A synthetic inhibitor of factor Xa, DX-9065a, reduces proliferation of vascular smooth muscle cells in vivo in rats

Effect of Rivaroxaban and Clopidogrel Combination Therapy on In-Stent Responses After Everolimus-Eluting Stent Implantation in a Porcine Coronary Model

Aim: According to recent clinical trials, a combination of direct oral anticoagulants with antiplatelet drugs is often recommended for atrial fibrillation patients who receive drug-eluting stents (DESs). Although the optimal combination comprises direct factor Xa inhibitors and a P2Y ₁₂ receptor antagonist (or aspirin), their influence on vascular responses to DESs remains unclear.

Methods: Pigs were given either aspirin and clopidogrel (dual antiplatelet therapy [DAPT] group), aspirin and rivaroxaban (AR group), or clopidogrel and rivaroxaban (CR group), followed by everolimus-eluting stent (Promus Element) implantation into the coronary artery. Stented coronary arteries were evaluated via intravascular optical coherence tomography (OCT) and histological analysis at 1 and 3 months.

Results: OCT revealed lower neointimal thickness in the DAPT group and comparable thickness among all groups at 1 and 3 months, respectively. Histological analyses revealed comparable neointimal area among all groups and the smallest neointimal area in the CR group at 1 and 3 months, respectively. In the DAPT and AR groups, the neointima continued to grow from 1 to 3 months. A shortened time course for neointima growth was observed in the CR group, with rapid growth within a month (maintained for 3 months). A higher incidence of in-stent thrombi was observed in the AR group at 1 month; no thrombi were found in either group at 3 months. More smooth muscle cells with contractile features were found in the CR group at both 1 and 3 months.

Conclusions: Our results proved the noninferiority of the combination of rivaroxaban with an antiplatelet drug, particularly the dual therapy using rivaroxaban and clopidogrel, compared to DAPT after DES implantation.

A direct oral factor Xa inhibitor edoxaban ameliorates neointimal hyperplasia following vascular injury and thrombosis in apolipoprotein E-deficient mice

Vascular injury activates the coagulation cascade. Some studies report that coagulation factor Xa and thrombin are implicated in proliferation of vascular smooth muscle cells and neointimal hyperplasia after vascular injury. The aim of this study was to determine the effect of an oral direct factor Xa inhibitor, edoxaban, on neointimal hyperplasia following the carotid artery injury in apolipoprotein E (ApoE)-deficient mice. Vascular injury was induced by the application of 10% ferric chloride to the carotid artery for 3 min in ApoE-deficient mice. After vascular injury, all animals were fed with high-cholesterol chow for 6 weeks. Edoxaban at 15 mg/kg was orally administered to the mice 1 h before (n = 10) or 1 h after (n = 9) ferric chloride injury, and thereafter 10 mg/kg edoxaban was orally administered b.i.d. for 6 weeks. Thrombus formation and neointimal hyperplasia were evaluated. Treatment with 15 mg/kg edoxaban before vascular injury almost completely inhibited thrombus formation, and following chronic administration of edoxaban significantly suppressed neointimal hyperplasia. In the mice treated with edoxaban after vascular injury, there was wide interindividual variability. In some mice (four out of nine) the neointimal hyperplasia was inhibited like in edoxaban-pretreated mice, but there was no statistical difference compared with control. This study demonstrated that inhibition of the coagulation and thrombosis by edoxaban ameliorated neointimal hyperplasia caused by vascular injury and high-cholesterol diets in ApoE-deficient mice. This suggests that factor Xa has a crucial role in the formation of neointima following vascular injury.The abstract should be followed by 3-4 bullet points that highlight major findings. The final bullet point should emphasize future directions for research.

