Activated Platelet-Derived and Leukocyte-Derived Circulating Microparticles and the Risk of Thrombosis in Heparin-Induced Thrombocytopenia: A Role for PF4-Bearing Microparticles?

Cryptogenic ischemic stroke in cardiac transthyretin amyloidosis and sinus rhythm: a case report

Cardiac amyloidosis is a group of diseases characterized by the deposition of amyloid fibers in cardiac tissue. Two forms are mainly reported: light chain (AL) and transthyretin (ATTR) amyloidosis. Among the complications of transthyretin amyloidosis there are thrombotic events and, to a lesser extent, hemorrhagic events. The latter are likely caused by perivascular amyloid deposition resulting in capillary fragility, in addition to INR lability during anticoagulant therapy. The onset of thrombotic events may be caused by the high prevalence of atrial fibrillation (AF), mechanical cardiac dysfunction and atrial myopathy observed in patients with transthyretin amyloidosis. It remains unclear why thromboembolic events occur even in patients with sinus rhythm or adequate anticoagulation, though a hypercoagulable state or underlying inflammation may be involved. We report a case of cryptogenic ischemic stroke in an 86-year-old woman with transthyretin amyloidosis and sinus rhythm. Traditional coagulation tests, whole blood rotational thromboelastometry and impedance aggregometry did not show a hypercoagulable state. The thrombin generation assay did not reveal a prothrombotic state. However, the study of extracellular vesicles highlighted underlying immune-mediated endothelial damage likely responsible for the thrombotic diathesis. It could be hypothesized that inflammation plays a role in the hypercoagulability of patients with transthyretin amyloidosis. Larger prospective studies are needed to validate our hypothesis.

Distribution of Signal Peptides in Microvesicles from Activated Macrophage Cells

Extracellular vesicles, such as microvesicles (LEV) and exosomes (SEV), play an important role in intercellular signaling by encapsulating functional molecules and delivering them to specific cells. Recent studies showed that signal peptides (SPs), which are derived from sequences at the N-terminal of newly synthesized proteins, exhibited biological activity in the extracellular fluid. We previously reported that SPs were secreted into the extracellular fluid via SEV; however, it remains unclear whether the release of SPs occurs via LEV. In the present study, we demonstrated that SP fragments from human placental secreted alkaline phosphatase (SEAP) were present in LEV as well as SEV released from RAW-Blue cells, which stably express an NF-κB-inducible SEAP reporter. When RAW-Blue cells were treated with LPS at 0-10,000 ng/mL, SEAP SP fragments per particle were more abundant in LEV than in SEV, with fragments in LEV and SEV reaching a maximum at 1000 and 100 ng/mL, respectively. The content of SEAP SP fragments in LEV from IFNγ-stimulated RAW-Blue cells was higher than those from TNFα-stimulated cells, whereas that in SEV from TNFα-stimulated RAW-Blue cells was higher than those from IFNγ-stimulated cells. Moreover, the content of SEAP SP fragments in LEV and SEV decreased in the presence of W13, a calmodulin inhibitor. Collectively, these results indicate that the transportation of SP fragments to extracellular vesicles was changed by cellular activation, and calmodulin was involved in their transportation to LEV and SEV.

Long-term hypercoagulability, endotheliopathy and inflammation following acute SARS-CoV-2 infection

INTRODUCTION

both symptomatic and asymptomatic SARS-CoV-2 infections - coined Coronavirus disease 2019 (COVID-19) - have been linked to a higher risk of cardiovascular events after recovery.

AREAS COVERED

our review aims to summarize the latest evidence on the increased thrombotic and cardiovascular risk in recovered COVID-19 patients and to examine the pathophysiological mechanisms underlying the interplay among endothelial dysfunction, inflammatory response and coagulation in long-COVID. We performed a systematic search of studies on hypercoagulability, endothelial dysfunction and inflammation after SARS-CoV-2 infection.

EXPERT OPINION

endothelial dysfunction is a major pathophysiological mechanism responsible for most clinical manifestations in COVID-19. The pathological activation of endothelial cells by a virus infection results in a pro-adhesive and chemokine-secreting phenotype, which in turn promotes the recruitment of circulating leukocytes. Cardiovascular events after COVID-19 appear to be related to persistent immune dysregulation. Patients with long-lasting symptoms display higher amounts of proinflammatory molecules such as tumor necrosis factor-α, interferon γ and interleukins 2 and 6. Immune dysregulation can trigger the activation of the coagulation pathway. The formation of extensive microclots in vivo, both during acute COVID-19 and in long-COVID-19, appears to be a relevant mechanism responsible for persistent symptoms and cardiovascular events.

Mechanisms of Thrombosis in Heparin-Induced Thrombocytopenia and Vaccine-Induced Immune Thrombotic Thrombocytopenia

Heparin-induced thrombocytopenia (HIT) and vaccine-induced immune thrombotic thrombocytopenia (VITT) are rare, iatrogenic immune-mediated conditions with high rates of thrombosis-related morbidity and mortality. HIT is a long-recognized reaction to the administration of the common parenterally administered anticoagulant heparin (or its derivatives), while VITT is a new, distinct syndrome occurring in response to adenovirus-based vaccines against coronavirus disease 2019 and potentially other types of vaccines. A feature of both HIT and VITT is paradoxical thrombosis despite a characteristic low platelet count, mediated by the presence of platelet-activating antibodies to platelet factor 4. Several additional factors have also been suggested to contribute to clot formation in HIT and/or VITT, including monocytes, tissue factor, microparticles, endothelium, the formation of neutrophil extracellular traps, complement, procoagulant platelets, and vaccine components. In this review, we discuss the literature to date regarding mechanisms contributing to thrombosis in both HIT and VITT and explore the pathophysiological similarities and differences between the two conditions.

