Phosphatidylcholine metabolism: masochistic enzymology, metabolic regulation, and lipoprotein assembly

1990 ◽  
Vol 68 (10) ◽  
pp. 1151-1165 ◽  
Author(s):  
Dennis E. Vance
Keyword(s):  
Fatty Acids ◽  
Endoplasmic Reticulum ◽  
Metabolic Regulation ◽  
Alternative Pathway ◽  
Plasma Lipoproteins ◽  
High Density Lipoproteins ◽  
Very Low Density Lipoproteins ◽  
Major Pathway ◽  
Phosphatidylcholine Biosynthesis ◽  
Membrane Bound

Phosphatidylcholine is apparently essential for mammalian life, since there are no known inherited diseases in the biosynthesis of this lipid. One of its critical roles appears to be in the structure of the eucaryotic membranes. Why phosphatidylcholine is required and why other phospholipids will not substitute are unknown. The major pathway for the biosynthesis of phosphatidylcholine occurs via the CDP-choline pathway. Choline kinase, the initial enzyme in the sequence, has been purified to homogeneity from kidney and liver and also catalyzes the phosphorylation of ethanolamine. Most evidence suggests that the next enzyme in the pathway, CTP:phosphocholine cytidylyltransferase, catalyzes the rate-limiting and regulated step in phosphatidylcholine biosynthesis. This enzyme has also been completely purified from liver. Cytidylyltransferase appears to exist in the cytosol as an inactive reservoir of enzyme and as a membrane-bound form (largely associated with the endoplasmic reticulum), which is activated by the phospholipid environment. There is evidence that the activity of this enzyme and the rate of phosphatidylcholine biosynthesis are regulated by the reversible translocation of the cytidylyltransferase between membranes and cytosol. Three major mechanisms appear to govern the distribution and cellular activity of this enzyme. (i) The enzyme is phosphorylated by cAMP-dependent protein kinase, which results in release of the enzyme into the cytosol. Reactivation of cytidylyltransferase by binding to membranes can occur by the action of protein phosphatase 1 or 2A. (ii) Fatty acids added to cells in culture or in vitro causes the enzyme to bind to membranes where it is activated. Removal of the fatty acids dissociates the enzyme from the membrane, (iii) Perhaps most importandy, the concentration of phosphatidylcholine in the endoplasmic reticulum feedback regulates the distribution of cytidylyltransferase. A decrease in the level of phosphatidylcholine causes the enzyme to be activated by binding to the membrane, whereas an increase in phosphatidylcholine mediates the release of enzyme into the cytosol. The third enzyme in the CDP-choline pathway, CDP-choline: 1,2-diacylglycerol cholinephosphotransferase, has been cloned from yeast but never purified from any source. In liver an alternative pathway for phosphatidylcholine biosynthesis is the methylation of phosphatidylethanolamine by phosphatidylethanolamine N-methyltransferase. This enzyme is membrane bound and has been purified to homogeneity. It catalyzes all three methylation reactions involved in the conversion of phosphatidylethanolamine to phosphatidylcholine. The activity of this enzyme is 100- to 1000-fold lower in other cells and tissues derived from animals. In yeast there are two phospholipid methyltransferases involved in the methylation of phosphatidylethanolamine. The genes encoding both of these enzymes have been cloned and the primary structure of the enzymes have been deduced. Phosphatidylcholine is also catabolized in liver. Only one enzyme involved in this process has been purified to homogeneity, that is, phospholipase A2 from mitochondria. The mechanisms involved in the regulation of phosphatidylcholine catabolism are largely unknown. Phosphatidylcholine is a major component of plasma lipoproteins and the active synthesis of phosphatidylcholine is required for the secretion of very low density lipoproteins from liver. In contrast, the secretion of high density lipoproteins, albumin, and all other secreted proteins do not require the active biosynthesis of phosphatidylcholine. Other phospholipids will not substitute for the phosphatidylcholine requirement. It is also apparent that newly made phosphatidylcholine, rather than preexisting phosphatidylcholine, is preferentially utilized for lipoprotein secretion.Key words: phosphatidylcholine, glycerophosphocholine, cytidylyltransferase, methyltransferase, cholinephosphotransferase.

