The multifunctional protein C system

Potential Beneficial Effects of Vitamin K in SARS-CoV-2 Induced Vascular Disease?

Prevalent coagulopathy and thromboembolism are observed in severe COVID-19 patients with 40% of COVID-19 mortality being associated with cardiovascular complications. Abnormal coagulation parameters are related to poor prognosis in COVID-19 patients. Victims also displayed presence of extensive thrombosis in infected lungs. Vitamin K is well-known to play an essential role in the coagulation system. Latest study revealed an existing correlation between vitamin K deficiency and COVID-19 severity, highlighting a role of vitamin K, probably via coagulation modulation. In agreement, other recent studies also indicated that anti-coagulant treatments can reduce mortality in severe cases. Altogether, potential mechanisms linking COVID-19 with coagulopathy in which vitamin K may exert its modulating role in coagulation related with disease pathogenesis are established. In this review, we discuss the recent evidence supporting COVID-19 as a vascular disease and explore the potential benefits of using vitamin K against COVID-19 to improve disease outcomes.

Expression of Pinopodes in the Endometrium from Recurrent Pregnancy Loss Women. Role of Thrombomodulin and Ezrin

BACKGROUND

Pinopode expression has been suggested as a marker of endometrial receptivity.

METHODS

We set up an experimental study comparing endometrial tissue from recurrent pregnancy loss (RPL, n = 30) and fertile control (CTR, n = 20) women in terms of pinopode expression/morphology; expression of thrombomodulin (TM) and ezrin; cytoskeletal organization. Endometrial samples were collected during implantation window and evaluated by scanning electron microscopy, western blot, and immunofluorescence.

RESULTS

We found that RPL endometrial tissue showed: (i) increased pinopodes density (* p < 0.05); (ii) a reduced diameter of pinopodes (* p < 0.05); (iii) a decreased TM and ezrin expression (p < 0.05). Additionally, confocal images showed a significantly reduced expression of phosphorylated (p)-ezrin, confirming the results obtained through immunoblot analysis. Immunofluorescence staining showed that in CTR samples, junctions between cells are intact and clearly visible, whereas actin filaments appear completely lost in RPL endometrial samples; this suggests that, due to the impaired expression and activity of TM and ezrin, actin does not bind to plasma membrane in order to orchestrate the cytoskeletal actin filaments.

CONCLUSIONS

Our findings suggest that an impaired expression of TM and expression/activation of ezrin may affect the connection between the TM and actin cytoskeleton, impairing the organization of cytoskeleton and, eventually, the adequate pinopode development.

Increase of Neutrophil Activation Markers in Venous Thrombosis-Contribution of Circulating Activated Protein C

Upon activation, neutrophils release their content through different mechanisms like degranulation and NETosis, thus prompting thrombosis. The natural anticoagulant activated protein C (APC) inhibits neutrophil NETosis and, consequently, this may lower the levels of neutrophil activation markers in plasma, further diminishing the thrombotic risk exerted by this anticoagulant. We aimed to describe the status of markers of neutrophil activation in plasma of patients with venous thrombosis, their association with the thrombotic risk and the potential contribution of APC. We quantified three markers of neutrophil activation (cell-free DNA, calprotectin, and myeloperoxidase) in 253 patients with venous thromboembolism (VTE) in a stable phase (192 lower extremity VTE and 61 splanchnic vein thrombosis) and in 249 healthy controls. In them, we also quantified plasma APC, soluble endothelial protein C receptor (EPCR), and soluble thrombomodulin (TM), and we genotyped two genetic regulators of APC: the EPCR gene (PROCR) haplotypes (H) and the TM gene (THBD) c.1418C>T polymorphism. We found a significant increase in plasma cell-free DNA (p < 0.0001), calprotectin (p = 0.0001) and myeloperoxidase (p = 0.005) in VTE patients compared to controls. Furthermore, all three neutrophil activation markers were associated with an increase in the thrombotic risk. Cell-free DNA and calprotectin plasma levels were significantly correlated (Spearman r = 0.28; p < 0.0001). As expected, the natural anticoagulant APC was significantly decreased in VTE patients (p < 0.0001) compared to controls, what was mediated by its genetic regulators PROCR-H1, PROCR-H3, and THBD-c.1418T, and inversely correlated with cell-free DNA levels. This is the largest case-control study that demonstrates the increase in markers of neutrophil activation in vivo in VTE patients and their association with an increased thrombotic risk. This increase could be mediated by low APC levels and its genetic regulators, which could also increase NETosis, further enhancing thrombosis and inflammation.