ABO O blood group as a risk factor for platelet reactivity in heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is an unpredictable, potentially catastrophic adverse effect resulting from an immune response to platelet factor 4 (PF4)/heparin complexes. We performed a genome-wide association study (GWAS) with positive functional assay as the outcome in a large discovery cohort of patients divided into 3 groups: (1) functional assay-positive cases (n = 1269), (2) antibody-positive (functional assay-negative) controls (n = 1131), and (3) antibody-negative controls (n = 1766). Significant associations (α = 5 × 10-8) were investigated in a replication cohort (α = 0.05) of functional assay-confirmed HIT cases (n = 177), antibody-positive (function assay-negative) controls (n = 258), and antibody-negative controls (n = 351). We observed a strong association for positive functional assay with increasing PF4/heparin immunoglobulin-G (IgG) level (odds ratio [OR], 16.53; 95% confidence interval [CI], 13.83-19.74; P = 1.51 × 10-209) and female sex (OR, 1.15; 95% CI, 1.01-1.32; P = .034). The rs8176719 C insertion variant in ABO was significantly associated with positive functional assay status in the discovery cohort (frequency = 0.41; OR, 0.751; 95% CI, 0.682-0.828; P = 7.80 × 10-9) and in the replication cohort (OR, 0.467; 95% CI, 0.228-0.954; P = .0367). The rs8176719 C insertion, which encodes all non-O blood group alleles, had a protective effect, indicating that the rs8176719 C deletion and the O blood group were risk factors for HIT (O blood group OR, 1.42; 95% CI, 1.26-1.61; P = 3.09 × 10-8). Meta-analyses indicated that the ABO association was independent of PF4/heparin IgG levels and was stronger when functional assay-positive cases were compared with antibody-positive (functional assay-negative) controls than with antibody-negative controls. Sequencing and fine-mapping of ABO demonstrated that rs8176719 was the causal single nucleotide polymorphism (SNP). Our results clarify the biology underlying HIT pathogenesis with ramifications for prediction and may have important implications for related conditions, such as vaccine-induced thrombotic thrombocytopenia.

Platelet and extracellular vesicles in COVID-19 infection and its vaccines

Platelets are at the crossroads between thrombosis and inflammation. When activated, platelets can shed bioactive extracellular vesicles [pEVs] that share the hemostatic potential of their parent cells and act as bioactive shuttles of their granular contents. In a viral infection, platelets are activated, and pEVs are generated with occasional virion integration. Both platelets and pEVs are engaged in a bidirectional interaction with neutrophils and other cells of the immune system and the hemostatic pathways. Severe COVID-19 infection is characterized by a stormy thromboinflammatory response with platelets and their EVs at the center stage of this reaction. This review sheds light on the interactions of platelets, pEVS and SARS-CoV-2 infection and prognostic and potential therapeutic role of pEVs. The review also describes the role of pEVs in the rare adenovirus-based COVID-19 vaccine-induced thrombosis thrombocytopenia.

Longitudinal Trend of Plasma Concentrations of Extracellular Vesicles in Patients Hospitalized for COVID-19

Plasma concentrations of extracellular vesicles (EVs) originating from cells involved in COVID-19-associated coagulopathy (CAC), their longitudinal trend and association with clinical outcomes were evaluated. Blood samples of consecutive COVID-19 patients admitted to a medical Unit were longitudinally collected within 48 h of admission, at discharge and 30 days post-discharge. EVs were analyzed using high sensitivity flow cytometry and phospholipid-dependent clotting time (PPL). The following EVs were measured: endothelium-, platelet-, leukocyte-derived, bearing tissue factor (TF)+, angiotensin-converting enzyme (ACE2)+, platelet-derived growth factor receptor-β (PDGF-β)+ and SARS-CoV-2-nucleoprotein (NP)+. 91 patients were recruited for baseline EV analysis (mean age 67 ± 14 years, 50.5% male) and 48 underwent the longitudinal evaluation. From baseline to 30-days post-discharge, we observed significantly decreased plasma concentrations of endothelium-derived EVs (E-Selectin+), endothelium-derived bearing TF (E-Selectin+ TF+), endothelium-derived bearing ACE2 (E-Selectin+ACE2+) and leukocyte-EVs bearing TF (CD45+TF+), p < 0.001, p = 0.03, p = 0.001, p = 0.001, respectively. Conversely, platelet-derived (P-Selectin+) and leukocyte-derived EVs (CD45+) increased from baseline to 30-days post-discharge (p = 0.038 and 0.032, respectively). EVs TF+, ACE2+, PDGF-β+, and SARS-CoV-2-NP+ did not significantly change during the monitoring. PPL increased from baseline to 30-days post-discharge (+ 6.3 s, p = 0.006). P-Selectin + EVs >1,054/µL were associated with thrombosis (p = 0.024), E-Selectin + EVs ≤531/µL with worsening/death (p 0.026) and 30-days P-Selectin+ and CD45 + EVs with persistent symptoms (p < 0.0001). We confirmed increased EVs originating from cells involved in CAC at admission and discharge. EVs derived from activated pericytes and expressing SARS-CoV-2-NP were also detected. 30-days post-discharge, endothelium-EVs decreased, while platelet- and leukocyte-EVs further increased, indicating that cellular activation persists long after the acute phase.

