Rapid regression of atherosclerosis: insights from the clinical and experimental literature

Cholesterol-induced membrane microvesicles as novel carriers of damage-associated molecular patterns: mechanisms of formation, action, and detoxification

OBJECTIVE

Cholesterol enrichment occurs in vivo when phagocytes ingest retained and aggregated lipoproteins, damaged or senescent cells, and related debris. We previously reported that enrichment of human monocyte/macrophages with unesterified cholesterol (UC) triggers the release of highly procoagulant microvesicles ([MVs], also called microparticles) through induction of apoptosis. We determined whether UC-induced MVs (UCMVs) might transmit endogenous danger signals and, if so, what molecular processes might be responsible for their production, recognition, and detoxification.

METHODS AND RESULTS

Injection of UCMVs into rats provoked extensive leukocyte rolling and adherence to postcapillary venules in vivo. Likewise, exposure of mouse aortic explants or cultured human endothelial cells to UCMVs augmented the adhesion of human monocytes by several fold and increased endothelial cell intercellular adhesion molecule-1 via nuclear factor-κB activation. To explore molecular mechanisms, we found that UC enrichment of human monocytes, in the absence of other stimuli, induced mitochondrial complex II-dependent accumulation of superoxide and peroxides. A subset of these moieties was exported on UCMVs and mediated endothelial activation. Strikingly, aortic explants from mice lacking lectin-like oxidized low-density lipoprotein receptor-1, a pattern-recognition receptor, were essentially unable to respond to UCMVs, whereas simultaneously treated explants from wild-type mice responded robustly by increasing monocyte recruitment. Moreover, high-density lipoprotein and its associated enzyme paraoxonase-1 exerted unexpected roles in the detoxification of UCMVs.

CONCLUSIONS

Overall, our study implicates MVs from cholesterol-loaded human cells as novel carriers of danger signals. By promoting maladaptive immunologic and thrombotic responses, these particles may contribute to atherothrombosis and other conditions in vivo.

Macrophages, dendritic cells, and regression of atherosclerosis

Atherosclerosis is the number one cause of death in the Western world. It results from the interaction between modified lipoproteins and cells such as macrophages, dendritic cells (DCs), T cells, and other cellular elements present in the arterial wall. This inflammatory process can ultimately lead to the development of complex lesions, or plaques, that protrude into the arterial lumen. Ultimately, plaque rupture and thrombosis can occur leading to the clinical complications of myocardial infarction or stroke. Although each of the cell types plays roles in the pathogenesis of atherosclerosis, the focus of this review will be primarily on the macrophages and DCs. The role of these two cell types in atherosclerosis is discussed, with a particular emphasis on their involvement in atherosclerosis regression.

Plaque neovascularization: defense mechanisms, betrayal, or a war in progress

Angiogenesis is induced from sprouting of preexisting endothelial cells leading to neovascularization. Imbalance in the angiogenic and antiangiogenic mediators triggers angiogenesis, which may be physiological in the normal state or pathological in malignancy and atherosclerosis. Physiologic angiogenesis is instrumental for restoration of vessel wall normoxia and resolution inflammation, leading to atherosclerosis regression. However, pathological angiogenesis enhances disease progression, increasing macrophage infiltration and vessel wall thickness, perpetuating hypoxia and necrosis. In addition, thin-walled fragile neovessels may rupture, leading to intraplaque hemorrhage. Lipid-rich red blood cell membranes and free hemoglobin are detrimental to plaque composition, increasing inflammation, lipid core expansion, and oxidative stress. In addition, associated risk factors that include polymorphysms in the haptoglobin genotype and diabetes mellitus may modulate the features of plaque vulnerability. This review will focus on physiological and pathological angiogenesis in atherosclerosis and summarizes the current status of anti-vascular endothelial growth factor (VEGF) therapy, microvascular rarefaction, and possible statin-mediated effects in atherosclerosis neovascularization.

Regression of atherosclerosis is characterized by broad changes in the plaque macrophage transcriptome

We have developed a mouse model of atherosclerotic plaque regression in which an atherosclerotic aortic arch from a hyperlipidemic donor is transplanted into a normolipidemic recipient, resulting in rapid elimination of cholesterol and monocyte-derived macrophage cells (CD68+) from transplanted vessel walls. To gain a comprehensive view of the differences in gene expression patterns in macrophages associated with regressing compared with progressing atherosclerotic plaque, we compared mRNA expression patterns in CD68+ macrophages extracted from plaque in aortic aches transplanted into normolipidemic or into hyperlipidemic recipients. In CD68+ cells from regressing plaque we observed that genes associated with the contractile apparatus responsible for cellular movement (e.g. actin and myosin) were up-regulated whereas genes related to cell adhesion (e.g. cadherins, vinculin) were down-regulated. In addition, CD68+ cells from regressing plaque were characterized by enhanced expression of genes associated with an anti-inflammatory M2 macrophage phenotype, including arginase I, CD163 and the C-lectin receptor. Our analysis suggests that in regressing plaque CD68+ cells preferentially express genes that reduce cellular adhesion, enhance cellular motility, and overall act to suppress inflammation.

Notch ligand delta-like 4 blockade attenuates atherosclerosis and metabolic disorders

Atherosclerosis and insulin resistance are major components of the cardiometabolic syndrome, a global health threat associated with a systemic inflammatory state. Notch signaling regulates tissue development and participates in innate and adaptive immunity in adults. The role of Notch signaling in cardiometabolic inflammation, however, remains obscure. We noted that a high-fat, high-cholesterol diet increased expression of the Notch ligand Delta-like 4 (Dll4) in atheromata and fat tissue in LDL-receptor-deficient mice. Blockade of Dll4-Notch signaling using neutralizing anti-Dll4 antibody attenuated the development of atherosclerosis, diminished plaque calcification, improved insulin resistance, and decreased fat accumulation. These changes were accompanied by decreased macrophage accumulation, diminished expression of monocyte chemoattractant protein-1 (MCP-1), and lower levels of nuclear factor-κB (NF-κB) activation. In vitro cell culture experiments revealed that Dll4-mediated Notch signaling increases MCP-1 expression via NF-κB, providing a possible mechanism for in vivo effects. Furthermore, Dll4 skewed macrophages toward a proinflammatory phenotype ("M1"). These results suggest that Dll4-Notch signaling plays a central role in the shared mechanism for the pathogenesis of cardiometabolic disorders.

Lymphocytes and the adventitial immune response in atherosclerosis

Although much of the research on atherosclerosis has focused on the intimal accumulation of lipids and inflammatory cells, there is an increasing amount of interest in the role of the adventitia in coordinating the immune response in atherosclerosis. In this review of the contributions of the adventitia and adventitial lymphocytes to the development of atherosclerosis, we discuss recent research on the formation and structural nature of adventitial immune aggregates, potential mechanisms of crosstalk between the intima, media, and adventitia, specific contributions of B lymphocytes and T lymphocytes, and the role of the vasa vasorum and surrounding perivascular adipose tissue. Furthermore, we highlight techniques for the imaging of lymphocytes in the vasculature.

Macrophage differentiation and function in atherosclerosis: opportunities for therapeutic intervention?

The macrophage is exquisitely sensitive to its microenvironment, as demonstrated primarily through in vitro study. Changes in macrophage phenotype and function within the atherosclerotic plaque have profound consequences for plaque biology, including rupture and arterial thrombosis leading to clinical events such as myocardial infarction. We review the evidence for dynamic changes in macrophage numbers and macrophage differentiation within the atherosclerotic plaque microenvironment and discuss potential approaches to target macrophage differentiation for therapeutic benefit in cardiovascular disease.

