Extracellular vesicles and coagulation in blood from healthy humans revisited

Background: In 2001, we studied the presence and coagulant properties of “microparticles” in the blood of healthy humans. Since then, multiple improvements in detection, isolation and functional characterization of the now called “extracellular vesicles” (EVs) have been made, and shortcomings were identified. Aim: To revisit the presence and function of EVs in blood from healthy humans. Methods: Blood was collected from 20 healthy donors. EV-containing plasma was prepared according to new guidelines, and plasma was diluted to prevent swarm detection. Single EVs were measured by flow cytometry with known sensitivity of fluorescence and light scatter. The haemostatic properties of EVs were measured by thrombin-, fibrin-, and plasmin generation. Plasma concentrations of thrombin-antithrombin complexes and prothrombin fragment 1 + 2 were measured to assess the coagulation status in vivo. Results: Compared to 2001, the total concentrations of detected EVs increased from 190- to 264-fold. In contrast to 2001, however, EVs are non-coagulant which we show can be attributed to improvements in blood collection and plasma preparation. No relation is present between the plasma concentrations of EVs and either TAT or F1 + 2. Finally, we show that EVs support plasmin generation. Discussion: Improvements in blood collection, plasma preparation and detection of EVs reveal that results from earlier studies have to be interpreted with care. Compared to 2001, higher concentrations of EVs are detected in blood of healthy humans which promote fibrinolysis rather than coagulation.

Randomized controlled trial protocol to investigate the antiplatelet therapy effect on extracellular vesicles (AFFECT EV) in acute myocardial infarction

Activated platelets contribute to thrombosis and inflammation by the release of extracellular vesicles (EVs) exposing P-selectin, phosphatidylserine (PS) and fibrinogen. P2Y12 receptor antagonists are routinely administered to inhibit platelet activation in patients after acute myocardial infarction (AMI), being a combined antithrombotic and anti-inflammatory therapy. The more potent P2Y12 antagonist ticagrelor improves cardiovascular outcome in patients after AMI compared to the less potent clopidogrel, suggesting that greater inhibition of platelet aggregation is associated with better prognosis. The effect of ticagrelor and clopidogrel on the release of EVs from platelets and other P2Y12-exposing cells is unknown. This study compares the effects of ticagrelor and clopidogrel on (1) the concentrations of EVs from activated platelets (primary end point), (2) the concentrations of EVs exposing fibrinogen, exposing PS, from leukocytes and from endothelial cells (secondary end points) and (3) the procoagulant activity of plasma EVs (tertiary end points) in 60 consecutive AMI patients. After the percutaneous coronary intervention, patients will be randomized to antiplatelet therapy with ticagrelor (study group) or clopidogrel (control group). Blood will be collected from patients at randomization, 48 hours after randomization and 6 months following the index hospitalization. In addition, 30 age- and gender-matched healthy volunteers will be enrolled in the study to investigate the physiological concentrations and procoagulant activity of EVs using recently standardized protocols and EV-dedicated flow cytometry. Concentrations of EVs will be determined by flow cytometry. Procoagulant activity of EVs will be determined by fibrin generation test. The compliance and response to antiplatelet therapy will be assessed by impedance aggregometry. We expect that plasma from patients treated with ticagrelor (1) contains lower concentrations of EVs from activated platelets, exposing fibrinogen, exposing PS, from leukocytes and from endothelial cells and (2) has lower procoagulant activity, when compared to patients treated with clopidogrel. Antiplatelet therapy effect on EVs may identify a new mechanism of action of ticagrelor, as well as create a basis for future studies to investigate whether lower EV concentrations are associated with improved clinical outcomes in patients treated with P2Y12 antagonists.

Human Blood Platelet Membrane Glycoproteins

The separation of the major platelet membrane glycoproteins of normal subjects and subjects with well defined platelet membrane glycoprotein abnormalities have been examined using four different polyacrylamide gel electrophoretic techniques (continuous and discontinuous). The mobilities of the resolved glycoprotein bands have been correlated with the glycoprotein nomenclature proposed for the conventional sodium dodecyl sulphate- phosphate buffer system. Since the glycoprotein distribution varies depending on the system used, the merits of each method should be considered before application to a specific problem.

Thrombin-Antithrombin III Complexes in the Prediction of Deep Vein Thrombosis Following Total Hip Replacement

In 196 consecutive patients who underwent elective total hip surgery we investigated the diagnostic accuracy of the thrombinantithrombin III complex immunoassay, as assessed on the first, fourth and tenth postoperative day, for the development of deep vein thrombosis (DVT). Patients received either LMWheparinoid (n = 97) or placebo (n = 99) and underwent contrast venography on the tenth postoperative day.

Thrombin-antithrombin III (T-AT) plasma levels were raised in all patients on the first postoperative day and gradually decreased during the study period. T-AT plasma levels were significantly higher in patients developing DVT when compared to patients without DVT and remained so until day 10. This difference was apparent both in the LMW-heparinoid group as well as in the placebo-treated patients.

ROC-curve analysis revealed no satisfactory discriminative power for the diagnosis of developing DVT at any of the studied cut-off values for T-AT.

We conclude that the postoperative determination of T-AT complex plasma concentrations in hip surgery patients has no clinical utility in the prediction of postoperative DVT.

Detection of Carriers in Glanzmann's Thrombasthenia

Quantitative glycoprotein (GP) analysis of whole platelets or platelet membranes was performed by SDS-polyacrylamide gelelectrophoresis (SDS-PAGE) and periodic acid Schiff staining in the families of two unrelated Glanzmann’s thrombasthenia (GT) patients. Each family consisted of two symptom free parents, a symptom free daughter and a GT daughter. All symptom free members had a normal bleeding time, clot retraction and platelet aggregation response to adenosine 5’-diphosphate (ADP), collagen and adrenalin. Platelet Zw* antigen was normally expressed in these subjects. GT patiens, classified as a type I and II subject, showed reduced amounts of GP lib and of GP nia. Analysis of isolated membranes in the non-reduced state, however, showed that the amount of GP Ilia was also reduced in three of the four parents, whereas one parent (of the GT type I patient) and the two unaffected daughters had normal amounts of GP Ilia. Quantitative SDS-PAGE may therefore provide a method for the detection of asymptomatic carriers in GT type I and II.

