Metabolic heterogeneity of post-lipolysis rat mesenteric lymph small chylomicrons produced in vitro

Human milk phospholipid analog improved the digestion and absorption of 1,3-dioleoyl-2-palmitoyl-glycerol

The present study investigated the effects of a human milk phospholipid analog (HPLA) on the digestion and absorption of 1,3-dioleoyl-2-palmitoyl-glycerol (OPO). The HPLA contained 26.48% phosphatidylethanolamine (PE), 24.64% phosphatidylcholine (PC), 36.19% sphingomyelin (SM), 6.35% phosphatidylinositol (PI), and 6.32% phosphatidylserine (PS), with 40.51% C16:0, 17.02% C18:0, 29.19% C18:1, and 13.26% C18:2. The HPLA prevented OPO from hydrolysis during the in vitro gastric phase, while it facilitated the digestion of OPO during the in vitro intestinal stage, resulting in the production of large amounts of diglycerides (DAGs) and monoglycerides (MAGs). In vivo experimental results showed that the HPLA might increase the gastric emptying rate of OPO and increase the hydrolysis and absorption of OPO at an early stage of intestinal digestion. Notably, fatty acids in the serum of the OPO group decreased to their initial value at 5 h, while the serum of the OPO + HPLA (OPOH) group still contained a high level of fatty acids indicating that the HPLA was helpful in maintaining serum lipid at a high level, which might be beneficial for sustainably providing energy for babies. The present study provides data support for the potential application of Chinese human milk phospholipid analogs in infant formulas.

Milk Polar Lipids Affect In Vitro Digestive Lipolysis and Postprandial Lipid Metabolism in Mice

BACKGROUND

Polar lipid (PL) emulsifiers such as milk PLs (MPLs) may affect digestion and subsequent lipid metabolism, but focused studies on postprandial lipemia are lacking.

OBJECTIVE

We evaluated the impact of MPLs on postprandial lipemia in mice and on lipid digestion in vitro.

METHODS

Female Swiss mice were gavaged with 150 μL of an oil-in-water emulsion stabilized with 5.7 mg of either MPLs or soybean PLs (SPLs) and killed after 1, 2, or 4 h. Plasma lipids were quantified and in the small intestine, gene expression was analyzed by reverse transcriptase-quantitative polymerase chain reaction. Emulsions were lipolyzed in vitro using a static human digestion model; triglyceride (TG) disappearance was followed by thin-layer chromatography.

RESULTS

In mice, after 1 h, plasma TGs tended to be higher in the MPL group than in the SPL group (141 μg/mL vs. 90 μg/mL; P = 0.07) and nonesterified fatty acids (NEFAs) were significantly higher (64 μg/mL vs. 44 μg/mL; P < 0.05). The opposite was observed after 4 h with lower TGs (21 μg/mL vs. 35 μg/mL; P < 0.01) and NEFAs (20 μg/mL vs. 32 μg/mL; P < 0.01) in the MPL group compared with the SPL group. This was associated at 4 h with a lower gene expression of apolipoprotein B (Apob) and Secretion Associated, Ras related GTPase 1 gene homolog B (Sar1b), in the duodenum of MPL mice compared with SPL mice (P < 0.05). In vitro, during the intestinal phase, TGs were hydrolyzed more in the MPL emulsion than in the SPL emulsion (decremental AUCs were 1750%/min vs. 180%/min; P < 0.01). MPLs enhance lipid intestinal hydrolysis and promote more rapid intestinal lipid absorption and sharper kinetics of lipemia.

CONCLUSIONS

Postprandial lipemia in mice can be modulated by emulsifying with MPLs compared with SPLs, partly through differences in chylomicron assembly, and TG hydrolysis rate as observed in vitro. MPLs may thereby contribute to the long-term regulation of lipid metabolism.

