Immune effector mechanisms implicated in atherosclerosis: from mice to humans

The influence of dysfunctional signaling and lipid homeostasis in mediating the inflammatory responses during atherosclerosis

Atherosclerosis, the underlying cause of myocardial infarction and thrombotic cerebrovascular events, is responsible for the majority of deaths in westernized societies. Mortality from this disease is also increasing at a marked rate in developing countries due to the acquisition of a westernized lifestyle accompanied with elevated rates of obesity and diabetes. Atherosclerosis is recognized as a chronic inflammatory disorder associated with lipid accumulation and the development of fibrotic plaques within the walls of medium and large arteries. A range of immune cells, such as macrophages and T-lymphocytes, through the action of various cytokines, such as interleukins-1 and -33, transforming growth factor-β and interferon-γ, orchestrates the inflammatory response in this disease. The disease is also characterized by marked dysfunction in lipid homeostasis and signaling pathways that control the inflammatory response. This review will discuss the molecular basis of atherosclerosis with particular emphasis on the roles of the immune cells and cytokines along with the dysfunctional lipid homeostasis and cell signaling associated with this disease.

Treatment with sulphated galactan inhibits macrophage chemotaxis and reduces intraplaque macrophage content in atherosclerotic mice

Experimental data from animal models and clinical studies support connections between the haemostasis and inflammation in atherogenesis. These interfaces among inflammation and thrombogenesis have been suggested as targets for pharmacological intervention to reduce disease progression. We hypothesize that the recently discovered antithrombotic drug Sulphated Galactan (SG) (isolated from the red marine alga Acanthophora muscoides) might reduce atherosclerotic plaque vulnerability and inflammatory gene expression in 10-week aged apolipoprotein E deficient (ApoE-/-) mice under high-cholesterol diet for additional 11weeks. Then, the underlying cellular mechanisms were investigated in vitro. SG (10mg/kg) or Vehicle was subcutaneously injected from week 6 until week 11 of the diet. Treatment with SG reduced intraplaque macrophage and Tissue Factor (TF) content as compared to Vehicle-treated animals. Intraplaque TF co-localized and positively correlated with macrophage rich-areas. No changes on atherosclerotic plaque size, and other intraplaque features of vulnerability (such as lipid, neutrophil, MMP-9 and collagen contents) were observed. Moreover, mRNA expression of MMPs, chemokines and genetic markers of Th1/2/reg/17 lymphocyte polarization within mouse aortic arches and spleens was not affected by SG treatment. In vitro, treatment with SG dose-dependently reduced macrophage chemotaxis without affecting TF production. Overall, the chronic SG treatment was well tolerated. In conclusion, our results indicate that SG treatment reduced intraplaque macrophage content (by impacting on cell recruitment) and, concomitantly, intraplaque TF content of potential macrophage origin in atherosclerotic mice.

The microbiota and microbiome in aging: potential implications in health and age-related diseases

Advances in bacterial deoxyribonucleic acid sequencing allow for characterization of the human commensal bacterial community (microbiota) and its corresponding genome (microbiome). Surveys of healthy adults reveal that a signature composite of bacteria characterizes each unique body habitat (e.g., gut, skin, oral cavity, vagina). A myriad of clinical changes, including a basal proinflammatory state (inflamm-aging), that directly interface with the microbiota of older adults and enhance susceptibility to disease accompany aging. Studies in older adults demonstrate that the gut microbiota correlates with diet, location of residence (e.g., community dwelling, long-term care settings), and basal level of inflammation. Links exist between the microbiota and a variety of clinical problems plaguing older adults, including physical frailty, Clostridium difficile colitis, vulvovaginal atrophy, colorectal carcinoma, and atherosclerotic disease. Manipulation of the microbiota and microbiome of older adults holds promise as an innovative strategy to influence the development of comorbidities associated with aging.

Targeting the adaptive immune system: new strategies in the treatment of atherosclerosis

Atherosclerosis is a lipid-driven chronic inflammatory disease of the arterial wall. Current treatment of atherosclerosis is focused on limiting its risk factors, such as hyperlipidemia or hypertension. However, treatments that target the inflammatory nature of atherosclerosis are still under development. Discovery of novel targets involved in the inflammation of the arterial wall creates opportunities to design new therapeutics that successfully modulate atherosclerosis. Here, we review drug targets that have proven to play pivotal roles in the adaptive immune system in atherosclerosis, and we discuss their potential as novel therapeutics.

Inflammatory bowel disease and risk of coronary heart disease

Emerging data have shown consistent evidence of an association between inflammation and development of atherosclerosis. Systemic autoimmune diseases are characterized by chronic inflammation and immune dysregulation, and diseases such as rheumatoid arthritis and lupus erythematosus are now commonly accepted to associate with development of cardiovascular disease, including coronary artery disease. However, the risk of cardiovascular disease in inflammatory bowel disease (IBD), a chronic inflammatory disease of the gut, is still unclear and the magnitude of a potentially increased risk is continuously debated. The aim of this review is to give an update on the existing literature on the association between inflammatory bowel disease and risk of cardiovascular disease, in particular coronary artery disease, and further to discuss traditional and non-traditional risk factors in patients with inflammatory bowel disease.

Co-morbidity and systemic inflammation as drivers of cognitive decline: new experimental models adopting a broader paradigm in dementia research

Dementia prevalence increases with age and Alzheimer’s disease (AD) accounts for up to 75% of cases. However, significant variability and overlap exists in the extent of amyloid-β and Tau pathology in AD and non-demented populations and it is clear that other factors must influence progression of cognitive decline, perhaps independent of effects on amyloid pathology. Coupled with the failure of amyloid-clearing strategies to provide benefits for AD patients, it seems necessary to broaden the paradigm in dementia research beyond amyloid deposition and clearance. Evidence has emerged from alternative animal model approaches as well as clinical and population epidemiological studies that co-morbidities contribute significantly to neurodegeneration/cognitive decline and systemic inflammation has been a strong common theme in these approaches. We hypothesise, and discuss in this review, that a disproportionate inflammatory response to infection, injury or chronic peripheral disease is a key determinant of cognitive decline. We propose that detailed study of alternative models, which encompass acute and chronic systemic inflammatory co-morbidities, is an important priority for the field and we examine the cognitive consequences of several of these alternative experimental approaches. Experimental models of severe sepsis in normal animals or moderate acute systemic inflammation in animals with existing neurodegenerative pathology have uncovered roles for inflammatory mediators interleukin-1β, tumour necrosis factor-α, inducible nitric oxide synthase, complement, prostaglandins and NADPH oxidase in inflammation-induced cognitive dysfunction and neuronal death. Moreover, microglia are primed by existing neurodegenerative pathology to produce exaggerated responses to subsequent stimulation with bacterial lipopolysaccharide or other inflammatory stimuli and these insults drive acute dysfunction and negatively affect disease trajectory. Chronic co-morbidities, such as arthritis, atherosclerosis, obesity and diabetes, are risk factors for subsequent dementia and those with high inflammatory status are particularly at risk. Models of chronic co-morbidities, and indeed low grade systemic inflammation in the absence of specific pathology, indicate that interleukin-1β, tumour necrosis factor-α and other inflammatory mediators drive insulin resistance, hypothalamic dysfunction, impaired neurogenesis and cognitive function and impact on functional decline. Detailed study of these pathways will uncover important mechanisms of peripheral inflammation-driven cognitive decline and are already driving clinical initiatives to mitigate AD progression through minimising systemic inflammation.

