Venous thrombosis-associated inflammation and attenuation with neutralizing antibodies to cytokines and adhesion molecules

Mice with reduced protease-activated receptor 4 reactivity show decreased venous thrombosis and platelet procoagulant activity

BACKGROUND

Hypercoagulation and thrombin generation are major risk factors for venous thrombosis. Sustained thrombin signaling through protease-activated receptor (PAR) 4 promotes platelet activation, phosphatidylserine exposure, and subsequent thrombin generation. A single nucleotide polymorphism in PAR4 (rs2227376) changes proline to leucine extracellular loop 3, which decreases PAR4 reactivity and is associated with a lower risk for venous thromboembolism (VTE) in a genome wide association studies meta-analysis.

OBJECTIVES

The goal of this study was to determine the mechanism for the association of rs2227376 with a reduced risk of VTE using mice with a homologous mutation (PAR4-P322L).

METHODS

Venous thrombosis was examined using our recently generated PAR4-P322L mice in the inferior vena cava stasis and stenosis models. Coagulation and clot stability were measured using rotational thromboelastometry. Thrombin-generating potential was measured in platelet-rich plasma. Phosphatidylserine surface expression and platelet-neutrophil aggregates were analyzed using flow cytometry.

RESULTS

Mice heterozygous (PAR4P/L) or homozygous (PAR4L/L) at position 310 had reduced sizes of venous clots at 48 hours. PAR4P/L and PAR4L/L platelets had progressively decreased phosphatidylserine in response to thrombin and convulxin, in addition to decreased thrombin generation and decreased PAR4-mediated platelet-neutrophil aggregation.

CONCLUSION

The leucine allele in extracellular loop 3, PAR4-322L, leads to fewer procoagulant platelets, decreased endogenous thrombin potential, and reduced platelet-neutrophil aggregation. This decreased ability to generate thrombin and bind to neutrophils offers a mechanism for PAR4's role in VTE, highlighting a key role for PAR4 signaling.

Current development of severe acute respiratory syndrome coronavirus 2 neutralizing antibodies (Review)

The coronavirus disease 2019 pandemic due to severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) seriously affected global public health security. Studies on vaccines, neutralizing antibodies (NAbs) and small molecule antiviral drugs are currently ongoing. In particular, NAbs have emerged as promising therapeutic agents due to their well‑defined mechanism, high specificity, superior safety profile, ease of large‑scale production and simultaneous application for both prevention and treatment of viral infection. Numerous NAb therapeutics have entered the clinical research stages, demonstrating promising therapeutic and preventive effects. These agents have been used for outbreak prevention and control under urgent authorization processes. The present review summarizes the molecular targets of SARS‑CoV‑2‑associated NAbs and screening and identification techniques for NAb development. Moreover, the current shortcomings and challenges that persist with the use of NAbs are discussed. The aim of the present review is to offer a reference for the development of NAbs for any future emergent infectious diseases, including SARS‑CoV‑2.

Platelet lifespan and mechanisms for clearance

PURPOSE OF REVIEW

Activated or aged platelets are removed from circulation under (patho)physiologic conditions, the exact mechanism of platelet clearance under such conditions remains unclear and are currently being investigated. This review focuses on recent findings and controversies regarding platelet clearance and the disruption of platelet life cycle.

RECENT FINDINGS

The platelet life span is determined by glycosylation of platelet surface receptors with sialic acid. Recently, it was shown that platelet activation and granule release leads to desialylation of glycans and accelerated clearance of platelets under pathological conditions. This phenomenon was demonstrated to be a main reason for thrombocytopenia being a complication in several infections and immune disorders.

SUMMARY

Although we have recently gained some insight into how aged platelets are cleared from circulation, we are still not seeing the full picture. Further investigations of the platelet clearance pathways under pathophysiologic conditions are needed as well as studies to unravel the connection between platelet clearance and platelet production.

Acute Pulmonary Embolism and Immunity in Animal Models

Venous thromboembolism, encompassing acute pulmonary embolism (APE) and deep vein thrombosis (DVT), is a potentially fatal disease with complex pathophysiology. Traditionally, the Virchow triad provided a framework for understanding the pathogenic contributors to thrombus formation, which include endothelial dysfunction, alterations in blood flow and blood hypercoagulability. In the last years, it has become apparent that immunity plays a central role in thrombosis, interacting with classical prothrombotic mechanisms, oxidative stress and vascular factors. Thrombosis amplifies inflammation, and exaggerated inflammatory processes can trigger thrombosis mainly due to the activation of leukocytes, platelets, and endothelial cells. APE-related endothelium injury is a major trigger for immune system activation. Endothelium is also a key component mediating inflammatory reaction and it is relevant to maintain vascular permeability. Exaggerated right ventricular wall stress and overload, with coexisting systemic hypotension and hypoxemia, result in myocardial injury and necrosis. Hypoxia, tissue factor activation and cytokine storm are engaged in the thrombo-inflammatory processes. Thrombus development is characterized by inflammatory state vascular wall caused mainly by an early extravasation of leukocytes and intense selectins and cytokines production. Nevertheless, immunity of DVT is well described, little is known about potential chemokine and cellular differences between thrombus that develops in the vein and thrombus that detaches and lodges in the pulmonary circulation being a cause of APE. There is a paucity of data considering inflammatory state in the pulmonary artery wall during an acute episode of pulmonary embolism. The main aim of this review is to summarize the knowledge of immunity in acute phase of pulmonary embolism in experimental models.

Intravital Imaging of Thrombosis Models in Mice

Intravital microscopy is a powerful tool to study thrombosis in real time. The kinetics of thrombus formation and progression in vivo is studied after inflicting damage to the endothelium through mechanical, chemical, or laser injury. Mouse models of atherosclerosis are also used to induce thrombus formation. Vessels of different sizes and from different vascular beds such as carotid artery or vena cava, mesenteric or cremaster arterioles, can be targeted. Using fluorescent dyes, antibodies, or reporter mouse strains allows to visualize key cells and factors mediating the thrombotic processes. Here, we review the latest literature on using intravital microscopy to study thrombosis as well as thromboinflammation following transient middle cerebral artery occlusion, infection-induced immunothrombosis, and liver ischemia reperfusion.

The role of monocytes in thrombotic diseases: a review

Cardiovascular and cerebrovascular diseases are the number one killer threatening people's life and health, among which cardiovascular thrombotic events are the most common. As the cause of particularly serious cardiovascular events, thrombosis can trigger fatal crises such as acute coronary syndrome (myocardial infarction and unstable angina), cerebral infarction and so on. Circulating monocytes are an important part of innate immunity. Their main physiological functions are phagocytosis, removal of injured and senescent cells and their debris, and development into macrophages and dendritic cells. At the same time, they also participate in the pathophysiological processes of pro-coagulation and anticoagulation. According to recent studies, monocytes have been found to play a significant role in thrombosis and thrombotic diseases of the immune system. In this manuscript, we review the relationship between monocyte subsets and cardiovascular thrombotic events and analyze the role of monocytes in arterial thrombosis and their involvement in intravenous thrombolysis. Finally, we summarize the mechanism and therapeutic regimen of monocyte and thrombosis in hypertension, antiphospholipid syndrome, atherosclerosis, rheumatic heart disease, lower extremity deep venous thrombosis, and diabetic nephropathy.

Clinical application of three-dimensional T1-weighted BrainVIEW in magnetic resonance imaging of cerebral venous thrombosis: a case report and literature review

To date, there is no clinical scoring system or laboratory indicator that can rule out cerebral venous thrombosis (CVT) or provide diagnostic proof for evaluating post-treatment thrombosis recanalization during follow-up. We therefore explored an imaging method for quantitative assessment of CVT and assessed thrombotic changes during follow-up. A patient presented with severe posterior occipital distension extending to the top of the forehead and an elevated plasma D-dimer (DD2) level. Computed tomography and pre-contrast-enhanced magnetic resonance imaging revealed only a small amount of cerebral hemorrhage. Three-dimensional (3D) T1-weighted (T1W) BrainVIEW pre-contrast-enhanced magnetic resonance scanning showed subacute thrombosis in the venous sinus, and the post-contrast-enhanced scan combined with volume rendering reconstruction showed cerebral thrombosis of the venous sinus and allowed for measurement of the thrombus volume. On days 30 and 60 of post-treatment follow-up, post-contrast-enhanced scans showed progressive reduction of the thrombus volume as well as recanalization and fibrotic flow voids in the chronic thrombosis. 3D T1W BrainVIEW was helpful to observe the size of the thrombi and the situation of venous sinus recanalization during the follow-up after clinical treatment of CVT. This technique can reflect the imaging manifestations of CVT throughout the whole process to guide clinical treatment decisions.

