Palmitic acid and linoleic acid metabolism in Caco-2 cells: different triglyceride synthesis and lipoprotein secretion

Ketogenic Diet High in Saturated Fat Promotes Colonic Claudin Expression without Changes in Intestinal Permeability to Iohexol in Healthy Mice

Ketogenic diets (KDs) have been studied in preclinical models of intestinal diseases. However, little is known of how the fat source of these diets influences the intestinal barrier. Herein, we studied the impact of four-week feeding with KD high either in saturated fatty acids (SFA-KD) or polyunsaturated linoleic acid (LA-KD) on paracellular permeability of the intestine to iohexol in healthy male C57BL/6J mice. We investigated jejunal and colonic tight junction protein expression, histological changes, and inflammatory markers (Il1b, Il6, Tnf, and Lcn2), as well as the activity and expression of intestinal alkaline phosphatase (IAP) in feces and jejunal tissue, respectively, and plasma lipopolysaccharide. KDs did not change intestinal permeability to iohexol after two or twenty-six days of feeding regardless of fat quality. SFA-KD, but not LA-KD, upregulated the colonic expression of tight junction proteins claudin-1 and -4, as well as the activity of IAP. Both KDs resulted in increased epithelial vacuolation in jejunum, and this was pronounced in SFA-KD. Jejunal Il1β expression was lower and colonic Il6 expression higher in LA-KD compared to SFA-KD. In colon, Tnf mRNA was increased in LA-KD when compared to controls. Overall, the results suggest that KDs do not influence intestinal permeability to iohexol but elicit changes in colonic tight junction proteins and inflammatory markers in both jejunum and colon. Future research will show whether these changes become of importance upon proinflammatory insults.

The Role of Dietary Fats in the Development and Prevention of Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is a significant cause of mortality and morbidity in preterm infants. The pathogenesis of NEC is not completely understood; however, intestinal immaturity and excessive immunoreactivity of intestinal mucosa to intraluminal microbes and nutrients appear to have critical roles. Dietary fats are not only the main source of energy for preterm infants, but also exert potent effects on intestinal development, intestinal microbial colonization, immune function, and inflammatory response. Preterm infants have a relatively low capacity to digest and absorb triglyceride fat. Fat may thereby accumulate in the ileum and contribute to the development of NEC by inducing oxidative stress and inflammation. Some fat components, such as long-chain polyunsaturated fatty acids (LC-PUFAs), also exert immunomodulatory roles during the early postnatal period when the immune system is rapidly developing. LC-PUFAs may have the ability to modulate the inflammatory process of NEC, particularly when the balance between n3 and n6 LC-PUFAs derivatives is maintained. Supplementation with n3 LC-PUFAs alone may have limited effect on NEC prevention. In this review, we describe how various fatty acids play different roles in the pathogenesis of NEC in preterm infants.

ZmCTLP1 is required for the maintenance of lipid homeostasis and the basal endosperm transfer layer in maize kernels

Maize kernel weight is influenced by the unloading of nutrients from the maternal placenta and their passage through the transfer tissue of the basal endosperm transfer layer (BETL) and the basal intermediate zone (BIZ) to the upper part of the endosperm. Here, we show that Small kernel 10 (Smk10) encodes a choline transporter-like protein 1 (ZmCTLP1) that facilitates choline uptake and is located in the trans-Golgi network (TGN). Its loss of function results in reduced choline content, leading to smaller kernels with a lower starch content. Mutation of ZmCTLP1 disrupts membrane lipid homeostasis and the normal development of wall in-growths. Expression levels of Mn1 and ZmSWEET4c, two kernel filling-related genes, are downregulated in the smk10, which is likely to be one of the major causes of incompletely differentiated transfer cells. Mutation of ZmCTLP1 also reduces the number of plasmodesmata (PD) in transfer cells, indicating that the smk10 mutant is impaired in PD formation. Intriguingly, we also observed premature cell death in the BETL and BIZ of the smk10 mutant. Together, our results suggest that ZmCTLP1-mediated choline transport affects kernel development, highlighting its important role in lipid homeostasis, wall in-growth formation and PD development in transfer cells.

Palmitic Acid Affects Intestinal Epithelial Barrier Integrity and Permeability In Vitro

Palmitic acid (PA), a long-chain saturated fatty acid, might activate innate immune cells. PA plays a role in chronic liver disease, diabetes and Crohn’s disease, all of which are associated with impaired intestinal permeability. We investigated the effect of PA, at physiological postprandial intestinal concentrations, on gut epithelium as compared to lipopolysaccharide (LPS) and ethanol, using an in vitro gut model, the human intestinal epithelial cell line Caco-2 grown on transwell inserts. Cytotoxicity and oxidative stress were evaluated; epithelial barrier integrity was investigated by measuring the paracellular flux of fluorescein, and through RT-qPCR and immunofluorescence of tight junction (TJ) and adherens junction (AJ) mRNAs and proteins, respectively. In PA-exposed Caco-2 monolayers, cytotoxicity and oxidative stress were not detected. A significant increase in fluorescein flux was observed in PA-treated monolayers, after 90 min and up to 360 min, whereas with LPS and ethanol, this was only observed at later time-points. Gene expression and immunofluorescence analysis showed TJ and AJ alterations only in PA-exposed monolayers. In conclusion, PA affected intestinal permeability without inducing cytotoxicity or oxidative stress. This effect seemed to be faster and stronger than those with LPS and ethanol. Thus, we hypothesized that PA, besides having an immunomodulatory effect, might play a role in inflammatory and functional intestinal disorders in which the intestinal permeability is altered.

Effects of fatty acids composition in a breakfast meal on the postprandial lipid responses: a systematic review and meta-analysis of randomised controlled trials

Replacement of food rich in saturated fatty acids (SFAs) with unsaturated fatty acids (UFAs) is a well-known dietary strategy to reduce the risk of cardiovascular disease while its impact on postprandial blood lipids is less examined. This study assessed the effects of fatty acids composition on the postprandial triglycerides and cholesterol responses. Seventeen randomised controlled trials were identified and pooled analysis results revealed that consumption of a UFAs-rich or an SFAs-rich breakfast meal did not acutely affect postprandial triglycerides and cholesterol responses. However, subgroup analysis observed that triglycerides incremental area under the curve was lower with an SFAs-rich meal (SMD: -0.36; 95% CI: -0.57, -0.15) over a less than 8 h duration, while was higher (SMD: 0.59; 95% CI: 0.05, 1.23) over a longer postprandial duration. It suggests that the postprandial duration is of importance when evaluating the effects of fatty acids composition on blood lipid responses.

Effects of ZnO nanoparticles on intestinal function and structure in normal/high fat diet-fed rats and Caco-2 cells

Aim: The present study was carried out to determine the effects of ZnO nanoparticles (ZnO–NPs) on intestinal function and pathophysiological alteration. Materials & methods: ZnO–NPs were synthesized and their characterizations were performed using various techniques. The Wistar male rats fed with normal diet and/or high fat diet (HFD) for 8 weeks and then orally received ZnO–NPs (5, 50 and 100 mg/kg bodyweight) for 28 days. The oxidative stress (SOD, CAT, GPx), inflammatory (TNF-α, iNOS) and apoptosis pathways (Bcl2, Bax and p53) genes expression and protein levels were measured by real-time polymerase chain reaction and available kit, respectively. The activity of Caspase-3, antioxidant capacity, as well as inflammatory markers were determined. The histological alterations of the large and small intestine were also evaluated with haematoxylin and eosin (H&E) as well as TdT dUTP nick end labeling (TUNEL) assay. The biochemical factors, viability and antioxidant activity were also determined in Caco-2 cells. Results: It was found that the antioxidant enzymes activity and genes expression markedly increased, while inflammatory and apoptosis pathways and TNF-α levels significantly decreased in the intestine of HFD-fed rats treated with 5 mg/kg ZnO–NPs. Intestinal morphological changes were also restored by 5 mg/kg ZnO–NPs in HFD group. Conclusion: Treatment of rats with 50 and 100 mg/kg ZnO–NPs significantly induced intestinal injury, while treatment with 5 mg/kg ZnO nanoparticle normalized intestinal functions and structure. This study showed the synergistic effects of ZnO–NPs and HFD administration on liver enzyme, oxidative stress, apoptosis, inflammation, morphological changes and cell toxicity.

