Intravenous iron supplementation in heart failure patients induces temporary endothelial dysfunction with release of endothelial microvesicles

Background

Intravenous iron supplementation is an established therapy for patients with heart failure (HF) and concomitant iron deficiency reducing the risk of HF hospitalization. However, concerns persist regarding potential adverse vascular effects, since iron may induce oxidative stress, inflammation, and apoptosis of endothelial cells. To assess endothelial health following ferric carboxymaltose (FCM) administration, we analyzed the profile of circulating endothelial microvesicles (EMVs) and endothelial progenitor cells (EPCs) in a cohort of 23 HF patients using flow cytometry.

Results

Compared to healthy subjects, baseline levels of CD31+/CD41- EMVs were higher and EMVs featured a more apoptotic phenotype in HF patients. Following FCM administration, EMV levels showed a rapid but transient increase and displayed an altered phenotype profile with dominant augmentation of EMVs expressing inducible markers CD62E and CD54, indicating endothelial inflammatory activation and injury. Levels of circulating vasoregenerative CD45lowCD34+KDR+ EPCs were lower in HF patients and FCM application resulted in an early decrease of EPCs followed by substantial mobilization into the circulation after one week. Levels of EMVs and EPCs returned to baseline values within two and four weeks, respectively. HF patients with additional chronic kidney disease showed an elevated EMV/EPC ratio and diminished EPC mobilization, suggesting impaired vascular repair capacity. Providing a mechanistic link, in vitro experiments with cultured endothelial cells revealed that FCM dose-dependently promotes endothelial apoptosis, increases expression of adhesion molecules and CXCL12, and triggers generation of EMVs.

Conclusion

Intravenous iron supplementation with FCM in HF patients induces a biphasic response with initial increased release of CD62E+ and CD54+ enriched EMVs and subsequent mobilization of EPCs, indicating endothelial dysfunction upon FCM and suggesting consecutive engagement of a defense program aimed to reconstitute vascular health.

Endothelial Progenitor Cells Modulate the Phenotype of Smooth Muscle Cells and Increase Their Neointimal Accumulation Following Vascular Injury

BACKGROUND

 Smooth muscle cells (SMCs) are the main driver of neointima formation and restenosis following vascular injury. In animal models, endothelial progenitor cells (EPCs) accelerate endothelial regeneration and reduce neointima formation after arterial injury; however, EPC-capture stents do not reduce target vessel failure compared with conventional stents. Here we examined the influence of EPCs on features of SMCs pivotal for their impact on injury-induced neointima formation including proliferation, migration, and phenotype switch.

METHODS AND RESULTS

 EPCs, their conditioned medium, and EPC-derived microparticles induced proliferation of SMCs while limiting their apoptosis. In transwell membrane experiments and scratch assays, EPCs stimulated migration of SMCs and accelerated their recovery from scratch-induced injury. Treatment of SMCs with an EPC-derived conditioned medium or microparticles triggered transformation of SMCs toward a synthetic phenotype. However, co-cultivation of EPCs and SMCs enabling direct cell-cell contacts preserved their original phenotype and protected from the transformative effect of SMC cholesterol loading. Adhesion of EPCs to SMCs was stimulated by SMC injury and reduced by blocking CXCR2 and CCR5. Interaction of EPCs with SMCs modulated their secretory products and synergistically increased the release of selected chemokines. Following carotid wire injury in athymic mice, injection of EPCs resulted not only in reduced neointima formation but also in altered cellular composition of the neointima with augmented accumulation of SMCs.

CONCLUSION

 EPCs stimulate proliferation and migration of SMCs and increase their neointimal accumulation following vascular injury. Furthermore, EPCs context-dependently modify the SMC phenotype with protection from the transformative effect of cholesterol when a direct cell-cell contact is established.

Validation of commercially available ELISAs for the detection of circulating sclerostin in hemodialysis patients

BACKGROUND

Sclerostin is an endocrine regulator in chronic kidney disease - mineral and bone disorder (CKD-MBD). Validation of assay comparability and pre-analytical handling is mandatory for establishment of sclerostin as a biomarker.

METHODS

Blood samples (serum, EDTA, heparin and citrate plasma) were obtained from 12 hemodialysis (HD) patients after the long dialysis interval. Passing-Bablok regression analysis and Bland-Altman difference plots were used to evaluate the agreement between sclerostin levels measured with two commercially available ELISAs from TECOmedical and Biomedica.

RESULTS

Independent of the sample type, the agreement of the two assays was poor with a strong proportional but no systematic bias. Compared to the TECOmedical assay, the Biomedica test yielded almost 2-fold higher sclerostin values throughout all sample types. Spike recovery and linear dilution studies revealed a higher accuracy of the TECOmedical assay (97% and 96%) compared to the Biomedica assay (118% and 78%). Sclerostin levels were stable within 4 hours after sample collection, in particular when analyzed in plasma. In contrast to the Biomedica assay, the TECOmedical showed a systematic but no proportional bias between serum and plasma samples with higher values for plasma samples. Among the 3 different plasma samples no systematic error could be documented.