Inflammation and immunity in diseases of the arterial tree: players and layers

The hypothesis that immunity and inflammation participate in the pathogenesis of vascular diseases has now gained widespread recognition and stimulated work around the globe. Broadening knowledge has extended the recognition of the role of immune and inflammatory mechanisms to all of the layers of the artery, to all levels of the arterial tree, and implicated virtually all arms, cellular players, and effector molecules and pathways involved in these crucial host defenses, that turn against us in disease. We provide here a guide to a compendium series of articles that aimed to look forward and broaden the traditional focus of immunopathogenesis of arterial disease, with the goal of integrating the players and the layers involved. Although the field has advanced remarkably, much remains to be done, and this commentary also aims to highlight some of the gaps that future research should strive to close on the participation of inflammation and immunity in arterial diseases.

A prospective study of the incidence of myocarditis/pericarditis and new onset cardiac symptoms following smallpox and influenza vaccination

Background

Although myocarditis/pericarditis (MP) has been identified as an adverse event following smallpox vaccine (SPX), the prospective incidence of this reaction and new onset cardiac symptoms, including possible subclinical injury, has not been prospectively defined.

Purpose

The study’s primary objective was to determine the prospective incidence of new onset cardiac symptoms, clinical and possible subclinical MP in temporal association with immunization.

Methods

New onset cardiac symptoms, clinical MP and cardiac specific troponin T (cTnT) elevations following SPX (above individual baseline values) were measured in a multi-center prospective, active surveillance cohort study of healthy subjects receiving either smallpox vaccine or trivalent influenza vaccine (TIV).

Results

New onset chest pain, dyspnea, and/or palpitations occurred in 10.6% of SPX-vaccinees and 2.6% of TIV-vaccinees within 30 days of immunization (relative risk (RR) 4.0, 95% CI: 1.7-9.3). Among the 1081 SPX-vaccinees with complete follow-up, 4 Caucasian males were diagnosed with probable myocarditis and 1 female with suspected pericarditis. This indicates a post-SPX incidence rate more than 200-times higher than the pre-SPX background population surveillance rate of myocarditis/pericarditis (RR 214, 95% CI 65-558). Additionally, 31 SPX-vaccinees without specific cardiac symptoms were found to have over 2-fold increases in cTnT (>99th percentile) from baseline (pre-SPX) during the window of risk for clinical myocarditis/pericarditis and meeting a proposed case definition for possible subclinical myocarditis. This rate is 60-times higher than the incidence rate of overt clinical cases. No clinical or possible subclinical myocarditis cases were identified in the TIV-vaccinated group.

Conclusions

Passive surveillance significantly underestimates the true incidence of myocarditis/pericarditis after smallpox immunization. Evidence of subclinical transient cardiac muscle injury post-vaccinia immunization is a finding that requires further study to include long-term outcomes surveillance. Active safety surveillance is needed to identify adverse events that are not well understood or previously recognized.

The role of T and B cells in human atherosclerosis and atherothrombosis

Far from being merely a passive cholesterol accumulation within the arterial wall, the development of atherosclerosis is currently known to imply both inflammation and immune effector mechanisms. Adaptive immunity has been implicated in the process of disease initiation and progression interwined with traditional cardiovascular risk factors. Although the body of knowledge regarding the correlation between atherosclerosis and immunity in humans is growing rapidly, a relevant proportion of it derives from studies carried out in animal models of cardiovascular disease (CVD). However, while the mouse is a well-suited model, the results obtained therein are not fully transferrable to the human setting due to intrinsic genomic and environmental differences. In the present review, we will discuss mainly human findings, obtained either by examination of post-mortem and surgical atherosclerotic material or through the analysis of the immunological profile of peripheral blood cells. In particular, we will discuss the findings supporting a pro-atherogenic role of T cell subsets, such as effector memory T cells or the potential protective function of regulatory T cells. Recent studies suggest that traditional T cell-driven B2 cell responses appear to be atherogenic, while innate B1 cells appear to exert a protective action through the secretion of naturally occurring antibodies. The insights into the immune pathogenesis of atherosclerosis can provide new targets in the quest for novel therapeutic targets to abate CVD morbidity and mortality.

Free Light Chains in patients with acute coronary syndromes: Relationships to inflammation and renal function

AIMS

We assessed changes of serum combined free immunoglobulin light chains (cFLC) levels, which are associated with increased all-cause mortality, in ST-elevation myocardial infarction (STEMI) in relation to inflammation and renal function indices.

METHODS

cFLC were measured in 48 patients with STEMI on days 1, 3, 7 and 30 with assessment of their relationships with monocyte subsets, high sensitivity C-reactive protein (hsCRP), and cystatin C. Day 1 levels in STEMI patients were compared to 40 patients with stable coronary artery disease, and 37 healthy controls.

RESULTS

There were no significant differences in cFLC levels between the study groups. In STEMI patients, cFLC values peaked on day 7 post-MI and remained elevated on day 30 (p<0.001 vs. day 1 for both). hsCRP concentrations peaked on day 3 of STEMI followed by their gradual reduction to the levels seen in the controls (p<0.001). In STEMI cFLC correlated with cystatin C (r=0.55, p<0.001), and negatively correlated with counts of CD14++CD16- monocytes (r=-0.55, p<0.001). On multivariate Cox regression analysis, cFLC concentrations were associated with increased need for future percutaneous coronary intervention (PCI) (p=0.019).

CONCLUSION

cFLC levels increase during STEMI with peak values on day 7 after presentation and predict the need for future PCI.

Cryptotanshinone, an orally bioactive herbal compound from Danshen, attenuates atherosclerosis in apolipoprotein E-deficient mice: role of lectin-like oxidized LDL receptor-1 (LOX-1)

BACKGROUND AND PURPOSE

Cryptotanshinone (CTS) is a major bioactive diterpenoid isolated from Danshen, an eminent medicinal herb that is used to treat cardiovascular disorders in Asian medicine. However, it is not known whether CTS can prevent experimental atherosclerosis. The present study was designed to investigate the protective effects of CTS on atherosclerosis and its molecular mechanisms of action.

EXPERIMENTAL APPROACH

Apolipoprotein E-deficient (ApoE(-/-)) mice, fed an atherogenic diet, were dosed daily with CTS (15, 45 mg kg(-1) day(-1)) by oral gavage. In vitro studies were carried out in oxidized LDL (oxLDL)-stimulated HUVECs treated with or without CTS.

KEY RESULTS

CTS significantly attenuated atherosclerotic plaque formation and enhanced plaque stability in ApoE(-/-) mice by inhibiting the expression of lectin-like oxLDL receptor-1 (LOX-1) and MMP-9, as well as inhibiting reactive oxygen species (ROS) generation and NF-κB activation. CTS treatment significantly decreased the levels of serum pro-inflammatory mediators without altering the serum lipid profile. In vitro, CTS decreased oxLDL-induced LOX-1 mRNA and protein expression and, thereby, inhibited LOX-1-mediated adhesion of monocytes to HUVECs, by reducing the expression of adhesion molecules (intracellular adhesion molecule 1 and vascular cellular adhesion molecule 1). Furthermore, CTS inhibited NADPH oxidase subunit 4 (NOX4)-mediated ROS generation and consequent activation of NF-κB in HUVECs.

