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Lipids are carried in plasma by lipoproteins, which have an external hydrophilic region containing proteins, phospholipids, and nonsterified cholesterol, and an internal hydrophobic core, containing triacylglycerols (TAGs) and cholesterol esters. Based on their density, different lipoprotein groups can be distinguished in blood. (1) Chylomicrons, which contain mainly TAGs synthesized in the intestinal mucosa from fatty acids (FAs) and monoacylglycerols from the diet. A lipoprotein lipase (LpL) in capillary endothelial cells hydrolyze TAG. The freed FA enter the cells, where they are oxidized (muscle) or stored (adipose tissue). The chylomicron remnants, reduced to its protein component (apolipoprotein B-48, or apo-48) bind to liver receptors and are internalized and cleared from circulation. (2) Very low density lipoproteins (VLDLs) are synthesized in hepatocytes. They are rich in TAG and contains protein B-100. In the capillaries, TAGs are hydrolyzed by LpL and they exchange TAG for cholesterol esters from high-density lipoproteins (HDLs). VLDLs are converted to intermediate density lipoproteins (IDLs). TAGs are hydrolyzed by liver lipase, apo E returns to HDL. Hepatocytes remove more than 50% of IDL from the circulation. The rest are the low density density lipoproteins (LDLs), rich in Chol. All cells have receptors that bind B-100 and internalize LDL composed of apos B-100 and E, Chol, mostly CholE, and low proportion of TAG. (3) HDLs are synthesized in the liver and intestine and contain apo A, C, and E, lecithin-cholesterol acyltransferase (LCAT) and phospholipids. In blood, HDL donates apo C and E to VLDL and chylomicrons. In extrahepatic tissues, HDL binds to the capillary endothelium and receives cholesterol from the cells, which is esterified by LCAT and transferred to VLDL and chylomicrons (reverse cholesterol transport). Remnants of these particles are taken up by the liver. Fat metabolism starts with the hydrolysis of TAG into glycerol (Glyc) and FA, by the action of intracellular lipase and LpL. Glycerol is converted into glyceraldehyde-3-P that can be directed to glycolysis or gluconeogenesis. FAs are catabolyzed in mitochondria by β-oxidation. β-oxidation follows a series of oxidative steps and the release of acyl-CoA. Ketogenesis produces ketone bodies from acetoacetate, 3-OH butyrate, and acetone. Muscle, heart, and other tissues are capable of activating acetoacetate and can use ketone bodies as fuel; the liver cannot. FA biosynthesis takes place from acetyl-CoA (generated mainly by degradation of glucose and amino acid carbon chains) by the FA synthase multienzyme system. Essential polyunsaturated FA cannot be synthesized, they must be obtained from the diet. Eicosanoids (prostaglandins, thromboxanes, and leukotrienes) are synthesized from arachidonic acid and catalyzed by cyclo-oxigenase. Biosynthesis of triacylglycerols (TAG) starts with the activation of glycerol to glycerol-3-P and FAs to acyl-CoA. Glycerol-3-phosphate is esterified at carbons 1 and 2 by two acyl groups transferred from acyl-CoA to form 1,2-diacylglycerolphosphate, also called phosphatidic acid. A new acyl-CoA molecule transfers another acyl to 1,2-diacylglycerol and triacylglycerol is produced. Phospholipids in higher animals are synthesized from phosphatidic acid. Cholesterol synthesis comprises three stages: acetate to mevalonate, mevalonate to squalene, and squalene to Chol. It is removed from plasma by LDL receptors in all cells. Bile acids and steroid hormones are synthesized from cholesterol.

Background We hypothesized that adolescents with obesity have higher remnant B48 concentrations associated with lipoprotein lipase dysregulation. Methods Cross-sectional study of 32 adolescents with obesity and 27 control subjects. Results As compared to lean controls, obese participants showed 35% higher concentrations of apoB48: 3.60 (2.93–4.30) vs 2.65 (1.64–3.68) ng/ml; 28% of apoC-III: (72.7 (58.6–89.7) vs 56.9 (44.8–79.8 ug/ml and 17% ANGPTL 3: (72.2 ± 20.2 vs 61.2 ± 19.2 ng/ml). This was accompanied by a 33% reduction in LPL: 13.1 ± 5.1 vs 18.9 ± 4.7 ng/ml. Obese participants had 25% lower adiponectin 2.9 (1.9–3.8) vs 4.4 (3.2.-5.2) μg/ml; 260% higher leptin 25.7 (11.2–44.8) vs 9.3 (2.8–20.7) ng/ml c and 83% higher Il-6: 2.2 (1.3–5.4) vs 1.2 (0.8–1.4) pg/ml. ApoC-III and ANGPTL3 correlated positively with VAI; ANGPTL3 negatively with HDL-C; LDL size and VLDL-C. ApoB48 correlated negatively with LDL-C. Conclusions Adolescents with obesity show higher ANGPTL3 compounded with increased apoC-III associated with increased CR and lower LPL mass. This is associated with inflammation and visceral fat. The significance of these findings resides in that they shed light on a mechanism for TRL dyslipidemia in adolescents: increased LPL inhibition impairs VLDL and chylomicron catabolism leading to atherogenic remnants.

Elevated triglycerides are associated with an increased risk of cardiovascular disease (CVD). Therefore, it is very important to understand the metabolism of triglyceride-rich lipoproteins (TRLs) and their atherogenic role in animal models. Using low-density lipoprotein receptor knockout (LDLR−/−) Syrian golden hamsters, this study showed that unlike LDLR−/− mice, when LDLR−/− hamsters were fed a high cholesterol high-fat diet (HFD), they had very high plasma levels of triglycerides and cholesterol. We found that LDLR−/− hamsters exhibited increased serum TRLs and the ApoB100 and 48 in these particles after being fed with HFD. Treatment with ezetimibe for 2 weeks decreased these large particles but not the LDL. In addition, ezetimibe simultaneously reduced ApoB48 and ApoE in plasma and TRLs. The expression of LRP1 did not change in the liver. These findings suggested that the significantly reduced large particles were mainly chylomicron remnants, and further, the remnants were mainly cleared by the LDL receptor in hamsters. After 40 days on an HFD, LDLR−/− hamsters had accelerated aortic atherosclerosis, accompanied by severe fatty liver, and ezetimibe treatment reduced the consequences of hyperlipidemia. Compared with the serum from LDLR−/− hamsters, that from ezetimibe-treated LDLR−/− hamsters decreased the expression of vascular adhesion factors in vascular endothelial cells and lipid uptake by macrophages. Our results suggested that in the LDLR−/− hamster model, intestinally-derived lipoprotein remnants are highly atherogenic and the inflammatory response of the endothelium and foam cells from macrophages triggered atherosclerosis. The LDL receptor might be very important for chylomicrons remnant clearance in the Syrian golden hamster, and this may not be compensated by another pathway. We suggest that the LDLR−/− hamster is a good model for the study of TRLs-related diseases as it mimics more complex hyperlipidemia.

This article reviews the literature on capillarization of hepatic sinusoids since its discovery in 1963. Liver sinusoidal endothelial cells are uniquely fenestrated and lack an underlying basement membrane. In chronic liver disease, the sinusoids capillarize and transform into systemic capillaries, a process termed capillarization of sinusoids. The histopathology is marked by defenestration, basement membrane formation, and space of Disse fibrogenesis. Capillarized sinusoids compromise the bidirectional exchange of materials between sinusoids and hepatocytes, leading to hepatocellular dysfunction. Sinusoidal capillarization was first described in active cirrhosis of alcoholics in 1963. Since then, it has been found in early and progressive stages of alcoholic hepatic fibrosis before the onset of cirrhosis. The sinusoidal structure is not altered in alcoholic steatosis without fibrosis. Defenestration impairs the ability of the endothelium to filter chylomicron remnants from sinusoids into the Disse's space, contributing to alcohol-induced postprandial hyperlipidemia and possibly atherosclerosis. Ethanol also modulates the fenestration dynamics in animals. In baboons, chronic alcohol consumption diminishes endothelial porosity in concomitance with hepatic fibrogenesis and in rats defenestrates the endothelium in the absence of fibrosis, and sometimes capillarizes the sinusoids. Acute ethanol ingestion enlarges fenestrations in rats and contracts fenestrations in rabbits. In sinusoidal endothelial cell culture, ethanol elicits fenestration dilation, which is likely related to its interaction with fenestration-associated cytoskeleton. Ethanol potentiates sinusoidal injury caused by cocaine, acetaminophen or lipopolysaccharide in mice and rats. Understanding ethanol's mechanisms on pathogenesis of sinusoidal capillarization and fenestration dynamics will lead to development of methods to prevent risks for atherosclerosis in alcoholism.

