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Lewis ED, Kosik SJ, Zhao YY, Jacobs RL, Curtis JM, Field CJ. Total choline and choline-containing moieties of commercially available pulses. Plant Foods Hum Nutr 2014; 69:115-21. [PMID: 24682658 DOI: 10.1007/s11130-014-0412-2] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Estimating dietary choline intake can be challenging due to missing foods in the current United States Department of Agriculture (USDA) database. The objectives of the study were to quantify the choline-containing moieties and the total choline content of a variety of pulses available in North America and use the expanded compositional database to determine the potential contribution of pulses to dietary choline intake. Commonly consumed pulses (n = 32) were analyzed by hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC LC-MS/MS) and compared to the current USDA database. Cooking was found to reduce the relative percent from free choline and increased the contribution of phosphatidylcholine to total choline for most pulses (P < 0.05). Using the expanded database to estimate choline content of recipes using pulses as meat alternatives, resulted in a different estimation of choline content per serving (±30%), compared to the USDA database. These results suggest that when pulses are a large part of a meal or diet, the use of accurate food composition data should be used.
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Affiliation(s)
- Erin D Lewis
- Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB, Canada
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Abstract
Folate is an essential B vitamin required for the maintenance of AdoMet-dependent methylation. The liver is responsible for many methylation reactions that are used for post-translational modification of proteins, methylation of DNA, and the synthesis of hormones, creatine, carnitine, and phosphatidylcholine. Conditions where methylation capacity is compromised, including folate deficiency, are associated with impaired phosphatidylcholine synthesis resulting in non-alcoholic fatty liver disease and steatohepatitis. In addition, folate intake and folate status have been associated with changes in the expression of genes involved in lipid metabolism, obesity, and metabolic syndrome. In this review, we provide insight on the relationship between folate and lipid metabolism, and an outlook for the future of lipid-related folate research.
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Affiliation(s)
| | | | | | - René L Jacobs
- *Address for correspondence: René L. Jacobs, Ph.D., Department of Agricultural, Food & Nutritional Science, 4-002 Li Ka Shing (LKS) Centre for Health Research Innovation, University of Alberta, Edmonton, AB T6G 2E1, Canada. Fax: +780-492-9270; E-mail:
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Jacome-Sosa MM, Borthwick F, Mangat R, Uwiera R, Reaney MJ, Shen J, Quiroga AD, Jacobs RL, Lehner R, Proctor SD, Nelson RC. Diets enriched in trans-11 vaccenic acid alleviate ectopic lipid accumulation in a rat model of NAFLD and metabolic syndrome. J Nutr Biochem 2014; 25:692-701. [PMID: 24775093 DOI: 10.1016/j.jnutbio.2014.02.011] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2013] [Revised: 02/02/2014] [Accepted: 02/12/2014] [Indexed: 12/19/2022]
Abstract
Trans11-18:1 (vaccenic acid, VA) is one of the most predominant naturally occurring trans fats in our food chain and has recently been shown to exert hypolipidemic effects in animal models. In this study, we reveal new mechanism(s) by which VA can alter body fat distribution, energy utilization and dysfunctional lipid metabolism in an animal model of obesity displaying features of the metabolic syndrome (MetS). Obese JCR:LA-cp rats were assigned to a control diet that included dairy-derived fat or the control diet supplemented with 1% VA. VA reduced total body fat (-6%), stimulated adipose tissue redistribution [reduced mesenteric fat (-17%) while increasing inguinal fat mass (29%)] and decreased adipocyte size (-44%) versus control rats. VA supplementation also increased metabolic rate (7%) concomitantly with an increased preference for whole-body glucose utilization for oxidation and increased insulin sensitivity [lower HOMA-IR (-59%)]. Further, VA decreased nonalcoholic fatty liver disease activity scores (-34%) and reduced hepatic (-27%) and intestinal (-39%) triglyceride secretion relative to control diet, while exerting differential transcriptional regulation of SREBP1 and FAS amongst other key genes in the liver and the intestine. Adding VA to dairy fat alleviates features of MetS potentially by remodeling adipose tissue and attenuating ectopic lipid accumulation in a rat model of obesity and MetS. Increasing VA content in the diet (naturally or by fortification) may be a useful approach to maximize the health value of dairy-derived fats.
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Affiliation(s)
- M Miriam Jacome-Sosa
- Metabolic and Cardiovascular Disease Laboratory, Group on Molecular and Cell Biology of Lipids, Alberta Diabetes and Mazankowski Heart Institutes, University of Alberta, Edmonton, AB, Canada
| | - Faye Borthwick
- Metabolic and Cardiovascular Disease Laboratory, Group on Molecular and Cell Biology of Lipids, Alberta Diabetes and Mazankowski Heart Institutes, University of Alberta, Edmonton, AB, Canada
| | - Rabban Mangat
- Metabolic and Cardiovascular Disease Laboratory, Group on Molecular and Cell Biology of Lipids, Alberta Diabetes and Mazankowski Heart Institutes, University of Alberta, Edmonton, AB, Canada
| | - Richard Uwiera
- Department of Agricultural Food and Nutritional Science, University of Alberta, Edmonton, AB, Canada
| | - Martin J Reaney
- Department of Plant Science, University of Saskatchewan, Saskatoon, SK, Canada
| | - Jianheng Shen
- Department of Plant Science, University of Saskatchewan, Saskatoon, SK, Canada
| | - Ariel D Quiroga
- Department of Pediatrics, Group on Molecular and Cell Biology of Lipids, University of Alberta, AB, Canada
| | - René L Jacobs
- Metabolic and Cardiovascular Disease Laboratory, Group on Molecular and Cell Biology of Lipids, Alberta Diabetes and Mazankowski Heart Institutes, University of Alberta, Edmonton, AB, Canada
| | - Richard Lehner
- Department of Pediatrics, Group on Molecular and Cell Biology of Lipids, University of Alberta, AB, Canada
| | - Spencer D Proctor
- Metabolic and Cardiovascular Disease Laboratory, Group on Molecular and Cell Biology of Lipids, Alberta Diabetes and Mazankowski Heart Institutes, University of Alberta, Edmonton, AB, Canada.