CONCLUSION

Careful consideration of the pre-analytical handling and comparative assay validation are necessary to facilitate a more differentiated interpretation of studies reporting circulating sclerostin levels. The presence of a proportional bias demonstrates that in HD patients the two ELISAs for measuring sclerostin should not be used interchangeably. Furthermore, caution is necessary when comparing sclerostin results obtained from different blood sample types.

Microvesicles from platelets: novel drivers of vascular inflammation

Microvesicles are receiving increased attention not only as biomarkers but also as mediators of cell communication and as integral effectors of disease. Platelets present a major source of microvesicles and release these microvesicles either spontaneously or upon activation. Platelet-derived microvesicles retain many features of their parent cells and have been shown to exert modulatory effects on vascular and immune cells. Accordingly, microvesicles from platelets can be measured at increased levels in patients with cardiovascular disease or individuals at risk. In addition, isolated microvesicles from platelets were shown to exert immunomodulatory actions on various cell types. In this review the various aspects of platelet-derived microvesicles including release, clearance, measurement, occurrence during disease and relevance for the pathophysiology of vascular inflammation will be discussed.

Inflammatory role and prognostic value of platelet chemokines in acute coronary syndrome

Activated platelets and neutrophils exacerbate atherosclerosis. Platelets release the chemokines CXCL4, CXCL4L1 and CCL5, whereas myeloperoxidase (MPO) and azurocidin are neutrophil-derived. We investigated whether plasma levels of these platelet and neutrophil mediators are affected by the acute coronary syndrome (ACS), its medical treatment, concomitant clinical or laboratory parameters, and predictive for the progression of coronary artery disease (CAD). In an observational study, the association of various factors with plasma concentrations of platelet chemokines and neutrophil mediators in 204 patients, either upon admission with ACS and 6 hours later or without ACS or CAD, was determined by multiple linear regression. Mediator release was further analysed after activation of blood with ACS-associated triggers such as plaque material. CXCL4, CXCL4L1, CCL5, MPO and azurocidin levels were elevated in ACS. CXCL4 and CCL5 but not CXCL4L1 or MPO were associated with platelet counts and CRP. CXCL4 (in association with heparin treatment) and MPO declined over 6 hours during ACS. Elevated CCL5 was associated with a progression of CAD. Incubating blood with plaque material, PAR1 and PAR4 activation induced a marked release of CXCL4 and CCL5, whereas CXCL4L1 and MPO were hardly or not altered. Platelet chemokines and neutrophil products are concomitantly elevated in ACS and differentially modulated by heparin treatment. CCL5 levels during ACS predict a progression of preexisting CAD. Platelet-derived products appear to dominate the inflammatory response during ACS, adding to the emerging evidence that ACS per se may promote vascular inflammation.

Neutrophil-derived cathelicidin protects from neointimal hyperplasia

Percutaneous transluminal angioplasty with stent implantation is used to dilate arteries narrowed by atherosclerotic plaques and to revascularize coronary arteries occluded by atherothrombosis in myocardial infarction. Commonly applied drug-eluting stents release antiproliferative or anti-inflammatory agents to reduce the incidence of in-stent stenosis. However, these stents may still lead to in-stent stenosis; they also show increased rates of late stent thrombosis, an obstacle to optimal revascularization possibly related to endothelial recovery. Here, we examined the contribution of neutrophils and neutrophilic granule proteins to arterial healing after injury. We found that neutrophil-borne cathelicidin (mouse CRAMP, human LL-37) promoted reendothelization and thereby limited neointima formation after stent implantation. We then translated these findings to an animal model using a neutrophil-instructing, biofunctionalized, miniaturized Nitinol stent coated with LL-37. This stent reduced in-stent stenosis in a mouse model of atherosclerosis, suggesting that LL-37 may promote vascular healing after interventional therapy.

