Monocyte subset dynamics in human atherosclerosis can be profiled with magnetic nano-sensors

Epidrugs in the clinical management of atherosclerosis: Mechanisms, challenges and promises

Atherosclerosis is a complex and multigenic pathology associated with significant epigenetic reprogramming. Traditional factors (age, sex, obesity, hyperglycaemia, dyslipidaemia, hypertension) and non-traditional factors (foetal indices, microbiome alteration, clonal hematopoiesis, air pollution, sleep disorders) induce endothelial dysfunction, resulting in reduced vascular tone and increased vascular permeability, inflammation and shear stress. These factors induce paracrine and autocrine interactions between several cell types, including vascular smooth muscle cells, endothelial cells, monocytes/macrophages, dendritic cells and T cells. Such cellular interactions lead to tissue-specific epigenetic reprogramming regulated by DNA methylation, histone modifications and microRNAs, which manifests in atherosclerosis. Our review outlines epigenetic signatures during atherosclerosis, which are viewed as potential clinical biomarkers that may be adopted as new therapeutic targets. Additionally, we emphasize epigenetic modifiers referred to as 'epidrugs' as potential therapeutic molecules to correct gene expression patterns and restore vascular homeostasis during atherosclerosis. Further, we suggest nanomedicine-based strategies involving the use of epidrugs, which may selectively target cells in the atherosclerotic microenvironment and reduce off-target effects.

Monocyte Subsets in Cardiovascular Disease: A Biomarker Perspective

Endothelial dysfunctions together with a dysregulated immune response and lipid accumulation are important confounding factors in the onset and chronic development of atherosclerosis. Recently, a large body of data has emerged on the sequential involvement of different immune cell types, including monocytes, in the pathology of this disease. In this condensed review, we aim to highlight some of the recent basic research and clinical findings on monocyte subsets published since our joint European Society of Cardiology consensus document, and re-evaluate their potential relevance as surrogate biomarkers in coronary artery disease.

Nanoparticles targeting monocytes and macrophages as diagnostic and therapeutic tools for autoimmune diseases

Autoimmune diseases are chronic conditions that result from an inadequate immune response to self-antigens and affect many people worldwide. Their signs, symptoms, and clinical severity change throughout the course of the disease, therefore the diagnosis and treatment of autoimmune diseases are major challenges. Current diagnostic tools are often invasive and tend to identify the issue at advanced stages. Moreover, the available treatments for autoimmune diseases do not typically lead to complete remission and are associated with numerous side effects upon long-term usage. A promising strategy is the use of nanoparticles that can be used as contrast agents in diagnostic imaging techniques to detect specific cells present at the inflammatory infiltrates in tissues that are not easily accessible by biopsy. In addition, NPs can be designed to deliver drugs to a cell population or tissue. Considering the significant role played by monocytes in the development of chronic inflammatory conditions and their emergence as a target for extracorporeal monitoring and precise interventions, this review focuses on recent advancements in nanoparticle-based strategies for diagnosing and treating autoimmune diseases, with a particular emphasis on targeting monocyte populations.

Kinetics of monocyte subpopulations during experimental cerebral malaria and its resolution in a model of late chloroquine treatment

Cerebral malaria (CM) is one of the most severe forms of malaria and is a neuropathology that can lead to death. Monocytes have been shown to accumulate in the brain microvasculature at the onset of neurological symptoms during CM. Monocytes have a remarkable ability to adapt their function to their microenvironment from pro-inflammatory to resolving activities. This study aimed to describe the behavior of monocyte subpopulations during infection and its resolution. C57BL/6 mice were infected with the Plasmodium berghei ANKA strain and treated or not with chloroquine (CQ) on the first day of the onset of neurological symptoms (day 6) for 4 days and followed until day 12 to mimic neuroinflammation and its resolution during experimental CM. Ly6C monocyte subpopulations were identified by flow cytometry of cells from the spleen, peripheral blood, and brain and then quantified and characterized at different time points. In the brain, the Ly6C^int and Ly6C^low monocytes were associated with neuroinflammation, while Ly6C^hi and Ly6C^int were mobilized from the peripheral blood to the brain for resolution. During neuroinflammation, CD36 and CD163 were both involved via splenic monocytes, whereas our results suggest that the low CD36 expression in the brain during the neuroinflammation phase was due to degradation. The resolution phase was characterized by increased expressions of CD36 and CD163 in blood Ly6C^low monocytes, a higher expression of CD36 in the microglia, and restored high expression levels of CD163 in Ly6C^hi monocytes localized in the brain. Thus, our results suggest that increasing the expressions of CD36 and CD163 specifically in the brain during the neuroinflammatory phase contributes to its resolution.

Increased biomarkers of cardiovascular risk in HIV-1 viremic controllers and low persistent inflammation in elite controllers and art-suppressed individuals

HIV controllers (HICs) are models of HIV functional cure, although some studies have shown persistent inflammation and increased rates of atherosclerosis in HICs. Since immune activation/inflammation contributes to the pathogenesis of cardiovascular diseases (CVD), we evaluated clinical data and inflammation markers in HIV-1 viremic controllers (VC), elite controllers (EC), and control groups (HIV positive individuals with virological suppression by antiretroviral therapy-cART; HIV negative individuals-HIVneg) to assess whether they presented elevated levels of inflammation markers also associated with CVD. We observed the highest frequencies of activated CD8+ T cells in VCs, while EC and cART groups presented similar but slightly altered frequencies of this marker when compared to the HIVneg group. Regarding platelet activation, both HICs groups presented higher expression of P-selectin in platelets when compared to control groups. Monocyte subset analyses revealed lower frequencies of classical monocytes and increased frequencies of non-classical and intermediate monocytes among cART individuals and in EC when compared to HIV negative individuals, but none of the differences were significant. For VC, however, significant decreases in frequencies of classical monocytes and increases in the frequency of intermediate monocytes were observed in comparison to HIV negative individuals. The frequency of monocytes expressing tissue factor was similar among the groups on all subsets. In terms of plasma markers, VC had higher levels of many inflammatory markers, while EC had higher levels of VCAM-1 and ICAM-1 compared to control groups. Our data showed that VCs display increased levels of inflammation markers that have been associated with CVD risk. Meanwhile, ECs show signals of lower but persistent inflammation, comparable to the cART group, indicating the potential benefits of alternative therapies to decrease inflammation in this group.