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Al Rajabi A, Castro GSF, da Silva RP, Nelson RC, Thiesen A, Vannucchi H, Vine DF, Proctor SD, Field CJ, Curtis JM, Jacobs RL. Choline supplementation protects against liver damage by normalizing cholesterol metabolism in Pemt/Ldlr knockout mice fed a high-fat diet. J Nutr 2014; 144:252-7. [PMID: 24368431 DOI: 10.3945/jn.113.185389] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Dietary choline is required for proper structure and dynamics of cell membranes, lipoprotein synthesis, and methyl-group metabolism. In mammals, choline is synthesized via phosphatidylethanolamine N-methyltransferase (Pemt), which converts phosphatidylethanolamine to phosphatidylcholine. Pemt(-/-) mice have impaired VLDL secretion and developed fatty liver when fed a high-fat (HF) diet. Because of the reduction in plasma lipids, Pemt(-/-)/low-density lipoprotein receptor knockout (Ldlr(-/-)) mice are protected from atherosclerosis. The goal of this study was to investigate the importance of dietary choline in the metabolic phenotype of Pemt(-/-)/Ldlr(-/-) male mice. At 10-12 wk of age, Pemt(+/+)/Ldlr(-/-) (HF(+/+)) and half of the Pemt(-/-)/Ldlr(-/-) (HF(-/-)) mice were fed an HF diet with normal (1.3 g/kg) choline. The remaining Pemt(-/-)/Ldlr(-/-) mice were fed an HF diet supplemented (5 g/kg) with choline (HFCS(-/-) mice). The HF diet contained 60% of calories from fat and 1% cholesterol, and the mice were fed for 16 d. HF(-/-) mice lost weight and developed hepatomegaly, steatohepatitis, and liver damage. Hepatic concentrations of free cholesterol, cholesterol-esters, and triglyceride (TG) were elevated by 30%, 1.1-fold and 3.1-fold, respectively, in HF(-/-) compared with HF(+/+) mice. Choline supplementation normalized hepatic cholesterol, but not TG, and dramatically improved liver function. The expression of genes involved in cholesterol transport and esterification increased by 50% to 5.6-fold in HF(-/-) mice when compared with HF(+/+) mice. Markers of macrophages, oxidative stress, and fibrosis were elevated in the HF(-/-) mice. Choline supplementation normalized the expression of these genes. In conclusion, HF(-/-) mice develop liver failure associated with altered cholesterol metabolism when fed an HF/normal choline diet. Choline supplementation normalized cholesterol metabolism, which was sufficient to prevent nonalcoholic steatohepatitis development and improve liver function. Our data suggest that choline can promote liver health by maintaining cholesterol homeostasis.
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Affiliation(s)
- Ala Al Rajabi
- Departments of Agricultural, Food, and Nutritional Science, and
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Jacobs RL, van der Veen JN, Vance DE. Finding the balance: the role of S-adenosylmethionine and phosphatidylcholine metabolism in development of nonalcoholic fatty liver disease. Hepatology 2013; 58:1207-9. [PMID: 23703836 DOI: 10.1002/hep.26499] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/11/2013] [Revised: 04/17/2013] [Accepted: 04/21/2013] [Indexed: 12/23/2022]
Affiliation(s)
- René L Jacobs
- Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada; Group on the Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, Alberta, Canada
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Lewis ED, Goruk S, Curtis JM, Jacobs RL, Field CJ. Supplementation with phosphatidylcholine during suckling improves the immune response of the offspring. FASEB J 2013. [DOI: 10.1096/fasebj.27.1_supplement.123.8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Erin Diane Lewis
- Agricultural, Food & Nutritional ScienceUniversity of AlbertaEdmontonABCanada
| | - Susan Goruk
- Agricultural, Food & Nutritional ScienceUniversity of AlbertaEdmontonABCanada
| | - Jonathan M Curtis
- Agricultural, Food & Nutritional ScienceUniversity of AlbertaEdmontonABCanada
| | - René L Jacobs
- Agricultural, Food & Nutritional ScienceUniversity of AlbertaEdmontonABCanada
| | - Catherine J Field
- Agricultural, Food & Nutritional ScienceUniversity of AlbertaEdmontonABCanada
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Yu Z, Thomson ELS, Liu J, Dennis JJ, Jacobs RL, Kaufman WR. Antimicrobial activity in the egg wax of the tick Amblyomma hebraeum (Acari: Ixodidae) is associated with free fatty acids C16:1 and C18:2. Exp Appl Acarol 2012; 58:453-470. [PMID: 22692850 DOI: 10.1007/s10493-012-9586-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2012] [Accepted: 05/26/2012] [Indexed: 06/01/2023]
Abstract
Untreated eggs of the tick Amblyomma hebraeum Koch (Acari: Ixodidae) exhibited antimicrobial activity (AMA) against Gram-negative but not Gram-positive bacteria; eggs denuded of wax by solvent extraction showed no AMA. The unfractionated egg wax extract, however, showed AMA against Gram-positive but not Gram-negative bacteria, as also shown by Arrieta et al. (Exp Appl Acarol 39: 297-313, 2006). In this study we partitioned the egg wax into various fractions, using a variety of techniques, analyzed their compositions, and tested them for AMA. The crude aqueous extract exhibited AMA. However, although more than 30 metabolites were identified in this extract by nuclear magnetic resonance analysis, none of them seemed likely to be responsible for the observed AMA. In the crude organic extract, cholesterol esters were the most abundant lipids, but were devoid of AMA. Fatty acids (FAs), with chain lengths between C13 and C26 were the next most abundant lipids. After lipid fractionation and gas chromatography/mass spectroscopy, free FAs, especially C16:1 and C18:2, accounted for most of the AMA in the organic extract. The material responsible for AMA in the crude aqueous extract remains unidentified. No AMA was detected in the intracellular contents of untreated eggs.
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Affiliation(s)
- Zhijun Yu
- College of Life Sciences, Hebei Normal University, Shijiazhuang, 050016 Hebei, China
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58
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Xiong Y, Zhao YY, Goruk S, Oilund K, Field CJ, Jacobs RL, Curtis JM. Validation of an LC–MS/MS method for the quantification of choline-related compounds and phospholipids in foods and tissues. J Chromatogr B Analyt Technol Biomed Life Sci 2012; 911:170-9. [DOI: 10.1016/j.jchromb.2012.10.038] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2012] [Revised: 09/14/2012] [Accepted: 10/29/2012] [Indexed: 10/27/2022]
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Wu G, Zhang L, Li T, Zuniga A, Lopaschuk GD, Li L, Jacobs RL, Vance DE. Choline supplementation promotes hepatic insulin resistance in phosphatidylethanolamine N-methyltransferase-deficient mice via increased glucagon action. J Biol Chem 2012. [PMID: 23179947 DOI: 10.1074/jbc.m112.415117] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Biosynthesis of hepatic choline via phosphatidylethanolamine N-methyltransferase (PEMT) plays an important role in the development of type 2 diabetes and obesity. We investigated the mechanism(s) by which choline modulates insulin sensitivity. PEMT wild-type (Pemt(+/+)) and knock-out (Pemt(-/-)) mice received either a high fat diet (HF; 60% kcal of fat) or a high fat, high choline diet (HFHC; 4 g of choline/kg of HF diet) for 1 week. Hepatic insulin signaling and glucose and lipid homeostasis were investigated. Glucose and insulin intolerance occurred in Pemt(-/-) mice fed the HFHC diet, but not in their Pemt(-/-) littermates fed the HF diet. Plasma glucagon was elevated in Pemt(-/-) mice fed the HFHC diet compared with Pemt(-/-) mice fed the HF diet, concomitant with increased hepatic expression of glucagon receptor, phosphorylated AMP-activated protein kinase (AMPK), and phosphorylated insulin receptor substrate 1 at serine 307 (IRS1-s307). Gluconeogenesis and mitochondrial oxidative stress were markedly enhanced, whereas glucose oxidation and triacylglycerol biosynthesis were diminished in Pemt(-/-) mice fed the HFHC diet. A glucagon receptor antagonist (2-aminobenzimidazole) attenuated choline-induced hyperglycemia and insulin intolerance and blunted up-regulation of phosphorylated AMPK and IRS1-s307. Choline induces glucose and insulin intolerance in Pemt(-/-) mice through modulating plasma glucagon and its action in liver.
