Reduction of atherosclerosis in low-density lipoprotein receptor-deficient mice by passive administration of antiphospholipid antibody

OBJECTIVE: Patients with antiphospholipid syndrome (APS) are at a high risk of developing atherosclerotic complications. Conversely, individuals with primary atherosclerosis have an increased prevalence of antiphospholipid antibodies (aPL) and antibodies to oxidized low-density lipoproteins (ox-LDL). Several studies suggest that these two antibody populations may in fact overlap, although it is unclear how aPL contribute to pathogenesis. In this study, we characterized an IgG monoclonal aPL and assessed its ability to modulate atherosclerosis in low-density lipoprotein receptor-deficient (LDLR(-/-)) mice. METHODS: The cardiolipin-reactive monoclonal antibody FB1 was obtained from an (NZW x BXSB)F(1) mouse, a strain with APS features that make it prone to fatal myocardial infarctions. Using an enzyme-linked immunosorbent assay, we investigated the binding of this antibody to phospholipid and LDL antigens. We also passively administered FB1 to atherosclerosis-prone mice to determine its effect on atherogenesis. RESULTS: In contrast to earlier studies of aPL that were specific for oxidized forms of LDL, FB1 cross-reacted with both native LDL and ox-LDL. In vivo, passive administration of FB1 significantly reduced plaque formation in atherosclerosis-prone LDLR(-/-) mice. CONCLUSION: These results indicate that some aPL may play a protective role in atherogenesis and suggest a novel approach to the prevention of atherosclerosis.     

Inhibition of injury-induced arterial remodelling and carotid atherosclerosis by recombinant human antibodies against aldehyde-modified apoB-100

OBJECTIVE: The immune system plays an important regulatory role in the development of atherosclerotic plaques and neointima formation following various types of angioplasty. In the present study we investigated the effect of antibodies against aldehyde-modified apolipoprotein B-100 (apoB-100), a component of oxidized LDL, on atherosclerosis and response to arterial injury in mice. METHODS: The ability of a high affinity human recombinant antibody (2D03), specific for malondialdehyde-modified apoB-100, to influence formation of atherosclerosis as well as remodelling and neointima formation after a collar-induced injury of the carotid artery was studied in LDL receptor(-/-) mice over-expressing human apoB-100. RESULTS: The antibody recognized epitopes present in mouse plasma and reduced the plasma level of oxidized LDL by 34%. Antibody treatment inhibited injury-induced restrictive vascular remodelling but did not influence the size of the neointima. Atherosclerosis in the uninjured contra lateral carotid artery was determined by computerized image analysis and the mean plaque area in animals given control IgG1 was 7608+/-10,336 micro m(2). In contrast, essentially no plaques were present in animals treated with the 2D03 antibody (397+/-235 micro m(2), P<0.01 versus control IgG1). CONCLUSIONS: Treatment with antibodies against aldehyde-modified apoB-100 dramatically reduces atherosclerosis and inhibits restrictive vascular remodelling in mice expressing human apoB-100.     

Low carbohydrate, high protein diet promotes atherosclerosis in apolipoprotein E/low-density lipoprotein receptor double knockout mice (apoE/LDLR(-/-))

Although in apoE/LDLR(-/-) mice atherosclerotic plaques develop spontaneously, various atherogenic diets (e.g. Western diet) are frequently used to accelerate the disease in this model. The objective of this study was to compare the effects on atherosclerosis of Western diet and other types of high-fat, high cholesterol, hypertriglyceridemic diets with the effects of the low carbohydrate, high protein (LCHP) diet. 16-18 week old mice with pre-established atherosclerosis were assigned to experimental groups and fed for the next 10 weeks with control diet, margarine diet (margarine 7%), hypertrigliceridemic diet (fructose 62%), high-fat diet (Western diet), high cholesterol diet (egg yolk diet) or with LCHP diet. No differences in body weight were observed among experimental groups. Plasma cholesterol concentration was significantly increased in egg yolk diet- and LCHP diet-fed apoE/LDLR(-/-) mice as compared to other types of diets. Plasma concentration of triacylglycerols was significantly elevated in egg yolk diet- and LCHP diet-fed apoE/LDLR(-/-) mice. The area of atherosclerotic plaques in the aortic root was substantially increased in LCHP diet-fed mice as compared to other types of diets. Furthermore, in brachiocephalic arteries of LCHP diet-fed mice there was evidence of plaque rupture. In conclusion, the LCHP diet promoted atherosclerosis in apoE/LDLR(-/-) mice more intensively than classical Western diet and favored the development of unstable lesions.     