Circulating monocyte populations in patients with coronary atherosclerosis

Aims: The authors examined the phenotype of circulating monocytes in patients with coronary atherosclerosis depending on age. Methods: A total of 121 patients were categorized into three groups according to the severity of coronary atherosclerosis assessed by angiography and into two groups depending on age above/below the median 60.0 (range: 56.0-66.0). Classical CD14++CD16-, intermediate CD14++CD16+ and non-classical CD14+CD16+ monocytes were analyzed via direct immunofluorescence and flow cytometry. Results and conclusions: In patients >60 years of age, the severity of atherosclerosis was associated with the decreased number of classical monocytes in the blood. In patients under 60 years of age, this relationship was not observed. The authors hypothesize that the contribution of different subtypes of blood monocytes to the development of atherosclerosis may vary with age.

Tumor-Associated Macrophages-Implications for Molecular Oncology and Imaging

Tumor-associated macrophages (TAMs) represent the largest group of leukocytes within the tumor microenvironment (TME) of solid tumors and orchestrate the composition of anti- as well as pro-tumorigenic factors. This makes TAMs an excellent target for novel cancer therapies. The plasticity of TAMs resulting in varying membrane receptors and expression of intracellular proteins allow the specific characterization of different subsets of TAMs. Those markers similarly allow tracking of TAMs by different means of molecular imaging. This review aims to provides an overview of the origin of tumor-associated macrophages, their polarization in different subtypes, and how characteristic markers of the subtypes can be used as targets for molecular imaging and theranostic approaches.

Nonclassical Monocytes in Health and Disease

Monocytes are innate blood cells that maintain vascular homeostasis and are early responders to pathogens in acute infections. There are three well-characterized classes of monocytes: classical (CD14+CD16−in humans and Ly6Chiin mice), intermediate (CD14+CD16+in humans and Ly6C+Treml4+in mice), and nonclassical (CD14−CD16+in humans and Ly6Cloin mice). Classical monocytes are critical for the initial inflammatory response. Classical monocytes can differentiate into macrophages in tissue and can contribute to chronic disease. Nonclassical monocytes have been widely viewed as anti-inflammatory, as they maintain vascular homeostasis. They are a first line of defense in recognition and clearance of pathogens. However, their roles in chronic disease are less clear. They have been shown to be protective as well as positively associated with disease burden. This review focuses on the state of the monocyte biology field and the functions of monocytes, particularly nonclassical monocytes, in health and disease.

Iron oxide nanoparticles: Diagnostic, therapeutic and theranostic applications

Many different iron oxide nanoparticles have been evaluated over the years, for a wide variety of biomedical applications. We here summarize the synthesis, surface functionalization and characterization of iron oxide nanoparticles, as well as their (pre-) clinical use in diagnostic, therapeutic and theranostic settings. Diagnostic applications include liver, lymph node, inflammation and vascular imaging, employing mostly magnetic resonance imaging but recently also magnetic particle imaging. Therapeutic applications encompass iron supplementation in anemia and advanced cancer treatments, such as modulation of macrophage polarization, magnetic fluid hyperthermia and magnetic drug targeting. Because of their properties, iron oxide nanoparticles are particularly useful for theranostic purposes. Examples of such setups, in which diagnosis and therapy are intimately combined and in which iron oxide nanoparticles are used, are image-guided drug delivery, image-guided and microbubble-mediated opening of the blood-brain barrier, and theranostic tissue engineering. Together, these directions highlight the versatility and the broad applicability of iron oxide nanoparticles, and indicate the integration in future medical practice of multiple iron oxide nanoparticle-based materials.

Iron oxide nanoparticles: Diagnostic, therapeutic and theranostic applications

Many different iron oxide nanoparticles have been evaluated over the years, for a wide variety of biomedical applications. We here summarize the synthesis, surface functionalization and characterization of iron oxide nanoparticles, as well as their (pre-) clinical use in diagnostic, therapeutic and theranostic settings. Diagnostic applications include liver, lymph node, inflammation and vascular imaging, employing mostly magnetic resonance imaging but recently also magnetic particle imaging. Therapeutic applications encompass iron supplementation in anemia and advanced cancer treatments, such as modulation of macrophage polarization, magnetic fluid hyperthermia and magnetic drug targeting. Because of their properties, iron oxide nanoparticles are particularly useful for theranostic purposes. Examples of such setups, in which diagnosis and therapy are intimately combined and in which iron oxide nanoparticles are used, are image-guided drug delivery, image-guided and microbubble-mediated opening of the blood-brain barrier, and theranostic tissue engineering. Together, these directions highlight the versatility and the broad applicability of iron oxide nanoparticles, and indicate the integration in future medical practice of multiple iron oxide nanoparticle-based materials.

Magnetic Force-Based Microfluidic Techniques for Cellular and Tissue Bioengineering

Live cell manipulation is an important biotechnological tool for cellular and tissue level bioengineering applications due to its capacity for guiding cells for separation, isolation, concentration, and patterning. Magnetic force-based cell manipulation methods offer several advantages, such as low adverse effects on cell viability and low interference with the cellular environment. Furthermore, magnetic-based operations can be readily combined with microfluidic principles by precisely allowing control over the spatiotemporal distribution of physical and chemical factors for cell manipulation. In this review, we present recent applications of magnetic force-based cell manipulation in cellular and tissue bioengineering with an emphasis on applications with microfluidic components. Following an introduction of the theoretical background of magnetic manipulation, components of magnetic force-based cell manipulation systems are described. Thereafter, different applications, including separation of certain cell fractions, enrichment of rare cells, and guidance of cells into specific macro- or micro-arrangements to mimic natural cell organization and function, are explained. Finally, we discuss the current challenges and limitations of magnetic cell manipulation technologies in microfluidic devices with an outlook on future developments in the field.