scholarly journals Stimulation of triacylglycerol synthesis in rat adipocytes by plasma very-low-density lipoproteins

1978 ◽  
Vol 176 (1) ◽  
pp. 169-174 ◽  
Author(s):  
P Thomopoulos ◽  
M Berthelier ◽  
D Lagrange ◽  
M J Chapman ◽  
M H Laudat
Keyword(s):  
Fatty Acids ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Low Density Lipoproteins ◽  
High Density Lipoproteins ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Very Low Density Lipoproteins ◽  
Rat Adipocytes ◽  
Triacylglycerol Synthesis

The effect of human plasma lipoproteins on lipogenesis from glucose has been studied in isolated rat adipocytes. The very-low-density lipoproteins increased lipogenesis specifically, whereas low-density lipoproteins and high-density lipoproteins were without effect. Such stimulation could be reproduced with partially delipidated very-low-density lipoproteins. Nod-esterified fatty acids and glycerol were also without effect. Pretreatment of the adipocytes with trypsin did not alter the effect of very-low-density lipoprotein. The presence of Ca2+ was required for the full activation of lipogenesis. The synthesis of acylglycerol fatty acids and of acylglycerol glycerol were equally increased. The effect of very-low-density lipoprotein was not additive to that of insulin. It is suggested that very-low-density lipoprotein may directly stimulate lipogenesis in fat-cells, particularly in states when the lipoproteins are present at high concentration in the circulation.

Insufficient accuracy and specificity of polyanion precipitation methods for quantifying low-density lipoproteins

1990 ◽  
Vol 36 (12) ◽  
pp. 2109-2113 ◽  
Author(s):  
R Siekmeier ◽  
W März ◽  
W Gross
Keyword(s):  
Fatty Acids ◽  
Dextran Sulfate ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Low Density Lipoproteins ◽  
High Density Lipoproteins ◽  
Low Density ◽  
Very Low Density Lipoproteins ◽  
Nonesterified Fatty Acids ◽  
High Concentrations

Abstract Recently, polyanion precipitation assays for low-density lipoprotein (LDL)-cholesterol have been found to underestimate their analyte in normolipidemic samples (Siekmeier et al., Clin Chim Acta 1988;177:221-30). Therefore, accuracy, specificity, and interference by nonesterified fatty acids have been studied for three precipitants (obtained by heparin, dextran sulfate, or polyvinyl sulfate precipitation). At normal concentrations of LDL, precipitation is incomplete, whereas it is nearly quantitative at high concentrations of LDL. The polyvinyl sulfate reagent markedly responds to variations in the amount of non-LDL protein present in the precipitation mixture. In the dextran sulfate and the polyvinyl sulfate method, but not in the heparin method, the percentages of LDL precipitated notably increase as the concentration of the polyanion compound is decreased. In either assay, very-low-density lipoproteins, but not high-density lipoproteins, are significantly coprecipitated (dextran sulfate 28%, polyvinyl sulfate and heparin 66%) in a concentration-independent fashion. Increased concentrations of nonesterified fatty acids markedly interfere with the dextran sulfate and polyvinyl sulfate assay, but do not much affect results with the heparin reagent.

scholarly journals Characterization of plasma lipoproteins separated and purified by agarose-column chromatography

1974 ◽  
Vol 139 (1) ◽  
pp. 89-95 ◽  
Author(s):  
Lawrence L. Rudel ◽  
Jason A. Lee ◽  
Manford D. Morris ◽  
James M. Felts
Keyword(s):  
Human Plasma ◽  
Column Chromatography ◽  
Low Density Lipoproteins ◽  
High Density ◽  
Plasma Lipoproteins ◽  
High Density Lipoproteins ◽  
Low Density ◽  
Very Low Density Lipoproteins ◽  
Simple Method ◽  
Lipoprotein Class

