Cytometric analysis of high shear-induced platelet microparticles and effect of cytokines on microparticle generation

The role of biomechanical stress in extracellular vesicle formation, composition and activity

Extracellular vesicles (EVs) are cornerstones of intercellular communication with exciting fundamental, clinical, and more broadly biotechnological applications. However, variability in EV composition, which results from the culture conditions used to generate the EVs, poses significant fundamental and applied challenges and a hurdle for scalable bioprocessing. Thus, an understanding of the relationship between EV production (and for clinical applications, manufacturing) and EV composition is increasingly recognized as important and necessary. While chemical stimulation and culture conditions such as cell density are known to influence EV biology, the impact of biomechanical forces on the generation, properties, and biological activity of EVs remains poorly understood. Given the omnipresence of these forces in EV preparation and in biomanufacturing, expanding the understanding of their impact on EV composition-and thus, activity-is vital. Although several publications have examined EV preparation and bioprocessing and briefly discussed biomechanical stresses as variables of interest, this review represents the first comprehensive evaluation of the impact of such stresses on EV production, composition and biological activity. We review how EV biogenesis, cargo, efficacy, and uptake are uniquely affected by various types, magnitudes, and durations of biomechanical forces, identifying trends that emerge both generically and for individual cell types. We also describe implications for scalable bioprocessing, evaluating processes inherent in common EV production and isolation methods, and propose a path forward for rigorous EV quality control.

A Review on Biological Effects of Ultrasounds: Key Messages for Clinicians

Ultrasound (US) is acoustic energy that interacts with human tissues, thus, producing bioeffects that may be hazardous, especially in sensitive organs (i.e., brain, eye, heart, lung, and digestive tract) and embryos/fetuses. Two basic mechanisms of US interaction with biological systems have been identified: thermal and non-thermal. As a result, thermal and mechanical indexes have been developed to provide a means of assessing the potential for biological effects from exposure to diagnostic US. The main aims of this paper were to describe the models and assumptions used to estimate the "safety" of acoustic outputs and indices and to summarize the current state of knowledge about US-induced effects on living systems deriving from in vitro models and in vivo experiments on animals. This review work has made it possible to highlight the limits associated with the use of the estimated safety values of thermal and mechanical indices relating above all to the use of new US technologies, such as contrast-enhanced ultrasound (CEUS) and acoustic radiation force impulse (ARFI) shear wave elastography (SWE). US for diagnostic and research purposes has been officially declared safe, and no harmful biological effects in humans have yet been demonstrated with new imaging modalities; however, physicians should be adequately informed on the potential risks of biological effects. US exposure, according to the ALARA (As Low As Reasonably Achievable) principle, should be as low as reasonably possible.

Dynamic in vitro hemocompatibility of oligoproline self-assembled monolayer surfaces

The blood compatibility of self-assembled monolayers (SAMs) of oligoproline, a nonionic antifouling peptide, was investigated using the cone-and-plate assay imitating arterial blood flow conditions. End-capped oligoprolines composed of 6 and 9 proline residues (Pro6 and Pro9) and a Cys residue were synthesized for preparing SAMs (Pro-SAMs) on Au-sputtered glass. The surface of Pro-SAMs indicated hydrophilic property with a smooth topology. The adsorption of blood components and the adhesion of blood cells, including leukocytes and platelets, were strongly suppressed on Pro-SAMs. Moreover, Pro9-SAM did not trigger the activation of platelets (i.e., the conformational change of GPIIb/IIIa and P-selectin (CD62P) expression on platelets and the formation of aggregates). Our results demonstrate that Pro9-SAM completely inhibited acute thrombogenic responses and the activation of platelets under dynamic conditions.

Inter-Relationship between Platelet-Derived Microparticles and Oxidative Stress in Patients with Venous Thromboembolism

Background: Hypercoagulative conditions play a key role in venous thromboembolism (VTE). Inflammation is currently linked to VTE, but the potential role of circulating microparticles and oxidative stress (OxS) must be elucidated. The aim of this study was to evaluate platelet-derived microparticles and surrogate OxS biomarkers in patients diagnosed with VTE through a case–control study. Methods: Platelet-derived microparticles (MPs), pro-thrombinase-induced clotting time assay (PiCT), phospholipids (PLPs), malondialdehyde (MDA), 4-hydroxynonenale (4-HNE), thiobarbituric acid reactive substances (TBARs), superoxide dismutase (SOD), and galectin-3 (Gal-3) were measured in VTE patients and in healthy controls. Results: PLPs, 4-HNE, TBARs, and Gal-3 were higher in VTE patients compared to controls; conversely, SOD was lower. A significant non-linear regression between OxS biomarkers and the markers of platelet degranulation was found. Conclusion: Our results suggest that OxS and platelet degranulation are concomitant pathophysiological mechanisms in VTE.

Platelet-Derived Microparticles (MPs) and Thrombin Generation Velocity in Deep Vein Thrombosis (DVT): Results of a Case-Control Study

Introduction

The role of platelets (Ps) and platelet-derived microparticles (MPs) in venous thromboembolism (VTE) is still being debated.

Methods

We measured MPs, velocity of thrombin formation (PiCT) and phospholipid generation (PLPs) in 40 patients with unprovoked deep vein thrombosis (DVT), who were compared with 40 healthy controls.

Results

MPs were higher in DVT (7.12 nM; 25th–75th percentile 5.26–9.12) than in controls (5.45 nM; 25th–75th percentile 1.67–8.96) (p = 0.19). PiCT velocity was lower in DVT (1.87 sec; 25th–75th percentile 1.75–1.93 sec) compared with controls (1.95 sec; 25th–75th percentile 1.84–2.24 sec) (p = 0.04). PLPs were higher in DVT (77.03 µg/mL; 25th–75th percentile 72.12–103.59 µg/mL) compared with controls (68.65 µg/mL, 25th–75th percentile 55.31–78.20 µg/mL) (p = 0.02).

Discussion

We hypothesize that MPs could be integrated with the lab network assay in evaluating Ps’ role as an activated procoagulative condition. We encourage research on Ps and P-derived microvesicle pathways in patients with unprovoked DVT and not only in patients with cancer-induced DVT.

Therapeutic Potential of Extracellular Vesicles in Hypertension-Associated Kidney Disease

Hypertension-mediated organ damage frequently includes renal function decline in which several mechanisms are involved. The present review outlines the state of the art on extracellular vesicles in hypertension and hypertension-related renal damage. Emerging evidence indicates that extracellular vesicles, small vesicles secreted by most cell types and body fluids, are involved in cell-to-cell communication and are key players mediating biological processes such as inflammation, endothelial dysfunction or fibrosis, mechanisms present the onset and progression of hypertension-associated kidney disease. We address the potential use of extracellular vesicles as markers of hypertension-mediated kidney damage severity and their application as therapeutic agents in hypertension-associated renal damage. The capacity of exosomes to deliver a wide variety of cargos to the target cell efficiently makes them a potential drug delivery system for treatment of renal diseases.

Circulating Microparticles in Patients with Symptomatic Carotid Disease Are Related to Embolic Plaque Activity and Recent Cerebral Ischaemia

Background and Purpose

In order to assess the association of microparticles derived from activated platelets (PMP) or endothelial cells (EMP) with risk markers for recurrent embolic events in patients with symptomatic carotid artery disease, we studied the associations between PMP/EMP and three risk markers: plaque haemorrhage (PH), micro-embolic signals and cerebral diffusion abnormalities.

Methods

Patients with recently symptomatic high-grade carotid artery stenosis (60–99%, 42 patients, 31 men; mean age 75 ± 8 years) and 30 healthy volunteers (HV, 11 men; mean age 56 ± 12 years) were prospectively recruited. Patients were characterised by carotid magnetic resonance imaging (presence of PH [MRI PH]), brain diffusion MRI (cerebral ischaemia [DWI+]) and transcranial Doppler ultrasound (micro-embolic signals [MES+]). PMP and EMP were classified by flow cytometry and expressed as log-transformed counts per microlitre.