Ginkgo biloba Induces Thrombomodulin Expression and Tissue-Type Plasminogen Activator Secretion via the Activation of Krüppel-Like Factor 2 within Endothelial Cells

The effects of thrombo-prevention, such as antiplatelet and anticoagulant activity, have been reported with the usage of Ginkgo biloba extract (GbE); however, the detailed mechanism has not yet been fully investigated, especially the role of Krüppel-like factor 2 (KLF2). This study aimed to investigate whether GbE can activate KLF2 and then induce thrombomodulin (TM) and tissue-type plasminogen activator (t-PA) secretion to enhance the effects of thrombo-prevention. Different concentrations of GbE were incubated with human umbilical vein endothelial cells (HUVECs) to evaluate its effect on endothelial cells. We found that KLF2 expression is correlated to the risk of atherosclerosis and venous thromboembolism in clinical practice. In the HUVEC cell model, GbE stimulated the expression of KLF2 in a dose-dependent manner. Moreover, TM and t-PA secretion increased when the cells were cultured with GbE. Both the expressions and activities of TM and t-PA in the GbE-treated cells declined after KLF2 was blocked by shKLF2. In sum, with GbE treatment, KLF2 expression in human endothelial cells was significantly activated, which in turn induced an increase in the protein expression and activity of TM and t-PA. After shRNA inhibited the KLF2 expression, GbE stopped inducing the expression and activity of TM and t-PA. These findings suggest that GbE exerts an antithrombotic effect on endothelial cells by increasing the TM expression and t-PA secretion; further, KLF2 is a key factor in this mechanism.

Current and emerging pharmacotherapy for ischemic stroke prevention in patients with atrial fibrillation

Introduction: Atrial fibrillation (AF) is associated with high morbidity and mortality rates due to thromboembolic complications, and anticoagulation is central to the management of this common arrhythmia to prevent acute thromboembolic events. The traditional anticoagulants: heparin, fondaparinux, and vitamin K antagonists (VKA, e.g. warfarin, acenocoumarol or phenprocoumin) have long served as pharmacotherapy for ischemic stroke prophylaxis. Areas covered: In this review article, the authors provide an overview on current and emerging pharmacotherapy for ischemic stroke prevention. Furthermore, they review the data from novel therapeutic targets in the coagulation cascade, and investigational anticoagulant drugs currently assessed in preclinical and clinical studies. Expert opinion: The introduction of nonvitamin K antagonist oral anticoagulants (NOACs) was an important milestone, as these drugs show relative efficacy, safety, and convenience compared to the VKAs. Nevertheless, their clinical use still has some limitations with, for example, patients with severe renal impairment and those with mechanical heart valves, high bleeding risks, lack of standard laboratory monitoring and (some) reversal agents. To overcome some of these limitations, various attempts are now underway to discover new strategies and targets via the hemostatic pathway in order to develop new coagulation inhibiting drugs.

α2-Macroglobulin Is a Significant In Vivo Inhibitor of Activated Protein C and Low APC:α2M Levels Are Associated with Venous Thromboembolism

BACKGROUND

Activated protein C (APC) is a major regulator of thrombin formation. Two major plasma inhibitors form complexes with APC, protein C inhibitor (PCI) and α₁-antitrypsin (α₁AT), and these complexes have been quantified by specific enzyme-linked immunosorbent assays (ELISAs). Also, complexes of APC with α₂-macroglobulin (α₂M) have been observed by immunoblotting. Here, we report an ELISA for APC:α₂M complexes in plasma.