1. A simple method for isolation of individual human plasma lipoprotein classes is presented. In this technique, lipoproteins are removed from plasma at d1.225 by ultracentrifugation, after which they are separated and purified by agarose-column chromatography. 2. Three major classes are obtained after agarose-column chromatography. Separation between classes is excellent; more than 95% of the lipoproteins eluted from the column are recovered in the form of a purified lipoprotein class. 3. Each lipoprotein class was characterized immunologically, chemically, electrophoretically and by electron microscopy. A comparison of the properties of the column-isolated lipoproteins was made with very-low-density lipoproteins, low-density lipoproteins, and high-density lipoproteins separated by sequential ultracentrifugation at densities of 1.006, 1.063 and 1.21 respectively. 4. By each criterion, peak-I lipoproteins from the agarose column are the same as very-low-density lipoproteins, peak-II lipoproteins are the same as low-density lipoproteins, and peak-III lipoproteins are the same as high-density lipoproteins. Thus the lipoprotein classes isolated by both methods are similar if not identical. 5. The agarose-column separation technique offers the advantage of a two- to three-fold saving in time. In addition, the column-elution pattern serves as a recording of the size distribution of lipoproteins in plasma. 6. The most complete characterization is reported for human plasma lipoproteins. The results with rhesus-monkey and rabbit lipoproteins were identical.

scholarly journals Determination of the intracellular distribution and pool sizes of apolipoprotein B in rabbit liver

1992 ◽  
Vol 288 (2) ◽  
pp. 413-419 ◽  
Author(s):  
J Wilkinson ◽  
J A Higgins ◽  
P H E Groot ◽  
E Gherardi ◽  
D E Bowyer
Keyword(s):  
Endoplasmic Reticulum ◽  
Apolipoprotein B ◽  
Intracellular Distribution ◽  
Subcellular Fractions ◽  
Rabbit Liver ◽  
Very Low Density Lipoproteins ◽  
Apo B ◽  
Golgi Region ◽  
Membrane Bound ◽  
Vldl Assembly

We have investigated the intracellular distribution of apolipoprotein B (apo B) in rabbit liver by immunoblotting, radioimmunoassay (r.i.a.) and enzyme-linked immunoassay (e.l.i.s.a.). Apo B100 was detected in total microsomes, rough microsomes, smooth microsomes, trans-enriched Golgi and cis-enriched Golgi and membrane and cisternal-content subfractions prepared from these fractions. There was also evidence of degradation of apo B100 in the Golgi membrane fractions. The amount of apo B in the subcellular fractions detected by competitive r.i.a. or e.l.i.s.a. ranged from 1.5 micrograms/mg of protein in the rough endoplasmic reticulum to 13 micrograms/mg of protein in the trans-Golgi fraction. Using internal standards (NADPH-cytochrome c reductase for the endoplasmic reticulum and galactosyltransferase for the Golgi membranes) it was calculated that all the apo B of liver is recovered within the secretory compartment, with 63% of the total apo B in the endoplasmic reticulum and the remainder in the Golgi. When the subcellular fractions were separated into membranes and cisternal contents, 60%, 50%, 60% and 30% of the total apo B was recovered in the membrane of the rough microsomes, smooth microsomes, cis-Golgi and trans-Golgi respectively. Using competitive e.l.i.s.a. we found that the membrane-bound form of the apo B was exposed at the cytosolic surface of the intact subcellular fractions. These observations are consistent with a model for assembly of very-low-density lipoproteins (VLDL) in which newly synthesized apo B is incorporated into a membrane-bound pool and a lumenal pool. The membrane-bound pool not used for VLDL assembly may be degraded, possibly in the Golgi region.

scholarly journals Plasma Lipid Profiles of Transgenic mice expressing the Human ApoB100XCETP are altered differentially by Diets enriched with defined Fatty Acids

