Apolipoprotein E Structure and Substrate and Receptor-Binding Activities of Triglyceride-Rich Human Plasma Lipoproteins in Normo- and Hypertriglyceridemia

Cysteine-arginine interchanges along the primary sequence of human plasma apolipoprotein E (apoE) play an important role in determining its biological functions due to a high mutation frequency of cytosine in CGX triplet that codes 33 of 34 apolipoprotein arginine residues. The contribution of apoE secondary structure to apolipoprotein-lipid interaction is described. The significance of apolipoprotein in triglyceride synthesis, lipoprotein lipolysis, and receptor-mediated clearance of lipolytic remnants of triglyceride-rich lipoproteins is discussed as well. The metabolic flow of lipoproteins in normo- and hypertriglyceridemia can be described by separate compartments that contribute to lipoprotein interaction with at least six different receptors: 1) low density lipoprotein (LDL) receptor; 2) LDL receptor-related protein (LRP); 3) apoB(48) macrophage receptor for hypertriglyceridemic very low density lipoproteins (VLDL); 4) scavenger receptors; 5) VLDL receptor; 6) lipolysis-stimulated receptor. The contribution of the exposure of apoE molecules on the surface of triglyceride-rich particles sensitive both to lipolysis and plasma triglyceride content to the interaction with LDL receptor and LRP is emphasized.     

Heparan sulfate proteoglycans and triglyceride-rich lipoprotein metabolism

PURPOSE OF REVIEW: Clearance of triglyceride-rich lipoprotein remnants by the liver is a key step in preventing hypertriglyceridemia, an independent risk factor for cardiovascular disease. We review recent genetic evidence that heparan sulfate proteoglycans work in concert with the LDL receptor in the liver to facilitate binding and clearance of both triglyceride and cholesterol-rich lipoproteins from the circulation. RECENT FINDINGS: Partial reduction of sulfation of liver heparan sulfate using the Cre-loxP system caused accumulation of hepatic and dietary triglyceride-rich lipoprotein particles due to delayed clearance. Compounding the mutation with LDL receptor deficiency caused enhanced accumulation of both cholesterol and triglyceride-rich particles compared with mice lacking only LDL receptors. These findings provide the first genetic evidence that hepatic heparan sulfate proteoglycans play a central role in the clearance of lipoproteins by the liver and work independently of LDL receptors. SUMMARY: A role for hepatocyte heparan sulfate in lipoprotein metabolism has now been genetically established in mice. Given this finding, mild, but clinically relevant, hyperlipidemias in human patients may be a result of alterations in heparan sulfate structure or possible genetic polymorphisms in the relevant biosynthetic genes.     

Rapid turnover of apolipoprotein C-III-containing triglyceride-rich lipoproteins contributing to the formation of LDL subfractions

The atherogenicity theory for triglyceride-rich lipoproteins (TRLs; VLDL + intermediate density lipoprotein) generally cites the action of apolipoprotein C-III (apoC-III), a component of some TRLs, to retard their metabolism in plasma. We studied the kinetics of multiple TRL and LDL subfractions according to the content of apoC-III and apoE in 11 hypertriglyceridemic and normolipidemic persons. The liver secretes mainly two types of apoB lipoproteins: TRL with apoC-III and LDL without apoC-III. Approximately 45% of TRLs with apoC-III are secreted together with apoE. Contrary to expectation, TRLs with apoC-III but not apoE have fast catabolism, losing some or all of their apoC-III and becoming LDL. In contrast, apoE directs TRL flux toward rapid clearance, limiting LDL formation. Direct clearance of TRL with apoC-III is suppressed among particles also containing apoE. TRLs without apoC-III or apoE are a minor, slow-metabolizing precursor of LDL with little direct removal. Increased VLDL apoC-III levels are correlated with increased VLDL production rather than with slow particle turnover. Finally, hypertriglyceridemic subjects have significantly greater production of apoC-III-containing VLDL and global prolongation in residence time of all particle types. ApoE may be the key determinant of the metabolic fate of atherogenic apoC-III-containing TRLs in plasma, channeling them toward removal from the circulation and reducing the formation of LDLs, both those with apoC-III and the main type without apoC-III.     

