Rapid analysis of S-adenosylmethionine (SAM) and S- adenosylhomocysteine (SAH) isotopologues in stable isotope-resolved metabolomics (SIRM) using direct infusion nanoelectrospray ultra- high-resolution Fourier transform mass spectrometry (DI-nESI-UHR- FTMS)

S-Adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH) are important metabolites in the one-carbon cycle that modulates cellular methylation required for proliferation and epigenetic regulation. Their concentrations, synthesis, and turnover are difficult to determine conveniently and reliably. We have developed such a method by coupling a simple and rapid purification scheme that efficiently captures both compounds, with high sensitivity, sample throughput direct infusion nanoelectrospray ultra-high-resolution Fourier transform mass spectrometry (DI-nESI-UHR-FTMS). This method is compatible with Stable Isotope-Resolved Metabolomic (SIRM) analysis of numerous other metabolites. The limits of detection for both SAM and SAH were < 1 nM, and the linearity range was up to 1000 nM. The method was first illustrated for SAM/SAH analysis of mouse livers, and lung adenocarcinoma A549 cells. We then applied the method to track 13C1-CH3-Met incorporation into SAM and 13C6-glucose transformation into SAM and SAH via de novo synthesis. We further used the method to show the distinct effects on A549 and H1299 cells with treatment of anti-cancer methylseleninic acid (MSA), selenite, and selenomethionine, notably SAM depletion and increased SAM to SAH ratio by MSA, which implicates altered epigenetic regulation. (c) 2021 Elsevier B.V. All rights reserved. Superscript/Subscript Available

Automated summary

A new method has been developed to conveniently and reliably determine the concentrations, synthesis, and turnover of SAM and SAH, important metabolites in the one-carbon cycle. This method is compatible with Stable Isotope-Resolved Metabolomic (SIRM) analysis and allows for tracking metabolite incorporation and effects of anti-cancer substances on cells.