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Bile acid-modified nanoparticles provide a convenient strategy to improve oral bioavailability of poorly permeable drugs by exploiting specific interactions with bile acid transporters. However, the underlying mechanisms are unknown, especially considering the different absorption sites of free bile acids (ileum) and digested fat molecules from bile acid-emulsified fat droplets (duodenum). Here, glycocholic acid (GCA)-conjugated polystyrene nanoparticles (GCPNs) are synthesized and their transport in Caco-2 cell models is studied. GCA conjugation enhances the uptake by interactions with apical sodium-dependent bile acid transporter (ASBT). A new pathway correlated with both ASBT and chylomicron pathways is identified. Meanwhile, the higher uptake of GCPNs does not lead to higher transcytosis to the same degree compared with unmodified nanoparticles (CPNs). The pharmacological and genomics study confirm that GCA conjugation changes the endocytosis mechanisms and downregulates the cellular response to the transport at gene levels, which works as a negative feedback loop and explains the higher cellular retention of GCPNs. These findings offer a solid foundation in the bile acid-based nanomedicine design, with utilizing advantages of the ASBT-mediated uptake, as well as inspiration to take comprehensive consideration of the cellular response with more developed technologies., (© 2022 The Authors. Advanced Science published by Wiley-VCH GmbH.)

Background: Statins suppress the progression of atherosclerosis by reducing low-density lipoprotein (LDL) cholesterol levels. Pemafibrate (K-877), a novel selective peroxisome proliferator-activated receptor α modulator, is expected to reduce residual risk factors including high triglycerides (TGs) and low high-density lipoprotein (HDL) cholesterol during statin treatment. However, it is not known if statin therapy with add-on pemafibrate improves the progression of atherosclerosis. The aim of this study was to assess the effect of combination therapy with pitavastatin and pemafibrate on lipid profiles and endothelial dysfunction in hypertension and insulin resistance model rats., Methods: Seven-week-old male Dahl salt-sensitive (DS) rats were divided into the following five treatment groups (normal diet (ND) plus vehicle, high-salt and high-fat diet (HD) plus vehicle, HD plus pitavastatin (0.3 mg/kg/day), HD plus pemafibrate (K-877) (0.5 mg/kg/day), and HD plus combination of pitavastatin and pemafibrate) and treated for 12 weeks. At 19 weeks, endothelium-dependent relaxation of the thoracic aorta in response to acetylcholine was evaluated., Results: After feeding for 12 weeks, systolic blood pressure and plasma levels of total cholesterol were significantly higher in the HD-vehicle group compared with the ND-vehicle group. Combination therapy with pitavastatin and pemafibrate significantly reduced systolic blood pressure, TG levels, including total, chylomicron (CM), very LDL (VLDL), HDL-TG, and cholesterol levels, including total, CM, VLDL, and LDL-cholesterol, compared with vehicle treatment. Acetylcholine caused concentration-dependent relaxation of thoracic aorta rings that were pre-contracted with phenylephrine in all rats. Relaxation rates in the HD-vehicle group were significantly lower compared with the ND-vehicle group. Relaxation rates in the HD-combination of pitavastatin and pemafibrate group significantly increased compared with the HD-vehicle group, although neither medication alone ameliorated relaxation rates significantly. Western blotting experiments showed increased phosphorylated endothelial nitric oxide synthase protein expression in aortas from rats in the HD-pemafibrate group and the HD-combination group compared with the HD-vehicle group. However, the expression levels did not respond significantly to pitavastatin alone., Conclusions: Combination therapy with pitavastatin and pemafibrate improved lipid profiles and endothelial dysfunction in hypertension and insulin resistance model rats. Pemafibrate as an add-on strategy to statins may be useful for preventing atherosclerosis progression.

Objective: Intestinal overproduction of atherogenic chylomicron particles postprandially is an important component of diabetic dyslipidemia in insulin-resistant states. In addition to enhancing insulin secretion, peripheral glucagon-like peptide-1 (GLP-1) receptor stimulation has the added benefit of reducing this chylomicron overproduction in patients with type 2 diabetes mellitus. Given the presence of central GLP-1 receptors and GLP-1-producing neurons, we assessed whether central GLP-1 exerts an integral layer of neuronal control during the production of these potentially atherogenic particles., Approach and Results: Postprandial production of triglyceride-rich lipoproteins was assessed in Syrian hamsters administered a single intracerebroventricular injection of the GLP-1 receptor agonist exendin-4. Intracerebroventricular exendin-4 reduced triglyceride-rich lipoprotein-triglyceride and -apolipoprotein B48 accumulation relative to vehicle-treated controls. This was mirrored by intracerebroventricular MK-0626, an inhibitor of endogenous GLP-1 degradation, and prevented by central exendin9-39, a GLP-1 receptor antagonist. The effects of intracerebroventricular exendin-4 were also lost during peripheral adrenergic receptor and central melanocortin-4 receptor inhibition, achieved using intravenous propranolol and phentolamine and intracerebroventricular HS014, respectively. However, central exendin9-39 did not preclude the effects of peripheral exendin-4 treatment on chylomicron output., Conclusions: Central GLP-1 is a novel regulator of chylomicron production via melanocortin-4 receptors. Our findings point to the relative importance of central accessibility of GLP-1-based therapies and compel further studies examining the status of this brain-gut axis in the development of diabetic dyslipidemia and chylomicron overproduction., (© 2015 American Heart Association, Inc.)

Background & Aims: The intestine efficiently incorporates and rapidly secretes dietary fat as chylomicrons (lipoprotein particles comprising triglycerides, phospholipids, cholesterol, and proteins) that contain the apolipoprotein isoform apoB-48. The gut can store lipids for many hours after their ingestion, and release them in chylomicrons in response to oral glucose, sham feeding, or unidentified stimuli. The gut hormone glucagon-like peptide-2 (GLP-2) facilitates intestinal absorption of lipids, but its role in chylomicron secretion in human beings is unknown., Methods: We performed a randomized, single-blind, cross-over study, with 2 study visits 4 weeks apart, to assess the effects of GLP-2 administration on triglyceride-rich lipoprotein (TRL) apoB-48 in 6 healthy men compared with placebo. Subjects underwent constant intraduodenal feeding, with a pancreatic clamp and primed constant infusion of deuterated leucine. In a separate randomized, single-blind, cross-over validation study, 6 additional healthy men ingested a high-fat meal containing retinyl palmitate and were given either GLP-2 or placebo 7 hours later with measurement of TRL triglyceride, TRL retinyl palmitate, and TRL apoB-48 levels., Results: GLP-2 administration resulted in a rapid (within 30 minutes) and transient increase in the concentration of TRL apoB-48, compared with placebo (P = .03). Mathematic modeling of stable isotope enrichment and the mass of the TRL apoB-48 suggested that the increase resulted from the release of stored, presynthesized apoB-48 from the gut. In the validation study, administration of GLP-2 at 7 hours after the meal, in the absence of additional food intake, robustly increased levels of TRL triglycerides (P = .007), TRL retinyl palmitate (P = .002), and TRL apoB-48 (P = .04) compared with placebo., Conclusions: Administration of GLP-2 to men causes the release of chylomicrons that comprise previously synthesized and stored apoB-48 and lipids. This transiently increases TRL apoB-48 levels compared with placebo. Clinical trials number at www.clinicaltrials.gov: NCT 01958775., (Copyright © 2014 AGA Institute. Published by Elsevier Inc. All rights reserved.)

