Effects of granulocyte-macrophage colony-stimulating factor on the levels of VLDL and LDL receptor mRNAs in vivo

We investigated the mechanism by which granulocyte-macrophage colony-stimulating factor (GM-CSF) lowers plasma cholesterol levels. Recombinant human GM-CSF (rhGM-CSF) was administered to normal and Watanabe heritable hyperlipidemic (WHHL) rabbits. Treatment with rhGM-CSF reduced the levels of cholesterol and triglyceride in these animals. In vitro colony assay for hematopoietic progenitors indicated that rhGM-CSF was capable of supporting granulocyte-macrophage colony formation in rabbits, suggesting that rhGM-CSF stimulates macrophage function even in rabbits. Northern blot analysis of rabbit very-low density lipoprotein (VLDL) receptor showed that rhGM-CSF elevated the levels of VLDL receptor mRNA 2.6- and 1.8-fold in muscles of normal WHHL rabbits, respectively, 1.5 hours after a single injection. Increases of 1.5- and 1.4-fold were observed in muscles of these rabbits after 5 days of administration. No changes were found in the LDL receptor mRNA levels in liver, spleen or bone marrow. These findings show that the lowering of lipids by GM-CSF may be mediated through the up-regulation of the VLDL receptor mRNA and the enhancement of macrophage function.

Effects of particle size on cell uptake of model triglyceride-rich particles with and without apoprotein E

The effect of apoprotein E on cellular uptake of "VLDL-size" and "IDL-size" triacylglycerol-phospholipid emulsion particles was studied in J-774 macrophages and fibroblasts. In the absence of apoprotein E (apo E), uptake of the smaller IDL-size particles was up to 2-fold higher by mass and 100-fold higher as calculated by particle number. Apo E enhanced the uptake of both VLDL-size and IDL-size emulsion particles, but the effect was greater on the uptake of larger particles (4-5-fold) as compared to up to a 2-fold increase in the uptake of IDL-size particles. In fibroblasts, particle uptake was less than in macrophages (30-50%), but preferential uptake of smaller particles was similarly observed. Particle internalization was demonstrated by 125I-apo E degradation and resistance to particle release by heparin-suramin. In the absence of apo E, cholesteryl ester of emulsion particles (prepared with trace amounts of [3H]cholesteryl ester) was hydrolyzed to free cholesterol, proving internalization and intracellular metabolism. Double-label experiments using DiI-labeled emulsion particles, in the absence and presence of apo E, showed that emulsion particles are rapidly targeted to perinuclear lysosomes. Thus, at physiological concentrations of triglyceride-rich particles, non-receptor-mediated uptake is a mechanism for the uptake of VLDL-size and IDL-size particles into cells.

Diet-induced type IV-like hyperlipidemia and increased body weight are associated with cholesterol gallstones in hamsters

Male Syrian hamsters (60-70 g) were fed purified diets containing 5% fat (American Fat Blend) and 15% fiber with or without 0.3% cholesterol (0.86 mg/kcal), for 12 weeks. Hamsters fed the cholesterol-supplemented challenge diet revealed a major increase in plasma triglyceride between 9 and 12 weeks, whereas plasma cholesterol (which reflected body weight dynamics) increased three-fold up to nine weeks and plateaued (342 +/- 22 vs. 122 +/- 5 mg/dL). The greatest increases in cholesterol occurred in the very low density lipoprotein (VLDL) and high density lipoprotein (HDL2) fractions. Gallstone incidence was similar (69% vs. 78%) for cholesterol-supplemented vs. control hamsters, but the type of stones differed. Of the cholesterol-supplemented hamsters with gallstones, 45% had cholesterol stones and 55% had pigment stones. Only pigment stones were seen in control hamsters. Hamsters with cholesterol stones were 25% heavier and transported most cholesterol in VLDL (33 +/- 5%), approximately double that in VLDL of cholesterol-supplemented hamsters with no stones (19 +/- 3%) or cholesterol-supplemented hamsters with pigment stones (21 +/- 3%). Hamsters with pigment stones or no stones (regardless of diet fed) transported the majority of their cholesterol in HDL2 (44%), whereas this figure was only 27% in hamsters that developed cholesterol stones. Thus pigment stones develop routinely in hamsters fed casein-based purified diets. Adding dietary cholesterol resulted in cholesterol gallstones only in those hamsters that gained the most weight and whose terminal VLDL/HDL cholesterol ratio exceeded 1.0, not unlike the lipoprotein profile of obese humans who develop cholesterol gallstones.

