Electrolytic inferior vena cava model (EIM) of venous thrombosis

Establishment of a Modified and Standardized Ferric Chloride-Induced Rat Carotid Artery Thrombosis Model

BACKGROUND

Ferric chloride is widely utilized in inducing thrombosis in small vessels of experimental animals. However, the lack of its application in large blood vessels of experimental animals and inconsistent concentration has limited its application. Therefore, we systematically tested the most suitable concentration and reliable induction time in the experiment of using ferric chloride to induce rat carotid artery thrombosis.

METHODS

In this study, we selected the common carotid artery of 59 Sprague-Dawley rats as the target vessel. The exploration process was divided into three stages. First, to determine the optimum induction concentration, we compared the effects of 30-60% ferric chloride on thrombus formation within 24 h. Second, to confirm the handling time, we tested different induction times from 3 min to 10 min. Lastly, we used the thrombolytic drug rt-PA to detect whether the formed thrombus can be lysed. Doppler blood flow imaging and H-E staining were employed to estimate the blood flow and thrombus. The ATP levels in the brain were measured using a bioluminescence ATP assay kit.

RESULTS

We found that the application of 50% ferric chloride for 10 min was enough to successfully induce thrombosis in the rat carotid artery and without spontaneous thrombolysis after 24 h. It is better than other concentrations and will lead to the decline of the ATP content in the ischemic hemisphere.

CONCLUSIONS

Our results indicate that the rat carotid artery thrombosis model induced by 50% ferric chloride for 10 min is stable and reliable.

Understanding the Pathophysiology of Thrombotic APS through Animal Models

Antiphospholipid syndrome (APS) is a leading acquired cause of thrombotic events, with a notable tendency to promote thrombosis in vascular beds of all sizes, including both arterial and venous circuits. While pathogenic antiphospholipid antibodies circulate at relatively stable levels in blood, thrombosis tends to manifest as discrete and acute events, suggesting the requirement for a “second hit.” While this two-hit model is generally accepted, much remains to be learned about exactly how antiphospholipid antibodies predispose to thrombosis in vivo and exactly how this predisposition interacts with the second hit. To this end, investigators have turned to animal models. Numerous approaches for modeling APS in animals have been described to date, each with potential advantages and disadvantages. This review will attempt to describe the most common APS models employed so far while discussing some pros and cons of each. Mechanisms of thrombotic APS that have thus far been explored in animal models will also be briefly addressed.

Extracellular DNA-A Danger Signal Triggering Immunothrombosis

Clotting and inflammation are effective danger response patterns positively selected by evolution to limit fatal bleeding and pathogen invasion upon traumatic injuries. As a trade-off, thrombotic, and thromboembolic events complicate severe forms of infectious and non-infectious states of acute and chronic inflammation, i.e., immunothrombosis. Factors linked to thrombosis and inflammation include mediators released by platelet granules, complement, and lipid mediators and certain integrins. Extracellular deoxyribonucleic acid (DNA) was a previously unrecognized cellular component in the blood, which elicits profound proinflammatory and prothrombotic effects. Pathogens trigger the release of extracellular DNA together with other pathogen-associated molecular patterns. Dying cells in the inflamed or infected tissue release extracellular DNA together with other danger associated molecular pattern (DAMPs). Neutrophils release DNA by forming neutrophil extracellular traps (NETs) during infection, trauma or other forms of vascular injury. Fluorescence tissue imaging localized extracellular DNA to sites of injury and to intravascular thrombi. Functional studies using deoxyribonuclease (DNase)-deficient mouse strains or recombinant DNase show that extracellular DNA contributes to the process of immunothrombosis. Here, we review rodent models of immunothrombosis and the evolving evidence for extracellular DNA as a driver of immunothrombosis and discuss challenges and prospects for extracellular DNA as a potential therapeutic target.

By word of mouse: using animal models in venous thrombosis research

Deep vein thrombosis (DVT) is a disease with high prevalence and morbidity. It can lead to pulmonary embolism with severe respiratory insufficiency and risk of death. Mechanisms behind all stages of DVT, such as thrombosis commencement, propagation, and resolution, remain incompletely understood. Animal models represent an invaluable tool to explore these problems and identify new targets for DVT prevention and treatment. In this review, we discuss existing models of venous thrombosis, their advantages and disadvantages, and applicability to studying different aspects of DVT pathophysiology. We also speculate about requirements for an "ideal model" that would best recapitulate features of human DVT and discuss readouts of various models.

