s-adenosylhomocysteine and Choline-Deficiency

Choline is an essential nutrient for humans, and part of this requirement is met by endogenous synthesis catalyzed by hepatic phosphatidylethanolamine N-methyltransferase (PEMT). PEMT activity is difficult to estimate in humans because it requires a liver biopsy. Previously, we showed that mice that lack functional PEMT have dramatically reduced concentrations of docosahexaenoic acid (DHA; 22:6n-3) in plasma and of liver phosphatidylcholine (PtdCho)-a phospholipid formed by PEMT.. The objective was to evaluate plasma PtdCho-DHA concentrations as a noninvasive marker of liver PEMT activity in humans.. Plasma PtdCho-DHA concentrations were measured in 72 humans before and after they consumed a low-choline diet, and correlations were analyzed in relation to estrogen status, PEMT polymorphism rs12325817, the ratio of plasma S-adenosylmethionine (AdoMet) to S-adenosylhomocysteine (AdoHcy), and dietary choline intake; all of these factors are associated with changes in liver PEMT activity. PtdCho-DHA and PEMT activity were also measured in human liver specimens.. At baseline, the portion of PtdCho species containing DHA (pmol PtdCho-DHA/nmol PtdCho) was higher in premenopausal women than in men and postmenopausal women (P < 0.01). This ratio was lower in premenopausal women with the rs12325817 polymorphism in the PEMT gene (P < 0.05), and PtdCho-DHA concentration and PEMT activity were lower in human liver samples from women who were homozygous for PEMT rs12325817 (P < 0.05). The ratio of DHA-PtdCho to PtdCho in plasma was directly correlated with the ratio of AdoMet to AdoHcy (P = 0.0001). The portion of PtdCho species containing DHA in plasma was altered in subjects who consumed a low-choline diet.. PtdCho-DHA may be useful as a surrogate marker for in vivo hepatic PEMT activity in humans. This trial was registered at clinicaltrials.gov as NCT00065546.

Topics: Adolescent; Adult; Aged; Biomarkers; Cholesterol, Dietary; Choline; Choline Deficiency; Docosahexaenoic Acids; Female; Genetic Association Studies; Humans; Liver; Male; Menopause; Middle Aged; Phosphatidylcholines; Phosphatidylethanolamine N-Methyltransferase; Polymorphism, Single Nucleotide; S-Adenosylhomocysteine; S-Adenosylmethionine; Young Adult

Methionine is required for protein synthesis and provides a methyl group for >50 critical transmethylation reactions including creatine and phosphatidylcholine synthesis as well as DNA and protein methylation. However, the availability of methionine depends on dietary sources as well as remethylation of demethylated methionine (i.e., homocysteine) by the dietary methyl donors folate and choline (via betaine). By restricting dietary methyl supply, we aimed to determine the extent that dietary methyl donors contribute to methionine availability for protein synthesis and transmethylation reactions in neonatal piglets. Piglets 4-8 days of age were fed a diet deficient (MD-) (n=8) or sufficient (MS+) (n=7) in folate, choline and betaine. After 5 days, dietary methionine was reduced to 80% of requirement in both groups to elicit a response. On day 8, animals were fed [(3)H-methyl]methionine for 6h to measure methionine partitioning into hepatic protein, phosphatidylcholine, creatine and DNA. MD- feeding reduced plasma choline, betaine and folate (P<.05) and increased homocysteine ~3-fold (P<.05). With MD- feeding, hepatic phosphatidylcholine synthesis was 60% higher (P<.05) at the expense of creatine synthesis, which was 30% lower during MD- feeding (P<.05); protein synthesis as well as DNA and protein methylation were unchanged. In the liver, ~30% of dietary label was traced to phosphatidylcholine and creatine together, with ~50% traced to methylation of proteins and ~20% incorporated in synthesized protein. Dietary methyl donors are integral to neonatal methionine requirements and can affect methionine availability for transmethylation pathways.

