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Folate deficiency inhibits pancreatic amylase secretion in rats.

Previous studies have suggested that the metabolism of methyl groups is an important factor in the function of the exocrine pancreas. Ethionine, an inhibitor of cellular methylation reactions, produces hemorrhagic pancreatitis when administered to mice fed a choline-deficient diet. Glycine N-methyltransferase, an enzyme which regulates the ratio of S-adenosylmethionine to S-adenosylhomocysteine, is particularly abundant in the exocrine pancreas. Since de novo synthesis of methyl groups requires the participation of folate coenzymes, we investigated the effect of folate deficiency on pancreatic exocrine function. Rats were fed an amino acid-defined folate-deficient diet or the same diet supplemented with folate ad libitum. A third group received the folate supplemented diet pair-fed to the deficient group. After 3 and 5 wk, pancreatic amylase secretion was measured in perfused duodenal segments of anesthetized animals before and after cholecystokinin injection. Pancreatic secretion was significantly reduced in the deficient group compared with the pair-fed control group after 5 wk. These results indicate that severe folate deficiency impairs pancreatic exocrine function.

Aging↗

Pentoxifylline does not prevent neither liver damage nor early profibrogenic events in a rat model of non-alcoholic steatohepatitis.

BACKGROUND: Non-alcoholic steatohepatitis (NASH) is a metabolic disorder of the liver, which may evolve to fibrosis or cirrhosis. Pentoxifylline (PTX) has been postulated to act as an antifibrogenic agent able to inhibit hepatic stellate cell proliferation and collagen synthesis in vitro. Short-term studies suggest beneficial effects of PTX in experimental models of NASH. AIM: To study whether PTX can influence liver fibrogenesis in an animal model of NASH. METHODS: To induce NASH, a choline-deficient diet (CDD) was given to Sprague- Dawley rats for 8 weeks. Rats were allocated to two experimental groups one receiving PTX (9 mg/kg/day) in drinking water. Control rats received a choline-supplemented diet. Biochemical and histological evaluation of fatty liver was performed by conventional techniques. In addition, mRNA levels of Pro-collagen I and transforming growth factor beta-1 were assessed by semi-quantitative RT-PCR and stellate cell activation by alpha-actin immunofluorescence stain. RESULTS: After 8 weeks CDD induced a marked elevation of serum aminotransferases, a marked decrease in both hepatic and biliary glutathione and a severe fatty liver infiltration with mild histological inflammation and fibrosis. A significant increase in mRNA levels of both Pro-collagen I and TGFbeta-1 was seen after CDD feeding. No differences were seen between rats receiving PTX and rats on CDD diet alone with regard to the biochemical, morphological or molecular alterations induced by the CDD. CONCLUSION: PTX does influence neither liver injury nor early profibrogenic events in the CDD model of NASH.

Animals↗

Biosynthesis of carnitine and 4-N-trimethylaminobutyrate from lysine.

The conversion of l-[U-(14)C]lysine into carnitine was demonstrated in normal, choline-deficient and lysine-deficient rats. In other experiments in vivo radioactivity from l-[4,5-(3)H]lysine and dl-[6-(14)C]lysine was incorporated into carnitine; however, radioactivity from dl-[1-(14)C]lysine and dl-[2-(14)C]lysine was not incorporated. Administered l-[Me-(14)C]methionine labelled only the 4-N-methyl groups whereas lysine did not label these groups. Therefore lysine must be incorporated into the main carbon chain of carnitine. The methylation of lysine by a methionine source to form 6-N-trimethyl-lysine is postulated as an intermediate step in the biosynthesis of carnitine. Radioactive 4-N-trimethylaminobutyrate (butyrobetaine) was recovered from the urine of lysine-deficient rats injected with [U-(14)C]lysine. This lysine-derived label was incorporated only into the butyrate carbon chain. The specific radioactivity of the trimethylaminobutyrate was 12 times that of carnitine isolated from the urine or carcasses of the same animals. These data further support the idea that the last step in the formation of carnitine from lysine was the hydroxylation of trimethylaminobutyric acid, and are consistent with the following sequence: lysine+methionine --> 6-N-trimethyl-lysine --> --> 4-N-trimethylaminobutyrate --> carnitine.

