Metabolism of larger high density lipoproteins accumulating in some families of baboons fed a high cholesterol and high saturated fat diet

Progeny of certain baboon sires accumulate lipoproteins in high density lipoprotein-1 (HDL1) when challenged with a high cholesterol, high saturated fat diet. These studies were conducted to determine the apoprotein composition and metabolic fate of HDL1 in the plasma. HDL1 particles containing apoA-I with and without apoE were detected. The majority of particles, however, contained apoA-I without any detectable apoE. To determine the metabolic fate of HDL1 in plasma, HDL1 labeled with iodinated apoA-I from animals with high levels of HDL1 and iodinated apoA-I-labeled autologous HDL were coinjected into both high and low HDL1 animals. The data for the decay of radioactivity in HDL1 and HDL were analyzed by multicompartment modelling. The radioactivity from HDL1 was cleared from the plasma either via direct removal (9.1 +/- 4.7% in low and 21.7 +/- 8.3% in high HDL1 animals) or via its conversion to HDL. A large proportion of radioactivity from HDL1 was rapidly transferred to HDL directly or metabolized via an intermediate compartment. Most of the radioactivity from apoE-poor HDL1, however, was transferred to HDL. Both high and low HDL1 animals catabolized HDL1 and HDL similarly. Low HDL1 animals transferred HDL1 radioactivity to HDL much faster. No detectable radioactivity from HDL was transferred to HDL1. Thus, HDL1 that accumulates in high HDL1 animals is mainly a precursor for HDL. Our hypothesis is that this accumulation of HDL1 is due to the slower cholesteryl ester transfer from HDL to lower density lipoproteins, thus affecting reverse cholesterol transport in high HDL1 baboons.     

Plasma turnover of HDL apoC-I,apoC-III,and apoE in humans: in vivo evidence for a link between HDL apoC-III and apoA-I metabolism

Numerous factors are known to affect the plasma metabolism of HDL, including lipoprotein receptors, lipid transfer protein, lipolytic enzymes and HDL apolipoproteins. In order to better define the role of HDL apolipoproteins in determining plasma HDL concentrations, the aims of the present study were: a) to compare the in vivo rate of plasma turnover of HDL apolipoproteins [i.e., apolipoprotein A-I (apoA-I), apoC-I, apoC-III, and apoE], and b) to investigate to what extent these metabolic parameters are related to plasma HDL levels. We thus studied 16 individuals with HDL cholesterol levels ranging from 0.56-1.66 mmol/l and HDL apoA-I levels ranging from 89-149 mg/dl. Plasma kinetics of HDL apolipoproteins were investigated using a primed constant (12 h) infusion of deuterated leucine. Plasma HDL apolipoprotein levels were 41.8 +/- 1.5, 9.7 +/- 0.5, 4.9 +/- 0.5, and 0.7 +/- 0.1 micromol/l for apoA-I, apoC-I, apoC-III and apoE. Plasma transport rates (TRs) were 388.6 +/- 24.7, 131.5 +/- 12.5, 66.5 +/- 9.1, and 31.4 +/- 3.3 nmol.kg-1.day-1; and residence times (RTs) were 5.1 +/- 0.4, 3.7 +/- 0.3, 3.6 +/- 0.3, and 1.1 +/- 0.1 days, respectively. HDL cholesterol and apoA-I levels were significantly correlated with HDL apoA-I RT (r = 0.69 and r = 0.56), and were not significantly correlated with HDL apoA-I TR. In contrast, HDL apoC-I, apoC-III, and apoB levels were all positively related to their TRs and not their RTs. HDL apoC-III TR was positively correlated with levels of HDL apoC-III (r = 0.73, P < 0.01), and with those of HDL cholesterol and apoA-I (r = 0.54 and r = 0.53, P < 0.05, respectively). HDL apoC-III TR was in turn related to HDL apoA-I RT (r = 0.51, P < 0.05). Together, these results provide in vivo evidence for a link between the metabolism of HDL apoC-III and apoA-I, and suggest a role for apoC-III in the regulation of plasma HDL levels.     