Venous Thrombosis and Post-Thrombotic Syndrome: From Novel Biomarkers to Biology

Deep vein thrombosis (DVT) is a common disease that carries serious ramifications for patients, including pulmonary embolism and post-thrombotic syndrome (PTS). Although standard treatment for DVT is anticoagulation, this carries an added risk of bleeding and increased medication monitoring. Identifying those at risk for DVT and PTS can be difficult, and current research with murine models is helping to illuminate the biologic changes associated with these two disorders. Potential novel biomarkers for improving the diagnosis of DVT and PTS include ICAM-1, P-selectin, and cell-free DNA. Inhibition of factor XI, P- and E-selectin, and neutrophil extracellular traps holds promise for novel clinical treatment of DVT. Experimental research on PTS suggests potential cellular and mediator therapy targets of TLR9, MMP-2 and-9, PAI-1, and IL-6. Although many important concepts and mechanisms have been elucidated through research on DVT and PTS, more work must be done to translate experimental findings to the clinical arena. This review examines the currently used murine models of DVT, biomarkers involved in the pathophysiology and diagnosis of DVT and PTS, and potential pharmacologic targets for PTS treatment.

Effect of a new inhibitor of factor Xa zifaxaban, on thrombosis in the inferior vena cava in rabbits

In recent years, oral factor Xa inhibitors have become a research focus as anticoagulant drugs. Zifaxaban is the first oral FXa inhibitor to enter clinical trials in China. The aim of this study was to determine the inhibitory effect of zifaxaban on thrombosisthrough a model ofinferior vena cava (IVC) thrombosis in rabbits. IVC thrombosis model was established by electrical injury and stenosis, and zifaxaban was administered (p.o.) for 5 consecutive days, then coagulation indicators and bleeding were observed. The results showed that zifaxaban had obvious inhibitory effects on FXa, and had a significant inhibitory effect on IVC thrombosis induced by electrical damage and stenosis. The effect of zifaxaban was similar to that of rivaroxaban, but the bleeding side-effects of zifaxaban were less severe than those of rivaroxaban. Zifaxaban could prolong the prothrombin time and activated partial thromboplastin time of plasma similar to that of other oral FXa inhibitors. Zifaxaban had a significant inhibitory effect on FXa, but it had no obvious effect on other coagulation factors, major anticoagulant factors or fibrinolytic indices. Our results suggest that zifaxaban had specific inhibitory effects on FXa and inhibited IVC thrombosis in rabbits with its hemorrhagic effect was less than that of rivaroxaban. Zifaxaban is ecpected to be developed as a new drug for the prevention of deep venous thrombosis, providing more medication options for patients with such disease, more research is required to support it in the future.

Platelet-targeted dual pathway antithrombotic inhibits thrombosis with preserved hemostasis

Despite advances in antithrombotic therapy, the risk of recurrent coronary/cerebrovascular ischemia or venous thromboembolism remains high. Dual pathway antithrombotic blockade, using both antiplatelet and anticoagulant therapy, offers the promise of improved thrombotic protection; however, widespread adoption remains tempered by substantial risk of major bleeding. Here, we report a dual pathway therapeutic capable of site-specific targeting to activated platelets and therapeutic enrichment at the site of thrombus growth to allow reduced dosing without compromised antithrombotic efficacy. We engineered a recombinant fusion protein, SCE5-TAP, which consists of a single-chain antibody (SCE5) that targets and blocks the activated GPIIb/IIIa complex, and tick anticoagulant peptide (TAP), a potent direct inhibitor of activated factor X (FXa). SCE5-TAP demonstrated selective platelet targeting and inhibition of thrombosis in murine models of both carotid artery and inferior vena cava thrombosis, without a significant impact on hemostasis. Selective targeting to activated platelets provides an attractive strategy to achieve high antithrombotic efficacy with reduced risk of bleeding complications.