Animals↗

Dietary choline requirement of juvenile red drum (Sciaenops ocellatus).

A 6-wk feeding experiment was conducted to determine the maximal dietary choline requirement of juvenile red drum (Sciaenops ocellatus). Diets were formulated to provide 35 g crude protein/ 100 g dry weight from solvent-extracted lyophilized red drum muscle and an amino acid premix. This premix provided methionine precisely at the minimum requirement determined for red drum so that potential synthesis of choline from methionine would be limited. Menhaden oil and dextrin were added to all diets to provide 13.8 kJ metabolizable energy/g diet as estimated by physiological fuel values. The diets were supplemented with choline chloride to provide 0, 250, 500, 750, 1000 and 1500 mg choline/kg diet. Each diet was fed to triplicate groups of red drum initially averaging 5.5 g/fish in a closed, recirculating system consisting of 110-L glass aquaria. Dietary choline concentration significantly (P < 0.05) affected weight gain, feed efficiency, total lipid in liver and plasma, as well as plasma cholesterol ester, triglyceride, cholesterol and phosphatidylcholine concentrations. Least-squares regression of these responses yielded requirements ranging from 330 to 676 mg choline/kg diet. Based on weight gain data, a maximal requirement estimate (+/- SEM) of 588 (+/- 35) mg choline/kg diet was established. Red drum appear to differ from other animals in regard to the response of total lipid in liver because fish fed choline-deficient diets had reduced liver lipid rather than lipid accumulation. Cultured red drum normally store high levels of lipid in the liver.

Animals↗

Formation of aliphatic amine precursors of N-nitrosodimethylamine after oral administration of choline and choline analogues in the rat.

Trimethylamine and dimethylamine are important precursors of N-nitrosodimethylamine, which is a potent carcinogen in a wide variety of animal species. Choline, a component of the normal human diet, is metabolized by bacteria within the intestine to form trimethylamine and dimethylamine. However, animals on a choline-free diet continue to excrete some trimethylamine and dimethylamine, suggesting that other dietary precursors of these methylamines might exist. To determine whether C-N bond cleavage by the intestinal bacteria is specific to the choline molecule, we measured monomethylamine, dimethylamine, trimethylamine and trimethylamine oxide excretion in rat urine after the administration of compounds that shared structural features with choline. Water, choline, dimethylaminoethanol, diethylaminoethanol, phosphocholine, betaine, carnitine, beta-methylcholine or dimethylaminoethyl chloride were administered by orogastric intubation, and the urine was collected for 24 hr. Administration of choline (15 mmol/kg body weight) resulted in increased urinary excretion of dimethylamine, trimethylamine and trimethylamine oxide (increases of approximately twofold, 500-fold and 50-fold, respectively). Of the administered choline, 12% was converted to trimethylamine or trimethylamine oxide and excreted in the urine within 24 hr. Phosphocholine administration resulted in similar increases in dimethylamine, trimethylamine and trimethylamine oxide excretion by rats. Modification of the ethyl-backbone or quaternary amine end of the choline molecule resulted in marked suppression of methylamine formation. Though administration of some analogues of choline (methylcholine, betaine and carnitine) resulted in the formation of small amounts of trimethylamine or trimethylamine oxide, and the administration of others (dimethylaminoethanol and dimethylaminoethyl chloride) resulted in the formation of some dimethylamine, the amounts formed were minimal compared with the amounts of trimethylamine and trimethylamine oxide formed after choline administration. Thus, of the many components of foods, only choline and its esters are likely to be significant substrates for trimethylamine and dimethylamine formation. How then can we explain the persistence of trimethylamine and dimethylamine excretion observed in choline-deficient rats? We suggest that endogenous (non-bacterial) synthesis of trimethylamine and dimethylamine occurs within some tissue of the rat.

Administration, Oral↗

Effects of chronic choline and lecithin on mouse hippocampal dendritic spine density.

