Pulling down the plug on atherosclerosis: finding the culprit in your heart

Peroxisome proliferator-activated receptor δ improves the features of atherosclerotic plaque vulnerability by regulating smooth muscle cell phenotypic switching

BACKGROUND AND PURPOSE

Vascular smooth muscle cells (SMCs) undergo phenotypic switching during sustained inflammation, contributing to an unfavourable atherosclerotic plaque phenotype. PPARδ plays an important role in regulating SMC functions; however, its role in atherosclerotic plaque vulnerability remains unclear. Here, we explored the pathological roles of PPARδ in atherosclerotic plaque vulnerability in severe atherosclerosis and elucidated the underlying mechanisms.

EXPERIMENTAL APPROACH

Plasma levels of PPARδ were measured in patients with acute coronary syndrome (ACS) and stable angina (SA). SMC contractile and synthetic phenotypic markers, endoplasmic reticulum (ER) stress, and features of atherosclerotic plaque vulnerability were analysed for the brachiocephalic artery of apolipoprotein E-knockout (ApoE-/- ) mice, fed a high-cholesterol diet (HCD) and treated with or without the PPARδ agonist GW501516. In vitro, the role of PPARδ was elucidated using human aortic SMCs (HASMCs).

KEY RESULTS

Patients with ACS had significantly lower plasma PPARδ levels than those with SA. GW501516 reduced atherosclerotic plaque vulnerability, a synthetic SMC phenotype, ER stress markers, and NLRP3 inflammasome expression in HCD-fed ApoE-/- mice. ER stress suppressed PPARδ expression in HASMCs. PPARδ activation inhibited ER stress-induced synthetic phenotype development, ER stress-NLRP3 inflammasome axis activation and matrix metalloproteinase 2 (MMP2) expression in HASMCs. PPARδ inhibited NFκB signalling and alleviated ER stress-induced SMC phenotypic switching.

CONCLUSIONS AND IMPLICATIONS

Low plasma PPARδ levels may be associated with atherosclerotic plaque vulnerability. Our findings provide new insights into the mechanisms underlying the protective effect of PPARδ on SMC phenotypic switching and improvement the features of atherosclerotic plaque vulnerability.

Anti-CXCR2 antibody-coated nanoparticles with an erythrocyte-platelet hybrid membrane layer for atherosclerosis therapy

Atherosclerosis is the leading cause of mortality globally. RBC-platelet hybrid membrane-coated nanoparticles ([RBC-P]NPs), which biologically mimic platelets in vivo, display evidence of anti-atherosclerotic activity. The efficacy of a targeted RBC-platelet hybrid membrane-coated nanoparticles ([RBC-P]NP)-based approach was investigated as a primary preventive measure against atherosclerosis. A ligand-receptor interactome analysis conducted with circulating platelets and monocytes derived from CAD patients and healthy controls identified CXCL8-CXCR2 as a key platelet ligand-monocyte receptor dyad in CAD patients. Based on this analysis, a novel anti-CXCR2 [RBC-P]NP that specifically binds to CXCR2 and blocks the interaction between CXCL8 and CXCR2 was engineered and characterized. Administering anti-CXCR2 [RBC-P]NPs to Western diet-fed Ldlr^-/- mice led to diminished plaque size, necrosis, and intraplaque macrophage accumulation relative to control [RBC-P]NPs or vehicle. Importantly, anti-CXCR2 [RBC-P]NPs demonstrated no adverse bleeding/hemorrhagic effects. A series of in vitro experiments was conducted to characterize anti-CXCR2 [RBC-P]NP's mechanism of action in plaque macrophages. Mechanistically, anti-CXCR2 [RBC-P]NPs inhibited p38α (Mapk14)-mediated, pro-inflammatory M1 skewing and corrected efferocytosis in plaque macrophages. This targeted [RBC-P]NP-based approach, in which the cardioprotective effects of anti-CXCR2 [RBC-P]NP therapy overweighs its bleeding/hemorrhagic risks, could potentially be used to proactively manage atherosclerotic progression in at-risk populations.