Dietary Cholesterol Concentration and Duration Degrade Long-Term Memory of Classical Conditioning of the Rabbit's Nictitating Membrane Response

A rabbit model of Alzheimer's disease based on feeding a cholesterol diet for eight weeks shows sixteen hallmarks of the disease, including learning and memory changes. Although we have shown 2% cholesterol and copper in water can retard learning, other studies show feeding dietary cholesterol before learning can improve acquisition whereas feeding cholesterol after learning can degrade long-term memory. We explored this issue by manipulating cholesterol concentration and duration following classical trace conditioning of the rabbit's nictitating membrane response and assessed conditioned responding after eight weeks on cholesterol. First, rabbits given trace classical conditioning followed by 0.5%, 1%, or 2% cholesterol for eight weeks showed body weight and serum cholesterol levels that were a function of dietary cholesterol. Although all concentrations of cholesterol showed some sign of retarding long-term memory, the level of memory retardation was correlated with serum cholesterol levels. Second, rabbits given trace conditioning followed by different durations of a 2% cholesterol diet combined with different durations of a 0% control diet for 8 weeks showed duration and timing of a 2% cholesterol diet were important in affecting recall. The data support the idea that dietary cholesterol may retard long-term memory.

Microvesicles: potential markers and mediators of endothelial dysfunction

PURPOSE OF REVIEW

Microvesicles (also known as microparticles) are small membranous structures that are released from platelets and cells upon activation or during apoptosis. Microvesicles have been found in blood, urine, synovial fluid, extracellular spaces of solid organs, atherosclerotic plaques, tumors, and elsewhere. Here, we focus on new clinical and basic work that implicates microvesicles as markers and mediators of endothelial dysfunction and hence novel contributors to cardiovascular and other diseases.

RECENT FINDINGS

Advances in the detection of microvesicles and the use of cell type-specific markers to determine their origin have allowed studies that associated plasma concentrations of specific microvesicles with major types of endothelial dysfunction - namely, inappropriate or maladaptive vascular tone, leukocyte recruitment, and thrombosis. Recent investigations have highlighted microvesicular transport of key biologically active molecules besides tissue factor, such as ligands for pattern-recognition receptors, elements of the inflammasome, and morphogens. Microvesicles generated from human cells under different pathologic circumstances, for example, during cholesterol loading or exposure to endotoxin, carry different subsets of these molecules and thereby alter endothelial function through several distinct, well characterized molecular pathways.

SUMMARY

Clinical and basic studies indicate that microvesicles may be novel markers and mediators of endothelial dysfunction. This work has advanced our understanding of the development of cardiovascular and other diseases. Opportunities and obstacles to clinical applications are discussed.

Preclinical mouse models and methods for the discovery of the causes and treatments of atherosclerosis

INTRODUCTION

Atherosclerosis is the leading cause of death in the Western world. Despite huge advances in understanding its pathophysiological mechanisms, current treatment is mostly based on 'traditional' risk factors. The introduction of statins more than 20 years ago reduced morbidity and mortality of atherosclerosis by 30%, leaving a residual cardiovascular risk. Therefore, efforts continue toward the development of novel therapies that can be added to established treatments. Besides targeting dyslipidemia, recent focus has been put on preventing or resolving inflammatory processes involved in atherosclerosis.

AREAS COVERED

The article discusses therapeutic and diagnostic targets in atherosclerosis and how they can be discovered and studied in preclinical animal models. The roles of immune cells, specifically macrophages and monocytes, in plaque inflammation are discussed. The article also describes current preclinical models of atherosclerosis, specifically the mouse, study designs (for progression and regression studies), basic and advanced methods of analysis of atherosclerotic lesions, and discusses the challenges of translating the findings to humans.

EXPERT OPINION

Advances in genomics, proteomics, lipidomics and the development of high-throughput screening techniques help to improve our understanding of atherosclerosis disease mechanisms immensely and facilitate the discovery of new diagnostic and therapeutic targets. Preclinical studies in animals are still indispensable to uncover pathways involved in atherosclerotic disease and to evaluate novel drug targets. The translation of these targets, however, from animal studies to humans remains challenging. There is a strong need for novel biomarkers that can be used to prove the concept of a new target in humans.

The neuroimmune guidance cue netrin-1 promotes atherosclerosis by inhibiting the emigration of macrophages from plaques

Atherosclerotic plaque formation is fueled by the persistence of lipid-laden macrophages in the artery wall. The mechanisms by which these cells become trapped, thereby establishing chronic inflammation, remain unknown. Netrin-1, a neuroimmune guidance cue, was secreted by macrophages in human and mouse atheroma, where it inactivated macrophage migration to chemokines implicated in their egress from plaques. Acting via its receptor UNC5b, netrin-1 inhibited CCL2- and CCL19-directed macrophage migration, Rac1 activation and actin polymerization. Targeted deletion of netrin-1 in macrophagesseverely diminished atherosclerosis progression in Ldlr^−/− mice and promoted macrophage emigration from plaques. Thus, netrin-1 promotes atherosclerosis by retaining macrophages in the artery wall and establish a causative role for negative regulators of leukocyte migration in chronic inflammation.

Statins promote the regression of atherosclerosis via activation of the CCR7-dependent emigration pathway in macrophages

HMG-CoA reductase inhibitors (statins) decrease atherosclerosis by lowering low-density-lipoprotein cholesterol. Statins are also thought to have additional anti-atherogenic properties, yet defining these non-conventional modes of statin action remains incomplete. We have previously developed a novel mouse transplant model of atherosclerosis regression in which aortic segments from diseased donors are placed into normolipidemic recipients. With this model, we demonstrated the rapid loss of CD68+ cells (mainly macrophages) in plaques through the induction of a chemokine receptor CCR7-dependent emigration process. Because the human and mouse CCR7 promoter contain Sterol Response Elements (SREs), we hypothesized that Sterol Regulatory Element Binding Proteins (SREBPs) are involved in increasing CCR7 expression and through this mechanism, statins would promote CD68+ cell emigration from plaques. We examined whether statin activation of the SREBP pathway in vivo would induce CCR7 expression and promote macrophage emigration from plaques. We found that western diet-fed apoE^-/- mice treated with either atorvastatin or rosuvastatin led to a substantial reduction in the CD68+ cell content in the plaques despite continued hyperlipidemia. We also observed a significant increase in CCR7 mRNA in CD68+ cells from both the atorvastatin and rosuvastatin treated mice associated with emigration of CD68+ cells from plaques. Importantly, CCR7^-/-/apoE^-/- double knockout mice failed to display a reduction in CD68+ cell content upon statin treatment. Statins also affected the recruitment of transcriptional regulatory proteins and the organization of the chromatin at the CCR7 promoter to increase the transcriptional activity. Statins promote the beneficial remodeling of plaques in diseased mouse arteries through the stimulation of the CCR7 emigration pathway in macrophages. Therefore, statins may exhibit some of their clinical benefits by not only retarding the progression of atherosclerosis, but also accelerating its regression.

Interleukin-7 induces recruitment of monocytes/macrophages to endothelium

AIMS

Interleukin-7 (IL-7) is a master regulator of T-cell development and homoeostasis. Increased IL-7 levels are associated with inflammatory diseases. The aims of this study were to determine whether IL-7 is a biomarker for inflammatory conditions or an active participant in atherogenesis.