In vivo uptake of radiolabeled MDA2, an oxidation-specific monoclonal antibody, provides an accurate measure of atherosclerotic lesions rich in oxidized LDL and is highly sensitive to their regression

To determine whether labeled antibodies against oxidized LDL (OxLDL) offer advantages for quantifying atherosclerosis, we compared in vivo aortic uptake of (125)I-labeled MDA2, a monoclonal antibody against malondialdehyde-lysine epitopes), atherosclerotic surface area, and aortic weight in Watanabe heritable hyperlipidemic and New Zealand White rabbits and in low density lipoprotein receptor-deficient (LDLR(-/-)) and apolipoprotein E-deficient (apoE(-/-)) mice. Absolute and specific uptakes of (125)I-MDA2 were significantly greater in plaque than in normal aortas. Uptake of (125)I-MDA2 significantly correlated with aortic weight and percent atherosclerotic surface area in rabbits and mice. To assess whether (125)I-MDA2 uptake reflects changes in lesion content of OxLDL, in a separate study, extensive atherosclerosis was induced in 4 groups of LDLR(-/-) mice by feeding them a high fat/cholesterol diet for 6 months. A baseline group was euthanized at this time. The remaining groups were fed "regression" diets (chow or chow+1% vitamin E+0.05% vitamin C) or the high fat/cholesterol diet for 6 more months. When atherosclerosis was measured as percent surface area or aortic weight, there was strong progression in the high fat/cholesterol group, moderate progression in the chow group, and no progression in the chow+vitamin E+vitamin C group compared with the baseline group. The (125)I-MDA2 method also yielded a significant increase in atherosclerosis in the high fat/cholesterol group but significant decreases in the chow and chow+vitamin E+vitamin C groups. Immunocytochemistry showed fewer oxidation-specific epitopes in lesions from the chow and chow+vitamin E+vitamin C groups. Thus, the uptake of (125)I-MDA2 correlates well with traditional measures of atherosclerosis but also reflects reduced plaque OxLDL content after hypocholesterolemic intervention.     

Antibodies against various forms of mildly oxidized low-density lipoprotein are not associated with carotid intima-media thickness in patients with primary hyperlipidemia

The carotid intima-media thickness (IMT) can reflect early atherosclerosis. Oxidative modification of low-density lipoprotein (LDL) leads to the formation of several immunogenic epitopes and different forms of antibodies against oxidized LDL (oxLDL). We investigated the possible relationship between autoantibody titers against various forms of mildly oxLDL and carotid IMT in patients (n=100) with primary hyperlipidemia. Three different types of mildly oxidized LDL-oxLDL(L), oxLDL(P), and oxLDL(D)-were prepared at the end of lag, propagation, and decomposition phases of oxidation, respectively. Similar types of oxLDL were also prepared from the same LDL preparations after inactivation of the LDL-associated platelet-activating factor acetylhydrolase (PAF-AH). These types were denoted as oxLDL(-)(L), oxLDL(-)(P), and oxLDL(-)(D). OxLDL types are primarily enriched in lysophosphatidylcholine (lyso-PC) due to hydrolysis of oxidized phospholipids (oxPL) by PAF-AH. OxLDL(-) types are mainly enriched in intact oxPL due to the inactivation of the LDL-associated PAF-AH before oxidation. IgG autoantibodies against all types of oxLDL were determined and IMT was evaluated ultrasonographically. IMT values were significantly associated with age, systolic blood pressure and serum triglyceride levels, whereas no correlation was found between IMT values and antibody titers against all types of either oxLDL or oxLDL(-). We suggest that autoantibodies against various types of mildly oxidized LDL enriched either in lyso-PC or in oxPL are not associated with the extent of carotid atherosclerosis. This supports the concept that extensively oxidized LDL enriched in aldehydes rather than mildly oxidized LDL may play a prominent role in the early stage of atherosclerosis.     

The two-receptor model of lipoprotein clearance: tests of the hypothesis in "knockout" mice lacking the low density lipoprotein receptor, apolipoprotein E, or both proteins.

