[New AHA and ACC guidelines on the treatment of blood cholesterol to reduce atherosclerotic cardiovascular risk : Statement of the D•A•CH Society for Prevention of Cardiovascular Diseases, the Austrian Atherosclerosis Society and the Working Group on Lipids and Atherosclerosis (AGLA) of the Swiss Society for Cardiology]. / Neue AHA- und ACC-Leitlinie zur Risikoreduktion von Herz-Kreislauf-Erkrankungen durch Cholesterinsenkung : Stellungnahme der D•A•CH-Gesellschaft Prävention von Herz-Kreislauf-Erkrankungen e. V., der Österreichischen Atherosklerose Gesellschaft und der Arbeitsgruppe Lipide und Atherosklerose (AGLA) der Schweizer Gesellschaft für Kardiologie.

Guidelines for the reduction of cholesterol to prevent atherosclerotic vascular events were recently released by the American Heart Association and the American College of Cardiology. The authors claim to refer entirely to evidence from randomized controlled trials, thereby confining their guidelines to statins as the primary therapeutic option. The guidelines derived from these trials do not specify treatment goals, but refer to the percentage of cholesterol reduction by statin medication with low, moderate, and high intensity. However, these targets are just as little tested in randomized trials as are the cholesterol goals derived from clinical experience. The same applies to the guidelines of the four patient groups which are defined by vascular risk. No major statin trial has included patients on the basis of their global risk; thus the allocation criteria are also arbitrarily chosen. These would actually lead to a significant increase in the number of patients to be treated with high or maximum dosages of statins. Also, adhering to dosage regulations instead of cholesterol goals contradicts the principles of individualized patient care. The option of the new risk score to calculate lifetime risk up to the age of 80 years in addition to the 10-year risk can be appreciated. Unfortunately it is not considered in the therapeutic recommendations provided, despite evidence from population and genetic studies showing that even a moderate lifetime reduction of low-density lipoprotein (LDL) cholesterol or non-HDL cholesterol has a much stronger effect than an aggressive treatment at an advanced age. In respect to secondary prevention, the new American guidelines broadly match the European guidelines. Thus, the involved societies from Germany, Austria and Switzerland recommend continuing according to established standards, such as the EAS/ESC guidelines.

Turnover of lipoprotein (a) in man.

An elevated concentration of lipoprotein (a) [Lp(a)] in the serum has been considered a risk factor for coronary heart disease by various investigators. In the present study, the turnover of Lp(a) was investigated in nine individuals with serum Lp(a) levels ranging from 1 to 68 mg/100 ml. After intravenous injection of radioiodinated Lp(a), the radioactivity time-curve of the serum and the specific activitity time-curves of the isolated Lp(a) and Lp(a) apolipoproteins were measured for 14 d. More than 97% of the label was found in the protein moiety of Lp(a). During the entire study period, the serum radioactivity remained with Lp(a), only insignificant amounts of radioactivity were detectable in other lipoprotein fractions. The serum radioactivity time-curves and the specific activity time-curves of the isolated Lp(a) and Lp(a) apolipoproteins were identical. The kinetic parameters of Lp(a) turnover were calculated in terms of a two-compartment model. 76.5+/-5.1% (mean+/-1 SD) of total Lp(a) was contained in the intravascular space. The biological half-life of Lp(a) was 3.32+/-0.52 d, the fractional catabolic rate (FCR) was 0.306+/-0.054/d, and the rate of synthesis was 5.00+/-3.37 mg/kg/d. A positive correlation was found between serum concentration and synthetic rate of Lp(a) apoprotein. No relationship could be demonstrated between serum level and FCR of Lp(a). The results of this study indicate that Lp(a) is not converted to other serum lipoproteins. From the correlations between serum concentration and kinetic parameters of Lp(a) it is concluded that an elevated Lp(a) level is the consequence of an increased Lp(a) apoprotein synthesis.

Studies on the role of specific cell surface receptors in the removal of lipoprotein (a) in man.

