Association of monocyte subsets with vulnerability characteristics of coronary plaques as assessed by 64-slice multidetector computed tomography in patients with stable angina pectoris

Monocyte subsets and monocyte-platelet aggregates in patients with unstable angina

Monocyte subsets and monocyte-platelet aggregates (MPAs) play important role in atherosclerosis and thrombosis. We aimed to determine their changes in patients with unstable angina (UA). In this cross-sectional case-control study, Global Registry of Acute Coronary Events (GRACE) score was determined in 95 UA patients without elevated troponin level. Thirty age-and-sex matched stable coronary heart disease (CHD) subjects served as control group. The classical (CD14++CD16-, Mon1), the intermediate (CD14++CD16+, Mon2) and the non-classical (CD14+CD16++, Mon3) monocytes, as well as subset-specific MPAs, were measured by flow cytometry. Compared with stable CHD patients, UA patients had increased Mon2 and Mon3 counts (all P < 0.001). For UA subjects, compared with GRACE score-determined low risk patients (GRACE score ≤108, n = 70), intermediate-to-high risk patients (GRACE score >108, n = 25) had higher counts of Mon2 and total MPAs, as well as Mon1- and Mon2-associated MPAs (all P < 0.001). Adjusted binary logistic regression analysis revealed that increased counts of Mon2 subset (for per 5 cells/μL increase, OR 1.186, 95% CI 1.044-1.347, P = 0.009), Mon2 MPAs (for per 5 cells/μL increase, OR 1.228, 95% CI 1.062-1.421, P = 0.006) and total MPAs (for per 5 cells/μL increase, OR 1.072, 95 % CI 1.010-1.137, P = 0.022) independently associated with GRACE score-determined intermediate-to-high risk UA patients. In UA patients with intermediate-to-high risk (determined by GRACE score), counts of Mon2 subset, Mon2-associated MPAs and total MPAs are increased, which are independent of traditional risk factors.

Correlation Between High-Density Lipoprotein and Monocyte Subsets in Patients with Stable Coronary Heart Disease

Background

High-density lipoprotein (HDL) consists of heterogeneous particles with a variety of structures and functions. Its role in atherosclerosis has been gradually recognized. Studies have shown dysfunction of small HDL in patients with coronary artery disease (CAD). Monocytes play an important role in atherosclerosis, which can be divided into 3 subgroups based on the expression of surface markers CD14 and CD16. This study aimed to investigate the association between HDL and monocyte subsets in CAD patients.

Material/Methods

A total of 90 patients with stable CAD were selected in this study. Monocytes were divided into classical monocytes (CM, CD14++CD16−), intermediate monocytes (IM, CD14++CD16+), and non-classical monocytes (NCM, CD14+CD16++). HDL components in serum were determined by high-resolution polyacrylamide gel electrophoresis (detected by Quantimetrix HDL Lipoprint system, referring to HDL subfractions analysis: A new laboratory diagnostic assay for patients with cardiovascular diseases and dyslipoproteinemia).

Results

Serum level of small HDL was positively correlated with circulating proinflammatory NCM (r=0.30; p=0.004), negatively correlated with CM, and not correlated with IM. We also found that disease severity was not associated with diabetes mellitus, glycosylated hemoglobin, hypertension, smoking history, or statin dosage.

Conclusions

Our study confirmed that small HDL level is associated with an increase in NCM and a decrease in CM, suggesting the proinflammatory relationship between small HDL and intrinsic immune function during the progression of stable CAD.

Monocyte subset distribution in patients with stable atherosclerosis and elevated levels of lipoprotein(a)

Background

Lipoprotein(a) (Lp(a)) is a proatherogenic plasma lipoprotein currently established as an independent risk factor for the development of atherosclerotic disease and as a predictor for acute thrombotic complications. In addition, Lp(a) is the major carrier of proinflammatory oxidized phospholipids (OxPL). Today, atherosclerosis is considered to be an inflammatory disease of the vessel wall in which monocytes and monocyte-derived macrophages are crucially involved. Circulating monocytes can be divided according to their surface expression pattern of CD14 and CD16 into at least 3 subsets with distinct inflammatory and atherogenic potential.

Objective

The aim of this study was to examine whether elevated levels of Lp(a) and OxPL on apolipoprotein B-100–containing lipoproteins (OxPL/apoB) are associated with changes in monocyte subset distribution.

Methods

We included 90 patients with stable coronary artery disease. Lp(a) and OxPL/apoB were measured, and monocyte subsets were identified as classical monocytes (CMs; CD14++CD16−), intermediate monocytes (IMs; CD14++CD16+), and nonclassical monocytes (NCMs; CD14+CD16++) by flow cytometry.

