Effects of high-density lipoprotein and the apoprotein of high-density lipoprotein on prostacyclin synthesis by endothelial cells.
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6-Ketoprostaglandin F1 alpha↗
Biomedical subjects
A R Tall
Publications and source records attributed to A R Tall.
Facilitation of phosphatidylcholine transfer into high density lipoproteins by an apolipoprotein in the density 1.20-1.26 g/ml fraction of plasma.
Incubation of unilamellar vesicles of egg phosphatidylcholine (PC) in human plasma results in rapid transfer of phospholipid into high density lipoproteins (HDL). A similar but much slower transfer occurs upon incubation of PC vesicles with centrifugally isolated HDL. Experiments were conducted to characterize a plasma factor that might facilitate PC transfer into HDL. Addition of the d greater than 1.21 g/ml fraction of plasma to isolated HDL caused a marked increase in the rate of transfer of PC from vesicles to HDL. Fractionation of plasma by vertical rotor density gradient ultracentrifugation revealed that the factor that facilitated transfer of PC into HDL resided in the density 1.20-1.26 g/ml fraction, associated with a lipoprotein particle of apparent Stokes' diameter 10.2 nm. This fraction caused facilitated transfer of PC mass from vesicles into HDL3, resulting in formation of larger, less dense "HDL2a"-like particles. A partially purified preparation of phospholipid transfer activity was obtained from the d 1.20-1.26 g/ml fraction by a sequence of phenyl-Sepharose, heparin-Sepharose, and carboxymethylcellulose chromatography. The most purified fraction facilitated transfer of 4 micrograms of 14C-labeled PC/microgram protein per 60 min and also promoted transfer of radioactive cholesteryl esters from HDL to LDL. The results suggest that during lipoprotein metabolism the insertion of PC molecules into HDL may be facilitated by a plasma lipid transfer protein.
Biological Transport, Active↗
Stimulation of arterial endothelial cell prostacyclin synthesis by high density lipoproteins.
Prostacyclin (PGI2) is a vasoactive prostaglandin synthesized by vascular endothelial and smooth muscle cells. In order to investigate whether plasma lipoproteins influence the biosynthesis and release of prostacyclin by vascular tissues, human high density lipoproteins (HDL) and low density lipoproteins (LDL) were incubated with porcine arterial endothelial cells grown in tissue culture. PGI2 production was measured by radioimmunoassay of its stable metabolite, 6-keto-PGF1 alpha. In incubations of HDL with endothelial cells for 24 h, levels of 6-keto-PGF1 alpha in the medium increased significantly in a dose-dependent fashion to values 5-fold above control. This effect was less pronounced in confluent than in subconfluent cultures and did not occur in the presence of an inhibitor of cyclooxygenase. No significant stimulation of 6-keto-PGF1 alpha was observed when the endothelial cells were incubated with LDL. In time course experiments with HDL, 6-keto-PGF1 alpha levels increased continuously over 24 h. Rat HDL, containing a high content of arachidonate in its cholesterol ester fatty acids, caused a 2-4-fold greater release of 6-keto-PGF1 alpha than human HDL. The delipidated apoprotein of both human and rat HDL caused similar stimulation of 6-keto-PGF1 alpha production, but much less than intact HDL. The data indicate that HDL stimulates PGI2 synthesis by cultured arterial endothelial cells, possibly by providing the cells with arachidonate.
6-Ketoprostaglandin F1 alpha↗
Changes in the distribution and composition of plasma high density lipoproteins after ingestion of fat.