The binding of 125I-lipoprotein (a) [Lp(a)] to cell surface receptors was studied on cultured human fibroblasts. The results were compared with corresponding data obtained with 125I-low density lipoproteins (LDL). Equilibrium binding studies showed that Lp(a) is bound with high affinity by the cell surface receptors. The maximum binding capacity for Lp(a) was 37% lower than for LDL. For Lp(a) and LDL, the Scatchard plots displayed linearity, indicating a single category of binding sites. Half-maximal saturation occurred at a concentration of 9.52 +/- 1.04 nM for Lp(a) and 7.76 +/- 1.29 nM for LDL. Competition binding experiments revealed that Lp(a) and LDL are nearly equally potent in competing each other for the binding sites. Binding of Lp(a) and LDL were followed by suppression of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity. Cyclohexanedione treatment of Lp(a) and LDL completely abolished receptor binding. Neither Lp(a) nor LDL were specifically bound by fibroblasts obtained from a patient with homozygous familial hypercholesterolemia (FH). The removal mechanisms for Lp(a) and LDL were further compared by in vivo studies. Radioiodinated Lp(a) and LDL were injected intravenously into 12 normolipemic individuals to measure kinetic parameters of these two lipoproteins simultaneously in each subject. Mean fractional catabolic rate (FCR) of Lp(a) was 0.260 +/- 0.060 and mean FCR of LDL was 0.377 +/- 0.077 (mean +/- SD). In each subject, FCR of Lp(a) was lower than the FCR of LDL; the mean difference was 31%. The absolute synthetic rate of Lp(a) was significantly lower than the corresponding value of LDL. In each individual, the percentage of total Lp(a) that was contained in the intravascular space was higher than the corresponding value of LDL; the mean difference was 19%. A highly significant positive correlation was found between FCR of LDL and FCR of Lp(a) (r = 0.853, P less than 0.01). No relationship was found between the serum concentration of LDL-apolipoprotein B and Lp(a). The serum level of Lp(a) was positively related to the absolute rate of Lp(a) synthesis (r = 0.979, P less than 0.01). The serum level of LDL-apolipoprotein B was inversely related to FCR of LDL (r = 0.613, P less than 0.05). In a patient with homozygous FH, FCR of LDL was 0.205 and FCR of Lp(a) was 0.210. The results of these studies show that Lp(a) is specifically bound with high affinity to the same receptors of human fibroblasts as LDL. The affinity and maximum binding capacity are slightly lower for Lp(a) than for LDL. The results of the turnover studies are consistent with the assumption that Lp(a) is removed from the plasma by similar mechanisms as LDL.

Lipoprotein binding to cultured human hepatoma cells.

Binding of various 125I-lipoproteins to hepatic receptors was studied on cultured human hepatoma cells (Hep G2). Chylomicrons, isolated from a chylothorax, chylomicron remnants, hypertriglyceridemic very low-density lipoproteins, normotriglyceridemic very low-density lipoproteins (NTG-VLDL), their remnants, low-density lipoproteins (LDL), and HDL-E (an Apo E-rich high-density lipoprotein isolated from the plasma of a patient with primary biliary cirrhosis) were bound by high-affinity receptors. Chylomicron remnants and HDL-E were bound with the highest affinity. The results, obtained from competitive binding experiments, are consistent with the existence of two distinct receptors on Hep G2 cells: (a) a remnant receptor capable of high-affinity binding of triglyceride-rich lipoproteins and HDL-E, but not of Apo E free LDL, and (b) a LDL receptor capable of high-affinity binding of LDL, NTG-VLDL, and HDL-E. Specific binding of Apo E-free LDL was completely abolished in the presence of 3 mM EDTA, indicating that binding to the LDL receptor is calcium dependent. Specific binding of chylomicron remnants was not inhibited by the presence of even 10 mM EDTA. Preincubation of the Hep G2 cells in lipoprotein-containing medium resulted in complete suppression of LDL receptors but did not affect the remnant receptors. Hep G2 cells seem to be a suitable model for the study of hepatic receptors for lipoprotein in man.

The role of lecithin: cholesterol acyltransferase for lipoprotein (a) assembly. Structural integrity of low density lipoproteins is a prerequisite for Lp(a) formation in human plasma.

