High-density Lipoprotein Maturation Research Articles

Relationship between apolipoprotein C-III concentrations and high-density lipoprotein subclass distribution

High-density lipoprotein (HDL) subclasses have different antiatherogenic potentials and functional properties. This work presents our findings and discussions on their metabolic implications on apolipoprotein (apo) C-III together with other apolipoprotein levels and HDL subclass distribution profile. Apolipoprotein A-I contents of plasma HDL subclasses were quantitated by 2-dimensional gel electrophoresis coupled with immunodetection in 511 subjects. Concentrations of triglycerides and of apo B-100, C-II, and C-III were higher, whereas those of HDL cholesterol were lower, for subjects in the highest tertile of apo C-III levels group, which presented a typical hypertriglyceridemic lipid profile. Subjects in the middle and highest tertile of apo C-III levels groups had increased pre β 1-HDL, HDL 3c, HDL 3b (only in the highest tertile of apo C-III group), and HDL 3a, but decreased HDL 2a and HDL 2b contents compared with subjects in the lowest tertile of apo C-III levels group. With the elevation of apo C-III together with apo C-II levels, contents of small-sized pre β 1-HDL increased successively and significantly; but those of large-sized HDL 2b reduced successively and significantly. With a rise in apo C-III and apo A-I levels, those of pre β 1-HDL increased significantly. Moreover, subjects with high apo A-I levels showed a substantial increase in HDL 2b; on the contrary, HDL 2b declined progressively and obviously for subjects in the low apo A-I levels with the elevation of apo C-III levels. Correlation analysis illustrated that apo C-III levels were positively associated with pre β 1-HDL, pre β 2-HDL, and HDL 3a. The particle size of HDL shifted toward smaller sizes with the increase of plasma apo C-III levels, and the shift was more remarkable when the elevation of apo C-III and apo C-II was simultaneous; and besides, higher apo A-I concentrations could modify the effect of apo C-III on HDL subclass distribution profile. Large-sized HDL 2b particles decreased greatly for hypertriglyceridemic subjects who were characterized by elevated apo C-III and C-II accompanied with significantly lower apo A-I, which, in turn, blocked the maturation of HDL.

High-Density Lipoprotein Transport Through Aortic Endothelial Cells Involves Scavenger Receptor BI and ATP-Binding Cassette Transporter G1

Cholesterol efflux from macrophage foam cells is a rate-limiting step in reverse cholesterol transport. In this process cholesterol acceptors like high-density lipoproteins (HDL) and apolipoprotein (apo)A-I must cross the endothelium to get access to the donor cells in the arterial intima. Previously, we have shown that apoA-I passes a monolayer of aortic endothelial cells (ECs) from the apical to the basolateral side by transcytosis, which is modulated by the ATP-binding cassette transporter (ABC)A1. Here, we analyzed the interaction of mature HDL with ECs. ECs bind HDL in a specific and saturable manner. Both cell surface biotinylation experiments and immunofluorescence microscopy of HDL recovered approximately 30% of the cell-associated HDL intracellularly. Cultivated on inserts ECs bind, internalize, and translocate HDL from the apical to the basolateral compartment in a specific and temperature-dependent manner. The size of the translocated particle was reduced, but its protein moiety remained intact. Using RNA interference, we investigated the impact of SR-BI, ABCA1, and ABCG1 on binding, internalization, and transcytosis of HDL by ECs. HDL binding was reduced by 50% and 30% after silencing of SR-BI and ABCG1, respectively, but not at all after diminishing ABCA1 expression. Knock down of SR-BI and, even more so, ABCG1 reduced HDL transcytosis but did not affect inulin permeability. Cosilencing of both proteins did not further reduce HDL binding, internalization, or transport. In conclusion, ECs transcytose HDL by mechanisms that involve either SR-BI or ABCG1 but not ABCA1.