Vaccine-induced thrombotic thrombocytopenia following coronavirus vaccine: A narrative review

The novel coronavirus pandemic has taken a toll on the global healthcare systems and economy. Safety precautions, along with vaccination, are the most effective preventive measures. The global vaccination program against COVID-19 has dramatically reduced the number of deaths and cases. However, the incidence of thrombotic events and thrombocytopenia post-COVID-19 vaccination known as vaccine-induced thrombotic thrombocytopenia has raised safety concerns. This has led to an element of vaccine hesitancy. The exact mechanism for vaccine-induced thrombotic thrombocytopenia is unknown. Although the incidence of thrombosis associated with COVID-19 vaccination is low, it still requires attention, especially in older people, smokers, and people with preexisting comorbidities. This study aims to review the pathophysiology, diagnosis, and management of vaccine-induced thrombotic thrombocytopenia, to provide a concise and comprehensive update.

Mechanisms of Immunothrombosis by SARS-CoV-2

SARS-CoV-2 contains certain molecules that are related to the presence of immunothrombosis. Here, we review the pathogen and damage-associated molecular patterns. We also study the imbalance of different molecules participating in immunothrombosis, such as tissue factor, factors of the contact system, histones, and the role of cells, such as endothelial cells, platelets, and neutrophil extracellular traps. Regarding the pathogenetic mechanism, we discuss clinical trials, case-control studies, comparative and translational studies, and observational studies of regulatory or inhibitory molecules, more specifically, extracellular DNA and RNA, histones, sensors for RNA and DNA, as well as heparin and heparinoids. Overall, it appears that a network of cells and molecules identified in this axis is simultaneously but differentially affecting patients at different stages of COVID-19, and this is characterized by endothelial damage, microthrombosis, and inflammation.

Vaccine-induced immune thrombotic thrombocytopenia: current evidence, potential mechanisms, clinical implications, and future directions

Vaccine-induced immune thrombotic thrombocytopenia (VITT) (also termed thrombosis with thrombocytopenia syndrome or vaccine-induced thrombotic thrombocytopenia or vaccine-induced immune thrombocytopenia) is characterized by (i) venous or arterial thrombosis; (ii) mild-to-severe thrombocytopenia; (iii) positive antiplatelet factor 4 (PF4)-polyanion antibodies or anti-PF4-heparin antibodies detected by the HIT (heparin-induced thrombocytopenia) ELISA; (iv) occurring 5-30 days after ChAdOx1 nCoV-19 (AstraZeneca) or Ad26.COV2.S (Johnson & Johnson/Janssen) vaccination. VITT's incidence is 1 per 100 000 vaccinated people irrespective of age and up to 1 in 50 000 for people <50 years of age with the AstraZeneca COVID-19 vaccine. The exact mechanism by which adenovirus-vectored COVID-19 vaccines trigger this syndrome is still unclear, as for the increased risk for acute cerebral sinus venous thrombosis and splanchnic vein thrombosis as compared to other locations of venous thrombotic events. VITT is associated with the detection of anti-PF4 antibodies, unrelated to previous use of heparin therapy. PF4 antibodies are thought to activate platelets via the platelet FcγRIIA receptors leading to further platelet activation that causes thrombosis and thrombocytopenia.

The Role of P-Selectin in COVID-19 Coagulopathy: An Updated Review

In severe COVID-19, which is characterized by blood clots and neutrophil-platelet aggregates in the circulating blood and different tissues, an increased incidence of cardiovascular complications and venous thrombotic events has been reported. The inflammatory storm that characterizes severe infections may act as a driver capable of profoundly disrupting the complex interplay between platelets, endothelium, and leukocytes, thus contributing to the definition of COVID-19-associated coagulopathy. In this frame, P-selectin represents a key molecule expressed on endothelial cells and on activated platelets, and contributes to endothelial activation, leucocyte recruitment, rolling, and tissue migration. Briefly, we describe the current state of knowledge about P-selectin involvement in COVID-19 pathogenesis, its possible use as a severity marker and as a target for host-directed therapeutic intervention.

Research Advances in the Subtype of Sepsis-Associated Thrombocytopenia

The incidence and mortality of sepsis in the intensive care unit (ICU) are extremely high. Thrombocytopenia, one of the most common laboratory abnormalities, is correlated with prognosis in sepsis. The pathophysiology of sepsis-associated thrombocytopenia (SAT) remains unclear and may be associated with several factors such as platelet activation due to vascular injury and pathogen, suppression of bone marrow, platelet-targeted antibodies and desialylation. This review summarized all these possible mechanisms in the 3 subtypes of SAT: increased platelet consumption, reduced platelet production and increased platelet destruction. Based on the clinically available platelet parameters, the evidence for identifying SAT subtypes and the recent progress in treatments according to these subtypes are proposed to provide new prospects for the management of SAT.

Acute kidney injury is associated with increased levels of circulating microvesicles in patients with decompensated cirrhosis

BACKGROUND

Microvesicles (MVs) play a role in inflammation, coagulation, and vascular homeostasis in liver disease.