The composition of lipoproteins in the plasma of patients with LCAT deficiency (LCAT-D) is grossly altered due to the lack of cholesteryl esters which form the core of normal lipoproteins. When plasma from LCAT-D patients and their relatives was examined we found that nine heterozygotes had plasma Lp(a) levels of 2-13 mg/dl whereas none of 11 affected homozygous individuals from different families contained detectable amounts of Lp(a) in their plasma. Therefore, the binding of apo(a) to LDL density particles was studied in vitro using LDL density fractions prepared from patients, and recombinant apo(a) [r-apo(a)], which was expressed and secreted by transfected COS-7 cells. The LDL from heterozygotes were chemically indistinguishable from normal LDL and homogeneous with regard to morphology, whereas the crude LDL floating fraction from homozygotes consisted of a heterogeneous mixture of large vesicles, and small spheres resembling normal LDL. The LDL density fraction from the LCAT-D patient lacked almost completely cholesteryl esters. Incubation of LCAT-D plasma with active LCAT caused a substantial augmentation of the original subfraction which morphologically resembled normal LDL. Using r-apo(a) and normal LDL or LDL of heterozygous individuals, apoB:r-apo(a) complexes were formed when incubated at 37 degrees C in vitro for 20 h. In contrast, the total LDL floating fraction from a homozygous LCAT-D patient failed to form apoB:r-apo(a) complexes. After treatment with active LCAT, a significant apoB:r-apo(a) association was observed with LCAT-D LDL-density particles. Our data emphasize the importance of the integrity of LDL structure and composition for the formation of Lp(a). In addition, we demonstrate that the absence of LCAT activity has a fundamental impact on the regulation of plasma Lp(a) levels.

Diagnosis of families with familial hypercholesterolaemia and/or Apo B-100 defect by means of DNA analysis of LDL-receptor gene mutations.

BACKGROUND: One major problem of using hypercholesterolaemia alone as a primary criterion for diagnosing familial hypercholesterolaemia (FH) is that 15-40% of relatives may be misdiagnosed because plasma lipid levels in FH heterozygotes overlap with those in the general population. SETTING: General Hospital/University of Vienna, Department of Pediatrics, Outpatient lipid clinic. METHODS: As a part of the MED-PED (make early diagnosis-prevent early death) project we are currently investigating children, adolescents and their relatives who are suspected to be affected with FH in our out-patient clinic for metabolic diseases using MED-PED inclusion criteria and confirming the diagnosis by means of DNA analysis. PATIENTS: 263 patients with premature atherosclerosis and/or hypercholesterolaemia: 116 children (mean age 11.6 +/- 4.1 years; 57 girls and 59 boys) and 147 adults (64 women, mean age 41.5 +/- 13.7 years; 83 men, mean age 42.8 +/- 10.8 years). RESULTS: 119 patients with mutations have been detected; 56 children with either low density lipoprotein receptor (LDLR) and/or ApoB mutations (27 girls and 29 boys; mean total cholesterol (TC) 275 +/- 71 mg/dl, triglycerides (TG) 101 +/- 57 mg/dl, high-density lipoprotein cholesterol (HDL-C) 49 +/- 12 mg/dl, low-density lipoprotein cholesterol (LDL-C) 198 +/- 67 mg/dl) and one boy with a homozygous. LDLR mutation. A further 62 adults with LDLR and/or ApoB mutations were documented; 33 women (mean age 36.9 +/- 11.1 years; mean TC 283 +/- 76 mg/dl, TG 137 +/- 78 mg/dl, HDL-C 55 +/- 17 mg/dl, LDL-C 210 +/- 67 mg/dl) and 29 men (mean age 45.0 +/- 10.6 years; mean TC 301 +/- 87 mg/dl, TG 163 +/- 112 mg/dl, HDL-C 42 +/- 12 mg/dl, LDL-C 233 +/- 83 mg/dl). In 32 of these subjects (11 children (21%), 21 adults (42%)), serum lipid levels were lower than the diagnostic MED-PED limits adopted, so that they might have been misclassified without an additional DNA analysis. CONCLUSION: In our study, diagnosis of FH and related disorders (ApoB-100 defect) by means of conventional laboratory methods missed at least 21% in children and 42% in adults affected with LDLR and/or ApoB gene mutations. Genetic FH diagnosis provides a tool for specific diagnosis of mutation carrier status.

