Fractalkine levels are elevated early after PCI-treated ST-elevation myocardial infarction; no influence of autologous bone marrow derived stem cell injection

CX3CL1 (Fractalkine)-CX3CR1 Axis in Inflammation-Induced Angiogenesis and Tumorigenesis

The chemotactic cytokine fractalkine (FKN, chemokine CX3CL1) has unique properties resulting from the combination of chemoattractants and adhesion molecules. The soluble form (sFKN) has chemotactic properties and strongly attracts T cells and monocytes. The membrane-bound form (mFKN) facilitates diapedesis and is responsible for cell-to-cell adhesion, especially by promoting the strong adhesion of leukocytes (monocytes) to activated endothelial cells with the subsequent formation of an extracellular matrix and angiogenesis. FKN signaling occurs via CX3CR1, which is the only known member of the CX3C chemokine receptor subfamily. Signaling within the FKN-CX3CR1 axis plays an important role in many processes related to inflammation and the immune response, which often occur simultaneously and overlap. FKN is strongly upregulated by hypoxia and/or inflammation-induced inflammatory cytokine release, and it may act locally as a key angiogenic factor in the highly hypoxic tumor microenvironment. The importance of the FKN/CX3CR1 signaling pathway in tumorigenesis and cancer metastasis results from its influence on cell adhesion, apoptosis, and cell migration. This review presents the role of the FKN signaling pathway in the context of angiogenesis in inflammation and cancer. The mechanisms determining the pro- or anti-tumor effects are presented, which are the cause of the seemingly contradictory results that create confusion regarding the therapeutic goals.

Chemokine Fractalkine and Non-Obstructive Coronary Artery Disease-Is There a Link?

Non-obstructive coronary artery disease (NO-CAD) constitutes a heterogeneous group of conditions collectively characterized by less than 50% narrowing in at least one major coronary artery with a fractional flow reserve (FFR) of ≤0.80 observed in coronary angiography. The pathogenesis and progression of NO-CAD are still not fully understood, however, inflammatory processes, particularly atherosclerosis and microvascular dysfunction are known to play a major role in it. Chemokine fractalkine (FKN/CX3CL1) is inherently linked to these processes. FKN/CX3CL1 functions predominantly as a chemoattractant for immune cells, facilitating their transmigration through the vessel wall and inhibiting their apoptosis. Its concentrations correlate positively with major cardiovascular risk factors. Moreover, promising preliminary results have shown that FKN/CX3CL1 receptor inhibitor (KAND567) administered in the population of patients with ST-elevation myocardial infarction (STEMI) undergoing percutaneous coronary intervention (PCI), inhibits the adverse reaction of the immune system that causes hyperinflammation. Whereas the link between FKN/CX3CL1 and NO-CAD appears evident, further studies are necessary to unveil this complex relationship. In this review, we critically overview the current data on FKN/CX3CL1 in the context of NO-CAD and present the novel clinical implications of the unique structure and function of FKN/CX3CL1 as a compound which distinctively contributes to the pathomechanism of this condition.

Fractalkine Signalling (CX3CL1/CX3CR1 Axis) as an Emerging Target in Coronary Artery Disease

Acute myocardial infarction (MI) is the most common and dramatic complication of atherosclerosis, which, despite successful reperfusion therapy, can lead to incident heart failure (HF). HF occurs when the healing process is impaired due to adverse left ventricular remodelling, and can be the result of so-called ischaemia/reperfusion injury (IRI), visualised by the development of intramyocardial haemorrhage (IMH) or microvascular obstruction (MVO) in cardiac MRI. Thus far, translation of novel pharmacological strategies from preclinical studies to target either IRI or HF post MI have been largely unsuccessful. Anti-inflammatory therapies also carry the risk of affecting the immune system. Fractalkine (FKN, CX3CL1) is a unique chemokine, present as a transmembrane protein on the endothelium, or following cleavage as a soluble ligand, attracting leukocyte subsets expressing the corresponding receptor CX3CR1. We have shown previously that the fractalkine receptor CX3CR1 is associated with MVO in patients undergoing primary PCI. Moreover, inhibition of CX3CR1 with an allosteric small molecule antagonist (KAND567) in the rat MI model reduces acute infarct size, inflammation, and IMH. Here we review the cellular biology of fractalkine and its receptor, along with ongoing studies that introduce CX3CR1 as a future target in coronary artery disease, specifically in patients with myocardial infarction.