Circulating inflammatory monocytes contribute to impaired influenza vaccine responses in HIV-infected participants

OBJECTIVE

Antibody responses are often impaired in old age and in HIV-positive (HIV+) infection despite virologic control with antiretroviral therapy but innate immunologic determinants are not well understood.

DESIGN

Monocytes and natural killer cells were examined for relationships to age, HIV infection and influenza vaccine responses.

METHODS

Virologically suppressed HIV+ (n = 139) and HIV-negative (HIV-) (n = 137) participants classified by age as young (18-39 years), middle-aged (40-59 years) and old (≥60 years) were evaluated preinfluenza and postinfluenza vaccination.

RESULTS

Prevaccination frequencies of inflammatory monocytes were highest in old HIV+ and HIV-, with old HIV+ exhibiting higher frequency of integrin CD11b on inflammatory monocytes that was correlated with age, expression of C-C chemokine receptor-2 (CCR2) and plasma soluble tumor necrosis factor receptor-1 (sTNFR1), with inverse correlation with postvaccination influenza H1N1 antibody titers. Higher frequencies of CD11b+ inflammatory monocytes (CD11b(hi), >48.4%) compared with low frequencies of CD11b+ inflammatory monocytes (<15.8%) was associated with higher prevaccination frequencies of total and inflammatory monocytes and higher CCR2 MFI, higher plasma sTNFR1 and CXCL-10 with higher lipopolysaccharide stimulated expression of TNFα and IL-6, concomitant with lower postvaccination influenza antibody titers. In HIV+ CD11b(hi) expressers, the depletion of inflammatory monocytes from peripheral blood mononuclear cells resulted in enhanced antigen-specific CD4+ T-cell proliferation. Immature CD56(hi) natural killer cells were lower in young HIV+ compared with young HIV- participants.

CONCLUSION

Perturbations of innate immunity and inflammation signified by high CD11b on inflammatory monocytes are exacerbated with aging in HIV+ and negatively impact immune function involved in Ab response to influenza vaccination.

Proportions of Proinflammatory Monocytes Are Important Predictors of Mortality Risk in Hemodialysis Patients

Despite the continuous progression in dialysis medicine, mortality and the burden of cardiovascular disease (CVD) among hemodialysis patients are still substantial. Substantial evidence suggests that proinflammatory (CD16+) monocytes contribute to the development of atherosclerosis. A cohort of 136 stable hemodialysis patients (follow-up: 6.25 year) was assessed to investigate the association between the proportion of CD16+ monocytes for all-cause and CVD mortalities. The CD16+ monocytes were associated with both mortalities after adjusting for a preexisting CVD history. Compared to the reference group (CD16+ monocytes within [15.6–18.6], the first and second quartile), patients with CD16+ monocytes above the highest quartile level (>21.5) had an adjusted hazard ratio (HR) of 30.85 (95% confidence interval [CI]: 7.12–133.8) for CVD mortality and 5.28 (2.07–13.49) for all-cause mortality, and those with CD16+ monocytes below the lowest quartile ≤15.6), had significantly elevated death risks after 3.5-year follow-up (HR [95% CI]: 10.9 [2.42–48.96] and 4.38 [1.45–13.24] for CV and all-cause mortalities, respectively). The hemodialysis patients with CD16+ monocyte level in a low but mostly covering normal range also portended a poor prognosis. The findings shed some light for nephrologists on future prospects of early recognizing immune dysfunction and improving early intervention outcomes.

The "Intermediate" CD14++CD16+ monocyte subset increases in severe peripheral artery disease in humans

Monocytes are key players in atherosclerotic. Human monocytes display a considerable heterogeneity and at least three subsets can be distinguished. While the role of monocyte subset heterogeneity has already been well investigated in coronary artery disease (CAD), the knowledge about monocytes and their heterogeneity in peripheral artery occlusive disease (PAOD) still is limited. Therefore, we aimed to investigate monocyte subset heterogeneity in patients with PAOD. Peripheral blood was obtained from 143 patients suffering from PAOD (Rutherford stage I to VI) and three monocyte subsets were identified by flow cytometry: CD14⁺⁺CD16⁻ classical monocytes, CD14⁺CD16⁺⁺ non-classical monocytes and CD14⁺⁺CD16⁺ intermediate monocytes. Additionally the expression of distinct surface markers (CD106, CD162 and myeloperoxidase MPO) was analyzed. Proportions of CD14⁺⁺CD16⁺ intermediate monocyte levels were significantly increased in advanced stages of PAOD, while classical and non-classical monocytes displayed no such trend. Moreover, CD162 and MPO expression increased significantly in intermediate monocyte subsets in advanced disease stages. Likewise, increased CD162 and MPO expression was noted in CD14⁺⁺CD16⁻ classical monocytes. These data suggest substantial dynamics in monocyte subset distributions and phenotypes in different stages of PAOD, which can either serve as biomarkers or as potential therapeutic targets to decrease the inflammatory burden in advanced stages of atherosclerosis.

Increased intermediate CD14++CD16++ monocyte subset levels associate with restenosis after peripheral percutaneous transluminal angioplasty

BACKGROUND AND AIMS

We aimed at studying the association of three major human monocyte subsets after percutaneous transluminal angioplasty (PTA) in patients with femoropopliteal disease.

METHODS

We prospectively studied 67 sequential patients (40 male, 27 female; mean age 71 ± 11 years) treated with femoropopliteal angioplasty. Multi-color flow cytometry characterized monocyte subsets from venous blood for expression of CD14 and CD16 and intracellular myeloperoxidase (MPO) prior to, and 3, 6 and 12 months post PTA. Analyses tested associations between monocyte subsets and risk for restenosis.