Structural organization of free and esterified cholesterol in human high density lipoproteins. A 100.6 MHz 13C NMR study.

The structural organization of free and esterified cholesterol in human high density lipoproteins has been studied by high-field 1H and 13C NMR. The measurements are consistent with free cholesterol being present in at least two different environments. Part of the free cholesterol is oriented in the outer surface layer of the high density lipoprotein particle in contact with phospholipid or apoprotein, or both. The rest is probably present in the liquid, hydrophobic core of the HDL particle.

The separation of human serum high density lipoproteins by hydroxy apatite column chromatography. Evidence for the presence of discrete subfractions.

Human serum high density lipoprotein subfractions 2 and 3, isolated by preparative ultracentrifugation after blocking the enzyme phosphatidylcholine: cholesterol acyl transferase, have been subfractionated further by hydroxyapatite column chromatography. From subfraction 2 we reproducibly obtained 5 and from subfraction 3, 6 fractions differing in chemical composition and apolipoprotein content. The fractions eluting at low salt concentrations were composed primarily of apolipoprotein-A polypeptides while those eluting at high salt concentrations consisted primarily of apolipoprotein-C. From all the 11 subfractions only one contained the "arginine-rich" polypeptide. The apolipoprotein-C-containing fractions were richer in triacylglycerol, phospholipids and free cholesterol as compared to the apolipoprotein-A-containing ones. Although small differences of their partial specific volumes existed, the obtained values indicate that all subfractions belonged to the parent density class. The implications of these results to the current view of lipoprotein metabolism are discussed.

Activation of lecithin-cholesterol acyltransferase by apolipoprotein D: comparison of proteoliposomes containing apolipoprotein D, A-I or C-I.

To study the activation of lecithin-cholesterol acyl transferase (LCAT) (phosphatidylcholine:sterol O-acyltransferase, EC 2.3.1.43) by apolipoprotein D in comparison to apolipoproteins A-I and C-I, proteoliposomes with a phosphatidylcholine/free cholesterol molar ratio of 24:1, containing 10-300 micrograms/ml of apolipoproteins were used. The proteoliposomes were prepared by the cholate dialysis technique. In all proteoliposome preparations we found rouleaux structures and stacked discs. The particles formed with apolipoprotein A-I were the most homogeneous, followed by apolipoprotein D- and apolipoprotein C-I-containing particles. Apolipoprotein A-I was the most potent LCAT activator in our system followed by apolipoproteins C-I and D. The fractional esterification rate observed with apolipoprotein D-containing substrates amounted to 15-48% that of apolipoprotein A-I-containing ones. Neither apolipoprotein A-I- nor C-I-containing proteoliposomes gave linear reaction kinetics with LCAT. Even during the first 15-30 min of incubation, the kinetics deviated strikingly from linearity at all apolipoprotein concentrations. In contrast, proteoliposomes containing apolipoprotein D exhibited linear reaction kinetics up to 60-90 min. At low apolipoprotein A-I concentrations (5 micrograms/ml), the addition of apolipoprotein D to the incubates resulted in significantly higher esterification rates as compared to substrates containing apolipoprotein A-I only. This was not the case using substrates with high apolipoprotein A-I concentrations (50 micrograms/ml). From our results we speculate that apolipoprotein D may have some stabilizing effect on the enzyme LCAT.

Studies on the composition of pig serum lipoproteins. Isolation and characterization of different apoproteins.

