ATP-binding cassette transporters A1 and G1, HDL metabolism, cholesterol efflux, and inflammation: important targets for the treatment of atherosclerosis.

Atherosclerosis has been characterized as a chronic inflammatory response to cholesterol deposition in arteries. Plasma high density lipoprotein (HDL) levels bear a strong independent inverse relationship with atherosclerotic cardiovascular disease. One central antiatherogenic role of HDL is believed to be its ability to remove excessive peripheral cholesterol back to the liver for subsequent catabolism and excretion, a physiologic process termed reverse cholesterol transport (RCT). Cholesterol efflux from macrophage foam cells, the initial step of RCT is the most relevant step with respect to atherosclerosis. The ATP-binding cassette (ABC) transporters ABCA1 and ABCG1 play crucial roles in the efflux of cellular cholesterol to HDL and its apolipoproteins. Moreover, ABCA1 and ABCG1 affect cellular inflammatory cytokine secretion by modulating cholesterol content in the plasma membrane and within intracellular compartments. In humans, ABCA1 mutations can cause a severe HDL-deficiency syndrome characterized by cholesterol deposition in tissue macrophages and prevalent atherosclerosis. Disrupting Abca1 or Abcg1 in mice promotes accumulation of excessive cholesterol in macrophages, and physiological manipulation of ABCA1 expression affects atherogenesis. Here we review recent advances in the role of ABCA1 and ABCG1 in HDL metabolism, macrophage cholesterol efflux, inflammation, and atherogenesis. Next, we summarize the structure, expression, and regulation of ABCA1 and ABCG1. Finally, we give an update on the progress and pitfalls of therapeutic approaches that target ABCA1 and ABCG1 to stimulate the flux of lipids through the RCT pathway.

Vaccination against Foxp3(+) regulatory T cells aggravates atherosclerosis.

OBJECTIVE: Regulatory T cells are crucial for immune homeostasis and an impaired regulatory T cell function results in many pathological conditions. Regulatory T cells have already been described to be protective in atherosclerosis. However the exact contribution of Foxp3-expressing natural regulatory T cells in atherosclerosis has not been elucidated yet. METHODS AND RESULTS: In this study we vaccinated LDL receptor deficient mice with dendritic cells which are transfected with Foxp3 encoding mRNA and studied the effect on initial atherosclerosis. Vaccination against Foxp3 resulted in a reduction of Foxp3(+) regulatory T cells in several organs and in an increase in initial atherosclerotic lesion formation. Furthermore we observed an increase in plaque cellularity and increased T cell proliferation in the Foxp3 vaccinated mice. CONCLUSION: We further establish the protective role of Tregs in atherosclerosis. The results illustrate the important role for Foxp3-expressing regulatory T cells in atherosclerosis, thereby providing a potential opportunity for therapeutic intervention against this disease.

Reduced leucocyte cholesteryl ester transfer protein expression in acute coronary syndromes.

OBJECTIVE: Cholesterol ester transfer protein (CETP) plays an important role in HDL cholesterol metabolism. Leucocytes, including monocyte-derived macrophages in the arterial wall synthesize and secrete CETP, but its role in atherosclerosis is unclear. The aim of the current study was to investigate the effect of acute coronary syndromes (ACS) on leucocyte CETP expression. RESEARCH DESIGN: Peripheral blood mononuclear cells (PBMCs) were freshly isolated from hospitalized ACS patients displaying Braunwald class IIIB unstable angina pectoris (UAP) on admission (t = 0) and at 180 days post inclusion (t = 180) for analysis of CETP expression. In addition, to prove the potential correlation between leucocyte CETP and ACS the effect of acute myocardial infarction on leucocyte CETP expression was studied in CETP transgenic mice. RESULTS: Upon admission, UAP patients displayed approximately 3-6 fold (P < 0.01) lower CETP mRNA and nearly absent CETP protein expression in PBMCs, as compared to healthy age-/sex-matched controls. Interestingly, CETP mRNA and protein levels were significantly elevated in PBMCs isolated from UAP patients (both stabilized and refractory) at t = 180 as compared to t = 0 (P < 0.01), which was correlated with a reduced inflammatory status after medical treatment. In agreement with the data obtained in UAP patients, markedly down-regulated leucocyte CETP mRNA expression was observed after coronary artery ligation in CETP transgenic mice, which also correlated with increased serum amyloid A levels. CONCLUSIONS: We are the first to report that episodes of UAP in humans and myocardial infarction in CETP transgenic mice are associated with reduced leucocyte CETP expression. We propose that the impairment in leucocyte CETP production is associated with an enhanced inflammatory status, which could be clinically relevant for the pathogenesis of ACS.