RESULTS

16/67 patients (24%) developed restenosis within 12 months after PTA. Patients with hyperlipidemia had increased risk for restenosis (HR = 1.7, 95% CI 0.7-2.9, p = 0.001). Increased baseline monocytes associated with an increased risk of late restenosis (HR = 4.9, 95% CI: 1.3-18.6, p = 0.047). CD14⁺⁺CD16⁺⁺ 'intermediate' monocytes assessed at baseline, and after 3, 6, and 12 months significantly associated with the risk for subsequent restenosis: HR = 3.9 (95% CI: 2.4-6.5, p = 0.029), HR = 5.7 (95% CI = 0.7-44.7, p = 0.013), HR = 6.5 (95% CI: 2.5-16.9, p = 0.001) and HR = 1.5 (95% CI = 1.4-15.5 p = 0.001), respectively. Moreover, the probability for freedom of restenosis decreased with increased levels of intermediate subsets at 12 months after PTA. Additionally, intracellular MPO expression in CD14⁺⁺CD16⁺⁺ measured at 3, 6 and 12 months associated with an increased restenosis risk (HR = 1.5, 95% CI: 0.8-2.1, p = 0.214, HR = 1.9, 95% CI: 1.0-2.3 p = 0.051 and HR = 1.4, 95% CI: 1.0-1.8, p = 0.052).

CONCLUSIONS

Our results imply altered innate immunity after angioplasty. Elevated CD14⁺⁺CD16⁺⁺ intermediate monocyte frequencies and increased MPO expression may identify individuals at heightened risk for restenosis.

Disordered haematopoiesis and athero-thrombosis

Atherosclerosis, the major underlying cause of cardiovascular disease, is characterized by a lipid-driven infiltration of inflammatory cells in large and medium arteries. Increased production and activation of monocytes, neutrophils, and platelets, driven by hypercholesterolaemia and defective high-density lipoproteins-mediated cholesterol efflux, tissue necrosis and cytokine production after myocardial infarction, or metabolic abnormalities associated with diabetes, contribute to atherogenesis and athero-thrombosis. This suggests that in addition to traditional approaches of low-density lipoproteins lowering and anti-platelet drugs, therapies directed at abnormal haematopoiesis, including anti-inflammatory agents, drugs that suppress myelopoiesis, and excessive platelet production, rHDL infusions and anti-obesity and anti-diabetic agents, may help to prevent athero-thrombosis.

Native LDL promotes differentiation of human monocytes to macrophages with an inflammatory phenotype

Recruitment of monocytes in atherosclerosis is dependent upon increased levels of plasma lipoproteins which accumulate in the blood vessel wall. The extracellular milieu can influence the phenotype of monocyte subsets (classical: CD14++CD16-, intermediate: CD14+CD16+ and non-classical: CD14dimCD16++) and macrophages (M1 or M2) and consequently the initiation, progression and/or regression of atherosclerosis. However, it is not known what effect lipoproteins, in particular native low-density lipoproteins (nLDL), have on the polarisation of monocyte-derived macrophages. Monocytes were differentiated into macrophages in the presence of nLDL. nLDL increased gene expression of the inflammatory cytokines TNFα and IL-6 in macrophages polarised towards the M1 phenotype while decreasing the M2 surface markers, CD206 and CD200R and the anti-inflammatory cytokines TGFβ and IL-10. Compared to the classical and intermediate subsets, the non-classical subset-derived macrophages had a reduced ability to respond to M1 stimuli (LPS and IFNγ). nLDL enhanced the TNFα and IL-6 gene expression in macrophages from all monocyte subsets, indicating an inflammatory effect of nLDL. Further, the classical and intermediate subsets both responded to M2 stimuli (IL-4) with upregulation of TGFβ and SR-B1 mRNA; an effect, which was reduced by nLDL. In contrast, the non-classical subset failed to respond to IL-4 or nLDL, suggesting it may be unable to polarise into M2 macrophages. Our data suggests that monocyte interaction with nLDL significantly affects macrophage polarisation and that this interaction appears to be subset dependent.

g-force induced giant efficiency of nanoparticles internalization into living cells

Nanotechnology plays an increasingly important role in the biomedical arena. Iron oxide nanoparticles (IONPs)-labelled cells is one of the most promising approaches for a fast and reliable evaluation of grafted cells in both preclinical studies and clinical trials. Current procedures to label living cells with IONPs are based on direct incubation or physical approaches based on magnetic or electrical fields, which always display very low cellular uptake efficiencies. Here we show that centrifugation-mediated internalization (CMI) promotes a high uptake of IONPs in glioblastoma tumour cells, just in a few minutes, and via clathrin-independent endocytosis pathway. CMI results in controllable cellular uptake efficiencies at least three orders of magnitude larger than current procedures. Similar trends are found in human mesenchymal stem cells, thereby demonstrating the general feasibility of the methodology, which is easily transferable to any laboratory with great potential for the development of improved biomedical applications.

Molecular imaging of inflammation in atherosclerosis

Acute rupture of vulnerable plaques frequently leads to myocardial infarction and stroke. Within the last decades, several cellular and molecular players have been identified that promote atherosclerotic lesion formation, maturation and plaque rupture. It is now widely recognized that inflammation of the vessel wall and distinct leukocyte subsets are involved throughout all phases of atherosclerotic lesion development. The mechanisms that render a stable plaque unstable and prone to rupture, however, remain unknown and the identification of the vulnerable plaque remains a major challenge in cardiovascular medicine. Imaging technologies used in the clinic offer minimal information about the underlying biology and potential risk for rupture. New imaging technologies are therefore being developed, and in the preclinical setting have enabled new and dynamic insights into the vessel wall for a better understanding of this complex disease. Molecular imaging has the potential to track biological processes, such as the activity of cellular and molecular biomarkers in vivo and over time. Similarly, novel imaging technologies specifically detect effects of therapies that aim to stabilize vulnerable plaques and silence vascular inflammation. Here we will review the potential of established and new molecular imaging technologies in the setting of atherosclerosis, and discuss the cumbersome steps required for translating molecular imaging approaches into the clinic.