The glucagon-like peptides (GLP-1 and GLP-2) are processed from the proglucagon polypeptide and secreted in equimolar amounts but have opposite effects on chylomicron (CM) production, with GLP-1 significantly reducing and GLP-2 increasing postprandial chylomicronemia. In the current study, we evaluated the apparent paradoxical roles of GLP-1 and GLP-2 under physiological conditions in the Syrian golden hamster, a model with close similarity to humans in terms of lipoprotein metabolism. A short (30-min) intravenous infusion of GLP-2 resulted in a marked increase in postprandial apolipoprotein B48 (apoB48) and triglyceride (TG) levels in the TG-rich lipoprotein (TRL) fraction, whereas GLP-1 infusion decreased lipid absorption and levels of TRL-TG and apoB48. GLP-1 and GLP-2 coinfusion resulted in net increased lipid absorption and an increase in TRL-TG and apoB48. However, prolonged (120-min) coinfusion of GLP-1 and GLP-2 decreased postprandial lipemia. Blocking dipeptidyl peptidase-4 activity resulted in decreased postprandial lipemia. Interestingly, fructose-fed, insulin-resistant hamsters showed a more pronounced response, including possible hypersensitivity to GLP-2 or reduced sensitivity to GLP-1. In conclusion, under normal physiological conditions, the actions of GLP-2 predominate; however, when GLP-1 activity is sustained, the hypolipidemic action of GLP-1 predominates. Pharmacological inhibition of GLP-1 degradation tips the balance toward an inhibitory effect on intestinal production of atherogenic CM particles.

A major function of the enterocytes is absorption, processing, and export of dietary lipids into the lymphatic system. Pluronic L-81 is a non-ionic hydrophobic surfactant, which specifically inhibits lipid absorption in the intestine when administered in vivo. This compound is therefore an attractive probe to perturb and investigate the molecular and intracellular events in chylomicron assembly in the enterocytes. In the present study pluronic acid was administered to hamsters followed by isolation of the enterocytes and cell fractionation to investigate the effect of pluronic acid on intracellular events in lipid absorption. Four types of diet were administered to hamsters for three weeks; low-fat chow, high-fat chow and each diet with or without added pluronic acid. Sub-cellular fractions of freshly isolated enterocytes were prepared. Consistent with morphological observation, the high fat diet resulted in a three-fold increase in the triacylglycerol (TAG) content of the enterocytes and addition of pluronic acid to either the low fat or the high fat diets resulted in a ten-fold increase in cellular TAG levels. Determination of the mass of TAG and the time course of incorporation of 3H-triolein, administered by gavage, showed that the increased TAG was recovered in the microsomal (endoplasmic reticulum) fraction and the cytosol. In microsomes, increased TAG was recovered mainly in the membrane although there was a significant amount in the microsomal luminal contents. Pluronic acid therefore acts at the level of the endoplasmic reticulum and inhibits the assembly of apo-B48 with chylomicron TAG. The excess TAG is transferred to cytosolic stores.

The metabolic syndrome (MetS) and conditions of insulin resistance are often characterized by an increase in cardiovascular disease (CVD) risk without a concomitant increase in low-density lipoprotein cholesterol (LDL-C), suggesting that other atherogenic pathways maybe involved. Intestinally derived chylomicron remnants (CM-r) are also thought to contribute to atherogenic dyslipidemia during insulin resistance. Recent animal and human studies suggest that insulin resistance leads to an over-production of intestinal chylomicrons (CM), which can contribute to fasting and post-prandial dyslipidemia during these conditions. We and others have contributed new insights into the mucosal absorption, efflux and secretion of cholesterol and triglyceride (TG) in intestinal CM during conditions of insulin resistance. One of the pertinent discoveries has been that the intestine has the capacity to increase the secretion of CM during conditions of hyper-insulinemia (observed in the JCR:LA-cp rat model). Advances to identify cholesterol-transporter targets have highlighted the contribution of the intestine to whole body cholesterol metabolism. Ezetimibe (EZ) is a novel pharmaceutical compound that reduces intestinal cholesterol absorption. We know that ezetimibe either alone, or in combination with a HMG-CoA reductase inhibitor (such as simvastatin [SV]) can decrease both plasma LDL-C and CM-r concentrations. However, the combined effects of these compounds (EZ+SV) on post-prandial dyslipidemia and/or impact on arterial deposition of cholesterol during MetS have not been studied. The focus of this review is to highlight studies using an animal model of MetS and CM over-production (the JCR:LA-cp rat), and to summarize the effects of ezetimibe on intestinal cholesterol flux, CM metabolism and uptake of cholesterol into arterial vessels., (Copyright © 2010 Elsevier Ireland Ltd. All rights reserved.)

Trans-11 vaccenic acid (VA) is the predominant trans isomer in ruminant fat and a major precursor to the endogenous synthesis of cis9,trans11-conjugated linoleic acid in humans and animals. We have previously shown that 3-wk VA supplementation has a triglyceride (TG)-lowering effect in a rat model of dyslipidemia, obesity, and metabolic syndrome (JCR:LA-cp rats). The objective of this study was to assess the chronic effect (16 wk) of VA on lipid homeostasis in both the liver and intestine in obese JCR:LA-cp rats. Plasma TG (P < 0.001), total cholesterol (P < 0.001), LDL cholesterol (P < 0.01), and nonesterified fatty acid concentrations, as well as the serum haptoglobin concentration, were all lower in obese rats fed the VA diet compared with obese controls (P < 0.05). In addition, there was a decrease in the postprandial plasma apolipoprotein (apo)B48 area under the curve (P < 0.05) for VA-treated obese rats compared with obese controls. The hepatic TG concentration and the relative abundance of fatty acid synthase and acetyl-CoA carboxylase proteins were all lower (P < 0.05) in the VA-treated group compared with obese controls. Following acute gastrointestinal infusion of a VA-triolein emulsion in obese rats that had been fed the control diet for 3 wk, the TG concentration was reduced by 40% (P < 0.05) and the number of chylomicron (CM) particles (apoB48) in nascent mesenteric lymph was reduced by 30% (P < 0.01) relative to rats infused with a triolein emulsion alone. In conclusion, chronic VA supplementation significantly improved dyslipidemia in both the food-deprived and postprandial state in JCR:LA-cp rats. The appreciable hypolipidemic benefits of VA may be attributed to a reduction in both intestinal CM and hepatic de novo lipogenesis pathways.