Apolipoprotein E (apoE) is hypothesized to mediate lipoprotein clearance by binding to two receptors: (i) the low density lipoprotein receptor (LDLR) and (ii) a chylomicron remnant receptor. To test this hypothesis, we have compared plasma lipoproteins in mice that are homozygous for targeted disruptions of the genes for apoE [apoE(-/-)], the LDLR [LDLR(-/-)], and both molecules [poE(-/-); LDLR(-/-)]. On a normal chow diet, apoE(-/-) mice had higher mean plasma cholesterol levels than LDLR(-/-) mice (579 vs. 268 mg/dl). Cholesterol levels in the apoE(-/-); LDLR(-/-) mice were not significantly different from those in the apoE(-/-) mice. LDLR(-/-) mice had a relatively isolated elevation in plasma LDL, whereas apoE(-/-) mice had a marked increase in larger lipoproteins corresponding to very low density lipoproteins and chylomicron remnants. The lipoprotein pattern in apoE(-/-); LDLR(-/-) mice resembled that of apoE(-/-) mice. The LDLR(-/-) mice had a marked elevation in apoB-100 and a modest increase in apoB-48. In contrast, the apoE(-/-) mice had a marked elevation in apoB-48 but not in apoB-100. The LDLR(-/-); apoE(-/-) double homozygotes had marked elevations of both apolipoproteins. The observation that apoB-48 increases more dramatically with apoE deficiency than with LDLR deficiency supports the notion that apoE binds to a second receptor in addition to the LDLR. This conclusion is also supported by the observation that superimposition of a LDLR deficiency onto an apoE deficiency [apoE(-/-); LDLR(-/-) double homozygotes] does not increase hypercholesterolemia beyond the level observed with apoE deficiency alone.     

Stabilization of advanced atherosclerosis in low-density lipoprotein receptor-deficient mice by aspirin

COX-1-dependent eicosanoid formation accelerates atherogenesis, and low-dose aspirin reduces early atherosclerosis. However, the role of aspirin in modulating progression of vascular atherosclerotic lesions once established is less investigated. We wished to determine the effect of low-dose aspirin on vascular inflammation, plaque composition, and progression of established atherosclerosis. Low-density lipoprotein receptor-deficient mice (LDLR(-/-)) were fed a high-fat diet for 3 months. At this time, one group of mice underwent baseline analysis. Two additional groups, while continuing the high-fat diet, were randomized to receive placebo or aspirin for additional 3 months. At the end of the study, LDLR(-/-) mice that had received aspirin had suppressed biosynthesis of thromboxane B2, the major products of COX-1 activity, reduced monocyte chemoattractant protein-1, and soluble intercellular adhesion molecule-1 levels compared with controls. Compared with baseline, the placebo group had significant progression of atherosclerosis. In contrast, aspirin treated mice showed a significant reduction in progression of atherosclerosis, and a significant decrease in foam cell content. These results suggest that in murine atherosclerosis, low-dose aspirin retards progression of established and advanced vascular atherosclerotic lesions by suppressing the formation of bioactive lipids and vascular inflammation.     

Atherosclerosis quantitative trait loci are sex- and lineage-dependent in an intercross of C57BL/6 and FVB/N low-density lipoprotein receptor-/- mice

Atherosclerosis is a complex disease that is affected by environmental as well as genetic factors. The aim of the present study was to identify loci of atherosclerosis susceptibility in a cross of atherosclerosis-susceptible C57BL/6 and atherosclerosis-resistant FVB/N mice on the low-density lipoprotein (LDL) receptor (LDLR)-deficient background (LDLR(-/-)) and to test whether these loci are affected by lineage. A total of 459 F(2)s were generated in two ways: In cross "mB6xfFVB," male B6.LDLR(-/-) mice were crossed to female FVB.LDLR(-/-) mice to generate 107 female and 112 male F(2)s. In cross "mFVBxfB6," male FVB.LDLR(-/-) mice were crossed to female B6.LDLR(-/-) mice to generate 120 female and 120 male F(2)s. Animals were phenotyped for cross-sectional atherosclerotic lesion area at the aortic root, and a genome scan was carried out with 192 microsatellite markers. Quantitative trait locus mapping revealed significant loci of atherosclerosis susceptibility on chromosomes 3, 10, and 12. On chromosome 10 maximal logarithm of odds (LOD) scores of 13.1 (D10Mit16, 16 cM) and 5.7 (D10Mit168, 9 cM) were found in female and male mice, respectively. On chromosome 3, a maximal LOD score of 5.1 (D3Mit45, 79 cM) was detected only in females. On proximal chromosome 12 significant LOD scores were lineage-dependent, with maximal LOD scores of 3.9 (D12Mit82, 3 cM) and 4.8 (D12Mit189, 24 cM) present only in female mice of cross mB6xfFVB and male mice of cross mFVBxfB6, respectively. We conclude that, in this intercross, loci of atherosclerosis susceptibility are in part sex- and lineage-dependent. Awareness of these complexities may have major consequences for the identification of atherosclerosis susceptibility genes by quantitative trait locus mapping.     