Differential Stability of High-density Lipoprotein Subclasses: Effects of Particle Size and Protein Composition

High-density lipoproteins (HDLs) are complexes of proteins (mainly apoA-I and apoA-II) and lipids that remove cholesterol and prevent atherosclerosis. Understanding the distinct properties of the heterogeneous HDL population may aid the development of new diagnostic tools and therapies for atherosclerosis. Mature human HDLs form two major subclasses differing in particle diameter and metabolic properties, HDL 2 (large) and HDL 3 (small). These subclasses are comprised of HDL(A-I) containing only apoA-I, and HDL(A-I/A-II) containing apoA-I and apoA-II. ApoA-I is strongly cardioprotective, but the function of the smaller, more hydrophobic apoA-II is unclear. ApoA-II is thought to counteract the cardioprotective action of apoA-I by stabilizing HDL particles and inhibiting their remodeling. To test this notion, we performed the first kinetic stability study of human HDL subclasses. The results revealed that the stability of plasma spherical HDL decreases with increasing particle diameter; which may facilitate preferential cholesterol ester uptake from large lipid-loaded HDL 2. Surprisingly, size-matched plasma HDL(A-I/A-II) showed comparable or slightly lower stability than HDL(A-I); this is consistent with the destabilization of model discoidal HDL observed upon increasing the A-II to A-I ratio. These results clarify the roles of the particle size and protein composition in HDL remodeling, and help reconcile conflicting reports regarding the role of apoA-II in this remodeling.

Human Endothelial Cells of the Placental Barrier Efficiently Deliver Cholesterol to the Fetal Circulation via ABCA1 and ABCG1

Although maternal-fetal cholesterol transfer may serve to compensate for insufficient fetal cholesterol biosynthesis under pathological conditions, it may have detrimental consequences under conditions of maternal hypercholesterolemia leading to preatherosclerotic lesion development in fetal aortas. Maternal cholesterol may enter fetal circulation by traversing syncytiotrophoblast and endothelial layers of the placenta. We hypothesized that endothelial cells (ECs) of the fetoplacental vasculature display a high and tightly regulated capacity for cholesterol release. Using ECs isolated from human term placenta (HPECs), we investigated cholesterol release capacity and examined transporters involved in cholesterol efflux pathways controlled by liver-X-receptors (LXRs). HPECs demonstrated 2.5-fold higher cholesterol release to lipid-free apolipoprotein (apo)A-I than human umbilical vein ECs (HUVECs), whereas both cell types showed similar cholesterol efflux to high-density lipoproteins (HDLs). Interestingly, treatment of HPECs with LXR activators increased cholesterol efflux to both types of acceptors, whereas no such response could be observed for HUVECs. In line with enhanced cholesterol efflux, LXR activation in HPECs increased expression of ATP-binding cassette transporters ABCA1 and ABCG1, while not altering expression of ABCG4 and scavenger receptor class B type I (SR-BI). Inhibition of ABCA1 or silencing of ABCG1 decreased cholesterol efflux to apoA-I (-70%) and HDL(3) (-57%), respectively. Immunohistochemistry localized both transporters predominantly to the apical membranes of placental ECs in situ. Thus, ECs of human term placenta exhibit unique, efficient and LXR-regulated cholesterol efflux mechanisms. We propose a sequential pathway mediated by ABCA1 and ABCG1, respectively, by which HPECs participate in forming mature HDL in the fetal blood.

Influence of ApolipoproteinCII Concentrations on HDL Subclass Distribution

To demonstrate the interrelationship between plasma apolipoprotein(apo)CII concentrations and the pattern of high-density lipoprotein (HDL) subclass distribution. ApolipoproteinA-I contents of plasma HDL subclasses were quantified by 2-dimensional gel electrophoresis associated with immunodetection in 504 Chinese subjects. Compared with subjects in the lowest tertile of the apoCII group, the contents of prebeta(1)- HDL, HDL(3b), and HDL(3a) were significantly higher than HDL(2a) and HDL(2b) in subjects in the middle and highest tertiles of the apoCII group. Moreover, regardless of whether apoB100 increased, prebeta(1)-HDL contents increased, but HDL(2b) fell when apoCII rose while, at any apoCII levels, HDL(2b) rose with the elevation of apoA-I. Additionally, a reduction in prebeta(1)-HDL (from 131.9 to 90.6 mg/L) but an increase in HDL(2b) (from 269.1 to 382.7 mg/L) with a rise in the apoCIII/CIi value (between 0.8 and 5.6) were also observed. The particle size of HDL become smaller with the increase of apoCII levels, implying that the efficiency of reverse cholesterol transport (RCT) was impaired and blocked the maturation of HDL. ApoCII might be an independent factor affecting the distribution of HDL subclasses. Further, the apoCIII/CII ratio correlated with the size of HDL particles.