2015 ◽  
Vol 3 (3) ◽  
pp. 207-218
Author(s):  
Wael Hatahet ◽  
Abdul Soofi ◽  
Oyonumo Ntekim ◽  
Thomas Fungwe
Keyword(s):  
Fatty Acids ◽  
Transgenic Mice ◽  
Cholesterol Acyltransferase ◽  
Plasma Lipid ◽  
Lipid Profiles ◽  
Dietary Fats ◽  
Plasma Lipoproteins ◽  
High Density Lipoproteins ◽  
Type I ◽  
Protective Effects

Dietary fat is known to modulate plasma lipid profiles. Synthesis of high density lipoproteins (HDL), which has protective effects on vascular disease is also influenced by dietary fats, but the mechanisms are unclear. The hapoB100XCETP transgenic mouse was used to investigate the effects of fatty acids on the metabolism of plasma lipoproteins, including the pathway leading to synthesis HDL. Male transgenic mice were fed with diets formulated to provide TG (33% energy) as tripalmitin (TP), triolein (TO), tristearin (TS) or equicaloric substitution of fat with carbohydrate (sucrose) for 4 weeks. Analysis of plasma profile showed that HDL-cholesterol were 53.7+14; 64.6+8.6; 50.2+3.3; 47.0+9.2 and 45.2+4.9 mg/dL for control, oleate, palmitate, stearate and sucrose based diets, respectively. LDL-cholesterol levels were 51.7+7.0; 23.1+7.0; 38.9+2.2; 75.1+1.8 and 46.8.1.0 mg/dl, for control, TO, TP, TS and sucrose, respectively. Hepatic Lecithin-cholesterol acyltransferase (LCAT) protein levels increased by 2-fold in mice fed TS or TO diets, compared to TP, while sucrose had no effect. The scavenger receptor class B type I (SR-B1) which plays an important role in meditating the uptake of HDL-derived cholesterol and cholesteryl ester in the liver and steroidogenic tissues increased in livers of animals fed TP and TO, while TS and sucrose did not have a similar effects. These results suggests that fatty acids can uniquely impact HDL, in addition, the ApoB100XCETP mouse is a useful model for the evaluation of how dietary components affect the risk of developing atherosclerosis and heart disease.

Metabolism of palmitate and linoleate in intact dogs

1962 ◽  
Vol 203 (5) ◽  
pp. 914-918 ◽  
Author(s):  
P. J. Nestel ◽  
A. Bezman ◽  
R. J. Havel
Keyword(s):  
Fatty Acids ◽  
Free Fatty Acids ◽  
Milk Fat ◽  
Plasma Lipids ◽  
Corn Oil ◽  
Low Density Lipoproteins ◽  
High Density Lipoproteins ◽  
Low Density ◽  
Very Low Density Lipoproteins ◽  
Two Populations

Palmitate-9, 10-H3 and linoleate-1-C14 were infused simultaneously into intact dogs as albumin-bound free fatty acids or as esterified fatty acids in chylomicrons. Linoleate bound to albumin was removed more rapidly from the plasma and was incorporated more extensively into triglycerides of very low density lipoproteins of plasma than palmitate. Both linoleate and palmitate were incorporated more slowly into triglyceride fatty acids of low density and high density lipoproteins than into those of very low density lipoproteins. When chylomicrons obtained separately from dogs fed palmitate-9, 10-H3 with milk fat and linoleate-1-C14 with corn oil were mixed and infused into recipients, the rates of removal from the blood of both triglycerides and phospholipids of the two populations of chylomicrons differed, but this did not seem to depend on their chemical composition. Linoleate derived from chylomicron triglycerides disappeared from hepatic triglycerides and phospholipids more rapidly than palmitate and was incorporated more extensively into plasma lipids. Palmitate and linoleate were incorporated in equivalent amounts into circulating free fatty acids, but more linoleate was found in lipids of adipose tissue.

scholarly journals Membrane receptors for very low density lipoprotein (VLDL) inhibitor of lymphocyte proliferation