ICAM-1 deficiency reduces atherosclerotic lesions in double-knockout mice (ApoE(-/-)/ICAM-1(-/-)) fed a fat or a chow diet

Intercellular adhesion molecule (ICAM)-1, a major adhesion molecule, plays a critical role in the homing of leukocytes to sites of atherosclerotic lesions. However, very little is known on the role of ICAM-1 in initiating and perpetuating vascular lesions in ApoE(-/-) mice fed a chow or a fat diet. This study has investigated the mean aortic lesions in mice (C57BL6 background) with a single-knockout (ApoE(-/-)) or double-knockout (DKO; ApoE(-/-), ICAM-1(-/-)) fed a chow or a fat diet over a period of 3, 6, 15, and 20 weeks. A 3-fold reduction in lesion size was observed at all time points in DKO mice fed a chow diet. However, in DKO mice fed a fat diet, a marked reduction in the aortic lesion was observed at 3 and 15 weeks, which did not reach a significant level at 6 and 20 weeks. This study shows in essence that DKO mice are protected from developing significant lesions for up to 6 weeks when fed a chow diet and from 3 to 6 weeks when fed a fat diet. After 6 weeks, the lesion size of the DKO mice follows that of the single-knockout mice when fed a chow diet and gets to the same level in mice fed a fat diet. Plasma cholesterol levels were not altered as a result of ICAM-1 deficiency. These studies show that ICAM-1 is implicated in the formation and progression of atherosclerotic lesions.     

Autoantibodies against oxidized low-density lipoprotein (LDL) and carotid atherosclerosis in patients with rheumatoid arthritis

OBJECTIVES: To examine the relationship between autoantibodies against oxidized low-density lipoprotein (oxLDL-Abs) and the progression of carotid atherosclerosis in patients with rheumatoid arthritis (RA). METHODS: Fifty RA patients without evidence of risk factors for atherosclerosis (RA group) and 30 healthy volunteers (normal group) were investigated. The mean intima-media thickness of the common carotid artery (mean CCA-IMT) was measured by high-resolution B-mode ultrasonography. The titer of IgG oxLDL-Abs was measured by enzyme-linked immunosorbent assay. The relationships among mean CCA-IMT, IgG oxLDL-Ab titer and patient factors such as body mass index, systolic blood pressure, diastolic blood pressure, C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and serum lipid levels were examined. RESULTS: Mean CCA-IMT, CRP, ESR and titer of IgG oxLDL-Abs were significantly higher in the RA group than in the normal group. Although mean CCA-IMT showed a positive correlation only with age in multivariate analysis, IgG oxLDL-Ab titers in the RA group were positively associated with mean CCA-IMT and independently with age and sex by multiple regression analysis. CONCLUSIONS: IgG oxLDL-Abs appear to be associated with the degree of carotid atherosclerosis in patients with RA, and are independent of traditional risk factors for atherosclerotic diseases. These results suggest a possible link between autoimmune mechanisms and accelerated atherosclerosis in RA.     

Phosphorylcholine-targeting immunization reduces atherosclerosis.