CC chemokine ligand-5 (CCL5/RANTES) and CC chemokine ligand-18 (CCL18/PARC) are specific markers of refractory unstable angina pectoris and are transiently raised during severe ischemic symptoms.

BACKGROUND: Chemokines play an important role in atherogenesis and in ischemic injury and repair; however, prospective data on individual chemokines in unstable angina pectoris (UAP) are scarce. Therefore, we assessed chemokine patterns in a prospective cohort of patients with UAP. METHODS AND RESULTS: Plasma samples of 54 patients with Braunwald class IIIB UAP were examined at baseline for 11 chemokines and 5 inflammatory mediators via multiplex analysis. Levels of CC chemokine ligand (CCL)-5 (also known as RANTES [regulated on activation, normally T-cell expressed, and secreted]; 32.7 versus 23.1 ng/mL, P=0.018) and CCL18 (also known as PARC [pulmonary and activation-regulated chemokine]; 104.4 versus 53.7 ng/mL, P=0.011) were significantly elevated in patients with refractory ischemic symptoms versus stabilized patients. Temporal monitoring by ELISA of CCL5, CCL18, and soluble CD40 ligand (sCD40) levels revealed a drop in CCL5 and sCD40L levels in all UAP patients from day 2 onward (CCL5 12.1 ng/mL, P<0.001; sCD40L 1.35 ng/mL, P<0.05), whereas elevated CCL18 levels were sustained for at least 2 days, then were decreased at 180 days after inclusion (34.5 ng/mL, P<0.001). Peripheral blood mononuclear cells showed increased protein expression of chemokine receptors CCR3 and CCR5 in CD3+ and CD14+ cells at baseline compared with 180 days after inclusion, whereas mRNA levels were downregulated, which was attributable in part to a postischemic release of human neutrophil peptide-3-positive neutrophils and in part to negative feedback. Finally, elevated CCL5 and CCL18 levels predicted future cardiovascular adverse events, whereas C-reactive protein and sCD40L levels did not. CONCLUSIONS: We are the first to report that CCL18 and CCL5 are transiently raised during episodes of UAP, and peak levels of both chemokines are indicative of refractory symptoms. Because levels of both chemokines, as well as of cognate receptor expression by circulating peripheral blood mononuclear cells, are increased during cardiac ischemia, this may point to an involvement of CCL5/CCL18 in the pathophysiology of UAP and/or post-UAP responses.

Chemokines and atherosclerotic plaque progression: towards therapeutic targeting?

Atherosclerosis is currently viewed as an inflammatory disease in which the initiation and progression of the atherosclerotic plaque towards a rupture prone, unstable plaque is driven by leukocyte recruitment mediated by various inflammatory mediators. Recently, interest in chemotactic cytokines or chemokines with regard to atherosclerosis has been growing as chemokines mediate the influx of leukocytes that is typical of atherothrombosis. The activity of the majority of chemokines is overlapping and chemokines are not only produced by the various cellular constituents of the atherosclerotic plaque but also by activated platelets. Consequently, the direct influence of individual chemokines on plaque destabilisation and rupture is widespread and rather unclear. Experimental research has already established the role of a number of chemokines in advanced atherosclerosis. Nevertheless, given the complexity and size of the chemokine family, further screening of cardiovascular disease for chemokine level and genetic polymorphisms for chemokines will be warranted as the search for viable biomarkers of plaque destabilization as well as novel therapeutic targets for specific atheroregressive therapeutic compounds is ongoing. With regard to the latter, clinical trials with specific chemokine inhibitory strategies, like chemokine receptor antagonists, are already underway in other inflammatory disorders. Summarizing, chemokine inhibition likely constitutes an important therapeutic option next to already established drugs in the management of cardiovascular disease.

