Quantitative profiling of folate and one-carbon metabolism in large-scale epidemiological studies by mass spectrometry.
BACKGROUND
Derangements of one-carbon metabolism have been related to the development of chronic diseases. Metabolic profiling as part of epidemiological studies in this area should include intermediates involved in the transfer of one-carbon units, cofactors for the relevant enzymes and markers of inflammation, kidney function and smoking.


METHODS
We established five platforms that measured 6-16 analytes each. Platforms A (gas chromatography-mass spectrometry; GC-MS) and B (gas chromatography-tandem mass spectrometry; GC-MS/MS) involved methylchloroformate derivatization of primary amines, thiols and carboxylic acids. Platform C determined basic compounds by liquid chromatography-tandem mass spectrometry (LC-MS/MS), using an ether-linked phenyl reversed-phase column. Platforms D and E (LC-MS/MS) exploited the efficient ionization and high sensitivity obtained for a wide range of analytes, using a mobile phase containing a high concentration of acetic acid. The chromatographic run times ranged from 3 to 8 min.


RESULTS
The analyte concentrations ranged from 0.2 nmol/L to 400 micromol/L. Platforms A and B both measured methylmalonic acid, total homocysteine and related amino acids. Platform B also included sarcosine, cystathionine, tryptophan and kynurenine. Platform C was optimized for the measurement of choline and betaine, but also included arginine, asymmetric and symmetric dimethylarginine and creatinine. A diversity of low abundance compounds mainly occurring in the nanomolar range were measured on platform D. These were vitamin B(2) and B(6) species, neopterin, cotinine and tryptophan metabolites. Platform E measured folates and folate catabolites.


CONCLUSIONS
Approximately 40 analytes related to one-carbon metabolism were determined in less than 1 mL of plasma/serum using five complementary analytical platforms. As a method control, several metabolites were measured on two or more platforms. Logistics and data handling were carried out by specially designed software. This strategy allows profiling of one-carbon metabolism in large-scale epidemiological studies.
Ueland
Per Magne
PM
LOCUS for Homocysteine and Related Vitamins, University of Bergen, Bergen, Norway. per.ueland@ikb.uib.no
Midttun
Oivind
O
Windelberg
Amrei
A
Svardal
Asbjørn
A
Skålevik
Rita
R
Hustad
Steinar
S
D002244:Carbon / Q000378:metabolism*; D002853:Chromatography, Liquid; D016021:Epidemiologic Studies; D005492:Folic Acid / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D006801:Humans; D053719:Tandem Mass Spectrometry / Q000379:methods*
D002244:Carbon; D005492:Folic Acid