Analysis of hydrophilic and lipophilic choline compounds in radioresistant and radiosensitive glioblastoma cell lines by HILIC-ESI-MS/MS

A new method based on hydrophilic interaction chromatography-electrospray ionisation-tandem mass spectrometry (HILIC-ESI-MS/MS) coupled to the use of a stable isotope labelled substrate was developed to study the metabolism of choline (Cho) compounds in two human glioblastoma multiform (GBM) cell lines with different responses to ionising radiation. Analysis was performed in the positive ion mode using multiple reaction monitoring. This fast, sensitive and selective method enabled the profiling of both hydrophilic and lipophilic Cho-containing compounds, to analyse specifically different phosphatidylcholine (PtdCho) molecular species, and to measure simultaneously native and labelled Cho metabolites. Radioresistant (SF763) and radiosensitive (SF767) cells were incubated for 8 h with d (9)-Cho. Higher native Cho and phosphocholine (PCho) concentrations and higher uptake of d (9)-Cho and formation of d (9)-PCho were found in the radioresistant cell line. The similar low concentrations of native cytidine 5'-diphosphocholine (CDP-Cho) and d (9)-CDP-Cho in both cell lines show that CDP-Cho is the limiting metabolite in the two models. The turnovers (percentage of each d (9)-Cho compound in its respective pool, i.e. native + labelled) were lower in radioresistant cells for all Cho compounds, suggesting a global PtdCho metabolism more active in radiosensitive cells that could be related to their higher proliferation rate.