Impact of various emulsifiers on ALA bioavailability and chylomicron synthesis through changes in gastrointestinal lipolysis

Formulating healthy food rich in omega 3 fatty acids requires prior knowledge of the parameters influencing their bioavailability and their metabolic fate. In this context, we studied the effects of various emulsifiers widely used in the food industry, on the gastrointestinal lipolysis of flaxseed oil emulsions in an in vitro model and on the intestinal absorption and lymphatic secretion of alpha-linolenic acid (ALA) in rats. In vitro data showed that the emulsification of flaxseed oil with soya lecithin improved the gastric lipolysis of the oil (+30%), while the presence of Tween 80 or of sodium caseinate decreased it (-80% and -40%, respectively). The in vivo data demonstrated that the intestinal absorption and the lymphatic secretion of ALA were improved with soya lecithin (Cmax = 24 mg mL(-1)) and reduced in the presence of sodium caseinate (Cmax = 7 mg mL(-1)) compared to unemulsified flaxseed oil (Cmax = 16 mg mL(-1)); Tween 80 had no effect. In addition, the synthesized chylomicrons were notably larger and more numerous with soya lecithin whereas they were smaller in the presence of sodium caseinate (p < 0.05). This study shows that the intestinal bioavailability of ALA was increased by the emulsification of flaxseed oil with soya lecithin via an improved lipolysis, favouring the intestinal absorption of ALA and the secretion of many large chylomicrons in lymph.

Carboxylesterase1/Esterase-x regulates chylomicron production in mice

Elevated postprandial plasma triacylglycerol (TG) concentrations are commonly associated with obesity and the risk of cardiovascular disease. Dietary fat contributes to this condition through the production of chylomicrons. Carboxylesterases have been mainly studied for their role in drug metabolism, but recently they have been shown to participate in lipid metabolism; however, their role in intestinal lipid metabolism is unknown. Carboxylesterase1/esterase-x (Ces1/Es-x) deficient mice become obese, hyperlipidemic and develop hepatic steatosis even on standard chow diet. Here, we aimed to explore the role of Ces1/Es-x in intestinal lipid metabolism. Six-month old wild-type and Ces1/Es-x deficient mice were maintained on chow diet and intestinal lipid metabolism and plasma chylomicron clearance were analyzed. Along the intestine Ces1/Es-x protein is expressed only in proximal jejunum. Ablation of Ces1/Es-x expression results in postprandial hyperlipidemia due to increased secretion of chylomicrons. The secreted chylomicrons have aberrant protein composition, which results in their reduced clearance. In conclusion, Ces1/Es-x participates in the regulation of chylomicron assembly and secretion. Ces1/Es-x might act as a lipid sensor in enterocytes regulating chylomicron secretion rate. Ces1/Es-x might represent an attractive pharmacological target for the treatment of lipid abnormalities associated with obesity, insulin resistance and fatty liver disease.

Effect of acute and chronic moderate red or white wine consumption on fasted and postprandial lipemia in the rat

The effects of acute and chronic (10 wk) red or white wine consumption on fasted and postprandial lipemia in the rat model are reported. Fasted rats, in the acute study, were loaded intragastrically with 5 ml of an olive oil emulsion (30% w/v) in the presence or absence of wine (8% v/v ethanol), and either mesenteric lymph or blood was collected 3 h postprandially. Animals in the chronic study received either red or white wine in drinking water for a period of 10 wk (3% v/v ethanol). Blood samples were collected from animals in either the fasted state or after fat-wine loading. Postprandially, wine delayed gastric emptying, reduced lymph triacylglycerol (TAG) secretion concomitantly with increased number and decreased chylomicron (CM) size, and increased plasma TAG and CM concentrations. Phospholipid and cholesterol contents of CM, but not very-low-density lipoprotein (VLDL), were increased, indicating enhanced liver bile secretion; however, a significant increase in plasma VLDL concentration was observed. In the chronic study, a wine-fat load resulted in increased high-density lipoprotein (HDL) cholesterol concentration and less pronounced postprandial hypertriglyceridemia and hyperchylomicronemia. In the fasted state, plasma TAG and total apolipoprotein B concentrations were not modified in these animals, and an increase in HDL and a decrease in low-density lipoprotein (LDL)/HDL cholesterol ratios were observed. No liver function or intestinal lipid absorption impairment was observed. In conclusion, unlike binge drinking, chronic moderate wine consumption appears to have a cardioprotective effect in the fasted state, an effect attenuated by the observed temporary postprandial hyperchylomicronemia and hypertriglyceridemia resulting from a direct effect of alcohol on CM size and number.

