Clearance Of Remnants Research Articles

Dyslipidemia in chronic kidney disease: Causes and consequences

Cardiovascular risk increases with each decrement in renal function. Abnormalities in plasma lipoprotein composition among patients with end-stage renal disease represent a change both in lipoprotein level and structure. Low-density lipoprotein (LDL) cholesterol is not increased and LDL level is not strongly correlated with outcome. In contrast, high-density lipoprotein (HDL) levels are decreased and are inversely associated with cardiovascular risk. HDL is decreased because of an increased rate of catabolism associated with a predominance of small dense HDL. HDL fails to mature normally as a result of decreased lecithin cholesterol ester (CE) transfer protein (lecithin:cholesterol acyltransferase), leaving CE poor, triglyceride (TG) rich HDL3, and pre β HDL. Chronic kidney disease (CKD) also causes insulin resistance, and this may also contribute to low HDL levels. Plasma TG levels are increased and TGs are found in an expanded intermediate density lipoprotein (IDL) pool. These are composed of chylomicron and very low-density lipoprotein remnants resulting from delayed lipolysis on the endothelium and impaired hepatic uptake. IDL in contrast to LDL is associated with vascular disease in dialysis patients. Lipoprotein (a) (Lp (a)) levels are also increased. In patients without renal disease. The concentration of Lp (a) is inversely associated with the size of the apolipoprotein (a) isoform inherited; Lp (a) levels are increased in patients with kidney disease as a consequence of increased concentrations, primarily of the high molecular weight isoform. Lp (a) levels are also associated with cardiovascular outcome among dialysis patients.

Heritability and genetic loci of fatty liver in familial combined hyperlipidemia

VLDL overproduction, a process that is driven by an excess amount of hepatic fat, is a well-documented feature of familial combined hyperlipidemia (FCHL). The aims of this study were to investigate whether fatty liver, measured with ultrasound and as plasma alanine aminotransferase (ALT) levels, develops against a genetic background in FCHL and to identify chromosomal loci that are linked to these traits. In total, 157 FCHL family members and 20 spouses participated in this study. Radiological evidence of fatty liver was more prevalent not only in FCHL probands (40%) but also in their relatives (35%) compared with spouses (15%) (P < 0.05). Heritability calculations revealed that 20-36% of the variability in ALT levels could be attributed to genetic factors. Nonparametric quantitative trait locus (QTL) analysis revealed three significant (P < 0.001) loci with either the ultrasound or the ALT trait in the male sample: 1q42.3, 7p12-21, and 22p13-q11; none was found in the female sample or the entire group. Of these QTLs, the 7p region was consistent over time, because reanalysis with ALT levels that were determined during a visit 5 years earlier yielded similar results. This study shows that fatty liver is a heritable aspect of FCHL. Replication of particularly the 7p region is awaited.

Regulation of fatty acid transport and storage: influence of acylation-stimulating protein

Postprandial lipemia and fatty acid fluxes occur several times daily, resulting in very efficient absorption of dietary fat and redistribution to various tissues. Absorbed dietary lipids are incorporated into chylomicrons to distribute triglycerides either for storage in adipose tissue or for immediate use in muscle. Commonly, the dietary sources of fat exceed the actual needs and the tissues are faced with dealing with the excess. Under these circumstances, the removal process of dietary triglycerides and fatty acids becomes overloaded, resulting in excessive postprandial lipemia and accumulation of chylomicrons, remnant particles and non-esterified fatty acids. These particles are associated with disruptions in lipoprotein metabolism and changes in inflammatory factors, thus their association with cardiovascular disease, metabolic syndrome and diabetes is not surprising. Dietary factors, not just fat, influence postprandial fluxes. This leads to the question: do we need a standardized fat tolerance test? The recognition of the factors influencing postprandial lipemia and fatty acid uptake and clearance is constantly increasing. Numerous proteins, transporters, enzymes and hormones have been shown to affect fatty acid flux at the level of absorption, peripheral uptake and hepatic remnant clearance. This summary targets fatty acid fluxes, with a focus on acylation-stimulating protein. Keywords: C3adesArg; lipoprotein lipase; postprandial; triglyceride

