Intracellular apoA-I and apoB distribution in rat intestine is altered by lipid feeding

Association of cerebrospinal fluid NPY with peripheral ApoA: a moderation effect of BMI

BACKGROUND

Apoprotein A-I (ApoA-I) and Apoprotein B (ApoB) have emerged as novel cardiovascular risk biomarkers influenced by feeding behavior. Hypothalamic appetite peptides regulate feeding behavior and impact lipoprotein levels, which effects vary in different weight states. This study explores the intricate relationship between body mass index (BMI), hypothalamic appetite peptides, and apolipoproteins with emphasis on the moderating role of body weight in the association between neuropeptide Y (NPY), ghrelin, orexin A (OXA), oxytocin in cerebrospinal fluid (CSF) and peripheral ApoA-I and ApoB.

METHODS

In this cross-sectional study, we included participants with a mean age of 31.77 ± 10.25 years, categorized into a normal weight (NW) (n = 73) and an overweight/obese (OW/OB) (n = 117) group based on BMI. NPY, ghrelin, OXA, and oxytocin levels in CSF were measured.

RESULTS

In the NW group, peripheral ApoA-I levels were higher, while ApoB levels were lower than in the OW/OB group (all p < 0.05). CSF NPY exhibited a positive correlation with peripheral ApoA-I in the NW group (r = 0.39, p = 0.001). Notably, participants with higher CSF NPY levels had higher peripheral ApoA-I levels in the NW group and lower peripheral ApoA-I levels in the OW/OB group, showing the significant moderating effect of BMI on this association (R2 = 0.144, β=-0.54, p < 0.001). The correlation between ghrelin, OXA and oxytocin in CSF and peripheral ApoB in both groups exhibited opposing trends (Ghrelin: r = -0.03 and r = 0.04; OXA: r = 0.23 and r=-0.01; Oxytocin: r=-0.09 and r = 0.04).

CONCLUSION

This study provides hitherto undocumented evidence that BMI moderates the relationship between CSF NPY and peripheral ApoA-I levels. It also reveals the protective role of NPY in the NW population, contrasting with its risk factor role in the OW/OB population, which was associated with the at-risk for cardiovascular disease.

Vegetable lecithins: A review of their compositional diversity, impact on lipid metabolism and potential in cardiometabolic disease prevention

Vegetable lecithins, widely used in the food industry as emulsifiers, are a mixture of naturally occurring lipids containing more than 50% of phospholipids (PL). PL exert numerous important physiological effects. Their amphiphilic nature notably enables them to stabilise endogenous lipid droplets, conferring them an important role in lipoprotein transport, functionality and metabolism. In addition, beneficial effects of dietary lecithin on metabolic disorders have been reported since the 1990s. This review attempts to summarize the effects of various vegetable lecithins on lipid and lipoprotein metabolism, as well as their potential application in the treatment of dyslipidemia associated with metabolic disorders. Despite controversial data concerning the impact of vegetable lecithins on lipid digestion and intestinal absorption, the beneficial effect of lecithin supplementation on plasma and hepatic lipoprotein and cholesterol levels is unequivocal. This is especially true in hyperlipidemic patients. Furthermore, the immense compositional diversity of vegetable lecithins endows them with a vast range of biochemical and biological properties, which remain to be explored in detail. Data on the effects of vegetable lecithins alternative to soybean, both as supplements and as ingredients in different foods, is undoubtedly lacking. Given the exponential demand for vegetable products alternative to those of animal origin, it is of primordial importance that future research is undertaken in order to elucidate the mechanisms by which individual fatty acids and PL from various vegetable lecithins modulate lipid metabolism. The extent to which they may influence parameters associated with metabolic disorders, such as intestinal integrity, low-grade inflammation and gut microbiota must also be assessed.

A New Look for the Red Macroalga Palmaria palmata: A Seafood with Polar Lipids Rich in EPA and with Antioxidant Properties