Impaired antioxidant activity of high-density lipoprotein in chronic kidney disease

Chronic kidney disease (CKD) is associated with accelerated atherosclerosis and increased mortality from cardiovascular disease. CKD results in oxidative stress, inflammation, and high-density lipoprotein (HDL) deficiency, which work in concert to promote atherosclerosis. Normal HDL confers protection against atherosclerosis by inhibiting the oxidation of lipids and lipoproteins and by retrieving surplus cholesterol and phospholipids from lipid-laden cells in the artery wall for disposal in the liver (reverse cholesterol transport). The plasma level of oxidized low-density lipoprotein (LDL) is increased, plasma HDL-cholesterol is reduced, and HDL maturation is impaired in CKD. This study was designed to examine the antioxidant properties of HDL in patients with CKD. In all, 32 stable hemodialysis-dependent patients and 13 age-matched controls were studied. HDL was isolated and used for determination of in vitro antioxidant activity. In addition, the plasma level of key components of HDL, namely paraoxonase (PON), glutathione peroxidase (GPX), platelet activating factor acetylhydrolase (PAF-AH), lecithin cholesterol acyltransferase (LCAT), and apolipoprotein A-I (ApoA-I), were measured. The end-stage renal disease (ESRD) patients exhibited significant reductions of HDL-cholesterol, ApoA-I (-41%), GPX (-50%), and LCAT (-60%) concentrations, and a decrease in PON (-30%) and GPX (-50%) activities. These results were accompanied by a marked reduction of antioxidant activity of HDL (-127%), which was unaffected by the hemodialysis procedure. Thus, in addition to diminished plasma HDL concentration, the composition and antioxidant activity of HDL are altered in CKD; these events can contribute to a heightened risk of atherosclerosis.

Metformin Increases HDL3–Cholesterol and Decreases Subcutaneous Truncal Fat in Nondiabetic Patients with HIV-Associated Lipodystrophy

The purpose of this study was to assess metformin effects on high-density lipoprotein (HDL) composition of patients with HIV-associated lipodystrophy (LDHIV). Twenty-four adult outpatients were enrolled to receive metformin (1700 mg/d) during 6 months, but 2 were lost to follow-up and 6 stopped the drug due to adverse events (gastrointestinal in 5, and excessive weight loss in 1). From the 16 subjects who completed the study, 69% were female. At baseline, 3 and 6 months, we assessed: weight, waist and hip circumferences, blood pressure, fasting glucose and insulin, homeostasis model assessment of insulin resistance (HOMA2-IR), lipids, and HDL subfractions by microultracentrifugation. At 0 and 6 months, body fat distribution was assessed by computed tomography (CT) scan (L4 and middle femur). Metformin use was associated with reduction of mean weight (-2.4Kg at 6 months; p < 0.001), body mass index, waist, waist-to-hip ratio and a marked decrease in blood pressure (p < 0.001). Subcutaneous (p = 0.01) and total abdominal fat (p = 0.002) were reduced, but no change was found in visceral or thigh fat. No difference was detected on plasma glucose, insulin, HOMA2-IR, cholesterol or triglycerides, except for an increase in HDL3-cholesterol (from 21 mg/dL to 24 mg/dL, p = 0.002) and a reduction of nascent HDL (the fraction of plasma HDL-cholesterol not associated to subfractions HDL2 or HDL3) (p = 0.008). Adverse effects were very common, but most were gastrointestinal and mild. Thus, metformin use in LDHIV increases HDL3-cholesterol (probably due to improved maturation of HDL) and decreases blood pressure, weight, waist, and subcutaneous truncal fat, making this an attractive option for preventing cardiovascular disease in this population.