OBJECTIVES: The present study evaluated the effect of phosphorylcholine (PC) immunization on the extent of experimental atherosclerosis. BACKGROUND: Immunization against oxidized lipoprotein (oxLDL) or Streptococcus pneumoconiae reduces atherosclerosis. Phosphorylcholine is the main epitope recognized by both antipneumococcus and anti-oxLDL antibodies. Therefore we reasoned that PC-specific antibodies might play an important role in atherogenesis. METHODS: Apolipoprotein E knockout mice were immunized with PC every second week over 4 months. At the end of the study, serum antibodies directed to either PC or oxLDL were measured. Splenic and peritoneal B cells were analyzed by flow cytometry. Aortic root atherosclerotic lesions were quantified by morphometry and phenotyped by immunohistochemistry. Immune and control sera were also tested for their effect on foam cell formation in macrophage culture in the presence of oxLDL. RESULTS: The PC-immunized mice showed 3-fold increase in titers of anti-PC and -oxLDL antibodies compared with control mice (p < 0.01). The PC-immunized mice also showed a significant increase in the number of splenic mature B cells. The extent of atherosclerotic aorta root lesions was reduced by >40% in the PC-immunized mice (p < 0.01). Immunohistochemistry showed reduced expression of major histocompatibility complex class II antigens (p < 0.05) and the presence of B-cell clusters in plaques of PC-immunized mice. Finally, PC-immune serum was able to reduce macrophage-derived foam cell formation in the presence of oxLDL in vitro. CONCLUSIONS: Phosphorylcholine immunization drives a specific humoral immune response that reduces foam cell formation in vitro and is atheroprotective in vivo.     

Atherogenic oxidized low-density lipoprotein/beta2-glycoprotein I (oxLDL/beta2GPI) complexes in patients with systemic lupus erythematosus and antiphospholipid syndrome

Oxidized low-density lipoprotein (oxLDL) interacts in vitro with beta2-glycoprotein I (beta2GPI) via LDL-derived specific ligands forming oxLDL/beta2GPI complexes. Circulating oxLDL/beta2GPI complexes have been demonstrated in patients with systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS). Autoimmune vascular inflammation and oxidative stress contribute to oxLDL/beta2GPI complex formation. Immunohistochemical staining of atherosclerotic lesions suggest that these complexes are formed in the arterial wall and released into circulation. The demonstration of antibodies to oxLDL/beta2GPI complexes indicates that these complexes are immunogenic, and the coexistence of complexes and antibodies suggest an active pro-thrombotic/pro-atherogenic role in the development of autoimmune vascular complications. Circulating oxLDL/beta2GPI complexes can be measured by ELISA using a monoclonal antibody specific to complexed human beta2GPI to capture beta2GPI bound to oxLDL. An enzyme-conjugated monoclonal antibody to human Apo B 100 allows the specific detection of oxLDL/beta2GPI complexes. OxLDL/beta2GPI complexes were common in SLE and APS patients suggesting an underlying process of inflammation and oxidation. Using oxLDL/beta2GPI complexes as capture antigen, antibodies to oxLDL/beta2GPI can be measured by ELISA. Serum levels of IgG anti-oxLDL/beta2GPI antibodies were significantly higher in SLE patients with APS compared to SLE controls without APS. Further, high titers of these IgG antibodies were observed in APS patients with a history of arterial thrombosis. The presence of circulating oxLDL/beta2GPI complexes and IgG antibodies to these complexes indicates significant vascular injury and oxidative stress as well as an active role in autoimmune-mediated atherothrombosis.     

Timing affects the efficacy of LDL immunization on atherosclerotic lesions in apo E (-/-) mice

BACKGROUND: Immunization of animals with LDL reduces atherosclerosis. However, whether the timing of immunization affects its efficacy is not known. In this study, we evaluated the influence of timing of immunization on the athero-protective effects of LDL immunization in apo E (-/-) mice. METHODS AND RESULTS: Hypercholesterolemic apo E (-/-) mice were immunized with native LDL (nLDL) at age of 6-7 weeks old or at 20 weeks old. Compared to adjuvant group, mice that were immunized at the age of 6-7 weeks developed significantly smaller aortic sinus plaques with reduced gelatinolytic activity and increased collagen content. This was associated with an increase of oxidized LDL (oxLDL) antibody titer and a marked decrease in splenic IL-4 mRNA expression. Immunization at 20 weeks of age also increased oxLDL antibody titer but did not reduce plaque size, gelatinolytic activity or collagen content but resulted in a modest decrease in macrophage infiltration. Late immunization did not alter splenic IL-4 mRNA expression. CONCLUSIONS: Our findings demonstrate that, only early nLDL immunization modulates humoral and cellular immune responses and affects plaques size and composition in apo E (-/-) mice, indicating the critical importance of timing of immunization for its antiatherogenic efficacy.     

