Platelet Extracellular Vesicles Research Articles

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

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.

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, VO 2peak: 15.4 ± 0.6 mL/kg/min, BMI: 34.1 ± 1.7 kg/m2) and PF (n = 13, VO 2peak: 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 VO 2peak (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.

Initiation and Propagation of Vascular Calcification Is Regulated by a Concert of Platelet- and Smooth Muscle Cell-Derived Extracellular Vesicles.

The ageing population continues to suffer from its primary killer, cardiovascular disease (CVD). Despite recent advances in interventional medicinal and surgical therapies towards the end of the 20th century, the epidemic of cardiovascular disease has not been halted. Yet, rather than receding globally, the burden of CVD has risen to become a top cause of morbidity and mortality worldwide. Most CVD arises from thrombotic rupture of an atherosclerotic plaque, the pathologic thickening of coronary and carotid artery segments and subsequent distal ischemia in heart or brain. In fact, one-fifth of deaths are directly attributable to thrombotic rupture of a vulnerable plaque. Atherosclerotic lesion formation is caused by a concert of interactions between circulating leukocytes and platelets, interacting with the endothelial barrier, signalling into the arterial wall by the release of cytokines and extracellular vesicles (EVs). Both platelet- and cell-derived EVs represent a novel mechanism of cellular communication, particularly by the transport and transfer of cargo and by reprogramming of the recipient cell. These interactions result in phenotypic switching of vascular smooth muscle cells (VSMCs) causing migration and proliferation, and subsequent secretion of EVs. Loss of VSMCs attracts perivascular Mesenchymal Stem Cells (MSCs) from the adventitia, which are a source of VSMCs and contribute to repair after vascular injury. However, continuous stress stimuli eventually switch phenotype of cells into osteochondrogenic VSMCs facilitating vascular calcification. Although Virchow’s triad is over 100 years old, it is a reality that is accurate today. It can be briefly summarised as changes in the composition of blood (platelet EVs), alterations in the vessel wall (VSMC phenotypic switching, MSC infiltration and EV release) and disruption of blood flow (atherothrombosis). In this paper, we review the latest relevant advances in the identification of extracellular vesicle pathways as well as VSMCs and pericyte/MSC phenotypic switching, underlying vascular calcification.

Procoagulant Effects of Low-Level Platelet Activation and Its Inhibition by Colchicine.

Platelets play an important role in diseases such as cardiovascular disease and cancer, especially through their release of extracellular vesicles (EVs) and role in thrombosis. The effects of the anti-inflammatory drug colchicine on platelets are not well understood. We investigated the effect of colchicine on the release of pro-coagulant EVs from platelets under low-level activation. Citrated platelet-rich plasma (PRP) from healthy donors was incubated with 2 mM colchicine or vehicle at 37°C for 30 minutes with gentle rotation. The incubation conditions caused mild platelet activation (expression of CD62P and increased surface lactadherin binding) and release of EVs expressing phosphatidylserine (PS, measured by binding of lactadherin), CD61 and CD62P, both of which were attenuated by colchicine. The incubation conditions shortened the delay to fibrin generation and this correlated with elevated levels of PS+/CD61+ EVs. Removal of EVs from plasma abrogated clot formation in the overall haemostatic potential (OHP) assay. Colchicine decreased levels of both PS+/CD61+ and CD62P+ EVs and abrogated the shortened delay to fibrin generation achieved by platelet activation. Similar results were observed after incubation of PRP with 200 µM vinblastine, suggesting a microtubular effect. An alternative method of platelet activation using platelet agonists 20 µM ADP or 10 µM epinephrine also increased CD62P+ EV levels, and this too was attenuated by prior incubation with colchicine. Our novel findings demonstrate procoagulant effects of low-level platelet activation and EV formation which are inhibited by colchicine.

Dissecting the biochemical architecture and morphological release pathways of the human platelet extracellular vesiculome.