Trans fatty acids exacerbate dextran sodium sulphate-induced colitis by promoting the up-regulation of macrophage-derived proinflammatory cytokines involved in T helper 17 cell polarization

Numerous reports have shown that a diet containing large amounts of trans fatty acids (TFAs) is a major risk factor for metabolic disorders. Although recent studies have shown that TFAs promote intestinal inflammation, the underlying mechanisms are unknown. In this study, we examined the effects of dietary fat containing TFAs on dextran sodium sulphate (DSS)-induced colitis. C57 BL/6 mice were fed a diet containing 1·3% TFAs (mainly C16:1, C18:1, C18:2, C20:1, C20:2 and C22:1), and then colitis was induced with 1·5% DSS. Colonic damage was assessed, and the mRNA levels of proinflammatory cytokines and major regulators of T cell differentiation were measured. The TFA diet reduced survival and exacerbated histological damage in mice administered DSS compared with those fed a TFA-free diet. The TFA diet significantly elevated interleukin (IL)-6, IL-12p40, IL-23p19 and retinoic acid-related orphan receptor (ROR)γt mRNA levels in the colons of DSS-treated animals. Moreover, IL-17A mRNA levels were elevated significantly by the TFA diet, with or without DSS treatment. We also examined the expression of proinflammatory cytokines in lipopolysaccharide (LPS)-stimulated RAW264.7 cells and peritoneal macrophages. These cells were exposed to TFAs (linoelaidic acid or elaidic acid) with or without LPS and the mRNA levels of various cytokines were measured. IL-23p19 mRNA levels were increased significantly by TFAs in the absence of LPS. Cytokine expression was also higher in LPS-stimulated cells exposed to TFAs than in unexposed LPS-stimulated cells. Collectively, our results suggest that TFAs exacerbate colonic inflammation by promoting Th17 polarization and by up-regulating the expression of proinflammatory cytokines in the inflamed colonic mucosa.

Antiproliferative Action of Conjugated Linoleic Acid on Human MCF-7 Breast Cancer Cells Mediated by Enhancement of Gap Junctional Intercellular Communication through Inactivation of NF- κ B

The major conjugated linoleic acid (CLA) isomers, c9,t11-CLA and t10,c12-CLA, have anticancer effects; however, the exact mechanisms underlying these effects are unknown. Evidence suggests that reversal of reduced gap junctional intercellular communication (GJIC) in cancer cells inhibits cell growth and induces cell death. Hence, we determined that CLA isomers enhance GJIC in human MCF-7 breast cancer cells and investigated the underlying molecular mechanisms. The CLA isomers significantly enhanced GJIC of MCF-7 cells at 40 μM concentration, whereas CLA inhibited cell growth and induced caspase-dependent apoptosis. CLA increased connexin43 (Cx43) expression both at the transcriptional and translational levels. CLA inhibited nuclear factor-κB (NF-κB) activity and enhanced reactive oxygen species (ROS) generation. No significant difference was observed in the efficacy of c9,t11-CLA and t10,c12-CLA. These results suggest that the anticancer effect of CLA is associated with upregulation of GJIC mediated by enhanced Cx43 expression through inactivation of NF-κB and generation of ROS in MCF-7 cells.

Differential effect of 14 free fatty acids in the expression of inflammation markers on human arterial coronary cells

Cardiovascular disease is the leading cause of death in the United States, and circulating free fatty acids (FFAs) are known risk factors associated with cardiovascular inflammation. The influence of 14 dietary FFAs (including saturated, mono- and polyunsaturated, and trans) on the expression of inflammatory markers in human coronary arterial smooth muscle (HCASM) and endothelial (HCEC) cells using a cell culture model was investigated. HCASM and HCEC cell cultures were incubated with 200 μM of each FFA for 8 or 24 h, respectively, at 37 °C in a 5% CO2 humidified incubator. Inflammatory markers were assessed by ELISA or Western blot in the supernatant or cell lysates respectively. Results showed significant differences in the expression of inflammatory markers among the fatty acid treatments and the control, with myristic and palmitic acids being identified as the most and linoleic acid as the least pro-inflammatory. This suggests that FFAs may induce low-grade inflammation in human coronary arterial cells and provides more information on mode of action.

Trans fatty acids: induction of a pro-inflammatory phenotype in endothelial cells

Epidemiological data have shown an association of the intake of industrial produced trans fatty acids (TFA) and sudden cardiac death. The present study examines the impact of elaidic acid (t18:1n-9) and linoelaidic acid (t18:2n-6) on the human aortic endothelial cell functional response. Trans fatty acids predominately incorporated into the phospholipid component while only a minute fraction of the total fatty acids (FA) incorporated into triacylglycerol. Trans fatty acids incorporated into the plasma membranes at the expense of the saturated-FA, stearic, palmitic, and to a lesser extent, myristic acid. Both t18:1n-9 and t18:2n-6 induced a pro-inflammatory response by elevating surface expression of intercellular adhesion molecule-1 (ICAM-1). Neither oleic nor linoleic evoked a pro-inflammatory phenotype under the maximal 50 µM treatments. Both TFA and stearic acid increased phosphorylation of the ICAM-1 transcriptional regulator, nuclear factor-κβ (NF-κβ), while oleic and linoleic acids did not appear to alter the phosphorylation status. Elaidic acid minimally affected endothelial cell growth, whereas linoelaidic acid completely inhibited growth at 100 µM and imparted limited cytotoxicity up to 300 µM. Stearic acid induced cytotoxicity at concentrations above 75 µM, while oleic and linoleic acids evoked gradual dose-dependent growth inhibition with cytotoxicity occurring only at linoleic acid concentrations greater than 200 µM. In conclusion, t18:1n-9 and t18:2n-6 fatty acids effectively incorporated into the phospholipid component of endothelial cells and subsequently induce a pro-inflammatory phenotype.

Visualizing digestive organ morphology and function using differential fatty acid metabolism in live zebrafish

Lipids are essential for cellular function as sources of fuel, critical signaling molecules and membrane components. Deficiencies in lipid processing and transport underlie many metabolic diseases. To better understand metabolic function as it relates to disease etiology, a whole animal approach is advantageous, one in which multiple organs and cell types can be assessed simultaneously in vivo. Towards this end, we have developed an assay to visualize fatty acid (FA) metabolism in larval zebrafish (Danio rerio). The method utilizes egg yolk liposomes to deliver different chain length FA analogs (BODIPY-FL) to six day-old larvae. Following liposome incubation, larvae accumulate the analogs throughout their digestive organs, providing a comprehensive readout of organ structure and physiology. Using this assay we have observed that different chain length FAs are differentially transported and metabolized by the larval digestive system. We show that this assay can also reveal structural and metabolic defects in digestive mutants. Because this labeling technique can be used to investigate digestive organ morphology and function, we foresee its application in diverse studies of organ development and physiology.

