Persistent abnormalities in lipoprotein composition and cholesteryl ester transfer following lovastatin treatment

Optimally effective lipid-lowering agents should not only restore plasma lipids to normal levels but also correct potentially atherogenic alterations in lipoprotein composition and function often present in hyperlipidemic patients. Lovastatin, a competitive inhibitor of cholesterol biosynthesis, clearly lowers plasma cholesterol levels. Its effects on lipoprotein composition and cholesteryl ester transfer (CET), a key step in reverse cholesterol transport, however, are not known. Since abnormalities in CET and lipoprotein composition are present in patients with hypercholesterolemia, we studied these parameters of plasma lipoprotein transport in twelve hypercholesterolemic (HC; Type IIa) subjects (six male, six female) before and 2 months after lovastatin treatment (20 mg qd). Before lovastatin, the free cholesterol (FC)/lecithin (L) ratio in plasma, a new index of cardiovascular risk that reflects lipoprotein surface composition, was abnormally increased (1.18 +/- 0.26 vs controls 0.83 +/- 0.14; P less than 0.001) in very low density lipoproteins (VLDL) and high density lipoprotein-3 (HDL3), and remained so after treatment despite significant declines in whole plasma cholesterol (311.7 +/- 68.2 vs 215.6 +/- 27.2 mg/dl; P less than 0.001), low density lipoprotein (LDL)-cholesterol (206.3 +/- 47.9 vs 146.8 +/- 29.4; P less than 0.001), and apolipoprotein B (149 +/- 30 vs 110 +/- 17; P less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)     

Enrichment of apolipoprotein B-48 in the LDL density class following in vivo inhibition of hepatic lipase

In order to explore the in vivo function of hepatic lipase, rats were injected with goat anti-rat hepatic lipase serum which produced a complete and specific inhibition of heparin-releasable hepatic lipase. In the fasting rats, protein, phospholipid and free cholesterol expressed as either mass or percent weight increased significantly in low-density lipoprotein (LDL) and high-density lipoprotein 2 (HDL-2) fractions. These three constituents were not affected in the VLDL and HDL-3 lipoproteins. In the fat-loaded (1 ml corn oil) rat, 6 h post inhibition of hepatic lipase triacylglycerol, phospholipid and free cholesterol concentrations in the d less than 1.006 fraction were 2.5-fold higher in the inhibited animals than in the control rats. The composition of the d less than 1.006 fraction was also affected. Expressed as percent mass, protein was lower (5.2 +/- 1.2 vs. 10.3 +/- 1.5, P less than 0.001) as was cholesteryl ester (1.7 +/- 0.7 vs. 2.6 +/- 0.4, P less than 0.01); triacylglycerol was elevated (77.2 +/- 4.0 vs. 72.6 +/- 2.4, P less than 0.025), as was free cholesterol (3.0 +/- 0.6 vs. 2.4 +/- 0.2, P less than 0.025). Overall, inhibition lowered the ratio of surface-to-core constituents suggesting a larger mean particle diameter. SDS-polyacrylamide gel electrophoresis showed the intermediate- and low-density lipoprotein from treated rats to be significantly enriched in apolipoprotein B-48. In the LDL fraction, apolipoprotein B-48 accounted for 62 +/- 14% of the total apolipoprotein B in the inhibited rats, vs. 12 +/- 2% in the control rats. The above results support the previously described in vivo function of hepatic lipase as a phospholipase. In addition, the results demonstrate a role of hepatic lipase in the catabolism of chylomicrons. Since removal of apolipoprotein B-48-containing lipoproteins is dependent upon apolipoprotein E, their appearance in the LDL fraction implies a masking of apolipoprotein E-binding determinants.     

Alterations in erythrocyte membrane lipid composition and fluidity in primary lipoprotein lipase deficiency.

