High Density Lipoprotein Apoprotein Research Articles

Apoprotein D in a healthy, male population and in male myocardial infarction patients and their male, first-degree relatives

This report examines the correlation of serum apoprotein D with other lipoprotein lipids and apoproteins in a healthy, male population and compares the levels of high density lipoprotein apoprotein D of this control population with 2 samples composed of male, acute myocardial infarction patients and their healthy, male, first-degree relatives. Highly significant correlations were observed with very low density lipoprotein lipids (negative), high density lipoprotein lipids (positive) and serum triglycerides (negative). Serum and low density lipoprotein apoprotein B was not correlated with serum apoprotein D, whereas apoprotein A-1 from serum and high density lipoproteins was strongly correlated with apoprotein D. A significant reduction in high density lipoprotein apoprotein D was observed in male, myocardial infarction patients. Their male, first-degree relatives also had lower apoprotein D levels, but the difference was not significant.

Conversion of human plasma high density lipoprotein-2 to high density lipoprotein-3. Roles of neutral lipid exchange and triglyceride lipases.

Cholesterol esters accumulating in human plasma high density lipoproteins (HDL) are important in conversion of HDL3 to larger HDL2. We studied whether mechanisms of removal of cholesterol esters from HDL might be important in a reverse direction, i.e. conversion of HDL2 to HDL3. Native HDL2 or HDL3 is incubated with very low density lipoproteins (VLDL) and lipoprotein-poor plasma (d greater than 1.21 g/ml) at 37 degrees C. After incubation, "modified" (M) VLDL, and HDL2 or HDL3 are reisolated by ultracentrifugation. In modified M-HDL2 or M-HDL3, triglyceride becomes the major core lipid as the triglyceride/cholesterol ester weight ratio increases 8-10-fold relative to native HDL. With only small changes in protein/phospholipid ratios in M-HDLs, the large decrease in cholesterol ester/protein ratios suggest net cholesterol ester loss from HDL. Quantitative recovery analyses prove that the cholesterol esters lost from HDL are transferred to M-VLDL, which is now richer in cholesterol ester and poorer in triglyceride. These substantial exchanges of HDL lipids are not associated by significant transfer of HDL apoproteins but are dependent on neutral lipid transfer factors present in human lipoprotein-poor plasma (d greater than 1.21 g/ml). Similar results are obtained when purified core lipid transfer protein replaces d greater than 1.21 g/ml plasma in these incubations. After depletion of cholesterol ester from HDL, most but not all, exchanged triglyceride can be removed by lipolysis with either hepatic or lipoprotein lipase, resulting in a post-lipolysis HDL2 with an increased triglyceride content relative to normal HDL. With successive incubations with VLDL, and core lipid transfer factors, HDL2 loses more than two-thirds of its cholesterol esters. After lipolysis of acquired triglyceride, HDL2 is remodeled, in both composition and flotation parameters, toward HDL3.

In vivo interaction of synthetic acylated apopeptides with high density lipoproteins in rat.

The metabolism of synthetic peptide analogues of high density lipoprotein (HDL) apoproteins has been studied in the rat. These compounds are 15-amino acid lipid associating peptides (LAPs) bearing acyl chains of various lengths (0-16 carbon units). After injection of each 125I-LAP, the serum decay curves suggested a two-compartment process with a clearance rate decreasing when the acyl chain lengths increased. The similarity between the apparent half-life of C16-LAP and that of apoprotein A-I as well as the chromatographic analysis of rat serum were consistent with a partitioning of the LAPs between HDL and the aqueous phase. This was strongly dependent upon the acyl chain length of the LAPs. The distribution volumes of the 125I-LAPs in organs were measured 10 min after injection. The results were analyzed using a model explicitly predicting the organ distribution volumes of HDL and the equilibrium constant (Keq) of the binding of each LAP to HDL. HDL distributed significantly in the adrenals (250 microliters/g), liver (80 microliters/g), and ovaries (55 microliters/g), but not in the kidneys. This suggests that the binding of HDL apoproteins to kidneys, reported by others, was due to the uptake of free apoproteins. The Keqs exhibited a log-linear relationship with respect to the acyl chain length of the LAPs. Each carbon unit added to the acyl chain decreased the free energy of association by a constant value (0.3 kcal mol-1). This clearly showed a strict hydrophobic effect similar to that previously observed in vitro.