Topics: Animals; Animals, Newborn; Betaine; Choline Deficiency; Creatine; Diet; Female; Folic Acid Deficiency; Homocysteine; Hyperhomocysteinemia; Liver; Male; Methionine; Methylation; Phosphatidylcholines; Protein Biosynthesis; Protein Processing, Post-Translational; S-Adenosylhomocysteine; S-Adenosylmethionine; Swine; Swine, Miniature; Tritium

Methyl-deficient diets are known to induce various liver disorders, in which DNA methylation changes are implicated. Recent studies have clarified the existence of the active DNA demethylation pathways that start with oxidization of 5-methylcytosine (5meC) to 5-hydroxymethylcytosine by ten-eleven translocation (Tet) enzymes, followed by the action of base-excision-repair pathways. Here, we investigated the effects of a methionine-choline-deficient (MCD) diet on the hepatic DNA methylation of mice by precisely quantifying 5meC using a liquid chromatography-electrospray ionization-mass spectrometry and by investigating the regulatory pathways, including DNA demethylation. Although feeding the MCD diet for 1 week induced hepatic steatosis and lower level of the methyl donor S-adenosylmethionine, it did not cause a significant reduction in the 5meC content. On the other hand, the MCD diet significantly upregulated the gene expression of the Tet enzymes, Tet2 and Tet3, and the base-excision-repair enzymes, thymine DNA glycosylase and apurinic/apyrimidinic-endonuclease 1. At the same time, the gene expression of DNA methyltransferase 1 and a, was also significantly increased by the MCD diet. These results suggest that the DNA methylation level is precisely regulated even when dietary methyl donors are restricted. Methyl-deficient diets are well known to induce oxidative stress and the oxidative-stress-induced DNA damage, 8-hydroxy-2'-deoxyguanosine (8OHdG), is reported to inhibit DNA methylation. In this study, we also clarified that the increase in 8OHdG number per DNA by the MCD diet is approximately 10 000 times smaller than the reduction in 5meC number, suggesting the contribution of 8OHdG formation to DNA methylation would not be significant.

Topics: 5-Methylcytosine; 8-Hydroxy-2'-Deoxyguanosine; Animals; Choline Deficiency; Cytosine; Deoxyguanosine; DNA Methylation; Fatty Liver; Gene Expression Regulation, Enzymologic; Liver; Male; Methionine; Mice, Inbred C57BL; Oxidative Stress; S-Adenosylhomocysteine; S-Adenosylmethionine

Arsenic, a carcinogen, is assumed to induce global DNA hypomethylation by consuming the universal methyl donor S-adenosylmethionine (SAM) in the body. A previous study reported that a methyl-deficient diet (MDD) with arsenic intake greatly reduced global DNA methylation (the content of 5-methylcytosine) in the liver of male C57BL/6 mice. In the present study, we investigated the DNA methylation level, SAM content, and expression of DNA methyltransferases (DNMTs) in the liver of male and female C57BL/6 mice fed a methyl-sufficient diet (MSD), an MDD, or an MDD + arsenic. The DNA methylation level was accurately determined by measuring the content of genomic 5-methyldeoxycytidine (5medC) by high-performance liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) using stable-isotope-labeled 5medC and deoxycytidine (dC) as internal standards. The results of this study revealed that while the MDD and arsenic tended to reduce the genomic 5meC content in the male mice livers, the MDD + arsenic significantly increased the 5meC content in the female mice livers. Another unexpected finding was the small differences in 5meC content among the groups. The MDD and MDD + arsenic suppressed DNMT1 expression only in the male mice livers. In contrast, SAM content was reduced by the MDD and MDD + arsenic only in the livers of female mice, showing that the changes in 5meC content were not attributable to SAM content. The sex-dependent changes in 5meC content induced by methyl deficiency and arsenic may be involved in differences in male and female susceptibility to diseases via epigenetic modification of physiological functions.