Immune Factors in Deep Vein Thrombosis Initiation

Deep vein thrombosis (DVT) is a major origin of morbidity and mortality. While DVT has long been considered as blood coagulation disorder, several recent lines of evidence demonstrate that immune cells and inflammatory processes are involved in DVT initiation. Here, we discuss these mechanisms, in particular, the role of immune cells in endothelial activation, and the immune cascades leading to expression of adhesion receptors on endothelial cells. We analyze the specific recruitment and functional roles of different immune cells, such as mast cells and leukocytes, in DVT. Importantly, we also speculate how immune modulation could be used for DVT prevention with a lower risk of bleeding complications than conventional therapeutic approaches.

Pre-Clinical Model to Study Recurrent Venous Thrombosis in the Inferior Vena Cava

BACKGROUND

Patients undergoing deep vein thrombosis (VT) have over 30% recurrence, directly increasing their risk of post-thrombotic syndrome. Current murine models of inferior vena cava (IVC) VT model host one thrombosis event.

OBJECTIVE

We aimed to develop a murine model to study IVC recurrent VT in mice.

MATERIALS AND METHODS

An initial VT was induced using the electrolytic IVC model (EIM) with constant blood flow. This approach takes advantage of the restored vein lumen 21 days after a single VT event in the EIM demonstrated by ultrasound. We then induced a second VT 21 days later, using either EIM or an IVC ligation model for comparison. The control groups were a sham surgery and, 21 days later, either EIM or IVC ligation. IVC wall and thrombus were harvested 2 days after the second insult and analysed for IVC and thrombus size, gene expression of fibrotic markers, histology for collagen and Western blot for citrullinated histone 3 (Cit-H3) and fibrin.

RESULTS

Ultrasound confirmed the first VT and its progressive resolution with an anatomical channel allowing room for the second thrombus by day 21. As compared with a primary VT, recurrent VT has heavier walls with significant up-regulation of transforming growth factor-β (TGF-β), elastin, interleukin (IL)-6, matrix metallopeptidase 9 (MMP9), MMP2 and a thrombus with high citrullinated histone-3 and fibrin content.

CONCLUSION

Experimental recurrent thrombi are structurally and compositionally different from the primary VT, with a greater pro-fibrotic remodelling vein wall profile. This work provides a VT recurrence IVC model that will help to improve the current understanding of the biological mechanisms and directed treatment of recurrent VT.

Update on the electrolytic IVC model for pre-clinical studies of venous thrombosis

BACKGROUND

The electrolytic inferior vena cava model (EIM) is a murine venous thrombosis (VT) model that produces a non-occlusive thrombus. The thrombus forms in the direction of blood flow, as observed in patients. The EIM is valuable for investigations of therapeutics due to the presence of continuous blood flow. However, the equipment used to induce thrombosis in the original model description was expensive and has since been discontinued. Further, the fibrinolytic system had not been previously studied in the EIM.

OBJECTIVES

We aimed to provide an equipment alternative. Additionally, we further characterized the model through mapping the current and time dependency of thrombus resolution dynamics, and investigated the fibrinolytic system from acute to chronic VT.

RESULTS

A voltage to current converter powered by a direct current power supply was constructed and validated, providing an added benefit of significantly reducing costs. The current and time dependency of thrombus volume dynamics was assessed by MRI, demonstrating the flexibility of the EIM to investigate both pro-thrombotic and anti-thrombotic conditions. Additionally, the fibrinolytic system was characterized in EIM. Centripetal distribution of plasminogen was observed over time, with peak staining at day 6 post thrombus induction. Both active circulating plasminogen activator inhibitor-1 (PAI-1) and vein wall gene expression of PAI-1 peaked at day 2, coinciding with a relative decrease in tissue plasminogen activator and urokinase plasminogen activator.

CONCLUSIONS

The EIM is a valuable model of VT that can now be performed at low cost and may be beneficial in investigations of the fibrinolytic system.