METHODS AND RESULTS

Advanced atherosclerotic lesions in Apoe(-/-) mice were regressed by long-term cholesterol lowering through treatment with a helper-dependent adenovirus expressing apolipoprotein E (n= 6-10). Using this model, gene expression patterns in the aorta were analysed at an early phase of regression by microarray. After stringent statistical analysis, we found that IL-7 expression is significantly reduced in response to lowering of cholesterol (n= 6). To understand the importance of IL-7 down-regulation for atherosclerotic regression, we studied the effects and mechanisms of action of IL-7 on endothelial cells (ECs) in vitro as well as in vivo. Our major findings are: (i) IL-7 up-regulates cell adhesion molecules and monocyte chemoattractant protein-1 in ECs and promotes monocyte adhesion to ECs; (ii) this regulation is mediated by phosphatidylinositol 3-kinase (PI3K)/AKT-dependent and -independent activation of NF-κB; (iii) elevation of plasma IL-7 induces recruitment of monocytes/macrophages to endothelium without affecting plasma cholesterol (n= 5, 6); and (4) lack of IL-7 in bone marrow-derived cells reduces migration of monocytes/macrophages to the lesions (n= 5, 6).

CONCLUSION

These results suggest that IL-7 inflames endothelium via PI3K/AKT-dependent and -independent activation of NF-κB and recruits monocytes/macrophages to the endothelium, thus playing an active role in atherogenesis.

Atherosclerotic lesion progression is attenuated by reconstitution with bone marrow from macrophage-specific cholesteryl ester hydrolase transgenic mice

Accumulation of cholesteryl ester (CE)-enriched macrophage foam cells is central to the development of atherosclerotic lesions. Intracellular CE hydrolysis is the rate-limiting step in the removal of free cholesterol from macrophage foam cells. Enhancing this process by transgenic overexpression of CE hydrolase (CEH) resulted in a significant decrease in diet-induced atherosclerosis in LDL receptor-deficient (LDLR-/-) mice. However, for development of this step as an antiatherosclerotic target it is imperative to demonstrate that increase in CE hydrolysis after initiation of lesion formation will also attenuate further lesion progression. The objective of the present study was to directly address this issue using an animal model. LDLR-/- mice were fed a high-fat high-cholesterol diet (Western Diet) for 8 wk to initiate lesion formation and were then divided into three groups. Group 1 mice were killed to determine baseline lesion development. Mice in groups 2 and 3 were irradiated and transplanted with either LDLR-/- or LDLR-/-CEH transgenic bone marrow and maintained on Western Diet. Atherosclerotic lesion progression was assessed after 12 wk. While a more than fourfold increase in total lesions (compared to group 1) was seen in group 2 receiving LDLR-/- marrow, a significantly lower increase (<2-fold) was noted in mice reconstituted with CEH transgenic marrow (group 3). Lesions in group 3 mice were also more cellular with smaller necrotic cores. Lesion progression is associated with a switch in macrophage phenotype from anti-inflammatory M2 to proinflammatory M1 phenotype and is consistent with reduced lesion progression. Aortas from group 3 mice contained a significantly higher percentage of macrophages in M2 phenotype (Ly6C(lo)). These data demonstrate for the first time that enhancing macrophage CE hydrolysis even after lesion initiation can still attenuate further lesion progression and also switches the phenotype of lesion-associated macrophages to anti-inflammatory M2 phenotype establishing intracellular CE hydrolysis as an anti-atherosclerotic as well as anti-inflammatory target.

LXRα regulates macrophage arginase 1 through PU.1 and interferon regulatory factor 8

RATIONALE

Activation of liver X receptors (LXRs) inhibits the progression of atherosclerosis and promotes regression of existing lesions. In addition, LXRα levels are high in regressive plaques. Macrophage arginase 1 (Arg1) expression is inversely correlated with atherosclerosis progression and is markedly decreased in foam cells within the lesion.

OBJECTIVE

To investigate LXRα regulation of Arg1 expression in cultured macrophages and atherosclerotic regressive lesions.

METHODS AND RESULTS

We found that Arg1 expression is enhanced in CD68+ cells from regressive versus progressive lesions in a murine aortic arch transplant model. In cultured macrophages, ligand-activated LXRα markedly enhances basal and interleukin-4-induced Arg1 mRNA and protein expression as well as promoter activity. This LXRα-enhanced Arg1 expression correlates with a reduction in nitric oxide levels. Moreover, Arg1 expression within regressive atherosclerotic plaques is LXRα-dependent, as enhanced expression of Arg1 in regressive lesions is impaired in LXRα-deficient CD68+ cells. LXRα does not bind to the Arg1 promoter but instead promotes the interaction between PU.1 and interferon regulatory factor (IRF)8 transcription factors and induces their binding of a novel composite element. Accordingly, knockdown of either IRF8 or PU.1 strongly impairs LXRα regulation of Arg1 expression in macrophage cells. Finally, we demonstrate that LXRα binds the IRF8 locus and its activation increases IRF8 mRNA and protein levels in these cells.

CONCLUSIONS

This work implicates Arg1 in atherosclerosis regression and identifies LXRα as a novel regulator of Arg1 and IRF8 in macrophages. Furthermore, it provides a unique molecular mechanism by which LXRα regulates macrophage target gene expression through PU.1 and IRF8.

PON-dering differences in HDL function in coronary artery disease

HDL cholesterol activates endothelial cell production of the atheroprotective signaling molecule NO, and it promotes endothelial repair. In this issue of the JCI, Besler et al. provide new data indicating that HDL from stable coronary artery disease (CAD) or acute coronary syndrome patients inhibits rather than stimulates endothelial NO synthesis and endothelial repair. This may be related to decreased HDL-associated paraoxonase 1 (PON1) activity. These observations support the concept that the cardiovascular impact of HDL is not simply related to its abundance, and the translation of the present findings to prospective studies of CAD risk and to evaluations of HDL-targeted therapeutics is a logical future goal.

Suppressed monocyte recruitment drives macrophage removal from atherosclerotic plaques of Apoe-/- mice during disease regression

Experimental models of atherosclerosis suggest that recruitment of monocytes into plaques drives the progression of this chronic inflammatory condition. Cholesterol-lowering therapy leads to plaque stabilization or regression in human atherosclerosis, characterized by reduced macrophage content, but the mechanisms that underlie this reduction are incompletely understood. Mice lacking the gene Apoe (Apoe-/- mice) have high levels of cholesterol and spontaneously develop atherosclerotic lesions. Here, we treated Apoe-/- mice with apoE-encoding adenoviral vectors that induce plaque regression, and investigated whether macrophage removal from plaques during this regression resulted from quantitative alterations in the ability of monocytes to either enter or exit plaques. Within 2 days after apoE complementation, plasma cholesterol was normalized to wild-type levels, and HDL levels were increased 4-fold. Oil red O staining and quantitative mass spectroscopy revealed that esterified cholesterol content was markedly reduced. Plaque macrophage content decreased gradually and was 72% lower than baseline 4 weeks after apoE complementation. Importantly, this reduction in macrophages did not involve migratory egress from plaques or CCR7, a mediator of leukocyte emigration. Instead, marked suppression of monocyte recruitment coupled with a stable rate of apoptosis accounted for loss of plaque macrophages. These data suggest that therapies to inhibit monocyte recruitment to plaques may constitute a more viable strategy to reduce plaque macrophage burden than attempts to promote migratory egress.