Antithrombin Acts as a Negative Acute Phase Protein as Established with Studies on HepG2 Cells and in Baboons

Patients with sepsis or after major surgery have decreased plasma levels of the anticoagulant protein antithrombin. In such patients elevated levels of interleukin-6 (IL-6) are present and this interleukin is known to induce positive and negative acute phase responses. To investigate the possibility that antithrombin acts as a negative acute phase response-protein we performed studies on the human hepatoma cell line HepG2 in vitro and baboons in vivo. HepG2 cells were treated with recombinant human IL-6, ILß3, or combinations of the latter two, and tested for production of antithrombin, fibrinogen and prealbumin (transthyretin). This treatment resulted in a dose dependent increase in fibrinogen concentration (with a maximum effect of 2.8-2.9-fold) and a dose dependent decrease in prealbumin (with a maximum effect of 0.6-0.7-fold) and antithrombin concentrations (with a maximum effect of 0.6-0.8-fold). Simultaneous treatment of the HepG2 cells with IL-6 (1,000 pg/ml or 2,500 pg/ml) and IL-1β (25 pg/ml), provided more extensively decreased prealbumin (0.8 and 0.6-fold, respectively) and antithrombin concentration (0.7 and 0.6-fold, respectively) compared to the single interleukin treatment at these concentrations. Baboons treated with 2 µg IL-6 · kg body-weight-1 · day1 showed increased plasma CRP levels (59-fold, p <0.05) and decreased prealbumin (0.9-fold, p <0.05) and antithrombin (0.8-fold, p <0.05) plasma levels, without evidence for coagulation activation. Our results indicate that antithrombin acts as a negative acute phase protein, which may contribute to the decreased antithrombin plasma levels observed after major surgery or in sepsis.

Early Markers of Blood Coagulation and Fibrinolysis Activation in Argentine Hemorrhagic Fever

Junin virus, an arenaviridae, is the etiological agent of Argentine hemorrhagic fever. In addition to thrombocytopenia, patients present several alterations in both the blood coagulation and the fibrinolytic system, but diffuse intravascular coagulation could not be demonstrated. To investigate further the activation status of the two systems, levels of thrombin-antithrombin complexes (TAT), prothrombin fragment 1+2, protein C, total and free protein S, C4bBP, antithrombin III, t-PA, PAI-1 and D-dimer were measured. Fourteen patients with a confirmed diagnosis of Argentine hemorrhagic fever were included in the study, 2 were severe, 3 moderate and 9 mild clinical cases, but hemorrhages were slight throughout. Blood samples were collected for 6 consecutive days on admission and on remission. At admission TAT and F1+2 levels were increased in 13/14 patients, reaching 0.33 nM (0.06-0.87) and 2.16 nM (0.96-6.5), respectively. PC was low in 4 cases, fPS in 6 and tPS in 2, whereas C4bBP and ATIII values were within normal range. t-PA and D-dimer levels were high in 11/14 patients, reaching 20 ng/ml (2.7-106) and 1660 ng/ml (877-3780) respectively, while PAI-1 was considerably increased in the 2 severe cases and normal in the remainder. These results suggest low level though persistent process of blood coagulation and fibrinolysis activation in this viral hemorrhagic disease. We believe these abnormalities may lead to the well described bleeding manifestations in these patients.

Standardization of extracellular vesicle measurements by flow cytometry through vesicle diameter approximation

Essentials Platelet extracellular vesicles (EVs) concentrations measured by flow cytometers are incomparable. A model is applied to convert ambiguous scatter units to EV diameter in nanometer. Most included flow cytometers lack the sensitivity to detect EVs of 600 nm and smaller. The model outperforms polystyrene beads for comparability of platelet EV concentrations.

SUMMARY

Background Detection of extracellular vesicles (EVs) by flow cytometry has poor interlaboratory comparability, owing to differences in flow cytometer (FCM) sensitivity. Previous workshops distributed polystyrene beads to set a scatter-based diameter gate in order to improve the comparability of EV concentration measurements. However, polystyrene beads provide limited insights into the diameter of detected EVs. Objectives To evaluate gates based on the estimated diameter of EVs instead of beads. Methods A calibration bead mixture and platelet EV samples were distributed to 33 participants. Beads and a light scattering model were used to set EV diameter gates in order to measure the concentration of CD61-phycoerythrin-positive platelet EVs. Results Of the 46 evaluated FCMs, 21 FCMs detected the 600-1200-nm EV diameter gate. The 1200-3000-nm EV diameter gate was detected by 31 FCMs, with a measured EV concentration interlaboratory variability of 81% as compared with 139% with the bead diameter gate. Part of the variation in both approaches is caused by precipitation in some of the provided platelet EV samples. Flow rate calibration proved essential because systems configured to 60 μL min-1 differed six-fold in measured flow rates between instruments. Conclusions EV diameter gates improve the interlaboratory variability as compared with previous approaches. Of the evaluated FCMs, 24% could not detect 400-nm polystyrene beads, and such instruments have limited utility for EV research. Finally, considerable differences were observed in sensitivity between optically similar instruments, indicating that maintenance and training affect the sensitivity.

Extracellular vesicles from human saliva promote hemostasis by delivering coagulant tissue factor to activated platelets

Essentials Human salivary extracellular vesicles (EVs) expose coagulant tissue factor (TF). Salivary EVs expose CD24, a ligand of P-selectin. CD24 and coagulant TF co-localize on salivary EVs. TF+ /CD24+ salivary EVs bind to activated platelets and trigger coagulation.

SUMMARY

Background Extracellular vesicles (EVs) from human saliva expose coagulant tissue factor (TF). Whether such TF-exposing EVs contribute to hemostasis, however, is unknown. Recently, in a mice model, tumor cell-derived EVs were shown to deliver coagulant TF to activated platelets at a site of vascular injury via interaction between P-selectin glycoprotein ligand-1 (PSGL-1) and P-selectin. Objectives We hypothesized that salivary EVs may deliver coagulant TF to activated platelets via interaction with P-selectin. Methods We investigated the presence of two ligands of P-selectin on salivary EVs, PSGL-1 and CD24. Results Salivary EVs expose CD24 but PSGL-1 was not detected. Immune depletion of CD24-exposing EVs completely abolished the TF-dependent coagulant activity of cell-free saliva, showing that coagulant TF and CD24 co-localize on salivary EVs. In a whole blood perfusion model, salivary EVs accumulated at the surface of activated platelets and promoted fibrin generation, which was abolished by an inhibitory antibody against human CD24. Conclusions A subset of EVs in human saliva expose coagulant TF and CD24, a ligand of P-selectin, suggesting that such EVs may facilitate hemostasis at a site of skin injury where the wound is licked in a reflex action.

Tissue Factor Coagulant Activity is Regulated by the Plasma Membrane Microenvironment

BACKGROUND

Tissue factor (TF) can be present in a non-coagulant and coagulant form. Whether the coagulant activity is affected by the plasma membrane microenvironment is unexplored.

OBJECTIVE

This article studies the presence and coagulant activity of human TF in plasma membrane micro-domains.