Lipid composition of plasma lipoproteins and erythrocyte ghost membranes has been studied in 16 healthy normolipidaemic subjects and in 16 patients affected by primary lipoprotein lipase deficiency, resulting in severe chylomicronaemia and in cholesterol-depleted low-density lipoproteins and high-density lipoproteins. A significant decrease in membrane cholesterol/phospholipid ratio was observed in lipoprotein lipase deficient patients compared to controls (3.27 +/- 0.33 vs. 3.95 +/- 0.50, mean +/- S.D.; P less than 0.0001). There was also an increase in the erythrocyte membrane phosphatidylcholine/sphingomyelin ratio in lipoprotein lipase deficient patients compared to controls (1.53 +/- 0.10 vs. 1.05 +/- 0.13; P less than 0.0001) due to a concurrent increase in phosphatidylcholine and decrease in sphingomyelin relative concentrations in these patients. Erythrocyte ghost membrane fluidity was determined by fluorescence anisotropy and found to be higher in membranes from lipoprotein lipase deficient patients. This increase in membrane fluidity can be attributed in part to changes in membrane cholesterol and phospholipid concentrations in response to abnormal plasma lipoprotein composition.     

Reactivity of human lipoproteins with purified lecithin: cholesterol acyltransferase during incubations in vitro

Studies have been performed to determine the proportion of the esterified cholesterol in high-density lipoproteins (HDL), low-density lipoproteins (LDL) and very-low-density lipoproteins (VLDL) that is attributable to a direct action of lecithin: cholesterol acyltransferase on each lipoprotein fraction. Esterification of [3H]cholesterol was examined in 37 degrees C incubations of either: (a) unseparated whole plasma, (b) plasma reconstituted after prior ultracentrifugation to separate the 1.21 g/ml supernatant, (c) a mixture comprising the 1.21 g/ml supernatant of plasma and purified lecithin: cholesterol acyltransferase or (d) the same mixture as (c) after supplementation with a preparation of partially purified lipid transfer protein. Each of these incubations was performed using samples collected from four different subjects, two of whom had normal and two of whom had elevated concentrations of plasma triacylglycerol. At the completion of 3-h incubations, the lipoproteins were separated into multiple fractions by gel filtration to obtain a continuous profile of esterified [3H]cholesterol across the whole spectrum of lipoproteins. There was an appearance of esterified [3H]cholesterol in each of the major lipoprotein fractions in all incubations. In unseparated plasma, 56% of the total (mean of four experiments) was in HDL, 33% in LDL and 11% in VLDL. A comparable distribution was observed in the incubations of reconstituted plasma and in the samples to which partially purified lipid transfer protein had been added. In the absence of lipid transfer protein activity in incubations containing purified lecithin: cholesterol acyltransferase, 73% of the esterified [3H]cholesterol was in HDL, 25% in LDL and only 1% in VLDL. It has been concluded that at physiological concentrations of lipoproteins, 70-80% of the cholesterol esterifying action of lecithin: cholesterol acyltransferase is confined to the HDL fraction, with most of the remainder involving the LDL fraction. Of the newly formed esterified cholesterol incorporated into LDL during incubations of unseparated plasma, it was apparent that more than 70% was independent of activity of the lipid transfer protein. Of that incorporated into VLDL in unseparated plasma, in contrast, almost 90% was derived as a transfer from other fractions as a consequence of activity of the lipid transfer protein.     

Disappearance and effects of exogenous lipid transfer activity in rats

These studies were performed to determine the role of plasma lipid transfer activity in the regulation of plasma total and lipoprotein cholesterol in vivo. Partially purified human lipid transfer activity was injected into rats at a level similar to that of normal rabbit plasma, d greater than 1.21. The disappearance of exogenous lipid transfer activity from rat plasma was biphasic, with a 70% loss within 6 h. The remaining 30% was lost with a half-time of about 14 h. In the rat, short-term exposure (6 h) to high levels of lipid transfer activity resulted in a net transfer of cholesteryl esters from high density to d less than 1.019 lipoproteins, without affecting plasma total cholesterol. However, the lipid transfer activity-induced changes in lipoprotein cholesterol were not evident after 24 h, despite the fact that the lipid transfer activity of rat plasma d greater than 1.21 was similar to that of human plasma d greater than 1.21 during the preceding 18 h.     