Experimental venous thrombus resolution is driven by IL-6 mediated monocyte actions

Deep venous thrombosis and residual thrombus burden correlates with circulating IL-6 levels in humans. To investigate the cellular source and role of IL-6 in thrombus resolution, Wild type C57BL/6J (WT), and IL-6-/- mice underwent induction of VT via inferior vena cava (IVC) stenosis or stasis. Vein wall (VW) and thrombus were analyzed by western blot, immunohistochemistry, and flow cytometry. Adoptive transfer of WT bone marrow derived monocytes was performed into IL6-/- mice to assess for rescue. Cultured BMDMs from WT and IL-6-/- mice underwent quantitative real time PCR and immunoblotting for fibrinolytic factors and matrix metalloproteinase activity. No differences in baseline coagulation function or platelet function were found between WT and IL-6-/- mice. VW and thrombus IL-6 and IL-6 leukocyte-specific receptor CD126 were elevated in a time-dependent fashion in both VT models. Ly6Clo Mo/MØ were the predominant leukocyte source of IL-6. IL-6-/- mice demonstrated larger, non-resolving stasis thrombi with less neovascularization, despite a similar number of monocytes/macrophages (Mo/MØ). Adoptive transfer of WT BMDM into IL-6-/- mice undergoing stasis VT resulted in phenotype rescue. Human specimens of endophlebectomized tissue showed co-staining of Monocyte and IL-6 receptor. Thrombosis matrix analysis revealed significantly increased thrombus fibronectin and collagen in IL-6-/- mice. MMP9 activity in vitro depended on endogenous IL-6 expression in Mo/MØ, and IL-6-/- mice exhibited stunted matrix metalloproteinase activity. Lack of IL-6 signaling impairs thrombus resolution potentially via dysregulation of MMP-9 leading to impaired thrombus recanalization and resolution. Restoring or augmenting monocyte-mediated IL-6 signaling in IL-6 deficient or normal subjects, respectively, may represent a non-anticoagulant target to improve thrombus resolution.

A vein wall cell atlas of murine venous thrombosis determined by single-cell RNA sequencing

Deep vein thrombosis (DVT) is a common clinical problem, but its cellular and molecular mechanisms remain incompletely understood. In this study, we performed single-cell RNA sequencing on mouse inferior vena cava (IVC) 24 h after thrombus-inducing IVC ligation or sham operation. 9 cell types composed of multiple subpopulations were identified. Notable transcriptomic changes induced by DVT included a marked inflammatory response, elevated hypoxia, and globally reduced myogenesis. Analysis of individual cell populations revealed increased inflammation and reduced extracellular matrix production across smooth muscle cells and fibroblasts, juxtaposed against an early phenotypic shift in smooth muscle cell populations away from a contractile state. By characterizing the transcriptomic changes in the vein wall during acute venous thrombosis at the single-cell level, this work provides novel insights into early pathological events in the vein wall that may potentiate thrombus formation and result in long term adverse venous remodeling.

Neutrophil Extracellular Traps in Atherosclerosis and Thrombosis

Despite effective therapeutic and preventive strategies, atherosclerosis and its complications still represent a substantial health burden. Leukocytes and inflammatory mechanisms are increasingly recognized as drivers of atherosclerosis. Neutrophil granulocytes within the circulation were recently shown to undergo neutrophil extracellular trap (NET) formation, linking innate immunity with acute complications of atherosclerosis. In this chapter, we summarize mechanisms of NET formation, evidence for their involvement in atherosclerosis and thrombosis, and potential therapeutic regimens specifically targeting NET components.

The Emerging Role of Neutrophil Extracellular Traps in Arterial, Venous and Cancer-Associated Thrombosis

Neutrophils play a vital role in the formation of arterial, venous and cancer-related thrombosis. Recent studies have shown that in a process known as NETosis, neutrophils release proteins and enzymes complexed to DNA fibers, collectively called neutrophil extracellular traps (NETs). Although NETs were originally described as a way for the host to capture and kill bacteria, current knowledge indicates that NETs also play an important role in thrombosis. According to recent studies, the destruction of vascular microenvironmental homeostasis and excessive NET formation lead to pathological thrombosis. In vitro experiments have found that NETs provide skeletal support for platelets, red blood cells and procoagulant molecules to promote thrombosis. The protein components contained in NETs activate the endogenous coagulation pathway to promote thrombosis. Therefore, NETs play an important role in the formation of arterial thrombosis, venous thrombosis and cancer-related thrombosis. This review will systematically summarize and explain the study of NETs in thrombosis in animal models and in vivo experiments to provide new targets for thrombosis prevention and treatment.

Strength and deformability of fibrin clots: Biomechanics, thermodynamics, and mechanisms of rupture

Fibrin is the major determinant of the mechanical stability and integrity of blood clots and thrombi. To explore the rupture of blood clots, emulating thrombus breakage, we stretched fibrin gels with single-edge cracks of varying size. Ultrastructural alterations of the fibrin network correlated with three regimes of stress vs. strain profiles: the weakly non-linear regime due to alignment of fibrin fibers; linear regime owing to further alignment and stretching of fibers; and the rupture regime for large deformations reaching the critical strain and stress, at which irreversible breakage of fibers ahead of the crack tip occurs. To interpret the stress-strain curves, we developed a new Fluctuating Spring model, which maps the fibrin alignment at the characteristic strain, network stretching with the Young modulus, and simultaneous cooperative rupture of coupled fibrin fibers into a theoretical framework to obtain the closed-form expressions for the strain-dependent stress profiles. Cracks render network rupture stochastic, and the free energy change for fiber deformation and rupture decreases with the crack length, making network rupture more spontaneous. By contrast, mechanical cooperativity due to the presence of inter-fiber contacts strengthens fibrin networks. The results obtained provide a fundamental understanding of blood clot breakage that underlies thrombotic embolization. STATEMENT OF SIGNIFICANCE: Fibrin, a naturally occurring biomaterial, is the major determinant of mechanical stability and integrity of blood clots and obstructive thrombi. We tested mechanically fibrin gels with single-edge cracks and followed ultrastructural alterations of the fibrin network. Rupture of fibrin gel involves initial alignment and elastic stretching of fibers followed by their eventual rupture for deformations reaching the critical level. To interpret the stress-strain curves, we developed Fluctuating Spring model, which showed that cracks render rupture of fibrin networks more spontaneous; yet, coupled fibrin fibers reinforce cracked fibrin networks. The results obtained provide fundamental understanding of blood clot breakage that underlies thrombotic embolization. Fluctuating Spring model can be applied to other protein networks with cracks and to interpret the stress-strain profiles.

Evaluation and management of patients with chronic thromboembolic pulmonary hypertension - consensus statement from the ISHLT

ISHLT members have recognized the importance of a consensus statement on the evaluation and management of patients with chronic thromboembolic pulmonary hypertension. The creation of this document required multiple steps, including the engagement of the ISHLT councils, approval by the Standards and Guidelines Committee, identification and selection of experts in the field, and the development of 6 working groups. Each working group provided a separate section based on an extensive literature search. These sections were then coalesced into a single document that was circulated to all members of the working groups. Key points were summarized at the end of each section. Due to the limited number of comparative trials in this field, the document was written as a literature review with expert opinion rather than based on level of evidence.