Lipolysis stimulated lipoprotein receptor: a novel molecular link between hyperlipidemia, weight gain, and atherosclerosis in mice

The lipolysis-stimulated lipoprotein receptor, LSR, is a multimeric protein complex in the liver that undergoes conformational changes upon binding of free fatty acids, thereby revealing a binding site (s) that recognizes both apoB and apoE. Complete inactivation of the LSR gene is embryonic lethal in mice. Here we show that removal of a single LSR allele (LSR(-/+)) caused statistically significant increases in both plasma triglyceride and cholesterol levels, a 2-fold increase in plasma triglyceride changes during the post-prandial phase, and delayed clearance of lipid emulsions or a high fat meal. The longer postprandial lipoprotein clearance time observed in LSR(-/+) mice was further increased in LSR(-/+) mice lacking functional low density lipoprotein (LDL) receptors. LSR(-/+) mice placed on a Western-type diet displayed higher plasma triglycerides and cholesterol levels, increased triglyceride-rich lipoproteins and LDL, and increased aorta lipid content, as compared with control mice on the same diet. Furthermore, a direct correlation was observed between the hyperlipidemia and weight gain but only in the LSR(-/+) mice. Knockdown of LSR expression by small interfering RNA in mouse Hepa1-6 cells led to decreased internalization of both DiI-labeled cyclohexanedione-LDL and very low density lipoprotein in the presence of oleate. These data led us to conclude that LSR contributes to the physiological clearance of atherogenic triglyceride-rich lipoproteins and LDL. We propose that LSR cooperates with the LDL receptor in the final hepatic processing of apoB-containing lipoproteins and represents a novel therapeutic target for the treatment of hyperlipidemia associated with obesity and atherosclerosis.     

Properties of an apolipoprotein E-enriched fraction of triglyceride-rich lipoproteins isolated from human blood plasma with a monoclonal antibody to apolipoprotein B-100.

A monoclonal antibody to apolipoprotein (apo) B-100 (JI-H) with unique binding properties has been used to separate a population of triglyceride-rich lipoproteins from blood plasma of normotriglyceridemic individuals and patients with various forms of hypertriglyceridemia. This antibody fails to recognize an apoE-rich population of very low density lipoproteins (VLDL) containing apoB-100 as well as all triglyceride-rich lipoproteins containing apoB-48, but it binds other VLDL that contain apoE and almost all lipoproteins that contain apoB-100, but no apoE. The unbound triglyceride-rich lipoproteins separated by ultracentrifugation after separation from plasma by immunoaffinity chromatography contained 10-13% of the apoB of triglyceride-rich lipoproteins from three normotriglyceridemic individuals, 10-29% of that from five patients with endogenous hypertriglyceridemia, 40-48% of that from three patients with familial dysbetablipoproteinemia, and 65% of that from a patient with lipoprotein lipase deficiency. In all cases, the unbound triglyceride-rich lipoproteins contained more molecules of apoE and cholesteryl esters per particle than those that were bound to monoclonal antibody JI-H, and they were generally depleted of C apolipoproteins. These properties resemble those described for partially catabolized remnants of chylomicrons and VLDL. The affinity of the unbound lipoproteins for the low density lipoprotein (LDL) receptor varied widely, and closely resembled that of the total triglyceride-rich lipoproteins from individual subjects. Our results demonstrate that remnant-like chylomicrons and a population of remnant-like VLDL can be isolated and quantified in blood plasma obtained in the postabsorptive state from normotriglyceridemic and hypertriglyceridemic individuals alike.     