Inhibition of activated factor X by rivaroxaban attenuates neointima formation after wire-mediated vascular injury

Accumulating evidence suggests that activated factor X (FXa), a key coagulation factor, plays an important role in the development of vascular inflammation through activation of many cell types. Here, we investigated whether pharmacological blockade of FXa attenuates neointima formation after wire-mediated vascular injury. Transluminal femoral artery injury was induced in C57BL/6 mice by inserting a straight wire. Rivaroxaban (5mg/kg/day), a direct FXa inhibitor, was administered from one week before surgery until killed. At four weeks after surgery, rivaroxaban significantly attenuated neointima formation in the injured arteries compared with control (P<0.01). Plasma lipid levels and blood pressure were similar between the rivaroxaban-treated group and non-treated group. Quantitative RT-PCR analyses demonstrated that rivaroxaban reduced the expression of inflammatory molecules (e.g., IL-1β and TNF-α) in injured arteries at seven days after surgery (P<0.05, respectively). In vitro experiments using mouse peritoneal macrophages demonstrated that FXa increased the expression of inflammatory molecules (e.g., IL-1β and TNF-α), which was blocked in the presence of rivaroxaban (P<0.05). Also, in vitro experiments using rat vascular smooth muscle cells (VSMC) demonstrated that FXa promoted both proliferation and migration of this cell type (P<0.05), which were blocked in the presence of rivaroxaban. Inhibition of FXa by rivaroxaban attenuates neointima formation after wire-mediated vascular injury through inhibition of inflammatory activation of macrophages and VSMC.

Factor Xa Signaling Contributes to the Pathogenesis of Inflammatory Diseases

The coagulation protease Factor Xa (FXa) triggers a variety of signaling pathways through activation of protease-activated receptors (PARs) and non-PAR receptors. FXa-mediated signaling is strongly implicated in the pathogenesis of several inflammatory diseases including fibrosis, cardiovascular diseases, and cancer. Thus, targeting of FXa can have great clinical significance in terms of the treatment of these disorders. This review summarizes the current knowledge about the mechanism of FXa signaling in cellular and animal systems under (patho) physiological conditions for a better understanding and hence a better management of FXa-induced disorders. J. Cell. Physiol. 232: 1966-1970, 2017. © 2016 Wiley Periodicals, Inc.

Complement and coagulation: strangers or partners in crime?

The convergence between complement and the clotting system extends far beyond the chemical nature of the complement and coagulation components, both of which form proteolytic cascades. Complement effectors directly enhance coagulation. These effects are supplemented by the interactions of complement with other inflammatory mediators that can increase the thrombogenicity of blood. In addition, complement inhibits anticoagulant factors. The crosstalk between complement and coagulation is also well illustrated by the ability of certain coagulation enzymes to activate complement components. Understanding the interplay between complement and coagulation has fundamental clinical implications in the context of diseases with an inflammatory pathogenesis, in which complement-coagulation interactions contribute to the development of life-threatening complications. Here, we review the interactions of the complement system with hemostasis and their roles in various diseases.

Roles of coagulation pathway and factor Xa in rat mesangioproliferative glomerulonephritis

Tissue factor initiates the extrinsic coagulation pathway by activating coagulation factor X to factor Xa, and factor V is a cofactor for the prothrombin activation by factor Xa. As factor Xa is known to promote the proliferation of mesangial cells in culture, the roles of the coagulation pathway and factor Xa were studied in an animal model of mesangioproliferative glomerulonephritis (MsPGN). MsPGN was induced in Wistar rats by an intravenous injection of anti-Thy 1.1 monoclonal antibody, OX-7. To clarify the role of factor Xa in MsPGN, a specific factor Xa inhibitor, DX-9065a, was injected intravenously at 2.5 or 10 mg/kg at the same time as OX-7, and kidney involvement was assessed by immunohistological analyses. We also examined p44/42 mitogen-activated protein (MAP) kinase activation. Time-course study revealed that expressions of tissue factor, factor V, and protease-activated receptor 2 (PAR2) were peaked on day 3, followed by factor X accumulation and mesangial proliferation. DX-9065a treatment significantly ameliorated proteinuria in a dose-dependent manner on day 8. Histological analyses showed a significant reduction in the size of glomeruli, the total number of glomerular cells, and crescent formation by DX-9065a treatment. Macrophage infiltration, which was rapidly observed on day 1 in disease control rats was not inhibited on days 1-3 by DX-9065a treatment, however it was suppressed on days 5-8. The deposition of fibrin, the number of PCNA-positive cells, and phosphorylation of p44/42 MAP kinase were markedly increased in the disease control group, whereas they were significantly reduced in the treatment group. Tissue factor and factor V induction may accelerate MsPGN through the activation and accumulation of factor X via proinflammatory and procoagulant mechanisms, and the inhibition of factor Xa would be a promising method to regulate the disease process.