Elevated plasma concentration of complement factor C5 is associated with risk of future venous thromboembolism

The role of complement in the pathogenesis of venous thromboembolism (VTE) is unclear. We aimed to (i) investigate whether plasma complement component C5 levels are influenced by genetic variants or chronic inflammation, and (ii) investigate the association between plasma C5 and risk of future VTE in a nested case-control study with 415 VTE patients and 848 age- and sex-matched controls derived from the Tromsø study. Plasma C5 levels were measured at inclusion. Odds ratios (ORs) with 95% confidence intervals (95% CI) for provoked and unprovoked VTE across tertiles of C5 concentrations were estimated using logistic regression. C-reactive protein (CRP) was adjusted for as a proxy for general inflammation. Whole exome sequencing and protein quantitative trait loci analyses were performed to assess genetic influence on C5 concentrations. There was no association between genome-wide or C5-related gene variants and C5 levels. The association between plasma C5 levels and VTE risk displayed a threshold effect, where subjects with C5 levels above the lowest tertile had increased VTE risk. Subjects in tertile 3 (highest C5 levels) had an age and sex-adjusted OR of 1.45 (95% CI 1.07-1.96) compared to tertile 1 (lowest). This was more pronounced for unprovoked VTE (OR 1.70, 95% CI 1.11-2.60). Adjustments for body mass index and CRP had minor impact on risk estimates. The ORs increased substantially with shorter time between blood sampling and VTE event. In conclusion, plasma C5 was associated with risk of future VTE. C5 levels were not genetically regulated and only slightly influenced by chronic inflammation.

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.

Magnetic resonance black-blood thrombus imaging can confirm chronic cerebral venous thrombosis: a case report and literature review

Background

Cerebral venous thrombosis (CVT) is easily missed or misdiagnosed in clinical settings because of its high variability in terms of symptoms and radiological findings. Herein, we aimed to explore a promising modality for confirming presumed CVT in the hope to uncover its superior diagnostic performance to conventional imaging modalities.

Case presentation: The patient complained of intolerable pain in her forehead and left eye. Her lumbar puncture opening pressure was 140 mmH₂O, and her cerebrospinal fluid composition was normal. No marked abnormalities were observed in routine brain images, including non-contrast computed tomography, magnetic resonance imaging, and contrast-enhanced magnetic resonance venography. However, chronic mural thrombi in the lumen of the left cortical veins, transverse/sigmoid sinus, and superior sagittal sinus were identified in magnetic resonance black-blood thrombus imaging (MRBTI) maps.

Conclusions

MRBTI can be used to directly and non-invasively visualize thrombi, and may thus be a promising tool over alternative routine techniques for confirming the diagnosis of CVT.

The Neutrophil Secretome as a Crucial Link between Inflammation and Thrombosis

Cardiovascular diseases are a leading cause of death. Blood-cell interactions and endothelial dysfunction are fundamental in thrombus formation, and so further knowledge of the pathways involved in such cellular crosstalk could lead to new therapeutical approaches. Neutrophils are secretory cells that release well-known soluble inflammatory signaling mediators and other complex cellular structures whose role is not fully understood. Studies have reported that neutrophil extracellular vesicles (EVs) and neutrophil extracellular traps (NETs) contribute to thrombosis. The objective of this review is to study the role of EVs and NETs as key factors in the transition from inflammation to thrombosis. The neutrophil secretome can promote thrombosis due to the presence of different factors in the EVs bilayer that can trigger blood clotting, and to the release of soluble mediators that induce platelet activation or aggregation. On the other hand, one of the main pathways by which NETs induce thrombosis is through the creation of a scaffold to which platelets and other blood cells adhere. In this context, platelet activation has been associated with the induction of NETs release. Hence, the structure and composition of EVs and NETs, as well as the feedback mechanism between the two processes that causes pathological thrombus formation, require exhaustive analysis to clarify their role in thrombosis.

Visualizing thrombosis to improve thrombus resolution

The severity, course, and outcomes of thrombosis are determined mainly by the size and location of the thrombus, but studying thrombus structure and composition has been an important but challenging task. The substantial progress in determination of thrombus morphology has become possible due to new intravital imaging methodologies in combination with mechanical thrombectomy, which allows extraction of a fresh thrombus from a patient followed by microscopy. Thrombi have been found to contain various structural forms of fibrin along with platelet aggregates, leukocytes, and red blood cells, many of which acquire a polyhedral shape (polyhedrocytes) as a result of intravital platelet-driven contraction. The relative volume fractions of thrombus components and their structural forms vary substantially, depending on the clinical and pathogenic characteristics. This review summarizes recent research that describes quantitative and qualitative morphologic characteristics of arterial and venous thrombi that are relevant for the pathogenesis, prophylaxis, diagnosis, and treatment of thrombosis.

Insights from experimental post-thrombotic syndrome and potential for novel therapies

Post-thrombotic syndrome (PTS) is an end stage manifestation of deep vein thrombosis. This is an inherently inflammatory process, with consequent fibrosis. Multiple cellular types are involved, and are likely driven by leukocytes. Herein, we review the current gaps in therapy, and insights from rodent models of venous thrombosis that suggest possible targets to treat and prevent PTS.

miR-150 regulates endothelial progenitor cell differentiation via Akt and promotes thrombus resolution

Background

Deep venous thrombosis (DVT) constitutes a major global disease burden. Endothelial progenitor cells (EPCs) have been described in association with recanalization of venous thrombus. Furthermore, emerging evidence suggests microRNAs are involved in this progression. The goal of this study was to investigate the influence of miR-150 on the behavior of EPCs and its potential contribution in venous thrombosis resolution.

Methods

We isolated and cultured EPCs from healthy adults. Next, early EPCs or endothelial colony-forming cells (ECFCs or late EPCs) were transfected with miR-150 agomir and antagomir. Gene expression profiles, proliferation, cytokine secretion, and angiogenic capacity of early EPCs and ECFCs were examined. The effects of miR-150 on c-Myb expression and Akt/FOXO1 signaling were also evaluated. Furthermore, a rat model of venous thrombosis was constructed to determine the in vivo function of EPCs.

Results

Our results showed that miR-150 overexpression in early EPCs significantly promoted differentiation to ECFCs and contributed to proliferation and tube formation. However, suppression of miR-150 in late EPCs inhibited proliferation and tube formation. Moreover, we identified that this progression is regulated by inhibition of c-Myb and activation of the Akt/FOXO1 pathway. Our findings also showed that miR-150 led to the enhanced resolution ability of EPCs in a rat venous thrombosis model.

Conclusions

In this study, we present a novel mechanism of miRNA-mediated regulation of EPCs and Akt activation in thrombus resolution.

Oxidative Stress and Thrombosis during Aging: The Roles of Oxidative Stress in RBCs in Venous Thrombosis

Mid-life stage adults are at higher risk of developing venous thrombosis (VT)/thromboembolism (VT/E). Aging is characterized by an overproduction of reactive oxygen species (ROS), which could evoke a series of physiological changes involved in thrombosis. Here, we focus on the critical role of ROS within the red blood cell (RBC) in initiating venous thrombosis during aging. Growing evidence has shifted our interest in the role of unjustifiably unvalued RBCs in blood coagulation. RBCs can be a major source of oxidative stress during aging, since RBC redox homeostasis is generally compromised due to the discrepancy between prooxidants and antioxidants. As a result, ROS accumulate within the RBC due to the constant endogenous hemoglobin (Hb) autoxidation and NADPH oxidase activation, and the uptake of extracellular ROS released by other cells in the circulation. The elevated RBC ROS level affects the RBC membrane structure and function, causing loss of membrane integrity, and decreased deformability. These changes impair RBC function in hemostasis and thrombosis, favoring a hypercoagulable state through enhanced RBC aggregation, RBC binding to endothelial cells affecting nitric oxide availability, RBC-induced platelet activation consequently modulating their activity, RBC interaction with and activation of coagulation factors, increased RBC phosphatidylserine exposure and release of microvesicles, accelerated aging and hemolysis. Thus, RBC oxidative stress during aging typifies an ultimate mechanism in system failure, which can affect major processes involved in the development of venous thrombosis in a variety of ways. The reevaluated concept of the critical role of RBC ROS in the activation of thrombotic events during aging will help identify potential targets for novel strategies to prevent/reduce the risk for VT/E or VT/E recurrences in mid-life stage adults.