CONCLUSIONS AND IMPLICATIONS

CTS was shown to have anti-atherosclerotic activity, which was mediated through inhibition of the LOX-1-mediated signalling pathway. This suggests that CTS is a vasculoprotective drug that has potential therapeutic value for the clinical treatment of atherosclerotic cardiovascular diseases.

Caspase-1-mediated pathway promotes generation of thromboinflammatory microparticles

Extracellular ATP is a signal of tissue damage and induces macrophage responses that amplify inflammation and coagulation. Here we demonstrate that ATP signaling through macrophage P2X7 receptors uncouples the thioredoxin (TRX)/TRX reductase (TRXR) system and activates the inflammasome through endosome-generated ROS. TRXR and inflammasome activity promoted filopodia formation, cellular release of reduced TRX, and generation of extracellular thiol pathway-dependent, procoagulant microparticles (MPs). Additionally, inflammasome-induced activation of an intracellular caspase-1/calpain cysteine protease cascade degraded filamin, thereby severing bonds between the cytoskeleton and tissue factor (TF), the cell surface receptor responsible for coagulation activation. This cascade enabled TF trafficking from rafts to filopodia and ultimately onto phosphatidylserine-positive, highly procoagulant MPs. Furthermore, caspase-1 specifically facilitated cell surface actin exposure, which was required for the final release of highly procoagulant MPs from filopodia. Together, the results of this study delineate a thromboinflammatory pathway and suggest that components of this pathway have potential as pharmacological targets to simultaneously attenuate inflammation and innate immune cell-induced thrombosis.

Magnetoliposomes loaded with poly-unsaturated fatty acids as novel theranostic anti-inflammatory formulations

We describe the preparation, physico-chemical characterization and anti-inflammatory properties of liposomes containing the superparamagnetic nanoparticle Nanotex, the fluorescent dye Rhodamine-100 and omega-3 polyunsaturated fatty acid ethyl ester (ω-3 PUFA-EE), as theranostic anti-inflammatory agents. Liposomes were prepared after drying chloroform suspensions of egg phosphatidylcholine, hydration of the lipid film with aqueous phases containing or not Nanotex, Rhodamine-100 dye or ω-3 PUFA-EE, and eleven extrusion steps through nanometric membrane filters. This resulted in uniform preparations of liposomes of approximately 200 nm diameter. Extraliposomal contents were removed from the preparation by gel filtration chromatography. High Resolution Magic Angle Spinning ¹H NMR Spectroscopy of the liposomal preparations containing ω-3 PUFA-EE revealed well resolved ¹H resonances from highly mobile ω-3 PUFA-EE, suggesting the formation of very small (ca. 10 nm) ω-3 PUFA-EE nanogoticules, tumbling fast in the NMR timescale. Chloroform extraction of the liposomal preparations revealed additionally the incorporation of ω-3 PUFA-EE within the membrane domain. Water diffusion weighted spectra, indicated that the goticules of ω-3 PUFA-EE or its insertion in the membrane did not affect the average translational diffusion coefficient of water, suggesting an intraliposomal localization, that was confirmed by ultrafiltration. The therapeutic efficacy of these preparations was tested in two different models of inflammatory disease as inflammatory colitis or the inflammatory component associated to glioma development. Results indicate that the magnetoliposomes loaded with ω-3 PUFA-EE allowed MRI visualization in vivo and improved the outcome of inflammatory disease in both animal models, decreasing significantly colonic inflammation and delaying, or even reversing, glioma development. Together, our results indicate that magnetoliposomes loaded with ω-3 PUFA-EE may become useful anti-inflammatory agents for image guided drug delivery.

Cholesterol, inflammation and innate immunity

Hypercholesterolaemia leads to cholesterol accumulation in macrophages and other immune cells, which promotes inflammatory responses, including augmentation of Toll-like receptor (TLR) signalling, inflammasome activation, and the production of monocytes and neutrophils in the bone marrow and spleen. On a cellular level, activation of TLR signalling leads to decreased cholesterol efflux, which results in further cholesterol accumulation and the amplification of inflammatory responses. Although cholesterol accumulation through the promotion of inflammatory responses probably has beneficial effects in the response to infections, it worsens diseases that are associated with chronic metabolic inflammation, including atherosclerosis and obesity. Therapeutic interventions such as increased production or infusion of high-density lipoproteins may sever the links between cholesterol accumulation and inflammation, and have beneficial effects in patients with metabolic diseases.

IRF5 deficiency ameliorates lupus but promotes atherosclerosis and metabolic dysfunction in a mouse model of lupus-associated atherosclerosis

Premature atherosclerosis is a severe complication of lupus and other systemic autoimmune disorders. Gain-of-function polymorphisms in IFN regulatory factor 5 (IRF5) are associated with an increased risk of developing lupus, and IRF5 deficiency in lupus mouse models ameliorates disease. However, whether IRF5 deficiency also protects against atherosclerosis development in lupus is not known. In this study, we addressed this question using the gld.apoE(-/-) mouse model. IRF5 deficiency markedly reduced lupus disease severity. Unexpectedly, despite the reduction in systemic immune activation, IRF5-deficient mice developed increased atherosclerosis and also exhibited metabolic dysregulation characterized by hyperlipidemia, increased adiposity, and insulin resistance. Levels of the atheroprotective cytokine IL-10 were reduced in aortae of IRF5-deficient mice, and in vitro studies demonstrated that IRF5 is required for IL-10 production downstream of TLR7 and TLR9 signaling in multiple immune cell types. Chimera studies showed that IRF5 deficiency in bone marrow-derived cells prevents lupus development and contributes in part to the increased atherosclerosis. Notably, IRF5 deficiency in non-bone marrow-derived cells also contributes to the increased atherosclerosis through the generation of hyperlipidemia and increased adiposity. Together, our results reveal a protective role for IRF5 in lupus-associated atherosclerosis that is mediated through the effects of IRF5 in both immune and nonimmune cells. These findings have implications for the proposed targeting of IRF5 in the treatment of autoimmune disease as global IRF5 inhibition may exacerbate cardiovascular disease in these patients.

Towards a molecular systems model of coronary artery disease

Coronary artery disease (CAD) is a complex disease driven by myriad interactions of genetics and environmental factors. Traditionally, studies have analyzed only 1 disease factor at a time, providing useful but limited understanding of the underlying etiology. Recent advances in cost-effective and high-throughput technologies, such as single nucleotide polymorphism (SNP) genotyping, exome/genome/RNA sequencing, gene expression microarrays, and metabolomics assays have enabled the collection of millions of data points in many thousands of individuals. In order to make sense of such 'omics' data, effective analytical methods are needed. We review and highlight some of the main results in this area, focusing on integrative approaches that consider multiple modalities simultaneously. Such analyses have the potential to uncover the genetic basis of CAD, produce genomic risk scores (GRS) for disease prediction, disentangle the complex interactions underlying disease, and predict response to treatment.