Results

MES+ patients (n = 18) had elevated PMP (MES+ 9.61 ± 0.57) compared to HV (8.80 ± 0.73; p < 0.0001) and to MES– patients (8.55 ± 0.85; p < 0.0001). Stroke patients had elevated PMP (9.49 ± 0.64) and EMP (6.13 ± 1.0) compared to non-stroke patients (PMP 8.81 ± 0.73, p = 0.026, EMP 5.52 ± 0.65, p = 0.011) and HV (PMP 8.80 ± 0.73, p = 0.007, and EMP 5.44 ± 0.47, p = 0.006). DWI+ patients (n = 16) showed elevated PMP (DWI+ 9.53 ± 0.64; vs. HV, p = 0.002) and EMP (DWI+ 5.91 ± 0.99 vs. HV 5.44 ± 0.47; p = 0.037). Only PMP but not EMP were higher in DWI+ versus DWI– patients (8.67 ± 0.90; p = 0.002). No association was found between PMP and EMP with MRI PH.

Conclusion

PMP and EMP were associated with stroke and recent cerebrovascular events (DWI+) but only PMP were also associated with ongoing (MES+) thrombo-embolic activity suggesting a differential biomarker potential for EMP to index cerebral ischaemia while PMP may predict on-going thrombo-embolic activity.

An Oral Glucose Load Decreases Postprandial Extracellular Vesicles in Obese Adults with and without Prediabetes

Although extracellular vesicles (EVs) are a novel biomediator of type 2 diabetes (T2D) and cardiovascular disease (CVD), the effects of hyperglycemia on EVs in humans is unknown. We tested the hypothesis that a 75-g oral glucose tolerance test (OGTT) would promote changes in EVs in relation to CVD risk. Twenty-five obese adults (Age: 52.4 ± 3.2 year, BMI: 32.5 ± 1.2 kg/m²) were screened for normal glucose tolerance (NGT, n = 8) and prediabetes (PD, n = 17) using American Diabetes Association criteria (75 g OGTT and/or HbA1c). Body composition (bioelectrical impedance) and fitness (VO₂peak) were measured. Arterial stiffness (augmentation index; AIx) was measured at 0, 60- and 120-min while insulin, glucose, and free fatty acids were evaluated every 30 min during the OGTT to assess CVD risk. Annexin V positive (AV+) and Annexin V negative (AV-) total EVs, platelet EVs (CD31⁺/CD41⁺; CD41⁺), leukocyte EVs (CD45⁺; CD45⁺/CD41-), platelet endothelial cell adhesion molecule (PECAM) (CD31⁺) and endothelial EVs (CD 31⁺/CD41-; CD105⁺) were collected at 0 and 120 min. There were no differences in age, BMI, or body fat between NGT and PD (all P > 0.63). Total EVs, AV+ CD31+ (PECAM), and AV+ CD31⁺/CD41- (endothelial) EVs decreased after the OGTT (P ≤ 0.04). Circulating insulin at 2-h correlated with elevated post-prandial AV- CD45⁺ (r = 0.48, P = 0.04) while arterial stiffness related to reduced total EVs (r = -0.49, P = 0.03) and AV+CD41⁺ (platelet) (r = -0.52, P = 0.02). An oral glucose load lowers post-prandial total, platelet, and endothelial EVs in obese adults with NGT and prediabetes in relation to CVD risk.

Exosomes and microvesicles in normal physiology, pathophysiology, and renal diseases

Extracellular vesicles are cell-derived membrane particles ranging from 30 to 5,000 nm in size, including exosomes, microvesicles, and apoptotic bodies. They are released under physiological conditions, but also upon cellular activation, senescence, and apoptosis. They play an important role in intercellular communication. Their release may also maintain cellular integrity by ridding the cell of damaging substances. This review describes the biogenesis, uptake, and detection of extracellular vesicles in addition to the impact that they have on recipient cells, focusing on mechanisms important in the pathophysiology of kidney diseases, such as thrombosis, angiogenesis, tissue regeneration, immune modulation, and inflammation. In kidney diseases, extracellular vesicles may be utilized as biomarkers, as they are detected in both blood and urine. Furthermore, they may contribute to the pathophysiology of renal disease while also having beneficial effects associated with tissue repair. Because of their role in the promotion of thrombosis, inflammation, and immune-mediated disease, they could be the target of drug therapy, whereas their favorable effects could be utilized therapeutically in acute and chronic kidney injury.

Low cardiorespiratory fitness is associated with higher extracellular vesicle counts in obese adults

Low cardiorespiratory fitness (CRF) is associated with cardiovascular disease (CVD) independent of obesity. Extracellular vesicles (EVs) are a novel target of CVD, however, it remains unknown if obese individuals with very poor fitness (VPF) have elevated EVs versus people with poor fitness (PF). Thus, we tested whether VPF was associated with greater EV subtypes in obese adults. Subjects with VPF (n = 13, VO2 peak: 15.4 ± 0.6 mL/kg/min, BMI: 34.1 ± 1.7 kg/m2 ) and PF (n = 13, VO2 peak: 25.9 ± 3.0 mL/kg/min, BMI: 32.1 ± 1.2 kg/m2 ) were compared in this cross-sectional study. After an overnight fast, AnnexinV (AV) +/- platelet (CD31+ /CD41+ ), leukocyte (CD45+ /CD41- ), and endothelial EVs (CD105+ , CD31+ /CD41- ) were analyzed from fresh platelet poor plasma via imaging flow cytometry. Body fat, blood pressure (BP), and glucose tolerance (OGTT) were also tested. Body weight, BP, and circulating glucose were similar between groups, although VPF subjects were older than PF (64.0 ± 2.1 vs. 49.8 ± 4.2 year; P < 0.05). People with VPF, compared with PF, had higher total AV- EVs (P = 0.04), AV- platelet EVs (CD31+ /CD41+ ; P = 0.006), and AV- endothelial EVs (CD31+ /CD41- ; P = 0.005) independent of age and body fat. Higher AV- platelet and endothelial EVs were associated with lower VO2 peak (r = -0.56, P = 0.006 and r = -0.55, P = 0.005, respectively). Endothelial-derived AV- /CD31+ /CD41- EVs were also related to pulse pressure (r = 0.45, P = 0.03), whereas AV- /CD105 was linked to postprandial glucose (r = 0.41, P = 0.04). VPF is associated with higher AnnexinV- total, endothelial, and platelet EVs in obese adults, suggesting that subtle differences in fitness may reduce type 2 diabetes and CVD risk through an EV-related mechanism.

Physiologic Impact of Circulating RBC Microparticles upon Blood-Vascular Interactions

Here, we review current data elucidating the role of red blood cell derived microparticles (RMPs) in normal vascular physiology and disease progression. Microparticles (MPs) are submicron-size, membrane-encapsulated vesicles derived from various parent cell types. MPs are produced in response to numerous stimuli that promote a sequence of cytoskeletal and membrane phospholipid changes and resulting MP genesis. MPs were originally considered as potential biomarkers for multiple disease processes and more recently are recognized to have pleiotropic biological effects, most notably in: promotion of coagulation, production and handling of reactive oxygen species, immune modulation, angiogenesis, and in initiating apoptosis. RMPs, specifically, form normally during RBC maturation in response to injury during circulation, and are copiously produced during processing and storage for transfusion. Notably, several factors during RBC storage are known to trigger RMP production, including: increased intracellular calcium, increased potassium leakage, and energy failure with ATP depletion. Of note, RMP composition differs markedly from that of intact RBCs and the nature/composition of RMP components are affected by the specific circumstances of RMP genesis. Described RMP bioactivities include: promotion of coagulation, immune modulation, and promotion of endothelial adhesion as well as influence upon vasoregulation via influence upon nitric oxide (NO) bioavailability. Of particular relevance, RMPs scavenge NO more avidly than do intact RBCs; this physiology has been proposed to contribute to the impaired oxygen delivery homeostasis that may be observed following transfusion. In summary, RMPs are submicron particles released from RBCs, with demonstrated vasoactive properties that appear to disturb oxygen delivery homeostasis. The clinical impact of RMPs in normal and patho-physiology and in transfusion recipients is an area of continued investigation.