Objective: We assessed the ability of novel lipid structures including medium-chain triacylglycerols (MCTs) and 1,3-diacylglycerol (DG) oil to lower postprandial triacylglycerol (TG) elevation and increase hepatic fat oxidation when substituted for dietary TG, which may be useful in the prevention and treatment of obesity and other related metabolic conditions, such as dyslipidemias., Methods: This double-blind, randomized, crossover trial evaluated the effects of an oral fat load containing DG or MCTs compared with equivalent intakes of long-chain triacylglycerols (LCTs) on the postprandial metabolic responses of insulin-resistant men and women (n = 36). Each subject consumed a single oral fat load on each test day. The fat loads were delivered in milkshakes that contained 30 g of one of the three test oils., Results: The postprandial TG incremental area under the curve after MCT was 73% lower, and that for DG was 22% lower, compared with the response after LCT oil. The incremental area under the curve values for chylomicron TG were reduced versus LCT by 89% and 28%, respectively, in the MCT and DG conditions. Compared with the LCT treatment, beta-hydroxybutyrate concentration was increased after MCT oil, but not after DG., Conclusion: These results indicate that dietary DG decreased postprandial triglyceridemia compared with LCT, but to a lesser extent than MCT.

Lipoprotein lipase (LPL) deficiency is an extremely rare congenital metabolic disorder with an accumulation of chylomicrons in the blood. We encountered a patient with an LPL deficiency leading to multiple bone xanthomas associated with hyperlipidemia. Radiographs and MRI of the humerus and femur revealed symmetrical bone lesions, and there is a possibility that these symmetrical lesions may therefore be a characteristic feature for this disorder.

Objective: The purpose of this study was to evaluate the impact of torcetrapib on atherogenic TG-rich lipoprotein subfractions in the postprandial phase in Type IIB hyperlipidemia., Methods and Results: The quantitative and qualitative features of the postprandial profile of TG-rich lipoproteins were determined at baseline, after treatment for 6 weeks with 10 mg/d atorvastatin, and subsequently with an atorvastatin/torcetrapib combination (10/60 mg/d) in Type IIB patients (n=18). After ingestion of a standardized mixed meal, TG-rich lipoprotein subfractions were evaluated over 8 hours after each experimental period. On a background of atorvastatin, torcetrapib significantly attenuated the incremental postprandial area under the curve (iAUC 0 to 8 hours) for VLDL-1 (-40%), and the AUC 0 to 8 hours for VLDL-2 (-53%), with minor effect on chylomicron iAUC (-24%); concomitantly, the CE/TG ratio in both VLDL-1 and VLDL-2 was significantly reduced (-27% to -42%). Such reduction was attributable to torcetrapib-mediated attenuation of postprandial CE transfer to Chylomicrons (-17%) and VLDL-1 (-33%). Marked reduction in postprandial VLDL-1 levels was associated with apoE enrichment., Conclusions: On a background of atorvastatin, torcetrapib attenuated the quantitative and qualitative features of the atherogenic postprandial profile of chylomicrons, VLDL-1 and VLDL-2. Such changes reflect the sum of torcetrapib-mediated effects on TG-rich lipoprotein production, intravascular remodeling, and catabolism.

Objective: The aim of the present study was to investigate the effect of trans-18:1 isomers compared to other fatty acids, especially saturates, on the postprandial fatty acid composition of triacylglycerols (TAG) in chylomicrons and VLDL., Design: A randomised crossover experiment where five interesterified test fats with equal amounts of palmitic acid (P fat), stearic acid (S fat), trans-18:1 isomers (T fat), oleic acid (O fat), or linoleic acid (L fat) were tested., Subjects: A total of 16 healthy, normolipidaemic males (age 23+/-2 y) were recruited., Interventions: The participants ingested fat-rich test meals (1 g fat per kg body weight) and the fatty acid profiles of chylomicron and VLDL TAG were followed for 8 h., Results: The postprandial fatty acid composition of chylomicron TAG resembled that of the ingested fats. The fatty acids in chylomicron TAG were randomly distributed among the three positions in accordance with the distributions in test fats. Calculations of postprandial TAG concentrations from fatty acid data revealed increasing amounts up to 4 h but lower response curves (IAUC) for the two saturated fats in accordance with previous published data. The T fat gave results comparable to the O and L fats. The test fatty acids were much less reflected in VLDL TAG and there was no dietary influence on the response curves., Conclusions: The fatty acid composition in the test fats as well as the positional distributions of these were maintained in the chylomicrons. No specific clearing of chylomicron TAG was observed in relation to time.

The effect of short-term bezafibrate (BF) administration over time on the expression of adiponectin mRNA in the tissues was examined in Otsuka Long Evans Tokushima Fatty (OLETF) rats. Eight-week-old rats were divided into the high-dose (100 mg/kg) BF group (n=15), the low-dose (10 mg/kg) BF group (n=15), or the control group (n=15) and followed up for 14 d. Tri-glyceride and free fatty acid levels significantly decreased in a dose-dependent manner in the high-dose BF group. The insulin levels increased with time, although they were significantly lower in the high-dose BF group on d 3 and 7 than the control group. Adiponectin levels significantly increased in the high-dose BF group. On d 14 of BF administration, the levels of VLDL and chy-lomicron were significantly lower in BF groups, and adiponectin mRNA expression in the white adipose tissue was significantly higher in the high-dose BF group. Findings from this study suggest that in type 2 diabetes with insulin resistance, hypertriglyceridemia is closely linked to adiponectin.

Purpose: To compare the effects of a low-carbohydrate diet and a conventional (fat- and calorie-restricted) diet on lipoprotein subfractions and inflammation in severely obese subjects., Methods: We compared changes in lipoprotein subfractions and C-reactive protein levels in 78 severely obese subjects, including 86% with either diabetes or metabolic syndrome, who were randomly assigned to either a low-carbohydrate or conventional diet for 6 months., Results: Subjects on a low-carbohydrate diet experienced a greater decrease in large very low-density lipoprotein (VLDL) levels (difference = -0.26 mg/dL, P = 0.03) but more frequently developed detectable chylomicrons (44% vs. 22%, P = 0.04). Both diet groups experienced similar decreases in the number of low-density lipoprotein (LDL) particles (difference = -30 nmol/L, P = 0.74) and increases in large high-density lipoprotein (HDL) concentrations (difference = 0.70 mg/dL, P = 0.63). Overall, C-reactive protein levels decreased modestly in both diet groups. However, patients with a high-risk baseline level (>3 mg/dL, n = 48) experienced a greater decrease in C-reactive protein levels on a low-carbohydrate diet (adjusted difference = -2.0 mg/dL, P = 0.005), independent of weight loss., Conclusion: In this 6-month study involving severely obese subjects, we found an overall favorable effect of a low-carbohydrate diet on lipoprotein subfractions, and on inflammation in high-risk subjects. Both diets had similar effects on LDL and HDL subfractions., (Copyright 2004 Elsevier Inc.)

Background: The amount of dietary fat required for optimal bioavailability of carotenoids in plant matrices is not clearly defined., Objective: The objective was to quantify the appearance of carotenoids in plasma chylomicrons after subjects ingested fresh vegetable salads with fat-free, reduced-fat, or full-fat salad dressings., Design: The subjects (n = 7) each consumed 3 salads consisting of equivalent amounts of spinach, romaine lettuce, cherry tomatoes, and carrots with salad dressings containing 0, 6, or 28 g canola oil. The salads were consumed in random order separated by washout periods of > or =2 wk. Blood samples were collected hourly from 0 to 12 h. Chylomicrons were isolated by ultracentrifugation, and carotenoid absorption was analyzed by HPLC with coulometric array detection., Results: After ingestion of the salads with fat-free salad dressing, the appearance of alpha-carotene, beta-carotene, and lycopene in chylomicrons was negligible. After ingestion of the salads with reduced-fat salad dressing, the appearance of the carotenoids in plasma chylomicrons increased relative to that after ingestion of the salads with fat-free salad dressing (P < 0.04). Similarly, the appearance of the carotenoids in plasma chylomicrons was higher after the ingestion of salads with full-fat than with reduced-fat salad dressing (P < 0.02)., Conclusions: High-sensitivity HPLC with coulometric array detection enabled us to quantify the intestinal absorption of carotenoids ingested from a single vegetable salad. Essentially no absorption of carotenoids was observed when salads with fat-free salad dressing were consumed. A substantially greater absorption of carotenoids was observed when salads were consumed with full-fat than with reduced-fat salad dressing.

