Perturbations in choline metabolism cause neural tube defects in mouse embryos in vitro.
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A role for choline during early stages of mammalian embryogenesis has not been established, although recent studies show that inhibitors of choline uptake and metabolism, 2-dimethylaminoethanol (DMAE), and 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3), produce neural tube defects in mouse embryos grown in vitro. To determine potential mechanisms responsible for these abnormalities, choline metabolism in the presence or absence of these inhibitors was evaluated in cultured, neurulating mouse embryos by using chromatographic techniques. Results showed that 90%-95% of 14C-choline was incorporated into phosphocholine and phosphatidylcholine (PtdCho), which was metabolized to sphingomyelin. Choline was oxidized to betaine, and betaine homocysteine methyltransferase was expressed. Acetylcholine was synthesized in yolk sacs, but 70 kDa choline acetyltransferase was undetectable by immunoblot. DMAE reduced embryonic choline uptake and inhibited phosphocholine, PtdCho, phosphatidylethanolamine (PtdEtn), and sphingomyelin synthesis. ET-18-OCH3 also inhibited PtdCho synthesis. In embryos and yolk sacs incubated with 3H-ethanolamine, 95% of recovered label was PtdEtn, but PtdEtn was not converted to PtdCho, which suggested that phosphatidylethanolamine methyltransferase (PeMT) activity was absent. In ET-18-OCH3 treated yolk sacs, PtdEtn was increased, but PtdCho was still not generated through PeMT. Results suggest that endogenous PtdCho synthesis is important during neurulation and that perturbed choline metabolism contributes to neural tube defects produced by DMAE and ET-18-OCH3. (+info)
The sea urchin embryo as a model for mammalian developmental neurotoxicity: ontogenesis of the high-affinity choline transporter and its role in cholinergic trophic activity.
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Embryonic development in the sea urchin requires trophic actions of the same neurotransmitters that participate in mammalian brain assembly. We evaluated the development of the high-affinity choline transporter, which controls acetylcholine synthesis. A variety of developmental neurotoxicants affect this transporter in mammalian brain. [3H]Hemicholinium-3 binding to the transporter was found in the cell membrane fraction at stages from the unfertilized egg to pluteus, with a binding affinity comparable with that seen in mammalian brain. Over the course of development, the concentration of transporter sites rose more than 3-fold, achieving concentrations comparable with those of cholinergically enriched mammalian brain regions. Dimethylaminoethanol (DMAE), a competitive inhibitor of choline transport, elicited dysmorphology beginning at the mid-blastula stage, with anomalies beginning progressively later as the concentration of DMAE was lowered. Pretreatment, cotreatment, or delayed treatment with acetylcholine or choline prevented the adverse effects of DMAE. Because acetylcholine was protective at a lower threshold, the DMAE-induced defects were most likely mediated by its effects on acetylcholine synthesis. Transient removal of the hyaline layer enabled a charged transport inhibitor, hemicholinium-3, to penetrate sufficiently to elicit similar anomalies, which were again prevented by acetylcholine or choline. These results indicate that the developing sea urchin possesses a high-affinity choline transporter analogous to that found in the mammalian brain, and, as in mammals, the functioning of this transporter plays a key role in the developmental, trophic activity of acetylcholine. The sea urchin model may thus be useful in high-throughput screening of suspected developmental neurotoxicants. (+info)
Dimethylethanolamine does not prevent liver failure in phosphatidylethanolamine N-methyltransferase-deficient mice fed a choline-deficient diet.
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Mice that lack phosphatidylethanolamine-N-methyltransferase (PEMT) and are fed a choline-deficient (CD) diet suffer severe liver damage and do not survive. Since phosphatidyldimethylethanolamine (PDME) has physical properties similar to those of phosphatidylcholine (PC), we hypothesized that dimethylethanolamine (DME) would be converted into PDME that might substitute for PC, and therefore abrogate the liver damage in the Pemt -/- mice fed a CD diet. We fed Pemt -/- mice either a CD diet, a CD diet supplemented with choline, or a CD diet supplemented with DME (CD + DME). Pemt -/- mice fed the CD diet developed severe liver failure by 4 days while CD + DME-fed mice developed severe liver failure by 5 days. The hepatic PC level in choline-supplemented (CS) mice was 67 +/- 4 nmol/mg protein, whereas the PC content was reduced in CD- and CD + DME-fed mice (49 +/- 3 and 30 +/- 3 nmol/mg protein, respectively). Upon supplementation of the CD diet with DME the amount of hepatic PDME was 81 +/- 9 nmol/mg protein so that the hepatic content of PC + PDME combined was 111 nmol/mg protein. Moreover, plasma apolipoprotein B100 and Al levels were markedly lower in mice fed the CD + DME diet compared to mice fed the CS diet, as was the plasma content of PC. Thus, despite replacement of the deficit in hepatic PC with PDME in Pemt -/- mice fed a CD diet, normal liver function was not restored. We conclude that although PC and PDME exhibit similar physical properties, the three methyl groups of choline are required for hepatic function in mice. (+info)
2-dimethylaminoethanol (Deanol) in Huntington's chorea.
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A double-blind crossover trial with 2-dimethylaminoethanol (Deanol), a possible precursor of brain acetylcholine, was carried out in nine patients with Huntington's chorea. It was found to be ineffective in inducing any alteration in hyperkinesia. (+info)
Functionalization of 6-nitrobenzo[1,3]dioxole with carbonyl compounds via TDAE methodology.
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We report herein the synthesis of substituted 2-(6-nitrobenzo[1,3]dioxol-5-yl)-1- aryl ethanols and 2-(6-nitrobenzo[1,3]dioxol-5-yl)-propionic acid ethyl esters from the reaction of 5-chloromethyl-6-nitrobenzo[1,3]dioxole with various aromatic carbonyl and alpha- carbonyl ester derivatives using the tetrakis(dimethylamino)ethylene (TDAE) methodology. (+info)
Head-group specificity for feedback regulation of CTP:phosphocholine cytidylyltransferase.
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The specificity of the phospholipid head-group for feedback regulation of CTP: phosphocholine cytidylyltransferase was examined in rat hepatocytes. In choline-deficient cells there is a 2-fold increase in binding of cytidylyltransferase to cellular membranes, compared with choline-supplemented cells. Supplementation of choline-deficient cells with choline, dimethylethanolamine, monomethylethanolamine or ethanolamine resulted in an increase in the concentration of the corresponding phospholipid. Release of cytidylyltransferase into cytosol was only observed in hepatocytes supplemented with choline or dimethylethanolamine. The apparent EC50 values (concn. giving half of maximal effect) for cytidylyltransferase translocation were similar for choline and dimethylethanolamine (25 and 27 microM respectively). The maximum amount of cytidylyltransferase released into cytosol with choline supplementation (1.13 m-units/mg membrane protein) was twice that (0.62) observed with dimethylethanolamine. Supplementation of choline-deficient hepatocytes with NN'-diethylethanolamine, N-ethylethanolamine or 3-aminopropanol also did not cause release of cytidylyltransferase from cellular membranes. The translocation of cytidylyltransferase appeared to be mediated by the concentration of phosphatidylcholine in the membranes and not the ratio of phosphatidylcholine to phosphatidylethanolamine. The results provide further evidence for feedback regulation of phosphatidylcholine biosynthesis by phosphatidylcholine. (+info)
Conditional mutagenesis of a novel choline kinase demonstrates plasticity of phosphatidylcholine biogenesis and gene expression in Toxoplasma gondii.
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