Dietary homocysteine promotes atherosclerosis in apoE-deficient mice by inducing scavenger receptors expression

Elevated plasma homocysteine (Hcy) levels have been recognized as an independent risk factor for atherosclerosis leading to cardiovascular diseases. However, the mechanisms contributing to atherosclerosis have not been delineated. Since, scavenger receptors mediated uptake of oxidized-LDL (oxLDL) by macrophages resulting in foam cell formation is an early event in atherosclerosis, we hypothesized that atherogenic effects of Hcy may be mediated via regulating expression of scavenger receptor(s). We have tested this hypothesis using apoE-/- female mice fed normal rodent chow (NC) diet or NC supplemented with Hcy in drinking water (9 g/L). Hcy-fed mice showed increased fatty streak lesions in aortic sinus/root compared to NC group without alterations in plasma lipid profiles. Similar findings were observed in the enface analysis of the descending aorta. To determine the molecular mechanisms underlying Hcy-mediated progression of fatty streak lesions, expression of scavenger receptors such as CD36 and lectin-like oxidized LDL binding protein-1 (LOX-1) in the aortic lesions were analyzed. Interestingly, Hcy-fed mice had increased immuno-positive staining for CD36 and LOX-1 in the atherosclerotic lesions compared to NC-fed mice. In vitro analyses showed neither Hcy nor HcyLDL directly affect the expression of CD36 and LOX-1 on mouse macrophages. However, Hcy supplementation in apoE-/- mice resulted in elevated oxLDL levels in plasma. Since oxLDL has been shown to upregulate the expression of CD36 and LOX-1, these findings suggest that Hcy may exert its atherogenic effect in part by elevating the levels of oxLDL. Interestingly, interaction of monocytes with Hcy-activated endothelial cells resulted in upregulation of CD36 expression on monocytes, suggesting a possible mechanism by which Hcy may upregulate CD36 expression at the lesion site. Further, these findings suggest a novel mechanism by which Hcy may promote atherogenesis.     

LOX-1 deletion decreases collagen accumulation in atherosclerotic plaque in low-density lipoprotein receptor knockout mice fed a high-cholesterol diet

AIMS: Collagen, as a component of the extracellular matrix, has been linked to atherosclerotic plaque formation and stability. Activation of LOX-1, a lectin-like oxidized low-density lipoprotein (LDL) receptor-1, exerts a significant role in collagen formation. We examine the hypothesis that LOX-1 deletion may inhibit collagen accumulation in atherosclerotic arteries in LDL receptor (LDLR) knockout (KO) mice. METHODS AND RESULTS: We generated LOX-1 KO and LOX-1/LDLR double KO mice on a C57BL/6 (wild-type mice) background and fed a 4% cholesterol/10% cocoa butter diet for 18 weeks. Vessel wall collagen accumulation was increased in association with atherogenesis in the LDLR KO mice (P < 0.01 vs. wild-type mice), but much less so in the double KO mice (P < 0.01 vs. LDLR KO mice). Collagen accumulation data were corroborated with pro-collagen I measurements. Expression/activity of osteopontin, fibronectin, and matrix metalloproteinases (MMP-2 and MMP-9) was also increased in the LDLR KO mice (P < 0.01 vs. wild-type mice), but not in the mice with LOX-1 deletion (P < 0.01 vs. LDLR KO mice). The expression of NADPH oxidase (p47(phox), p22(phox), gp91(phox), and Nox-4 subunits) and nitrotyrosine was increased in the LDLR KO mice (P < 0.01 vs. wild-type mice) and not in mice with LOX-1 deletion (P < 0.01 vs. LDLR KO mice). Phosphorylation of Akt-1 and endothelial nitric oxide synthase and expression of haem-oxygenase-1 were found to be reduced in the LDLR KO mice (P < 0.01 vs. wild-type mice), but not in the mice with LOX-1 deletion (P < 0.01 vs. LDLR KO mice). CONCLUSION: LOX-1 deletion reduces enhanced collagen deposition and MMP expression in atherosclerotic regions via inhibition of pro-oxidant signals.     

