Venous valvular stasis-associated hypoxia and thrombosis: what is the link?

Serial values of hematologic variables and deep venous thrombosis: Red cell distribution width is associated with deep venous thrombosis

INTRODUCTION

As 30 to 50% of deep venous thrombosis (DVT) cases remain idiopathic, an increased focus on hematologic variables may therefore reveal novel correlates of DVT. Very few studies have investigated the association of hematological parameters with DVT and the causal relationship between them is still to be elucidated. Therefore, we aimed to investigate the association between serial values of hematologic variables and DVT.

METHODS

Complete blood count parameters were serially measured at baseline and then at approximately 3-month intervals for 12 months in 152 adults with the first episode of DVT and 152 age- and sex-matched controls. The odds ratio (OR) with the 95% confidence interval (95%CI) was calculated as a measure of association between hematological parameters and DVT.

RESULTS

The red cell distribution width (RDW) was the only hematologic variable which showed an independent and consistent association with DVT at all time points (multivariable-adjusted OR [95%CI] 3.38 [1.28 - 8.91] at baseline, 2.24 [0.85 - 5.92] at 3 months and 2.12 [0.81 - 5.55] at 12 months for RDW > 14.0%). This association was higher for provoked DVT than unprovoked DVT and for DVT plus pulmonary embolism than DVT alone. No significant correlation was found between the high RDW and classical thrombotic risk factors, except malignancy.

CONCLUSIONS

We demonstrated an independent and consistent association of the high RDW with the first episode of DVT in adult patients. The study was probably underpowered to evaluate the association between the high RDW and recurrent DVT. Further large studies with long follow-up are needed to confirm this association.

Recent Advances on the Molecular Mechanism and Clinical Trials of Venous Thromboembolism

Venous thromboembolism is a condition that includes deep vein thrombosis and pulmonary embolism. It is the third most common cardiovascular disease behind acute coronary heart disease and stroke. Over the past few years, growing research suggests that venous thrombosis is also related to the immune system and inflammatory factors have been confirmed to be involved in venous thrombosis. The role of inflammation and inflammation-related biomarkers in cerebrovascular thrombotic disease is the subject of ongoing debate. P-selectin leads to platelet-monocyte aggregation and stimulates vascular inflammation and thrombosis. The dysregulation of miRNAs has also been reported in venous thrombosis, suggesting the involvement of miRNAs in the progression of venous thrombosis. Plasminogen activator inhibitor-1 (PAI-1) is a crucial component of the plasminogen-plasmin system, and elevated levels of PAI-1 in conjunction with advanced age are significant risk factors for thrombosis. In addition, it has been showed that one of the ways that neutrophils promote venous thrombosis is the formation of neutrophil extracellular traps (NETs). In recent years, the role of extracellular vesicles (EVs) in the occurrence and development of VTE has been continuously revealed. With the advancement of research technology, the complex regulatory role of EVs on the coagulation process has been gradually discovered. However, our understanding of the causes and consequences of these changes in venous thrombosis is still limited. Therefore, we review our current understanding the molecular mechanisms of venous thrombosis and the related clinical trials, which is crucial for the future treatment of venous thrombosis.

Stroke risk in multiple sclerosis: a critical appraisal of the literature

Observational studies suggest that the occurrence of stroke on multiple sclerosis (MS) patients is higher compared to the general population. MS is a heterogeneous disease that involves an interplay of genetic, environmental and immune factors. The occurrence of stroke is subject to a wide range of both modifiable and non-modifiable, short- and long-term risk factors. Both MS and stroke share common risk factors. The immune mechanisms that underlie stroke are similar to neurodegenerative diseases and are attributed to neuroinflammation. The inflammation in autoimmune diseases may, therefore, predispose to an increased risk for stroke or potentiate the effect of conventional stroke risk factors. There are, however, additional determinants that contribute to a higher risk and incidence of stroke in MS. Due to the challenges that are associated with their differential diagnosis, the objective is to present an overview of the factors that may contribute to increased susceptibility or occurrence of stroke in MSpatients by performing a review of the available to date literature. As both MS and stroke can individually detrimentally affect the quality of life of afflicted patients, the identification of factors that contribute to an increased risk for stroke in MS is crucial for the prompt implementation of preventative therapeutic measures to limit the additive burden that stroke imposes.

Protective Role of Endothelial SIRT1 in Deep Vein Thrombosis and Hypoxia-induced Endothelial Dysfunction Mediated by NF-κB Deacetylation

Venous hypoxia is considered as the major pathogenetic mechanism linking blood flow stagnancy with deep vein thrombosis (DVT). Our previous study showed that activating SIRT1 may attenuate inferior vena cava (IVC) stenosis-induced DVT in rats. This study was aimed to investigate the role of endothelial SIRT1 in DVT and hypoxia-induced endothelial dysfunction as well as the underlying mechanism. Protein profiling of IVCs and blood plasma of DVT rats induced by IVC stenosis was analysed by 4D Label free proteomics analysis. To verify the independent role of SIRT1 in DVT and oxygen-glucose deprivation (OGD)-induced endothelial dysfunction, SIRT1 specific activator SRT1720 and SIRT1 knockdown in both local IVCs and endothelial cells were employed. Moreover, the role of the NF-κB were investigated using NF-κB inhibitor caffeic acid phenethyl ester (CAPE). SRT1720 significantly inhibited thrombus burden, leukocytes infiltration, protein expressions of cell adhesion molecules and chemokines, as well as acetylation level of NF-κB/p65 in wild DVT rats, while these protective effects of SRT1720 were abolished in rats with SIRT1 knockdown in local IVCs. In vitro, SRT1720 protected endothelial cells against OGD-induced dysfunction characterized with enhanced adhesion of monocytes as well as the protein expressions of cell adhesion molecules and chemokines, whereas these protective effects of SRT1720 were vanished by SIRT1 stable knockdown. Furthermore, CAPE attenuated endothelial cell dysfunction and abolished these effects of SIRT1 knockdown. Collectively, these data suggested that endothelial SIRT1 plays an independent role in ameliorating hypoxia-induced endothelial dysfunction and thrombotic inflammation in DVT, and this effect is mediated by NF-κB deacetylation.

New Therapeutic Targets for the Prevention and Treatment of Venous Thromboembolism With a Focus on Factor XI Inhibitors

FXI (factor XI) and FXII (factor XII) have emerged as targets for new anticoagulants that have the potential to be both more efficacious and safer than the currently available direct oral anticoagulants for the prevention and treatment of venous thromboembolism. In this review, we discuss the role of FXI and FXII in the pathogenesis of venous thromboembolism, explain why FXI is a better target, and explain why FXI inhibitors have potential advantages over currently available anticoagulants. Finally, we describe the FXI inhibitors under development and discuss their potential to address unmet needs in venous thromboembolism management.

Dynamic observation of circRNA and mRNA profiles in a rat model of deep vein thrombosis

The goal of the present study was to identify different transcriptome expression profiles involved in the pathogenesis of deep vein thrombosis (DVT), and to illustrate the diagnostic and therapeutic potential of circular RNAs (circRNAs) and mRNAs in DVT progression. A Sprague-Dawley rat model of DVT was successfully established through the stenosis method and samples were sequenced at four time points (1, 6 and 12 h, and 3 days after ligation) to observe the dynamic changes in circRNAs and mRNAs during DVT progression. RNA sequencing was used to analyze the circRNA and mRNA expression profiles, and associated functions and pathways, in the blood of DVT rats at the four time points. In addition, Short Time Series Expression Miner (STEM) analysis was performed to explore temporal gene expression. Differential expression of 1,680, 4,018, 3,724, and 3,036 circRNAs, and 400, 1,176, 373, and 573 mRNAs was observed in the 1, 6 and 12 h, and 3-day groups, respectively, compared with the sham group (fold change >2.0 or <-2.0, P<0.05). Functional enrichment analysis indicated that differentially expressed mRNAs were associated with the following terms: Immune response, cell activation, blood stasis facilitated organelle, extracellular membrane-bounded organelle, and blood microparticle, oxygen transporter activity. STEM analysis indicated that the expression of 366 circRNAs in circRNA profile 45 and 270 mRNAs in mRNA profile 45 was consistent with thrombus progression. Enrichment analysis was performed on mRNA profile 45. The main Gene Ontology annotations were chromosome segregation, mitotic sister chromatid segregation, cell cycle process, and ligand-dependent nuclear receptor transcription coactivator activity. Pathway enrichment analysis identified the platelet-associated pathway, immune-associated pathway, and inflammation-relation pathway. According to the enriched platelet-associated pathways, four mRNAs and ten candidate circRNAs were selected for reverse transcription-quantitative PCR verification. The expression of nine of the ten circRNAs and all four mRNAs was consistent with the sequencing results. In summary, differentially expressed circRNAs and mRNAs are dynamically involved in DVT development. Dysregulated transcriptome profiles and the corresponding functions and pathways may provide mechanistic insights into DVT diagnosis and treatment.