Concerted actions of cholesteryl ester transfer protein and phospholipid transfer protein in type 2 diabetes: effects of apolipoproteins

PURPOSE OF REVIEW: Type 2 diabetes frequently coincides with dyslipidemia, characterized by elevated plasma triglycerides, low high-density lipoprotein cholesterol levels and the presence of small dense low-density lipoprotein particles. Plasma lipid transfer proteins play an essential role in lipoprotein metabolism. It is thus vital to understand their pathophysiology and determine which factors influence their functioning in type 2 diabetes. RECENT FINDINGS: Cholesteryl ester transfer protein-mediated transfer is increased in diabetic patients and contributes to low plasma high-density lipoprotein cholesterol levels. Apolipoproteins A-I, A-II and E are components of the donor lipoprotein particles that participate in the transfer of cholesteryl esters from high-density lipoprotein to apolipoprotein B-containing lipoproteins. Current evidence for functional roles of apolipoproteins C-I, F and A-IV as modulators of cholesteryl ester transfer is discussed. Phospholipid transfer protein activity is increased in diabetic patients and may contribute to hepatic very low-density lipoprotein synthesis and secretion and vitamin E transfer. Apolipoprotein E could stimulate the phospholipid transfer protein-mediated transfer of surface fragments of triglyceride-rich lipoproteins to high-density lipoprotein, and promote high-density lipoprotein remodelling. SUMMARY: Both phospholipid and cholesteryl ester transfer proteins are important in very low and high-density lipoprotein metabolism and display concerted actions in patients with type 2 diabetes.     

Neutral lipid transfer and lipolysis convert high molecular weight LDL from cholesterol-fed nonhuman primates towards normal: a molecular analysis

In cynomolgus monkeys (Macaca fascicularis) fed an atherogenic diet, large, cholesterol ester-rich LDL (Mr greater than 3.5.10(6] are found at the same time that the plasma triacylglycerol levels are low. We studied whether the presence of higher concentrations of triacylglycerol-rich lipoproteins (VLDL) during in vitro incubations would allows depletion from LDL of cholesterol ester and a decreased LDL molecular weight. Three high Mr LDL (Mr = (3.7-4.8).10(6)), rich in cholesterol ester (50 +/- 1.4% by weight), were isolated from three animals by zonal ultracentrifugation, and were then incubated with human VLDL at 37 degrees C for 18 h in lipoprotein-deficient human plasma containing neutral lipid transfer activity. After incubation, modified LDL (M-LDL) was isolated by zonal ultracentrifugation. M-LDL was triacylglycerol-rich (36 +/- 5% by weight) and cholesterol ester-poor (20 +/- 3%), and cholesterol ester had transferred into VLDL. Purified lipoprotein lipase was added to the M-LDL, and triacylglycerol was hydrolyzed. The size of the post-lipolysis M-LDL (Mp-LDL) particles became smaller (mean diameters of 253 A and 228 A for two native LDLs and 215 A and 193 A for Mp-LDL, respectively). Both analytical and zonal ultracentrifugation showed Mp-LDL to be more dense than native LDL. Estimated molecular weights for Mp-LDL were 40%-50% less than that of the original LDL, and fell within the molecular weight range for normal human and monkey LDL. Lipid exchanges, but not apoprotein transfers, were responsible for LDL remodelling, as supported by three separate methods of analysis. Cholesterol ester losses accounted for about two-thirds of the molecular weight decrease. These in vitro results suggest that cholesterol ester enrichment of apoprotein B lipoprotein particles can be reversed by providing adequate levels of VLDL in the presence of neutral lipid transfer processes and lipolytic activity.     

Interaction of bovine serum high density lipoprotein with mixed vesicles of phosphatidylcholine and cholesterol.