Topics: Animals; Arsenites; Carcinogens; Choline Deficiency; Deoxycytidine; Diet; DNA; DNA Methylation; DNA Modification Methylases; Female; Folic Acid Deficiency; Gene Expression Regulation, Enzymologic; Isoenzymes; Liver; Male; Methionine; Mice; Mice, Inbred C57BL; RNA, Messenger; S-Adenosylhomocysteine; S-Adenosylmethionine; Sex Characteristics; Sodium Compounds

Deficiency in nutritional determinants of homocysteine (HCY) metabolism, such as vitamin B(12) and folate, during pregnancy is known to influence HCY levels in the progeny, which in turn may exert adverse effects during development, including liver defects. Since short hypoxia has been shown to induce tolerance to subsequent stress in various cells including hepatocytes, and as vitamins B deficiency and hypoxic episodes may simultaneously occur in neonates, we aimed to investigate the influence of brief postnatal hypoxia (100% N(2) for 5 min) on the liver of rat pups born from dams fed a deficient regimen, i.e., depleted in vitamins B(12), B(2), folate, and choline. Four experimental groups were studied: control, hypoxia, deficiency, and hypoxia + deficiency. Although hypoxia transiently stimulated HCY catabolic pathways, it was associated with a progressive increase of hyperhomocysteinemia in deficient pups, with a fall of cystathionine beta-synthase activity at 21 days. At this stage, inducible NO synthase activity was dramatically increased and glutathione reductase decreased, specifically in the group combining hypoxia and deficiency. Also, hypoxia enhanced the deficiency-induced drop of the S-adenosylmethionine/S-adenosylhomocysteine ratio. In parallel, early exposure to the methyl-deficient regimen induced oxidative stress and led to hepatic steatosis, which was found to be more severe in pups additionally exposed to hypoxia. In conclusion, brief neonatal hypoxia may accentuate the long-term adverse effects of impaired HCY metabolism in the liver resulting from an inadequate nutritional regimen during pregnancy, and our data emphasize the importance of early factors on adult disease.

Topics: Animals; Animals, Newborn; Apoptosis; Cell Proliferation; Choline Deficiency; Cystathionine beta-Synthase; Female; Folic Acid; Folic Acid Deficiency; Food, Formulated; Glutathione; Homocysteine; Hypoxia; Liver; Nitric Oxide Synthase Type II; Pregnancy; Rats; Rats, Wistar; Riboflavin; Riboflavin Deficiency; S-Adenosylhomocysteine; S-Adenosylmethionine; Vitamin B 12; Vitamin B 12 Deficiency; Vitamin B Deficiency

Hepatic steatosis and fat malabsorption are common in cystic fibrosis (CF). Choline deficiency results in decreased phosphatidylcholine synthesis through the cytidine diphosphocholine-choline pathway and hepatic steatosis and in increased synthesis of phosphatidylcholine from phosphatidylethanolamine using methyl groups from S-adenosylmethionine. The intestinal absorption of phosphatidylcholine in CF is unknown.. The objective was to determine whether excretion of choline phosphoglyceride (phosphatidylcholine and lysophosphatidylcholine) is increased in CF and whether loss of fecal choline phosphoglyceride is associated with altered plasma methionine cycle metabolites.. A cross-sectional study involved 53 children with CF and 18 control children without CF. Blood was collected from all participants. A subset of 18 children with CF and 8 control children provided 72-h fecal samples and 5-d food records.. Fat absorption was significantly lower (x+/- SEM: 86.2 +/- 1.6% and 94.1 +/- 1.2%) and excretion of fecal fat (12.9 +/- 1.7 and 3.9 +/- 0.7 g/d), phospholipid (median: 130 and 47.7 mg/d), phosphatidylcholine (19.6 and 2.1 mg/d), and lysophosphatidylcholine (60.3 and 16.9 mg/d) was significantly higher in children with CF than in control children, respectively (P < 0.05). Choline phosphoglyceride excretion was positively correlated with plasma homocysteine and S-adenosylhomocysteine and inversely related with plasma methionine (P < 0.05).. Choline phosphoglyceride excretion is increased in children with CF and is associated with decreased plasma methionine and increased homocysteine and S-adenosylhomocysteine. These findings suggest choline depletion and an increased choline synthesis by S-adenosylmethionine-dependent methylation in CF, as well as a metabolic link between phosphatidylcholine metabolism and the methionine-homocysteine cycle in humans.