Apolipoprotein A5 S19W May Play a Role in Dysbetalipoproteinemia in Patients with the Apo E2/E2 Genotype

Apolipoprotein (apo) E is one of the constituents of triglyceride-rich lipoproteins (chylomicrons and VLDL). Its interaction with the LDL receptor (LDLR), LDL-receptor related protein (LRP), and VLDL receptor permits clearance of triglyceride-rich lipoprotein remnants. The 3 common isoforms of the apo E protein, apo E2, apo E3, and apo E4, differ in their ability to bind lipoprotein receptors. Apo E3 is the most common isoform (frequency 75%). Apo E2 and apo E4 result from nucleotide substitutions affecting amino acid residues 158 and 112, respectively. Homozygosity for apo E2 is the cause of familial dysbetalipoproteinemia (Fdisβ), an autosomal, recessively transmitted disease in which reduced catabolism leads to dyslipemic phenotype type III, a characteristic accumulation of chylomicrons and VLDL remnants. Because only a small proportion (10%–20%) of persons with apo E2/E2 develop the dysbetalipoproteinemic phenotype, the clinical expression of this …

Accelerated Lipid Absorption in Mice Overexpressing Intestinal SR-BI

Dietary cholesterol absorption contributes to a large part of the circulating cholesterol. However, the mechanism of sterol intestinal uptake is not clearly elucidated. Scavenger receptor class B type I (SR-BI), major component in the control of cholesterol homeostasis, is expressed in the intestine, but its role in this organ remains unclear. We have generated transgenic mice overexpressing SR-BI primarily in the intestine by using the mouse SR-BI gene under the control of intestinal specific "apoC-III enhancer coupled with apoA-IV promoter." We found SR-BI overexpression with respect to the natural protein along the intestine and at the top of the villosities. After a meal containing [(14)C]cholesterol and [(3)H]triolein, SR-BI transgenic mice presented a rise in intestinal absorption of both lipids that was not due to a defect in chylomicron clearance nor to a change in the bile flow or the bile acid content. Nevertheless, SR-BI transgenic mice showed a decrease of total cholesterol but an increase of triglyceride content in plasma without any change in the high density lipoprotein apoA-I level. Thus, we described for the first time a functional role in vivo for SR-BI in cholesterol but also in triglyceride intestinal absorption.

Apolipoprotein CI causes hypertriglyceridemia independent of the very-low-density lipoprotein receptor and apolipoprotein CIII in mice

We have recently shown that the predominant hypertriglyceridemia in human apolipoprotein C1 ( APOC1) transgenic mice is mainly explained by apoCI-mediated inhibition of the lipoprotein lipase (LPL)-dependent triglyceride (TG)-hydrolysis pathway. Since the very-low-density lipoprotein receptor (VLDLr) and apoCIII are potent modifiers of LPL activity, our current aim was to study whether the lipolysis-inhibiting action of apoCI would be dependent on the presence of the VLDLr and apoCIII in vivo. Hereto, we employed liver-specific expression of human apoCI by using a novel recombinant adenovirus (Ad APOC1). In wild-type mice, moderate apoCI expression leading to plasma human apoCI levels of 12–33 mg/dl dose-dependently and specifically increased plasma TG (up to 6.6-fold, P < 0.001), yielding the same hypertriglyceridemic phenotype as observed in human APOC1 transgenic mice. Ad APOC1 still increased plasma TG in vldlr −/− mice (4.1-fold, P < 0.001) and in apoc3 −/− mice (6.8-fold, P < 0.001) that were also deficient for the low-density lipoprotein receptor (LDLr) and LDLr-related protein (LRP) or apoE, respectively. Thus, irrespective of receptor-mediated remnant clearance by the liver, liver-specific expression of human apoCI causes hypertriglyceridemia in the absence of the VLDLr and apoCIII. We conclude that apoCI is a powerful and direct inhibitor of LPL activity independent of the VLDLr and apoCIII.