The interaction of sonicated, small vesicles of egg phosphatidylcholine and cholesterol (2:1, mol/mol) with bovine high density serum lipoproteins was examined in terms of lipid transfer between both types of particles and the resulting changes in lipoprotein structure. Saturation of high density lipoprotein preparations with vesicle lipids gave final lipoprotein particles with essentially unchanged protein content and composition, unchanged cholesterylester and nonpolar lipid content, but with markedly increased phospholipid content (59% increas by weight) and moderately increased cholesterol content (20% increase by weight). The lipoproteins enriched in lipid were relatively uniform, spherical particles, 110 +/- 3.6 A in diameter (6 A larger than the original lipoproteins); they had a markedly decreased intrinsic protein fluorescence, a red-shifted fluorescence wavelength maximum, and more fluid lipid domains. These results indicate that the direct addition of excess lipids from membranes or other lipoproteins is a possible mechanism for lipid transfer to high density lipoproteins. Also they suggest a structural flexibility of high density lipoproteins that allows the addition of significant amounts of surface components.     

Effects of sucrose feeding and injection of lipid transfer protein on rat plasma lipoproteins

Sucrose feeding increased rat plasma very-low-density lipoprotein (VLDL) triacylglycerol concentration and decreased the cholesterol level in high-density lipoprotein (HDL). Gel filtration chromatography cholesterol profiles of both normal-fed and sucrose-fed plasma lipoproteins showed a small peak of VLDL and a large peak of HDL. Injection of a partially purified human lipid transfer protein preparation into normal-fed rats did not alter the concentration of cholesterol in either VLDL or HDL to a great extent, but there was a disappearance of the larger HDL particles. Injection of lipid transfer protein into sucrose-fed rats resulted in an overall 35% reduction in the concentration of HDL cholesterol, a more dramatic loss of larger HDL particles and a slight decrease in the mean particle size of the major HDL population.     

The effect of growth hormone administration on lipids and lipoproteins in growth hormone-deficient patients

Plasma lipids, lipoproteins, and lipoprotein cholesterol levels were studied in a group (n = 8) of prepubertal growth hormone-deficient patients before and after growth hormone (GH) administration. Determination of plasma lipoproteins by a sensitive agarose gel electrophoretic technique demonstrated: (a) in the patients with two prebeta bands an intensification of the fast prebeta lipoprotein fraction after growth hormone administration; and (b) in the patients with one prebeta band the appearance of a second prebeta band after growth hormone administration. The mean (+/- SD) plasma triglyceride level before GH was 86 +/- 60 mg/dl and 158 +/- 95 mg/dl after GH (P less than 0.01). Mean (+/- SD) plasma cholesterol level before GH was 196 +/- 25 mg/dl and 174 +/- 28 mg/dl after GH (P less than 0.05). High-density lipoprotein cholesterol concentrations decreased significantly (P less than 0.001) from mean (+/- SD) 55 +/- 12 mg/dl before GH to 37 +/- 10 mg/dl after GH. Very-low-density lipoprotein cholesterol concentrations increased significantly (P less than 0.05) from mean (+/- SD) 13 +/- 12 mg/dl before GH to 23 +/- 15 mg/dl after GH. Low-density lipoprotein cholesterol concentrations decreased (N.S.) from mean (+/- SD) 123 +/- 15 mg/dl before GH to 114 +/- 15 mg/dl after GH. These lipid and lipoprotein changes could be mediated through the insulin antagonism, hyperinsulinemia, and a decrease in lipoprotein lipase activity caused by growth hormone.     

Reduction in the concentration and activity of plasma cholesteryl ester transfer protein by alcohol.