The value of HDL genetics

To review studies on hereditary disorders of high-density lipoprotein (HDL) metabolism and studies on HDL genetics in mice, which have both provided valuable insight into the pathways of this intriguing lipoprotein and moreover revealed targets to raise HDLc to reduce atherosclerosis. To date, as many as 11 genes are considered key players in the synthesis, maturation, conversion and/or catabolism of HDL. Five of these genes have been identified in humans, APOA1, LCAT, ABCA1, LIPC, and CETP, whereas the other six genes have been identified in mice, SCARB1, ABCG1, ATPB5, PLTP, LIPG and APOM. Genetic association studies are as yet the best line of evidence of the roles of the 'murine genes' in human HDL pathways. In addition to recent genetic association studies, a third section describes exciting news on six newly proposed HDL genes VNN1, GALNT2, MMAB/MVK, CTalpha, BMP-1 and SIRT1. This review provides a summary of the current literature on the genetics of HDL. New information from this research area may assist us in obtaining a better understanding of HDL biology and identifying novel pharmacological targets.

Depletion of High‐density Lipoprotein and Appearance of Triglyceride‐rich Low‐density Lipoprotein in a Japanese Patient With FIC1 Deficiency Manifesting Benign Recurrent Intrahepatic Cholestasis

Lipoprotein metabolism in FIC1 deficiency due to ATP8B1 mutations has never been studied sufficiently. This study was performed to investigate the detailed lipoprotein metabolism in benign recurrent intrahepatic cholestasis (BRIC) caused by FIC1 deficiency. Lipoprotein profile and major lipoprotein regulators such as lecithin:cholesterol acyltransferase (LCAT), hepatic triglyceride lipase (HTGL), lipoprotein lipase, and cholesteryl ester transfer protein in a Japanese patient with BRIC were serially examined during a bout of cholestasis. Liver expression of farnesoid X receptor (FXR), which suppresses high-density lipoprotein (HDL) generation, was also examined. Hypercholesterolemia and lipoprotein X accumulation were never observed throughout this study. When the cholestasis was severe, triglyceride-rich low-density lipoprotein (LDL) accounted for most of the plasma lipoproteins whereas HDL was hardly detectable. Concurrently, activities of all regulators were decreased, together with decreases of the serum parameter for liver protein synthesis. In particular, suppressions of LCAT and HTGL activities were severe and greatly contributed to the appearance of triglyceride-rich LDL. As the cholestasis improved, this LDL gradually transformed into normal LDL with the recoveries of LCAT and HTGL activities. The activities of all regulators for the last 1 to 2 months were normal but HDL remained depleted. His liver showed low FXR expression compared with control livers. The present study showed an appearance of triglyceride-rich LDL due to suppressions of LCAT and HTGL activities and a depletion of HDL that is not able to be explained by lipoprotein regulators or FXR in our patient.

Molecular regulation of macrophage reverse cholesterol transport

Macrophage reverse cholesterol transport is one of the key mechanisms mediating the protective effects of high-density lipoproteins on atherosclerosis. This review focuses on the recent developments in our understanding of molecular mechanisms of macrophage reverse transport and regulators that play important roles during this process. Macrophage reverse cholesterol transport is promoted by apolipoprotein A-I overexpression and reduced in the setting of apolipoprotein A-I deficiency. A liver X receptor agonist markedly increases macrophage reverse cholesterol transport. ATP-binding cassette transporter A1 and ATP-binding cassette transporter G1 are liver X receptor-responsive macrophage genes that promote cholesterol efflux to lipid-free apolipoprotein A-I and mature high-density lipoprotein, respectively. The direct roles of ATP-binding cassette transporter A1 and ATP-binding cassette transporter G1 in macrophage reverse cholesterol transport in vivo remain unclear. Therapeutically promoting macrophage reverse cholesterol transport has been recognized as one of the promising means to prevent atherosclerosis. Increasing evidence has suggested that ATP-binding cassette transporter A1 and ATP-binding cassette transporter G1 are involved in macrophage reverse cholesterol transport. In-depth understanding of the molecular mechanisms will enable us to develop new therapeutic means to protect against atherosclerosis.