Defective efferocytosis of vascular cells in heart disease

The efficient phagocytic clearance of dying cells and apoptotic cells is one of the processes that is essential for the maintenance of physiologic tissue function and homeostasis, which is termed "efferocytosis." Under normal conditions, "find me" and "eat me" signals are released by apoptotic cells to stimulate the engulfment and efferocytosis of apoptotic cells. In contrast, abnormal efferocytosis is related to chronic and non-resolving inflammatory diseases such as atherosclerosis. In the initial steps of atherosclerotic lesion development, monocyte-derived macrophages display efficient efferocytosis that restricts plaque progression; however, this capacity is reduced in more advanced lesions. Macrophage reprogramming as a result of the accumulation of apoptotic cells and augmented inflammation accounts for this diminishment of efferocytosis. Furthermore, defective efferocytosis plays an important role in necrotic core formation, which triggers plaque rupture and acute thrombotic cardiovascular events. Recent publications have focused on the essential role of macrophage efferocytosis in cardiac pathophysiology and have pointed toward new therapeutic strategies to modulate macrophage efferocytosis for cardiac tissue repair. In this review, we discuss the molecular and cellular mechanisms that regulate efferocytosis in vascular cells, including macrophages and other phagocytic cells and detail how efferocytosis-related molecules contribute to the maintenance of vascular hemostasis and how defective efferocytosis leads to the formation and progression of atherosclerotic plaques.

Potential Role of Protein Kinase C in the Pathophysiology of Diabetes-Associated Atherosclerosis

Diabetes mellitus is a metabolic syndrome that affects millions of people worldwide. Recent studies have demonstrated that protein kinase C (PKC) activation plays an important role in hyperglycemia-induced atherosclerosis. PKC activation is involved in several cellular responses such as the expression of various growth factors, activation of signaling pathways, and enhancement of oxidative stress in hyperglycemia. However, the role of PKC activation in pro-atherogenic and anti-atherogenic mechanisms remains controversial, especially under hyperglycemic condition. In this review, we discuss the role of different PKC isoforms in lipid regulation, oxidative stress, inflammatory response, and apoptosis. These intracellular events are linked to the pathogenesis of atherosclerosis in diabetes. PKC deletion or treatment with PKC inhibitors has been studied in the regulation of atherosclerotic plaque formation and evolution. Furthermore, some preclinical and clinical studies have indicated that PKCβ and PKCδ are potential targets for the treatment of diabetic vascular complications. The current review summarizes these multiple signaling pathways and cellular responses regulated by PKC activation and the potential therapeutic targets of PKC in diabetic complications.

Platelet regulation of myeloid suppressor of cytokine signaling 3 accelerates atherosclerosis

Platelets are best known as mediators of hemostasis and thrombosis; however, their inflammatory effector properties are increasingly recognized. Atherosclerosis, a chronic vascular inflammatory disease, represents the interplay between lipid deposition in the artery wall and unresolved inflammation. Here, we reveal that platelets induce monocyte migration and recruitment into atherosclerotic plaques, resulting in plaque platelet-macrophage aggregates. In Ldlr ^-/- mice fed a Western diet, platelet depletion decreased plaque size and necrotic area and attenuated macrophage accumulation. Platelets drive atherogenesis by skewing plaque macrophages to an inflammatory phenotype, increasing myeloid suppressor of cytokine signaling 3 (SOCS3) expression and reducing the Socs1:Socs3 ratio. Platelet-induced Socs3 expression regulates plaque macrophage reprogramming by promoting inflammatory cytokine production (Il6, Il1b, and Tnfa) and impairing phagocytic capacity, dysfunctions that contribute to unresolved inflammation and sustained plaque growth. Translating our data to humans with cardiovascular disease, we found that women with, versus without, myocardial infarction have up-regulation of SOCS3, lower SOCS1:SOCS3, and increased monocyte-platelet aggregate. A second cohort of patients with lower extremity atherosclerosis demonstrated that SOCS3 and the SOCS1:SOCS3 ratio correlated with platelet activity and inflammation. Collectively, these data provide a causative link between platelet-mediated myeloid inflammation and dysfunction, SOCS3, and cardiovascular disease. Our findings define an atherogenic role of platelets and highlight how, in the absence of thrombosis, platelets contribute to inflammation.

Analysis of repeated leukocyte DNA methylation assessments reveals persistent epigenetic alterations after an incident myocardial infarction

Background

Most research into myocardial infarctions (MIs) have focused on preventative efforts. For survivors, the occurrence of an MI represents a major clinical event that can have long-lasting consequences. There has been little to no research into the molecular changes that can occur as a result of an incident MI. Here, we use three cohorts to identify epigenetic changes that are indicative of an incident MI and their association with gene expression and metabolomics.