Sustained and intermittent hypoxia differentially modulate primary monocyte immunothrombotic responses to IL-1β stimulation

Venous thromboembolism (VTE) is a leading cause of preventable deaths in hospitals, and its incidence is not decreasing despite extensive efforts in clinical and laboratory research. Venous thrombi are primarily formed in the valve pockets of deep veins, where activated monocytes play a crucial role in bridging innate immune activation and hemostatic pathways through the production of inflammatory cytokines, chemokines, and tissue factor (TF) - a principal initiator of coagulation. In the valve pocket inflammation and hypoxia (sustained/intermittent) coexist, however their combined effects on immunothrombotic processes are poorly understood. Inflammation is strongly associated with VTE, while the additional contribution of hypoxia remains largely unexplored. To investigate this, we modelled the intricate conditions of the venous valve pocket using a state-of-the-art hypoxia chamber with software-controlled oxygen cycling. We comprehensively studied the effects of sustained and intermittent hypoxia alone, and in combination with VTE-associated inflammatory stimuli on primary monocytes. TF expression and activity was measured in monocytes subjected to sustained and intermittent hypoxia alone, or in combination with IL-1β. Monocyte responses were further analyzed in detailed by RNA sequencing and validated by ELISA. Stimulation with IL-1β alone promoted both transcription and activity of TF. Interestingly, the stimulatory effect of IL-1β on TF was attenuated by sustained hypoxia, but not by intermittent hypoxia. Our transcriptome analysis further confirmed that sustained hypoxia limited the pro-inflammatory response induced by IL-1β, and triggered a metabolic shift in monocytes. Intermittent hypoxia alone had a modest effect on monocyte transcript. However, in combination with IL-1β intermittent hypoxia significantly altered the expression of 2207 genes and enhanced the IL-1β-stimulatory effects on several chemokine and interleukin genes (e.g., IL-19, IL-24, IL-32, MIF), as well as genes involved in coagulation (thrombomodulin) and fibrinolysis (VEGFA, MMP9, MMP14 and PAI-1). Increased production of CCL2, IL-6 and TNF following stimulation with intermittent hypoxia and IL-1β was confirmed by ELISA. Our findings provide valuable insights into how the different hypoxic profiles shape the immunothrombotic response of monocytes and shed new light on the early events in the pathogenesis of venous thrombosis.

A combination of strongly associated prothrombotic single nucleotide polymorphisms could efficiently predict venous thrombosis risk

Background

Venous thrombosis (VT) is multifactorial trait that contributes to the global burden of cardiovascular diseases. Although abundant single nucleotide polymorphisms (SNPs) provoke the susceptibility of an individual to VT, research has found that the five most strongly associated SNPs, namely, rs6025 (F5 Leiden), rs2066865 (FGG), rs2036914 (F11), rs8176719 (ABO), and rs1799963 (F2), play the greatest role. Association and risk prediction models are rarely established by using merely the five strongly associated SNPs. This study aims to explore the combined VT risk predictability of the five SNPs and well-known non-genetic VT risk factors such as aging and obesity in the Hungarian population.

Methods

SNPs were genotyped in the VT group (n = 298) and control group (n = 400). Associations were established using standard genetic models. Genetic risk scores (GRS) [unweighted GRS (unGRS), weighted GRS (wGRS)] were also computed. Correspondingly, the areas under the receiver operating characteristic curves (AUCs) for genetic and non-genetic risk factors were estimated to explore their VT risk predictability in the study population.

Results

rs6025 was the most prevalent VT risk allele in the Hungarian population. Its risk allele frequency was 3.52-fold higher in the VT group than that in the control group [adjusted odds ratio (AOR) = 3.52, 95% CI: 2.50-4.95]. Using all genetic models, we found that rs6025 and rs2036914 remained significantly associated with VT risk after multiple correction testing was performed. However, rs8176719 remained statistically significant only in the multiplicative (AOR = 1.33, 95% CI: 1.07-1.64) and genotypic models (AOR = 1.77, 95% CI: 1.14-2.73). In addition, rs2066865 lost its significant association with VT risk after multiple correction testing was performed. Conversely, the prothrombin mutation (rs1799963) did not show any significant association. The AUC of Leiden mutation (rs6025) showed better discriminative accuracy than that of other SNPs (AUC = 0.62, 95% CI: 0.57-0.66). The wGRS was a better predictor for VT than the unGRS (AUC = 0.67 vs. 0.65). Furthermore, combining genetic and non-genetic VT risk factors significantly increased the AUC to 0.89 with statistically significant differences (Z = 3.924, p < 0.0001).

Conclusions

Our study revealed that the five strongly associated SNPs combined with non-genetic factors could efficiently predict individual VT risk susceptibility. The combined model was the best predictor of VT risk, so stratifying high-risk individuals based on their genetic profiling and well-known non-modifiable VT risk factors was important for the effective and efficient utilization of VT risk preventive and control measures. Furthermore, we urged further study that compares the VT risk predictability in the Hungarian population using the formerly discovered VT SNPs with the novel strongly associated VT SNPs.

A nomogram model based on the combination of the systemic immune-inflammation index, body mass index, and neutrophil/lymphocyte ratio to predict the risk of preoperative deep venous thrombosis in elderly patients with intertrochanteric femoral fracture: a retrospective cohort study

OBJECTIVES

Deep vein thrombosis (DVT) has been considered as a frequent and serious consequence of intertrochanteric femoral fractures in the elderly. Several negative repercussions of DVT can be considerably mitigated by its timely recognition and treatment. The current work was aimed at exploring the factors independently predicting DVT among cases suffering from intertrochanteric femoral fractures and validate their predictive usefulness in diagnosing DVT.

METHODS

Between April 2017 and July 2022, clinical information from 209 cases showing preoperative DVT for femoral intertrochanteric fractures were retrospectively evaluated. In patients with femoral intertrochanteric fractures, logistic regression analysis with a backward stepwise method was adopted for detecting independent predictors for the diagnosis of preoperative DVT. Using multivariate logistic regression, a nomogram prediction model was developed and verified with the testing group.

RESULTS

According to multivariate logistic regression model, body mass index (BMI) (OR 0.79, 95% CI 0.63-0.99, P = 0.042), neutrophil/lymphocyte ratio (NLR) (OR 7.29, 95% CI 1.53, 34.64, P = 0.0012), and systemic immune-inflammation index (SII) (OR 6.61, 95% CI 2.35, 18.59, P = 0.001) were independent predictors for DVT before surgery among cases developing intertrochanteric femoral fracture. AUC values were 0.862 and 0.767 for training and testing groups, separately, while their mean errors in the calibration curve were 0.027 and 0.038 separately. Decision curve analysis (DCA) curve revealed a high value of clinical application for both groups.

CONCLUSION

Upon admission, BMI, NLR, and SII are independent predictors of DVT before surgery among cases developing intertrochanteric femoral fractures. Additionally, the nomogram based on the BMI, NLR, and SII can assist clinicians in determining if preventive and symptomatic therapies are required to improve DVT prognosis and reduce its associated mortality.

