IN-VITRO AND IN-VIVO C-13 AND P-31 NMR ANALYSES OF PHOSPHOCHOLINE METABOLISM IN RAT GLIOMA-CELLS

In vivo magnetic resonance spectroscopy (MRS) has revealed that phsoph omonoesters (PME) such as phosphocholine (PCho) and phosphoethanolamin e (PEth) are elevated in tumors and rapidly proliferating tissues. The regulation of PME levels and their relationship to proliferation are not well known. In the present study, we investigated the regulation o f PCho and PEth levels in rat glioma cells grown in vivo and in vitro using P-31 and C-13 MRS. However, the ability of cells to produce chol ine endogenously is variable. To fully understand regulation of PCho l evels, it is necessary to characterize the activity of the endogenous pathway, if it exists. This was first investigated by following the me tabolic fate of C-13-labeled methionine of 9L glioma tumors in vivo. O ur results indicate that there is a significant amount of de novo chol ine synthesis in vivo. However, similar experiments performed in vitro using cells cultured in bioreactors indicated that glioma cells thems elves are unable to synthesize choline de novo, suggesting that the in vivo results were due to the involvement of extratumoral organs, e.g. , liver. Further in vitro experiments demonstrated that the uptake and phosphorylation of physiologically relevant concentrations of exogeno us choline is very active in these systems. Thus, it appears that the exogenous pathway for PCho biosynthesis predominates and regulates PCh o levels in glioma cells. Our results also demonstrate that PCho level s are lowest, and PEth levels are highest, in nonproliferating cells. These observations indicate that there is a decrease in the biosynthes is of PCho concomitant with a reduction in culture growth. The source of the increased PEth is, as yet, undefined.