METHODS

Plasma samples were pre-treated with dithiothreitol and then with iodoacetamide. The detection range of the newly developed APC:α₂M assay was 0.031 to 8.0 ng/mL of complexed APC. Following infusions of APC in humans and baboons, complexes of APC with α₂M, PCI and α₁AT were quantified. These complexes as well as circulating APC were also measured in 121 patients with a history of venous thromboembolism (VTE) and 119 matched controls.

RESULTS

In all the in vivo experiments, α₂M was a significant APC inhibitor. The VTE case-control study showed that VTE patients had significantly lower APC:α₂M and APC levels than the controls (p < 0.001). Individuals in the lowest quartile of APC:α₂M or the lowest quartile of APC had approximately four times more VTE risk than those in the highest quartile of APC:α₂M or of APC. The risk increased for individuals with low levels of both parameters.

CONCLUSION

The APC:α₂M assay reported here may be useful to help monitor the in vivo fate of APC in plasma. In addition, our results show that a low APC:α₂M level is associated with increased VTE risk.

Effects of oral anticoagulant therapy and haplotype 1 of the endothelial protein C receptor gene on activated protein C levels

Oral anticoagulants (OACs) reduce activated protein C (APC) plasma levels less than those of protein C (PC) in lupus erythematosus and cardiac patients. Carriers of the H1 haplotype of the endothelial PC receptor gene (PROCR) have higher APC levels than non-carriers. We aimed to confirm these results in a large group of patients treated with OACs because of venous thromboembolism (VTE) and to assess whether the effect is influenced by the PROCR H1 haplotype. We evaluated APC, PC, and factor (F)II levels in 502 VTE patients (158 with and 344 without OACs) and in 322 healthy individuals. Mean APC, PC and FII levels were significantly lower in OAC patients than in patients not taking OACs. During anticoagulant therapy, the FII/PC ratios were independent of the PC values, whereas APC/FII and APC/PC ratios significantly increased when FII and PC levels decreased. Of the 22 OAC patients carrying the H1H1genotype, 11 (50%) showed APC/PCag ≥2.0 and 10 (45%) APC/ FIIag ratios ≥2.0, whereas for the 49 OAC patients non-carrying the H1 haplotype these figures were 6 (12%) and 4 (8%), respectively (p<0.001). Barium citrate adsorption of plasma from OAC patients showed that most of the circulating free and complexed APC, but only part of PCag, is fully carboxylated. In conclusion, during anticoagulant therapy VT patients have APC levels disproportionately higher than the corresponding PC levels, mainly due to the presence of the PROCR H1 haplotype. Furthermore, a sufficiently carboxylated PC Gla-domain seems to be essential for PC activation in vivo.

Trauma-induced coagulopathy: from biology to therapy

Trauma is a leading cause of death and disability. Hemorrhage is the major mechanism responsible for death during the first 24 hours following trauma. One quarter of severely injured patients present in the emergency room with acute coagulopathy of trauma and shock (ACOT). The drivers of ACOT are tissue hypoperfusion, inflammation, and activation of the neurohumoral system. ACOT is a result of protein C activation with cleavage of activated factor VIII and V and inhibition of plasminogen activator inhibitor-1 (PAI-1). The resuscitation-associated coagulopathy (RAC) is secondary to a combination of acidosis, hypothermia and dilution from intravenous blood and fluid therapy. RAC may further aggravate acidosis and hypoxia resulting in a vicious cycle. This review focuses on the biology of the trauma-associated coagulopathy, and reviews current therapeutic strategies.

Association of the Thrombomodulin Gene c.1418C>T Polymorphism With Thrombomodulin Levels and With Venous Thrombosis Risk

Objective—

To investigate the association of the THBD c.1418C>T polymorphism, which encodes for the replacement of Ala455 by Val in thrombomodulin (TM), with venous thromboembolism (VTE), plasma soluble TM, and activated protein C levels. In addition, human umbilical vein endothelial cells (HUVEC) isolated from 100 umbilical cords were used to analyze the relation between this polymorphism and THBD mRNA and TM protein expression.

