scholarly journals Control of Hep G2-cell triacylglycerol and apolipoprotein B synthesis and secretion by polyunsaturated non-esterified fatty acids and insulin

1992 ◽  
Vol 288 (1) ◽  
pp. 101-107 ◽  
Author(s):  
C D Byrne ◽  
T W M Wang ◽  
C N Hales
Keyword(s):  
Fatty Acids ◽  
Apolipoprotein B ◽  
Cellular Protein ◽  
Mrna Levels ◽  
Hep G2 ◽  
Apo B ◽  
Esterified Fatty Acids ◽  
Affect Cell Viability ◽  
Intracellular Content ◽  
Cellular Protein Content

Non-esterified fatty acids (NEFAs) and insulin are important factors in the control of lipoprotein secretion, but the mechanism of action is unclear. The present study was undertaken to determine whether insulin and NEFAs modulated hepatic secretion of triacylglycerol and apolipoprotein B (apo-B) by regulation of hepatic intracellular apo-B content. The experiments were performed with the human hepatoblastoma cell line Hep G2, for periods of up to 72 h in the presence and absence of NEFAs and insulin. Higher concentrations of eicosapentanoate (EPA) sustained for 72 h decreased cellular protein content (at 250 microM) or caused cell death (at 750 microM), and this effect was not observed with the other NEFAs studied, whereas 75 microM-EPA did not affect cell viability. Compared with the absence of NEFA, 75 microM-EPA did not alter the intracellular triacylglycerol content, but decreased the intracellular content of apo-B by 47% (P < 0.01) and decreased secreted triacylglycerol and secreted apo-B by 13% (P < 0.05) and 21% (P < 0.01) respectively, after 72 h. However 250 microM-oleate increased the intracellular triacylglycerol by 36% (P < 0.01), intracellular apo-B by 22% (P < 0.05) and secreted triacylglycerol and apo-B by 20-30% (P < 0.05-0.01). Insulin decreased secreted triacylglycerol and apo-B in the presence of each NEFA studied by 20-30%. There was no correlation between the changes in intracellular triacylglycerol and the rate of secretion. However, when the secreted triacylglycerol or apo-B was plotted against intracellular apo-B content a significant correlation was observed (r = 0.89, P < 0.001 for both analyses). Apo-B mRNA levels did not change after 72 h incubation with oleate or EPA. These results demonstrate that EPA can be toxic to hepatocytes and that NEFAs and insulin control secretion of triacylglycerol and apo-B by regulation of the intracellular apo-B concentration, thus controlling assembly of apo-B with triacylglycerol to form lipoproteins.

scholarly journals Endurance training increases stimulation of uncoupling of skeletal muscle mitochondria in humans by non-esterified fatty acids: an uncoupling-protein-mediated effect?

2000 ◽  
Vol 351 (3) ◽  
pp. 805-810 ◽  
Author(s):  
Michail TONKONOGI ◽  
Anna KROOK ◽  
Brandon WALSH ◽  
Kent SAHLIN
Keyword(s):  
Fatty Acids ◽  
Endurance Training ◽  
Uncoupling Protein ◽  
Mrna Level ◽  
Relative Increase ◽  
Essential Property ◽  
Mrna Levels ◽  
Purine Nucleotides ◽  
Muscle Mitochondria ◽  
Esterified Fatty Acids

Uncoupled respiration (UCR) is an essential property of muscle mitochondria and has several functions in the cell. We hypothesized that endurance training may alter the magnitude and properties of UCR in human muscle. Isolated mitochondria from muscle biopsies taken before and after 6 weeks of endurance exercise training (n = 8) were analysed for UCR. To investigate the role of uncoupling protein 2 (UCP2) and UCP3 in UCR, the sensitivity of UCR to UCP-regulating ligands (non-esterified fatty acids and purine nucleotides) and UCP2 and UCP3 mRNA expression in muscle were examined. Oleate increased the mitochondrial oxygen consumption rate, an effect that was not attenuated by GDP and/or cyclosporin A. The effect of oleate was significantly greater after compared with before training. Training had no effect on UCP2 or UCP3 mRNA levels, but after training the relative increase in respiration rate induced by oleate was positively correlated with the UCP2 mRNA level. In conclusion, we show that the sensitivity of UCR to non-esterified fatty acids is up-regulated by endurance training. This suggests that endurance training causes intrinsic changes in mitochondrial function, which may enhance the potential for regulation of aerobic energy production, prevent excess free radical generation and contribute to a higher basal metabolic rate.