Lymphatic chylomicron size is inversely related to biliary phospholipid secretion in mice

Biliary phospholipids (PL) stimulate dietary fat absorption by facilitating intraluminal lipid solubilization and by providing surface components for chylomicron (CM) assembly. Impaired hepatic PL availability induces secretion of large very-low-density lipoproteins, but it is unclear whether CM size depends on biliary PL availability. Biliary PL secretion is absent in multidrug resistance protein 2-deficient (Mdr2(-/-)) mice, whereas it is strongly increased in essential fatty acid (EFA)-deficient mice. We investigated lymphatic CM size and composition in mice with absent (Mdr2(-/-)) or enhanced (EFA deficient) biliary PL secretion and in their respective controls under basal conditions and during enteral lipid administration. EFA deficiency was induced by feeding mice a high-fat, EFA-deficient diet for 8 wk. Lymph was collected by mesenteric lymph duct cannulation with or without intraduodenal lipid administration. Lymph was collected in 30-min fractions for up to 4 h, and lymphatic lipoprotein size was determined by dynamic light-scattering techniques. Lymph lipoprotein subfractions were isolated by ultracentrifugation, and lipid composition was measured. Lymphatic CMs were significantly larger in Mdr2(-/-) mice than in Mdr2(+/+) controls either without (+50%) or with (+25%) enteral lipid administration, and molar core-surface ratios were increased [triglyceride (TG)-to-PL ratio: 4.4 +/- 1.4 in Mdr2(-/-) mice vs. 2.7 +/- 0.8 in Mdr2(+/+) mice, P < 0.001]. In contrast, EFA-deficient mice secreted lipoproteins into lymph that were significantly smaller than in EFA-sufficient controls (173 +/- 32 vs. 236 +/- 47 nm), with correspondingly decreased core-surface ratios (TG-to-PL ratio: 3.0 +/- 1.0 in EFA-deficient mice vs. 6.0 +/- 1.9 in EFA-sufficient mice, P < 0.001). CM size increased during fat absorption in both EFA-deficient and EFA-sufficient mice, but the difference between the groups persisted. In conclusion, the present results strongly suggest that the availability of biliary PL is a major determinant of the size of intestinally produced lipoproteins both under basal conditions and during lipid absorption. Altered CM size may have physiological consequences for postprandial CM processing.

Essential fatty acid deficiency in mice is associated with hepatic steatosis and secretion of large VLDL particles

Essential fatty acid (EFA) deficiency in mice decreases plasma triglyceride (TG) concentrations and increases hepatic TG content. We evaluated in vivo and in vitro whether decreased hepatic secretion of TG-rich very low-density lipoprotein (VLDL) contributes to this consequence of EFA deficiency. EFA deficiency was induced in mice by feeding an EFA-deficient (EFAD) diet for 8 wk. Hepatic VLDL secretion was quantified in fasted EFAD and EFA-sufficient (EFAS) mice using the Triton WR-1339 method. In cultured hepatocytes from EFAD and EFAS mice, VLDL secretion into medium was measured by quantifying [(3)H]-labeled glycerol incorporation into TG and phospholipids. Hepatic expression of genes involved in VLDL synthesis and clearance was measured, as were plasma activities of lipolytic enzymes. TG secretion rates were quantitatively similar in EFAD and EFAS mice in vivo and in primary hepatocytes from EFAD and EFAS mice in vitro. However, EFA deficiency increased the size of secreted VLDL particles, as determined by calculation of particle diameter, particle sizing by light scattering, and evaluation of the TG-to-apoB ratio. EFA deficiency did not inhibit hepatic lipase and lipoprotein lipase activities in plasma, but increased hepatic mRNA levels of apoAV and apoCII, both involved in control of lipolytic degradation of TG-rich lipoproteins. EFA deficiency does not affect hepatic TG secretion rate in mice, but increases the size of secreted VLDL particles. Present data suggest that hypotriglyceridemia during EFA deficiency is related to enhanced clearance of altered VLDL particles.

Effect of acute and chronic moderate alcohol consumption on fasted and postprandial lipemia in the rat