Following ingestion of a fatty meal there is an increase in concentration of phospholipids and proteins in the plasma high density lipoproteins (HDL). To evaluate the resulting changes in HDL subclasses, the plasma HDL of six subjects were analyzed 4 to 8 h after ingestion of 100 ml of corn oil or 80 ml of corn oil with four eggs. Isopycnic density gradient ultracentrifugation of fasting plasma showed two broad components of HDL: a major peak of density (d) 1.11 to 1.17 g/ml (HDL3) and a smaller peak of d 1.07 to 1.11 g/ml (HDL2). Following ingestion of either type of fatty meal, there was an increase in lipoprotein mass in both peaks of HDL and their centers of mass were shifted to lower density (1.140 leads to 1.120 to 1.130 g/ml; 1.095 leads to 1.090 g/ml). Calculation of changes in HDL concentration (lipemic minus fasting) showed that the alterations in density gradient profile were due to a major increase in lipoproteins of d 1.102 to 1.137 g/ml, a smaller increase in a separate lipoprotein peak of 1.080 to 1.102 g/ml, and a small decrease in lipoproteins of d 1.137 to 1.165 g/ml. Redistribution of HDL mass into larger, less dense lipoproteins was also demonstrated by agarose gel chromatography or by minimal spin density gradient ultracentrifugation in a vertical rotor. The increase in mass of 1.080 to 1.102 lipoproteins was largely due to increased concentrations of phospholipid, cholesterol ester, and apoA-I, while the increase in 1.102 to 1.137 lipoproteins was due to increased concentrations of apoA-I, apoA-II, phospholipids, cholesterol, and cholesterol esters. Analytical ultracentrifugation of representative samples within these density intervals showed lipoprotein species with molecular weights and sedimentation coefficients, respectively, of 378,000, 5.8 (d 1.080 to 1.095); 248,000, 3.5 (d 1.110 to 1.120); and 173,000, 1.6 (d 1.135 to 1.150). Polyacrylamide gradient gel electrophoresis showed that the 1.080 to 1.102 lipoproteins contained a single lipoprotein band of diameter approximately 10.7 nm; the 1.102 to 1.137 lipoproteins contained a single band which varied in size fro 10.0 to 9.2 nm: and the 1.137 to 1.165 lipoproteins contained three species of diameters approximately 9.2, 8.8, and 8.2 nm. Within density intervals, the molecular weights, sedimentation coefficients, and diameters of the different lipoproteins were similar in fasting and lipemic plasma. Calculation of average molecular compositions shows that the major incremental HDL of d approximately 1.12 g/ml could be derived by addition of lipids to the largest species of fasting HDL3. Within density intervals, the particle contents of apoA-I and apoA-II were unchanged during lipemia, suggesting that apoprotein transfer causes interconversion of existing HDL species or formation of new particles with the same content of apoA-I and apoA-II as existing species.
Adult↗
Effect of biliary diversion on rat mesenteric lymph apolipoprotein-I and high density lipoprotein.
The effect of biliary diversion on intestinal apolipoprotein (apoA)-I and high density lipoprotein formation was studied in mesenteric lymph fistula rats. Bile diversion was produced by an exteriorized catheter that allowed interruption and reconstitution of the enterohepatic circulation. Bile diversion reduced lymph cholesterol output from 0.47+/-0.05 mumol/h to 0.17+/-0.03 mumol/h (P < 0.025), and lymph triglyceride output from 3.6+/-0.3mumol/h to 0.6+/-0.05 mumol/h (P < 0.025) after 24 h. This was due to depletion of lymph chylomicrons and very low density lipoprotein (VLDL). Despite the reduced lipid outputs, lymph apoA-I output was maintained during biliary diversion (basal: 119+/-15 mug/h; diverted 140+/-20 mug/h, n = 12). During biliary diversion, high density lipoprotein (HDL) were maintained in mesenteric lymph as shown by lipoprotein and immunoelectrophoresis. Bile diversion altered the lipid composition of lymph HDL. Bile-diverted lymph HDL was depleted in total cholesterol and has a greater phospholipid/cholesterol ester ratio than basal lymph HDL. Lymph HDL contained discoidal particles when examined by negative stain electron microscopy. Bile diversion was associated with a reduction in the size of discoidal HDL particles (basal, nondiverted, 165+/-7A (n = 112) compared with diverted 126+/-5A (n = 98, P < 0.025). Experiments were then carried out to determine the source of the apoA-I and HDL found in lymph from bile-diverted animals. The transfer of HDL from plasma into lymph was determined by the intravenous infusion of (125)I-apoA-I labeled HDL into lymph fistula rats. In both nonbile-diverted and diverted rats, the specific activity of apoA-I in the HDL fraction of lymph was 23% of the specific activity of apoA-I in plasma HDL, indicating that the major portion (75%) of mesenteric lymph apoA-I did not come from plasma filtration. In other experiments the intraduodenal infusion of [(3)H]leucine to bile fistula, lymph fistula rats resulted in relative fivefold increase in the specific activity in apoA-I in lymph HDL when compared with the specific activity of apoA-I in plasma HDL from the same animal. We conclude that intestinal apoA-I secretion is maintained during biliary diversion and that synthesis of this apoprotein occurs in the absence of chylomicron formation. We also conclude that discoidal HDL are present in mesenteric lymph despite reduced triglyceride absorption and secretion into lymph.
