Increased venous versus arterial thrombosis in the Factor V Leiden mouse

Safety of DIEP Flap Reconstruction in Patients with Factor V Leiden: A Retrospective Cohort Study

Background:

Factor V Leiden (FVL) is the most common inherited thrombophilia in White people. Thrombotic complications resulting from free flap breast reconstruction in FVL patients have been studied to a limited degree. We evaluated whether patients heterozygous for a FVL mutation undergoing deep inferior epigastric perforator flap reconstruction had increased risk of micro- or macrovascular thrombotic complications compared with patients without a diagnosed thrombophilia.

Methods:

We performed a retrospective cohort study of deep inferior epigastric perforator flap reconstructions at Brigham and Women’s Hospital (1/2015–12/2020) comparing patients diagnosed as FVL heterozygotes compared with matched controls without a diagnosed thrombophilia. Patients were matched using coarsened exact matching algorithm based on clinical characteristics. The primary outcomes were micro- (return to OR for flap compromise, flap loss) and macrovascular (venous thromboembolism) complications.

Results:

A total of 506 patients (812 flaps) were included in this study. Eleven patients (17 flaps) were FVL heterozygotes. After matching, 10 patients (16 flaps) with FVL were matched to 55 patients (94 flaps). The return to OR for flap compromise was 0% in the FVL cohort compared with 5% (n = 5/94, 3/94 flaps lost, P = 1.00) in the matched controls (1.9%, n = 15/795 in unmatched controls, 0.6%, n = 5/795 loss rate). There were zero venous thromboembolism events among FVL patients compared with 2% of controls (n = 1/55).

Conclusions:

FVL heterozygosity did not increase the risk of micro- or macrovascular complications in patients undergoing deep inferior epigastric perforator flap breast reconstruction. This study supports the safety of microvascular reconstruction in this group of patients when appropriate venous thromboembolism prophylaxis is given.

Large intestine embryogenesis: Molecular pathways and related disorders (Review)

The large intestine, part of the gastrointestinal tract (GI), is composed of all three germ layers, namely the endoderm, the mesoderm and the ectoderm, forming the epithelium, the smooth muscle layers and the enteric nervous system, respectively. Since gastrulation, these layers develop simultaneously during embryogenesis, signaling to each other continuously until adult age. Two invaginations, the anterior intestinal portal (AIP) and the caudal/posterior intestinal portal (CIP), elongate and fuse, creating the primitive gut tube, which is then patterned along the antero‑posterior (AP) axis and the radial (RAD) axis in the context of left‑right (LR) asymmetry. These events lead to the formation of three distinct regions, the foregut, midgut and hindgut. All the above‑mentioned phenomena are under strict control from various molecular pathways, which are critical for the normal intestinal development and function. Specifically, the intestinal epithelium constitutes a constantly developing tissue, deriving from the progenitor stem cells at the bottom of the intestinal crypt. Epithelial differentiation strongly depends on the crosstalk with the adjacent mesoderm. Major molecular pathways that are implicated in the embryogenesis of the large intestine include the canonical and non‑canonical wingless‑related integration site (Wnt), bone morphogenetic protein (BMP), Notch and hedgehog systems. The aberrant regulation of these pathways inevitably leads to several intestinal malformation syndromes, such as atresia, stenosis, or agangliosis. Novel theories, involving the regulation and homeostasis of intestinal stem cells, suggest an embryological basis for the pathogenesis of colorectal cancer (CRC). Thus, the present review article summarizes the diverse roles of these molecular factors in intestinal embryogenesis and related disorders.

Animal Models of Thrombosis From Zebrafish to Nonhuman Primates: Use in the Elucidation of New Pathologic Pathways and the Development of Antithrombotic Drugs

Thrombosis is a leading cause of morbidity and mortality worldwide. Animal models are used to understand the pathological pathways involved in thrombosis and to test the efficacy and safety of new antithrombotic drugs. In this review, we will first describe the central role a variety of animal models of thrombosis and hemostasis has played in the development of new antiplatelet and anticoagulant drugs. These include the widely used P2Y12 antagonists and the recently developed orally available anticoagulants that directly target factor Xa or thrombin. Next, we will describe the new players, such as polyphosphate, neutrophil extracellular traps, and microparticles, which have been shown to contribute to thrombosis in mouse models, particularly venous thrombosis models. Other mouse studies have demonstrated roles for the factor XIIa and factor XIa in thrombosis. This has spurred the development of strategies to reduce their levels or activities as a new approach for preventing thrombosis. Finally, we will discuss the emergence of zebrafish as a model to study thrombosis and its potential use in the discovery of novel factors involved in thrombosis and hemostasis. Animal models of thrombosis from zebrafish to nonhuman primates are vital in identifying pathological pathways of thrombosis that can be safely targeted with a minimal effect on hemostasis. Future studies should focus on understanding the different triggers of thrombosis and the best drugs to prevent each type of thrombotic event.