Plasma cholesteryl esters, synthesized within high density lipoproteins (HDL), may be transferred from HDL particles to other lipoproteins by plasma cholesteryl ester transfer protein (CETP). Alcohol consumption is associated with increased HDL cholesterol concentration and reduced plasma CETP activity. The alcohol-induced decrease in CETP activity may be due to a low concentration of CETP in plasma or the inhibition of CETP by specific inhibitor proteins or alterations in the composition of plasma lipoproteins. The first two possibilities are studied further in this paper using data on 47 alcohol abusers and 31 control subjects. The activity of CETP was measured as the rate of cholesteryl ester transfer between radio-labeled low density lipoproteins and unlabeled HDL using an in vitro method independent of endogenous plasma lipoproteins. Plasma CETP concentration was determined by a Triton-based radioimmunoassay. The alcohol abusers consuming alcohol (on average 154 g/day) had 28% higher HDL cholesterol (P less than 0.01), 27% lower plasma CETP concentration (P less than 0.001), and 22% lower plasma CETP activity (P less than 0.001) than the controls. Plasma CETP concentration showed a negative correlation with HDL cholesterol among all the subjects (r = -0.317, P less than 0.01) but not among the alcohol abusers alone (r = -0.102, N. S.). During 2 weeks of alcohol withdrawal, plasma CETP concentration and activity of 8 subjects increased, whereas HDL cholesterol decreased by 42% (P less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)     

Modulation of lipid homeostasis in response to continuous or intermittent high-fat diet in pigs

A high-fat diet is known to induce atherosclerosis in animal models. Dietary factors and timing of atherogenic food delivery may affect plasma lipoprotein content composition and its potential atherogenic effect. Increasingly often, humans spend periods/days eating in a completely unregulated way, ingesting excessive amounts of food rich in oils and fats, alternating with periods/days when food intake is more or less correct. We investigate the effect on lipid homeostasis of a high-fat diet administered either continuously or intermittently. We investigated control pigs receiving standard diet (C, n=7), pigs receiving a high-fat diet every day for 10 weeks (CHF, n=5), and pigs receiving a high-fat diet every other week for 10 weeks (IHF, n=7). IHF animals were shown to have a different lipid profile compared with CHF animals, with a significant increase in high-density lipoproteins (HDL) levels with respect to C and CHF groups. CHF also showed significantly higher values of TC/HDL cholesterol compared with C and IHF. Hepatic expression analysis of genes involved in lipid homeostasis showed an increasing trend of nuclear receptor LXRα along with its target genes in the CHF group and in the IHF group, whereas SREBP2 and LDLr were significantly inhibited. A significant correlation was found between ABCA1 expression and circulating levels of HDL-C. Periodic withdrawals of a high-fat atherogenic diet compared with a regular administration results in a different adaptive response of lipoprotein metabolism, which leads to a significantly higher plasma level of HDL-C and lower TC/HDL-C.     

Plasma lipoprotein and platelet function after heparin injection: studies in normal fasted and postprandial and in type V hyperlipoproteinemic subjects

The effect of heparin injection (50 IU/kg body weight) on plasma lipoprotein concentration and composition as well as on platelet aggregation and 14C-serotonin release was studied in normal fasted subjects, normal subjects 4 hr after a fatty meal (postprandial state), and in primary type V hyperlipoproteinemic patients. Heparin injection resulted in a reduction in plasma triglyceride, cholesterol, and phospholipids as well as in the inhibition of platelet function in either the presence or the absence of the plasma environment. Heparin injection resulted in catabolism of triglyceride-rich lipoproteins and increment of cholesterol and protein in the high-density lipoprotein (HDL) density range. In fasted normal subjects, very-low-density lipoprotein (VLDL) was reduced by 50%; in the postprandial state, both VLDL and chylomicrons decreased similarly; but in phenotype V hyperlipoproteinemia, only chylomicrons (but not VLDL) degraded. Heparin injection also caused increased electrophoretic mobility of plasma lipoprotein. Upon incubation of similar lipoprotein concentration, derived before and after heparin injection, with normal washed platelets, we found that in all the groups all the lipoproteins (except HDL) derived after heparin injection caused reduction in platelet activity. High-density lipoproteins derived after heparin injection, especially from type V hyperlipoproteinemic subjects, increased normal platelet activity, and this probably represents an effect of chylomicron remnant particles in the HDL density range. Our study thus demonstrates altered composition and concentration of plasma lipoprotein after heparin injection and may suggest the appearance of remnant particles with atherogenic properties.     