We-P13:347 Lower waist circumference threshold for metabolic syndrome in a Malay Asian population

Physiological levels of wild-type (wt) apolipoprotein E (apoE) in plasma mediate the clearance of cholesterol-rich atherogenic lipoprotein remnants while higher than normal plasma apoE concentrations fail to do so and trigger hypertriglyceridemia. This property of wt apoE reduces significantly its therapeutic value as a lead biological for the treatment of dyslipidemia. Recently, we reported the generation of a recombinant apoE variant, apoE4 [L261A, W264A, F265A, L268A, V269A] (apoE4mut1) with improved biological functions. Specifically, in apoE-deficient (apoE−/−) mice this variant can normalize high plasma cholesterol levels without triggering hypertriglyceridemia, even at supraphysiological levels of expression. In the present study we performed pharmacodynamic and pharmacokinetic analysis of apoE4mut1 in experimental mice. Using adenovirus-mediated gene transfer in LDL receptor deficient (LDLr−/−) mice, we show that the cholesterol lowering potential of apoE4mut1 is dependent on the expression of a functional classical LDLr. Bolus infusion of apoE4mut1-containing proteoliposomes in apoE−/− mice fed western-type diet for 6 weeks indicated that exogenously synthesized apoE4mut1 maintains intact its ability to normalize the high cholesterol levels of these mice with a maximum pharmacological effect obtained at 10 h post-treatment. Interestingly, plasma cholesterol levels remained significantly reduced up to 24 h following intravenous administration of apoE4mut1 proteoliposomes. Measurements of plasma apoE levels indicated that apoE4mut1 in the form of proteoliposomes used in the study has a half-life of 15.8 h. Our data suggest that purified apoE4mut1 may be an attractive new candidate for the acute correction of hypercholesterolemia in subjects expressing functional LDL receptor.

HIV Protease Inhibitors and Hyperlipidemia

Treatment with a combination of highly active antiretroviral agents considerably reduces the morbidity and mortality of human immunodeficiency virus (HIV) infection.1 Although the clinical benefits are considerable, the protease inhibitors contained in these antiretroviral regimens produce a lipodystrophy syndrome characterized by changes in body fat distribution, hyperlipidemia, and insulin resistance.2 The hyperlipidemia is attributable to increases in very low density lipoproteins (VLDL) and intermediate density lipoproteins (IDL), and it can produce serious cardiovascular complications including endothelial dysfunction and atherosclerosis.3,4 See page 124 A number of studies indicate that the hyperlipidemia produced by HIV protease inhibitors is attributable to an increase in VLDL production. Data from HIV positive patients indicate that excessive free fatty acid (FFA) mobilization occurs because of insulin resistance in the adipose tissue,5 resulting in increased VLDL–triglyceride production and apoB synthesis. Likewise, studies in C57BL/6 mice treated with HIV protease inhibitors demonstrate increased VLDL-triglyceride production and apoB synthesis,6 and increased triglyceride synthesis also was observed in HepG2 cells and AKR/J mice incubated with protease inhibitors.7 The hyperlipidemia in the mice was attributed to elevated fatty acid and cholesterol synthesis in the liver and adipose tissue caused by activation of sterol regulatory element binding protein (SREBP) 1 and 2,8 whereas studies in cultured liver cells suggest that the mechanism involves decreased degradation of nascent apoB attributable to inhibition of the 20S proteasome.9 There is also evidence that HIV protease inhibitors do not reduce the clearance of either VLDL or triglyceride-rich lipoprotein remnants,5,6,10 providing additional support for a mechanism based on increased VLDL production. However, other studies indicate that impaired lipoprotein …