Use of Mouse Models in Atherosclerosis Research

Cardiovascular disease is the major cause of death in most developed nations and the social and economic burden of this disease is quite high. Atherosclerosis is a major underlying basis for most cardiovascular diseases including myocardial infarction and stroke. Genetically modified mouse models, particularly mice deficient in apoprotein E or the LDL receptor, have been widely used in preclinical atherosclerosis studies to gain insight into the mechanisms underlying this pathology. This chapter reviews several mouse models of atherosclerosis progression and regression as well as the role of immune cells in disease progression and the genetics of murine atherogenesis.

Lymphatic vessels: an emerging actor in atherosclerotic plaque development

BACKGROUND

Atherosclerosis is a chronic inflammatory disease of large- to medium-sized arteries and is the main underlying cause of death worldwide. The lymphatic vasculature is critical for processes that are intimately linked to atherogenesis such as the immune response and cholesterol metabolism. However, whether lymphatic vessels truly contribute to the pathogenesis of atherosclerosis is less clear despite increasing research efforts in this field.

DESIGN

PubMed and Ovid MEDLINE databases were searched. In addition, key review articles were screened for relevant original publications.

RESULTS

Current knowledge about lymphatic vessels in the arterial wall came from studies that examined the presence and location of such vessels in human atherosclerotic plaque specimens, as well as in a variety of arteries in animal models for atherosclerosis (e.g. rabbits, dogs, rats and mice). Generally, three experimental approaches have been used to investigate the functional role of plaque-associated lymphatic vessels; experimental lymphostasis was used to investigate lymphatic drainage of the arterial wall, and more recently, studies with genetic interventions and/or surgical transplantation have been performed.

CONCLUSIONS

Lymphatic vessels seem to be mostly present in the adventitial layer of the arterial walls of animals and humans. They are involved in reverse cholesterol transport from atherosclerotic lesions, and arteries with a dense lymphatic network seem naturally protected against atherosclerosis. Lymphangiogenesis is a process that is an important part of the inflammatory loop in atherosclerosis. However, how augmenting or impeding the distribution of lymphatic vessels impacts disease progression remains to be investigated in future studies.

Proteasome-mediated reduction in proapoptotic molecule Bim renders CD4⁺CD28null T cells resistant to apoptosis in acute coronary syndrome

BACKGROUND

The number of CD4(+)CD28(null) (CD28(null)) T cells, a unique subset of T lymphocytes with proinflammatory and cell-lytic phenotype, increases markedly in patients with acute coronary syndrome (ACS). ACS patients harboring high numbers of CD28(null) T cells have increased risk of recurrent severe acute coronary events and unfavorable prognosis. The mechanisms that govern the increase in CD28(null) T cells in ACS remain elusive. We investigated whether apoptosis pathways regulating T-cell homeostasis are perturbed in CD28(null) T cells in ACS.

METHODS AND RESULTS

We found that CD28(null) T cells in ACS were resistant to apoptosis induction via Fas-ligation or ceramide. This was attributable to a dramatic reduction in proapoptotic molecules Bim, Bax, and Fas in CD28(null) T cells, whereas antiapoptotic molecules Bcl-2 and Bcl-xL were similar in CD28(null) and CD28(+) T cells. We also show that Bim is phosphorylated in CD28(null) T cells and degraded by the proteasome. Moreover, we demonstrate for the first time that proteasomal inhibition restores the apoptosis sensitivity of CD28(null) T cells in ACS.

CONCLUSIONS

We show that CD28(null) T cells in ACS harbor marked defects in molecules that regulate T-cell apoptosis, which tips the balance in favor of antiapoptotic signals and endows these cells with resistance to apoptosis. We demonstrate that the inhibition of proteasomal activity allows CD28(null) T cells to regain sensitivity to apoptosis. A better understanding of the molecular switches that control the apoptosis sensitivity of CD28(null) T cells may reveal novel strategies for targeted elimination of these T cells in ACS patients.

Circulating microparticles carry oxidation-specific epitopes and are recognized by natural IgM antibodies

Oxidation-specific epitopes (OSEs) present on apoptotic cells and oxidized low density lipoprotein (OxLDL) represent danger-associated molecular patterns that are recognized by different arcs of innate immunity, including natural IgM antibodies. Here, we investigated whether circulating microparticles (MPs), which are small membrane vesicles released by apoptotic or activated cells, are physiological carriers of OSEs. OSEs on circulating MPs isolated from healthy donors and patients with ST-segment elevation myocardial infarction (STE-MI) were characterized by flow cytometry using a panel of OSE-specific monoclonal antibodies. We found that a subset of MPs carry OSEs on their surface, predominantly malondialdehyde (MDA) epitopes. Consistent with this, a majority of IgM antibodies bound on the surface of circulating MPs were found to have specificity for MDA-modified LDL. Moreover, we show that MPs can stimulate THP-1 (human acute monocytic leukemia cell line) and human primary monocytes to produce interleukin 8, which can be inhibited by a monoclonal IgM with specificity for MDA epitopes. Finally, we show that MDA⁺ MPs are elevated at the culprit lesion site of patients with STE-MI. Our results identify a subset of OSE⁺ MPs that are bound by OxLDL-specific IgM. These findings demonstrate a novel mechanism by which anti-OxLDL IgM antibodies could mediate protective functions in CVD.

Angiotensin II and vascular injury

Vascular injury, characterized by endothelial dysfunction, structural remodelling, inflammation and fibrosis, plays an important role in cardiovascular diseases. Cellular processes underlying this include altered vascular smooth muscle cell (VSMC) growth/apoptosis, fibrosis, increased contractility and vascular calcification. Associated with these events is VSMC differentiation and phenotypic switching from a contractile to a proliferative/secretory phenotype. Inflammation, associated with macrophage infiltration and increased expression of redox-sensitive pro-inflammatory genes, also contributes to vascular remodelling. Among the many factors involved in vascular injury is Ang II. Ang II, previously thought to be the sole biologically active downstream peptide of the renin-angiotensin system (RAS), is converted to smaller peptides, [Ang III, Ang IV, Ang-(1-7)], that are functional and that modulate vascular tone and structure. The actions of Ang II are mediated via signalling pathways activated upon binding to AT1R and AT2R. AT1R activation induces effects through PLC-IP3-DAG, MAP kinases, tyrosine kinases, tyrosine phosphatases and RhoA/Rho kinase. Ang II elicits many of its (patho)physiological actions by stimulating reactive oxygen species (ROS) generation through activation of vascular NAD(P)H oxidase (Nox). ROS in turn influence redox-sensitive signalling molecules. Here we discuss the role of Ang II in vascular injury, focusing on molecular mechanisms and cellular processes. Implications in vascular remodelling, inflammation, calcification and atherosclerosis are highlighted.