Results

In patients with elevated levels of Lp(a) (>50 mg/dL), monocyte subset distribution was skewed toward an increase in the proportion of IM (7.0 ± 3.8% vs 5.2 ± 3.0%; P = .026), whereas CM (82.6 ± 6.5% vs 82.0 ± 6.8%; P = .73) and NCM (10.5 ± 5.3 vs 12.8 ± 6.0; P = .10) were not significantly different. This association was independent of clinical risk factors, choice of statin treatment regime, and inflammatory markers. In addition, OxPL/apoB was higher in patients with elevated Lp(a) and correlated with IM but not CM and NCM.

Conclusions

In conclusion, we provide a potential link between elevated levels of Lp(a) and a proatherogenic distribution of monocyte subtypes in patients with stable atherosclerotic disease.

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Lipoprotein(a) serves as an independent risk factor in atherosclerotic disease.

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Monocyte subsets exhibit distinct inflammatory and atherogenic properties.

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Patients with elevated levels of Lp(a) show a shift towards intermediate monocytes.

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This association was independent of clinical properties and inflammatory markers.

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Those patients also exhibited higher OxPL/apoB concentrations.

Association of small dense LDL serum levels and circulating monocyte subsets in stable coronary artery disease

Objective

Atherosclerosis is considered to be an inflammatory disease in which monocytes and monocyte-derived macrophages play a key role. Circulating monocytes can be divided into three distinct subtypes, namely in classical monocytes (CM; CD14++CD16-), intermediate monocytes (IM; CD14++CD16+) and non-classical monocytes (NCM; CD14+CD16++). Low density lipoprotein particles are heterogeneous in size and density, with small, dense LDL (sdLDL) crucially implicated in atherogenesis. The aim of this study was to examine whether monocyte subsets are associated with sdLDL serum levels.

Methods

We included 90 patients with angiographically documented stable coronary artery disease and determined monocyte subtypes by flow cytometry. sdLDL was measured by an electrophoresis method on polyacrylamide gel.

Results

Patients with sdLDL levels in the highest tertile (sdLDL≥4mg/dL;T3) showed the highest levels of pro-inflammatory NCM (15.2±7% vs. 11.4±6% and 10.9±4%, respectively; p<0.01) when compared with patients in the middle (sdLDL=2-3mg/dL;T2) and lowest tertile (sdLDL=0-1mg/dL;T1). Furthermore, patients in the highest sdLDL tertile showed lower CM levels than patients in the middle and lowest tertile (79.2±8% vs. 83.9±7% and 82.7±5%; p<0.01 for T3 vs. T2+T1). Levels of IM were not related to sdLDL levels (5.6±4% vs. 4.6±3% vs. 6.4±3% for T3, T2 and T1, respectively). In contrast to monocyte subset distribution, levels of circulating pro- and anti-inflammatory markers were not associated with sdLDL levels.

Conclusion

The atherogenic lipoprotein fraction sdLDL is associated with an increase of NCM and a decrease of CM. This could be a new link between lipid metabolism dysregulation, innate immunity and atherosclerosis.

Nonclassical patrolling monocyte function in the vasculature

Nonclassical patrolling monocytes are characterized by their unique ability to actively patrol the vascular endothelium under homeostatic and inflammatory conditions. Patrolling monocyte subsets (CX3CR1(high)Ly6C(-) in mouse and CX3CR1(high)CD14(dim)CD16(+) in humans) are distinct from the classical monocyte subsets (CCR2(high)Ly6C(+) in mouse and CCR2(high)CD14(+)CD16(-) in humans) and exhibit unique functions in the vasculature and inflammatory disease. Patrolling monocytes function in several disease settings to remove damaged cells and debris from the vasculature and have been associated with wound healing and the resolution of inflammation in damaged tissues. This review highlights the unique functions of these patrolling monocytes in the vasculature and during inflammation.

Monocyte-targeting supramolecular micellar assemblies: a molecular diagnostic tool for atherosclerosis

Atherosclerosis is a multifactorial inflammatory disease that can progress silently for decades and result in myocardial infarction, stroke, and death. Diagnostic imaging technologies have made great strides to define the degree of atherosclerotic plaque burden through the severity of arterial stenosis. However, current technologies cannot differentiate more lethal "vulnerable plaques," and are not sensitive enough for preventive medicine. Imaging early molecular markers and quantifying the extent of disease progression continues to be a major challenge in the field. To this end, monocyte-targeting, peptide amphiphile micelles (PAMs) are engineered through the incorporation of the chemokine receptor CCR2-binding motif of monocyte chemoattractant protein-1 (MCP-1) and MCP-1 PAMs are evaluated preclinically as diagnostic tools for atherosclerosis. Monocyte-targeting is desirable as the influx of monocytes is a marker of early lesions, accumulation of monocytes is linked to atherosclerosis progression, and rupture-prone plaques have higher numbers of monocytes. MCP-1 PAMs bind to monocytes in vitro, and MCP-1 PAMs detect and discriminate between early- and late-stage atherosclerotic aortas. Moreover, MCP-1 PAMs are found to be eliminated via renal clearance and the mononuclear phagocyte system (MPS) without adverse side effects. Thus, MCP-1 PAMs are a promising new class of diagnostic agents capable of monitoring the progression of atherosclerosis.