Apolipoproteins C-I and C-III Inhibit Lipoprotein Lipase Activity by Displacement of the Enzyme from Lipid Droplets

Apolipoproteins (apo) C-I and C-III are known to inhibit lipoprotein lipase (LPL) activity, but the molecular mechanisms for this remain obscure. We present evidence that either apoC-I or apoC-III, when bound to triglyceride-rich lipoproteins, prevent binding of LPL to the lipid/water interface. This results in decreased lipolytic activity of the enzyme. Site-directed mutagenesis revealed that hydrophobic amino acid residues centrally located in the apoC-III molecule are critical for attachment to lipid emulsion particles and consequently inhibition of LPL activity. Triglyceride-rich lipoproteins stabilize LPL and protect the enzyme from inactivating factors such as angiopoietin-like protein 4 (angptl4). The addition of either apoC-I or apoC-III to triglyceride-rich particles severely diminished their protective effect on LPL and rendered the enzyme more susceptible to inactivation by angptl4. These observations were seen using chylomicrons as well as the synthetic lipid emulsion Intralipid. In the presence of the LPL activator protein apoC-II, more of apoC-I or apoC-III was needed for displacement of LPL from the lipid/water interface. In conclusion, we show that apoC-I and apoC-III inhibit lipolysis by displacing LPL from lipid emulsion particles. We also propose a role for these apolipoproteins in the irreversible inactivation of LPL by factors such as angptl4.     

LDL receptor deficiency or apoE mutations prevent remnant clearance and induce hypertriglyceridemia in mice

We have used adenovirus-mediated gene transfer and bolus injection of purified apolipoprotein E (apoE) in mice to determine the contribution of LDL receptor family members in the clearance of apoE-containing lipoproteins in vivo and the factors that trigger hypertriglyceridemia. A low dose [5 x 10(8) plaque-forming units (pfu)] of an adenovirus expressing apoE4 did not normalize plasma cholesterol levels of apolipoprotein E-deficient (apoE(-/-)) x low density lipoprotein receptor-deficient (LDLr(-/-)) mice and induced hypertriglyceridemia. A similar phenotype of combined dyslipidemia was induced in apoE(-/-) or apoE(-/-) x LDLr(-/-) mice after infection with a low dose (4 x 10(8) pfu) of an adenovirus expressing the apoE4[R142V/R145V] mutant previously shown to be defective in receptor binding. In contrast, a low dose of 5 x 10(8) pfu of the apoE4-expressing adenovirus corrected hypercholesterolemia in apoE(-/-) mice and did not trigger hypertriglyceridemia. Bolus injection of purified apoE in apoE(-/-) x LDLr(-/-) mice did not clear plasma cholesterol levels and induced mild hypertriglyceridemia. In contrast, similar injection of apoE in apoE(-/-) mice cleared plasma cholesterol and caused transiently mild hypertriglyceridemia. These findings suggest that a) the LDL receptor alone can account for the clearance of apoE-containing lipoproteins in mice, and the contribution of other receptors is minimal, and b) defects in either the LDL receptor or in apoE that affect its interactions with the LDL receptor, increase the sensitivity to apoE-induced hypertriglyceridemia in mice.     

ApoC-III content of apoB-containing lipoproteins is associated with binding to the vascular proteoglycan biglycan

Retention of apolipoprotein (apo)B and apoE-containing lipoproteins by extracellular vascular proteoglycans is critical in atherogenesis. Moreover, high circulating apoC-III levels are associated with increased atherosclerosis risk. To test whether apoC-III content of apoB-containing lipoproteins affects their ability to bind to the vascular proteoglycan biglycan, we evaluated the impact of apoC-III on the interaction of [(35)S]SO(4)-biglycan derived from cultured arterial smooth muscle cells with lipoproteins obtained from individuals across a spectrum of lipid concentrations. The extent of biglycan binding correlated positively with apoC-III levels within VLDL (r = 0.78, P < 0.01), IDL (r = 0.67, P < 0.01), and LDL (r = 0.52, P < 0.05). Moreover, the biglycan binding of VLDL, IDL, and LDL was reduced after depletion of apoC-III-containing lipoprotein particles in plasma by anti-apoC-III immunoaffinity chromatography. Since apoC-III does not bind biglycan directly, enhanced biglycan binding may result from a conformational change associated with increased apo C-III content by which apoB and/or apoE become more accessible to proteoglycans. This may be an intrinsic property of lipoproteins, since exogenous apoC-III enrichment of LDL and VLDL did not increase binding. ApoC-III content may thus be a marker for lipoproteins characterized as having an increased ability to bind proteoglycans.     