Dendritic spines, which project from the dendrites of central neurons, are thought to contribute to the amount of contact area available for synaptic connections. The density of these spines has been found to correlate with learning and memory function, and there is a progressive decrease in dendritic spine density with aging. In addition, experimental animals given a choline-enriched diet have an increase in neocortical spine density compared to controls. In this study, the dendritic spine density of hippocampal pyramidal cells was examined in aged mice which had received life-long choline enriched, choline deficient or lecithin enriched diets. These treatments had no effect on hippocampal dendritic spine density compared to control. The results indicate that dietary supplementation may have different effects in different brain areas and that the relative increase in learning and memory function in aged animals given a choline or lecithin enriched diet is not due to an increase in hippocampal dendritic spine density.

Aging↗

Plasma choline concentrations in children requiring long-term home parenteral nutrition: a case control study.

BACKGROUND: Low plasma free choline concentration has been associated with elevated serum hepatic aminotransferase concentrations and hepatic steatosis in adults who need home parenteral nutrition (HPN). We sought to determine if plasma free choline is similarly reduced in children who need home total parenteral nutrition (TPN). METHODS: We compared the plasma free choline concentration in 21 children who required long-term HPN with 31 normal controls. Patients had received HPN for 75 +/- 13 (SD) months (range 3-206 months). All control children ingested a normal, mixed, nonvegetarian diet. RESULTS: The mean plasma free choline concentration in the children receiving HPN was significantly lower than normal children (6.6 +/- 4.3 vs 8.0 +/- 2.3 nmol/mL, p = .002). Plasma free choline concentration was correlated with age (r = -0.43, p = .049). Using multiple linear regression analysis for age, sex, and squared age (considered in order to account for possible nonlinearity between choline and age), HPN children showed a steady and significant decline in plasma free choline concentration with increased age at the rate of 0.03 nmol/mL per month. Plasma lipid bound choline concentration did not vary with age. No relationship was seen between either plasma free and lipid bound choline concentration and amount of daily IV lipid infusion. A significant negative correlation was observed between plasma free choline concentration and aspartate aminotransferase (AST) and alanine aminostransferase (ALT) (r = -0.72, p = .04 and r = -0.80, p = .02, respectively). CONCLUSION: Our data support the notion that patients who need long-term HPN without significant enteral feeding have a significant risk for the development of choline deficiency with its associated hepatic dysfunction.

Adolescent↗

Selectivity and sensitivity of changes in serum bile acids during induction of cirrhosis in rats.

Because some patients with cirrhosis have serum transaminase levels within the normal range, a prospective study was undertaken to determine whether the concentration of individual serum bile acids would be a sensitive indicator of development of cirrhosis. The choline-deficient rat has been used as a model for study of these changes. Using high-performance liquid chromatography, we measured the concentrations of individual serum bile acids at 3, 6, 10, 20 and 30 wk of dietary intake. Serum levels of total glycine- and taurine-conjugated bile acids were elevated at all stages tested as compared with levels in control groups (choline supplemented). Similarly, unconjugated bile acids and, particularly, cholic acid showed significantly higher levels at all stages except with the occurrence of cirrhosis at 30 wk, at which time there was a significantly lower level for unconjugated bile acids (0.48 +/- 0.11 vs. 1.40 +/- 0.36 in controls) and for cholic acid (0.17 +/- 0.05 vs. 0.91 +/- 0.39 in controls). The ratio of serum cholic acid to serum chenodeoxycholic acid changed in temporal relationship to progression in the histological lesions in livers of these rats. The ratio was at its highest at 78 +/- 3 at 3 wk (no histological change) and decreased with increasing time and changes in histological appearance until 30 wk, at which time it was down to 1.6 +/- 0.6. The routinely used markers of liver injury (serum ALT, alkaline phosphatase and bilirubin), however, did not match the progression of hepatic histological changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Alanine Transaminase↗

Alkylphosphocholines inhibit choline uptake and phosphatidylcholine biosynthesis in rat sympathetic neurons and impair axonal extension.