Dynamic structure of the lower density lipoproteins. II. Deuterium NMR studies of the monolayer of very low and low density lipoproteins

The order of phosphatidylcholine (PC) acyl chains in the surface monolayer of very low density lipoproteins (VLDL) and low density lipoproteins (LDL) has been determined from 2H nuclear magnetic resonance order parameters, SCD, using selectively deuterated PC or palmitic acids. From the computer simulated line shapes, we find two distinct phospholipid domains within the amphiphilic monolayer of both VLDL and LDL. In the more ordered domain of LDL, SCD was approximately 0.3 for the "plateau" chain region. The SCD values of VLDL particles are similar to those of LDL for the 5,6- and 11,12-positions, hence we suggest the organization of the more ordered region of VLDL and LDL are similar. The domain of low order in LDL comprises less than 10% of the phospholipid molecules (we do not distinguish between PC and sphingomyelin), having approximately the same order (SCD less than 0.1) as egg PC - sphingomyelin unilamellar vesicles. In VLDL, the domain of low order comprises between approximately 10 and approximately 20% of the phospholipid molecules and the entire acyl chain is in an essentially isotropic environment (SCD less than 0.02). We prepared VLDL-sized microemulsions composed of egg PC, deuterated PC, and triolein to test whether the apoproteins were responsible for creating the two differently organized domains in VLDL and LDL. Surprisingly, these protein-free particles also showed two domains of different order at two temperatures. The high order region, however, is less ordered than in VLDL and LDL. We explain two surface domains of PC in terms of lipid organization and the unique interactions of lipids in the various lipoprotein particles.

Effect of plasmapheresis on the liver uptake of ApoB-lipoproteins labeled with technetium-99m

To study liver low density lipoprotein (LDL)-receptor activity before and after plasmapheresis, [99mTc] very low density lipoprotein (VLDL) was used. Autologous VLDL was labeled, sterilized by filtration, and administered intravenously to patients under a gamma camera. The uptake of lipoproteins in the liver was measured by scintiscanning. Liver activity curves were generated for each patient. The liver activity in patients with the heterozygous form of familial hypercholesterolemia (FH) and in patients with symptomatic atherosclerosis (SA) without hereditary deficit of LDL receptors was reduced as compared to healthy people. Plasmapheresis enhanced the liver uptake of the 99mTc-labeled lipoproteins in atherosclerotic patients. Thus, labeled metabolites could presumably be of use in assessing the effect of plasmapheresis on liver function.

Effect of corticosterone on circulating concentrations of corticosterone, prolactin, thyroid hormones and somatomedin C and on fattening in broilers selected for high or low fat content

Daily changes in the concentrations of plasma corticosterone, prolactin, thyroid hormones and somatomedin C were measured in 28-day-old fat and lean lines of broilers produced by selection for high and low concentrations of very low density lipoproteins (VLDL). The effects of daily injections of corticosterone on the concentrations of these hormones and on fattening were compared in the two lines. The selection procedure had no effect on the concentrations of any of the hormones. However, daily rhythms in concentrations of plasma corticosterone, tri-iodothyronine (T3) and prolactin were less often observed in the fat line than in the lean line. No differences were seen between lines in the daily rhythms in plasma thyroxine (T4) and somatomedin C. Daily injections of 2500 micrograms corticosterone/kg body weight, in both lines, depressed mean concentrations of plasma prolactin, T3 and somatomedin C and body weight. This dose of corticosterone also increased abdominal fat pad and liver weights expressed as a percentage of body weight. The liver and fat pad responses to 2500 micrograms corticosterone in both lines were greater when the steroid was injected at the end rather than towards the beginning of the 14-h daily photoperiod. There was no difference between the lines in the fattening response to corticosterone. Lower doses of 100 and 500 micrograms corticosterone per day did not induce fattening or affect concentrations of plasma prolactin. They did, however, depress concentrations of plasma T3. Concentrations of plasma T4 were increased in both lines treated with 2500, but not with 100 or 500 micrograms corticosterone, towards the beginning of the daily photoperiod.(ABSTRACT TRUNCATED AT 250 WORDS)