1. Different lipoprotein density fractions from pig serum were isolated by phosphotungstate precipitation followed by purification in the preparative ultra-centrifuge. 2. The protein part of very low density lipoproteins was composed of approximately 52 percent lipoprotein B apoprotein and the rest of lipoprotein C II apoprotein and other as yet unidentified peptides. 3. The protein moiety of low density lipoproteins consisted primarily of lipoprotein B apoprotein (over 95 percent); the amino acid compositions of lipoprotein B apoprotein of very low and low density lipoproteins were practically identical. 4. The predominant polypeptide of pig serum high density lipoproteins exhibited an amino acid composition and a molecular weight very similar to human liprotein A I apoprotein. In contrast to human lipoprotein A I apoprotein, the apoprotein from pigs was found to release leucine first followed by alanine, threonine, and lysine upon incubation with carboxypeptidase A. 5. In pig serum the major lipoprotein C apoprotein was found to be a polypeptide similar in amino acid composition to lipoprotein C II apoprotein from human serum. The molecular weight of this polypeptide is approximately 8000. Incubation experiments with carboxypeptidase A indicate serine to be the most likely C-terminal amino acid.

Lipoprotein (a) is not a metabolic product of other lipoproteins containing apolipoprotein B.

125I-Labeled autologous very low density lipoprotein (VLDL) was injected intravenously into three lipoprotein (a) positive individuals. One other lipoprotein (a) positive subject received 125I-labeled VLDL from a a lipoprotein (a) negative donor. Specific activity of apolipoprotein B in VLDL, low density lipoprotein (LDL) and lipoprotein (a) was measured for 5 days. In the lipoprotein (a) fraction only traces of radioactivity could be detected, which were caused by contamination with labeled LDL. No precursor-product relationship existed between apolipoprotein B in VLDL or LDL and apolipoprotein B in lipoprotein (a). One lipoprotein (a)-positive individual was kept on a fat-free diet for 4 days to prevent chylomicron formation; no change in the serum level of lipoprotein (a) could be detected under these conditions. The data of this study indicate that lipoprotein (a) is not a metabolic product of VLDL or LDL. Also chylomicrons are not likely to play role as a precursor for lipoprotein (a). It is concluded that lipoprotein (a) is synthesized as a separate lipoprotein.

The structure and morphology of the abnormal serum lipoprotein-X.

The structure and morphology of an abnormal lipoprotein particle present in the serum of patients with obstructive jaundice has been investigated by gel filtration, electron microscopy and NMR spectroscopy. Lipoprotein-X is a spherical lipoprotein particle with an average Stokes diameter of approximately 40 nm and a wide size distribution ranging from 20 to 70 nm. Different from all lipoprotein structures known so far lipoprotein-X is a hollow particle (= vesicle) with a water-filled internal cavity surrounded by a continuous, single bilayer which is impermeable to cations and K3Fe(CN)6. The packing of the bilayer is tighter and the segmental motion of both the polar group and the hydrocarbon chains are significantly reduced relative to typical phosphatidylcholine bilayers. In terms of segmental motion and anisotropy of packing the lipoprotein-X bilayer closely resembles a model bilayer system consisting of phosphatidylcholine, lysophosphatidylcholine, sphingomyelin and cholesterol mixed in the same molar ratio as in lipoprotein-X. In that model system the phospholipid distribution between the two layers of the bilayer is asymmetric with (sphingomyelin + lysophosphatidylcholine) being preferentially located on the inner layer and phosphatidylcholine preferentially on the outer layer of the bilayer. By analogy with the model system the phospholipid distribution in lipoprotein-X bilayers is proposed to be also asymmetric.

Oxidation of lipoprotein Lp(a). A comparison with low-density lipoproteins.