Blood ◽  
1981 ◽  
Vol 57 (6) ◽  
pp. 1055-1064 ◽  
Author(s):  
PI Yi ◽  
G Beck ◽  
S Zucker
Keyword(s):  
Dna Synthesis ◽  
Lymphocyte Proliferation ◽  
Human Lymphocytes ◽  
Low Density Lipoproteins ◽  
Membrane Receptors ◽  
Plasma Lipoproteins ◽  
High Density Lipoproteins ◽  
Scatchard Analysis ◽  
Low Density ◽  
Very Low Density Lipoproteins

Abstract Physiologic concentrations of human plasma very low density lipoproteins inhibit the DNA synthesis of lymphocytes stimulated by allogeneic cells or lectins. In this report we have compared the effects of isolated lipoproteins [very low density lipoproteins (VLDL), low density lipoproteins (LDL), and high density lipoproteins (HDL)] and lipoprotein-depleted plasma (LDP) on DNA synthesis by phytohemagglutinin-stimulated human lymphocytes. The relative potency for the inhibition of lymphocyte proliferation was VLDL greater than LDL greater than HDL greater than LDP. Fifty percent inhibition of DNA synthesis was observed at a VLDL protein concentration of 1.5--2.0 microgram/ml. We have further demonstrated the presence of specific receptors for VLDL on human lymphocytes. Native VLDL was more effective than LDL in competing for 125I-VLDL binding sites. Subsequent to binding to lymphocytes, 125I-VLDL was internalized and degraded to acid- soluble products. Based on a Scatchard analysis of VLDL binding at 4 degrees C, the number of VLDL receptors per lymphocyte was estimated at 28,000 +/- 1300. Based on an estimated mean binding affinity for the VLDL receptor complex at half saturation of approximately 8.8 X 10(7) liter/mole, it is estimated that 91% of lymphocyte VLDL receptors are occupied at physiologic VLDL concentrations in blood. Although the immune regulatory role of plasma lipoproteins is uncertain, we suggest tha VLDL and LDL-In may maintain circulating blood lymphocytes in a nonproliferative state via their respective cell receptor mechanisms.

Binding of thyroxine and 3,5,3'-triiodothyronine to trout plasma lipoproteins

1992 ◽  
Vol 262 (5) ◽  
pp. E712-E720 ◽  
Author(s):  
P. J. Babin
Keyword(s):  
Nutritional Status ◽  
Binding Sites ◽  
Density Lipoprotein ◽  
High Density ◽  
Plasma Lipoproteins ◽  
High Density Lipoproteins ◽  
Minor Role ◽  
Very Low Density Lipoproteins

The plasma vectors of thyroid hormones (TH) in trout have been characterized. Plasma components were separated by density gradient ultracentrifugation after first labeling binding sites with trace levels of radioactive hormones, both in vivo and in vitro. Lipoproteins play only a minor role in humans but are major carriers of thyroxine (T4) and 3,5,3'-triiodothyronine (T3) in trout plasma. More than 67% of T4 and 89% of T3 were bound to lipoproteins (density less than 1.210 g/ml), predominantly to high-density lipoproteins (HDL), regardless of the nutritional status of the animals. The percentage of hormone bound to very-low-density lipoproteins, on the other hand, was proportional to their concentration and thus to nutritional status. T3 and T4 could also bind to vitellogenin, a very-high-density lipoprotein, which could transfer TH to the yolk of oocytes. Homologous ligand displacement indicated that T3 could bind to at least two classes of saturable sites in the plasma. In addition, plasma HDL were the major binding sites with low affinity (1.7 +/- 0.4 x 10(5) M-1) but with high capacity (3.1 +/- 0.3 x 10(-5) M). In conclusion, these results show that lipoproteins are the principal binding sites of TH in trout plasma.

scholarly journals Inhibition of lymphocyte proliferation stimulated by lectins and allogeneic cells by normal plasma lipoproteins.