Induction of oral tolerance to oxidized low-density lipoprotein ameliorates atherosclerosis.

BACKGROUND: Oxidation of low-density lipoprotein (LDL) and the subsequent processing of oxidized LDL (oxLDL) by macrophages results in activation of specific T cells, which contributes to the development of atherosclerosis. Oral tolerance induction and the subsequent activation of regulatory T cells may be an adequate therapy for the treatment of atherosclerosis. METHODS AND RESULTS: Tolerance to oxLDL and malondialdehyde-treated LDL (MDA-LDL) was induced in LDL receptor-/- mice fed a Western-type diet by oral administration of oxLDL or MDA-LDL before the induction of atherogenesis. Oral tolerance to oxLDL resulted in a significant attenuation of the initiation (30% to 71%; P<0.05) and progression (45%; P<0.05) of atherogenesis. Tolerance to oxLDL induced a significant increase in CD4+ CD25+ Foxp3+ cells in spleen and mesenteric lymph nodes, and these cells specifically responded to oxLDL with increased transforming growth factor-beta production. Tolerance to oxLDL also increased the mRNA expression of Foxp3, CTLA-4, and CD25 in the plaque. In contrast, tolerance to MDA-LDL did not affect atherogenesis. CONCLUSIONS: OxLDL-specific T cells, present in LDL receptor-/- mice and important contributors in the immune response leading to atherosclerotic plaque, can be counteracted by oxLDL-specific CD4+ CD25+ Foxp3+ regulatory T cells activated via oral tolerance induction to oxLDL. We conclude that the induction of oral tolerance to oxLDL may be a promising strategy to modulate the immune response during atherogenesis and a new way to treat atherosclerosis.

Efficient targeting of adenoviral vectors to integrin positive vascular cells utilizing a CAR-cyclic RGD linker protein.

Vascular smooth muscle (VSMC) and endothelial cells (EC) are particularly resistant to infection by type 5 adenovirus (Ad) vectors. To overcome this limitation and target Ad vectors to ubiquitously expressed alpha(V)beta(3/5) integrins, we have generated a linker protein consisting of the extracellular domain of the coxsackie adenovirus receptor (CAR) connected via avidin to a biotinylated cyclic (c) RGD peptide. After optimization of CAR to cRGD and to Ad coupling, infection of mouse heart endothelial cells (H5V) could be augmented significantly, as demonstrated by 600-fold increased transgene expression levels. In EOMAs, a hemangioendothelioma-derived cell line, the fraction of infected cells was enhanced 4- to 6-fold. Furthermore, the fraction of infected primary mouse VSMC was increased from virtually 0% to 25%. Finally, in human umbilical vein endothelial cells, the number of GFP positive cells was enhanced from 2% to 75%. In conclusion, CAR-cRGD is a versatile and highly efficient construct to target Ad vectors to both transformed and primary VSMC and EC.

Blockade of interleukin-12 function by protein vaccination attenuates atherosclerosis.

BACKGROUND: Interleukin-12 (IL-12) has been identified as a key inducer of a type 1 T-helper cell cytokine pattern, which is thought to contribute to the development of atherosclerosis. We sought to study the role of IL-12 in atherosclerosis by inhibition of IL-12 using a newly developed vaccination technique that fully blocks the action of IL-12. METHODS AND RESULTS: LDL receptor-deficient (LDLr(-/-)) mice were vaccinated against IL-12 by 5 intramuscular injections of IL-12-PADRE complex in combination with adjuvant oil-in-water emulsion (low dose)/MPL/QS21 every 2 weeks. Two weeks thereafter, atherogenesis was initiated in the carotid artery by perivascular placement of silicone elastomer collars. IL-12 vaccination resulted in the induction of anti-IL-12 antibodies that functionally blocked the action of IL-12 as determined in an IL-12 bioassay. Blockade of IL-12 by vaccination of LDLr(-/-) mice resulted in significantly reduced (68.5%; P<0.01) atherogenesis compared with control mice without a change in serum cholesterol levels. IL-12 vaccination also resulted in a significant decrease in intima/media ratios (66.7%; P<0.01) and in the degree of stenosis (57.8%; P<0.01). On IL-12 vaccination, smooth muscle cell and collagen content in the neointima increased 2.8-fold (P<0.01) and 4.2-fold (P<0.01), respectively. CONCLUSIONS: Functional blockade of endogenous IL-12 by vaccination resulted in a significant 68.5% reduction in atherogenesis in LDLr(-/-) mice. Vaccination against IL-12 also improved plaque stability, from which we conclude that the blockade of IL-12 by vaccination may be considered a promising new strategy in the treatment of atherosclerosis.