Hyperhomocysteinemia potentiates hyperglycemia-induced inflammatory monocyte differentiation and atherosclerosis

Hyperhomocysteinemia (HHcy) is associated with increased diabetic cardiovascular diseases. However, the role of HHcy in atherogenesis associated with hyperglycemia (HG) remains unknown. To examine the role and mechanisms by which HHcy accelerates HG-induced atherosclerosis, we established an atherosclerosis-susceptible HHcy and HG mouse model. HHcy was established in mice deficient in cystathionine β-synthase (Cbs) in which the homocysteine (Hcy) level could be lowered by inducing transgenic human CBS (Tg-hCBS) using Zn supplementation. HG was induced by streptozotocin injection. Atherosclerosis was induced by crossing Tg-hCBS Cbs mice with apolipoprotein E-deficient (ApoE(-/-)) mice and feeding them a high-fat diet for 2 weeks. We demonstrated that HHcy and HG accelerated atherosclerosis and increased lesion monocytes (MCs) and macrophages (MØs) and further increased inflammatory MC and MØ levels in peripheral tissues. Furthermore, Hcy-lowering reversed circulating mononuclear cells, MC, and inflammatory MC and MC-derived MØ levels. In addition, inflammatory MC correlated positively with plasma Hcy levels and negatively with plasma s-adenosylmethionine-to-s-adenosylhomocysteine ratios. Finally, l-Hcy and d-glucose promoted inflammatory MC differentiation in primary mouse splenocytes, which was reversed by adenoviral DNA methyltransferase-1. HHcy and HG, individually and synergistically, accelerated atherosclerosis and inflammatory MC and MØ differentiation, at least in part, via DNA hypomethylation.

The mutual interplay of lipid metabolism and the cells of the immune system in relation to atherosclerosis

Atherosclerosis is a chronic inflammation in the arterial wall involving cells of the innate and adaptive immune system that is promoted by hyperlipidemia. In addition, the immune system can influence lipids and lipoprotein levels and cellular lipid homeostasis can influence the level and function of the immune cells. We will review the effects of manipulation of adaptive immune cells and immune cell products on lipids and lipoproteins, focusing mainly on studies performed in murine models of atherosclerosis. We also review how lipoproteins and cellular lipid levels, particularly cholesterol levels, influence the function of cells of the innate and adaptive immune systems. The overriding theme is that these interactions are driven by the need to provide the energy and membrane components for cell proliferation and migration, membrane expansion and other functions that are so important in the functioning of the immune cells.

Targeting sortilin in immune cells reduces proinflammatory cytokines and atherosclerosis

Genome-wide association studies have identified a link between genetic variation at the human chromosomal locus 1p13.3 and coronary artery disease. The gene encoding sortilin (SORT1) has been implicated as the causative gene within the locus, as sortilin regulates hepatic lipoprotein metabolism. Here we demonstrated that sortilin also directly affects atherogenesis, independent of its regulatory role in lipoprotein metabolism. In a mouse model of atherosclerosis, deletion of Sort1 did not alter plasma cholesterol levels, but reduced the development of both early and late atherosclerotic lesions. We determined that sortilin is a high-affinity receptor for the proinflammatory cytokines IL-6 and IFN-γ. Moreover, macrophages and Th1 cells (both of which mediate atherosclerotic plaque formation) lacking sortilin had reduced secretion of IL-6 and IFN-γ, but not of other measured cytokines. Transfer of sortilin-deficient BM into irradiated atherosclerotic mice reduced atherosclerosis and systemic markers of inflammation. Together, these data demonstrate that sortilin influences cytokine secretion and that targeting sortilin in immune cells attenuates inflammation and reduces atherosclerosis.

Myocardial ischemia and reperfusion leads to transient CD8 immune deficiency and accelerated immunosenescence in CMV-seropositive patients

RATIONALE

There is mounting evidence of a higher incidence of coronary heart disease in cytomegalovirus-seropositive individuals.

OBJECTIVE

The aim of this study was to investigate whether acute myocardial infarction triggers an inflammatory T-cell response that might lead to accelerated immunosenescence in cytomegalovirus-seropositive patients.

METHODS AND RESULTS

Thirty-four patients with acute myocardial infarction undergoing primary percutaneous coronary intervention were longitudinally studied within 3 months after reperfusion (Cohort A). In addition, 54 patients with acute myocardial infarction and chronic myocardial infarction were analyzed in a cross-sectional study (Cohort B). Cytomegalovirus-seropositive patients demonstrated a greater fall in the concentration of terminally differentiated CD8 effector memory T cells (TEMRA) in peripheral blood during the first 30 minutes of reperfusion compared with cytomegalovirus-seronegative patients (-192 versus -63 cells/μL; P=0.008), correlating with the expression of programmed cell death-1 before primary percutaneous coronary intervention (r=0.8; P=0.0002). A significant proportion of TEMRA cells remained depleted for ≥3 months in cytomegalovirus-seropositive patients. Using high-throughput 13-parameter flow cytometry and human leukocyte antigen class I cytomegalovirus-specific dextramers, we confirmed an acute and persistent depletion of terminally differentiated TEMRA and cytomegalovirus-specific CD8(+) cells in cytomegalovirus-seropositive patients. Long-term reconstitution of the TEMRA pool in chronic cytomegalovirus-seropositive postmyocardial infarction patients was associated with signs of terminal differentiation including an increase in killer cell lectin-like receptor subfamily G member 1 and shorter telomere length in CD8(+) T cells (2225 versus 3397 bp; P<0.001).

CONCLUSIONS

Myocardial ischemia and reperfusion in cytomegalovirus-seropositive patients undergoing primary percutaneous coronary intervention leads to acute loss of antigen-specific, terminally differentiated CD8 T cells, possibly through programmed cell death-1-dependent programmed cell death. Our results suggest that acute myocardial infarction and reperfusion accelerate immunosenescence in cytomegalovirus-seropositive patients.

Placental lesions associated with acute atherosis

OBJECTIVE

Acute atherosis is a lesion of the spiral arteries characterized by fibrinoid necrosis of the vessel wall, an accumulation of fat-containing macrophages, and a mononuclear perivascular infiltrate, which can be found in patients with preeclampsia, fetal death, small-for-gestational age, spontaneous preterm labor/premature prelabor rupture of membrane, and spontaneous mid-trimester abortion. This lesion is thought to decrease blood flow to the intervillous space which may lead to other vascular lesions of the placenta. The objective of this study was to test whether there is an association between acute atherosis and placental lesions that are consistent with maternal vascular underperfusion (MVU), amniotic fluid infection (AFI), fetal vascular thrombo-occlusive disease (FVTOD) or chronic inflammation.

MATERIAL AND METHODS

A retrospective cohort study of pregnant women who delivered between July 1998 and July 2014 at Hutzel Women's Hospital/Detroit Medical Center was conducted examine 16 457 placentas. The frequency of placenta lesions (diagnosed using the criteria of the Perinatal Section of the Society for Pediatric Pathology) was compared between pregnancies with and without acute atherosis.

RESULTS

Among 16 457 women who were enrolled, 10.2% (1671/16 457) were excluded, leaving 14 786 women who contributed data for analysis. Among them, the prevalence of acute atherosis was 2.2% (326/14 786). Women with acute atherosis were more than six times as likely as those without to have placental lesions consistent with maternal underperfusion (adjusted odds ratio - aOR: 6.7; 95% CI 5.2-8.6). To a lesser degree, acute atherosis was also associated with greater risks of having either lesions consistent with FVTOD (aOR 1.7; 95% CI 1.2-2.3) or chronic chorioamnionitis (aOR 1.9; 95% CI 1.3-3), but not with other chronic inflammatory lesions, after adjusting for gestational age at delivery. In contrast, women with acute atherosis were 60% less likely to have lesions consistent with AFI, adjusting for gestational age at delivery (aOR 0.4; 95% CI 0.3-0.5).