Effects of acute and chronic alcohol intake on fasted and postprandial lipemia in the rat model are reported. In the acute study, fasted rats are loaded with a 30% w/w olive oil emulsion with or without 8% alcohol in the form of ethanol, beer or whisky. After 3 h, either mesenteric lymph or blood is collected and the TAG-rich lipoprotein fractions are isolated. In the chronic study, animals received, for a period of 10 weeks, 3% alcohol in drinking water in the form of ethanol, beer or whisky. Blood samples were collected from animals in either the fasted state or after being loaded with the fat load as described above. Alcohol ingestion along with a fat load increases the number (increased net apoB48 secretion) and reduces the size (reduced TAG/apoB48 ratio) of CM secreted into the mesenteric lymph duct. It also delays gastric emptying, reduces trans-enterocyte TAG flux rates and increases plasma concentrations of TAG, cholesterol and CM. Similar conditions also results in increased total phospholipid and cholesterol content of CM but not of VLDL, indicating an enhanced liver bile secretion into the gut; however, a significant increase in plasma VLDL concentration is observed. Unlike the acute study, an alcohol-fat load in animals put on chronic alcohol intake results in increased HDL cholesterol concentrations and less pronounced postprandial hypertriglyceridemia and hypercholesterolemia but not hyperchylomicronemia. In the fasted state, plasma TAG and total apoB concentrations are not modified in these animals, and an increase in HDL and a decrease in total and LDL cholesterol concentrations are observed. No liver function impairment is observed following the 10-week period of chronic alcohol intake. In conclusion, unlike binge drinking, chronic moderate alcohol consumption appears to have a cardioprotective effect in the fasted state, an effect attenuated by the observed temporary postprandial hyperchylomicronemia and hypertriglyceridemia resulting from a direct effect of alcohol on CM size and number.

Effect of a surfactant, Tween 80, on the formation and secretion of chylomicrons in the rat

Effects of Tween 80, a nonionic surfactant, on size and number of chylomicrons (CM) secreted during lipid absorption in the rat model are reported. Fasted rats were loaded with either 154 mM NaCl or 25% (w/w) olive oil emulsion in 154 mM NaCl with 0, 0.1, 1 or 10% (w/w) Tween 80. After 3 h, either mesenteric lymph or blood was collected and their triacylglycerol-rich lipoprotein fraction (Sf>20 and Sf>400, respectively) isolated. Triacylglycerol (TAG) and apolipoprotein B48 (apoB48) concentrations in the lipoprotein fractions were assayed and their fluxes (lymph) calculated. TAG:apoB48 ratios, indicative of CM size, were determined. The data support the hypothesis that fat loading is accommodated mainly by increased average size, rather than number, of CM. Co-administration of Tween 80 with olive oil resulted in a significant increase in CM apoB48 secretion into the mesenteric lymph duct and in an increased concentration of apoB48 in the blood (Sf>400). Also, Tween 80-treated groups exhibited smaller mean CM size relative to the olive oil only group in both lymph and blood. The observed effect on CM size and number did not appear to be dose dependent at concentrations of Tween 80 above 0.1% (w/w). Incorporation of Tween 80 in the diet at 1 or 10% (w/w) concentrations reduced the TAG concentration in the stools; however, a significant increase in water content was observed at 10% (w/w) concentration. In conclusion, Tween 80 at 1 or 10% (w/w) doses can improve the efficiency of the digestive system to absorb dietary fat but at high concentrations (10%, w/w) it appeared to have a toxic or irritating effect on the gastrointestinal system. More importantly, the effect of Tween 80 on size and number of CM is a condition that favours a delay in their clearance rate.

Bile salt-stimulated carboxyl ester lipase influences lipoprotein assembly and secretion in intestine: a process mediated via ceramide hydrolysis

Bile salt-stimulated carboxyl ester lipase (CEL), also called cholesterol esterase, is one of the major proteins secreted by the pancreas. The physiological role of CEL was originally thought to be its mediation of dietary cholesterol absorption. However, recent studies showed no difference between wild type and CEL knockout mice in the total amount of cholesterol absorbed in a single meal. The current study tests the hypothesis that CEL in the intestinal lumen may influence the type of lipoproteins produced. A lipid emulsion containing 4 mm phospholipid, 13.33 mm [(3)H]triolein, and 2.6 mm [(14)C]cholesterol in 19 mm taurocholate was infused into the duodenum of lymph fistula CEL(+/+) and CEL(-/-) mice at a rate of 0.3 ml/h. Results showed no difference between CEL(+/+) and CEL(-/-) mice in the rate of cholesterol and triglyceride transport from the intestinal lumen to the lymph. However, CEL(-/-) mice produced predominantly smaller lipoproteins, whereas the CEL(+/+) mice produced primarily large chylomicrons and very low density lipoprotein. The proximal intestine of CEL(-/-) mice was also found to possess significantly less ceramide hydrolytic activity than that present in CEL(+/+) mice. By using Caco2 cells grown on Transwell membranes as a model, sphingomyelinase treatment inhibited the secretion of larger chylomicron-like lipoproteins without affecting total cholesterol secretion. In contrast, the addition of CEL to the apical medium increased the amount of large lipoproteins produced and alleviated the inhibition induced by sphingomyelinase. Taken together, this study identified a novel and physiologically significant role for CEL, namely the promotion of large chylomicron production in the intestine. The mechanism appears to be mediated through CEL hydrolysis of ceramide generated during the lipid absorption process.