METHODS

Plasma membranes were isolated from human MIA PaCa2 cells, MDA-MB-231 cells and human vascular smooth muscle cells by Percoll gradient ultracentrifugation after cell disruption. Plasma membranes were fractionated by OptiPrep gradient ultracentrifugation, and the presence of TF, flotillin, caveolin, clathrin, protein disulphide isomerase (PDI), TF pathway inhibitor (TFPI) and phosphatidylserine (PS) were determined.

RESULTS

Plasma membranes contain two detergent-resistant membrane (DRM) compartments differing in density and biochemical composition. High-density DRMs (DRM-H) have a density (ρ) of 1.15 to 1.20 g/mL and contain clathrin, whereas low-density DRMs (DRM-L) have a density between 1.09 and 1.13 g/mL and do not contain clathrin. Both DRMs contain TF, flotillin and caveolin. PDI is detectable in DRM-H, TFPI is not detectable in either DMR-H or DRM-L and PS is detectable in DRM-L. The DRM-H-associated TF (> 95% of the TF antigen) lacks detectable coagulant activity, whereas the DRM-L-associated TF triggers coagulation. This coagulant activity is inhibited by lactadherin and thus PS-dependent, but seemed insensitive to 16F16, an inhibitor of PDI.

CONCLUSION

Non-coagulant and coagulant TF are present within different types of DRMs in the plasma membrane, and the composition of these DRMs may affect the TF coagulant activity.

Comparison of Generic Fluorescent Markers for Detection of Extracellular Vesicles by Flow Cytometry

BACKGROUND

Extracellular vesicles (EVs) in biofluids are potential biomarkers of disease. To explore the clinical relevance of EVs, a specific generic EV marker would be useful, one that does not require antibodies and binds to all EVs. Here we evaluated 5 commonly used generic markers for flow cytometry.

METHODS

Flow cytometry (A60-Micro, Apogee) was used to evaluate the ability of the generic EV markers calcein acetoxymethyl ester, calcein acetoxymethyl ester violet, carboxyfluorescein succinimidyl ester (CFSE), 4-(2-[6-(dioctylamino)-2-naphthalenyl]ethenyl)-1-(3-sulfopropyl)pyridinium (di-8-ANEPPS), and lactadherin to stain EVs from MCF7 human breast adenocarcinoma cell line-conditioned culture medium [epithelial cell adhesion molecule positive (EpCAM+)] or platelet EVs from human plasma [integrin β3 positive (CD61+)]. Side scatter triggering was applied as a reference, and the influence of non-EV components (proteins and lipoproteins) was evaluated.

RESULTS

Di-8-ANEPPS, lactadherin, and side scatter detected 100% of EpCAM+ MCF7 EVs. Lactadherin and side scatter detected 33% and 61% of CD61+ EVs, respectively. Di-8-ANEPPS detected platelet EVs only if soluble protein was first removed. Because all generic markers stained proteins, at best 33% of platelet EVs in plasma were detected. The calcein markers and CFSE were either insensitive to EVs in both samples or associated with swarm detection.

CONCLUSIONS

None of the generic markers detected all and only EVs in plasma. Side scatter triggering detected the highest concentration of plasma EVs on our A60-Micro, followed by lactadherin. The choice between scatter or lactadherin primarily depends on the analytical sensitivity of the flow cytometer used.

Increased Levels of Factor VIII and Fibrinogen in Patients with Venous Thrombosis Are not Caused by Acute Phase Reactions

Factor VIII activity (factor VIII:C) levels ≥150 IU/dl are associated with a 5- to 6-fold increased risk of venous thrombosis compared to levels <100 IU/dl, and fibrinogen levels ≥5.0 g/l increase the thrombosis risk 4-fold. These high levels are present in 25% resp. 3% of the patients with a first episode of venous thrombosis. These findings were based on measurements after the thrombotic event, so the factor VIII and fibrinogen levels in thrombosis patients may have been influenced by acute phase reactions or ongoing inflammatory responses. In the present study we measured plasma C-reactive protein (CRP) as a sensitive marker of an acute phase reaction in 474 thrombosis patients and 474 age- and sex-matched healthy controls, that were part of the Leiden Thrombophilia Study (LETS). Mean and median CRP levels were higher in thrombosis patients than in the controls, suggesting inflammation in some patients. CRP affected both factor VIII and fibrinogen levels, in patients and controls alike. After adjustment for the effect of CRP, high factor VIII:C levels still increased the thrombosis risk 6-fold and high fibrinogen levels 4-fold, which is for both very similar to the risk before correction for CRP levels. These results show that although systemic inflammation may be present in some of the patients, elevated levels of factor VIII:C and fibrinogen were in general not caused by acute phase reactions. This further supports a causal relationship between both high factor VIII:C and fibrinogen levels and venous thrombosis.

Prothrombin Time Ratio Is Reduced by Magnesium Contamination in Evacuated Blood Collection Tubes

Magnesium ions were detected in sodium citrate solutions in several lots of evacuated blood collection tubes. The mean concentrations ranged between 1.3 and 1.6 mmol/L. Magnesium was also present in the rubber stoppers of the blood collection tubes and could be leached into the citrate solution. It was shown that magnesium added to citrated plasma shortened the prothrombin time of both coumarin and normal plasma. The effect of magnesium was relatively greater on coumarin than on normal plasma resulting in reduced prothrombin time ratio. Shortening of the prothrombin time was also observed when magnesium chloride was added to dialysed plasma, i.e., in the absence of citrate. These results indicate that magnesium contamination can interfere with accurate INR determination in the control of oral anticoagulant therapy.

Development of Peritoneal Carcinomatosis in Epithelial Ovarian Cancer: A Review

Epithelial ovarian cancer (EOC) metastasizes intra-abdominally with often numerous, superficial, small-sized lesions. This so-called peritoneal carcinomatosis is difficult to treat, and peritoneal recurrences are frequently observed, leading to a poor prognosis. Underlying mechanisms of interactions between EOC and peritoneal cells are incompletely understood. This review summarizes and discusses the development of peritoneal carcinomatosis from a cell-biological perspective, focusing on characteristics of EOC and peritoneal cells. We aim to provide insight into how peritoneum facilitates tumor adhesion but limits size of lesions and depth of invasion. The development of peritoneal carcinomatosis is a multistep process that requires adaptations of EOC and peritoneal cells. Mechanisms that enable tumor adhesion and growth involve cadherin restructuring on EOC cells, integrin-mediated adhesion, and mesothelial evasion by mechanical forces driven by integrin-ligand interactions. Clinical trials targeting these mechanisms, however, showed only limited effects. Other factors that inhibit tumor growth and deep invasion are virtually unknown. Future studies are needed to elucidate the exact mechanisms that underlie the development and limited growth of peritoneal carcinomatosis. This review on development of peritoneal carcinomatosis of EOC summarizes the current knowledge and its limitations. Clarification of the stepwise process may inspire future research to investigate new treatment approaches of peritoneal carcinomatosis.