HDL promotes rapid atherosclerosis regression in mice and alters inflammatory properties of plaque monocyte-derived cells

HDL cholesterol (HDL-C) plasma levels are inversely related to cardiovascular disease risk. Previous studies have shown in animals and humans that HDL promotes regression of atherosclerosis. We hypothesized that this was related to an ability to promote the loss of monocyte-derived cells (CD68(+), primarily macrophages and macrophage foam cells) from plaques. To test this hypothesis, we used an established model of atherosclerosis regression in which plaque-bearing aortic arches from apolipoprotein E-deficient (apoE(-/-)) mice (low HDL-C, high non-HDL-C) were transplanted into recipient mice with differing levels of HDL-C and non-HDL-C: C57BL6 mice (normal HDL-C, low non-HDL-C), apoAI(-/-) mice (low HDL-C, low non-HDL-C), or apoE(-/-) mice transgenic for human apoAI (hAI/apoE(-/-); normal HDL-C, high non-HDL-C). Remarkably, despite persistent elevated non-HDL-C in hAI/apoE(-/-) recipients, plaque CD68(+) cell content decreased by >50% by 1 wk after transplantation, whereas there was little change in apoAI(-/-) recipient mice despite hypolipidemia. The decreased content of plaque CD68(+) cells after HDL-C normalization was associated with their emigration and induction of their chemokine receptor CCR7. Furthermore, in CD68(+) cells laser-captured from the plaques, normalization of HDL-C led to decreased expression of inflammatory factors and enrichment of markers of the M2 (tissue repair) macrophage state. Again, none of these beneficial changes were observed in the apoAI(-/-) recipients, suggesting a major requirement for reverse cholesterol transport for the beneficial effects of HDL. Overall, these results establish HDL as a regulator in vivo of the migratory and inflammatory properties of monocyte-derived cells in mouse atherosclerotic plaques, and highlight the phenotypic plasticity of these cells.

Reversal of hyperlipidemia with a genetic switch favorably affects the content and inflammatory state of macrophages in atherosclerotic plaques

BACKGROUND

We previously showed that the progression of atherosclerosis in the Reversa mouse (Ldlr(-/-Apob100/100Mttpfl/fl) Mx1Cre(+/+)) was arrested when the hyperlipidemia was normalized by inactivating the gene for microsomal triglyceride transfer protein. Here, we tested whether atherosclerosis would regress if the lipid levels were reduced after advanced plaques formed.

METHODS AND RESULTS

Reversa mice were fed an atherogenic diet for 16 weeks. Plasma lipid levels were then reduced. Within 2 weeks, this reduction led to decreased monocyte-derived (CD68(+)) cells in atherosclerotic plaques and was associated with emigration of these cells out of plaques. In addition, the fall in lipid levels was accompanied by lower plaque lipid content and by reduced expression in plaque CD68(+) cells of inflammatory genes and higher expression of genes for markers of antiinflammatory M2 macrophages. Plaque composition was affected more than plaque size, with the decreased content of lipid and CD68(+) cells balanced by a higher content of collagen. When the reduced lipid level was combined with the administration of pioglitazone to simulate the clinical aggressive lipid management and proliferator-activated receptor-γ agonist treatment, the rate of depletion of plaque CD68(+) cells was unaffected, but there was a further increase in their expression of antiinflammatory macrophage markers.

CONCLUSION

The Reversa mouse is a new model of atherosclerosis regression. After lipid lowering, favorable changes in plaque composition were independent of changes in size. In addition, plaque CD68(+) cells became less inflammatory, an effect enhanced by treatment with pioglitazone.

Regression and stabilization of advanced murine atherosclerotic lesions: a comparison of LDL lowering and HDL raising gene transfer strategies

Both reductions in atherogenic lipoproteins and increases in high-density lipoprotein (HDL) levels may affect atherosclerosis regression. Here, the relative potential of low-density lipoprotein (LDL) lowering and HDL raising gene transfer strategies to induce regression of complex murine atherosclerotic lesions was directly compared. Male C57BL/6 LDL receptor (LDLr)^−/− mice were fed an atherogenic diet (1.25% cholesterol and 10% coconut oil) to induce advanced atherosclerotic lesions. A baseline group was killed after 6 months and remaining mice were randomized into a control progression (Adnull or saline), an apolipoprotein (apo) A-I (AdA-I), an LDLr (AdLDLr), or a combined apo A-I/LDLr (AdA-I/AdLDLr) adenoviral gene transfer group and followed-up for another 12 weeks with continuation of the atherogenic diet. Gene transfer with AdLDLr decreased non-HDL cholesterol levels persistently by 95% (p < 0.001) compared with baseline. This drastic reduction of non-HDL cholesterol levels induced lesion regression by 28% (p < 0.001) in the aortic root and by 25% (p < 0.05) in the brachiocephalic artery at 12 weeks after transfer. Change in lesion size was accompanied by enhanced plaque stability, as evidenced by increased collagen content, reduced lesional macrophage content, a drastic reduction of necrotic core area, and decreased expression of inflammatory genes. Elevated HDL cholesterol following AdA-I transfer increased collagen content in lesions, but did not induce regression. Apo A-I gene transfer on top of AdLDLr transfer resulted in additive effects, particularly on inflammatory gene expression. In conclusion, drastic lipid lowering induced by a powerful gene transfer strategy leads to pronounced regression and stabilization of advanced murine atherosclerosis.

Atherosclerosis in chronic kidney disease: the role of macrophages

Patients with chronic kidney disease (CKD) are at increased risk of atherosclerotic cardiovascular disease and loss of renal parenchyma accelerates atherosclerosis in animal models. Macrophages are central to atherogenesis because they regulate cholesterol traffic and inflammation in the arterial wall. CKD influences macrophage behavior at multiple levels, rendering them proatherogenic. Even at normal creatinine levels, macrophages from uninephrectomized Apoe(-/-) mice are enriched in cholesterol owing to downregulation of cholesterol transporter ATP-binding cassette subfamily A member 1 levels and activation of nuclear factor κB, which leads to impaired cholesterol efflux. Interestingly, treatment with an angiotensin-II-receptor blocker (ARB) improves these effects. Moreover, atherosclerotic aortas from Apoe(-/-) mice transplanted into renal-ablated normocholesterolemic recipients show plaque progression and increased macrophage content instead of the substantial regression seen in recipient mice with intact kidneys. ARBs reduce atherosclerosis development in mice with partial renal ablation. These results, combined with the clinical benefits of angiotensin-converting-enzyme (ACE) inhibitors and ARBs in patients with CKD, suggest an important role for the angiotensin system in the enhanced susceptibility to atherosclerosis seen across the spectrum of CKD. The role of macrophages could explain why these therapies may be effective in end-stage renal disease, one of the few conditions in which statins show no clinical benefit.

Deletion of ABCA1 and ABCG1 impairs macrophage migration because of increased Rac1 signaling

RATIONALE

Reduced plasma cholesterol and increased high-density lipoprotein (HDL) levels promote regression of atherosclerosis, in a process characterized by lipid unloading and emigration of macrophages from lesions. In contrast free cholesterol loading of macrophages leads to imbalanced Rac1/Rho activities and impaired chemotaxis.

OBJECTIVE

To study the role of HDL and the ATP-binding cassette transporters ABCA1 and ABCG1 in modulating the chemotaxis of macrophages.