Monocyte chemokine receptors as therapeutic targets in cardiovascular diseases

Chemokine receptors are fundamental in many processes related to cardiovascular diseases, such as monocyte migration to vessel walls, cell adhesion, and angiogenesis, among others. Even though many experimental studies have shown the utility of blocking these receptors or their ligands in the treatment of atherosclerosis, the findings in clinical research are still poor. Thus, in the current review we aimed to describe some promising results concerning the blockade of chemokine receptors as therapeutic targets in the treatment of cardiovascular diseases and also to discuss some challenges that need to be overcome before using these strategies in clinical practice.

Dapagliflozin protects H9c2 cells against injury induced by lipopolysaccharide via suppression of CX3CL1/CX3CR1 axis and NF-κB activity

BACKGROUND

Dapagliflozin, a selective Sodium-glucose cotransporter-2 (SGLT2) inhibitor, has been shown to play a key role in the control and management of the metabolic and cardiac disease.

OBJECTIVE

The current study aims to address the effects of dapagliflozin on the expression of fractalkine (FKN), known as CX3CL1, and its receptors CX3CR1, Nuclear factor-kappa B(NF-κB) p65 activity, Reactive oxygen species (ROS), and inflammation in LPS-treated H9c2 cell line.

METHODS

H9c2 cells were cultured with lipopolysaccharide (LPS) to establish a model of LPS-induced damage and then subsequently were treated with dapagliflozin for 72 h. Our work included measurement of cell viability (MTT), Malondialdehyde (MDA), intracellular ROS, tumor necrosis factor-α (TNF-α), NF-κB activity, and expression CX3CL1/CX3CR1.

RESULTS

The results showed that LPS-induced reduction of cell viability was successfully rescued by dapagliflozin treatment. The cellular levels of MDA, ROS, and TNF-α, as an indication of cellular oxidative stress and inflammation, were significantly elevated in H9c2 cells compared to the control group. Furthermore, dapagliflozin ameliorated inflammation and oxidative stress through the modulation of the levels of MDA, TNF-α, and ROS. Correspondingly, dapagliflozin reduced the expression of CX3CL1/CX3CR1, NF-κB p65 DNA binding activity and it also attenuated nuclear acetylated NF-κB p65 in LPS-induced injury in H9c2 cells compared to untreated cells.

CONCLUSION

These findings shed light on the novel pharmacological potential of dapagliflozin in the alleviation of LPS-induced CX3CL1/CX3CR1-mediated injury in inflammatory conditions such as sepsis-induced cardiomyopathy.

Targeting the chemokine network in atherosclerosis

Chemokines and their receptors represent a potential target for immunotherapy in chronic inflammation. They comprise a large family of cytokines with chemotactic activity, and their cognate receptors are expressed on all cells of the body. This network dictates leukocyte recruitment and activation, angiogenesis, cell proliferation and maturation. Dysregulation of chemokine and chemokine receptor expression as well as function participates in many pathologies including cancer, autoimmune diseases and chronic inflammation. In atherosclerosis, a lipid-driven chronic inflammation of middle-sized and large arteries, chemokines and their receptors participates in almost all stages of the disease from initiation of fatty streaks to mature atherosclerotic plaque formation. Atherosclerosis and its complications are the main driver of mortality and morbidity in cardiovascular diseases (CVD). Hence, exploring new fields of therapeutic targeting of atherosclerosis is of key importance. This review gives an overview of the recent advances on the role of key chemokines and chemokine receptors in atherosclerosis, addresses chemokine-based biomarkers at biochemical, imaging and genetic level in human studies, and highlights the clinial trials targeting atherosclerosis.

