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 (LC-HRMS) 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 G₂M 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.

中文翻译：

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绘制正常细胞和转化细胞中的胆碱代谢物

介绍

胆碱是人体必需的营养素，对增殖细胞特别重要，胆碱代谢的改变与癌症转化有关。然而，尚未系统地研究胆碱在增殖细胞中的各种代谢命运。

目标

本研究旨在绘制正常和癌性增殖细胞中胆碱的代谢产物。

方法

我们对正常和体外转化（肿瘤形成）上皮细胞以及肿瘤来源的癌细胞系中的代谢产物进行了¹³ C-胆碱示踪，然后进行了液相色谱-高分辨率质谱 (LC-HRMS) 分析。选定的代谢物通过内标进行定量。

结果

非靶向分析揭示了 121 个 LCMS 峰，这些峰是来自胆碱的¹³ C 标记，包括各种磷脂种类，但也包括以前未知的产物，例如单甲基乙醇胺和二甲基乙醇胺。有趣的是，我们观察到胆碱特别是在肿瘤衍生细胞中形成甜菜碱。催化甜菜碱合成第一步的胆碱脱氢酶 (CHDH) 的表达与所研究的细胞系中的甜菜碱合成相关。尽管我们观察到 G _{2 的}比例增加，但 CHDH 的 RNAi 沉默不影响细胞增殖M 期细胞具有一些 RNAi 序列，表明 CHDH 及其产物甜菜碱可能在细胞周期进程中发挥作用。甜菜碱细胞浓度约为 10 µM，反对渗透功能，并且不用作甲基供体。甜菜碱在这些肿瘤衍生细胞中的功能目前尚不清楚。

结论

这项研究确定了癌症和正常细胞系中胆碱的新代谢物，并揭示了癌细胞中胆碱代谢的改变。