Dietary triacylglycerol structure and its role in infant nutrition

Human milk TG are a remarkable example of stereo-specific positioning of fatty acids with structures that are highly conserved and unusual. Not only does human milk contain high amounts of fat and 16:0, but ~70% of the 16:0 is esterified at the TG stereo-specifically numbered (sn)-2 position, with preferential positioning of 18:1(n-9) and 18:2(n-6) at the TG sn-1,3 positions. The milk TG structures and digestive lipases combine to enable efficient digestion and absorption of 16:0 by conserving 16:0 in sn-2 monoacylglycerols, which are absorbed, reassembled, and secreted in plasma conserving the original milk TG configuration; these studies are reviewed in this article. The reason why the mammary gland invests in enzymes to provide the infant with 20-25% milk fatty acids as 16:0 rather than selecting against 16:0 is unknown, yet likely has a purpose given the mammary gland capacity for 10:0, 12:0, and 14:0 synthesis. Recent advances in the development-, tissue-, and species-specific activity of enzymes of TG synthesis and knowledge that dietary TG structures are maintained postabsorption suggest that the purpose of the milk TG structures is more sophisticated than simply avoiding 16:0 malabsorption. The overall aim is to expand consideration of fatty acids in the infant diet from a simple view of average fatty acid compositions to the complex lipids and molecular structures in which fatty acids are provided to tissues during early life and the biology through which the unique features of human milk enable the infant to grow and thrive on a high-fat, high-saturated-fat milk diet.

Preventive effect of t,t-conjugated linoleic acid on 12-O-tetradecanoylphorbol-13-acetate-induced inhibition of gap junctional intercellular communication in human mammary epithelial MCF-10A cells

The anti-tumor promotional effects of t9,t11-conjugated linoleic acid (t9,t11-CLA) and t10,t12-CLA were evaluated on the 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced inhibition of gap junctional intercellular communication (GJIC) in the human mammary epithelial cell line MCF-10A. The results were compared to those obtained from c9,t11-CLA, which is a more effective anti-tumor promoter on TPA-induced GJIC inhibition in MCF-10A cells than t10,c12-CLA. Cells were treated with 20 μM t9,t11-CLA, t10,t12-CLA, or c9,t11-CLA for 24 h followed by 60 nM TPA for 1 h. Both t9,t11-CLA and t10,t12-CLA equally protected MCF-10A cells from TPA-induced inhibition of GJIC with inferior efficacy to c9,t11-CLA.The protection was due to the ameliorated phosphorylation of connexin43 via suppression of extracellular signal-regulated kinases (ERK1/2) activation. Suppression of TPA-induced reactive oxygen species (ROS) generation by t9,t11-CLA and t10,t12-CLA was less effective, relative to c9,t11-CLA. The results suggest that the anti-promotional activities of t9,t11-CLA and t10,t12-CLA are equal but less potent than c9,t11-CLA in TPA-treated MCF-10A cells. The activity might be mediated by the attenuation of ROS production in MCF-10A cells by preventing the downregulation of GJIC during the cancer promotion stage.

Attenuation of 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced gap junctional intercellular communication (GJIC) inhibition in MCF-10A cells by c9,t11-conjugated linoleic acid

The protective effect of c9,t11-conjugated linoleic acid (CLA) on the inhibition of gap junctional intercellular communication (GJIC) was examined in a human mammary epithelial cell line (MCF-10A) treated with 12-O-tetradecanoylphorbol-13-acetate (TPA), relative to t10,c12-CLA isomer. TPA inhibited GJIC in a dose-dependent and reversible manner and was associated with connexin 43 phosphorylation. Pretreatment of 20 μM c9,t11-CLA for 24 h prior to 60 nM TPA for 1 h prevented the inhibition of GJIC by reducing the phosphorylation of connexin 43 via suppressing extracellular signal-regulated kinases (ERK1/2) activation. Reactive oxygen species (ROS) accumulation by TPA was attenuated by c9,t11-CLA. The efficacy of c9,t11-CLA in protecting inhibition of GJIC, connexin 43 phosphorylation, and ROS production was superior to that of t10,c12-CLA. These results suggest that c9,t11-CLA, including t10,c12-CLA, prevents the carcinogenesis of MCF-10A cells by protecting down-regulation of GJIC during the cancer promotion stage, and lack of their toxicities could be an excellent indicator for the chemoprevention of breast cancer.

Oleic acid inhibits stearic acid-induced inhibition of cell growth and pro-inflammatory responses in human aortic endothelial cells

Saturated fatty acids (SFAs), significant components of both enteral/parenteral nutritional formulations (including diet), are linked to cardiovascular disease complications, such as atherosclerosis. We investigated whether oleic acid (C18:1n-9) reduces the growth inhibitory and pro-inflammatory effects of the stearic acid (C18:0) in human aortic endothelial cells (HAEC). Stearic acid induced growth inhibition at concentrations less than 50 μM, whereas higher concentrations invoked cytotoxicity. Stearic acid-induced growth inhibition and cytotoxic effects were eradicated upon cosupplementation with oleic acid (25 μM). Oleic acid (as low as 5 μM) also inhibited the stearic acid-induced increase in intercellular adhesion molecule-1 (ICAM-1) expression. Stearic acid-induced phosphorylation of nuclear factor-kappa B (NF-κB), a transcriptional regulator of ICAM-1, was also reduced by oleic acid. HAECs supplemented with either stearic or oleic acid resulted in cellular incorporation of C18:0 and C18:1n-9, respectively. Stearic acid primarily incorporated into phospholipids without increasing the total fatty acid content in HAECs. In contrast, oleic acid, with or without stearic acid, incorporated into both phospholipids and triglycerides, with a significant increase in total fatty acid amounts in triglycerides. Our data suggest that oleic acid has the ability to reduce the inflammatory effects of long-chain SFAs in HAECs through reducing cellular stearic acid incorporation and NF-κB activation.

Long-chain saturated fatty acids induce pro-inflammatory responses and impact endothelial cell growth

BACKGROUND & AIMS

Saturated fatty acids (SFAs), significant components of enteral and parenteral formulations, have been linked to cardiovascular complications. However, the effect of SFAs upon vascular inflammation is less clear. Endothelial cells (EC) play an important role in the acute inflammatory responses. We, therefore, evaluated the acute effects of different chain-length SFAs upon EC functions.

METHODS

Endothelial cells were cultured with various SFAs. Growth and cytotoxicity were determined by WST-1 assay. Apoptosis and pro-inflammatory adhesion molecule (ICAM-1) expression was assayed using flow cytometry. Activation of NF-kappaB was analyzed using western blot analysis.

RESULTS

Long-chain SFAs (C14:0-C20:0) inhibited EC growth in a chain-length dependent manner. Medium-chain SFAs (C6:0-C12:0) did not significantly affect EC growth. In contrast, the short-chain SFA (C4:0) stimulated cellular growth. Stearic acid induced significantly more EC apoptosis and necrosis than palmitic acid or myristic acids. Stearic acid (>10muM) treatment also significantly increased ICAM-1 expression. Stearic acid's pro-inflammatory response was confirmed by phosphorylation of IkappaB-alpha and NF-kappaB in a dose dependent manner.

CONCLUSIONS

Long-chain SFAs can induce pro-inflammatory responses and significantly impact growth and viability of EC. Our data suggest that the presence of long-chain SFAs in parenteral formulations may have harmful effects on the vascular system.