Results

Using paired samples from the KORA cohort, we screened for DNA methylation loci (CpGs) whose change in methylation is potentially indicative of the occurrence of an incident MI between the baseline and follow-up exams. We used paired samples from the NAS cohort to identify 11 CpGs which were predictive in an independent cohort. After removing two CpGs associated with medication usage, we were left with an “epigenetic fingerprint” of MI composed of nine CpGs. We tested this fingerprint in the InCHIANTI cohort where it moderately discriminated incident MI occurrence (AUC = 0.61, P = 6.5 × 10⁻³). Returning to KORA, we associated the epigenetic fingerprint loci with cis-gene expression and integrated it into a gene expression-metabolomic network, which revealed links between the epigenetic fingerprint CpGs and branched chain amino acid (BCAA) metabolism.

Conclusions

There are significant changes in DNA methylation after an incident MI. Nine of these CpGs show consistent changes in multiple cohorts, significantly discriminate MI in independent cohorts, and were independent of medication usage. Integration with gene expression and metabolomics data indicates a link between MI-associated epigenetic changes and BCAA metabolism.

Electronic supplementary material

The online version of this article (10.1186/s13148-018-0588-7) contains supplementary material, which is available to authorized users.

Mitochondrial Oxidative Stress Promotes Atherosclerosis and Neutrophil Extracellular Traps in Aged Mice

RATIONALE

Mitochondrial oxidative stress (mitoOS) has been shown to be increased in various cell types in human atherosclerosis and with aging. However, the role of cell type-specific mitoOS in atherosclerosis in the setting of advanced age and the molecular mechanisms remains to be determined in vivo.

OBJECTIVE

The aim of this study was to examine the role of myeloid cell mitoOS in atherosclerosis in aged mice.

APPROACH AND RESULTS

Lethally irradiated low-density lipoprotein receptor-deficient mice (Ldlr^-/-) were reconstituted with bone marrow from either wild-type or mitochondrial catalase (mCAT) mice. mCAT transgenic mice contain ectopically expressed human catalase gene in mitochondria, which reduces mitoOS. Starting at the age of 36 weeks, mice were fed the Western-type diet for 16 weeks. We found that mitoOS in lesional myeloid cells was suppressed in aged mCAT→Ldlr^-/- chimeric mice compared with aged controls, and this led to a significant reduction in aortic root atherosclerotic lesion area despite higher plasma cholesterol levels. Neutrophil extracellular traps (NETs), a proinflammatory extracellular structure that contributes to atherosclerosis progression, were significantly increased in the lesions of aged mice compared with lesions of younger mice. Aged mCAT→Ldlr^-/- mice had less lesional neutrophils and decreased NETs compared with age-matched wild-type→Ldlr^-/- mice, whereas young mCAT→ and wild-type→Ldlr^-/- mice had comparable numbers of neutrophils and similar low levels of lesional NETs. Using cultured neutrophils, we showed that suppression of mitoOS reduced 7-ketocholesterol-induced NET release from neutrophils of aged but not younger mice.

CONCLUSIONS

MitoOS in lesional myeloid cells enhanced atherosclerosis development in aged mice, and this enhancement was associated with increased lesional NETs. Thus, mitoOS-induced NET formation is a potentially new therapeutic target to prevent atherosclerosis progression during aging.

The Role of Efferocytosis in Atherosclerosis

The necrotic core has long been a hallmark of the vulnerable atherosclerotic plaque. Although apoptotic cells are cleared quickly in almost all other tissue beds, their removal appears to be significantly impaired in the diseased blood vessel. Emerging evidence indicates that this phenomenon is caused by a defect in efferocytosis, the process by which apoptotic tissue is recognized for engulfment by phagocytic cells such as macrophages. Genetic and experimental data suggest that efferocytosis is impaired during atherogenesis caused by dysregulation of so-called eat me ligands, which govern the edibility of cells undergoing programmed cell death. The following is a summary of recent data indicating that efferocytosis is a major unappreciated driver of lesion expansion but also a reversible defect that can potentially be targeted as a means to prevent plaque progression.