Palmaria palmata is an edible red macroalga widely used for human consumption and valued for its high protein value. Despite its low total lipid content, it is rich in eicosapentaenoic acid (EPA). This seaweed has been scarcely explored with regard to its lipid composition. The polar lipids of seaweeds are nowadays recognized as important phytochemicals contributing to their add value valorization and providing support for claims of potential health benefits. The present study aimed to disclose the polar lipid profile of P. palmata, farmed in an integrated multi-trophic aquaculture (IMTA) through modern lipidomic approaches using high-resolution LC-MS and MS/MS and to screen for the antioxidant properties of this red macroalga. A total of 143 molecular species of lipids were identified, belonging to several classes of polar lipids, such as glycolipids, phospholipids, and betaine lipids. It is noteworthy that the most abundant lipid species in each class were esterified with eicosapentaenoic acid (EPA), accounting for more than 50% of the lipid content. The polar lipid extract rich in EPA showed antioxidant activity with an inhibition concentration (IC) of IC30 = 171 ± 19.8 µg/mL for α,α-diphenyl-β-picrylhydrazyl radical (DPPH^●) and IC50 = 26.2 ± 0.1 µg/mL for 2,20-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid radical cation (ABTS^●+). Overall, this study highlights that P. palmata farmed in an IMTA framework can be a sustainable source of beneficial lipids with antioxidant activity. Moreover, this red macroalga can be exploited for future applications as a source of lipids rich in EPA for food and feed, nutraceuticals, and cosmetics.

Immunoglobulin-like domain containing receptor 1 mediates fat-stimulated cholecystokinin secretion

Cholecystokinin (CCK) is a satiety hormone produced by discrete enteroendocrine cells scattered among absorptive cells of the small intestine. CCK is released into blood following a meal; however, the mechanisms inducing hormone secretion are largely unknown. Ingested fat is the major stimulant of CCK secretion. We recently identified a novel member of the lipoprotein remnant receptor family known as immunoglobulin-like domain containing receptor 1 (ILDR1) in intestinal CCK cells and postulated that this receptor conveyed the signal for fat-stimulated CCK secretion. In the intestine, ILDR1 is expressed exclusively in CCK cells. Orogastric administration of fatty acids elevated blood levels of CCK in wild-type mice but not Ildr1-deficient mice, although the CCK secretory response to trypsin inhibitor was retained. The uptake of fluorescently labeled lipoproteins in ILDR1-transfected CHO cells and release of CCK from isolated intestinal cells required a unique combination of fatty acid plus HDL. CCK secretion secondary to ILDR1 activation was associated with increased [Ca2+]i, consistent with regulated hormone release. These findings demonstrate that ILDR1 regulates CCK release through a mechanism dependent on fatty acids and lipoproteins and that absorbed fatty acids regulate gastrointestinal hormone secretion.

Marine omega-3 phospholipids: metabolism and biological activities

The biological activities of omega-3 fatty acids (n-3 FAs) have been under extensive study for several decades. However, not much attention has been paid to differences of dietary forms, such as triglycerides (TGs) versus ethyl esters or phospholipids (PLs). New innovative marine raw materials, like krill and fish by-products, present n-3 FAs mainly in the PL form. With their increasing availability, new evidence has emerged on n-3 PL biological activities and differences to n-3 TGs. In this review, we describe the recently discovered nutritional properties of n-3 PLs on different parameters of metabolic syndrome and highlight their different metabolic bioavailability in comparison to other dietary forms of n-3 FAs.

Inhibition of cholesterol absorption: targeting the intestine

Atherosclerosis, the gradual formation of a lipid-rich plaque in the arterial wall is the primary cause of Coronary Artery Disease (CAD), the leading cause of mortality worldwide. Hypercholesterolemia, elevated circulating cholesterol, was identified as a key risk factor for CAD in epidemiological studies. Since the approval of Mevacor in 1987, the primary therapeutic intervention for hypercholesterolemia has been statins, drugs that inhibit the biosynthesis of cholesterol. With improved understanding of the risks associated with elevated cholesterol levels, health agencies are recommending reductions in cholesterol that are not achievable in every patient with statins alone, underlying the need for improved combination therapies. The whole body cholesterol pool is derived from two sources, biosynthesis and diet. Although statins are effective at reducing the biosynthesis of cholesterol, they do not inhibit the absorption of cholesterol, making this an attractive target for adjunct therapies. This report summarizes the efforts to target the gastrointestinal absorption of cholesterol, with emphasis on specifically targeting the gastrointestinal tract to avoid the off-target effects sometimes associated with systemic exposure.

CFTR knockdown stimulates lipid synthesis and transport in intestinal Caco-2/15 cells

Cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride channel highly expressed in epithelial cells of the gastrointestinal tract. Mutations in the CFTR gene cause cystic fibrosis (CF), a disease characterized by pancreatic insufficiency, fat malabsorption, and steatorrhea. Despite the administration of pancreatic enzymes to normalize malabsorption, CF patients still experienced lipid fecal loss, nutritional deficiencies, and abnormalities in serum lipid profile, suggesting the presence of intrinsic defects in the intestinal handling of nutrients. The objective of the present study was to assess the impact of CFTR gene knockdown on intracellular lipid metabolism of the intestinal Caco-2/15 cell line. Partial CFTR gene inactivation led to cellular lipid accretion of phospholipids, triglycerides, and cholesteryl esters. Likewise, secretion of these lipid fractions was significantly increased following CFTR gene manipulation. As expected from these findings, the output of triglyceride-rich lipoproteins showed the same increasing pattern. Investigation of the mechanisms underlying these changes revealed that CFTR knockdown resulted in raised levels of apolipoproteins in cells and media and microsomal transfer protein activity, two important factors for the efficient assembly and secretion of lipoproteins. Similarly, scrutiny of the enzymatic monoacylglycerol acyltransferase and diacylglycerol acyltransferase, which exhibit dynamic function in triacylglycerol resynthesis and chylomicron formation in enterocytes, revealed a significant augmentation in their activity. Conversely, cholesterol uptake mediated by Niemann-Pick C1 like 1, Scavenger Receptor Class B Type I, and ATP-binding cassette G8 remains unaffected by genetic modification of CFTR. Collectively, these results highlight the role played by CFTR in intestinal handling of lipids and may suggest that factors other than defective CFTR are responsible for the abnormal intracellular events leading to fat malabsorption in CF patients.

Molecular processes that handle -- and mishandle -- dietary lipids

Overconsumption of lipid-rich diets, in conjunction with physical inactivity, disables and kills staggering numbers of people worldwide. Recent advances in our molecular understanding of cholesterol and triglyceride transport from the small intestine to the rest of the body provide a detailed picture of the fed/fasted and active/sedentary states. Key surprises include the unexpected nature of many pivotal molecular mediators, as well as their dysregulation - but possible reversibility - in obesity, diabetes, inactivity, and related conditions. These mechanistic insights provide new opportunities to correct dyslipoproteinemia, accelerated atherosclerosis, insulin resistance, and other deadly sequelae of overnutrition and underexertion.

Dietary phospholipids, hepatic lipid metabolism and cardiovascular disease

PURPOSE OF REVIEW

An increasing number of studies in experimental animals suggest that dietary phospholipids might be of benefit in the treatment of fatty liver disease. This raises the possibility that synthetic or naturally occurring phospholipid isolates could be used as hepatoprotective nutraceuticals or functional foods. The aim of the present article is to review published data describing the beneficial effects of dietary phospholipids on hepatic lipid metabolism and their potential to affect atherosclerosis and cardiovascular disease.

RECENT FINDINGS

Consistent results have been obtained supporting the concept that phospholipid from various sources (i.e., soybean, safflower, egg and fish roe) can reduce liver lipid levels. The primary site of action for this effect appears to be in the intestinal lumen, where dietary phospholipids are able to interfere with neutral sterol absorption. Results have also been obtained suggesting that dietary phospholipids can stimulate bile acid and cholesterol secretion. Additional work suggests that dietary phospholipids can have a beneficial effect on plasma lipid and lipoprotein levels.

SUMMARY

The concept of using naturally occurring compounds such as phospholipid to treat or prevent hepatic steatosis is very attractive. Controlled human trials are, however, required to verify the efficacy of this approach. It is also important that additional research be conducted to determine the extent to which certain phospholipids have the ability to increase plasma HDL levels and potentially affect the onset or development of cardiovascular disease.

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.

Effect of acute feeding of diets of varying fatty acid composition on intestinal apolipoprotein expression in the newborn swine

The purpose of this study was to determine the effects of dietary fatty acids of varying chain lengths and degrees of saturation on intestinal apolipoprotein (apo) B and A-I expression in the newborn piglet. Two-day-old female piglets received one of three isocaloric formulas containing 48% of total calories (120 kcal/kg/24 h) as medium-chain triglycerides (MCT) from MCT oil, intermediate-chain saturated triglycerides (ICST) from coconut oil, or long-chain polyunsaturated triglycerides (LCPUT) from safflower oil by continuous duodenal infusion for 24 h. After in situ radiolabeling, jejunal and ileal mucosal apo B-48 and A-I were immunoprecipitated, and synthesis was expressed as percentage of total protein synthesis. Mucosal apo B and A-I mass was measured by ELISA as nanograms of apoprotein/microgram of total protein. Fifty percent less apo B jejunal synthesis was present in the ICST group versus the MCT and LCPUT groups (0.67 +/- 0.07, 1.19 +/- 0.20, and 1.25 +/- 0.15, respectively, mean +/- SEM, p < 0.05). Jejunal apo B mass was lower in the MCT group versus the ICST and LCPUT groups (0.10 +/- 0.02, 0.21 +/- 0.03, and 0.16 +/- 0.03, respectively, p < 0.05). Ileal apo B synthesis was lowest in the ICST group. No differences were found in ileal apo B mass. Two-fold higher jejunal apo A-I synthesis was found in the LCPUT group versus the MCT and ICST groups (14.18 +/- 1.69, 7.56 +/- 2.63, and 6.36 +/- 0.58, respectively, p < 0.01). No differences were found for jejunal apo A-I mass. In the ileum, the only difference was a higher apo A-I mass in the LCPUT group (p < 0.05). We conclude that in the newborn piglet intestinal apo B and A-I expression is acutely and differentially regulated by dietary lipid varying in fatty acid chain length and saturation. The patterns of regulation are complex and vary among specific apolipoproteins and regions of the small intestine and include co- and posttranslational mechanisms.