Wall shear gradient dependent thrombosis studied in blood-on-a-chip with stenotic, branched, and valvular constructions

Thrombosis is the leading cause of death, while the effect of the shear flow on the formation of thrombus in vascular constructions has not been thoroughly understood, and one of the challenges is to observe the origination of thrombus with a controlled flow field. In this work, we use blood-on-a-chip technology to mimic the flow conditions in coronary artery stenosis, neonatal aortic arch, and deep venous valve. The flow field is measured by the microparticle image velocimeter (μPIV). In the experiment, we find that the thrombus often originates at the constructions of stenosis, bifurcation, and the entrance of valve, where the flow stream lines change suddenly, and the maximum wall shear rate gradient appears. Using the blood-on-a-chip technology, the effect of the wall shear rate gradients on the formation of the thrombus has been illustrated, and the blood-on-a-chip is demonstrated to be a perspective tool for further studies on the flow-induced formation of thrombosis.

Enhanced in vivo and ex vivo thrombin generation after lower-leg trauma, but not after knee arthroscopy

BACKGROUND

There is room for improvement of prevention of venous thromboembolism (VTE) after lower-leg cast application or knee arthroscopy. Information about the mechanism of clot formation in these patients may be useful to identify new prophylaxis targets. We aimed to study the effect of 1) lower-leg injury and 2) knee arthroscopy on thrombin generation.

METHODS

A cross-sectional study was conducted using plasma samples of POT-(K)CAST trials to measure ex vivo thrombin generation (Calibrated Automated Thrombography [CAT]) and plasma levels of prothrombin fragment 1 + 2 (F1 + 2), thrombin-antithrombin (TAT), fibrinopeptide A (FPA). Plasma was obtained shortly after lower-leg trauma or before and after (< 4 h) knee arthroscopy. Participants were randomly selected from those who did not develop VTE. For aim 1, samples of 88 patients with lower-leg injury were compared with 89 control samples (i.e., preoperative samples of arthroscopy patients). Linear regression was used to obtain mean differences (or ratios if ln-retransformed because of skewedness) adjusted for age, sex, body mass index, comorbidities. For aim 2, pre- and postoperative samples of 85 arthroscopy patients were compared, for which mean changes were obtained.

RESULTS

In patients with lower-leg injury (aim 1), endogenous thrombin potential, thrombin peak, velocity index, FPA and TAT were increased as compared with controls. In arthroscopy patients (aim 2), pre- and postoperative levels were similar for all parameters.

CONCLUSION

Lower-leg trauma increases thrombin generation both ex vivo and in vivo, in contrast to knee arthroscopy. This may imply that the pathogenesis of VTE is different in both situations.

Platelet accumulation in an endothelium-coated elastic vein valve model of deep vein thrombosis is mediated by GPIbα-VWF interaction

Deep vein thrombosis is a life-threatening disease that takes millions of people's lives worldwide. Given both technical and ethical issues of using animals in research, it is necessary to develop an appropriate in vitro model that would recapitulate the conditions of venous thrombus development. We present here a novel microfluidics vein-on-a-chip with moving valve leaflets to mimic the hydrodynamics in a vein, and Human Umbilical Vein Endothelial Cell (HUVEC) monolayer. A pulsatile flow pattern, typical for veins, was used in the experiments. Unstimulated human platelets, reconstituted with the whole blood, accumulated at the luminal side of the leaflet tips proportionally to the leaflet flexibility. Platelet activation by thrombin induced robust platelet accrual at the leaflet tips. Inhibition of glycoprotein (GP) IIb-IIIa did not decrease but, paradoxically, slightly increased platelet accumulation. In contrast, blockade of the interaction between platelet GPIbα and A1 domain of von Willebrand factor completely abolished platelet deposition. Stimulation of the endothelium with histamine, a known secretagogue of Weibel-Palade bodies, promoted platelet accrual at the basal side of the leaflets, where human thrombi are usually observed. Thus, platelet deposition depends on the leaflet flexibility, and accumulation of activated platelets at the valve leaflets is mediated by GPIbα-VWF interaction.

The effects of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on ischemic stroke and the possible underlying mechanisms

Purpose: As of November 28, 2020, COVID-19 has been reported in 220 countries with 61,036,793 confirmed cases and 1,433,316 confirmed deaths; countries became vigilant around the world. In addition to SARS-CoV-2 causing pneumonia, many studies have reported ischemic stroke in patients with COVID-19. This article describes the effects and possible underlying mechanisms of SARS-CoV-2 on ischemic stroke.Materials and methods: A literature search was performed using PubMed, Web of Science, and other COVID-dedicated databases and the combination of the keywords 'SARS-CoV-2', 'COVID-19' and 'ischemic stroke' up to November 28, 2020.Results: SARS-CoV-2 invades the host through angiotensin converting enzyme 2 (ACE2). ACE2 is expressed not only in the lungs, but also in the brain and vascular endothelial cells. SARS-CoV-2 infection might cause direct vascular disease or enhance the immunogenic thrombosis environment through several mechanisms. SARS-CoV-2 infection can modulate the host immune response and can cause inflammation, coagulation disorders, renin angiotensin system disorders, hypoxia, and stress disorders, which may lead to the occurrence of ischemic stroke.Conclusions: Some patients with COVID-19 can develop ischemic stroke. Ischemic stroke has a high risk of causing disability and is associated with a high mortality rate. It is hoped that when medical staff treat patients with COVID-19, they would pay attention to the occurrence of ischemic stroke to improve the prognosis of patients with COVID-19.

Pathophysiological mechanisms of thrombosis in acute and long COVID-19

COVID-19 patients have a high incidence of thrombosis, and thromboembolic complications are associated with severe COVID-19 and high mortality. COVID-19 disease is associated with a hyper-inflammatory response (cytokine storm) mediated by the immune system. However, the role of the inflammatory response in thrombosis remains incompletely understood. In this review, we investigate the crosstalk between inflammation and thrombosis in the context of COVID-19, focusing on the contributions of inflammation to the pathogenesis of thrombosis, and propose combined use of anti-inflammatory and anticoagulant therapeutics. Under inflammatory conditions, the interactions between neutrophils and platelets, platelet activation, monocyte tissue factor expression, microparticle release, and phosphatidylserine (PS) externalization as well as complement activation are collectively involved in immune-thrombosis. Inflammation results in the activation and apoptosis of blood cells, leading to microparticle release and PS externalization on blood cells and microparticles, which significantly enhances the catalytic efficiency of the tenase and prothrombinase complexes, and promotes thrombin-mediated fibrin generation and local blood clot formation. Given the risk of thrombosis in the COVID-19, the importance of antithrombotic therapies has been generally recognized, but certain deficiencies and treatment gaps in remain. Antiplatelet drugs are not in combination with anticoagulant treatments, thus fail to dampen platelet procoagulant activity. Current treatments also do not propose an optimal time for anticoagulation. The efficacy of anticoagulant treatments depends on the time of therapy initiation. The best time for antithrombotic therapy is as early as possible after diagnosis, ideally in the early stage of the disease. We also elaborate on the possible mechanisms of long COVID thromboembolic complications, including persistent inflammation, endothelial injury and dysfunction, and coagulation abnormalities. The above-mentioned contents provide therapeutic strategies for COVID-19 patients and further improve patient outcomes.

