Amino acids in a targeted versus a non-targeted metabolomics LC-MS/MS assay. Are the results consistent?
BACKGROUND
The results of plasma amino acid patterns in samples from kidney transplant patients with good and impaired renal function using a targeted LC-MS/MS amino acid assay and a non-targeted metabolomics assay were compared.


METHODS
EDTA plasma samples were prospectively collected at baseline, 1, 2, 4 and 6months post-transplant (n=116 patients, n=398 samples). Each sample was analyzed using both a commercial amino acid LC-MS/MS assay and a non-targeted metabolomics assay also based on MS/MS ion transitions. The results of both assays were independently statistically analyzed to identify amino acids associated with estimated glomerular filtration rates using correlation and partial least squares-discriminant analysis.


RESULTS
Although there was overlap between the results of the targeted and non-targeted metabolomics assays (tryptophan, 1-methyl histidine), there were also substantial inconsistencies, with the non-targeted assay resulting in more "hits" than the targeted assay. Without further verification of the hits detected by the non-targeted discovery assay, this would have led to different interpretation of the results. There were also false negative results when the non-targeted assay was used (hydroxy proline). Several of said discrepancies could be explained by loss of sensitivity during analytical runs for selected amino acids (serine and threonine), retention time shifts, signals above the range of linear detector response and integration of peaks not separated from background and interferences (aspartate) when the non-targeted metabolomics assay was used.


CONCLUSIONS
Whenever assessment of a specific pathway such as amino acids is the focus of interest, a targeted seems preferable to a non-targeted metabolomics assay.
iC42 Clinical Research and Development, University of Colorado Anschutz Medical Campus, Aurora, CO, United States. Electronic address: jacek.klepacki@ucdenver.edu.
Jacek
J
Klepacki
iC42 Clinical Research and Development, University of Colorado Anschutz Medical Campus, Aurora, CO, United States.
Jost
J
Klawitter
iC42 Clinical Research and Development, University of Colorado Anschutz Medical Campus, Aurora, CO, United States.
Jelena
J
Klawitter
Center for Computational Biology, University of Colorado Anschutz Medical Campus, Aurora, CO, United States.
Anis
A
Karimpour-Fard
Division of Nephrology, University of Colorado Anschutz Medical Campus, Aurora, CO, United States.
Joshua
J
Thurman
Novartis Pharmaceuticals, East Hanover, NJ, United States.
Gordon
G
Ingle
Novartis Pharmaceuticals, East Hanover, NJ, United States.
Dharmesh
D
Patel
iC42 Clinical Research and Development, University of Colorado Anschutz Medical Campus, Aurora, CO, United States.
Uwe
U
Christians
D000596:Amino Acids / Q000378:metabolism*; D002853:Chromatography, Liquid / Q000379:methods*; D006801:Humans; D055432:Metabolomics; D011446:Prospective Studies; D053719:Tandem Mass Spectrometry / Q000379:methods*
D000596:Amino Acids
Amino acids; Kidney transplantation; LC-MS/MS; Multi-analyte LC-MS/MS; Non-targeted metabolomics; Targeted metabolomics; eGFR