title: Identification and quantification of the atypical metabolite ornithine-lactam in human plasma by liquid chromatography-tandem mass spectrometry (LC-MS/MS).
abstract: In the late 1970s the atypical metabolite of ornithine, ornithine-lactam, has been observed in urine samples of patients suffering from hyperornithinemia. However, not least due to insufficient analytical methods, until now there are no data available about ornithine-lactam in human plasma. Here, we describe a new method, which is, for the first time, suitable to identify and quantify ornithine-lactam in human EDTA-plasma. The method was validated according to the requirements of the FDA guidance for bioanalytical method validation. The analytes were extracted on mixed mode cation exchange SPE columns, separated on a silica analytical HPLC column working in the HILIC mode and detected on a tandem mass spectrometer equipped with an ESI ion source. As internal standard newly synthesized stable isotope labeled D(6)-ornithine-lactam was used. The calibration function was linear in the range of 0.1-5 microM. Intra- and inter-day precision and accuracy was better than 14% at all concentration levels. In EDTA-plasma samples from 30 volunteers ornithine-lactam concentrations ranging from 0.136 to 0.653 microM were determined. These concentrations correlated significantly (p<0.001, R(2)=0.784) to those of ornithine in EDTA-plasma.
authors.affiliation: Institute of Clinical Pharmacology, Otto-von-Guericke University, 39120 Magdeburg, Germany. jens.martens-lobenhoffer@med.ovgu.de
authors.forename: Jens
authors.initials: J
authors.lastname: Martens-Lobenhoffer
authors.forename: Achim
authors.initials: A
authors.lastname: Becker
authors.forename: Horst
authors.initials: H
authors.lastname: Freude
authors.forename: Stefanie M
authors.initials: SM
authors.lastname: Bode-Böger
mesh_terms: D000328:Adult; D000368:Aged; D002853:Chromatography, Liquid / Q000379:methods*; D005260:Female; D006801:Humans; D007769:Lactams / Q000097:blood*; D008297:Male; D008875:Middle Aged; D009952:Ornithine / Q000097:blood*; D053719:Tandem Mass Spectrometry / Q000379:methods*; D055815:Young Adult
chemical_list: D007769:Lactams; D009952:Ornithine