Development and validation of an LC-MS/MS assay for the quantification of the trans-methylation pathway intermediates S-adenosylmethionine and S-adenosylhomocysteine in human plasma

Background: Although increased levels of S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH) have been implicated as markers for renal and vascular dysfunction, until now there have been no studies investigating their association with clinical post-transplant events such as organ rejection and immunosuppressant nephrotoxicity. Methods: A newly developed and validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for the quantification of SAM and SAH in human EDTA plasma was used for a clinical proof-of-concept pilot study. Retrospective analysis was performed using samples from a longitudinal clinical study following de novo kidney transplant patients for the first year (n = 16). Results: The ranges of reliable response were 8 to 1024 nmol/l for SAM and 16 to 1024 nmol/l for SAH. The inter-day accuracies were 96.7-103.9% and 97.9-993% for SAM and SAH, respectively. Inter-day imprecisions were 8.1-9.1% and 8.4-9.8%. The total assay run time was 5 min. SAM and SAH concentrations were significantly elevated in renal transplant patients preceding documented acute rejection and nephrotoxicity events when compared to healthy controls (n = 8) as well as transplant patients void of allograft dysfunction (n = 8). Conclusion: The LC-MS/MS assay will provide the basis for further large-scale clinical studies to explore these thiol metabolites as molecular markers for the management of renal transplant patients. (C) 2013 Elsevier B.V. All rights reserved.