Topics: Case-Control Studies; Child; Choline Deficiency; Cross-Sectional Studies; Cystic Fibrosis; Diet Records; Dietary Fats; Feces; Female; Homocysteine; Humans; Intestinal Absorption; Lysophosphatidylcholines; Male; Phosphatidylcholines; S-Adenosylhomocysteine; S-Adenosylmethionine

Several epidemiological studies have suggested a modulatory effect of dietary folate intake on the risk of colorectal cancer. The molecular basis for this inverse association is not clearly understood, but may involve alterations in DNA methylation. In this study, we examined the levels of methylation intermediates [S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH)] and of global DNA methylation in the pre-neoplastic small intestine of Min (multiple intestinal neoplasia) mice. We also studied the effect of folate/choline deficiency on these parameters and on tumor multiplicity in this animal model. In folate-adequate Min mice, we identified positive linear correlations between SAM or SAH and tumor numbers (R(2) = 0.38, P < 0.005; R(2) = 0.26, P = 0.025, respectively). A positive correlation between global DNA hypomethylation and tumor multiplicity was also observed (R(2) = 0.29, P = 0.014). These three biochemical determinants (SAM, SAH and DNA hypomethylation) may, therefore, serve as early markers of cell transformation. Folate/choline deficiency, however, did not produce a consistent effect on tumor numbers in three separate experiments. As an increase in tumor numbers was observed only in folate- and choline-deficient mice with low levels of SAM and DNA hypomethylation, the modulatory role of folate may be dependent on the transformation state of the cell.

Topics: Animals; Biomarkers; Choline Deficiency; Diet; DNA Methylation; Folic Acid Deficiency; Intestinal Neoplasms; Methionine; Mice; Neoplasms; Precancerous Conditions; S-Adenosylhomocysteine; S-Adenosylmethionine

The purpose of the present experiments was to test the hypothesis that diethanolamine (DEA), an alkanolamine shown to be hepatocarcinogenic in mice, induces hepatic choline deficiency and to determine whether altered choline homeostasis was causally related to the carcinogenic outcome. To examine this hypothesis, the biochemical and histopathological changes in male B6C3F1 mice made choline deficient by dietary deprivation were first determined. Phosphocholine (PCho), the intracellular storage form of choline was severely depleted, decreasing to about 20% of control values with 2 weeks of dietary choline deficiency. Other metabolites, including choline, glycerophosphocholine (GPC), and phosphatidylcholine (PC) also decreased. Hepatic concentrations of S-adenosylmethionine (SAM) decreased, whereas levels of S-adenosylhomocysteine (SAH) increased. Despite these biochemical changes, fatty liver, which is often associated with choline deficiency, was not observed in the mice. The dose response, reversibility, and strain-dependence of the effects of DEA on choline metabolites were studied. B6C3F1 mice were dosed dermally with DEA (0, 10, 20, 40, 80, and 160 mg/kg) for 4 weeks (5 days/week). Control animals received either no treatment or dermal application of 95% ethanol (1.8 ml/kg). PCho was most sensitive to DEA treatment, decreasing at dosages of 20 mg/kg and higher and reaching a maximum 50% depletion at 160 mg/kg/day. GPC, choline, and PC also decreased in a dose-dependent manner. At 80 and 160 mg/kg/day, SAM levels decreased while SAH levels increased in liver. A no-observed effect level (NOEL) for DEA-induced changes in choline homeostasis was 10 mg/kg/day. Choline metabolites, SAM and SAH returned to control levels in mice dosed at 160 mg/kg for 4 weeks and allowed a 2-week recovery period prior to necropsy. In a manner similar to dietary choline deficiency, no fatty change was observed in the liver of DEA-treated mice. In C57BL/6 mice, DEA treatment (160 mg/kg) also decreased PCho concentrations, without affecting hepatic SAM levels, suggesting that strain-specific differences in intracellular methyl group regulation may influence carcinogenic outcome with DEA treatment. Finally, in addition to the direct effects of DEA on choline homeostasis, dermal application of 95% ethanol for 4 weeks decreased hepatic betaine levels, suggesting that the use of ethanol as a vehicle for dermal application of DEA may exacerbate or confound the biochemical actions of

Topics: Administration, Cutaneous; Animals; Betaine; Carcinogens; Choline Deficiency; Dose-Response Relationship, Drug; Drug Synergism; Ethanol; Ethanolamines; Glycerylphosphorylcholine; Liver; Male; Mice; Mice, Inbred C57BL; No-Observed-Adverse-Effect Level; Phosphatidylcholines; Phosphorylcholine; S-Adenosylhomocysteine; S-Adenosylmethionine; Species Specificity

