title: A method for the determination of D-kynurenine in biological tissues.
abstract: D-kynurenine (D-KYN), a metabolite of D-tryptophan, can serve as the bioprecursor of kynurenic acid (KYNA) and 3-hydroxykynurenine, two neuroactive compounds that are believed to play a role in the pathophysiology of several neurological and psychiatric diseases. In order to investigate the possible presence of D-KYN in biological tissues, we developed a novel assay based on the conversion of D-KYN to KYNA by purified D-amino acid oxidase (D-AAO). Samples were incubated with D-AAO under optimal conditions for measuring D-AAO activity (100 mM borate buffer, pH 9.0), and newly produced KYNA was detected by high-performance liquid chromatography (HPLC) with fluorimetric detection. The detection limit for D-KYN was 300 fmol, and linearity of the assay was ascertained up to 300 pmol. No assay interference was noted when other D-amino acids, including D-serine and D-aspartate, were present in the incubation mixture at 50-fold higher concentrations than D-KYN. Using this new method, D-KYN was readily detected in the brain, liver, and plasma of mice treated systemically with D-KYN (300 mg/kg). In these experiments, enantioselectivity was confirmed by determining total kynurenine levels in the same samples using a conventional HPLC assay. Availability of a sensitive, specific, and simple method for D-KYN measurement will be instrumental for evaluating whether D-KYN should be considered for a role in physiology and pathology.
authors.affiliation: Maryland Psychiatric Research Center, University of Maryland School of Medicine, P.O. Box 21247, Baltimore, MD, 21228, USA.
authors.forename: Xiao-Dan
authors.initials: XD
authors.lastname: Wang
authors.forename: Kyle J
authors.initials: KJ
authors.lastname: Horning
authors.forename: Francesca M
authors.initials: FM
authors.lastname: Notarangelo
authors.forename: Robert
authors.initials: R
authors.lastname: Schwarcz
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D003605:D-Amino-Acid Oxidase / Q000378:metabolism; D005260:Female; D005470:Fluorometry / Q000379:methods*; D007736:Kynurenic Acid / Q000378:metabolism; D007737:Kynurenine / Q000031:analogs & derivatives / Q000032:analysis* / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008297:Male; D051379:Mice; D010949:Plasma
chemical_list: C005045:3-hydroxykynurenine; D007737:Kynurenine; D003605:D-Amino-Acid Oxidase; D007736:Kynurenic Acid