METHYL-GROUP DONORS CANNOT PREVENT APOPTOTIC DEATH OF RAT HEPATOCYTESINDUCED BY CHOLINE-DEFICIENCY

Choline-deficiency causes liver cells to die by apoptosis, and it has not been clear whether the effects of choline-deficiency are mediated by methyl-deficiency or by lack of choline moieties. SV40 immortalized CWSV-1 hepatocytes were cultivated in media that were choline-suffici ent, choline-deficient, choline-deficient with methyl-donors (betaine or methionine), or choline-deficient with extra folate/vitamin B-12. C holine-deficient CWSV-1 hepatocytes were not methyl-deficient as they had increased intracellular S-adenosylmethionine concentrations (132% of control; P < 0.01). Despite increased phosphatidylcholine synthesis via sequential methylation of phosphatidylethanol amine, choline-defi cient hepatocytes had significantly decreased (P < 0.01) intracellular concentrations of choline (20% of control), phosphocholine (6% of con trol); glycerophosphocholine (15% of control), and phosphatidylcholine (55% of control). Methyl-supplementation in choline-deficiency enhanc ed intracellular methyl-group availability, but did not correct cholin e-deficiency induced abnormalities in either choline metabolite or pho spholipid content in hepatocytes. Methyl-supplemented, choline-deficie nt cells died by apoptosis. in a rat study, 2 weeks of a choline-defic ient diet supplemented with betaine did not prevent the occurrence of fatty liver and the increased DNA strand breakage induced by choline-d eficiency. Though dietary supplementation with betaine restored hepati c betaine concentration and increased hepatic S-adenosylmethionine/S-a denosylhomocysteine ratio, it did not correct depleted choline (15% of control), phosphocholine (6% control), or phosphatidylcholine (48% of control) concentrations in deficient livers. These data show that dec reased intracellular choline and/or choline metabolite concentrations, and not methyl deficiency, are associated with apoptotic death of hep atocytes. (C) 1997 Wiley-Liss, Inc.