Surface Plasmon Resonance is an Analytically Sensitive Method for Antigen Profiling of Extracellular Vesicles

BACKGROUND

Identification, enumeration, and characterization of extracellular vesicles (EVs) are hampered by the small size of EVs, a low refractive index, and low numbers of antigens on their surface.

METHODS

We investigated the potential of a 48-multiplex surface plasmon resonance imaging (SPRi) system to perform EV phenotyping. Antigen surface density of 11 antigens was measured on the human breast cancer cell lines HS578T, MCF7, and SKBR3 and their EVs by use of both SPRi and the widely used flow cytometry (FCM).

RESULTS

For cells, the SPRi and FCM signals for antigen exposure correlated (R_{HS578T cells}² = 0.66, R_{MCF7 cells}² = 0.78, R_{SKBR3 cells}² = 0.60). With regard to EVs, SPRi detected 31 out of 33 tested antibody-EV pairs, whereas our flow cytometer detected 5 antibody-EV pairs because of high blank and isotype control signals. For HS578T-derived EVs, the SPRi and FCM signals correlated (R²_{HS578T EVs} = 0.98). However, on MCF7- and SKBR3-derived EVs, insufficient antigens were detected by our flow cytometer. To confirm that the SPRi responses correlated with mean antigen density on EVs, the SPRi responses of EVs were correlated with antigen density on parental cells as measured by FCM (R_HS578T² = 0.77, R_MCF7² = 0.49, R_SKBR3² = 0.52).

CONCLUSIONS

SPRi responses correlate with mean antigen density. Moreover, SPRi detects lower antigen-exposure levels than FCM because SPRi measures an ensemble of EVs binding to the sensor surface, whereas FCM detects antigens of single EV.

Endotoxin, interleukin-6 and tumor necrosis factor concentrations in equine acute abdominal disease: relation to clinical outcome

Serial peri-operative plasma and serum samples from 55 horses suffering from acute abdominal disease and presented for surgical intervention were assayed for the presence of endotoxins (lipopolysaccharides; LPS), tumor necrosis factor (TNF) and interleukin-6 (IL-6). At study entry, venous blood was collected for blood cultures. Intra-operatively collected ascitic fluid samples were assayed for the presence of LPS. The clinical course of the disease was documented. Four horses were excluded from the study. At study entry, 21 of the 51 horses (41%) had increased platelet-rich plasma LPS concentrations, i.e. ≥ 5 ng/l (mean 35.5; range 7-197 ng/l), in 34 horses (67%) IL-6 concentrations were increased, i.e. exceeding 35 ng/l (mean 364; range 36—1762 ng/l). Detectable TNF was present in 5 horses (10%); 3 of them died spontaneously during surgery. In all TNF positive samples, markedly increased LPS and IL-6 concentrations were detected. Study entry IL-6 concentrations were significantly higher in non-surviving (mean 394; range < 20—1762 ng/l) than in surviving horses (mean 116; range < 20—894 ng/l; P < 0.0002). This was most evident when non-surviving horses with inflamed bowel disease were considered (mean 1096; range 650—1762 ng/l; P < 0.0001). Positive ascitic fluid LPS concentrations (≥ 3 ng/l) were encountered in 18 horses. There was no significant correlation between the LPS concentrations in ascites and plasma. Study entry concentrations of IL-6 were significantly correlated with LPS concentrations (r = 0.62; P < 0.001) and were inversely correlated with platelet counts (r = -0.46; P < 0.002). The magnitude of a calculated LPS-cytokine score strongly correlated with mortality (P < 0.001). Receiver operating characteristic (ROC) curve analysis showed that the IL-6 assay had reasonable accuracy for the prediction of unfavorable outcome (i.e. the area under the curve equalled 0.72), in contrast to the LPS assay. The results indicate that LPS, TNF and IL-6 are predominantly released in the systemic circulation of horses suffering from inflamed and ischemic bowel disease. IL-6 concentrations have predictive value for unfavorable outcome and the simultaneous presence of increased LPS, TNF and IL-6 concentrations is especially associated with a poor clinical condition and outcome.

Handling and storage of human body fluids for analysis of extracellular vesicles

Because procedures of handling and storage of body fluids affect numbers and composition of extracellular vesicles (EVs), standardization is important to ensure reliable and comparable measurements of EVs in a clinical environment. We aimed to develop standard protocols for handling and storage of human body fluids for EV analysis. Conditions such as centrifugation, single freeze-thaw cycle, effect of time delay between blood collection and plasma preparation and storage were investigated. Plasma is the most commonly studied body fluid in EV research. We mainly focused on EVs originating from platelets and erythrocytes and investigated the behaviour of these 2 types of EVs independently as well as in plasma samples of healthy subjects. EVs in urine and saliva were also studied for comparison. All samples were analysed simultaneously before and after freeze-thawing by resistive pulse sensing, nanoparticle tracking analysis, conventional flow cytometry (FCM) and transmission (scanning) electron microscopy. Our main finding is that the effect of centrifugation markedly depends on the cellular origin of EVs. Whereas erythrocyte EVs remain present as single EVs after centrifugation, platelet EVs form aggregates, which affect their measured concentration in plasma. Single erythrocyte and platelet EVs are present mainly in the range of 100-200 nm, far below the lower limit of what can be measured by conventional FCM. Furthermore, the effects of single freeze-thaw cycle, time delay between blood collection and plasma preparation up to 1 hour and storage up to 1 year are insignificant (p>0.05) on the measured concentration and diameter of EVs from erythrocyte and platelet concentrates and EVs in plasma, urine and saliva. In conclusion, in standard protocols for EV studies, centrifugation to isolate EVs from collected body fluids should be avoided. Freezing and storage of collected body fluids, albeit their insignificant effects, should be performed identically for comparative EV studies and to create reliable biorepositories.

Accuracy and Reproducibility in Quantification of Plasma Protein Concentrations by Mass Spectrometry without the Use of Isotopic Standards

Background

Quantitative proteomic analysis with mass spectrometry holds great promise for simultaneously quantifying proteins in various biosamples, such as human plasma. Thus far, studies addressing the reproducible measurement of endogenous protein concentrations in human plasma have focussed on targeted analyses employing isotopically labelled standards. Non-targeted proteomics, on the other hand, has been less employed to this end, even though it has been instrumental in discovery proteomics, generating large datasets in multiple fields of research.