Identification of an internalising peptide in differentiated Calu-3 cells by phage display technology; application to gene delivery to the airways.

Differentiated, human submucosal-gland carcinoma, Calu-3 cell monolayers were used as in vitro model for the airway epithelium. Internalised phage were selected from a recombinant pComb8 phage library by repetitive cycles of bio-panning on Calu-3 monolayers, protease K degradation, cell-lysis and amplification. After four selection rounds, sequence analysis of 15 enriched phage colonies revealed two clones of 73 and 27% abundancy, named IB1 and IB2, respectively. The IB2 sequence was eliminated due to a frame shift. IB1-phage internalisation at 4 degrees C was significantly lower (P < 0.05) than at 37 degrees C, suggesting involvement of a receptor-mediated endocytosis pathway. The IB1 peptide was synthesised, biotinylated and complexed to streptavidin. IB1/streptavidin-complexes co-administrated with PEI/DNA-polyplexes, enhanced polyplex transfection efficiency, dose dependently, by 6- and 4-fold in Calu-3 cells. IB1/Alexa488-streptavidin complexes were used for confocal laser-scanning microscopy (CLSM) visualisation and showed basolateral localisation in membrane associated and internalising vesicles. This study demonstrates the potential of phage display technology for identification of internalising peptide-epitopes that can enhance gene delivery efficiency in differentiated airway epithelial cells.

Scavenger receptor-like receptors for the binding of lipopolysaccharide and lipoteichoic acid to liver endothelial and Kupffer cells.

This study was undertaken to identify the role of scavenger receptors in the catabolism of lipopolysaccharide (LPS) and lipoteichoic acid (LTA). LPS is mainly cleared from the blood by the liver. The Kupffer cells are primarily responsible for this clearance. Although several binding sites have been described for LPS and LTA, only CD14 is involved in LPS signalling. Scavenger receptor type A (SR-A) is expressed in the liver on endothelial cells and Kupffer cells, and macrosialin (class D scavenger receptor) is expressed on Kupffer cells. Fucoidin and poly-I are both good inhibitors of scavenger receptors. Fucoidin significantly reduced the serum clearance of [125I]-LPS and decreased liver uptake of [125I]-LPS by approximately 40%. Poly-I inhibited the binding of [125I]-LPS to isolated Kupffer and endothelial cells by 75%, while poly-A, a polyanionic substrate that does not block scavenger receptors, had no effect. LPS significantly inhibited the binding of acetylated LDL and oxidized LDL (two well-described scavenger receptor ligands) to isolated Kupffer and liver endothelial cells. OxLDL and acLDL did not affect the binding of LPS to these cells. We conclude that on both endothelial cells and Kupffer cells, LPS mainly binds to scavenger receptors, but SR-A and macrosialin contribute to a limited extent to the binding of LPS. Injection of LTA into C57Bl6 mice resulted in a maximal liver uptake of 20% of the injected dose. In the liver, 50% was bound by the Kupffer cells, 20% by parenchymal cells and 30% by liver endothelial cells. The contribution of SR-A to the plasma clearance of LTA was limited. A main component in the catabolism of LTA is the interaction of LTA with plasma lipoproteins, which limit the uptake of LTA by tissues and extend the plasma half-life of LTA.

Attenuation of atherogenesis by systemic and local adenovirus-mediated gene transfer of interleukin-10 in LDLr-/- mice.