Objective: We tested the hypothesis that enlarged, dysfunctional HDL (high-density lipoprotein) particles contribute to the augmented atherosclerosis susceptibility associated with SR-BI (scavenger receptor BI) deficiency in mice. Approach and Results: We eliminated the ability of HDL particles to fully mature by targeting PLTP (phospholipid transfer protein) functionality. Particle size of the HDL population was almost fully normalized in male and female SR-BI×PLTP double knockout mice. In contrast, the plasma unesterified cholesterol to cholesteryl ester ratio remained elevated. The PLTP deficiency-induced reduction in HDL size in SR-BI knockout mice resulted in a normalized aortic tissue oxidative stress status on Western-type diet. Atherosclerosis susceptibility was—however—only partially reversed in double knockout mice, which can likely be attributed to the fact that they developed a metabolic syndrome-like phenotype characterized by obesity, hypertriglyceridemia, and a reduced glucose tolerance. Mechanistic studies in chow diet–fed mice revealed that the diminished glucose tolerance was probably secondary to the exaggerated postprandial triglyceride response. The absence of PLTP did not affect LPL (lipoprotein lipase)-mediated triglyceride lipolysis but rather modified the ability of VLDL (very low-density lipoprotein)/chylomicron remnants to be cleared from the circulation by the liver through receptors other than SR-BI. As a result, livers of double knockout mice only cleared 26% of the fractional dose of [ 14 C]cholesteryl oleate after intravenous VLDL-like particle injection. Conclusions: We have shown that disruption of PLTP-mediated HDL maturation reduces SR-BI deficiency-driven atherosclerosis susceptibility in mice despite the induction of proatherogenic metabolic complications in the double knockout mice.

Postprandial lipemia is an independent risk factor for CVD, due to effects on lipoprotein remodelling, oxidative stress, inflammation, haemostasis and endothelial dysfunction. However, it is unknown whether the total, peak or duration of the lipemic response determines risk. The PREDICT I study is the largest study to date to measure postprandial lipemic responses and intermediary acutely changing cardiometabolic risk factors at multiple time points using a standardized test meal model.A multi-center postprandial study of 1,000 individuals from the UK (unrelated, identical and non-identical twins) and 100 unrelated individuals from the US, assessed postprandial (hourly 0–6h) metabolic responses to sequential mixed-nutrient dietary challenges (50 g fat, 85 g carbohydrate at 0 h; 22 g fat, 71 g carbohydrate at 4h) in a clinic setting. We investigated the relationship of different postprandial triacylglycerol (TG) measures (4 and 6 h TG iAUC, 4 and 6 h TG concentration, 4 and 6 h TG increase from fasting) with lipoprotein remodelling (XXL-VLDL (including chylomicron remnants and VLDL particles) and XL-VLDL particle concentrations (average diameters > 75, 64 nm respectively), HDL-C) and levels of glycosylated acute phase proteins (GlycA; marker of cardiovascular inflammation), all of which have been implicated as independent predictors of CVD risk.Following adjustment (for use of medication, demographic characteristics, fasting TG, insulin and glucose levels), all six postprandial TG measures (4 and 6 h TG iAUC, 4 and 6 h TG concentration, 4 and 6 h TG increase from fasting) were strongly correlated with markers of atherogenic lipoprotein remodelling and the marker of cardiovascular inflammation (GlycA). The strongest correlation (interim analysis) was observed for the 6 h TG increase from fasting (all P < 0.001, Pearson's coefficient r = 0.94 [95%CI's; 0.93, 0.95] for XXL-VLDL-P; r = 0.95 [95%CI's; 0.95, 0.96] for XL-VLDL-P; r = 0.89 [95%CI's; 0.88, 0.91] for GlycA ; r = -0.61 [95%CI's; -0.66, -0.55] for HDL-C). Inter-individual variability in postprandial lipemic responses was high in the tightly controlled clinic setting (interim analysis, n = 656); IQR (median) was; iAUC (0–6h) 2.39 (2.31) mmol/L.h; Cmax 1.32 (2.06) mmol/L; Tmax 30.0 (300) min; and increase above fasting at 6 h 0.78 (0.62) mmol/L.This is the most detailed postprandial study performed to date and suggests that identifying predictors of the postprandial 6 h TG rise will have the highest CVD relevance. Ongoing exploration in PREDICT I of the determinants of postprandial lipemic responses considering environmental, genetic and microbiome variables will significantly advance our ability to predict an individual's postprandial response and its links to cardiovascular risk.

Supplemental Digital Content is available in the text., Objective— Studies into the role of LRP1 (low-density lipoprotein receptor–related protein 1) in human lipid metabolism are scarce. Although it is known that a common variant in LRP1 (rs116133520) is significantly associated with HDL-C (high-density lipoprotein cholesterol), the mechanism underlying this observation is unclear. In this study, we set out to study the functional effects of 2 rare LRP1 variants identified in subjects with extremely low HDL-C levels. Approach and Results— In 2 subjects with HDL-C below the first percentile for age and sex and moderately elevated triglycerides, we identified 2 rare variants in LRP1: p.Val3244Ile and p.Glu3983Asp. Both variants decrease LRP1 expression and stability. We show in a series of translational experiments that these variants culminate in reduced trafficking of ABCA1 (ATP-binding cassette A1) to the cell membrane. This is accompanied by an increase in cell surface expression of SR-B1 (scavenger receptor class B type 1). Combined these effects may contribute to low HDL-C levels in our study subjects. Supporting these findings, we provide epidemiological evidence that rs116133520 is associated with apo (apolipoprotein) A1 but not with apoB levels. Conclusions— This study provides the first evidence that rare variants in LRP1 are associated with changes in human lipid metabolism. Specifically, this study shows that LRP1 may affect HDL metabolism by virtue of its effect on both ABCA1 and SR-B1.

BACKGROUND: Trapping of apoB lipoprotein particles within the arterial wall initiates and drives the atherosclerotic process from beginning to end. Very low-density lipoprotein particles (VLDL) contain most of the triglyceride in plasma whereas low-density lipoprotein particles (LDL) particles contain most of the cholesterol. Smaller numbers of chylomicron and Lp(a) particles are also present in plasma. All these particles have one molecule of apoB. Therefore, plasma apoB equals the total number of apoB particles. Because the lipid content of apoB particles is variable, plasma triglyceride and cholesterol are not always accurate-measures of the number of apoB particles. THE CHOLESTEROL MODEL OF ATHEROSCLEROSIS: The conventional model of atherosclerosis presumes that the mass of cholesterol within VLDL and LDL particles is the principal determinant of the mass of cholesterol that will be deposited within the arterial wall and will drive atherogenesis. But cholesterol can only enter the arterial wall within apoB particles and the mass of cholesterol that will be deposited is determined by the rate at which apoB particles are trapped within the arterial wall rather than passing harmless through. THE APOB PARTICLE MODEL OF ATHEROGENESIS: The number of apoB particles that enter and are trapped within the arterial wall is determined primarily by the number of apoB particles within the arterial lumen. However, once within the arterial wall, smaller cholesterol-depleted apoB particles have a greater tendency to be trapped than larger cholesterol-enriched apoB particles because they bind more avidly to the glycosaminoglycans within the subintimal space of the arterial wall. If so, a cholesterol-enriched particle would deposit more cholesterol than a cholesterol-depleted apoB particle. By contrast, more smaller apoB particles that enter the arterial wall will be trapped than larger apoB particles. The net result is, with the exceptions of the abnormal chylomicron remnants in type III hyperlipoproteinemia and Lp(a), all apoB particles are equally atherogenic. ApoB, therefore, unifies, amplifies, and simplifies the information from the conventional lipid markers as to the atherogenic risk attributable to the apoB lipoproteins.