Results

Using a non-targeted mass spectrometric assay (LCMS^E), we quantified abundant plasma proteins (43 mg/mL—40 ug/mL range) in human blood plasma specimens from 30 healthy volunteers and one blood serum sample (ProteomeXchange: PXD000347). Quantitative results were obtained by label-free mass spectrometry using a single internal standard to estimate protein concentrations. This approach resulted in quantitative results for 59 proteins (cut off ≥11 samples quantified) of which 41 proteins were quantified in all 31 samples and 23 of these with an inter-assay variability of ≤ 20%. Results for 7 apolipoproteins were compared with those obtained using isotope-labelled standards, while 12 proteins were compared to routine immunoassays. Comparison of quantitative data obtained by LCMS^E and immunoassays showed good to excellent correlations in relative protein abundance (r = 0.72–0.96) and comparable median concentrations for 8 out of 12 proteins tested. Plasma concentrations of 56 proteins determined by LCMS^E were of similar accuracy as those reported by targeted studies and 7 apolipoproteins quantified by isotope-labelled standards, when compared to reference concentrations from literature.

Conclusions

This study shows that LCMS^E offers good quantification of relative abundance as well as reasonable estimations of concentrations of abundant plasma proteins.

Refractive index determination of nanoparticles in suspension using nanoparticle tracking analysis

The refractive index (RI) dictates interaction between light and nanoparticles and therefore is important to health, environmental, and materials sciences. Using nanoparticle tracking analysis, we have determined the RI of heterogeneous particles <500 nm in suspension. We demonstrate feasibility of distinguishing silica and polystyrene beads based on their RI. The hitherto unknown RI of extracellular vesicles from human urine was determined at 1.37 (mean). This method enables differentiation of single nanoparticles based on their RI.

Single-step isolation of extracellular vesicles by size-exclusion chromatography

Background

Isolation of extracellular vesicles from plasma is a challenge due to the presence of proteins and lipoproteins. Isolation of vesicles using differential centrifugation or density-gradient ultracentrifugation results in co-isolation of contaminants such as protein aggregates and incomplete separation of vesicles from lipoproteins, respectively.

Aim

To develop a single-step protocol to isolate vesicles from human body fluids.

Methods

Platelet-free supernatant, derived from platelet concentrates, was loaded on a sepharose CL-2B column to perform size-exclusion chromatography (SEC; n=3). Fractions were collected and analysed by nanoparticle tracking analysis, resistive pulse sensing, flow cytometry and transmission electron microscopy. The concentrations of high-density lipoprotein cholesterol (HDL) and protein were measured in each fraction.

Results

Fractions 9–12 contained the highest concentrations of particles larger than 70 nm and platelet-derived vesicles (46%±6 and 61%±2 of totals present in all collected fractions, respectively), but less than 5% of HDL and less than 1% of protein (4.8%±1 and 0.65%±0.3, respectively). HDL was present mainly in fractions 18–20 (32%±2 of total), and protein in fractions 19–21 (36%±2 of total). Compared to the starting material, recovery of platelet-derived vesicles was 43%±23 in fractions 9–12, with an 8-fold and 70-fold enrichment compared to HDL and protein.

Conclusions

SEC efficiently isolates extracellular vesicles with a diameter larger than 70 nm from platelet-free supernatant of platelet concentrates. Application SEC will improve studies on the dimensional, structural and functional properties of extracellular vesicles.

Co-isolation of extracellular vesicles and high-density lipoproteins using density gradient ultracentrifugation

Extracellular vesicles (EVs) facilitate intercellular communication by carrying bioactive molecules such as proteins, messenger RNA, and micro (mi)RNAs. Recently, high-density lipoproteins (HDL) isolated from human plasma were also reported to transport miRNA to other cells. HDL, when isolated from human plasma, ranges in density between 1.063 and 1.21 g/mL, which grossly overlap with the reported density of EVs. Consequently, HDL and EV will be co-isolated when using density gradient ultracentrifugation. Thus, more stringent isolation/separation procedures of EV and HDL are essential to know their relative contribution to the pool of circulating bioactive molecules.

Particle size distribution of exosomes and microvesicles determined by transmission electron microscopy, flow cytometry, nanoparticle tracking analysis, and resistive pulse sensing

BACKGROUND

Enumeration of extracellular vesicles has clinical potential as a biomarker for disease. In biological samples, the smallest and largest vesicles typically differ 25-fold in size, 300,000-fold in concentration, 20,000-fold in volume, and 10,000,000-fold in scattered light. Because of this heterogeneity, the currently employed techniques detect concentrations ranging from 10(4) to 10(12) vesicles mL(-1) .

OBJECTIVES

To investigate whether the large variation in the detected concentration of vesicles is caused by the minimum detectable vesicle size of five widely used techniques.

METHODS

The size and concentration of vesicles and reference beads were measured with transmission electron microscopy (TEM), a conventional flow cytometer, a flow cytometer dedicated to detecting submicrometer particles, nanoparticle tracking analysis (NTA), and resistive pulse sensing (RPS).

RESULTS

Each technique gave a different size distribution and a different concentration for the same vesicle sample.

CONCLUSION

Differences between the detected vesicle concentrations are primarily caused by differences between the minimum detectable vesicle sizes. The minimum detectable vesicle sizes were 70-90 nm for NTA, 70-100 nm for RPS, 150-190 nm for dedicated flow cytometry, and 270-600 nm for conventional flow cytometry. TEM could detect the smallest vesicles present, albeit after adhesion on a surface. Dedicated flow cytometry was most accurate in determining the size of reference beads, but is expected to be less accurate on vesicles, owing to heterogeneity of the refractive index of vesicles. Nevertheless, dedicated flow cytometry is relatively fast and allows multiplex fluorescence detection, making it most applicable to clinical research.

Effects of cancer on platelets

The main function of circulating platelets is to stop bleeding upon vascular injury by the formation of a hemostatic plug. The presence of cancer results in numerical and functional abnormalities of platelets. Thrombocytosis is commonly observed in cancer patients and is associated with decreased survival. Conversely, thrombocytopenia has been shown to have antimetastatic effects in experimental models. Tumor cells also can induce changes in the platelet activation status, both in direct and indirect manners. Direct tumor cell-induced platelet aggregation enables the formation of a cloak of aggregated platelets around circulating tumor cells (CTCs) that shields them from attacks by the immune system and facilitates metastasis to distant sites. Cancer also can induce platelet activation in various indirect ways. Tumor cells shed small extracellular vesicles that expose the transmembrane protein tissue factor (TF)--the initiator of the extrinsic coagulation cascade. The abundant presence of TF in the circulation of cancer patients can result in local generation of thrombin, the most potent platelet activator. Another pathway of indirect platelet activation is by increased formation of neutrophil extracellular traps in the presence of tumor-secreted granulocyte colony-stimulating factor (G-CSF). Last, tumor cells may regulate the selective secretion of angiogenic proteins from platelet granules, which enables the tumor to stimulate and stabilize the immature neovasculature in the tumor environment. Since there is little doubt that the cancer-induced platelet alterations are beneficial to tumor growth and dissemination, it could be worthwhile to intervene in the underlying mechanisms for anticancer purposes. Antiplatelet and anticoagulant agents that inhibit platelet activation and thrombin generation can potentially slow cancer progression, although the clinical evidence thus far is not unequivocal.