Platelet extracellular vesicles (PEVs) have emerged as potential mediators in intercellular communication. PEVs exhibit several activities with pathophysiological importance and may serve as diagnostic biomarkers. Here, imaging and analytical techniques were employed to unveil morphological pathways of the release, structure, composition, and surface properties of PEVs derived from human platelets (PLTs) activated with the thrombin receptor activating peptide (TRAP). Based on extensive electron microscopy analysis, we propose four morphological pathways for PEVs release from TRAP-activated PLTs: (1) plasma membrane budding, (2) extrusion of multivesicular α-granules and cytoplasmic vacuoles, (3) plasma membrane blistering and (4) "pearling" of PLT pseudopodia. The PLT extracellular vesiculome encompasses ectosomes, exosomes, free mitochondria, mitochondria-containing vesicles, "podiasomes" and PLT "ghosts". Interestingly, a flow cytometry showed a population of TOM20+LC3+ PEVs, likely products of platelet mitophagy. We found that lipidomic and proteomic profiles were different between the small PEV (S-PEVs; mean diameter 103nm) and the large vesicle (L-PEVs; mean diameter 350nm) fractions separated by differential centrifugation. In addition, the majority of PEVs released by activated PLTs was composed of S-PEVs which have markedly higher thrombin generation activity per unit of PEV surface area compared to L-PEVs, and contribute approximately 60% of the PLT vesiculome procoagulant potency.

Hairy Platelet-Derived Extracellular Vesicles Promote Lung Vaso-Occlusion in Sickle Cell Disease

Background: Acute chest syndrome (ACS) is a type of acute lung injury and the leading cause of mortality in Sickle Cell Disease (SCD). Current treatments for ACS are primarily supportive, and there is a critical need for rescue therapies. ACS is often a sequela of acute systemic vaso-occlusive crisis and preceded by thrombocytopenia. However, the role of platelets in the pathogenesis of ACS remains largely unknown.Methods: We used our validated model of vaso-occlusive crisis in transgenic, humanized SCD mice, which is triggered by intravenous challenge with nanogram levels of the TLR4 ligand, lipopolysaccharide (LPS). Platelet-neutrophil aggregates and blood flow in the lung microcirculation was visualized in real time in vivo, using multi-photon-excitation microscopy of intact lung in live SCD mice. SCD or control human blood was perfused through microfluidic channels in vitro and neutrophil-platelet aggregation was visualized using fluorescence microscopy. Platelet derived extracellular vesicles were characterized using nanoparticle tracking and biochemical approaches.Results: We have made a novel finding that the arrest of blood flow and injury in the lung is secondary to blockade of pulmonary arterioles by platelet-neutrophil aggregates. Using in vitro microfluidic studies, we confirmed that platelet-neutrophil aggregation is higher in LPS-treated SCD patient blood compared with healthy controls, and this correlates with increased numbers of platelet-derived extracellular vesicles (EVs) that express IL-1β. Our studies also reveal that platelet-neutrophil aggregation in pulmonary arterioles of SCD mice is associated with an increase in peripheral blood levels of platelet-derived EVs containing IL-1β. Remarkably, inhibition of TLR4 or TLR4/NLRP3-inflammasome activated caspase-1, or inhibition of IL-1β signaling, attenuated release of platelet EVs and platelet-neutrophil aggregation in the lung arterioles of SCD mice in vivo and SCD human blood in vitro .Conclusions: TLR4 and NLRP3-inflammasome-mediated caspase-1 activation in platelets during vaso-occlusive crisis leads to release of IL-1β-containing EVs into the circulation. These circulating platelet EVs promote platelet-neutrophil aggregation in pulmonary arterioles, which results in arrest of blood flow in the lung, leading to ACS. Therapeutic inhibition of TLR4/NLRP3-caspase-1 signaling in platelets or IL-1β signaling is a potential therapy for ACS in SCD patients.Acknowledgments: This study was supported by 1R01HL128297-01 (P.S.) and VMI startup funds (P.S.). DisclosuresNo relevant conflicts of interest to declare.