Microparticles: protagonists of a novel communication network for intercellular information exchange

Microparticles represent a heterogeneous population of vesicles with a diameter of 100 to 1000 nm that are released by budding of the plasma membrane and express antigens specific of their parental cells. Although microparticle formation represents a physiological phenomenon, a multitude of pathologies are associated with a considerable increase in circulating microparticles, including inflammatory and autoimmune diseases, atherosclerosis, and malignancies. Microparticles display an broad spectrum of bioactive substances and receptors on their surface and harbor a concentrated set of cytokines, signaling proteins, mRNA, and microRNA. Recent studies provided evidence for the concept of microparticles as veritable vectors for the intercellular exchange of biological signals and information. Indeed, microparticles may transfer part of their components and content to selected target cells, thus mediating cell activation, phenotypic modification, and reprogramming of cell function. Because microparticles readily circulate in the vasculature, they may serve as shuttle modules and signaling transducers not only in their local environment but also at remarkable distance from their site of origin. Altogether, this transcellular delivery system may extend the confines of the limited transcriptome and proteome of recipient cells and establishes a communication network in which specific properties and information among cells can be efficiently shared. At least in same cases, the sequential steps of the transfer process underlie complex regulatory mechanisms, including selective sorting ("packaging") of microparticle components and content, specificity of interactions with target cells determined by surface receptors, and ultimately finely tuned and signal-dependent release and delivery of microparticle content.

C5a Receptor Targeting in Neointima Formation After Arterial Injury in Atherosclerosis-Prone Mice

Background— Receptor binding of complement C5a leads to proinflammatory activation of many cell types, but the role of receptor-mediated action during arterial remodeling after injury has not been studied. In the present study, we examined the contribution of the C5a receptor (C5aR) to neointima formation in apolipoprotein E–deficient mice employing a C5aR antagonist (C5aRA) and a C5aR-blocking monoclonal antibody.

Methods and Results— Mice fed an atherogenic diet were subjected to wire-induced endothelial denudation of the carotid artery and treated with C5aRA and anti-C5aR-blocking monoclonal antibody or vehicle control. Compared with controls, neointima formation was significantly reduced in mice receiving C5aRA or anti-C5aR-blocking monoclonal antibody for 1 week but not for 3 weeks, attributable to an increased content of vascular smooth muscle cells, whereas a marked decrease in monocyte and neutrophil content was associated with reduced vascular cell adhesion molecule-1. As assessed by immunohistochemistry, reverse transcription polymerase chain reaction, and flow cytometry, C5aR was expressed in lesional and cultured vascular smooth muscle cells, upregulated by injury or tumor necrosis factor-α, and reduced by C5aRA. Plasma levels and neointimal plasminogen activator inhibitor-1 peaked 1 week after injury and were downregulated in C5aRA-treated mice. In vitro, C5a induced plasminogen activator inhibitor-1 expression in endothelial cells and vascular smooth muscle cells in a C5aRA-dependent manner, possibly accounting for higher vascular smooth muscle cell immigration.

Conclusions— One-week treatment with C5aRA or anti-C5aR-blocking monoclonal antibody limited neointimal hyperplasia and inflammatory cell content and was associated with reduced vascular cell adhesion molecule-1 expression. However, treatment for 3 weeks failed to reduce but rather stabilized plaques, likely by reducing vascular plasminogen activator inhibitor-1 and increasing vascular smooth muscle cell migration.

Platelet microparticles enhance the vasoregenerative potential of angiogenic early outgrowth cells after vascular injury

BACKGROUND

Angiogenic early outgrowth cells (EOCs) have been reported to contribute to endothelial regeneration and to limit neointima formation after vascular injury. Vascular pathologies comprise platelet activation and concomitant generation of platelet microparticles (PMPs). We hypothesized that PMPs may interact with EOCs in the context of vascular injury and modulate their regenerative potential.

METHODS AND RESULTS

Using flow cytometry, confocal microscopy, and scanning electron microscopy, we demonstrated the binding of thrombin/collagen-induced PMPs to EOCs with subsequent membrane assimilation and incorporation. This interaction promoted phenotypic alterations of EOCs with increased expression of endothelial cell markers and transfer of the chemokine receptor CXCR4 to EOCs with enhanced responsiveness to its ligand CXCL12/SDF-1alpha. In addition, PMPs augmented the adhesion of EOCs to extracellular matrix components and to the injured vessel wall and accelerated cytoskeletal reorganization and migration of EOCs. PMPs induced changes in the EOC secretome toward a more proangiogenic profile and amplified the EOC-mediated induction of proliferation, migration, and capillary tube formation by mature endothelial cells. Compared with untreated EOCs, the injection of PMP-treated EOCs resulted in accelerated reendothelialization after arterial denudation injury in athymic nude mice, whereas the EOC-mediated reduction of neointima formation remained unchanged.

CONCLUSIONS

Our data provide evidence that PMPs can boost the potential of EOCs to restore endothelial integrity after vascular injury. Major mechanisms involve the enhancement of EOC recruitment, migration, differentiation, and release of proangiogenic factors.