Stenosis of the Inferior Vena Cava: A Murine Model of Deep Vein Thrombosis

Deep vein thrombosis (DVT) and its devastating complication, pulmonary embolism, are a severe health problem with high mortality. Mechanisms of thrombus formation in veins remain obscure. Lack of mobility (e.g., after surgery or long-haul flights) is one of the main factors leading to DVT. The pathophysiological consequence of the lack of mobility is blood flow stagnation in venous valves. Here, a model is described that mimics such flow disturbance as a thrombosis-driving factor. In this model, partial flow restriction (stenosis) in the inferior vena cava (IVC) is created. Closure of about 90% of the IVC lumen for 48 h results in development of thrombi structurally similar to those in humans. The similarities are: i) most of the thrombus volume is red, i.e., consists of red blood cells and fibrin, ii) presence of a white part (lines of Zahn), iii) non-denuded endothelial monolayer, iv) elevated plasma D-Dimer levels, and v) possibility to prevent thrombosis by low molecular weight heparin. Limitations include variable size of thrombi and the fact that a certain percentage of wild-type mice (0 - 35%) may not produce a thrombus. In addition to visual observation and measurement, thrombi may be visualized by non-invasive technologies, such as ultrasonography, which allows for monitoring the dynamics of thrombus development. At shorter time points (1 - 6 h), intravital microscopy may be applied to directly observe events (e.g., recruitment of cells to the vessel wall) preceding thrombus formation. Use of this method by several teams around the world has made it possible to uncover basic mechanisms of DVT initiation and identify potential targets that might be beneficial for its prevention.

Animal models of venous thrombosis

Venous thrombosis (VT) is a prevalent clinical condition with significant adverse sequela or mortality. Anticoagulation and pharmacologic or pharmacomechanical thrombolytic therapies are the mainstays of VT treatment. An understanding of thrombosis biology will allow for more effective VT-tailored diagnosis and therapy. In vivo models of thrombosis provide indispensable tools to study the pathogenesis of thrombus formation and to evaluate novel therapeutic or preventive adjuncts for VT management or prevention. In this article, we review the most prominent in vivo models of VT created in rodents and swine species and outline how each model can serve as a useful tool to promote our understanding of VT pathogenesis and to examine novel therapies.

Mouse models of deep vein thrombosis

The pathogenesis of venous thromboembolism (VTE) is still not completely understood. Experimental animals in which human deep vein thrombosis can be modeled are useful tools to investigate the pathogenesis of VTE. Besides the availability of transgenic and genetically modified mice, the use of high frequency ultrasound and intravital microscopy plays an important role in identifying thrombotic processes in mouse models. In this article, an overview about the application of various new technologies and existing mouse models is provided, and the impact of venous side branches on deep vein thrombosis in the mouse model is discussed.

Tissue factor expressed by circulating cancer cell-derived microparticles drastically increases the incidence of deep vein thrombosis in mice

BACKGROUND

The risk of thrombotic complications such as deep vein thrombosis (DVT) during tumor development is well known. Tumors release into the circulation procoagulant microparticles (MPs) that can participate in thrombus formation following vessel injury. The importance of this MP tissue factor (TF) in the initiation of cancer-associated DVT remains uncertain.

OBJECTIVE

To investigate how pancreatic cancer MPs promote DVT in vivo.

METHODS

We combined a DVT mouse model in which thrombosis is induced by flow restriction in the inferior vena cava with one of subcutaneous pancreatic cancer in C57BL/6J mice. We infused high-TF and low-TF tumor MPs to determine the importance of TF in experimental cancer-associated DVT.

RESULTS

Both tumor-bearing mice and mice infused with tumor MPs subjected to 3 h of partial flow restriction developed an occlusive thrombus; fewer than one-third of the control mice did. We observed that MPs adhered to neutrophil extracellular traps (NETs), which are functionally important players during DVT, whereas neither P-selectin nor glycoprotein Ib were required for MP recruitment in DVT. The thrombotic phenotype induced by MP infusion was suppressed by hirudin, suggesting the importance of thrombin generation. TF carried by tumor MPs was essential to promote DVT, as mice infused with low-TF tumor MPs had less thrombosis than mice infused with high-TF tumor MPs.

CONCLUSIONS

TF expressed on tumor MPs contributes to the increased incidence of cancer-associated venous thrombosis in mice in vivo. These MPs may adhere to NETs formed at the site of thrombosis.