CONCLUSIONS

Acute atherosis is associated with increased risks of having placental lesions consistent with MVU, and to a lesser extent, chronic chorioamnionitis and those consistent with FVTOD.

Lipopolysaccharide augments the uptake of oxidized LDL by up-regulating lectin-like oxidized LDL receptor-1 in macrophages

There is a growing body of evidence supporting an intimate association of immune activation with the pathogenesis of cardiovascular diseases, including atherosclerosis. Uptake of oxidized low-density lipoprotein (oxLDL) through scavenging receptors promotes the formation of mature lipid-laden macrophages, which subsequently leads to exacerbation of regional inflammation and atherosclerotic plaque formation. In this study, we first examined changes in the mRNA level of the lectin-like oxLDL receptor-1 (LOX-1) in the mouse macrophage cell line RAW264.7 and the human PMA-induced macrophage cell line THP-1 after LPS stimulation. LPS significantly up-regulated LOX-1 mRNA in RAW264.7 cells; LOX-1 cell-surface protein expression was also increased. Flow cytometry and fluorescence microscopy analyses showed that cellular uptake of fluorescence (Dil)-labeled oxLDL was significantly augmented with LPS stimulation. The augmented uptake of Dil-oxLDL was almost completely abrogated by treatment with an anti-LOX-1 antibody. Of note, knockdown of Erk1/2 resulted in a significant reduction of LPS-induced LOX-1 up-regulation. Treatment with U0126, a specific inhibitor of MEK, significantly suppressed LPS-induced expression of LOX-1 at both the mRNA and protein levels. Furthermore, LOX-1 promoter activity was significantly augmented by LPS stimulation; this augmentation was prevented by U0126 treatment. Similar results were also observed in human PMA-induced THP-1 macrophages. Taken together, our results indicate that LPS up-regulates LOX-1, at least in part through activation of the Erk1/2 signaling pathway, followed by augmented cellular oxLDL uptake, thus highlighting a critical role of TLR4-mediated aberrant LOX-1 signaling in the pathogenesis of atherosclerosis.

Classical and Alternative Activation and Metalloproteinase Expression Occurs in Foam Cell Macrophages in Male and Female ApoE Null Mice in the Absence of T and B Lymphocytes

BACKGROUND

Rupture of advanced atherosclerotic plaques accounts for most life-threatening myocardial infarctions. Classical (M1) and alternative (M2) macrophage activation could promote atherosclerotic plaque progression and rupture by increasing production of proteases, including matrix metalloproteinases (MMPs). Lymphocyte-derived cytokines may be essential for generating M1 and M2 phenotypes in plaques, although this has not been rigorously tested until now.

METHODS AND RESULTS

We validated the expression of M1 markers (iNOS and COX-2) and M2 markers (arginase-1, Ym-1, and CD206) and then measured MMP mRNA levels in mouse macrophages during classical and alternative activation in vitro. We then compared mRNA expression of these genes ex vivo in foam cells from subcutaneous granulomas in fat-fed immune-competent ApoE knockout (KO) and immune-compromised ApoE/Rag-1 double-KO mice, which lack all T and B cells. Furthermore, we performed immunohistochemistry in subcutaneous granulomas and in aortic root and brachiocephalic artery atherosclerotic plaques to measure the extent of M1/M2 marker and MMP protein expression in vivo. Classical activation of mouse macrophages with bacterial lipopolysaccharide in vitro increased MMPs-13, -14, and -25 but decreased MMP-19 and TIMP-2 mRNA expressions. Alternative activation with IL-4 increased MMP-19 expression. Foam cells in subcutaneous granulomas expressed all M1/M2 markers and MMPs at ex vivo mRNA and in vivo protein levels, irrespective of Rag-1 genotype. There were also similar percentages of foam cell macrophages (FCMs) carrying M1/M2 markers and MMPs in atherosclerotic plaques from ApoE KO and ApoE/Rag-1 double-KO mice.

CONCLUSION

Classical and alternative activation leads to distinct MMP expression patterns in mouse macrophages in vitro. M1 and M2 polarization in vivo occurs in the absence of T and B lymphocytes in either granuloma or plaque FCMs.

Heme oxygenase-1: an emerging therapeutic target to curb cardiac pathology

Activation of heme oxygenase-1 (HO-1), a heme-degrading enzyme responsive to a wide range of cellular stress, is traditionally considered to convey adaptive responses to oxidative stress, inflammation and vasoconstriction. These diversified effects are achieved through the degradation of heme to carbon monoxide (CO), biliverdin (which is rapidly converted to bilirubin by biliverdin reductase) and ferric iron. Recent findings have added antiproliferative and angiogenic effects to the list of HO-1/CO actions. HO-1 along with its reaction products bilirubin and CO are protective against ischemia-induced injury (myocardial infarction, ischemia-reperfusion (IR)-injury and post-infarct structural remodelling). Moreover, HO-1, and CO in particular, possess acute antihypertensive effects. As opposed to these curative potentials, the long-believed protective effect of HO-1 in cardiac remodelling in response to pressure overload and type 2 diabetes mellitus (DM) has been questioned by recent work. These challenges, coupled with emerging regulatory mechanisms, motivate further in-depth studies to help understand untapped layers of HO-1 regulation and action. The outcomes of these efforts may shed new light on critical mechanisms that could be used to harness the protective potential of this enzyme for the therapeutic benefit of patients suffering from such highly prevalent cardiovascular disorders.

The role of the FPR2/ALX receptor in atherosclerosis development and plaque stability

AIMS

The formyl peptide receptor (FPR) subtype FPR2/ALX transduces pro-inflammatory responses and participates in the resolution of inflammation depending on activation. The aim of the present study was to unravel the role of FPR2/ALX signalling in atherosclerosis.

METHODS AND RESULTS

Expression of FPR2/ALX was analysed in 127 human carotid atherosclerotic lesions and revealed that this receptor was expressed on macrophages, smooth muscle cells (SMCs), and endothelial cells. Furthermore, FPR2/ALX mRNA levels were significantly up-regulated in atherosclerotic lesions compared with healthy vessels. In multiple regression, age, creatinine, and clinical signs of increased cerebral ischaemia were independent predictors of FPR2/ALX expression. To provide mechanistic insights into these observations, we generated Ldlr(-/-)xFpr2(-/-) mice, which exhibited delayed atherosclerosis development and less macrophage infiltration compared with Ldlr(-/-)xFpr2(+/+) mice. These findings were reproduced by transplantation of Fpr2(-/-) bone marrow into Ldlr(-/-) mice and further extended by in vitro experiments, demonstrating a lower inflammatory state in Fpr2(-/-) macrophages. FPR2/ALX expression correlated with chemo- and cytokines in human atherosclerotic lesions and leucocytes. Finally, atherosclerotic lesions in Ldlr(-/-)xFpr2(-/-) mice exhibited decreased collagen content, and Fpr2(-/-) SMCs exhibited a profile of increased collagenase and decreased collagen production pathways.

CONCLUSION

FPR2/ALX is proatherogenic due to effects on bone marrow-derived cells, but promoted a more stable plaque phenotype through effects on SMCs. Taken together, these results suggest a dual role of FPR2/ALX signalling in atherosclerosis by way of promoting disease progression and but increasing plaque stability.