Both atorvastatin and fenofibrate are known to lower postprandial chylomicrons and chylomicron remnants. However, until now it has not been investigated which of the two drugs is more effective in one and the same patient and, secondly, whether these drugs exert different effects on chylomicron remnants of different sizes. To this end 12 patients with mixed hyperlipidemia were treated in a crossover study with 40 mg atorvastatin or with 200 mg micronized fenofibrate once daily for 6 weeks. Oral fat loading was given before and after each treatment. Chylomicron remnants of various sizes were determined by fluorometric determinations of retinyl palmitate after lipoprotein separation by size-exclusion chromatography. As expected, atorvastatin was more effective than fenofibrate on total and LDL-cholesterol (P < 0.05). Fenofibrate, in contrast, was more effective on all triglyceride-rich lipoproteins in both the fasting and the postprandial state. The stronger effect of fenofibrate affected not only chylomicrons and VLDL but also chylomicron remnants. It reduced large chylomicron remnants by 66% at 6h and by 74% at 8 h. The action of atorvastatin was less pronounced, with corresponding reductions of 42 and 65% (P < 0.05 only after 8 h). Fenofibrate was even more effective on small chylomicron remnants, yielding reductions of 47, 74, and 66% at 4, 6, and 8 h. Atorvastatin, in contrast, gave reductions of 30 and 26% after 6 and 8 h, the effect reaching statistical significance only after 6h. Fenofibrate is therefore more effective than atorvastatin in lowering all triglyceride-rich lipoproteins, including large and small chylomicron remnants., (Copyright 2003 Elsevier Ireland Ltd.)

Omega-3 fatty acids (FAs) reduce postprandial triacylglycerol (TG) concentrations. This study was undertaken to determine whether this effect was due to reduced production or increased clearance of chylomicrons. Healthy subjects (n = 33) began with a 4-week, olive oil placebo (4 g/d) run-in period. After a 4-week wash-out period, subjects were randomized to supplementation with 4 g/d of ethyl esters of either safflower oil (SAF), eicosapentaenoic acid (EPA), or docosahexaenoic acid (DHA) for 4 weeks. Results for EPA and DHA were similar, and therefore the data were combined into one omega-3 FA group. Omega-3 FA supplementation reduced the postprandial TG and apolipoprotein B (apo B)-48 and apoB-100 concentrations by 16% (P = 0.08), 28% (P < 0.001), and 24% (P < 0.01), respectively. Chylomicron TG half-lives in the fed state were reduced after omega-3 FA treatment (6.0 +/- 0.5 vs. 5.1 +/- 0.4 min; P < 0.05), but not after SAF (6.9 +/- 0.7 vs. 7.1 +/- 0.7 min). Omega-3 FA supplementation decreased chylomicron particle sizes (mean diameter; 293 +/- 44 vs. 175 +/- 25 nm; P < 0.01) and increased preheparin lipoprotein lipase (LPL; 0.6 +/- 0.1 vs. 0.9 +/- 0.1 micromol/h/ml; P < 0.05) activity during the fed state, but had no effect on postheparin LPL or hepatic lipase activities. The results suggest that omega-3 FA supplementation accelerates chylomicron TG clearance by increasing LPL activity, and that EPA and DHA are equally effective.

Bacterial endotoxin (LPS) elicits dramatic responses in the host including elevated plasma lipid levels due to the increased synthesis and secretion of triglyceride (TG)-rich lipoproteins by the liver. We postulate that this cytokine-induced hyperlipoproteinemia, clinically termed the 'lipemia of sepsis', represents an innate, non-adaptive host immune response to infection. Data in support of this hypothesis include the capacity of TG-rich lipoproteins (VLDL and chylomicrons, CM) to bind and neutralize LPS. Herein, we present evidence that CM-bound LPS attenuates the hepatocellular response to pro-inflammatory cytokines. Primary rodent hepatocytes pretreated with CM-LPS complexes for 2 h demonstrated a near 70% reduction in cytokine-induced NO production as compared to non-pretreated control cells (P > or = 0.04). Whereas hepatocytes were maximally tolerant to cytokine stimulation 6 h after CM-LPS pretreatment, the cells spontaneously regained cytokine responsiveness within 40 h. The induction of cytokine tolerance in hepatocytes follows the internalization of CM-LPS complexes and is a process regulated by the LDL receptor. CM-LPS complexes failed to induce cytokine tolerance in hepatocytes wherein lipoprotein receptor activity was inhibited with high dose receptor associated protein (30 microg/ml). Similarly, CM-bound LPS did not induce tolerance in hepatocytes from ldlr(-/-) mice. Thus, the biochemical or genetic inhibition of LDL receptor activity effectively prevented the CM-mediated induction of the cytokine tolerant phenotype. In conclusion, the lipemia of sepsis likely represents a mechanism by which the host combats sporadic, non-life-threatening episodes of endotoxemia. Also, it may indicate a negative regulatory mechanism for the hepatic response to sepsis, serving to effectively down-regulate the acute phase response. A better understanding of how TG-rich lipoproteins modulate the host response to LPS could yield novel biological insights with important clinical implications, including the development of lipid-based therapies for bacterial infections.

The triglyceride-lowering effect of pitavastatin, a potent 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor, was investigated in a rat model of postprandial lipemia. Plasma triglyceride levels started to increase 4 h after the fat load, reached the maximum at 6 h and then gradually decreased. A single dose of pitavastatin (1 mg/kg) significantly suppressed chylomicron-triglyceride secretion into the lymph by 40% and delayed the elevation of plasma triglyceride. Pitavastatin at 1 mg/kg decreased the 6-h plasma triglyceride levels by 53% and at 0.5 mg/kg decreased the 0-12 h area under the curve (AUC) of triglyceride levels by 56%. Atorvastatin also caused decreases, but to a lesser extent. Pitavastatin, and atorvastatin to a lesser extent, reduced the activity of the intestinal microsomal triglyceride transfer protein (MTP) at 6 h. These results suggested that a single dose of pitavastatin lowered postprandial triglyceride levels in rats by decreasing chylomicron-triglyceride secretion, probably through a reduction of intestinal MTP activity and triglyceride droplet formation in the endoplasmic reticulum.