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Affiliation(s)
- Gengshu Wu
- Group on the Molecular and Cell Biology of Lipids and Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2S2
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60
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Ling J, Zhu LF, Vance DE, Jacobs RL. Impaired phosphatidylcholine biosynthesis does not attenuate liver regeneration after 70% partial hepatectomy in hepatic CTP:phosphocholine cytidylyltransferase-α deficient mice. Can J Physiol Pharmacol 2012; 90:1403-12. [DOI: 10.1139/y2012-116] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Phosphatidylcholine (PC) is the major component of mammalian membranes, and the induction of PC biosynthesis has been shown to be an essential step in cell proliferation in various cell lines. Cytidine triphosphate (CTP):phosphocholine cytidylyltransferase α (CTα) regulates the primary pathway of PC biosynthesis in the liver. The targeted disruption of CTα in murine liver (LCTα−/− mice) decreases hepatic PC mass and the number of cells in the liver, suggesting CTα as an important factor for hepatocyte proliferation. To elucidate the role of CTα in hepatic cell division in vivo, we monitored liver regeneration after 70% partial hepatectomy in LCTα−/− and loxP flanked (floxed) LCTα (control) mice. To our surprise, liver re-growth, DNA synthesis, and PC mass after surgery were not impaired in LCTα−/− mice, despite reduced total PC synthesis. Furthermore, PC synthesis in the control mice was not induced after 70% partial hepatectomy. We conclude that CTα is not essential for proliferation of hepatocytes in vivo, and that basal hepatic PC biosynthesis is sufficient to sustain regeneration after 70% partial hepatectomy.
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Affiliation(s)
- Ji Ling
- Group on the Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, AB T6G 2S2, Canada
- Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2S2, Canada
| | - Lin Fu Zhu
- Department of Surgery, University of Alberta, Edmonton, AB T6G 2S2, Canada
| | - Dennis E. Vance
- Group on the Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, AB T6G 2S2, Canada
- Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2S2, Canada
| | - René L. Jacobs
- Group on the Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, AB T6G 2S2, Canada
- Department of Agricultural, Food, and Nutritional Science, University of Alberta, Edmonton, AB T6G 2S2, Canada
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Ling J, Chaba T, Zhu LF, Jacobs RL, Vance DE. Hepatic ratio of phosphatidylcholine to phosphatidylethanolamine predicts survival after partial hepatectomy in mice. Hepatology 2012; 55:1094-102. [PMID: 22095799 DOI: 10.1002/hep.24782] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/26/2011] [Accepted: 10/11/2011] [Indexed: 01/12/2023]
Abstract
UNLABELLED A major predictor of failed liver resection and transplantation is nonalcoholic fatty liver disease (NAFLD). NAFLD is linked to a wide spectrum of diseases including obesity and diabetes that are increasingly prevalent in Western populations. Thus, it is important to develop therapies aimed at improving posthepatectomy outcomes in patients with NAFLD, as well as to improve the evaluation of patients slated for hepatic surgery. Decreased hepatic phosphatidylcholine (PC) content and decreased ratio of hepatic PC to phosphatidylethanolamine (PE) have previously been linked to NAFLD. To determine if decreased hepatic PC/PE could predict survival after hepatectomy, we used mouse models lacking key enzymes in PC biosynthesis, namely, phosphatidylethanolamine N-methyltransferase and hepatic-specific CTP:phosphocholine cytidylyltransferase α. These mice were fed a high-fat diet to induce NAFLD. We then performed a 70% partial hepatectomy and monitored postoperative survival. We identified hepatic PC/PE to be inversely correlated with the development of steatosis and inflammation in the progression of NAFLD. Decreased hepatic PC/PE before surgery was also strongly associated with decreased rates of survival after partial hepatectomy. Choline supplementation to the diet increased hepatic PC/PE in Pemt(-/-) mice with NAFLD, decreased inflammation, and increased the survival rate after partial hepatectomy. CONCLUSION Decreased hepatic PC/PE is a predictor of NAFLD and survival following partial hepatectomy. Choline supplementation may serve as a potential therapy to prevent the progression of NAFLD and to improve postoperative outcome after liver surgery.
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Affiliation(s)
- Ji Ling
- Group on the Molecular and Cell Biology of Lipids, Department of Biochemistry, University of Alberta, Edmonton, AB, Canada
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Wu G, Zhang L, Li T, Lopaschuk G, Vance DE, Jacobs RL. Choline Deficiency Attenuates Body Weight Gain and Improves Glucose Tolerance in ob/ob Mice. J Obes 2012; 2012:319172. [PMID: 22778916 PMCID: PMC3385711 DOI: 10.1155/2012/319172] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/01/2011] [Revised: 02/02/2012] [Accepted: 02/16/2012] [Indexed: 02/07/2023] Open
Abstract
Previous studies demonstrated that choline supply is directly linked to high-fat-diet-induced obesity and insulin resistance in mice. The aim of this study was to evaluate if choline supply could also modulate obesity and insulin resistance caused by a genetic defect. Eight-week-old male ob/ob mice were fed for two months with either choline-deficient or choline-supplemented diet. Tissue weight including fat mass and lean mass was assessed. Intracellular signaling, plasma glucagon and insulin, and glucose and insulin tolerance tests were also investigated. The choline-deficient diet slowed body weight gain and decreased fat mass. Choline deficiency also decreased plasma glucose level and improved glucose and insulin tolerance although fatty liver was exacerbated. Increased adipose lipolytic activity, decreased plasma glucagon and reduced expression of hepatic glucagon receptor were also observed with the choline-deficient diet. Our results demonstrate that a choline-deficient diet can decrease fat mass and improve glucose tolerance in obese and diabetic mice caused by a genetic defect.
