A glimpse on the phenomenon of macrophage polarization during atherosclerosis

Novel cutting edge nano-strategies to address old long-standing complications in cardiovascular diseases. A comprehensive review

BACKGROUND

Cardiovascular diseases (CVD) impact a substantial portion of the global population and represent a significant threat to experiencing life-threatening outcomes, such as atherosclerosis, myocardial infarction, stroke and heart failure. Despite remarkable progress in pharmacology and medical interventions, CVD persists as a major public health concern, and now ranks as the primary global cause of death and the highest consumer of global budgets. Ongoing research endeavours persist in seeking novel therapeutic avenues and interventions to deepen our understanding of CVD, enhance prevention measures, and refine treatment strategies.

METHODS

Nanotechnology applied to the development of new molecular probes with diagnostic and theranostic properties represents one of the greatest technological challenges in preclinical and clinical research.

RESULTS

The application of nanotechnology in cardiovascular medicine holds great promise for advancing our understanding of CVDs and revolutionizing their diagnosis and treatment strategies, ultimately improving patient care and outcomes. In addition, the capacity of drug encapsulation in nanoparticles has significantly bolstered their biological safety, bioavailability and solubility. In combination with imaging technologies, molecular imaging has emerged as a pivotal therapeutic tool, offering insight into the molecular events underlying disease and facilitating targeted treatment approaches.

CONCLUSION

Here, we present a comprehensive overview of the recent advancements in targeted nanoparticle approaches for diagnosing CVDs, encompassing molecular imaging techniques, underscoring the significant progress in theranostic, as a novel and promising therapeutic strategy.

Targeting systemic inflammation in metabolic disorders. A therapeutic candidate for the prevention of cardiovascular diseases?

Cardiovascular disease (CVD) remains the leading cause of death and disability worldwide. While many factors can contribute to CVD, atherosclerosis is the cardinal underlying pathology, and its development is associated with several metabolic risk factors including dyslipidemia and obesity. Recent studies have definitively demonstrated a link between low-grade systemic inflammation and two relevant metabolic abnormalities: hypercholesterolemia and obesity. Interestingly, both metabolic disorders are also associated with endothelial dysfunction/activation, a proinflammatory and prothrombotic phenotype of the endothelium that involves leukocyte infiltration into the arterial wall, one of the earliest stages of atherogenesis. This article reviews the current literature on the intricate relationship between hypercholesterolemia and obesity and the associated systemic inflammation and endothelial dysfunction, and discusses the effectiveness of present, emerging and in-development pharmacological therapies used to treat these metabolic disorders with a focus on their effects on the associated systemic inflammatory state and cardiovascular risk.

Non-Mouse Models of Atherosclerosis: Approaches to Exploring the Translational Potential of New Therapies

Cardiovascular disease is the largest single cause of disease-related mortality worldwide and the major underlying pathology is atherosclerosis. Atherosclerosis develops as a complex process of vascular lipid deposition and retention by modified proteoglycans, endothelial dysfunction and unresolved chronic inflammation. There are a multitude of current therapeutic agents, most based on lowering plasma lipid levels, but, overall, they have a lower than optimum level of efficacy and many deaths continue to arise from cardiovascular disease world-wide. To identify and evaluate potential novel cardiovascular drugs, suitable animal models that reproduce human atherosclerosis with a high degree of fidelity are required as essential pre-clinical research tools. Commonly used animal models of atherosclerosis include mice (ApoE-/-, LDLR-/- mice and others), rabbits (WHHL rabbits and others), rats, pigs, hamster, zebrafish and non-human primates. Models based on various wild-type and genetically modified mice have been extensively reviewed but mice may not always be appropriate. Thus, here, we provide an overview of the advantages and shortcomings of various non-mouse animal models of atherosclerotic plaque formation, and plaque rupture, as well as commonly used interventional strategies. Taken together, the combinatorial selection of suitable animal models readily facilitates reproducible and rigorous translational research in discovering and validating novel anti-atherosclerotic drugs.

Isolation and Culturing of Primary Mouse and Human Macrophages

Macrophages are mature immune cells involved in the defense of the organism. Since their discovery, the main function attributed to macrophages has been phagocytosis. However, in recent years, several new functions such as angiogenesis, tissue remodeling, clearance of apoptotic cells, pro- and anti-inflammatory properties and tumor growth have been attributed to macrophages. To perform such varied functions, macrophages acquire specific phenotypes in response to external signals. The possibility of replicating these phenotypes in vitro represents a cutting-edge tool to understand potential macrophage functions in vivo. This chapter outlines protocols used to isolate and culture murine bone marrow-derived and human monocyte-derived macrophages. Furthermore, macrophage polarization processes into different phenotypes, with special relevance to atherosclerosis, are indicated.

Curcumin in Metabolic Health and Disease

In recent years, epidemiological studies have suggested that metabolic disorders are nutritionally dependent. A healthy diet that is rich in polyphenols may be beneficial in the treatment of metabolic diseases such as polycystic ovary syndrome, metabolic syndrome, non-alcoholic fatty liver disease, cardiovascular disease, and, in particular, atherosclerosis. Curcumin is a polyphenol found in turmeric and has been reported to have antioxidant, anti-inflammatory, hepatoprotective, anti-atherosclerotic, and antidiabetic properties, among others. This review summarizes the influence of supplementation with curcumin on metabolic parameters in selected metabolic disorders.

M2 Monocyte Polarization in Dialyzed Patients Is Associated with Increased Levels of M-CSF and Myeloperoxidase-Associated Oxidative Stress: Preliminary Results

Cardiovascular diseases represent a major issue in terms of morbidity and mortality for dialysis patients. This morbidity is due to the accelerated atherosclerosis observed in these patients. Atherosclerosis is a chronic inflammatory disease characterized by key players such as monocytes, macrophages, or oxidized LDLs. Monocytes-macrophages are classified into subsets of polarized cells, with M1 and M2 macrophages considered, respectively, as pro- and anti-inflammatory. (1) Methods: The monocyte subsets and phenotypes were analyzed by flow cytometry. These data were completed by the quantification of plasma M-CSF, IL-8, CRP, Mox-LDLs, Apo-B, Apo-AI, chloro-tyrosine, and homocitrulline concentrations. The statistical differences and associations between two continuous variables were assessed using the Mann-Whitney U test and Spearman's correlation coefficient, respectively. (2) Results: Hemodialyzed patients showed a significant increase in their concentrations of CRP, M-CSF, and IL-8 (inflammation biomarkers), as well as chloro-tyrosine and homocitrulline (myeloperoxidase-associated oxidative stress biomarkers). Moreover, we observed a higher percentage of M2 monocytes in the plasma of hemodialysis patients as compared to the controls. (3) Conclusions: Our data suggest that oxidative stress and an inflammatory environment, which is amplified in hemodialysis patients, seems to favor an increase in the concentration of circulating M-CSF, therefore leading to an increase in M2 polarization among circulating monocytes.