At least 50% of the major axonal membrane lipid, phosphatidylcholine, of rat sympathetic neurons is synthesized in situ in axons [Posse de Chaves, Vance, Campenot and Vance (1995) J. Cell Biol. 128, 913-918]. In the same study we reported that, in a choline-deficient model for neuron growth, phosphatidylcholine synthesis in cell bodies is neither necessary nor sufficient for growth of distal axons. Rather, the local synthesis of phosphatidylcholine in distal axons is required for normal axon growth. We have now used three alkylphosphocholines (hexadecylphosphocholine, dodecylphosphocholine and octadecylphosphocholine) as inhibitors of PtdCho biosynthesis in a compartmented model for culture of rat sympathetic neurons. The experiments reveal that alkylphosphocholines decrease the uptake of choline into these neurons and inhibit PtdCho synthesis, but not via an effect on the activity of the enzyme CTP: phosphocholine cytidylyltransferase. We also show that when the distal axons, but not the cell bodies, are exposed to alkylphosphocholines, axonal elongation is inhibited, which is consistent with the hypothesis that phosphatidylcholine synthesis in axons, but not in cell bodies, is required for axonal elongation. The inhibitory effect of alkylphosphocholines on axon growth is most likely not mediated via a decrease in the activity of protein kinase C, since when this enzyme activity is down-regulated by treatment of the cells with phorbol ester, the alkylphosphocholines retain their ability to inhibit axonal growth.

Animals↗

Effects of peroxidative stress and age on the concentration of a deoxyguanosine-malondialdehyde adduct in rat DNA.

The effect of age and peroxidative stress on the concentration of a deoxyguanosine malondialdehyde adduct (dG-MDA) in rat tissues was investigated. Vitamin E deficiency had no effect on the dG-MDA content of liver DNA in rats fed a diet containing 10% corn oil. When 2% cod liver oil was added to this diet, the dG-MDA content of liver DNA doubled in the positive controls fed a high level of vitamin E (100 ppm dl-alpha-tocopherol), and there was a further increase when vitamin E was deleted. Neither iron nitrilotriacetate administration nor choline deficiency had any effect on the dG-MDA content of liver DNA. Carbon tetrachloride had a lowering effect. The failure of iron or carbon tetrachloride administration and of vitamin E deficiency to increase liver dG-MDA is consistent with their failure in previous experiments to affect the urinary excretion of dG-MDA. In contrast, these forms of peroxidative stress produce large increments in the urinary excretion of MDA adducts with lysine, reflecting increased formation and degradation of MDA-modified proteins. DNA appears to be protected from modification by MDA produced at extranuclear sites. The frequency of dG-MDA in different tissues of 4-month-old rats varied markedly: brain >> liver > kidneys and testes. Higher concentrations of dG-MDA were found in the liver and kidneys, but not the testes, of 25-month-old rats. The determinants of the concentration of dG-MDA in DNA merit further investigation.

Aging↗

Phosphatidylcholine homeostasis and liver failure.

In mammals, the only endogenous pathway for choline biosynthesis is the methylation of phosphatidylethanolamine to phosphatidylcholine (PC) by phosphatidylethanolamine N-methyltransferase (PEMT) coupled to PC degradation. Complete choline deprivation in mice by feeding Pemt(-/-) mice a choline-deficient (CD) diet decreases hepatic PC by 50% and is lethal within 5 days. PC secretion into bile is mediated by a PC-specific flippase, multiple drug-resistant protein 2 (MDR2). Here, we report that mice that lack both PEMT and MDR2 and are fed a CD diet survive for >90 days. Unexpectedly, the amount of PC also decreases by 50% in the livers of Mdr2(-/-)/Pemt(-/-) mice. The Mdr2(-/-)/Pemt(-/-) mice adapt to the severe choline deprivation via choline recycling by induction of phospholipase A(2), choline kinase, and CTP:phosphocholine cytidylyltransferase activities and by a strikingly decreased expression of choline oxidase. The ability of Mdr2(-/-)/Pemt(-/-) mice to survive complete choline deprivation suggests that acute lethality in CD-Pemt(-/-) mice results from rapid depletion of hepatic PC via biliary secretion.

ATP Binding Cassette Transporter, Subfamily B↗

Placental thrombosis and spontaneous fetal death in mice deficient in ethanolamine kinase 2.