Mammalian Wnt3a is released on lipoprotein particles

Little is known about the release and intercellular transport of Wnt proteins from mammalian cells. Lipoproteins may act as carriers for the intercellular movement and gradient formation of the lipid-linked morphogens Wingless and Hedgehog in Drosophila. To investigate whether such a mechanism can occur in mammals, we have studied Wnt release in cultured mammalian cells. Wnt3a associated with lipoproteins in the culture medium and not with extracellular vesicles or exosomes. Although Wnt3a was associated with both high-density lipoproteins (HDL) and low-density lipoproteins, only HDL allowed Wnt3a release from mouse fibroblasts. Remarkably, Wnt3a lacking its palmitate moiety was released in a lipoprotein-independent manner, demonstrating the dual role of palmitoylation in membrane and lipoprotein binding. We additionally found that Wnt3a can be released from enterocyte cell lines on endogenously expressed lipoproteins. We further discuss the physiological implications of our findings.

A vegetable oil feeding history affects digestibility and intestinal fatty acid uptake in juvenile rainbow trout Oncorhynchus mykiss

Future expansion of aquaculture relies on the use of alternatives to fish oil in fish feed. This study examined to what extent the nature of the feed oil affects intestinal lipid uptake properties in rainbow trout. The fish were fed a diet containing fish (FO), rapeseed (RO) or linseed (LO) oil for 8 weeks after which absorptive properties were assessed. Differences in digestibility due to feed oil history were measured using diet FO with an indigestible marker. Intestinal integrity, paracellular permeability, in vitro transepithelial fatty acid transport (3H-18:3n-3 and 14C-16:0) and their incorporation into intestinal epithelia were compared using Ussing chambers. Feed oil history did not affect the triacylglycerol/phosphatidylcholine ratio (TAG/PC) of the newly synthesized lipids in the segments. The lower TAG/PC ratio with 16:0 (2:1) than with 18:3 (10:1) showed the preferential incorporation of 16:0 into polar lipids. The FO-feeding history decreased permeability and increased transepithelial resistance of the intestinal segments. Transepithelial passage rates of 18:3n-3 were higher when pre-fed LO compared to RO or FO. Similarly, pre-feeding LO increased apparent lipid and fatty acid digestibilities compared to RO or FO. These results demonstrate that the absorptive intestinal functions in fish can be altered by the feed oil history and that the effect remains after a return to a standard fish oil diet.

A mixture of trans, trans conjugated linoleic acid induces apoptosis in MCF-7 human breast cancer cells with reciprocal expression of Bax and Bcl-2

The growth inhibitory effect of a mixture of trans, trans conjugated linoleic acid isomers (t, t CLA) was investigated in a human breast cancer cell line, MCF-7, with references to c9, t11 CLA, t10, c12 CLA, and linoleic acid. The t, t CLA treatment effectively induced a cytotoxic effect in a time-dependent (0-6 days) and concentration-dependent (0-40 microM) manner, as compared to the reference and control treatments. The apoptotic parameters were measured on cells treated with 40 microM t, t CLA for 4 days. The occurrence of the characteristic morphological changes and DNA fragmentation confirmed apoptosis. The t, t CLA treatment led to an increase in the level of p53 tumor suppressor protein and Bax protein, but suppressed the expression of Bcl-2 protein. In addition, cytochrome c was released from the mitochondria into the cytosol, and the activation of caspase-3 led to the cleavage of poly(ADP-ribose) polymerase (PARP). Moreover, the composition of the linoleic and arachidonic acids was decreased in cellular membranes. These findings suggest that incorporation of t, t CLA in the membrane induces a mitochondria-mediated apoptosis that can enhance the antiproliferative effect of t, t CLA in MCF-7 cells.

Transport properties of bovine and reindeer β-lactoglobulin in the Caco-2 cell model

Beta-lactoglobulin (betaLG) is a protein that binds ligands like fatty acids and retinol into the hydrophobic pocket. Our purpose was to study bovine and reindeer betaLG as transporter molecules and compare their transport properties across Caco-2 cell membrane. The reindeer betaLG has more valuable binder characteristics than bovine betaLG because it has only one genetic phenotype and it seems to exhibit better immunological properties. The permeation of betaLG in Caco-2 cells was evaluated by immunoblotting, and the permeation of the model substances retinol, palmitic acid and cholesterol with and without betaLG was determined using [(3)H]-labelled ligands. Both bovine and reindeer betaLG were able to pass across a Caco-2 cell monolayer similarly. Unbound and betaLG-bound [(3)H]retinol and [(3)H]palmitic acid were equally transported across the Caco-2 cell layer, whereas [(3)H]cholesterol could not pass across Caco-2 cells with or without betaLG at any of the studied circumstances. Thus, the bovine and reindeer milk betaLG is not a suitable protein to enhance transport of ligands across the Caco-2 cell membrane, used for predicting intestinal absorption.

Trans-fatty acids induce pro-inflammatory responses and endothelial cell dysfunction

Epidemiological data indicate that there is a strong association between intake of trans-18 : 2 fatty acids (TFA) and sudden cardiac death. There is little known about the mechanisms by which TFA exert harmful effects on the cardiovascular system. The present in vitro study is the first to demonstrate the effects of membrane-incorporated C18 : 2 TFA on human aortic endothelial cell (HAEC) function. Trans-18 : 2 fatty acids were incorporated to a greater extent (2-fold) in the phospholipid fraction of endothelial cells than that of cis-18 : 2; furthermore, these fatty acids were enriched to a similar extent in the TAG fraction. Flow cytometric analysis indicated that TFA treatment of HAEC significantly increased the expression of endothelial adhesion molecules, including intercellular adhesion molecule-1 (CD54) and vitronectin receptor (CD51/CD61). Incorporation of TFA into membranes increased HAEC adhesion to fibronectin- or vitronectin-coated plates by 1.5- to 2-fold, respectively. Neutrophil and monocyte adhesion to HAEC monolayers was nearly proportional to adhesion molecule expression. TFA treatment also induced the release of monocyte chemoattractant protein-1 by nearly 3-fold in non-stimulated HAEC. Furthermore, we examined the role of TFA on in vitro angiogenic assays. Chemotactic migration of TFA-treated HAEC toward sphingosine-1-phosphate (SPP) was significantly increased compared with controls. Conversely, capillary morphogenesis of TFA-treated HAEC was significantly inhibited in response to SPP, suggesting that TFA incorporation suppresses endothelial cell differentiation. In conclusion, these in vitro studies demonstrated that TFA play a role in the induction of pro-inflammatory responses and endothelial cell dysfunction.

Dietary neutral lipid level and source in Senegalese sole (Solea senegalensis) larvae: effect on growth, lipid metabolism and digestive capacity

Contrary to larval essential fatty acid (EFA) requirements, the effect of dietary neutral lipid supply has been little investigated in marine fish larvae. The present work investigates the effect of feeding Senegalese sole larvae on Artemia enriched with higher or lower doses of lipid emulsion. Two lipid sources - soybean oil and fish oil - were compared. From 16 days after hatching (DAH) onwards, larvae were fed one of four experimental treatments: Artemia enriched on a high or low dose of soybean oil emulsion (HS and LS) or Artemia enriched on a high or low dose of fish oil emulsion (HF and LF). In terms of growth, the dietary lipid level did not have a significant effect while the soybean oil treatments induced a lower growth than the fish oil-enriched Artemia. The fatty acid (FA) composition of the larvae closely reflected the dietary quantitative and qualitative FA profile. Only slight dietary effects were noted in the activity of trypsin, lipase and alkaline phosphatase. A higher amount of lipid droplets was noticeable in the posterior intestine epithelia and in the hepatocytes of larvae fed Artemia enriched with higher lipid doses, while LS-Artemia induced the lower lipid accumulation on the basal zone of the enterocytes, in accordance with the lowest total lipid level measured in this treatment. These results suggest an important effect of dietary total lipid level on lipid accumulation in the enterocytes and on FA absorption. At 33 DAH a tube feeding trial was conducted with 14C-labelled oleic acid (OA) or triolein (TRI), showing that the lower accumulation of lipid droplets in the larvae fed LS was associated with a significantly higher absorption and retention in the gut and body tissues of the TRI label. For OA no significant differences between treatments were found. TRI label was considerably more evacuated than OA, indicating that sole larvae may have a lower capacity to incorporate a triacylglycerol, which needs to be digested. Finally, OA appears to be preferentially utilized for energy production, accumulating more in larval tissues when absorbed in higher amounts.