HSP60 knockdown exerts differential response in endothelial cells and monocyte derived macrophages during atherogenic transformation

Ectopic expression of HSP60 in vascular cells is known to activate auto-immune response that is critical to atherogenic initiation. However, the pathogenic relevance of the aberrant HSP60 upregulation in intracellular signaling pathways associated with atherogenic consequences in vascular cells remains unclear. The aim of the present study was to determine the role of endogenous HSP60 in atherogenic transformation of endothelial cells and macrophages. After generating primary evidence of oxidized low density lipoprotein (OxLDL) induced HSP60 upregulation in human umbilical vein endothelial cells (HUVEC), its physiological relevance in high fat high fructose (HFHF) induced early atherogenic remodelling was investigated in C57BL/6J mice. Prominent HSP60 expression was recorded in tunica intima and media of thoracic aorta that showed hypertrophy, lumen dilation, elastin fragmentation and collagen deposition. Further, HSP60 overexpression was found to be prerequisite for its surface localization and secretion in HUVEC. eNOS downregulation and MCP-1, VCAM-1 and ICAM-1 upregulation with subsequent macrophage accumulation provided compelling evidences on HFHF induced endothelial dysfunction and activation that were also observed in OxLDL treated- and HSP60 overexpressing-HUVEC. OxLDL induced concomitant reduction in NO production and monocyte adhesion were prevented by HSP60 knockdown, implying towards HSP60 mediated possible regulation of the said genes. OxLDL induced HSP60 upregulation and secretion was also recorded in THP-1 derived macrophages (TDMs). HSP60 knockdown in TDMs accounted for higher OxLDL accumulation that correlated with altered scavenger receptors (SR-A1, CD36 and SR-B1) expression further culminating in M1 polarization. Collectively, the results highlight HSP60 upregulation as a critical vascular alteration that exerts differential regulatory role in atherogenic transformation of endothelial cells and macrophages.

Characterization of Immature Myofibroblasts of Stellate Cell or Mesenchymal Cell Origin in D-Galactosamine-Induced Liver Injury in Rats

Lesions of D-galactosamine (D-GalN)-induced hepatotoxicity resemble those of human acute viral hepatitis. This study investigated hepatic mesenchymal cells including hepatic stellate cells (HSCs) and myofibroblasts in D-GalN-induced hepatotoxicity. Rats, injected with D-GalN (800 mg/kg body weight, once, intraperitoneally) were examined on post single injection (PSI) at 8 hours and days 1 to 5. Lesions consisting of hepatocyte necrosis and reparative fibrosis were present diffusely or focally within the hepatic lobules on PSI days 1 and 2, and then the injury recovered on PSI days 3 and 5. Myofibroblasts expressing vimentin, desmin, and α-smooth muscle actin (α-SMA) were present in the lesions. Double immunofluorescence showed that myofibroblasts reacted simultaneously to vimentin/α-SMA, desmin/α-SMA, and desmin/vimentin; furthermore, myofibroblasts reacting to vimentin, desmin, and α-SMA also co-expressed glial fibrillary acidic protein (GFAP), a marker of HSCs. Additionally, GFAP-expressing myofibroblasts reacted to nestin and A3 (both are markers of immature mesenchymal cells). Cells reacting to Thy-1, a marker for immature mesenchymal cells, also appeared in fibrotic lesions. In agreement with the myofibroblastic appearance, mRNAs of fibrosis-related factors (TGF-β1, PDGF-β, TNF-α, Timp2, and Mmp2) increased mainly on PSI days 1 and 2. Myofibroblasts with expression of various cytoskeletal proteins were present in diffuse or focal hepatic lesions, and they might be derived partly from immature HSCs and from immature mesenchymal cells.

Dual-Targeted Synthetic Nanoparticles for Cardiovascular Diseases

Atherosclerosis is one of the world's most aggressive diseases, claiming over 17.5 million lives per year. This disease is usually caused by high amounts of lipoproteins circulating in the blood stream, which leads to plaque formation. Ultimately, these plaques can undergo thrombosis and lead to major heart damage. A major contributor to these vulnerable plaques is macrophage apoptosis. Development of nanovehicles that carry contrast and therapeutic agents to the mitochondria within these macrophages is attractive for the diagnosis and treatment of atherosclerosis. Here, we report the design and synthesis of a dual-targeted synthetic nanoparticle (NP) to perform the double duty of diagnosis and therapy in atherosclerosis treatment regime. A library of dual-targeted NPs with an encapsulated iron oxide NP, mito-magneto (MM), with a magnetic resonance imaging (MRI) contrast enhancement capability was elucidated. Relaxivity measurements revealed that there is a substantial enhancement in transverse relaxivities upon the encapsulation of MM inside the dual-targeted NPs, highlighting the MRI contrast-enhancing ability of these NPs. Successful in vivo imaging documenting the distribution of MM-encapsulated dual-targeted NPs in the heart and aorta in mice ensured the diagnostic potential. The presence of mannose receptor targeting ligands and the optimization of the NP composition facilitated its ability to perform therapeutic duty by targeting the macrophages at the plaque. These dual-targeted NPs with the encapsulated MM were able to show therapeutic potential and did not trigger any toxic immunogenic response.

Characterization of Macrophages and Myofibroblasts Appearing in Dibutyltin Dichloride-Induced Rat Pancreatic Fibrosis

Macrophages and myofibroblasts are important in fibrogenesis. The cellular characteristics in pancreatic fibrosis remain to be investigated. Pancreatic fibrosis was induced in F344 rats by a single intravenous injection of dibutyltin dichloride. Histopathologically, the induced pancreatic fibrosis was divided into 3 grades (1+, 2+, and 3+), based on collagen deposition. Immunohistochemically, CD68-expressing M1 macrophages increased with grade and CD163-expressing M2 macrophages also increased later than M1 macrophage appearance. Double immunofluorescence showed that there were macrophages coexpressing CD68 and CD163, suggesting a possible shift from M1 to M2 types; similarly, increased major histocompatibility complex class II- and CD204-expressing macrophages were polarized toward M1 and M2 types, respectively. These findings indicated the participation of M1- and M2-polarized macrophages. Mesenchymal cells staining positive for vimentin, desmin, and α-smooth muscle actin (α-SMA) increased with grade. There were mesenchymal cells coexpressing vimentin/α-SMA, desmin/α-SMA, and glial fibrillary acidic protein (GFAP)/α-SMA; Thy-1-expressing immature mesenchymal cells also increased in fibrotic lesions. Because α-SMA expression is a reliable marker for myofibroblasts, α-SMA-expressing pancreatic myofibroblasts might be originated from GFAP-expressing pancreatic stellate cells or Thy-1-expressing immature mesenchymal cells; the myofibroblasts could simultaneously express cytoskeletal proteins such as vimentin and desmin. The present findings would provide useful information for analyses based on features of macrophages and myofibroblasts in chemically induced pancreatic fibrosis.

Monocyte Subsets, Stanford-A Acute Aortic Dissection, and Carotid Artery Stenosis: New Evidences

Monocytes are a heterogeneous cell population distinguished into three subsets with distinctive phenotypic and functional properties: “classical” (CD14++CD16-), “intermediate” (CD14++CD16+), and “nonclassical” (CD14+CD16++). Monocyte subsets play a pivotal role in many inflammatory systemic diseases including atherosclerosis (ATS). Only a low number of studies evaluated monocyte behavior in patients affected by cardiovascular diseases, and data about their role in acute aortic dissection (AAD) are lacking. Thus, the aim of this study was to investigate CD14++CD16-, CD14++CD16+, and CD14+CD16++ cells in patients with Stanford-A AAD and in patients with carotid artery stenosis (CAS). Methods. 20 patients with carotid artery stenosis (CAS group), 17 patients with Stanford-A AAD (AAD group), and 17 subjects with traditional cardiovascular risk factors (RF group) were enrolled. Monocyte subset frequency was determined by flow cytometry. Results. Classical monocytes were significantly increased in the AAD group versus CAS and RF groups, whereas intermediate monocytes were significantly decreased in the AAD group versus CAS and RF groups. Conclusions. Results of this study identify in AAD patients a peculiar monocyte array that can partly explain depletion of T CD4+ lymphocyte subpopulations observed in patients affected by AAD.