In view of its multifaceted anti-inflammatory properties, interleukin-10 (IL-10) has been deemed to be potentially anti-atherogenic. We have evaluated the capacity of adenoviral gene transfer of IL-10 for the modulation of de novo atherosclerotic lesion formation by systemic and by local overexpression. Atherogenesis was initiated in the carotid arteries of low-density lipoprotein receptor deficient mice by perivascular placement of silastic collars. One week after collar placement, mice were injected intravenously with 1 x 109 plaque-forming units (pfu's) of IL-10 (AdV.IL-10) or control adenovirus (AdV.empty). Administration of AdV.IL-10 resulted in extended systemic expression of IL-10 (peak serum level 3.0 +/- 1.1 ng/ml) and a reduction in atherosclerotic lumen stenosis by 62.2% (P<0.02). This finding was accompanied by monocyte deactivation and lowering of serum cholesterol levels (maximum decrease 44%). In a second experiment, collared arteries were transfected locally by transluminal instillation of adenovirus (titer 1.5x1010 pfu/ml). Systemic parameters remained unchanged following local transfection, but the degree of stenosis was, nonetheless, decreased by 44.9% (P<0.05). We conclude that a marked inhibition of atherogenesis can be achieved by systemic overexpression of AdV.IL-10, owing to its metabolic and immunomodulatory effects. Local IL-10 transfer is virtually equipotent, however, and it may represent a valuable addition to the armory of anti-atherosclerotic therapies.

Midazolam is a phenobarbital-like cytochrome p450 inducer in rats.

Midazolam is almost exclusively metabolized by cytochrome P450 3A (CYP3A) isoenzymes. Therefore, midazolam is used as a probe to determine CYP3A levels in humans and rats. A prerequisite for longitudinal determination of CYP3A expression levels using midazolam as a probe is that midazolam itself has no effect on the expression of CYP3A. In the present study, we analyzed the mRNA levels and enzyme activities of the major CYP isoforms in the rat liver after intraperitoneal injection of midazolam (50 mg/kg) for 3 consecutive days. CYP3A1 mRNA levels were increased 4-fold in midazolam-treated animals compared with controls, whereas the mRNA levels of CYP3A2, CYP3A9, and CYP3A18 were not altered. The increase in CYP3A1 mRNA was accompanied by a 25% increase in microsomal testosterone 6beta-hydroxylation activity. More strikingly, CYP2B1/2 mRNA levels were increased 22-fold upon midazolam treatment, leading to an 11- to 95-fold enhancement of CYP2B enzyme activity. CYP2C6 mRNA levels were 4 times higher in midazolam-treated animals. Formation of 2alpha-hydroxy-testosterone, mainly catalyzed by CYP2C11, was 2.6-fold lower in liver microsomes from midazolam-treated animals. Midazolam induced CYP2E enzyme activity 2.5-fold at the post-transcriptional level. The induction of CYP2B1/2 mRNA levels by midazolam was dose-dependent (4.5-fold increase at 10 mg/kg). Induction of CYP3A1 and CYP2B expression was also observed in isolated rat hepatocytes cultured with 100 microM midazolam. We conclude that midazolam is a phenobarbital-like CYP inducer in rats. Induction of CYP3A1 by midazolam may have implications for the longitudinal use of midazolam as a probe for analysis of CYP3A expression levels in rats.

Delivery of cholesteryl-conjugated phosphorothioate oligodeoxynucleotides to Kupffer cells by lactosylated low-density lipoprotein.