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

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

Different Potential of Extracellular Vesicles to Support Thrombin Generation: Contributions of Phosphatidylserine, Tissue Factor, and Cellular Origin

Cells release diverse types of vesicles constitutively or in response to proliferation, injury, inflammation, or stress. Extracellular vesicles (EVs) are crucial in intercellular communication, and there is emerging evidence for their roles in inflammation, cancer, and thrombosis. We investigated the thrombogenicity of platelet-derived EVs, which constitute the majority of circulating EVs in human blood, and assessed the contributions of phosphatidylserine and tissue factor exposure on thrombin generation. Addition of platelet EVs to vesicle-free human plasma induced thrombin generation in a dose-dependent manner, which was efficiently inhibited by annexin V, but not by anti-tissue factor antibodies, indicating that it was primarily due to the exposure of phosphatidylserine on platelet EVs. Platelet EVs exhibited higher thrombogenicity than EVs from unstimulated monocytic THP-1 cells, but blockade of contact activation significantly reduced thrombin generation by platelet EVs. Stimulation of monocytic cells with lipopolysaccharide enhanced their thrombogenicity both in the presence and in the absence of contact activation, and thrombin generation was efficiently blocked by anti-tissue factor antibodies. Our study provides evidence that irrespective of their cellular origin, EVs support the propagation of coagulation via the exposure of phosphatidylserine, while the expression of functional tissue factor on EVs appears to be limited to pathological conditions.

Metabolomic Profiling of Extracellular Vesicles and Alternative Normalization Methods Reveal Enriched Metabolites and Strategies to Study Prostate Cancer-Related Changes.

Body fluids are a rich source of extracellular vesicles (EVs), which carry cargo derived from the secreting cells. So far, biomarkers for pathological conditions have been mainly searched from their protein, (mi)RNA, DNA and lipid cargo. Here, we explored the small molecule metabolites from urinary and platelet EVs relative to their matched source samples. As a proof-of-concept study of intra-EV metabolites, we compared alternative normalization methods to profile urinary EVs from prostate cancer patients before and after prostatectomy and from healthy controls.Methods: We employed targeted ultra-performance liquid chromatography-tandem mass spectrometry to profile over 100 metabolites in the isolated EVs, original urine samples and platelets. We determined the enrichment of the metabolites in the EVs and analyzed their subcellular origin, pathways and relevant enzymes or transporters through data base searches. EV- and urine-derived factors and ratios between metabolites were tested for normalization of the metabolomics data.Results: Approximately 1 x 1010 EVs were sufficient for detection of metabolite profiles from EVs. The profiles of the urinary and platelet EVs overlapped with each other and with those of the source materials, but they also contained unique metabolites. The EVs enriched a selection of cytosolic metabolites including members from the nucleotide and spermidine pathways, which linked to a number of EV-resident enzymes or transporters. Analysis of the urinary EVs from the patients indicated that the levels of glucuronate, D-ribose 5-phosphate and isobutyryl-L-carnitine were 2-26-fold lower in all pre-prostatectomy samples compared to the healthy control and post-prostatectomy samples (p < 0.05). These changes were only detected from EVs by normalization to EV-derived factors or with metabolite ratios, and not from the original urine samples.Conclusions: Our results suggest that metabolite analysis of EVs from different samples is feasible using a high-throughput platform and relatively small amount of sample material. With the knowledge about the specific enrichment of metabolites and normalization methods, EV metabolomics could be used to gain novel biomarker data not revealed by the analysis of the original EV source materials.