Distribution of high-density lipoprotein 2 and 3 constituents during in vitro phospholipid hydrolysis

Human high-density lipoproteins HDL2 (d = 1.068-1.125) and HDL3 (d = 1.125-1.210) doubly labelled with [3H]cholesterol/cholesteryl ester and with [acyl-14C]phosphatidylcholine were further incubated with phospholipases. Highly purified phospholipase A2 from Crotalus adamanteus allowed gradual degrees of lipolysis (30-90%) on both HDL2 and HDL3. Moderate phospholipid hydrolyses were achieved using hepatic triacylglycerol lipase, partially purified from post-heparin plasma. Moreover, the latter enzyme seemed to exert a lysophospholipase activity, acting on the 2-acyl-sn-glycero-3-phosphocholine generated. A purified sphingomyelinase C from Staphylococcus aureus was also used and completely hydrolysed HDL sphingomyelin. After incubation, doubly labelled HDL2/HDL3 were reisolated in their appropriate density interval. In the presence of albumin, which bound most of the lipolysis products, phospholipolysis induced a phospholipid depletion of the particles and a heterogeneous partition of all HDL2 constituents between the HDL2 and HDL3 density intervals. Radioactivity distributions correlated with mass movements. The 'HDL3-like' particles isolated after HDL2 lipolysis were twice as rich in cholesterol as plasma HDL3. No loss of apoprotein A1 was recorded due to phospholipolysis. In the absence of albumin, the density distributions of HDL2 or HDL3 constituents were unaffected by phospholipolysis, the products of lipolysis being reisolated with the stable particles. Control and treated HDL were also reisolated by equilibrium density gradient ultracentrifugation, gel chromatography or by gradient gel electrophoresis. Phospholipase treatment in the presence of albumin induced a shift of the HDL2 or HDL3 whole distribution towards particles of higher density and lower apparent size. Lipolysed HDL2 thus showed characteristics intermediate between those of HDL2 and HDL3. So, phospholipolysis may affect the physical parameters of HDL particles, but additional pathways such as cholesterol movements and apoprotein loss must be linked to achieve the HDL2----HDL3 interconversion.     

Is the oxidation of high-density lipoprotein lipids different than the oxidation of low-density lipoprotein lipids?

This article gives detailed insight into the kinetics of high-density lipoprotein (HDL) oxidation catalyzed by azobis(2-amidinopropane).dihydrochloride (ABAP) or by copper. ABAP initialized oxidation of human HDL 3-4 times faster than non-human primate HDL with a similar composition. The oxidizability of non-human primate HDL was 1000 times lower than the oxidizability calculated from rate constants derived from liposome oxidation, suggesting that there is a slow step in HDL oxidation not present in liposomes. Saturable binding of copper to HDL was a significant feature of copper-catalyzed oxidation. Binding constants (K(m)) for non-human primate HDL were 2-3-fold lower than those for human HDL. Copper-catalyzed oxidation of non-human primate HDL was slower than that of human HDL, but human HDL(2) and HDL(3) oxidized at about the same rate. Overall, the kinetics describing the oxidation of HDL were mechanistically similar to those reported for LDL, suggesting that HDL lipids were as easily oxidized as LDL lipids and that HDL will be easily oxidized in vivo when exposed to agents that oxidize LDL.     