Combined hyperlipidemia/hyperalphalipoproteinemia associated with premature spontaneous atherosclerosis in mice lacking hepatic lipase and low density lipoprotein receptor

Background and methods Hepatic lipase (HL) is an enzyme which hydrolyzes triglycerides from plasma lipoproteins and thus takes part in the metabolism of triglyceride-rich lipoprotein remnants and high density lipoproteins. The search described here concentrated on the description of the double invalidation of the HL and LDL receptor genes in mice in order to better understand the possible role of HL in combined hyperlipidemia/hyperalphalipoproteinemia and development of atherosclerosis. Results We show here that mice lacking both endogenous HL and LDL receptor (HL−/−:LDLR−/−) dramatically increased their plasma triglyceride-rich lipoproteins and their remnants as a consequence of reduced liver uptake. This result is strenghthened by the fact that HL−/−:LDLR−/− were found to overexpress LRP, LSR, and apoE genes. Interestingly, HL−/−:LDLR−/− mice showed premature spontaneous atherosclerosis and aortic lesions from 1-year-old animals were two-fold larger than those of LDLR−/− single mutants. We confirmed that HL−/− and wild-type mice did not develop atherosclerosis lesion even 1 year after birth. Conclusions Analysis of this double HL–LDLR knockout mouse model provides in vivo evidence that HL has a major role in the clearance of TRL remnants when LDLR is deficient and in the reduction of the development of atherosclerosis.

Heterogeneous Nuclear Ribonucleoprotein P2 Is an Autoantibody Target in Mice Deficient for Mer, Axl, and Tyro3 Receptor Tyrosine Kinases

Deficiencies in clearance of apoptotic cells predispose to the development of autoimmune disease. This is evident in mice lacking the receptor tyrosine kinases Tyro3, Axl, and Mer. Deficient mice exhibit an increased abundance of apoptotic cells in tissues and manifest diverse autoimmune conditions. To test these mice for the presence of autoantibodies to apoptotic cells, we generated spontaneous splenic B cell hybridomas and used a novel microscopy screen to detect Ab binding to apoptotic Jurkat cells. From hybridomas secreting IgG Abs reactive with apoptotic cells, we selected one that recreated the major serum specificity for apoptotic cells. The Ab LHC7.15 bound to an Ag that is differentially distributed between the nucleus and the cytoplasm in live and apoptotic cells. In late apoptotic cells, the Ag coalesces into aggregates that bleb from the cell surface. Immunopurification of the Ag, followed by mass spectrometry, identified a protein of 69 kDa whose partial sequence matched heterogeneous nuclear ribonucleoprotein P2. This multifunctional protein binds DNA, RNA, and several known ribonucleoprotein autoantigens. Our observations indicate that a ribonucleoprotein complex, formed and translocated to the cell surface in apoptosis, represents a potent stimulus for breaking tolerance and inducing systemic autoimmunity in mice with defective clearance of cell remnants.

Direct Interaction of Dietary Lipids Carried in Chylomicron Remnants with Cells of the Artery Wall: Implications for Atherosclerosis Development

The development of atherosclerotic lesions in the artery wall is a complex process involving the endothelium, lipid engorged macrophages (foam cells) and smooth muscle cells. In recent years it has become clear that chylomicron remnants, the lipoproteins which carry lipids of dietary origin in the blood, are strongly atherogenic, and there is increasing evidence to indicate that this is due to direct interaction of the remnant particles with cells of the artery wall. Chylomicron remnants have been demonstrated to inhibit endothelium dependent vasorelaxation and to activate signal transduction pathways associated with inflammation in cultured endothelial cells. They have also been shown to be taken up by smooth muscle cells and macrophages, and to cause the extensive lipid accumulation associated with foam cell formation, as well as influencing the expression of key genes regulating macrophage lipid uptake and metabolism. Furthermore, oxidative modification of the remnant particles is not required for many of these effects. Chylomicron remnants, therefore, have multiple direct effects on three major cell types of the arterial wall which are likely to promote the development of atherosclerotic lesions. These effects may be modulated by various lipids carried by the particles, including the type of fat (saturated or unsaturated or oxidised fat), micronutrients such as vitamins and carotenoids which have antioxidant properties, and orally administered lipophilic drugs. Delayed clearance of chylomicron remnants from the blood occurs in a number of dyslipidemias associated with premature atherosclerosis development, and the potentially atherogenic effects of the particles would clearly be enhanced in these circumstances. Thus, elucidation of the mechanisms involved will aid in the identification of new drug targets which may be particularly useful for these conditions.