Amiodarone-induced changes in lipid metabolism

Hypothyroidism is a major cause of secondary hypercholesterolemia. Amiodarone treatment alters both the levels of serum lipids and thyroid hormones. We investigated whether the amiodarone-induced changes in lipid metabolism are related to the changes in thyroid hormone levels. Eighteen patients received amiodarone (31 +/- 3 g cumulative dose) for six weeks. Serum triglyceride, total-cholesterol, high density lipoprotein-cholesterol and its subfractions, apolipoproteins B and AI, and plasma post-heparin lipoprotein lipase and hepatic triglyceride lipase activities were determined. Amiodarone treatment caused significant increases in serum total-cholesterol (baseline 4.4 +/- 0.21 (SE), 6 weeks 5.12 +/- 0.26 mmol/l, P less than 0.01), in low density lipoprotein cholesterol (baseline 2.61 +/- 0.26, 6 weeks 3.36 +/- 0.21 mmol/l, P less than 0.05) and in apolipoprotein B (baseline 1.95 +/- 0.15, 6 weeks 2.26 +/- 0.13 mmol/l, P less than 0.01) concentrations. Serum high density lipoprotein and its subfractions, or apolipoprotein AI levels did not change. Plasma post-heparin lipoprotein lipase activity increased (baseline 137 +/- 21, 6 weeks 168 +/- 21 U/ml, P less than 0.01) while hepatic triglyceride lipase did not change. Amiodarone also caused an increase in serum thyroxine (baseline 110 +/- 8, 6 weeks 136 +/- 6 mmol/l, P less than 0.05), although values remained in euthyroid range. In summary, amiodarone therapy increased the concentrations of atherogenic lipoproteins in the serum similar to that seen in hypothyroidism. On the other hand the effect of amiodarone on lipoprotein lipase was opposite to that seen in hypothyroidism. Therefore, amiodarone-induced changes in lipid metabolism cannot be explained solely on the basis of the changes in circulating thyroid hormone levels.     

Inhibition of CETP activity by torcetrapib reduces susceptibility to diet-induced atherosclerosis in New Zealand White rabbits

Cholesteryl ester transfer protein (CETP) inhibitors increase high density lipoprotein-cholesterol (HDL-C) in animals and humans, but whether CETP inhibition will be antiatherogenic is still uncertain. We tested the CETP inhibitor torcetrapib in rabbits fed an atherogenic diet at a dose sufficient to increase HDL-C by at least 3-fold (207 +/- 32 vs. 57 +/- 6 mg/dl in controls at 16 weeks). CETP activity was inhibited by 70-80% throughout the study. Non-HDL-C increased in both groups, but there was no difference apparent by the study's end. At 16 weeks, aortic atherosclerosis was 60% lower in torcetrapib-treated animals (16.4 +/- 3.4% vs. 39.8 +/- 5.4% in controls) and aortic cholesterol content was reduced proportionally. Sera from a separate group of rabbits administered torcetrapib effluxed 48% more cholesterol from Fu5AH cells than did sera from control animals, possibly explaining the reduced aortic cholesterol content. Regression analyses indicated that lesion area in the torcetrapib-treated group was strongly correlated with the ratio of total plasma cholesterol to HDL-C but not with changes in other lipid or lipoprotein levels. CETP inhibition with torcetrapib retards atherosclerosis in rabbits, and the reduced lesion area is associated with increased levels of HDL-C.     

Identification of lipoprotein X-like particles in rat plasma following Intralipid infusion.