Behaviour of phospholipase-modified HDL towards cultured hepatocytes. I. Enhanced transfers of HDL sterols and apoproteins

Human HDL subfractions (HDL2, HDL3, or HDL separated by heparin affinity chromatography) were labelled either on their apolipoprotein moiety with 125I or on their sterols: unesterified [14C]cholesterol and [3H]cholesteryl linoleyl ether, a non-hydrolysable analog of esterified cholesterol. HDL subfractions were then treated with or without phospholipase A2 from Crotalus adamanteus in presence of albumin leading to a 72-82% phosphatidylcholine degradation. Control and treated HDL were reisolated and then addressed to cultured rat hepatocytes. (A) During incubations, unesterified [14C]cholesterol from HDL3 readily appeared in hepatocytes. The specific uptake of HDL esterified cholesterol calculated from [3H]cholesteryl ether was 2-4-times less important. Uptake of HDL cholesterol tended to saturate at 150-200 micrograms/ml HDL protein. A prior phospholipase treatment of HDL3 stimulated by 2-5-fold the uptake of [3H]cholesteryl ether, whereas the transfer of free [14C]cholesterol was minimally increased. The uptake of 3H/14C-labelled sterols from HDL2 was 2-3-times higher than from HDL3. (B) Parallel experiments were conducted with 125I-labelled HDL subfractions. At 37 degrees C, the specific uptake and degradation of HDL3 125I-apolipoprotein were about 2-fold enhanced following treatment of HDL3 with phospholipase A2. Uptakes of apolipoprotein and of esterified cholesterol were compared, indicating a preferential delivery of the sterol over apoprotein (X5). The dissociation was still more pronounced with phospholipase-treated HDL3. Competition experiments showed that 12-times more unlabelled HDL3 were required to half reduce the uptake of HDL3 [3H]cholesteryl ether than to impede similarly the HDL 125I-apolipoprotein recovered in cells. Uptake of 125I-labelled apolipoprotein from HDL2 was quantitatively comparable to that from HDL3. (C) Binding of 125I-HDL subfractions was followed at 4 degrees C. A specific binding was observed for HDL2 and HDL3, although kinetic parameters were quite different (KD of 9 and 25 micrograms/ml, respectively). Following phospholipolysis, both the specific and non-specific contributions to total binding were increased. Hence, hepatocytes take up more 125I-labelled apolipoprotein and 3H/14C-labelled sterols from lipolysed HDL than from unmodified particles. This is associated to changes in the binding characteristics.     

eNOS Activation by HDL Is Impaired in Genetic CETP Deficiency

Mutations in the CETP gene resulting in defective CETP activity have been shown to cause remarkable elevations of plasma HDL-C levels, with the accumulation in plasma of large, buoyant HDL particles enriched in apolipoprotein E. Genetic CETP deficiency thus represents a unique tool to evaluate how structural alterations of HDL impact on HDL atheroprotective functions. Aim of the present study was to assess the ability of HDL obtained from CETP-deficient subjects to protect endothelial cells from the development of endothelial dysfunction. HDL isolated from one homozygous and seven heterozygous carriers of CETP null mutations were evaluated for their ability to down-regulate cytokine-induced cell adhesion molecule expression and to promote NO production in cultured endothelial cells. When compared at the same protein concentration, HDL and HDL3 from carriers proved to be as effective as control HDL and HDL3 in down-regulating cytokine-induced VCAM-1, while carrier HDL2 were more effective than control HDL2 in inhibiting VCAM-1 expression. On the other hand, HDL and HDL fractions from carriers of CETP deficiency were significantly less effective than control HDL and HDL fractions in stimulating NO production, due to a reduced eNOS activating capacity, likely because of a reduced S1P content. In conclusion, the present findings support the notion that genetic CETP deficiency, by affecting HDL particle structure, impacts on HDL vasculoprotective functions. Understanding of these effects might be important for predicting the outcomes of pharmacological CETP inhibition.     