METHODS AND RESULTS

Abca1(-/-)Abcg1(-/-) mouse macrophages displayed profoundly impaired chemotaxis both in a Transwell chamber assay and in the peritoneal cavity of wild-type (WT) mice. HDL reversed impaired chemotaxis in free cholesterol-loaded WT macrophages but was without effect in Abca1(-/-)Abcg1(-/-) cells, whereas cyclodextrin was effective in both. Abca1(-/-)Abcg1(-/-) macrophages had markedly increased Rac1 activity and increased association of Rac1 with the plasma membrane (PM). Their defective chemotaxis was reversed by a Rac1 inhibitor. To gain a better understanding of the role of transporters in PM cholesterol movement, we measured transbilayer PM sterol distribution. In WT macrophages, the majority of cholesterol was located on the inner leaflet, whereas on upregulation of transporters by liver X receptor activation, PM sterol was shifted to the outer leaflet, where it could be removed by HDL. Abca1(-/-)Abcg1(-/-) macrophages showed increased PM sterol content and defective redistribution of sterol to the outer leaflet.

CONCLUSIONS

Deletion of ABCA1 and ABCG1 causes an increased cholesterol content on the inner leaflet of the PM, associated with increased Rac1 PM localization, activation, and impairment of migration. ABCA1 and ABCG1 facilitate macrophage chemotaxis by promoting PM transbilayer cholesterol movement and may contribute to the ability of HDL to promote regression of atherosclerosis.

Atherosclerosis regression study in rabbits upon olive pomace polar lipid extract administration

BACKGROUND AND AIMS

Virgin olive oil polar lipid extract (OOPL) and olive pomace polar lipid extract (PPL) have similar antiatherosclerotic effects in cholesterol-fed rabbits. Our aim was to compare the effect of PPL with that of simvastatin on the progression of atherogenesis.

METHODS AND RESULTS

Rabbits were fed an atherogenic diet for 6 weeks in order to develop dyslipidemia and atheromatous lesions. Following documentation of these events in random animals (group A, n=6), the remaining were fed for 3 weeks with: standard chow alone (group B, n=6), chow supplemented with PPL (group C, n=6), and chow supplemented with simvastatin (group D, n=6). Blood was collected at 0, 6 and 9 weeks, to determine plasma lipid levels, plasma PAF-AH activity, platelet aggregation (PAF-EC(50)), resistance of plasma to oxidation (RPO) and extent of atheromatous lesions in aortas. The atherogenic diet induced dyslipidemia and increased PAF-AH activity. Dyslipidemia and PAF-activity reduced more effectively in groups C and D. RPO decreased in group B only. PAF-EC(50) values decreased in group C only. Atherogenesis progression in group C was prevented to an extent indistinguishable from that in group D. PAF-AH activity was positively correlated, whereas RPO was negatively correlated with the extent of atheromatous lesions.

CONCLUSION

PPL, as a dietary supplement, is equipotent to simvastatin in preventing the progression of atherogenesis.

The dynamic nature of coronary artery lesion morphology assessed by serial virtual histology intravascular ultrasound tissue characterization

OBJECTIVES

We used virtual histology intravascular ultrasound (VH-IVUS) to investigate the natural history of coronary artery lesion morphology.

BACKGROUND

Plaque stability is related to its histological composition.

METHODS

We performed serial (baseline and 12-month follow-up) VH-IVUS studies and examined 216 nonculprit lesions (plaque burden >or=40%) in 99 patients. Lesions were classified into pathological intimal thickening (PIT), VH-IVUS-derived thin-capped fibroatheroma (VH-TCFA), thick-capped fibroatheroma (ThCFA), fibrotic plaque, and fibrocalcific plaque.

RESULTS

At baseline, 20 lesions were VH-TCFAs; during follow-up, 15 (75%) VH-TCFAs "healed," 13 became ThCFAs, 2 became fibrotic plaque, and 5 (25%) VH-TCFAs remained unchanged. Compared with VH-TCFAs that healed, VH-TCFAs that remained VH-TCFAs located more proximally (values are median [interquartile range]) (16 mm [15 to 18 mm] vs. 31 mm [22 to 47 mm], p = 0.013) and had larger lumen (9.1 mm(2) [8.2 to 10.7 mm(2)] vs. 6.9 mm(2) [6.0 to 8.2 mm(2)], p = 0.021), vessel (18.7 mm(2) [17.3 to 28.6 mm(2)] vs. 15.5 mm(2) [13.3 to 16.6 mm(2)]; p = 0.010), and plaque (9.7 mm(2) [9.6 to 15.7 mm(2)] vs. 8.4 mm(2) [7 to 9.7 mm(2)], p = 0.027) areas; however, baseline VH-IVUS plaque composition did not differ between VH-TCFAs that healed and VH-TCFAs that remained VH-TCFAs. Conversely, 12 new VH-TCFAs developed; 6 late-developing VH-TCFAs were PITs, and 6 were ThCFAs at baseline. In addition, plaque area at minimum lumen sites increased significantly in PITs (7.8 mm(2) [6.2 to 10.0 mm(2)] to 9.0 mm(2) [6.5 to 12.0 mm(2)], p < 0.001), VH-TCFAs (8.6 mm(2) [7.3 to 9.9 mm(2)] to 9.5 mm(2) [7.8 to 10.8 mm(2)], p = 0.024), and ThCFAs (8.6 mm(2) [6.8 to 10.2 mm(2)] to 8.8 mm(2) [7.1 to 11.4 mm(2)], p < 0.001) with a corresponding decrease lumen areas, but not in fibrous or fibrocalcific plaque.

CONCLUSIONS

Most VH-TCFAs healed during 12-month follow-up, whereas new VH-TCFAs also developed. PITs, VH-TCFAs, and ThCFAs showed significant plaque progression compared with fibrous and fibrocalcific plaque.

Gene therapy for dyslipidemia: a review of gene replacement and gene inhibition strategies

Despite numerous technological and pharmacological advances and more detailed knowledge of molecular etiologies, cardiovascular diseases remain the leading cause of morbidity and mortality worldwide claiming over 17 million lives a year. Abnormalities in the synthesis, processing and catabolism of lipoprotein particles can result in severe hypercholesterolemia, hypertriglyceridemia or low HDL-C. Although a plethora of antidyslipidemic pharmacological agents are available, these drugs are relatively ineffective in many patients with Mendelian lipid disorders, indicating the need for new and more effective interventions. In vivo somatic gene therapy is one such intervention. This article summarizes current strategies being pursued for the development of clinical gene therapy for dyslipidemias that cannot effectively be treated with existing drugs.

Diabetes mellitus is a major negative determinant of coronary plaque regression during statin therapy in patients with acute coronary syndrome--serial intravascular ultrasound observations from the Japan Assessment of Pitavastatin and Atorvastatin in Acute Coronary Syndrome Trial (the JAPAN-ACS Trial)

BACKGROUND

The Japan Assessment of Pitavastatin and Atorvastatin in Acute Coronary Syndrome (JAPAN-ACS) trial has found that early aggressive statin therapy in patients with acute coronary syndrome (ACS) significantly reduces the plaque volume (PV) of non-culprit coronary lesions. The purpose of the present study was to evaluate clinical factors that have an impact on plaque regression using statin therapy.

METHODS AND RESULTS

Serial intravascular ultrasound observations over 8-12 months were performed in 252 ACS patients receiving pitavastatin or atorvastatin. Linear regression analysis identified the presence of diabetes mellitus (DM) and PV at baseline as inhibiting factors, and serum remnant-like particle-cholesterol level at baseline as a significant factor significantly affecting the degree of plaque regression. Significant correlation between % change of PV and low-density lipoprotein cholesterol (LDL-C) level was found in patients with DM (n=73, P<0.05, r=0.4), whereas there was no significant correlation between the 2 parameters in patients without DM (n=178).