Enhanced and prolonged postprandial lipaemia is implicated in coronary and carotid artery disease. This study assessed the effects of atorvastatin, a 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor, on postprandial plasma concentrations of triglyceride-rich lipoproteins (TRLs). Sixteen middle-aged men with combined hyperlipidaemia (baseline low density lipoprotein (LDL) cholesterol and plasma triglyceride concentrations (median (interquartile range) of 4.54 (4.17-5.26)) and 2.66 (2.04-3.20) mmol/l, respectively) and previous myocardial infarction were randomised to atorvastatin 40 mg or placebo once daily for 8 weeks in a double-blind, cross-over design. The apolipoprotein (apo) B-48 and B-100 contents were determined in subfractions of TRLs as a measure of chylomicron remnant and very low density lipoprotein (VLDL) particle concentrations (expressed as mg apo B-48 or apo B-100 per litre of plasma), in the fasting state and after intake of a mixed meal. Atorvastatin treatment reduced significantly the fasting plasma concentrations of VLDL cholesterol, LDL cholesterol and VLDL triglycerides (median% change) by 29, 44 and 27%, respectively, and increased high density lipoprotein (HDL) cholesterol by 19%, compared with baseline. The postprandial plasma concentrations of large (Svedberg flotation rate (Sf) 60-400) and small (Sf 20-60) VLDLs and chylomicron remnants were almost halved compared with baseline (mean 0-6 h plasma concentrations were reduced by 48% for Sf 60-400 apo B-100, by 46% for Sf 60-400 apo B-48, by 46% for Sf 20-60 apo B-100 and by 27% for Sf 20-60 apo B-48), and the postprandial triglyceridaemia was reduced by 23% during active treatment. In conclusion, atorvastatin 40 mg once daily causes profound reductions of postprandial plasma concentrations of all TRLs in combined hyperlipidaemic patients with premature coronary artery disease.

Elevated plasma concentration of chylomicron remnants may be causally related to atherosclerosis in obesity. We examined the effect of atorvastatin on chylomicron remnant metabolism in 25 obese men with dyslipidaemia. A remnant-like emulsion labeled with cholesteryl [(13)C]oleate was injected intravenously into patients; the fractional catabolic rate (FCR) of the remnant-like emulsion was determined by measurement of (13)CO(2) in the breath and analyzed using compartmental modelling. Compared with placebo, atorvastatin significantly decreased the plasma concentrations of total cholesterol, triglycerides, LDL cholesterol, apolipoprotein B (apoB), and lathosterol (P < 0.001). ApoB-48 and remnant-like particle-cholesterol (RLP-C) both decreased significantly by 23% (P = 0.002) and 33% (P = 0.045), respectively. The FCR of the remnant-like emulsion increased significantly from 0.054 +/- 0.008 to 0.090 +/- 0.010 pools/h (P = 0.002). The decrease in RLP-C was associated with the decrease in plasma triglycerides (r = 0.750, P = 0.003). Furthermore, the change in FCR of remnant-like emulsions was inversely associated with the change in LDL-C (r = -0.575, P = 0.040), suggesting removal of LDL and chylomicron remnants by similar hepatic receptor pathways. We conclude that in obese subjects, inhibition of cholesterol synthesis with atorvastatin decreases the plasma concentrations of both LDL-C and triglyceride-rich remnants and that this may be partially due to an enhancement in hepatic clearance of these lipoproteins.

Background: Hypertriglyceridemia over 1,000 mg/dl can provoke acute pancreatitis and its persistence can worsen the clinical outcome. On the contrary, a rapid decrease in triglyceride level is beneficial. Plasmapheresis has been performed in some patients to remove chylomicrons from the circulation, while heparin and/or insulin have been administered in some other cases to rapidly reduce blood triglycerides. Heparin and insulin stimulate lipoprotein-lipase activity and accelerate chylomicron degradation., Aim: To report five patients with acute pancreatitis treated with heparin and insulin., Patients and Methods: Five patients (4 females and 1 male) seen in the last two years, who suffered acute pancreatitis induced by hypertriglyceridemia are reported. Initial blood triglyceride levels were above 1,000 mg/dl (range 1,590-8,690 mg/dl). Besides the usual treatment of acute pancreatitis, heparin and/or insulin were administered intravenously in continuous infusion. Heparin dose was guided by usual parameters of blood coagulation, and insulin dose, by serial determinations of blood glucose. Pancreatic necrosis was demonstrated in 4 patients., Results: Serum triglyceride levels decreased to < 500 mg/dl within 3 days in all cases. No complication of treatment was observed and all patients survived. Early and late complications of pancreatitis occurred in one patient., Conclusion: Administration of heparin and/or insulin is an efficient alternative to reduce triglyceride levels in patients with acute pancreatitis and hypertriglyceridemia.

The effects of positional distribution of triacylglycerol (TAG) fatty acids to TAG structures in chylomicrons and VLDL, and to postprandial lipemia, were studied in 10 healthy premenopausal women using a 6-h oral fat load test and a randomized, double-blind cross-over design. Molecular level information of TAG regioisomerism was obtained with a tandem mass spectrometric method. The positional distribution of fatty acids in chylomicron TAGs was similar to the respective dietary fat; 79% of the analyzed regioisomers in palm oil and 84% of the analyzed regioisomers in transesterified oil were found in chylomicron TAGs 3 h after the oral fat loads. VLDL TAGs were equal after the two fat loads in all but one regioisomer. Similarities in the fatty acid compositions of chylomicron TAGs suggest that palmitic acid was absorbed equally from both test fats. The proportion of palmitoleic acid in the chylomicrons was increased. Fat with palmitic acid predominantly in the sn-1 and sn-3 positions caused a larger incremental area of total TAGs in plasma and reduced plasma insulin values at the beginning of the postprandial response (0-90 min) compared with fat with palmitic acid randomly distributed. The relationship between TAG molecular structures in dietary fats and in lipoproteins provides new means for understanding the effects of fatty acid positional distribution on human lipid metabolism.

Anti-atherosclerotic effects of human macrophage colony-stimulating factor were investigated using rabbits fed a high cholesterol diet. Rabbits fed a diet containing 2% cholesterol for 59 days developed hyperlipidemia and atheromatous aortic plaques. They were then administered 80 microg/kg/day of either macrophage colony-stimulating factor or human serum albumin, as a control, for the next 12 weeks. Compared with the control group, rabbits treated with macrophage colony-stimulating factor had significantly fewer plaques on the inner surface of the thoracic and abdominal aortae, and half the sectional area of thickened intima in the aortic arch, as well as in the thoracic and abdominal aortae. Macrophage colony-stimulating factor also decreased the cholesterol content of the atherosclerotic lesions. Serobiochemical analyses revealed that macrophage colony-stimulating factor increased the levels of high density lipoprotein-cholesterol significantly, without influencing other lipid parameters such as the level of low density lipoproteins. The effects of macrophage colony-stimulating factor were evident until the fourth week of drug injection, at which time anti-human macrophage colony-stimulating factor antibodies were clearly induced in the serum. These results indicate that exogenously administered macrophage colony-stimulating factor suppresses atherosclerotic lesions induced by a high cholesterol diet by activating lipid metabolism in vivo.