Association Between Blood Lipid Levels and Lower Extremity Deep Venous Thrombosis: A Population-Based Cohort Study

ObjectsTo investigate the potential clinical significance between blood lipid levels and lower extremity deep venous thrombosis (LEDVT). Methods: This cohort study included 500 participants, contains 246 patients with LEDVT and 254 patients without LEDVT. The characteristics including age, sex, body mass index (BMI), disease course, ill position, smoking history, history of current illness, drug administration were collected. And blood lipid levels and other clinical parameters including triglyceride (TG), total cholesterol (TC), high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), apolipoprotein A1 (ApoA1), apolipoprotein B (ApoB), activated partial thromboplastin time (APTT), thromboplastin time (TT), prothrombin time (PT), and fibrinogen (FIB), neutrophils (NEUT), platelet (PLT), lymphocyte count (LY) were observed. Univariate and multivariate logistic regression analyses were applied. In the present study we particularly focused on the potential associations between blood lipid levels and LEDVT. Results: The risk of LEDVT in participants with HDL-C levels of 0.965 to 1.14 mmol/L, 1.14 to 1.36 mmol/L, and >1.36 mmol/L were 0.366, 0.183, 0.203 times than in controls (<0.965 mmol/L), respectively. Compared to individuals with ApoA1 <1.06 mmol/L, individuals with ApoA1 levels of 1.06 to 1.22 mmol/L, 1.22 to 1.38 mmol/L, and >1.38 mmol/L were related to a decreased risk of LEDVT. The risk of LEDVT in patients with TG levels of 0.985 to 1.37 mmol/L, 1.37 to 1.91 mmol/L, and >1.91 mmol/L were 2.243, 2.224, and 2.540 times higher than that of those with TG <0.985 mmol/L, respectively. The risk of LEDVT in subjects with 4.57< TC <5.17 mmol/L was 0.471-fold than that of those with TC <3.97 mmol/L. Conclusion: The present study indicates that higher levesl of HDL-C and ApoA1 could be associated with a decreased risk of LEDVT, while higher TG levels might be associated with an increased risk of LEDVT. In addition, within the normal range, high TC levels were associated with decreased risk of LEDVT. These findings may help clinicals to identify early and treat those patients with a high-risk of LEDVT at proper time, which could improve patients’ life quality.

Pathophysiological Aspects of Aging in Venous Thromboembolism: An Update

The aim of this review is to highlight all the factors that associate venous thromboembolism (VTE) with aging. Elderly people are characterized by a higher incidence of thrombosis taking into account the co-existing comorbidities, complications and fatality that arise. Based on the Virchow triad, pathophysiological aspects of venous stasis, endothelium injury and hypercoagulability in elderly people (≥65 years) are described in detail. More precisely, venous wall structure, nitric oxide (NO) and endothelin-1 expression are impaired in this age group. Furthermore, an increase in high-molecular-weight kininogen (HMWK), prekallikrein, factors V, VII, VIII, IX and XI, clot lysis time (CLT) and von Willebrand factor (vWF) is observed. Age-dependent platelet dysfunction and changes in anticoagulant factors are also illustrated. A “low-grade inflammation stage” is delineated as a possible risk factor for thrombosis in the elderly. Consequently, clinical implications for frail elderly people related to diagnosis, treatment, bleeding danger and VTE recurrence emerge. We conclude that aging is an acquired thrombotic factor closely related to pathophysiological changes.

High Levels of Complement Activating Enzyme MASP-2 Are Associated With the Risk of Future Incident Venous Thromboembolism

BACKGROUND

Experimental studies have shown that the complement activating enzyme MASP-2 (mannose-binding lectin associated serine protease 2) exhibits a thrombin-like activity and that inhibition of MASP-2 protects against thrombosis. In this study, we investigated whether plasma MASP-2 levels were associated with risk of future venous thromboembolism (VTE) and whether genetic variants linked to MASP-2 levels were associated with VTE risk.

METHODS

We conducted a population-based nested case-control study involving 410 VTE patients and 842 age- and sex-matched controls derived from the Norwegian Tromsø Study. Logistic regression was used to estimate odds ratios (ORs) of VTE across MASP-2 quartiles. Whole-exome sequencing and protein quantitative trait loci analyses were performed to assess genetic variants associated with MASP-2 levels. A 2-sample Mendelian randomization study, also including data from the INVENT consortium (International Network of Venous Thrombosis), was performed to assess causality.

RESULTS

Subjects with plasma MASP-2 in the highest quartile had a 48% higher OR of VTE (OR, 1.48 [95% CI, 1.06-2.06]) and 83% higher OR of deep vein thrombosis (OR, 1.83 [95% CI, 1.23-2.73]) compared with those with MASP-2 levels in the lowest quartile. The protein quantitative trait loci analysis revealed that 3 previously described gene variants, rs12711521 (minor allele frequency, 0.153), rs72550870 (minor allele frequency, 0.045; missense variants in the MASP2 gene), and rs2275527 (minor allele frequency, 0.220; exon variant in the adjacent MTOR gene) explained 39% of the variation of MASP-2 plasma concentration. The OR of VTE per 1 SD increase in genetically predicted MASP-2 was 1.03 ([95% CI, 1.01-1.05] P=0.0011).

CONCLUSIONS

Our findings suggest that high plasma MASP-2 levels are causally associated with risk of future VTE.

Effect of lower‐leg trauma and knee arthroscopy on procoagulant phospholipid‐dependent activity

Background

Lower-leg injury and knee arthroscopy are both associated with venous thromboembolism (VTE). The mechanism of VTE in both situations is unknown, including the role of procoagulant microparticles. This may provide useful information for individualizing thromboprophylactic treatment in both patient groups.

Objective

We aimed to study the effect of (1) lower-leg trauma and (2) knee arthroscopy on procoagulant phospholipid-dependent (PPL) activity plasma levels.

Methods

POT-(K)CAST trial participants who did not develop VTE were randomly selected for the current study. Plasma was collected shortly after lower-leg trauma or before and after knee arthroscopy. For aim 1, samples of 67 patients with lower-leg injury were compared with control samples (preoperative samples of 74 patients undergoing arthroscopy). Linear regression was used to obtain mean ratios (natural logarithm retransformed data), adjusted for age, sex, body mass index, infections, and comorbidities. For aim 2, pre- and postoperative samples of 49 patients undergoing arthroscopy were compared using paired t tests. PPL activity was measured using modified activated factor X-dependent PPL clotting assay.

Results

For aim 1, PPL activity levels were almost threefold higher in patients with lower-leg injury compared with controls, that is, mean ratio, 2.82 (95% confidence interval [CI], 1.98-4.03). For aim 2, postoperative PPL activity levels did not change significantly, that is, mean change, -0.72 mU/mL (95% CI, -2.03 to 0.59).

Conclusion

Lower-leg trauma was associated with increased plasma levels of PPL activity, in contrast to knee arthroscopy. Lower-leg trauma triggers the release of procoagulant microparticles.

Pathophysiology of deep vein thrombosis

Deep venous thrombosis is a frequent, multifactorial disease and a leading cause of morbidity and mortality. Most of the time deep venous thrombosis is triggered by the interaction between acquired risk factors, such as hip fracture, pregnancy, and immobility, and hereditary risk factors such as thrombophilias. The mechanisms underlying deep venous thrombosis are not fully elucidated; however, in recent years, important advances have shed light on the role of venous flow, endothelium, platelets, leukocytes, and the interaction between inflammation and hemostasis. It has been described that the alteration of venous blood flow produces endothelial activation, favoring the adhesion of platelets and leukocytes, which, through tissue factor expression and neutrophil extracellular traps formation, contribute to the activation of coagulation, trapping more cells, such as red blood cells. Thus, the concerted interaction of these phenomena allows the formation and growth of the thrombus. In this work, the main mechanisms involved in the pathophysiology of deep vein thrombosis will be described.

The interaction of vortical flows with red cells in venous valve mimics

The motion of cells orthogonal to the direction of main flow is of importance in natural and engineered systems. The lateral movement of red blood cells (RBCs) distal to sudden expansion is considered to influence the formation and progression of thrombosis in venous valves, aortic aneurysms, and blood-circulating devices and is also a determining parameter for cell separation applications in flow-focusing microfluidic devices. Although it is known that the unique geometry of venous valves alters the blood flow patterns and cell distribution in venous valve sinuses, the interactions between fluid flow and RBCs have not been elucidated. Here, using a dilute cell suspension in an in vitro microfluidic model of a venous valve, we quantified the spatial distribution of RBCs by microscopy and image analysis, and using micro-particle image velocimetry and 3D computational fluid dynamics simulations, we analyzed the complex flow patterns. The results show that the local hematocrit in the valve pockets is spatially heterogeneous and is significantly different from the feed hematocrit. Above a threshold shear rate, the inertial separation of streamlines and lift forces contribute to an uneven distribution of RBCs in the vortices, the entrapment of RBCs in the vortices, and non-monotonic wall shear stresses in the valve pockets. Our experimental and computational characterization provides insights into the complex interactions between fluid flow, RBC distribution, and wall shear rates in venous valve mimics, which is of relevance to understanding the pathophysiology of thrombosis and improving cell separation efficiency.