Phlebosclerosis in lower extremities veins - a systematic review

Phlebosclerosis is a venous wall degenerative disease which has gained little popularity in the literature due to its uncertain clinical significance. The objective of this review is to evaluate the epidemiology, etiology and clinical significance of phlebosclerosis in lower extremities veins, particularly the effect of preexisting phlebosclerosis of the great saphenous vein on vein graft patency. Medline was searched from inception until November 1, 2019. Reference lists of included studies were scanned. Only articles published after 1949 were included. Two reviewers independently screened titles/abstracts and full-text papers for any study design in relation to phlebosclerosis in lower extremities veins and abstracted data. A total of 16 Cohort studies and one case-control study (3708 participants, mean age 61.8 years, 59.3 % men, and 40.7 % women) were included after screening 317 titles and abstracts, and 80 full-text articles. The incidence of phlebosclerosis ranged from 1.5-9.7 % depending on the radiological features. On the contrary, the incidence of the phlebosclerotic great saphenous vein prior to its use as a vein graft was 26.9-91 % on histological examination. The small saphenous vein was the most common location of phlebosclerosis followed by the great saphenous vein. There is a link between phlebosclerosis and age, venous insufficiency and haemodialysis. As for the vein graft patency seven studies demonstrated a correlation between preexisting phlebosclerosis and vein graft stenosis, whereas three studies failed to prove any association. In conclusion, the radiological incidence of phlebosclerosis depended on the ultrasound findings. Its presence in the great saphenous vein prior to its use as a vein graft is established on histological examination. The small saphenous vein is mainly affected. Risk factors included age, haemodialysis, and venous insufficiency. Preexisting wall thickness of the great saphenous vein graft seemed to affect negatively its patency in bypass surgery.

Depletion of CD4 and CD8 Positive T Cells Impairs Venous Thrombus Resolution in Mice

Resolution of deep venous thrombosis involves coordinated inflammatory processes. T cells regulate inflammation in vivo and modulate vascular remodeling in other settings, but their role in venous thrombus resolution remains undefined. To determine the role of T cells in venous thrombus resolution in vivo, stasis induced thrombi were created by vena cava ligation in outbred CD-1 mice. CD4 and CD8 positive T cells, as determined by flow cytometry, were present in thrombi both during thrombus formation and resolution. Depletion of the CD4 and CD8 positive T cells by antibody treatment selectively impaired thrombus resolution compared to animals treated with isotype control antibodies, without an effect on venous thrombus formation. Quantitation of intra-thrombus macrophage numbers, fibrinolytic marker expression, and gelatinolytic activity by zymography revealed that T cell depletion decreased the number of macrophages, reduced the expression of fibrinolytic marker urokinase plasminogen activator (uPA), and decreased the activity of matrix metalloprotinease-9 (MMP-9). These data implicate CD4 and CD8 positive T cells in functionally contributing to venous thrombus resolution, thus representing a potential therapeutic target, but also underscoring potential risks involved in T cell depletion used clinically for solid organ and hematopoietic transplantation procedures.

Crucial Involvement of IL-6 in Thrombus Resolution in Mice via Macrophage Recruitment and the Induction of Proteolytic Enzymes

After the ligation of the inferior vena cava (IVC) of wild-type (WT) mice, venous thrombi formed and grew progressively until 5 days and resolved thereafter. Concomitantly, intrathrombotic gene expression of Il6 was enhanced later than 5 days after IVC ligation. IL-6 protein expression was detected mainly in F4/80-positive macrophages in thrombus. When Il6-deficient (Il6^−/−) mice were treated in the same manner, thrombus mass was significantly larger than in WT mice. Moreover, the recovery of thrombosed IVC blood flow was markedly delayed in Il6^−/− compared with WT mice. F4/80-positive macrophages in thrombus expressed proteolytic enzymes such as matrix metalloproteinase (Mmp) 2, Mmp9, and urokinase-type plasminogen activator (Plau); and their mRNA expression was significantly reduced in Il6^−/− mice. Consistently, the administration of anti-IL-6 antibody delayed the thrombus resolution in WT mice, whereas IL-6 administration accelerated thrombus resolution in WT and Il6^−/− mice. Moreover, IL-6 in vitro enhanced Mmp2, Mmp9, and Plau mRNA expression in WT-derived peritoneal macrophages in a dose-dependent manner; and the enhancement was abrogated by a specific Stat3 inhibitor, Stattic. Thus, IL-6/Stat3 signaling pathway can promote thrombus resolution by enhancing Mmp2, Mmp9, and Plau expression in macrophages.

Factors influencing recanalization of thrombotic venous occlusions

Summary. The outcome of a thrombotic vessel occlusion is related to the resolution of thrombus and restitution of blood flow. Thrombus formation simultaneously activates an enzymatic process that mediates endogenous fibrinolysis to maintain vessel patency. The balance between coagulation and fibrinolysis determines the extent of thrombus formation, its resolution, and clinical outcome. Endogenic fibrinolysis is frequently unable to overcome coagulation and to resolve the thrombus. Therefore, for a complete resolution of thrombus in an acute phase, exogenic fibrinolytic agents are needed. Currently, tissue plasminogen activator (tPA) is most frequently used for therapeutic thrombolysis. Also, heparins, particularly low-molecular-weight heparins and direct oral anticoagulants which are known as anticoagulant drugs, have some pro-fibrinolytic properties. Besides the extent and age of a clot, different other factors influence the lysis of thrombus. Thrombus structure is one of the most important determinants of thrombus lysis. The concentration of thrombolytic agent (tPA) around and inside of thrombus importantly determines clot lysis velocity. Further, flow-induced mechanical forces which stimulate the transport of thrombolytic agent into the clot influence thrombolysis. Inflammation most probably represents a basic pathogenetic mechanism of activation of coagulation and influences the activity of the fibrinolytic system. Inflammation increases tissue factor release, platelet activity, fibrinogen concentration and inhibits fibrinolysis by increasing plasminogen activator inhibitor 1. Therefore, recanalization of a thrombotic vessel occlusion is inversely related to levels of some circulating inflammatory agents. Consequently, inhibition of inflammation with anti-inflammatory drugs may improve the efficacy of prevention of thromboembolic events and stimulate recanalization of thrombotic occlusions of veins.

Reduced Contraction of Blood Clots in Venous Thromboembolism Is a Potential Thrombogenic and Embologenic Mechanism

Contraction (retraction) of the blood clot is a part of the clotting process driven by activated platelets attached to fibrin that can potentially modulate the obstructiveness and integrity of thrombi. The aim of this work was to reveal the pathogenic importance of contraction of clots and thrombi in venous thromboembolism (VTE). We investigated the kinetics of clot contraction in the blood of 55 patients with VTE. In addition, we studied the ultrastructure of ex vivo venous thrombi as well as the morphology and functionality of isolated platelets. Thrombi from VTE patients contained compressed polyhedral erythrocytes, a marker for clot contraction in vivo. The extent and rate of contraction were reduced by twofold in clots from the blood of VTE patients compared with healthy controls. The contraction of clots from the blood of patients with pulmonary embolism was significantly impaired compared with that of those with isolated venous thrombosis, suggesting that less compacted thrombi are prone to embolization. The reduced ability of clots to contract correlated with continuous platelet activation followed by their partial refractoriness. Morphologically, 75% of platelets from VTE patients were spontaneously activated (with filopodia) compared with only 21% from healthy controls. At the same time, platelets from VTE patients showed a 1.4-fold reduction in activation markers expressed in response to chemical activation when compared with healthy individuals. The results obtained suggest that the impaired contraction of thrombi is an underappreciated pathogenic mechanism in VTE that may regulate the obstructiveness and embologenicity of venous thrombi.

Lack of T-bet reduces monocytic interleukin-12 formation and accelerates thrombus resolution in deep vein thrombosis

The role of leukocytes in deep vein thrombosis (DVT) resolution is incompletely understood. We determined how depletion of lysozyme positive (LysM⁺) cells and a switched-off type 1 immune response influences thrombus resolution. DVT was induced in 12-week-old male mice by inferior vena cava (IVC) stenosis. Toxin mediated depletion of myeloid cells improved thrombus resolution in mice with Cre-inducible expression of the diphtheria toxin receptor in LysM⁺ cells. This correlated with decreased CD45⁺ cells, a population shift of Gr-1⁺ to Gr-1^- CD11b⁺ myelomonocytic cells (flow cytometry) and an increase in CC-chemokine ligand 2, interleukin-4 and interleukin-10 mRNA expressions. Tbx21^-/- mice (lacking transcription factor T-bet and marked by an attenuated type 1 immune response) with DVT had faster thrombus resolution, a reduction of pro-inflammatory Ly6C^hi monocytes in thrombi and decreased interleukin-12p40 mRNA expression than control mice resulting in increased vascular endothelial growth factor mRNA expression and improved neovascularization of thrombotic veins. Transfer of Tbx21^-/- bone marrow into irradiated Tbx21^+/+ recipients lead to accelerated thrombus resolution with lower T-bet-dependent interleukin-12p40 mRNA levels following IVC-stenosis. We conclude that inhibition of Tbet⁺ interleukin-12 forming myelomonocytic cells accelerated thrombus resolution. Modulating the inflammatory immune response might be an approach to improve therapy of DVT.

