Methyl group donors cannot prevent apoptotic death of hepatocytes induced by choline deficiency

Patients fed parenterally with low choline solutions develop liver damage which can be reversed by treatment with choline containing compounds. We have recently reported thai choline deficiency causes liver cells to die by apoptosis. Choline deficient livers show a decrease in both hepatic methyl group availability and choline metabolites. These studies seek to identify the mechanisms by which choline deficiency damages liver. We investigated whether supplementation of methyl group donors can prevent apoptotic death of hepatocytes induced by choline deficiency. SV 40 immortalized, nontum-Tigenic CWSV-1 hepatocytes were cultivated in choline sufficient (CS; 70 (jM choline) serum free medium for 4 days, and then cultivated in CS medium, choline deficient (CD; 0 (J.M choline) medium, and CD medium supplemented with betaine (120×B; 70-1400μM betaine) or extra methionine (1-10×M; 70-700 μM extra methionine). Choline deficient CWSV-1 hepatocytes increased intracellular S-adenosy I methionine anil phosphatidylcholine (PC) synthesis via sequential methylation of phosphatidylethanolamine (PE). However, choline deficient CWSV-1 cells decreased major choline metabolites such as choline. phosphocholine, glycerophosphochohne. and PC. Choline deficient CWSV-I hepatocytes increased their PE, phosphatidylinositol, and sphingomyelin composition. With these biochemical changes, choline deficient CWSV-1 hepatocytes died by apoptosis (200 bp DNA fragmentation, cell detachment. morphological changes). CWSV-1 hepatocytes cultivated in CD medium supplemented with betaine or extra methionine did not correci abnormalities in eilher choline metabolites or phospholipid composition, even though sufficient methyl groups were available. CWSV-I hepatocytes cultivated in methyl supplemented media died by apoptosis. In a rat study, dietary betaine did not prevent fatty livers and DNA fragmentation (TUNEL labeling) induced by choline deficiency, even though dietary betaine restored the hepatic betaine pool and increased S-adenosylmethionine/Sadenosylhomocysteine ratio. These data show that choline is an essential nutrienl for survival of hepatocytes. Apoptosis induced by choline deficiency is not due 10 a decrease in methyl group availability, but instead may be related to the abnormalities in choline meiaholites or Ihe nhosnhotioid composition of cells.