The interactive effects of dietary methyl insufficiency and the estrogenic compound ethynylestradiol (EE) on the levels of S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH) were examined in the liver, lungs and pancreas of rats. In addition, such effects on the hepatic content of 5-methyl-deoxycytidine (5-MC) in nuclear DNA were determined. Castrated male Wistar/Furth rats were fed various levels of EE in either: (i) a complete, amino acid-defined diet (diet 1); (ii) the same diet lacking in choline and methionine and supplemented with 0.9% of DL-homocystine (equimolar to methionine) (diet 2); or (iii) diet 2 but only with 0.3% DL-homocystine (diet 2M). Methyl deficiency and EE each independently produced decreased weight gains and increased relative liver weights (liver weight relative to total body weight) compared with control animals. Livers from rats fed diets 2 and 2M without EE had lower levels of SAM and lower SAM:SAH ratios than did the livers from diet 1-fed rats not treated with EE. Hepatic SAM:SAH ratios in diet 1-fed rats were not altered by EE treatment. However, EE treatment increased the hepatic contents of SAM and restored the SAM:SAH levels to normal in rats fed diet 2 or 2M. The levels of SAM + SAH in the livers of rats fed the low homocystine diet (diet 2M) were less than in those fed either diet 1 or diet 2. Thus, the addition of EE at 10 p.p.m. gave protection against reduced levels of SAM, and reduced SAM:SAH ratios in the liver, but had little effect when added to the methyl-adequate diet. No differences in hepatic 5-MC levels were observed in any of the groups as a result of either methyl deficiency or EE treatment. Methyl deprivation alone caused no discernible difference in pancreatic SAM levels but did result in a significant rise in SAH levels and thus in decreased SAM:SAH ratios. EE had no consistent effect on pancreatic SAM, SAH or SAM:SAH ratios in any of the diet groups examined. Similarly, the chronic feeding of diet 2, diet 2M or of EE had no significant effect on the SAM contents of lungs, compared with the corresponding levels in control rats. The protection conferred by EE against SAM insufficiency in the livers of rats fed a methionine- and choline-deficient diet is consistent with the relative insensitivity of female rats to the hepatotoxicity of dietary methyl insufficiency.

Topics: Animals; Body Weight; Castration; Choline Deficiency; Ethinyl Estradiol; Liver; Lung; Male; Methionine; Organ Size; Pancreas; Rats; Rats, Inbred WF; S-Adenosylhomocysteine; S-Adenosylmethionine

Because of evidence linking methyl group deficiency and increased tumor formation in experimental animals, we explored other possible methods of producing a methyl group deficiency. Rats fed a low methionine diet lacking choline (MCD) were injected intraperitoneally daily for 3 wk with large doses of nicotinamide. Hepatic levels of lipids were elevated, S-adenosylmethionine (SAM) levels and the SAM:S-adenosylhomocysteine (SAH) ratio were decreased, and SAH level was not consistently changed. In livers of rats fed the MCD diet without folate (MCFD), lipids were also elevated and SAM reduced as compared to MCD-fed rats. In rats fed the MCD diet plus a methionine (Met) supplement (MCD + Met), hepatic SAM levels and the SAM:SAH ratio were higher and lipid levels lower than in MCD-fed rats, indicating that the MCD diet is marginally deficient in methyl donor groups. The injection of nicotinamide or the removal of folate from the MCD diet increased the severity of methyl donor deficiency, as shown by lower hepatic SAM levels and higher hepatic lipid levels. Hepatic glutathione levels were similar in MCD- and MCFD-fed rats and were lower than in rats fed the methionine-supplemented MCD diet or injected with nicotinamide.