Small high-density lipoprotein is associated with monocyte subsets in stable coronary artery disease

Objective: High-density lipoprotein (HDL) particles are heterogeneous in structure and function and the role of HDL subfractions in atherogenesis is not well understood. It has been suggested that small HDL may be dysfunctional in patients with coronary artery disease (CAD). Monocytes are considered to play a key role in atherosclerotic diseases. Circulating monocytes can be divided into three subtypes according to their surface expression of CD14 and CD16. Our aim was to examine whether monocyte subsets are associated with HDL subfractions in patients with atherosclerosis. Methods: We included 90 patients with angiographically stable CAD. Monocyte subsets were defined as classical monocytes (CD14++CD16-; CM), intermediate monocytes (CD14++CD16+; IM) and non-classical monocytes (CD14+CD16++; NCM). HDL subfractions were measured by electrophoresis on polyacrylamide gel. Results: Serum levels of small HDL correlated with circulating pro-inflammatory NCM and showed an inverse relationship to circulating CM independently from other lipid parameters, risk factors, inflammatory parameters or statin treatment regime, respectively. IM were not associated with small HDL. In particular, patients with small HDL levels in the highest tertile showed dramatically increased levels of NCM (14.7 ± 7% vs. 10.7 ± 5% and 10.8 ± 5%; p = 0.006) and a decreased proportion of CM (79.3 ± 7% vs. 83.7 ± 6% and 83.9 ± 6%; p = 0.004) compared to patients in the two lower tertiles. In contrast, intermediate HDL, large HDL and total HDL were not associated with monocyte subset distribution. Conclusion: Small HDL levels are associated with pro-inflammatory NCM and inversely correlated with CM. This may suggest that small HDL could have dysfunctional anti-inflammatory properties in patients with established CAD.

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Small HDL levels are associated with non-classical monocytes in stable CAD.

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Classical monocytes are inversely associated with small HDL levels.

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Associations are independent of other lipid parameters, risk factors, inflammatory parameters or statin treatment regime.

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Inflammatory markers do not vary according to small HDL levels.

Neutrophil/Lymphocyte ratio is associated with non-calcified plaque burden in patients with coronary artery disease

Background

Elevations in soluble markers of inflammation and changes in leukocyte subset distribution are frequently reported in patients with coronary artery disease (CAD). Lately, the neutrophil/lymphocyte ratio has emerged as a potential marker of both CAD severity and cardiovascular prognosis.

Objectives

The aim of the study was to investigate whether neutrophil/lymphocyte ratio and other immune-inflammatory markers were related to plaque burden, as assessed by coronary computed tomography angiography (CCTA), in patients with CAD.

Methods

Twenty patients with non-ST-elevation acute coronary syndrome (NSTE-ACS) and 30 patients with stable angina (SA) underwent CCTA at two occasions, immediately prior to coronary angiography and after three months. Atherosclerotic plaques were classified as calcified, mixed and non-calcified. Blood samples were drawn at both occasions. Leukocyte subsets were analyzed by white blood cell differential counts and flow cytometry. Levels of C-reactive protein (CRP) and interleukin(IL)-6 were measured in plasma. Blood analyses were also performed in 37 healthy controls.

Results

Plaque variables did not change over 3 months, total plaque burden being similar in NSTE-ACS and SA. However, non-calcified/total plaque ratio was higher in NSTE-ACS, 0.25(0.09–0.44) vs 0.11(0.00–0.25), p<0.05. At admission, levels of monocytes, neutrophils, neutrophil/lymphocyte ratios, CD4+ T cells, CRP and IL-6 were significantly elevated, while levels of NK cells were reduced, in both patient groups as compared to controls. After 3 months, levels of monocytes, neutrophils, neutrophil/lymphocyte ratios and CD4+ T cells remained elevated in patients. Neutrophil/lymphocyte ratios and neutrophil counts correlated significantly with numbers of non-calcified plaques and also with non-calcified/total plaque ratio (r = 0.403, p = 0.010 and r = 0.382, p = 0.024, respectively), but not with total plaque burden.