Differential and additive effects of platelet-derived chemokines on monocyte arrest on inflamed endothelium under flow conditions

Platelet-derived chemokines, such as regulated on activation, normal T expressed and secreted (RANTES; CC chemokine ligand 5), platelet factor 4 [PF4; CXC chemokine ligand 4 (CXCL4)], and epithelial neutrophil-activating protein 78 (ENA-78; CXCL5), or precursors, such as beta-thromboglobulin, which can be processed to neutrophil-activating protein-2 (NAP-2; CXCL7), may play an important role in monocyte recruitment during atherogenesis. Platelets can deposit chemokines on inflamed endothelium; however, little is known about differential or additive effects of platelet chemokines on monocyte arrest. Here, we demonstrate that preincubation of activated human microvascular endothelial cells (HMVECs) with RANTES, PF4, or NAP-2 but not ENA-78 dose-dependently increased surface immobilization and subsequent monocyte arrest in flow. RANTES was the most potent and efficient arrest chemokine. Pretreatment of HMVECs with beta-thromboglobulin enhanced monocyte arrest in the presence of cathepsin G generating NAP-2. Combined pretreatment of HMVECs with RANTES and PF4 at suboptimal concentrations synergistically increased arrest, and preincubation with chondroitinase ABC abrogated RANTES- and PF4-induced monocyte arrest. This was associated with reduced expression of chondroitin sulfate, RANTES, and PF4 on the HMVEC surface. Perfusion of HMVECs with platelets known to deposit RANTES and PF4 on the endothelial surface enhanced monocyte arrest, which was inhibited by Met-RANTES, chondroitinase, or a blocking antibody to PF4 but not to ENA-78. The relevance of platelet-derived chemokines was confirmed in adhesion assays with activated whole blood, where Met-RANTES and to a lesser extent, antibodies to PF4 and NAP-2 inhibited arrest of CD14-positive monocytes. Thus, multiple platelet-derived chemokines and processable precursors, which can be presented by specific endothelial proteoglycans, may contribute and cooperate differentially to induce monocyte recruitment.

Platelet microparticles: a transcellular delivery system for RANTES promoting monocyte recruitment on endothelium

OBJECTIVE

Platelet activation mediates multiple cellular responses, including secretion of chemokines such as RANTES (CCL5), and formation of platelet microparticles (PMPs). We studied the role of PMPs in delivering RANTES and promoting monocyte recruitment.

METHODS AND RESULTS

Here we show that PMPs contain substantial amounts of RANTES and deposit RANTES on activated endothelium or murine atherosclerotic carotid arteries. RANTES deposition is facilitated by flow conditions and more efficient than that conferred by PMP supernatants. Interactions of PMPs with activated endothelium in flow were mostly characterized by rolling. RANTES deposition showed a diffuse distribution pattern and was rarely colocalized with firmly adherent PMPs, substantiating that RANTES deposition occurs during transient interactions. Importantly, preperfusion with PMPs enhanced monocyte arrest on activated endothelium or atherosclerotic carotid arteries, which could be inhibited by a blocking antibody or a RANTES receptor antagonist. Blockade or deficiency of PMP-expressed adhesion receptors demonstrated differential requirement of P-selectin, glycoprotein Ib (GPIb), GPIIb/IIIa, and junctional adhesion molecule-A for PMP interactions with endothelium, PMP-dependent RANTES deposition, and subsequent monocyte arrest.

CONCLUSION

Circulating PMPs may serve as a finely tuned transcellular delivery system for RANTES, triggering monocyte arrest to inflamed and atherosclerotic endothelium, introducing a novel mechanism for platelet-dependent monocyte recruitment in inflammation and atherosclerosis.

Heterophilic interactions of platelet factor 4 and RANTES promote monocyte arrest on endothelium

The chemokines platelet factor 4 (PF4) and RANTES (regulated on activation normal T cell expressed and secreted) are secreted by activated platelets and influence multiple cell types and biologic processes. For instance, PF4 inhibits progenitor cell proliferation and angiogenesis, while platelet-derived RANTES is involved in vascular recruitment of monocytes. However, little is known about functional interactions of PF4 and RANTES. Here we show that the presence of PF4 enhanced the arrest of RANTES-stimulated monocytes and monocytic cells on activated endothelial cells under flow conditions, while binding of PF4 to the monocyte surface was increased by RANTES. Both RANTES-triggered arrest and PF4 binding involved monocytic chondroitin sulfate. Ligand blots and surface plasmon resonance revealed a robust heterophilic interaction of PF4 with RANTES but not with RANTES variants defective in higher order oligomerization. The tetrameric mutant E26A bound to the monocyte surface without increasing PF4 binding, and monocyte arrest induced by E26A-RANTES was not enhanced by PF4. Stimulation of monocytes with supernatants of activated platelets triggered arrest involving RANTES and PF4, as shown by inhibition studies. Our results suggest that heterophilic interactions with PF4 require structural motifs important in RANTES oligomerization and amplify RANTES-triggered effects on monocyte adhesion. This may have implications for the modulation of inflammatory recruitment by platelet-derived chemokines.