title: Molecular speciated isotope dilution mass spectrometric methods for accurate, reproducible and direct quantification of reduced, oxidized and total glutathione in biological samples.
abstract: Novel protocols were developed to accurately quantify reduced (GSH), oxidized (GSSG) and total (tGSH) glutathione in biological samples using molecular speciated isotope dilution mass spectrometry (SIDMS). For GSH and GSSG measurement, the sample was spiked with isotopically enriched analogues of the analytes ((310)GSH and (616)GSSG), along with N-ethylmaleimide (NEM), and treated with acetonitrile to solubilize the endogenous analytes via protein precipitation and equilibrate them with the spikes. The supernatant was analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and the analytes were quantified with simultaneous tracking and correction for auto-oxidation of GSH to GSSG. For tGSH assay, a (310)GSH-spiked sample was treated with dithiothreitol (DTT) to convert disulfide-bonded glutathione to GSH. After removing the protein, the supernatant was analyzed by LC-MS/MS and the analyte was quantified by single-spiking isotope dilution mass spectrometry (IDMS). The mathematical relationships in IDMS and SIDMS quantifications are based on isotopic ratios and do not involve calibration curves. The protocols were validated using spike recovery tests and by analyzing synthetic standard solutions. Red blood cell (RBC) and saliva samples obtained from healthy subjects, and whole blood samples collected and shipped from a remote location were analyzed. The concentrations of tGSH in the RBC and whole blood samples were 2 orders of magnitude higher than those found in saliva. The fractions of GSSG were 0.2-2.2% (RBC and blood) and 15-47% (saliva) of the free glutathione (GSH + 2xGSSG) in the corresponding samples. Up to 3% GSH was auto-oxidized to GSSG during sample workup; the highest oxidations (>1%) were in the saliva samples.
authors.affiliation: Department of Chemistry and Biochemistry, Duquesne University , 600 Forbes Avenue, Pittsburgh, Pennsylvania 15282, United States.
authors.forename: Timothy
authors.initials: T
authors.lastname: Fahrenholz
authors.forename: Mesay Mulugeta
authors.initials: MM
authors.lastname: Wolle
authors.forename: H M Skip
authors.initials: HM
authors.lastname: Kingston
authors.forename: Scott
authors.initials: S
authors.lastname: Faber
authors.forename: John C
authors.initials: JC
authors.lastname: Kern
authors.forename: Matt
authors.initials: M
authors.lastname: Pamuku
authors.forename: Logan
authors.initials: L
authors.lastname: Miller
authors.forename: Hemasudha
authors.initials: H
authors.lastname: Chatragadda
authors.forename: Andreas
authors.initials: A
authors.lastname: Kogelnik
mesh_terms: D000328:Adult; D002648:Child; D002675:Child, Preschool; D002853:Chromatography, Liquid / Q000379:methods; D004912:Erythrocytes / Q000737:chemistry; D005978:Glutathione / Q000032:analysis* / Q000097:blood*; D019803:Glutathione Disulfide / Q000032:analysis* / Q000097:blood*; D006801:Humans; D007201:Indicator Dilution Techniques; D008875:Middle Aged; D010084:Oxidation-Reduction; D015203:Reproducibility of Results; D012463:Saliva / Q000737:chemistry*; D053719:Tandem Mass Spectrometry / Q000379:methods*; D055815:Young Adult
chemical_list: D005978:Glutathione; D019803:Glutathione Disulfide