Purpose of review Oxidized low-density lipoprotein (Ox-LDL) and chylomicron remnants were previously proposed as the most atherogenic lipoproteins for the causal lipoproteins of atherosclerosis. However, there are still controversies on these hypothesizes. Therefore, we have proposed a new hypothesis based on our recent findings of remnant lipoproteins (RLPs) in postprandial plasma. Recent findings Plasma RLP-C and RLP-TG increased significantly after fat load. More than 80% of the increased triglycerides after fat load consisted of the triglycerides in RLP, which contained greater amount of apoB100 than apoB48 particles as mostly very low density lipoproteins (VLDL) remnants. The majority of lipoprotein lipase (LPL) in plasma was found in RLP as RLP-LPL complex, which is released into circulation after hydrolysis. LPL activity and concentration in plasma did not increase after food intake associated with the insufficient hydrolysis of chylomicrons and VLDL and resulted in the significant increase of RLP-TG. Plasma LPL was inversely correlated with RLP particle size and number. Summary VLDL remnants have been shown as the major atherogenic lipoproteins in postprandial plasma associated with LPL activity as the targets for prevention of atherosclerosis. We also proposed a new definition of RLPs, 'LPL bound TG-rich lipoproteins' based on the findings of RLP-LPL complex.

This study aimed to explore lipoprotein metabolism in obstructive sleep apnea (OSA) and the effects of continuous positive airway pressure (CPAP). We studied 15 men with severe OSA [apnea-hypopnea index (AHI) ≥30 events/hour] and 12 age-, BMI-, and waist circumference-matched volunteers without OSA (AHI

Background Methyglyoxal (MG) is a toxic molecule that mediates damage produced by glycation, a key pathogenic factor in diabetes mellitus. We have previously shown that the MG catabolic product, D-lactate, is higher in obese adolescents (1) and that apoB48 is higher in adolescents with insulin resistance (IR) (2). Hypothesis and aims: We tested the hypothesis that increased D-lactate is associated with ApoB48 (remnant) dyslipoproteinemia and IR in adolescents. Material and Methods This cross-sectional study in anew cohort included euglycemic adolescents between 15 and 19 years old, classified in 4 groups according to BMI and HOMA-IR: lean adolescents without (MHL) alterations (n = 20), lean adolescents with metabolic alterations (MUL, n=20) metabolically healthy obese (MHO) n = 20 and metabolically unhealthy obese adolescents (MUO) n = 24. Results D-lactate levels did not differ between MHL and MUL participants (0.29 +/- 0.15 vs 0.29 +/- 0.13 mmol/L), they show a trend to be higher in MHO (0.38 +/- 0.15 mmol/L) and are significantly higher (0.46 +/- 0.15 mmol/L) in MUO vs MUL or MHL (p=0.003. D-lactate correlated with BMI (Rho=0.39, p=0.0002); HOMA-IR (Rho=0.33, p=0.002) and apoB48 HOMA-IR (Rho=0.33, p=0.002). Conclusion: MUO displayed 58% higher levels of D-lactate than lean adolescents. D-lactate correlates with BMI, HOMA-IR and with chylomicron remnants. We suggest that IR does not suffice to produce increased MG metabolism (MHL and MUL have the same levels) but potentiates the effect of obesity. Increased D-lactate show dysregulation of glycolysis leading to MG production, in association with poor chylomicron catabolism. 1. Rodriguez-Mortera, Reyna, Claudia Luevano-Contreras, Sergio Solorio-Meza, Russell Caccavello, Yasmin Bains, Ma Eugenia Garay-Sevilla, and Alejandro Gugliucci. Clinical Chemistry and Laboratory Medicine (CCLM) 56, no. 7 (2018): 1100-1108. 2. Rodriguez-Mortera R, Caccavello R, Garay-Sevilla ME, Gugliucci A. Clin Chim Acta. 2020; 508:61-68. doi:10.1016/j.cca.2020.05.014

Apolipoprotein (apo) B, the critical structural protein of the atherogenic lipoproteins, has two major isoforms: apoB48 and apoB100. ApoB48 is found in chylomicrons and chylomicron remnants with one apoB48 molecule per chylomicron particle. Similarly, a single apoB100 molecule is contained per particle of very-low-density lipoprotein (VLDL), intermediate density lipoprotein, LDL and lipoprotein(a). This unique one apoB per particle ratio makes plasma apoB concentration a direct measure of the number of circulating atherogenic lipoproteins. ApoB levels indicate the atherogenic particle concentration independent of the particle cholesterol content, which is variable. While LDL, the major cholesterol-carrying serum lipoprotein, is the primary therapeutic target for management and prevention of atherosclerotic cardiovascular disease, there is strong evidence that apoB is a more accurate indicator of cardiovascular risk than either total cholesterol or LDL cholesterol. This review examines multiple aspects of apoB structure and function, with a focus on the controversy over use of apoB as a therapeutic target in clinical practice. Ongoing coronary artery disease residual risk, despite lipid-lowering treatment, has left patients and clinicians with unsatisfactory options for monitoring cardiovascular health. At the present time, the substitution of apoB for LDL-C in cardiovascular disease prevention guidelines has been deemed unjustified, but discussions continue.

Purpose of review Clearing of atherogenic lipoprotein particles by the liver requires hepatic low-density lipoprotein receptor (LDLR) and LDLR-related protein 1 (LRP1). This review highlights recent studies that have expanded our understanding of the molecular regulation and metabolic functions of LDLR and LRP1 in the liver. Recent findings Various proteins orchestrate the intracellular trafficking of LDLR and LRP1. After internalization, the receptors are redirected via recycling endosomes to the cell surface. Several new endocytic proteins that facilitate the endosomal trafficking of LDLR and consequently the clearance of circulating LDL cholesterol have recently been reported. Mutations in some of these proteins cause hypercholesterolemia in human. In addition, LRP1 controls cellular cholesterol efflux by modulating the expression of ABCA1 and ABCG1, and hepatic LRP1 protects against diet-induced hepatic insulin resistance and steatosis through the regulation of insulin receptor trafficking. Summary LDLR and LRP1 have prominent roles in cellular and organismal cholesterol homeostasis. Their functioning, including their trafficking in the cell, is controlled by numerous proteins. Comprehensive studies into the molecular regulation of LDLR and LRP1 trafficking have advanced our fundamental understanding of cholesterol homeostasis, and these insights may lead to novel therapeutic strategies for atherosclerosis, hyperlipidemia and insulin resistance in the future.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a serine protease involved in the regulation of LDL receptor (LDLR) expression and apolipoprotein B lipoprotein cholesterol metabolism. Hepatic PCSK9 protein expression, activity, and secretion have been shown to affect cholesterol homeostasis. An upregulation of hepatic PSCK9 protein leads to increased LDLR degradation, resulting in decreased uptake of apoB lipoproteins and a consequent increase in the plasma concentration of these lipoproteins, including LDL and chylomicron remnants. Hence, PCSK9 has become a novel target for lipid-lowering therapies. The aim of this review is to outline current findings on the metabolic and dietary regulation of PCSK9 and effects on cholesterol, apoB lipoprotein metabolism, and cardiovascular disease (CVD) risk. PCSK9 gene and protein expression have been shown to be regulated by metabolic status and the diurnal pattern. In the fasting state, plasma PCSK9 is reduced via modulation of the nuclear transcriptional factors, including sterol regulatory element-binding protein (SREBP) 1c, SREBP2, and hepatocyte nuclear factor 1α. Plasma PCSK9 concentrations are also known to be positively associated with plasma insulin and homeostasis model assessment of insulin resistance, and appear to be regulated by SREBP1c independently of glucose status. Plasma PCSK9 concentrations are stable in response to high-fat or high-protein diets in healthy individuals; however, this response may differ in altered metabolic conditions. Dietary n-3 polyunsaturated fatty acids have been shown to reduce plasma PCSK9 concentration and hepatic PCSK9 mRNA expression, consistent with their lipid-lowering effects, whereas dietary fructose appears to upregulate PCSK9 mRNA expression and plasma PCSK9 concentrations. Further studies are needed to elucidate the mechanisms of how dietary components regulate PCSK9 and effects on cholesterol and apoB lipoprotein metabolism, as well as to delineate the clinical impact of diet on PCSK9 in terms of CVD risk.