Speciation of Human Plasma High-Density Lipoprotein (HDL): HDL Stability and Apolipoprotein A-I Partitioning

The distribution of apolipoprotein (apo) A-I between human high-density lipoproteins (HDL) and water is an important component of reverse cholesterol transport and the atheroprotective effects of HDL. Chaotropic perturbation (CP) with guanidinium chloride (Gdm-Cl) reveals HDL instability by inducing the unfolding and transfer of apo A-I but not apo A-II into the aqueous phase while forming larger apo A-I deficient HDL-like particles and small amounts of cholesteryl ester-rich microemulsions (CERMs). Our kinetic and hydrodynamic studies of the CP of HDL species separated according to size and density show that (1) CP mediated an increase in HDL size, which involves quasi-fusion of surface and core lipids, and release of lipid-free apo A-I (these processes correlate linearly), (2) >94% of the HDL lipids remain with an apo A-I deficient particle, (3) apo A-II remains associated with a very stable HDL-like particle even at high levels of Gdm-Cl, and (4) apo A-I unfolding and transfer from HDL to water vary among HDL subfractions with the larger and more buoyant species exhibiting greater stability. Our data indicate that apo A-I's on small HDL (HDL-S) are highly dynamic and, relative to apo A-I on the larger more mature HDL, partition more readily into the aqueous phase, where they initiate the formation of new HDL species. Our data suggest that the greater instability of HDL-S generates free apo A-I and an apo A-I deficient HDL-S that readily fuses with the more stable HDL-L. Thus, the presence of HDL-L drives the CP remodeling of HDL to an equilibrium with even larger HDL-L and more lipid-free apo A-I than with either HDL-L or HDL-S alone. Moreover, according to dilution studies of HDL in 3 M Gdm-Cl, CP of HDL fits a model of apo A-I partitioning between HDL phospholipids and water that is controlled by the principal of opposing forces. These findings suggest that the size and relative amount of HDL lipid determine the HDL stability and the fraction of apo A-I that partitions into the aqueous phase where it is destined for interaction with ABCA1 transporters, thereby initiating reverse cholesterol transport or, alternatively, renal clearance.

Pathway of biogenesis of apolipoprotein E-containing HDL in vivo with the participation of ABCA1 and LCAT

We have investigated the ability of apoE (apolipoprotein E) to participate in the biogenesis of HDL (high-density lipoprotein) particles in vivo using adenovirus-mediated gene transfer in apoA-I-/- (apolipoprotein A-I) or ABCA1-/- (ATP-binding cassette A1) mice. Infection of apoA-I-/- mice with 2x10(9) pfu (plaque-forming units) of an apoE4-expressing adenovirus increased both HDL and the triacylglycerol-rich VLDL (very-low-density lipoprotein)/IDL (intermediate-density lipoprotein)/LDL (low-density lipoprotein) fraction and generated discoidal HDL particles. ABCA1-/- mice treated similarly failed to form HDL particles, suggesting that ABCA1 is essential for the generation of apoE-containing HDL. Combined infection of apoA-I-/- mice with a mixture of adenoviruses expressing both apoE4 (2x10(9) pfu) and human LCAT (lecithin:cholesterol acyltransferase) (5x10(8) pfu) cleared the triacylglycerol-rich lipoproteins, increased HDL and converted the discoidal HDL into spherical HDL. Similarly, co-infection of apoE-/- mice with apoE4 and human LCAT corrected the hypercholesterolaemia and generated spherical particles, suggesting that LCAT is essential for the maturation of apoE-containing HDL. Overall, the findings indicate that apoE has a dual functionality. In addition to its documented functions in the clearance of triacylglycerol-rich lipoproteins, it participates in the biogenesis of HDL-sized apoE-containing particles. HDL particles generated by this pathway may account at least for some of the atheroprotective functions of apoE.