Thermotropic properties and molecular dynamics of cholesteryl ester rich very low density lipoproteins: effect of hydrophobic core on polar surface

Cholesteryl ester rich very low density lipoproteins (CER-VLDL), isolated from the plasma of rabbits fed a hypercholesterolemic diet, have been studied by differential scanning calorimetry (DSC), 13C nuclear magnetic resonance (NMR), and spin-label electron paramagnetic resonance (EPR) to determine the temperature-dependent dynamics of cholesteryl esters in the hydrophobic core and of phospholipids on the polar surface. Intact CER-VLDL exhibit two DSC heating endotherms; these occur at 40-42 and 45-48 degrees C. Cholesteryl esters isolated from CER-VLDL also exhibit two DSC endotherms; these occur at 50.0 and 55.1 degrees C and correspond to the smectic----cholesteric and cholesteric----isotropic liquid-crystalline phase transitions. A model mixture containing cholesteryl linoleate, oleate, and palmitate in a ratio (0.21, 0.51, and 0.28 mol fraction) similar to that in CER-VLDL exhibited comparable DSC endotherms at 45.2 and 51.5 degrees C. CER-VLDL at 37 degrees C gave 13C NMR spectra that contained no resonances assignable to cholesteryl ring carbons but detectable broad resonances for some fatty acyl chain carbons, suggesting the cholesteryl esters were in a liquid-crystalline state. When the mixture was heated to 42 degrees C, broad ring carbon resonances became detectable; at 48 degrees C, they became narrow, indicating the cholesteryl esters were in an isotropic, liquid-like state. With increasing temperature over the range 38-60 degrees C, the resonances for cholesteryl ring carbons C3 and C6 in CER-VLDL narrowed differentially. Similar spectral changes were observed for the synthetic cholesteryl ester mixture, except they occurred at temperatures about 10 degrees C higher. These results indicate that the two DSC transitions in CER-VLDL do not directly correlate with the smectic----cholesteric and cholesteric----isotropic transitions exhibited by pure cholesteryl esters. (5-Doxylpalmitoyl)-phosphatidylcholine (5-DP-PC) and (12-doxylstearoyl)phosphatidylcholine (12-DS-PC) were used to probe the polar surface monolayer of CER-VLDL; the corresponding cholesteryl esters (5-DP-CE and 12-DS-CE) were used to probe the hydrophobic core. None of these probes in CER-VLDL detected an abrupt change in EPR order parameters, S, or maximum splitting, 2T max, over the temperature range 20-58 degrees C even though 12-DS-PC and 5-DP-PC can detect phase transitions in phospholipid bilayers and 12-DS-CE and 5-DP-CE can detect phase transitions in neat cholesteryl esters. However, 12-DS-CE and 5-DP-CE did detect a much greater acyl chain order for the neutral lipids of CER-VLDL than for those of normal triglyceride-rich VLDL.(ABSTRACT TRUNCATED AT 400 WORDS)

[Determination of the radius, volume and surface area of plasma lipoproteins using fluorescent probes]

The effect of radiationless energy transfer between the fluorescent probes was used to determine the radius, volume and surface area of the blood plasma lipoprotein. Anthracene and p-terphenyl, distributed over the whole volume of lipids of a lipoprotein particle, and HSPH-14 localized on its surface served as energy donor and acceptor probes. Human blood lipoproteins of very low (LVLD), low (LLD2), and high (LHD2 and LHD3) density were studied. All the fluorescence-measured lipoprotein volumes were rather close to the data resulted from the weight analysis. The surface areas were equal to 230, 210, 400 and 330 m2 per 1 g of lipoprotein and the radii--11, 11, 7.5, 7.2 nm, respectively. All the measurements were made in solutions, without any denaturating effects on lipoprotein, its concentration being 1 mg/ml and lower.