The association of lipophilic statins with plasma lipoproteins in the presence of disturbed acid-base balance can modify the pharmacokinetics and tissue distribution of these drugs, resulting in alteration in their efficacy and toxicity profiles. The purpose of this study is to elucidate the role of hyperlipidaemia alone or in combination with acidosis/alkalosis in the development and potentiation of statin-induced myotoxicity. Statins association with plasma lipoproteins was examined under conditions of physiological and altered pH levels. The effect of this association on cellular uptake and myotoxicity of statins was also assessed at different pH levels using C2C12 cells that overexpress lipoprotein lipase. Lipophilic simvastatin displayed considerable association with the non-polar lipoprotein fractions (triglyceride-rich lipoproteins and low-density lipoprotein). This association contributed to increased cellular uptake of simvastatin by C2C12 cells through lipoprotein lipase-mediated process, resulting in enhanced muscle toxicity in hyperlipidaemic conditions. Furthermore, a combination of low pH environment (representing acidosis) and hyperlipidaemia increased the association of simvastatin with plasma lipoproteins causing potentiation of cellular uptake and myotoxicity of this drug. Comorbidities such as hyperlipidaemia, especially when coincident with acidosis, can enhance statin-associated muscle toxicity, and therefore require extra caution by prescribing clinicians. Hydrophilic rather than lipophilic statins could be a preferable choice in this patient population.

TAG depleted remnants of postprandial chylomicrons are a risk factor for atherosclerosis. Recent studies have demonstrated that in the fasted state, the majority of chylomicrons are small enough for transcytosis to arterial subendothelial space and accelerate atherogenesis. However, the size distribution of chylomicrons in the absorptive state is unclear. This study explored in normolipidaemic subjects the postprandial distribution of the chylomicron marker, apoB-48, in a TAG-rich lipoprotein plasma fraction (Svedberg flotation rate (Sf>400), in partially hydrolysed remnants (Sf 20–400) and in a TAG-deplete fraction (Sf

Aim: Evaluation of serum lipoprotein profiles including triglyceride (TG)-rich lipoprotein, that is, intermediate-density lipoprotein (IDL), very low-density lipoprotein (VLDL), and chylomicron (CM) remnant is important to manage coronary heart disease (CHD) risk. The purpose of this study was to investigate CHD or cardiovascular disease (CVD) risk scores with cholesterol levels of six fractionated lipoprotein classes {high-density lipoprotein [HDL], low-density lipoprotein [LDL], IDL, VLDL, CM including CM remnant, and lipoprotein (a) [Lp (a)]} in Japanese healthy men. Methods: The present study enrolled 161 healthy men without any medications. Lipoprotein profiles (fractionated lipoprotein cholesterol levels) were measured by anion-exchange high-performance liquid chromatography (AEX-HPLC) method and were compared with age, estimated glomerular filtration rate (eGFR), and three risk scores, that is, NIPPON DATA, Hisayama risk predicting model, and Suita score. Results: Levels of LDL-cholesterol (C), VLDL-C, and CM-C significantly differed with age, while values of HDL-C, IDL-C, and Lp(a)-C were not different. The eGFR inversely correlated with LDL-C, IDL-C, VLDL-C, and CM-C. In a stepwise multiple logistic regression analysis, VLDL-C only correlated independently with eGFR. Three risk scores significantly correlated with CM-C. Conclusions: These results suggested that VLDL-C concentration contributes to an increased risk at early stages of renal dysfunction, and CM-C may serve as a marker for estimating CHD risk in Japanese healthy men.

Cluster of differentiation 36 (CD36) variants influence fasting lipids and risk of metabolic syndrome, but their impact on postprandial lipids, an independent risk factor for cardiovascular disease, is unclear. We determined the effects of SNPs within a ~410 kb region encompassing CD36 and its proximal and distal promoters on chylomicron (CM) remnants and LDL particles at fasting and at 3.5 and 6 h following a high-fat meal (Genetics of Lipid Lowering Drugs and Diet Network study, n = 1,117). Five promoter variants associated with CMs, four with delayed TG clearance and five with LDL particle number. To assess mechanisms underlying the associations, we queried expression quantitative trait loci, DNA methylation, and ChIP-seq datasets for adipose and heart tissues that function in postprandial lipid clearance. Several SNPs that associated with higher serum lipids correlated with lower adipose and heart CD36 mRNA and aligned to active motifs for PPARγ, a major CD36 regulator. The SNPs also associated with DNA methylation sites that related to reduced CD36 mRNA and higher serum lipids, but mixed-model analyses indicated that the SNPs and methylation independently influence CD36 mRNA. The findings support contributions of CD36 SNPs that reduce adipose and heart CD36 RNA expression to inter-individual variability of postprandial lipid metabolism and document changes in CD36 DNA methylation that influence both CD36 expression and lipids.

We thank Drs Stellaard and Lütjohann for their interest in our study and for their question regarding the nature of apoB48‐containing lipoprotein particles found in the VLDL1 and VLDL2 density ranges (1). The correspondents are correct in pointing out that chylomicron remnants and apoB100‐containing VLDL of liver origin co‐exist in the VLDL1 (Sf60‐400) and VLDL2 (Sf20‐60) fractions, especially after a fat‐rich meal.

Lycopene, like other lipophilic dietary components, is absorbed from the intestine in chylomicrons. These large, triacylglycerol-rich lipoproteins are metabolized in the blood by removal of some of the triacylglycerol, leaving smaller chylomicron remnants particles that deliver the remaining lipids to the liver. Lycopene may then re-enter the circulation and is transported in low density lipoprotein. The proportion of dietary lycopene absorbed in chylomicrons is relatively low and is influenced by a number of factors. It is increased by the consumption of tomato products rather than the raw fruit, as well as by the presence of fat in the diet, and the cis isomer is more easily incorporated into chylomicrons than the all-trans form. Conversely, absorption is reduced by non-absorbable fat substitutes such as sucrose polyester, and in older as compared to younger subjects. In addition, other carotenoids in the diet may compete with lycopene for absorption in chylomicrons, although this does not appear to influence its bioavailability in the medium term. Some studies have suggested that lycopene may protect against atherosclerosis, possibly because its antioxidant properties protect low density lipoprotein from oxidation. However, the presence of lycopene in chylomicron remnants, which are also known to be atherogenic, has been found to increase their induction of macrophage foam cell formation and decrease their uptake by the liver, thus potentially promoting atherosclerotic lesion development. The type of 160lipoprotein carrier of lycopene, therefore, may be important for its effects on atherosclerosis, with its presence being beneficial in low density lipoprotein, but deleterious in chylomicron remnants. Since chylomicron remnants are normally rapidly cleared from the blood, the beneficial effect may predominate in healthy subjects. However, remnant particles accumulate in the blood in some conditions, including obesity and diabetes, and the potentially detrimental effects may be more important in these circumstances. Despite the potential protective effects of dietary lycopene against cardiovascular and other diseases, the mechanisms regulating its absorption in chylomicrons are not completely understood, and more research is essential to establish the optimum conditions for the dietary intake of lycopene in order to obtain the maximum benefit for health.

Lipoproteins are one of the major risk factors for atherosclerotic cardiovascular disease (ASCVD), among which, low-density lipoprotein (LDL) particles have been definitively shown to be causally associated with the development of ASCVD. Additionally, the concept of remnant lipoproteins has emerged as lipoprotein metabolism has been fully investigated. The principal concept of this lipoprotein category is triglyceride-rich lipoproteins significantly increase at the postprandial state. Although there is no clear definition of remnant lipoproteins, they typically include chylomicron remnants, which are lipolyzed particles from chylomicron, as well as very low-density lipoprotein (VLDL) and intermediate-density lipoprotein (IDL) remnants that are lipolyzed particles from VLDL and IDL particles. However, the most important factor of these lipoproteins is such remnant lipoproteins seem to be causally associated with ASCVD, independent of LDL particles or LDL cholesterol. It has been challenging to assert a causal association of remnant lipoproteins and ASCVD; however, accumulated evidence from epidemiological studies, as well as recent Mendelian randomization studies from common and rare genetic variations strongly support this association. In this article, a basic explanation of lipoprotein metabolism is presented, including remnant lipoproteins and the important causal associations with ASCVD from a clinical point of view.