HSP70 Is Increased in Circulating Extracellular Vesicles from Transfusion-Dependent β-Thalassemia Patients: Potential Biomarker for Ineffective Erythropoiesis

Heat-shock protein 70 (HSP70) is a chaperone protein involved in cellular protein homeostasis. It protects proteins from, or targets them for degradation, regulates the cellular response against stress injury, and has a key role in erythropoiesis. In β-thalassemia (β-TM) erythroblasts, HSP70 is retained in the cytoplasm by free α-globin chains; the transcription factor GATA1 is unprotected in the nucleus and therefore degraded, resulting in erythroblast apoptosis, which further aggravates the ineffective erythropoiesis observed in β-TM (Arlet et al, Nature 2014). Extracellular vesicles (EVs) are secreted from cells and are involved in intercellular communication and transport of biologically active molecules. The current study aimed to explore HSP70 in EVs as a potential biomarker in β-TM.EVs of 35 transfusion-dependent β-TM children and adults and matched healthy controls were characterized. Patients were treated under a standard protocol at Emek Medical Center. Clinical and laboratory data were collected from patients' files.EV count, cellular origin and membrane antigens were evaluated in platelet-poor plasma (PPP) by nanoparticle tracking analysis to assess concentration and size distribution of particles in the diameter range of 50-1000 nm, and by FACS to visualize >500 nm particles.Protein content was evaluated in EV pellets (obtained from centrifugation of PPP for 1 h, 18,000g at 4°C, washing in PBS and recentrifugation). Human protein antibody arrays for angiogenesis, inflammation and apoptosis were used to evaluate pooled EV pellets obtained from controls and patient subgroups: hypersplenism (Hy), No-Hy and splenectomized (Sp). The level of HSP70 was evaluated by ELISA.Nanoparticle tracking analysis demonstrated a sharp increase in EV concentration in patients vs. controls (2.15 ± 1.1 vs. 0.66 ± 0.2 E+9 particles/μl; P< 0.001), with mean sizes of 91.9 ± 22 nm and 80.1 ± 6.4 nm, respectively. The concentration of annexin-V-labeled EVs was slightly higher in patients than in controls (7.5 ± 11 vs. 2 ± 0.6 E+5 particles/μl), with mean sizes of 261.6 ± 74 nm and 295.6 ± 140 nm, respectively.FACS analysis showed significantly lower RBC (CD235+) EV and CD14+ EV levels in patients vs. controls. Similar percentages of platelet EVs (CD41+), activated platelet EVs (CD62P+), endothelial cell EVs (CD31+41-) and leukocyte EVs (CD11+) were found in patients and controls.We found significant differences in several angiogenic/inflammatory proteins between the patients and controls. Increased levels (over 200%) of 11 proteins were observed in the Sp group, among them growth-regulated oncogene and platelet-derived growth factor BB, while levels of only 3 proteins were increased in Hy and No-Hy groups. Levels of 14 proteins seemed to decrease (less than 75%) in Hy and No-Hy groups, whereas 5 proteins decreased in the Sp group. Several differences in the apoptotic protein profile were found between patients and controls; however a uniform pattern was observed in the patient subgroups. Increased levels of insulin-like growth factor-binding protein (IGFBP) 2 and caspase 8, decreased levels of IGFBP 3 and 6, and a high increase in HSP70 were found.The increased HSP70 levels were validated in the study cohort: patients (n = 32) 3.46 ± 3 ng/ml vs. healthy controls (n = 11) 1.7 ± 0.2 ng/ml; P< 0.0001. HSP70 showed a moderate positive correlation with patients’ reticulocyte count and lactate dehydrogenase (n = 31, R = 0.47 and n = 32, R = 0.43, respectively) and a moderate negative correlation with hemoglobin (Hb) levels (study Hb n = 32, R = -0.4 and mean 5-yr Hb n = 31, R = -0.51) and annual transfusion requirement (mL /kg weight) (n = 29, R = -0.48). Thus HSP70 reflects the degree of ineffective erythropoiesis, hemolysis and severity of anemia in patients. However, no correlation was found with iron-overload parameters (iron, transferrin saturation and ferritin).Overall, important differences were found between the properties of patient and control EVs, probably reflecting and affecting the pathophysiology of β-TM. We show that circulating EVs in β-TM contain high levels of HSP70 that are correlated with hematological disease severity but not with iron-overload status. These results create a foundation for the potential use of HSP70 in circulating EVs as a novel biomarker for monitoring ineffective erythropoiesis in β-TM. Further studies are required to explore the consequences of high HSP70 in β-TM EVs. DisclosuresNo relevant conflicts of interest to declare.