Ethanolamine kinase catalyzes the first step in the CDP-ethanolamine pathway for the formation of the major membrane phospholipid phosphatidylethanolamine (PtdEtn). In this work, the predicted Etnk2 cDNA was established as a soluble protein with ethanolamine-specific kinase activity that was most highly expressed in liver. Mice with an inactivated Etnk2 gene were derived, and its absence reduced the rate of PtdEtn synthesis from exogenous ethanolamine in hepatocytes. PtdEtn is a major precursor to phosphatidylcholine in liver; however, Etnk2(-/-) mice did not have reduced amounts of either PtdEtn or phosphatidylcholine or an altered phospholipid molecular species distribution. The knock-out animals were able to adapt to a choline-deficient diet. The Etnk2(-/-) mice exhibited a maternal-specific intrauterine growth retardation phenotype that resulted in a 33% reduction in litter size and frequent perinatal death. Histological analysis of pregnant Etnk2(-/-) females showed that fetal development failed at the late stage of pregnancy in a significant percentage of embryos because of the appearance of extensive placental thrombosis. These results illustrate a non-redundant role for EtnK2 expression in regulating placental hemostasis.

Amino Acid Sequence↗

Diethanolamine inhibits choline uptake and phosphatidylcholine synthesis in Chinese hamster ovary cells.

Diethanolamine (DEA), an alkanolamine used widely in industry, is hepatocarcinogenic in mice. The goal of this work was to determine whether DEA altered choline homeostasis in cultured cells, so as to ascertain whether the liver tumor response may be related to choline deficiency. CHO cells were cultured in Ham's F-12 medium containing DEA (0-1000 microgram/ml) and [(33)P]-phosphorus was used to label phospholipid pools. After 48 hours incubation, lipids were extracted and [(33)P]-labeled phospholipids were quantified by autoradiography after thin layer chromatographic separation. In control cells, phosphatidylcholine (PC) accounted for 51 +/- 0.7% of the total lipid (33)P incorporation. DEA had no effect on cell number or total phospholipid biosynthesis, but it significantly decreased the incorporation of (33)P into PC at concentrations >/=50 microgram/ml. DEA (>/=20 microgram/ml) also inhibited the uptake of [(3)H]-choline into CHO cells, with 95% inhibition observed at 250 microgram/ml. To determine whether supplemental choline prevented PC synthesis inhibition by DEA, CHO cells were cultured with or without excess choline (30 mM) and DEA (500 microgram/ml). DEA reduced PC synthesis to 27 +/- 3% of total phospholipids, but had no effect on PC synthesis in choline-supplemented cells. When [(14)C]-DEA was incubated with CHO cells, it was also incorporated into the phospholipid fraction. Collectively, these results indicate that DEA reversibly inhibits PC synthesis by blocking choline uptake and competing for utilization in the CDP-choline pathway in CHO cells.

Animals↗

Coordinate regulation of phosphatidylserine decarboxylase activity and phospholipid N-methylation in yeast.

Membranes isolated from Saccharomyces cerevisiae, strain ATCC 26615, catalyze the decarboxylation of exogenous phosphatidylserine added as an aqueous dispersion in detergent. Active preparations of the decarboxylase can be obtained by extracting salt-washed membranes with 0.5% Cutscum . The properties of the phosphatidylserine decarboxylase activity associated with a particulate fraction and the detergent extracts have been characterized by assaying the enzymatic conversion of exogenous [14C]phosphatidylserine to [14C]phosphatidylethanolamine. The yeast decarboxylase does not require a divalent cation and is inhibited by hydroxylamine and p-hydroxymercuribenzoate. The rate of decarboxylation of exogenous phosphatidylserine catalyzed by membranes prepared from cells grown in the presence of choline is reduced by approximately 60% compared to membranes from cells grown in a choline-deficient medium. Relatively smaller reductions in phosphatidylserine decarboxylase activity are also seen in cells grown in the presence of mono- or dimethylethanolamine. In vitro incorporation studies with [14C]serine demonstrate that endogenous, prelabeled phosphatidylserine can be utilized for the biosynthesis of phosphatidylcholine by the coupled action of the hydroxylamine-sensitive decarboxylase and the phospholipid N-methyltransferases in the presence of 2 mM S-adenosylmethionine. A similar comparative enzymatic study shows that the rates of synthesis and decarboxylation of [14C]phosphatidylserine, as well as phospholipid N-methylation, are lower for membranes prepared from cells grown in the presence of choline relative to identical preparations from cells grown in the absence of choline. These studies describe the properties of particulate and detergent-solubilized phosphatidylserine decarboxylase activity in S. cerevisiae and provide evidence that its activity is regulated in coordination with other enzymes in the pathway for phosphatidylcholine biosynthesis involving N-methylation.