Identification of Rev-erbalpha as a physiological repressor of apoC-III gene transcription

Elevated serum levels of triglyceride-rich remnant lipoproteins (TRL) are a major risk factor predisposing a subject to atherosclerosis. Apolipoprotein C-III (apoC-III) is a major constituent of TRL that impedes triglyceride hydrolysis and remnant clearance and, as such, may exert pro-atherogenic activities. In the present study, transient cotransfection experiments in rat hepatocytes in primary culture and rabbit kidney RK13 cells demonstrated that overexpression of Rev-erbalpha specifically decreases basal and HNF-4 stimulated human apoC-III promoter activity. A Rev-erbalpha response element was mapped by promoter deletion, mutation analysis, and gel-shift experiments to a AGGTCA half-site located at position -23/-18 (downstream of the TATA box) in the apoC-III promoter. Finally, Rev-erbalpha-deficient mice displayed elevated serum and liver mRNA levels of apoC-III together with increased serum VLDL triglycerides. Taken together, our data identify Rev-erbalpha as a regulator of apoC-III gene expression, providing a novel, physiological role for this nuclear receptor in the regulation of lipid metabolism.     

The low density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor binds and mediates catabolism of bovine milk lipoprotein lipase.

Lipoprotein lipase (LPL), the major lipolytic enzyme involved in the conversion of triglyceride-rich lipoproteins to remnants, was found to compete with binding of activated alpha 2-macroglobulin (alpha 2M*) to the low density lipoprotein receptor-related protein (LRP)/alpha 2-macroglobulin receptor. Bovine milk LPL displaced both 125I-labeled alpha 2M* and 39-kDa alpha 2M receptor-associated protein (RAP) from the surface of cultured mutant fibroblasts lacking LDL receptors with apparent KI values at 4 degrees C of 6.8 and 30 nM, respectively. Furthermore, LPL inhibited the cellular degradation of 125I-alpha 2M* at 37 degrees C. Because both alpha 2M* and RAP interact with LRP, these data suggest that LPL binds specifically to this receptor. This was further supported by observing that an immunoaffinity-isolated polyclonal antibody against LRP blocked cellular degradation of 125I-LPL in a dose-dependent manner. In addition, 125I-LPL bound to highly purified LRP in a solid-phase assay with a KD of 18 nM, and this binding could be partially displaced with alpha 2M* (KI = 7 nM) and RAP (KI = 3 nM). Taken together, these data establish that LPL binds with high affinity to LRP and undergoes LRP-mediated cellular uptake. The implication of these findings for lipoprotein catabolism in vivo may be important if LRP binding is preserved when LPL is attached to lipoproteins. If so, LPL might facilitate LRP-mediated clearance of lipoproteins.     

An extrahepatic receptor-associated protein-sensitive mechanism is involved in the metabolism of triglyceride-rich lipoproteins

We have used adenovirus-mediated gene transfer in mice to investigate low density lipoprotein receptor (LDLR) and LDLR-related protein (LRP)-independent mechanisms that control the metabolism of chylomicron and very low density lipoprotein (VLDL) remnants in vivo. Overexpression of receptor-associated protein (RAP) in mice that lack both LRP and LDLR (MX1cre(+)LRP(flox/flox)LDLR(-/-)) in their livers elicited a marked hypertriglyceridemia in addition to the pre-existing hypercholesterolemia in these animals, resulting in a shift in the distribution of plasma lipids from LDL-sized lipoproteins to large VLDL-sized particles. This dramatic increase in plasma lipids was not due to a RAP-mediated inhibition of a unknown hepatic high affinity binding site involved in lipoprotein metabolism, because no RAP binding could be detected in livers of MX1cre(+)LRP(flox/flox)LDLR(-/-) mice using both membrane binding studies and ligand blotting experiments. Remarkably, RAP overexpression also resulted in a 7-fold increase (from 13.6 to 95.6 ng/ml) of circulating, but largely inactive, lipoprotein lipase (LPL). In contrast, plasma hepatic lipase levels and activity were unaffected. In vitro studies showed that RAP binds to LPL with high affinity (K(d) = 5 nM) but does not affect its catalytic activity, in vitro or in vivo. Our findings suggest that an extrahepatic RAP-sensitive process that is independent of the LDLR or LRP is involved in metabolism of triglyceride-rich lipoproteins. There, RAP may affect the functional maturation of LPL, thus causing the accumulation of triglyceride-rich lipoproteins in the circulation.     