A functional role for inducible costimulator (ICOS) in atherosclerosis

BACKGROUND: Lymphocytes appear to influence atherosclerosis by altering cytokine production. Whereas primary lymphocyte activation requires T cell receptor ligation, costimulatory signals also appear requisite for generation of a functional T cell response. Inducible costimulator (ICOS) is a newly discovered T cell molecule with a dual role in immune mediated disorders. Herein, we tested the importance of ICOS in atherosclerosis. METHODS AND RESULTS: Atherosclerotic plaques from ApoE-KO mice were studied immunohistochemically for the presence and localization of ICOS and its receptors and its expression in splenocytes. ApoE-KO mice were immunized with human ICOS/Fc-chimera or non-fused Fc and either provided a chow diet for 6 weeks, or a high fat diet for 8 weeks. ICOS and its ligand were abundantly expressed within plaques from ApoE-KO mice: Spleen cells from atherosclerotic mice exhibited lowered constitutive expression of ICOS yet priming with oxLDL enhanced ICOS expression dose-dependently. In mice induced to develop fatty streaks and to generate ICOS blocking antibodies, early atherosclerosis was increased by approximately 77% whereas upon inducing more advanced lesions, the increase in plaque area upon ICOS blockade group was approximately 36%. IFN-gamma secretion by oxLDL-primed splenocytes in ICOS-immunized mice increased whereas IL-10 secretion diminished as compared to control animals. A similar trend in cytokine production was evident in the lesion by immunohistochemistry. CONCLUSION: ICOS appears as an influential costimulatory pathway in atherosclerosis that may play a protective rather that a proatherogenic role.     

The effects of lipid-lowering therapy on low-density lipoprotein auto-antibodies: relationship with low-density lipoprotein oxidation and plasma total antioxidant status

BACKGROUND: Oxidized low-density lipoprotein (Ox-LDL) is believed to play an important role in the progression of atherosclerosis. Oxidative modification of low-density lipoprotein (LDL) is a prerequisite for rapid accumulation of LDL in macrophages and for the formation of foam cells. Because of high antioxidant levels in plasma, LDL oxidation is suggested to occur mainly in the subendothelial space of the arterial wall, where there is the concomitant presence of large amounts of reactive oxygen species generated by endothelial cells and activated leukocytes. After Ox-LDL formation, antibodies against this form of LDL may occur. Auto-antibodies against Ox-LDL (AuAb-Ox-LDL) show directly in in-vivo LDL oxidation. Many studies have indicated that the amount of antibodies in serum is positively correlated to the rate of progression of atherosclerotic plaques. DESIGN AND METHODS: In this study the effect of lipid-lowering therapy on the levels of AuAb-Ox-LDL in patients with dyslipidemia was determined using atorvastatin (10 mg/day), and the relationship between the antibodies and plasma total antioxidant status (TAS) and LDL oxidation capacity was also investigated. Serum levels of AuAb-Ox-LDL, lipids, lipoproteins, TAS and susceptibility of LDL to oxidation were determined using lag time in 44 patients with dyslipidemia (29 with hypercholesterolemia and 15 with mixed-type hyperlipidemia). RESULTS: After lipid-lowering therapy, serum levels of AuAb-Ox-LDL were found to be significantly decreased, by 18.7%, while lag time and plasma TAS were increased (31.3% and 7.6% respectively) in patients with dyslipidemia. The percentage change in lag time was found to be negatively correlated to the percentage change in AuAb-Ox-LDL (r = -0.31, P < 0.05). The percentage change in lag time also showed a positive correlation with the percentage change in TAS (r = 0.58, P < 0.01). AuAb-Ox-LDL levels decreased by 21.7% in patients with hypercholesterolemia and by 12.6% in patients with mixed-type hyperlipidemia. Also AuAb-Ox-LDL levels in patients with hypercholesterolemia were higher than in those with mixed-type hyperlipidemia (367 +/- 294 compared with 300 +/- 176 mU/l). CONCLUSION: It was concluded that lipid-lowering therapy may contribute to the reduction in levels of AuAb-Ox-LDL and the increase in the antioxidant capacity of plasma LDL and TAS. It was also suggested that the measurement of antibodies against Ox-LDL during lipid-lowering therapy may be used as an important marker for representing in-vivo LDL oxidation and atherosclerotic processes.     