Rotational mobility associated with the protein moiety of human serum lipoproteins from tryptophan phosphorescence anisotropy measurements

The steady-state phosphorescence anisotropy of human low density (LDL) and very low density (VLDL) serum lipoproteins in a glycerol--buffer solvent has been investigated. By virtue of the long lifetime of the triplet state, depolarization of the emission resulting from slow rotational motions is observed between -90 and -50 degrees C. Despite the number of emitting residues within these complexes, the rotational behavior can be represented within experimental error by a single correlation time. The magnitude and temperature dependence of the rotational correlation times observed for LDL are consistent with overall rotation of essentially spherical rigid particles as the source of the phosphorescence depolarization. Preliminary data for VLDL indicate the presence of internal peptide motions which are more rapid than those of the overall complex.

Ascites chylomicron: a poor substrate for hepatic triglyceride lipase

A patient with nephrotic syndrome and morbus Kimura (eosinophilic granuloma) showed chylous ascites. Ascites chylomicrons were analyzed and used to study the substrate specificity of lipoprotein lipase and hepatic triglyceride lipase. Ascites triglyceride and cholesterol concentrations were 191 and 12 mg/dl, respectively. Both apo CII and apo CIII content in ascites were approximately one-third of those of plasma from normal subjects. Ascites chylomicrons were incubated with either lipoprotein lipase or hepatic triglyceride lipase, which were prepared from postheparin plasma using heparin-Sepharose affinity chromatography. Lipoprotein lipase hydrolyzed ascites chylomicrons, while hepatic triglyceride lipase did not. These results suggest different functions of these two lipases in chylomicron catabolism.

[Effect of hyperalphalipoproteinemia on structural characteristics of plasma lipoproteins according to electron paramagnetic resonance spin probe findings]

Spin probe, a stearic acid derivative, was used to study the structural features of different lipoproteins (LP) from plasma of subjects with different plasma level of high density LP (HDLP). Access of spin probe located in the internal nonpolar regions of HDLP for the reducer, ascorbic acid, was higher in hyperalphalipoproteinemia than in mean values of HDLP cholesterol concentration. An analogous effect was seen in subjects with LP of very low density. Possible causes of such differences as well as their role in biochemical reactions that proceed with LP participation are discussed.

[Elastic properties of lipid bilayer membranes during incorporation of plasma lipoproteins]

Interaction between lipoproteins of very low density /LPVLD/ with bilayer lipid membranes was studied in blood plasma of healthy rabbits and in rabbits with alimentary hyperlipoproteinemia. The LPVLD of healthy animals did not produce any alterations in elasticity and volume of bilayer lipid membranes within 120 sec, whereas the lipid fraction from animals with hyperlipoproteinemia altered these physical properties of the membranes at the period studied. The factors, which are responsible for the action of LPVLD on the bilayer lipid membranes, were both composition and structure of lipoprotein particles. The importance of nitial parameters of the membrane structure in its interaction with lipoproteins was shown using the model system.

Antibody-independent neutralization of vesicular stomatitis virus by human complement. II. Formation of VSV-lipoprotein complexes in human serum and complement-dependent viral lysis

Vesicular stomatitis virus (VSV) is efficiently neutralized by normal, nonimmune human serum without the participation of antibody. Neutralization is complement- (C) dependent and requires the early-acting components of the classical pathway, C1, C4, C2, and C3, but not later-acting C components. In further studies, normal human serum was found to markedly increase the density of a variable but significant proportion of virus-associated RNA and to markedly decrease the density of the remainder of virus-associated RNA. The RNA of increased density was found to be dense ribonucleocapsid cores released from VSV by C-dependent viral lysis mediated through the classical pathway. The released ribonucleocapsid cores found at the bottom of sucrose density gradient after incubation of VSV with human serum were resistant to degradation by proteolytic enzymes. The VSV-derived RNA found floating on the tops of sucrose density gradients performed on serum-treated VSV was infectious virus. The decreased density was due to binding of VSV to human serum lipoproteins (LP), primarily very low density lipoproteins (VLDL). Binding of VLDL to VSV required the presence of the viral envelope and the external glycoprotein, G. Despite the binding of LP to VSV, LP did not neutralize VSV, and LP-depleted sera were fully active in neutralizing VSV. Thus, LP do not represent an accessory factor for the C-dependent neutralization of VSV.