Unidirectional inversion of ibuprofen in Caco-2 cells: developing a suitable model for presystemic chiral inversion study

Intestinal chiral inversion of ibuprofen is still lacking direct evidence. In a preliminary experiment, ibuprofen was found to undergo inversion in Caco-2 cells. This investigation was thus conducted to determine the characteristics and influence of some biochemical factors on the chiral inversion of ibuprofen in Caco-2 cells. The effects of substrate concentration (2.5-40 microg/ml), cell density (0.5-2 x 10(6) cells/well), content of serum (0-20%), coexistence of S ibuprofen (corresponding doses), sodium azide (10 mM), exogenous Coenzyme A (CoA) (0.1-0.4 mM), and palmitic acid (5-25 microM) on inversion were examined. A stereoselective HPLC method based on the Chromasil-CHI-TBB column was developed for quantitative analysis of the drug in cell culture medium. The inversion ratio (F(i)) and elimination rate constant were calculated as the indexes of inversion extent. Inversion of ibuprofen in Caco-2 cells was found to be both dose and cell density dependent, indicating saturable characteristics. Addition of serum significantly inhibited the inversion, to an extent of 2.7 fold decrease at 20% content. Preexistence of S enantiomer exerted a significant inhibitory effect (p<0.01 for all tests). Sodium azide decreased the inversion ratio from 0.43 to 0.32 (p<0.01). Exogenous CoA and palmitic acid significantly promoted the inversion at all tested doses (p<0.01 for all tests). This research provided strong evidence to the capacity and capability of intestinal chiral inversion. Although long incubation times up to 120 h were required, Caco-2 cells should be a suitable model for chiral inversion research of 2-APAs considering the human-resourced and well-defined characteristics from the present study.

Greater enrichment of triacylglycerol-rich lipoproteins with apolipoproteins E and C-III after meals rich in saturated fatty acids than after meals rich in unsaturated fatty acids

BACKGROUND

Although there is considerable interest in the postprandial events involved in the absorption of dietary fats and the subsequent metabolism of diet-derived triacylglycerol-rich lipoproteins, little is known about the effects of meal fatty acids on the composition of these particles.

OBJECTIVE

We examined the effect of meal fatty acids on the lipid and apolipoprotein contents of triacylglycerol-rich lipoproteins.

DESIGN

Ten normolipidemic men received in random order a mixed meal containing 50 g of a mixture of palm oil and cocoa butter [rich in saturated fatty acids (SFAs)], safflower oil [n-6 polyunsaturated fatty acids (PUFAs)], or olive oil [monounsaturated fatty acids (MUFAs)] on 3 occasions. Fasting and postprandial apolipoproteins B-48, B-100, E, C-II, and C-III and lipids (triacylglycerol and cholesterol) were measured in plasma fractions with Svedberg flotation rates (S(f)) >400, S(f) 60-400, and S(f) 20-60.

RESULTS

Calculation of the composition of the triacylglycerol-rich lipoproteins (expressed per mole of apolipoprotein B) showed notable differences in the lipid and apolipoprotein contents of the SFA-enriched particles in the S(f) > 400 and S(f) 60-400 fractions. After the SFA meal, triacylglycerol-rich lipoproteins in these fractions showed significantly greater amounts of triacylglycerol and of apolipoproteins C-II (S(f) 60-400 fraction only), C-III, and E than were found after the MUFA meal (P < 0.02) and more cholesterol, apolipoprotein C-III (S(f) > 400 fraction only), and apolipoprotein E than after the PUFA meal (P < 0.02).

CONCLUSIONS

Differences in the composition of S(f) > 400 and S(f) 60-400 triacylglycerol-rich lipoproteins formed after saturated compared with unsaturated fatty acid-rich meals may explain differences in the metabolic handling of dietary fats.

Lipid micelles stimulate the secretion of triglyceride-enriched apolipoprotein B48-containing lipoproteins by Caco-2 cells

Intestinal triglyceride-rich lipoproteins (TRL) are synthesized from dietary lipids. This study was designed to evaluate the effects of lipid micelles, mimicking post-digestive duodenal micelles, on the fate of apolipoprotein B (apoB)48-containing lipoproteins by Caco-2 cells. Such micelles, consisting of oleic acid (OA), taurocholate, 2-monooleoylglycerol (2-MO), cholesterol (Chol), and L-alpha-lysophospatidylcholine, were the most efficient inducers of OA uptake and esterification. The efficiency of TG and apoB48 secretion increased specifically as a function of cell differentiation. PAGE analysis of secreted lipoproteins separated by sequential ultracentrifugation after [35S] labeling revealed differences in the secretion of apoB100- and apoB48-containing lipoproteins. In absence of micelles, apoB48 was secreted mostly in "HDL-like" particles, as observed in enterocytes in vivo. Micelle application increased 2.7-fold the secretion of apoB, resulting in 53 times more apoB48 being recovered as TG-enriched lipoproteins at d < 1.006 g/ml. Electron microscopy revealed the presence of lipid droplets in the secretory pathway and the accumulation of newly synthesized TG in cytoplasmic lipid droplets, as in enterocytes in vivo. We showed that these droplets could be used for secretion. However, apoB48 preferentially bound to newly synthesized TG in the presence of micelles, accounting in part for the functional advantage of apoB editing in the intestine. While Caco-2 cells express both apoB isoforms, our results show that the apical supply of complex lipid micelles favors the physiological route of apoB48-containing TG-enriched lipoproteins.

Distribution of fatty acids from dietary oils into phospholipid classes of triacylglycerol-rich lipoproteins in healthy subjects

Several studies have suggested that lipoprotein metabolism can be affected by lipoprotein phospholipid composition. We investigated the effect of virgin olive oil (VOO) and high-oleic sunflower oil (HOSO) intake on the distribution of fatty acids in triacylglycerols (TG), cholesteryl esters (CE) and phospholipid (PL) classes of triacylglycerol-rich lipoproteins (TRL) from normolipidemic males throughout a 7 h postprandial metabolism. Particularly, changes in oleic acid (18:1n-9) concentration of PL were used as a marker of in vivo hydrolysis of TRL external monolayer. Both oils equally promoted the incorporation of oleic acid into the TG and CE of postprandial TRL. However, PL was enriched in oleic acid (18:1n-9) and n-3 polyunsaturated fatty acids (PUFA) after VOO meal, whereas in stearic (18:0) and linoleic (18:2n-6) acids after HOSO meal. We also found that VOO produced TRL which PL 18:1n-9 content was dramatically reduced along the postprandial period. We conclude that the fatty acid composition of PL can be a crucial determinant for the clearance of TRL during the postprandial metabolism of fats.