Nonclinical evaluation of novel cationically modified polysaccharide antidotes for unfractionated heparin

Protamine, the only registered antidote of unfractionated heparin (UFH), may produce a number of adverse effects, such as anaphylactic shock or serious hypotension. We aimed to develop an alternative UFH antidote as efficient as protamine, but safer and easier to produce. As a starting material, we have chosen generally non-toxic, biocompatible, widely available, inexpensive, and easy to functionalize polysaccharides. Our approach was to synthesize, purify and characterize cationic derivatives of dextran, hydroxypropylcellulose, pullulan and γ-cyclodextrin, then to screen them for potential heparin-reversal activity using an in vitro assay and finally examine efficacy and safety of the most active polymers in Wistar rat and BALB/c mouse models of experimentally induced arterial and venous thrombosis. Efficacy studies included the measurement of thrombus formation, activated partial thromboplastin time, bleeding time, and anti-factor Xa activity; safety studies included the measurement of hemodynamic, hematologic and immunologic parameters. Linear, high molecular weight dextran substituted with glycidyltrimethylammonium chloride groups at a ratio of 0.65 per glucose unit (Dex40-GTMAC3) is the most potent and the safest UFH inhibitor showing activity comparable to that of protamine while possessing lower immunogenicity. Cationic polysaccharides of various structures neutralize UFH. Dex40-GTMAC3 is a promising and potentially better UFH antidote than protamine.

Evaluation of antithrombotic activity of thrombin DNA aptamers by a murine thrombosis model

Aptamers are nucleic acid based molecular recognition elements with a high potential for the theranostics. Some of the aptamers are under development for therapeutic applications as promising antithrombotic agents; and G-quadruplex DNA aptamers, which directly inhibit the thrombin activity, are among them. RA-36, the 31-meric DNA aptamer, consists of two thrombin binding pharmacophores joined with the thymine linker. It has been shown earlier that RA-36 directly inhibits thrombin in the reaction of fibrinogen hydrolysis, and also it inhibits plasma and blood coagulation. Studies of both inhibitory and anticoagulation effects had indicated rather high species specificity of the aptamer. Further R&D of RA-36 requires exploring its efficiency in vivo. Therefore the development of a robust and adequate animal model for effective physiological studies of aptamers is in high current demand. This work is devoted to in vivo study of the antithrombotic effect of RA-36 aptamer. A murine model of thrombosis has been applied to reveal a lag and even prevention of thrombus formation when RA-36 was intravenous bolus injected in high doses of 1.4–7.1 µmol/kg (14–70 mg/kg). A comparative study of RA-36 aptamer and bivalirudin reveals that both direct thrombin inhibitors have similar antithrombotic effects for the murine model of thrombosis; though in vitro bivalirudin has anticoagulation activity several times higher compared to RA-36. The results indicate that both RA-36 aptamer and bivalirudin are direct thrombin inhibitors of different potency, but possible interactions of the thrombin-inhibitor complex with other components of blood coagulation cascade level the physiological effects for both inhibitors.

The electrolytic inferior vena cava model (EIM) to study thrombogenesis and thrombus resolution with continuous blood flow in the mouse

Previously, we presented the electrolytic inferior vena cava (IVC) model (EIM) during acute venous thrombosis (VT). Here, we present our evaluation of the EIM for chronic VT time points in order to determine whether this model allows for the study of thrombus resolution. C57BL/6 mice (n=191) were utilised. In this model a copper-wire, inserted into a 25-gauge needle, is placed in the distal IVC and another subcutaneously. An electrical current (250 μAmp/15 minutes) activates the endothelial cells, inducing thrombogenesis. Ultrasound, thrombus weight (TW), vein wall leukocyte counts, vein wall thickness/fibrosis scoring, thrombus area and soluble P-selectin (sP-sel) were performed at baseline, days 1, 2, 4, 6, 9, 11 and 14, post EIM. A correlation between TW and sP-sel was also determined. A thrombus formed in each mouse undergoing EIM. Blood flow was documented by ultrasound at all time points. IVC thrombus size increased up to day 2 and then decreased over time, as shown by ultrasound, TW, and sP-sel levels. TW and sP-sel showed a strong positive correlation (r=0.48, p<0.0002). Vein wall neutrophils were the most common cell type present in acute VT (up to day 2) with monocytes becoming the most prevalent in chronic VT (from day 6 to day 14). Thrombus resolution was demonstrated by ultrasound, TW and thrombus area. In conclusion, the EIM produces a non-occlusive and consistent IVC thrombus, in the presence of constant blood flow, allowing for the study of VT at both acute and chronic time points. Thrombus resolution was demonstrated by all modalities utilised in this study.