Suppression of 3-hydroxy-3-methylglutaryl-CoA reductase by low density lipoproteins produced in vitro by lipoprotein lipase action on nonsuppressive very low density lipoproteins

Very low density lipoproteins (VLDL), Sf60 to 400, from normolipemic individuals do not suppress 3-hydroxy-3-methylglutaryl-CoA reductase activity in cultured normal human fibroblasts at concentrations 20-fold higher than those of low density lipoproteins (LDL) that give total suppression. To determine if these VLDL contain all of the structural elements necessary for receptor-mediated suppression, they were converted in vitro with bovine milk lipoprotein lipase to low density lipoproteins. These LDL-like lipoproteins were as effective in suppression as LDL isolated directly from plasma, with half-maximal and complete suppression at 1 and 4 microgram of cholesterol ml-1. Neither native LDL nor LDL produced in vitro suppressed receptor-negative fibroblasts. We conclude that action of lipoprotein lipase on VLDL leads to a rearrangement of lipoprotein components that permits interaction of LDL produced in vitro with the LDL-specific cell surface receptor of fibroblasts and subsequent suppression of 3-hydroxy-3-methylglutaryl-CoA reductase.

Ultrastructure and cytochemistry of the yolk syncytial layer in the alevin of trout (Salmo fario trutta L. and Salmo gairdneri R.) after hatching. II. The cytoplasmic zone

In contrast to the vitellolysis zone which is involved in the degradation of the yolk, the cytoplasmic zone of the yolk syncytial layer, composed of many cytoplasmic organelles, is implicated in a secretory process. The granular endoplasmic reticulum of the latter is extremely well developed and organized into trabeculae. The yolk nuclei show a RNA positive reaction. The Golgi apparatus is implicated in the elaboration of very low density lipoproteins (VLDL) and of acid phosphatase. The numerous mitochondria seem to suggest an important energy metabolism in the solubilisation area. The appearance of certain special structures (crystalline bodies, pseudovesicular structures, lipochondria) as well as their relation with the organelles of the cytoplasmic zone, re-inforces the impression of a layer with a secretory nature and suggests its participation in the remodelling of the yolk products produced in the vitellolysis zone. The results of the investigations concerning the acid phosphatase activity suggest that this enzyme plays a role on the one hand in the degradation of certain platelets which penetrate into the cytoplasmic zone, and on the other hand in the regulation of VLDL, in the lysis of secretory products elaborated by the cytoplasmic zone. The possible presence of microperoxisomes is discussed as well as the positive detection of glucose-6-phosphate dehydrogenase.

Structure of the dimyristoylphosphatidylcholine vesicle and the complex formed by its interaction with apolipoprotein C-III: X-ray small-angle scattering studies

Single bilayer vesicles of dimyristoylphosphatidylcholine have been investigated by small-angle X-ray scattering at 28 degrees C. The results indicate that these vesicles are hollow spherical shell structures with an outer radius of approximately 12 nm and a molecular weight of (3.2 +/- 0.5) X 10(6). The shell was found to be 4.4 +/- 0.2 nm thick with a cross-sectional electron-density profile characteristic for a single phospholipid bilayer. Upon interaction of these vesicles with apolipoprotein C-III from human very low density lipoproteins at a protein/lipid ratio greater than 0.08 (g/g), a complex containing 0.25 g of protein/g of lipid, with molecular weight of (3.9 +/- 0.4) X 10(5), is formed. The shape analysis indicates a highly asymmetric particle with an internal partition of low and high electron density resembling that produced by a bilayer structure. Model calculations and curve-fitting procedures show good agreement between the experimental scattering curve and that computed for an oblate ellipsoidal structure with dimensions of 17 X 17 X 5 nm and a 1 nm thick shell of high electron density surrounding the core of low electron density.