New findings on venous thrombogenesis

Venous thrombosis (VT) is the third most common cause of cardiovascular death worldwide. Complications from VT and pulmonary embolism are the leading cause of lost disability-adjusted life years. Risks include genetic (e.g., non-O blood group, activated protein C resistance, hyperprothrombinemia) and acquired (e.g., age, surgery, cancer, pregnancy, immobilisation, female hormone use) factors. Pathophysiologic mechanisms that promote VT are incompletely understood, but involve abnormalities in blood coagulability, vessel function, and flow (so-called Virchow's Triad). Epidemiologic studies of humans, animal models, and biochemical and biophysical investigations have revealed contributions from extrinsic, intrinsic, and common pathways of coagulation, endothelial cells, leukocytes, red blood cells, platelets, cell-derived microvesicles, stasis-induced changes in vascular cells, and blood rheology. Knowledge of these mechanisms may yield new therapeutic targets. Characterisation of mechanisms that mediate VT formation and stability, particularly in aging, are needed to advance understanding of VT.

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.

Thrombodynamics of microvascular repairs: effects of antithrombotic therapy on platelets and fibrin

PURPOSE

To evaluate the hypothesis that platelets and fibrin differentially accrue at microvascular anastomoses in arteries versus veins and under different pharmacologic conditions.

METHODS

We evaluated mouse arterial and venous anastomoses with intravital fluorescence imaging, using fluorophore-labeled platelets and anti-fibrin antibodies to measure the extent of thrombus component development in the intraluminal anastomotic site. We evaluated systemic heparin or eptifibatide (platelet aggregation inhibitor) to determine their relative influences on thrombus composition.

RESULTS

Platelets accumulated rapidly in both arterial and venous repairs, and then fell in number after 10 to 30 minutes of reflow. Fibrin had a relatively steady development over 60 minutes in veins, with a more variable increase in arteries. Heparin reduced platelet accumulation in arteries and fibrin development in veins. Eptifibatide reduced platelets in both arteries and veins and had an apparent effect on lowering the amount of fibrin in veins.

CONCLUSIONS

These findings show that platelets have a rapid, transient response, whereas fibrin has a slower, more sustained accrual in both arterial and venous anastomoses. Furthermore, inhibition of either coagulation or platelet aggregation can influence presumably non-targeted components of thrombosis in vascular repairs of both arteries and veins.

CLINICAL RELEVANCE

Preventing replantation failure using antithrombotic therapies requires a better understanding of the effect of each pharmacologic compound on the various aspects of thrombogenesis.

Regional block anesthesia in a patient with factor V Leiden mutation and axillary artery occlusion

Anesthetic management of patients with coagulation disorders presents safety and technical challenges. This case describes a 58-year-old woman with factor V Leiden mutation who required distal saphenous vein harvest and axillo-brachial bypass to treat axillary artery occlusion. The patient underwent surgery with satisfactory anesthesia using infraclavicular brachial plexus block, thoracic paravertebral block, and unilateral subarachnoid block. These three regional anesthetic interventions were performed in lieu of general anesthesia to minimize risks of thrombotic events, pain, and to decrease recovery time. Despite higher failure rates of regional anesthesia, longer time required for procedures, and added discomforts during surgery, the benefits may outweigh risks for selected high-risk patients, including those with factor V Leiden mutations.

Two-photon intravital imaging of thrombus development

Thrombus development in mouse mesenteric vessels following laser-induced injury was monitored by high-resolution, near-real-time, two-photon, intravital microscopy. In addition to the use of fluorescently tagged fibrin(ogen) and platelets, plasma was labeled with fluorescently tagged dextran. Because blood cells exclude the dextran in the single plane, blood cells appear as black silhouettes. Thus, in addition to monitoring the accumulation of platelets and fibrin in the thrombus, the protocol detects the movement and incorporation of unlabeled cells in and around it. The developing thrombus perturbs the blood flow near the thrombus surface, which affects the incorporation of platelets and blood cells into the structure. The hemodynamic effects and incorporation of blood cells lead to the development of thrombi with heterogeneous domain structures. Additionally, image processing algorithms and simulations were used to quantify structural features of developing thrombi. This analysis suggests a novel mechanism to stop the growth of developing thrombus.