AIM

To characterize circulating plasma MVs profile in patients with decompensated cirrhosis and acute kidney injury (AKI).

METHODS

We measured the levels of total, endothelial, platelet, tissue factor (TF)+, leukocyte and hepatocyte MVs by new generation flow-cytometry in a prospective cohort of patients with decompensated cirrhosis with and without AKI.

RESULTS

Eighty patients with decompensated cirrhosis were recruited (40 each with and without AKI). Patients with cirrhosis with AKI had significantly higher calcein+ (total), endothelial, and platelet-MVs. Conversely, TF+, leukocyte, and hepatocyte-MVs were comparable between groups. Resolution of AKI was associated with significantly decreased total and endothelial-MVs that became comparable with those in patients without AKI. Platelet MVs significantly decreased but remained higher compared to patients without AKI. TF+MVs significantly decreased and became lower than patients without AKI. Leukocyte and hepatocyte-MVs remained unchanged. Creatinine (OR 4.3 [95%CI 1.8-10.7]), MELD (OR 1.13 [95%CI 1.02-1.27]), any bleeding (OR 9.07 [95%CI 2.02-40.6]), and hepatocyte-MVs (OR 1.04 [95%CI 1.02-1.07]) were independently associated with 30-day mortality.

CONCLUSION

AKI worsened vascular and cellular homeostasis in patients with cirrhosis, particularly by inducing endothelial dysfunction and platelet activation. AKI did not worsen systemic inflammation and hepatocytes activation.

PAR-4/Ca2+-calpain pathway activation stimulates platelet-derived microparticles in hyperglycemic type 2 diabetes

Background

Patients with type 2 diabetes (T2DM) have a prothrombotic state that needs to be fully clarified; microparticles (MPs) have emerged as mediators and markers of this condition. Thus, we investigate, in vivo, in T2DM either with good (HbA1c ≤ 7.0%; GGC) or poor (HbA1c > 7.0%; PGC) glycemic control, the circulating levels of MPs, and in vitro, the molecular pathways involved in the release of MPs from platelets (PMP) and tested their pro-inflammatory effects on THP-1 transformed macrophages.

Methods

In 59 T2DM, and 23 control subjects with normal glucose tolerance (NGT), circulating levels of CD62E+, CD62P+, CD142+, CD45+ MPs were determined by flow cytometry, while plasma levels of ICAM-1, VCAM-1, IL-6 by ELISA. In vitro, PMP release and activation of isolated platelets from GGC and PGC were investigated, along with their effect on IL-6 secretion in THP-1 transformed macrophages.

Results

We found that MPs CD62P⁺ (PMP) and CD142⁺ (tissue factor-bearing MP) were significantly higher in PGC T2DM than GGC T2DM and NGT. Among MPs, PMP were also correlated with HbA1c and IL-6. In vitro, we showed that acute thrombin exposure stimulated a significantly higher PMP release in PGC T2DM than GGC T2DM through a more robust activation of PAR-4 receptor than PAR-1 receptor. Treatment with PAR-4 agonist induced an increased release of PMP in PGC with a Ca²⁺-calpain dependent mechanism since this effect was blunted by calpain inhibitor. Finally, the uptake of PMP derived from PAR-4 treated PGC platelets into THP-1 transformed macrophages promoted a marked increase of IL-6 release compared to PMP derived from GGC through the activation of the NF-kB pathway.

Conclusions

These results identify PAR-4 as a mediator of platelet activation, microparticle release, and inflammation, in poorly controlled T2DM.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12933-021-01267-w.

Diets and Cellular-Derived Microparticles: Weighing a Plausible Link With Cerebral Small Vessel Disease

Cerebral small vessel disease (CSVD) represents a spectrum of pathological processes of various etiologies affecting the brain microcirculation that can trigger neuroinflammation and the subsequent neurodegenerative cascade. Prevalent with aging, CSVD is a recognized risk factor for stroke, vascular dementia, Alzheimer disease, and Parkinson disease. Despite being the most common neurodegenerative condition with cerebrocardiovascular axis, understanding about it remains poor. Interestingly, modifiable risk factors such as unhealthy diet including high intake of processed food, high-fat foods, and animal by-products are known to influence the non-neural peripheral events, such as in the gastrointestinal tract and cardiovascular stress through cellular inflammation and oxidation. One key outcome from such events, among others, includes the cellular activations that lead to elevated levels of endogenous cellular-derived circulating microparticles (MPs). MPs can be produced from various cellular origins including leukocytes, platelets, endothelial cells, microbiota, and microglia. MPs could act as microthrombogenic procoagulant that served as a plausible culprit for the vulnerable end-artery microcirculation in the brain as the end-organ leading to CSVD manifestations. However, little attention has been paid on the potential role of MPs in the onset and progression of CSVD spectrum. Corroboratively, the formation of MPs is known to be influenced by diet-induced cellular stress. Thus, this review aims to appraise the body of evidence on the dietary-related impacts on circulating MPs from non-neural peripheral origins that could serve as a plausible microthrombosis in CSVD manifestation as a precursor of neurodegeneration. Here, we elaborate on the pathomechanical features of MPs in health and disease states; relevance of dietary patterns on MP release; preclinical studies pertaining to diet-based MPs contribution to disease; MP level as putative surrogates for early disease biomarkers; and lastly, the potential of MPs manipulation with diet-based approach as a novel preventive measure for CSVD in an aging society worldwide.