Overactivation of IL6 cis‑signaling in leukocytes is an inflammatory hallmark of deep vein thrombosis

Inflammation is a protective response of the body to various injuries, which is strictly regulated by a variety of factors, including immune cells and soluble mediators. However, dysfunction of this defensive mechanism often results in inflammation‑driven diseases, such as deep vein thrombosis (DVT). The complex relationship between inflammatory cell activity and DVT has not been fully elucidated. The present study aimed to investigate the role of interleukin‑6 (IL6) signaling transduction in DVT. To this aim, the expression levels of transmembrane isoforms of the IL6 receptor (IL6R) and the glycoprotein 130 responsible for the IL6 cis‑signaling were evaluated in the peripheral blood mononuclear cells of patients with DVT and of healthy controls. The results indicated that leukocytes from patients with DVT exhibited overexpression of both IL6R and gp130 membrane isoforms and that these were strongly associated with the occurrence of DVT. Overall, the present findings indicated that IL6 cis‑signaling may have a direct involvement in the leukocyte activation in DVT and may serve as a predictive biomarker of DVT development.

In silico analyses of blood flow and oxygen transport in human micro-veins and valves

BACKGROUND

Almost 95% of the venous valves are micron scale found in veins smaller than 300μm diameter. The fluid dynamics of blood flow and transport through these micro venous valves and their contribution to thrombosis is not yet well understood or characterized due to difficulty in making direct measurements in murine models.

OBJECTIVE

The unique flow patterns that may arise in physiological and pathological non-actuating micro venous valves are predicted.

METHODS

Computational fluid and transport simulations are used to model blood flow and oxygen gradients in a microfluidic vein.

RESULTS

The model successfully recreates the typical non-Newtonian vortical flow within the valve cusps seen in preclinical experimental models and in clinic. The analysis further reveals variation in the vortex strengths due to temporal changes in blood flow. The cusp oxygen is typically low from the main lumen, and it is regulated by systemic venous flow.

CONCLUSIONS

The analysis leads to a clinically-relevant hypothesis that micro venous valves may not create a hypoxic environment needed for endothelial inflammation, which is one of the main causes of thrombosis. However, incompetent micro venous valves are still locations for complex fluid dynamics of blood leading to low shear regions that may contribute to thrombosis through other pathways.

Endothelial thrombomodulin downregulation caused by hypoxia contributes to severe infiltration and coagulopathy in COVID-19 patient lungs

BACKGROUND

Thromboembolism is a life-threatening manifestation of coronavirus disease 2019 (COVID-19). We investigated a dysfunctional phenotype of vascular endothelial cells in the lungs during COVID-19.

METHODS

We obtained the lung specimens from the patients who died of COVID-19. The phenotype of endothelial cells and immune cells was examined by flow cytometry and immunohistochemistry (IHC) analysis. We tested the presence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the endothelium using IHC and electron microscopy.

FINDINGS

The autopsy lungs of COVID-19 patients exhibited severe coagulation abnormalities, immune cell infiltration, and platelet activation. Pulmonary endothelial cells of COVID-19 patients showed increased expression of procoagulant von Willebrand factor (VWF) and decreased expression of anticoagulants thrombomodulin and endothelial protein C receptor (EPCR). In the autopsy lungs of COVID-19 patients, the number of macrophages, monocytes, and T cells was increased, showing an activated phenotype. Despite increased immune cells, adhesion molecules such as ICAM-1, VCAM-1, E-selectin, and P-selectin were downregulated in pulmonary endothelial cells of COVID-19 patients. Notably, decreased thrombomodulin expression in endothelial cells was associated with increased immune cell infiltration in the COVID-19 patient lungs. There were no SARS-CoV-2 particles detected in the lung endothelium of COVID-19 patients despite their dysfunctional phenotype. Meanwhile, the autopsy lungs of COVID-19 patients showed SARS-CoV-2 virions in damaged alveolar epithelium and evidence of hypoxic injury.

INTERPRETATION

Pulmonary endothelial cells become dysfunctional during COVID-19, showing a loss of thrombomodulin expression related to severe thrombosis and infiltration, and endothelial cell dysfunction might be caused by a pathologic condition in COVID-19 patient lungs rather than a direct infection with SARS-CoV-2.

FUNDING

This work was supported by the Johns Hopkins University, the American Heart Association, and the National Institutes of Health.

Acute Cerebellar Stroke in a Military Active-Duty Pilot

BACKGROUND: Cryptogenic stroke leading to cerebellar infarction is a rare but serious cause of acute nausea and vomiting. This has the potential of devastating consequences if this occurs in aviators during flight. We present a case of cryptogenic stroke causing incapacitating nausea and vomiting in a U.S. Air Force pilot.CASE REPORT: A 36-yr-old active-duty U.S. Air Force male pilot developed acute onset severe vertigo, nausea, and vomiting during initial descent. Initial computed tomography imaging was normal and his initial assessment yielded a diagnosis of benign paroxysmal positional vertigo. MRI-Brain at 1 mo revealed a small right inferomedial cerebellar infarct. Echocardiography revealed a patent foramen ovale and bilateral atrial enlargement. He made a full neurological recovery and was eventually returned to active flight status with Flying Class IIC waiver.DISCUSSION: Cryptogenic stroke caused by patent foramen ovale (PFO) is uncommon. However, this is increased in patients younger than 50 yr of age. This can lead to an acute incapacitation with varying degrees of dysfunction. There is controversial discussion of treatment options for secondary stroke prevention with PFO. However, there is no significant literature on primary prevention in these patients. A small subset of patients benefit from closure of PFO and most patients benefit from antiplatelet therapy after a stroke occurs. There may also be a significant subset of patients with PFO that may benefit from antiplatelet therapy as a primary prevention of stroke.Lytle ME, Martin BR. Acute cerebellar stroke in a military active-duty pilot. Aerosp Med Hum Perform. 2021; 92(11): 919-923.

Identification of genes, pathways and transcription factor-miRNA-target gene networks and experimental verification in venous thromboembolism

Venous thromboembolism (VTE) is a complex, multifactorial life-threatening disease that involves vascular endothelial cell (VEC) dysfunction. However, the exact pathogenesis and underlying mechanisms of VTE are not completely clear. The aim of this study was to identify the core genes and pathways in VECs that are involved in the development and progression of unprovoked VTE (uVTE). The microarray dataset GSE118259 was downloaded from the Gene Expression Omnibus database, and 341 up-regulated and 8 down-regulated genes were identified in the VTE patients relative to the healthy controls, including CREB1, HIF1α, CBL, ILK, ESM1 and the ribosomal protein family genes. The protein–protein interaction (PPI) network and the transcription factor (TF)-miRNA-target gene network were constructed with these differentially expressed genes (DEGs), and visualized using Cytoscape software 3.6.1. Eighty-nine miRNAs were predicted as the targeting miRNAs of the DEGs, and 197 TFs were predicted as regulators of these miRNAs. In addition, 237 node genes and 4 modules were identified in the PPI network. The significantly enriched pathways included metabolic, cell adhesion, cell proliferation and cellular response to growth factor stimulus pathways. CREB1 was a differentially expressed TF in the TF-miRNA-target gene network, which regulated six miRNA-target gene pairs. The up-regulation of ESM1, HIF1α and CREB1 was confirmed at the mRNA and protein level in the plasma of uVTE patients. Taken together, ESM1, HIF1α and the CREB1-miRNA-target genes axis play potential mechanistic roles in uVTE development.

