Changes in cell phospholipid metabolism in vitro in the presence of HEMA and its degradation products.
OBJECTIVE
Diacylglycerol-kinase (DAG-kinase) is an enzyme that phosphorylates diacylglycerol (DAG) to phosphatidic acid (PA), which serves as a precursor to phosphoglycerides involved in cell signaling or as cell membrane structural components. DAG-kinase can be inhibited by diacylethylene glycols (DAEG). We hypothesize that 2-hydroxyethyl methacrylate (HEMA) may alter phosphorylation of DAG to PA following intracellular formation of DAEG.


METHODS
Cultured rabbit kidney (RK13) epithelial cells were treated with HEMA, EG, or known inhibitors of DAG-kinase for 24 h, then exposed to [32P]O4- in the presence of a synthetic diacylglycerol for 2 h. Other cultures were radiolabeled with [3H]-oleic acid for 24 h, then exposed to HEMA for an additional 24 h. The cells were harvested and the lipids extracted. Radioactive lipids were separated by thin layer chromatography, located by autoradiography, and quantitated as cpm/ug protein. Cell cultures treated with HEMA were homogenized and the DAG-kinase activity was assayed and expressed as cpm/ug protein. Data were analyzed by one-way ANOVA and Newman-Keuls Multiple Comparison Test.


RESULTS
Cultures exposed to HEMA or known DAG-kinase inhibitors exhibited reduced incorporation of radioactivity in the PA fraction compared to control cultures. Direct assays of DAG-kinase activity from cells exposed to HEMA demonstrated decreased enzyme activity. Evaluation of cell phospholipid synthesis showed altered formation of phosphatidylethanolamine and phosphatidylcholine.


CONCLUSIONS
Results suggest that HEMA impairs formation of PA, possibly by acylation of EG released by hydrolysis of the HEMA and resultant production of the inhibitor DAEG. The decreased availability of PA may alter PA-dependent cell structural lipid pathways and lipid-dependent signaling pathways, altering cell growth.
Schuster
G S
GS
Department of Oral Biology and Maxillofacial Pathology, Medical College of Georgia School of Dentistry, Augusta, GA 30912-1126, USA. gschuste@mail.mcg.edu
Caughman
G B
GB
Rueggeberg
F A
FA
D000704:Analysis of Variance; D000818:Animals; D001345:Autoradiography; D002478:Cells, Cultured; D002855:Chromatography, Thin Layer; D017220:Dentin-Bonding Agents / Q000494:pharmacology*; D019852:Diacylglycerol Kinase / Q000037:antagonists & inhibitors; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D006868:Hydrolysis; D007668:Kidney / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D008689:Methacrylates / Q000494:pharmacology*; D019301:Oleic Acid / Q000378:metabolism; D010712:Phosphatidic Acids / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000378:metabolism; D010714:Phosphatidylethanolamines / Q000378:metabolism; D010766:Phosphorylation; D011817:Rabbits; D019275:Radiopharmaceuticals; D013223:Statistics as Topic; D014316:Tritium
D017220:Dentin-Bonding Agents; D004791:Enzyme Inhibitors; D008689:Methacrylates; D010712:Phosphatidic Acids; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D019275:Radiopharmaceuticals; D014316:Tritium; D019301:Oleic Acid; C005044:hydroxyethyl methacrylate; D019852:Diacylglycerol Kinase