Conclusions

Among immune-inflammatory markers in NSTE-ACS and SA patients, neutrophil counts and neutrophil/lymphocyte ratios were significantly correlated with non-calcified plaques. Data suggest that these easily measured biomarkers reflect the burden of vulnerable plaques in CAD.

Impact of glucose fluctuation and monocyte subsets on coronary plaque rupture

BACKGROUND AND AIMS

It remains unclear whether glycemic fluctuation can affect plaque rupture in acute myocardial infarction (AMI). Here we investigate the impact of glucose fluctuation on plaque rupture, as observed by optical coherence tomography (OCT), and monocyte subsets in patients with AMI.

METHODS AND RESULTS

We studied 37 consecutive patients with AMI. All patients underwent OCT examination, which revealed 24 patients with plaque rupture and 13 patients without plaque rupture at the culprit site. Peripheral blood sampling was performed on admission. Three monocyte subsets (CD14(+)CD16(-), CD14(bright)CD16(+), and CD14(dim)CD16(+)) were assessed by flow cytometry. Glycemic variability, expressed as the mean amplitude of glycemic excursion (MAGE), was determined by a continuous glucose monitoring system 7 days after the onset of AMI. MAGE was significantly higher in the rupture patients than in the non-rupture patients (P=0.036). Levels of CD14(bright)CD16(+) monocytes from the rupture patients were significantly higher than those from the non-rupture patients (P=0.042). Of interest, levels of CD14(bright)CD16(+) monocytes correlated positively and significantly with MAGE (r=0.39, P=0.02).

CONCLUSION

Dynamic glucose fluctuation may be associated with coronary plaque rupture, possibly through the preferential increase in CD14(bright)CD16(+) monocyte levels.

Increased proatherogenic monocyte-platelet cross-talk in monocyte subpopulations of patients with stable coronary artery disease

BACKGROUND

Monocytes and platelets are important cellular mediators of atherosclerosis. Human monocytes can be divided into CD14(++) CD16(-) , CD14(++) CD16(+) and CD14(+) CD16(++) cells, which differ in their functional properties. The aim of this study was to examine monocyte subset distribution, monocyte-platelet aggregate (MPA) formation and expression of CCR5, the receptor of the platelet-derived chemokine CCL5, and to determine whether these parameters are altered in individuals with coronary atherosclerosis.

METHODS

Peripheral blood cells from 64 healthy blood donors (HBDs) and 60 patients with stable coronary artery disease (CAD) were stained with antibodies against CD14, CD16, CD42b and CCR5 and analysed by flow cytometry. Circulating CCL5 levels were determined using an enzyme-linked immunosorbent assay.

RESULTS

In patients with CAD, the relative proportion of the CD14(++) CD16(-) monocyte subset was elevated (P < 0.05) and of the CD14(+) CD16(++) subset was reduced (P < 0.001) compared with the HBD group. Furthermore, MPA formation significantly increased in patients with CAD in all three monocyte subsets. In both study groups, the majority of CCR5(+) cells was detected in CD14(++) CD16(+) monocytes (P < 0.001 versus CD14(++) CD16(-) and CD14(+) CD16(++) ), although the CCR5(+) monocyte number was reduced in patients with CAD (CD14(++) CD16(-) /CD14(+) CD16(++) , P < 0.001; CD14(++) CD16(+) , P < 0.05) compared with the HBD group, particularly in those who were not taking statins. Ex vivo incubation of monocytes from HBDs with plasma from patients with CAD also decreased CCR5(+) expression (P < 0.05 versus plasma from HBDs). Serum CCL5 levels were similar in both groups.

CONCLUSIONS

The increased monocyte-platelet cross-talk in patients with CAD might have contributed to atherosclerosis progression. The decreased CCR5(+) monocyte numbers in patients with CAD could have resulted from CCR5(+) cell recruitment into atherosclerotic lesions or CCR5 downregulation in response to circulating factors.

Monocyte and macrophage differentiation: circulation inflammatory monocyte as biomarker for inflammatory diseases

Monocytes express various receptors, which monitor and sense environmental changes. Monocytes are highly plastic and heterogeneous, and change their functional phenotype in response to environmental stimulation. Evidence from murine and human studies has suggested that monocytosis can be an indicator of various inflammatory diseases. Monocytes can differentiate into inflammatory or anti-inflammatory subsets. Upon tissue damage or infection, monocytes are rapidly recruited to the tissue, where they can differentiate into tissue macrophages or dendritic cells. Given the rapid progress in monocyte research from broad spectrum of inflammatory diseases, there is a need to summarize our knowledge in monocyte heterogeneity and its impact in human disease. In this review, we describe the current understanding of heterogeneity of human and murine monocytes, the function of distinct subsets of monocytes, and a potential mechanism for monocyte differentiation. We emphasize that inflammatory monocyte subsets are valuable biomarkers for inflammatory diseases, including cardiovascular diseases.