Modelling Particle Agglomeration on through Elastic Valves under Flow

This work proposes a model of particle agglomeration in elastic valves replicating the geometry and the fluid dynamics of a venous valve. The fluid dynamics is simulated with Smooth Particle Hydrodynamics, the elastic leaflets of the valve with the Lattice Spring Model, while agglomeration is modelled with a 4-2 Lennard-Jones potential. All the models are combined together within a single Discrete Multiphysics framework. The results show that particle agglomeration occurs near the leaflets, supporting the hypothesis, proposed in previous experimental work, that clot formation in deep venous thrombosis is driven by the fluid dynamics in the valve.

Current Strategies for Microbubble-Based Thrombus Targeting: Activation-Specific Epitopes and Small Molecular Ligands

Microbubbles with enhanced ultrasound represent a potentially potent evolution to the administration of a free drug in the treatment of thrombotic diseases. Conformational and expressional changes of several thrombotic biological components during active coagulation provide epitopes that allow site-specific delivery of microbubble-based agents to the thrombus for theranostic purpose. Through the interaction with these epitopes, emerging high-affinity small molecular ligands are able to selectively target the thrombi with tremendous advantages over traditional antibody-based strategy. In this mini-review, we summarize recent novel strategies for microbubble-based targeting of thrombus through epitopes located at activated platelets and fibrin. We also discuss the challenges of current targeting modalities and supramolecular carrier systems for their translational use in thrombotic pathologies.

The recombinant plant Bauhinia bauhinioides elastase inhibitor reduces rat thrombus without alterations in hemostatic parameters

The anti-inflammatory effects of the plant protease inhibitor BbCI (Bauhinia bauhinioides cruzipain inhibitor), which blocks elastase, cathepsin G, and L, and proteinase 3 has been demonstrated. Here, we investigated the recombinant rBbCI-His(6) (containing a histidine tail) in an experimental venous thrombosis model of vena cava (VC) ligature in rats, comparing to heparin. We evaluate the effects of the inhibitors (native or recombinant) or heparin on the activated partial thromboplastin time (aPTT) and prothrombin time (PT) in human and rat plasmas. The rats undergoing treatment received a saline solution or increasing concentrations of rBbCI-His(6), heparin, or a mixture of both. After 4 h of ligature VC, thrombus, if present was removed and weighed. aPTT, PT, and cytokines were measured in blood collected by cardiac puncture. aPTT, PT, and bleeding time (BT) were also measured at the time of VC (vena cava) ligature. rBbCI-His(6) (0.45 or 1.40 mg/kg) does not alter aPTT, PT or BT. No differences in coagulation parameters were detected in rBbCI-His(6) treated rats at the time of VC ligature or when the thrombus was removed. There was a significant decrease in the weight of thrombus in the animals of the groups treated with the rBbCI-His(6) (1.40 mg/kg), with the rBbCI-His(6) mixture (1.40 mg/kg) + heparin (50 IU/kg) and heparin (100 IU/kg) in relation to control group (saline). The growth-related oncogene/keratinocyte chemoattractant (GRO/KC) serum levels in rats treated with rBbCI-His(6) (1.40 mg/kg) or heparin (200 IU/kg) were reduced. In the experimental model used, rBbCI-His(6) alone had an antithrombotic effect, not altering blood clotting or bleeding time.

Inflammasome activation promotes venous thrombosis through pyroptosis

Crosstalk between coagulation and innate immunity contributes to the progression of many diseases, including infection and cardiovascular disease. Venous thromboembolism (VTE), including pulmonary embolism and deep vein thrombosis (DVT), is among the most common causes of cardiovascular death. Here, we show that inflammasome activation and subsequent pyroptosis play an important role in the development of venous thrombosis. Using a flow restriction-induced mouse venous thrombosis model in the inferior vena cava (IVC), we show that deficiency of caspase-1, but not caspase-11, protected against flow restriction-induced thrombosis. Interleukin-1β expression increased in the IVC following ligation, indicating that inflammasome is activated during injury. Deficiency of gasdermin D (GSDMD), an essential mediator of pyroptosis, protected against restriction-induced venous thrombosis. After induction of venous thrombosis, fibrin was deposited in the veins of wild-type mice, as detected using immunoblotting with a monoclonal antibody that specifically recognizes mouse fibrin, but not in the caspase-1-deficient or GSDMD-deficient mice. Depletion of macrophages by gadolinium chloride or deficiency of tissue factor also protected against venous thrombosis. Our data reveal that tissue factor released from pyroptotic monocytes and macrophages following inflammasome activation triggers thrombosis.

Thrombin: A Pivotal Player in Hemostasis and Beyond

The serine protease thrombin, a naturally derived enzyme, plays a key role in hemostasis by converting fibrinogen to fibrin and activating coagulation factor XIII whereby the fibrin clot is stabilized. Furthermore, thrombin activates platelets through protease-activated receptors on the platelet surface. Conversely, thrombin also exerts anticoagulant effects, enhancing the protein C activity while complexed with thrombomodulin. During recent years, it has become evident that thrombin has significant effects beyond hemostasis, as it contributes also to modulation of the endothelium, promotes inflammation and angiogenesis, and plays a role in tumor progression. Yet, due to the very short half-life and almost immediate inhibition in fluid phase by antithrombin, thrombin itself remains elusive, and only indirect measurement of thrombin generation is possible. This review provides a description of structure and mechanisms of action of thrombin both in physiological and pathological processes. Furthermore, it summarizes laboratory tests that measure in vivo or ex vivo thrombin generation, and presents knowledge on the value of these biomarkers in bleeding disorders, cardiopulmonary bypass surgery, and thromboembolic risk assessment in different patient populations. Finally, this review outlines further perspectives on using thrombin generation biomarkers for research purposes and in clinical practice.

Inflammation, Infection and Venous Thromboembolism

The association between inflammation, infection, and venous thrombosis has long been recognized; yet, only in the last decades have we begun to understand the mechanisms through which the immune and coagulation systems interact and reciprocally regulate one another. These interconnected networks mount an effective response to injury and pathogen invasion, but if unregulated can result in pathological thrombosis and organ damage. Neutrophils, monocytes, and platelets interact with each other and the endothelium in host defense and also play critical roles in the formation of venous thromboembolism. This knowledge has advanced our understanding of both human physiology and pathophysiology, as well as identified mechanisms of anticoagulant resistance and novel therapeutic targets for the prevention and treatment of thrombosis. In this review, we discuss the contributions of inflammation and infection to venous thromboembolism.

Role of angiopoietin-2 in venous thrombus resolution and chronic thromboembolic disease

Defective angiogenesis, incomplete thrombus revascularisation and fibrosis are considered critical pathomechanisms of chronic thromboembolic pulmonary hypertension (CTEPH) after pulmonary embolism (PE). Angiopoietin-2 (ANGPT2) has been shown to regulate angiogenesis, but its importance for thrombus resolution and remodelling is unknown.ANGPT2 plasma concentrations were measured in patients with CTEPH (n=68) and acute PE (n=84). Tissue removed during pulmonary endarterectomy (PEA) for CTEPH was analysed (immuno)histologically. A mouse model of inferior vena cava ligation was used to study the kinetics of venous thrombus resolution in wild-type mice receiving recombinant ANGPT2 via osmotic pumps, and in transgenic mice overexpressing ANGPT2 in endothelial cells.Circulating ANGPT2 levels were higher in CTEPH patients compared to patients with idiopathic pulmonary arterial hypertension and healthy controls, and decreased after PEA. Plasma ANGPT2 levels were also elevated in patients with PE and diagnosis of CTEPH during follow-up. Histological analysis of PEA specimens confirmed increased ANGPT2 expression, and low levels of phosphorylated TIE2 were observed in regions with early-organised pulmonary thrombi, myofibroblasts and fibrosis. Microarray and high-resolution microscopy analysis could localise ANGPT2 overexpression to endothelial cells, and hypoxia and TGF-β1 were identified as potential stimuli. Gain-of-function experiments in mice demonstrated that exogenous ANGPT2 administration and transgenic endothelial ANGPT2 overexpression resulted in delayed venous thrombus resolution, and thrombi were characterised by lower TIE2 phosphorylation and fewer microvessels.Our findings suggest that ANGPT2 delays venous thrombus resolution and that overexpression of ANGPT2 contributes to thrombofibrosis and may thus support the transition from PE to CTEPH.