γδT cells are prevalent in the proximal aorta and drive nascent atherosclerotic lesion progression and neutrophilia in hypercholesterolemic mice

Unique innate immunity-linked γδT cells have been seen in early human artery lesions, but their role in lesion development has received little attention. Here we investigated whether γδT cells modulate atherogenesis in apolipoprotein E-deficient (ApoE KO) mice. We found that γδT cell numbers were markedly increased in the proximal aorta of ApoE-deficient vs. wild-type mice during early atherogenesis, particularly in the aortic root and arch, where they comprised most of the T cells and lesion progression is most rapid. γδT cells infiltrated intimal lesions in ApoE KO mice, but only the adventitia in wild-type mice, and were more prevalent than CD4⁺ T cells in early nascent lesions, as evaluated by en face confocal microscopy. These aortic γδT cells produced IL-17, but not IFN-γ, analyzed by ex vivo FACS. Furthermore, aortic arch lipid accumulation correlated strongly with abundance of IL-17-expressing splenic γδT cells in individual ApoE KO mice. To investigate the role of these γδT cells in early atherogenesis, we analyzed ApoE/γδT double knockout (DKO) compared to ApoE KO mice. We observed reduced early intimal lipid accumulation at sites of nascent lesion formation, both in chow-fed (by 40%) and Western diet-fed (by 44%) ApoE/γδT DKO mice. In addition, circulating neutrophils were drastically reduced in these DKO mice on Western diet, while expansion of inflammatory monocytes and splenic Th1 or Th17 lymphocytes was not affected. These data reveal, for the first time, a pathogenic role of γδT cells in early atherogenesis in ApoE KO mice, by mechanisms likely to involve their IL-17 production and induction of neutrophilia. Targeting γδT cells thus might offer therapeutic benefit in atherosclerosis or other inflammatory vascular diseases.

Imaging of oxidation-specific epitopes with targeted nanoparticles to detect high-risk atherosclerotic lesions: progress and future directions

Oxidation-specific epitopes (OSE) within developing atherosclerotic lesions are key antigens that drive innate and adaptive immune responses in atherosclerosis, leading to chronic inflammation. Oxidized phospholipids and malondialdehyde-lysine epitopes are well-characterized OSE present in human atherosclerotic lesions, particularly in pathologically defined vulnerable plaques. Using murine and human OSE-specific antibodies as targeting agents, we have developed radionuclide and magnetic resonance based nanoparticles, containing gadolinium, manganese or lipid-coated ultrasmall superparamagnetic iron oxide, to non-invasively image OSE within experimental atherosclerotic lesions. These methods quantitate plaque burden, allow detection of lesion progression and regression, plaque stabilization, and accumulation of OSE within macrophage-rich areas of the artery wall, suggesting they detect the most active lesions. Future studies will focus on using "natural" antibodies, lipopeptides, and mimotopes for imaging applications. These approaches should enhance the clinical translation of this technique to image, monitor, evaluate efficacy of novel therapeutic agents, and guide optimal therapy of high-risk atherosclerotic lesions.

Obese hypertensive men have plasma concentrations of C-reactive protein similar to that of obese normotensive men

BACKGROUND

Low-grade chronic inflammation is a characteristic feature of obesity, the most important lifestyle risk factor for hypertension. Elevated plasma concentrations of the inflammatory biomarker C-reactive protein (CRP) are associated with an increased risk of hypertension, but elevated plasma CRP concentrations are also closely associated with obesity. It is uncertain whether CRP is directly involved in the pathogenesis of hypertension or is only a marker of other pathogenic processes closely related to obesity.

METHODS

We studied 103 obese men (body mass index (BMI) ≥ 30.0 kg/m(2)); 63 of these men had 24-hour ambulatory blood pressure (ABP) ≥ 130/80 mm Hg and comprised the obese hypertensive (OHT) group. The 40 remaining obese men had 24-hour ABP < 130/80 mm Hg and comprised the obese normotensive (ONT) group. Our control group comprised 27 lean normotensive (LNT) men. All participants were medication-free. We measured plasma CRP concentrations with a high-sensitivity assay and determined body composition by dual energy x-ray absorptiometry scanning.

RESULTS

There were no differences in anthropometric measures (BMI, waist circumference, or total fat mass percentage) between OHT and ONT groups (P ≥ 0.08). The obese groups had higher CRP concentrations than the LNT group (OHT: median = 2.30, interquartile range (IQR) = 1.10-4.10mg/L; ONT: median = 2.55, IQR = 1.25-4.80 mg/L; LNT: median = 0.60, IQR = 0.30-1.00 mg/L; P < 0.001), but there was no difference in CRP concentrations between OHT and ONT groups (P = 1.00). In the obese men, CRP was not correlated with either 24-hour systolic (r = 0.04; P = 0.71) or 24-hour diastolic ABP (r = -0.03; P = 0.78).

CONCLUSIONS

Obese hypertensive men, matched for anthropometric measurements, have plasma CRP concentrations similar to those of obese normotensive men.

IL-17 and Th17 cells in atherosclerosis: subtle and contextual roles

Atherosclerosis is a chronic inflammatory arterial disease driven by both innate and adaptive immune responses to modified lipoproteins and components of the injured vascular wall. Specific T lymphocyte responses driven by T helper-1 or T regulatory cells play distinct and opposing roles in atherosclerosis. More recently, T helper-17 cells, which produce the prototype cytokine interleukin-17, have been characterized and shown to be critical in mucosal host defense against microbial and fungal pathogens. Sustained production of interleukin-17 in an inflammatory context has been linked to the pathology of several autoimmune and inflammatory diseases. However, regulatory and protective roles have also been reported in selective disease settings. Studies in atherosclerosis led to conflicting results on the roles of interleukin-17 and T helper-17 cells in disease development and plaque stability. The present review provides a summary of the available evidence and putative mechanisms linking this pathway to atherosclerosis, as well as a perspective on the risks and benefits of interleukin-17-targeted cytokine therapy in patients at high cardiovascular risk.

Innate immune receptor NOD2 promotes vascular inflammation and formation of lipid-rich necrotic cores in hypercholesterolemic mice

Atherosclerosis is an inflammatory disease associated with the activation of innate immune TLRs and nucleotide-binding oligomerization domain-containing protein (NOD)-like receptor pathways. However, the function of most innate immune receptors in atherosclerosis remains unclear. Here, we show that NOD2 is a crucial innate immune receptor influencing vascular inflammation and atherosclerosis severity. 10-week stimulation with muramyl dipeptide (MDP), the NOD2 cognate ligand, aggravated atherosclerosis, as indicated by the augmented lesion burden, increased vascular inflammation and enlarged lipid-rich necrotic cores in Ldlr(-/-) mice. Myeloid-specific ablation of NOD2, but not its downstream kinase, receptor-interacting serine/threonine-protein kinase 2, restrained the expansion of the lipid-rich necrotic core in Ldlr(-/-) chimeric mice. In vitro stimulation of macrophages with MDP enhanced the uptake of oxidized low-density lipoprotein and impaired cholesterol efflux in concordance with upregulation of scavenger receptor A1/2 and downregulation of ATP-binding cassette transporter A1. Ex vivo stimulation of human carotid plaques with MDP led to increased activation of inflammatory signaling pathways p38 MAPK and NF-κB-mediated release of proinflammatory cytokines. Altogether, this study suggests that NOD2 contributes to the expansion of the lipid-rich necrotic core and promotes vascular inflammation in atherosclerosis.

