Eicosapentaenoic acid inhibits synthesis and secretion of triacylglycerols by cultured rat hepatocytes (original) (raw)
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The Journal of Lipid Research
The mechanism for the reduced hepatic production of triacylglycerol in the presence of eicosapentaenoic acid was explored in short-term experiments using cultured parenchymal cells and microsomes from rat liver. Oleic, palmitic, stearic, and linoleic acids were the most potent stimulators of tria~yl[~H]glycerol synthesis and secretion by hepatocytes, whereas erucic, a-linolenic, y-linolenic, arachidonic, docosahexaenoic, and eicosapentaenoic acids (in decreasing order) were less stimulatory. There was a linear correlation (r= 0.85, PcO.01) between synthesis and secretion of tria~yl[~H]glycerol for the fatty acids examined. The extreme and opposite effects of eicosapentaenoic and oleic acids on triacylglycerol metabolism were studied in more detail. With increasing number of free fatty acid molecules bound per molecule of albumin, the rate of synthesis and secretion of tria~yl[~H]glycerol increased, most markedly for oleic acid. Cellular uptake of the two fatty acids was similar, but more free eicosapentaenoic acid accumulated intracellularly. Eicosapentaenoic acid caused higher incorporation of ['Hlwater into phospholipid and lower incorporation into triacylglycerol and cholesteryl ester as compared to oleic acid. No difference was observed between the fatty acids on incorporation into cellular free fatty acids, monoacylglycerol and diacylglycerol. The amount of some 16-and 18-carbon fatty acids in triacylglycerol was significantly higher in the presence of oleic acid compared with eicosapentaenoic acid. Rat liver microsomes in the presence of added 1,2-dioleoylglycerol incorporated eicosapentaenoic acid and eicosapentaenoyl-CoA into triacylglycerol to a lesser extent than oleic acid and its CoA derivative. Decreased formatiop of triacylglycerol was also observed when eicosapentaenoyl-CoA was given together with oleoyl-CoA, whereas palmitoyl-CoA, stearoyl-CoA, linoleoyl-CoA, linolenoyl-CoA, and arachidonoyl-CoA had no inhibitory effect.
Biochemical Journal, 1999
Hypolipidaemic fatty acid derivatives and polyunsaturated fatty acids decrease concentrations of plasma triacylglycerol by mechanisms that are not fully understood. Because poor susceptibility to β-and\or ω-oxidation is apparently a determinant of the peroxisome proliferating and hypolipidaemic capacity of fatty acids and derivatives, the relative importance of activation of the peroxisome-proliferator-activated receptor α (PPARα), fatty acid oxidation and triacylglycerol synthesis were examined. We have compared the effects of differentially β-oxidizable fatty acids on these parameters in primary cultures of rat hepatocytes. Tetradecylthioacetic acid (TTA), 2-methyleicosapentaenoic acid and 3-thia-octadecatetraenoic acid, which are non-β-oxidizable fatty acid derivatives, were potent activators of a glucocorticoid receptor (GR)-PPARα chimaera. This activation was paradoxically reflected in an substantially increased oxidation of [1-"%C]palmitic acid and\or oleic acid. The incorporation of [1-"%C]palmitic acid and\or oleic acid into cell-associated and secreted triacylglycerol was decreased by 15-20 % and 30 % respectively with these non-β-oxidizable fatty acid derivatives. The CoA ester of TTA inhibited the esterification of 1,2-
Atherosclerosis, 1987
The consumption of long chain polyunsaturated fatty acids by fish oils leads to profound lowering of plasma triacylglycerol but not of plasma cholesterol. Reasons for this were investigated with the human hepatoma cell line, the Hep G2 cell. Incubations with oleic acid (18 : 1 n9), linoleic acid (18 : 2 n6) and the characteristic marine fatty acid eicosapentaenoic acid (EPA, 20 : 5 n3) enriched cellular triacylglycerol mass, though least with EPA. However, secretion of very low density lipoprotein (VLDL) triacylglycerol and apoprotein B (measured by formation from [ 3 HIglycerol and [ 3 Hlleucine) was markedly inhibited by EPA. Preincubation with linoleic acid reduced VLDL triacylglycerol but not apo B secretion in comparison with oleic acid which stimulated both.