Application and side effects of blood flow restriction technique: A cross-sectional questionnaire survey of professionals

The physiological benefits of applying blood flow restriction (BFR) in isolation or in the presence of physical exercise have been widely documented in the scientific literature. Most investigations carried out under controlled laboratory conditions have found the technique to be safe. However, few studies have analyzed the use of the technique in clinical settings.To analyze how the BFR technique has been applied by professionals working in the clinical area and the prevalence of side effects (SEs) resulting from the use of this technique.This is a cross-sectional study. A total of 136 Brazilian professionals who perform some function related to physical rehabilitation, sports science, or physical conditioning participated in this study. Participants answered a self-administered online questionnaire consisting of 21 questions related to the professional profile and methodological aspects and SEs of the BFR technique.Professionals reported applying the BFR technique on individuals from different age groups from youth (≤18 years; 3.5%) to older adults (60-80 years; 30.7%), but mainly on people within the age group of 20 to 29 years (74.6%). A total of 99.1% of the professionals coupled the BFR technique with resistance exercise. Their main goals were muscle hypertrophy and physical rehabilitation. The majority (60.9%) of interviewees reported using BFR in durations of less than 5 minutes and the pressure used was mainly determined through the values of brachial blood pressure and arterial occlusion. Moreover, 92% of professionals declared observing at least 1 SE resulting from the BFR technique. Most professionals observed tingling (71.2%) and delayed onset of muscle soreness (55.8%). Rhabdomyolysis, fainting, and subcutaneous hemorrhaging were reported less frequently (1.9%, 3.8%, and 4.8%, respectively).Our findings indicate that the prescription of blood flow restriction technique results in minimal serious side effects when it is done in a proper clinical environment and follows the proposed recommendations found in relevant scientific literature.

Phosphatidylserine-exposing tumor-derived microparticles exacerbate coagulation and cancer cell transendothelial migration in triple-negative breast cancer

Background: Neoadjuvant chemotherapy is relevant to the formation of thromboembolism and secondary neoplasms in triple-negative breast cancer (TNBC). Chemotherapy-induced breast cancer cell-derived microparticles (BCMPs) may have important thrombogenic and pro-metastatic effects on platelets and endothelium, which may be related to the expression and distribution of phosphatidylserine (PS). However, investigating these interactions is challenging due to technical limitations. Methods: A study was conducted in 20 healthy individuals and 18 patients who had been recently diagnosed with TNBC and were undergoing neoadjuvant chemotherapy with doxorubicin and cyclophosphamide. BCMPs were isolated from patient blood samples and doxorubicin-treated breast cancer cell lines. Their structure and morphology were studied by electron microscopy and antigen levels were measured by fluorescence-activated cell sorting. In an inhibition assay, isolated BCMPs were pretreated with lactadherin or tissue factor antibodies. Platelets isolated from healthy subjects were treated with BCMPs and coagulation time, fibrin formation, and expression of intrinsic/extrinsic factor Xase (FXa) and thrombin were evaluated. The effects of BCMPs on endothelial thrombogenicity and integrity were assessed by confocal microscopy, electron microscopy, measurement of intrinsic/extrinsic FXa, prothrombinase assay, and transwell permeability assay. Results: Neoadjuvant chemotherapy significantly increased the expression of PS+ BCMPs in patient plasma. Its expression was associated with a rapid increase in procoagulant activity. Treatment with lactadherin, a PS-binding scavenging molecule, markedly reduced the adhesion of BCMPs and abolished their procoagulant activity, but this was not observed with tissue factor antibody treatment. Intravenous injection of BCMPs in mice induced a significant hypercoagulable state, reducing the extent of plasma fibrinogen and promoting the appearance of new thrombus. Cancer cells incubated with doxorubicin released large numbers of PS+ BCMPs, which stimulated and transformed endothelial cells into a procoagulant phenotype and increased the aggregation and activation of platelets. Moreover, cancer cells exploited this BCMP-induced endothelial leakiness and showed promoted metastasis. Pretreatment with lactadherin increased uptake of both PS+ BCMPs and cancer cells by endothelial cells and limited the transendothelial migration of cancer cells. Conclusion: Lactadherin, a biosensor that we developed, was used to study the extracellular vesicle distribution of PS, which revealed a novel PS+ BCMPs administrative axis that initiated a local coagulation cascade and facilitated metastatic colonization of circulating cancer cells.

"Silent Hypoxemia" Leads to Vicious Cycle of Infection, Coagulopathy and Cytokine Storm in COVID-19: Can Prophylactic Oxygen Therapy Prevent It?

Humankind is facing its worst pandemic of the twenty-first century, due to infection of a novel coronavirus named as SARS-CoV2, started from Wuhan in China. Till now, 15 million people are infected, causing more than 600,000 deaths. The disease, commonly known as, COVID-19, was initially thought to be associated with ARDS only, but later on revealed to have many unexplained and atypical clinical features like coagulopathy and cytokinemia, leading to multi-organ involvements. The patients also suffer from 'Silent Hypoxemia', where there is no immediate respiratory signs and symptoms even though alarmingly low SpO₂ level. We hypothesize that this covert hypoxemia may lead to molecular changes exacerbating coagulopathy and cytokine storm in COVID19 patients, which again, in turn, causes a vicious cycle of more hypoxemia/hypoxia and progression of the infection to more severe stages through HIF-1α dependent pathway. Although molecular mechanisms are yet to be substantiated by scientific evidence, hypoxemia remains an independent worsening factor in serious COVID 19 patients. Keeping all in mind, we propose that even in the early and asymptomatic cases, prophylactic oxygen therapy to be initiated to break the vicious cycle and to reduce the mortality in COVID 19 to save precious human lives.

Thromboembolic Adverse Drug Reactions in Janus Kinase (JAK) Inhibitors: Does the Inhibitor Specificity Play a Role?

Recent advances in immunology enabled the characterization of several signal transmitting pathways responsible for proper cytokine and chemokine signaling. Among them, Janus kinases (JAKs) are essential components of receptor activation systems. The discovery of JAK kinases enabled the synthesis of JAK kinase inhibitors (JAKi or Jakinibs), which have proven to be efficacious in the treatment of hematologic malignancies and several rheumatological disorders and continue to be investigated in many clinical indications. Blocking multiple cytokines belonging to several cytokine families with a single small molecule may, however, create a potential risk for the patients. Recently, a higher risk of thromboembolic complications, namely, deep vein thrombosis and pulmonary embolism, has been recognized as the main concern during treatment with Jakinibs. At present, it is not entirely clear whether this increased risk is related to direct cytokine blockade, the presence of concomitant diseases in treated patients or other unknown circumstances that work together to increase the risk of this side effect. In this review, we discuss data on the risk of thromboembolic side effects, with special emphasis on the mechanism that may be responsible for this increased risk. Many indirect data indicate that higher thromboembolic risk may be related to the specificity of JAK inhibitor action, such that preferentially blocking one signaling pathway upsets the balance between pro and anti-thrombotic activities.

In vitro flow-based assay: From simple toward more sophisticated models for mimicking hemostasis and thrombosis

In vitro flow-based assays are widely used to investigate the role of platelets and coagulation in hemostasis and thrombosis. Their main advantage over other assays relies on the fact that they integrate blood flow that regulates many aspects of platelet function, including adhesion, activation, and aggregation. Blood flow is also central in the regulation of coagulation through its ability to modulate the local concentrations of coagulation factors within and around thrombi. The most broadly used assay to study thrombus formation consists in perfusing whole blood over immobilized fibrillar collagen through a single channel, which helps to reproduce thrombus formation as it occurs in vivo after vascular injury, with platelets adhering, becoming activated, and forming a mural thrombus. This process can also be studied under conditions of thrombin generation, notably by recalcifying blood collected in sodium citrate. In this manuscript, we briefly discuss the advantages and limits of this broadly used "in vitro thrombus formation model." The main emphasis is on the description of the most recent developments regarding design of new flow models and new techniques, and how these may advance the landscape of in vitro studies into the formation of physiological or pathophysiological thrombi. Challenges linked to mimicking the formation of a hemostatic plug in a healthy vessel or a thrombus in diseased arteries and the complexity of reproducing the various aspects of venous thrombosis are discussed. Future directions are proposed to improve the physiological or pathophysiological relevance of current flow-based assays.