Binding characteristics of high density lipoprotein subclasses to porcine liver, adrenal and skeletal muscle plasma membranes

1. We compared binding characteristics of 125I-labeled high density lipoprotein (HDL) subclasses to porcine liver, adrenal and skeletal muscle plasma membranes. 2. HDL subclasses were discriminated by their buoyant densities (HDL2 and HDL3) or by their apolipoprotein (apo) content (Lp-AI (particles containing apoA-I but no apoA-II) and LpA-I/A-II (particles containing both apoA-I and apoA-II)). 3. HDL2 and HDL3 showed saturable binding to the three types of membrane preparations. 4. No differences were found in the Kds within one HDL subclass. 5. Kds and maximal binding of HDL2 were lower than these of HDL3. Unlabeled HDL2 and HDL3, but not LDL, effectively displaced 125I-HDL2 and 125I-HDL3. 6. Binding of HDL was independent of the concentration of NaCl and did not require calcium. 7. These results suggest a process mediated by a single specific receptor in porcine liver, adrenal and skeletal muscle plasma membranes. 8. We also studied binding characteristics of HDL subclasses Lp-AI and LpA-I/A-II to porcine liver membranes. LpA-I showed the highest Kd and maximal binding. 9. All types of HDL subclasses studied (i.e. HDL2, HDL3, LpA-I and LpA-I/A-II) effectively competed for binding of both Lp-AI and LpA-I/A-II, suggesting that the HDL subclasses studied bind to the same receptor by their apoA-I moiety.     

High-density lipoprotein cholesterol subfractions HDL2 and HDL3 are reduced in women with rheumatoid arthritis and may augment the cardiovascular risk of women with RA: a cross-sectional study

IntroductionHigher levels of high density lipoprotein (HDL) subfractions HDL3-chol and particularly HDL2-chol protect against cardiovascular disease (CVD), but inflammation reduces the HDL level and may impair its anti-atherogenic effect. Changed HDL composition through the impact of inflammation on HDL subfractions may contribute to the excess risk of CVD in rheumatoid arthritis (RA). In this study, we investigated whether HDL2-chol and HDL3-chol concentrations differ between RA patients and healthy controls, and whether these levels are related to the level of RA disease activity.MethodsNon-fasting blood samples were collected from 45 RA patients and 45 healthy controls. None of the participants had a history of CVD, diabetes, or used lipid-lowering drugs. HDL2-chol and HDL3-chol concentrations were obtained by ultracentrifugation. Regression modeling was used to compare HDL subfraction levels between RA patients and healthy controls, and to analyze the effect of disease activity on HDL2-chol and HDL3-chol.ResultsHDL2-chol and HDL3-chol were significantly lower in RA patients compared to healthy controls (P = 0.01, P = 0.005, respectively). The HDL2:HDL3 ratio was significantly lower in patients compared to controls (P = 0.04). Reduced HDL2-chol and HDL3-chol levels were primarily present in female RA patients and not in male RA patients. A modest effect of the disease activity score in 28 joins ( DAS28) on HDL2-chol concentrations was found, after correction for disease duration, glucocorticosteroid use and body mass index (BMI), with a 0.06 mmol/L decrease with every point increase in DAS28 (P = 0.05). DAS28 did not significantly affect HDL3-chol concentrations (P = 0.186).ConclusionsBoth HDL subfractions but particularly HDL2-chol concentrations were decreased in RA, primarily in women. This seems to be associated with disease activity and is of clinical relevance. The reduction of the HDL subfraction concentrations, particularly the supposedly beneficial HDL2-chol, may negatively impact the cardiovascular risk profile of women with RA.     

Proliferative effect of high density lipoprotein (HDL) and HDL fractions (HDL1,2, HDL3) on virus transformed lymphoblastoid cells

The growth-promoting activities of plasma lipoproteins (LDL, HDL, HDL1,2, HDL3) and total HDL apolipoproteins on a virus transformed lymphoblastoid cell line in vitro, has been compared. When maintained in lipoprotein-deficient serum-supplemented medium, these cells do not proliferate optimally. The addition of either HDL, HDL1,2 or HDL3 induced optimal cell proliferation as compared to the result observed in fetal calf serum-supplemented medium. The HDL1,2 subfraction was found to be more potent than the HDL3 subfraction in supporting cell growth. Total HDL apolipoproteins were able to support significant cell proliferation. In contrast, LDL did not promote cell growth. In serum-free conditions and in the presence of transferrin, only HDL and HDL subfractions induced cell proliferation. These results suggest that HDL and HDL subfractions could initiate B lymphoblastoid cell growth and that total HDL apolipoproteins could support a part of cell proliferation.     

