Electric injury model of murine arterial thrombosis

Antithrombotic efficacy of direct oral anticoagulants on patency rate following microsurgical anastomosis in crushed rat arteries

BACKGROUND

During the last decade direct oral anticoagulants (DOAC) have been established in various fields of medicine.Their use in microsurgery has not been evaluated yet though. This study aims to evaluate their efficacy in microsurgery and additionally compare them with a well established antithrombotic agent.

MATERIALS AND METHODS

The right femoral artery of 101 rats divided into 4 groups, was crushed and anastomosed. Group A (20 rats) received placebo therapy (1 ml NaCl 0.9%, orally), while Group B (27 rats), Group C (27 rats) and Group D (27 rats) received rivaroxaban (3 mg/kg, orally), dabigatran (30 mg/kg, orally) and enoxaparin (30 mg/kg, subcutaneously) respectively. All drugs were administered 3 h preoperatively and once daily for the following postoperative days until the sacrifice of the animals. Patency was evaluated at 1st, 7th and 20th postoperative day. Following patency evaluation the rats were sacrificed and the vessels were harvested for histological examination.

RESULTS

None of the rats died postoperatively. Patency rates of rivaroxaban group (78%), dabigatran group (70%) and enoxaparin group (63%) were statistically similar, but significantly higher than the placebo-treated control group (p < 0.05). Cells with morphologic features of endothelial cells were evident 7 days after the injury.

CONCLUSION

The results of this study demonstrate the following: (1) rivaroxaban and dabigatran through inhibition of thrombus formation significantly enhanced the patency rate compared to placebo treatment (2) the antithrombotic efficacy of rivaroxaban and dabigatran in compromised microvessels was similar to that of enoxaparin, the most widely used antithrombotic agent.

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.

Acute Stroke due to Electrocution: Uncommon or Unrecognized?

The growing dependence on electricity in our daily lives has increased the incidence of electrocution injuries. Although several neurological injuries have been described previously, acute stroke due to electrocution is rare. Our patient, a previously healthy man, was electrocuted after he grabbed a “live” high-voltage wire. Although he was hemodynamically stable, he remained confused with language defects. MRI of the brain showed acute stroke in the bilateral anterior cerebral artery territory and watershed regions of the left middle cerebral artery territory. MR angiogram incidentally showed A1 segment aplasia of the right anterior cerebral artery. Electrocution is known to cause vasospasm leading to end-organ damage similar to that seen in stroke. In our patient, vasospasm of the left anterior circulation likely led to watershed infarcts in the left parietal lobe and bilateral frontal lobes. Due to aplasia of the A1 segment on the right side, perfusion to both frontal lobes was solely from the left anterior cerebral artery.

Imaging of small animal peripheral artery disease models: recent advancements and translational potential

Peripheral artery disease (PAD) is a broad disorder encompassing multiple forms of arterial disease outside of the heart. As such, PAD development is a multifactorial process with a variety of manifestations. For example, aneurysms are pathological expansions of an artery that can lead to rupture, while ischemic atherosclerosis reduces blood flow, increasing the risk of claudication, poor wound healing, limb amputation, and stroke. Current PAD treatment is often ineffective or associated with serious risks, largely because these disorders are commonly undiagnosed or misdiagnosed. Active areas of research are focused on detecting and characterizing deleterious arterial changes at early stages using non-invasive imaging strategies, such as ultrasound, as well as emerging technologies like photoacoustic imaging. Earlier disease detection and characterization could improve interventional strategies, leading to better prognosis in PAD patients. While rodents are being used to investigate PAD pathophysiology, imaging of these animal models has been underutilized. This review focuses on structural and molecular information and disease progression revealed by recent imaging efforts of aortic, cerebral, and peripheral vascular disease models in mice, rats, and rabbits. Effective translation to humans involves better understanding of underlying PAD pathophysiology to develop novel therapeutics and apply non-invasive imaging techniques in the clinic.

Murine arterial thrombus induction mechanism influences subsequent thrombodynamics

BACKGROUND

The mechanism of thrombotic induction in experimental models can vary greatly, as can the applied evaluative measures, making comparisons among models difficult.

OBJECTIVES

This study comparatively evaluated the arterial thrombodynamic response among injury mechanisms.