Microparticles in vascular disorders: how tissue factor-exposing vesicles contribute to pathology and physiology

Coagulation is initiated by tissue factor (TF). Coagulant TF is constitutively expressed by extravascular cells, but there is increasing evidence that TF can also be present within the blood, in particular during pathological conditions. Such TF is exposed on circulating cell-derived vesicles, and its presence has been associated with development of disseminated intravascular coagulation and venous thrombosis. For example, the presence of TF-exposing vesicles in the blood of cancer patients may be associated with their high risk of developing venous thromboembolism. Remarkably, high levels of coagulant TF-exposing vesicles are present in other body fluids such as saliva and urine of healthy persons, suggesting that these vesicles play a physiological role. We postulate that the presence of TF-exposing vesicles in body fluids as saliva and urine provides an additional source of coagulant TF that promotes coagulation, thereby reducing blood loss and contributing to host defence by reducing the risk of microorganisms entering the "milieu intérieur".

Active caspase-3 is removed from cells by release of caspase-3-enriched vesicles

Cleavage of Rho associated Coiled Coil kinase I (ROCK I) by caspase-3 contributes to membrane blebbing. Whether caspase-3 and ROCK I also play a role in the release of membrane vesicles is unknown. Therefore, we transfected a human breast cancer cell line (MCF-7) that is caspase-3 deficient, lacks membrane blebbing, and does not release membrane vesicles, with caspase-3. Cells expressing caspase-3 demonstrate both ROCK I-mediated membrane blebbing, and release of small (400-600nm) membrane vesicles in a ROCK I-independent manner. These membrane vesicles contain caspase-3, and are enriched in caspase-3 activity compared to the releasing cells. Caspase-3-containing vesicles are taken up by untransfected cells but the cells do not show any sign of apoptosis. In conclusion, we show that the release of caspase-3-enriched membrane vesicles and membrane blebbing are two differentially regulated processes. Furthermore, we hypothesize that packaging of caspase-3 into membrane vesicles contributes to cellular homeostasis by the removal of caspase-3, and concurrently, protects the cells' environment from direct exposure to caspase-3 activity.

Single vs. swarm detection of microparticles and exosomes by flow cytometry

BACKGROUND

Microparticles and exosomes are cell-derived vesicles and potential biomarkers for disease. Recently, the Scientific Standardization Committee collaborative workshop of the ISTH initiated standardization of vesicle detection by flow cytometry with polystyrene beads. Because polystyrene beads have different optical properties from biological vesicles, and because the mechanisms causing the detection signal are incompletely understood, there are contradictions between expected and observed results.

OBJECTIVES

To develop a model with which to relate the detection signal of a flow cytometer to the diameter of vesicles and clarify observed discrepancies.

METHODS

We combined measurements of polystyrene and silica beads with an estimated refractive index of vesicles and performed Mie calculations of light scattering.

RESULTS

We established the relationship between measured light scattering and the diameter of vesicles. The Megamix gating strategy proposed by the Scientific Standardization Committee selects single vesicles and cells with diameters between 800 and 2400 nm when applied on the forward-scattering detector of regular flow cytometers. Nevertheless, we demonstrated that, irrespective of the applied gating, multiple vesicles smaller than 220 nm or multiple 89-nm silica beads were counted as a single event signal at sufficiently high concentrations.

CONCLUSIONS

Vesicle detection by flow cytometry is attributed to large single vesicles and swarm detection of smaller vesicles; that is, multiple vesicles are simultaneously illuminated by the laser beam and counted as a single event signal. Swarm detection allows the detection of smaller vesicles than previously thought possible, and explains the finding that flow cytometry underestimates the concentration of vesicles.

Coagulation activation and microparticle-associated coagulant activity in cancer patients. An exploratory prospective study

Cancer increases the risk of venous thromboembolism (VTE). Here, we investigated the contribution of microparticle (MP)-dependent procoagulant activity to the prothrombotic state in these patients. In 43 cancer patients without VTE at study entry and 22 healthy volunteers, markers of in vivo and MP-dependent coagulation were measured and patients were prospectively followed for six months for the development of VTE. Procoagulant activity of MPs was measured in vitro using a tissue factor (TF)-independent phospholipid dependent test, a factor Xa-generation assay with and without anti-TF, and a fibrin generation test (FGT) with and without anti-factor VII(a). Markers of in vivo coagulation activation and total number of MPs at baseline were significantly elevated in cancer patients compared to controls (F1+2 246 vs. 156 pM, thrombin-antithrombin complexes 4.1 vs. 3.0 mg/l, D-dimer 0.76 vs. 0.22 mg/l and 5.53 x 10⁶ vs. 3.37 x 10⁶ MPs/ml). Five patients (11.6%) developed VTE. Patients with VTE had comparable levels of coagulation activation markers and phospholipid-dependent MP procoagulant activity. However, median TF-mediated Xa-generation (0.82 vs. 0.21 pg/ml, p=0.016) and median VIIa-dependent FGT (13% vs. 0%, p=0.036) were higher in the VTE group compared with the non-VTE group. In this exploratory study the overall hypercoagulable state in cancer patients was not associated directly with the MP phospholipid-dependent procoagulant activity. However, in the patients who developed VTE within six months when compared to those who did not, an increased MP procoagulant activity was present already at baseline, suggesting this activity can be used to predict VTE.

The functions of microparticles in pre-eclampsia

Pre-eclampsia (P-EC), a heterogenic multisystem disorder characterized by hypertension and proteinuria, usually develops in the second half of pregnancy. The incidence is 2 to 5%, and P-EC is therefore a major cause of maternal and perinatal morbidity and mortality. Although the exact etiology is unknown, placental factors released into the maternal circulation lead to systemic maternal inflammation and endothelial dysfunction. Growing evidence indicates that placenta-derived microparticles, best known as syncytiotrophoblast microparticles (STBM), are important among these factors. This review provides an overview of the presence and function(s) of STBM and other cell-derived microparticles and exosomes.