The Structure of Apolipoprotein A-II in Discoidal High Density Lipoproteins

It is well accepted that high levels of high density lipoproteins (HDL) reduce the risk of atherosclerosis in humans. Apolipoprotein A-I (apoA-I) and apoA-II are the first and second most common protein constituents of HDL. Unlike apoA-I, detailed structural models for apoA-II in HDL are not available. Here, we present a structural model of apoA-II in reconstituted HDL (rHDL) based on two well established experimental approaches: chemical cross-linking/mass spectrometry (MS) and internal reflection infrared spectroscopy. Homogeneous apoA-II rHDL were reacted with a cross-linking agent to link proximal lysine residues. Upon tryptic digestion, cross-linked peptides were identified by electrospray mass spectrometry. 14 cross-links were identified and confirmed by tandem mass spectrometry (MS/MS). Infrared spectroscopy indicated a beltlike molecular arrangement for apoA-II in which the protein helices wrap around the lipid bilayer rHDL disc. The cross-links were then evaluated on three potential belt arrangements. The data clearly refute a parallel model but support two antiparallel models, especially a "double hairpin" form. These models form the basis for understanding apoA-II structure in more complex HDL particles.

Disorders in High-Density Metabolism With Insulin Resistance and Chronic Kidney Disease

Cardiovascular risk increases with each decrement in renal function. Low-density lipoprotein (LDL) cholesterol levels are not associated with increased mortality, but high-density lipoprotein (HDL) levels are inversely associated with cardiovascular risk. Lipoprotein composition with increased abundance of small dense LDL and HDL and reduced levels of more buoyant isoforms is similar to what is found in states of insulin resistance and in the metabolic syndrome (MS). In both cases, high triglyceride levels are associated with reduced HDL levels. Chronic kidney disease (CKD) is itself associated with increasing insulin resistance as renal function fails. In both instances, decreased levels of apo A-I and apo A-II are a consequence of increased fractional catabolic rate (FCR), resulting from a predominance of small HDL particles. HDL maturation is impaired in CKD through decreased activity of lecithin:cholesterol acyltransferase (LCAT), and increased cholesterol ester transfer protein (CETP) activity in MS shuttles triglycerides back into HDL, thereby destabilizing it. Whether insulin resistance is entirely responsible for disorders of HDL metabolism in CKD, or whether the process is a result of unrelated pathophysiology, is currently unknown.

Alterations of high-density lipoprotein subclasses in hypercholesterolemia and combined hyperlipidemia

Background Alterations in plasma lipid levels can influence the composition, content, and distribution of plasma lipoprotein subclasses that effect atherosclerosis risk. Hypercholesterolemia and combined hyperlipidemia are common forms of atherogenic dyslipoproteinemia. This study evaluates the alterations of high-density lipoprotein (HDL) subclasses in hypercholesterolemic and combined hyperlipidemic subjects. Methods Apolipoprotein A-I contents of plasma HDL subclasses were quantitated by 2-dimensional gel electrophoresis in 242 normolipidemic subjects, 66 hypercholesterolemic subjects and 59 combined hyperlipidemic subjects. Results Compared with the normolipidemic subjects, apolipoprotein A-I contents of small-sized pre-β 1-HDL, HDL 3c, HDL 3band HDL 3awere significantly higher in both hypercholesterolemic subjects ( p < .01, p < .05, p < .01 and p < .05, respectively) and combined hyperlipidemic subjects ( p < .01, p < .05, p < .01 and p < .01, respectively). In contrast, apolipoprotein A-I contents of large-sized HDL 2a and HDL 2b were significantly lower in hypercholesterolemic subjects ( p < .05 and p < .01, respectively) as well as combined hyperlipidemic subjects ( p < .01 and p < .01, respectively). In addition, pre-β 1-HDL increased significantly ( p < .05) while HDL 2aand HDL 2b decreased significantly ( p < .05 and p < .01, respectively) in combined hyperlipidemic group versus hypercholesterolemic subjects. With the elevation of triglyceride levels, pre-β 1-HDL, and HDL 3a increased successively, however, HDL 2aand HDL 2b decreased successively in subjects with total cholesterol levels greater than 240 mg/dl. Conclusions The particle size of HDL shifted towards smaller size in hypercholesterolemic subjects, and that the shift was more prominent in combined hyperlipidemic subjects. The alternations mentioned above indicate that HDL maturation might be abnormal, and reverse cholesterol transport (RCT) might be weakened.