Slow chylomicron intravascular catabolism has been associated with coronary artery disease and screening for drugs that can speed-up this process can be important. In this study, the effects of etofibrate upon chylomicron metabolism was tested by determination of the plasma kinetics of a chylomicron-like emulsion model in 12 patients with coronary artery disease, aged 59+/-11 years, (total cholesterol: 240+/-41 mg/dl; triglycerides: 188+/-42 mg/dl) submitted to a randomized, crossover, double-blind, placebo-controlled study with administration of 1 g per day etofibrate or placebo for 1-month. A 1-month washout period was inserted between the treatment periods. Patients were intravenously injected a chylomicron-like emulsion doubly labeled with 14C-cholesteryl oleate and 3H-triolein at baseline and after treatments. After etofibrate treatment, there was decrease of total cholesterol and triglyceride plasma levels and a trend to increase high-density lipoprotein cholesterol plasma levels. Etofibrate elicited 62% enhancement of post-heparin lipolytic activity and 100% increase of 3H-triglyceride fractional clearance rate compared with placebo treatment. 14C-cholesterol ester fractional clearance rate was 260% greater after etofibrate than after placebo. Therefore, a potent effect of etofibrate on both chylomicron lipolysis and remnant removal was achieved, indicating that this drug can be used to improve this metabolism in future prospective studies.

Objective: The effects of dietary diacylglycerol (DG) on postprandial lipemia in healthy humans were investigated., Methods: Forty normolipidemic male volunteers ingested fat emulsions containing either DG oil or triacylglycerol (TG) oil, at different doses: 10 g (n = 13), 20 g (n = 10) and 44 g (n = 17). Two test emulsions were given at seven-days intervals in random order. Fatty acid compositions of the test oils had been adjusted to be equal. Fasting and postprandial serum lipid concentrations in each group and plasma lipoprotein lipids in the 20 g-fat ingestion group were measured during the postprandial intervals., Results: When DG emulsion was ingested, serum TG concentrations were significantly lower (p < 0.05) in the late postprandial phase, i.e., 4 hours, 6 hours as compared to the TG emulsion. The magnitude of postprandial lipemia (the area bounded by the curve above the fasting concentration) after ingestion of 44 g-DG emulsion was significantly less than that of 44 g-TG emulsion (6.54 +/- 5.12 and 8.45 +/- 7.54 mmol x h/L, mean +/- SD, respectively). Chylomicron TG, cholesterol, and phospholipid concentrations at 4 hours after ingestion of DG emulsion were significantly lower (p < 0.05) than those after the ingestion of TG emulsion at the same time point. No marked differences were observed for VLDL, LDL and HDL lipids between the test emulsions., Conclusion: In the usual range of fat intake (10-44 g), postprandial response after ingestion of DG emulsion was significantly less than that after ingestion of TG emulsion in healthy human subjects.

The speed of the plasma removal of chylomicrons, the lipoproteins that carry dietary lipids absorbed in the intestine, may influence atherogenesis. Thus, the effects of a 30-day pravastatin or placebo treatment on the plasma kinetics of chylomicron-like emulsions were evaluated in 25 patients with coronary artery disease who were not hypertriglyceridemic in a randomized, single-blinded study. Eleven patients (53 +/- 4 years, 10 men) received pravastatin 40 mg/day and 14 received placebo (52 +/- 3 years, 13 men). Emulsions labeled with triolein ((3)H-TO) and cholesteryl oleate ((14)C-CO) to assess lipolysis and clearance of chylomicron and remnants, respectively, were injected intravenously in a bolus after a 12-hour fast. Blood samples were collected during 60 minutes to determine radio isotope decaying curves and fractional catabolic rates. Subjects were studied at baseline and after the treatment period. Compared with placebo (data expressed as mean +/- SEM), pravastatin treatment increased the (14)C-CO fractional catabolic rates (70 +/- 45% vs 18 +/- 10%, p = 0.01), reduced total cholesterol (-21 +/- 3% vs -3 +/- 2% p = 0.0001), low-density lipoprotein (LDL) cholesterol (-25 +/- 5% vs 4 +/- 6%, p = 0.0001), and apolipoprotein B levels (-22 +/- 3% vs -7 +/- 3% p = 0.01). (3)H-TO fractional catabolic rates, plasma triglycerides, very-low-density lipoprotein (VLDL) cholesterol and high-density lipoprotein (HDL) cholesterol variations did not differ between the groups. The fractional catabolic rate of (14)C-CO was inversely correlated with plasma apolipoprotein B levels (r = -0.7, p = 0.04). This suggests that besides reducing LDL cholesterol, pravastatin also increases chylomicron remnant clearance, with possible antiatherogenic implications.

1. Amylin is a pancreatic peptide that has been shown to be able to induce a state of peripheral insulin resistance. Hyperamylinaemia, which occurs in type 2 diabetes, may be central to a number of metabolic abnormalities present in the diabetic state. Because lipoprotein metabolism is often disturbed in diabetes, we investigated whether amylin was a regulating factor of lipoprotein metabolism in rats; specifically, whether exogenous amylin influences production and clearance of triglyceride (TG)-rich lipoproteins. 2. When amylin was given acutely to rats or by way of infusion, total plasma TG was significantly elevated. Acute doses of amylin decreased fractional clearance rates of TG-rich lipoproteins by 45%. Hydrolysis of lipoproteins by endothelial lipases was not decreased; rather, amylin appeared to reduce hepatic uptake of TG-rich lipoproteins, following conversion to the remnant form. Consistent with the kinetic data in vivo, cell culture studies found that amylin reduced the high-affinity uptake of remnant lipoproteins, probably by inhibiting low-density lipoprotein receptor expression. 3. We have found that amylin can influence the kinetics of TG-rich lipoproteins in vivo and in vitro. Amylin can reduce chylomicron uptake, most probably by regulating lipoprotein receptors either directly, or via modulation of insulin activity. Increased levels of amylin in type 2 diabetes may contribute to the raised concentration of TG-rich remnant lipoproteins present in this disease.

Apolipoprotein (apo) A-IV is a glycoprotein synthesized by the human intestine. In rodents, both the small intestine and the liver secrete apo A-IV; the small intestine, however, is by far the major organ responsible for the circulating apo A-IV. Intestinal apo A-IV synthesis is markedly stimulated by fat absorption and appears not to be mediated by the uptake or reesterification of fatty acids to form triglycerides. Rather, it is the formation of chylomicrons that acts as a signal for the induction of intestinal apo A-IV synthesis. Intestinal apo A-IV synthesis is also enhanced by a factor from the ileum and that factor is probably peptide tyrosine-tyrosine (PYY). The inhibition of food intake by apo A-IV is probably mediated centrally. The stimulation of intestinal synthesis and secretion of apo A-IV by lipid absorption are rapid; thus, apo A-IV likely plays a role in the short-term regulation of food intake. Other evidence suggests that apo A-IV may also be involved in the long-term regulation of food intake and body weight. Chronic ingestion of a high fat diet blunts the intestinal apo A-IV response to lipid feeding and may explain why the chronic ingestion of a high fat diet predisposes both animals and humans to obesity.