A genome-wide trans-ethnic interaction study links the PIGR-FCAMR locus to coronary atherosclerosis via interactions between genetic variants and residential exposure to traffic

Air pollution is a worldwide contributor to cardiovascular disease mortality and morbidity. Traffic-related air pollution is a widespread environmental exposure and is associated with multiple cardiovascular outcomes such as coronary atherosclerosis, peripheral arterial disease, and myocardial infarction. Despite the recognition of the importance of both genetic and environmental exposures to the pathogenesis of cardiovascular disease, studies of how these two contributors operate jointly are rare. We performed a genome-wide interaction study (GWIS) to examine gene-traffic exposure interactions associated with coronary atherosclerosis. Using race-stratified cohorts of 538 African-Americans (AA) and 1562 European-Americans (EA) from a cardiac catheterization cohort (CATHGEN), we identify gene-by-traffic exposure interactions associated with the number of significantly diseased coronary vessels as a measure of chronic atherosclerosis. We found five suggestive (P<1x10^-5) interactions in the AA GWIS, of which two (rs1856746 and rs2791713) replicated in the EA cohort (P < 0.05). Both SNPs are in the PIGR-FCAMR locus and are eQTLs in lymphocytes. The protein products of both PIGR and FCAMR are implicated in inflammatory processes. In the EA GWIS, there were three suggestive interactions; none of these replicated in the AA GWIS. All three were intergenic; the most significant interaction was in a regulatory region associated with SAMSN1, a gene previously associated with atherosclerosis and B cell activation. In conclusion, we have uncovered several novel genes associated with coronary atherosclerosis in individuals chronically exposed to increased ambient concentrations of traffic air pollution. These genes point towards inflammatory pathways that may modify the effects of air pollution on cardiovascular disease risk.

Chronic intermittent hypoxia exposure-induced atherosclerosis: a brief review

Obstructive sleep apnea (OSA) is highly prevalent in the USA and is recognized as an independent risk factor for atherosclerotic cardiovascular disease. Identification of atherosclerosis risk factor attributable to OSA may provide opportunity to develop preventive measures for cardiovascular risk reduction. Chronic intermittent hypoxia (CIH) is a prominent feature of OSA pathophysiology and may be a major mechanism linking OSA to arteriosclerosis. Animal studies demonstrated that CIH exposure facilitated high-cholesterol diet (HCD)-induced atherosclerosis, accelerated the progression of existing atherosclerosis, and induced atherosclerotic lesions in the absence of other atherosclerosis risk factors, demonstrating that CIH is an independent causal factor of atherosclerosis. Comparative studies revealed major differences between CIH-induced and the classic HCD-induced atherosclerosis. Systemically, CIH was a much weaker inducer of atherosclerosis. CIH and HCD differentially activated inflammatory pathways. Histologically, CIH-induced atherosclerotic plaques had no clear necrotic core, contained a large number of CD31+ endothelial cells, and had mainly elastin deposition, whereas HCD-induced plaques had typical necrotic cores and fibrous caps, contained few endothelial cells, and had mainly collagen deposition. Metabolically, CIH caused mild, but HCD caused more severe dyslipidemia. Mechanistically, CIH did not, but HCD did, cause macrophage foam cell formation. NF-κB p50 gene deletion augmented CIH-induced, but not HCD-induced atherosclerosis. These differences reflect the intrinsic differences between the two types of atherosclerosis in terms of pathological nature and underlying mechanisms and support the notion that CIH-induced atherosclerosis is a new paradigm that differs from the classic HCD-induced atherosclerosis.

Association of Roadway Proximity with Fasting Plasma Glucose and Metabolic Risk Factors for Cardiovascular Disease in a Cross-Sectional Study of Cardiac Catheterization Patients

BACKGROUND

The relationship between traffic-related air pollution (TRAP) and risk factors for cardiovascular disease needs to be better understood in order to address the adverse impact of air pollution on human health.

OBJECTIVE

We examined associations between roadway proximity and traffic exposure zones, as markers of TRAP exposure, and metabolic biomarkers for cardiovascular disease risk in a cohort of patients undergoing cardiac catheterization.

METHODS

We performed a cross-sectional study of 2,124 individuals residing in North Carolina (USA). Roadway proximity was assessed via distance to primary and secondary roadways, and we used residence in traffic exposure zones (TEZs) as a proxy for TRAP. Two categories of metabolic outcomes were studied: measures associated with glucose control, and measures associated with lipid metabolism. Statistical models were adjusted for race, sex, smoking, body mass index, and socioeconomic status (SES).