Effect of serum-antigen incubation times on the expression of non-specific inhibitors of rubella hemagglutination

Under certain conditions, serum very low-density lipoproteins (VLDL) and high-density lipoproteins (HDL) can inhibit rubella hemagglutination. The level of this non-specific hemagglutination-inhibition (HI) activity increases as the incubation period between serum and antigen is increased. Treatment of serum with heparin-MnCl2 does not precipitate HDL, and may not effect complete removal of all VLDL. This treatment method, therefore, should be considered a source of false-positive reactions, especially when extended serum-antigen incubation periods are used to enhance HI activity and to detect low levels of IgM.

Relative increase in apolipoprotein CII content of VLDL and chylomicrons in a case with massive type V hyperlipoproteinaemia by nicotinic acid treatment

VLDL of fasting serum was fractionated into 4 fractions of decreasing particle size by preparative ultracentrifugation in a density gradient from a patient with massive type V hyperlipoproteinaemia before and after treatment with 12 g daily of nicotinic acid. Serum triglycerides fell from 58 to 9 mmol/1 in response to treatment due particularly to reduction of larger VLDL particles. Total, insoluble (apoprotein B) and soluble protein of all VLDL fractions also fell but the ratio of these 3 protein fractions to triglyceride rose particularly in the smaller VLDL fractions. The relative amount of apolipoprotein CII increased in all fractions and the ratio apo CII to triglycerides increased by 60--90% in all VLDL fractions. The relative amounts of apo CI, apo CII-2 and apo E appeared also to increase. The results are consistent with the hypothesis that low amounts of apo CII may play a role for the development of hypertriglyceridaemia.

Physical properties of the dimyristoylphosphatidylcholine vesicle and of complexes formed by its interaction with apolipoprotein C-III

The structure of a single bilayer vesicle of dimyristoylphosphatidylcholine has been characterized by sedimentation, densimetry, and light-scattering measurements. The molecular weight, partial specific volume, Stokes radius, and degree by hydration were found to be 2.68 X 10(6), 0.972 cm3/g, 125 A, and 0.86 g/g, respectively. From these quantities, a spherically symmetrical model has been derived that features a phospholipid bilayer 35.5 A thick and a hydration shell 9.3 A thick. This particle was shown to bind apolipoprotein C-III (apoC-III) up to 0.08 g/g without loss of its original vesicular structure. At protein-lipid ratios in excess of 0.08 g/g, sedimentation, gel chromatography, and light-scattering measurement indicated a dramatic decrease in Stokes radius and molecular weight. The sedimentation data showed these parameters to become constant at protein-lipid ratios in excess of 0.25 g/g. In this region, the Stokes radius and molecular weight were found to be approximately 80 A and 442 000, respectively. Within the constraints of these values and other data, several models for this complex are discussed.

Selective solubilization of apolipoproteins from hen's egg yolk very low density lipoprotein with guanidine hydrochloride and urea

The selective solubilization of apo-very low density lipoprotein (apo VLDL) of hen's egg yolk was achieved from intact VLDL with guanidine hydrochloride (GuHCl) or urea. The amount of extracted apoVLDL increased with increase of the reagent concentration. GuHCl was more effective than urea and more than 60% of apoVLDL was solubilized with 6 M GuHCl. Previously we reported the presence of five major apoVLDL components, GPI, ApoA, GPII, ApoB, and ApoC in order of size, and found that GPI and GPII were periodic acid-Schiff staining positive, while ApoA, ApoB, and ApoC were negative. With GuHCl or urea, GPI and GPII were easily solubilized, while ApoA and ApoB could not be extracted. The solubilized apoVLDL was rich in carbohydrates, especially sialic acid, compared with the residual apoVLDL. However, only slight differences in amino acid compositon were found between the soluble and the residual apoVLDL. After the partial removal of apoVLDL with GuHCl or urea, VLDL retained its particulate nature, and no destruction of the lipid core was observed. These results were interpreted as indicating that the release of apoVLDL with GuHCl or urea occurred from the surface of the VLDL particle and that the selectively solubilized apoVLDL fractions, such as GPI and GPII, were weakly bound to lipids on the surface of VLDL, while ApoA and ApoB were tightly associated with the VLDL particle.