DX-9065a, a direct inhibitor of factor Xa

The synthetic compound DX-9065a represents a low molecular weight, direct, competitive inhibitor of factor Xa (FXa) with a high affinity and selectivity for the enzyme. Under experimental conditions DX-9065a exerts strong anticoagulant actions in vitro and in vivo and is antithrombotically effective in various thrombosis models. It inhibits proliferation of vascular smooth muscle cells in cell culture systems as well as in in vivo models. As a small molecule inhibitor, DX-9065a inactivates both free and fibrin-bound FXa. By this mechanism it effectively affects the clot-associated procoagulant activity which might be responsible for the propagation of intravascular thrombi as well as for recurrent thrombosis and thrombotic reocclusion after lysis. Although DX-9065a is effective after oral administration, its oral bioavailability is relatively low and seems not to be sufficient for a long-term therapeutic use of the drug. However, first clinical trials in healthy volunteers and in patients with cardiovascular diseases demonstrated a predictable pharmacokinetic and pharmacodynamic behavior of DX-9065a after either intravenous bolus injection or constant infusion, as well as its high safety, especially a lower bleeding risk compared with other commonly used drugs. Further experimental studies and ongoing clinical trials will evaluate the inhibitory profile of the drug, its effectiveness and its possible superiority over other drug regimens in various cardiovascular indications.

Coagulation factor Xa synergistically interacts with serotonin in inducing vascular smooth muscle cell proliferation

INTRODUCTION

Initial events following vascular interventions include activation of platelets and coagulation cascade. Activated platelets release several vasoactive mediators including serotonin. Activation of coagulation cascade results in conversion of inactive zymogens such as factor X to its active form (factor Xa). So this study designed to examine the effect of factor Xa on rabbit vascular smooth muscle cell (VSMC) proliferation and its interaction with serotonin.

METHODS

Growth-arrested VSMCs were incubated in a serum-free medium with different concentrations of factor Xa with or without serotonin. VSMC proliferation was examined by increase in incorporation of [3H]thymidine into DNA and by increase in cell number.

RESULTS

Factor Xa and serotonin stimulated DNA synthesis in a dose-dependent manner. Factor Xa had a maximal effect at 100 nM (1180+/-110%) and serotonin at 50 microM (345+/-21%). When added together, at nonmitogenic concentrations, factor Xa (0.1 nM) and serotonin (1 micoM) synergistically induced DNA synthesis (312+/-12%). These increases in DNA synthesis were paralleled by an increase in cell number. Serine protease inhibitors, active site blockers and platelet-derived growth factor receptor tyrosine kinase inhibitor blocked the mitogenic effect of factor Xa and its interaction with serotonin. Similarly, serotonin type 2 receptor inhibitor and Gi-protein-coupled receptor inhibitor inhibited the mitogenic effect of serotonin and its interaction with factor Xa. When used in combination, they blocked the interaction between factor Xa and serotonin.

CONCLUSION

Coagulation factor Xa and serotonin are mitogenic to VSMCs and also function as amplification factors to each other, suggesting that inhibition of neointimal proliferation after vascular injury may require the combined use of multiple growth factor inhibitors to simultaneously block several critical cellular activation pathways.

Global anticoagulant effects of a synthetic anti-factor Xa inhibitor (DX-9065a): implications for interventional use

Heparin has been conventionally used as an anticoagulant for medical and surgical indications. Because factor Xa is an essential component of the prothrombinase complex and leads to the generation of thrombin, its inhibition has become a focus of newer antithrombotic drug development. The in vitro anticoagulant profile of DX-9065a, a synthetic direct factor Xa inhibitor, was studied using activated clotting time assay, thrombelastography, and global clotting tests, such as prothrombin time (PT), activated partial thromboplastin time (aPTT), diluted aPTT, Heptest, Heptest-HI, dilute Russell's viper venom time (dRVVT), thrombin time, ecarin clotting time, and amidolytic anti-Xa assay. In addition, the effect of DX-9065a on platelet aggregation and inhibition of thrombin generation markers (FPA, F1+2, and TAT) were studied. The pharmacokinetic and pharmacodynamic profiles of DX-9065a were also studied in a non-human primate (Macaca mulatta) model. DX-9065a produced a concentration-dependent increase in the Hemochron celite ACT and HemoTec ACT. Clotting times of 538 +/- 19 and 401 +/- 12, respectively, were reached at a concentration of 25 microg/mL signifying that DX-9065a may be useful in interventional cardiological procedures. DX-9065a prolonged the r-time on thrombelastography. DX-9065a did not show any effect on adenosine diphosphate (ADP)-, collagen-, epinephrine-, and arachidonic acid-induced platelet aggregation at concentrations up to 10 microgram/mL. DX-9065a exhibited a concentration-dependent prolongation of the PT, aPTT, diluted aPTT, Heptest, dRVVT, and reached the clotting times of 51.6, 132, 193, 47.9, 129.9 seconds, respectively, at a final concentration of 12.5 microgram/mL; compared to a control value of 10.6, 30.2, 41.9, 14, 32.2 seconds, respectively. DX-9065a did not affect the ecarin clotting time and thrombin time at concentrations up to 12.5 microgram/mL. Because DX-9065a prolonged the dRVVT, this may impact diagnostic screening of patients with systemic lupus erythematosus.