Low-density lipoprotein inhibits secretion of phospholipid transfer protein in human trophoblastic BeWo cells

Human plasma phospholipid transfer protein (PLTP) plays an important role in lipoprotein metabolism. In this study, we investigated the effects of lipoproteins on the secretion of PLTP in cultured BeWo choriocarcinoma cells. Low-density lipoproteins (LDLs) decreased PLTP secretion in a dose- and time-dependent manner, whereas very low density lipoproteins and high-density lipoproteins (HDLs) had little effect. LDL suppression of PLTP secretion was not altered by the inhibition of both LDL receptor and LDL receptor-related protein with receptor-associated protein. Mitogen-activated protein kinase (MAPK) kinase (MEK) inhibitor, U0126, could abolish the LDL-mediated inhibition of PLTP secretion. Furthermore, LDL, but not HDL, could stimulate the expression of MAPK phosphatase-1 (MKP-1) in BeWo cells that resulted in the inactivation of p44/p42 extracellular signal-regulated kinase (ERK) 1 and 2, the family members of MAPKs. These results support the conclusion that LDL-mediated suppression of PLTP secretion in BeWo cells is through a LDL receptor-independent MAPK signaling pathway.     

Distinct patterns of lipoproteins with apoB defined by presence of apoE or apoC-III in hypercholesterolemia and hypertriglyceridemia

Apolipoprotein (apo) E and apoC-III concentrations in VLDL and LDL are associated with coronary heart disease. We studied the relationship between apoE and apoC-III and the abnormal concentrations and distribution of apoB lipoproteins in 10 hypercholesterolemic and 13 hypertriglyceridemic patients compared with 12 normolipidemic subjects (mean age, 45 years). Sixteen distinct types of apoB lipoprotein particles were separated by first using anti-apoE and anti-apoC-III immunoaffinity chromatography in sequence and then ultracentrifugation [light VLDL, dense VLDL, IDL, and LDL, with apoE with or without apoC-III (E(+)C-III(+), E(+)C-III(-)) or without apoE with or without apoC-III (E(-)C-III(+), E(-)C-III(-))]. The concentrations of VLDL particles with apoC-III (E(+)C-III(+), E(-)C-III(+)) were increased in the hypertriglyceridemic group compared with the hypercholesterolemic and normolipidemic groups. These particles were the most triglyceride rich of the particle types, and their triglyceride content was twice as high in hypertriglyceridemics compared with the other two groups. Hypertriglyceridemics had a similar concentration of total E(-)C-III(-) particles compared with normolipidemics, but the E(-)C-III(-) particles were distributed more to VLDL and IDL than to LDL. Hypercholesterolemics, in contrast, were distinguished from the normolipidemic group by 2-fold higher concentrations of apoB lipoproteins without apoE or apoC-III (E(-)C-III(-)), mainly LDL, which had high cholesterol content. Nonetheless, both normolipidemics and hypercholesterolemics had apoC-III-containing VLDL, which comprised 68% and 43% of their total VLDL particles. E(+)C-III(-) particles were a minor type, comprising <10% of particles in all lipoproteins and patient groups. Therefore, VLDL particles with apoC-III may play a central role in identifying the high risk of coronary heart disease in hypertriglyceridemia, but their substantial prevalence in normolipidemics may be of clinical significance as well.     

Capillary isotachophoresis study of lipoprotein network sensitive to apolipoprotein E phenotype. 1. ApoE distribution between lipoproteins