Circulating levels of chylomicron remnants (CMRs) increase postprandially and their composition directly reflects dietary lipid intake. These TG-rich lipoproteins likely contribute to the development of endothelial dysfunction, albeit via unknown mechanisms. Here, we investigated how the FA composition of CMRs influences their actions on human aortic endothelial cells (HAECs) by comparing the effects of model CMRs—artificial TG-rich CMR-like particles (A-CRLPs)—containing TGs extracted from fish, DHA-rich algal, corn, or palm oils. HAECs responded with distinct transcriptional programs according to A-CRLP TG content and oxidation status, with genes involved in antioxidant defense and cytoprotection most prominently affected by n-3 PUFA-containing A-CRLPs. These particles were significantly more efficacious inducers of heme oxygenase-1 (HO-1) than n-6 PUFA corn or saturated FA-rich palm CRLPs. Mechanistically, HO-1 induction by all CRLPs requires NADPH oxidase 4, with PUFA-containing particles additionally dependent upon mitochondrial reactive oxygen species. Activation of both p38 MAPK and PPARβ/δ culminates in increased nuclear factor erythroid 2-related factor 2 (Nrf2) expression/nuclear translocation and HO-1 induction. These studies define new molecular pathways coupling endothelial cell activation by model CMRs with adaptive regulation of Nrf2-dependent HO-1 expression and may represent key mechanisms through which dietary FAs differentially impact progression of endothelial dysfunction.

Low-density lipoprotein receptor-related protein-1 (LRP1) is a multifunctional uptake receptor for chylomicron remnants in the liver. In vascular smooth muscle cells LRP1 controls reverse cholesterol transport through platelet-derived growth factor receptor β (PDGFR-β) trafficking and tyrosine kinase activity. Here we show that LRP1 regulates hepatic energy homeostasis by integrating insulin signaling with lipid uptake and secretion. Somatic inactivation of LRP1 in the liver (hLRP1KO) predisposes to diet-induced insulin resistance with dyslipidemia and non-alcoholic hepatic steatosis. On a high-fat diet, hLRP1KO mice develop a severe Metabolic Syndrome secondary to hepatic insulin resistance, reduced expression of insulin receptors on the hepatocyte surface and decreased glucose transporter 2 (GLUT2) translocation. While LRP1 is also required for efficient cell surface insulin receptor expression in the absence of exogenous lipids, this latent state of insulin resistance is unmasked by exposure to fatty acids. This further impairs insulin receptor trafficking and results in increased hepatic lipogenesis, impaired fatty acid oxidation and reduced very low density lipoprotein (VLDL) triglyceride secretion.

Hypertension, advanced age, postprandial hyperlipidemia, and insulin resistance are major risk factors for atherosclerosis. The calcium channel blocker nifedipine is reported to ameliorate insulin resistance possibly by activating PPARγ. This is expected to become accentuated in elderly individuals due to age-related insulin resistance. Insulin resistance modulates lipoprotein metabolism. Therefore, we reasoned that nifedipne offers the potential for improving postprandial lipemia in association with increasing age. We studied the effect of nifedipine on fasting lipids, postprandial lipemia, insulin sensitivity, and plasma lipolytic activity in 24 and 15 hypertensive subjects aged 70-75 years and 40-45 years, respectively. As expected, nifedipine significantly lowered systolic and diastolic blood pressure. Nifedipine decreased fasting triglyceride level (23%) and increased HDL-C (15%) in the elderly group. At baseline, postprandial triglyceride levels were remarkably elevated in elderly compared to younger patients (1 288±798 vs. 501±260 mg·dl(-1)·h, p

In this issue of the journal, Puri et al1 examines the association of on-treatment concentrations of non–high-density lipoprotein (non-HDL) cholesterol and triglycerides with coronary atheroma progression and clinical events. They used data from 9 clinical trials, originally designed to examine effects of different medical therapies on regression of coronary atheroma burden, assessed by intravascular ultrasound. The main finding was that achieved concentrations of non-HDL cholesterol and achieved concentrations of triglycerides were closely associated with coronary atheroma progression and regression, irrespective of achieved concentrations of low-density lipoprotein (LDL) cholesterol, C-reactive protein concentration, and diabetes mellitus status. See accompanying article on page 2220 Non-HDL cholesterol is a combined measure of the cholesterol content of LDL, lipoprotein(a), and triglyceride-rich lipoproteins, the latter also known as remnants (Figure). Remnants are here a combined term for intermediate-density lipoproteins, very-low-density lipoproteins, and chylomicron remnants. These lipoproteins likely are atherogenic by penetrating the arterial wall, leading to accumulation of cholesterol in the intimal space, foam cell formation, and atherosclerosis2–5 (Figure). Triglycerides are primarily carried by remnants, and concentrations of triglycerides are highly correlated with the cholesterol content of remnants, that is, remnant cholesterol.6 It is most likely that the cholesterol content of remnants, and not triglycerides, causes atherosclerosis because most cells can degrade triglycerides but not cholesterol2,5 and because cholesterol, and not …

Metabolic syndrome (MetS) is a highly prevalent disorder which can be used to identify individuals with a higher risk for cardiovascular disease and type 2 diabetes. This metabolic syndrome is characterized by a combination of physiological, metabolic, and molecular alterations such as insulin resistance, dyslipidemia, and central obesity. The low-density lipoprotein receptor-related protein 1 (LRP1—A member of the LDL receptor family) is an endocytic and signaling receptor that is expressed in several tissues. It is involved in the clearance of chylomicron remnants from circulation, and has been demonstrated to play a key role in the lipid metabolism at the hepatic level. Recent studies have shown that LRP1 is involved in insulin receptor (IR) trafficking and intracellular signaling activity, which have an impact on the regulation of glucose homeostasis in adipocytes, muscle cells, and brain. In addition, LRP1 has the potential to inhibit or sustain inflammation in macrophages, depending on its cellular expression, as well as the presence of particular types of ligands in the extracellular microenvironment. In this review, we summarize existing perspectives and the latest innovations concerning the role of tissue-specific LRP1 in lipoprotein and glucose metabolism, and examine its ability to mediate inflammatory processes related to MetS and atherosclerosis. Fil: Actis Dato, Virginia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Bioquímica Clínica e Inmunología; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Bioquímica Clínica; Argentina Fil: Chiabrando, Gustavo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Bioquímica Clínica e Inmunología; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Bioquímica Clínica; Argentina

What you need to know ### Sources and selection criteria We carried out an electronic search through PubMed and Cochrane database of systematic reviews using the following search terms: “primary prevention,” “dyslipidaemia,” “cardiovascular disease,” “statins,” “statin intolerance,” “ezetimibe,” “PCSK9,” “hypercholesterolaemia diagnosis and treatment.” We also interrogated relevant dyslipidaemia guidelines and personal archives for supporting evidence as discussed and as referenced. Cardiovascular disease (CVD) is the most common underlying cause of death worldwide, accounting for 17.3 million of 54 million total deaths per year. Of these, 8.2 million were caused by ischaemic heart disease and 6.5 million by stroke.1 Mean total cholesterol, calculated low density lipoprotein (LDLc), and triglyceride concentrations have declined over the last 20 years. However, some observational cohort evidence suggests that long term exposure to even modestly elevated cholesterol concentrations is associated with CVD in later life.12 Cholesterol made in the liver and from the diet is transported to peripheral cells by apoB-containing lipoproteins in the blood (fig 1). In a fasting sample, the LDL particles constitute most of the circulating apoB lipoproteins. However, in clinical practice LDL is not measured directly but is calculated (LDLc) (box 1). LDLc has become a metric for treatment success and for diagnosis. Fig 1 Apolipoprotein B, non-HDL lipid transport, and atherosclerosis. Lipoproteins involved in cholesterol are transported from gut and liver to the peripheral tissues, providing fuel, membrane structure, and hormones. Lipoproteins carrying apolipoprotein B (apart from chylomicrons) have the potential to be atherogenic. APOE: apoliprotein e receptor; Chol: cholesterol; FA: fatty acids; IDL: intermediate density lipoprotein; TG: triglyceride; C: chylomicron; CR: chylomicron remnant; LDL: low density …

Objective— Dyslipidemia is one of the key factors behind coronary heart disease. Blood and lymphatic vessels play pivotal roles in both lipoprotein metabolism and development of atherosclerotic plaques. Recent studies have linked members of VEGF (vascular endothelial growth factor) family to lipid metabolism, but the function of VEGF-D has remained unexplored. Here, we investigated how the deletion of VEGF-D affects lipid and lipoprotein metabolism in atherogenic LDLR −/− ApoB 100/100 mice. Approach and Results— Deletion of VEGF-D (VEGF-D −/− LDLR −/− ApoB 100/100 ) led to markedly elevated plasma cholesterol and triglyceride levels without an increase in atherogenesis. Size distribution and hepatic lipid uptake studies confirmed a delayed clearance of large chylomicron remnant particles that cannot easily penetrate through the vascular endothelium. Mechanistically, the inhibition of VEGF-D signaling significantly decreased the hepatic expression of SDC1 (syndecan 1), which is one of the main receptors for chylomicron remnant uptake when LDLR is absent. Immunohistochemical staining confirmed reduced expression of SDC1 in the sinusoidal surface of hepatocytes in VEGF-D deficient mice. Furthermore, hepatic RNA-sequencing revealed that VEGF-D is also an important regulator of genes related to lipid metabolism and inflammation. The lack of VEGF-D signaling via VEGFR3 (VEGF receptor 3) led to lowered expression of genes regulating triglyceride and cholesterol production, as well as downregulation of peroxisomal β-oxidation pathway. Conclusions— These results demonstrate that VEGF-D, a powerful lymphangiogenic and angiogenic growth factor, is also a major regulator of chylomicron metabolism in mice.