Effects of a synthetic factor Xa inhibitor (JTV-803) on various laboratory tests

Synthetic direct inhibitors of factor Xa are capable of prolonging the global anticoagulant assay times in a concentration-dependent fashion. The relative degree of thrombin generation inhibition at an equivalent prolongation is not similar to the results observed with heparins and oral anticoagulant drugs. In addition, the direct factor Xa inhibitors prolong the Russell's viper venom test (RWT) and Heptest clotting times. Ecarin clotting time (ECT) and thrombin time (TT) remain unaffected. The kinetics of factor Xa inhibition are markedly different than those observed with pentasaccharide and heparins. Therefore, the methods developed for heparins and pentasaccharides may not be applicable for the monitoring of factor Xa inhibitors. To test the feasibility of using the prothrombin time (PT), International Normalized Ratio (INR), activated partial thromboplastin time (aPTT), Heptest, thrombin time, RVVT, ECT, and a modified anti-Xa amidolytic assay, to monitor a synthetic factor Xa inhibitor, normal human pool plasma samples were spiked with a synthetic factor Xa inhibitor in the concentration range of 0 to 1 microg/mL and 0 to 25 microg/mL. Different laboratory tests were performed and INR and other ratios were calculated. The anticoagulant effects on whole blood were measured using the activated clotting time (ACT). Further studies on the effect of factor Xa inhibitor on platelet aggregation; factor II, VII, and X functional levels; and fibrinopeptide A (FPA) generation were carried out at equivalent INR levels in comparison to oral anticoagulant and antithrombin agents. FPA generation at equivalent anticoagulant level in comparison to heparin (twice the baseline) was also carried out. Factor Xa inhibitor produced a concentration-dependent prolongation of the ACT. ACT was doubled at a concentration of 4 to 5 microg/mL. There was a marked difference in the prolongation of the PT by a synthetic factor Xa inhibitor dependent on the ISI of the PT reagent used. When the results were calculated to determine INR, marked variations were noted between the recombinant thromboplastin and rabbit brain thromboplastin. The rabbit brain thromboplastin reagent gave markedly high INR values. Similar results were observed when different aPTT reagents were studied. In the anti-Xa assay, modification of the incubation time was employed to extend the proper sensitivity range. These studies warrant further investigation to understand the mechanism of action of factor Xa inhibitors.

Factor Xa releases matrix metalloproteinase-2 (MMP-2) from human vascular smooth muscle cells and stimulates the conversion of pro-MMP-2 to MMP-2: role of MMP-2 in factor Xa-induced DNA synthesis and matrix invasion

Pro-matrix metalloproteinase-2 (pro-MMP-2) is expressed in vascular smooth muscle cells (SMCs). We report that activated coagulation factor X (FXa) induces the release of MMP-2 (65 kDa) from human SMCs. In addition, FXa cleaves pro-MMP-2 (72 kDa) into MMP-2. Pro-MMP-2 and MMP-2 were determined by gelatin zymography. MMP-2 was generated in conditioned medium containing pro-MMP-2 in a concentration-dependent fashion by FXa (3 to 100 nmol/L). FX at concentrations up to 300 nmol/L was ineffective. The conversion of pro-MMP-2 to MMP-2 was inhibited by a selective FXa inhibitor (DX-9065a) at 3 to 10 micromol/L. There was a concentration-dependent induction of an intermediate MMP-2 form (68 kDa) in lysates of FXa-treated cells. This indicates that cellular mechanisms are involved in FXa-induced conversion of pro-MMP-2. As a possible biological consequence of MMP-2 activation by FXa, DNA synthesis and matrix invasion of SMCs were determined. Both were stimulated by FXa and inhibited by the selective FXa inhibitor DX-9065a and the MMP inhibitor GM 6001 but not by hirudin or aprotinin. It is concluded that stimulation of SMCs by FXa increases the levels of MMP-2 in the extracellular space and that two different mechanisms are involved: release of active MMP-2 and cleavage of secreted pro-MMP-2. Both might contribute to the mitogenic potency of FXa and FXa-stimulated matrix invasion of SMCs.