Elevated Circulating Microparticle Subpopulations in Incidental Cerebral White Matter Hyperintensities: A Multimodal Study

Asymptomatic (or "silent") manifestations of cerebral small vessel disease (CSVD) are widely recognized through incidental findings of white matter hyperintensities (WMHs) as a result of magnetic resonance imaging (MRI). This study aims to examine the potential associations of surrogate markers for the evaluation of white matter integrity in CSVD among asymptomatic individuals through a battery of profiling involving QRISK2 cardiocerebrovascular risk prediction, neuroimaging, neurocognitive evaluation, and microparticles (MPs) titers. Sixty asymptomatic subjects (mean age: 39.83 ± 11.50 years) with low to moderate QRISK2 scores were recruited and underwent neurocognitive evaluation for memory and cognitive performance, peripheral venous blood collection for enumeration of selected MPs subpopulations, and 3T MRI brain scan with specific diffusion MRI (dMRI) sequences inclusive of diffusion tensor imaging (DTI). WMHs were detected in 20 subjects (33%). Older subjects (mean age: 46.00 ± 12.00 years) had higher WMHs prevalence, associated with higher QRISK2 score and reduced processing speed. They also had significantly higher mean percentage of platelet (CD62P)- and leukocyte (CD62L)-derived MPs. No association was found between reduced white matter integrity-especially at the left superior longitudinal fasciculus (LSLF)-with age and neurocognitive function; however, LSLF was associated with higher QRISK2 score, total MPs, and CD62L- and endothelial cell-derived MPs (CD146). Therefore, this study establishes these multimodal associations as potential surrogate markers for "silent" CSVD manifestations in the well-characterized cardiocerebrovascular demographic of relatively young, neurologically asymptomatic adults. Furthermore, to the best of our knowledge, this study is the first to exhibit elevated MP counts in asymptomatic CSVD (i.e., CD62P and CD62L), which warrants further delineation.

Methodological Approaches to Assessing the Size and Morphology of Microvesicles of Cell Lines

Morphological properties and the size of microvesicles were assessed using atomic force microscopy, electron microscopy, and granulometric analysis. As these methods require significant numbers of microvesicles, we chose microvesicles derived from cell lines for our research.

Platelet-Derived Microparticles Bearing PF4 and Anti-GAGS Immunoglobulins in Patients with Sepsis

PF4 is a megakaryocyte-derived cationic chemokine that plays a part in innate immunity through its activity on the macrophages. In bacterial sepsis, PF4 binds to glycosaminoglycans (GAGs) on the surface of aerobic bacteria, giving rise to an antigenic complex that induces the early formation of anti-PF4 IgG-IgA-IgM. This triggers the immune response in patients receiving heparin therapy who develop heparin-induced thrombocytopenia (HIT). These antibodies have also been identified in patients with chronic Gram-negative infections. Given the complexity of this innate immune response network, our study on 45 patients with sepsis focused on the immune response mediated by platelet PF4. We analyzed the role of IgG-IgA-IgM against PF4-GAGs, and the presence of specific PF4-bearing platelet microparticles (PMPs). Anti-GAGs/PF4 IgG-IgA-IgM levels were significantly higher in septic patients than in control groups (healthy controls or acute patients without sepsis, p < 0.001). PF4-bearing PMP levels were only significantly higher in septic patients (p < 0.001). The occurrence of IgG-IgA-IgM against PF4-GAGs and PF4+ PMPs correlated with an improvement in patients’ sepsis. In conclusion, we demonstrated that, in the course of bacterial sepsis, platelet activation leads to the formation of specific PF4-bearing PMPs. These specific microparticles bind to polyanionic sequences on the surface of aerobic bacteria, giving rise to an antigenic complex that induces the early formation of IgG-IgA-IgM against PF4-GAGs as an innate immune response to infection.

The haemostatic system in acromegaly: a single-centre case-control study

PURPOSE

Although the mortality from acromegaly is due in most cases to an increased cardiovascular risk, no study has globally evaluated the haemostatic balance in acromegaly to ascertain the presence of hypercoagulability. We endeavoured to assess the overall coagulation profile in patients with acromegaly using both traditional and global coagulation assays.

METHODS

Consecutive outpatients with a diagnosis of acromegaly were enrolled and matched with healthy subjects. Whole blood thromboelastometry and impedance aggregometry, procoagulant, anticoagulant and fibrinolytic factors, as well as thrombin-generation assay and circulating endothelium-derived microvesicles were measured.

RESULTS

Forty patients (M/F 14/26, median age 59 years) with either new diagnosis (naïve, 14 cases) or treated acromegaly (26 cases) were enrolled in this study. Median time from diagnosis was 11 years. Levels of factor VIII and fibrinogen were significantly higher in acromegalic patients vs. controls (p = 0.029 and < 0.003, respectively). Overall, thromboelastometry parameters showed a faster coagulation formation with a more stable clot. Acromegaly patients showed significantly higher endogenous thrombin potential [ETP] and thrombin peak compared to controls (p = 0.016 and p < 0.001, respectively). ETP remained significantly higher (p < 0.001) when thrombomodulin was added. Endothelial-derived microvesicles were significantly higher in acromegaly patients than controls (52 [40.5-67] MVs/µL and 30 [18-80] MVs/µL, p = 0.03). Patients with untreated (naïve) acromegaly showed significantly reduced ETP with and without thrombomodulin vs. patients with treated acromegaly (p = 0.01).