Monocyte heterogeneity in cardiovascular disease

Only a few decades ago, students of the pathophysiology of cardiovascular disease paid little heed to the involvement of inflammation and immunity. Multiple lines of evidence now point to the participation of innate and adaptive immunity and inflammatory signaling in a variety of cardiovascular conditions. Hence, interest has burgeoned in this intersection. This review will focus on the contribution of innate immunity to both acute injury to the heart muscle itself, notably myocardial infarction, and to chronic inflammation in the artery wall, namely atherosclerosis, the cause of most myocardial infarctions. Our discussion of the operation of innate immunity in cardiovascular diseases will focus on functions of the mononuclear phagocytes, with special attention to emerging data regarding the participation of different functional subsets of these cells in cardiovascular pathophysiology.

Making a difference: monocyte heterogeneity in cardiovascular disease

Monocytes are frequently described as bone marrow-derived precursors of macrophages. Although many studies support this view, we now appreciate that monocytes neither develop exclusively in the bone marrow nor give rise to all macrophages and dendritic cells. In addition to differentiating to specific leukocyte populations, monocytes, as monocytes, are functionally and ontogenically heterogeneous. In this review we will focus on the development and activity of monocytes and their subsets in mice (Ly-6 C(high/low)) and humans (CD14(+/dim/-) CD16(+/-)) in the context of atherosclerosis and its complications.

Novel immune signals and atherosclerosis

Atherosclerosis underlies coronary artery disease (CAD) and cerebrovascular disease, which are the most common forms of life-threatening cardiovascular disorders. To minimize the risk of atherosclerotic complications, primary and secondary prevention strategies seek to control risk factors. Reducing low-density lipoprotein (LDL) cholesterol through lipid-lowering drugs, such as statins, in particular yields a proportional decrease in cardiovascular disease risk. Atherosclerosis is considered to be a complex chronic inflammatory process triggered by cardiovascular risk factors which cause endothelial dysfunction and inflammatory cell infiltration within the artery wall. In this review, we summarize the current understanding of the underling molecular mechanisms of the immune signals in the development and progression of atherosclerosis. Among various molecular mechanisms, toll like receptors (TLRs) are potent proinflammatory cytokines that operate to induce inflammation play an important role in the pathogenesis of atherosclerosis. Moreover, we discuss current knowledge regarding monocyte/macrophage biology that contributes to the progression of atherosclerosis, including macrophage polarization and heterogeneity. Understanding the molecular mechanisms in conjunction with orchestration of monocyte/macrophage biology should provide a basis for novel treatment strategies to prevent the development and progression of atherosclerosis.

Reactive oxygen species and thiol redox signaling in the macrophage biology of atherosclerosis

SIGNIFICANCE

Despite the recent decline in the prevalence of cardiovascular diseases, atherosclerosis remains the leading cause of death in industrialized countries. Monocyte recruitment into the vessel wall is a rate-limiting step in atherogenesis. Death of macrophage-derived foam cells promotes lesion progression and the majority of acute complications of atherosclerotic disease (e.g., myocardial infarction) occur in lesions that are intensely infiltrated with monocyte-derived macrophages, underlining the critical roles monocytes and macrophages play in this complex chronic inflammatory disease.

RECENT ADVANCES

A rapidly growing body of literature supports a critical role for reactive oxygen species (ROS) in the regulation of monocyte and macrophage (dys)function associated with atherogenesis and macrophage death in atherosclerotic plaque.

CRITICAL ISSUES

In this review we highlight the important roles of NADHP oxidase 4 recently identified in monocytes and macrophages and the role of ROS and (thiol) redox signaling in different aspects of monocytes and macrophage biology associated with atherosclerosis.

FUTURE DIRECTIONS

Studies aimed at identifying the intracellular targets of ROS involved in redox signaling in macrophages and at elucidating the redox signaling mechanisms that control differentiation, activation, polarization, and death of monocytes and macrophages may ultimately lead to the development of novel preventive and therapeutic strategies for atherosclerosis.

Self-assembled poly(ε-caprolactone)-g-chondroitin sulfate copolymers as an intracellular doxorubicin delivery carrier against lung cancer cells

The aim of this study was to utilize self-assembled polycaprolactone (PCL)-grafted chondroitin sulfate (CS) as an anticancer drug carrier. We separately introduced double bonds to the hydrophobic PCL and the hydrophilic CS. The modified PCL was reacted with the modified CS through a radical reaction (CSMA-g-PCL). The copolymer without doxorubicin (DOX) was noncytotoxic in CRL-5802 and NCI-H358 cells at a concentration ranging from 5–1000 μg/mL and DOX-loaded CSMA-g-PCL (Micelle DOX) had the lowest inhibitory concentration of 50% cell growth values against the NCI-H358 cells among test samples. The cellular uptake of Micelle DOX into the cells was confirmed by flow cytometric data and confocal laser scanning microscopic images. The in vivo tumor-targeting efficacy of Micelle DOX was realized using an NCI-H358 xenograft nude mouse model. The mice administered with Micelle DOX showed suppressed growth of the NCI-H358 lung tumor compared with those administered with phosphate-buffered saline and free DOX.

NR4A1 (Nur77) deletion polarizes macrophages toward an inflammatory phenotype and increases atherosclerosis

RATIONALE

NR4A1 (Nur77) is a nuclear receptor that is expressed in macrophages and within atherosclerotic lesions, yet its function in atherosclerosis is unknown.

OBJECTIVE

Nur77 regulates the development of monocytes, particularly patrolling Ly6C(-) monocytes that may be involved in resolution of inflammation. We sought to determine how absence of nuclear receptor subfamily 4, group A, member 1 (NR4A1) in hematopoietic cells affected atherosclerosis development.

METHODS AND RESULTS

Nur77(-/-) chimeric mice on a Ldlr(-/-) background showed a 3-fold increase in atherosclerosis development when fed a Western diet for 20 weeks, despite having a drastic reduction in Ly6C(-) patrolling monocytes. In a second model, mice deficient in both Nur77 and ApoE (ApoE(-/-)Nur77(-/-)) also showed increased atherosclerosis after 11 weeks of Western diet. Atherosclerosis was associated with a significant change in macrophage polarization toward a proinflammatory phenotype, with high expression of tumor necrosis factor-α and nitric oxide and low expression of Arginase-I. Moreover, we found increased expression of toll-like receptor 4 mRNA and protein in Nur77(-/-) macrophages as well as increased phosphorylation of the p65 subunit of NFκB. Inhibition of NFκB activity blocked excess activation of Nur77(-/-) macrophages.