Platelets and Cardiovascular Disease

Platelets play an important, but often under-recognized role in cardiovascular disease. For example, the normal response of the platelet can be altered, either by increased pro-aggregatory stimuli or by diminished anti-aggregatory substances to produce conditions of increased platelet activation/aggregation and occur in active cardiovascular disease states both on a chronic (e.g. stable angina pectoris) and acute basis (e.g. acute myocardial infarction). In addition, platelet hyperaggregability is also associated with the risk factors for coronary artery disease (e.g. smoking, hypertension, and hypercholesterolaemia). Finally, the utility of an increasing range of anti-platelet therapies in the management of the above disease states further emphasizes the pivotal role platelets play in the pathogenesis of cardiovascular disease. This paper provides a comprehensive overview of the normal physiologic role of platelets in maintain homeostasis, the pathophysiologic processes that contribute to platelet dysfunction in cardiovascular disease and the associated role and benefits of anti-platelet therapies.

Microparticles as Biomarkers of Blood Coagulation in Cancer

Cancer is associated with hypercoagulopathy and increased risk of thrombosis. This negatively influences patient morbidity and mortality. Cancer is also frequently complicated by the development of venous thromboembolism (VTE). Tumor-derived tissue factor (TF)-bearing microparticles (MPs) are associated with VTE events in malignancy. MPs are small membrane vesicles released from many different cell types by exocytic budding of the plasma membrane in response to cellular activation or apoptosis. MPs may also be involved in clinical diseases through expression of procoagulative phospholipids. The detection of TF-expressing MPs in cancer patients may be clinically useful. In lung and breast cancer patients, MPs induce metastasis and angiogenesis and may be indicators of vascular complications. Additionally, MPs in patients with various types of cancer possess adhesion proteins and bind target cells to promoting cancer progression or metastasis. Overexpression of TF by cancer cells is closely associated with tumor progression, and shedding of TF-expressing MPs by cancer cells correlates with the genetic status of cancer. Consequently, TF-expressing MPs represent important markers to consider in the prevention of and therapy for VTE complications in cancer patients.

Microparticle and Atherothrombotic Diseases

Microparticles (MPs) are small membrane vesicles that are released from many different cell types by exocytotic budding of the plasma membrane in response to cellular activation or apoptosis. MPs may be involved in both physiological processes and clinical treatments because they express phospholipids, which function as procoagulants. Elevated levels of platelet-derived MPs, endothelial cell-derived MPs, and monocyte-derived MPs are observed in almost all thrombotic diseases occurring in venous and arterial beds. Several studies have shown that the quantity, cellular origin, and composition of circulating MPs depend on the type of disease, the disease state, and medical treatment. Although MPs were initially thought to be small particles with only procoagulant activity, they are now known to have many different functions. An increasing number of studies have identified new implications of elevated MPs in clinical disorders. On the basis of evidence available till date, the present review suggests that MPs may be a useful biomarker in identifying atherothrombosis.

Microvesicles in the brain: Biomarker, messenger or mediator?

Microvesicles (MVs) are cell-derived vesicles produced after membrane remodeling of eukaryotic cells during activation or apoptosis. MVs are considered a novel biomarker/messenger for many diseases. Neurons, astrocytes, microglia, as well as neural stem cells, have been described to release MVs, many studies have demonstrated the involvement of platelets and endothelial MVs in some central nervous diseases. This review is focused on understanding the role of MVs in the brain; new findings demonstrated that MVs can contribute to the onset and progression of some neurodegenerative and neuroinflammatory diseases, as well as to the development and regeneration of the nervous system.

Clinical significance of procoagulant microparticles

Microparticles (MPs) are small membrane vesicles that are released from many different cell types by exocytic budding of the plasma membrane in response to cellular activation or apoptosis. MPs may also be involved in clinical diseases because they express phospholipids, which function as procoagulants. Although flow cytometry is the most widely used method for studying MPs, some novel assays, such as tissue factor-dependent procoagulant assay or the ELISA method, have been reported. However, the use of quantification of MP as a clinical tool is still controversial. Elevated platelet-derived MP, endothelial cell-derived MP, and monocyte-derived MP concentrations are documented in almost all thrombotic diseases occurring in venous and arterial beds. However, the significance of MPs in various clinical conditions remains controversial. An example of this controversy is that it is unknown if MPs found in peripheral blood vessels cause thrombosis or whether they are the result of thrombosis. Numerous studies have shown that not only the quantity, but also the cellular origin and composition of circulating MPs, are dependent on the type of disease, the disease state, and medical treatment. Additionally, many different functions have been attributed to MPs. Therefore, the number and type of clinical disorders associated with elevated MPs are currently increasing. However, MPs were initially thought to be small particles with procoagulant activity. Taken together, our review suggests that MPs may be a useful biomarker to identify thrombosis.

The emerging roles of microvesicles in liver diseases

Microvesicles (MVs) are extracellular vesicles released by virtually all cells, under both physiological and pathological conditions. They contain lipids, proteins, RNAs and microRNAs and act as vectors of information that regulate the function of target cells. This Review provides an overview of the studies assessing circulating MV levels in patients with liver diseases, together with an insight into the mechanisms that could account for these changes. We also present a detailed analysis of the implication of MVs in key processes of liver diseases. MVs have a dual role in fibrosis as certain types of MVs promote fibrolysis by increasing expression of matrix metalloproteinases, whereas others promote fibrosis by stimulating processes such as angiogenesis. MVs probably enhance portal hypertension by contributing to intrahepatic vasoconstriction, splanchnic vasodilation and angiogenesis. As MVs can modulate vascular permeability, vascular tone and angiogenesis, they might contribute to several complications of cirrhosis including hepatic encephalopathy, hepatopulmonary syndrome and hepatorenal syndrome. Several results also suggest that MVs have a role in hepatocellular carcinoma. Although MVs represent promising biomarkers in patients with liver disease, methods of isolation and subsequent analysis must be standardized.

Microparticles: a new perspective in central nervous system disorders

Microparticles (MPs) are a heterogeneous population of small cell-derived vesicles, ranging in size from 0.1 to 1 μm. They contain a variety of bioactive molecules, including proteins, biolipids, and nucleic acids, which can be transferred between cells without direct cell-to-cell contact. Consequently, MPs represent a novel form of intercellular communication, which could play a role in both physiological and pathological processes. Growing evidence indicates that circulating MPs contribute to the development of cancer, inflammation, and autoimmune and cardiovascular diseases. Most cell types of the central nervous system (CNS) have also been shown to release MPs, which could be important for neurodevelopment, CNS maintenance, and pathologies. In disease, levels of certain MPs appear elevated; therefore, they may serve as biomarkers allowing for the development of new diagnostic tools for detecting the early stages of CNS pathologies. Quantification and characterization of MPs could also provide useful information for making decisions on treatment options and for monitoring success of therapies, particularly for such difficult-to-treat diseases as cerebral malaria, multiple sclerosis, and Alzheimer's disease. Overall, studies on MPs in the CNS represent a novel area of research, which promises to expand the knowledge on the mechanisms governing some of the physiological and pathophysiological processes of the CNS.