Structure of an apolipoprotein-phospholipid complex: apoC-III induced changes in the physical properties of dimyristoylphosphatidylcholine

The effect of ApoC-III, a major apoprotein constituent of human very low density lipoproteins, on the physical properties of dimyristoylphosphatidylcholine (DMPC) vesicles has been studied by magnetic resonance and fluorescence techniques. The sharp gel-liquid crystalline transition usually observed at 23 C in DMPC is both broadened and elevated when ApoC-III is bound as determined (a) from measurements of microscopic viscosity by pyrene excimer fluorescence, (b) from the distribution of di-tert-butyl nitroxide between the bulk aqueous phase and the fluid lipid phase, and (c) from the motion of fatty acyl chains of spin-labeled phosphatdylcholine. Experiments involving the translocation of ascorbate and charged nitroxide ions and the movement of paramagnetic Eu 3+ ions indicate that when ApoC-III binds to DMPC vesicles, it increases their permeability or destroys their original bilayer structure. These two possibilities were distinguishable by gel filtration of the DMPC-ApoC-III complex (approximately 34 mol mol) that indicated that the product particles were significantly smaller than the original vesicles. Taken together, the data indicate that ApoC-III binding to DMPC not only decreases the acyl chain motion of individual lipid molecules, but also induces break-down of bilamellar vesicular structure to give significantly smaller complexes.

The solid phase synthesis of a protein activator for lecithin-cholesterol acyltransferase corresponding to human plasma apoC-I

Apolipoprotein C-I, a protein constituent of the very low density lipoproteins of human plasma, consists of a single chain of 57 amino acids. The total synthesis of a protein corresponding to apolipoprotein C-I in physical properties and compositions was accomplished by solid phase techniques employing a modified polystrene incorporating spacer groups between the point of attachment of the first residue and the polymer matrix. The synthetic apoprotein was shown to activate lecithin:cholesterol acyltransferase to the same extent as the native protein. Comparative lipid-binding studies with dimyristoyl phosphatidylcholine gave complexes for native and synthetic apoprotein which floated at the same density after ultracentrifugation in KBr gradients and had virtually the same lipid:protein ratios.

Interaction of apoliprotein C-III with phosphatidylcholine vesicles. Dependence of aproprotein-phospholipid complex formation on vesicle structure

We have studied the interaction of an apolipoprotein from human very low density lipoproteins (apoC-III) with egg yolk phosphatidylcholine in the form of single- and multi-bilayer vesicles. The reactivity of single-bilayer vesicles with apoC-III appears to be greater than that of the multi-bilayer vesicles according to several thermodynamic and spectrosconic criteria. In the complexes formed by the association of apoC-III with single-bilayer vesicles, the alpha-helical content of the peptide backbone and the apolarity of the environment around the tryptophan residues are greater than that observed in the complexes formed with the multibilayer vesicles. A higher yield and more homogeneous density distribution of lipid-apoprotein complexes results from the interaction of apoC-III with the single-bilayer vesicles relative to those obtained with the multi-bilayer vesicles. The enthalpy of association of apoC-III with phospholipid was greater for the single-shelled vesicles (25 kcal/mol apoC-III) than for the multi-shelled ones (18 kcal/mol apoC-III). The difference in reactivity of these two types of liposomes is not due to a difference in their fluidities since their fatty acid compositions are identical, but may be due to a difference in their areas of sterically accessible phospholipid, their permeabilities to the apoprotein, their radii of curvation, or a combination of these factors.

[Biological examination in hyperlipemia]

The authors review the various methods of investigation useful in the classification of hyperlipoproteinaemias. Estimation of cholesterol and triglycerides remain the most important elements but do not suffice alone to reach a conclusion and measurement of phospholipids would seem to be a useful addition. Electrophoresis on agar, isolating a larger quantity of prebetalipoproteins, does not always facilitate classification. Finally, ultracentrifugation is often necessary in those forms which are difficult to classify, these representing almost 20 p.cent of patients.