Lipolysis-induced degradation of apolipoproteins B and E of human very low density lipoproteins.

We have found that in vitro lipolysis of human very low density lipoproteins (VLDL) by purified bovine milk lipoprotein lipase (LpL) promotes degradation of the apolipoprotein (apo) B moiety of VLDL. Analysis by sodium dodecyl sulfate-polyacrylamide gradient gel electrophoresis showed that lipolysis of VLDL by purified LpL for 1 h at 37 degrees C induced the selective degradation of the high Mr apo-B (apo-B-100) from most hypertriglyceridemic VLDL and from a few normolipidemic VLDL into several small fragments with molecular weights ranging from 90,000-490,000. No detectable degradation of apo-B occurred in control VLDL when incubated without LpL. The apo-E moiety of VLDL from certain individuals was also degraded following lipolysis of VLDL, and the extent of degradation of apo-B and -E in VLDL was varied among the individual VLDL. The major degradation products of apo-E, identified from the gel, were 31,000- and/or 28,000-Da species. In contrast to the apo-E moiety of VLDL, purified apo-E was not degraded when incubated with LpL. Incubation of low density lipoproteins (LDL) with LpL showed only a minimal effect on the apoproteins of LDL. When high density lipoprotein (HDL) was included in the lipolysis mixture as an acceptor of lipolytic surface remnants, the apoproteins of HDL remained unaltered, while the apo-B moiety of VLDL remnants in the mixture was degraded. Inclusion of protease inhibitors in the lipolysis mixture prevented the degradation of apo-B, but the hydrolysis of VLDL-triglyceride was minimally affected. A selective degradation of apo-B in VLDL also occurred during lipolysis of VLDL when VLDL was perfused through rat hearts. These results suggest that conformational changes in apo-B and apo-E caused by VLDL lipolysis may increase the susceptibility of apo-B and apo-E to degradation by the proteases co-isolated with VLDL. The consequences of the lipolysis-induced degradation of apo-B and apo-E on changes in metabolic properties of VLDL remnants remain to be determined.

Effects of Indoramin and Metoprolol on Plasma Lipids and Lipoproteins

The effects of indoramin (n = 29) and metoprolol (n = 15) on lipid profiles in hypertensive patients were compared in a double-blind study. Blood samples were taken at baseline, weeks 3 and 4 of placebo administration, and after 4 and 8 weeks of active treatment. The following assays were performed: total cholesterol, total triglycerides, high density lipoprotein (HDL) cholesterol, HDL3 cholesterol, and apoproteins A, AI, and B. The following values were calculated: HDL2 cholesterol, low density lipoprotein (LDL) cholesterol, total cholesterol/HDL cholesterol ratio (Castelli risk ratio I), and LDL cholesterol/HDL cholesterol (Castelli risk ratio II). The results of an overall analysis showed the following significant changes (mean +/- SD) for indoramin: LDL cholesterol, from 129.50 +/- 38.29 to 114.00 +/- 32.41 mg/dl (p less than or equal to 0.001); apoprotein A, from 169.51 +/- 39.83 to 232.48 +/- 34.08 mg/dl (p less than or equal to 0.001); apoprotein AI, from 105.62 +/- 20.70 to 134.68 +/- 21.58 mg/dl; apoprotein B, from 110.13 +/- 34.88 to 122.34 +/- 32.13 mg/dl (p less than or equal to 0.05); and Castelli risk ratio II, from 2.38 to 1.96 (p less than or equal to 0.01). The following significant variations occurred for metoprolol: total cholesterol, from 201.54 +/- 49.21 to 191.80 +/- 51.88 mg/dl (p less than or equal to 0.05); apoprotein A, from 186.78 +/- 62.63 to 227.68 +/- 44.78 mg/dl (p less than or equal to 0.001); apoprotein AI, from 109.12 +/- 34.72 to 131.95 +/- 21.79 mg/dl (p less than or equal to 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Binding of high density lipoprotein to cultured fibroblasts after chemical alteration of apoprotein amino acid residues.

