Mapping choline metabolites in normal and transformed cells
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ORIGINAL ARTICLE
Mapping choline metabolites in normal and transformed cells Irena Roci1,2,3 · Jeramie D. Watrous4 · Kim A. Lagerborg4 · Mohit Jain4 · Roland Nilsson1,2,3 Received: 6 July 2020 / Accepted: 12 November 2020 © The Author(s) 2020
Abstract Introduction Choline is an essential human nutrient that is particular important for proliferating cells, and altered choline metabolism has been associated with cancer transformation. Yet, the various metabolic fates of choline in proliferating cells have not been investigated systematically. Objectives This study aims to map the metabolic products of choline in normal and cancerous proliferating cells. Methods We performed 13C-choline tracing followed by liquid chromatography-high resolution mass spectrometry (LCHRMS) analysis of metabolic products in normal and in vitro-transformed (tumor-forming) epithelial cells, and also in tumor-derived cancer cell lines. Selected metabolites were quantified by internal standards. Results Untargeted analysis revealed 121 LCMS peaks that were 13C-labeled from choline, including various phospholipid species, but also previously unknown products such as monomethyl- and dimethyl-ethanolamines. Interestingly, we observed formation of betaine from choline specifically in tumor-derived cells. Expression of choline dehydrogenase (CHDH), which catalyzes the first step of betaine synthesis, correlated with betaine synthesis across the cell lines studied. RNAi silencing of CHDH did not affect cell proliferation, although we observed an increased fraction of G 2M phase cells with some RNAi sequences, suggesting that CHDH and its product betaine may play a role in cell cycle progression. Betaine cell concentration was around 10 µM, arguing against an osmotic function, and was not used as a methyl donor. The function of betaine in these tumor-derived cells is presently unknown. Conclusion This study identifies novel metabolites of choline in cancer and normal cell lines, and reveals altered choline metabolism in cancer cells. Keywords 13C3 choline · Betaine · CHDH · Methylation · Isotope tracing
1 Introduction
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11306-020-01749-0) contains supplementary material, which is available to authorized users. * Roland Nilsson [email protected] 1
Cardiovascular Medicine Unit, Department of Medicine, Karolinska Institutet, 171 76 Stockholm, Sweden
2
Division of Cardiovascular Medicine, Karolinska University Hospital, 171 76 Stockholm, Sweden
3
Center for Molecular Medicine, Karolinska Institutet, 171 76 Stockholm, Sweden
4
Department of Medicine & Pharmacology, University of California, San Diego, 9500 Gilman Avenue,, La Jolla, CA 92093, USA
Choline is a central nutrient in human metabolism. Choline forms the head group of phosphatidylcholine, the most abundant lipid in cell membranes (van der Veen et al. 2017), and choline is therefore required in substantial amounts by proliferating cells to synthesize membranes. Althoug
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