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

Protection against neutrophil extracellular trap (NET) toxicity by antioxidant monoHER

Background: Neutrophil extracellular traps (NET) are extracellular fibers produced by activated neutrophils to kill bacteria. NET was recently found to be associated with several diseases, such as autoimmune diseases. NET formation, called NETosis, is reactive oxygen species (ROS) dependent, thereby, prompting us to study its inhibition by potent antioxidant monoHER as well as to study monoHER protection against NET toxicity caused by NET constituent histone 3 on endothelial cells. Methods: Freshly isolated neutrophils from male donors were stimulated with PMA to induce NET formation. The effect of monoHER (50 µM) on oxidative burst (O2 ●− production) and NET formation was determined by fluorescence microscopy. Flow cytometry was used to determine the protective effect of monoHER against NET toxicity constituent histone 3 in EA.hy926 cells. Data was evaluated using ANOVA followed by the Bonferroni post-hoc test. Results: MonoHER significantly reduced (p < 0.01) O2 ●− production of PMA-stimulated neutrophils and consequently inhibited NET formation. MonoHER could also counteract histone 3 toxicity in EA.hy926 cells. Conclusions: MonoHER might inhibit ROS-dependent NETosis pathway and also protect the endothelial cells against NET toxicity

Protection against neutrophil extracellular trap (NET) toxicity by antioxidant monoHER

Background: Neutrophil extracellular traps (NET) are extracellular fibers produced by activated neutrophils to kill bacteria. NET was recently found to be associated with several diseases, such as autoimmune diseases. NET formation, called NETosis, is reactive oxygen species (ROS) dependent, thereby, prompting us to study its inhibition by potent antioxidant monoHER as well as to study monoHER protection against NET toxicity caused by NET constituent histone 3 on endothelial cells. Methods: Freshly isolated neutrophils from male donors were stimulated with PMA to induce NET formation. The effect of monoHER (50 µM) on oxidative burst (O2 ●− production) and NET formation was determined by fluorescence microscopy. Flow cytometry was used to determine the protective effect of monoHER against NET toxicity constituent histone 3 in EA.hy926 cells. Data was evaluated using ANOVA followed by the Bonferroni post-hoc test. Results: MonoHER significantly reduced (p < 0.01) O2 ●− production of PMA-stimulated neutrophils and consequently inhibited NET formation. MonoHER could also counteract histone 3 toxicity in EA.hy926 cells. Conclusions: MonoHER might inhibit ROS-dependent NETosis pathway and also protect the endothelial cells against NET toxicity

Platelet extracellular vesicles induce a pro-inflammatory smooth muscle cell phenotype

Extracellular vesicles (EVs) are mediators of cell communication during health and disease, and abundantly released by platelets upon activation or during ageing. Platelet EVs exert modulatory effects on immune and vascular cells. Platelet EVs may modulate the function of vascular smooth muscle cells (SMC). Platelet EVs were isolated from platelet-rich plasma and incubated with SMC in order to assess binding, proliferation, migration and pro-inflammatory phenotype of the cells. Platelet EVs firmly bound to resting SMC through the platelet integrin αIIbβ3, while binding also occurred in a CX3CL1–CX3CR1-dependent manner after cytokine stimulation. Platelet EVs increased SMC migration comparable to platelet derived growth factor or platelet factor 4 and induced SMC proliferation, which relied on CD40- and P-selectin interactions. Flow-resistant monocyte adhesion to platelet EV-treated SMC was increased compared with resting SMC. Again, this adhesion depended on integrin αIIbβ3 and P-selectin, and to a lesser extent on CD40 and CX3CR1. Treatment of SMC with platelet EVs induced interleukin 6 secretion. Finally, platelet EVs induced a synthetic SMC morphology and decreased calponin expression. Collectively, these data indicate that platelet EVs exert a strong immunomodulatory activity on SMC. In particular, platelet EVs induce a switch towards a pro-inflammatory phenotype, stimulating vascular remodelling.Netherlands Foundation for Scientific ResearchLandsteiner Foundation for Blood Transfusion ResearchDeutsche ForschungsgemeinschaftNutrim NWO Graduate Programme (Netherlands Foundation for Scientific Research

Combined Antiplatelet Therapy Reduces the Proinflammatory Properties of Activated Platelets

The cause of atherothrombosis is rupture or erosion of atherosclerotic lesions, leading to an increased risk of myocardial infarction or stroke. Here, platelet activation plays a major role, leading to the release of bioactive molecules, for example, chemokines and coagulation factors, and to platelet clot formation. Several antiplatelet therapies have been developed for secondary prevention of cardiovascular events, in which anticoagulant drugs are often combined. Besides playing a role in hemostasis, platelets are also involved in inflammation. However, it is unclear whether current antiplatelet therapies also affect platelet immune functions. In this study, the possible anti-inflammatory effects of antiplatelet medications on chemokine release were investigated using enzyme-linked immunosorbent assay and on the chemotaxis of THP-1 cells toward platelet releasates. We found that antiplatelet medication acetylsalicylic acid (ASA) led to reduced chemokine (CC motif) ligand 5 (CCL5) and chemokine (CXC motif) ligand 4 (CXCL4) release from platelets, while leukocyte chemotaxis was not affected. Depending on the agonist, α (IIb) β (3) and P2Y (12) inhibitors also affected CCL5 or CXCL4 release. The combination of ASA with a P2Y (12) inhibitor or a phosphodiesterase (PDE) inhibitor did not lead to an additive reduction in CCL5 or CXCL4 release. Interestingly, these combinations did reduce leukocyte chemotaxis. This study provides evidence that combined therapy of ASA and a P2Y (12) or PDE3 inhibitor can decrease the inflammatory leukocyte recruiting potential of the releasate of activated platelets

Platelet extracellular vesicles induce a pro-inflammatory smooth muscle cell phenotype

Extracellular vesicles (EVs) are mediators of cell communication during health and disease, and abundantly released by platelets upon activation or during ageing. Platelet EVs exert modulatory effects on immune and vascular cells. Platelet EVs may modulate the function of vascular smooth muscle cells (SMC). Platelet EVs were isolated from platelet-rich plasma and incubated with SMC in order to assess binding, proliferation, migration and pro-inflammatory phenotype of the cells. Platelet EVs firmly bound to resting SMC through the platelet integrin a(11b)beta(3), while binding also occurred in a CX3CL1-CX3CR1-dependent manner after cytokine stimulation. Platelet EVs increased SMC migration comparable to platelet derived growth factor or platelet factor 4 and induced SMC proliferation, which relied on CD40-and P-selectin interactions. Flow-resistant monocyte adhesion to platelet EV-treated SMC was increased compared with resting SMC. Again, this adhesion depended on integrin a(11b)beta(3) and P-selectin, and to a lesser extent on CD40 and CX3CR1. Treatment of SMC with platelet EVs induced interleukin 6 secretion. Finally, platelet EVs induced a synthetic SMC morphology and decreased calponin expression. Collectively, these data indicate that platelet EVs exert a strong immunomodulatory activity on SMC. In particular, platelet EVs induce a switch towards a pro-inflammatory phenotype, stimulating vascular remodelling