Cultured extrahepatic cells possess a specific high affinity binding site (receptor) for high density lipoprotein (HDL) that is induced by cholesterol delivery to cells. To characterize the binding recognition site(s) on HDL, the ability of HDL to interact with cultured human fibroblasts was assayed after chemical alteration of specific apoprotein amino acid residues. Reduction and alkylation, acetylation, and cyclohexanedione treatment of HDL3 had little or no effect on its cellular binding. Treatment of HDL3 with tetranitromethane (TNM), however, caused a large dose-dependent decrease in binding, with maximum inhibition at 3 mM. Amino acid analysis of the TNM-treated particles showed specific alteration of tyrosine residues, but sodium dodecyl sulfate-gel electrophoresis demonstrated apoprotein cross-linking coincident with decreased binding. These results suggest that modification of HDL tyrosine residues and/or cross-linking of HDL apoproteins alters the ligand site recognized by the HDL receptor. Gradient gel electrophoresis, molecular sieve chromatography, and electron microscopy showed only minor changes in size distribution and shape of HDL3 particles after treatment with 3 mM TNM, but at higher TNM concentrations, coalescence and aggregation of particles was evident. Treatment of HDL3 with 3 mM TNM affected neither its promotion of the low affinity (receptor-independent) cholesterol efflux from cells nor its ability to accept cholesterol from an albumin suspension, yet promotion of high affinity (receptor-dependent) cholesterol efflux from cells was abolished. The finding that TNM treatment of HDL3 decreases both its receptor binding and its promotion of cholesterol efflux from cells without substantial alteration of its physical properties supports the hypothesis that the HDL receptor functions to facilitate cholesterol transport from cells.

Abnormal interaction of the human apolipoprotein A-I variant [Lys 107→0] with high density lipoproteins

Several isoforms of apoprotein A-I [apoA-I], the major apoprotein of high density lipoproteins [HDL], have been described. We compared the in vivo and in vitro properties of normal human apoA-I with those of apoA-I [Lys 107→0]. Fluorescence and circular dichroic spectra showed that deletion of Lys 107 decreases apoprotein self-association. In vivo metabolic studies in the rat indicated that the interaction of apoA-I [Lys 107→0] with HDL was lower than normal. We conclude that deletion of Lys 107 results in a reorganization of the apoprotein structure that decreases its potential to form hydrophobic associations.

Characterization of plasma lipoproteins of grain- and cholesterol-fed White Carneau and Show Racer pigeons.

Plasma cholesterol concentrations from White Carneau (WC) and Show Racer (SR) pigeons consuming a cholesterol-free grain diet averaged about 300 mg/dl, approximately 200 mg/dl as high density lipoproteins (HDL) and the remainder as low density lipoproteins (LDL). Consumption of a cholesterol-containing diet increased plasma cholesterol concentrations in both breeds to greater than 2000 mg/dl. Approximately one-half of this increase was as LDL with the remainder as beta-migrating very low density lipoproteins (beta-VLDL). There was little change in HDL concentration. LDL from cholesterol-fed animals had a greater net negative charge than control LDL, and was larger (Mr = 10 X 10(6) vs 3.2 X 10(60)) due to an increase in the number of cholesteryl ester molecules per particle. The principal apoprotein of LDL was apoB-100 with smaller amounts of apoA-I and several minor unidentified apoproteins. beta-VLDL was cholesteryl ester-rich, could be separated into two size populations by gel chromatography, and contained apoB-100 as its principal apoprotein. Apoprotein E was not detected in any of the plasma lipoproteins. HDL from control and cholesterol-fed animals was composed of a single class of particles with virtually identical composition resembling HDL2. The major apoprotein of HDL was apoA-I. There were no consistent quantitative or qualitative differences in the lipoproteins of the two breeds of pigeons that could help to explain the susceptibility to atherosclerosis of the WC or the resistance of the SR.

Specific targeting of high density lipoproteins to liver hepatocytes by incorporation of a tris-galactoside-terminated cholesterol derivative.