Comparison of gradient gel electrophoresis and zonal ultracentrifugation for quantitation of high density lipoproteins

The study was conducted to compare gradient gel electrophoresis (GGE) and zonal ultracentrifugation for quantitation of human plasma high density lipoproteins (HDL). Plasma samples were obtained from seven normal subjects consuming a high fat diet (65% total calories) followed by a high carbohydrate diet (65% total calories). HDL were fractionated into HDL2 and HDL3 by zonal ultracentrifugation and lipid and protein mass were determined. HDL were also fractionated by GGE and the results were compared to the zonal method. Zonally isolated HDL2 represented a homogeneous particle population that was equivalent to HDL2b as determined by GGE. By the zonal method, HDL2 accounted for 27 +/- 4% (mean +/- SEM) of total HDL mass in subjects on the high fat diet as compared to 16 +/- 2% in subjects fed the high carbohydrate diet; by GGE, the HDL2b values were 27 +/- 4% and 14 +/- 1%, respectively. The coefficient of correlation (n = 25) for the two methods was 0.894 (P less than 0.001).     

Measurement of normative HDL subfraction cholesterol levels by Gaussian summation analysis of gradient gels

This report describes development of a computerized method for analyzing polyacrylamide gradient gels of high density lipoproteins (HDL) by Gaussian summation, a simple technique to obtain standardized measurements of size and amount of HDL subfractions. Conditions for reproducibility and ranges of linearity were established. By Gaussian summation analysis, five or six HDL subfractions could be found in the plasma of most normolipidemic people. The relationship of staining intensity to cholesterol level was determined for Coomassie Blue R-250, permitting determination of the cholesterol levels in the individual subfractions, with standard errors of repeated measurements of 2% or less of the total HDL area, and accuracy, limited by the standard error of the chromogenicity, of 1-2 mg/dl for the least abundant fractions and 3-4 mg/dl for the most abundant subfractions. Levels of HDL2b measured by this method were statistically the same as levels of HDL2 measured by dextran sulfate-Mg2+ precipitation. Gaussian summation analysis of gradient gels was used to measure HDL subfraction cholesterol levels in subjects from the Baltimore Longitudinal Study on Aging to obtain normative levels for men and women for the major HDL subfractions. Comparisons of these levels with each other and with triglyceride and cholesterol levels showed that triglyceride levels were inversely correlated with levels of HDL2a and HDL2b, cholesterol levels were directly correlated with levels of HDL3b and HDL3a, and that HDL3b levels were inversely correlated with levels of both HDL2a and HDL2b.     

Semaphorin 3A is a marker for disease activity and a potential immunoregulator in systemic lupus erythematosus

Introduction

Higher levels of high density lipoprotein (HDL) subfractions HDL3-chol and particularly HDL2-chol protect against cardiovascular disease (CVD), but inflammation reduces the HDL level and may impair its anti-atherogenic effect. Changed HDL composition through the impact of inflammation on HDL subfractions may contribute to the excess risk of CVD in rheumatoid arthritis (RA). In this study, we investigated whether HDL2-chol and HDL3-chol concentrations differ between RA patients and healthy controls, and whether these levels are related to the level of RA disease activity.

Methods

Non-fasting blood samples were collected from 45 RA patients and 45 healthy controls. None of the participants had a history of CVD, diabetes, or used lipid-lowering drugs. HDL2-chol and HDL3-chol concentrations were obtained by ultracentrifugation. Regression modeling was used to compare HDL subfraction levels between RA patients and healthy controls, and to analyze the effect of disease activity on HDL2-chol and HDL3-chol.