Topics: Animals; Biomarkers; Choline Deficiency; Cysteine; Diet; Fatty Liver; Folic Acid Deficiency; Glutathione; Homocysteine; Lipids; Liver; Male; Methionine; Methylation; Niacinamide; Rats; Rats, Inbred Strains; S-Adenosylhomocysteine; S-Adenosylmethionine

Amino acid-defined diets deficient in methyl groups have been shown to result in a very high incidence of hepatocellular carcinoma. It has been suggested that this is a result of decreased levels of S-adenosylmethionine and the undermethylation of DNA. Accordingly, the enzyme glycine N-methyltransferase (GNMT, EC 2.1.1.20) may play a major role in maintaining the levels of S-adenosylmethionine in liver in response to changes in dietary methionine. The effect of methyl-deficient, amino acid-defined diets on GNMT activity and S-adenosylmethionine levels in rat liver was therefore investigated. When rats were fed a defined amino acid diet containing no choline in which homocysteine was substituted for the methionine of the control diet at an equimolar level, there was a rapid and marked decrease in growth rate in spite of the fact that the rats consumed 85% of the food eaten by control rats fed a nutritionally adequate, defined amino acid diet. The GNMT activity in livers of methyl-deficient rats decreased rapidly, but there was no difference in amount of GNMT protein as measured immunologically. In methyl-deficient rats, the levels of S-adenosylmethionine were maintained but the levels of S-adenosylhomocysteine were rapidly elevated compared to control values. These changes are consistent with the postulated role of GNMT in regulating methyl group metabolism.

Topics: Amino Acids; Animals; Carbon; Choline Deficiency; Diet; Glycine N-Methyltransferase; Liver; Male; Methionine; Methylation; Methyltransferases; Organ Size; Rats; Rats, Inbred F344; S-Adenosylhomocysteine; S-Adenosylmethionine; Weight Gain

Methotrexate (MTX) affects homocysteine (Hcy) metabolism in both cultured cells and patients, and this may be explained by a lack of the 5-methyltetrahydrofolate required for salvage of Hcy to methionine. We here report the effect of MTX on Hcy in serum and Hcy, S-adenosylhomocysteine (AdoHcy), S-adenosylmethionine (AdoMet) and reduced glutathione (GSH) in tissues of rats fed either a normal or a defined, choline-deficient (CD) diet. The CD diet alone did not affect the amounts of Hcy in serum and tissues, but decreased the amount of AdoMet in most tissues and increased the GSH content in the liver. MTX increased the amount of Hcy about 2-fold in serum, liver and kidney, and decreased the amount of AdoMet in liver and kidney, whereas the AdoHcy content in these tissues was essentially unaffected. Accordingly, both choline deficiency and MTX treatment reduced the AdoMet to AdoHcy ratio. The increased GSH in the liver induced by CD diet seemed to be abolished by MTX. In the spleen MTX had only a marginal effect on the Hcy and AdoMet content and decreased the GSH content. It is concluded that the increase in serum Hcy during MTX exposure probably reflects a disturbance of the Hcy metabolism in some tissues, and especially in the liver. Altered metabolism of other sulfur-containing metabolites may only partly be related to the inhibition of Hcy salvage, and some metabolic effects of MTX may be modulated by tissue-specific metabolic pathways as well as by the diet.

Topics: Analysis of Variance; Animals; Choline Deficiency; Diet; Glutathione; Homocysteine; Kidney; Liver; Male; Methotrexate; Rats; Rats, Inbred Strains; S-Adenosylhomocysteine; S-Adenosylmethionine; Spleen

A progressive decrease was observed in the 5-methyldeoxycytidine content of hepatic DNA in male F344 rats fed with a hepatocarcinogenic methyl-deficient diet. The same dietary regimen resulted in altered hepatic contents of S-adenosylmethionine, the methyl-donating species, and S-adenosylhomocysteine, an inhibitor of DNA methylase. The data indicate that this carcinogenic dietary manipulation is sufficient to alter a possible regulatory process, DNA methylation.