CONCLUSIONS

We conclude that the absence of Nur77 in monocytes and macrophages results in enhanced toll-like receptor signaling and polarization of macrophages toward a proinflammatory M1 phenotype. Despite having fewer monocytes, Nur77(-/-) mice developed significant atherosclerosis when fed a Western diet. These studies indicate that Nur77 is a novel target for modulating the inflammatory phenotype of monocytes and macrophages and may be important for regulation of atherogenesis.

Different capacity of monocyte subsets to phagocytose iron-oxide nanoparticles

Objective

To explore the capacity of human CD14⁺CD16⁺⁺ and CD14⁺⁺CD16^- monocytes to phagocyte iron-oxide nanoparticles in vitro.

Methods

Human monocytes were labeled with four different magnetic nanoparticle preparations (Ferumoxides, SHU 555C, CLIO-680, MION-48) exhibiting distinct properties and cellular uptake was quantitatively assessed by flow cytometry, fluorescence microscopy, atomic absorption spectrometry and Magnetic Resonance Imaging (MRI). Additionally we determined whether cellular uptake of the nanoparticles resulted in phenotypic changes of cell surface markers.

Results

Cellular uptake differed between the four nanoparticle preparations. However for each nanoparticle tested, CD14⁺⁺CD16^- monocytes displayed a significantly higher uptake compared to CD14⁺CD16⁺⁺ monocytes, this resulted in significantly lower T1 and T2 relaxation times of these cells. The uptake of iron-oxide nanoparticles further resulted in a remarkable shift of expression of cell surface proteins indicating that the labeling procedure affects the phenotype of CD14⁺CD16⁺⁺ and CD14⁺⁺CD16^- monocytes differently.

Conclusion

Human monocyte subsets internalize different magnetic nanoparticle preparations differently, resulting in variable loading capacities, imaging phenotypes and likely biological properties.

Differential role of monocyte subsets in atherosclerosis

Endothelial dysfunction and inflammation of the arterial wall continuously drive the development of atherosclerosis. Details regarding the sequential involvement of different monocyte subsets in the pathology of this disease have recently emerged. This review concentrates on major monocyte subpopulations in mouse and men and specifically addresses their phenotype, function and recruitment during primary atherosclerosis as well as their contribution to angiogenesis and tissue regeneration secondary to plaque rupture.

CD14dimCD16+ and CD14+CD16+ monocytes in obesity and during weight loss: relationships with fat mass and subclinical atherosclerosis

OBJECTIVE

Studies suggest the implication of CD16(+) subpopulations (CD14(+)CD16(+), CD14(dim)CD16(+)) in inflammatory diseases. We aimed to determine the frequency of these subpopulations during weight loss in obesity and diabetes, conditions associated with changes in systemic inflammation, and we tested the link with subclinical atherosclerosis.

METHODS AND RESULTS

CD14(dim)CD16(+) and CD14(+)CD16(+) frequencies were measured by flow cytometry in lean subjects, obese subjects before and after a hypocaloric diet or gastric surgery, and obese diabetic subjects before and after gastric surgery. Both monocyte subsets were increased in obese subjects, with a significant enrichment of the CD14(dim)CD16(+) subpopulation in obese diabetic patients. Multivariate analysis demonstrated a link between the percentages of CD14(dim)CD16(+) monocytes and glycemia, independent of fat mass. Drastic weight loss led to a sharp decrease of this subset, the variations of which were strongly related to fat mass changes. A reduction of at least 5% of fat mass was sufficient to observe a significant decrease of CD14(dim)CD16(+) monocytes. A diminution of the CD14(+)CD16(+) subset was also observed during weight loss and was associated with a decrease in intima-media thickness.

CONCLUSIONS

This work demonstrates a major impact of fat mass variations on CD14(dim)CD16(+) monocyte subsets and that the decrease in the CD14(+)CD16(+) subpopulation is linked to a reduction of subclinical atherosclerosis.

CLINICAL TRIAL REGISTRATION

URL: http://clinicaltrials.gov. Unique identifier: NCT00476658.

Micro-NMR for rapid molecular analysis of human tumor samples

Although tumor cells obtained from human patients by image-guided intervention are a valuable source for diagnosing cancer, conventional means of analysis are limited. Here, we report the development of a quantitative micro-NMR (nuclear magnetic resonance) system for rapid, multiplexed analysis of human tumors. We implemented the technology in a clinical setting to analyze cells obtained by fine-needle aspirates from suspected lesions in 50 patients and validated the results in an independent cohort of another 20 patients. Single fine-needle aspirates yielded sufficient numbers of cells to enable quantification of multiple protein markers in all patients within 60 min. Moreover, using a four-protein signature, we report a 96% accuracy for establishing a cancer diagnosis, surpassing conventional clinical analyses by immunohistochemistry. Our results also show that protein expression patterns decay with time, underscoring the need for rapid sampling and diagnosis close to the patient bedside. We also observed a surprising degree of heterogeneity in protein expression both across the different patient samples and even within the same tumor, which has important implications for molecular diagnostics and therapeutic drug targeting. Our quantitative point-of-care micro-NMR technique shows potential for cancer diagnosis in the clinic.

Innate immunity and monocyte-macrophage activation in atherosclerosis

Innate inflammation is a hallmark of both experimental and human atherosclerosis. The predominant innate immune cell in the atherosclerotic plaque is the monocyte-macrophage. The behaviour of this cell type within the plaque is heterogeneous and depends on the recruitment of diverse monocyte subsets. Furthermore, the plaque microenvironment offers polarisation and activation signals which impact on phenotype. Microenvironmental signals are sensed through pattern recognition receptors, including toll-like and NOD-like receptors - the latter of which are components of the inflammasome - thus dictating macrophage behaviour and outcome in atherosclerosis. Recently cholesterol crystals and modified lipoproteins have been recognised as able to directly engage these pattern recognition receptors. The convergent role of such pathways in terms of macrophage activation is discussed in this review.