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.

Comparison of different cellular models measuring in vitro the whole human serum cholesterol efflux capacity

Fu5AH rat hepatoma cells and cAMP (cyclic AMP)-pretreated J774 mouse macrophages are commonly used as models for SR-BI (scavenger receptor class B type I) and ABCA1 (ATP binding cassette transporter 1)-mediated free cholesterol efflux to whole serum, respectively. However, the responsiveness of Fu5AH, control or cAMP pretreated J774 cells to the various lipids and HDL (high-density lipoprotein)-parameters from both normo- and dyslipidaemic subjects has never been compared within the same study. Fifty-eight men were classified into four groups: type IIa hypercholesterolaemic (n = 12), type IIb dyslipidaemic (n = 13), type IV hypertriglyceridaemic (n = 18) and normolipidaemic (n = 15) were recruited. A complete lipid profile including prebeta-HDL was performed. Cholesterol efflux from Fu5AH cells as well as from control or cAMP pretreated J774 cells were measured; the difference between these two latter values being taken as the ABCA1-mediated efflux. The Fu5AH and the control J774 cells delivered cholesterol to mature HDLs, especially to phospholipid (PL)-rich HDL. Using cAMP pretreated cells, the ABCA1-dependent efflux was highly sensitive to prebeta-HDL, which appeared to be a factor in determining the efflux. Consistent with the dependence of the SR-BI-mediated efflux on HDL-PL levels, which are not different between groups, all sera displayed similar efflux capacities from the Fu5AH cells. Conversely, in accordance with their high prebeta-HDL levels, the ABCA1-dependent efflux highlighted the efficiency of type IV sera. Two complementary cellular models providing SR-BI and ABCA1-dependent efflux should be used to measure the capacity of a biological fluid which contains a wide variety of components to promote cholesterol efflux.

Effects of Salt on the Thermal Stability of Human Plasma High-Density Lipoprotein

High-density lipoproteins (HDL) mediate cholesterol removal and thereby protect against atherosclerosis. Mature spherical HDL contain the apolar lipid core and polar surface of proteins and phospholipids. Earlier, we showed that the structural integrity of HDL is modulated by kinetic barriers that prevent spontaneous protein dissociation and lipoprotein fusion and rupture. To determine the role of electrostatic interactions in the kinetic stability of mature HDL, here we analyze the effects of salt and pH on their thermal denaturation. In low-salt buffer at pH 5.7-7.7, HDL are highly thermostable. Increasing the salt concentration from 0 to 0.3 M NaCl causes low-temperature shifts in the calorimetric HDL transitions of up to -14 degrees C. This salt-induced destabilization leads to protein unfolding below 100 degrees C, facilitating the first Arrhenius analysis of HDL denaturation by circular dichroism spectroscopy. In 150 mM NaCl, two kinetic phases in HDL protein unfolding are observed: a faster phase with an activation energy E(a,fast) < or =15 kcal/mol and a slower phase with an E(a,slow) = 50 +/- 7 kcal/mol. Gel electrophoresis and electron microscopic data suggest that the faster phase involves partial protein unfolding but no significant protein dissociation or changes in HDL size, while the slower phase involves complete protein unfolding, partial protein dissociation, and HDL fusion. Hence, the slower phase may resemble HDL remodeling and fusion by plasma enzymes during metabolism. Analysis of the effects of various salts, sucrose, and pH suggests that HDL destabilization by salt results from ionic screening of favorable short-range electrostatic interactions such as salt bridges. Consequently, electrostatic interactions significantly contribute to the high thermostability of HDL in low-salt solutions.