Sixteen patients differing widely in plasma triglyceride content were divided into three groups by their apolipoprotein E (apoE) phenotype—E33 homozygotes, E23, and E34 heterozygotes. The plasma lipid and apoE distribution between individual lipoproteins was followed by capillary isotachophoresis (CITP) of plasma samples pre-stained with lipid fluorescent probe NBD-C6-ceramide and by fluorescein-labeled apoE, respectively. Among 12 peaks visualized by ceramide staining, an individual peak with very low density lipoproteins (VLDL) was identified. The VLDL cholesterol and apoE content determined by CITP directly in whole plasma were significantly related to their content as determined by conventional analysis with isolated VLDL. The ceramide distribution among lipoprotein pools was insensitive to apoE phenotype (49–53 : 7–11 : 39–43% for HDL, VLDL, and IDL/LDL, respectively) while the preferential binding of apoE to VLDL was observed in E34 patients compared to E33 (62 : 19 : 20 vs. 70 : 9 : 22%). In a study of apoE/F displacement from lipoproteins at plasma titration by apoC-III in vitro, apoE was found to bind more tightly to VLDL from E34 compared to E33 patients as evidenced by both the increased non-displaceable apoE pool, the increased VLDL sorbtion capacity for apoE, and the decreased displacement parameter in a “container” model of lipoprotein binding. Two different types of apoE package in a whole lipoprotein profile were observed. ApoE structure in a particular lipoprotein may underlie the phenotype-sensitive apoE distribution and apoC-III interference in hypertriglyceridemia.     

Apolipoprotein C-III displacement of apolipoprotein E from VLDL: effect of particle size.

ApoC-III and apoE are important determinants of intravascular lipolysis and clearance of triglyceride-rich chylomicrons and VLDL from the blood plasma. Interactions of these two apolipoproteins were studied by adding purified human apoC-III to human plasma at levels observed in hypertriglyceridemic subjects and incubating under specific conditions (2 h, 37 degrees C). As plasma concentrations of apoC-III protein were increased, the contents in both VLDL and HDL were also increased. Addition of apoC-III at concentrations up to four times the intrinsic concentration resulted in the decreasing incremental binding of apoC-III to VLDL while HDL bound increasing amounts without evidence of saturation. No changes were found in lipid content or in particle size of any lipoprotein in these experiments. However, distribution of the intrinsic apoE in different lipoprotein particles changed markedly with displacement of apoE from VLDL to HDL. The fraction of VLDL apoE that was displaced from VLDL to HDL at these high apoC-III concentrations varied among individuals from 20% to 100% its intrinsic level. The proportion of VLDL apoE that was tightly bound (0% to 80%) was found to be reproducible and to correlate with several indices of VLDL particle size. In the group of subjects studied, strongly adherent apoE was essentially absent from VLDL particles having an average content of less than 50,000 molecules of triglyceride.Addition of apoC-III to plasma almost completely displaces apoE from small VLDL particles. Larger VLDL contain tightly bound apoE which are not displaced by increasing concentration of apoC-III.     

Saturated fat-induced changes in Sf 60-400 particle composition reduces uptake of LDL by HepG2 cells

The ability of human postprandial triacylglycerol-rich lipoproteins (TRLs), isolated after meals enriched in saturated fatty acids (SFAs), n-6 PUFAs, and MUFAs, to inhibit the uptake of 125I-labeled LDL by the LDL receptor was investigated in HepG2 cells. Addition of TRLs resulted in a dose-dependent inhibition of heparin-releasable binding, cell-associated radioactivity, and degradation products of 125I-labeled LDL (P < 0.001). SFA-rich Svedberg flotation rate (Sf) 60-400 resulted in significantly greater inhibition of cell-associated radioactivity than PUFA-rich particles (P = 0.016) and total uptake of 125I-labeled LDL compared with PUFA- and MUFA-rich particles (P < 0.02). Normalization of the apolipoprotein (apo)E but not apoC-III content of the TRLs removed the effect of meal fatty acid composition, and addition of an anti-apoE antibody reversed the inhibitory effect of TRLs on the total uptake of 125I-labeled LDL. Real time RT-PCR showed that the SFA-rich Sf 60-400 increased the expression of genes involved in hepatic lipid synthesis (P < 0.05) and decreased the expression of the LDL receptor-related protein 1 compared with MUFAs (P = 0.008). In conclusion, these findings suggest an alternative or additional mechanism whereby acute fat ingestion can influence LDL clearance via competitive apoE-dependent effects of TRL on the LDL receptor.     