Animals↗
Role of apolipoprotein E-containing lipoproteins in abetalipoproteinemia.
Detailed studies of apolipoprotein E (apoE)-containing lipoproteins in abetalipoproteinemia have been performed in an attempt to resolve the apparent paradox of a suppressed low density lipoprotein (LDL) receptor pathway in the absence of apoB-containing lipoproteins. It was hypothesized that apoE-containing high density lipoproteins (HDL) in abetalipoproteinemia might functionally substitute for LDL in regulation of cholesterol metabolism in these patients. The mean (+/-standard deviation) plasma concentration of apoE in nine patients with abetalipoproteinemia was 44.8+/-8.2 mug/ml, slightly higher than the corresponding value for a group of 50 normal volunteers, 36.3+/-11 mug/ml. Fractionation of plasma lipoproteins by agarose column chromatography or by ultracentrifugation indicated that in abetalipoproteinemia, plasma apoE was restricted to a subfraction of HDL. This was in contrast to the results obtained with plasma from 30 normal volunteers, in whom apoE was distributed between very low density lipoproteins (VLDL) and HDL. Consequently, the mean apoE content of HDL in abetalipoproteinemia (44.8 mug/ml) was more than twice that found in the normal volunteers (20.3 mug/ml).ApoE-rich and apoE-poor subfractions of HDL(2) were isolated by heparin-agarose affinity chromatography. ApoE comprised a mean of 81% of the protein mass of the apoE-rich subfraction. Compared with the apoE-poor subfraction, the apoE-rich HDL(2) was of larger mean particle diameter (141+/-7 vs. 115+/-15 A) and had a higher ratio of total cholesterol/protein (1.01+/-0.11 vs. 0.63+/-0.14). Plasma and HDL fractions from three patients were studied with respect to their ability to compete with (125)I-LDL in specific binding to receptors on cultured human fibroblasts. The binding activity of plasma from patients (per milligram of protein) was about half that of plasma from normal volunteers. All binding activity in the patients' plasma was found to reside in the HDL fraction. The binding activity of the patients' HDL (on a total protein basis) was intermediate between that of normal HDL and normal LDL. However, the large differences in binding between patients' HDL and normal HDL entirely disappeared when data were expressed in terms of the apoE content of these lipoproteins. This suggested that the binding activity was restricted to that subfraction of HDL particles that contain apoE. These apoE-rich HDL particles had calculated binding potencies per milligram of protein 10-25 times that of normal LDL. Direct binding studies using (125)I-apoE-rich HDL(2) and (125)I-apoE-poor HDL(2), confirmed the suggestion that binding is restricted to the subfraction of HDL particles containing apoE. The apoE-rich HDL(2) were found to be very potent inhibitors of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase activity in cultured fibroblasts, providing direct evidence of the ability of these lipoproteins to regulate cholesterol metabolism. On the basis of binding potencies of apoE-rich HDL, apoE concentrations, and the composition of apoE-rich HDL, it could be calculated that apoE-rich HDL in abetalipoproteinemia have a capacity to deliver cholesterol to tissues via the LDL receptor pathway equivalent to an LDL concentration of 50-150 mg/dl of cholesterol. Thus, these apoE-rich lipoproteins are capable of producing the suppression of cholesterol synthesis and LDL receptor activity previously observed in abetalipoproteinemia.