The activation of factors XII (FXII) and VII (FVII) has been shown to occur on the surface of lipoproteins in the presence of lipoprotein lipase and may be modulated by beta2glycoprotein-1 (beta2GP1). In the postprandial state FVII is activated without apparent activation of FXII in plasma. We investigated whether beta2GP1, FXIIa and FVIIa are associated with triglyceride-rich lipoproteins in the fasting and postprandial state. Six normal subjects were studied while fasting and 1, 2 and 4 h after ingestion of 100 g fat. We confirmed that plasma FVIIa activity, but not FXIIa antigen, was increased in the postprandial period. FXIIa, FVIIa and beta2GP1 were associated with chylomicra-rich lipoproteins, and lipase or Triton X-100 treatment caused an increase in FXIIa in plasma and chylomicra without an increase in FVIIa. This suggests that FXIIa may be formed in the postprandial period, but its antigenic determinants are masked by the association with lipoprotein particles, although it could still express proteolytic activity. Alternatively a FXII-independent mechanism or surface other than triglyceride-rich lipoproteins may be responsible for FVII activation in the postprandial state.

The effect of a novel inhibitor of acylcoenzyme A:cholesterol acyltransferase (EC 2.3.1.26, ACAT), EAB309 (EAB) on plasma lipid metabolism was studied in cholesterol-fed rats. Orally administered EAB was not detected in the portal vein or the liver but distributed exclusively in the intestine, suggesting that this agent selectively inhibits intestinal ACAT. The rats were fed with either a cholesterol-diet or a cholesterol-diet containing 0.005% EAB (w/w) ad. libium for three weeks. ACAT activity in intestinal microsomes was significantly inhibited in EAB-treated rats. Hepatic ACAT activity was also decreased in EAB-treated rats, however, this was attenuated by the addition of excess cholesterol to the liver microsome, indicating that substrate availability is tightly associated with this enzyme's activity and the inhibition of hepatic ACAT by EAB is not direct. Incorporation of [3H]-cholesterol to cholesteryl ester (CE) in mesenteric lymph were markedly suppressed by EAB treatment. Chylomicrons (CMs) were doubly labeled with [3H]-vitamin A and [14C]-triglyceride (TG) in EAB-treated or non-treated rats and injected into normal chow-fed rats. The CMs from EAB-treated rats were cleared faster from the plasma and taken up more by the liver compared with the CMs from non-treated rats. The content of CE in newly secreted VLDL was remarkably decreased by EAB treatment without affecting TG output. These results demonstrate that EAB, a novel inhibitor of intestinal ACAT, significantly suppresses both intestinal and hepatic CE output and stimulates CM removal. This suggests that the inhibition of intestinal ACAT can subsequently suppress hepatic ACAT by decreased CE delivery from the intestine to the liver.

The effect of the apolipoprotein C-II/C-III1 ratio on the capacity of purified bovine milk lipoprotein lipase to hydrolyse triglycerides was measured in a controlled model of pyrene-labeled nonanoyltriglycerides (1-2 ditetradecyl 3-pyrene nonanoyl glyceride) monolayer vesicles. Monolayer was composed of triglycerides, a non-hydrolysable phospholipid ether and cholesterol, a model system where the quality of the interface can be controlled. LPL released fatty acids from pyrene-triglycerides which were transferred from the lipoprotein structure to albumin. This transfer induces a decrease in the excimer production and in the excimer fluorescence intensity. Apolipoprotein C-II and C-III0 and C-III1 were purified from apolipoprotein VLDL. The 2 fragments, C-III1 A (peptide 1-40) and C-III1 B (peptide 41-79), were obtained after thrombin cleavage. Apolipoproteins C-III0 and C-III1 had a similar inhibitory effect on LPL. Inhibition with apo C-III0 or apo C-III1 was 85% of full LPL activity without inhibitor: Apo C-III1 B inhibited 62% of basal activity. It was 27% less effective than apo C-III1. Fragment C-III1 A did not inhibit LPL. The effect of change in both apo C-II (0-0.6 microM) and apo C-III1 (0-1.0 microM) on triglyceride hydrolysis shows the importance of the apo C-II/C-III1 ratio for the release of free fatty acids from triglycerides by LPL. The activating effect of apo C-II in the absence of the apo C-III inhibitor was maximal at 0.06 microM. No further activation was obtained between 0.06 and 0.30 microM. Higher concentrations decreased LPL activity. Apo C-III1 (0.1 microM) decreased the maximum activation by apo C-II from 0.0196 to 0.063 nmol/min/nmol LPL. Higher concentrations of apo C-III1 (0.1-0.5 microM) required higher apo C-II concentrations (0.30 microM instead of 0.06 microM) for maximal activation than when apo C-III1 was absent. The activity of the enzyme without apo C-II was decreased by 65% by 0.12 microM apo C-III1. Increasing the apo C-II/apo C-III1 ratio from 0.1 to 1, increased the activation of the enzyme by a given apo C-II concentration. Moreover, for a given apo C-II/C-III1 ratio, the LPL activation increased with the apo C-II concentration (between 0 and 0.010 microM), until a plateau was reached. This is important, as the change in the C-II/C-III1 ratio is not the only factor affecting LPL activity, and inhibition by apo C-III1 also depends on the overall quantity of apolipoproteins. Extrapolation of these results suggests that hyperlipoproteinemia seems to be more likely due to overproduction of VLDL, than to a decrease in lipoprotein lipase activity.

On intravenous injection to rats, decasaccharides gave rise to a short-lived peak of lipoprotein lipase (LPL) activity, whereas octa- and hexasaccharides caused only marginal increases. In isolated hearts perfused by a single pass, decasaccharides released LPL more efficiently than conventional heparin on a mass basis. Octa- and hexasaccharides were much less efficient. Similar results were obtained for hepatic lipase, which was studied both in vivo and by liver perfusion. In the intact rat, the heparin fragments themselves disappeared rapidly from the circulating blood. The decay of hepatic lipase activity after the early peak roughly paralleled the decay of decasaccharide concentration, but for LPL the decay was faster, presumably because the liver extracted this lipase from plasma. To assess the lipase activities remaining in contact with blood a large dose of conventional heparin was injected at a series of times after the decasaccharides. LPL was decreased by 40% after 1 h. At that time, the LPL activity that could be released from isolated hearts by single-pass perfusion with heparin for 2 min ("functional LPL') was decreased by 75%. Chylomicrons labelled in vivo with [14C]oleic acid (primarily in triacylglycerols, providing a tracer for lipolysis) and [3H]retinol (primarily in ester form, providing a tracer for the particles) were injected intravenously to explore the effects of the LPL depletion on lipoprotein metabolism. Triacylglycerol lipolysis and particle clearance was markedly delayed from 30 min to 2 h after injection of decasaccharides. After 1 h the fractional catabolic rate was only one-third of the control value and the catabolism of chylomicron triacylglycerols by perfused hearts was delayed to a similar extent. Thus injection of decasaccharides leads to accelerated turnover of LPL with loss of functional LPL from extrahepatic tissues. This in turn leads to a period of delayed lipolysis and removal of chylomicron particles.