The efficacy of antisense oligonucleotides depends on the ability to reach in vivo their target cells. We aim to develop strategies to enhance uptake of phosphorothioate oligodeoxynucleotides by Kupffer cells. To this end, we conjugated cholesterol to ISIS-3082, a phosphorothioate oligodeoxynucleotide specific for intercellular adhesion molecule-1. The cholesterol-conjugated oligonucleotide, denoted ISIS-9388, associated readily with lactosylated low-density lipoprotein (LacLDL), a lipidic carrier that is taken up by galactose receptors on Kupffer cells. Association of up to 10 molecules of ISIS-9388 per LacLDL particle did not induce aggregation. LacLDL-associated [3H]ISIS-9388 was rapidly taken up by the liver after injection into rats (52.9+/-1.8% of the dose within 2 min versus 18.6+/-2.8% for ISIS-3082). N-acetylgalactosamine inhibited hepatic uptake, indicating involvement of galactose-specific receptors. Liver cells were isolated at 60 min after injection of LacLDL-associated [3H]ISIS-9388. Kupffer cells displayed the highest uptake: 88.1+/-24.7 ng of oligonucleotide/mg of cell protein, which is 6-14 times higher than after injection of free ISIS-9388 or ISIS-3082 (15.0+/-3.8 ng and 6.3+/-1.4 ng, respectively). It can be calculated that Kupffer cells contribute 43.9+/-5.4% to the liver uptake (free ISIS-9388 and ISIS-3083 14.5+/-3.1% and 8.3+/-3.2%, respectively). In conclusion, conjugation of a phosphorothioate oligodeoxynucleotide with cholesterol and its subsequent association with LacLDL results in a substantially increased Kupffer cell uptake of the oligonucleotide. As Kupffer cells play a key role in inflammation, our approach may be utilized to improve antisense-based therapeutic intervention during inflammation.

Apolipoprotein C-III deficiency accelerates triglyceride hydrolysis by lipoprotein lipase in wild-type and apoE knockout mice.

Previous studies with hypertriglyceridemic APOC3 transgenic mice have suggested that apolipoprotein C-III (apoC-III) may inhibit either the apoE-mediated hepatic uptake of TG-rich lipoproteins and/or the lipoprotein lipase (LPL)-mediated hydrolysis of TG. Accordingly, apoC3 knockout (apoC3(-/-)) mice are hypotriglyceridemic. In the present study, we attempted to elucidate the mechanism(s) underlying these phenomena by intercrossing apoC3(-/-) mice with apoE(-/-) mice to study the effects of apoC-III deficiency against a hyperlipidemic background. Similar to apoE(+/+) apoC3(-/-) mice, apoE(-/-)apoC3(-/-) mice exhibited a marked reduction in VLDL cholesterol and TG, indicating that the mechanism(s) by which apoC-III deficiency exerts its lipid-lowering effect act independent of apoE. On both backgrounds, apoC3(-/-) mice showed normal intestinal lipid absorption and hepatic VLDL TG secretion. However, turnover studies showed that TG-labeled emulsion particles were cleared much more rapidly in apoC3(-/-) mice, whereas the clearance of VLDL apoB, as a marker for whole particle uptake by the liver, was not affected. Furthermore, it was shown that cholesteryl oleate-labeled particles were also cleared faster in apoC3(-/-) mice. Thus the mechanisms underlying the hypolipidemia in apoC3(-/-) mice involve both a more efficient hydrolysis of VLDL TG as well as an enhanced selective clearance of VLDL cholesteryl esters from plasma. In summary, our studies of apoC3(-/-) mice support the concept that apoC-III is an effective inhibitor of VLDL TG hydrolysis and reveal a potential regulating role for apoC-III with respect to the selective uptake of cholesteryl esters.

Tissue distribution of factor VIII gene expression in vivo--a closer look.

Previous studies have shown that factor VIII (FVIII) is expressed by multiple tissues. However, little is known about its cellular origin or its level of expression in different organs. In the present study, we examined FVIII gene expression in different tissues on a quantitative basis. Most of the tissues, especially liver and kidney, expressed high levels of FVIII mRNA compared to their level of expression of other hemostatic proteins, including von Willebrand factor (VWF). This was unexpected since FVIII is a trace protein. In situ hybridization analysis confirmed that liver and kidney were rich in FVIII mRNA. In the liver, a clear hybridization signal was detected in cells lining the sinusoids. FVIII mRNA analysis of purified liver cells confirmed the expression of FVIII mRNA by sinusoidal endothelial cells and Kupffer cells. Low but significant levels of FVIII mRNA were also detected in the hepatocytes. VWF mRNA was not detectable in these cells. Similarly, immunohistochemical staining of liver tissue revealed that FVIII protein is primarily associated with sinusoidal cells. VWF protein was predominantly located in the endothelium of larger vessels. In the kidney, FVIII synthesis was localized to the glomeruli and to tubular epithelial cells. Taken together, these results suggest that besides hepatocytes, non-parenchymal cells (e.g. sinusoidal endothelial cells) contribute to FVIII synthesis. VWF synthesis is primarily confined to extra-hepatic tissues.

