Circulating endothelial microparticles: a new marker of vascular injury

Cell activation or apoptosis leads to plasma membrane blebbing and microparticles (MPs) release. MPs are submicron membrane vesicles expressing a panel of oxidized phospholipids and proteins specific of the cells they originate from. Exposure of negatively charged phospholipids and tissue factor confers a procoagulant potential to MPs. Increases in plasma MPs levels, particularly those of endothelial origin, reflects cellular injury and appears now as a surrogate marker of vascular dysfunction. MPs are also biologically active and stimulate pro-inflammatory responses in target cells. Thus, MPs can promote a prothrombogenic and pro-inflammatory vicious circle leading to vascular dysfunction. A better understanding of MPs composition, as well as their effects and the mechanisms leading to their clearance will likely open new therapeutic approaches in the treatment and the prognosis of cardiovascular diseases.     

Cellular microparticles: a disseminated storage pool of bioactive vascular effectors

PURPOSE OF REVIEW: Microparticles (MP) or microvesicles are fragments shed from the plasma membrane of stimulated or apoptotic cells. Having long been considered inert debris reflecting cellular activation or damage, MP are now acknowledged as cellular effectors involved in cell-cell crosstalk. This review focuses on procoagulant MP circulating in the vascular compartment, their role in hemostasis and thrombosis, and possible impact in vascular functions. RECENT FINDINGS: Microparticles can be viewed as a "storage pool" by themselves, disseminating blood-borne tissue factor activity and procoagulant phospholipids. Increasing evidences of integrated loops involving dynamic exchanges and transfer events through multiple MP-cell interactions are summarized. SUMMARY: Microparticles can be considered true targets in the pharmacological control of thrombosis. Another challenging issue is to take advantage of their procoagulant potential for the management of hemophilia.     

Early endotoxin-mediated haemostatic and inflammatory responses in the clopidogrel-treated pig

We have previously shown that the thrombin inhibiting agent melagatran markedly prolongs aPTT and counteracts creatinine increase in endotoxemic pigs. Against this background the effects of the platelet-inhibiting agent, clopidogrel on basic haemostatic, inflammatory and physiological variables were evaluated during porcine endotoxemia. Clopidogrel (10 mg/kg) or saline was randomly injected i.v. 30 min before start of a 6-h continuous infusion of endotoxin in 12 anaesthetised pigs. Another three pigs were given clopidogrel but not endotoxin. Clopidogrel did not affect physiological variables, formation of activated platelet microparticles, PK, aPTT, platelet count, plasma fibrinogen, TNF-alpha, or IL-6 during porcine endotoxemia. Although renal function, as evaluated by creatinine clearance (CLcr) deteriorated significantly (P = 0.01) in the saline-endotoxin, but not in the clopidogrel-endotoxin group, there was no significant difference between the saline-endotoxin and the clopidogrel-endotoxin groups. Renal biopsies were marked with a FITC-labelled chicken anti-fibrinogen antibody detecting fibrinogen and platelet bound fibrinogen, as a marker of porcine platelet activation, and examined by light microscopy. Evaluation of these immunohistochemical slides did not indicate that clopidogrel, significantly reduced the amount of intrarenal fibrin or fibrinogen depositions. Besides a trend to preserve renal function, clopidogrel did not affect haemodynamics or the coagulatory and inflammatory responses in porcine endotoxemia.     

Platelet microparticles and platelet adhesion: Therapeutic implications for the prevention and treatment of stroke

Opinion statement Platelets are believed to play a part in all stages of the pathogenesis of ischemic stroke, from the initial formation of the atherosclerotic plaque, through plaque destabilization to the development of neuronal cell death. A process common to all of these pathogenic changes is the ability of the activated platelet to adhere to the site of disease. In addition, the release of the membrane vesicles from platelets enhances many of these processes. Therefore, an understanding of platelet adhesion and platelet microparticle release can aid the development toward the treatment and prevention of stroke. There has been much research into interventions that can reduce platelet activation in atherosclerosis and stroke. The benefits of nonpharmacologic interventions in stroke, such as diet and lifestyle modification, may in part be mediated by their effects on platelet activation. In addition, the antiplatelet drug aspirin has been shown to be useful in both the treatment of acute stroke and the secondary prevention of atherothrombosis. Other antiplatelet agents, such as the glycoprotein IIb/IIIa inhibitors and triflusal, are currently being evaluated for the treatment of acute atherothrombotic stroke.     