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Affiliation(s)
- Gengshu Wu
- Group on the Molecular and Cell Biology of Lipids and Department of Biochemistry, University of Alberta, Edmonton, AB, Canada T6G 2S2
| | - Liyan Zhang
- Cardiovascular Research Group, University of Alberta, Edmonton, AB, Canada T6G 2S2
| | - Tete Li
- Group on the Molecular and Cell Biology of Lipids and Department of Biochemistry, University of Alberta, Edmonton, AB, Canada T6G 2S2
| | - Gary Lopaschuk
- Cardiovascular Research Group, University of Alberta, Edmonton, AB, Canada T6G 2S2
| | - Dennis E. Vance
- Group on the Molecular and Cell Biology of Lipids and Department of Biochemistry, University of Alberta, Edmonton, AB, Canada T6G 2S2
- *Dennis E. Vance:
| | - René L. Jacobs
- Department of Agricultural, Food and Nutritional Sciences, University of Alberta, Edmonton, AB, Canada T6G 2S2
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63
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Walker AK, Jacobs RL, Watts JL, Rottiers V, Jiang K, Finnegan DM, Shioda T, Hansen M, Yang F, Niebergall LJ, Vance DE, Tzoneva M, Hart AC, Näär AM. A conserved SREBP-1/phosphatidylcholine feedback circuit regulates lipogenesis in metazoans. Cell 2011; 147:840-52. [PMID: 22035958 DOI: 10.1016/j.cell.2011.09.045] [Citation(s) in RCA: 310] [Impact Index Per Article: 23.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2011] [Revised: 06/14/2011] [Accepted: 09/19/2011] [Indexed: 12/17/2022]
Abstract
Sterol regulatory element-binding proteins (SREBPs) activate genes involved in the synthesis and trafficking of cholesterol and other lipids and are critical for maintaining lipid homeostasis. Aberrant SREBP activity, however, can contribute to obesity, fatty liver disease, and insulin resistance, hallmarks of metabolic syndrome. Our studies identify a conserved regulatory circuit in which SREBP-1 controls genes in the one-carbon cycle, which produces the methyl donor S-adenosylmethionine (SAMe). Methylation is critical for the synthesis of phosphatidylcholine (PC), a major membrane component, and we find that blocking SAMe or PC synthesis in C. elegans, mouse liver, and human cells causes elevated SREBP-1-dependent transcription and lipid droplet accumulation. Distinct from negative regulation of SREBP-2 by cholesterol, our data suggest a feedback mechanism whereby maturation of nuclear, transcriptionally active SREBP-1 is controlled by levels of PC. Thus, nutritional or genetic conditions limiting SAMe or PC production may activate SREBP-1, contributing to human metabolic disorders.
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Affiliation(s)
- Amy K Walker
- Massachusetts General Hospital Cancer Center, Building 149, 13th Street, Charlestown, MA 02129, USA.
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64
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Deminice R, da Silva RP, Lamarre SG, Brown C, Furey GN, McCarter SA, Jordao AA, Kelly KB, King-Jones K, Jacobs RL, Brosnan ME, Brosnan JT. Creatine supplementation prevents the accumulation of fat in the livers of rats fed a high-fat diet. J Nutr 2011; 141:1799-804. [PMID: 21880953 DOI: 10.3945/jn.111.144857] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The aim of the present study was to examine the effects of creatine supplementation on liver fat accumulation induced by a high-fat diet in rats. Rats were fed 1 of 3 different diets for 3 wk: a control liquid diet (C), a high-fat liquid diet (HF), or a high-fat liquid diet supplemented with creatine (HFC). The C and HF diets contained, respectively, 35 and 71% of energy derived from fat. Creatine supplementation involved the addition of 1% (wt:v) of creatine monohydrate to the liquid diet. The HF diet increased total liver fat concentration, liver TG, and liver TBARS and decreased the hepatic S-adenosylmethionine (SAM) concentration. Creatine supplementation normalized all of these perturbations. Creatine supplementation significantly decreased the renal activity of l-arginine:glycine amidinotransferase and plasma guanidinoacetate and prevented the decrease in hepatic SAM concentration in rats fed the HF diet. However, there was no change in either the phosphatidylcholine:phosphatidylethanolamine (PE) ratio or PE N-methyltransferase activity. The HF diet decreased mRNA for PPARα as well as 2 of its targets, carnitine palmitoyltransferase and long-chain acylCoA dehydrogenase. Creatine supplementation normalized these mRNA levels. In conclusion, creatine supplementation prevented the fatty liver induced by feeding rats a HF diet, probably by normalization of the expression of key genes of β-oxidation.
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Affiliation(s)
- Rafael Deminice
- Department of Biochemistry, Memorial University of Newfoundland, St. John's, Canada
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Frier BC, Jacobs RL, Wright DC. Interactions between the consumption of a high-fat diet and fasting in the regulation of fatty acid oxidation enzyme gene expression: an evaluation of potential mechanisms. Am J Physiol Regul Integr Comp Physiol 2011; 300:R212-21. [DOI: 10.1152/ajpregu.00367.2010] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The consumption of high-fat diets (HFDs) and fasting are known to increase the expression of enzymes involved in fatty acid oxidation (FAO). However, it has been reported that the ability of physiological stressors to induce enzymes of FAO in skeletal muscle is blunted with obesity. In this regard, we sought to explore the effects and potential mechanisms of an HFD on the expression of FAO enzymes in the fed and fasted state. The consumption of an HFD increased the mRNA expression or protein content of medium-chain acyl-CoA dehydrogenase (MCAD), uncoupling protein-3 (UCP3), and pyruvate dehydrogenase kinase 4 (PDK4) in the fed state. Fasting increased the mRNA expression of PDK4, MCAD, and UCP-3, and the protein content of UCP-3 in chow but not HFD rats. HFDs did not increase carnitine palmitoyl transfer-1 (CPT-1) mRNA levels in the fed state and the effects of fasting were markedly reduced compared with chow-fed rats. The expression of peroxisome-proliferator-activated receptor-γ coactivator-1β (PGC-1β) was increased in muscle from HFD rats in the fed state, while PGC-1-related coactivator (PRC) was increased with fasting in chow-fed but not HFD rats. Plasma fatty acid levels were elevated in the fed state from HFD rats but not increased further with fasting, whereas fasting increased plasma fatty acids in chow-fed animals. Fasting-mediated increases in plasma epinephrine, and the activation of PKA and AMPK in skeletal muscle were similar between chow and HFD rats. p38 MAPK phosphorylation was increased with fasting in chow-fed but not HFD rats. Our findings suggest that a blunted effect of fasting on the induction of PDK4, MCAD, and UCP3 in skeletal muscle from HFD rats is likely a result of already elevated levels of these enzymes, the induction of which is associated with increases in plasma fatty acid and PGC-1β. On the other hand, a blunted induction of PRC and CPT-1 mRNA may be explained by decreases in p38 MAPK signaling.
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Affiliation(s)
- Bruce C. Frier
- Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
| | - René L. Jacobs
- Group on the Molecular and Cellular Biology of Lipids and Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada; and
| | - David C. Wright
- Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
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Abstract
UNLABELLED Tamoxifen is an anti-estrogen drug widely used for the treatment of hormone-sensitive breast cancer. Approximately 43% of breast cancer patients treated with tamoxifen develop hepatic steatosis. The mechanism or mechanisms by which tamoxifen may induce lipid accumulation in the liver are unclear. Mice were injected with tamoxifen or vehicle (sesame oil containing 1% benzyl alcohol) for 5 consecutive days. In comparison with the vehicle, tamoxifen increased hepatic triacylglycerol levels by 72%. The levels of plasma triacylglycerol were similar between the tamoxifen-treated and control groups. We found increased radiolabeling of triacylglycerol and phospholipids from [(3)H]acetate (∼50%) but not [(14)C]oleate in hepatocytes from tamoxifen-treated mice versus control mice. Fatty acid uptake, triacylglycerol secretion, and fatty acid oxidation remained unchanged in isolated hepatocytes after tamoxifen treatment. The apparent increase in fatty acid synthesis was explained by a marked decrease in the phosphorylation of acetyl coenzyme A carboxylase, which resulted in its activation. CONCLUSION Our data suggest that increased de novo fatty acid synthesis is the primary event leading to tamoxifen-induced steatosis in the mouse liver. Inhibition of fatty acid synthesis might, therefore, ameliorate steatosis/steatohepatitis in breast cancer patients treated with tamoxifen.
