scholarly journals Effects of fasting on phosphatidylcholine biosynthesis in hamster liver: regulation of cholinephosphotransferase activity by endogenous argininosuccinate

1993 ◽  
Vol 289 (3) ◽  
pp. 727-733 ◽  
Author(s):  
K M O ◽  
P C Choy
Keyword(s):  
Enzyme Activity ◽  
Substantial Decrease ◽  
Compensatory Mechanism ◽  
Choline Uptake ◽  
Endogenous Inhibitor ◽  
Short Term ◽  
Phosphatidylcholine Biosynthesis ◽  
Choline Phosphotransferase ◽  
Pool Sizes

The control of phosphatidylcholine biosynthesis in the hamster liver was examined. Livers of hamsters fasted for 24 and 48 h were perfused with labelled choline. Under both fasting conditions, the incorporation of labelled choline into phosphatidylcholine was reduced. After 48 h of fasting, the 52% reduction in phosphatidylcholine biosynthesis was caused by changes in several factors including a diminishing rate of choline uptake and severe reductions in the pool sizes of ATP and CTP (to 33-37% control values) which resulted in a decrease in the pools of choline-containing metabolites. The activation of cytidylyltransferase after 48 h of fasting might be regarded as a compensatory mechanism for the maintenance of phosphatidylcholine biosynthesis. After 24 h of fasting, a 25% reduction in phosphatidylcholine biosynthesis was observed. The ATP and CTP levels were decreased but the reduction was not severe enough to affect the choline uptake or the labelling of the phosphocholine fraction. The activities of the cytidylyltransferase remained unchanged but an accumulation of labelled CDP-choline was detected. Although choline-phosphotransferase activity was not changed in the microsomes, the enzyme activity was attenuated in the postmitochondrial fraction. Further analysis revealed that cholinephosphotransferase in the liver was inhibited by an endogenous inhibitor in the cytosol which was later identified as argininosuccinate. The level of argininosuccinate was elevated during fasting and the change quantitatively accounted for the attenuation of cholinephosphotransferase activity. The inhibition of choline-phosphotransferase by argininosuccinate, coupled with a substantial decrease in the diacylglycerol level, would provide the hamster liver with an immediate mechanism for the transient modulation of phosphatidylcholine biosynthesis during short-term fasting.

Glucagon inhibits phosphatidylcholine biosynthesis via the CDP-choline and transmethylation pathways in cultured rat hepatocytes

1984 ◽  
Vol 62 (4) ◽  
pp. 196-202 ◽  
Author(s):  
Steven L. Pelech ◽  
P. Haydn Pritchard ◽  
Eric F. Sommerman ◽  
Anthony Percival-Smith ◽  
Dennis E. Vance
Keyword(s):  
Fatty Acid ◽  
Rat Hepatocytes ◽  
Biosynthetic Enzymes ◽  
Choline Uptake ◽  
Acetate Incorporation ◽  
Short Term ◽  
Monolayer Cultures ◽  
Phosphatidylcholine Biosynthesis ◽  
Cultured Rat Hepatocytes ◽  
In Cells

The short-term influence of insulin and glucagon on phosphatidylcholine biosynthesis in monolayer cultures of rat hepatocytes was investigated. Under conditions in which insulin (100 nM) stimulated [3H]acetate incorporation into fatty acid almost twofold, synthesis of phosphatidylcholine via CDP-choline and from phosphatidylethanolamine were unaffected. By contrast, glucagon (100 nM), even in the presence of insulin (100 nM), reduced the rate of phosphatidylcholine formation from [Me-3H]phosphocholine by approximately 25% (p < 0.05) within 1 h. Similarly, [3H]phosphatidylethanolamine incorporation into phosphatidylcholine was inhibited in cells exposed to glucagon. Insulin and glucagon had little or no effect on [Me-3H] choline uptake by the hepatocytes. No changes in the activities of the phosphatidylcholine biosynthetic enzymes in cytosol and microsomes from glucagon-treated cells could be detected.

scholarly journals Expression of human cholesterol 7α-hydroxylase in atherosclerosis-susceptible mice via adenovirus infection

1997 ◽  
Vol 324 (3) ◽  
pp. 863-867 ◽  
Author(s):  
Gina L. MOORE ◽  
Christian A. DREVON ◽  
Dietrich MACHLEDER ◽  
John D. TRAWICK ◽  
Alan McCLELLAND ◽  
...  
Keyword(s):  
Enzyme Activity ◽  
Transcriptional Repression ◽  
Adenovirus Vector ◽  
Chow Diet ◽  
Adenovirus Infection ◽  
Hepatic Inflammation ◽  
Short Term ◽  
Rous Sarcoma ◽  
Sarcoma Virus ◽  
Virus Promoter

Adenovirus is a vector for the delivery of genes mainly to the liver. Short-term (~3 days) studies using adenovirus transfection have provided valuable insights into how genes can complement normal and pathological phenotypes. When atherosclerosis-susceptible C57BL/6 mice were infected with an adenovirus vector containing the human 7α-hydroxylase cDNA (AV17h1) and fed on a chow diet, human 7α-hydroxylase mRNA and enzyme activity doubled compared with that in mice infected with an adenovirus vector (AV1Null) alone. In AV17h1-infected mice fed on a high fat cholic acid (HFCA) diet, mRNA expression and activity of both the endogenous and adenovirus (human) 7α-hydroxylase were repressed. AV17h1-infected mice fed on a HFCA diet and killed at mid-light had increased 7α-hydroxylase activity and mRNA compared with mice killed at mid-dark. Since expression of AV17h1 is driven by a constitutive Rous sarcoma virus promoter, the repression of human 7α-hydroxylase by the HFCA diet was unexpected. In spite of this post-transcriptional repression by the HFCA diet, AV17h1-infected mice expressed the human 7α-hydroxylase mRNA, causing its enzyme activity to be 3-fold greater than in AV1Null-infected mice. In AV17h1-infected mice, the 7α-hydroxylase enzyme activity varied as a linear function of human mRNA abundance. In conclusion, the accumulation of apolipoprotein B-containing lipoproteins in plasma of C57BL/6 mice fed on the HFCA diet was not reduced by longer-term (2 weeks) 7α-hydroxylase expression, probably because of its diminished expression caused by the diet and hepatic inflammation from the adenovirus infection. These results may suggest that adenovirus is effective in promoting longer-term (2 weeks) expression of 7α-hydroxylase.

