Determination of S-adenosylmethionine and S-adenosylhomocysteine in plasma and cerebrospinal fluid by stable-isotope dilution tandem mass spectrometry.
BACKGROUND
Available methods for the determination of nanomolar concentrations of S:-adenosylmethionine (SAM) and S:-adenosylhomocysteine (SAH) in plasma and cerebrospinal fluid (CSF) are time-consuming. We wished to develop a method for their rapid and simultaneous measurement.


METHODS
We used tandem mass spectrometry (MS/MS) for the simultaneous determination of SAM and SAH, with stable-isotope-labeled internal standards. The (13)C(5)-SAH internal standard was enzymatically prepared using SAH-hydrolase and [(13)C(5)]adenosine. The method comprises a weak anion-exchange solid-phase extraction procedure serving as clean-up step for the deproteinized plasma and CSF samples. After clean-up, samples were injected on a C(18) HPLC column, which was connected directly to the tandem mass spectrometer, operating in MS/MS mode.


RESULTS
In plasma samples, the intraassay CVs for SAM and SAH were 4.2% and 4.0%, respectively, and the interassay CVs were 7.6% and 5. 9%, respectively. In CSF, the intraassay CVs for SAM and SAH were 6. 8% and 6.9%, respectively, and the interassay CVs were 4.2% and 5.5%, respectively. Mean recovery of SAM and SAH for both matrices at two concentrations was 93%. Detection limits for SAM and SAH in samples were 7.5 and 2.5 nmol/L, respectively. Concentrations of SAM and SAH in plasma from healthy subjects were within the previously reported ranges. In 10 CSF samples, the mean concentrations (range) were 248 (137-385) nmol/L for SAM and 11.3 (8.9-14.1) nmol/L for SAH.


CONCLUSIONS
SAM and SAH can be analyzed by MS/MS, taking optimal advantage of the speed and high sensitivity and specificity of this relatively new analytical technique.
Struys
E A
EA
Metabolic Unit, Department of Clinical Chemistry, Free University Hospital, De Boelelaan 1117, 1081 HV Amsterdam, The Netherlands.
Jansen
E E
EE
de Meer
K
K
Jakobs
C
C
D002247:Carbon Isotopes; D002648:Child; D002853:Chromatography, Liquid; D005260:Female; D006801:Humans; D007201:Indicator Dilution Techniques; D013058:Mass Spectrometry; D017697:Premenopause; D012435:S-Adenosylhomocysteine / Q000097:blood* / Q000134:cerebrospinal fluid*; D012436:S-Adenosylmethionine / Q000097:blood* / Q000134:cerebrospinal fluid*
D002247:Carbon Isotopes; D012436:S-Adenosylmethionine; D012435:S-Adenosylhomocysteine