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Affiliation(s)
- Laura K Cole
- Group on Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, Alberta, Canada
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Koonen DP, Sung MM, Kao CK, Dolinsky VW, Koves TR, Ilkayeva O, Jacobs RL, Vance DE, Light PE, Muoio DM, Febbraio M, Dyck JR. Alterations in skeletal muscle fatty acid handling predisposes middle-aged mice to diet-induced insulin resistance. Diabetes 2010; 59:1366-75. [PMID: 20299464 PMCID: PMC2874697 DOI: 10.2337/db09-1142] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
OBJECTIVE Although advanced age is a risk factor for type 2 diabetes, a clear understanding of the changes that occur during middle age that contribute to the development of skeletal muscle insulin resistance is currently lacking. Therefore, we sought to investigate how middle age impacts skeletal muscle fatty acid handling and to determine how this contributes to the development of diet-induced insulin resistance. RESEARCH DESIGN AND METHODS Whole-body and skeletal muscle insulin resistance were studied in young and middle-aged wild-type and CD36 knockout (KO) mice fed either a standard or a high-fat diet for 12 weeks. Molecular signaling pathways, intramuscular triglycerides accumulation, and targeted metabolomics of in vivo mitochondrial substrate flux were also analyzed in the skeletal muscle of mice of all ages. RESULTS Middle-aged mice fed a standard diet demonstrated an increase in intramuscular triglycerides without a concomitant increase in insulin resistance. However, middle-aged mice fed a high-fat diet were more susceptible to the development of insulin resistance-a condition that could be prevented by limiting skeletal muscle fatty acid transport and excessive lipid accumulation in middle-aged CD36 KO mice. CONCLUSION Our data provide insight into the mechanisms by which aging becomes a risk factor for the development of insulin resistance. Our data also demonstrate that limiting skeletal muscle fatty acid transport is an effective approach for delaying the development of age-associated insulin resistance and metabolic disease during exposure to a high-fat diet.
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Affiliation(s)
- Debby P.Y. Koonen
- Department of Pediatrics, Cardiovascular Research Centre, University of Alberta, Edmonton, Alberta, Canada
- Department of Pathology and Medical Biology, Medical Biology Section, Division Molecular Genetics, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands
| | - Miranda M.Y. Sung
- Department of Pediatrics, Cardiovascular Research Centre, University of Alberta, Edmonton, Alberta, Canada
| | - Cindy K.C. Kao
- Department of Pediatrics, Cardiovascular Research Centre, University of Alberta, Edmonton, Alberta, Canada
| | - Vernon W. Dolinsky
- Department of Pediatrics, Cardiovascular Research Centre, University of Alberta, Edmonton, Alberta, Canada
| | - Timothy R. Koves
- Sarah W. Stedman Nutrition and Metabolism Center, Departments of Medicine, Pharmacology, and Cancer Biology, Duke University, Durham, North Carolina
| | - Olga Ilkayeva
- Sarah W. Stedman Nutrition and Metabolism Center, Departments of Medicine, Pharmacology, and Cancer Biology, Duke University, Durham, North Carolina
| | - René L. Jacobs
- Group on the Molecular and Cell Biology of Lipids, Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada
| | - Dennis E. Vance
- Group on the Molecular and Cell Biology of Lipids, Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada
| | - Peter E. Light
- Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada
| | - Deborah M. Muoio
- Sarah W. Stedman Nutrition and Metabolism Center, Departments of Medicine, Pharmacology, and Cancer Biology, Duke University, Durham, North Carolina
| | - Maria Febbraio
- Department of Cell Biology, Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, Ohio; and
| | - Jason R.B. Dyck
- Department of Pediatrics, Cardiovascular Research Centre, University of Alberta, Edmonton, Alberta, Canada
- Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada
- Corresponding author: Jason R.B. Dyck,
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Jacobs RL, Zhao Y, Koonen DPY, Sletten T, Su B, Lingrell S, Cao G, Peake DA, Kuo MS, Proctor SD, Kennedy BP, Dyck JRB, Vance DE. Impaired de novo choline synthesis explains why phosphatidylethanolamine N-methyltransferase-deficient mice are protected from diet-induced obesity. J Biol Chem 2010; 285:22403-13. [PMID: 20452975 DOI: 10.1074/jbc.m110.108514] [Citation(s) in RCA: 152] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Phosphatidylcholine (PC) is synthesized from choline via the CDP-choline pathway. Liver cells can also synthesize PC via the sequential methylation of phosphatidylethanolamine, catalyzed by phosphatidylethanolamine N-methyltransferase (PEMT). The current study investigates whether or not hepatic PC biosynthesis is linked to diet-induced obesity. Pemt(+/+) mice fed a high fat diet for 10 weeks increased in body mass by 60% and displayed insulin resistance, whereas Pemt(-/-) mice did not. Compared with Pemt(+/+) mice, Pemt(-/-) mice had increased energy expenditure and maintained normal peripheral insulin sensitivity; however, they developed hepatomegaly and steatosis. In contrast, mice with impaired biosynthesis of PC via the CDP-choline pathway in liver became obese when fed a high fat diet. We, therefore, hypothesized that insufficient choline, rather than decreased hepatic phosphatidylcholine, was responsible for the lack of weight gain in Pemt(-/-) mice despite the presence of 1.3 g of choline/kg high fat diet. Supplementation with an additional 2.7 g of choline (but not betaine)/kg of diet normalized energy metabolism, weight gain, and insulin resistance in high fat diet-fed Pemt(-/-) mice. Furthermore, Pemt(+/+) mice that were fed a choline-deficient diet had increased oxygen consumption, had improved glucose tolerance, and gained less weight. Thus, de novo synthesis of choline via PEMT has a previously unappreciated role in regulating whole body energy metabolism.