Biochimica et biophysica acta, 1995
We compared the effects of eicosapentaenoic acid (EPA) and oleic acid (OA) on glycerolipid and apolipoprotein B (apoB) metabolism in primary human hepatocytes, HepG2 cells and primary rat hepatocytes. Cells were incubated for 1 to 5 h with 0.25 mM bovine serum albumin in the absence (control) or presence of 1 mM of EPA or OA. Synthesis and secretion of [3H]glycerolipid were determined after 1 h incubation with [3H]glycerol. Cellular and medium apoB abundance was semi-quantitatively estimated in human cells by Western blotting. The following observations were made. (1) Compared to control, OA induced a 7-fold increase in [3H]triacylglycerol (TG) synthesis in human hepatocytes and a 4-fold increase in rat hepatocytes and HepG2 cells. EPA enhanced [3H]TG synthesis about 2-fold in all three cell types although it stimulated [3H]diacylglycerol (DG) synthesis to an extent (i.e., 2.5- to 5-fold) similar to OA. (2) In contrast to OA, which stimulated VLDL-associated [3H]TG secretion 2.5- to...
Journal of Biological Chemistry
The effects of eicosapentaenoic acid on synthesis and secretion of cholesterol and cholesterol ester by cultured rat hepatocytes were studied. In the presence of eicosapentaenoic acid cellular cholesterol esterification was decreased by SO-76% compared to oleic acid as measured by radioactive precursors and mass. Secretion of cholesterol ester was reduced by 60-80% in the presence of eicosapentaenoic acid as evaluated by radiolabeled fatty acids, mevalonolactone, and mass measurement. Oleic, palmitic, and stearic acid increased, whereas eicosapentaenoic and docosahexaenoic acid decreased synthesis and secretion of cholesterol ester as compared to a fatty acid-free control. Cellular and secreted free cholesterol were unaffected by eicosapentaenoic acid in comparison with oleic acid. The reduced cholesterol esterification was observed within 1 h and lasted for at least 20 h. Eicosapentaenoic acid caused lower cholesterol esterification than oleic acid in the concentration range 0.2-1.0 mM fatty acid and reduced the stimulatory effect of oleic acid on cholesterol ester formation. Cholesterol esterification and release of cholesterol ester were markedly increased by 26-hydroxycholesterol in the presence of eicosapentaenoic acid as well as oleic acid. Experiments with liver microsomes revealed that radioactive eicosapentaenoic acid and eicosapentaenoyl-CoA were poorer substrates (7-30%) for cholesterol esterification than oleic acid and oleoyl-CoA. Reduced formation of cholesterol ester was also observed when eicosapentaenoyl-CoA was given together with labeled oleoyl-CoA, whereas palmitoyl-CoA, stearoyl-CoA, linolenoyl-CoA, and arachidonoyl-CoA had no inhibitory effect. In conclusion, eicosapentaenoic acid reduced cellular cholesterol esterification by inhibiting the activity of acyl-CoAxholesterol acyltransferase. The lowered cholesterol esterification caused by eicosapentaenoic acid secondly decreased secretion of very low density lipoprotein cholesterol ester.