Optical and non-optical methods for detection and characterization of microparticles and exosomes

Microparticles and exosomes are cell-derived microvesicles present in body fluids that play a role in coagulation, inflammation, cellular homeostasis and survival, intercellular communication, and transport. Despite increasing scientific and clinical interest, no standard procedures are available for the isolation, detection and characterization of microparticles and exosomes, because their size is below the reach of conventional detection methods. Our objective is to give an overview of currently available and potentially applicable methods for optical and non-optical determination of the size, concentration, morphology, biochemical composition and cellular origin of microparticles and exosomes. The working principle of all methods is briefly discussed, as well as their applications and limitations based on the underlying physical parameters of the technique. For most methods, the expected size distribution for a given microvesicle population is determined. The explanations of the physical background and the outcomes of our calculations provide insights into the capabilities of each method and make a comparison possible between the discussed methods. In conclusion, several (combinations of) methods can detect clinically relevant properties of microparticles and exosomes. These methods should be further explored and validated by comparing measurement results so that accurate, reliable and fast solutions come within reach.

Complement activation on the surface of cell-derived microparticles during cardiac surgery with cardiopulmonary bypass - is retransfusion of pericardial blood harmful?

OBJECTIVES

To investigate whether cell-derived microparticles play a role in complement activation in pericardial blood of patients undergoing cardiac surgery with cardiopulmonary bypass (CPB) and whether microparticles in pericardial blood contribute to systemic complement activation upon retransfusion.

METHODS

Pericardial blood of 13 patients was retransfused in 9 and discarded in 4 cases. Microparticles were isolated from systemic blood collected before anesthesia (T1) and at the end of CPB (T2), and from pericardial blood. The microparticles were analyzed by flow cytometry for bound complement components C1q, C4 and C3, and bound complement activator molecules C-reactive protein (CRP), serum amyloid P-component (SAP), immunoglobulin (Ig)M and IgG. Fluid-phase complement activation products (C4b/c, C3b/c) and activator molecules were determined by ELISA.

RESULTS

Compared with systemic T1 blood, pericardial blood contained increased C4b/c and C3b/c, and increased levels of microparticles with bound complement components. In systemic T1 samples, microparticle-bound CRP, whereas in pericardial blood, microparticle-bound SAP and IgM were associated with complement activation. At the end of CPB, increased C3b/c (but not C4b/c) was present in systemic T2 blood compared with T1, while concentrations of microparticles binding complement components and of those binding complement activator molecules were similar. Concentrations of fluid-phase complement activation products and microparticles were similar in patients whether or not retransfused with pericardial blood.

CONCLUSIONS

In pericardial blood of patients undergoing cardiac surgery with CPB, microparticles contribute to activation of the complement system via bound SAP and IgM. Retransfusion of pericardial blood, however, does not contribute to systemic complement activation.

C-reactive protein in myocardial infarction binds to circulating microparticles but is not associated with complement activation

BACKGROUND

C-reactive protein (CRP) is elevated in patients with acute myocardial infarction (AMI). When CRP binds to membrane phospholipids or Fc receptors, it activates the complement system. Recent studies show that CRP can be exposed on cell-derived microparticles (MP) and is associated complement activation.

OBJECTIVES

We studied complement activation on circulating MP in AMI patients and healthy controls.

METHODS

MP were isolated from plasma of AMI patients (n=21) and sex- and age-matched healthy individuals (n=10), and analyzed by flow cytometry for bound complement components (C1q, C4, C3) and complement inhibitor and activator molecules (C4bp, CRP, serum amyloid P component, immunoglobulins IgM and IgG). Concurrently, the levels of fluid phase complement activation products and inhibitor and activator molecules were determined.

RESULTS

Fluid phase CRP, MP with bound CRP (CRP + MP), and C3 activation products were elevated in AMI patients compared to controls (P=0.032, P=0.031 and P=0.023, respectively), and fluid phase CRP correlated with CRP+ MP (r=0.84, P<0.001). Although CRP+ MP were elevated, they were not associated with C1q+ MP (r=0.32, P=0.174). In contrast, IgG+ MP were associated with C1q+ MP (r=0.73, P<0.001), C4+ MP and C3+ MP (r=0.78 and r=0.87, respectively; both P<0.001), and C4bp (r=0.63, P=0.004). In healthy individuals, CRP+ MP were strongly associated with C1q+ MP (r=0.82, P=0.007), which in turn were associated with C4+ MP and C3+ MP (r=0.68, P=0.032 and r=0.68, P=0.031, respectively).

CONCLUSIONS

Despite CRP-associated complement activation on the surface of MP in healthy individuals and a strong correlation between MP-bound CRP and fluid phase CRP in AMI patients, the MP-associated complement activation is IgG- but not CRP-dependent in AMI patients.

Phospholipid composition of in vitro endothelial microparticles and their in vivo thrombogenic properties

INTRODUCTION

Microparticles from activated endothelial cells (EMP) are well known to expose tissue factor (TF) and initiate coagulation in vitro. TF coagulant activity is critically dependent on the presence of aminophospholipids, such as phosphatidylserine (PS) and phosphatidylethanolamine (PE), but it is unknown whether or not TF-exposing EMP are enriched in such aminophospholipids. Furthermore, despite the fact that EMP have been reported in several pathological conditions, direct evidence for their (putative) coagulant properties in vivo is still lacking. We investigated the phospholipid composition of endothelial MP (EMP) and their thrombogenic properties in vivo.

MATERIALS AND METHODS

Human umbilical vein endothelial cells (HUVEC; n=3) were incubated with or without interleukin (IL)-1alpha (5 ng/mL; 0-72 h). Phospholipid composition of EMP was determined by high-performance thin layer chromatography. The association between EMP, TF antigen and activity was confirmed in vitro (ELISA, Western blot and thrombin generation). Thrombogenic activity of EMP in vivo was determined in a rat venous stasis model.

RESULTS

Levels of TF antigen increased 3-fold in culture medium of IL-1alpha-treated cells (P<0.0001). This TF antigen was associated with EMP and appeared as a 45-47 kDa protein on Western blot. In addition, EMP from activated cells were enriched in both PS (P<0.0001) and PE (P<0.0001), and triggered TF-dependent thrombin formation in vitro and thrombus formation in vivo. In contrast, EMP from control cells neither initiated coagulation in vitro nor thrombus formation in vivo.

CONCLUSIONS

EMP from activated endothelial cells expose coagulant tissue factor and are enriched in its cofactors PS and PE.

Cell-Derived Microparticles and Complement Activation in Preeclampsia Versus Normal Pregnancy

BACKGROUND

Inflammation plays a major role in the vascular dysfunction seen in preeclampsia, and several studies suggest involvement of the complement system.

OBJECTIVES

To investigate whether complement activation on the surface of microparticles is increased in plasma of preeclamptic patients versus healthy pregnant controls.