Neutrophils in atherosclerosis: from mice to man

Infiltration of leukocyte subsets is a driving force of atherosclerotic lesion growth, and during the past decade, neutrophils have received growing attention in chronic inflammatory processes, such as atherosclerosis. Equipped with various ready to be released mediators, evolved to fight invading pathogens, neutrophils may also hold key functions in affecting sterile inflammation, such as in atherosclerosis. Many of their secretion products might instruct or activate other immune cells (particularly monocytes) to, for example, enter atherosclerotic lesions or release proinflammatory mediators. Despite the emerging evidence for the mechanistic contribution of neutrophils to early atherosclerosis in mice, their role in human atherogenesis, atheroprogression, and atherosclerotic plaque destabilization is still poorly understood. This brief review will summarize latest findings on the role of neutrophils in atherosclerosis and will pay special attention to studies describing a translation approach by combining measurements in mouse and human.

Atheroprotective immunization with malondialdehyde-modified LDL is hapten specific and dependent on advanced MDA adducts: implications for development of an atheroprotective vaccine

Immunization with homologous malondialdehyde (MDA)-modified LDL (MDA-LDL) leads to atheroprotection in experimental models supporting the concept that a vaccine to oxidation-specific epitopes (OSEs) of oxidized LDL could limit atherogenesis. However, modification of human LDL with OSE to use as an immunogen would be impractical for generalized use. Furthermore, when MDA is used to modify LDL, a wide variety of related MDA adducts are formed, both simple and more complex. To define the relevant epitopes that would reproduce the atheroprotective effects of immunization with MDA-LDL, we sought to determine the responsible immunodominant and atheroprotective adducts. We now demonstrate that fluorescent adducts of MDA involving the condensation of two or more MDA molecules with lysine to form malondialdehyde-acetaldehyde (MAA)-type adducts generate immunodominant epitopes that lead to atheroprotective responses. We further demonstrate that a T helper (Th) 2-biased hapten-specific humoral and cellular response is sufficient, and thus, MAA-modified homologous albumin is an equally effective immunogen. We further show that such Th2-biased humoral responses per se are not atheroprotective if they do not target relevant antigens. These data demonstrate the feasibility of development of a small-molecule immunogen that could stimulate MAA-specific immune responses, which could be used to develop a vaccine approach to retard or prevent atherogenesis.

Mast cells as effectors in atherosclerosis

The mast cell is a potent immune cell known for its functions in host defense responses and diseases, such as asthma and allergies. In the past years, accumulating evidence established the contribution of the mast cell to cardiovascular diseases as well, in particular, by its effects on atherosclerotic plaque progression and destabilization. Through its release not only of mediators, such as the mast cell-specific proteases chymase and tryptase, but also of growth factors, histamine, and chemokines, activated mast cells can have detrimental effects on its immediate surroundings in the vessel wall. This results in matrix degradation, apoptosis, and enhanced recruitment of inflammatory cells, thereby actively contributing to cardiovascular diseases. In this review, we will discuss the current knowledge on mast cell function in cardiovascular diseases and speculate on potential novel therapeutic strategies to prevent acute cardiovascular syndromes via targeting of mast cells.

LDL-cholesterol reduction in patients with hypercholesterolemia by modulation of adenosine triphosphate-citrate lyase and adenosine monophosphate-activated protein kinase

PURPOSE OF REVIEW

To review the profile of ETC-1002, as shown in preclinical and clinical studies, including LDL-cholesterol (LDL-C)-lowering activity and beneficial effects on other cardiometabolic risk markers as they relate to the inhibition of adenosine triphosphate-citrate lyase and the activation of adenosine monophosphate-activated protein kinase.

RECENT FINDINGS

ETC-1002 is an adenosine triphosphate-citrate lyase inhibitor/adenosine monophosphate-activated protein kinase activator currently in Phase 2b clinical development. In seven Phase 1 and Phase 2a clinical studies, ETC-1002 dosed once daily for 2-12 weeks has lowered LDL-C and reduced high-sensitivity C-reactive protein by up to 40%, with neutral to positive effects on glucose levels, blood pressure, and body weight. Importantly, use of ETC-1002 in statin-intolerant patients has shown statin-like lowering of LDL-C without the muscle pain and weakness responsible for discontinuation of statin use by many patients. ETC-1002 has also been shown to produce an incremental benefit, lowering LDL-C as an add-on therapy to a low-dose statin. In over 300 individuals in studies of up to 12 weeks, ETC-1002 has been well tolerated with no serious adverse effects.

SUMMARY

Because adenosine triphosphate-citrate lyase and adenosine monophosphate-activated protein kinase play central roles in regulating lipid and glucose metabolism, pharmacological modulation of these two enzymes could provide an important therapeutic alternative for statin-intolerant patients with hypercholesterolemia.

Murine aortic smooth muscle cells acquire, though fail to present exogenous protein antigens on major histocompatibility complex class II molecules

In the present study aortic murine smooth muscle cell (SMC) antigen presentation capacity was evaluated using the Eα-GFP/Y-Ae system to visualize antigen uptake through a GFP tag and tracking of Eα peptide/MHCII presentation using the Y-Ae Ab. Stimulation with IFN-γ (100 ng/mL) for 72 h caused a significant (P < 0.01) increase in the percentage of MHC class II positive SMCs, compared with unstimulated cells. Treatment with Eα-GFP (100 μg/mL) for 48 h induced a significant (P < 0.05) increase in the percentage of GFP positive SMCs while it did not affect the percentage of Y-Ae positive cells, being indicative of antigen uptake without its presentation in the context of MHC class II. After IFN-γ-stimulation, ovalbumin- (OVA, 1 mg/mL) or OVA_323–339 peptide-(0.5 μg/mL) treated SMCs failed to induce OT-II CD4⁺ T cell activation/proliferation; this was also accompanied by a lack of expression of key costimulatory molecules (OX40L, CD40, CD70, and CD86) on SMCs. Finally, OVA-treated SMCs failed to induce DO11.10-GFP hybridoma activation, a process independent of costimulation. Our results demonstrate that while murine primary aortic SMCs express MHC class II and can acquire exogenous antigens, they fail to activate T cells through a failure in antigen presentation and a lack of costimulatory molecule expression.

B cells and humoral immunity in atherosclerosis

Insights into the important contribution of inflammation and immune functions in the development and progression of atherosclerosis have greatly improved our understanding of this disease. Although the role of T cells has been extensively studied for decades, only recently has the role of B cells gained more attention. Recent studies have identified differential effects of different B-cell subsets and helped to clarify the still poorly understood mechanisms by which these act. B1 cells have been shown to prevent lesion formation, whereas B2 cells have been suggested to promote it. Natural IgM antibodies, mainly derived from B1 cells, have been shown to mediate atheroprotective effects, but the functional role of other immunoglobulin classes, particularly IgG, still remains elusive. In this review, we will focus on recent insights on the role of B cells and various immunoglobulin classes and how these may mediate their effects in atherosclerotic lesion formation. Moreover, we will highlight potential therapeutic approaches focusing on B-cell depletion that could be used to translate experimental evidence to human disease.