Neutrophil extracellular traps and monocyte subsets at the culprit lesion site of myocardial infarction patients

Neutrophils release their chromatin into the extracellular space upon activation. These web-like structures are called neutrophil extracellular traps (NETs) and have potent prothrombotic and proinflammatory properties. In ST-elevation myocardial infarction (STEMI), NETs correlate with increased infarct size. The interplay of neutrophils and monocytes impacts cardiac remodeling. Monocyte subsets are classified as classical, intermediate and non-classical monocytes. In the present study, in vitro stimulation with NETs led to an increase of intermediate monocytes and reduced expression of CX3CR1 in all subsets. Intermediate monocytes have been associated with poor outcome, while non-classical CX3CR1-positive monocytes could have reparative function after STEMI. We characterized monocyte subsets and NET markers at the culprit lesion site of STEMI patients (n = 91). NET surrogate markers were increased and correlated with larger infarct size and with fewer non-classical monocytes. Intermediate and especially non-classical monocytes were increased at the culprit site compared to the femoral site. Low CX3CR1 expression of monocytes correlated with high NET markers and increased infarct size. In this translational system, causality cannot be proven. However, our data suggest that NETs interfere with monocytic differentiation and receptor expression, presumably promoting a subset shift at the culprit lesion site. Reduced monocyte CX3CR1 expression may compromise myocardial salvage.

Lymphocyte Communication in Myocardial Ischemia/Reperfusion Injury

SIGNIFICANCE

Myocardial ischemia/reperfusion (I/R) is an important complication of reperfusion therapy for myocardial infarction (MI). It is a complex process involving metabolic and immunological factors. To date, no effective treatment has been identified. Recent Advances: Previous research has focused on the role of innate immune cells in I/R injury. In recent years, increasing evidence has accumulated for an important role for adaptive immune cells, particularly T lymphocytes. Data from ST elevation MI patients have identified prognostic significance for lymphocyte counts, particularly postreperfusion lymphopenia. Dynamic changes in circulating CD4⁺ T cell subsets occurring early after reperfusion are associated with development of I/R injury in the form of microvascular obstruction. Transcoronary gradients in cell counts suggest sequestration of these cells into the reperfused myocardium. These findings support existing data from mouse models indicating a role for CD4⁺ T cells in I/R injury. It is clear, however, the effects of lymphocytes in the ischemic myocardium are time and subset specific, with some having protective effects, while others are pathogenic.

CRITICAL ISSUES

An understanding of the cellular events that lead to accumulation of lymphocytes in the myocardium, and their actions once there, is key to manipulating this process. Chemokines produced in response to ischemia and cellular injury have an important role, while lymphocyte-derived cytokines are critical in the balance between inflammation and healing.

FUTURE DIRECTIONS

Further research into the involvement of lymphocytes in myocardial I/R injury may allow development of targeted therapies, opening a new avenue of considerable therapeutic potential. Antioxid. Redox Signal. 26, 660-675.

Transplantation of Autologous Bone Marrow Mononuclear Cells Regulates Inflammation in a Rabbit Model of Carotid Artery Atherosclerosis

OBJECTIVE

It is well known that inflammation plays key roles in the development of atherosclerosis and that the transplantation of bone marrow mononuclear cells (BMMNCs) can suppress inflammation in rodent models of ischemic diseases. Here, we explored whether transplantation of autologous BMMNCs could prevent the progression of atherosclerosis by the alleviation of inflammatory responses in a rabbit model of carotid artery atherosclerosis.

METHODS AND RESULTS

The atherosclerotic rabbit model was established by air desiccation followed by a high-cholesterol diet for 8 weeks. Then, 1 × 107 BMMNCs labeled with BrdU or an equal volume of vehicle were injected into the rabbits via the ear vein. Using an ultrasonographic imaging method, we found that autologous BMMNC treatment significantly decreased the area of atherosclerotic plaques compared to the vehicle-treated group (p < 0.05). The results were further confirmed by hematoxylin-eosin staining. RT-PCR results demonstrated that BMMNC treatment significantly reduced the expression of interleukin (IL)-6 and CD147 but increased the expression of IL-10 and transforming growth factor-β compared with vehicle treatment (p < 0.05), which was consistent with Western blot results.