Urinary podocyte microparticles identify prealbuminuric diabetic glomerular injury

Microparticles (MPs) are small (0.1-1.0 µm) vesicles shed from the surface of cells in response to stress. Whether podocytes produce MPs and whether this production reflects glomerular injury are unclear. We examined MP formation in cultured human podocytes (hPODs) and diabetic mice. hPODs were exposed to cyclical stretch, high glucose (HG; 25 mM), angiotensin II, or TGF-β. Urinary podocyte MPs were assessed in three mouse models of diabetic nephropathy: streptozotocin (STZ)-treated, OVE26, and Akita mice. Cyclic stretch and HG increased MP release as assessed by flow cytometry (P<0.01 and P<0.05, respectively, versus controls). Inhibition of Rho-kinase (ROCK) with fasudil blocked HG-induced podocyte MP formation. STZ-treated (8 weeks) mice exhibited increased urinary podocyte MPs compared with age-matched nondiabetic mice. Similarly, 16-week-old OVE26 mice had elevated levels of urinary podocyte MPs compared with wild-type littermates (P<0.01). In 1 week post-STZ-treated and 6- and 12-week-old Akita mice, urinary podocyte MPs increased significantly compared with those MPs in nondiabetic mice, despite normal urinary albumin levels. Our results indicate that podocytes produce MPs that are released into urine. Podocyte-derived MPs are generated by exposure to mechanical stretch and high glucose in vitro and could represent early markers of glomerular injury in diabetic nephropathy.

Therapeutic drug-induced platelet apoptosis: an overlooked issue in pharmacotoxicology

The surfacing of the applied fields of biology such as, biotechnology, pharmacology and drug discovery was a boon to the modern man. However, it had its share of disadvantages too. The indiscriminate use of antibiotics and other biological drugs resulted in numerous adverse reactions including thrombocytopenia. One of the reasons for drug-induced thrombocytopenia could be attributed to an enhanced rate of platelet apoptosis, which is a less investigated aspect. The present essay sheds light on the adverse (pro-apoptotic) effects of some of the commonly used drugs and antibiotics on platelets viz. cisplatin, aspirin, vancomycin and balhimycin. Furthermore, the undesirable reactions resulting from chemotherapy could be attributed at least to some extent to the systemic stress induced by microparticles, which in turn are the byproducts of platelet apoptosis. Thereby, the essay aims to highlight the challenges in the emerging trend of cross-disciplinary implications, i.e., drug-induced platelet apoptosis, which is a nascent field. Thus, the different mechanisms through which drugs induce platelet apoptosis are discussed, which also opens up a new perspective through which the adverse effects of commonly used drugs could be dealt. The drug-associated platelet toxicity is of grave concern and demands immediate attention. Besides, it would also be appealing to examine the platelet pro-apoptotic effects of other commonly used therapeutic drugs.

Microparticles in health and disease

Microparticles (MPs), small membrane-derived vesicles, are derived from many cell types and released into the circulation. Microparticles can express antigens, and contain cell surface proteins, cytoplasmic contents, and nuclear components from their cell of origin that determines their composition, characterization, and transfer of biologic information. Certain prompts for this release include shear stress, complement activation, proapoptotic stimulation, cellular damage, or agonist interaction with cell surface receptors. Release can be physiologic or pathologic and is associated with proinflammatory and procoagulant effects and has been implicated in thrombotic states. Microparticles also contribute to systemic inflammation and cardiovascular, hematologic, and oncologic disease states. The study of MPs in human medicine is rapidly advancing and extends into the physiology of health, the pathophysiology of disease, and the role of MPs in transfusion medicine. In veterinary medicine, published work on MPs has been limited to the area of inherited disorders, blood storage, and leukoreduction (LR). Microparticle research is still in its infancy, and this review should be seen as a snapshot of what is currently known. As research continues important limitations, including variations in preanalytic variables such as collection, storage, or centrifugation, and limitations of quantitation are coming to the forefront. Correlation of quantitation of MPs with assays of activity will hopefully shed light on the true nature of MPs in health and disease. This review will focus on the role of cellular exocytic vesiculation in health, disease, and transfusion medicine.

Microparticles: biomarkers and beyond

Membrane microparticles are submicron fragments of membrane shed into extracellular space from cells under conditions of stress/injury. They may be distinguished from other classes of extracellular vesicles (i.e. exosomes) on the basis of size, content and mechanism of formation. Microparticles are found in plasma and other biological fluids from healthy individuals and their levels are altered in various diseases, including diabetes, chronic kidney disease, pre-eclampsia and hypertension among others. Accordingly, they have been considered biomarkers of vascular injury and pro-thrombotic or pro-inflammatory conditions. In addition to this, emerging evidence suggests that microparticles are not simply a consequence of disease, but that they themselves may contribute to pathological processes. Thus microparticles appear to serve as both markers and mediators of pathology. The present review examines the evidence for microparticles as both biomarkers of, and contributors to, the progression of disease. Approaches for the detection of microparticles are summarized and novel concepts relating to the formation of microparticles and their biological effects are examined.

Microparticles, Vascular Function, and Atherothrombosis

Membrane-shed submicron microparticles (MPs) are released after cell activation or apoptosis. High levels of MPs circulate in the blood of patients with atherothrombotic diseases, where they could serve as a useful biomarker of vascular injury and a potential predictor of cardiovascular mortality and major adverse cardiovascular events. Atherosclerotic lesions also accumulate large numbers of MPs of leukocyte, smooth muscle cell, endothelial, and erythrocyte origin. A large body of evidence supports the role of MPs at different steps of atherosclerosis development, progression, and complications. Circulating MPs impair the atheroprotective function of the vascular endothelium, at least partly, by decreased nitric oxide synthesis. Plaque MPs favor local inflammation by augmenting the expression of adhesion molecule, such as intercellular adhesion molecule -1 at the surface of endothelial cell, and monocyte recruitment within the lesion. In addition, plaque MPs stimulate angiogenesis, a key event in the transition from stable to unstable lesions. MPs also may promote local cell apoptosis, leading to the release and accumulation of new MPs, and thus creating a vicious circle. Furthermore, highly thrombogenic plaque MPs could increase thrombus formation at the time of rupture, together with circulating MPs released in this context by activated platelets and leukocytes. Finally, MPs also could participate in repairing the consequences of arterial occlusion and tissue ischemia by promoting postischemic neovascularization.

Cellular phenotype switching and microvesicles

Cell phenotype alteration by cell-derived vesicles presents a new aspect for consideration of cell fate. Accumulating data indicates that vesicles from many cells interact with or enter different target cells from other tissues, altering their phenotype toward that of the cell releasing the vesicles. Cells may be changed by direct interactions, transfer of cell surface receptors or epigenetic reprogramming via transcriptional regulators. Induced epigenetic changes appear to be stable and result in significant functional effects. These data force a reconsideration of the cellular context in which transcription regulates the proliferative and differentiative fate of tissues and suggests a highly plastic cellular system, which might underlay a relatively stable tissue system. The capacity of marrow to convert to non-hematopoietic cells related to vesicle cross-communication may underlie the phenomena of stem cell plasticity. Additionally, vesicles have promise in the clinical arenas of disease biomarkers, tissue restoration and control of neoplastic cell growth.

Stem cell plasticity revisited: the continuum marrow model and phenotypic changes mediated by microvesicles

The phenotype of marrow hematopoietic stem cells is determined by cell-cycle state and microvesicle entry into the stem cells. The stem cell population is continually changing based on cell-cycle transit and can only be defined on a population basis. Purification of marrow stem cells only addresses the heterogeneity of these populations. When whole marrow is studied, the long-term repopulating stem cells are in active cell cycle. However, with some variability, when highly purified stem cells are studied, the cells appear to be dormant. Thus, the study of purified stem cells is intrinsically misleading. Tissue-derived microvesicles enhanced by injury effect the phenotype of different cell classes. We propose that previously described stem cell plasticity is due to microvesicle modulation. We further propose a stem cell population model in which the individual cell phenotypes continually change, but the population phenotype is relatively stable. This, in turn, is modulated by microvesicle and microenvironmental influences.

Microparticles, vascular function and hypertension

PURPOSE OF REVIEW

To summarize the potential role of microparticles in hypertension and in cardiovascular diseases. Microparticles are submicron vesicles shed from the membrane in response to cell activation or apoptosis. Microparticles of different cellular origins are found in the plasma of healthy individuals and their circulating levels augment in patients with cardiovascular diseases.