Lipoprotein metabolism of pregnant women is associated with both their genetic polymorphisms and those of their newborn children

To explore whether the placenta contributes to the lipoprotein metabolism of pregnant women, we took advantage of the fact that placental proteins are encoded from the fetal genome and examined the associations between lipids of 525 pregnant women and the presence, in their newborns, of genetic polymorphisms of LPL and apolipoprotein E (APOE), two genes expressed in placenta. After adjustment for maternal polymorphisms, newborn LPL*S447X was associated with lower triglycerides (-21 +/- 9 mg/dl), lower LDL-cholesterol (LDL-C; -12 +/- 5 mg/dl), lower apoB (-14 +/- 4 mg/dl), higher HDL-C (5 +/- 2 mg/dl), and higher apoA-I (9 +/- 4 mg/dl) in their mothers; newborn LPL*N291S was associated with higher maternal triglycerides (114 +/- 31 mg/dl); and newborn APOE*E2 (compared to E3E3) was associated with higher maternal LDL-C (14 +/- 6 mg/dl) and higher maternal apoB (14 +/- 5 mg/dl). These associations (all P < 0.05) were independent of polymorphisms carried by the mothers and of lipid concentrations in newborns and were similar in amplitude to the associations between maternal polymorphisms and maternal lipids. Such findings support the active role of placental LPL and APOE in the metabolism of maternal lipoproteins and suggest that fetal genes may modulate the risk for problems related to maternal dyslipidemia (preeclampsia, pancreatitis, and future cardiovascular disease).

SR-BI-mediated selective lipid uptake segregates apoA-I and apoA-II catabolism

The HDL receptor scavenger receptor class B type I (SR-BI) binds HDL and mediates the selective uptake of cholesteryl ester. We previously showed that remnants, produced when human HDL(2) is catabolized in mice overexpressing SR-BI, become incrementally smaller, ultimately consisting of small alpha-migrating particles, distinct from pre-beta HDL. When mixed with mouse plasma, some remnant particles rapidly increase in size by associating with HDL without the mediation of cholesteryl ester transfer protein, LCAT, or phospholipid transfer protein. Here, we show that processing of HDL(2) by SR-BI-overexpressing mice resulted in the preferential loss of apolipoprotein A-II (apoA-II). Short-term processing generated two distinct, small alpha-migrating particles. One particle (8.0 nm diameter) contained apoA-I and apoA-II; the other particle (7.7 nm diameter) contained only apoA-I. With extensive SR-BI processing, only the 7.7 nm particle remained. Only the 8.0 nm remnants were able to associate with HDL. Compared with HDL(2), this remnant was more readily taken up by the liver than by the kidney. We conclude that SR-BI-generated HDL remnants consist of particles with or without apoA-II and that only those containing apoA-II associate with HDL in an enzyme-independent manner. Extensive SR-BI processing generates small apoA-II-depleted particles unable to reassociate with HDL and readily taken up by the liver. This represents a pathway by which apoA-I and apoA-II catabolism are segregated.