A triantennary galactose-terminated cholesterol derivative, N-(tris(beta-D-galactopyranosyloxymethyl) methyl)-N alpha-(4(5-cholesten-3 beta-yloxy)succinyl)glycinamide (Tris-Gal-Chol), which dissolves easily in water, was added to human apolipoprotein E-free high density lipoproteins (HDL) in varying quantities. Incorporation of 5 or 13 micrograms of Tris-Gal-Chol into HDL (20 micrograms of protein) stimulates the liver association of the HDL apoprotein radioactivity 24- and 55-fold, respectively, at 10 min after intravenous injection into rats. The increased interaction of Tris-Gal-Chol HDL with the liver is blocked by preinjection of asialofetuin or N-acetylgalactosamine but not influenced by N-acetylglucosamine. The parenchymal liver cell uptake of HDL is stimulated 42- or 105-fold, respectively, by incorporation of 5 or 13 micrograms of Tris-Gal-Chol into HDL (20 micrograms of protein), while the association with nonparenchymal cells is stimulated only 1.7- or 5-fold. It can be calculated that 98.0% of the Tris-Gal-Chol HDL is associated with parenchymal cells. In contrast, incorporation of 13 micrograms of Tris-Gal-Chol into LDL (20 micrograms of protein) leads to a selective association of LDL with nonparenchymal cells (92.3% of the total liver uptake). It is concluded that Tris-Gal-Chol incorporation into HDL leads to a specific interaction of HDL with the asialoglycoprotein (galactose) receptor on parenchymal cells whereas Tris-Gal-Chol incorporation into LDL leads mainly to an interaction with a galactose receptor from Kupffer cells. Probably this highly selective cellular targeting of LDL and HDL by Tris-Gal-Chol is caused by the difference in size between these lipoproteins. The increased interaction of HDL with the parenchymal cells upon Tris-Gal-Chol incorporation is followed by degradation of the apolipoprotein in the lysosomes. It is concluded that Tris-Gal-Chol incorporation into LDL or HDL leads to a markedly increased catabolism of LDL by way of the Kupffer cells and HDL by parenchymal cells which might be used for lowering serum cholesterol levels. The use of Tris-Gal-Chol might also find application for targeting drugs or other compounds of interest to either Kupffer or parenchymal liver cells.

Relationship of the parameters of body cholesterol metabolism with plasma levels of HDL cholesterol and the major HDL apoproteins.

The inverse relationship between plasma levels of high density lipoprotein (HDL) and coronary heart disease rates has suggested that HDL might influence body stores of cholesterol. Therefore, we have investigated potential relationships between the parameters of body cholesterol metabolism and the plasma levels of HDL cholesterol and the major HDL apoproteins. The study involved 55 human subjects who underwent long-term cholesterol turnover studies, as well as plasma lipoprotein and apolipoprotein assays. In order to maximize the likelihood of detecting existing relationships, the subjects were selected to span a wide range of plasma levels of lipids, lipoproteins, and apolipoproteins. Single univariate correlation analyses suggested weak but statistically significant inverse relationships of HDL cholesterol and apoA-I levels with the following model parameters: production rate (PR), the mass of rapidly exchanging body cholesterol (M1), the minimum estimate of the mass of slowly exchanging body cholesterol (M3min), and of the mass of total exchangeable body cholesterol (Mtotmin). These correlations, however, were quantitatively quite small (/r/ = 0.28-0.42) in comparison to the strength of the univariate relationships between body weight and PR (r = 0.76), M1 (r = 0.61), M3min (r = 0.58), and Mtotmin (r = 0.78). Correlations for apoA-II and apoE levels were even smaller than those for apoA-I and HDL cholesterol. In additional analyses using multivariate approaches, HDL cholesterol, apoA-I, apoA-II, and apoE levels were all found not to be independent determinants of the parameters of body cholesterol metabolism (/partial r/ less than 0.17, P greater than 0.3 in all cases). Thus the weak univariate correlations reflect relationships of HDL cholesterol and apoA-I levels with physiological variables, such as body size, which are primarily related to the model parameters. We conclude that plasma levels of HDL cholesterol and apoproteins A-I, A-II, and E are not quantitatively important independent determinants of the mass of slowly exchanging body cholesterol or of other parameters of long-term cholesterol turnover in humans. These studies give no support to the hypothesis that the inverse relationship between HDL cholesterol levels and coronary heart disease rates is mediated via an influence of HDL on body stores of cholesterol.