CONCLUSION

Hypercoagulability in acromegaly is mainly due to higher levels of fibrinogen, factor VIII and thrombin generation, and appears to be more linked to the chronic phase of the disease.

Changes in plasma circulating microvesicles in patients with HCV-related cirrhosis after treatment with direct-acting antivirals

BACKGROUND & AIMS

The eradication of Hepatitis C (HCV) infection by direct-acting antiviral (DAAs) agents has been linked to an amelioration of liver synthesis and regression of fibrosis. Although changes in number and type of circulating microvesicles (MVs) have been reported in cirrhosis, conclusive data on the effect of DAAs treatment on MVs profile in HCV cirrhotic patients remain scarce.

METHODS

We measured the levels of endothelial, platelet and hepatocyte MVs, as well as MVs-expressing versican core protein (VCAN+) in patients with HCV-related cirrhosis at baseline, end of treatment (EOT), at 12, 24 and 48 weeks (W) after EOT by new generation flow cytometry.

RESULTS

Fifty-eight patients were enrolled (86% Child's A). MVs were increased at EOT vs baseline, though only platelet MVs revealed a statistically significant difference (P < .01). MV levels did not change significantly after EOT notwithstanding a steady downward trend towards baseline levels. Conversely, VCAN + MVs dropped significantly at EOT (P < .001) and remained low throughout the follow-up. Hepatocyte MVs significantly correlated with liver stiffness (r = .40, P = .0021). Eight composite outcomes occurred during the 1-year follow-up: three portal vein thromboses (PVTs), two hepatocellular carcinomas (HCCs) and three liver decompensation. Child's B, the presence of F2 oesophageal varices (OR for interaction 19.2 [95% CI 1.45-253.7], P = .023) and platelet MVs (OR 1.026 [95% CI 1.00-1.05, P = .023) correlated significantly with clinical outcomes.

CONCLUSIONS

VCAN + MVs appear to mirror the profibrotic status of the cirrhotic disease; hepatocyte MVs correlate with liver stiffness and increased platelet MV levels could be associated with a worse clinical outcome.

The Mediterranean diet decreases prothrombotic microvesicle release in asymptomatic individuals at high cardiovascular risk

BACKGROUND & AIMS

Circulating microvesicles (cMV) are small phospholipid-rich vesicles that contribute to the atherothrombotic process, and are biomarkers of cardiovascular disease (CVD) burden and progression. Diet is a cornerstone for CVD prevention, but dietary effects on cMV shedding are poorly characterized. We aimed at assessing the long term effects of a Mediterranean diet compared to a low-fat diet (LFD) on MV shedding by cells of the blood and vascular compartments in patients at high cardiovascular risk treated as per guidelines.

METHODS

A total of 155 participants from the PREDIMED trial free of cardiovascular events after a mean follow-up of 5 years (n = 53 from the Mediterranean diet supplemented with extra-virgin olive oil -EVOO-; n = 49 from the Mediterranean diet supplemented with mixed nuts -Nuts-; and n = 53 from the LFD) were included in the study. At baseline and after one-year intervention, cMV were quantified and characterized by flow cytometry to identify their activated parental cell origin and prothrombotic potential by Annexin V (AV) binding.

RESULTS

After one year of dietary intervention, platelet-derived PAC-1⁺/AV⁺ and CD62P⁺/AV⁺ cMV concentrations were lower in the Nuts group compared with the LFD and EVOO interventions (P = 0.036 and 0.003, respectively). In addition, prothrombotic cMV carrying tissue factor (CD142⁺/AV⁺) and CD11a⁺/AV⁺ cMV derived from activated cells, were significantly lower in both Mediterranean diet (EVOO and Nuts) interventions compared to one year of LFD (P < 0.0001 and 0.028, respectively). SMAα⁺/AV^- cMV were lower in the LFD compared to the Nuts group after one year of intervention (P = 0.038).

CONCLUSIONS

cMV are markers of cell activation and vascular injury that appear to be sensitive to dietary changes. Following a Mediterranean diet rich in EVOO or nuts is associated with lower cell activation towards a pro-atherothrombotic phenotype, suggesting a delay in the development of CV complications.

The role of microvesicles and its active molecules in regulating cellular biology

Cell‐derived microvesicles are membrane vesicles produced by the outward budding of the plasma membrane and released by almost all types of cells. These have been considered as another mechanism of intercellular communication, because they carry active molecules, such as proteins, lipids and nucleic acids. Furthermore, these are present in circulating fluids, such as blood and urine, and are closely correlated to the progression of pathophysiological conditions in many diseases. Recent studies have revealed that microvesicles have a dual effect of damage and protection of receptor cells. However, the nature of the active molecules involved in this effect remains unclear. The present study mainly emphasized the mechanism of microvesicles and the active molecules mediating the different biological effects of receptor cells by affecting autophagy, apoptosis and inflammation pathways. The effective ways of blocking microvesicles and its active molecules in mediating cell damage when microvesicles exert harmful effects were also discussed.