Abetalipoproteinemia↗
Incorporation of phosphatidylcholine into spherical and discoidal lipoproteins during incubation of egg phosphatidylcholine vesicles with isolated high density lipoproteins or with plasma.
Incubation of phosphatidylcholine vesicles with isolated high density lipoproteins (HDL) or with whole plasma results in transfer of phospholipid into HDL. To investigate the mechanisms of this process, small unilamellar vesicles of egg phosphatidylcholine were incubated with human HDL3 (d 1.125 to 1.210 g/ml) or with plasma and were subsequently analyzed by density gradient ultracentrifugation and negative stain electron microscopy. Incubation of vesicles with isolated HDL3 resulted in formation of both discoidal lipoproteins (1.04 to 1.06 g/ml) and phospholipid-enriched spherical lipoproteins (1.10 to 1.14 g/ml). The lipid bilayer discoidal lipoproteins had dimensions approximately 22 X 5.4 nm and contained phospholipid, apoA-I, and apoA-II. The phospholipid-enriched sperical HDL were increased in diameter and decreased in density compared to HDL3. With maximum phospholipid uptake these lipoproteins had a similar density, size, and lipid composition to HDL2a, a phospholipid-rich subfraction of HDL isolated from human plasma between 1.100 to 1.125 g/ml. Scanning microcalorimetry of the phospholipid-enriched HDL showed, compared to HDL3, a decrease in the temperature and enthalpy of lipoprotein denaturation. This altered denaturation pattern was similar to that of plasma HDL2a. Following incubation of vesicles in plasma, there was an increase in phospholipid-rich lipoproteins within the HDL2 density range (1.070 to 1.125 g/ml), and disappearance of lipoproteins from the HDL3 density range (1.125 to 1.210 g/ml). The phospholipid-rich HDL2 contained a major peak (d 1.095 to 1.125 g/ml), which consisted of only spherical particles and a smaller peak (d 1.070 to 1.095 g/ml), which included a population of lipid bilayer discs. Thus, during incubation of vesicles with isolated HDL3, there is insertion of phospholipid into HDL3, producing spherical lipoproteins which have some properties in common with HDL2a. Discoidal lipoproteins are also formed, probably as a result of interaction of vesicles with small amounts of apoA-I and apoA-II released from HDL3. The uptake of phosphatidylcholine by HDL in whole plasma occurs by similar mechanisms.
Calorimetry, Differential Scanning↗
Organization of the core lipids of high density lipoproteins in the lactating bovine.
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Animals↗
Thermotropic transitions in rat intestinal plasma membranes studied by differential scanning calorimetry and fluorescence polarization.
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Animals↗
Products of delipidation of intestinal chylomicrons with diethyl ether.
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Animals↗
Structure of plasma lipoproteins: view from calorimetric studies.
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Animals↗
Body cholesterol removal: role of plasma high-density lipoproteins.
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Animals↗
Studies on the transfer of phosphatidylcholine from unilamellar vesicles into plasma high density lipoproteins in the rat.