The role of monocyte phenotype switching in peri-procedural myocardial injury and its involvement in statin therapy

Peri-procedural myocardial injury, which is associated with worse long-term clinical outcome, is a common complication related to inflammatory pathogenetic mechanisms. Monocytes and macrophages play key roles in the initiation and progression of atherosclerosis. Recent studies have demonstrated that monocytes in human peripheral blood are heterogeneous, including CD14⁺CD16⁻ monocytes and CD14⁺CD16⁺ monocytes. Several lines of evidence suggested that CD14⁺CD16⁺ monocytes might contribute to the accelerated atherosclerosis. In view of the heightened appreciation of the heterogeneity of circulating monocytes, we hypothesized that an up-shifting subset of CD14⁺CD16⁺ monocytes might be induced by percutaneous coronary intervention (PCI), which subsequently leads to peri-procedural myocardial injury. Moreover, statins loading before PCI could exert anti-inflammatory effects partly by modulating monocyte phenotype and thus prevent peri-procedural myocardial injury.

Comparison of diagnostic accuracy between multidetector computed tomography and virtual histology intravascular ultrasound for detecting optical coherence tomography-derived fibroatheroma

Histopathological studies have reported that optical coherence tomography (OCT) can accurately detect fibroatheroma that is involved in not only culprit lesion of acute coronary syndrome but also no-reflow phenomenon after percutaneous coronary intervention. Studies have demonstrated superiority of OCT in plaque characterization and interruption of arterial wall component. At current, multidetector computed tomography (MDCT) and virtual histology intravascular ultrasound (VH-IVUS) are considered as alternative imaging devices for coronary plaque characterization. This study aimed to compare the diagnostic accuracy for detecting fibroatheroma between MDCT and VH-IVUS using OCT as the reference standard. Forty-three lesions from 27 patients assessed by MDCT, VH-IVUS, and OCT were included in this study. Fibroatheroma was defined by OCT as a signal-poor region with a fast signal drop-off and little or no signal backscattering within the lesion. From 43 lesions, OCT revealed 21 fibroatheromas. Ring-like sign assessed by MDCT and positive remodeling assessed by IVUS were more frequently observed in OCT-fibroatheroma than non-OCT-fibroatheroma. The remodeling index of OCT-fibroatheroma assessed by MDCT and IVUS were higher than those of non-OCT-fibroatheroma. The sensitivity, specificity, positive predict values, negative predict values and accuracy of ring-like sign by MDCT and VH-IVUS for detecting OCT-fibroatheroma were 43, 95, 90, 64, 70 % and 71, 45, 56, 63, 58 %, respectively. Our results suggest that both accuracies of MDCT and VH-IVUS to detect OCT-fibroatheroma are insufficient. We need to apply appropriate device for searching vulnerable plaque.

Inflammation and coagulation in atherosclerosis

Cardiovascular diseases remain to be the leading cause of death in Western societies. Despite major findings in vascular biology that lead to a better understanding of the pathomechanisms involved in atherosclerosis, treatment of the disease has only changed slightly within the last years. A big body of evidence suggests that atherosclerosis is a chronic inflammatory disease of the vessel wall. Accumulation and peroxidation of LDL-particles within the vessel wall trigger a strong inflammatory response, causing macrophage and T-cell accumulation within the vessel wall. Additionally, B-cells and specific antibodies against LDL-particles, as well as the complement system are implicated in atherogenesis. Besides data from clinical trials and autopsy studies it was the implementation of mouse models of atherosclerosis and the emerging field of direct gen-modification that lead to a thorough description of the pathophysiological mechanisms involved in the disease and created overwhelming evidence for a participation of the immune system. Recently, the cross-talk between coagulation and inflammation in atherogenesis has gained attention. Serious limitations and disparities in the pathophysiology of atherosclerosis in mice and men complicated the translation of experimental data into clinical practice. Despite these limitations, new anti-inflammatory medical therapies in cardiovascular disease are currently being tested in clinical trials.

Immunological aspects of atherosclerosis

Cardiovascular disease is the leading cause of death in several countries. The underlying process is atherosclerosis, a slowly progressing chronic disorder that can lead to intravascular thrombosis. There is overwhelming evidence for the underlying importance of our immune system in atherosclerosis. Monocytes, which comprise part of the innate immune system, can be recruited to inflamed endothelium and this recruitment has been shown to be proportional to the extent of atherosclerotic disease. Monocytes undergo migration into the vasculature, they differentiate into macrophage phenotypes, which are highly phagocytic and can scavenge modified lipids, leading to foam cell formation and development of the lipid-rich atheroma core. This increased influx leads to a highly inflammatory environment and along with other immune cells can increase the risk in the development of the unstable atherosclerotic plaque phenotype. The present review provides an overview and description of the immunological aspect of innate and adaptive immune cell subsets in atherosclerosis, by defining their interaction with the vascular environment, modified lipids and other cellular exchanges. There is a particular focus on monocytes and macrophages, but shorter descriptions of dendritic cells, lymphocyte populations, neutrophils, mast cells and platelets are also included.