Carrier-mediated delivery improves the efficacy of 9-(2-phosphonylmethoxyethyl)adenine against hepatitis B virus.

We recently synthesized a lipophilic prodrug of 9-(2-phosphonyl-methoxyethyl)adenine (PMEA), designated PMEA-LO, and incorporated it into reconstituted lactosylated high-density lipoprotein (LacNeoHDL). In a rat model, LacNeoHDL-associated PMEA-LO was internalized by the asialoglycoprotein receptor on parenchymal liver cells and converted into its active diphosphorylated metabolite. To further evaluate the therapeutic potential of the carrier-associated prodrug, we examined in this study the processing of (125)I-labeled PMEA-LO--loaded LacNeoHDL by HepG2 cells. Upon incubation with HepG2 cells, PMEA-LO--loaded LacNeoHDL became rapidly cell-associated. The association was saturable and of high-affinity (k(d) = 3.8 +/- 0.4 nM). Asialofetuin, an established ligand for the asialoglycoprotein receptor, inhibited the association by >75%, which confirms the role of the asialoglycoprotein receptor. Association of the prodrug-loaded particles to HepG2 cells was coupled to degradation. Radiolabeled degradation products appeared in the culture medium with a lag phase of 2 h. Asialofetuin and chloroquine inhibited secretion of degradation products by 75 to 80%, indicating that PMEA-LO--loaded LacNeoHDL is internalized via the asialoglycoprotein receptor and lysosomally processed. The therapeutic potential of LacNeoHDL-associated PMEA-LO was studied by measuring its effects on hepatitis B virus (HBV) replication in Hep AD38 cells (HBV-transfected HepG2 cells). LacNeoHDL-associated PMEA-LO effectively inhibited HBV DNA synthesis. The EC(50) value of carrier-associated PMEA-LO was 35 times lower than that of free PMEA (3.4 +/- 0.4 and 120 +/- 18 ng of PMEA/ml, respectively). We conclude that the present results, combined with our earlier in vivo disposition data, underscore the therapeutic potential and utility of PMEA-LO--loaded LacNeoHDL for treatment of chronic hepatitis B.

Determination of the upper size limit for uptake and processing of ligands by the asialoglycoprotein receptor on hepatocytes in vitro and in vivo.

The asialoglycoprotein receptor (ASGPr) on hepatocytes plays a role in the clearance of desialylated proteins from the serum. Although its sugar preference (N-acetylgalactosamine (GalNAc) >> galactose) and the effects of ligand valency (tetraantennary > triantennary >> diantennary >> monoantennary) and sugar spacing (20 A 10 A 4 A) are well documented, the effect of particle size on recognition and uptake of ligands by the receptor is poorly defined. In the present study, we assessed the maximum ligand size that still allows effective processing by the ASGPr of mouse hepatocytes in vivo and in vitro. Here too, we synthesized a novel glycolipid, which possesses a highly hydrophobic steroid moiety for stable incorporation into liposomes, and a triantennary GalNAc(3)-terminated cluster glycoside with a high nanomolar affinity (2 nm) for the ASGPr. Incorporation of the glycolipid into small (30 nm) [(3)H]cholesteryl oleate-labeled long circulating liposomes (1-50%, w/w) caused a concentration-dependent increase in particle clearance that was liver-specific (reaching 85 +/- 7% of the injected dose at 30 min after injection) and mediated by the ASGPr on hepatocytes, as shown by competition studies with asialoorosomucoid in vivo. By using glycolipid-laden liposomes of various sizes between 30 and 90 nm, it was demonstrated that particles with a diameter of >70 nm could no longer be recognized and processed by the ASGPr in vivo. This threshold size for effective uptake was not related to the physical barrier raised by the fenestrated sinusoidal endothelium, which shields hepatocytes from the circulation, because similar results were obtained by studying the uptake of liposomes on isolated mouse hepatocytes in vitro. From these data we conclude that in addition to the species, valency, and orientation of sugar residues, size is also an important determinant for effective recognition and processing of substrates by the ASGPr. Therefore, these data have important implications for the design of ASGPr-specific carriers that are aimed at hepatocyte-directed delivery of drugs and genes.