Mechanism of the hypertriglyceridemia induced by tumor necrosis factor administration to rats

4 h after intravenous injection of recombinant HuTNF-alpha to fed rats, an increase in heart, diaphragm, and plasma lipoprotein lipase activity was observed. At the same time, a 40-60% decrease in enzymic activity in epididymal fat pad and kidney and 40% decrease in hepatic lipase activity in liver had occurred. Similar results were obtained 20 h after injection of recombinant HuTNF-alpha into fasted rats. Pretreatment with Indomethacin did not affect the changes in tissue lipoprotein lipase activity observed following recombinant HuTNF-alpha administration. Serum triacylglycerol concentration increased by 2- and 6-fold; 4 and 20 h after recombinant HuTNF-alpha administration. Disappearance of 14C-labeled triacylglycerol from the circulation after injection of small chylomicrons, biosynthetically labeled in their triacylglycerol and cholesterol moieties, was lower in TNF-treated than in control rats. However, the clearance rate of triacylglycerol was the same or even higher in recombinant HuTNF-alpha treated rats (assuming that 14C-labeled chylomicron triacylglycerol represents the serum triacylglycerol pool). The livers of recombinant HuTNF-alpha-treated rats and controls contained similar amounts of 14C-labeled lipids, but less [3H]cholesterol, suggesting that in recombinant HuTNF-alpha-treated rats, the liver took up chylomicron remnant particles enriched with triacylglycerol. Separation of the d less than 1.04 g/ml fraction of serum obtained from control and recombinant HuTNF-alpha treated rats by zonal ultracentrifugation revealed that in recombinant HuTNF-alpha-treated rats the lipoprotein particles were less lipolyzed than in controls. The secretion rate of [3H]triacylglycerol into the serum was determined 90 min after injection of [3H]palmitate albumin complex and Triton WR 1339. In recombinant HuTNF-alpha-treated rats, the secretion of [3H]triacylglycerol into plasma was 48% higher than in controls. It is suggested that the increase in lipoprotein lipase activity of heart and diaphragm resulted from an indirect effect of TNF. It is concluded that the increase in serum triacylglycerol in the recombinant HuTNF-alpha-treated rats is due mainly to an increased secretion of triacylglycerol by the liver. Impaired lipolysis, probably due to a fall in hepatic lipase could also contribute to the rise in plasma triacylglycerol.

Plasma lipoprotein and platelet function after heparin injection: studies in normal fasted and postprandial and in type V hyperlipoproteinemic subjects

The effect of heparin injection (50 IU/kg body weight) on plasma lipoprotein concentration and composition as well as on platelet aggregation and 14C-serotonin release was studied in normal fasted subjects, normal subjects 4 hr after a fatty meal (postprandial state), and in primary type V hyperlipoproteinemic patients. Heparin injection resulted in a reduction in plasma triglyceride, cholesterol, and phospholipids as well as in the inhibition of platelet function in either the presence or the absence of the plasma environment. Heparin injection resulted in catabolism of triglyceride-rich lipoproteins and increment of cholesterol and protein in the high-density lipoprotein (HDL) density range. In fasted normal subjects, very-low-density lipoprotein (VLDL) was reduced by 50%; in the postprandial state, both VLDL and chylomicrons decreased similarly; but in phenotype V hyperlipoproteinemia, only chylomicrons (but not VLDL) degraded. Heparin injection also caused increased electrophoretic mobility of plasma lipoprotein. Upon incubation of similar lipoprotein concentration, derived before and after heparin injection, with normal washed platelets, we found that in all the groups all the lipoproteins (except HDL) derived after heparin injection caused reduction in platelet activity. High-density lipoproteins derived after heparin injection, especially from type V hyperlipoproteinemic subjects, increased normal platelet activity, and this probably represents an effect of chylomicron remnant particles in the HDL density range. Our study thus demonstrates altered composition and concentration of plasma lipoprotein after heparin injection and may suggest the appearance of remnant particles with atherogenic properties.