The use of flow cytometry in the diagnosis of heparin-induced thrombocytopenia (HIT)

Heparin-induced thrombocytopenia (HIT) affects some of the patients exposed to heparin. It is mediated by antibodies that recognize neoepitopes on platelet factor 4 (PF4)/heparin complexes. A HIT diagnosis requires both clinical and laboratory evaluation and remains a challenge. Since many patients develop antibodies in response to heparin, but only a few of them generate anti-PF4/heparin antibodies capable of activating platelets which consequently cause clinical complications, the performance of serologic assays is not enough to diagnose HIT. Functional assays can identify pathogenic antibodies capable of platelet activation, but they are more demanding and their limited availability contributes to the problem of diagnosing HIT. Restricted laboratories usually collect sera of multiple patients to perform functional assays only once or twice a week; hence, a HIT diagnosis can take several days. The use of flow cytometry appears to be a promising alternative in the confirmation of pathogenic anti-PF4/heparin antibodies. Flow cytometric assays detect either activation markers on a healthy donor's platelet surfaces or platelet derived microparticles formed after platelet incubation with a patient's serum. Flow cytometers are readily available in many clinical laboratories, so this technology introduces the possibility of an earlier HIT diagnosis. The objective of this review was to collect findings on flow cytometric HIT confirmations to the present date, and to review the currently available flow cytometric assays used in the diagnosis of HIT.

Platelet factor 4-containing immune complexes induce platelet activation followed by calpain-dependent platelet death

Heparin-induced thrombocytopenia (HIT) is a complication of heparin therapy sometimes associated with thrombosis. The hallmark of HIT is antibodies to the heparin/platelet factor 4 (PF4) complex that cause thrombocytopenia and thrombosis through platelet activation. Despite the clinical importance, the molecular mechanisms and late consequences of immune platelet activation are not fully understood. Here, we studied immediate and delayed effects of the complexes formed by human PF4 and HIT-like monoclonal mouse anti-human-PF4/heparin IgG antibodies (named KKO) on isolated human platelets in vitro. Direct platelet-activating effect of the KKO/PF4 complexes was corroborated by the overexpression of phosphatidylserine (PS) and P-selectin on the platelet surface. The immune platelet activation was accompanied by a decrease of the mitochondrial transmembrane potential (ΔΨm), concurrent with a significant gradual reduction of the ATP content in platelets, indicating disruption of energy metabolism. A combination of PS expression and mitochondrial depolarization induced by the PF4-containing immune complexes observed in a substantial fraction of platelets was considered as a sign of ongoing platelet death, as opposed to a subpopulation of activated live platelets with PS on the plasma membrane but normal ΔΨm. Both activated and dying platelets treated with KKO/PF4 formed procoagulant extracellular microvesicles bearing PS on their surface. Scanning and transmission electron microscopy revealed dramatic morphological changes of KKO/PF4-treated platelets, including their fragmentation, another indicator of cell death. Most of the effects of KKO/PF4 were prevented by an anti-FcγRII monoclonal antibody IV.3. The adverse functional and structural changes in platelets induced by the KKO/PF4 complexes were associated with strong time-dependent activation of calpain, but only trace cleavage of caspase 3. The results indicate that the pathogenic PF4-containing HIT-like immune complexes induce direct prothrombotic platelet activation via FcγRIIA receptors followed by non-apoptotic calpain-dependent death of platelets, which can be an important mechanism of thrombocytopenia during HIT development.

Biology and Role of Extracellular Vesicles (EVs) in the Pathogenesis of Thrombosis

Extracellular vesicles (EVs) are well-established mediators of cell-to-cell communication. EVs can be released by every cell type and they can be classified into three major groups according to their biogenesis, dimension, density, and predominant protein markers: exosomes, microvesicles, and apoptotic bodies. During their formation, EVs associate with specific cargo from their parental cell that can include RNAs, free fatty acids, surface receptors, and proteins. The biological function of EVs is to maintain cellular and tissue homeostasis by transferring critical biological cargos to distal or neighboring recipient cells. On the other hand, their role in intercellular communication may also contribute to the pathogenesis of several diseases, including thrombosis. More recently, their physiological and biochemical properties have suggested their use as a therapeutic tool in tissue regeneration as well as a novel option for drug delivery. In this review, we will summarize the impact of EVs released from blood and vascular cells in arterial and venous thrombosis, describing the mechanisms by which EVs affect thrombosis and their potential clinical applications.

Levels of circulating microparticles in septic shock and sepsis-related complications: a case-control study

BACKGROUND

Microparticles (MP) have been largely studied as potential biomarkers in septic shock (SS) though their biological and clinical relevance is still unclear. This case-control study describes the trend of various MP subtypes during SS to evaluate their possible association with severity of illness and sepsis-related complications (disseminated intravascular coagulation [DIC] and acute kidney injury [AKI]).

METHODS

Forty patients admitted to the Intensive Care Unit with SS and 40 matched healthy volunteers were recruited. AnnexinV+, E-selectin+, thrombomodulin (TM+), leukocyte-derived (CD45+, CD36+) and platelet-derived MP (PMP-expressed as PMP/platelets ratio) were measured by flow-cytometry at baseline, on day 1, 3 and 7 after diagnosis. Severity of illness was assessed by Sequential Organ Failure Assessment Score, duration of vasoactive support and mechanical ventilation. Sepsis-related complications were considered.

RESULTS

Overall, septic patients showed higher levels of all MP considered compared to controls. TM+MP were significantly lower in more severe sepsis, while CD36+MP and PMP/platelets ratio were significantly increased in patients requiring longer vasoactive support and mechanical ventilation. As for sepsis-related complications, a higher PMP/platelets ratio in patients who developed DIC and increased E-selectin+MP in subjects who developed AKI were observed. PMP/platelets ratio at baseline was significantly associated with longer vasoactive support (OR=1.59 [1.05-2.42]), longer mechanical ventilation (OR=1.6 [1.06-2.42]) and DIC occurrence (OR=1.45 [1.08-1.96]).