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Affiliation(s)
- René L Jacobs
- Group on the Molecular and Cell Biology of Lipids and Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2S2, Canada
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Zhao Y, Su B, Jacobs RL, Kennedy B, Francis GA, Waddington E, Brosnan JT, Vance JE, Vance DE. Lack of phosphatidylethanolamine N-methyltransferase alters plasma VLDL phospholipids and attenuates atherosclerosis in mice. Arterioscler Thromb Vasc Biol 2009; 29:1349-55. [PMID: 19520976 DOI: 10.1161/atvbaha.109.188672] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE Impaired hepatic phosphatidylcholine (PC) synthesis lowers plasma lipids. We, therefore, tested the hypothesis that lack of phosphatidylethanolamine N-methyltransferase (PEMT), a hepatic enzyme catalyzing PC biosynthesis, attenuates the development of atherosclerosis. METHODS AND RESULTS Mice deficient in both PEMT and low-density lipoprotein receptors (Pemt(-/-)/Ldlr(-/-) mice) were fed a high-fat/high-cholesterol diet for 16 weeks. Atherosclerotic lesion area was approximately 80% lower (P<0.01) in Pemt(-/-)/Ldlr(-/-) mice than in Pemt(+/+)/Ldlr(-/-) mice, consistent with the atheroprotective plasma lipoprotein profile (ie, significant reduction in very low-density lipoprotein [VLDL]/intermediate-density lipoprotein/low-density lipoprotein-associated phospholipids [approximately 45%], triacylglycerols [approximately 65%], cholesterol [approximately 58%], and cholesteryl esters [approximately 68%]). Plasma apoB was decreased by 40% to 60%, whereas high-density lipoprotein levels were not altered. In addition, PEMT deficiency reduced plasma homocysteine by 34% to 52% in Pemt(-/-)/Ldlr(-/-) mice. The molar ratio of PC/phosphatidylethanolamine in nascent VLDLs produced by Pemt(-/-)/Ldlr(-/-) mice was lower than in VLDLs in Pemt(+/+)/Ldlr(-/-) mice. Furthermore, deletion of PEMT modestly reduced hepatic VLDL secretion in Ldlr(-/-) mice and altered the rate of VLDL clearance from plasma. CONCLUSIONS This is the first report showing that inhibition of hepatic phospholipid biosynthesis attenuates atherosclerosis.
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Affiliation(s)
- Yang Zhao
- Department of Biochemistry, University of Alberta, Edmonton, Canada
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70
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Jacobs RL, Lingrell S, Zhao Y, Francis GA, Vance DE. Hepatic CTP:Phosphocholine Cytidylyltransferase-α Is a Critical Predictor of Plasma High Density Lipoprotein and Very Low Density Lipoprotein. J Biol Chem 2008; 283:2147-55. [DOI: 10.1074/jbc.m706628200] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
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Koonen DPY, Jacobs RL, Febbraio M, Young ME, Soltys CLM, Ong H, Vance DE, Dyck JRB. Increased hepatic CD36 expression contributes to dyslipidemia associated with diet-induced obesity. Diabetes 2007; 56:2863-71. [PMID: 17728375 DOI: 10.2337/db07-0907] [Citation(s) in RCA: 351] [Impact Index Per Article: 20.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
OBJECTIVE The etiology of type 2 diabetes often involves diet-induced obesity (DIO), which is associated with elevated plasma fatty acids and lipoprotein associated triglycerides. Since aberrant hepatic fatty acid uptake may contribute to this, we investigated whether increased expression of a fatty acid transport protein (CD36) in the liver during DIO contributes to the dyslipidemia that precedes development of type 2 diabetes. RESEARCH DESIGN AND METHODS We determined the effect DIO has on hepatic CD36 protein expression and the functional consequence of this in terms of hepatic triglyceride storage and secretion. In addition, in vivo adenoviral gene delivery of CD36 to the livers of lean mice was performed to determine if increased hepatic CD36 protein was sufficient to alter hepatic fatty acid uptake and triglyceride storage and secretion. RESULTS During DIO, CD36 protein levels in the liver are significantly elevated, and these elevated levels correlate with increased hepatic triglyceride storage and secretion. These alterations in liver lipid storage and secretion were also observed upon forced expression of hepatic CD36 in the absence of DIO and were accompanied with a marked rise in hepatic fatty acid uptake in vivo, demonstrating that increased CD36 expression is sufficient to recapitulate the aberrant liver lipid handling observed in DIO. CONCLUSIONS Increased expression of hepatic CD36 protein in response to DIO is sufficient to exacerbate hepatic triglyceride storage and secretion. As these CD36-mediated effects contribute to the dyslipidemia that often precedes the development of type 2 diabetes, increased hepatic CD36 expression likely plays a causative role in the pathogenesis of type 2 diabetes.
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Affiliation(s)
- Debby P Y Koonen
- Department of Pediatrics, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
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Vance DE, Li Z, Jacobs RL. Hepatic phosphatidylethanolamine N-methyltransferase, unexpected roles in animal biochemistry and physiology. J Biol Chem 2007; 282:33237-41. [PMID: 17881348 DOI: 10.1074/jbc.r700028200] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Affiliation(s)
- Dennis E Vance
- Canadian Institutes of Health Research Group on the Molecular and Cell Biology of Lipids, Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2S2, Canada.
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Abstract
Various questions have been raised about labile methyl balance and total transmethylation fluxes, and further discussion has been encouraged. This report reviews and discusses some of the relevant evidence now available. The fact that, if needed, labile methyl balance is maintained by methylneogenesis appears to be established, but several aspects of transmethylation remain uncertain: definitive measurements of the rate of total transmethylation in humans of both sexes on various diets and at various ages; the extent to which synthesis of phosphatidylcholine has been underestimated; and the relative contributions of the 2 pathways for the formation of sarcosine (ie, N-methylglycine). The available evidence indicates that the quantitatively most important pathways for S-adenosylmethionine-dependent transmethylation in mammals are the syntheses of creatine by guanidinoacetate methyltransferase, of phosphatidylcholine by phosphatidylethanolamine methyltransferase, and of sarcosine by glycine N-methyltransferase. Data presented in this report show that S-adenosylmethionine and methionine accumulate abnormally in the plasma of humans with glycine N-methyltransferase deficiency but not of those with guanidinoacetate N-methyltransferase deficiency or in the plasma or livers of mice devoid of phosphatidylethanolamine N-methyltransferase activity. The absence of such accumulations in the latter 2 conditions may be due to removal of S-adenosylmethionine by synthesis of sarcosine. Steps that may help clarify the remaining issues include the determination of the relative rates of synthesis of sarcosine, creatine, and phosphatidylcholine by rapid measurement of the rates of radiolabel incorporation into these compounds from L-[methyl-3H]methionine administered intraportally to an experimental animal; clarification of the intracellular hepatic isotope enrichment value during stable-isotope infusion studies to enhance the certainty of methyl flux estimates during such studies; and definitive measurement of the dietary betaine intake from various diets.
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Affiliation(s)
- S Harvey Mudd
- Laboratory of Molecular Biology, National Institute of Mental Health, Bethesda, MD 20892, USA.
