wallace
L J
LJ
Uretsky
N J
NJ
Bauer
J A
JA
D000818:Animals; D002452:Cell Count; D003342:Corpus Striatum / Q000187:drug effects* / Q000201:enzymology / Q000473:pathology; D003913:Dextroamphetamine / Q000494:pharmacology; D004195:Disease Models, Animal; D007150:Immunohistochemistry; D051379:Mice; D009043:Motor Activity / Q000187:drug effects; D019636:Neurodegenerative Diseases / Q000139:chemically induced* / Q000201:enzymology / Q000473:pathology; D009474:Neurons / Q000187:drug effects / Q000201:enzymology / Q000473:pathology; D016627:Oxidopamine / Q000008:administration & dosage / Q000633:toxicity; D013378:Substantia Nigra / Q000187:drug effects / Q000201:enzymology / Q000473:pathology; D014443:Tyrosine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000633:toxicity*; D014446:Tyrosine 3-Monooxygenase / Q000032:analysis / Q000378:metabolism
C002744:3-nitrotyrosine; D014443:Tyrosine; D016627:Oxidopamine; D014446:Tyrosine 3-Monooxygenase; D003913:Dextroamphetamine