Anticoagulation beyond direct thrombin and factor Xa inhibitors: indications for targeting the intrinsic pathway?

Antithrombotic drugs like vitamin K antagonists and heparin have been the gold standard for the treatment and prevention of thromboembolic disease for many years. Unfortunately, there are several disadvantages of these antithrombotic drugs: they are accompanied by serious bleeding problems, it is necessary to monitor the therapeutic window, and there are various interactions with food and other drugs. This has led to the development of new oral anticoagulants, specifically inhibiting either thrombin or factor Xa. In terms of effectiveness, these drugs are comparable to the currently available anticoagulants; however, they are still associated with issues such as bleeding, reversal of the drug and complicated laboratory monitoring. Vitamin K antagonists, heparin, direct thrombin and factor Xa inhibitors have in common that they target key proteins of the haemostatic system. In an attempt to overcome these difficulties we investigated whether the intrinsic coagulation factors (VIII, IX, XI, XII, prekallikrein and high-molecular-weight kininogen) are superior targets for anticoagulation. We analysed epidemiological data concerning thrombosis and bleeding in patients deficient in one of the intrinsic pathway proteins. Furthermore, we discuss several thrombotic models in intrinsic coagulation factor-deficient animals. The combined results suggest that intrinsic coagulation factors could be suitable targets for anticoagulant drugs.

Open surgery for iliofemoral deep vein thrombosis with temporary arteriovenous fistula remains valuable

Objective We assessed outcomes of open surgical venous thrombectomy with temporary arteriovenous fistula, and the procedure's effect on health-related quality of life. Method We retrospectively analyzed 48 (26 at long-term) patient medical records. Mortality rates, patency, and risk of post-thrombotic syndrome were analyzed using Kaplan-Meier estimation. The association between risk factors/coagulation disorders and patency/post-thrombotic syndrome along with patient health-related quality of life at long-term was analyzed employing various statistical methods. Results Patient one-year survival rate was 93 ± 4% and primary one-year patency rate was 89 ± 5% (secondary one-year patency rate 97 ± 3%). Freedom from post-thrombotic syndrome after eight years was 80 ± 12% (post-thrombotic syndrome rate 20 ± 12%). Health-related quality of life was impaired vs. normative data in the physical and social subscales, and in the mental component score ( p < .05). Conclusions Open surgical venous thrombectomy appears safe compared with literature-reported outcomes in similar patients using alternative approaches. Iliofemoral deep vein thrombosis impairs physical, social, and mental health-related quality of life.

Cytokine Signature in End-Stage Renal Disease Patients on Hemodialysis

Hemodialysis is a modality of blood filtration in which accumulated toxins and water are removed from the body. This treatment is indicated for patients at the end stage of renal disease. Vascular access complications are responsible for 20–25% of all hospitalizations in dialyzed patients. The occurrence of thrombosis in the vascular access is a serious problem that may severely compromise or even make the hemodialysis impossible, which is vital for the patient. The aim of this study was to investigate inflammatory profile in patients undergoing hemodialysis as well as the association between these alterations and vascular access thrombosis. A total of 195 patients undergoing hemodialysis have been evaluated; of which, 149 patients had not experienced vascular access thrombosis (group I) and 46 patients had previously presented this complication (group II). Plasma levels of cytokines including interleukin (IL-) 2, IL-4, IL-5, IL-10, TNF-α, and IFN-γ were measured by cytometric bead array. Our results showed that patients with previous thrombotic events (group II) had higher levels of the IL-2, IL-4, IL-5, and IFN-γ when compared to those in group I. Furthermore, a different cytokine signature was detected in dialyzed patients according to previous occurrences or not of thrombotic events, suggesting that elevated levels of T-helper 1 and T-helper 2 cytokines might, at least in part, contribute to this complication.

Effect of pathological heterogeneity on shear wave elasticity imaging in the staging of deep venous thrombosis

Background

We aimed to observe the relationship between the pathological components of a deep venous thrombus (DVT), which was divided into three parts, and the findings on quantitative ultrasonic shear wave elastography (SWE) to increase the accuracy of thrombus staging in a rabbit model.

Methods

A flow stenosis-induced vein thrombosis model was used, and the thrombus was divided into three parts (head, body and tail), which were associated with corresponding observation points. Elasticity was quantified in vivo using SWE over a 2-week period. A quantitative pathologic image analysis (QPIA) was performed to obtain the relative percentages of the components of the main clots.

Results

DVT maturity occurred at 2 weeks, and the elasticity of the whole thrombus and the three parts (head, body and tail) showed an increasing trend, with the Young's modulus values varying from 2.36 ± 0.41 kPa to 13.24 ± 1.71 kPa; 2.01 ± 0.28 kPa to 13.29 ± 1.48 kPa; 3.27 ± 0.57 kPa to 15.91 ± 2.05 kPa; and 1.79 ± 0.36 kPa to 10.51 ± 1.61 kPa, respectively. Significant increases occurred on different days for the different parts: the head showed significant increases on days 4 and 6; the body showed significant increases on days 4 and 7; and the tail showed significant increases on days 3 and 6. The QPIA showed that the thrombus composition changed dynamically as the thrombus matured, with the fibrin and calcium salt deposition gradually increasing and the red blood cells (RBCs) and platelet trabecula gradually decreasing. Significant changes were observed on days 4 and 7, which may represent the transition points for acute, sub-acute and chronic thrombi. Significant heterogeneity was observed between and within the thrombi.

Conclusions

Variations in the thrombus components were generally consistent between the SWE and QPIA. Days 4 and 7 after thrombus induction may represent the transition points for acute, sub-acute and chronic thrombi in rabbit models. A dynamic examination of the same part of the thrombus may be helpful for improving the sensitivity and reproducibility of SWE for DVT diagnosis and staging.

Current understanding of the pathophysiology of chronic thromboembolic pulmonary hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) is a unique form of pulmonary hypertension arising from fibrotic obliteration of major pulmonary arteries. Pro-thrombotic states, large clot burden and impaired dissolution are believed to contribute to the occurrence and progression of thrombosis after an acute pulmonary embolic event. Recent data utilizing several models have facilitated the understanding of clot resolution. This review summarizes current knowledge on pathophysiological mechanisms of major vessel occlusion in CTEPH.

Myeloid p53 regulates macrophage polarization and venous thrombus resolution by inflammatory vascular remodeling in mice

Deep venous thrombosis (DVT) remains a common and serious cardiovascular problem with both fatal and long-term consequences. The consequences of DVT include the development of postthrombotic syndrome in 25% to 60% of DVT patients. Despite the clinical importance of venous thrombus resolution, the cellular and molecular mediators involved are poorly understood, and currently there is no molecular therapy to accelerate this process. Several lines of evidence suggest that a complex and interrelated array of molecular signaling processes are involved in the inflammatory vascular remodeling associated with the resolution of DVT. Here, we have identified a role for the tumor suppressor gene p53 in regulating venous thrombus resolution. Using the stasis model of venous thrombosis and resolution in mice, we found that genetic deficiency of p53 or pharmacologic inhibition by pifithrin impairs thrombus resolution and is associated with increased fibrosis and altered expression of matrix metalloproteinase-2. The effect of p53 loss was mediated by cells of the myeloid lineage, resulting in enhanced polarization of the cytokine milieu toward an M1-like phenotype. Furthermore, augmentation of p53 activity using the pharmacological agonist of p53, quinacrine, accelerates venous thrombus resolution in a p53-dependent manner, even after establishment of thrombosis. Together, these studies define mechanisms by which p53 regulates thrombus resolution by increasing inflammatory vascular remodeling of venous thrombi in vivo, and the potential therapeutic application of a p53 agonist as a treatment to accelerate this process in patients with DVT.