Heterogeneity of human monocytes: an optimized four-color flow cytometry protocol for analysis of monocyte subsets

Monocytes are central mediators in the development of atherosclerotic plaques. They circulate in blood and eventually migrate into tissue including the vessel wall where they give rise to macrophages and dendritic cells. The existence of monocyte subsets with distinct roles in homeostasis and inflammation suggests specialization of function. These subsets are identified based on expression of the CD14 and CD16 markers. Routinely applicable protocols remain elusive, however. Here, we present an optimized four-color flow cytometry protocol for analysis of human blood monocyte subsets using a specific PE-Cy5-conjugated monoclonal antibody (mAb) to HLA-DR, a PE-Cy7-conjugated mAb to CD14, a FITC-conjugated mAb to CD16, and PE-conjugated mAbs to additional markers relevant to monocyte function. Classical CD14(+)CD16(-) monocytes (here termed "Mo1" subset) expressed high CCR2, CD36, CD64, and CD62L, but low CX(3)CR1, whereas "nonclassical" CD14(lo)CD16(+) monocytes (Mo3) essentially showed the inverse expression pattern. CD14(+)CD16(+) monocytes (Mo2) expressed high HLA-DR, CD36, and CD64. In patients with stable coronary artery disease (n = 13), classical monocytes were decreased, whereas "nonclassical" monocytes were increased 90% compared with healthy subjects with angiographically normal coronary arteries (n = 14). Classical monocytes from CAD patients expressed higher CX(3)CR1 and CCR2 than controls. Thus, stable CAD is associated with expansion of the nonclassical monocyte subset and increased expression of inflammatory markers on monocytes. Flow cytometric analysis of monocyte subsets and marker expression may provide valuable information on vascular inflammation. This may translate into the identification of monocyte subsets as selective therapeutic targets, thus avoiding adverse events associated with indiscriminate monocyte inhibition.

Insights into atherosclerosis using nanotechnology

A developing forefront in vascular disease research is the application of nanotechnology, the engineering of devices at the molecular scale, for diagnostic and therapeutic applications in atherosclerosis. Promising research in this field over the past decade has resulted in the preclinical validation of nanoscale devices that target cellular and molecular components of the atherosclerotic plaque, including one of its prominent cell types, the macrophage. Nanoscale contrast agents targeting constituents of plaque biology have been adapted for application in multiple imaging modalities, leading toward more detailed diagnostic readouts, whereas nanoscale drug delivery devices can be tailored for site-specific therapeutic activity. This review highlights recent progress in utilizing nanotechnology for the clinical management of atherosclerosis, drawing upon recent preclinical studies relevant to diagnosis and treatment of the plaque and promising future applications.

Molecular diagnostics in transplantation

The past few decades are characterized by an explosive evolution of genetics and molecular cell biology. Advances in chemistry and engineering have enabled increased data throughput, permitting the study of complete sets of molecules with increasing speed and accuracy using techniques such as genomics, transcriptomics, proteomics, and metabolomics. Prediction of long-term outcomes in transplantation is hampered by the absence of sufficiently robust biomarkers and a lack of adequate insight into the mechanisms of acute and chronic alloimmune injury and the adaptive mechanisms of immunological quiescence that may support transplantation tolerance. Here, we discuss some of the great opportunities that molecular diagnostic tools have to offer both basic scientists and translational researchers for bench-to-bedside clinical application in transplantation medicine, with special focus on genomics and genome-wide association studies, epigenetics (DNA methylation and histone modifications), gene expression studies and transcriptomics (including microRNA and small interfering RNA studies), proteomics and peptidomics, antibodyomics, metabolomics, chemical genomics and functional imaging with nanoparticles. We address the challenges and opportunities associated with the newer high-throughput sequencing technologies, especially in the field of bioinformatics and biostatistics, and demonstrate the importance of integrative approaches. Although this Review focuses on transplantation research and clinical transplantation, the concepts addressed are valid for all translational research.

The multiple roles of monocyte subsets in steady state and inflammation

Monocytes participate importantly in immunity. Produced in the bone marrow and released into the blood, they circulate in blood or reside in a spleen reservoir before entering tissue and giving rise to macrophages or dendritic cells. Monocytes are more than transitional cells that adapt to a particular tissue environment indiscriminately. Accumulating evidence now indicates that monocytes are heterogeneous in several species and are themselves predetermined for particular function in the steady state and inflammation. Future therapeutics may harness this heterogeneity to target harmful functions while sparing those that are beneficial. Here, we review recent advances on the ontogeny and function of monocytes and their subsets in humans and mice.

M1-activated macrophages migration, a marker of aortic atheroma progression: a preclinical MRI study in mice

BACKGROUND

M1-activated Macrophages (M1M) play a major role in atherosclerotic lesions of aortic arch, promoting proinflammatory response. In vivo trafficking of M1M in aortic plaques is therefore critical.

METHODS

M1M from bone marrow cell culture were magnetically labeled, using iron nanoparticles, intravenously injected and followed up with 3 day magnetic resonance imaging (MRI) in mice developing macrophage-laden atheroma (ApoE2 knock-in mice). M1M recruitment in aortic arch lesions was assessed both by MRI and histology.

RESULTS

In all ApoE2 knock-in mice injected with labeled cells, high resolution MRI showed localized signal loss regions in the thickened aortic wall, with a maximal effect at day 2 (-34% +/- 7.3% P < 0.001 compared with baseline). This was confirmed with Prussian blue (iron) staining and corresponded to M1M (Major Histo-compatibility Complex II positive). Clear different intraplaque and adventitial dynamic distribution profiles of labeled cells were observed during the 3 days.

CONCLUSION

M1M dynamic MRI is a promising marker to noninvasively assess the macrophage trafficking underlying aortic arch plaque progression.