Increased plasma non-esterified fatty acids and platelet-activating factor acetylhydrolase are associated with susceptibility to atherosclerosis in mice

2004 ◽  
Vol 106 (4) ◽  
pp. 421-432 ◽  
Author(s):  
Uma SINGH ◽  
Shumei ZHONG ◽  
Momiao XIONG ◽  
Tong-bin LI ◽  
Allan SNIDERMAN ◽  
...  
Keyword(s):  
Gene Expression ◽  
Fatty Acids ◽  
Animal Models ◽  
Enzyme Activities ◽  
Platelet Activating Factor ◽  
Density Lipoprotein ◽  
Mrna Levels ◽  
Wild Type ◽  
Platelet Activating Factor Acetylhydrolase ◽  
Esterified Fatty Acids

Animal models provide vital tools to explicate the pathogenesis of atherosclerosis. Accordingly, we established two atherosclerosis-prone mice models: (i) mice lacking the LDL (low-density lipoprotein) receptor (LDLR) and the ability to edit apo (apolipoprotein) B mRNA (Apobec1; designated LDb: LDLR-/-Apobec1-/-), and (ii) mice with the LDb background, who also overexpressed human apoB100 (designated LTp: LDLR-/-Apobec1-/-ERhB+/+). Both LDb and LTp mice had markedly elevated levels of LDL and increased levels of NEFAs (non-esterified fatty acids) compared with C57BL/6 wild-type mice. However, fasting glucose and insulin levels in both animals were not different than those in C57BL/6 wild-type mice. It has been suggested that PAF-AH (platelet-activating factor acetylhydrolase) increases susceptibility to vascular disease. Both LDb and LTp mice had significantly higher PAF-AH mRNA levels compared with C57BL/6 wild-type mice. PAF-AH gene expression was also significantly influenced by age and sex. Interestingly, PAF-AH mRNA levels were significantly higher in both LTp male and female mice than in the LDb mice. This increased PAF-AH gene expression was associated with elevated plasma PAF-AH enzyme activities (LTp>LDb>C57BL/6). Moreover, a greater proportion of PAF-AH activity was associated with the apoB-containing lipoproteins: 29% in LTp and 13% in LDb mice compared with C57BL/6 wild-type animals (6.7%). This may explain why LTp mice developed more atherosclerotic lesions than LDb mice by 8 months of age. In summary, increased plasma NEFAs, PAF-AH mRNA and enzyme activities are associated with accelerated atherogenesis in these animal models.

The effects of fatty acids on apolipoprotein B secretion by human hepatoma cells (HEP G2)

2000 ◽  
Vol 150 (2) ◽  
pp. 255-264 ◽  
Author(s):  
Sharon Arrol ◽  
Michael I Mackness ◽  
Paul N Durrington
Keyword(s):  
Fatty Acids ◽  
Apolipoprotein B ◽  
Hepatoma Cells ◽  
Human Hepatoma ◽  
Hep G2 ◽  
Human Hepatoma Cells

Effects of lipid administration on lymphatic apolipoprotein A-IV and B output and synthesis

1996 ◽  
Vol 271 (2) ◽  
pp. G322-G329
Author(s):  
M. Nishimura ◽  
M. Seishima ◽  
H. Ohashi ◽  
A. Noma
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Free Fatty Acids ◽  
The Other ◽  
Mrna Levels ◽  
Control Solution ◽  
Apo B ◽  
Apolipoprotein A ◽  
Lipoprotein Assembly ◽  
Long Chain

We examined the mesenteric lymphatic and portal venous transport of triglyceride (TG), free fatty acids (FFA), apolipoproteins (apo)A-IV and B in response to a bolus duodenal infusion of a TG-free control solution, and long-chain (18:1) and medium-chain (8:0) TG (LCT and MCT, respectively) emulsions in the rat. Additionally, intestinal and hepatic apo A-IV and apo B mRNA levels were also measured. Lymph apo A-IV, apo B (B-48), FFA, and TG output increased after LCT infusion, whereas only apo A-IV and FFA outputs increased after MCT infusion. On the other hand, portal FFA and apo A-IV transports increased at 15 min after MCT infusion but not after LCT infusion. Portal TG and apo B transports were not altered by either MCT or LCT infusion. Jejunal apo A-IV mRNA was increased after both MCT and LCT infusions. Hepatic apo A-IV mRNA levels increased only after MCT infusion. Conversely, neither LCT nor MCT had any effect on apo B mRNA levels in intestine or liver. These results indicate that apo A-IV is regulated by MCT absorption and that fatty acid reesterification and lipoprotein assembly are not prerequisite for such regulation. Conversely, it is likely that apo B-48 participates only in the formation and/or transport of chylomicrons after LCT absorption.

scholarly journals Effects of a thyromimetic on apolipoprotein B-100 in rats

2000 ◽  
Vol 25 (3) ◽  
pp. 299-308 ◽  
Author(s):  
Y Wada ◽  
S Matsubara ◽  
J Dufresne ◽  
GM Hargrove ◽  
ZF Stephan ◽  
...  
Keyword(s):  
Apolipoprotein B ◽  
Mrna Levels ◽  
Dependent Manner ◽  
Mrna Editing ◽  
Human Hepatoma Cells ◽  
Apo B ◽  
Editing Activity ◽  
Cardiac Sparing ◽  
Dose Dependent