Triacylglycerol Fatty Acid Positional Distribution and Postprandial Lipid Metabolism

Triacylglycerol (TAG) structure affects the biochemical properties of fat. According to studies with animals and infants, absorption of palmitic and stearic acids is inferior from the stereospecifically numbered (sn) positions sn-1 and sn-3 compared with from the sn-2 position of TAGs, and saturated fatty acids in the sn-2 position, delay the clearance of chylomicron remnants. Medium chain fatty acids are transported both in lymph and in portal blood, lymphatic absorption being more efficient from the sn-2 position.Recently, new information has arisen on the variation in TAG composition within the postprandial period and on differences in the TAG structure-dependent formation and clearance of chylomicron and very low density lipoprotein TAGs. This article reviews the metabolism of TAG fatty acids in different sn positions.

An Apolipoprotein(a) Peptide Delays Chylomicron Remnant Clearance and Increases Plasma Remnant Lipoproteins and Atherosclerosis In Vivo

Humans with high expression of apolipoprotein(a) [apo(a)] and high plasma levels of lipoprotein(a) [Lp(a)] are at increased risk for atherosclerosis, but the mechanism is not known. We have previously shown that the KIV(5-8) domain of apo(a) has unique cell-surface binding properties, and naturally occurring fragments of apo(a) encompassing this domain are thought to be atherogenic in humans. To investigate the effect of KIV(5-8) on lipoprotein metabolism and atherosclerosis in vivo, we created several independent lines of liver-targeted KIV(5-8) transgenic mice. The transgenic mice have plasma apo(a) peptide concentrations that are similar to Lp(a) concentrations in humans at risk for coronary artery disease. Remarkably, the transgenic mice had a 2- to 4-fold increase in cholesterol-rich remnant lipoproteins (RLPs) when fed a cholesterol-rich diet, and a 5- to 20-fold increase in atherosclerosis lesion area in the aortic root. Using an in vivo clearance study, we found only slight differences in the triglyceride and apolipoprotein B secretion rates between the 2 groups of mice, suggesting an RLP clearance defect. Using an isolated perfused mouse liver system, we showed that transgenic livers had a slower rate of RLP removal, which was retarded further when KIV(5-8), full-length apo(a), or Lp(a) were added to the perfusate. An apo(a) peptide that does not interact with cells, K(IV2)3, did not retard RLP removal, and low-density lipoprotein (LDL) had a much smaller effect than Lp(a). We propose that high levels of apo(a)/Lp(a), perhaps acting via a specific cell-surface binding domain, inhibit hepatic clearance of remnants, leading to high plasma levels of RLPs and markedly enhanced atherosclerosis. We speculate that the KIV(5-8) region of apo(a) competes with one or more receptors for remnant clearance in the liver and that this process may represent one mechanism accounting for increased atherosclerosis in humans with high secretion levels of apo(a).

Growth Hormone Receptor Is a Target for Presenilin-dependent γ-Secretase Cleavage

Growth hormone receptor (GHR) is a cytokine receptor superfamily member that binds growth hormone (GH) via its extracellular domain and signals via interaction of its cytoplasmic domain with JAK2 and other signaling molecules. GHR is a target for inducible metalloprotease-mediated cleavage in its perimembranous extracellular domain, a process that liberates the extracellular domain as the soluble GH-binding protein and leaves behind a cell-associated GHR remnant protein containing the transmembrane and cytoplasmic domains. GHR metalloproteolysis can be catalyzed by tumor necrosis factor-alpha-converting enzyme (ADAM-17) and is associated with down-modulation of GH signaling. We now study the fate of the GHR remnant protein. By anti-GHR cytoplasmic domain immunoblotting, we observed that the remnant induced in response to phorbol ester or platelet-derived growth factor has a reliable pattern of appearance and disappearance in both mouse preadipocytes endogenously expressing GHR and transfected fibroblasts expressing rabbit GHR. Lactacystin, a specific proteasome inhibitor, did not appreciably change the time course of remnant appearance or clearance but allowed detection of the GHR stub, a receptor fragment slightly smaller than the remnant but containing the C terminus of the remnant (receptor cytoplasmic domain). In contrast, MG132, another (less specific) proteasome inhibitor, strongly inhibited remnant clearance and prevented stub appearance. Inhibitors of gamma-secretase, an aspartyl protease, also prevented the appearance of the stub, even in the presence of lactacystin, and concomitantly inhibited remnant clearance in the same fashion as MG132. In addition, mouse embryonic fibroblasts derived from presenilin 1 and 2 (PS1/2) knockouts recapitulated the gamma-secretase inhibitor studies, as compared with their littermate controls (PS1/2 wild type). Confocal microscopy indicated that the GHR cytoplasmic domain became localized to the nucleus in a fashion dependent on PS1/2 activity. These data indicate that the GHR is subject to sequential proteolysis by metalloprotease and gamma-secretase activities and may suggest GH-independent roles for the GHR.