Biological profile of monocyte-derived macrophages in coronary heart disease patients: implications for plaque morphology

The prevalence of a macrophage phenotype in atherosclerotic plaque may drive its progression and/or instability. Macrophages from coronary plaques are not available, and monocyte-derived macrophages (MDMs) are usually considered as a surrogate. We compared the MDM profile obtained from coronary artery disease (CAD) patients and healthy subjects, and we evaluated the association between CAD MDM profile and in vivo coronary plaque characteristics assessed by optical coherence tomography (OCT). At morphological analysis, MDMs of CAD patients had a higher prevalence of round than spindle cells, whereas in healthy subjects the prevalence of the two morphotypes was similar. Compared to healthy subjects, MDMs of CAD patients had reduced efferocytosis, lower transglutaminase-2, CD206 and CD163 receptor levels, and higher tissue factor (TF) levels. At OCT, patients with a higher prevalence of round MDMs showed more frequently a lipid-rich plaque, a thin-cap fibroatheroma, a greater intra-plaque macrophage accumulation, and a ruptured plaque. The MDM efferocytosis correlated with minimal lumen area, and TF levels in MDMs correlated with the presence of ruptured plaque. MDMs obtained from CAD patients are characterized by a morpho-phenotypic heterogeneity with a prevalence of round cells, showing pro-inflammatory and pro-thrombotic properties. The MDM profile allows identifying CAD patients at high risk.

miR-146a deficiency in hematopoietic cells is not involved in the development of atherosclerosis

Background

Atherosclerosis involves activation of the IRAK1/TRAF6/NF-κB inflammatory cascade, which is negatively regulated by miR146a. Previous studies showed that the TT genotype of rs2431697, located near the miR-146a gene, drives lower miR-146a transcription and predicts adverse cardiovascular events in anticoagulated atrial fibrillation patients. Moreover, systemic miR-146a administration protects mice from atherosclerosis. Here we evaluated the ability of miR-146a expression in the hematopoietic component to regulate atherosclerosis in low-density lipoprotein receptor-null mice (Ldlr^-/-).

Methods and results

Lethally-irradiated Ldlr^-/- mice transplanted with bone marrow from wild-type or miR-146a-null mice were fed an atherogenic diet for 8 and 20 weeks. Irak1, Traf6 and MIR146A expression were quantified in thoracic aorta by qRT-PCR and Western blot. Aortic plaque size and composition were characterized by Oil-Red staining and immunohistochemistry and leukocyte recruitment by intravital microscopy. Blood cell counts were similar in fat-fed Ldlr^-/-mice with or without hematopoietic miR-146a expression. However, plasma cholesterol decreased in fat-fed Ldlr^-/-mice transplanted with bone marrow deficient for miR-146a. Finally, aortic atherosclerosis burden and recruitment of leukocytes into the vessel wall were undistinguishable between the two groups, despite higher levels of Irak1 and Traf6 mRNA and protein in the aorta of fat-fed mice lacking hematopoietic miR-146a expression.

Conclusions

miR-146a deficiency exclusively in hematopoietic cells modulates cholesterol levels in plasma and the expression of its targets in the artery wall of fat-fed Ldlr^-/- mice, but does not accelerate atherosclerosis. Atheroprotection upon systemic miR-146a administration may therefore be caused by specific effects on vascular cells.

Hepatic lipase inactivation decreases atherosclerosis in insulin resistance by reducing LIGHT/Lymphotoxin β-Receptor pathway

Coexistence of insulin resistance (IR) and metabolic syndrome (MetS) increases the risk of cardiovascular disease (CVD). Genetic studies in diabetes have linked Hepatic Lipase (HL) to an enhanced risk of CVD while others indicate a role of HL in inflammatory cells. Thus, we explored the role of HL on atherosclerosis and inflammation in a mouse model of MetS/IR, (apoE-/-Irs2+/- mice) and in patients with MetS and IR. HL-deficiency in apoE-/-Irs2+/- mice reduced atheroma size, plaque vulnerability, leukocyte infiltration and macrophage proliferation. Compared with apoE-/-Irs2+/-HL+/+ mice, MCP1, TNFa and IL6 plasma levels, pro-inflammatory Ly6Chi monocytes and activated(CD69+)-T lymphocytes were also decreased in apoE-/-Irs2+/-HL-/- mice. The LIGHT (Tumour necrosis factor ligand superfamily member 14, TNFSF14)/ Lymphotoxin β-Receptor(LTβ-R) pathway, which is involved in T-cell and macrophage activation, was diminished in plasma and in apoE-/-Irs2+/-HL-/- mouse atheromas. Treatment of apoE-/-Irs2+/-HL-/- mice with LIGHT increased the number of Ly6Chi-monocytes and lesion size. Acutely LIGHT-treated apoE-/- mice displayed enhanced proliferating Ly6Chi-monocytes and increased activation of the mitogen-activated protein kinase p38, suggesting that LIGHT/LTβ-R axis might promote atherogenesis by increasing proinflammatory monocytes and proliferation. Notably, MetS-IR subjects with increased atherosclerosis displayed up-regulation of the LIGHT/LTβ-R axis, enhanced inflammatory monocytes and augmented HL mRNA expression in circulating leukocytes. Thus, HL-deficiency decreases atherosclerosis in MetS/IR states by reducing inflammation and macrophage proliferation which are partly attributed to reduced LIGHT/LTβ-R pathway. These studies identify the LIGHT/LTβ-R axis as a main pathway in atherosclerosis and suggest that its inactivation might ameliorate inflammation and macrophage proliferation associated with atherosclerosis burden in MetS/IR.

Supplementary Material to this article is available at www.thrombosis-online.com.

Novel phosphate-activated macrophages prevent ectopic calcification by increasing extracellular ATP and pyrophosphate

PURPOSE

Phosphorus is an essential nutrient involved in many pathobiological processes. Less than 1% of phosphorus is found in extracellular fluids as inorganic phosphate ion (Pi) in solution. High serum Pi level promotes ectopic calcification in many tissues, including blood vessels. Here, we studied the effect of elevated Pi concentration on macrophage polarization and calcification. Macrophages, present in virtually all tissues, play key roles in health and disease and display remarkable plasticity, being able to change their physiology in response to environmental cues.

METHODS AND RESULTS

High-throughput transcriptomic analysis and functional studies demonstrated that Pi induces unpolarized macrophages to adopt a phenotype closely resembling that of alternatively-activated M2 macrophages, as revealed by arginine hydrolysis and energetic and antioxidant profiles. Pi-induced macrophages showed an anti-calcifying action mediated by increased availability of extracellular ATP and pyrophosphate.

CONCLUSION

We conclude that the ability of Pi-activated macrophages to prevent calcium-phosphate deposition is a compensatory mechanism protecting tissues from hyperphosphatemia-induced pathologic calcification.

Macrophage molecular signaling and inflammatory responses during ingestion of atherogenic lipoproteins are modulated by complement protein C1q

BACKGROUND AND AIMS

This study investigated the effect of innate immune protein C1q on macrophage programmed responses during the ingestion of atherogenic lipoproteins. C1q plays a dual role in atherosclerosis where activation of complement by C1q is known to drive inflammation and promote disease progression. However, C1q is atheroprotective in early disease using mouse models. Our previous studies have highlighted a non-complement associated role for C1q in polarizing macrophages towards an M2-like anti-inflammatory phenotype during ingestion of targets such as atherogenic lipoproteins. This study aims to investigate the molecular mechanisms involved.

METHODS

We investigated the molecular signaling mechanisms involved in macrophage polarization using an unbiased examination of gene expression profiles in human monocyte derived macrophages ingesting oxidized or acetylated low density lipoproteins in the presence or absence of C1q.

