Diethanolamine inhibits choline uptake and phosphatidylcholine synthesis in Chinese hamster ovary cells

Diethanolamine (DEA), an alkanolamine used widely in industry, is hepatocarcinogenic in mice. The goal of this work was to determine whether DEA altered choline homeostasis in cultured cells, so as to ascertain whether the liver tumor response may be related to choline deficiency. CHO cells were cultured in Ham's F-12 medium containing DEA (0-1000 microgram/ml) and [(33)P]-phosphorus was used to label phospholipid pools. After 48 hours incubation, lipids were extracted and [(33)P]-labeled phospholipids were quantified by autoradiography after thin layer chromatographic separation. In control cells, phosphatidylcholine (PC) accounted for 51 +/- 0.7% of the total lipid (33)P incorporation. DEA had no effect on cell number or total phospholipid biosynthesis, but it significantly decreased the incorporation of (33)P into PC at concentrations >/=50 microgram/ml. DEA (>/=20 microgram/ml) also inhibited the uptake of [(3)H]-choline into CHO cells, with 95% inhibition observed at 250 microgram/ml. To determine whether supplemental choline prevented PC synthesis inhibition by DEA, CHO cells were cultured with or without excess choline (30 mM) and DEA (500 microgram/ml). DEA reduced PC synthesis to 27 +/- 3% of total phospholipids, but had no effect on PC synthesis in choline-supplemented cells. When [(14)C]-DEA was incubated with CHO cells, it was also incorporated into the phospholipid fraction. Collectively, these results indicate that DEA reversibly inhibits PC synthesis by blocking choline uptake and competing for utilization in the CDP-choline pathway in CHO cells.