METHODS

Thrombotic responses were induced in mouse carotid arteries, with subsequent intravital imaging using rhodamine-6G-labeled platelets to quantitate platelet accumulation over 30minutes. Nine induction methods were evaluated: brief pinch, temporary hard ligation, cautery/heat, needle puncture, intralumenal wire (scratch), intralumenal adventitia/collagen (2 different models), and brief exposures to either iron-based surface electrolytic injury or ferric chloride.

RESULTS

The accumulation of platelets was variable among induction methods, with a greater response to more severe injury mechanisms, free radical injury, and exposed collagen. Temporal profiles were generated by normalizing data to peak platelet accumulation for each run; rapid platelet development and subsequent detachment were found for mechanical injuries that maintained vessel integrity (pinch and ligation injuries), with more sustained growth for more severe mechanical (wire) injury or breach of the vessel (needle puncture or intralumenal collagen). A delayed but extended temporal response was seen with free radical injury (both electrolytic and ferric chloride).

CONCLUSIONS

These findings demonstrate a dependence of platelet thrombodynamics on the method of induction, with collagen exposure causing greater, more prolonged activity, while free-radical injury effected a delayed but sustained platelet thrombus formation with slower resolution. A better understanding of how these various injury models relate to clinical causes of arterial thrombosis is needed for optimal translational interpretation of murine models of thrombosis.

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.

A rat model of thrombosis in common carotid artery induced by implantable wireless light-emitting diode device

This work has developed a novel approach to form common carotid artery (CCA) thrombus in rats with a wireless implantable light-emitting diode (LED) device. The device mainly consists of an external controller and an internal LED assembly. The controller was responsible for wirelessly transmitting electrical power. The internal LED assembly served as an implant to receive the power and irradiate light on CCA. The thrombus formation was identified with animal sonography, 7 T magnetic resonance imaging, and histopathologic examination. The present study showed that a LED assembly implanted on the outer surface of CCA could induce acute occlusion with single irradiation with 6 mW/cm(2) LED for 4 h. If intermittent irradiation with 4.3-4.5 mW/cm(2) LED for 2 h was shut off for 30 min, then irradiation for another 2 h was applied; the thrombus was observed to grow gradually and was totally occluded at 7 days. Compared with the contralateral CCA without LED irradiation, the arterial endothelium in the LED-irradiated artery was discontinued. Our study has shown that, by adjusting the duration of irradiation and the power intensity of LED, it is possible to produce acute occlusion and progressive thrombosis, which can be used as an animal model for antithrombotic drug development.

Electroablation: a method for neurectomy and localized tissue injury

BACKGROUND

Tissue injury has been employed to study diverse biological processes such as regeneration and inflammation. In addition to physical or surgical based methods for tissue injury, current protocols for localized tissue damage include laser and two-photon wounding, which allow a high degree of accuracy, but are expensive and difficult to apply. In contrast, electrical injury is a simple and inexpensive technique, which allows reproducible and localized cell or tissue damage in a variety of contexts.

RESULTS

We describe a novel technique that combines the advantages of zebrafish for in vivo visualization of cells with those of electrical injury methods in a simple and versatile protocol which allows the study of regeneration and inflammation. The source of the electrical pulse is a microelectrode that can be placed with precision adjacent to specific cells expressing fluorescent proteins. We demonstrate the use of this technique in zebrafish larvae by damaging different cell types and structures. Neurectomy can be carried out in peripheral nerves or in the spinal cord allowing the study of degeneration and regeneration of nerve fibers. We also apply this method for the ablation of single lateral line mechanosensory neuromasts, showing the utility of this approach as a tool for the study of organ regeneration. In addition, we show that electrical injury induces immune cell recruitment to damaged tissues, allowing in vivo studies of leukocyte dynamics during inflammation within a confined and localized injury. Finally, we show that it is possible to apply electroablation as a method of tissue injury and inflammation induction in adult fish.

CONCLUSIONS

Electrical injury using a fine microelectrode can be used for axotomy of neurons, as a general tissue ablation tool and as a method to induce a powerful inflammatory response. We demonstrate its utility to studies in both larvae and in adult zebrafish but we expect that this technique can be readily applied to other organisms as well. We have called this method of electrical based tissue ablation, electroablation.