Effects of amino acids and ethanolamine on choline uptake and phosphatidylcholine biosynthesis in baby hamster kidney-21 cells

1992 ◽  
Vol 70 (12) ◽  
pp. 1319-1324 ◽  
Author(s):  
Xiliang Zha ◽  
Francis T. Jay ◽  
Patrick C. Choy
Keyword(s):  
Amino Acids ◽  
Culture Media ◽  
Specific Radioactivity ◽  
Kinetic Studies ◽  
Choline Uptake ◽  
Dependent Manner ◽  
Baby Hamster Kidney ◽  
Concentration Dependent Manner ◽  
Cell Culture Media ◽  
Phosphatidylcholine Biosynthesis

The effects of amino acids and ethanolamine on choline uptake and phosphatidylcholine biosynthesis in baby hamster kidney (BHK-21) cells were investigated. The cells were incubated with labelled choline in the presence of an amino acid or ethanolamine. The uptake of labelled choline was noncompetitively inhibited by amino acids. Glycine, L-alanine, L-serine, L-leucine, L-aspartate, and L-arginine were effective inhibitors and a maximum of 22% inhibition of choline uptake was obtained with 5 mM glycine. Analyses of the labellings in the choline-containing metabolites revealed that the conversion of choline to CDP-choline and subsequently phosphatidylcholine was not affected by the presence of amino acids. The uptake of choline was also inhibited by ethanolamine in a concentration-dependent manner. Kinetic studies on the uptake of choline indicated that the inhibition by ethanolamine was competitive in nature. Although ethanolamine is a potent inhibitor of choline kinase, analyses of the labellings in the choline-containing metabolites indicated that the conversion of choline to phosphocholine was not affected in the cells incubated with ethanolamine. Ethanolamine did not change the pool sizes of phosphocholine and CDP-choline. Based on the specific radioactivity of CDP-choline and the labelling of phosphatidylcholine, the rates of phosphatidylcholine biosynthesis were not significantly different between the control and the ethanolamine-treated cells. In view of the concentrations of amino acids (millimolar) and ethanolamine (micromolar) in most cell culture media, it appeared that only amino acids were important metabolites for the regulation of choline uptake in BHK-21 cells. We conclude that both amino acids and ethanolamine have no direct effect on the biosynthesis of phosphatidylcholine.Key words: choline uptake, phosphatidylcholine biosynthesis, amino acids, ethanolamine, BHK-21 cells.

Short-Term Retinoic Acid Treatment Increases In Vivo, but Decreases In Vitro, Epidermal Transglutaminase-K Enzyme Activity and Immunoreactivity

1992 ◽  
Vol 99 (3) ◽  
pp. 283-288 ◽  
Author(s):  
Christopher E M Griffiths ◽  
Dean S Rosenthal ◽  
Ambati P Reddy ◽  
James T Elder ◽  
Anders. Astrom ◽  
...  
Keyword(s):  
Enzyme Activity ◽  
Retinoic Acid ◽  
Acid Treatment ◽  
Short Term ◽  
Retinoic Acid Treatment ◽  
Epidermal Transglutaminase

Endogenous hydrogen sulfide in perivascular adipose tissue: role in the regulation of vascular tone in physiology and pathology

2013 ◽  
Vol 91 (11) ◽  
pp. 889-898 ◽  
Author(s):  
Jerzy Bełtowski
Keyword(s):  
Insulin Resistance ◽  
Adipose Tissue ◽  
Hydrogen Sulfide ◽  
Vascular Tone ◽  
Compensatory Mechanism ◽  
Short Term ◽  
Insulin Sensitizer ◽  
Perivascular Adipose Tissue ◽  
S Oxidation ◽  
Lipophilic Statin

Hydrogen sulfide (H2S) is synthesized from l-cysteine by cystathionine β-synthase (CBS) or cystathionine γ-lyase (CSE), and is enzymatically metabolized in mitochondria by sulfide:quinone oxidoreductase (SQR). Recent studies have indicated that H2S is synthesized by CSE in perivascular adipose tissue (PVAT), and is responsible for the anticontractile effect of PVAT on adjacent vessels. The lipophilic statin atorvastatin increases PVAT-derived H2S by suppressing its mitochondrial oxidation; the effect that results from statin-induced depletion of ubiquinone. Experimental obesity induced by a highly palatable diet has a time-dependent effect on H2S in PVAT. Adipose tissue hypoxia suppresses H2S oxidation and increases its level in short-term obesity not associated with insulin resistance. In contrast, in long-term obesity, insulin resistance and (or) hyperinsulinemia result in the down-regulation of CSE and H2S deficiency, which is corrected by treatment with the insulin sensitizer rosiglitazone. In addition, cannabinoid CB1 receptor agonist administered for 2 weeks increases H2S by impairing mitochondria biogenesis. This indicates that the rate of mitochondrial H2S oxidation plays an important role in the regulation of H2S level in PVAT. Up-regulation of H2S signaling in short-term obesity and (or) by elevated endocannabinoids may be a compensatory mechanism that maintains vascular tone, despite endothelial dysfunction.

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