Aimed at identifying possible mechanisms of the suggested high atherogenicity of Lp(a), its susceptibility for Cu(II)-induced oxidation was studied and compared with that of LDL. Since the content of antioxidants as well as the fatty acid pattern of a lipoprotein greatly affects its oxidizability, Lp(a) and LDL were characterized first with respect to these substances. Paired samples of low-density lipoproteins (LDL) and Lp(a) were isolated from seven individual donors and compared with each other. This study showed that LDL and Lp(a) are very similar with respect to their fatty acid and antioxidant composition. LDL contains approx. 1132 nmol of total fatty acids/mg lipoprotein and LDL 1466 nmol total fatty acids/mg lipoprotein. Analysis of the fatty acid composition of individual lipid classes (cholesteryl esters, phospholipids and triacylglycerols) revealed also a high similarity in the composition of these lipid classes between the two lipoproteins. A comparison of the antioxidant composition showed that Lp(a) contains less alpha-tocopherol than LDL (1.6 +/- 0.35 nmol/mg vs. 2.1 +/- 0.25 nmol/mg LDL). In copper(II)-induced lipid peroxidation experiments we found a striking difference in the susceptibility of individual lipoprotein classes between all donors. In addition, Lp(a) exhibited a 1.2 to 2.4 longer lag-phase than the corresponding LDL preparation from the same blood donor. Treatment of Lp(a) with neuraminidase resulted in a drastic decrease of the lag-phase of Lp(a). Neuraminidase treatment of LDL on the other hand had no significant effects on its susceptibility to oxidation. Supplementation of neuraminidase-treated Lp(a) with N-acetylneuraminic acid (NANA) at concentrations comparable to the naturally occurring amounts of NANA in the Lp(a) protein moiety led to an increase of the lag-phase yielding values which were comparable to those observed with native Lp(a). These results demonstrate that the fatty acid composition as well as the antioxidant concentrations of Lp(a) and LDL are quite similar; despite this fact, Cu2(+)-mediated oxidation of Lp(a) is retarded in comparison to LDL which might be due to the higher content of NANA in Lp(a).

Effect of tranexamic acid and delta-aminovaleric acid on lipoprotein(a) metabolism in transgenic mice.

The assembly of lipoprotein(a) (Lp(a)) is a two-step process which involves the interaction of kringle-4 (K-IV) domains in apolipoprotein(a) (apo(a)) with Lys groups in apoB-100. Lys analogues such as tranexamic acid (TXA) or delta-aminovaleric acid (delta-AVA) proved to prevent the Lp(a) assembly in vitro. In order to study the in vivo effect of Lys analogues, transgenic apo(a) or Lp(a) mice were treated with TXA or delta-AVA and plasma levels of free and low density lipoprotein bound apo(a) were measured. In parallel experiments, McA-RH 7777 cells, stably transfected with apo(a), were also treated with these substances and apo(a) secretion was followed. Treatment of transgenic mice with Lys analogues caused a doubling of plasma Lp(a) levels, while the ratio of free:apoB-100 bound apo(a) remained unchanged. In transgenic apo(a) mice a 1. 5-fold increase in plasma apo(a) levels was noticed. TXA significantly increased Lp(a) half-life from 6 h to 8 h. Incubation of McA-RH 7777 cells with Lys analogues resulted in an up to 1. 4-fold increase in apo(a) in the medium. The amount of intracellular low molecular weight apo(a) precursor remained unchanged. We hypothesize that Lys analogues increase plasma Lp(a) levels by increasing the dissociation of cell bound apo(a) in combination with reducing Lp(a) catabolism.

Factors affecting the conversion of high-density lipoproteins: experiments with pig and human plasma.

The conversion of pig high-density lipoproteins (HDL) (mainly HDL3) to fractions of lower densities was studied by incubating pig plasma for 24 h at 37 degrees C in the presence and absence of lipoprotein lipase from bovine milk, lecithin:cholesterol acyltransferase, cholesteryl ester transfer protein and triacylglycerol-rich particles (very-low-density lipoproteins (VLDL) or Intralipid). The results can be summarized as follows. In the presence of lipoprotein lipase and at a VLDL/HDL mass ratio of 2, the F-1.210 of pig HDL was shifted from 3.3 to 4.2, which is characteristic for human HDL2. This shift was caused by the excessive increase in the free fatty acid content in HDL. If 50 g/l of bovine serum albumin were added prior to incubation, the flotation rate of HDL remained in the HDL2a region. If lecithin:cholesterol acyltransferase was active in fasting pig plasma during incubation, we observed only a negligible increase of F-1.210 in HDL. If pig lipoproteins were incubated with human lipoprotein-free serum as a source of cholesteryl ester transfer activity, a slight increase in the flotation rate of HDL was observed, which was amplified in the presence of active lecithin:cholesterol acyltransferase. Pig HDL was converted to a fraction with F-1.210 of 4.2, which is typical for human HDL2, only if active lecithin:cholesterol acyltransferase, cholesteryl ester transfer protein and triacylglycerol-rich particles were present in the incubation mixture. From our results we also concluded that apolipoprotein A-II plays no role in the HDL2 formation.