RECENT FINDINGS

Recent studies demonstrate that circulating levels of microparticles originating from endothelial cells, which represent a small fraction of the overall pool of plasma microparticles, augment with increased endothelial dysfunction in patients with cardiovascular diseases. Therefore, endothelial microparticles constitute an emerging surrogate marker of endothelial dysfunction, with potential prognostic value for major adverse events in patients with cardiovascular diseases. In addition, microparticles of endothelial and other cellular origins are also potential biological effectors in inflammation, vascular injury, angiogenesis and thrombosis.

SUMMARY

In summary, circulating endothelial microparticles may serve not only as an index of arterial damage but also as a trigger of vascular repair.

Microvesicle entry into marrow cells mediates tissue-specific changes in mRNA by direct delivery of mRNA and induction of transcription

OBJECTIVE

Microvesicles have been shown to mediate intercellular communication. Previously, we have correlated entry of murine lung-derived microvesicles into murine bone marrow cells with expression of pulmonary epithelial cell-specific messenger RNA (mRNA) in these marrow cells. The present studies establish that entry of lung-derived microvesicles into marrow cells is a prerequisite for marrow expression of pulmonary epithelial cell-derived mRNA.

MATERIALS AND METHODS

Murine bone marrow cells cocultured with rat lung, but separated from them using a cell-impermeable membrane (0.4-microm pore size), were analyzed using species-specific primers (for rat or mouse).

RESULTS

These studies revealed that surfactant B and C mRNA produced by murine marrow cells were of both rat and mouse origin. Similar results were obtained using murine lung cocultured with rat bone marrow cells or when bone marrow cells were analyzed for the presence of species-specific albumin mRNA after coculture with rat or murine liver. These studies show that microvesicles both deliver mRNA to marrow cells and mediate marrow cell transcription of tissue-specific mRNA. The latter likely underlies the longer-term stable change in genetic phenotype that has been observed. We have also observed microRNA in lung-derived microvesicles, and studies with RNase-treated microvesicles indicate that microRNA negatively modulates pulmonary epithelial cell-specific mRNA levels in cocultured marrow cells. In addition, we have also observed tissue-specific expression of brain, heart, and liver mRNA in cocultured marrow cells, suggesting that microvesicle-mediated cellular phenotype change is a universal phenomena.

CONCLUSION

These studies suggest that cellular systems are more phenotypically labile than previously considered.

Development of a real-time PCR detection method for a FCGR2A polymorphism in the LightCycler and application in the heparin-induced thrombocytopenia syndrome

OBJECTIVE

The FcgammaRIIa receptor is responsible for the activation of platelets by antibodies in heparin-induced thrombocytopenia (HIT). The c.497G>A polymorphism in the corresponding FCG2RA gene (H131R) has been implicated in the HIT syndrome and we aimed at its rapid and reliable determination.

DESIGN AND METHODS

We designed a novel asymmetric real-time PCR method in the LightCycler that uses two hybridization probes and is followed by melting curve analysis. Seventy-one post-cardiac-surgery HIT Greek patients well ascertained by clinical data, immunological and functional tests (PAT, CD62P-selectin and microparticle flow cytometric detection) were studied, along with a clinically relevant group of 49 thrombocytopenic control patients and 119 healthy subjects.

RESULTS

The developed method has excellent analytical characteristics (linear and efficient amplification, precision), has wide DeltaT(m) between the two alleles H and R (11.53 degrees C), and is in 100% concordance with validated controls and another commonly used screening method. The RR percentage increased from 10% in the control populations to 24% in the HIT patient group.

CONCLUSION

The described method is technically simple, robust, fast, and accurate. A statistically significant difference was found in the comparison between the groups of HIT patients and healthy subjects [RR vs. RH+ HH, chi(2) test, p=0.01, OR (95% C.I.) 2.81 (1.21-4.68)]. The RR frequency in the Greek population was found to be the lowest among Caucasians.

The paradoxical dynamism of marrow stem cells: considerations of stem cells, niches, and microvesicles

Marrow stem cell regulation represents a complex and flexible system. It has been assumed that the system was intrinsically hierarchical in nature, but recent data has indicated that at the progenitor/stem cell level the system may represent a continuum with reversible alterations in phenotype occurring as the stem cells transit cell cycle. Short and long-term engraftment, in vivo and in vitro differentiation, gene expression, and progenitor numbers have all been found to vary reversibly with cell cycle. In essence, the stem cells appear to show variable potential, probably based on transcription factor access, as they proceed through cell cycle. Another critical component of the stem cell regulation is the microenvironment, so-called niches. We propose that there are not just several unique niche cells, but a wide variety of niche cells which continually change phenotype to appropriately interact with the continuum of stem cell phenotypes. A third component of the regulatory system is microvesicle transfer of genetic information between cells. We have shown that marrow cells can express the genetic phenotype of pulmonary epithelial cells after microvesicle transfer from lung to marrow cells. Similar transfers of tissue specific mRNA occur between liver, brain, and heart to marrow cells. Thus, there would appear to be a continuous genetic modulation of cells through microvesicle transfer between cells. We propose that there is an interactive triangulated Venn diagram with continuously changing stem cells interacting with continuously changing areas of influence, both being modulated by transfer of genetic information by microvesicles.

Alteration of marrow cell gene expression, protein production, and engraftment into lung by lung-derived microvesicles: a novel mechanism for phenotype modulation

Numerous animal studies have demonstrated that adult marrow-derived cells can contribute to the cellular component of the lung. Lung injury is a major variable in this process; however, the mechanism remains unknown. We hypothesize that injured lung is capable of inducing epigenetic modifications of marrow cells, influencing them to assume phenotypic characteristics of lung cells. We report that under certain conditions, radiation-injured lung induced expression of pulmonary epithelial cell-specific genes and prosurfactant B protein in cocultured whole bone marrow cells separated by a cell-impermeable membrane. Lung-conditioned media had a similar effect on cocultured whole bone marrow cells and was found to contain pulmonary epithelial cell-specific RNA-filled microvesicles that entered whole bone marrow cells in culture. Also, whole bone marrow cells cocultured with lung had a greater propensity to produce type II pneumocytes after transplantation into irradiated mice. These findings demonstrate alterations of marrow cell phenotype by lung-derived microvesicles and suggest a novel mechanism for marrow cell-directed repair of injured tissue.

Embryonic stem cell-derived microvesicles reprogram hematopoietic progenitors: evidence for horizontal transfer of mRNA and protein delivery

Membrane-derived vesicles (MV) are released from the surface of activated eucaryotic cells and exert pleiotropic effects on surrounding cells. Since the maintenance of pluripotency and undifferentiated propagation of embryonic stem (ES) cells in vitro requires tight cell to cell contacts and effective intercellular signaling, we hypothesize that MV derived from ES cells (ES-MV) express stem cell-specific molecules that may also support self-renewal and expansion of adult stem cells. To address this hypothesis, we employed expansion of hematopoietic progenitor cells (HPC) as a model. We found that ES-MV (10 microg/ml) isolated from murine ES cells (ES-D3) in serum-free cultures significantly (i) enhanced survival and improved expansion of murine HPC, (ii) upregulated the expression of early pluripotent (Oct-4, Nanog and Rex-1) and early hematopoietic stem cells (Scl, HoxB4 and GATA 2) markers in these cells, and (iii) induced phosphorylation of MAPK p42/44 and serine-threonine kinase AKT. Furthermore, molecular analysis revealed that ES-MV express Wnt-3 protein and are selectively highly enriched in mRNA for several pluripotent transcription factors as compared to parental ES cells. More important, this mRNA could be delivered by ES-MV to target cells and translated into the corresponding proteins. The biological effects of ES-MV were inhibited after heat inactivation or pretreatment with RNAse, indicating a major involvement of protein and mRNA components of ES-MV in the observed phenomena. We postulate that ES-MV may efficiently expand HPC by stimulating them with ES-MV expressed ligands (e.g., Wnt-3) as well as increase their pluripotency after horizontal transfer of ES-derived mRNA.