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.

Monocyte gene expression and coronary artery disease

PURPOSE OF REVIEW

Despite current therapy, coronary artery disease (CAD) remains the major cause of morbidity and mortality worldwide. CAD is the consequence of a complex array of deranged metabolic processes including the immune system. In this context, monocytes and macrophages are indisputable players. Thus, monocyte gene expression analysis could be a powerful tool to provide new insights in the pathophysiology of CAD and improve identification of individuals at risk. We discuss current literature assessing monocyte gene expression and its association with CAD.

RECENT FINDINGS

Monocyte surface markers CD14 ⁺⁺and CD16⁺ have been established as biomarkers for increased cardiovascular disease risk in a large number of studies. More in-depth gene expression analysis identified several interesting genes, such as ABCA1, CD36 and MSR1 with an increased expression in circulating monocytes from patients with CAD. The results for CD36 were replicated in one other study. For ABCA1 and MSR1 conflicting data are published.

SUMMARY

Recent findings indicate that genetic differences exist in circulating monocytes of patients suffering from CAD, giving us more insights into the underlying mechanisms. However, larger studies are required to prove that monocytes' expression signature could serve as a marker for diagnostic purposes in the future.

Beyond Coronary Stenosis: Coronary Computed Tomographic Angiography for the Assessment of Atherosclerotic Plaque Burden

Coronary computed tomographic angiography (CCTA) is emerging as a key non-invasive method for assessing cardiovascular risk by measurement of coronary stenosis and coronary artery calcium (CAC). New advancements in CCTA technology have led to the ability to directly identify and quantify the so-called "vulnerable" plaques that have features of positive remodeling and low density components. In addition, CCTA presents a new opportunity for noninvasive measurement of total coronary plaque burden that has not previously been available. The use of CCTA needs also to be balanced by its risks and, in particular, the associated radiation exposure. We review current uses of CCTA, CCTA's ability to measure plaque quantity and characteristics, and new developments in risk stratification and CCTA technology. CCTA represents a quickly developing field that will play a growing role in the non-invasive management of cardiovascular disease.

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.

Distribution, frequency and clinical implications of napkin-ring sign assessed by multidetector computed tomography

BACKGROUND

Plaque rupture and secondary thrombus formation play key roles in the onset of acute coronary syndrome (ACS). Plaques showing the napkin-ring sign in multidetector computed tomography (MDCT) have been reported as thin-cap fibroatheroma that is recognized as a precursor lesion for plaque rupture. The purpose of this study was to investigate distribution and frequency of napkin-ring sign and its relationship to features indicating coronary plaque vulnerability on MDCT in patients with coronary artery disease.

METHODS

We enrolled 273 patients with ACS (n=61) or stable angina pectoris (SAP, n=212) who were assessed by MDCT. The definition of the napkin-ring sign was the presence of a ring of high attenuation and the CT attenuation of a ring presenting higher than those of the adjacent plaque and no greater than 130HU.

RESULTS

The culprit plaques with the napkin-ring sign show higher remodeling index and lower CT attenuation (1.15±0.12 vs. 1.02±0.12, p<0.01 and 39.9±22.8 vs. 72.7±26.6, p<0.01, respectively). Napkin-ring sign at culprit lesions was more frequent in patients with ACS than those with SAP (49.0% vs. 11.2%, p<0.01). Moreover, napkin-ring sign at non-culprit lesions was more frequently observed in ACS patients compared with SAP patients (12.7% vs. 2.8%, p<0.01). The distribution of the napkin-ring sign in the right coronary arteries and left circumflex arteries of our population was relatively even, whereas the napkin-ring sign in the left anterior descending artery was common in the proximal sites (p<0.01).

CONCLUSIONS

The napkin-ring sign assessed by MDCT represents similar clinical features of fibroatheroma. MDCT could contribute to the search for fibroatheroma.

Elevated markers of inflammation and endothelial activation and increased counts of intermediate monocytes in adult survivors of childhood acute lymphoblastic leukemia

BACKGROUND

Adult survivors of childhood malignancy are prone to accelerated atherogenesis and late cardiovascular complications. Plaque formation is initiated by recruitment of monocytes and T-cells into the intima, mediated by adhesion molecules and chemokines expressed by activated endothelial cells.