Dyslipidemia of chronic renal failure: the nature, mechanisms, and potential consequences

Chronic renal failure (CRF) results in profound lipid disorders, which stem largely from dysregulation of high-density lipoprotein (HDL) and triglyceride-rich lipoprotein metabolism. Specifically, maturation of HDL is impaired and its composition is altered in CRF. In addition, clearance of triglyceride-rich lipoproteins and their atherogenic remnants is impaired, their composition is altered, and their plasma concentrations are elevated in CRF. Impaired maturation of HDL in CRF is primarily due to downregulation of lecithin-cholesterol acyltransferase (LCAT) and, to a lesser extent, increased plasma cholesteryl ester transfer protein (CETP). Triglyceride enrichment of HDL in CRF is primarily due to hepatic lipase deficiency and elevated CETP activity. The CRF-induced hypertriglyceridemia, abnormal composition, and impaired clearance of triglyceride-rich lipoproteins and their remnants are primarily due to downregulation of lipoprotein lipase, hepatic lipase, and the very-low-density lipoprotein receptor, as well as, upregulation of hepatic acyl-CoA cholesterol acyltransferase (ACAT). In addition, impaired HDL metabolism contributes to the disturbances of triglyceride-rich lipoprotein metabolism. These abnormalities are compounded by downregulation of apolipoproteins apoA-I, apoA-II, and apoC-II in CRF. Together, these abnormalities may contribute to the risk of arteriosclerotic cardiovascular disease and may adversely affect progression of renal disease and energy metabolism in CRF.

Th-P15:91 Efficience of triglycerides/s HDL-cholesterol ration in comparison to homa and quicki values as atherogenic markers

Background: It is generally accepted that different high-density lipoprotein (HDL) subclasses have distinct but interrelated metabolic functions. HDL is known to directly influence the atherogenic process and changes in HDL subclasses distribution may be related to the incidence and prevalence of atherosclerosis. Method: The relative apolipoprotein (apo)A-I contents (% apoA-I) of plasma HDL subclasses were determined by two-dimensional gel electrophoresis coupled with immunodetection for apoA-I, in 39 hypercholesterolemic (HTC) subjects, 97 hypertriglyceridemic (HTG) subjects and 32 mixed hyperlipidemic (MHL) subjects, and 124 normolipidemic subjects. Results: The relative apoA-I contents of preβ1-HDL, preβ2-HDL, HDL3c, HDL3b and HDL3a significantly increased while HDL2a and HDL2b significantly decreased in hyperlipidemic subjects. In HTC subjects of hyperlipidemia, the concentrations of preβ1-HDL were significantly lower and HDL2b concentrations were significantly higher than in HTG and MHL subjects. In HTG subjects, the concentrations of HDL3a were significantly higher and the concentrations of HDL2b were lower than in HTC and MHL subjects. In total hyperlipidemic subjects, plasma triglyceride (TG) concentrations showed positive correlation with preβ1-HDL, preβ2-HDL, HDL3b and HDL3a and negative correlation with HDL2a and HDL2b. The total cholesterol (TC) concentrations showed positive correlation with the relative apoA-I contents of preβ1-HDL and HDL3b, whereas the HDL-C concentrations showed negative correlation with the relative apoA-I contents of preβ1-HDL and HDL3a and positive correlation with those of HDL2a and HDL2b. The relative apoA-I contents of preβ1-HDL, preβ2-HDL, HDL3b, and HDL3a were positively correlated whereas those of HDL2a and HDL2b were negatively correlated with TG/HDL-C ratio. Conclusion: The particle size of HDL in hyperlipidemic subjects shifted towards smaller sizes, which, in turn, indicates that the maturation of HDL may be abnormal in hyperlipidemic subjects.