Chylomicron particle size and number, factor VII activation and dietary monounsaturated fatty acids

This study evaluated the effects of substituting dietary saturated fatty acids (SFAs) with monounsaturated fatty acids (MUFAs) on postprandial chylomicron (triacylglycerol (TAG), apolipoprotein B-48 (apo B-48) and retinyl ester (RE)), chylomicron particle size and factor VII (FVII) response when subjects were given a standard meal. In a controlled sequential design, 51 healthy young subjects followed an SFA-rich diet (Reference diet) for 8 weeks after which half of the subjects followed a moderate MUFA diet (n=25) and half followed a high MUFA diet (n=26) for 16 weeks. Fasting lipoprotein and lipid measurements were evaluated at baseline and at 8-week intervals during the Reference and MUFA diets. In 25 of the subjects (n=12 moderate MUFA, n=13 high MUFA), postprandial responses to a standard test meal containing RE and 13C-tripalmitin were investigated at the end of the Reference and the MUFA diet periods. Although there were no differences in the postprandial lipid markers (TAG, RE, 13C-TAG) on the two diets, the postprandial apo B-48 response (incremental area under the curve (IAUC)) was reduced by 21% on the moderate MUFA diet (NS) and by 54% on the high MUFA diet (P<0.01). The postprandial peak concentrations of apo B-48 were reduced by 33% on the moderate MUFA diet (P<0.01) and 48% on the high MUFA diet (P<0.001). Fasting values for factor VII activity (FVIIc), activated factor VII (FVIIa) or factor VII antigen (FVIIag) did not differ significantly when subjects were transferred from Reference to MUFA diets. However, the postprandial increases in coagulation FVII activity (FVIIc) were 18% lower and of activated FVII (FVIIa) were 17% lower on the moderate MUFA diet (NS). Postprandial increases in FVIIc and FVIIa were 50% (P<0.05) and 29% (P<0.07) lower on the high MUFA diet and the area under the postprandial FVIIc response curve (AUC) was also lower on the high MUFA diet (P<0.05). Significantly higher ratios of RE:apo B-48 (P<0.001) and 13C-palmitic acid:apo B-48 (P<0.01) during both MUFA diets suggest that the CMs formed carry larger amounts of dietary lipids per particle, reflecting an adaptation to form larger lipid droplets in the enterocyte when increased amounts of dietary MUFAs are fed. Smaller numbers of larger chylomicrons may explain attenuated activation of factor VII during the postprandial state when the background diet is rich in MUFA.

Acute-on-chronic effects of fatty acids on intestinal triacylglycerol-rich lipoprotein metabolism

Postprandial triacylglycerol (TAG) metabolism is an important metabolic state that has been associated with cardiovascular disease. The magnitude of the postprandial TAG response is determined by dietary fat composition, which alters intestinal and hepatic TAG-rich lipoprotein (TRL) metabolism. Caco-2 cell monolayers are morphologically and physiologically similar to the human intestinal enterocytes, hence they are a good model to study intestinal lipoprotein metabolism. To date only the acute effect of fatty acid composition on intestinal TRL metabolism in Caco-2 cells has been investigated. Little is known of the effect of habitual, or chronic, dietary fat composition on intestinal TRL metabolism. Using the Caco-2 cell model, the present study investigated the acute-on-chronic effect of fatty acid composition on TRL metabolism. Caco-2 cells were grown in the presence of 0.05 mm-palmitic acid (PA; 16 : 0), -oleic acid (OA; 18 : 1n-9),-eicosapentaenoic acid (EPA; 20 : 5n-3) or no fatty acid (control) for 19 d, then one of four acute treatments (control (bovine serum albumin (BSA; 5 g/l)) or BSA (5 g/l) plus 0.5 mm-PA, -OA or -EPA) were administered for 22 h. Significant acutexchronic interactions for the effect of fatty acid composition on cellular TAG:secreted de novo TAG, and cellular de novo TAG:de novo phospholipid were observed. Thus the effect of a fatty acid was determined by the duration of exposure to the fatty acid intervention. Acute PA treatment increased de novo TAG synthesis, but chronic PA supplementation did not. Acute and chronic OA treatments increased de novo TAG secretion. For EPA, chronic supplementation had the greatest effect on TAG synthesis and secretion. The acute-on-chronic effects of fatty acids on apolipoprotein B metabolism were relatively minor compared with the changes noted for TRL lipid composition. The present study shows that the Caco-2 cell model is valuable for studying intestinal TRL metabolism and that fatty acids modulate this process, the nature of which can be determined by the length of exposure of the cell to the fatty acid.

Trans polyunsaturated fatty acids have more adverse effects than saturated fatty acids on the concentration and composition of lipoproteins secreted by human hepatoma HepG2 cells

The objective of this study was to assess the relative long-term effects of linoleic (cis, cis 18:2), linolelaidic (trans, trans 18:2), and palmitic (16:0) acids on hepatic lipoprotein production in HepG2 cells. All fatty acids increased the mass of triglycerides (TG) in the medium and the incorporation of [(3)H]-glycerol into secreted TG; the increase was more pronounced with linoleic acid than with linolelaidic and palmitic acids. The net accumulation in the medium of apolipoprotein (apo) A-I was not affected by the fatty acids tested and moderate changes in that of apoB resulted in apoB/apoA-I mass ratios of 1.05, 1.27 and 0.86 with linoleic, linolelaidic and palmitic acids, respectively. The incorporation of [(14)C]-acetate into cellular plus secreted total sterols was 9.1%, 33.6% and 17.4% of total [(14)C]-labeled lipids with linoleic, linolelaidic and palmitic acids, respectively. Relative to linoleic acid, palmitic acid, and to a greater extent (P < 0.05) linolelaidic acid, increased the secretion and cellular accumulation of [(14)C]-labeled free cholesterol (FC) and cholesteryl esters and decreased those of TG and phospholipids (PL). Compared with linoleic acid, linolelaidic acid increased LDL-cholesterol (C) and HDL-C by 154% (P < 0.001) and 50% (P = 0.016), respectively, whereas palmitic acid increased LDL-C by 17% (P > 0.1) and did not affect HDL-C. The LDL-C to HDL-C ratios were 0.70, 1.18 and 0.96 with linoleic, linolelaidic and palmitic acids, respectively. These differences were not due to altered LDL receptor activity. The PL to C ratios of HDL particles were 1.61, 0.40 and 0.77 with linoleic acid, linolelaidic acid and palmitic acid, respectively. These results suggest that relative to cis polyunsaturated and saturated fatty acids, trans PUFA more adversely affect the concentration and composition of apoA-I- and apoB-containing lipoproteins secreted by HepG2 cells.

Chronic but not acute treatment with conjugated linoleic acid (CLA) isomers (trans-10, cis-12 CLA and cis-9, trans-11 CLA) affects lipid metabolism in Caco-2 cells

Conjugated linoleic acid (CLA) has profound effects on hepatic and adipocyte lipid metabolism, but little is known about its effects on intestinal lipid metabolism. We investigated the acute (22 h) and acute-after-chronic (22 h after 19 d) effects of trans-10, cis-12 CLA (t10,c12-CLA) and cis-9, trans-11 CLA (c9, t11-CLA) on triacylglycerol (TAG)-rich lipoprotein (TRL) metabolism, de novo TAG, phospholipid (PL) ((14)C-glycerol) and apolipoprotein B (apoB) ((35)S-methionine) synthesis and secretion, in the colon carcinoma (Caco-2) cell model of intestinal lipoprotein metabolism. Acute treatment with either CLA isomer did not affect TRL metabolism. However, chronic t10,c12-CLA and c9,t11-CLA supplementation followed by acute palmitic acid (PA) treatment increased the ratio of cellular to secreted de novo TAG (cTAG/sTAG) (P < or = 0.03) as a result of increased cellular de novo TAG levels. Chronic Caco-2 cell t10,c12-CLA supplementation, prior to the acute oleic acid (OA) treatment, significantly increased (P = 0.005) the ratio of cellular de novo TAG to de novo PL (cTAG/cPL), to a greater extent than that following chronic linoleic acid (LA) (P = 0.001) or c9,t11-CLA supplementation (P = 0.005). Again, this effect was attributed to increased cellular de novo TAG synthesis. Neither CLA isomer affected the ratio of secreted de novo TAG to de novo PL (sTAG/sPL). No effects on Caco-2 cell apoB synthesis and secretion were observed after acute or chronic CLA treatments. In conclusion, chronic t10,c12-CLA supplementation modulated intestinal TRL metabolism, by increasing cellular de novo TAG synthesis but had no effect on de novo TAG secretion in Caco-2 cells.