Results

HDL2-chol and HDL3-chol were significantly lower in RA patients compared to healthy controls (P = 0.01, P = 0.005, respectively). The HDL2:HDL3 ratio was significantly lower in patients compared to controls (P = 0.04). Reduced HDL2-chol and HDL3-chol levels were primarily present in female RA patients and not in male RA patients. A modest effect of the disease activity score in 28 joins ( DAS28) on HDL2-chol concentrations was found, after correction for disease duration, glucocorticosteroid use and body mass index (BMI), with a 0.06 mmol/L decrease with every point increase in DAS28 (P = 0.05). DAS28 did not significantly affect HDL3-chol concentrations (P = 0.186).

Conclusions

Both HDL subfractions but particularly HDL2-chol concentrations were decreased in RA, primarily in women. This seems to be associated with disease activity and is of clinical relevance. The reduction of the HDL subfraction concentrations, particularly the supposedly beneficial HDL2-chol, may negatively impact the cardiovascular risk profile of women with RA.     

Apolipoprotein AIMilano. Disulfide-linked dimers increase high density lipoprotein stability and hinder particle interconversion in carrier plasma

The in vitro metabolism of high density lipoproteins (HDL) in carriers of the apolipoprotein AIMilano (apoAIM) mutant was investigated during incubation of whole plasma and isolated lipoprotein fractions. A reduced cholesterol esterification (16.5 versus 25.0% for controls) and a decreased exchange of lipids between HDL and lower density lipoproteins was observed during incubation (6 h at 37 degrees C) of AIM plasma. Control HDL3 were converted to larger, faster-floating HDL particles, whereas only a fraction of AIM HDL3 followed the same pathway. Incubations were also carried out by mixing HDL3 from controls and AIM carriers with a lipoprotein-depleted plasma fraction in the presence of triglyceride-rich particles isolated from Intralipid. AIM HDL3 again showed a reduced capacity for lipid exchange; some HDL3 particles followed a "normal" conversion to faster-floating, larger HDL, whereas the small AIM HDL3 were not modified, indicating that AIM HDL3 are a mixture of metabolically functional and nonfunctional particles. Following transformation of the apoAIM homo- and heterodimers into their normal counterparts, i.e. monomeric apoAI and -AII, by reduction and carboxamidomethylation of AIM HDL3, the modified HDL3 behave like control HDL3 during incubation with lipoprotein-depleted plasma and triglyceride-rich particles. The presence of AIM dimers is most likely responsible for the increased HDL3 stability in the AIM carriers, indicating that apolipoprotein composition plays a major role in HDL particle interconversion.     

Intravascular metabolism of the cholesteryl ester moiety of rat plasma lipoproteins

The intravascular metabolism of the cholesteryl ester moiety of rat plasma LDL, HDL1, and HDL2 was determined in intact male rats. Biosynthetically labeled lipoproteins were prepared by zonal ultracentrifugation from the plasma of rats injected with [3H]cholesterol. The lipoproteins were concentrated by vacuum ultrafiltration as other procedures were found to alter the biological properties of the lipoproteins. After injection of labeled LDL, [3H]cholesteryl esters remained with the injected lipoprotein and decayed from plasma with a t1/2 of 7-8 hours. [3H]Cholesteryl esters in HDL1 behaved similarly and decayed with a t1/2 of 10.5 hours. With HDL2, however, a different metabolic pattern was observed with intraplasma conversion of some [3H]cholesteryl ester HDL2 particles to HDL1. Since such conversion of HDL2 to HDL1 was not observed after in vitro incubations of rat plasma, this process seems to depend on metabolic events that occur in vivo. [3H]Cholesteryl esters disappeared from HDL2 with a t1/2 of 6-7 hours, while the esters that were transferred to HDL1 decayed with a t1/2 of 10-11 hours, similar to labeled cholesteryl esters injected with HDL1. The study demonstrated that the high apoE content of rat plasma HDL1 is not associated with rapid catabolism of the lipoprotein and that a major source of HDL1 in the rat is the intraplasma conversion of HDL2 particles to HDL1.     