METHODS

Microparticles from plasma of preeclamptic (n=10), healthy pregnant (n=10) and healthy nonpregnant (n=10) women were analyzed by flow cytometry for bound complement components (C1q, C4, C3) and complement activator molecules (C-reactive protein [CRP], serum amyloid P component [SAP], immunoglobulin [Ig]M, IgG). Fluid phase complement activation products and activator molecules were also determined.

RESULTS

Levels of microparticles with bound complement components showed no increase in complement activation on the microparticle surface in preeclamptic women, in line with levels of fluid phase complement activation products. In healthy nonpregnant and pregnant women, bound CRP was associated with classical pathway activation on the microparticle surface, and in healthy pregnant women IgM and IgG molecules also contributed. In preeclamptic women, microparticles with bound SAP and those with IgG seemed to contribute to C1q binding without a clear association to further classical pathway activation. Furthermore, significantly increased levels of microparticles with bound CRP were present in preeclamptic compared with healthy pregnant women (median 178x10(6)/L versus 47x10(6)/L, P<0.01), but without concomitant increases in complement activation.

CONCLUSIONS

We found no evidence of increased complement activation on the microparticle surface in preeclamptic women. Microparticles with bound CRP were significantly increased, but in contrast to healthy pregnant and nonpregnant women, this was not associated with increased classical pathway activation on the surface of the microparticles.

Lorenzo's oil and platelet activation in adrenomyeloneuropathy and asymptomatic X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD) is an inherited disorder of peroxisomal beta-oxidation, which results in accumulation of very long-chain fatty acids, causing damage to the nervous system, adrenal cortex and testis. The two most frequent phenotypes are childhood cerebral adrenoleukodystrophy (CCALD) and adrenomyeloneuropathy (AMN). Some affected males demonstrate no clinical signs (asymptomatic ALD), whereas female carriers can also be affected. Patients with X-ALD have been treated with Lorenzo's oil, a 4:1 combination of oleic acid and erucic acid, with thrombocytopenia as the main side effect and sometimes leading to a hemorrhagic diathesis. We studied platelet count, size and membrane surface exposure of platelet activation antigens in 17 adult X-ALD patients. Eight patients used the prescribed amount of erucic acid (as glyceroltrierucate) or more (very compliant), five used less(compliant), and four did not use the diet. All eight very compliant patients had highly enlarged platelets and seven manifested thrombocytopenia. An enhanced in vivo platelet activation status was established by increased platelet surface expression of P-selectin (CD62P, PADGEM, GMP-140) in five of the seven thrombocytopenic patients, and of increased fibrinogen receptor exposure (measured with the antibody PAC-1) in three of these five patients. The other nine compliant or untreated patients had normal platelet counts and, generally, normal P-selection and fibrinogen receptor expression. A diet-induced 7- to 27-fold enrichment of erucic acid was observed in the platelets of the four patients studied. We conclude that the thrombocytopenia in AMN patients using Lorenzo'soil is associated with circulating platelets that have an increased erucic acid content, size and activation status. We hypothesize that the erucic acid in some way induces the increased size and thus, directly or indirectly, increased platelet activation or instability in vivo. This then causes the thrombocytopenia, with circulating platelets representing a population that has not yet been sufficiently changed to be removed, but has clear signs of activation.

Two consecutive high-fat meals affect endothelial-dependent vasodilation, oxidative stress and cellular microparticles in healthy men

BACKGROUND

A large body of evidence has accumulated indicating a relation between postprandial hyperglycemia and hypertriglyceridemia, and the risk of cardiovascular disease.

OBJECTIVE

We studied possible mechanisms underlying the postprandial proatherogenic state by exposing healthy males to two consecutive high-fat mixed meals.

PATIENTS/METHODS

Seventeen healthy males [age 25.4 +/- 3 years, body mass index 23.6 +/- 2 kg m(-2)] were studied during two randomized visits. During the meal visit, subjects consumed standardized meals (50 g of fat, 55 g of carbohydrates and 30 g of proteins) as breakfast and 4 h later as lunch. During the control visit, subjects remained fasted. Prior to each blood collection (before and every 2 h after the first meal), flow-mediated dilation (FMD) of the brachial artery was measured.

RESULTS

Although within the normal range, postprandial plasma glucose and triacylglycerol concentrations increased significantly, especially after the second meal, as compared with baseline (4.8 +/- 0.3 to 5.4 +/- 0.4, 0.8 +/- 0.2 to 1.7 +/- 0.7 mmol L(-1), respectively; both P < 0.05) and the fasting visit. After the second meal, FMD was significantly impaired (6.9% vs. 3.7%, P < 0.05) whereas oxidized low-density lipoprotein (oxLDL)/LDL cholesterol ratio and malondialdehyde concentrations were markedly elevated (both P < 0.01). Finally, an increase in total microparticle (MP) numbers was observed during the meal visit (P < 0.05).

CONCLUSIONS

In healthy males, after two consecutive fat-rich meals, mild elevations in plasma glucose and triacylglycerol were paralleled by impaired FMD, increased markers of oxidative stress and circulating MPs, in particular, after the second meal. These findings may have consequences for subjects with postprandial dysmetabolism, including those with Type 2 diabetes.

The phospholipid composition and cholesterol content of platelet-derived microparticles: a comparison with platelet membrane fractions

BACKGROUND

The processes that govern the distribution of molecules between platelets and the microparticles (MP) they release are unknown. Certain proteins are sorted selectively into MP, but lipid sorting has not been studied.

OBJECTIVES

To compare the phospholipid composition and cholesterol content of platelet-derived MP obtained with various stimuli with that of isolated platelet membrane fractions.

METHODS

Washed platelets from venous blood of healthy individuals (n = 6) were stimulated with collagen, thrombin, collagen plus thrombin, or A23187. Platelet activation, MP release and antigen exposure were assessed by flow cytometry. MPs were isolated by differential centrifugation. Platelet plasma-, granule- and intracellular membranes were isolated from platelet concentrates (n = 3; 10 donors each) by pressure homogenization and Percoll density gradient fractionation. The phospholipid composition and cholesterol content of MPs and membrane fractions were analyzed by high performance thin layer chromatography.

RESULTS

The phospholipid composition of MPs was intermediate compared with that of platelet plasma- and granule membranes, and differed significantly from that of intracellular membranes. There were small but significant differences in phospholipid composition between the MPs produced by the various agonists, which paralleled differences in P-selectin exposure in case of the physiological agonists collagen, thrombin, or collagen plus thrombin. The cholesterol content of MPs tended to be higher than that of the three-platelet membrane fractions.

CONCLUSIONS

Regarding its phospholipid content, the MP membrane is a composite of the platelet plasma- and granule membranes, showing subtle differences depending on the platelet agonist. The higher cholesterol content of MPs suggests their enrichment in lipid rafts.