Lipid-based formulations for intestinal lymphatic delivery

The current state of the art of intestinal lymphatic transport is given by reviewing the more recent publications, which have utilized lipid-based vehicles. The results published often show variable trends depending on, the design of the vehicle, the components used, the physicochemical properties of the drug, the animal model and experimental techniques, these variables often make direct comparisons difficult. Traditionally intestinal lymphatic delivery has been expressed as a percentage of the dose transported in the lymph. Using this parameter results obtained to date, with lipid-based vehicles, are somewhat disappointing maximising at approximately 20-30%, for highly lipophilic compounds including DDT and halofantrine (Hf). Recent data, monitoring Hf, in a fed versus fasted dog study, have shown that a higher degree of lymphatic transport is possible (>50% dose) in the postprandial state, this study should result in stimulating renewed interest in the potential of achieving significant levels of lymphatic targeting. Although some relevant features controlling lymphatic transport have been identified over the years a deeper appreciation of all the mechanisms, which is vital for therapeutic exploitation of lymphatic transport, is still unrealized. This review analyses the success and limitations of a formulation approach using lipid-based vehicles and highlights potential areas for further research.

Hypobetalipoproteinemic mice with a targeted apolipoprotein (Apo) B-27.6-specifying mutation: in vivo evidence for an important role of amino acids 1254-1744 of ApoB in lipid transport and metabolism of the apoB-containing lipoprotein

Carboxyl-terminal deletion of apoB-100 may impair its triglyceride (TG)-transporting capability and alter its catabolism. Here, we compare our newly generated apoB gene (Apob)-targeted apoB-27.6-bearing mice to our previously reported apoB-38.9 mice to understand further the relationship between the size of a truncated apoB variant and its function/metabolism in vivo. The apoB-27.6-specifying mutation produces a premature stop codon six amino acids (aa) downstream of the last codon of mouse Apob exon 24 (corresponding to aa 1254 of human apoB-100). ApoB-27.6 transcripts were 3- and 5-fold more abundant than apoB wild type and apoB-38.9 transcripts in the liver. Likewise, hepatic secretion rates of apoB-27.6 were 7-fold higher than those of apoB-48 and apoB-38.9. In contrast, apoB-27.6 heterozygotes (Apob(27.6/+)) had lower hepatic TG secretion rates and higher liver TG contents than both apoB-38.9 heterozygotes (Apob(38.9/+)) and apoB wild type mice (Apob(+/+)). ApoB-27.6 was secreted by Apob(27.6/+) hepatocytes as dense high density lipoprotein particles. Moreover, despite its high secretion rates, apoB-27.6 was barely detectable in plasma. Disruption of apoE gene in Apob(38.9/+) and Apob(27.6/+) dramatically increased plasma levels of apoB-38.9 as well as apoB-48 but caused no change in plasma apoB-27.6 concentrations. Finally, the birth rate of apoB-27.6 homozygotes (Apob(27.6/27.6)) from intercrosses of Apob(27.6/+) was 7-fold lower than that of Apob(38.9/38.9) from Apob(38.9/+) intercrosses (1.8% versus 12%). Crossbreeding of Apob(27.6/27.6) and Apob(38.9/38.9) produced viable Apob(27.6/38.9) offspring, but Apob(27.6/27.6) intercrosses produced no offspring. Together, these results demonstrate in vivo that the apoB-27.6-apoB-38.9 peptide segment (aa 1254-1744) plays a critical role, not only in supporting hepatic TG-secretion and in modulating catabolism of apoB-containing lipoproteins, but also in normal mouse embryonic development.

Monoacylglycerol metabolism in human intestinal Caco-2 cells: evidence for metabolic compartmentation and hydrolysis

Free fatty acids (FFA) and sn-2-monoacylglycerol (MG), the two major hydrolysis products of dietary triacylglycerol (TG), are absorbed from the lumen into polarized enterocytes that line the small intestine. Intensive studies regarding FFA metabolism in the intestine have been published; however, little is known regarding the metabolism of MG. In these studies, we examined the metabolism of sn-2-monoolein (sn-2-18:1) by human intestinal Caco-2 cells. To mimic the physiological presentation of MG to the enterocyte, the metabolism of [(3)H]sn-2-monoolein was examined by adding taurocholate-mixed sn-2-18:1 and albumin-bound sn-2-18:1 at the apical (AP) and basolateral (BL) surfaces of the Caco-2 cell, respectively. The results demonstrate that more sn-2-18:1 was incorporated into TG from AP taurocholate-mixed sn-2-18:1, whereas more phospholipid was synthesized from BL albumin-bound sn-2-18:1. The TG:phospholipid ratio was approximately 5-fold higher for AP relative to BL MG incubation. Qualitatively similar results were observed for bovine serum albumin-bound MG added at the apical surface. It was also found that substantial sn-2-18:1 radioactivity was recovered in the FFA fraction, suggesting that sn-2-18:1 may be directly hydrolyzed within the Caco-2. We therefore used reverse transcription-PCR with primers designed from the murine MG lipase (MGL) gene, and detected the presence of MG lipase mRNA in Caco-2. The human MGL gene was cloned and found to be 83% identical to the murine MGL, and identical to a previously described lysophospholipase-like protein. Northern blot analysis showed the expression of MGL throughout Caco-2 differentiation. Thus, MG metabolism in Caco-2 cells may include not only well established anabolic processes, but also catabolic processes. Further, the observed polarity of MG metabolism suggests that, as for fatty acids, separate precursor and/or product pools of lipid may exist in the intestinal enterocyte.

Regulation of surfactant-like particle secretion by Caco-2 cells

Surfactant-like particle (SLP) is a phosphatidylcholine (PC)-rich membrane produced in the small intestine, and its secretion is increased by fat feeding. In Caco-2 cells known to produce SLP, preincubation with [(3)H]palmitate labelled the SLP and was used as a marker for newly secreted membrane. SLP-associated PC and protein (d=1.07-1.08 g/ml in a linear non-equilibrium NaBr gradient) were secreted in parallel with triacylglycerols (TG) and at a rate about twice the control rate in response to feeding cells with an oleate/egg PC mixture. Cholesterol and apolipoprotein A-I identified only a small peak corresponding to high-density lipoprotein (HDL), but the largest peak corresponded with SLP (d=1.07-1.08). Palmitate incorporation into PC showed a similar small peak migrating at the density of HDL, but most labelled PC secreted from the cells was due to SLP. PC secretion, alkaline phosphatase activity, and newly synthesized immunoprecipitated SLP proteins from conditioned serum-free media migrated together at a density of >/=1.21 g/ml in a lipoprotein NaBr step gradient, and represented SLP. Glycerol incorporated into TG migrated at a peak density of 1.12 g/ml, consistent with HDL secretion from cells incubated in serum-free media. These data confirm that the secreted PC in SLP is distinct from lipoprotein particles. Incorporation of [(3)H]palmitate into the PC fraction of either whole cell homogenate or isolated brush border membranes was not affected by oleate/egg PC feeding. Both Pluronic L-81, an inhibitor of chylomicron secretion, and BMS-197636-02, a microsomal triglyceride transfer protein inhibitor, blocked the secretion of both TG and PC. Elevation of intracellular cAMP levels that stimulate surfactant secretion from type II pneumocytes caused a 50% reduction in SLP and TG secretion from Caco-2 cells. These results confirm the SLP response to fat feeding found in vivo, further supporting a role for SLP in TG secretion from the enterocyte, and show that the regulation of SLP secretion differs from that of pulmonary surfactant.