RESULTS

An interquartile-range (990 m) decrease in distance to roadways was associated with higher fasting plasma glucose (β = 2.17 mg/dL; 95% CI: -0.24, 4.59), and the association appeared to be limited to women (β = 5.16 mg/dL; 95% CI: 1.48, 8.84 compared with β = 0.14 mg/dL; 95% CI: -3.04, 3.33 in men). Residence in TEZ 5 (high-speed traffic) and TEZ 6 (stop-and-go traffic), the two traffic zones assumed to have the highest levels of TRAP, was positively associated with high-density lipoprotein cholesterol (HDL-C; β = 8.36; 95% CI: -0.15, 16.9 and β = 5.98; 95% CI: -3.96, 15.9, for TEZ 5 and 6, respectively).

CONCLUSION

Proxy measures of TRAP exposure were associated with intermediate metabolic traits associated with cardiovascular disease, including fasting plasma glucose and possibly HDL-C.

Osteoporosis Is Associated With High Risk for Coronary Heart Disease: A Population-Based Cohort Study

We employed a population-based cohort sample to explore the risk of coronary heart disease (CHD) in relation to osteoporosis in an Asian population.We designed a retrospective population-based cohort study from 2000 to 2010 with data obtained from Taiwan's Longitudinal Health Insurance Database. A total of 19,456 patients aged 45 years or older who had no history of CHD and had a diagnosis of osteoporosis were identified as the osteoporosis cohort. The patients in the comparison cohort were randomly selected and frequency matched according to age, sex, and year of index date at a 1:1 ratio. Both cohorts were followed from the index date until a new diagnosis of CHD was made. Baseline variables, comorbidities, and bisphosphonate and estrogen prescriptions were collected.The overall incidence of CHD was 23.5 (per 1000 person-years) for the osteoporosis cohort and 16.7 for the comparison cohort, with a mean follow-up of 6.54 years and 6.63 years, respectively. The hazard ratio (HR) for developing CHD during follow-up was 1.30 (95% confidence interval [CI], 1.23-1.38) for the osteoporosis cohort compared with the comparison cohort after adjusting for age, sex, comorbidities, and estrogen medication. Patients with osteoporosis who received treatment with bisphosphonates or with both bisphosphonates and estrogen exhibited a significantly lower risk for CHD (adjusted HR = 0.37 and 0.23) than those who did not receive either of these 2 medications.The results support an association between osteoporosis and CHD in Asian population.

ADAM-10 could mediate cleavage of N-cadherin promoting apoptosis in human atherosclerotic lesions leading to vulnerable plaque: a morphological and immunohistochemical study

Atherosclerosis remains a major cause of mortality. Whereas the histopathological progression of atherosclerotic lesions is well documented, much less is known about the development of unstable or vulnerable plaque, which can rupture leading to thrombus, luminal occlusion and infarct. Apoptosis in the fibrous cap, which is rich in vascular smooth muscle cells (VSMCs) and macrophages, and its subsequent weakening or erosion seems to be an important regulator of plaque stability. The aim of our study was to improve our knowledge on the biological mechanisms that cause plaque instability in order to develop new therapies to maintain atherosclerotic plaque stability and avoid its rupture. In our study, we collected surgical specimens from atherosclerotic plaques in the right or left internal carotid artery of 62 patients with evident clinical symptoms. Histopathology and histochemistry were performed on wax-embedded sections. Immunohistochemical localization of caspase-3, N-cadherin and ADAM-10 was undertaken in order to highlight links between apoptosis, as expressed by caspase-3 immunostaining, and possible roles of N-cadherin, a cell-cell junction protein in VSMCs and macrophages that provides a pro-survival signal reducing apoptosis, and ADAM-10, a "disintegrin and metalloproteases" that is able to cleave N-cadherin in glioblastomas. Our results showed that when apoptosis, expressed by caspase-3 immunostaining, increased in the fibrous cap, rich in VSMCs and macrophages, the expression of N-cadherin decreased. The decreased N-cadherin expression, in turn, was linked to increased ADAM-10 expression. This study shows that apoptotic events are probably involved in the vulnerability of atherosclerotic plaque.