Carboxy-Lyases↗

Novel surface attachment mechanism of the Streptococcus pneumoniae protein PspA.

Pneumococcal surface protein A (PspA) of Streptococcus pneumoniae has been found to utilize a novel mechanism for anchoring to the bacterial cell surface. In contrast to that of surface proteins from other gram-positive bacteria, PspA anchoring required choline-mediated interactions between the membrane-associated lipoteichoic acid and the C-terminal repeat region of PspA. Release of PspA from the cell surface could be effected by deletion of 5 of the 10 C-terminal repeat units, by high concentrations of choline, or by growth in choline-deficient medium. Other pneumococcal proteins, including autolysin, which has a similar C-terminal repeat region, were not released by these treatments. The attachment mechanism utilized by PspA thus appears to be uniquely adapted to exploit the unusual structure of the pneumococcal cell surface. Further, it has provided the means for rapid and simple isolation of immunogenic PspA from S. pneumoniae.

Amino Acid Sequence↗

Hepatocyte CYP2E1 overexpression and steatohepatitis lead to impaired hepatic insulin signaling.

Insulin resistance and increased cytochrome P450 2E1 (CYP2E1) expression are both associated with and mechanistically implicated in the development of nonalcoholic fatty liver disease. Although currently viewed as distinct factors, insulin resistance and CYP2E1 expression may be interrelated through the ability of CYP2E1-induced oxidant stress to impair hepatic insulin signaling. To test this possibility, the effects of in vitro and in vivo CYP2E1 overexpression on hepatocyte insulin signaling were examined. CYP2E1 overexpression in a hepatocyte cell line decreased tyrosine phosphorylation of insulin receptor substrate (IRS)-1 and IRS-2 in response to insulin. CYP2E1 overexpression was also associated with increased inhibitory serine 307 and 636/639 IRS-1 phosphorylation. In parallel, the effects of insulin on Akt activation, glycogen synthase kinase 3, and FoxO1a phosphorylation, and glucose secretion were all significantly decreased in CYP2E1 overexpressing cells. This inhibition of insulin signaling by CYP2E1 overexpression was partially c-Jun N-terminal kinase dependent. In the methionine- and choline-deficient diet mouse model of steatohepatitis with CYP2E1 overexpression, insulin-induced IRS-1, IRS-2, and Akt phosphorylation were similarly decreased. These findings indicate that increased hepatocyte CYP2E1 expression and the presence of steatohepatitis result in the down-regulation of insulin signaling, potentially contributing to the insulin resistance associated with nonalcoholic fatty liver disease.

Adenoviridae↗

Maternal dietary choline availability alters mitosis, apoptosis and the localization of TOAD-64 protein in the developing fetal rat septum.

Maternal changes in dietary choline availability alter brain biochemistry and hippocampal development in the offspring resulting in lifelong behavioral changes in the offspring. In order to better understand the relationship between maternal diet, brain cytoarchitecture and behavior, we investigated the effects of choline availability on cell proliferation, apoptosis and differentiation in the fetal rat brain septum. Timed-pregnant rats on day E12 were fed AIN-76 diet with varying levels of dietary choline for 6 days. We found that choline deficiency (CD) significantly decreased the rate of mitosis in the progenitor neuroepithelium adjacent to the septum. In addition, we found an increased number of apoptotic cells in the septum of CD animals compared to controls (3.5+/-0.5 vs. 1.7+/-0.5 apoptotic cells per section; p<0.05). However, CD had no effect on apoptosis in the indusium griseum (IG), a region of cortex dorsal to the septum. Using an unbiased image analysis method and a monoclonal antibody we found a decreased expression of the TOAD-64 kDa protein, a marker of commitment to neuronal differentiation during fetal development, in the dorsal lateral septum of CD animals. CD also decreased the expression of TOAD-64 kDa protein in the IG and cortical plate adjacent to the septum. These results show that dietary choline availability during pregnancy alters the timing of mitosis, apoptosis and the early commitment to neuronal differentiation by progenitor cells in regions of the fetal brain septum, as well as hippocampus, two brain regions known to be associated with learning and memory.

Animals↗