Human serum amyloid A (SAA): biosynthesis and postsynthetic processing of preSAA and structural variants defined by complementary DNA.

To study structural variants of human serum amyloid A (SAA), an apoprotein of high-density lipoprotein, complementary DNA clones were isolated from a human liver library with the use of two synthetic oligonucleotide mixtures containing sequences that could code for residues 33-38 and 90-95 of the protein sequence. The SAA-specific cDNA clone (pA1) contains the nucleotide sequence coding for the mature SAA and 10 amino acids of the 18-residue signal peptide. It also includes a 70 nucleotide long 3'-untranslated region and approximately 120 bases of the poly(A) tail. The derived amino acid sequence of pA1 is identical with the alpha form of apoSAA1. A fragment of pA1 containing the conserved (residues 33-38) region of SAA also hybridized with RNA from human acute phase liver and acute phase stimulated, but not unstimulated, mouse and rabbit liver. In contrast, a fragment corresponding to the variable region hybridized to a much greater extent with human than with rabbit or murine RNA. Human acute phase liver SAA mRNA (approximately 600 nucleotides in length) directs synthesis of preSAA (Mr 14 000) in a cell-free translating system. In a Xenopus oocyte translation system preSAA is synthesized and processed to the mature Mr 12 000 product. The complete 18 amino acid signal peptide sequence of preSAA was derived from sequencing cDNA synthesized by "primer extension" from the region of SAA mRNA corresponding to the amino terminus of the mature product. Two other SAA-specific cDNA clones (pA6 and pA10) differed from pA1 in that they lack the internal PstI restriction enzyme site spanning residues 54-56 of pA1.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of etophylline clofibrate on HDL subfractions

The effect of etophylline clofibrate on lipids and apolipoproteins of the high density lipoprotein (HDL) subfractions HDL 2 and HDL 3 as well as on very low density (VLDL) and low density lipoproteins (LDL) and the post heparin lipolytic activities (PHLA) of lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) has been studied in 14 patients with type II hyperlipoproteinemia (HLP). The study was preceded by a 4-week washout phase, followed by a 6-week placebo period. During the next 12 weeks, the patients received 750 mg etophylline clofibrate per day. Then the drug was again replaced by placebo for another 6 weeks. During the study the patients were on a low fat diet poor in cholesterol with a P/S ratio over 1.0. HDL cholesterol and apoproteins increased significantly during treatment. In the first verum phase this effect was related to the rise in HDL 2 components with minor changes in HDL 3 concentrations, whereas in the second verum period a distinct increase of the HDL 3 components could be detected. This development was accompanied by a significant increase of the LPL activities during the first 6 weeks of treatment, followed by a decrease to initially measured values after 12 weeks. The drug lowered plasma- and LDL-cholesterol levels by 19% and 22%, and plasma and VLDL triglycerides by 22% and 25%, respectively. VLDL-C apoproteins (C-I, C-II, C-III) declined by 31% with a percentage increase of apo C-II compared with apo C-I and apo C-III.

70 The effect of Danazol on high density lipoprotein cholesterol and apoproteins

70 The effect of Danazol on high density lipoprotein cholesterol and apoproteins

Equilibrium of apoproteins between high density lipoprotein and the aqueous phase: Modelling of in vivo metabolism

There is a growing body of evidence that apoproteins of the high density lipoproteins (HDL) exchange between lipoprotein particles through the aqueous phase and that there is always a finite but physiologically important quantity of lipid-free apoprotein in plasma. We have studied the theoretical consequences of this concept on the catabolism of apoproteins and developed a testable model for studying the in vivo metabolism of HDL apoproteins. This model describes the putative modification of the apparent tissue distribution spaces of the apoprotein that would result from a change in the partitioning of this apoprotein between HDL and the aqueous phase. The main parameters predicted by the model include the tissue distribution spaces of free monomeric apoprotein, those of HDL-bound apoprotein and the partition coefficient of the apoprotein between HDL and the aqueous phase in blood. We have designed several ways of testing this model in vivo including the use of model synthetic apoproteins. This model can be generalized to a number of other binding systems.