RESULTS

Expression of genes involved in Janus kinase and signal transducer and activator of transcription (JAK-STAT) signaling, peroxisome proliferator activating receptor (PPAR) signaling and toll-like receptor (TLR) signaling were modulated by C1q in this screen. C1q was also shown to significantly suppress JAK-STAT pathway activation (a maximum 55% ± 13% reduction, p = 0.044) and increase transcriptional activation of PPARs (a maximum 229% ± 54% increase, p = 0.0002), consistent with an M2-like polarized response. These pathways were regulated in macrophages by C1q bound to different types of modified atherogenic lipoprotein and led to a reduction in the release of pro-inflammatory cytokine IL-6.

CONCLUSIONS

This study identifies potential molecular mechanisms for the beneficial role C1q plays in early atherosclerosis.

M1-/M2-macrophage polarization in pseudolobules consisting of adipohilin-rich hepatocytes in thioacetamide (TAA)-induced rat hepatic cirrhosis

INTRODUCTION

Liver steatosis is the most frequent liver disease and may further develop into non-alcoholic steatohepatitis (NASH), liver cirrhosis, and finally hepatocellular carcinoma. Adipophilin (Adp) is localized on lipid droplet membrane in cytoplasm, and its increased expression is related to development of steatosis and NASH. The relationship between M1-/M2-macrophage polarization and Adp-rich hepatocyte-consisting pseudolobules (PLs) was investigated in thioacetamide (TAA)-induced rat cirrhosis.

MATERIALS AND METHOD

F344 rats were injected twice weekly with TAA (100mg/kg bodyweight) and sacrificed at post-first injection (PFI) weeks 5, 10, 15, 20, 25 and 32. Macrophage immunophenotypes and Adp-containing hepatocytes were analyzed by single immunolabeling. Adp and M1-/M2-related factors were analyzed by real -time RT-PCR.

RESULTS

PLs consisting exclusively of Adp-containing hepatocytes (Adp-positive) and PLs consisting of few Adp-containing hepatocytes (Adp-negative) were clearly distinguishable at PFI week 20 onwards. The numbers of M1-macrophages (reacting to CD68 and Iba1) and M2- macrophages (reacting to CD163, CD204 and Gal-3) were considerably greater in Adp-positive PLs. Expressions for both M1 (TNF-α, MCP-1, and Iba1)- and M2 (IL-4, TGF-β1, Gal-3, and Hsp25)-related factors were markedly higher in Adp-positive PLs at PFI week 25. Interestingly, MHC class II-positive macrophages/dendritic cells were increased in Adp-positive clusters/foci at the early stages at PFI weeks 5 and 10, and the level was gradually decreased thereafter.

CONCLUSIONS

M1-/M2-macrophages may simultaneously participate in the pathogenesis of steatosis in TAA-induced cirrhosis through M1- and M2-related factors. MHC class II cells may be responsible for steatosis at early stages, suggesting different functions from the above M1-/M2-macropahges.

Acute hyperlipidemia initiates proinflammatory and proatherogenic changes in circulation and adipose tissue in obese women

BACKGROUND

Obesity represents a high risk factor for the development of atherosclerosis and is associated with a low-grade inflammation and activation of immune cells.

AIMS

The aim of our study was to investigate the effect of a short-term lipid infusion on immune cells in blood and subcutaneous abdominal adipose tissue (SAAT) in obese women.

METHODS

Seven-hour intravenous lipid/control infusions were performed in two groups of women (n = 15, n = 10, respectively). Before and at the end of the infusion, SAAT and blood samples were obtained and relative content and phenotype of immune cells were analyzed using flow cytometry. Analysis of immune cell markers, inflammation and angiogenesis markers was performed in SAAT by RT-PCR and in plasma by immunoassays.

RESULTS

Relative content of CD45+/14+ and CD45+/14+/16+ populations of monocytes was reduced in circulation by 21% (p = 0.004) and by 46% (p = 0.0002), respectively, in response to hyperlipidemia, which suggested the increased adhesion of these cells to endothelium. In line with this, the levels of sICAM and sVCAM in plasma were increased by 9.4% (p = 0.016), 11.8% (p = 0.008), respectively. In SAAT, the relative content of M2 monocyte/macrophages subpopulation CD45+/14+/206+/16+ decreased by 27% (p = 0.012) and subpopulations CD14+/CD206- and CD14/+TLR4+ cells increased (p = 0.026; p = 0.049, respectively). Intralipid infusion promoted an increase of mRNA levels in SAAT: RORC (marker of proinflammatory Th17 lymphocytes) by 43% (p = 0.048), MCP-1 (78%, p = 0.028) and VEGF (68.5%, p = 0.0001).

CONCLUSIONS

Acute hyperlipidemia induces a proinflammatory and proatherogenic response associated with altered relative content of immune cells in blood and SAAT in obese women.

Aldosterone Induces Renal Fibrosis and Inflammatory M1-Macrophage Subtype via Mineralocorticoid Receptor in Rats

We aimed to evaluate macrophages heterogeneity and structural, functional and inflammatory alterations in rat kidney by aldosterone + salt administration. The effects of treatment with spironolactone on above parameters were also analyzed. Male Wistar rats received aldosterone (1 mgkg^-1d^-1) + 1% NaCl for 3 weeks. Half of the animals were treated with spironolactone (200 mg kg^-1d^-1). Systolic and diastolic blood pressures were elevated (p<0.05) in aldosterone + salt–treated rats. Relative kidney weight, collagen content, fibronectin, macrophage infiltrate, CTGF, Col I, MMP2, TNF-α, CD68, Arg2, and SGK-1 were increased (p<0.05) in aldosterone + salt–treated rats, being reduced by spironolactone (p<0.05). Increased iNOS and IFN-γ mRNA gene expression (M1 macrophage markers) was observed in aldosterone + salt rats, whereas no significant differences were observed in IL-10 and gene ArgI mRNA expression or ED2 protein content (M2 macrophage markers). All the observed changes were blocked with spironolactone treatment. Macrophage depletion with liposomal clodronate reduced macrophage influx and inflammatory M1 markers (INF-γ or iNOS), whereas interstitial fibrosis was only partially reduced after this intervention, in aldosterone plus salt-treated rats. In conclusion, aldosterone + salt administration mediates inflammatory M1 macrophage phenotype and increased fibrosis throughout mineralocorticoid receptors activation.

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.

Immunophenotypical characterization and influence on liver homeostasis of depleting and repopulating hepatic macrophages in rats injected with clodronate

Hepatic macrophages (including Kupffer cells) play a crucial role in the homeostasis and act as mediators of inflammatory response in the liver. Hepatic macrophages were depleted in male F344 rats by a single intravenous injection of liposomal clodronate (CLD; 50mg/kg body weight), and immunophenotypical characteristics of depleting and repopulating macrophages were analyzed by different antibodies specific for macrophages. CD163(+) Kupffer cells were almost completely depleted on post-injection (PI) days 1-12. Macrophages reacting to CD68, Iba-1, and Gal-3 were drastically reduced in number on PI day 1 and then recovered gradually until PI day 12. MHC class II(+) and CD204(+) macrophages were moderately decreased during the observation period. Although hepatic macrophages detectable by different antibodies were reduced in varying degrees, Kupffer cells were the most susceptible to CLD. Liver situation influenced by depleted hepatic macrophages was also investigated. No marked histological changes were seen in the liver, but the proliferating activity of hepatocytes was significantly increased, supported by changes of gene profiles relating to cell proliferation on microarray analysis on PI day 1; the values of AST and ALT were significantly elevated; macrophage induction/activation factors (such as MCP-1, CSF-1, IL-6 and IL-4) were increased exclusively on PI day 1, whereas anti-inflammatory factors such as IL-10 and TGF-β1 remained significantly decreased after macrophage depletion. The present study confirmed importance of hepatic macrophages in liver homeostasis. The condition of hepatic macrophages should be taken into consideration when chemicals capable of inhibiting macrophage functions are evaluated.