CONCLUSIONS

The regression of coronary plaque induced by statin therapy after ACS was weaker in diabetic patients than their counterparts. Moreover, vigorous reduction of the LDL-C levels might induce a greater degree of plaque regression in ACS patients with DM.

Short Communication: Dating Components of Human Atherosclerotic Plaques

Rationale : Atherosclerotic plaques that give rise to acute clinical symptoms are typically characterized by degradation of the connective tissue and plaque rupture. Experimental studies have shown that mechanisms to repair vulnerable lesions exist, but the rate of remodeling of human plaque tissue has not been studied.

Objective : In the present study, we determined the biological age of different components of advanced human atherosclerotic plaques by analyzing tissue levels of 14 C released into the atmosphere during the nuclear weapons tests in the late 1950s and early 1960s.

Methods and Results : Atherosclerotic plaques were obtained from 10 patients (age 46 to 80 years) undergoing carotid surgery. Different regions of the plaques were dissected and analyzed for 14 C content using accelerator mass spectrometry. At the time of surgery, the mean biological age of the cap region was 6.4±3.2 years, which was significantly lower than that of the shoulder region (12.9±3.0 years, P <0.01), the interface toward the media (12.4±3.3 years, P <0.01), and the core (9.8±4.5 years, P <0.05). Analysis of proliferative activity and rate of apoptosis showed no signs of increased cellular turnover in the cap, suggesting that the lower 14 C content reflected a more recent time of formation.

Conclusions : These results show that the turnover time of human plaque tissue is very long and may explain why regression of atherosclerotic plaque size rarely is observed in cardiovascular intervention trials.

Resident peritoneal inflammatory cells are pivotal in the development of experimental atherosclerosis

AIM

Based on evidence that ionizing radiation can ameliorate chronic and autoimmune diseases in patients and experimental animals, we investigated the effects of radiation on the induction and development of experimental atherogenesis.

METHODS

Male New Zealand rabbits were divided into 5 groups and given an atherogenic diet for 90 days. Peritoneal and thoracic areas (9 Gy) were irradiated on the 1st and 45th days for groups 1 and 2, the 45th day for groups 3 and 4, and not at all for group 5. Prior to irradiation, the peritoneal cavity of animals from groups 1 and 3 was washed with buffered saline. Cells collected by peritoneal washing were reinfused into the peritoneal cavity of the same animal after irradiation. Animals from groups 2 and 4 were intraperitoneally injected with saline as a control.

RESULTS

Despite similar lipid profiles among the experimental groups, the percentage of aortas covered by plaques was remarkably reduced (p<0.001) among animals submitted to irradiation (groups 2 and 4). These differences were completely abolished in irradiated animals reconstituted with their own peritoneal cells.

CONCLUSIONS

These findings point to an important role of resident inflammatory peritoneal cells in experimental atherogenesis.

Inflammatory cell recruitment in cardiovascular disease: murine models and potential clinical applications

Atherosclerosis is the pathological process that underlies the development of cardiovascular disease, a leading cause of mortality. Atherosclerotic plaque formation is driven by the recruitment of inflammatory monocytes into the artery wall, their differentiation into macrophages and the subsequent transformation of macrophages into cholesterol-laden foam cells. Models of hypercholesterolaemia such as the ApoE (apolipoprotein E)-/- mouse and the application of transgenic technologies have allowed us to undertake a thorough dissection of the cellular and molecular biology of the atherosclerotic disease process. Murine models have emphasized the central role of inflammation in atherogenesis and have been instrumental in the identification of adhesion molecules that support monocyte recruitment, scavenger receptors that facilitate cholesterol uptake by macrophages and other macrophage activation receptors. The study of mice deficient in multiple members of the chemokine family, and their receptors, has shown that chemokines play a critical role in promoting atherosclerotic plaque formation. In the present review, we will discuss novel therapeutic avenues for the treatment of cardiovascular disease that derive directly from our current understanding of atherogenesis gained in experimental animal models.

A2A adenosine receptor stimulation decreases foam cell formation by enhancing ABCA1-dependent cholesterol efflux

Immune and inflammatory cells play a critical role in the pathogenesis of atherosclerotic plaques. We have demonstrated that A2ARs inhibit foam cell formation and stimulate production of ABCA1, the primary transporter of lipoproteins. We asked whether the effects of A2ARs on foam cell formation in vitro are mediated by transporters involved in reverse cholesterol transport, ABCA1 and ABCG1. Foam cells were generated from THP-1 cells by incubation with 100 nM PMA for 2 days and incubated with acLDL (50 microg/mL) plus IFN-gamma (500 U/mL) +/- A2AR agonist CGS-21680 (1 microM). Radiolabeled cholesterol (0.2 microCi/ml) was added to cells, and efflux was measured using a liquid scintillation counter. Lentiviral siRNA infection markedly reduces ABCA1 or ABCG1 mRNA in THP-1 cells. Despite diminished ABCG1 expression (KD), CGS-21680 inhibits foam cell formation (81+5% inhibition; P<0.0001 vs. IFN-gamma alone; n=3) but has no effect on foam cell formation in ABCA1 KD cells (5+3% inhibition; P<0.85 vs. IFN-gamma alone; n=3). The A2A agonist increases apoA-I-mediated cholesterol efflux nearly twofold in THP-1-derived macrophages (from 9.5% to 17.5+2.5% [3H]-cholesterol efflux; P<0.0090 vs. control; n=3) but not in ABCA1 KD cells. Activation of Epac, a signaling molecule downstream of the A2AR, increased ABCA1 (23+5%; P<0.0007 vs. control; n=3) and phospho-ABCA1 (13+5%; P<0.0003 vs. control; n=3) protein. These results demonstrate that A2AR occupancy diminishes foam cell formation by stimulating increased reverse cholesterol transport via ABCA1.

Macrophage death and defective inflammation resolution in atherosclerosis

A key event in atherosclerosis is a maladaptive inflammatory response to subendothelial lipoproteins. A crucial aspect of this response is a failure to resolve inflammation, which normally involves the suppression of inflammatory cell influx, effective clearance of apoptotic cells and promotion of inflammatory cell egress. Defects in these processes promote the progression of atherosclerotic lesions into dangerous plaques, which can trigger atherothrombotic vascular disease, the leading cause of death in industrialized societies. In this Review I provide an overview of these concepts, with a focus on macrophage death and defective apoptotic cell clearance, and discuss new therapeutic strategies designed to boost inflammation resolution in atherosclerosis.

Moderate kidney disease inhibits atherosclerosis regression

Chronic kidney disease (CKD) accelerates cardiovascular disease. The mechanisms that explain this independent, excess risk associated with CKD have not been fully elucidated.

OBJECTIVES

We propose that impaired regression of atherosclerosis in renal disease represents a novel risk factor for the heightened morbidity and mortality and resistance to treatment observed in patients with CKD.

METHODS AND RESULTS

Using a transplant model to study atherosclerosis regression, we transplanted atheromatous aortic segments generated in Apolipoprotein E knock-out (ApoE(-/-)) mice, into either control or moderately uremic, normolipidemic, wild-type mice. In non-uremic mice, lesions regressed 55%, whereas lesions in uremic mice increased in size by 17% (p<0.01 for control vs. uremic). The lesions in uremic mice were also characterized by a greater presence of macrophages (36,300 microm(2) vs. 12,600 microm(2), p<0.01). This finding was despite upregulation of chemokine receptor 7 (CCR7), normally a migration factor, in uremic lesion macrophages. Gene expression analysis of lesion macrophages showed relative down-regulation of serum response factor (SRF) target genes in the uremic group, consistent with impaired CCR7 signaling.