1977 ◽  
Vol 146 (6) ◽  
pp. 1791-1803 ◽  
Author(s):  
J H Morse ◽  
L D Witte ◽  
D S Goodman
Keyword(s):  
Human Plasma ◽  
Rank Order ◽  
Human Lymphocytes ◽  
Low Density Lipoproteins ◽  
Plasma Lipoproteins ◽  
High Density Lipoproteins ◽  
Low Density ◽  
Very Low Density Lipoproteins ◽  
Normal Plasma

Lipoproteins, isolated by sequential flotation at densities 1.006, 1.019, 1.063, and 1.21, were examined for their ability to inhibit human lymphocytes stimulated by allogeneic cells and by lectins (phytohemagglutinin-P and concanavalin A). All the classes of normal plasma lipoproteins inhibited lymphoproliferation when peripheral blood lymphocytes were cultured in autologous, heterologous, or lipoprotein-deficient plasma (d greater than 1.21). The rank order of inhibitory potency was intermediate density lipoprotein (IDL) greater than very low density lipoproteins (VLDL) greater than low density lipoproteins (LDL) greater than high density lipoproteins (HDL), regardless of the mode of stimulation. The concentrations of IDL, VLDL, and LDL required for complete inhibition of stimulated lymphoproliferation were considerably below the levels of each of these lipoproteins normally found in human plasma. In addition, the concentration of HDL required for 50-90% inhibition was in the range of HDL levels normally found in human plasma. Moreover, at relatively higher concentrations, lipoproteins suppressed the incorporation of [3H]thymidine into DNA below the levels seen with reseting, unstimulated lymphocytes. The results suggest that circulating lymphocytes may normally be highly suppressed by the combined effects of all the endogenous lipoproteins and that the lipoproteins may play important roles in vivo in modulating lymphocyte functions and responses.

scholarly journals The Effect of Infection by Toxocariasis on Some Biochemical Parameters in Some Areas of Salah Al-Din Governorate

2020 ◽  
Vol 1 (3) ◽  
pp. 89-92
Author(s):  
Enas Ermeith ◽  
Ashraf Jamal Mahmoud ◽  
Buthaina Jassim Yousef
Keyword(s):  
Fatty Acids ◽  
Low Density Lipoproteins ◽  
The Body ◽  
High Density Lipoproteins ◽  
Low Density ◽  
Age Group ◽  
Very Low Density Lipoproteins ◽  
Large Numbers ◽  
Rate Of Increase ◽  
Group 15

The current study examined 277 blood samples of people, from both sexes of different ages, living in different areas of Salah Al-Din Governorate (Tikrit, Al-Alam and Baiji districts). The study was conducted from November, 2018 to June, 2019. All participants were secrened to investigate the incidence of toxocariasis using IgG TES-ELISA technique. The results showed that the rate of infection with toxocariasis was 22%. It was found an increase in cholesterol concentrations within age group 48-58 years and amounted to 185.8 mg/dl, and highest rate of increase in triglycerides was recorded within age group 15-25 years (168.1 mg/dl). The highest percentage of total protein was recorded within age group 26- 36 years (6.67 mg/dl). As for lipoprotein tests, highest percentage of high-density lipoproteins in age group 48-58 years was recorded (53 mg/dl), while low-density lipoproteins were highest in age group 48-58 years (100.8 mg/dl), and in very low-density lipoproteins the highest percentage within age group 15-25 years (33.5 mg/dl). The highest percentage of AST liver enzymes was recorded in age group 15-25 years and the percentage was 20.6 u/l. The highest percentage of ALT was recorded in age group 26-36 years (20.1 u/l) and 15-25 years (20 u/l). It is concluded that This age group continues to be exposed to infection with toxocariasis, which leads to presence large numbers of live larvae which secrete their antigens in the body and thus spread of toxoplasmosis, and the increase in proportion of fats is caused by poor oxidation of fatty acids and increased production of hepatic fatty acids Which leads to a delay in breakdown of lipoproteins, and the increase in level of AST, ALT enzyme occurs in cases of hepatitis and cirrhosis and may be associated with advanced cases of toxocariasis.

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