Voluntary Exercise Stabilizes Established Angiotensin II-Dependent Atherosclerosis in Mice through Systemic Anti-Inflammatory Effects

We have previously demonstrated that exercise training prevents the development of Angiotensin (Ang) II-induced atherosclerosis and vulnerable plaques in Apolipoprotein E-deficient (ApoE^-/-) mice. In this report, we investigated whether exercise attenuates progression and promotes stability in pre-established vulnerable lesions. To this end, ApoE^-/- mice with already established Ang II-mediated advanced and vulnerable lesions (2-kidney, 1-clip [2K1C] renovascular hypertension model), were subjected to sedentary (SED) or voluntary wheel running training (EXE) regimens for 4 weeks. Mean blood pressure and plasma renin activity did not significantly differ between the two groups, while total plasma cholesterol significantly decreased in 2K1C EXE mice. Aortic plaque size was significantly reduced by 63% in 2K1C EXE compared to SED mice. Plaque stability score was significantly higher in 2K1C EXE mice than in SED ones. Aortic ICAM-1 mRNA expression was significantly down-regulated following EXE. Moreover, EXE significantly down-regulated splenic pro-inflammatory cytokines IL-18, and IL-1β mRNA expression while increasing that of anti-inflammatory cytokine IL-4. Reduction in plasma IL-18 levels was also observed in response to EXE. There was no significant difference in aortic and splenic Th1/Th2 and M1/M2 polarization markers mRNA expression between the two groups. Our results indicate that voluntary EXE is effective in slowing progression and promoting stabilization of pre-existing Ang II-dependent vulnerable lesions by ameliorating systemic inflammatory state. Our findings support a therapeutic role for voluntary EXE in patients with established atherosclerosis.

Ink4/Arf locus restores glucose tolerance and insulin sensitivity by reducing hepatic steatosis and inflammation in mice with impaired IRS2-dependent signalling

Single nucleotide polymorphisms near the Ink4/Arf locus have been associated with type-2 diabetes mellitus. Previous studies indicate a protective role of the locus in the carbohydrate metabolism derangement associated with ageing in wild-type mice. The present study demonstrates that the increased Ink4/Arf locus expression in 1-year-old mice, partially-deficient for the insulin receptor substrate (IRS)2 (Irs2+/-SuperInk4/Arf mice) ameliorates hepatic steatosis, inflammation and insulin resistance. Irs2+/-SuperInk4/Arf mice displayed improved glucose tolerance and insulin sensitivity compared with Irs2+/- mice which were glucose intolerant and insulin resistant compared with age-matched wild-type mice. These changes in Irs2+/- mice were accompanied by enhanced hepatic steatosis, proinflammatory macrophage phenotype, increased Ly6C(hi)-monocyte percentage, T-lymphocyte activation and MCP1 and TNF-α cytokine levels. In Irs2+/-SuperInk4/Arf mice, steatosis and inflammatory parameters were markedly reduced and similar to those of wild-type counterparts. In vivo insulin signalling also revealed reduced activation of the IRS/AKT-dependent signalling in Irs2+/- mice. This was restored upon increased locus expression in Irs2+/-SuperInk4/Arf mice which display similar activation levels as those for wild-type mice. In vivo treatment of Irs2+/-SuperInk4/Arf mice with TNF-α diminished insulin canonical IRS/AKT-signalling and enhanced the stress SAPK/JNK-phosphoSer307IRS1-pathway suggesting that cytokine levels might potentially affect glucose homeostasis through changes in these insulin-signalling pathways. Altogether, these results indicate that enhanced Ink4/Arf locus expression restores glucose homeostasis and that this is associated with diminished hepatic steatosis and inflammation in mice with insulin resistance. Therefore, pharmacological interventions targeted to modulate the Ink4/Arf locus expression could be a tentative therapeutic approach to alleviate the inflammation associated with insulin resistance.

Molecular analysis of curcumin-induced polarization of murine RAW264.7 macrophages

This study aimed to investigate the effects of curcumin on macrophages polarization and possible mechanism involved, and to analyze the molecular basis of its antiatherosclerosis activity. RAW264.7 macrophages (M0) and M1 macrophages were treated with curcumin at 0, 6.25, 12.5, and 25 μmol/L with or without GW9662. Using real-time polymerase chain reaction and Western blot analysis, we examined the phenotype markers of M1 [iNOS, interleukin (IL)-1β, IL-6, and MCP-1] and M2 (KLF4, FIZZ1, and MGL1] macrophages. Curcumin reduced the expression of the M1 phenotype markers and upregulated the expression of proliferator-activated receptor γ in M0 and M1 macrophages and IKBα in M1 macrophages. When M1 macrophages were incubated with curcumin and GW9662, the expression of the M1 phenotype markers was decreased, while IKBα was upregulated. The expression of the M2 phenotype markers in M0 and M1 macrophages was upregulated after the curcumin treatment. When M0 and M1 macrophages were incubated with curcumin and GW9662, the expression of the M2 phenotype markers was reduced. Curcumin inhibited the M1 inflammation phenotype as a result of the direct activation of IKBα and polarized the macrophages to become M2 phenotype through the activation of proliferator-activated receptor γ. These findings provide new clues to develop new drug therapy for atherosclerosis.

Isolation, Culture, and Polarization of Murine Bone Marrow-Derived and Peritoneal Macrophages

Macrophages are the most specialized phagocytic cells, and acquire specific phenotypes and functions in response to a variety of external triggers. Culture of bone marrow-derived or peritoneal macrophages from mice represents an exceptionally powerful technique to investigate macrophage phenotypes and functions in response to specific stimuli, resembling as much as possible the conditions observed in various pathophysiological settings. This chapter outlines protocols used to isolate and culture murine bone marrow-derived and peritoneal macrophages. Furthermore, we describe how these macrophages can be "polarized" to obtain specific macrophage subsets with special relevance to atherosclerosis.

Mechanical, biological and structural characterization of human atherosclerotic femoral plaque tissue

The failure of endovascular treatments of peripheral arterial disease represents a critical clinical issue. Specialized data are required to tailor such procedures to account for the mechanical response of the diseased femoral arterial tissue to medical device deployment. The purpose of this study is to characterize the mechanical response of atherosclerotic femoral arterial tissue to large deformation, the conditions typical of angioplasty and stenting, and also to determine the mechanically induced failure properties and to relate this behaviour to biological content and structural composition using uniaxial testing, Fourier transform infrared spectroscopy and scanning electron microscopy. Mechanical and biological characterization of 20 plaque samples obtained from femoral endarterectomy identified three distinct classifications. "Lightly calcified" samples display linear mechanical responses and fail at relatively high stretch. "Moderately calcified" samples undergo an increase in stiffness and ultimate strength coupled with a decrease in ductility. Structural characterization reveals calcified nodules within this group that may be acting to reinforce the tissue matrix, thus increasing the stiffness and ultimate strength. "Heavily calcified" samples account for the majority of samples tested and exhibit significantly reduced ultimate strength and ductility compared to the preceding groups. Structural characterization of this group reveals large areas of calcified tissue dominating the failure cross-sections of the samples. The frequency and structural dominance of these features solely within this group offers an explanation as to the reduced ultimate strength and ductility and highlights the need for modern peripheral endovascular devices to account for this behaviour during novel medical device design.