Fasting rats were infused with 10% Intralipid for 24 h (0.33 mL/h per 100 g body weight) and the plasma lipoproteins isolated and compared with those of fed animals and animals with bile duct ligatures as controls. There was a 6- to 10-fold increase in the free cholesterol and phospholipid content of total plasma in animals infused with Intralipid or with ligated bile ducts. The changes were largely restricted to the low density lipoproteins (d=1.019--1.063 g/mL) where free cholesterol and phospholipid increased 30- to 60-fold compared with fed control animals. Hydroxylapatite chromatography of the low density lipoprotein fractions of both Intralipid-infused and bile duct ligated animals yielded a subfraction which was rich in free cholesterol (27%), phosphatidylcholine (66%), and protein (6%); the latter was composed primarily of albumin and apo C proteins. The electrophoretic mobility and polyanionic precipitation properties of the abnormal lipoprotein were indistinguishable from those of lipoprotein X isolated from the animals with bile duct ligatures. The albumin in the abnormal lipoprotein from both groups of experimental animals was detected immunochemically only after delipidation of the lipoprotein. Twice as much of the lipoprotein X accumulated in Intralipid-infused than in the bile duct ligated animals. On rechromatography of the residual low density lipoprotein other subfractions could be isolated which possessed lipid and protein proportions intermediate between those of the lipoprotein X and of normal rat plasma low density lipoprotein. The activity of lecithin cholesterol acyl transferase was increased twofold in the Intralipid-infused animals when compared with control animals, but it decreased by 50% in the animals with bile duct ligatures. It is concluded that the unusual lipoprotein X accumulates in the plasma of Intralipid-infused animals owing to incomplete clearance of the exogenous phospholipid, which mobilized tissue cholesterol and in the form of vesicular particles serves as a lipid phase for apo C proteins. A comparable mechanism is suggested for the formation of lipoprotein X in the animals with bile duct ligature.     

Lecithin:cholesterol acyltransferase deficiency increases atherosclerosis in the low density lipoprotein receptor and apolipoprotein E knockout mice.

The purpose of the present study was to test the hypothesis that lecithin:cholesterol acyltransferase (LCAT) deficiency would accelerate atherosclerosis development in low density lipoprotein (LDL) receptor (LDLr-/-) and apoE (apoE-/-) knockout mice. After 16 weeks of atherogenic diet (0.1% cholesterol, 10% calories from palm oil) consumption, LDLr-/- LCAT-/- double knockout mice, compared with LDLr-/- mice, had similar plasma concentrations of free (FC), esterified (EC), and apoB lipoprotein cholesterol, increased plasma concentrations of phospholipid and triglyceride, decreased HDL cholesterol, and 2-fold more aortic FC (142 +/- 28 versus 61 +/- 20 mg/g protein) and EC (102 +/- 27 versus 61+/- 27 mg/g). ApoE-/- LCAT-/- mice fed the atherogenic diet, compared with apoE-/- mice, had higher concentrations of plasma FC, EC, apoB lipoprotein cholesterol, and phospholipid, and significantly more aortic FC (149 +/- 62 versus 109 +/- 33 mg/g) and EC (101 +/- 23 versus 69 +/- 20 mg/g) than did the apoE-/- mice. LCAT deficiency resulted in a 12-fold increase in the ratio of saturated + monounsaturated to polyunsaturated cholesteryl esters in apoB lipoproteins in LDLr-/- mice and a 3-fold increase in the apoE-/- mice compared with their counterparts with active LCAT. We conclude that LCAT deficiency in LDLr-/- and apoE-/- mice fed an atherogenic diet resulted in increased aortic cholesterol deposition, likely due to a reduction in plasma HDL, an increased saturation of cholesteryl esters in apoB lipoproteins and, in the apoE-/- background, an increased plasma concentration of apoB lipoproteins.     

Combined (n-3 and n-6) essential fatty deficiency is a potent modulator of plasma lipids, lipoprotein composition, and lipolytic enzymes