Successful reduction of inflammatory responses and arachidonic acid-cyclooxygenase 2 pathway in human pulmonary artery endothelial cells by silencing adipocyte fatty acid-binding protein

Background

Adipocyte fatty acid-binding protein, also known as aP2 or fatty acid-binding protein 4 (FABP4), plays an important role in inflammatory and metabolic responses in adipocytes and macrophages. Recent work has demonstrated that macrophage FABP4 integrates inflammatory and lipid metabolic responses, thereby contributing to the development of insulin resistance and atherosclerosis. However, it is not known whether FABP4 in human pulmonary artery endothelial cells(HPAECs) modulates inflammation.

Results

Here, we demonstrate that FABP4 and inflammatory cytokines are upregulated in lipopolysaccharide(LPS)-stimulated HPAECs. In addition, LPS increases the expression of molecules in the arachidonic acid(AA)–cyclooxygenase (COX) 2 signaling pathway in FABP4-expressing, but not FABP4-deficient, HPAECs.

Conclusions

Our findings demonstrate that silencing FABP4 could decrease inflammatory cytokines, which were reported to be expressed via the AA–COX2 pathway, in HPAECs. In addition, silencing FABP4 could inhibit the expression of molecules in the AA–COX2 pathways. So we speculate silencing FABP4 could decrease the inflammatory response in HPAECs, which involves in the AA–COX2 signaling pathway. Our study suggests that FABP4 could be a potential biomarker and intervention point for the inflammation-related disease in HPAECs such as pulmonary thromboembolism.

E-selectin inhibition with GMI-1271 decreases venous thrombosis without profoundly affecting tail vein bleeding in a mouse model

Selectins, such as E-selectin (CD62E), function in venous thrombosis by binding and activating immune cells to initiate the coagulation cascade. GMI-1271 is a small molecule antagonist that inhibits E-selectin activity. Here we determine whether inhibition of E-selectin is sufficient to decrease acute venous thrombosis and associated inflammatory events in both prophylactic and treatment protocols without significantly affecting haemostasis. Male C57BL/6 mice underwent surgery for experimental thrombosis induction and were harvested at peak thrombus formation in our animal model, two days post induction. Groups included non-thrombosed true controls, shams, controls, and prophylactic or treatment groups of GMI-1271 (10 mg/kg intraperitoneal BID (twice a day) and low-molecular-weight heparin (LMWH, Lovenox 6 mg/kg subcutaneously (SC), once a day (SID). Compared with control animals, prophylaxis or treatment with LMWH and GMI-1271 in a dose-dependent manner significantly decreased thrombosis. GMI-1271 significantly lowered tail bleeding times when compared to LMWH. GMI-1271 and LMWH prophylactically administered significantly decreased vein wall neutrophil cell extravasation. However, all treatment and prophylactic therapies significantly decreased vein wall monocyte extravasation versus controls. GMI-1271 prophylactic therapy significantly decreased intra-thrombus cell counts versus control animals and other treatment groups. Immunohistochemistry confirmed that both treatments with GMI-1271 and LMWH significantly decreased activated leukocyte migration. GMI-1271 therapy significantly decreased thrombus weight and resulted in significantly lower bleeding times than LMWH. GMI-1271 treated mice showed decreased local and systemic inflammatory effects while modulating neutrophil activation, suggesting that GMI-1271 is a viable therapeutic candidate for venous thrombosis prophylaxis and treatment.

Zedoary Guaiane-Type Sesquiterpenes-Eluting Stents Accelerate Endothelial Healing Without Neointimal Hyperplasia in a Porcine Coronary Artery Model

Objective:

The effects of zedoary guaiane-type sesquiterpenes (ZGS)-based eluting stent (ZES) in accelerating reendothelialization and inhibiting neointimal hyperplasia were examined in a porcine coronary artery model.

Methods:

The ZES was prepared by polymer-free 316L stainless metal stents. Sirolimus-eluting stents (SES) and bare metal stents (BMS) with identical platforms were used as controls. Stents with 15 mm in length and 2.0 to 3.5 mm in diameter were implanted in porcine coronary arteries. Scanning electron microscopy (SEM) and histopathology were performed to assess the reendothelialization and neointimal hyperplasia. The 3-(4, 5-dimethylthiazol-2yl)-2, 5-diphenyl-2H-tetrazoliumbromide assay and flow cytometry were used to assess the influence of ZGS on human umbilical vascular endothelial cells (HUVECs).

Results:

At 7 days, SEM showed that percentage of endothelial coverage area was 94.04% ± 5.01% for ZES, 47.59% ± 19.91% for SES ( P < .01 for ZES vs SES), and 59.58% ± 19.61% for BMS ( P < .05 for ZES vs BMS). At 28 days, the percentage of coverage area was 98.51% ± 1.86% for ZES, 86.18% ± 8.16% for SES ( P < .05 for ZES vs SES), and 94.26% ± 5.58% for BMS. Neointimal area and stenosis were significantly lower in ZES (1.07 ± 0.48 mm2, 27.66% ± 12.20%) compared to BMS (1.73 ± 0.69 mm2, 44.08% ± 15.03%, both P < .01, respectively), with no difference in SES (0.94 ± 0.12 mm2, 28.87% ± 6.00%, both P > .05, respectively). The ZGS also promoted HUVECs viability and improved HUVECs proliferation compared to sirolimus.

Conclusion:

The ZES accelerated reendothelialization and suppressed neointimal hyperplasia in a porcine coronary artery model, with beneficial effects on HUVECs.

Endotoxaemia-augmented murine venous thrombosis is dependent on TLR-4 and ICAM-1, and potentiated by neutropenia

Venous thromboembolism is a major cause of death during and immediately post-sepsis. Venous thrombosis (VT) is mediated by cell adhesion molecules and leukocytes, including neutrophil extracellular traps (NETs). Sepsis, or experimentally, endotoxaemia, shares similar characteristics and is modulated via toll like receptor 4 (TLR4). This study was undertaken to determine if endotoxaemia potentiates early stasis thrombogenesis, and secondarily to determine the role of VT TLR4, ICAM-1 and neutrophils (PMNs). Wild-type (WT), ICAM-1^-/- and TLR4^-/- mice underwent treatment with saline or LPS (10 mg/kg i. p.) alone, or followed by inferior vena cava (IVC) ligation to generate stasis VT. In vivo microscopy of leukocyte trafficking was performed in non-thrombosed mice, and tissue and plasma were harvested during early VT formation. Pre-thrombosis, circulating ICAM-1 was elevated and increased leukocyte adhesion and rolling occurred on the IVC of LPS-treated mice. Post-thrombosis, endotoxaemic mice formed larger, platelet-poor thrombi. Endotoxaemic TLR4^-/- mice did not have an augmented thrombotic response and exhibited significantly decreased circulating ICAM-1 compared to endotoxaemic WT controls. Endotoxaemic ICAM-1^-/- mice had significantly smaller thrombi compared to controls. Hypothesising that PMNs localised to the inflamed endothelium were promoting thrombosis, PMN depletion using anti-Ly6G antibody was performed. Paradoxically, VT formed without PMNs was amplified, potentially related to endotoxaemia induced elevation of PAI-1 and circulating FXIII, and decreased uPA. Endotoxaemia enhanced early VT occurs in a TLR-4 and ICAM-1 dependent fashion, and is potentiated by neutropenia. ICAM-1 and/or TLR-4 inhibition may be a unique strategy to prevent sepsis-associated VT.

Serum from Varicose Patients Induces Senescence-Related Dysfunction of Vascular Endothelium Generating Local and Systemic Proinflammatory Conditions

Although the role of endothelium in varicose vein development is indisputable, the effect of the pathology on biological properties of endothelial cells remains unclear. Here we examined if the presence of varicose veins affects senescence of endothelial cells (HUVECs) and, if so, what will be the local and systemic outcome of this effect. Experiments showed that HUVECs subjected to serum from varicose patients display improved proliferation, increased expression of senescence marker, SA-β-Gal, and increased generation of reactive oxygen species (ROS), as compared with serum from healthy donors. Both increased SA-β-Gal activity and ROS release were mediated by TGF-β1, the concentration of which in varicose serum was elevated and the activity of which in vitro was prevented using specific neutralizing antibody. Senescent HUVECs exposed to varicose serum generated increased amounts of ICAM-1, VCAM-1, P-selectin, uPA, PAI-1, and ET-1. Direct comparison of sera from varicose and healthy donors showed that pathological serum contained increased level of ICAM-1, VCAM-1, P-selectin, uPA, and ET-1. Calendar age of healthy subjects correlated positively with serum uPA and negatively with P-selectin. Age of varicose patients correlated positively with ICAM-1, VCAM-1, and ET-1. Collectively, our findings indicate that the presence of varicose veins causes a senescence-related dysfunction of vascular endothelium, which leads to the development of local and systemic proinflammatory environment.