Chylomicron assembly and catabolism: role of apolipoproteins and receptors

Chylomicrons are lipoproteins synthesized exclusively by the intestine to transport dietary fat and fat-soluble vitamins. Synthesis of apoB48, a translational product of the apob gene, is required for the assembly of chylomicrons. The apob gene transcription in the intestine results in 14 and 7 kb mRNAs. These mRNAs are post-transcriptionally edited creating a stop codon. The edited mRNAs chylomicrons from the shorter apoB48 peptide remains to be elucidated. In addition, the roles of proteins involved in the assembly pathway, e.g. apobec-1, MTP and apoA-IV, needs to be studied. Cloning of enzymes involved in the intestinal biosynthesis of triglycerides will be crucial to fully appreciate the assembly of chylomicrons. There is a need for cell culture and transgenic animal models that can be used for intestinal lipoprotein assembly. The catabolism of chylomicrons is far more complex and efficient than the catabolism of VLDL. Even though the major steps involved in the catabolism of chylomicrons are now known, the determinants for apolipoprotein exchange, processing of remnants in the space of Disse, as well as the mechanism of uptake of these particles by extra-hepatic tissue needs further exploration.

Effect of fat feeding on human intestinal apolipoprotein B mRNA levels and editing

Our purpose was to assess the effect of a fat-rich meal on intestinal apolipoprotein B (apoB) mRNA levels and editing. We obtained jejunal biopsies from eight healthy adults in the fasting state and 3 h after a meal containing 1 g/kg of fat. In the fasting state, 93% of the apoB mRNA contained the editing sequence resulting in apoB-48 production. Feeding induced no significant changes in apoB mRNA levels or editing. Our data are consistent with the concept that the significant increase in apoB-48 within triglyceride-rich lipoproteins in postprandial plasma is not due to alterations in apoB gene expression or editing.

Ontogenetic regulation of apolipoprotein B mRNA editing during human and rat development in vivo

The solubilization and delivery of lipids in plasma rely on both forms of apolipoprotein B (apo B): apo B-100 and apo B-48. Apo B-48 is the translational product of apo B-100 mRNA that undergoes peritranscriptional conversion of C----U, replacing codon CAA (glutamine 2,153) with the inframe stop codon (UAA). We examined mRNA editing activity in the human and the rat by reverse transcription-polymerase chain reaction primer-extension analysis of intestine and liver total RNA. In rat intestine the percentage of apo B transcripts that undergo editing increases dramatically the day before birth (from approximately 1% to 80%), whereas the rat liver acquires an adult level of editing activity during the third postnatal week (rising from approximately 8% to 30%), when weaning is completed, bile acid composition matures, and plasma thyroid hormone levels peak. In contrast to the rat, the human intestine acquires adult levels of apo B mRNA editing relatively early in fetal development, rising from 10% at 10 weeks to approximately 80% by the end of the second trimester. Our results establish that apo B mRNA editing is 1) developmentally regulated in a tissue- and species-specific manner; 2) fully developed prenatally in both human and rat intestine, suggesting a crucial role of apo B-48 in mammalian fetal adaptation to extrauterine life; and 3) acquired early in human fetal intestine, implying a potential role for apo B-48 in prenatal lipid metabolism.

Apolipoprotein B gene expression in rat intestine. The effect of dietary fiber

The effect of the dietary fiber on apo B mRNA level was studied in the intestine of rats that were fed either fiber-free or high-fiber (30% sugar-beet fiber) low-fat diets for 3 weeks. The fiber diet studied does not affect jejunal apo B mRNA levels but decreases the level of ileal apo B mRNA. In the rat cecum, in both fiber-free and fiber groups, we failed to detect the apo B mRNA. The test fiber diet feeding markedly increased fecal bile salt and cholesterol excretions. We suggest that dietary fiber can modify apo B expression in the intestine. The increased fecal bile salt excretion might be involved in such a modification.