The purpose of this review is to summarize our current understanding of the physiological roles of apoA-IV in metabolism, and to underscore the potential for apoA-IV to be a focus for new therapies aimed at the treatment of diabetes and obesity-related disorders. ApoA-IV is primarily synthesized by the small intestine, attached to chylomicrons by enterocytes, and secreted into intestinal lymph during fat absorption. In circulation, apoA-IV is associated with HDL and chylomicron remnants, but a large portion is lipoprotein free. Due to its anti-oxidative and anti-inflammatory properties, and because it can mediate reverse-cholesterol transport, proposed functions of circulating apoA-IV have been related to protection from cardiovascular disease. This review, however, focuses primarily on several properties of apoA-IV that impact other metabolic functions related to food intake, obesity, and diabetes. In addition to participating in triglyceride absorption, apoA-IV can act as an acute satiation factor through both peripheral and central routes of action. It also modulates glucose homeostasis through incretin-like effects on insulin secretion, and by moderating hepatic glucose production. While apoA-IV receptors remain to be conclusively identified, the latter modes of action suggest that this protein holds therapeutic promise for treating metabolic disease.

Apolipoprotein E (apoE) has long been recognized as an important regulator of plasma lipoprotein metabolism and cholesterol homeostasis. However, despite decades of research into the biology of apoE, new aspects of its function continue to emerge. In this issue, Li et al1 demonstrate that apoE regulates the expression of an anti-inflammatory microRNA, miR-146a, in monocytes/macrophages. The authors reveal that miR-146a represses nuclear factor-κB (NF-κB) signaling in these cells and that intravascular delivery of miR-146a mimetics can inhibit atherogenesis in mouse models. These findings establish that enhancing miR-146a expression can antagonize atherogenesis and provide an impetus to pursue microRNA-based therapies for vascular inflammatory diseases. Article, see p e1 Initial work that characterized apoE function in the cardiovascular system demonstrated that apoE mediates the uptake of chylomicron remnants and triglyceride-rich very low and intermediate density lipoproteins in the liver. In arteries, together with apoA-I, apoE facilitates cellular cholesterol efflux from macrophage foam cells.2 Genetically engineered deficiency of Apoe in mice results in elevated plasma very low and intermediate density lipoproteins and spontaneous atherogenesis.3,4 Over the past 2 decades, this model has served as the mainstay of atherosclerosis research. Global Apoe deficiency can be rescued by transplantation of wild-type bone marrow, which normalizes plasma cholesterol levels and dramatically reduces atherosclerosis.5,6 Attenuated atherosclerosis is also observed in Apoe -null mice bred with transgenic mice expressing human apoE specifically in macrophages. These mice have plasma cholesterol levels comparable with control littermates.7 Interestingly, a recent study revealed that global hypomorphic expression of apoE has no effect on plasma cholesterol, yet atherosclerosis is suppressed and the expression of monocyte and endothelial cell inflammatory genes are reduced relative to complete Apoe deficiency in the low-density lipoprotein receptor–deficient ( Ldlr −/−) background.8 These studies highlight the importance of apoE in …

Objective: Familial Hypercholesterolemia (FH) is associated with an increased risk of cardiovascular disease (CVD). However, whether an individual heterozygous FH patient will develop CVD depends on other genetic-and environmental risk factors as well. LDL receptor-related protein with 11 ligand binding repeat (LR11) and its soluble form (sLR11) play a role in the progression of atherosclerosis. We investigated the involvement of LR11 and sLR11 in CVD development in FH patients and in LDLR deficient (Ldlr(-/-)) mice. Approach and results: In statin-treated asymptomatic male heterozygous FH subjects, plasma sLR11 levels correlated with carotid intima-media thickness. Increased plasma sLR11 levels were found in Ldlr(-/-) and also in wild-type mice exclusively after high-fat feeding. Hepatic LR11 mRNA levels, however, were higher in chow-fed Ldlr(-/-) in comparison with wild-type mice and were further increased after a high fat diet. Similar results were obtained with Apoe(-/-) mice, but not with wild-type mice. LR11 mRNA and protein levels and release of sLR11 from cultured HepG2 and aortic smooth muscle cells were upregulated by postprandial triglyceride-rich lipoproteins (TGRL). Overexpression of human LR11 in CHO cells resulted in increased binding and association of 12I-labeled TGRL, but not of 12I-labeled LDL. Conclusion: Our data strongly suggest an involvement of LR11 in mediating the harmful effects of a high-fat diet on CVD progression. Elevated sLR11 levels may increase the CVD risk especially in subjects with delayed clearance of triglyceride-rich remnants, such as in FH patients. (C) 2015 Elsevier Ireland Ltd. All rights reserved.

BACKGROUND Levels of apolipoprotein (apo) B48 may be increased in conditions associated with systemic inflammation and increased cardiovascular disease (CVD) risk such as rheumatoid arthritis (RA). We aimed to evaluate apo B48 levels in patients with RA in relation to subclinical atherosclerosis. METHODS Patients with RA (without CVD) and controls without RA but with high CVD risk (based on the presence of diabetes mellitus or a history of CVD) and healthy controls were included in this cross-sectional study. Carotid intima-media thickness (cIMT) was measured as a surrogate for vascular damage. RESULTS In total, 312 patients with RA, 65 controls with high CVD risk and 36 healthy controls were included. Patients with RA had the highest mean apo B48 (10.00 ± 6.65 mg/L) compared to controls with high CVD risk and healthy controls (8.37 ± 5.16 and 5.22 ± 2.46, P

Aims Fasting and postprandial hypertriglyceridemia (PHTG) are caused by the accumulation of triglyceride (TG)-rich lipoproteins and their remnants, which have atherogenic effects. Fibrates can improve fasting and PHTG; however, reduction of remnants is clinically needed to improve health outcomes. In the current study, we investigated the effects of a novel selective peroxisome proliferator-activated receptor α modulator (SPPARMα), K-877 (Pemafibrate), on PHTG and remnant metabolism. Methods Male C57BL/6J mice were fed a high-fat diet (HFD) only, or an HFD containing 0.0005% K-877 or 0.05% fenofibrate, from 8 to 12 weeks of age. After 4 weeks of feeding, we measured plasma levels of TG, free fatty acids (FFA), total cholesterol (TC), HDL-C, and apolipoprotein (apo) B-48/B-100 during fasting and after oral fat loading (OFL). Plasma lipoprotein profiles after OFL, which were assessed by high performance liquid chromatography (HPLC), and fasting lipoprotein lipase (LPL) activity were compared among the groups. Results Both K-877 and fenofibrate suppressed body weight gain and fasting and postprandial TG levels and enhanced LPL activity in mice fed an HFD. As determined by HPLC, K-877 and fenofibrate significantly decreased the abundance of TG-rich lipoproteins, including remnants, in postprandial plasma. Both K-877 and fenofibrate decreased intestinal mRNA expression of ApoB and Npc1l1; however, hepatic expression of Srebp1c and Mttp was increased by fenofibrate but not by K-877.Hepatic mRNA expression of apoC-3 was decreased by K-877 but not by fenofibrate. Conclusion K-877 may attenuate PHTG by suppressing the postprandial increase of chylomicrons and the accumulation of chylomicron remnants more effectively than fenofibrate.