Platelets in Pulmonary Immune Responses and Inflammatory Lung Diseases

Platelets are essential for physiological hemostasis and are central in pathological thrombosis. These are their traditional and best known activities in health and disease. In addition, however, platelets have specializations that broaden their functional repertoire considerably. These functional capabilities, some of which are recently discovered, include the ability to sense and respond to infectious and immune signals and to act as inflammatory effector cells. Human platelets and platelets from mice and other experimental animals can link the innate and adaptive limbs of the immune system and act across the immune continuum, often also linking immune and hemostatic functions. Traditional and newly recognized facets of the biology of platelets are relevant to defensive, physiological immune responses of the lungs and to inflammatory lung diseases. The emerging view of platelets as blood cells that are much more diverse and versatile than previously thought further predicts that additional features of the biology of platelets and of megakaryocytes, the precursors of platelets, will be discovered and that some of these will also influence pulmonary immune defenses and inflammatory injury.

Abnormal pulmonary endothelial cells may underlie the enigmatic pathogenesis of chronic thromboembolic pulmonary hypertension

BACKGROUND

Chronic thromboembolic pulmonary hypertension results from chronic mechanical obstruction of the pulmonary arteries after acute venous thromboembolism. However, the mechanisms that result in the progression from unresolved thrombus to fibrotic vascular remodeling are unknown. We hypothesized that pulmonary artery endothelial cells contribute to this phenomenon via paracrine growth factor and cytokine signaling.

METHODS

Using enzyme-linked immunosorbent assay and cell migration assays, we investigated the circulating growth factors and cytokines of chronic thromboembolic pulmonary hypertension patients as well as the cross talk between pulmonary endothelial cells and pulmonary artery smooth muscle cells and monocytes from patients with chronic thromboembolic pulmonary hypertension in vitro.

RESULTS

Culture medium from the pulmonary endothelial cells of chronic thromboembolic pulmonary hypertension patients contained higher levels of growth factors (fibroblast growth factor 2), inflammatory cytokines (interleukin 1β, interleukin 6, monocyte chemoattractant protein 1), and cell adhesion molecules (vascular cell adhesion molecule 1 and intercellular adhesion molecule 1). Furthermore, exposure to the culture medium of pulmonary endothelial cells from patients with chronic thromboembolic pulmonary hypertension elicited marked pulmonary artery smooth muscle cell growth and monocyte migration.

CONCLUSIONS

These findings implicate pulmonary endothelial cells as key regulators of pulmonary artery smooth muscle cell and monocyte behavior in chronic thromboembolic pulmonary hypertension and suggest a potential mechanism for the progression from unresolved thrombus to fibrotic vascular remodeling.

Polymorphonuclear Leukocyte Integrinsin Deep Venous Thrombosis

The polymorphonuclear leukocytes (PMN) have a role in the pathophysiology of deep venous thrombosis (DVT). We examined the phenotypical expression of PMN beta2-integrins (CD l l a, CDl l b, CD 11c) in a group of 19 subjects with leg DVT. PMN cells were incubated with fluorescent monoclonal antibodies against CD11a, CD11b, CD11c, and the evaluation was made by flow cytofluorimetry. The same integrins were determined after in vitro activation with 4-phorbol 12-myristate 13-acetate (PMA) and N-formylmethionyl-leucyl-phenylalanine (fMLP). In DVT subjects, at baseline, the phenotypical expression of CD11b was decreased and that of CD11c increased when compared with normal controls. In normal subjects PMN activation with PMA and fMLP led to a constant increase of all PMN adhesion molecules, while in DVT subjects the CDl l a did not show any change. These data might have therapeutical ap plications, especially with the aim of preventing post-thrombotic deterioration of vein function.

The role of leukocytes in thrombosis

In recent years, the traditional view of the hemostatic system as being regulated by a coagulation factor cascade coupled with platelet activation has been increasingly challenged by new evidence that activation of the immune system strongly influences blood coagulation and pathological thrombus formation. Leukocytes can be induced to express tissue factor and release proinflammatory and procoagulant molecules such as granular enzymes, cytokines, and damage-associated molecular patterns. These mediators can influence all aspects of thrombus formation, including platelet activation and adhesion, and activation of the intrinsic and extrinsic coagulation pathways. Leukocyte-released procoagulant mediators increase systemic thrombogenicity, and leukocytes are actively recruited to the site of thrombus formation through interactions with platelets and endothelial cell adhesion molecules. Additionally, phagocytic leukocytes are involved in fibrinolysis and thrombus resolution, and can regulate clearance of platelets and coagulation factors. Dysregulated activation of leukocyte innate immune functions thus plays a role in pathological thrombus formation. Modulation of the interactions between leukocytes or leukocyte-derived procoagulant materials and the traditional hemostatic system is an attractive target for the development of novel antithrombotic strategies.

Plasmin and Matrix Metalloproteinase System in Deep Venous Thrombosis Resolution

Deep venous thrombosis (DVT) is a common event in hospitalized medical and surgical patients. Outside of anticoagulation, few good options exist for decreasing the vein wall damage that results after natural thrombolysis. DVT resolution is complex and involves chemokines, leukocytes, and native vein wall cells. Herein some aspects of DVT resolution related to the intersection of inflammation, the plasminogen and matrix metalloproteinase systems, and their respective inhibitors are reviewed. Ultimately, better knowledge of these natural thrombolytic systems may allow local, directed, and specific acceleration of DVT resolution and decreased vein wall damage.

Immunomodulatory effects of therapeutic plasma exchange on monocytes in antiphospholipid syndrome

Antiphospholipid syndrome (APS) is a systemic autoimmune disorder characterized by thrombosis and recurrent fetal loss, with the persistent presence of antiphospholipid antibodies (aPLs). aPLs exert their pathogenic effect via the overproduction of tissue factor and activation of complement and several cell types, including endothelial cells, platelets and notably monocytes. As a result, a hypercoagulable state develops leading to APS-associated obstetric complications and fetal loss. Despite being far from optimal, treatment of APS usually includes heparin and low dose aspirin. Recently, plasma exchange (PE) therapy was successfully used in patients with APS with obstetric complications who did not respond to the standard treatment. Therefore, the present study investigated the mechanism underlying PE action, and aimed to determine whether PE affects the functional activity of APS monocytes by examining the expression of 11 mRNA transcripts encoding cytokines, signaling molecules and transcription factors. Monocytes were collected prior to and following the PE treatment from women with APS who experienced recurrent pregnancy losses, as well as from healthy volunteers. Compared with control cells, APS monocytes showed deregulated expression of interleukin (IL)-1β, IL-6, IL-23, chemokine (C-C motif) ligand 2 (CCL2), C-X-C motif chemokine 10 (CXCL10), toll-like receptor 2, and signal transducer and activator of transcription 3. PE treatment resulted in increased IL-1β, IL-6, IL-23, CCL2, P2X7 and tumor necrosis factor-α mRNA transcripts in APS monocytes, restoring the mRNA expression levels to within normal ranges. Furthermore, PE therapy counterbalanced the expression levels of CCL2 and CXCL10, the levels of which are indicative of T helper cell 1/2 balance. The results of the present study indicate that the altered transcriptional profile in APS monocytes was restored by the immunomodulatory effect of plasmapheresis.

Assessment of arterial stiffness in patients with venous thromboembolism: Separate or continuous circuits?