Effects of shear stress on endothelial cells: possible relevance for ultrasound applications

This review forms part of a series of papers resulting from a workshop on safety of ultrasound applications. The physical effects of ultrasound include generation of steady streaming in large fluid volumes, and micro-streaming around contrast bubbles. Such streaming induces shear stress acting on the vascular endothelium. This review provides a discussion on the levels of endothelial shear stress associated with diagnostic ultrasound applications, and on the biological effects of shear stress acting on the endothelial cells. Depending on vessel size and ultrasound characteristics, shear stresses associated with streaming and micro-streaming may exceed the physiological levels associated with the flow of blood by many orders of magnitude. The resulting biological effects could range anywhere from activation of normal shear stress sensors such as ion channels, damage of the endothelial surface layer, reversible perforation of the membrane, to cell detachment and lysis. The possible presence of such biological effects does not necessarily mean that the effects are harmful for the individual. However, considering the ever-increasing use of ultrasound, a further investigation into these shear stress-related effects, using both experiments and modelling, is desired. Apart from safety concerns, such effects may provide a base for strategies aimed at targeted delivery of drugs.

Cytoprotective doses of erythropoietin or carbamylated erythropoietin have markedly different procoagulant and vasoactive activities

Recombinant human erythropoietin (rhEPO) is receiving increasing attention as a potential therapy for prevention of injury and restoration of function in nonhematopoietic tissues. However, the minimum effective dose required to mimic and augment these normal paracrine functions of erythropoietin (EPO) in some organs (e.g., the brain) is higher than for treatment of anemia. Notably, a dose-dependent risk of adverse effects has been associated with rhEPO administration, especially in high-risk groups, including polycythemia-hyperviscosity syndrome, hypertension, and vascular thrombosis. Of note, several clinical trials employing relatively high dosages of rhEPO in oncology patients were recently halted after an increase in mortality and morbidity, primarily because of thrombotic events. We recently identified a heteromeric EPO receptor complex that mediates tissue protection and is distinct from the homodimeric receptor responsible for the support of erythropoiesis. Moreover, we developed receptor-selective ligands that provide tools to assess which receptor isoform mediates which biological consequence of rhEPO therapy. Here, we demonstrate that rhEPO administration in the rat increases systemic blood pressure, reduces regional renal blood flow, and increases platelet counts and procoagulant activities. In contrast, carbamylated rhEPO, a heteromeric receptor-specific ligand that is fully tissue protective, increases renal blood flow, promotes sodium excretion, reduces injury-induced elevation in procoagulant activity, and does not effect platelet production. These preclinical findings suggest that nonerythropoietic tissue-protective ligands, which appear to elicit fewer adverse effects, may be especially useful in clinical settings for tissue protection.

Role of platelet-derived chemokines (RANTES and ENA-78) after stem cell transplantation

Stem cell transplantation (SCT) is being used for hematopoietic reconstitution following high-dose chemotherapy for malignancy. Some patients seem to have an imbalance of the immune response after SCT and cytokines are known to regulate this response. Recently, platelets have been shown to contain members of the chemokine family, suggesting a role of platelets as inflammatory cells. We measured and compared levels of platelet activation markers, chemokines, and soluble factors in patients undergoing SCT. IL-8 and GROalpha exhibited a significant elevation in the early phase (1 or 2 weeks) after SCT; this trend was marked after autologous SCT. Furthermore, these levels significantly and positively correlated with the change in G-CSF. In contrast, ENA-78 exhibited a significant elevation in the later phase (3 or 4 weeks) after SCT. In addition, its level negatively correlated with the change in G-CSF. Soluble CD40 ligand and platelet-derived microparticles significantly increased after both auto- and allo-SCT. In addition, ENA-78 positively correlated with the level of platelet-derived microparticles. The increase of RANTES seems to be related to platelet activation, since RANTES was in the dynamic phase similar to soluble CD40 ligand and platelet-derived microparticles. RANTES exhibited changes similar to IL-6, TNFalpha, and soluble IL-2 receptors, which are GVHD markers. Thus, the platelet-derived chemokines ENA-78 and RANTES exhibited particular changes after SCT. Our results suggest that ENA-78 play a role in hematopoietic conditions in which G-CSF is not involved, and RANTES generation after allo-SCT relates to GVHD.

Effect of doxazosin gastrointestinal therapeutic system on platelet degranulation and platelet-leukocyte microaggregate formation induced by physiologic shear stress in hypertension

INTRODUCTION

In this prospective, ex vivo, single-blind study, the effect of doxazosin on platelet function was studied in patients with hypertension.

MATERIALS AND METHODS

Platelet activation by shear stress was measured in whole blood samples of 22 hypertensive patients and 22 normotensive controls, using flow cytometry. Sheared samples were evaluated for CD62 expression, microaggregate formation, and Ca2+ mobilization. Results were collected at baseline and after 1 and 2 months of single-dose (4 mg/d) extended-release doxazosin gastrointestinal therapeutic system therapy.

RESULTS

Doxazosin normalized blood pressure in hypertensive patients after 1 and 2 months of treatment. Hypertensive patients had a higher baseline percentage (mean+/-SD) of degranulated platelets (CD62+) than the normotensive control group (4.14+/-1.05 vs. 2.47+/-0.68, P<0.01). After 2 months of doxazosin gastrointestinal therapeutic system treatment, the percentage of CD62+ in the experimental group significantly decreased (P<0.05). At baseline, the number of platelet-leukocyte aggregates in vivo was greater in hypertensive patients (P<0.01); doxazosin did not normalize this measurement. Following shearing, platelet expression of CD62 increased significantly in the hypertensive group (P<0.001 vs. control). Shear stress-induced platelet activation and microaggregate formation were also greater in hypertensive patients. Intraplatelet-free calcium concentration was higher in hypertensive patients at baseline than in the normotensive group (P<0.001). At 2 months, doxazosin significantly reduced thrombin-stimulated Ca2+ mobilization in hypertensive patients (P<0.01 vs. baseline).

CONCLUSIONS

Platelets from hypertensive patients are more readily activated by shear stress and demonstrate significant alterations in cytoplasmic-free calcium mobilization. Doxazosin treatment reduced blood pressure and normalized alterations in platelet function.

Losartan and simvastatin inhibit platelet activation in hypertensive patients

BACKGROUND

Diabetic patients also show hypercoagulability and platelet hyperaggregability, with increased levels of platelet activation-markers such as P-selectin (CD62P) and platelet-derived microparticles. We investigated the effects of losartan and simvastatin on circulating levels of platelet activation markers, microparticles, soluble selectins, and soluble cell adhesion molecules in hypertensive and hyperlipidemic patients with or without Type 2 diabetes.

METHODS

The subjects included 25 normotensive healthy controls and 41 hypertensive patients. The 41 hypertensive patients were divided into three groups: group A had hypertension and hyperlipidemia (n = 11), group B had hypertension and Type 2 diabetes (n = 14), and group C had hypertension, hyperlipidemia, and diabetes (n = 16). Losartan was administered to all of the patients at a dose of 50 mg/day for 24 weeks. In addition, simvastatin was administered to the hyperlipidemic patients at a dose of 10 mg/day for 24 weeks.

RESULTS

There were significant differences in the levels of CD62P, CD63, PAC-1, platelet microparticles, endothelial microparticles, sE-selectin, and sVCAM-1 between the hypertensive patients and healthy controls. These markers were all significantly increased in hypertensive and hyperlipidemic patients with Type 2 diabetes. In hypertensive patients with diabetes, CD62P, CD63, PAC-1, platelet and endothelial microparticles, and soluble adhesion markers were all decreased by losartan monotherapy. The decrease of each marker in hypertensive and hyperlipidemic patients given combined therapy with losartan plus simvastatin was greater among those with than without Type 2 diabetes. Low-density lipoprotein was decreased significantly by simvastatin and was correlated with CD62P or platelet microparticles in all of the patients.