CONCLUSION

Moderate kidney disease inhibits regression of atherosclerosis in a mouse transplant model. This inhibition may be a result of impaired CCR7 signaling.

Macrophage apoptosis in advanced atherosclerosis

Plaque necrosis in advanced atheromata, which triggers acute atherothrombotic vascular events, is caused by the apoptosis of lesional macrophages coupled with defective phagocytic clearance of the dead cells. The central enabling event in macrophage apoptosis relevant to advanced atherosclerosis is the unfolded protein response (UPR), an endoplasmic reticulum (ER) stress pathway. The UPR effector CHOP (GADD153) amplifies release of ER Ca(2+) stores, which activates a central integrator of apoptosis signaling, calcium/calmodulin-dependent protein kinase II (CaMKII). CaMKII, in turn, leads to activation of pro-apoptotic STAT1, induction of the death receptor Fas, and stimulation of the mitochondria-cytochrome c pathway of apoptosis. While these pathways are necessary for apoptosis, apoptosis occurs only when the cells are also exposed to one or more additional "hits." These hits amplify pro-apoptotic pathways and/or suppress compensatory cell-survival pathways. A second hit relevant to atherosclerosis is activation of pattern recognition receptors (PRRs), such as scavenger and toll-like receptors. In vivo relevance is suggested by the fact that advanced human lesions express markers of UPR activation that correlate closely with the degree of plaque vulnerability and macrophage apoptosis. Moreover, studies with genetically altered mice have shown that ER stress and PRR activation are causative for advanced lesional macrophage apoptosis and plaque necrosis. In summary, a key cellular event in the conversion of benign to vulnerable atherosclerotic plaques is ER stress-induced macrophage apoptosis. Further understanding of the mechanisms and consequences of this event may lead to novel therapies directed at preventing the clinical progression of atheromata.

Macrophages create an acidic extracellular hydrolytic compartment to digest aggregated lipoproteins

A critical event in atherogenesis is the interaction of macrophages with subendothelial lipoproteins. Although most studies model this interaction by incubating macrophages with monomeric lipoproteins, macrophages in vivo encounter lipoproteins that are aggregated. The physical features of the lipoproteins require distinctive mechanisms for their uptake. We show that macrophages create an extracellular, acidic, hydrolytic compartment to carry out digestion of aggregated low-density lipoproteins. We demonstrate delivery of lysosomal contents to these specialized compartments and their acidification by vacuolar ATPase, enabling aggregate catabolism by lysosomal acid hydrolases. We observe transient sealing of portions of the compartments, allowing formation of an "extracellular" proton gradient. An increase in free cholesterol is observed in aggregates contained in these compartments. Thus, cholesteryl ester hydrolysis can occur extracellularly in a specialized compartment, a lysosomal synapse, during the interaction of macrophages with aggregated low-density lipoprotein. A detailed understanding of these processes is essential for developing strategies to prevent atherosclerosis.

[Comparative analysis of lower extremities tissue perfusion by the use of perfusion scintigraphy method after hyperbaric oxygenation and lumbar sympathectomy]

BACKGROUND/AIM

Lumbar sympathectomy (LS) increases pheripheral blood flow primarily by the arteriolar vasodilatation within the skin vascular net. Increase in tissue nutrition takes place only in the distal blood vessels of the skin. Nevertheless, in some patients sympathectomy brings about improvement in ischemic ulcerations healing. Hyperbaric oxigenation (HBO) is a medical treatment in which a patient breathes 100% oxygen under pressure higher than atmospheric implemented in special units allowing the whole body be in a chamber. The aim of the study was to determine efficacy of the applied therapies for the treatment of inoperable occlussive lower extremities (LE) arteries diseases according to the obtained results.

METHODS

The study included 30 patients divided into two grups (15 patients each) in which stenosis level of the lower extremities arteries had been determined using aortography due to further treatment with HBO and LS. All the patients were clinically examined, their objective condition evaluation based on claudication distance, pain in rest, skin and skin adnexa atrophy, and temperature and LE functionality, as well as exposed to perfusion scintigraphy prior to the treatment and within 30 days after the treatment finishing.

RESULTS

Analysing patients' status prior to and after the treatments applied the number of patients with obvious improvement was higher in those treated by HBO than those treated by LS. Measuring claudication distance revealed significantly greater changes in patients treated by HBO (from 178.57 m to 754.76 m) than in those treated by LS (from 229 m to 253 m). Other clinical symptoms, such as parasthesia, status of the skin adnexes (hair, nails), skin colour and temperature were also improved after the treatment by HBO.

CONCLUSION

The results obtained in this study confirm the advantages of HBO over LS in therapy of inoperable occlussive LE disease, so LS could be definitely abandoned as a choice for treating such disease.

Effects of cardiovascular lifestyle change on lipoprotein subclass profiles defined by nuclear magnetic resonance spectroscopy

Background

Low-density lipoprotein (LDL) cholesterol lowering is a primary goal in clinical management of patients with cardiovascular disease, but traditional cholesterol levels may not accurately reflect the true atherogenicity of plasma lipid profiles. The size and concentration of lipoprotein particles, which transport cholesterol and triglycerides, may provide additional information for accurately assessing cardiovascular risk. This study evaluated changes in plasma lipoprotein profiles determined by nuclear magnetic resonance (NMR) spectroscopy in patients participating in a prospective, nonrandomized lifestyle modification program designed to reverse or stabilize progression of coronary artery disease (CAD) to improve our understanding of lipoprotein management in cardiac patients.

Results

The lifestyle intervention was effective in producing significant changes in lipoprotein subclasses that contribute to CAD risk. There was a clear beneficial effect on the total number of LDL particles (-8.3%, p < 0.05 compared to matched controls), small dense LDL particles (-9.5%, p < 0.05), and LDL particle size (+0.8%; p < 0.05). Likewise, participants showed significant improvement in traditional CAD risk factors such as body mass index (-9.9%, p < 0.01 compared to controls), total cholesterol (-5.5%, p < 0.05), physical fitness (+37.2%, p < 0.01), and future risk for CAD (-7.9%, p < 0.01). Men and women responded differently to the program for all clinically-relevant variables, with men deriving greater benefit in terms of lipoprotein atherogenicity. Plasma lipid and lipoprotein responses to the lifestyle change program were not confounded by lipid-lowering medications.

Conclusion

In at risk patients motivated to participate, an intensive lifestyle change program can effectively alter traditional CAD risk factors and plasma lipoprotein subclasses and may reduce risk for cardiovascular events. Improvements in lipoprotein subclasses are more evident in men compared to women.

Lowering plasma cholesterol levels halts progression of aortic valve disease in mice

BACKGROUND

Treatment of hyperlipidemia produces functional and structural improvements in atherosclerotic vessels. However, the effects of treating hyperlipidemia on the structure and function of the aortic valve have been controversial, and any effects could be confounded by pleiotropic effects of hypolipidemic treatment. The goal of this study was to determine whether reducing elevated plasma lipid levels with a "genetic switch" in Reversa mice (Ldlr-/-/Apob(100/100)/Mttp(fl/fl)/Mx1-Cre+/+) reduces oxidative stress, reduces pro-osteogenic signaling, and retards the progression of aortic valve disease.