The metabolic availability of dietary triacylglycerols from two high oleic oils during the postprandial period does not depend on the amount of oleic acid ingested by healthy men

Monounsaturated oils, virgin olive oil (VOO) and high oleic sunflower oil (HOSO) are suggested to have selective physiologic effects on humans in the fasting state. The aim of the study was to evaluate whether two oils with equal amounts of oleic acid but with different compositions of minor fatty acids and triacylglycerol molecular species (TAG) could produce different triacylglycerol-rich lipoprotein (TRL)-TAG responses in the postprandial state. Eight normolipidemic men consumed the following three meals in random order on separate occasions with 2 wk between meals: control meal, control meal plus VOO and control meal plus HOSO. Plasma total TAG and TRL-TAG were measured hourly for 7 h after ingestion. TAG and sn-2 positional fatty acids within TAG were analyzed in the TRL fraction. Plasma total TAG concentrations in response to the dietary oils did not differ. However, TRL triglyceridemia was significantly lower after VOO intake (P < 0.05). The molecular species in the TRL fraction returned toward basal levels more quickly (P < 0.05) after VOO than HOSO intake. 2-Positional fatty acid analysis demonstrated higher proportions of stearic and palmitic acids and a lower proportion of oleic acid (P < 0.05) in TRL-TAG derived from HOSO. This study shows that VOO intake results in attenuated postprandial TAG concentration and faster TRL-TAG disappearance from blood compared with HOSO, suggesting that the oleic acid content may not be the main factor affecting TAG metabolism. Minor fatty acids such as linoleic acid and the 2-positional distribution of saturated stearic and palmitic acids into the TAG molecule may be important determinants of postprandial lipemia in normolipidemic men.

Caco-2 cells secrete two independent classes of lipoproteins with distinct density: effect of the ratio of unsaturated to saturated fatty acid

Polarized Caco-2 cells can synthesize two distinct density classes of lipoproteins, i.e. chylomicron/VLDL (d<1.006 g/ml) or IDL/LDL density (1.009<d<1.068 g/ml). When saturated fatty acid in the incubation medium is replaced with unsaturated fatty acid, this results in an increase in the basolateral secretion of triglycerides from 18.6+/-3.6 nmol/filter (with 0.5 mmol/l 16:0) to 21.4+/-6.2, 27. 5+/-4.8 and 28.9+/-5.3 nmol/filter when 10, 20 or 30% of 16:0 were substituted by 18:1. The secretion of IDL/LDL-sized lipoproteins diminished and chylomicron/VLDL secretion increased in proportion to the increase of unsaturated fatty acid in the medium. To gain insight into the relationship between these lipoprotein classes, we determined their secretion at several time intervals (0-4, 4-8 and 22-26 h) after incubation with a fatty acid mixture containing 16:0 and 18:1 in a 9:1 molar ratio (total fatty acid concentration was 0.5 mmol/l). Chylomicron/VLDL secretion was detectable immediately upon the start of the incubation and persisted during all intervals. In contrast, IDL/LDL density lipoproteins were first detectable in the 4-8 h time interval and their secretion was highest in the final phase of the incubation (22-26 h). We conclude that Caco-2 cells secrete two distinct density classes of lipoproteins that show no precursor-product relation.

Chylomicron synthesis by intestinal cells in vitro and in vivo

Synthesis and secretion of chylomicrons by the intestine is essential to transport dietary fats in the circulation and to deliver these fats to the appropriate peripheral tissues. The assembly of chylomicrons within the enterocyte and the subsequent secretion of these lipoprotein particles into the lymph is a complex, multi-step process that includes absorption of lipids by the enterocytes, cellular lipid (re)synthesis and translocation of cellular lipid pools, synthesis and post-translational modification of various apolipoproteins and, finally, the assembly of lipid and lipoprotein components into a chylomicron. The key process in chylomicron synthesis is the intracellular association of apolipoprotein (apo)B48, the structural protein of chylomicrons, with lipids.

Assembly and secretion of VLDL in nondifferentiated Caco-2 cells stably transfected with human recombinant ApoB48 cDNA

Intestinal cells secrete apoB48-containing very low density lipoproteins (VLDLs) and chylomicrons for the transport of biliary and dietary lipids. The molecular mechanisms regulating the assembly of intestinal lipoproteins are not known due to a lack of reliable and specific cell culture models. Caco-2 (a human colon carcinoma) cells have been used to study intestinal lipid metabolism. These cells have been shown to secrete both apoB100- and apoB48-containing triglyceride (TG)-rich lipoproteins only after differentiation into enterocyte-like cells. To study lipoprotein assembly in nondifferentiated Caco-2 cells, we stably expressed human recombinant apoB48 cDNA under the control of a constitutive cytomegalovirus promoter. Pulse-chase analysis revealed that the majority (> 50%) of apoB48 synthesized was degraded intracellularly in the presence or absence of oleic acid. Transfected nondifferentiated cells secreted lipoproteins with flotation densities similar to those of plasma HDL or LDL when cultured in serum-free or serum-containing media, respectively. Incubation of cells with media containing serum and oleic acid resulted in the secretion of VLDL-like particles. Secretion of VLDL was inhibited (> 80%) by triacsin C due to > 60% inhibition of oleate-induced TG synthesis. However, inhibition of cholesteryl ester synthesis by 70% with an acyl coenzyme A:cholesterol acyltransferase inhibitor did not affect VLDL secretion. Efficient assembly of lipoproteins usually requires the microsomal TG transfer protein (MTP). The presence of MTP in transfected Caco-2 cells was investigated by measuring TG transfer activity in microsomal fractions. Microsomal fractions had 0.2% TG transfer activity per hour per microgram of protein, which corresponds to 30% to 60% of the MTP activity present in liver-derived cells. To determine whether MTP activity was required for lipoprotein assembly, transfected cells were incubated in the presence of the MTP inhibitor CP-10,447. This compound completely abolished the secretion of apoB. These data show that the transfected cell lines secrete lipoproteins of different densities under different culture conditions and that the assembly of larger VLDL particles requires active TG synthesis and MTP activity. Thus, in nondifferentiated Caco-2 cells, the amount of apoB secreted and not the MTP activity is the limiting factor for lipoprotein assembly.

Olive oil increases the magnitude of postprandial chylomicron remnants compared to milk fat and safflower oil

OBJECTIVE

The acute effects of olive oil, milk fat and safflower oil on postprandial lipemia and remnant lipoprotein metabolism were investigated.

METHODS

Eight Healthy male volunteers randomly underwent three types of oral fat-vitamin A loading tests. The test drink was a mixture of retinyl palmitate (RP)(50,000 IU of aqueous vitamin A/m2 body surface area) and one of the three types of oils (40 g of fat/m2 body surface area): olive oil (70.7% oleic acid of total fatty acids); milk fat (69.3% saturated fatty acid); safflower oil (74.2% linoleic acid).

RESULTS

Olive oil significantly increased plasma triacylglycerol and RP concentrations 4 hours after fat loading, as compared to other fats. Increases of remnant like particle concentrations were higher after olive oil than after the other two fats.

CONCLUSION

These results show that olive oil increases the magnitude of postprandial chylomicrons and chylomicron remnants compared to milk fat and safflower oil.