The ability of chyle chylomicrons to bind prothrombin has been studied. Rat chyle chylomicrons were incubated with human 125I-prothrombin and binding was examined by separating the chylomicrons from free 125-I-prothrombin by density-gradient ultracentrifugation, and by gel filtration on Sepharose CL-2B. A significant binding of prothrombin to chyle chylomicrons occurred. The complex formation was calcium dependent, and decreased markedly when the temperature was lowered from 37 degrees C to 20 degrees C and when PH was raised above 8. The time course for the binding at 37 degrees C in presence of 2 mmol/L CaCl2 exhibited an initial lag phase at about 10 minutes. Thereafter most of the binding occurred within 30 minutes. Bound prothrombin could not be removed from chyle chylomicrons by treatment with EDTA, suggesting that this binding is not a simple Ca2+ dependent association between prothrombin and chyle chylomicrons. Inclusion of 1% purified human serum albumin caused a 50% decrease in binding, half of which was reversed by increasing the Ca2+ ion concentration. Addition of pancreatic phospholipase A2 (PLA2) in doses sufficient to hydrolyze more than 95% of the phosphatidylethanolamine (PE) and 37% of the phosphatidylcholine (PC) decreased the binding by 50%. Doses of PLA2 that hydrolyze more than 95% of the phosphatidylethanolamine (PE) and 37% of the phosphatidylcholine (PC) decreased the binding by 50%. Doses of PLA2 that hydrolyzed 60-80% of (PE and 4-10% of the PC decreased the binding by only 7-15%. It is suggested that the binding of prothrombin to chyle chylomicrons is in part mediated by negatively charged phospholipids of the chylomicron surface, although a specific role of the PE could not be demonstrated.

The metabolism of the postprandial intestinal-derived lipoproteins, chylomicron and chylomicron remnants, is not known in patients with essential hypertension. After a fat meal, using the vitamin A test as a marker, retinyl palmitate was measured in the total plasma, chylomicron, and chylomicron remnant fractions in 14 untreated nondiabetic essential hypertensive patients with normal fasting lipids and lipoproteins. The vitamin A fat loading test was repeated in eight hypertensive patients after 3 months of captopril therapy. Fifteen matched normotensive subjects were used as controls. The untreated essential hypertensive patients had significantly higher chylomicron fraction concentration curves (AUC 17,469 +/- 2553 micrograms/L/h) P < .001 compared with the control group (AUC 13,208 +/- 1245 micrograms/L/h), by two-way analysis of variance with repeated measurements. After 3 months of captopril therapy, the chylomicron fraction (AUC 9701 +/- 1566 micrograms/L/h), and chylomicron remnants fraction (AUC 3487 +/- 580 micrograms/L/h) were much lower (P < .001) than before captopril therapy. Oral glucose tolerance tests were borderline in five of the eight hypertensives before captopril treatment but returned to normal after 3 months of therapy. In summary, postprandial intestinal-derived lipoprotein metabolism is altered in essential hypertensive patients. Captopril therapy caused significant improvement in the postprandial chylomicron metabolism.

In 11 patients with IIB hyperlipoproteinemia we studied fasting lipids, lipoproteins, lipoprotein-modifying enzymes, and postprandial lipid metabolism after a standardized oral fat load supplemented with vitamin A before and 12 weeks after treatment with fenofibrate, a third-generation fibric acid derivative. Fasting plasma cholesterol, triglycerides, low-density lipoprotein cholesterol decreased significantly (P < 0.05, P < 0.01, P < 0.01), high-density lipoprotein subfraction 3 cholesterol increased significantly (P < 0.05), and high-density lipoprotein subfraction 2 cholesterol remained unchanged. Postprandial lipemia, i.e., the integrated postprandial triglyceride concentrations corrected for the fasting triglyceride level, and postprandial chylomicron concentrations, as assessed by biosynthetic labeling of chylomicrons with retinyl palmitate, decreased by 40.6% and 60.1% (P < 0.05; P < 0.05), respectively. The activity of lipoprotein lipase (LPL) increased by 33.6% (P < 0.05); the increase in LPL during fenofibrate treatment was positively correlated with the increase in high-density lipoprotein cholesterol (r = 0.84; P < 0.005). Hepatic lipase and cholesteryl ester transfer protein mass and activity remained unchanged. We conclude that lipid-lowering therapy with fenofibrate ameliorates fasting and, more profoundly, postprandial lipoprotein transport in hypertriglyceridemia by curbing postprandial triglyceride and chylomicron accumulation, at least in part, through an increase in LPL activity.

Heparin is a well-known, widely used anticoagulant drug. In addition to its anticoagulant properties, however, it also has a marked influence on fat metabolism. Postprandial lipoproteins may contribute significantly to the development of coronary heart disease. Therefore, it is important to evaluate the effects of heparin on these lipoproteins. The effect of continuous heparin administration on postprandial lipoprotein metabolism was studied in 11 patients with thromboembolic disease. Results were compared with those in a group of six patients given no heparin. Two vitamin A-fat loading tests were done: the first, 5 days before heparin was started and the second, on the fourth day of continuous heparin drip of 1000 U/h, maintaining PTT levels at twice the baseline. To study the effect of acute heparin, an additional fat loading test was done in five patients on the first day of heparin treatment. Vitamin A, specifically labels intestinally derived lipoproteins with retinyl palmitate (RP). The concentrations of chylomicron (Sf > 1000)- and nonchylomicron (Sf < 100)-retinyl palmitate were measured for 10 h postprandially. Four days of continuous intravenous heparin administration increased the area below the chylomicron RP curve from 11091 +/- 4393 to 17684 +/- 5949 micrograms/l.h (P < 0.003). When measured on the first day of heparin treatment in five patients, the area of the chylomicron fraction was reduced from 16678 +/- 6895 to 10474 +/- 3893 micrograms/l.h (P < 0.05). Postheparin lipoprotein lipase activity was significantly lower on the fourth day of heparin, administration than before treatment: 1.8 +/- 1.1 vs. 4.1 +/- 1.3 mumol/FFA per ml per h, respectively (P < 0.0005). In the six control patients with thromboembolic disease in whom heparin therapy was not indicated, no changes in postprandial lipoprotein levels or in lipolytic activity during hospitalization were found. The study demonstrates that 4 days of heparin administration causes an accumulation of chylomicrons in the circulation, most probably as a result of a marked decrease in serum lipolytic activity.

The contribution of the low density lipoprotein (LDL) receptor to the removal of chylomicron remnants was determined in vitro and in vivo by using interventions that up- or down-regulate the LDL receptor but not the LDL receptor-related protein (LRP). In vitro, chylomicron remnants and beta-very low density lipoprotein (VLDL) bind to the LDL receptor on endosomal membranes; their binding can be competed by LDL and beta-VLDL and the binding capacity is greatly augmented in membranes from estradiol-treated rats. Likewise, estradiol treatment almost doubled the removal of chylomicron remnants during a single pass through perfused rat livers. However, in vivo the removal of chylomicron remnants and beta-VLDL was very rapid even in untreated rats so that the effect of the stimulation by estradiol was barely detectable when trace amounts of lipoproteins were injected. Yet, when saturating doses of either lipoprotein were injected, the effect of estradiol treatment on the removal of chylomicron remnants and beta-VLDL was readily disclosed. In rats fed a diet containing lard, cholesterol, and bile acids, removal of chylomicron remnants or beta-VLDL was significantly retarded. Likewise, perfused livers from diet-fed rats removed only a mean of 16% of chylomicron remnants during a single passage as compared to 29% in livers from control animals. Also, when large doses of beta-VLDL had been infused into rats for 4 h, in subsequent perfusions of the livers the removal of chylomicron remnants was decreased to 11%. From these results it is concluded that the LDL receptor mediates the hepatic removal of a major fraction of chylomicron remnants and beta-VLDL.