Endogenously produced glycosaminoglycans affecting the release of lipoprotein lipase from macrophages and the interaction with lipoproteins.

Macrophages are intimately involved in the pathogenesis of atherosclerotic diseases. A key feature of this process is their uptake of various lipoproteins and subsequent transformation to foam cells. Since lipoprotein lipase (LPL) is believed to play a role in foam cell formation, we investigated if endogenously produced proteoglycans (PGs) affect the release of this enzyme from macrophages. The human leukaemic cell line THP-1 which differentiates into macrophages by treatment with phorbol ester (phorbol 12-myristate 13-acetate) served as a model. The differentiation of THP-1 macrophages promoted the release of PGs into the cell medium which caused the detachment of LPL activity from the cell surface, and prevented LPL re-uptake and inactivation. These PGs were mainly composed of chondroitin sulfate type and exerted a heparin-like effect on LPL release. LPL is known to increase the cell association of lipoproteins by the well known bridging function. Exogenous bovine LPL at a concentration of 1 microg/ml enhanced low density lipoprotein (LDL)-binding 10-fold. Endogenously produced PGs reduced LPL-mediated binding of LDL. It is proposed that the differentiation-dependent increase in the release of PGs interferes with binding of LPL and reduces lipoprotein-binding to macrophages.

Lipoprotein (a) and plasminogen are immunochemically related.

Earlier studies demonstrated that lipoprotein (a), a lipoprotein of high atherogenicity, possesses proteolytic activity. In this report, we provide evidence that the lipoprotein (a)-specific antigen, apoprotein (a) is immunochemically related to plasminogen. This was demonstrated by polyclonal antisera from rabbit, sheep and horse, and with three monoclonal antibodies from mouse. Using immunospecific adsorbers against lipoprotein (a), all plasminogen could be adsorbed from lipoprotein (a)-positive and apparently lipoprotein (a)-negative plasma. As an additional similarity to plasminogen, lipoprotein (a) binds selectively to lysine-Sepharose, but with a somewhat lower affinity. In an assay system for measuring the fibrinolytic activity challenged with streptokinase, lipoprotein (a) prolonged strikingly the fibrinolysis time under certain experimental conditions.

In vitro formation of HDL-2 from HDL-3 and triacylglycerol-rich lipoproteins by the action of lecithin:cholesterol acyltransferase and cholesterol ester transfer protein.

In order to study the factors responsible for the formation of high-density lipoprotein subfraction-2 (HDL-2), very-low-density lipoproteins (VLDL) and HDL-3 were mixed and incubated with purified bovine milk lipoprotein lipase, human serum lecithin:cholesterol acyltransferase, cholesteryl ester transfer protein and mixtures thereof. The results can be summarized as follows: Incubation of HDL-3 and VLDL for 24 h at 37 degrees C without enzymes did not cause any significant change in the protein:lipid ratio or in the flotation constant of the HDL. Cholesteryl ester transfer protein treatment caused only an exchange of part of the HDL cholesteryl esters with VLDL triacylglycerols. Lipoprotein lipase caused a slight shift of HDL-hydrated density to lower values; HDL-2b, however, was not formed. Incubation of HDL-3 and VLDL with lecithin:cholesterol acyltransferase or mixtures of lecithin:cholesterol acyltransferase and lipoprotein lipase reduced the HDL-protein:lipid ratio and increased the HDL-flotation rate. The newly formed HDL resembled that of native HDL-2a. The incubation of HDL-3 and VLDL with lecithin:cholesterol acyltransferase and cholesteryl ester transfer protein caused a shift of the HDL-3 into an HDL-2b-like fraction. Particles resembling HDL-2b in the analytical ultracentrifuge were also formed if VLDL + HDL-3 were incubated with lipoprotein lipase or lipoprotein lipase + cholesteryl ester transfer protein in a medium containing low amounts of albumin, insufficient for binding all liberated fatty acids during hydrolysis. The incubation of mixtures of HDL-3 and chylomicrons enriched with apoAI in the presence of lecithin:cholesterol acyltransferase and cholesteryl ester transfer protein caused the formation of HDL-2-like particles which resembled those of native HDL-2 also with respect to the apoAI/AII ratio.