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74
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Jacobs RL, Lingrell S, Dyck JRB, Vance DE. Inhibition of hepatic phosphatidylcholine synthesis by 5-aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside is independent of AMP-activated protein kinase activation. J Biol Chem 2006; 282:4516-4523. [PMID: 17179149 DOI: 10.1074/jbc.m605702200] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
5-Aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside (AICAr), a commonly used indirect activator of AMP-activated protein kinase (AMPK), inhibits phosphatidylcholine (PC) biosynthesis in freshly isolated hepatocytes. In all nucleated mammalian cells, PC is synthesized from choline via the Kennedy (CDP-choline) pathway. The purpose of our study was to provide direct evidence that AMPK regulates phospholipid biosynthesis and to elucidate the mechanism(s) by which AMPK inhibits hepatic PC synthesis. Incubations of hepatocytes with AICAr resulted in a dose-dependent activation of AMPK and inhibition of PC biosynthesis. Surprisingly, adenoviral delivery of constitutively active AMPK did not alter PC biosynthesis. In addition, expression of dominant negative mutants of AMPK was unable to block the AICAr-dependent inhibition of PC biosynthesis, indicating that AICAr was acting independently of AMPK activation. Determination of aqueous intermediates of the CDP-choline pathway indicated that choline kinase, the first enzyme in the pathway, was inhibited by AICAr administration. Flux through the CDP-choline pathway was directly correlated to the level of intracellular ATP concentrations. Therefore, it is possible that inhibition of PC biosynthesis is another process by which the cell can reduce ATP consumption in times of energetic stress. However, unlike cholesterol and triacylglycerol biosynthesis, PC production is not regulated by AMPK.
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Affiliation(s)
- René L Jacobs
- Canadian Institutes of Health Research Group on the Molecular and Cell Biology of Lipids and Department of Biochemistry and the University of Alberta, Edmonton, Alberta T6G 2S2, Canada
| | - Susanne Lingrell
- Canadian Institutes of Health Research Group on the Molecular and Cell Biology of Lipids and Department of Biochemistry and the University of Alberta, Edmonton, Alberta T6G 2S2, Canada
| | - Jason R B Dyck
- Cardiovascular Research Group, Departments of Pediatrics and Pharmacology, University of Alberta, Edmonton, Alberta T6G 2S2, Canada
| | - Dennis E Vance
- Canadian Institutes of Health Research Group on the Molecular and Cell Biology of Lipids and Department of Biochemistry and the University of Alberta, Edmonton, Alberta T6G 2S2, Canada.
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Hartz CS, Nieman KM, Jacobs RL, Vance DE, Schalinske KL. Hepatic phosphatidylethanolamine N-methyltransferase expression is increased in diabetic rats. J Nutr 2006; 136:3005-9. [PMID: 17116711 DOI: 10.1093/jn/136.12.3005] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Phosphatidylcholine is an essential phospholipid that is synthesized by 2 different pathways, the CDP-choline pathway and the methylation of phosphatidylethanolamine by phosphatidylethanolamine N-methyltransferase (PEMT). Recent studies have suggested that PEMT is an important consumer of methyl groups from S-adenosylmethionine (SAM) and is a major determinant of homocysteine pools. Diabetes and all-trans-retinoic acid (ATRA) have been shown to alter the activities of several enzymes involved in methyl group metabolism. Thus, we investigated how diabetes and ATRA, individually and together, affect SAM-dependent phospholipid methylation. Rats received a single injection of streptozotocin (60 mg/kg body wt) or vehicle followed by administration of ATRA (30 mumol/kg body wt) or vehicle for 5 d. The hepatic activity of PEMT increased 50% in both diabetic rat groups, whereas administration of ATRA was without effect. In diabetic rats, plasma total homocysteine decreased 30-35% in all treatment groups as compared with the control group. Thus, alterations in the activity of PEMT were not directly correlated to changes in homocysteine concentrations. Moreover, treatment of diabetic rats with insulin prevented the increase in PEMT activity and abundance. Because these observations support an increased need for SAM-dependent phosphatidylcholine synthesis, this may also indicate an increased choline requirement in diabetes.
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Affiliation(s)
- Cara S Hartz
- Department of Food Science and Human Nutrition, Iowa State University, Ames, IA 50011, USA
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Lingrell S, Jacobs RL, Dyck JR, Vance DE. Inhibition of hepatic phosphatidylcholine synthesis by AICAR and phenformin is independent of AMP‐activated protein kinase (AMPK) activation. FASEB J 2006. [DOI: 10.1096/fasebj.20.4.a91-b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Susanne Lingrell
- Dept. of BiochemistryUniversity of Alberta320 HMRCEdmontonAlbertaT6G 2S2Canada
| | - René L Jacobs
- Dept. of BiochemistryUniversity of Alberta320 HMRCEdmontonAlbertaT6G 2S2Canada
| | - Jason R.B. Dyck
- Dept. of MedicineUniversity of AlbertaHMRCEdmontonAlbertaT6G 2S2Canada
| | - Dennis E Vance
- Dept. of BiochemistryUniversity of Alberta320 HMRCEdmontonAlbertaT6G 2S2Canada
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Jacobs RL, Vance DE. Liver‐specific phosphocholine cytidylyltransferase‐ α knockout mice develop insulin resistance despite having lower plasma lipid levels. FASEB J 2006. [DOI: 10.1096/fasebj.20.4.a87-c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- René L Jacobs
- BiochemistryUniversity of Alberta320 HMRCEdmontonAlbertaT6G 2S2Canada
| | - Dennis E Vance
- BiochemistryUniversity of Alberta320 HMRCEdmontonAlbertaT6G 2S2Canada
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Abstract
S-Adenosylmethionine (AdoMet) is the major biological methyl donor. AdoMet's methyl group arises both from the diet (eg, methionine, choline, and betaine) and from de novo synthesis by the process of methylneogenesis. At least 50 AdoMet-dependent methylation reactions have been identified in mammals, and genomic analyses suggest that the final number will be much higher. Such methylation reactions play major roles in biosynthesis, regulation, and detoxification. Creatine synthesis is thought to account for the use of >70% of AdoMet-derived methyl groups in humans. This is not consistent with recent studies in mice, in which the phosphatidylethanolamine methyltransferase gene was deleted (PEMT-/-). Loss of this hepatic enzyme resulted in a 50% decrease in plasma homocysteine, which suggests that it accounts for a major component of whole-body AdoMet utilization. A reexamination of human creatine metabolism showed that dietary creatine can account for as much as 50% of daily creatine requirements in nonvegetarians and, therefore, that estimates of creatine synthesis need to be reduced. We suggest that creatine synthesis is responsible for a smaller proportion of AdoMet-derived methyl groups than has been suggested and that phosphatidylcholine synthesis via phosphatidylethanolamine methyltransferase is a major consumer of these methyl groups.