Approach and Results—

The THBD c.1418C>T polymorphism was genotyped in 1173 patients with VTE and 1262 control subjects. Levels of soluble TM and activated protein C were measured in 414 patients with VTE (not on oral anticoagulants) and 451 controls. HUVECs were genotyped for the polymorphism and analyzed for THBD mRNA and TM protein expression and for the ability to enhance protein C activation by thrombin. The 1418T allele frequency was lower in patients than in controls ( P <0.001), and its presence was associated with a reduced VTE risk, reduced soluble TM levels, and increased circulating activated protein C levels ( P <0.001). In cultured HUVEC, the 1418T allele did not influence THBD expression but was associated with increased TM in cell lysates, increased rate of protein C activation, and reduced soluble TM levels in conditioned medium.

Conclusions—

The THBD 1418T allele is associated with lower soluble TM, both in plasma and in HUVEC-conditioned medium, and with an increase in functional membrane–bound TM in HUVEC, which could explain the increased activated protein C levels and the reduced VTE risk observed in individuals carrying this allele.

Thrombomodulin as a regulator of the anticoagulant pathway: implication in the development of thrombosis

Thrombomodulin is a cell surface-expressed glycoprotein that serves as a cofactor for thrombin-mediated activation of protein C (PC), an event further amplified by the endothelial cell PC receptor. The PC pathway is a major anticoagulant mechanism that downregulates thrombin formation and hedges thrombus formation. The objectives of this review were to review recent findings regarding thrombomodulin structure, its involvement in the regulation of hemostasis and further discuss the implication, if any, of the genetic polymorphisms in the thrombomodulin gene in the risk of development of thrombosis. We performed a literature search by using electronic bibliographic databases. Although the direct evaluation of risk situations associated with thrombomodulin mutations/polymorphisms could be of clinical significance, it appears that mutations that affect the function of thrombomodulin are rarely associated with venous thromboembolism. However, several polymorphisms are reported to be associated with increased risk for arterial thrombosis. Additionally studies on knock out mice as well studies on humans bearing rare mutations suggest that thrombomodulin dysfunction may be implicated in the pathogenesis of myocardial infraction.

Textilinin-1, an alternative anti-bleeding agent to aprotinin: Importance of plasmin inhibition in controlling blood loss

Aprotinin has been used widely in surgery as an anti-bleeding agent but is associated with a number of side effects. We report that textilinin-1, a serine protease inhibitor from Pseudonaja textilis venom with sequence relatedness to aprotinin, is a potent but reversible plasmin inhibitor and has a narrower range of protease inhibition compared to aprotinin. Like aprotinin, textilinin-1 at 5 micromol/l gave almost complete inhibition of tissue plasminogen activator-induced fibrinolysis of whole blood clots. The activated partial thromboplastin time for plasma was markedly increased by aprotinin but unaffected by textilinin-1. In a mouse tail-vein bleeding model, intravenous textilinin-1 and aprotinin caused similar decreases in blood loss but time to haemostasis in the textilinin-treated animals was significantly shorter than in aprotinin-treated mice. Based on these data, textilinin-1 merits further investigation as a therapeutic alternative to aprotinin.

Significance of endothelial dysfunction in the pathogenesis of early and delayed radiation enteropathy

This review summarizes the current state of knowledge regarding the role of endothelial dysfunction in the pathogenesis of early and delayed intestinal radiation toxicity and discusses various endothelial-oriented interventions aimed at reducing the risk of radiation enteropathy. Studies published in the biomedical literature during the past four decades and cited in PubMed, as well as clinical and laboratory data from our own research program are reviewed. The risk of injury to normal tissues limits the cancer cure rates that can be achieved with radiation therapy. During treatment of abdominal and pelvic tumors, the intestine is frequently a major dose-limiting factor. Microvascular injury is a prominent feature of both early (inflammatory), as well as delayed (fibroproliferative) radiation injuries in the intestine and in many other normal tissues. Evidence from our and other laboratories suggests that endothelial dysfunction, notably a deficiency of endothelial thrombomodulin, plays a key role in the pathogenesis of these radiation responses. Deficient levels of thrombomodulin cause loss of vascular thromboresistance, excessive activation of cellular thrombin receptors by thrombin, and insufficient activation of protein C, a plasma protein with anticoagulant, anti-inflammatory, and cytoprotective properties. These changes are presumed to be critically involved in many aspects of early intestinal radiation toxicity and may sustain the fibroproliferative processes that lead to delayed intestinal dysfunction, fibrosis, and clinical complications. In conclusion, injury of vascular endothelium is important in the pathogenesis of the intestinal radiation response. Endothelial-oriented interventions are appealing strategies to prevent or treat normal tissue toxicity associated with radiation treatment of cancer.