Lipoprotein-associated alpha-tocopheryl-succinate inhibits cell growth and induces apoptosis in human MCF-7 and HBL-100 breast cancer cells.

alpha-Tocopheryl succinate (alpha-TS) is a potent inhibitor of tumor cell proliferation. The goal of the present study was to investigate whether and to what extent alpha-TS associates with plasma lipoproteins and if alpha-TS-enriched lipoproteins inhibit breast cancer cell growth in a manner comparable to the free drug. In vitro enrichment of human plasma revealed that alpha-TS readily associated with the main lipoprotein classes, findings confirmed in vivo in mice. At the highest alpha-TS concentrations, lipoproteins carrying 50000 (VLDL), 5000 (LDL) and 700 (HDL) alpha-TS molecules per lipoprotein particle were generated. alpha-TS enrichment generated lipoprotein particles with slightly decreased density and increased particle radius. To study whether the level of LDL-receptor (LDL-R) expression affects alpha-TS uptake from apoB/E containing lipoprotein particles human breast cancer cells with low (MCF-7) and normal (HBL-100) LDL-R expression were used. The uptake of free, VLDL- and (apoE-free) HDL(3)-associated alpha-TS was nearly identical for both cell lines. In contrast, uptake of LDL-associated alpha-TS by HBL-100 cells (normal LDL-R expression) was about twice as high as compared to MCF-7 cells (low LDL-R expression). VLDL and LDL-associated alpha-TS inhibited proliferation most effectively at the highest concentration of alpha-TS used (100% inhibition of MCF-7 growth with 20 microg/ml of lipoprotein-associated alpha-TS). However, also alpha-TS-free VLDL and LDL inhibited HBL-100 cell proliferation up to 55%. In both cell lines, alpha-TS-enriched HDL(3) inhibited cell growth by 40-60%. Incubation of both cell lines in the presence of free or lipoprotein-associated alpha-TS resulted in DNA fragmentation indicative of apoptosis. Collectively, the present findings demonstrate that: (1) alpha-TS readily associates with lipoproteins in vitro and in vivo; (2) the lipoprotein-enrichment efficacy was dependent on the particle size and/or the triglyceride content of the lipoprotein; (3) uptake of LDL-associated alpha-TS was apparently dependent on the level of LDL-R expression; and (4) lipoproteins were efficient alpha-TS carriers inducing reduced cell proliferation rates and apoptosis in human breast cancer cells as observed for the free drug.

Prothrombinase activity of human platelets is inhibited by beta 2-glycoprotein-I.

In the present paper the influence of beta 2-glycoprotein-I, also known as apolipoprotein H, upon the prothrombinase activity of platelets and phospholipid vesicles was investigated. The results can be summarized as follows. 1. The prothrombinase activity of resting, non-activated platelets, lysed platelets and vesicles composed of phosphatidylserine and phosphatidylcholine at different molar ratios is inhibited by beta 2-glycoprotein-I in a dose-dependent manner. The concentration of glycoprotein which produces marked inhibition is within the physiological plasma concentration range of beta 2-glycoprotein-I. 2. The time dependence of this inhibition is a relatively slow process, which is not fully expressed before 1 h of incubation. 3. The effect of the glycoprotein is not due to a direct interaction with the components of the prothrombinase complex, i.e. factors Xa, Va, Ca2+ or prothrombin, nor is the inhibitory action abolished by increasing concentrations of coagulation factors Xa and Va. This suggests that beta 2-glycoprotein-I causes a reduction of the prothrombinase binding sites of these coagulation factors to platelets or phospholipid vesicles. 4. The prothrombinase activity of platelets stimulated with ionophore A23187 or with collagen plus thrombin is also inhibited by beta 2-glycoprotein-I in a manner similar to that observed for phospholipid vesicles or for lysed platelets. These findings suggest a regulatory role for beta 2-glycoprotein-I in the pathway of blood coagulation.