The omega-3 fatty acid docosahexaenoic acid favorably modulates the inflammatory pathways and macrophage polarization within aorta of LDLR(-/-) mice

The omega-3 fatty acid docosahexaenoic acid (DHA) has potent anti-atherogenic properties but its mechanisms of action at the vascular level remain poorly explored. Knowing the broad range of molecular targets of omega-3 fatty acids, microarray analysis was used to open-mindedly evaluate the effects of DHA on aorta gene expression in LDLR(-/-) mice and better understand its local anti-atherogenic action. Mice were fed an atherogenic diet and received daily oral gavages with oils rich in oleic acid or DHA. Bioinformatics analysis of microarray data first identified inflammation and innate immunity as processes the most affected by DHA supplementation within aorta. More precisely, several down-regulated genes were associated with the inflammatory functions of macrophages (e.g., CCL5 and CCR7), cell movement (e.g., ICAM-2, SELP, and PECAM-1), and the major histocompatibility complex (e.g., HLA-DQA1 and HLA-DRB1). Interestingly, several genes were identified as specific biomarkers of macrophage polarization, and their changes suggested a preferential orientation toward a M2 reparative phenotype. This observation was supported by the upstream regulator analysis highlighting the involvement of three main regulators of macrophage polarization, namely PPARγ (z-score = 2.367, p = 1.50 × 10(-13)), INFγ (z-score = -2.797, p = 2.81 × 10(-14)), and NFκB (z-score = 2.360, p = 6.32 × 10(-9)). Moreover, immunohistological analysis of aortic root revealed an increased abundance of Arg1 (+111 %, p = 0.01), a specific biomarker of M2 macrophage. The present study showed for the first time that DHA supplementation during atherogenesis is associated with protective modulation of inflammation and innate immunity pathways within aorta putatively through the orientation of plaque macrophages toward a M2 reparative phenotype.

Complement protein C1q promotes macrophage anti-inflammatory M2-like polarization during the clearance of atherogenic lipoproteins

OBJECTIVE

Innate immune protein C1q plays a dual role in the chronic inflammatory disease of atherosclerosis. Complement activation via C1q exacerbates pathology in the atherosclerotic lesion in later stages of the disease. However, in early stages of disease C1q is protective. We hypothesize that complement-independent activities of C1q are involved in reprogramming macrophage inflammatory polarization.

METHODS

The influence of C1q on macrophage inflammatory responses during clearance of oxLDL was examined. Changes in cytokines at the gene and protein level were measured by quantitative PCR and ELISA assay.

RESULTS

C1q modulated cytokine expression in Raw264.7 macrophages during ingestion of oxLDL. Levels of pro-inflammatory cytokines IL-1β and IL-6 were downregulated by C1q, whereas levels of the anti-inflammatory cytokine IL-10 were increased. In addition, data from an NFκB-luciferase gene reporter assay suggest that C1q suppresses activation of NFκB during lipoprotein clearance in macrophages, providing one mechanism by which C1q downregulates pro-inflammatory cytokine production.

CONCLUSIONS

C1q-polarization of macrophages toward an anti-inflammatory (M2-like) phenotype may be important in dampening inflammation in the early atherosclerotic lesion. Further investigation of molecular pathways targeted by C1q may provide novel therapeutic targets for this disease.

Haemodynamical stress in mouse aortic arch with atherosclerotic plaques: Preliminary study of plaque progression

Atherosclerotic plaques develop at particular sites in the arterial tree, and this regional localisation depends largely on haemodynamic parameters (such as wall shear stress; WSS) as described in the literature. Plaque rupture can result in heart attack or stroke and hence understanding the development and vulnerability of atherosclerotic plaques is critically important. The purpose of this study is to characterise the haemodynamics of blood flow in the mouse aortic arch using numerical modelling. The geometries are digitalised from synchrotron imaging and realistic pulsatile blood flow is considered under rigid wall assumptions. Two cases are considered; arteries with and without plaque. Mice that are fed under fat diet present plaques in the aortic arch whose size is dependent on the number of weeks under the diet. The plaque distribution in the region is however relatively constant through the different samples. This result underlines the influence of the geometry and consequently of the wall shear stresses for plaque formation with plaques growing in region of relative low shear stresses. A discussion of the flow field in real geometry in the presence and absence of plaques is conducted. The presence of plaques was shown to alter the blood flow and hence WSS distribution, with regions of localised high WSS, mainly on the wall of the brachiocephalic artery where luminal narrowing is most pronounced. In addition, arch plaques are shown to induce recirculation in the blood flow, a phenomenon with potential influence on the progression of the plaques. The oscillatory shear index and the relative residence time have been calculated on the geometry with plaques to show the presence of this recirculation in the arch, an approach that may be useful for future studies on plaque progression.

Uremic conditions drive human monocytes to pro-atherogenic differentiation via an angiotensin-dependent mechanism

Aims

Elevated expression levels of monocytic-ACE have been found in haemodialysis patients. They are not only epidemiologically linked with increased mortality and cardiovascular disease, but may also directly participate in the initial steps of atherosclerosis. To further address this question we tested the role of monocytic-ACE in promotion of atherosclerotic events in vitro under conditions mimicking those of chronic renal failure.

Methods and Results

Treatment of human primary monocytes or THP-1 cells with uremic serum as well as PMA-induced differentiation led to significantly up-regulated expression of ACE, further increased by additional treatment with LPS. Functionally, these monocytes revealed significantly increased adhesion and transmigration through endothelial monolayers. Overexpression of ACE in transfected monocytes or THP-1 cells led to development of more differentiated, macrophage-like phenotype with up-regulated expression of Arg1, MCSF, MCP-1 and CCR2. Expression of pro-inflammatory cytokines TNFa and IL-6 were also noticeably up-regulated. ACE overexpression resulted in significantly increased adhesion and transmigration properties. Transcriptional screening of ACE-overexpressing monocytes revealed noticeably increased expression of Angiotensin II receptors and adhesion- as well as atherosclerosis-related ICAM-1 and VCAM1. Inhibition of monocyte ACE or AngII-receptor signalling led to decreased adhesion potential of ACE-overexpressing cells.

Conclusions

Taken together, these data demonstrate that uremia induced expression of monocytic-ACE mediates the development of highly pro-atherogenic cells via an AngII-dependent mechanism.

Nitric oxide production by monocytes in children with OSA and endothelial dysfunction

Endothelial dysfunction in the context of paediatric sleep apnoea is associated with distinctive alterations in circulating monocyte subsets and reduced NO production by monocytes.

Expression of endoglin isoforms in the myeloid lineage and their role during aging and macrophage polarization

Endoglin plays a crucial role in pathophysiological processes such as hereditary hemorrhagic telangiectasia (HHT), preeclampsia and cancer. Endoglin expression is upregulated during the monocyte-to-macrophage transition, but little is known about its regulation and function in these immune cells. Two different alternatively spliced isoforms of endoglin have been reported, L-endoglin and S-endoglin. Although L-endoglin is the predominant variant, here, we found that there was an increased expression of the S-endoglin isoform during senescence of the myeloid lineage in human and murine models. We performed a stable isotope labelling of amino acids in cell culture (SILAC) analysis of both L-endoglin and S-endoglin transfectants in the human promonocytic cell line U937. Analysis of differentially expressed protein clusters allowed the identification of cellular activities affected during aging. S-endoglin expression led to decreased cellular proliferation and a decreased survival response to granulocyte-macrophage colony-stimulating factor (GM-CSF)-induced apoptosis, as well as increased oxidative stress. Gene expression and functional studies suggested that there was a non-redundant role for each endoglin isoform in monocyte biology. In addition, we found that S-endoglin impairs the monocytic differentiation into the pro-inflammatory M1 phenotype and contributes to the compromised status of macrophage functions during aging.

Comparison of fluorodeoxyglucose uptake in symptomatic carotid artery and stable femoral artery plaques

BACKGROUND

Fluorine-18-labelled fluoroxdeoxyglucose (FDG) positron emission tomography (PET) has been used to evaluate atherosclerotic plaque metabolic activity, and through its uptake by macrophages is believed to have the potential to identify vulnerable plaques. The aims were to compare FDG uptake in carotid plaques from patients who had sustained a recent thromboembolic cerebrovascular event with that in femoral artery plaques from patients with leg ischaemia, and to correlate FDG uptake with the proportion of M1 and M2 macrophages present.