Effect of dietary elaidic versus vaccenic acid on blood and liver lipids in the hamster.

Male hamsters (30 per group) were fed five different semi-purified diets ad libitum. The diets, containing 30% of energy (en%) as fat, differed in their dietary fat composition (specified fatty acids exchanged at 10 en%) and were fed for 4 weeks. The five fatty acids compared in mixed triglycerides were elaidic acid (C18:1 9t), vaccenic acid (C18:1 11t), their cis-counterpart oleic acid (C18:1 9c), medium-chain fatty acids (MCFA; C8:0 and C10:0), and palmitic acid (C16:0). Compared with oleic acid, dietary MCFA and palmitic acid tended to increase blood cholesterol levels in the hamsters. The effect of elaidic and vaccenic acid on blood cholesterol did not differ from that of oleic acid. When elaidic acid and vaccenic acids were compared directly, the ratio of LDL/HDL-cholesterol in plasma was significantly higher in hamsters fed vaccenic acid than in those fed elaidic acid, and elaidic acid was incorporated at low levels, but more efficiently than vaccenic acid at the sn-2 position of platelet phospholipids. Biological consequences of this low incorporation are considered unlikely as levels of arachidonic acid (C20:4 n-6) and docosohexaenoic acid (C22:6 n-3) in the platelet phospholipids of all dietary groups did not differ. With respect to the effect on the LDL/HDL-cholesterol ratio, elaidic acid may be preferable to vaccenic acid. We conclude that this animal study does not provide evidence for the suggestion, based on epidemiological observations, that elaidic acid would be more detrimental to cardiovascular risk than vaccenic acid.

Macrophage p53 deficiency leads to enhanced atherosclerosis in APOE*3-Leiden transgenic mice.

Cell proliferation and cell death (either necrosis or apoptosis) are key processes in the progression of atherosclerosis. The tumor suppressor gene p53 is an essential gene in cell proliferation and cell death and is upregulated in human atherosclerotic plaques, both in smooth muscle cells and in macrophages. In the present study, we investigated the importance of macrophage p53 in the progression of atherosclerosis using bone marrow transplantation in APOE*3-Leiden transgenic mice, an animal model for human-like atherosclerosis. APOE*3-Leiden mice were lethally irradiated and reconstituted with bone marrow derived from either p53-deficient (p53(-/-)) or control (p53(+/+)) donor mice. Reconstitution of mice with p53(-/-) bone marrow did not result in any hemopoietic abnormalities as compared with p53(+/+) transplanted mice. After 12 weeks on an atherogenic diet, APOE*3-Leiden mice reconstituted with p53(-/-) bone marrow showed a significant (P=0.006) 2.3-fold increase in total atherosclerotic lesion area as compared with mice reconstituted with p53(+/+) bone marrow. Although likely a secondary effect of the increased lesion area, p53(-/-) transplanted mice also showed significantly more lesion necrosis (necrotic index, 1.1+/-1.3 versus 0.2+/-0.7; P=0.04) and lesion macrophages (macrophage area, 79.9+/-40.0 versus 39.7+/-27.3x10(3) micrometer(2) per section; P=0.02). These observations coincided with a tendency toward decreased apoptosis (terminal deoxynucleotidyl transferase end-labeling [TUNEL]-positive nuclei going from 0.42+/-0.39 to 0.14+/-0.15%, P=0.071), whereas the number of proliferating cells (5'-bromo-2'-deoxyuridine-positive nuclei) was not affected (3.75+/-0.98 versus 4.77+/-2.30%; P=0.59). These studies indicate that macrophage p53 is important in suppressing the progression of atherosclerosis and identify a novel therapeutic target for regulating plaque stability.