CONCLUSIONS

Transplantation of autologous BMMNCs delays the development of atherosclerosis, most probably via the attenuation of inflammatory responses, which could be a new approach for treating carotid atherosclerosis.

Associations between circulating proteins and corresponding genes expressed in coronary thrombi in patients with acute myocardial infarction

INTRODUCTION

Several genes are expressed in aspirated coronary thrombi in acute myocardial infarction (AMI), exhibiting dynamic changes along ischemic time. Whether soluble biomarkers reflect the local gene environment and ischemic time is unclear. We explored whether circulating biomarkers were associated with corresponding coronary thrombi genes and total ischemic time.

MATERIAL AND METHODS

In 33 AMI patients undergoing percutaneous coronary intervention (PCI), blood samples were collected within 6-24h for markers related to plaque rupture (metalloproteinase 9, tissue inhibitor of metalloproteinases 1), platelet and endothelial cell activation (P-selectin, CD40 ligand, PAR-1), hemostasis (tissue factor, tissue plasminogen activator, plasminogen activator inhibitor 1, free and total tissue factor pathway inhibitor, D-dimer, prothrombin fragment 1+2), inflammation (interleukin 8 and 18, fractalkine, monocyte chemoattractant protein 1 (MCP-1), CXCL1, pentraxin 3, myeloperoxidase) and galectin 3, caspase 8 and epidermal growth factor (EGF). Laboratory analyses were performed by Proximity Extension Assay (Proseek Multiplex CVD I(96 × 96)), ELISAs and RT-PCR.

RESULTS

Only circulating P-selectin correlated to the corresponding P-selectin gene expression in thrombi (r=0.530, p=0.002). Plasma galectin 3, fractalkine, MCP-1 and caspase 8 correlated inversely to ischemic time (r=-0.38-0.50, all p <0.05), while plasma MCP-1, galectin 3 and EGF were higher at short (≤ 4 h) vs. long (>4h) ischemic time (all p <0.05).

CONCLUSIONS

The dynamic changes in circulating mediators along ischemic time were not reflected in the profile of locally expressed genes. These observations indicate a locally confined milieu within the site of atherothrombosis, which may be important for selective therapy.

T lymphocytes and fractalkine contribute to myocardial ischemia/reperfusion injury in patients

BACKGROUND

Lymphocytes contribute to ischemia/reperfusion (I/R) injury in several organ systems, but their relevance in ST elevation myocardial infarction (STEMI) is unknown. Our goal was to characterize lymphocyte dynamics in individuals after primary percutaneous coronary intervention (PPCI), assess the prognostic relevance of these cells, and explore mechanisms of lymphocyte-associated injury.

METHODS

Lymphocyte counts were retrospectively analyzed in 1,377 STEMI patients, and the prognostic relevance of post-PPCI lymphopenia was assessed by Cox proportional hazards regression. Blood from 59 prospectively recruited STEMI patients undergoing PPCI was sampled, and leukocyte subpopulations were quantified. Microvascular obstruction (MVO), a component of I/R injury, was assessed using MRI.

RESULTS

In the retrospective cohort, lymphopenia was associated with a lower rate of survival at 3 years (82.8% vs. 96.3%, lowest vs. highest tertile; hazard ratio 2.42). In the prospective cohort, lymphocyte counts fell 90 minutes after reperfusion, primarily due to loss of T cells. CD8+ T cells decreased more than CD4+ T cells, and effector subsets exhibited the largest decline. The early decrease in effector T cell levels was greater in individuals that developed substantial MVO. The drop in T cell subsets correlated with expression of the fractalkine receptor CX3CR1 (r2 = 0.99, P = 0.006). Serum fractalkine concentration peaked at 90 minutes after reperfusion, coinciding with the T cell count nadir.

CONCLUSIONS

Lymphopenia following PPCI is associated with poor prognosis. Our data suggest that fractalkine contributes to lymphocyte shifts, which may influence development of MVO through the action of effector T cells.

TRIAL REGISTRATION

Not applicable.