METHODS AND RESULTS

After 6 months of hypercholesterolemia, Reversa mice exhibited increases in superoxide, lipid deposition, myofibroblast activation, calcium deposition, and pro-osteogenic protein expression in the aortic valve. Maximum aortic valve cusp separation, as judged by echocardiography, was not altered. During an additional 6 months of hypercholesterolemia, superoxide levels, valvular lipid deposition, and myofibroblast activation remained elevated. Furthermore, calcium deposition and pro-osteogenic gene expression became more pronounced, and the aortic cusp separation decreased from 0.85+/-0.04 to 0.70+/-0.04 mm (mean+/-SE; P<0.05). Rapid normalization of cholesterol levels at 6 months of age (by inducing expression of Cre recombinase) normalized aortic valve superoxide levels, decreased myofibroblast activation, reduced valvular calcium burden, suppressed pro-osteogenic signaling cascades, and prevented reductions in aortic valve cusp separation.

CONCLUSIONS

Collectively, these data indicate that reducing plasma lipid levels by genetic inactivation of the mttp gene in hypercholesterolemic mice with early aortic valve disease normalizes oxidative stress, reduces pro-osteogenic signaling, and halts the progression of aortic valve stenosis.

Human carotid atherosclerotic plaque increases oxidative state of macrophages and low-density lipoproteins, whereas paraoxonase 1 (PON1) decreases such atherogenic effects

Human atherosclerotic plaque contains a variety of oxidized lipids, which can facilitate further oxidation. Paraoxonase 1 (PON1) is a high-density lipoprotein (HDL)-associated esterase (lipolactonase), exhibiting antiatherogenic properties. The aims of the present study were to examine the oxidizing potency of the human carotid plaque lipid extract (LE), and the antiatherogenic role of PON1 on LE oxidation competence. Human carotid plaques were extracted by organic solvent, and the extract was incubated with lipoprotein particles, with macrophages, or with probes sensitive to oxidative stress, with or without preincubation with PON1, followed by oxidative-stress assessment. Our findings imply that the LE oxidized LDL, macrophages, and exogenous probes and decreases HDL-mediated cholesterol efflux from macrophages, in a dose-dependent manner. Incubation of PON1 with LE significantly affects LE composition, reduces LE atherogenic properties, and decreases the extract's total peroxide concentration by 44%, macrophage oxidation by 25%, and probe oxidation by up to 52%. We conclude that these results expand our understanding of how the plaque itself accelerates atherogenesis and provides an important mechanism for attenuation of atherosclerosis development by the antioxidant action of PON1 on the atherosclerotic plaque.

Thieno[2,3-c]isoquinolin-5-one, a potent poly(ADP-ribose) polymerase inhibitor, promotes atherosclerotic plaque regression in high-fat diet-fed apolipoprotein E-deficient mice: effects on inflammatory markers and lipid content

We recently showed that poly(ADP-ribose) polymerase (PARP) is activated within atherosclerotic plaques in an animal model of atherosclerosis. Pharmacological inhibition of PARP or reduced expression in heterozygous animals interferes with atherogenesis and may promote factors of plaque stability, possibly reflecting changes in inflammatory and cellular factors consistent with plaque stability. The current study addresses the hypothesis that pharmacological inhibition of PARP promotes atherosclerotic plaque regression. Using a high-fat diet-induced atherosclerosis apolipoprotein E(-/-) mouse model, we demonstrate that administration of the potent PARP inhibitor, thieno[2,3-c]isoquinolin-5-one (TIQ-A), when combined with a regular diet regimen during treatment, induced regression of established plaques. Plaque regression was associated with a reduction in total cholesterol and low-density lipoproteins. Furthermore, plaques of TIQ-A-treated mice were highly enriched with collagen and smooth muscle cells, displayed thick fibrous caps, and exhibited a marked reduction in CD68-positive macrophage recruitment and associated foam cell presence. These changes correlated with a significant decrease in expression of monocyte chemoattractant protein-1 and intercellular cell adhesion molecule-1, potentially as a result of a robust reduction in tumor necrosis factor expression. The PARP inhibitor appeared to affect cholesterol metabolism by affecting acyl-coenzymeA/cholesterol acyltransferase-1 expression but exerted no effect on cholesterol influx or efflux as assessed by an examination of the ATP-binding cassette transporter-1 and the scavenger receptor-A expression levels in the different experimental groups. In accordance, PARP inhibition may prove beneficial not only in preventing atherogenesis but also in promoting regression of preexisting plaques.

Core2 1-6-N-glucosaminyltransferase-I is crucial for the formation of atherosclerotic lesions in apolipoprotein E-deficient mice

OBJECTIVE

Core2 1-6-N-glucosaminyltransferase-I (C2GlcNAcT-I) modification of adhesion molecules is required for optimal binding to target ligands. The objective of this study was to determine the role of C2GlcNAcT-I in the recruitment of Ly-6C(hi) monocytes to atherosclerotic lesions and in lesion formation in mice.

METHODS AND RESULTS

In a whole-blood binding assay, Ly-6C(hi) monocytes and certain lymphocytes and natural killer cells from wild-type mice bound to P- and E-selectin. C2GlcNAcT-I deficiency abrogated leukocyte binding to P- and E-selectin in this assay as well as in an in vitro flow chamber assay. Moreover, C2GlcNAcT-I deficiency decreased Ly-6C(hi) monocyte interactions with atherosclerotic arteries under physiological flow conditions and also inhibited monocyte recruitment to the peritoneal cavity in mice challenged with thioglycollate. In apolipoprotein E-deficient (apoE(-/-)) mice, lack of C2GlcNAcT-I resulted in fewer and smaller atherosclerotic lesions in mouse aortas. Atherosclerosis was also suppressed in C2GlcNAcT-I(-/-)/apoE(-/-) chimeric mice transplanted with C2GlcNAcT-I(+/+) bone marrow cells.

CONCLUSIONS

C2GlcNAcT-I in both leukocytes and blood vessel wall cells contributes to leukocyte recruitment to the arterial wall. C2GlcNAcT-I deficiency leads to the formation of small, macrophage-poor, and collagen-rich atherosclerotic lesions.

Molecular processes that handle -- and mishandle -- dietary lipids

Overconsumption of lipid-rich diets, in conjunction with physical inactivity, disables and kills staggering numbers of people worldwide. Recent advances in our molecular understanding of cholesterol and triglyceride transport from the small intestine to the rest of the body provide a detailed picture of the fed/fasted and active/sedentary states. Key surprises include the unexpected nature of many pivotal molecular mediators, as well as their dysregulation - but possible reversibility - in obesity, diabetes, inactivity, and related conditions. These mechanistic insights provide new opportunities to correct dyslipoproteinemia, accelerated atherosclerosis, insulin resistance, and other deadly sequelae of overnutrition and underexertion.

Emigration of monocyte-derived cells to lymph nodes during resolution of inflammation and its failure in atherosclerosis

PURPOSE OF REVIEW

This review compares the fate of monocyte-derived cells that enter atherosclerotic plaques with those that accumulate at other sites of inflammation.

RECENT FINDINGS

Resolution of inflammatory reactions involves emigration of monocyte-derived cells out of the inflamed site through nearby lymphatic vessels. However, this emigratory process associated with resolution is impaired in atherosclerosis. The mechanism for impeded emigration from plaques in vivo remains to be determined, but multiple factors are likely involved, including specialized properties of artery walls and a negative impact of lipid mediators on monocyte-derived cell migration.

SUMMARY

Impaired egress would be expected to compound macrophage accumulation within plaques, contribute to build-up of necrotic pools, and explain in part the reticence of many plaques to regress, or resolve. Restoration of the capacity of monocyte-derived cells to leave plaques would, by contrast, be expected to facilitate regression, but it remains to be determined whether restoring egress may sometimes provoke unwanted outcomes as well.