高トリグリセライド血症における超低比重リポ蛋白のアポ蛋白異常

The percentages of apo C-II and C-III proteins in very low density lipoprotein (VLDL) were high in the patients with hypertriglyceridemia (type IIb and IV) when compared with normal control subjects and those of apo A-I, A-II and B proteins were low. Positive correlation was shown between serum VLDL concentration and the percentage of apo C proteins, and the inverse relationship was between VLDL concentration and the percent apo B protein. Consequently, C/B and C/E ratios were higher in these patients than in healthy control.By contrast, there were no significant difference in high density lipoprotein apoprotein composition between normal subjects and the patients with high triglyceride concentration.

Synthesis, transport, and processing of apolipoproteins of high density lipoproteins

Cell biology methods have greatly influenced the elucidation of the biosynthetic pathways of apolipoproteins. In vitro and tissue culture systems allow the study, to a large extent, of the process of synthesis, intracellular processing, secretion, and extracellular processing of the major high density lipoprotein apoproteins apoA-I and A-II and also of a minor component, apoA-IV. Whereas the latter apoprotein is equipped only with a signal sequence, the primary translation products of apoA-I and apoA-II carry N-terminal extensions of preprosequence of 24 amino acids for apoA-I and 23 amino acid residues for apoA-II. The pro-form of apoA-I characterized by a hexapeptide extension is completely stable intracellularly and is secreted as such. The pro-form is further processed by a serum protease specific for an unusual -Gln-Gln-Asp-Glu-sequence site. Pro-apoA-II, a pentapeptide sequence, is partially processed intracellularly to its mature form and secreted together with the residual pro-form. The cleavage site of pro-apoA-II is characterized by two basic amino acid residues Arg-Arg, present also in other known pro-proteins. The biological function of the N-terminal pro-sequences and details of their final processing by the serum protease(s) have yet to be established.

A hepatocyte receptor for high-density lipoproteins specific for apolipoprotein A-I.

Apolipoprotein (apo) E-deficient rat high-density lipoproteins (HDL) bind to isolated rat hepatocytes at 4 degrees C by a process shown to be saturable and competed for by an excess of unlabeled HDL. Uptake (binding and internalization) at 37 degrees C was also saturable and competed for by an excess of unlabeled HDL. At 37 degrees C the HDL apoprotein was degraded as evidenced by the appearance of trichloroacetic acid-soluble radioactivity in the incubation media. The binding of a constant amount of 125I-apo-E-deficient HDL was measured in the presence of increasing concentrations of various lipoproteins. HDL and dimyristoyl phosphatidylcholine (DMPC) X apo-A-I complexes decreased binding by 80 and 65%, respectively. Human low-density lipoproteins, DMPC X apo-E complexes, and DMPC vesicles alone did not compete for apo-E-deficient HDL binding. However, DMPC X apo-E complexes did compete for the binding of the total HDL fraction that contained apo-E but to a lesser extent than did DMPC X apo-A-I. DMPC X 125I-apo-A-I complexes also bound to hepatocytes, and this binding was competed for by excess HDL (70%) and DMPC X apo-A-I complexes (65%), but there was no competition for binding by DMPC vesicles or DMPC X apo-E complexes. It thus appears that hepatocytes have a specific receptor for HDL and that apo-A-I is the ligand for this receptor.

Abnormalities of high density lipoproteins in homozygous familial hypercholesterolemia.

The possibility that low high density lipoprotein (HDL) levels may add to the risk of occlusive atherosclerosis in familial hypercholesterolemia (FH) is supported by the frequency and severity of this finding in these patients, particularly homozygotes. To investigate this abnormality in greater detail, we measured HDL lipid and apoprotein values in nine homozygotes with FH. Compared to their unaffected relatives, they had markedly reduced HDL cholesterol and apo A-I and A-II levels. The values found in heterozygote relatives were between those of homozygotes and those of controls. Density gradient ultracentrifugation of serum or isolated HDL from homozygotes demonstrated little or no HDL2; there was also a shift of homozygotes' HDL to an above normal peak density (d = 1.15 g/ml). Heterozygotes had milder abnormalities. The reduced HDL in FH seems to be related to elevated low density lipoprotein levels although the pathophysiology is unknown. These findings add weight to the concept that HDL abnormalities contribute to the relentless course of atherosclerosis in familial hypercholesterolemia.