Dietary fats absorbed in the intestine are transported in the circulation as chylomicrons and remnants that have atherogenic potential. Although postprandial lipidemia is increased in older subjects, the specific chylomicron metabolism has not been explored in older subjects nor compared to young subjects, which is the focus of this study. After a 12 h fast, artificially-made emulsions similar to lymph chylomicrons and doubly labeled with radioactive cholesteryl esters and triglycerides were intravenously injected in 23 older (66±4 years) and 20 young (24±3 years) subjects. Sequential blood samples were collected to determine fractional clearance rates (FCR, in min-1) by compartmental analysis. Older subjects had higher LDL-cholesterol (p

Lipid accumulation is a key characteristic of advancing atherosclerotic lesions. Herein, we analyzed the ultrastructure of the accumulated Lipids in endarterectomized human carotid atherosclerotic plaques using three-dimensional (3D) electron microscopy, a method never used in this context before. 3D electron microscopy revealed intracellular lipid droplets and extracellular Lipoprotein particles. Most of the particles were aggregated, and some connected to needle-shaped or sheet-like cholesterol crystals. Proteomic analysis of isolated extracellular Lipoprotein particles revealed that apolipoprotein B is their main protein component, indicating their origin from low-density lipoprotein, intermediate-density Lipoprotein, very-Low-density lipoprotein, lipoprotein (a), or chylomicron remnants. The particles also contained small exchangeable apolipoproteins, complement components, and immunoglobulins. Lipidomic analysis revealed differences between plasma lipoproteins and the particles, thereby indicating involvement of lipolytic enzymes in their generation. Incubation of human monocyte-derived macrophages with the isolated extracellular lipoprotein particles or with plasma lipoproteins that had been Lipolytically modified in vitro induced intracellular Lipid accumulation and triggered inflammasome activation in them. Taken together, extracellular Lipids accumulate in human carotid plaques as distinct 3D structures that include aggregated and fused lipoprotein particles and cholesterol crystals. The particles originate from plasma lipoproteins, show signs of lipolytic modifications, and associate with cholesterol crystals. By inducing intracellular cholesterol accumulation (ie, foam cell formation) and inflammasome activation, the extracellular lipoprotein particles may actively enhance atherogenesis.

The metabolic syndrome is an escalating worldwide public health concern. Defined by a combination of physiological, metabolic, and biochemical factors, the metabolic syndrome is used as a clinical guideline to identify individuals with a higher risk for type 2 diabetes and cardiovascular disease. Although risk factors for type 2 diabetes and cardiovascular disease have been known for decades, the molecular mechanisms involved in the pathophysiology of these diseases and their interrelationship remain unclear. The LDL receptor-related protein 1 (LRP1) is a large endocytic and signaling receptor that is widely expressed in several tissues. As a member of the LDL receptor family, LRP1 is involved in the clearance of chylomicron remnants from the circulation and has been demonstrated to be atheroprotective. Recently, studies have shown that LRP1 is involved in insulin receptor trafficking and regulation and glucose metabolism. This review summarizes the role of tissue-specific LRP1 in insulin signaling and its potential role as a link between lipoprotein and glucose metabolism in diabetes.

The Apolipoprotein (Apo) family is implicated in lipid metabolism. There are five types ofApo:Apoa,Apob,Apoc,Apod, andApoe.Apoehas been demonstrated to play a central role in lipoprotein metabolism and to be essential for efficient receptor-mediated plasma clearance of chylomicron remnants and VLDL remnant particles by the liver.Apoe-deficient (Apoe−/−) mice develop atherosclerotic plaques spontaneously, followed by obesity. In this study, we investigated whether lipid deposition caused byApoeknockout affects reproduction in female mice. The results demonstrated thatApoe−/−mice were severely hypercholesterolemic, with their cholesterol metabolism disordered, and lipid accumulating in the ovaries causing the ovaries to be heavier compared with the WT counterparts. In addition, estrogen and progesterone decreased significantly at D 100. Quantitative PCR analysis demonstrated that at D 100 the expression of cytochromeP450 aromatase (Cyp19a1), 3β-hydroxysteroid dehydrogenase (Hsd3b), mechanistic target of rapamycin (Mtor), and nuclear factor-κB (Nfkb) decreased significantly, while that of BCL2-associated agonist of cell death (Bad) and tuberous sclerosis complex 2 (Tsc2) increased significantly in theApoe−/−mice. However, there was no difference in the fertility rates of theApoe−/−and WT mice; that is, obesity induced byApoeknockout has no significant effect on reproduction. However, the deletion ofApoeincreased the number of ovarian follicles and the ratio of ovarian follicle atresia and apoptosis. We believe that this work will augment our understanding of the role ofApoein reproduction.

Aim Apolipoprotein B-48 (apoB-48) is a constituent of chylomicrons and their remnants (chylomicron remnants). A high concentration of serum apoB-48 is suspected to be a major risk factor for the development of atherosclerotic cardiovascular disease. Proteinuria and a reduced estimated glomerular filtration rate (eGFR) are independent risk factors for cardiovascular events and renal dysfunction. In the present study, we examined whether the serum apoB-48 concentration is associated with renal dysfunction. Methods A total of 264 patients was enrolled and classified into four groups according to the eGFR and level of proteinuria: a high eGFR (＞60mL/min/1.73m(2)) without proteinuria (≥1＋ by urine dipstick) (n=50); a high eGFR with proteinuria (n=75); a low eGFR (＞60mL/min/1.73m(2)) without proteinuria (n=74); and a low eGFR with proteinuria (n=65). Biochemical markers of lipid metabolism, including the fasting serum apoB-48 concentration, were compared between the four groups. Results The serum log-apoB-48 and log-apoB-48/TG levels were significantly higher in the patients with a high eGFR with proteinuria, low eGFR with proteinuria and low eGFR without proteinuria than in those with a high eGFR without proteinuria, with the most significant differences for these parameters. The eGFR was found to be significantly correlated with the log-apoB-48 and log-apoB-48/TG levels, whereas urinary protein was found to be significantly correlated with the log-apoB-48 level only. A multiple regression analysis indicated that the log-apoB-48/TG level was a significant determinant of a reduced eGFR. Conclusions Both a low eGFR (＜60) and proteinuria (≥1＋) are independent determinants of a high apoB-48 concentration. Taken together, the present results suggest that an increased serum apoB-48 concentration contributes to an increased risk of cardiovascular events.

Cholesterol is of vital importance for vertebrate cell membrane structure and function. It is obvious that adequate regulation of cholesterol homeostasis is essential. Hypercholesterolemia promotes atherosclerosis and thereby represents a major risk factor for cardiovascular disease. The liver has been considered the major site of control in maintenance of cholesterol homeostasis. The liver facilitates clearance of (very) low density lipoprotein particles and cholesterol-containing chylomicron remnants, synthesizes cholesterol, synthesizes and secretes (nascent) high density lipoprotein particles, secretes cholesterol and bile salts to bile, and is involved in reverse cholesterol transport. In recent years, however, the importance of the intestine in many aspects of cholesterol physiology is increasingly recognized. It has become apparent that direct secretion of cholesterol from the blood compartment into the intestine, or transintestinal cholesterol excretion, plays a major role in disposal of cholesterol via the feces. This review will discuss current knowledge on the physiology of cholesterol homeostasis, with emphasis on cholesterol absorption, cholesterol synthesis and fecal excretion, and therapeutic options for hypercholesterolemia.

Apolipoprotein A-IV (apoA-IV) is a lipid-binding protein, which is primarily synthesized in the small intestine, packaged into chylomicrons, and secreted into intestinal lymph during fat absorption. In the circulation, apoA-IV is present on chylomicron remnants, high-density lipoproteins, and also in lipid-free form. ApoA-IV is involved in a myriad of physiological processes such as lipid absorption and metabolism, anti-atherosclerosis, platelet aggregation and thrombosis, glucose homeostasis, and food intake. ApoA-IV deficiency is associated with atherosclerosis and diabetes, which renders it as a potential therapeutic target for treatment of these diseases. While much has been learned about the physiological functions of apoA-IV using rodent models, the action of apoA-IV at the cellular and molecular levels is less understood, let alone apoA-IV-interacting partners. In this review, we will summarize the findings on the molecular function of apoA-IV and apoA-IV-interacting proteins. The information will shed light on the discovery of apoA-IV receptors and the understanding of the molecular mechanism underlying its mode of action.