AIM

To assess markers of inflammatory activity, endothelial activation as well as monocyte heterogeneity in adult survivors of childhood acute lymphoblastic leukemia (ALL) who had been treated with chemotherapy without cranial irradiation.

METHODS AND RESULTS

We studied 27 (age: 18-28 years) healthy survivors of childhood ALL and 20 controls (age: 20-31 years). Flow cytometry was used to identify monocyte subsets: classical CD14(++)CD16(-), intermediate CD14(++)CD16(+) and nonclassical CD14(+)CD16(++) monocytes which were further characterized by their expression of HLA-DR and β2-integrins CD11b/CD18 and CD11c/CD18. In ALL survivors we found increased levels of pentraxin-3 (median [interquartile range]: 0.63 [0.36-0.94] vs. 0.40 [0.32-0.57] ng/ml; p = 0.03), soluble vascular cell adhesion molecule-1 (687 [597-761] vs. 558 [534-702]ng/ml; p = 0.02), osteoprotegerin (mean ± SD: 5.24 ± 1.00 vs. 4.42 ± 1.34 pmol/l; p = 0.02) and tumor necrosis factor (TNF)-related apoptosis-inducing ligand (107.0 ± 23.6 vs. 89.5 ± 18.9 pg/ml; p = 0.01), whereas C-reactive protein, interleukin 6 and 18, TNF-α, monocyte chemotactic protein-1 and soluble intercellular adhesion molecule-1 were unchanged. Former ALL patients exhibited elevated counts of intermediate monocytes (6.3 ± 4.0 vs. 4.3 ± 1.5% of blood monocytes; p = 0.03). CD11b/CD18 and CD11c/CD18 expression on intermediate monocytes tended to be higher in ALL survivors (1917 ± 993 vs. 1396 ± 673 MFI [median fluorescence intensity]; p = 0.06 and 3883 ± 1445 vs. 3185 ± 645 MFI; p = 0.05, respectively).

CONCLUSION

Our findings suggest chronic inflammatory activation and immune dysregulation in adult survivors of childhood ALL, which can translate into late cardiovascular morbidity.

CD14++CD16+ monocytes independently predict cardiovascular events: a cohort study of 951 patients referred for elective coronary angiography

OBJECTIVES

The aim of this study was to analyze the yet ill-defined relationship of distinct human monocyte subsets with cardiovascular outcomes in a broad patient population at cardiovascular risk.

BACKGROUND

Monocytes, the most abundant immune cell type found in atherosclerotic plaques, are crucial promoters of atherogenesis. Three distinct human monocyte subsets exist: classical CD14++CD16-, intermediate CD14++CD16+, and nonclassical CD14+CD16++ monocytes. Immunomodulation of distinct monocyte subsets has recently been discussed as a new therapeutic avenue in atherosclerosis.

METHODS

Cardiovascular events in 951 subjects referred for elective coronary angiography were prospectively analyzed. Monocyte subset analysis was performed using flow cytometry, blinded to patients' clinical characteristics, and patients were categorized according to quartiles of total monocyte and monocyte subset counts. The primary endpoint was defined a priori as the first occurrence of cardiovascular death, acute myocardial infarction, or nonhemorrhagic stroke. Endpoint adjudication was done blinded to monocyte subset distribution.

RESULTS

During a mean follow-up period of 2.6 ± 1.0 years, 93 patients experienced the primary endpoint. In univariate Kaplan-Meier analysis, counts of total (p = 0.010), classical CD14++CD16- (p = 0.024), and intermediate CD14++CD16+ (p < 0.001) monocytes predicted the primary endpoint, whereas nonclassical monocytes did not (p = 0.158). After full adjustment for confounders, CD14++CD16+ monocytes remained the only monocyte subset independently related to cardiovascular events (fourth vs. first quartile: hazard ratio: 3.019; 95% confidence interval: 1.315 to 6.928; p = 0.009).

CONCLUSIONS

CD14++CD16+ monocytes independently predicted cardiovascular events in subjects referred for elective coronary angiography. Future studies will be needed to elucidate whether CD14++CD16+ monocytes may become a target cell population for new therapeutic strategies in atherosclerosis.