Topics: Animals; Cell Nucleus; Choline Deficiency; Deoxycytidine; Diet; Diethylnitrosamine; DNA; Liver; Liver Neoplasms; Male; Methionine; Methylation; Rats; Rats, Inbred F344; S-Adenosylhomocysteine; S-Adenosylmethionine

The levels of S-adenosylmethionine (AdoMet) and of S-adenosylhomocysteine (AdoHcy) as well as the ratio of AdoMet/AdoHcy were determined in the liver, lungs, testes and kidneys of weanling male rats fed a commercial chow diet or 5 different amino acid-defined diets for 1-5 weeks. The amino acid-defined diets used were as follows: diet 1, supplemented with methionine, choline, folic acid and vitamin B12; diet 2, deficient in methionine and choline; diet 3, deficient in methionine alone; diet 4, deficient in choline alone; diet 5, deficient in methionine, choline, folic acid and vitamin B12. All methionine-deficient diets were supplemented with an equimolar dose of its metabolic precursor, homocystine. The animals were sacrificed after 1, 3 and 5 weeks of treatment. In animals fed either the chow diet or diet 1, liver was the organ found to contain the highest levels of AdoMet and AdoHcy. Similarly, in animals fed diet 1 or chow, the testes and lungs contained the lowest level of AdoMet, while the lungs contained the lowest levels of AdoHcy. In general, the tissue levels of AdoHcy and AdoMet in rats fed diet 1 were very similar to the corresponding values found in chow-fed rats. Diet 1 feeding, however, led to higher hepatic levels of AdoMet than did the administration of the chow diet. The administration of the methyl-deficient diets generally led to decreased hepatic AdoMet contents at 3 and 5 weeks; the methyl-deficient diets also led to increased AdoHcy contents and decreased AdoMet:AdoHcy ratios when compared with diet 1. Linear regression analysis showed a significant direct correlation between the observed hepatic AdoMet levels and the methyl content of the diet as well as an inverse correlation between hepatic AdoHcy levels and dietary methyl contents. Unlike liver, the lung and testes did not show any decrease in AdoMet content following feeding of the methyl-deficient diets. These tissues did show, however, early significant increases in AdoHcy contents and corresponding decreases in the ratios of AdoMet:AdoHcy. These changes were found to be proportional to the dietary methyl content. The renal contents of AdoMet, AdoHcy and the ratio of AdoMet/AdoHcy were unaffected by any of the diets administered except for diet 5. The administration of diet 5 to rats for 5 weeks led to a significant increase in renal AdoHcy. These results provide evidence indicating that dietary methyl insufficiency may exert its role in carcinogenesis through a decreased ava

Topics: Animals; Body Weight; Choline Deficiency; Diet; Folic Acid Deficiency; Homocysteine; Kinetics; Liver; Lung; Male; Methionine; Methylation; Rats; Rats, Inbred F344; S-Adenosylhomocysteine; S-Adenosylmethionine; Testis; Tissue Distribution; Vitamin B 12 Deficiency

To produce a severe choline-methionine deficiency, a synthetic L-amino acid diet, free of choline, methionine, vitamin B12, and folic acid and supplemented with guanidoacetic acid, a methyl group acceptor, was fed to female rats for 2 weeks. The in vitro activity of liver microsomal phosphatidylethanolamine methyltransferase was stimulated twofold when compared with basal diet controls. The activity of choline phosphotransferase was depressed by 86%; thus, the contribution of the methyltransferase in the overall synthesis of phosphatidylcholine apparently increased. However, measurement of the in vivo methylation of phosphatidylethanolamine by incorporation of [1,2-14C]ethanolamine into phosphatidylcholine indicates that the methylation pathway is markedly depressed in methyl deficiency. Hepatic concentrations of the methyltransferase substrate, S-adenosylmethionine, and the inhibitory metabolite, S-adenosylhomocysteine, were significantly altered such that an unfavorable environment for methylation was present in the deficient animal. The ratio of substrate to inhibitor was depressed from 5.2:1 in the controls to 1.7:1 in the livers of methyl-depleted rats. Control of transmethylation in accordance with the availability of substrates, phosphatidylethanolamine, or S-adenosylmethionine, and the level of S-adenosylhomocysteine is discussed.

Topics: Animals; Choline Deficiency; Diacylglycerol Cholinephosphotransferase; Diet; Female; Liver; Methionine; Methylation; Methyltransferases; Phosphatidylcholines; Phosphatidylethanolamine N-Methyltransferase; Phosphatidylethanolamines; Rats; Rats, Inbred Strains; S-Adenosylhomocysteine; S-Adenosylmethionine