CONCLUSION

Administration of losartan plus simvastatin to hypertensive and hyperlipidemic patients with Type 2 diabetes may prevent the development of cardiovascular complications caused by activated platelets and microparticles via another mechanism in addition to reduction of the blood pressure or lipid levels.

Microvesicles derived from activated platelets induce metastasis and angiogenesis in lung cancer

The role of platelets in tumor progression and metastasis has been recognized but the mechanism of their action remains unclear. Five human lung cancer cell lines (A549, CRL 2066, CRL 2062, HTB 183, HTB 177) and a murine Lewis lung carcinoma (LCC) cell line (for an in vivo model of metastasis) were used to investigate how platelet-derived microvesicles (PMV), which are circular fragments shed from the surface membranes of activated platelets, and exosomes released from platelet alpha-granules, could contribute to metastatic spread. We found that PMV transferred the platelet-derived integrin CD41 to most of the lung cancer cell lines tested and stimulated the phosphorylation of mitogen-activated protein kinase p42/44 and serine/threonine kinase as well as the expression of membrane type 1-matrix metalloproteinase (MT1-MMP). PMV chemoattracted 4 of the 5 cell lines, with the highly metastatic A549 cells exhibiting the strongest response. In A549 cells, PMV were shown to stimulate proliferation, upregulate cyclin D2 expression and increase trans-Matrigel chemoinvasion. Furthermore, in these cells, PMV stimulated mRNA expression for angiogenic factors such as MMP-9, vascular endothelial growth factor, interleukin-8 and hepatocyte growth factor, as well as adhesion to fibrinogen and human umbilical vein endothelial cells. Intravenous injection of murine PMV-covered LLC cells into syngeneic mice resulted in significantly more metastatic foci in their lungs and LLC cells in bone marrow than in control animals injected with LCC cells not covered with PMV. Based on these findings, we suggest that PMV play an important role in tumor progression/metastasis and angiogenesis in lung cancer.

Serotonin and thromboxane A2 stimulate platelet-derived microparticle-induced smooth muscle cell proliferation

INTRODUCTION

At the sites of vascular injury, activated and aggregating platelets release small vesiculated structures called platelet microparticles (PMPs). Apart from PMPs they also release several vasoactive mediators including serotonin and thromboxane A2 (TXA2). PMPs, serotonin, and TXA2 have been shown to stimulate vascular smooth muscle cell (VSMC) proliferation. Thus, this study is designed to examine the interaction between PMPs and serotonin or TXA2 in inducing rabbit VSMC proliferation.

METHODS

Growth-arrested rabbit SMCs were incubated in serum-free medium with different concentrations of PMPs with or without serotonin or TXA2. VSMC proliferation was examined by increase in incorporation of [3H]thymidine into DNA and by increase in cell number.

RESULTS

PMPs stimulated DNA synthesis in a dose-dependent manner; up to an added concentration of 30 microg/ml (1489 +/- 90%) they stimulated SMC proliferation in a logarithmic fashion. Serotonin at 50 microM (345 +/- 21%) and TXA2 at 7.5 microM (900 +/- 36%) had their maximal effect. When added together, PMPs (10 microg/ml) and serotonin (5 microM), synergistically induced DNA synthesis (581 +/- 36% and 211 +/- 11% when added alone and 1201 +/- 95% when added together), whereas PMPs (10 microg/ml) and TXA2 (5 microM) additively induced DNA synthesis (581 +/- 36% and 781 +/- 56% when added alone and 1262 +/- 115% when added together). These increases in DNA synthesis were paralleled by increase in cell number.

CONCLUSION

PMPs, serotonin, and TXA2 are mitogenic to SMC, and function as amplification factors to each other, suggesting that inhibition of neointimal proliferation after vascular injury may require the combined use of multiple growth factor inhibitors to simultaneously block several critical cellular activation pathways.

Platelet activation markers, microparticles and soluble adhesion molecules are elevated in patients with arteriosclerosis obliterans: therapeutic effects by cilostazol and potentiation by dipyridamole

We evaluated the plasma concentrations of platelet activation markers, microparticles and soluble adhesion molecules in patients with arteriosclerosis obliterans (ASO) and compared the beneficial effects of cilostazol alone and combination therapy of cilostazol and dipyridamole in these patients. There was a significant elevation of CD62P, CD63, PAC-1, annexin V, platelet-derived microparticles (PDMPs), sP-selectin, sE-selectin, sICAM-1 and sVCAM-1 in the ASO patients compared with the controls. Platelet aggregation was decreased by 2 weeks of cilostazol monotherapy in the ASO patients. Adding dipyridamole to the cilostazol therapy for 2 weeks further reduced platelet aggregation. While treatment with cilostazol alone reduced levels of CD62P, CD63, PAC-1, annexin V, PDMP, and sP-selectin, the combination therapy reduced these parameters further. While sE-selectin and cell adhesion molecules did not change significantly after 2 weeks of combination therapy, they exhibited a remarkable decrease after 16 weeks of combination treatment. These findings suggest that platelets are activated in ASO patients, and cilostazol is effective to reduce platelet activation. Furthermore, dipyridamole may potentiate the beneficial effect of cilostazol in ASO patients. Combination use of both drugs may help to prevent the onset of cardiovascular complications in patients with ASO by activated platelets and PDMP.

Increased platelet-derived microparticles in the coronary circulation of percutaneous transluminal coronary angioplasty patients

Platelet-derived microparticles that are produced during platelet activation are capable of adhesion and aggregation. Endothelial trauma that occurs during percutaneous transluminal coronary angioplasty (PTCA) may support platelet-derived microparticle adhesion and contribute to development of restenosis. We have previously reported an increase in platelet-derived microparticles in peripheral arterial blood with angioplasty. This finding raised concerns regarding the role of platelet-derived microparticles in restenosis, and therefore the aim of this study was to monitor levels in the coronary circulation. The study population consisted of 19 angioplasty patients. Paired coronary artery and sinus samples were obtained following heparinization, following contrast administration, and subsequent to all vessel manipulation. Platelet-derived microparticles were identified with an anti-CD61 (glycoprotein IIIa) fluorescence-conjugated antibody using flow cytometry. There was a significant decrease in arterial platelet-derived microparticles from heparinization to contrast administration (P = 0.001), followed by a significant increase to the end of angioplasty (P = 0.004). However, there was no significant change throughout the venous samples. These results indicate that the higher level of platelet-derived microparticles after angioplasty in arterial blood remained in the coronary circulation. Interestingly, levels of thrombin-antithrombin complexes did not rise during PTCA. This may have implications for the development of coronary restenosis post-PTCA, although this remains to be determined.

Probucol and ticlopidine: effect on platelet and monocyte activation markers in hyperlipidemic patients with and without type 2 diabetes

We investigated the effects of probucol and ticlopidine on circulating levels of platelet activation markers, microparticles, soluble selectins, and malondialdehyde-low density lipoprotein (MDA-LDL) in hyperlipidemic patients with or without type 2 diabetes. There were significant differences in the levels of CD62P, PAC-1, annexin V, PDMP, MDMP, sP-selectin, sE-selectin and MDA-LDL between the hyperlipidemic patients and the controls. In particular, these markers were significantly increased in hyperlipidemic patients who had type 2 diabetes. In the hyperlipidemic patients with diabetes, MDA-LDL was decreased by both monotherapy with probucol and combination therapy (probucol and ticlopidine). In these patients, CD62P, PAC-1, annexin V, MDMP, PDMP, sP-selectin, and sE-selectin were also significantly decreased after treatment. The decreases of CD62P, PAC-1, annexin V, PDMP and sP-selectin were greater combination therapy than with monotherapy. These findings suggest that administration of probucol and ticlopidine to hyperlipidemic patients with type 2 diabetes may help to prevent the development of cardiovascular complications caused by modified LDL, selectins, or activated platelets and monocytes.