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Affiliation(s)
- Lori M Stead
- Department of Biochemistry, Memorial University of Newfoundland, St John's, Canada
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Jacobs RL, Stead LM, Devlin C, Tabas I, Brosnan ME, Brosnan JT, Vance DE. Physiological regulation of phospholipid methylation alters plasma homocysteine in mice. J Biol Chem 2005; 280:28299-305. [PMID: 15958390 DOI: 10.1074/jbc.m501971200] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Biological methylation reactions and homocysteine (Hcy) metabolism are intimately linked. In previous work, we have shown that phosphatidylethanolamine N-methyltransferase, an enzyme that methylates phosphatidylethanolamine to form phosphatidylcholine, plays a significant role in the regulation of plasma Hcy levels through an effect on methylation demand (Noga, A. A., Stead, L. M., Zhao, Y., Brosnan, M. E., Brosnan, J. T., and Vance, D. E. (2003) J. Biol. Chem. 278, 5952-5955). We have further investigated methylation demand and Hcy metabolism in liver-specific CTP:phosphocholine cytidylyltransferase-alpha (CTalpha) knockout mice, since flux through the phosphatidylethanolamine N-methyltransferase pathway is increased 2-fold to meet hepatic demand for phosphatidylcholine. Our data show that plasma Hcy is elevated by 20-40% in mice lacking hepatic CTalpha. CTalpha-deficient hepatocytes secrete 40% more Hcy into the medium than do control hepatocytes. Liver activity of betaine:homocysteine methyltransferase and methionine adenosyltransferase are elevated in the knockout mice as a mechanism for maintaining normal hepatic S-adenosylmethionine and S-adenosylhomocysteine levels. These data suggest that phospholipid methylation in the liver is a major consumer of AdoMet and a significant source of plasma Hcy.
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Affiliation(s)
- René L Jacobs
- Canadian Institutes of Health Research Group on the Molecular and Cell Biology of Lipids and Department of Biochemistry, University of Alberta, Edmonton, Canada
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Affiliation(s)
- Lori M Stead
- Department of Biochemistry, Memorial University of Newfoundland, St. John's, NL, Canada A1B 3X9
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Jacobs RL, Devlin C, Tabas I, Vance DE. Targeted deletion of hepatic CTP:phosphocholine cytidylyltransferase alpha in mice decreases plasma high density and very low density lipoproteins. J Biol Chem 2004; 279:47402-10. [PMID: 15331603 DOI: 10.1074/jbc.m404027200] [Citation(s) in RCA: 144] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
CTP:phosphocholine cytidylyltransferase (CT) is the key regulatory enzyme in the CDP-choline pathway for the biosynthesis of phosphatidylcholine. Hepatic cells express both an alpha and a beta2 isoform of CT and can also synthesize phosphatidylcholine via the sequential methylation of phosphatidylethanolamine catalyzed by phosphatidylethanolamine N-methyltransferase. To ascertain the functional importance of CTalpha, we created a mouse in which the hepatic CTalpha gene was specifically inactivated by the Cre/LoxP procedure. In CTalpha knockout mice, hepatic CT activity (due to residual CTbeta2 activity as well as activity in nonhepatic cells) was 15% of normal, whereas phosphatidylethanolamine N-methyltransferase activity was elevated 2-fold compared with controls. Lipid analyses of the liver indicated that female knockout mice had reduced phosphatidylcholine levels and accumulated triacylglycerols. The plasma phosphatidylcholine concentration was reduced in the CTalpha knockout (independent of gender), as were levels of high density lipoproteins (cholesterol and apoAI) and very low density lipoproteins (triacylglycerols and apoB100). Experiments in which mice were injected with Triton WR1339 indicated that apoB secretion was decreased in hepatic-specific CTalpha knockout mice compared with controls. These results suggest an important role for hepatic CTalpha in regulating both hepatic and systemic lipid and lipoprotein metabolism.
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Affiliation(s)
- René L Jacobs
- Canadian Institutes of Health Research Group on the Molecular and Cell Biology of Lipids and Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada
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Jacobs RL, Stead LM, Brosnan ME, Brosnan JT. Hyperglucagonemia in rats results in decreased plasma homocysteine and increased flux through the transsulfuration pathway in liver. J Biol Chem 2001; 276:43740-7. [PMID: 11559709 DOI: 10.1074/jbc.m107553200] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
An elevated plasma level of homocysteine is a risk factor for the development of cardiovascular disease. The purpose of this study was to investigate the effect of glucagon on homocysteine metabolism in the rat. Male Sprague-Dawley rats were treated with 4 mg/kg/day (3 injections per day) glucagon for 2 days while control rats received vehicle injections. Glucagon treatment resulted in a 30% decrease in total plasma homocysteine and increased hepatic activities of glycine N-methyltransferase, cystathionine beta-synthase, and cystathionine gamma-lyase. Enzyme activities of the remethylation pathway were unaffected. The 90% elevation in activity of cystathionine beta-synthase was accompanied by a 2-fold increase in its mRNA level. Hepatocytes prepared from glucagon-injected rats exported less homocysteine, when incubated with methionine, than did hepatocytes of saline-treated rats. Flux through cystathionine beta-synthase was increased 5-fold in hepatocytes isolated from glucagon-treated rats as determined by production of (14)CO(2) and alpha-[1-(14)C]ketobutyrate from l-[1-(14)C]methionine. Methionine transport was elevated 2-fold in hepatocytes isolated from glucagon-treated rats resulting in increased hepatic methionine levels. Hepatic concentrations of S-adenosylmethionine and S-adenosylhomocysteine, allosteric activators of cystathionine beta-synthase, were also increased following glucagon treatment. These results indicate that glucagon can regulate plasma homocysteine through its effects on the hepatic transsulfuration pathway.
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Affiliation(s)
- R L Jacobs
- Department of Biochemistry, Memorial University of Newfoundland, St. John's, Newfoundland A1B 3X9, Canada
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Stead LM, Au KP, Jacobs RL, Brosnan ME, Brosnan JT. Methylation demand and homocysteine metabolism: effects of dietary provision of creatine and guanidinoacetate. Am J Physiol Endocrinol Metab 2001; 281:E1095-100. [PMID: 11595668 DOI: 10.1152/ajpendo.2001.281.5.e1095] [Citation(s) in RCA: 127] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
S-adenosylmethionine, formed by the adenylation of methionine via S-adenosylmethionine synthase, is the methyl donor in virtually all known biological methylations. These methylation reactions produce a methylated substrate and S-adenosylhomocysteine, which is subsequently metabolized to homocysteine. The methylation of guanidinoacetate to form creatine consumes more methyl groups than all other methylation reactions combined. Therefore, we examined the effects of increased or decreased methyl demand by these physiological substrates on plasma homocysteine by feeding rats guanidinoacetate- or creatine-supplemented diets for 2 wk. Plasma homocysteine was significantly increased (~50%) in rats maintained on guanidinoacetate-supplemented diets, whereas rats maintained on creatine-supplemented diets exhibited a significantly lower (~25%) plasma homocysteine level. Plasma creatine and muscle total creatine were significantly increased in rats fed the creatine-supplemented or guanidinoacetate-supplemented diets. The activity of kidney L-arginine:glycine amidinotransferase, the enzyme catalyzing the synthesis of guanidinoacetate, was significantly decreased in both supplementation groups. To examine the role of the liver in mediating these changes in plasma homocysteine, isolated rat hepatocytes were incubated with methionine in the presence and absence of guanidinoacetate and creatine, and homocysteine export was measured. Homocysteine export was significantly increased in the presence of guanidinoacetate. Creatine, however, was without effect. These results suggest that homocysteine metabolism is sensitive to methylation demand imposed by physiological substrates.
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Affiliation(s)
- L M Stead
- Department of Biochemistry, Memorial University of Newfoundland, St. John's, Newfoundland, Canada A1B 3X9
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