Monocytes as a diagnostic marker of cardiovascular diseases

Inflammation is an important pathogenic factor of cardiovascular diseases. Inflammatory processes induce the organism systemic changes that are sensed by the cells of innate immune system. These systemic changes include increased concentrations of soluble factors capable of activating monocytes in the blood circulation therefore monocytes represent highly attractive cell population for diagnostic use. To date various parameters of circulating monocytes were associated with cardiovascular diseases. These comprise monocyte count, increased adhesive properties, alteration of lipid metabolism, phagocytosis and endocytosis of LDL. Search for markers, better suitable for clinical use led to identification of monocyte population heterogeneity. One of the best studied markers for identification of monocyte subpopulation is CD16. Although there is no consensus regarding the origin and composition of various monocyte subpopulations, association of increased size of CD16+ monocyte population with atherosclerosis is well established. Further surface markers of monocytes found to be associated with cardiovascular diseases are CD18, CD11b, CXCR1, CD36 and STAB1. Functional studies performed on primary human monocytes support the importance of these molecules for the pathogenesis of cardiovascular diseases. Continuous research on monocyte biology leads to identification of perspective markers that show significant potential of clinical use. These include analysis of monocyte response to a challenge and level of mitochondrial DNA heteroplasmy. Further research involving genomic, proteomic and cell biology techniques supplemented with systems biology approaches for data analysis and computer simulations are required for defining molecular and functional parameters of monocytes to be used as a diagnostic tool or therapeutic target.

Elevated CD14++CD16- monocytes predict cardiovascular events

BACKGROUND

Although monocytes in peripheral blood are no longer considered to be a homogeneous population, associations between distinct monocyte subsets and cardiovascular disease have not been highlighted in large epidemiological studies.

METHODS AND RESULTS

The study included 700 randomly selected subjects from the cardiovascular arm of the Malmö Diet and Cancer study. Among these, 123 subjects experienced ischemic cardiovascular events during the follow-up until December 2008. Mononuclear leukocytes frozen at the baseline investigation in 1991 to 1994 were thawed and analyzed with flow cytometry to enumerate monocyte subsets, based on CD14 and CD16 expression. The percentage and number of classical CD14(++)CD16(-) monocytes were increased in the cardiovascular-event group compared with the event-free subjects (median, 69% [interquartile range, 62% to 76%] versus 67% [59% to 72%], P=0.017; 344 [251 to 419] cells/μL versus 297 [212 to 384] cells/μL, P=0.003). The hazard ratio was 1.66 for suffering a cardiovascular event in the highest tertile of the number of CD14(++)CD16(-) monocytes compared with the lowest tertile, even after adjustment for common risk factors (HR, 1.66; 95% CI: 1.02 to 2.72). CD14(++)CD16(-) monocytes did not, however, associate with the extent of atherosclerosis at baseline. In contrast, the percentage of monocytes expressing CD16 was negatively associated to the extent of carotid atherosclerosis measured as intima-media thickness at baseline. The chemokine receptors CCR2, CX3CR1, and CCR5 were not differentially expressed between cases and controls on any of the monocyte subsets, but CCR5 expression on CD14(+)CD16(++) monocytes was negatively associated to carotid intima-media thickness.

CONCLUSIONS

This study shows that classical CD14(++)CD16(-) monocytes can predict future cardiovascular risk independently of other risk factors in a randomly selected population.

Differential expression of Toll-like receptor 4 and human monocyte subsets in acute myocardial infarction

OBJECTIVE

To investigate the involvement of Toll-like receptor 4 (TLR4) expression on two monocyte subsets in the pathologic processes related to acute coronary syndrome. How monocytes, which have recently been shown to comprise two distinct subsets, mediate the process of coronary plaque rupture remains to be fully elucidated. Recent studies have shown that TLR4 is involved in monocyte activation of patients with accelerated forms of atherosclerosis.

METHODS

We enrolled 65 patients with acute myocardial infarction (AMI, n=22), unstable angina pectoris (UAP, n=16), and stable angina pectoris (SAP, n=27) who underwent coronary angiography and 15 healthy controls. The expression of TLR4 on two monocyte subsets (CD14(+)CD16(-) and CD14(+)CD16(+)) was measured by flow cytometry.

RESULTS

In patients with AMI, TLR4 was more expressed on circulating CD14(+)CD16(+) monocytes than on CD14(+)CD16(-) monocytes (p<0.001). The expression levels of TLR4 on CD14(+)CD16(+) monocytes were significantly elevated in patients with AMI compared with other 3 groups. TLR4 expression levels on CD14(+)CD16(+) monocytes were significantly elevated at the culprit site compared with the systemic level (p=0.044). The up-regulation of TLR4 on admission was remarkably decreased 12 days after AMI (p<0.001). In addition, plasma levels of tumor necrosis factor-α were positively correlated with TLR4 expression levels on monocytes in patients with AMI (r=0.47, p=0.027).

CONCLUSION

TLR overexpression on CD14(+)CD16(+) monocytes in AMI, as demonstrated both in the circulation and at the coronary culprit site, might be associated with the pathogenesis of AMI.

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.

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.