Influence of eicosapentaenoic acid (20:5, n-3) on secretion of lipoproteins in CaCo-2 cells
The Journal of Lipid Research
CaCo-2 cells, grown on filter membranes, were used to study the effects of fatty acids on cellular metabolism of triacylglycerol and phospholipids. The rate of triacylglycerol secretion was enhanced more than 2-fold, from 1 to 2 weeks after reaching confluency, in the presence of 0.6 mM fatty acids. Triacylglycerol secretion and oxidation of oleic acid increased 2and 9-fold, respectively, with this culture system, as compared to cells grown on conventional plastic dishes. Eicosapentaenoic acid (20:5 n-3), when compared to oleic acid, did not reduce formation of triacylglycerol or enhance phospholipid synthesis in CaCo-2 cells during short term (< 24 h) experiments, when the cells resided on membranes, regardless of what type of radioisotopes were used as precursors in the incubation media. However, the n-3 fatty acid was preferentially incorporated into phosphatidylinositol, lysophosphatidylcholine, and sphingomyelin, as compared to oleic acid. The disappearance from the apical medium and cellular uptake of labeled eicosapentaenoic and oleic acid were similar during incubations u p to 24 h, and the metabolism of these fatty acids to acid-soluble materials and COZ was equal. Light scattering analysis indicated that secreted lipoproteins of density <1.006 g/ml were in the same size-range as chylomicrons derived from human plasma. Assessment of Downloaded from Ranheim et al. Fish oil and lipid metabolism in CaCo-2 cells Runhim d ul. Fish oil and lipid metabolism in CaCo-2 cells
Lipids, 1996
Fish oils rich in n-3 fatty acids have been shown to decrease plasma lipid levels, but the underlying mechanism has not yet been elucidated. This investigation was performed in order to further clarify the effects of purified ethyl esters of eicosapentaenoic acid (EPA-EE) and docosahexaenoic acid (DHA-EE) on lipid metabolism in rats. The animals were fed EPA-EE, DHA-EE, palmitic acid, or corn oil (1 g/kg/d) by orogastrif intubation along with a chow background diet for three months. At the end the animals were sacrificed. Plasma and liver lipids were measured, as well as lipid-related enzyme activities and mRNA levels. The fatty acid composition of plasma and different tissues was also determined. This study shows that, compared to the corn oil control, EPA-EE and DHA-EE lowered plasma cholesterol level, whereas only EPA-EE lowered the amount of plasma triacylglycerol. In liver peroxisomes, both EE preparations increased fatty acyI-CoA oxidase FAO activities, and neither altered 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase activities. In liver microsomes, EPA-EE raised HMG-CoA reductase and acyI-CoAicholesterol acyltransferase activities, whereas DHA-EE lowered the former and did not affect the latter. Neither product altered mRNA levels for HMG-CoA reductase, low density lipoprotein-receptor, or low density lipoprotein-receptor related protein. EPA-EE lowered plasma triacylglycerol, reflecting lowered very low density lipoprotein secretion, thus the cholesterol lowering effect in EPA-EE-treated rats may be secondary to the hypotriacylglycerolemic effect. An inhibition of HMG-CoA reductase activity in DHA-EE treated rats may contribute to the hypocholesterolemic effect. The present study reports that 20:5n-3, and not 22:6n-3, is the fatty acid primarily responsible for the triacylglycerol lowering effect of fish oil. Finally, 20:5n-3 was not converted to 22:6n-3, whereas retroconversion of 22:6n-3 to 20:5n-3 was observed. Abbreviations: ACAT, acyl-CoA:cholesterol acyltransferase; DHA, docosahexaenoic acid; DHA-EE, DHA as ethyl ester; EPA, eicosapentaenoic acid; EPA-EE, EPA as ethyl ester; HMGq2oA, 3-hydroxy-3-methylglutaryl-CoA; LDL, low density lipoprotein; LRP-4, LDL-receptor related protein; VLDL, very low density lipoprotein.