Screening for Dysbetalipoproteinemia by Plasma Cholesterol and Apolipoprotein B Concentrations

Dysbetalipoproteinemia (type III hyperlipidemia) is a highly atherogenic mixed hyperlipidemia characterized by the accumulation of remnants of triglyceride-rich lipoproteins (chylomicrons and VLDL) (1). The binding of these remnants to hepatic lipoprotein receptors is mediated by apolipoprotein E (apoE). At the apoE gene locus, there are three common alleles: e2, e3, and e4 (2). ApoE2 binds poorly to hepatic lipoprotein receptors, leading to impaired remnant clearance. Consequently, remnants become enriched with cholesterol and migrate abnormally on electrophoresis. More than 90% of dysbetalipoproteinemic patients are homozygous for apoE2, but only a minority (1 in 20) of apoE2 homozygotes will be overtly hyperlipidemic. Remnant accumulation sufficient to cause hyperlipidemia usually occurs only when a second metabolic hit increases lipoprotein production (e.g., diabetes) or further decreases remnant clearance (e.g., hypothyroidism) (3). Dysbetalipoproteinemia is highly atherogenic but responds well to lifestyle changes and lipid-modifying medications. Genetic counseling is important, particularly in areas where there is a high local prevalence of autosomal dominant apoE mutations (4)(5). Dysbetalipoproteinemia is often suspected when both the total cholesterol (TC) and triglyceride (TG) concentrations are increased and the TC/TG molar ratio approximates 2:1. Clinically, pathognomonic palmar crease xanthomata are found in only ∼20% of patients (4)(6)(7). There are no simple diagnostic tests for dysbetalipoproteinemia. Diagnostic tests are based either on the demonstration of remnant accumulation or characterization of apoE. Electrophoretic techniques include serum agarose gel electrophoresis, but a broad β band is found in less than one half of patients (8)(9). Ultracentrifugation is required to demonstrate β-migrating VLDL. Nondenaturing polyacrylamide gradient gel electrophoresis is an effective screening technique (9). Cholesterol-enriched VLDL is diagnostic of dysbetalipoproteinemia (10)(11)(12), but sample preparation requires ultracentrifugation, which is not available in routine diagnostic laboratories. ApoE phenotyping requires isoelectric focusing, and genotyping is …

The apolipoprotein CI content of triglyceride-rich lipoproteins independently predicts early atherosclerosis in healthy middle-aged men

