title: 6-hydroxydopamine increases the hydroxylation and nitration of phenylalanine in vivo: implication of peroxynitrite formation.
abstract: In the present study, we investigated the effect of the dopaminergic neurotoxin 6-hydroxydopamine (6-OHDA) on hydroxyl free radical and peroxynitrite formation in vivo using D-phenylalanine as a novel mechanistic probe. In vivo microdialysis was carried out in the striatum of freely moving male Wistar rats. The microdialysis probes were perfused with artificial cerebrospinal fluid containing 5 mM D-phenylalanine (flow rate 2 microL/min). After obtaining a stable baseline 6-OHDA was delivered into the striatum via reverse microdialysis for 60 min. HPLC measurements of the effluent were performed using photodiode array detection for determination of phenylalanine derived o-tyrosine and m-tyrosine (as hydroxylation markers) as well as of nitrotyrosine and nitrophenylalanine (as nitration markers). The basal levels of the hydroxylation derived products of phenylalanine were approximately 100-fold higher than those of the nitration derived products. 6-OHDA (0.1, 1, 10 mM) significantly increased o- and m-tyrosine up to nine- and 13-fold, respectively, whereas levels of 3-nitrotyrosine and 4-nitrophenylalanine were significantly increased up to 422- and 358-fold, respectively. The results demonstrate that phenylalanine is a sensitive in vivo marker for 6-OHDA-induced hydroxylation and nitration reactions which are clearly concentration dependent. We conclude that peroxynitrite formation is involved in 6-OHDA-induced neurochemical effects.
authors.affiliation: Wolfson Centre for Age-Related Diseases, Guy's, King's & St Thomas' School of Biomedical Sciences, King's College London, London, UK. ferger@toxi.biol.ethz.ch
authors.forename: B
authors.initials: B
authors.lastname: Ferger
authors.forename: C
authors.initials: C
authors.lastname: Themann
authors.forename: S
authors.initials: S
authors.lastname: Rose
authors.forename: B
authors.initials: B
authors.lastname: Halliwell
authors.forename: P
authors.initials: P
authors.lastname: Jenner
mesh_terms: D018663:Adrenergic Agents / Q000737:chemistry / Q000494:pharmacology; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D003342:Corpus Striatum / Q000378:metabolism*; D004298:Dopamine / Q000494:pharmacology; D006900:Hydroxylation; D008297:Male; D017551:Microdialysis / Q000379:methods; D009566:Nitrates / Q000378:metabolism*; D016877:Oxidants / Q000096:biosynthesis; D016627:Oxidopamine / Q000737:chemistry / Q000494:pharmacology*; D010649:Phenylalanine / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
chemical_list: D018663:Adrenergic Agents; D009566:Nitrates; D016877:Oxidants; C039642:peroxynitric acid; D010649:Phenylalanine; D016627:Oxidopamine; D004298:Dopamine