Fibrin architecture in clots: a quantitative polarized light microscopy analysis

Fibrin plays a vital structural role in thrombus integrity. Thus, the ability to assess fibrin architecture has a potential to provide insight into thrombosis and thrombolysis. Fibrin has an anisotropic molecular structure, which enables it to be seen with polarized light. Therefore, we aimed to determine if automated polarized light microscopy methods of quantifying two structural parameters; fibrin fiber bundle orientation and fibrin's optical retardation (OR: a measure of molecular anisotropy) could be used to assess thrombi. To compare fibrin fiber bundle orientation we analyzed picrosirius red-stained sections obtained from clots formed: (A) in vitro, (B) in injured and stenotic coronary arteries, and (C) in surgically created aortic aneurysms (n=6 for each group). To assess potential changes in OR, we examined fibrin in picrosirius red-stained clots formed after ischemic preconditioning (10 min ischemia+10 min reflow; a circumstance shown to enhance lysability) and in control clots (n=8 each group). The degree of fibrin organization differed significantly according to the location of clot formation; fibrin was most aligned in the aneurysms and least aligned in vitro whereas fibrin in the coronary clots had an intermediate organization. The OR of fibrin in the clots formed after ischemic preconditioning was lower than that in controls (2.9+/-0.5 nm versus 5.4+/-1.0 nm, P<0.05). The automated polarized light analysis methods not only enabled fibrin architecture to be assessed, but also revealed structural differences in clots formed under different circumstances.

Factor v leiden mutation in reocclusion after intra-arterial thrombolysis

BACKGROUND AND PURPOSE

Reocclusion of intracranial arteries after successful recanalization is associated with poor clinical outcome. The role of Factor V Leiden mutation in intracranial arterial thrombosis/rethrombosis is unclear.

SUMMARY OF REPORT

We report the case of a patient who developed recurrent reocclusions of the middle cerebral artery after intra-arterial thrombolysis for acute ischemic stroke. The patient subsequently underwent transcatheter clot retrieval followed by successful stent-supported angioplasty of the occluded segment. He underwent a detailed workup for thrombophilia. The patient was detected to be heterozygous for Factor V Leiden mutation without any other cause for thrombophilia.

CONCLUSIONS

Factor V Leiden mutation could be a contributing etiology for reocclusion after endovascular interventions in stroke. Systematic studies looking for thrombophilic mutations in patients with arterial reocclusion might be warranted.

Electric injury model of murine arterial thrombosis

BACKGROUND AND PURPOSE

Murine models of arterial thrombosis have gained utility with applications in genetically manipulated mice. Implementation of current models requires specialized equipment and provides limited outcome measures. A new murine model of continuously monitored arterial thrombosis was created.

METHODS

An electric injury was delivered to the exterior surface of the common carotid artery using the flat end of a 140-mum steel microsurgery needle connected to the anode of a 3-V battery source. Direct current was delivered for 30 s. The developing thrombus was apparent as a white, platelet-dominated region at the site of injury. This region was continuously monitored and recorded by videotape for 30 min. Subsequently, the thrombus area was measured directly on the TV monitor, generating a time course for thrombogenesis. In a further evaluation of the model, three pharmacologically treated groups of mice were evaluated, with drug infusion immediately before thrombus induction: (1) saline (control), (2) heparin (60 units/kg), and (3) GR144053, a GPIIb/IIIa-specific antagonist (10 mg/kg).

RESULTS

The basic model showed consistent thrombus development by 7-9 min, occasionally forming an occlusive thrombus. Most of the thrombi underwent one or more cycles of embolization and thrombus regrowth. In the experimental series, the heparin-treated group had a significantly decreased thrombus area versus controls (p<0.0001); the GR144053-treated mice had no apparent thrombus, supporting a dominant role of platelet aggregation in arterial thrombogenesis.

CONCLUSION

This new model is simple to do, uses readily available instrumentation, and provides a continuously recorded quantifiable measure of thrombogenesis.