Diabetic hypertriglyceridemia

The conference opened with the clinical presentation of a 50-year-old male with fasting hyperglycemia (296 mg per cent) and hypertriglyceridemia (2736 mg per cent). The discussion began with a summary of current concepts regarding the manner in which chylomicra (intestine) and very low density lipoproteins (intestine and liver) are formed, transported into the plasma, and removed from the circulation. This was followed by a consideration of diabetic hypertriglyceridemia in which this syndrome was subdivided into two categories. The first form is seen in patients with severe fasting hyperglycemia, and is characterized by marked insulin deficiency, decreased very low density lipoprotein production, a fall in the activity of lipoprotein lipase, and hypertriglyceridemia secondary to a defect in removal of lipoproteins from the plasma. In contrast the other form of diabetic hypertriglyceridemia is seen in patients with minimal abnormalities of carbohydrate tolerance, and in this instance insulin resistance, not insulin lack, seems to play the pivotal role. In these patients, the rise in plasma triglyceride levels seems to be secondary to increased production of very low density lipoproteins, presumably as a result of the hyperinsulinemia associated with the insulin resistance. The conference ended with an attempt to relate the patient presented to the models of diabetic hypertriglyceridemia that had been defined.

The structure of human high density lipoprotein and the levels of apolipoprotein A-I in plasma as determined by radioimmunoassay

The major apoprotein of high density lipoprotein is apolipoprotein A-I (ApoA-I). In addition to being a structural component of this class of lipoproteins, ApoA-I also has a physiologic role as an activator of lecithin-cholesterol acyl transferase, an enzyme important in the metabolism of all lipoproteins. To measure ApoA-I content in human plasma, to assess its immunologic activity in hyperlipoproteinemia, and to carry out certain structural studies of high density lipoproteins, we have developed a double antibody radioimmunoassay. ApoA-I, isolated by gel filtration, was used to produce monospecific antisera. ApoA-I was iodinated by chloramine-T and the resulting [(125)I]-ApoA-I was purified by gel filtration. > 85% of [(125)I]-ApoA-I was precipitated by antibody, and 90% of bound [(125)I]ApoA-I was displaced by "cold" ApoA-I. Other lipoproteins and apoproteins did not react. Plasma and high density lipoprotein from normals and subjects with hyperlipoproteinemia displaced counts in parallel with ApoA-I, suggesting that the same antigenic determinants were reacting with antibody on lipid-free and lipid-associated ApoA-I. However, less than 5% of ApoA-I of high density lipoprotein reacted in the assay. Removal of the lipid by extraction increased the reactivity of ApoA-I in high density lipoprotein 15-20-fold; thus more than 95% of the ApoA-I molecules in "intact" high density lipoprotein are unreactive with antibody. Normal and hyperlipoproteinemic plasma and high density lipoproteins isolated from the same subjects continued to display parallelism with ApoA-I standard after lipid extraction, suggesting that ApoA-I of normal and hyperliproteinemic subjects are immunologically identical. About 90% of ApoA-I was in the d 1.063-1.21 fractions of normal plasma, trace quantities were found in the lipoproteins of d < 1.063, and the rest (about 10%) was in the d > 1.21 fraction. Normal plasma levels, assessed in extracted plasmas with a precision of 8%, were 100+/-35 mg/dl. Levels were normal in small groups of subjects with types II and IV hyperlipoproteinemia and high in pregnancy. However, larger population studies need to be performed to determine the distribution of ApoA-I levels in the various hyperlipoproteinemias.

31P nuclear magnetic resonance spectroscopy of native and recombined lipoproteins

Native and recombined lipoproteins have been studied by (31)P nuclear magnetic resonance spectroscopy. Very low-, low-, and high-density lipoproteins exhibited characteristic spectra. The main resonances were assigned to phosphatidylcholine and sphingomyelin. Relaxation times for these phospholipids were separately measured in low-density lipoproteins and high-density lipoproteins. The effect of paramagnetic ions (Eu(+++)) on the nuclear magnetic resonance spectrum of high-density lipoproteins is reported.