title: Quantitative assay of plasma homocysteine thiolactone by gas chromatography/mass spectrometry.
abstract: Enzymatic cyclization of homocysteine forms a reactive thiolactone that may play an important role in its cardiovascular toxicity, but reliable quantitation of the free thiolactone metabolite in physiological fluids has not been reported. We have therefore used a highly selective gas chromatography/mass spectrometry (GC/MS) technique combined with the sensitivity of negative chemical ionization (NCI) to develop a quantitative method for the detection of homocysteine thiolactone (HcyTL) in plasma. To improve accuracy the deuterated isomer d(4)-HcyTL was synthesized and added to plasma as internal standard. The plasma was then treated with silica solid-phase extraction and derivatized with heptafluorobutyric anhydride. The derivative was analyzed by GC/MS in NCI mode with methane as the reagent gas and quantified by analyzing for the HcyTL ion [M(-)[bond]HF] and its d(4)-HcyTL counterpart in single-ion monitoring mode. The calibration curve showed a dynamic linear range up to 40 nmol/L. Within-day precision (n = 20, nominal concentration 5.2 nmol/L) was 0.96% and between-day precision was 3.9%, with a detection limit of 1.7 nmol/L and quantification limit of 5.2 nmol/L. Two human plasma samples had HcyTL concentrations of 18 and 25 nmol/L. This facile method for quantitation of homocysteine thiolactone opens the way for more detailed clinical studies of its potential role in homocysteine-induced arteriosclerosis and vaso-occlusive disease.
authors.affiliation: Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto ON M5G 1L5, Canada.
authors.forename: Parham
authors.initials: P
authors.lastname: Daneshvar
authors.forename: Mehrdad
authors.initials: M
authors.lastname: Yazdanpanah
authors.forename: Carla
authors.initials: C
authors.lastname: Cuthbert
authors.forename: David E C
authors.initials: DE
authors.lastname: Cole
mesh_terms: D015415:Biomarkers / Q000097:blood / Q000737:chemistry; D003903:Deuterium; D008401:Gas Chromatography-Mass Spectrometry; D006710:Homocysteine / Q000031:analogs & derivatives* / Q000097:blood* / Q000138:chemical synthesis / Q000737:chemistry; D006801:Humans; D015394:Molecular Structure; D012015:Reference Standards; D012680:Sensitivity and Specificity; D012822:Silicon Dioxide
chemical_list: D015415:Biomarkers; D006710:Homocysteine; D012822:Silicon Dioxide; D003903:Deuterium; C007957:homocysteine thiolactone