Evolution of enzyme cascades from embryonic development to blood coagulation

Recent delineation of the serine protease cascade controlling dorsal-ventral patterning during Drosophila embryogenesis allows this cascade to be compared with those controlling clotting and complement in vertebrates and invertebrates. The identification of discrete markers of serine protease evolution has made it possible to reconstruct the probable chronology of enzyme evolution and to gain new insights into functional linkages among the cascades. Here, it is proposed that a single ancestral developmental/immunity cascade gave rise to the protostome and deuterostome developmental, clotting and complement cascades. Extensive similarities suggest that these cascades were built by adding enzymes from the bottom of the cascade up and from similar macromolecular building blocks.

Role of short-term inhibition of factor Xa by FXV673 in arterial passivation: a study in a chronic model of thrombosis in conscious dogs

Factor Xa (fXa) plays a pivotal role in the activation of the coagulation system during thrombosis, but, unlike GPIIb/IIIa receptor antagonists, the role of fXa inhibition in arterial passivation is not well defined. We compared the long-term antithrombotic efficacy of a direct fXa inhibitor, FXV673, and heparin after short-term infusion in conscious dogs. Dogs were instrumented surgically to induce carotid artery thrombosis by electrolytic injury. On day 1, dogs received a 3-h infusion of placebo (n = 10), FXV673 (100 microg/kg + 10 microg/kg/min, n = 7), or heparin (60 U/kg + 0.7 U/kg/min, n 7). Injury (100 microA) was initiated concomitantly for 1 h. The procedure was repeated on day 2 with injury of 200 microA for 3 h. Carotid artery blood flow (CBF) and coagulation parameters were monitored continuously for 3 h on days 1 and 2 and for 30 min on days 3, 4, and 5. On day 1 at 3 h, CBF in the placebo-treated group was 26% of baseline with 70% incidence of occlusion. None of the vessels occluded in the heparin and FXV673 groups; however, the CBF was significantly higher in the FXV673 group (92+/-8 ml/min versus 39+/-12 ml/min). Before injury on day 2, CBF recovered in all groups to 71-89% of baseline. After the second injury, all vessels in the placebo-treated group progressed to complete occlusion by 3 h. CBF was significantly higher in FXV673 group compared with heparin throughout the 3-h period. On days 3, 4, and 5 the placebo-treated vessels remained occluded, but the CBF in the heparin group was 33+/-20 ml/min, 55+/-11 ml/min and 68+/-12 ml/min, respectively, compared with 84+/-10 ml/min, 98+/-7 ml/min, and 99+/-10 ml/min in the FXV673 group. The arterial thrombus mass was significantly lower in FXV673 group (13+/-4 mg) compared with placebo (103+/-10 mg) and heparin (44+/-11 mg). In summary, these data demonstrate that short-term infusion of FXV673 was associated with long-term efficacy that was superior to standard heparin and underscore the role of direct fXa inhibition in arterial passivation.

The role of proteinases in angiogenesis, heart development, restenosis, atherosclerosis, myocardial ischemia, and stroke: insights from genetic studies

The development of novel gene technologies in mice has provided an elegant tool to identify gene products that are causally linked to certain physiologic processes as well as the pathogenesis of numerous disorders. Using these techniques, three major proteolytic systems -- the plasminogen, the matrix metalloproteinase (MMP) and the coagulation systems -- have been shown to be involved in cardiovascular diseases, which still constitute the leading cause of death in Western societies. This overview summarizes the role of these proteolytic systems in angiogenesis, arterial stenosis, allograft transplant stenosis, vein graft stenosis, atherosclerosis, myocardial infarction, cardiac development and ischemic stroke and discusses possible therapeutic implications.