Age-related changes of serum apoprotein SAS SAM, apoprotein A-I and low-density lipoprotein levels in senescence accelerated mouse (SAM)

Age-related changes of serum concentration of apo SAS SAM, an apoprotein of high density lipoprotein (HDL) which cross-reacts with antiserum against murine senile amyloid fibril protein (AS SAM) were estimated in senescence accelerated mouse (SAM-P) and in senescence resistant series (SAM-R), as a control, using a single radial immuno fxdiffusion technique. Serum concentrations of apo A-I, a major apoprotein of HDL, and low density lipoprotein (LDL) were also measured. In SAM-P (SAM-P/1 and SAM-P/2) with a high incidence of senile systemic amyloidosis, we observed age-associated decreases in serum apo SAS SAM levels. The concentrations of apo SAS SAM at 16 months of age were below 40% of the concentration at 2 months of age, regardless of the sex. In contrast with SAM-P, we observed no age-associated decrease of serum apo SAS SAM levels in SAM-R (SAM-R/1 and SAM-R/2) with a low incidence of amyloidosis. Serum apo SAS SAM concentration was higher in SAM-R/1 than in any other strain of mice observed. Serum apo A-1 concentration was highly and significantly correlated with the serum concentration of apo SAS SAM and decreased with advancing age in SAM-P but not in SAM-R. Age-related changes of LDL were not observed in any strain, but the concentration was lower in the females. In old SAM-P (16 months' old), the concentration of apo SAS SAM decreased to one-third of that in the young SAM-P (4 months' old) and the serum concentrations of albumin and total protein did not decrease, compared with those in the young mice. All these findings taken together suggest that abnormality of metabolism in apo SAS SAM, putative precursor of AS SAM, might occur in SAM-P.

Stimulation of vascular smooth muscle cell prostacyclin and prostaglandin E2 synthesis by plasma high and low density lipoproteins.

We studied the effects of plasma high density and low density lipoproteins upon the synthesis of prostacyclin and prostaglandin E2 by vascular smooth muscle cells. Prostaglandin synthesis was measured in 24-hour cultures by radioimmunoassay of the stable metabolites of prostacyclin, 6-keto-prostaglandin F1 alpha and of prostaglandin E2. High density lipoproteins induced dose-dependent increases in the release of 6-keto-prostaglandin F1 alpha and of prostaglandin E2 from smooth muscle cells to values 14- and 50-fold above control. Incubations with low density lipoproteins at comparable cholesterol concentrations also induced dose-dependent release of 6-keto-prostaglandin F1 alpha and prostaglandin E2, but to a lesser extent. Rat high density lipoprotein, which contained 2.5 times more cholesteryl arachidonate than human high density lipoproteins, stimulated 6-keto-prostaglandin F1 alpha and prostaglandin E2 release 2- to 3-fold more than human high density lipoproteins, whereas the delipidated apoproteins of high density lipoproteins had no significant effect on prostaglandin synthesis. Recombinant high density lipoproteins containing cholesteryl-[1- 14C]arachidonate stimulated release of [14C]-6-keto-prostaglandin F1 alpha and [14C]prostaglandin E2 by smooth muscle cells. The ionophore, A 23187, released labeled 6-keto-prostaglandin F1 alpha and prostaglandin E2 from cells preincubated with recombinant high density lipoprotein containing cholesteryl-[1- 14C]arachidonate. Unlabeled high density lipoproteins, in contrast, did not cause release of radioactive prostaglandins from cells preincubated with [1- 14C]arachidonate. Phospholipase activators were synergistic (bradykinin) or additive (angiotensin II) with high density lipoprotein in stimulation of prostaglandin synthesis. The data indicate that both high and low density lipoproteins stimulate the synthesis of prostacyclin and prostaglandin E2 by vascular smooth muscle cells. The results suggest that the lipoproteins provide arachidonate to a phospholipase-sensitive pool accessible to cyclooxygenase.