High-density lipoprotein binding to guinea-pig hepatic membranes. Comparison of guinea-pig and human ligands

Human and guinea-pig apo-E-free HDL were incubated with isolated guinea-pig hepatic membranes at 4 and 37 degrees C to determine the effects of temperature and heterologous systems on the equilibrium parameters of HDL binding. Receptor mediated HDL binding was highest at 37 degrees C for both lipoproteins. At 4 degrees C, a higher affinity constant (Kd) was observed when guinea-pig HDL was the ligand relative to human HDL; in contrast, both HDL preparations had similar Kd values at 37 degrees C. Calculated binding and receptor number (Bmax) were higher at both temperatures when guinea-pig HDL was the ligand. These results demonstrate a significant species difference in HDL binding to hepatic membrane which is partially temperature-dependent.     

Behaviour of phospholipase modified-HDL towards cultured hepatocytes. II. Increased cell cholesterol storage and bile acid synthesis

Human total HDL (hydrated density 1.070-1.210), HDL2 (1.070-1.125), HDL3 (1.125-1.210) or HDL separated by heparin affinity chromatography were treated with or without purified phospholipase A2 from Crotalus adamanteus. Control and treated HDL were reisolated and were then incubated with cultured hepatocytes. 1. Mass measurements evidenced a time-dependent cholesterol enrichment in hepatocytes cultured in the absence of lipoproteins. Addition of HDL2 still enhanced by 25% the cell cholesterol content and down-regulated endogenous sterol synthesis in similar proportions. Conversely, HDL3 slightly decreased the amount of free cholesterol in hepatocytes (-12%). 2. Incubations with phospholipase A2-treated HDL resulted in a 35%-50% increase of both the cellular cholesterol esterification and the cholesterylester accumulation, when compared to cells cultured in the presence of control-HDL. This effect was observed with HDL2, HDL3 and combining the data with all subfractions. 3. Cultured hepatocytes secreted cholic and beta-muricholic acids as major bile acids and HDL2 showed a tendency to stimulate their secretion. Phospholipase treatment of HDL again induced an increased production by hepatocytes of those two bile acids. Thus, whereas HDL2 and HDL3 display different behaviours with respect to cell cholesterol content, neosynthesis and bile acid secretion, their modifications by phospholipases always orientate the cell sterol metabolism in the same direction: increased cholesterylester accumulation and bile acid production.     

Properties of serum high-density lipoproteins in the crab, Cancer antennarius Stimpson

Two classes of high-density lipoprotein (HDL) comprise virtually all the lipoprotein mass in female hemolymph. These lipoproteins have hydrated densities of 1.187 g/ml (HDL3) and 1.112 g/ml (HDL2). A third species (HDL1, density 1.080 g/ml) appeared in ovigerous crabs. The mean annual HDL protein concentration was 109 mg/dl of which 67% was HDL3. HDL proteins of both HDL2 and HDL3 were mostly insoluble in tetramethylurea. Three major components with apparent mol. wts of 185,000, 100,000 and 84,000 daltons were identified by gel electrophoresis in SDS. Amino acid compositions are reported. Electron microscopy indicated that the HDL are polymorphic and discoidal. Similarities in shape and differences in size of HDL3 and HDL2 particles were consistent with their lipid and protein composition. Phospholipids, mostly phosphatidylcholine, were the dominant lipid class (74%); no cholesteryl esters were detected. Palmitic and oleic acids were the major fatty acid components of esterified lipids.     