METHODS

Consecutive patients who had carotid endarterectomy for symptomatic, significant carotid stenosis and patients with severe leg ischaemia and significant stenosis of the common femoral artery underwent FDG-PET and histological plaque analysis. The voxel with the greatest activity in the region of interest was calculated using the Patlak method over 60 min. Plaques were dual-stained for CD68, and M1 and M2 macrophage subsets.

RESULTS

There were 29 carotid and 25 femoral artery plaques for study. The maximum dynamic uptake was similar in carotid compared with femoral plaques: median (range) 9·7 (7·1-12·2) versus 10·0 (7·4-16·6) respectively (P = 0·281). CD68 macrophage counts were significantly increased in carotid compared with femoral plaques (39·5 (33·9-50·1) versus 11·5 (7·7-21·3) respectively; P < 0·001), as was the proportion of M1 proinflammatory macrophages. The degree of carotid stenosis correlated with the maximum dynamic FDG uptake (rs  = 0·48, P = 0·008).

CONCLUSION

FDG uptake was no greater in symptomatic carotid plaques than in the less inflammatory femoral plaques. In patients on statin therapy. FDG uptake occurred in areas of significant arterial stenosis, irrespective of the degree of inflammation.

β-Glucan attenuates inflammatory responses in oxidized LDL-induced THP-1 cells via the p38 MAPK pathway

AIM

To investigate the immunomodulatory effects of β-(1,3/1,6)-d-glucan on atherosclerosis as well as on the molecular mechanisms of its transition.

METHODS AND RESULTS

Human monocytic leukemia (THP-1) cells were differentiated into the macrophage phenotype by incubation with oxLDL in the absence or presence of β-glucan. β-glucan attenuated CD86 and CD80 expression and simultaneously reduced secretion of the inflammatory cytokines IL-2, IL-8, IL-12, TNF-α and IFN-γ. Western blot analysis showed that oxLDL treatment induced phosphorylation of p38 MAPK and ERK1/2 in PMA-differentiated THP-1 cells. However, β-glucan inhibited p38 MAPK activation. In experiments with monocytes derived from healthy donors, β-glucan inhibited IL-8, IL-12 and TNF-α production. The anti-inflammatory effects of β-glucan were also observed in atherosclerotic plaque cells.

CONCLUSIONS

β-glucan inhibited oxLDL-induced pro-inflammatory effects in macrophages via regulation of p38 MAPK phosphorylation. This novel finding may provide insight for new therapeutic strategies.

Potential beneficial effects of ixmyelocel-T in the treatment of atherosclerotic diseases

Introduction

Advanced atherosclerotic lesions are characterized by lipid accumulation, inflammation, and defective efferocytosis. An ideal therapy should address all aspects of this multifactorial disease. Ixmyelocel-T therapy, an expanded autologous multicellular therapy showing clinical promise in the treatment of diseases associated with advanced atherosclerosis, includes a novel population of M2-like macrophages. Here, we examine the macrophages of ixmyelocel-T and determine their ability to influx modified cholesterol in an atheroprotective manner, maintaining cholesterol homeostasis and preventing cellular dysfunction and death, ultimately promoting reverse cholesterol efflux.

Methods

Approximately 50 ml of whole bone marrow was obtained from healthy donors and shipped overnight. Bone marrow mononuclear cells (BMMNCs) were produced by using density gradient separation and cultured for approximately 12 days to generate ixmyelocel-T. CD14+ cells were isolated from ixmyelocel-T via positive selection for analysis. Ixmyelocel-T and human leukemia monocyte (THP-1) cells were loaded with acetylated low-density lipoprotein (Ac-LDL) for analysis. Flow cytometry and immunofluorescence were used to examine Ac-LDL uptake, expression of cytokines was analyzed by enzyme-linked immunofluorescence assay (ELISA), and quantitative real-time PCR was used to analyze expression of cholesterol-transport genes. Both the in vitro cholesterol efflux assay and in vivo reverse cholesterol transport assay were used to examine cholesterol transport.

Results

Ixmyelocel-T macrophages take up acetylated low-density lipoprotein and express the scavenger receptors CD36 and scavenger receptor-B1 (SR-B1). Ixmyelocel-T did not become apoptotic or proinflammatory after lipid loading. The cholesterol transporter genes ABAC1 and ABCG1 were both statistically significantly upregulated when ixmyelocel-T macrophages were loaded with cholesterol. Ixmyelocel-T also exhibited enhanced apolipoprotein A-I (ApoAI)-mediated cholesterol efflux. In addition, in vivo reverse cholesterol-transport assay demonstrated that ixmyelocel-T was able to efflux cholesterol in this model.

Conclusions

Ixmyelocel-T macrophages influx modified cholesterol, remained anti-inflammatory in the face of lipid loading and inflammatory challenge, and displayed enhanced cholesterol efflux capabilities. These combined features suggest that this autologous multicellular therapy may exert beneficial effects in atherosclerotic diseases.

Insulin resistance and atherosclerosis: convergence between metabolic pathways and inflammatory nodes

For some time now it has been known that diabetes and atherosclerosis are chronic inflammatory diseases that are closely associated with one another and often develop together. In both there is an increase in tissue-wide inflammation that is exhibited by the infiltration of immune cells into the adipose tissue and the vascular walls respectively. The monocyte/macrophage populations that are recruited in these seemingly different settings also display a high similarity by exhibiting similar phenotypes in both conditions. In the insulin resistant as well as the atherosclerotic setting there is a distinct switch in the macrophage populations present from an anti-inflammatory (M2) population to an inflammatory (M1) population, which releases cytokines and chemotactic factors with the ability to worsen the local environment and thus aggravate the situation by creating a vicious circle. However, although some discoveries suggest that preventing the development of M1 macrophages reduces inflammation and thereby aggravation of these diseases, there are currently no clear-cut opinions on how to achieve a switch from M2 to M1.

Gene Deficiency in Activating Fcγ Receptors Influences the Macrophage Phenotypic Balance and Reduces Atherosclerosis in Mice

Immunity contributes to arterial inflammation during atherosclerosis. Oxidized low-density lipoproteins induce an autoimmune response characterized by specific antibodies and immune complexes in atherosclerotic patients. We hypothesize that specific Fcγ receptors for IgG constant region participate in atherogenesis by regulating the inflammatory state of lesional macrophages. In vivo we examined the role of activating Fcγ receptors in atherosclerosis progression using bone marrow transplantation from mice deficient in γ-chain (the common signaling subunit of activating Fcγ receptors) to hyperlipidemic mice. Hematopoietic deficiency of Fcγ receptors significantly reduced atherosclerotic lesion size, which was associated with decreased number of macrophages and T lymphocytes, and increased T regulatory cell function. Lesions of Fcγ receptor deficient mice exhibited increased plaque stability, as evidenced by higher collagen and smooth muscle cell content and decreased apoptosis. These effects were independent of changes in serum lipids and antibody response to oxidized low-density lipoproteins. Activating Fcγ receptor deficiency reduced pro-inflammatory gene expression, nuclear factor-κB activity, and M1 macrophages at the lesion site, while increasing anti-inflammatory genes and M2 macrophages. The decreased inflammation in the lesions was mirrored by a reduced number of classical inflammatory monocytes in blood. In vitro, lack of activating Fcγ receptors attenuated foam cell formation, oxidative stress and pro-inflammatory gene expression, and increased M2-associated genes in murine macrophages. Our study demonstrates that activating Fcγ receptors influence the macrophage phenotypic balance in the artery wall of atherosclerotic mice and suggests that modulation of Fcγ receptor-mediated inflammatory responses could effectively suppress atherosclerosis.