In this study, we examined the apolipoprotein (apo) CI content of triglyceride-rich lipoproteins (TRLs) in relation to established coronary heart disease (CHD) risk factors and early atherosclerosis. In Western society, the postprandial state constitutes a nearly constant stress on the vasculature and the metabolism of lipoproteins. Delayed clearance of postprandial TRL remnants has repeatedly been associated with premature CHD and may include the enrichment of these remnants with apoCI. We examined 72 healthy 50-year-old men with an apoE3/E3 genotype who had undergone an oral fat load test and B-mode ultrasound examination of the intima-media thickness (IMT) of the common carotid artery. In the fasting state, plasma, very-low-density lipoprotein (VLDL), and low-density lipoprotein cholesterol, proinsulin, and apoB100-containing intermediate density lipoprotein levels were related to IMT (p < 0.05). In the postprandial state, IMT was related to triglycerides at 2 h (p < 0.01), large VLDL concentration at 3 h (p < 0.05), the apoCI plasma and TRL concentrations at 6 h (p < 0.05, p < 0.05), and the apoCI content of TRLs at 6 h (p < 0.002). Multivariate analysis revealed that the apoCI content of TRLs at 6 h (p < 0.0001), plasma triglyceride concentrations at 2 h (p < 0.006), and fasting plasma cholesterol concentration (p < 0.05) independently predicted IMT. In addition, the apoCI content of postprandial TRLs correlated strongly with the cholesterol content (r = 0.64, p < 0.0001). Our results indicate that the apoCI content of postprandial TRLs is a novel independent risk factor for early atherosclerosis in normolipidemic healthy middle-aged men with possible implication for the enrichment of TRL remnant lipoproteins with cholesterol.

Down-regulation of hepatic LDL receptor-related protein (LRP) in chronic renal failure

Chronic renal failure (CRF) is associated with premature atherosclerosis, impaired high-density lipoprotein (HDL)-mediated reverse cholesterol transport, depressed clearance, and elevated plasma concentrations of very low-density lipoprotein (VLDL), chylomicrons, and their atherogenic remnants. LDL receptor-related protein (LRP) is a member of the LDL receptor gene family that is heavily expressed in the liver, and mediates removal of at least 30 different ligands, including VLDL remnants (IDL) and chylomicron remnants. This study was conducted to test the hypothesis that the well-known defect in clearance of IDL and chylomicron remnants in CRF may be indicative of diminished hepatic LRP abundance. Hepatic tissue LRP mRNA abundance [reverse transcription-polymerase chain reaction (RT-PCR)] and protein abundance (Western blot analysis) were determined in rats 8 weeks after 5/6 nephrectomy (CRF group) or sham operation (control group). The CRF group exhibited hypertension, diminished creatinine clearance, increased plasma triglyceride concentration, and elevated total cholesterol-to-HDL cholesterol concentration ratio compared to the corresponding values found in the control group. This was associated with a significant down-regulation of hepatic LRP mRNA expression and immunodetectable LRP protein. CRF results in down-regulation of hepatic LRP. This abnormality can, at least in part, account for the previously documented elevation of plasma concentration and depressed clearance of chylomicron remnants and IDL in CRF.

High cholesterol absorption efficiency and rapid biliary secretion of chylomicron remnant cholesterol enhance cholelithogenesis in gallstone-susceptible mice

The study of chylomicron pathway through which it exerts its metabolic effects on biliary cholesterol secretion is crucial for understanding how high dietary cholesterol influences cholelithogenesis. We explored a relationship between cholesterol absorption efficiency and gallstone prevalence in 15 strains of inbred male mice and the metabolic fate of chylomicron and chylomicron remnant cholesterol in gallstone-susceptible C57L and gallstone-resistant AKR mice. Our results show a positive and significant ( P<0.0001, r=0.87) correlation between percent cholesterol absorption and gallstone prevalence rates. Compared with AKR mice, C57L mice displayed significantly greater absorption of cholesterol from the small intestine, more rapid plasma clearance of chylomicrons and chylomicron remnants, higher activities of lipoprotein lipase and hepatic lipase, greater hepatic uptake of chylomicron remnants, and faster secretion of chylomicron remnant cholesterol from plasma into bile. All of these increased susceptibility to cholesterol gallstone formation in C57L mice. We conclude that genetic variations in cholesterol absorption efficiency are associated with cholesterol gallstone formation in inbred mice and cholesterol absorbed from the intestine provides an important source for biliary hypersecretion. Differential metabolism of the chylomicron remnant cholesterol between C57L and AKR mice clearly plays a crucial role in the formation of lithogenic bile and gallstones.