Essential fatty acids (EFA) are important structural and functional components of cell membranes. Their deficiency has been associated with several clinical and biochemical abnormalities. In the present study, the lipid profile as well as the concentration, composition, and metabolism of lipoproteins were examined in rats rendered EFA-deficient over a period of 12 weeks. Changes in plasma fatty acids mainly induced an increase of palmitoleic (16:1 n-7) and eicosatrienoic (20:3 n-9) acids, while linoleic (18:2 n-6), arachidonic (20:4 n-6), linolenic (18:3 n-3), and docosahexaenoic (22:6 n-3) acids were decreased. The results show increased concentrations of free fatty acids (FFA) (P less than 0.001), triglycerides (P less than 0.001), total cholesterol (P less than 0.02), free cholesterol (P less than 0.005), and phospholipids (P less than 0.05) when compared to pair-fed controls. Similar levels of cholesteryl esters were found in the two groups, and lecithin: cholesterol acyltransferase activity (nmol/100 microliters plasma per h) (8.98 +/- 1.44 vs 8.72 +/- 0.50) did not differ. On the other hand, postheparin extrahepatic lipoprotein lipase (LPL) activity was significantly (P less than 0.002) decreased (5.96 +/- 0.29 vs 7.29 +/- 0.68 mumol FFA/ml per h) and could account for the hypertriglyceridemia as well for the relative triglyceride enrichment of very low density lipoprotein, intermediate density lipoprotein, and low density lipoprotein particles. This enzymatic depletion of LPL was mainly due to the adipose tissue, since a higher level (P less than 0.001) of hepatic lipase (325.8 +/- 16.0 vs 130.8 +/- 9.5 nmol FFA/mg protein per h) was found in liver acetone powder extracts.(ABSTRACT TRUNCATED AT 250 WORDS)     

Plasma lipoprotein profile and composition in White Carneau and Show Racer breeds of pigeons.

Plasma lipoprotein profile and composition in atherosclerosis-susceptible White Carneau and atherosclerosis-resistant Show Racer pigeons were investigated while consuming a regular pigeon chow diet free of cholesterol. Plasma was studied by analytical and preparative ultracentrifugation and paper electrophoresis. Lipid composition of each lipoprotein was determined by combined TLC-GLC techniques. The major plasma lipoprotein of both breeds was high density lipoprotein (HDL) with some low density lipoprotein (LDL) and no very low density lipoprotein (VLDL). Cholesterol was mainly found in the HDL in both breeds (71.7%), and no difference was noticed in the total cholesterol content of whole plasma or in various lipoproteins. The LDL fraction in White Carneaux showed a significantly lower (P less than 0.05) percentage of cholesterol esters compared with Show Racers (58.63 +/- 4.9 in White Carneaux vs. 72.12 +/- 2.1 in Show Racers). In LDL, the percentage of the triglyceride concentration in White Carneaux was significantly lower (P less than 0.01) than that of Show Racers while the percentage of protein content in White Carneaux was higher than in Show Racers. No significant differences were observed in fatty acid composition of steryl esters phospholipids, and triglycerides in the lipoprotein fractions of the two breeds. These studies show important differences in the cholesterol esters, protein, and triglyceride content of LDL in the atherosclerosis-susceptible breed of pigeons.     

Oral nicotine induces an atherogenic lipoprotein profile

Male squirrel monkeys were used to evaluate the effect of chronic oral nicotine intake on lipoprotein composition and metabolism. Eighteen yearling monkeys were divided into two groups: 1) Controls fed isocaloric liquid diet; and 2) Nicotine primates given liquid diet supplemented with nicotine at 6 mg/kg body wt/day. Animals were weighed biweekly, plasma lipid, glucose, and lipoprotein parameters were measured monthly, and detailed lipoprotein composition, along with postheparin plasma lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) activity, was assessed after 24 months of treatment. Although nicotine had no effect on plasma triglyceride or high density lipoproteins (HDL), the alkaloid caused a significant increase in plasma glucose, cholesterol, and low density lipoprotein (LDL) cholesterol plus protein while simultaneously reducing the HDL cholesterol/plasma cholesterol ratio and animal body weight. Levels of LDL precursors, very low density (VLDL) and intermediate density (IDL) lipoproteins, were also lower in nicotine-treated primates while total postheparin lipase (LPL + HTGL) activity was significantly elevated. Our data indicate that long-term consumption of oral nicotine induces an atherogenic lipoprotein profile (increases LDL, decreases HDL/total cholesterol ratio) by enhancing lipolytic conversion of VLDL to LDL. These results have important health implications for humans who use smokeless tobacco products or chew nicotine gum for prolonged periods.