CONCLUSIONS

A global response through extra-vesiculation of endothelial cells, leukocytes and platelets during the early stages of SS was confirmed. The cellular activation was detected until day 3 after diagnosis. PMP/platelets ratio at diagnosis may be useful to evaluate SS severity and DIC occurrence.

Neutrophil microparticle production and inflammasome activation by hyperglycemia due to cytoskeletal instability

Microparticles are lipid bilayer-enclosed vesicles produced by cells under oxidative stress. MP production is elevated in patients with diabetes, but the underlying cellular mechanisms are poorly understood. We hypothesized that raising glucose above the physiological level of 5.5 mm would stimulate leukocytes to produce MPs and activate the nucleotide-binding domain, leucine-rich repeat pyrin domain-containing 3 (NLRP3) inflammasome. We found that when incubated in buffer with up to 20 mm glucose, human and murine neutrophils, but not monocytes, generate progressively more MPs with high interleukin (IL)-1β content. Enhanced MP production required generation of reactive chemical species by mitochondria, NADPH oxidase, and type 2 nitric-oxide synthase (NOS-2) and resulted in S-nitrosylation of actin. Depleting cells of capon (C-terminal PDZ ligand of neuronal nitric-oxide synthase protein), apoptosis-associated speck-like protein containing C-terminal caspase recruitment domain (ASC), or pro-IL-1β prevented the hyperglycemia-induced enhancement of reactive species production, MP generation, and IL-1β synthesis. Additional components required for these responses included inositol 1,3,5-triphosphate receptors, PKC, and enhancement of filamentous-actin turnover. Numerous proteins become localized to short filamentous actin in response to S-nitrosylation, including vasodilator-stimulated phosphoprotein, focal adhesion kinase, the membrane phospholipid translocation enzymes flippase and floppase, capon, NLRP3, and ASC. We conclude that an interdependent oxidative stress response to hyperglycemia perturbs neutrophil cytoskeletal stability leading to MP production and IL-1β synthesis.

Circulating levels and characterization of microparticles in patients with different degrees of glucose tolerance

Background

Microparticles (MPs) are vesicular structures shed from endothelial or circulating blood cells, after activation or apoptosis, and can be considered markers of vascular damage. We aimed to determine the levels of circulating MPs, their content of miRNA-126-3p and 5p, and their relationship with early endothelial activation/damage, in patients with different degree of glucose tolerance.

Methods

CD62E⁺, CD62P⁺, CD142⁺, CD45⁺ circulating MPs, their apoptotic (AnnexinV⁺) fractions, and miRNA-126 expression were determined in 39 prediabetic (PreDM), 68 type 2 diabetic (T2DM), and 53 control (NGT) subjects, along with main anthropometric and biochemical measurements. MPs were analysed by flow cytometry. miRNA-126 was measured by quantitative real-time PCR. Plasma antioxidant capacity was determined by electronic spin resonance; ICAM-1, and VCAM-1 by ELISA.

Results

Activated endothelial cell-derived MPs (CD62E⁺) were significantly increased in PreDM and T2DM in comparison to NGT (p < 0.0001). AnnexinV⁺/CD62E⁺ MPs and Annexin V⁺ MPs were significantly increased in T2DM compared to PreDM and NGT (p < 0.001); other MPs were not significantly different among groups. Plasma antioxidant capacity was significantly decreased in PreDM and T2DM compared to NGT (p = 0.001); VCAM-1 significantly increased in PreDM and T2DM in comparison to NGT (p = 0.001). miR-126-3p expression, but not miR-126-5p, in MPs, decreased significantly and progressively from NGT, to PreDM, and T2DM (p < 0.001). In PreDM and T2DM, CD62E⁺ MPs level was significantly and negatively associated with plasma glucose (p = 0.004).

Conclusion

We show for the first time that circulating CD62E⁺ MPs level and miR-126-3p content in MPs are abnormal in subjects with pre-diabetes; the content of miR-126-3p correlates with markers of endothelial inflammation, such as VCAM-1, plasma antioxidant capacity, and microparticles, well-accepted markers of endothelial dysfunction.

Functional Assays in the Diagnosis of Heparin-Induced Thrombocytopenia: A Review

A rapid and accurate diagnosis in patients with suspected heparin-induced thrombocytopenia (HIT) is essential for patient management but remains challenging. Current HIT diagnosis ideally relies on a combination of clinical information, immunoassay and functional assay results. Platelet activation assays or functional assays detect HIT antibodies that are more clinically significant. Several functional assays have been developed and evaluated in the literature. They differ in the activation endpoint studied; the technique or technology used; the platelet donor selection; the platelet suspension (washed platelets, platelet rich plasma or whole blood); the patient sample (serum or plasma); and the heparin used (type and concentrations). Inconsistencies in controls performed and associated results interpretation are common. Thresholds and performances are determined differently among papers. Functional assays suffer from interlaboratory variability. This lack of standardization limits the evaluation and the accessibility of functional assays in laboratories. In the present article, we review all the current activation endpoints, techniques and methodologies of functional assays developed for HIT diagnosis.