P-selectin and platelet-derived microparticles associated with monocyte activation markers in patients with pulmonary embolism

Platelet activation markers (platelet-derived microparticles and P-selectin on activated platelets), chemokines (monocyte chemotactic peptide and regulated on activation normally T-cell expressed and secreted), and soluble markers (sP-selectin, sE-selectin, sVCAM-1, and sCD14) were measured and compared in patients with pulmonary embolism (PE). These substances are thought to participate in the pathogenesis of PE. Levels of all of the platelet activation markers, chemokines, and soluble markers were higher in the patients with PE than in normal controls. Levels of platelet activation markers were also significantly increased postoperatively after total knee arthroplasty. Anti-platelet therapy significantly inhibited the elevation of platelet activation markers after total knee arthroplasty. These findings suggest that antiplatelet therapy may be useful for PE-related interaction of platelets, leukocytes, and endothelial cells.

Elevation of Platelet Activation Markers and Chemokines during Peripheral Blood Stem Cell Harvest with G-CSF

The kinetics of peripheral blood stem cell mobilization in response to recombinant human granulocyte colony-stimulating factor is well established. However, there have been few investigations of platelet activation markers during peripheral blood stem cell harvest. We measured the levels of the platelet activation markers, chemokines, and soluble factors in plasma obtained from patients undergoing peripheral blood stem cell harvest. The number of leukocytes, CD34+ cells, neutrophils, monocytes, and lymphocytes peaked on day 5 after granulocyte colony-stimulating factor treatment, but the numbers of eosinophils and basophils showed no significant change. Regulated on activation normally T-cell expressed and secreted (RANTES) level increased through day 10, and the monocyte chemotactic peptide-1 (MCP-1) level peaked on day 5. Platelet counts continued to increase through day 10. The level of thrombopoietin significantly increased on day 3, peaked on day 5, and decreased slightly by day 10. The levels of soluble CD40 ligand and soluble P-selectin increased up to day 5. The platelet-derived microparticle level peaked on day 5, and then began to decline. CD34+ cell numbers significantly correlated with those of leucocytes, neutrophils, monocytes, and lymphocytes, as well as levels of MCP-1, and the CD34+ cells exhibited changes similar to platelet-derived microparticles. The patterns of change in MCP-1, platelet-derived microparticles, and the CD34+ cell count are similar in that each peaks on day 5 and decreases thereafter. Further study is required to determine if a cause-and-effect relationship in their pattern of change exists among them.

Increased platelet aggregation and production of platelet-derived microparticles after surgery for upper gastrointestinal malignancy

BACKGROUND

Since platelet function is known to play a major role in arterial thrombosis, we investigated postsurgery alterations in platelet function that might predispose patients with upper gastrointestinal malignancy to postoperative thrombotic complications.

SUBJECTS AND METHODS

Shear-induced platelet aggregation (SIPA) in platelet-rich plasma was measured in 23 patients who elected to undergo abdominal surgery. Measurement was done by cone-plate viscometer under low shear stress (12 dyn/cm(2)), a physiological condition, and under high shear stress (108 dyn/cm(2)), a pathological condition that simulates in vivo conditions such as those in stenotic arteries. Platelet microparticle (PMP) formation was analyzed by flow cytometry. Plasma von Willebrand factor (vWF) was also measured.

RESULTS

SIPA under high shear stress was significantly enhanced from 44.0 +/- 13.4% preoperatively to 69.5 +/- 15.8% on postoperative day (POD) 1, and it returned to preoperative levels on POD 14. PMP formation under high shear stress was enhanced before surgery (140.8 +/- 38.7%) compared to that under a static condition, and the enhancement was further augmented on POD 1 (219.1 +/- 49.3%). The enhancement of SIPA and PMP formation had no association with disease stage. vWF levels increased significantly on POD 1. Exogenous vWF augmented SIPA and PMP formation under high shear stress, and this augmentation was inhibited by anti-vWF antibody.

CONCLUSIONS

Because PMPs are highly procoagulant, increased SIPA and PMP formation induced by surgical intervention possibly contribute to thrombotic complications. Blockage of platelet interaction with vWF may prevent arterial thrombus formation perioperatively.

Increased generation of platelet-derived microparticles following percutaneous transluminal coronary angioplasty

Platelet-derived microparticles that are produced during platelet activation bind to traumatized endothelium. Such endothelial injury occurs during percutaneous transluminal coronary angioplasty. Approximately 20% of these patients subsequently develop restenosis, although this is improved by treatment with the anti-platelet glycoprotein IIb/IIIa receptor drug abciximab. As platelet activation occurs during angioplasty, it is likely that platelet-derived microparticles may be produced and hence contribute to restenosis. This study population consisted of 113 angioplasty patients, of whom 38 received abciximab. Paired peripheral arterial blood samples were obtained following heparinization and subsequent to all vessel manipulation. Platelet-derived microparticles were identified using an anti-CD61 (glycoprotein IIIa) fluorescence-conjugated antibody and flow cytometry. Baseline clinical characteristics between patient groups were similar. The level of platelet-derived microparticles increased significantly following angioplasty in the group without abciximab (paired t test, P = 0.019). However, there was no significant change in the level of platelet-derived microparticles following angioplasty in patients who received abciximab, despite requiring more complex angioplasty procedures. In this study, we have demonstrated that the level of platelet-derived microparticles increased during percutaneous transluminal coronary angioplasty, with no such increase with abciximab treatment. The increased platelet-derived microparticles may adhere to traumatized endothelium, contributing to re-occlusion of the arteries, but this remains to be determined.

Effects of eicosapentaenoic acid on platelet activation markers and cell adhesion molecules in hyperlipidemic patients with Type 2 diabetes mellitus

We compared the levels of microparticles, platelet activation markers, soluble cell adhesion molecules, soluble selectins, and antioxidized low-density lipoprotein (anti-Ox LDL) antibody between patients with hyperlipidemia and control subjects. Binding of anti-glycoprotein (GP) IIb/IIIa and anti-GPIb monoclonal antibodies to platelets did not differ significantly between the hyperlipidemic patients and controls. However, expression of activation markers (CD62P, CD63, PAC-1, and annexin V) by platelets was higher in the hyperlipidemic patients with Type 2 diabetes. The levels of platelet-derived microparticles (PDMPs) and monocyte-derived microparticles (MDMPs) were significantly different in hyperlipidemic patients with Type 2 diabetes and controls. Soluble P-selectin (sP-selectin), soluble E-selectin (sE-selectin), and anti-Ox LDL antibody also showed higher levels in the hyperlipidemic patients with Type 2 diabetes. After treatment with eicosapentaenoic acid (EPA), the levels of CD62P, CD63, annexin V, PDMPs, and MDMPs, sE-selectin, and oxidized LDL antibody were reduced significantly. Triglyceride (TG) and total cholesterol levels were also decreased. Anti-Ox LDL antibodies and MDMPs were correlated positively with platelet CD62P (plt-CD62P) levels. These findings suggest that in hyperlipidemic patients with Type 2 diabetes, EPA may prevent complications caused by oxidized LDL, E-selectin, and activated platelets or monocytes.

Effects of severe hypertension on endothelial and platelet microparticles

The molecular mechanisms by which extreme blood pressure elevation leads to vascular injury are not defined. To explore the hypothesis that activation of endothelium and platelets as manifested by increased concentrations of circulating endothelial microparticles and platelet microparticles could play a role in this target organ injury, we conducted a cross-sectional study of these markers in 3 groups: (1) untreated patients referred specifically for treatment of severe uncontrolled hypertension; (2) untreated patients with established mild hypertension; and (3) normotensive volunteer subjects. By ANOVA, endothelial (P=0.002) and platelet (P=0.01) microparticles were greatest in the severely hypertensive group. There was a significant correlation between both of these markers and blood pressure, even in the setting of multiple risk factors. Our results suggest that these markers may be useful and specific for pressure-induced endothelial and platelet activation in hypertension. Furthermore, because of the combined effects of endothelial and platelet microparticles on coagulation, leukocytes, and endothelium, it is possible that they may play a pathogenic role in mediating target organ injury in severe hypertension.