To investigate the metabolic disposition of phosphatidylcholine vesicles, unilamellar vesicles of egg phosphatidylcholine or cholesterol/phosphatidylcholine were injected intravenously into rats. Ten minutes after injection of 0.5 to 3.0 mg phosphatidylcholine vesicles, a major fraction of their radioactivity and mass had been incorporated into high density lipoproteins (HDL). Agarose gel chromatography showed that the phospholipid of vesicles was incorporated into the plasma HDL region, in association with release of a trapped marker, [3H]inulin. Density gradient ultracentrifugtion showed that the highest specific activity of phospholipid was present in HDL of d 1.08-1.12 g/ml, consisting of homogenous spherical particles by negative stain electron microscopy. With increasing cholesterol/phosphatidylcholine ratio of injected vesicles, there was progressively less incorporation of phospholipid into HDL and vesicles retaining [3H]inulin were re-isolated from plasma. Sixty minutes after injection of cholesterol/phosphatidylcholines vesicles, phospholipid appeared to be partly transferred into HDL and partly taken up by the liver. In summary, injection of unilamellar egg phosphatidylcholine vesicles results in a rapid incorporation of vesicle phospholipid into plasma HDL, primarily as a result of insertion of phospholipid into pre-existing HDL. This process is inhibited by a high content of vesicle unesterified cholesterol. These studies may have relevance to the mechanisms of transfer of phosphatidylcholine from chylomicrons into plasma.
Animals↗
The effect of chronic cholesterol feeding on intestinal lipoproteins in the rat.
Chronic cholesterol feeding has been shown to produce abnormal plasma lipoproteins in a variety of experimental animals and man. In order to explore the role of the intestine in the production of these abnormal lipoproteins, rats were chronically fed a diet containing 1% cholesterol and 10% olive oil and were compared to control animals, fed either normal chow or normal chow containing 10% olive oil. Mesenteric lymph lipoproteins from fasting lymph and from lymph obtained after acutely infusing cholesterol and olive oil were examined and compared to plasma lipoproteins from these animals. There were no differences in apoA-I output, cholesterol output, or distribution in lymph lipoproteins between the two groups of controls. The cholesterol-olive oil diet produced a mild hyperlipidemia (plasma cholesterol 81 --> 95 mg/dl, plasma triglyceride 95 --> 162 mg/dl). Plasma lipoprotein electrophoresis revealed an abnormal band with broad beta mobility and a reduction in HDL. Lipid analysis of ultracentrifugally separated fractions demonstrated the appearance of an intermediate density (1.006-1.030 g/ml) lipoprotein in plasma markedly enriched in cholesteryl esters. Analysis of fasting mesenteric lymph from chronically cholesterol-fed animals revealed similar apoA-I, cholesterol, and triglyceride outputs when compared to controls. Although in both groups most of the cholesterol was transported in d < 1.006 g/ml lipoproteins, there was a redistribution of cholesterol transport in d > 1.006 g/ml lipoproteins. In the chronically cholesterol-fed animals, 19% of fasting lymph cholesterol was transported in a lipoprotein of density 1.006-1.030 g/ml, compared to 4% in this density in controls. During the acute infusion of cholesterol and olive oil, the output of lymph apoA-I (226 +/- 20 versus 374 +/- 5 micro g/hr, P < 0.025) and lymph cholesterol (970 +/- 82 +/- 1774 micro g/hr, P < 0.01) was significantly lower in the chronically cholesterol-fed group, despite no significant change in triglyceride outputs (49 +/- 2 versus 58 +/- 7 mg/hr). Analysis of individual lymph lipoproteins from chronically cholesterol-fed animals revealed that significantly less apoA-I and cholesterol was carried in d < 1.006 g/ml lipoproteins than in controls. There was however, both a relative and absolute increase in the cholesterol and apoA-I content of intermediate and low density lymph subfractions. Particularly prominent in lymph from chronically cholesterol-fed animals was a lipoprotein (d 1.006-1.030 g/ml) which was inconsistently found in controls. This particle was rich in cholesterol and contained apoA-I. [(3)H]Retinol infusion studies revealed that this particle contained increased retinyl ester when compared to plasma, suggesting an intestinal origin. These results demonstrate that chronic cholesterol feeding in the rat results in altered mesenteric lymph lipoproteins which may contribute to the abnormalities found in plasma.-Riley, J. W., R. M. Glickman, P. H. R. Green, and A. R. Tall. The effect of chronic cholesterol feeding on intestinal lipoproteins in the rat.