The respective and combined anticoagulant effects of recombinant human activated protein C, melagatran and heparins using CAT

INTRODUCTION

Combinations of anticoagulants might be beneficial in some patients with sepsis, but most anticoagulants require specific clotting assays for monitoring. Thrombin generation assay, however, is a global function test of hemostasis.

MATERIALS AND METHODS

We performed an in vitro investigation of the respective effects of recombinant human activated protein C (rhAPC) alone and in combination with either melagatran (a new direct thrombin inhibitor), unfractionated heparin (UH) or low molecular weight heparin (LMWH) in varying concentrations on the thrombin generation (TG) using the calibrated automated thrombography.

RESULTS

RhAPC, UH, LMWH and melagatran dose-dependently prolonged the lag time and the time to peak, and significantly suppressed the endogenous thrombin potential (ETP). Combined application of rhAPC with either melagatran, UH or LMWH induced an additive prolongation of the lag time; this effect was more pronounced in a combination of rhAPC with UH or LMWH.

CONCLUSION

In our in vitro study adding either melagatran, UH or LMWH augmented the capacity of rhAPC to suppress thrombin generation in human plasma. These findings suggest that patients with severe sepsis might benefit from a treatment with combinations of anticoagulant agents.

PAR4, but not PAR1, signals human platelet aggregation via Ca2+ mobilization and synergistic P2Y12 receptor activation

Regulation of platelet activation plays a central role in hemostasis and pathophysiological processes such as coronary artery disease. Thrombin is the most potent activator of platelets. Human platelets express two thrombin receptors, PAR1 and PAR4, both of which signal platelet activation. Evidence is lacking on the mechanism by which PAR1 and PAR4 may differentially signal platelet aggregation. Here we show that at the relatively high concentration of agonist most likely found at the site of a local thrombus, dual inhibition of the P2Y12 receptor and calcium mobilization result in a complete inhibition of PAR4-induced aggregation, while having no effect on either thrombin or PAR1-mediated platelet aggregation. Both PAR1- and PAR4mediated aggregation are independent of calcium mobilization. Furthermore, we show that P2Y12 receptor activation is not required for protease-activated receptor-mediated aggregation at higher agonist concentrations and is only partially required for Rap1 as well as GPIIbIIIa activation. P2Y12 receptor inhibitors clinically in use such as clopidogrel are postulated to decrease platelet aggregation through partial inhibition of PAR1 signaling. Our data, however, indicate that at high local concentrations of thrombin, it is the signaling through PAR4 rather than PAR1 that may be regulated through purinergic feedback. Thus, our data identify an intra-platelet mechanism that may function as a future site for therapeutic intervention.

Coagulation Defects

The present understanding of the coagulation process emphasizes the final common pathway and the proteolytic systems that result in the degradation of formed clots and the prevention of unwanted clot formations, as well as a variety of defense systems that include tissue repair, autoimmune processes, arteriosclerosis, tumor growth, the spread of metastases, and defense systems against micro-organisms. This article discusses diagnosis and management of some of the most common bleeding disorders. The goals are to provide a simple guide on how best to manage patients afflicted with congenital or acquired clotting abnormalities during the perioperative period, present a brief overview of the methods of testing and monitoring the coagulation defects, and discuss the appropriate pharmacologic or blood component therapies for each disease.

The rule of four: a systematic approach to diagnosis of common pediatric hematologic and oncologic disorders

The "Rule of Four" facilitates a rapid and focused approach to the diagnosis of the common hematologic and oncologic disorders encountered in general pediatric practice. This system relies on four recurrent but different clinical entities or laboratory tests relevant to the diagnosis of children with anemia, excessive bleeding or clotting, and common malignancies. For each disorder, there is a discussion of a variety of four lab tests or factors pertinent to a differential diagnosis.