Extension of the mitochondria dysfunction hypothesis of metabolic syndrome to atherosclerosis with emphasis on the endocrine-disrupting chemicals and biophysical laws

Metabolic syndrome and its component phenotypes, hyperglycemia, hypertension, (abdominal) obesity and hypertriglyceridemia, are major risk factors for atherosclerosis. Recently, associations between exposure to endocrine‐disrupting chemicals (EDCs), mitochondrial dysfunction, metabolic syndrome and atherosclerosis have been established, suggesting a possible common mechanism underlying these phenomena. Extending a previously proposed mitochondria dysfunction theory of metabolic syndrome and using biophysical laws, such as metabolic scaling, Murray's law and fractal geometry of the vascular branching system, we propose that atherosclerosis could be explained as an ill‐adaptive change occurring in nutrient‐supplying arteries in response to the decreasing tissue energy demand caused by tissue mitochondrial dysfunction. Various aspects of this new hypothesis are discussed.

Biomechanical regulation of vascular smooth muscle cell functions: from in vitro to in vivo understanding

Vascular smooth muscle cells (VSMCs) have critical functions in vascular diseases. Haemodynamic factors are important regulators of VSMC functions in vascular pathophysiology. VSMCs are physiologically active in the three-dimensional matrix and interact with the shear stress sensor of endothelial cells (ECs). The purpose of this review is to illustrate how haemodynamic factors regulate VSMC functions under two-dimensional conditions in vitro or three-dimensional co-culture conditions in vivo. Recent advances show that high shear stress induces VSMC apoptosis through endothelial-released nitric oxide and low shear stress upregulates VSMC proliferation and migration through platelet-derived growth factor released by ECs. This differential regulation emphasizes the need to construct more actual environments for future research on vascular diseases (such as atherosclerosis and hypertension) and cardiovascular tissue engineering.

A novel mouse model of atherosclerotic plaque instability for drug testing and mechanistic/therapeutic discoveries using gene and microRNA expression profiling

RATIONALE

The high morbidity/mortality of atherosclerosis is typically precipitated by plaque rupture and consequent thrombosis. However, research on underlying mechanisms and therapeutic approaches is limited by the lack of animal models that reproduce plaque instability observed in humans.

OBJECTIVE

Development and use of a mouse model of plaque rupture that reflects the end stage of human atherosclerosis.

METHODS AND RESULTS

On the basis of flow measurements and computational fluid dynamics, we applied a tandem stenosis to the carotid artery of apolipoprotein E-deficient mice on high-fat diet. At 7 weeks postoperatively, we observed intraplaque hemorrhage in ≈50% of mice, as well as disruption of fibrous caps, intraluminal thrombosis, neovascularization, and further characteristics typically seen in human unstable plaques. Administration of atorvastatin was associated with plaque stabilization and downregulation of monocyte chemoattractant protein-1 and ubiquitin. Microarray profiling of mRNA and microRNA (miR) and, in particular, its combined analysis demonstrated major differences in the hierarchical clustering of genes and miRs among nonatherosclerotic arteries, stable, and unstable plaques and allows the identification of distinct genes/miRs, potentially representing novel therapeutic targets for plaque stabilization. The feasibility of the described animal model as a discovery tool was established in a pilot approach, identifying a disintegrin and metalloprotease with thrombospondin motifs 4 (ADAMTS4) and miR-322 as potential pathogenic factors of plaque instability in mice and validated in human plaques.

CONCLUSIONS

The newly described mouse model reflects human atherosclerotic plaque instability and represents a discovery tool toward the development and testing of therapeutic strategies aimed at preventing plaque rupture. Distinctly expressed genes and miRs can be linked to plaque instability.

Foam cell specific LXRα ligand

Objective

The liver X receptor α (LXRα) is a ligand-dependent nuclear receptor and the major regulator of reverse cholesterol transport in macrophages. This makes it an interesting target for mechanistic study and treatment of atherosclerosis.

Methods and Results

We optimized a promising stilbenoid structure (STX4) in order to reach nanomolar effective concentrations in LXRα reporter-gene assays. STX4 displayed the unique property to activate LXRα effectively but not its subtype LXRβ. The potential of STX4 to increase transcriptional activity as an LXRα ligand was tested with gene expression analyses in THP1-derived human macrophages and oxLDL-loaded human foam cells. Only in foam cells but not in macrophage cells STX4 treatment showed athero-protective effects with similar potency as the synthetic LXR ligand T0901317 (T09). Surprisingly, combinatorial treatment with STX4 and T09 resulted in an additive effect on reporter-gene activation and target gene expression. In physiological tests the cellular content of total and esterified cholesterol was significantly reduced by STX4 without the undesirable increase in triglyceride levels as observed for T09.

Conclusions

STX4 is a new LXRα-ligand to study transcriptional regulation of anti-atherogenic processes in cell or ex vivo models, and provides a promising lead structure for pharmaceutical development.