Abstract 355: Progenitor Cells and Extracellular Vesicles as Biomarkers for Vasculitis

Background: Patients with vasculitis (VS) have complex organ- and life-threatening disease manifestations due to autoimmune-mediated inflammatory vascular damage and an increased risk of cardiovascular disease (CVD). Accurate biomarkers do not exist for VS. Cells release extracellular vesicles (EVs) in the setting of activation, injury, or death. In patients with diabetes mellitus and CVD, the effects of the inflammatory cascade, platelets and endothelium, positively correlate with levels of EVs bearing receptors for CD3, CD41, or CD105, and negatively correlate with levels of circulating endothelial progenitor cells (CPCs). Because VS is characterized by systemic inflammation, platelet activation and endothelial damage, this group of diseases may have unique effects on EVs and CPCs. This study evaluated a high dimensional flow cytometry approach to profiling EVs and CPCs in plasma to discern a biomarker pattern in VS. Methods: Levels of CPCs and EVs were measured with a panel of cell surface markers in 10 VS patients and 5 age-similar healthy controls (HC). Data were acquired on a modified Becton Dickinson FACSCanto. Results: Although no significant increase in CPCs in VS compared with HC was detected, the standard deviation of CPC levels in VS was more than double that in HC (SD=574 vs. 165, p=0.081), suggesting heterogeneity in the VS group. EV subsets with lower concentrations in VS, compared with HC, included: Annexin + CD3 + double-positive T Lymphocyte (p=0.026) and CD105 + CD64 + double-positive activated Macrophage (p=0.030). CD144 + CD105 + double-positive endothelial EVs were only detected in a subset of VS and not in HC. CD31 + CD41a + double-positive platelet EVs were increased in VS compared with HC (894 (580) vs. 416 (128), p=0.004). Conclusion: This proof of concept study discovered a distinct EV pattern that correlates with a diagnosis of VS, suggesting that cell- and vesicle-based assays could be useful biomarkers in evaluating VS. This pattern is different from that found in patients with diabetes mellitus and CVD. Larger studies could seek to elucidate correlations between CPCs and disease activity and identify a unique EV signature for VS with increased risk for CVD.

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.

High‐density lipoprotein 3 and apolipoprotein A‐I alleviate platelet storage lesion and release of platelet extracellular vesicles

Stored platelet (PLT) concentrates (PLCs) for transfusion develop a PLT storage lesion (PSL), decreasing PLT viability and function with profound lipidomic changes and PLT extracellular vesicle (PL-EV) release. High-density lipoprotein 3 (HDL3 ) improves PLT homeostasis through silencing effects on PLT activation in vivo. This prompted us to investigate HDL3 and apolipoprotein A-I (apoA-I) as PSL-antagonizing agents. Healthy donor PLCs were split into low-volume standard PLC storage bags and incubated with native (n)HDL3 or apoA-I from plasma ethanol fractionation (precipitate IV) for 5 days under standard blood banking conditions. Flow cytometry, Born aggregometry, and lipid mass spectrometry were carried out to analyze PL-EV release, PLT aggregation, agonist-induced PLT surface marker expression, and PLT and plasma lipid compositions. Compared to control, added nHDL3 and apoA-I significantly reduced PL-EV release by up to -62% during 5 days, correlating with the added apoA-I concentration. At the lipid level, nHDL3 and apoA-I antagonized PLT lipid loss (+12%) and decreased cholesteryl ester (CE)/free cholesterol (FC) ratios (-69%), whereas in plasma polyunsaturated/saturated CE ratios increased (+3%) and CE 16:0/20:4 ratios decreased (-5%). Administration of nHDL3 increased PLT bis(monoacylglycero)phosphate/phosphatidylglycerol (+102%) and phosphatidic acid/lysophosphatidic acid (+255%) ratios and improved thrombin receptor-activating peptide 6-induced PLT aggregation (+5%). nHDL3 and apoA-I improve PLT membrane homeostasis and intracellular lipid processing and increase CE efflux, antagonizing PSL-related reduction in PLT viability and function and PL-EV release. We suggest uptake and catabolism of nHDL3 into the PLT open canalicular system. As supplement in PLCs, nHDL3 or apoA-I from Fraction IV of plasma ethanol fractionation have the potential to improve PLC quality to prolong storage.