FUNDING

British Heart Foundation (FS/12/31/29533) and National Institute of Health Research (NIHR) Newcastle Biomedical Research Centre.

Modulation of platelet and monocyte function by the chemokine fractalkine (CX3 CL1) in cardiovascular disease

BACKGROUND

The chemokine fractalkine, CX3CL1, bears unique features within the chemokine family: it exists in a membrane bound form acting as an adhesion molecule and surface receptor; however, when cleaved by ADAM 10, it functions as a soluble chemokine. Fractalkine and its chemokine receptor CX3CR1 are known to have multiple roles in diverse human diseases, for example inflammatory diseases, rheumatoid arthritis, renal diseases and atherosclerosis.

MATERIALS AND METHODS

This review is based on the material obtained via PubMed up to November 2014. The key search terms used were 'fractalkine', 'CX3CL1', 'CX3CR1', 'cardiovascular disease', 'platelets', 'monocytes' and 'platelet-monocyte complexes'.

RESULTS

Atherosclerosis is recognized as a highly inflammatory disease, and it has become increasingly evident that the immune system plays an important role in atherogenesis and atheroprogression. Two blood cell populations are crucially involved in the early development of atherosclerotic lesions: monocytes and platelets. They are detected at vascular sites of endothelial dysfunction and are involved in inflammatory immune responses. These cells directly interact with each other, forming platelet-monocyte complexes that are increased in cardiovascular diseases. During the development of atherosclerosis, fractalkine mediates leukocyte recruitment to the inflamed endothelium, which promotes early formation of lesions. This process only effectively works in the presence of activated platelets. It has been suggested that fractalkine and its receptor contribute to platelet-monocyte aggregate formation underlining the two important impacts of this chemokine for platelets as well as monocytes.

CONCLUSION

Interesting data hint at a role of fractalkine for platelet activation, adhesion and subsequent monocyte recruitment to activated endothelial cells in cardiovascular diseases. However, the exact mechanisms remain to become unravelled.

Fractalkine neutralization improves cardiac function after myocardial infarction

NEW FINDINGS

What is the central question of this study? What is the cardioprotective role of fractalkine neutralization in heart failure and what are the mechanisms responsible? What is the main finding and its importance? The concentration of fractalkine is increased in the left ventricle of mice with myocardial infarction, similar to the increases in plasma from heart failure patients. The present study shows a clear beneficial effect of neutralizing fractalkine in a model of myocardial infarction, which results in increased survival. Such an approach may be worthwhile in human patients. Concentrations of the chemokine fractalkine (FKN) are increased in patients with chronic heart failure, and our previous studies show that aged mice lacking the prostaglandin E2 EP4 receptor subtype (EP4-KO) have increased cardiac FKN, with a phenotype of dilated cardiomyopathy. However, how FKN participates in the pathogenesis of heart failure has rarely been studied. We hypothesized that FKN contributes to the pathogenesis of heart failure and that anti-FKN treatment prevents heart failure induced by myocardial infarction (MI) more effectively in EP4-KO mice. Male EP4-KO mice and wild-type littermates underwent sham or MI surgery and were treated with an anti-FKN antibody or control IgG. At 2 weeks post-MI, echocardiography was performed and hearts were excised for determination of infarct size, immunohistochemistry and Western blot of signalling molecules. Given that FKN protein levels in the left ventricle were increased to a similar extent in both strains after MI and that anti-FKN treatment improved survival and cardiac function in both strains, we subsequently used only wild-type mice to examine the mechanisms whereby anti-FKN is cardioprotective. Myocyte cross-sectional area and interstitial collagen fraction were reduced after anti-FKN treatment, as were macrophage migration and gelatinase activity. Activation of ERK1/2 and p38 MAPK were reduced after neutralization of FKN. In vitro, FKN increased fibroblast proliferation. In conclusion, increased FKN contributes to heart failure after MI. This effect is not exacerbated in EP4-KO mice, suggesting that there is no link between FKN and lack of EP4. Overall, inhibition of FKN may be important to preserve cardiac function post-MI.