Molecular imaging to identify the vulnerable plaque--from basic research to clinical practice

Cardiovascular disease (CVD) is still the leading cause of death in the Western World. Adverse outcomes of CVD include stroke, myocardial infarction, and heart failure. Atherosclerosis is considered to be the major cause of CVD and is estimated to cause half of all deaths in developed countries. Atherosclerotic lesions of the vessel wall may obstruct blood flow mechanically through stenosis, but rupture of atherosclerotic plaques causing formation of occlusive thrombi is far more prevalent. Unfortunately, conventional diagnostic tools fail to assess whether a plaque is vulnerable to rupture. Research over the past decade identified the biological processes that are implicated in the course towards plaque rupture, like cell death and inflammation. Knowledge about plaque biology propelled the development of imaging techniques that target biologic processes in order to predict the vulnerable plaque. This paper discusses novel and existing molecular imaging targets and addresses advantages and disadvantages of these targets and respective imaging techniques in respect of clinical application and socio-economic impact.

Quantitation of acute necrosis after experimental myocardial infarction

Myocardial infarction (MI) is death and necrosis of myocardial tissue secondary to ischemia. MI is associated with adverse cardiac remodeling, progressive heart chamber dilation, ventricular wall thinning, and loss of cardiac function. Myocardial necrosis can be experimentally induced in rodents to simulate human MI by surgical occlusion of coronary arteries. When induced in knockout or transgenic mice, this model is useful for the identification of molecular modulators of cell death, cardiac remodeling, and preclinical therapeutic potential. Herein we outline in tandem, methods for microsurgical ligation of the left anterior descending artery followed by quantitation of myocardial necrosis. Necrosis is quantified after staining the heart with triphenyltetrazolium chloride.

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.

Annexin A5 prevents post-interventional accelerated atherosclerosis development in a dose-dependent fashion in mice

BACKGROUND

Activated cells in atherosclerotic lesions expose phosphatidylserine (PS) on their surface. Annexin A5 (AnxA5) binds to PS and is used for imaging atherosclerotic lesions. Recently, AnxA5 was shown to inhibit vascular inflammatory processes after vein grafting. Here, we report a therapeutic role for AnxA5 in post-interventional vascular remodeling in a mouse model mimicking percutaneous coronary intervention (PCI).

METHODS AND RESULTS

Associations between the rs4833229 (OR = 1.29 (CI 95%), p(allelic) = 0.011) and rs6830321 (OR = 1.35 (CI 95%), p(allelic) = 0.003) SNPs in the AnxA5 gene and increased restenosis-risk in patients undergoing PCI were found in the GENDER study. To evaluate AnxA5 effects on post-interventional vascular remodeling and accelerated atherosclerosis development in vivo, hypercholesterolemic ApoE(-/-) mice underwent femoral arterial cuff placement to induce intimal thickening. Dose-dependent effects were investigated after 3 days (effects on inflammation and leukocyte recruitment) or 14 days (effects on remodeling) after cuff placement. Systemically administered AnxA5 in doses of 0.1, 0.3 and 1.0mg/kg compared to vehicle reduced early leukocyte and macrophage adherence up to 48.3% (p = 0.001) and diminished atherosclerosis development by 71.2% (p = 0.012) with a reduction in macrophage/foam cell presence. Moreover, it reduced the expression of the endoplasmic reticulum stress marker GRP78/BiP, indicating lower inflammatory activity of the cells present.

CONCLUSIONS

AnxA5 SNPs could serve as markers for restenosis after PCI and AnxA5 therapeutically prevents vascular remodeling in a dose-dependent fashion, together indicating clinical potential for AnxA5 against post-interventional remodeling.

Insulin resistance, hyperglycemia, and atherosclerosis

Progress in preventing atherosclerotic coronary artery disease (CAD) has been stalled by the epidemic of type 2 diabetes. Further advances in this area demand a thorough understanding of how two major features of type 2 diabetes, insulin resistance and hyperglycemia, impact atherosclerosis. Insulin resistance is associated with systemic CAD risk factors, but increasing evidence suggests that defective insulin signaling in atherosclerotic lesional cells also plays an important role. The role of hyperglycemia in CAD associated with type 2 diabetes is less clear. Understanding the mechanisms whereby type 2 diabetes exacerbates CAD offers hope for new therapeutic strategies to prevent and treat atherosclerotic vascular disease.