Isolation and characterization of platelet-derived extracellular vesicles

BackgroundPlatelet-derived extracellular vesicles (EVs) participate, for example, in haemostasis, immunity and development. Most studies of platelet EVs have targeted microparticles, whereas exosomes and EV characterization under various conditions have been less analyzed. Studies have been hampered by the difficulty in obtaining EVs free from contaminating cells and platelet remnants. Therefore, we optimized an EV isolation protocol and compared the quantity and protein content of EVs induced by different agonists.MethodsPlatelets isolated with iodixanol gradient were activated by thrombin and collagen, lipopolysaccharide (LPS) or Ca2+ ionophore. Microparticles and exosomes were isolated by differential centrifugations. EVs were quantitated by nanoparticle tracking analysis (NTA) and total protein. Size distributions were determined by NTA and electron microscopy. Proteomics was used to characterize the differentially induced EVs.ResultsThe main EV populations were 100–250 nm and over 90% were <500 nm irrespective of the activation. However, activation pathways differentially regulated the quantity and the quality of EVs, which also formed constitutively. Thrombogenic activation was the most potent physiological EV-generator. LPS was a weak inducer of EVs, which had a selective protein content from the thrombogenic EVs. Ca2+ ionophore generated a large population of protein-poor and unselectively packed EVs. By proteomic analysis, EVs were highly heterogeneous after the different activations and between the vesicle subpopulations.ConclusionsAlthough platelets constitutively release EVs, vesiculation can be increased, and the activation pathway determines the number and the cargo of the formed EVs. These activation-dependent variations render the use of protein content in sample normalization invalid. Since most platelet EVs are 100–250 nm, only a fraction has been analyzed by previously used methods, for example, flow cytometry. As the EV subpopulations could not be distinguished and large vesicle populations may be lost by differential centrifugation, novel methods are required for the isolation and the differentiation of all EVs.

Multicolor Flow Cytometry and Nanoparticle Tracking Analysis of Extracellular Vesicles in the Plasma of Normal Pregnant and Pre-eclamptic Women1

Excessive release of syncytiotrophoblast extracellular vesicles (STBMs) from the placenta into the maternal circulation may contribute to the systemic inflammation that is characteristic of pre-eclampsia (PE). Other intravascular cells types (platelets, leukocytes, red blood cells [RBCs], and endothelium) may also be activated and release extracellular vesicles (EVs). We developed a multicolor flow cytometry antibody panel to enumerate and phenotype STBMs in relation to other EVs in plasma from nonpregnant (NonP) and normal pregnant (NormP) women, and women with late-onset PE. Nanoparticle tracking analysis (NTA) was used to determine EV size and concentration. In vitro-derived STBMs and EVs from platelets, leukocytes, RBCs, and endothelial cells were examined to select suitable antibodies to analyze the corresponding plasma EVs. Flow cytometry analysis of plasma from NonP, NormP, and PE showed that STBMs comprised the smallest group of circulating EVs, whereas most were derived from platelets. The next most abundant group comprised unidentified orphan EVs (which did not label with any of the antibodies in the panel), followed by EVs from RBCs and leukocytes. NTA showed that the total number of EVs in plasma was significantly elevated in NormP and late-onset PE women compared to NonP controls, and that EVs were smaller in size. In general, EVs were elevated in pregnancy plasma apart from platelet EVs, which were reduced. These studies did not show any differences in EVs between NormP and PE, probably because late-onset PE was studied.