Objectives The aim of this study is to evaluate the association of venous thromboembolism with arterial stiffness by cardio-ankle vascular index method. Method We included 52 patients with a documented lower extremity venous thromboembolism within the last six months and 52 healthy subjects to this cross sectional observational study. Results Cardio-ankle vascular index (8.58 ± 1.60 versus 7.05 ± 1.44, p < 0.001, respectively) and systolic blood pressure (128.02 ± 7.13 mmHg versus 123.94 ± 8.12 mmHg, p = 0.008, respectively) were significantly higher among patients with venous thromboembolism than controls. Cardio-ankle vascular index was an independent predictor of venous thromboembolism in multivariate logistic regression analysis (p < 0.001, odds ratio = 1.864, 95% confidence interval = 1.370-2.536). Cardio-ankle vascular index value > 7.8 had a sensitivity of 82.7% and a specificity of 80.8% for predicting venous thromboembolism (area under curve = 0.789, 95% confidence interval = 0.698-0.863, p < 0.001) in receiver operating characteristic curve analysis. Conclusion We found that arterial stiffness was increased in patients with venous thromboembolism which highlights the fact that arterial and venous circulation is in continuum and an insult may affect both of these circuits.

Granulocytes in coronary thrombus evolution after myocardial infarction--time-dependent changes in expression of matrix metalloproteinases

BACKGROUND

Remodeling of extracellular matrix is a key process during wound healing, which is strictly regulated by matrix metalloproteinases (MMPs) and their tissue inhibitors [tissue inhibitors of metalloproteinases (TIMPs)]. In this study, we evaluated intrathrombotic MMPs and TIMPs and their cellular origin during thrombus evolution after disruption of coronary atherosclerotic plaque.

MATERIALS AND METHODS

Thrombectomy materials (N=120) obtained from patients with acute myocardial infarction were histologically classified in three groups based on thrombus age: fresh (<1day), lytic (1-5days), or organized (>5days) thrombi; materials showing a heterogeneous composition were classified according to oldest part. Presence and cellular origin of MMPs (MMP-1, MMP-2, MMP-8, MMP-9, and MMP-14) and TIMPs (TIMP-1, TIMP-2, and TIMP-3) was evaluated with immunostains (double) and with polymerase chain reaction.

RESULTS AND CONCLUSION

MMPs and TIMPs were present in all the thrombectomy samples. A distinct temporal change in extent and cellular origin of MMPs and TIMPs during thrombus evolution was observed. In the early (fresh and lytic) stages of thrombus, high numbers of neutrophilic granulocytes occupy the thrombus mass and produce large amounts of MMPs and TIMPs. However, with progression of thrombus evolution (organizing stage) and diminishment of neutrophil granulocytes, there is disappearance of MMP-8 and MMP-9, steep decline of MMP-1 and TIMP-2, and progressive decrease of TIMP-3. In contrast, intrathrombotic MMP-2 and MMP-14 are present at a constant high level during the entire process of thrombus evolution. These temporal changes indicate a complex time-dependent function of MMPs, which are largely granulocyte derived, in the healing process of thrombus after plaque disruption.

Matrix Metalloproteinase 9 (MMP-9) Regulates Vein Wall Biomechanics in Murine Thrombus Resolution

Objective

Deep venous thrombosis is a common vascular problem with long-term complications including post-thrombotic syndrome. Post-thrombotic syndrome consists of leg pain, swelling and ulceration that is related to incomplete or maladaptive resolution of the venous thrombus as well as loss of compliance of the vein wall. We examine the role of metalloproteinase-9 (MMP-9), a gene important in extracellular remodeling in other vascular diseases, in mediating thrombus resolution and biomechanical changes of the vein wall.

Methods and Results

The effects of targeted deletion of MMP-9 were studied in an in vivo murine model of thrombus resolution using the FVB strain of mice. MMP-9 expression and activity significantly increased on day 3 after DVT. The lack of MMP-9 impaired thrombus resolution by 27% and this phenotype was rescued by the transplantation of wildtype bone marrow cells. Using novel biomechanical techniques, we demonstrated that the lack of MMP-9 significantly decreased thrombus-induced loss of vein wall compliance. Biomechanical analysis of the contribution of individual structural components showed that MMP-9 affected the elasticity of the extracellular matrix and collagen-elastin fibers. Biochemical and histological analyses correlated with these biomechanical effects as thrombi of mice lacking MMP-9 had significantly fewer macrophages and collagen as compared to those of wildtype mice.

Conclusions

MMP-9 mediates thrombus-induced loss of vein wall compliance by increasing stiffness of the extracellular matrix and collagen-elastin fibers during thrombus resolution. MMP-9 also mediates macrophage and collagen content of the resolving thrombus and bone-marrow derived MMP-9 plays a role in resolution of thrombus mass. These disparate effects of MMP-9 on various aspects of thrombus illustrate the complexity of individual protease function on biomechanical and morphometric aspects of thrombus resolution.

Association between inflammation biomarkers, anatomic extent of deep venous thrombosis, and venous symptoms after deep venous thrombosis

OBJECTIVE

Inflammation may play a role in pathogenesis of venous thromboembolism, but the nature of this relationship is not yet understood. The objective of this study was to assess whether inflammation marker levels measured at diagnosis of deep venous thrombosis (DVT) and change in levels during the first month after DVT are associated with anatomic extent of DVT and severity of venous signs and symptoms at baseline and 1 month.

METHODS

The BioSOX study is a biomarker substudy of the Compression Stockings to Prevent the Post-Thrombotic Syndrome (SOX) trial, a multicenter, randomized controlled trial that included patients with a first, acute, symptomatic, proximal DVT. Blood samples were collected from participants at baseline and 1 month, and C-reactive protein (CRP), intercellular adhesion molecule 1, interleukin (IL)-6, and IL-10 were measured by established assays. Linear regression was used to assess the association between continuous log-transformed baseline biomarker levels and anatomic extent of DVT, classified as iliac or common femoral DVT vs femoral or popliteal DVT (reference). Proportional odds ordinal logistic regression models were used to analyze the association between biomarker level and Villalta score (as a measure of severity of venous signs and symptoms) at baseline and 1 month.

RESULTS

Among 717 patients, 60.2% were male, and the mean age was 55.2 years. There was a significant association between more extensive DVT (common femoral or iliac) and levels of CRP and IL-6 at DVT diagnosis. Median (interquartile range) CRP level was 11.6 mg/L (3.84-39.5) in patients with common femoral or iliac DVT vs 6.86 mg/L (3.11-22) in patients with popliteal or femoral DVT, and median IL-6 level was 6.36 pg/mL (1.09-14.37) vs 4.40 pg/mL (2.35-8.27), respectively. These differences were statistically significant in linear regression analyses. In addition, compared with those in the lowest quartile, each higher quartile of baseline CRP concentration was associated with an odds ratio of 2.89 (1.93-4.33) for having a more severe Villalta category at baseline and 1.98 (1.28-3.08) for having a more severe Villalta category 1 month after DVT. Higher baseline levels of IL-6 were associated with Villalta severity category at baseline (odds ratio, 2.40 [1.61-3.59]). Change in biomarker levels during the first month after DVT was not strongly associated with the 1-month Villalta score.

CONCLUSIONS

Levels of CRP and IL-6 at DVT diagnosis were associated with thrombotic disease burden, as measured by DVT extent, and severity of DVT symptoms and signs. Further studies are required to more fully elucidate the role of inflammation in DVT and its clinical course.

Venous thrombosis

Venous thromboembolism (VTE) encompasses deep-vein thrombosis (DVT) and pulmonary embolism. VTE is the leading cause of lost disability-adjusted life years and the third leading cause of cardiovascular death in the world. DVT leads to post-thrombotic syndrome, whereas pulmonary embolism can cause chronic pulmonary hypertension, both of which reduce quality of life. Genetic and acquired risk factors for thrombosis include non-O blood groups, factor V Leiden mutation, oral contraceptive use, hormone replacement therapy, advanced age, surgery, hospitalization and long-haul travel. A combination of blood stasis, plasma hypercoagulability and endothelial dysfunction is thought to trigger thrombosis, which starts most often in the valve pockets of large veins. Animal studies have revealed pathogenic roles for leukocytes, platelets, tissue factor-positive microvesicles, neutrophil extracellular traps and factors XI and XII. Diagnosis of VTE requires testing and exclusion of other pathologies, and typically involves laboratory measures (such as D-dimer) and diagnostic imaging. VTE is treated with anticoagulants and occasionally with thrombolytics to prevent thrombus extension and to reduce thrombus size. Anticoagulants are also used to reduce recurrence. New therapies with improved safety profiles are needed to prevent and treat venous thrombosis. For an illustrated summary of this Primer, visit: http://go.nature.com/8ZyCuY.