title: Stable isotope dilution analysis of cystine in granulocyte suspensions as cysteine: a powerful method for the diagnosis, the follow-up, and treatment of patients with cystinosis.
abstract: A stable isotope dilution method was developed for the determination of cystine in granulocytes. Granulocytes were isolated from blood samples of treated cystinosis patients. Cystine in the granulocyte suspension was decoupled from proteins and converted to cysteine by treatment with a tri-butyl phosphine solution. Tertiary butyldimethyl silyl derivatives were prepared and analyzed by gas chromatography/mass spectrometry. Selective ion monitoring was carried out at m/z 304.3 (M-159 and m/z 406.4 (M-57) for the natural, and at m/z 306.3 and 408.4 for the labelled compound. [3,3,3',3'-2H]-DL-cystine was used as internal standard for the isotope dilution analysis. Concentrations of cystine in granulocytes could be accurately measured. There was a distinct difference in cystine concentrations in healthy individuals and treated patients.
authors.affiliation: Nutrition Science, Nestlé Research Centre, Nestec Ltd., Lausanne, Switzerland.
authors.forename: H
authors.initials: H
authors.lastname: Schierbeek
authors.forename: K
authors.initials: K
authors.lastname: Bijsterveld
authors.forename: T E
authors.initials: TE
authors.lastname: Chapman
authors.forename: W H
authors.initials: WH
authors.lastname: van Luijk
authors.forename: D J
authors.initials: DJ
authors.lastname: Reijngoud
authors.forename: R
authors.initials: R
authors.lastname: Berger
mesh_terms: D000293:Adolescent; D000328:Adult; D002469:Cell Separation; D002648:Child; D003543:Cysteamine / Q000627:therapeutic use; D003545:Cysteine / Q000097:blood*; D003553:Cystine / Q000097:blood*; D003554:Cystinosis / Q000097:blood / Q000175:diagnosis* / Q000188:drug therapy; D008401:Gas Chromatography-Mass Spectrometry; D006098:Granulocytes / Q000737:chemistry*; D006801:Humans; D007201:Indicator Dilution Techniques; D012016:Reference Values
chemical_list: D003553:Cystine; D003543:Cysteamine; D003545:Cysteine