We have studied the effects of a cardiac sparing thyromimetic, CGS 23425, on postprandial levels of triglycerides, abundance of apolipoprotein B (apo B) protein and hepatic apo B mRNA expression in rats. When compared with control rats, triglyceride clearance was significantly accelerated by treatment with CGS 23425. A full return to baseline values was achieved within 8 h after ingesting a large quantity of fat, as compared to >24 h in control animals. The abundance of apo B-100 protein in CGS 23425-treated hyperlipidemic rats decreased in a dose-dependent manner, but levels of apo B-48 were not significantly affected. Like L-tri-iodothyronine (L-T(3)), treatment with 30 microg/kg CGS 23425 for 6 or 9 days decreased the levels of apo B-100 protein by 80% and 40% respectively. This change was paralleled by a 27% reduction in hepatic apo B-100 mRNA. To investigate a potential mechanism of CGS 23425 action, we measured in vitro apo B mRNA editing activity in hepatocellular extract from control or CGS 23425-treated rats. Treatment with CGS 23425 increased activity of the hepatic apo B-100 editosome, apobec-1. In human hepatoma cells which lack apobec-1 activity, apo B-100 mRNA levels remained the same in cells treated with or without the agent. In summary, these observations show that CGS 23425 decreases the levels of apo B-100 in rats. This action of CGS 23425 involves apo B-100 mRNA editing activity.

Oncotic pressure regulates gene transcriptions of albumin and apolipoprotein B in cultured rat hepatoma cells

1992 ◽  
Vol 263 (2) ◽  
pp. C397-C404 ◽  
Author(s):  
A. Yamauchi ◽  
Y. Fukuhara ◽  
S. Yamamoto ◽  
F. Yano ◽  
M. Takenaka ◽  
...  
Keyword(s):  
Apolipoprotein B ◽  
Protein S ◽  
Hepatoma Cells ◽  
Mrna Levels ◽  
Dependent Manner ◽  
Oncotic Pressure ◽  
Regulation Of Expression ◽  
Apo B ◽  
Albumin Mrna ◽  
Rat Hepatoma

The mechanism of the accelerated syntheses of albumin and apolipoprotein B (apo B) in response to decreased oncotic pressure was investigated in cultured rat hepatoma H4-II-E cells. Addition of dextran (mol wt 6-9 x 10(4)) to the culture medium decreased the levels of albumin and apo B mRNAs in an oncotic pressure-dependent manner. The reductions of both mRNAs were attenuated with increase in the molecular weight of dextran, which resulted in a decrease in oncotic pressure. Addition of macromolecule increased the viscosity in medium; however, alteration of viscosity appeared not to correlate with albumin and apo B mRNA levels. Transcriptional run-on assays with isolated nuclei from dextran-treated vs. untreated hepatoma cells indicated that the changes in steady-state mRNA levels were mainly controlled at the transcriptional step. Treatment with cycloheximide increased albumin mRNA to the basal level, which was effectively suppressed by dextran, and resulted in superinduction of apo B mRNA. These changes occurred primarily at the transcriptional step. These results suggest that regulations of the expressions of the albumin and apo B genes for adaptive increases in the mRNAs may require the continued synthesis of a labile protein(s) or a limiting transcription factor(s). We conclude that oncotic pressure plays an important role in regulation of expression of the albumin and apo B genes at the transcriptional step.

Regulation of apolipoprotein secretion by long-chain polyunsaturated fatty acids in newborn swine enterocytes

2001 ◽  
Vol 280 (6) ◽  
pp. G1137-G1144 ◽  
Author(s):  
Heng Wang ◽  
Song Lu ◽  
Jianhui Du ◽  
Ying Yao ◽  
Helen M. Berschneider ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Polyunsaturated Fatty Acids ◽  
Infant Formula ◽  
Lipid Synthesis ◽  
Density Lipoprotein ◽  
Mrna Levels ◽  
Apo B ◽  
Cellular Phospholipid ◽  
Long Chain

Long-chain polyunsaturated fatty acids (LC-PUFA) are important in the development of the immature nervous system, and adding these fatty acids to infant formula has been proposed. To determine the effect of n-3 LC-PUFA on apolipoprotein secretion and lipid synthesis in newborn swine enterocytes, differentiated IPEC-1 cells were incubated for 24 h with docosahexaenoic acid (DHA; 22:6) or eicosapentaenoic acid (EPA; 20:5) complexed with albumin at a fatty acid concentration of 0.8 mM or albumin alone (control) added to the apical medium. Oleic acid (OA; 18:1) was used a control for lipid-labeling studies. Both DHA and EPA reduced apolipoprotein (apo) B secretion by one-half, whereas EPA increased apo A-I secretion. The increased apo A-I secretion occurred primarily in the high-density lipoprotein fraction. These changes in apoprotein secretion were not accompanied by significant changes in synthesis. Modest decreases in apo B mRNA levels were observed for DHA and EPA, whereas there were no changes in apo A-I mRNA abundance. EPA reduced cellular triacylglycerol labeling by one-half, and DHA and EPA decreased cellular phospholipid labeling compared with OA. Labeled triacylglycerol secretion was decreased 75% by EPA, and DHA doubled labeled phospholipid secretion. If present in vivo, these effects should be considered before supplementing infant formula with these fatty acids.

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