Biochemical Journal, 1988
1. The synthesis and secretion of glycerolipids by monolayer cultures of rat hepatocytes was measured by using radioactive choline, glycerol and fatty acids and by measuring the concentration of triacylglycerols in the cells. 2. The incorporation of glycerol into triacylglycerol and the accumulation of this lipid in hepatocytes showed little specificity for fatty acids, except for eicosapentaenoate, which stimulated least. Oleate was more effective at stimulating triacylglycerol secretion than were palmitate, stearate, arachidonate and eicosapentaenoate. 3. Linoleate, linolenate, arachidonate and eicosapentaenoate stimulated the incorporation of glycerol and choline into phosphatidylcholine that was secreted into the medium. By contrast, palmitate and stearate produced relatively high incorporations into the phosphatidylcholine that remained in the cells. 4. The incorporation of glycerol and choline into lysophosphatidylcholine in the medium was stimulated 2-3-fold by all of the uns...
Prostaglandins, Leukotrienes and Essential Fatty Acids, 2009
Eicosapentaenoic acid (EPA) is a member of the family of n-3 polyunsaturated fatty acids (PUFAs) that are clinically used to treat hypertriglyceridemia. The triglyceride (TG) lowering effect is likely due to an alteration in lipid metabolism in the liver, but details have not been fully elucidated. To assess the effects of EPA on hepatic TG metabolism, mice were fed a high-fat and high-sucrose diet (HFHSD) for 2 weeks and were given highly purified EPA ethyl ester (EPA-E) daily by gavage. The HFHSD diet increased the hepatic TG content and the composition of monounsaturated fatty acids (MUFAs). EPA significantly suppressed the hepatic TG content that was increased by the HFHSD diet. EPA also altered the composition of fatty acids by lowering the MUFAs C16:1 and C18:1 and increasing n-3 PUFAs, including EPA and docosahexaenoic acid (DHA). Linear regression analysis revealed that hepatic TG content was significantly correlated with the ratios of C16:1/C16:0, C18:1/C18:0, and MUFA/n-3 PUFA, but was not correlated with the n-6/n-3 PUFA ratio. EPA also decreased the hepatic mRNA expression and nuclear protein level of sterol regulatory element binding protein-1c (SREBP-1c). This was reflected in the levels of lipogenic genes, such as acetyl-CoA carboxylase a (ACCa), fatty acid synthase, stearoyl-CoA desaturase 1 (SCD1), and glycerol-3-phosphate acyltransferase (GPAT), which are regulated by SREBP-1c. In conclusion, oral administration of EPA-E ameliorates hepatic fat accumulation by suppressing TG synthesis enzymes regulated by SREBP-1 and decreases hepatic MUFAs accumulation by SCD1.
Lipids, 1998
Fourteen healthy volunteers were randomly allocated to receive 4 g highly purified ethyl esters of eicosapentaenoic acid (EPA) (95% pure, n = 7) or docosahexaenoic acid (DHA) (90% pure, n = 7) daily for 5 wk in supplement to their ordinary diet. The n-3 fatty acids were given with a standard high-fat meal at the beginning and the end of the supplementation period. EPA and DHA induced a similar incorporation into chylomicrons which peaked 6 h after the meal. The relative uptake of EPA and DHA from the meal was >90% compared with the uptake of oleic acid. During absorption, there was no significant elongation or retroconversion of EPA or DHA in total chylomicron fatty acids. The concentration of EPA decreased by 13% and DHA by 62% (P < 0.001) between 6 and 8 h after the meal. During the 5-wk supplementation period, EPA showed a more rapid and comprehensive increase in serum phospholipids than did DHA. DHA was retroconverted to EPA, whereas EPA was elongated to docosapentaenoic acid (DPA). The postprandial triglyceridemia was suppressed by 19 and 49% after prolonged intake of EPA and DHA, respectively, indicating that prolonged intake of DHA is equivalent to or even more efficient than that of EPA in lowering postprandial triglyceridemia. This study indicates that there are metabolic differences between EPA and DHA which may have implications for the use of n-3 fatty acids in preventive and clinical medicine. FIG. 4. Chylomicron triglyceride (TG) concentrations after a standard high-fat meal before (-) and after (---) a daily intake of 4 g EPA (A) or DHA (B) for 5 wk. Symbols are means ± SD.