Ischemic stroke after low-voltage electric injury in a diabetic and coagulopathic woman

Electric injury is a common physical injury in daily life. Because of the low resistance of vascular tissue, vascular injury and thrombosis are frequently found in cases of high-voltage electric injury but are rarely reported in low-voltage conditions. We present the case of a diabetic woman who suffered symptomatic brainstem stroke after a short duration of 60 Hz/110 V alternate current electric contact with a home washer socket. A stroke risk factor survey did not reveal remarkable cardiac or vascular abnormality, except increased glycohemoglobin levels and decreased protein C activity. In contrast to a direct and adequate energy transfer in high-voltage electric injury, a pre-existing vasculohemostatic deficit, such as coagulopathy, has been proposed to provide a predisposition to thrombosis in low-voltage electric injury. Nevertheless, the findings in this patient remind the possibility of physical triggering factor for stroke occurrence in our environment as new technology and product generates rapidly enough for understanding their safety and biologic effect.

Murine hematopoietic cell tissue factor pathway inhibitor limits thrombus growth

OBJECTIVE

Tissue factor (TF)-factor VIIa initiates blood coagulation and is found on microparticles that accumulate within intravascular thrombi. Tissue factor pathway inhibitor (TFPI), a factor Xa (fXa)-dependent inhibitor of TF-factor VIIa, is produced by megakaryocytes and is present in platelets. We sought to determine the role of platelet TFPI in regulation of thrombus growth.

METHODS AND RESULTS

Western blot analyses demonstrated that murine platelets produce TFPIα, the most evolutionarily conserved alternatively spliced isoform of TFPI. A mouse model of hematopoietic cell TFPI deficiency was developed by transplanting irradiated TFPI(+/-) mice with TFPI(-/-) fetal liver cells. Platelets from transplanted mice totally lack TFPI inhibitory activity. An electrolytic vascular injury model was used to assess thrombus growth in the femoral vein and carotid artery. Mice lacking hematopoietic TFPI developed larger femoral vein and carotid artery thrombi than TFPI(+/-) mice transplanted with TFPI(+/+) hematopoietic cells, as evidenced by increased platelet accumulation.

CONCLUSIONS

Hematopoietic TFPI limits thrombus growth following vascular injury. Because platelets are the primary hematopoietic cell accumulating within a growing thrombus, these findings suggest that TFPI present within platelets functions to limit intravascular thrombus growth, likely through inhibition of the procoagulant activity of blood borne TF.

A ferric chloride induced arterial injury model used as haemostatic effect model

A number of experimental bleeding models have been applied to animal models of haemophilia in order to evaluate the acute haemostatic effect of procoagulant compounds. In contrast, in vivo thrombosis models (including the FeCl(3) induced injury model) have mainly been used to study antithrombotic pharmacological intervention. However, as there are limitations to existing bleeding models and as new recombinant FVIII, FIX, and FVIIa variants with increased and prolonged activity are generated there is an increasing need for new and optimized in vivo animal models for testing the efficacy of these haemostatic drug candidates. This led us to look at existing thrombosis models in a new perspective. We have studied the effect of a FeCl(3) induced arterial injury in both F8-KO and F9-KO mice using optimized conditions where exposure to FeCl(3) induces occlusion within 4.2 +/- 0.2 min in wild type mice with a normal coagulation system. In contrast, no occlusion was observed in haemophilic mice providing a therapeutic window in the model making it suitable for pharmacological testing of therapeutic intervention. We demonstrate that replacement therapy with a clinical relevant dose of rFVIII (Advate 20-80 U kg(-1)) and rFIX [(0.75 mg kg(-1) BeneFIX) approximately 50 IU kg(-1)] restored coagulation and normalized the time to occlusion following FeCl(3) induced injury in F8-KO mice and restored coagulation and nearly normalized the time to occlusion in F9-KO mice. In conclusion, we have demonstrated that under optimized conditions the FeCl(3) induced arterial injury model provides a therapeutic window that makes it an useful effect model for evaluation of the haemostatic potential of procoagulant drugs.

Overview of murine thrombosis models

There are a myriad of options on where and how to perform thrombosis studies in mice. Models have been developed for systemic thrombosis, larger and smaller vessels of both the arterial and venous systems as well as several different microvascular beds. However, there are important differences between the models and investigators need to be careful and thoughtful when they choose which model to use.