Aberrant antibody responses to oxidized LDL and increased intimal thickening in apoE-/- mice exposed to cigarette smoke

Cigarette smoking is associated with increased atherosclerosis and intimal thickening, and has immune-suppressive effects. The immune system modulates atherosclerosis and intimal thickening. We hypothesized that detrimental effects of cigarette smoke (CS) involves modulation of the immune response to oxidized low-density lipoprotein (oxLDL). ApoE-/- mice fed Western diet were exposed to CS starting at 20 weeks of age. Control mice were exposed to air. After 5 weeks of CS, mice were subjected to carotid arterial cuffing for 21 days. Intimal thickening was significantly increased in CS mice compared to control (0.050 +/- 0.034 mm(2) versus 0.023 +/- 0.021 mm(2); P < 0.05). Spleen lymphocyte population, cytokine mRNA expression, and total IgM and IgG levels were similar. Anti-MDA oxLDL IgG was reduced by 40% (P < 0.05) in CS mice compared to control. Copper-oxidized LDL IgG antibodies remained unchanged but IgM increased in CS mice, associated with increased intimal thickening. Anti-phosphorylcholine (PC) IgM was also increased in the CS mice, associated with increased intimal thickening. Lymphocyte signaling molecule lymphotoxin beta (LTbeta) expression was significantly decreased in spleens of CS exposed mice. Our results suggest that immune modulation by CS characterized by aberrant antibody responses to oxLDL and reduced LTbeta mRNA expression is associated with increased intimal thickening after arterial cuffing.     

Oxidized low-density lipoprotein and high-density lipoprotein cholesterol modulate coronary arterial remodeling: an intravascular ultrasound study

BACKGROUND: Oxidized low-density lipoprotein (oxLDL) not only plays an important role in plaque formation, but also impairs the endothelium-dependent relaxation. Constrictive remodeling rather than intimal hyperplasia mainly contributes to restenosis after balloon angioplasty. Probucol (powerful antioxidant) reduced restenosis rate by improving constrictive remodeling. Thus, oxLDL may modulate coronary arterial remodeling. HYPOTHESIS: The study was designed for using intravascular ultrasound to test the hypothesis that arterial constrictive remodeling (CR) was associated with oxLDL in patients with coronary artery disease. METHODS: Intravascular ultrasound was performed in 36 patients with de novo atherosclerotic coronary. Remodeling was defined and evaluated as follows: remodeling index (RI) = lesion vessel area (VA)/(proximal reference VA + distal reference VA)/2. Constrictive remodeling (CR) was defined as remodeling index (RI) < 0.9. Neutral and expansive remodeling (NER) was defined as RI > or = 0.9. The level of plasma ox-LDL was measured by sandwich ELISA using the monoclonal antibody (DLH3)-recognized oxidatively modified lipoproteins and the antihuman apoprotein B monoclonal antibody. RESULTS: Neutral and expansive remodeling was found in 24 lesions, and CR in 12 lesions. Remodeling index was significantly lower in the CR group than in the NER group (0.8 +/- 0.1 vs. 1.0 +/- 0.1, p < 0.001). The level of oxLDL in the CR group was significantly higher than that in the NER group (24.0 +/- 12.1 vs. 16.4 +/- 6.2 U/ml, p < 0.05). The level of high-density lipoprotein-cholesterol (HDL-C) in the CR group was significantly lower than that in the NER group (40.5 +/- 4.8 vs. 46.2 +/- 10.6 mg/ml, p < 0.05). There was a statistically significant correlation between the value of HDL-C/ ox-LDL and the RI (r = -0.48, p < 0.005). CONCLUSIONS: Oxidized LDL and HDL-C were associated with arterial remodeling in de novo atherosclerotic lesions.     

Oxidized LDL/beta2-glycoprotein I complexes: new aspects in atherosclerosis

beta2-glycoprotein I (beta2GPI) is a major antigenic target for antiphospholipid antibodies. Oxidized low-density lipoprotein (oxLDL) is the principal lipoprotein found in atherosclerotic lesions, and it colocalizes with beta2GPI and immunoreactive lymphocytes. oxLDL/beta2GPI complexes appeared in the blood circulation of patients with diseases, such as systemic lupus erythematosus (SLE), antiphospholipid syndrome (APS), systemic sclerosis, diabetes mellitus and chronic renal diseases. Thus, the complexes may be associated with systemic and chronic inflammation of the vasculature. IgG anti-oxLDL/beta2GPI complexes autoantibodies and their immune complexes were detected only in SLE/APS patients and in its animal model and were strongly associated with arterial thrombosis. The oxLDL/beta2GPI complexes were internalized by macrophages via IgG anti-beta2GPI antibody-mediated phagocytosis. In contrast, IgM anti-oxLDL antibodies derived from hyperlipidemic mice reduced the incidence of atherosclerosis. The distribution patterns of IgG and IgM anti-oxLDL antibodies in patients suggest the different roles of these antibodies.