前β_1-HDL与细胞HDL受体结合活性的研究

The activities of pre\|β 1HDL and apoE\|deficient HDL 3 binding to HDL receptors on human SMC,HepG2 and macrophage were detected using enzyme linked immune receptor assay(ELIRA).The results showed the value of K d of pre\|β 1 HDL binding to HDL receptor was significantly lower than that of apoE\|deficient HDL 3( P <0.05),but B max showed no difference.The results suggested that the affinity of pre\|β 1 HDL to HDL receptor was significantly higher than that of apoE\|deficient HDL 3.     

High-density lipoprotein nitration and chlorination catalyzed by myeloperoxidase impair its effect of promoting endothelial repair

High-density lipoprotein (HDL) plays a key role in protecting against atherosclerosis. In cardiovascular disease, HDL can be nitrated and chlorinated by myeloperoxidase (MPO). In this study, we discovered that MPO-oxidized HDL is dysfunctional in promoting endothelial repair compared to normal HDL. Proliferation assay, wound healing, and transwell migration experiments showed that MPO-oxidized HDL was associated with a reduced stimulation of endothelial cell (EC) proliferation and migration. In addition, we found that Akt and ERK1/2 phosphorylation in ECs was significantly lower when ECs were incubated with oxidized HDL compared with normal HDL. To further determine whether oxidized HDL diminished EC migration through the PI3K/Akt and MEK/ERK pathways, we performed experiments with inhibitors of both these pathways. The transwell experiments performed in the presence of these inhibitors showed that the migration capacity was reduced and the differences observed between normal HDL and oxidized HDL were diminished. Furthermore, to study the effects of oxidized HDL on endothelial cells in vivo, we performed a carotid artery electric injury model on nude mice injected with either normal or oxidized HDL. Oxidized HDL inhibited reendothelialization compared to normal HDL in vivo. These findings implicate a key role for MPO-oxidized HDL in the pathogenesis of cardiovascular disease.     

ApoA-IV metabolism in the rat: role of lipoprotein lipase and apolipoprotein transfer

Factors influencing the association of apoA-IV with high density lipoproteins (HDL) were investigated by employing a crossed immunoelectrophoresis assay to estimate the distribution of rat plasma apoA-IV between the lipoprotein-free and HDL fractions. Incubation of rat plasma at 37 degrees C resulted in the complete transfer of lipoprotein-free apoA-IV to HDL within 45 min. When plasma obtained from fat-fed rats was incubated at 37 degrees C in the presence of postheparin plasma as a source of lipolytic activity, there was a complete transfer of HDL apoA-IV to the lipoprotein-free fraction within 30 min. With extended incubation (120 min), lipoprotein-free apoA-IV began to transfer back to HDL. Similar patterns of apoA-IV redistribution were seen when plasma from fat-fed rats was incubated with postheparin heart perfusate or was perfused through a beating heart. Incubations conducted with plasma obtained from fasted rats showed similar but markedly attenuated apoA-IV responses. Similar observations were found in vivo following intravenous heparin administration. To determine whether the transfer of apolipoproteins from triglyceride-rich lipoproteins to HDL was partially responsible for the lipolysis-induced redistribution of apoA-IV, purified apoA-I, apoE, and C apolipoproteins were added to plasma from fasted rats. When added to plasma, all of the apolipoproteins tested displaced apoA-IV from HDL in a dose-dependent manner. Conversely, apolipoproteins were removed from HDL by adding Intralipid to plasma from fasted rats. With increasing concentrations of Intralipid, there was a progressive loss of HDL apoC-III and a progressive increase in HDL apoA-IV. Intravenous injection of a bolus of Intralipid to fasted rats resulted in a transient decrease of HDL apoC-III and concomitant increase in HDL apoA-IV. From these studies, we conclude that the binding of apoA-IV to HDL is favored under conditions that result in a relative deficit of HDL surface components, such as following cholesterol esterification by LCAT or transfer of apolipoproteins to nascent triglyceride-rich lipoproteins.