Animals↗
Absence of liquid crystalline transitions of cholesterol esters in reconstituted low density lipoproteins.
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Calorimetry, Differential Scanning↗
Interaction between unilamellar egg yolk lecithin vesicles and human high density lipoprotein.
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Adult↗
Drugs, alcohol and malabsorption.
Alcohol and a number of drugs (e.g., neomycin, cholestyramine, antacids, laxatives, paraminosalicyclic acid, colchicine and oral hypoglycemic agents) can cause malabsorption due to drugs and alcohol is surveyed. Examined in detail are the mechanisms of malabsorption produced by neomycin and cholestyramine, and the factors responsible for malabsorption in the chronic alcoholic.
Alcoholism↗
Human intestinal lipoproteins. Studies in chyluric subjects.
To explore the role of the human intestine as a source of apolipoproteins, we have studied intestinal lipoproteins and apoprotein secretion in two subjects with chyluria (mesenteric lymphatic-urinary fistulae). After oral corn oil, apolipoprotein A-I (apoA-I) and apolipoprotein A-II (apoA-II) output in urine increased in parallel to urinary triglyceride. One subject, on two occasions, after 40 g of corn oil, excreted 8.4 and 8.6 g of triglyceride together with 196 and 199 mg apoA-I and on one occasion, 56 mg apoA-II. The other subject, after 40 g corn oil, excreted 0.3 g triglyceride and 17.5 mg apoA-I, and, after 100 g of corn oil, excreted 44.8 mg apoA-I and 5.8 mg apoA-II. 14.5+/-2.1% of apoA-I and 17.7+/-4.3% of apoA-II in chylous urine was in the d < 1.006 fraction (chylomicrons and very low density lipoprotein). Calculations based on the amount of apoA-I and apoA-II excreted on triglyceride-rich lipoproteins revealed that for these lipid loads, intestinal secretion could account for 50 and 33% of the calculated daily synthetic rate of apoA-I and apoA-II, respectively. Similarly, subject 2 excreted 48-70% and 14% of the calculated daily synthetic rate of apoA-I and apoA-II, respectively. Chylous urine contained chylomicrons, very low density lipoproteins and high density lipoproteins, all of which contained apoA-I. Chylomicrons and very low density lipoproteins contained a previously unreported human apoprotein of 46,000 mol wt. We have called this apoprotein apoA-IV because of the similarity of its molecular weight and amino acid composition to rat apoA-IV. In sodium dodecyl sulfate gels, chylomicron apoproteins consisted of apoB 3.4+/-0.7%, apoA-IV 10.0+/-3.3%, apoE 4.4+/-0.3%, apoA-I 15.0+/-1.8%, and apoC and apoA-II 43.3+/-11.3%. Very low density lipoprotein contained more apoB and apoA-IV and less apoC than chylomicrons. Ouchterlony immunodiffusion of chylomicron apoproteins revealed the presence of apoC-I, apoC-II, and apoC-III. In contrast, plasma chylomicrons isolated during a nonchyluric phase revealed a markedly altered chylomicron apoprotein pattern when compared with urinary chylomicrons. The major apoproteins in plasma chylomicrons were apoB, apoE, and the C peptides: no apoA-I or apoA-IV were present in sodium dodecyl sulfate gels indicating that major changes in chylomicron apoproteins occur during chylomicron metabolism. When incubated in vitro with plasma, urinary chylomicrons lost apoA-I and apoA-IV and gained apoE and apoC. Loss of apoA-I and apoA-IV was dependent upon the concentration of high density lipoproteins in the incubation mixture. These studies demonstrate that the human intestine secretes significant amounts of apoA-I and apoA-II during lipid absorption. Subsequent transfer of apoproteins from triglyceride-rich lipoproteins to other plasma lipoproteins may represent a mechanism whereby the intestine contributes to plasma apoprotein levels.
Adult↗