Molecular basis of hyperlipidemia in golden hamsters during experimental infection with Ancylostoma ceylanicum (Nematoda:Strongylidae)

An infection of golden hamsters with Ancylostoma ceylanicum, a hookworm parasite, induced profound hyperlipidemia, particularly hypertriglyceridemia, and the effect was directly related to the degree of infection. A significant increase was also noticed in serum cholesterol and phospholipid levels. The appearance of lipoprotein-X, an abnormal low density lipoprotein, was detected in the serum of hookworm-infected animals. The hyperlipidemia was further characterized by an increase in very low density lipoproteins (VLDL) and low density lipoproteins (LDL) with a concomitant decline in high density lipoproteins (HDL). Decreased lipolytic activities, especially triglyceride lipase, in hepatic tissue and induction of lipolytic activities in intestine and adipose tissues indicated mobilization of fats from adipose and jejunum with a defective removal of triglyceride-rich lipoproteins in hepatic tissues. Accumulation of lipids in liver and depletion in adipose tissue supported these results. The derangement may have a significant effect on host parasite interaction and is an important pathophysiological feature occurring during experimental ancylostomiasis.     

Antisense inhibition of apoB synthesis with mipomersen reduces plasma apoC-III and apoC-III-containing lipoproteins

Mipomersen, an antisense oligonucleotide that reduces hepatic production of apoB, has been shown in phase 2 studies to decrease plasma apoB, LDL cholesterol (LDL-C), and triglycerides. ApoC-III inhibits VLDL and LDL clearance, and it stimulates inflammatory responses in vascular cells. Concentrations of VLDL or LDL with apoC-III independently predict cardiovascular disease. We performed an exploratory posthoc analysis on a subset of hypercholesterolemic subjects obtained from a randomized controlled dose-ranging phase 2 study of mipomersen receiving 100, 200, or 300 mg/wk, or placebo for 13 wk (n = 8 each). ApoC-III-containing lipoproteins were isolated by immuno-affinity chromatography and ultracentrifugation. Mipomersen 200 and 300 mg/wk reduced total apoC-III from baseline by 6 mg/dl (38-42%) compared with placebo group (P < 0.01), and it reduced apoC-III in both apoB lipoproteins and HDL. Mipomersen 100, 200, and 300 mg doses reduced apoB concentration of LDL with apoC-III (27%, 38%, and 46%; P < 0.05). Mipomersen reduced apoC-III concentration in HDL. The drug had no effect on apoE concentration in total plasma and in apoB lipoproteins. In summary, antisense inhibition of apoB synthesis reduced plasma concentrations of apoC-III and apoC-III-containing lipoproteins. Lower concentrations of apoC-III and LDL with apoC-III are associated with reduced risk of coronary heart disease (CHD) in epidemiologic studies independent of traditional risk factors.     

Synthesis of reconstituted high density lipoprotein (rHDL) containing apoA-I and apoC-III: the functional role of apoC-III in rHDL

Apolipoprotein (apo) C-III is a marker protein of triacylglycerol (TG)-rich lipoproteins and high-density lipoproteins (HDL), and has been proposed as a risk factor of coronary heart disease. To compare the physiologic role of reconstituted HDL (rHDL) with or without apoC-III, we synthesized rHDL with molar ratios of apoA-I:apoC-III of 1:0, 1:0.5, 1:1, and 1:2. Increasing the apoC-III content in rHDL produced smaller rHDL particles with a lower number of apoA-I molecules. Furthermore, increasing the molar ratio of apoC-III in rHDL enhanced the surfactant-like properties and the ability to lyse dimyristoyl phosphatidylcholine. Furthermore, rHDL containing apoC-III was found to be more resistant to particle rearrangement in the presence of low-density lipoprotein (LDL) than rHDL that contained apoA-I alone. In addition, the lecithin:cholesterol acyltransferase (LCAT) activation ability was reduced as the apoC-III content of the rHDL increased; however, the CE transfer ability was not decreased by the increase of apoC-III. Finally, rHDL containing apoC-III aggravated the production of MDA in cell culture media, which led to increased cellular uptake of LDL. Thus, the addition of apoC-III to rHDL induced changes in the structural and functional properties of the rHDL, especially in particle size and rearrangement and LCAT activation. These alterations may lead to beneficial functions of HDL, which is involved in anti-atherogenic properties in the circulation.