Background Liver vitamin A (VA) concentration is the gold standard for VA status, but is not routinely accessible. Adipose tissue VA concentrations, as retinol and retinyl esters, may be correlated to liver VA. α-VA (as α-retinol) is a cleavage product of α-carotene that traces postprandial VA distribution to tissues but cannot recirculate from hepatic stores, providing insight into tissue VA sources. Objective We performed a secondary analysis of VA and α-VA in Mongolian gerbil liver and adipose to determine the suitability of adipose tissue VA as a biomarker of VA status. Methods Gerbils (n = 186) consumed feeds containing 0–15.9 μg (0–55.6 nmol) retinol activity equivalents/g as preformed VA and/or provitamin A carotenoids for 36–62 d in 3 studies. Body fat percentage was determined in the final study by MRI. Serum and liver retinol, α-retinol, and retinyl esters were extracted and analyzed by HPLC or ultra-performance LC (UPLC). Epididymal and retroperitoneal adipose tissue retinol and α-retinol were determined by UPLC after homogenization, saponification, and extraction. Linear regression models with appropriate data transformations identified determinants of adipose VA concentrations. Results Liver VA did not predict serum retinol concentrations. After logarithmic transformation of adipose and liver values, liver VA positively predicted both adipose depots’ VA concentrations (P 0.7). Adding serum retinol or body fat percentage did not significantly increase the adjusted R2. In liver, α-VA concentration explained much of the variation of VA (P 0.7), but far less in epididymal and retroperitoneal adipose (P = 0.004 and 0.012, respectively, R2

Chylomicrons labeled in vivo with (14)C-oleic acid (primarily in triglycerides, providing a tracer for lipolysis) and (3)H-retinol (primarily in ester form, providing a tracer for the core lipids) were injected into rats. Radioactivity in tissues was followed at a series of times up to 40 min and the data were analyzed by compartmental modeling. For heart-like tissues it was necessary to allow the chylomicrons to enter into a compartment where lipolysis is rapid and then transfer to a second compartment where lipolysis is slower. The particles remained in these compartments for minutes and when they returned to blood they had reduced affinity for binding in the tissue. In contrast, the data for liver could readily be fitted with a single compartment for native and lipolyzed chylomicrons in blood, and there was no need for a pathway back to blood. A composite model was built from the individual tissue models. This whole-body model could simultaneously fit all data for both fed and fasted rats and allowed estimation of fluxes and residence times in the four compartments; native and lipolyzed chylomicrons ("remnants") in blood, and particles in the tissue compartments where lipolysis is rapid and slow, respectively.

Blood levels of triglyceride-rich lipoproteins (TRL) increase postprandially, and a delay in their clearance results in postprandial hyperlipidemia, an important risk factor in atherosclerosis development. Atherosclerosis is a multifactorial inflammatory disease, and its initiation involves endothelial dysfunction, invasion of the artery wall by leukocytes and subsequent formation of foam cells. TRL are implicated in several of these inflammatory processes, including the formation of damaging free radicals, leukocyte activation, endothelial dysfunction and foam cell formation. Recent studies have provided insights into the mechanisms of uptake and the signal transduction pathways mediating the interactions of TRL with leukocytes and vascular cells, and how they are modified by dietary lipids. Multiple receptor and non-receptor mediated pathways function in macrophage uptake of TRL. TRL also induce expression of adhesion molecules, cyclooxygenase-2 and heme-oxygenase-1 in endothelial cells, and activate intracellular signaling pathways involving mitogen-activated protein kinases, NF-κB and Nrf2. Many of these effects are strongly influenced by dietary components carried in TRL. There is extensive evidence indicating that raised postprandial TRL levels are a risk factor for atherosclerosis, but the molecular mechanisms involved are only now becoming appreciated. Here, we review current understanding of the mechanisms by which TRL influence vascular cell function.

Acute pancreatitis is a potentially life-threatening complication of severe hypertriglyceridemia. In some cases, inborn errors of metabolism such as lipoprotein lipase deficiency, apoprotein C-II deficiency, and familial hypertriglyceridemia have been reported as causes of severe hypertriglyceridemia. More often, severe hypertriglyceridemia describes various clinical conditions characterized by high plasma levels of triglycerides (>1000 mg/dL), chylomicron remnants, or intermediate density lipoprotein like particles, and/or chylomicrons. International guidelines on the management of acute pancreatitis are currently available. Standard therapeutic measures are based on the use of lipid-lowering agents (fenofibrate, gemfibrozil, niacin, Ω-3 fatty acids), low molecular weight heparin, and insulin in diabetic patients. However, when standard medical therapies have failed, non-pharmacological approaches based upon the removal of triglycerides with therapeutic plasma exchange can also provide benefit to patients with severe hypertriglyceridemia and acute pancreatitis. Plasma exchange could be very helpful in reducing triglycerides levels during the acute phase of hyperlipidemic pancreatitis, and in the prevention of recurrence. The current evidence on management of acute pancreatitis and severe hypertriglyceridemia, focusing on symptoms, treatment and potential complications is reviewed herein.

The hepatic removal of triglyceride-rich chylomicrons during the postprandial phase represents an important step towards determining the bioavailability of dietary lipids amongst the peripheral tissues. Indeed, elevated postprandial lipemia is often associated with obesity and increased risk of coronary heart disease. The milk protein, lactoferrin, has been shown to inhibit hepatic chylomicron remnant removal by the liver, resulting in increased postprandial lipemia. Despite numerous studies on potential targets for lactoferrin, the molecular mechanisms underlying the effect of lactoferrin remain unclear. We recently demonstrated that the lipolysis stimulated lipoprotein receptor (LSR) contributes to the removal of triglyceride-rich lipoproteins during the postprandial phase. Here, we report that while lactoferrin does not have any significant effect on LSR protein levels in mouse Hepa1–6 cells, this protein colocalizes with LSR in cells but only in the presence of oleate, which is needed to obtain LSR in its active form as lipoprotein receptor. Ligand blotting using purified LSR revealed that lactoferrin binds directly to the receptor in the presence of oleate and prevents the binding of triglyceride-rich lipoproteins. Both C- and N-lobes of lactoferrin as well as a mixture of peptides derived from its hydrolysis retained the ability to bind LSR in its active form. We propose then that the elevated postprandial lipemia observed upon lactoferrin treatment in vivo is mediated in part by its direct interaction with free fatty acid activated LSR, thus preventing clearance of chylomicrons and their remnants through the LSR pathway. Structured digital abstract • Lsr and Lsr bind by comigration in gel electrophoresis (View interaction) • Lsr binds to Lf by filter binding (View interaction) • Lf and Lsr colocalize by fluorescence microscopy (View interaction) • Lsr physically interacts with VLDL by filter binding (View interaction)

Die diabetische Dyslipidamie stellt bei Menschen mit Typ-2-Diabetes einen wichtigen kardiovaskularen Risikofaktor dar. Verantwortlich fur die Veranderungen im Lipidstoffwechsel ist insbesondere die Insulinresistenz, die die exzessive Bildung von grosen, triglyzeridreichen Very-low-density-Lipoprotein(VLDL)-1-Partikeln und somit die Hypertriglyzeridamie begunstigt. Die erhohten VLDL-Plasma-Spiegel entstehen zum einem durch vermehrte Produktion infolge des gesteigerten Zuflusses freier Fettsauren zur Leber und zum anderen durch verminderten Abbau infolge von Insulinresistenz und niedrigem Adiponektinplasmaspiegel. Eine Ansammlung triglyzeridreicher Lipoproteine fuhrt zur vermehrten Anzahl kleiner, dichter Low-density Lipoproteins („small-dense-LDL“, sdLDL) und verringerter Konzentration der Cholesterin rucktransportierenden High-density-Lipoprotein(HDL)-Partikel. Durch das Cholesterinestertransferprotein (CETP) wird der Austausch von Triglyzeriden der VLDL oder Chylomikronen gegen Cholesterinester der LDL- bzw. HDL-Partikel vermittelt. Durch Hydrolyse der triglyzeridreichen LDL bzw. HDL entsteht schlieslich die atherogene Komposition aus sdLDL und kleineren, dysfunktionalen HDL-Partikeln, die rasch abgebaut werden.