Macrophages heterogeneity in atherosclerosis - implications for therapy

Atherosclerosis is a chronic inflammatory disease occurring within the artery wall and is an underlying cause of cardiovascular complications, including myocardial infarction, stroke and peripheral vascular disease. Its pathogenesis involves many immune cell types with a well accepted role for monocyte/macrophages. Cholesterol-loaded macrophages are a characteristic feature of plaques and are major players in all stages of plaque development. As well as modulating lipid metabolism, macrophages secrete inflammatory cytokines, chemokines and reactive oxygen and nitrogen species that drive pathogenesis. They also produce proteases and tissue factor that contribute to plaque rupture and thrombosis. Macrophages are however heterogeneous cells and when appropriately activated, they phagocytose cytotoxic lipoproteins, clear apoptotic bodies, secrete anti-inflammatory cytokines and synthesize matrix repair proteins that stabilize vulnerable plaques. Pharmacological modulation of macrophage activity therefore represents a potential therapeutic strategy for atherosclerosis. The aim of this review is to provide an overview of the current understanding of the different macrophage subsets and their monocyte precursors, and, the implications of these subsets for atherosclerosis. This will present a foundation for highlighting novel opportunities to exploit the heterogeneity of macrophages as important diagnostic and therapeutic targets for atherosclerosis and its associated diseases.

Hybrid PET-optical imaging using targeted probes

Fusion imaging of radionuclide-based molecular (PET) and structural data [x-ray computed tomography (CT)] has been firmly established. Here we show that optical measurements [fluorescence-mediated tomography (FMT)] show exquisite congruence to radionuclide measurements and that information can be seamlessly integrated and visualized. Using biocompatible nanoparticles as a generic platform (containing a (18)F isotope and a far red fluorochrome), we show good correlations between FMT and PET in probe concentration (r(2) > 0.99) and spatial signal distribution (r(2) > 0.85). Using a mouse model of cancer and different imaging probes to measure tumoral proteases, macrophage content and integrin expression simultaneously, we demonstrate the distinct tumoral locations of probes in multiple channels in vivo. The findings also suggest that FMT can serve as a surrogate modality for the screening and development of radionuclide-based imaging agents.

High intracellular iron oxide nanoparticle concentrations affect cellular cytoskeleton and focal adhesion kinase-mediated signaling

Iron oxide nanoparticle internalization exerts detrimental effects on cell physiology for a variety of particles, but little is known about the mechanism involved. The effects of high intracellular levels of four types of iron oxide particles (Resovist, Endorem, very small organic particles, and magnetoliposomes (MLs)) on the viability and physiology of murine C17.2 neural progenitor cells and human blood outgrowth endothelial cells are reported. The particles diminish cellular proliferation and affect the actin cytoskeleton and microtubule network architectures as well as focal adhesion formation and maturation. The extent of the effects correlates with the intracellular concentration (= iron mass) of the particles, with the biggest effects for Resovist and MLs at the highest concentration (1000 microg Fe mL(-1)). Similarly, the expression of focal adhesion kinase (FAK) and the amount of activated kinase (pY397-FAK) are affected. The data suggest that high levels of perinuclear localized iron oxide nanoparticles diminish the efficiency of protein expression and sterically hinder the mature actin fibers, and could have detrimental effects on cell migration and differentiation.

Monocytes in atherosclerosis: subsets and functions

Chronic inflammation drives atherosclerosis, the leading cause of cardiovascular disease. Over the past two decades, data have emerged showing that immune cells are involved in the pathogenesis of atherosclerotic plaques. The accumulation and continued recruitment of leukocytes are associated with the development of 'vulnerable' plaques. These plaques are prone to rupture, leading to thrombosis, myocardial infarction or stroke, all of which are frequent causes of death. Plaque macrophages account for the majority of leukocytes in plaques, and are believed to differentiate from monocytes recruited from circulating blood. However, monocytes represent a heterogenous circulating population of cells. Experiments are needed to address whether monocyte recruitment to plaques and effector functions, such as the formation of foam cells, the production of nitric oxide and reactive oxygen species, and proteolysis are critical for the development and rupture of plaques, and thus for the pathophysiology of atherosclerosis, as well as elucidate the precise mechanisms involved.

Comparison of gene expression profiles between human and mouse monocyte subsets

Blood of both humans and mice contains 2 main monocyte subsets. Here, we investigated the extent of their similarity using a microarray approach. Approximately 270 genes in humans and 550 genes in mice were differentially expressed between subsets by 2-fold or more. More than 130 of these gene expression differences were conserved between mouse and human monocyte subsets. We confirmed numerous of these differences at the cell surface protein level. Despite overall conservation, some molecules were conversely expressed between the 2 species' subsets, including CD36, CD9, and TREM-1. Other differences included a prominent peroxisome proliferator-activated receptor gamma (PPARgamma) signature in mouse monocytes, which is absent in humans, and strikingly opposed patterns of receptors involved in uptake of apoptotic cells and other phagocytic cargo between human and mouse monocyte subsets. Thus, whereas human and mouse monocyte subsets are far more broadly conserved than currently recognized, important differences between the species deserve consideration when models of human disease are studied in mice.

Regulation of the migration and survival of monocyte subsets by chemokine receptors and its relevance to atherosclerosis

Monocytes are central mediators in the advance of atherosclerotic plaque, making them a natural therapeutic target for reducing disease burden. Here, we highlight recent advances in our current understanding of monocyte heterogeneity and its relevance to regulation of monocyte accumulation and function within atherosclerotic plaques. Differences that distinguish monocyte subsets include differential expression of chemokine receptors, especially CCR2 and CX3CR1. Ablation of expression of these 2 receptors (or their ligands) in mice has an additive inhibition on monocyte recruitment to atherosclerotic plaques. Moreover, simultaneously interfering with 3 key pathways--CCR2, CX3CR1, and CCR5--essentially abolishes atherosclerosis in mice. Here, we discuss how these chemokine receptors act at multiple points on at least 1 monocyte subset, regulating their mobilization from bone marrow, survival, or recruitment to plaques. Finally, we discuss how this knowledge may be useful clinically, emphasizing that CX3CR1 may in particular be a viable target for therapeutic manipulation of monocyte-derived cell fate in cardiovascular disease.