Microengineered Human Vein-Chip Recreates Venous Valve Architecture and Its Contribution to Thrombosis

Deep vein thrombosis (DVT) and its consequences are lethal, but current models cannot completely dissect its determinants-endothelium, flow, and blood constituents-together called Virchow's triad. Most models for studying DVT forego assessment of venous valves that serve as the primary sites of DVT formation. Therefore, the knowledge of DVT formed at the venous cusps has remained obscure due to lack of experimental models. Here, organ-on-chip methodology is leveraged to create a Vein-Chip platform integrating fully vascularized venous valves and its hemodynamic, as seen in vivo. These Vein-Chips reveal that vascular endothelium of valve cusps adapts to the locally disturbed microenvironment by expressing a different phenotype from the regions of uniform flow. This spatial adaptation of endothelial function recreated on the in vitro Vein-Chip platform is shown to protect the vein from thrombosis from disturbed flow in valves, but interestingly, cytokine stimulation reverses the effect and switches the valve endothelium to becoming prothrombotic. The platform eventually modulates the three factors of Virchow's triad and provides a systematic approach to investigate the determinants of fibrin and platelet dynamics of DVT. Therefore, this Vein-Chip offers a new preclinical approach to study venous pathophysiology and show effects of antithrombotic drug treatment.

The role of bone marrow-derived cells in venous thromboembolism

Venous thrombosis is a life-threatening condition with high morbidity and mortality. Abnormal functioning of different cells in the blood is an integral part of its pathogenesis. In this review, we describe the contribution of bone marrow-derived cells to the development of this debilitating disease. We present both epidemiological and clinical data demonstrating involvement of various cell types in venous thrombosis, and discuss potential mechanisms underlying these effects. Modern concepts including recently discovered new paradigms in thrombosis, such as neutrophil extracellular traps, mast cells, and polyphosphate, are summarized.

The role of valve stiffness in the insurgence of deep vein thrombosis

Deep vein thrombosis is a life-threatening development of blood clots in deep veins. Immobility and blood flow stagnancy are typical risk factors indicating that fluid dynamics play an important role in the initiation of venous clots. However, the roles of physical parameters of the valves and flow conditions in deep vein thrombosis initiation have not been fully understood. Here, we describe a microfluidics in vitro method that enabled us to explore the role of valve elasticity using in situ fabrication and characterisation. In our experimental model the stiffness of each valve leaflet can be controlled independently, and various flow conditions were tested. The resulting complex flow patterns were detected using ghost particle velocimetry and linked to localised thrombus formation using whole blood and an aqueous suspension of polystyrene particles. In particular, valves with leaflets of similar stiffness had clot formation on the valve tips whereas valves with leaflets of different stiffness had clot formation in the valve pocket.

The Effect of Sequential Compression Devices on Fibrinolysis in Plastic Surgery Outpatients: A Randomized Trial

BACKGROUND

Sequential compression devices are often considered a mainstay of prophylaxis against deep venous thromboses in surgical patients. The devices are believed to produce a milking action on the deep veins to prevent venous stasis. A systemic fibrinolytic effect has also been proposed, adding a second mechanism of action. The plasma levels of tissue plasminogen activator and plasminogen activator inhibitor-1 reflect fibrinolytic activity.

METHODS

A randomized trial was conducted among 50 consecutive plastic surgery outpatients undergoing cosmetic surgery performed by the author under total intravenous anesthesia and without paralysis. Patients were randomized to receive calf-length sequential compression devices or no sequential compression devices during surgery. Blood samples were obtained from the upper extremity preoperatively and at hourly intervals until the patient was discharged from the postanesthesia care unit. Tissue plasminogen activator and plasminogen activator inhibitor-1 levels were measured. Ultrasound surveillance was used in all patients. There was no outside funding for the study.

RESULTS

All patients agreed to participate (inclusion rate, 100 percent). No patient developed clinical signs or ultrasound evidence of a deep venous thrombosis. There were no significant changes in tissue plasminogen activator levels or plasminogen activator inhibitor-1 levels from the preoperative measurements at any hourly interval and no differences in levels comparing patients treated with or without sequential compression devices.

CONCLUSIONS

No significant change in systemic fibrinolytic activity occurs during outpatient plastic surgery under total intravenous anesthesia. Sequential compression devices do not affect tissue plasminogen activator or plasminogen activator inhibitor-1 levels, suggesting no fibrinolytic benefit.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, I.

Tuning the Thromboinflammatory Response to Venous Flow Interruption by the Ectonucleotidase CD39

Objective- Leukocyte flux contributes to thrombus formation in deep veins under pathological conditions, but mechanisms that inhibit venous thrombosis are incompletely understood. Ectonucleotide di(tri)phosphohydrolase 1 ( ENTPD1 or Cd39), an ectoenzyme that catabolizes extracellular adenine nucleotides, is embedded on the surface of endothelial cells and leukocytes. We hypothesized that under venous stasis conditions, CD39 regulates inflammation at the vein:blood interface in a murine model of deep vein thrombosis. Approach and Results- CD39-null mice developed significantly larger venous thrombi under venous stasis, with more leukocyte recruitment compared with wild-type mice. Gene expression profiling of wild-type and Cd39-null mice revealed 76 differentially expressed inflammatory genes that were significantly upregulated in Cd39-deleted mice after venous thrombosis, and validation experiments confirmed high expression of several key inflammatory mediators. P-selectin, known to have proximal involvement in venous inflammatory and thrombotic events, was upregulated in Cd39-null mice. Inferior vena caval ligation resulted in thrombosis and a corresponding increase in both P-selectin and VWF (von Willebrand Factor) levels which were strikingly higher in mice lacking the Cd39 gene. These mice also manifest an increase in circulating platelet-leukocyte heteroaggregates suggesting heterotypic crosstalk between coagulation and inflammatory systems, which is amplified in the absence of CD39. Conclusions- These data suggest that CD39 mitigates the venous thromboinflammatory response to flow interruption.

Microparticles from aged packed red blood cell units stimulate pulmonary microthrombus formation via P-selectin

INTRODUCTION

During storage, packed red blood cells undergo a series of physical, metabolic, and chemical changes collectively known as the red blood cell storage lesion. One key component of the red blood cell storage lesion is the accumulation of microparticles, which are submicron vesicles shed from erythrocytes as part of the aging process. Previous studies from our laboratory indicate that transfusion of these microparticles leads to lung injury, but the mechanism underlying this process is unknown. In the present study, we hypothesized that microparticles from aged packed red blood cell units induce pulmonary thrombosis.

MATERIALS AND METHODS

Leukoreduced, platelet-depleted, murine packed red blood cells (pRBCS) were prepared then stored for up to 14 days. Microparticles were isolated from stored units via high-speed centrifugation. Mice were transfused with microparticles. The presence of pulmonary microthrombi was determined with light microscopy, Martius Scarlet Blue, and thrombocyte stains. In additional studies microparticles were labelled with CFSE prior to injection. Murine lung endothelial cells were cultured and P-selectin concentrations determined by ELISA. In subsequent studies, P-selectin was inhibited by PSI-697 injection prior to transfusion.

RESULTS

We observed an increase in microthrombi formation in lung vasculature in mice receiving microparticles from stored packed red blood cell units as compared with controls. These microthrombi contained platelets, fibrin, and microparticles. Treatment of cultured lung endothelial cells with microparticles led to increased P-selectin in the media. Treatment of mice with a P-selectin inhibitor prior to microparticle infusion decreased microthrombi formation.

CONCLUSIONS

These data suggest that microparticles isolated from aged packed red blood cell units promote the development of pulmonary microthrombi in a murine model of transfusion. This pro-thrombotic event appears to be mediated by P-selectin.