The involvement of the monocytes/macrophages in chronic inflammation associated with atherosclerosis

Atherosclerosis is a progressive chronic disease of large and medium arteries, characterized by the formation of atherosclerotic plaques. Monocytes and macrophages are key factors in lesion development, participating to the processes that mediate the progression of the atherosclerotic plaque (lipid accumulation, secretion of pro-inflammatory and cytotoxic factors, extracellular matrix remodeling). The recruitment of the monocytes in the vascular wall represents a hallmark in the pathology of the atherosclerotic lesion. Monocyte adhesion and transmigration are dependent on the complementary adhesion molecules expressed on the endothelial surface, whose expression is modulated by chemical mediators. The atherosclerotic plaque is characterized by a heterogeneous population of macrophages reflecting the complexity and diversity of the micro-environment to which cells are exposed after entering the arterial wall. Within the atherosclerotic lesions, macrophages differentiate, proliferate and undergo apoptosis. Taking into account that their behavior has a direct and critical influence on all lesional stages, the development of therapeutic approaches to target monocytes/macrophages in the atherosclerotic plaque became a focal interest point for researchers in the field.

Macrophage function and polarization in cardiovascular disease: a role of estrogen signaling?

Macrophages are plastic and versatile cells adapting their function/phenotype to the microenvironment. Distinct macrophage subpopulations with different functions, including classically (M1) and (M2) activated macrophages, have been described. Reciprocal skewing of macrophage polarization between the M1 and M2 state is a process modulated by transcription factors, such as the nuclear peroxisome proliferator-activated receptors. However, whether the estrogen/estrogen receptor pathways control the balance between M1/M2 macrophages is only partially understood. Estrogen-dependent effects on the macrophage system may be regarded as potential targets of pharmacological approaches to protect postmenopausal women from the elevated risk of cardiovascular disease.

A clinical evaluation of statin pleiotropy: statins selectively and dose-dependently reduce vascular inflammation

Statins are thought to reduce vascular inflammation through lipid independent mechanisms. Evaluation of such an effect in atherosclerotic disease is complicated by simultaneous effects on lipid metabolism. Abdominal aortic aneurysms (AAA) are part of the atherosclerotic spectrum of diseases. Unlike atherosclerotic occlusive disease, AAA is not lipid driven, thus allowing direct evaluation of putative anti-inflammatory effects. The anti-inflammatory potency of increasing doses (0, 20 or 40 mg/day) simvastatin or atorvastatin was evaluated in 63 patients that were at least 6 weeks on statin therapy and who underwent open AAA repair. A comprehensive analysis using immunohistochemistry, mRNA and protein analyses was applied on aortic wall samples collected during surgery. The effect of statins on AAA growth was analyzed in a separate prospective study in incorporating 142 patients. Both statins equally effectively and dose-dependently reduced aortic wall expression of NFκB regulated mediators (i.e. IL-6 (P<0.001) and MCP-1 (P<0.001)); shifted macrophage polarization towards a M2 phenotype (P<0.0003); selectively reduced macrophage-related markers such as cathepsin K and S (P<0.009 and 0.0027 respectively), and ALOX5 (P<0.0009), and reduced vascular wall NFκB activity (40 mg/day group, P<0.016). No effect was found on other cell types. Evaluation of the clinical efficacy of statins to reduce AAA progression did not indicate an effect of statins on aneurysm growth (P<0.337). Hence, in the context of AAA the clinical relevance of statins pleiotropy appears minimal.

Neutrophil gelatinase-associated lipocalin and interleukin-10 regulate intramacrophage Chlamydia pneumoniae replication by modulating intracellular iron homeostasis

Neutrophil gelatinase-associated lipocalin (NGAL/Lipocalin-2/Lcn-2) is a 25 kDa protein which is involved in host defence against certain Gram negative bacteria upon binding of iron loaded bacterial siderophores thereby limiting the availability of this essential nutrient to bacteria resulting in inhibition of their growth and pathogenicity. As iron is important for the growth of the intracellular bacterium Chlamydia pneumoniae we questioned whether Lcn-2 affects the course of this infection. We employed primary peritoneal macrophages obtained from wildtype and Lcn-2 −/− mice and RAW 264.7 cells which were infected with C. pneumoniae. In addition, we studied C. pneumoniae multiplication in vivo in mice receiving diets with varying iron contents. We analyzed C. pneumoniae numbers by immunohistochemistry and RT-PCR and studied the expression of iron metabolism and cytokine genes by RT-PCR, Western blot or ELISA.

Infection with Chlamydiae ex vivo and in vivo revealed a significantly higher bacterial growth in peritoneal macrophages of Lcn-2 −/− than of wildtype mice. These differences were significantly more pronounced upon iron challenge, which stimulated bacterial growth. Accordingly, treatment with an anti-Lnc-2 antibody increased whereas addition of recombinant Lcn-2 reduced bacterial growth in infected macrophages. When investigating the underlying mechanisms we observed partly different expression of several iron metabolism genes between Lcn-2 +/+ and Lcn-2 −/− macrophages and most strikingly an increased formation of the anti-inflammatory cytokine IL-10 by Lcn-2 −/− macrophages. Upon treatment with an anti-IL10 antibody we experienced a significant increase of Chlamydial growth within Lcn-2 −/− macrophages along with a reduction of the major iron storage protein ferritin. Herein we provide first time evidence that Lcn-2 is involved in host defence against Chlamydia presumably by limiting the availability of iron to the pathogen. In the absence of Lcn-2, increased formation of IL-10 exerts protective effects by increasing the intracellular formation of ferritin, thereby reducing the access of iron for bacteria.

Aldosterone and the mineralocorticoid receptor in the cerebral circulation and stroke

Ischemic stroke is a leading cause of morbidity and mortality worldwide. Elevated plasma aldosterone levels are an independent cardiovascular risk factor and are thought to contribute to hypertension, a major risk factor for stroke. Evidence from both experimental and human studies supports a role for aldosterone and/or the mineralocorticoid receptor (MR) in contributing to detrimental effects in the cerebral vasculature and to the incidence and outcome of ischemic stroke. This article reviews the evidence, including the protective effects of MR antagonism. Specifically, the effects of aldosterone and/or MR activation on cerebral vascular structure and on immune cells will be reviewed. The existing evidence suggests that aldosterone and the MR contribute to cerebral vascular pathology and to the incidence and outcome of stroke. We suggest that further research into the signaling mechanisms underlying the effects of aldosterone and MR activation in the brain and its vasculature, especially with regard to cell-specific actions, will provide important insight into causes and potential treatments for cerebrovascular disease and stroke.

Cellular and molecular players in the atherosclerotic plaque progression

Atherosclerosis initiation and progression is controlled by inflammatory molecular and cellular mediators. Cells of innate immunity, stimulated by various endogenous molecules that have undergone a transformation following an oxidative stress or nonenzymatic glycation processes, activate cells of the adaptive immunity, found at the borders of atheromas. In this way, an immune response against endogenous modified antigens takes place and gives rise to chronic low-level inflammation leading to the slow development of complex atherosclerotic plaques. These lesions will occasionally ulcerate, thus ending with fatal clinical events. Plaque macrophages represent the majority of leukocytes in the atherosclerotic lesions, and their secretory activity, including proinflammatory cytokines and matrix-degrading proteases, may be related to the fragilization of the fibrous cap and then to the rupture of the plaque. A considerable amount of work is currently focused on the identification of locally released proinflammatory factors that influence the evolution of the plaque to an unstable phenotype. A better understanding of these molecular processes may contribute to new treatment strategies. Mediators released by the immune system and associated with the development of carotid atherosclerosis are discussed.