Platelet characteristic antigens of CD34+ cells in cryopreserved cord blood: a study of platelet-derived microparticles in transplant processing

BACKGROUND AND OBJECTIVES: In previous studies, we found that platelet microparticles (PMPs) bind to cord blood (CB) CD34+ cells and transfer adhesion molecules to them, which enhances their engraftment. Before applying this phenomenon in actual transplants, we investigated the effect of PMPs on cryopreserved CD34+ cells in CB. MATERIALS AND METHODS: We cryopreserved 18 CB units, then evaluated the binding of PMPs to CD34+ cells after thawing, by varying the expression of platelet characteristic antigens (CD41a, CD61, CD62P and CXCR4) on these cells. Adherence of the CD34+ cells, coated with freeze/thaw-induced PMPs, to endothelium and fibronectin was also studied, as were the effects of thrombin-induced PMPs from both fresh and preserved CB platelets. RESULTS: PMPs induced by freezing and thawing adhered less well to CD34+ cells than did those from fresh CB, and cells coated with these PMPs had poor adherence. However, thrombin-induced PMPs from both fresh and preserved CB platelets bound equally well to cryopreserved CD34+ cells and improved their adhesion properties. CONCLUSIONS: PMPs could be a useful tool for enhancing engraftment after CB transplantation.     

Menstrual cycle hormones induce changes in functional interactions between lymphocytes and decidual vascular endothelial cells

During the secretory phase of the menstrual cycle, a natural killer (NK) cell subset expressing cluster of differentiation (CD)56bright appears in the decidualizing uterus and remains until onset of menses. If pregnancy occurs, decidual NK cells increase to become the predominant uterine lymphocytes of early pregnancy. To elucidate mechanisms of CD56bright cell recruitment to the uterus, an in vitro adhesion assay was used to assess the effect of the menstrual cycle, as well as cycle-associated hormones on adhesive properties of human lymphocytes. Adhesion of human peripheral blood lymphocytes to pregnant mouse lymph nodes and Peyer's Patches tissue sections was constant throughout the cycle. When uterine tissue was used as the substrate, adhesive CD56+ cells were found only in decidua basalis. Adhesion increased at the LH surge. Adhesion was mediated through both L-selectin and alpha4-integrin-dependent mechanisms. Furthermore, we observed increased adhesive function in CD56+ cells from male donors which had been cultured with estradiol or LH compared with cell aliquots cultured without additives. Lymphocytes adherent to mouse uterine tissue were predominantly CD56bright, suggesting that peripheral NK cells may be actively recruited to the uterus in an important, brief endocrine-regulated fashion at the time of ovulation to establish the decidual NK population of early pregnancy.     

Strategies for researches on the interactions between skeletal and vascular tissues

Osteoporosis and vascular disease are commonly found together in estrogen-deficient and elderly people. The common factors such as estrogen deficiency, abnormalities of vitamin D metabolism, and lipid oxidation have been suggested to contribute to the development of osteoporosis and atherosclerosis. Recent research works on the mechanism of arterial calcification using in vitro models and mouse genetics have unraveled the potential molecular link between osteoporosis and arterial calcification.     

Platelet endothelial cell adhesion molecule-1 and mechanotransduction in vascular endothelial cells

Endothelial cells are known to respond to mechanical forces such as fluid shear stress and cyclic stretch, but elucidating the mechanism for mechanosensing has been difficult. Experimental data indicate that there are probably several sensing mechanisms. We have recently proposed a novel mechanoresponse mechanism that involves platelet endothelial cell adhesion molecule-1 (PECAM-1). When endothelial cells are stimulated by fluid shear stress, PECAM-1 is tyrosine phosphorylated and activates the extracellular signal-regulated kinase 1 and 2 (ERK1/2) signalling cascade. The same signalling events occurred when we applied pulling force directly on PECAM-1 on the endothelial cell surface using magnetic beads coated with antibodies against the external domain of PECAM-1. These results appear to indicate that PECAM-1 is a mechanotransduction molecule. To our knowledge, this is the first mammalian molecule that is shown to respond to mechanical force directly exerted to it.