Rosuvastatin reduced deep vein thrombosis in ApoE gene deleted mice with hyperlipidemia through non-lipid lowering effects

INTRODUCTION

Statins, particularly rosuvastatin, have recently become relevant in the setting of venous thrombosis. The objective of this study was to study the non-lipid lowering effects of rosuvastatin in venous thrombosis in mice with hyperlipidemia.

MATERIALS AND METHODS

An inferior vena cava ligation model of venous thrombosis in mice was utilized. Saline or 5mg/kg of rosuvastatin was administered by gavage 48hs previous to thrombosis. Blood, the inferior vena cava, thrombus, and liver were harvested 3, 6hours, and 2days post-thrombosis. Thrombus weight, inflammatory markers, and plasminogen activator inhibitor-1 expression and plasma levels were measured. Also, neutrophil migration to the IVC was assessed.

RESULTS

Rosuvastatin significantly decreased thrombus weight, plasminogen activator inhibitor-1 expression and plasma levels, expression of molecules related to the interleukin-6 pathway, and neutrophil migration into the vein wall.

CONCLUSIONS

This work supports the beneficial effects of rosuvastatin on venous thrombosis in mice with hyperlipidemia, due to its non-lipid lowering effects.

Critical review of mouse models of venous thrombosis

Deep vein thrombosis and pulmonary embolism are a significant health care concern, representing a major source of mortality and morbidity. In order to understand the pathophysiology of thrombogenesis and thrombus resolution, animal models are necessary. Mouse models of venous thrombosis contribute to our understanding of the initiation, propagation, and resolution of venous thrombus, as well as allow for the evaluation of new pharmaceutical approaches to prophylaxis and treatment of deep vein thrombosis. In this work we review the ferric chloride model, the inferior vena cava ligation model, the inferior vena cava stenosis models, and the electrolytic inferior vena cava model and compare their advantages and disadvantages.

Myeloid cell tissue factor does not contribute to venous thrombogenesis in an electrolytic injury model

INTRODUCTION

Tissue factor (TF) is a potent initiator of the extrinsic coagulation cascade. The role and source of TF in venous thrombotic disease is not clearly defined. Our study objective was to identify the contribution of myeloid cell TF to venous thrombogenesis in mice.

MATERIALS AND METHODS

The mouse electrolytic inferior vena cava model was used to induce thrombosis. The following groups of mice were used (1) TF(flox/flox)LysMCre(+) mice that have reduced TF expression in myeloid cells, (2) TF(flox/flox)LysMCre(-) littermate controls, (3) Wild type mice given a monoclonal anti-mouse TF antibody (1H1) to inhibit TF activity, and (4) Wild type mice given rat IgG. Evaluations at baseline, day 2, and day 6 post thrombosis included thrombus weight, vein wall inflammatory cell migration, vein wall TF mRNA, and plasma D-dimer levels.

RESULTS

Inhibition of TF significantly decreased thrombus weight 2days post venous thrombosis. In contrast, TF(flox/flox)LysMCre(+) had no change in thrombus weight when compared to littermate controls. The absence of myeloid cell TF did not affect infiltration of neutrophils or monocytes into the vein wall. TF mRNA expression in the vein wall decreased at 2days but then returned to baseline levels by 6days post thrombosis. D-dimer levels peaked at 2days post thrombosis in mice with or without myeloid cell TF.

CONCLUSIONS

TF is important in the formation of venous thrombi in the macrovasculature. However, TF expression by myeloid cells does not significantly contribute to venous thrombogenesis in this model.